OH radical-induced charge migration in oligodeoxynucleotides

Using the technique of pulse radiolysis with spectrophotometric detection, OH radical ((OH)-O-.)-induced electron transfer by intramolecular processes was studied in aqueous solutions containing either equimolar binary mixtur es of deoxynucleosides or di- and oligodeoxynucleotides at pH 7.4. The time -resolved optical absorbance changes in mixtures of monodeoxynucleosides di d not reveal significant electron transfer, indicating the lack of intermol ecular electron transfer induced by (OH)-O-.. Of the dinucleotides studied, only 2'-dH-induced intramolecular electron transfer, This reaction involve s electron transfer from guanine to the adeoxyadenylyl-(3'->5')-2'-deoxygua nosine (dApdG) shows (OH)-O-.-induced intramolecular electron transfer. Thi s reaction involves electron transfer from guanine to the adenine radicle w hich results from dehydration of its C(4)-(OH)-O-. adduct and was monitored at 400 nm, The rate-determining step of electron transfer is the dehydrati on of the C(4)(OH)-O-. adduct of adenine. With the single-stranded oligodeo xynucleotides, 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)-O-. adduct. In contrast. (OH)-O-. interactions with dATG AA and dATGTA do not induce electron on transfer from guanine to the adenin e radical produced by dehydration of the C(4)-(OH)-O-. adduct, These result s indicate that the dehydrated adenine radical 5' to the guanine is prefere ntially involved in the electron-transfer process.