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1

Reduction Potentials of Rieske Clusters: Importance of the Coupling between Oxidation State and Histidine Protonation State  

E-print Network

state. Implications for the mechanism of quinol oxidation at the QO site of the cytochrome bc1 and b6f- quinol oxidizing cytochrome bc1 or b6f complex to -150 mV for a Rieske-type ferredoxin (1). In RieskeReduction Potentials of Rieske Clusters: Importance of the Coupling between Oxidation State

Crofts, Antony R.

2

Oxidation reduction potential automatic control potential of intermittently aerated membrane bioreactor for nitrification and denitrification.  

PubMed

An intermittently aerated membrane bioreactor (IAMBR) process is designed to achieve greater removal efficiency of organic matter and nutrients than a regular membrane bioreactor (MBR) through the control on and off of an aerator. In this paper, we have investigated Oxidation/Reduction Potential (ORP) and Dissolved Oxygen (DO) values compared to NH4(+)-N and NO3(-)-N concentrations at SRTs of 20, 30 and 40 days and C/N ratios of 4.5, 7, and 10. Additionally, the paper addresses a comprehensive approach to evaluate ORP as an appropriate factor for the auto-control of IAMBR process on the nitrification and denitrification and present DeltaORP/Deltat curve to confirm accurate completion time of aeration on and off. As the results of ORP and DO curve, it is proven that points of ORP bending and knee are appropriate factors for auto-control of the process in both aeration on and off time and ORP as well as DO relate to the dynamic behavior of nutrient concentration during a cycle. A peak point at aerobic state and a slump point at anoxic state on DeltaORP/Deltat curve obviously present the ORP bending point. Hence, it could find that peak point and slump point indicated the relatively accurate completion time of nitrification and denitrification respectively in IAMBR. PMID:19587414

Choi, Changkyoo; Kim, Moonil; Lee, Kwangho; Park, Heekyung

2009-01-01

3

The reduction potential of nitric oxide (NO) and its importance to NO biochemistry  

PubMed Central

A potential of about ?0.8 (±0.2) V (at 1 M versus normal hydrogen electrode) for the reduction of nitric oxide (NO) to its one-electron reduced species, nitroxyl anion (3NO?) has been determined by a combination of quantum mechanical calculations, cyclic voltammetry measurements, and chemical reduction experiments. This value is in accord with some, but not the most commonly accepted, previous electrochemical measurements involving NO. Reduction of NO to 1NO? is highly unfavorable, with a predicted reduction potential of about ?1.7 (±0.2) V at 1 M versus normal hydrogen electrode. These results represent a substantial revision of the derived and widely cited values of +0.39 V and ?0.35 V for the NO/3NO? and NO/1NO? couples, respectively, and provide support for previous measurements obtained by electrochemical and photoelectrochemical means. With such highly negative reduction potentials, NO is inert to reduction compared with physiological events that reduce molecular oxygen to superoxide. From these reduction potentials, the pKa of 3NO? has been reevaluated as 11.6 (±3.4). Thus, nitroxyl exists almost exclusively in its protonated form, HNO, under physiological conditions. The singlet state of nitroxyl anion, 1NO?, is physiologically inaccessible. The significance of these potentials to physiological and pathophysiological processes involving NO and O2 under reductive conditions is discussed. PMID:12177417

Bartberger, Michael D.; Liu, Wei; Ford, Eleonora; Miranda, Katrina M.; Switzer, Christopher; Fukuto, Jon M.; Farmer, Patrick J.; Wink, David A.; Houk, Kendall N.

2002-01-01

4

Chapter A6. Section 6.5. Reduction-Oxidation Potential (Electrode Method)  

USGS Publications Warehouse

Reduction-oxidation (redox) potential--also referred to as Eh--is a measure of the equilibrium potential, relative to the standard hydrogen electrode, developed at the interface between a noble metal electrode and an aqueous solution containing electroactive chemical species. Measurements of Eh are used to evaluate geochemical speciation models, and Eh data can provide insights on the evolution and status of water chemistry in an aqueous system. Nevertheless, the measurement is fraught with inherent interferences and limitations that must be understood and considered to determine applicability to the aqueous system being studied. For this reason, Eh determination is not one of the field parameters routinely measured by the U.S. Geological Survey (USGS). This section of the National Field Manual (NFM) describes the equipment and procedures needed to measure Eh in water using a platinum electrode. Guidance as to the limitations and interpretation of Eh measurement also is included.

Nordstrom, Darrell Kirk; Wilde, Franceska D.

2005-01-01

5

Electrode measurements of the oxidation reduction potential in the Gotland Deep using a moored profiling instrumentation  

NASA Astrophysics Data System (ADS)

The Gotland Deep Environmental Sampling Station (GODESS) operating between 30 m and 185 m was used to assess the variation of in situ redox potential (Eh) in the stratified water column of the central Baltic Sea, for a period of 56 days (November 2010-January 2011). The aim of this study was to acquire in-depth understanding of redox variations with the overall objective to identify the processes controlling Eh. At an interval of 8 h basic hydro-physical parameters were registered, including the oxidation-reduction potential, dissolved oxygen, chlorophyll a fluorescence, turbidity, temperature and conductivity. In total 170 profiles of all parameters were obtained. The measured Eh (with respect to standard hydrogen electrode, SHE) ranged from -0.055 V to 0.167 V. After temperature and pH correction of the standard reduction potentials, a comparison of the measured Eh with that calculated for the particular redox couples was carried out by applying the Nernst-equation. Furthermore, the concentrations of the most important redox elements such as Fe, Mn, N, O, C and S used for comparison were estimated by using empirical functions or were based on measurements of discrete water samples, taken at the time of deployment and recovery of the mooring. The obtained results reveal that the reduction of Fe(III) and O2 may be the main processes controlling the Eh potential in the Gotland basin. Below the redoxcline the reduction of hematite and then ferric oxyhydroxide could be related to the redox potential and somewhat deeper Fe(III)/Fe(II) was found to be the dominant redox couple. Although mixed potential theory could have been applied, the Fe couples appear to dominate over many other possible redox equilibria. This may be explained by the relatively high exchange current of Fe and by high Fe concentrations (up to 1.5 ?M). Finally, a close correspondence to the Eh potentials measured in the oxic/hypoxic part of the water column was found considering the O2/O2-· and the O2-·/H2O2 couples. This suggests that one-electron transfer reactions determined the Eh under oxic/hypoxic conditions.

Meyer, David; Prien, Ralf D.; Dellwig, Olaf; Waniek, Joanna J.; Schulz–Bull, Detlef E.

2014-03-01

6

Influence of protein interactions on oxidation/reduction midpoint potentials of cofactors in natural and de novo metalloproteins.  

PubMed

As discussed throughout this special issue, oxidation and reduction reactions play critical roles in the function of many organisms. In photosynthetic organisms, the conversion of light energy drives oxidation and reduction reactions through the transfer of electrons and protons in order to create energy-rich compounds. These reactions occur in proteins such as cytochrome c, a heme-containing water-soluble protein, the bacteriochlorophyll-containing reaction center, and photosystem II where water is oxidized at the manganese cluster. A critical measure describing the ability of cofactors in proteins to participate in such reactions is the oxidation/reduction midpoint potential. In this review, the basic concepts of oxidation/reduction reactions are reviewed with a summary of the experimental approaches used to measure the midpoint potential of metal cofactors. For cofactors in proteins, the midpoint potential not only depends upon the specific chemical characteristics of cofactors but also upon interactions with the surrounding protein, such as the nature of the coordinating ligands and protein environment. These interactions can be tailored to optimize an oxidation/reduction reaction carried out by the protein. As examples, the midpoint potentials of hemes in cytochromes, bacteriochlorophylls in reaction centers, and the manganese cluster of photosystem II are discussed with an emphasis on the influence that protein interactions have on these potentials. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. PMID:23466333

Olson, T L; Williams, J C; Allen, J P

2013-01-01

7

Analysis of flow decay potential on Galileo. [oxidizer flow rate reduction by iron nitrate precipitates  

NASA Technical Reports Server (NTRS)

The risks posed to the NASA's Galileo spacecraft by the oxidizer flow decay during its extended mission to Jupiter is discussed. The Galileo spacecraft will use nitrogen tetroxide (NTO)/monomethyl hydrazine bipropellant system with one large engine thrust-rated at a nominal 400 N, and 12 smaller engines each thrust-rated at a nominal 10 N. These smaller thrusters, because of their small valve inlet filters and small injector ports, are especially vulnerable to clogging by iron nitrate precipitates formed by NTO-wetted stainless steel components. To quantify the corrosion rates and solubility levels which will be seen during the Galileo mission, corrosion and solubility testing experiments were performed with simulated Galileo materials, propellants, and environments. The results show the potential benefits of propellant sieving in terms of iron and water impurity reduction.

Cole, T. W.; Frisbee, R. H.; Yavrouian, A. H.

1987-01-01

8

The oxidation-reduction potential of aqueous soil solutions at the Mars Phoenix landing site  

NASA Astrophysics Data System (ADS)

Results from the Mars Phoenix mission Wet Chemistry Laboratory (WCL) are used to determine the oxidation-reduction potential (Eh) of the Phoenix WCL Rosy Red sample soil solution. The measured Eh of the Rosy Red sample in the WCL aqueous test solution was 253 ± 6 mV at a pH of 7.7 ± 0.1. Measured solution Eh changes correspond to changes in solution H+ activity, which is controlled mainly by changes in headspace PCO2 and solution CO32-, HCO3-, and CO2 concentrations. If measured at a PCO2 of 8 mbar in water, rather than in WCL test solution, the Eh of the Rosy Red soil solution would be ˜300 mV. The results of laboratory experiments using analog salt mixtures are compatible with the possible presence of low levels (ppm) of metal peroxides or other oxidants and indicate that levels of readily soluble ferrous iron in the soil are below 1 ppm.

Quinn, Richard C.; Chittenden, Julie D.; Kounaves, Samuel P.; Hecht, Michael H.

2011-07-01

9

Effect of voltage polarity on oxidation-reduction potential by plasma in water  

NASA Astrophysics Data System (ADS)

Use of plasma in water for water treatment and medical treatment is growing and raises expectations of finding advanced functions such as an increase of biological compatibility. In the present study with a focus on the variation of oxidation-reduction potential (ORP), relationships between the electrode polarities of plasma in water and the change of water quality such as conductivity, H2O2 concentration, dissolved hydrogen concentration, pH and ORP were revealed. Similar line spectra of radiation at the electrode tip were observed for each case of positive and negative electrode polarity. The emission intensities of OH (309 nm), H? (656 nm), and OI (777 nm) for the positive discharge were significantly higher than those for the negative one, though the energy consumption during the discharge period of both cases was nearly the same. Positive electrode polarity was found to be more suitable than negative electrode polarity for increasing dissolved hydrogen gas and hydrogen peroxide. The ORP for the positive polarity decreased from 460 to 45 mV and that for the negative polarity decreased from 460 to 183 mV, although the pH and conductivity were not significantly changed.

Miyahara, Takashi; Oizumi, Masanobu; Nakatani, Tatsuyuki; Sato, Takehiko

2014-04-01

10

Differential Effects of Oxygen and Oxidation Reduction Potential on the Multiplication of Three Species of Anaerobic Intestinal Bacteria  

PubMed Central

The sensitivity of three strains of anaerobic intestinal bacteria, Clostridium perfringens, Bacteroides fragilis, and Peptococcus magnus, to the differential effects of oxygen and adverse oxidation-reduction potential was measured. The multiplication of the three organisms was inhibited in the presence of oxygen whether the medium was at a negative oxidation-reduction potential (Eh of -50 mV), poised by the intermittent addition of dithiothreitol, or at a positive oxidation-reduction potential (Eh of near +500 mV). However, when these organisms were cultured in the absence of oxygen, no inhibition was observed, even when the oxidation-reduction potential was maintained at an average Eh of +325 mV by the addition of potassium ferricyanide. When the cultures were aerated, the growth patterns of the three organisms demonstrated different sensitivities to oxygen. P. magnus was found to be the most sensitive. After 2 h of aerobic incubation, no viable organisms could be detected. B. fragilis was intermediately sensitive to oxygen with no viable organisms detected after 5 h of aerobic incubation. C. perfringens was the least sensitive. Under conditions of aerobic incubation, viable organisms survived for 10 h. During the experiments with Clostridium, no spores were observed by spore staining. PMID:173238

Walden, William C.; Hentges, David J.

1975-01-01

11

Determination of chemical oxygen demand (COD) using ultrasound digestion and oxidation-reduction potential-based titration  

Microsoft Academic Search

A new method for determining wastewater chemical oxygen demand (COD) using ultrasonic digestion and titration based on oxidation reduction potential (ORP) was developed. COD values of potassium hydrogen phthalate solution obtained by ultrasonic digestion were well matched with those obtained using Standard Methods. When applied to determine COD of real wastewater collected from a local treatment plant, results from the

Hyunook Kim; Honglae Lim; Mark F. Colosimo

2007-01-01

12

Oxidation/Reduction  

NSDL National Science Digital Library

Created by team members from Kapi'olani Community College and Leeward Community College, this site provides educators and students with a colorful background lesson in oxidation and reduction. The site is divided into concepts, exercises, and everyday examples of oxidation and reduction. Each exercise allows users to check all answers.

13

Soil Oxidation-Reduction Potential and Plant Photosynthetic Capacity in the Northern Pantanal of Mato Grosso, Brazil  

NASA Astrophysics Data System (ADS)

Plant communities of the Pantanal wetland are able to survive long periods of climatic and physiological stress in the dry and wet seasons. During inundation, soil oxygen demand increases dramatically as reducing soil conditions create stress in the root system with possible impacts on photosynthetic capacity of plants. We look at inundation cycles of a tree island (locally known as a cordilheira) in the Northern Pantanal near Poconé, Mato Grosso, and relate soil oxidation-reduction potential and soil oxygen depletion to the photosynthetic capacity of two plant communities of flooded scrub forest (Vochysia divergens and Curatela americana). Results show a drop in soil oxidation-reduction potential of over 400 mV, to levels below the absolute value of -200 mV, following inundation around the tree island. Both plant species showed increased carbon assimilation at highest soil oxygen demand despite a change in stomatal conductance, suggesting adaptation to the inundated environment. Absolute values of soil oxidation-reduction potential also allow for the determination of specific soil chemical reactions characteristic of the tree island environment, namely the reduction of iron(III), or carbon dioxide which in turn produces methane. Our combined analysis of soil chemistry with plant ecophysiology allows for a better understanding of soil-plant interactions in the Pantanal, specifically the drivers of biogeochemical processes between inundation periods.

Lathuilliere, M. J.; Johnson, M. S.; Dalmagro, H. J.; Pinto Junior, O. B.; Couto, E. G.

2013-12-01

14

GAMMA RADIATION INTERACTS WITH MELANIN TO ALTER ITS OXIDATION-REDUCTION POTENTIAL AND RESULTS IN ELECTRIC CURRENT PRODUCTION  

SciTech Connect

The presence of melanin pigments in organisms is implicated in radioprotection and in some cases, enhanced growth in the presence of high levels of ionizing radiation. An understanding of this phenomenon will be useful in the design of radioprotective materials. However, the protective mechanism of microbial melanin in ionizing radiation fields has not yet been elucidated. Here we demonstrate through the electrochemical techniques of chronoamperometry, chronopotentiometry and cyclic voltammetry that microbial melanin is continuously oxidized in the presence of gamma radiation. Our findings establish that ionizing radiation interacts with melanin to alter its oxidation-reduction potential. Sustained oxidation resulted in electric current production and was most pronounced in the presence of a reductant, which extended the redox cycling capacity of melanin. This work is the first to establish that gamma radiation alters the oxidation-reduction behavior of melanin, resulting in electric current production. The significance of the work is that it provides the first step in understanding the initial interactions between melanin and ionizing radiation taking place and offers some insight for production of biomimetic radioprotective materials.

Turick, C.; Ekechukwu, A.; Milliken, C.

2011-05-17

15

Oxidation-Reduction Equilibria  

NSDL National Science Digital Library

This 11-page PDF document is part of an environmental geochemistry course taught by Dr. David Sherman at the University of Bristol. Topics include oxidation-reduction reactions and oxidation states, the Nerst Equation, Eh-pH diagrams, and redox environments in nature. Also included are the calculation of Eh from concentrations and the prediction of stable oxidation states. Helpful diagrams accompany the text.

Sherman, David M.; Bristol, University O.

16

Requirement of low oxidation-reduction potential for photosynthesis in a blue-green alga (Phormidium sp.).  

PubMed

Photosynthesis in a Phormidium species which forms dense conical-shaped structures in thermal springs is strongly inhibited by aeration but is stimulated by sulfide and other agents (cysteine, thioglycolate, sulfite) which lower the oxidation-reduction potential. The compact structures which this alga forms in nature may restrict oxygen penetration from the enviroment so that the anaerobic or microaerophilic conditions necessary ofr photosynthesis can develop. The alga may be defective in a regulatory mechanism that controls the reoxidation of reduced pyridine nucleotides formed during photosynthesis. It is suggested that other mat-forming and benthic blue-green algae may also prefer anaerobib conditions for growth and photosynthesis. PMID:808187

Weller, D; Doemel, W; Brock, T D

1975-06-20

17

Effects of oxidation reduction potential in the bypass micro-aerobic sludge zone on sludge reduction for a modified oxic-settling-anaerobic process.  

PubMed

Batch experiments were conducted to determine the effect of oxidation reduction potential (ORP) on sludge reduction in a bypass micro-aerobic sludge reduction system. The system was composed of a modified oxic-settling-anaerobic process with a sludge holding tank in the sludge recycle loop. The ORPs in the micro-aerobic tanks were set at approximately +350, -90, -150, -200 and -250 mV, by varying the length of aeration time for the tanks. The results show that lower ORP result in greater sludge volume reduction, and the sludge production was reduced by 60% at the lowest ORP. In addition, low ORP caused extracellular polymer substances dissociation and slightly reduced sludge activity. Comparing the sludge backflow characteristics of the micro-aerobic tank's ORP controlled at -250 mV with that of +350 mV, the average soluble chemical oxygen (SCOD), TN and TP increased by 7, 0.4 and 2 times, median particle diameter decreased by 8.5 ?m and the specific oxygen uptake rate (SOUR) decreased by 0.0043 milligram O2 per gram suspended solids per minute. For the effluent, SCOD and TN and TP fluctuated around 30, 8.7 and 0.66 mg/L, respectively. Therefore, the effective assignment of ORP in the micro-aerobic tank can remarkably reduce sludge volume and does not affect final effluent quality. PMID:24845332

Li, Kexun; Wang, Yi; Zhang, Zhongpin; Liu, Dongfang

2014-01-01

18

Reversible potentials for steps in methanol and formic acid oxidation to CO2; adsorption energies of intermediates on the ideal electrocatalyst for methanol oxidation and CO2 reduction.  

PubMed

Quantum chemical theory is used to identify the reasons for platinum's limitations as an electrocatalyst for oxidizing methanol at fuel cell anodes. The linear Gibbs energy relation (LGER) method is employed to predict reversible potentials for reaction steps for intermediates on the electrode surface. In this procedure, standard reversible potentials are calculated for the reactions in bulk solution phase and then they are perturbed using calculated adsorption bond strengths to the electrode surface, yielding the equilibrium potentials for each electron transfer step for adsorbed intermediates. Adsorption properties of ideal electrocatalysts for the methanol oxidation are found by imposing the condition that the reversible potential of each electron transfer step equals that for the overall reaction. The adsorption bond strengths that provide the ideal properties also apply to formic acid oxidation and carbon dioxide reduction. It is instructive to think of the ideal electrocatalyst as a lens that focusses the reversible potentials for the n individual electron transfer steps to the reversible potential for the n-electron process. It is found that the ideal catalyst will adsorb many intermediates, including HOOC, CO, OCH, HOC, HOCH, HOCH2, and OCH3 more weakly than platinum, and OOCH and OH more strongly. For example, for one possible pathway it is necessary to weaken adsorption bond strengths for HOCH2, HOCH, OCH, HOOC by about 0.5 eV, weaken adsorption CO by about 1.1 eV and strengthen OH adsorption by about 0.6 eV. These results imply a need for developing new multi-component catalysts. PMID:24741672

Anderson, Alfred B; Asiri, Haleema Aied

2014-06-14

19

Primary sequence, oxidation-reduction potentials and tertiary-structure prediction of Desulfovibrio desulfuricans ATCC 27774 flavodoxin.  

PubMed

Flavodoxin was isolated and purified from Desulfovibrio desulfuricans ATCC 27774, a sulfate-reducing organism that can also utilize nitrate as an alternative electron acceptor. Mid-point oxidation-reduction potentials of this flavodoxin were determined by ultraviolet/visible and EPR methods coupled to potentiometric measurements and their pH dependence studied in detail. The redox potential E2, for the couple oxidized/semiquinone forms at pH 6.7 and 25 degrees C is -40 mV, while the value for the semiquinone/hydroquinone forms (E1), at the same pH, -387 mV. E2 varies linearly with pH, while E1 is independent of pH at high values. However, at low pH (< 7.0), this value is less negative, compatible with a redox-linked protonation of the flavodoxin hydroquinone. A comparative study is presented for Desulfovibrio salexigens NCIB 8403 flavodoxin [Moura, I., Moura, J.J.G., Bruschi, M. & LeGall, J. (1980) Biochim. Biophys. Acta 591, 1-8]. The complete primary amino acid sequence was obtained by automated Edman degradation from peptides obtained by chemical and enzymic procedures. The amino acid sequence was confirmed by FAB/MS. Using the previously determined tridimensional structure of Desulfovibrio vulgaris flavodoxin as a model [similarity, 48.6%; Watenpaugh, K.D., Sieker, L.C., Jensen, L.H., LeGall, J. & Dubourdieu M. (1972) Proc. Natl Acad. Sci. USA 69, 3185-3188], the tridimensional structure of D. desulfuricans ATCC 27774 flavodoxin was predicted using AMBER force-field calculations. PMID:8143752

Caldeira, J; Palma, P N; Regalla, M; Lampreia, J; Calvete, J; Schäfer, W; Legall, J; Moura, I; Moura, J J

1994-03-15

20

Effects of molecular oxygen, oxidation-reduction potential, and antioxidants upon in vitro replication of Treponema pallidum subsp. pallidum.  

PubMed Central

The effects of various concentrations of dithiothreitol, molecular oxygen, and several antioxidants upon the in vitro replication of Treponema pallidum were studied. The optimal dithiothreitol concentration was between 0.65 and 1.62 mM, and the optimum oxygen concentration was 3.0% +/- 0.5% in both the presence and absence of additional antioxidants. It was discovered that the reduced sulfhydryl concentration and the oxidation-reduction potential of the medium were stabilized after 5 days. The water-soluble antioxidants cobalt chloride, cocarboxylase, mannitol, and histidine were individually tested for their ability to increase treponemal growth in vitro. The optimum concentrations for these antioxidants were 21 nM, 4.3 nM, 0.55 mM, and 0.23 mM, respectively. When combined at these concentrations, the mixture of antioxidants stimulated the in vitro replication of T. pallidum. The number of treponemes in cultures with the antioxidants averaged a 59-fold increase, compared with a 43-fold increase in cultures lacking the antioxidants. It was further demonstrated that histidine and mannitol were the most critical components of this mixture. Catalase and superoxide dismutase were investigated for their ability to promote the growth and maintain viability of T. pallidum in tissue culture. The optimum concentrations for these enzymes were 10,000 U/liter and 25,000 U/liter, respectively. When these enzymes and the above antioxidants were combined and added to a chemically reduced modified Eagle medium, the treponemes increased an average of 70-fold, compared with an average of 35-fold in cultures lacking them. Furthermore, this medium, T. pallidum culture medium, supported the replication of T. pallidum at oxygen concentrations from 5 to 7% with little loss in yield or viability. The lipid-soluble antioxidants vitamin A and vitamin E acetate were also shown to enhance the in vitro growth of T. pallidum in this medium. PMID:2285317

Cox, D L; Riley, B; Chang, P; Sayahtaheri, S; Tassell, S; Hevelone, J

1990-01-01

21

Electro-catalytic reduction of nitrogen oxides  

SciTech Connect

Nitrogen oxides have been linked to a broad range of air pollution problems including acid rain and the atmospheric production of photochemical ozone. Over twenty million tons of nitrogen oxides are emitted into the atmosphere each year as a result of the high temperature combustion of fossil fuels. Efforts to control nitrogen oxides emissions have lagged because of the generally low discharge concentrations of nitrogen oxides in combustion exhaust and because nitrogen oxides are more difficult to remove due to their lower reactivity. No catalyst has yet been found that will achieve significant reduction of nitrogen oxides in an oxidizing environment. Oxygen in the exhaust stream competes with nitrogen oxides for the active catalyst sites. Also, the dissociated oxygen atoms produced by decomposition of nitrogen oxides deactivate the surface of the catalyst. Externally applied electric fields have been used to control oxygen adsorption on metal and semi-conductor surfaces. In this investigation, a stream containing nitric oxide has been subjected to intense electric fields in the presence of catalyst materials including steel, stainless steel, and gold plated stainless steel wools and glass wool. The electric fields have been generated using DC, AC and rectified AC potentials in the range of 0--20 KV. The effect of parameters such as inlet nitric oxide concentration, oxygen and water content, gas residence time and temperature have also been studied.

McLarnon, C.R.

1989-12-01

22

Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria  

PubMed Central

Microorganisms have been observed to oxidize Fe(II) at neutral pH under anoxic and microoxic conditions. While most of the mixotrophic nitrate-reducing Fe(II)-oxidizing bacteria become encrusted with Fe(III)-rich minerals, photoautotrophic and microaerophilic Fe(II) oxidizers avoid cell encrustation. The Fe(II) oxidation mechanisms and the reasons for encrustation remain largely unresolved. Here we used cultivation-based methods and electron microscopy to compare two previously described nitrate-reducing Fe(II) oxidizers ( Acidovorax sp. strain BoFeN1 and Pseudogulbenkiania sp. strain 2002) and two heterotrophic nitrate reducers (Paracoccus denitrificans ATCC 19367 and P. denitrificans Pd 1222). All four strains oxidized ?8 mM Fe(II) within 5 days in the presence of 5 mM acetate and accumulated nitrite (maximum concentrations of 0.8 to 1.0 mM) in the culture media. Iron(III) minerals, mainly goethite, formed and precipitated extracellularly in close proximity to the cell surface. Interestingly, mineral formation was also observed within the periplasm and cytoplasm; intracellular mineralization is expected to be physiologically disadvantageous, yet acetate consumption continued to be observed even at an advanced stage of Fe(II) oxidation. Extracellular polymeric substances (EPS) were detected by lectin staining with fluorescence microscopy, particularly in the presence of Fe(II), suggesting that EPS production is a response to Fe(II) toxicity or a strategy to decrease encrustation. Based on the data presented here, we propose a nitrite-driven, indirect mechanism of cell encrustation whereby nitrite forms during heterotrophic denitrification and abiotically oxidizes Fe(II). This work adds to the known assemblage of Fe(II)-oxidizing bacteria in nature and complicates our ability to delineate microbial Fe(II) oxidation in ancient microbes preserved as fossils in the geological record. PMID:24271182

Klueglein, Nicole; Zeitvogel, Fabian; Stierhof, York-Dieter; Floetenmeyer, Matthias; Konhauser, Kurt O.; Obst, Martin

2014-01-01

23

ChemTeacher Resource: Oxidation Reduction Reactions  

NSDL National Science Digital Library

This computer resource goes over oxidation reduction reactions and how they are broken down into half reactions. It explains which half reaction is the oxidation reaction and which one is the reduction, then has some summary questions at the end.

Dr. Martin McClinton, Debbie McClinton, Dr. Miriam Douglass

2011-01-01

24

Molecular Modeling of Environmentally Important Processes: Reduction Potentials  

ERIC Educational Resources Information Center

The increasing use of computational quantum chemistry in the modeling of environmentally important processes is described. The employment of computational quantum mechanics for the prediction of oxidation-reduction potential for solutes in an aqueous medium is discussed.

Lewis, Anne; Bumpus, John A.; Truhlar, Donald G.; Cramer, Christopher J.

2004-01-01

25

Oxidation and Reduction Reactions in Organic Chemistry  

ERIC Educational Resources Information Center

A variety of approaches to the concept of oxidation and reduction appear in organic textbooks. The method proposed here is different than most published approaches. The oxidation state is calculated by totaling the number of heterogeneous atoms, [pi]-bonds, and rings. A comparison of the oxidation states of reactant and product determine what type…

Shibley, Ivan A., Jr.; Amaral, Katie E.; Aurentz, David J.; McCaully, Ronald J.

2010-01-01

26

Effect of active site and surface mutations on the reduction potential of yeast cytochrome c peroxidase and spectroscopic properties of the oxidized and reduced enzyme  

Microsoft Academic Search

The reduction potentials of 22 yeast cytochrome c peroxidase (CcP) mutants were determined at pH 7.0 in order to determine the effect of both heme pocket and surface mutations on the Fe(III)\\/Fe(II) redox couple of CcP, as well as to determine the range in redox potentials that could be obtained through point mutations in the enzyme. Spectroscopic properties of the

Cory M. DiCarlo; Lidia B. Vitello; James E. Erman

2007-01-01

27

Dechlorination by combined electrochemical reduction and oxidation*  

PubMed Central

Chlorophenols are typical priority pollutants listed by USEPA (U.S. Environmental Protection Agency). The removal of chlorophenol could be carried out by a combination of electrochemical reduction and oxidation method. Results showed that it was feasible to degrade contaminants containing chlorine atoms by electrochemical reduction to form phenol, which was further degraded on the anode by electrochemical oxidation. Chlorophenol removal rate was more than 90% by the combined electrochemical reduction and oxidation at current of 6 mA and pH 6. The hydrogen atom is a powerful reducing agent that reductively dechlorinates chlorophenols. The instantaneous current efficiency was calculated and the results indicated that cathodic reduction was the main contributor to the degradation of chlorophenol. PMID:15909345

Cong, Yan-qing; Wu, Zu-cheng; Tan, Tian-en

2005-01-01

28

Reduction of metal oxides through mechanochemical processing  

DOEpatents

The low temperature reduction of a metal oxide using mechanochemical processing techniques. The reduction reactions are induced mechanically by milling the reactants. In one embodiment of the invention, titanium oxide TiO.sub.2 is milled with CaH.sub.2 to produce TiH.sub.2. Low temperature heat treating, in the range of 400.degree. C. to 700.degree. C., can be used to remove the hydrogen in the titanium hydride.

Froes, Francis H. (Moscow, ID); Eranezhuth, Baburaj G. (Moscow, ID); Senkov, Oleg N. (Moscow, ID)

2000-01-01

29

Stabilized tin-oxide-based oxidation/reduction catalysts  

NASA Technical Reports Server (NTRS)

The invention described herein involves a novel approach to the production of oxidation/reduction catalytic systems. The present invention serves to stabilize the tin oxide reducible metal-oxide coating by co-incorporating at least another metal-oxide species, such as zirconium. In one embodiment, a third metal-oxide species is incorporated, selected from the group consisting of cerium, lanthanum, hafnium, and ruthenium. The incorporation of the additional metal oxide components serves to stabilize the active tin-oxide layer in the catalytic process during high-temperature operation in a reducing environment (e.g., automobile exhaust). Moreover, the additional metal oxides are active components due to their oxygen-retention capabilities. Together, these features provide a mechanism to extend the range of operation of the tin-oxide-based catalyst system for automotive applications, while maintaining the existing advantages.

Jordan, Jeffrey D. (Inventor); Schryer, David R. (Inventor); Davis, Patricia P. (Inventor); Leighty, Bradley D. (Inventor); Watkins, Anthony Neal (Inventor); Schryer, Jacqueline L. (Inventor); Oglesby, Donald M. (Inventor); Gulati, Suresh T. (Inventor); Summers, Jerry C. (Inventor)

2008-01-01

30

41 CFR 101-30.702 - Determining item reduction potential.  

Code of Federal Regulations, 2011 CFR

...2007-07-01 true Determining item reduction potential. 101-30.702 Section 101-30...101-30.702 Determining item reduction potential. Item reduction studies are...determine whether sufficient item reduction potential appears to exist. Item reduction...

2011-07-01

31

41 CFR 101-30.702 - Determining item reduction potential.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 true Determining item reduction potential. 101-30.702 Section 101-30...101-30.702 Determining item reduction potential. Item reduction studies are...determine whether sufficient item reduction potential appears to exist. Item reduction...

2010-07-01

32

Role of Ser457 of NADPH-cytochrome P450 oxidoreductase in catalysis and control of FAD oxidation-reduction potential.  

PubMed

Site-directed mutagenesis of Ser457 of NADPH-cytochrome P450 oxidoreductase demonstrates that this residue plays a major role in both hydride transfer from NADPH to FAD and modulation of FAD redox potential. Substitution of Ser457 with alanine or cysteine decreases the rates of reduction of the substrates cytochrome c and potassium ferricyanide approximately 100-fold, while substitution with threonine produces a 20-fold decrease in activity. No changes are observed in k(m)NADPH, KiNADP+, or flavin content, indicating that these substitutions have no effect on cofactor binding but affect catalysis only. k(m)cyt c values are decreased in parallel with the observed decreases in the rates of the reductive half-reaction. Stopped-flow studies with the S457A mutant show a 100-fold decrease in the rate of flavin reduction. The primary deuterium isotope effect on Kcat for cytochrome c reduction increases from 2.7 for the wild-type enzyme to 9.0 for the S457A mutant, consistent with a change in the rate-determining step from NADP+ release in the wild-type enzyme to hydride transfer in the S457A mutant. The primary deuterium isotope effect on K1 for flavin reduction at high ionic strength (I = 535 mM) increases from 12.2 for the wild-type enzyme to > 20 for the S457A mutant, consistent again with an increase in the relative rate limitation of hydride transfer. Furthermore, anaerobic titration of S457A indicates that the redox potential of the FAD semiquinone has been decreased. Data presented in this study support the hypothesis that Ser457 is involved in hydrogen bonding interactions which stabilize both the transition state for hydride transfer and the reduced FAD. PMID:8755724

Shen, A L; Kasper, C B

1996-07-23

33

Pulsed laser assisted reduction of graphene oxide  

Microsoft Academic Search

We report a simple approach to reduce graphene oxide (GO) solution by pulsed laser irradiation. The reduction was rapidly carried out at room temperature in only 5min. The reduced graphene oxide (r-GO) was characterized with UV–visible spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermo-gravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. Based on this

Lei Huang; Yang Liu; Le-Chun Ji; Yi-Qun Xie; Tao Wang; Wang-Zhou Shi

2011-01-01

34

Bacterial Reduction of Uranium in Mineralogically Heterogeneous Media: Impact of Mn and Fe-oxides  

Microsoft Academic Search

Dissimilatory reduction of uranium can have a profound impact on the transport of uranium within surface and subsurface environments. The rate and extent of biological uranium reduction, and stability of reduced uranium phases, will be influenced by sediment mineralogy. Both Fe- and Mn-oxide phases have the potential to retard U(VI) reduction and may even serve as oxidants of reduced U

M. A. Ginder-Vogel; S. Fendorf

2003-01-01

35

Microbial reduction of manganese oxides - Interactions with iron and sulfur  

NASA Technical Reports Server (NTRS)

Alteromonas putrefaciens (strain MR-1) is capable of rapid Mn(IV) reduction under conditions of neutral pH and temperatures characteristic of the Oneida Lake, New York, sediments from which it was isolated. MR-1 also reduces Fe(3+) to Fe(2+), and disproportionates thiosulfate to sulfide and sulfite; independently, the Fe(2+) and sulfide act as rapid reductants of Mn. The addition of Fe(3+) or thiosulfate to cultures of MR-1 in the presence of oxidized Mn increases the rate and the extent of Mn reduction relative to that observed in the absence of Fe(3+) or thiosulfate. Furthermore, when Fe(3+) and Mn oxides are present conjointly, Fe(2+) does not appear until the reduction of the oxidized Mn is complete. These results demonstrate that the observed rates of Fe(2+) and sulfide production may underestimate the total rates of Fe and sulfate reduction in those environments containing oxidized Mn. These results also demonstrate the potential impact that a single microbe can exert on sediment geochemistry, and provide the basis for preliminary models of the complexity of microbial and geochemical interactions that occur.

Myers, Charles R.; Nealson, Kenneth H.

1988-01-01

36

Hydrogen reduction of oxidized nickel concentrates  

NASA Astrophysics Data System (ADS)

Thermal gravimetric analysis was used to investigate the weight change of Ni/Cu/Co calcines upon heating in an inert as well as hydrogen atmosphere. The two calcines investigated contained approximately 50 wt pct combined of hematite and magnetite in addition to sulfides of Ni, Cu, Co, and Fe. Mass spectrometry was used to analyze the gas species evolved during heating and reduction. The calcine samples are 100 pct less than 100 µm with hematite/magnetite rims around a central sulfide core. When heating the calcines at 10 °C/min in hydrogen, reduction starts at around 400 °C and is nearly complete at about 700 °C with all the reducible oxygen removed. Isothermal reduction tests show that at temperatures from 650 °C to 800 °C, half the oxygen is removed in less than 4 min. The TGA results combined with microscopic analysis show that the reduction followed a uniform internal reduction model. The reduced calcines will quickly get re-oxidized if they are allowed to contact air while they remain hot.

Crowe, C. J. B.; Utigard, T. A.

2003-12-01

37

Oxidation-reduction catalyst and its process of use  

NASA Technical Reports Server (NTRS)

This invention relates generally to a ruthenium stabilized oxidation-reduction catalyst useful for oxidizing carbon monoxide, and volatile organic compounds, and reducing nitrogen oxide species in oxidizing environments, substantially without the formation of toxic and volatile ruthenium oxide species upon said oxidizing environment being at high temperatures.

Jordan, Jeffrey D. (Inventor); Watkins, Anthony Neal (Inventor); Schryer, Jacqueline L. (Inventor); Oglesby, Donald M. (Inventor)

2008-01-01

38

In situ reduction and oxidation of nickel from solid oxide fuel cells in a Titan ETEM  

E-print Network

In situ reduction and oxidation of nickel from solid oxide fuel cells in a Titan ETEM A. Faes1. The in situ reduction and re-oxidation of the FIB prepared TEM lamellae is performed in a FEI Titan equipped

Dunin-Borkowski, Rafal E.

39

Analysis of potential helicopter vibration reduction concepts  

NASA Technical Reports Server (NTRS)

Results of analytical investigations to develop, understand, and evaluate potential helicopter vibration reduction concepts are presented in the following areas: identification of the fundamental sources of vibratory loads, blade design for low vibration, application of design optimization techniques, active higher harmonic control, blade appended aeromechanical devices, and the prediction of vibratory airloads. Primary sources of vibration are identified for a selected four-bladed articulated rotor operating in high speed level flight. The application of analytical design procedures and optimization techniques are shown to have the potential for establishing reduced vibration blade designs through variations in blade mass and stiffness distributions, and chordwise center-of-gravity location.

Landgrebe, A. J.; Davis, M. W.

1985-01-01

40

Calculating Standard Reduction Potentials of [4Fe-4S] Proteins  

PubMed Central

The oxidation-reduction potentials of electron transfer proteins determine the driving forces for their electron transfer reactions. While the type of redox site determines the intrinsic energy required to add or remove an electron, the electrostatic interaction energy between the redox site and its surrounding environment can greatly shift the redox potentials. Here, a method for calculating the reduction potential versus the standard hydrogen electrode, E°, of a metalloprotein using a combination of density functional theory and continuum electrostatics is presented. This work focuses on the methodology for the continuum electrostatics calculations, including various factors that may affect the accuracy. The calculations are demonstrated using crystal structures of six homologous HiPIPs, which give E° that are in excellent agreement with experimental results. PMID:23115132

Perrin, Bradley Scott; Niu, Shuqiang; Ichiye, Toshiko

2012-01-01

41

CHARACTERIZATION OF OXIDATION REDUCTION PROCESSES IN CONSTRUCTED WETLANDS FOR SWINE WASTEWATER TREATMENT  

Microsoft Academic Search

Constructed wetlands designed and properly operated for treatment of swine wastewater may enhance oxidation -reduction processes and nutrient treatment performance. The objective of this investigation was to characterize soil wetland processes related to nitrogen (N) treatment (nitrification-denitrification) and phosphorus (P) removal using soil oxidation -reduction potential (ORP) data. We evaluated three surface-flow wetland systems constructed for treatment of swine wastewater

A. A. Szögi; P. G. Hunt; E. J. Sadler; D. E. Evans

42

Relationships between polarographic oxidation and reduction half-wave potentials, electronic spectra, and Hammett substituent constants for a series of 5-substituted 3-nitroanilines  

E-print Network

Rl:I AT! ONSIII I'S Bll'I IV!:I:N I-'Cl 9 ROGRARlll C OX IDA'I'TON AND [I!'DUCT! ON I!A!. I: -', ~ AVI'. I'O'I'];N. ' I ~ I S, EI, EC I'RON! C SPI. '. C I I AND ib 'DI. I'T SUI'ST I TUI:NT COI'S'I'AN'IS I OR A SFR II: 0" 5 ? +UI'ST! Tll'I DD 3 ? N...-nitroanilines, peaked oxidation waves, as described by Lund, were obtained. The other members of the series 13 gave "g' shaped oxidation s='. "s. . 't was obse: vcd that ii the s otating platinum electr=Je uas not rigorously cleaned after e, ch. oxIda ion th...

Brown, Robert Allan

2012-06-07

43

Potential reduction of DSN uplink energy cost  

NASA Technical Reports Server (NTRS)

DSN Earth stations typically transmit more power than that required to meet minimum specifications for uplink performance. Energy and cost savings that could result from matching the uplink power to the amount required for specified performance are studied. The Galileo mission was selected as a case study. Although substantial reduction in transmitted energy is possible, potential savings in source energy (oil or electricity) savings are much less. This is because of the rising inefficiency in power conversion and radio frequency power generation that accompanies reduced power output.

Dolinsky, S.; Degroot, N. F.

1982-01-01

44

Plutonium Oxidation and Subsequent Reduction by Mn (IV) Minerals  

SciTech Connect

Plutonium sorbed to rock tuff was preferentially associated with manganese oxides. On tuff and synthetic pyrolusite (Mn{sup IV}O{sub 2}), Pu(IV) or Pu(V) was initially oxidized, but over time Pu(IV) became the predominant oxidation state of sorbed Pu. Reduction of Pu(V/VI), even on non-oxidizing surfaces, is proposed to result from a lower Gibbs free energy of the hydrolyzed Pu(IV) surface species versus that of the Pu(V) or Pu(VI) surface species. This work suggests that despite initial oxidation of sorbed Pu by oxidizing surfaces to more soluble forms, the less mobile form of Pu, Pu(IV), will dominate Pu solid phase speciation during long term geologic storage. The safe design of a radioactive waste or spent nuclear fuel geologic repository requires a risk assessment of radionuclides that may potentially be released into the surrounding environment. Geochemical knowledge of the radionuclide and the surrounding environment is required for predicting subsurface fate and transport. Although difficult even in simple systems, this task grows increasingly complicated for constituents, like Pu, that exhibit complex environmental chemistries. The environmental behavior of Pu can be influenced by complexation, precipitation, adsorption, colloid formation, and oxidation/reduction (redox) reactions (1-3). To predict the environmental mobility of Pu, the most important of these factors is Pu oxidation state. This is because Pu(IV) is generally 2 to 3 orders of magnitude less mobile than Pu(V) in most environments (4). Further complicating matters, Pu commonly exists simultaneously in several oxidation states (5, 6). Choppin (7) reported Pu may exist as Pu(IV), Pu(V), or Pu(VI) oxic natural groundwaters. It is generally accepted that plutonium associated with suspended particulate matter is predominantly Pu(IV) (8-10), whereas Pu in the aqueous phase is predominantly Pu(V) (2, 11-13). The influence of the character of Mn-containing minerals expected to be found in subsurface repository environments on Pu oxidation state distributions has been the subject of much recent research. Kenney-Kennicutt and Morse (14), Duff et al. (15), and Morgenstern and Choppin (16) observed oxidation of Pu facilitated by Mn(IV)-bearing minerals. Conversely, Shaughnessy et al. (17) used X-ray Absorption near-edge spectroscopy (XANES) to show reduction of Pu(VI) by hausmannite (Mn{sup II}Mn{sub 2}{sup III}O{sub 4}) and manganite ({gamma}-Mn{sup III}OOH) and Kersting et al., (18) observed reduction of Pu(VI) by pyrolusite (Mn{sup IV}O{sub 2}). In this paper, we attempt to reconcile the apparently conflicting datasets by showing that Mn-bearing minerals can indeed oxidize Pu, however, if the oxidized species remains on the solid phase, the oxidation step competes with the formation of Pu(IV) that becomes the predominant solid phase Pu species with time. The experimental approach we took was to conduct longer term (approximately two years later) oxidation state analyses on the Pu sorbed to Yucca Mountain tuff (initial analysis reported by Duff et al., (15)) and measure the time-dependant changes in the oxidation state distribution of Pu in the presence of the Mn mineral pyrolusite.

KAPLAN, DANIEL

2005-09-13

45

Graphite Oxide: Structure, Reduction and Applications  

NASA Astrophysics Data System (ADS)

This thesis proposes a modified structure model for graphite oxide (GO), an important precursor in graphene chemistry, develops a new strategy to convert GO back to graphene-like structure, and demonstrates its possible applications in both water purification and supercapacitor technologies. GO, a nontraditional compound first obtained from graphite oxidation over 150 years ago, is now becoming an important player in the production of graphene-based materials, which has high technological relevance. GO structure and reduction have been vigorously investigated, but its precise chemical structure still remains obscure, and the complete restoration of the sp2 carbon lattice has not yet been achieved. In our work, solid state 13C NMR (MAS) analysis offered a piece of evidence for five or six-membered ring lactol structure existing in GO that had never been assigned before, leading to a modified Lerf-Klinowski model for GO. A three-step reduction strategy, involving sodium borohydride (NaBH4), sulfuric acid, and high temperature thermal annealing, described in the thesis, successfully reduced GO back to chemically converted graphene (CCG) with the lowest heteroatom abundance among all those previously reported. In addition to the chemical significance of graphene/CCG production, GO and its derivatives were used as novel adsorbents in water purification. GO-coated sand showed higher retention than ordinary sand for both Rhodamine B and mercuric ion (Hg2+) contaminants in water. Further functionalization of GO with thiophenol resulted in better adsorption capacity toward Hg2+ than that of activated carbon. In addition, free-standing films of GO were treated and reduced with a CO 2 laser beam into different conductive reduced GO (RGO) patterns, and directly used as supercapacitor devices which showed good cyclic stability and energy storage capacities comparable to that of existing thin film ultracapacitors. GO turned out to be a solid electrolyte with anisotropic proton conductivity similar to Nafion, while the large amount of trapped water in GO played an important role.

Gao, Wei

46

Nitrogen oxide reduction in Wolinella succinogenes and Campylobacter species.  

PubMed Central

Wolinella succinogenes cells and extracts reduced nitric oxide, and cells, but not extracts, reduced nitrous oxide. Formate-reduced W. succinogenes extracts generated the 573-nm peak in difference spectra seen previously in response to nitric oxide in denitrifiers. The type strains of several Campylobacter species did not reduce either gaseous oxide. Cells, but not extracts, of C. fetus subspecies (fetus and venerealis) reduced nitrous oxide; acetylene inhibited reduction. Neither cells nor extracts reduced nitric oxide. PMID:7130133

Payne, W J; Grant, M A; Shapleigh, J; Hoffman, P

1982-01-01

47

REPEATED REDUCTIVE AND OXIDATIVE TREATMENTS ON GRANULAR ACTIVATED CARBON  

EPA Science Inventory

Fenton oxidation and Fenton oxidation preceded by reduction solutions were applied to granular activated carbon (GAC) to chemically regenerate the adsorbent. No adsorbate was present on the GAC so physicochemical effects from chemically aggressive regeneration of the carbon coul...

48

Iron reduction potentiates hydroxyl radical formation only in flavonols.  

PubMed

Flavonoids, substantial components of the human diet, are generally considered to be beneficial. However, they may possess possible pro-oxidative effects, which could be based on their reducing potential. The aims of this study were to evaluate the ability of 26 flavonoids to reduce ferric ions at relevant pH conditions and to find a possible relationship with potentiation of hydroxyl radical production. A substantial ferric ions reduction was achieved under acidic conditions, particularly by flavonols and flavanols with the catecholic ring B. Apparently corresponding bell-shaped curves displaying the pro-oxidant effect of flavonols quercetin and kaempferol on iron-based Fenton reaction were documented. Several flavonoids were efficient antioxidants at very low concentrations but rather inefficient or pro-oxidative at higher concentrations. Flavonols, morin and rutin were progressively pro-oxidant, while 7-hydroxyflavone and hesperetin were the only flavonoids with dose-dependent inhibition of hydroxyl radical production. Conclusively, administration of flavonoids may lead to unpredictable consequences with few exceptions. PMID:22980846

Macáková, Kate?ina; Mlad?nka, P?emysl; Filipský, Tomáš; ?íha, Michal; Jahodá?, Lud?k; Trejtnar, František; Bovicelli, Paolo; Proietti Silvestri, Ilaria; Hrdina, Radomír; Saso, Luciano

2012-12-15

49

Oxidation-Reduction Resistance of Advanced Copper Alloys  

NASA Technical Reports Server (NTRS)

Resistance to oxidation and blanching is a key issue for advanced copper alloys under development for NASA's next generation of reusable launch vehicles. Candidate alloys, including dispersion-strengthened Cu-Cr-Nb, solution-strengthened Cu-Ag-Zr, and ODS Cu-Al2O3, are being evaluated for oxidation resistance by static TGA exposures in low-p(O2) and cyclic oxidation in air, and by cyclic oxidation-reduction exposures (using air for oxidation and CO/CO2 or H2/Ar for reduction) to simulate expected service environments. The test protocol and results are presented.

Greenbauer-Seng, L. (Technical Monitor); Thomas-Ogbuji, L.; Humphrey, D. L.; Setlock, J. A.

2003-01-01

50

Highly active oxide photocathode for photoelectrochemical water reduction  

NASA Astrophysics Data System (ADS)

A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H2 production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6?mA?cm-2 at a potential of 0?V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1?h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

Paracchino, Adriana; Laporte, Vincent; Sivula, Kevin; Grätzel, Michael; Thimsen, Elijah

2011-06-01

51

One-step reduction of graphene oxide with l-glutathione  

Microsoft Academic Search

The preparation of graphene nanosheets from graphene oxide by chemical reduction is one of the important topics in areas of nanotechnology because graphene-based nanomaterials have potential applications. Herein, we developed a green and facile approach to produce graphene by using an environmentally friendly reagent, namely, l-glutathione as a reducing agent. Graphene was prepared via one-step reduction from graphene oxide under

Tuan Anh Pham; Jeong Sik Kim; Jeong Su Kim; Yeon Tae Jeong

2011-01-01

52

REDUCTION OF NITRIC OXIDE WITH METAL SULFIDES  

EPA Science Inventory

The report gives results of research to determine the technical feasibility of using metal sulfide for the chemical reduction of NOx to N2. Nineteen different metal sulfides were investigated, using a test gas of pure NO. Although most sulfides resulted in some NO reduction, BaS,...

53

Three-Electrode Metal Oxide Reduction Cell  

DOEpatents

A method of electrochemically reducing a metal oxide to the metal in an electrochemical cell is disclosed along with the cell. Each of the anode and cathode operate at their respective maximum reaction rates. An electrolyte and an anode at which oxygen can be evolved, and a cathode including a metal oxide to be reduced are included as is a third electrode with independent power supplies connecting the anode and the third electrode and the cathode and the third electrode.

Dees, Dennis W. (Downers Grove, IL); Ackerman, John P. (Downers Grove, IL)

2005-06-28

54

DEVELOPMENT OF ELECTROCHEMICAL REDUCTION TECHNOLOGY FOR SPENT OXIDE FUELS  

SciTech Connect

The Advanced Spent Fuel Conditioning Process (ACP) has been under development at Korea Atomic Energy Research Institute (KAERI) since 1997. The concept is to convert spent oxide fuel into metallic form and to remove high heat-load fission products such as Cs and Sr from the spent fuel. The heat power, volume, and radioactivity of spent fuel can decrease by a factor of a quarter via this process. For the realization of ACP, a concept of electrochemical reduction of spent oxide fuel in Li2O-LiCl molten salt was proposed and several cold tests using fresh uranium oxides have been carried out. In this new electrochemical reduction process, electrolysis of Li2O and reduction of uranium oxide are taking place simultaneously at the cathode part of electrolysis cell. The conversion of uranium oxide to uranium metal can reach more than 99% ensuring the feasibility of this process.

Hur, Jin-Mok; Seo, Chung-Seok; Kim, Ik-Soo; Hong, Sun-Seok; Kang, Dae-Seung; Park, Seong-Won

2003-02-27

55

Benzene Oxidation Coupled to Sulfate Reduction  

Microsoft Academic Search

(14C)benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as 14CO2. Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of 14CO2from ( 14 C)benzene. Benzene metabolism stopped when the sediments became sulfate depleted,andbenzeneuptakeresumedwhensulfatewasaddedagain.Thestoichiometryofbenzeneuptakeand sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for

DEREK R. LOVLEY; JOHN D. COATES; JOAN C. WOODWARD; ANDELIZABETH J. P. PHILLIPS

1995-01-01

56

Reduction of oral malodor by oxidizing lozenges.  

