The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Kai Finster - One of the best experts on this subject based on the ideXlab platform.
-
Disproportionation of elemental sulfur by haloalkaliphilic bacteria from soda lakes
Extremophiles, 2013Co-Authors: Alexander Poser, Regina Lohmayer, Carsten Vogt, Kay Knoeller, Britta Planerfriedrich, Dimitry Y Sorokin, Hans H Richnow, Kai FinsterAbstract:Microbial Disproportionation of elemental sulfur to sulfide and sulfate is a poorly characterized part of the anoxic sulfur cycle. So far, only a few bacterial strains have been described that can couple this reaction to cell growth. Continuous removal of the produced sulfide, for instance by oxidation and/or precipitation with metal ions such as iron, is essential to keep the reaction exergonic. Hitherto, the process has exclusively been reported for neutrophilic anaerobic bacteria. Here, we report for the first time Disproportionation of elemental sulfur by three pure cultures of haloalkaliphilic bacteria isolated from soda lakes: the Deltaproteobacteria Desulfurivibrio alkaliphilus and Desulfurivibrio sp. AMeS2, and a member of the Clostridia, Dethiobacter alkaliphilus. All cultures grew in saline media at pH 10 by sulfur Disproportionation in the absence of metals as sulfide scavengers. Our data indicate that polysulfides are the dominant sulfur species under highly alkaline conditions and that they might be disproportionated. Furthermore, we report the first organism (Dt. alkaliphilus) from the class Clostridia that is able to grow by sulfur Disproportionation.
-
Sulfite-oxido-reductase is involved in the oxidation of sulfite in Desulfocapsa sulfoexigens during Disproportionation of thiosulfate and elemental sulfur
Biodegradation, 2003Co-Authors: Trine-maria Frederiksen, Kai FinsterAbstract:The enzymatic pathways of elemental sulfur and thiosulfate Disproportionation were investigated using cell-free extract of Desulfocapsa sulfoexigens . Sulfite was observed to be an intermediate in the metabolism of both compounds. Two distinct pathways for the oxidation of sulfite have been identified. One pathway involves APS reductase and ATP sulfurylase and can be described as the reversion of the initial steps of the dissimilatory sulfate reduction pathway. The second pathway is the direct oxidation of sulfite to sulfate by sulfite oxidoreductase. This enzyme has not been reported from sulfate reducers before. Thiosulfate reductase, which cleaves thiosulfate into sulfite and sulfide, was only present in cell-free extract from thiosulfate disproportionating cultures. We propose that this enzyme catalyzes the first step in thiosulfate Disproportionation. The initial step in sulfur Disproportionation was not identified. Dissimilatory sulfite reductase was present in sulfur and thiosulfate disproportionating cultures. The metabolic function of this enzyme in relation to elemental sulfur or thiosulfate Disproportionation was not identified. The presence of the uncouplers HQNO and CCCP in growing cultures had negative effects on both thiosulfate and sulfur Disproportionation. CCCP totally inhibited sulfur Disproportionation and reduced thiosulfate Disproportionation by 80% compared to an unamended control. HQNO reduced thiosulfate Disproportionation by 80% and sulfur Disproportionation by 90%.
Virgil Percec - One of the best experts on this subject based on the ideXlab platform.
-
where is cu 0 generated by Disproportionation during set lrp
Polymer Chemistry, 2013Co-Authors: Nga H Nguyen, Sven Fleischmann, Martin E Levere, Virgil PercecAbstract:The nucleation and growth of nascent Cu(0) nanoparticles formed by Disproportionation during SET-LRP on the surface of Cu(0) wire was demonstrated by Scanning Electron Microscopy analysis of the surface of Cu(0) wire before and after Disproportionation and polymerization. The dynamics of nascent Cu(0) formation, activation of dormant species and their nucleation and growth on the existing Cu(0) surface determines the Cu(0) consumption during polymerization.
