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. 1974 Apr;71(4):1326–1329. doi: 10.1073/pnas.71.4.1326

Structure of an Iron(II) Dioxygen Complex; A Model for Oxygen Carrying Hemeproteins

James P Collman †,*, Robert R Gagne †, Christopher A Reed †,‡, Ward T Robinson §, Gordon A Rodley §
PMCID: PMC388220  PMID: 4524640

Abstract

The preliminary structural characterization of a reversible ferrous dioxygen complex is reported. Mono(N-methyl imidazole) (dioxygen) meso-tetra (α,α,α,α-o-pivalamidephenyl) porphinatorino(II), [Fe(O2)-(N-Me imid) (α,α,α,α-TpivPP)], 1, isolated from toluene solution, crystallizes in the monoclinic system with four molecules in a unit cell of dimensions a = 18.690 (3), b = 19.514 (3), c = 18.638 (3) Å, and β = 91.00 (1)°. R = 0.15 for 841 reflections having F2 > 3σ (F2).

The complex 1 has four pivalamido groups on one side of the porphyrin forming a hydrophobic pocket of 5.4-Å depth which encloses coordinated dioxygen. The dioxygen is coordinated “end-on,” with a bent Fe-O-O bond. The Fe-O-O plane bisects an N-Fe-N right angle of the equatorial iron porphyrin plane and is four way statistically disordered. In addition there is a crystallographic 2-fold axis through iron, coordinated oxygen, and nitrogen of the axially bound N-methyl imidazole. Thus there are two types of coordinated dioxygen with the Fe-O-O plane either parallel or perpendicular to the trans axial imidazole plane. Corresponding values for the Fe-O-O bond angles are 135-(4)° and 137(4)° and for the O-O bond lengths are 1.23 (0.08) and 1.26 (0.08) Å, with a dihedral angle of 90° between alternative orientations of the Fe-O-O plane. The Fe-O distance is 1.75 (0.02) Å and Fe-N (imidazole) is 2.07 (0.02) Å, suggesting multiple bond character in the Fe-O moiety. The similarity of the Mössbauer spectrum of the model complex, 1, with oxyhemoglobin indicates that 1 may be a good model for oxygen binding in the oxygen transport hemeproteins.

Keywords: picket fence porphyrin, x-ray diffraction

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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