Two new dicopper(II) complexes with oxamido-bridged ligand: Synthesis, crystal structures, DNA binding/cleavage and BSA binding activity

Abstract

New oxamido-bridged copper(II) complexes, [Cu2(oxbp)(H2O)2(NCS)2] (1) and [Cu2(oxbp)(μ-DMSO)2(NCS)2][Cu2(oxbp)(DMSO)2(NCS)2] (2) (H2oxbp=N,N′-bis(2-(diethylamino)ethyl)oxalamide), were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR, and electronic spectra. X-ray analysis revealed that complex 1 consists of neutral binuclear [Cu2(oxbp)(H2O)2(NCS)2] units which forms a two-dimensional network through intermolecular hydrogen bonds and complex 2 is constructed by neutral [Cu2(oxbp)(μ-DMSO)2(NCS)2] (2a) and [Cu2(oxbp)(DMSO)2(NCS)2] (2b) entities which alternately distribute to form a two-dimensional network by means of quasi μ-DMSO bridge and intermolecular hydrogen bonds. In both 1 and 2, bicopper centers are linked by the “trans-form” oxamido bridges with the distances of 5.272Å for 1 and av. 5.296Å for 2, respectively. The interaction of Cu(II) complexes with DNA was investigated by UV-visible, fluorescence emission spectrometry and agarose gel electrophoresis. The apparent binding constant (Kapp) values of 3.16×105M−1 for 1 and 4.9×105M−1 for 2 suggest moderate intercalative binding modes between the complexes and DNA. Complex 1 displayed efficient oxidative cleavage of supercoiled DNA, which might indicate that the underlying mechanism involves singlet oxygen (1O2) as reactive oxygen species. Complex 2 is characteristic of the involvement of a singlet oxygen-like entity and hydrogen peroxide in the cleavage process. In addition, our present work showed, by fluorescence spectrometry of BSA with complexes, both 1 and 2 bind to BSA with a medium affinity through a static mode which is tentatively assigned binding to Trp134 in BSA.