No description available.

No description available.

Complex biosynthetic pathways are required for the assembly and insertion of iron-sulfur (Fe-S) cluster cofactors. The four cluster biogenesis systems that have been discovered require at least one ATPase, but generally the function of nucleotide hydrolysis is understudied. In the cytosolic iron sulfur cluster assembly (CIA) system, responsible for delivering [Fe4-S4] cluster cofactors for cytosolic and nuclear enzymes, the assembly scaffold comprises two homologous ATPases, called Nbp35 and Cfd1 in Saccharomyces cerevisiae. Genetic studies have discovered that the ATPase sites are required for scaffold function in vivo, but in vitro studies have failed to reveal why. The ATPase sites of the Nbp35 and Cfd1 contain a conserved P-loop nucleotide-binding protein fold with a deviant Walker A motif. Known metal trafficking P-loop NTPases’ metallochaperone mechanisms rely on both nucleotide binding and hydrolysis to properly assemble and deliver metal cargo. Furthermore, P-loop NTPases with a deviant Walker A motif commonly serve as central regulatory switches whose hydrolysis activity is modulated by small molecule cargos and/or protein partners. Therefore, it is proposed that the role of Nbp35-Cfd1’s ATPase sites is to direct Fe-S cluster movement by regulating protein and metal cargo interactions. The goal of this thesis is to better understand the scaffold reaction cycle by investigating the metallochaperone mechanism through Nbp35-Cfd1’s protein communications with its ATPase sites. To do this, the identification of at least one nucleotide-dependent partner protein must first be discovered. Herein, in vitro methods have been developed to uncover the scaffold’s ATPase site regulation of protein interactions. We describe a qualitative affinity copurification assay and a quantitative analysis for evaluating the dissociation constant and the kcat and Km values for ATP hydrolysis for the scaffold–partner protein complex. Additionally, the execution of these ATPase assays in an anaerobic environment can be applied to study nucleotide hydrolases involved in metallocluster biogenesis. These in vitro methods are applied to Nbp35-Cfd1 and it is discovered that ATP binding and hydrolysis regulates Nbp35-Cfd1 binding with two CIA factors: Dre2, a reductase proposed to assist in Fe-S cluster assembly, and Nar1, an adaptor between the early and late CIA factors. Although reconstitution of the scaffold’s Fe-S clusters results in a two-fold increase in its ATPase activity, the Dre2 and Nar1 ATP hydrolysis stimulation is dampened, demonstrating that both the Fe-S cargo and partner proteins regulate the scaffold’s ATPase reaction cycle. Next, the domains required for binding and ATPase stimulation were identified for Nbp35-Cfd1 with its partner proteins Dre2 and Nar1. The C-terminal Fe-S binding domain of Dre2 is sufficient for ATPase stimulation, while the Nar1 requires both its N- and C-terminal Fe-S binding domains to activate Nbp35-Cfd1’s ATP hydrolysis. The N-terminal Fe-S binding domain of Nbp35 is dispensable for binding and ATPase stimulation of both Dre2 and Nar1. The CIA targeting complex protein Cia1, which binds to Nar1, competes off Nbp35-Cfd1, indicating a shared binding domain. This data both validates and refines the current working model of the CIA system. To test whether the communication between the ATPase and Fe-S cluster binding domains of the CIA scaffold functions in an analogous manner across multiple species, a preliminary analysis was completed for whether Chaetomium thermophilum and Homo sapien Nbp35-Cfd1 exhibit similar ATPase characteristics and partner protein interaction as their S. cerevisiae ortholog. Human and fungal Nbp35-Cfd1 exhibit ATP binding and demonstrate nucleotide-dependent interactions with Dre2 and Nar1, suggesting that these interactions in a similar manner to effectively communicate in the CIA pathway. Overall, our study uncovers striking similarities between the CIA pathway and other systems which exploit a deviant Walker A NTPase to coordinate complex, multiprotein processes. Identification of the scaffold’s partner proteins significantly advances our understanding as to why the Nbp35/MRP-type Fe-S cluster biogenesis proteins are nucleotide hydrolases. This work provides some mechanistic insight into the functions of these proteins and provides a roadmap for how to investigate this large and widely distributed family and other P-loop NTPase metallochaperones. / 2024-09-19T00:00:00Z

