Friedreich's ataxia is a neurodegenerative disorder caused by the low expression of a mitochondrial protein called frataxin. Studies in the yeast Saccharomyces cerevisiae have unraveled a role for the frataxin homologue (Yfh1p) in iron-sulfur cluster (Fe/S) biosynthesis, probably by interacting with the scaffold protein, Isu1p, and providing iron to the machinery. Yfh1p possesses a large â-sheet platform that may be involved in the interaction with other proteins through conserved residues at its surface. We have used directed mutagenesis associated with polymerase chain reaction (PCR) to study conserved residues localizing either at the surface of the protein, Thr110, Thr118, Val120, Asn122, Gln124, Gln129, Trp131, Ser137 and Arg141, or buried in the core of the protein, Ile130 and Leu132. Mutants T110A, T118A, V120A, N122A, Q124A, Q129A, I130A, W131A, L132A, S137A and R141A were generated in yeast. Growth on iron- or copper-containing medium was severely impaired for mutants Q129A, I130A, W131A and R141A. Others were roughly growing as well as the wild-type strain. We assessed the efficiency of Fe/S biosynthesis by measuring aconitase activity. The results confirmed those obtained on metal-containing medium: mutants Q129A, I130A, W131A and R141A showed a high decrease in their aconitase activity that dropped to the deleted strain level. Moreover, S137A showed also a decreased aconitase activity. We monitored the interaction between Yfh1p and Isu1p by co-immunoprecipitation and it turned out that only the W131A mutation affects directly this interaction. Even if the amount of Yfh1p determined by western blot analysis was highly decreased for several mutants, it is not sufficient to explain the phenotypes as they were poorly restored by overexpression of the mutant proteins to wild-type levels, except for W131F. We have concluded that Gln129, Trp131, and Arg141 are important for Yfh1p function, while Ile130 and Ser137 are required for the folding of the protein. All these residues cluster to the 4th and 5th â-strand of the protein. Our work has demonstrated for the first time the importance of this area for Yfh1p function and shows that Trp131 is involved in the interaction with Isu1p.

Cerium(IV) oxide (CeO2), ceria, is an active metal oxide used in solid oxide fuel cells and for the purification of exhaust gases in vehicle emissions control. Behind these technically important applications of ceria lies one overriding feature, namely ceria's exceptional reduction-oxidation properties. These are enabled by the duality of the cerium ion which easily toggles between Ce4+ and Ce3+. Here the cerium 4f electrons and oxygen vacancies (missing oxygen ions in the structure) are key players. In this thesis, the nature of ceria's f electrons and oxygen vacancies are in focus, and examined with theoretical calculations. It is shown that for single oxygen vacancies at ceria surfaces, the intimate coupling between geometrical structure and electron localisation gives a multitude of almost degenerate local energy mimima. With many vacancies, the situation becomes even more complex, and not even state-of-the-art quantum-mechanical calculations manage to predict the experimentally observed phenomenon of vacancy clustering. Instead, an alternative set of computer experiments managed to produce stable vacancy chains and trimers consistent with experimental findings from the literature and revealed a new general principle for surface vacancy clustering. The rich surface chemistry of ceria involves not only oxygen vacancies but also other active oxygen species such as superoxide ions (O2−). Experiments have shown that nanocrystalline ceria demonstrates an unusually large oxygen storage capacity (OSC) and an appreciable low-temperature redox activity, which have been ascribed to superoxide species. A mechanism explaining these phenomena is presented. The ceria surface is also known to interact with SOx molecules, which is relevant both in the context of sulfur poisoning of ceria-based catalysts and sulfur recovery from them. In this thesis, the sulfur species and key mechanisms involved are identified.

The presence and synthesis of transfer RNA (tRNA) is highly conserved in all organisms and a lot of genetic material is dedicated to its synthesis. tRNA contains a large number of modified nucleosides and several diverse functions have been found but much about their function is still unknown. By using a novel frameshifting system to select for tRNA modification mutants, new mutations were isolated and subsequently analyzed. This thesis examines the synthesis and function of a subset of tRNA modifications that have a sulfur (thio) -group as part of the modification. The isc operon encodes for proteins synthesizing iron sulfur centers ([Fe-S]) that are a part of the active site of many key enzymes in the cell and the thiolated nucleosides are dependant on a functional iron sulfur gene (iscS) for their synthesis. By studying thiolated tRNA it is not only possible to learn more about the synthesis of the modifications themselves, but also about the synthesis of [Fe-S] clusters. Based on an analysis of mutations in three of the isc operon genes (iscS, iscU, and iscA), a two-model pathway is proposed for the synthesis of Salmonella enterica Serovar Typhimurium thiolated tRNA modifications. The interactions of IscS with other proteins in the tRNA modification thiolation pathways suggest a more complex sulfur relay than had previously been envisioned. Some of the specificities and the effect of an iscA mutant on the levels of tRNA modifications lead to an examination of the role of IscA in [Fe-S] formation and its importance for tRNA modifications.

