Syntheses, X-ray crystal structures, DNA binding, oxidative cleavage activities and antimicrobial studies of two Cu(II) hydrazone complexes

From a mononuclear Cu(II)-hydrazone complex [Cu(PBH)(2)] (1), one mu(1,1)-azido bridged dinuclear Cu(II) complex having the formula [{Cu(PBH)(mu(1,1)-NNN)}(2)] (2) (where HPBH = 2-pyridinecarboxaldehyde benzoyl hydrazone) has been synthesised. Both the complexes are characterised by elemental analyses, IR and UV-Vis spectroscopic studies. The tridentate hydrazone pro-ligand (HPBH) is obtained by the condensation of benzhydrazide and pyridine-2-carboxaldehyde. The structures of the complexes have conclusively been established by the X-ray single crystal diffraction method. Complex I and 2 both display DNA binding ability, which is ascertained by UV-Vis titration and cyclic voltammetric studies using calf thymus DNA (CT-DNA). The apparent binding constants (K-app) are of moderate values and are 2.048 x 10(4) M-1 (+/- 0.006) and 1.644 x 10(4) M-1 (+/- 0.005), respectively. The modes of binding of the complexes with CT-DNA has been investigated using circular dichroism, ethidium bromide displacement assay and viscosity measurements. The cleavage properties of these complexes as well as the free proligand with super coiled (SC) pUC19 are studied using the gel electrophoresis method, where both the complexes displayed chemical nuclease activity in the presence of H2O2 via an oxidative mechanism. The antimicrobial study using the free pro-ligand, 1 and 2 against both Gram positive and Gram negative bacteria are performed, 2 showed antimicrobial activity against both Gram negative and Gram positive bacteria whereas the free ligand and I show no antibacterial activity. (C) 2009 Elsevier Ltd. All rights reserved.