The oxidation of refractory gold concentrates containing arsenopyrite and pyrite and the simultaneous dissolution of gold in aerated alkaline solutions at ambient temperatures and pressures without the addition of cyanide has been studied. It involves the following aspects: the chemistry of the oxidation of pure arsenopyrite and pyrite minerals in aerated alkaline solutions; the kinetics of oxidation of arsenopyrite and the simultaneous dissolution of gold in such solutions; the kinetics of simultaneous dissolution of gold during the alkaline oxidation of refractory gold concentrates; the electrochemistry of gold in alkaline solutions containing thiosulfate or monothioarsenate; the effect of copper on the leaching of gold in alkaline thiosulfate solutions; and the leaching of gold in alkaline solutions with thioarsenites. The nature and proportions of the products of the oxidation of arsenopyrite in aerated alkaline solutions have been studied using high pressure ion chromatography techniques that have shown that thiosulfate and a new species, monothioarsenate, are the main oxidation products of arsenopyrite apart from arsenate and sulfite. The alkaline oxidation of pyrite primarily yields thiosulfate and sulfite. A kinetic investigation of the oxidation of arsenopyrite with air or oxygen has shown that the initial rate of arsenopyrite oxidation is proportional to the concentration of dissolved oxygen. A reaction mechanism for the oxidation of arsenopyrite has been proposed, which involves an anodic oxidation of the mineral involving hydroxyl ions coupled to a cathodic process for oxygen reduction which is partially controlled by mass transfer of dissolved oxygen to the mineral surface. Detailed studies of the dissolution behaviour of gold in aerated alkaline solutions in the presence of thiosulfate or monothioarsenate by electrochemical and leaching methods have demonstrated that the dissolution rate is very low as compared to that of gold in alkaline cyanide or ammoniacal thiosulfate solutions. It has been found that copper ions catalyze the dissolution of gold in the thiosulfate solutions in the absence of ammonia. The leaching experiments also have shown that gold may dissolve in alkaline thioarsenite solutions, which provides a possible new process option for the leaching of gold. The oxidation of refractory arsenical gold concentrates in aerated alkaline solutions results in the formation of thiosulfate, arsenate and sulfate as well as the dissolution of gold, copper and iron. It appears that the dissolution of gold is due to the complex reactions of gold with thiosulfate ions promoted by the catalytic effect of copper ions. Up to 80% of the gold may be extracted during the oxidation of selected refractory arsenical

