The reductions of WO₃ with hydrogen, with CO, and with carbon, as well as the reduction of WO₃/graphite mixtures with hydrogen, were studied using thermogravimetry, evolved gas analysis, X-ray powder diffraction, and scanning electron microscopy. The intermediate phases W₂₀O₅₈, W₁₈O₄₉ and WO₂, were observed in the reductions. The final product of the reductions with hydrogen and carbon was tungsten, and we was formed in the reduction with CO. The reaction paths in the overall processes were determined. The reactant/product gas ratio had a considerable influence on which reactions took place. The morphology of the sample was characterised at different stages of the reduction. The shape of the WO₃ particles was retained during the reduction. Particle growth was observed in the reduction with hydrogen and was attributed to the formation of WO₂(OH)₂(g). The kinetics of the reductions were investigated , and the reaction mechanisms determined. The reduction of WO₃ with CO was studied from 650 to 900°C, and occurred at a phase boundary with an activation energy of 40 kJ mol⁻¹ . The reduction of WO₂, was studied under the same conditions. The reaction also occurred at a phase boundary and had an activation energy of 62 kJ mol⁻¹. The reduction of WO₃ with carbon was studied from 935 to 1100°C and took place via CO and CO₂. Two stages were observed in the reduction . The first stage, which corresponded approximately to the formation of WO₂ had an activation energy of 66 kJ mol⁻¹ and was limited by diffusion through the porous reacting particles. The second stage was first order and had an activation energy of 40 kJ mol⁻¹. The reduction of WO₃ and WO₃ graphite mixtures with hydrogen were studied from 575 to 975 °C. The reactions were controlled by mass-transfer under the conditions investigated. The addition of carbon increased the rate of the reduction process , but did not affect the phases formed in the system. CO₂ was evolved mainly at the start, and CO mainly at the end of the process.

The redox behavior of a series of organometallic complexes containing Cp'M(NO) groups (Cp' = ƞ⁵-C₅H₅(Cp) or ƞ⁵-C₅Me₅(Cp*) ; M = Mo or W) has been investigated both by cyclic voltammetry and by chemical means. The neutral 16-electron Cp'Mo(N0)X₂ compounds (X = CL, Br or I) undergo a single, essentially reversible, one-electron reduction in CH₂CL₂/O.1M [n-Bu₄N]PF₆ at relatively low potentials (<-0.1 V vs SCE). The electrochemically observed reductions can be effected on a preparative scale by employing CP₂C0 as the chemical reductant. The isolable 17-electron [Cp'Mo (NO)X₂]•⁻ radical anions are cleanly reconverted to their 16-electron neutral precursors by treatment with [Cp₂Fe]BF₄. In contrast, the Cp'W(NO)I₂ compounds undergo rapid decomposition to their [Cp'W(NO)I]₂ monohalo dimers upon electrochemical reduction. Electrophiles NE⁺ (E = O or ϱ-O₂NC₆H₄N) undergo unprecedented insertions into the Cr-C ϭ-bonds of CpCr(NO)₂R complexes (R = Me, CH₂SiMe₃ or Ph) to afford [CpCr(N0)₂{N(E)R}]⁺ cationic complexes. Present evidence is consistent with these insertions occurring via charge-controlled, intermolecular attacks by NE⁺ at the Cr-R groups in classical SE2 processes. The newly-formed N(E)R ligands function as Lewis bases through nitrogen atoms toward the formally 16-electron [CpCr(NO)₂]⁺ cations and may be displaced from the chromium's coordination sphere by the more strongly coordinating CL⁻ anion. The resulting CpCr(NO)₂CL can be reconverted to CpCr(NO)₂R. thereby completing a cycle by regenerating the initial organometallic reactant. The entire sequence of stoichiometric reactions forming the cycle thus constitutes a selective method for the formation of new carbon-nitrogen bonds, the net organic conversions mediated by the CpCr(NO)₂ group being NE⁺ + R⁻ → N(E)R. The electrophilic [Cp'M(NO)₂]⁺ cations (Cp'=Cp or Cp* ; M = Cr, Mo or W) condense with methyl propiolate and 2,3-dimethyl-2-butene to afford cationic organometallic lactone complexes. These complexes undergo facile ⍜-dealkylation to yield the neutral Cp'M(NO)₂(ƞ¹-lactone) derivatives. Furthermore, the neutral Cp'W(NO)₂(ƞ¹-lactone) compounds decompose in air to their Cp'W(O)₂(ƞ¹-lactone) dioxo products. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

No description available.

