Inorganic-organic hybrid copper phosphate nanoflower coated with an upper rim tetra-imidazolyl-phenanthroline derivatized calix[4]arene: synthesis, characterization and its application as a peroxidase mimic catalyst
Dinda S.K., Areti S., Rao C.P.
Article, New Journal of Chemistry, 2025, DOI Link
View abstract ⏷
An upper rim tetra-imidazolyl-phenanthroline derivatized calix[4]arene conjugate (L) was synthesized and characterized using different analytical, spectral, microscopic and diffraction techniques. The incubation of L with CuSO4·5H2O in PBS buffer (20 mM) for 1 h resulted in the formation of a nanoflower material. The L-coated copper phosphate nanoflowers (L@CuPNFs) were characterized through Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, and microscopy techniques. The peroxidase mimetic activity of L@CuPNFs was assessed, and the results were compared with those of unmodified CuPNFs as a control. The peroxidase activity was demonstrated using three different substrates, viz., tetramethylbenzidine (TMB), ortho-phenylenediamine (OPD) and guaiacol. The progress of the oxidation reaction of the model substrates in the presence of L@CuPNFs and H2O2 was demonstrated through absorption spectra measured as a function of time. The changes could be qualitatively gauged from the observed visual colour variation. The oxidized species were identified by measuring the ESI-MS spectrum of the reaction mixture. The rate of oxidation of these substrates in the presence of H2O2 was higher when L@CuPNFs were used as a catalyst, and this was much greater than the reaction rate observed with the unmodified CuPNF, which was not coated with L. All these results confirmed that the coating of L enhanced the peroxidase mimetic activity of the nanoflowers.
Supramolecular Logic Gates Based on the Conjugates of Calixarenes and Carbohydrates
Nag R., Sivaiah A., Rao C.P.
Review, Langmuir, 2024, DOI Link
View abstract ⏷
In the era of application-oriented research, laboratory to real life translation is highly regarded and in great demand. This could mean that molecular science developed for sensing and detecting a variety of chemical species awaits conversion to devices. In that, the molecular logic gates are the most promising ones where the information storage and/or data processing can be easily carried out in terms of molecular inputs and electrical response outputs. This would facilitate the simultaneous execution of a diverse array of molecular sensing functions. The recent progress in molecular logic gates based on supramolecular optical receptors, in particular, fluorescent ones, such as calixarene derivatives and carbohydrate conjugates will have a transformative impact on molecular devices and will encourage this science to yield technology. Therefore, this review provides a critical evaluation of recent publications on molecular logic gates based on the derivatives of calixarenes and glyco-conjugates, including several from our own research group, with the view that the corresponding applications are a beneficiary in laboratory-to-device translation. In addition, this review is also expected to assist young researchers in planning their research focus in the broad area of supramolecular-based logic gates targeting some specific applications.
Selective Sensing and Removal of Mercury Ions by Encapsulating Dansyl Appended Calix[4]Conjugate in a Zeolitic Imidazolate Framework as an Organic-Inorganic Hybrid Nanomaterial
Uttam B., Polepalli S., Sinha S., Majumder A., Rao C.P.
Article, ACS Applied Nano Materials, 2022, DOI Link
View abstract ⏷
A lower rim dansyl appended calix[4]arene, DanC4A has been synthesized and characterized. DanC4A is a promising sensor for selective detection of toxic metal ions, Hg2+, among the twelve separate metal ions studied. The fluorescence titration of DanC4A with Hg2+ shows approximately 80% quenching. Competitive metal ion studies suggest the selective binding of Hg2+ to DanC4A. The biocompatibility of DanC4A has been confirmed by an MTT assay performed using HeLa cells. Confocal microscopy and fluorescence microscopy studies suggest that DanC4A exhibits strong green fluorescence in HeLa cells, and the same is quenched as the concentration of Hg2+ increases in the cells. Apart from sensing, the main concern is the removal of Hg2+ from water and this is not possible with the direct use of DanC4A due to its solubility. Therefore, DanC4A has been embedded into a zeolitic imidazolate framework (ZIF8) to result in an inorganic-organic hybrid nanomaterial, DanC4A_ZIF8_MOFs, by an in situ reaction. Approximately 95% of the Hg2+ ions were removed from water by using the hybrid material, viz., DanC4A_ZIF8_MOFs. Thus, DanC4A is not only a superior sensor for Hg2+ in solution and in mammalian cells but can be converted into an organic-inorganic hybrid material, DanC4A_ZIF8_MOFs, for efficient removal of Hg2+ from water.
Synthetic strategies for the functionalization of upper or lower rim of supramolecular calix[4]arene platform
Uttam B., Polepalli S., Rao C.P.
Review, Arkivoc, 2022, DOI Link
View abstract ⏷
In the broad area of supramolecular chemistry, the calix[n]arene provides a congenial platform for synthetic modifications, and further has been a highly studied system and thereby occupies a unique position among the supramolecular scaffolds. This is attributable to its pre-organised hydrophobic cavity, amenability to synthetic modifications to generate derivatives, presence of pre-organised ion binding cores along with reporter moieties both at its lower and upper rims. Such derivatizations lead to well defined conformations, and tunable functionalization at both these rims. Among various possible derivatizations, the synthetic strategies of those leading to cone conformation have been rationalized in this review article. In addition, some insights into the synthesis of calix[4]arene dimers and tubes, and a variety of different macrocyclic derivatives of the calixarene have also been taken into consideration. All the conjugated derivatives of calix[4]arene platform reported in this article have been provided with a relevance to highlight their application potential.
Calixarene-mediated host-guest interactions leading to supramolecular assemblies: visualization by microscopy
Article, Chemical Communications, 2022, DOI Link
View abstract ⏷
Host-guest chemistry, particularly of supramolecules, has been an intriguing topic for researchers for a long time due to its multiplicative applications ranging from chemical to biological to materials science. Supramolecules, such as calixarenes, are excellent host molecular systems due to their controllable cavity along with the ease of functionalization both at the lower and upper rims. The host-guest interactions involving calixarenes have been primarily studied using physical methods, such as absorption, fluorescence and nuclear magnetic resonance spectroscopy, isothermal titration calorimetry and mass spectrometry. The corresponding literature as disseminated through review articles triggered broadening of the spectrum of research. Depending upon the nature of the derivatization, the supramolecular conjugates of calixarenes have been shown to form different morphologies of micro and nanometric size as reported in the literature. Pertinent research performed in our own group was based on atomic force microscopy, transmission electron microscopy and scanning electron microscopy studies. The literature reveals that such morphologies are modified in the presence of guest species. Thus, the supramolecular host-guest complexation of calixarenes leading to the formation of various architectures has been studied using both spectroscopy and microscopy techniques to obtain complimentary data. However, there are no review articles that provide discussions on this exciting area of supramolecular science involving microscopy. Therefore, in the present article, for the first time, we have brought together the research reported in the literature during the past decade, including ours, in demonstrating the supramolecular architectures formed from the host-guest interactions extended by the conjugates of calixarenes, and their applications using microscopy. The scope of this article spans across various features of interaction in these systems: (i) in solution, (ii) at the air-water interface and (iii) on solid surfaces. The application domain includes sensing of organic explosives and drugs, exhibiting antibacterial activity, supramolecular self-assembly or co-assembly resulting in gels, micelles and vesicles, and the consequent aggregation-induced emission and a few others.
Development of hybrid DNA-copper phosphate nanoflowers as peroxidase enzyme mimics and for colorimetric sensing of phenol
Article, Inorganica Chimica Acta, 2022, DOI Link
View abstract ⏷
A facile co-precipitation method was adapted for the synthesis of DNA coated copper phosphate nanoflowers (CuPNF_ctDNA) using calf thymus DNA (ctDNA) and the copper salt in phosphate buffer saline (PBS). The flower growth was monitored using scanning electron microscopy (SEM), wherein a fully formed floral morphology was observed after 36 h. The SEM data further supported a decrease in the size of the nanoflower (NF) and an increase in the density of petals upon increasing the added ctDNA concentration. The coated nanoflowers, viz., CuPNF_ctDNAx {‘x’ is the concentration of ctDNA used for coating} were characterized using spectroscopy, microscopy and diffraction techniques. The petals of the NFs were observed in transmission electron microscopy and the inorganic copper phosphate framework was characterized by powder X-ray diffraction. The surface charge of the NFs (CuPNF_ctDNAx) were measured using zeta potential equipment at different values of ‘x’ used in the preparation. The presence of phosphorous in DNA and that in the copper phosphate were confirmed using X-ray photoelectron spectra. The peroxidase mimetic activity of CuPNF_ctDNA0.3 was measured using 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of H2O2 in acetate buffer at pH 4.5. The enzyme kinetics were evaluated using the Michaelis–Menten steady state curve along with the Lineweaver – Burk plot and the derived Km values were 0.011 and 1.36 mM for TMB and H2O2 respectively. Micromolar detection of phenol in phosphate buffer saline (PBS) at pH = 7.4 was performed using 4-aminoantipyrine as substrate to a limit of detection of 5.2 μM. Thus, the hybrid material, viz., CuPNF_ctDNA0.3 exhibited peroxidase enzyme mimetic activity, besides sensing the common pollutant, phenol.
Enhanced DNA nuclease activity of Momordica charantia lectin by biomimetic mineralization as hybrid copper phosphate nanoflowers and as zeolitic imidazole frameworks
Article, International Journal of Biological Macromolecules, 2022, DOI Link
View abstract ⏷
Biomimetic mineralization of enzymes for enhanced stability and activity is an important area of research due to its potential applications. Inorganic materials with enzymes coated and or embedded in them, viz., protein-inorganic hybrid nanomaterials with distinctive morphology and surface characteristics are promising candidates for exploring their elevated enzymatic activity. In this work, we have developed two different types of protein inorganic nanohybrid materials using a 120 kDa lectin purified from bitter gourd seeds (Momordica charantia lectin, MCL), and (i) copper phosphate nanoflowers to result in a protein – inorganic nano hybrid material CuPNF_MCL and (ii) encapsulating the protein in zeolitic imidazole framework, ZIF8_MCL. While CuPNF_MCL showed floral morphology, the ZIF8_MCL mostly showed hexapod morphology as noticed from the microscopy data. Both the nanomaterials showed a distinctive trend of decrease in size with increase in the protein concentration used during the preparation. The nanoflowers also showed an increase in the tightness of the packing of petals with increase in the protein concentration. Powder X-Ray diffraction studies confirmed the crystallinity of the inorganic frameworks. The Fourier Transform infrared spectroscopy studies coupled with confocal imaging of the fluorophore tagged MCL embedded hybrids confirmed the presence of the protein. The MCL protein was examined for its ability to cleave DNA, i.e., nuclease activity using pBR322, wherein the form I plasmid is completely transformed into the form II / III at 2 mg/mL concentration of the protein. However, both the hybrids showed a superior nuclease activity as compared to the protein, wherein the CuPNF_MCL showed a threefold greater nuclease activity as compared to the ZIF8_MCL. The greater nuclease activity of CuPNF_MCL is attributable to its mesoporous nature with higher pore size and pore volume as compared to that in case of ZIF8_MCL, which is microporous in nature. Thus, in this paper, we have purified a nuclease like lectin from bitter gourd seeds and improved its nuclease property by converting it into inorganic hybrid nanomaterial of two types wherein higher activity was observed in the material having better porosity and surface area characteristics.
Advanced Oxidation Processes: A Promising Route for Abatement of Emerging Contaminants in Water
Kusuma T.D., Naga Jyothi M.S.V., Rao C.P., Maliyekkal S.M.
Book chapter, Energy, Environment, and Sustainability, 2021, DOI Link
View abstract ⏷
The importance of clean water and the link between water and health are well-documented. Ailment and disease from the consumption of polluted water is a significant cause of human misery in the world. With the advancements in chemistry in general and in analytical chemistry in particular, our ability to detect and analyze pollutants in trace quantities has increased significantly over the years. Currently, many freshwater bodies are contaminated not only with conventional pollutants but also with several organic molecules, such as pharmaceutically active compounds, endocrine-disrupting compounds, surfactants, personal care products, and several others. These emerging contaminants (ECs) require special attention due to their toxicity to all forms of life. Besides, some of these pollutants are bio-resistant and can even sustain after primary and secondary treatments of wastewater. Advanced oxidation is a promising technique and has gained immense importance in recent years due to its ability to degrade and mineralize complex organic molecules, including ECs. Advanced oxidation processes (AOPs) rely on the in-situ generation of reactive chemical species such as hydroxyl radicals for degradation. This chapter discusses the principles and working mechanisms of various AOPs, including ozonation, Fenton, photolysis, plasma, sonolysis, and photocatalysis, and their combinations. The application of AOPs in degrading ECs such as pesticides, pharmaceutically active compounds (PACs), personal care products (PCPs), and endocrine-disrupting compounds (EDCs) are discussed. This chapter also elucidates the origin, fate, and human and ecological health impacts of ECs in water bodies.
Development and demonstration of functionalized inorganic-organic hybrid copper phosphate nanoflowers for mimicking the oxidative reactions of metalloenzymes by working as a nanozyme
Article, Journal of Materials Chemistry B, 2021, DOI Link
View abstract ⏷
Copper phosphate nanoflowers (CuPNFs) have been synthesized in the presence of different aromatic phenanthroline derivatives (Ln), leading to inorganic-organic hybrid materials (Ln-CuPNFs). Studies revealed that the morphology of nanoflowers varies as a function of the aromatic moiety present in the derivative,Ln(where ‘n’ corresponds to phenyl, naphthyl, anthracenyl, and pyrenyl) used for coating the nanomaterial. Other noticeable changes were the increase in the size of the flower by ∼2-3 fold in the presence of these derivatives. In the absence of such aromatic phenanthroline derivatives,i.e., the use of 1,10-phenanthroline-5-amine did not induce the formation of nanoflowers, suggesting that the organic derivatization used in the present study stabilizes the nanoflower structure. Nanoflowers were characterized using X-ray diffraction, Brunauer-Emmett-Teller (BET) isotherm, X-ray photoelectron spectroscopy, Raman and Infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy, thus covering a range of diffraction, spectroscopy, and microscopy techniques. Nanoflowers,Ln-CuPNFs, have been demonstrated for the oxidative reactions mimicking copper metalloenzymes in the presence and absence of hydrogen peroxide using different substrates. Thus, hybridLn-CuPNFs mediate the complete oxidation ofo-phenylenediamine, dopamine, ascorbate oxidase, and terephthalic acid without causing much change in the morphology of the hybrid nanoflower material and with the retention of the activity supporting the hybrid as an acceptable enzyme mimicking material. Oxidation is mediated through hydroxyl radical formation and the order of the oxidative activity is pyrenyl > anthracenyl > naphthyl > phenyl for the inorganic-organic hybrid nanoflowers. The copper complex of pyrenyl-appended phenanthroline derivative also showed similar biomimetic activity.
Supramolecular conjugates of calixarenes in biological cells by microscopy
Review, Journal of Chemical Sciences, 2021, DOI Link
View abstract ⏷
During the past two decades, the supramolecular conjugates of calixarenes have turned intriguing to the researchers due to their versatility in functionalization and applications spanning across various fields, such as chemical, biological and materials sciences. Though several review articles discuss host-guest and other functional aspects of the supramolecular conjugates of calixarenes, there is no such article that consolidates the role of the conjugates in the context of cell science. In this article, we focus on the utility of such conjugates in the biological cells as studied primarily using microscopy techniques that include endeavours emerging from our research group. Therefore, this will assist researchers working in this area in order to understand the microscopy aspects of calixarene based supramolecular conjugates inside the biological cells and thereby support the design of newer conjugates planned to target a specific purpose. Thus, this article focuses on the aspects, such as drug loading and bactericidal activity, gene transfer, selective ion sensing, and cell imaging by localizing in mitochondria, cytosol or Golgi apparatus, i.e., in any one of the subcellular components. Graphic abstract: [Figure not available: see fulltext.] Synopsis Supramolecular conjugates of calixarenes turned intriguing to the researchers due to their versatility in functionalization and in exhibiting diverse applications. This article focusses on the microscopy data for drug loading, bactericidal activity, gene transfer, ion sensing and cell imaging and thereby support the design of newer conjugates to target specific purposes.
Protein-inorganic nano hybrid sheets of Pd embedded BSA as a robust catalyst in water for oxidase mimic activity and C-C coupling reactions, and as a sustainable material for micromolar sensing of dopamine
Polepalli S., Uttam B., Rao C.P.
Article, Materials Advances, 2020, DOI Link
View abstract ⏷
Protein-inorganic hybrids with tunable morphology offer excellent applications in several fields due to their versatile characteristics. Herein, we report a new hybrid material prepared using commercially available protein bovine serum albumin (BSA) and a palladium salt. Employing a green process, distinctive colonies of Pd-nanoparticles (Pd_NPs) (2-5 nm) embedded in BSA hybrid sheets (Pd_NP@BSAsheet) were synthesized and characterized using different microscopy techniques. While naked Pd_NPs show larger particles of ∼52 nm in size, the size of the Pd_NPs embedded in BSA sheets is as small as ∼4 nm and they form well separated colonies by providing a much greater number of distinct reaction centers. Further characterization was performed using thermal, spectral and diffraction techniques. Pd_NP@BSAsheet shows excellent oxidase enzyme mimic activity as demonstrated using 3,3′,5,5′-tetramethylbenzidine (TMB) and o-phenylenediamine (OPD) as substrates. The selective detection of the neurotransmitter dopamine by the in situ generated oxidized species of TMB has been demonstrated in buffer, human serum and urine samples to a micromolar detection limit. The hybrid Pd_NP@BSAsheet was also shown to have superior catalytic activity in Suzuki coupling reactions performed in water as compared to several other literature reported Pd-based catalysts and its reusability has been demonstrated. Thus, the hybrid Pd_NP@BSAsheet material is promising and sustainable as an oxidase enzyme mimic, as a biosensor for sensing crucial neurotransmitter dopamine and as a catalyst for C-C coupling in aqueous medium.
Lysozyme coated copper nanoclusters for green fluorescence and their utility in cell imaging
Thawari A.G., Kumar P., Srivastava R., Rao C.P.
Article, Materials Advances, 2020, DOI Link
View abstract ⏷
Fluorescent, pH dependent and water soluble copper nanoclusters (CuNCs) were synthesized using lysozyme (lyz) as the stabilizing agent to give lysozyme coated copper nanoclusters, viz., lyz-CuNCs. The lyz-CuNCs were 3-5 nm in size at neutral pH and exhibit green fluorescence (λem ∼ 510 nm) when excited at 490 nm and exhibited a maximum quantum yield of 18%. However, under basic conditions, aggregates of lyz-CuNCs were seen with a particle size of ∼100 nm. The emission of lyz-CuNCs observed at 510 nm complements that from the blue (λem = 450 nm) and the red (λem = 650 nm) nanoclusters and thus bridges the gap. On the other hand, under acidic conditions, these show a size of 5-10 nm but weakly fluoresce. The particle size and aggregations were monitored by TEM studies carried out using the samples prepared under both the acidic and the basic conditions. The lyz-CuNCs prepared at neutral pH show >90% cell viability and hence can be used as a probe for cellular imaging. The imaging was carried out with both healthy and cancer cell lines, viz., NIH3T3 cells (mouse embryonic fibroblast cell), MCF7 cells (human breast cancer cells) and MDA-MB-231 cells (human estrogen negative breast cancer cells). The Z-stack study suggested the presence of lyz-CuNCs in the cells in cytoplasm. Thus, the green fluorescent lyz-CuNCs can be an alternate to green fluorescent protein (GFP) that is used for cell imaging purposes, since the latter needs a tedious procedure to express, purify and to conjugate.
Binding of Fe(ii)-complex of phenanthroline appended glycoconjugate with DNA, plasmid and an agglutinin protein
Dinda S.K., Polepalli S., Rao C.P.
Article, New Journal of Chemistry, 2020, DOI Link
View abstract ⏷
The phenanthroline appended glycoconjugate (L) and its Fe(ii)-complex were synthesized and characterized using analytical and spectral methods. The complexation of Fe2+ with L has been shown using absorption and fluorescence spectral studies. 1H NMR titration of L with Fe2+ supports that the phenanthroline moiety acts as the metal binding core. The interaction and binding of the Fe-complex with calf thymus DNA (ct-DNA) were studied using spectral techniques, such as UV-Vis absorption, circular dichroism (CD) and DNA melting temperatures. The corresponding data supported the minor groove binding of ct-DNA by the Fe-complex along with electrostatic interactions. The gel electrophoresis studies carried out using pBR322 plasmid showed a tight binding of the iron complex with the plasmid and this resulted in the condensation of the pBR322 plasmid as revealed by the blob-like structures observed in the atomic force microscopy data. The binding of the Fe-complex by WGA was demonstrated by absorption, fluorescence and CD spectra, and the microstructures were observed via scanning electron microscopy (SEM). Star-like nanostructures observed via SEM support that the octahedral iron complex connects the protein molecules in three dimensions through their carbohydrate terminal moieties. Thus, a new Fe-complex possessing a biocompatible glucosyl moiety interacts and binds to biomolecules, such as DNA and protein, and the resulting species are of importance in biological applications.
Coumarin-Calix[4]arene Conjugate-Anchored SiO2Nanoparticles as an Ultrasensor Material for Fe3+to Work in Water, in Serum, and in Biological Cells
Uttam B., Jahan I., Sen S., Rao C.P.
Article, ACS Omega, 2020, DOI Link
View abstract ⏷
A coumarin-appended calixarene derivative (CouC4A) and a hybrid material generated by covalently linking this onto a silica surface (CouC4A@SiO2) were synthesized and were characterized by various analytical, spectroscopy, and microscopy methods. Both these materials are capable of sensing Fe3+ with greater sensitivity and selectivity. The sensitivity is enhanced by 30,000 fold on going from a simple solution phase to the silica surface with the limit of Fe3+ detection being 1.75 ± 0.4 pM when CouC4A@SiO2 is used, and the sensing is partially reversible with phosphates, while it is completely reversible with adenosine 5′-triphosphate (ATP). While the calix precursor, CouC4A, has a limitation to work in water, anchoring this onto SiO2 endowed it with the benefit of its use in water as well as in buffer and thereby extends its application toward Fe3+ sensing even in the biorelevant medium such as fetal bovine serum and human serum. The hybrid material is biocompatible and shows ∼90% cell viability in the case of MDA-MB231 and 3T3 cell lines. CouC4A@SiO2 functions as a reversible sensor for Fe3+ with the use of ATP in vitro as well as in biological cells. Thus, the inorganic-organic hybrid material, such as, CouC4A@SiO2, is an indispensable material for sensitive and selective detection of Fe3+ in a picomolar range in solution and in nanomolar to micromolar range in biorelevant fluids and biological cells, respectively.
1,3-Di-naphthalimide Conjugate of Calix[4]arene as a Sensitive and Selective Sensor for Trinitrophenol and This Turns Reversible when Hybridized with Carrageenan as Beads
Narula A., Hussain M.A., Upadhyay A., Rao C.P.
Article, ACS Omega, 2020, DOI Link
View abstract ⏷
A fluorescent naphthalimide conjugate of calix[4]arene (L1) has been synthesized and characterized. The selective and efficient detection of trinitrophenol (TNP) by L1 among nine other different nitroaromatic compounds was demonstrated using absorption and fluorescence spectroscopy. The minimum detection limit is 29 nM, which is the lowest reported so far by any conjugate of calixarene toward TNP. The fluorescence quenching is associated with a high Stern-Volmer constant of 3.3 ± 0.4 × 105 M-1. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data revealed a network structure with pores having a weighted average size of 0.66 ± 0.08 μm for L1. When incubated with TNP, the pores were filled with fibril structures, as supported by both SEM and TEM data. In order to demonstrate the real time applications, the L1 has been coated onto a Whatman filter paper and the imprint of TNP contaminated thumb has been detected upon physical contact. The 1HNMR titration and the studies carried out using the control molecule support the necessity of both the naphthalimide moiety and the calixarene platform for sensing. In order to mend L1 as a reversible sensor for TNP, the same is incorporated into carrageenan beads (L1@Cb) and the reversible sensing has been shown for three cycles by reusing the same material upon recovery followed by washing it. The solid-state detection of TNP has also been demonstrated using the lyophilized L1@Cb bead powder. The fluorescence intensity of L1 was quenched upon addition of solid TNP to the lyophilized bead powder of L1@Cb as studied by fluorescence microscopy. The computational studies show that one of the arms of the calixarene takes a bent conformation, and the 1:1 TNP complex of L1 is stabilized by exhibiting differential extents of hydrogen bonding interactions with the two arms owing to their conformational difference. The result of such complexation was already felt through the shifts observed in the experimentally measured 1HNMR spectra.
Copper-Based Metallogel of Bovine Serum Albumin and Its Derived Hybrid Biomaterials as Aerogel and Sheet: Comparative Study of the Adsorption and Reduction of Dyes and Nitroaromatics
Upadhyay A., Narula A., Rao C.P.
Article, ACS Applied Bio Materials, 2020, DOI Link
View abstract ⏷
This paper deals with the synthesis of a protein-inorganic hybrid hydrogel and its derived materials, including aerogel and sheet, and the demonstration of their application potentials. For this, a common and abundant protein, bovine serum albumin (BSA), and a copper salt were used in order to prepare a hydrogel by cross-linking the protein molecules using epichlorohydrin and embedding Cu2+ ions to give BSA_Cuhydrogel (1). When this material was lyophilized, it resulted in the product powder BSA_Cuaerogel (2); however, when dried under vacuum, it yielded a blue sheet material, BSA_Cusheet (3). All three of these biomaterials were characterized by spectroscopy and microscopy and further studied for three different applications, and the data were compared in order to establish the material vs property/activity relationship. The applications include (i) adsorption of organic dyes, (ii) reductive degradation of these dyes, and (iii) the reductive transformation of nitroaromatic compounds. The study revealed the efficient adsorption of the anionic and neutral dyes, while the adsorption of the cationic dye was much lower. The adsorption capacities (in mg/g) of Congo red followed the trend BSA_Cuaerogel (367 ± 6) > BSA_Cuhydrogel (274 ± 4) > BSA_Cusheet (204 ± 3). The comparison of the rate of reductive degradation of Congo red and methylene blue follows the same trend as that of the adsorption of the dyes. The reductive degradation was demonstrated for six cycles by reusing the recovered catalyst after every cycle. More than half a dozen nitroaromatics were studied for their reduction using BSA_Cuaerogel. In the case of p-nitrophenol, the rate of reduction follows the trend 2 > 1 > 3. Thus, this paper deals with a methodology to synthesize both a robust hydrogel incorporating metal ions and other derived protein-based biomaterials, viz., an aerogel and sheet, and a comparison of their activity toward the adsorption and degradation of dyes and nitroaromatics.
Porous, pH-Responsive, and Reusable Hydrogel Beads of Bovine Serum Albumin-Au Hybrid as Smart Nanofactories for the Removal of Organic and Inorganic Pollutants from Water: A Detailed Demonstration by Spectroscopy and Microscopy
Article, ACS Applied Materials and Interfaces, 2019, DOI Link
View abstract ⏷
The availability of potable water is one of the major concerns in many countries today. This brings in a need to design molecular scaffolds suitable for efficient adsorption of the contaminants present in water. In this paper, an unprecedented strategy is demonstrated in order to synthesize highly porous bovine serum albumin-Au (BSA-Au) beads and was employed for the removal of water contaminants. The beads stored in acidic medium (Bead a ) and in basic medium (Bead b ) selectively adsorb anionic and cationic species that includes organic dyes and inorganic species, respectively, by showing a pH-responsive behavior. This phenomenon bestowed the beads with the recyclability and reusability as demonstrated for eight cycles wherein almost 100% efficiency is retained by the beads without any deterioration. The porous nature of these beads is retained even after switching the pH for several cycles of adsorption-desorption processes as judged based by the SEM data. Thus, the reported beads are demonstrated for their selective and efficient removal of both organic and inorganic contaminants from water wherein the beads can be recycled by triggering pH changes that would also release the captured species. The biologically benign beads act as reusable smart nanofactories in the purification of water from industrial contaminants.
Role of Aromatic Moiety in the Probe Property toward Picric Acid: Synthesis, Crystal Structure, Spectroscopy, Microscopy, and Computational Modeling of a Knoevenagel Condensation Product of d -Glucose
Areti S., Bandaru S., Kandi R., Rao C.P.
Article, ACS Omega, 2019, DOI Link
View abstract ⏷
Molecular probes for picric acid (PA) in both solution and solid states are important owing to their wide usage in industry. This paper deals with the design and development of a glucosyl conjugate of pyrene (L1) along with control molecular systems, possessing anthracenyl (L2), naphtyl (L3), and phenyl (L4) moieties, via Knoevenagel condensation of 2,4-pentanedione with d-glucose. The selectivity of L1 toward PA has been demonstrated on the basis of fluorescence and absorption spectroscopy, and the species of recognition by electrospray ionization mass spectrometry. The role of the aromatic group in the selective receptor property has been addressed among L1, L2, L3, and L4. The structural features of the {L1 + PA} complex were established by density functional theory computations. L1 was demonstrated to detect PA in solid state selectively over other nitroaromatic compounds (NACs). To study the utility of L1 in film, cellulose paper strips coated with L1 were used and demonstrated the selective detection of PA. The observed microstructural features of L1 and its complex {L1 + PA} differ distinctly in both atomic force microscopy and scanning electron microscopy, all in the support of the complex formation. Thus, L1 was demonstrated as a sensitive, selective, and inexpensive probe for PA over several NACs by visual, spectral, and microscopy methods.
Calixarene-Assisted Pd Nanoparticles in Organic Transformations: Synthesis, Characterization, and Catalytic Applications in Water for C-C Coupling and for the Reduction of Nitroaromatics and Organic Dyes
Narkhede N., Uttam B., Rao C.P.
Article, ACS Omega, 2019, DOI Link
View abstract ⏷
A new type of ternary hybrid, Pd@MCM-Calix ox , based on mesoporous silica, calixarene conjugate, and Pd(0) nanoparticles (NPs) was synthesized by sacrificial oxidation of allylic calixarene conjugate eventually functionalized with mesoporous silica without using any external reducing agent. The role of the calix conjugate in the formation of Pd@MCM-Calix ox has been established. The hybrid, Pd@MCM-Calix ox , was characterized by different techniques to support the formation of well-dispersed Pd(0) NPs of 12 ± 2 nm size. The catalyst, Pd@MCM-Calix ox , has been proven to be a resourceful one in water in three different types of reactions, namely, Suzuki C-C cross coupling, reduction of both hydrophilic and hydrophobic nitroaromatic compounds, and reduction and degradation of cationic, anionic, and neutral organic dyes. The catalyst exhibited higher turnover frequencies for all these transformations even when a very low concentration of Pd-based catalyst was used. The Pd@MCM-Calix ox hybrid catalyst can be recycled several times without experiencing any significant loss in the activity. Also, the regenerated catalyst showed retention of well-spread Pd(0) species even after several catalytic cycles. The tetraallyl calixarene, allylCalix, conjugate acts as a reducing agent, also controls the size, and yields the well-dispersed Pd(0) NPs. The calix conjugate further provides a hydrophobic core in assisting the diffusion of hydrophobic substrates toward catalytic sites.
Hydrogel of the Supramolecular Complex of Graphene Oxide and Sulfonatocalix[4]arene as Reusable Material for the Degradation of Organic Dyes: Demonstration of Adsorption and Degradation by Spectroscopy and Microscopy
Article, ACS Omega, 2019, DOI Link
View abstract ⏷
Industrial modernization causes severe contamination of water resources due to which the presence of organic dyes poses a great threat to human life. To address this, we have synthesized a hydrogel GSCg using graphene oxide (GO), sulphonatocalix[4]arene (SC4a), and l-Cys by heating at 90 °C for 30 min and characterized by analytic, spectroscopy, and microscopy techniques. The GSCg possessing porous structure and adsorbs all three types of dyes, viz., eosin yellow (anionic), neutral red, and methylene blue (cationic), as shown by scanning electron microscopy, and the adsorption kinetics are addressed. The dye adsorbed by the gel (dye@GSCg) has been degraded by the treatment of Cu 2+ /N 2 H 4 , which regenerates the gel. The regenerated gel has been demonstrated for further cycles of adsorption followed by degradation. Alternatively, the degradation of the organic dyes was also demonstrated by an in situ approach by taking GO, SC4a, l-Cys, and the organic dye together and subjecting the mixture to hydrothermal conditions and the process leaves out free gel (GSCgd). This was proven to be true in the case of each of the 12 dyes studied individually and also for their mixture, supporting that this methodology can be employed for large scale purification of contaminated water with high efficiency. GSCgd was repeatedly used for the adsorption and degradation (with the use of Cu 2+ /N 2 H 4 ) cycles wherein the gel does not lose its adsorption capability even after several cycles. Therefore, {GO···SC4a} hybrid is a smart, sustainable, and reusable material suitable for the purification of water contaminated with industrial organic dye effluents.
Development of Nitrobenzoxadiazole-Appended Calix[4]arene Conjugate (L) for Selective Sensing of Trivalent Cr 3+ , Fe 3+ , and Al 3+ Ions in Solution and in the Solid State and Imaging MCF7 cells by { L + Al 3+ }
Dinda S.K., Upadhyay A., Polepalli S., Althaf Hussain M., Rao C.P.
