Syntheses and DNA-binding studies of two ruthenium(II) complexes containing one ancillary ligand of bpy or phen: [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)2

Two new ruthenium(II) complexes of [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)2 (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, pp[2,3]p = pyrido[2′,3′:5,6]pyrazino[2,3-f][1,10]phenanthroline) have been synthesized and characterized by elemental analysis and 1H NMR spectra. The calf thymus DNA-binding properties of the two complexes were investigated by UV-visible and emission spectroscopy, competitive binding experiments with ethidium bromide and viscosity measurements. The results indicate that the two complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA-binding constants of 3.08 × 106 and 6.53 × 106 M−1 in buffered 50 mM NaCl, respectively, which are much larger than 6.9 × 105 M−1 for [Ru(bpy)2(pp[2,3]p)](ClO4)2 containing two ancillary ligands of bpy.