This research project is a part of our endeavor to developing a new hydrogen sulfide (H2S) splitting cycle for hydrogen production. In view of that the Bunsen reaction is the key step for the overall efficiency, the objective of this research is to develop an effective and efficient process to carry out the Bunsen reaction in the presence of organic solvents. Organic solvents can help dissolve iodine crystal, lower the reaction temperature and reduce the corrosiveness accompanying the reaction. Through screening of the ordinary organic solvents, aromatic hydrocarbons stood out and toluene was used in this project.<p> In order to study the Bunsen reaction rate in the presence of toluene, the iodine solubility in HI solution was extensively explored at room temperature. Although the iodine solubility in water is small (0.3404g/L at 25â), it was found that the iodine solubility in HI solution increases greatly as the [HI] increases. At lower [HI] (0~0.238 M), the iodine solubility is linear to [HI] with a relationship of [iodine solubility] = 0.57[HI] + 0.0030; at higher [HI] (0.238 ~7.6 M), the relationship of the iodine solubility and [HI] conforms to [iodine solubility]/[HI] = 0.190[HI] + 0.58.<p> In the second part, the iodine distribution behavior between HI solution and toluene phase was studied at room temperature. It was determined that the iodine distribution coefficient (D = [I2]HI solution/[I2]toluene) increases as the increase of [HI]. At lower [HI] (0~1.89 M), the distribution coefficient has a quadratic relationship with [HI] as D = 1.4027[HI]2 + 0.8638[HI] + 0.0088; at higher [HI] (1.89~7.54 M) the distribution coefficient is linear to [HI] with a relationship of D=5.5937[HI]-3.5632.<p> On the basis of the above work, in a semi-batch reactor, the Bunsen reaction rate in the presence of toluene was measured. In a mixture of toluene and water, iodine prefers to stay in toluene phase. The Bunsen reaction was readily initiated by feeding SO2 into water phase. Experimental results indicated that the rate of the Bunsen reaction in the presence of toluene is equal to the molar flow rate of feeding SO2 when the iodine concentration is higher than a certain value. This specific value depends on the reaction conditions, such as the interface area between water and toluene phase, the dispersion efficiency and the flow rate of SO2.

Because of the high demand for hydrogen in the oil industries, new technologies for hydrogen production are being investigated. The thermochemical splitting cycle is one of them. Among the cycles that have been investigated, sulfur-iodine (S-I) water splitting is the most studied. In the S-I cycle, there are three reactions: H2SO4 decomposition, Bunsen reaction and HI decomposition. A new thermochemical cycle has been developed based on the S-I cycle, which is a H2S splitting cycle. In the H2S cycle, there are also three reactions. The only difference between S-I and H2S cycle is that the H2SO4 decomposition reaction is replaced by a reaction between hydrogen sulfide and sulfuric acid which produces sulfur dioxide, elemental sulfur and water. Research on this reaction has been done for many years, studying thermodynamic, kinetics and mass transfer. This reaction produces sulfur, sulfur dioxide and water. The SO2 produced is the used in the second reaction in the H2S cycle; the Bunsen reaction.<p> The main objective of this research was to find an operating condition to increase the production of SO2 from the reaction between H2S and H2SO4. This study investigated different conditions such as temperature, stirring rate and sulfuric acid concentration to maximize the production of SO2. The temperature and stirring rate range used in the reaction were from 120 to 160°C and from 0 to 400 rpm, respectively. The sulfuric acid concentrations were between 90 and 96 wt%. The results showed that increasing the temperature and the acid concentration in the reaction between H2S and H2SO4, the SO2 produced from this reaction will increase. There is no need to apply stirring in the reaction, because the stirring will increase the surface area which allows the produced sulfur dioxide in the gas phase to be dissolved more in sulfuric acid solution, which favors the unwanted side-reaction between SO2 and H2S. A model that was developed to predict the partial pressure change of SO2 in closed reactor. This model was used to compare the data between experimental and simulation through Matlab software. The simulated data was compared to the experimental data and the results indicated that the model fits the data satisfactorily. Additionally, study on the separation between the remaining sulfuric acid and produced elemental sulfur from the reaction between H2S and H2SO4 were performed. The mixture was placed in an oven at140°C of temperature for two hours. It was found that all small droplets of sulfur produced during the reaction between hydrogen sulfide and sulfuric acid agglomerated and the sulfuric acid solution became clearer.