Article, ACS Omega, 2019, DOI Link
View abstract ⏷
A nitrobenzoxadiazole (NBD)-appended calix[4]arene conjugate (L) possessing a cyclic core formed by connecting the 1,3-positions at the lower rim has been designed. The L has been developed as a receptor for the selective recognition of biologically and ecologically relevant trivalent metal ions, viz., Cr 3+ , Fe 3+ , and Al 3+ . The interaction and region of binding of these metal ions by the receptor L have been explored by isothermal titration calorimetry, spectroscopy, microscopy, and density functional theory (DFT) computational studies. The probe L itself exhibits weak fluorescence emission intensity, and the quantum yield is enhanced by ∼4-fold upon addition of the M 3+ ion due to the chelate enhanced fluorescence effect. Fluorescence enhancement also takes place in L when it interacts with M 3+ even in the solid state and in the MCF7 cancer cells. The binding constant (K b ) for M 3+ by L is ∼10 4 M -1 , supporting that these ions bind to L with moderate strength. The detection limit for all the three metal ions is as low as 4-5 μM. The 1 H NMR data reflects the region of binding of the M 3+ ion to L. The binding is further supported by DFT studies where the space filling structures evidently shows the binding core in L, and the M 3+ ion is buried in this core. As a result of this, the microscopy features are almost the same for L and {L + M 3+ }. The reversible utility of the sensor has been achieved by the addition of H 2 PO4- Based on the input-output information, a molecular logic circuit (INHIBIT logic gate) has been built, which will provide an electronic basis for designing a memory device by the concerned experts.
Fluorophoric Conjugate of N-Alkyl Naphthalimide in Sodium Dodecyl Sulfate As a Tunable and Sustainable Sensing System: Differential Sensing of Zn2+ and Al3+ and the Application of Its Zn2+ Complex in Detecting Dipicolinic Acid, a Component of Anthrax Bacterial Endospores
Article, Journal of Physical Chemistry C, 2019, DOI Link
View abstract ⏷
A naphthalimide-based fluorophore has been conjugated by an octyl chain on one side and an ethylenediamine ("en") moiety on the other to result in a conjugate (L1) that was adapted to exhibit selective ion sensing. Since L1 is not a receptor for metal ions in water or in organic solvents, this has been introduced into the self-assembly formed by the surfactant, i.e., sodium dodecyl sulfate (SDS), and its ion sensing was studied by varying the concentration of the SDS since it is known to form premicellar as well as micellar assemblies. Thus, the L1 was successfully converted to a specific, selective, and sustainable chemo-receptor system for Al3+ and Zn2+ with the support of such assemblies of SDS. The selectivity was among three trivalent and eight divalent ions studied. The ion recognition ability was dependent on the nature of the assembly of SDS formed and is efficient in the premicellar media. Both the Al3+ and Zn2+ were differentially recognized just by tuning the SDS concentration. The results were ratified by comparing with several control experiments. The excited-state lifetime measurements and the size of these assemblies measured by dynamic light scattering (DLS) reveal that at >4 mM SDS concentration (critical micellar concentration is 8 mM) the probe L1 is not accessible for any of the metal ions studied. The two other derivatives possessing a shorter (propyl, L2) and a longer (dodecyl, L3) alkyl chain showed that the L1 with an octyl chain performs much better at all the premicellar SDS concentrations. The Zn2+-bound assembly of L1 in 4 mM SDS was demonstrated for sensing the dipicolinic acid (DPA) which happens to be an endospore component of anthrax bacteria. This study was extended to several other carboxylic acid derivatives which would act as control molecular systems. Even in the DPA sensing, the assemblies possessing an octyl derivative stand out when compared to the propyl or the dodecyl derivatives.
Ratiometric Cu2+ Binding, Cell Imaging, Mitochondrial Targeting, and Anticancer Activity with Nanomolar IC50 by Spiro-Indoline-Conjugated Calix[4]arene
Nag R., Polepalli S., Althaf Hussain M., Rao C.P.
Article, ACS Omega, 2019, DOI Link
View abstract ⏷
A triazole-derivatized, spiro-indoline-linked, 1,3-di-derivative of calix[4]arene (L) has been synthesized to take advantage of its ion-binding capability in the ring-open form. Indeed, the spiro-indoline moiety is well known for its photochromic, acidochromic, and metallochromic properties. Therefore, the L has been explored for Cu2+ binding, cell imaging, and anticancer activity of the corresponding complex since Cu2+ complexes are known for such activity. The conversion from the closed to open form of L is expedited by light or proton, while the metal ion can open as well as stabilize it. The open form of L showed binding of Cu2+ ratiometrically as demonstrated by absorption and fluorescence spectroscopy. This leads to the formation of 1:1 complex with a binding constant of (6.9 ± 2.3) × 105 M-1, with the lowest detection limit being 1.9 nM. In the complex, the Cu2+ is bound by two triazole-N and two phenolic-O groups resulting in a distorted tetrahedral coordination core of CuN2O2 as demonstrated based on density functional theory studies. To form such coordination core, the arms underwent considerable changes in some of the dihedral angles. The binding of Cu2+ to L induces self-assembly of L by varying from simple particles to rodlike structures when bound to Cu2+. The on-off fluorescence intensity of L and its Cu2+-bound species are responsible for imaging cancer cells. The L shows red fluorescence in MDA-MB-231 cancer cells by targeting mitochondria as proved based on the colocalization study carried out using MitoTracker Green. While the L alone is nontoxic to cancer cells, the presence of Cu2+ brings cell death to an extent of 90% with an IC50 value of 165 nM by bringing a substantial quench in the fluorescence of L. A shift of population from G0/G1 and G2M phases to the Sub-G1 phase was observed as the concentration of the complex was increased, indicating cell death as studied by fluorescence-activated cell sorting. Thus, the present work clearly proved that a calix[4]arene functionalized at the lower rim with spiro-indoline moieities when complexed with Cu2+ acts as an efficient anticancer agent and is capable of imaging cancer cells.
Supramolecular Sensing of 2,4,6-Trinitrophenol by a Tetrapyrenyl Conjugate of Calix[4]arene: Applicability in Solution, in Solid State, and on the Strips of Cellulose and Silica Gel and the Image Processing by a Cellular Phone
Dinda S.K., Althaf Hussain M., Upadhyay A., Rao C.P.
Article, ACS Omega, 2019, DOI Link
View abstract ⏷
A calix[4]arene conjugate possessing a tetrapyrenyl moiety at its upper rim (R) is designed as a receptor for sensing trinitrophenol (TNP). To understand the role of the calix[4]arene platform and that of pyrenyl moieties in R, two other control molecules were synthesized. These are as follows: The one possessing a tetraphenyl moiety in place of tetrapyrenyl (R1) and the other one is a p-pyrenyl-hydroxy benzene (R2) that is devoid of the calix[4]arene platform. The R shows high sensitivity toward TNP in tetrahydrofuran (THF) over eleven other nitroaromatic compounds (NACs) studied by exhibiting large fluorescence enhancement and hence is selective to TNP over the other NACs studied. However, the control molecules R1 and R2 showed only marginal fluorescence enhancement, supporting the need of a calixarene platform and the presence of a tetrapyrenyl moiety in the receptor system for the selective sensing of TNP. Further, R1 and R2 are not suitable for sensing, since these exhibit similar fluorescence response over several NACs studied. The binding of TNP by R has been addressed by fluorescence titration and isothermal titration calorimetry. The nature of the complexation of TNP by R has been revealed by the computational calculations, wherein the data showed the entrapment of TNP by two adjacent pyrene moieties via Ï-πstacking interactions. Such host-guest complexation is expected to restrict the mobility of the pyrene moieties present in R. The reduction of the flexibility of the pyrenyl moieties of R upon TNP binding is evidenced by the 1H NMR spectral study, wherein this acts as an additional evidence for the complexation. In the present study, the sensing of TNP by R has been shown in THF solution, on the surface of silica gel and the cellulose paper to result in lowest detection limits (LODs) of 1.5, 3.5, and 6.5 μM, respectively. Even the solid mixture of R and TNP showed LOD of 2.1 μmol. Since R is expected to show supramolecular aggregation that is dependent on the guest species, the corresponding details were probed by microscopy techniques, using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy methods, and significant changes in the aggregation of R upon interaction with TNP were found. Such aggregation is responsible for the observed fluorescence enhancement. Thus, the tetrapyrenyl calix[4]arene conjugate (R) acts as a sensitive and robust platform for selective detection of TNP from a mixture of nitroaromatic compounds (NACs) wherein the fluorescence intensities can be imaged and managed by a cellular phone.
Interaction of the Zn2+ and Cu2+ complexes of terpyridine appended glucosyl-conjugate with wheat germ agglutinin and DNA
Dinda S.K., Upadhyay A., Hussain M.A., Rao C.P.
Article, Polyhedron, 2019, DOI Link
View abstract ⏷
The terpyridine appended glucosyl-conjugate ligand L and its complexes of Zn2+ (1) and Cu2+ (2) were synthesized and characterized by spectroscopy techniques. The changes in the absorption and fluorescence spectra of L in presence of Zn2+ and Cu2+ is supportive of interaction of L through terpyridyl metal binding core which was further confirmed by 1H NMR. The coordination and structural features emerged from the spectroscopy were used in order to optimize the structures of 1 and 2 by DFT computational calculations. The isolated complex 2 shows binding with ct-DNA through minor groove binding and intercalation modes and increases the thermal stability of ct-DNA by ∼20 °C. Due to the presence of Cu2+ in 2, this complex showed cleavage of the plasmid pBR322 through hydroxy radical formation. The presence of glucosyl moiety at both the ends of the complex 1 interacts with the WGA and imparts dendrimeric-like micro structures due to the protein aggregation as demonstrated by SEM.
Cytotoxicity of apo bovine α-lactalbumin complexed with La 3+ on cancer cells supported by its high resolution crystal structure
Yarramala D.S., Prakash P., Ranade D.S., Doshi S., Kulkarni P.P., Bhaumik P., Rao C.P.
Article, Scientific Reports, 2019, DOI Link
View abstract ⏷
Cancer remains one of the biggest threats to human society. There are massive demands for compounds to selectively kill cancerous cells. Earlier studies have shown that bovine α -lactalbumin made lethal to tumor cells (BAMLET) becomes cytotoxic against cancer cells in complex with oleic acid {Hoque, M. et. al., PLoSOne8, e68390 (2013)}. In our study, we obtained bovine α-lactalbumin complexed with lanthanum ion (La 3+ -B-α-LA) and determined its high resolution crystal structure. The natural calcium binding site of bovine α-lactalbumin is replaced by lanthanum. The La 3+ complex formation by B-α-apo-LA was also supported by various biophysical methods. Interestingly, our complex, La 3+ -B-α-LA exhibits much greater anticancer activity against breast cancer cells as compared to the reported BAMLET-oleic acid complex. This study shows that La 3+ -B-α-LA complex is preferentially more toxic to MCF-7 cells as compared to KB (oral cancer) and HeLa (cervical) cells, while almost non-toxic to the healthy cells that we studied. Our data indicates that the cytotoxicity of La 3+ -B-α-LA against cancer cells is through apoptotic path way. The higher anticancer activity of La 3+ -B-α-LA is attributable to the requisite structural changes induced in the protein by La 3+ binding as supported by the crystal structure of the complex.
Switching the ion selectivity from Fe3+ to Al3+ by a triazole-appended calix[4]arene-based amphiphile
Nag R., Vashishtha M., Rao C.P.
Article, ChemistrySelect, 2018, DOI Link
View abstract ⏷
A triazole appended benzaldehydic lower rim derivative of calix [4]arene (L) has been synthesized and was thoroughly characterized. In CH3CN solution, the L showed greater sensitivity for Fe3+ by a 5-fold increase in the absorbance and 37% quenching in the fluorescence intensity, by forming a 1:1 complex. The Fe3+ induces aggregation in L as studied by microscopy. The Langmuir film formed at the air-water interface was characterized by pressure-area isotherm and Brewster angle micrographs, both in the presence and absence of metal ions. The Langmuir films of pure L, {L+Al3+} and {L+Zn2+} were transferred onto H-terminated Si-wafer and characterized using Atomic Force Microscopy, contact angle, Grazing Incidence Fourier Transform Infrared Spectrscopy and X-ray Photoelectron Spectroscopy. The study resulted selective binding of Al3+ to the Langmuir film of L among the nine metal ions studied. Thus, the calix[4]arene-conjugate L is sensitive and selective to Fe3+ in acetonitrile solution whereas to Al3+ in Langmuir film and hence acts as an ion switch depending upon the physical state of L.
Wheat germ agglutinin modified magnetic iron oxide nanocomplex as a cell membrane specific receptor target material for killing breast cancer cells
Upadhyay A., Kandi R., Rao C.P.
Article, Journal of Materials Chemistry B, 2018, DOI Link
View abstract ⏷
Lectins are known for their specificity for carbohydrate binding. However, a few specific carbohydrate residues are over expressed in cancer cells, which may be an advantage for using a lectin that is specific to such residues. Herein, we report the strategic design of wheat germ agglutinin (WGA) and a fluorescent torch, FITC immobilized on Fe3O4 NPs as a cell membrane specific receptor target for breast cancer cells, viz., MCF-7 and MDA-MB-231. The resultant nanocomplexes were well characterized by using microscopy and spectroscopy. The WGA tagged nanocomplex was further loaded with the anticancer drug 5-fluorouracil (5-FU) to selectively kill the cancer cells. The loading efficiency of 5-FU is ∼356 μg mg-1. The nanocomplex itself shows ∼90% cell viability for all the four cell lines (HEK, HeLa, MCF-7 and MDA-MB-231) studied and is therefore a suitable targeting drug delivery vehicle. However, the nanocomplex loaded with {WGA + 5-FU} shows a ∼1.5-fold decrease in cell viability in the case of specific cells (MCF-7 and MDA-MB-231) when compared to non-specific cells (HeLa and HEK). The internalization of the nanocomplex is supported by fluorescence microscopy and confocal laser scanning microscopy techniques by tracking with the fluorescent torch, FITC. The nanocomplex can be internalized ∼2 times more in the specific cells as compared to the non-specific cells. It is observed that the internalization is ∼2 fold increased when the MDA-MB-231 cells are exposed to a magnetic field for 24 h as compared to in the absence of a magnetic field. Live-dead cell assay of the 5-FU loaded nanocomplex was done by propidium iodide (PI) staining. There is an increase in the cell death by ∼2.5 fold when the cells are under a magnetic field as measured from the PI uptake. Such strategic designing of the nanocomplex can lead to the development of a better method to selectively target and kill the cancer cells by acting as a carrier to deliver a suitable drug, as a result of which the medical field can benefit.
Injectable, Self-Healing, and Stress Sustainable Hydrogel of BSA as a Functional Biocompatible Material for Controlled Drug Delivery in Cancer Cells
Upadhyay A., Kandi R., Rao C.P.
Article, ACS Sustainable Chemistry and Engineering, 2018, DOI Link
View abstract ⏷
Hydrogels have been used in the literature in tissue engineering, in drug delivery, and as enzyme biomimics. Herein, we report the synthesis of a functional biomaterial using BSA as scaffold and epichlorohydrin as cross-linker. The hydrogels reported in this paper were shown to exhibit tunable pore size as a function of BSA concentration by scanning electron microscopy (SEM) and, therefore, are well suited to encapsulate drug molecules for delivery applications. These are injectable, shear thinning, self-healing, and has the ability to withstand a physical weight of ∼300 times of its own. In trypsin medium, the gel is degraded by 50% in 36 h supporting that these are biodegradable. The loading of Dox by the gel was confirmed by the emission of red fluorescence and also by filling the pores by fibrillar structures as demonstrated by SEM. The controlled release of Dox occurs over 5 days to an extent of 37 ± 2%, 26 ± 0.5%, and 21 ± 1.5% in PBS at pH 5.5, 6.8, and 7.4 respectively. Since these hydrogels are made of BSA as matrix, their biocompatibility was proven by MCF-7, HeLa, and MDA-MB-231 cells wherein 95 ± 5% of cells are viable when treated with unloaded hydrogel. However, the Dox loaded hydrogel results in 70-80% of killing in the case of all three cancer cells. Fluorescence microscopy and FACS studies support controlled and time dependent release of Dox in MCF-7 cells for 24 h where the drug goes into cytoplasm initially and then into nucleus. The cell cycle analysis carried out using MCF-7 cells clearly showed that the cell death is due to apoptosis, and this is by arresting the G2/M phase as a function of time. All of the data supports the utility of the synthesized BSA hydrogel as a biomaterial that will find application in controlled drug delivery.
Silica-Calix Hybrid Composite of Allyl Calix[4]arene Covalently Linked to MCM-41 Nanoparticles for Sustained Release of Doxorubicin into Cancer Cells
Narkhede N., Uttam B., Kandi R., Rao C.P.
Article, ACS Omega, 2018, DOI Link
View abstract ⏷
An inorganic-organic hybrid material, MCM-allylCalix, was synthesized by covalent modification of an MCM-41 surface with a tetra-allyl calixarene conjugate. The synthesized hybrid was characterized by 13C and 29Si MAS-NMR, Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller surface area, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) analyses. The application of this MCM-allylCalix hybrid has been demonstrated for loading and in vitro release of doxorubicin (Dox) in phosphate-buffered saline (PBS) buffer as well as in the cancer cells, viz., MCF7, HeLa, and MDA-MB231. The Dox-loaded hybrid, MCM-allylCalix-Dox, was characterized by TEM, FT-IR, TGA, N2 sorption, diffuse refectance spectroscopy-UV, and fluorescence microscopy to confirm the presence of the drug. The release study of the drug from MCM-allylCalix-Dox was carried out in PBS buffer at pH 5 and 7.4. The results showed ∼140% increase in the release of Dox at pH 5 compared to that at pH 7.4 in 144 h, suggesting a pH-triggered release of the drug. MCM-allylCalix-Dox releases a greater amount of Dox compared to that released from unmodified MCM-Dox. Cytotoxicity studies suggested that MCM-allylCalix-Dox exhibits anticancer activity that is dependent on the nature of the cell. The Dox-loaded hybrid shows more cytotoxicity for MCF7 compared to that for the HeLa and MDA-MB231 cells. This was further supported by ∼120% more internalization of Dox into MCF7 cells compared to that in the other two cell lines. Both fluorescence microscopy and fluorescence-activated cell sorting studies suggested concentration-dependent internalization of Dox into the MCF7 and HeLa cells. The results suggested that the inorganic-organic hybrid can be useful in sustained drug delivery into cancer cells.
Host-Guest Complexation of a Lipoic Acid Conjugate of Calix[4]arene with Pyridinium Moiety on Gold Nanorods for Mitochondrial Tracking Followed by Cytotoxicity in HeLa Cells under 633 nm Laser Light
Nag R., Kandi R., Rao C.P.
Article, ACS Sustainable Chemistry and Engineering, 2018, DOI Link
View abstract ⏷
A new 1,3-lower rim-lipoic acid appended calix[4]arene (L) has been synthesized and characterized by different spectral techniques. Lipoic acid functionality helps L to anchor onto a noble metal surface, and in the present case these are the gold nanorods (GNRs). As the conjugate of calix[4]arene acts as a host due to the presence of its arene cavity, pyridinium containing guests have been explored to study their complexation, since the pyridinium containing molecules will accumulate in mitochondria in cells. The host-guest complexation has been explored in solution by 1H NMR, ESI-MS, UV-vis, and fluorescence spectral titration studies. The loading of host and the guest onto the GNR surface has been analyzed by spectroscopy and microscopy and found that their combination results in nanocomplexation. The presence of pyridinium functionality on the guest leads to targeted delivery to mitochondria of GNR nanocomposites as shown by confocal laser scanning microscopy imaging. The nanocomplex has been studied for cancer cell imaging and laser-induced cell killing with the help of plasmonic gold nanorods. When excited at the longitudinal SPR band of GNRs using laser (λ = 633 nm), cancer cell killing was observed due to laser-induced cell death. The flow cytometry studies supported ∼97% killing when the GNR-nanocomplex administered HeLa cells were irradiated under laser light for 10 min, which is a ∼4 fold increase in their cell as compared to the study carried out in the absence of laser light irradiation, and this has been partly attributed to the greater internalization of these into cells.
Fluorescent Lower Rim 1,3-Dibenzooxadiazole Conjugate of Calix[4]arene in Selective Sensing of Fluoride in Solution and in Biological Cells Using Confocal Microscopy
Uttam B., Kandi R., Hussain M.A., Rao C.P.
Article, Journal of Organic Chemistry, 2018, DOI Link
View abstract ⏷
p-tert-Butyl-calix[4]arene was derivatized by integrating a benzooxadiazole fluorescent tag into its 1,3-arms at the lower rim to result in L and was characterized. L was titrated with 17 anions in THF and found selective for F- ions with lowest detection limit of 109 ppb. L and F- form a 1:1 complex. L self-assembles in THF to result in sheet like structures which converts into smaller spherical particles upon addition of F-. The site of interaction of F- was deduced based on 1H NMR spectroscopy and the coordination features by density functional theory (DFT) computations wherein six noncovalent interactions of the type X-H···F (where X = O, N, or C) were noticed. The sensing of F- is reversible when titrated with Ca2+, and the reversibility was demonstrated for 10 cycles without losing sensitivity. The study has been extended to the biological cells using fluorescence and confocal microscopy. While L shows strong fluorescence in HeLa cells, increasing concentrations of F- exhibited greater fluorescence quenching. Thus, L acts as a good sensor for F- in solution as well as in biological cells, a rare and unique combination for a calixarene conjugate to exhibit such sensing behavior in dual media.
Inorganic-organic covalent hybrid of polyoxometalate-calixarene: Synthesis, characterization and enzyme mimetic activity
Narkhede N., Uttam B., Rao C.P.
Article, Inorganica Chimica Acta, 2018, DOI Link
View abstract ⏷
The inorganic-organic hybrid based on covalently attached trilacunary phosphotungstate and calixarene conjugate (POM-Calix hybrid) has been synthesized via facile click chemistry approach. The characterization studies showed that both the moieties are present together in the hybrid upon covalent modification. The morphology of the hybrid was studied by SEM, TEM and AFM analyses suggesting spherical shaped nanoparticles of 40–60 nm size for the hybrid. The POM-Calix hybrid was successfully employed to demonstrate peroxidase-like activity for the oxidation of the model substrate, viz., o-phenylenediamine (OPD), for the enzyme. The activity of the POM-Calix hybrid was ∼170% greater than that exhibited by simple POM and this is mainly attributed to the introduction of hydrophobic character by the covalently attached calixarene conjugate and the hydrophobicity is supported by the contact angle measurement. From the kinetic studies, the Michaelis constants, Km and Vmax were estimated to be 2.55 mM and 0.756 × 10−8 M s−1, respectively. It was observed that, the POM-Calix hybrid facilitates the formation of [rad]OH radicals when treated with H2O2 which eventually results in the oxidation of the substrate. The POM-Calix hybrid exhibits excellent enzyme-like activity over a wide pH range, which would enable its bio-applications at physiological conditions.
Drum Stick Seed Powder as Smart Material for Water Purification: Role of Moringa oleifera Coagulant Protein-Coated Copper Phosphate Nanoflowers for the Removal of Heavy Toxic Metal Ions and Oxidative Degradation of Dyes from Water
Article, ACS Sustainable Chemistry and Engineering, 2018, DOI Link
View abstract ⏷
Seed powder of vegetable drum stick (Moringa oleifera) is a household known material for the coagulation of impurities from water. We find from our lab experiments that this material indeed removes toxic inorganic heavy metal ions and organic dyes; however, the latter can be degraded in the presence of H2O2 under Cu2+ as catalyst. To understand the details of the treatment of water that is taking place by this seed powder, a simple inorganic-protein nanoflower system was developed using copper phosphate (CuP), and a low molecular weight, cationic, and coagulant protein of Moringa oleifera (MOCP), to result in the nanoflowers (NFs), CuPNF-MOCP. The CuPNF-MOCPs were synthesized at different ratios of inorganic versus protein components and characterized by spectroscopy and microscopy techniques. Both the time- and the protein concentration-dependent flower growth showed complete flower morphology within 24 h with tightly packed petals having smooth surface upon increasing the protein concentration as noticed from SEM. The anionic dyes were adsorbed more preferentially over the cationic ones by these NFs, due to the cationic charge present on MOCP, as understood by studying six different dyes of which three are anionic and three are cationic in nature. The dyes are oxidatively degraded by a Fenton-type mechanism that takes place between Cu2+ present in the NFs and added H2O2 with the generation of •OH radicals. These NFs also adsorb heavy metal ions, such as Pb2+, Cd2+, and Hg2+, with high selectivity of >99% for Pb2+. Upon adsorption of Pb2+, the surface of the NFs revealed needle-shaped structures at petal edges in their micrographs, where the needles were confirmed by elemental mapping, powder XRD, and energy dispersive X-ray spectroscopy. Thus, the water purification routinely carried out by the households using the drum stick seed powder is essentially due to the coagulant protein present in it. This has been demonstrated in the form of CuPNF-MOCP for scavenging toxic heavy metal ions and organic dyes from water sources. Hence, this study provides a lead for the purification of water in a sustainable manner.
Selective recognition of Zn2+ by a triazole linked thiophene-methylimine based derivative of calix[6]arene and the secondary sensing of biothiols by the corresponding zinc complex
Nehra A., Hinge V.K., Nag R., Rao C.P.
Article, Journal of the Indian Chemical Society, 2018,
View abstract ⏷
A 1,3,5-tris-triazole linked thiophene-methylimino appended calix[6]arene conjugate, L has been shown to bind to Zn2+ selectively in ethanol among the metal ions studied which include, alkali and alkaline earth ions, transition metal ions and lanthanides by fluorescence, absorption and ESI-MS. The conjugate, L exhibited ~25 fold increase in its fluorescence intensity at λem = 450 nm in presence of Zn2+ upon exciting at 330 nm with a limit of detection of 25±4 ppb while the Ka is (2.31±0.1)×105 M-1. The control molecules, C1 and C2 which lack iminophenolic core and calix[6]arene platform respectively have been studied. These do not show considerable changes in their fluorescence emission in presence of Zn2+ implying the essential role of both the arene cavity as well as the role of the three arms to bind to Zn2+. Absorption studies further support the binding of Zn2+ to L by exhibiting isosbestic points at 294 and 344 nm and stoichiometry of the 1:1 complex formed between L and Zn2+ was confirmed by ESI-MS. The computationally optimized structure of {L+Zn2+} complex exhibited distorted octahedral geometry about Zn2+ with N3O3 core. The in situ generated complex, {L+Zn2+} interacts with biologically relevant thiols by exhibiting fluorescence quenching of the complex due to the release of Zn2+ from its complex which is further supported by absorption and ESI-MS studies.
Physicochemical and Ion-Sensing Properties of Benzofurazan-Appended Calix[4]arene in Solution and on Gold Nanoparticles: Spectroscopy, Microscopy, and DFT Computations in Support of the Species of Recognition
Uttam B., Hussain M.A., Joshi S., Rao C.P.
Article, ACS Omega, 2018, DOI Link
View abstract ⏷
A calix[4]arene conjugate (L) functionalized at the lower rim with a benzofurazan fluorophore (NBD) and at the upper rim with a thioether moiety has been synthesized and characterized by 1H NMR, 13C NMR, and mass spectrometry techniques. Both the absorption and emission spectral data for L in different solvents exhibited progressive changes with an increase in polarity. Ion recognition studies were performed by absorption and fluorescence spectroscopy using 10 different metal ions. Among these, Hg2+ exhibited greater changes in these spectra, whereas Cu2+ showed only significant changes and all other ions showed no change in the spectral features. Although the Hg2+ has dominant influence on the spectral features and provides a detection limit of 56.0 ± 0.6 ppb, the selectivity was hampered because of the presence of the derivatizations present on both the rims of L for ion interaction in solution. Therefore, L was immobilized onto gold nanoparticles (AuNPL's) so that the upper rim derivatizations anchor onto the gold surface through Au-S interactions, and this leaves out only the lower rim NBD derivatization for interaction with ions selectively. The AuNPL's were characterized by transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The surface characteristics were analyzed by contact angle measurements. The AuNPL's exhibit greater selectivity and enhanced sensitivity for Hg2+ ions with a lowest detection limit of 48.0 ± 0.8 ppb. The immobilization of L onto AuNPs was reflected in the corresponding fluorescence lifetime values, and the addition of Hg2+ to either L or AuNPL showed fluorescence quenching. The reversible recognition of Hg2+ by L was demonstrated by titrating L or AuNPL with Hg2+ followed by tetra-butyl ammonium iodide for several cycles. The structural features of Hg2+-bound species were demonstrated by density functional theory computations and were supported by the XPS data. The Hg2+ induces aggregated fibrillar morphology into supramolecular L, as demonstrated by microscopy when Hg2+ was added either to L or to AuNPL, supporting aggregation-caused quenching.
Integrating glucosyl moiety with the reporting group through linker resulting in conjugates suitable for ion and molecular recognition: Critical analysis of our own demonstrations
Article, Trends in Carbohydrate Research, 2017,
View abstract ⏷
This perspective article prepared based on the doctoral thesis work of one of the authors mainly focuses to provide a comprehensive and comparative view of designing glucosyl-based molecular systems possessing binding cores to act as receptors for ions and molecules in solution and on solid surface and to provide cellular imaging in demonstrating their practical applicability.
A Bimodal, Cationic, and Water-Soluble Calix[4]arene Conjugate: Design, Synthesis, Characterization, and Transfection of Red Fluorescent Protein Encoded Plasmid in Cancer Cells
Samanta K., Ranade D.S., Upadhyay A., Kulkarni P.P., Rao C.P.
Article, ACS Applied Materials and Interfaces, 2017, DOI Link
View abstract ⏷
A new bimodal fluorescent cationic calix[4]arene (L1) conjugate has been synthesized in multiple steps and well characterized by NMR and electrospray ionization-mass spectrometry (ESI-MS) techniques. L1 has been investigated for its DNA binding ability by various spectroscopy techniques like absorption, fluorescence, and circular dichroism (CD). The formation of L1-DNA complex has been confirmed by the gel electrophoresis in the presence of incremental concentration of L1. To visualize the packing of the plasmid (pBR322), detailed tapping mode atomic force microscopy study has been performed, which revealed blob-like structure of plasmid upon addition of the incremental amount of L1. Concentration dependent transfection ability of L1 has been established in MCF-7 cells by confocal microscopy by carrying the red fluorescent protein (RFP) encoded plasmid pCMV-tdTomato-N1 to emit both intrinsic fluorescence of L1 as well as that from RFP. All this has been possible in the absence of any adjuvant phospholipids (DOPE) that are commonly used as helper. Further transfection efficiency of L1 has been compared with the commercially available lipofectamine (LTX) in two cancer cell lines, MCF 7 and SH-SY5Y, and found that the L1 is as efficient as that of LTX. Hence, L1 is an efficient and effective cargo to transport genetic material into the cells.
Green Synthesis of Protein-Protected Fluorescent Gold Nanoclusters (AuNCs): Reducing the Size of AuNCs by Partially Occupying the Ca2+ Site by La3+ in Apo-α-Lactalbumin
Yarramala D.S., Baksi A., Pradeep T., Rao C.P.
Article, ACS Sustainable Chemistry and Engineering, 2017, DOI Link
View abstract ⏷
In this paper, we report the studies relevant to controlling the size of protein-protected gold nanoclusters (AuNCs). In order to demonstrate this, we have chosen bovine apo α-Lactalbumin (apo-α-LA), which has a specific binding site for Ca2+, and La3+ occupies this position when apo-α-LA is treated with lanthanum trichloride. When the Apo-α-LA is treated with Au3+, it results in the formation of a protein-coated Au10 nanocluster where the protein reduces Au3+ to Au0 and protects the nanoclusters (apo-α-LA-AuNCs) which are luminescent. In these protein-protected luminescent gold nanoclusters, the protein is involved both in reduction as well as protection, thereby supporting green synthesis. As La3+ occupies the Ca2+ site in apo-α-LA, the size of AuNCs formed is reduced to smaller than the Au10, where the size is dependent on the extent to which La3+ is bound to the protein with a concomitant increase in luminescence. The apo-α-LA-AuNCs and the same formed in the presence of different concentrations of La3+-bound protein were all characterized by analytical, spectral, and microscopy techniques. Control of the size of AuNCs formed was also studied by using Gd3+ instead of La3+ and found similar results. In particular, the size variation of AuNCs was clearly demonstrated by MALDI-TOF-MS and HRTEM. Thus, the apo-α-LA protein-coated gold nanocluster is a useful green material for suitable applications.
Tuning glycoconjugates to acquire selectivity for toxic Hg2+ ion
Article, Trends in Carbohydrate Research, 2016,
View abstract ⏷
The development of probes for Hg2+ ion has been an active area of research in recent years because of the ill effects of this ion on the human health and environment. Hence the probe that needs to be developed should be sensitive as well as biologically compatible. This review mainly focuses to provide a comprehensive and comparative view of advances reported over the past ten years of literature, including our own contributions, in the design and application of the carbohydrate-based conjugates as fluorescent sensors for mercury. Therefore, this review covers aspects, such as, Hg2+ ion recognition, sensing and complexation by carbohydrate conjugates addressed using different spectral techniques and their critical analysis in a comparative manner.
