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Sample records for active oxygen forms

  1. [Relationship between the oxidation-reduction system of astrocytes with production of active forms of oxygen].

    PubMed

    Semenkova, G N; Kvacheva, Z B; Obydennikova, S V; Cherenkevich, S N; Titov, L P

    1998-01-01

    Cells of neuroglia--the astrocytes are of interest from the point of view of their participation in phagocytosis. Phagocyte ability to generate active oxygen forms (AOF) as used as the basic criterion of the estimation of their functional activity. For the purpose to clear up molecular and cellular mechanisms of phagocytosis a study of astrocyte redox-systems, participating in production of AOF, was undertaken. Registration of AOF in astrocytes was carried out using a method of luminol-dependent chemiluminescence. Primary culture of guinea pig astrocytes was used. Spontaneous chemiluminescence of low intensity was found for the astrocytes at the presence of luminol. The destruction of the cells was accompanied by a significant growth of the intensity of spontaneous chemiluminescence. Suspension of endocutosis inductors, particle of latex and phytohemagglutinin, added to astrocytes did not result in formation of AOF, characteristic for other cells, possessing phagocytosis. It was established, that addition of hydrogen peroxide destroys astrocytes at the presence of luminol and gives rise to the emission. Chemiluminescence was not observed in similar experiments with intact cells. A conclusion was made that inside astrocytes there are structures, which show peroxidase-like activity. PMID:9848214

  2. [Active forms of oxygen: cytotoxic effects and methodological approaches to laboratory control of liver lesions (literature review)].

    PubMed

    Matiushin, B N; Loginov, A S

    1996-01-01

    The injurious effects of active oxygen forms (AOF) on the cell caused by destruction of its membranous structures and impairment of their functional characteristics are discussed. Disorders of the processes of formation and inactivation of AOF in hepatocytes may be the metabolic mechanisms mediating the status and development of the pathological process in the liver. The problem of prospective approaches to assessing chronic diseases of the liver at the level of "free-radical pathology" is discussed. PMID:8963562

  3. [Generation of active oxygen forms in rat thymocytes under action of hydrogen peroxide and fullerene C60].

    PubMed

    Hrebinyk, S M; Hryniuk, I I; Pryluts'ka, S V; Matyshevs'ka, O P

    2012-01-01

    The dynamics of active oxygen forms (AOF) generation in rat thymocytes 50 min after treatment with 0.1 and 0.5 mM H2O2 was estimated with the use of fluorescent probe DCFDA. Both enhanced AOF generation, which was dependent on H2O2 concentration, and glutathione peroxidase and superoxide dismutase activation, followed by a decrease of thymocytes viability were demonstrated. Preincubation of cells with 10(-5) M fullerene C60 was shown not only to prevent H2O2--induced AOF generation but to increase viability of H2O2-treated thymocytes at more prolonged time period. The data obtained indicate to fullerene C60 ability to prevent oxidative stress in thymocytes. PMID:22642121

  4. Oxygen-dependent upstream activation sites of Saccharomyces cerevisiae cytochrome c genes are related forms of the same sequence

    SciTech Connect

    Cerdan, M.E.; Zitomer, R.S.

    1988-06-01

    In Sacchariomyces cerevisiae, the two genes, CYC1 and CYC7, that encode the isoforms of cytochrome c are expressed at different levels. Oxygen regulation is indicated by the expression of the CYP1 gene, and the CYP1 protein interacts with both CYC1 upstream activation sequence 1 (UAS1) and CYC7 UAS/sub 0/. In this study, the homology between the CYP1-binding sites of both genes was investigated. The most noticeable difference between the CYC1 and CYC7 UASs is the presence of GC base pairs at the same positions in a repeated sequence in CYC7 compared with CG base pairs in CYC1. Directed mutagenesis changing these GC residues to CG residues in CYC7 led to CYC1-like expression of CYC7 both in a CYP1 wild-type strain and in a strain carrying the semidominant mutation CYP1-16 which reverses the oxygen-dependent expression of the two genes. The authors' results strongly support the hypothesis that the CYP1-binding sites in CYC1 and CYC7 are related forms of the same sequence and that the CYP1-16 protein has altered specificity for the variant forms of the concensus sequences in both genes.

  5. The Three Forms of Molecular Oxygen.

    ERIC Educational Resources Information Center

    Laing, Michael

    1989-01-01

    Finds that a logical application of the simple rules of the molecular orbital bonding theory for diatomic molecules predicted the existence of three spin isomers of the oxygen molecule: one triplet form with two unpaired electrons and two singlet forms with all electrons paired. (MVL)

  6. [Cytotoxic action of active forms of oxygen and mechanisms of development of a chronic process in the liver in liver disease].

    PubMed

    Loginov, A S; Matiushin, B N

    1996-01-01

    The paper deals with the damaging action of active oxygen forms (AOF) on the cell, which is associated with impairments of membranous structures and their functional properties. Based on the results of their own investigations, the authors forward a concept of the stereotypic pattern of changes in the enzyme mechanisms of AOF utilization in chronic hepatic diseases of viral etiology. It is suggested that impaired hepatocytic AOF formation and inactivation may be metabolic mechanisms mediating the status and development of a chronic process in the liver in its viral damage. Promising approaches to treating oxidative impairments are also discussed. PMID:9082318

  7. Reactive oxygen species formed in organic lithium-oxygen batteries.

    PubMed

    Schwager, Patrick; Dongmo, Saustin; Fenske, Daniela; Wittstock, Gunther

    2016-04-20

    Li-oxygen batteries with organic electrolytes are of general interest because of their theoretically high gravimetric energy density. Among the great challenges for this storage technology is the generation of reactive oxygen species such as superoxides and peroxides that may react with the organic solvent molecules and other cell components. The generation of such species has been assumed to occur during the charging reaction. Here we show that superoxide is formed also during the discharge reaction in lithium ion-containing dimethyl sulfoxide electrolytes and is released into the solution. This is shown independently by fluorescence microscopy after reaction with the selective reagent 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole and by local detection using a microelectrode of a scanning electrochemcial microscope positioned in a defined distance of 10 to 90 μm above the gas diffusion electrode. PMID:26911793

  8. [Role of the lungs in the regulation of the generation of active oxygen forms by leukocytes under normal and pathological conditions].

    PubMed

    Kogan, A Kh; Losev, N I; Biriukov, Iu V; Sandrikov, V A; Tsypin, A B; Al'-Khadidi, M; Manuĭlov, B M; Syrkin, A L; Krotovskiĭ, G S; Pogromov, A P

    1991-01-01

    Studies conducted in the clinic (in patients with cardiac diseases) and experiments (performed on intact dogs) by means of the hemiluminescent method and the nitroblue tetrazolium test showed that the lungs, in distinction to other organs (heart and others), have a stimulating effect on the generation of active oxygen forms (AOF) by the leukocytes. In this way the lungs may probably play a double role in the organism: potentiate its defence (by intensifying the microbicidal activity of the phagocytes) and facilitate damage (by secretion of AOF by the phagocytes beyond them--into the tissues); the resultant effect depends on the balance of these two types of action. In carcinoma of the lung the stimulating effect of its involved lobe (part) on the leukocytes diminishes. PMID:2057236

  9. Photoadaptation and protection against active forms of oxygen in the symbiotic procaryote Prochloron sp. and its ascidian host

    SciTech Connect

    Lesser, M.P.; Stochaj, W.R. )

    1990-06-01

    Superoxide dismutase, ascorbate, peroxidase, and catalase activities were studied in the symbiotic photosynthetic procaryote Prochloron sp. and its ascidian host Lissoclinum patella. The protein-specific activities of these antioxidant enzymes in the Prochloron sp. and L. patella collected at different depths from the Great Barrier Reef, Australia, were directly proportional to irradiance, whereas the pigment concentrations in the Prochloron sp. were inversely proportional to irradiance. The presence of a cyanide-sensitive superoxide dismutase, presumably a Cu-An metalloprotein, in the Prochloron sp. extends the possible phylogenetic distribution of this protein. The concentration of UV-absorbing mycosporine-like amino acids in inversely proportional to irradiance in both the host and symbiont, suggesting that these compounds may not provide sufficient protection against UV radiation in high-irradiance environments. The significant differences in the specific activities of these antioxidant enzymes, cellular photosynthetic pigment concentrations, and UV-absorbing compounds from high- and low-irradiance habitats constitute an adaptive response to different photic environments. These photoadaptive responses are essential to prevent inhibition of photosynthesis by high fluxes of visible and UV radiation.

  10. Photoadaptation and Protection against Active Forms of Oxygen in the Symbiotic Procaryote Prochloron sp. and Its Ascidian Host

    PubMed Central

    Lesser, Michael P.; Stochaj, Wayne R.

    1990-01-01

    Superoxide dismutase, ascorbate peroxidase, and catalase activities were studied in the symbiotic photosynthetic procaryote Prochloron sp. and its ascidian host Lissoclinum patella. The protein-specific activities of these antioxidant enzymes in the Prochloron sp. and L. patella collected at different depths from the Great Barrier Reef, Australia, were directly proportional to irradiance, whereas the pigment concentrations in the Prochloron sp. were inversely proportional to irradiance. The presence of a cyanide-sensitive superoxide dismutase, presumably a Cu-Zn metalloprotein, in the Prochloron sp. extends the possible phylogenetic distribution of this protein. The concentration of UV-absorbing mycosporine-like amino acids is inversely proportional to irradiance in both the host and symbiont, suggesting that these compounds may not provide sufficient protection against UV radiation in high-irradiance environments. The significant differences in the specific activities of these antioxidant enzymes, cellular photosynthetic pigment concentrations, and UV-absorbing compounds from high- and low-irradiance habitats constitute an adaptive response to different photic environments. These photoadaptive responses are essential to prevent inhibition of photosynthesis by high fluxes of visible and UV radiation. PMID:16348202

  11. [Induction of heat resistance in wheat coleoptiles by salicylic and succinic acids: connection of the effect with the generation and neutralization of active oxygen forms].

    PubMed

    Kolupaev, Iu E; Iastreb, T O; Shvidenko, N V; Karpets, Iu V

    2012-01-01

    The influence of salicylic (SaA) and succinic (SuA) acids on the generation of active oxygen forms (AOFs) and the heat resistance of wheat (Triticum aestivum L.) coleoptiles has been studied. The treatment of coleoptiles with 10 microM SaA or SuA results in the accumulation of hydrogen peroxide and enhanced formation of a superoxide anion radical. This effect is partially suppressed by both alpha-naphthol (the NADPH oxidase inhibitor) and salicylhydroxamic acid (peroxidase inhibitor). SaA and SuA cause an increase in the activity of antioxidant enzymes, such as superoxide dismutase, catalase, and soluble peroxidase, and improve the heat resistance ofcoleoptiles. Antioxidant ionol and compounds, which inhibit the NADPH oxidase and peroxidase, significantly reduce the positive influence of SaA and SuA on the heat resistance of wheat coleoptiles. AOFs are considered to be intermediates for heat resistance induction in coleoptiles, treated with SaA and SuA; enhanced AOF generation can be caused by an increased activity of the NADPH oxidase and peroxidase. PMID:23101394

  12. [Carbon dioxide inhibits the generation of active forms of oxygen in human and animal cells and the significance of the phenomenon in biology and medicine].

    PubMed

    Boljevic, S; Kogan, A H; Gracev, S V; Jelisejeva, S V; Daniljak, I G

    1996-01-01

    Carbon dioxide (CO2) influence in generation of active oxygen forms (AOF) in human mononuclear cells (blood phagocytes and alveolar macrophages) and animal cells (tissue phagocytes, parenchymal and interstitial cells of liver, kidney, lung, brain and stomach) was investigated. The AOF generation was examined by the methods of chemiluminiscence (CL) using luminol, lucigenin and NBT (nitro blue tetrazolium) reaction. It was established that CO2 in concentrations similar to those in blood (5.1%, pCO2 37.5 mmHg) and at high concentrations (8.2%, pCO2 60 mmHg; 20%, pCO2 146 mmHg) showed pronounced inhibitory effect on the AOF generation in all the studied cells (usually reducing it 2 to 4 times). Those results were obtained not only after the direct contact of isolated cells with CO2, but also after the whole body exposure to CO2. Besides, it was established that venous blood gas mixture (CO2 - 45 mmHg, +O2 - 39 mmHg, + N2 - 646 mmHg) inhibited the AOF generation in cited cells more than the arterial blood gas mixture (CO2 - 40 mmHg, + O2 - 95 mmHg, + N2 - 595 mmHg). Carbon dioxide action mechanism was developed partially through the inhibition of the OAF generation in mitochondria and through deceleration of NADPH oxidative activity. Finally, it was established that CO2 led to the better coordination of oxidation and phosphorylation and increased the phosphorylation velocity in liver mitochondria. The results clearly confirmed the general property of CO2 to inhibit significantly the AOF generation in all the cell types. This favors the new explanation of the well-known evolutionary paradox: the Earth life and organisms preservation when the oxygen, that shows toxic effects on the cells through the AOF, occurs in the atmosphere. The results can also be used to explain in a new way the vasodilating effect of CO2 and the favorable hypercapnotherapy influence on the course of some bronchial asthma forms. The results are probably significant for the analysis of important

  13. Free radicals and activated oxygen.

    PubMed

    Famaey, J P

    1982-01-01

    Superoxide anion (0(-2)), hydrogen peroxide (H2O2) and hydroxyl radical (OH.) are products of the biological reduction of 0(2). They are very reactive and poorly tolerated within living systems and enzymes that catalytically scavenge these products have been evolved as defense mechanisms. These include superoxide dismutases (SOD), catalase and peroxidases. Large amounts of O-2 are produced by different enzymatic and non enzymatic biological processes. Large amounts of activated oxygens are produced by phagocytosing cells such as macrophages and polymorphonuclear cells. This production is associated with the bactericidal actions of these cells but it also largely contributes to exacerbate and sustain the inflammation where these cells congregate. The arachidonic acid pathway triggered by the inflammatory stimuli is also a source for these oxidizing radicals. The production of activated oxygens has been associated with the normal aging process but also with various toxic reactions (e.g. the toxicity of the herbicide paraquat, of the ionizing radiations, of certain antibiotics such as streptonigrin, etc. . . .). O-2 induces the depolymerization of hyaluronic acid which lends viscosity and lubricating properties to synovial fluids. SOD possess antiinflammatory properties and a bovine SOD, orgotein, has now been largely investigated by intramuscular and intraarticular injections in the treatment of rheumatic diseases. Various antiinflammatory compounds (e.g. the salicylates) are able either to inhibit the production of these oxygen radicals or to scavenge them which seems of importance for their antiinflammatory properties. Singlet oxygen, another activated oxygen, might also play a role in the inflammatory process. PMID:6295769

  14. Active oxygen doctors the evidence

    NASA Astrophysics Data System (ADS)

    Castelló, Ana; Francès, Francesc; Corella, Dolores; Verdú, Fernando

    2009-02-01

    Investigation at the scene of a crime begins with the search for clues. In the case of bloodstains, the most frequently used reagents are luminol and reduced phenolphthalein (or phenolphthalin that is also known as the Kastle-Meyer colour test). The limitations of these reagents have been studied and are well known. Household cleaning products have evolved with the times, and new products with active oxygen are currently widely used, as they are considered to be highly efficient at removing all kinds of stains on a wide range of surfaces. In this study, we investigated the possible effects of these new cleaning products on latent bloodstains that may be left at a scene of a crime. To do so, various fabrics were stained with blood and then washed using cleaning agents containing active oxygen. The results of reduced phenolphthalein, luminol and human haemoglobin tests on the washed fabrics were negative. The conclusion is that these new products alter blood to such an extent that it can no longer be detected by currently accepted methods employed in criminal investigations. This inability to locate bloodstains means that highly important evidence (e.g. a DNA profile) may be lost. Consequently, it is important that investigators are aware of this problem so as to compensate for it.

