The effect of axial ligands and porphyrin substituents on the dynamic and electronic properties of model hemes.

Persistent Link:
http://hdl.handle.net/10150/186734
Title:
The effect of axial ligands and porphyrin substituents on the dynamic and electronic properties of model hemes.
Author:
Nesset, Marlys Jean McAuliffe.
Issue Date:
1994
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This study involved the use of model heme compounds for the structural elucidation of membrane bound cytochromes b which play an integral role in the respiration process. This research entailed observing the electronic and dynamic properties of various "hindered" iron tetraphenylporphyrin compounds with axially coordinated imidazoles (N-methylimidazole and 2-methylimidazole) and pyridines of widely differing basicities (4-cyanopyridine, pyridine, 3,4-lutidine, and 4-dimethylaminopyridine). The "hindered" aspect of the porphyrin complexes consisted of substituents of varying size and electronegativity (CH ₃, OCH ₃, Cl, and Br) at the ortho positions of each phenyl ring of the tetraphenylporphyrin. The syntheses of the "hindered" tetraphenylporphyrinatoiron(III) perchlorate complexes were developed and optimized for each compound. The formation constants for the bis-axially ligated iron(III) and iron(II) porphyrinates were determined by cyclic voltammetry. The magnitude of the iron(III) formation constants followed predominantly the size of the ortho-phenyl substituents with the largest substituents having the largest formation constants. The weaker bases had the smaller formation constants as exhibited in the following ordering where the numbers following the ortho substituent give the range of log β ₂'s determined - Br(0.8 - > 9) > Cl(-0.2-8.4) > CH ₃ (0.2-8.3) > OCH ₃ (-0.2-7.5) > H(-1.4-6.8). The iron(II) formation constants were slightly influenced by the electronegativity of the ortho-phenyl substituents while the pyridine base strength had virtually no effect - Br(8.9 - > 9) > Cl(7.8-8.4) > CH ₃ (7.3-7.9) > H(5.3-6.7) > OCH ₃ (5.1-6.6). The electron self-exchange rates were measured for iron tetramesitylporphyrin complexed with each of the pyridines and imidazoles. These electron self-exchange rates were determined by proton NMR line broadening techniques. The exchange rates were all in the fast exchange regime (k ∼ 10⁷ M- ¹ (s- ¹) and were not influenced by the varying basicity of the axial ligands with the possible exception of the most weakly basic pyridines.
Type:
text; Dissertation-Reproduction (electronic)
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Walker, F. Ann

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleThe effect of axial ligands and porphyrin substituents on the dynamic and electronic properties of model hemes.en_US
dc.creatorNesset, Marlys Jean McAuliffe.en_US
dc.contributor.authorNesset, Marlys Jean McAuliffe.en_US
dc.date.issued1994en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis study involved the use of model heme compounds for the structural elucidation of membrane bound cytochromes b which play an integral role in the respiration process. This research entailed observing the electronic and dynamic properties of various "hindered" iron tetraphenylporphyrin compounds with axially coordinated imidazoles (N-methylimidazole and 2-methylimidazole) and pyridines of widely differing basicities (4-cyanopyridine, pyridine, 3,4-lutidine, and 4-dimethylaminopyridine). The "hindered" aspect of the porphyrin complexes consisted of substituents of varying size and electronegativity (CH ₃, OCH ₃, Cl, and Br) at the ortho positions of each phenyl ring of the tetraphenylporphyrin. The syntheses of the "hindered" tetraphenylporphyrinatoiron(III) perchlorate complexes were developed and optimized for each compound. The formation constants for the bis-axially ligated iron(III) and iron(II) porphyrinates were determined by cyclic voltammetry. The magnitude of the iron(III) formation constants followed predominantly the size of the ortho-phenyl substituents with the largest substituents having the largest formation constants. The weaker bases had the smaller formation constants as exhibited in the following ordering where the numbers following the ortho substituent give the range of log β ₂'s determined - Br(0.8 - > 9) > Cl(-0.2-8.4) > CH ₃ (0.2-8.3) > OCH ₃ (-0.2-7.5) > H(-1.4-6.8). The iron(II) formation constants were slightly influenced by the electronegativity of the ortho-phenyl substituents while the pyridine base strength had virtually no effect - Br(8.9 - > 9) > Cl(7.8-8.4) > CH ₃ (7.3-7.9) > H(5.3-6.7) > OCH ₃ (5.1-6.6). The electron self-exchange rates were measured for iron tetramesitylporphyrin complexed with each of the pyridines and imidazoles. These electron self-exchange rates were determined by proton NMR line broadening techniques. The exchange rates were all in the fast exchange regime (k ∼ 10⁷ M- ¹ (s- ¹) and were not influenced by the varying basicity of the axial ligands with the possible exception of the most weakly basic pyridines.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairWalker, F. Annen_US
dc.contributor.committeememberBurke, Michael F.en_US
dc.contributor.committeememberFernando, Quintusen_US
dc.contributor.committeememberPemberton, Jeanne E.en_US
dc.contributor.committeememberEnemark, John H.en_US
dc.identifier.proquest9426563en_US
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