Theoretical Studies of Proton-Coupled Electron Transfer Reactions

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Sharon Hammes-Schiffer of the Pennsylvania State University is supported by an award from the Theory, Models and Computational Methods program in the Chemistry division to carry out research on theoretical studies of proton-coupled electron transfer (PCET) reactions. The PI and her research group are pursuing four related projects: 1) developing both grid and nuclear-electronic orbital(NEO) methods for analyzing the electron-proton nonadiabatic effects to elucidate the mechanisms of PCET reactions. The degree of electronic nonadiabaticity for the proton transfer reaction provides a quantitative diagnostic for differentiating between hydrogen atom transfer (HAT) and PCET, where HAT is electronically adiabatic and PCET is electronically nonadiabatic. 2) developing methods to calculate electron-proton vibronic couplings to enable the prediction of trends in rate constants and kinetic isotope effects for PCET reactions. 3) developing methods for studying the dynamics of photoinduced PCET reactions. The solvent and solute nuclei are propagated on adiabatic electron-proton vibronic surfaces using a surface hopping method to incorporate nonadiabatic transitions among the adiabatic states 4) modeling the ultrafast dynamics of photo-excited PCET in DNA. Proton-coupled electron transfer (PCET) reactions play a critical role in a wide range of chemical and biological processes, including electrochemistry, photosynthesis, respiration, and enzyme reactions. Software resulting from this project is made widely available to the broader community by being included in the public version of the GAMESS computational chemistry software package. The advances from this research are provided to the public through a website devoted to PCET that contains tutorials, code and interactive Java servletes (https://webpcet.chem.psu.edu).