ABSTRACT: To evaluate the role of adenosine in low energy
electron (LEE) induced DNA strand breaks, theoretical investigations
of the LEE attachment induced CO σ bonds and Nglycosidic
bond breaking of 20-deoxyadenosine-30,50-diphosphate
(30,50-dAMP) were performed at the B3LYP/DZP++
level of theory. The results indicate that, although adenine-rich
oligonucleotides are capable of capturing the near 0 eV electron
to form the electronically stable radical anions in the gas phase,
it is unlikely to undergo either CO σ bond cleavage or the
glycosidic processes due to the low electron detachment energy
(VDE) of 30,50-dADP unit (0.26 eV). Instead, these radical anions should directly yield an electron detachment product in the gas
phase. In the presence of polarizable surroundings, due to the large increase of the electron detachment energy (VDE increases to
1.59 eV), the adenine-centered radical anions could directly lead to strand breaks in the adenine-rich DNA single strands through
either σ bond orN-glycosidic bond breaking. The values of activation energy for rupture of the C50O50 σ bond (22.5 kcal/mol), the
N-glycosidic bond (20.2 kcal/mol), and the C30O30 σ bond (13.2 kcal/mol) indicate that C30O30 σ bond breaking should
dominate. Moreover, along with the previous research, the predicted ratio of the activation energy barrier of the C50O50 σ bond
breakage in 30,50-dXDP (X = G, A, T) partly explains the observation in the femtosecond time-resolved laser spectroscopic
experiment that the C50O50 σ bond breaking only occurs in dGMP and dTMP not in dAMP. This study completes the series
of LEE-induced DNA single strand breaking investigations for the four basic DNA units 30,50-dXDP (X = G, A, T, C). The obtained
results are vital for elucidating the experimental observations. Combined with the previous studies, the information revealed in this
study is crucial for understanding the mechanisms of the interactions between the LEE and the DNA stands.