Abstract
High energy radiation to DNA is suspected to proceed from the formation of transient charged radicals of cation and anion within the strand. In contrast to the mechanism in the oxidative process of cation radicals, much less is known about the process of excess electron transfer. It was suggested that pyrimidine radical anions C•‒ and T•‒ are most likely to serve as primary carriers for excess electron transfer. Protonation of C•‒ and T•‒ interfere with the electron hopping. However, there has been no previous report of direct observation of the protonation process of base in DNA. This report describes pulse radiolysis method with nanosecond time resolution to follow the protonation of radical anion of bases dA, dT, dG, dC and DNA. The anion radicals of deoxynucleotides were formed by the reaction of hydrated electron (eaq-). Subsequently, dT anion radical reacts with H+ to for neutral radical dT(H)• within 2.4 X 1010 M-1s-1. In dC, corresponding reaction of H+ was found to occur within 50 ns. The transient spectra of oligonucleotide AT and GC anion radicals were different from corresponding base anion radicals.
