Faculty Publications
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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 Partitioning studies of ?-lactalbumin in environmental friendly poly (ethylene glycol) - Citrate salt aqueous two phase systems(2013) Kalaivani, S.; Iyyaswami, I.Aqueous two-phase systems (ATPS) formed by polymer and salt have been utilized to enrich the desired biomolecule into one of the phase with higher yield and purity. The eco-friendly, biodegradable poly ethylene glycol (PEG) and different citrate salts were chosen as ATPS phase components to investigate the partitioning behavior of ?-lactalbumin (?-La). System factors and process parameters such as type and concentration of salt, molecular weight and concentration of PEG, pH, temperature and the effect of additives were studied and the results are discussed in detail. PEG 1000-tri-potassium citrate system yields high partition coefficient of 20 with a better yield of 98 % in the top phase. The addition of NaCl as an additive and acidic pH lowers the yield of ?-La in the top phase. Influence of phase volume ratio (V r) on partitioning was studied and found that the partition coefficient remains almost constant along the tie line. High yield was achieved at a V r of 3.5 at the tie line length of 50.63 (%, w/w). © 2013 Springer-Verlag Berlin Heidelberg.Item Identification of robust synthon in the molecular salts of 2-aminothiazole with substituted benzoic acids: A case study(Springer India sanjiv.goswami@springer.co.in, 2014) Oruganti, M.; Pallepogu, R.; Trivedi, D.R.Six new salts of an API intermediate 2-aminothiazole with different carboxylic acid coformers were synthesized and characterized by IR (Infrared spectroscopy), 1H-NMR, DSC (Differential scanning calorimetry), XRPD (X-ray powder diffraction) and single crystal XRD. The crystal structure of the salts with benzoic acid, 2,3-, 2,4-, 2,5-, 2,6- dihydroxybenzoic acids and 2,4-dinitrobenzoic acid were determined. The thiazole moiety exhibited solvent (polarity) assisted tautomerism in all reported salts and proton transfer was noticed to the ring N of thiazole due to which two point supramolecular synthon N+-H(thiazole)?O-(acid), N-H(amine)?O-(acid) was observed. The crystal structures were studied with respect to the positional effect of the competing functional groups like hydroxyl (-OH) and nitro (-NO2) as well as their donor and acceptor abilities for hydrogen bonding. The presence of the non-conventional hydrogen bond (C-H?O) has been found to play a critical role in the formation of secondary supramolecular architectures. © 2014 Indian Academy of Sciences.Item The hierarchies of hydrogen bonds in salts/cocrystals of isoniazid and its Schiff base - A case study(Royal Society of Chemistry, 2016) Oruganti, M.; Khade, P.; Das, U.K.; Trivedi, D.R.A series of two salts of isoniazid and two cocrystals of its Schiff base have been synthesised and characterized using FT-IR, 1H-NMR, DSC, XRPD and SCXRD. The crystal structures with 2,5-dihydroxybenzoic acid, 2,6-dihydroxy benzoic acid, 3-aminobenzoic acid and o-phthalic acid have been deduced. In all complexes the involvement of pyridine N (proton transfer/robust synthon) is noticed. The unit cell similarity index was calculated between two cocrystals (N-(propan-2-ylidene)isonicotinohydrazide)·(2,5-dihydroxybenzoic acid) and (3-aminobenozic acid)·(N-(propan-2-ylidene)isonicotinohydrazide). Furthermore, the index was compared with the reported complexes and it was found to be close to zero indicating isostructurality. The correlation between the NPyr-H?O (acid) hydrogen bond distance for the reported cocrystals and their corresponding pKa values has been deduced and validated. © The Royal Society of Chemistry 2016.