Effects of anthracene and pyrene units on the interactions of novel polypyridylruthenium(II) mixed-ligand complexes with DNA

Abstract

2-(9-Anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip) and [2-(1-pyrenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (pyip) and their complexes [Ru(phen)₂(aip)]²⁺ (1) and [Ru(phen)₂(pyip)]²⁺ (2) (phen=1,10-phenanthroline) have been synthesized and characterized by elemental analysis, UV/Vis, IR and 1H NMR spectroscopy, FAB-MS and cyclic voltammetry methods. Both 1 and 2 are redox-active and undergo oxidation at 1.43 and 1.47 V (vs. SCE), respectively. Both 1 and 2 show only the MLCT emission typical of any polypyridylruthenium(II) complex. These new complexes are seen to be excellent binders of calf-thymus (CT) DNA, as revealed by the results of absorption, luminescence, viscometric titrations, and thermal denaturation studies. These results also indicate that while ruthenium-bound aip and pyip intercalate within the base pairs of the duplex, the phen moieties act only as spectator ligands in each case. Steady-state emission studies carried out in aqueous media with and without DNA reveal that [Ru(phen)₂(pyip)]²⁺ is a better "molecular light switch" for DNA than [Ru(phen)₂(aip)]²⁺. Under an identical set of experimental conditions of light and drug dose, the DNA photocleavage ability of [Ru(phen)₂(pyip)]²⁺ is also higher than that of [Ru(phen)₂(aip)]²⁺. "Inhibitor studies" suggest that the oxygen species are mainly responsible for the DNA photocleavage by these complexes.