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Abstract

Photoreceptor proteins are molecular sensors that translate photon energy into biological information. The BLUF (Blue Light using FAD) protein is such a sensor that switches between its dark and light states by means of photoinduced proton-coupled electron transfer (PCET). In this thesis, I present the first detailed and systematic computational study of photoinduced PCET in BLUF using state-of-the-art electronic-structure methods. The photoactivation in BLUF results in the tautomerization and rotation of a conserved glutamine side chain. The computed potential-energy landscapes presented in this thesis reveal the energies of glutamine rotamers and tautomers and serve as a basis to identify the structure of the glutamine side chain in the functional dark and light states of BLUF. To map the pathway connecting the dark and light states on the excited-state potential-energy surface, I established a computational procedure employing multi-configurational multi-reference electronic-structure methods, and built and characterized quantum-mechanical cluster and hybrid quantum-mechanical/molecular-mechanical models. After establishing and benchmarking the computational protocol, I computed several PCET photoreaction pathways. The energy profiles obtained serve as a basis to answer, for the first time, questions related to how PCET is realized in photoactivation, photostability, and redox tuning in BLUF.