This proposal describes continued development of molecular simulation techniques, correlated ab initio quantum chemical methods, and new force fields, and application of these developments to studying the photosynthetic bacterial reaction center. Novel electronic structure methods, multiple timescale simulation methods, and continuum dielectric methods will allow high accuracy to be obtained for the large reaction center protein and its constituent bacteriochlorophyll chromophores. The project has a number of specific goals. Firstly, we will determine the energies of the chromophores in their neutral ground state, excited state, and charged states, as well as off-diagonal electronic couplings between diabetic states, in the protein environment. This will allow the basic mechanism of charge separation to be effectively addressed (e.g. what is the role of the intermediate bacteriochlorophyll) and will provide an explanation as to why the M branch of the reaction center is inactive. Secondly, we will use molecular dynamics and quantum dynamical methods to calculate the electron transfer rate constants for both wild type and mutant reaction centers, employing parameters obtained from high level quantum chemistry. Finally, we will continue our studies of reaction center spectroscopy, incorporating information from quantum chemical excited state calculations and including additional experiments (e.g. resonance Raman) in our lineshape simulation analysis. From these efforts, a detailed molecular level understanding of the mechanism of primary charge separation in bacterial photosynthesis will emerge. There will be a strong emphasis on cross checks of both quantum chemistry and parametrized models by insisting upon extensive comparison with spectroscopic and dynamical experiments on mutant reaction centers. The methodology developed in the course of this effort will be useful in the study of other metalloprotein systems, particularly those involved in electron transfer.
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