| We study multiple proton transfer (MPT) reactions along water chains and proton coupled electron transfer (PCET) reactions in solution to investigate the effects governing multiple charge transfer reactions in the condensed phase. MPT and PCET reactions have been observed in numerous chemical and biological systems, but the mechanisms by which they occur are not fully understood. The translocation of multiple protons along water chains occurs in several transmembrane proteins, including photosynthetic reaction centers and cytochrome c. PCET reactions play a key role in biological processes such as respiration, photosynthesis and numerous enzyme reactions. Furthermore, PCET reactions occur in electrochemical processes and in solid state materials. The theoretical study of these types of reactions provides a better understanding of the fundamental physical principles of these important chemical and biological processes.; We use a mixed quantum/classical method to study the impact of model protein environments on the dynamics of proton wires. The protein environment is modeled by applying structural constraints to the heavy atoms in the chains, by applying external electric fields, and by including solvating water molecules hydrogen-bonded to the ends of the water chain. Our simulations of proton translocation along water chains illustrate that the protein environment can strongly impact the dynamics of proton wires through a combination of structural constraints, fluctuating electric fields, solvation and hydrogen bonding. We also find that quantum effects such as hydrogen tunneling and nonadiabatic transitions play a significant role under certain nonequilibrium conditions resulting in a wide range of observed mechanisms.; We use a multistate continuum theory to perform a comprehensive study of model PCET reactions and predict how the rates, mechanisms and kinetic isotope effects depend on the physical properties of the system. The basic model system consists of an electron donor and acceptor connected by a symmetric proton transfer interface represented by a protonated water dimer. We vary several physical parameters, including the distance for electron transfer, the distance for proton transfer, the exothermicity (or endothermicity) of the proton transfer reaction, the exothermicity (or endothermicity) of the electron transfer reaction, the temperature, the solvent polarity and the size of the electron donor and acceptor. These calculations allow us to predict trends in the rates, mechanisms and kinetic isotope effects as these physical properties are varied. |