The wide applications of energy storage systems in consumer electronics, electric vehicles, and grid storage in the recent decade has created an enormous market globally. The electrochemical flow system has many applications in Li-ion battery recycling and energy storage system design. First, research work on a scalable electrochemical flow system is presented to effectively restore the lithium concentration in end-of-life Li-ion cathode materials. An effective recycling process for end-of-life lithium-ion batteries could relieve the environmental burden and retrieve valuable cathode battery materials. The design is validated in a static configuration with both cathode loose powder and cathode electrode sheet. Materials with comparable electrochemical performance to virgin cathode materials are produced after post heat treatment. Second, research contributions in sulfur-based flow battery systems for long-duration energy storage are presented. Sulfur-based redox flow batteries are promising due to their high theoretical capacity, low cost, and high abundance. The speciation of aqueous sulfur solutions with different nominal concentrations, sulfur concentrations, and pH are studied by Raman spectroscopy. Next, a promising aqueous manganese catholyte to couple with the sulfur anolyte for a full flow battery is investigated. Test protocols and quantification metrics for the catholyte are developed. The stability of the catholyte, including self-discharge rate and precipitation rate, is measured via ex-situ characterizations. The electrochemical performance of the catholyte is investigated and optimized via in-situ experiments. The reaction pathway for the precipitation of catholyte is discussed and several mitigation strategies are proposed. Finally, a semi-solid sodium-sulfur flow battery is developed. The electrochemical performance of the sodium-sulfur battery is studied first in a static configuration at an intermediate temperature (150°C). Then a Na-S semi-solid flow cell is assembled and cycled under the two-aliquots and three-aliquots intermittent flow. / Doctor of Philosophy / The market of energy storage systems has been expanding dramatically in recent years due to their wide applications in portable electronics, electric vehicles, and large-scale grid storage. First, the research on the development of an electrochemical flow system in the Li-ion batteries (LIB) recycling process is presented. The improper disposal of end-of-life LIBs will generate flammable hazardous waste. Recycling spent LIBs could ease the environmental burden and replenish valuable resources such as lithium, cobalt, and nickel, and reduce the cost of battery manufacturing. In this study, an electrochemical flow system is designed to restore the end-of-life cathode materials in LIBs. The design has the potential to scale up and is validated with a static configuration. The recycled materials show comparable electrochemical performance to virgin battery cathode materials. Life cycle analysis shows that the recycling process consumes less energy and is more environmentally friendly. Second, the research contribution in sulfur-based flow battery systems for long-duration energy storage is presented. The aqueous sulfur solutions with different nominal concentrations, sulfur concentrations, and pH are studied by Raman spectroscopy. Next, a promising aqueous manganese catholyte to couple with the sulfur anolyte for a full redox flow battery is investigated. The chemical stability of the catholyte, including self-discharge rate and precipitation rate, is measured via ex-situ characterizations. The electrochemical performance of the catholyte is studied and optimized via in-situ experiments. The reaction mechanisms for the precipitation of aqueous manganese solutions are discussed. Finally, a semi-solid sodium-sulfur (Na-S) flow battery is developed. The electrochemical performance of the sodium-sulfur battery is studied first in a static cell at intermediate temperature. Then a Na-S semi-solid flow cell is demonstrated and cycled under the two-aliquots and three-aliquots intermittent flow.

