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)(2) {Happip=2-(4-(β-D-allopyranoside)phenyl)imidazo[4,5-f][1,10]phenanthroline} was synthesized and characterized by elemental analysis, (1)H 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) were also studied and compared with those of Ru(bpy)(2)(Happip) and Ru(bpy)(2)(Hpip){bpy=2,2'-bipyridine, Hpip=2-(4-phenyl)imidazo[4,5-f][1,10]phenanthroline}.