Proton-Assisted Electron Transfer in Irradiated DNA−Acrylamide Complexes:  Modeled by Theory

Theoretical calculations at the density functional theory (DFT) level are employed to elucidate a proton-assisted electron transfer (PA-ET) reaction within a DNA base (thymine)−acrylamide hydrogen-bonded complex, a process suggested from previous experimental results. Calculations with a 6-31+G* basis set are performed with full geometry optimizations and with vibrational analysis. Theory predicts the initial unpaired spin is delocalized over both thymine and acrylamide, and proton transfer then serves to fully localize the spin to the acrylamide. The PA-ET reaction is found to be exergonic by 1.6 kcal/mol. The final step of the reaction, i.e., an intramolecular proton transfer from the oxygen to the terminal carbon on acrylamide, results in the experimentally observed radical, i.e., CH 3 CH(•)CONH 2, and is also predicted to be highly exergonic (18 kcal/mol).