Experimental electronic structures of the FeIV=O bond in S=1 heme vs. nonheme sites: Effect of the porphyrin ligand

• 成果类型: Article
• 署名作者: Braun, Augustin; Gee, Leland B.; Waters, Max D. J.; Jose, Anex; Baker, Michael L.; Mara, Michael W.; Babicz, Jeffrey T., Jr.; Ehudin, Melanie A.; Quist, David A.; Zhou, Ang; Kroll, Thomas; Titus, Charles J.; Lee, Sang-Jun; Nordlund, Dennis; Sokaras, Dimosthenis; Yoda, Yoshitaka; Kobayashi, Yasuhiro; Tamasaku, Kenji; Hedman, Britt; Hodgson, Keith O.; Karlin, Kenneth D.; Que, Lawrence, Jr.; Solomon, Edward I.
• 署名单位: Stanford University; Stanford University; United States Department of Energy (DOE); SLAC National Accelerator Laboratory; Johns Hopkins University; University of Minnesota System; University of Minnesota Twin Cities; Stanford University; Japan Synchrotron Radiation Research Institute; Kyoto University; RIKEN; University of Manchester; Diamond Light Source; United States Department of Energy (DOE); Argonne National Laboratory
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-14571
• DOI: 10.1073/pnas.2420205122
• 发表日期: 2025-02-25
• 关键词: high-valent iron; resonance raman-spectroscopy; ray-absorption spectroscopy; horseradish-peroxidase; k-edge; oxoiron(iv) complex; compound-i; activation; intermediate; prediction

摘要

High-valent FeIV=O species are common intermediates in biological and artificial catalysts. Heme and nonheme S=1 FeIV=O sites have been synthesized and studied for decades but little quantitative experimental comparison of their electronic structures has been available, due to the lack of direct methods focused on the iron. This study allows a rigorous determination of the electronic structure of a nonheme FeIV=O center and its comparison to an FeIV=O heme site using 1s2p resonant inelastic X-ray scattering (RIXS) and Fe L-edge X-ray absorption spectroscopy (XAS). Further, variable temperature magnetic circular dichroism (VT-MCD) of the ligand field transitions, combined with nuclear resonance vibrational spectroscopy of the two S=1 FeIV=O systems show that the equatorial ligand field decreases from a nonheme to a heme FeIV=O site. Alternatively, RIXS and Fe L-edge XAS combined with MCD show that the Fe dit orbitals are unperturbed in the FeIV=O heme relative to the nonheme site because the strong axial Fe-O bond uncouples the Fe dit orbitals from the porphyrin it-system. As a consequence, the thermodynamics and kinetics of the H-atom abstraction reactions are actually very similar for heme compound II and nonheme FeIV=O active sites.