De senaste åren har utsläppsreglerna för sjöfarten blivit allt hårdare och under de kommande åren skärps de ännu mer. För att svaveldirektiven för sjöfarten ska fungera effektivt så krävs det också att de efterlevs. Syftet med den här studien var därför att undersöka hur länderna i Europeiska SECA områdena agerar och kommer att agera i framtiden för att se till att svaveldirektiven efterlevs. Studien syftar också till att undersöka hur efterlevnadskontroller genomförs, samt se om länderna har infört sanktioner mot överträdelser och vad dessa innebär. För att få svar på detta studerades lagar och förordningar, men framförallt skickades frågeformulär ut till de ansvariga myndigheterna i flera olika länder kring SECA områdena. Slutsatsen av det här arbetet är att samtliga länder anser att efterlevnadskontroll sker i tillräcklig omfattning och alla länder använder sig av samma metod. I Sverige pågår utveckling av en optisk mätmetod för att mäta svavelhalt i avgaserna ifrån luften, men än är metoden inte tillräckligt säker för att kunna användas. Det framkom också att i flera länder anses det på grund av flera faktorer vara svårt att fälla någon ifall de bryter mot gällande svavelförordningar, därför anses det också finnas en risk för överträdelser. Detta trots att det i andra länder faktiskt sker ingripande mot överträdelser och samtliga länder använder sig av samma metoder för efterlevnadskontroll. Det saknas i dagsläget även sanktioner mot överträdelser i flera länder.

<p>Natural and constructed clay liners are routinely used to contain waste and wastewater. The impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at pH > 1.0. The impact of sulfuric acid leachate characterized by pH < 1.0, including potentially negative pH values on the geochemistry and mineralogy of clays is, however, not clear.</p> <p>To address this deficiency a series of batch and diffusion cell studies, investigating the geochemical and mineralogical impacts of H₂SO₄ solutions (pH 5.0 to -3.0), were conducted on three mineralogically distinct clays (Kc, Km, and BK). Batch testing was conducted at seven pH treatments (5.0, 3.0, 1.0, 0.0, -1.0, -2.0 and -3.0) using standardized sulfuric acid solutions for four exposure periods (14, 90, 180, and 365 d). Aqueous geochemical, XRD, and Si and Al XANES analyses showed: increased dissolution of aluminosilicates with decreasing pH and increasing exposure period; preferential dissolution of aluminosilicate Al-octahedral layers relative to Si-tetrahedral layers; formation of an amorphous silica-like phase that was confined to the surface layer of the altered clay samples at pH ⤠0.0 and t ⥠90 d; and precipitation of anhydrite and a Al-SO₄-rich phase (pH ⤠-1.0, t ⥠90 d).</p> <p>The diffusive transport of H₂SO₄ (pH =1.0, -1.0, and -3.0) through the Kc and Km clays for 216 d was examined using single reservoir, constant concentration, diffusion cells. The diffusive transport of H⁺ within the cells was modeled using 1-D transport models that assumed no absorption, linear absorption, and non-linear absorption of H⁺. The absorption isotherms were calculated from the pH 5.0, 3.0, and 1.0 batch experiment results, which were assumed representative of H⁺ absorption at pH < 1.0. However, model results indicated that the batch test results can not account for the observed H⁺ consumption in all cells and greatly underestimate the amount of H⁺ consumption in the pH -1.0 and -3.0. In the Kc and Km diffusion cells, above-background Ca, Al, Fe, and Si aqueous concentrations were associated with depth intervals characterized by decreased pH values. Respective peak concentrations of 325, 403, 176, 11.7, and 1.38 x 10³ μmol g^-1 (Kc) and 32.4, 426, 199, 7.2, and 1.22 x 10³ μmol g^-1 (Km) were measured in the pH -3.0 cells. XRD results showed that the elevated concentrations corresponded to the loss of carbonates and montmorillonite peaks and decreased peak intensities for illite and kaolinite in depth intervals with pH ⤠1.0, in the Kc and Km pH -1.0 and -3.0 cells.</p> <p>The combined results of these studies indicated that the long-term diffusion of H₂SO₄ through clays at pH < 1.0 will result in a large amount of primary phase dissolution; however, this will be accompanied by precipitation of soluble Ca and Al sulfate salts and amorphous silica, especially at pH ⤠0.0. Additionally, the presence of even a small amount of carbonate will serve to greatly buffer the diffusive transport of H₂SO₄ through clays, even at a source pH of -3.0.</p>

