THE PHOTOCHEMISTRY OF ADENOSINE - INTERMEDIATES CONTRIBUTING TO ITS PHOTODEGRADATION MECHANISM IN AQUEOUS-SOLUTION AT 298-K AND CHARACTERIZATION OF THE MAJOR PRODUCT

The steady-state (254 nm) photolysis of 9-(beta-D-erythropentofuranosy l)adenine (adenosine) in aqueous solution was studied. Photodestructio n yields on the order of 1.3 x 10(-3) were determined at room temperat ure by measuring the initial decrease in the absorption maximum as a f unction of irradiation time. The use of high performance liquid chroma tography (HPLC) permitted a more exact determination of the yield (2.5 x 10(-3)). The formation of photoproducts was also studied using HPLC . In the photolysis of 50 muM aqueous solutions of adenosine under ana erobic conditions at least 11 stable photoproducts are formed that abs orb at 260 nm, the wavelength of maximum absorption of adenosine. The major photoproduct was also isolated and characterized as adenine; its formation yield was determined to be 4.5 X 10(-4). This yield is affe cted by the presence of oxygen and by the initial concentration of ade nosine employed. Fluorescence emission and excitation spectra were use d to monitor the formation of highly fluorescent photoproducts that em it with maxima at 365, 398, and 430 nm and absorb in the wavelength re gion of 240-380 nm. The reactive species in the photodestruction mecha nism were established using substrates that react selectively with the respective short-lived species. Photoionization is a primary photopro cess implied by these studies. The triplet state of adenosine also con tributes to the photodestruction mechanism.