Four new copper(II) complexes with 1,3-tpbd ligand: Synthesis, crystal structures, magnetism, oxidative and hydrolytic cleavage of pBR322 DNA

Abstract Four copper(II) complexes [Cu 2 (1,3-tpbd)Cl 4 ]·EtOH ( 1 ), {[Cu 2 (1,3-tpbd)(μ-Cl) 2 ](ClO 4 ) 2 (H 2 O) 4.5 (NaClO 4 )} ∞ ( 2 ), [Cu 2 (1,3-tpbd)(1,10-phen) 2 (H 2 O) 2 ](ClO 4 ) 4 ( 3 ) and [Cu 2 (1,3-tpbd)(2,2′-bpy) 2 (H 2 O) 2 ](ClO 4 ) 4 ( 4 ) (1,3-tpbd =  N , N , N ′, N ′-tetrakis(2-pyridylmethyl)benzene-1,3-diamine) have been synthesized and characterized by X-ray single crystal structure analysis. Variable–temperature magnetic susceptibility studies (2–300 K) indicate the existence of antiferromagnetic coupling between the copper(II) ions in complexes 2 and 3 . The interactions of the four complexes with calf thymus DNA (CT-DNA) have been investigated by UV absorption, fluorescent spectroscopy, circular dichroism spectroscopy, viscosity and cyclic voltammetry, and the modes of CT-DNA binding to the complexes have been proposed. Furthermore, DNA cleavage activities by the four complexes were performed in the presence and absence of external agents, the results indicate that their cleavage activities have been promoted in the presence of external agents. Mechanism investigation shows that the four complexes could cleave DNA through both oxidative and hydrolytic processes. In the four copper(II) complexes, complex 2 showed highest cleavage activity with the pseudo-Michaelis–Menten kinetic paraments k cat  = 5.16 h −1 and K m  = 3.6 × 10 −5  M.