A new, bioactive structural motif: Visible light induced DNA photobinding and oxygen independent photocleavage by RuII, RhIII bimetallics

Abstract

The Ru,Rh bimetallic complexes, [(bpy)(2)Ru(dpp)RhCl(2)(phen)](3+) and [(bpy)(2)Ru(bpm)RhCl(2)(phen)](3+) (bpy=2,2'-bipyridine, dpp=2,3-bis(2-pyridyl)pyrazine, phen=1,10-phenanthroline, and bpm=2,2'-bipyrimidine), couple one ruthenium polyazine light absorber to a cis-Rh(III)Cl(2) center through a dpp or bpm bridging ligand in contrast to the previously studied Ru,Rh,Ru trimetallics. This motif provides a sterically accessible Rh reactive site. These bimetallics are efficient visible light absorbers possessing many advantages compared to the previously reported trimetallics: lower cationic charges, reduced stereoisomerization, and independent variation of terminal ligands at each metal center to modulate properties. The bimetallic systems display efficient visible light induced bioreactivities with DNA. In addition to the known DNA photocleavage in related Ru,Rh,Ru trimetallics, these Ru,Rh bimetallic systems display visible light induced DNA binding. Low lying triplet metal to metal charge transfer ((3)MMCT) excited states provide oxygen independent photoreactivity. This previously unexplored structural motif for DNA modification holds promises in photodynamic therapy and DNA modification schemes.