RUTHENIUM(II) COMPLEXES WITH 1,4,5,8,9,12-HEXAAZATRIPHENYLENE AND 1,4,5,8-TETRAAZAPHENANTHRENE LIGANDS - KEY ROLE PLAYED BY THE PHOTOELECTRON TRANSFER IN DNA CLEAVAGE AND ADDUCT FORMATION

The interaction and photoreaction of a series of ruthenium(II) complex es containing 1,4,5,8,9,12-hexaazatriphenylene (hat) and 1,4,5,8-tetra azaphenanthrene (tap) ligands with nucleotides and DNA have been studi ed. The rate constant of quenching of the excited states of the comple xes by guanosine-5'-monophosphate (GMP) is shown to depend on the redu ction potentials of the metal complex excited state, suggesting that t he quenching is due to electron transfer from the guanine. The more st rongly oxidizing metal complex excited state species are also quenched by adenosine-5'-monophosphate (AMP). Electron transfer has been verif ied for Ru(hat)(3)(2+), Ru(tap)(3)(2+), and Ru(tap)(2)(hat)(2+) by las er flash photolysis, which indicates the formation of Ru(I) species an d oxidized nucleotide intermediates with cage escape yields in the ran ge 20-35%. Application of the Marcus theory yields a value of 1.16 V ( vs NHE) for E(G.+/G) in GMP. The luminescence from Ru(hat)(3)(2+), Ru( tap)(3)(2+), Ru(tap)(2)L(2+), or Ru(hat)(2)L(2+) (L = 2,2'-bipyridine or 1,10-phenanthroline) is also quenched when the complexes are bound to DNA, and these oxidizing complexes are shown to be more efficient p hotosensitisers for single strand breaks in plasmid DNA. Covalently bo und adducts are formed between the metal complexes and calf thymus DNA for those complexes whose excited states can oxidize guanine.