Industrial activities of mankind are feared to damage the environment irretrievably. Especially the release of huge amounts of harmful gases causes concern. In this regard the environmental pollution caused by the one billion motor vehicles on earth is particularly important. The platinum-group metals (PGM) are well known for their catalytic activity. They are used extensively for reducing the amounts of hydrocarbons, carbon monoxide and nitrogen oxides from the exhausts gas emitted by automobiles. In 2012 20% of platinum and 27% of palladium produced were used in the manufacture of catalytic converters. With the increasing use of PGM-containing autocatalysts, the reclaiming of PGMs from spent catalysts has become essential. Particularly attractive hydrometallurgical methods are those based on the use of halide ions e.g. sodium chloride, as complexing agent in conjunction with nitric acid as oxidant. The chemical reactions between mixtures of aluminium chloride and nitric acid have been studied, but the electrochemical reactions have received little attention. The research reported in this dissertation is aimed at providing data relating to the electrochemical behaviour of platinum in mixtures of aluminium chloride and nitric acid. The construction of Pourbaix diagrams of platinum in chloride environments confirmed that the stable chloro-complexes [PtCl4]2- and PtCl6]2-, as well as platinum oxides (PtO and PtO2) could play a role under the experimental conditions employed in this study. From the thermodynamic results it can be concluded that the systems deserving consideration favour high chloride concentrations and high temperatures. Notable anodic reactions found were the adsorption of chloride on the platinum surface and the gradual formation of [PtCl6]2-, followed by the formation of platinum oxides at 1.00 to 1.01 V. The results show that anodic currents diminished with lower chloride concentrations. A seemingly anomalous anodic behaviour at 35 °C and 45 °C could be explained in terms of a competition between platinum oxide formation and the formation of platinum chloro-complexes. Evidence for the following cathodic reduction reactions was found: hydrogen evolution, reduction of dissolved oxygen to hydrogen dioxide (-1.3 V SHE), nitrate ion reduction to nitrite ions (-0.01 V SHE), nitrite ion reduction to nitric oxide (-0.85 V SHE) and reduction of PtO and PtO2 to Pt (at -1.00 V and 1.01 V SHE, respectively). A brief study was undertaken in an attempt to relate the electrochemical results to the leaching of platinum from a virgin automotive exhaust catalyst. The recovery was low for mixtures with low chloride concentrations, which could be expected from the electrochemical polarisation curves obtained in electrolytes with different chloride concentrations. The maximum platinum recovery attained, was 60% at 45 °C in a mixture containing 0.6 M AlCl3 and 0.9 M HNO3. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Faraday modulation spectroscopy (FAMOS) is a technique for detection of paramagnetic molecules. By applying a magnetic field over a gaseous sample, the presence of paramagnetic species will rotate the polarization plane of light, addressing a transition in such a species. By placing a gas containing paramagnetic molecules between almost crossed polarizers and modulating the magnetic field, the intensity of the transmitted light will consequently be modulated. Since the rotation of the polarization plane of light is proportional to the concentration of species, this technique can be used for quantitative analysis of paramagnetic molecules. Since FAMOS is solely sensitive to paramagnetic molecules it is superior to many other types of laser-based detection techniques, drastically decreasing various types of noise, background signals, as well as signals from other molecules; e.g. flicker noise, etalon effects and signals from water and CO2 molecules. An experimental setup for detection of nitric oxide (NO) by FAMOS has been developed and optimized. This system is based on a quantum cascade laser emitting light at 5.331 μm, addressing the—for FAMOS—most sensitive transition in NO, Q3/2(3/2). Optimized parameters include a pressure of 60 mbar, a magnetic field of 190 G and a polarizer uncrossing angle of 0.75°. In its present configuration, this system has demonstrated a detection of NO down to 200 ppb for a detection rate of 10 measurements per second. It is very possible that the limit of detection is even lower than this number since this lowest acquirable concentration is limited by the specifications of the gas mixer. A standard deviation between subsequent measurements, of 15 s time separation, is calculated to 30 ppb. However, this is far from the expected ultimate detection limit of this system and this technique in general. One process that causes a weakening of the signal is outgassing. When measuring on an emptied system this phenomenon is greatly reduced and a standard deviation of measurements is then measured and calculated to 7.6 ppb. The detection limit is presumed to be in the very low ppb, or sub-ppb, regime and this limit should be obtainable by further optimization of the system. / Gasen kvävemonoxid är en restprodukt vid förbränning av fossila bränslen, men den återfinns också i människokroppen som en signalsubstans. I stora mängder är den giftig då den interagerar med cellandningen och påverkar arvsmassan. I kombination med syre övergår den sakta till gasen kvävedioxid som i sin tur övergår till salpetersyra. Detta innebär att det är viktigt att kunna detektera denna gas i miljöer där risk för spridning kan anses vara stor. Kvävemonoxid används inom sjukvården som inhalationsgas för tidigt födda barn. Den förekommer även i ökad koncentration i utandningsluft hos människor med astma, Alzheimers eller Parkinsons sjukdom. Därmed finns det också ett intresse av att kunna mäta denna noggrant inom sjukvården, för att ge rätt dosering av gasen samt för att enklare kunna ställa korrekta diagnoser. Att mäta koncentration av kvävemonoxid görs ofta på kemiska vägar. Då detta är tidskrävande finns det anledning att utveckla nya och snabbare sätt att detektera denna gas. En effektiv teknik för att mäta kvävemonoxid är Faraday-moduleringsspektroskopi, FAMOS. Denna teknik bygger på att man med ett magnetfält, genom den så kallade Faradayeffekten, utnyttjar somliga fysikaliska egenskaper hos just kvävemonoxid, för att vidare bestämma dess mängd. FAMOS möjliggör mätningar i realtid och har en låg minsta detektionsgräns i jämförelse med andra laserbaserade tekniker. Framtidsutsikterna för denna teknik är mycket goda och möjligheterna utökas allt eftersom optisk utrustning förbättras. Denna rapport ger grunderna för FAMOS och den jämförs speciellt med en mer konventionell laserbaserad spektroskopisk teknik, våglängdsmodulering. Avhandlingen beskriver dessutom konstruktionen av ett FAMOS-system som baseras kring en kvantkaskadlaser vilken verkar med infrarött ljus på den, för kvävemonoxid, optimala energiövergången.

