Date of Award

Spring 2000

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

N D Chasteen

Abstract

Several modifications were made on a Varian Q-band EPR/ENDOR spectrometer, including the installation of a microwave amplifier in the E110 bridge, design and assembly of a new cavity coupler, addition of frequency counting capability, as well as other useful minor changes. The performance of the spectrometer was improved in signal-to-noise ratio, convenience of tuning and operation and accuracy of g-value and hyperfine coupling measurements. The signal-to-noise ratio was increased by a factor of six.

Improvements were also achieved with our X-band EPR/ENDOR spectrometer by design and assembly of a new printed ENDOR coil for use in a TE104 rectangular cavity. The Dewar and sample holder were changed to accommodate EPR tubes of 5 mm o.d. The ENDOR signal-to-noise ratio of a sucrose standard sample was increased by a factor of three by these changes.

1H ENDOR studies of ferritin iron nitrosyl complexes and other model complexes were carried out with the new ENDOR system. The proton ENDOR signals of ferritin iron nitrosyl complexes were first observed in this laboratory. Molecular modeling calculations and the equations derived for the iron nitrosyl complexes enable one to undertake a complete ENDOR data analysis. The ENDOR studies suggested that the local structure of the iron site in the ferritin iron nitrosyl complex was identical to that of a model complex of penicillamine with the iron atom coordinated to a sulphur atom of a cysteine residue, a nitrogen atom in the protein backbone and two nitric oxide radicals.

EPR/ENDOR studies of copper cis,cis-1,3,5-triaminocyclohexane have shown the complexes to have a rhombic magnetic symmetry in powders, but axial symmetry in aqueous solution. When the complex was prepared in methanol, it retained its molecular configuration as in the crystal. However, when prepared in aqueous solution, two water molecules might replace one or two of the chloride ions in the equatorial plane of the complex. The sample in aqueous solution had covalent in-plane sigma bonding. The out-plane pi bonds and the in-plane pi bond were ionic for the aqueous sample.

Finally, Q-band EPR studies of fossil tooth enamel demonstrated that X-band EPR could be used for routine dating of fossil teeth samples by slightly over modulating the overlapping signals of the dating and interfering radical centers. The interfering peak in some of the fossil tooth enamel samples appears to arise from a slight structural deformation of the radical center in hydroxyapatite. The age of the measured fossil teeth sample was determined to be about 1400 years old.

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