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

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-Melmz)](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'-pyridyl-methylenimine, 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 Cu-63/65 nucleus (I = 3/2, natural abundances: Cu-63, 69.17%; Cu-65, 30.83%) with the isotropic coupling constant (A(iso)) values of 80 +/- 1.5 G 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 -0.20 V 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. (C) 2016 Elsevier B.V. All rights reserved.