This research project is a part of our endeavor to developing a new hydrogen sulfide (H2S) splitting cycle for hydrogen production. In view of that the Bunsen reaction is the key step for the overall efficiency, the objective of this research is to develop an effective and efficient process to carry out the Bunsen reaction in the presence of organic solvents. Organic solvents can help dissolve iodine crystal, lower the reaction temperature and reduce the corrosiveness accompanying the reaction. Through screening of the ordinary organic solvents, aromatic hydrocarbons stood out and toluene was used in this project.<p> In order to study the Bunsen reaction rate in the presence of toluene, the iodine solubility in HI solution was extensively explored at room temperature. Although the iodine solubility in water is small (0.3404g/L at 25â), it was found that the iodine solubility in HI solution increases greatly as the [HI] increases. At lower [HI] (0~0.238 M), the iodine solubility is linear to [HI] with a relationship of [iodine solubility] = 0.57[HI] + 0.0030; at higher [HI] (0.238 ~7.6 M), the relationship of the iodine solubility and [HI] conforms to [iodine solubility]/[HI] = 0.190[HI] + 0.58.<p> In the second part, the iodine distribution behavior between HI solution and toluene phase was studied at room temperature. It was determined that the iodine distribution coefficient (D = [I2]HI solution/[I2]toluene) increases as the increase of [HI]. At lower [HI] (0~1.89 M), the distribution coefficient has a quadratic relationship with [HI] as D = 1.4027[HI]2 + 0.8638[HI] + 0.0088; at higher [HI] (1.89~7.54 M) the distribution coefficient is linear to [HI] with a relationship of D=5.5937[HI]-3.5632.<p> On the basis of the above work, in a semi-batch reactor, the Bunsen reaction rate in the presence of toluene was measured. In a mixture of toluene and water, iodine prefers to stay in toluene phase. The Bunsen reaction was readily initiated by feeding SO2 into water phase. Experimental results indicated that the rate of the Bunsen reaction in the presence of toluene is equal to the molar flow rate of feeding SO2 when the iodine concentration is higher than a certain value. This specific value depends on the reaction conditions, such as the interface area between water and toluene phase, the dispersion efficiency and the flow rate of SO2.

Biogas, composed principally of methane, has limited use in energy generation due to the presence of hydrogen sulphide (H2S). Biogas cannot be burned directly in an engine as H2S present causes corrosion in the reaction chamber. There currently exist various technologies for the removal of H2S from a gas stream, but most are chemically based, expensive, and are limited in use. The purpose of this study was to determine a biogas purification technique suitable for a small scale farm application; including using a technology inexpensive, efficient, robust and easy to operate. As such, biofiltration was investigated for H2S removal from biogas. Factors considered in the design of the biofiltration system included the source and conditioning of inoculum, type of packing material, and general operating conditions including inlet gas flow rate and H2S loading rate to the biofilter. Activated sludge conditioned in A. ferrooxidans media was an effective inoculum source. This was tested for growth support compatibility with gravel packing material, to be used in the biofilter. The inoculated packing material was loaded into the biofilter initially during start-up and acclimatization. In this study, synthetic biogas (49.9%volCH4, 49.9%volCO2, 2000ppmv H2S) mixed with air (totalling 4%vol O2) was added at 5-10L/hr to a biofilter of 0.4L gravel packing inoculated with conditioned activated sludge. Baseline H2S removal studies in a non-inoculated biofilter were performed with anticipated operating conditions, including an inlet gas stream at 7.5L/h (25oC, 1atm), resulting in 31-56% H2S removal. A factorial test performed found that air content in the inlet gas stream was the significant factor affecting the removal of H2S in the non-inoculated biofilter. Operation of the biofilter with biogas was done for 61 days, including 41 days for start-up and acclimatization and 20 days of H2S loading tests. Start-up and acclimatization with biogas resulted in complete H2S removal after 2 days, with an average overall H2S removal of 98.1%±2.9 std deviation over 34 days. Loading tests performed on the system ranged 5-12.4L/h (25oC, 1atm), with a loading rate of 27.8 to 69.5gH2S/m3h of filter bed. Throughout this test the average H2S removal rate was 98.9%±2.1 std deviation over 20 days. Although complete H2S breakthrough studies were not performed, these results indicate that biofiltration is a promising technology for H2S removal from biogas in a small scale application.

