R.N. Patel

E.P.R. study of an imidazolate-bridged Cu-Zn complex of glycylglycine

Abstract An imidazolate-bridged heterometallic binuclear copper–zinc complex Na[(glygly)Cu–im–Zn(glygly)], where H 2 glygly is glycylglycine and imH is imidazole, has been synthesized. X-band e.p.r. spectra of the complex at different pH values in frozen solution (50% DMSO, 77 K) suggest that the imidazolate bridged complex is stable in the pH range 7–10. At lower pH ( 10), the e.p.r. changes suggest either hydroxylation of the copper centre or breaking of the imidazolate bridge on the zinc side.

E.s.r., magnetic, optical and biological (SOD and antimicrobial) studies of imidazolate bridged CuII–ZnII and CuII–NiII complexes with tris(2-amino ethyl)amine as capping ligand: a plausible model for superoxide dismutase

X-band e.s.r. and optical absorption spectra of the imidazolate bridged heterobimetallic complexes [(tren)Cu-E-Im-Zn-(tren)](ClO(4))(3) and [(tren)Cu-E-Im-Ni-(tren)](ClO(4))(3), where trentris(2-aminoethyl)amine, E-Im=2-ethylimidazolate ion and the related mononuclear complexes [Cu(tren)](ClO(4))(2) and [(tren)Cu-E-ImH)](ClO(4))(2) have been described. Biological activities (superoxide dismutase and antimicrobial) have also been measured and compared with reported complexes.

Spectral, structural, and superoxide dismutase activity of some octahedral nickel(II) complexes with tri-tetradentate ligands

Three nickel(II) complexes, [Ni(L1)2] ⋅ 3H2O (1), [Ni(L2)2](ClO4)2 (2), and [Ni(L3)(bipy)](ClO4)2 (3), where L1 = N′-[phenyl(pyridin-2-yl)methylidene]furan-2-carbohydrazide, L2 = 2,6-bis[N,N′-(4-methoxyphenyl)ethanimidoyl]pyridine, and L3 = N-(methoxy-phenyl-pyridin-2-yl-methyl)-N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine, have been synthesized and characterized by physico-chemical and spectroscopic methods. The solid-state structures of 1–3 were determined by single crystal X-ray crystallography, which revealed distorted octahedral geometry. In solid-state structure, 3 is self-assembled via intermolecular π ··· π stacking and intramolecular CH(methyl) ··· π(phenyl) non-covalent interactions. Infrared spectra, ligand-field spectra, and magnetic susceptibility measurements agree with the observed crystal structures. These complexes have also been revealed to catalyze effectively the dismutation of superoxide ( ) in alkaline dimethyl superoxide-nitro blue tetrazolium assay.

Synthesis, characterization, and biological activity of nickel(II) complexes with a tridentate Schiff base derived from heterocyclic aldehyde

A series of nickel(II) complexes, namely [Ni(L)2] (1), [Ni(L)(HL)](ClO4)(H2O) (2), [Ni(HL)(bipy)(H2O)](NO3)(ClO4)(H2O) (3), and [Ni(HL)(dien)](ClO4)2(H2O) (4) have been synthesized with Schiff base (L) derived from 2-pyridinecarboxaldehyde and benzoylhydrazine. The elemental analyses of the complexes indicate stoichiometry ML2 and M(L)(B), where L = N-[(1)-pyridin-2-ylmethylidene]benzohydrazide, B = diethylenetriamine/2,2′-bipyridine. L is a deprotonated as well as neutral tridentate ligand. Single-crystal X-ray structures of 1–4 reveal distorted octahedral geometry in the complexes. The molecules are connected by various hydrogen-bonding interactions. Magnetic susceptibility measurements at room temperature were 2.79–2.91 MB. The electrochemical behavior, superoxide dismutase, and antibacterial activities of these complexes were made by cyclic voltammetry, the alkaline DMSO-nitro blue tetrazolium chloride assay, and the paper disc diffusion method, respectively.

Structural, spectroscopic, and biological studies of N,O donor Schiff base copper(II) complexes

The Schiff bases (L1 and L2) and their complexes [Cu(L)2] (L1 = N-[(1)-1-(4-methylphenyl)ethylidene]benzolhydrazide and L2 = N-[(1)-1-(2-methoxyphenyl)ethylidene]benzolhydrazide) have been prepared and characterized by elemental analysis, magnetic, and conductivity measurements. Crystal structure of the two complexes determined by single crystal X-ray analysis shows distorted square planar CuN2O2 coordination. Electron paramagnetic resonance spectra of these complexes in frozen DMSO show a signal at g ca 2. The trend in g-value (g ‖ > g ⊥ > 2.0023) suggests that the unpaired electron on copper(II) has character. The superoxide dismutase and biological (antimicrobial) activities of these complexes have also been screened.

