Dinuclear Cu(II) complexes based on p-xylylene-bridged bis(1,4,7-triazacyclononane) ligands: Synthesis, characterization, DNA cleavage abilities and evaluation of superoxide dismutase- and catalase-like activities

Three new dinuclear Cu(II) complexes with the formulas [Cu2(pxdmbtacn)Cl4] (1), [Cu2(pxdmbtacn)Cl0.7(NO3)1.3(OH)2(H2O)1.3]⋅6H2O (2) and [Cu2(pxdiprbtacn)Cl4] (3) together with one previously reported complex, [Cu2(pxbtacn)Cl4] (4), were obtained from Cu(II) salts with three p-xylylene-bridged bis-tacn ligands bearing pendant alkyl substituents or without pendant group. Complex 2 was structurally characterized as a centrosymmetric dinuclear molecule with each metal center being coordinated to some labile ligands in addition to one tacn ring. Based on the results of mass spectrometry and UV–visible spectroscopy, complexes 1 and 3 are capable of existing in aqueous solution as dinuclear species but 4 can partially form a dimer of the original dinuclear motif. Complexes 1, 3 and 4 can all effectively cleave supercoiled DNA oxidatively in the presence of hydrogen peroxide. The superoxide dismutase (SOD) activities of 1 and 3 measured under physiological conditions are comparable to that of the native CuZnSOD enzyme but the enzymatic activity of 4 is about three- to fourfold lower. Furthermore, complexes 1, 3 and 4 demonstrate moderate scavenging effect on hydrogen peroxide and their catalase activities are in the decreasing order of 3 > 1 > 4.