  15. High-temperature oxygen sensors for glass-forming melts.

    PubMed

    Baucke, F G

    1996-09-01

    Electrochemical sensors are reported for the on-line measurement of oxygen partial pressures of oxidic glass-forming melts on a laboratory and technical scale. Based on the principle of solid electrolyte cells without transference, they are principally simple units. The extreme chemical and temperature conditions of their applications, however, demanded extensive fundamental investigations and resulted in specific forms of reference and measuring electrodes, a thermo-dynamic procedure of verifying the correct functioning of such cells, and a method of measuring thermoelectric voltages of non-isothermal glass melts. PMID:15048355

  16. Probing Oxygen Activation Sites in Two Flavoprotein Oxidases Using Chloride as an Oxygen Surrogate

    SciTech Connect

    Kommoju, Phaneeswara-Rao; Chen, Zhi-wei; Bruckner, Robert C.; Mathews, F. Scott; Jorns, Marilyn Schuman

    2011-08-16

    A single basic residue above the si-face of the flavin ring is the site of oxygen activation in glucose oxidase (GOX) (His516) and monomeric sarcosine oxidase (MSOX) (Lys265). Crystal structures of both flavoenzymes exhibit a small pocket at the oxygen activation site that might provide a preorganized binding site for superoxide anion, an obligatory intermediate in the two-electron reduction of oxygen. Chloride binds at these polar oxygen activation sites, as judged by solution and structural studies. First, chloride forms spectrally detectable complexes with GOX and MSOX. The protonated form of His516 is required for tight binding of chloride to oxidized GOX and for rapid reaction of reduced GOX with oxygen. Formation of a binary MSOX-chloride complex requires Lys265 and is not observed with Lys265Met. Binding of chloride to MSOX does not affect the binding of a sarcosine analogue (MTA, methylthioactetate) above the re-face of the flavin ring. Definitive evidence is provided by crystal structures determined for a binary MSOX-chloride complex and a ternary MSOX-chloride-MTA complex. Chloride binds in the small pocket at a position otherwise occupied by a water molecule and forms hydrogen bonds to four ligands that are arranged in approximate tetrahedral geometry: Lys265:NZ, Arg49:NH1, and two water molecules, one of which is hydrogen bonded to FAD:N5. The results show that chloride (i) acts as an oxygen surrogate, (ii) is an effective probe of polar oxygen activation sites, and (iii) provides a valuable complementary tool to the xenon gas method that is used to map nonpolar oxygen-binding cavities.

  17. Prolyl Hydroxylase PHD3 Activates Oxygen-dependent Protein Aggregation

    PubMed Central

    Rantanen, Krista; Pursiheimo, Juha; Högel, Heidi; Himanen, Virpi; Metzen, Eric

    2008-01-01

    The HIF prolyl hydroxylases (PHDs/EGLNs) are central regulators of the molecular responses to oxygen availability. One isoform, PHD3, is expressed in response to hypoxia and causes apoptosis in oxygenated conditions in neural cells. Here we show that PHD3 forms subcellular aggregates in an oxygen-dependent manner. The aggregation of PHD3 was seen under normoxia and was strongly reduced under hypoxia or by the inactivation of the PHD3 hydroxylase activity. The PHD3 aggregates were dependent on microtubular integrity and contained components of the 26S proteasome, chaperones, and ubiquitin, thus demonstrating features that are characteristic for aggresome-like structures. Forced expression of the active PHD3 induced the aggregation of proteasomal components and activated apoptosis under normoxia in HeLa cells. The apoptosis was seen in cells prone to PHD3 aggregation and the PHD3 aggregation preceded apoptosis. The data demonstrates the cellular oxygen sensor PHD3 as a regulator of protein aggregation in response to varying oxygen availability. PMID:18337469

  18. Biochar activated by oxygen plasma for supercapacitors

    NASA Astrophysics Data System (ADS)

    Gupta, Rakesh Kumar; Dubey, Mukul; Kharel, Parashu; Gu, Zhengrong; Fan, Qi Hua

    2015-01-01

    Biochar, also known as black carbon, is a byproduct of biomass pyrolysis. As a low-cost, environmental-friendly material, biochar has the potential to replace more expensive synthesized carbon nanomaterials (e.g. carbon nanotubes) for use in future supercapacitors. To achieve high capacitance, biochar requires proper activation. A conventional approach involves mixing biochar with a strong base and baking at a high temperature. However, this process is time consuming and energy inefficient (requiring temperatures >900 °C). This work demonstrates a low-temperature (<150 °C) plasma treatment that efficiently activates a yellow pine biochar. Particularly, the effects of oxygen plasma on the biochar microstructure and supercapacitor characteristics are studied. Significant enhancement of the capacitance is achieved: 171.4 F g-1 for a 5-min oxygen plasma activation, in comparison to 99.5 F g-1 for a conventional chemical activation and 60.4 F g-1 for untreated biochar. This enhancement of the charge storage capacity is attributed to the creation of a broad distribution in pore size and a larger surface area. The plasma activation mechanisms in terms of the evolution of the biochar surface and microstructure are further discussed.

  19. Quantifying consumption rates of dissolved oxygen along bed forms

    NASA Astrophysics Data System (ADS)

    Boano, Fulvio; De Falco, Natalie; Arnon, Shai

    2016-04-01

    Streambed interfaces represent hotspots for nutrient transformations because they host different microbial species, and the evaluation of these reaction rates is important to assess the fate of nutrients in riverine environments. In this work we analyze a series of flume experiments on oxygen demand in dune-shaped hyporheic sediments under losing and gaining flow conditions. We employ a new modeling code to quantify oxygen consumption rates from observed vertical profiles of oxygen concentration. The code accounts for transport by molecular diffusion and water advection, and automatically determines the reaction rates that provide the best fit between observed and modeled concentration values. The results show that reaction rates are not uniformly distributed across the streambed, in agreement with the expected behavior predicted by hyporheic exchange theory. Oxygen consumption was found to be highly influenced by the presence of gaining or losing flow conditions, which controlled the delivery of labile DOC to streambed microorganisms.

  20. Removal of Biologically Active Organic Contaminants using Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Banks, Michael A. (Inventor); Banks, Eric B. (Inventor)

    2003-01-01

    Biomedical devices that are to come into contact with living tissue, such as prosthetic and other implants for the human body and the containers used to store and transport them, are together cleaned of non-living, but biologically active organic materials, including endotoxins such as lipopolysaccharides, and assembled into a hermetically sealed package without recontamination. This is achieved by cleaning both the device and package components together in an apparatus, which includes a hermetically sealed chamber, in which they are contacted with atomic oxygen which biocleans them, by oxidizing the biologically active organic materials. The apparatus also includes means for manipulating the device and container and hermetically sealing the cleaned device into the cleaned container to form the package. A calibrated witness coupon visually indicates whether or not the device and container have received enough exposure to the atomic oxygen to have removed the organic materials from their surfaces. Gamma radiation is then used to sterilize the device in the sealed container.

  1. Activation of molecular oxygen and the nature of the active oxygen species for CO oxidation on oxide supported Au catalysts.

    PubMed

    Widmann, D; Behm, R J

    2014-03-18

    Although highly dispersed Au catalysts with Au nanoparticles (NPs) of a few nanometers in diameter are well-known for their high catalytic activity for several oxidation and reduction reactions already at rather low temperatures for almost 30 years, central aspects of the reaction mechanism are still unresolved. While most studies focused on the active site, the active Au species, and the effect of the support material, the most crucial step during oxidation reactions, the activation of molecular oxygen and the nature of the resulting active oxygen species (Oact), received more attention just recently. This is topic of this Account, which focuses on the formation, location, and nature of the Oact species present on metal oxide supported Au catalysts under typical reaction conditions, at room temperature and above. It is mainly based on quantitative temporal analysis of products (TAP) reactor measurements, which different from most spectroscopic techniques are able to detect and quantify these species even at the extremely low concentrations present under realistic reaction conditions. Different types of pulse experiments were performed, during which the highly dispersed, realistic powder catalysts are exposed to very low amounts of reactants, CO and/or O2, in order to form and reactively remove Oact species and gain information on their formation, nature, and the active site for Oact formation. Our investigations have shown that the active oxygen species for CO oxidation on Au/TiO2 for reaction at 80 °C and higher is a highly stable atomic species, which at 80 °C is formed only at the perimeter of the Au-oxide interface and whose reactive removal by CO is activated, but not its formation. From these findings, it is concluded that surface lattice oxygen represents the Oact species for the CO oxidation. Accordingly, the CO oxidation proceeds via a Au-assisted Mars-van Krevelen mechanism, during which surface lattice oxygen close to the Au NPs is removed by reaction

  2. Effects of MCI-186 upon neutrophil-derived active oxygens.

    PubMed

    Sumitomo, K; Shishido, N; Aizawa, H; Hasebe, N; Kikuchi, K; Nakamura, M

    2007-01-01

    Reactions of 3-methyl-1-phenyl-2-pyrazoline-5-one (MCI-186) with hypochlorous acid and superoxide were analysed by spectrophotometry and mass spectrometry. The results were applied to the neutrophil system to evaluate the scavenging activity of neutrophil-derived active oxygen species by MCI-186. MCI-186 reacted rapidly with hypochlorous acid (1 x 10(6) M(-1)s(-1)) to form a chlorinated intermediate, followed by a slow conversion to a new spectrum. MCI-186 consumed 3 moles of hypochlorous acid and did not react with superoxide. The newly synthesized fluorescence probes, 2-[6-(4'-amino)-phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (APF) and 2-[6-(4'-hydroxy)phenoxy-3H-anthen-3-on-9-yl]benzoic acid (HPF) successfully detected neutrophil-derived active oxygens (Setsukinai K, Urano Y, Kakinuma K, Majima HJ, Nagano T. Development of novel fluorescence probes that can reliably detect reactive oxygen species and distinguish specific species. J Biol Chem 2003; 278: 3170-3175). The rate constants for the reaction of hypochlorous acid with MCI-186 and fluorescence probes was in the order of MCI-186 > APF > HPF. Fluorescence due to the oxidation of APF and HPF was observed with the stimulated neutrophils. The result that the intensity from APF oxidation was higher than that from HPF oxidation is compatible with reports that APF selectively reacts with hypochlorous acid. Fluorescence due to oxidation of both APF and HPF decreased when the reactions were carried out in the presence of a fluorescence probe and MCI-186 in a dose-dependent manner. These results indicate that MCI-186 effectively scavenges neutrophil-derived hypochlorous acid and other active oxygens. PMID:17705989

  3. SAFETY ASPECTS OF OXYGEN AERATION ACTIVATED SLUDGE SYSTEMS

    EPA Science Inventory

    This project was carried out to assess the impact of the use of oxygen and oxygen-enriched air for aeration of activated sludge systems on the safety of municipal waste-water treatment plants and their personnel. The tasks included (1) determination of oxygen combustion hazards f...

  4. Henry's Law Activity of Oxygen in Molten Iron

    NASA Astrophysics Data System (ADS)

    Matousek, J. W.

    2015-09-01

    A model is proposed for the solubility of oxygen in molten iron in dilute solutions in which the oxygen exists in two states, free and associated. Only the free oxygen has thermodynamic activity in the sense of interaction with an electrochemical cell to produce the voltage described by the Nernst equation.

  5. BIOLOGICALLY ENHANCED OXYGEN TRANSFER IN THE ACTIVATED SLUDGE PROCESS (JOURNAL)

    EPA Science Inventory

    Biologically enhanced oxgyen transfer has been a hypothesis to explain observed oxygen transfer rates in activated sludge systems that were well above that predicted from aerator clean-water testing. The enhanced oxygen transfer rates were based on tests using BOD bottle oxygen ...

  6. Multiple forms of soluble monophenol, dihydroxyphenylalanine: oxygen oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum). III. Influence of pH on the molecular weight distribution of enzyme activity in potato juice.

    PubMed

    Matheis, G; Belitz, H D

    1979-09-01

    Gel chromatography on Sepharose and on Sephadex was used to separate the soluble phenol oxidase in various potato juices into multiple molecular forms ranging from 36,000 to 800,000 daltons. Adjustment of potato juice from physiological pH (ca. 6) to pH 4.5 or to pH 7.8 resulted in the predominance of low-mol.-wt. (less than 150,000 daltons) or high-mol.-wt. (greater than 150,000 daltons) enzyme forms, respectively. This suggests association phenomena of subunits. In potato juice of physiological pH and in potato juice adjusted to pH 4.5, all enzyme forms exhibited both monophenol and o-diphenol oxidase activities (assayed at pH 6.0). In potato juice adjusted to pH 7.8 considerable loss of monophenol oxidase activity (assayed at pH 6.0) occurred. This suggests that o-diphenol oxidase is more alkali-stable than monophenol oxidase. The significance of these findings for enzyme purifications and for the in vivo action of the enzyme is discussed. PMID:41378

  7. Oxygen consumption along bed forms under losing and gaining streamflow conditions

    NASA Astrophysics Data System (ADS)

    De Falco, Natalie; Arnon, Shai; Boano, Fulvio

    2016-04-01

    Recent studies have demonstrated that bed forms are the most significant geomorphological structure that drives hyporheic exchange and biogeochemical processes in stream networks. Other studies also demonstrated that due to the hyporheic flow patterns within bed form, biogeochemical processes do not occur uniformly along and within the bed forms. The objective of this work was to systematically evaluate how losing or gaining flow conditions affect oxygen consumption by biofilm along sandy bed forms. We measured the effects of losing and gaining flow conditions on oxygen consumption by combining modeling and experiments in a novel laboratory flume system that enable the control of losing and gaining fluxes. Oxygen consumption was measured after growing a benthic biofilm fed with Sodium Benzoate (as a carbon source) and measuring the distribution of oxygen in the streambed with microelectrodes. The experimental results were analyzed using a novel code that calculates vertical profiles of reaction rates in the presence of hyporheic water fluxes. These experimental observations and modeling revealed that oxygen distribution varied along the bed forms. The zone of oxygen consumption (i.e. depth of penetration) was the largest at the upstream side of the bed form and the smallest in the lee side (at the lowest part of the bed form), regardless of the flow conditions. Also, the zone of oxygen consumption was the largest under losing conditions, the smallest under gaining conditions, and in-between under neutral conditions. The distribution of oxygen consumption rates determined with our new model will be also discussed. Our preliminary results enable us to show the importance of the coupling between flow conditions and oxygen consumption along bed forms and are expected to improve our understanding of nutrient cycling in streams.

