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Iron sulfur [Fe-S] proteins are essential components of many major biological processes including electron transport, respiration, photosynthesis, hormone biosynthesis, and environmental sensing. The process of [Fe-S] cluster assembly in living cells is a controlled mechanism that is highly conserved across all kingdoms. Considerable progress has been made in deciphering this mechanism in bacteria, yeast, and mammals. The key players are the NifS/IscS/SufS proteins, which act as the sulfur donor, and the NifU/IscU/SufU proteins, which serve as a scaffold that binds Fe and upon which the cluster is assembled. Additional proteins are involved in the maturation and transport of the clusters. In eukaryotes there is redundancy in the proteins involved in this mechanism and the process is compartmentalized. Not much is known about the [Fe-S] cluster assembly mechanism in plants. In addition to the redundancy and compartmentalization seen in this machinery in eukaryotes, plants present a further challenge by offering chloroplasts as an additional site for [Fe-S] cluster assembly. The objective of this project has been to characterize Arabidopsis AtNFS1 and AtISU1-3, which show high homology to NifS/IscS and NifU/IscU, respectively, and are hypothesized to be key players in [Fe-S] cluster biogenesis in plants. Subcellular localization results of the AtNFS1 and AtISU1-3 proteins fused to GFP from this study are consistent with the presence of dual machinery in plants, with both mitochondria and chloroplasts as sites for [Fe-S] cluster assembly. Furthermore, observations also showed that AtISU2 mRNA may be unstable. The results of these experiments, together with promoter analysis described in this dissertation using GUS fusions suggested that the genes encoding the AtISU scaffold proteins are regulated at the transcriptional and probably also at the posttranscriptional level. Gene silencing experiments performed in this dissertation research using antisense and RNAi constructs indicated that these genes have the potential to impact respiration, photosynthesis, phytohormone biosynthesis, and environmental sensing, diverse processes that rely on [Fe-S] proteins. These observations, together with previous in vitro evidence that AtNFS1 and AtISU1 can participate in [Fe-S] cluster assembly, provide strong evidence that these proteins are part of two distinct cluster assembly systems that function in different subcellular locations and perhaps under different environmental conditions. Information gathered here has made it possible to begin developing a detailed model of [Fe-S] cluster biogenesis in plants. / Ph. D.

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One of the environmental concerns associated with mining waste is the contamination of soil. This study addresses the decontamination of soil, particularly of Co and Ni using Berkheya coddii (B. coddii). B. coddii is a hyperaccumulater plant that is able to decontaminate Co and Ni from the contaminated land. The use of B. coddii to decontaminate soil or waste must be based on a cognizance of the complicated, integrated effects of pollutant sources and soil-plant variables. Phytoextraction pot trials using B. coddii were carried out under green house condition, with controlled watering. A contaminated metallurgical waste residue known as Rustenburg Base Mine Refineries waste (RBMR waste soil) collected from Rustenburg while a serpentine (native) soil (N soil) where B. coddii grows naturally was collected from Mpumalanga. The experiment involved the addition of sulfur doses to both soils in order to test whether acidification and higher sulfur availability could enhance the uptake of both Co and Ni by B. coddii. The results indicate that the addition of sulfur from 2.0 to 8.0 g per kilogram decreased pH in both substrates. RBMR waste soil pH was found to have decreased from 7.8 to 7.4 while the N soil pH was found to have decreased from 6.4 to 4.7. The reduction oxidation potential (redox potential) in both substrates was observed to have decreased along with the increase in sulfur dosage. The mean redox potential for RBMR waste soil was found to be 350 mV and 506 mV for the N soil after the addition of sulfur. Conductivity increased along with the increase in sulfur dosage in both substrates. The mean conductivity for the N soil was found to be 961 μS/cm while that of the RBMR waste soil was found to be 1453 μS/cm after the addition of sulfur. The decrease in soil pH was significant (p = 0.00115) in the N soil than RBMR waste soil. Despite the increase in sulfur dosage and decrease in soil pH in both substrates, B. coddii observed growing. Although it was evident that B. coddii is able to grow in the RBMR waste soil, it was observed that the RBMR waste soil limits the root depth of the B. coddii, reducing chances for the roots to penetrate into the ground especially when dry. The RBMR waste soil becomes more compacted than the N soil when dry. It is therefore crucial to ensure that there is enough moisture to allow for the B. coddii being able to survive effectively in the RBMR waste soil. B. coddii plant height in the RBMR waste soil after four months was observed to be in the range of 190 to 200 mm tall. This was found to be less than the height observed for the B. coddii planted in the N soil, which was in the range of 350 to 400 mm. Nonetheless, plants grown in both substrates were able to absorb Ni and Co into their tissues. More Co and Ni were found to have accumulated into the leaf tissues than in other parts of the plant. This could be an advantage since one would harvest only the leaf part or the canopy (shoots) and allow B. coddii to resprout in order to continue taking up more Co and Ni from the same waste substrate to remediation levels that could be stipulated by Government as desirable for the ecosystem and the protection of human health. Although the accumulated Ni and Co can be recovered from biomass, this alone might not provide sufficient economic justification for phytoextraction due to the low concentrations that could be recovered. B. coddii was found to absorb higher concentrations of Co and Ni from the N soil than from the RBMR waste soil. However, the results found in this study may not be conclusive. This could be due to many variables that could control metal uptake which were not investigated. These include mycorrhizal fungi and metal forms in the soil. Moreover, this study was performed in a green house and not in the outdoor environment. Ni is generally toxic to most plants, hyperaccumulators (i.e. B.coddii) contain elements that nullify the toxic effect of nickel, and in this case the accumulated nickel is bound to malate to form a harmless nickel complex which could be absorbed by the plants as nutrients.