Developing next generation secondary batteries has attracted much attention in recent years due to the increasing demand of high energy and high power density energy storage for portable electronics, electric vehicles and renewable sources of energy. This dissertation investigates sulfur based advanced electrode materials in Lithium/Sodium batteries. The electrochemical performances of the electrode materials have been enhanced due to their unique nano structures as well as the formation of novel composites. First, a nitrogen-doped graphene nanosheets/sulfur (NGNSs/S) composite was synthesized via a facile chemical reaction deposition. In this composite, NGNSs were employed as a conductive host to entrap S/polysulfides in the cathode part. The NGNSs/S composite delivered an initial discharge capacity of 856.7 mAh g-1 and a reversible capacity of 319.3 mAh g-1 at 0.1C with good recoverable rate capability. Second, NGNS/S nanocomposites, synthesized using chemical reaction-deposition method and low temperature heat treatment, were further studied as active cathode materials for room temperature Na-S batteries. Both high loading composite with 86% gamma-S8 and low loading composite with 25% gamma-S8 have been electrochemically evaluated and compared with both NGNS and S control electrodes. It was found that low loading NGNS/S composite exhibited better electrochemical performance with specific capacity of 110 and 48 mAh g-1 at 0.1C at the 1st and 300th cycle, respectively. The Coulombic efficiency of 100% was obtained at the 300th cycle. Third, high purity rock-salt (RS), zinc-blende (ZB) and wurtzite (WZ) MnS nanocrystals with different morphologies were successfully synthesized via a facile solvothermal method. RS-, ZB- and WZ-MnS electrodes showed the capacities of 232.5 mAh g-1, 287.9 mAh g-1 and 79.8 mAh g-1 at the 600th cycle, respectively. ZB-MnS displayed the best performance in terms of specific capacity and cyclability. Interestingly, MnS electrodes exhibited an unusual phenomenon of capacity increase upon cycling which was ascribed to the decreased cell resistance and enhanced interfacial charge storage. In summary, this dissertation provides investigation of sulfur based electrode materials with sulfur/N-doped graphene composites and MnS nanocrystals. Their electrochemical performances have been evaluated and discussed. The understanding of their reaction mechanisms and electrochemical enhancement could make progress on development of secondary batteries.

Doctor of Philosophy / Department of Animal Sciences and Industry / James S. Drouillard / Four studies evaluated effects of dry distillers grains with solubles (DDGS) containing high S concentrations on feedlot performance, ruminal fermentation, and diet digestibility by finishing cattle. Trial 1 used finishing steers fed diets based on steam-flaked corn (SFC) or dry-rolled corn (DRC), and containing 30% DDGS (DM) with 0.42% S (0.42S) or 0.65% S (0.65S). No interaction (P ≥ 0.15) between dietary S and grain processing occurred, but feeding 0.65S decreased DMI (P < 0.001) and ADG (P = 0.006) by 8.9% and 12.9%, respectively, whereas G:F was unaffected by S concentration (P = 0.25). Steers fed 0.65S had 4.3% lighter HCW (P = 0.006), lower KPH (P = 0.009), and lower yield grades (P = 0.04) than steers fed 0.42S. Concentration of H2S was inversely related (P ≤ 0.01) to ADG (r = -0.58) and DMI (r = -0.67) in cattle fed SFC, and DMI (r = -0.40) in cattle fed DRC. Trial 2 used the same treatments as in the first stud, and investigated ruminal fermentation characteristics and diet digestibility by feedlot cattle. Feeding 0.65S increased ruminal pH (P < 0.05), but decreased total VFA concentrations (P = 0.05). Steers fed 0.65S had greater ruminal NH3 concentrations (P < 0.01) than steers fed 0.42S. The magnitudes of these effects were greater in steers fed DRC than in steers fed SFC (interaction, P < 0.01). Feeding 0.65S yielded greater apparent total tract digestibilities of DM (P = 0.04) and ether extract (P = 0.03). The 3rd study evaluated effects of in vitro S titration (0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6% of DM) in substrates based on ground corn and DDGS (GC-DDGS) or ground corn with urea and soybean meal (GC-SBM). Concentrations of NH3, total VFA, IVDMD, in vitro gas production, and gas composition were unaffected by S (P > 0.05) or by the S × substrate interaction (P > 0.05). Study 4 evaluated cattle feedlot performance when exposed to DDGS containing high S levels, either continuously or intermittently. Treatments were chronic high S (CHS; 0.60% DM), chronic intermediate S (CIS; 0.50% DM), and sporadic intermediate S (SIS; oscillating from 0.40 or 0.60% S DM basis). Steers fed CHS had 11.2 and 6.1% less (P < 0.05) DMI than steers fed CIS and SIS, respectively, but there were no treatment effects on ADG, G:F, or carcass characteristics (P > 0.10). These studies suggest that changes in cattle performance and digestibility associated with high S are primarily attributable to decreased DMI, but infrequent exposure to high levels is no more harmful than continuous exposure.

