Synthesis and DNA interaction studies of a binuclear ruthenium(II) complex with 2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline as bridging and intercalating ligand.

A novel binuclear complex [(bpy)2Ru(mu-bipp)Ru(bpy)2](ClO4)4, where bpy=2,2'-bipyridine and bipp=2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline has been synthesized. Photophysical results reveal that this complex interacts with calf-thymus DNA with intrinsic binding constant 2.6 x 10(5) M(-1) in the buffer containing 5 mM Tris and 50 mM NaCl. The fact that the intraligand transition of bipp around 370 nm decreased by up to 50% in the presence of DNA, much more pronounced than the metal to ligand charge transfer band around 445 nm indicates the bridging ligand bipp is also the intercalating ligand into DNA base pairs. The emission band around at 601 nm increased by 1.4-fold, and red shifted 14 nm when DNA was added to saturation. The emission quenching of this complex by K4[Fe(CN)6] was depressed greatly when DNA was present. Viscometric measurements also proved the intercalative binding mode.