Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
9 results
Search Results
Item Supramolecular synthons in noncovalent synthesis of a class of gelators derived from simple organic salts: Instant gelation of organic fluids at room temperature via in situ synthesis of the gelators(2009) Das, U.K.; Trivedi, D.R.; Adarsh, N.N.; Dastidar, P.(Chemical Equation Presented) The supramolecular synthon approach has been employed to synthesize noncovalently a series of low molecular mass organic gelators (LMOGs) derived from benzylammonium salts of variously substituted benzoic acids. The majority of the salts (75%) prepared showed interesting gelation properties. Instant gelation of an organic fluid, namely methyl salicylate, was achieved at room temperature by using most of the gelator salts by in situ synthesis of the gelators. Table top rheology and scanning electron microscopy (SEM) were used to characterize the gels. Single crystal X-ray diffraction studies revealed the presence of both 1D and 2D supramolecular synthons. X-ray powder diffraction (XRPD) studies indicated the presence of various crystalline phases in the fibers of the xerogels. By using these data, a structure-property correlation has been attempted and the working hypothesis for designing the gelator has been reinforced. © 2009 American Chemical Society.Item A catalyst- and solvent-free three-component reaction for the regioselective one-pot access to polyfunctionalized pyrroles(2013) Bhat, S.I.; Trivedi, D.R.A facile method for the regioselective synthesis of tetrasubstituted pyrroles, from readily accessible 1,3-dicarbonyls, benzoin derivatives and ammonium acetate, has been developed. The one-pot three-component reactions were performed to afford tetrasubstituted pyrroles under solvent- and catalyst-free conditions. © 2013 Elsevier Ltd. All rights reserved.Item Pharmaceutical salts of ethionamide with GRAS counter ion donors to enhance the solubility(Elsevier B.V., 2017) Nechipadappu, S.K.; Trivedi, D.R.Pharmaceutical salts of BCS class II second line anti-tuberculosis drug ethionamide (ETH) with various counter ions namely, 2-chloro-4-nitrobenzoic acid (CNB), 2,6-dihydroxybenzoic acid (2,6HBA), 2,3-dihydroxybenzoic acid (2,3HBA) and 2,4-dinitrobenzoic acid (DNB) were synthesized by crystal engineering approach. All the synthesized salts were characterized by various spectroscopic (NMR, FT-IR,), thermal (DSC & TGA) and PXRD techniques. The crystal structure of the synthesized salts was determined by single-crystal X-ray diffraction techniques. All the reported salts, except ETH-2,3HBA exhibited charge assisted acid pyridine heterosynthon. In ETH-2,3HBA hydoxyl pyridine heterosynthon is observed. In ETH-CNB salt, both ionic and neutral acid pyridine heterosynthon were observed in the asymmetric unit. ETH-DNB salt consists of both partial and complete proton transfer from DNB to ETH in the asymmetric unit. All the synthesized salts were found to be non-hygroscopic at accelerated humid condition (~ 75% RH). Solubility experiment has been performed in purified water and in 0.1 N HCl (pH = 1) solution and found that the solubility of ETH-CNB salt was about eight-fold higher soluble than ETH in purified water. The solubility of synthesized salts follows the order of ETH < ETH-2,3HBA < ETH-2,6HBA < ETH-CNB in purified water. © 2016 Elsevier B.V.Item Pharmaceutical Co-Crystal of Flufenamic Acid: Synthesis and Characterization of Two Novel Drug-Drug Co-Crystal(Elsevier B.V., 2017) Nechipadappu, S.K.; Tekuri, V.; Trivedi, D.R.Two novel pharmaceutical co-crystals of anti-inflammatory drug flufenamic acid (FFA) with 2-chloro-4-nitrobenzoic acid (CNB) and ethenzamide (ETZ) have been synthesized by solvent evaporation method as well as by solvent drop-assisted grinding method. The synthesized co-crystals were characterized thoroughly by various spectroscopic methods and crystal structures were determined by single-crystal x-ray diffraction technique. In FFA-CNB co-crystal, robust supramolecular acid-acid homosynthon was observed. FFA-ETZ co-crystal is formed via robust supramolecular acid-amide heterosynthon. In FTIR spectra, a significant shift in the carbonyl stretching frequency was observed for the co-crystals due to the presence of intermolecular hydrogen bond. 1H nuclear magnetic resonance study suggests the presence of hydrogen bond in the solution state of FFA-ETZ co-crystal; however, it was absent for FFA-CNB co-crystal. Solubility study in Millipore water revealed that the solubility of FFA is increased by 2-fold when it is in the form of FFA-CNB co-crystal and no increment in the solubility of FFA was observed in FFA-ETZ co-crystal. About 5-fold increment in the solubility of FFA was observed in both the co-crystals in 0.1 N HCl (pH 1) solution. The synthesized co-crystals were found to be non-hygroscopic at ?75% relative humidity and stable for a period of 6 months at ambient temperature (?25°C). © 2017 American Pharmacists Association®Item Synthesis of cocrystals/salts of flucytosine: Structure and stability(Royal Society of Chemistry, 2018) Nechipadappu, S.K.; Ramachandran, J.; Naveen, N.; Lokanath, N.K.; Trivedi, D.R.5-Fluorocytosine or flucytosine (FLC) is a well-known drug for anti-fungal treatment and is one of the essential medicines needed in a health system. The main disadvantage of FLC drugs is their instability due to hydration under storage conditions. In the present work, cocrystal/salt screening experiments resulted in three molecular salts of FLC with dihydroxybenzoic acid derivatives, 2,3-dihydroxybenzoic acid (2,3HBA), 3,5-dihydroxybenzoic acid (3,5HBA), and 2,6-dihydroxybenzoic acid (2,6HBA), and two cocrystals with gallic acid (GAA) and glutaric acid (GLA). Since FLC drugs are highly susceptible to hydration, the present work concentrated on the stability of the synthesized molecular salts/cocrystals under different relative humidity (RH) conditions. All the newly formed crystalline adducts were characterized structurally, and the crystal structures were determined using single-crystal X-ray diffraction techniques (SCXRD). The FLC-2,6HBA salt was found to be a monohydrate, whereas the FLC-3,5HBA salt was crystallized as a hemipentahydrate. FLC-2,3HBA and FLC-GLA were crystallized in 2:1 equimolar ratios of FLC and the coformer. The FLC-GAA cocrystal crystallized in a 1:1 equimolar ratio. Two point heterosynthons between FLC and the coformer were observed in all the crystalline structures except FLC-GLA, where the structure was formed through a single point heterosynthon. Stability studies under different relative humidity conditions showed the non-hygroscopicity of the synthesized molecular salts/cocrystals. It was found that the FLC-2,3HBA salt, and the FLC-GAA and FLC-GLA cocrystals did not experience any hydration under the accelerated humidity conditions (both 70-75% RH and 90-95% RH) at ambient temperature (?30 °C). However, FLC-2,6HBA and FLC-3,5HBA were found to be hygroscopic under 70-75% RH conditions. Furthermore, all the synthesized salts/cocrystals except FLC-3,5HBA were found to be stable for 2 months under ambient conditions (?30 °C, 60-65% RH). Therefore, the FLC-2,3HBA salt, and the FLC-GAA and FLC-GLA cocrystals are better candidates for the preparation of new drug products of FLC. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Colorimetric and fluorometric turn-on sensor for selective detection of fluoride ions: Sol-gel transition studies and theoretical insights(Royal Society of Chemistry, 2018) Pangannaya, S.; Mohan, M.; Trivedi, D.R.A new organic receptor R1 based on a naphthyl unit covalently linked to a long alkyl chain has been designed, synthesized and characterized by standard spectroscopic techniques. The colorimetric response of receptor R1 from colorless to a pale yellow color and blue fluorescence emission in the presence of F- ions revealed its selective sensing ability in the solution phase. UV-Vis titration, fluorescence titration and 1H NMR titration studies confirmed the formation of the R1-F- complex. Receptor R1 formed a stable gel in DMSO and was confirmed through the standard heating-and-cooling method. Addition of F- ions resulted in disruption of the gel forming a solution that exhibited blue fluorescence emission. The binding constant of the R1-F- complex was found to be of the order of 5.9 × 105 M-1. DFT studies revealed the formation of the receptor-anion complex agreeing well with the experimental results. The detection limit was calculated and found to be 0.8 ppm, implying the potential for application of receptor R1 in environmental applications. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Photophysics of proton transfer in hydrazides: A combined theoretical and experimental analysis towards OLED device application(Royal Society of Chemistry, 2019) Mohan, M.; Satyanarayan, M.N.; Trivedi, D.R.Hydrazides generate phototautomers and thus, a mechanistic interpretation to uncover the excited state dynamics of such systems is highly necessary to theorize principles based on experimental speculations. Accordingly, focus on the proton transfer barrier, which is a questionable step-wise or hypothetical simultaneous double proton transfer on structurally favored species, is quintessential; however, to the best of our knowledge, theoretical insights into such findings remain rare. Thus, TX, PX and FX (where X = 2 and 3) were designed and synthesized by incorporating hydrazides, which exhibit the phenomenon of excited state intramolecular proton transfer (ESIPT). Some of the molecules exhibited electroluminescence when employed as an active emitter material in fabricated OLED devices. Theoretical predictions support the presence of extended conjugation in TX, PX and FX (where X = 2 and 3) to support ESIPT efficiently in comparison with TX, PX and FX (where X = 1). The solvatochromic study revealed that TX, PX and FX (where X = 2 and 3) exhibit a distinct double peak in THF solvent, characteristic of ESIPT. Interestingly, for some of the molecules, emission in thin film form showed a double peak, which indicates ESIPT in the solid state. However, it was found that aggregation induced emission (AIE) was inactive in these molecules. The geometrical attributes of the molecules and the nature of electronic orbital distribution well underline the principle supporting excited state proton translocation. The theoretically estimated energy transitions exhibited good correlation with the experimental results. Also, the potential energy scans revealed the molecules possess a lower forward barrier at their excited state in comparison with that of their ground state, promoting ESIPT. The potential energy surface scans performed on structurally favored species confirmed the impossible double proton transfer and highly difficult step-wise double proton transfer. © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Design and synthesis new colorimetric receptors for naked-eye detection of biologically important fluoride and acetate anions in organic and arsenite in aqueous medium based on ICT mechanism: DFT study and test strip application(Elsevier B.V., 2020) Singh, A.; Mohan, M.; Trivedi, D.R.Novel three colorimetric anion receptors R1, R2 and R3 have been designed and synthesized via condensation reaction and characterized using IR, MS, and NMR spectroscopic techniques. Anion sensing properties were studied using colorimetric, UV–vis titration, 1H NMR titration, and Cyclic Voltammetric Studies. Comparing the UV–visible titration data of the receptors R1 and R2, R2 showed high redshift (??max) in the mixed competitive solution (DMSO: H2O, 9: 1; v/v) of about 155 nm, 157 nm, 169 nm for Na+F?, Na+AcO?, and Na+AsO2 ? ions with LOD of 0.23 ppm, 0.18 ppm, and 0.30 ppm, respectively. The observed spectral change of receptor R2 is due to the anion-induced deprotonation of the OH proton, which is confirmed by UV–vis titration, 1HNMR titration, and cyclic voltammetric studies. Theoretical studies via DFT calculation were carried for R1 and R2 to optimize the structure and to explain the anion-binding mechanism. The application of designed receptor R2 was successfully demonstrated for the detection of F? and AsO2 ? ions using a test strip. The receptors R1 and R2 proved itself to be potentially useful for real-life application by sensing F? and AcO? ions in real samples like toothpaste, mouthwash, vinegar and seawater in a complete aqueous medium. © 2019 Elsevier B.V.Item Design and synthesis of malonohydrazide based colorimetric receptors for discrimination of maleate over fumarate and detection of F?, AcO? and AsO2 ? ions(Elsevier B.V., 2020) Singh, A.; Mohan, M.; Trivedi, D.R.In this study, we have designed and synthesized two new organic receptors R1 and R2 based on malonohydrazide for the recognition of biologically important anions. The receptor R1 capable of colorimetric discrimination of maleate over fumarate ion, exhibit significant color change from pale yellow to wine red due to intermolecular hydrogen bond between the R1 and maleate ion, supported by 1HNMR titration, where the peak at ?12.0 ppm attributed to the NH proton experiences a downfield shift upon binding with maleate ion. Receptor R1, equipped with two electron-withdrawing [sbnd]NO2 moieties as the chromogenic signaling unit enhance the hydrogen bonding tendency and acidity, and thus when comparing with receptor R2, R1 displayed substantial higher redshift (??max) of 148 nm, 143 nm, and 140 nm towards F?, AcO?, and maleate anion in the DMSO. In addition, the synthesized receptors R1 and R2 are able to detect F?, AcO?, and AsO2 ? ions as their sodium salts in an aqueous solution with visual color change. Receptor R1 exhibit electrochemical response towards F? and AcO? ions. The receptors R1 and R2 are successfully applied for quantitative detection of F? ion in the toothpaste solution in an aqueous medium. Additionally, R1 and R2 exhibit fluorescence enhancement towards F? and AcO? ions in the DMSO. As well, R1 and R2 demonstrate to be potentially useful colorimetric chemosensor for sensing maleate ion using the test strip. The theoretical calculation based on TD-DFT corroborates well with the experimental results of the receptors R1 and R2 with fluoride, acetate and maleate. © 2019 Elsevier B.V.