Low energy electron induced DNA damage: effects of terminal phosphate and base moieties on the distribution of damage.

Low energy electrons (LEE) induce DNA damage by dissociative electron attachment, which involves base release (N-glycosidic bond (N-C) cleavage) and the formation of strand breaks (phosphodiester-sugar bond (C-O) cleavage). The effect of terminal phosphate and base moieties was assessed by exposing DNA model compounds to LEE in the condensed phase followed by HPLC-UV analysis of products remaining on the surface. First, we report that the presence of terminal phosphate groups in monomers (pT, Tp, pTp) and dimers (pTpT, TpTp, pTpTp) increases overall damage by 2-3-fold while it decreases N-C and C-O bond cleavage by 2-10-fold. This suggests that the capture of LEE directly by the terminal phosphate does not contribute to N-C and C-O bond cleavage. Second, we report that terminal bases appear to shield the internal base from damage, resulting in a bias of damage toward the termini. In summary, the presence of terminal phosphate base moieties greatly affects the distribution of LEE induced damage in DNA model compounds.