Because of the high demand for hydrogen in the oil industries, new technologies for hydrogen production are being investigated. The thermochemical splitting cycle is one of them. Among the cycles that have been investigated, sulfur-iodine (S-I) water splitting is the most studied. In the S-I cycle, there are three reactions: H2SO4 decomposition, Bunsen reaction and HI decomposition. A new thermochemical cycle has been developed based on the S-I cycle, which is a H2S splitting cycle. In the H2S cycle, there are also three reactions. The only difference between S-I and H2S cycle is that the H2SO4 decomposition reaction is replaced by a reaction between hydrogen sulfide and sulfuric acid which produces sulfur dioxide, elemental sulfur and water. Research on this reaction has been done for many years, studying thermodynamic, kinetics and mass transfer. This reaction produces sulfur, sulfur dioxide and water. The SO2 produced is the used in the second reaction in the H2S cycle; the Bunsen reaction.<p> The main objective of this research was to find an operating condition to increase the production of SO2 from the reaction between H2S and H2SO4. This study investigated different conditions such as temperature, stirring rate and sulfuric acid concentration to maximize the production of SO2. The temperature and stirring rate range used in the reaction were from 120 to 160°C and from 0 to 400 rpm, respectively. The sulfuric acid concentrations were between 90 and 96 wt%. The results showed that increasing the temperature and the acid concentration in the reaction between H2S and H2SO4, the SO2 produced from this reaction will increase. There is no need to apply stirring in the reaction, because the stirring will increase the surface area which allows the produced sulfur dioxide in the gas phase to be dissolved more in sulfuric acid solution, which favors the unwanted side-reaction between SO2 and H2S. A model that was developed to predict the partial pressure change of SO2 in closed reactor. This model was used to compare the data between experimental and simulation through Matlab software. The simulated data was compared to the experimental data and the results indicated that the model fits the data satisfactorily. Additionally, study on the separation between the remaining sulfuric acid and produced elemental sulfur from the reaction between H2S and H2SO4 were performed. The mixture was placed in an oven at140°C of temperature for two hours. It was found that all small droplets of sulfur produced during the reaction between hydrogen sulfide and sulfuric acid agglomerated and the sulfuric acid solution became clearer.

Biogas, composed principally of methane, has limited use in energy generation due to the presence of hydrogen sulphide (H2S). Biogas cannot be burned directly in an engine as H2S present causes corrosion in the reaction chamber. There currently exist various technologies for the removal of H2S from a gas stream, but most are chemically based, expensive, and are limited in use. The purpose of this study was to determine a biogas purification technique suitable for a small scale farm application; including using a technology inexpensive, efficient, robust and easy to operate. As such, biofiltration was investigated for H2S removal from biogas. Factors considered in the design of the biofiltration system included the source and conditioning of inoculum, type of packing material, and general operating conditions including inlet gas flow rate and H2S loading rate to the biofilter. Activated sludge conditioned in A. ferrooxidans media was an effective inoculum source. This was tested for growth support compatibility with gravel packing material, to be used in the biofilter. The inoculated packing material was loaded into the biofilter initially during start-up and acclimatization. In this study, synthetic biogas (49.9%volCH4, 49.9%volCO2, 2000ppmv H2S) mixed with air (totalling 4%vol O2) was added at 5-10L/hr to a biofilter of 0.4L gravel packing inoculated with conditioned activated sludge. Baseline H2S removal studies in a non-inoculated biofilter were performed with anticipated operating conditions, including an inlet gas stream at 7.5L/h (25oC, 1atm), resulting in 31-56% H2S removal. A factorial test performed found that air content in the inlet gas stream was the significant factor affecting the removal of H2S in the non-inoculated biofilter. Operation of the biofilter with biogas was done for 61 days, including 41 days for start-up and acclimatization and 20 days of H2S loading tests. Start-up and acclimatization with biogas resulted in complete H2S removal after 2 days, with an average overall H2S removal of 98.1%±2.9 std deviation over 34 days. Loading tests performed on the system ranged 5-12.4L/h (25oC, 1atm), with a loading rate of 27.8 to 69.5gH2S/m3h of filter bed. Throughout this test the average H2S removal rate was 98.9%±2.1 std deviation over 20 days. Although complete H2S breakthrough studies were not performed, these results indicate that biofiltration is a promising technology for H2S removal from biogas in a small scale application.

No description available.

