title: Probing the electronic structure of the hemoglobin active center in physiological solutions.
abstract: Soft-x-ray absorption spectroscopy at the L_{2,3} edge of the iron center in bovine hemoglobin and hemin under physiological conditions is reported for the first time. Spectra of the same compounds in solid form are presented for comparison. Striking differences in the electronic structure of the metalloporphyrin are observed between the liquid and solid compounds. We unambiguously show that hemoglobin and hemin are in a high-spin ferric state in solution, and that the 2p spin-orbit coupling decreases for hemin compared to the hemoglobin, while this is not the case in solids. The spectra were simulated using ligand field multiplet theory, in good agreement with the experiment, allowing quantification of the amount of charge transfer between the porphyrin and Fe3+ ion in hemoglobin and in hemin.
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany. Emad.Aziz@bessy.de
authors.forename: Emad F
authors.initials: EF
authors.lastname: Aziz
authors.forename: Niklas
authors.initials: N
authors.lastname: Ottosson
authors.forename: Sébastien
authors.initials: S
authors.lastname: Bonhommeau
authors.forename: Nora
authors.initials: N
authors.lastname: Bergmann
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eberhardt
authors.forename: Majed
authors.initials: M
authors.lastname: Chergui
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D002417:Cattle; D005290:Ferric Compounds / Q000737:chemistry; D006427:Hemin / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry*; D008958:Models, Molecular; D012996:Solutions; D013052:Spectrometry, X-Ray Emission / Q000379:methods
chemical_list: D005290:Ferric Compounds; D006454:Hemoglobins; D012996:Solutions; D006427:Hemin