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Title: Is Deprotonation of the Oxygen-Evolving Complex of Photosystem II during the S 1 → S 2 Transition Suppressed by Proton Quantum Delocalization?

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/jacs.1c00633· OSTI ID:1784465

We address the protonation state of the water-derived ligands in the oxygen-evolving complex (OEC) of photosystem II (PSII), prepared in the S2 state of the Kok cycle. We perform quantum mechanics/molecular mechanics calculations of isotropic proton hyperfine coupling constants, with direct comparisons to experimental data from two-dimensional hyperfine sublevel correlation (HYSCORE) spectroscopy and extended X-ray absorption fine structure (EXAFS). We find a low-barrier hydrogen bond with significant delocalization of the proton shared by the water-derived ligand, W1, and the aspartic acid residue D1–D61 of the D1 polypeptide. The lowering of the zero-point energy of a shared proton due to quantum delocalization precludes its release to the lumen during the S1→ S2 transition. Retention of the proton facilitates the shuttling of a proton during the isomerization of the tetranuclear manganese–calcium–oxo (Mn4Ca–oxo) cluster, from the “open” to “closed” conformation, a step suggested to be necessary for oxygen evolution from previous studies. Our findings suggest that quantum-delocalized protons, stabilized by low-barrier hydrogen bonds in model catalytic systems, can facilitate the accumulation of multiple oxidizing equivalents at low overpotentials.

Research Organization:
Yale Univ., New Haven, CT (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
FG02-05ER15646; FG02-07ER15903; DESC0001423; SC0001423
OSTI ID:
1784465
Alternate ID(s):
OSTI ID: 1787806; OSTI ID: 1812295
Journal Information:
Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Vol. 143 Journal Issue: 22; ISSN 0002-7863
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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