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Steven K Lower - One of the best experts on this subject based on the ideXlab platform.
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antibody recognition force microscopy shows that outer membrane cytochromes omca and mtrc are expressed on the exterior surface of shewanella oneidensis mr 1
Applied and Environmental Microbiology, 2009Co-Authors: Brian H Lower, Grigoriy E. Pinchuk, Ruchirej Yongsunthon, Linda Wildling, Nicholas S Wigginton, Timothy C Droubay, Jeanfrancois Boily, Hermann J Gruber, Catherine L Reardon, Steven K LowerAbstract:Antibody recognition force microscopy showed that OmcA and MtrC are expressed on the exterior surface of living Shewanella oneidensis MR-1 cells when Fe(III), including solid-phase Hematite (fe2o3), was the terminal electron acceptor. OmcA was localized to the interface between the cell and mineral. MtrC displayed a more uniform distribution across the cell surface. Both cytochromes were associated with an extracellular polymeric substance.
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specific bonds between an iron oxide surface and outer membrane cytochromes mtrc and omca from shewanella oneidensis mr 1
Journal of Bacteriology, 2007Co-Authors: Brian H Lower, Ruchirej Yongsunthon, Timothy C Droubay, David E Mccready, Steven K LowerAbstract:Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly to Fe(III) in a mineral during anaerobic respiration. A prerequisite for this type of reaction would be the formation of a stable bond between a cytochrome and an iron oxide surface. Atomic force microscopy (AFM) was used to detect whether a specific bond forms between a Hematite (fe2o3) thin film, created with oxygen plasma-assisted molecular beam epitaxy, and recombinant MtrC or OmcA molecules coupled to gold substrates. Force spectra displayed a unique force signature indicative of a specific bond between each cytochrome and the Hematite surface. The strength of the OmcA-Hematite bond was approximately twice that of the MtrC-Hematite bond, but direct binding to Hematite was twice as favorable for MtrC. Reversible folding/unfolding reactions were observed for mechanically denatured MtrC molecules bound to Hematite. The force measurements for the Hematite-cytochrome pairs were compared to spectra collected for an iron oxide and S. oneidensis under anaerobic conditions. There is a strong correlation between the whole-cell and pure-protein force spectra, suggesting that the unique binding attributes of each cytochrome complement one another and allow both MtrC and OmcA to play a prominent role in the transfer of electrons to Fe(III) in minerals. Finally, by comparing the magnitudes of binding force for the whole-cell versus pure-protein data, we were able to estimate that a single bacterium of S. oneidensis (2 by 0.5 μm) expresses ∼104 cytochromes on its outer surface.
Brian H Lower - One of the best experts on this subject based on the ideXlab platform.
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antibody recognition force microscopy shows that outer membrane cytochromes omca and mtrc are expressed on the exterior surface of shewanella oneidensis mr 1
Applied and Environmental Microbiology, 2009Co-Authors: Brian H Lower, Grigoriy E. Pinchuk, Ruchirej Yongsunthon, Linda Wildling, Nicholas S Wigginton, Timothy C Droubay, Jeanfrancois Boily, Hermann J Gruber, Catherine L Reardon, Steven K LowerAbstract:Antibody recognition force microscopy showed that OmcA and MtrC are expressed on the exterior surface of living Shewanella oneidensis MR-1 cells when Fe(III), including solid-phase Hematite (fe2o3), was the terminal electron acceptor. OmcA was localized to the interface between the cell and mineral. MtrC displayed a more uniform distribution across the cell surface. Both cytochromes were associated with an extracellular polymeric substance.
