Two enantiomerically pure polypyridyl ruthenium(Ⅱ) complexes Δ- and Λ-[Ru(bpy) 2HPIP](PF 6) 2{HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline} were synthesized and characterized. DNA-binding studies indicated that both enantiomers bound to calf thymus DNA by intercalation, the Δ- enantiomer exhibited a stronger binding affinity than the Λ- enantiomer. Upon irradiation at 302 nm, both enantiomers were found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form Ⅰ to the open circular form Ⅱ, but the Δ-enantiomer exhibited a higher cleaving efficiency for DNA due to the different binding affinities to DNA. The cleaving mechanisms for Δ- and Λ-[Ru(bpy) 2HPIP] 2+ were identical, the hydroxyl radical(OH ·) was likely to be the reactive specie responsible for the cleavage of plasmid pBR 322, and the photoreduction of Ru(Ⅱ) complex with concomitant hydroxide oxidation was the important step in the DNA cleavage reaction.
