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Gas phase kinetics of the reactions involving hydroxyl radical and hydrogen atom were studied using experimental and ab initio theoretical techniques. The rate constant for the H + H2S reaction has been measured from 298 to 598 K by the laser photolysis/resonance fluorescence (LP-RF) technique. The transition state theory (TST) analysis coupled with the measurements support the suggestion that the reaction shows significant curvature in the Arrhenius plot. The LP-RF technique was also used to measure the rate constant of the H + CH3Br reaction over the temperature range 400-813 K. TST and density functional theory (DFT) calculations show that the dominant reaction channel is Br-abstraction. The reaction H + CF2=CF-CF=CF2 was first studied by flash photolysis/resonance fluorescence (FP-RF) method. The experiments of this work revealed distinctly non-Arrhenius behavior, which was interpreted in terms of a change in mechanism. DFT calculations suggest that the adduct is CF2H-CF•-CF=CF2. At lower temperatures a mixture of this molecule and CF2•-CFH-CF=CF2 is likely. The theoretical calculations show that H atom migrates in the fluoroethyl radicals through a bridging intermediate, and the barrier height for this process is lower in the less fluorinated ethyl radical. High level computations were also employed in studies of the rate constants of OH + chloroethylenes reactions. VTST calculations indicate that, except the reaction of OH + C2Cl4, these reactions present a complex behavior. For OH + C2Cl4, conventional TST calculation shows a simple positive temperature-dependence behavior.

Choline oxidase catalyzes the flavin-dependent, two-step oxidation of choline to glycine betaine via the formation of an aldehyde intermediate. The oxidation of choline includes two reductive half-reactions followed by oxidative half-reactions. In the first oxidation reaction, the alcohol substrate is activated to its alkoxide via proton abstraction and oxidized via transfer of a hydride from the alkoxide α-carbon to the N(5) atom of the enzyme-bound flavin. In the wild-type enzyme, proton and hydride transfers are mechanistically and kinetically uncoupled. The role of Ser101 was investigated in this dissertation. Replacement of Ser101 with threonine, alanine, cysteine, or valine demonstrated the importance of the hydroxyl group of Ser101 in proton abstraction and in hydride transfer. Moreover, the kinetic studies on the Ser101Ala variant have revealed the importance of a specific residue for the optimization of the overall turnover of choline oxidase. The UV-visbible absorbance of Ser101Cys suggests Cys101 can form an adduct with the C4a atom of the flavin. The mechanism of formation of the C4a-cysteinyl adduct has been elucidated. D-arginine dehydrogenase (DADH) catalyzes the oxidation of D-amino acids to the corresponding imino acids, which are non-enzymatically hydrolyzed to α-keto acids and ammonia. The enzyme is strick dehrogenase and deoesnot react with molecular oxygen. Steady state kinetic studies wirh D-arginine and D-histidine as a substrate and PMS as the electron acceptor has been investigated. The enzyme has broad substrate specificity for D-amino acids except aspartate, glutamate and glycine, with preference for arginine and lysine. Leucine is the slowest substrate in which steady state kinetic parameters can be obtained. The chemical mechanism of leucine dehydrogenation catalyzed by DADH was explored with a combination of pH, substrate and solvent kinetic isotope effects (KIE) and proton inventories by using rapid kinetics in a stopped-flow spectrophotometer. The data are discussed in the context of the crystallographic structures at high resolutions (<1.3 Å) of the enzyme in complex with iminoarginine or iminohistidine.

In medical and health physics, we are interested in the effects of ionizing radiation on biological systems, in particular, human biology. The main process by which ionizing radiations causes damage to biological systems, is through the creation of radicals close to DNA strands. The radicals are very reactive and those created within close proximity to DNA will react with the DNA causing damage, in particular single strand or double strand breaks. This damage to the DNA can cause mutations that can kill the cell, either mitotically or apoptotically, or possibly lead to a cancerous formation. Therefore it is important to study how these radicals interact with DNA strands for a correlation between the resultant products of radical reactions and DNA strand breaks. For this study, we look at the most important radical, the OH radical and it's addition to DNA bases. We will study, through quantum chemistry, the thermodynamics of OH radical addition to the four bases, Adenine, Guanine, Cytosine and Thymine. The Jaguar program developed by Schrodinger was used for DFT calculations of the Gibbs free energy of the addition. In addition, calculations for the partial charge, HOMO's and Fukui indices were calculated and compared to experiment.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1969. / Includes bibliographical references (p. 119-122).

Radical chemistry has always been a very active area of research. This is due to the fact that radicals are both very numerous in variety and very reactive. A radical is any chemical species that possesses one or more unpaired electrons. These unpaired electrons usually lead to the extremely reactive characteristics of the chemical species. This reactivity can be beneficial; this is true in the case of polymer chemistry. For instance, some plastics are synthesized through a radical chain reaction. In addition, radicals are used in the synthesis of novel organic compounds with the goal of creating new pharmaceuticals. Radical reactivity can be detrimental as well; radicals have been implicated in a number of ailments including heart disease and cancer. One particular view of cancer cells is that their DNA is somehow mutated; a radical could cause this mutation. In fact, one radical species in particular is known to oxidize DNA, the hydroxyl radical.Unfortunately, the electronic structures of most radicals do not lend themselves to direct study by modem spectroscopic methods. Recently, researchers have discovered that hydroxyl radical, being very reactive in nature, easily complexes with other species. If these complexes are spectrosopically active, then we can study the radical reactivity indirectly through a "reporter" molecule. One such approach uses the transient visible absorbance of the complexes of hydroxyl radical with the thiocyanate anion. In addition, there is other experimental evidence that suggests that thiocyanate anion complexes with other radicals as well. These experiments have been very successful in improving our understanding of radical chemistry, but very little is known about the electronic structure or connectivities of these complexes.Our research is comprised of a systematic theoretical study of the structure, vibrational frequencies, and spectroscopic properties of complexes of hydroxyl radical with thiocyanate anion. In addition, we will investigate the structures, vibrational frequencies, and spectroscopic properties of complexes of thiocyanate anion and other radical species.The ultimate goal of our research is to determine the feasibility of utilizing thiocyanate anion as an LFP reporter for radical species other than hydroxyl radical.Our theoretical approach is based in computerized, mathematical models of the properties of the species being studied, based on quantum mechanics and density functional theory as implemented in the computational chemistry software Gaussian 03. Our study includes calculations that provide the energies, optimized geometry, vibrational frequencies, charge and spin densities, and other properties of the various species. This consists of the various isolated radicals and anions, complexes, transitions states, pre-reactive complexes, and structural isomers. / Department of Chemistry

Thesis (Ph.D.)--McMaster University (Canada), 1991. / Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0308. Supervisor: John Warkentin.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 196-214).