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specific bonds between an iron oxide surface and outer membrane cytochromes mtrc and omca from shewanella oneidensis mr 1
Journal of Bacteriology, 2007Co-Authors: Brian H Lower, Ruchirej Yongsunthon, Timothy C Droubay, David E Mccready, Steven K LowerAbstract:Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly to Fe(III) in a mineral during anaerobic respiration. A prerequisite for this type of reaction would be the formation of a stable bond between a cytochrome and an iron oxide surface. Atomic force microscopy (AFM) was used to detect whether a specific bond forms between a Hematite (fe2o3) thin film, created with oxygen plasma-assisted molecular beam epitaxy, and recombinant MtrC or OmcA molecules coupled to gold substrates. Force spectra displayed a unique force signature indicative of a specific bond between each cytochrome and the Hematite surface. The strength of the OmcA-Hematite bond was approximately twice that of the MtrC-Hematite bond, but direct binding to Hematite was twice as favorable for MtrC. Reversible folding/unfolding reactions were observed for mechanically denatured MtrC molecules bound to Hematite. The force measurements for the Hematite-cytochrome pairs were compared to spectra collected for an iron oxide and S. oneidensis under anaerobic conditions. There is a strong correlation between the whole-cell and pure-protein force spectra, suggesting that the unique binding attributes of each cytochrome complement one another and allow both MtrC and OmcA to play a prominent role in the transfer of electrons to Fe(III) in minerals. Finally, by comparing the magnitudes of binding force for the whole-cell versus pure-protein data, we were able to estimate that a single bacterium of S. oneidensis (2 by 0.5 μm) expresses ∼104 cytochromes on its outer surface.
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high affinity binding and direct electron transfer to solid metals by the shewanella oneidensis mr 1 outer membrane c type cytochrome omca
Journal of the American Chemical Society, 2006Co-Authors: Yijia Xiong, Brian H Lower, Baowei Chen, Uljana M Mayer, Yuri Londer, Saumyaditya Bose, Michael F Hochella, James K Fredrickson, Thomas C SquierAbstract:The purified outer membrane bacterial protein OmcA binds densely to the surface of Hematite (fe2o3), permitting direct electron transfer to this solid mineral to reduce Fe (III) with an electron flux of about 1013 electrons /cm2/s. In the presence of Hematite, there is a substantial increase in the amplitude of internal protein motions that correlate with metal reduction. Binding is highly favorable, with a partition coefficient of approximately 2 × 105 (ΔGo‘ = −28 kJ/mol), where approximately 1014 OmcA proteins bind per cm2 to the solid metal surface, indicating the utility of using purified OmcA in the construction of a biofuel cell.
James Barber - One of the best experts on this subject based on the ideXlab platform.
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understanding charge transport in non doped pristine and surface passivated Hematite fe2o3 nanorods under front and backside illumination in the context of light induced water splitting
Physical Chemistry Chemical Physics, 2016Co-Authors: Prince Saurabh Bassi, James Barber, Li Xianglin, Yanan Fang, Joachim Say Chye Loo, Lydia Helena WongAbstract:Hematite (fe2o3) nanorods on FTO substrates have been proven to be promising photoanodes for solar fuel production but only with high temperature thermal activation which allows diffusion of tin (Sn) ions from FTO, eventually enhancing their conductivity. Hence, there is a trade-off between the conductivity of fe2o3, and the degradation of FTO occurring at high annealing temperatures (>750 °C). Here, we present a comprehensive study on undoped fe2o3 nanorods under front and back illumination to find the optimum annealing temperature. Bulk/surface charge transport efficiency analysis demonstrates minimum bulk recombination indicating overall high quality crystalline fe2o3 and the preservation of FTO conductivity. Surface recombination is further improved by growing a TiOx overlayer, which improves the photocurrent density from 0.2 mA cm−2 (backside) to 1.2 mA cm−2 under front side and 0.8 mA cm−2 under backside illumination. It is evident from this study that the performance of undoped and unpassivated Hematite nanorods is limited by electron transport, whereas that of doped/passivated Hematite nanorods is limited by hole transport.
