title: Toward models for the full oxygen-evolving complex of photosystem II by ligand coordination to lower the symmetry of the Mn3CaO4 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 Mn4CaOn cluster. Herein, low-symmetry Mn(IV)3GdO4 and Mn(IV)3CaO4 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 μ3-oxo moiety of the Mn3CaO4 unit becomes more basic allowing for selective protonation. Coordination of a fifth metal ion, Ag(+), to the same site gives a Mn3CaAgO4 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.
authors.affiliation: Divison of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Jacob S
authors.initials: JS
authors.lastname: Kanady
authors.forename: Po-Heng
authors.initials: PH
authors.lastname: Lin
authors.forename: Kurtis M
authors.initials: KM
authors.lastname: Carsch
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Nielsen
authors.forename: Michael K
authors.initials: MK
authors.lastname: Takase
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.forename: Theodor
authors.initials: T
authors.lastname: Agapie
mesh_terms: D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D004583:Electrons; D008024:Ligands; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008024:Ligands; D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen; D002118:Calcium