Decomposition of Thymidine by Low-Energy Electrons: Implications for the Molecular Mechanisms of Single-Strand Breaks in DNA

摘要

Low-energy electrons decompose gas-phase thymidine (a thymine unit coupled to a sugar unit) through dissociative electron attachment (DEA) involving two low-lying resonances at 1.2 and 1.8 eV and a broad resonant feature located between 5.5 and 12 eV. The peak at 1.2 eV arises from the rupture of the glycosidic N1-C1 bond (observable through the anion of the sugar moiety), whereas the resonance located at 1.8 eV results from the loss of a neutral hydrogen atom from the N3 position of the thymine moiety within thymidine. The broad resonant feature in the energy range 5.5-12 eV is associated with the rupture of the N1-C1 bond, in this case observable through the thymine anion generated. From the analysis of the DEA signatures it follows that excess-electron transfer from the thymine to the sugar unit within thymidine and vice versa is not operative.