Synthesis, characterization and evaluation of antimicrobial potential of zinc(II) complexes of nitro-substituted hydroxamic acid chelators

The nitro-substituted hydroxamic acid chelators potassium 4-nitrobenzohydroxamate (4-(NO2)C6H4CONHOK) (KHL1) and 3,5-dinitrosalicylhydroxamate (3,5-(NO2)(2)(OH)C6H2CONHOK) (KHL2) on reaction with anhydrous zinc(II) chloride (ZnCl2) in 1:2 metal:ligand ratio in MeOH + THF afforded new zinc(II) complexes, [Zn(4-(NO2)C6H4CONHO)(2)] (1) and [Zn(3,5-(NO2)(2)(OH)C6H2CONHO)(2)] (2). The structural characterization of 1 and 2 has been accomplished by physicochemical studies; elemental analyses, molar conductivity, cyclic voltammetry and spectroscopic techniques in the solid state (IR) and in solution (H-1 NMR and UV-visible). The stoichiometric composition of 1 and 2 has been authenticated by mole ratio method and the stability constants were determined. IR spectral studies suggested the bidentate nature of ligands involving bonding through carbonyl and hydroxamic oxygen atoms (O,O'-coordination). The mass spectral data of 1 and 2 have indicated these to be mononuclear. In order to infer the biological relevance of newly synthesized complexes, the in vitro antimicrobial activity assay against pathogenic gram-ve bacteria, viz. Salmonella typhi and Escherichia coli; gram + ve bacteria Bacillus cereus and Staphylococcus aureus and fungi Rhizoctoniasolani and Fusarium sambucinum by MIC method has shown appreciable antimicrobial potential. The results have been compared with standard Tetracycline and Nystatin drugs.