PubMed

The main purpose of the study was to examine the anti-malodor properties of oxidizing lozenges, as compared to breath mints and chewing gum. Healthy, young adult volunteers (N = 123; mean age 24.5 years) were measured for oral malodor-related parameters (whole mouth odor measured by 2 judges; tongue dorsum posterior odor using the spoon test; volatile sulphide levels; salivary levels of cadaverine and putrescine; and 2 versions of an oral rinse test) on the first afternoon of the study. They were then assigned randomly to one of 6 groups (2 brands of breath mints, chewing gum with no active ingredients, regular and full-strength oxidizing lozenges, and a no-treatment control), and instructed to employ the treatment before bedtime, the next morning, and in the early afternoon 3 hours prior to measurements, which were carried out 24 hours following baseline measurements. Volunteers also estimated the level of their own whole mouth and tongue odors at baseline and post-treatment. The data showed that, among treatments, only the full-strength oxidizing lozenge significantly reduced tongue dorsum malodor, as determined by the spoon test. The full-strength lozenge also yielded a significant increase in the modified oral rinse test, presumably due, at least in part, to residual oxidizing activity retained in the oral cavity. Self-estimations of whole mouth and tongue malodor by volunteers were significantly correlated with corresponding-judge assessments, suggesting some degree of objectivity in assessing one's own oral malodor. PMID:9444592

Greenstein, R B; Goldberg, S; Marku-Cohen, S; Sterer, N; Rosenberg, M

1997-12-01

57

Kinetics of oxidation and reduction of Ni\\/YSZ cermets  

Microsoft Academic Search

A cyclic reduction and oxidation of Ni\\/YSZ-cermet anodes for Solid Oxide Fuel Cells (SOFC) resulted in an increase of the\\u000a polarization resistance. Therefore, investigations concerning kinetics of oxidation\\/reduction and the impact of redox cycles\\u000a on the mi-crostructure of Ni\\/YSZ bulk ceramics were made. The reaction process of the basic system Ni\\/NiO was compared with\\u000a cermet bulk samples and the influence

D. Fouquet; A. C. Müller; A. Weber; E. Ivers-Tiffée

2003-01-01

58

Phyto-reduction of graphene oxide using the aqueous extract of Eichhornia crassipes (Mart.) Solms  

NASA Astrophysics Data System (ADS)

The aqueous extract of Eichhornia crassipes was used as reductant to produce graphene from graphene oxide by refluxing method. The complete reduction of graphene oxide was monitored using UV-Vis spectrophotometer. Characterization of graphene was made through FTIR, XRD, and Raman spectroscopy analysis. The stability of graphene was studied by thermal gravimetric analysis and zeta potential measurements. The nature and surface morphology of the synthesized graphene was analyzed by transmission electron microscopy. The production of graphene using phytoextract as reductant emphasizes on the facile method of synthesis and greener nanotechnology.

Firdhouse, M. Jannathul; Lalitha, P.

2014-10-01

59

Titanium(III) Citrate as a Nontoxic Oxidation-Reduction Buffering System for the Culture of Obligate Anaerobes  

Microsoft Academic Search

An oxidation-reduction buffering system based on titanium(III) citrate eliminates any traces of oxygen in a culture medium, serves as an indicator for low oxidation-reduction potentials, and prevents the growth of facultative anaerobes, which frequently contaminate anaerobic cultures.

Alexander J. B. Zehnder; Karl Wuhrmann

1976-01-01

60

Reduction-Oxidation Photocycle Dynamics of Flavins in Starch Films  

PubMed Central

The blue-light photo-reduction (conversion of oxidized flavin quinone via flavin semiquinone to fully reduced flavin hydroquinone) and dark re-oxidation of the flavins riboflavin and lumiflavin in starch (?-amylose) films was studied by absorption and luminescence spectroscopy. Blue-light photo-excitation caused an absorption, fluorescence, and phosphorescence decrease which recovered in the dark. The photo-reduction dark-oxidation cycle could be repeated. The efficiency of photo-reduction decreased with exposed excitation energy, and the speed of re-oxidation in the dark slowed down with time after excitation. The absorption did not fully recover. The fluorescence efficiency after a long time of storage in the dark increased beyond the initial flavin quinone fluorescence efficiency. Flavin photo-excitation is thought to cause starch-flavin restructuring (static fluorescence quenching center formation), enabling enhanced photo-induced starch to flavin electron transfer with subsequent flavin reduction and starch oxidation. In the dark, after light switch-off, thermal reversion of flavin reduction and starch oxidation occurred. PMID:22942758

Penzkofer, Alfons

2012-01-01

61

Reductive mobilization of oxide-bound metals  

SciTech Connect

We have completed a large number of experiments which examine the release of MnO{sub 2}-bound Co, Ni, and Cu. Our work has focused upon the following areas: (1) competitive adsorption among the three toxic metals and Mn(II); (2) toxic metal release upon addition of low MW organic reductants and complexants; and (3) toxic metal release upon addition of natural organic matter-rich surface waters and IHSS organic matter reference material.

Stone, A.T.

1991-01-01

62

Oxide reduction during triggered-lightning fulgurite formation  

NASA Astrophysics Data System (ADS)

In this study triggered-lightning induced fulgurites were formed in 99.9% pure binary oxides of manganese (MnO) and nickel (NiO) in order to study oxide reduction mechanisms. The fulgurite formation process involved packing the oxide in PVC holders and using the standard rocket-and-wire technique to trigger a lightning strike through the oxide at the International Center for Lightning Research and Testing in Camp Blanding, Florida. These two oxides were chosen from the thermodynamic extrapolation of the oxide stability using the Ellingham Diagram. This diagram indicates that NiO is significantly less stable than MnO. Fulgurites from the pure oxides were analyzed in a scanning electron microscope (SEM); secondary electron images, backscattered images and energy dispersive spectroscopy (EDS) were used to determine the microstructure and composition of the fulgurites. SEM/EDS analysis of the NiO and MnO prior to fulgurite formation confirmed they were pure binary oxides with no metallic contamination. After fulgurite formation, it was found that the nickel oxide fulgurite contained metallic nickel particles; the manganese oxide fulgurite showed no metallic phase formation. Transmission electron microscopy (TEM) examination confirmed that the MnO was a pure oxide with no sign of metallic phase formation. However, TEM results of the NiO showed that approximately 50% of the NiO was reduced to metallic face-centered cubic Ni. The Ni and NiO were observed to be coherent with the [1 0 0]Ni//[1 0 0]NiO and [1 1 0]Ni//[1 1 0]NiO. These results are consistent with the aforementioned thermodynamic stability calculations and show that the presence of carbonaceous material or mixtures of oxides is not necessary for oxide reduction during fulgurite formation. These studies do not rule out the possibility that electrolysis plays a role in oxide reduction. However, these fulgurites were made simultaneously during the same lightning strike and therefore were subjected to the same electrical current, and thus it is proposed the thermodynamic stability of the oxide must play a role in oxide reduction.

Jones, B. E.; Jones, K. S.; Rambo, K. J.; Rakov, V. A.; Jerald, J.; Uman, M. A.

2005-03-01

63

Reductive mobilization of oxide-bound metals  

SciTech Connect

This project is concerned with the mobilization of MnO{sub 2}- and FeOOH-bound toxic metals in subsurface environments arising from an influx of natural organic matter or organic-containing wastes. Our work to date emphasizes the importance of characterizing the reductant, complexant, and adsorptive characteristics of constituent organic chemicals. Organic chemicals may interact with pollutant metals directly, or may bring about changes in speciation and solubility indirectly by acting upon MnO{sub 2} and FeOOH host phases. The primary application of this work is the understanding of metal sorption and release processes within subsurface environments undergoing changes in redox status.

Stone, A.T.

1992-01-01

64

Visible light-induced photocatalytic reduction of graphene oxide by tungsten oxide thin films  

NASA Astrophysics Data System (ADS)

Tungsten oxide thin films (deposited by thermal evaporation or sol gel method) were used for photocatalytic reduction of graphene oxide (GO) platelets (synthesized through a chemical exfoliation method) on surface of the films under UV or visible light of the environment, in the absence of any aqueous ambient at room temperature. Atomic force microscopy (AFM) technique was employed to characterize surface morphology of the GO sheets and the tungsten oxide films. Moreover, using X-ray photoelectron spectroscopy (XPS), chemical state of the tungsten oxide films and the photocatalytic reduction of the GO platelets were quantitatively investigated. The better performance of the sol-gel tungsten oxide films in photocatalytic reduction of GO platelets as compared to the evaporated tungsten oxide films was assigned to lower W5+/W6+ ratio (i.e., a better stoichiometry) and higher surface water content of the sol-gel film. The GO reduction level achieved after 24 h UV-assisted photocatalytic reduction on surface of the sol-gel tungsten oxide film was comparable with the reduction level usually obtainable by hydrazine. The sol-gel tungsten oxide film even showed an efficient photocatalytic reduction of the GO platelets after exposure to the visible light of the environment for 2 days.

Choobtashani, M.; Akhavan, O.

2013-07-01

65

ASSESSMENT OF HOUSEHOLD CARBON FOOTPRINT REDUCTION POTENTIALS  

SciTech Connect

The term ?household carbon footprint? refers to the total annual carbon emissions associated with household consumption of energy, goods, and services. In this project, Lawrence Berkeley National Laboratory developed a carbon footprint modeling framework that characterizes the key underlying technologies and processes that contribute to household carbon footprints in California and the United States. The approach breaks down the carbon footprint by 35 different household fuel end uses and 32 different supply chain fuel end uses. This level of end use detail allows energy and policy analysts to better understand the underlying technologies and processes contributing to the carbon footprint of California households. The modeling framework was applied to estimate the annual home energy and supply chain carbon footprints of a prototypical California household. A preliminary assessment of parameter uncertainty associated with key model input data was also conducted. To illustrate the policy-relevance of this modeling framework, a case study was conducted that analyzed the achievable carbon footprint reductions associated with the adoption of energy efficient household and supply chain technologies.

Kramer, Klaas Jan; Homan, Greg; Brown, Rich; Worrell, Ernst; Masanet, Eric

2009-04-15

66

Size-reduction of nanodiamonds via air oxidation  

E-print Network

Here we report the size reduction and effects on nitrogen-vacancy centres in nanodiamonds by air oxidation using a combined atomic force and confocal microscope. The average height reduction of individual crystals as measured by atomic force microscopy was 10.6 nm/h at 600 {\\deg}C air oxidation at atmospheric pressure. The oxidation process modified the surface including removal of non-diamond carbon and organic material which also led to a decrease in background fluorescence. During the course of the nanodiamond size reduction, we observed the annihilation of nitrogen-vacancy centres which provided important insight into the formation of colour centres in small crystals. In these unirradiated samples, the smallest nanodiamond still hosting a stable nitrogen-vacancy centre observed was 8 nm.

T. Gaebel; C. Bradac; J. Chen; P. Hemmer; J. R. Rabeau

2011-04-27

67

Size-reduction of nanodiamonds via air oxidation  

E-print Network

Here we report the size reduction and effects on nitrogen-vacancy centres in nanodiamonds by air oxidation using a combined atomic force and confocal microscope. The average height reduction of individual crystals as measured by atomic force microscopy was 10.6 nm/h at 600 {\\deg}C air oxidation at atmospheric pressure. The oxidation process modified the surface including removal of non-diamond carbon and organic material which also led to a decrease in background fluorescence. During the course of the nanodiamond size reduction, we observed the annihilation of nitrogen-vacancy centres which provided important insight into the formation of colour centres in small crystals. In these unirradiated samples, the smallest nanodiamond still hosting a stable nitrogen-vacancy centre observed was 8 nm.

Gaebel, T; Chen, J; Hemmer, P; Rabeau, J R

2011-01-01

68

Abiotic sulfide oxidation via manganese reduction fuels the deep biosphere  

Microsoft Academic Search

The deep biosphere in marine sediments consists of large populations of metabolically active Bacteria and Archaea [1, 2]. Buried organic carbon is the main energy source for the deep biosphere and is anaerobically oxidized via nitrate-, Mn(IV)-, Fe(III)-, sulfate or carbonate-reduction. Sulfate reduction has been identified as the most important of these processes [3, 4] yet sulfate is typically quantitatively

S. Bottrell; M. E. Böttcher; A. Schippers; R. Parkes; R. Raiswell

2009-01-01

69

Sulfate reduction and anaerobic methane oxidation in Black Sea sediments  

Microsoft Academic Search

Beyond the shelf break at ca. 150m water depth, sulfate reduction is the only important process of organic matter oxidation in Black Sea sediments from the surface down to the sulfate–methane transition at 2–4m depth. Sulfate reduction rates were measured experimentally with 35SO42?, and the rates were compared with results of two diffusion-reaction models. The results showed that, even in

Bo Barker Jørgensen; Andreas Weber; Jakob Zopfi

2001-01-01

70

Spectroscopic Characterization and Assignment of Reduction Potentials in the Tetraheme Cytochrome c554 from  

E-print Network

Spectroscopic Characterization and Assignment of Reduction Potentials in the Tetraheme Cytochrome c, Minnesota 55108 Received July 8, 2002 ; E-mail: hendrich@andrew.cmu.edu Abstract: The tetraheme cytochrome c in the biological oxidation of ammonia. The protein contains one 5-coordinate heme and three bis-His coordinated

Hendrich, Mike

71

Oxidation of aromatic contaminants coupled to microbial iron reduction  

USGS Publications Warehouse

THE contamination of sub-surface water supplies with aromatic compounds is a significant environmental concern1,2. As these contaminated sub-surface environments are generally anaerobic, the microbial oxidation of aromatic compounds coupled to nitrate reduction, sulphate reduction and methane production has been studied intensively1-7. In addition, geochemical evidence suggests that Fe(III) can be an important electron acceptor for the oxidation of aromatic compounds in anaerobic groundwater. Until now, only abiological mechanisms for the oxidation of aromatic compounds with Fe(III) have been reported8-12. Here we show that in aquatic sediments, microbial activity is necessary for the oxidation of model aromatic compounds coupled to Fe(III) reduction. Furthermore, a pure culture of the Fe(III)-reducing bacterium GS-15 can obtain energy for growth by oxidizing benzoate, toluene, phenol or p-cresol with Fe(III) as the sole electron acceptor. These results extend the known physiological capabilities of Fe(III)-reducing organisms and provide the first example of an organism of any type which can oxidize an aromatic hydrocarbon anaerobically. ?? 1989 Nature Publishing Group.

Lovley, D.R.; Baedecker, M.J.; Lonergan, D.J.; Cozzarelli, I.M.; Phillips, E.J.P.; Siegel, D.I.

1989-01-01

72

Changes in hydrogen-bond strengths explain reduction potentials in 10 rubredoxin variants  

PubMed Central

The rubredoxin from Clostridium pasteurianum (CpRd) provides an excellent system for investigating how the protein sequence modulates the reduction potential of the active site in an iron–sulfur protein. 15N NMR spectroscopy has allowed us to determine with unprecedented accuracy the strengths of all six key hydrogen bonds between protein backbone amides and the sulfur atoms of the four cysteine residues that ligate the iron in the oxidized (FeIII) and reduced (FeII) forms of wild-type CpRd and nine mutants (V44G, V44A, V44I, V44L, V8G, V8A, V8I, V8L, and V8G/V44G). The length (or strength) of each hydrogen bond was inferred from the magnitude of electron spin delocalized across the hydrogen bond from the iron atom onto the nitrogen. The aggregate lengths of these six hydrogen bonds are shorter in both oxidation states in variants with higher reduction potential than in those with lower reduction potential. Differences in aggregate hydrogen bonding upon reduction correlate linearly with the published reduction potentials for the 10 CpRd variants, which span 126 mV. Sequence effects on the reduction potential can be explained fully by their influence on hydrogen-bond strengths. PMID:16199518

Lin, I-Jin; Gebel, Erika B.; Machonkin, Timothy E.; Westler, William M.; Markley, John L.

2005-01-01

73

Measuring the poverty reduction potential of land in rural Mexico  

E-print Network

-3310, United States Received 1 October 2002; accepted 1 February 2004 Abstract To help inform the currentMeasuring the poverty reduction potential of land in rural Mexico Frederico Finan, Elisabeth debate on the role of land as an instrument for poverty reduction, we analyze the conditions under which

Sadoulet, Elisabeth

74

Identifying Sequence Determinants of Reduction Potentials of Metalloproteins  

PubMed Central

The reduction potential of an electron transfer protein is one of its most important functional characteristics. While the type of redox site and the protein fold are the major determinants of the reduction potential of a redox active protein, its amino acid sequence may tune the reduction potential as well. Thus, homologous proteins can often be divided into different classes, with each class characterized by a biological function and a reduction potential. Site-specific mutagenesis of the sequence determinants of the differences in the reduction potential between classes should change the reduction potential of a protein in one class to that of the other class. Here, a procedure is presented that combines energetic and bioinformatics analysis of homologous proteins for identifying sequence determinants that are also good candidates for site-specific mutations, using the [4Fe-4S]-ferredoxins and the [4Fe-4S]-HiPIPs as examples. This procedure is designed to guide site-specific mutations or more computationally expensive studies, such as molecular dynamics simulations. To make the procedure more accessible to the general scientific community, it is being implemented into CHARMMing, a web-based portal, with a library of density functional theory results for the redox site that used in the set up of Poisson-Boltzmann continuum electrostatics calculations for the protein energetics. PMID:23690205

Perrin, Bradley Scott; Ichiye, Toshiko

2013-01-01

75

Mechanisms of oxidative vs. reductive nitrobenzene transformation by microorganisms  

Microsoft Academic Search

Nitroaromatic compounds such as nitrobenzene (NB), are widespread environmental contaminants. In natural attenuation processes selected microorganisms are able to degrade nitrobenzene via two different pathways, that is oxidation of nitrobenzene to catechol and reduction to aniline, respectively. Since both processes occur under oxic conditions but the latter leads to products of similar toxicity than the initial contaminant, it is necessary

Ivo Caravatti; Thomas Hofstetter

76

Direct plutonium oxide reduction\\/electrorefining interface program  

Microsoft Academic Search

Research test work and production data evaluation were performed by the Direct Oxide Reduction (DOR)\\/Electrorefining (ER) Interface Task Team to determine the cause for poor efficiency and yields during ER of DOR metal product. Production data and preliminary test results provided a working hypothesis. Extremely high loadings of impurities (whatever their exact source and identity) in the DOR product metal

C. E. Baldwin; J. W. Berry; R. E. Giebel; J. L. Long; W. S. Moser; J. D. Navratil; S. F. Tibbitts

1986-01-01

77

Tyrosine can protect against oxidative stress through ferryl hemoglobin reduction.  

PubMed

The toxic mechanism of hemoglobin (Hb) under oxidative stress is linked to the formations of highly cytotoxic ferryl species and subsequently heme-to-protein cross-linked derivative of Hb (Hb-X). In this study, we have examined the effects of free tyrosine and its analogues (3-chlorotyrosine, phenylalanine) on the stability of ferryl hemoglobin and the formation of Hb-X. The results showed that free tyrosine (not phenylalanine, 10-500 ?M) was an efficient reducing agent of ferryl species and also effective at preventing the formation of cytotoxic Hb-X. Meanwhile, the dimeric tyrosine was formed as the oxidation product of tyrosine during Hb redox reaction. Compared with free tyrosine, 3-chlorotyrosine, an oxidation product of tyrosine and a proposed biomarker for hypochlorous acid (HOCl) in vivo, exhibited stronger antioxidant properties in Hb-induced oxidative stress, which was consistent with its more efficient ability in the reduction of ferryl species. These results showed that the presence of tyrosine and its derivative in vivo and vitro could ameliorate oxidative damage through ferryl heme reduction. The antioxidant ability, therefore, may provide new insights into the nutritional and physiological significance of free tyrosine with redox active heme proteins-related oxidative stress. PMID:24698734

Lu, Naihao; He, Yingjie; Chen, Chao; Tian, Rong; Xiao, Qiang; Peng, Yi-Yuan

2014-08-01

78

Biological reduction of graphene oxide using plant leaf extracts.  

PubMed

Two-dimensional graphene has attracted significant attention due to its unique mechanical, electrical, thermal, and optical properties. Most commonly employed methods to chemically reduce graphene oxide to graphene use hydrazine or its derivatives as the reducing agent. However, they are highly hazardous and explosive. Various phytochemicals obtained from different natural sources such as leaves and peels of a plant are used as reducing agents in the preparation of different gold, silver, copper, and platinum nanoparticles. In this study, seven plant leaf extracts (Cherry, Magnolia, Platanus, Persimmon, Pine, Maple, and Ginkgo) were compared for their abilities to reduce graphene oxide. The optimized reaction conditions for the reduction of graphene oxide were determined as follows. Type of plant: Cherry (Prunus serrulata), reaction time: 12 h, composition of the reaction mixture: 16.7% v/v of plant leaf extract in total suspension, and temperature: 95°C. The degree of reduction caused by Cherry leaf extract was analyzed by elemental analysis and X-ray photoelectron spectroscopy. The reduction of graphene oxide was also confirmed by ultraviolet-visible spectroscopy, Fourier transform-infrared spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and thermogravimetric analysis. PMID:24375994

Lee, Geummi; Kim, Beom Soo

2014-01-01

79

Nanosized Iron Oxide Colloids Strongly Enhance Microbial Iron Reduction? †  

PubMed Central

Microbial iron reduction is considered to be a significant subsurface process. The rate-limiting bioavailability of the insoluble iron oxyhydroxides, however, is a topic for debate. Surface area and mineral structure are recognized as crucial parameters for microbial reduction rates of bulk, macroaggregate iron minerals. However, a significant fraction of iron oxide minerals in the subsurface is supposed to be present as nanosized colloids. We therefore studied the role of colloidal iron oxides in microbial iron reduction. In batch growth experiments with Geobacter sulfurreducens, colloids of ferrihydrite (hydrodynamic diameter, 336 nm), hematite (123 nm), goethite (157 nm), and akaganeite (64 nm) were added as electron acceptors. The colloidal iron oxides were reduced up to 2 orders of magnitude more rapidly (up to 1,255 pmol h?1 cell?1) than bulk macroaggregates of the same iron phases (6 to 70 pmol h?1 cell?1). The increased reactivity was not only due to the large surface areas of the colloidal aggregates but also was due to a higher reactivity per unit surface. We hypothesize that this can be attributed to the high bioavailability of the nanosized aggregates and their colloidal suspension. Furthermore, a strong enhancement of reduction rates of bulk ferrihydrite was observed when nanosized ferrihydrite aggregates were added. PMID:19915036

Bosch, Julian; Heister, Katja; Hofmann, Thilo; Meckenstock, Rainer U.

2010-01-01

80

Anaerobic oxidation of arsenite linked to chlorate reduction.  

PubMed

Microorganisms play a significant role in the speciation and mobility of arsenic in the environment. In this study, the oxidation of arsenite [As(III)] to arsenate [As(V)] linked to chlorate (ClO??) reduction was shown to be catalyzed by sludge samples, enrichment cultures (ECs), and pure cultures incubated under anaerobic conditions. No activity was observed in treatments lacking inoculum or with heat-killed sludge, or in controls lacking ClO??. The As(III) oxidation was linked to the complete reduction of ClO?? to Cl?, and the molar ratio of As(V) formed to ClO?? consumed approached the theoretical value of 3:1 assuming the e? equivalents from As(III) were used to completely reduce ClO??. In keeping with O? as a putative intermediate of ClO?? reduction, the ECs could also oxidize As(III) to As(V) with O? at low concentrations. Low levels of organic carbon were essential in heterotrophic ECs but not in autotrophic ECs. 16S rRNA gene clone libraries indicated that the ECs were dominated by clones of Rhodocyclaceae (including Dechloromonas, Azospira, and Azonexus phylotypes) and Stenotrophomonas under autotrophic conditions. Additional phylotypes (Alicycliphilus, Agrobacterium, and Pseudoxanthomonas) were identified in heterotrophic ECs. Two isolated autotrophic pure cultures, Dechloromonas sp. strain ECC1-pb1 and Azospira sp. strain ECC1-pb2, were able to grow by linking the oxidation of As(III) to As(V) with the reduction of ClO??. The presence of the arsenite oxidase subunit A (aroA) gene was demonstrated with PCR in the ECs and pure cultures. This study demonstrates that ClO?? is an alternative electron acceptor to support the microbial oxidation of As(III). PMID:20729322

Sun, Wenjie; Sierra-Alvarez, Reyes; Milner, Lily; Field, Jim A

2010-10-01

81

Anaerobic Oxidation of Arsenite Linked to Chlorate Reduction? †  

PubMed Central

Microorganisms play a significant role in the speciation and mobility of arsenic in the environment. In this study, the oxidation of arsenite [As(III)] to arsenate [As(V)] linked to chlorate (ClO3?) reduction was shown to be catalyzed by sludge samples, enrichment cultures (ECs), and pure cultures incubated under anaerobic conditions. No activity was observed in treatments lacking inoculum or with heat-killed sludge, or in controls lacking ClO3?. The As(III) oxidation was linked to the complete reduction of ClO3? to Cl?, and the molar ratio of As(V) formed to ClO3? consumed approached the theoretical value of 3:1 assuming the e? equivalents from As(III) were used to completely reduce ClO3?. In keeping with O2 as a putative intermediate of ClO3? reduction, the ECs could also oxidize As(III) to As(V) with O2 at low concentrations. Low levels of organic carbon were essential in heterotrophic ECs but not in autotrophic ECs. 16S rRNA gene clone libraries indicated that the ECs were dominated by clones of Rhodocyclaceae (including Dechloromonas, Azospira, and Azonexus phylotypes) and Stenotrophomonas under autotrophic conditions. Additional phylotypes (Alicycliphilus, Agrobacterium, and Pseudoxanthomonas) were identified in heterotrophic ECs. Two isolated autotrophic pure cultures, Dechloromonas sp. strain ECC1-pb1 and Azospira sp. strain ECC1-pb2, were able to grow by linking the oxidation of As(III) to As(V) with the reduction of ClO3?. The presence of the arsenite oxidase subunit A (aroA) gene was demonstrated with PCR in the ECs and pure cultures. This study demonstrates that ClO3? is an alternative electron acceptor to support the microbial oxidation of As(III). PMID:20729322

Sun, Wenjie; Sierra-Alvarez, Reyes; Milner, Lily; Field, Jim A.

2010-01-01

82

Selective insertion of sulfur dioxide reduction intermediates on graphene oxide.  

PubMed

Graphite microparticles (d50 6.20 ?m) were oxidized by strong acids, and the resultant graphite oxide was thermally exfoliated to graphene oxide sheets (MPGO, C/O 1.53). Graphene oxide was treated with nonthermal plasma under a SO2 atmosphere at room temperature. The XPS spectrum showed that SO2 was inserted only as the oxidized intermediate at 168.7 eV in the S 2p region. Short thermal shocks at 600 and 400 °C, under an Ar atmosphere, produced reduced sulfur and carbon dioxide as shown by the XPS spectrum and TGA analysis coupled to FTIR. MPGO was also submitted to thermal reaction with SO2 at 630 °C, and the XPS spectrum in the S 2p region at 164.0 eV showed that this time only the nonoxidized episulfide intermediate was inserted. Plasma and thermal treatment produced a partial reduction of MPGO. The sequence of thermal reaction followed by plasma treatment inserted both sulfur intermediates. Because oxidized and nonoxidized intermediates have different reactivities, this selective insertion would allow the addition of selective types of organic fragments to the surface of graphene oxide. PMID:24605942

Humeres, Eduardo; Debacher, Nito A; Smaniotto, Alessandra; de Castro, Karen M; Benetoli, Luís O B; de Souza, Eduardo P; Moreira, Regina de F P M; Lopes, Cristiane N; Schreiner, Wido H; Canle, Moisés; Santaballa, J Arturo

2014-04-22

83

Landscape Planning for Agricultural Nonpoint Source Pollution Reduction III: Assessing Phosphorus and Sediment Reduction Potential  

Microsoft Academic Search

Riparian buffers have the potential to improve stream water quality in agricultural landscapes. This potential may vary in response to landscape characteristics such as soils, topography, land use, and human activities, including legacies of historical land management. We built a predictive model to estimate the sediment and phosphorus load reduction that should be achievable following the implementation of riparian buffers;

Matthew W. Diebel; Jeffrey T. Maxted; Dale M. Robertson; Seungbong Han; M. Jake Vander Zanden

2009-01-01

84

Oxidation-Reduction Properties of Mixed Oxides in Lanthanum-Uranium-Oxygen System  

Microsoft Academic Search

The oxidation-reduction properties and the phase relations of mixed oxides in the system La-U-O were examined by means of thermogravimetry and X-ray diffraction method. The O\\/M ratios of the mixed oxides LayU1-yO2±x, prepared at 1,650°C in vacuo by the reaction of La2O3 and UO2, were expressed as 2–0.5 y except 0.2?y?0.4. The oxides were the single fluorite phase at y0.7.

Hiroaki TAGAWA; Takeo FUJINO; Kinji OUCHI; Kenju WATANABE; Koji SAITA; Takao MORIMOTO

1983-01-01

85

Oxidation Potentials in Iron and Steel Making  

NASA Astrophysics Data System (ADS)

The state of oxidation of a pyrometallurgical process given by the partial pressure of oxygen and the temperature (the oxidation potential) is one of the important properties monitored and controlled in the smelting and refining of iron and the nonferrous metals. Solid electrolyte sensors based on ZrO2 and a reference electrode such as Cr/Cr2O3 to measure the oxygen pressure found early application in the steel industry, followed soon after in copper, nickel, lead, and zinc smelting. Similar devices are installed in automobile postcombustion/exhaust trains as part of emission control systems. The current discussion reviews this technology as applied in the primary steps of iron and steel making and refining.

Matousek, J. W.

2013-11-01

86

Isoniazid: Radical-induced oxidation and reduction chemistry.  

PubMed

Isoniazid is a potent and selective therapeutic prodrug agent used to treat infections by Mycobacterium tuberculosis. Although it has been used clinically for over five decades its full mechanism of action is still being elucidated. Essential to its mechanism of action is the activation of isoniazid to a reactive intermediate, the isonicotinyl acyl radical, by the catalase-peroxidase KatG. The isonicotinyl acyl radical then reacts with NAD producing an inhibitor of the NADH-dependent enoyl ACP reductase responsible for mycolic acid synthesis as its primary target. However, the initial oxidation of isoniazid by KatG has also revealed alternative reaction pathways leading to an array of carbon-, oxygen-, and nitrogen-centered radical intermediates. It has also been reported that isoniazid produces nitric oxide in the presence of KatG and hydrogen peroxide. In this study, the temperature-dependent rate constants for the hydroxyl radical oxidation and solvated electron reduction of isoniazid and two model compounds have been studied. Based on these data the initial oxidation of isoniazid by the hydroxyl radical has been shown to predominantly occur at the primary nitrogen of the hydrazyl moiety, consistent with the postulated mechanism for the formation of the isonicotinyl radical. The hydrated electron reduction occurred mostly at the pyridine ring. Concomitant EPR spin-trap measurements under a variety of oxidizing and reducing conditions did not show any evidence of nitric oxide production as had been previously reported. Finally, examination of the transient absorption spectra obtained for hydrated electron reaction with isoniazid demonstrated for the first time an initial reduced transient identified as the isonicotinyl acyl radical produced from isoniazid. PMID:23562055

Rickman, Kimberly A; Swancutt, Katy L; Mezyk, Stephen P; Kiddle, James J

2013-05-15

87

Potential role of bicarbonate during pyrite oxidation  

SciTech Connect

The need to prevent the development of acid mine drainage (AMD) by oxidation of pyrite has triggered numerous investigations into the mechanisms of its oxidation. According to Frontier molecular orbital (FMO) theory, the surface-exposed sulfur atom of pyrite possesses an unshared electron pair which produces a slightly negatively charged pyrite surface that can attract cations such as Fe{sup 2+}. Because of surface electroneutrality and pH considerations, however, the pyrite surface Fe{sup 2+} coordinates OH. The authors proposed that this surface Fe{sup 2+} OH when in the presence of CO{sub 2} is converted to {minus}FeCO{sub 3} or {minus}FeHCO{sub 3}, depending on pH. In this study, using Fourier transform infrared spectroscopy (FT-IR) they demonstrated that such complexes form on the surface of pyrite and continue to persist even after a significant fraction of the surface Fe{sup 2+} was oxidized to Fe{sup 3+}. FT-IR spectra also showed the presence of two carbonyl absorption bands (1,682 and 1,653 cm{sup {minus}1}) on the surface of pyrite upon exposure to CO{sub 2} which suggested that pyrite surface carbon complexes existed in two different surface chemical environments, pointing out two potential mechanisms of pyrite surface-CO{sub 2} interactions. One potential mechanism involved formation of a pyrite surface-Fe(II)HCO{sub 3} complex, whereas a second potential mechanism involved formation of a pyrite surface-carboxylic acid group complex [{minus}Fe(II)SSCOOFe-(II)].

Evangelou, V.P.; Holt, A. [Univ. of Kentucky, Lexington, KY (United States). Dept. of Agronomy] [Univ. of Kentucky, Lexington, KY (United States). Dept. of Agronomy; Seta, A.K. [Univ. Bengkulu (Indonesia). Fakultas Pertanian] [Univ. Bengkulu (Indonesia). Fakultas Pertanian

1998-07-15

88

Long-step strategies in interior point potential reduction methods  

SciTech Connect

We analyze from a unique point of view the behavior of path-following and primal-dual potential reduction methods on nonlinear conic problems. We demonstrate that the most of the interior-point methods with O({radical}n ln {sub {epsilon}} {sup 1}) efficiency estimate can be considered as different strategies of minimization of a convex primal-dual potential in an extended primal-dual space. Their efficiency estimate is a direct consequence of large local norm of the gradient of the potential along a central path. It is shown that the neighborhood of this path is a region of the fastest decrease of the convex potential. Therefore the long-step path-following methods are, in a sense, the best potential-reduction strategies. We present three examples of such long-step strategies. We prove also the efficiency estimate for a pure primal-dual potential reduction method, which can be considered as an implementation of a penalty strategy based on a {open_quotes}functional{close_quotes} proximity measure.

Nesterov, Y.

1994-12-31

89

An Investigation Into the Potential for PVC Reduction in  

E-print Network

An Investigation Into the Potential for PVC Reduction in Residential Building Drainage Lines A Triple Bottom Line Analysis of PVC vs. HDPE For Penny Martyn, Stakeholder of Project, Green Building for flexibility and cheap cost, PVC comes with numerous harmful side-effects to both the environment

90

1. West facade of Plutonium Concentration Facility (Building 233S), ReductionOxidation ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. West facade of Plutonium Concentration Facility (Building 233-S), Reduction-Oxidation Building (REDOX-202-S) to the right. Looking east. - Reduction-Oxidation Complex, Plutonium Concentration Facility, 200 West Area, Richland, Benton County, WA

91

Landscape Planning for Agricultural Nonpoint Source Pollution Reduction III: Assessing Phosphorus and Sediment Reduction Potential  

NASA Astrophysics Data System (ADS)

Riparian buffers have the potential to improve stream water quality in agricultural landscapes. This potential may vary in response to landscape characteristics such as soils, topography, land use, and human activities, including legacies of historical land management. We built a predictive model to estimate the sediment and phosphorus load reduction that should be achievable following the implementation of riparian buffers; then we estimated load reduction potential for a set of 1598 watersheds (average 54 km2) in Wisconsin. Our results indicate that land cover is generally the most important driver of constituent loads in Wisconsin streams, but its influence varies among pollutants and according to the scale at which it is measured. Physiographic (drainage density) variation also influenced sediment and phosphorus loads. The effect of historical land use on present-day channel erosion and variation in soil texture are the most important sources of phosphorus and sediment that riparian buffers cannot attenuate. However, in most watersheds, a large proportion (approximately 70%) of these pollutants can be eliminated from streams with buffers. Cumulative frequency distributions of load reduction potential indicate that targeting pollution reduction in the highest 10% of Wisconsin watersheds would reduce total phosphorus and sediment loads in the entire state by approximately 20%. These results support our approach of geographically targeting nonpoint source pollution reduction at multiple scales, including the watershed scale.

Diebel, Matthew W.; Maxted, Jeffrey T.; Robertson, Dale M.; Han, Seungbong; Vander Zanden, M. Jake

2009-01-01

92

Landscape planning for agricultural nonpoint source pollution reduction III: Assessing phosphorus and sediment reduction potential  

USGS Publications Warehouse

Riparian buffers have the potential to improve stream water quality in agricultural landscapes. This potential may vary in response to landscape characteristics such as soils, topography, land use, and human activities, including legacies of historical land management. We built a predictive model to estimate the sediment and phosphorus load reduction that should be achievable following the implementation of riparian buffers; then we estimated load reduction potential for a set of 1598 watersheds (average 54 km2) in Wisconsin. Our results indicate that land cover is generally the most important driver of constituent loads in Wisconsin streams, but its influence varies among pollutants and according to the scale at which it is measured. Physiographic (drainage density) variation also influenced sediment and phosphorus loads. The effect of historical land use on present-day channel erosion and variation in soil texture are the most important sources of phosphorus and sediment that riparian buffers cannot attenuate. However, in most watersheds, a large proportion (approximately 70%) of these pollutants can be eliminated from streams with buffers. Cumulative frequency distributions of load reduction potential indicate that targeting pollution reduction in the highest 10% of Wisconsin watersheds would reduce total phosphorus and sediment loads in the entire state by approximately 20%. These results support our approach of geographically targeting nonpoint source pollution reduction at multiple scales, including the watershed scale. ?? 2008 Springer Science+Business Media, LLC.

Diebel, M.W.; Maxted, J.T.; Robertson, D.M.; Han, S.; Vander Zanden, M. J.

2009-01-01

93

Oxidation-Reduction Calculations in the Biochemistry Course  

ERIC Educational Resources Information Center

Redox calculations have the potential to reinforce important concepts in bioenergetics. The intermediacy of the NAD[superscript +]/NADH couple in the oxidation of food by oxygen, for example, can be brought out by such calculations. In practice, students have great difficulty and, even when adept at the calculations, frequently do not understand…

Feinman, Richard D.

2004-01-01

94

Extent of Reduction of Vanadium Oxides during Catalytic Oxidation of Alkanes Measured by in-Situ UV-Visible Spectroscopy  

E-print Network

Extent of Reduction of Vanadium Oxides during Catalytic Oxidation of Alkanes Measured by in-Situ UV to oxidation reactions using lattice oxygens as reactive intermediates. Introduction Oxidative alkane-visible spectroscopy probes the electronic structure of oxide domains commonly used in alkane ODH catalysis.6

Bell, Alexis T.

95

Multiple reaction fronts in the oxidation-reduction of iron-rich uranium ores  

SciTech Connect

When a container of radioactive waste is buried underground, it eventually corrodes, and leakage of radioactive material to the surrounding rock occurs. Depending on the chemistry of the rock, many different reactions may occur. A particular case concerns the oxidation and reduction of uranium ores by infiltrating groundwater, since UO[sub 3] is relatively soluble (and hence potentially transportable to the water supply), whereas UO[sub 2] is essentially insoluble. It is therefore of concern to those involved with radioactive waste disposal to understand the mechanics of uranium transport through reduction and oxidation reactions. This paper describes the oxidation of iron-rich uranium-bearing rocks by infiltration of groundwater. A reaction-diffusion model is set up to describe the sequence of reactions involving iron oxidation, uranium oxidation and reduction, sulfuric acid production, and dissolution of the host rock that occur. On a geological timescale of millions of years, the reactions occur very fast in very thin reaction fronts. It is shown that the redox front that separates oxidized (orange) rock from reduced (black) rock must actually consist of two separate fronts that move together, at which the two separate processes of uranium oxidation and iron reduction occur, respectively. Between these fronts, a high concentration of uranium is predicted. The mechanics of this process are not specific to uranium-mediated redox reactions, but apply generally and may be used to explain the formation of concentrated ore deposits in extended veins. On the long timescales of relevance, a quasi-static response results, and the problem can be solved explicitly in one dimension. This provides a framework for studying more realistic two-dimensional problems in fissured rocks and also for the future study of uraninite nodule formation.

Dewynne, J.N. (Univ. of Southampton (United Kingdom). Faculty of Mathematical Studies); Fowler, A.C. (Oxford Univ. (United Kingdom). Mathematical Inst.); Hagan, P.S. (Los Alamos National Lab., NM (United States))

1993-08-01

96

Pre-converted nitric oxide gas in catalytic reduction system  

DOEpatents

A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO.sub.2 in the presence of O.sub.2. The second stage serves to convert NO.sub.2 to environmentally benign gases that include N2, CO2, and H.sub.2 O. By preconverting NO to NO.sub.2 in the first stage, the efficiency of the second stage for NO.sub.x reduction is enhanced. For example, an internal combustion engine exhaust is connected by a pipe to a first chamber. An oxidizing first catalyst converts NO to NO.sub.2 in the presence of O.sub.2 and includes platinum/alumina, e.g., Pt/Al.sub.2 O.sub.3 catalyst. A flow of hydrocarbons (C.sub.x H.sub.y) is input from a pipe into a second chamber. For example, propene can be used as a source of hydrocarbons. The NO.sub.2 from the first catalyst mixes with the hydrocarbons in the second chamber. The mixture proceeds to a second reduction catalyst that converts NO.sub.2 to N2, CO2, and H.sub.2 O, and includes a gamma-alumina .gamma.-Al.sub.2 O.sub.3. The hydrocarbons and NO.sub.x are simultaneously reduced while passing through the second catalyst.

Hsiao, Mark C. (Livermore, CA); Merritt, Bernard T. (Livermore, CA); Penetrante, Bernardino M. (San Ramon, CA); Vogtlin, George E. (Fremont, CA)

1999-01-01

97

Pre-converted nitric oxide gas in catalytic reduction system  

DOEpatents

A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO{sub 2} in the presence of O{sub 2}. The second stage serves to convert NO{sub 2} to environmentally benign gases that include N{sub 2}, CO{sub 2}, and H{sub 2}O. By preconverting NO to NO{sub 2} in the first stage, the efficiency of the second stage for NO{sub x} reduction is enhanced. For example, an internal combustion engine exhaust is connected by a pipe to a first chamber. An oxidizing first catalyst converts NO to NO{sub 2} in the presence of O{sub 2} and includes platinum/alumina, e.g., Pt/Al{sub 2}O{sub 3} catalyst. A flow of hydrocarbons (C{sub x}H{sub y}) is input from a pipe into a second chamber. For example, propene can be used as a source of hydrocarbons. The NO{sub 2} from the first catalyst mixes with the hydrocarbons in the second chamber. The mixture proceeds to a second reduction catalyst that converts NO{sub 2} to N{sub 2}, CO{sub 2}, and H{sub 2}O, and includes a {gamma}-Al{sub 2}O{sub 3}. The hydrocarbons and NO{sub x} are simultaneously reduced while passing through the second catalyst. 9 figs.

Hsiao, M.C.; Merritt, B.T.; Penetrante, B.M.; Vogtlin, G.E.

1999-04-06

98

Landscape Planning for Agricultural Nonpoint Source Pollution Reduction III: Assessing Phosphorus and Sediment Reduction Potential  

Microsoft Academic Search

Riparian buffers have the potential to improve stream water quality in agricultural landscapes. This potential may vary in\\u000a response to landscape characteristics such as soils, topography, land use, and human activities, including legacies of historical\\u000a land management. We built a predictive model to estimate the sediment and phosphorus load reduction that should be achievable\\u000a following the implementation of riparian buffers;

Matthew W. Diebel; Jeffrey T. Maxted; Dale M. Robertson; Seungbong Han; M. Jake Vander Zanden

2009-01-01

99

Aggregate-scale heterogeneity in iron (hydr)oxide reductive transformations  

Microsoft Academic Search

There is growing awareness of the complexity of potential reaction pathways and the associated solid-phase transformations during the reduction of Fe (hydr)oxides, especially ferrihydrite. An important observation in static and advective-dominated systems is that microbially produced Fe(II) accelerates Ostwald ripening of ferrihydrite, thus promoting the formation of thermodynamically more stable ferric phases (lepidocrocite and goethite) and, at higher Fe(II) surface

Katharine J. Tufano; Shawn G. Benner; Klaus U. Mayer; Matthew A. Marcus; Peter S. Nico; Scott Fendorf

2009-01-01

100

Abiotic sulfide oxidation via manganese reduction fuels the deep biosphere  

NASA Astrophysics Data System (ADS)

The deep biosphere in marine sediments consists of large populations of metabolically active Bacteria and Archaea [1, 2]. Buried organic carbon is the main energy source for the deep biosphere and is anaerobically oxidized via nitrate-, Mn(IV)-, Fe(III)-, sulfate or carbonate-reduction. Sulfate reduction has been identified as the most important of these processes [3, 4] yet sulfate is typically quantitatively removed from pore waters in the upper few meters of marine sediments. A key question remains: “How is continued metabolic activity maintained in the deep biosphere?”. Buried organic carbon remains as an electron donor but the source of electron acceptors is less clear. Stable isotope compositions of sulfur and oxygen in sulfate are particularly useful in the study of biogeochemical processes and sediment-pore fluid interactions e.g. [5, 6]. Here we use stable sulfur and oxygen isotope compositions to show that the oxidant sulfate is generated by anoxic sulfide oxidation in deeply buried sediments of the Cascadia margin and Blake Ridge and controlled anoxic experiments to constrain the mechanisms involved on this reaction. Pore fluid sulfate in deep Cascadia margin and Blake Ridge sediments contained sulfur with similar isotopic composition to diagenetic sulfide in the sediment and oxygen that was depleted in 18O (in some cases depleted in 18O relative to pore water). Experiments with Mn(IV)-containing oxides confirmed that these can abiotically oxidize iron sulfides and also produce sulfate depleted in 18O relative to water. In another set of anoxic experiments, pyrite was mixed with different Fe(III) minerals. Crucially, experiments with synthesized pure Fe(III) minerals produced no sulfate but identical experiments with natural Fe(III) minerals containing trace Mn did. Sulfate concentrations in solution were stoichiometrically balanced by Mn concentrations, showing trace Mn(IV) in the natural minerals to be the oxidizing agent generating sulfate. Sulfate formed was again depleted in 18O relative to water. Experiments with 18O-labelled water show that all oxygen atoms in the sulfate formed are derived from water molecules, thus the sulfate oxygen isotopic composition represents a true fractionation from water. The depletion of 18O in sulfate relative to water thus acts as a fingerprint for sulfate produced by Mn (IV) reduction. Oxidized manganese stored within the mineral fraction of marine sediments can thus drive abiotic anaerobic sulfide oxidation which, together with microbial sulfate reduction, forms a closed sulfur cycle feeding the deep biosphere in marine sediments. [1] Parkes et al. (2005) Nature 436, 390. [2] Schippers et al. (2005) Nature 433, 861. [3] D’Hondt et al. (2002) Science 295, 2067. [4] D’Hondt et al. (2004) Science 306, 2216. Bottrell et al. (2000) J. Geol. Soc. Lond. 157, 711. [6] Böttcher et al. (2006) Proc. ODP Sci. Res. 201-109, 1.

Bottrell, S.; Böttcher, M. E.; Schippers, A.; Parkes, R.; Raiswell, R.

2009-12-01

101

Transparent Conducting Oxides as Potential Thermoelectrics  

NASA Astrophysics Data System (ADS)

Transparent conducting oxides (TCOs) in their less-doped semiconducting states have potential as thermoelectric oxides or TEOs. They are attractive as TEOs owing to: 1) their good thermochemical stability, 2) their n-type character (to complement existing p-type TEOs), and 3) their high electronic mobilities. The numerator of the TE figure of merit (Z), also known as the ``power factor'' (PF), is the product of the electronic conductivity and the square of the Seebeck coefficient. An experimental procedure named after its developer, ``Jonker'' analysis plots Seebeck coefficient vs. the natural logarithm of the electronic conductivity. Data for bulk ceramic specimens just prior to the onset of degeneracy tend to fall on a line of slope, k/e (k=Boltzmann constant, e=charge of the electron). From this line, the doping composition corresponding to the highest power factor can be determined and the PF optimized, based upon data from a few carefully chosen compositions. Subsequently, following a procedure originally derived by Ioffe, the zero-thermopower intercept of these Jonker lines can be directly related to the maximum achievable power factor for a given TEO. So-called ``Ioffe'' plots allow for meaningful comparisons between candidate TEO materials, and also indicate the minimum thermal conductivity required to achieve a target ZT value at the temperature of measurement. Results for TCO-based TEOs will be discussed for both simple and compound (including layered) materials.

Mason, Thomas

2013-03-01

102

Floating Potential Probe Langmuir Probe Data Reduction Results  

NASA Technical Reports Server (NTRS)

During its first five months of operations, the Langmuir Probe on the Floating Potential Probe (FPP) obtained data on ionospheric electron densities and temperatures in the ISS orbit. In this paper, the algorithms for data reduction are presented, and comparisons are made of FPP data with ground-based ionosonde and Incoherent Scattering Radar (ISR) results. Implications for ISS operations are detailed, and the need for a permanent FPP on ISS is examined.

Morton, Thomas L.; Minow, Joseph I.

2002-01-01

103

Removal of oxides from alkali metal melts by reductive titration to electrical resistance-change end points  

DOEpatents

Alkali metal oxides dissolved in alkali metal melts are reduced with soluble metals which are converted to insoluble oxides. The end points of the reduction is detected as an increase in electrical resistance across an alkali metal ion-conductive membrane interposed between the oxide-containing melt and a material capable of accepting the alkali metal ions from the membrane when a difference in electrical potential, of the appropriate polarity, is established across it. The resistance increase results from blocking of the membrane face by ions of the excess reductant metal, to which the membrane is essentially non-conductive.

Tsang, Floris Y. (Walnut Creek, CA)

1980-01-01

104

Design Principles for Oxygen Reduction and Evolution on Oxide Catalysts  

NASA Astrophysics Data System (ADS)

Driven by growing concerns about global warming and the depletion of petroleum resources, developing renewable energy production and storage technologies represent one of the major scientific challenges of the 21^st century. A critical element in pursuit of this quest is the discovery of efficient and cost-effective catalysts used in solar fuel production via electrochemical energy conversion processes such as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), both of which are central to the efficiencies of direct-solar and electrolytic water-splitting devices, fuel cells, and metal-air batteries. Although the Sabatier's principle provides a qualitative argument in tuning catalytic activity by varying the bond strength between catalyst surface and reactant/product (neither too strong nor too weak leading to the maximum activity at moderate bond strength), it has no predictive power to find catalysts with enhanced activity. Identifying a ``design principle'' that links catalyst properties to the catalytic activity is critical to accelerate the search for highly active catalysts based on abundant elements, and minimize the use of precious metals. Here we establish a molecular principle that governs the activities of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) for oxide catalysts, where the activities primarily correlate to the ?* orbital (``eg'') occupation of surface transition-metal cations established by systematic examination of more than ten to fifteen transition-metal oxides. The intrinsic ORR and OER activities exhibit a volcano-shaped dependence on the eg occupancy and the activities peak at an eg occupancy close to unity. Our findings reflect the critical influence of the ?* orbital on the energetics of surface reaction intermediates on surface transition metal ions such as the O2^2-/OH^- displacement and the OH^- regeneration, and thus highlight the importance of surface oxide electronic structure in controlling catalytic activities. Using the established molecular principle, we further demonstrate that an alkaline earth cobalt oxide with a chemical formula of Ba0.5Sr0.5Co0.8Fe0.2O3-? (BSCF), catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than the state-of-the-art iridium oxide catalyst in basic solutions. [4pt] [1] J. Suntivich, H.A. Gasteiger, N. Yabuuchi, H. Nakanishi, J. B. Goodenough and Y. Shao-Horn, Design Principles for Oxygen Reduction Activity on Perovskite Oxide Catalysts for Fuel Cells and Metal-Air Batteries, Nature Chemistry, 3, 546--550 (2011).[0pt] [2] Jin Suntivich, Kevin J. May, Hubert A. Gasteiger, John B. Goodenough and Yang Shao-Horn, A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital Principles, ScienceExpress, Science DOI: 10.1126/science.1212858, (2011).

Shao-Horn, Yang

2012-02-01

105

Nitrous oxide emission reduction in temperate biochar-amended soils  

NASA Astrophysics Data System (ADS)

Biochar, a pyrolysis product of organic residues, is an amendment for agricultural soils to improve soil fertility, sequester CO2 and reduce greenhouse gas (GHG) emissions. In highly weathered tropical soils laboratory incubations of soil-biochar mixtures revealed substantial reductions for nitrous oxide (N2O) and carbon dioxide (CO2). In contrast, evidence is scarce for temperate soils. In a three-factorial laboratory incubation experiment two different temperate agricultural soils were amended with green waste and coffee grounds biochar. N2O and CO2 emissions were measured at the beginning and end of a three month incubation. The experiments were conducted under three different conditions (no additional nutrients, glucose addition, and nitrate and glucose addition) representing different field conditions. We found mean N2O emission reductions of 60 % compared to soils without addition of biochar. The reduction depended on biochar type and soil type as well as on the age of the samples. CO2 emissions were slightly reduced, too. NO3- but not NH4+ concentrations were significantly reduced shortly after biochar incorporation. Despite the highly significant suppression of N2O emissions biochar effects should not be transferred one-to-one to field conditions but need to be tested accordingly.

Felber, R.; Hüppi, R.; Leifeld, J.; Neftel, A.

2012-01-01

106

Redox-Inactive Metals Modulate the Reduction Potential in Heterometallic Manganese-Oxido Clusters  

PubMed Central

Redox-inactive metals are found in biological and heterogeneous water oxidation catalysts, but their roles in catalysis are currently not well understood. A series of high oxidation state tetranuclear-dioxido clusters comprised of three manganese centers and a redox-inactive metal (M) of various charge is reported. Crystallographic studies show an unprecedented Mn3M(?4-O)(?2-O) core that remains intact upon changing M or the manganese oxidation state. Electrochemical studies reveal that the reduction potentials span a window of 700 mV, dependent upon the Lewis acidity of the second metal. With the pKa of the redox-inactive metal-aqua complex as a measure of Lewis acidity, these compounds display a linear dependence between reduction potential and acidity with a slope of ca. 100 mV per pKa unit. The Sr2+ and Ca2+ compounds show similar potentials, an observation that correlates with the behavior of the OEC, which is active only in the presence of one of these two metals. PMID:23511417

Tsui, Emily Y.; Tran, Rosalie; Yano, Junko; Agapie, Theodor

2013-01-01

107

Dose reduction potential with photon counting computed tomography  

NASA Astrophysics Data System (ADS)

Electronic noise becomes a major source of signal degradation in low-dose clinical computed tomography (CT). In current clinical scanners based on energy integrating x-ray detectors, electronic noise from the readout circuits adds a noise of constant variance, which is negligible at high counts but can be significant at low count levels. On the other hand, in a photon counting detector (PCD) with pulse height discrimination capability, electronic noise has little to no impact on the measured signal. PCDs are known for their abilities to provide useful spectral information. In this work, we investigate this dose reduction to improve low-dose single-energy CT. We perform low-dose single-energy CT simulations using both energy integrating and photon counting detectors, and compare results with both analytical and iterative reconstructions (IR). The results demonstrate the dose reduction potential of PCDs in conventional low-dose single-energy CT examinations, when spectral information is not required.

