Physical Sciences and Mathematics Commons^™

Instrument And Application Development In Saturation Recovery And Rapid Scan Electron Paramagnetic Resonance, Joseph E. Mcpeak

Electronic Theses and Dissertations

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 …

Rapid-Scan Epr And Imaging, Yilin Shi

Electronic Theses and Dissertations

EPR imaging at low frequency is a powerful tool to obtain important biological information in vivo in a non-invasive way. Properties of nitroxide and trityl radical imaging reagents have been studied. Developments in rapid scan imaging techniques are reported that improve efficiency of experiments and user-friendliness of software.

Relaxation and signal-to-noise ratio (S/N) in pulse experiments on trityl radicals were measured at frequencies between 400 MHz and 1.5 GHz. Relaxation time increases as the frequency increases and the radical concentration decreases. Since relaxation time is a sensitive and accurate measure of oxygen pressure, this study provides criteria for the selection …

Electron Paramagnetic Resonance Imaging And Probes, Hanan B. Elajaili

Electronic Theses and Dissertations

EPR imaging at low frequency is an important method to measure in vivo physiology. Because native paramagnetic species exist at low concentrations in living systems, exogenous paramagnetic species are needed for in vivo EPR. Selection of the appropriate EPR probe allows the experimenter to obtain information about the environment of the imaged probe and its spatial distribution. Relaxation times for several nitroxide radicals were studied with the aim of understanding the relaxation mechanisms, which provides criteria for design of suitable in vivo imaging probes.

Amino-substituted trityl radicals have the potential to monitor pH in vivo, and the suitability for this …

Applications Of Epr With An Emphasis On Tau Fibril Structure, Virginia Meyer

Electronic Theses and Dissertations

Substances containing unpaired electrons have been studied by electron paramagnetic resonance (EPR) for nearly 70 years. With continual development and enhancement of EPR techniques, questions have arisen regarding optimum method selection for a given sample based on its properties. In this work, radiation defects, natural lattice defects, solid organic radicals, radicals in solution, and spin-labeled proteins were analyzed using CW, pulse, and rapid scan EPR to compare methods. Studies of solid BDPA, E' in quartz, N_s⁰ in diamond, and a-Si:H, showed that rapid scan could overcome many obstacles presented by other techniques, cementing rapid scan as an effective …

X-Band Rapid-Scan Epr, Deborah Gale Mitchell

Electronic Theses and Dissertations

The advantages of rapid-scan EPR relative to CW and pulse techniques for samples with long longitudinal relaxation time T₁ (N_s⁰ defects in diamond, N@C₆₀, and amorphous hydrogenated silicon), heterogeneous samples (crystalline 1:1 α,γ-bisdiphenylene-β-phenylallyl (BDPA):benzene), lossy samples (aqueous nitroxyl radicals), and transient radicals (5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO)-superoxide adduct) were studied.

For samples with long relaxation times, CW (continuous wave) EPR is challenging due to power saturation and distortions from passage effects. In rapid-scan EPR, the field is swept through resonance in a time that is short relative to T₂. In rapid-scan EPR, the magnetic field is …

Structural Polymorphism In Tau Filaments: An Implication For Neurodegenerative Diseases, Ayisha Siddiqua

Electronic Theses and Dissertations

Tau filaments are the pathological hallmark of >20 neurodegenerative diseases including Alzheimer's disease, Pick's disease, and progressive supranuclear palsy. In the adult human brain, six isoforms of tau are expressed that differ by presence or absence of the second of the four semiconserved repeats. As a consequence, half of the tau isoforms have three repeats (3R tau), whereas the other half has four repeats (4R tau).

Site-directed spin labeling of recombinant tau in conjunction with electron paramagnetic resonance spectroscopy was used to obtain structural insights into tau filaments. The studies showed that the filaments of 4R tau and 3R tau …

The Fabrication Of Polymer-Derived Sicn/Sibcn Ceramic Nanostructures And Investigation Of Their Structure-Property Relationship, Sourangsu Sarkar

Electronic Theses and Dissertations

Polymer-derived Ceramics (PDCs) represent a unique class of high-temperature stable materials synthesized directly by the thermal decomposition of polymers. This research first focuses on the fabrication of high temperature stable siliconcarbonitride (SiCN) fibers by electrospinning for ceramic matrix composite (CMC) applications. Ceraset™ VL20, a commercially available liquid cyclosilazane, was functionalized with aluminum sec-butoxide in order to be electrospinnable. The surface morphology of the electrospun fibers was investigated using the fibers produced from solvents. The electrospun fibers produced from the chloroform/N,N-dimethylformamide solutions had hierarchical structures that led to superhydrophobic surfaces. A “dry skin” model was proposed to explain the formation of …

Mechanistic Importance Of Redox Potentials And Conformational Flexibility In Electron-Transferring Flavoproteins, Michael Anthony Swanson

Electronic Theses and Dissertations

The mitochondrial matrix flavoproteins electron transfer flavoprotein (ETF) and electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) are responsible for linking fatty acid β-oxidation with the main mitochondrial respiratory chain. Electrons derived from flavoprotein dehydrogenases are transferred sequentially through ETF and ETF-QO to ubiquinone and then into the respiratory chain via complex III. In this study, the effects of changes in ETF-QO redox potentials on its activity and the conformational flexibility of ETF were investigated.

ETF-QO contains one [4Fe-4S]^2+,1+ and one flavin adenine dinucleotide (FAD). In the porcine protein, threonine 367 is hydrogen bonded to N1 and O2 of the flavin ring …