Date of Award

2020

Document Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry and Biochemistry

First Advisor

Gareth R. Eaton

Second Advisor

Sandra S. Eaton

Third Advisor

Bryan J. Cowen

Fourth Advisor

Alex Huffman

Fifth Advisor

Brian J. Majestic

Sixth Advisor

Anneliese Andrews

Keywords

Electron paramagnetic resonance, Instrumentation, Magnetic resonance, Physical chemistry, Rapid scan, Saturation recovery

Abstract

Enhanced signal sensitivity by the use of Rapid Scan (RS) electron paramagnetic resonance (EPR), a technique that allows for much faster magnetic field scans than traditional field-swept techniques, has facilitated improved data acquisition for many types of samples. For example, irradiated fingernails for radiation dosimetry have been studied using RS-EPR, which resulted in substantial decreases in detection limits. Samarium-mediated reduction mechanisms in organic synthesis have been investigated by RS-EPR providing evidence for a radical intermediate. Spectra of organic radicals exhibiting both narrow lines and closely spaced hyperfine interactions have been recorded via RS-EPR. Well-resolved spectra can be recorded at a rate of 40 spectra/minute to gain insight into molecular changes on this timescale. RS-EPR performed at low temperatures using a closed cycle helium system and a cryostat containing a region with low electrical conductivity provides very wide (>9000 G) spectra free of passage effects near 5 K, expanding the capabilities of RS-EPR.

Recent developments in arbitrary wave form generators (AWGs) provide digital waveform synthesis at high enough frequencies to be used in EPR experiments at ca. 9 GHz (X-band). A new saturation recovery (SR) EPR spectrometer has been constructed with an AWG as the microwave source. Circuit design focuses on implementation of an X-band crossed-loop resonator with a reduced quality factor (Q) to minimize dead time due to resonator ring down processes. Increased accuracy of the AWG instrument relative to conventional sources has made nitroxide spin-lattice relaxation time measurements possible via SR-EPR with S/N high enough to permit separation of electron and nuclear spin-lattice relaxation contributions. These results enabled more accurate estimation of the saturation factor in dynamic nuclear polarization (DNP) experiments.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Provenance

Received from ProQuest

Rights holder

Joseph E. McPeak

File size

206 p.

File format

application/pdf

Language

en

Discipline

Chemistry, Physical chemistry, Electrical engineering

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