Synthesis, pH-induced "on-off-on" luminescence switching, and partially intercalative DNA-binding and DNA photocleavage properties of an β-D-allopyranoside-grafted ruthenium (II) complex

A new ruthenium(II) complex [Ru(Happip)(3)](ClO4)(2) {Happip = 2-(4-(beta-D-allopyranoside)phenyl)imidazo [4,5-f][1,10]phenanthroline} was synthesized and characterized by elemental analysis, H-1 NMR and matrix-assisted laser desorption ionization mass spectrometry. Calf-thymus DNA-binding properties were studied by DNA viscosity measurements and spectroscopic methods of UV-visible (UV-vis) absorption and luminescence titrations, steady-state emission quenching. DNA competitive binding with ethidium bromide and DNA melting experiments, indicating that the complex partially intercalates into the DNA with a large binding constant greater than 10(6) M-1. The pH effects on UV-vis absorption and emission spectra of the complex were studied, demonstrating that the complex acted as an excellent pH-induced "on-off-on" luminescence switch with large on-off intensity ratios of 88 and 50 with one of luminescence on/off switching actions occurring in near-physiological pH region (pK(a2) = 7.33). The DNA photocleaving properties of [Ru(Happip)(3)](2+) were also studied and compared with those of [Ru(bpy)(2)(Happip)](2+) and [Ru(bpy)(2)(Hpip)](2+){bpy = 2,2'-bipyridine, Hpip = 2-(4-phenyl)imidazo[4,5-f][1,10]phenanthroline}. (C) 2012 Elsevier Inc. All rights reserved.