A Bifunctional Thioether Linked Coumarin Appended Calix[4]arene Acquires Selectivity Toward Cu2+ Sensing on Going from Solution to SAM on Gold
Article, ACS Applied Materials and Interfaces, 2016, DOI Link
View abstract ⏷
A bifunctional calix[4]arene molecule bearing coumarin moiety on the lower rim and thioether moiety on the upper rim (L1), has been synthesized and well characterized by 1H, 13C NMR and mass spectrometry. Suitably functionalized coumarin moieties are well suited for selective recognition of various cations and anions. Among the 10 different metal ions studied, only Cu2+ and Fe3+ exhibit appreciable changes in the absorption spectra owing to the availability of functional moieties present at both the lower as well as the upper rim of free L1 in acetonitrile solution. To bring better selectivity, we blocked one of these functional moieties by coating on to a surface so that only the other one is exposed to the environment for sensing. Such a study carried out in the present case using the self-assembled monolayer (SAM) of L1 on Au(111) resulted in selective sensing of Cu2+ over several other metal ions as studied by surface plasmon resonance (SPR). The SAM of L1 on Au(111) was confirmed by different techniques, such as grazing incidence FT-IR, contact angle measurement, cyclic voltammetry and scanning tunneling microscopy. Thus, L1 is proven to be a suitable sensor for Cu2+ when attached to gold surface
Peroxidase-like Catalytic Activity of Copper-Mediated Protein-Inorganic Hybrid Nanoflowers and Nanofibers of β-Lactoglobulin and α-Lactalbumin: Synthesis, Spectral Characterization, Microscopic Features, and Catalytic Activity
Article, ACS Applied Materials and Interfaces, 2016, DOI Link
View abstract ⏷
A free Cys-SH-containing protein, β-lactoglobulin (β-LG), and another protein not possessing the same, viz., apo-α-lactoglobulin (apo-α-LA), were used in studies to demonstrate the role of this amino acid, along with its secondary structure, in the formation of a protein dimer and a protein-inorganic hybrid nanoflower and in the creation of the peroxidase-like activity of the nanomaterials produced when the proteins were treated with varying Cu2+ concentration under different pH conditions. An increase in the pH as well as the Cu2+ mole ratio results in increasing dimer formation in case of β-LG due to the presence of free Cys121-SH, while the dimer is not formed in case of apo-α-LA under the same conditions. The role of Cys in the dimer formation has been demonstrated both by MALDI and sodium dodecyl sulfate-polyacrylamide gel electrophoresis studies. Both of the proteins exhibited changes in their secondary structures to different extents as a function of pH, and the structures were stabilized by Cu2+ interactions, as studied by CD and fluorescence spectroscopy. The small and spherical nanoparticles formed at pH 7 with lower equivalents of Cu2+ join together to form larger aggregates at higher equivalents of Cu2+. For the same concentration at pH 9, both the aggregates and the nanoflowers were noticed. However, at pH 12, the Cu2+ binding induces the formation of fibers along with the flowers. Both the nanoflowers and nanofibers exhibited peroxidase-like activity in a catalytic manner. Nanoflowers were also shown to detect phenol in the concentration range from 10 to 200 μM. The copper-induced nanobiomaterial obtained in the case of apo-α-LA also exhibited peroxidase-like activity. Thus, this paper deals with the green synthesis of copper-induced protein (β-LG/apo-α-LA)-inorganic hybrid nanomaterials that are important due to their applications as nanobiomaterials.
Structure of a di-zinc complex of a bis-calix[4]arene conjugate and its sensing of cysteine among the amino acids
Mummidivarapu V.V.S., Pathak R.K., Rao C.P.
Article, Supramolecular Chemistry, 2016, DOI Link
View abstract ⏷
A triethylene glycol di-imine locked triazole linked bis-calix[4]arene conjugate (L) and its Zn2+ complex [Zn2L], were synthesised, characterised and the three-dimentional (3-D) structure of the complex was established by single crystal XRD. In this complex, the Zn2+ centre exhibits distorted tetrahedral geometry with N2O2 binding core. The complex showed selectivity towards cysteine (Cys) with greater sensitivity followed by histidine (His) among the naturally occurring amino acids studied based on fluorescence and absorption spectroscopy. The fluorescence quenching of the complex is much greater with Cys as compared to that of His. The detection limit of Cys is 650 ppb. Release of Zn2+ from its complex [Zn2L] followed by its capture by -SH containing molecules was shown based on absorption and emission spectroscopy. This was also shown in one case by 1H NMR spectroscopy.
Differential Recognition of Anions with Selectivity towards F−by a Calix[6]arene–Thiourea Conjugate Investigated by Spectroscopy, Microscopy, and Computational Modeling by DFT
Nehra A., Bandaru S., Yarramala D.S., Rao C.P.
Article, Chemistry - A European Journal, 2016, DOI Link
View abstract ⏷
Anion recognition studies were performed with triazole-appended thiourea conjugates of calix[6]arene (i.e., compound6L) by absorption and1H NMR spectroscopy by using nineteen different anions. The composition of the species of recognition was derived from ESI mass spectrometry. The absorption spectra of compound6L showed a new band at λ=455 nm in the presence of F−due to a charge transfer from the anion to the thiourea moiety and the absorbance increases almost linearly in the concentration range 5 to 200 μm. This is associated with a strong visual color change of the solution. Other anions, such as H2PO4−and HSO4−, exhibit a redshift of the λ=345 nm band and the spectral changes are associated with the formation of an isosbestic point at λ=343 nm.1H NMR studies further confirm the binding of F−efficiently to the thiourea group among the halides by shifting the thiourea proton signals downfield followed by their disappearance after the addition of more than one equivalent of F−. The other anions also showed interactions with compound6L, however, their binding strength follows the order F−>CO32−>H2PO4−≈CH3COO−>HSO4−. The NMR spectral changes clearly revealed the anion-binding region of the arms in case of all these anions. The anion binding to compound6L indeed stabilizes a flattened-cone conformation as deduced based on the calix-aromatic proton signals and was further confirmed by VT1H NMR experiments. The stabilization of the flattened-cone conformation was further augmented by the interaction of the butyl moiety of the nBu4N+counterion. The structural features of the anion-bound species were demonstrated by DFT computations and the resultant structures carried the features that were predicted based on the1H NMR spectroscopic measurements. In addition, SEM images showed a marigold flower-type morphology for compound6L and this has been transformed into a chain-like structure of connected spherical particles in the presence of F−. The anion-induced microstructural features are reflective of the binding strength, size, and shape of the anions. The binding strengths of the anions by compound6L were further compared with that of compound4L, a calix[4]arene analogue of compound6L, in order to address the role of the number of arms built on the calixarene platform based on absorption spectroscopy,1H NMR spectroscopy, and DFT computations and it was found that compound6L is a better receptor for F−, which extends its interactions from all the three arms.
A 1,3-Capped Calix[4] Conjugate Possessing an Amine Moiety as an Anion Receptor: Reversible Anion Sensing Detected by Spectroscopy and Characterization of the Supramolecular Features by Microscopy
Nehra A., Yarramala D.S., Rao C.P.
Article, Chemistry - A European Journal, 2016, DOI Link
View abstract ⏷
A phenylenediamine-capped conjugate of calix[4]arene (Lamino) was synthesized by reducing its precursor, Limino, with sodium borohydride in methanol. The Laminosample binds to anions due to the more flexible and bent conformation of the capped aminophenolic binding core, compared to the precursor Limino. The Laminosample showed selectivity towards H2PO4−by exhibiting a ratiometric increase in emission by about 11-fold with a detection limit of (1.2±0.2) μm ((116±20) ppb) over 15 anions studied, including other phosphates, such as P2O74−, adenosine monophosphate (AMP2−), adenosine diphosphate (ADP2−), and adenosine triphosphate (ATP2−). The Laminosample shows an increase in the absorbance at λ=315 nm in the presence of H2PO4−, CO32−, HCO3−, CH3CO2−, and F−. The1H NMR spectroscopic titration of Laminowith H2PO4−, F−, and CH3CO2−showed major changes in the phenylene-capped and salicyl moieties, and thereby, confirming the aminophenolic region as the binding core. However, the binding strength of these anions followed the trend H2PO4−>F−≫CH3CO2−>HSO4−. The heat changes observed by isothermal titration calorimetry support this trend. The Laminosample showed reversible sensing towards H2PO4−and F−in the presence of Mg2+and Ca2+, respectively. NOESY studies of Lamino, in comparison with its anionic complexes, revealed that major conformational changes occurred in the capping region to facilitate the binding of anion. ESI-MS and the Job's method revealed 1:1 stoichiometry between Laminoand H2PO4−or F−. In the SEM micrographs of Lamino, the spherical particles are converted into spherical aggregates and further form large agglomerates and even branched sheets in the presence of anions, depending upon their binding strength.
Selenocysteine vs Cysteine: Tuning the Derivatization on Benzenesulfonyl Moiety of a Triazole Linked Dansyl Connected Glycoconjugate for Selective Recognition of Selenocysteine and the Applicability of the Conjugate in Buffer, in Serum, on Silica Gel, and in HepG2 Cells
Areti S., Verma S.K., Bellare J., Rao C.P.
Article, Analytical Chemistry, 2016, DOI Link
View abstract ⏷
A dansyl derivatized triazole linked glucopyranosyl conjugate (NO2L) has been synthesized and characterized and was used in the present study. The conjugate NO2L releases a fluorescent product upon reaction by Cys-SeH in aqueous PBS buffer by exhibiting a ∼210-fold fluorescence enhancement even in the presence of 20 other amino acids with a minimum detection limit of (1.5 ± 0.2) × 10-7 M. The selectivity of the Cys-SeH to NO2L was further proven by extending the fluorescence study to different other selenium compounds. The role of para-nitrobenzenesulfonyl (pNBS) center in NO2L in the selective recognition of Cys-SeH was confirmed when the fluorescence emission studies were carried out using five different derivatizations possessing two NO2, five fluoro, two fluoro, one fluoro, and no fluoro groups. The nucleophilic substitution reaction of Cys-SeH on NO2L has been clearly demonstrated on the basis of 1H NMR, ESI-MS, and absorption spectroscopy, and the heat changes were monitored by isothermal titration calorimetry. The application potential of NO2L has been demonstrated by studying its selectivity toward Cys-SeH in aqueous PBS buffer, in bovine serum, and on the silica gel surface that lead to minimum detection limits of (25 ± 2), (80 ± 5), and (168 ± 16) ppb, respectively. The biological applicability of NO2L for Cys-SeH was further demonstrated in HepG2 cells by fluorescence microscopy. Thus, NO2L is aqueous soluble and a biologically acceptable probe for Cys-SeH.
Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn2+, Cd2+, and Hg2+ Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn2+ and the Structure of the Complex Using DFT
Areti S., Bandaru S., Rao C.P.
Article, ACS Omega, 2016, DOI Link
View abstract ⏷
A water-soluble triazole-linked quinoline conjugate of glucopyranose (L) has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of L toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate L detects Zn2+ and Cd2+ with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg2+, only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn2+ and Cd2+ resulting in [Zn(L)2] and [Cd(L)2], and it is 1:1 in the case of Hg2+, as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn2+ shows greater exothermicity over Cd2+, whereas Hg2+ shows endothermicity, which supports the differences in their binding strength and the nature of the corresponding complex. L exhibits rod-shaped particles and upon complexation with Zn2+, it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd2+, whereas the [HgL] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the syn-[Zn(L)2] complex is stabilized by 9.7 kcal mol-1 more than that in the case of anti-[Zn(L)2] owing to the formation of hydrogen bonds between the two glucosyl moieties within the syn-complex. Among the anions studied, [Zn(L)2] is sensitive and selective toward the phosphate ion (H2PO4-) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [HgL] can act as a secondary sensor for CN- while also exhibiting reversibility. Based on the input-output characteristics, INHIBIT logic gate was built in the case of Zn2+ vs H2PO4- and IMPLICATION logic gate was built in the case of Hg2+ vs CN-.
Green synthesis, characterization and anticancer activity of luminescent gold nanoparticles capped with apo-α-lactalbumin
Yarramala D.S., Doshi S., Rao C.P.
Article, RSC Advances, 2015, DOI Link
View abstract ⏷
A green synthesis was developed in order to prepare protein coated gold nanoparticles using a metal free, α-helical protein, i.e., apo-α-LA, that acts as both the reducing as well as stabilizing agent to result in Au0 nanoparticles from Au3+ which are luminescent and hence can be used for biological imaging, including of cells. The nanoparticles, apo-α-LA-AuNPs, thus synthesized were characterized by multiple techniques, such as, analytical, spectral, microscopy and light scattering, in order to support the presence of NPs in terms of their size and shape, involvement of Au0 and the protein encapsulation and its structural changes upon coating. The 10-16 nm sized apo-α-LA-AuNPs were shown to be non-toxic to healthy cells as studied using normal mouse fibroblast cells (L929). Having found that these NPs are biocompatible and possess structurally altered apo-α-LA protein, the luminescent apo-α-LA-AuNPs were demonstrated to have cytotoxicity towards cancer cells as studied by cell viability tests as well as fluorescence microscopy. While these NPs kill ∼75% of MCF-7 cells, at the same concentration these are capable of killing only ∼30% of HeLa cells, thus exhibiting cell dependency. The present study clearly demonstrates the advantage of the luminescent apo-α-LA-AuNPs in their attack of cancer cells in general and selective killing of breast cancer cells in particular. Thus coating AuNPs with the protein apo-α-LA enhanced their anticancer activity several fold. This journal is
Zn2+ and Cu2+ induced nanosheets and nanotubes in six different lectins by TEM
Article, RSC Advances, 2015, DOI Link
View abstract ⏷
Self assembly of biomolecules is important not only in unravelling the fundamental aspects of biology but also in exhibiting their supramolecular structures wherein the self assembly acts as a basic principle. Therefore, proteins having different side chains and structures with varying binding affinities towards metal ions can certainly be manifested in generating myriad supramolecular structures. In order to demonstrate this, we have chosen several β-sheet lectins, such as, Horse gram lectin (DBL), Pisum sativum agglutinin (PSA), Wheat germ agglutinin (WGA), Allium sativum agglutinin also known as garlic lectin (ASA) and Concanavalin A (Con A) lectin, in conjunction with Zn2+ and Cu2+ as biologically important ions and showed that these form nanostructures, such as, open-, rolled- and stacked sheets, and tubes. The Zn2+ induces mainly the sheets in the lectins studied so far though some of these are thin and others are thick, while some are folded and others are not. However, Cu2+ induces mainly tubes in ASA and DBL, predominantly sheets in Con A and a mixture of tubes and sheets in PSA and WGA as shown by TEM and supported by SEM. The tubes formed were thick as well as thin, solid as well as hollow in nature, straight, cylindrical as well as twisted and ribbon shaped. Plasmid PBR322 treated nanostructures formed from PSA in the presence of Cu2+ showed the presence of the plasmid in the corresponding tubes and sheets. These nanostructures are unprecedented and could lead to major advances in biomaterials science by providing potential applications. This journal is
Binding and ratiometric dual ion recognition of Zn2+ and Cu2+ by 1,3,5-tris-amidoquinoline conjugate of calix[6]arene by spectroscopy and its supramolecular features by microscopy
Mummidivarapu V.V.S., Bandaru S., Yarramala D.S., Samanta K., Mhatre D.S., Rao C.P.
Article, Analytical Chemistry, 2015, DOI Link
View abstract ⏷
Lower rim amide linked 8-amino quinoline and 8-amino naphthalene moiety 1,3,5-triderivatives of calix[6]arene L1 and L2 have been synthesized and characterized. While the L1 acts as a receptor molecule, the L2 acts as a control molecule. The complexation between L1 and Cu2+ or Zn2+ was delineated by the absorption and electrospray ionization (ESI) MS spectra. The binding ability of these molecules toward biologically important metal ions was studied by fluorescence and absorption spectroscopy. The derivative L1 detects Zn2+ by bringing ratiometric change in the fluorescence signals at 390 and 490 nm, but in the case of Cu2+, it is only the fluorescence quenching of 390 nm band that is observed, while no new band is observed at 390 nm. The stoichiometry of both the complexes is 1:1 and was confirmed in both the cases by measuring the ESI mass spectra. The isotopic peak pattern observed in the ESI MS confirmed the presence of Zn2+ or Cu2+ present in the corresponding complex formed with L1. Among these two ions, the Cu2+ exhibits higher sensitivity. The density-functional theory (DFT) studies revealed the conformational changes in the arms and also revealed the coordination features in the case of the metal complexes. The arm conformational changes upon Zn2+ binding were supported by nuclear Overhauser effect spectrometry (NOESY) studies. The stronger binding of Cu2+ over that of Zn2+ observed from the absorption study was further supported by the complexational energies computed from the computational data. While the L1 exhibited spherical particles, upon complexation with Cu2+, it exhibits chain like morphological features in scanning electron microscopy (SEM) but only small aggregates in the case of Zn2+. Thus, even the microscopy data can differentiate the complex formed between L1 and Cu2+ from that formed with Zn2+.
Coumarine-imino-C2-glucosyl conjugate as receptor for Cu2+ in blood serum milieu, on silica gel sheet and in Hep G2 cells and the characterization of the species of recognition
Areti S., Khedkar J.K., Bandaru S., Teotia R., Bellare J., Rao C.P.
Article, Analytica Chimica Acta, 2015, DOI Link
View abstract ⏷
A coumarine-imino-C2-glucosyl conjugate (L) was synthesized and characterized. The conjugate L is found to recognize Cu2+ in aqueous HEPES buffer by exhibiting a 95% fluorescence quenching in pH range 7-10 even in the presence of several biologically and ecologically relevant metal ions. Fluorescence on-off behavior has been clearly demonstrated on the basis of the binding variability of Cu2+ to L. The binding has been elicited through the changes observed in fluorescence, absorption, ESI-MS and 1H NMR titrations. All the other thirteen metal ions studied did not show any change in the fluorescence emission. These ions do not interfere with the recognition of Cu2+ by L. The structural features of [CuL]2 complex in both the isomeric forms were established by DFT computational calculations. The utility of L has been demonstrated by showing its sensitivity toward Cu2+ on a thin layer of silica gel. The L gives sensitive fluorescence signals for Cu2+ even in blood serum and exhibits appropriate fluorescence responses in living cells.
Versatile, reversible, and reusable gel of a monocholesteryl conjugated calix[4]arene as functional material to store and release dyes and drugs including doxorubicin, curcumin, and tocopherol
Bandela A.K., Hinge V.K., Yarramala D.S., Rao C.P.
Article, ACS Applied Materials and Interfaces, 2015, DOI Link
View abstract ⏷
Gels are interesting soft materials owing to their functional properties leading to potential applications. This paper deals with the synthesis of monocholesteryl derivatized calix[4]arene (G) and its instantaneous gelation at a minimum gelator concentration of 0.6% in 1:1 v/v THF/acetonitrile. The gel shows remarkable thermoreversibility by exhibiting T<inf>gel?sol</inf> at ?48 °C and is demonstrated for several cycles. The gel shows an organized network of nanobundles, while that of the sol shows spherical nanoaggregates in microscopy. A bundle with ?12 nm diameter possessing hydrophobic pockets in itself is obtained from computationally modeled gel, and hence the gel is suitable for storage and release applications. The guest-entrapped gels exhibit the same microstructures as that observed with simple gels, while fluorescence spectra and molecular mechanics suggests that the drug molecules occupy the hydrophobic pockets. All the entrapped drug molecules are released into water, suggesting a complete recovery of the trapped species. The reusability of the gel for the storage and release of the drug into water is demonstrated for four consecutive cycles, and hence the gel formed from G acts as a functional material that finds application in drug delivery.
A Fluorescent 1,3-Diaminonaphthalimide Conjugate of Calix[4]arene for Sensitive and Selective Detection of Trinitrophenol: Spectroscopy, Microscopy, and Computational Studies, and Its Applicability using Cellulose Strips
Bandela A.K., Bandaru S., Rao C.P.
Article, Chemistry - A European Journal, 2015, DOI Link
View abstract ⏷
A new fluorescent 1,3-diaminonaphthalimide conjugate of calix[4]arene receptor (R) was synthesized and characterized. The receptor displays good selectivity towards trinitrophenol (TNP) over other explosive aromatic- and aliphatic-nitro compounds by exhibiting changes in its fluorescence emission. Receptor-coated cellulose paper strips are equally effective in terms of their selective detection of TNP over other aromatic- and aliphatic-nitro compounds. When used in solution or on cellulose paper strips, R can detect up to submicromolar concentration of TNP by exhibiting changes in its fluorescence emission and in its supramolecular structure upon interaction. Interestingly, the microscopy features of R, TNP, and {R+TNP} are quite distinct, indicating the interactions present between R and TNP, as studied by using AFM and TEM. Computationally modeled complexes of receptor with TNP and TNT show enormous difference in their interaction energies in the favor of TNP by showing the host-guest interaction of cation ⋯ anion type in the presence of TNP but not TNT. This is because the receptor adopts an "arms-open"-type structure in the case of the TNP complex, whereas it adopts an "arms-closed"-type structure in the presence of TNT. Both the experimental and the computational studies reveal that the receptor selectively binds to TNP over TNT. Thus, R-coated Whatman No.1 filter paper strips provide easy, rapid, and economical detection of trace amounts of TNP both by visual and spectral measurement. Open arms for TNP: A new fluorescent 1,3-diaminonaphthalimide conjugate of a calix[4]arene receptor (R) was synthesized and characterized. The receptor displays good selectivity towards trinitrophenol (TNP) over other explosive aromatic and aliphatic nitro compounds, like trinitrotoluene (TNT). R can detect up to submicromolar concentrations of TNP by exhibiting changes in its fluorescence emission and in its supramolecular structure upon interaction (see figure).
Pb2+ binding to lentil lectin and its influence on the protein aggregation
Thawari A.G., Tabbasum K., Hinge V.K., Rao C.P.
Article, RSC Advances, 2015, DOI Link
View abstract ⏷
Binding of Pb2+ to lentil lectin (LL) was studied by spectroscopy, microscopy and thermodynamics and the species were modelled by molecular dynamics (MD). The effect of pH on Pb2+ binding was studied at pH = 5 in acetate buffer and pH = 7.2 in Tris buffer. Based on ITC, multiple binding sites were found for Pb2+ at pH = 7.2. No binding is noticed at pH = 5. The MD results showed the involvement of aspartate and glutamate with hemi-directed geometry for Pb2+. Pb2+ mediated β sheet to α-helix transition was noticed at pH = 7.2. At physiological pH, morphological changes were observed in the reduction of size of the particles of LL (160 ± 30 nm) to those in {LL + Pb2+} (45 ± 10 nm) as derived based on AFM and TEM. In presence of Pb2+, the larger particles break down to smaller ones because of the coordination ability of Pb2+ towards carboxylate and imidazole moieties. At pH = 5, the TEM shows much higher aggregation than that observed at pH = 7.2 for the protein alone, leading to linear aggregated species which were further broken down by Pb2+ into smaller ones.
Differentiating Phosphates by an Mg2+ Complex of the Conjugate of Calix[4]arene via the Formation of Ternary Species and Causing Changes in the Aggregation: Spectroscopy, Microscopy, and Computational Modeling
Nehra A., Yarramala D.S., Hinge V.K., Samanta K., Rao C.P.
Article, Analytical Chemistry, 2015, DOI Link
View abstract ⏷
A phenylene diimine capped conjugate of 1,3-calix[4]arene (L) was synthesized and characterized, and its Mg2+ complex has been isolated and characterized. The chemo sensing ensemble of Mg2+ bound L provides distinguishable features of response toward phosphates, viz., HPO42-, P2O74-, and AMP2- (Set A) and H2PO4-, ATP2-, and ADP2- (Set B). While the Set A shows the formation of ternary complex, the Set B does not exhibit any intermediate complex, but both show the release of Mg2+ and L at different equivalents. The structures of {L + Mg2+} and its phosphate bound ternary complexes have been established by computational calculations, and the corresponding results agree well with the experimental ones. The microscopy studies show an aggregation-disaggregation phenomenon in the presence of different equivalents of phosphates in both of the sets. Using the fluorescence data, an INHIBIT logic gate has been built.
A water soluble glucopyranosyl conjugate as a selective and reactive probe for cysteine in a buffer and its application to living cells
Areti S., Teotia R., Rao C.P.
Article, Analyst, 2015, DOI Link
View abstract ⏷
A water soluble and biocompatible glucopyranosyl conjugate (L) has been synthesized and characterized by various techniques. The L has been employed to recognize Cys selectively among the naturally occurring amino acids in HEPES buffer at physiological pH. A minimum detection limit of 2.5 × 10-7 M was shown by L for Cys in the buffer at pH = 7.4. The reactivity of L towards biological thiols as demonstrated by emission and absorption is supported by the observed increase in the fluorescence intensity; however, Cys shows a maximum increase owing to its better nucleophilicity. The reactivity of Cys on L is demonstrated by 1H NMR, ESI MS, emission and absorption spectroscopy, and the formation of the binary complex was supported by ESI MS. The control molecular study revealed the necessity of the glyco-moiety to bring water solubility and biological adaptability. The cellular studies support that the conjugate L is biologically adaptable and shows effective intracellular fluorescence emission upon reacting with intracellular thiols.
Water-Soluble 8-Hydroxyquinoline Conjugate of Amino-Glucose As Receptor for La3+ in HEPES Buffer, on Whatman Cellulose Paper and in Living Cells
Areti S., Bandaru S., Teotia R., Rao C.P.
Article, Analytical Chemistry, 2015, DOI Link
View abstract ⏷
A water-soluble glucopyranosyl conjugate, L, has been synthesized and characterized by different analytical and spectral techniques. The L has been demonstrated to have switch-on fluorescence enhancement of ∼75 fold in the presence of La3+ among the nine lanthanide ions studied in the HEPES buffer at pH 7.4. A minimum detection limit of 140 nM (16 ± 2 ppb) was shown by L for La3+ in the buffer at physiological pH. The utility of L has been demonstrated by showing its sensitivity toward La3+ on Whatman filter paper strips. The reversible and reusable action of L has been demonstrated by monitoring the fluorescence changes as a function of the addition of La3+ followed by F- and HPO42- ions. The complexation of L by La3+ was shown by absorption spectra wherein isosbestic behavior was observed. The Jobs plot suggests a 2:1 complex between L and La3+, and the same was supported by ESI-MS. The control molecular study revealed the necessity of hydroxy quinoline and the amine group for La3+ ion binding and the glyco-moiety to bring water solubility and biocompatibility. The structural features of the [2L+La3+] complex were established by DFT computational calculations. The chemo-ensemble, [2L+La3+], is shown responsible for providing intracellular fluorescence imaging in HepG2 cells.
Optimizing the Electron-Withdrawing Character on Benzenesulfonyl Moiety Attached to a Glyco-Conjugate to Impart Sensitive and Selective Sensing of Cyanide in HEPES Buffer and on Cellulose Paper and Silica Gel Strips
Areti S., Bandaru S., Yarramala D.S., Rao C.P.
Article, Analytical Chemistry, 2015, DOI Link
View abstract ⏷
Dansyl-derivatized, triazole-linked, glucopyranosyl conjugates, 5FLOH, 2FLOH, 1FLOH, and 0FLOH were synthesized and characterized. While the 5FLOH acts as a molecular probe for CN-, 2FLOH, 1FLOH, and 0FLOH acts as control molecules. The reactivity of CN- toward 5FLOH has been elicited through the changes observed in NMR, ESI MS, emission, and absorption spectroscopy. The conjugate 5FLOH releases a fluorescent product upon reaction by CN- in aqueous acetonitrile medium by exhibiting an ∼125-fold fluorescence enhancement even in the presence of other anions. Fluorescence switch-on behavior has been clearly demonstrated on the basis of the nucleophilic substitution reaction of CN- on 5FLOH. A minimum detection limit of (2.3 ± 0.3) × 10-7 M (6 ± 1 ppb) was shown by 5FLOH for CN- in solution. All the other anions studied showed no change in the fluorescence emission. The utility of 5FLOH has been demonstrated by showing its reactivity toward CN- on a thin layer of silica gel as well as on Whatman No. 1 cellulose filter paper strips. The role of glucose moiety and the penta-fluorobenzenesulfonyl reactive center present in 5FLOH in the selectivity of CN- over other anions has been demonstrated by fluorescence, absorption and thermodynamics study. Similar studies carried out with the control molecules showed no selectivity for CN-. The mechanistic aspects of the reactivity of CN- toward 5FLOH were supported by DFT computational study.
Mercuration of apo-α-lactalbumin: Binding of Hg2+ followed by protein-mediated nanoparticle formation
Thawari A.G., Hinge V.K., Temgire M., Rao C.P.
Article, RSC Advances, 2014, DOI Link
View abstract ⏷
Nanoparticles and nanocrystals of mercury are formed when Hg2+ salt reacts with apo-α-lactalbumin (apo-α-LA). Reduction followed by nanoparticle formation is further augmented by the protein, as it also acts as a coating agent. The initial interaction of Hg2+ with apo-α-LA was demonstrated by changes observed in absorption, emission, and CD spectroscopy, where the latter technique also detected structural changes in the protein. Such structural changes are expected when Hg2+ binds to the protein, and therefore, the binding was determined by isothermal titration calorimetry (ITC). The binding was further proven by MALDI, which showed mercurated species of protein with a Gaussian distribution exhibiting a weighted average of 6 and 9 Hg2+ ions bound to protein when apo-α-LA was treated with 10 and 100 equivalents, respectively. The molecular dynamics studies revealed the binding of Hg2+ ions followed by the structural changes that occurred in the protein. The reaction between Hg2+ and apo-α-LA yields non-crystalline nanoparticles at lower molar ratios of Hg2+ and crystalline ones at higher molar ratios. The existence of both of these nanoparticles was proven by extensive TEM studies, and the mercury nanocrystals were further studied using fluorescence microscopy. X-ray photoelectron spectroscopy demonstrated that the protein has the ability to convert Hg2+ to Hg0, and the resultant Hg0 cluster is known to be less harmful than Hg2+ to the organism. All of these studies support the use of apo-α-LA in the form of nanoparticles and nanocrystals to detoxify Hg2+. This journal is
Chemosensing ability of hydroxynaphthylidene derivatives of hydrazine towards Cu 2 + : Experimental and computational studies
Dessingiou J., Khedkar J.K., Rao C.P.
Article, Journal of Chemical Sciences, 2014, DOI Link
View abstract ⏷
2-Hydroxynaphthylidene derivatives of hydrazine, namely L 1, L 2 and L 3, were synthesized by going through two-step reactions and the products were characterized. The ion recognition properties of these receptors were studied using fluorescence and absorption spectroscopy. The receptors were found to be sensitive and selective towards Cu2+ in methanol solution among the 13 metal ions studied, namely Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn 2+, Cd2+, Hg2+, Pb2+, Na +, K+, Ca2+ and Mg2+, by exhibiting switch off fluorescence. The stoichiometry of the complexed species was found to be 2:1. The fluorescence quenching with Cu2+ is in the order of L 1 > L 2 > L 3 . These conjugates were also found to act as colorimetric sensors for Cu2+ in solution by exhibiting visual colour change. The 2:1 complex shows a centrosymmetric structure based on DFT computations. © 2014 Indian Academy of Sciences.
Zn2+, Cd2+ and Cu2+ mediated formation of amyloid like fibrils by the monomers of β-sheet rich peanut agglutinin
Article, RSC Advances, 2014, DOI Link
View abstract ⏷
A broad spectrum of peptides and proteins can self assemble to form amyloid or amyloid like fibrils under appropriate conditions. Although amyloid fibrils have recently been exploited for their potential use as biomaterials, their applications remain challenging. In this paper, we have shown the formation of amyloid like fibrils of peanut agglutinin isolated from leguminacea class that is rich in beta sheet secondary structure under thermal conditions in the presence of Zn2+, Cd2+ and Cu2+. Formation of such fibrils has been followed and also assayed by different spectroscopy techniques. This was further evaluated by transmission electron microscopy, atomic force microscopy and scanning electron microscopy revealing their morphological features at the nano-scale. The blue-green fluorescence of these fibrils treated with dansyl chloride was micrographed. The role of these metal ions has been revealed by carrying out the experiments in the presence of EDTA that chelates these metal ions. Furthermore, the Energy Dispersive X-ray Analysis clearly showed that the fibrils are enriched with these metal ions. During the formation of fibrils, the presence of granular, sponge-like, network-like and proto-filaments has been witnessed. In order to demonstrate the utility of such self assembled fibrils induced by metal ions, these were shown to bind and possess circular-PBR322 plasmid, and hence are expected to have potential applications in gene delivery and related therapy.
Glyco-conjugate as selective switch-on molecule for Hg2+ in the presence of albumin proteins, blood serum milieu and on silica gel solid support
Areti S., Yarramala D.S., Samanta K., Hinge V.K., Khedkar J., Rao C.P.
