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Calcium Valence-to-Core X‑ray Emission Spectroscopy: A Sensitive Probe of Oxo Protonation in Structural Models of the Oxygen-Evolving Complex
Version 2 2020-01-29, 18:33
Version 1 2019-11-19, 20:36
journal contribution
posted on 2020-01-29, 18:33 authored by Zachary Mathe, Dimitrios A. Pantazis, Heui Beom Lee, Richard Gnewkow, Benjamin E. Van Kuiken, Theodor Agapie, Serena DeBeerCalcium is an abundant, nontoxic metal that finds many
roles in synthetic and biological systems including the oxygen-evolving
complex (OEC) of photosystem II. Characterization methods for calcium
centers, however, are underdeveloped compared to those available for
transition metals. Valence-to-core X-ray emission spectroscopy (VtC
XES) selectively probes the electronic structure of an element’s
chemical environment, providing insight that complements the geometric
information available from other techniques. Here, the utility of
calcium VtC XES is established using an in-house dispersive spectrometer
in combination with density functional theory. Spectral trends are
rationalized within a molecular orbital framework, and Kβ2,5 transitions, derived from molecular orbitals with primarily
ligand p character, are found to be a promising probe of the calcium
coordination environment. In particular, it is shown that calcium
VtC XES is sensitive to the electronic structure changes that accompany
oxo protonation in Mn3CaO4-based molecular mimics
of the OEC. Through correlation to calculations, the potential of
calcium VtC XES to address unresolved questions regarding the mechanism
of biological water oxidation is highlighted.
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probeOxygen-Evolving Complex CalciumValence-to-core X-ray emission spectroscopyligand p characteroxo protonationcalcium VtC XESdispersive spectrometerstructure changeswater oxidationcalcium centerscalcium coordination environmentMn 3 CaO 4Oxo Protonationtransition metalsphotosystem IIVtC XESOECSensitive ProbeCharacterization methodsStructural ModelsSpectral trends
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