pH effects on optical and DNA binding properties of a thiophene-containing ruthenium(II) complex

A new ruthenium(II) complex, [Ru(bpy)(2)(Htip)]Cl-2 {where bpy = 2,2'-bipyridine and Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline}, has been synthesized and characterized by H-1 NMR spectroscopy, elemental analysis, and mass spectrometry. The pH effects on UV-Vis absorption and emission spectra of the complex have been studied, and the ground-and excited-state acidity ionization constant values have been derived. The calf thymus (ct) DNA binding properties of the complex have been investigated with UV-Vis absorption and luminescence titrations, steady-state emission quenching by [Fe(CN)(6)](4) , DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. The molecular structures and electronic properties of [Ru(bpy)(2)(Htip)](2+) and deprotonated form [Ru(bpy)(2)(tip)](+) have also been investigated by means of density functional theory calculations in an effort to understand the DNA binding properties. The results suggest that the complex undergo three-step successive protonation/deprotonation reactions with one of which occurring over physiological pH region, and act as a ct-DNA intercalator with an intrinsic DNA binding constant value on 10(5) M (1) order of magnitude that is insensitive to pH. (C) 2011 Elsevier B.V. All rights reserved.