Article, RSC Advances, 2014, DOI Link
View abstract ⏷
The glyco-conjugate, LS, its Hg2+ complex, and the LO were synthesized and characterized in their solid state by FTIR, diffuse reflectance, and powder XRD. The mercury complex shows dumbbell-like microstructures as a result of the metal ion-induced aggregation of the glyco-conjugate as studied based on scanning electron microscopy. The aggregation was also supported by atomic force microscopy. The Hg2+ was detected on LS-coated silica gel sheets by switch-on fluorescence, wherein, the enhancement in the fluorescence intensity varies linearly with the added Hg2+ in the concentration range 5-60 μM. The concentration-dependent variation was also detected on silica gel sheets by viewing their colour under 365 nm light. Hg2+ was detected by the LS-coated silica gel sheets by switch-on fluorescence even in the presence of blood serum. Thus, this method is extendable for the detection and quantification of Hg2+ present in blood and or in biological fluids using disposable silica gel sheets. The sensing of Hg2+ in HEPES buffer solution is well demonstrated in this paper using various techniques, such as fluorescence, absorption, visual color, ESI MS, and 1H NMR. In the buffer medium, the LS exhibit selective chromogenic as well as fluorogenic properties towards Hg2+ by showing ∼75-fold higher fluorescence emission intensity and the studies were further extended to show that none of the 13 ions studied compete for Hg2+. A minimum detection limit of 25 ± 4 ppb was shown by LS for Hg 2+ in the buffer. All the experimental studies carried out support the formation of 2:1 complex between LS and Hg2+. At higher mole ratios of Hg2+, the same yields the oxo-product, viz., LO. The structure of the 2:1 complex was modeled by DFT using B3LYP/LANL2DZ. This journal is © the Partner Organisations 2014.
Structural comparisons of the binding cores formed by 1,3-di-amide derivatives of p-tert-Butylcalix[4]arene: Arms Stabilization through intra-molecular interactions including N-H···O, O-H···Cl and π···Cl types
Dey M., Guionneau P., Hinge V.K., Rao C.P.
Article, Proceedings of the National Academy of Sciences India Section A - Physical Sciences, 2014, DOI Link
View abstract ⏷
This paper deals with the development of a receptor with selectively functionalized at the lower rim of p-tert-butyl calix[4]arene linked through amide bond, resulting in the diamide derivatives (L1, L2 and L3) suitable for sensing ions and molecules. All the derivatives were thoroughly characterized by analytical and spectral methods. These derivatives were structurally characterized by single crystal X-ray diffraction and the conformational features of the calix[4]arene as well as the pendants are discussed. The L1 and L2 exhibited intramolecular hydrogen bond interaction between the N-H and the lower rim phenolic oxygen in addition to the circular hydrogen bonding between the phenolic O-H and the ether oxygen of the adjacent strand. The corresponding H-bond is absent when no 'H' is present on amide-N as in case of L3. Such intramolecular N-H ···O interactions observed with the pendant results in a conformational bend responsible for the orientation of the arms and there by the nature of the binding core formed. Thus the binding cores formed differ largely between L3 and the other two. © The National Academy of Sciences, India 2014.
Phenylene-diimine-capped conjugate of lower rim 1,3-Calix[4]arene as molecular receptor for Mg2+ via arm conformational changes followed by aggregation and mimicking the species by molecular mechanics
Nehra A., Hinge V.K., Rao C.P.
Article, Journal of Organic Chemistry, 2014, DOI Link
View abstract ⏷
A phenylene-diimine-capped conjugate of lower rim 1,3-calix[4]arene (L) was synthesized, characterized, and shown to selectively bind to Mg2+ using its capped arms. This results in a selective recognition of Mg 2+ through eliciting fluorescence enhancement of ∼70 fold with a detection limit of 40 ± 5 ppb. However, in the presence of blood serum, the lowest detection limit is 209 ± 10 ppb (0.2 μM). The binding of Mg2+ to L is authenticated by absorption and 1H NMR data. The Jobs plot derived on the basis of the absorption data showed 1:1 stoichiometry between the receptor and Mg2+. The 1:1 species was further confirmed through ESI MS, that is, being supported by the isotope peak pattern authenticating the presence of Mg2+ in the complex. The L binds Mg2+ octahedrally using the tetradentate L2- and two additional acetic acid moieties by bringing conformational changes as studied on the basis of MM computations. The conformational changes that occur in the capped arms upon Mg2+ binding were supported experimentally by NOESY. AFM and SEM studies showed that spherical particles of L are modified into flower and chain type aggregates upon complexation with Mg2+, confirming the supramolecular behavior of the species formed. © 2014 American Chemical Society.
A fluorescent di-zinc(II) complex of bis-calix[4]arene conjugate as chemosensing-ensemble for the selective recognition of ATP
Mummidivarapu V.V.S., Pathak R.K., Hinge V.K., Dessingou J., Rao C.P.
Conference paper, Supramolecular Chemistry, 2014, DOI Link
View abstract ⏷
A triethylene glycol di-imine locked triazole linked bis-calix[4]arene conjugate L has been synthesised and characterised. Conjugate L exhibits high fluorescence enhancement towards Zn2+ among the 13 metal ions studied down to a lower detection limit of ∼12 ppb. The absorption and visual colour change experiments differentiated the Zn2+ from the other metal ions studied. The isolated zinc complex, [Zn2L] has been used as a chemo-sensing ensemble for the recognition of anions based on their binding affinities towards Zn2+. [Zn2L] was found to be sensitive and selective towards phosphate-bearing species and in particular to adenosine triphosphate (ATP2-) among the other 20 anions studied as observed based on the changes occurred in the fluorescence intensity. The selectivity of the ATP2- has been shown on the basis of the changes observed in the emission and absorption spectral studies. The lowest detectable concentration for ATP2- with the chemo-sensing ensemble [Zn2L] is 348 ppb in methanol. The fluorescence quenching by the phosphate-based anions has been modelled by molecular mechanics studies and found that the anions possessing two or more phosphate moieties can only bridge between the two zinc centres, and hence those possessing only one phosphate moiety (H 2PO-4 and AMP2-) are ineffective. © 2014 Taylor & Francis.
Supramolecular complexation of biological phosphates with an acyclic triazolium-linked anthracenyl-1,3-diconjugate of calix[4]arene: Synthesis, characterization, spectroscopy, microscopy, and computational studies
Mummidivarapu V.V.S., Hinge V.K., Samanta K., Yarramala D.S., Rao C.P.
Article, Chemistry - A European Journal, 2014, DOI Link
View abstract ⏷
A triazolium-anthracenyl calix[4]arene conjugate (L) was synthesized by methylating the precursor triazole derivative and then characterized. The potential of the cationic L to differentiate nucleoside triphosphates (NTPs) from their mono- and diphosphates was demonstrated. Due to its unique combination of arms with the calix-platform, a fluorescence enhancement was observed for L with all the NTPs, whereas there is no report with such enhancement being exhibited in case of all the NTPs. This has been supported by the aggregation of L observed from microscopy. Selectivity of L towards NTPs over other phosphates was a result of specific weak interactions, namely, ion-ion, hydrogen bonding and π·π, present in the 1:2 complex of L and NTPs (based on ESI MS), which were absent in their congener-phosphates as delineated by NMR and computational studies. Thus, L stands as a unique receptor for NTPs.
Time- and concentration-dependent reactivity of Cys, Hcy, and GSH on the diels-alder-grafted 1,3,5-tris conjugate of calix[6]arene to bring selectivity for Cys: Spectroscopy, microscopy, and its reactivity in cells
Mummidivarapu V.V.S., Yarramala D.S., Kondaveeti K.K., Rao C.P.
Article, Journal of Organic Chemistry, 2014, DOI Link
View abstract ⏷
Herein we report the synthesis and characterization of 7-oxanorbornadiene (OND)-appended 1,3,5-tris conjugate of calix[6]arene (L<inf>2</inf>). L<inf>2</inf> has been shown to exhibit selective reactivity toward cysteine (Cys) over homocysteine (Hcy) and glutathione (GSH) under stoichiometric conditions. The selectivity of L<inf>2</inf> is attributed to the steric crowding of three Diels-Alder centers possessing OND units present on the calix[6]arene platform, while a control molecular system possessing only one such unit without the calix[6]arene platform (L<inf>1</inf>) does not show any selectivity toward Cys. While L<inf>2</inf> exhibited spherical particles, its reactivity with Cys resulted in flowerlike morphological features, as revealed by scanning electron microscopy. However, the reaction with GSH did not result in any such morphological features, a result that is in agreement with that observed from fluorescence studies in solution. L<inf>2</inf> has been shown to react with Cys present in HeLa and Jurkat E6 cells by fluorescence microscopy.
Pyrenyl-imino-C2-glucosyl conjugate: Synthesis, characterization, and ratiometric and reversible OFF-ON receptor for Hg2+
Areti S., Hinge V.K., Rao C.P.
Article, Carbohydrate Research, 2014, DOI Link
View abstract ⏷
A pyrenyl-imino-C2-glucosyl conjugate, L, has been synthesized and characterized. The L exhibits selective chromogenic as well as fluorescent property towards Hg2+ in a ratiometric manner by showing ∼30 fold enhanced fluorescence emission intensity. The fluorescence enhancement continues to be there even in the presence of thirteen other competitive metal ions studied. The sensing of Hg2+ is well demonstrated using various techniques, such as, fluorescence, absorption, visual color under UV light and ESI MS. A minimum detection limit of 18 ± 2 ppb was shown by L for Hg2+ in ethanol. All the experimental studies carried out supported the formation of 2:1 complex between L and Hg2+. The structure of the 2:1 complex was modeled at ab initio using HF and found a structure where Hg2+ is sandwiched between the two pyrenyl moieties. The reversibility and reusability of L has been demonstrated using fluoride ion.
Interaction of a dinuclear fluorescent Cd(ii) complex of calix[4]arene conjugate with phosphates and its applicability in cell imaging
Sreenivasu Mummidivarapu V.V., Hinge V.K., Rao C.P.
Article, Dalton Transactions, 2014, DOI Link
View abstract ⏷
A triazole-linked hydroxyethylimino conjugate of calix[4]arene (L) and its cadmium complex have been synthesized and characterized, and their structures have been established. In the complex, both the Cd2+ centers are bound by an N2O4 core, and one of it is a distorted octahedral, whereas the other is a trigonal anti-prism. The fluorescence intensity of the di-nuclear Cd(ii) complex is quenched only in the presence of phosphates and not with other anions studied owing to their binding affinities and the nature of the interaction of the phosphates with Cd2+. These are evident even from their absorption spectra. Different phosphates exhibit changes in both their fluorescence as well as absorption spectra to varying extents, suggesting their differential interactions. Among the six phosphates, H2PO4- has higher fluorescence quenching even at low equivalents of this ion, whereas P2O74- shows only 50% quenching even at 10 equivalents. The fluorescence quenching is considerable even at 20 ppb (0.2 μM) of H2PO4-, whereas all other phosphates require a concentration of 50-580 ppb to exhibit the same effect on fluorescence spectra. Thus, the interaction of H2PO4- is more effective by ∼30 fold as compared to that of P2O74-. Fluorescence quenching by phosphate is due to the release of L from its original cadmium complex via the formation of a ternary species followed by the capture of Cd2+ by the phosphate, as delineated based on the combination of spectral techniques, such as absorption, emission, 1H NMR and ESI MS. The relative interactive abilities of the six phosphates differ from each other. The removal of Cd2+ is demonstrated to be reversible by the repeated addition of the phosphate followed by Cd2+. The characteristics of the ternary species formed in each of these six phosphates have been computationally modeled using molecular mechanics. The computational study revealed that the coordination between cadmium and -CH2-CH2-OH breaks and new coordination is established through the phosphate oxygens, and as a result the Cd2+ center acquires a distorted octahedral geometry. The utility of the complex was demonstrated in HeLa cells. This journal is
Chemico-biological aspects of plant lectins with a preference to legume lectins
John F.C., Tabbasum K., Rao C.P.
Book chapter, Studies in Natural Products Chemistry, 2013, DOI Link
View abstract ⏷
The discovery of lectins, a class of carbohydrate-binding proteins, dates back to 1888 when Stillmark first noticed a hemagglutinating factor in castor bean extracts. Ever since, the field of lectins has been steadily growing as new lectins with unique binding specificities are being discovered from various sources. Moreover, newer technologies and synthetic approaches have helped unravel unknown aspects of lectins that have potential for the use of these proteins in biomedicine and biomaterial sciences. Lectins are, by the new definition, proteins with the presence of at least one noncatalytic domain that binds reversibly to a specific carbohydrate. The ability of lectins to bind carbohydrate moieties of glycoprotein and glycolipid cell-surface receptors often results in important biological events. They also bind various glycoses and/or glycoconjugates, including certain drugs, a potential that can be used in prophylaxis of disease. As a result of these findings, studies on lectins have escalated from both chemical and biological points of view, and it is difficult to keep track of the new discoveries and developments in this field in order to reap their benefits and develop the science and the emerging technology from them. Therefore, this review deals with the new discoveries and key developments in the field of lectins, especially with reference to their isolation, structure elucidation, and their chemico-biological applications including those in drug discovery and medicine. Lectins have been isolated from various sources, including plant, viral, bacterial, fungal, and animal. However, the most well-studied class of lectins is the plant lectins, followed by fungal ones. Plant lectins have been shown to possess antitumor and anticarcinogenic activity. Like the antitumor drugs that trigger the apoptotic death of tumor cells, plant lectins have also shown cytotoxic effects mediated via apoptosis. During the last decade, there has been a growing interest in lectins, which exhibit anticancer activities. A few kinds of plant lectins have been identified that induce apoptosis activity in tumor cells, for example, mistletoe (Viscum album L.). Interaction of lectins with cells is also known to induce mitogenicity. As lectins are specific to certain carbohydrates, they are very often able to distinguish between normal and cancer cells and can be used in targeted delivery of organic or inorganic drugs to certain cancer cells and bring about their destruction, a potential that needs to be exploited to its fullest extent. Therefore, this chapter attempts to put into meaningful perspective the latest information available on lectins, which includes practical aspects of isolation, structure elucidation, and lectin-drug interactions, and the structure-activity relationship of lectins that helps us to understand how their activity can be optimized. Many lectins studied to date have numerous biological activities, of which some may have applicability in the biomedical industry. Advancements in computational and bioinformatics studies, and efficient screening mechanisms available in the pharmaceutical industries to pick out the most efficient of these proteins and turn them into drugs for medical use, have all led to a renewed interest in lectins in drug discovery. © 2013 Elsevier B.V. All rights reserved.
Synthesis, characterization and ion recognition studies of lower rim 1,3-di{rhodamine} conjugate of calix[4]arene
Chinta J.P., Dessingou J., Rao C.P.
Article, Journal of Chemical Sciences, 2013, DOI Link
View abstract ⏷
An amido-linked rhodamine conjugate of calix[4]arene, L has been synthesized and characterized. Metal ion recognition properties of L have been studied by emission and absorption techniques with 14 different metal ions including the transition ones. Results show that, L exhibits ratiometric emission intensity towards Hg2+, Fe2+, Fe3+, Cu2+, Pb2+ and Zn2+. Composition of the complex formed in the solution has been found to be 1:2 (L:Mn+), based on the Job's plot. The L can also act as a chemosensor for Hg2+ through naked eye detection. Fluorescence quenching observed at 485 nm follows an order, Hg2+ >> Fe3+ - Cu2+ > Zn2+ > Pb2+ > Ca2+, while the enhancement observed at 580 nm follows, Hg2+ >> Fe2+ - Pb2+ > Zn2+. Mode of interaction of Mn+ with L is by the ring opening of spirolactam moiety. © Indian Academy of Sciences.
Triazole linked lower rim glycosyl appended 1,3-calix[4]arene conjugates: Synthesis, characterization, and their interaction with jacalin
Article, Carbohydrate Research, 2013, DOI Link
View abstract ⏷
Triazole linked lower rim galactosyl and lactosyl appended calix[4]arene conjugates have been synthesized by 1,3 dipolar addition of glycosyl azide and calix[4]arene alkyne. All these conjugates were characterized by 1H and 13C NMR, IR and mass spectrometry. Interaction of amino acids with the galactosyl conjugate of calix[4]arene (5) was studied using absorption and 1H NMR techniques. Absorption studies showed that Trp interacts with triazole ring of 5. This was further confirmed by 1H NMR study which showed an upfield shift in the triazole proton of 5 upon titrating with Trp. The preliminary studies of interaction of these conjugates with Jacalin were demonstrated by fluorescence and circular dichroism (CD) spectroscopy techniques. © 2013 Elsevier Inc. All rights reserved.
Quinoline driven fluorescence turn on 1,3-bis-calix[4]arene conjugate-based receptor to discriminate Fe3+ from Fe2+
Pathak R.K., Dessingou J., Hinge V.K., Thawari A.G., Basu S.K., Rao C.P.
Article, Analytical Chemistry, 2013, DOI Link
View abstract ⏷
The synthesis and characterization of a triazole linked quinoline appended calix[4]arene conjugate, L, and its fluorescence turn on receptor property for Fe3+ have been demonstrated. The selective and sensitive discrimination of Fe3+ has been shown using fluorescence and absorption titration experiments. The Fe3+ binding to L has been further shown by ITC and ESI MS. The mode of binding of Fe3+ by calix[4]arene conjugate has been shown by absorption, 1H NMR and visual color change and the species were modeled based on DFT computations. The {L + Fe3+} has been shown to label cells with fluorescence imaging. Moreover the utility of this conjugate has been demonstrated by the combination logic gate system. © 2013 American Chemical Society.
Triazole-linked anthracenyl-appended calix[4]arene conjugate as receptor for co(II): Synthesis, spectroscopy, microscopy, and computational studies
Mummidivarapu V.V.S., Hinge V.K., Tabbasum K., Gonnade R.G., Rao C.P.
Article, Journal of Organic Chemistry, 2013, DOI Link
View abstract ⏷
A new triazole-linked anthracenyl-appended calix[4]arene-1,3-diconjugate (L) has been synthesized and characterized, and its single crystal XRD structure has been established. Binding properties of L toward different biologically relevant metal ions have been studied by fluorescence and absorption spectroscopy in ethanol. L exhibits selective recognition of Co2+ and can detect down to a concentration of 55 ppb (0.92 μM). The roles of the calix[4]arene platform as well as the preorganized binding core in L's selective recognition have been demonstrated by studying appropriate control molecules. The mode of binding of L with Co2+ has been modeled both by DFT and MD computational calculations. L and its Co2+ complex could be differentiated on the basis of the nanostructural features observed in AFM and TEM. © 2013 American Chemical Society.
Thiourea linked peracetylated glucopyranosyl-anthraquinone conjugate as reversible ON-OFF receptor for fluoride in acetonitrile
Areti S., Khedkar J.K., Chilukula R., Rao C.P.
Article, Tetrahedron Letters, 2013, DOI Link
View abstract ⏷
A new thiourea linked peracetylated glucopyranosyl-anthraquinone conjugate (L) has been synthesized and characterized. The binding properties of L have been studied with nineteen different anions. The L exhibited selective chromogenic as well as fluorescent chemosensor property toward F- by a ∼13-fold increase in the emission intensity upon binding with F -. The minimal detection limit for F- is 185 ± 5 ppb in acetonitrile. Interaction of F- led to a bathochromic shift of 80 nm in the absorption band. An INHIBIT logic gate has been proposed using the output obtained from the fluorescence studies. The structure of the species formed upon the interaction of F- with L has been established by DFT computations. © 2013 Elsevier Ltd. All rights reserved.
Fluorescence and piezoresistive cantilever sensing of trinitrotoluene by an upper-rim tetrabenzimidazole conjugate of calix[4]arene and delineation of the features of the complex by molecular dynamics
Kandpal M., Bandela A.K., Hinge V.K., Rao V.R., Rao C.P.
Article, ACS Applied Materials and Interfaces, 2013, DOI Link
View abstract ⏷
A new benzimidazole-functionalized calix[4]arene receptor (R) was synthesized and characterized. The receptor R shows better selectivity toward trinitrotoluene (TNT) compared to the other nitro explosives in solution, which also retains its effectiveness for solid-phase detection. The chemical interactions of the molecule with different nitro explosive analytes were studied by fluorescence spectroscopy and by a molecular dynamics approach. The molecular dynamics studies show a 1:3 complex between R and TNT, and hence high sensitivity was imparted by fluorescence studies. The detection of explosive vapors in ambient conditions was tested by using a sensitive coating layer of R on an SU-8/CB-based piezoresistive cantilever surface. The developed device showed large sensitivity toward TNT compared to cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) in the solid state at their respective vapor pressures at room temperature. The detection sensitivity of the device was estimated to be 35 mV for TNT at ambient conditions. Moreover, the sensor does not show a response when exposed to humidity. These results demonstrate that R can be used as one of the coating materials for a cantilever for the detection of TNT using piezoresistivity measurement. R can also detect the explosives in solution with high sensitivity and selectivity by fluorescence spectroscopy. © 2013 American Chemical Society.
Synthesis, characterization of the amido-conjugates of 1,1′- methylene-bis(2-naphthol) and recognition of Cu2+ in aqueous acetonitrile
Baghel G.S., Chinta J.P., Rao C.P.
Article, New Journal of Chemistry, 2012, DOI Link
View abstract ⏷
Di-amido-derivatives of 1,1′-methylene-bis(2-naphthol) (mbn), viz.; L1 to L6 and L7, have been synthesized and characterized. The single crystal X-ray structure of L2 has been established. All these derivatives have been studied for metal ion recognition by fluorescence and absorption techniques. Among these, L6 and L 7 were found to be selective towards Cu2+ even in the presence of other metal ions in aqueous acetonitrile owing to the presence of the N,O-binding core up to the lowest concentration of 210 ± 11 and 144 ± 3 ppb, respectively. The binding region has been identified by 1H NMR studies. The proposed mode of binding has been modelled by DFT computations. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Structural comparisons of the species of recognition of Ni 2+, Cu 2+, Zn 2+, Cd 2+, Hg 2+ and Ag + with 1,3-di-conjugates of calix[4]arene by DFT computations
Ramanujam B., Chinta J.P., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2012,
View abstract ⏷
Calixarenes are versatile macromolecular systems, which would exhibit better host-guest chemistry upon appropriate derivatization. Our group has been involved in the synthesis of a variety of calix[4]arene conjugates, which were found to selectively recognize metal ions. Though such recognitions have been demonstrated, based on different experimental studies, the qualitative and semi-quantitative understanding of the coordination aspects are still lacking owing to the non-availability of the crystal structures of the species of recognition. Hence, in order to understand the coordination chemistry of the interactions between the host calix[4]arene receptor and the guest metal ion species, computational modelling studies have been carried out. In this regard, five conjugates of calix[4]arene, which are 1,3-di-O-derivised at the lower-rim and appended over an amide as well as Schiff base linker have been studied. The computational modelling studies have been carried out at the level of density functional theory to yield coordination geometries, which are intune with the experimental observations and comparable to those reported in the literature in the case of similar receptor systems. The species of recognition obtained with the metal ions are found to have some structural resemblances with the metal sites present in metalloproteins. The modelling studies and the coordination geometries are discussed in this article.
Benzimidazole conjugate of 1,1′-thiobis(2-naphthol) as switch-on fluorescence receptor for Ag + and the complex as secondary recognition ensemble toward Cys, Asp, and Glu in aqueous methanolic solution: Synthesis, characterization, ion and amino acid recognition, computational studies, and microscopy features
Dessingou J., Mitra A., Tabbasum K., Baghel G.S., Rao C.P.
Article, Journal of Organic Chemistry, 2012, DOI Link
View abstract ⏷
A new 1,1′-thiobis(2-naphthoxy)-based receptor molecule (L) containing a benzimidazole moiety has been synthesized and characterized by 1H NMR, ESI-MS, and elemental analysis. The selectivity of L has been explored in aqueous methanol, resulting in selective (7.5 ± 0.5)-fold switch-on fluorescence response toward Ag + among 14 different transition, alkali, and alkaline earth metal ions studied. The complexation of Ag + by L has been addressed by ESI-MS, 1H NMR, and UV-vis spectra. Microstructural features of L and its Ag + complex have been measured by AFM and TEM. The morphological features of L alone and L in the presence of Ag + differ dramatically both in shape and size, and the ion induces the formation of chains owing to its coordinating ability toward benzimidazole. Further, the in situ [Ag +-L] complex was titrated against 20 naturally occurring amino acids and found that this complex acts as a secondary recognition ensemble toward Cys, Asp, and Glu by switch-off fluorescence. © 2011 American Chemical Society.
Lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene: Synthesis, characterization, and selective recognition of Hg2+and its sensitivity toward pyrimidine bases
Dessingou J., Tabbasum K., Mitra A., Hinge V.K., Rao C.P.
Article, Journal of Organic Chemistry, 2012, DOI Link
View abstract ⏷
The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg2+ among other biologically important metal ions, viz., Na+, K +, Ca2+, Mg2+, Mn2+, Fe 2+, Co2+, Ni2+, Cu2+, Zn 2+, Cd2+, Hg2+, Pb2+, and Ag + as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg2+ by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg2+ is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg2+ is bound through an N2O2 extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg2+ complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest. © 2012 American Chemical Society.
Coordination polymers formed by the mono- and dinuclear Cu(II) complexes of 1,1′-methylene/thio-bis(2-naphthoxy) acetic acid
Baghel G.S., Chinta J.P., Kaiba A., Guionneau P., Rao C.P.
Article, Crystal Growth and Design, 2012, DOI Link
View abstract ⏷
A series of five new Cu 2+ coordination polymers, namely, {[CuL CH2(DMF)](DMF)} n (1), {[CuL CH2(DMF)(2,2'- bipy)](CH 3OH)} n (2), {[CuL CH2(2,2'- bipy)](2H 2O)} n (3), {[CuL CH2(H 2O)(2,2'-bipy)](2H 2O)} n (5), {[Cu 2(L S) 2(DMF) 2](DMF)(CH 3OH)(2H 2O)} n (6), and three discrete coordination complexes {[Cu 2L CH2(2,2'- bipy) 2(CH 3O)](ClO 4)(CH 3OH)} (4), {[CuL S(2,2'bipy)]- (CH 3OH)} (7), and {[CuL S(1,10-phen)](DMF)} (8) have been prepared by the reaction of Cu(ClO 4) 2·6H 2O and 1,1'- methylene-bis(2-naphthoxy acetic acid) (L CH2) or 1,1'-thiobis( 2-naphthoxy acetic acid) (L S), with or without the presence of 2,2'-bipyridine, under varying reaction conditions or methods of crystallization or both. All the compounds were characterized by elemental analysis, IR, thermogravimetric analysis, and single crystal X-ray diffraction (XRD). The structures of L CH2 and L S obtained by single crystal XRD indicated antiorientation of the pendant arms which upon metal complexation may turn into cis- orientation leading to discrete metal ion complexes or may remain in anti- orientation leading to extended multidimensional co-ordination polymers. The complexation with Cu 2+ led to five different coordination spheres which in turn resulted in five different lattice structures. Thus, the present paper demonstrates the design of coordination polymers that are rich with mononuclear as well as dinuclear Cu 2+ centers wherein L CH2 or L S coordinates in a monodentate as well as a bridging fashion leading to the formation of one-dimensional curving, helical, and two-dimensional networks. © 2012 American Chemical Society.
1,3-Di-amidoquinoline conjugate of calix[4]arene (L) as a ratiometric and colorimetric sensor for Zn 2+: Spectroscopy, microscopy and computational studies
Mummidivarapu V.V.S., Tabbasum K., Chinta J.P., Rao C.P.
Article, Dalton Transactions, 2012, DOI Link
View abstract ⏷
Carboxamidoquinoline appended calix[4]arene-1,3-di-conjugate (L) has been synthesized and characterized and its single crystal XRD structure has been established. L has been shown to act as selective ratiometric turn-on fluorescence sensor for Zn 2+ up to a lowest concentration of 183 ± 18 ppb (2.82 μM) with a nine-fold enhancement by exhibiting blue-green emission. The coordination features of the species of recognition have been computationally evaluated by DFT methods and found to have distorted tetrahedral Zn 2+ center in an N 4 core. The spherical nano-structural features observed for L in TEM are being transformed into the Koosh nano-flower like structure when complexed with Zn 2+ and hence these two can be easily differentiated. Even the features observed in AFM can distinctly differentiate L from its Zn 2+ complex. © 2012 The Royal Society of Chemistry.
Erratum: Lower rim 1,3-Di{4-antipyrine}amide conjugate of calix[4]arene: Synthesis, characterization, and selective recognition of Hg 2+ and its sensitivity toward pyrimidine bases (Journal of Organic Chemistry (2012) 58 (1406-1413) DOI: 10.1021/jo2022372)
Dessingou J., Tabbasum K., Mitra A., Hinge V.K., Rao C.P.
Erratum, Journal of Organic Chemistry, 2012, DOI Link
Triazole linked picolylimine conjugate of calix[6]arene as a sequential sensor for La 3+ followed by F –
Mummidivarapu V.V.S., Nehra A., Hinge V.K., Rao C.P.
Article, Organic Letters, 2012, DOI Link
View abstract ⏷
A new 1,3,5-tris-triazole linked picolylimine conjugate of calix[6]arene (L) has been shown to be selective toward La 3+ by turn on fluorescence with ∼70-fold enhancement and emits blue, with a minimal detection limit of 65 ± 5 ppb (490 nM). The species of recognition has been modeled computationally to have a monocapped twisted square antiprism with a N 6O 3 binding core about La 3+. The in situ complex of L with La 3+ recognizes F - via fluorescence quenching. The reversible response of sensing La 3+ and F - sequentially by L has been demonstrated. © 2012 American Chemical Society.
Pyrophosphate sensing by a fluorescent Zn2+ bound triazole linked imino-thiophenyl conjugate of calix[4]arene in HEPES buffer medium: Spectroscopy, microscopy, and cellular studies
Pathak R.K., Tabbasum K., Rai A., Panda D., Rao C.P.
Article, Analytical Chemistry, 2012, DOI Link
View abstract ⏷
An in situ prepared Zn2+ complex of triazole linked imino-thiophenyl conjugate of calix[4]arene, [ZnL], was demonstrated to be highly fluorescent in HEPES buffer solution. [ZnL] has been used as a chemo-sensing ensemble for the recognition of phosphates in general and pyrophosphates in particular among the eighteen different anions studied. The chemo-sensing behavior of the [ZnL] has been demonstrated through fluorescence, absorption, visual fluorescent color changes, ESI MS, and 1H NMR titrations. Variations in the microstructural features of L, its zinc complex and the complex upon addition of PPi have been demonstrated through atomic force microscopy and transmission electron microscopy. Such studies have been extended to see the permeability of the conjugate into the HeLa cells by fluorescence microscopy. In accession, a reversible "write-read-erase- read" logic gate property of L has been demonstrated through a feedback loop in the presence of Zn2+ and PPi. © 2012 American Chemical Society.
Cd 2+ complex of a triazole-based calix[4]arene conjugate as a selective fluorescent chemosensor for Cys
Pathak R.K., Hinge V.K., Mahesh K., Rai A., Panda D., Rao C.P.
Article, Analytical Chemistry, 2012, DOI Link
View abstract ⏷
An N,N-Dimethylamine ethylimino-appended triazole-linked calix[4]arene conjugate, L, has been synthesized and characterized, and its Cd 2+ complex has been isolated and characterized. The structure of [CdL] was established by computational calculation using B3LYP/LANL2DZ. Time-dependent density functional theory calculations were performed to demonstrate the electronic properties of [CdL]. This highly fluorescing [CdL] has been used to recognize Cys selectively among the 20 naturally occurring amino acids. [CdL] exhibits a minimum detection limit of 58 ppb for Cys, with reusability and reversibility being imparted to the system during sensing. Thus, the sensing of Cys was well demonstrated using various techniques, viz., fluorescence, absorption, visual color change, electrospray ionization MS, 1H NMR, and live cell imaging experiments. © 2012 American Chemical Society.
Conjugates of calixarenes emerging as molecular entities of nanoscience
Acharya A., Samanta K., Rao C.P.
Review, Coordination Chemistry Reviews, 2012, DOI Link
View abstract ⏷
Calixarenes, along with cyclodextrins (viz. β-CD) and crown ethers, are the most commonly studied macrocyclic compounds. These bucket shaped molecules have gained tremendous importance for having both hydrophilic and hydrophobic compartments together in the same species. The primary target of this review is to give the readers of various disciplines an updated overview of the recent advancements of the conjugates of calixarenes with respect to their nano chemistry in understanding the nanoscience of these supramolecular systems. Calixarenes now compete with cyclodextrins and calixresorcinols. Thus it is important to look into the current advancement in the literature to draw appropriate comparisons and to provide appropriate designs for their nano science aspects. This review is expected to provide all this. The review covers over 113 conjugates of calixarenes published in 106 references that include contributions from our research group. All the conjugates and their nanoscience aspects were depicted through 63 figures and two schemes. The characterization of these nano systems has been carried out by a variety of techniques that includes spectroscopy and microscopy. The advancement of the conjugates of calixarenes in the nanoworld can be considered as one of the most recent encroachment in the calixarene chemistry and is expected to come out as a major thrust research area in near future. © 2012 Elsevier B.V.
A Zn2+ specific triazole based calix[4]arene conjugate (L) as a fluorescence sensor for histidine and cysteine in HEPES buffer milieu
Pathak R.K., Tabbasum K., Rai A., Panda D., Rao C.P.
Article, Analyst, 2012, DOI Link
View abstract ⏷
A highly fluorescent Zn2+ complex of the triazole linked salicyl-imino-thiophenyl conjugate of calix[4]arene, [ZnL] has been demonstrated to be a chemo-sensing ensemble for the recognition of His and Cys among the naturally occurring amino acids in HEPES buffer milieu. The recognition behaviour of the [ZnL] towards these amino acids has been shown on the basis of fluorescence, absorption and visual fluorescent colour changes. The species of recognition were shown by ESI MS titrations, AFM & TEM microscopy and cell studies. © 2012 The Royal Society of Chemistry.
Ratiometric fluorescence off-on-off sensor for Cu2+ in aqueous buffer by a lower rim triazole linked benzimidazole conjugate of calix[4]arene
Pathak R.K., Hinge V.K., Mondal P., Rao C.P.
