Ruthenium(ii) complex of 2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline: synthesis, spectrophotometric pH titrations and DNA interaction

Abstract

A Ru(II) complex of [(bpy)₂Ru(aip)](ClO₄)₂·H₂O (bpy = 2,2′-bipyridine, aip = 2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline) was newly synthesized. The ground- and excited-state acid–base properties of the complex were studied by UV–visible and emission spectrophotometric pH titrations. The excited-state ionization constants of pK_a1* = 2.57, pK_a2* = 8.47 are comparable to and 1.3 orders of magnitude greater than the ground-state ones, respectively. The interaction of the complex with calf thymus DNA was investigated by UV–visible and emission spectroscopy, steady-state emission quenching by [Fe(CN)₆]^4–, competitive binding with ethidium bromide, reverse salt titrations, DNA melting experiments, as well as viscosity measurements. The results indicated that the complex bound to the DNA by interaction of the anthryl moiety of the complex with an intrinsic binding constant of the order of 10⁴ M⁻¹ in buffered 50 mM NaCl at room temperature, and non-electrostatic binding free energy made a predominant contribution to the binding free energy.