Cette thèse porte sur l'écophysiologie et la physiologie d'une bactérie hyperthermophile et microaérophile, Aquifex aeolicus, cultivée dans différentes conditions d'oxygénation. Au cours de ce travail, trois systèmes expérimentaux (jarres, microcosmes et fermenteur) ont été testés : (1) le nouveau système de jarres qui été mis au point est muni de microplaques de 24 puits couplé à un robot. Il permet d'étudier un grand nombre de facteurs trophiques ou de formulations de milieux de cultures tout en conservant une atmosphère de composition constante, (2) pour l'étude de facteurs trophiques gazeux, l'utilisation des microcosmes a été montrée peu adaptée, amenant même dans certains cas, à des interprétations erronées, et, 3) le fermenteur reste le meilleur outil pour étudier l'influence de la concentration en O2 dissous (pO2) sur le métabolisme d'A. aeolicus. A partir des cinétiques de croissance obtenues en fermenteur, il a été établi que la densité de biomasse est constante et que la vitesse de croissance est maximale pour une pO2 comprise, respectivement, entre 0.006 et 6 mg/L et, entre 1 et 2 mg/L. Pour des pO2 supérieures à 2 mg/L, il a été montré que l'oxygène a un effet toxique sur la croissance d'A. aeolicus. Pour des conditions optimales d'oxygénation (pO2=1.5 mg/L) et lorsque l'H2 (100 mL/min) limite la croissance, le catabolisme énergétique est alors dévié vers la consommation du thiosulfate. En effet, pour les débits d'H2 de 450 et 100 mL/min, d'une part 97 et 79 % de l'O2 sont respectivement réduits par l'hydrogène et d'autre part 3 et 21 % de l'O2 sont respectivement réduits par le thiosulfate. / This manuscript addresses the physiology and ecophysiology of the microaerophilic hyperthermophilic bacterium Aquifex aeolicus, grown under different oxygen-supply conditions. Three experimental systems, jar, microcosm and fermentor were tested in those experiments: (1) a newly-engineered jar system containing 24-well microplates coupled to an automated controller. This system allows to study a broad spectrum of trophic factors or culture media formulations while maintaining a constant atmospheric composition; (2) microcosm systems were, here, proved ill-adapted to studying gas-phase trophic factors, and in some cases even to leading to false interpretations; 3) the fermentor system remains the best tool to studying the influence of dissolved O2 concentration (pO2) on A. aeolicus metabolism. Based on in-fermentor growth kinetic curves, we established that biomass density was maximum and constant at a pO2 in the range 0.006 to 6 mg/L and growth rate was maximum at a pO2 of about 2 mg/L. At a pO2 over 2 mg/L, oxygen level had a toxic effect on A. aeolicus growth. Under optimal oxygen supply (pO2 = 1.5 mg/L) and when H2 (100 mL/min) is the growth-limiting factor, energy catabolism is diverted towards thiosulfate consumption: at H2 flow-rates of 450 and 100 mL/min, 97% and 79% of O2 is reduced by hydrogen while 3% and 21% of O2 is reduced by thiosulfate, respectively. Under over-oxygenation conditions (pO2 = 10.5 and 12 mg/L), growth was correlated to high thiosulfate consumption whereas the expression of genes encoding hydrogenases was significantly downregulated and hydrogenase activity was null.

No description available.

Complementary electrochemical and spectroscopic techniques were used to characterize the behavior and composition of the passive layer formed at the gold-thiosulfate interface in the presence of copper. Raman studies of three different cationic (calcium, ammonium and sodium) thiosulfate leaching solutions showed that the concentrations of sulfate, thiosulfate, trithionate and tetrathionate remained constant. Initial leaching current densities for the three systems were identical, however, significant differences were noted in the open circuit potentials of these systems. Gold nanorod electrodes were employed as substrates for Surface Enhanced Raman Spectroscopy (SERS) studies of the gold-thiosulfate interface. The composition and behavior of the passive layer at the gold- thiosulfate interface greatly differed from that of the bulk solutions. Higher order polythionate species were not observed, and significant differences were noted in the behavior of species common between the three thiosulfate leaching solutions. Passivation levels determined from SERS indicate that in the presence of copper, the cation associated with thiosulfate may play a key role in the extent of passivation on the gold surface. / Barrick Gold Corp., NSERC

The research work presented in this thesis investigates the mechanistic details of conventional as well as electrochemically directed self-assembly of alkylthiosulfates and explores the use of conjugated semiconducting polymers for organic electronic applications. Here, the significance of the use of conjugated polymers is twofold; first, to explore their applications in nanoelectronics and second, the possibility of using them as a top contact on the self-assembled monolayers (SAMs) for molecular electronic applications. Throughout this work, deposition of the organic materials was performed on prefabricated device structures that required no further lithographic or metal deposition steps after modification of the electrodes with the organic molecules. Self-assembly of alkylthiosulfates on gold are reported to form monolayers identical to those formed from the corresponding alkanethiols. However, these self-assembly processes follow more complex mechanisms of monolayer formation than originally recognized. Studies on the mechanism of alkylthiosulfate chemisorption on gold shows that the self-assembly process is influenced by electrolyte and solvent. Plausible mechanisms have been proposed for the role of trace water in the solvent on conventional as well as electrochemically assisted self-assembly of alkylthiosulfates on gold. Electroanalytical and spectroscopic techniques have been used to explore the mechanistic details of electrochemically directed self-assembly of alkylthiosulfates on gold. It has been found that the self-assembly process is dynamic under electrochemical conditions and the heterogeneous electron transfer process between the organosulfur compound and gold is mediated through gold surface oxide and accompanied by corrosion. Conducting polymers are serious candidates for organic electronic applications since their properties can be controlled by the manipulation of molecular architecture. Unique electronic properties of conjugated polypyrrole hybrid materials (PPy0DBS-Li+) with immobile dopant anions and mobile cations have been observed and explained on the basis of movement of the cations in an applied electric field. Based on this principle, functioning polymer resistive memory devices have been demonstrated which can be scalable to lower dimensions for nanoelectronics applications. Finally, proof of concept for using a conducting polymer as a top contact in molecular electronic devices created using electrochemically directed self-assembly is demonstrated.

