Effect of hydrogen bonding on the photo-oxidation of DNA

The one-electron oxidation of DNA has been extensively studied as it leads to the formation of oxidative lesions that cause carcinogenesis and aging. In this paper, experimental results specifically addressing the effect of hydrogen bonding on the one-electron oxidation rate of nucleosides are presented. To separate the hydrogen bonding from the π-stacking effect, experiments were performed in dichloromethane, in which base-pair formation is possible at the monomer level. The effect of base pairing of guanine with cytosine on the rate constant of the electron transfer from guanine to electron acceptor molecules in the triplet excited state was investigated, and a selective enhancement of the electron transfer was observed for the guanine:cytosine base pair. By introducing a methyl or bromo group to the C5 position of cytosine, acceleration or suppression, respectively, of the one-electron oxidation relative to the guanine:cytosine base pair was observed. The results demonstrate that the one-electron oxidation rate of guanine in DNA can be regulated by introducing a substituent on the base-pairing cytosine.