The Reactions of the 2′-deoxyadenosine Electron Adduct in Aqueous Solution. The Effects of the Radiosensitizer <i>p</i> -nitroacetophenone. A Pulse Spectroscopic and Pulse Conductometric Study

Abstract

The reactions of the one electron adduct of 2'-deoxyadenosine dA(-), in aqueous solutions have been studied using pulse radiolysis techniques with optical absorption and conductivity detection. The dA(-) radical anion itself shows a weak and featureless optical absorption at greater than 300 nm. It reacts rapidly with H20 (k equals 6 x 10(4)M(-1)s(-1); t1/2 equals 210 ns) to yield at least three different protonated structures (dAH., dA'H., dA"H.). In neutral solutions the most important of these (dAH., lambda(max) equals 315 nm) decays by a first order process (t1/2 approximately equal to 9 microseconds). In basic solutions dAH. undergoes on OH- catalysed rearrangement into another neutral radical (dA"'H., lambda(max) equals 355 nm; k(dAH. plus OH-) equals 1.7 x 10(8)M(-1)s(-1)). p-Nitroacetophenone (PNAP) reacts rapidly with the protonated electron adducts of 2'-deoxyadenosine (k equals 5 x 10(9)M(-1)s(-1)). An electron transfer occurs with dAH to yield PNAP and a reoxidized form of 2'-deoxyadenosine. As indicated by its pK value of 8.8 the latter is not, however, simply a repaired 2'-deoxyadenosine molecule, but is suggested to include the elements of water. Species dA"'H.(and dA'H.) react with PNAP in a process which is clearly not an electron transfer but likely an addition reaction.