METAL (II) COMPLEXES OF BIOINORGANIC AND MEDICINAL RELEVANCE: ANTIBACTERIAL, ANTIOXIDANT AND DNA CLEAVAGE STUDIES OF TETRADENTATE COMPLEXES INVOLVING O, N-DONOR ENVIRONMENT OF 3, 3'-DIHYDROXYBENZIDINE-BASED SCHIFF BASES

A new potentially tetradentate Schiff base ligand H2L and their binuclear metal complexes have been prepared on the condensation of 3, 3′dihydroxybenzidine, o- phthalaldehyde and 2-aminophenol in the molar ratio of 1:2:2. The Schiff base, H2L, ligand acts as dibasic with two N2O2tetradentate sites and can coordinate with two metal ions to form binuclear complexes after the deprotonation of the hydrogen atoms of the phenolic groups in all the complexes. All the metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and Spectral studies. The analytical data helped to elucidate the structure of the metal complexes. All the complexes are non-electrolyte in DMF due to their low molar conductance value. The IR spectral data suggest the involvement of azomethine nitrogen in co-ordination to the central metal ion. Electronic, ESR and magnetic data proposed the square planar geometry for Cu(II), Ni(II) and square pyramidal for VO(II) complexes under investigations. Cyclic voltammetry and controlled electrolysis studies indicate that the metal ion in the binuclear complexes undergo quasireversible one electron reduction and oxidation. The nucleolytic cleavage activities of the complexes were assayed on pUC18 plasmid DNA using gel electrophoresis in the presence and absence of H2O2 and the complexes show promising nuclease activity. The complexes show significant growth inhibitory activity against the bacteria like Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Klebsilla pneumonia than the free ligands. In addition, the antioxidant activities of the complexes were also investigated through scavenging effect on DPPH radicals. The obtained IC50 value of the DPPH activity for the copper complex (IC50 = 5.46 mg/ml) was higher than other compounds.