This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Multi-edge x-ray absorption spectroscopic investigations of modified Fe-S mineral surfaces and nanoparticles are proposed in order to map the Fe-S phase diagrams as a function of length scale (micrometer vs. nanometer), synthesis (surface/beam, protein-cage controlled synthesis), and preparation conditions (exposure time, temperature, pH, presence of other ions). We hypothesize that using energy- (surface/beam) and structure- (protein cage or viral capsid) controlled synthesis of Fe-S systems, areas of Fe-S phase diagrams can be accessed that would not be possible by conventional synthetic methods. Recently obtained preliminary data already indicate the existence of a previously unobserved reduced state of pyrite, which was prepared by exposing pristine [100] pyrite surface to hydrogen atom/hydrogen gas plasma. We will take advantage of the complementarity of XAS data at the Fe K-edge, Fe L-edge, and S K-edge. Recent beamline development at BL4-3 now allows for collection of sulfur EXAFS, which in combination with iron EXAFS can provide more reliable fits of geometric structure for hard to characterize intermediates or transition states. XANES analysis of preedge and rising-edge features of Fe L-edge and S K-edge spectra provides electronic structural information about effective nuclear charges of metal/ligand centers, orbital compositions, ligand-field splitting of metal centers, and non-innocent behavior of ligands. Structural insights from the proposed experiments have an impact on the role of Fe-S systems as pre-biotic metabolic catalysts (NASA Astrobiology Institute supported research program at MSU), as well as, potential in proposing novel industrial catalysts from abundant Fe-S containing materials for activation of small molecules such as dinitrogen or dihydrogen.
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