Synthesis, X-ray crystal structures, magnetism, and DNA cleavage properties of copper(ii) complexes with 1,4-tpbd ligand

Abstract

Four new copper(II) complexes, [Cu(1,4-tpbd)Br₂] (1), [Cu₂(1,4-tpbd)(H₂O)₄](ClO₄)₄ (2), [Cu₂(1,4-tpbd)(1,10-phen)₂(DMF)₂](ClO₄)₄ (3) and [Cu₂(1,4-tpbd)(2,2′-bpy)₂(ClO₄)₂](ClO₄)₂ (4), [1,4-tpbd = N,N,N′,N′-tetrakis(2-pyridylmethyl)benzene-1,4-diamine], have been synthesized to serve as artificial nucleases. Single crystal X-ray diffraction reveals that the copper(II) atom has a distorted intermediate between square pyramidal and trigonal bipyramidal configuration for 1 and a distorted square pyramidal geometry for 2, while a distorted octahedral environment for 3 and 4. Variable-temperature magnetic susceptibility studies (2–300 K) indicate the existence of antiferromagnetic coupling between the copper(II) ions in complex 2. The interactions of the four complexes with calf thymus DNA (CT-DNA) have been investigated by UV absorption, fluorescent spectroscopy and cyclic voltammetry, and the modes of CT-DNA binding for the complexes have been proposed. In the absence of external agents, supercoiled plasmid DNA cleavage by the complexes was performed under aerobic conditions, the influence on the DNA cleavage process of different complex concentrations, reaction times was also studied. The DNA cleavage mechanisms were demonstrated with radical scavengers and anaerobic conditions, indicating all complexes cleaved pBR322 DNA in 50 mM Tris-HCl/18 mM NaCl buffer (pH = 7.2) at 37 °C through a hydrolytic process. In the four copper(II) complexes, complex 2 showed highest cleavage activity with the pseudo-Michaelis–Menten kinetic parameters k_cat = 4.23 h⁻¹ and K_m = 2.4 × 10⁻⁵ M.