The photochemistry of adenine and some of its derivatives in aqueous glasses at low temperatures: reactive intermediates and quantum yields

Abstract

Reactive intermediates produced by UV irradiation of frozen aqueous glasses containing adenine, 2′-deoxyadenosine, 2′-deoxyadenosine-5′-phosphate and 2′-deoxyadenylyl-(3′,5′)-2′ deoxyadenosine were detected and characterized by means of electron paramagnetic resonance, UV and visible absorption spectroscopy. In neutral (12 M LiCl) and basic (8 M NaOH) glasses at 77 K, photo-ionization occurs and is the principal photodestruction route. Photo-ionization is evidenced by the formation of trapped electrons and radical cations in yields of the order of 10 −3 after 30 s of UV irradiation in both media. Prolonged irradiation induces partial bleaching of the trapped electron and recombination with its geminate cation. Photo-destruction yields determined after 300 s irradiation are of the order of 10 −4 in both glasses. The dinucleoside phosphate shows the largest photoreactivity yield of the adenine derivatives. UV irradiation of these purines in 12 M LiCl also results in reaction with the solvent producing Cl 2 − ions. Photo-ionization, as well as the reaction with the solvent, involves the excited triplet state. Neutral and negatively charged species of the adenine derivatives show similar photoreactivity with the exception of 2′-deoxyadenosine-5′-phosphate for which its negatively charged species is more photoreactive.