Article, Dalton Transactions, 2012, DOI Link
View abstract ⏷
A benzimidazole appended triazole linked 1,3-diconjugate of calix[4]arene (L) has been synthesized and characterized. The conjugate L has been found to recognize Cu2+ among the thirteen different metal ions studied by exhibiting ratiometric fluorescence changes through newly generated excimer band at ∼380 nm. Fluorescence off-on-off behavior has been clearly demonstrated on the basis of the binding variability of Cu2+ to L. The binding has been elicited through the changes observed in the fluorescence, ESI MS and 1H NMR titrations. All the other metal ions studied do not show any new band and further do not interfere with the recognition of Cu2+ by L, even when these are present in the same medium. The structural features of both the mono- and di-nuclear complexes were established by DFT computational calculations and found to display highly distorted geometry about the copper centers that deviate from both the tetrahedral and the square planar. © 2012 The Royal Society of Chemistry.
Multiple sensor array of Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ complexes of a triazole linked imino-phenol based calix[4]arene conjugate for the selective recognition of Asp, Glu, Cys, and his
Pathak R.K., Dessingou J., Rao C.P.
Article, Analytical Chemistry, 2012, DOI Link
View abstract ⏷
The triazole linked o-imino phenol appended calix[4]arene conjugate (L) has been synthesized and characterized. The structure of L has been established based on single crystal XRD. The binding and recognition behavior of conjugate, L toward the transition metal ions, such as Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+, has been demonstrated using fluorescence, absorption and ESI-MS techniques. The in situ prepared complexes of these metal ions, namely, [Mn2L], [Fe 2L], [Co2L], [Ni2L], [Cu2L], and [Zn2L] have shown recognition toward Glu, Asp, His and Cys. Hence L provides a multiple sensing molecular tool where the response for the recognition of biologically active amino acids of metalloproteins is elicited by the presence of specific metal ion. © 2012 American Chemical Society.
Cu(II) complexes of glyco-imino-aromatic conjugates in DNA binding, plasmid cleavage and cell cytotoxicity
Kumar A., Mitra A., Ajay A.K., Bhat M.K., Rao C.P.
Conference paper, Journal of Chemical Sciences, 2012, DOI Link
View abstract ⏷
Binding of metal complexes of C2-glucosyl conjugates with DNA has been established by absorption and fluorescence studies. Conformational changes occurred in DNA upon binding have been studied by circular dichroism. All these studies are suggestive that the metal complexes bind to DNA through intercalation. Binding of di-nuclear copper complex 5 was found to be stronger when compared to the other complexes studied. Copper complexes were found to cleave the plasmid DNA in the absence of oxidizing or reducing agent, whereas, zinc complexes do not cleave. Metal complexes have shown toxicity to the HeLa and MCF-7 cell lines. Morphological studies, western blot and FACS analysis are suggestive of apoptotic cell death induced by the metal complexes. Di-nuclear copper complexes were found to be better as compared to the mononuclear ones in binding, plasmid cleavage and also in causing more cell death. © 2012 Indian Academy of Sciences.
Structural aspects of the metal ion complexes of the conjugates of calix[4]arene: Crystal structures and computational models
Chinta J.P., Ramanujam B., Rao C.P.
Review, Coordination Chemistry Reviews, 2012, DOI Link
View abstract ⏷
In this review, the structural aspects of the metal ion complexes of calix[4]arene and its derivatives have been discussed. Aspects, such as the coordination geometry about the metal ions and conformational mobility of the arms of the calix[4]arene as well as the calix[4]arene platform were discussed and compared appropriately. Structures derived based on the computational modeling of the metal ion complexes of the calix[4]arene derivatives have also been reviewed. The complexation of the metal ions with the derivatives was observed mainly through the heteroatoms which were further strengthened by cation... π interactions extended from the phenyl moieties of calix[4]arene. Solvent molecules play an important role in preorganizing the cavity to optimize the binding of metal ions. Conformational changes were observed in the arms upon metal ion binding. However, conformational changes were also observed in the calix[4]arene moiety, particularly when no arms were built on these platforms for coordination. This review covers the structural information of ∼125 metal ion complexes from a list of 145 literature references and thus covers the relevant literature in its entirety starting from the year 1989. Thus the present review covers the metal ion complexes of the calix[4]arene and its derivatives, viz., alkali and alkaline earth, transition (first, second and third row), main group and lanthanides, that may be of use in designing the conjugates of calix[4]arene for their possible applications. © 2012 Elsevier B.V.
1,3-diamido-calix[4]arene conjugates of amino acids: Recognition of -COOH side chain present in amino acids, peptides, and proteins by experimental and computational studies
Acharya A., Ramanujam B., Chinta J.P., Rao C.P.
Article, Journal of Organic Chemistry, 2011, DOI Link
View abstract ⏷
Lower rim 1,3-diamido conjugates of calix[4]arene have been synthesized and characterized, and the structures of some of these have been established by single crystal XRD. The amido-calix conjugates possessing a terminal -COOH moiety have been shown to exhibit recognition toward guest molecules possessing -COOH moiety, viz., Asp, Glu, and reduced and oxidized glutathione (GSH, GSSG), by switch-on fluorescence in aqueous acetonitrile and methanol solutions when compared to the control molecules via forming a 1:1 complex. The complex formed has been shown by mass spectrometry, and the structural features of the complexes were derived on the basis of DFT computations. The association constants observed for the recognition of Asp/Glu by Phe-calix conjugate, viz., 532/676 M-1, are higher than that reported for the recognition of Val, Leu, Phe, His, and Trp (16-63 M-1) by a water-soluble calixarene (Arena, G., et al. Tetrahedron Lett. 1999, 40, 1597). For this recognition, there should be a free -COOH moiety from the guest molecule. AFM, SEM, and DLS data exhibited spherical particles with a hundred-fold reduction in the size of the complexes when compared to the particles of the precursors. These spherical particles have been computationally modeled to possess hexameric species reminiscent of the hexameric micellar structures shown for a Ag+ complex of a calix[6]arene reported in the literature (Houmadi, S., et al. Langmuir 2007, 23, 4849). Both AFM and TEM studies demonstrated the formation of nanospheres in the case of GSH-capped Ag nanoparticles in interaction with the amido-calix conjugate that possesses terminal -COOH moiety. The AFM studies demonstrated in this paper have been very well applied to albumin proteins to differentiate the aggregational behavior and nanostructural features exhibited by the complexes of proteins from those of the uncomplexed ones. To our knowledge, this is the first report wherein a amido-calix[4]arene conjugate and its amino acid/peptide/protein complexes have been differentiated on the basis of spectroscopy and microscopy studies followed by species modeling by computations. © 2010 American Chemical Society.
Recognition of polycyclic aromatic hydrocarbons and their derivatives by the 1,3-dinaphthalimide conjugate of calix[4]arene: Emission, absorption, crystal structures, and computational studies
Bandela A., Prakash Chinta J., Kumar Hinge V., Dikundwar A.G., Row Guru T.N., Rao C.P.
Article, Journal of Organic Chemistry, 2011, DOI Link
View abstract ⏷
Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants as well as well-known carcinogens. Therefore, it is important to develop an effective receptor for the detection and quantification of such molecules in solution. In view of this, a 1,3-dinaphthalimide derivative of calix[4]- arene (L) has been synthesized and characterized, and the structure has been established by single crystal XRD. In the crystal lattice, intermolecular arm-to-arm π 3 3 3 π overlap dominates and thus L becomes a promising receptor for providing interactions with the aromatic species in solution, which can be monitored by following the changes that occur in its fluorescence and absorption spectra. On the basis of the solution studies carried out with about 17 derivatives of the aromatic guest molecular systems, it may be concluded that the changes that occur in the fluorescence intensity seem to be proportional to the number of aromatic rings present and thus proportional to the extent of π 3 3 3 π interaction present between the naphthalimidemoieties and the aromatic portion of the guest molecule. Though the nonaromatic portion of the guest species affects the fluorescence quenching, the trend is still based on the number of rings present in these. Four guest aldehydes are bound to L with Kass of 2000-6000M-1 and their minimum detection limit is in the range of 8-35 μM. The crystal structure of a naphthaldehyde complex, L.2b, exhibits intermolecular arm-to-arm as well as arm-to-naphthaldehyde π 3 3 3 π interactions. Molecular dynamics studies of L carried out in the presence of aromatic aldehydes under vacuum as well as in acetonitrile resulted in exhibiting interactions observed in the solid state and hence the changes observed in the fluorescence and absorption spectra are attributable for such interactions. Complex formation has also been delineated through ESI MS studies. Thus L is a promising receptor that can recognize PAHs by providing spectral changes proportional to the aromatic conjugation of the guest and the extent of aromatic π 3 3 3 π interactions present between L and the guest.© 2011 American Chemical Society.
Carbohydrate assisted fluorescence turn-on gluco-imino-anthracenyl conjugate as a Hg(II) sensor in milk and blood serum milieu
Mitra A., Mittal A.K., Rao C.P.
Article, Chemical Communications, 2011, DOI Link
View abstract ⏷
A new anthracenyl-imino-glucosyl conjugate (L) selectively senses Hg2+ by turn-on fluorescence with a 13 ± 1 fold enhancement by forming a 2 : 1 complex in pH 5 to 10 even in the presence of several biologically and ecologically relevant metal ions, with a 25 ± 2% fluorescence enhancement at the EPA limit of 2 ppb. L is equally sensitive towards Hg2+ in the presence of albumin proteins and in blood serum and milk. © 2011 The Royal Society of Chemistry.
A zinc-sensing glucose-based naphthyl imino conjugate as a detecting agent for inorganic and organic phosphates, including DNA
Mitra A., Hinge V.K., Mittal A., Bhakta S., Guionneau P., Rao C.P.
Article, Chemistry - A European Journal, 2011, DOI Link
View abstract ⏷
Sugars sense of zinc: A glucose-based naphthylimino conjugate (L) has been synthesized and structurally characterized. L has been shown to exhibit selective turn-on fluorescence towards Zn2+ in an aqueous alcoholic medium. The zinc complex, in turn, recognizes phosphates, nucleotides, and DNA by turn-off fluorescence, which has been further investigated by molecular dynamics simulations. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Calix[4]arene-based 1,3-diconjugate of salicylyl imine having dibenzyl amine moiety (L): Synthesis, characterization, receptor properties toward Fe 2+, Cu 2+, and Zn 2+, crystal structures of its Zn 2+ and Cu 2+ complexes, and selective phosphate sensing by the [ZnL]
Joseph R., Chinta J.P., Rao C.P.
Article, Inorganic Chemistry, 2011, DOI Link
View abstract ⏷
A calix[4]arene conjugate bearing salicylyl imine having dibenzyl moiety (L) has been synthesized and characterized, and its ability to recognize three most important essential elements of human system, viz., iron, copper, and zinc, has been addressed by colorimetry and fluorescence techniques. L acts as a sensor for Cu 2+ and Fe 2+ by exhibiting visual color change and for Zn 2+ based on fluorescence spectroscopy. L shows a minimum detection limit of 3.96 ± 0.42 and 4.51 ± 0.53 ppm and 45 ± 4 ppb, respectively, toward Fe 2+, Cu 2+, and Zn 2+. The in situ prepared [ZnL] exhibits phosphate sensing among 14 anions studied with a detection limit of 247 ± 25 ppb. The complexes of Zn 2+, Cu 2+, and Fe 2+ of L have been synthesized and characterized by different techniques. The crystalline nature of the zinc and copper complexes and the noncrystalline nature of simple L and its iron complex have been demonstrated by powder XRD. The structures of Cu 2+ and Zn 2+ complexes have been established by single crystal XRD wherein these were found to be 1:1 monomeric and 2:2 dimeric, respectively, using N 2O 2 as binding core. The geometries exhibited by the Zn 2+ and the Cu 2+ complexes were found to be distorted tetrahedral and distorted square planar, respectively. The iron complex of L exists in 1:1 stoichiometry as evident from the mass spectrometry and elemental analysis. © 2011 American Chemical Society.
Ion and molecular recognition by lower rim 1,3-di-conjugates of calix[4]arene as receptors
Review, Chemical Reviews, 2011, DOI Link
View abstract ⏷
The ion and molecular recognition properties of 1, 3-diconjugates of calix[4]arene were studied. These recognitions were carried out in different solvent systems by using various spectroscopy techniques, and in some cases the species of recognition have been demonstrated by single crystal X-ray structure determination and/or by computational modeling studies. An aspect that requires further attention is the aqueous solubility of calix[4]arene conjugates. It is possible to build more binding sites on the calix[4]arene platform by introducing various donor groups in the vicinity of the lower rim phenolic group of calix[4]arene to provide higher coordination for lanthanides and other demanding ions. All of these receptors primarily possesses O- and N-binding centers, but are mostly deprived of carboxylato- and/or thiolato-moieties that may be required to mimic the selective recognition of metal ions by the corresponding apo-proteins.
Synthesis, characterization, plasmid cleavage and cytotoxicity of cancer cells by a copper(ii) complex of anthracenyl-terpyridine
Kumar A., Prakash Chinta J., Kumar Ajay A., Kumar Bhat M., Rao C.P.
Article, Dalton Transactions, 2011, DOI Link
View abstract ⏷
Metallo-organic compounds are interesting to study for their antitumor activity and related applications. This paper deals with the syntheses, characterization, structure determination of a copper complex of anthracenyl terpyridine (1) and its plasmid cleavage and cytotoxicity towards different cancer cell lines. The complex binds CT-DNA through partial intercalation mode. The plasmid cleavage studies carried out using pBR322 and pUC18 resulted in the formation of all the three forms of the plasmid DNA. Plasmid cleavage studies carried out with a non-redoxable Zn 2+ complex (2) supported the role of the redox activity of copper in 1. The complex 1 showed remarkable antiproliferative activity against cancer cell lines, viz., cervical (HeLa, SiHa, CaSki), breast (MCF-7), liver (HepG2) and lung (H1299). A considerable lowering was observed in the IC 50 values of HPV-infected (viz., HeLa, SiHa, CaSki) vs. non-HPV-infected cell lines (MCF-7, HepG2, H1299). Antiproliferative activity of 1 was found to be much higher than the carboplatin when treated with the same cell lines. Incubation of the cells with 1 results in granular structures only with the HPV-infected cells and not with others as studied by phase contrast and fluorescence microscopy. The lower IC 50 value observed in case of 1 with HPV-infected cell lines may be correlated with the involvement of HPV oncoprotein. The role of HPV has been further augmented by transfecting the MCF-7 cells (originally not possessing HPV copy) with e6 oncoprotein cDNA. To our knowledge this is the first copper complex that causes cell death by interacting with HPV oncoprotein followed by exhibition of remarkable antiproliferative activity. © 2011 The Royal Society of Chemistry.
Role of the conformational changes brought in the arms of the 1,3-di-capped conjugate of calix[4]arene (L) in turning on the fluorescence of L by Hg 2+
Bandela A., Chinta J.P., Rao C.P.
Article, Dalton Transactions, 2011, DOI Link
View abstract ⏷
A new 1,3-di-capped calix[4]arene conjugate of salicylidene (L) has been synthesized, characterized and the structure has been established by single crystal XRD. L shows selectivity towards Hg 2+ in ethanol by turn-on fluorescence among the biologically important metal ions studied. The species of recognition has been modeled by DFT computational calculations to result in conformational changes in the arms that support the turn-on fluorescence behaviour. © 2011 The Royal Society of Chemistry.
Naked eye sensing of Hg 2+ using glucose based anthracenyl imino derivative
Article, Trends in Carbohydrate Research, 2011,
View abstract ⏷
A new and simple glucose based receptor molecular system, Glc-2-AI (L), linked to anthracenyl through imine moiety has been shown to sense Hg 2++ by a recognizable colour change, among eight different ions studied.
Spectroscopic investigation of hydrogen bonding interaction in di-O-isopropylidene derivatives of monosaccharides
Rajaganesh R., Karthik Kumar K., Mohan Das T., Rao C.P.
Article, Trends in Carbohydrate Research, 2011,
View abstract ⏷
Di-O-isopropylidene derivatives of D-glucose and D-mannose were synthesized, and characterized based on different spectral techniques. Both the derivatives exhibit different extents of intra and inter molecular hydrogen bonding in different solvents. Absorption, FT-IR and NMR studies in different solvents shows 2,3:5,6-di-O-isopropylidene-D-mannofuranose derivative to exhibit hydrogen bonding different from the corresponding D-glucofuranose derivative.
Triazole-linked-thiophene conjugate of calix[4]arene: Its selective recognition of Zn 2+ and as biomimetic model in supporting the events of the metal detoxification and oxidative stress involving metallothionein
Pathak R.K., Hinge V.K., Mondal M., Rao C.P.
Article, Journal of Organic Chemistry, 2011, DOI Link
View abstract ⏷
Supramolecular calix[4]arene conjugate (L) has been developed as a sensitive and selective sensor for Zn 2+ in HEPES buffer among the 12 metal ion by using fluorescence, absorption and ESI MS and also by visual fluorescent color. The structural, electronic, and emission properties of the calix[4]arene conjugates L and its zinc complex, [ZnL], have been demonstrated using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. The TDDFT calculations reveal the switch on fluorescence behavior of L is mainly due to the utilization of the lone pair of electrons on imine moiety by the Zn 2+. The resultant fluorescent complex, [ZnL], has been used as a secondary sensing chemo-ensemble for the detection of -SH containing molecules by removing Zn 2+ from [ZnL] and forming {Cys/DTT·Zn} adducts as equivalent to those present in metallothioneins. The displacement followed by the release of the coordinated zinc from its Cys/DTT complex by heavy metal ion (viz. Cd 2+ and Hg 2+), as in the metal detoxification process or by ROS (such as H 2O 2) as in the oxidative stress, has been well demonstrated using the conjugate L through the fluorescence intensity retrieval wherein the fluorescence intensity is the same as that observed with [ZnL], which in turn mimics the zinc sensing element (MTF) in biology (Figure presented). © 2011 American Chemical Society.
A lower rim triazole linked calix[4]arene conjugate as a fluorescence switch on sensor for Zn2+ in blood serum milieu
Pathak R.K., Dikundwar A.G., Row T.N.G., Rao C.P.
Article, Chemical Communications, 2010, DOI Link
View abstract ⏷
A fluorescence turn-on receptor based on triazole linked calix[4]arene (L) for selective recognition of Zn2+ in aqueous-methanolic HEPES buffer has been developed and showed its utility for sensing Zn2+ in blood serum milieu. © 2010 The Royal Society of Chemistry.
1-(d-Glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxybenzene as chemosensor for aromatic amino acids by switch-on fluorescence
Mitra A., Chinta J.P., Rao C.P.
Article, Tetrahedron Letters, 2010, DOI Link
View abstract ⏷
A glucose based C2-glyco-conjugate, that is, 1-(d-glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxybenzene (L), has been synthesized in a high yield and characterized. Titration of L with all the 20 naturally occurring amino acids resulted in a large fluorescence intensity enhancement only in case of aromatic amino acids, that is, Phe, Trp, His, and Tyr and not with the others. This has been attributed to the initial formation of 1:1 hydrogen bonded complex followed by π-π interactions present between the aromatic moieties of such complexes as demonstrated by absorption and computational methods. Thus L has been able to recognize aromatic amino acids down to 1.5-3 ppm through switch-on fluorescence behavior. © 2009 Elsevier Ltd. All rights reserved.
Synthesis and characterization of a (1+1) cyclic Schiff base of a lower rim 1,3-diderivative of p-tert-butylcalix[4]arene and its complexes of VO2+, UO22 +, Fe3+, Ni2+, Cu2+ and Zn2+
Ali A., Joseph R., Mahieu B., Rao C.P.
Article, Polyhedron, 2010, DOI Link
View abstract ⏷
A (1+1) macrocyclic calix[4]arene based Schiff base derivative has been synthesized and was subjected to complexation with different ions or ionic species, viz., VO2+, UO22 +, Fe3+, Ni2+, Cu2+ and Zn2+. Both the conjugate and the complexes were characterized using various spectral techniques, viz.; FTIR, 1H, 13C NMR and FAB mass. The complexes have been further characterized by UV-Vis, EPR and magnetic susceptibility, while the iron complex was studied further by Mössbauer spectroscopy. On the basis of all these studies, the VO2+ and UO22 + complexes were found to be mononuclear, whereas all the other complexes were found to be dinuclear. Based on the studies, the iron complex was found have a distorted octahedral high spin Fe(III) center with an antiferromagnetically coupled dinuclear core in the complex. © 2009 Elsevier Ltd. All rights reserved.
Lower rim 1,3-diderivative of calix[4]arene-appended salicylidene imine (H2L): Experimental and computational studies of the selective recognition of H2L toward Zn2+ and sensing phosphate and amino acid by [ZnL]
Joseph R., Chinta J.P., Rao C.P.
Article, Journal of Organic Chemistry, 2010, DOI Link
View abstract ⏷
A new 1,3-diderivative of calix[4]arene appended with hydroxymethyl salicylyl imine has been synthesized and its ion recognition toward biologically relevant Mn+ ions studied. The receptor H2L showed selectivity toward Zn2+ by switch-on fluorescence among the 12 metal ions studied with a detection limit of 192 ppb. The interaction of Zn 2+ with H2L has been further supported by absorption studies, and the stoichiometry of the complex formed (1:1) has been established on the basis of absorption and ESI MS. Competitive ion titrations carried out reveal that the Zn2+ can be detected even in the presence of other metal ions of bioimportance. The mode of interaction of Zn2+ with conjugate has been established by a fleet of computational calculations carried out in a cascade manner, either on the ligand or on the complex, wherein the final optimizations were carried out by the density functional theory (DFT) and found that the Zn2+ and Cd2+ indeed bind differently. In situ prepared [ZnL] complex responds to both inorganic phosphate as well as AMP, ADP, and ATP with a minimum detection limit of 426 ppb wherein the Zn 2+ from the complex is detached and recomplexed by the added phosphate moiety. It has been possible to build an INHIBIT logic gate for the conjugate using Zn2+ and HPO42- as inputs by monitoring the fluorescence emission band at 444 nm as output. The amino acid sensing abilities of [ZnL] have been explored by fluorescence and absorbance spectroscopy where it showed selectivity toward Cys, Asp, and His through the formation of the Zn2+ complex of these amino acids by chelating through their side chain moieties. Thus, while H2L is selective for Zn2+ among a number of cations, the [ZnL] is selective toward phosphate among a number of anions and also toward Asp, Cys, and His among the naturally occurring amino acids. © 2010 American Chemical Society.
1,3-Di-peptido-conjugates of calix[4]arene and its di-OCH3 derivatives: Synthesis, characterization and phosphate recognition
Dey M., Ali A., Acharya A., Rao C.P.
Article, Indian Journal of Chemistry - Section B Organic and Medicinal Chemistry, 2010,
View abstract ⏷
Novel double-armed peptido-conjugates of calix[4]arene have been developed on the lower rim of the macrocycle. The functional group pendants exhibit conformational bend through the involvement of 11-atom N-H...O hydrogen bond inscribed in a 14-atom O-H...O interaction. As a result, only the terminal -COOR and -COOH groups are exposed to the environment, but not the amide moiety. The cowe-conformation of the calix[4]arene is further stabilized through the O-H...O interactions at the lower rim. In effect, the conjugates exhibit a binding core at the lower rim along with hydrophobic cavity formed by the enclosure of arene moieties. Conformational mobility induced by the replacement of lower rim phenolic-OH by -OCH3 has also been demonstrated by variable temperature NMR studies in case of the corresponding - OCH3 derivatives. Differential receptor binding characteristics of these conjugates towards phosphate are demonstrated using absorption spectroscopy. The negatively charged phosphate group is received preferentially by the carboxylic terminal over the ester terminal conjugate.
Nanofibers formed through π···π stacking of the complexes of glucosyl- C2-salicyl-imine and phenylalanine: Characterization by microscopy, modeling by molecular mechanics, and interaction by α-helical and β-sheet proteins
Acharya A., Ramanujam B., Mitra A., Rao C.P.
Article, ACS Nano, 2010, DOI Link
View abstract ⏷
This paper deals with the self-assembly of the 1:1 complex of two different amphiphiles, namely, a glucosyl-salicyl-imino conjugate (L) and phenylalanine (Phe), forming nanofibers over a period of time through π·· ·π interactions. Significant enhancement observed in the fluorescence intensity of L at ∼423 nm band and the significant decrease observed in the absorbance of the ∼215 nm band are some characteristics of this self-assembly. Matrix-assisted laser desorption ionization/time of flight titration carried out at different time intervals supports the formation of higher aggregates. Atomic force microscopy (AFM), transmission electron microscopy, and scanning electron miscroscopy results showed the formation of nanofibers for the solutions of L with phenylalanine. In dynamic light scattering measurements, the distribution of the particles extends to a higher diameter range over time, indicating a slow kinetic process of assembly. Similar spectral and microscopy studies carried out with the control molecules support the role of the amino acid moiety over the simple - COOH moiety as well as the side chain phenyl moiety in association with the amino acid, in the formation of these fibers. All these observations support the presence of π···π interactions between the initially formed 1:1 complexes leading to the fiber formation. The aggregation of 1:1 complexes leading to fibers followed by the formation of bundles has been modeled by molecular mechanics studies. Thus the fiber formation with L is limited to phenylalanine and not to any other naturally occurring amino acid and hence a polymer composed of two different biocompatible amphiphiles. AFM studies carried out between the fiber forming mixture and proteins resulted in the observation that only BSA selectively adheres to the fiber among the three α-helical and two β-sheet proteins studied and hence may be of use in some medical applications. © 2010 American Chemical Society.
Benzothiazole appended lower rim 1,3-di-amido-derivative of calix[4]arene: Synthesis, structure, receptor properties towards Cu2+, iodide recognition and computational modeling
Joseph R., Chinta J.P., Rao C.P.
Article, Inorganica Chimica Acta, 2010, DOI Link
View abstract ⏷
A new molecular fluorescent sensor (L) for Cu2+ has been synthesized by derivatizing the lower rim of calix[4]arene with benzothiazole moiety, through amide linkage to result in 1,3-di-derivative. The receptor molecule, L exhibited fluorescence quenching towards Cu2+ among eleven divalent ions, viz., Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg 2+, Ca2+, Mg2+ and Pb2+, studied. The 1:1 stoichiometry of the complex formed between L and Cu2+ has been demonstrated by electronic absorption and ESI-MS. The role of calix[4]arene for the selective sensing of Cu2+ has been established by comparing the data with that obtained for an appropriate control molecule. The minimum concentration at which L can detect Cu2+ has been found to be 403 ppb. The computations carried out at DFT level have provided the coordination and structural features of the Cu2+ complex of L as species of recognition. The Cu2+ complex thus formed recognizes iodide by bringing change in the color, among the 14 anions studied. © 2010 Elsevier B.V. All rights reserved.
Interaction of aromatic imino glycoconjugates with jacalin: Experimental and computational docking studies
Kumar A., Ramanujam B., Singhal N.K., Mitra A., Rao C.P.
Article, Carbohydrate Research, 2010, DOI Link
View abstract ⏷
Altering the lectin properties by chemically modified glycoconjugates can have profound effect on their biological applications. In the present case, jacalin has been chosen to study the binding aspects toward glycoconjugates modified by connecting aromatic moieties through imine conjugation at their C-1- or C-2-positions. Out of 10 glycoconjugates, the galactosyl-naphthyl imine (1c) was found to be most effective toward agglutination inhibition (260 times better than galactose), quenching fluorescence intensity, and exhibiting greater binding (Ka, 1.3 × 104 M-1) with jacalin. The specific binding of galactose conjugates and the nonspecific binding of other conjugates have been demonstrated based on ITC. Changes in the secondary structures have been addressed by far- and near-UV CD spectroscopy. The present studies demonstrated that galactose-based conjugates bind at carbohydrate recognition domain (CRD) mainly through polar interactions in addition to exhibiting some nonpolar/hydrophobic interactions, whereas the conjugates other than galactose primarily interact through hydrophobic interactions. Binding of galactosyl conjugates at CRD has been further demonstrated by rigid docking. © 2010 Elsevier Ltd. All rights reserved.
1-(d-Glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxynaphth alene as chemo-sensor for Fe3+ in aqueous HEPES buffer based on colour changes observable with the naked eye
Mitra A., Ramanujam B., Rao C.P.
Article, Tetrahedron Letters, 2009, DOI Link
View abstract ⏷
A new glucose-based C2-derivatized colorimetric chemo-sensor (L1) has been synthesized by a one-step condensation of glucosamine and 2-hydroxy-1-naphthaldehyde for the recognition of transition metal ions. Among the eleven metal ions studied, viz., Mg2+, Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Hg2+, L1 results in visual colour change only in the presence of Fe2+, Fe3+and Cu2+ in methanol. However, in an aqueous HEPES buffer (pH 7.2) it is only the Fe3+ that gives a distinct visual colour change even in the presence of other metal ions, up to a concentration of 280 ppb. The changes have been explained based on the complex formed, and the composition has been determined to be 2:1 between L1 and Fe3+ based on Job's plot as well as ESI MS. The structure of the proposed complex has been derived based on HF/6-31G calculations. © 2008 Elsevier Ltd. All rights reserved.
Selective recognition of Cu2+ by di-O-picolyl derivative of 1,1′-methylene-bis(2-naphthol)
Baghel G.S., Ramanujam B., Rao C.P.
Article, Journal of Photochemistry and Photobiology A: Chemistry, 2009, DOI Link
View abstract ⏷
Di-derivatives of 1,1′-methylene-bis(2-naphthol) (L1) possessing ester (L2), carboxylic acid (L3) or picolyl (L4) as end groups of the pendants have been synthesized and characterized. Titration of these derivatives for their recognition towards M2+ (where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn) were performed by following the fluorescence emission intensities in methanol solution. The picolyl derivative (L4) has been found to be well suited for Cu2+ recognition (≤630 ppb) via the formation of 1:1 complex that was further proven based on absorption as well as ESI MS studies. On the other hand, L1 and L2 were mainly insensitive towards M2+, where as the carboxylic derivative (L3) shows fluorescence changes with almost all the metal ions and hence none of the L1, L2 and L3 are suited for any M2+ recognition. The studies clearly suggested that the chemical nature of the functional groups and the coordination preferences of the metal ion seem to play important role in the selective recognition of the metal ion. © 2008 Elsevier B.V. All rights reserved.
Coordination characteristics of di-O-picolyl derivative of 1,1′-methylene-bis(2-naphthol): First crystal structure of a monomeric Cu(II) complex of bis{2-[(pyridin-2-yl)methoxy] naphthalen-1-yl}methane
Baghel G.S., Mobin S.M., Rao C.P.
Article, Inorganica Chimica Acta, 2009, DOI Link
View abstract ⏷
Monomeric Cu(II) complex of bis{2-[(pyridin-2-yl)methoxy] naphthalen-1-yl}methane (L) having a composition, {[Cu(L)(H2O)(ClO4)](ClO4)(CH3OH)2} (1) has been synthesized and characterized by analytical, spectral and magnetic methods and the structure has been established for the first time based on single crystal XRD. The Cu2+ center shows axially elongated octahedron with a bound water and perchlorate moieties, where two of the coordinations were long but within the van der Waals distance. The bound water, perchlorate ions and the methanol of crystallization are primarily responsible for the formation of extended lattice structure resulted from the intra-helical interactions. Complex 1 exhibit catecholase activity as studied using 3,5-di-tert-butyl catechol. © 2008 Elsevier B.V. All rights reserved.
C1-/C2-aromatic-imino-glyco-conjugates: Experimental and computational studies of binding, inhibition and docking aspects towards glycosidases isolated from soybean and jack bean
Kumar A., Singhal N.K., Ramanujam B., Mitra A., Rameshwaram N.R., Nadimpalli S.K., Rao C.P.
Article, Glycoconjugate Journal, 2009, DOI Link
View abstract ⏷
Several C1-imino conjugates of d-galactose, d-lactose and d-ribose, where the nitrogen center was substituted by the salicylidene or naphthylidene, were synthesized and characterized. Similar C2-imino conjugates of d-glucose have also been synthesized. All the glyco-imino- conjugates, which are transition state analogues, exhibited 100% inhibition of the activity towards glycosidases extracted from soybean and jack bean meal. Among these, a galactosyl-napthyl-imine-conjugate (1c) showed 50% inhibition of the activity of pure α-mannosidase from jack bean at 22∈± ∈2.5 μM, and a ribosyl-naphthyl-imine-conjugate (3c) showed at 31∈±∈5.5 μM and hence these conjugates are potent inhibitors of glycosidases. The kinetic studies suggested non-competitive inhibition by these conjugates. The studies are also suggestive of the involvement of aromatic, imine and carbohydrate moieties of the glyco-imino-conjugates in the effective inhibition. The binding of glyco-imino-conjugate has been established by extensive studies carried out using fluorescence emission and isothermal titration calorimetry. The conformational changes resulted in the enzyme upon interaction of these derivatives has been established by studying the fluorescence quench of the enzyme by KI as well as from the secondary structural changes noticed in CD spectra. All these studies revealed the difference in the binding strengths of the naphthylidene vs. salicylidene as well as galactosyl vs. lactosyl moieties present in these conjugates. The differential inhibition of these glyco-conjugates has been addressed by quantifying the specific interactions present between the glyco-conjugates and the enzyme by using rigid docking studies. © 2008 Springer Science+Business Media, LLC.