  8. Protocyanobacteria: Oxygenic and Anoxygenic photosynthesis in mat-forming bacteria

    NASA Technical Reports Server (NTRS)

    Cohen, Y.

    1985-01-01

    The oldest record of life is preserved in prePhanerozoic stromatolites dated 3500 million years old and is most likely of filamentous mat-forming cyanobacteria. The sedimentary records of cyanobacterial mats in stromatolites are the most abundant record of life throughout the prePhanerozoic. Stromatolites persisted into the Phanerozoic Eon, yet they become much less pronounced relative to earlier ones. The abundance and persistence of cyanobacterial mats throughout most of geological time point to the evolutionary success of these kinds of microbial communities and their possible role in the evolution of the earth and atmosphere.

  9. On the determination of oxygen abundances in chromospherically active stars

    NASA Astrophysics Data System (ADS)

    Morel, T.; Micela, G.

    2004-08-01

    We discuss oxygen abundances derived from [O I] λ6300s and the O I triplet in stars spanning a wide range in chromospheric activity level, and show that these two indicators yield increasingly discrepant results with higher chromospheric/coronal activity measures. While the forbidden and permitted lines give fairly consistent results for solar-type disk dwarfs, spuriously high O I triplet abundances are observed in young Hyades and Pleiades stars, as well as in individual components of RS CVn binaries (up to 1.8 dex). The distinct behaviour of the [O I]-based abundances which consistently remain near-solar suggests that this phenomenon mostly results from large departures from LTE affecting the O I triplet at high activity level that are currently unaccounted for, but also possibly from a failure to adequately model the atmospheres of K-type stars. These results suggest that some caution should be exercised when interpreting oxygen abundances in active binaries or young open cluster stars. Based on observations collected at the European Southern Observatory, Chile (Proposals 64.L-0249 and 071.D-0260). Table \\ref{tab_data} is only available in electronic form at http://www.edpsciences.org

  10. Electrochemically Formed Ultrafine Metal Oxide Nanocatalysts for High-Performance Lithium-Oxygen Batteries.

    PubMed

    Liu, Bin; Yan, Pengfei; Xu, Wu; Zheng, Jianming; He, Yang; Luo, Langli; Bowden, Mark E; Wang, Chong-Min; Zhang, Ji-Guang

    2016-08-10

    Lithium-oxygen (Li-O2) batteries have an extremely high theoretical specific energy density when compared with conventional energy-storage systems. However, practical application of the Li-O2 battery system still faces significant challenges. In this work, we report a new approach for synthesis of ultrafine metal oxide nanocatalysts through an electrochemical prelithiation process. This process reduces the size of NiCo2O4 (NCO) particles from 20-30 nm to a uniformly distributed domain of ∼2 nm and significantly improves their catalytic activity. Structurally, the prelithiated NCO nanowires feature ultrafine NiO/CoO nanoparticles that are highly stable during prolonged cycles in terms of morphology and particle size, thus maintaining an excellent catalytic effect to oxygen reduction and evolution reactions. A Li-O2 battery using this catalyst demonstrated an initial capacity of 29 280 mAh g(-1) and retained a capacity of >1000 mAh g(-1) after 100 cycles based on the weight of the NCO active material. Direct in situ transmission electron microscopy observations conclusively revealed the lithiation/delithiation process of as-prepared NCO nanowires and provided in-depth understanding for both catalyst and battery chemistries of transition-metal oxides. This unique electrochemical approach could also be used to form ultrafine nanoparticles of a broad range of materials for catalyst and other applications. PMID:27380300

  11. PARALLEL EVALUATION OF AIR- AND OXYGEN-ACTIVATED SLUDGE

    EPA Science Inventory

    To provide data on the relative merits of air and oxygen in the activated sludge process, two 1900-cu m/day (0.5-mgd) activated sludge pilot plant, one air and one oxygen system, were operated side-by-side at the Joint Water Pollution Control Plant, Carson, California. Both of th...

  12. Reactive oxygen species-activated nanomaterials as theranostic agents.

    PubMed

    Kim, Kye S; Lee, Dongwon; Song, Chul Gyu; Kang, Peter M

    2015-01-01

    Reactive oxygen species (ROS) are generated from the endogenous oxidative metabolism or from exogenous pro-oxidant exposure. Oxidative stress occurs when there is excessive production of ROS, outweighing the antioxidant defense mechanisms which may lead to disease states. Hydrogen peroxide (H2O2) is one of the most abundant and stable forms of ROS, implicated in inflammation, cellular dysfunction and apoptosis, which ultimately lead to tissue and organ damage. This review is an overview of the role of ROS in different diseases. We will also examine ROS-activated nanomaterials with emphasis on hydrogen peroxide, and their potential medical implications. Further development of the biocompatible, stimuli-activated agent responding to disease causing oxidative stress, may lead to a promising clinical use. PMID:26328770

  13. Reactive oxygen species-activated nanomaterials as theranostic agents

    PubMed Central

    Kim, Kye S; Lee, Dongwon; Song, Chul Gyu; Kang, Peter M

    2015-01-01

    Reactive oxygen species (ROS) are generated from the endogenous oxidative metabolism or from exogenous pro-oxidant exposure. Oxidative stress occurs when there is excessive production of ROS, outweighing the antioxidant defense mechanisms which may lead to disease states. Hydrogen peroxide (H2O2) is one of the most abundant and stable forms of ROS, implicated in inflammation, cellular dysfunction and apoptosis, which ultimately lead to tissue and organ damage. This review is an overview of the role of ROS in different diseases. We will also examine ROS-activated nanomaterials with emphasis on hydrogen peroxide, and their potential medical implications. Further development of the biocompatible, stimuli-activated agent responding to disease causing oxidative stress, may lead to a promising clinical use. PMID:26328770

  14. Molecular dioxygen enters the active site of 12/15-lipoxygenase via dynamic oxygen access channels.

    PubMed

    Saam, Jan; Ivanov, Igor; Walther, Matthias; Holzhütter, Hermann-Georg; Kuhn, Hartmut

    2007-08-14

    Cells contain numerous enzymes that use molecular oxygen for their reactions. Often, their active sites are buried deeply inside the protein, which raises the question whether there are specific access channels guiding oxygen to the site of catalysis. Choosing 12/15-lipoxygenase as a typical example for such oxygen-dependent enzymes, we determined the oxygen distribution within the protein and defined potential routes for oxygen access. For this purpose, we have applied an integrated strategy of structural modeling, molecular dynamics simulations, site-directed mutagenesis, and kinetic measurements. First, we computed the 3D free-energy distribution for oxygen, which led to identification of four oxygen channels in the protein. All channels connect the protein surface with a region of high oxygen affinity at the active site. This region is localized opposite to the nonheme iron providing a structural explanation for the reaction specificity of this lipoxygenase isoform. The catalytically most relevant path can be obstructed by L367F exchange, which leads to a strongly increased Michaelis constant for oxygen. The blocking mechanism is explained in detail by reordering the hydrogen-bonding network of water molecules. Our results provide strong evidence that the main route for oxygen access to the active site of the enzyme follows a channel formed by transiently interconnected cavities whereby the opening and closure are governed by side chain dynamics. PMID:17675410

  15. Active site densities, oxygen activation and adsorbed reactive oxygen in alcohol activation on npAu catalysts.

    PubMed

    Wang, Lu-Cun; Friend, C M; Fushimi, Rebecca; Madix, Robert J

    2016-07-01

    The activation of molecular O2 as well as the reactivity of adsorbed oxygen species is of central importance in aerobic selective oxidation chemistry on Au-based catalysts. Herein, we address the issue of O2 activation on unsupported nanoporous gold (npAu) catalysts by applying a transient pressure technique, a temporal analysis of products (TAP) reactor, to measure the saturation coverage of atomic oxygen, its collisional dissociation probability, the activation barrier for O2 dissociation, and the facility with which adsorbed O species activate methanol, the initial step in the catalytic cycle of esterification. The results from these experiments indicate that molecular O2 dissociation is associated with surface silver, that the density of reactive sites is quite low, that adsorbed oxygen atoms do not spill over from the sites of activation onto the surrounding surface, and that methanol reacts quite facilely with the adsorbed oxygen atoms. In addition, the O species from O2 dissociation exhibits reactivity for the selective oxidation of methanol but not for CO. The TAP experiments also revealed that the surface of the npAu catalyst is saturated with adsorbed O under steady state reaction conditions, at least for the pulse reaction. PMID:27376884

  16. A ligand field chemistry of oxygen generation by the oxygen-evolving complex and synthetic active sites

    PubMed Central

    Betley, Theodore A; Surendranath, Yogesh; Childress, Montana V; Alliger, Glen E; Fu, Ross; Cummins, Christopher C; Nocera, Daniel G

    2007-01-01

    Oxygen–oxygen bond formation and O2 generation occur from the S4 state of the oxygen-evolving complex (OEC). Several mechanistic possibilities have been proposed for water oxidation, depending on the formal oxidation state of the Mn atoms. All fall under two general classifications: the AB mechanism in which nucleophilic oxygen (base, B) attacks electrophilic oxygen (acid, A) of the Mn4Ca cluster or the RC mechanism in which radical-like oxygen species couple within OEC. The critical intermediate in either mechanism involves a metal oxo, though the nature of this oxo for AB and RC mechanisms is disparate. In the case of the AB mechanism, assembly of an even-electron count, high-valent metal-oxo proximate to a hydroxide is needed whereas, in an RC mechanism, two odd-electron count, high-valent metal oxos are required. Thus the two mechanisms give rise to very different design criteria for functional models of the OEC active site. This discussion presents the electron counts and ligand geometries that support metal oxos for AB and RC O–O bond-forming reactions. The construction of architectures that bring two oxygen functionalities together under the purview of the AB and RC scenarios are described. PMID:17971328

  17. Oxygen requirements for formation and activity of the squalene expoxidase in Saccharomyces cerevisiae

    NASA Technical Reports Server (NTRS)

    Jahnke, L.; Klein, H. P.

    1983-01-01

    The effect of oxygen on squalene epoxidase activity in Saccharomyces cerevisiae was investigated. In cells grown in standing cultures, the epoxidase was localized mainly in the 'mitochondrial' fraction. Upon aeration, enzyme activity increased and the newly formed enzyme was associated with the 'microsomal' fraction. At 0.03 percent (vol/vol) oxygen, epoxidase levels doubled, whereas the ergosterol level was only slightly increased. Cycloheximide inhibited the increase in epoxidase under these conditions. An apparent K sub m for oxygen of 0.38 percent (vol/vol) was determined from a crude particulate preparation for the epoxidase.

  18. Oxygen-independent induction of enzyme activities related to oxygen metabolism in yeast by copper.

    PubMed

    Galiazzo, F; Schiesser, A; Rotilio, G

    1988-04-14

    Aerobic growth of Saccharomyces cerevisiae in the presence of CuSO4 (between 0.1 and 1 mM) caused a generalized induction of major enzyme activities involved in 'housekeeping' routes of oxygen metabolism (cytochrome oxidase, glutathione peroxidases and catalase) which were comparable to or higher than that observed with Cu,Zn-superoxide dismutase. Fumarase and glutathione transferase, tested as controls for oxygen-unrelated activities, were found to decrease under the same conditions. In the absence of oxygen, copper addition to yeast resulted in significant increases of Cu,Zn-superoxide dismutase and glutathione peroxidases and a slight increase of cytochrome oxidase, with catalase remaining undetectable irrespective of whether or not copper was present. Other metal ions tested (Mn2+, Co2+) were unable to produce such effects. It is concluded that copper has a general inducing effect on enzymes related to metabolism of oxygen and oxygen derivatives, which is mediated neither by formation of O2-. and H2O2 nor by interaction with copper-specific apoproteins. These results point to a general role of copper as regulator of the expression of major enzyme activities involved in biological oxygen activation. PMID:2831994

  19. Oxygen fugacity of basaltic magmas and the role of gas-forming elements

    NASA Technical Reports Server (NTRS)

    Sato, M.

    1978-01-01

    It is suggested that major variations in the relative oxygen fugacity of a basaltic magma are caused primarily by gas-forming elements, especially carbon and hydrogen. According to this theory, carbon, present in the source region of a basaltic magma, reduces the host magma during ascent, as isothermally carbon becomes more reducing with decreasing pressure. For an anhydrous magma such as lunar basalts, this reduction continues through the extrusive phase and the relative oxygen fugacity decreases rapidly until buffered by the precipitation of a metallic phase. For hydrous magmas such as terrestrial basalts, reduction by carbon is eventually superceded by oxidation due to loss of H2 generated by the reaction of C with H2O and by thermal dissociation of H2O. The relative oxygen fugacity of a hydrous magma initially decreases as a magma ascends from the source region and then increases until magnetite crystallization curbs the rising trend of the relative oxygen fugacity.

  20. Kinetic studies on the oxidation of semiquinone and hydroquinone forms of Arabidopsis cryptochrome by molecular oxygen.

    PubMed

    van Wilderen, Luuk J G W; Silkstone, Gary; Mason, Maria; van Thor, Jasper J; Wilson, Michael T

    2015-01-01

    Cryptochromes (crys) are flavoprotein photoreceptors present throughout the biological kingdom that play important roles in plant development and entrainment of the circadian clock in several organisms. Crys non-covalently bind flavin adenine dinucleotide (FAD) which undergoes photoreduction from the oxidised state to a radical form suggested to be active in signalling in vivo. Although the photoreduction reactions have been well characterised by a number of approaches, little is known of the oxidation reactions of crys and their mechanisms. In this work, a stopped-flow kinetics approach is used to investigate the mechanism of cry oxidation in the presence and absence of an external electron donor. This in vitro study extends earlier investigations of the oxidation of Arabidopsis cryptochrome1 by molecular oxygen and demonstrates that, under some conditions, a more complex model for oxidation of the flavin than was previously proposed is required to accommodate the spectral evidence (see P. Müller and M. Ahmad (2011) J. Biol. Chem. 286, 21033-21040 [1]). In the absence of an electron donor, photoreduction leads predominantly to the formation of the radical FADH(•). Dark recovery most likely forms flavin hydroperoxide (FADHOOH) requiring superoxide. In the presence of reductant (DTT), illumination yields the fully reduced flavin species (FADH(-)). Reaction of this with dioxygen leads to transient radical (FADH(•)) and simultaneous accumulation of oxidised species (FAD), possibly governed by interplay between different cryptochrome molecules or cooperativity effects within the cry homodimer. PMID:26649273

  1. Kinetic studies on the oxidation of semiquinone and hydroquinone forms of Arabidopsis cryptochrome by molecular oxygen

    PubMed Central

    van Wilderen, Luuk J.G.W.; Silkstone, Gary; Mason, Maria; van Thor, Jasper J.; Wilson, Michael T.

