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

Abstract

A new class of mono [CuL] ( 1) and binuclear copper(II) complexes [Cu 2LB](ClO 4) 2 ( 2 and 3), where L (6,6-piprazine-1,4 diyl-dimethylene bis(4-methyl phenol) is a N 2O 2 donor ligand and B is a N,N-donor heterocyclic 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 μ 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 (−2 J = 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 × 10 −7, 6.8 × 10 −5 and 2.3 × 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) × 10 5 ( s = 0.1) and 0.44(± 0.2) × 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.