Proton-coupled electron transfer in DNA-acrylamide complexes

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 wave function. In this application, the ground and 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 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 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.