Advanced X-ray Spectroscopy for Biological Chemistry

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X-ray absorption spectroscopy (XAS) uses synchrotron radiation to probe the electronic structure and physical arrangement of other atoms around a target element in almost any matrix. While XAS is well-established, bringing important insights in a range of disciplines, like any method it has inherent limitations that curb its utility. In this proposal I lay out plans to push the boundaries of this important synchrotron technique and to make these advances available to the wider research community. Four limitations of XAS include: (1) poor bond-length resolution; (2) little or no geometrical information; (3) poor spectroscopic resolution; and (4) lack of access to very low concentrations. My previous work explored methods of overcoming limitations (1) and (2); here I focus on addressing limitations (3) and (4), through a suite of methods known collectively as advanced X-ray spectroscopy (AXS). AXS methods are photon-in/photon-out spectroscopies, where both incident and emitted photons are measured with very high energy resolution. The so-called high energy resolution fluorescence detection (HERFD) overcomes the inherent broadening of the spectra, which is due to the lifetime of the core-hole created when an electron is excited. Instead HERFD is sensitive to the much longer lifetime of the core-hole created upon emission. The exquisitely sharper spectra that result from HERFD allow greater sensitivity to speciation of chemical forms and studies of electronic structure. At the same time, the enormously improved background rejection allows access to the ultra-dilute concentration regime - an unusual spectroscopic win-win! OBJECTIVES AND SCIENTIFIC APPROACH: I seek to develop AXS methodology in both tender (2-5 keV) and hard (>5keV) X-ray energy regimes, moving it from a highly-specialized to a mainstream technique. I achieve this through targeted research projects using AXS in my career interests of bioinorganic and biological chemistry. These include studies of elements essential for life such as Mo, W, and Cu; and of toxic elements such as As and Hg, and their relationship with the essential element Se. NOVELTY AND EXPECTED SIGNIFICANCE: The opportunities afforded by AXS are no less than revolutionary, poised to transform the use of XAS in environmental and health science, amongst many other disciplines. Since AXS facilities are now emerging at synchrotron facilities worldwide, our proposed work will position the Canadian community to be among the world leaders in this area, and provide unparalleled opportunities for cross-disciplinary training of highly qualified personnel at the forefront of synchrotron technique development.