Intermediates and quantum yields in the photolysis of guanine and its derivatives in neutral glasses at 77 k

Abstract

A comparative study on the photochemical properties of guanine (Gua), guanosine (Guo) and guanosine monophosphate (GMP), based on the detection and characterization of the reactive intermediates and on the determination of the photodestruction and intersystem crossing yields, has been undertaken. UV irradiation of Gua, Guo or GMP in neutral aqueous glasses at 77 K produces intermediates such as trapped electrons, base radical cations and anions, hydrogen addition radicals and solvent radicals. These have been studied and characterized by electron paramagnetic resonance and UV-visible spectroscopy. Photodestruction yields are similar for the three Gua derivatives within experimental error while photoionization decreases in the order Guo (0.0009) = GMP (0.0009) &>; Gua (0.0008). Photoionization occurs through a biphotonic mechanism involving the triplet state, for which yields of 0.15, 0.31 and 0.29 have been determined for Gua, Guo and GMP.