Call number: LD2668 .T4 1979 P63 / Master of Science

Submitted in partial compliance with the requirements of the Master’s Degree in Technology: Homoeopathy, Durban University of Technology, Durban, South Africa, 2016. / Aim The aim of this study was to compare the nuclear magnetic resonance spectra of Sulphur 12c samples produced by the traditional Hahnemannian method with Sulphur 12c samples produced using sonication as an alternative method of agitation. Sonication, while not widely employed as an agitating technique in the homoeopathic potentisation process, is a highly effective agitation process which produces effects on liquids that closely resemble the effect of traditional Hahnemannian hand succussion (Bhattacharyya et al. 2008). Thus, this study sought to reveal whether or not homoeopathic remedies produced by sonication bore a close enough physicochemical resemblance to traditional hand succussed remedies to be considered as a viable equivalent. Methodology Five sample groups were manufactured for analysis, all by means of serial dilution at the centesimal ratio (1:100) to the 12c potency, and with agitation between dilution levels where applicable. Three of the sample groups were experimental, namely the Sulphur 12c Hahnemannian, Sulphur 12c sonicated and Sulphur 12c both (succussion and sonication). The Sulphur 12c Hahnemannian samples were produced by hand according to the German Homoeopathic Pharmacopoeia (Benyunes 2005), which includes an agitation phase of 10 hand succussions. Sonicated samples were produced according to the Hahnemannian method as far as possible, however the agitation phase consisted of 30 seconds of sonication in a sonication bath at 40Hz in accordance with related studies (Sukul, Sinhabau, and Sukul 1999: 58-59; Sukul et al. 2001a: 187). Sulphur 12c both (succussion and sonication) samples underwent ten hand succussions and 30 seconds of sonication at 40Hz between dilution levels. Two of the sample groups were controls, namely Sulphur 12c unagitated and Lactose 12c unagitated, neither of which underwent agitation between dilution phases but were otherwise produced according to the German Homoeopathic Pharmacopoeia specification (Benyunes 2005). All samples were raised to the 12c potency level in 87% alcohol from a 3CH triturate. The Lactose 12c unagitated control was derived from a 3CH triturate of lactose, while the other samples were all derived from a 3CH triturate of Sulphur. The sample groups were sent for nuclear magnetic resonance (NMR) spectroscopy at the Department of Chemistry at Stellenbosch University. The NMR device used was the Varian UnityInova 600 NMR Spectrometer ®, with a Deuterated DMSO insert added as an instrument frequency lock. Samples were drawn and analysed by Dr D.J. Brand. One sample was drawn from each sample group. The chemical shift and relative integration values for the OH, H2O, CH2, and CH3 peaks of the NMR spectra were captured and tabulated using Microsoft Excel© 2013. The statistical analysis was performed with the aid of SPSS Version 22. The chemical shift and relative integration values for the H2O, OH, CH2 and CH3 peaks were used in the statistical analysis. The Kruskal-Wallis method was performed for the five sample groups to ascertain whether or not a statistically significant difference existed between the five sample groups. Comparisons between individual paired groups were conducted by means of the non-parametric Mann-Whitney test. The significance interval was set at α = Results The chemical shift values of the CH2 peaks of the samples showed a clear similarity between the samples produced by Hahnemannian hand succussion, sonication and both (succussion and sonication) as well as a clear difference between these three samples and the two controls. The relative integration values, however, showed no clear trends in support of or detracting from the hypotheses. Conclusion In terms of the CH2 peak chemical shift values it can be concluded that distinct similarities exist between 12c potency level of Sulphur produced by Hahnemannian hand succussion and sonication, and that the two methods of agitation produce similar structural properties in samples of the 12c potency level. Furthermore in terms of the chemical shift values, succussion and sonication develop remedies that are distinct from unagitated remedies of equivalent potency level. Thus, these findings support the use of sonication as a potentially viable alternative to hand succussion as a method of agitation in the potentisation process. Further studies need to be conducted however, with the inclusion of a greater variety of potency levels in order to possibly reveal more trends in terms of the relative integration values as these values were inconclusive in this study. / M

No description available.

