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Abstract
Seven new transition metal complexes formulated as [M2(1,4-tpbd)(diimine)2(H2O)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: [Zn2(1,4-tpbd)(phen)2(H2O)2]4+ (1), [Zn2(1,4-tpbd)(bpy)2(H2O)2]4+ (2), [Co2(1,4-tpbd)(phen)2(H2O)2]4+ (3), [Ni2(1,4-tpbd)(phen)2(H2O)2]4+ (4), [Ni2(1,4-tpbd)(bpy)2(H2O)2]4+ (5), [Ni2(1,4-tpbd)(dafo)2(H2O)2]4+ (6) and [Cd2(1,4-tpbd)(phen)2(H2O)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 (Kapp) are calculated to be 5.2 × 105 M−1 for 1, 1.05 × 105 M−1 for 2, 5.76 × 105 M−1 for 3, 4.57 × 105 M−1 for 4, 1.29 × 105 M−1 for 5, 1.7 × 105 M−1 for 6, 2.53 × 105 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)/H2O2 and Cd(II)/H2O2 systems efficiently cleave DNA attributed to the peroxide ion coordinated to the Zn(II) and Cd(II), which enhanced their nucleophilicity, this is rare.
Notes
Project supported by China Postdoctoral Science Foundation [number 2011M500526].