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.
Kelle
S O
SO
Beckman Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125, USA.
Orellana
G
G
Barton
J K
JK
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