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

The reactions of (OH)-O-., O.- and SO4.- with purine, adenine, adenosine an d guanosine were studied by pulse radiolysis with optical detection. The se cond order rate constants for both O.- and SO4.- with these compounds range from (0.25 - 4.2) x 10(9) dm(3) mol(-1) s(-1) and the k values for the O.- reaction are lower by an order of magnitude than those obtained for the co rresponding (OH)-O-. reaction except in the case of purine where the rates are nearly the same. The transient absorption spectra measured in the react ion of (OH)-O-. with purine, adenine and adenosine have characteristic peak s at 335 and 450 nm while absorption only in the lower wavelength region wi th peaks at 300 and 335 nm was observed in the O.- reaction. The rate of ri ng opening of the (C-8-O)(.-) adduct of adenine is lower than that found fo r the (OH)-O-. reaction with practically no ring opening in the case of pur ine. 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 p roduct analysis confirm that the H-abstraction by the O.- from the sugar mo iety leading to the base release is an important reaction channel. The tran sient absorption spectra obtained in the SO4.- reaction with adenine and ad enosine showed maxima at 290 and 335 nm with weak and broad absorption arou nd 580 nm which are assigned to the neutral nitrogen centered radical.