Ruthenium(II) complexes of bipyridine-glycoluril and their interactions with DNA

Nine complexes of the type [Ru(N-N)(2)(BPG)]Cl(2) 1-4, [Ru(N-N)(BPG)(2)]Cl(2) 5-8, and [Ru(BPG)(3)]Cl(2) 9 where N-N is 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), dipyrido[3,2-a:2',3'-c]phenazine (dppz), which incorporates bipyridine-glycoluril (BPG-4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f][1,10]phenanthroline-6,13-dione) as the ancillary ligand, have been synthesized and characterized. These complexes with the peripheral polypyridyl ligands have the ability to form conjugates with DNA. The DNA binding (absorption spectroscopy, steady-state and time-resolved emission measurements, steady-state emission quenching measurements) and cleavage (under dark and irradiated conditions) by these complexes has been studied to investigate the influence of the ancillary ligand. The binding ability of these complexes to DNA is dependent on the planarity of the intercalative polypyridyl ligand, which is further affected by the ancillary bipyridine-glycoluril ligand. The complexes 3, 4, 7, and 8 bind to CT-DNA with binding constants on the order of 10(4) M(-1). Time-resolved emission measurements on the DNA-bound complexes 1, 3, 5-7, and 9 show monoexponential decay of the excited states, whereas complexes 2, 4, and 8 show biexponential decay with short- and long-lived components. Interaction of complexes 2-9 with plasmid pBR322 DNA studied by gel electrophoresis experiments reveals that all complexes cleave DNA efficiently at micromolar concentrations under dark and anaerobic conditions probably by a hydrolytic mechanism. Complexes 3, 4, 7, 8, and [Ru(bpy)(2)(dppz)](2+) show extensive DNA cleavage in the presence of light with a shift in mobility of form I of DNA probably due to the high molecular weight of DNA-complex conjugates. However, the extent of the cleavage is augmented on irradiation in the case of complexes 3, 4, 7, and 8, which include the planar dpq and dppz ligands, suggesting a combination of hydrolytic and oxidative mechanism for the DNA scission. Molecular mechanics calculations of these systems corroborate the DNA binding and cleavage mechanisms.