Hydrogen sulfide (H2S) is an essential small molecule in human physiology. Although quite toxic, H2S is produced endogenously and performs important regulatory functions in the cardiovascular, immune, nervous, and respiratory systems. Varied interactions with intracellular thiols, reactive oxidants, and protein transition-metal centers are highly dynamic and sensitive to fluctuations in redox homeostasis. Furthermore, H2S is implicated in a number of diseases such as cancer, neurodegeneration, and heart disease. Hence, exogenously delivered H2S as a therapeutic agent is an active area of intrigue and research. The complexity and interconnectivity of these processes has stimulated the development of advanced chemical tools with which to study biological H2S, including reaction-based fluorescent probes and slow-releasing H2S donors. Toward these goals, I present several significant advances in the fields of H2S detection and delivery. An azide reduction-based probe, MeRho-Az, provides a rapid >1,000-fold fluorescence response when treated with H2S. MeRho-Az is sufficiently sensitive to detect endogenous H2S in C6 cells and was used to image H2S in live zebrafish larvae using light sheet fluorescence microscopy, representing the first analyte-responsive experiments with this imaging technology. Using a ratiometric dual-fluorophore fragmentation strategy, NBD-Coum simultaneously detects, differentiates, and measures relative concentration ratios of H2S versus cysteine/homocysteine, two important metabolites in H2S biosynthesis. NBD-Coum was used to monitor changes in redox homeostasis in a simulated sulfur pool and is useful for studying H2S-thiol dynamics. The synthesis and amide-coupling conditions of ADT-NH2, a highly sought dithiolethione H2S donor, allow for hydrolytically stable, H2S-releasing non-steroidal anti-inflammatory drug hybrids. Finally, inspired by polysulfide-containing natural products, functionalized tetrasulfides are a new class of accessible, customizable, and versatile H2S donors with controllable H2S release rates. I hope that by using these investigative tools, chemists and biologists are able to refine our understanding of physiological H2S and exploit H2S activities in disease treatments.

Yes / Living longer without simultaneously extending years spent in good health ("health span") is an increasing societal burden, demanding new therapeutic strategies. Hydrogen sulfide (H2S) can correct disease-related mitochondrial metabolic deficiencies, and supraphysiological H2S concentrations can pro health span. However, the efficacy and mechanisms of mitochondrion-targeted sulfide delivery molecules (mtH2S) administered across the adult life course are unknown. Using a Caenorhabditis elegans aging model, we compared untargeted H2S (NaGYY4137, 100 µM and 100 nM) and mtH2S (AP39, 100 nM) donor effects on life span, neuromuscular health span, and mitochondrial integrity. H2S donors were administered from birth or in young/middle-aged animals (day 0, 2, or 4 postadulthood). RNAi pharmacogenetic interventions and transcriptomics/network analysis explored molecular events governing mtH2S donor-mediated health span. Developmentally administered mtH2S (100 nM) improved life/health span vs. equivalent untargeted H2S doses. mtH2S preserved aging mitochondrial structure, content (citrate synthase activity) and neuromuscular strength. Knockdown of H2S metabolism enzymes and FoxO/daf-16 prevented the positive health span effects of mtH2S, whereas DCAF11/wdr-23 - Nrf2/skn-1 oxidative stress protection pathways were dispensable. Health span, but not life span, increased with all adult-onset mtH2S treatments. Adult mtH2S treatment also rejuvenated aging transcriptomes by minimizing expression declines of mitochondria and cytoskeletal components, and peroxisome metabolism hub components, under mechanistic control by the elt-6/elt-3 transcription factor circuit. H2S health span extension likely acts at the mitochondrial level, the mechanisms of which dissociate from life span across adult vs. developmental treatment timings. The small mtH2S doses required for health span extension, combined with efficacy in adult animals, suggest mtH2S is a potential healthy aging therapeutic. / A.R.V., M.W., and T.E. were supported by the US Army Research Office (W911NF-19-1-0235). L.S., M.W., and T.E. were supported by the United Mitochondrial Disease Foundation (PI-19-0985). L.S. was also supported by the University of Exeter Jubilee Scholarship. M.C., N.J.S., and T.E. were supported by the UK Space Agency (ST/R005737/1). N.J.S. and T.E. were supported by BBSRC (BB/N015894/1). S.A.V. was supported by NASA (NNX15AL16G). N.J.S. was supported by grants from NASA [NSSC22K0250; NSSC22K0278] and acknowledges the support of the Osteopathic Heritage Foundation through funding for the Osteopathic Heritage Foundation Ralph S. Licklider, D.O., Research Endowment in the Heritage College of Osteopathic Medicine.

