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Understanding the structure and kinetics of electrochemical oxidation of platinum single-crystal surfaces at the atomic level is important to understanding and improving the electrocatalysis of platinum in fuel cells. This thesis concerns the analysis of data from combined electrochemical and surface X-ray diffraction (SXRD) experiments on Pt(111) and Pt(100). In the early stages of oxidation, Pt atoms are extracted from their metal lattice sites and become part of a metal oxide. Their locations have been measured by collaborators using SXRD. The corresponding charges measured electrochemically are determined by integration of cyclic voltammetry, potential step and potential sweep-hold experiments, and used to propose reactions that are occurring in the oxidation. The measured charge consists of the wanted charge that passes in the electrochemical reactions and a capacitive charge associated with charging the electrical double-layer. Different ways of subtracting the double-layer charge were investigated. Reactions were proposed for optimally corrected charges, and for the worst case where no correction is made, in order to determine the reliability of the proposed reactions. From cyclic voltammetry experiments on Pt(111) surfaces, during oxidation 0.5 ML adsorbed oxygen and a few extracted PtO (less than 0.1 ML) are formed. Without baseline correction the data are consistent with 0.5 ML Oads and a few extracted PtO2. After fast scans, the Pt(111) surface is restructured as shown by the X-ray signal, but the oxide peaks in CV are nearly unchanged, which suggests that the electron transfer and Pt extraction do not need to be tightly coupled. From CV experiments on Pt(100) surfaces, during oxidation many more extracted Pt are formed than on Pt(111). These form long chains with PtO2 units (0.25 to 0.39 ML) together with Oads and a total coverage of 0.5 ML. If CV isn't baseline corrected, the data is not consistent with long chains with PtO2 units, but short Pt3O8 chains with equal numbers of independent PtO2 groups. From potential step experiments on Pt(100), there is an expectation from the literature that the charge will grow linearly with log t. However, this relationship was only found during the first second of each step, and then is unchanged after ~1 s. The slopes of the logarithmic plots are linearly related to potential. From sweep hold experiments on Pt(100), both charges and coverage of extracted Pt atoms are not very linear vs log t, and their slopes are also not linearly related to potential but change sharply during the potential range of Pt extraction. / Graduate

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The essential nutrient choline is known to serve as a precursor for phospholipids and the neurotransmitter acetylcholine, and to feed into methylation pathways. The role and fate of choline in immune cells, however, is not yet fully elucidated. To act as a methyl group donor, choline must first undergo oxidation in mitochondria, a process which has long been thought to occur exclusively in the liver and kidney. The recent identification of choline transporters on the mitochondrial membrane has highlighted the possibility of mitochondrial choline oxidation in other cell types. Here, I show that choline transporters are present on the mitochondrial membrane of primary and immortalized mouse macrophages. The interaction of CTL2 with mitochondria is further augmented following pro-inflammatory polarization with the bacterial endotoxin lipopolysaccharide. I show that mitochondrial choline uptake occurs in macrophages using radiolabelled choline assays; however, it remains unclear whether this process is conducted through the identified transporters. Preliminary data suggest that mitochondrial choline oxidation to betaine was increased in LPS-stimulated macrophages, revealing a potential additional input into one-carbon metabolism in polarized macrophages. This project broadens the existing paradigm that choline oxidation occurs strictly in hepatic and renal tissue and suggests that choline oxidation may be a regulated process in macrophage polarization.

A study of the photo-oxidation of the 2,6-dichlorophenol indophenol-ascorbic couple was undertaken with a view to investigating the postulated mechanism of oxidation by a component of the oxygen evolving sequence operative in photosynthesis. A spectrophotometric method for the measurement of the progress of photo-oxidation was developed. Temperature and pH dependence were determined and the effect of various common inhibitors and physiological substances tested. None of the common Hill reaction inhibitors were effective in the ascorbic acid photo-oxidation in the system used. KCN and catalase as well as a few other high molecular weight proteins were able to inhibit dark auto-oxidation of DPIP, presumably through the absorption or complexing of metal ions. The presence of catalase or peroxidase at levels of 5 x 10-7 and 1 x 10-6 Molar respectively was necessary for photo-oxidation of DPIP when KCN was added to the system in a concentration of 1 x 10-3 Molar. Many of the effects of catalase, peroxidase and KCN are unexplained. It was found that riboflavin mono-nucleotide sensitization accounted for all the photo-oxidation observed in the system used. The optimum concentration was 1 x 10-4 M. Neither chlorophyll nor chloroplasts had any effect on the reaction. It was also found that FMN could sensitize the photo-oxidation of mammalian cytochrome c Catalase, peroxidase and KCN were without effect in this reaction. The effect of ethanol concentration on the chlorophyll a sensitized photo-oxidation of DPIP and it was shown that this reaction probably does not take place in an aqueous medium as photo-oxidation decreases rapidly with ethanol concentration. The effect of light intensity on the FMN sensitized photo-oxidation of DPIP was studied and found to exhibit no inhibitory effect at levels as high as 1600 foot-candles. The possible implication of FMN in light inhibited photo-synthesis was noted. The possible implication of FMN in previously reported photo-oxidations was discussed as well as its possible role in photo-synthesis.

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