published_or_final_version / abstract / Medicine / Master / Master of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Pharmacology / Master / Master of Philosophy

published_or_final_version / Medicine / Master / Master of Philosophy

published_or_final_version / Pharmacology and Pharmacy / Master / Master of Philosophy

Barrett's esophagus (BE) is a premalignant disease associated with esophageal adenocarcinoma (EAC). This condition is highly associated with gastroesophageal reflux disease (GERD) which is characterized as chronic exposure of the esophagus to acid and bile acids. An understanding of the cytotoxic and tumorigenic capacity of bile acids and acid during a reflux episode will lead to the identification of markers for therapeutic intervention. The major goal of the following studies was to determine the mechanisms responsible for bile acid-induced alteration in intracellular pH (pHi) the effect on DNA damage, apoptosis and the adaptive resistance to reflux episodes in cells derived from normal esophagus (HET1A) or BE (CP-A) and EAC (JH-EsoAd1). In addition, I explored the therapeutic potential of UDCA oral therapy in BE cells.Here we show a novel mechanism of bile acid-induced, nitric oxide-mediated inhibition of the sodium-hydrogen exchanger (NHE) is a pathway bile acids utilize to induce acid-mediated DNA damage. This same mechanism can elicit apoptosis-resistance which we demonstrate by the complete inhibition of NHE with pharmacological inhibitor of NHE, EIPA. In addition, chronic exposure of bile acids and acid, in-vitro, confers resistance to cytotoxicity and makes cells derived from the squamous epithelium of the esophagus resemble BE and EAC. Finally, modifying the bile acid composition with glycol-Ursodeoxycholic acid (GUDCA) prevents many of the malignant effects of bile acids and acid and suggests a possible therapeutic strategy for those that suffer from GERD. The conclusion from this study suggest that bile acid reflux should be controlled in patients who suffer from GERD

Sex dimorphism in the prevalence, onset, development and progression of cardiovascular disease (CVD) is well recognized. Sex-specific differences in adaptation to cardiac pathological progressions such as cardiac hypertrophy (CH), and the extent to which they are attributable to sex hormones requires further delineation. The objective of this dissertation was to determine which cardiac vasoactive systems are responsible for sex-specific differences in CH modulation using the atrial natriuretic peptide gene-disrupted (ANP-/-) mouse model. First, sex-specific differences in the expression of the cardiac natriuretic peptide (NP) and nitric oxide synthase (NOS) systems were evaluated. Next, the influence of 17β-Estradiol (E2) on the expression and signaling of the cardiac NP and NOS systems was determined in ovariectomized (OVX) female ANP+/+ and ANP-/- mice. Finally, sex-specific differences in cardiac adaptation to Angiotensin II (ANGII) pressure overload were elucidated in male and intact female ANP+/+ and ANP-/- mice. These studies revealed that males predominantly use the NP system and females predominantly use the NOS system. Sex-specific differences in the cardiac NOS system were further enhanced by E2 in OVX female ANP+/+ and ANP-/- mice. In the female ANP-/- mouse, E2 was found to signal through the NOS system to significantly increase plasma cGMP. Finally, male and female differences were demonstrated in the sex-specific patterns of cardiac vasoactive gene system expression and development of cardiac dysfunction in response to ANGII treatment. Sex dimorphism was observed in the expression of BNP and NPR-A in male and female ANP-/- mice treated with ANGII. Female ANP+/+ and ANP-/- ANGII-treated mice exhibited elevated E/E’ ratios that were not found to the same extent in genotype matched ANGII-treated male mice, demonstrating that female mice developed ANGII-mediated mild left ventricle diastolic dysfunction. Based on the results of this dissertation, we conclude that sex-specific differences do indeed exist in the cardiac adaptation to pathological stresses. These data support the understanding that a progression towards sex-specific CVD treatments is warranted, with a particular emphasis on the potential benefits of female-specific targeting of the cardiac NOS system. / Thesis (Ph.D, Anatomy & Cell Biology) -- Queen's University, 2013-08-23 14:21:45.324

The freezing kinetics of binary nitric acid/water aerosols is of fundamental importance to the modelling of polar stratospheric clouds and the role they in ozone depletion over the Arctic/Antarctic regions. Cirrus clouds are also often composed of nitric acid solutions, hence an understanding of freezing process in these aerosols also aids in modelling the earth's radiation budget and global warming. This thesis explores the kinetic phase diagram of nitric acid/water aerosols with sizes ranging between 0. 2 and 1. 5 mm in radius and concentrations ranging between pure water and 0. 45 mole fraction HNO3. Although the kinetic phase diagram has now been studied between 0. 46 mole fraction HNO3 and pure water, more data is needed in the region between 0. 18 and 0. 25 mole fraction HNO3 to confirm the results reported. The project described in this thesis are a continuation of a project begun by Allan Bertram. The measurements involving aerosols with compositions greater than 0. 25 mole fraction HNO3 were carried out as part of Allan Bertram's Ph. D. thesis (see ref. 20) These data were later examined using a more comprehensive data analysis method (as presented in this thesis) in an effort to obtain a more complete understanding of this system.