Theoretica chimica acta

, Volume 36, Issue 1, pp 67-76

First online:

Mössbauer and molecular orbital study of the myoglobin-CO complex

  • Alfred TrautweinAffiliated withAngewandte Physik, Universität des Saarlandes
  • , Yutaka MaedaAffiliated withAngewandte Physik, Universität des Saarlandes
  • , Frank E. HarrisAffiliated withDepartment of Physics, University of Utah
  • , Helmuth FormanekAffiliated withBotanisches Institut, Universität München

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Experimental Mössbauer spectra of the Fe57-enriched CO complex of sperm whale myoglobin (MbCO) at T= 4.2 K with and without applied magnetic field (H⊥γ) were measured to derive the sign of the electric field gradient (EFG), the quadrupole splitting ΔE Q, and the isomer shift δ of the heme iron. We find a positive EFG, δE Q = 0.363 mm/sec, and δ + 0.266 mm/sec. Molecular orbital calculations were carried out to obtain theoretical estimates of EFG and ΔE Q for several steric arrangements of the CO ligand relative to the heme group. Our results are most consistent with the conclusion that the iron is situated in the heme plane, and that a bent geometry with a Fe-C-O angle of about 135 ° is more favorable than a more symmetric structure with a linear Fe-C-O geometry.

Key words

Mössbauer spectra Myoglobin-CO complex