Fluorescence switch-on sensor for Cu2+ by an amide linked lower rim 1,3-bis(2-picolyl)amine derivative of calix[4]arene in aqueous methanol
Joseph R., Ramanujam B., Acharya A., Rao C.P.
Article, Tetrahedron Letters, 2009, DOI Link
View abstract ⏷
A highly selective fluorescence switch on sensor, L for detecting Cu2+ has been synthesized by introducing a bis-(2-picolyl)amine moiety at the lower rim of a calix[4]arene platform via amide linkage. Binding properties of L toward ten different biologically relevant Mn+ ions have been studied by fluorescence and absorption spectroscopy in methanol and aqueous methanol. L was found to detect Cu2+ selectively down to a concentration of 196 and 341 ppb, respectively, in methanol and 1:1 aqueous methanol even in the presence of other metal ions. The composition of the complex has been found to be 1:1 based on the Job plot and is further confirmed by ESI MS. The role of calix[4]arene platform as well as the pre-organized binding core in the selective recognition of Cu2+ has been demonstrated by studying appropriate reference molecules. The possible modes of binding of L with Cu2+ have been modeled by computational calculations. L and its Cu2+ complex could very well be differentiated based on the nano-structural features observed in SEM and AFM. © 2009 Elsevier Ltd. All rights reserved.
Selective recognition of Zn2+ by salicylaldimine appended triazole-linked di-derivatives of calix[4]arene by enhanced fluorescence emission in aqueous-organic solutions: role of terminal -CH2OH moietieefs in conjunction with the imine in recognition
Pathak R.K., Ibrahim Sk.Md., Rao C.P.
Article, Tetrahedron Letters, 2009, DOI Link
View abstract ⏷
A series of lower rim 1,3-di-derivatives possessing Schiff's base cores were synthesized using triazole unit as linker moiety by further introducing butyl (L2), one -CH2OH (L3) and two -CH2OH (L4)-containing moieties, respectively, in order to bring additional support for ion binding. Based on fluorescence and absorption spectroscopies it has been shown that Zn2+ could be selectively recognized by the Schiff's base core and not by the triazole core among the ten metal ions studied both in methanol and in aqueous solutions of methanol and acetonitrile, wherein the -CH2OH moieties augment the fluorescence response by providing additional coordinations to the Zn2+. Thus L4 exhibited a fluorescence enhancement of ∼65, ∼48 and ∼25-fold in methanol, aqueous solutions of methanol and acetonitrile, with minimum detection limits of 174, 313 and 320 ppb, respectively. Both the excitation and emission wavelengths fall in visible region. © 2009 Elsevier Ltd. All rights reserved.
Spectroscopy and microscopy studies of the recognition of amino acids and aggregation of proteins by Zn(II) complex of lower rim naphthylidene conjugate of calix[4]arene
Chinta J.P., Acharya A., Kumar A., Rao C.P.
Article, Journal of Physical Chemistry B, 2009, DOI Link
View abstract ⏷
A lower rim naphthylidene conjugate of calix[4]arene [L] has been synthesized and characterized, and the structure has been established on the basis of single crystal XRD. The L has been found to be selective toward Zn 2-, which induces appropriate changes in the arms of L so that the N2O2 coordination results in the formation of a tetrahedral complex; namely, [ZnL]. [ZnL] recognizes Asp, Cys, His, and Glu from among the naturally occurring amino acids owing to the protonation and chelating ability of the amino acid and the π-π interaction ability of the side chain of the amino acid with [ZnL]. AU of these features have been demonstrated on the basis of fluorescence, absorption, and lifetime measurements. The rechelation of Zn2- by the amino acid used in the titration has been demonstrated on the basis of ESI-MS studies in the case of Cys to result in a Zn2+ complex having either 5- or 6-coordination. [ZnL] has also been shown to be selective toward glutathione and glutathione oxidized. The amino acids present in the proteins also interact with [ZnL], resulting in dechelation of [ZnL] as well as aggregation of the protein, as demonstrated on the basis of absorption and fluorescence spectroscopy and atomic force microscopy. The α-helical proteins (namely, albumins) exhibit greater conformational changes, as compared to the β-sheet proteins (namely, lectins), as studied on the basis of CD spectroscopy. The aggregation of the proteins when treated with [ZnL] follows a trend: peanut agglutinin < bovine serum albumin < jacalin < human serum albumin. The present studies clearly demonstrated the recognition features of [ZnL] toward Asp, Cys, His, and Glu, and the peptides and proteins containing these by spectroscopy and microscopy studies. © 2009 American Chemical Society.
Synthesis and characterization of complexes of Fe(III), Co(III), Ni(II), Cu(II), Zn(II) and UO22+ with p-tert-butylcalix[4]arene bearing two imine pendants linked through salicylyl moiety at the lower rim
Dey M., Chinta J.P., Long G.J., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2009,
View abstract ⏷
Metal ion complexes of the double-armed p-tert-butylcatix[4]arene derivative possessing ¡mine functionality linked through salicylyl moiety at the lower rim has been synthesized for the first time and characterized by analytical, spectral and magnetic methods. The 1, 3- di-calix[4]arene-imine conjugate exhibits variable coordination behavior, from tctradcntatc to hexadentate, depending upon the metal ion to which it is bound, by always acting as di-anionic. While it uses both the ether oxygens of the pendants to coordinate in the case of Fc(III), Co(III) and Ni(II) complexes, it uses only the pendant salicylidene moieties in the case of Cu(II) and Zn(II) complexes. The Zn(II) complex catalysis ester hydrolysis through the formation of Zn(II)-hydroxo species.
Role of the orientation of –OH groups in the sensitivity and selectivity of the interaction of M2+ with ribosyl- and galactosyl-imino-conjugates
Singhal N.K., Mitra A., Rajsekhar G., Shaikh M.M., Kumar S., Guionneau P., Rao C.P.
Article, Journal of the Chemical Society. Dalton Transactions, 2009, DOI Link
View abstract ⏷
Three glyco-conjugates, viz., L1, L2and L3, which differ either in their carbohydrate moiety or in their aromatic moiety or both, were synthesized and characterized and were shown to have β-anomeric form based on1 H NMR and optical rotation studies. Metal ion interaction studies carried out in solution by emission and absorption spectral techniques exhibited selectivity towards Cu2+ in HEPES buffer and a two fold higher sensitivity for L2as compared to L1. The composition of the complexed species has been established based on ESI MS. Dinuclear-Cu(II) complexes of all these conjugates have been synthesized and characterized based on analytical and spectral methods including FTIR,1 H NMR, FAB MS, EPR, ORD, CD and magnetism, and the structures of 1 and 3 have been established based on single crystal XRD. The structures revealed subtle differences present in the orientation of the –OH groups and also their ion binding preferences both at the molecular level as well as at the lattice levels. In the dinuclear-Cu(II) complexes, while C3-O- of ribosyl acts as a bridging moiety in 1, it is the C2-O- of galactosyl that bridges in 3 and the Cu2O2cores are stabilized by two intra-complex H-bond interactions formed using C4-OH in the case of 1 and C3-OH in the case of 3. While the glyco-moiety is poised perpendicular to the average plane of the Cu2O2core in 1, this is in plane in the case of 3. © 2009 The Royal Society of Chemistry.
Pamoic acid in forming metallo-organic framework: Synthesis, characterization and first crystal structure of a dimeric Ti(IV) complex
Article, Polyhedron, 2009, DOI Link
View abstract ⏷
Two novel dinuclear Ti(IV) complexes of the ligand, 4,4′-methylene-bis (3-hydroxy-2-naphthalene carboxylic acid) (H4L) or pamoic acid having compositions, [(HL)2Ti2(μ-O)(DMF)2]·(DMF)6 (1) and [(L)2Ti2(μ-O)(DMF)2]·(DMF)4(4,4′-Bipy-2H)(H2O), (2) have been synthesized and characterized by analytical and spectral methods and the structure has been established by single crystal XRD. Unlike the reported polymeric structures observed in case of H4L or pamoic acid, the anti-conformation of H4L changes to syn - orientation to avoid poly-metallic complex formation, as noticed in 1 and 2. The dimeric Ti(IV) units stack in the lattice to form helical columns and the space between the adjacent columns is being filled by the solvent molecules in 1 and solvent plus the protonated 4,4′-bipy in the lattice of 2 and thus the neighbor columns are connected through weak interactions. © 2009 Elsevier Ltd. All rights reserved.
Lower rim 1,3-di{bis(2-picolyl)}amide derivative of calix[4]arene (L) as ratiometric primary sensor toward Ag+ and the complex of Ag + as secondary sensor toward cys: Experimental, computational, and microscopy studies and INHIBIT logic gate properties of L
Joseph R., Ramanujam B., Acharya A., Rao C.P.
Article, Journal of Organic Chemistry, 2009, DOI Link
View abstract ⏷
(Figure Presented) Astructurally characterized lower rim 1,3-di{bis(2-picolyl)}amide derivative of calix[4]arene (L) exhibits high selectivity toward Ag+ by forming a 1:1 complex, among nine other biologically important metal ions, viz., Na+, K+, Mg 2+, Ca2+, Mn2+, Fe2+, Co 2+, Ni2+, and Zn2+, as studied by fluorescence, absorption, and 1H NMR spectroscopy. The 1:1 complex formed between L and Ag+ has been further proven on the basis of ESI mass spectrometry and has been shown to have an association constant, Ka, of 11117 ± 190 M-1 based on fluorescence data. L acts as a primary ratiometric sensor toward Ag+ by switch-on fluorescence and exhibits a lowest detectable concentration of 450 ppb. DFT computational studies carried out in mimicking the formation of a 1:1 complex between L and Ag + resulted in a tetrahedral complex wherein the nitrogens of all four pyridyl moieties present on both arms are being coordinated. Whereas these pyridyls are located farther apart in the crystal structure, appropriate dihedral changes are induced in the arms in the presence of silver ion in order to form a coordination complex. Even the nanostructural features obtained in TEM clearly differentiates L from its Ag+ complex. The in situ prepared silver complex of L detects Cys ratiometrically among the naturally occurring amino acids to a lowest concentration of 514 ppb by releasing L from the complex followed by formation of the cysteine complex of Ag+. These were demonstrated on the basis of emission, absorption, 1H NMR, and ESI mass spectra. The INH logic gate has also been generated by choosing Ag + and Cys as input and by monitoring the output signal at 445 nm that originates from the excimer emission of L in the presence of Ag+. Thus L is a potential primary sensor toward Ag+and is a secondary sensor toward Cys. ©2009 American Chemical Society.
Influence of alkali and alkaline earth ions on the O-alkylation of the lower rim phenolic-OH groups of p-tert-butyl-calix[4]arene to result in amide-pendants: Template action of K+ and the structure of K + bound tetra-amide derivative crystallized with a p-tert-butyl-calix[4]arene anion
Ali A., Rao C.P., Guionneau P.
Article, Journal of Chemical Sciences, 2008, DOI Link
View abstract ⏷
Role of alkali and alkaline earth ions on the formation of calix[4]arene-amide derivatives through O-alkylation of the lower rim phenolic-OH groups in general and template action of K+ in particular have been explored. Na+ and K+ ions among alkali, and Ca2+ and Sr2+ ions among alkaline earth have shown tetra-amide derivatives bound to metal ion species. Among all these, potassium salts act as template and yields a K+ bound tetra-amide derivative where the charge is counter balanced by a calix[4] arene-monoanion and the product is crystallographically characterized. Change in the amide precursor used in these O-alkylation reactions has no effect on the type of the amide derivative formed. Also demonstrated is a direct one-step reaction for the preparation of 1,3-di-amide derivative in high yield and low reaction period using CsHCO3. © Indian Academy of Sciences.
Lower rim 1,3-di-amide-derivative of calix[4]arene possessing bis-{N-(2,2′-dipyridylamide)} pendants: a dual fluorescence sensor for Zn2+ and Ni2+
Joseph R., Ramanujam B., Pal H., Rao C.P.
Article, Tetrahedron Letters, 2008, DOI Link
View abstract ⏷
Single crystal XRD structure of the lower rim 1,3-di-amide-derivative of calix[4]arene possessing bis-{N-(2,2′-dipyridylamide)} pendants (L) exhibit two distinct binding cores, viz., N4 and O6. L was found to be selective for Zn2+ by switch-on and for Ni2+ by switch-off fluorescence by forming 1:1 complexes. The binding and the composition of the complex formed have been addressed based on steady state and time-resolved fluorescence spectroscopy in addition to the absorption and ESI MS. As L can detect Zn2+ and Ni2+ to a concentration as low as 142 and 203 ppb, respectively, L can be a very sensitive molecular probe for these ions. The coordination details of the metal ion-bound complexes have been addressed based on ab initio calculations showing that the stabilization energies are commensurate with the coordination formed. © 2008 Elsevier Ltd. All rights reserved.
Experimental and computational studies of selective recognition of Hg 2+ by amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene: Species characterization in solution and that in the isolated complex, including the delineation of the nanostructures
Joseph R., Ramanujam B., Acharya A., Khutia A., Rao C.P.
Article, Journal of Organic Chemistry, 2008, DOI Link
View abstract ⏷
(Chemical Equation Presented) Amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene, L has been shown to be sensitive and selective to Hg2+ in aqueous acetonitrile solution based on fluorescence spectroscopy, and the stoichiometry of the complexed species has been found to be 1:1. The selectivity of L toward Hg2+ has been shown among 11 M2+ ions, viz., Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg 2+, Pb2+, Ca2+, and Mg2+ studied, including those of the mercury group and none of these ions impede the recognition of Hg2+ by L. Role of the solvent on the recognition of Hg2+ has been demonstrated. The role of calix[4]arene platform and the benzimidazole moieties in the recognition of Hg2+ by L has been delineated upon performing such studies with five different molecules of relevance as reference molecular systems. The binding cores formed by the receptor L and the reference compounds have been established based on the single crystal XRD structures, and the preferential metal ion binding cores have been discussed. The binding of Hg2+ with L has been further established based on 1H and 13C NMR, ESI MS, absorption, and fluorescence lifetime measurements. Some of these techniques have been used to establish the stoichiometry of the species formed. The complex species formed between L and Hg2+ have been isolated and characterized and found to be 1:1 species even in the isolated complex. Whereas transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) provided the nanostructural behavior of L, the TEM and SEM demonstrated that the mercury complex has different characteristics when compared to L. The TEM, SEM, and powder XRD studies revealed that whereas L is crystalline, that of the mercury complex is not, perhaps a reason for not being able to obtain single crystals of the complex. Binding characteristics of Hg2+ toward L have been established based on the DFT computational calculations. © 2008 American Chemical Society.
Experimental and computational studies of the recognition of amino acids by galactosyl-imine and -amine derivatives: An attempt to understand the lectin-carbohydrate interactions
Ahuja R., Singhal N.K., Ramanujam B., Ravikumar M., Rao C.P.
Article, Journal of Organic Chemistry, 2007, DOI Link
View abstract ⏷
(Chemical Equation Presented) A galactosyl-naphthyl-imine-based derivative, 1-(β-D-galactopyranosyl-1′-deoxy-1′-iminomethyl)-2- hydroxynaphthalene (GNI), and a galactosyl-naphthyl-amine-based derivative, 1-(galactopyranosyl-1′-deoxy-1′-aminomethyl)-2-hydroxynaphthalene (GNA), possessing an ONO binding core were studied for their recognition of naturally occurring amino acids using fluorescence and absorption spectroscopy, and the corresponding association constants were derived for the complexes formed. The complexes formed between GNI/GNA and amino acids were supported by electrospray ionization mass spectrometry (ESI/MS). The structures of the complexes were optimized by computational studies using density functional theory, and stabilization energies were computed for the complexes to substantiate the interactions present between GNI/GNA and amino acid. The interactions were found to be primarily hydrogen bonding in nature. These interactions are reminiscent of those present in the lectin-carbohydrate and glycosidase substrate. Thus, the carbohydrate moiety present in GNI shows high specificity toward the -COOH group of the amino acid, which may be relevant to such interactions present between the carbohydrates and the polypeptides. © 2007 American Chemical Society.
Fluorescence and absorption studies on the selective recognition of iodide by lower rim 1,3-bis(aminoethoxy)-p-t-butyl-calix[4]arene derivative
Joseph R., Gupta A., Ali A., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2007,
View abstract ⏷
Lower rim 1,3-bis(aminoethoxy)-p-t-butyl-calix[4]arene derivative (L) has been subjected to fluorescence and absorption studies to evaluate its utility to recognize halides. This derivative has been found to be selective towards iodide, immaterial of its counter cation as well as the presence of other halide ions. Combining this data with that of the negative ion mass spectrometry and 1H NMR spectra, an arene cavity bound iodide species is proposed.
Photophysical properties of the interaction of lower rim 1,3-bis(aminoethoxy)-calix[4]arene derivative with Pb2+, Hg2+ and Cd2+ions: Recognition of Hg2+
Joseph R., Gupta A., Rao C.P.
Article, Journal of Photochemistry and Photobiology A: Chemistry, 2007, DOI Link
View abstract ⏷
Interaction of heavy metal ions, viz., Pb2+, Hg2+ and Cd2+ with 1,3-bis(aminoethoxy)-calix[4]arene was studied using emission spectroscopy and the corresponding binding parameters were derived. Based on the changes observed in the fluorescence during titration with these metal ions, two types of species were proposed, viz., one in which the metal ion is bound at the lower rim, the other in which the metal ion interacts through the hydrophobic arene cavity. The extent to which these species were present depends upon the type of the metal ion as well as the number of metal ion equivalents added. The results were compared with unmodified calix[4]arene titration data. Based on these studies, Hg2+ can distinctly be recognized from the other heavy metal ions. © 2006 Elsevier B.V. All rights reserved.
Synthesis and characterization of Sn(IV) complexes of lower rim 1,3-diacid derivative of calix[4]arene and their protective effects on tissue oxidative stress and essential metal concentration in lead exposed male Wistar rats
Ali A., Flora S.J.S., Saxena G., Kolehmainen E., Mahieu B., Rao C.P.
Article, Journal of Inorganic Biochemistry, 2006, DOI Link
View abstract ⏷
The two Sn(IV) complexes synthesized using calix[4]arene-1,3-di-acid derivative were characterized by analytical, 1H, 13C and 119Sn NMR, matrix assisted laser desorption ionization mass, and 119Sn Mossbauer techniques and found that the complexes are tetranuclear possessing structurally two different types of tin centers. These complexes were evaluated for their protective value against blood and tissue oxidative stress in lead exposed male albino rats of Wistar strain. The results suggest that the two tin complexes significantly protect changes in lead induced biochemical variables indicative of heme synthesis pathway and exhibit only moderate effect on tissue oxidative stress. The beneficial effects could be attributed mainly to the ability of Sn(IV) complexes in preventing absorption of lead to the target sites/tissues. © 2005 Elsevier Inc. All rights reserved.
Photo-physical behavior as chemosensor properties of anthracene-anchored 1,3-di-derivatives of lower rim calix[4]arene towards divalent transition metal ions
Kumar A., Ali A., Rao C.P.
Article, Journal of Photochemistry and Photobiology A: Chemistry, 2006, DOI Link
View abstract ⏷
Anthracene anchored 1,3-di-derivatives of lower rim p-tert-butyl-calix[4]arene were synthesized and characterized. These derivatives were subjected to the binding studies with the divalent metal ions, viz., Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+ using fluorescence and absorption spectra. The imine moiety that is in conjugation with the anthryl unit is responsible for quenching the fluorescence in the absence of metal ion, however, in the presence of Fe2+ and Cu2+, the spectra showed very high enhancement in fluorescence intensity indicating that the lone pair present on the imine-N is involved in the metal ion binding and as a result the photo-induced electron transfer is prevented. Based on the photo-physical studies, it has been found that the anthracene derivative that is coupled with the calix[4]arene unit through an imine bond acts as a chemosensor for Fe2+ and Cu2+. The fluorescence studies are further augmented by the absorption spectra. © 2005 Elsevier B.V. All rights reserved.
Mono- and di-nuclear Cu(II) complexes of p-tert-butyl-calix[4]arene-1,3- diacid derivative: A comparative study of their characterization and catecholase mimetic activity
Ali A., Salunke-Gawali S., Rao C.P., Linares J.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2006,
View abstract ⏷
Reaction of copper(II) perchlorate with p-tert-butyl-calix[4]arene-1,3- diacid gives mono-nuclear complex in acetonitrile and dinuclear complex in methanol which have been isolated as their pyridine bound adducts. The dinuclear complex exhibits different characteristics in its EPR and magnetic studies. The reactivity studies clearly indicate that the dinuclear complex has higher catecholase mimetic activity over its mononuclear counterpart owing to its coordination favourability.
Carbohydrate-based switch-on molecular sensor for Cu(II) in buffer: Absorption and fluorescence study of the selective recognition of Cu(II) ions by galactosyl derivatives in HEPES buffer
Singhal N.K., Ramanujam B., Mariappanadar V., Rao C.P.
Article, Organic Letters, 2006, DOI Link
View abstract ⏷
1-(β-D-Galactopyranosyl-1′-deoxy-1′-iminomethyl) -2-hydroxynaphthalene (L1), possessing an ONO binding core, was found to be selective for Cu2+ ions in N-[2-hydroxyethyl]piperazine- N′-[2-ethanesulfonic acid] buffer, at concentrations ≤580 ppb, at physiological pH by eliciting switch-on behavior, whereas the other ions, viz., Mg2+, Ca2+, Mn2+, Fe2+, Co 2+, Ni2+, Zn2+, and Cd2+, caused no significant change in the fluorescence. Whereas the binding characteristics were ascertained by absorption spectroscopy, the species formed were shown by Q-TOF ES MS. © 2006 American Chemical Society.
Lectins: Chemical, structural and biological aspects including drug targeting
Ahuja R., Singhal N.K., Rao C.P.
Review, Chemistry, 2006,
View abstract ⏷
This review is primarily intended to attract the attention of amateurs into the field of lectins, an interdisciplinary science that promises its future impact in disease diagnosis and therapy, by providing simple and yet informative features of lectins highlighting chemical, structural and biological aspects including its applications in drug targeting and use of lectin-gold complexes in diagnosis.
Formation of mono- and di-amide-calix[4]arene derivatives from the reaction of p-tert-butyl-calix[4]arene and α-chloro-N,N-diethylacetamide in the presence of sodium hydride
Article, Indian Journal of Chemistry - Section B Organic and Medicinal Chemistry, 2005,
View abstract ⏷
The formation of mono- and di (1,2 and 1,3)-amide derivatives of p-tert-butylcalix[4]arene in the presence of sodium hydride has been demonstrated. All the compounds have been purified and characterized by various spectral methods. Both 1H and 13C NMR spectra exhibit clear-cut differences between the 1,2-di- and 1,3-di-amide derivatives.
Structural characterization and reactivity of Cu(II) complex of p-tert-butyl-calix[4]arene bearing two imine pendants at lower rim
Dey M., Rao C.P., Guionneau P.
Article, Inorganic Chemistry Communications, 2005, DOI Link
View abstract ⏷
Cu(II) complex of the double-armed p-tert-butylcalix[4]arene conjugate possessing imine functionality at the lower rim was synthesized and was characterized by analytical, spectral and crystallographic methods and its catecholase activity was evaluated. © 2005 Elsevier B.V. All rights reserved.
A direct fluorescence-on chemo-sensor for selective recognition of Zn(II) by a lower rim 1,3-di-derivative of calix[4]arene possessing bis-{N-(2-hydroxynaphthyl-1-methylimine)} pendants
Dessingou J., Joseph R., Rao C.P.
Article, Tetrahedron Letters, 2005, DOI Link
View abstract ⏷
The bis-{N-(2-hydroxynaphthyl-1-methylimine)} anchored 1,3-di-derivative of lower rim p-tert-butyl-calix[4]arene possessing a N2O2, N2O4 or N2O6 binding core was found to be selective for Zn(II) ions even at ≤60 ppb by eliciting fluorescence-on behaviour while the other ions, viz., Ti4+, VO2+, Cr 3+, Mn2+, Fe2+, Co2+, Ni 2+, Cu2+, Mg2+, Cd2+ and Hg 2+ caused no change in the fluorescence. The reaction between 1 and Zn2+ was found to be stoichiometric with the formation of a 1:1 complex; while H+ quenched the fluorescence of the complex, OH - restored it. The studies of the 1:1 isolated complexes of Zn 2+, Ni2+ and Cu2+ augmented the results. © 2005 Elsevier Ltd. All rights reserved.
Complexation behaviour of hexadentate ligands possessing N 2O4 and N2O2S2 cores: Differential reactivity towards Co(II), Ni(II) and Zn(II) salts and structures of the products
Rajsekhar G., Rao C.P., Saarenketo P., Nattinen K., Rissanen K.
Article, New Journal of Chemistry, 2004, DOI Link
View abstract ⏷
Reactions of divalent metal salts of Co, Ni and Zn with 1,2-di(salicylaldimino-o-phenylthio)ethane (H2L1) and 1,2-di(naphthaldimino-o-phenylthio)ethane (H2L2), having N2O2S2 cores, and 1,2-di(O-salicylaldimino-o- hydroxyphenyl)ethane (H2L3), having a N2O 4 core, have been explored. Out of the three ligands and the nine products obtained from the corresponding reactions, two ligands and seven products were crystallographically characterized. However, all the ligands and the products were characterized by analytical and spectral methods. Reaction of H2L1 and H2L2 with Co(II) salts results in oxidative cleavage of the C-S bond to produce a CO(III) product bound to two dissimilar tridentate ligands formed as a result of the cleavage. The reaction of H2L1 and H2L2 with Co(III)acac in the presence of methanolic NaOH also shows cleavage of the C-S bond to give compounds similar to those obtained by reacting H2L 1 and H2L2 with Co(II) salts in the absence of additional external base. However, the reaction of Co(II) salt with H 2L3 did not lead to any C-O bond cleavage; rather it produced an octahedral CO(II) complex of the hexadentate H2L 3. Reactions of all these three ligands with Ni(II) salt resulted in octahedral complexes of the corresponding hexadentate ligands. In the case of Zn(II), while H2L3 with a N2O4 core resulted in an octahedral complex, H2L1 and H 2L2, both with a N2O2S2 core, produced pseudo-octahedral complexes whose Zn-S bond lengths are rather long. The conformations of both the 5-membered and 6-membered chelate rings formed in the products were evaluated. The extent of distortion exhibited in the geometry of these octahedral complexes was computed and appropriately compared.
A first report of the complexes of 5,11,17,23-tetra-tert-butyl-25,27- diethoxycarboxymethoxy-26,28-dihydroxycalix[4]arene with Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II)
Ali A., Salunke-Gawali S., Rao C.P., Linares J.
Article, Inorganic Chemistry Communications, 2004, DOI Link
View abstract ⏷
Complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) of 5,11,17,23-tetra-tert-butyl-25,27-diethoxy-carboxymethoxy-26, 28-dihydroxycalix[4]arene were synthesized for the first time and were well characterized. Totally six dinuclear complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) of calix[4]arene derivatized with two pendants possessing terminal -COOH functions at two of its alternate phenolic -OH groups were synthesized for the first time and were well characterized. © 2004 Elsevier B.V. All rights reserved.
2-Hydroxy-1-naphthaldehyde-derived Schiff bases: Synthesis, characterization, and structure
Rao P.V., Rao C.P., Wegelius E.K., Rissanen K.
Article, Journal of Chemical Crystallography, 2003, DOI Link
View abstract ⏷
Four Schiff base molecules were synthesized from the condensation of 2-hydroxy1-naphthaldehyde with various amines having additional ligating centers, and the resulting products were characterized by analytical and spectral methods, and also by single crystal X-ray diffraction. 2-(β-Naphthalideneamino)-2-methyl-1-propanol, 1, is orthorhombic, P2 12121, a = 9.918(1), b = 12.629(1), c = 10.416(1) Å. 2-(β-Naphthalideneamino)-2-hydroxymethyl-1-propanol, 2, is monoclinic, P21/c, a = 14.522(3), b = 9.723(2), c = 9.534(9) Å, β= 107.75(4)°. 2-(β-Naphthalideneamino)-2-hydroxymethyl- 1,3-propanediol, 3, is monoclinic, P21/c, a = 20.981(9), b = 5.943(3), c = 10.549(5) Å, β= 91.23(3)°. 2-(β- Naphthalideneamino)-pyridine, 4, is monoclinic, P21/c, a = 5.804(4), b = 17.363(2), c = 24.032(11) Å, β = 92.03(5)°. The molecular structures of these were found to be in extended conformation where the aromatic moiety is coplanar with that of the imine bond and the imine bond exhibited trans-geometry. The naphthyl moiety in each of these molecules is stabilized in quinoid form in the solid state. Interesting lattice structures were noticed owing to intermolecular interactions.
Saccharide complexes of lanthanides
Review, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2003,
View abstract ⏷
The main focus of this review article is to bring out different aspects of interactions of saccharides with lanthanide ions. Various characteristic properties of lanthanide-saccharide complexes have been compared appropriately with those of the transition metal ones.
First crystallographic evidence for the formation of β-D-ribopyranosylamine from the reaction of ammonia with of D-ribose
Rajsekhar G., Rao C.P., Guionneau P.
Article, Carbohydrate Research, 2003, DOI Link
View abstract ⏷
β-D-Ribopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. The molecule exists in the chair form with the 4C1 conformation. The β anomeric form of C-1 is supported by the dihedral angles. The molecule exhibits both intra- and intermolecular hydrogen-bond interactions of the type O-H⋯O, N-H⋯O and C-H⋯O, and these are interconnected to each other to form chains. © 2003 Elsevier Science Ltd. All rights reserved.
Synthesis and crystallographic characterization of some derivatives of benzimidazole
Das T.M., Rao C.P., Kalle N., Rissanen K.
Article, Indian Journal of Chemistry - Section B Organic and Medicinal Chemistry, 2003,
View abstract ⏷
Three derivatives of benzimidazole have been synthesized and characterized based on 1H and 13C NMR, FTIR, FAB-mass and UV spectra, and the structures of two compounds are characterized based on single crystal XRD studies. Existence of both interand intra-molecular hydrogen bonds has been identified in the case of 2-(o-aminophenyl)benzimidazole amine and not in case of N-methyl-2-(o-nitrophenyl)benzimidazole. While the former is a completely planar molecule, the latter is not. Both the compounds exhibit interesting lattice structures.
A soluble complex of Zn(II) with N2O4 core: A structural study
Sah A.K., Ali A., Wegelius E.K., Rissanen K., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2003,
View abstract ⏷
A soluble complex of Zn(II) with 1-hydroxy-3-hydroxy-2-hydroxymethyl-2-(5′-formyl-salicylidimino) propane resulting in a distorted octahedral ZnN2O4 core has been synthesized and characterized by analytical and spectral methods and the structure has been established by single crystal XRD.
Unusual interaction extended between the pyranose ring oxygen and Zn(II) center in the complexes derived from 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o- hydroxybenzylidene)-β-D-glucopyranosylamine: Evidence for a pseudo-bicapped tetrahedral complex of Zn(II) based on the crystal structure
Rajsekhar G., Rao C.P., Nattinen K., Rissanen K.
Article, Inorganic Chemistry Communications, 2003, DOI Link
View abstract ⏷
The Zn(II) complexes of 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o- hydroxybenzylidene)-β-D-glucopyranosyl-amine have been synthesized and characterized using spectral and analytical methods and structure for one of the products was established. The geometry of the complexes vary from unusual distorted trigonal bipyramidal to pseudo-bicapped tetrahedron depending upon the extent of binding of pyranose ring oxygens to the Zn(II) ion, as evidenced from crystal structures. Such interaction is also reflected on the optical rotation and CD spectral properties of these complexes in solution. © 2003 Published by Elsevier B.V.
Bis-(μ-saccharide-C-2-oxo) dinuclear Cu(II) complexes of 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o- hydroxybenzylidene/5-bromo-o-hydroxybenzylidene)-β-D-glucopyranosylamine: Structural aspects and data correlations
Rajsekhar G., Sah A.K., Rao C.P., Guionneau P., Bharathy M., Gururow T.N.
Article, Dalton Transactions, 2003, DOI Link
View abstract ⏷
A total of five dinuclear copper complexes were synthesized using 4,6-O-butylidene/ethylidene-N-(α-hydroxy-naphthylidene/ o-hydroxybenzylidene/5-bromo-o-hydroxybenzylidene)-β-D-glucopyranosylamine. Upon recrystallisation from different solvents, viz., dmso/MeOH/pyridine, seven different dinuclear copper complexes were generated, wherein the geometry around one or both of the copper centers changes from square planar to square pyramidal due to the binding of solvent molecule as the fifth ligand. The ligands and their complexes were characterized by elemental analysis, 1H and 13C NMR, FT-IR, FABMS, UV-Vis, optical rotation, CD and magnetic susceptibility measurements. The 3D structures of all the seven complexes were established by single crystal XRD. All the complexes are neutral and dinuclear with the metal to the glycosylamine ratio being 1:1. Each glycosylamine acts as tridentate with di-negative charge and bridges between the two copper centers through the C-2-oxo group of the saccharide part and further the coupling between the copper centers is antiferromagnetic. At least four different types of Cu2O22+ core structures were identified depending upon the presence or absence of a fifth ligand at the Cu(II) center. The ß-4C1-pyranose form of the glycosylamine is retained even in complexes. The dinuclear complex is stabilized through intra-complex hydrogen bond interaction. The inter-molecular C-H ⋯ O interactions are manifested in the formation of a helical structure where the water molecules occupy the cavity. The structural diversity observed in the complexes and several data correlations are discussed in detail. © The Royal Society of Chemistry 2003.
