Abstract
To evaluate the possibility of the decomposition of 2‐deoxyribose moiety of thymidine induced by low energy electrons (LEE) attachment, the transition states and the energy barriers of the bond breaking processes of the ribose of the nucleoside have been studied theoretically by applying the density functional theory with the double zeta basis sets (DZP++). The energy barriers for the breakage of the CC bonds (C~1′~C~2′~, C~2′~C~3′~, C~3′~C~4′~, and C~4′~C~5′~) of the ribose group of the radical anion of thymidine are found to be high (ca. 42–57 kcal/mol). The total energies of the CC bond‐broken products are significantly higher than that of the radical anion dT^•−^. The decomposition of dT^•−^ through the CC bond rupture is unlikely to take place. The rupture of the C~1′~O~4′~ bond of dT^•−^ needs an activation energy as low as 10.4 kcal/mol. However, the reversed reaction (C~1′~O~4′~ bond formation) needs the activation energy low as 0.3 kcal/mol. Therefore, the intermediate product LM1~C1′~~O4′~ is unlikely to be stable and the C~1′~O~4′~ bond‐broken is not favored. The activation energy of the C~4′~O~4′~ bond rupture process amounts to 20.5 kcal/mol. The total energy of the C~4′~O~4′~ bond broken product is about 6.5 kcal/mol lower than that of the reactant dT^•−^. The subsequent N1‐glycosidic bond breaking process is found to have a very low energy barrier. Therefore, the LEE‐induced base release through the C~4′~O~4′~ bond rupture might be a possible pathway. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008