Description of the Electronic Structure of Oxyhemoglobin Using Fe L-Edge X-ray Absorption Spectroscopy

Braun, Augustin; Titus, Charles J.; Gee, Leland B.; Baker, Michael L.; Waters, Max D. J.; Yan, James J.; Lee, Sang-Jun; Nordlund, Dennis; Doriese, William B.; O’Neil, Galen C.; Schmidt, Daniel R.; Swetz, Daniel S.; Ullom, Joel N.; Irwin, Kent D.; Solomon, Edward I.

doi:10.1021/jacs.5c05261

Description of the Electronic Structure of Oxyhemoglobin Using Fe L-Edge X-ray Absorption Spectroscopy

Journal Article · Wed Jun 11 00:00:00 EDT 2025 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.5c05261· OSTI ID:2575165

^[1]; Titus, Charles J. ^[2]; Gee, Leland B. ^[1]; ^[1]; ^[1]; ^[1]; ^[3]; Nordlund, Dennis ^[3]; ^[4]; ^[4]; Schmidt, Daniel R. ^[4]; Swetz, Daniel S. ^[4]; Ullom, Joel N. ^[4]; Irwin, Kent D. ^[5]; ^[1]

Stanford Univ., CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL); Stanford Univ., CA (United States); National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL); Stanford Univ., CA (United States)
National Inst. of Standards and Technology (NIST), Boulder, CO (United States)
Stanford Univ., CA (United States)

The electronic structure of oxyhemoglobin has been controversial since the discovery of the compound’s diamagnetism in 1936. Here, 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 O₂-bound iron site. The spectrum is very different from typical low-spin Fe^II and Fe^III heme spectra, and multiplet simulations indicate a mixed ground configuration with ∼57% low-spin Fe^III and ∼43% low-spin Fe^II character. This is also very different from the Fe^II character found for the picket-fence porphyrin model complex. The oxyhemoglobin L-edge XAS data further show that the O₂ ligand engages in a weak σ- but strong π-bond with the iron ion, leading to the overall strong Fe–O₂ bond required for O₂ transport.

View Accepted Manuscript (DOE)

Research Organization:: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Organization:: National Institutes of Health (NIH); Royal Society of Chemistry (RSC); Swiss National Science Foundation (SNSF); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: AC02-76SF00515

OSTI ID:: 2575165

Journal Information:: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 25 Vol. 147; ISSN 0002-7863; ISSN 1520-5126

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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