2-Hydroxynaphthalene-1-carbaldehyde- and 2-(Aminomethyl)pyridine-Based Schiff Base CuII Complexes for DNA Binding and Cleavage

Three mononuclear CuII complexes, [CuCl(naph-pa)] (1), [Cu(bipy)(naph-pa)]Cl (2), and [Cu(naph-pa)(phen)]Cl (3) ((naph-pa)=Schiff base derived from the condensation of 2-hydroxynaphthalene-1-carbaldehyde and 2-picolylamine (=2-(aminomethyl)pyridine), bipy=2,2'-bypiridine, and phen=1,10-phenanthroline) were synthesized and characterized. Complex 1 exhibits square-planar geometry, and 2 and 3 exhibit square pyramidal geometry, where Schiff base and bipy/phen act as NNO and as NN donor ligands, respectively. CT (Calf thymus)-DNA-binding studies revealed that the complexes bind through intercalative mode and show good binding propensity (intrinsic binding constant Kb: 0.98x105, 2.22 x105, and 2.67x105 M-1 for 13, resp.). The oxidative and hydrolytic DNA-cleavage activity of these complexes has been studied by gel electrophoresis: all the complexes displayed chemical nuclease activity in the presence and absence of H2O2. From the kinetic experiments, hydrolytic DNA cleavage rate constants were determined as 2.48, 3.32, and 4.10 h-1 for 13, respectively. It amounts to (0.681.14)x108-fold rate enhancement compared to non-catalyzed DNA cleavage, which is impressive. The complexes display binding and cleavage propensity to DNA in the order of 3>2>1.