Luminescence quenching by DNA-bound viologens: effect of reactant identity on efficiency and dynamics of electron transfer in DNA.
Photoinduced electron transfer from two intercalating photoactive donors, Ru(phen)2dppz2+ and ethidium, to intercalating viologen acceptors of the N,N'-dialkyl-6-(2'-pyridiniumyl)phenanthridinium family has been investigated through steady-state and time-resolved luminescence quenching measurements. Efficient quenching of the emission from these donors bound to DNA is observed at low concentrations of acceptor (1-10 eq.), and in time-resolved emission experiments it is determined that electron transfer occurs on the nanosecond time scale. Furthermore, transient absorption measurements confirm that the quenching is the result of a charge-transfer process; upon photoreaction of intercalated Ru(phen)2dppz2+ with a viologen acceptor, an intermediate with spectral properties resembling the expected charge-separated pair is observed. The quenching yields and kinetics obtained with this quencher are in marked contrast to those observed with these same donors paired with Rh(phi)2bpy3+ as an acceptor. The differing efficiencies of electron transfer for these donor/acceptor pairs bound to DNA as compared to others previously described are discussed qualitatively in terms of the structural and electronic properties of the different reactants.
Beckman Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125, USA.
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D004247:DNA / Q000737:chemistry* / Q000528:radiation effects*; D004579:Electron Transport / Q000528:radiation effects; D004996:Ethidium / Q000737:chemistry / Q000528:radiation effects; D007364:Intercalating Agents / Q000737:chemistry / Q000528:radiation effects; D007700:Kinetics; D008163:Luminescent Measurements; D009942:Organometallic Compounds / Q000737:chemistry / Q000528:radiation effects; D010617:Phenanthridines / Q000737:chemistry / Q000528:radiation effects; D010618:Phenanthrolines / Q000737:chemistry / Q000528:radiation effects; D010777:Photochemistry; D014755:Viologens / Q000737:chemistry* / Q000528:radiation effects*
D007364:Intercalating Agents; C094137:N,N'-ethylene-6-(2-pyridinium)phenanthridinium; C094138:N,N'-propylene-6-(2-pyridinium)phenanthridinium; D009942:Organometallic Compounds; D010617:Phenanthridines; D010618:Phenanthrolines; D014755:Viologens; C084261:bis(phenanthroline)(dipyridophenazine)ruthenium(II); D004247:DNA; D004996:Ethidium