Electrochemical, magnetic, catalytic, DNA binding and cleavage studies of new mono and binuclear copper(II) complexes

A new class of mono [CuL] (1) and binuclear copper(II) complexes [Cu2LB](ClO4)(2) (2 and 3), where L (6,6-piprazine-1,4 diyl-dimethylene bis(4-methyl phenol) is a N2O2 donor ligand and B is a N,N-donor hetero-cyclic base, viz. 2,2-bipyridyl (bipy) (2) and 1,10-phenanthroline (phen) (3), has been synthesized. These complexes were characterized by elemental and spectroscopic techniques. The redox, magnetic, catalytic, DNA binding and cleavage activities of the copper(II) complexes (1-3) were studied. Cyclic voltammetric investigation of the mononuclear Cu(II) complex (1) shows a quasi-reversible one electron reduction wave (E-1/2 = -0.87 V) and the binuclear Cu(II) complexes show two quasi-reversible one electron reduction processes around E-1/2(1) = -0.28 V, -0.18 V and E-1/2(2) = -0.72 V, -0.66 V versus Ag/AgCl in DMF, 0.1 M TBAP. ESR spectra of the copper(II) complexes 2 and 3 show a broad signal at g = 2.08 and 2.10, and mu(eff) values 1.32 and 1.35 BM respectively, which convey spin-spin interactions between the two copper(II) ions. Cryomagnetic investigation of the binuclear complexes reveals a weak antiferromagnetic spin exchange interaction between the Cu(II) ions within the complexes (-2J = 228.3 (2) and 237.5 cm(-1)(3)). The initial rate values for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the mono and binuclear Cu(II) complexes 1,2 and 3 are 2.6 x 10(-7), 6.8 x 10(-5) and 2.3 x 10(-5) M s(-1) respectively. The complexes 2 and 3 show good binding propensity to calf thymus DNA, giving binding constant values of 0.37(+/- 0.1) x 10(5) (s = 0.1) and 0.44(+/- 0.2) x 10(5) M-1 (s = 0.1) respectively. The complexes display significant oxidative cleavage of circular plasmid pBR322 DNA in the presence of mercaptoethanol using singlet oxygen as a reactive species. The phenanthroline containing binuclear Cu(II) complex 3 displays a better DNA interaction and significant chemical nuclease activity compared to the bypyridyl analog 2 and the mononuclear complex 1. (C) 2010 Elsevier Ltd. All rights reserved.