PNNL

Abstract

We propose a mechanism of DNA single strand breaks induced by low-energy electrons. Density functional theory calculations have been performed on a nucleotide of cytosine to identify barriers for the phosphate-sugar O-C bond cleavage. Attachment of the first excess electron induces intermolecular proton transfer to cytosine. The resulting neutral radical of hydrogenated cytosine binds another excess electron, and the excess charge is localized primarily on the C6 atom. A barrier based of free enthalpies of 4.2 kcal/mol is encountered for proton transfer from the C2’ atom of the adjacent sugar unit to the C6 atom of cytosine. The proton transfer is followed by a barrier-free sugar-phosphate C-O bond cleavage. The rate of the C-O bond cleavage in the anion of hydrogenated nucleotide of cytosine is estimated to be in a range 5x108 to 2x1010 s-1, which makes the proposed mechanism probable to take place in DNA. The process proceeds through bound anionic states, not through metastable states with finite lifetimes and discrete energy positions with respect to the neutral target. The results suggest that even very low-energy electrons may cleave the DNA backbon