    2015-01-01

    Cryptochromes (crys) are flavoprotein photoreceptors present throughout the biological kingdom that play important roles in plant development and entrainment of the circadian clock in several organisms. Crys non-covalently bind flavin adenine dinucleotide (FAD) which undergoes photoreduction from the oxidised state to a radical form suggested to be active in signalling in vivo. Although the photoreduction reactions have been well characterised by a number of approaches, little is known of the oxidation reactions of crys and their mechanisms. In this work, a stopped-flow kinetics approach is used to investigate the mechanism of cry oxidation in the presence and absence of an external electron donor. This in vitro study extends earlier investigations of the oxidation of Arabidopsis cryptochrome1 by molecular oxygen and demonstrates that, under some conditions, a more complex model for oxidation of the flavin than was previously proposed is required to accommodate the spectral evidence (see P. Müller and M. Ahmad (2011) J. Biol. Chem. 286, 21033–21040 [1]). In the absence of an electron donor, photoreduction leads predominantly to the formation of the radical FADH•. Dark recovery most likely forms flavin hydroperoxide (FADHOOH) requiring superoxide. In the presence of reductant (DTT), illumination yields the fully reduced flavin species (FADH−). Reaction of this with dioxygen leads to transient radical (FADH•) and simultaneous accumulation of oxidised species (FAD), possibly governed by interplay between different cryptochrome molecules or cooperativity effects within the cry homodimer. PMID:26649273

  2. Active superconducting devices formed of thin films

    DOEpatents

    Martens, Jon S.; Beyer, James B.; Nordman, James E.; Hohenwarter, Gert K. G.

    1991-05-28

    Active superconducting devices are formed of thin films of superconductor which include a main conduction channel which has an active weak link region. The weak link region is composed of an array of links of thin film superconductor spaced from one another by voids and selected in size and thickness such that magnetic flux can propagate across the weak link region when it is superconducting. Magnetic flux applied to the weak link region will propagate across the array of links causing localized loss of superconductivity in the links and changing the effective resistance across the links. The magnetic flux can be applied from a control line formed of a superconducting film deposited coplanar with the main conduction channel and weak link region on a substrate. The devices can be formed of any type to superconductor but are particularly well suited to the high temperature superconductors since the devices can be entirely formed from coplanar films with no overlying regions. The devices can be utilized for a variety of electrical components, including switching circuits, amplifiers, oscillators and modulators, and are well suited to microwave frequency applications.

  3. Leukocytic oxygen activation and microbicidal oxidative toxins.

    PubMed

    Hurst, J K; Barrette, W C

    1989-01-01

    Following a brief introduction of cellular response to stimulation comprising leukocyte activation, three major areas are discussed: (1) the neutrophil oxidase; (2) myeloperoxidase (MPO)-dependent oxidative microbicidal reactions; and (3) MPO-independent oxidative reactions. Topics included in section (A) are current views on the activation mechanism, redox composition, structural and topographic organization of the oxidase, and its respiratory products. In section (B), emphasis is placed on recent research on cidal mechanisms of HOCl, including the oxidative biochemistry of active chlorine compounds, identification of sites of lesions in bacteria, and attendant metabolic consequences. In section (C), we review the (bio)chemistry of H2O2 and .OH microbicidal reactions, with particular attention being given to addressing the controversial issue of probe methods to identify .OH radical and critical assessment of the recent proposal that MPO-independent killing arises from site-specific metal-catalyzed Fenton-type chemistry. PMID:2548810

  4. OXYGEN UTILIZATION IN ACTIVATED SLUDGE PLANTS: SIMULATION AND MODEL CALIBRATION

    EPA Science Inventory

    The objective of the research described in the report is to apply recent advances in activated sludge process modeling to the simulation of oxygen utilization rates in full scale activated sludge treatment plants. This is accomplished by calibrating the International Association ...

  5. Oxygen tension limits nitric oxide synthesis by activated macrophages.

    PubMed Central

    McCormick, C C; Li, W P; Calero, M

    2000-01-01

    Previous studies have established that constitutive calcium-dependent ('low-output') nitric oxide synthase (NOS) is regulated by oxygen tension. We have investigated the role of oxygen tension in the synthesis of NO by the 'high-output' calcium-independent NOS in activated macrophages. Hypoxia increased macrophage NOS gene expression in the presence of one additional activator, such as lipopolysaccharide or interferon-gamma, but not in the presence of both. Hypoxia markedly reduced the synthesis of NO by activated macrophages (as measured by accumulation of nitrite and citrulline), such that, at 1% oxygen tension, NO accumulation was reduced by 80-90%. The apparent K(m) for oxygen calculated from cells exposed to a range of oxygen tensions was found to be 10.8%, or 137 microM, O(2) This value is considerably higher than the oxygen tension in tissues, and is virtually identical to that reported recently for purified recombinant macrophage NOS. The decrease in NO synthesis did not appear to be due to diminished arginine or cofactor availability, since arginine transport and NO synthesis during recovery in normoxia were normal. Analysis of NO synthesis during hypoxia as a function of extracellular arginine indicated that an altered V(max), but not K(m)(Arg), accounted for the observed decrease in NO synthesis. We conclude that oxygen tension regulates the synthesis of NO in macrophages by a mechanism similar to that described previously for the calcium-dependent low-output NOS. Our data suggest that oxygen tension may be an important physiological regulator of macrophage NO synthesis in vivo. PMID:10970783

  6. Associative oxygen species on the oxidized silver surface formed under O 2 microwave excitation

    NASA Astrophysics Data System (ADS)

    Boronin, A. I.; Koscheev, S. V.; Murzakhmetov, K. T.; Avdeev, V. I.; Zhidomirov, G. M.

    2000-09-01

    The experimental methods of X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS, respectively) and the quantum mechanical calculations are applied for analysis of oxygen states on the silver oxide surface. At low temperatures ( T<470 K), the silver surface is intensively oxidized by a microwave oxygen discharge to form cuprite Ag 2O. Two adsorbed oxygen species of the atomic (dissociative) and molecular (associative) nature can be adsorbed on the cuprite Ag 2O surface. A comparison of the UPS data and the DFT calculations of molecular models Ag 2-O 2 and Ag 2-O 3 shows that the formation of ozonide-like structures is preferable to that of peroxide species. Thermal stability and the reaction probability of the adsorbed states are investigated.

  7. Microfluidic Platform Generates Oxygen Landscapes for Localized Hypoxic Activation

    PubMed Central

    Rexius, Megan L.; Mauleon, Gerardo; Malik, Asrar B.; Rehman, Jalees; Eddington, David T.

    2014-01-01

    An open-well microfluidic platform generates an oxygen landscape using gas-perfused networks which diffuse across a membrane. The device enables real-time analysis of cellular and tissue responses to oxygen tension to define how cells adapt to heterogeneous oxygen conditions found in the physiological setting. We demonstrate that localized hypoxic activation of cells elicited specific metabolic and gene responses in human microvascular endothelial cells and bone marrow-derived mesenchymal stem cells. A robust demonstration of the compatibility of the device with standard laboratory techniques demonstrates the wide utility of the method. This platform is ideally suited to study real-time cell responses and cell-cell interactions within physiologically relevant oxygen landscapes. PMID:25315003

  8. Reactive Oxygen Species Mediated Activation of a Dormant Singlet Oxygen Photosensitizer: From Autocatalytic Singlet Oxygen Amplification to Chemicontrolled Photodynamic Therapy.

    PubMed

    Durantini, Andrés M; Greene, Lana E; Lincoln, Richard; Martínez, Sol R; Cosa, Gonzalo

    2016-02-01

    Here we show the design, preparation, and characterization of a dormant singlet oxygen ((1)O2) photosensitizer that is activated upon its reaction with reactive oxygen species (ROS), including (1)O2 itself, in what constitutes an autocatalytic process. The compound is based on a two segment photosensitizer-trap molecule where the photosensitizer segment consists of a Br-substituted boron-dipyrromethene (BODIPY) dye. The trap segment consists of the chromanol ring of α-tocopherol, the most potent naturally occurring lipid soluble antioxidant. Time-resolved absorption, fluorescence, and (1)O2 phosphorescence studies together with fluorescence and (1)O2 phosphorescence emission quantum yields collected on Br2B-PMHC and related bromo and iodo-substituted BODIPY dyes show that the trap segment provides a total of three layers of intramolecular suppression of (1)O2 production. Oxidation of the trap segment with ROS restores the sensitizing properties of the photosensitizer segment resulting in ∼40-fold enhancement in (1)O2 production. The juxtaposed antioxidant (chromanol) and prooxidant (Br-BODIPY) antagonistic chemical activities of the two-segment compound enable the autocatalytic, and in general ROS-mediated, activation of (1)O2 sensitization providing a chemical cue for the spatiotemporal control of (1)O2.The usefulness of this approach to selectively photoactivate the production of singlet oxygen in ROS stressed vs regular cells was successfully tested via the photodynamic inactivation of a ROS stressed Gram negative Escherichia coli strain. PMID:26789198

  9. OXYGEN-ACTIVATED SLUDGE PLANT COMPLETES TWO YEARS OF SUCCESSFUL OPERATION

    EPA Science Inventory

    A detailed report of the conversion to and operational performance of an oxygen-activated sludge system at the Westgate wastewater treatment plant in Fairfax County, Virginia, is given in this report. It is presented in the form of a case history including the time span leading u...

  10. [Effect of substances which change the proton-motive force on activity of methane microbe oxygenation].

    PubMed

    Malashenko, Iu P; Sokolov, I G; Rokitko, P V; Romanovskaia, V A

    2006-01-01

    High extracellular concentration of K+ stimulated methane oxygenation with Methylomonas rubra 15 [Russian character: see text], Methylococcus thermophilus 111 [Russian character: see text] and Methylococcus capsulatus 494 at neutral value of pH. That was determined by K+ arrival to the cells at neutral medium pH that resulted in the increase of pH difference between the exterior and interior sides of the membrane (ApH) and, respectively, in the increase of the methane oxygenation rate. Thus, methane monooxygenation depends on the availability of ion gradients on a membrane. Ionophores valinomycin and monensin inhibited methane oxygenation by the cells of Methylomonas rubra 15 [Russian character: see text] that evidenced for the methane oxygenation dependence on the protone-motive force which could be formed as the result both of protons displacement with oxygenation of methane monooxygenation products and of the gradient of potassium and sodium ions. Protonophore FCCP suppressed completely methane oxygenation in Methylococcus capsulatus 494 and M. thermophilus 111 [Russian character: see text] at neutral pH, and took no effect at the alkaline values of pH. This suggests that FCCP dissipates the proton-motive force and does not inhibit methane monooxygenase activity. The results obtained indicate that the process of methane oxygenation should be combined with energy generation in a form of the transmembrane electric charge (delta psi) and proton gradient (deltapH). PMID:17243361

  11. Excited states in the active media of oxygen - iodine lasers

    SciTech Connect

    Azyazov, V N

    2009-11-30

    A review of investigations of kinetic processes in active media oxygen - iodine lasers (OILs) performed in the last decade is presented. The mechanisms of pumping and quenching of electronically and vibrationally excited O{sub 2} and I{sub 2} molecules are considered, and dissociation mechanisms of I{sub 2} in the active medium of the OIL are analysed. The values of kinetic constants of processes proceeding in the active media of OILs are recommended. (review)

  12. Apparatus in the form of a disk for the separation of oxygen from other gases and/or for the pumping of oxygen and the method of removing the oxygen

    NASA Technical Reports Server (NTRS)

    Suitor, Jerry W. (Inventor); Berdahl, C. Martin (Inventor); Marner, Wilbur J. (Inventor)

    1989-01-01

    An apparatus in the form of a disk for the separation of oxygen from gases, or for the pumping of oxygen, uses a substantially circular disk geometry for the solid electrolyte with radial flow of gas from the outside edge of the disk to the center of the disk. The reduction in available surface area as the gas flows toward the center of the disk reduces the oxygen removal area proportionally to provide for a more uniform removal of oxygen.

  13. Early oxygen-utilization and brain activity in preterm infants.

    PubMed

    Tataranno, Maria Luisa; Alderliesten, Thomas; de Vries, Linda S; Groenendaal, Floris; Toet, Mona C; Lemmers, Petra M A; Vosse van de, Renè E; van Bel, Frank; Benders, Manon J N L

    2015-01-01

    The combined monitoring of oxygen supply and delivery using Near-InfraRed spectroscopy (NIRS) and cerebral activity using amplitude-integrated EEG (aEEG) could yield new insights into brain metabolism and detect potentially vulnerable conditions soon after birth. The relationship between NIRS and quantitative aEEG/EEG parameters has not yet been investigated. Our aim was to study the association between oxygen utilization during the first 6 h after birth and simultaneously continuously monitored brain activity measured by aEEG/EEG. Forty-four hemodynamically stable babies with a GA < 28 weeks, with good quality NIRS and aEEG/EEG data available and who did not receive morphine were included in the study. aEEG and NIRS monitoring started at NICU admission. The relation between regional cerebral oxygen saturation (rScO2) and cerebral fractional tissue oxygen extraction (cFTOE), and quantitative measurements of brain activity such as number of spontaneous activity transients (SAT) per minute (SAT rate), the interval in seconds (i.e. time) between SATs (ISI) and the minimum amplitude of the EEG in μV (min aEEG) were evaluated. rScO2 was negatively associated with SAT rate (β=-3.45 [CI=-5.76- -1.15], p=0.004) and positively associated with ISI (β=1.45 [CI=0.44-2.45], p=0.006). cFTOE was positively associated with SAT rate (β=0.034 [CI=0.009-0.059], p=0.008) and negatively associated with ISI (β=-0.015 [CI=-0.026- -0.004], p=0.007). Oxygen delivery and utilization, as indicated by rScO2 and cFTOE, are directly related to functional brain activity, expressed by SAT rate and ISI during the first hours after birth, showing an increase in oxygen extraction in preterm infants with increased early electro-cerebral activity. NIRS monitored oxygenation may be a useful biomarker of brain vulnerability in high-risk infants. PMID:25965343

  14. Optically active surfaces formed by ion implantation and thermal treatment

    SciTech Connect

    Gea, L.A.; Boatner, L.A.; Evans, H.M.; Zuhr, R.

