Se Kalpha HERFD XAS/EXAFS and VtC XES of Se-incorporated Nitrogenase intermediates

Nitrogenase, the only natural enzyme to reduce nitrogen to ammonia. In the nitrogenase catalytic cycle, H+/e- are sequentially delivered to its active site, however open questions exist as to the specific sites of these protonation steps. The probable sites are thought to be the bridging sulfides and the iron centres. Recently researchers were successful in selectively replacing the sulfide bridges within the FeMoco active site by Se, which provides a selective spectroscopic handle, allowing the bridging Se to serve as a unique spectator for the two irons it interacts with and thus enabling protonation at the Se and/or Fe in different intermediates to be experimentally probed. Herein, we intend to pursue selenium Kalpha HERFD XAS, together with EXAFS and Se valence to core X-ray emission spectroscopy (VtC XES) in order to obtain electronic and geometric structural insights into the changes that occur at the FeMo-co active site of molybdenum nitrogenase.

固氮酶（Nitrogenase）是唯一可将氮气还原为氨的天然酶。在固氮酶的催化循环中，质子（H+）与电子（e-）会依次被递送至其活性位点，但目前针对这些质子化步骤的具体发生位点仍存在诸多未解问题。目前推测潜在的质子化位点为桥联硫化物与铁中心（iron centres）。近期研究人员成功实现了对铁钼辅因子（FeMoco）活性位点内桥联硫化物的硒（Se）选择性替换，该策略为体系提供了一种选择性光谱探针，使得桥联硒原子可作为与其相互作用的两个铁原子的独特旁观者配体，从而能够通过实验探究不同中间体中硒原子与/或铁原子处的质子化过程。本研究拟采用硒Kα高能量分辨率荧光检测X射线吸收谱（selenium Kalpha HERFD XAS），结合扩展X射线吸收精细结构谱（EXAFS）与价层至芯层X射线发射光谱（VtC XES），以获取钼固氮酶FeMoco活性位点所发生的电子结构与几何结构变化的相关洞察。