Regulation of one-electron oxidation rate of guanine by base pairing with cytosine derivatives

Effects of base pairing on the one-electron oxidation rate of guanine derivatives, guanine, 8-bromoguanine, and 8-oxo-7,8-dihydroguanine have been studied. The one-electron oxidation rate of guanine derivatives was determined by triplet-quenching experiments, using N,N'-dibutylnaphthaldiimide (NDI) in the triplet excited state (3NDI*) and fullerene (C(60)) in the triplet excited state ((3)C(60*)) as oxidants. In all three guanine derivatives studied here, acceleration of the one-electron oxidation was observed upon hydrogen bonding with cytosine, which demonstrates lowering of the oxidation potential of guanine derivatives by base pairing with cytosine. When a methyl or bromo group was introduced to the C5 position of cytosine, acceleration or suppression of the one-electron oxidation relative to the guanine:cytosine base pair was observed, respectively. The results demonstrate that the one-electron oxidation rate of guanine in DNA can be regulated by introducing a substituent on base pairing cytosine.