    1996-08-01

    Embedded VO{sub 2} precipitates have been formed in single-crystal sapphire by the ion co-implantation of vanadium and oxygen and subsequent thermal annealing. The embedded VO{sub 2} particles have been shown to exhibit an optical switching behavior that is comparable to that of continuous thin films. In this work, the mechanisms of formation of these optically active particles are investigated. It is shown that precipitation of the vanadium dioxide phase is favored when the thermal treatment is performed on an ion-damaged but still crystalline (rather than amorphized) Al{sub 2}O{sub 3} substrate. The best optical switching behavior is observed in this case, and this behavior is apparently correlated with a more-favorable dispersion of VO{sub 2} small particles inside the matrix.

  15. Changes to coral health and metabolic activity under oxygen deprivation.

    PubMed

    Murphy, James W A; Richmond, Robert H

    2016-01-01

    On Hawaiian reefs, the fast-growing, invasive algae Gracilaria salicornia overgrows coral heads, restricting water flow and light, thereby smothering corals. Field data shows hypoxic conditions (dissolved oxygen (DO2) < 2 mg/L) occurring underneath algal mats at night, and concurrent bleaching and partial tissue loss of shaded corals. To analyze the impact of nighttime oxygen-deprivation on coral health, this study evaluated changes in coral metabolism through the exposure of corals to chronic hypoxic conditions and subsequent analyses of lactate, octopine, alanopine, and strombine dehydrogenase activities, critical enzymes employed through anaerobic respiration. Following treatments, lactate and octopine dehydrogenase activities were found to have no significant response in activities with treatment and time. However, corals subjected to chronic nighttime hypoxia were found to exhibit significant increases in alanopine dehydrogenase activity after three days of exposure and strombine dehydrogenase activity starting after one overnight exposure cycle. These findings provide new insights into coral metabolic shifts in extremely low-oxygen environments and point to ADH and SDH assays as tools for quantifying the impact of hypoxia on coral health. PMID:27114888

  16. Changes to coral health and metabolic activity under oxygen deprivation

    PubMed Central

    Richmond, Robert H.

    2016-01-01

    On Hawaiian reefs, the fast-growing, invasive algae Gracilaria salicornia overgrows coral heads, restricting water flow and light, thereby smothering corals. Field data shows hypoxic conditions (dissolved oxygen (DO2) < 2 mg/L) occurring underneath algal mats at night, and concurrent bleaching and partial tissue loss of shaded corals. To analyze the impact of nighttime oxygen-deprivation on coral health, this study evaluated changes in coral metabolism through the exposure of corals to chronic hypoxic conditions and subsequent analyses of lactate, octopine, alanopine, and strombine dehydrogenase activities, critical enzymes employed through anaerobic respiration. Following treatments, lactate and octopine dehydrogenase activities were found to have no significant response in activities with treatment and time. However, corals subjected to chronic nighttime hypoxia were found to exhibit significant increases in alanopine dehydrogenase activity after three days of exposure and strombine dehydrogenase activity starting after one overnight exposure cycle. These findings provide new insights into coral metabolic shifts in extremely low-oxygen environments and point to ADH and SDH assays as tools for quantifying the impact of hypoxia on coral health. PMID:27114888

  17. Activated oxygen alters cerebral microvascular responses in newborn pigs

    SciTech Connect

    Leffler, C.W.; Busiia, D.W.; Armstead, W.M.; Mirro, R.; Thelin, O. )

    1990-02-26

    In piglets, cerebral ischemia/reperfusion blocks prostanoid dependent cerebral vasodilation to hypercapnia (CO{sub 2}) and hypotension but not prostanoid independent dilation to isoproterenol (Isu) or constriction to norepinephrine (NE). Ischemia/reperfusion increases activated-O{sub 2} production by piglet brains. Using cranial windows in piglets, the authors investigated the hypothesis that activated oxygen can block prostanoid dependent cerebral vasodilator responses to CO{sub 2} and hypotension without altering responses to Isu and NE. Exposure to an activated oxygen generating system of xanthine oxidase, hypoxanthine, and Fe that made about 3 times the activated-O{sub 2} on the brain surface as ischemia/reperfusion caused reversible pial arteriolar dilation. After exposure, pial arteriolar dilation was reduced to CO{sub 2} and hypotension but not to Isu. NE constrictor responses were also unaltered. H{sub 2}O{sub 2} or H{sub 2}O{sub 2} + Fe caused constriction followed by reversible dilation. After exposure, pial arteriolar dilation in response to CO{sub 2} and hypotension was not altered. However, addition of xanthine oxidase and hypoxanthine with H{sub 2}O{sub 2} and Fe totally eliminated pial arteriolar dilator responses to CO{sub 2} and hypotension but did not decrease dilation caused by Isu or constriction caused by NE. The authors conclude that activated oxygen could produce the altered prostanoid dependent pial arteriolar responses observed following ischemia in piglets.

  18. Electron Spin Resonance (ESR) detection of active oxygen species and organic phases in Martian soils

    NASA Technical Reports Server (NTRS)

    Tsay, Fun-Dow; Kim, Soon Sam; Liang, Ranty H.

    1989-01-01

    The presence of active oxygen species (O(-), O2(-), O3(-)) and other strong oxidants (Fe2O3 and Fe3O4) was invoked in interpretations of the Viking biological experiments and a model was also suggested for Martian surface chemistry. The non-biological interpretations of the biological results gain futher support as no organic compounds were detected in the Viking pyrolysis-gas chromatography mass spectrometer (GCSM) experiments at concentrations as low as 10 ppb. Electron spin resonance (ESR) measures the absorption of microwaves by a paramagnetic and/or ferromagnetic center in the presence of an external field. In many instances, ESR has the advantage of detailed submicroscopic identification of the transient species and/or unstable reaction intermediates in their environments. Since the higly active oxygen species (O(-), O2(-), O3(-), and R-O-O(-)) are all paramagnetic in nature, they can be readily detected in native form by the ESR method. Active oxygen species likely to occur in the Martian surface samples were detected by ESR in UV-irradiated samples containing MgO. A miniaturized ESR spectrometer system can be developed for the Mars Rover Sample Return Mission. The instrument can perform the following in situ Martian samples analyses: detection of active oxygen species; characterization of Martian surface chemistry and photooxidation processes; and searching for organic compounds in the form of free radicals preserved in subsoils, and detection of microfossils with Martian carbonate sediments.

  19. Reactive oxygen scavenging activity of matured whiskey and its active polyphenols.

    PubMed

    Koga, K; Taguchi, A; Koshimizu, S; Suwa, Y; Yamada, Y; Shirasaka, N; Yoshizumi, H

    2007-04-01

    The quality of whiskey is known to improve remarkably by its storage over many years. This process is commonly termed "maturing." In this process, polyphenols derived from lignin and tannin of the barrel have an important role in not only forming the matured flavor and taste but also contributing to the advance of clustering ethanol and water in whiskey. It is also likely that polyphenols generally possess reactive oxygen (RO) scavenging activity. The present study evaluated the RO scavenging activity (free-radical scavenging activity, H(2)O(2) reduction activity under peroxidase coculture, and H(2)O(2)scavenging activity) of 24 single malt whiskeys with a maturation age of 10 to 30 y produced in Japanese, Scotch (Islay), or Scotch (Speyside and Highland) regions. Single malt whiskey not only showed RO scavenging activity but there was also a positive correlation between this activity and the maturation age of whiskey exceeding the difference resulting from the manufacturing region. A nonvolatile fraction derived from the barrel was responsible for RO scavenging activity. In particular, the contents of ellagic and gallic acids and lyoniresinol, the main polyphenolic compounds in whiskey, increased with maturation age. For the free-radical scavenging activity per molecule, each compound was 1.68 to 3.14 times that of trolox (a water-soluble vitamin E). The activities of ellagic acid, gallic acid, and lyoniresinol in the whiskey (Yamazaki 18) were equivalent to that of 80.3, 31.2, and 11.1 ppm trolox, respectively. Accordingly, the total activity of these 3 compounds accounted for about 20% of the activity of the whiskey (630.7 ppm trolox). PMID:17995817

  20. The role of oxygen diffusion in the release of technetium from reducing cementitious waste forms

    SciTech Connect

    Smith, R.W.; Walton, J.C.

    1993-12-31

    Cementitious materials provide an ideal geochemical environment (e.g., high pH pore fluids and large surface areas for sorption) for immobilizing nuclear waste. The inclusion of reducing agents, such as blast furnace slag (BFS) can immobilize radionuclides by forming of solid sulfide phases. Thermodynamic calculations using the MINTEQ geochemical computer code indicate the elemental sulfur present in BPS reacts with the highly mobile pertechnetate anion (TcO{sub 4}{sup -}) anion to form an insoluble technetium sulfide phase (Tc{sub 2}S{sub 7(s)}). Initially, the waste form very effectively immobilizes technetium. However, as oxygen diffuses into the waste form, an outer zone of oxidized concrete and a shrinking core of reduced intact concrete develops. Oxidation of sulfur in the outer zone results in increased technetium concentrations in the pore fluid because Tc{sub 2}S{sub 7(a)} oxidizes to the mobile TcO{sub 4}{sup -} anion. The TcO{sub 4}{sup -} anion can then diffuse from the waste form into the environment. A mathematical model that accounts for diffusion of oxygen into concrete coupled with oxidation of sulfur and sulfide to sulfate has been developed. This model assumes the existence of an oxidized outer layer of concrete surrounding a shrinking core of reducing intact concrete. A sharp boundary between the two zones moves slowly inward resulting in oxidation of Tc{sub 2}S{sub 7(s)} and subsequent release of TcO{sub 4}{sup -} via aqueous diffusion in the concrete pore fluids. The model indicates that this mechanism results in a linear dependance of release with the square root of time similar to pure diffusion. In addition, the release of technetium is related to the inverse of the square root of the concentration of BFS, indicating that performance will significantly increases with the addition of approximately 20 percent BFS to the cement mix.

  1. Thickness independent reduced forming voltage in oxygen engineered HfO{sub 2} based resistive switching memories

    SciTech Connect

    Sharath, S. U. Kurian, J.; Komissinskiy, P.; Hildebrandt, E.; Alff, L.; Bertaud, T.; Walczyk, C.; Calka, P.; Schroeder, T.

    2014-08-18

    The conducting filament forming voltage of stoichiometric hafnium oxide based resistive switching layers increases linearly with layer thickness. Using strongly reduced oxygen deficient hafnium oxide thin films grown on polycrystalline TiN/Si(001) substrates, the thickness dependence of the forming voltage is strongly suppressed. Instead, an almost constant forming voltage of about 3 V is observed up to 200 nm layer thickness. This effect suggests that filament formation and switching occurs for all samples in an oxidized HfO{sub 2} surface layer of a few nanometer thickness while the highly oxygen deficient thin film itself merely serves as a oxygen vacancy reservoir.

  2. Charge transfer induced activity of graphene for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Shen, Anli; Xia, Weijun; Zhang, Lipeng; Dou, Shuo; Xia, Zhenhai; Wang, Shuangyin

    2016-05-01

    Tetracyanoethylene (TCNE), with its strong electron-accepting ability, was used to dope graphene as a metal-free electrocatalyst for the oxygen reduction reaction (ORR). The charge transfer process was observed from graphene to TCNE by x-ray photoelectron spectroscopy and Raman characterizations. Our density functional theory calculations found that the charge transfer behavior led to an enhancement of the electrocatalytic activity for the ORR.

  3. A new resin technology: a glaze/composite sealant that cures without forming an oxygen-inhibited layer.

    PubMed

    Suh, Byoung I

    2003-08-01

    Until now, intraoral composite resin sealants cured with an oxygen-inhibited layer. In addition, resin glazes used for temporaries and processed appliances could not be used intraorally. This article describes the strategies behind the development of a new resin product that can be used intra- and extraorally as a sealant/glaze without forming an oxygen-inhibited layer after curing. PMID:14692216

  4. Distribution and Origin of Oxygen-Dependent and Oxygen-Independent Forms of Mg-Protoporphyrin Monomethylester Cyclase among Phototrophic Proteobacteria

    PubMed Central

    Boldareva-Nuianzina, Ekaterina N.; Bláhová, Zuzana; Sobotka, Roman

    2013-01-01

    Magnesium-protoporphyrin IX monomethylester cyclase is one of the key enzymes of the bacteriochlorophyll biosynthesis pathway. There exist two fundamentally different forms of this enzyme. The oxygen-dependent form, encoded by the gene acsF, catalyzes the formation of the bacteriochlorophyll fifth ring using oxygen, whereas the oxygen-independent form encoded by the gene bchE utilizes an oxygen atom extracted from water. The presence of acsF and bchE genes was surveyed in various phototrophic Proteobacteria using the available genomic data and newly designed degenerated primers. It was found that while the majority of purple nonsulfur bacteria contained both forms of the cyclase, the purple sulfur bacteria contained only the oxygen-independent form. All tested species of aerobic anoxygenic phototrophs contained acsF genes, but some of them also retained the bchE gene. In contrast to bchE phylogeny, the acsF phylogeny was in good agreement with 16S inferred phylogeny. Moreover, the survey of the genome data documented that the acsF gene occupies a conserved position inside the photosynthesis gene cluster, whereas the bchE location in the genome varied largely between the species. This suggests that the oxygen-dependent cyclase was recruited by purple phototrophic bacteria very early during their evolution. The primary sequence and immunochemical similarity with its cyanobacterial counterparts suggests that acsF may have been acquired by Proteobacteria via horizontal gene transfer from cyanobacteria. The acquisition of the gene allowed purple nonsulfur phototrophic bacteria to proliferate in the mildly oxygenated conditions of the Proterozoic era. PMID:23396335

  5. Multiple active forms of thrombin. IV. Relative activities of meizothrombins

    SciTech Connect

    Doyle, M.F.; Mann, K.G. )

    1990-06-25

    The prothrombin activation intermediates meizothrombin and meizothrombin(desF1) (meizothrombin that has been autoproteolyzed to remove fragment 1) have been obtained in a relatively pure, active form with minimal autolysis, making them suitable for enzymatic characterization. When compared at equimolar concentrations, alpha-thrombin, fragment 1.2+ alpha-thrombin, meizothrombin(desF1), and meizothrombin have approximately 100, 100, 10, and 1% activity, respectively, toward the macromolecular substrates factor V, fibrinogen, and platelets. The difference in activity of these four enzymes cannot be attributed to alterations in the catalytic triad, as all four enzymes have nearly identical catalytic efficiency toward the chromogenic substrate S2238. Further, the ability of meizothrombin and meizothrombin(desF1) to activate protein C was 75% of the activity exhibited by alpha-thrombin or fragment 1.2+ alpha-thrombin. All four enzymes bind to thrombomodulin, as judged by the enhanced rate of protein C activation upon preincubation of the enzymes with thrombomodulin. The extent of rate enhancement varied, with meizothrombin/thrombomodulin exhibiting only 50% of the alpha-thrombin/thrombomodulin rate. This difference in rate is not due to a decreased affinity of the meizothrombin for thrombomodulin since the apparent dissociation constants for the alpha-thrombin-thrombomodulin complex and the meizothrombin-thrombomodulin complex are virtually identical. The difference in the observed rate is due in part to the higher Km for protein C exhibited by the meizothrombin-thrombomodulin complex. Incubation of the thrombomodulin-enzyme complex with phospholipid vesicles caused an increase in the protein C activation rates. The kinetic constants for protein C activation in the presence of phospholipid are virtually identical for these enzyme-thrombomodulin complexes.

