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Published October 15, 2014 | Supplemental Material + Published
Journal Article Open

Toward Models for the Full Oxygen-Evolving Complex of Photosystem II by Ligand Coordination To Lower the Symmetry of the Mn_3CaO_4 Cubane: Demonstration That Electronic Effects Facilitate Binding of a Fifth Metal

Abstract

Synthetic model compounds have been targeted to benchmark and better understand the electronic structure, geometry, spectroscopy, and reactivity of the oxygen-evolving complex (OEC) of photosystem II, a low-symmetry Mn_4CaO_n cluster. Herein, low-symmetry Mn^(IV)_3GdO_4 and Mn^(IV_)3CaO_4 cubanes are synthesized in a rational, stepwise fashion through desymmetrization by ligand substitution, causing significant cubane distortions. As a result of increased electron richness and desymmetrization, a specific μ_3-oxo moiety of the Mn_3CaO_4 unit becomes more basic allowing for selective protonation. Coordination of a fifth metal ion, Ag+, to the same site gives a Mn_3CaAgO_4 cluster that models the topology of the OEC by displaying both a cubane motif and a "dangler" transition metal. The present synthetic strategy provides a rational roadmap for accessing more accurate models of the biological catalyst.

Additional Information

© 2014 American Chemical Society. ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: August 8, 2014. Publication Date (Web): September 20, 2014. This work was supported by the California Institute of Technology, the NIH (R01 GM102687A, T.A.), the NSF GRFP (J.S.K.), and NSF (CHE-1214158, W.A.G.). T.A. is a Sloan, Dreyfus, and Cottrell fellow. We thank Lawrence M. Henling for assistance with crystallography. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF Chemistry Research Instrumentation award to Caltech (CHE-0639094).

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Supplemental Material - ja508160x_si_001.pdf

Supplemental Material - ja508160x_si_002.cif

Supplemental Material - ja508160x_si_003.cif

Supplemental Material - ja508160x_si_004.cif

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August 20, 2023
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