Effect of copper ion on DNA intercalating behavior of a chelation unsaturated diruthenium polypyridyl complex

The effect of Cu2+ on the DNA interaction of [(bpy)2Ru(μ-bipp)Ru(bpy)2]4+ (bpy = 2,2′-bipyridine, bipp = 2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline) was studied by electronic absorption and emission methods. Bipp has vacant chelating sites in the middle phenanthroline moiety and can bite a Cu2+ in the absence of DNA, as evidenced by the absorptive and emissive decrease of diruthenium complex. The resulted heterometallic complex binds to DNA via intercalation of the middle part of bipp into the DNA base pairs, demonstrated by the dramatic hypochromism and emission enhancement. The maximum emission enhancement is 1.9-fold, larger than the case without copper. The DNA bound [(bpy)2Ru(μ-bipp)Ru(bpy)2]4+ cannot bite Cu2+ due to the difficult access of the vacant chelating sites of bipp caused by the deep insertion of bipp in the DNA base pairs, as can be told since Cu2+ did not disturb the absorption and emission spectra of the DNA bound diruthenium complex.