In this thesis, a combination of laboratory experimentation under well defined conditions coupled with a kinetic modelling approach is used to verify the existence and respective kinetic rates of previously unconfirmed or postulated mechanisms that drive and limit dark Fenton (Fe(II)/H2O2) - mediated As(III) oxidation at pH 3 and 8 and dark Cu(II) - H2O2 - mediated As(III) oxidation at pH 8. Dark Fenton - mediated oxidation of As(III) at pH 3 is first examined and the effects of the variation in the concentration of reactants (As(III), Fe(II) and H2O2), oxygen, phosphate and organics (2 - propanol, formate, and citrate) are reported and analysed. The kinetic models developed for these systems show high applicability to full scale water treatment application and key mechanistic findings include the significance of the cycling of Fe(II) / Fe(III) via HO2 ???/O2 ??????, the effects of As(IV) termination reactions in the absence of oxygen and the retarding effects of phosphate due to the postulated formation of a Fe(III) - phosphate complex (at a derived rate constant of 2.2 x 106 M-1s-1, that also appears to have negligible kinetic activity in terms of reduction to Fe(II) by HO2 ???/O2 ??????). The work also demonstrates the significance of the free radical by products of formate and citrate oxidation by ???OH (HCOO???/CO2 ?????? and 3HGA???2???). The examination of the dark Cu(II) - H2O2 - mediated oxidation of As(III) at pH 8 with variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate and organics (2 - propanol, formate and citrate) demonstrated for the first time the high applicability of this system to the pre - oxidation of As(III) in water treatment and mechanistically that ???OH and CO3 ?????? are the dominant As(III) oxidants in this system. The As(III) oxidant CO3 ??????, is suggested to be generated by the interaction of ???OH and O2 ?????? with the carbonate matrix, at the respective rate constants of 4.9 x 107 M-1s-1 and 5.5 x 106 M-1s-1. Examination of the dark Fenton - mediated oxidation of As(III) at pH 8 and the effects of variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate, organics (2 - propanol, formate and citrate) and Cu(II) demonstrates the varied potential mechanistic pathways in relation to the generation of As(III) oxidants from the Fenton reaction, Fe(II) + H2O2 such as Fe(IV) and CO3 ?????? and the previously dismissed ???OH, due to the presence of Fe(II) - citrate complexes. This work also demonstrates and models the enhancement of As(III) oxidation in the presence of an additional transitional metal ion, Cu(II).

The physiologically important free radicals, nitrogen monoxide and superoxide, can combine to form the reactive intermediate peroxynitrite. Peroxynitrite can react with proteins and their constituent amino acids, such as tyrosine, resulting in protein peroxidation, oxidation and nitration. The nitration of proteins, assessed by the analysis of 3-nitrotyrosine, is a proposed index of pathophysiological activity of peroxynitrite. The aim of the work was to investigate the reaction products between peroxynitrite and protein, develop an assay for 3-nitrotyrosine and measure its levels in biological samples. To study the amino acid products arising from the reaction of peroxynitrite and protein, both liquid chromatography (LC) and gas chromatography (GC) combined with mass spectrometry (MS) were adopted. Approaches to 3-nitrotyrosine assay development were first, to take advantage of the intrinsic sensitivity of electron capture negative ionization GC-MS. Secondly, to avoid possible artefactual problems associated with the derivatisation step in GC-MS, an assay for 3-nitrotyrosine based on combined LC-MS-MS was developed. When a selection of peptides was exposed to peroxynitrite under physiological conditions in vitro, the hydrolysis products showed that 3-nitrotyrosine was the major product. Detectable minor products were 3,5-dinitrotyrosine and DOPA. The GC-MS assay was found to be fraught with difficulty due to artefactual formation of 3-nitrotyrosine. In order to quantify and correct for artefact formation, this complication was approached by incorporating a second isotopomer. This method, however, was confounded by large errors that reduced the overall sensitivity. Either negative or zero levels of endogenous 3-nitrotyrosine were found in tested samples after correction for artefact formation. The LC-MS-MS assay was then used to analyse 3-nitrotyrosine levels in a range of biological samples, including human plasma from healthy volunteers, synovial fluid samples from arthritis patients and tissue extracts from a mouse model of amyotropic lateral sclerosis. In contrast to published data, 3-nitrotyrosine levels were found to be below the limit of detection (1 pg/????L, 10 pg o/c) for all samples - a result somewhat consistent with the negative GC-MS data. It is suggested that the high 3-nitrotyrosine levels previously reported in the literature might reflect artefactual generation of 3-nitrotyrosine and that other approaches to assessing pathophysiological nitration should be sought in future.

