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

Abstract

<p>Light-driven water oxidation in algae, cyanobacteria, and higher plants generates dioxygen that supports life on Earth. The water-oxidation reaction is catalyzed by the oxygen-evolving complex (OEC) in photosystem II (PSII) that is comprised of the tetranuclear manganese calcium-oxo (Mn<sub>4</sub>CaO<sub>5</sub>) cluster, with participation of the redox-active tyrosine residue (Y<sub>Z</sub>) and a hydrogen-bonded network of amino acids and water molecules. Y<sub>Z</sub> mediates successive proton-coupled electron transfer (PCET) reactions that are essential for the oxidation of water to dioxygen at the Mn<sub>4</sub>CaO<sub>5</sub> cluster. It has been proposed that the strong hydrogen bond between Y<sub>Z</sub> and and its conjugate base, D1-His190, likely renders Y<sub>Z</sub> kinetically and thermodynamically competent leading to highly efficient water oxidation.<sup>1</sup> However, a detailed understanding of PCET at Y<sub>Z</sub> remains elusive due to the transient nature of its intermediate states. In this study, we utilize a combination of high-resolution two-dimensional (2D) <sup>14</sup>N hyperfine sublevel correlation (HYSCORE) spectroscopy and density functional theory (DFT) methods to investigate the electronic structure of a bioinspired artificial photosynthetic reaction center, benzimidazole-phenol porphyrin (BiP–PF<sub>10</sub>), that mimics the PCET process at the Y<sub>Z</sub> residue of PSII. The results of these studies underscore the importance of proximal water molecules and charge delocalization on the electronic structure of the artificial reaction center.</p>

Benchmarking computational methods to calculate the octanol/water partition coefficients of a diverse set of organic molecules

“…to be essential to reproduce some experimental results [30][31][32] and this could further improve the correlations, although some reports claim the contrary. 29…”