Radiation chemical study of OH, O and SO₄ - reactions with purines

Abstract

The reactions of 'OH, O.^- and SO₄.^- with purine, adenine, adenosine and guanosine were studied by pulse radiolysis with optical detection. The second order rate constants for both O.^- and SO₄.^- with these compounds range from (0.25 - 4.2) × 10⁹ dm³ mol^-1 s^-1 and the k values for the O.^- reaction are lower by an order of magnitude than those obtained for the corresponding 'OH reaction except in the case of purine where the rates are nearly the same. The transient absorption spectra measured in the reaction of .OH with purine, adenine and adenosine have characteristic peaks at 335 and 450 nm while absorption only in the lower wavelength region with peaks at 300 and 335 nm was observed in the O.^- reaction. The rate of ring opening of the (C-8-O).^- adduct of adenine is lower than that found for the 'OH reaction with practically no ring opening in the case of purine. In contrast, a single peak at 300 nm was observed in the O.^- reaction with the nucleosides adenosine and guanosine. The spectral nature and the product analysis confirm that the H-abstraction by the O.^- from the sugar moiety leading to the base release is an important reaction channel. The transient absorption spectra obtained in the SO₄.^- reaction with adenine and adenosine showed maxima at 290 and 335 nm with weak and broad absorption around 580 nm which are assigned to the neutral nitrogen centered radical.