Synthesis and characterization of dinuclear macrocyclic cobalt(II), copper(II) and zinc(II) complexes derived from 2,2,2 ′,2 ′- S, S[bis(bis- N, N-2-thiobenzimidazolyloxalato-1,2-ethane)]: DNA binding and cleavage studies

Abstract

New homodinuclear macrocyclic complexes of cobalt(II), copper(II) and zinc(II) were isolated from the newly synthesized ligand 2,2,2′,2′- S, S[bis(bis- N, N-2-thiobenzimidazolyloxalato-1,2-ethane)]. The structures of the complexes were elucidated by elemental analysis, molar conductance measurements, IR, 1H NMR, 13C NMR, electronic and ESI-MS spectroscopic techniques. In complex 1, Co(II) ions possess a tetrahedral coordination environment composed of O 2S 2 donor atoms while its Cu(II) and Zn(II) counterparts 2 and 3, respectively, reveal a six coordinate octahedral structure, defined by the O 2S 2 donors from the macrocyclic ring and two chloride ions. Molar conductance and spectroscopic data also support the proposed geometry of the complexes. DNA binding properties of complexes 1– 3 were investigated using electronic absorption spectroscopy, fluorescence spectroscopy, viscosity measurements and cyclic voltammetry. The absorption spectra of complexes 2 and 3 with calf thymus DNA showed hypochromism, while complex 1 showed hyperchromism attributed to a partial intercalation and electrostatic binding modes, respectively. The intrinsic binding constant K b of complexes 1– 3 were determined as 16.6 × 10 4 M −1, 4.25 × 10 4 M −1 and 3.0 × 10 4 M −1, respectively. The decrease in the relative specific viscosity of calf thymus DNA with increasing concentration of the complexes authenticates the partial intercalation binding mode. Gel electrophoresis of complex 2 with plasmid DNA demonstrated that complex exhibits excellent “artificial” nuclease activity.