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.