Theoretical Investigation of the Production of Strand Breaks in DNA by Water Radicals

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Abstract
A calculation has been made of the indirect action of radiation on SV40 DNA in dilute aqueous solution, including the extent of OH reaction with both the sugar moiety and the bases. A realistic DNA model is used along with a track model that gives the correct decay rates of hydrated electrons and OH radicals in pure water with the same calculational techniques. We find, in agreement with experiment, that 80% of the OH attack on DNA is on the bases and 20% is on the sugar. We estimate that the probability is almost non-existent (-6) for two OH radicals from the same track or from two tracks to reach sugars on opposite strands within 12 base pairs from each other. Thus double strand breaks that depend linearly on the dose (as we find in a companion experimental programme) must arise from some other mechanism. Our calculated single strand break probabilities are in good agreement with experiment.

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