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Density Functional Calculations of 55 Mn, 14 N and 13 C Electron Paramagnetic Resonance Parameters Support an Energetically Feasible Model System for the S 2 State of the Oxygen‐Evolving Complex of Photosystem II
Author(s) -
Schinzel Sandra,
Schraut Johannes,
Arbuznikov Alexei V.,
Siegbahn Per E. M.,
Kaupp Martin
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000584
Subject(s) - hyperfine structure , electron paramagnetic resonance , chemistry , manganese , quadrupole , cluster (spacecraft) , spectral line , density functional theory , crystallography , spin (aerodynamics) , electron nuclear double resonance , atomic physics , molecular physics , nuclear magnetic resonance , physics , computational chemistry , organic chemistry , computer science , thermodynamics , programming language , astronomy
Metal and ligand hyperfine couplings of a previously suggested, energetically feasible Mn 4 Ca model cluster ( SG2009 −1 ) for the S 2 state of the oxygen‐evolving complex (OEC) of photosystem II (PSII) have been studied by broken‐symmetry density functional methods and compared with other suggested structural and spectroscopic models. This was carried out explicitly for different spin‐coupling patterns of the S =1/2 ground state of the Mn III (Mn IV ) 3 cluster. By applying spin‐projection techniques and a scaling of the manganese hyperfine couplings, computation of the hyperfine and nuclear quadrupole coupling parameters allows a direct evaluation of the proposed models in comparison with data obtained from the simulation of EPR, ENDOR, and ESEEM spectra. The computation of 55 Mn hyperfine couplings (HFCs) for SG2009 −1 gives excellent agreement with experiment. However, at the current level of spin projection, the 55 Mn HFCs do not appear sufficiently accurate to distinguish between different structural models. Yet, of all the models studied, SG2009 −1 is the only one with the Mn III site at the Mn C center, which is coordinated by histidine (D1‐His332). The computed histidine 14 N HFC anisotropy for SG2009 −1 gives much better agreement with ESEEM data than the other models, in which Mn C is an Mn IV site, thus supporting the validity of the model. The 13 C HFCs of various carboxylates have been compared with 13 C ENDOR data for PSII preparations with 13 C‐labelled alanine.