Wang, Xiaolan; Zamyatin, Alexander; Shi, Daxin

2012-03-01

108

Role of thickness and intercalated water in the facile reduction of graphene oxide employing camera flash  

NASA Astrophysics Data System (ADS)

Graphene oxide (GO) is a potential precursor for the bulk production of graphene as the synthetic route is simple and cost-effective. Typically, reduction of GO is a time-consuming process and involves either toxic/hazardous reducing agents or high temperature treatment. Herein, we report the role of intercalated water and thickness of GO films towards the reduction of GO employing simple camera flash. A fast, simple and single camera flash instantaneously causes the deoxygenation reaction of GO without employing hazardous/toxic chemical reductants at room temperature. Successful reduction of GO employing camera flash has been verified via XRD, Raman and UV-vis spectroscopic analyses. Flash-reduced graphene shows a relatively high conductivity value of 740 S m-1 with a C/O ratio of around 9.5. Intercalated water molecules facilitate the reduction by electron-hole pair formation. It has also been found that the intercalated water facilitates the reduction of GO up to a certain film thickness. However, the intensity of light passing through to the backside of a too thick film decreases significantly, causing incomplete reduction.

Bose, Saswata; Drzal, Lawrence T.

2014-02-01

109

Nitrate reduction functional genes and nitrate reduction potentials persist in deeper estuarine sediments. Why?  

PubMed

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are processes occurring simultaneously under oxygen-limited or anaerobic conditions, where both compete for nitrate and organic carbon. Despite their ecological importance, there has been little investigation of how denitrification and DNRA potentials and related functional genes vary vertically with sediment depth. Nitrate reduction potentials measured in sediment depth profiles along the Colne estuary were in the upper range of nitrate reduction rates reported from other sediments and showed the existence of strong decreasing trends both with increasing depth and along the estuary. Denitrification potential decreased along the estuary, decreasing more rapidly with depth towards the estuary mouth. In contrast, DNRA potential increased along the estuary. Significant decreases in copy numbers of 16S rRNA and nitrate reducing genes were observed along the estuary and from surface to deeper sediments. Both metabolic potentials and functional genes persisted at sediment depths where porewater nitrate was absent. Transport of nitrate by bioturbation, based on macrofauna distributions, could only account for the upper 10 cm depth of sediment. A several fold higher combined freeze-lysable KCl-extractable nitrate pool compared to porewater nitrate was detected. We hypothesised that his could be attributed to intracellular nitrate pools from nitrate accumulating microorganisms like Thioploca or Beggiatoa. However, pyrosequencing analysis did not detect any such organisms, leaving other bacteria, microbenthic algae, or foraminiferans which have also been shown to accumulate nitrate, as possible candidates. The importance and bioavailability of a KCl-extractable nitrate sediment pool remains to be tested. The significant variation in the vertical pattern and abundance of the various nitrate reducing genes phylotypes reasonably suggests differences in their activity throughout the sediment column. This raises interesting questions as to what the alternative metabolic roles for the various nitrate reductases could be, analogous to the alternative metabolic roles found for nitrite reductases. PMID:24728381

Papaspyrou, Sokratis; Smith, Cindy J; Dong, Liang F; Whitby, Corinne; Dumbrell, Alex J; Nedwell, David B

2014-01-01

110

Facile Synthesis of Graphene Nanosheets via Fe Reduction of Exfoliated Graphite Oxide  

Microsoft Academic Search

The synthesis of graphene nanosheets from graphite oxide typically involves harmful chemical reductants that are undesirable for most practical applications of graphene. Here, we demonstrate a green and facile approach to the synthesis of graphene nanosheets based on Fe reduction of exfoliated graphite oxide, resulting in a substantial removal of oxygen functionalities of the graphite oxide. More interestingly, the resulting

Zhuang-Jun Fan; Wang Kai; Jun Yan; Tong Wei; Lin-Jie Zhi; Jing Feng; Yue-ming Ren; Li-Ping Song; Fei Wei

2011-01-01

111

The Effect of Iron Oxide on Dissimilatory Nitrate Reduction to Ammonium (DNRA) in Lignin Cellulose medium  

E-print Network

The Effect of Iron Oxide on Dissimilatory Nitrate Reduction to Ammonium (DNRA) in Lignin Cellulose that may be more harmful than nitrate. In order to reduce ammonium production I proposed to add iron oxide oxidizing bacteria capable of DNRA. It was concluded that the iron addition actually prevented the reduction

Vallino, Joseph J.

112

Excimer laser reduction and patterning of graphite oxide Denis A. Sokolov a  

E-print Network

Excimer laser reduction and patterning of graphite oxide Denis A. Sokolov a , Christopher M of graphite oxide (GO) to multilayer graphene using 248 nm excimer laser irradiation in both vacuum of graphite oxide (GO) [4­16]. To date, many GO reduction schemes have been proposed, and these can

Geohegan, David B.

113

Thermogravimetric study of reduction of oxides present in oxidized nickel-base alloy powders  

NASA Technical Reports Server (NTRS)

Carbon, hydrogen, and hydrogen plus carbon reduction of three oxidized nickel-base alloy powders (a solid solution strengthened alloy both with and without the gamma prime formers aluminum and titanium and the solid solution strengthened alloy NiCrAlY) were evaluated by thermogravimetry. Hydrogen and hydrogen plus carbon were completely effective in reducing an alloy containing chromium, columbium, tantalum, molybdenum, and tungsten. However, with aluminum and titanium present the reduction was limited to a weight loss of about 81 percent. Carbon alone was not effective in reducing any of the alloys, and none of the reducing conditions were effective for use with NiCrAlY.

Herbell, T. P.

1976-01-01

114

Lightning-induced reduction of phosphorus oxidation state  

NASA Astrophysics Data System (ADS)

Phosphorus is frequently the limiting nutrient in marine and terrestrial ecosystems, largely owing to its poor solubility and slow movement through the rock cycle. Phosphorus is viewed to exist in geological systems almost exclusively in its fully oxidized state as orthophosphate. However, many microorganisms use the partially oxidized forms-phosphite and hypophosphite-as alternative phosphorus sources, and genomic evidence suggests that this selectivity is ancient. Elucidating the processes that reduce phosphate is therefore key to understanding the biological cycling of phosphorus. Here we show that cloud-to-ground lightning reduces phosphate in lightning-derived glass compounds, termed fulgurites. We analysed the phosphorus chemistry of ten fulgurites retrieved from North America, Africa and Australia, using microprobes and 31P nuclear magnetic resonance. Half of the fulgurites contained reduced phosphorus, mainly in the form of phosphite. The amount and type of reduced phosphorus was dependent on the composition of the fulgurite section examined: carbon-rich sections contained around 22% reduced phosphorus in the form of iron phosphide, whereas other fulgurites contained between 37 and 68% in the form of phosphite. We suggest that lightning provides some portion of the reduced phosphorus used by microbes, and that phosphate reduction by lightning can be locally important to phosphorus biogeochemistry.

Pasek, Matthew; Block, Kristin

2009-08-01

115

(11,12/94)(4,5/97)(02,3/07)(01/08) Neuman Chapter 17 Oxidation and Reduction  

E-print Network

(11,12/94)(4,5/97)(02,3/07)(01/08) Neuman Chapter 17 0 Chapter 17 Oxidation and Reduction from and Substitution Reactions 17. Oxidation and Reduction Reactions 18. Reactions of Enolate Ions and Enols 19 Chapter 17 1 17: Oxidation and Reduction 17.1 Oxidation and Reduction Occur Together 17-3 Redox Reactions

Reed, Christopher A.

116

Effects of oxidants and reductants on the efficiency of excitation transfer in green photosynthetic bacteria  

NASA Technical Reports Server (NTRS)

The efficiency of energy transfer in chlorosome antennas in the green sulfur bacteria Chlorobium vibrioforme and Chlorobium limicola was found to be highly sensitive to the redox potential of the suspension. Energy transfer efficiencies were measured by comparing the absorption spectrum of the bacteriochlorophyll c or d pigments in the chlorosome to the excitation spectrum for fluorescence arising from the chlorosome baseplate and membrane-bound antenna complexes. The efficiency of energy transfer approaches 100% at low redox potentials induced by addition of sodium dithionite or other strong reductants, and is lowered to 10-20% under aerobic conditions or after addition of a variety of membrane-permeable oxidizing agents. The redox effect on energy transfer is observed in whole cells, isolated membranes and purified chlorosomes, indicating that the modulation of energy transfer efficiency arises within the antenna complexes and is not directly mediated by the redox state of the reaction center. It is proposed that chlorosomes contain a component that acts as a highly quenching center in its oxidized state, but is an inefficient quencher when reduced by endogenous or exogenous reductants. This effect may be a control mechanism that prevents cellular damage resulting from reaction of oxygen with reduced low-potential electron acceptors found in the green sulfur bacteria. The redox modulation effect is not observed in the green gliding bacterium Chloroflexus aurantiacus, which contains chlorosomes but does not contain low-potential electron acceptors.

Wang, J.; Brune, D. C.; Blankenship, R. E.

1990-01-01

117

Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella Oneidensis MR-1  

PubMed Central

In the absence of O2 and other electron acceptors, the Gram-negative bacterium Shewanella oneidensis MR-1 can use ferric [Fe(III)] (oxy)(hydr)oxide minerals as the terminal electron acceptors for anaerobic respiration. At circumneutral pH and in the absence of strong complexing ligands, Fe(III) oxides are relatively insoluble and thus are external to the bacterial cells. S. oneidensis MR-1 and related strains of metal-reducing Shewanella have evolved machinery (i.e., metal-reducing or Mtr pathway) for transferring electrons from the inner-membrane, through the periplasm and across the outer-membrane to the surface of extracellular Fe(III) oxides. The protein components identified to date for the Mtr pathway include CymA, MtrA, MtrB, MtrC, and OmcA. CymA is an inner-membrane tetraheme c-type cytochrome (c-Cyt) that belongs to the NapC/NrfH family of quinol dehydrogenases. It is proposed that CymA oxidizes the quinol in the inner-membrane and transfers the released electrons to MtrA either directly or indirectly through other periplasmic proteins. A decaheme c-Cyt, MtrA is thought to be embedded in the trans outer-membrane and porin-like protein MtrB. Together, MtrAB deliver the electrons through the outer-membrane to the MtrC and OmcA on the outmost bacterial surface. MtrC and OmcA are the outer-membrane decaheme c-Cyts that are translocated across the outer-membrane by the bacterial type II secretion system. Functioning as terminal reductases, MtrC and OmcA can bind the surface of Fe(III) oxides and transfer electrons directly to these minerals via their solvent-exposed hemes. To increase their reaction rates, MtrC and OmcA can use the flavins secreted by S. oneidensis MR-1 cells as diffusible co-factors for reduction of Fe(III) oxides. Because of their extracellular location and broad redox potentials, MtrC and OmcA can also serve as the terminal reductases for soluble forms of Fe(III). In addition to Fe(III) oxides, Mtr pathway is also involved in reduction of manganese oxides and other metals. Although our understanding of the Mtr pathway is still far from complete, it is the best characterized microbial pathway used for extracellular electron exchange. Characterizations of the Mtr pathway have made significant contributions to the molecular understanding of microbial reduction of Fe(III) oxides. PMID:22363328

Shi, Liang; Rosso, Kevin M.; Clarke, Tomas A.; Richardson, David J.; Zachara, John M.; Fredrickson, James K.

2012-01-01

118

Reduction potentials of heterometallic manganese-oxido cubane complexes modulated by redox-inactive metals  

PubMed Central

Understanding the effect of redox-inactive metals on the properties of biological and heterogeneous water oxidation catalysts is important both fundamentally and for improvement of future catalyst designs. In this work, heterometallic manganese–oxido cubane clusters [MMn3O4] (M = Sr2+, Zn2+, Sc3+, Y3+) structurally relevant to the oxygen-evolving complex (OEC) of photosystem II were prepared and characterized. The reduction potentials of these clusters and other related mixed metal manganese–tetraoxido complexes are correlated with the Lewis acidity of the apical redox-inactive metal in a manner similar to a related series of heterometallic manganese–dioxido clusters. The redox potentials of the [SrMn3O4] and [CaMn3O4] clusters are close, which is consistent with the observation that the OEC is functional only with one of these two metals. Considering our previous studies of [MMn3O2] moieties, the present results with more structurally accurate models of the OEC ([MMn3O4]) suggest a general relationship between the reduction potentials of heterometallic oxido clusters and the Lewis acidities of incorporated cations that applies to diverse structural motifs. These findings support proposals that one function of calcium in the OEC is to modulate the reduction potential of the cluster to allow electron transfer. PMID:23744039

Tsui, Emily Y.; Agapie, Theodor

2013-01-01

119

Reduction potentials of heterometallic manganese-oxido cubane complexes modulated by redox-inactive metals.  

PubMed

Understanding the effect of redox-inactive metals on the properties of biological and heterogeneous water oxidation catalysts is important both fundamentally and for improvement of future catalyst designs. In this work, heterometallic manganese-oxido cubane clusters [MMn3O4] (M = Sr(2+), Zn(2+), Sc(3+), Y(3+)) structurally relevant to the oxygen-evolving complex (OEC) of photosystem II were prepared and characterized. The reduction potentials of these clusters and other related mixed metal manganese-tetraoxido complexes are correlated with the Lewis acidity of the apical redox-inactive metal in a manner similar to a related series of heterometallic manganese-dioxido clusters. The redox potentials of the [SrMn3O4] and [CaMn3O4] clusters are close, which is consistent with the observation that the OEC is functional only with one of these two metals. Considering our previous studies of [MMn3O2] moieties, the present results with more structurally accurate models of the OEC ([MMn3O4]) suggest a general relationship between the reduction potentials of heterometallic oxido clusters and the Lewis acidities of incorporated cations that applies to diverse structural motifs. These findings support proposals that one function of calcium in the OEC is to modulate the reduction potential of the cluster to allow electron transfer. PMID:23744039

Tsui, Emily Y; Agapie, Theodor

2013-06-18

120

Bacterial Manganese Reduction and Growth with Manganese Oxide as the Sole Electron Acceptor  

Microsoft Academic Search

Microbes that couple growth to the reduction of manganese could play an important role in the biogeochemistry of certain anaerobic environments. Such a bacterium, Alteromonas putrefaciens MR-1, couples its growth to the reduction of manganese oxides only under anaerobic conditions. The characteristics of this reduction are consistent with a biological, and not an indirect chemical, reduction of manganese, which suggest

Charles R. Myers; Kenneth H. Nealson

1988-01-01

121

Inhibition of bacterially promoted uranium reduction: Ferric (hydr)oxides as competitive electron acceptors.  

SciTech Connect

Reduction of hexavalent to tetravalent uranium results in a marked decrease in the mobility of this hazardous element. Microbial reduction is the most kinetic viable mechanism for such a reaction. Unfortunately, alternate terminal electron acceptors may thus compete with uranyl. We examine the role of common iron oxides on uranyl reduction. Only poorly ordered iron oxides altered the degree and rate of hexavalent uranium reduction and the effect was transitory.

Wielinga, B.; B. Bostick; R.F. Rosenzweig; S. Fendorf

2000-05-15

122

Iron isotope fractionation during microbial dissimilatory iron oxide reduction in simulated Archaean seawater.  

PubMed

The largest Fe isotope excursion yet measured in marine sedimentary rocks occurs in shales, carbonates, and banded iron formations of Neoarchaean and Paleoproterozoic age. The results of field and laboratory studies suggest a potential role for microbial dissimilatory iron reduction (DIR) in producing this excursion. However, most experimental studies of Fe isotope fractionation during DIR have been conducted in simple geochemical systems, using pure Fe(III) oxide substrates that are not direct analogues to phases likely to have been present in Precambrian marine environments. In this study, Fe isotope fractionation was investigated during microbial reduction of an amorphous Fe(III) oxide-silica coprecipitate in anoxic, high-silica, low-sulphate artificial Archaean seawater at 30 °C to determine if such conditions alter the extent of reduction or isotopic fractionations relative to those observed in simple systems. The Fe(III)-Si coprecipitate was highly reducible (c. 80% reduction) in the presence of excess acetate. The coprecipitate did not undergo phase conversion (e.g. to green rust, magnetite or siderite) during reduction. Iron isotope fractionations suggest that rapid and near-complete isotope exchange took place among all Fe(II) and Fe(III) components, in contrast to previous work on goethite and hematite, where exchange was limited to the outer few atom layers of the substrate. Large quantities of low-?(56)Fe Fe(II) (aqueous and solid phase) were produced during reduction of the Fe(III)-Si coprecipitate. These findings shed new light on DIR as a mechanism for producing Fe isotope variations observed in Neoarchaean and Paleoproterozoic marine sedimentary rocks. PMID:21504536

Percak-Dennett, E M; Beard, B L; Xu, H; Konishi, H; Johnson, C M; Roden, E E

2011-05-01

123

Oxidized Phospholipids as Potential Novel Drug Targets  

PubMed Central

The interactions of three therapeutic agents, viz. the antipsychotics HPD and CPZ, and the antineoplastic anthracycline DOX, with oxidatively modified phospholipids were studied by monitoring the quenching of fluorescence of an incorporated pyrene-labeled lipid derivative. All three drugs bound avidly to the two oxidized PCs bearing either an aldehyde or carboxylic function at the end of the sn-2 nonanoyl chain, with the highest affinity measured between CPZ and the latter oxidized lipid. Subsequent dissociation of the above drugs from the oxidized lipids by DNA, acidic phospholipids, and NaCl revealed the binding of these drugs with the aldehyde lipid to be driven by hydrophobicity similarly to their binding to lysophosphatidylcholine, whereas a significant contribution of electrostatics was evident for the lipid with the carboxylic moiety. These results connect to previous experimental data, demonstrating the induction by these drugs of oxidative stress and binding to membrane phospholipids. These issues are elaborated with reference to their clinical use and side effects. PMID:17604316

Mattila, Juha-Pekka; Sabatini, Karen; Kinnunen, Paavo K. J.

2007-01-01

124

Biological Oxidation of Fe(II) in Reduced Nontronite Coupled with Nitrate Reduction by Pseudogulbenkiania sp. Strain 2002  

SciTech Connect

Nitrate contamination in soils, sediments, and water bodies is a significant issue. Although much is known about nitrate degradation in these environments, especially via microbial pathways, a complete understanding of all degradation processes, especially in clay mineral-rich soils, is still lacking. The objective of this study was to study the potential of removing nitrate contaminant using structural Fe(II) in clay mineral nontronite. Specifically, the coupled processes of microbial oxidation of Fe(II) in microbially reduced nontronite (NAu-2) and nitrate reduction by Pseudogulbenkiania species strain 2002 was investigated. Bio-oxidation experiments were conducted in bicarbonate-buffered medium under both growth and nongrowth conditions. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57Fe-Mössbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in nontronite. The bio-oxidation extent under growth and nongrowth conditions reached 93% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N2), via an intermediate product nitrite. Magnetite was a mineral product of nitrate-dependent Fe(II) oxidation, as evidenced by XRD data and TEM diffraction patterns. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in soils.

Zhao, Linduo; Dong, Hailiang; Kukkadapu, Ravi K.; Agrawal, A.; Liu, Deng; Zhang, Jing; Edelmann, Richard E.

2013-10-15

125

Kinetics of Microbial Bromate Reduction in a Hydrogen-Oxidizing, Denitrifying Biofilm Reactor  

E-print Network

ARTICLE Kinetics of Microbial Bromate Reduction in a Hydrogen-Oxidizing, Denitrifying Biofilm a hydrogen-based, deni- trifying membrane-biofilm reactor (MBfR) for bromate reduction, and report the first; denitrification; biofilm; hollow-fiber membrane biofilm reactor Introduction Bromate (BrOÃ? 3 ) is an oxidized

Nerenberg, Robert

126

Reduction of Sintering during Annealing of FePt Nanoparticles Coated with Iron Oxide  

E-print Network

thermal decomposition of iron pentacarbonyl and polyol reduction of platinum salt.4 How- everReduction of Sintering during Annealing of FePt Nanoparticles Coated with Iron Oxide Chao LiuVised Manuscript ReceiVed October 12, 2004 FePt/iron oxide core/shell nanoparticles are synthesized by a two step

Laughlin, David E.

127

Potential oxidative stress due to Pb exposure  

E-print Network

increases in oxidation of glutathione in K 562 myelogenous leukemia cells at low Pb levels. The approach consisted of incubating K 562 cells in solutions of 0, 300, and 700 ppb Pb dissolved in RPMI cell medium for a total of 96 hours. After this period...

Elms, Rene' Davina

2013-02-22

128

Microbial reduction of graphene oxide by Escherichia coli: a green chemistry approach.  

PubMed

Graphene and graphene related materials are an important area of research in recent years due to their unique properties. The extensive industrial application of graphene and related compounds has led researchers to devise novel and simple methods for the synthesis of high quality graphene. In this paper, we developed an environment friendly, cost effective, simple method and green approaches for the reduction of graphene oxide (GO) using Escherichia coli biomass. In biological method, we can avoid use of toxic and environmentally harmful reducing agents commonly used in the chemical reduction of GO to obtain graphene. The biomass of E. coli reduces exfoliated GO to graphene at 37°C in an aqueous medium. The E. coli reduced graphene oxide (ERGO) was characterized with UV-visible absorption spectroscopy, particle analyzer, high resolution X-ray diffractometer, scanning electron microscopy and Raman spectroscopy. Besides the reduction potential, the biomass could also play an important role as stabilizing agent, in which synthesized graphene exhibited good stability in water. This method can open up the new avenue for preparing graphene in cost effective and large scale production. Our findings suggest that GO can be reduced by simple eco-friendly method by using E. coli biomass to produce water dispersible graphene. PMID:23107955

Gurunathan, Sangiliyandi; Han, Jae Woong; Eppakayala, Vasuki; Kim, Jin-Hoi

2013-02-01

129

Biological oxidation of Fe(II) in reduced nontronite coupled with nitrate reduction by Pseudogulbenkiania sp. Strain 2002  

NASA Astrophysics Data System (ADS)

The importance of microbial nitrate-dependent Fe(II) oxidation to iron biogeochemistry is well recognized. Past research has focused on oxidation of aqueous Fe2+ and structural Fe(II) in oxides, carbonates, and phosphate, but the importance of structural Fe(II) in phyllosilicates in this reaction is only recently studied. However, the effect of clay mineralogy on the rate and the mechanism of the reaction, and subsequent mineralogical end products are still poorly known. The objective of this research was to study the coupled process of microbial oxidation of Fe(II) in clay mineral nontronite (NAu-2), and nitrate reduction by Pseudogulbenkiania species strain 2002, and to determine mineralogical changes associated with this process. Bio-oxidation experiments were conducted using Fe(II) in microbially reduced nontronite as electron donor and nitrate as electron acceptor in bicarbonate-buffered medium under both growth and nongrowth conditions to investigate cell growth on this process. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57Fe-Mössbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in NAu-2. The bio-oxidation extent under growth and nongrowth conditions reached 67% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N2), via an intermediate product nitrite. Abiotic oxidation by nitrite partly accelerated Fe(II) oxidation rate under the growth condition. The oxidized Fe(III) largely remained in the nontronite structure, but secondary minerals such as vivianite, ferrihydrite, and magnetite formed depending on specific experimental conditions. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in natural environments.

Zhao, Linduo; Dong, Hailiang; Kukkadapu, Ravi; Agrawal, Abinash; Liu, Deng; Zhang, Jing; Edelmann, Richard E.

2013-10-01

130

Direct reduction of actinide oxide and carbide to metal: Application to the preparation of plutonium metal  

NASA Astrophysics Data System (ADS)

Three different conversion and refining methods for the preparation of high purity plutonium metal are described: the calciothermic reduction of plutonium oxide followed by electrorefining; the thoriothermic reduction of plutonium oxide followed by selective evaporation; the tantalothermic reduction of plutonium carbide followed by selective evaporation. The calciothermic reduction of plutonium oxide followed by electrorefining is used for the semi-industrial or large scale production of high purity plutonium metal. The rate and yield of preparation and refining is high. With high purity reactants the reduction of the oxide with thorium is well adapted to obtain high purity plutonium metal on the laboratory scale. The tantalothermic reduction of plutonium carbide gives high purity plutonium metal even with impure plutonium starting material (recovered from waste). This results from the high selectivity at the different steps of the process.

Spirlet, J. C.; Müller, W.; Van Audenhove, J.

1985-06-01

131

Regulatory Interactions between Ubiquinol Oxidation and Ubiquinone Reduction Sites in the Dimeric Cytochrome  

E-print Network

transports one electron from the QH2 oxidation site (center P) in cytochrome b to cytochrome c1 between the cytochrome b subunits would favor the formation of SQ with oxidized bH heme at each center NRegulatory Interactions between Ubiquinol Oxidation and Ubiquinone Reduction Sites in the Dimeric

Trumpower, Bernard L.

132

Particulate Matter Oxidative Potential from Waste Transfer Station Activity  

PubMed Central

Background Adverse cardiorespiratory health is associated with exposure to ambient particulate matter (PM). The highest PM concentrations in London occur in proximity to waste transfer stations (WTS), sites that experience high numbers of dust-laden, heavy-duty diesel vehicles transporting industrial and household waste. Objective Our goal was to quantify the contribution of WTS emissions to ambient PM mass concentrations and oxidative potential. Methods PM with a diameter < 10 ?m (PM10) samples were collected daily close to a WTS. PM10 mass concentrations measurements were source apportioned to estimate local versus background sources. PM oxidative potential was assessed using the extent of antioxidant depletion from a respiratory tract lining fluid model. Total trace metal and bioavailable iron concentrations were measured to determine their contribution to PM oxidative potential. Results Elevated diurnal PM10 mass concentrations were observed on all days with WTS activity (Monday–Saturday). Variable PM oxidative potential, bioavailable iron, and total metal concentrations were observed on these days. The contribution of WTS emissions to PM at the sampling site, as predicted by microscale wind direction measurements, was correlated with ascorbate (r = 0.80; p = 0.030) and glutathione depletion (r = 0.76; p = 0.046). Increased PM oxidative potential was associated with aluminum, lead, and iron content. Conclusions PM arising from WTS activity has elevated trace metal concentrations and, as a consequence, increased oxidative potential. PM released by WTS activity should be considered a potential health risk to the nearby residential community. PMID:20368130

Godri, Krystal J.; Duggan, Sean T.; Fuller, Gary W.; Baker, Tim; Green, David; Kelly, Frank J.; Mudway, Ian S.

2010-01-01

133

Role of ammonia oxidation in selective catalytic reduction of nitric oxide over vanadia catalysts  

SciTech Connect

The role of direct oxidation of ammonia in SCR reactions and the catalytic anisotropy of V[sub 2]O[sub 5] catalysts in this reaction network were investigated. The catalysts were characterized using BET surface area measurement, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and 3-D imaging. Temperature-programmed reduction experiments using ammonia and hydrogen as reducing agents and temperature-programmed desorption studies were also performed. A steady-state fixed-bed reactor system was used for activity and selectivity measurements. The product analysis was carried out by a combination of techniques including chemiluminescence NO[sub x] analysis, on-line gas chromatography and on-line mass spectrometry, and chemical titration methods. The results obtained in this study, when combined with our previous studies in SCR reactions, indicate that over vanadium pentoxide catalysts, ammonia oxidation and NO reduction reactions are closely coupled. The results suggest that ammonia adsorption takes place on at least two types of sites located on the (010) and (100) planes of V[sub 2]O[sub 5]. The sites that selectively reduce NO to N[sub 2] are the V-O-V sites located on the side planes, whereas V[double bond]O sites promote direct oxidation of ammonia to NO and the formation of N[sub 2]O from NO and NH[sub 3] interaction more readily. It is found that the V[double bond]O sites are more easily reduced with both hydrogen and ammonia. 35 refs., 13 figs., 2 tabs.

Ozkan, U.S.; Cai, Y.; Kumthekar, M.W.; Zhang, L. (Ohio State Univ., Columbus (United States))

1993-07-01

134

Mechanisms and factors affecting chromium oxide particle reduction in iron-chromium honeycombs  

NASA Astrophysics Data System (ADS)

In the production of iron chromium honeycombs, iron oxide and chromium oxide mixtures are reduced by hydrogen at elevated temperatures to produce a metallic alloy. The complete reduction of the iron oxide occurs prior to the reduction of the chromium oxide. The reduction of the chromium oxide particles within the iron matrix is affected by factors that include the diffusion of the reduced chromium away from the chromium oxide particle into the iron matrix, the diffusion of the gaseous reactants and products to and from the chromium oxide particles, and the porosity of the iron matrix, which changes as a result of sintering. The type of heat-treatment used, (isothermal or non-isothermal, i.e., holding at a specific temperature versus using a steadily increasing temperature) plays a vital role in how these factors will affect chromium oxide reduction. Experimental data were used in conjunction with sintering and dissolution models to obtain an understanding of the environment in which the chromium oxide particles reduce as a function of heat-treatment. This understanding will assist in the development of more effective processing steps for the reduction of metallic honeycombs from oxide mixtures.

McIntosh, Monique Sandra

135

Microorganisms pumping iron: anaerobic microbial iron oxidation and reduction.  

PubMed

Iron (Fe) has long been a recognized physiological requirement for life, yet for many microorganisms that persist in water, soils and sediments, its role extends well beyond that of a nutritional necessity. Fe(II) can function as an electron source for iron-oxidizing microorganisms under both oxic and anoxic conditions and Fe(III) can function as a terminal electron acceptor under anoxic conditions for iron-reducing microorganisms. Given that iron is the fourth most abundant element in the Earth's crust, iron redox reactions have the potential to support substantial microbial populations in soil and sedimentary environments. As such, biological iron apportionment has been described as one of the most ancient forms of microbial metabolism on Earth, and as a conceivable extraterrestrial metabolism on other iron-mineral-rich planets such as Mars. Furthermore, the metabolic versatility of the microorganisms involved in these reactions has resulted in the development of biotechnological applications to remediate contaminated environments and harvest energy. PMID:16980937

Weber, Karrie A; Achenbach, Laurie A; Coates, John D

2006-10-01

136

A wide visible-light-responsive tunneled MgTa2O6-xNx photocatalyst for water oxidation and reduction.  

PubMed

We demonstrate for the first time that a nitrogen-doped tunneled oxide MgTa2O6-xNx with an absorption edge of ca. 570 nm can drive both water oxidation and reduction half reactions in the presence of scavengers under visible light irradiation, showing great potential in solar water splitting. PMID:25300157

Chen, Shanshan; Qi, Yu; Liu, Guiji; Yang, Jingxiu; Zhang, Fuxiang; Li, Can

2014-10-23

137

Oxidation Potentials in Matte Smelting of Copper and Nickel  

NASA Astrophysics Data System (ADS)

The oxidation potential, given as the base-ten logarithm of the oxygen partial pressure in bars and the temperature [log pO2/ T, °C], defines the state of oxidation of pyrometallurgical extraction and refining processes. This property varies from copper making, [-6/1150]; to lead/zinc smelting, [-10/1200]; to iron smelting, [-13/1600]. The current article extends the analysis to the smelting of copper and nickel/copper sulfide concentrates to produce mattes of the type Cu(Ni)FeS(O) and iron silicate slags, FeOxSiO2—with oxidation potentials of [-7.5/1250].

Matousek, Jan W.

2014-09-01

138

Monitoring of the Oxidation-Reduction State of Brain Structures in Freely Moving Rats during Sleep–Waking Cycles by Potentiometric Recording  

Microsoft Academic Search

Freely mobile mongrel male rats weighing 300–350 g were used for studies of changes in the oxidative-reductive (redox) state of brain tissue during cycles of waking, slow-wave sleep, and paradoxical sleep, by recording the potential of the oxidative-reductive state of brain tissue with platinum electrodes implanted into the cerebral cortex ad hippocampus. Electromyograms were also recorded from the cervical muscles,

T. B. Shvets-Ténéta-Gurii; G. I. Troshin; M. R. Novikova; N. M. Khonicheva; O. A. Shostak; I. V. Borovskaya

2003-01-01

139

Aggregate-scale heterogeneity in iron (hydr)oxide reductive transformations  

SciTech Connect

There is growing awareness of the complexity of potential reaction pathways and the associated solid-phase transformations during the reduction of Fe (hydr)oxides, especially ferrihydrite. An important observation in static and advective-dominated systems is that microbially produced Fe(II) accelerates Ostwald ripening of ferrihydrite, thus promoting the formation of thermodynamically more stable ferric phases (lepidocrocite and goethite) and, at higher Fe(II) surface loadings, the precipitation of magnetite; high Fe(II) levels can also lead to green rust formation, and with high carbonate levels siderite may also be formed. This study expands this emerging conceptual model to a diffusion-dominated system that mimics an idealized micropore of a ferrihydrite-coated soil aggregate undergoing reduction. Using a novel diffusion cell, coupled with micro-x-ray fluorescence and absorption spectroscopies, we determined that diffusion-controlled gradients in Fe{sup 2+}{sub (aq)} result in a complex array of spatially distributed secondary mineral phases. At the diffusive pore entrance, where Fe{sup 2+} concentrations are highest, green rust and magnetite are the dominant secondary Fe (hydr)oxides (30 mol% Fe each). At intermediate distances from the inlet, green rust is not observed and the proportion of magnetite decreases from approximately 30 to <10%. Across this same transect, the proportion of goethite increases from undetectable up to >50%. At greater distances from the advective-diffusive boundary, goethite is the dominant phase, comprising between 40 and 95% of the Fe. In the presence of magnetite, lepidocrocite forms as a transient-intermediate phase during ferrihydrite-to-goethite conversion; in the absence of magnetite, conversion to goethite is more limited. These experimental observations, coupled with results of reactive transport modeling, confirm the conceptual model and illustrate the potential importance of diffusion-generated concentration gradients in dissolved Fe{sup 2+} on the fate of ferrihydrite during reduction in structured soils.

Tufano, K.J.; Benner, S.G.; Mayer, K.U.; Marcus, M.A.; Nico, P.S.; Fendorf, S.

2009-06-15

140

DISSOLVED OXYGEN AND OXIDATION-REDUCTION POTENTIALS IN GROUND WATER  

EPA Science Inventory

Water samples were collected from various depths in a pristine sand and gravel water table aquifer at monthly intervals over a period of one year. Dissolved oxygen concentrations were near saturation 9 feet below the water table and decreased to nearly zero at 78 feet below the w...

141

Synthesis of transition-metal phosphides from oxidic precursors by reduction in hydrogen plasma  

SciTech Connect

A series of transition metal phosphides, including MoP, WP, CoP, Co{sub 2}P, and Ni{sub 2}P, were synthesized from their oxidic precursors by means of hydrogen plasma reduction under mild conditions. The effects of reduction conditions, such as metal to phosphorus molar ratio, power input, and reduction time, on the synthesis of metal phosphides were investigated. The products were identified by means of XRD characterization. It is indicated that metal phosphides were readily synthesized stoichiometrically from their oxides in hydrogen plasma under mild conditions. - Graphical abstract: Metal phosphides were obtained stoichiometrically from their oxidic precursors by hydrogen plasma reaction under mild conditions.

Guan Jie [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Wang Yao [Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China); Qin Minglei; Yang Ying [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Li Xiang [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China); Wang Anjie, E-mail: ajwang@dlut.edu.c [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China)

2009-06-15

142

Graphene produced by radiation-induced reduction of graphene oxide  

Microsoft Academic Search

Effect of irradiation on graphene oxide by sunlight, UV light and KrF excimer laser has been investigated in detail. Both sunlight and ultraviolet light reduce graphene oxide well after prolonged irradiation, but laser irradiation produces graphene with negligible oxygen functionalities within a short time. Laser irradiation is also useful for one-step synthesis of metal particle decorated graphene. Laser irradiation of

Prashant Kumar; K. S. Subrahmanyam; C. N. R. Rao

2010-01-01

143

IN-SITU CHEMICAL OXIDATION - DNAPL MASS REDUCTION TECHNOLOGY  

EPA Science Inventory

In-situ chemical oxidation (ISCO) is a rapidly developing technology used at hazardous waste sites where oxidants and complimentary reagents are injected into the subsurface to transform organic contaminants into less toxic byproducts. This technology is being used at new sites ...

144

High-Quality Reduced Graphene Oxide by a Dual-Function Chemical Reduction and Healing Process  

PubMed Central

A new chemical dual-functional reducing agent, thiophene, was used to produce high-quality reduced graphene oxide (rGO) as a result of a chemical reduction of graphene oxide (GO) and the healing of rGO. Thiophene reduced GO by donation of electrons with acceptance of oxygen while it was converted into an intermediate oxidised polymerised thiophene that was eventually transformed into polyhydrocarbon by loss of sulphur atoms. Surprisingly, the polyhydrocarbon template helped to produce good-quality rGOC (chemically reduced) and high-quality rGOCT after thermal treatment. The resulting rGOCT nanosheets did not contain any nitrogen or sulphur impurities, were highly deoxygenated and showed a healing effect. Thus the electrical properties of the as-prepared rGOCT were superior to those of conventional hydrazine-produced rGO that require harsh reaction conditions. Our novel dual reduction and healing method with thiophene could potentially save energy and facilitate the commercial mass production of high-quality graphene. PMID:23722643

Some, Surajit; Kim, Youngmin; Yoon, Yeoheung; Yoo, HeeJoun; Lee, Saemi; Park, Younghun; Lee, Hyoyoung

2013-01-01

145

A novel bimediator amperometric sensor for electrocatalytic oxidation of gallic acid and reduction of hydrogen peroxide.  

PubMed

A novel bimediator amperometric sensor is fabricated for the first time by surface modification of graphite electrode with thionine (TH) and nickel hexacyanoferrate (NiHCF). The electrochemical behavior of the TH/NiHCF bimediator modified electrode was characterized by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The TH/NiHCF bimediator modified electrode exhibited a pair of distinct redox peaks for NiHCF and TH with formal potentials of 0.33V and -0.27V vs. SCE at a scan rate of 50mV s(-1) in 0.1M NaNO3 and 0.1M NH4NO3 respectively. The electrocatalytic activity of the bimediator modified electrode towards oxidation of gallic acid with NiHCF and reduction of hydrogen peroxide with TH was evaluated and it was observed that the modified electrode showed an electrocatalytic activity towards the oxidation of gallic acid in the concentration range of 4.99×10(-6)-1.20×10(-3)M with a detection limit of 1.66×10(-6)M (S/N=3) and reduction of H2O2 in the concentration range of 1.67×10(-6)-1.11×10(-3)M with a detection limit of 5.57×10(-7)M (S/N=3). The bimediator modified electrode was found to exhibit good stability and reproducibility. PMID:24845813

Sangeetha, N S; Narayanan, S Sriman

2014-05-30

146

Using FISH-SIMS to Study Marine Methane Oxidation Coupled to the Reduction of Metal Oxides, a Plausible Microbial Metabolism for Subsurface Mars  

NASA Astrophysics Data System (ADS)

In the shallow martian subsurface, microbial life could be supported by methane oxidation coupled to the reduction of sulfate or metal oxides. Here, we report results of efforts to characterize the organisms involved in manganese-dependent marine methane oxidation.

House, C. H.; Beal, E. J.; Orphan, V. J.

2010-04-01

147

A NEW SOURCE REDUCTION PROJECT: THE POTENTIAL FOR SAFE SUBSTITUTES  

EPA Science Inventory

One of the clean product research projects being funded by the EPA's Pollution Prevention Research Branch in Cincinnati, Ohio, involves evaluating the possibility of dramatic reductions in hazardous waste and toxic chemical exposure associated with commercial products. y identify...

148

Bacterial manganese reduction and growth with manganese oxide as the sole electron acceptor  

NASA Technical Reports Server (NTRS)

Microbes that couple growth to the reduction of manganese could play an important role in the biogeochemistry of certain anaerobic environments. Such a bacterium, Alteromonas putrefaciens MR-1, couples its growth to the reduction of manganese oxides only under anaerobic conditions. The characteristics of this reduction are consistent with a biological, and not an indirect chemical, reduction of manganese, which suggest that this bacterium uses manganic oxide as a terminal electron acceptor. It can also utilize a large number of other compounds as terminal electron acceptors; this versatility could provide a distinct advantage in environments where electron-acceptor concentrations may vary.

Myers, Charles R.; Nealson, Kenneth H.

1988-01-01

149

Step like surface potential on few layered graphene oxide  

NASA Astrophysics Data System (ADS)

We report surface potential maps of few layered graphene oxide films on different substrates. Kelvin probe force microscopy images reveal that the surface potential decreases in steps with increasing number of layers on the substrate until five layers are reached, where it saturates to a constant value. This intrinsic behavior is smeared out in the presence of ambient humidity where the surface potential is shielded by the presence of a thin water layer on the surface. This effect can be exploited to quickly determine the number of layers of graphene oxide on a substrate.

Jaafar, M.; López-Polín, G.; Gómez-Navarro, C.; Gómez-Herrero, J.

2012-12-01

150

A bifunctional nonprecious metal catalyst for oxygen reduction and water oxidation.  

PubMed

There is a growing interest in oxygen electrochemistry as conversions between O(2) and H(2)O play an important role in a variety of renewable energy technologies. The goal of this work is to develop active bifunctional catalyst materials for water oxidation and oxygen reduction. Drawing inspiration from a cubane-like CaMn(4)O(x), the biological catalyst found in the oxygen evolving center (OEC) in photosystem II, nanostructured manganese oxide surfaces were investigated for these reactions. Thin films of nanostructured manganese oxide were found to be active for both oxygen reduction and water oxidation, with similar overall oxygen electrode activity to the best known precious metal nanoparticle catalysts: platinum, ruthenium, and iridium. Physical and chemical characterization of the nanostructured Mn oxide bifunctional catalyst reveals an oxidation state of Mn(III), akin to one of the most commonly observed Mn oxidation states found in the OEC. PMID:20839797

Gorlin, Yelena; Jaramillo, Thomas F

2010-10-01

151

Comparative survey of potential nitrate and sulfate reduction rates in aquatic sediments  

NASA Astrophysics Data System (ADS)

Nitrate and sulfate are two major terminal electron acceptors of anaerobic respiration in nearshore sediments. Potential nitrate and sulfate reduction rates (NRR and SRR) were determined on surficial sediments sampled at 14 sites representing a wide range of shallow-water depositional environments. The rates were obtained by supplying undisturbed slices of sediments with nitrate, sulfate or both using a flow-through reactor technique. No external electron donor was added to the sediments. The results indicate that all studied sediments harbored viable and coexisting nitrate- and sulfate-reducing communities, which were able to instantaneously consume the electron acceptors supplied to the reactors. On average, NRR exceeded SRR by about one order of magnitude (309 ± 180 nmol NO3- cm-3 h-1versus 37 ± 29 nmol SO42- cm-3 h-1). The NRR:SRR molar ratio, however, varied significantly from site to site, with values ranging from 1.7 to 59. Nitrite production, indicative of incomplete nitrate reduction, was observed in all studied sediments and, on average, accounted for 45% of NRR (range 3-80%). Production of sulfate under nitrate-reducing conditions was observed in 10 out of 14 of the studied sediments, suggesting a common occurrence of sulfide oxidation coupled to nitrate reduction. Oxidation of sulfide accounted for 0 to 40% of NRR in the nitrate-only experiments. When both electron acceptors were supplied simultaneously, net sulfate consumption decreased on average by 45%. The effect of nitrate on SRR was highly variable, however, ranging from near complete inhibition to a 25% enhancement of SRR. Overall, the results of this study point to the need to critically reassess the model formulations used to represent anaerobic respiration processes and their interactions in early diagenetic models.

Laverman, Anniet M.; Pallud, Céline; Abell, Jeffrey; Cappellen, Philippe Van

2012-01-01

152

Standard reduction potentials of all couples of the peroxidase cycle of lactoperoxidase.  

PubMed

Lactoperoxidase (LPO) is found in mucosal surfaces and exocrine secretions including milk, tears and saliva and has physiological significance in antimicrobial defense. Its predominant physiological role is to convert hydrogen peroxide and thiocyanate in hypothiocyanite. In this study, the standard reduction potentials of all redox couples involved in the halogenation and peroxidase cycle of LPO have been determined by multi-mixing stopped-flow spectroscopy. The standard reduction potentials of the redox couples compound I/native LPO, compound I/compound II of LPO, and compound II/native LPO are (1.09 +/- 0.01) V, (1.14 +/- 0.02) V, and (1.04 +/- 0.02) V, respectively, at pH 7 and 25 degrees C. Thus, for the first time, a full description of these important thermodynamic parameters of lactoperoxidase has been performed, allowing a better understanding in the substantial differences in the oxidation of two- and one-electron donors by LPO and other members of the mammalian heme peroxidase superfamily. PMID:15833345

Furtmüller, Paul Georg; Arnhold, Jürgen; Jantschko, Walter; Zederbauer, Martina; Jakopitsch, Christa; Obinger, Christian

2005-05-01

153

Variation of electronic transitions and reduction potentials of cerium(iv) complexes.  

PubMed

The trivalent compound K[Ce[N(SiHMe2)2]4] was synthesized and oxidized, providing a convenient route to the reported cerium(iv) compound Ce[N(SiHMe2)2]4. Protonolysis reactions of Ce[N(SiHMe2)2]4 with tert-butanol, substituted benzyl alcohols, and 2,6-diphenylphenol yielded the neutral tetravalent compounds Ce(O(t)Bu)4(py)2, Ce2(OCH2C6R5)8(thf)2 (R = Me, F), and Ce(Odpp)4 (dpp = 2,6-(C6H5)2-C6H3). Spectroscopic and electrochemical characterization of the monometallic cerium(iv) silylamide, alkoxide, and aryloxide compounds revealed variable ligand-to-metal charge transfer transitions and metal-based reduction potentials. Computational bonding analyses were performed to complement the physical characterization of the complexes. PMID:25148646

Williams, Ursula J; Schneider, David; Dorfner, Walter L; Maichle-Mössmer, Cäcilia; Carroll, Patrick J; Anwander, Reiner; Schelter, Eric J

2014-10-14

154

Developing Investigation Skills in an Introductory Multistep Synthesis Using Fluorene Oxidation and Reduction  

ERIC Educational Resources Information Center

A two-step oxidation-reduction sequence that incorporates several important aspects of synthesis into introductory organic chemistry laboratories is described. This experiment is an excellent vehicle for introducing elements of discovery and intermediate yield improvement strategies.

Stocksdale, Mark G; Pointer, Roy D; Benson, Barret W.; Fletcher, Steven E. S.; Henry, Ian; Ogren, Paul J.; Berg, Michael A. G.

2004-01-01

155

Sequential Oxidative and Reductive Bleaching in a Multicomponent Single Liquor System.  

National Technical Information Service (NTIS)

The present invention relates to processes for oxidative (using hydrogen peroxide) and reductive bleaching of fibers, and fibers bleached by the aforementioned processes. Both of the bleaching processes of the present invention may be utilized to great ad...

W. N. Marmer

1989-01-01

156

Hydrogen production using solid oxide membrane electrolyzer with solid carbon reductant in liquid metal anode  

SciTech Connect

A laboratory-scale solid oxide membrane (SOM) steam electrolyzer that can potentially utilize the energy value of coal or any hydrocarbon reductant to produce high purity hydrogen has been fabricated and evaluated. The SOM electrolyzer consists of an oxygen-ion-conducting yttria-stabilized zirconia (YSZ) electrolyte with a Ni-YSZ cermet cathode coated on one side and liquid tin anode on the other side. Hydrogen production using the SOM electrolyzer was successfully demonstrated between 900 and 1000{sup o}C by feeding a steam-rich gas to the Ni-YSZ cermet cathode and solid carbon reductant into the liquid tin anode. It was confirmed that the energy required for hydrogen production can be effectively lowered by feeding a solid carbon reductant in the liquid tin anode. A polarization model for the SOM electrolyzer was developed. The experimental data obtained under different operating conditions were curve fitted into the model to identify the various polarization losses. Based on the results of this study, work needed toward increasing the electrochemical performance of the SOM electrolyzer is discussed.

Pati, S.; Yoon, K.J.; Gopalan, S.; Pal, U.B. [Boston University, Boston, MA (United States). Dept. of Mechanical Engineering

2009-07-01

157

Graphene produced by radiation-induced reduction of graphene oxide  

Microsoft Academic Search

Effect of irradiation on graphene oxide by sunlight, UV light and KrF excimer\\u000alaser has been investigated in detail. Both sunlight and ultraviolet light\\u000areduce graphene oxide well after prolonged irradiation, but laser irradiation\\u000aproduces graphene with negligible oxygen functionalities within a short time.\\u000aLaser irradiation is also useful for one-step synthesis of metal particle\\u000adecorated graphene. Laser irradiation of

Prashant Kumar; K. S. Subrahmanyam; C. N. R. Rao

2010-01-01

158

Fluidized reduction of oxides on fine metal powders without sintering  

NASA Technical Reports Server (NTRS)

In the process of reducing extremely fine metal particles (av. particle size or = 1000 angstroms) covered with an oxide layer, the metal particles are fluidized by a gas flow contg. H, heated, and reduced. The method uniformly and easily reduces surface oxide layers of the extremely fine metal particles without causing sintering. The metal particles are useful for magnetic recording materials, conductive paste, powder metallurgy materials, chem. reagents, and catalysts.

Hayashi, T.

1985-01-01

159

Microbial reduction of manganese oxides: Interactions with iron and sulfur  

Microsoft Academic Search

Alteromonas putrefaciens (strain MR-1) is capable of rapid Mn(IV) reduction under conditions of neutral pH and temperatures characteristic of the Oneida Lake, New York, sediments from which it was isolated. MR-1 also reduces Fe{sup 3+} to Fe{sup 2+}, and disproportionates thiosulfate to sulfide and sulfite; independently, the Fe{sup 2+} and sulfide act as rapid reductants of Mn. The addition of

C. R. Myers; K. H. Nealson

1988-01-01

160

Coupled reductive and oxidative sulfur cycling in the phototrophic plate of a meromictic lake.  

PubMed

Mahoney Lake represents an extreme meromictic model system and is a valuable site for examining the organisms and processes that sustain photic zone euxinia (PZE). A single population of purple sulfur bacteria (PSB) living in a dense phototrophic plate in the chemocline is responsible for most of the primary production in Mahoney Lake. Here, we present metagenomic data from this phototrophic plate--including the genome of the major PSB, as obtained from both a highly enriched culture and from the metagenomic data--as well as evidence for multiple other taxa that contribute to the oxidative sulfur cycle and to sulfate reduction. The planktonic PSB is a member of the Chromatiaceae, here renamed Thiohalocapsa sp. strain ML1. It produces the carotenoid okenone, yet its closest relatives are benthic PSB isolates, a finding that may complicate the use of okenone (okenane) as a biomarker for ancient PZE. Favorable thermodynamics for non-phototrophic sulfide oxidation and sulfate reduction reactions also occur in the plate, and a suite of organisms capable of oxidizing and reducing sulfur is apparent in the metagenome. Fluctuating supplies of both reduced carbon and reduced sulfur to the chemocline may partly account for the diversity of both autotrophic and heterotrophic species. Collectively, the data demonstrate the physiological potential for maintaining complex sulfur and carbon cycles in an anoxic water column, driven by the input of exogenous organic matter. This is consistent with suggestions that high levels of oxygenic primary production maintain episodes of PZE in Earth's history and that such communities should support a diversity of sulfur cycle reactions. PMID:24976102

Hamilton, T L; Bovee, R J; Thiel, V; Sattin, S R; Mohr, W; Schaperdoth, I; Vogl, K; Gilhooly, W P; Lyons, T W; Tomsho, L P; Schuster, S C; Overmann, J; Bryant, D A; Pearson, A; Macalady, J L

2014-09-01

161

Crystallographic studies of V44 mutants of Clostridium pasteurianum rubredoxin: Effects of side-chain size on reduction potential  

SciTech Connect

Understanding the structural origins of differences in reduction potentials is crucial to understanding how various electron transfer proteins modulate their reduction potentials and how they evolve for diverse functional roles. Here, the high-resolution structures of several Clostridium pasteurianum rubredoxin (Cp Rd) variants with changes in the vicinity of the redox site are reported in order to increase this understanding. Our crystal structures of [V44L] (at 1.8 {angstrom} resolution), [V44A] (1.6 {angstrom}), [V44G] (2.0 {angstrom}) and [V44A, G45P] (1.5 {angstrom}) Rd (all in their oxidized states) show that there is a gradual decrease in the distance between Fe and the amide nitrogen of residue 44 upon reduction in the size of the side chain of residue 44; the decrease occurs from leucine to valine, alanine or glycine and is accompanied by a gradual increase in their reduction potentials. Mutation of Cp Rd at position 44 also changes the hydrogen-bond distance between the amide nitrogen of residue 44 and the sulfur of cysteine 42 in a size-dependent manner. Our results suggest that residue 44 is an important determinant of Rd reduction potential in a manner dictated by side-chain size. Along with the electric dipole moment of the 43-44 peptide bond and the 44-42 NHS type hydrogen bond, a modulation mechanism for solvent accessibility through residue 41 might regulate the redox reaction of the Rds. Proteins 2004.

