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 1H 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 1 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.

Photoactivated cleavage of pBR-322 DNA in the presence of 1 (a) or 2 (b) after 60 min of irradiation at 400 nm. Lane 0, DNA alone; Lanes 1–5, at 5, 10, 15, 20 and 25 μM, Ru(II) complex, respectively.Figure optionsDownload as PowerPoint slide