Electron transfer in DNA from guanine and 8-oxoguanine to a radical cationof the carbohydrate backbone

Photolysis of a 4'-pivaloyl-substituted nucleotide in single- and double-st randed DNA (1) generated an enol ether radical cation 4 that was reduced to enol ether 17 by electron transfer from the nearest guanoside (G). Variati on of the nucleotide sequence demonstrated a strong distance dependence of this electron-transfer rate with beta = 1.0 +/- 0.1 Angstrom(-1). When 8-ox oguanosine (G(oxo)) was used as the electron donor, the rate of the electro n transfer increased by a factor of 4 but the distance dependence of the tr ansfer remained unchanged within experimental error. In single strands, the number of intervening A, T, and C nucleotides had a much smaller effect; t he rate remained nearly constant for two, three, or four intervening nucleo tides. This is explained by the flexibility of the single-stranded oligonuc leotides.