This thesis was devised as a fundamental study of the Li-S system by the use of 7Li Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), X-ray Absorption Near-Edge Structure (XANES), and Non-Resonant Inelastic X-ray Scattering (NRIXS). The first part of this thesis is dedicated to the synthesis of solid state linear chain polysulfides in order to use them as reference compounds in the following experiments. 7Li NMR shows that Li2S and Li2S6 exhibit single but different Li environments, while the others stoichiometry targeted consist of a mixture of them. This is the first report of a stable solid-phase intermediate between elemental sulfur (α-S8) and Li2S. The second part of this thesis is based on operando XANES measurements made in the Argonne Photon Source (APS). Linear combination fit (LCF) analyses are performed to interpret the data; and, noticeably, the distinction between short-chain and long-chain polysulfides can be made due to the use of proper reference materials. The results reveal the first detailed observation of typical sulfur redox chemistry upon cycling, showing how sulfur fraction (under-utilization) and sulfide precipitation impact capacity. It also gives new insights into the differences between the charge and discharge mechanisms, resulting in the hysteresis of the cycling profile. Heat-treated PCNS/S exhibits a particular electrochemical signature, which has never explained. Operando XANES measurements at the sulfur K-edge are performed on heat-treated PCNS. Noticeably, the difference in the XANES signatures of the pristine and the recharged state shows the irreversible process that occurs during the first discharges. At last, electrolytes are investigated by the compilation of quantitative physico-chemical parameters on novel class of solvents that are glymes with non-polar groups and acetonitrile (ACN) complexed with LiTFSI. (ACN)2:LiTFSI attracts particular attention because of the particularly low Li2Sn solubility and. Its good electrochemical performance when mixed with 50 vol% HFE. Operando XANES proves the formation of polysulfides in this electrolyte, and the low energy feature evolution shows a more progressive mechanism involved in this electrolyte, which could be linked to the particularly low Li2Sn solubility.

Anaerobic digestion is a common process for treatment of wastewater sludge from municipal sewage systems. Volatile sulfur compounds, including volatile organic sulfur compounds (VOSCs) and hydrogen sulfide, have been reported as the most odorous compounds in digestion emissions and impurities which can damage facilities for generation, transportation, storage, and utilization of biogas. There has been no comprehensive study on biological generation and degradation kinetics of VOSC or modeling VOSC behaviors through anaerobic sludge digestion. The goal of the present study was to establish a model for VOSC conversions in anaerobic sludge digestion which could facilitate quantitative analysis of VOSC emissions in anaerobic digestion. VOSCs and methionine were employed in dosed batch tests. VOSC conversion processes in anaerobic methionine digestion have been identified. The kinetics for the identified VOSC degradation and conversion processes were determined at 35 and 55 °C respectively. Mixed-second order kinetics were found to best fit the conversion processes. A model was established based on the identified processes and estimated kinetic constants. To extend the model to VOSC release in anaerobic sludge digestion, mesophilic and thermophilic incubations were conducted with four different sludge samples. The effects of temperature and sludge source on VOSC release patterns were assessed. It was found that an unidentified DMS generation mechanism was triggered in the mesophilic incubation of activated sludge in which iron was dosed. To apply the model which was established based on methionine degradation in sludge digestion, hydrolysis of particulate materials was incorporated. The model simulations for VOSC behavior in thermophilic batch incubation were able to represent the observed VOSC releases. However, the simulations could not well fit the observed VOSC release at 35 ° because the model did not include the unidentified DMS generation mechanism. Application of the model to bench-scale digesters was lack-of-fit. It may have been due to imprecise estimation of the degradable sulfur in the feed sludge. In addition, in the batch tests and digester operation the ratios of the raw and digested sludge were different. This might have resulted in different concentrations of the microorganisms which mediated biotransformations and hence resulted in different kinetic constants.