The reaction between various forms of manganese dioxide and halide ions has been investigated. Analytical techniques for the study of this heterogeneous liquid-solid reaction have been developed. The appearance of the reaction products, I₂ and Mn²⁺, was monitored in the aqueous phase of the reaction mixture. I₂ was monitored using amperometry. Mn²⁺ was monitored by a novel application of flow injection analysis. A molecular mechanism was postulated which accounts for the complex pH dependence of the reaction and the inhibition of the reaction under conditions of lower hydrogen ion concentration. The potential of the manganese dioxide-iodide reaction for the metallurgical processing of ferromanganese nodules has been demonstrated. Studies show that there is a preferential dissolution of the manganese portion of the nodules by the action of iodide in acidic conditions. The use of deconvolution techniques for obtaining information from overlapping flow injection analysis peaks has been shown to be feasible. Deconvolution techniques allow an increase in the sampling rates which will broaden the application of flow injection analysis in kinetic studies.

The kinetics of reduction by free flavin semiquinones of the individual components of 1:1 complexes of yeast cytochrome c peroxidase and the cytochrome c from horse, tuna, and yeast, including several site-specific mutants of either the cytochrome c or cytochrome c peroxidase, have been studied. The orientations of the various cytochromes c within electrostatically-stabilized complexes with the peroxidase are not equivalent. This is shown by differential decreases in the rate constants for cytochrome reduction by neutral flavin semiquinones upon complexation which are in the order: tuna ≫ horse > yeast iso-2 > yeast iso-1. We have also directly measured the physiologically-significant intracomplex one-electron transfer rate constants from the ferrous cytochromes c to the peroxide-oxidized species of the peroxidase at several ionic strengths. The rate constants at low ionic strength are highly species dependent, again consistent with the contention that the orientations of the various cytochromes within the complex with CcP are not the same. Increasing the ionic strength in all cases resulted in an increase in the rate constant for the first-order process which controls electron transfer from cytochrome c to the peroxidase Compound I species of the peroxidase. When the two proteins are immobilized by covalent cross-linking, no such rate enhancement is observed, suggesting that the ionic strength effect is manifested by an increase in the number of geometric orientations between the two proteins which results in more rapid electron transfer. Similar rate enhancing effects are observed when positively charged residues on the surface of cytochrome c are converted to electrostatically neutral amino acids by site-specific mutagenesis. The effect of site-specific mutagenesis of two residues of cytochrome c peroxidase have also been studied. His-181, when converted to a glycine has little effect on the electron transfer rate constant, whereas when Trp-191 is converted to a phenylalanine no intracomplex electron transfer could be observed, indicating an obligatory role of this residue in the electron transfer process.

The structure of cytochrome c₅₅₅ from the green sulfur bacterium Chlorobium thiosulfatophilum was determined by using a single isomorphous derivative, K₂HgI₄, in combination with its anomalous signal. The initial 2.25 angstrom map was modified by the technique of Fourier inversion. The smoothing function for the electron density map addressed three different features in the map, the solvent density, the protein density and the volume surrounding the heavy atom binding sites known to contain spurious peaks. This structure determination was undertaken for three reasons. First, Chlorobium thiosulfatophilum is a very primitive sulfur metabolizing bacterium and so its cytochrome c₅₅₅ structure is important for its evolutionary implications. Second, the oxidation-reduction potential of cytochrome c₅₅₅ is significantly different from the oxidation-reduction potential of other cytochromes whose structures have been determined. Comparisons with the other structures would provide information concerning the factors that are important in regulating oxidation-reduction potentials. Finally, the three dimensional structure may aid in explaining the pattern of reactivity cytochrome c₅₅₅ displays with mitochondrial cytochrome c oxidase and reductase, which is reversed when compared to other bacterial c-type cytochromes. The resulting structure contains three alpha helices. These features are consistent with other c-type cytochrome molecules previously determined. Two regions of the map appear to be disordered and are difficult to interpret. Possible causes of this observation are discussed and related to the significance of the structure.

Mitochondria are a major source of reactive oxygen species and are particularly vulnerable to oxidative stress. Mitochondrial dysfunction, methionine oxidation, and oxidative stress are thought to play a role in both the aging process and several neurodegenerative diseases. Two major classes of methionine sulfoxide reductases, designated MsrA and MsrB are enzymes that function to repair the enatiomers of methionine sulfoxide, met-(o)-S and met-(o)- R, respectively. This study focuses on the effect of Msr deficiencies on mitochondrial function by utilizing mutant alleles of MsrA and MsrB. The data show that loss of only one form of Msr in the mitochondria does not completely impair the function of the mitochondria. However, loss of both Msr proteins within the mitochondria leads to an increased ROS production and a diminished energy output of the mitochondria. These results support the hypothesis that Msr plays a key role in proper mitochondrial function. / by Jennifer Verriotto. / Thesis (M.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 95-96. / by Cordelia Mae Price. / M.S.

