Synthesis, characterization and DNA-binding properties of novel dipyridophenazine complex of ruthenium (II) : [Ru(IP)2(DPPZ)]2+

A novel ruthenium(II) complex of dipyridophenazine (DPPZ) with the ancillary ligand imidazole[4,5- f ] [1,10]phenanthroline (IP), [Ru(IP) 2 (DPPZ)] (PF 6 ) 2 , has been synthesized and characterized by elemental analysis, 1D and 2D 1 H NMR, fast-atom bombardment mass spectra (FABMS), electronic spectroscopy and cyclic voltammetry. The DNA-binding properties of the complex were studied by spectroscopic methods. The intrinsic binding constant, K =2.1 × 10 7 M −1 , of the complex to calf thymus DNA has been determined by absorption titration in 5 mmol dm −3 Tris-HCl, 50 mmol dm −3 NaCl buffer (pH 7.0). The excited state lifetimes and luminescence quenching with [Fe(CN) 6 ] 4− as the quencher in the presence of DNA were also tested and mono-exponentiality was observed for the emission decay curves. Viscosity measurements together with the optical titrations unambiguously proved that the complex bound with DNA intercalatively and that the binding affinity to DNA was several times larger than that of the parent complex [Ru(bpy) 2 (DPPZ)] 2+ .