Darshak R. Trivedi

Bovine serum albumin catalyzed one-pot, three-component synthesis of dihydropyrano[2,3-c]pyrazole derivatives in aqueous ethanol

Bovine serum albumin (BSA) catalyzed synthesis of dihydropyrano[2,3-c]pyrazole derivatives via a one pot, three component reaction of an aldehyde/ketone/isatin, malononitrile and 3-methyl-1H-pyrazol-5-(4H)-one in H2O–EtOH (7 : 3) at ambient temperature was developed in this work. The catalyst was found to work efficiently for aldehydes, ketones and isatins to give the corresponding dihydropyrano[2,3-c]pyrazole and spiro[indoline-3,4′-pyrano[2,3-c]pyrazole] derivatives in high yields. BSA showed a broad range of catalytic promiscuity towards various aldehydes, aromatic/aliphatic ketones and substituted isatins. The use of an environmentally benign protocol, reusability of the catalyst, avoidance of hazardous solvents, excellent yields, easy work up and no byproduct formation make BSA an attractive candidate for further applications as a biocatalyst.

Condensation of malononitrile with salicylaldehydes and o-aminobenzaldehydes revisited: solvent and catalyst free synthesis of 4H-chromenes and quinolines

The reaction of malononitrile with salicylaldehyde under solvent and catalyst free conditions was re-investigated using mechanochemical mixing, thermal heating and a direct crystallization process. The resulting condensation product by all three types of molecular activation, was found to be (2-amino-3-cyano-4H-chromene-4-yl)malononitrile, which is not the previously reported benzofuran-2-carbonitrile. The structure of the resulting chromene derivative was confirmed by FT-IR, MS, 1H, 13C NMR and single crystal and powder X-ray diffraction. The reaction pathway under neat conditions (mechanochemical mixing) at ambient temperature was monitored by IR spectral measurements. The versatility of the current green protocol was examined through the reaction of eleven derivatives of o-hydroxybenzaldehyde with malononitrile to obtain 2-amino-3-cyano-4H-chromene derivatives. In addition, malononitrile was further reacted with o-aminobenzaldehydes under neat conditions to yield quinoline derivatives.

Colorimetric receptors for naked eye detection of inorganic fluoride ion in aqueous media using ICT mechanism

A new series of receptors were designed and synthesized based on benzohydrazide for the colorimetric detection of fluoride ion. The receptors L1 and L2 are highly selective towards fluoride ion over other anions. These receptors are able to detect inorganic fluoride such as NaF in aqueous solutions. The presence of two carbonyl groups in the receptor molecule makes the –NH proton highly acidic and hence these receptors are capable of competing with water molecules to bind fluoride ion. The receptors L1 and L2 showed a significant colour change from colourless to yellow in aqueous solutions of NaF with a Δλmax of 149 nm and 147 nm respectively. The mechanism involved in the colour change was deprotonation, formation of imidic acid intermediate followed by stabilization of complex through Intramolecular Charge Transfer (ICT). This was further confirmed by 1H NMR titrations where the formation of imidic acid was observed. The receptor L1 proved itself to be potentially useful for real-life applications by detecting fluoride ion quantitatively in sea water and commercially available mouth wash.

Dual colorimetric receptor with logic gate operations: anion induced solvatochromism

A receptor R1 was designed and synthesised for colorimetric detection of F− ions as well as Cu2+ ions via intramolecular charge transfer mechanism. Upon addition of F− ions in dry DMSO, the color of the receptor R1 changed from pale yellow to blue. The receptor showed a unique property of solvatochromism by displaying different coloration with different solvents only in the presence of F− ions, which were applied to determine the percentage composition of binary solvent mixtures. The receptor R1 was able to detect Cu2+ ions colorimetrically where it exhibited a color change from pale yellow to orange-red. In addition, the receptor was subjected to molecular logic gate applications, wherein it showed ‘ON–OFF’ switching operations.

Pharmaceutical salts of ethionamide with GRAS counter ion donors to enhance the solubility.

&NA; 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. Graphical abstract Four novel molecular salts of anti‐tuberculosis drug ethionamide with various counter ions namely 2‐chloro‐4‐nitrobenzoic acid, 2,6‐dihydroxybenzoic acid, 2,3‐dihydroxybenzoic acid and 2,4‐dinitrobenzoic acid are reported. Physico‐chemical properties associated with ETH‐CNB, ETH‐2,6HBA and ETH‐2,3HBA are evaluated in the present study. Figure. No caption available.

