Syntheses, crystal structures and DNA-binding studies of Cu(II) and Zn(II) complexes bearing asymmetrical aroylhydrazone ligand

Zn(II) and Cu(II) complexes with benzophenone benzoyl hydrazone (HBBH) and benzophenone salicylylhydrazone (HBSH) have been synthesized and characterized by different physico-chemical and spectroscopic techniques (UV-vis, IR and NMR). The molecular structures of these complexes [Zn(BBH)(2), Cu(BBH)(2) and Cu(BSH)(2)Cl2H2O] have also been determined by single X-ray diffraction technique. In Zn(BBH)(2) and Cu(BBH)(2) complexes, each ligand coordinates to metal through enol tautomeric form by azomethine-N and carbonylate-O resulting a 4-coordinate distorted tetrahedral geometry. While in Cu(BSH)(2)Cl2H2O, each ligand coordinates to metal through keto tautomeric form resulting distorted octahedral geometry in which two chlorine atoms occupy the axial positions. The DNA interaction propensity of the complexes with Herring sperm DNA, studied at physiological pH by spectrophotometric, spectrofluorometric, viscometric techniques and cyclic voltammetry, revealed intercalation as the possible binding mode. Fascinatingly, Cu(BSH)(2)Cl2H2O was found to exhibit greater binding strength than the others. A strong hyperchromism effect and a slight red shift were exhibited by all complexes. The intrinsic binding constants are of moderate values and are about 3.28 x 10(4) M-1, 4.73 x 10(4) M-1 and 5.80 x 10(4) M-1, respectively. Cyclic voltammetry studies of the complexes binding with DNA indicate quasireversible oxidation and reduction potentials. The results suggest that the binding affinity of complexes lies in the order Cu(BSH)(2)Cl2H2O > Cu(BBH)(2) > Zn(BBH)(2). (C) 2016 Elsevier B.V. All rights reserved.