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iron based photoanodes for solar fuel production
Physical Chemistry Chemical Physics, 2014Co-Authors: Prince Saurabh Bassi, Lydia Helena Wong, James BarberAbstract:In natural photosynthesis, the water splitting reaction of photosystem II is the source of the electrons/reducing equivalents for the reduction of carbon dioxide to carbohydrate while oxygen is formed as the by-product. Similarly, for artificial photosynthesis where the end product is a solar fuel such as hydrogen, a water splitting-oxygen evolving system is required to supply high energy electrons to drive the reductive reactions. Very attractive candidates for this purpose are iron based semiconductors which have band gaps corresponding to visible light and valence band energies sufficient to oxidise water. The most studied system is Hematite (fe2o3) which is highly abundant with many attributes for incorporation into photoelectrochemical (PEC) cells. We review the recent progress in manipulating Hematite for this purpose through nanostructuring, doping and surface modifications. We also consider several hybrid iron-based semiconducting systems like ferrites and iron titanates as alternatives to Hematite for light driven water splitting emphasizing their advantages with respect to their band levels and charge transport properties.
Ranjani Siriwardane - One of the best experts on this subject based on the ideXlab platform.
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fluidized bed testing of commercially prepared mgo promoted Hematite and cuo fe2o3 mixed metal oxide oxygen carriers for methane and coal chemical looping combustion
Applied Energy, 2015Co-Authors: Ranjani Siriwardane, Hanjing Tian, Duane D Miller, George A RichardsAbstract:Performance data of two commercially prepared oxygen carriers, MgO-promoted natural mineral Hematite (fe2o3) and synthetic mixed metal CuO–fe2o3/alumina, are described in this paper. Large, 180-kg (400-pound) batches of both oxygen carriers were successfully prepared at a commercial catalyst preparation facility.
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Kinetics of Magnetite (Fe3O4) Oxidation to Hematite (fe2o3) in Air for Chemical Looping Combustion
Industrial & Engineering Chemistry Research, 2014Co-Authors: Esmail R. Monazam, Ronald W. Breault, Ranjani SiriwardaneAbstract:Thermogravimetric analysis (TGA) of magnetite (Fe3O4) oxidation was conducted at temperatures ranging from 750 to 900 °C over 10 oxidation cycles. Oxidation experiments were carried out in a continuous stream of air for period of 30 min. The oxidized magnetite (Fe3O4), which resulted in formation of Hematite (fe2o3), was then reduced by using continuous stream of CO (5% and 10%) with N2 balance. The rate of oxidation was determined by the oxygen weight gain. Analysis of the data indicated that the oxidation behavior followed a two-stage process. The initial oxidation, which was very fast, took place in 2 min and was described using nucleation and growth processes with a low activation energy of about 4.21 ± 0.45 kJ/mol. As the reaction developed within the surface, oxygen transport through the product layer become the rate-controlling step with activation energy of 53.58 ± 3.56 kJ/mol.
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reduction of Hematite fe2o3 to wustite feo by carbon monoxide co for chemical looping combustion
Chemical Engineering Journal, 2014Co-Authors: Esmail R. Monazam, Ronald W. Breault, Ranjani SiriwardaneAbstract:Abstract Thermogravimetric analysis (TGA) of the reduction behavior of Hematite by using continuous streams of 5%, 10%, and 20% CO concentrations in N 2 was conducted at temperatures ranging from 750 to 900 °C over ten cycles. The reduced Hematite was then oxidized using dry air. The rate of reduction was determined by the sample weight loss. Analysis of the data indicated that the reduction behavior can be described by single rate-determining step and it was controlled by the chemical reaction at the particle surface. The mass spectroscopy analysis of product gas indicated that no carbon deposition was found when operating at these temperature ranges (750–900 °C). The analysis of reduction showed that two reduction steps (Fe 2 O 3 → Fe 3 O 4 , Fe 3 O 4 → FeO) proceed simultaneously. The activation energy was estimated to be 19.0 ± 0.14 kJ/mole.