-
the Disproportionation of cu i x mediated by ligand and solvent into cu 0 and cu ii x2 and its implications for set lrp
Journal of Polymer Science Part A, 2009Co-Authors: Brad M Rosen, Xuan Jiang, Christopher J L Wilson, Nga H Nguyen, Michael J Monteiro, Virgil PercecAbstract:Disproportionation of Cu(I)X is the major step in Single-Electron Transfer Living Radical Polymerization (SET-LRP). The Disproportionation of Cu(I)X mediated by Me-6-TREN in various solvents was studied through UV-vis spectroscopy and Dynamic Light Scattering (DLS). UV-vis experiments reveal that Disproportionation is dependent on both solvent composition and concentration of Me-6-TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of Disproportionation in the presence of Me6-TREN. Exemplified by DMSO, a favored solvent for SET-LRP, LTV-vis spectroscopy shows that under certain conditions Disproportionation is four-orders of magnitude greater than the value reported from electrochemistry experiments. Through LTV-vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H2O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET-LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of Disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET-LRP are discussed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5606-5628, 2009
-
new efficient reaction media for set lrp produced from binary mixtures of organic solvents and h2o
Journal of Polymer Science Part A, 2009Co-Authors: Nga H Nguyen, Brad M Rosen, Xuan Jiang, Sven Fleischmann, Virgil PercecAbstract:SET-LRP is mediated by a combination of solvent and ligand that promotes Disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 . Therefore, the diversity of solvents suitable for SET-LRP is limited. SET-LRP of MA in a library of solvents with different equilibrium constants for Disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H 2 O was examined. H 2 O exhibits the highest equilibrium constant for Disproportionation of Cu(I)X. The apparent rate constant of the polymerization exhibits a linear increase with the addition of H 2 O. This is consistent with higher equilibrium constants for Disproportionation generated by addition of H 2 O to organic solvents. Furthermore, with the exception of alcohols and carbonates, the rate constant of polymerization in binary mixtures could be correlated with the Dimroth-Reichardt solvent polarity parameter. This is consistent with the single-electron transfer mechanism proposed for SET-LRP that involves a polar transition state. These experiments demonstrate that the use of binary mixtures of solvents with H 2 O provides a new, simple and efficient method for the elaboration of a large diversity of reaction media that are suitable for SET-LRP even when one of the two solvents does not mediate Disproportionation of Cu(I)X.
Satoshi Hirosawa - One of the best experts on this subject based on the ideXlab platform.
-
intermediate hydrogenation phase in the hydrogenation Disproportionation desorption recombination process of nd2fe14b based anisotropic magnets
Acta Materialia, 1999Co-Authors: Toshiro Tomida, Naoyuki Sano, Kenji Hanafusa, Hiroyuki Tomizawa, Satoshi HirosawaAbstract:Abstract To understand the Disproportionation and anisotropy-inducing mechanism of the hydrogenation–Disproportionation–desorption–recombination process of Nd 2 Fe 14 B-based anisotropic magnets, the disproportionated structure of Nd 13.0 Fe 67.9 Co 11.0 B 7.0 Ga 1.0 Zr 0.1 alloys has been investigated via transmission electron microscopy. An intermediate hydrogenation phase of the tetragonal Fe 3 B (t-Fe 3 B) has been revealed to appear in the early stage of Disproportionation. The t-Fe 3 B possesses lattice coherency and an associated “one-to-one” orientation relationship with the parent Nd 2 Fe 14 B phase. Within the t-Fe 3 B grain, fine Nd 2 Fe 14 B particles exist along with NdH 2 particles. The diameter of the Nd 2 Fe 14 B particles is around 50 nm, and they have close orientation to that of original Nd 2 Fe 14 B. An anisotropy-mediating Disproportionation scheme with the intermediate hydrogenation phase is proposed.
I.r. Harris - One of the best experts on this subject based on the ideXlab platform.
