Ajnesh Singh

Fluorescent Organic Nanoparticles of Biginelli-Based Molecules: Recognition of Hg2+ and Cl– in an Aqueous Medium

Biginelli-based molecules (1-3) have been synthesized and developed as a new class of fluorescent organic nanoparticle-based chemosensors. Chemosensor 2 has shown excellent selectivity and sensitivity for detection of Hg(2+) in an aqueous medium. It can detect Hg(2+) up to 1 nM, and the resultant 2Hg(2+) complex can detect Cl(-) ions (micromolar level) in an aqueous medium.

Comparative DNA binding abilities and phosphatase-like activities of mono-, di-, and trinuclear Ni(II) complexes: the influence of ligand denticity, metal-metal distance, and coordinating solvent/anion on kinetics studies.

Six novel Ni(II) complexes, namely, [Ni2(HL(1))(OAc)2] (1), [Ni3L(1)2]·H2O·2CH3CN (2), [Ni2(L(2))(L(3))(CH3CN)] (3), [Ni2(L(2))2(H2O)2] (4), [Ni2(L(2))2(DMF)2]2·2H2O (5), and [Ni(HL(2))2]·H2O (6), were synthesized by reacting nitrophenol-based tripodal (H3L(1)) and dipodal (H2L(2)) Schiff base ligands with Ni(II) metal salts at ambient conditions. All the complexes were fully characterized with different spectroscopic techniques such as elemental analyses, IR, UV-vis spectroscopy, and electrospray ionization mass spectrometry. The solid-state structures of 2, 3, 5, and 6 were determined using single-crystal X-ray crystallography. The compounds 1, 3, 4, and 5 are dinuclear complexes where the two Ni(II) centers have octahedral geometry with bridging phenoxo groups. Compound 2 is a trinuclear complex with two different types of Ni(II) centers. In compound 3 one of the Ni(II) centers has a coordinated acetonitrile molecule, whereas in compound 4, a water molecule has occupied one coordination site of each Ni(II) center. In complex 5, the coordinated water of complex 4 was displaced by the dimethylformamide (DMF) during its crystallization. Complex 6 is mononuclear with two amine-bis(phenolate) ligands in scissorlike fashion around the Ni(II) metal center. The single crystals of 1 and 4 could not be obtained; however, from the spectroscopic data and physicochemical properties (electronic and redox properties) it was assumed that the structures of these complexes are quite similar to other analogues. DNA binding abilities and phosphatase-like activities of all characterized complexes were also investigated. The ligand denticity, coordinated anions/solvents (such as acetate, acetonitrile, water, and DMF), and cooperative action of two metal centers play a significant role in the phosphate ester bond cleavage of 2-hydroxypropyl-p-nitropenylphosphate by transesterification mechanism. Complex 3 exhibits highest activity among complexes 1-6 with 3.86 × 10(5) times greater rate enhancement than uncatalyzed reaction.

A benzimidazolium-based organic trication: a selective fluorescent sensor for detecting cysteine in water

A benzimidazolium- and imidazolium-based trication was developed as a fluorescence probe for cysteine (Cys). The probe exhibits fluorescence responses to Cys in water with high selectivity and a nano-molar detection limit. Such specificity towards Cys is based on differences in the hydrogen bonding of R1 with Cys, and it provides a method for detecting Cys in the presence of other analytes in a real biological system such as human serum. Density functional theory (DFT) calculations and 1H NMR titration confirmed the cavity-based recognition of Cys.

Water-mediated supramolecular architecture of Co(III)–phenanthroline complexes: organizational control to 2D-layers and 3D-square cavities through substituted aryl carboxylate anions

To explore the variation in the supramolecular architecture of cobalt(III)–1,10-phenanthroline–aryl carboxylate complexes in tune with aryl substitution, eight new supramolecular inorganic–organic framework complexes have been synthesized. These have the general formula [Co(phen)2CO3]L·nH2O, where phen = 1,10-phenanthroline, L = 3-nitrobenzoate (P, Z = 2, n = 4; 1), 4-nitrobenzoate (P, Z = 2, n = 5; 2), 2-chloro-4-nitrobenzoate (P, Z = 2, n = 5; 3), 3-methyl-4-nitrobenzoate (P, Z = 2, n = 5; 4), 4-chlorobenzoate (P21/c, Z = 4, n = 7; 5), 2-iodobenzoate (P, Z = 2, n = 7; 6), 2-phenoxybenzoate (P, Z = 2, n = 8; 7) and 2-napthleneacetate (P21/c, Z = 4, n = 7; 8) and were unequivocally characterized by physicochemical methods, spectroscopic techniques and single crystal X-ray crystallography. Solubility, conductivity measurements and X-ray structure determination revealed the ionic nature of complexes 1–8. While the complexes 1–4, 7 and 8 prefer a 2D layer structure; the complexes 5 and 6 favor a 3D square cavity and in all these complexes, water molecules act as stabilizing linkers between anions and cations. The weak non-covalent interactions of the type O–H⋯O (carboxylate/water/carbonato), C–H⋯O (carboxylate/water/carbonato), π⋯π, C–H⋯π and anion⋯π interactions play a crucial role in stabilizing the crystal lattices.

Stabilization of tetrameric metavanadate ion by tris(1,10-phenanthroline)cobalt(III): Synthesis, spectroscopic and X-ray structural study of [Co(phen)(3)](3)(V(4)O(12))(2)Cl·27H(2)O.

A new complex salt of composition [Co(phen)3]3(V4O12)2Cl ⋅ 27H2O (phen = 1,10-phenanthroline and [V4O12]4− = tetrameric metavanadate, dodecaoxotetravanadate ion) was synthesized by the reaction of appropriate salts in aqueous medium. The complex salt has been characterized by elemental analyses, thermogravimetric analysis, cyclic voltammetry, FT-IR, and UV-Vis spectroscopies, solubility product and conductance measurements. Single crystal X-ray structure determination revealed ionic structure consisting of three complex cations, [Co(phen)3]3+, two [V4O12]4− anions, one chloride and 27 lattice water molecules. Detailed structural and spectroscopic analyses of [Co(phen)3]3(V4O12)2Cl ⋅ 27H2O showed that the large anion is stabilized by large cationic metal complex as there is preferred shape compatibility that leads to a large number of lattice-stabilizing non-covalent interactions.