  6. Activation energies for oxygen reduction on platinum alloys: theory and experiment.

    PubMed

    Anderson, Alfred B; Roques, Jérôme; Mukerjee, Sanjeev; Murthi, Vivek S; Markovic, Nenad M; Stamenkovic, Vojislav

    2005-01-27

    A combined theoretical and experimental analysis of the electrode potential dependencies of activation energies is presented for the first step in oxygen reduction over platinum and platinum alloy catalysts in both polycrystalline and carbon supported form. Tafel data for several of the catalysts are used to predict potential-dependent activation energies for oxygen reduction over the 0.6-0.9 V range in strong and weak acid. Comparisons with the theoretical curve show good agreement above 0.8 V, suggesting a fairly constant preexponential factor. Arrhenius determinations of activation energies over the 0.7-0.9 V range yield little trend for weak acid, possibly because of the larger uncertainties in the Arrhenius fits, but the strong acid results have smaller uncertainties and for them the measured activation energies trend up with potential. PMID:16851081

  7. Origin of Active Oxygen in a Ternary CuOx /Co3O4–CeO 2 Catalyst for CO Oxidation

    DOE PAGESBeta

    Liu, Zhigang; Wu, Zili; Peng, Xihong; Binder, Andrew; Chai, Songhai; Dai, Sheng

    2014-11-14

    In this paper, we have studied CO oxidation over a ternary CuOx/Co3O4-CeO2 catalyst and employed the techniques of N2 adsorption/desporption, XRD, TPR, TEM, in situ DRIFTS and QMS (Quadrupole mass spectrometer) to explore the origin of active oxygen. DRIFTS-QMS results with labeled 18O2 indicate that the origin of active oxygens in CuOx/Co3O4-CeO2 obeys a model, called as queue mechanism. Namely gas-phase molecular oxygens are dissociated to atomic oxygens and then incorporate in oxygen vacancies located at the interface of Co3O4-CeO2 to form active crystalline oxygens, and these active oxygens diffuse to the CO-Cu+ sites thanks to the oxygen vacancy concentrationmore » magnitude and react with the activated CO to form CO2. This process, obeying a queue rule, provides active oxygens to form CO2 from gas-phase O2 via oxygen vacancies and crystalline oxygen at the interface of Co3O4-CeO2.« less

  8. Support nanostructure boosts oxygen transfer to catalytically active platinum nanoparticles.

    PubMed

    Vayssilov, Georgi N; Lykhach, Yaroslava; Migani, Annapaola; Staudt, Thorsten; Petrova, Galina P; Tsud, Nataliya; Skála, Tomáš; Bruix, Albert; Illas, Francesc; Prince, Kevin C; Matolín, Vladimír; Neyman, Konstantin M; Libuda, Jörg

    2011-04-01

    Interactions of metal particles with oxide supports can radically enhance the performance of supported catalysts. At the microscopic level, the details of such metal-oxide interactions usually remain obscure. This study identifies two types of oxidative metal-oxide interaction on well-defined models of technologically important Pt-ceria catalysts: (1) electron transfer from the Pt nanoparticle to the support, and (2) oxygen transfer from ceria to Pt. The electron transfer is favourable on ceria supports, irrespective of their morphology. Remarkably, the oxygen transfer is shown to require the presence of nanostructured ceria in close contact with Pt and, thus, is inherently a nanoscale effect. Our findings enable us to detail the formation mechanism of the catalytically indispensable Pt-O species on ceria and to elucidate the extraordinary structure-activity dependence of ceria-based catalysts in general. PMID:21423188

  9. Support nanostructure boosts oxygen transfer to catalytically active platinum nanoparticles

    NASA Astrophysics Data System (ADS)

    Vayssilov, Georgi N.; Lykhach, Yaroslava; Migani, Annapaola; Staudt, Thorsten; Petrova, Galina P.; Tsud, Nataliya; Skála, Tomáš; Bruix, Albert; Illas, Francesc; Prince, Kevin C.; MatolíN, VladimíR.; Neyman, Konstantin M.; Libuda, Jörg

    2011-04-01

    Interactions of metal particles with oxide supports can radically enhance the performance of supported catalysts. At the microscopic level, the details of such metal-oxide interactions usually remain obscure. This study identifies two types of oxidative metal-oxide interaction on well-defined models of technologically important Pt-ceria catalysts: (1) electron transfer from the Pt nanoparticle to the support, and (2) oxygen transfer from ceria to Pt. The electron transfer is favourable on ceria supports, irrespective of their morphology. Remarkably, the oxygen transfer is shown to require the presence of nanostructured ceria in close contact with Pt and, thus, is inherently a nanoscale effect. Our findings enable us to detail the formation mechanism of the catalytically indispensable Pt-O species on ceria and to elucidate the extraordinary structure-activity dependence of ceria-based catalysts in general.

  10. Biological Apatite Formed from Polyphosphate and Alkaline Phosphatase May Exchange Oxygen Isotopes from Water through Carbonate

    NASA Astrophysics Data System (ADS)

    Omelon, S. J.; Stanley, S. Y.; Gorelikov, I.; Matsuura, N.

    2011-12-01

    The oxygen isotopic composition in bone mineral phosphate is known to reflect the local water composition, environmental humidity, and diet1. Once ingested, biochemical processes presumably equilibrate PO43- with "body water" by the many biochemical reactions involving PO43- 2. Blake et al. demonstrated that enzymatic release of PO43- from organophosphorus compounds, and microbial metabolism of dissolved orthophosphate, significantly exchange the oxygen in precipitated apatite within environmental water3,4, which otherwise does not exchange with water at low temperatures. One of the enzymes that can cleave phosphates from organic substrates is alkaline phosphastase5, the enzyme also associated with bone mineralization. The literature often states that the mineral in bone in hydroxylapatite, however the mineral in bone is carbonated apatite that also contains some fluoride6. Deprotonation of HPO32- occurs at pH 12, which is impossibly high for biological system, and the predominate carbonate species in solution at neutral pH is HCO3-. To produce an apatite mineral without a significant hydroxyl content, it is possible that apatite biomineralization occurs through a polyphosphate pathway, where the oxygen atom required to transform polyphosphate into individual phosphate ions is from carbonate: [PO3-]n + CO32- -> [PO3-]n-1 + PO43- + CO2. Alkaline phosphatase can depolymerise polyphosphate into orthophosphate5. If alkaline phosphatase cleaves an oxygen atom from a calcium-carbonate complex, then there is no requirement for removing a hydrogen atom from the HCO3- or HPO43- ions of body water to form bioapatite. A mix of 1 mL of 1 M calcium polyphosphate hydogel, or nano-particles of calcium polyphosphate, and amorphous calcium carbonate were reacted with alkaline phosphatase, and maintained at neutral to basic pH. After two weeks, carbonated apatite and other calcium phosphate minerals were identified by powder x-ray diffraction. Orthophosphate and unreacted

  11. Active medium gain study of electric-discharge oxygen-iodine laser

    NASA Astrophysics Data System (ADS)

    Kolobyanin, Yuriy; Adamenkov, Yuriy; Vyskubenko, Boris; Goryachev, Leonid; Ilyin, Sergey; Kalashnik, Anatoliy; Rakhimova, Tatiana; Rogozhnikov, Georgiy

    2007-05-01

    The paper reports on experimental studies of the active medium gain in supersonic electric-discharge oxygen-iodine laser (DOIL) based on traveling mw discharge. The measurements have included: absolute concentration, yield, and energy efficiency of production of SO in pure oxygen and oxygen-helium mixes at an oxygen partial pressure 3 to 15 Torr. For the gas flow to get rid of atomic oxygen, both heterogeneous mercury oxide coatings of the tube walls and homogeneous additives to the work mix, such as nitrogen oxide, have been used. The active medium of DOIL was formed using a nozzle array of the type of ejector sized as 10*50 mm2. The singlet oxygen-helium mix was supplied through three rows of sonic cylindrical nozzles, while the iodine-carrier gas mix - through two rows of supersonic conical nozzles with a half-opening angle of 10°(arc). The gas-phase iodine was produced in a quartz cell filled with iodine crystals. Room-temperature iodine vapors were picked up with a carrier gas (nitrogen or helium) and thus delivered into the nozzle array. The active medium was investigated by the high-resolution laser diode spectroscopy approach that used the laser type Vortex 6025 purchased from New Focus, Inc. The laser medium gain factor was determined by the intra-cavity approach having a sensitivity about 1*10 -6 cm -1. The static temperature of the medium was determined from the measurements of gain half-width. The gain of the active medium of electric-discharge OIL has been investigated. The DOIL in use was operating on a mix composed as O II:He=1:1 at a total pressure of 6 Torr and flowrate - about 1 mmol/s. With helium as an iodine carrier gas at a flowrate ~3 mmol/s, we have recorded a positive gain in the DOIL medium.

  12. Studies of reductive elimination reactions to form carbon-oxygen bonds from Pt(IV) complexes.

    PubMed

    Williams, B S; Goldberg, K I

    2001-03-21

    The platinum(IV) complexes fac-L(2)PtMe(3)(OR) (L(2) = bis(diphenylphosphino)ethane, o-bis(diphenylphosphino)benzene, R = carboxyl, aryl; L = PMe(3), R = aryl) undergo reductive elimination reactions to form carbon-oxygen bonds and/or carbon-carbon bonds. The carbon-oxygen reductive elimination reaction produces either methyl esters or methyl aryl ethers (anisoles) and L(2)PtMe(2), while the carbon-carbon reductive elimination reaction affords ethane and L(2)PtMe(OR). Choice of reaction conditions allows the selection of either type of coupling over the other. A detailed mechanistic study of the reductive elimination reactions supports dissociation of the OR(-) ligand as the initial step for the C-O bond formation reaction. This is followed by a nucleophilic attack of OR(-) upon a methyl group bound to the Pt(IV) cation to produce the products MeOR and L(2)PtMe(2). C-C reductive elimination proceeds from L(2)PtMe(3)(OR) by initial L (L = PMe(3)) or OR(-) (L(2) = dppe, dppbz) dissociation, followed by C-C coupling from the resulting five-coordinate intermediate. Our studies demonstrate that both C-C and C-O reductive elimination reactions from Pt(IV) are more facile in polar solvents, in the presence of Lewis acids, and for OR(-) groups that contain electron withdrawing substituents. PMID:11456927

  13. Ozone-forming potential of a series of oxygenated organic compounds

    SciTech Connect

    Japar, S.M.; Wallington, T.J.; Rudy, S.J.; Chang, Tai Y. )

    1991-03-01

    An incremental reactivity approach has been used to assess the relative ozone-forming potentials of various important oxygenated fuels/fuel additives, i.e., tert-butyl alcohol (TBA), dimethyl ether (DME), diethyl ether (DEE), methyl tert-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE), in a variety of environments. Calculations were performed using a single-cell trajectory model, combined with the Lurmann-Carter-Coyner chemical mechanism, with (NMOC)/(NO{sub x}) ratios ranging from 4 to 20. This work provides the first quantitative assessment of the air quality impact of release of these important oxygenated compounds. ETBE and DEE are the two most reactive compounds on a per carbon equivalent basis, while TBA is the least reactive species. At a (NMOC)/(NO{sub x}) ratio of 8, which is generally typical of polluted urban areas in the United States, TBA, DME, MTBE, and ETBE all have incremental reactivities less than or equal to that of the urban NMHC mix. Thus, use of these additives in fuels may have a beneficial impact on urban ozone levels.

  14. Catalytic activity trends of oxygen reduction reaction for nonaqueous Li-air batteries.

    PubMed

    Lu, Yi-Chun; Gasteiger, Hubert A; Shao-Horn, Yang

    2011-11-30

    We report the intrinsic oxygen reduction reaction (ORR) activity of polycrystalline palladium, platinum, ruthenium, gold, and glassy carbon surfaces in 0.1 M LiClO(4) 1,2-dimethoxyethane via rotating disk electrode measurements. The nonaqueous Li(+)-ORR activity of these surfaces primarily correlates to oxygen adsorption energy, forming a "volcano-type" trend. The activity trend found on the polycrystalline surfaces was in good agreement with the trend in the discharge voltage of Li-O(2) cells catalyzed by nanoparticle catalysts. Our findings provide insights into Li(+)-ORR mechanisms in nonaqueous media and design of efficient air electrodes for Li-air battery applications. PMID:22044022

  15. Trend in the Catalytic Activity of Transition Metals for the Oxygen Reduction Reaction by Lithium

    SciTech Connect

    Dathar, Gopi Krishna Phani; Shelton Jr, William Allison; Xu, Ye

    2012-01-01

    Periodic density functional theory (DFT) calculations indicate that the intrinsic activity of Au, Ag, Pt, Pd, Ir, and Ru for the oxygen reduction reaction by Li (Li-ORR) forms a volcano-like trend with respect to the adsorption energy of oxygen, with Pt and Pd being the most active. The trend is based on two mechanisms: the reduction of molecular O{sub 2} on Au and Ag and of atomic O on the remaining metals. Step edges are found to be more active for catalyzing the Li-ORR than close-packed surfaces. Our findings identify important considerations in the design of catalyst-promoted air cathodes for nonaqueous Li-air batteries.

  16. Device for measuring oxygen activity in liquid sodium

    DOEpatents

    Roy, P.; Young, R.S.

