Ligand-dependent interaction of ruthenium(II) polypyridyl complexes with DNA probed by emission spectroscopy
The nature of the interaction in buffered aqueous solution of several homo and heteroleptic ruthenium(II) polypyridyl complexes containing 2,2'-bipyridine (bpy), 2,2'-bipyrazine (bpz), 1,10-phenanthroline (phen), 4,7-diphenyl-l,10-phenanthroline (dip), 3,4,7,8-tetramethyl-l,10-phenanthroline (tmp), 1,4,5,8-tetraazaphenanthrene (tap), and 1,4,5,8,9,12-hexaazatriphenylene (hat) with calf thymus DNA and poly(dA-dT)-poly(dA-dT) (pdAT) has been investigated by steady-state spectroscopy and emission lifetime measurements. Those complexes containing two or more tap/hat ligands photo-oxidize the guanine base upon binding to DNA with efficiencies that parallel their excited state redox potentials, but display "normal" behavior (increase of both the emission intensity and lifetime) when bound to pdAT. However Ru(tap)(hat)^(2/2+) and Ru(hat)^(2/3+) even photooxidize the adenine base of pdAT, so that their excited states are also quenched in the presence of either polynucleotide. The electron transfer quenching mechanism has been confirmed previously by detection of the monoreduced complex in laser flash photolysis experiments in the presence of mononucleotides. Most of the complexes investigated appear to bind to DNA, at least in part via intercalation, with affinities being dependent on the nature of the largest ligand (hat shows the highest ability in heteroleptic complexes). From lifetime quenching experiments, in the presence of moderate amounts of NaCl, surface binding does not appear to be a general mode for the complexes investigated, and it has been demonstrated unequivocally only for Ru(phen)^(2/3+). In addition, the intercalation of complexes into DNA increases as the ionic strength of the medium decreases, the DNA/Ru ratio increases, or when water is partially replaced by glycerol.
© 1990 Pergamon Press. (Received 25 October 1989; accepted 26 January 1990) The authors gratefully acknowledge the NATO for a Scientific Research Grant (A.K.D.) and the Spanish Mistry of Education and Science and the U.S. Government for a Fulbright Postdoctoral Fellowship under which this work was done (G.O.). They are also grateful to Professor J. Nasielski, F. de Buyl, and L. Jacquet for their gift of tap and hat complexes and thank the NIH (GM 33309) for its generous support.