The hierarchies of hydrogen bonds in salts/cocrystals of isoniazid and its Schiff base – a case study

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.

Multi-signaling thiocarbohydrazide based colorimetric sensors for the selective recognition of heavy metal ions in an aqueous medium

A series of colorimetric chemosensors R1-R6 have been developed from thiocarbohydrazide derivatives, for the selective detection of heavy metal ions. The structures of the receptors R1-R6 were well characterized by standard spectroscopic techniques like FT-IR, 1H NMR, and ESI-MS. The solid structure of receptor R1 and R2 were derived by single crystal X-ray diffraction (SC-XRD). The cation reorganization abilities of receptors R1-R6 were studied by UV-Vis spectroscopy. The receptors R1, R3 and R4 acts as a tremendous sensitive probe for heavy metal ions (Hg2+, Cd2+ and Pb2+) with the μM detection (R1 for Hg2+, 2.72, R3 for Cd2+, 3.22, R4 for Hg2+, Cd2+ & Pb2+, 0.70, 0.20 & 0.30μM) and the receptors R2, R5 &R6 are sensitive towards Cu2+ ions with the μM detection (3.34, 0.90 & 1.20μM) in an aqueous medium among all other tested cations. The receptor R4 shows a multi-color response towards Hg2+, Cu2+, Cd2+ and Pb2+ ions. The recognition mechanism, stoichiometric binding ratio and detection limit (DL) have been examined by UV-Visible spectroscopic titration experiments and Benesi-Hildebrand (B-H) plot, receptor R1-R6 sowed 1:1 binding ratio with good binding constant range of 103 to 105M-1 with Hg2+, Cu2+, Cd2+ and Pb2+ ions metal ions.

A highly efficient and green cascade synthesis of 3-methyl-substituted-4-hydroxy-1-methyl-quinolin-2(1H)-ones under solvent- and catalyst-free conditions

An expeditious and green protocol for the synthesis of 3,3′-methanediylbis(4-hydroxy-1-methylquinolin-2(1H)-one) (MDBHQ) derivatives and 3-((2-amino-6-oxocyclohex-1-enyl)methyl)-4-hydroxy-1-methylquinolin-2(1H)-one (AOCHQ) derivatives has been developed via a cascade Knoevenagel–Michael reaction. The products were obtained in high yield under neat reaction conditions without any work-up or chromatographic purification. The generality and functional tolerance of this environmentally benign protocol is demonstrated.

Design and synthesis of a new organic receptor and evaluation of colorimetric anion sensing ability in organo-aqueous medium

A new organic receptor has been designed and synthesized by the combination of aromatic dialdehyde with nitro-substituted aminophenol resulting in a Schiff base compound. The receptor exhibited a colorimetric response for F(-) and AcO(-) ion with a distinct color change from pale yellow to red and pink respectively in dry DMSO solvent and yellow to pale greenish yellow in DMSO:H2O (9:1, v/v). UV-Vis titration studies displayed a significant shift in absorption maxima in comparison with the free receptor. The shift could be attributed to the hydrogen bonding interactions between the active anions and the hydroxyl functionality aided by the electron withdrawing nitro substituent on the receptor. (1)H NMR titration and density functionality studies have been performed to understand the nature of interaction of receptor and anions. The lower detection limit of 1.12ppm was obtained in organic media for F(-) ion confirming the real time application of the receptor.

Insights into the electrooptical anion sensing properties of a new organic receptor: solvent dependent chromogenic response and DFT studies

A highly selective hydrazine based electrooptical receptor featuring solvent based color transition properties in the presence of acetate ions has been developed. The AcO− ion mediated color transition properties of a new organic receptor in solvents of varying polarity highlights the influence of dipole moment in stabilizing the excited state. Selective detection of acetate ions by a new organic receptor in the presence of DMSO : Tris HCl buffer (9 : 1, v/v) has been the pivotal concept of the present work. 1H-NMR titration and DFT studies provide quantitative proof of the underlying detection mechanism. Solution and solid state sensing response of anions by the receptor reflects the practical utility in real time sample analysis.