The steps involved in plant reductive assimilation of sulphate to sulphide for incorporation into cysteine are not clear. The aim of the project described in this thesis was the isolation of genes encoding sulphate assimilation enzymes which will provide molecular tools for unravelling this key metabolic pathway. Functional complementation of the Escherichia coli cysteine auxotrophic strain JM15 (serine acetyltransferase deficient) using an Arabidopsis thaliana cDNA library in the expression vector YES resulted in the isolation of at least three members of an A. thaliana multigene family encoding serine acetyltransferase. Characterisation of one clone, Sat-1, showed that it conferred serine acetyltransferase activity (with apparent KM for substrates acetyl CoA and L-serine of 0.043 and 3.47 mM, respectively) on strain JM15. The 1515 bp full-length cDNA encodes a deduced protein of 391 amino acids, SAT-1, that has significant identity with bacterial and plant serine acetyltransferases, and that contains a putative N-terminal organellar targeting peptide. Southern hybridisation indicated that Sat-1 is present as a single copy in A. thaliana, while northern analysis revealed a single message of 1.5 kb. Using the A. thaliana cDNA library in the expression vector YES, cDNAs encoding a novel putative "APS reductase" were obtained by functional complementation of E. coli cysteine auxotrophic strains JM81A (adenosine 5'-phosphosulphate [APS] kinase deficient) and JM96 (3'-phosphoadenosine-5'-phosphosulphate [PAPS] reductase deficient). Retransformation of three clones (Papsr-19, Papsr-26 and Papsr-43) encoding different putative APS kinase isoforms into strain JM96 conferred low PAPS reductase activity on the mutant, although this activity was thioredoxin-independent unlike wild-type bacterial activity. The putative APS reductase has a PAPS reductase-like C-terminal domain, but further analysis demonstrated that the enzyme accepts APS in preference to PAPS as substrate and has a thioredoxin-like C-terminal domain. Isolation and characterisation of these genes invites a new hypothesis for plant reductive sulphate assimilation and provides direction for future research.

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Made available in DSpace on 2014-06-11T19:29:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-04-12Bitstream added on 2014-06-13T19:17:24Z : No. of bitstreams: 1 modenesjunior_ma_me_araiq.pdf: 555705 bytes, checksum: 92da4dab4fc7933ad296384b8fb75eed (MD5) / O enxofre presente no biodiesel é um contaminante que mesmo em baixas quantidades está associado ao mau funcionamento de conversores catalíticos, emissão de gases e materiais particulados, e a corrosão de partes do motor. Neste trabalho, foi desenvolvido um eletrodo de amálgama sólido de prata (AgSAE) para determinação de enxofre em microemulsões de biodiesel. A caracterização eletroquímica do AgSAE foi realizada em solução eletrólito tampão amônia/amônio devido as melhores condições de análise do enxofre ser em meio alcalino. Através dos experimentos de voltametria cíclica de redissolução adsortiva, sugere-se que o processo redox envolvido se distância da reversibilidade possivelmente devido a uma reação química acoplada. Antes de cada medida foi estipulado um tempo de acúmulo de 120 segundos, devido ao processo adsortivo que ocorre entre o sulfeto em solução e a superfície do AgSAE. Essa característica adsortiva permitiu alcançar um LD da ordem de 10-8 mol L-1 em meio aquoso para as técnica de LSAdSV, SWAdSV e DPAdSV. Um diagrama de fase ternário foi construído a fim de estipular a região onde se forma uma microemulsão caracterizando a sua composição. Avaliou-se o comportamento eletroquímico do sulfeto em dez diferentes composições, observando que em apenas quatro há redução. A microemulsão que apresentou melhor resposta em termos de intensidade de corrente de pico catódica e resolução foi 25% de solução tampão (pH 9,0), 5% de biodiesel e 70% de propanol. A validação do método foi realizada em um material de referência certificado de biodiesel de soja, os LD e LQ obtidos para LSAdSV, SWAdSV e DPAdSV foram da ordem de 10-7 mol L-1. O estudo de recuperação apresentou valores próximos de 100%. A metodologia foi aplicada na determinação de enxofre em... / The sulfur present in biodiesel is a contaminant that even at low quantities is associated with the malfunctioning of catalytic converters, gaseous and particulate materials, and corrosion of engine parts. In this work, we developed a solid amalgam electrode silver (AgSAE) for determination of sulfur in biodiesel microemulsions. The electrochemical characterization was performed