Park, Il Yeong; Eidsness, Marly K.; Lin, I-Jin; Gebel, Erika B.; Youn, Buhyun; Harley, Jill L.; Machonkin, Timothy E.; Frederick, Ronnie O.; Markley, John L.; Smith, Eugene T.; Ichiye, Toshiko; Kang, ChulHee (Wilkes); (Georgetown); (UW); (WSUP); (Georgia)

2010-11-16

162

In situ reduction and evaluation of anode supported single chamber solid oxide fuel cells  

E-print Network

In situ reduction and evaluation of anode supported single chamber solid oxide fuel cells D conditions. hal-00840106,version1-1Jul2013 #12;1. Introduction Single Chamber Solid Oxide Fuel Cells (SC microstructure. For both cells tested, the Open Circuit Voltage (OCV), the power density and the fuel utilization

Paris-Sud XI, Université de

163

Xanthine oxidoreductase catalyses the reduction of nitrates and nitrite to nitric oxide under hypoxic conditions  

Microsoft Academic Search

Xanthine oxidoreductase (XOR) catalyses the reduction of the therapeutic organic nitrate, nitroglycerin (glyceryl trinitrate, GTN), as well as inorganic nitrate and nitrite, to nitric oxide (NO) under hypoxic conditions in the presence of NADH. Generation of nitric oxide is not detectable under normoxic conditions and is inhibited by the molybdenum site-specific inhibitors, oxypurinol and (?)BOF 4272. These enzymic reactions provide

Timothy M Millar; Cliff R Stevens; Nigel Benjamin; Robert Eisenthal; Roger Harrison; David R Blake

1998-01-01

164

Extracellular Metabolites of Hydrocarbon-Oxidizing Bacteria as Substrates for Sulfate Reduction  

Microsoft Academic Search

The relationship between bacterial oxidation of hydrocarbons and sulfate reduction was studied in an experimental system with liquid paraffin used as a source of organic compounds inoculated with silt taken from a reservoir. Pseudomonads dominated in the hydrocarbon-oxidizing silt bacteriocenosis. However, Rodococcusand Arthrobacteria amounted to no more than 3%. Arthrobacteria dominated the microbial association formed in the paraffin film of

T. V. Koronelli; T. I. Komarova; O. V. Porshneva; L. F. Tkebuchava

2001-01-01

165

Synthesis of graphene nanosheets via oxalic acid-induced chemical reduction of exfoliated graphite oxide  

Microsoft Academic Search

Preparing high-quality graphene through reduction of graphene oxide (GO) by oxalic acid is demonstrated in this paper. Transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectrometry, X-ray diffraction and Raman spectrometry were taken to confirm the reduction of GO and the formation of graphene under these mild conditions. Thermogravimetric analysis and conductivity measurements further testify the excellent thermal stability

Peng Song; Xiao-Yan Zhang; Mingxun Sun; Xiao-Li Cui; Yuehe Lin

2012-01-01

166

Author's personal copy Microbial reduction of chlorite and uranium followed by air oxidation  

E-print Network

Author's personal copy Microbial reduction of chlorite and uranium followed by air oxidation, we examined the reduction of structural Fe(III) in chlorite CCa-2 and uranium(VI) by Shewanella oneidensis MR-1, and the reoxidation of these minerals (after pasteurization) via the introduction of oxygen

Burgos, William

167

Nitrous oxide reduction by members of the family Rhodospirillaceae and the nitrous oxide reductase of Rhodopseudomonas capsulata  

SciTech Connect

After growth in the absence of nitrogenous oxides under anaerobic phototrophic conditions, several strains of Rhodopseudomonas capsulata were shown to possess a nitrous oxide reductase activity. The enzyme responsible for this activity had a periplasmic location and resembled a nitrous oxide reductase purified from Pseudomonas perfectomarinus. Electron flow to nitrous oxide reductase was coupled to generation of a membrane potential and inhibited by rotenone but not antimycin. It is suggested that electron flow to nitrous oxide reductase branches at the level of ubiquinone from the previously characterized electron transfer components of R. capsulata. R. capsulata grew under dark anaerobic conditions in the presence of malate as carbon source and nitrous oxide as electron acceptor. This confirms that nitrous oxide respiration is linked to ATP synthesis. Phototrophically and anaerobically grown cultures of nondenitrifying strains of Rhodopseudomonas sphaeroides, Rhodopseudomonas palustris, and Rhodospirillum rubrum also possessed nitrous oxide reductase activity.

McEwan, A.G.; Greenfield, A.J.; Wetzstein, H.G.; Jackson, J.B.; Ferguson, S.J.

1985-11-01

168

Oxidation versus reductive detoxification of SO sub 2 by chloroplasts  

SciTech Connect

Intact chloroplasts isolated from spinach (Spinacia oleracea L. cv Yates) both oxidized and reduced added sulfite in the light. Oxidation was fast only when endogenous superoxide dismutase was inhibited by cyanide. It was largely suppressed by scavengers of oxygen radicals. After addition of O-acetylserine, chloroplasts reduced sulfite to cysteine and exhibited sulfite-dependent oxygen evolution. Cysteine synthesis from sulfite was faster than from sulfate. The results are discussed in relation to species-specific differences in the phytotoxicity of SO{sub 2}.

Ghisi, R.; Dittrich, A.P.M.; Heber, U. (Universitaet Wuerzburg (West Germany))

1990-03-01

169

Nitrogen oxides reduction by staged combustion of LCV gas  

E-print Network

TABLES OF THE STATISTICAL ANALYSES Primary Equivalence Ratio Overall Equivalence Ratio Delay Time between Stages Inlet Reynolds Number Combustion Temperature F/A Ratio in Gasifier D COMPUTER PROGRAM USED IN THE CAMAC SYSTEM E EXAMPLE . 162 163... of nitrogen that can be present in the ambient air: nitric oxide (NO), nitrogen dioxide (NO z), nitrous oxide (NzO), unsymmetrical nitrogen trioxide (OONO), symmetrical nitrogen trioxide (ON(D P ), dinitrogen trioxide (N zO s), dinitrogen tetroxide (NzO4...

Cabrera Sixto, Jose Manuel

2012-06-07

170

Elevated acetate concentrations in the rhizosphere of Spartina alterniflora and potential influences on sulfate reduction  

NASA Technical Reports Server (NTRS)

Acetate is important in anaerobic metabolism of non-vegetated sediments but its role in salt marsh soils was not investigated thoroughly. Acetate concentrations, oxidation (C-14) and SO4(2-) reduction (S-35) were measured in S. alterniflora soils in NH and MA. Pore water from cores contained greater than 0.1 mM acetate and in some instances greater than 1.0 mM. Non-destructive samples contained less than 0.01 mM. Acetate was associated with roots and concentrations were highest during vegetative growth and varied with changes in plant physiology. Acetate turnover was very low whether whole core or slurry incubations were used. Radiotracers injected directly into soils yielded rates of SO4(2-) reduction and acetate oxidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account for a significant percentage of SO4(2-) reduction. These results differ markedly from data for non-vegetated coastal sediments where acetate levels are low, oxidation rate constants are high and acetate oxidation rates greatly exceed rates of SO4(2-) reduction. The discrepancy between rates of acetate oxidation and SO4(2-) reduction in marsh soils may be due either to the utilization of substrates other than acetate by SO4(2-) reducers or artifacts associated with measurements of organic utilization by rhizosphere bacteria.

Hines, Mark E.; Tugel, Joyce B.; Giblin, A. E.; Banta, G. T.; Hobbie, J. E.

1992-01-01

171

Observations of Oxygen Ion Behavior in the Lithium-Based Electrolytic Reduction of Uranium Oxide  

Microsoft Academic Search

Parametric studies were performed on a lithium-based electrolytic reduction process at bench-scale to investigate the behavior of oxygen ions in the reduction of uranium oxide for various electrochemical cell configurations. Specifically, a series of eight electrolytic reduction runs was performed in a common salt bath of LiCl 1 wt% Li2O. The variable parameters included fuel basket containment material (i.e., stainless

Steven D. Herrmann; Shelly X. Li; Brenda E. Serrano-Rodriguez

2009-01-01

172

Crystal growth of tungsten during hydrogen reduction of tungsten oxide at high temperature  

Microsoft Academic Search

Crystal growth of tungsten during hydrogen reduction of tungsten oxide (WO3) to prepare coarse grain tungsten powder at high temperature (950 °C) was studied. The phase composition and morphologies of products were investigated by means of XRD and SEM. The results show that the reduction sequence of hydrogen reduction of WO3 is WO3?WO2.9?W18O49?WO2?W. The step of WO2?W is the critical

Xiang-wei WU; Jing-song LUO; Bi-zhi LU; Chen-hui XIE; Zhi-ming PI; Mao-zhong HU; Tao XU; Guo-gen WU; Zhi-ming YU; Dan-qing YI

2009-01-01

173

EQUILIBRIUM STUDIES IN THE REDUCTION OF THORIUM OXIDE BY ALUMINUM  

Microsoft Academic Search

Thorium-- aluminum melts were equilibrated with a molten fluoride salt ; that was saturated with thoria and alumina and contained a solid excess of both. ; Under these conditions, the dissolved and solid oxides are in equilibrium. By ; determining the equilibrium concentration of thorium in aluminum in this system, ; it was shown that the primary driving force for

Douglas O. Raleigh

1962-01-01

174

Potential of solar cooling systems for peak demand reduction  

SciTech Connect

We investigated the technical feasibility of solar cooling for peak demand reduction using a building energy simulation program (DOE2.1D). The system studied was an absorption cooling system with a thermal coefficient of performance of 0.8 driven by a solar collector system with an efficiency of 50% with no thermal storage. The analysis for three different climates showed that, on the day with peak cooling load, about 17% of the peak load could be met satisfactorily with the solar-assisted cooling system without any thermal storage. A performance availability analysis indicated that the solar cooling system should be designed for lower amounts of available solar resources that coincide with the hours during which peak demand reduction is required. The analysis indicated that in dry climates, direct-normal concentrating collectors work well for solar cooling; however, in humid climates, collectors that absorb diffuse radiation work better.

Pesaran, A.A. [National Renewable Energy Lab., Golden, CO (United States)] [National Renewable Energy Lab., Golden, CO (United States); Neymark, J. [Neymark (Joel), Golden, CO (United States)] [Neymark (Joel), Golden, CO (United States)

1994-11-01

175

Technological Potential for CO 2 Emission Reductions of Passenger Cars  

Microsoft Academic Search

\\u000a Nowadays, the relation between car transport and climate change is according to recent surveys obvious to most people in Europe.\\u000a Despite this cognition the necessary behavioural change only proceeds slowly. Hence, the significance of innovative technologies\\u000a reducing CO2 emissions from cars rises as behavioural change may take longer and remains uncertain. This paper focuses on technically\\u000a feasible CO2 emission reduction

Michael Krail; Wolfgang Schade

176

The Fundamental Role of Nano-Scale Oxide Films in the Oxidation of Hydrogen and the Reduction of Oxygen on Noble Metal Electrocatalysts  

SciTech Connect

The derivation of successful fuel cell technologies requires the development of more effective, cheaper, and poison-resistant electrocatalysts for both the anode (H{sub 2} oxidation in the presence of small amounts of CO from the reforming of carbonaceous fuels) and the cathode (reduction of oxygen in the presence of carried-over fuel). The proposed work is tightly focused on one specific aspect of electrocatalysis; the fundamental role(s) played by nanoscale (1-2 nm thick) oxide (''passive'') films that form on the electrocatalyst surfaces above substrate-dependent, critical potentials, on charge transfer reactions, particularly at elevated temperatures (25 C < T < 200 C). Once the role(s) of these films is (are) adequately understood, we will then use this information to specify, at the molecular level, optimal properties of the passive layer for the efficient electrocatalysis of the oxygen reduction reaction.

Digby Macdonald

2005-04-15

177

In Vitro Enzymatic Reduction Kinetics of Mineral Oxides by Membrane Fractions from Shewanella oneidensis MR-1  

SciTech Connect

This study documents the first example of in vitro solid-phase mineral oxide reduction by enzyme-containing membrane fractions. Previous in vitro studies have only reported the reduction of aqueous ions. Total membrane (TM) fractions from iron-grown cultures of Shewanella oneidensis MR-1 were isolated and shown to catalyze the reduction of goethite, hematite, birnessite, and ramsdellite/pyrolusite using formate. In contrast, nicotinamide adenine dinucleotide (NADH) and succinate cannot function as electron donors. The significant implications of observations related to this cell-free system are: (i) both iron and manganese mineral oxides are reduced by the TM fraction, but aqueous U(VI) is not; (ii) TM fractions from anaerobically grown, but not aerobically grown, cells can reduce the mineral oxides; (iii) electron shuttles and iron chelators are not needed for this in vitro reduction, documenting conclusively that reduction can occur by direct contact with the mineral oxide; (iv) electron shuttles and EDTA stimulate the in vitro Fe(III) reduction, documenting that exogenous molecules can enhance rates of enzymatic mineral reduction; and (v) multiple membrane components are involved in solid-phase oxide reduction. The membrane fractions, consisting of liposomes of cytoplasmic and outer membrane segments, contain at least 100 proteins including the enzyme that oxidizes formate, formate dehydrogenase. Mineral oxide reduction was inhibited by the addition of detergent Triton X-100, which solubilizes membranes and their associated proteins, consistent with the involvement of multiple electron carriers that are disrupted by detergent addition. In contrast, formate dehydrogenase activity was not inhibited by Triton X-100. The addition of anthraquinone-2,6-disulfonate (AQDS) and menaquinone-4 was unable to restore activity; however, menadione (MD) restored 33% of the activity. The addition of AQDS and MD to reactions without added detergent increased the rate of goethite reduction. The Michaelis-Menten K{sub m} values of 71 {+-} 22 m{sup 2}/L for hematite and 50 {+-} 16 m{sup 2}/L for goethite were calculated as a function of surface area of the two insoluble minerals. V{sub max} was determined to be 123 {+-} 14 and 156 {+-} 13 nmol Fe(II)/min/mg of TM protein for hematite and goethite, respectively. These values are consistent with in vivo rates of reduction reported in the literature. These observations are consistent with our conclusion that the enzymatic reduction of mineral oxides is an effective probe that will allow elucidation of molecular chemistry of the membrane-mineral interface where electron transfer occurs.

Ruebush,S.; Icopini, G.; Brantley, S.; Tien, M.

2006-01-01

178

Environmental Catalysis on Iron Oxide–Silica Aerogels: Selective Oxidation of NH 3 and Reduction of NO by NH 3  

Microsoft Academic Search

The catalytic properties of mesoporous iron oxide–silica aerogels prepared by a sol–gel process combined with ensuing supercritical extraction with CO2 was investigated in the selective oxidation (SCO) of ammonia and the selective reduction (SCR) of NO by ammonia. The main parameters changed in the aerogel preparation were the type of base used as gelation agent, the iron content, and the

P. Fabrizioli; T. Bürgi; A. Baiker

2002-01-01

179

Comparison of effects of nitrate, nitrite, and nitric oxide on reduction of nitrous oxide to dinitrogen by soil microorganisms  

SciTech Connect

Recent work has shown that nitrate inhibits reduction of nitrous oxide (N/sub 2/O) to dinitrogen (N/sub 2/) by soil microorganisms under anaerobic conditions. Studies to investigate the possibility that this inhibition is caused by nitrite or nitric oxide (NO) formed through microbial reduction of nitrate showed that both NO and nitrite inhibit reduction of N/sub 2/O to N/sub 2/ by soil microorganisms under anaerobic conditions (helium atmosphere) but that the inhibitory effect of NO on N/sub 2/O reduction is much smaller than the effects of nitrate or nitrite. Comparison of the effects of nitrate, nitrite, and mixtures of nitrate and nitrite on reduction of N/sub 2/O to N/sub 2/ by soils incubated under He showed that nitrate per se inhibits N/sub 2/O reduction and did not confirm a recent suggestion that the inhibitory effect of nitrate on N/sub 2/O reduction is due to nitrite formed through microbial reduction of nitrate.

Gaskell, J.F.; Blackmer, A.M.; Bremner, J.M.

1981-11-01

180

Voltammetry of a flavocytochrome c(3): the lowest potential heme modulates fumarate reduction rates.  

PubMed Central

Iron-induced flavocytochrome c(3), Ifc(3), from Shewanella frigidimarina NCIMB400, derivatized with a 2-pyridyl disulfide label, self-assembles on gold electrodes as a functional array whose fumarate reductase activity as viewed by direct electrochemistry is indistinguishable from that of Ifc(3) adsorbed on gold or graphite electrodes. The enhanced stability of the labeled protein's array permits analysis at a rotating electrode and limiting catalytic currents fit well to a Michaelis-Menten description of enzyme kinetics with K(M) = 56 +/- 20 microM, pH 7.5, comparable to that obtained in solution assays. At fumarate concentrations above 145 microM cyclic voltammetry shows the catalytic response to contain two features. The position and width of the lower potential component centered on -290 mV and corresponding to a one-electron wave implicates the oxidation state of the lowest potential heme of Ifc(3) as a defining feature in the mechanism of fumarate reduction at high turnover rates. We propose the operation of dual pathways for electron transfer to the active site of Ifc(3) with the lowest potential heme acting as an electron relay on one of these pathways. PMID:10653813

Butt, J N; Thornton, J; Richardson, D J; Dobbin, P S

2000-01-01

181

Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment.  

PubMed

Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide. Sulfidic marine sediment was incubated with overlying nitrate-amended anoxic seawater. Within 2 months, electric coupling of spatially segregated nitrate reduction and sulfide oxidation was evident from: (1) the formation of a 4-6-mm-deep zone separating sulfide oxidation from the associated nitrate reduction, and (2) the presence of pH signatures consistent with proton consumption by cathodic nitrate reduction, and proton production by anodic sulfide oxidation. Filamentous Desulfobulbaceae with the longitudinal structures characteristic of cable bacteria were detected in anoxic, nitrate-amended incubations but not in anoxic, nitrate-free controls. Nitrate reduction by cable bacteria using long-distance electron transport to get privileged access to distant electron donors is a hitherto unknown mechanism in nitrogen and sulfur transformations, and the quantitative importance for elements cycling remains to be addressed. PMID:24577351

Marzocchi, Ugo; Trojan, Daniela; Larsen, Steffen; Meyer, Rikke Louise; Revsbech, Niels Peter; Schramm, Andreas; Nielsen, Lars Peter; Risgaard-Petersen, Nils

2014-08-01

182

In-situ X-Ray Absorption Spectroscopy (XAS) Investigation of a Bifunctional Manganese Oxide Catalyst with High Activity for Electrochemical Water Oxidation and Oxygen Reduction  

PubMed Central

In-situ x-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochemical systems, with the ability to elucidate the chemical nature of electrocatalysts under reaction conditions. In this study, we perform in-situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Using x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS), we find that exposure to an ORR-relevant potential of 0.7 V vs. RHE produces a disordered Mn3II,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs. RHE, relevant to the OER, we observe an oxidation of approximately 80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged Mn3II,III,IIIO4. XAS and electrochemical characterization of two thin film catalysts with different MnOx thicknesses reveals no significant influence of thickness on the measured oxidation states, at either ORR or OER potentials, but demonstrates that the OER activity scales with film thickness. This result suggests that the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film. As the portion of the catalyst film that is most likely to be oxidized at the high potentials necessary for the OER is that which is closest to the electrolyte interface, we hypothesize that the MnIII,IV oxide, rather than Mn3II,III,IIIO4, is the phase pertinent to the observed OER activity. PMID:23758050

Benck, Jesse D.; Gul, Sheraz; Webb, Samuel M.; Yachandra, Vittal K.; Yano, Junko; Jaramillo, Thomas F.

2013-01-01

183

Tin oxide dependence of the CO2 reduction efficiency on tin electrodes and enhanced activity for tin/tin oxide thin-film catalysts.  

PubMed

The importance of tin oxide (SnO(x)) to the efficiency of CO(2) reduction on Sn was evaluated by comparing the activity of Sn electrodes that had been subjected to different pre-electrolysis treatments. In aqueous NaHCO(3) solution saturated with CO(2), a Sn electrode with a native SnO(x) layer exhibited potential-dependent CO(2) reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn(0) surface exhibited higher overall current densities but almost exclusive H(2) evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn(0) and SnO(x) on a Ti electrode. This catalyst exhibited up to 8-fold higher partial current density and 4-fold higher faradaic efficiency for CO(2) reduction than a Sn electrode with a native SnO(x) layer. Our results implicate the participation of SnO(x) in the CO(2) reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis. PMID:22239243

Chen, Yihong; Kanan, Matthew W

2012-02-01

184

Thermogravimetric study of the reduction of oxides of nickel and chromium  

NASA Technical Reports Server (NTRS)

The controlled hydrogen, carbon, and hydrogen-carbon reductions of the oxides of nickel and chromium were evaluated by thermogravimetric means. The materials studied were nickel (nickelous) oxide (NiO) and chromic sesquioxide (Cr2O3), mixed NiO-Cr2O3, and oxidized nickel - 20-percent chromium (Ni-20Cr). NiO was effectively reduced by all three atmospheres, Cr2O3 only by hydrogen-carbon, NiO-Cr2O3 by hydrogen and hydrogen-carbon, and oxidized Ni-20Cr by hydrogen and hydrogen-carbon and to a considerable extent by carbon alone. The results suggest that the presence of nickel promotes the reduction of Cr2O3. However, no definite explanation could be reached for the effectiveness of the hydrogen-carbon reduction of Cr2O3.

Herbell, T. P.

1973-01-01

185

Aqueous CO2 reduction at very low overpotential on oxide-derived Au nanoparticles.  

PubMed

Carbon dioxide reduction is an essential component of many prospective technologies for the renewable synthesis of carbon-containing fuels. Known catalysts for this reaction generally suffer from low energetic efficiency, poor product selectivity, and rapid deactivation. We show that the reduction of thick Au oxide films results in the formation of Au nanoparticles ("oxide-derived Au") that exhibit highly selective CO(2) reduction to CO in water at overpotentials as low as 140 mV and retain their activity for at least 8 h. Under identical conditions, polycrystalline Au electrodes and several other nanostructured Au electrodes prepared via alternative methods require at least 200 mV of additional overpotential to attain comparable CO(2) reduction activity and rapidly lose their activity. Electrokinetic studies indicate that the improved catalysis is linked to dramatically increased stabilization of the CO(2)(•-) intermediate on the surfaces of the oxide-derived Au electrodes. PMID:23171134

Chen, Yihong; Li, Christina W; Kanan, Matthew W

2012-12-12

186

Hydrogen and formate oxidation coupled to dissimilatory reduction of iron or manganese by Alteromonas putrefaciens  

USGS Publications Warehouse

The ability of Alteromonas putrefaciens to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory Fe(III) or Mn(IV) reduction was investigated. A. putrefaciens grew with hydrogen, formate, lactate, or pyruvate as the sole electron donor and Fe(III) as the sole electron acceptor. Lactate and pyruvate were oxidized to acetate, which was not metabolized further. With Fe(III) as the electron acceptor, A. putrefaciens had a high affinity for hydrogen and formate and metabolized hydrogen at partial pressures that were 25-fold lower than those of hydrogen that can be metabolized by pure cultures of sulfate reducers or methanogens. The electron donors for Fe(III) reduction also supported Mn(IV) reduction. The electron donors for Fe(III) and Mn(IV) reduction and the inability of A. putrefaciens to completely oxidize multicarbon substrates to carbon dioxide distinguish A. putrefaciens from GS-15, the only other organism that is known to obtain energy for growth by coupling the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). The ability of A. putrefaciens to reduce large quantities of Fe(III) and to grow in a defined medium distinguishes it from a Pseudomonas sp., which is the only other known hydrogen-oxidizing, Fe(III)-reducing microorganism. Furthermore, A. putrefaciens is the first organism that is known to grow with hydrogen as the electron donor and Mn(IV) as the electron acceptor and is the first organism that is known to couple the oxidation of formate to the reduction of Fe(III) or Mn(IV). Thus, A. putrefaciens provides a much needed microbial model for key reactions in the oxidation of sediment organic matter coupled to Fe(III) and Mn(IV) reduction.

Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.

1989-01-01

187

Geochemical control of microbial Fe(III) reduction potential in wetlands: Comparison of the rhizosphere to non-rhizosphere soil  

USGS Publications Warehouse

We compared the reactivity and microbial reduction potential of Fe(III) minerals in the rhizosphere and non-rhizosphere soil to test the hypothesis that rapid Fe(III) reduction rates in wetland soils are explained by rhizosphere processes. The rhizosphere was defined as the area immediately adjacent to a root encrusted with Fe(III)-oxides or Fe plaque, and non-rhizosphere soil was 0.5 cm from the root surface. The rhizosphere had a significantly higher percentage of poorly crystalline Fe (66??7%) than non-rhizosphere soil (23??7%); conversely, non-rhizosphere soil had a significantly higher proportion of crystalline Fe (50??7%) than the rhizosphere (18??7%, P<0.05 in all cases). The percentage of poorly crystalline Fe(III) was significantly correlated with the percentage of FeRB (r=0.76), reflecting the fact that poorly crystalline Fe(III) minerals are labile with respect to microbial reduction. Abiotic reductive dissolution consumed about 75% of the rhizosphere Fe(III)-oxide pool in 4 h compared to 23% of the soil Fe(III)-oxide pool. Similarly, microbial reduction consumed 75-80% of the rhizosphere pool in 10 days compared to 30-40% of the non-rhizosphere soil pool. Differences between the two pools persisted when samples were amended with an electron-shuttling compound (AQDS), an Fe(III)-reducing bacterium (Geobacter metallireducens), and organic carbon. Thus, Fe(III)-oxide mineralogy contributed strongly to differences in the Fe(III) reduction potential of the two pools. Higher amounts of poorly crystalline Fe(III) and possibly humic substances, and a higher Fe(III) reduction potential in the rhizosphere compared to the non-rhizosphere soil, suggested the rhizosphere is a site of unusually active microbial Fe cycling. The results were consistent with previous speculation that rapid Fe cycling in wetlands is due to the activity of wetland plant roots. ?? 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.

Weiss, J.V.; Emerson, D.; Megonigal, J.P.

2004-01-01

188

Potential genotoxicity of chronically elevated nitric oxide: A review  

Microsoft Academic Search

Several human cancers are associated with chronic bacterial, viral and parasitic infections. Nitric oxide, which is a short-lived free radical produced by many types of cells for a number of important physiological functions, is elevated in these infections. Long-term exposure to elevated NO · cells could have potential genotoxic effects on hosts. There are at least three mechanisms by which

Rui Hai Liu; Joseph H. Hotchkiss

1995-01-01

189

Nitrite reduction to nitrous oxide by propionibacteria: Detoxication mechanism  

Microsoft Academic Search

Characteristics of dissimilatory nitrate reduction by Propionibacterium acidi-propionici, P. freudenreichii, P. jensenii, P. shermanii and P. thoenii were studied. All strains reduced nitrate to nitrite and further to N2O. Recovery of added nitrite-N as N2O-N approached 100%, so that no other end product existed in a significant quantity. Specific rates of N2O production were 3 to 6 orders of magnitude

Heinrich F. Kaspar

1982-01-01

190

Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1  

SciTech Connect

In the absence of O2 and other electron acceptors, the Gram-negative bacterium Shewanella oneidensis MR-1 can use ferric [Fe(III)] (oxy)(hydr)oxide minerals as the terminal electron acceptors for anaerobic respiration. At circumneutral pH and in the absence of strong complexing ligands, Fe(III) oxides are relatively insoluble and thus are external to the bacterial cells. S. oneidensis MR-1 and related strains of metal-reducing Shewanella have evolved the machinery (i.e., metal-reducing or Mtr pathway) for transferring electrons from the inner-membrane, through the periplasm and across the outer-membrane to the surface of extracellular Fe(III) oxides. The protein components identified to date for the Mtr pathway include CymA, MtrA, MtrB, MtrC and OmcA. CymA is an inner-membrane tetraheme c-type cytochrome (c-Cyt) that belongs to the NapC/NrfH family of quinol dehydrogenases. It is proposed that CymA oxidizes the quinol in the inner-membrane and transfers the released electrons to redox proteins in the periplasm. Although the periplasmic proteins receiving electrons from CymA during Fe(III) oxidation have not been identified, they are believed to relay the electrons in the periplasm to MtrA. A decaheme c-Cyt, MtrA is thought to be embedded in the trans outer-membrane and porin-like protein MtrB. Together, MtrAB deliver the electrons through the outer-membrane to the MtrC and OmcA on the outmost bacterial surface. MtrC and OmcA are the outer-membrane decaheme c-Cyts that are translocated across the outer-membrane by the bacterial type II secretion system. Functioning as terminal reductases, MtrC and OmcA can bind the surface of Fe(III) oxides and transfer electrons directly to these minerals via their solvent-exposed hemes. To increase their reaction rates, MtrC and OmcA can use the flavins secreted by S. oneidensis MR-1 cells as diffusible co-factors for reduction of Fe(III) oxides. Because of their extracellular location and broad redox potentials, MtrC and OmcA can also serve as the terminal reductases for soluble forms of Fe(III). Although our understanding of the Mtr pathway is still far from complete, it is the best characterized microbial pathway used for extracellular electron exchange. Characterizations of the Mtr pathway have made significant contributions to the molecular understanding of microbial reduction of Fe(III) oxides.

Shi, Liang; Rosso, Kevin M.; Clarke, Thomas A.; Richardson, David J.; Zachara, John M.; Fredrickson, Jim K.

2012-02-15

191

Influence of the oxidizing species on the reactivity of iron-based Bimetallic reductants.  

PubMed

Anticipating which pollutants are amenable to treatment by iron-based bimetallic reductants requires an understanding of the mechanism(s) driving pollutant reduction. Here, batch studies with six bimetals (Au/Fe, Co/Fe, Cu/Fe, Ni/ Fe, Pd/Fe, and Pt/Fe) and four oxidants (alkyl polyhalides, vinyl polyhalides, alkynes, and water) explored the influence of the electron acceptor on reductant reactivity. Bimetals exhibited disparate reactivity toward some oxidant classes. For example, Pt/Fe enhanced rates of cis-dichloroethylene reduction, but it inhibited the reduction of several alkyl polyhalides. Moreover, the rate increase for vinyl polyhalide reduction by Ni/Fe (approximately 100-fold) and Pd/Fe (approximately 1000-fold) was far greater than that measured for alkyl polyhalides (approximately 10-fold), and reactivity toward vinyl polyhalides exhibited a more pronounced dependence on Ni and Pd loadings than did reactivity toward alkyl polyhalides. These results suggest that the reactions of alkyl and vinyl polyhalides with iron-based bimetals involve different active reductants. Neither rates of alkyl nor vinyl polyhalide reduction correlated with rates of iron corrosion by water, contrary to expectations if galvanic corrosion was primarily responsible for organohalide reduction. Trends observed for the hydrogenation of 2-butyne did mirror the sequence we identified for 1,1,1-trichloroethane reduction, consistent with a role for atomic hydrogen as the principal electron donor in these two systems. PMID:17547205

Cwiertny, David M; Bransfield, Stephen J; Roberts, A Lynn

2007-05-15

192

Sulfonamide antibiotic reduction in aquatic environment by application of fenton oxidation process  

PubMed Central

Presence of antibiotics in the environment may cause potential risk for aquatic environment and organisms. In this research, Fenton oxidation process was offered as an effective method for removal of antibiotic sulfamethoxazole from aqueous solutions. The experiments were performed on laboratory-scale study under complete mixing at 25±2°C. The effects of initial antibiotic concentration, molar ratio of H2O2/Fe+2, solution pH, concentration of H2O2, Fe+2 and reaction time was studied on the oxidation of sulfamethoxazole in three level. The results indicated that the optimal parameters for Fenton process were as follows: molar ratio of [H2O2]/[Fe+2] = 1.5, pH= 4.5, and contact time= 15 min. In this situation, the antibiotic removal and COD reduction were achieved 99.99% and 64.7-70.67%, respectively. Although, Fenton reaction could effectively degrade antibiotic sulfamethoxazole under optimum experimental conditions, however, the rate of mineralization was not completed. This process can be considered to eliminate other refractory antibiotics with similar structure or to increase their biodegradability. PMID:23570238

2013-01-01

193

Characterization of methionine oxidation and methionine sulfoxide reduction using methionine-rich cysteine-free proteins  

PubMed Central

Background Methionine (Met) residues in proteins can be readily oxidized by reactive oxygen species to Met sulfoxide (MetO). MetO is a promising physiological marker of oxidative stress and its inefficient repair by MetO reductases (Msrs) has been linked to neurodegeneration and aging. Conventional methods of assaying MetO formation and reduction rely on chromatographic or mass spectrometry procedures, but the use of Met-rich proteins (MRPs) may offer a more streamlined alternative. Results We carried out a computational search of completely sequenced genomes for MRPs deficient in cysteine (Cys) residues and identified several proteins containing 20% or more Met residues. We used these MRPs to examine Met oxidation and MetO reduction by in-gel shift assays and immunoblot assays with antibodies generated against various oxidized MRPs. The oxidation of Cys-free MRPs by hydrogen peroxide could be conveniently monitored by SDS-PAGE and was specific for Met, as evidenced by quantitative reduction of these proteins with Msrs in DTT- and thioredoxin-dependent assays. We found that hypochlorite was especially efficient in oxidizing MRPs. Finally, we further developed a procedure wherein antibodies made against oxidized MRPs were isolated on affinity resins containing same or other oxidized or reduced MRPs. This procedure yielded reagents specific for MetO in these proteins, but proved to be ineffective in developing antibodies with broad MetO specificity. Conclusion Our data show that MRPs provide a convenient tool for characterization of Met oxidation, MetO reduction and Msr activities, and could be used for various aspects of redox biology involving reversible Met oxidation. PMID:23088625

2012-01-01

194

Gold Decorated Graphene for Rapid Dye Reduction and Efficient Electro Catalytic Oxidation of Ethanol  

NASA Astrophysics Data System (ADS)

A well known disadvantage in fabrication of metal-graphene composite is the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. Here, we demonstrate a novel one pot synthesis of gold nanoparticles (AuNPs) by laser ablation of gold strip and simultaneous decoration of these on functionalized graphene derivatives. Not only the impregnation of AuNPs was linker free, but also the synthesis by itself was surfactant free. This resulted in in-situ decoration of pristine AuNPs on functionalized graphene derivatives. These materials were well characterized and tested for catalytic applications pertaining to dye reduction and electrooxidation. The catalytic reduction rates are 1.4 x 10^2 and 9.4x10^2 times faster for Rhodamine B and Methylene Blue dyes respectively, compared to earlier reports. The enhanced rate involves synergistic interplay of electronic relay between AuNPs and the dye, also charge transfer between the graphene system and dye. In addition, the onset potential for ethanol oxidation was found to be more negative ˜ 100 mV, an indication of its promising application in direct ethanol fuel cells.

Sai Siddhardha, R. S.; v, Lakshman Kumar; Kaniyoor, A.; Podila, R.; Muthu Kumar, V. S.; Venkataramaniah, K.; Ramaprabhu, S.; Rao, A.; Ramamurthy, S. S.

2013-03-01

195

Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation  

NASA Astrophysics Data System (ADS)

Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform.

Gonçalves, Gil; Vila, Mercedes; Bdikin, Igor; de Andrés, Alicia; Emami, Nazanin; Ferreira, Rute A. S.; Carlos, Luís D.; Grácio, José; Marques, Paula A. A. P.

2014-10-01

196

Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation.  

PubMed

Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform. PMID:25339424

Gonçalves, Gil; Vila, Mercedes; Bdikin, Igor; de Andrés, Alicia; Emami, Nazanin; Ferreira, Rute A S; Carlos, Luís D; Grácio, José; Marques, Paula A A P

2014-01-01

197

Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation  

PubMed Central

Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform. PMID:25339424

Goncalves, Gil; Vila, Mercedes; Bdikin, Igor; de Andres, Alicia; Emami, Nazanin; Ferreira, Rute A. S.; Carlos, Luis D.; Gracio, Jose; Marques, Paula A. A. P.

2014-01-01

198

Anaerobic methane oxidation in metalliferous hydrothermal sediments: influence on carbon flux and decoupling from sulfate reduction.  

PubMed

The anaerobic oxidation of methane (AOM) is a globally significant sink that regulates methane flux from sediments into the oceans and atmosphere. Here we examine mesophilic to thermophilic AOM in hydrothermal sediments recovered from the Middle Valley vent field, on the Juan de Fuca Ridge. Using continuous-flow sediment bioreactors and batch incubations, we characterized (i) the degree to which AOM contributes to net dissolved inorganic carbon flux, (ii) AOM and sulfate reduction (SR) rates as a function of temperature and (iii) the distribution and density of known anaerobic methanotrophs (ANMEs). In sediment bioreactors, inorganic carbon stable isotope mass balances results indicated that AOM accounted for between 16% and 86% of the inorganic carbon produced, underscoring the role of AOM in governing inorganic carbon flux from these sediments. At 90°C, AOM occurred in the absence of SR, demonstrating a striking decoupling of AOM from SR. An abundance of Fe(III)-bearing minerals resembling mixed valent Fe oxides, such as green rust, suggests the potential for a coupling of AOM to Fe(III) reduction in these metalliferous sediments. While SR bacteria were only observed in cooler temperature sediments, ANMEs allied to ANME-1 ribotypes, including a putative ANME-1c group, were found across all temperature regimes and represented a substantial proportion of the archaeal community. In concert, these results extend and reshape our understanding of the nature of high temperature methane biogeochemistry, providing insight into the physiology and ecology of thermophilic anaerobic methanotrophy and suggesting that AOM may play a central role in regulating biological dissolved inorganic carbon fluxes to the deep ocean from the organic-poor, metalliferous sediments of the global mid-ocean ridge hydrothermal vent system. PMID:22827909

Wankel, Scott D; Adams, Melissa M; Johnston, David T; Hansel, Colleen M; Joye, Samantha B; Girguis, Peter R

2012-10-01

199

Bystanding F+ Oxidants Enable Selective Reductive Elimination from High-Valent Metal Centers in Catalysis  

PubMed Central

Reductive elimination from partially or completely oxidized metal centers is a vital step in a myriad of carbon–carbon and carbon–heteroatom bond–forming reactions. One strategy for promoting otherwise challenging reductive elimination reactions is to oxidize the metal center using a two-electron oxidant (i.e., from M(n) to M(n+2)). However, many of the commonly used oxidants for this type of transformation contain oxygen, nitrogen, or halogen moieties that are subsequently capable of participating in reductive elimination, leading to a mixture of products. This minireview examines an emerging solution to this widespread problem in organometallic chemistry, the use of bystanding F+ oxidants, and describes recent applications in Pd(II)/Pd(IV) and Au(I)/Au(III) catalysis. We then briefly discuss a rare example in which one-electron oxidants have been shown to promote selective reductive elimination in Pd(II)-catalyzed C–H functionalization, which we view as a promising future directing in the field. PMID:21264991

Engle, Keary M.; Mei, Tian-Sheng; Wang, Xisheng; Yu, Jin-Quan

2011-01-01

200

Remote fabrication and irradiation test of recycled nuclear fuel prepared by the oxidation and reduction of spent oxide fuel  

NASA Astrophysics Data System (ADS)

A direct dry recycling process was developed in order to reuse spent pressurized light water reactor (LWR) nuclear fuel in CANDU reactors without the separation of sensitive nuclear materials such as plutonium. The benefits of the dry recycling process are the saving of uranium resources and the reduction of spent fuel accumulation as well as a higher proliferation resistance. In the process of direct dry recycling, fuel pellets separated from spent LWR fuel rods are oxidized from UO2 to U3O8 at 500 °C in an air atmosphere and reduced into UO2 at 700 °C in a hydrogen atmosphere, which is called OREOX (oxidation and reduction of oxide fuel). The pellets are pulverized during the oxidation and reduction processes due to the phase transformation between cubic UO2 and orthorhombic U3O8. Using the oxide powder prepared from the OREOX process, the compaction and sintering processes are performed in a remote manner in a shielded hot cell due to the high radioactivity of the spent fuel. Most of the fission gas and volatile fission products are removed during the OREOX and sintering processes. The mini-elements fabricated by the direct dry recycling process are irradiated in the HANARO research reactor for the performance evaluation of the recycled fuel pellets. Post-irradiation examination of the irradiated fuel showed that microstructural evolution and fission gas release behavior of the dry-recycled fuel were similar to high burnup UO2 fuel.

Jin Ryu, Ho; Chan Song, Kee; Il Park, Geun; Won Lee, Jung; Seung Yang, Myung

2005-02-01

201

Jet Noise Reduction Potential From Emerging Variable Cycle Technologies  

NASA Technical Reports Server (NTRS)

Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts utilized ejectors, inverted velocity profiles, and fluidic shields. One of the ejector concepts was found to produce stagnant flow within the ejector and the other ejector concept produced discrete-frequency tones that degraded the acoustic performance of the model. The concept incorporating an inverted velocity profile and fluid shield produced overall-sound-pressure-level reductions of 6 dB relative to a single stream nozzle at the peak jet noise angle for some nozzle pressure ratios. Flow separations in the nozzle degraded the acoustic performance of the inverted velocity profile model at low nozzle pressure ratios.

2012-01-01

202

Jet Noise Reduction Potential from Emerging Variable Cycle Technologies  

NASA Technical Reports Server (NTRS)

Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts utilized ejectors, inverted velocity profiles, and fluidic shields. One of the ejector concepts was found to produce stagnant flow within the ejector and the other ejector concept produced discrete-frequency tones that degraded the acoustic performance of the model. The concept incorporating an inverted velocity profile and fluid shield produced overall-sound-pressure-level reductions of 6 dB relative to a single stream nozzle at the peak jet noise angle for some nozzle pressure ratios. Flow separations in the nozzle degraded the acoustic performance of the inverted velocity profile model at low nozzle pressure ratios.

Henderson, Brenda; Bridges, James; Wernet, Mark

2012-01-01

203

Potential CO2 Emission Reduction by Development of Non-Grain-Based Bioethanol in China  

NASA Astrophysics Data System (ADS)

Assessment of the potential CO2 emission reduction by development of non-grain-based ethanol in China is valuable for both setting up countermeasures against climate change and formulating bioethanol policies. Based on the land occupation property, feedstock classification and selection are conducted, identifying sweet sorghum, cassava, and sweet potato as plantation feedstocks cultivated from low-quality arable marginal land resources and molasses and agricultural straws as nonplantation feedstocks derived from agricultural by-products. The feedstock utilization degree, CO2 reduction coefficient of bioethanol, and assessment model of CO2 emission reduction potential of bioethanol are proposed and established to assess the potential CO2 emission reduction by development of non-grain-based bioethanol. The results show that China can obtain emission reduction potentials of 10.947 and 49.027 Mt CO2 with non-grain-based bioethanol in 2015 and 2030, which are much higher than the present capacity, calculated as 1.95 Mt. It is found that nonplantation feedstock can produce more bioethanol so as to obtain a higher potential than plantation feedstock in both 2015 and 2030. Another finding is that developing non-grain-based bioethanol can make only a limited contribution to China’s greenhouse gas emission reduction. Moreover, this study reveals that the regions with low and very low potentials for emission reduction will dominate the spatial distribution in 2015, and regions with high and very high potentials will be the majority in 2030.

Li, Hongqiang; Wang, Limao; Shen, Lei

2010-10-01

204

Potential CO2 emission reduction by development of non-grain-based bioethanol in China.  

PubMed

Assessment of the potential CO(2) emission reduction by development of non-grain-based ethanol in China is valuable for both setting up countermeasures against climate change and formulating bioethanol policies. Based on the land occupation property, feedstock classification and selection are conducted, identifying sweet sorghum, cassava, and sweet potato as plantation feedstocks cultivated from low-quality arable marginal land resources and molasses and agricultural straws as nonplantation feedstocks derived from agricultural by-products. The feedstock utilization degree, CO(2) reduction coefficient of bioethanol, and assessment model of CO(2) emission reduction potential of bioethanol are proposed and established to assess the potential CO(2) emission reduction by development of non-grain-based bioethanol. The results show that China can obtain emission reduction potentials of 10.947 and 49.027 Mt CO(2) with non-grain-based bioethanol in 2015 and 2030, which are much higher than the present capacity, calculated as 1.95 Mt. It is found that nonplantation feedstock can produce more bioethanol so as to obtain a higher potential than plantation feedstock in both 2015 and 2030. Another finding is that developing non-grain-based bioethanol can make only a limited contribution to China's greenhouse gas emission reduction. Moreover, this study reveals that the regions with low and very low potentials for emission reduction will dominate the spatial distribution in 2015, and regions with high and very high potentials will be the majority in 2030. PMID:20087584

Li, Hongqiang; Wang, Limao; Shen, Lei

2010-10-01

205

Visible light-mediated atom transfer radical addition via oxidative and reductive quenching of photocatalysts.  

PubMed

Herein, the development of visible light-mediated atom transfer radical addition (ATRA) of haloalkanes onto alkenes and alkynes using the reductive and oxidative quenching of [Ir{dF(CF(3))ppy}(2)(dtbbpy)]PF(6) and [Ru(bpy)(3)]Cl(2) is presented. Initial investigations indicated that the oxidative quenching of photocatalysts could effectively be utilized for ATRA, and since that report, the protocol has been expanded by broadening the scope of the reaction in terms of the photocatalysts, substrates, and solvents. In addition, further modifications of the reaction conditions allowed for the efficient ATRA of perfluoroalkyl iodides onto alkenes and alkynes utilizing the reductive quenching cycle of [Ru(bpy)(3)]Cl(2) with sodium ascorbate as the sacrificial electron donor. These results signify the complementary nature of the oxidative and reductive quenching pathways of photocatalysts and the ability to predictably direct reaction outcome through modification of the reaction conditions. PMID:22486313

Wallentin, Carl-Johan; Nguyen, John D; Finkbeiner, Peter; Stephenson, Corey R J

2012-05-30

206

Holographic patterning of graphene-oxide films by light-driven reduction.  

PubMed

We report on the patterning and reduction of graphene-oxide films by holographic lithography. Light reduction can be used to engineer low-cost graphene-based devices by performing a local conversion of insulating oxide into the conductive graphene. In this work, computer-generated holograms have been exploited to realize complex graphene patterns in a single shot, different from serial laser writing or mask-based photolithographic processes. The technique has been further improved by achieving speckle noise reduction: submicron and diffraction-limited features have been obtained. In addition we have also demonstrated that the gray-scale lithography capability can be used to obtain different reduction levels in a single exposure. PMID:25121702

Orabona, E; Ambrosio, A; Longo, A; Carotenuto, G; Nicolais, L; Maddalena, P

2014-07-15

207

A simple method for the determination of reduction potentials in heme proteins  

PubMed Central

We describe a simple method for the determination of heme protein reduction potentials. We use the method to determine the reduction potentials for the PAS-A domains of the regulatory heme proteins human NPAS2 (Em = ?115 mV ± 2 mV, pH 7.0) and human CLOCK (Em = ?111 mV ± 2 mV, pH 7.0). We suggest that the method can be easily and routinely applied to the determination of reduction potentials across the family of heme proteins. PMID:24440354

Millett, Elizabeth S.; Glenday, Jennifer; Chan, Cheuk K.; Weedon, Holly; Randhawa, Harpreet; Basran, Jaswir; Raven, Emma L.

2014-01-01

208

Reduction of a phosphorus oxide and acid reaction set  

SciTech Connect

It has been predicted for some time that hypersonic aircraft will suffer from diminished fuel efficiency due to the slow speed of radical recombination in the nozzle of the aircraft and the consequent expulsion of high-energy fragments during high Mach number flight. The addition of small amounts of phosphine combustion products (phosphorus oxides and acids) to water vapor has been found to result in a faster relaxation rate of OH to its equilibrium density following H{sub 2}O photolysis. This article describes the systematic construction of a reaction model of 162 phosphorus reactions among 17 phosphorus-containing species. Those reactions that contribute to the reestablishment of equilibrium following the perturbation of the system by H{sub 2}O photolysis or by an increase in temperature are identified. A thermodynamic free energy function is used to quantify the rate of system relaxation back to equilibrium for a series of 36 reaction conditions covering a temperature range of 1,500 to 3,000 K, a gas density range of 5 {times} 10{sup {minus}7} to 5 {times} 10{sup {minus}5} mol/cm{sup 3} and a fuel equivalence ratio of 0.8 to 1.2.

Twarowski, A. [Rockwell International Science Center, Thousand Oaks, CA (United States)] [Rockwell International Science Center, Thousand Oaks, CA (United States)

1995-07-01

209

Fabrication of palladium/graphene oxide composite by plasma reduction at room temperature.  

PubMed

Pd nanoparticles were fabricated on graphene oxide (GO) using a deposition-precipitation method with a glow discharge plasma reduction at room temperature. Argon was employed as the plasma-generating gas. The novel plasma method selectively reduces the metal ions. The graphene oxide has no change with this plasma reduction according to the Fourier transform infrared analysis. The Pd nanoparticles on the GO were uniformly distributed with an average diameter of 1.6 nm. The functional groups on the GO not only prevent Pd nanoparticles from further aggregation but also provide a strong hydrophilic property to the Pd/GO composite, which can form stable colloidal dispersions in water. PMID:22533915

Yu, Yue; Li, Yingzhi; Pan, Yunxiang; Liu, Chang-Jun

2012-01-01

210

Localized reduction of graphene oxide by electrogenerated naphthalene radical anions and subsequent diazonium electrografting.  

PubMed

Herein, we describe a new localized functionalization method of graphene oxide (GO) deposited on a silicon oxide surface. The functionalization starts with the reduction of GO by electrogenerated naphthalene radical anions. The source of reducers is a microelectrode moving close to the substrate in a typical scanning electrochemical microscopy (SECM) configuration. Then, the recovery of electronic conductivity upon reduction enables the selective electrochemical functionalization of the patterns. The illustrative example is the electrografting of reduced-GO with a diazonium salt bearing a protonated amino group that can further immobilize gold nanoparticles by simple immersion. This study opens new routes for the construction of multifunctional patterned surfaces. PMID:24628490

Azevedo, Joël; Fillaud, Laure; Bourdillon, Céline; Noël, Jean-Marc; Kanoufi, Fréderic; Jousselme, Bruno; Derycke, Vincent; Campidelli, Stéphane; Cornut, Renaud

2014-04-01

211

LC-MS/MS analysis and comparison of oxidative damages on peptides induced by pathogen reduction technologies for platelets.  

PubMed

Pathogen reduction technologies (PRT) are photochemical processes that use a combination of photosensitizers and UV-light to inactivate pathogens in platelet concentrates (PCs), a blood-derived product used to prevent hemorrhage. However, different studies have questioned the impact of PRT on platelet function and transfusion efficacy, and several proteomic analyses revealed possible oxidative damages to proteins. The present work focused on the oxidative damages produced by the two main PRT on peptides. Model peptides containing residues prone to oxidation (tyrosine, histidine, tryptophane, and cysteine) were irradiated with a combination of amotosalen/UVA (Intercept process) or riboflavin/UVB (Mirasol-like process). Modifications were identified and quantified by liquid chromatography coupled to tandem mass spectrometry. Cysteine-containing peptides formed disulfide bridges (R-SS-R, -2 Da; favored following amotosalen/UVA), sulfenic and sulfonic acids (R-SOH, +16 Da, R-SO3H, +48 Da, favored following riboflavin/UVB) upon treatment and the other amino acids exhibited different oxidations revealed by mass shifts from +4 to +34 Da involving different mechanisms; no photoadducts were detected. These amino acids were not equally affected by the PRT and the combination riboflavin/UVB generated more oxidation than amotosalen/UVA. This work identifies the different types and sites of peptide oxidations under the photochemical treatments and demonstrates that the two PRT may behave differently. The potential impact on proteins and platelet functions may thus be PRT-dependent. PMID:24470194

Prudent, Michel; Sonego, Giona; Abonnenc, Mélanie; Tissot, Jean-Daniel; Lion, Niels

2014-04-01

212

Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions  

NASA Astrophysics Data System (ADS)

Development of efficient, affordable electrocatalysts for the oxygen evolution reaction and the oxygen reduction reaction is critical for rechargeable metal-air batteries. Here we present lithium cobalt oxide, synthesized at 400?°C (designated as LT-LiCoO2) that adopts a lithiated spinel structure, as an inexpensive, efficient electrocatalyst for the oxygen evolution reaction. The catalytic activity of LT-LiCoO2 is higher than that of both spinel cobalt oxide and layered lithium cobalt oxide synthesized at 800?°C (designated as HT-LiCoO2) for the oxygen evolution reaction. Although LT-LiCoO2 exhibits poor activity for the oxygen reduction reaction, the chemically delithiated LT-Li1-xCoO2 samples exhibit a combination of high oxygen reduction reaction and oxygen evolution reaction activities, making the spinel-type LT-Li0,5CoO2 a potential bifunctional electrocatalyst for rechargeable metal-air batteries. The high activities of these delithiated compositions are attributed to the Co4O4 cubane subunits and a pinning of the Co3+/4+:3d energy with the top of the O2-:2p band.

Maiyalagan, Thandavarayan; Jarvis, Karalee A.; Therese, Soosairaj; Ferreira, Paulo J.; Manthiram, Arumugam

2014-05-01

213

Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions.  

PubMed

Development of efficient, affordable electrocatalysts for the oxygen evolution reaction and the oxygen reduction reaction is critical for rechargeable metal-air batteries. Here we present lithium cobalt oxide, synthesized at 400?°C (designated as LT-LiCoO2) that adopts a lithiated spinel structure, as an inexpensive, efficient electrocatalyst for the oxygen evolution reaction. The catalytic activity of LT-LiCoO2 is higher than that of both spinel cobalt oxide and layered lithium cobalt oxide synthesized at 800?°C (designated as HT-LiCoO2) for the oxygen evolution reaction. Although LT-LiCoO2 exhibits poor activity for the oxygen reduction reaction, the chemically delithiated LT-Li1-xCoO2 samples exhibit a combination of high oxygen reduction reaction and oxygen evolution reaction activities, making the spinel-type LT-Li0,5CoO2 a potential bifunctional electrocatalyst for rechargeable metal-air batteries. The high activities of these delithiated compositions are attributed to the Co4O4 cubane subunits and a pinning of the Co(3+/4+):3d energy with the top of the O(2-):2p band. PMID:24862287

Maiyalagan, Thandavarayan; Jarvis, Karalee A; Therese, Soosairaj; Ferreira, Paulo J; Manthiram, Arumugam

2014-01-01

214

Potential toxicity of superparamagnetic iron oxide nanoparticles (SPION)  

PubMed Central

Superparamagnetic iron oxide nanoparticles (SPION) are being widely used for various biomedical applications, for example, magnetic resonance imaging, targeted delivery of drugs or genes, and in hyperthermia. Although, the potential benefits of SPION are considerable, there is a distinct need to identify any potential cellular damage associated with these nanoparticles. Besides focussing on cytotoxicity, the most commonly used determinant of toxicity as a result of exposure to SPION, this review also mentions the importance of studying the subtle cellular alterations in the form of DNA damage and oxidative stress. We review current studies and discuss how SPION, with or without different surface coating, may cause cellular perturbations including modulation of actin cytoskeleton, alteration in gene expression profiles, disturbance in iron homeostasis and altered cellular responses such as activation of signalling pathways and impairment of cell cycle regulation. The importance of protein-SPION interaction and various safety considerations relating to SPION exposure are also addressed. PMID:22110864

Singh, Neenu; Jenkins, Gareth J.S.; Asadi, Romisa; Doak, Shareen H.

2010-01-01

215

Doping metal-organic frameworks for water oxidation, carbon dioxide reduction, and organic photocatalysis.  

