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Direct Detection of Oxygen Ligation to the Mn4Ca Cluster of Photosystem II by X-ray Emission Spectroscopy


  • This work was supported by the NIH grant (GM 55302) and the DOE, Director, Office of Science, Office of Basic Energy Sciences (OBES), Chemical Sciences, Geosciences, and Biosciences Division, under Contract DE-AC02-05CH11231. Portions of this research were carried out at SSRL, operated by Stanford University for DOE, OBES. The SSRL SMB Program is supported by the DOE, OBER and by the NIH, NCRR. We thank Prof. Steve Cramer for the use of his emission spectrometer (NIH Grant EB-001962) for some of the work and Prof. Ken Sauer for many useful discussions.


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Seeing O: Mn Kβ2,5 and Kβ′′ X-ray emission spectra arise from transitions from the ligand 2s and 2p shells of the metal complexes to the metal 1s levels. In biological systems, it is difficult to specifically probe the O and N ligands. This spectroscopic technique is used to study the O ligands of the Mn4Ca cluster that catalyzes photosynthetic water splitting and allows direct detection for the first time of the bridging oxo groups of Mn.