on the AgSAE electrolyte solution buffered ammonia/ammonium due to better analysis of the sulfur being in an alkaline medium, as the pH study shows conducted. Through the adsorptive stripping cyclic voltammetry experiments, it is suggested that the redox process involved becomes far from reversibility possibly due to a chemical reaction coupled. Before each measurement one was fixed accumulation time of 120 seconds, due to adsorptive process that occurs between the sulfite solution and the surface of AgSAE. This characteristic achieves an adsorptive LD of the order of 10-8 mol L-1 in aqueous medium. A ternary phase diagram was constructed to stipulate the region where it forms a microemulsion characterizing its composition. We evaluated the electrochemical behavior of sulfate in ten different compositions, noting that there are only four in reduction. The microemulsion showed better response in terms of intensity and cathodic peak current resolution was 25% of buffer (pH 9,0), 5% biodiesel and 70% propanol. The method validation was performed in a certified reference material of biodiesel from soybeans, LOD and LOQ obtained for LSAdSV, and SWAdSV DPAdSV were the order of 10-7 mol L-1, and the study showed recovery values close to 100%. The methodology was applied in the determination of sulfur in biodiesel sample, the sulfur content in the samples was... (Complete abstract click electronic access below)

Orientador: José Anchieta Gomes Neto / Banca: Joaquim de Araújo Nóbrega / Banca: Marcia Andréia Mesquita Silva da Veiga / Resumo: Foi desenvolvido e validado um método para determinação de enxofre em amostras agroindustriais por espectrometria de absorção molecular em chama com fonte contínua e alta resolução (HR-CS MAS), por meio da medida da absorção molecular do monosulfeto de carbono (CS) em 257,595; 257,958 e 258,056 nm e do hidreto de enxofre (SH) em 323,658; 324,064 e 327,990 nm, associados aos espectros com que possuem estruturas rotacionais finas comparáveis a linhas atômicas. Em chama acetileno-ar, a altura de observação ótima foi de 7 mm e razão da vazão dos gases para CS e SH de 0,211 e 0,231 com 110 L h-1 de acetileno. Para chama a acetileno-N2O, a altura ótima de observação para todas as linhas de CS foi 5 mm e para SH 12 mm em 323,658 nm e 6 mm para 324,064 nm e 327,990 nm. A condição ótima de chama foi de 250 L h-1 de acetileno (razão acetileno/ar 0,617) para CS e variável entre 190-220 L h-1 (razão 0,467-0,541) para as três linhas de SH. A natureza dos reagentes H2SO4 e (NH4)2SO4 no preparo dos padrões de enxofre foi avaliada com relação a produção das espécies CS e SH, apresentando influência insignificante. A influência da medida da absorbância integrada no comprimento de onda foi avaliada do pixel central (CP) até 7 pixels (CP±3), observando melhoria de sensibilidade com o aumento de pixels e correspondente diminuição da precisão. As principais figuras de mérito foram estabelecidas. Intervalos lineares entre 100-5000 mg L-1 S (CS) e 2000-40000 mg L-1 S (SH), limites de detecção entre 15,1-22,4 mg L-1 S (CS) e 955,8-2558,3 mg L-1 S (SH) e desvios padrão relativos inferiores a 5,7% (CS) e 8,5% (SH), foram obtidos utilizandose o (NH4)2SO4 na calibração e medidas para 1 pixel (CP). As linhas de CS se mostraram livres de interferências espectrais, enquanto que para SH... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: A method was developed and validated for sulfur determination in agroindustrial samples by high-resolution continuum source molecular absorption spectrometry in flame (HR-CS MAS), using the molecular absorption of the carbon monosulfide (CS) at 257.595; 257.958 and 258.056 nm and for sulfur hydride (SH) at 323.658; 324.064 and 327.990 nm, associated to sharp rotational structures comparable to atomic lines. In acetylene-air flame, the optimum burner height was of 7 mm and gases flow ratio for CS and SH of 0.211 and 0.231 with 110 L h-1 of acetylene. For acetylene-N2O flame, the optimum burner height for all CS lines was 5 mm and 12 mm at 323.658 nm and 6 mm for 324.064 and 327.990 nm for SH. The optimum flame condition was 250 L h-1 of acetylene (acetylene/air ratio 0.617) for CS and variable between 190-220 L h-1 (ratio 0.467-0.541) for SH. The characteristics of the reagents H2SO4 and (NH4)2SO4 in the preparation of sulfur standard solutions were evaluated to product the CS and SH species, and their influence were insignificant. The influence of wavelength integrated absorbance was evaluated measuring the central pixel (CP) up to 7 pixels (CP±3). This procedure improved the sensibility but reduced the precision when the number of pixels evaluated was increased. The main figures of merit were established. Linear dynamic ranges between 100-5000 mg L-1 S (CS) and 2000-40000 mg L-1 S (SH), limits of detection between 15.1-22.4 mg L-1 S (CS) e 955.8-2558.3 mg L-1 S (SH) and relative standard deviations less than 5.7% (CS) e 8.5% (SH), were obtained using (NH4)2SO4 in calibration and 1 pixel (CP) evaluation. The CS lines presented free of spectral interferences, but for SH at 323.658 nm in presence of some elements like Ca, Cu, Fe, Mn, P, Si, Zn, this interferences were considerable. The performance of fungicide samples prepare in closed vessel microwave-assisted acid-digestion system was... (Complete abstract click electronic access below) / Mestre