PubMed

Catalytically competent Ir, Re, and Ru complexes H(2)L(1)-H(2)L(6) with dicarboxylic acid functionalities were incorporated into a highly stable and porous Zr(6)O(4)(OH)(4)(bpdc)(6) (UiO-67, bpdc = para-biphenyldicarboxylic acid) framework using a mix-and-match synthetic strategy. The matching ligand lengths between bpdc and L(1)-L(6) ligands allowed the construction of highly crystalline UiO-67 frameworks (metal-organic frameworks (MOFs) 1-6) that were doped with L(1)-L(6) ligands. MOFs 1-6 were isostructural to the parent UiO-67 framework as shown by powder X-ray diffraction (PXRD) and exhibited high surface areas ranging from 1092 to 1497 m(2)/g. MOFs 1-6 were stable in air up to 400 °C and active catalysts in a range of reactions that are relevant to solar energy utilization. MOFs 1-3 containing [Cp*Ir(III)(dcppy)Cl] (H(2)L(1)), [Cp*Ir(III)(dcbpy)Cl]Cl (H(2)L(2)), and [Ir(III)(dcppy)(2)(H(2)O)(2)]OTf (H(2)L(3)) (where Cp* is pentamethylcyclopentadienyl, dcppy is 2-phenylpyridine-5,4'-dicarboxylic acid, and dcbpy is 2,2'-bipyridine-5,5'-dicarboxylic acid) were effective water oxidation catalysts (WOCs), with turnover frequencies (TOFs) of up to 4.8 h(-1). The [Re(I)(CO)(3)(dcbpy)Cl] (H(2)L(4)) derivatized MOF 4 served as an active catalyst for photocatalytic CO(2) reduction with a total turnover number (TON) of 10.9, three times higher than that of the homogeneous complex H(2)L(4). MOFs 5 and 6 contained phosphorescent [Ir(III)(ppy)(2)(dcbpy)]Cl (H(2)L(5)) and [Ru(II)(bpy)(2)(dcbpy)]Cl(2) (H(2)L(6)) (where ppy is 2-phenylpyridine and bpy is 2,2'-bipyridine) and were used in three photocatalytic organic transformations (aza-Henry reaction, aerobic amine coupling, and aerobic oxidation of thioanisole) with very high activities. The inactivity of the parent UiO-67 framework and the reaction supernatants in catalytic water oxidation, CO(2) reduction, and organic transformations indicate both the molecular origin and heterogeneous nature of these catalytic processes. The stability of the doped UiO-67 catalysts under catalytic conditions was also demonstrated by comparing PXRD patterns before and after catalysis. This work illustrates the potential of combining molecular catalysts and MOF structures in developing highly active heterogeneous catalysts for solar energy utilization. PMID:21780787

Wang, Cheng; Xie, Zhigang; deKrafft, Kathryn E; Lin, Wenbin

2011-08-31

216

Evidence of alloy formation during reduction of platinized tin oxide surfaces  

NASA Technical Reports Server (NTRS)

Ion scattering spectroscopy, Auger electron spectroscopy, and electron spectroscopy for chemical analysis have been used to examine a platinized tin oxide catalyst surface before, during, and after reduction by annealing under vacuum at 250 to 450 C. These techniques were then used to examine the reduced surface after a room-temperature, low-pressure oxygen exposure. The spectral results and the behavior of the reduced surface toward oxygen exposure both indicate that a Pt/Sn alloy is produced during reduction.

Gardner, Steven D.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1989-01-01

217

Tuning the nonlinear optical absorption of reduced graphene oxide by chemical reduction.  

PubMed

Reduced graphene oxides with varying degrees of reduction have been produced by hydrazine reduction of graphene oxide. The linear and nonlinear optical properties of both graphene oxide as well as the reduced graphene oxides have been measured by single beam Z-scan measurement in the picosecond region. The results reveal both saturable absorption and two-photon absorption, strongly dependent on the intensity of the pump pulse: saturable absorption occurs at lower pump pulse intensity (~1.5 GW/cm2 saturation intensity) whereas two-photon absorption dominates at higher intensities (?5.7 GW/cm2). Intriguingly, we find that the two-photon absorption coefficient (from 1.5 cm/GW to 4.5cm/GW) and the saturation intensity (from 1 GW/cm2 to 2 GW/cm2) vary with chemical reduction, which is ascribed to the varying concentrations of sp2 domains and sp2 clusters in the reduced graphene oxides. Our results not only provide an insight into the evolution of the nonlinear optical coefficient in reduced graphene oxide, but also suggest that chemical engineering techniques may usefully be applied to tune the nonlinear optical properties of various nano-materials, including atomically thick graphene sheets. PMID:25321022

Shi, Hongfei; Wang, Can; Sun, Zhipei; Zhou, Yueliang; Jin, Kuijuan; Redfern, Simon A T; Yang, Guozhen

2014-08-11

218

Mercury reduction and oxidation by reduced natural organic matter in anoxic environments  

SciTech Connect

Natural organic matter (NOM)-mediated redox cycling of elemental mercury Hg(0) and mercuric Hg(II) is critically important in affecting inorganic mercury transformation and bioavailability. However, these processes are not well understood, particularly in anoxic water and sediments where NOM can be reduced and toxic methylmercury is formed. We show that under dark anoxic conditions reduced organic matter (NOMre) simultaneously reduces and oxidizes Hg via different reaction mechanisms. Reduction of Hg(II) is primarily caused by reduced quinones. However, Hg(0) oxidation is controlled by thiol functional groups via oxidative complexation, which is demonstrated by the oxidation of Hg(0) by low-molecular-weight thiol compounds, including glutathione and mercaptoacetic acid under reducing conditions. Depending on the NOM source, oxidation state, and NOM:Hg ratio, NOM reduces Hg(II) at initial rates ranging from 0.4 to 5.5 h-1, which are about 2 to 6 times higher than observed for photochemical reduction of Hg(II) in open surface waters. However, rapid reduction of Hg(II) by NOMre can be offset by oxidation of Hg(0) with an estimated initial rate as high as 5.4 h-1. This dual role of NOMre is expected to strongly influence the availability of reactive Hg and thus to have important implications for microbial uptake and methylation in anoxic environments.

Zheng, Wang [ORNL; Liang, Liyuan [ORNL; Gu, Baohua [ORNL

2012-01-01

219

The potential reduction of microbial contamination of central venous catheters.  

PubMed

The microbial contamination of stopcock entry ports attached to central venous catheters (CVC) was determined using a specially designed swab. The swab was made of a highly porous material, Porex, and was designed to fit exactly into the entry port of stopcocks. The swab was used to determine the frequency of microbial contamination of entry ports attached to CVC in patients located on an Intensive Care Unit. Of the 200 swabs obtained 44 (22%) contained microorganisms. Coagulase-negative staphylococci were recovered from 43 of the swabs and diphtheroid bacilli from 1 swab. In vitro studies were carried out to investigate the efficiency of the swab in removing excess residual fluid and organisms from entry ports. The swab absorbed relatively large numbers of bacteria within seconds. When entry ports were inoculated with between 10(3) and 10(5) cfu of either Staphylococcus epidermidis or Klebsiella pneumoniae greater than 99% of the organisms were absorbed by the swab (P < 0.01). The absorbent swab was more efficient at removing S. epidermidis from the entry port when compared to a standard cotton swab (P < 0.01). In vitro this absorbent swab reduced the potential for catheter contamination resulting from migration of organisms from the entry port via the intraluminal route. The use of the swab in the clinical situation may reduce the incidence of CVC-related infections. PMID:7636276

Tebbs, S E; Trend, V; Elliott, T S

1995-03-01

220

Reduction of local velocity spreads by linear potentials  

NASA Astrophysics Data System (ADS)

We study the spreading of the wave function of a Bose-Einstein condensate accelerated by a constant force both in the absence and in the presence of atom-atom interactions. We show that, despite the initial velocity dispersion, the local velocity dispersion defined at a given position downward can reach ultralow values and be used to probe very narrow energetic structures. We explain how one can define quantum mechanically and without ambiguities the different velocity moments at a given position by extension of their classical counterparts. We provide a common theoretical framework for interacting and noninteracting regimes based on the Wigner transform of the initial wave function that encapsulates the dynamics in a scaling parameter. In the absence of interaction, our approach is exact. Using a numerical simulation of the one-dimensional Gross-Pitaevskii equation, we provide the range of validity of our scaling approach and find a very good agreement in the Thomas-Fermi regime. We apply this approach to the study of the scattering of a matter wave packet on a double barrier potential. We show that a Fabry-Perot resonance in such a cavity with an energy width below the pK range can be probed in this manner. We show that our approach can be readily transposed to a large class of many-body quantum systems that exhibit self-similar dynamics.

Damon, F.; Vermersch, F.; Muga, J. G.; Guéry-Odelin, D.

2014-05-01

221

Yttrium oxide/gadolinium oxide-modified platinum nanoparticles as cathodes for the oxygen reduction reaction.  

PubMed

Rare-earth-element (Y, Gd) modified Pt nanoparticles (NPs) supported on a carbon substrate (Vulcan XC-72) are synthesized via a water-in-oil chemical route. In both cases, X-ray diffraction (XRD) measurements show the non-formation of an alloyed material. Photoemission spectroscopy (XPS) results reveal that Y and Gd are oxidized. Additionally, no evidence of an electronic modification of Pt can be brought to light. Transmission electron microscopy (TEM) studies indicate that Pt-Y(2)O(3) and Pt-Gd(2)O(3) particles are well dispersed on the substrate-and that their average particle sizes are smaller than the Pt-NP sizes. The catalytic activity of the Pt-Y(2)O(3)/C and Pt-Gd(2)O(3)/C catalysts towards the oxygen reduction reaction (ORR) is studied in a 0.5?M H(2)SO(4) electrolyte. The surface and mass specific activities of the Pt-Y(2)O(3)/C catalyst towards the ORR at 0.9 V (vs. the reversible hydrogen electrode, RHE) are (54.3±1.2) ?A?cm(-2)(Pt) and MA=(23.1±0.5) mA?mg(-1)(Pt), respectively. These values are 1.3-, and 1.6-fold higher than the values obtained with a Pt/C catalyst. Although the as-prepared Pt-Gd(2)O(3)/C catalyst has a lower catalytic activity for the ORR compared to Pt/C, the heat-treated sample shows a surface specific activity of about (53.0±0.7) ?A?cm(-2) Pt , and a mass specific activity (MA) of about (18.2±0.5) mA?mg(-1) Pt at 0.9 V (vs. RHE). The enhancement of the ORR kinetics on the Pt-Y(2)O(3)/C and heat-treated Pt-Gd(2)O(3)/C catalysts could be associated with the formation of platinum NPs presenting modified surface properties. PMID:24819164

Luo, Yun; Habrioux, Aurélien; Calvillo, Laura; Granozzi, Gaetano; Alonso-Vante, Nicolas

2014-07-21

222

Oxygen potential studies on hypostoichiometric uranium-cerium mixed oxide  

NASA Astrophysics Data System (ADS)

Oxygen potential measurements on (U,Ce)0 2-x with Ce/U + Ce ratios of 0.2 to 0.5 were carried out at 1073 and 1173 K by a gas equilibration method employing H 20/H 2 carrier gas. A new wet chemical method based on potentiometric titrations was used to determine and cross check the O/M ratios of the equilibrated samples. Lattice parameters of stoichiometric oxides were determined by x-ray diffraction. The oxygen potentials and their dependence on O/M and composition are discussed and compared with available literature data.

Nagarajan, K.; Saha, Rita; Yadav, R. B.; Rajagopalan, S.; Kutty, K. V. G.; Saibaba, M.; Rao, P. R. Vasudeva; Mathews, C. K.

1985-02-01

223

Redox Potentials, Laccase Oxidation, and Antilarval Activities of Substituted Phenols  

PubMed Central

Laccases are copper-containing oxidases that are involved in sclerotization of the cuticle of mosquitoes and other insects. Oxidation of exogenous compounds by insect laccases may have the potential to produce reactive species toxic to insects. We investigated two classes of substituted phenolic compounds, halogenated di- and trihydroxybenzenes and substituted di-tert-butylphenols, on redox potential, oxidation by laccase and effects on mosquito larval growth. An inverse correlation between the oxidation potentials and laccase activity of halogenated hydroxybenzenes was found. Substituted di-tert-butylphenols however were found to impact mosquito larval growth and survival. In particular, 2,4-di-tert-butyl-6-(3-methyl-2-butenyl)phenol (15) caused greater than 98% mortality of Anopheles gambiae larvae in a concentration of 180 nM, whereas 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-2-methylpropanal oxime (13) and 6,8-di-tert-butyl-2,2-dimethyl-3,4-dihydro-2H-chromene (33) caused 93% and 92% mortalities in concentrations of 3.4 and 3.7 ?M, respectively. Larvae treated with di-tert-butylphenolic compounds died just before pupation. PMID:22300888

Prasain, Keshar; Nguyen, Thi D. T.; Gorman, Maureen J.; Barrigan, Lydia M.; Peng, Zeyu; Kanost, Michael R.; Syed, Lateef U.; Li, Jun; Zhu, Kun Yan; Hua, Duy H.

2012-01-01

224

Slide fastener reduction of graphene-oxide edges by calcium: insight from ab initio molecular dynamics.  

PubMed

The reduction of graphene oxide can be used as a simple way to produce graphene on a large scale. However, the numerous edges produced by the oxidation of graphite seriously degrade the quality of the graphene and its carrier transport property. In this work, the reduction of oxygen-passivated graphene edges and the subsequent linking of separated graphene sheets by calcium are investigated by using first-principles calculations. The calculations show that calcium can effectively remove the oxygen groups from two adjacent edges. The joining point of the edges serves as the starting point of the reduction and facilitates the reaction. Once the oxygen groups are removed, the crack is sutured. If the joining point is lacking, it becomes difficult to zip the separated fragments. A general electron-reduction model and a random atom-reduction model are suggested for these two situations. The present study sheds light on the reduction of graphene-oxide edges by using reactive metals to give large-sized graphene through a simple chemical reaction. PMID:24925117

Xie, Sheng-Yi; Li, Xian-Bin; Tian, Wei Quan; Wang, Dan; Chen, Nian-Ke; Han, Dong; Sun, Hong-Bo

2014-09-15

225

Biochimica et Biophysica Acta, 725 (1983) 25-33 25 MEMBRANE POTENTIAL-DEPENDENT REDUCTION OF CYTOCHROME b-6 IN AN ALGAL  

E-print Network

-S protein), so that the whole process is trig- gered by the prior oxidation of cytochrome f by PS I. A very-DEPENDENT REDUCTION OF CYTOCHROME b-6 IN AN ALGAL MUTANT LACKING PHOTOSYSTEM I CENTERS JER(3ME LAVERGNE Institut de) Key words." Cytochrome b-6," Membrane potential; Photosynthesis," Photosystem I," (Chlorella sorokinia

226

A simple and efficient method to prepare graphene by reduction of graphite oxide with sodium hydrosulfite.  

PubMed

Inspired by an ancient reducing method used in textile production, sodium hydrosulfite was used to reduce graphite oxide as an efficient reducing agent in our work. The reduced materials were characterized by x-ray photoelectron spectroscopy, thermogravimetric analysis, wide-angle x-ray scattering, Raman spectroscopy, solid state (13)C NMR spectroscopy and electrical conductivity measurements, respectively. The results showed that graphite oxide can be reduced with sodium hydrosulfite in a few minutes, with a degree of reduction comparable to those achieved with hydrazine. It provides an efficient method to reduce graphite oxide and could be used as a method to prepare novel composites. PMID:21169657

Zhou, Tiannan; Chen, Feng; Liu, Kai; Deng, Hua; Zhang, Qin; Feng, Jiwen; Fu, Qiang

2011-01-28

227

A simple and efficient method to prepare graphene by reduction of graphite oxide with sodium hydrosulfite  

NASA Astrophysics Data System (ADS)

Inspired by an ancient reducing method used in textile production, sodium hydrosulfite was used to reduce graphite oxide as an efficient reducing agent in our work. The reduced materials were characterized by x-ray photoelectron spectroscopy, thermogravimetric analysis, wide-angle x-ray scattering, Raman spectroscopy, solid state 13C NMR spectroscopy and electrical conductivity measurements, respectively. The results showed that graphite oxide can be reduced with sodium hydrosulfite in a few minutes, with a degree of reduction comparable to those achieved with hydrazine. It provides an efficient method to reduce graphite oxide and could be used as a method to prepare novel composites.

Zhou, Tiannan; Chen, Feng; Liu, Kai; Deng, Hua; Zhang, Qin; Feng, Jiwen; Fu, Qiang

2011-01-01

228

Policy resistance to harm reduction for drug users and potential effect of change  

Microsoft Academic Search

Despite good evidence for its effectiveness in HIV prevention, countries such as Russia remain resistant to harm reduction. Tim Rhodes and colleagues show the obstacles to and potential benefits of changing policy on opiate substitution treatment

Tim Rhodes; Anya Sarang; Peter Vickerman; Matthew Hickman

2010-01-01

229

Reductions in Northeast Refining Activity: Potential Implications for Petroleum Product Markets  

EIA Publications

This report is the Energy Information Administration's (EIA) initial effort to provide information and analysis on the potential impacts on petroleum product markets from reductions in Northeast petroleum refining activity.

2011-01-01

230

Nanophase transition metal oxides show large thermodynamically driven shifts in oxidation-reduction equilibria.  

PubMed

Knowing the thermodynamic stability of transition metal oxide nanoparticles is important for understanding and controlling their role in a variety of industrial and environmental systems. Using calorimetric data on surface energies for cobalt, iron, manganese, and nickel oxide systems, we show that surface energy strongly influences their redox equilibria and phase stability. Spinels (M(3)O(4)) commonly have lower surface energies than metals (M), rocksalt oxides (MO), and trivalent oxides (M(2)O(3)) of the same metal; thus, the contraction of the stability field of the divalent oxide and expansion of the spinel field appear to be general phenomena. Using tabulated thermodynamic data for bulk phases to calculate redox phase equilibria at the nanoscale can lead to errors of several orders of magnitude in oxygen fugacity and of 100 to 200 kelvin in temperature. PMID:20929770

Navrotsky, Alexandra; Ma, Chengcheng; Lilova, Kristina; Birkner, Nancy

2010-10-01

231

Two Types of Potential Oscillation During the Reduction of Dichromate on Gold Electrode in H2SO4 Solution  

NASA Astrophysics Data System (ADS)

Two different types of potential oscillations have been identified for the first time during dichromate reduction on a gold electrode in a solution of dilute sulfuric acid. One occurs before hydrogen evolution due to the formation and dissolution of passivating films of low-valence chromium oxides, and the other generates, accompanying periodic hydrogen evolution, from the coupling of electrochemical reactions with diffusive and convective mass transport. More interestingly, these two types of oscillations correspond to two crossing loops in the cyclic voltammogram (CV). Such a relation of oscillations with crossed CVs will provide a new way to find electrochemical oscillatory systems systematically and rapidly.

Jiang, Xiao-chun; Chen, Shu; Li, Ze-lin

2006-06-01

232

Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO  

NASA Technical Reports Server (NTRS)

Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.

Drawdy, Jean E.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1990-01-01

233

wild type showed a significant deuterium kinetic isotope effect on cytochrome b reduction/oxidation kinetics whereas D2O had little  

E-print Network

wild type showed a significant deuterium kinetic isotope effect on cytochrome b reduction/oxidation. These functional data define cytochrome b6 arginine 214 as a key residue for Qi-site func- tion, cytochrome bf (Yan & Cramer 2003) and PetB-R214H in the low potential chain (current study) slow overall cytochrome

Allen, John F.

234

Nanoscale tunable reduction of graphene oxide for graphene electronics , D. Wang2*  

E-print Network

in graphene oxide (GO) has risen for producing large-scale flexible conductors and for its potential to open conductive nanoribbons with dimensions down to 12 nm have been produced in oxidized epitaxial graphene films), leading to transistors operating at GHz frequency (10). Techniques to produce nanometer scale graphene

235

Reduction of coherence of the human brain electric potentials  

NASA Astrophysics Data System (ADS)

Plenty of technological processes are known to be damaged by magnetic storms. But technology is controlled by men and their functional systems may be damaged as well. We are going to consider the electro-neurophysiological aspect of the general problem: men surrounded by physical fields including ones of cosmic origination. Magnetic storms’ influence had been observed for a group of 13 students (practically healthy girls and boys from 18 to 23 years old, Moscow). To control the main functional systems of the examinees, their electroencephalograms (EEG) were being registered along with electrocardiograms, respiratory rhythms, arterial blood pressure and other characteristics during a year. All of these characteristics, save for the EEG, were within the normal range for all of the examinees during measurements. According to the EEG investigations by implementation of the computer proof-reading test in absence of magnetic storms, the values of the coherence function of time series of the theta-rhythm oscillations (f = 4 - 7.9 Hz, A = 20 ?V) of electric potentials of the frontal-polar and occipital areas of the head belong to the interval [0.3, 0.8] for all of the students under investigation. (As the proof-reading test, it was necessary to choose given symbols from a random sequence of ones demonstrated at a monitor and to enter the number of the symbols discovered in a computer. Everyone was known that the time for determination of symbols is unlimited. On the other hand, nobody was known that the EEG and other registrations mentioned are connected with electromagnetic geophysical researches and geomagnetic storms). Let us formulate the main result: by implementation of the same test during a magnetic storm, 5 ? K ? 6, or no later then 24 hours after its beginning (different types of moderate magnetic storms occurred, the data of IZMIRAN were used), the values of the theta-rhythm frontal - occipital coherence function of all of the students of the group under consideration decreased by a factor of two or more, including the zero coherence function value. The similar result was obtained for another basic low-frequency electro-neurophysiological rhythm delta (f = 0.5 - 3.9 Hz, A = 20 ?V). The usual coherence function values from the interval [0.3, 0.8] were being registered, typically, about 48 hours after the magnetic storm end. The result about decreasing of the coherence of the brain low frequency bioelectric oscillations under a magnetic storm influence was obtained by two methods: 1) comparison of the time series of bioelectric oscillations of a given person without a magnetic storm and under its influence; 2) comparison of two sets of time series of oscillations: a) the set A of time series measured without a magnetic storm and b) the set B of time series measured under its influence, regardless to an individual. Surely, the total number of the EEGs available for the investigation by the set’s approach, i.e. without personification, is more than the number of the EEGs available by the individual approach because there were ones investigated without a magnetic storm only as well as ones investigated under its influence only. By the EEG measurements with closed or open eyes, but without a functional load on the brain in the form of the proof-reading test, a distinctive decrease of the coherence function was not observed during a magnetic storm as well as for pairs of points from other parts of the head (see above) or other rhythms.

Novik, Oleg; Smirnov, Fedor

236

Potential Impacts of Reductions in Refinery Activity on Northeast Petroleum Product Markets  

EIA Publications

Potential Impacts of Reductions in Refinery Activity on Northeast Petroleum Product Markets is an update to a previous Energy Information Administration (EIA) report, Reductions in Northeast Refining Activity: Potential Implications for Petroleum Product Markets, released in December 2011. This update analyzes possible market responses and impacts in the event Sunoco's Philadelphia refinery closes this summer, in addition to the recently idled refineries on the East Coast and in the U.S. Virgin Islands.

2012-01-01

237

Mechanism of oxygen reduction reaction on transition metal oxide catalysts for high temperature fuel cells  

E-print Network

The solid oxide fuel cell (SOFC) with its high energy conversion efficiency, low emissions, silent operation and its ability to utilize commercial fuels has the potential to create a large impact on the energy landscape. ...

La O', Gerardo Jose Cordova

2008-01-01

238

Explosive thermal reduction of graphene oxide-based materials: mechanism and safety implications  

PubMed Central

Thermal reduction of graphene oxide or graphite oxide (GO) is an important processing step in the fabrication of many graphene-based materials and devices. Here we show that some bulk solid GO samples can undergo explosive decomposition when small samples are heated slowly in inert gas environments, while others do not. These micro-explosions can occur for samples as small as few milligrams and are sufficiently energetic to cause laboratory equipment damage. Thermochemical analysis methods are used to understand the factors that lead to the explosive reduction mode. The studies show that the explosive mode of reduction is caused by the exothermicity of GO reduction coupled with a threshold sample mass/size that causes heat and mass transfer limitations leading to local temperature rise and a thermal runaway reaction. The explosive mode of reduction is not caused or promoted by interstitial water, and its onset temperature can be lowered by immersion in potassium hydroxide solution. By allowing early release of internal gas pressure, the explosive mode reduces the extent of surface area development in GO exfoliation from an optimum value of 1470 m2g?1 obtained under non-explosive reduction conditions. Explosive reduction of bulk GO poses industrial safety hazards during large-scale storage, handling, and processing. PMID:25018560

Qiu, Yang; Guo, Fei; Hurt, Robert; Kulaots, Indrek

2014-01-01

239

Multifunctional Low-Pressure Turbine for Core Noise Reduction, Improved Efficiency, and Nitrogen Oxide (NOx) Reduction  

NASA Technical Reports Server (NTRS)

This work studied the feasibility of using Helmholtz resonator cavities embedded in low-pressure-turbine (LPT) airfoils to (1) reduce core noise by damping acoustic modes; (2) use the synthetic jets produced by the liner hole acoustic oscillations to improve engine efficiency by maintaining turbulent attached flow in the LPT at low-Reynolds-number cruise conditions; and (3) reduce engine nitrogen oxide emissions by lining the internal cavities with materials capable of catalytic conversion. Flat plates with embedded Helmholtz resonators, designed to resonate at either 3000 or at 400 Hz, were simulated using computational fluid dynamics. The simulations were conducted for two inlet Mach numbers, 0.25 and 0.5, corresponding to Reynolds numbers of 90 000 and 164 000 based on the effective chordwise distance to the resonator orifice. The results of this study are (1) the region of acoustic treatment may be large enough to have a benefit; (2) the jets may not possess sufficient strength to reduce flow separation (based on prior work by researchers in the flow control area); and (3) the additional catalytic surface area is not exposed to a high velocity, so it probably does not have any benefit.

Miller, Christopher J.; Shyam, Vikram; Rigby, David L.

2013-01-01

240

Prediction of Reduction Potential Changes in Rubredoxin: A Molecular Mechanics Approach  

PubMed Central

Predicting the effects of mutation on the reduction potential of proteins is crucial in understanding how reduction potentials are modulated by the protein environment. Previously, we proposed that an alanine vs. a valine at residue 44 leads to a 50-mV difference in reduction potential found in homologous rubredoxins because of a shift in the polar backbone relative to the iron site due to the different side-chain sizes. Here, the aim is to determine the effects of mutations to glycine, isoleucine, and leucine at residue 44 on the structure and reduction potential of rubredoxin, and if the effects are proportional to side-chain size. Crystal structure analysis, molecular mechanics simulations, and experimental reduction potentials of wild-type and mutant Clostridium pasteurianum rubredoxin, along with sequence analysis of homologous rubredoxins, indicate that the backbone position relative to the redox site as well as solvent penetration near the redox site are both structural determinants of the reduction potential, although not proportionally to side-chain size. Thus, protein interactions are too complex to be predicted by simple relationships, indicating the utility of molecular mechanics methods in understanding them. PMID:14581187

Ergenekan, Can E.; Thomas, Dustin; Fischer, Justin T.; Tan, Ming-Liang; Eidsness, Marly K.; Kang, ChulHee; Ichiye, Toshiko

2003-01-01

241

Kinetics of manganese oxide reduction from basic slags by carbon dissolved in liquid iron  

Microsoft Academic Search

The reduction of manganese oxide from a basic slag by carbon dissolved in liquid iron is a slow reaction, failing to approach equilibrium closely in 20 hr. Furthermore, the rate of stirring has no apparent effect on the reaction rate. This identifies the rate-controlling step as a chemical reaction at the interface. Only the model for the reaction O 2-

Weldon L. Daines; Robert D. Pehlke

1971-01-01

242

Synthesis of carbon-encapsulated iron nanoparticles via solid state reduction of iron oxide nanoparticles  

SciTech Connect

The encapsulation of iron nanoparticles in protective carbon cages leads to unique hybrid core-shell nanomaterials. Recent literature reports suggest that such nanocomposites can be obtained in a relatively simple process involving the solid state carbothermal reduction of iron oxide nanoparticles. This approach is very attractive because it does not require advanced equipment and consumes less energy in comparison to widely used plasma methods. The presented more-in-depth study shows that the carbothermal approach is sensitive to temperature and the process yield strongly depends on the morphology and crystallinity of the carbon material used as a reductant. - Graphical abstract: Reduction of iron oxide nanoparticles by carbon black at 1200 deg. C yields well crystallized carbon-encapsulated iron nanoparticles. Highlights: > Carbon-encapsulated iron nanoparticles were synthesized by carbothermal reduction of iron oxide nanoparticles. > The process has the highest selectivity at 1200 C. > Lower temperatures result in iron oxide nanoparticles wrapped in carbon matrix. > The encapsulation rate of Fe at 1200 deg. C was found to be 15%.

Bystrzejewski, M., E-mail: mibys@chem.uw.edu.pl [Dept of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw (Poland)

2011-06-15

243

Formation and reduction of nitric oxide in fixed-bed combustion of straw  

Microsoft Academic Search

Mechanisms of nitric oxide (NO) formation and reduction in fixed-bed combustion of straw have been modeled mathematically and verified experimentally. The model for the straw combustion and nitrogen chemistry consists of sub-models for evaporation, pyrolysis, tar and char combustion, nitrogen conversion, and energy and mass conservation. Twenty chemical reactions are included, of which 12 belong to the fuel nitrogen reaction

H. Zhou; A. D. Jensen; P. Glarborg; A. Kavaliauskas

2006-01-01

244

Reduction and oxidation of peptide nucleic acid and DNA at mercury and carbon electrodes  

Microsoft Academic Search

Peptide nucleic acid (PNA) is a DNA mimic that binds strongly and specifically to complementary DNA or RNA oligomers, but in contrast to DNA its backbone does not carry any electric charge. We used voltammetry in cyclic and square-wave modes to study reduction and oxidation signals of single stranded (ss)PNA and DNA decamers and pentadecamers with the same base sequences

Miroslav Tomschik; František Jelen; Lud?k Havran; Libuše Trnková; Peter E Nielsen; Emil Pale?ek

1999-01-01

245

The kinetic isotope effect in the bacterial reduction and oxidation of sulfur  

Microsoft Academic Search

The kinetic isotope effect in the bacterial reduction of sulfate to sulfide and oxidation of native sulfur and sulfide to sulfate has been investigated at the temperature of 32°C. In these studies, mixed culture techniques were used in order to more closely approximate isotopic fractionation as it occurs in nature. In addition, the S 34 compositions of sulfur in coexisting

M. L. Jensen; Nobuyuki Nakai

1964-01-01

246

OZONE PRECURSOR LEVELS AND RESPONSES TO EMISSIONS REDUCTIONS:ANALYSIS OF REGIONAL OXIDANT MODEL RESULTS  

EPA Science Inventory

An analysis of results from the Regional Oxidant Modeling for Northeast Transport (ROMNET) study (U.S. EPA, 1991, EPA-450/4-91-002a) has investigated the chemical conditions under which air quality was predicted to improve with reductions in ROG and/or NOx emissions, or with chan...

247

Oxidation potential and state of some vanadium ores and the relation of woody material to their deposition  

USGS Publications Warehouse

Oxidation potential studies with a multiple pH-potential recorder designed and constructed for this purpose demonstrated that some uranium-vanadium ores in the Colorado Plateau were in a reduced state when deposited. Any oxidation which took place occurred after deposition. Experimental and theoretical reducing studies on fresh wood, wood degraded by burial for 450 years, and lignite, indicate that such ores may have been deposited by reduction of oxidized vanadium solutions by woody material. A vanadium (III) mineral, V2O(OH)4, was prepared synthetically by reduction of a vanadium (V) solution with wood. This is the only reported synthesis of any reduced vanadium mineral by any method. It was shown that the origin of almost all vanadium deposits currently of commercial importance involves life processes and products.

Pommer, Alfred Michael

1956-01-01

248

Intermolecular potential energy surface and thermophysical properties of ethylene oxide.  

PubMed

A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C2H4O) molecules was determined from high-level quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the MP2 and CCSD(T) levels of theory was utilized to determine interaction energies for 10178 configurations of two molecules. An analytical site-site potential function with 19 sites per ethylene oxide molecule was fitted to the interaction energies and fine tuned to agree with data for the second acoustic virial coefficient from accurate speed of sound measurements. The PES was validated by computing the second virial coefficient, shear viscosity, and thermal conductivity. The values of these properties are substantiated by the best experimental data as they tend to fall within the uncertainty intervals and also obey the experimental temperature functions, except for viscosity, where experimental data are insufficient. Due to the lack of reliable data, especially for the transport properties, our calculated values are currently the most accurate estimates for these properties of ethylene oxide. PMID:25362314

Crusius, Johann-Philipp; Hellmann, Robert; Hassel, Egon; Bich, Eckard

2014-10-28

249

Intermolecular potential energy surface and thermophysical properties of ethylene oxide  

NASA Astrophysics Data System (ADS)

A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C2H4O) molecules was determined from high-level quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the MP2 and CCSD(T) levels of theory was utilized to determine interaction energies for 10178 configurations of two molecules. An analytical site-site potential function with 19 sites per ethylene oxide molecule was fitted to the interaction energies and fine tuned to agree with data for the second acoustic virial coefficient from accurate speed of sound measurements. The PES was validated by computing the second virial coefficient, shear viscosity, and thermal conductivity. The values of these properties are substantiated by the best experimental data as they tend to fall within the uncertainty intervals and also obey the experimental temperature functions, except for viscosity, where experimental data are insufficient. Due to the lack of reliable data, especially for the transport properties, our calculated values are currently the most accurate estimates for these properties of ethylene oxide.

Crusius, Johann-Philipp; Hellmann, Robert; Hassel, Egon; Bich, Eckard

2014-10-01

250

Oxidation Potential, Not Crystal Structure, Controls the Oxidation State of Iron in Perovskite  

NASA Astrophysics Data System (ADS)

The mantle's oxidation state has broad implications on the state and evolution of the earth's interior. The relatively high oxidation potential of the upper mantle is such that iron is predominantly Fe2+ with small amounts of Fe3+ . Fe3+ is more stable than Fe2+ in the dominant lower mantle mineral, perovskite, despite the fact that the effect of pressure is to reduce the oxidizing potential of a system. It is therefore suggested that iron undergoes a disproportionation reaction of 3Fe2+ =2Fe3+ +Fe0 , controlled by the crystallography instead of oxidation potential. We crystallized synthetic enstatite glass with 5% Al2O3, 14% FeO, and 3% Fe2O3 in the laser-heated diamond anvil cell at 25-63 GPa and 1700-2800 K. We find that for temperatures <2200 K, the sample crystallizes to only perovskite, while at higher temperatures, the sample crystallizes to perovskite and stishovite as evident in x-ray diffraction, with 5-50 nm iron precipitates on grain boundaries. The precipitates have small amounts of dissolved oxygen, but are Mg- and Al- free. We interpret that the stishovite is forming due to the oxidation of the ferric iron to ferrous iron according to (Mg2+,Al3+)(Fe3+,Si4+)O3 +SiO2 + Fe0 while the lower-temperature samples crystallizing as approximately (Mg2+ Fe2+ Al3+ )(Fe3+ Al3+ Si4+ )O3. We observe 2.8(2) Å3 volume expansion of the perovskite and a 28(2) GPa decrease in compressibility of the perovskite relative to the perovskite forming at lower temperature, consistent with the proposed compositions of the perovskites. As the increased temperature increases the oxidation potential of the system, we suggest that the oxidation state of iron in perovskite is dependent on oxidation potential as opposed to perovskite's crystal structure. Transmission Electron Microscopy (TEM) coupled with Electron Energy Loss Spectroscopy (EELS) show iron precipitation on grain boundaries supporting the conclusion. We present a discussion of the results and implications for core formation and lower mantle dynamics.

Panero, W. R.; Pigott, J. S.; Watson, H. C.; Scharenberg, M.; Green, H. W.; McComb, D. W.; Williams, R. E.

2013-12-01

251

Leakage Current Reduction Mechanism of Oxide-Nitride-Oxide Inter-Poly Dielectrics through the Post Plasma Oxidation Treatment  

NASA Astrophysics Data System (ADS)

High quality oxide-nitride-oxide (ONO) inter-poly dielectrics were successfully fabricated by the optimized plasma oxidation without H2. The bottom low pressure chemical vapor deposition (LPCVD) oxides treated by the conventional N2O annealing step were subjected to the post deposition process using a plasma treatment. This process reduces both the leakage current and the stress-induced leakage current (SILC), while no thickness increase of the bottom LPCVD oxides was observed due to the plasma treatment. Based on the photo electron injection technique, it is found that the O2 plasma oxidation method significantly reduces the defect centers located at 1.67 nm away from the bottom oxide/floating gate interface.

Lee, Woong; Jee, Jeonggeun; Yoo, Dae-Han; Lee, Eun-Young; Bok, Jinkwon; Hyung, Younwoo; Kim, Seoksik; Kang, Chang-Jin; Moon, Joo-Tae; Roh, Yonghan

2011-04-01

252

Anodic Oxidation of m-terphenyl thio-, seleno-and telluroethers: Lowered oxidation potentials due to chalcogen.•••? interaction  

E-print Network

The electrochemistry of m-terphenylthio-, seleno-, and telluroethers was studied using cyclic voltammetry in acetonitrile. All of the compounds studied showed irreversible oxidations. The first oxidation potentials for ...

Wilson, George S.; Ammam, Malika; Zakai, Uzma I.; Glass, Richard S.

2010-02-01

253

Palladium and gold nanotubes as oxygen reduction reaction and alcohol oxidation reaction catalysts in base.  

PubMed

Palladium (PdNTs) and gold nanotubes (AuNTs) were synthesized by the galvanic displacement of silver nanowires. PdNTs and AuNTs have wall thicknesses of 6?nm, outer diameters of 60?nm, and lengths of 5-10 and 5-20??m, respectively. Rotating disk electrode experiments showed that the PdNTs and AuNTs have higher area normalized activities for the oxygen reduction reaction (ORR) than conventional nanoparticle catalysts. The PdNTs produced an ORR area activity that was 3.4, 2.2, and 3.7?times greater than that on carbon-supported palladium nanoparticles (Pd/C), bulk polycrystalline palladium, and carbon-supported platinum nanoparticles (Pt/C), respectively. The AuNTs produced an ORR area activity that was 2.3, 9.0, and 2.0?times greater than that on carbon-supported gold nanoparticles (Au/C), bulk polycrystalline gold, and Pt/C, respectively. The PdNTs also had lower onset potentials than Pd/C and Pt/C for the oxidation of methanol (0.236?V), ethanol (0.215?V), and ethylene glycol (0.251?V). In comparison to Pt/C, the PdNTs and AuNTs further demonstrated improved alcohol tolerance during the ORR. PMID:24757078

Alia, Shaun M; Duong, Kathlynne; Liu, Toby; Jensen, Kurt; Yan, Yushan

2014-06-01

254

Bacterial reduction of crystalline Fe{sup 3+} oxides in single phase suspensions and subsurface materials  

SciTech Connect

Microbiologic reduction of synthetic and geologic Fe{sup 3+} oxides associated with four Pleistocene-age, Atlantic coastal plain sediments was investigated using a dissimilatory Fe reducing bacterium (Shewanella putrefaciens, strain CN32) in bicarbonate buffer. Experiments investigated whether phosphate and anthraquinone-2,6-disulfonate, (AQDS, a humic acid analogue) influenced the extent of crystalline Fe{sup 3+} oxide bioreduction and whether crystalline Fe{sup 3+} oxides in geologic materials are more or less reducible than comparable synthetic phases. Anaerobic incubations (10{sup 8} organisms/mL) were performed both with and without PO{sub 4} and AQDS that functions as an electron repository and shuttle. The production of Fe{sup 2+} (solid and aqueous) was followed with time, as was mineralogy by X-ray diffraction. The synthetic oxides were reduced in a qualitative trend consistent with their surface area and free energy: hydrous ferric oxide (HFO) > goethite > hematite. Bacterial reduction of the crystalline oxides was incomplete in spite of excess electron donor. Biogenic formation of vivianite [Fe{sub 3}(PO{sub 4}){sub 2}{center_dot}8H{sub 2}O] and siderite (FeCO{sub 3}) was observed; the conditions of their formation was consistent with their solubility. The geologic Fe{sup 3+} oxides showed a large range in reducibility, approaching 100% in some materials. The natural oxides were equally or more reducible than their synthetic counterparts, in spite of association with non-reducible mineral phases (e.g., kaolinite). The reducibility of the synthetic and geologic oxides was weakly effected by PO{sub 4}, but was accelerated by AQDS. CN32 produced the hydroquinone form of AQDS (AHDS), that, in turn, had thermodynamic power to reduce the Fe{sup 3+} oxides. As a chemical reductant, it could reach physical regions of the oxide not accessible by the organism. Electron microscopy showed that crystallite size was not the primary factor that caused differences in reducibility between natural and synthetic crystalline Fe{sup 3+} oxide phases. Crystalline disorder and microheterogeneities may be more important.

Zachara, J.M.; Fredrickson, J.K.; Li, S.M.; Kennedy, D.W.; Smith, S.C.; Gassman, P.L. [Pacific Northwest National Lab., Richland, WA (United States)

1998-11-01

255

Biomineralization Associated with Microbial Reduction of Fe3+ and Oxidation of Fe2+ in Solid Minerals  

SciTech Connect

Iron- reducing and oxidizing microorganisms gain energy through reduction or oxidation of iron, and by doing so they play an important role in geochemical cycling of iron in a wide range of environments. This study was undertaken to investigate iron redox cycling in the deep subsurface by taking an advantage of the Chinese Continental Scientific Deep Drilling project. A fluid sample from 2450 m was collected and Fe(III)-reducing microorganisms were enriched using specific media (pH 6.2). Nontronite, an Fe(III)-rich clay mineral, was used in initial enrichments with lactate and acetate as electron donors under strictly anaerobic condition at the in-situ temperature of the fluid sample (65oC). Instead of a monotonic increase in Fe(II) concentration with time as would have been expected if Fe(III) bioreduction was the sole process, Fe(II) concentration initially increased, reached a peak, but then decreased to a minimum level. Continued incubation revealed an iron cycling with a cycling period of five to ten days. These initial results suggested that there might be Fe(III) reducers and Fe(II) oxidizers in the enrichment culture. Subsequently, multiple transfers were made with an attempt to isolate individual Fe(III) reducers and Fe(II) oxidizers. However, iron cycling persisted after multiple transfers. Additional experiments were conducted to ensure that iron reduction and oxidation was indeed biological. Biological Fe(II) oxidation was further confirmed in a series of roll tubes (with a pH gradient) where FeS and siderite were used as the sole electron donor. The oxidation of FeS occurred only at pH 10, and goethite, lepidocrocite, and ferrihydrite formed as oxidation products. Although molecular evidence (16S rRNA gene analysis) collectively suggested that only a single organism (a strain of Thermoanaerobacter ethanolicus) might be responsible for both Fe(III) reduction and Fe(II) oxidation, we could not rule out the possibility that Fe(III) reduction and Fe(II) oxidation may be accomplished by a consortia of organisms. Nonetheless, our data were definitive in showing that iron redox cycling exists in the deep subsurface.

Zhang, Gengxin; Dong, Hailiang; Jiang, Hongchen; Kukkadapu, Ravi K.; Kim, Jinwook; Eberl, Dennis D.; Xu, Zhiqin

2009-07-01

256

Two Oxidation Sites for Low Redox Potential Substrates  

PubMed Central

Versatile peroxidase shares with manganese peroxidase and lignin peroxidase the ability to oxidize Mn2+ and high redox potential aromatic compounds, respectively. Moreover, it is also able to oxidize phenols (and low redox potential dyes) at two catalytic sites, as shown by biphasic kinetics. A high efficiency site (with 2,6-dimethoxyphenol and p-hydroquinone catalytic efficiencies of ?70 and ?700 s?1 mm?1, respectively) was localized at the same exposed Trp-164 responsible for high redox potential substrate oxidation (as shown by activity loss in the W164S variant). The second site, characterized by low catalytic efficiency (?3 and ?50 s?1 mm?1 for 2,6-dimethoxyphenol and p-hydroquinone, respectively) was localized at the main heme access channel. Steady-state and transient-state kinetics for oxidation of phenols and dyes at the latter site were improved when side chains of residues forming the heme channel edge were removed in single and multiple variants. Among them, the E140G/K176G, E140G/P141G/K176G, and E140G/W164S/K176G variants attained catalytic efficiencies for oxidation of 2,2?-azino-bis(3-ethylbenzothiazoline-6-sulfonate) at the heme channel similar to those of the exposed tryptophan site. The heme channel enlargement shown by x-ray diffraction of the E140G, P141G, K176G, and E140G/K176G variants would allow a better substrate accommodation near the heme, as revealed by the up to 26-fold lower Km values (compared with native VP). The resulting interactions were shown by the x-ray structure of the E140G-guaiacol complex, which includes two H-bonds of the substrate with Arg-43 and Pro-139 in the distal heme pocket (at the end of the heme channel) and several hydrophobic interactions with other residues and the heme cofactor. PMID:23071108

Morales, Maria; Mate, Maria J.; Romero, Antonio; Martinez, Maria Jesus; Martinez, Angel T.; Ruiz-Duenas, Francisco J.

2012-01-01

257

Effect of applied voltage, initial concentration and natural organic matter on sequential reduction/oxidation of nitrobenzene by graphite electrodes  

PubMed Central

Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H2 at the cathode and oxidizing conditions and O2 at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (kNB) and NSB (kNSB) increased with applied voltage between 2V and 3.5 V (when the initial NB concentration was 100 µM, kNB=0.3 d?1 and kNSB=0.04 d?1at 2V; kNB=1.6 d?1 and kNSB=0.64 d?1at 3.5 V) but stopped increasing beyond the threshold of 3.5V. When initial NB concentration decreased from 100 to 5 µM, kNB and kNSB became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased kNB while slightly increased kNSB, but only to a limited extent (~factor of 3) for dissolved organic carbon content up to 100 mg/l. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation. PMID:22571797

Sun, Mei; Reible, Danny D.; Lowry, Gregory V.; Gregory, Kelvin B.

2012-01-01

258

Reduction of bacteria on spinach, lettuce, and surfaces in food service areas using neutral electrolyzed oxidizing water.  

PubMed

Food safety issues and increases in food borne illnesses have promulgated the development of new sanitation methods to eliminate pathogenic organisms on foods and surfaces in food service areas. Electrolyzed oxidizing water (EO water) shows promise as an environmentally friendly broad spectrum microbial decontamination agent. EO water is generated by the passage of a dilute salt solution ( approximately 1% NaCl) through an electrochemical cell. This electrolytic process converts chloride ions and water molecules into chlorine oxidants (Cl(2), HOCl/ClO(-)). At a near-neutral pH (pH 6.3-6.5), the predominant chemical species is the highly biocidal hypochlorous acid species (HOCl) with the oxidation reduction potential (ORP) of the solution ranging from 800 to 900mV. The biocidal activity of near-neutral EO water was evaluated at 25 degrees C using pure cultures of Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis. Treatment of these organisms, in pure culture, with EO water at concentrations of 20, 50, 100, and 120ppm total residual chlorine (TRC) and 10min of contact time resulted in 100% inactivation of all five organisms (reduction of 6.1-6.7log(10)CFU/mL). Spray treatment of surfaces in food service areas with EO water containing 278-310ppm TRC (pH 6.38) resulted in a 79-100% reduction of microbial growth. Dip (10min) treatment of spinach at 100 and 120ppm TRC resulted in a 4.0-5.0log(10)CFU/mL reduction of bacterial counts for all organisms tested. Dipping (10min) of lettuce at 100 and 120ppm TRC reduced bacterial counts of E. coli by 0.24-0.25log(10)CFU/mL and reduced all other organisms by 2.43-3.81log(10)CFU/mL. PMID:17993375

Guentzel, Jane L; Liang Lam, Kang; Callan, Michael A; Emmons, Stuart A; Dunham, Valgene L

2008-02-01

259

Microsensor measurements of sulfate reduction and sulfide oxidation in compact microbial communities of aerobic biofilms  

SciTech Connect

The microzonation of O{sub 2} respiration, H{sub 2}S oxidation, and SO{sub 4}{sup 2{minus}} reduction in aerobic trickling-filter biofilms was studied by measuring concentration profiles at high spatial resolution (25 to 100 {mu}m) with microsensors for O{sub 2}, S{sup 2{minus}}, and pH. Specific reaction rates were calculated from measured concentration profiles by using a simple one-dimensional diffusion reaction model. The importance of electron acceptor and electron donor availability for the microzonation of respiratory processes and their reaction rates was investigated. Oxygen respiration was found in the upper 0.2 to 0.4 mm of the biofilm, whereas sulfate reduction occurred in deeper, anoxic parts of the biofilm. Sulfate reduction accounted for up to 50% of the total mineralization of organic carbon in the biofilms. All H{sub 2}S produced from sulfate reduction was reoxidized by O{sub 2} in a narrow reaction zone, and no H{sub 2}S escaped to the overlying water. Turnover times of H{sub 2}S and O{sub 2} in the reaction zone were only a few seconds owing to rapid bacterial H{sub 2}S oxidation. Anaerobic H{sub 2}S oxidation with NO{sub 3}{sup {minus}} could be induced by addition of nitrate to the medium. Total sulfate reduction rates increased when the availability of SO{sub 4}{sup 2{minus}} or organic substrate increased as a result of deepening of the sulfate reduction zone or an increase in the sulfate reduction intensity, respectively.

Kuehl, M.; Joergensen, B.B. (Univ. of Aarhus (Denmark))

1992-04-01

260

Prediction of the reduction potential of tris(2,2'-bipyridinyl)iron(III/II) derivatives.  

PubMed

The reduction potentials of a tris(2,2'-bipyridinyl)iron (III/II) and iron(III/II) couples complexed with 2,2'-bipyridinyl derivatives in acetonitrile are predicted using density functional theory. The calculation protocol proposed by Kim et al. (Kim, J. Park, Y. S. Lee, J. Comput. Chem. 2013, 34, 2233) showing reliable performance for the reduction potential is used. The four kinds of the functional groups, a methoxy group, a methyl group, a chlorine atom, and a cyanide group, are substituted at the ligands to examine the electronic effect on the reduction potential. Electron donating/withdrawing effect is analyzed by comparing the reduction potential having different substituents at the same position. The influence of the geometrical strain on the reduction potential is investigated. The good correlation between the experimental results and the calculated results is obtained. Not only the general trend, but also the detailed phenomena are correctly reproduced. The maximum deviation from the experimental value is 0.083 V for the methyl substitution at the position 4. The mean absolute error for the seven couples is 0.047 V. The difference of the reduction potential between the chlorine atom substituted at the positions 4 and 5, 0.1 V, is well described. The difference between the CN and the Cl substitution of 0.318 and 0.228 V for the position 4 and 5 is correctly obtained as 0.325 and 0.213 V, respectively. The simple linear relation between the lowest unoccupied molecular orbital (LUMO) energy of the Fe(III) complexes in solution and the calculated reduction potentials is obtained with the R(2) of 0.977. © 2014 Wiley Periodicals, Inc. PMID:25348486

Kim, Hyungjun; Park, Joungwon; Lee, Yoon Sup

2015-01-01

261

Potential of front-face fluorescence to monitor OM reduction in drinking water during potabilization process  

NASA Astrophysics Data System (ADS)

Elimination of OM in drinking water represents a great challenge for municipalities and technical actors to ensure that it can be safely used for consumption purposes. Indeed, current indicators such as Total Organic Carbon (TOC), turbidity or UV-Absorbance at 254 nm (UVA254) enable only non-specific overview of the amount of organic residuals in water. Fluorescence EEMs are a potent tool for discrimination and deep analysis of OM detailed composition and behaviour. It has been shown that several forms of OM co-exist in raw water, and come from various origins (bacteria, humic compounds…). Potabilization operation is composed of different steps that aim at decreasing all forms of OM using chemical as well as physical methods (ozone oxidation, filtration on activated carbon or sand, flocculation etc.). Unfortunately, it has been observed that reduction of OM during this process was not identical for all the forms, and the process showed a particular lack of efficiency during raining periods. 130 samples of water at various stages of potabilization were analyzed using home-made compact fluorometer, an apparatus composed of UV excitation LEDs. Using chemometrical treatment of spectral data, we put into highlight 5 different forms of OM that were identified according to litterature data. We evidenced the critical steps of the purification on OM reduction, as well as the relative content of each form from raw to product water. In particular, we showed that two forms were less reduced than the other three, so that progressive enrichment of total OM in the former was observed throughout the process. Moreover, a study was carried out in order to establish calibration models over conventional analyses using the spectral information. Highly satisfying models were thus obtained over TOC, turbidity and UVA254, with average RMSEC values of 13%, 7% and 16% respectively. These results demonstrate the potential of the fluorescence analyzer to simultaneously predict three major OM-related quality parameters of water. Finally, study of relationships between the different OM forms, climate parameters (temperature, raw water flow, rainfall) and coagulant amounts showeds that each OM form was specifically linked to these parameters. In particular, we were able to pinpoint one of the five forms that was most associated with the water flow, and also the most flocculated by the coagulant. In conclusion, this work demonstrates that our fluorescence analyzer helps to get improved knowledge of OM behavior during potabilization process. Five different OM forms were identified and their respective evolution was characterized. Furthermore, we evidenced a potential use of a compact and small-size analyzer to monitor water purification steps through simultaneous prediction of quality parameters related to OM content.

Lacotte, Pierre

2014-05-01

262

Wet air oxidation pretreatment of biomethanated distillery effluent: mapping pretreatment efficiency in terms color, toxicity reduction and biogas generation.  

