Department of Chemistry, 152 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802 (USA)

Abstract: A theoretical study of proton-coupled electron transfer (PCET) in the radical anionic thymine-acrylamide
complex is presented. This study is based on a multistate continuum theory, in which the solute is represented by
a multistate valence bond model, the solvent is described by a dielectric continuum, and the transferring hydrogen
nucleus is represented by a quantum mechanical wavefunction. In this application, the ground and the excited
electronic states are calculated with the complete active space self-consistent-field (CASSCF) method, the
electronic coupling for the electron transfer reaction is calculated with the Generalized Mulliken-Hush method,
and the solvation properties are calculated with the frequency resolved cavity model. The influence of the
neighboring DNA base pairs is determined by studying solvated DNA-acrylamide models in addition to the
solvated thymine-acrylamide complex. The calculations indicate that the final product corresponds to the single
electron transfer (ET) for the solvated thymine-acrylamide complex but to a net PCET reaction for the solvated
DNA-acrylamide complex. This difference is due to a decrease in solvent accessibility in the presence of DNA,
which alters the relative free energies of the ET and PCET product states. Thus, the balance between ET and
PCET in the DNA-acrylamide system is highly sensitive to the solvation properties of the system.