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No description available.

The literature on acid rain provides evidence that large (>5 μm) alkaline particles in the atmosphere, which derived from surface soil, play an important role in mitigating the effect of acid rain. Not only do they help to neutralize acidity but they also are a source of nutrients to the terrestrial and aquatic environments. While ground-up limestone has been added to the forests and the lakes of regions deficient in alkalinity, this mode of application is prohibitively expensive. An economic alternative method of distribution would utilize the advective and turbulent diffusive processes within the troposhere in order to supply limestone particles of approximately 10 μm diameter to the terrestrial and the aquatic environments. However, while the particles are being transported through the atmosphere they will also interact to some degree with the atmospheric pollutants (SO₂, NOx, photochemical oxidants, etc.). While the two-phase chemical interaction of water droplets and gaseous pollutants has been extensively studied, little is known about the reaction between limestone particles and gaseous pollutants under ambient conditions. As a first step in understanding these processes laboratory experiments were conducted in order to measure the rate of the heterogeneous reaction between limestone particles and sulphur dioxide (SO₂) gas in clean humid air. Calcitic limestone (200-270 mesh Tyler) from Texada Island, B.C., was reacted with 30-80 ppb SO₂ at room temperature (17-22°C) over a humidity range of 70-100%. Ancillary experiments were also conducted to determine the maximum dissolution rate of these limestone particles in an acidic, aqueous environment. The overall rate (r) for the SO₂ reaction with Texada Island limestone was determined to be approximately first-order with respect to the SO₂ concentration and to be strongly dependent upon the relative humidity: [Formula Omitted] Limited experiments with precipitated dolomite indicated that it reacts with SO₂ somewhat faster than does the calcitic limestone. A study of the individual mass transfer and reaction processes indicated that the rate limiting step for the overall reaction was the aqueous phase oxidation of the bisulphite ion. Limestone dissolution (determined experimentally), and estimated gas and aqueous phase diffusive processes, were not rate limiting. In a clean humid atmosphere, free of photochemical oxidants, a limestone aerosol would react very slowly with SO₂ (SO₂ removal rate of about 3x10⁻³% per hour). However, in a humid polluted atmosphere rich in photochemical oxidants, similar to that responsible for acid fog and acid rain, the aqueous phase oxidation of dissolved SO₂ is not expected to be rate limiting. Under such conditions bisulphite dissociation: [Formula Omitted] Therefore in humid, polluted atmospheres limestone aerosol will act as a "sink." for SO₂ for soluble photochemical oxidants, and probably also for HNO₃ (nitric acid). Since the oxidants are considered to be phytotoxic while the other pollutants are responsible for creating acid rain we conclude that the deployment of a limestone aerosol may have a positive impact on the atmospheric environment, besides being beneficial to the aquatic and terrestrial environments. It is strongly recommended that further research be done in this area in order to better quantify the rate processes, and perhaps also to identify practical methods for increasing the atmospheric concentration of alkaline aerosol in those geographic regions which are deficient. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The oxidation of sulfidic mine tailings and subsequent acid and salt accumulation results in acid drainage and poses a severe reclamation problem. The objectives of this study were to quantify the processes leading to these problems and propose feasible solutions. Characterization of 120 sulfidic surface samples, collected from the Sullivan mine tailings ponds, was carried out for dominant physiological groups of microorganisms, sulfur forms, water and acid extractable cations qualitative physical characteristics, pH, conductivity, organic matter and moisture content. Acid tolerant fungi and iron, sulfur and acid tolerant heterotrophic bacteria were enumerated by the most-probable-number technique. Iron bacteria (Thiobacillus ferrooxidans) occurred often and can be implicated as the cause of Fe⁺² oxidation in samples not buffered at near neutral pH values by bases. Sulfur bacteria (thiobacillus species were commonly found and classified as T. thioparus, T. neapolitanus, or T. thiooxidans. A pH-dependent succession of these thiobacilli occurs in the tailings. Acid tolerant heterotrophic bacteria populations were highly correlated with those of the thiobacilli suggesting a symbiotic relationship, particularly in samples with pH >2.5. The numbers of acid tolerant fungi tended to increase proportionally with oxidation, suggesting increased colonization with time. Chemical analysis for major sulfur forms indicates that iron mono- sulfide oxidation is rapid resulting in the formation and persistence of Fe⁺³ (as amorphous Fe oxyhydroxides in mineralogical analysis) and elemental sulfur. Some accumulation of other oxidizable sulfur forms is indicated by the high levels of total oxidizable sulfur. A portion of this sulfur not accounted for by CS₂ extractable elemental sulfur may be present as amorphous elemental sulfur. The oxidation of elemental sulfur and other sulfur intermediates to sulfate is pronounced in the surface 0-2 cm based on the laboratory oxidation of a bulk tailings sample. Mineralogical analysis shows that gypsum is the predominant sulfate containing mineral at basic to slightly acid pH values. Under moderately to strongly acid conditions, jarosite type minerals occurred in high amounts. Mineralogical analysis also showed that the decomposition of basic minerals and chlorite occurred initially, with the dissolution of micas and K-feldspars being less rapid. The absence of detectable kaolinite or other Al silicate residues indicates that alumino-silicate dissolution may be congruent. Mineralogical results showing dissolution of minerals is supported by general increases in water extractable cations (including Fe, Al, Ca, Mg, K and Na) and decreases in these same acid extractable cations as weathering proceeds. These processes ultimately result in a highly oxidized surface in which acid production is slow. It is suggested that erosional processes be inhibited where an oxidized surface exists to prevent the exposure of reduced tailings beneath the surface. Furthermore, steps should be taken to minimize the addition of fresh tailings over oxidized surfaces. The use of correlations between the qualitative physical characteristics texture, structure and color, obtained in this study, can serve as guides to estimating the degree of tailings oxidation in the field. If more precision is required, the colorimetric determination of CS₂ extractable elemental sulfur is suggested, particularly on the more oxidized samples. Proper management of the tailings to maintain present oxidized surfaces should reduce the acid drainage considerably until reclamation is undertaken. The quantification of the changes in tailings properties with increases in weathering can be useful in evaluating reclamation strategies. / Land and Food Systems, Faculty of / Graduate

A high power pulsed CO_2 laser was used to induce reactions in gas mixtures containing either N_2F_4 or SF_6. The rate of laser induced dissociation of N_2F_4 to NF_2 was as much as 1000 times faster than the thermal rate, and the rate law was of lower order than the thermal, bimolecular rate law. Explosion threshold and induction time data were obtained for butene stabilized mixtures of N_2F_4 and H_2. HF laser gain was observed during the first few microseconds of CO_2 laser pulse, but it was strongly quenched by the explosion. The laser driven reaction of SF_6 with H_2 also exhibited HF laser gain at early times and laser energy threshold for reaction. All of the laser induced reactions studied occurred at rates that were faster than the rates of thermal reaction. This accelerated reaction rate was attributed to nonthermal vibrational excitation of the reactants. A computer model of the SF_6-H_2 electrical discharge chemical laser was employed to gain a better understanding of the fundamental processes that occur in this laser. Good agreement with experimental results were obtained, and several suggestions for further study were made.

No description available.