How Accurately Can Extended X-ray Absorption Spectra Be Predicted from First Principles? Implications for Modeling the Oxygen-Evolving Complex in Photosystem II.
First principle calculations of extended X-ray absorption fine structure (EXAFS) data have seen widespread use in bioinorganic chemistry, perhaps most notably for modeling the Mn4Ca site in the oxygen evolving complex (OEC) of photosystem II (PSII). The logic implied by the calculations rests on the assumption that it is possible to a priori predict an accurate EXAFS spectrum provided that the underlying geometric structure is correct. The present study investigates the extent to which this is possible using state of the art EXAFS theory. The FEFF program is used to evaluate the ability of a multiple scattering-based approach to directly calculate the EXAFS spectrum of crystallographically defined model complexes. The results of these parameter free predictions are compared with the more traditional approach of fitting FEFF calculated spectra to experimental data. A series of seven crystallographically characterized Mn monomers and dimers is used as a test set. The largest deviations between the FEFF calculated EXAFS spectra and the experimental EXAFS spectra arise from the amplitudes. The amplitude errors result from a combination of errors in calculated S0(2) and Debye-Waller values as well as uncertainties in background subtraction. Additional errors may be attributed to structural parameters, particularly in cases where reliable high-resolution crystal structures are not available. Based on these investigations, the strengths and weaknesses of using first-principle EXAFS calculations as a predictive tool are discussed. We demonstrate that a range of DFT optimized structures of the OEC may all be considered consistent with experimental EXAFS data and that caution must be exercised when using EXAFS data to obtain topological arrangements of complex clusters.
Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.|Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
Martha A
MA
Beckwith
Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.
William
W
Ames
Department of Physics, University of Washington , Seattle, Washington 98195, United States.
Fernando D
FD
Vila
Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.
Vera
V
Krewald
Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.
Dimitrios A
DA
Pantazis
Département de Chimie Moléculaire, Université Joseph Fourier Grenoble, CNRS , F-38000 Grenoble, France.
Claire
C
Mantel
Laboratoire de Reconnaissance Ionique et Chimie de Coordination, Service de Chimie Inorganique et Biologique, (UMR E-3 CEA/UJF, FRE3200 CNRS), CEA-Grenoble, INAC , 17 rue des Martyrs 38054 Grenoble cedex 9, France.
Jacques
J
Pécaut
Département de Chimie Moléculaire, Université Joseph Fourier Grenoble, CNRS , F-38000 Grenoble, France.
Marcello
M
Gennari
Département de Chimie Moléculaire, Université Joseph Fourier Grenoble, CNRS , F-38000 Grenoble, France.
Carole
C
Duboc
Département de Chimie Moléculaire, Université Joseph Fourier Grenoble, CNRS , F-38000 Grenoble, France.
Marie-Noëlle
MN
Collomb
Physical Biosciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Junko
J
Yano
Department of Physics, University of Washington , Seattle, Washington 98195, United States.
John J
JJ
Rehr
Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.
Frank
F
Neese
Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.|Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
Serena
S
DeBeer
D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*
D045332:Photosystem II Protein Complex; D010100:Oxygen