The research work presented in this thesis investigates the mechanistic details of conventional as well as electrochemically directed self-assembly of alkylthiosulfates and explores the use of conjugated semiconducting polymers for organic electronic applications. Here, the significance of the use of conjugated polymers is twofold; first, to explore their applications in nanoelectronics and second, the possibility of using them as a top contact on the self-assembled monolayers (SAMs) for molecular electronic applications. Throughout this work, deposition of the organic materials was performed on prefabricated device structures that required no further lithographic or metal deposition steps after modification of the electrodes with the organic molecules. Self-assembly of alkylthiosulfates on gold are reported to form monolayers identical to those formed from the corresponding alkanethiols. However, these self-assembly processes follow more complex mechanisms of monolayer formation than originally recognized. Studies on the mechanism of alkylthiosulfate chemisorption on gold shows that the self-assembly process is influenced by electrolyte and solvent. Plausible mechanisms have been proposed for the role of trace water in the solvent on conventional as well as electrochemically assisted self-assembly of alkylthiosulfates on gold. Electroanalytical and spectroscopic techniques have been used to explore the mechanistic details of electrochemically directed self-assembly of alkylthiosulfates on gold. It has been found that the self-assembly process is dynamic under electrochemical conditions and the heterogeneous electron transfer process between the organosulfur compound and gold is mediated through gold surface oxide and accompanied by corrosion. Conducting polymers are serious candidates for organic electronic applications since their properties can be controlled by the manipulation of molecular architecture. Unique electronic properties of conjugated polypyrrole hybrid materials (PPy0DBS-Li+) with immobile dopant anions and mobile cations have been observed and explained on the basis of movement of the cations in an applied electric field. Based on this principle, functioning polymer resistive memory devices have been demonstrated which can be scalable to lower dimensions for nanoelectronics applications. Finally, proof of concept for using a conducting polymer as a top contact in molecular electronic devices created using electrochemically directed self-assembly is demonstrated.

Köln, Universiẗat, Diss., 1999.

