Polypyridyl ruthenium(II) complexes containing intramolecular hydrogen-bond ligand: syntheses, characterization, and DNA-binding properties

Two new ligands containing an intramolecular hydrogen bond, 2-(2-hydroxyphenyl) imidazo[4,5-f] [1,10] phenanthroline (HPIP) and 2-(2-hydroxy-1-naphthyl)imidazo[4,5-f] [1,10]phenanthroline (HNAIP), and their complexes [Ru(bpy)(2)(HPIP)] (PF6)(2). H2O (1) and [Ru(bpy)(2)(HNAIP)] (PF6)(2). H2O (2) (bpy = 2,2'-bipyridine) have been synthesized and characterized by UV-Vis, IR, H-1 NMR, and mass spectra. The electrochemical behaviors of the two complexes were studied by cyclic voltammetry. The binding of the two complexes with calf thymus DNA has been investigated by absorption, luminescence titrations, steady-state emission quenching, and viscosity measurements. The results suggest that complex 1 intercalates into DNA base pairs via the ligand HPIP, while complex 2 binds with DNA by partially intercalating the ligand HNAIP. Complex 1 shows higher affinity to DNA than complex 2. The intrinsic binding constants K for complexes 1 (6.5 +/- 0.3 x 10(5) M-1) and 2 (8.3 +/- 0.4 x 10(4) M-1) together with [Ru(bpy)(2)PIP](2+) (4.7 +/- 0.2 x 10(5) M-1, PIP = 2-phenylimidazo[4,5-f] [1,10] phenanthroline) were determined by absorption titration. (C) 1999 Elsevier Science Inc. All rights reserved.