Towards polynuclear metal complexes with enhanced bioactivities: Synthesis, crystal structures and DNA cleaving activities of Cu~(II), Ni~(II), Zn~(II), Co~(II) and Mn~(II) complexes derived from 4-carboxy-1-(4-carboxybenzyl) pyridinium bromide

摘要

Six transition metal complexes, that is, {[Cu(Ccbp)_2] ·4H_2O}_n (1), [Ni(H_2O) _6](Ccbp)_2·4H_2O (2), [M(Ccbp) _2(H_2O)_4]·2H_2O·2MeOH (M = Zn~(II) (3), Co~(II) (4), Mn~(II) (5)), and [Cu(Cbp)_2(H_2O)_2](NO_3)_ 2·4H_2O (6) were synthesized from the reaction of 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide (H2CcbpBr) and N-(4-carboxybenzyl)pyridinium bromide (HCbpBr) with the corresponding metal salts in the presence of NaOH, respectively. All these metal complexes were characterized by IR, elemental analyses and single crystal X-ray crystallography. In complex 1, every two Ccbp ions bridge two Cu~(2+) ions through four terminal carboxylate ions in a monodentate coordination mode, thus forming a one-dimensional polymer structure. Complex 2 is an ionic metal complex consisting of isolated [M(H_2O)_6]~(2+) dications and Ccbp anions. Complexes 3-5 have similar structures, in which the central metal atom in [M(Ccbp)_2(H_2O)_4] unit adopts a slightly distorted octahedral geometry. In complex 6, the central Cu atom adopts a distorted tetrahedral coordination geometry that is formed from two unidentate Cbp ligands and two H_2O molecules. Agarose gel electrophoresis studies on the cleavage of plasmid pBR322 DNA by complexes 1-6 indicated that only complex 1 was capable of efficiently cleaving DNA, most probably via an oxidative mechanism. Kinetic assay of complex 1 afforded the maximal catalytic rate constant kmax of 0.50 h ~1 and Michaelis constant K_M of 0.60 mM, respectively. Ethidium bromide displacement experiments indicated that complex 1 had a binding affinity of (3.10 ±0.90) × 10~5 M ~1 toward calf-thymus DNA, 10- to 55-fold higher than those shown by H_2CcbpBr and complexes 2-5. The high cleaving efficacy of complex 1 is thought to be due to its polynuclear structure.