Proton-assisted electron transfer in irradiated DNA-acrylamide complexes: Modeled by theory

Theoretical calculations at the density functional theory (DFT) level are e mployed to elucidate a proton-assisted electron transfer (PA-ET) reaction w ithin a DNA base (thymine)-acrylamide hydrogen-bonded complex, a process su ggested from previous experimental results. Calculations with a 6-31+G* bas is set are performed with full geometry optimizations and with vibrational analysis. Theory predicts the initial unpaired spin is delocalized over bot h 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 prot on transfer from the oxygen to the terminal, carbon on acrylamide, results in the experimentally observed radical, i.e., CH3CH(circle dot )CONH2, and is also predicted to be highly exergonic (18 kcal/mol).