Dissimilatory metal-reducing bacteria (DMRB) play an important role in the biogeochemical cycling of metals. DMRB are unique in that they possess the ability to couple metal reduction with their metabolism. Microbial Fe(III) respiration is a central component of a variety of environmentally important processes, including the biogeochemical cycling of iron and carbon in redox stratified water and sediments, the bioremediation of radionuclide-contaminated water, the degradation of toxic hazardous pollutants, and the generation of electricity in microbial fuel cells. Despite this environmental and evolutionary importance, the molecular mechanism of microbial Fe(III) respiration is poorly understood. Current models of the molecular mechanism of microbial metal respiration are based on direct enzymatic, Fe(III) solubilization, and electron shuttling pathways. Fe(III) oxides are solid at circumneutral pH and therefore unable to come into direct contact with the microbial inner membrane, these bacteria must utilize an alternative strategy for iron reduction. Reduced organic compounds such as thiols are prominent in natural environments where DMRB are found. These thiol compounds are redox reactive and are capable of abiotically reducing Fe(III) oxides at high rates S. oneidensis wild-type and ΔluxS anaerobic biofilm formation phenotypes were examined under a variety of electron donor-electron acceptor pairs, including lactate or formate as the electron donor and fumarate, thiosulfate, or Fe(III) oxide-coated silica surfaces as the terminal electron acceptor. The rates of biofilm formation under the aforementioned growth conditions as well as in the presence of exogenous thiol compounds indicate that ∆luxS formed biofilms at rates only 5-10% of the wild-type strain and ∆luxS biofilm formation rates were restored to wild-type levels by addition of a variety of exogenous compounds including cysteine, glutathione, homocysteine, methionine, serine, and homoserine. Cell adsorption isotherm analyses results indicate that wild-type is can attach to the surface of hematite particles attachment , but ΔluxS is unable to attach the hematite surfaces. These results indicate that biofilm formation is not required for Fe(III) oxide reduction by S. oneidensis ∆luxS anaerobic biofilm formation rates were restored to wild-type levels by addition of exogenous auntoinducer-2 (AI-2), a by-product of homocysteine production in the Activated Methyl Cycle. This discovery led to subsequent experiments performed to detect the production and utilization of AI-2 by wild-type and ∆luxS strains under aerobic and anaerobic conditions. AI-2 production experiments showed wild-type, but not ΔluxS, was capable of producing AI-2. The addition of exogenous S. oneidensis and Vibrio harveyi-produced AI-2 to wild-type and ∆luxS resulted in the swift depletion of AI-2 from the media. These results provide evidence that S. oneidensis can produce AI-2 and subsequently utilize its’ own AI-2 as well as AI-2 produced by other bacteria as a carbon and electron source in the absence of preferred carbon sources. S. oneidensis produces and secretes a suite of extracellular thiols under anaerobic Fe(III)-reducing and Mn(III) and Mn(IV)-reducing conditions including cysteine, homocysteine, glutathione, and cyteamine. Exogenous thiols produced by S. oneidensis are intermediates of the Activated Methyl Cycle (AMC) and Transulfurylation Pathway (TSP). Reduced and oxidized thiols were detected, indicating that the thiols are in a constant state of flux between the reduced and oxidized forms and that the concentration of reduced thiols to its’ oxidized counterpart is indicative of the state of metal reduction by the microorganisms. Respiratory phenotypes Based on Fe(III) and Mn(IV) respiratory phenotypes observed in the AMC and TSP pathway mutants (∆luxS, ∆metB, ∆metC and ∆metY) we can infer that cysteine, glutathione, and cysteamine contribute to metal reduction by serving as efficient electron shuttling molecules, while homocysteine is critical for maintenance of the AMC, propagation of thiol biosynthesis, and maintenance of cellular metabolism via the AMC intermediate SAM. Furthermore, these findings suggest that all metal-reducing bacteria require thiol formation to reduce solid metal oxides. Direct contact mechanism is not the dominant means through electrons are transferred and metals are reduced, instead electron shuttles are the maid reduction mechanism.