Iron centers in [FeFe] hydrogenase and biomimetic coordination complexes studied by XAS/XES and DFT: hydrogen catalysis and oxygen inhibition

了解铁中心产生分子氢（H2）的机制以及氧气（O2）对该反应的抑制是可持续能源研究的重要课题。[FeFe]氢化酶蛋白是最有效的生物H2催化剂，它含有一个六价铁活性中心（[4Fe 4S]-2FeH），称为H-簇。合成化学已经产生了配位络合物，其模拟酶中二铁子簇的结构特征，但通常显示出不令人满意的活性和稳定性。[FeFe]氢化酶和二铁模型复合物中的反应的机理瓶颈将被研究，采用高分辨率X射线吸收和发射光谱（XAS/XES）结合密度泛函理论计算（DFT）。 使用XAS/XES表征H2裂解/生产和O2改性过程中的中间体，以确定其分子结构（金属-配体键长;金属-金属距离;连接变化;底物相互作用;活性氧物质形成）和电子构型（金属氧化态;自旋态;分子轨道结构、占据率和能量; HOMO-LUMO能隙）。位点选择性XAS/XES方法的发展和应用的歧视个别铁物种的多核配合物。通过密度泛函理论将光谱结果整合到几何优化的结构模型中，并从与H2和O2反应途径相关的电子结构方面进行定量解释，对[FeFe]氢化酶和模型复合物的比较研究将有助于在分子水平上深入理解H2周转和O2抑制的特定先决条件。此外，XAS/XES-DFT方法在生物学和化学中的金属中心的研究得到进一步发展。将获得对更有效的H2形成和增加O2耐受性的路线的一般见解，这将在基因工程氢化酶和定制的合成二铁催化剂中进行测试。

Understanding the mechanism of molecular hydrogen (H2) production at iron centers and inhibition of this reaction by oxygen (O2) is an important topic in sustainable energy research. [FeFe] hydrogenase proteins are the most efficient biological H2 catalysts, which contain a six-iron active site ([4Fe4S]-2FeH) denoted as H-cluster. Synthetic chemistry has produced coordination complexes, which mimic structural features of the diiron sub-cluster in the enzymes, but often show unsatisfying activity and stability. Mechanistic bottlenecks of the reactions in [FeFe] hydrogenase and diiron model complexes will be studied, employing high-resolution X-ray absorption and emission spectroscopy (XAS/XES) in combination with density functional theory calculations (DFT). Intermediates in the H2 cleavage/production and O2 modification processes are characterized using XAS/XES to determine their molecular structure (metal-ligand bond lengths; metal-metal distances; ligation changes; substrate interactions; reactive oxygen species formation) and electronic configuration (metal oxidation state; spin state; molecular orbitals structure, occupancy, and energy; HOMO-LUMO energy gap). Site-selective XAS/XES methods are developed and applied for the discrimination of individual iron species in the polynuclear complexes. By DFT the spectroscopic results are integrated in geometry-optimized structural models and quantitatively interpreted in terms of the electronic structure, which are related to the H2 and O2 reaction pathways.Comparative investigations on [FeFe] hydrogenase and model complexes will lead to an advanced understanding of the specific prerequisites of H2 turnover and O2 inhibition at the molecular level. In addition, the XAS/XES-DFT approach for the study of metal centers in biology and chemistry is further developed. General insights into routes towards more efficient H2 formation and increased O2 tolerance will be obtained, which will be tested in genetically engineered hydrogenase and tailored synthetic diiron catalysts.