<p>Natural and constructed clay liners are routinely used to contain waste and wastewater. The impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at pH > 1.0. The impact of sulfuric acid leachate characterized by pH < 1.0, including potentially negative pH values on the geochemistry and mineralogy of clays is, however, not clear.</p> <p>To address this deficiency a series of batch and diffusion cell studies, investigating the geochemical and mineralogical impacts of H₂SO₄ solutions (pH 5.0 to -3.0), were conducted on three mineralogically distinct clays (Kc, Km, and BK). Batch testing was conducted at seven pH treatments (5.0, 3.0, 1.0, 0.0, -1.0, -2.0 and -3.0) using standardized sulfuric acid solutions for four exposure periods (14, 90, 180, and 365 d). Aqueous geochemical, XRD, and Si and Al XANES analyses showed: increased dissolution of aluminosilicates with decreasing pH and increasing exposure period; preferential dissolution of aluminosilicate Al-octahedral layers relative to Si-tetrahedral layers; formation of an amorphous silica-like phase that was confined to the surface layer of the altered clay samples at pH ⤠0.0 and t ⥠90 d; and precipitation of anhydrite and a Al-SO₄-rich phase (pH ⤠-1.0, t ⥠90 d).</p> <p>The diffusive transport of H₂SO₄ (pH =1.0, -1.0, and -3.0) through the Kc and Km clays for 216 d was examined using single reservoir, constant concentration, diffusion cells. The diffusive transport of H⁺ within the cells was modeled using 1-D transport models that assumed no absorption, linear absorption, and non-linear absorption of H⁺. The absorption isotherms were calculated from the pH 5.0, 3.0, and 1.0 batch experiment results, which were assumed representative of H⁺ absorption at pH < 1.0. However, model results indicated that the batch test results can not account for the observed H⁺ consumption in all cells and greatly underestimate the amount of H⁺ consumption in the pH -1.0 and -3.0. In the Kc and Km diffusion cells, above-background Ca, Al, Fe, and Si aqueous concentrations were associated with depth intervals characterized by decreased pH values. Respective peak concentrations of 325, 403, 176, 11.7, and 1.38 x 10³ μmol g^-1 (Kc) and 32.4, 426, 199, 7.2, and 1.22 x 10³ μmol g^-1 (Km) were measured in the pH -3.0 cells. XRD results showed that the elevated concentrations corresponded to the loss of carbonates and montmorillonite peaks and decreased peak intensities for illite and kaolinite in depth intervals with pH ⤠1.0, in the Kc and Km pH -1.0 and -3.0 cells.</p> <p>The combined results of these studies indicated that the long-term diffusion of H₂SO₄ through clays at pH < 1.0 will result in a large amount of primary phase dissolution; however, this will be accompanied by precipitation of soluble Ca and Al sulfate salts and amorphous silica, especially at pH ⤠0.0. Additionally, the presence of even a small amount of carbonate will serve to greatly buffer the diffusive transport of H₂SO₄ through clays, even at a source pH of -3.0.</p>

The purpose of the present study was to determine olfactory detection thresholds in human subjects for a set of six sulfur-containing odorants which are known to be components of mammalian predator odors. Using a threealternative ascending staircase procedure, the olfactory sensitivity of 12 healthy adult human subjects, 6 males and 6 females was assessed with 2-propylthietane, 2,2-dimethylthietane, 3-mercapto-3-methylbutan-1-ol, 3-mercapto-3- methylbutyl formate, 3-methyl-1-butanethiol, and methyl-2-phenylethyl sulfide. The results showed that A) all six predator odorants were detected at concentrations below 1 ppb (parts per billion), and one of them (3-mercapto-3-methylbutyl formate) even at a concentration below 1 ppt (parts per trillion), B) structurally similar odorants yielded significantly different threshold values, and C) no significant sex differences were found in olfactory sensitivity with any of the six odorants. The findings obtained from the present study show that human subjects were not generally less sensitive to the predator odorants tested here compared to spider monkeys despite having a markedly lower number of olfactory receptor types. Further, they suggest that humans may be more sensitive to predator odorants compared to a variety of non-predator odorants. One possible explanation for the high olfactory sensitivity observed here is the fact that sulfur compounds typically can be detected at low concentrations. An alternative explanation derives from an evolutionary perspective as our human ancestors were a potential prey of large carnivores and  thus a high olfactory sensitivity for predator odors should be adaptive for humans.

No description available.