-
Metastable borides and the inducement of texture in Pr/sub 2/Fe/sub 14/B-type magnets produced by HDDR
IEEE Transactions on Magnetics, 2001Co-Authors: O. Gutfleisch, K.-h. Müller, A. Teresiak, B. Gebel, N.b. Cannesan, D. Brown, I.r. HarrisAbstract:A modified hydrogenation-Disproportionation-desorption-recombination (HDDR) process has been applied to Pr/sub 2/(Fe,Co,Zr)/sub 14/B-type alloys. XRD and Rietveld analysis show that a Fe/sub 3/B phase observed in a Pr/sub 13.7/Fe/sub 80.3/B/sub 6/ alloy solid-disproportionated at 875/spl deg/C is transformed to Fe/sub 2/B and bcc Fe on further hydrogen annealing and that the formation of Fe/sub 3/B is partly suppressed when the alloy is processed at 800/spl deg/C. No residual 2-14-1-type phases are observed after Disproportionation of Pr/sub 13.7/Fe/sub 63.5/Co/sub 16.7/Zr/sub 0.1/B/sub 6/ alloy but here a new intermediate boride phase, Pr(Fe,Co)/sub 12/B/sub 6/ (rhombohedral R~3m), is found. Pr(Fe,Co)/sub 12/B/sub 6/ transforms to (Fe,Co)/sub 2/B and /spl alpha/-(Fe,Co) on further hydrogen annealing or conventional Disproportionation. For both alloys it is found that processing at higher temperature leads to a better texture on recombination. The role of the Co and Zr additives is not primarily the stabilization of the 2-14-1 matrix phase against hydrogen Disproportionation but more importantly the stabilization of intermediate boride phases.
-
Hydrogenation and Disproportionation of Sm2Fe17−xGax at high hydrogen pressures
Journal of Applied Physics, 1998Co-Authors: M. Kubis, K.-h. Müller, L. Schutz, Oliver Gutfleisch, I.r. HarrisAbstract:In order to apply the hydrogenation-Disproportionation-desorption-recombination process for the preparation of highly coercive Sm2Fe15Ga2Cy, which exhibits excellent magnetic properties together with a high thermal stability, the Disproportionation of Sm2Fe17−xGax was investigated. A systematic study of the hydrogen absorption behavior of Sm2Fe17−xGax (x=0, 0.5, 1, and 2) at hydrogen pressures between 0.5 and 8 bar by means of hydrogen differential thermal analysis (HDTA) showed that increased hydrogen pressures promote the Disproportionation of the stabilized 2:17 phase. X-ray diffraction investigations of the HDTA samples showed a decreasing content of the 2:17 phase for increasing hydrogen pressures. It was possible to achieve a nearly full Disproportionation even for the most stable compound Sm2Fe15Ga2 by applying a pressure of 8 bar. Microstructural changes within the disproportionated mixture as a result of the applied pressure have been documented in detail by high resolution scanning electron micr...
-
In-situ electrical resistivity measurements: study of magnetic and phase transitions and solid-HDDR processes in Nd-Fe-B-type alloys
Journal of Materials Science, 1995Co-Authors: O. Gutfleisch, I.r. HarrisAbstract:Nd-Fe-B-type alloys have been characterized by means of in-situ electrical resistivity measurements. The potential of this technique for monitoring various phenomena relevant to the hydrogenation, Disproportionation, desorption and recombination (HDDR) processing of Nd-Fe-B-type alloys is assessed, together with an evaluation of its capacity for delineating magnetic and phase transitions. The effects of external parameters, such as hydrogen pressure and processing temperature, and of intrinsic parameters, such as alloy composition and initial microstructure, on the kinetics of the solid-HDDR process have been investigated. It was found that the amount of neodymium-rich intergranular phase present in the material had a significant influence on the rates of Disproportionation and recombination reactions. At 620‡C, the recombination process takes place as a solid-solid reaction, and this has a marked effect on the reaction rate. It was also found that the Disproportionation process is very sensitive to the hydrogen pressure and the dependence of the overall process on the processing temperature between 620 and 900‡C has been determined.
