Effects of the ancillary ligands of polypyridyl ruthenium(II) complexes on the DNA-binding and photocleavage behaviors

The new polypyridyl ligand MIP {MIP=2-(2,3-methylenedioxyphenyl)imidazo[4,5-f]1,10-phenanthroline} and its ruthenium(II) complexes [Ru(phen)(2)(MIP)](2+) (1) (phen = 1,10-phenanthroline) and [Ru(dmp)(2)(MIP)](2+) (2) (dmp = 2,9-dimethyl-1,10-phenanthroline) were synthesized and characterized by elemental analysis, MS and H-1 NMR spectroscopy. The DNA-binding properties of the two complexes to calf-thymus DNA (CT-DNA) were investigated by different spectrophotometric methods and viscosity measurements, as well as equilibrium dialysis and circular dichroism spectroscopy. The results suggest that complex I binds to CT-DNA through intercalation, and complex 2 binds to CT-DNA via a partial intercalative mode. This difference in binding mode probably is caused by the different ancillary ligands. Also, when irradiated at 400 nm, complex 1 was found to be a more-effective DNA-cleaving agent than complex 2. (C) 2007 Elsevier Ltd. All rights reserved.