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 Structural and physicochemical characterization of pyridine derivative salts of anti-inflammatory drugs(Elsevier B.V., 2017) Nechipadappu, S.K.; Trivedi, D.R.Salts of common anti-inflammatory drugs mefenamic acid (MFA), tolfenamic acid (TFA) and naproxen (NPX) with various pyridine derivatives (4-amino pyridine (4AP), 4-dimethylaminopyridine (DMAP) and 2-amino pyridine (2AP)) were synthesized by crystal engineering approach based on the pKa values of API's and the salt former. All the salts were characterized systematically by various spectroscopic methods including FT-IR and 1H NMR and the crystal structure was determined by single-crystal X-ray diffraction techniques (SCXRD). DMAP salt of NPX and 2AP salts of MFA and TFA were not obtained in the salt screening experiments. All the molecular salts exhibited 1:1 molecular stoichiometry in the asymmetric unit and except NPX-2AP salt, all the molecular salts included a water molecule in the crystal lattice. Physicochemical and structural properties between drug-drug molecular salts of MFA-4AP, TFA-4AP and NPX-4AP have been evaluated and it was found that these molecular salts were found to be stable for a time period of six months at ambient condition and further hydration of molecular salts were not observed even at accelerated humid conditions (?75% RH). It was found that 4AP salts of MFA and TFA and DMAP salts of MFA and TFA are isostructural. © 2017 Elsevier B.V.Item Estimation of spatially dependent heat flux transients during quenching of inconel probe in molten salt bath(ASTM International, 2017) Pranesh Rao, K.M.; Prabhu, K.N.Several industrial heat treatment processes, such as martempering and austempering, require a quench bath to be maintained at a temperature ranging between 150°C–600°C. Molten salts, molten alkali, and hot oils are the preferred quenchants for these processes. Molten salts and molten alkali are preferred over hot oil because they possess properties like wide operating temperature range, excellent thermal stability, and tolerance for contaminants. In the present work, the performance of a molten potassium nitrate (KNO3) quench bath was analyzed with an Inconel probe that measured 60 mm in height and 12.5 mm in diameter. The probe was heated to 850°C and subsequently quenched in a bath maintained at 450°C. Cooling curves at different locations of the probe were recorded using the K-type thermocouples inserted into the probe. Spatially dependent transient heat flux at the metal/quenchant interface was estimated using inverse heat conduction technique. The existence of two stages of quenching—boiling stage and convection stage—was confirmed by analyzing the heat flux. The heat transfer coefficient was calculated based on heat flux obtained by the inverse method. The nonuniformity in heat transfer along the length of the probe was quantified by calculating the range of surface temperatures at each instance. The hardness distribution in an AISI 4140 steel was predicted using the temperature distribution in the Inconel probe and obtained using inverse method. Uneven distribution of hardness predicted in the probe was attributed to the nonuniform cooling of the probe during quenching. © © 2017 by ASTM International.Item Colorimetric anion sensors based on positional effect of nitro group for recognition of biologically relevant anions in organic and aqueous medium, insight real-life application and DFT studies(Elsevier B.V., 2018) Singh, A.; Sahoo, S.K.; Trivedi, D.R.A new six colorimetric receptors A1-A6 were designed and synthesized, characterized by typical common spectroscopic techniques like FT-IR, UV–Visible, 1H NMR, 13C NMR and ESI-MS. The receptor A1 and A2 exhibit a significant naked-eye response towards F? and AcO? ions in DMSO. Due to presences of the NO2 group at para and ortho position with extended ?-conjugation of naphthyl group carrying –OH as a binding site. Compared to receptor A2, A1 is extremely capable of detecting F? and AcO? ions present in the form of sodium salts in an aqueous medium. This is owed to the occurrence of –NO2 group at para position induced in increasing the acidity of –OH proton. Consequently, it easily gets deprotonated in aqueous media. The detection limit of receptor A1 was turned out to be 0.40 and 0.35 ppm for F? and AcO? ions which is beneath WHO permission level (1.0 ppm). Receptor A1 shows a solitary property of solvatochromism in different aprotic solvents in presence of AcO? ion. Receptor A1 depicts high selectivity towards AcO? ion in DMSO: HEPES buffer (9:1, v/v). Receptor A1 proved itself for real life application by detecting anion in solution and solid state. The binding mechanism of receptor A1 with AcO? and F? ions was monitored from 1HNMR titration and DFT study. © 2017 Elsevier B.V.Item Salt/Cocrystal of Anti-Fibrinolytic