Description of the Electronic Structure of Oxyhemoglobin Using Fe L-Edge X-ray Absorption Spectroscopy
The electronic structure of oxyhemoglobin has been controversial since the discovery of the compound's diamagnetism in 1936. This study uses partial fluorescence yield Fe L-edge X-ray absorption spectroscopy (XAS) in the 3s→2p fluorescence on oxyhemoglobin solutions, measured using a transition-edge sensor detector, to obtain a quantitative experimental description of the electronic structure of the O<sub>2</sub>-bound iron site. The spectrum is very different from typical low-spin Fe<sup>II</sup> and Fe<sup>III</sup> heme spectra, and multiplet simulations indicate a mixed ground configuration with ∼57% low-spin Fe<sup>III</sup> and ∼43% low-spin Fe<sup>II</sup> character. This is also very different from the Fe<sup>II</sup> character found for the picket-fence porphyrin model complex. The oxyhemoglobin L-edge XAS data further show that the O<sub>2</sub> ligand engages in a weak σ- but strong π-bond with the iron ion, leading to the overall strong Fe-O<sub>2</sub> bond required for O<sub>2</sub> transport.
Authors
- Leland Bruce Gee (ORCID: https://orcid.org/0000-0002-5817-3997)
- Dennis Nordlund (ORCID: https://orcid.org/0000-0001-9524-6908)
- K. D. Irwin (ORCID: https://orcid.org/0000-0002-2998-9743)
- Edward I. Solomon (ORCID: https://orcid.org/0000-0003-0291-3199)
- Max D. J. Waters (ORCID: https://orcid.org/0000-0002-3505-627X)
- Charles J. Titus (ORCID: https://orcid.org/0000-0001-6312-8552)
- Daniel S. Swetz (ORCID: https://orcid.org/0000-0002-8192-2175)
- W. B. Doriese (ORCID: https://orcid.org/0000-0003-1107-6441)
- Augustin Braun (ORCID: https://orcid.org/0000-0002-9487-5769)
- Joel N. Ullom (ORCID: https://orcid.org/0000-0003-2486-4025)
- James J. Yan (ORCID: https://orcid.org/0000-0001-5516-3446)
- G. C. O’Neil (ORCID: https://orcid.org/0000-0003-3450-2263)
- Michael L. Baker (ORCID: https://orcid.org/0000-0002-8246-3177)
- Sang‐Jun Lee (ORCID: https://orcid.org/0000-0002-8199-3993)
- Daniel Schmidt (ORCID: https://orcid.org/0009-0009-1627-5790)
Institutions
- National Institute of Standards and Technology (US)
- SLAC National Accelerator Laboratory (US)
- Stanford Synchrotron Radiation Lightsource (US)
- National Institute of Standards (EG)
- Stanford University (US)
Publication Details
- Journal
- Journal of the American Chemical Society
- Published
- 2025-06-11
- DOI
- https://doi.org/10.1021/jacs.5c05261
- Citations
- 2
- Primary Topic
- Hemoglobin structure and function
- Type
- article
- Field-Weighted Citation Impact
- 2.30
Funders
- Royal Society of Chemistry
- Human Frontier Science Program
- Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
- National Institutes of Health
- Basic Energy Sciences
- SLAC National Accelerator Laboratory