Synthesis, structure, DNA binding, and cleavage activity of two copper(II) complexes

Two copper(II) complexes, [Cu(2)(L(1))(2)(H(2)O)](infinity) (1) and {[Cu(2)(L(2))(2)(H(2)O)]center dot H(2)O}infinity (2), have been synthesized and characterized by elemental analysis, UV-visible absorption spectra, and single-crystal X-ray diffraction. H(2)L(1) is an amino acid Schiff base derived from condensation of N-(2-hydroxybenzaldehyde) and L-methionine. H(2)L(2) is a reduced product of H(2)L(1) by sodium borohydride (scheme 1). Both complexes consist of one-dimensional covalently bonded polymeric chains. Complex 1 has two crystallographic independent copper centers. Cu1 has a distorted octahedral geometry and Cu2 a square pyramid. The copper(II)'s are bridged by carboxylate with a Cu1-Cu2 separation of 3.6399(5)angstrom. Complex 2 is a double phenolate-bridged complex with a Cu1-Cu2 separation of 3.0148(7)angstrom, where each copper is square pyramidal. Binding of the complexes with Calf thymus DNA (CT-DNA) has been investigated by UV-visible spectra and fluorescence quenching, showing intercalation to CT-DNA. DNA cleavage experiments have been also investigated by agarose gel electrophoresis. Both complexes show oxidative DNA cleavage in the presence of H(2)O(2)/sodium ascorbate. The reactive oxygen species responsible for the DNA cleavage is likely singlet oxygen ((1)O(2)).