Synthesis, structure, DNA-binding and photocleavage activity of a binuclear copper(II) complex

Abstract

A binuclear copper(II) complex [Cu(L)(NO₃)]₂ (1), where L is a NSO-donor reduced Schiff base ligand derived from salicylaldehyde and 2-mercaptoethylamine, is prepared, structurally characterized as 10.5MeCN by single crystal X-ray diffraction method and its DNA binding and photo-induced DNA cleavage activity studied. Complex 1 has a diphenoxo-bridged binuclear structure with a {Cu₂(μ-OAr)₂} core showing CuNO₃S coordination at each metal centre. The redox active complex displays two quasi-reversible cyclic voltammetric responses at 0.26 V (ΔEp = 390 mV) and at 0.078 V (ΔEp = 375 mV) versus SCE in DMF-0.1 M TBAP at scan rate of 50 mV s⁻¹. The complex exhibits a d-d band at 661 nm in DMF and shows moderate binding propensity to calf thymus DNA. It cleaves supercoiled (SC) DNA in the presence of 3-mercaptopropionic acid as a reducing agent. The complex is active in showing photo-induced cleavage of supercoiled pUC19 DNA in UV light of 365 nm and red light of 633 nm (He-Ne laser). The DNA photocleavage reaction involves formation of singlet oxygen (¹O₂) as the reactive species in a type-II pathway.