OH Radical-Induced Charge Migration in Oligodeoxynucleotides

Using the technique of pulse radiolysis with spectrophotometric detection, OH radical ( • OH)-induced electron transfer by intramolecular processes was studied in aqueous solutions containing either equimolar binary mixtures of deoxynucleosides or di- and oligodeoxynucleotides at pH 7.4. The time-resolved optical absorbance changes in mixtures of monodeoxynucleosides did not reveal significant electron transfer, indicating the lack of intermolecular electron transfer induced by • OH. Of the dinucleotides studied, only 2‘-deoxyadenylyl-(3‘→5‘)-2‘-deoxyguanosine (dApdG) shows • OH-induced intramolecular electron transfer. This reaction involves electron transfer from guanine to the adenine radical, which results from dehydration of its C(4)− • OH adduct and was monitored at 400 nm. The rate-determining step of electron transfer is the dehydration of the C(4)− • OH adduct of adenine. With the single-stranded oligodeoxynucleotides, dAGA, dAAGAA, and dAAGTA, the spectral changes with time are consistent with electron transfer occurring from guanine, but to only one of the possible neighboring adenine radicals produced by dehydration of the adenine C(4)− • OH adduct. In contrast, • OH interactions with dATGAA and dATGTA do not induce electron transfer from guanine to the adenine radical produced by dehydration of the C(4)− • OH adduct. These results indicate that the dehydrated adenine radical 5‘ to the guanine is preferentially involved in the electron-transfer process.