Fast protonation of adenosine and of its radical anion formed by hydrated electron attack; a nanosecond optical and dc-conductivity pulse radiolysis study.

The study of the reaction of the hydrated electron with adenosine by optical and dc-conductivity pulse radiolysis on nano- and microsecond timescales has been carried out in an attempt to answer the question whether the electron adduct radical becomes protonated or not. The following conclusions have been reached: (1) the reaction of the hydrated electron with adenosine is followed by a water-mediated protonation, which must be complete with 5 ns; (2) no spectral indication of a further protonation of the protonated electron adduct of adenosine of 2'-deoxyadenosine has been found between 40 and 5000 ns; (3) the equilibrium reaction between radiation produced H3O+ and adenosine with a pKa of 3.5 plays an important role in the kinetics of the conductivity transients.