Reactive intermediates in laser photolysis of guanosine

The photochemical reactions of aqueous solution guanosine with acetone as photosensitizer have been investigated by laser flash photolysis. From detailed kinetic analysis, the reaction mechanism has been derived: dehydrogenated guanosine radical G(-H)* and triplet guanosine ³G* were produced via electron transfer and triplet-triplet energy transfer respectively. The half-life time of ³G* has been determined to be 7.4 μs, and the quenching rate constant of Mn²⁺ on it was obtained to be 1.9 × 10⁸ M^-1 s^-1. Based on pH titration, the pKa value of ³G* was also obtained to be 8.7.