Hydrogen sulfide (H2S) is an endogenous gasotransmitter that regulates vascular function and blood pressure, and also protects the heart from injury associated with myocardial infarction (MI). The mitochondrial enzyme thiosulfate sulfurtransferase (TST) has a putative role in the breakdown of H2S but its role in the cardiovascular system is unknown. I hypothesised that TST reduces cardiovascular H2S availability and that inhibiting TST activity may therefore ameliorate cardiovascular pathology. In the heart, TST was expressed by cardiomyocytes and vascular smooth muscle cells. Tst-/- mice all survived to adulthood and had normal cardiac structure and function. Cardiac and hepatic H2S breakdown rates were reduced and H2S levels were higher in the blood of Tst-/- mice. However, in heart tissue, protein levels for the H2S-activated Nrf2 downstream targets, thioredoxin (Trx1) and heme oxygenase-1 (HO-1) were comparable. In contrast, protein levels for the cardiac specific H2S-synthetic enzyme, cystathionine gamma lyase (CSE) was reduced, suggesting a homeostatic negative feedback mechanism to maintain H2S at non-toxic levels. Respiration, measured using an oxygen-sensing electrode was normal in isolated mitochondria from whole Tst-/- compared to control C57BL6 hearts. Endothelial nitric oxide synthase (eNOS) protein expression was lower in Tst-/- hearts, highlighting potential cross talk between H2S and nitric oxide (NO) signalling. TST was expressed in whole aorta homogenates and in isolated endothelial cells from aorta and small intramuscular vessels of the hindlimb from C57BL/6N control mice. Myography and western blotting revealed a greater influence of NO in aorta from Tst-/- mice that was associated with increased phosphorylation of the activating serine1177 residue of eNOS (PeNOSSer1177). NO plays a lesser role in resistance arteries, but in comparison to control vessels, small mesenteric vessels from Tst-/- mice was more reliant on small and intermediate calcium activated potassium channels for relaxation. Tst-/- mice were normotensive, despite this alteration in the regulation of vascular tone. However, metabolic cage experiments identified that Tst-/- mice presented with diuresis, polydipsia, and increased urinary electrolyte excretion of sodium, potassium and chloride, possibly to compensate for increased vascular tone in order to maintain stable blood pressure. To investigate the role of TST in regulating the response to pathological challenge, MI was induced by coronary artery ligation (CAL). In control mice, gene expression of CSE was downregulated by 2 days after CAL, but TST expression was 12-fold increased, suggesting regulation of H2S bioavailability during the acute MI-healing phase. Tst-/- male mice had a 40% greater incidence of cardiac rupture during infarct healing and surviving Tst-/- mice had greater left ventricular dilatation and impaired function compared to controls. Ex vivo, isolated perfused hearts from Tst-/- mice were more susceptible to ischaemia/ reperfusion injury, suggesting an additional role of TST in determining cardiomyocyte susceptibility to injury. In conclusion, these data indicate that cardiovascular H2S bioavailability is regulated through degradation by TST. The data presented here provide evidence for significant tissue specific crosstalk between H2S synthetic and degradative mechanisms and between H2S and other local regulatory mechanisms, including ion channels and NOS. We infer TST has a physiological role in the kidney where its loss leads to changes in renal electrolyte and water handling, although other compensatory mechanisms prevent a change in blood pressure. Under conditions of pathological challenge following MI, loss of TST is detrimental, illustrating its key role in removal of H2S. The data refute the original hypothesis that TST inhibition would be protective against cardiovascular pathology. Further studies in mice with tissue specific deletion of TST are now required to more fully reveal the cardiovascular role of TST.

Inorganic sulfur-oxidising Bacteria are present throughout the Proteobacteria and inhabit all environments of Earth. Despite these facts they are still poorly understood in terms of taxonomy, physiology, biochemistry and genetics. Using phylogenetic and chemotaxonomic analysis two species that were erroneously classified as Thiobacillus trautweinii spp. in 1921 and 1934 are in fact novel chemolithoheterotrophic species for which the names Pseudomonas trautweiniana sp. nov. and Achromobacter starkeyanus sp. nov. are proposed, respectively. These species were found to oxidise thiosulfate in a “fortuitous” manor when grown in continuous culture and increases in maximum theoretical growth yield (YMAX) and maximum specific growth rate (μMAX) were observed. Cytochrome c linked thiosulfate-dependent ATP production was confirmed in both species, confirming “true” chemolithoheterotrophy. Evidence is presented that the ATP concentration governs the benefits of chemolithoheterotrophy. There were significant changes in enzyme activities, including enzymes of the TCA cycle that might be affecting amino acid synthesis. This is strong evidence that chemolithoheterotrophy gives a strong physiological boost and evolutionary advantage over strictly heterotrophic species. An autotrophic species that was historically placed in Thiobacillus was also shown to be a novel species for which the name Thermithiobacillus parkerianus sp. nov. is proposed. The enzyme profiles of Thermithiobacillus parkerianus differed significantly between different inorganic sulfur growth substrates and was the first time all TCA cycle enzymes were assayed in a member of the Acidithiobacillia. The properties of thiosulfate dehydrogenase varied significantly between Pseudomonas sp. Strain T, Achromobacter sp. Strain B and Thermithiobacillus sp. ParkerM both in terms of optimal parameters and the effect of inhibitors. This evidence adds to the increasing body of work indicating there to be at least two thiosulfate dehydrogenases present in the Bacteria.

No description available.