Synthesis, characterization, and DNA-binding and -cleavage properties of dinuclear Cu(II) --salophen/salen complexes.

Dinuclear Cu(II) complexes, [Cu(2) (salophen)(2) ] (1) and [Cu(2) (salen)(2) ] (2), with Schiff bases derived from salicylaldehyde and o-phenylenediamine (ophen) or ethylenediamine (en) were synthesized and characterized. They exhibit square-planar geometry with CuN(2) O(2) coordination, where the dianionic Schiff base acts as a tetradentate N(2) O(2) donor ligand. Calf thymus (CT)-DNA Binding studies revealed that the complexes possess good binding propensities (K(b) =3.13×10(5) for 1 and K(b) =2.99×10(5)  M(-1) for 2). They show good DNA-cleavage abilities under oxidative and hydrolytic conditions. Complex 1 binds and cleaves DNA more efficiently as compared to 2 due to the presence of an extended aromatic phenyl ring which might be involved in an additional stacking interaction with DNA bases. From the kinetic experiments, hydrolytic DNA-cleavage rate constants were determined as 1.54 for 1 and 0.72 h(-1) for 2. The nuclease activities of 1 and 2 are significant, giving rise to (2.03-2.88)×10(7) -fold rate enhancement compared to non-catalyzed DNA cleavage.