University of Illinois Urbana-Champaign

Synthetic Iron Porphyrins as Models for Heme Proteins

English, Daniel Roy

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Description

Title
Synthetic Iron Porphyrins as Models for Heme Proteins
Author(s)
English, Daniel Roy
Issue Date
1984
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Abstract
  • Various iron porphyrin complexes have been studied as models for the active sites of heme proteins. Spectroscopic studies of (FeTPP)(,2)N('+) (where TPP is the dianion of tetraphenylporphyrin) and (FeTPP)(,2)C indicate that these complexes contain iron(IV). This behavior can be contrasted with the isoelectronic complex (FeTPP)(,2)O('2+), which contains iron(III) and porphyrin pication radicals. (FePor)(,2)N('+) complexes (where Por can be one of several tetraarylporphyrins) can be further oxidized to yield (FePor)(,2)N('2+), a stable iron(IV) porphyrin pi-cation radical. The electronic structure of these species is dependent on the counterions and porphyrin substituents.
  • (FeTPP)(,2)N interacts with dioxygen in a polar frozen glass medium. This interaction is totally reversible. The optical spectrum of the oxygen adduct is equivalent to that of the unbound dimer; this indicates that the two iron atoms are inequivalent in the adduct while electron paramagnetic resonance data indicate a less anisotropic g tensor and appreciably diminished ('14)N and ('57)Fe hyperfine coupling relative to the nonadducted species. O(,2) titrations, as monitored by electron paramagnetic resonance, show that the adduct's stoichiometry is one O(,2) per dimer. All these data are consistent with a weak axial interaction of O(,2) with one side of the dimer.
  • To date, synthetic five-coordinate ferric porphyrin thiolates are all high-spin. Reaction of S(,8) and LiB(Et)(,3)H with Fe(TAP)Cl, where TAP is the dianion of p-methoxyphenylporphyrin, produces Fe(TAP)SH. Mossbauer, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopic studies and magnetic susceptibility measurements indicate that the product is a low-spin ferric species. The stereochemistry of Fe(TAP)SH has been determined by a single-crystal x-ray structure. The average Fe-N(,por) distance of 2.01 (ANGSTROM) is indicative of a low-spin iron center.
Graduation Semester
1984
Type of Resource
text
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