Production of volatile sulfur compounds in cheese is associated with desirable flavors. The direct source of these compounds has been assumed to arise from the metabolism of methionine and cysteine. However, the methionine concentration in cheese rises above the amount found in casein during aging, suggesting that alternative sulfur sources are present in milk. This led us to hypothesize that lactococci may acquire sulfur from the inorganic sulfur pool of milk, in addition to methionine and cysteine, to generate volatile sulfur compounds during cheese ripening. A turbidimetric method to determine total sulfate content in milk samples was developed. The average sulfate content of milk was determined to be ~49 mg/L ± 2.0 mg/L. The limit of detection of the test was ~2.5 mg/L in Tris buffer and ~10 mg/L in milk. Skim milk samples had significantly higher total sulfate content as compared to whole milk samples. Transport of sulfate by three strains of Lactococcus sp. was studied after we determined that milk had small, but measurable amounts of inorganic sulfate. A decrease in the environmental pH increased sulfate transport. The maximum transport occurred during exponential cellular growth phase. All strains tested had the ability to transport much more sulfate than is native in milk. The last phase of study was to determine the metabolic fate of sulfate. Incorporation of radio-labeled sulfate into cellular protein was studied by two-dimensional gel-electrophoresis of crude cellular lysate followed by auto-radiography. Production of volatile sulfur compounds from inorganic sulfur was determined with analysis of the head space gas with gas chromatography and scintillation counting. The incorporation of radio-labeled sulfur from sulfate was not detected in proteins on two-dimensional gels. Detectable volatile sulfur compounds were found only in the case of gas chromatographic analysis of ML3 head space. However, radio-labeled volatile sulfur was detected in the head space of all the three strains with scintillation counting. This study defined that lactococci can fix inorganic sulfur into volatile sulfur compounds in small amounts.

Lithium-ion batteries are leading the path for the power sources for various portable applications, such as laptops and cellular phones, which is due to their relatively high energy density, stable and long cycle life. However, the cost, safety and toxicity issues are restricting the wider application of early generations of lithium-ion batteries. Recently, cheaper and less toxic cathode materials, such as LiFePO₄ and a wide range of derivatives of LiMn₂O₄, have been successfully developed and commercialized. Furthermore, cathode material candidates, such as LiCoPO₄, which present a high redox potential at approximately 4.8 V versus Li⁺/Li, have received attention and are being investigated. However, the theoretical capacity of all of these materials is below 170 mAh g⁻¹, which cannot fully satisfy the requirements of large scale applications, such as hybrid electric vehicles and electric vehicles. Therefore, alternative high energy density and inexpensive cathode materials are needed to make lithium batteries more practical and economically feasible. Elemental sulfur has a theoretical specific capacity of 1672 mAh g⁻¹, which is higher than that of any other known cathode materials for lithium batteries. Sulfur is of abundance in nature (e.g., sulfur is produced as a by-product of oil extraction, and hundreds of millions of tons have been accumulated at the oil extraction sites) and low cost, and this makes it very promising for the next generation of cathode materials for rechargeable batteries. Despite the mentioned advantages, there are several challenges to make the sulfur cathode suitable for battery use, and the following are the main: (i) sulfur has low conductivity, which leads to low sulfur utilization and poor rate capability in the cathode; (ii) multistep electrochemical reduction processes generate various forms of soluble intermediate lithium polysulfides, which dissolve in the electrolyte, induce the so-called shuttle effect, and cause irreversible loss of sulfur active material over repeat cycles; (iii) volume change of sulfur upon cycling leads to its mechanical rupture and, consequently, rapid degradation of the electrochemical performance. A variety of strategies have been developed to improve the discharge capacity, cyclability, and Coulombic efficiency of the sulfur cathode in Li/S batteries. Among those techniques, preparation of sulfur/carbon and sulfur/conductive polymer composites has received considerable attention. Conductive carbon and polymer additives enhance the electrochemical connectivity between active material particles, thereby enhancing the utilization of sulfur and the reversibility of the system, i.e., improving the cell capacity and cyclability. Incorporation of conductive polymers into the sulfur composites provides a barrier to the diffusion of polysulfides, thus providing noticeable improvement in cyclability and hence electrochemical performance. Among the possible conductive polymers, polypyrrole (PPy) is one of the most promising candidates to prepare electrochemically active sulfur composites because PPy has a high electrical conductivity and a wide electrochemical stability window (0-5 V vs Li/Li⁺). In the first part of this thesis, the preparation of a novel nanostructured S/PPy based composites and investigation of their