Mn(IV) and Co(III)-complexes of -OH-rich ligands possessing O2N, O3N and O4N cores: Syntheses, characterization and crystal structures
Dey M., Rao C.P., Saarenketo P.K., Rissanen K., Kolehmainen E., Guionneau P.
Article, Polyhedron, 2003, DOI Link
View abstract ⏷
Mn(IV) and Co(III) complexes of tridentate -OH-rich ligands possessing O2N, O3N and O4N donor sets were synthesized, characterized and their structures were established by single crystal X-ray diffraction, where the binding core is O4N2. In the structurally characterized complexes, the coordination geometry about the metal ion was found to be distorted octahedral. © 2003 Elsevier Ltd. All rights reserved.
Synthesis, characterization and structure of Ti(IV) complexes of hydroxy-rich ligands
Rao V.P., Kolehmainen E., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2002,
View abstract ⏷
Coordination chemistry of two multi-hydroxy rich ligands has been explored with Ti(IV) by isolating the resultant products followed by their characterization. One of the products is also structurally characterized by single crystal XRD.
Crystal structure of 4,6-O-ethylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine
Sah A.K., Rao C.P., Saarenketo P.K., Rissanen K.
Article, Carbohydrate Research, 2002, DOI Link
View abstract ⏷
4,6-O-Ethylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. The anomeric nature of the saccharide moiety was proposed based on 1H NMR studies and was confirmed by the crystal structure. The lattice structure of this compound was compared with that of its analogues. © 2002 Published by Elsevier Science Ltd.
Glycosylamines of 4,6-O-butylidene-α-D-glucopyranose: Synthesis and characterization of glycosylamines, and the crystal structure of 4,6-O-butylidene-N-(o-chlorophenyl)-β-D-glucopyranosylamine
Rajsekhar G., Rao C.P., Saarenketo P.K., Kolehmainen E., Rissanen K.
Article, Carbohydrate Research, 2002, DOI Link
View abstract ⏷
A total of nine glycosylamines of 4,6-O-butylidene-α-D-glucopyranose were synthesized using primary amines having various groups in their ortho- or para-positions. Among these, six are monoglycosylamines, including one primary glycosylamine, and three are bis-glycosylamines. All these compounds were characterized by 1H, 1H-1H COSY, 1H-13C COSY and 13C NMR spectroscopy and FTIR spectra. The FAB mass spectra provided the molecular weights of the products by exhibiting the corresponding molecular ion peaks. The crystal structure of 4,6-O-butylidene-N-(o-chlorophenyl)-β-D-glucopyranosylamine revealed the C-1 glycosylation, the β-anomeric nature, and the 4C1 chair conformation of the saccharide unit in the product. In the lattice two types of dimers exist. While one type of dimer is formed through O-H···O type of interactions, the other type is formed via C-H···O type of interactions. In the direction of these C-H···O type of interactions, the dimeric units are connected to form a chain. © 2002 Published by Elsevier Science Ltd.
Dinuclear copper complexes of N-(2-hydroxybenzylidene or 5-bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine: Coordination variation and structural diversity
Sah A.K., Rao C.P., Saarenketo P.K., Rissanen K., Van Albada G.A., Reedijk J.
Article, Chemistry Letters, 2002, DOI Link
View abstract ⏷
Dinuclear Cu(II) complexes of N-(2-hydroxybenzylidene or 5-bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine with coordination variation and molecular and lattice structural variations are explored.
Interaction of metal ions with D-glucobenzothiazoline: Isolation and characterization of the resultant products
Das T.M., Rao C.P., Kolehmainen E., Kadam R.M., Sastry M.D.
Article, Carbohydrate Research, 2002, DOI Link
View abstract ⏷
Six different metal-ion complexes of D-glucobenzothiazoline were synthesized and characterized by analytical and spectral techniques. Formation of different types of species (ML and ML2) were observed with Cu2+, Ag+, Cd2+, Hg2+, and Zn2+ ions. Existence of an anomeric mixture in the case of the Cu2+ complex is identified from the EPR spectra, and the results were further supported by the simulated spectra. The structures were proposed based on different studies. © 2002 Published by Elsevier Science Ltd.
Synthesis, structural diversity, inter-conversion and reactivity of Cu(II) complexes of hydroxy-rich molecules
Dey M., Rao C.P., Saarenketo P.K., Rissanen K.
Article, Inorganic Chemistry Communications, 2002, DOI Link
View abstract ⏷
Tetranuclear Cu(II) complexes having linear, cubane and pseudodouble-cubane cores were synthesized using hydroxy-rich molecules possessing amine and imine groups. The products were structurally characterized and were studied for their ability to oxidize catechol as well as for their inter-conversion between mono- and tetra-nuclear complexes. © 2002 Elsevier Science B.V. All rights reserved.
C-S bond cleavage by cobalt: Synthesis, characterization and crystal structure determination of 1,2-di-(o-salicylaldiminophenylthio)ethane and its CO(III) product with C-S bond cleaved fragments
Rajsekhar G., Rao C.P., Saarenketo P.K., Kolehmainen E., Rissanen K.
Article, Inorganic Chemistry Communications, 2002, DOI Link
View abstract ⏷
1,2-Di-(o-salicylaldiminophenylthio)ethane reacts with Co(II) salts to form a complex with oxidative cleavage of the C-S bond, to result in the formation of a Co(III) complex of the cleaved ligands. © 2002 Elsevier Science B.V. All rights reserved.
Synthesis and characterisation of saccharide complexes of La(III) ion
Mukhopadhyay A., Kolehmainen E., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2002,
View abstract ⏷
A series of ten La(III)-saccharide complexes have been synthesised with eight different monosaccharides (D-glucose, D-fructose, D-galactose, D-mannose, L-sorbose, D-arabinose, D-ribose and D-xylose) and two disaccharides (D-maltose and D-lactose), and characterised by analytical, spectral and electrochemical techniques. 13C NMR spectra reveal interesting binding modes of saccharide molecules towards La(III).
Synthesis and characterization of 4,6-O-butylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine: Crystal structures of 4,6-O-butylidene-α-D-glucopyranose, 4,6-O-butylidene-β-D-glucopyranosylamine and 4,6-O-butylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine
Rajsekhar G., Gangadharmath U.B., Rao C.P., Guionneau P., Saarenketo P.K., Rissanen K.
Article, Carbohydrate Research, 2002, DOI Link
View abstract ⏷
4,6-O-Butylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. 1H and 13C NMR studies showed the presence of the β-anomer, which has also been confirmed by the crystal structure. The molecular structure of this compound showed the presence of the tridentate ONO ligation-core. Both precursors, 4,6-O-butylidene-α-D-glucopyranose and 4,6-O-butylidene-β-D-glucopyranosylamine were characterized using single crystal X-ray diffraction. The α-anomeric nature of the former and β-anomeric nature of the latter were proposed based on 1H NMR studies and were confirmed by determining the crystal structures. In addition, the crystal structure of 4,6-O-butylidene-β-D-glucopyranosylamine revealed the C-1-N-glycosylation. In all the three molecules, the saccharide unit exhibits a 4C1 chair conformation. In the lattice, the molecules are connected by hydrogen-bond interactions. The conformation of 4,6-O-butylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine is stabilized via an O-H⋯N intramolecular interaction, and each molecule in the lattice interacts with three neighboring molecules through hydrogen bonds of the type O-H⋯O and C-H⋯O. © 2002 Elsevier Science Ltd. All rights reserved.
Mono-, di- and tri-nuclear Ni(II) complexes of N-, O-donor ligands: Structural diversity and reactivity
Dey M., Rao C.P., Saarenketo P.K., Rissanen K.
Article, Inorganic Chemistry Communications, 2002, DOI Link
View abstract ⏷
A series of mono-, di- and tri-nuclear Ni(II) complexes of N, O-donating molecules possessing -H2C-NH- and -HC=N-moieties have been synthesized and characterized and the structures have been determined by single crystal x-ray diffraction. All these exhibited interesting molecular packing in their crystal lattices. Di-nuclear complexes were found to be cleaved in pyridine to result in mononuclear ones with additional coordinations being provided by pyridine. Di-nuclear complexes were found to form urea adducts as demonstrated based on absorption and vibrational studies. © 2002 Elsevier Science B.V. All rights reserved.
First crystallographic investigation of complexes of cis-VO2+, cis-MoO22+, and trans-UO22+ species with Schiff-base molecules derived from 4,6-O-ethylidene-β-D-glucopyranosylamine
Sah A.K., Rao C.P., Saarenketo P.K., Wegelius E.K., Kolehmainen E., Rissanen K.
Article, European Journal of Inorganic Chemistry, 2001, DOI Link
View abstract ⏷
The interaction of Schiff-base ligands derived from 4,6-O-ethylidene-β-D-glucopyranosylamine with cis-VO2+, cis-MoO22+, and trans-UO22+ species have been studied by isolating and characterizing the corresponding products. The structures of one complex of each type of species have been established by single-crystal X-ray diffraction analysis. In all the complexes, the saccharide moiety adopts a chair conformation and has a β-anomeric form. A gradual increase in coordination number (5, 6, and 7) and a gradual variation in the geometry (distorted trigonal-bipyramidal, distorted octahedral, and pentagonal-bipyramidal) are observed on going from the complexes of cis-VO2+ (mononuclear) to cis-MoO22+ (mononuclear) to trans-UO22+ (dinuclear). A variation in the binding mode of the ligand towards these dioxometal species is also observed. Intermolecular interactions of the type O-H⋯O, C-H⋯O, and N-H⋯O present in the lattices of these complexes lead to the formation of interesting structures. © Wiley-VCH Verlag GmbH, 2001.
Lower rim 1,3-disubstituted derivatives of calix[4]arene amides having amino acid ester and amines as pendants
Rao P.V., Rao C.P., Kolehmainen E., Wegelius E.K., Rissanen K.
Article, Chemistry Letters, 2001, DOI Link
View abstract ⏷
Lower rim modification of calix[4]arene at its 1,3-alternate positions to result in the molecules of potential importance possessing amide bonds and other functional moieties as generated from the reaction between calix[4]arene-1,3-diacid and the amino acids and/or substituted amines was carried out and the structural properties of the products were addressed.
Structure of the first tetranuclear Ni(II) complex derived from N-(2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine
Sah A.K., Rao C.P., Saarenketo P.K., Rissanen K.
Article, Chemistry Letters, 2001, DOI Link
View abstract ⏷
In order to understand the binding nature of the glycosylamines possessing imine functionality, a novel tetranuclear Ni(II) complex of N-(2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine having twisted Ni4O4 cubane core was synthesized and structurally characterized.
Rare earth-saccharide chemistry: Synthesis and characterisation of saccharide complexes of Sm(III) (f5), Eu(III) (f6) and Dy(III) (f9) ions
Mukhopadhyay A., Kolehmainen E., Rao C.P.
Article, Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry, 2001,
View abstract ⏷
Complexes of Sm(III), Eu(III) and Dy(III) ions with six monosaccharides (D-glucose, D-galactose, D -mannose, D-arabinose, D-ribose and D-xylose) and two disaccharides (D-maltose and D-lactose) have been synthesised. These are characterised by means of various analytical, spectral and electrochemical techniques. Based on the data, appropriate structures are assigned for these complexes.
Synthesis and characterisation of N-glycosyl amines from the reaction between 4,6-O-benzylidene-D-glucopyranose and substituted aromatic amines and also between 2-(o-aminophenyl)benzimidazole and pentoses or hexoses
Das T.M., Rao C.P., Kolehmainen E.
Article, Carbohydrate Research, 2001, DOI Link
View abstract ⏷
Twelve N-glycosyl amines were synthesised using 4,6-O-benzylidene-D-glucopyranose and different substituted aromatic amines, including some diamines that resulted in bis-glycosyl amines. Another set of six N-glycosyl amines was synthesised using different hexoses and pentoses and 2-(o-aminophenyl)benzimidazole. All compounds were isolated as solid products and purified, their elemental compositions were established, and these were characterised by NMR (1H and 13C), UV-Vis, and FTIR spectroscopy, by FAB mass spectrometry (molecular-ion peaks gave molecular weights), and by their optical rotations. While the protected saccharide, 4,6-O-benzylidene-D-glucopyranose, exists as a mixture of β and α anomers in solution, the corresponding N-glycosyl amines were of only the β anomeric form as determined by NMR and FTIR spectroscopy. On the other hand, N-glycosyl amines synthesised from 2-(o-aminophenyl)benzimidazole prefer the α anomeric form, and in two cases a mixture of both the β and the α anomers were observed. The trends observed in the chemical shifts were compared among different products. © 2001 Elsevier Science Ltd. All rights reserved.
Interaction of metal ions with N-glycosylamines: Isolation and characterization of the products of 4,6-O-benzylidene-N-(o-carboxyphenyl)-β-D-glucopyranosylamine with different metal ions
Mohan Das T., Rao C.P., Kolehmainen E.
Article, Carbohydrate Research, 2001, DOI Link
View abstract ⏷
Metal-ion complexes of Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Pb2+, Cd2+, Hg2+ with 4,6-O-benzylidene-N-(o-carboxyphenyl)-β-D-glucopyranosylamine were synthesized and isolated as solid products and characterized by analytical means as well as by spectral techniques, such as, 1H and 13C NMR, FTIR, absorption, FAB mass spectrometry, optical rotation and CD. While the alkali metal ions formed ML type of complexes, the other metal ions formed ML2 type complexes. Molecular weights of the complexes of Li+, Na+ and K+ were established based on the molecular-ion peaks in the FAB mass spectra. The saccharide portion remians in the β-anomeric form even after the complexation. The spectral data, as well as the trends observed in the chemical shifts, indicate the interaction preferences between this glycosyl amine and different metal ions, and further reveal certain structural features of the complexes. © 2001 Elsevier Science Ltd. All rights reserved.
Synthesis, characterisation and crystal structures of Schiff bases from the reaction of 4,6-O-ethylidene-β-D-glucopyranosylamine with substituted salicylaldehydes
Sah A.K., Rao C.P., Saarenketo P.K., Kolehmainen E., Rissanen K.
Article, Carbohydrate Research, 2001, DOI Link
View abstract ⏷
Multiple chemical modifications were carried out on D-glucose to result in the corresponding Schiff bases. Such modifications performed on D-glucose not only helped in increasing the solubility of the products in nonaqueous solvents, but also restricted the anomerisation of the saccharide moiety in solution. NMR study of the products revealed the presence of the β-anomeric form of the saccharide moiety in Me2SO solution. All the compounds were characterised by analytical and spectral methods. The literature is devoid of any crystal structures of saccharide-Schiff base combinations of the type reported in this paper. The crystal structures of these molecules exhibited a tridentate, ONO binding core. These studies further revealed that the compounds in the solid state were in the β-D-pyranose form with the 4C1 chair conformation. The compounds exhibited interesting lattice structures assisted through weak interactions of the type O-H···O and C-H···O. The lattice structure of one of these compounds exhibited channels filled with chloroform molecules. © 2001 Elsevier Science Ltd. All rights reserved.
Synthesis, characterization and the first crystal structure of the Zn(II) complex of 4,6-O-ethylidine-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine
Sah A.K., Rao C.P., Wegelius E.K., Kolehmainen E., Rissanen K.
Article, Carbohydrate Research, 2001, DOI Link
View abstract ⏷
4,6-O-Ethylidine-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine (H3L1) and N-(5-bromo-2-hydroxybenzylidene-4,6-O-ethylidine-β-D-glucopyranosylamine (H3L2) molecules possessing a -C-1-N=C(H)- moiety for metal-ion binding were synthesized by condensing the 4,6-O-ethylidene-β-D-glucopyranosylamine with salicylaldehyde or 5-bromosalicylaldehyde. Complexes of these ligands with Zn(II) were isolated and characterized using elemental analysis, FTIR, UV-Vis absorption, NMR spectroscopic and FAB mass spectrometric techniques. The structure of the Zn(II) complex derived from H3L1 was established for the first time by a single-crystal X-ray diffraction study. The anomeric nature of the saccharide moiety was established based on 1H NMR studies and was confirmed by the crystal structure. Further, the structure and binding aspects of the ligand, and the coordination features of this in its Zn(II) complex were derived from the corresponding crystal structure. © 2001 Published by Elsevier Science Ltd.
Transition metal saccharide chemistry and biology: Syntheses, characterization, solution stability and putative bio-relevant studies of iron-saccharide complexes
Rao C.P., Geetha K., Raghavan M.S.S., Sreedhara A., Tokunaga K., Yamaguchi T., Jadhav V., Ganesh K.N., Krishnamoorthy T., Ramaiah K.V.A., Bhattacharyya R.K.
Article, Inorganica Chimica Acta, 2000, DOI Link
View abstract ⏷
A number of Fe(III) complexes of saccharides and their derivatives, and those of ascorbic acid were synthesized, and characterized by a variety of analytical, spectral (FT-IR, UV-Vis, EPR, Mossbauer and EXAFS), magnetic and electrochemical techniques. Results obtained from various methods have shown good correlations. Data obtained from EPR, magnetic susceptibility and EXAFS techniques could be fitted well with the mono-, di- and trinuclear nature of the complexes. The solution stability of these complexes has been established using UV-Vis absorption and cyclic voltammetric techniques as a function of pH of the solution. Mixed valent, Fe(II,III) ascorbate complexes have also been synthesized and characterized. Reductive release of Fe(II) from the complexes using sodium dithionite has been addressed. In vitro absorption of Fe(III)-glucose complex has been studied using everted sacs of rat intestines and the results have been compared with that of simple ferric chloride. Fe(III)-saccharide complexes have shown regular protein synthesis even in hemin-deficient rabbit reticulocyte lysate indicating that these complexes play a role that is equivalent to that played by hemin in order to restore the normal synthesis of protein. These complexes have exhibited enhanced DNA cleavage properties in the presence of hydrogen peroxide with pUC-18 DNA, plasmid. (C) 2000 Elsevier Science S.A.
Interaction of saccharides with rare earth metal ions: Synthesis and characterisation of Pr(III)- and Nd(III)-saccharide complexes
Mukhopadhyay A., Kolehmainen E., Rao C.P.
Article, Carbohydrate Research, 2000, DOI Link
View abstract ⏷
A number of complexes are synthesised with Pr(III) and Nd(III) employing the mono- and disaccharides, D-glucose, D-galactose, D-mannose, D-arabinose, D-ribose, D-xylose, maltose and lactose. The complexes are characterised by various spectral and analytical techniques, and based on these data, appropriate structures were assigned for all complexes. (C) 2000 Elsevier Science Ltd.
N-Glycosylamines of 4,6-Oethylidene-α-D-gIucopyranose: Synthesis, characterisation and structure of CO2H, Cl and F ortho-substituted phenyl derivatives and metal ion complexes of the CO2H derivative
Sah A.K., Rao C.P., Saarenketo P.K., Wegelius E.K., Rissanen K., Kolehmainen E.
Article, Journal of the Chemical Society, Dalton Transactions, 2000, DOI Link
View abstract ⏷
A saccharide based ligand suitable for metal binding (HLCOOH) has been synthesized using 4,6-O-ethylidene-α-D-glucopyranose (4,6-O-EGP) and anthranilic acid. A few analogous glycosylamines with chloro and fluoro ortho substitutions have also been synthesized and characterised. Complexes of HLCOOHwith Na+, K+, Mg2+, Ca2+, Ba2+, Cd2+ and Hg2+ have been isolated and characterised fully. The crystal structures of 4,6-O-EGP, the chloro analogue of HLCOOH and the K+ complex of LCOOH are established. The anomeric nature, orientation of the binding core and the co-ordination aspects of K+ have been derived from these structures. ©The Royal Society of Chemistry 2000.
Synthesis, structure and reactivity of tmns-UO22+ complexes of OH-containing ligands
Venkateswara Rao P., Rao C.P., Srecdhara A., Wcgelius E.K., Rissancn K., Kolehmainen E.
Article, Journal of the Chemical Society, Dalton Transactions, 2000, DOI Link
View abstract ⏷
trans-Dioxouranium dinuclear complexes of a few OH-containing ligands possessing N-, O-binding sites were synthesized and characterised. Seven of these were also structurally characterised by single crystal X-ray diffraction. All these complexes exhibit symmetric U2O2 core structures in addition to having a seven-co-ordinated environment about each uranium centre. Even when the ligand possessed more than one CH2OH group, only one such group was found to be involved both in chelation as well as in bridging. These complexes exhibited facile transmetallation reactions with vanadium and molybdenum precursors. Though their core structures are alike, the complexes differ in their lattice arrangement by exhibiting novel types of structures such as channel, herringbone and corrugated sheets owing to the presence of a number of extended weak interactions. © The Royal Society of Chemistry 2000.
Oxo-metal complexes of alkoxo rich ligands and reactivity of vanadium complexes
Article, Proceedings of the Indian Academy of Sciences: Chemical Sciences, 1999,
View abstract ⏷
Oxo-metal centers, such as, VO3+, cis-VO2+, cis-MoO22+ and trans-UO22+ exhibited different coordination geometries and charge types to result in totally nine different types of structures, all of which were characterized by single crystal X-ray diffraction. Aqueous stability, reactivity towards acid, H2O2 and bromide of vanadium complexes are studied using absorption and 51V NMR spectra. Catalytic nature of the bromination reaction by vanadium complexes has also been addressed.
Reactivity of cis-bis(acetylacetonato)dichlorotitanium(IV) towards hydroxy-containing ligands: Isolation and characterisation of products
Rao P.V., Rao C.P., Wegelius E.K., Kolehmainen E., Rissanen K.
Article, Journal of the Chemical Society - Dalton Transactions, 1999, DOI Link
View abstract ⏷
The reactivity of cis-[Ti(acac)2Cl2] with a number of OH containing ligands has been explored. Corresponding products have been synthesized, isolated and characterised. Three dimensional structures of some of the products were established by single crystal X-ray diffraction. The reactivity of these ligands towards non-oxo titanium centres has been found to be different from that of oxometal centres of VV, MoVI and UVI. All the products of TiIV isolated were mononuclear complexes possessing one or two ligands. Both the molecular and crystal structures of the titanium products are found to be different from those of the oxometal ones. © The Royal Society of Chemistry 1999.
Reduction of potassium chromate by tannins
Arakawa H., Watanabe N., Tamura R., Rao C.P.
Article, Bulletin of the Chemical Society of Japan, 1998, DOI Link
View abstract ⏷
The reduction of potassium chromate has been carried out with several tannin substances, including gallic acid, pyrogallol, ethyl gallate, polygalloylglucose, and withered oak-leaf tannin. Each reaction was followed by colorimetry, EPR spectroscopy, electrochemistry, and molecular-sieve chromatography. The progress of the chromate reductions was monitored by measuring the VIS and EPR spectra as a function of time. The observed pseudo- first-order reaction rate constants for Cr(III) formation were derived based on the intensities of the Cr(III) signals of the EPR spectra. Cyclic voltammograms of the simple reductants and their final Cr(III)-containing products formed from the reductions of chromate have also been measured. The formation of Cr(III)-tannin complexes was indicated by separation on a Sephadex G-25 column. The results obtained from VIS, EPR, and cyclic voltammetry were found to be mutually dependent, and showed close correlations among the data. The rate of reduction for Cr(VI) revealed the following trend: gallic acid > pyrogallol > ethyl gallate > polygalloylglucose > withered oak-leaf tannin. The results obtained in the present study suggest that the rates of reduction for Cr(VI) in the tannins depend upon their peak oxidation potentials and stabilities for Cr(III)- tannin complexes.
Chromium toxicity: Spectral and electrochemical studies of Cr(VI) reduction by biomimicking molecules
Rao C.P., Kaiwar S.P., Raghavan M.S.S.
Article, International Journal of Environmental Studies, 1998, DOI Link
View abstract ⏷
The reductive abilities of a variety of biomimicking molecules, including OH-containing ones such as, saccharides and their derivatives, nucleotides and their components and mixed group ligands have been determined in vitro using absorption spectra and electrochemical characterizations and were explained based on the nature of the reductants. While the reductive coefficients of these molecules showed a linear correlation with respect to oxidation potential of the ligand (EPa) and/or reduction potential (Epc) of the final Cr(III)-products, in any given set, such as hexoses, pentoses, polyols, glycols, saccharide derivatives, nucleotides and their components and mixed group ligands, the plot of all the reductants reported in this paper exhibited interesting correlations with respect to these electrochemical parameters. These correlations are expected to be important in the identification of species in routine analysis carried out with pollutants. As reduction of Cr(VI) to Cr(III) by saccharides and their derivatives progresses via soluble and reactive intermediates of Cr(V) having long t1/2 periods, this may be implicated in the transport of toxic chromium salts from soil to plants and their ultimate entry into the biosphere causing ecological hazards. Based on the results obtained on chromate reduction studies, a working model has been proposed for the toxicity of Cr(VI). The reductive abilities of a variety of biomimicking molecules, including OH-containing ones such as, saccharides and their derivatives, nucleotides and their components and mixed group ligands have been determined in vitro using absorption spectra and electrochemical characterisations and were explained based on the nature of the reductants. While the reductive coefficients of these molecules showed a linear correlation with respect to oxidation potential of the ligand (E(p)/a) and/or reduction potential (E(p)(c)) of the final Cr(III)-products, in any given set, such as hexoses, pentoses, polyols, glycols, saccharide derivatives, nucleotides and their components and mixed group ligands, the plot of all the reductants reported in this paper exhibited interesting correlations with respect to these electrochemical parameters. These correlations are expected to be important in the identification of species in routine analysis carried out with pollutants. As reduction of Cr(VI) to Cr(III) by saccharides and their derivatives progresses via soluble and reactive intermediates of Cr(V) having long t(1/2) periods, this may be implicated in the transport of toxic chromium salts from soil to plants and their ultimate entry into the biosphere causing ecological hazards. Based on the results obtained on chromate reduction studies, a working model has been proposed for the toxicity of Cr(VI).
Reducing agents mitigate protein synthesis inhibition mediated by vanadate and vanadyl compounds in reticulocyte lysates
Krishnamoorthy T., Sreedhara A., Rao C.P., Ramaiah K.V.A.
Article, Archives of Biochemistry and Biophysics, 1998, DOI Link
View abstract ⏷
Recently, we synthesized and characterized vanadyl saccharides to evaluate the effects of various vanadate and vanadyl complexes, which differ in their oxidation states on various biomacromolecules and cellular activities. Here, we report that both vanadate (+V oxidation state) and different vanadyl species (+IV oxidation state) such as vanadyl D-glucose, vanadyl diascorbate, and vanadyl sulfate, impair the formation of polysomes and inhibit the initiation of protein synthesis in hemin-supplemented rabbit reticulocyte lysates. Vanadate inhibits protein synthesis more severely than vanadyl species and is consistent with the idea that vanadate is reduced to vanadyl state intracellularly. The inhibition of protein synthesis caused by low concentrations (10-20 μM) of vanadate and vanadyl species is effectively mitigated by reducing agents such as dithiothreitol, reduced glutathione (GSH), or reduced pyridine dinucleotide. A significant decrease in the protein synthesis inhibition in vanadate-treated lysates by GSH suggests that the mechanism of protein synthesis inhibition by vanadate is different than the action of other oxidants such as heavy metal ions and oxidized glutathione. This suggestion is also consistent with the findings that vanadium compounds do not stimulate phosphorylation of the alpha (α) subunit of initiation factor 2 (eIF2) or decrease the guanine nucleotide exchange activity of eIF2B, which is required to exchange GDP for GTP in eIF2 · GDP binary complex. The reduction of vanadate to vanadyl state and the subsequent complex formation of vanadyl species with the endogenous reducing compounds or with the -SH groups of certain proteins may be the cause for protein synthesis inhibition in lysates.
Syntheses, structure, reactivity and species recognition studies of oxo-vanadium(V) and -molybdenum(VI) complexes
Rao C.P., Sreedhara A., Rao P.V., Verghese M.B., Rissanen K., Kolehmainen E., Lokanath N.K., Sridhar M.A., Prasad J.S.
Article, Journal of the Chemical Society - Dalton Transactions, 1998, DOI Link
View abstract ⏷
Alkoxo-rich Schiff-bases of potentially tri-, tetra- and penta-dentate binding capacity, and their sodium tetrahydroborate-reduced derivatives, have been synthesized. Their oxo-vanadium(V) and -molybdenum(VI) complexes were synthesized and characterized using several analytical and spectral techniques including multinuclear NMR spectroscopy and single-crystal X-ray diffraction studies. Eight structurally different types of complexes possessing distorted square-pyramidal, trigonal-bipyramidal and octahedral geometries have been obtained. While VVO exhibits dimeric structures with 2-HOC6H4CH=NC(CH2OH)3 and 2-HOC6H4CH2-NHC(CH2OH)3 and related ligands through the formation of a symmetric V2O2 core as a result of bridging of one of the CH2O- groups, MoVIO gives only mononuclear complexes even when some unbound CH2OH groups are available and the metal center is co-ordinatively unsaturated. In all the complexes the nitrogen atom from a HC=N or H2CNH group of the ligand occupies a near trans position to the M=O bond. While the Schiff-base ligands act in a tri- and tetra-dentate manner in the vanadium(V) complexes, they are only tridentate in the molybdenum(VI) complexes. Proton NMR spectra in the region of bound CH2 provides a signature that helps to differentiate dinuclear from mononuclear complexes. Carbon-13 NMR co-ordination induced shifts of the bound CH2 group fit well with the charge on the oxometal species and the terminal or bridging nature of the ligand. The reactivity of the vanadium(V) complexes towards bromination of the dye xylene cyanole was studied. Transmetallation reactions of several preformed metal complexes of 2-HOC6H4CH=NC(CH2OH)3 with VO3+ were demonstrated as was selective extraction of VO3+ from a mixture of [VO(acac)2] and [MoO2(acac)2] using this Schiff base. The unusual selectivity and that of related derivatives for VO3+ is supported by binding constants and the solubility of the final products, and was established through a.c. conductivity measurements. The cis-MoO22+ complexes with alkoxo binding showed an average Mo-Oalk distance of 1.926 Å, a value that is close to that observed in the molybdenum(VI) enzyme dmso reductase (1.92 Å). Several correlations have been drawn based on the data.
Transition metal-saccharide chemistry: Synthesis, characterization and solution stability studies of cis-dioxomolybdenum saccharide complexes
Mukhopadhyay A., Karkamkar A., Kolehmainen E., Rao C.P.
Article, Carbohydrate Research, 1998, DOI Link
View abstract ⏷
Six cis-dioxomolybdenum(VI) complexes of simple monosaccharides (D-glucose, D-fructose, D-galactose, D-mannose, D-ribose and D-xylose) have been synthesized and characterized by a variety of analytical and spectral methods. Both the solution and solid-state studies have supported the presence of dimeric structures, formed through the cis-MoO2 moieties and the bridging saccharide units. Solution stability of these complexes as a function of time has also been addressed. Copyright (C) 1998 Elsevier Science Ltd.
Recognition of oxovanadium(V) species and its separation from other metal species through selective complexation by some acyclic ligands
Rao C.P., Sreedhara A., Rao P.V., Lokanath N.K., Sridhar M.A., Prasad J.S., Rissanen K.
Article, Polyhedron, 1998, DOI Link
View abstract ⏷
Acyclic molecules possessing -OH (phenoxo and alkoxo type) groups and imine or amine moieties have been developed to sense the specific preference for VO3 species. These molecules also showed a capability to quantitatively separate oxovanadium(V) species from a reaction mixture containing metal species of V, Mo, U, Fe, and Mn ions in solution. A cascade quantitative separation of VO3 followed by cis- MoO22 followed by trans- UO22 species is demonstrated from their mixture. Synthesis and structural details of oxo-species of vanadium molybdenum and uranium are also discussed. Factors influencing the complexation of these molecules towards oxo metal species of V, Mo and U are also addressed.
Synthesis and characterization of vanadyl(IV) complexes of schiff bases derived from anthranilic acid and salicylaldehyde (or its derivatives) or acetylacetone. Single crystal x-ray structures of the oxidized products
Asgedom G., Sreedhara A., Kivikoski J., Rao C.P.
Article, Polyhedron, 1997, DOI Link
View abstract ⏷
Anhydrous, dimeric vanadyl(IV) complexes of Schiff bases derived from [1+1] condensation of salicylaldehyde (or its derivatives) and anthranilic acid, have been synthesized from CH3CN and were characterized by elemental analysis, FTIR, EPR, absorption, TGA, cyclic voltammetry and room temperature magnetic susceptibility measurements. These complexes were found to be oxidized by air in polar solvents like MeOH and DMF to Vv products. The E1/2 values were found to be around 660 mV indicating that the carboxylate group favours vanadyl(IV) binding when compared to the alkoxo-bound vanadium complexes. Oxidative instability of these complexes are dependent on the substituent on the salicylaldehyde ring and follow an order, 5,6-benzo > H ≥ 3-OMe in MeOH and DMF. Attempted recrystallization of the dimeric vanadyl(IV) complex from pyridine led to products of oxidation, polymerization and loss of Schiff base ligand. Single crystal X-ray diffraction showed the oxidation product to be a decavanadate with the pyridinium counter cation, [C5NH6]6 V10O28·2H2O. When the dinuclear vanadyl(IV) complex was recrystallized from MeOH, it gave a product of mononuclear carboxylate bound octahedral VO3+ moiety along with the presence of both MeOH and OMe units in the coordination sphere with a formula, VO(L)(OMe)(MeOH), where L = 1+1 Schiff base derived from 5,6-benzosalicylaldehyde and anthranilic acid, as studied through single crystal X-ray diffraction. Copyright © 1996 Elsevier Science Ltd.