Les 3-mercaptopyruvate sulfurtransférases (3-MST) et les thiosulfate sulfurtransférases (TST) sont des enzymes ubiquitaires de la famille des thioltransférases à domaine rhodanèse qui catalysent le transfert d’un atome de soufre d’un substrat donneur vers un substrat accepteur via un intermédiaire Cys-persulfure. Les 3-MST sont impliquées dans la formation de sulfure d’hydrogène (H2S), un gazotransmetteur toxique à forte concentration, alors que les TST interviendraient dans son élimination. L’objectif de mon projet était de décrypter les mécanismes moléculaires impliquant ces thioltransférases afin de mieux comprendre leurs rôles physiologiques. Pour cela, le mécanisme catalytique et les spécificités de substrats des enzymes humaines (3-MST, TSTD1 et Rhodanèse) et d’Escherichia coli (3-MST et GlpE) ont été caractérisés grâce à la mise au point de méthodes spécifiques permettant l’étude de chacune des étapes du mécanisme (fluorescence, stopped-flow, sonde H2S) et par une étude des relations structure-fonction menée en collaboration pour les aspects chimie théorique et cristallographie RX. J’ai montré que le site actif de ces enzymes est adapté à la catalyse d’un transfert de S0 à partir de composés soufrés non activés. De plus, le mécanisme de formation de l’intermédiaire persulfure ne dépend pas de l’enzyme mais du substrat donneur. En effet, la rupture de la liaison C-S du 3-mercaptopyruvate requiert la déprotonation des fonctions thiols du substrat et de la Cys essentielle, fonction assurée par la boucle catalytique CysX5 qui constitue un véritable site de reconnaissance thiolate, et l’intervention concomitante d’une molécule d’eau comme catalyseur acide. En présence de thiosulfate, hormis l’activation de la Cys seule la neutralisation des charges négatives du substrat est indispensable à la réaction de transfert de soufre. Enfin, et de façon inattendue, la 3-MST humaine pourrait être impliquée dans l’élimination cytosolique du sulfite, un composé toxique pour les cellules. Quant aux deux TST mitochondriales humaines, elles pourraient intervenir à la fois dans la signalisation cellulaire H2S-dépendante, via la production d’espèces polysulfure, et dans l’élimination d’H2S / 3-mercaptopyruvate sulfurtransferases (3-MSTs) and thiosulfate sulfurtransferases (TSTs) are ubiquitous enzymes that belong to the rhodanese sulfurtransferase family and catalyze the transfer of a sulfur atom from a donor to an acceptor substrate via a cysteine-persulfide intermediate. While 3-MSTs are involved in the biogenesis of hydrogen sulfide (H2S), a gasotransmitter known to be toxic at high concentration, TSTs are likely responsible of its degradation. My project mainly focused on deciphering the sulfurtransferase-dependent molecular mechanisms to better define their physiological functions. To address these questions, their catalytic mechanisms and substrate specificities were investigated. This was achieved through the development of kinetic approaches (fluorescence, stopped-flow, H2S specific probe) to study each step of the reaction catalyzed by human (3-MST, TSTD1 and Rhodanese) and Escherichia coli (3-MST, GlpE) enzymes and structure-function relationship studies performed in collaboration for the theoretical chemistry and the X-ray crystallography parts. Here, I show that the active site of these enzymes is optimized to perform an efficient S0 transfer from non-activated sulfur compounds. Moreover, the mechanisms leading to formation of the persulfide intermediate do not depend on the enzyme but rather on the donor substrate. Indeed, the cleavage of the carbon-sulfur bond of 3-mercaptopyruvate critically depends on the CysX5 catalytic loop acting as a thiolate hole to favor the deprotonation of the essential Cys and the substrate, and on a water-mediated protonation step. In the presence of thiosulfate, the Cys activation mode remains unchanged and the reaction of sulfur transfer is only driven by the neutralization of the negative charges of the substrate. In addition, we propose a new physiological function for the human 3-MST in the cytoplasmic elimination of sulfite, a toxic compound for the cells. Finally, the two human mitochondrial TSTs are likely to be involved in the H2S-mediated cellular signaling, through the formation of polysulfide entities, but also in H2S catabolism