PubMed

The effluents from molasses-based distilleries after biomethanation are beset with problems of intensified dark brown color, high residual COD, low biodegradability index (BOD/COD ratio <0.2) and toxicity issues for possible land application as a potential fertilizer. Wet air oxidation (WAO) pretreatment of biomethanated distillery effluent resulted in substantial enhancement in the biodegradability index (BI) (up to 0.8). WAO pretreated effluent on anaerobic digestion indicated favorable biogas generation with methane content up to 64% along with concomitant COD reduction up to 54.75%. The HPLC analysis indicated that the pretreatment facilitated degradation of major color containing compounds-namely melanoidins, up to 97.8%. The pretreated effluent with enhanced biodegradability along with substantially reduced color also indicated positive effect on seed germination (up to 100%), implying toxicity reduction of the effluent post WAO pretreatment. PMID:24583914

Sarat Chandra, T; Malik, S N; Suvidha, G; Padmere, M L; Shanmugam, P; Mudliar, S N

2014-04-01

263

Shuttle to Shuttle 2: Subsystem weight reduction potential (estimated 1992 technology readiness date)  

NASA Technical Reports Server (NTRS)

The objective of this study was to make estimates of the weight savings that might be realized on all the subsystems on an advanced rocket-powered shuttle (designated Shuttle 2) by using advanced technologies having a projected maturity date of 1992. The current Shuttle with external tank was used as a baseline from which to make the estimates of weight savings on each subsystem. The subsystems with the greatest potential for weight reduction are the body shell and the thermal protection system. For the body shell, a reduction of 5.2 percent in the weight of the vehicle at main engine cutoff is projected through the application of new technologies, and an additional configuration-based reduction of 5 percent is projected through simplification of body shape. A reduction of 5 percent is projected for the thermal protection system through experience with the current Space Shuttle and the potential for reducing thermal protection system thicknesses in selected areas. Main propellant tanks are expected to increase slightly in weight. The main propulsion system is also projected to increase in weight because of the requirement to operate engines at derated power levels in order to accommodate one-engine-out capability. The projections for weight reductions through improvements in the remaining subsystems are relatively small. By summing all the technology factors, a projected reduction of 16 percent in the vehicle weight at main engine cutoff is obtained. By summarizing the configurational factors, a potential reduction of 12 percent in vehicle weight is obtained.

Macconochie, Ian O.

1988-01-01

264

Real-time monitoring of graphene oxide reduction in acrylic printable composite inks  

NASA Astrophysics Data System (ADS)

This work reports the electrical characterization of a water-based graphene oxide/acrylic composite material, which was directly inkjet printed to fabricate dissipative patterns. The graphene oxide filler, which is strongly hydrophilic due to its heavily oxygenated surface and can be readily dispersed in water, was reduced by UV irradiation during photo-curing of the polymeric matrix. The concurrent polymerization of the acrylic matrix and reduction of graphene oxide filler was demonstrated by real-time resistance measurements during UV light irradiation. The presence of graphene filler allowed decreasing the resistance of the pure polymeric matrix by nearly five orders of magnitude. This was explained by the fact that clusters of reduced graphene oxide inside the polymer matrix act as preferential pathways for the mobility of charge carriers, thus leading to an overall decrease of the material's resistance.

Porro, S.; Giardi, R.; Chiolerio, A.

2014-06-01

265

Development of Molecular Electrocatalysts for CO2 Reduction and H2 Production/Oxidation  

SciTech Connect

The conversion of solar energy to fuels in both natural and artificial photosynthesis requires components for both light harvesting and catalysis. The light-harvesting component generates the electrochemical potentials required to drive fuel-generating reactions that would otherwise be thermodynamically uphill. This review focuses on work from our laboratories on developing molecular electrocatalysts for CO2 reduction and for hydrogen production. A true analog of natural photosynthesis will require the ability to capture CO2 from the atmosphere and reduce it to a useful fuel. Work in our laboratories has focused on both aspects of this problem. Organic compounds such as quinones and inorganic metal complexes can serve as redox active CO2 carriers for concentrating CO2. Catalysts for CO2 reduction to form CO have also been developed based on a [Pd(triphosphine)(solvent)]2+ platform. A required feature for catalytic activity is the presence of a weakly coordinating solvent molecule that can dissociate during the catalytic cycle and provide a vacant coordination site for binding water and assisting C-O bond cleavage. Participation of a second metal in CO2 binding also appears to be required for achieving very active catalysts as suggested by structures of [NiFe] CO dehydrogenase enzymes and the results of studies on complexes containing two [Pd(triphosphine)(solvent)]2+ units. Molecular electrocatalysts for H2 production and oxidation based on [Ni(diphosphine)2]2+ complexes are also described. These catalysts require the optimization of both first and second coordination spheres similar to that of the palladium CO2 reduction catalysts. In this case, structural features of the first coordination sphere can be used to optimize the hydride acceptor ability of nickel needed to achieve heterolytic cleavage of H2. The second coordination sphere can be used to incorporate pendant bases that assist in a number of important functions including H2 binding, H2 cleavage, and the transfer of protons between nickel and solution. These pendant bases or proton relays are likely to be important in the design of catalysts for a wide range of fuel production and fuel utilization reactions involving multiple electron and proton transfer steps. The work described in this review has been supported by the Chemical Sciences program of the Office of Basic Energy Sciences of the Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Rakowski DuBois, Mary; DuBois, Daniel L.

2009-12-15

266

Reductive mobilization of oxide-bound metals: The role of reductant capacity and reductant reactivity in determining mobilization rates in soils and sediments  

SciTech Connect

We seek to identify environmental factors that exert a decisive influence on the mobilization of oxide-bound toxic metals in soils, sediments, and aquifers. Our objective is to examine how the complexant and reductant characteristics of organic compounds found in contaminated aquatic environments influence this mobilization process. Laboratory experiments begin by allowing toxic metals (Co, Ni, Pb, Cu) to adsorb onto host oxide phases (particulate MnO{sub 2} and FeOOH) for a period of 17 hours. Dissolved metal concentrations are then monitored after the addition of low molecular weight reference compounds (such as oxalate, malonate, and citrate) or natural organic matter. A variety of phenomena have been observed. Oxalate, for example, acts as a complexant at pH 6, solubilizing adsorbed Cu and Ni while leaving the MnO{sub 2} host phase intact. At pH 4, oxalate acts as both a complexant and reductant, causing solubilization of adsorbed Cu and Ni, and the MnO{sub 2} host phase. When toxic metals are equilibrated with NOM from the Great Dismal Swamp before MnO{sub 2} addition, the extent of adsorption is less than in NOM-free suspensions. As the host MnO{sub 2} phase is dissolved, the extent of toxic metal adsorption changes little. 4 refs., 8 figs., 1 tab.

Stone, A.T.

1990-10-01

267

Enhanced reduction of silicon oxide thin films on silicon under electron beam annealing  

NASA Astrophysics Data System (ADS)

Electron beam annealing is an interesting alternative to other annealing methods as it can provide high temperature, rapid heating and cooling and low level of impurity as it operates under high vacuum environment. Furthermore swamping the materials with electrons can lead to dramatic changes in the component valence states with the mechanism involving oxido-reduction reactions. This is illustrated in the present case with the enhancement of the reduction of SiO2. Commercial thermally grown 100 and 400 nm SiO2 films on Si were annealed under three different environments: furnace annealing in open atmosphere with O2 flow, high vacuum furnace annealing and electron beam annealing. The reduction and oxidation of SiO2 films on Si are investigated using ion beam analysis. The validity of the measurement method was confirmed by measuring the oxidation rate through successive Rutherford backscattering spectrometry (RBS) measurements. The oxidation kinetics were observed to be in excellent agreement with literature values. At 1000 °C reduction of the SiO2 film is observed only with electron beam annealing. A model is proposed to explain the effect of the electron beam.

Kennedy, J.; Leveneur, J.; Fang, F.; Markwitz, A.

2014-08-01

268

Characterization of the thrombogenic potential of surface oxides on stainless steel for implant purposes  

Microsoft Academic Search

Marketed stents are manufactured from various metals and passivated with different degrees of surface oxidation. The functional surface oxides on the degree of antithrombotic potential were explored through a canine femoral extracorporeal circuit model. Related properties of these oxide films were studied by open-circuit potential, current density detected at open-circuit potential, the electrochemical impedance spectroscopy, transmission electron microscopy, Auger spectroscopy

Chun-Che Shih; Chun-Ming Shih; Yea-Yang Su; Mau-Song Chang; Shing-Jong Lin

2003-01-01

269

Coupled Mercury-Cell Sorption, Reduction, and Oxidation on Methylmercury Production by Geobacter sulfurreducens PCA.  

PubMed

G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell-SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10(-19) to 25 × 10(-19) moles-Hg/cell (equivalent to Hg/cell-SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ?omcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn(2+) leads to increased Hg reduction and decreased methylation. These results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments. PMID:25268220

Lin, Hui; Morrell-Falvey, Jennifer L; Rao, Balaji; Liang, Liyuan; Gu, Baohua

2014-10-21

270

Restructuring transition metal oxide nanorods for 100% selectivity in reduction of nitric oxide with carbon monoxide.  

PubMed

Transition metal oxide is one of the main categories of heterogeneous catalysts. They exhibit multiple phases and oxidation states. Typically, they are prepared and/or synthesized in solution or by vapor deposition. Here we report that a controlled reaction, in a gaseous environment, after synthesis can restructure the as-synthesized transition metal oxide nanorods into a new catalytic phase. Co3O4 nanorods with a preferentially exposed (110) surface can be restructured into nonstoichiometric CoO1-x nanorods. Structure and surface chemistry during the process were tracked with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and environmental transmission electron microscopy (E-TEM). The restructured nanorods are highly active in reducing NO with CO, with 100% selectivity for the formation of N2 in temperatures of 250-520 °C. AP-XPS and E-TEM studies revealed the nonstoichiometric CoO1-x nanorods with a rock-salt structure as the active phase responsible for the 100% selectivity. This study suggests a route to generate new oxide catalysts. PMID:23731229

Zhang, Shiran; Shan, Junjun; Zhu, Yuan; Nguyen, Luan; Huang, Weixin; Yoshida, Hideto; Takeda, Seiji; Tao, Franklin Feng

2013-07-10

271

Potential oxidative stress in children with chronic constipation  

PubMed Central

AIM: To investigate the potential oxidative stress in children with chronic constipation and to explore its mechanisms. METHODS: Seventy children with chronic constipation and 70 age- and sex-matched healthy children were enrolled in a randomized controlled study. Plasma levels of vitamins C and E, activities of superoxide dismutase and catalase and lipoperoxide level in erythrocytes were determined by spectrophotometry. RESULTS: Compared with healthy children whose vitamin C, vitamin E, superoxide dismutase, catalase and lipoperoxide were 58.35±14.42 ?mol/L, 27.15±6.55 ?mol/L, 2 206±171 U/(g.Hb), 327.3±82.2 K/(g.Hb) and 19.18±4.27 nmol/(g.Hb) respectively, the levels of vitamin C, vitamin E, the activity of superoxide dismutase, and catalase in the children with chronic constipation significantly decreased [46.59±11.51 ?mol/L, 20.65±4.80 ?mol/L, 1943±147 U/(g.Hb) and 269.3±67.8 K/(g.Hb), respectively P<0.01], while the lipoperoxide significantly increased [25.22±5.01 nmol/(g.Hb), P<0.01]. With a prolonged course of disease, the levels of vitamin C, vitamin E, the activity of superoxide dismutase and catalase in the children with chronic constipation gradually decreased, while the level of lipoperoxide gradually increased. CONCLUSION: Chronic constipation can cause potential oxidative stress in children. PMID:15637746

Zhou, Jun-Fu; Lou, Jian-Guo; Zhou, Sheng-Li; Wang, Ji-Yue

2005-01-01

272

Isothermal reduction kinetics of nickel oxide using hydrogen: Conventional and Weibull kinetic analysis  

NASA Astrophysics Data System (ADS)

The powder sample of nickel oxide was synthesized by sol gel procedure. The isothermal reduction of nickel oxide using hydrogen was investigated by thermogravimetric analysis at five operating temperatures: 245, 255, 265, 275 and 300 °C. The kinetic triplet (Ea, A and f(?)) was determined using conventional and Weibull kinetic analysis. Both the kinetically procedures show that the reduction process considered can be explained with a two-step kinetic model. It is established that at lower temperatures (245 °C?T?255 °C), the reduction process considered is governed by two-parameter Šesták-Berggren autocatalytic model (first step) and at higher temperatures (T?265 °C), the reduction process is governed by Fn reaction model with different values of parameter n (second step). In this paper, the complex manner of dependence of the Weibull shape parameter (?) on temperature is established. With alterations of Weibull shape parameter from lower temperatures (?>1) to higher temperatures (?<1), it was concluded that isothermal reduction process of NiO using hydrogen can be described by a multistep reaction mechanism. These results are confirmed by the evaluated density distribution functions (ddf) of apparent activation energies (Ea), which show variations in basic characteristics at lower and higher operating temperature regions. Also, in this paper, it was shown that the shape parameter (?) of Weibull distribution function can represent the behaviour index, which indicates the kinetic pattern of the mechanism controlling the process studied.

Jankovi?, B.

2007-12-01

273

Inhibition by sulfide of nitric and nitrous oxide reduction by denitrifying Pseudomonas fluorescens  

SciTech Connect

The influence of low redox potentials and H/sub 2/S on NO and N/sub 2/O reduction by resting cells of dentrifying Pseudomonas fluorescens was studied. Hydrogen sulfide and Ti(III) were added to achieve redox potentials near -200 mv. The control without reductant had a redox potential near +200 mv. Production of /sup 13/No, (/sup 13/N)N/sub 2/O, and (/sup 13/N)N/sub 2/ from /sup 13/NO/sub 3//sup -/ and /sup 13/NO/sub 2//sup -/ was followed. Total gas production was similar for all three treatments. The accumulation of /sup 13/NO was most significant in the presence of sulfide. A parallel control with autoclaved cells indicated that the /sup 13/NO production was largely biological. The sulfide inhibition was more dramatic at the level of N/sub 2/O reduction; (/sup 13/N)NO/sub 2/ became the major product instead of (/sup 13/N)N/sub 2/, the dominant product when either no reductant or Ti(III) was present. The results indicate that the specific action of sulfide rather than the low redox potential caused a partial inhibition of NO reduction and a strong inhibition of N/sub 2/O reduction in denitrifying cells.

Sorensen, J.; Tiedje, J.M.; Firestone, R.B.

1980-01-01

274

Process for the catalytic reduction of nitrogen oxides in gaseous mixtures  

SciTech Connect

A process for the reductive removal of a nitrogen oxide from a gaseous stream, particularly a stream containing oxygen, water, sulfur dioxide, nitrogen oxide and nitrogen, by contacting the stream with ammonia in the presence of a mixture of two catalysts. The first catalyst comprises copper or a copper compound, preferably copper sulfate supported on a porous carrier material. The second catalyst is a combination of metals or compounds thereof, preferably sulfates of vanadium and iron or tungsten and iron, also dispersed on a porous carrier material.

Ginger, E.A.

1981-05-19

275

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution.  

PubMed

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO. PMID:24059434

Basirun, Wan J; Sookhakian, Mehran; Baradaran, Saeid; Mahmoudian, Mohammad R; Ebadi, Mehdi

2013-01-01

276

Selective catalytic reduction of nitric oxide with acetaldehyde over NaY zeolite catalyst in lean exhaust feed  

Microsoft Academic Search

Steady-state selective catalytic reduction (SCR) of nitric oxide (NO) was investigated under simulated lean-burn conditions using acetaldehyde (CH3CHO) as the reductant. This work describes the influence of catalyst space velocity and the impact of nitric oxide, acetaldehyde, oxygen, sulfur dioxide, and water on NOx reduction activity over NaY zeolite catalyst. Results indicate that with sufficient catalyst volume 90% NOx conversion

Steven J. Schmieg; Byong K. Cho; Se H. Oh

2004-01-01

277

Nitrogen oxides reduction by carbonaceous materials and carbon dioxide separation using regenerative metal oxides from fossil fuel based flue gas  

NASA Astrophysics Data System (ADS)

The ever-growing energy demands due to rising global population and continuing lifestyle improvements has placed indispensable emphasis on fossil fuels. Combustion of fossil fuels leads to the emission of harmful gaseous pollutants such as oxides of sulfur (SOx) and nitrogen (NOx), carbon dioxide (CO2), mercury, particulate matter, etc. Documented evidence has proved that this air pollution leads to adverse environmental health. This dissertation focuses on the development of technologies for the control of NOx and CO2 emissions. The first part of the thesis (Chapters 2--6) deals with the development of carbon based post combustion NOx reduction technology called CARBONOX process. High temperature combustion oxidizes both atmospheric nitrogen and organic nitrogen in coal to nitric oxide (NO). The reaction rate between graphite and NO is slow and requires high temperature (>900°C). The presence of metallic species in coal char catalyzes the reaction. The reaction temperature is lowered in the presence of oxygen to about 600--850°C. Chemical impregnation, specifically sodium compounds, further lowers the reaction temperature to 350--600°C. Activated high sodium lignite char (HSLC) provided the best performance for NO reduction. The requirement of char for NOx reduction is about 8--12 g carbon/g NO reduced in the presence of 2% oxygen in the inlet gas. The second part of this dissertation (chapter 7--8) focuses on the development of a reaction-based process for the separation of CO2 from combustion flue gas. Certain metal oxides react with CO2 forming metal carbonates under flue gas conditions. They can be calcined separately to yield CO2. Calcium oxide (CaO) has been identified as a viable metal oxide for the carbonation-calcination reaction (CCR) scheme. CaO synthesized from naturally occurring precursors (limestone and dolomite) attained 45--55% of their stoichiometric conversion due to the susceptibility of their microporous structure. High surface area precipitated calcium carbonate (PCC) was synthesized that provided a mesoporous CaO structure upon calcination. This CaO structure attained more than 90% conversion towards the carbonation reaction at 650°C. The reactivity of the novel CaO structure was maintained close to 95% over two reaction-regeneration cycles at 700°C. Vacuum calcination proved beneficial in maintaining the structural integrity of the sorbent.

Gupta, Himanshu

278

Axial ligation and polypeptide matrix effects on the reduction potential of heme proteins probed on their cyanide adducts.  

PubMed

The enthalpic and entropic changes accompanying the reduction reaction of the six-coordinate cyanide adducts of cytochrome c, microperoxidase-11 and a few plant peroxidases were measured electrochemically. Once the compensating changes in reduction enthalpy and entropy due to solvent reorganization effects are factorized out, it is found that cyanide binding stabilizes enthalpically the ferriheme following the order: cyochrome c > peroxidase > microperoxidase-11. The effect is inversely correlated to the solvent accessibility of the heme. Comparison of the reduction thermodynamics for the cyanide adducts of cytochrome c and plant peroxidases with those for microperoxidase-11 and myoglobin, respectively, yielded an estimate of the consequences of protein encapsulation and of the anionic character of the proximal histidine on the reduction potential of the heme-cyanide group. Insertion of the heme-CN group into the folded peptide chain of cyt c induces an enthalpy-based decrease in E degrees ' of approximately 100 mV, consistent with the lower net charge of the oxidized as compared to the reduced iron center, whereas a full imidazolate character of the proximal histidine stabilizes enthalpically the ferriheme by approximately 400 mV. The latter value should be best considered as an upper limit since it also includes some solvation effects arising from the nature of the protein systems being compared. PMID:16133205

Battistuzzi, G; Bellei, M; Borsari, M; Di Rocco, G; Ranieri, A; Sola, M

2005-10-01

279

Preparing hydrogenation catalysts via the simultaneous reduction of graphite oxide and platinum(IV)  

NASA Astrophysics Data System (ADS)

The simultaneous reduction of Pt(IV) and graphite oxide is performed for the preparation of hydrogenation catalysts. It is shown that of the four studied reducing agents (formate ion, ethylene glycol, sodium borohydride, and hydrazine), only NaBH4 and hydrazine can be used in the preparation of catalysts. It is assumed that Pt particles (?2 nm) are fixed to the defects, vacancies, and functional groups that are formed as a result of reduction. The prepared compositions catalyze the hydrogenation of decene-1 and nitrobenzene (45°C, 1 atm H2) with specific activities comparable to those in the literature.

Kushch, S. D.; Kuyunko, N. S.; Muradyan, V. E.; Tarasov, B. P.

2013-11-01

280

Catalytic decomposition of hydrogen peroxide on manganese oxides. IV. Catalytic activities and electrode potentials of platinum-supported manganese oxides  

Microsoft Academic Search

The decomposition of hydrogen peroxide on thin layers of platinum-supported manganese oxides was studied in the stationary and nonstationary regions. The catalytic activities and the electrode potentials of the oxides were simultaneously determined. In the stationary region the surface's oxidation state and structure are independent of the temperature, of the hydrogen peroxide concentration, and of the presence of KCl and

V. A. Sadykov; P. G. Tsyrulnikov

1977-01-01

281

Electrically rechargeable anionically active reduction-oxidation electrical storage-supply system  

SciTech Connect

An electrically rechargeable anionically active reduction-oxidation electric storage-supply system and process is disclosed using a sodium or potassium sulfidepolysulfide anolyte reaction and an iodide-polyiodide, chloride-chlorine or bromide-bromine species catholyte reaction. The catholyte and anolyte are separated by an ion selective membrane permeable to positive sodium and potassium ions and substantially impermeable to negative bromide, chloride, iodide, sulfide and polysulfide ions. A flowing electrolyte system is disclosed with external electrolyte storage vessels. The apparatus and process provide an electrically rechargeable anionically active reduction-oxidation system in which the electrolytes may be maintained at near neutral or slightly basic pH, with virtually no parasitic side reactions upon charging, such as hydrogen or oxygen evolution, and the disclosed storage and supply system provides higher energy densities than referenced prior art systems.

Remick, R.J.; Ang, P.G.P.

1984-11-27

282

pH dependence of copper geometry, reduction potential, and nitrite affinity in nitrite reductase.  

PubMed

Many properties of copper-containing nitrite reductase are pH-dependent, such as gene expression, enzyme activity, and substrate affinity. Here we use x-ray diffraction to investigate the structural basis for the pH dependence of activity and nitrite affinity by examining the type 2 copper site and its immediate surroundings in nitrite reductase from Rhodobacter sphaeroides 2.4.3. At active pH the geometry of the substrate-free oxidized type 2 copper site shows a near perfect tetrahedral geometry as defined by the positions of its ligands. At higher pH values the most favorable copper site geometry is altered toward a more distorted tetrahedral geometry whereby the solvent ligand adopts a position opposite to that of the His-131 ligand. This pH-dependent variation in type 2 copper site geometry is discussed in light of recent computational results. When co-crystallized with substrate, nitrite is seen to bind in a bidentate fashion with its two oxygen atoms ligating the type 2 copper, overlapping with the positions occupied by the solvent ligand in the high and low pH structures. Fourier transformation infrared spectroscopy is used to assign the pH dependence of the binding of nitrite to the active site, and EPR spectroscopy is used to characterize the pH dependence of the reduction potential of the type 2 copper site. Taken together, these spectroscopic and structural observations help to explain the pH dependence of nitrite reductase, highlighting the subtle relationship between copper site geometry, nitrite affinity, and enzyme activity. PMID:17148448

Jacobson, Frida; Pistorius, Arthur; Farkas, Daniel; De Grip, Willem; Hansson, Orjan; Sjölin, Lennart; Neutze, Richard

2007-03-01

283

Effects of microbial iron reduction and oxidation on the immobilization and mobilization of copper in synthesized Fe(III) minerals and Fe-rich soils.  

PubMed

The effects of microbial iron reduction and oxidation on the immobilization and mobilization of copper were investigated in a high concentration of sulfate with synthesized Fe(III) minerals and red earth soils rich in amorphous Fe (hydr)oxides. Batch microcosm experiments showed that red earth soil inoculated with subsurface sediments had a faster Fe(III) bioreduction rate than pure amorphous Fe(III) minerals and resulted in quicker immobilization of Cu in the aqueous fraction. Coinciding with the decrease of aqueous Cu, SO4(2-) in the inoculated red earth soil decreased acutely after incubation. The shift in the microbial community composite in the inoculated soil was analyzed through denaturing gradient gel electrophoresis. Results revealed the potential cooperative effect of microbial Fe(III) reduction and sulfate reduction on copper immobilization. After exposure to air for 144 h, more than 50% of the immobilized Cu was remobilized from the anaerobic matrices; aqueous sulfate increased significantly. Sequential extraction analysis demonstrated that the organic matter/sulfide-bound Cu increased by 52% after anaerobic incubation relative to the abiotic treatment but decreased by 32% after oxidation, indicating the generation and oxidation of Cu-sulfide coprecipitates in the inoculated red earth soil. These findings suggest that the immobilization of copper could be enhanced by mediating microbial Fe(III) reduction with sulfate reduction under anaerobic conditions. The findings have an important implication for bioremediation in Cucontaminated and Fe-rich soils, especially in acid-mine-drainage-affected sites. PMID:24448165

Hu, Chaohua; Zhang, Youchi; Zhang, Lei; Luo, Wensui

2014-04-01

284

Hidden symmetries in a gauge covariant approach, Hamiltonian reduction and oxidation  

E-print Network

Hidden symmetries in a covariant Hamiltonian formulation are investigated involving gauge covariant equations of motion. The special role of the Stackel-Killing tensors is pointed out. A reduction procedure is used to reduce the original phase space to another one in which the symmetries are divided out. The reverse of the reduction procedure is done by stages performing the unfolding of the gauge transformation followed by the Eisenhart lift in connection with scalar potentials.

Mihai Visinescu

2011-09-26

285

Kinetics of manganese oxide reduction from basic slags by carbon dissolved in liquid iron  

Microsoft Academic Search

The reduction of manganese oxide from a basic slag by carbon dissolved in liquid iron is a slow reaction, failing to approach\\u000a equilibrium closely in 20 hr. Furthermore, the rate of stirring has no apparent effect on the reaction rate. This identifies\\u000a the rate-controlling step as a chemical reaction at the interface. Only the model for the reactionO\\u000a 2? =O

Weldon L. Daines; Robert D. Pehlke

1971-01-01

286

Preparation of graphene by the rapid and mild thermal reduction of graphene oxide induced by microwaves  

Microsoft Academic Search

Rapid and mild thermal reduction of graphene oxide (GO) to graphene was achieved with the assistance of microwaves in a mixed solution of N,N-dimethylacetamide and water (DMAc\\/H2O). The mixed solution works as both a solvent for the produced graphene and a medium to control the temperature of the reactive system up to 165°C. Fourier transform infrared spectrometry, X-ray diffraction, atomic

Wufeng Chen; Lifeng Yan; Prakriti R. Bangal

2010-01-01

287

One-step reduction, characterization and magnetic behaviour of exfoliated graphene oxide  

NASA Astrophysics Data System (ADS)

The functionalized graphene (GO) was fabricated by a simple method of chemical reduction in a polar aprotic solvent. This paper therefore, describes a versatile and synthetic route for the preparation of reduced graphene oxide (RGO) and its behavior when exposed to magnetic field environment. The characterization results of transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy and the attenuated total reflectance-Fourier transform infra-red (ATR-FTIR) analysis indicate that graphite was exfoliated and reduced to graphene layers.

Dikio, E. D.; Thema, F. T.; Farah, A. M.; Shooto, N. D.

2013-01-01

288

Non-platinum electrocatalysts: Manganese oxide nanoparticle-cobaltporphyrin binary catalysts for oxygen reduction  

Microsoft Academic Search

This study is concerned with the development of non-platinum electrocatalysts for the efficient 4-electron reduction of molecular\\u000a oxygen to water in acidic media. A binary catalyst composed of electrodeposited manganese oxide nanoparticles (nano-MnO\\u000a x\\u000a ) and cobalt porphyrin macro complex (CoP) has been proposed in. The modification of glassy carbon (GC) electrode with CoP\\u000a alone resulted in a significant positive

Mohamed S. El-Deab; Sameh H. Othman; Takeyoshi Okajima; Takeo Ohsaka

2008-01-01

289

Biogenic gases and the oxidation and reduction of carbon in Amazon River and floodplain waters  

Microsoft Academic Search

Concentrations of COZ, 02, CH4, and N,O in the Amazon River system reflect an oxidation- reduction sequence in combination with physical mixing between the floodplain and the mainstem. Concentrations of CO, ranged from 150 PM in the Amazon mainstem to 200-300 PM in aerobic environments and up to 1,000 PM in oxygen-depleted environments of the floodplain. Apparent oxygen utilization (AOU)

JEFFREY E. RICHEY; ALLAN H. DEVOL; STEVEN C. WOFSY; REYNALDO VICTORIA; MARIA N. G. RIBERIO

1988-01-01

290

Noise and Fuel Burn Reduction Potential of an Innovative Subsonic Transport Configuration  

NASA Technical Reports Server (NTRS)

A study is presented for the noise and fuel burn reduction potential of an innovative double deck concept aircraft with two three-shaft direct-drive turbofan engines. The engines are mounted from the fuselage so that the engine inlet is over the main wing. It is shown that such an aircraft can achieve a cumulative Effective Perceived Noise Level (EPNL) about 28 dB below the current aircraft noise regulations of Stage 4. The combination of high bypass ratio engines and advanced wing design with laminar flow control technologies provide fuel burn reduction and low noise levels simultaneously. For example, the fuselage mounted engine position provides more than 4 EPNLdB of noise reduction by shielding the inlet radiated noise. To identify the potential effect of noise reduction technologies on this concept, parametric studies are presented to reveal the system level benefits of various emerging noise reduction concepts, for both engine and airframe noise reduction. These concepts are discussed both individually to show their respective incremental noise reduction potential and collectively to assess their aggregate effects on the total noise. Through these concepts approximately about 8 dB of additional noise reduction is possible, bringing the cumulative noise level of this aircraft to 36 EPNLdB below Stage 4, if the entire suite of noise reduction technologies would mature to practical application. In a final step, an estimate is made for this same aircraft concept but with higher bypass ratio, geared, turbofan engines. With this geared turbofan propulsion system, the noise is estimated to reach as low as 40-42 dB below Stage 4 with a fuel burn reduction of 43-47% below the 2005 best-in-class aircraft baseline. While just short of the NASA N+2 goals of 42 dB and 50% fuel burn reduction, for a 2025 in service timeframe, this assessment shows that this innovative concept warrants refined study. Furthermore, this design appears to be a viable potential future passenger aircraft, not only in meeting the regulatory requirements, but also in competing with aircraft of different advanced designs within this N+2 timeframe and goal framework.

Guo, Yueping; Nickol, Craig L.; Thomas, Russell H.

2014-01-01

291

Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts.  

PubMed

Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions. PMID:22280461

Liang, Yongye; Wang, Hailiang; Zhou, Jigang; Li, Yanguang; Wang, Jian; Regier, Tom; Dai, Hongjie

2012-02-22

292

Kinetics of the reduction of the zinc oxide in zinc ferrite with iron  

SciTech Connect

Electric arc furnace (EAF) dust, which can be considered as a by-product of the steel recycling process, contains significant quantities of recoverable zinc and iron, as well as hazardous elements such as cadmium, lead and chromium, which can be leached by ground water. The zinc in the EAF dust is found almost entirely in the form of either zinc oxide or zinc ferrite, the latter accounting for 20 to 50 percent of the total zinc. It is important that an efficient process be developed which renders the dust inert, while reclaiming the valuable metals to off-set processing costs. During the conventional carbothermic reduction processes, iron is formed, and this iron can participate in the reduction of the zinc oxide in zinc ferrite. In the present work, the reduction of the zinc oxide in zinc ferrite by iron according to the following reaction: ZnO{sup {sm_bullet}}Fe{sub 2}O{sub (s.s.)} + 2 Fe{sub (s)} = Zn{sub (g)} + 4 FeO{sub (s)} was studied in an argon atmosphere using a thermogravimetric technique. First, a thermodynamic analysis was performed using the F*A*C*T computational system. Then, the effects of briquette aspect ratio (l/d), temperature, zinc ferrite particle size, amount of iron added, as well as additions such as lime, sodium chloride, and calcium fluoride were investigated.

Donald, J.R.; Pickles, C.A. [Queen`s Univ., Kingston, Ontario (Canada). Dept. of Materials and Metallurgical Engineering

1995-12-31

293

Low-temperature aluminum reduction of graphene oxide, electrical properties, surface wettability, and energy storage applications.  

PubMed

Low-temperature aluminum (Al) reduction is first introduced to reduce graphene oxide (GO) at 100-200 °C in a two-zone furnace. The melted Al metal exhibits an excellent deoxygen ability to produce well-crystallized reduced graphene oxide (RGO) papers with a low O/C ratio of 0.058 (Al-RGO), compared with 0.201 in the thermally reduced one (T-RGO). The Al-RGO papers possess outstanding mechanical flexibility and extremely high electrical conductivities (sheet resistance R(s) ~ 1.75 ?/sq), compared with 20.12 ?/sq of T-RGO. More interestingly, very nice hydrophobic nature (90.5°) was observed, significantly superior to the reported chemically or thermally reduced papers. These enhanced properties are attributed to the low oxygen content in the RGO papers. During the aluminum reduction, highly active H atoms from H(2)O reacted with melted Al promise an efficient oxygen removal. This method was also applicable to reduce graphene oxide foams, which were used in the GO/SA (stearic acid) composite as a highly thermally conductive reservoir to hold the phase change material for thermal energy storage. The Al-reduced RGO/SnS(2) composites were further used in an anode material of lithium ion batteries possessing a higher specific capacity. Overall, low-temperature Al reduction is an effective method to prepare highly conductive RGO papers and related composites for flexible energy conversion and storage device applications. PMID:22984901

Wan, Dongyun; Yang, Chongyin; Lin, Tianquan; Tang, Yufeng; Zhou, Mi; Zhong, Yajuan; Huang, Fuqiang; Lin, Jianhua

2012-10-23

294

Essential role of Glu-C66 for menaquinol oxidation indicates transmembrane electrochemical potential generation by Wolinella succinogenes fumarate reductase  

PubMed Central

Quinol:fumarate reductase (QFR) is a membrane protein complex that couples the reduction of fumarate to succinate to the oxidation of quinol to quinone, in a reaction opposite to that catalyzed by the related enzyme succinate:quinone reductase (succinate dehydrogenase). In the previously determined structure of QFR from Wolinella succinogenes, the site of fumarate reduction in the flavoprotein subunit A of the enzyme was identified, but the site of menaquinol oxidation was not. In the crystal structure, the acidic residue Glu-66 of the membrane spanning, diheme-containing subunit C lines a cavity that could be occupied by the substrate menaquinol. Here we describe that, after replacement of Glu-C66 with Gln by site-directed mutagenesis, the resulting mutant is unable to grow on fumarate and the purified enzyme lacks quinol oxidation activity. X-ray crystal structure analysis of the Glu-C66 ? Gln variant enzyme at 3.1-? resolution rules out any major structural changes compared with the wild-type enzyme. The oxidation-reduction potentials of the heme groups are not significantly affected. We conclude that Glu-C66 is an essential constituent of the menaquinol oxidation site. Because Glu-C66 is oriented toward a cavity leading to the periplasm, the release of two protons on menaquinol oxidation is expected to occur to the periplasm, whereas the uptake of two protons on fumarate reduction occurs from the cytoplasm. Thus our results indicate that the reaction catalyzed by W. succinogenes QFR generates a transmembrane electrochemical potential. PMID:11186225

Lancaster, C. Roy D.; Gross, Roland; Haas, Alexander; Ritter, Michaela; Mantele, Werner; Simon, Jorg; Kroger, Achim

2000-01-01

295

One-pot green synthesis of silver/iron oxide composite nanoparticles for 4-nitrophenol reduction.  

PubMed

Silver/iron oxide composite nanoparticles have been synthesized successfully via a facile one-pot green route by the use of l-arginine, which created an aqueous solution of about pH 10 and acted as a reducing agent for the successive formation of iron oxide and Ag nanoparticles. The product was characterized to be silver-coated iron oxide and iron oxide hydroxide composite nanoparticles with a mean diameter of about 13.8 ± 3.0 nm and 8.53% of Ag in weight. It exhibited good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. The reduction reaction followed the pseudo-first-order kinetics. The corresponding rate constants increased with the increases of temperature and catalyst amount but decreased with the increase of initial 4-NP concentration, revealing an activation energy of 28.2 kJ/mol and a diffusion controlled mechanism. In addition, this product had quite good stability. No significant activity loss was observed after reuse for 5 cycles. PMID:23416483

Chiou, Jau-Rung; Lai, Bo-Hung; Hsu, Kai-Chih; Chen, Dong-Hwang

2013-03-15

296

Potentially toxic element release by fenton oxidation of sewage sludge.  

PubMed

The presence, in sewage sludge, of excess levels of the potentially toxic elements (PTE) copper, zinc, chromium, cadmium, nickel, lead and mercury, could impact on our ability to recycle these residues in the future. Far stricter limits on the levels of PTEs are likely in proposed legislation. A method involving the dosing of Fenton's reagent, a mixture of ferrous iron and hydrogen peroxide, under acidic conditions was evaluated for its potential to reduce metal levels. The [Fe]:[H2O2] (w/w) ratio was found to give a good indication of the percentage copper and zinc elution obtainable. Sites with no iron dosing as part of wastewater treatment required extra iron to be added in order to initiate the Fenton's reaction. A significant reduction, in excess of 70%, of the copper and zinc was eluted from both raw primary and activated sludge solid fractions. Cadmium and nickel could be reduced to below detection limits but elution of mercury, lead and chromium was less than 40%. The iron catalyst concentration was found to be a crucial parameter. This process has the potential to reduce the heavy metal content of the sludge and allow the recycling of sludge to continue in a sustainable manner. PMID:17087386

Andrews, J P; Asaadi, M; Clarke, B; Ouki, S

2006-01-01

297

Synthesis of high-performance graphene nanosheets by thermal reduction of graphene oxide  

SciTech Connect

Graphical abstract: High-performance graphene nanosheets were synthesized by thermal reduction of graphene oxide under ethanol atmosphere. X-ray photoelectron spectroscopy, Raman spectroscopy and electrical transport measurements indicate that the resulting graphene nanosheets can effectively restore its graphic structure in GO and present high mobility. Highlights: {yields} Graphene nanosheets were synthesized by reduction of GO under ethanol atmosphere. {yields} Raman and XPS results indicate the reduced graphene sheets have high-performance. {yields} Graphene sheets field-effect transistors present high mobility. -- Abstract: High-performance graphene nanosheets have been synthesized by thermal reduction of graphene oxide (GO) under ethanol atmosphere. The reduced GO nanosheets were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy and electrical transport measurements, respectively. The results indicated that the thermal reduction of GO under ethanol atmosphere can effectively remove the oxygen-containing functional groups and restore its graphic structure compared to the ones obtained using hydrazine or hydrogen. The electrical measurements indicated that the electrical mobility of single-layer graphene sheet reduced under ethanol atmosphere at 900 {sup o}C can reach 29.08 cm{sup 2} V{sup -1} S{sup -1}.

Wei, Ang; Wang, Jingxia; Long, Qing; Liu, Xiangmei; Li, Xingao [Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications NUPT, 9 Wenyuan Road, Nanjing 210046 (China)] [Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications NUPT, 9 Wenyuan Road, Nanjing 210046 (China); Dong, Xiaochen, E-mail: iamxcdong@njupt.edu.cn [Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications NUPT, 9 Wenyuan Road, Nanjing 210046 (China)] [Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications NUPT, 9 Wenyuan Road, Nanjing 210046 (China); Huang, Wei, E-mail: iamwhuang@njupt.edu.cn [Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications NUPT, 9 Wenyuan Road, Nanjing 210046 (China)] [Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications NUPT, 9 Wenyuan Road, Nanjing 210046 (China)

2011-11-15

298

Oxygen potentials of plutonium and uranium mixed oxide  

NASA Astrophysics Data System (ADS)

The oxygen potentials of (Pu 0.3U 0.7)O 2- x in the near stoichiometric region were measured by a thermogravimetric technique which was used to establish the equilibrium between the oxide phases and H 2/H 2O system gas. The experimental results of (Pu 0.3U 0.7)O 2- x show a consistent variation in PO 2 with O/M and temperature and are in agreement with other works. The relationship between the partial oxygen pressure and x in MO 2- x was evaluated by the lattice defect theory. The relationship in the hypo-stoichiometric region was x?PO2-1/2 near the stoichiometric composition, and became x?PO2-1/3 with a decrease in O/M.

Kato, Masato; Tamura, Tetsuya; Konashi, Kenji; Aono, Shigenori

2005-09-01

299

Oxidative dissolution potential of biogenic and abiogenic TcO 2 in subsurface sediments  

NASA Astrophysics Data System (ADS)

Technetium-99 (Tc) is an important fission product contaminant associated with sites of nuclear fuels reprocessing and geologic nuclear waste disposal. Tc is highly mobile in its most oxidized state [Tc(VII)O4-] and less mobile in the reduced form [Tc(IV)O 2· nH 2O]. Here we investigate the potential for oxidation of Tc(IV) that was heterogeneously reduced by reaction with biogenic Fe(II) in two sediments differing in mineralogy and aggregation state; unconsolidated Pliocene-age fluvial sediment from the upper Ringold (RG) Formation at the Hanford Site and a clay-rich saprolite from the Field Research Center (FRC) background site on the Oak Ridge Site. Both sediments contained Fe(III) and Mn(III/IV) as redox active phases, but FRC also contained mass-dominant Fe-phyllosilicates of different types. Shewanella putrefaciens CN32 reduced Mn(III/IV) oxides and generated Fe(II) that was reactive with Tc(VII) in heat-killed, bioreduced sediment. After bioreduction and heat-killing, biogenic Fe(II) in the FRC exceeded that in RG by a factor of two. More rapid reduction rates were observed in the RG that had lower biogenic Fe(II), and less particle aggregation. EXAFS measurements indicated that the primary reduction product was a TcO 2-like phase in both sediments. The biogenic redox product Tc(IV) oxidized rapidly and completely in RG when contacted with air. Oxidation, in contrast, was slow and incomplete in the FRC, in spite of similar molecular scale speciation of Tc compared to RG. X-ray microprobe, electron microprobe, X-ray absorption spectroscopy, and micro X-ray diffraction were applied to the whole sediment and isolated Tc-containing particles. These analyses revealed that non-oxidizable Tc(IV) in the FRC existed as complexes with octahedral Fe(III) within intra-grain domains of 50-100 ?m-sized, Fe-containing micas presumptively identified as celadonite. The markedly slower oxidation rates in FRC as compared to RG were attributed to mass-transfer-limited migration of O 2 into intra-aggregate and intraparticle domains where Tc(IV) existed; and the formation of unique, oxidation-resistant, intragrain Tc(IV)-Fe(III) molecular species.

Fredrickson, James K.; Zachara, John M.; Plymale, Andrew E.; Heald, Steve M.; McKinley, James P.; Kennedy, David W.; Liu, Chongxuan; Nachimuthu, Ponnusamy

2009-04-01

300

Fungicide use reduction in apple production—potentials or pipe dreams?  

Microsoft Academic Search

Reduction in pesticide use in response to consumer pressures is seen as a major issue in many crops. Fungicides comprise the greater proportion of pesticides applied to apples. Potential methods to reduce their usage have been available for a considerable period of time. These are examined under five broad areas: epidemiological (manipulation of current practices), non-conventional fungicides, biological control with

L. J. Penrose

1995-01-01

301

THEORETICAL INVESTIGATION INTO THE POTENTIAL OF HALOGENATED METHANES TO UNDERGO REDUCTIVE METABOLISM  

EPA Science Inventory

The density-functional theory (DFT) based computational chemistry software package DMol was used to provide insight into the reductive potentials of a series of halomethanes. t is known that certain members of this series are readily reduced in vivo via catalysis by cytochrome P4...

302

Potential for reduction in utility fuel oil consumption using natural gas  

Microsoft Academic Search

An examination of over 200 electric utility plants that consume residual fuel oil, indicates that in the short term any reduction in electric utility residual fuel oil consumption would be confined to dual-fuel plants and that these plants have the potential to reduce their resid consumption approximately 45 MB\\/D, or about 7% of total electric utility resid consumption in 1989.

S. Thumb; N. Pozar

1991-01-01

303

Unexpected C(carbene)-X (X: I, Br, Cl) Reductive Elimination From N-Heterocyclic Carbene Copper Halide Complexes Under Oxidative Conditions.  

PubMed

The non-innocent behaviors of NHC ligands have attracted wide attention due to their important implications for catalyst designs and reaction mechanisms. Herein, we report facile C(carbene)-halogen reductive eliminations from NHC copper halide complexes at RT under oxidative conditions. Density functional calculations on a simplified model system suggest that the reactions occur through oxidation of Cu(I) to Cu(III) species followed by C(carbene)-halogen reductive eliminations from NHC Cu(III) halide complexes. Remarkably short C(carbene)-chloride contacts and rare interactions between the chloride lone pair electrons and the C(carbene)p(?) orbital were found for the calculated NHC Cu(III) chlorides. The facile C(carbene)-X reductive elimination reported here warrants consideration as a potential decomposition pathway in reactions involving NHC-supported high-valent metal complexes, especially with late transition metals. PMID:21116469

Lin, Bo-Lin; Kang, Peng; Stack, T Daniel P

2010-09-13

304

Gadolinium oxide nanoparticles as potential multimodal imaging and therapeutic agents.  

PubMed

Potentials of hydrophilic and biocompatible ligand coated gadolinium oxide nanoparticles as multimodal imaging agents, drug carriers, and therapeutic agents are reviewed. First of all, they can be used as advanced T1 magnetic resonance imaging (MRI) contrast agents because they have r1 larger than those of Gd(III)-chelates due to a high density of Gd(III) per nanoparticle. They can be further functionalized by conjugating other imaging agents such as fluorescent imaging (FI), X-ray computed tomography (CT), positron emission tomography (PET), and single photon emission tomography (SPECT) agents. They can be also useful for drug carriers through morphology modifications. They themselves are also potential CT and ultrasound imaging (USI) contrast and thermal neutron capture therapeutic (NCT) agents, which are superior to commercial iodine compounds, air-filled albumin microspheres, and boron ((10)B) compounds, respectively. They, when conjugated with targeting agents such as antibodies and peptides, will provide enhanced images and be also very useful for diagnosis and therapy of diseases (so called theragnosis). PMID:23432005

Kim, Tae Jeong; Chae, Kwon Seok; Chang, Yongmin; Lee, Gang Ho

2013-01-01

305

The biogenic emission potential of nitric oxide from sandy soils  

NASA Astrophysics Data System (ADS)

There are about 160.9 Mha of sandy land in China, about 17.6% of total Chinese area, which mainly distributed in 35°-50° N. The western Songnen Plain, which located in the semi-arid region of Northeastern China, is one of the main sandy soil distribution regions. The changes of land use in sandy soil are accompanied by changes in biogeochemical cycles of nutrients, particularly of the air-surface exchange of trace gases like nitric oxide. Our study, based on results obtained by a laboratory incubation technique, focuses on (a) NO production and consumption in sandy soils from two types of land use as function of soil temperature and soil moisture, and (b) The biogenic emission potential of nitric oxide from sandy soils in semi-arid region. At 25?C, average NO production (in terms of mass of N) was 0.016,and 0.013 ng kg-1s-1 in sandy soils from soybean land (SL) and man-made forest (MF), re¬spectively. NO consumption rate constant ranged from 0.26×10-6 to 7.28×10-6 m3 kg-1s-1. At 25?C and under optimum soil moisture conditions for NO production, the NO compensation point mixing ratio was about 266 and 161 ug m-3 (465,and 281 ppb) for soils of SL and MF, respectively. Statistically sound relationships have been observed between NO fluxes and soil moisture (optimum curves). NO fluxes also increased exponentially with soil temperature at any given soil moisture. The optimum soil moisture for which maximum NO flux was observed was independent of soil temperature. The maximum of NO flux potentials for SL and MF soils (at 25°C) were 59.6 and 36.5 ng m-2s-1 at water-filled pore space (%WFPS) of 26 and 24, respectively. The NO flux potential was about 2 times larger for cropland soil than for man-made forest soils, most likely due to fertilizer application to the cropland soils.

Yu, J. B.; Meixner, F. X.; Sun, Z. G.; Chen, X. B.; Mamtimin, B.

2009-04-01

306

Pulsed laser irradiation for environment friendly reduction of graphene oxide suspensions  

NASA Astrophysics Data System (ADS)

Graphene oxide (GO) sheets were synthesized through a modified Hummers' method. Using high resolution transmission electron microscopy the thickness of the GO sheets in a multilayer structure of stacked GO sheets was found ˜0.8 nm. A nanosecond pulsed laser (with wavelength of 532 nm and average power of 0.3 W) was applied for effective and environment friendly reduction of the GO sheets in an ammonia solution (pH ˜9) at room temperature conditions. The deoxygenation of the GO sheets by the pulsed laser reduction method was confirmed by using UV-visible, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS) and thermo gravimetric analysis. Based on XPS analysis, the O/C ratio of the GO sheets decreased from 49% to 21% after 10 min laser irradiation. This reduction efficiency was comparable with the efficiency achieved by hydrazine which yielded the O/C ratio of 15% at 80 °C after 10 min. Using Raman spectroscopy it was found that the pulsed laser reduction method resulted in nearly no aggregation of the reduced GO sheets in the ammonia solution. These results can help to further promotion and application of pulsed lasers in environment friendly reduction of GO.

Ghadim, Ehsan Ezzatpour; Rashidi, Nasim; Kimiagar, Salimeh; Akhavan, Omid; Manouchehri, Firouzeh; Ghaderi, Elham

2014-05-01

307

Manganese sulfide formation via concomitant microbial manganese oxide and thiosulfate reduction.  

PubMed

The dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1 produced ?-MnS (rambergite) nanoparticles during the concurrent reduction of MnO? and thiosulfate coupled to H? oxidation. To investigate effect of direct microbial reduction of MnO? on MnS formation, two MR-1 mutants defective in outer membrane c-type cytochromes (?mtrC/?omcA and ?mtrC/?omcA/?mtrF) were also used and it was determined that direct reduction of MnO? was dominant relative to chemical reduction by biogenic sulfide generated from thiosulfate reduction. Although bicarbonate was excluded from the medium, incubations of strain MR-1 with lactate as the electron donor produced MnCO? (rhodochrosite) as well as MnS in nearly equivalent amounts as estimated by micro X-ray diffraction (micro-XRD) analysis. It was concluded that carbonate released from lactate metabolism promoted MnCO? formation and that Mn(II) mineralogy was strongly affected by carbonate ions even in the presence of abundant sulfide and weakly alkaline conditions expected to favour the precipitation of MnS. Formation of MnS, as determined by a combination of micro-XRD, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction analyses was consistent with equilibrium speciation modelling predictions. Biogenic manganese sulfide may be a manganese sink in the Mn biogeochemical cycle in select environments such as deep anoxic marine basins within the Baltic Sea. PMID:21951417

Lee, Ji-Hoon; Kennedy, David W; Dohnalkova, Alice; Moore, Dean A; Nachimuthu, Ponnusamy; Reed, Samantha B; Fredrickson, James K

2011-12-01

308

Small cell experiments for electrolytic reduction of uranium oxides to uranium metal using fluoride salts  

SciTech Connect

Electrolytic reduction of uranium oxide was proposed for the preparation of uranium metal feed for the atomic vapor laser isotope separation (AVLIS) process. A laboratory cell of 25-cm ID was operated to obtain additional information in areas important to design and operation of a pilot plant cell. Reproducible test results and useful operating and control procedures were demonstrated. About 20 kg of uranium metal of acceptable purity were prepared. A good supply of dissolved UO[sub 2] feed at the anode is the most important controlling requirement for efficient cell operation. A large fraction of the cell current is nonproductive in that it does not produce a metal product nor consume carbon anodes. All useful test conditions gave some reduction of UF[sub 4] to produce CF[sub 4] in addition to the reduction of UO[sub 2], but the fraction of metal from the reduction of UF[sub 4] can be decreased by increasing the concentration of dissolved UO[sub 2]. Operation of large continuous cells would probably be limited to current efficiencies of less than 60 pct, and more than 20 pct of the metal would result from the reduction of UF[sub 4].

Haas, P.A.; Adcock, P.W.; Coroneos, A.C.; Hendrix, D.E. (Oak Ridge National Lab., TN (United States))

1994-08-01

309

Organic carbon oxidation and suppression of methane production by microbial Fe(III) oxide reduction in vegetated and unvegetated freshwater wetland sediments  

Microsoft Academic Search

High concentrations (20-75 pmol cm-3) of amorphous Fe(III) oxide were observed in unvegetated surface and Juncus eflusus rhizosphere sediments of a freshwater wetland in the southeastern United States. Incu- bation experiments demonstrated that microbial Fe(III) oxide reduction suppressed sulfate reduction and methanogenesis in surface scdimcnts and mediated 240% of depth-integrated (O-10 cm) unvegetated sedi- ment carbon metabolism, compared to I

Eric E. Roden; Robert G. Wetzel

1996-01-01

310

Self-assembled platinum nanoflowers on polydopamine-coated reduced graphene oxide for methanol oxidation and oxygen reduction reactions.  

PubMed

The morphology- and size-controlled synthesis of branched Pt nanostructures on graphene is highly favorable for enhancing the electrocatalytic activity and stability of Pt. Herein, a facile approach is developed for the efficient synthesis of well-dispersed Pt nanoflowers (PtNFs) on the surface of polydopamine (PDA)-modified reduced graphene oxide (PDRGO), denoted as PtNFs/PDRGO, in high yield. The synthesis was performed by a simple heating treatment of an aqueous solution that contained K2 PtCl4 and PDA-modified graphene oxide (GO) without the need for any additional reducing agent, seed, surfactant, or organic solvent. The coated PDA serves not only as a reducing agent, but also as cross-linker to anchor and stabilize PtNFs on the PDRGO support. The as-prepared PtNFs/PDRGO hybrid, with spatially and locally separated PtNFs on PDRGO, exhibits superior electrocatalytic activity and stability toward both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) in alkaline solutions. PMID:25236885

Yu, Xueqing; Wang, Huan; Guo, Liping; Wang, Liang

2014-11-01

311

Complexation facilitated reduction of aromatic N-oxides by aqueous Fe(II)-tiron complex: reaction kinetics and mechanisms.  

