Synthesis and the Effect of a Peripheral N ‐Arylcarbazole Moiety on theAcid‐Base and DNA Binding Properties of a Novel Ru II Complex

A novel Ru II complex of [Ru(bpy) 2 (cpipH)](ClO 4 ) 2 (where bpy = 2,2′‐bipyridine, cpipH = 2‐[4‐(9 H ‐carbazol‐9‐yl)phenyl]‐1 H ‐imidazol[4,5‐ f ][1,10]phenanthroline) was synthesized. The binding of the complex to calf thymus DNA was investigated with UV/Vis absorption and luminescence titrations, steady‐state emission quenching by [Fe(CN) 6 ] 4– , DNA competitive binding with ethidium bromide, and thermal denaturation. The pH effects on the UV/Vis absorption and emission spectra of the complex were also studied, and the ground‐ and excited‐state ionization constants were derived. The results indicated that the complex intercalatively bound to the DNA, with an intrinsic binding constant of (8.2 ± 0.8) × 10 5 M –1 in buffered 50 m M NaCl, is stronger than the parent complex, [Ru(bpy) 2 (pip)] 2+ (pip = 2‐phenylimidazo[4,5‐ f ][1,10]phenanthroline), and its excited states are 0.7–0.8 p K a units more basic than those of the ground states. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)