Bibliography: leaves 192-193. / ix, 214, ix leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The focus of the thesis is to investigate the fundamental kinetics of the pyrite-nitric acid system. Particular attention is paid to the formation and oxidation of elemental sulfur. The study aims to elucidate the chemistry of the sulfide oxidation and of elemental sulfur formation and oxidation. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1997?

Includes bibliographical references (34 leaves). / xxi, 204 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates the in vitro antioxidant properties of red wine containing polphends and the isoflavone genistein. Subsequently the effect of red wine on low density lipoprotein oxidation and fatty streak lesion development in cholesterol-fed rabbits was examined. / Thesis (Ph.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 1998

Techn. Universiẗat, Diss., 2001--Berlin.

Humans have dramatically increased the amount of reactive nitrogen cycling through the biosphere. In coastal systems, excess nitrogen can lead to negative impacts. Thus, it is crucial to understand how nitrogen is cycled within, and eventually removed from, marine systems and the variables that regulate these processes. Sediment denitrification (the microbial conversion of nitrate (NO3^-) to dinitrogen (N2) gas) and water column nitrification (the two step oxidation of ammonium (NH4^+) to nitrite (NO2^-) and then nitrate (NO3^-)) rates were quantified along an in situ gradient of environmental conditions from an estuary to the continental shelf off Rhode Island, USA. Sediment net denitrification rates were directly measured over multiple seasonal cycles using the N2/Ar technique. Denitrification rates ranged from 20-75 μmol m^-2 hr^-1 (mean 44±4), indicating that this process removes ~5% of total reactive nitrogen entering the North Atlantic shelf region per year. Based on model results, these rates also represented a three-fold decrease in sediment nitrogen removal in New England continental shelf sediments over the past century. A literature review of marine water column nitrification observations were compiled to evaluate how ammonium, nitrite, and total oxidation rates vary worldwide. Rates of ammonium, nitrite, and total oxidation differed among estuary, continental shelf, and open ocean environments (p<0.05). This review highlights that as we continue to study marine "nitrification," it is necessary to consider both individual oxidation processes and environment type. Water column ammonium and nitrite oxidation rates were measured using stable isotope tracers off Rhode Island. At all study sites, nitrite oxidation rates (0-99 nM d^-1) outpaced ammonium oxidation rates (0-20 nM d^-1). These oxidation processes responded in dissimilar ways to in situ water column conditions (depth, salinity, dissolved oxygen, and pH), and these relationships varied with location. Nitrous oxide (N2O) production rates up to 10 times higher than ammonium oxidation indicated that ammonium oxidation may be underestimated if this byproduct is not measured. For the first time, the link between sediment metabolism and water column nitrification was also examined, and the results highlight the importance of benthic-pelagic coupling as controlling factor of water column ammonium and nitrite oxidation. / 2019-04-30T00:00:00Z

Carbon-carbon composite brakes are one third the weight of typical steel brakes, and they attain strength and frictional properties at temperatures up to 1600°C. C/C composite brakes can endure high temperatures, but in the presence of oxygen they will begin to oxidize at 400°C. Anti-oxidant systems must be applied to the non-rubbing surfaces of the C/C composite stators and rotors to prevent oxidation. Currently, commercial phosphorus based coating materials are made of crystalline metal phosphates that are derived from heat treated phosphoric acid-based liquid precursors painted on the non-rubbing surface of C/C composites. These crystalline metal phosphate coatings are very porous and tend to move to the friction surface when exposed to increased levels of relative humidity. This anti-oxidant migration towards the rubbing surface causes a drop in frictional properties. Migration reduction and oxidation inhibition was improved upon with advanced anti-oxidant systems. The advanced antioxidants analyzed protected the C/C composite from thermal and catalytic oxidation six to ten times better at 650°C than commercial materials. At 871°C, the antioxidants protected the C/C composite from thermal oxidation ten times better than commercial materials. Migration of the antioxidant to the rubbing surfaces was eliminated through the use of advanced antioxidant compositions. The predicted life of the antioxidants was modeled using Avrami's equation. Characterization of the antioxidants was further analyzed through the use of SEM, EDS, and XRD systems.

