The first dinuclear copper(ii) and zinc(ii) complexes containing novel Bis-TACN: syntheses, structures, and DNA cleavage activities

Abstract

Two novel binuclear complexes [Cu₂(L)]·(ClO₄)₂ (1) and [Zn₂(L)]·(ClO₄)₂ (2) were synthesized and crystallographically characterized {L = 1⁴,5⁴-dimethyl-1²,5²-dihydroxy-1(1,3),5(1,3)-dibenzene-3(1,4),7(1,4)-di-1,4,7-triazacyclononane}. The cation [Cu₂(L)]²⁺ structure of 1 is similar to that of [Zn₂(L)]²⁺ of 2. The central ion is bridged by the di-phenoxo of L and lies in a close to perfect square pyramidal geometry. 1 and 2 crystallize in the triclinic space group P. The two complexes effectively promote the cleavage of plasmid DNA in the presence of activating agents at physiological pH and temperature. The pseudo-Michaelis–Menten kinetic parameters k_cat = 1.61 h⁻¹, K_m = 1.35 × 10⁻⁵ M for complex 1 in the presence of mercaptoethanol; k_cat = 2.48 h⁻¹, K_m = 5.5 × 10⁻⁵M for complex 2 in the presence of hydrogen peroxide were obtained. The mechanism of plasmid DNA cleavage was studied by adding standard radical scavengers. DNA cleavage reaction by the binuclear Zn(II)/H₂O₂ system is a hydrolytic mechanism.