Effects of electron attachment on C_5′-O_5′ and C_1′-N₁ bond cleavages of pyrimidine nucleotides: A theoretical study

Sugar-base C_1′-N₁ and phosphate-sugar C _5′-O_5′ bond breakings of 2′- deoxycytidine-5′-monophosphates (dCMP) and 2′-deoxythymidine- 5′- monophosphates (dTMP) and their radical anions have been explored theoretically at the B3LYP/DZP++ level of theory. Calculations show that the low-energy electrons attachment to the pyrimidine nucleotides results in remarkable structural and chemical bonding changes. Predicted Gibbs free energies of reaction ΔG for the C_5′-O_5′ bond dissociation process of the radical anions are -14.6 and -11.5 kcal mol^-1, respectively, and such dissociation processes may be intrinsically spontaneous in the gas phase. Furthermore, the C _5′-O_5′ bond cleavage processes of the anionic dCMP and dTMP were predicted to have activation energies of 6.9 and 8.0 kcal mol^-1 in the gas phase, respectively, much lower than the barriers for the C_1′-N₁ bond breaking process, showing that the C-O bond dissociation in DNA single strand breaks is a dominant process as observed experimentally.