The formation of heterobimetallic complex [Co(bpy)2(ODHIP)Zn]5+ by [Co(bpy)2ODHIP]3+ and Zn2+ was investigated. The luminescent property of complex was also studied. The results indicated that the nonluminescent monometallic complex [Co(bpy)2ODHIP]3+ could coordinated with Zn2+ to form the luminescent heterobimetallic complex [Co(bpy)2(ODHIP)Zn]5+, the emission intensity increased as increasing the amounts of Zn2+. The luminescence became the strongest at the ratio of CZn / CCo of 1. After binding to DNA, [Co(bpy)2ODHIP]3+ must change its binding mode from partial intercalation to intercalation to make the peripheral coordination site on the ODHIP ligand accessible for Zn2+, the coordination occurred from the opposite side of helix with respect to the intercalated [Co(bpy)2ODHIP]3+, and the luminescent heterobimetallic complex [Co(bpy)2(ODHIP)Zn]5+ was formed. On the other hand, [Co(bpy)2(ODHIP)Zn]5+ bound to DNA by intercalation and situated the region of the intercalated [Co(bpy)2ODHIP]3+ between the base pairs of DNA, while the remained monometallic complex [Co(bpy)2ODHIP]3+ bound to DNA by partial intercalation.
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.