Hemostatic Drug Tranexamic acid: Structural, DFT, and Stability Study of Salt/Cocrystal with GRAS Molecules(American Chemical Society service@acs.org, 2019) Nechipadappu, S.K.; Reddy, I.R.; Tarafder, K.; Trivedi, D.R.Tranexamic acid (TXA) is an important and essential medicine needed in a health system and is approved by the US FDA for the treatment of excessive blood loss from trauma, postpartum bleeding, surgery, tooth removal, nosebleeds, and heavy menstruation. One of the notable disadvantages of the TXA drug is that has low absorption (â35-40%) in the gastrointestinal tract, possibly due to its amphoteric nature. In the present work, nine molecular salts and two cocrystals of the TXA molecule have been synthesized by a simple water-mediated solvent evaporation method. The coformers/counterions used were salicylic acid (SAL), 3-hydroxybenzoic acid (3HBA), 2,4-dihydroxybenzoic acid (2,4HBA), 2,5-dihydroxybenzoic acid (2,5HBA), 2,6-dihydroxybenzoic acid (2,6HBA), gallic acid (GAA), oxalic acid (TXA), tartaric acid (TTA), fumaric acid (FUM), succinic acid (SUA), and crotonic acid (CRA). The synthesized salts/cocrystals were characterized by various spectroscopic, thermal, and XRD techniques. The crystal structures of all of the molecular adducts were determined by SC-XRD techniques. In the synthesized salts, charge-assisted acid···amine heterosynthons and O-H···O hydrogen bonds between the acid group of TXA and the coformer are favored, and the salts TXA-FUM and TXA-SUA were found to be isostructural on the basis of the isostructural parameters Ï€ and Î? . In the cocrystal, molecules interacted through the acid group of the coformer with the carboxyl group of the TXA molecule. Further, these salts/cocrystals were found to be stable for a period of 6 months under ambient conditions (â25-30 °C, â60-65% RH). Furthermore, density functional theory (DFT) calculations were carried out to better understand the geometric structure of the molecules presented in our study. The interaction energies of the molecular salts and cocrystals were calculated, and they supported the reported structure of the crystalline adducts. The cocrystal formation in the case of TXA-GAA and TXA-CRA has been confirmed by a DFT calculation study, as the salt formation in these cases resulted in a higher interaction energy in comparison to the cocrystal. Consequently, these molecular salts offer promise for the development of new drug products of TXA, and a few salts, namely TXA-SAL and TXA-2,5HBA, offer the possibility of development of combination drugs. © 2018 American Chemical Society.Item Hydrophilicity of the hydrophobic group: Effect of cosolvents and ions(Elsevier B.V., 2019) Dilip, H.N.; Chakraborty, D.Classical molecular dynamics simulations were performed to study the effect of cosolvents and ions on the solvation structure of zwitterionic glycine in liquid water. Simulations were carried out for 2 M and 1 M concentration of TMAO, Urea, KCl and LiCl solutions to observe the changes in liquid structure of water near the glycine molecule. Radial distribution functions and spatial distribution functions showed the presence of protective hydration layer near the C ? in presence of TMAO which gets reduced in case of urea, KCl and minimum in case of LiCl. LiCl is found to disrupt severely the solvation structure near the glycine molecule. For LiCl system, a small hydration layer is found near C ? unit at higher distances which is mainly due to the first hydration shell of lithium ion bonded to the carboxylate group. Presence of these hydration layers gives extra stabilization energy to the glycine water system. Stabilizing and destabilizing effect of water near the glycine molecule is calculated in terms of Potential Mean Force. The anomalous behaviour of lithium salts with respect to Group I cation salts in protein stabilization can be explained on the basis of this behaviour. We found maximum hydrogen bond lifetime for water molecules in presence of TMAO followed by LiCl, KCl and least in case of urea. The higher lifetimes in presence of ions are found mainly due to their electrostatic force. The stabilization of the hydrophobic part of the glycine molecule can be correlated with the stabilization of proteins in presence of these cosolvents. © 2019 Elsevier B.V.