Advanced X-ray Spectroscopy for Biological Chemistry

x射线吸收光谱（XAS）使用同步辐射来探测几乎任何矩阵中目标元素周围其他原子的电子结构和物理排列。虽然XAS已经建立起来，在一系列学科中带来了重要的见解，但像任何方法一样，它有固有的限制，限制了它的实用性。在这个提议中，我列出了推动这一重要同步加速器技术的发展的计划，并将这些进步应用于更广泛的研究界。XAS的四个局限性包括：(1)键长分辨率差；(2)几何信息很少或没有；(3)光谱分辨率差；(4)无法获得极低浓度。我以前的工作探索了克服限制(1)和(2)的方法；在这里，我主要通过一套统称为先进x射线光谱学（AXS）的方法来解决局限性(3)和(4)。AXS方法是光子进/光子出光谱，其中入射和发射的光子都以非常高的能量分辨率进行测量。所谓的高能量分辨率荧光探测（HERFD）克服了固有的光谱展宽，这是由于电子被激发时产生的核心空穴的寿命。相反，HERFD对发射时产生的岩心孔的更长的寿命很敏感。由HERFD产生的精细清晰的光谱对化学形式的物种形成和电子结构的研究具有更高的灵敏度。同时，大大改善的背景抑制允许进入超稀浓度状态-一个不寻常的光谱双赢！目标和科学方法：我寻求在软x射线（2-5 keV）和硬x射线（50 - 5keV）能量体系中开发AXS方法，将其从高度专业化的技术转变为主流技术。我通过在我的职业兴趣生物无机和生物化学中使用AXS进行有针对性的研究项目来实现这一点。这些研究包括对生命必需元素的研究，如钼、钨和铜；砷和汞等有毒元素，以及它们与必需元素硒的关系。新奇和预期意义：AXS提供的机会不亚于革命性的，准备改变XAS在环境和健康科学以及许多其他学科中的使用。由于AXS设备现在正在世界各地的同步加速器设施中出现，我们提议的工作将使加拿大社区成为该领域的世界领导者之一，并为同步加速器技术发展前沿的高素质人才提供跨学科培训的无与伦比的机会。

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.