Study on the acid-base and DNA-binding properties of an indole group-containing ruthenium(II) complex

A novel ruthenium polypyridyl complex of [Ru(bpy)(2)(H(2)iip)](ClO4)(2)center dot 5H(2)O [bpy=2,2'-bipyridyl, H(2)iip=2-indole-3-yl-imidazol[4,5 f][1,10]phenanthroline], was synthesized and characterized by elemental analysis and H-1 NMR spectrum. The pH effects on the UV-visible and emission spectra of the complex were studied, and the three apparent ionization constants were derived. The binding of the complex to calf thymus (ct) DNA was investigated with electronic absorption and luminescence spectroscopic titrations, steady-state emission quenching, DNA competitive binding with ethidium bromide, viscosity measurements and thermal denaturation. The results indicated that the complex was bonded to ct-DNA through a classic intercalative mode with an intrinsic binding constant of (5.97 +/- 0.27) X 10(5) mol(-1)center dot L (50 mmol/L NaCl).