Transition metal Saccharide chemistry and biology: Vanadyl- monosaccharide complexes and their in vitro effect on pUC-18 DNA
Article, Journal of Inorganic Biochemistry, 1997, DOI Link
View abstract ⏷
Solid state complexes of VO2+ were synthesized from methanolic solutions of VOCl2 and sodium salts of the hexoses (D = Glc, D-Fru, D-Gal) and pentoses (D-Xyl, D-Rib). The complexes were characterized by diffuse reflectance, aqueous solution absorbance, CD, FTIR, EPR spectroscopies, CV, and elemental analysis. The complexes were found to be mononuclear with a general formula, Na2[VO(Sacch)2(OH)Cl] and these are different from those reported earlier which were synthesised by a different route. The aqueous solution stability and pH variation studies of these complexes have shown formation of polymeric species as monitored by UV-visible absorption spectroscopy and cyclic voltammetry. All the complexes exhibited enhanced structural alterations of pUC-18 DNA in the presence of hydrogen peroxide, based on in vitro studies.
Transition-metal saccharide chemistry: Synthesis and characterization of D-glucose, D-fructose, D-galactose, D-xylose, D-ribose, and maltose complexes of Ni(II)
Article, Carbohydrate Research, 1997, DOI Link
View abstract ⏷
Monosaccharide (D-Glc, D-Fru, D-Gal, D-Xyl, D-Rib) and disaccharide (Mall complexes of Ni(II) were synthesised using [NEt4]2[NiCl2Br2] or NiCl2 · 6H2O in nonaqueous medium. The compounds synthesised from these two starting materials are different. The isolated complexes were characterized by diffuse reflectance, aqueous solution absorbance, CD, FTIR, magnetic susceptibility, and EXAFS and XANES studies.
Transition-metal saccharide chemistry: Synthesis and characterization of D-glucose, D-fructose, D-galactose, D-xylose, D-ribose, and maltose complexes of Co(II)
Bandwar R.P., Sastry M.D., Kadam R.M., Rao C.P.
Article, Carbohydrate Research, 1997, DOI Link
View abstract ⏷
Monosaccharide (D-Glc, D-Fru, D-Gal, D-Xyl, and D-Rib) and disaccharide (Mall complexes of Co(II) were synthesised from nonaqueous solutions using [NEt4]2[CoCl2Br2] or CoCl2 · 6H2O and isolated in the solid state. The purified complexes were characterized by diffuse reflectance, aqueous solution absorbance, CD, FILR, magnetic susceptibility, EPR, and cyclic voltammetric studies. The complexes synthesised from [NEt4]2[CoCl2Br2] were found tobe primarily dinuclear, whereas those synthesised from CoCl2 · 6H2O were found to be di- or tetra-nuclear. The hydrolytic stability of the complexes followed a trend: D-Rib > Mal > D-Glc > D-Xyl > D-Fru >> D-Gal.
Transition-metal saccharide chemistry and biology: Saccharide complexes of cu(II) and their effect on in vivo metallothionein synthesis in mice
Bandwar R.P., Rao C.P., Giralt M., Hidalgo J., Kulkarni G.U.
Article, Journal of Inorganic Biochemistry, 1997, DOI Link
View abstract ⏷
Monosaccharide (D-Glc, D-Fru, D-Gal, D-Xyl, D-Rib) and disaccharide (Mal) complexes of Cu(II) were synthesized from two different precursors, viz. [NEt4]2 [CuCl2Br2] and CuCl2,2H2O, in nonaqueous media, and isolated in the solid state. The complexes were found to be primarily dimeric and trimeric and water soluble. These were characterized by diffuse reflectance, aqueous solution absorption, CD, FTIR, magnetic susceptibility, EPR, EXAFS, XANES, and elemental analysis. Aqueous solution stability in the pH range 4-8 was studied by cyclic voltammetry and absorption spectroscopy. The effect of subcutaneously injected Cu-Fru, Cu-Xyl, and Cu-Rib complexes on the in vivo metallothionein synthesis in mice was found to be significant in liver, but not in brain, in accordance with the observed copper accumulation in these tissues.
Transition metal-saccharide chemistry and biology: An emerging field of multidisciplinary interest
Article, Current Science, 1997,
View abstract ⏷
The interactions of transition metal ions with saccharides have been a subject of current interest. This review presents, in brief, the understanding of these interactions through our recent work in this promising field. Methodologies have been developed to synthesize and isolate a large number of complexes of transition metal ions with saccharides, using readily available and/or easy to prepare starting materials. The characterized complexes have been classified into various structurally diverse categories. Biological relevances of some of the transition metal-saccharide complexes have been discussed.
Vanadate and chromate reduction by saccharides and L-ascorbic acid: Effect of the isolated V(IV) and Cr(III) products on DNA nicking, lipid peroxidation, cytotoxicity and on enzymatic and non-enzymatic antioxidants
Sreedhara A., Susa N., Rao C.P.
Article, Inorganica Chimica Acta, 1997, DOI Link
View abstract ⏷
Vanadate and chromate reduction in the presence of biocomponents like saccharides and L-ascorbic acid is demonstrated to generate V(IV) and Cr(III) species, respectively. The incipiently formed V(IV) and Cr(III) species are demonstrated to cause single strand and plasmid DNA nicking, lipid pcroxidation and cytotoxicity in isolated rat hepatocytes. The V(IV) complexes depleted the levels of non-enzymatic antioxidants like L-ascorbic acid and glutathione and parallelly increased the levels of enzymatic antioxidants like glutathione reductase, glutathione S-transferase, glutathione peroxidase, superoxide dismutase and catalases. However, the Cr(III) species did not have any significant effect on the antioxidant enzymes. Thus the reducing and complexing abilities of biogenic ligands and the corresponding effects of the V(IV) and Cr(III) species generated from vanadate and chromate reduction, respectively, may lead to a better understanding of the toxic effects of the corresponding metal ions. © 1997 Elsevier Science S.A.
Influence of zinc-saccharide complexes on some haematological parameters in rats
Bandwar R.P., Flora S.J.S., Rao C.P.
Article, BioMetals, 1997, DOI Link
View abstract ⏷
The effects of three recently synthesized zinc-saccharide complexes (zinc-fructose, zinc-galactose and zinc-glucose) on blood δ-aminolevulinic acid dehydratase (ALAD) activity, glutathione (GSH), zinc-protoporphyrin (ZPP) and urinary δ-aminolevulinic acid (ALA) levels have been investigated to ascertain the utility of these complexes as zinc supplements and as preventive agents against lead intoxication in rats.
Alkoxo Bound Monooxo- and Dioxovanadium(V) Complexes: Synthesis, Characterization, X-ray Crystal Structures, and Solution Reactivity Studies
Asgedom G., Sreedhara A., Kivikoski J., Valkonen J., Kolehmainen E., Rao C.P.
Article, Inorganic Chemistry, 1996, DOI Link
View abstract ⏷
A large variety of oxovanadium(V) complexes, mononuclear VO2+ and VO3+ in addition to the dinuclear VO3+, of the structural type (VOL)2, (VOHL)2, VOLHQ, K(VO2HL), K(VO2H2L), or (salampr) (VO2L) {where L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyquinoline; salampr = cation of reduced Schiff base derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate and imine groups have been synthesized in high yields and characterized by several spectral and analytical methods, including single crystal X-ray studies. While the mononuclear VO2+ complexes have been synthesized at alkaline pH, the dinuclear VO3+ complexes have been synthesized under neutral conditions using alkoxo rich Schiff base ligands. The X-ray structures indicate that the cis-dioxo complexes showed longer V-Oalkoxo bond lengths compared to the monooxo counterparts. The plot of V-Ophen bond distances of several VO3+ complexes vs the 1mct showed a near linear correlation with a negative slope. The cyclic voltammograms revealed a reversible V(V)/V(IV) couple with the reduction potentials increasing to more negative ones as the number of alkoxo groups bound to V increases from 1 to 2. Moreover, the cis-dioxo VO2+ complexes are easier to reduce than their monooxo counterparts. The solution stability of these complexes was studied in the presence of added water (1:4, water: solvent), where no decomposition was observed, unlike other Schiff base complexes of V. The conversion of the dioxo complexes to their monooxo counterparts in the presence of catalytic amounts of acid is also demonstrated. The reactivity of alkoxo bound V(V) complexes is also reported. X-ray parameters are as follows. H4L3: monoclinic space group, P21/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) Å; β = 101.67(4)°; V = 1126(1) Å3; Z = 4; R = 0.060, Rw = 0.058. Complex 1: monoclinic space group, P21/n; a = 12.988(1), b = 9.306(2), c = 19.730(3) Å; β = 99.94(1)°; V = 2348.9(7) Å3; Z = 4; R = 0.031, Rw = 0.027. Complex 2: monoclinic space group, P21/n; a = 12.282(3), b = 11.664(2), c = 12.971(4) Å; β = 97.89(2)°; V = 1840.5(8) Å; Z = 4; R = 0.035, Rw = 0.038. Complex 5: monoclinic space group, P21/c; a = 17.274(2), b = 6.384(2), c = 16.122(2) Å; β = 116.67(1)°; V= 1588.7(7) Å3; Z= 4; R = 0.039, Rw = 0.043. Complex 8: monoclinic space group, P21/c; a = 11.991(1), b = 11.696(4), c = 12.564(3) Å; β = 110.47(1)°; V = 1650.8(8) Å3; Z = 2; R = 0.045, Rw = 0.049.
Synthesis, characterization and dna interaction studies of crIII products isolated from crVI reduction with – SH containing molecules
Kaiwar S.P., Sreedhara A., Raghavan M.S.S., Rao C.P., Jadhav V., Ganesh K.N.
Article, Polyhedron, 1996, DOI Link
View abstract ⏷
Chromium(III)-containing products were isolated from the reduction of chromate using molecules possessing the thiol function, i.e. L-cysteine, L-cysteine-ethyl ester and mercaptopropanediol. The products were characterized by various analytical, spectroscopic, magnetic and electrochemical studies. The in vitro interaction of these products with pUC18DNA has shown alterations in the DNA structure as established using agarose gel electrophoresis.
Structure, characterization and photoreactivity of monomeric dioxovanadium(V) Schiff-base complexes of trigonal-bipyramidal geometry
Asgedom G., Sreedhara A., Kivikoski J., Kolehmainen E., Rao C.P.
Article, Journal of the Chemical Society - Dalton Transactions, 1996, DOI Link
View abstract ⏷
Five mononuclear cis-dioxovanadium(V) complexes of tridentate Schiff bases derived from salicylaldehyde and its derivatives and 8-aminoquinoline have been synthesized and characterized. Single-crystal X-ray analyses were performed with [VO2L1] 1 and [VO2L2] 2 (L1 and L2 denote the [1 + 1] Schiff-base anions derived from salicylaldehyde or naphthaldehyde and 8-aminoquinoline). While the structure of 2 was refined to a final R = 0.074 (R′ = 0.055), that of 1 was refined only to R = 0.134(R′ = 0.139) due to its poor diffraction quality. The complexes contain cis-oxo groups in the equatorial plane and a trigonal-bipyramidal geometry around the vanadium at which the Schiff base binds meridionally. Photoirradiation of these complexes in CH2Cl2 yielded chloride-bound VO3+ species, as studied using absorption and 51V NMR spectroscopy. These species are convertible back to the dioxovanadium(V) complexes upon addition of water to the photoirradiated solution.
Role of saccharides in reduction and complexation of transition metal ions and the effect of zinc saccharides on some haematological variables
Article, Proceedings of the Indian Academy of Sciences - Chemical Sciences, 1996, DOI Link
Metal-saccharide chemistry and biology: Saccharide complexes of zinc and their effect on metallothionein synthesis in mice
Bandwar R.P., Giralt M., Hidalgo J., Rao C.P.
Article, Carbohydrate Research, 1996, DOI Link
View abstract ⏷
Monosaccharide (D-Fru, D-Gal, D-Glc, D-Xyl, and D-Rib) and disaccharide (Mal) complexes of Zn2+ were synthesised using different precursors and isolated in the solid state. These were found to be anionic with a Zn-to-saccharide ratio of 1:1 and 2:1 for monosaccharide and disaccharide complexes, respectively. Electrochemical behaviour in aqueous solution was studied by extensive cyclic voltammetric studies in the pH range 3.7-10.3. The effect of subcutaneously injected Zn-D-Fru, Zn-D-Gal and Zn-D-Glc complexes on the metallothionein synthesis in mice was found to be significant in the liver, but not in the brain.
Transition-metal-saccharide chemistry: Synthesis and characterisation of D-galactose, D-fructose, D-glucose, D-xylose, D-ribose, and maltose complexes of Mn(II)
Article, Carbohydrate Research, 1996, DOI Link
View abstract ⏷
Monosaccharide (D-Gal, D-Fru, D-Glc, D-Xyl, D-Rib) and disaccharide (D- Mal) complexes of Mn(ll) were synthesised from non-aqueous solutions using [NEt4]2[MnCl2Br2] and MnCl2·4H20. The isolated and purified complexes were characterised by diffuse reflectance, FTIR, EPR, DTA, TGA, magnetic susceptibility, and cyclic voltammetry techniques. Synthesis from [NEt4]2[MnCl2Br2] yielded dimeric complexes 1-3 and 9, and from MnCl2·4H2O it yielded trimeric complexes 4-8. These water-soluble complexes were found to be anionic with a Mn-to-saccharide ratio of 1:1 for monosaccharide complexes 1-8 and 2:1 for disaccharide complex 9. The complexes were found to be hydrolytically stable in solution at higher concentrations (≤ 4 mM), as studied by cyclic voltammetry.
One electron reduction of vanadate(V) to oxovanadium(IV) by low-molecular-weight biocomponents like saccharides and ascorbic acid: Effect of oxovanadium(IV) complexes on pUC18 DNA and on lipid peroxidation in isolated rat hepatocytes
Sreedhara A., Susa N., Patwardhan A., Rao C.P.
Article, Biochemical and Biophysical Research Communications, 1996, DOI Link
View abstract ⏷
One electron reduction of vanadate(V) to vanadyl(IV) occurs in the presence of biocomponents, such as, saccharides and L-ascorbic acid under physiological conditions. The vanadyl(IV) complexes thus generated have been demonstrated to introduce nicks in pUC18 DNA in the absence or in the presence of hydrogen peroxide and also exhibit lipid peroxidation in isolated rat hepatocytes. Thus the reducing and complexing abilities of these molecules may help in understanding the in vivo reduction and the resultant toxicity to cells incubated with vanadate(V).
Monooxovanadium(V) mixed ligand complexes of schiff bases and catecholates: Synthesis, spectral and electrochemical characterization
Asgedom G., Sreedhara A., Rao C.P., Kolehmainen E.
Article, Polyhedron, 1996, DOI Link
View abstract ⏷
Mixed ligand, monooxovanadium(V) complexes of Schiff bases with catechol, p-tertbutylcatechol or pyrogallol have been synthesized and characterized by various spectral techniques, such as FTIR, UV-vis, 51V NMR and electrochemistry. All of these complexes exhibited a six coordinated VO3+ center. The stability and the conversion of these complexes to pentacoordinated VO+2 species with the loss of a bidentate catecholate ligand in DMSO were demonstrated using absorption, 51V NMR and electrochemical studies. 51V NMR studies further suggested the formation of two possible isomers in the case of p-tertbutylcatechol and pyrogallol complexes of VO3+. Electrochemistry of these complexes showed one reversible V(V)/V(IV) couple and another irreversible V(IV)/V(III) response. The mixed ligand, VO3+ complexes are more resistant to reduction as compared to the corresponding tris catecholate complexes. Copyright © 1996 Elsevier Science Ltd.
Transition metal saccharide chemistry and biology: Synthesis, characterization, electrochemistry and EPR studies of oxovanadium(IV) complexes of saccharides and their derivatives and in vitro interaction of some of these with ribonuclease and deoxyribonuclease
Sreedhara A., Rao C.P., Rao B.J.
Article, Carbohydrate Research, 1996, DOI Link
View abstract ⏷
Low molecular weight, water-soluble saccharide complexes of oxovanadium(IV) have been synthesized and characterized by analytical, spectroscopic and electrochemical techniques. All the complexes were found to be mononuclear, possessing the VO2+ moiety. These are shown to be hydrolytically and oxidatively stable over a wide range of pH (1-12) and have been extensively characterized by absorption and EPR spectroscopy and by electrochemistry. Several correlations have been drawn from the data generated. Some of these complexes have been demonstrated to possess in vitro RNase inhibition activity with no effect on DNase. This suggests that these molecules closely mimic the substrate portion of the RNase-catalysed RNA hydrolysis and can act as transition-state analogues to RNase.
Oxovanadium(V) schiff base complexes of trishydroxymethylaminomethane with salicylaldehyde and its derivatives: Synthesis, characterization and redox reactivity
Asgedom G., Sreedhara A., Rao C.p.
Article, Polyhedron, 1995, DOI Link
View abstract ⏷
Five vanadium complexes possessing the VO3+ motif with NO4 coordination have been synthesized and characterized by 1H and 13C NMR, UV-Vis, FTIR and cyclic voltammetry. These complexes favour trigonal bipyramidal geometry. In DMF solution, complexes 1 and 5 have shown reversible redox behaviour in the presence of l-ascorbic acid or l-cysteine ethyl ester in air as monitored by electronic absorption and EPR studies. © 1995.
Transition metal-saccharide chemistry: d-glucose complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)
Bandwar R.P., Srinivasa Raghavan M.S., Rao C.P.
Article, Biometals, 1995, DOI Link
View abstract ⏷
Metal complexes of d-glucose (d-Glc) from large cation containing dibromo-dichloro salts of dipositive metals [NEt4]2[MBr2Cl2] (M = Mn, Co, Ni, Cu and Zn) and the disodium salt of glucose were synthesized from a MeOH:MeCN mixture. The complexes were characterized by UV-vis absorption, circular dichroism, IR and proton magnetic resonance spectroscopies, and by elemental analysis, and were found to be Na[M(d-Glc)(OMe)Cl]. Cyclic voltammetric studies of these complexes, in the acidic to neutral pH range, indicated no dissociation, even in highly acidic conditions. © 1995 Rapid Communications of Oxford Ltd.
Transition-metal saccharide chemistry: synthesis, spectroscopy, electrochemistry and magnetic susceptibility studies of iron(III) complexes of mono- and disaccharides
Geetha K., Raghavan M.S.S., Kulshreshtha S.K., Sasikala R., Rao C.P.
Article, Carbohydrate Research, 1995, DOI Link
View abstract ⏷
Low molecular weight, soluble and characterizable saccharide complexes of iron(III) were synthesised from MeOH using stoichiometric quantities of saccharides and sodium metal. Monosaccharides such as d-glucose, l-sorbose, d-fructose, d-mannose and d-galactose, and disaccharides such as lactose, maltose and sucrose were used for complexation. The final iron(III)-saccharide complexes were isolated, purified and characterised by various analytical, spectroscopic methods including Mossbauer, magnetic susceptibility and electrochemical methods. While half of these complexes were found to be mononuclear, the rest exhibited characteristics close to hydroxo-bridged dinuclear species. The inherent stability and hydrolytically robust nature of these complexes over a wide range of pH was demonstrated. The reductive release of iron from these complexes was shown to be better than that of the iron-dextran complex reported in the literature. Based on their demonstrated properties these may be considered as potentially important in the oral nutritional supplementation of iron. © 1995.
In vitro reduction of Cr(VI) by low molecular weight biomimetic components: a comparative study using UV-Vis spectroscopy
Article, Chemico-Biological Interactions, 1995, DOI Link
View abstract ⏷
Chromium(VI) reduction has been carried out by a variety of molecules of cellular and soil importance, such as thiol containing ones, ascorbic acid, saccharides and their derivatives, and nucleotides and their components using absorption spectroscopy. Based on the absorption data, the reductive abilities of these molecules have been obtained and the trend has been found to be ascorbic acid thiols ≫ saccharides nucleotides. © 1995.
Relative reducing abilities in vitro of some hydroxy-containing compounds, including monosaccharides, towards vanadium(V) and molybdenum(VI)
Article, Carbohydrate Research, 1995, DOI Link
View abstract ⏷
The reduction of vanadium(V) and molybdenum(VI) has been carried out in aqueous HCl by various hydroxy-containing compounds such as hexoses (d-glucose, d-fructose, and d-galactose), pentoses (d-ribose and d-xylose), glycols [ethylene glycol, di(ethylene glycol), tri(ethylene glycol), tetra(ethylene glycol), and poly(ethylene glycol)], and mono-, di-, and tri-ethanolamines. The relative reducing abilities of these compounds are compared with those of l-ascorbic acid and l-cysteine. The trend is similar to that reported earlier for chromium(VI) reduction. Based on this study it is concluded that hydroxy-containing compounds play important roles in complexation and reduction of metal ions. © 1995.
Mononuclear cis-dioxovanadium(V) anionic complexes [VO2L]-{H2L = [1 + 1] Schiff base derived from salicylaldehyde (or substituted derivatives) and 2-amino-2-methylpropan-l-ol}: Synthesis, structure, spectroscopy, electrochemistry and reactivity studies
Asgedom G., Sreedhara A., Kivikoski J., Valkonen J., Rao C.P.
Article, Journal of the Chemical Society, Dalton Transactions, 1995, DOI Link
View abstract ⏷
The compounds [H3NCMe2CH2OH][VO2L]{H2L = [1 + 1] Schiff base derived from salicyladehyde (or substituted derivatives) and 2-amino-2-methylpropan-l-ol} have been synthesized in good yields by reaction of the Schiff base (formed in situ) and a further equivalent of the amino alcohol with [VO(acac)2](Hacac = acetylacetone). The structures of three of the complexes have been solved by single-crystal X-ray studies. All the compounds were also characterized by UV/VIS, FTIR and NMR spectroscopy and by cyclic voltammetry. The three structurally characterized mononuclear complexes contain the cis-dioxovanadium(V) moiety and exhibit distorted square-pyramidal geometry at vanadium which is displaced from the equatorial plane by ≈0.5 Å. The crystal and molecular structures of these compounds showed extensive hydrogen bonding between the anionic portion of the complexes and the counter-cations of the amino alcohol which resulted in some unusual metric features of interest to the binding of vanadium in biological systems. Two of the compounds showed the longest V=O distances reported so far for mononuclear cis-dioxovanadium(V) complexes. Three of the complexes undergo photoreduction in the solid state which is attributed to their intermolecular interactions in the crystal.
Transition-metal saccharide chemistry and biology: Synthesis, characterisation, redox behaviour, biointeraction and data correlations of dinuclear chromium(III) complexes
Kaiwar S.P., Raghavan M.S.S., Rao C.P.
Article, Journal of the Chemical Society, Dalton Transactions, 1995, DOI Link
View abstract ⏷
A series of dinuclear chromium(III) complexes has been synthesised by reduction of chromate by a variety of saccharides and related compounds. The complexes have been characterised by various analytical (elemental and ICP-AES analysis, TLC, HPLC) and spectroscopic (UV/VIS, FTIR, EPR, 1H and 13C NMR) methods. Antiferromagnetic interactions between the two CrIII centres have been established by magnetic susceptibility measurements and the hydrolytic stability and redox behaviour of the complexes have been established by extensive electrochemical studies which gave several correlations. The interaction of some of the complexes with DNA has been studied by gel electrophoresis.
Fe(III) complexes of d-glucose and d-fructose
Rao Ch.P., Geetha K., Raghavan M.S.S.
Article, Biometals, 1994, DOI Link
View abstract ⏷
Fe(III)-saccharide complexes of d-glucose and d-fructose have been synthesized from methanol using stoichiometric quantities of sodium salts of the corresponding saccharides. Both the compounds were isolated in the solid state and characterized by various analytical, spectroscopic, magnetic and cyclic voltammetric methods. Both the complexes were found to be stable, in solution, in the pH range 2.5-12.0. © 1994 Rapid Communications of Oxford Ltd.
Transition metal saccharide chemistry: synthesis, spectroscopy, electrochemistry and magnetic studies of chromium(III)-hexose complexes and their in vitro interaction with DNA
Rao C.P., Kaiwar S.P., Raghavan M.S.S.
Article, Polyhedron, 1994, DOI Link
View abstract ⏷
Saccharide complexes of CrIII were synthesized via chromate reduction. Hexose monosaccharides such as d-glucose, d-fructose, d-galactose, d-mannose and l-sorbose and some acid derivatives, such as d-galacturonic acid and d-gluconic acid, were used. The final CrIII products were isolated, purified and characterized by various analytical, spectroscopic, magnetic and electrochemical methods. All the products reported here are shown to be dinuclear in nature. The inherent stability and robust nature of these complexes is demonstrated and they are shown to affect the pSV2neo plasmid (DNA) structure in gel electrophoretic experiments. © 1994.
In vitro reducing abilities towards chromate of various hydroxy-containing compounds, including saccharides and their derivatives
Kaiwar S.P., Srinivasa Raghavan M.S., Rao C.P.
Article, Carbohydrate Research, 1994, DOI Link
View abstract ⏷
The reduction of potassium chromate has been carried out with a variety of OH-containing compounds as reductants, which include pentoses, polyols, glycols, and sugar derivatives. The corresponding reactions were followed using UV-vis and EPR spectroscopies and electrochemistry. The progress of the chromate reduction reactions has been monitored by measuring UV-vis and EPR spectra as a function of time. The observed pseudo first-order reaction rate constants are derived based on the changes in the intensities of the Cr(VI), Cr(V), and Cr(III) signals. Cyclic voltammograms of the simple reductants and their final Cr(III) products formed from the reactions of chromate have also been measured. The reductive abilities of all these reductants have been derived from the spectral data and are discussed on a comparative basis. Based on the results, the aspects that makes a particular reductant more efficient has been addressed. The results obtained from UV-vis, EPR, and cyclic voltammetry are found to be mutually dependent and exhibit among themselves a linear correlation, suggesting that both the reducing and complexing nature of these molecules play important roles in the chromate reduction. © 1994.
Transition metal-saccharide interactions: Synthesis and characterization of vanadyl saccharides
Sreedhara A., Srinivasa Raghavan M.S., Rao C.P.
Article, Carbohydrate Research, 1994, DOI Link
View abstract ⏷
Low molecular weight saccharide complexes of vanadium of the type [VO(sacch)2]2-, were synthesized for the first time by simple and reproducible methods in nonaqueous media. These reactions yielded water-soluble products which were characterized by various analytical and spectroscopic techniques and by cyclic voltammetry. The vanadyl d-glucose complex 1 shows a resemblance to a natural vanadium-binding component vanadobin, isolated from the tunicate Ascidia sydneiensis samea. All the saccharide complexes are stable in solution for long periods under ambient conditions without being oxidised and showed no hydrolysis in the pH range 2-12. All the saccharide complexes reported in this paper show evidence for the V(IV) species. © 1994 Elsevier Science B.V. All rights reserved.
Transition metal-saccharide chemistry: Synthesis and characterization of some monosaccharide complexes
Kaiwar S.P., Bandwar R.P., Raghavan M.S.S., Rao C.P.
Article, Proceedings of the Indian Academy of Sciences - Chemical Sciences, 1994, DOI Link
View abstract ⏷
Synthesis and characterization of mononuclear complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with D-fructose and dinuclear complexes of Cr(III) with D-glucose, D-fructose, and L-sorbose are reported. Cyclic voltammetric studies of these complexes suggest their robustness over a wide pH range. Cr(III)-saccharide complexes are found to affect the structure of pSV2 neo DNA irreversibly. © 1994 Indian Academy of Sciences.
Reduction of potassium chromate by d-fructose, d-galactose, d-mannose, d-glucose, and l-sorbose
Article, Carbohydrate Research, 1993, DOI Link
View abstract ⏷
Chromate is readily reduced by various saccharides under different experimental conditions, and its reduction has been followed using absorption and EPR spectroscopies and electrochemistry. The reduction of Cr(VI) was found to be characteristic of the saccharide used and the reductive capabilities follow a trend, d-fructose > l-sorbose > d-galactose > d-mannose > d-glucose at pH 1.65 and d-fructose > d-galactose > d-mannose > l-sorbose > d-glucose at pH 0.35. Similar trends were noticed from EPR and electrochemistry studies. As the reduction of chromate was found to go via soluble, reactive, and relatively long-lived Cr(V) intermediates having different life times, the biological toxicity and ecological hazard created in the presence of Cr(VI) salts by various molecules containing such saccharide moieties is expected to follow a reverse trend. © 1993.
Solution stability of iron-saccharide complexes
Rao C.P., Geetha K., Bandwar R.P.
Article, Bioorganic and Medicinal Chemistry Letters, 1992, DOI Link
View abstract ⏷
Several soluble and low molecular weight complexes of mono- and disaccharides with iron were synthesized and found to be stable over a wide range of pH as studied through absorption spectroscopy and electrochemistry. These complexes are expected to act as better candidates for dietary supplementation of nutrient iron. © 1992.
Soluble complexes of early first-row transition-metal ions with d-glucose
Article, Carbohydrate Research, 1992, DOI Link
View abstract ⏷
Glucose complexes of Ti4+, V4+, Cr3+, and Mn2+ ions were synthesized by simple, reproducibleprocedures in nonaqueous media, isolated in the solid state, and characterized using several analytical and spectroscopic techniques. These are soluble both in water and in several polar organic solvents. © 1992 Elsevier Science Publishers B.V.
Chromate reduction: reduction of potassium chromateby d-glucose and d-fructose to form Cr(III)-saccharide complexes
Article, Carbohydrate Research, 1992, DOI Link
View abstract ⏷
The reduction of chromate by saccharides is of paramount importance in the context of chromiumtransport in biological and ecological systems. Potassium chromate has been shown to be reduced by d-glucose and D-fructose to form Cr(III)-saccharide complexes via an intermediate Cr(V) species. These saccharide complexes have been isolated in the solid state for the first time and characterized by analytical, spectroscopic, magnetic and electrochemical methods. Bridged dinuclear saccharide complexes of Cr(III) have been proposed. © 1992 Elsevier Science Publishers B.V.
Homoleptic glucose complexes of VO2+ and Cr3+
Article, Inorganica Chimica Acta, 1991, DOI Link
Chromate reductase activity: characterization of Cr(VI) to Cr(III) conversion
Rao C.P., Sarkar P.S., Kaiwar S.P., Vasudevan S.
Article, Proceedings of the Indian Academy of Sciences - Chemical Sciences, 1990, DOI Link
View abstract ⏷
In order to understand chromate reductase activity (CRA), related to cellular carcinogenecity and metal toxicity in ecological systems, we began studying the reduction of chromium(VI) salts using cysteine, ascorbic acid and several monosaccharides mainly through EPR and absorption spectroscopic methods. The present study indicates Cr(V) as a definite intermediate and also shows the relative trends of reducing capabilities among various reducing agents employed. Considerable progress has been achieved in the isolation of intermediates and final products as well. © 1990 Indian Academy of Sciences.
Neighbouring group participation and the tool of increasing electron demand: A review
Ravindranathan M., Rao C.G., Peters E.N.
Review, Proceedings of the Indian Academy of Sciences - Chemical Sciences, 1981, DOI Link
View abstract ⏷
Solvolytic reactions could be greatly influenced by the presence of neighbouring groups. The tool of increasing electron demand has been successfully used to detect such participation. For example, the tool has detected the presence of major π-participation in anti-7-norbornenyl and π-conjugation in cyclohexen-2-yl derivatives. The changes observed in the absolute values of p + with ring size in cyclic systems could be adequately explained by the I-strain concept. The tool has established major πδ-conjugation in cyclopropylcarbinyl and nortricyclyl derivatives. πδ-participation in the Coates' cation has been unambiguously established. However, this sensitive probe has failed to provide evidence for δ-participation in the solvolysis of 2-norbornyl system. It, is concluded that the tool of increasing electron demand is quite sensitive to detect the presence or absence or neighbouring group participation. © 1981 Indian Academy of Sciences.
Hydrophobic channels in crystals of an α-aminoisobutyric acid pentapeptide
Rao Ch.P., Shamala N., Nagaraj R., Rao C.N.R., Balaram P.
Article, Biochemical and Biophysical Research Communications, 1981, DOI Link
View abstract ⏷
The crystal structure of the pentapeptide p-toluene-sulfonyl-(α-aminoisobutyryl)5-methyl ester (Tosyl-(Aib)5-OMe) has been determined in the space group PI. Pentapeptide molecules are folded in the 310 helical conformation and packed together, so as to yield a hydrophobic channel with a minimim diameter of 5.2 Å. The channel contains crystallographically disordered material. This structure provides a model for channel formation by hydrophobic peptide aggregates and should prove useful in studies of alamethicin, suzukacillin and related Aib containing membrane channels. Triclinic (PI) crystals of the pentapeptide are obtained in the presence of LiClO4 in aqueous methanol, whereas crystallization from methanol alone yields crystals in the space group Pbca. The conformations of the peptide in the two crystal forms are very similar and only the molecular packing is dramatically different. © 1981.
Infrared spectroscopy as a probe for the development of secondary structure in the amino-terminal segment of alamethicin
Rao Ch.P., Nagaraj R., Rao C.N.R., Balaram P.
Article, FEBS Letters, 1979, DOI Link