    1973-12-01

    A composite ceramic electrolyte in a configuration (such as a closed end tube or a plate) suitable to separate liquid sodium from a reference electrode with a high impedance voltmeter connected to measure EMF between the sodium and the reference electrode as a measure of oxygen activity in the sodium is described. The composite electrolyte consists of zirconiacalcia with a bonded layer of thoria-yttria. The device is used with a gaseous reference electrode on the zirconia-calcia side and liquid sodium on the thoria-yttria side of the electrolyte. (Official Gazette)

  17. Bioreductively Activated Reactive Oxygen Species (ROS) Generators as MRSA Inhibitors.

    PubMed

    Khodade, Vinayak S; Sharath Chandra, Mallojjala; Banerjee, Ankita; Lahiri, Surobhi; Pulipeta, Mallikarjuna; Rangarajan, Radha; Chakrapani, Harinath

    2014-07-10

    The number of cases of drug resistant Staphylococcus aureus infections is on the rise globally and new strategies to identify drug candidates with novel mechanisms of action are in urgent need. Here, we report the synthesis and evaluation of a series of benzo[b]phenanthridine-5,7,12(6H)-triones, which were designed based on redox-active natural products. We find that the in vitro inhibitory activity of 6-(prop-2-ynyl)benzo[b]phenanthridine-5,7,12(6H)-trione (1f) against methicillin-resistant Staphylococcus aureus (MRSA), including a panel of patient-derived strains, is comparable or better than vancomycin. We show that the lead compound generates reactive oxygen species (ROS) in the cell, contributing to its antibacterial activity. PMID:25050164

  18. Catalytic reduction of NO by CO over rhodium catalysts. 2. Effect of oxygen on the nature, population, and reactivity of surface species formed under reaction conditions

    SciTech Connect

    Kondarides, D.I.; Chafik, T.; Verykios, X.E.

    2000-04-01

    The effect of oxygen on the nature, population, and reactivity of surface species formed during reduction of NO by CO over Rh/TiO{sub 2} catalysts has been examined employing FTIR and transient MS techniques. It has been found that the activity of Rh is hindered by accumulation of surface oxygen originating from NO decomposition and gas-phase oxygen in the feed. Adsorbed CO and reduced TiO{sub 2{minus}x} species in the vicinity of Rh particles act as oxygen atom scavengers and, under fuel-rich conditions, remove atomic oxygen from the surface and restore the catalytic properties. Results of the present study provide additional evidence that production of N{sub 2} is related to dissociation of adsorbed Rh-NO{sup {minus}} while production of N{sub 2}O is related to the presence of Rh(NO){sub 2}. The presence of reduced RH{sup 0} sites is necessary for the formation of both reduction products. In the absence of oxygen in the feed, surface isocyanate species are also observed under reaction conditions. Their formation requires the presence of adjacent Rh{sup 0}-CO and reduced Rh{sup 0} sites. Although these species are favored under conditions in which NO conversion to reduction products is observed, there is no evidence that they are catalytically active species.

  19. Nitroxyl (HNO) reacts with molecular oxygen and forms peroxynitrite at physiological pH. Biological Implications.

    PubMed

    Smulik, Renata; Dębski, Dawid; Zielonka, Jacek; Michałowski, Bartosz; Adamus, Jan; Marcinek, Andrzej; Kalyanaraman, Balaraman; Sikora, Adam

    2014-12-19

    Nitroxyl (HNO), the protonated one-electron reduction product of NO, remains an enigmatic reactive nitrogen species. Its chemical reactivity and biological activity are still not completely understood. HNO donors show biological effects different from NO donors. Although HNO reactivity with molecular oxygen is described in the literature, the product of this reaction has not yet been unambiguously identified. Here we report that the decomposition of HNO donors under aerobic conditions in aqueous solutions at physiological pH leads to the formation of peroxynitrite (ONOO(-)) as a major intermediate. We have specifically detected and quantified ONOO(-) with the aid of boronate probes, e.g. coumarin-7-boronic acid or 4-boronobenzyl derivative of fluorescein methyl ester. In addition to the major phenolic products, peroxynitrite-specific minor products of oxidation of boronate probes were detected under these conditions. Using the competition kinetics method and a set of HNO scavengers, the value of the second order rate constant of the HNO reaction with oxygen (k = 1.8 × 10(4) m(-1) s(-1)) was determined. The rate constant (k = 2 × 10(4) m(-1) s(-1)) was also determined using kinetic simulations. The kinetic parameters of the reactions of HNO with selected thiols, including cysteine, dithiothreitol, N-acetylcysteine, captopril, bovine and human serum albumins, and hydrogen sulfide, are reported. Biological and cardiovascular implications of nitroxyl reactions are discussed. PMID:25378389

  20. Nitroxyl (HNO) Reacts with Molecular Oxygen and Forms Peroxynitrite at Physiological pH

    PubMed Central

    Smulik, Renata; Dębski, Dawid; Zielonka, Jacek; Michałowski, Bartosz; Adamus, Jan; Marcinek, Andrzej; Kalyanaraman, Balaraman; Sikora, Adam

    2014-01-01

    Nitroxyl (HNO), the protonated one-electron reduction product of NO, remains an enigmatic reactive nitrogen species. Its chemical reactivity and biological activity are still not completely understood. HNO donors show biological effects different from NO donors. Although HNO reactivity with molecular oxygen is described in the literature, the product of this reaction has not yet been unambiguously identified. Here we report that the decomposition of HNO donors under aerobic conditions in aqueous solutions at physiological pH leads to the formation of peroxynitrite (ONOO−) as a major intermediate. We have specifically detected and quantified ONOO− with the aid of boronate probes, e.g. coumarin-7-boronic acid or 4-boronobenzyl derivative of fluorescein methyl ester. In addition to the major phenolic products, peroxynitrite-specific minor products of oxidation of boronate probes were detected under these conditions. Using the competition kinetics method and a set of HNO scavengers, the value of the second order rate constant of the HNO reaction with oxygen (k = 1.8 × 104 m−1 s−1) was determined. The rate constant (k = 2 × 104 m−1 s−1) was also determined using kinetic simulations. The kinetic parameters of the reactions of HNO with selected thiols, including cysteine, dithiothreitol, N-acetylcysteine, captopril, bovine and human serum albumins, and hydrogen sulfide, are reported. Biological and cardiovascular implications of nitroxyl reactions are discussed. PMID:25378389

  1. 76 FR 42129 - Agency Information Collection Activities: Case Submission Form, Case Assistance Form

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-18

    ... FY2010. We are requesting a two year approval for the form anticipating Government Paperwork Elimination... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF HOMELAND SECURITY Agency Information Collection Activities: Case Submission Form, Case Assistance Form (Form...

  2. Neural network with formed dynamics of activity

    SciTech Connect

    Dunin-Barkovskii, V.L.; Osovets, N.B.

    1995-03-01

    The problem of developing a neural network with a given pattern of the state sequence is considered. A neural network structure and an algorithm, of forming its bond matrix which lead to an approximate but robust solution of the problem are proposed and discussed. Limiting characteristics of the serviceability of the proposed structure are studied. Various methods of visualizing dynamic processes in a neural network are compared. Possible applications of the results obtained for interpretation of neurophysiological data and in neuroinformatics systems are discussed.

  3. 75 FR 26782 - Agency Information Collection Activities: Form I-864, Form I-864A, Form I-864EZ, and Form I-864W...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-12

    ... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form I-864, Form I- 864A, Form I-864EZ, and Form I-864W; Extension of an Existing Information Collection; Comment Request ACTION: 60-Day Notice of Information Collection Under Review; Form I- 864, Affidavit of...

  4. Doped LaFeO3 as SOFC Catalysts: Control of Oxygen Mobility Oxidation Activity

    SciTech Connect

    N Lakshminarayanan; J Kuhn; S Rykov; J Millet; U Ozkan; T Rao; J Smedley; E Wang; E Muller; et al.

    2011-12-31

    The bulk structure and surface properties of Fe-based perovskite-type oxides with the formula La{sub 0.6}Sr{sub 0.4}Co{sub y}Fe{sub 1-y}O{sub 3-{delta}} for y = 0.1, 0.2, and 0.3 have been investigated. The properties were found to strongly depend upon Co content, temperature, and environment. The materials were selected due to their potential use as solid oxide fuel cell cathodes. The intermediate Co loading formed oxygen vacancies most easily and several other properties including oxidation activity and surface sites showed a similar non-linear trend. Trends are related to a possible transition in electronic structure. Activity for oxidation of methane, oxygen storage and chemical compatibility was shown to be superior to that of the La{sub 0.6}Sr{sub 0.4}MnO{sub 3}.

  5. Silk microgels formed by proteolytic enzyme activity.

    PubMed

    Samal, Sangram K; Dash, Mamoni; Chiellini, Federica; Kaplan, David L; Chiellini, Emo

    2013-09-01

    The proteolytic enzyme α-chymotrypsin selectively cleaves the amorphous regions of silk fibroin protein (SFP) and allows the crystalline regions to self-assemble into silk microgels (SMGs) at physiological temperature. These microgels consist of lamellar crystals in the micrometer scale, in contrast to the nanometer-scaled crystals in native silkworm fibers. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and zeta potential results demonstrated that α-chymotrypsin utilized only the non-amorphous domains or segments of the heavy chain of SFP to form negatively charged SMGs. The SMGs were characterized in terms of size, charge, structure, morphology, crystallinity, swelling kinetics, water content and thermal properties. The results suggest that the present technique of preparing SMGs by α-chymotrypsin is simple and efficient, and that the prepared SMGs have useful features for studies related to biomaterial and pharmaceutical needs. This process is also an easy way to obtain the amorphous peptide chains for further study. PMID:23756227

  6. Oxygen Affects Gut Bacterial Colonization and Metabolic Activities in a Gnotobiotic Cockroach Model

    PubMed Central

    Tegtmeier, Dorothee; Thompson, Claire L.; Schauer, Christine

    2015-01-01

    The gut microbiota of termites and cockroaches represents complex metabolic networks of many diverse microbial populations. The distinct microenvironmental conditions within the gut and possible interactions among the microorganisms make it essential to investigate how far the metabolic properties of pure cultures reflect their activities in their natural environment. We established the cockroach Shelfordella lateralis as a gnotobiotic model and inoculated germfree nymphs with two bacterial strains isolated from the guts of conventional cockroaches. Fluorescence microscopy revealed that both strains specifically colonized the germfree hindgut. In diassociated cockroaches, the facultatively anaerobic strain EbSL (a new species of Enterobacteriaceae) always outnumbered the obligately anaerobic strain FuSL (a close relative of Fusobacterium varium), irrespective of the sequence of inoculation, which showed that precolonization by facultatively anaerobic bacteria does not necessarily favor colonization by obligate anaerobes. Comparison of the fermentation products of the cultures formed in vitro with those accumulated in situ indicated that the gut environment strongly affected the metabolic activities of both strains. The pure cultures formed the typical products of mixed-acid or butyrate fermentation, whereas the guts of gnotobiotic cockroaches accumulated mostly lactate and acetate. Similar shifts toward more-oxidized products were observed when the pure cultures were exposed to oxygen, which corroborated the strong effects of oxygen on the metabolic fluxes previously observed in termite guts. Oxygen microsensor profiles of the guts of germfree, gnotobiotic, and conventional cockroaches indicated that both gut tissue and microbiota contribute to oxygen consumption and suggest that the oxygen status influences the colonization success. PMID:26637604

  7. Oxygen Affects Gut Bacterial Colonization and Metabolic Activities in a Gnotobiotic Cockroach Model.

    PubMed

    Tegtmeier, Dorothee; Thompson, Claire L; Schauer, Christine; Brune, Andreas

    2016-02-01

    The gut microbiota of termites and cockroaches represents complex metabolic networks of many diverse microbial populations. The distinct microenvironmental conditions within the gut and possible interactions among the microorganisms make it essential to investigate how far the metabolic properties of pure cultures reflect their activities in their natural environment. We established the cockroach Shelfordella lateralis as a gnotobiotic model and inoculated germfree nymphs with two bacterial strains isolated from the guts of conventional cockroaches. Fluorescence microscopy revealed that both strains specifically colonized the germfree hindgut. In diassociated cockroaches, the facultatively anaerobic strain EbSL (a new species of Enterobacteriaceae) always outnumbered the obligately anaerobic strain FuSL (a close relative of Fusobacterium varium), irrespective of the sequence of inoculation, which showed that precolonization by facultatively anaerobic bacteria does not necessarily favor colonization by obligate anaerobes. Comparison of the fermentation products of the cultures formed in vitro with those accumulated in situ indicated that the gut environment strongly affected the metabolic activities of both strains. The pure cultures formed the typical products of mixed-acid or butyrate fermentation, whereas the guts of gnotobiotic cockroaches accumulated mostly lactate and acetate. Similar shifts toward more-oxidized products were observed when the pure cultures were exposed to oxygen, which corroborated the strong effects of oxygen on the metabolic fluxes previously observed in termite guts. Oxygen microsensor profiles of the guts of germfree, gnotobiotic, and conventional cockroaches indicated that both gut tissue and microbiota contribute to oxygen consumption and suggest that the oxygen status influences the colonization success. PMID:26637604

  8. The interrelationship between muscle oxygenation, muscle activation, and pulmonary oxygen uptake to incremental ramp exercise: influence of aerobic fitness.

    PubMed

    Boone, Jan; Barstow, Thomas J; Celie, Bert; Prieur, Fabrice; Bourgois, Jan

    2016-01-01

    We investigated whether muscle and ventilatory responses to incremental ramp exercise would be influenced by aerobic fitness status by means of a cross-sectional study with a large subject population. Sixty-four male students (age: 21.2 ± 3.2 years) with a heterogeneous peak oxygen uptake (51.9 ± 6.3 mL·min(-1)·kg(-1), range 39.7-66.2 mL·min(-1)·kg(-1)) performed an incremental ramp cycle test (20-35 W·min(-1)) to exhaustion. Breath-by-breath gas exchange was recorded, and muscle activation and oxygenation were measured with surface electromyography and near-infrared spectroscopy, respectively. The integrated electromyography (iEMG), mean power frequency (MPF), deoxygenated [hemoglobin and myoglobin] (deoxy[Hb+Mb]), and total[Hb+Mb] responses were set out as functions of work rate and fitted with a double linear function. The respiratory compensation point (RCP) was compared and correlated with the breakpoints (BPs) (as percentage of peak oxygen uptake) in muscle activation and oxygenation. The BP in total[Hb+Mb] (83.2% ± 3.0% peak oxygen uptake) preceded (P < 0.001) the BP in iEMG (86.7% ± 4.0% peak oxygen uptake) and MPF (86.3% ± 4.1% peak oxygen uptake), which in turn preceded (P < 0.01) the BP in deoxy[Hb+Mb] (88.2% ± 4.5% peak oxygen uptake) and RCP (87.4% ± 4.5% peak oxygen uptake). Furthermore, the peak oxygen uptake was significantly (P < 0.001) positively correlated to the BPs and RCP, indicating that the BPs in total[Hb+Mb] (r = 0.66; P < 0.001), deoxy[Hb+Mb] (r = 0.76; P < 0.001), iEMG (r = 0.61; P < 0.001), MPF (r = 0.63; P < 0.001), and RCP (r = 0.75; P < 0.001) occurred at a higher percentage of peak oxygen uptake in subjects with a higher peak oxygen uptake. In this study a close relationship between muscle oxygenation, activation, and pulmonary oxygen uptake was found, occurring in a cascade of events. In subjects with a higher aerobic fitness level this cascade occurred at a higher relative intensity. PMID:26701120

  9. Activated carbon becomes active for oxygen reduction and hydrogen evolution reactions.

    PubMed

    Yan, Xuecheng; Jia, Yi; Odedairo, Taiwo; Zhao, Xiaojun; Jin, Zhao; Zhu, Zhonghua; Yao, Xiangdong

    2016-06-21

    We utilized a facile method for creating unique defects in the activated carbon (AC), which makes it highly active for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). The ORR activity of the defective AC (D-AC) is comparable to the commercial Pt/C in alkaline medium, and the D-AC also exhibits excellent HER activity in acidic solution. PMID:27277286

  10. A CENSUS OF OXYGEN IN STAR-FORMING GALAXIES: AN EMPIRICAL MODEL LINKING METALLICITIES, STAR FORMATION RATES, AND OUTFLOWS

    SciTech Connect

    Zahid, H. J.; Dima, G. I.; Kewley, L. J.; Erb, D. K.; Dave, R.