Plasma electrolytic oxidation, or PEO, is a surface modification process for the production of ceramic oxide coatings upon substrates of metals such as aluminium, magnesium and titanium. Two methodologies for the quantitative study of electrical breakdown (discharge) events observed during plasma electrolytic oxidation processes were developed and are described in this work. One method presented involves direct measurement of electrical breakdowns during production of an oxide coating within an industrial scale PEO processing arrangement. The second methodology involves the generation and measurement of electrical breakdown events through coatings pre-deposited using full scale PEO processing equipment. The power supply used in the second technique is generally of much lower power output than the system used to initially generate the sample coatings. The application of these techniques was demonstrated with regard to PEO coating generation on aluminium substrates. Measurements of the probability distributions of discharge event characteristics are presented for the discharge initiation voltage; discharge peak current; event total duration; peak instantaneous power; charge transferred by the event and the energy dissipated by the discharge. Discharge events are shown to increase in scale with the voltage applied during the breakdown, and correlations between discharge characteristics such as peak discharge current and event duration are also detailed. Evidence was obtained which indicated a probabilistic dependence of the voltage required to initiate discharge events. Through the scaling behaviour observed for the discharge events, correspondence between the two measurement techniques is demonstrated. The complementary nature of the datasets obtainable from different techniques for measurement of PEO discharge event electrical characteristics is discussed with regards to the effects of interactions between concurrently active discharge events during large scale PEO processing.

No description available.

Thesis advisor: Matthias M. Waegele / Studying the adsorption and reaction kinetics of surface-bound chemical species, on different metal catalysts or electrodes, is of paramount importance in the development of inhomogeneous catalytic methodology. Our study of the oxidation of CO on platinum was accomplished by designing a thin layer flow cell in an external reflection configuration. A charge-injection circuit was successfully implemented which decreased the time required to charge the double layer in the electrochemical cell. We were able to obtain a signal via Stark shift spectrum, of the adsorbed CO, using the thin layer cell configuration. Additionally, electrochemical impedance spectroscopy was used as a diagnostic tool to assess the effect of electrode geometry, on the voltage response, in the thin layer cell. The coupling of visible light-driven photoexciation with transition metal catalytic plat- forms is emerging as a synthetic strategy to achieve unique reactivity that has previously been inaccessible. One such example is the iridium/nickel-dipyridyl system discovered recently. Characterizing the interactions between the iridium and nickel catalysts, under reaction conditions, is important to develop a better understanding of the system. In order to apply infrared spectroscopic measurement techniques, in-situ, we made modifications to the synthetic scheme by changing the solvent and by utilizing different iridium catalysts for the synthesis of the desired methyl 4-(benzoyloxy)benzoate product. Using our trans- mission infrared setup we effectively demonstrated in-situ product detection of the aryl- ester coupled product. Additionally, after constructing a transient infrared pump-probe setup, we collected preliminary results of the triplet state lifetime of the iridium dye. The surface morphology of copper has been shown to affect the electrochemical reduction of CO2. Using surface-enhanced Raman spectroscopies, the reversible formation of nanoscale metal clusters on a copper electrode was revealed at sufficiently cathodic potentials where we observed the appearance of a new band at 2080 cm-1 corresponding to C≡O adsorbed to undercoordinated copper defect sites. The formation of new undercoordinated sites additionally resulted in the surface enhancement of the Raman scattering which amplified the intensity of the other spectral bands. / Thesis (MS) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.