Carboxylate-bridged copper(II) complexes: synthesis, crystal structures, and superoxide dismutase activity

Two copper(II) complexes, [Cu2(μ-benzoato)(L1)2]NO3·2H2O (1) and [Cu2(μ-succinato)(L2)2(H2O)]ClO4 (2), have been synthesized, where L1 = N′-[(E)-phenyl(pyridin-2-yl)methylidene]benzoylhydrazone and L2 = N′-[(E)-pyridin-2-ylmethylidene]benzoylhydrazone. These complexes were characterized including by single-crystal X-ray diffraction studies. The copper is five-coordinate in 1 while in 2 one copper is five-coordinate and the other is six-coordinate. Electrochemical behavior of these complexes was measured by cyclic voltammetry. The conproportionation equilibrium constants (Kcon) for both complexes have been estimated. The superoxide dismutase (SOD) activities of 1 and 2 were measured by nitro blue tetrazolium assay. Complex 1 has better SOD activity than 2.

Synthesis and X-Band Electron Paramagnetic Resonance Study of an Imidazolato Bridged Binuclear Copper(II) - Glycylglycine Complex

Abstract EPR Spectra of an imidazolato-bridged binuclear copper(II) complex of glycylglycine are described. Spectra of related mononuclear complexes, viz., aquoglycylglycinatocopper(II) and imidazoleglycylglycinatocopper(II), are also described.

Synthesis and X-Band Spectra of An Imidazolate-Bridged Copper-Zinc Binuclear Complex

Abstract The pH-dependence of the EPR spectra of a newly synthesized imidazolate-bridged Cu(II)-Zn(II) complex, [(dien)Cu(im)Zn(dien)]3+ (dien = diethylenetriamine, im = imidazolate anion), has been studied in frozen solution (50% DMSO) to explore the mode of breaking of the imidazolate bridge. The data suggest that the imidazolate bridge in the complex is stable only at high pH (>9) and breaks on the zinc side at lower pH values.

Synthesis, spectral and structural study of sulfur-containing copper(II) complexes

A series of four new copper(II) complexes [Cu(H2L)(L1)] 1, [Cu(H2L)(PMDT)] 2, [Cu(H2L)(Dien)] 3 and [Cu(H2L)(L2)] 4 have been synthesized by template condensation (H2L=thiodiglycolic acid, L1=N-[(1)-1-(4-methylphenyl)ethylidene]benzohydrazide, PMDT=N,N,N′,N′,N ′′-pentamethyldiethylene- triamine, Dien=diethylenetriamine L2=N-[(1)-pyridin-2-ylmethylidene]benzohydrazide). The bonding and stereochemistry of the complexes have been characterized by molar conductance, elemental analysis, magnetic susceptibility, infrared, UV–visible, electron paramagnetic resonance structural studies and electrochemical studies. g-Values were calculated for all complexes in polycrystalline form as well as in DMSO solution. The magnetic and spectral data indicate square pyramidal geometry for 1 and octahedral geometry for 2–4 complexes. Cyclic voltammograms for all the complexes are similar and involve two irreversible redox processes. Their biological properties have also been studied. The thio complexes show more antibacterial activity than the controlled one. The antibacterial activities of the compounds have also been tested against Escherichia coli with different concentrations.

Design, synthesis, and characterization of a series of biologically active copper(II) Schiff-base coordination compounds

Four Schiff-base copper(II) complexes, [Cu(L1)(Phen)(H2O)](NO3)2 (1), [Cu(L1)(bipy)(H2O)](ClO4)(H2O)(NO3) (2), [Cu(L1)(Dien)](ClO4)2(H2O) (3), and [Cu(L1)(ImH)(H2O)](ClO4) (4) (L1  = N-[(1)-pyridin-2-ylmethylidene]benzohydrazide, Phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, Dien = diethylenetriamine, ImH = imidazole), have been synthesized and characterized using various physico-chemical techniques. L1 is coordinated to copper(II) neutral and uninegatively charged tridentate chelating agent via the azomethine nitrogen, pyridine nitrogen, and carbonyl oxygen. The copper(II) complexes are paramagnetic with octahedral stereochemistry. The crystal structures of the complexes reveal the presence of structure consisting of a tridentate N, N, O donor Schiff base, tridentate NNN donor polyamine or N, N donor heterocyclic base and the copper(II) center. In 1, 2, and 4, water is present as a coordinating molecule whereas in 2 and 4 it is also present as lattice water. In discrete monomeric species all complexes show significant hydrogen-bonding interactions. H-bridges are also present in the solid state structure. Complexes 1–4 effectively catalyze the dismutation of superoxide ( ) in alkaline nitro blue tetrazolium assay and IC50 values were determined. The susceptibility of certain strains of bacteria toward the precursors L1 and their complexes were also evaluated.