Studies on Photoinduced Electron and Proton Transfer Reactions of Nucleic Acid and Aromatic Ketone

The transient absorption spectra of two aromatic ketones (benzophenone (BP), xanthone (XT)) and four nucleic acids (guanosine 5'-monophosphate (GMP), adenosine 5'-monophosphate (AMP), cytidine 5'-monophosphate (CMP), thymidine 5'-monophosphate (TMP)) were obtained in 1 : 1 CH3CN/H2O solution by using time-resolved laser flash photolysis at 355 nm. From the changes of the transient absorption spectra the authors can conclude that photoinduced proton transfer following electron transfer from GMP and AMP to excited BP and XT occurs, which is in accordance with free energy change of the reactions. For CMP and TMP, electron transfer and proton transfer do not appear because no ketyl and anion radical are generated. In addition, the rate constants for electron transfer from GMP, AMP, CMP, and TMP to the excited BP and XT were determined. As can be seen, there is a good correlation between k(q) and the free energy changes (Delta G) of the electron transfer reaction.