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kinetics of the reduction of Hematite fe2o3 by methane ch4 during chemical looping combustion a global mechanism
Chemical Engineering Journal, 2013Co-Authors: Esmail R. Monazam, Ronald W. Breault, Ranjani Siriwardane, George A Richards, Stephen CarpenterAbstract:Abstract Chemical-looping combustion (CLC) has emerged as a promising technology for fossil fuel combustion which produces a sequestration ready concentrated CO 2 stream in power production. A CLC system is composed with two reactors, an air and a fuel reactor. An oxygen carrier such as Hematite (94%Fe 2 O 3 ) circulates between the reactors, which transfers the oxygen necessary for the fuel combustion from the air to the fuel. An important issue for the CLC process is the selection of metal oxide as oxygen carrier, since it must retain its reactivity through many cycles. The primary objective of this work is to develop a global mechanism with respective kinetics rate parameters such that CFD simulations can be performed for large systems. In this study, thermogravimetric analysis (TGA) of the reduction of Hematite (Fe 2 O 3 ) in a continuous stream of CH 4 (15%, 20%, and 35%) was conducted at temperatures ranging from 700 to 825 °C over ten reduction cycles. The mass spectroscopy analysis of product gas indicated the presence of CO 2 and H 2 O at the early stage of reaction and H 2 and CO at the final stage of reactions. A kinetic model based on two parallel reactions, (1) first-order irreversible rate kinetics and (2) Avrami equation describing nucleation and growth processes, was applied to the reduction data. It was found, that the reaction rates for both reactions increase with, both, temperature and the methane concentration in inlet gas.
Timothy C Droubay - One of the best experts on this subject based on the ideXlab platform.
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antibody recognition force microscopy shows that outer membrane cytochromes omca and mtrc are expressed on the exterior surface of shewanella oneidensis mr 1
Applied and Environmental Microbiology, 2009Co-Authors: Brian H Lower, Grigoriy E. Pinchuk, Ruchirej Yongsunthon, Linda Wildling, Nicholas S Wigginton, Timothy C Droubay, Jeanfrancois Boily, Hermann J Gruber, Catherine L Reardon, Steven K LowerAbstract:Antibody recognition force microscopy showed that OmcA and MtrC are expressed on the exterior surface of living Shewanella oneidensis MR-1 cells when Fe(III), including solid-phase Hematite (fe2o3), was the terminal electron acceptor. OmcA was localized to the interface between the cell and mineral. MtrC displayed a more uniform distribution across the cell surface. Both cytochromes were associated with an extracellular polymeric substance.
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specific bonds between an iron oxide surface and outer membrane cytochromes mtrc and omca from shewanella oneidensis mr 1
Journal of Bacteriology, 2007Co-Authors: Brian H Lower, Ruchirej Yongsunthon, Timothy C Droubay, David E Mccready, Steven K LowerAbstract:Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly to Fe(III) in a mineral during anaerobic respiration. A prerequisite for this type of reaction would be the formation of a stable bond between a cytochrome and an iron oxide surface. Atomic force microscopy (AFM) was used to detect whether a specific bond forms between a Hematite (fe2o3) thin film, created with oxygen plasma-assisted molecular beam epitaxy, and recombinant MtrC or OmcA molecules coupled to gold substrates. Force spectra displayed a unique force signature indicative of a specific bond between each cytochrome and the Hematite surface. The strength of the OmcA-Hematite bond was approximately twice that of the MtrC-Hematite bond, but direct binding to Hematite was twice as favorable for MtrC. Reversible folding/unfolding reactions were observed for mechanically denatured MtrC molecules bound to Hematite. The force measurements for the Hematite-cytochrome pairs were compared to spectra collected for an iron oxide and S. oneidensis under anaerobic conditions. There is a strong correlation between the whole-cell and pure-protein force spectra, suggesting that the unique binding attributes of each cytochrome complement one another and allow both MtrC and OmcA to play a prominent role in the transfer of electrons to Fe(III) in minerals. Finally, by comparing the magnitudes of binding force for the whole-cell versus pure-protein data, we were able to estimate that a single bacterium of S. oneidensis (2 by 0.5 μm) expresses ∼104 cytochromes on its outer surface.