In natural habitats bacteria predominantly grow and survive as biofilms, which are densely populated assemblages of cells encased in self-produced matrices. Biofilms face the challenge of resource limitation due to poor substrate diffusion and consumption by cells closer to the periphery. When terminal electron acceptors for metabolism, such as oxygen, are limiting, reducing equivalents accumulate in the cell, leading to an imbalanced redox state and disruption of metabolic processes. The opportunistic pathogen Pseudomonas aeruginosa possesses various redox-balancing strategies that facilitate disposal of excess reducing power, including (i) production of phenazines, redox-active compounds that mediate extracellular electron shuttling; (ii) use of nitrate as an electron acceptor via the denitrification pathway, and (iii) fermentation of pyruvate. However, if the biofilm grows to a point where these metabolic strategies become insufficient, the community adopts a “structural” strategy: the cells collectively produce extracellular matrix to form wrinkle features, which increase surface area and oxygen availability, ultimately oxidizing (i.e., rebalancing) the cellular redox state. Though the broad physiological effects of these metabolic and structural strategies are known, details of their regulation and coordination in biofilm communities have remained elusive. The work presented in this thesis was aimed at elucidating the (cross-)regulation and coordination of different redox-balancing strategies in biofilms of P. aeruginosa strain PA14. Studies described in Chapter 2 demonstrate novel regulatory links between phenazines and microaerobic denitrification, including a redox-mediated mechanism for control of the global transcription factor Anr, which is traditionally thought to be regulated solely by oxygen. This chapter also presents observations of the spatial segregation of denitrification enzymes in a colony biofilm, which is suggestive of metabolic specialization and substrate crossfeeding between different groups of cells. Chapters 3 and 4 describe work examining the physiological functions and regulation of pyruvate and lactate metabolism in P. aeruginosa. These studies were motivated by pyruvate’s role as a “hub” for central metabolism, the unique structural biochemistry of the P. aeruginosa pyruvate carboxylase, and the intriguing complement of “lactate dehydrogenase” genes in P. aeruginosa. These genes include two that encode canonical and non-canonical respiration-linked L-lactate dehydrogenases. My results in Chapter 3 show that the non-canonical L-lactate dehydrogenase gene can substitute for the canonical one to support aerobic L-lactate utilization and that it is induced specifically by the L- enantiomer of lactate. This enzymatic redundancy for L-lactate utilization could be an adaptation that enhances virulence, given that host organisms (e.g. humans and plants) produce L-lactate but not D-lactate. In addition, Chapter 3 includes studies of pyruvate-lactate metabolism in the context of biofilm communities, where aerobic and anaerobic zones coexist in proximity. Evidence is provided that cells in biofilms have the potential to engage in crossfeeding of anaerobically generated D-lactate, which would constitute a new instance of bacterial multicellular metabolism. Finally, Chapter 4 shows that mutants of pyruvate carboxylase, which converts pyruvate to oxaloacetate, have a matrix-overproducing, hyperwrinkling biofilm phenotype indicative of an imbalanced cellular redox state. This result suggests that disruption of pyruvate carboxylase shunts metabolic flow through pyruvate dehydrogenase, converting pyruvate to acetyl-CoA and generating an excess of reducing power. Together, the findings presented in Chapter 3 and 4 underscore the importance of pyruvate metabolism in the contexts of redox homeostasis and community behavior. When metabolic strategies are insufficient to balance the redox state, biofilms can ameliorate the problem of electron acceptor limitation by forming wrinkle structures, which increase the community’s surface area-to-volume ratio. Wrinkle formation depends on the production of extracellular matrix. Matrix production is also required for the formation of pellicles, biofilms that reside at air-liquid interfaces. Experiments described in Chapter 5 investigate properties of the P. aeruginosa matrix from a socio-evolutionary perspective. My results show that matrix production confers a competitive advantage in pellicle biofilms but not in colony biofilms. The evolutionary landscape of matrix production in biofilms is complex and context-specific; i.e., each microenvironment selects for a subset of phenotypes that confers fitness only in that specific microenvironment. Chapter 6 describes the dynamic processes of pellicle formation in the gram-positive bacterium Bacillus subtilis as well as the gram-negative P. aeruginosa in a time-resolved manner. In these two distantly related species, we observed a conserved mechanism for pellicle formation that involves motility, chemotaxis and aerotaxis. These findings indicate that motility is more than just a unicellular behavior: cells collectively migrate to a microniche and initiate biofilm formation. Finally, Appendix A describes efforts to characterize proteinaceous components of the matrix isolated from P. aeruginosa PA14. In conclusion, this work has elucidated mechanistic details of various redox-balancing strategies in P. aeruginosa, particularly from the perspective of multicellular community development.