DNA affinity and cleavage by naphthalene-based mononuclear and dinuclear copper(II) complexes

Two copper(II) complexes with naphthalene ring [Cu(L1)(H2O)](ClO4)2 center dot H2O (1) or [Cu2(L2)(ClO4)(H2O)3](ClO4)3 center dot H2O (2) (L1 = 1-[bis(pyridine-2-ylmethyl)aminomethyl]naphthalene and L2 = 1,4-di[bis(pyridine-2-ylmethyl)aminomethyl]naphthalene) were synthesized. Structural characterization of complex 2 by X-ray crystallography showed that the cations form a double-forficiform structure and each Cu(II) ion is bound by an in-plane N3Ow-coordination. Thermal melting curves and fluorescence spectroscopes of complex-DNA binding indicate that both complexes can efficiently interact with calf thymus DNA and that the binding ability of complex 2 is greater than that of complex 1. Viscosity measurements suggest that complex 2 partially intercalates between DNA base pairs via the naphthalene ring, whereas complex 1 most likely interacts with DNA through the electrostatic binding. In the presence of H2O2 and ascorbic acid, dinuclear complex 2 was more efficient than mononuclear complex 1 in cleaving double-stranded circular DNA into linear DNA. The interaction modes between the complexes and DNA were also discussed.