Description of the electronic structure of oxyhemoglobin using Fe L-edge X-ray absorption spectroscopy

Published

June 11, 2025

Author(s)

Augustin Braun, Charles Titus, Michael Baker, Max Waters, James Yan, Sang-Jun Lee, Dennis Nordlund, William Doriese, Galen O'Neil, Daniel Schmidt, Daniel Swetz, Joel Ullom, Kent Irwin, Edward Solomon

Abstract

The electronic structure of oxyhemoglobin (oxyHb), the O2-bound form of the oxygen carrier, has been controversial since the discovery of its diamagnetism in 1936. This study uses partial fluorescence yield Fe L-edge X-ray absorption spectroscopy (XAS) in the 3s→2p decay channel on oxyHb 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 FeII and FeIII heme spectra and multiplet simulations indicate a mixed ground configuration with around 57% low spin FeIII and 43% low spin FeII character. This is also very different from the dominantly FeII character found for the oxy-picket fence porphyrin model complex. The oxyHb L-edge XAS data further show that the O2 ligand engages in a weak σ- but strong π-donor bond with the iron ion, leading to the overall strong Fe-O2 bond required for O2 transport.

Citation

Journal of the American Chemical Society

Pub Type

Journals

Download Paper

https://doi.org/10.1021/jacs.5c05261

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Keywords

hemoglobin, xas, l edge, x-ray, oxyhemoglobin, Fe

Citation

Braun, A. , Titus, C. , Baker, M. , Waters, M. , Yan, J. , Lee, S. , Nordlund, D. , Doriese, W. , O'Neil, G. , Schmidt, D. , Swetz, D. , Ullom, J. , Irwin, K. and Solomon, E. (2025), Description of the electronic structure of oxyhemoglobin using Fe L-edge X-ray absorption spectroscopy, Journal of the American Chemical Society, [online], https://doi.org/10.1021/jacs.5c05261, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959817 (Accessed October 16, 2025)