Syntheses, characterization and DNA binding of mono- and diruthenium(II) complexes containing 2,2′-bis(1,2,4-triazino[5,6-f]phenanthren-3-yl)-4,4′-bipyridine and 2,2′-bipyridine ligands

A novel bridging ligand 2,2′-bis(1,2,4-triazino[5,6-f]phenanthren-3-yl)-4,4′-bipyridine (btpb) and its mononuclear ruthenium(II) complex [Ru(bpy)2(btpb)]2+ (Rubtpb; bpy = 2,2′-bipyridyl) and dinuclear ruthenium(II) complex [Ru(bpy)2(btpb)Ru(bpy)2]4+ (Ru2btpb) have been synthesized and characterized by elemental analyses, fast atom bombardment or electrospray mass spectra, 1H NMR, and electronic spectroscopy. Binding behaviors of the mono- and dinuclear complexes with calf thymus DNA (CT-DNA) have been investigated by absorption spectra, viscosity measurements, and equilibrium dialysis experiments. As the concentration of DNA is increased, the electronic absorption spectra bands at the metal–ligand charge transfer of the mononuclear complex Rubtpb at 501.0 nm exhibit hypochromism of about 17.4% and bathochromism of 2.0 nm, the dinuclear complex Ru2btpb at 511.0 nm exhibits hypochromism of about 24.8% and bathochromism of 1.0 nm. The increasing amounts of the complexes on the relative viscosities of CT-DNA are much smaller than that of the classic intercalators. The experiments suggest that the Rubtpb and Ru2btpb may be bound to DNA by non-intercalating binder.