Electron attachment induced proton transfer in a DNA nucleoside pair:: 2′-deoxyguanosine-2′-deoxycytidine

To elucidate electron attachment induced damage in the DNA double helix, electron attachment to the 2(')-deoxyribonucleoside pair dG:dC has been studied with the reliably calibrated B3LYP/DZP++ theoretical approach. The exploration of the potential energy surface of the neutral and anionic dG:dC pairs predicts a positive electron affinity for dG:dC [0.83 eV for adiabatic electron affinity (EA(ad)) and 0.16 eV for vertical electron affinity (VEA)]. The substantial increases in the electron affinity of dG:dC (by 0.50 eV for EA(ad) and 0.23 eV for VEA) compared to those of the dC nucleoside suggest that electron attachment to DNA double helices should be energetically favored with respect to the single strands. Most importantly, electron attachment to the dC moiety in the dG:dC pair is found to be able to trigger the proton transfer in the dG:dC(-center dot) pair, surprisingly resulting in the lower energy distonic anionic complex d(G-H)(-):d(C+H)(center dot). The negative charge for the latter system is located on the base of dC in the dG:dC(-center dot) pair, while it is transferred to d(G-H) in d(G-H)(-):d(C+H)(center dot), accompanied by the proton transfer from N1(dG) to N3(dC). The low energy barrier (2.4 kcal/mol) for proton transfer from dG to dC(-center dot) suggests that the distonic d(G-H)(-):d(C+H)(center dot) pair should be one of the important intermediates in the process of electron attachment to DNA double helices. The formation of the neutral nucleoside radical d(C+H)(center dot) is predicted to be the direct result of electron attachment to the DNA double helices. Since the neutral radical d(C+H)(center dot) nucleotide is the key element in the formation of this DNA lesion, electron attachment might be one of the important factors that trigger the formation of abasic sites in DNA double helices. (C) 2007 American Institute of Physics.