Based on a Ph.D. thesis in the Dept. of Electrical Engineering, 1963. / Bibliography: p. 81-83.

M.S. / Biochemistry / The EPR spectrum of the Tyr-Cys· free radical in oxidized apoGAOX has been investigated, using a combination of approaches. Power saturation analysis has been used to resolve two unique spectra through Evolving Factor Analysis (EFA) global fitting, indicating the presence of two distinct free radical species in the sample. The component that dominates at low microwave power arises from the Tyr-Cys· side chain, while the high power component has not yet been assigned. The experimental results show that the EPR spectrum collected at low power includes approximately 7% of the high power component. EPR spectra have been collected for ten different isotope derivatives of GAOX, including ²H-labeled, ¹³C-labeled, 17[superscript]O-labeled, and ³³S-labeled forms. XSophe simulation of the EPR spectra has been performed for the isotopically labeled samples in order to determine the spectroscopic parameters - g-values, hyperfine coupling constants, and linewidths. The g-values and the methylene proton hyperfine coupling constants obtained for the isotopically labeled samples are consistent with the literature values. The magnitude of the hyperfine coupling constants associated with each of the nuclei confirms that significant electron spin density is found on the methylene protons, the alternating carbon atoms within the aromatic π system and the 2p[subscript]z orbital of both sulfur and oxygen. Moreover, the rotation angle of the methylene protons to the phenoxyl ring around the C1-C7 bond has been evaluated based on the experimentally defined hyperfine coupling constants of the two methylene protons.

Diiron carboxylate proteins constitute an important class of metall-containing enzymes. These proteins perform a multitude of reactions in biological systems that normally involve activation of molecular oxygen at the diiron site. During activation and functioning of these proteins their diiron sites undergo redox changes in a rather wide range: from diferrous (FeII-FeII) to high potential intermediate Q(FeIV-FeIV). Two of these redox states are paramagnetic: (FeIV-FeIII), called high potential intermediate X, and (FeII-FeIII), called mixed-valent state of the diiron carboxylate proteins. In the present work it has been shown that these redox states are of functional relevance in two proteins with different functions. Ribonucleotide reductase (RNR) from the human parasite Chlamydia trachomatis is a class I RNR. It is typical for class I RNR to initiate the enzymatic reaction on its large subunit, protein R1, by activation from a stable tyrosyl free radical in its small subunit, protein R2. This radical, in its turn, is formed through oxygen activation by the diiron center. In C. trachomatis the tyrosine residue is replaced by phenylalanine, which cannot form a radical. We have shown in the present work, that active C. trachomatis RNR uses the FeIII-FeIV state of the diiron carboxylate cluster in R2 instead of a tyrosyl radical to initiate the catalytic reaction. The alternative oxidase (AOX) is a ubiquinol oxidase found in the mitochondrial respiratory chain of plants. The existence of the diiron carboxylate center in this protein was predicted on the basis of a conserved sequence motif consisting of the proposed iron ligands, four glutamate and two histidine residues. In experiments modeling the conditions of the enzyme catalytic cycle, i.e. reduction and reoxygenation of the overexpressed AOX in Escherichia coli membranes we were able to generate an EPR signal characteristic of a mixed-valent Fe(II)/Fe(III) binuclear iron center. The alternative oxidase is the first membrane protein where the existence of the diiron carboxylate center has been shown experimentally.

Electron paramagnetic resonance (EPR) dosimetry using the well established dosimeter material alanine is a generally accepted dosimetric method for measurements of high absorbed doses. Alanine EPR dosimetry is however not sensitive enough for high precision measurements of low (< 5 Gy) absorbed doses using reasonably measurement times and small dosimeters. It has therefore not been possible to fully exploit the benefits of EPR dosimetry for applications in radiation therapy. The aim of this thesis was to show that sensitive EPR dosimetry is a competitive method for applications in radiation therapy fulfilling the requirements of measurement precision. Our strategy for reaching this goal was to search for new, more sensitive, EPR dosimeter materials fulfilling the criteria of being tissue equivalent, having a high radical yield and having a narrow EPR spectrum suitable for dosimetry. The best materials were found among formates and dithionates. Doping with small amounts of metal ions and recrystallisation in D2O were tested to further increase the sensitivity. Four promising candidate materials were tested regarding radical stability and dose response and among them lithium formate was chosen for dosimetry in radiation therapy applications. A high precision EPR dosimetry method was developed using lithium formate. The method included the development of a production method for EPR dosimeters with very homogenous shape, mass and composition. A read-out process was developed with maximal measurement precision for reasonably short measurement times. The method also included a dosimeter quality control before actual dose measurements. Measurement accuracy was controlled for every new dosimeter batch. This high precision lithium formate EPR dosimetry method was evaluated for pretreatment verifications of intensity modulated radiation therapy (IMRT) treatment plans. The precision and accuracy was shown to be sufficient (< 5 %) for measurements of doses above 1.5 Gy using one single dosimeter and a measurement time of 15 minutes. The described evaluation is therefore a demonstration of the improved precision at low dose determinations that is available with our sensitive EPR dosimeter materials. While the EPR signal intensity is proportional to absorbed dose, the signal shape is in some cases dependent on the radiation quality. A new method is presented for simultaneous measurements of beam LET (linear energy transfer) and absorbed dose in heavy charged particle beams using potassium dithionate EPR dosimetry. The study shows that when irradiating a dosimeter with 35 MeV carbon ions, the ratio of the signal amplitudes from two radicals in potassium dithionate vary along the track indicating a dependence on linear energy transfer, LET. Potassium dithionate may therefore be a promising EPR dosimeter material for simultaneous measurements of absorbed dose and LET in heavy charged particle radiation fields.