PubMed

Rapid reduction of carbadox (CDX), olaquindox and several other aromatic N-oxides were investigated in aqueous solution containing Fe(II) and tiron. Consistent with previous work, the 1:2 Fe(II)-tiron complex, FeL2(6-), is the dominant reactive species as its concentration linearly correlates with the observed rate constant kobs under various conditions. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. UV-vis spectra suggest FeL2(6-) likely forms 5- or 7-membered rings with CDX and olaquindox through the N and O atoms on the side chain. The formed inner-sphere complexes significantly facilitated electron transfer from FeL2(6-) to the N-oxides. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. QSAR analysis indicated neither the first electron transfer nor N-O bond cleavage is the rate-limiting step. Calculations of the atomic spin densities of the anionic N-oxides confirmed the extensive delocalization between the aromatic ring and the side chain, suggesting complex formation can significantly affect the reduction kinetics. Our results suggest the complexation facilitated N-oxide reduction by Fe(II)-tiron involves a free radical mechanism, and the subsequent deoxygenation might also benefit from the weak complexation of Fe(II) with the N-oxide O atom. PMID:23957215

Chen, Yiling; Zhang, Huichun

2013-10-01

312

Nitrate reduction coupled with pyrite oxidation in the surface sediments of a sulfide-rich ecosystem  

NASA Astrophysics Data System (ADS)

studies of denitrification have focused on organic carbon as an electron donor, but reduced sulfur can also support denitrification. Few studies have reported nitrate (NO3-) reduction coupled with pyrite oxidation and its stoichiometry in surface sediments, especially without experimental pyrite addition. In this study, we evaluated NO3- reduction coupled with sulfur oxidation by long-term incubation of surface sediments from a sulfide-rich ecosystem in Akita Prefecture, Japan. The surface sediments were sampled from a mud pool and a riverbed. Fresh sediments and water were incubated under anoxic conditions (and one oxic condition) at 20°C. NO3- addition increased the SO42- concentration and decreased the NO3- concentration. SO42- production (?SO42-) was strongly and linearly correlated with NO3- consumption (?NO3-) during the incubation period (R2 = 0.983, P < 0.01, and n = 8), and the slope of the regression (?NO3-/?SO42-) and the stoichiometry indicated sulfur-driven NO3- reduction by indigenous autotrophic denitrifying bacteria. Framboidal pyrite and marcasite (both FeS2) were present in the sediments and functioned as the electron donors for autotrophic denitrification. Both ?NO3- and ?SO42- were higher in the riverbed sediment than in the mud pool sediment, likely because of the higher amount of easily oxidizable S (pyrite) in the riverbed sediment. Consistently low ammonium (NH4+) concentrations indicated that NO3- reduction by dissimilatory NO3- reduction to NH4+ was small but could not be disregarded. Our results demonstrate that sulfide-rich ecosystems with easily oxidizable metal-bound sulfides such as FeS2 near the ground surface may act as denitrification hot spots.

Hayakawa, Atsushi; Hatakeyama, Mizuho; Asano, Ryoki; Ishikawa, Yuichi; Hidaka, Shin

2013-06-01

313

The indirect global warming potential and global temperature change potential due to methane oxidation  

NASA Astrophysics Data System (ADS)

Methane is the second most important anthropogenic greenhouse gas in the atmosphere next to carbon dioxide. Its global warming potential (GWP) for a time horizon of 100 years is 25, which makes it an attractive target for climate mitigation policies. Although the methane GWP traditionally includes the methane indirect effects on the concentrations of ozone and stratospheric water vapour, it does not take into account the production of carbon dioxide from methane oxidation. We argue here that this CO2-induced effect should be included for fossil sources of methane, which results in slightly larger GWP values for all time horizons. If the global temperature change potential is used as an alternative climate metric, then the impact of the CO2-induced effect is proportionally much larger. We also discuss what the correction term should be for methane from anthropogenic biogenic sources.

Boucher, Olivier; Friedlingstein, Pierre; Collins, Bill; Shine, Keith P.

2009-10-01

314

Modeling Exposures to the Oxidative Potential of PM10  

PubMed Central

Differences in the toxicity of ambient particulate matter (PM) due to varying particle composition across locations may contribute to variability in results from air pollution epidemiologic studies. Though most studies have used PM mass concentration as the exposure metric, an alternative which accounts for particle toxicity due to varying particle composition may better elucidate whether PM from specific sources is responsible for observed health effects. The oxidative potential (OP) of PM < 10 ?m (PM10) was measured as the rate of depletion of the antioxidant reduced glutathione (GSH) in a model of human respiratory tract lining fluid. Using a database of GSH OP measures collected in greater London, U.K. from 2002 to 2006, we developed and validated a predictive spatiotemporal model of the weekly GSH OP of PM10 that included geographic predictors. Predicted levels of OP were then used in combination with those of weekly PM10 mass to estimate exposure to PM10 weighted by its OP. Using cross-validation (CV), brake and tire wear emissions of PM10 from traffic within 50 m and tailpipe emissions of nitrogen oxides from heavy-goods vehicles within 100 m were important predictors of GSH OP levels. Predictive accuracy of the models was high for PM10 (CV R2=0.83) but only moderate for GSH OP (CV R2 = 0.44) when comparing weekly levels; however, the GSH OP model predicted spatial trends well (spatial CV R2 = 0.73). Results suggest that PM10 emitted from traffic sources, specifically brake and tire wear, has a higher OP than that from other sources, and that this effect is very local, occurring within 50–100 m of roadways. PMID:22731499

2012-01-01

315

An inorganic geochemical argument for coupled anaerobic oxidation of methane and iron reduction in marine sediments.  

PubMed

Here, we present results from sediments collected in the Argentine Basin, a non-steady state depositional marine system characterized by abundant oxidized iron within methane-rich layers due to sediment reworking followed by rapid deposition. Our comprehensive inorganic data set shows that iron reduction in these sulfate and sulfide-depleted sediments is best explained by a microbially mediated process-implicating anaerobic oxidation of methane coupled to iron reduction (Fe-AOM) as the most likely major mechanism. Although important in many modern marine environments, iron-driven AOM may not consume similar amounts of methane compared with sulfate-dependent AOM. Nevertheless, it may have broad impact on the deep biosphere and dominate both iron and methane cycling in sulfate-lean marine settings. Fe-AOM might have been particularly relevant in the Archean ocean, >2.5 billion years ago, known for its production and accumulation of iron oxides (in iron formations) in a biosphere likely replete with methane but low in sulfate. Methane at that time was a critical greenhouse gas capable of sustaining a habitable climate under relatively low solar luminosity, and relationships to iron cycling may have impacted if not dominated methane loss from the biosphere. PMID:24460948

Riedinger, N; Formolo, M J; Lyons, T W; Henkel, S; Beck, A; Kasten, S

2014-03-01

316

An environmentally friendly approach to the reduction of graphene oxide by Escherichia fergusoni.  

PubMed

Graphene has attracted a great deal of scientific interest due to its unique properties and its various prospective applications. However, the use of graphene in technological purposes depends on the development of suitable methodologies for its mass production. Several environmentally safe methods have been emerging for the production of graphene from graphite oxide which are based on the solvothermal and the electrochemical processes. Herein, we developed a green, simple and cost effective approach to produce graphene by using an Escherichia fergusoni as a reducing agent. This reduction method avoids the use of environmentally harmful reagents such as hydrazine and hydrazine hydrate. The resulting reduced graphene oxide (rGO) was characterized by a wide range of analytical techniques. UV-Vis spectra of the samples confirm the transition of graphene oxide (GO) into graphene. Fourier transform infra-red spectroscopy (FT-IR) spectrum of the rGO indicates a significant reduction of the intensity of all oxygen containing moieties suggesting efficient conversion of GO to rGO. X-ray diffraction (XRD) was used to investigate the crystalline of graphene nanosheets, whereas high resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to investigate the morphologies of prepared graphene. Raman spectroscopy images provide clear evidence for the formation of graphene. All these findings clearly indicate that GO could be reduced by simple, eco-friendly method by using E. fergusoni to produce water dispersible graphene. PMID:23755651

Gurunathan, Sangiliyandi; Han, Jae Woong; Eppakayala, Vasuki; Jeyaraj, Muniyandi; Kim, Jin-Hoi

2013-03-01

317

The Effect of Thermal Reduction on the Photoluminescence and Electronic Structures of Graphene Oxides  

PubMed Central

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120–180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and K? XES spectra shows that the overlapping ? and ?* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C K? RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the ?-region and/or in the gap between the ? and ?* levels of the GO and rGOs. Two-dimensional C K? RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the ? and ? features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG. PMID:24717290

Chuang, C.-H.; Wang, Y.-F.; Shao, Y.-C.; Yeh, Y.-C.; Wang, D.-Y.; Chen, C.-W.; Chiou, J. W.; Ray, Sekhar C.; Pong, W. F.; Zhang, L.; Zhu, J. F.; Guo, J. H.

2014-01-01

318

Oxide shell reduction and magnetic property changes in core-shell Fe nanoclusters under ion irradiation  

NASA Astrophysics Data System (ADS)

Ion irradiation effects are studied on the Fe-based core-shell nanocluster (NC) films with core as Fe and shell as Fe3O4/Fe3N. These NC films were deposited on Si substrates to thickness of ˜0.5 ?m using a NC deposition system. The films were irradiated at room temperature with 5.5 MeV Si2+ ions to ion fluences of 1015 and 1016 ions/cm2. It is found that the irradiation induces grain growth, Fe valence reduction in the shell, and crystallization or growth of Fe3N. The film retained its Fe-core and its ferromagnetic properties after irradiation. The nature and mechanism of oxide shell reduction and composition dependence after irradiation were studied by synthesizing additional NC films of Fe3O4 and FeO + Fe3N and irradiating them under the same conditions. The presence of nanocrystalline Fe is found to be a major factor for the oxide shell reduction. The surface morphologies of these films show dramatic changes in the microstructures due to cluster growth and agglomeration as a result of ion irradiation.

Sundararajan, Jennifer A.; Kaur, Maninder; Jiang, Weilin; McCloy, John S.; Qiang, You

2014-05-01

319

The Effect of Thermal Reduction on the Photoluminescence and Electronic Structures of Graphene Oxides  

NASA Astrophysics Data System (ADS)

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120-180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and K? XES spectra shows that the overlapping ? and ?* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C K? RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the ?-region and/or in the gap between the ? and ?* levels of the GO and rGOs. Two-dimensional C K? RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the ? and ? features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

Chuang, C.-H.; Wang, Y.-F.; Shao, Y.-C.; Yeh, Y.-C.; Wang, D.-Y.; Chen, C.-W.; Chiou, J. W.; Ray, Sekhar C.; Pong, W. F.; Zhang, L.; Zhu, J. F.; Guo, J. H.

2014-04-01

320

Cerium oxide nanoparticles prevent apoptosis in primary cortical culture by stabilizing mitochondrial membrane potential.  

PubMed

Cerium oxide nanoparticles (CNPs) of spherical shape have unique antioxidant capacity primarily due to alternating + 3 and + 4 oxidation states and crystal defects. Several studies revealed the protective efficacies of CNPs in cells and tissues against the oxidative damage. However, its effect on mitochondrial functioning, downstream effectors of radical burst and apoptosis remains unknown. In this study, we investigated whether CNPs treatment could protect the primary cortical cells from loss of mitochondrial membrane potential (??m) and ??m-dependent cell death. CNPs with spherical morphology and size range 7-10 nm were synthesized and utilized at a concentration of 25 nM on primary neuronal culture challenged with 50 ?M of hydrogen peroxide (H2O2). We showed that optimal dose of CNPs minimized ROS content of the cells and also curbed related surge in cellular calcium flux. Importantly, CNPs treatment prevented apoptotic loss of cell viability. Reduction in the apoptosis could be successfully attributed to the maintenance of ??m and restoration of major redox equivalents NADH/NAD(+) ratio and cellular ATP. These findings, therefore, suggest possible route of CNPs protective efficacies in primary cortical culture. PMID:24650039

Arya, A; Sethy, N K; Das, M; Singh, S K; Das, A; Ujjain, S K; Sharma, R K; Sharma, M; Bhargava, K

2014-07-01

321

A Green and Mild Approach of Synthesis of Highly-Conductive Graphene Film by Zn Reduction of Exfoliated Graphite Oxide  

NASA Astrophysics Data System (ADS)

We report a simple and green approach to synthesize reduced graphene oxide (RGO) nanosheets at room temperature based on Zn reduction of exfoliated GO. The evolution of GO to RGO has been characterized by X-ray diffraction, UV-Vis absorption spectroscopy and Raman spectroscopy. The results of X-ray photoelectron spectroscopy reveal that the atomic ratio of carbon to oxygen in the RGO can be tuned from 1.67 to 13.7 through controlling the reduction time. Moreover, the conductivity of the RGO is measured to be 26.9±2.2 kS/m, much larger than those previously obtained by chemical reduction through other reducing agents. More importantly, the resistance of the RGO film with 20 nm thickness can be as low as 2 k?/square, while a high transparency over 70% within a broad spectral range from 0.45 ?m to 1.50 ?m can be retained. The proposed method is low-cost, eco-friendly and highly-efficient, the as-prepared thinner RGO films are useful in a variety of potential application fields such as optoelectronics, photovoltaics and electrochemistry by serving as an ultralight, flexible and transparent electrode material.

Geng, Zhi-gang; Zhang, Guang-hui; Lin, Yue; Yu, Xin-xin; Ren, Wen-zhen; Wu, Yu-kun; Pan, Nan; Wang, Xiao-ping

2012-08-01

322

Selective CO2 reduction conjugated with H2O oxidation utilizing semiconductor/metal-complex hybrid photocatalysts  

NASA Astrophysics Data System (ADS)

We developed a new hybrid photocatalyst for CO2 reduction, which is composed of a semiconductor and a metal complex. In the hybrid photocatalyst, ?G between the position of conduction band minimum (ECBM) of the semiconductor and the CO2 reduction potential of the complex is an essential factor for realizing fast electron transfer from the conduction band of semiconductor to metal complex leading to high photocatalytic activity. On the basis of this concept, the hybrid photocatalyst InP/Ru-complex, which functions in aqueous media, was developed. The photoreduction of CO2 to formate using water as an electron donor and a proton source was successfully achieved as a Z-scheme system by functionally conjugating the InP/Ru-complex photocatalyst for CO2 reduction with a TiO2 photocatalyst for water oxidation. The conversion efficiency from solar energy to chemical energy was ca. 0.04%, which approaches that for photosynthesis in a plant. Because this system can be applied to many other inorganic semiconductors and metal-complex catalysts, the efficiency and reaction selectivity can be enhanced by optimization of the electron transfer process including the energy-band configurations, conjugation conformations, and catalyst structures. This electrical-bias-free reaction is a huge leap forward for future practical applications of artificial photosynthesis under solar irradiation to produce organic species.

Morikawa, T.; Sato, S.; Arai, T.; Uemura, K.; Yamanaka, K. I.; Suzuki, T. M.; Kajino, T.; Motohiro, T.

2013-12-01

323

Catalytic Reduction of NO with CO on Active Carbon-Supported Copper, Manganese, and Copper–Manganese Oxides  

Microsoft Academic Search

The catalytic activity of copper, manganese, and copper–manganese oxide catalysts with respect to NO reduction with CO has been investigated in the temperature range 25–300°C. Copper–manganese oxide catalysts with Cu:Mn ratios of 1 : 2 and 1 : 1 where the two metals form spinel-like phases have shown the highest activity. With the three kinds of catalysts NO reduction proceeds

Neli B. Stankova; Mariana S. Khristova; Dimitar R. Mehandjiev

2001-01-01

324

Kinetics of microbial bromate reduction in a hydrogen-oxidizing, denitrifying biofilm reactor.  

PubMed

Bromate (BrO(3)(-)) is an oxidized contaminant produced from bromide (Br(-)) during ozonation and advanced oxidation of drinking water. Previous research shows that denitrifying bioreactors can reduce bromate to innocuous bromide. We studied a hydrogen-based, denitrifying membrane-biofilm reactor (MBfR) for bromate reduction, and report the first kinetics for a hydrogen-based bromate reduction process. A mixed-culture MBfR reduced up to 1,500 microg/L bromate to below 10 microg/L with a 50-min hydraulic residence time. Kinetics were determined using short-term tests on a completely mixed MBfR at steady state with an influent of 5 mg N/L nitrate plus 100 microg/L bromate. Short-term tests examined the impact of pH, nitrite, nitrate, and bromate on bromate reduction rates in the MBfR. Kinetic parameters for the process were estimated based on the short-term bromate tests. The q(max) for bromate reduction was 0.12 mg BrO(3)(-) x mg(x)(-1) x day(-1), and the K was 1.2 mg BrO(3)(-)/L. This q(max) is 2-3 times higher than reported for heterotrophic enrichments, and the K is the first reported in the literature. Nitrite and nitrate partially inhibited bromate reduction, with nitrite exerting a stronger inhibitory effect. Bromate was self-inhibitory at concentrations above 15 mg/L, but up to 50 mg/L of bromate had no inhibitory effect on denitrification. The optimum pH was approximately 7. We also examined the performance of an MBfR containing pure culture of the denitrifying bacterium Ralstonia eutropha. Under conditions similar to the mixed-culture tests, no bromate reduction was detected, showing that not all denitrifying bacteria are active in bromate reduction. Our results suggest the presence of specialized, dissimilatory bromate-reducing bacteria in the mixed-culture MBfR. PMID:17405178

Downing, Leon S; Nerenberg, Robert

2007-10-15

325

Simulation of reduction of iron-oxide-carbon composite pellets in a rotary hearth furnace  

NASA Astrophysics Data System (ADS)

The primary motivation of this work is to evaluate a new alternative ironmaking process which involves the combination of a Rotary Hearth Furnace (RHF) with an iron bath smelter. This work is concerned primarily, with the productivity of the RHF. It is known that the reduction in the RHF is controlled by chemical kinetics of the carbon oxidation and wustite reduction reactions as well as by heat transfer to the pellet surface and within the pellet. It is heat transfer to the pellet which limits the number of layers of pellets in the pellet bed in the RHF and thus, the overall productivity. Different types of carbon like graphite, coal-char and wood charcoal were examined. Part of the research was to investigate the chemical kinetics by de-coupling it from the influence of heat and mass transfer. This was accomplished by carrying out reduction experiments using small iron-oxide-carbon powder composite mixtures. The reaction rate constants were determined by fitting the experimental mass loss with a mixed reaction model. This model accounts for the carbon oxidation by CO2 and wustite reduction by CO, which are the primary rate controlling surface-chemical reactions in the composite system. The reaction rate constants have been obtained using wustite-coal-char powder mixtures and wustite-wood-charcoal mixtures. The wustite for these mixtures was obtained from two iron-oxide sources: artificial porous analytical hematite (PAH) and hematite ore tailings. In the next phase of this study, larger scale experiments were conducted in a RHF simulator using spherical composite pellets. Measurement of the reaction rates was accomplished using off-gas analysis. Different combinations of raw materials for the pellets were investigated. These included artificial ferric oxide as well as naturally existing hematite and taconite ores. Graphite, coal-char and wood-charcoal were the reductants. Experiments were conducted using a single layer, a double layer and a triple layer of composite pellets to look into the different aspects associated with multi-layer reduction in the RHF. The reduced pellets were examined for morphology and phase distribution using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. Efforts were made to interpret the differences in the observed rates from one kind of pellet to the other on the grounds of chemical kinetics of the carbon oxidation and wustite reduction reactions and the issues of external and internal heat transport to and within the pellets. It was concluded from the experiments that in the ore containing pellets, wood-charcoal appeared to be a faster reductant than coal-char. However, in the PAH containing pellets, the reverse was found to be true. This is because of the internal heat transport limitations imposed by two factors (a) lower thermal conductivity of wood-charcoal in comparison to coal-char and (b) swelling of the PAH-Wood-Charcoal pellets during the initial heat-up stage. For the same type of reductant, hematite containing pellets were observed to reduce faster than taconite containing pellets. This is in accordance with the higher reducibility of hematite because of development of internal porosity due to cracking and fissure formation during the Fe2O3 to Fe 3O4 transformation stage. This is however, absent during the reduction of taconite, which is primarily Fe3O4. The PAH-Wood-Charcoal pellets were found to undergo significant amounts of swelling under low temperature conditions. This behavior of the PAH-Wood-Charcoal pellets of a certain layer impeded the external heat transport to the lower layer and consequently, resulted in a relatively lower reduction rate for a multi-layer bed. The volume change phenomena associated with the reduction of composites were also studied. Volume changes influence the external heat transport, especially to the lower layers of a multi-layer bed. The volume change of the different kinds of composite pellets was studied as a function of reduction temperature and time. Empirical correlations were developed associating the volume

Halder, Sabuj

326

Giant refractive-index modulation by two-photon reduction of fluorescent graphene oxides for multimode optical recording  

PubMed Central

Graphene oxides (GOs) have emerged as precursors offering the potential of a cost-effective and large-scale production of graphene-based materials. Despite that their intrinsic fluorescence property has already brought interest of researchers for optical applications, to date, refractive-index modulation as one of the fundamental aspects of optical properties of GOs has received less attention. Here we reported on a giant refractive-index modulation on the order of 10?2 to 10?1, accompanied by a fluorescence intensity change, through the two-photon reduction of GOs. These features enabled a mechanism for multimode optical recording with the fluorescence contrast and the hologram-encoded refractive-index modulation in GO-dispersed polymers for security-enhanced high-capacity information technologies. Our results show that GO-polymer composites may provide a new material platform enabling flexible micro-/nano-photonic information devices. PMID:24085266

Li, Xiangping; Zhang, Qiming; Chen, Xi; Gu, Min

2013-01-01

327

Enhanced Oxygen Reduction Activity In Acid By Tin-Oxide Supported Au Nanoparticle Catalysts  

SciTech Connect

Gold nanoparticles supported on hydrous tin-oxide (Au-SnO{sub x}) are active for the four-electron oxygen reduction reaction in an acid electrolyte. The unique electrocatalytic of the Au-SnO is confirmed by the low amount of peroxide detected with rotating ring-disk electrode voltammetry and Koutecky-Levich analysis. In comparison, 10 wt % Au supported on Vulcan carbon and SnO{sub x} catalysts both produce significant peroxide in the acid electrolyte, indicating only a two-electron reduction reaction. Characterization of the Au-SnO{sub x} catalyst reveals a high-surface area, amorphous support with 1.7 nm gold metal particles. The high catalytic activity of the Au-SnO is attributed to metal support interactions. The results demonstrate a possible path to non-Pt catalysts for proton exchange membrane fuel cell cathodes.

Baker,W.; Pietron, J.; Teliska, M.; Bouwman, P.; Ramaker, D.; Swider-Lyons, K.

2006-01-01

328

Potential reduction exposure products and FDA tobacco and regulation: a CNS call to action.  

PubMed

A new generation of tobacco harm reduction products is stirring controversy and confusion among healthcare providers. These products, known as "potential reduction exposure products" (PREPs), can be described in terms of reported scientific evidence, as "the good, the bad, and the ugly." On the good side, there is sufficient scientific evidence to support the use of Commit, a new over-the-counter nicotine lozenge PREP, approved for smoking cessation. On the bad side, there is no scientific evidence to support the use of Ariva, another over-the-counter nicotine lozenge PREP, marketed as an alternative to cigarettes when smoking is restricted. On the ugly side, both of these PREPs are nicotine delivery systems with "candy-like" appearances; however, one (Commit) has the Food and Drug Administration (FDA) approval and the other (Ariva) does not. This article provides an overview of PREPs and strategies to help clinical nurse specialists (CNSs) address tobacco harm reduction issues. PMID:15061445

Heath, Janie; Andrews, Jeannette; Balkstra, Cindy R

2004-01-01

329

Favorite Demonstration: Demonstrating Indigo Carmine Oxidation-Reduction Reactions--A Choreography for Chemical Reactions  

NSDL National Science Digital Library

The indigo carmine demonstration (Ferguson et al. 1973), also referred to as a traffic-light demonstration (Flinn Scientific 2007a), is an example of a set of oxidation-reduction reactions that occurs within one solution. This type of demonstration can be used to introduce the concept of chemical reaction to undergraduate nonscience majors. Through their observations guided by the instructor, students begin to develop and construct the following concepts: color changes, reaction rates, reversible reactions, energy requirements (endothermic/exothermic), and equilibrium.

Majerich, David M.; Schmuckler, Joseph S.

2008-03-01

330

Investigation of NOx Reduction by Low Temperature Oxidation Using Ozone Produced by Dielectric Barrier Discharge  

NASA Astrophysics Data System (ADS)

NOx reduction by low temperature oxidation using ozone produced by a dielectric barrier discharge generator is investigated for different process parameters in a 6 m long reactor in serpentine arrangement using synthetic dry flue gas with NOx levels below 500 ppm, flows up to 50 slm and temperatures up to 80 °C. The role of different mixing schemes and the impact of a steep temperature gradient are also taken into consideration. The process chemistry is monitored by Fourier transform infrared spectroscopy, chemiluminescence and absorption spectroscopy. The kinetic mechanism during the mixing in a cross flow configuration is investigated using three-dimensional simulations.

Stamate, Eugen; Irimiea, Cornelia; Salewski, Mirko

2013-05-01

331

Reversibly phototunable TiO{sub 2} photonic crystal modulated by Ag nanoparticles' oxidation/reduction  

SciTech Connect

We report a reversibly phototunable photonic crystal system whose reflectance at the stop band position can be modulated by alternating UV/visible (UV/Vis) irradiation. The phototunable system consists of Ag nanoparticles and TiO{sub 2} photonic crystal. The stop bands intensity of Ag loaded TiO{sub 2} photonic crystals were found to be dependent on the redox states of Ag nanoparticles. The quasi 'on' and 'off' states of the stop band were reversibly modulated by the Ag nanoparticles' oxidation/reduction through alternating UV/Vis light irradiation.

Liu Jian; Zhou Jinming; Ye Changqing [Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Laboratory of New Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Graduate University of Chinese Academy of Sciences, Beijing 100049 (China); Li Mingzhu; Wang Jingxia; Jiang Lei; Song Yanlin [Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Laboratory of New Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

2011-01-10

332

Surface-layer formation by reductive decomposition of LiPF6 at relatively high potentials on negative electrodes in lithium ion batteries and its suppression  

NASA Astrophysics Data System (ADS)

In using a LiPF6/ethylene carbonate-dimethyl carbonate electrolyte for lithium ion batteries (LIBs), a certain reductive reaction is known to occur at a relatively high potential (ca. 2.6 V vs. Li+/Li) on Sn electrode, but its details are still unknown. By means of in-situ X-ray reflectometry, X-ray photoelectron spectroscopy, scanning electron microscopy observations and electrochemical measurements (by using mainly Sn electrode, and additionally Pt, graphite electrodes), we have found out that this reduction eventually forms an inactive passivation-layer consisting mainly of insulative LiF ascribed to the reductive decomposition of LiPF6, which significantly affects the battery cyclability. In contrast, a solid-electrolyte interphase (SEI) is formed by the reductive reaction of the solvent at ca. 1.5 V vs. Li+/Li, which is lower than the reduction potential of LiPF6. However, we have found that the formation of SEI preempts that of the passivation layer when holding the electrode at a potential lower than 1.5 V vs. Li+/Li. Consequently, the cyclability is improved by suppressing the formation of the inactive passivation layer. Such a pretreatment would be quite effective on improvement of the battery cyclability, especially for a relatively noble electrode whose oxidation potential is between 1.5 V and 2.6 V vs. Li+/Li.

Kawaguchi, Tomoya; Shimada, Koki; Ichitsubo, Tetsu; Yagi, Shunsuke; Matsubara, Eiichiro

2014-12-01

333

Carbohydrate oxidation coupled to Fe(III) reduction, a novel form of anaerobic metabolism  

USGS Publications Warehouse

An isolate, designated GC-29, that could incompletely oxidize glucose to acetate and carbon dioxide with Fe(III) serving as the electron acceptor was recovered from freshwater sediments of the Potomac River, Maryland. This metabolism yielded energy to support cell growth. Strain GC-29 is a facultatively anaerobic, Gram-negative motile rod which, in addition to glucose, also used sucrose, lactate, pyruvate, yeast extract, casamino acids or H2 as alternative electron donors for Fe(III) reduction. Stain GC-29 could reduce NO-3, Mn(IV), U(VI), fumarate, malate, S2O32-, and colloidal S0 as well as the humics analog, 2,6-anthraquinone disulfonate. Analysis of the almost complete 16S rRNA sequence indicated that strain GC-29 belongs in the Shewanella genus in the epsilon subdivision of the Proteobacteria. The name Shewanella saccharophilia is proposed. Shewanella saccharophilia differs from previously described fermentative microorganisms that metabolize glucose with the reduction of Fe(III) because it transfers significantly more electron equivalents to Fe(III); acetate and carbon dioxide are the only products of glucose metabolism; energy is conserved from Fe(III) reduction; and glucose is not metabolized in the absence of Fe(III). The metabolism of organisms like S. saccharophilia may account for the fact that glucose is metabolized primarily to acetate and carbon dioxide in a variety of sediments in which Fe(III) reduction is the terminal electron accepting process.

Coates, J.D.; Councell, T.; Ellis, D.J.; Lovley, D.R.

1998-01-01

334

Graphene oxide-facilitated reduction of nitrobenzene in sulfide-containing aqueous solutions.  

PubMed

The main objective of this study was to test the possibility that graphene-based nanomaterials can mediate environmentally relevant abiotic redox reactions of organic contaminants. We investigated the effect of graphene oxide (GO) on the reduction of nitrobenzene by Na2S in aqueous solutions. With the presence of GO (typically 5 mg/L), the observed pseudofirst-order rate constant (kobs) for the reduction of nitrobenzene was raised by nearly 2 orders of magnitude (from 7.83 × 10(-5) h(-1) to 7.77 × 10(-3) h(-1)), strongly suggesting reaction mediation by GO. As reflected by the combined spectroscopic analyses, GO was reduced in the beginning of the reaction, and hence the reduced GO (RGO) mediated the reduction of nitrobenzene. It was proposed that the zigzag edges of RGO acted as the catalytic active sites, while the basal plane of RGO served as the conductor for the electron transfer during the catalytic process. Furthermore, changing the pH (5.9-9.1) and the presence of dissolved humic acid (10 mg TOC/L) were found to greatly influence the catalytic activity of RGO. The results imply that graphene-based nanomaterials may effectively mediate the reductive transformation of nitroaromatic compounds and can contribute to the natural attenuation and remediation of these chemicals. PMID:23561007

Fu, Heyun; Zhu, Dongqiang

2013-05-01

335

Temperature and pH effect on reduction of graphene oxides in aqueous solution  

NASA Astrophysics Data System (ADS)

Reduced graphene oxides (RGOs) have usually been obtained by hydrazine reduction, but hydrazine-related compounds are corrosive, highly flammable and very hazardous, and the obtained RGOs heavily aggregated. Here we investigated extensively the effect of temperature and pH value on the structure of RGOs in hydrothermal environments without any reducing agents. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra showed that reduction rate of GOs remarkably increased with the temperature from 100 to 180 °C and with pH value from 3 to 10. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) exhibited the structural transition of the RGOs. Energy-dispersive x-ray analysis (EDX) showed the reduction degree of the RGO samples quantitatively. The results demonstrate that the GOs can be reduced controllably by a hydrothermal reduction process at pH value of 10 at 140 °C, and the large-scale RGOs are cut into small nanosheets with size from several to a few tens of nanometers with increasing temperature and duration. This study provides a feasible approach to controllably reduce GO with different nanostructures such as porous structures and quantum dots for applications in optoelectronics and biomedicals.

Tai, Guoan; Zeng, Tian; Li, Hongxiang; Liu, Jinsong; Kong, Jizhou; Lv, Fuyong

2014-09-01

336

Preparation of reduced graphene oxide by infrared irradiation induced photothermal reduction.  

PubMed

We present a green and scalable route toward the formation of reduced graphene oxide (r-GO) by photothermal reduction induced by infrared (IR) irradiation, utilizing a bathroom IR lamp as the source of IR light. Thermogravimetric analysis, Raman, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirm the reduction of r-GO by IR light. Ultraviolet-visible-infrared spectra indicate that adsorption of IR light by original GO films is less than that of UV and visible light; but when GO is exposed to IR light, its adsorption of IR light increases very rapidly with time. The influence of the power density of the IR light on the structure and properties of r-GO was investigated. At high IR power density, the reduction reaction was so fierce that r-GO became highly porous due to the rapid degassing and exfoliation of GO sheets. The r-GO powder revealed good performance as the anode material for lithium ion batteries. At relatively low IR power density, the reduction process was found to be mild but relatively slow. Crack-free and uniform conductive r-GO thin films with a volume conductivity of 1670 S m(-1) were then prepared by two-step IR irradiation, i.e. first at low IR power density and then at high IR power density. Moreover, the r-GO films were also observed to exhibit obvious and reversible IR light-sensing behavior. PMID:23934578

Guo, Honglei; Peng, Mao; Zhu, Zhongming; Sun, Lina

2013-10-01

337

Electrocatalytic oxidation of methanol on Pt catalyst supported on nitrogen-doped graphene induced by hydrazine reduction  

NASA Astrophysics Data System (ADS)

Hydrazine is often used to reduce graphene oxide (GO) to produce graphene. Recent observations suggested that when hydrazine is used to reduce GO, the resulting reduced graphene actually contains certain amounts of nitrogen dopants, which may influence the properties of the obtained material, and in some cases may be deployed for beneficial advantage. In this work, we prepared graphene oxide by the chemical oxidation method, then used either hydrazine or sodium borohydride (as a control) to reduce the graphene oxide to graphene and to explore the nature of the nitrogen functionalities introduced by hydrazine reduction. Pt nanoparticles were then deposited on the nitrogen doped (hydrazine-reduced) and undoped (control) graphene substrates, and the morphology, structure, and electrocatalytic methanol oxidation activity were characterized and evaluated. The results show that the nitrogen functional groups introduced into the graphene by hydrazine reduction greatly improve the electrocatalytic activity of the underlying Pt nanoparticles towards the methanol oxidation reaction.

Zhao, Yuanyuan; Zhou, Yingke; O'Hayre, Ryan; Shao, Zongping

2013-11-01

338

Synthesis of Pt-Ni/graphene via in situ reduction and its enhanced catalyst activity for methanol oxidation.  

PubMed

A simple in situ reduction approach was used to obtain Pt3Ni/reduced graphene oxide (rGO) with dominant {111} facets. The catalytic activity of Pt-Ni/rGO toward methanol electro-oxidation was studied by performing cyclic voltammetry. The Pt3Ni/rGO nanocatalysts exhibited improved catalytic activity and durability. PMID:23863973

Li, Lihong; Wu, Yuen; Lu, Jun; Nan, Caiyun; Li, Yadong

2013-09-01

339

A high pressure X-ray photoelectron spectroscopy study of oxidation and reduction of Rh(100) and Rh nanoparticles  

NASA Astrophysics Data System (ADS)

We have studied the oxidation and reduction of Rh(100) and SiO2 supported Rh particles using high pressure X-ray photoelectron spectroscopy. We show that the formation and reduction of Rh bulk oxide can be followed in situ in O2 and CO pressures in the range of 0.1 Torr. In general, the oxidation/reduction processes are similar on Rh(100) and the nanoparticles, but there are significant differences in temperature dependence. Already at a sample temperature of 140 °C, the particles show clear signs of a thin bulk oxide, while an ultra-thin so-called surface oxide covers the single crystal at the same temperature. Both of these oxide films, however, hinder further oxidation, and a thick oxide is only found at a temperature of at least 300 °C, for both samples. The reduction, in contrast, starts at a higher temperature on the particles as compared to the single crystal, but once started the particles are completely reduced at lower temperatures.

Blomberg, S.; Westerström, R.; Martin, N. M.; Lundgren, E.; Andersen, J. N.; Messing, M. E.; Gustafson, J.

2014-10-01

340

Accurate oxidation potentials of 40 benzene and biphenyl derivatives with heteroatom substituents.  

PubMed

The redox equilibrium method was used to determine accurate oxidation potentials in acetonitrile for 40 heteroatom-substituted compounds. These include methoxy-substituted benzenes and biphenyls, aromatic amines, and substituted acetanilides. The redox equilibrium method allowed oxidation potentials to be determined with high precision (? ±6 mV). Whereas most of the relative oxidation potentials follow well-established chemical trends, interestingly, the oxidation potentials of substituted N-methylacetanilides were found to be higher than those of the corresponding acetanilides. Density functional theory calculations provided insight into the origin of these surprising results in terms of the preferred conformations of the amides versus their cation radicals. PMID:25184671

Luo, Pu; Feinberg, Adam M; Guirado, Gonzalo; Farid, Samir; Dinnocenzo, Joseph P

2014-10-01

341

HYDROGEN-BASED, HOLLOW-FIBER MEMBRANE BIOFILM REACTOR FOR REDUCTION OF PERCHLORATE AND OTHER OXIDIZED CONTAMINANTS  

E-print Network

HYDROGEN-BASED, HOLLOW-FIBER MEMBRANE BIOFILM REACTOR FOR REDUCTION OF PERCHLORATE AND OTHER tested a hydrogen-based, hollow-fiber membrane biofilm reactor (MBfR) for reduction of perchlorate these and other oxidized contaminants in drinking water. Key Words: Biofilm reactor, hollow-fiber membrane

Nerenberg, Robert

342

Monoclinic hafnium oxynitride supported on reduced graphene oxide to catalyse the oxygen reduction reaction in acidic media.  

PubMed

Monoclinic HfO2 nanoparticles were doped with nitrogen via hydrothermal treatment that avoided high-cost pyrolysis with NH3 gas in order to develop a novel oxygen reduction reaction catalyst for use in acidic media. Catalyst size reduction was achieved using a reduced graphene oxide support, and activity above 0.8 V was obtained. PMID:25167377

Chisaka, M; Sasaki, H; Muramoto, H

2014-10-14

343

Formation of Green Rust and Immobilization of Nickel in Response to Bacterial Reduction of Hydrous Ferric Oxide  

SciTech Connect

This investigation documents the formation of Green Rust (GR) and immobilization of Ni2+ in response to bacterial reduction of hydrous ferric oxide (HFO) reduction experiments provided evidence that the solid-phase partitioning of Ni2+ in GR extended from equilibrium solid-solution behavior.

Parmar, N.; Gorby, Yuri A.; Beveridge, Terrance J.; Ferris, F G.

2001-04-01

344

Potential reduction of en route noise from an advanced turboprop aircraft  

NASA Technical Reports Server (NTRS)

When the en route noise of a representative aircraft powered by an eight-blade SR-7 propeller was previously calculated, the noise level was cited as a possible concern associated with the acceptance of advanced turboprop aircraft. Some potential methods for reducing the en route noise were then investigated and are reported. Source noise reductions from increasing the blade number and from operating at higher rotative speed to reach a local minimum noise point were investigated. Greater atmospheric attenuations for higher blade passing frequencies were also indicated. Potential en route noise reductions from these methods were calculated as 9.5 dB (6.5 dB(A)) for a 10-blade redesigned propeller and 15.5 dB (11 dB(A)) for a 12-blade redesigned propeller.

Dittmar, James H.

1990-01-01

345

Mechanism of flavin reduction and oxidation in the redox-sensing quinone reductase Lot6p from Saccharomyces cerevisiae†  

PubMed Central

Quinone reductases are flavin-containing enzymes that have been implicated in protecting organisms from redox stress and, more recently, as redox switches controlling the action of the proteasome. The reactions of the catalytic cycle of the dimeric quinone reductase Lot6p from Saccharomyces cerevisiae were studied in anaerobic stopped-flow experiments at 4° C. Both NADH and NADPH reacted similarly, reducing the FMN prosthetic group rapidly at saturation, but binding with very low affinity. The enzyme stereospecifically transferred the proS-hydride of NADPH with an isotope effect of 3.6, indicating that hydride transfer, and not an enzyme conformational change, is rate-determining in the reductive half-reaction. No intermediates such as charge-transfer complexes were detected. In the oxidative half-reaction, reduced enzyme reacted in a single phase with the six quinone substrates tested. The observed rate constants increased linearly with quinone concentration up to the limits allowed by solubility, indicating either a bimolecular reaction or very weak binding. The logarithm of the bimolecular rate constant increase linearly with the reduction potential of the quinone, consistent with the notion that quinone reductases strongly disfavor radical intermediates. Interestingly, both half-reactions of the catalytic cycle strongly resemble bioorganic model reactions; the reduction of Lot6p by NAD(P)H is moderately faster than non-enzymatic models, while the oxidation of Lot6p by quinones is actually slower than non-enzymatic reactions. This curious situation is consistent with the structure of Lot6p, which has a crease we propose to be the binding site for pyridine nucleotides, and space – but no obvious catalytic residues – near the flavin allowing the quinone to react. The decidedly sub-optimized catalytic cycle suggests that selective pressures other than maximizing quinone consumption shaped the evolution of Lot6p. This may reflect the importance of suppressing other potentially deleterious side-reactions, such as oxygen reduction, or it may indicate that the role Lot6p plays as a redox sensor in controlling the proteasome is more important than its role as a detoxifying enzyme. PMID:19618916

Sollner, Sonja; Deller, Sigrid; Macheroux, Peter; Palfey, Bruce A.

2010-01-01

346

The noise reduction potential of dual-stream coaxial rectangular improperly expanded jet flows  

NASA Technical Reports Server (NTRS)

The research performed began during Spring 1991 as a project to assess the noise reduction potential of rectangular coaxial nozzle configurations for improperly expanded jets. The research plan consisted of: (1) design of coaxial rectangular nozzle configuration by Syracuse graduate research assistant; (2) construction of nozzles by NASA Langley machinists; and (3) acquisition of preliminary acoustic and optical data for a variety of inner and outer jet pressure ratios.

Dosanjh, Darshan; Spina, Eric F.

1995-01-01

347

Calculating energy-saving potentials of heat-island reduction strategies  

Microsoft Academic Search

We have developed summary tables (sorted by heating- and cooling-degree-days) to estimate the potential of heat-island reduction (HIR) strategies (i.e., solar-reflective roofs, shade trees, reflective pavements, and urban vegetation) to reduce cooling-energy use in buildings. The tables provide estimates of savings for both direct effect (reducing heat gain through the building shell) and indirect effect (reducing the ambient air temperature).In

H. Akbari; S. Konopacki

2005-01-01

348

Symmetries and Special Solutions of Reductions of the Lattice Potential KdV Equation  

NASA Astrophysics Data System (ADS)

We identify a periodic reduction of the non-autonomous lattice potential Korteweg-de Vries equation with the additive discrete Painlevé equation with E_6^{(1)} symmetry. We present a description of a set of symmetries of the reduced equations and their relations to the symmetries of the discrete Painlevé equation. Finally, we exploit the simple symmetric form of the reduced equations to find rational and hypergeometric solutions of this discrete Painlevé equation.

Ormerod, Christopher M.

2014-01-01

349

CO 2 reduction potentials by utilizing waste plastics in steel works  

Microsoft Academic Search

Background, aim, and scope  Feedstock recycling has received attention as an effective method to recycle waste plastics. However, estimating the reduction\\u000a potential by life cycle assessment using coke oven and blast furnace in steel works has been a challenging task due to the\\u000a complex structure of energy flow in steel works. Municipal waste plastics consist of several plastic resins. Previous studies

Yu Sekine; Koichi Fukuda; Kenji Kato; Yoshihiro Adachi; Yasunari Matsuno

2009-01-01

350

Computational study of anomalous reduction potentials for hydrogen evolution catalyzed by cobalt dithiolene complexes.  

PubMed

The design of efficient hydrogen-evolving catalysts based on earth-abundant materials is important for developing alternative renewable energy sources. A series of four hydrogen-evolving cobalt dithiolene complexes in acetonitrile-water solvent is studied with computational methods. Co(mnt)(2) (mnt = maleonitrile-2,3-dithiolate) has been shown experimentally to be the least active electrocatalyst (i.e., to produce H(2) at the most negative potential) in this series, even though it has the most strongly electron-withdrawing substituents and the least negative Co(III/II) reduction potential. The calculations provide an explanation for this anomalous behavior in terms of protonation of the sulfur atoms on the dithiolene ligands after the initial Co(III/II) reduction. One fewer sulfur atom is protonated in the Co(II)(mnt)(2) complex than in the other three complexes in the series. As a result, the subsequent Co(II/I) reduction step occurs at the most negative potential for Co(mnt)(2). According to the proposed mechanism, the resulting Co(I) complex undergoes intramolecular proton transfer to form a catalytically active Co(III)-hydride that can further react to produce H(2). Understanding the impact of ligand protonation on electrocatalytic activity is important for designing more effective electrocatalysts for solar devices. PMID:22954257

Solis, Brian H; Hammes-Schiffer, Sharon

2012-09-19

351

Reduction of stress-induced leakage currents in thin oxides by application of a low post-stress gate bias  

NASA Astrophysics Data System (ADS)

We have observed that stress-induced leakage currents (SILC) in thin gate oxides (4.5 nm) could be reduced by applying a low gate bias to the oxides after stress, regardless of the polarity of the applied gate bias. The reduction of SILC increased with the applied gate bias and began to saturate after 105 s. In addition, the reduction of SILC was significantly enhanced in a hydrogen ambient, suggesting a strong link between the reduction of SILC and trapped-hole annealing.

Ang, C. H.; Ling, C. H.; Cheng, Z. Y.; Cho, B. J.; Kim, S. J.

2000-09-01

352

Intracellular distribution of the reductive and oxidative pentose phosphate pathways in two diatoms.  

PubMed

Diatoms contribute a large proportion to the worldwide primary production and are particularly effective in fixing carbon dioxide. Possibly because diatom plastids originate from a secondary endocytobiosis, their cellular structure is more complex and metabolic pathways are rearranged within diatom cells compared to cells containing primary plastids. We annotated genes encoding isozymes of the reductive and oxidative pentose phosphate pathways in the genomes of the centric diatom Thalassiosira pseudonana and the pennate diatom Phaeodactylum tricornutum and bioinformatically inferred their intracellular distribution. Prediction results were confirmed by fusion of selected presequences to Green Fluorescent Protein and expression of these constructs in P. tricornutum. Calvin cycle enzymes for the carbon fixation and reduction of 3-phosphoglycerate are present in single isoforms, while we found multiple isoenzymes involved in the regeneration of ribulose-1,5-bisphosphate. We only identified one cytosolic sedoheptulose-1,7-bisphosphatase in both investigated diatoms. The oxidative pentose phosphate pathway seems to be restricted to the cytosol in diatoms, since we did not find stromal glucose-6-phosphate dehydrogenase and 6-phosphogluconolactone dehydrogenase isoforms. However, the two species apparently possess a plastidic phosphogluconolactonase. A 6-phosphogluconolactone dehydrogenase is apparently plastid associated in P. tricornutum and might be active in the periplastidic compartment, suggesting that this compartment might be involved in metabolic processes in diatoms. PMID:19206144

Gruber, Ansgar; Weber, Till; Bártulos, Carolina Río; Vugrinec, Sascha; Kroth, Peter G

2009-02-01

353

Microbially mediated re-oxidation of sulfide during dissimilatory sulfate reduction by Desulfobacter latus  

NASA Astrophysics Data System (ADS)

Enzymatic reactions during dissimilatory sulfate reduction (DSR) are often treated as unidirectional with respect to dissolved sulfide. However, quantitative models describing kinetic sulfur isotope fractionations during DSR consider the individual enzymatic reactions as reversible ( Rees, 1973). Brunner and Bernasconi (2005) extended this line of thought, and suggested that as long as cell external sulfide (CES) concentrations are high enough, CES may diffuse back across the cytoplasmic cell membrane and may subsequently be re-oxidized to sulfate. Here, we test this hypothesis by measuring the time evolution of the ?34S-sulfate signal during DSR in closed system experiments under different levels of sulfide stress (0-20 mM and 0-40 mM total dissolved sulfide). Our results show that the measured ?34S-sulfate signal is markedly different in the latter case and that the observed sulfate S-isotope time-evolution is incompatible with a Rayleigh type fractionation model. In contrast, our results are consistent with a sulfate reduction and fractionation model that allows for a cell internal oxidation of dissolved sulfide by a sulfate reducer.

Eckert, T.; Brunner, B.; Edwards, E. A.; Wortmann, U. G.

2011-06-01

354

Supported transition-metal oxide catalysts for reduction of sulfur dioxide with hydrogen to elemental sulfur.  

PubMed

This work is for the purpose to find a high performance catalyst for the catalytic reduction of SO2 with H2 as a reducing agent. NiO/gamma-Al2O3 catalyst was found to be the most active catalyst among the seven gamma-Al2O3-supported metal-oxide catalysts tested. With NiO as the active species, of the supports tested, gamma-Al2O3 was the most suitable one and the optimal Ni content was 16 wt%. Using this NiO/gamma-Al2O3 catalyst, we found that the optimal feed ratio of H2/SO2 is 2:1 and the catalyst presulfided with H2 + H2S exhibits a higher performance than that pretreated with H2 or He. XRD patterns reveal that the nickel oxide experienced a transformation to Ni3S2 and NiS, and then to NiS2, the most active nickel sulfide, during the reaction process. The reason for the highest catalyst activity of 16 wt% Ni was attributed to the largest amount of NiS2. Water vapor in the feed gas reactant caused inhibition of catalyst activity, whereas H2S promoted the reduction of SO2. These phenomena were rationalized with the aid of Claus reaction. PMID:15212907

Chen, Chun-Liang; Wang, Ching-Huei; Weng, Hung-Shan

2004-08-01

355

Submerged liquid plasma for the synchronized reduction and functionalization of graphene oxide.  

PubMed

Formation of reduced and functionalized graphene oxide (r-FGO) at ambient temperature and pressure is demonstrated by generating liquid plasma submerged in acetonitrile and graphene oxide solution. The partial restoration of conjugation (sp(2) domain) and insertion of fluorophores such as nitrile and amine in r-FGO displays enhanced fluorescence property. Presence of nitrile and amine in r-FGO are confirmed by X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy. Morphology and optical property of r-FGO are studied with transmission electron microscopy, scanning tunneling microscopy and Ultraviolet-visible spectroscopy measurements. The nitrile and amine present in r-FGO undergo a surface-controlled reversible redox reaction and sp(2)- enriched r-FGO acts as an electrical double layer, providing additional hybrid capacitance or pseudocapacitance. r-FGO shows high cyclic stability with a specific capacitance value of 349?F/g at the scan rate of 10?mV/s. Only marginal reduction of specific capacitance (<10% reduction) is observed at the end of 1000 cycles. PMID:24637779

Senthilnathan, Jaganathan; Liu, Yung-Fang; Rao, Kodepelly Sanjeeva; Yoshimura, Masahiro

2014-01-01

356

Submerged Liquid Plasma for the Synchronized Reduction and Functionalization of Graphene Oxide  

NASA Astrophysics Data System (ADS)

Formation of reduced and functionalized graphene oxide (r-FGO) at ambient temperature and pressure is demonstrated by generating liquid plasma submerged in acetonitrile and graphene oxide solution. The partial restoration of conjugation (sp2 domain) and insertion of fluorophores such as nitrile and amine in r-FGO displays enhanced fluorescence property. Presence of nitrile and amine in r-FGO are confirmed by X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy. Morphology and optical property of r-FGO are studied with transmission electron microscopy, scanning tunneling microscopy and Ultraviolet-visible spectroscopy measurements. The nitrile and amine present in r-FGO undergo a surface-controlled reversible redox reaction and sp2- enriched r-FGO acts as an electrical double layer, providing additional hybrid capacitance or pseudocapacitance. r-FGO shows high cyclic stability with a specific capacitance value of 349 F/g at the scan rate of 10 mV/s. Only marginal reduction of specific capacitance (<10% reduction) is observed at the end of 1000 cycles.

Senthilnathan, Jaganathan; Liu, Yung-Fang; Rao, Kodepelly Sanjeeva; Yoshimura, Masahiro

2014-03-01

357

Manganese sulfide formation via concomitant microbial manganese oxide and thiosulfate reduction  

SciTech Connect

The dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1 produced {gamma}-MnS (rambergite) nanoparticles during the concurrent reduction of MnO{sub 2} and thiosulfate coupled to H{sub 2} oxidation. To investigate effect of direct microbial reduction of MnO{sub 2} on MnS formation, two MR-1 mutants defective in outer membrane c-type cytochromes ({Delta}mtrC/{Delta}omcA and {Delta}mtrC/{Delta}omcA/{Delta}mtrF) were also used and it was determined that direct reduction of MnO{sub 2} was dominant relative to chemical reduction by biogenic sulfide generated from thiosulfate reduction. Although bicarbonate was excluded from the medium, incubations of strain MR-1 with lactate as the electron donor produced MnCO{sub 3} (rhodochrosite) as well as MnS in nearly equivalent amounts as estimated by micro X-ray diffraction (micro-XRD) analysis. It was concluded that carbonate released from lactate metabolism promoted MnCO{sub 3} formation and that Mn(II) mineralogy was strongly affected by carbonate ions even in the presence of abundant sulfide and weakly alkaline conditions expected to favor the precipitation of MnS. Formation of MnS, as determined by a combination of micro-XRD, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction analyses was consistent with equilibrium speciation modeling predictions. Biogenic manganese sulfide may be a manganese sink in the Mn biogeochemical cycle in select environments such as deep anoxic marine basins within the Baltic Sea.

Lee, Ji-Hoon; Kennedy, David W.; Dohnalkova, Alice; Moore, Dean A.; Nachimuthu, Ponnusamy; Reed, Samantha B.; Fredrickson, Jim K.

2011-12-13

358

Oxidative and reductive routes of glycerol and glucose fermentation by Escherichia coli batch cultures and their regulation by oxidizing and reducing reagents at different pHs.  

PubMed

Glycerol and glucose fermentation redox routes by Escherichia coli and their regulation by oxidizing and reducing reagents were investigated at different pHs. Cell growth was followed by decrease of pH and redox potential (E ( h )). During glycerol utilization at pH 7.5 ?pH, the difference between initial and end pH, was lower compared with glucose fermentation. After 8 h growth, during glycerol utilization E ( h ) dropped down to negative values (-150 mV) but during glucose fermentation it was positive (+50 mV). In case of glycerol H(2) was evolved at the middle log phase while during glucose fermentation H(2) was produced during early log phase. Furthermore, upon glycerol utilization, oxidizer potassium ferricyanide (1 mM) inhibited both cell growth and H(2) formation. Reducing reagents DL-dithiothreitol (3 mM) and dithionite (1 mM) inhibited growth but stimulated H(2) production. The findings point out the importance of reductive conditions for glycerol fermentation and H(2) production by E. coli. PMID:23053487

Poladyan, Anna; Avagyan, Arev; Vassilian, Anait; Trchounian, Armen

2013-01-01

359

Plant growth promotion traits and Cr (VI) reduction potentials of Cr (VI) resistant Streptomyces strains.  

