title: Effect of Chloride Depletion on the Magnetic Properties and the Redox Leveling of the Oxygen-Evolving Complex in Photosystem II.
abstract: Chloride is an essential cofactor in the oxygen-evolution reaction that takes place in photosystem II (PSII). The oxygen-evolving complex (OEC) is oxidized in a linear four-step photocatalytic cycle in which chloride is required for the OEC to advance beyond the S2 state. Here, using density functional theory, we compare the energetics and spin configuration of two different states of the Mn4CaO5 cluster in the S2 state: state A with Mn1(3+) and B with Mn4(3+) with and without chloride. The calculations suggest that model B with an S = 5/2 ground state occurs in the chloride-depleted PSII, which may explain the presence of the EPR signal at g = 4.1. Moreover, we use multiconformer continuum electrostatics to study the effect of chloride depletion on the redox potential associated with the S1/S2 and S2/S3 transitions.
authors.affiliation: Center for Photonics and Smart Materials, Zewail City of Science and Technology, Sheikh Zayed District, 6th of October City, 12588 Giza, Egypt.
authors.forename: Muhamed
authors.initials: M
authors.lastname: Amin
authors.affiliation: The Dow Chemical Company, Marlborough, Massachusetts 01752, United States.
authors.forename: Ravi
authors.initials: R
authors.lastname: Pokhrel
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: Gary W
authors.initials: GW
authors.lastname: Brudvig
authors.affiliation: Center for Photonics and Smart Materials, Zewail City of Science and Technology, Sheikh Zayed District, 6th of October City, 12588 Giza, Egypt.
authors.forename: Ashraf
authors.initials: A
authors.lastname: Badawi
authors.affiliation: Center for Photonics and Smart Materials, Zewail City of Science and Technology, Sheikh Zayed District, 6th of October City, 12588 Giza, Egypt.
authors.forename: S S A
authors.initials: SS
authors.lastname: Obayya
mesh_terms: D002118:Calcium / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006860:Hydrogen Bonding; D008345:Manganese / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002712:Chlorides; D056831:Coordination Complexes; D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen; D002118:Calcium