Mixed-valence compounds are of interest as model systems for the study of electron transfer reactions. The intramolecular electron transfer processes and patterns of charge delocalization in such compounds depend on the interplay between the electronic (V) and the vibronic (L) coupling. One can obtain both parameters from a Hush analysis of the intervalence band that arises upon optical intramolecular electron transfer if the band is intense and well-separated from other bands. This is quite often the case for mixed-valence triarylamines. As such, both Hush analysis and simulation of the intervalence band are widely used to classify these compounds as charge localized (class-II) or delocalized (class-III). Yet one must estimate the diabatic electron transfer distance (R) to calculate V in the Hush formalism. For mixed-valence triarylamines, R is commonly taken as the N-N distance; we show this to be a poor approximation in many cases. The activation barrier to thermal intramolecular electron transfer in a class-II mixed-valence compound is also related to the parameters V and L. Thus, if one can capture the rate of thermal electron transfer at multiple temperatures, then two experimental methods exist by which to extract the microscopic parameters. One technique that is widely used for organic mixed-valence compounds is variable-temperature electron spin resonance (ESR) spectroscopy. But this method is only rarely used to determine thermal electron transfer rates in mixed-valence triarylamines, as the electron transfer in most of the class-II compounds with distinct intervalence bands is too fast to observe on the ESR timescale. We show, for the first time, that one can use ESR spectroscopy to measure thermal electron transfer rates in such compounds. Simulation of ESR spectra based on density functional theory calculation and comparison with optical data also uncover the nature (i.e., adiabatic or nonadiabatic) of the electron transfer process.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 148 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 124 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 81-87).

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains x, 210 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 154-185).

D. Tech. Chemistry. / Demonstrates the possibility of preparing large surface coatings of monodispersed spherical particles of chromium(III) oxide by using the ACG method for solar heating and magneto-optic technologies. t is aimed in the current study to investigate the photo-induced ESR phenomena in a-Cr2O3 mono-dispersed spherical particles using elimination of 160mW Nd:YAG laser of ˜1064 nm and a pulse repetition frequency of 30Hz, in the temperature range of 150 up to 315 K.

Variable temperature ESR studies of radicals generated photolytically from simple aliphatic alcohols and ethers in cyclopropane solution reveal complex linewidth effects. Isotropic modulation of the proton hyperfine splittings (hfs) through restricted rotation about C-0 and C-C single bonds is observable in the region 230>T>150K. Such effects can be distinguished from anisotropic viscosity-dependent line broadening. In spectra from alcohol radicals resolved 2nd order structure causes no ambiguity in the interpretation. Restricted rotation about Ca-0H modulates aaH and aBH out-of-phase with a0H in the series RCHOH [R= CH3, C2H5, C2H5CH2, (CH3)2CHCH2, (CH3)3CCH2]. A general model for the process is discussed. In cases three and four restricted Co-C rotation allows the diastereotopic inequivalence of the 6-protons to be manifested as a broadening of MB = 0 components. Preferred conformations consistent with all the foregoing modulation effects and with observed HB and HY splittings are presented. The analysis is supported by results for radicals RCHOR' from related ethers and by spectral simulation. The spectrum of the 1-hydroxycyclohexyl radical demonstrates previously unobserved fine structure and a low-temperature linewidth effect tentatively attributed to radical site inversion. A second series of alcohol-derived radicals R1R2R3CCHOH with an increasingly bulky Ca substituent has been studied. The Ha hfs provide evidence of a steric flattening not hitherto observed. This effect correlates well with literature values of steric parameters for the R1R2R3C substituent. In the case R1,R2 = CH3, R3 = C2H5 an observed specific y-H interaction is assigned to a locked conformation of the crowded system. A series of highly alkylated cyclic ethers has been examined. The dramatic temperature-dependent changes in the spectrum of the 5,5-dimethyl-l,3-dioxan-2-yl radical are attributed to restricted ring flipping. A fast exchange limit spectrum has been obtained for the first time in such systems, allowing evaluation of thermodynamic parameters. the 2,4,8,10-tetraoxyspiro[5,5]undecan-3-yl radical exhibits similar behaviour. The 2,2,5,5-tetramethyl and 5,5-diethyl-2,2-dimethyl-l,3--dioxan-4-yl radicals have fixed conformations which give rise to enhanced values of ayH in agreement with theoretical calculations. In the latter case a splitting of 4.27 G is assigned to a single y-methylene proton in behaviour analogous to R1R2R3CCHOH.