physical and electrochemical properties as a cathode for lithium secondary batteries are reported. An S/PPy composite with highly developed branched structure was obtained by a one-step ball-milling process without heat-treatment. The material exhibited a high initial discharge capacity of 1320 mAh g⁻¹ at a current density of 100 mA g⁻¹ (0.06 C) and retained about 500 mAh g⁻¹ after 40 cycles. Alternatively, in situ polymerization of the pyrrole monomer on the surface of nano-sulfur particles afforded a core-shell structure composite in which sulfur is a core and PPy is a shell. The composite showed an initial discharge capacity of 1199 mAh g⁻¹ at 0.2 C with capacity retention of 913 mAh g⁻¹ after 50 cycles, and of 437 mAh g⁻¹ at 2.5 C. Further improvement of the electrochemical performance was achieved by introducing multi-walled carbon nanotubes (MWNT), which provide a much more effective path for the electron transport, into the S/PPy composite. A novel S/PPy/MWNT ternary composite with a core-shell nano-tubular structure was developed using a two-step preparation method (in situ polymerization of pyrrole on the MWNT surface followed by mixing of the binary composite with nano-sulfur particles). This ternary composite cathode sustained 961 mAh g⁻¹ of reversible specific discharge capacity after 40 cycles at 0.1 C, and 523 mAh g⁻¹ after 40 cycles at 0.5 C. Yet another structure was prepared exploring the large surface area, superior electronic conductivity, and high mechanical flexibility graphene nanosheet (GNS). By taking advantage of both capillary force driven self-assembly of polypyrrole on graphene nanosheets and adhesion ability of polypyrrole to sulfur, an S/PPy/GNS composite with a dual-layered structure was developed. A very high initial discharge capacity of 1416 mAh g⁻¹ and retained a 642 mAh g⁻¹ reversible capacity after 40 cycles at 0.1 C rate. The electrochemical properties of the graphene loaded composite cathode represent a significant improvement in comparison to that exhibited by both the binary S/PPy and the MWCNT containing ternary composites. In the second part of this thesis, polyacrylonitrile (PAN) was investigated as a candidate to composite with sulfur to prepare high performance cathodes for Li/S battery. Unlike polypyrrole, which, in addition of being a conductive matrix, works as physical barrier for blocking polysulfides, PAN could react with sulfur to form inter- and/or intra-chain disulfide bonds, chemically confining sulfur and polysulfides. In the preliminary tests, PAN was ballmilled with an excess of elemental sulfur and the resulting mixture was heated at temperatures varying from 300°C to 350°C. During this step some H₂S gas was released as a result of the formation of rings with a conjugated π-system between sulfur and polymer backbone. These cyclic structures could ‘trap’ some of the soluble reaction products, improving the utilization of sulfur, as it was observed experimentally: the resulting S/PAN composite demonstrated a high sulfur utilization, large initial capacity, and high Coulombic efficiency. However, the poor electronic conductivity of the S/PAN binary composite compromises the rate capability and sulfur utilization at high C-rates. These issues were addressed by doping the composite with small amounts of components that positively affected the conductivity and reactivity of the cathode. Mg₀.₆Ni₀.₄O prepared by self-propagating high temperature synthesis was used as an additive in the S/PAN composite cathode and considerably improved its morphology stability, chemical uniformity, and electrochemical performance. The nanostructured composite containing Mg₀.₆Ni₀.₄O exhibited less sulfur agglomeration upon cycling, enhanced cathode utilization, improved rate capability, and superior reversibility, with a second cycle discharge capacity of over 1200 mAh g⁻¹, which was retained for over 100 cycles. Alternatively, graphene was used as conductive additive to form an S/PAN/Graphene composite with a well-connected conductive network structure. This ternary composite was prepared by ballmilling followed by low temperature heat treatment. The resulting material exhibited significantly improved rate capability and cycling performance delivering a discharge capacity of 1293 mAh g⁻¹ in the second cycle at 0.1 C. Even at up to 4 C, the cell still achieved a high discharge capacity of 762 mAh g⁻¹. Different approaches for the optimization of sulfur-based composite cathodes are described in this thesis. Experimental results indicate that the proposed methods constitute an important contribution in the development of the high capacity cathode for rechargeable Li/S battery technology. Furthermore, the innovative concept of sulfur/conductive polymer/conductive carbon ternary composites developed in this work could be used to prepare many other analogous composites, such as sulfur/polyaniline/carbon nanotube or sulfur/polythiophene/graphene, which could also lead to the development of new sulfur-based composites for high energy density applications. In particular, exploration of alternative polymeric matrices with high sulfur absorption ability is of importance for the attainment of composites that possess higher loading of sulfur, to increase the specific energy density of the cathode. Note that the material preparation techniques described here have the advantage of being reproducible, simple and inexpensive, compared with most procedures reported in the literature.

