Synthesis, structure, and DNA binding/cleavage of two novel binuclear Co(II) complexes

In this study, two novel binuclear Co(II) complexes, [Co₄(L₁)₂(CH₃CH₂O)₄·5.5H₂O (1) and [Co₂(L₂)₂(CH₃COO)(H₂O)]·2CH₃OH·3H₂O (2)], with the ligands H₃L₁ and H₂L₂ were synthesized and structurally characterized using single crystal X-ray diffraction. The crystal structures of complex 1 and 2 belong to a monoclinic system with space group of P2(1)/n and triclinic system with space group of P-1, respectively. Their interaction with CT-DNA was investigated using electron absorption and fluorescent spectroscopy. The apparent binding constants (K_app) of two complexes (1 and 2) were determined to be 5.34 × 10⁵ and 5.82 × 10⁵, respectively, and both exhibited a moderate intensity of insertion with 2 > 1. Fluorescence quenching studies indicated that the fluorescence quenching mechanism of complex 1 is dynamic quenching and that of complex 2 is a static quenching mechanism. The chemical nuclease activity of the complexes was studied using agarose gel electrophoresis. The results suggest that when H₂O₂ is added, complexes 1 and 2 exhibit chemical nuclease activity. The cleavage mechanisms between the complexes and plasmid DNA are the likely oxidative cleavage process of hydroxyl radical (OH) and singlet oxygen (¹O₂) as active species.