Nuclease activity of redoxon-redox active binuclear transition metal mixed-polypyridine complexes: [M_2(1,4-tpbd) (diimine)_2(H_2O)_2]~(4+), M = Zn, Co, Ni, Cd, diimine = phen, bpy, dafo

摘要

Seven new transition metal complexes formulated as [M_2(1,4-tpbd)(diimine)2(H_2O)_2]~(4+) [M = Zn, Co, Ni, Cd; 1,4-tpbd = N,N,N',N'-tetrakis(2-pyridylmethyl)benzene-1,4-diamine;;diimine is a N,N-donor heterocyclic base like 1,10-phenanthroline (phen), 2,2'-bipyridine (bpy), 4,5-diazafluoren-9-one (dafo)] have been synthesized and structurally characterized by X-ray crystallography: [Zn_2(1,4-tpbd) (phen)_2(H_2O)_2]~(4+) (1), [Zn_2(l,4-tpbd)(bpy)2(H_2O)_2]~(4+) (2), [Co_2( 1,4-tpbd)(phen)_2(H_2O)_2]~(4+) (3), [Ni_2(l,4-tpbd)(phen)_2(H_2O)_2]~(4+) (4), [Ni_2(l,4-tpbd)(bpy)2(H_2O)_2]~(4+) (5), [Ni_2(l,4-tpbd) (dafo)_2(H_2O)_2]~(4+) (6) and [Cd_2( 1,4-tpbd)(phen)_2(H_2O)_2]~(4+) (7). Single crystal diffraction reveals that the metals in the complexes are all in a distorted octahedral geometry. The interactions of the seven complexes with calf thymus DNA (CT-DNA) have been investigated by UV absorption, fluorescence, circular dichroism spectroscopy and viscosity measurements. The apparent binding constants (K_(app)) are calculated to be 5.2 × 10~5 M~(-1) for 1, 1.05 × 10~5 M~(-1) for 2, 5.76 × 10~5 M~(-1) for 3, 4.57 × 10~5 M~(-1) for 4, 1.29 × 10~5 M~(-1) for 5, 1.7 × 10~5 M~(-1) for 6, 2.53 × 10~5 M~(-1) for 7, the binding propensity to the calf thymus DNA in the order: 3 (Co-phen) > 1 (Zn-phen) > 4 (Ni-phen) > 7 (Cd-phen) > 6 (Ni-dafo) > 5 (Ni-bpy) > 2 (Zn-bpy). Furthermore, these complexes display efficient oxidative cleavage of supercoiled DNA;;the Zn(II)/H_2O_2 and Cd(II)/H_2O_2 systems efficiently cleave DNA attributed to the peroxide ion coordinated to the Zn(II) and Cd(II), which enhanced their nucleophilicity, this is rare.