-
The Disproportionation of Nd/sub 2/Fe/sub 14/B under hydrogen in Nd-Fe-B alloys
IEEE Transactions on Magnetics, 1992Co-Authors: D. Book, I.r. HarrisAbstract:The kinetics of the Disproportionation reaction in which the Nd/sub 2/Fe/sub 14/B phase forms Fe, Nd-hydride, and Fe/sub 2/B under hydrogen has been investigated by thermopiezic analysis. These studies have shown that the Disproportionation temperature is dependent on grain size, and is considerably lower for Nd-Fe-B alloys with submicron grain sizes when compared with the case material. Thus, melt-spun material disproportionates at a temperature about 300 degrees C below that of cast alloy (at a heating rate of 1 degrees C/min). In addition, the amount of Nd/sub 2/Fe/sub 14/B phase in the alloy can be related to the temperature range over which the reaction occurs and to the amount of Fe and Fe/sub 2/B that forms as a result of the Disproportionation reaction. The latter can be monitored by measuring the magnetization of the disproportionated material.
Nga H Nguyen - One of the best experts on this subject based on the ideXlab platform.
-
where is cu 0 generated by Disproportionation during set lrp
Polymer Chemistry, 2013Co-Authors: Nga H Nguyen, Sven Fleischmann, Martin E Levere, Virgil PercecAbstract:The nucleation and growth of nascent Cu(0) nanoparticles formed by Disproportionation during SET-LRP on the surface of Cu(0) wire was demonstrated by Scanning Electron Microscopy analysis of the surface of Cu(0) wire before and after Disproportionation and polymerization. The dynamics of nascent Cu(0) formation, activation of dormant species and their nucleation and growth on the existing Cu(0) surface determines the Cu(0) consumption during polymerization.
-
the Disproportionation of cu i x mediated by ligand and solvent into cu 0 and cu ii x2 and its implications for set lrp
Journal of Polymer Science Part A, 2009Co-Authors: Brad M Rosen, Xuan Jiang, Christopher J L Wilson, Nga H Nguyen, Michael J Monteiro, Virgil PercecAbstract:Disproportionation of Cu(I)X is the major step in Single-Electron Transfer Living Radical Polymerization (SET-LRP). The Disproportionation of Cu(I)X mediated by Me-6-TREN in various solvents was studied through UV-vis spectroscopy and Dynamic Light Scattering (DLS). UV-vis experiments reveal that Disproportionation is dependent on both solvent composition and concentration of Me-6-TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of Disproportionation in the presence of Me6-TREN. Exemplified by DMSO, a favored solvent for SET-LRP, LTV-vis spectroscopy shows that under certain conditions Disproportionation is four-orders of magnitude greater than the value reported from electrochemistry experiments. Through LTV-vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H2O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET-LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of Disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET-LRP are discussed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5606-5628, 2009
-
new efficient reaction media for set lrp produced from binary mixtures of organic solvents and h2o
Journal of Polymer Science Part A, 2009Co-Authors: Nga H Nguyen, Brad M Rosen, Xuan Jiang, Sven Fleischmann, Virgil PercecAbstract:SET-LRP is mediated by a combination of solvent and ligand that promotes Disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 . Therefore, the diversity of solvents suitable for SET-LRP is limited. SET-LRP of MA in a library of solvents with different equilibrium constants for Disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H 2 O was examined. H 2 O exhibits the highest equilibrium constant for Disproportionation of Cu(I)X. The apparent rate constant of the polymerization exhibits a linear increase with the addition of H 2 O. This is consistent with higher equilibrium constants for Disproportionation generated by addition of H 2 O to organic solvents. Furthermore, with the exception of alcohols and carbonates, the rate constant of polymerization in binary mixtures could be correlated with the Dimroth-Reichardt solvent polarity parameter. This is consistent with the single-electron transfer mechanism proposed for SET-LRP that involves a polar transition state. These experiments demonstrate that the use of binary mixtures of solvents with H 2 O provides a new, simple and efficient method for the elaboration of a large diversity of reaction media that are suitable for SET-LRP even when one of the two solvents does not mediate Disproportionation of Cu(I)X.