HYSCORE and DFT Studies of Proton-Coupled Electron Transfer in a Bioinspired Artificial Photosynthetic Reaction Center.

The photosynthetic water-oxidation reaction is catalyzed by the oxygen-evolving complex in photosystem II (PSII) that comprises the MnCaO cluster, with participation of the redox-active tyrosine residue (Y) and a hydrogen-bonded network of amino acids and water molecules. It has been proposed that the strong hydrogen bond between Y and D1-His190 likely renders Y kinetically and thermodynamically competent leading to highly efficient water oxidation. However, a detailed understanding of the proton-coupled electron transfer (PCET) at Y remains elusive owing to the transient nature of its intermediate states involving Y⋅. Herein, we employ a combination of high-resolution two-dimensional N hyperfine sublevel correlation spectroscopy and density functional theory methods to investigate a bioinspired artificial photosynthetic reaction center that mimics the PCET process involving the Y residue of PSII. Our results underscore the importance of proximal water molecules and charge delocalization on the electronic structure of the artificial reaction center.