This study consisted of laboratory and greenhouse experiments designed to determine the effect of sulfur waste materials on acidulation and other properties of calcareous soils. The laboratory experiment was conducted in the Soils, Water and Engineering Department, University of Arizona, for a period of nine weeks. Laveen soil (containing 6% CaCO₃) was treated with two levels of Morocco rock phosphate (0, 500 ppm P), and two different waste materials of sulfur, Cake S and Foam S, each with three levels (0, 5000, 10000 ppm). Treated soils were incubated for two periods (three and nine weeks) at 27°C and 66% water holding capacity. The design of the experiment was a complete randomized block with 24 treatments and two replications. Data were evaluated by analysis of variance and multiple means comparison tests for soil pH, soluble phosphorus, and sulfate, and regression analysis for the isotherm. Results showed that Foam sulfur had a greater effect as compared with Cake sulfur on soil pH, soluble phosphorus and sulfate and significantly shifted the isotherm to the right. Rock phosphate had no effect on soil pH and sulfate, but tended to decrease soluble phosphorus and shifted the isotherm to the left as compared with the control. The second experiment was conducted in the greenhouse near the Agricultural Sciences Building, University of Arizona, for a period of 32 weeks starting on August 20, 1979. Two calcareous soils, Pima and Laveen, (2% and 6% CaCO₃, respectively) were investigated with three levels of rock phosphate (0, 250, 500 ppm P), and three sources of sulfur (Cake, Foam and pure sulfur) each at two levels (0, 8000 ppm S). Two levels of super phosphate were used as a standard treatment. The chemical treatments were mixed with the soil and transferred to plastic pots and moistened to 70% water holding capacity, then covered with plastic sheets and incubated for eight weeks. Following the incubation, tomatoes were planted and grown for a six week period. Dry weights were measured only in the Pima soil but were eliminated due to poor stand in the Laveen soil. Barley was planted after the tomato harvest. Tomato and barley plants were irrigated with distilled water until the first harvest, after which barley was irrigated with tap water and CaSO₄ saturated to eliminate sulfur deficiency detected prior to the first harvest. The experiment was a complete randomized block design with 36 treatments and three replications. Data for soils and plants were evaluated by analysis of variance, multiple means comparison test, and regression analysis. From the results of this study the conclusions were as follows: (1) Foam sulfur tended to increase soluble P and Zn, lowered soil pH, and shifted the P isotherm to the right in the soil. Plant P and dry weight were increased more by the Foam S than Cake S and pure sulfur. However, Foam S tended to increase soluble salts more than Cake S and pure S. (2) Cake S also caused an increase in soluble P in the soil, reduced soil pH, and increased plant P and dry weight as well, although the effects were less than with Foam S. (3) Rock phosphate plus sulfur resulted in an increase in soluble P after 32 weeks of application. (4) Soils with low CaCO₃ content, higher organic matter content, and higher cation exchange capacity favored increased oxidation of sulfur to sulfate resulting in increased soluble P and lower soil pH. (5) Linear regression analysis of the P sorption isotherm was carried out by plotting the P remaining in the solution (ppm) on the X-axis versis P sorbed by the soil (ppm); a linear power function resulted. By this relationship, any regression equation can be used to evaluate the P status of a soil and the statistical differences between treatments.