The Reactions of the 2′-deoxyadenosine Electron Adduct in Aqueous Solution. The Effects of the Radiosensitizerp-nitroacetophenone. A Pulse Spectroscopic and Pulse Conductometric Study

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Abstract
The reactions of the 1 electron adduct of 2''-deoxyadenosine .**GRAPHIC**. in aqueous solution were studied using pulse radiolysis techniques with optical absorption and conductivity detection. The .**GRAPHIC**. radical anion showed a weak and featureless optical absorption at > 300 nm. It reacted rapidly with H2O (k [rate constant] = 6 .times. 104/M s; t1/2 [half time] = 210 ns) to yield at least 3 different protonated structures (daH., dAH., dA"H.). In neutral solutions the most important of these (dAH., .lambda.(max) = 315 nm) decays by a 1st order process (t 1/2 .apprxeq. 9 .mu.s). In basic solutions dAH. undergoes an OH- catalysed rearrangement into another neutral radical (dA"''H. .lambda.(max) = 355 nm; k(dAH. + OH-) = 1.7 .times. 108/M s). p-Nitroacetophenone (PNAP) reacted rapidly with the protonated electron adducts of 2''-deoxyadenosine (k = 5 .times. 109/M s). An electron transfer occurred with dAH. to yield .**GRAPHIC**. and a reoxidized form of .**GRAPHIC**. A pK of 8.8 implied this form was not simply a repaired 2''-deoxyadenosine molecule, but may include the elements of H2O. Species dA"''H. (and dA''H.) react with PNAP in a process which was clearly not an electron transfer but likely an addition reaction.