PubMed

The most toxic form of chromium [Cr (VI)] can be converted to less toxic Cr (III) by reduction with the help of microbes. A total of 6 Streptomyces strains (S. matansis BG5, Streptomyces sp. RSF17, S. vinaceus CRF2, Streptomyces sp. CRF14, S. pulcher CRF17, S. griseoincarnatus SCF18) which were previously isolated from saline farmlands of Punjab, Pakistan, were used in this work. These strains showed varying levels of resistance to Cr (VI) from 800??g?ml(-1) to 1000?mg l(-1) . Their plant growth promoting and Cr (VI) reduction potentials were assessed. Two strains showed positive phosphate solubilization activity. All the strains had ability to produce indole acetic acid (IAA) except one strain (CRF17). The maximum production of IAA was observed by strain BG5 that was 16?mg l(-1) in the presence of 50?mg l(-1) of Cr (VI). All the strains were able to produce ammonia both in the absence and presence of Cr (VI). The highest Cr (VI) reduction in majority of the strains was observed at 28?°C and pH 9. The complete reduction of 150?mg l(-1) of Cr (VI) occurred after 168?hrs. The chromium (VI) concentration of 200?mg l(-1) could be reduced above 90% by most of these strains. The presence of other metals also enhanced Cr (VI) reduction by most of the strains. The results indicate the potential capacity of Streptomyces strains as tool for plant growth promotion and Cr (VI) bioremediation and also is the first report about plant growth promoting traits of Cr (VI) resistant Streptomyces strains. PMID:22736528

Javaid, Mahwish; Sultan, Sikander

2013-05-01

360

Uncertainty assessment of spatially distributed nitrate reduction potential in groundwater using multiple geological realizations  

NASA Astrophysics Data System (ADS)

Spatially distributed nitrate reduction potential in groundwater was estimated for the clay till dominated Norsminde fjord catchment in Denmark using the distributed hydrological model MIKE SHE. The nitrate transport was simulated using particle tracking and nitrate was assumed to be instantaneously reduced at the redox interface. Spatially distributed depths of the redox interface were estimated based on the spatial patterns in groundwater recharge and sediment redox capacity. Uncertainty of the estimated nitrate reduction due to geological uncertainty was assessed using multiple geological realizations. The geological realizations were generated using the geostatistical software TProGS and either conditioned based on borehole data only or soft conditioned based on both borehole data and geophysical data. Finally an upscaling of the predicted nitrate reduction was done in order to evaluate the change in uncertainty with increasing scale. The study showed that the uncertainty (one standard deviation) of the estimated nitrate reduction potential (in percentage of nitrate input) on the original 100 m model scale was 25% if only using borehole data and 19% if combining the borehole data with geophysical data. The uncertainty on the model predictions decreased with increasing aggregation scale. The decrease in uncertainty was most apparent the first 500 m, where after the uncertainty started to level off. This scale corresponded well to the mean length of the sand units within the clay till. It is concluded that using geophysical data in combination with borehole data in generation of geological realizations can help decrease uncertainty on the estimated nitrate reduction and that the predictive capability of distributed models is constrained by the spatial resolution of key data such as geology.

Hansen, A. L.; Gunderman, D.; He, X.; Refsgaard, J. C.

2014-11-01

361

Monitoring of the oxidation-reduction state of brain structures in freely moving rats during sleep-waking cycles by potentiometric recording.  

PubMed

Freely mobile mongrel male rats weighing 300-350 g were used for studies of changes in the oxidative-reductive (redox) state of brain tissue during cycles of waking, slow-wave sleep, and paradoxical sleep, by recording the potential of the oxidative-reductive state of brain tissue with platinum electrodes implanted into the cerebral cortex ad hippocampus. Electromyograms were also recorded from the cervical muscles, and overall movement activity was also recorded. A common platinum reference electrode was implanted into the nasal bones. These experiments showed that in rats, episodes of waking and paradoxical sleep occurred on the background of increases in the oxidation-reduction potential state of brain tissue at a series of brain points, which we termed "metabolically active." Transitions from waking and paradoxical sleep to slow-wave sleep were accompanied by decreases in the potential of the redox state. The magnitude of changes in the tissue redox state varied up to 100 mV. It is suggested that transitions from waking and paradoxical sleep to slow-wave sleep are accompanied by dynamic changes in the balance of brain tissue energy metabolism between the main energy sources. Oxidative phosphorylation dominates in waking and paradoxical sleep, while aerobic glycolysis dominates slow-wave sleep. We suggest that this latter should be interpreted as a decrease in the potential of the tissue redox state and the formation within the tissue of oscillations during slow-wave sleep. Formation of oscillations is typical for acceleration of glycolytic processes. Recently published data suggest that the major compartment or aerobic glycolysis is the astroglia. PMID:14552530

Shvets-Ténéta-Gurii, T B; Troshin, G I; Novikova, M R; Khonicheva, N M; Shostak, O A; Borovskaya, I V

2003-09-01

362

Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation  

NASA Astrophysics Data System (ADS)

La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state.

Paneva, D.; Dimitrov, M.; Velinov, N.; Kolev, H.; Kozhukharov, V.; Tsoncheva, T.; Mitov, I.

2010-03-01

363

Preparation of reduced graphene oxide by infrared irradiation induced photothermal reduction  

NASA Astrophysics Data System (ADS)

We present a green and scalable route toward the formation of reduced graphene oxide (r-GO) by photothermal reduction induced by infrared (IR) irradiation, utilizing a bathroom IR lamp as the source of IR light. Thermogravimetric analysis, Raman, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirm the reduction of r-GO by IR light. Ultraviolet-visible-infrared spectra indicate that adsorption of IR light by original GO films is less than that of UV and visible light; but when GO is exposed to IR light, its adsorption of IR light increases very rapidly with time. The influence of the power density of the IR light on the structure and properties of r-GO was investigated. At high IR power density, the reduction reaction was so fierce that r-GO became highly porous due to the rapid degassing and exfoliation of GO sheets. The r-GO powder revealed good performance as the anode material for lithium ion batteries. At relatively low IR power density, the reduction process was found to be mild but relatively slow. Crack-free and uniform conductive r-GO thin films with a volume conductivity of 1670 S m-1 were then prepared by two-step IR irradiation, i.e. first at low IR power density and then at high IR power density. Moreover, the r-GO films were also observed to exhibit obvious and reversible IR light-sensing behavior.We present a green and scalable route toward the formation of reduced graphene oxide (r-GO) by photothermal reduction induced by infrared (IR) irradiation, utilizing a bathroom IR lamp as the source of IR light. Thermogravimetric analysis, Raman, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirm the reduction of r-GO by IR light. Ultraviolet-visible-infrared spectra indicate that adsorption of IR light by original GO films is less than that of UV and visible light; but when GO is exposed to IR light, its adsorption of IR light increases very rapidly with time. The influence of the power density of the IR light on the structure and properties of r-GO was investigated. At high IR power density, the reduction reaction was so fierce that r-GO became highly porous due to the rapid degassing and exfoliation of GO sheets. The r-GO powder revealed good performance as the anode material for lithium ion batteries. At relatively low IR power density, the reduction process was found to be mild but relatively slow. Crack-free and uniform conductive r-GO thin films with a volume conductivity of 1670 S m-1 were then prepared by two-step IR irradiation, i.e. first at low IR power density and then at high IR power density. Moreover, the r-GO films were also observed to exhibit obvious and reversible IR light-sensing behavior. Electronic supplementary information (ESI) available: Video of photothermal reduction of GO, temperature of the GO-coated thermocouple and details on the structure and properties of GO films. See DOI: 10.1039/c3nr02805d

Guo, Honglei; Peng, Mao; Zhu, Zhongming; Sun, Lina

2013-09-01

364

Protein kinase g i? oxidation paradoxically underlies blood pressure lowering by the reductant hydrogen sulfide.  

PubMed

Dysregulated blood pressure control leading to hypertension is prevalent and is a risk factor for several common diseases. Fully understanding blood pressure regulation offers the possibility of developing rationale therapies to alleviate hypertension and associated disease risks. Although hydrogen sulfide (H2S) is a well-established endogenous vasodilator, the molecular basis of its blood-pressure lowering action is incompletely understood. H2S-dependent vasodilation and blood pressure lowering in vivo was mediated by it catalyzing formation of an activating interprotein disulfide within protein kinase G (PKG) I?. However, this oxidative activation of PKG I? is counterintuitive because H2S is a thiol-reducing molecule that breaks disulfides, and so it is not generally anticipated to induce their formation. This apparent paradox was explained by H2S in the presence of molecular oxygen or hydrogen peroxide rapidly converting to polysulfides, which have oxidant properties that in turn activate PKG by inducing the disulfide. These observations are relevant in vivo because transgenic knockin mice in which the cysteine 42 redox sensor within PKG has been systemically replaced with a redox-dead serine residue are resistant to H2S-induced blood pressure lowering. Thus, a primary mechanism by which the reductant molecule H2S lowers blood pressure is mediated somewhat paradoxically by the oxidative activation of PKG. PMID:25267801

Stubbert, Daniel; Prysyazhna, Oleksandra; Rudyk, Olena; Scotcher, Jenna; Burgoyne, Joseph R; Eaton, Philip

2014-12-01

365

Automatic selection of tube potential for radiation dose reduction in CT: A general strategy  

SciTech Connect

Purpose: To optimize radiation dose efficiency in CT while maintaining image quality, it is important to select the optimal tube potential. The selection of optimal tube potential, however, is highly dependent on patient size and diagnostic task. The purpose of this work was to develop a general strategy that allows for automatic tube potential selection for each individual patient and each diagnostic task. Methods: The authors propose a general strategy that allows automatic adaptation of the tube potential as a function of patient size and diagnostic task, using a novel index of image quality, ''iodine contrast to noise ratio with a noise constraint (iCNR{sub N}C),'' to characterize the different image quality requirements by various clinical applications. The relative dose factor (RDF) at each tube potential to achieve a target image quality was then determined as a function of patient size and the noise constraint parameter. A workflow was developed to automatically identify the optimal tube potential that is both dose efficient and practically feasible, incorporating patient size and diagnostic task. An experimental study using a series of semianthropomorphic thoracic phantoms was used to demonstrate how the proposed general strategy can be implemented and how the radiation dose reduction achievable by the tube potential selection depends on phantom sizes and noise constraint parameters. Results: The proposed strategy provides a flexible and quantitative way to select the optimal tube potential based on the patient size and diagnostic task. The noise constraint parameter {alpha} can be adapted for different clinical applications. For example, {alpha}=1 for noncontrast routine exams; {alpha}=1.1-1.25 for contrast-enhanced routine exams; and {alpha}=1.5-2.0 for CT angiography. For the five thoracic phantoms in the experiment, when {alpha}=1, the optimal tube potentials were 80, 100, 100, 120, 120, respectively. The corresponding RDFs (relative to 120 kV) were 78.0%, 90.9%, 95.2%, 100%, and 100%. When {alpha}=1.5, the optimal tube potentials were 80, 80, 80, 100, 100, respectively, with corresponding RDFs of 34.7%, 44.7%, 54.7%, 60.8%, and 89.5%. Conclusions: A general strategy to automatically select the most dose efficient tube potential for CT exams was developed that takes into account patient size and diagnostic task. Dependent on the patient size and the selection of noise constraint parameter for different diagnostic tasks, the dose reduction at each tube potential, quantified explicitly with the RDF, varies significantly.

Yu Lifeng; Li Hua; Fletcher, Joel G.; McCollough, Cynthia H. [Department of Radiology, Mayo Clinic, Rochester, Minnesota 55905 (United States)

2010-01-15

366

Thermal, solution and reductive decomposition of Cu-Al layered double hydroxides into oxide products  

SciTech Connect

Cu-Al layered double hydroxides (LDHs) with [Cu]/[Al] ratio 2 adopt a structure with monoclinic symmetry while that with the ratio 0.25 adopt a structure with orthorhombic symmetry. The poor thermodynamic stability of the Cu-Al LDHs is due in part to the low enthalpies of formation of Cu(OH){sub 2} and CuCO{sub 3} and in part to the higher solubility of the LDH. Consequently, the Cu-Al LDH can be decomposed thermally (150 deg. C), hydrothermally (150 deg. C) and reductively (ascorbic acid, ambient temperature) to yield a variety of oxide products. Thermal decomposition at low (400 deg. C) temperature yields an X-ray amorphous residue, which reconstructs back to the LDH on soaking in water or standing in the ambient. Solution decomposition under hydrothermal conditions yields tenorite at 150 deg. C itself. Reductive decomposition yields a composite of Cu{sub 2}O and Al(OH){sub 3}, which on alkali-leaching of the latter, leads to the formation of fine particles of Cu{sub 2}O (<1 {mu}m). - Graphical abstract: SEM image of (a) the Cu{sub 2}O-Al(OH){sub 3} composite obtained on reductive decomposition of CuAl{sub 4}-LDH and (b) Cu{sub 2}O obtained on leaching of Al(OH){sub 3} from (a).

Britto, Sylvia [Department of Chemistry, Central College, Bangalore University, Bangalore 560 001 (India); Vishnu Kamath, P., E-mail: vishnukamath8@hotmail.co [Department of Chemistry, Central College, Bangalore University, Bangalore 560 001 (India)

2009-05-15

367

Oxidation and reduction processes of platinum nanoparticles observed at the atomic scale by environmental transmission electron microscopy  

NASA Astrophysics Data System (ADS)

Oxidation and reduction of the surfaces of Pt nanoparticles were in situ examined in reactive gases (O2, CO and H2O vapor) by aberration-corrected environmental transmission electron microscopy. Atomic layers of Pt oxides were gradually formed on the surface of Pt nanoparticles at room temperature in O2. The surface Pt oxides were reduced to Pt promptly in both vacuum and gas including CO. We showed that H2O vapor suppressed the surface oxidation. The processes found in this study were induced by gases that were most likely activated by electron irradiation. The observation results provide atomistic insight into the oxidation and reduction process of the surface of Pt nanoparticles that is exposed to activated gases.

Yoshida, Hideto; Omote, Hiroki; Takeda, Seiji

2014-10-01

368

An Examination of Drag Reduction Mechanisms in Marine Animals, with Potential Applications to Uninhabited Aerial Vehicles  

NASA Technical Reports Server (NTRS)

Previous engineering research and development has documented the plausibility of applying biomimetic approaches to aerospace engineering. Past cooperation between the Virginia Institute of Marine Science (VIMS) and NASA focused on the drag reduction qualities of the microscale dermal denticles of shark skin. This technology has subsequently been applied to submarines and aircraft. The present study aims to identify and document the three-dimensional geometry of additional macroscale morphologies that potentially confer drag reducing hydrodynamic qualities upon marine animals and which could be applied to enhance the range and endurance of Uninhabited Aerial Vehicles (UAVs). Such morphologies have evolved over eons to maximize organismal energetic efficiency by reducing the energetic input required to maintain cruising speeds in the viscous marine environment. These drag reduction qualities are manifested in several groups of active marine animals commonly encountered by ongoing VIMS research programs: namely sharks, bony fishes such as tunas, and sea turtles. Through spatial data acquired by molding and digital imagery analysis of marine specimens provided by VIMS, NASA aims to construct scale models of these features and to test these potential drag reduction morphologies for application to aircraft design. This report addresses the efforts of VIMS and NASA personnel on this project between January and November 2001.

Musick, John A.; Patterson, Mark R.; Dowd, Wesley W.

2002-01-01

369

Selective catalysts for the hydrogen oxidation and oxygen reduction reactions by patterning of platinum with calix[4]arene molecules  

NASA Astrophysics Data System (ADS)

The design of new catalysts for polymer electrolyte membrane fuel cells must be guided by two equally important fundamental principles: optimization of their catalytic behaviour as well as the long-term stability of the metal catalysts and supports in hostile electrochemical environments. The methods used to improve catalytic activity are diverse, ranging from the alloying and de-alloying of platinum to the synthesis of platinum core-shell catalysts. However, methods to improve the stability of the carbon supports and catalyst nanoparticles are limited, especially during shutdown (when hydrogen is purged from the anode by air) and startup (when air is purged from the anode by hydrogen) conditions when the cathode potential can be pushed up to 1.5V (ref. 11). Under the latter conditions, stability of the cathode materials is strongly affected (carbon oxidation reaction) by the undesired oxygen reduction reaction (ORR) on the anode side. This emphasizes the importance of designing selective anode catalysts that can efficiently suppress the ORR while fully preserving the Pt-like activity for the hydrogen oxidation reaction. Here, we demonstrate that chemically modified platinum with a self-assembled monolayer of calix[4]arene molecules meets this challenging requirement.

Genorio, Bostjan; Strmcnik, Dusan; Subbaraman, Ram; Tripkovic, Dusan; Karapetrov, Goran; Stamenkovic, Vojislav R.; Pejovnik, Stane; Markovi?, Nenad M.

2010-12-01

370

Carbon supported cobalt oxide nanoparticles-iron phthalocyanine as alternative cathode catalyst for oxygen reduction in microbial fuel cells  

NASA Astrophysics Data System (ADS)

The high cost and limited resources of precious metals as oxygen reduction catalysts (ORR) hindered the widespread use of microbial fuel cells (MFCs) in practice. Here, the feasibility of metal oxide assisted metal macrocyclic complex was investigated as a catalyst for ORR in an air-cathode MFC. Electrochemical results revealed that cobalt oxide (CoOx) incorporation increased the ORR activity of iron phthalocyanine (FePc). In MFCs, the maximum power density of 654 ± 32 mW m-2 was achieved from the C-CoOx-FePc cathode, which was 37% higher than the power density of carbon supported FePc (C-FePc). The voltage output of the MFC only decreased to 85% of its initial voltage after 50 cycles, suggesting that the synthesized catalyst showed acceptable long-term stability. The voltage drop partially resulted from the covering of biofilm on the catalyst layer. This work provided a potential alternative to Pt in MFCs for sustainable energy generation.

Ahmed, Jalal; Yuan, Yong; Zhou, Lihua; Kim, Sunghyun

2012-06-01

371

Simultaneous reduction of Cr(VI) and oxidation of As(III) by Bacillus firmus TE7 isolated from tannery effluent.  

PubMed

Hexavalent chromium [Cr(VI)] and arsenite [As(III)] are the most toxic forms of chromium and arsenic respectively, and reduction of Cr(VI) to Cr(III) and oxidation of As(III) to As(V) has great environmental implications as they affect toxicity and mobility of these toxic species. Bacillus firmus strain TE7, resistant to chromium and arsenic was isolated from tannery effluent. The strain exhibited ability to reduce Cr(VI) and oxidize As(III). It reduced 100 mg L(-1) Cr(VI) within 60 h in nutrient broth and oxidized 150 mg L(-1) As(III) within 10 h in minimal medium. It also completely reduced 15 mg L(-1) Cr(VI) and oxidized 50 mg L(-1) of As(III) simultaneously in minimal medium. To the best of our knowledge, this is the first bacterial strain showing simultaneous reduction of Cr(VI) and oxidation of As(III) and is a potential candidate for bioremediation of environments contaminated with these toxic metal species. PMID:23182111

Bachate, Sachin P; Nandre, Vinod S; Ghatpande, Niraj S; Kodam, Kisan M

2013-02-01

372

Passivated iodine pentoxide oxidizer for potential biocidal nanoenergetic applications.  

PubMed

Iodine pentoxide (I2O5), also known as diiodine pentoxide, is a strong oxidizer which has been recently proposed as an iodine-rich oxidizer in nanoenergetic formulations, whose combustion products lead to molecular iodine as a biocidal agent. However, its highly hygroscopic nature hinders its performance as a strong oxidizer and an iodine releasing agent and prevents its implementation. In this work, we developed a gas phase assisted aerosol spray pyrolysis which enables creation of iron oxide passivated I2O5. Transmission electron microscopy elemental imaging as well as temperature-jump mass spectrometry confirmed the core shell nature of the material and the fact that I2O5 could be encapsulated in pure unhydrated form. Combustion performance finds an optimal coating thickness that enables combustion performance similar to a high performing CuO based thermite. PMID:23988006

Feng, Jingyu; Jian, Guoqiang; Liu, Qing; Zachariah, Michael R

2013-09-25

373

Anaerobic oxidation of short-chain alkanes in hydrothermal sediments: potential influences on sulfur cycling and microbial diversity.  

PubMed

Short-chain alkanes play a substantial role in carbon and sulfur cycling at hydrocarbon-rich environments globally, yet few studies have examined the metabolism of ethane (C2), propane (C3), and butane (C4) in anoxic sediments in contrast to methane (C1). In hydrothermal vent systems, short-chain alkanes are formed over relatively short geological time scales via thermogenic processes and often exist at high concentrations. The sediment-covered hydrothermal vent systems at Middle Valley (MV, Juan de Fuca Ridge) are an ideal site for investigating the anaerobic oxidation of C1-C4 alkanes, given the elevated temperatures and dissolved hydrocarbon species characteristic of these metalliferous sediments. We examined whether MV microbial communities oxidized C1-C4 alkanes under mesophilic to thermophilic sulfate-reducing conditions. Here we present data from discrete temperature (25, 55, and 75°C) anaerobic batch reactor incubations of MV sediments supplemented with individual alkanes. Co-registered alkane consumption and sulfate reduction (SR) measurements provide clear evidence for C1-C4 alkane oxidation linked to SR over time and across temperatures. In these anaerobic batch reactor sediments, 16S ribosomal RNA pyrosequencing revealed that Deltaproteobacteria, particularly a novel sulfate-reducing lineage, were the likely phylotypes mediating the oxidation of C2-C4 alkanes. Maximum C1-C4 alkane oxidation rates occurred at 55°C, which reflects the mid-core sediment temperature profile and corroborates previous studies of rate maxima for the anaerobic oxidation of methane (AOM). Of the alkanes investigated, C3 was oxidized at the highest rate over time, then C4, C2, and C1, respectively. The implications of these results are discussed with respect to the potential competition between the anaerobic oxidation of C2-C4alkanes with AOM for available oxidants and the influence on the fate of C1 derived from these hydrothermal systems. PMID:23717305

Adams, Melissa M; Hoarfrost, Adrienne L; Bose, Arpita; Joye, Samantha B; Girguis, Peter R

2013-01-01

374

Anaerobic oxidation of short-chain alkanes in hydrothermal sediments: potential influences on sulfur cycling and microbial diversity  

PubMed Central

Short-chain alkanes play a substantial role in carbon and sulfur cycling at hydrocarbon-rich environments globally, yet few studies have examined the metabolism of ethane (C2), propane (C3), and butane (C4) in anoxic sediments in contrast to methane (C1). In hydrothermal vent systems, short-chain alkanes are formed over relatively short geological time scales via thermogenic processes and often exist at high concentrations. The sediment-covered hydrothermal vent systems at Middle Valley (MV, Juan de Fuca Ridge) are an ideal site for investigating the anaerobic oxidation of C1–C4 alkanes, given the elevated temperatures and dissolved hydrocarbon species characteristic of these metalliferous sediments. We examined whether MV microbial communities oxidized C1–C4 alkanes under mesophilic to thermophilic sulfate-reducing conditions. Here we present data from discrete temperature (25, 55, and 75°C) anaerobic batch reactor incubations of MV sediments supplemented with individual alkanes. Co-registered alkane consumption and sulfate reduction (SR) measurements provide clear evidence for C1–C4 alkane oxidation linked to SR over time and across temperatures. In these anaerobic batch reactor sediments, 16S ribosomal RNA pyrosequencing revealed that Deltaproteobacteria, particularly a novel sulfate-reducing lineage, were the likely phylotypes mediating the oxidation of C2–C4 alkanes. Maximum C1–C4 alkane oxidation rates occurred at 55°C, which reflects the mid-core sediment temperature profile and corroborates previous studies of rate maxima for the anaerobic oxidation of methane (AOM). Of the alkanes investigated, C3 was oxidized at the highest rate over time, then C4, C2, and C1, respectively. The implications of these results are discussed with respect to the potential competition between the anaerobic oxidation of C2–C4alkanes with AOM for available oxidants and the influence on the fate of C1 derived from these hydrothermal systems. PMID:23717305

Adams, Melissa M.; Hoarfrost, Adrienne L.; Bose, Arpita; Joye, Samantha B.; Girguis, Peter R.

2013-01-01

375

How Can a Single Second Sphere Amino Acid Substitution Cause Reduction Midpoint Potential Changes of Hundreds of Millivolts?  

SciTech Connect

The active site metal ion of superoxide dismutase (SOD) is reduced and reoxidized as it disproportionates superoxide to dioxygen and hydrogen peroxide. Thus, the reduction midpoint potential (E{sub m}) is a critical determinant of catalytic activity. In E. coli Fe-containing SOD (FeSOD), reduction of Fe{sup 3+} is accompanied by protonation of a coordinated OH{sup -}, to produce Fe{sup 2+} coordinated by H{sub 2}O. The coordinated solvent's only contact with the protein beyond the active site is a conserved Gln residue. Mutation of this Gln to His or Glu resulted in elevation of the E{sub m} by 220 mV and more than 660 mV, respectively [Yikilmaz et al., Biochemistry 2006, 45, 1151--1161], despite the fact that overall protein structure was preserved, His is a chemically conservative replacement for Gln, and neutral Glu is isostructural and isoelectronic with Gln. Therefore, we have investigated several possible bases for the elevated E{sub m}'s, including altered Fe electronic structure, altered active site electrostatics, altered H-bonding and altered redox-coupled proton transfer. Using EPR, MCD, and NMR spectroscopies, we find that the active site electronic structures of the two mutants resemble that of the WT enzyme, for both oxidation states, and Q69E-FeSOD's apparent deviation from WT-like Fe{sup 3+} coordination in the oxidized state can be explained by increased affinity for a small anion. Spontaneous coordination of an exogenous anion can only stabilize oxidized Q69E-Fe{sup 3+}SOD and, therefore, cannot account for the increased E{sub m} of Q69E FeSOD. WT-like anion binding affinities and active site pK's indicate that His69 of Q69H-FeSOD is neutral in both oxidation states, like Gln69 of WT-FeSOD, whereas Glu69 appears to be neutral in the oxidized state but ionized in the reduced state of Q69E-FeSOD. A 1.1 {angstrom} resolution crystal structure of Q69E-Fe{sup 2+}SOD indicates that Glu69 accepts a strong H-bond from coordinated solvent in the reduced state, in contrast to the case in WT-FeSOD where Gln69 donates an H-bond. These data and DFT calculations lead to the proposal that the elevated Em of Q69E-FeSOD can be substantially explained by (1) relief from enforced H-bond donation in the reduced state, (2) Glu69's capacity to provide a proton for proton-coupled Fe{sup 3+} reduction, and (3) strong hydrogen bond acceptance in the reduced state, which stabilizes coordinated H{sub 2}O. Our results thus support the hypothesis that the protein matrix can apply significant redox tuning via its influence over redox-coupled proton transfer and the energy associated with it.

Yikilmaz, E.; Porta, J.; Grove, L.E.; Vahedi-Faridi, A.; Bronshteyn, Y.; Brunold, T.C.; Borgstahl, G.E.O.; Miller, A.-F.

2009-06-04

376

Mulberry leaf phenolics ameliorate hyperglycemia-induced oxidative stress and stabilize mitochondrial membrane potential in HepG2 cells.  

PubMed

Abstract To investigate the effect of phenolics in mulberry leaves (mulberry leaf phenolics; MLP) on hyperglycemia-induced oxidative stress and mitochondrial membrane potential (??m) in HepG2 cells; we treated HepG2 with glucose [5.5 (N-Glc) or 50?mmol/L (Hi-Glc)] with or without MLP at 10 or 100?µmol/L gallic acid equivalents and assessed level of reactive oxidant species (ROS), ??m, malondialdehyde (MDA) and nuclear factor-kappaB (NF-?B) activation. Hi-Glc-induced oxidative damage was demonstrated by a series of increase in superoxides (560%, 0.5?h), MDA (400%, 24?h), NF-?B activation (474%, 4?h) and a wild fluctuation of ??m relative to the control cells (p???0.05). MLP treatments ameliorate Hi-Glc-induced negative effects by a 40% reduction in ROS production, 34-44% reduction in MDA production, over 35% inhibition of NF-?B activation, as well as exert protective effect on HepG2 cells from change in ??m. Our data show that MLP in vitro can protect hepatoctyes from hyperglycemia-induced oxidative damages. PMID:25026091

Zou, Yu-Xiao; Shen, Wei-Zhi; Liao, Sen-Tai; Liu, Fan; Zheng, Shan-Qing; Blumberg, Jeffrey B; Chen, C-Y Oliver

2014-12-01

377

Catalytic activity of oxidized (combusted) oil shale for removal of nitrogen oxides with ammonia as a reductant in combustion gas streams, Part 2  

SciTech Connect

Oxidized oil shale from the combustor in the LLNL Hot-Recycled-Solids (HRS) oil shale retorting process has been found to be a catalyst for removing nitrogen oxides from laboratory gas streams using NH{sub 3} as a reductant. Oxidized Green River oil shale heated at 10{degree}C/min in an Ar/O{sub 2}/NO/NH{sub 3} mixture ({approximately}93%/6%/2000 ppM/4000 ppM) with a gas residence time of {approximately}0.6 sec removed NO between 250 and 500{degree}C, with maximum removal of 70% at {approximately}400{degree}C. Under isothermal conditions with the same gas mixture, the maximum NO removal was {approximately}64%. When CO{sub 2} was added to the gas mixture at {approximately}8%, the NO removal dropped to {approximately}50%. However, increasing the gas residence time to {approximately}1.2 sec, increased NO removal to 63%. Nitrogen balances of these experiments suggest selective catalytic reduction of NO is occurring using NH{sub 3} as the reductant. These results are not based on completely optimized process conditions, but indicate oxidized oil shale is an effective catalyst for NO removal from combustion gas streams using NH{sub 3} as the reductant. Parameters calculated for implementing oxidized oil shale for NO{sub x} remediation on the current HRS retort indicate an abatement device is practical to construct.

Reynolds, J.G.; Taylor, R.W.; Morris, C.J.

1993-01-04

378

Catalytic activity of oxidized (combusted) oil shale for removal of nitrogen oxides with ammonia as a reductant in combustion gas streams, Part 2  

SciTech Connect

Oxidized oil shale from the combustor in the LLNL Hot-Recycled-Solids (HRS) oil shale retorting process has been found to be a catalyst for removing nitrogen oxides from laboratory gas streams using NH[sub 3] as a reductant. Oxidized Green River oil shale heated at 10[degree]C/min in an Ar/O[sub 2]/NO/NH[sub 3] mixture ([approximately]93%/6%/2000 ppM/4000 ppM) with a gas residence time of [approximately]0.6 sec removed NO between 250 and 500[degree]C, with maximum removal of 70% at [approximately]400[degree]C. Under isothermal conditions with the same gas mixture, the maximum NO removal was [approximately]64%. When CO[sub 2] was added to the gas mixture at [approximately]8%, the NO removal dropped to [approximately]50%. However, increasing the gas residence time to [approximately]1.2 sec, increased NO removal to 63%. Nitrogen balances of these experiments suggest selective catalytic reduction of NO is occurring using NH[sub 3] as the reductant. These results are not based on completely optimized process conditions, but indicate oxidized oil shale is an effective catalyst for NO removal from combustion gas streams using NH[sub 3] as the reductant. Parameters calculated for implementing oxidized oil shale for NO[sub x] remediation on the current HRS retort indicate an abatement device is practical to construct.

Reynolds, J.G.; Taylor, R.W.; Morris, C.J.

1993-01-04

379

Dramatic effective mass reduction driven by a strong potential of competing periodicity  

NASA Astrophysics Data System (ADS)

We present angle-resolved photoemission experiments on 1T-TiSe2 at temperatures ranging from 13 K to 288 K. The data evidence a dramatic renormalization of the conduction band below 100 K, whose origin can be related to the new potential responsible for the charge density wave phase at low temperature in this system. The renormalization translates into a substantial effective mass reduction of the dominant charge carriers and this observation is thus in opposition to the common belief that strong interactions produce heavier quasiparticles through an increased effective mass.

Monney, C.; Schwier, E. F.; Garnier, M. G.; Battaglia, C.; Mariotti, N.; Didiot, C.; Cercellier, H.; Marcus, J.; Berger, H.; Titov, A. N.; Beck, H.; Aebi, P.

2010-11-01

380

Metformin decreases glucose oxidation and increases the dependency of prostate cancer cells on reductive glutamine metabolism.  

PubMed

Metformin inhibits cancer cell proliferation, and epidemiology studies suggest an association with increased survival in patients with cancer taking metformin; however, the mechanism by which metformin improves cancer outcomes remains controversial. To explore how metformin might directly affect cancer cells, we analyzed how metformin altered the metabolism of prostate cancer cells and tumors. We found that metformin decreased glucose oxidation and increased dependency on reductive glutamine metabolism in both cancer cell lines and in a mouse model of prostate cancer. Inhibition of glutamine anaplerosis in the presence of metformin further attenuated proliferation, whereas increasing glutamine metabolism rescued the proliferative defect induced by metformin. These data suggest that interfering with glutamine may synergize with metformin to improve outcomes in patients with prostate cancer. PMID:23687346

Fendt, Sarah-Maria; Bell, Eric L; Keibler, Mark A; Davidson, Shawn M; Wirth, Gregory J; Fiske, Brian; Mayers, Jared R; Schwab, Matthias; Bellinger, Gary; Csibi, Alfredo; Patnaik, Akash; Blouin, Marie Jose; Cantley, Lewis C; Guarente, Leonard; Blenis, John; Pollak, Michael N; Olumi, Aria F; Vander Heiden, Matthew G; Stephanopoulos, Gregory

2013-07-15

381

Selective Oxidation/Reduction and Impact Melting in Experimental Metal-Silicate Craters  

NASA Astrophysics Data System (ADS)

We have produced thin veneers of crystalline to frothy projectile residues (where the projectiles varied from dunite, diopside, orthoclase or basalt cylinders) within small cm-sized craters formed in metal targets (where the targets varied from 1100 Al, Cu, SS304 or Mo). The morphology and mixing of the silicate residue with metal spherules is similar to that described in many natural impact melts including lunar samples, terrestrial impact crater melts and tektites, and shock features in some meteorites. Textural and chemical analysis suggests that local regions of these residues experienced high temperature gradients, fast rates of nucleation and crystal growth and minimal, but selective oxidation/reduction. Such inferences should help decipher the heterogeneous evolution of impact melts in terrestrial and extraterrestrial samples.

Rowan, L. R.; Horz, F.; Zolensky, M.

1996-03-01

382

Treatment of activated carbon to enhance catalytic activity for reduction of nitric oxide with ammonia  

SciTech Connect

Catalytic activity of activated carbon treated with various techniques was examined in a fixed bed reactor for the reduction of nitric oxide with ammonia at 150 C. Activated carbon derived from coconut shell impregnated with an aqueous solution of ammonium sulfate, further treated with sulfuric acid, dried at 120 C, and then heated in an inert gas stream at 400 C, showed the highest catalytic activity within the range of experimental conditions. The enhancement of catalytic activity of modified activated carbon could be attributed to the increase in the amount of oxygen function groups which increased the adsorption site for ammonia. Catalytic activity of activated carbons depended on the surface area and the oxygen content as well.

Ku, B.J.; Rhee, H.K. (Seoul National Univ. (Korea, Republic of). Dept. of Chemical Engineering); Lee, J.K.; Park, D. (Korea Inst. of Science and Technology, Seoul (Korea, Republic of))

1994-11-01

383

Branched platinum-on-palladium bimetallic heteronanostructures supported on reduced graphene oxide for highly efficient oxygen reduction reaction  

NASA Astrophysics Data System (ADS)

In this work, a facile one-pot wet-chemical approach is developed for synthesis of three-dimensional platinum-on-palladium (Pt-on-Pd) bimetallic nanodendrites supported on reduced graphene oxide (rGO), where octylphenoxypolye thoxyethanol (NP-40) acts as a growth-directing agent and formic acid serves as a reducing agent under mild conditions. The nanocomposites exhibit enhanced oxygen reduction reaction activity (onset potential of 0.05 V, half-wave potential of -0.15 V, electron transfer number >3.99) and better stability in alkaline media. The diffusion-limited current densities of Pt-on-Pd/rGO at -0.60 V (3.99 mA cm-2 and 22.72 mA mg-1) are much higher than those of PtPd/rGO, Pt/rGO, Pd/rGO, PtPd nanoparticles/rGO, Pt black, Pd black, Pt/C, and Pd/C catalysts. This method is general, facile, and green for preparation of rGO-supporting bimetallic electrocatalysts.

Li, Shan-Shan; Zheng, Jie-Ning; Wang, Ai-Jun; Tao, Fang-Lei; Feng, Jiu-Ju; Chen, Jian-Rong; Yu, Haiying

2014-12-01

384

Zinc immobilization and magnetite formation via ferric oxide reduction by Shewanella putrefaciens 200  

SciTech Connect

Long-term batch experiments in an artificial groundwater medium indicated that microbial reduction of synthetic, high-surface-area goethite and lepidocrocite by Shewanella putrefaciens 200 can act to immobilize surface-associated zinc into a new mineral phase that is not soluble in 0.5 M HCl. While Zn was incorporated in siderite grains in experiments with goethite, additional Zn immobilization may result from incorporation into as yet unidentified biogenic minerals or into a more crystalline goethite. Experiments with an oxide mixture primarily composed of lepidocrocite resulted in the production of magnetite, biphasic immobilization of Zn, and an enhanced overall degree of Zn immobilization. When NO{sub 3}{sup {minus}} was present as an alternate electron acceptor, microbial production of Fe(II) was inhibited, and the degree of Zn immobilization was subsequently reduced. These data indicate that (i) biologically induced mineralization can play a key role in the cycling of trace elements in natural systems, (ii) the nature of the oxide surface plays an important role in biologically induced mineralization, and (iii) conditions associated with Fe(II) production are necessary for these processes to immobilize surface-bound Zn within these new mineral phases.

Cooper, D.C.; Picardal, F.; Rivera, J.; Talbot, C.

2000-01-01

385

Diverse syntrophic relationships within a microbial community performing anaerobic oxidation of methane and sulfate reduction  

NASA Astrophysics Data System (ADS)

Here we report the metagenome and metatranscriptome analysis of a highly enriched, active AOM-SR (anaerobic oxidation of methane - sulfate reduction) community obtained through a continuous high-pressure bioreactor system. The community has a very high diversity of bacteria, besides SRB within delta-Proteobacteria, gamma-, beta-Proteobacteria and OP1 were found abundant. The archaeal components in the system are rather simple with only ANME2 and Marine Benthic Group D detected. FISH analysis revealed that most ANME cells form cell aggregates with SRB. A complete and functioning methanogenesis pathway from CO2 reduction was identified. Besides the methanogenesis and sulfate reducing pathways, pathways for complete denitrification and nitrogen fixation were also identified and expressed. Single cell aggregates in the community were captured and sequenced. Besides ANME and SRB, a third type of microorganisms were found present in certain cell aggregates, thus provide direct evidence for diverse syntrophic relationships among the microorganisms within the system fueled by AOM-SR.

Wang, F.; Chen, Y.; Zhang, Y.; He, Y.; Xiao, X.

2012-12-01

386

Oxidative potential and inflammatory impacts of source apportioned ambient air pollution in beijing.  

PubMed

Air pollution exposure is associated with a range of adverse health impacts. Knowledge of the chemical components and sources of air pollution most responsible for these health effects could lead to an improved understanding of the mechanisms of such effects and more targeted risk reduction strategies. We measured daily ambient fine particulate matter (<2.5 ?m in aerodynamic diameter; PM2.5) for 2 months in peri-urban and central Beijing, and assessed the contribution of its chemical components to the oxidative potential of ambient air pollution using the dithiothreitol (DTT) assay. The composition data were applied to a multivariate source apportionment model to determine the PM contributions of six sources or factors: a zinc factor, an aluminum factor, a lead point factor, a secondary source (e.g., SO4(2-), NO3(2-)), an iron source, and a soil dust source. Finally, we assessed the relationship between reactive oxygen species (ROS) activity-related PM sources and inflammatory responses in human bronchial epithelial cells. In peri-urban Beijing, the soil dust source accounted for the largest fraction (47%) of measured ROS variability. In central Beijing, a secondary source explained the greatest fraction (29%) of measured ROS variability. The ROS activities of PM collected in central Beijing were exponentially associated with in vivo inflammatory responses in epithelial cells (R(2) = 0.65-0.89). We also observed a high correlation between three ROS-related PM sources (a lead point factor, a zinc factor, and a secondary source) and expression of an inflammatory marker (r = 0.45-0.80). Our results suggest large differences in the contribution of different PM sources to ROS variability at the central versus peri-urban study sites in Beijing and that secondary sources may play an important role in PM2.5-related oxidative potential and inflammatory health impacts. PMID:25279798

Liu, Qingyang; Baumgartner, Jill; Zhang, Yuanxun; Liu, Yanju; Sun, Yongjun; Zhang, Meigen

2014-11-01

387

Acetylene Reduction (Nitrogen Fixation) and Metabolic Activities of Soybean Having Various Leaf and Nodule Water Potentials 1  

PubMed Central

An apparatus was designed that permitted acetylene reduction (N2 fixation) by root nodules to be measured in situ simultaneously with net photosynthesis, dark respiration, and transpiration of the shoot in soybean plants (Glycine max [L.] Merr. var. Beeson). Tests showed that acetylene reduction was linear with time for at least 5 hours, except for the first 30 to 60 minutes. Endogenous ethylene production did not affect the measurements. Successive determinations of acetylene reduction could be made without apparent aftereffects on the plant. This apparatus was used to investigate the effects of soil flooding and desiccation on acetylene reduction under conditions where soil, nodule, and leaf water potentials could be measured. No acetylene reduction was detectable in flooded soil or in soil desiccated to a water potential of ?19.5 bars. Between these extremes, acetylene reduction displayed a sharp optimum. Removing the soil eliminated the inhibitory effects of flooding, suggesting that rates of gas exchange were restricted between the nodules and the atnosphere at soil water potentials above ?2 bars. As the soil desiccated further, acetylene reduction decreased, and the decrease was correlated with decreases in photosynthesis and transpiration. Although dark respiration was inhibited, it was not affected to the extent that acetylene reduction, photosynthesis, or transpiration were. Consequently, it was concluded that photosynthesis, transpiration, or some direct effect on the nodules other than that caused by respiration were most likely to account for the inhibition of acetylene reduction at soil water potentials below ?2 bars. PMID:16659276

Huang, Chi-Ying; Boyer, John S.; Vanderhoef, Larry N.

1975-01-01

388

Absolute Standard Hydrogen Electrode Potential Measured by Reduction of Aqueous Nanodrops in the Gas Phase  

PubMed Central

In solution, half-cell potentials are measured relative to those of other half cells, thereby establishing a ladder of thermochemical values that are referenced to the standard hydrogen electrode (SHE), which is arbitrarily assigned a value of exactly 0 V. Although there has been considerable interest in, and efforts toward, establishing an absolute electrochemical half-cell potential in solution, there is no general consensus regarding the best approach to obtain this value. Here, ion-electron recombination energies resulting from electron capture by gas-phase nanodrops containing individual [M(NH3)6]3+, M = Ru, Co, Os, Cr, and Ir, and Cu2+ ions are obtained from the number of water molecules that are lost from the reduced precursors. These experimental data combined with nanodrop solvation energies estimated from Born theory and solution-phase entropies estimated from limited experimental data provide absolute reduction energies for these redox couples in bulk aqueous solution. A key advantage of this approach is that solvent effects well past two solvent shells, that are difficult to model accurately, are included in these experimental measurements. By evaluating these data relative to known solution-phase reduction potentials, an absolute value for the SHE of 4.2 ± 0.4 V versus a free electron is obtained. Although not achieved here, the uncertainty of this method could potentially be reduced to below 0.1 V, making this an attractive method for establishing an absolute electrochemical scale that bridges solution and gas-phase redox chemistry. PMID:18288835

Donald, William A.; Leib, Ryan D.; O'Brien, Jeremy T.; Bush, Matthew F.; Williams, Evan R.

2008-01-01

389

Oxidative stress mechanisms and potential therapeutics in Alzheimer disease  

Microsoft Academic Search

Summary. Oxidative damage of biological macromolecules is a hallmark of most neurodegenerative disorders such as Alzheimer, Parkinson and diffuse Lewy body diseases. Another important phenomenon involved in these disorders is the alteration of iron and copper homeostasis. Data from the literature support the involvement of metal homeostasis in mitochondrial dysfunction, protein alterations and nucleic acid damage which are relevant in

P. I. Moreira; S. L. Siedlak; G. Aliev; X. Zhu; A. D. Cash; M. A. Smith; G. Perry

2005-01-01

390

Hydroxylated HMPA enhances both reduction potential and proton donation in SmI? reactions.  

PubMed

HMPA is known to increase the reduction potential of SmI2. However, in many cases, the transferred electron returns from the radical anion of the substrate back to the Sm(3+). This could be avoided by an efficient trapping of the radical anion: e.g., by protonation. However, bimolecular protonation by a proton donor from the bulk may be too slow to compete with the back electron transfer process. An efficient unimolecular protonation could be achieved by using a proton donor which complexes to SmI2, in which case the proton is unimolecularly transferred within the ion pair. A derivative of HMPA in which one of the methyl groups was substituted by a CH2CH2OH unit was synthesized. Cyclic voltammetry studies have shown that it resembles HMPA in its ability to enhance the reduction potential of SmI2, and reactivity studies show that it has also efficient proton shift capabilities. The various aspects of this additive were examined in the reactions of SmI2 with three substrates: benzyl chloride, methyl cinnamate, and anthracene. PMID:24559471

Halder, Sandipan; Hoz, Shmaryahu

2014-03-21

391

Factors Driving Potential Ammonia Oxidation in Canadian Arctic Ecosystems: Does Spatial Scale Matter?  

PubMed Central

Ammonia oxidation is a major process in nitrogen cycling, and it plays a key role in nitrogen limited soil ecosystems such as those in the arctic. Although mm-scale spatial dependency of ammonia oxidizers has been investigated, little is known about the field-scale spatial dependency of aerobic ammonia oxidation processes and ammonia-oxidizing archaeal and bacterial communities, particularly in arctic soils. The purpose of this study was to explore the drivers of ammonia oxidation at the field scale in cryosols (soils with permafrost within 1 m of the surface). We measured aerobic ammonia oxidation potential (both autotrophic and heterotrophic) and functional gene abundance (bacterial amoA and archaeal amoA) in 279 soil samples collected from three arctic ecosystems. The variability associated with quantifying genes was substantially less than the spatial variability observed in these soils, suggesting that molecular methods can be used reliably evaluate spatial dependency in arctic ecosystems. Ammonia-oxidizing archaeal and bacterial communities and aerobic ammonia oxidation were spatially autocorrelated. Gene abundances were spatially structured within 4 m, whereas biochemical processes were structured within 40 m. Ammonia oxidation was driven at small scales (<1m) by moisture and total organic carbon, whereas gene abundance and other edaphic factors drove ammonia oxidation at medium (1 to 10 m) and large (10 to 100 m) scales. In these arctic soils heterotrophs contributed between 29 and 47% of total ammonia oxidation potential. The spatial scale for aerobic ammonia oxidation genes differed from potential ammonia oxidation, suggesting that in arctic ecosystems edaphic, rather than genetic, factors are an important control on ammonia oxidation. PMID:22081570

Banerjee, Samiran

2012-01-01

392

Oxygen potentials of uranium-plutonium oxides in the near stoichiometric region  

NASA Astrophysics Data System (ADS)

The change in stoichiometry of solid solutions of U 0.77Pu 0.23 and U 0.85 pu 0.15 oxides with oxygen potential between 1523 and 1823K has been determined. A thermogravimetric technique was used to establish the equilibrium between the oxide phases and CO/CO 2 gas mixtures of known oxygen potential. Particular attention was given to the relationship between the stoichiometry and the oxygen potential in the region very close to the stoichiometric composition. New data have been obtained for oxides with fO/M ratios 1.9984-2.0000.

Edwards, J.; Wood, R. N.; Chilton, G. R.

1985-02-01

393

Global perspective on the oxidative potential of airborne particulate matter: a synthesis of research findings.  

PubMed

An emerging hypothesis in the field of air pollution is that oxidative stress is one of the important pathways leading to adverse health effects of airborne particulate matter (PM). To advance our understanding of sources and chemical elements contributing to aerosol oxidative potential and provide global comparative data, we report here on the biological oxidative potential associated with size-segregated airborne PM in different urban areas of the world, measured by a biological (cell-based) reactive oxygen species (ROS) assay. Our synthesis indicates a generally greater intrinsic PM oxidative potential as well as higher levels of exposure to redox-active PM in developing areas of the world. Moreover, on the basis of our observations, smaller size fractions are generally associated with higher intrinsic ROS activity compared with larger PM size fractions. Another important outcome of our study is the identification of major species and sources that are associated with ROS activity. Water-soluble transition metals (e.g., Fe, Ni, Cu, Cr, Mn, Zn and V) and water-soluble organic carbon (WSOC) showed consistent correlations with the oxidative potential of airborne PM across different urban areas and size ranges. The major PM sources associated with these chemical species include residual/fuel oil combustion, traffic emissions, and secondary organic aerosol formation, indicating that these sources are major drivers of PM-induced oxidative potential. Moreover, comparison of ROS activity levels across different seasons indicated that photochemical aging increases the intrinsic oxidative potential of airborne PM. PMID:24873754

Saffari, Arian; Daher, Nancy; Shafer, Martin M; Schauer, James J; Sioutas, Constantinos

2014-07-01

394

Role of cation interactions in the reduction process in plutonium-americium mixed oxides.  

PubMed

The oxygen to metal ratio (O/M) is directly related to oxygen potential, which strongly influences the sintering and irradiation performance of nuclear fuels. A better understanding of these two parameters is therefore of major interest. To further ascertain the correlation between O/M ratio and oxygen potential in Am-bearing MOX, several thermodynamic descriptions are being developed. Despite their differences, they all involve the valence of actinide cations (e.g., U, Pu, and Am) as essential parameters. However, as no experimental data on their valence are available, these models rely on assumptions. In the present work, we coupled X-ray diffraction and X-ray absorption spectroscopy to follow the behavior of Pu and Am in three hypo-stoichiometric, U-free Pu(1-y)Am(y)O(2-x) compounds. We provide for the first time a quantitative determination of Pu and Am valences, demonstrating that plutonium reduction from Pu(4+) to Pu(3+) starts only when americium reduction from Am(4+) to Am(3+) is completed. This result fills in an important gap in experimental data, thereby improving the thermodynamic description of nuclear fuels. At last, we suggest that the O/M ratio may evolve at room temperature, especially for high Am content, which is of main concern for the fabrication of Am-loaded MOX and their storage prior to irradiation. PMID:23441886

Belin, Renaud C; Martin, Philippe M; Lechelle, Jacques; Reynaud, Muriel; Scheinost, Andreas C

2013-03-18

395

77 FR 44562 - Public Meeting: Potential Regulatory Implications of the Reduction of Lead in Drinking Water Act...  

Federal Register 2010, 2011, 2012, 2013

...FRL-9708-1] Public Meeting: Potential Regulatory Implications of the Reduction of Lead in Drinking Water Act of 2011 AGENCY: Environmental...States, manufacturers, drinking water systems, other interested groups...Reduction of Lead in Drinking Water Act of 2011 (``the...

2012-07-30

396

Activity of amine oxide against biofilms of Streptococcus mutans: a potential biocide for oral care formulations  

Microsoft Academic Search

Aims: To assess the potential bactericidal activity of amine oxide (C10-C16-alkyldimethyl N-oxides) against Streptococcus mutans grown as planktonic suspension and as biofilm on hydroxyapatite discs, and its ability to control acidification of the media. Methods: Amine oxide bacteriostasis was investigated using the Bioscreen C Microbiological Growth Analyser, while a standard suspension test was used to determine its bactericidal efficacy. In

Sebastien Fraud; Jean-Yves Maillard; Michael A. Kaminski; Geoffrey W. Hanlon

397

Redox potential measurements and Mössbauer spectrometry of Fe II adsorbed onto Fe III (oxyhydr)oxides  

Microsoft Academic Search

The redox properties of FeII adsorbed onto a series of FeIII (oxyhydr)oxides (goethite, lepidocrocite, nano-sized ferric oxide hydrate (nano-FOH), and hydrous ferric oxide (HFO)) have been investigated by rest potential measurements at a platinum electrode, as a function of pH (?log10[H+]) and surface coverage. Using the constant capacitance surface complexation model to describe FeII adsorption onto these substrates, theoretical values

Ewen Silvester; Laurent Charlet; Christophe Tournassat; Antoine Géhin; Jean-Marc Grenèche; Emmanuelle Liger

2005-01-01

398

Reducing Nitrous Oxide Emissions from US Row-Crop Agriculture through Nitrogen Fertilizer Management: Development of an Nitrous Oxide Emissions Reduction Protocol  

NASA Astrophysics Data System (ADS)

Nitrous oxide (N2O) is the major greenhouse gas emitted by US agriculture. About 80% of N2O emissions emanate from N fertilizer application and other soil management activities, with cropland emissions alone greater than 1 Tg yr-1. Manipulating fertilizer N inputs is a readily accessible management tool for increasing crop N use efficiency with fertilizer N rate, a crucial parameter for estimating both yield and N2O emissions in row-crop systems. Quantification of the trade-offs between N2O emissions, crop yield and fertilizer N rate is essential for proposing strategies which optimize productivity at economically and environmentally favorable N rates. The relationship between fertilizer N rate and subsequent N2O emissions is typically assumed linear and insensitive to increasing N rate. However, recent field studies at producer sites in Michigan, in winter wheat and corn, using static and automated chamber systems suggest that a non-linear relationship is more applicable. Emissions of N2O were low at fertilizer N rates below or coincident to those, optimizing crop yield but, sharply increased thereafter. This threshold response to increasing fertilizer N rate in row-crop agriculture suggests a substantial decrease in N2O emissions could be achieved with moderate reductions in N rate and little or no yield penalty. Our data, in conjunction with a recently developed approach for determining economically profitable N application rates for optimized crop yield in a number of Midwest states, have potential to be incorporated into agricultural N2O emission reduction protocols and utilized in future projects suitable for inclusion in the burgeoning nutrient cap-and-trade markets. We will present results from our 2007-2009 field seasons and outline a protocol framework for reducing N2O emissions from row-crop agriculture in the US Midwest.

Millar, N.; Robertson, G. P.; Grace, P. R.; Gehl, R.; Hoben, J.; Kahmark, K.; Bohm, S.

2009-12-01

399

The use of oxidation-reduction dyes in the determination of the shelf-life of meats  

E-print Network

PTee) (I!e ct c f l)etnart&noae) r (;1;ncb c: ) (hlemba . ) (tteinbc r ) {ii nilic. 'i ) (i'lanit- c r) Jo Iinll V {i?at. li) 19 7U {yc'er ) ABSTRACT The Use of Oxidation-Reduction Dyes in the Dctemsination of the -hclf-Life of Yeats !January..., 1970) Janis C. Bush, B. S. (Biology), Abilene Christian College Directed by: Dr. Carl Vanderzant A technique w's developed to carry out dye reduction tests with a m'nimum ot interference of tissu- in the reduction process. Tne technique e...