Spectroscopic, electrochemical and DNA binding studies of some monomeric copper(II) complexes containing N2S(thiolate)Cu core and N4S(disulfide)Cu core

Abstract

We report the synthesis, characterization and spectroscopic results of the Cu(II) complexes [Cu(pabt)(OH2)](ClO4) (1), [Cu(pabt)(Imz)](ClO4) (2), [Cu(pabt)(N-MeImz)](ClO4) (3), [Cu(pabt)Cl] (4), [Cu(pma)Cl] (5), [Cu(pdta)Cl]Cl (6) and [Cu(reduced-pdta)Cl]Cl (7), (Hpabt=N-(2-mercaptophenyl)-2′-pyridylmethylenimine, Hpma=N-(2-pyridylmethyl)-2-mercaptoaniline, pdta=2,2′-di(pyridyl-2-methyleneimine)diphenyl disulfide, reduced-pdta=2,2′-di(pyridyl-2-methylamine)diphenyl disulfide, Imz=imidazole, N-MeImz=N-methylimidazole). Electronic spectra of all these compounds display strong LMCT bands in the visible region mainly associated with S→Cu(II), and consistent with TDDFT results. A four-line EPR pattern originating from the interaction of the unpaired electron with the central 63/65Cu nucleus (I=3/2, natural abundances: 63Cu, 69.17%; 65Cu, 30.83%) with the isotropic coupling constant (Aiso) values of 80±1.5G at RT for all these complexes suggests monomeric nature in solution. The redox behavior of these compounds show either nearly reversible or quasi-reversible Cu(II)/Cu(I) couple with redox potentials within the range −0.08 to −0.20V versus Ag/AgCl. Some of these compounds show strong intercalative DNA binding and its complete cleavage. 1–3 exhibit remarkable cytotoxicity against C6 glioma cell line and human cervical cancer HeLa cell line. IC50 values of 2 and 3 for the cervical cancer HeLa cell line reveal that they exhibit higher cytotoxicity than many reported Cu(II) compounds.