    2012-09-20

    In this contribution, we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates (SFRs) at z = 0.07, 0.8, and 2.26, including the Sloan Digital Sky Survey (SDSS) and DEEP2 survey. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and SFR observed in our three samples. We show that the observed relation between stellar mass and SFR for our three samples is consistent with other samples in the literature. The mass-metallicity relation is well established for our three samples, and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the SFRs and metallicities of galaxies over cosmic time, allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature, we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies.

  11. 76 FR 61725 - Agency Information Collection Activities: Case Submission Form, Case Assistance Form; (Form DHS...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-05

    ... Federal Register on July 18, 2011 at 76 FR 42129, for a 60-day public comment period. No comments were... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF HOMELAND...-7001), Online Ombudsman Form DHS-7001 AGENCY: Office of the Citizenship and Immigration...

  12. Antioxidative activity of bound-form phenolics in potato peel.

    PubMed

    Nara, Kazuhiro; Miyoshi, Takayuki; Honma, Tamaki; Koga, Hidenori

    2006-06-01

    Free and bound-form phenolics were isolated from potato (cv. Toyoshiro) flesh and peel. The free and bound-form phenolics in the peel showed high DPPH radical scavenging activity, while those in the flesh showed low activity. The total amount of chlorogenic acid and caffeic acid in the free-form phenolics from the peel was highly correlated with the DPPH radical scavenging activity. Ferulic acid was identified as the active radical scavenging compound in the bound-form phenolics from the peel. The potato peel may therefore offer an effective source of an antioxidative. PMID:16794331

  13. 76 FR 41279 - Agency Information Collection Activities; Form I-864, Form I-864A, Form I-864EZ, and Form I-864W...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-13

    ... was previously published in the Federal Register on May 4, 2011, at 76 FR 25364, allowing for a 60-day... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities; Form I-864, Form I- 864A, Form I-864EZ, and Form I-864W; Extension of an Existing Information Collection;...

  14. 75 FR 51093 - Agency Information Collection Activities: Form I-864, Form I-864A, Form I-864EZ, and Form I-864W...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-18

    ... on May 12, 2010, at 75 FR 26782, allowing for a 60-day public comment period. USCIS received 2... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form I-864, Form I- 864A, Form I-864EZ, and Form I-864W; Extension of a Currently Approved Information...

  15. Production and Characterization of Active Transparent PET Films for Oxygen Sensitive Foods Packaging

    NASA Astrophysics Data System (ADS)

    Rosaria Galdi, Maria; Incarnato, Loredana

    2010-06-01

    The aim of this work is to investigate possible solutions to realize active, transparent PET film suitable for packaging oxygen sensitive foods. At this purpose, monolayer active PET films at different oxygen scavenger concentrations and multilayer active ones were produced by cast extrusion laboratory scale equipments. To assess their activity and to verify the efficacy of such solutions, O2 absorption analyses were carried out in continuous by an innovative oxygen meter.

  16. Towards forming-free resistive switching in oxygen engineered HfO{sub 2−x}

    SciTech Connect

    Sharath, S. U. Kurian, J.; Hildebrandt, E.; Alff, L.; Bertaud, T.; Walczyk, C.; Calka, P.; Zaumseil, P.; Sowinska, M.; Walczyk, D.; Gloskovskii, A.; Schroeder, T.

    2014-02-10

    We have investigated the resistive switching behavior in stoichiometric HfO{sub 2} and oxygen-deficient HfO{sub 2−x} thin films grown on TiN electrodes using reactive molecular beam epitaxy. Oxygen defect states were controlled by the flow of oxygen radicals during thin film growth. Hard X-ray photoelectron spectroscopy confirmed the presence of sub-stoichiometric hafnium oxide and defect states near the Fermi level. The oxygen deficient HfO{sub 2−x} thin films show bipolar switching with an electroforming occurring at low voltages and low operating currents, paving the way for almost forming-free devices for low-power applications.

  17. Bleaching in coral reef anthozoans: effects of irradiance, ultraviolet radiation, and temperature on the activities of protective enzymes against active oxygen

    NASA Astrophysics Data System (ADS)

    Lesser, M. P.; Stochaj, W. R.; Tapley, D. W.; Shick, J. M.

    1990-04-01

    Recent widespread bleaching of coral reef anthozoans has been observed on the Great Barrier Reef, the Pacific coast of Panama, and in the Caribbean Sea. Bleaching events have been correlated with anomalously high sea surface temperatures which are presumed to cause the expulsion of zooxanthellae from their hosts. Our experimental results show that increases in temperature significantly reduce the total number of zooxanthellae per polyp. At the same time temperature, irradiance (photosynthetically active radiation=PAR), and ultraviolet radiation (UV) independently increase the activities of the enzymes superoxide dismutase, catalase, and ascorbate peroxidase within the zooxanthellae of the zoanthid Palythoa caribaeorum. Enzyme activities within the host are only suggestive of similar changes. These enzymes are responsible for detoxifying active forms of oxygen, and their elevated activities indirectly indicate an increase in the production of active oxygen species by increases in these environmental factors. Historically, bleaching has been attributed to changes in temperature, salinity, and UV. Increases in temperature or highly energetic UV radiation can increase the flux of active forms of oxygen, particularly at the elevated oxygen concentrations that prevail in the tissues during photosynthesis, with oxygen toxicity potentially mediating the bleaching event. Additionally, the concentration of UV absorbing compounds within the symbiosis is inversely related to temperature, potentially increasing exposure of the host and zooxanthellae to the direct effects of UV.

  18. Communication: CO oxidation by silver and gold cluster cations: Identification of different active oxygen species

    SciTech Connect

    Popolan, Denisia M.; Bernhardt, Thorsten M.

    2011-03-07

    The oxidation of carbon monoxide with nitrous oxide on mass-selected Au{sub 3}{sup +} and Ag{sub 3}{sup +} clusters has been investigated under multicollision conditions in an octopole ion trap experiment. The comparative study reveals that for both gold and silver cations carbon dioxide is formed on the clusters. However, whereas in the case of Au{sub 3}{sup +} the cluster itself acts as reactive species that facilitates the formation of CO{sub 2} from N{sub 2}O and CO, for silver the oxidized clusters Ag{sub 3}O{sub x}{sup +} (n= 1-3) are identified as active in the CO oxidation reaction. Thus, in the case of the silver cluster cations N{sub 2}O is dissociated and one oxygen atom is suggested to directly react with CO, whereas a second kind of oxygen strongly bound to silver is acting as a substrate for the reaction.

  19. Effect of surface phosphorus functionalities of activated carbons containing oxygen and nitrogen on electrochemical capacitance

    PubMed Central

    Hulicova-Jurcakova, Denisa; Seredych, Mykola; Lu, Gao Qing; Kodiweera, N.K.A.C.; Stallworth, Phillip E.; Greenbaum, Steven; Bandosz, Teresa J.

    2009-01-01

    Micro/mesoporous activated carbons containing oxygen and phosphorus heteroatoms were modified by incorporation of nitrogen using melamine and urea precursors. The surface chemistry was analyzed by the means of elemental analysis, XPS, and 31P MAS NMR. The results indicate that upon the incorporation of nitrogen at high temperatures not only new species involving carbon/nitrogen/oxygen are formed but also the phosphorous environment is significantly altered. Both urea and melamine precursors have similar effects on formation of P–N and P–C bonds. These compounds, although present in small but measurable quantities seem to affect the performance of carbons in electrochemical capacitors. With an increase in the heterogeneity of phosphorus containing species and with a decrease in the content pyrophosphates the capacitance increases and the retention ratio of the capacitor is improved. PMID:20354586

  20. Direct determination of oxygen abundances in line-emitting star-forming galaxies at intermediate redshift

    NASA Astrophysics Data System (ADS)

    Pérez, José M.; Hoyos, Carlos; Díaz, Ángeles I.; Koo, David C.; Willmer, Christopher N. A.

    2016-01-01

    We present a sample of 22 blue [(B - V)AB < 0.45], luminous (MB,AB < -18.9), metal-poor galaxies in the 0.69 < z < 0.88 redshift range, selected from the DEEP2 galaxy redshift survey. Their spectra contain the [O III] λ4363 auroral line, the [O II] λλ3726, 3729 doublet and the strong nebular [O III] λλ4959, 5007 emission lines. The ionized gas-phase oxygen abundances of these galaxies lie between 7.62 < 12 + log O/H < 8.19, i.e., between 1/10 Z⊙ and 1/3 Z⊙. We find that galaxies in our sample have comparable metallicities to other intermediate-redshift samples, but are more metal poor than local systems of similar B-band luminosities and star formation activity. The galaxies here show similar properties to the green peas discovered at z ≃ 0.2-0.3, though our galaxies tend to be slightly less luminous.

  1. Determination of reactive oxygen species from ZnO micro-nano structures with shape-dependent photocatalytic activity

    SciTech Connect

    He, Weiwei; Zhao, Hongxiao; Jia, Huimin; Yin, Jun-Jie; Zheng, Zhi

    2014-05-01

    Graphical abstract: ZnO micro/nano structures with shape dependent photocatalytic activity were prepared by hydrothermal reaction. The generations of hydroxyl radical, superoxide and singlet oxygen from irradiated ZnO were identified precisely by electron spin resonance spectroscopy. The type of reactive oxygen species was determined by band gap structure of ZnO. - Highlights: • ZnO micro/nano structures with different morphologies were prepared by solvothermal reaction. • Multi-pod like ZnO structures exhibited superior photocatalytic activity. • The generations of hydroxyl radical, superoxide and singlet oxygen from irradiated ZnO were characterized precisely by electron spin resonance spectroscopy. • The type of reactive oxygen species was determined by band gap structure of ZnO. - Abstract: ZnO micro/nano structures with different morphologies have been prepared by the changing solvents used during their synthesis by solvothermal reaction. Three typical shapes of ZnO structures including hexagonal, bell bottom like and multi-pod formed and were characterized by scanning electron microscopy and X-ray diffraction. Multi pod like ZnO structures exhibited the highest photocatalytic activity toward degradation of methyl orange. Using electron spin resonance spectroscopy coupled with spin trapping techniques, we demonstrate an effective way to identify precisely the generation of hydroxyl radicals, superoxide and singlet oxygen from the irradiated ZnO multi pod structures. The type of reactive oxygen species formed was predictable from the band gap structure of ZnO. These results indicate that the shape of micro-nano structures significantly affects the photocatalytic activity of ZnO, and demonstrate the value of electron spin resonance spectroscopy for characterizing the type of reactive oxygen species formed during photoexcitation of semiconductors.

  2. Pu-238 fuel form activities, January 1-31, 1983

    SciTech Connect

    Not Available

    1983-03-01

    This monthly report for /sup 238/Pu Fuel Form Activities has two main sections: SRP-PuFF facility and SRL Fuel Form Activities. The program status, budget information, and milestone schedules are discussed in each main section. The Work Breakdown Structure (WBS) for this program is shown. Only one monthly report per year is processed for EDB.

  3. Pu-238 fuel form activities, January 1-31, 1981

    SciTech Connect

    Not Available

    1981-02-01

    This monthly report for /sup 238/Pu Fuel Form Activities has two main sections: SRP-PuFF facility and SRL Fuel Form Activities. The program status, budget information, and milestone schedules are discussed in each main section. The Work Breakdown Structure (WBS) for this program is shown. Only one monthly report per year is processed for EDB.

  4. Pu-238 fuel form activities, January 1-31, 1982

    SciTech Connect

    Not Available

    1982-03-01

    This monthly report for /sup 238/Pu fuel form activities has two main sections: SRP-PuFF facility and SRL fuel form activities. The program status, budget information, and milestone schedules are discussed in each main section. The Work Breakdown Structure (WBS) for this program is shown. Only one monthly report per year is processed for EDB.

  5. Effect of oxygen on the microbial activities of thermophilic anaerobic biomass.

    PubMed

    Pedizzi, C; Regueiro, L; Rodriguez-Verde, I; Lema, J M; Carballa, M

    2016-07-01

    Low oxygen levels (μgO2L(-1)) in anaerobic reactors are quite common and no relevant consequences are expected. On the contrary, higher concentrations could affect the process. This work aimed to study the influence of oxygen (4.3 and 8.8mgO2L(-1), respectively) on the different microbial activities (hydrolytic, acidogenic and methanogenic) of thermophilic anaerobic biomass and on the methanogenic community structure. Batch tests in presence of oxygen were conducted using specific substrates for each biological activity and a blank (with minimum oxygen) was included. No effect of oxygen was observed on the hydrolytic and acidogenic activities. In contrast, the methane production rate decreased by 40% in all oxygenated batches and the development of active archaeal community was slower in presence of 8.8mgO2L(-1). However, despite this sensitivity of methanogens to oxygen at saturation levels, the inhibition was reversible. PMID:27020398

  6. An ultrastable bimetallic carbide as platinum electrocatalyst support for highly active oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Yan, Zaoxue; Zhang, Mingmei; Xie, Jimin; Shen, Pei Kang

    2015-11-01

    Stable bimetallic carbide (Fe2MoC) with graphitized carbon (GC) as matrix has been synthesized through an ion-exchange method. The Pt nanoparticles are loaded on the GC-Fe2MoC composite to form Pt/GC-Fe2MoC electrocatalyst which shows much higher activity and stability than those of commercial Pt/C for oxygen reduction reaction in acidic media. The excellent performances of Pt/GC-Fe2MoC are mainly due to the inherent stability of GC-Fe2MoC and the promotion effect between Fe2MoC and Pt.

  7. OT2_dbrisbin_1: A z=1-2 oxygen survey. II. PAH-selected star forming and AGN sources

    NASA Astrophysics Data System (ADS)

    Brisbin, D.

    2011-09-01

    We are conducting a survey of the [CII] 158um line from galaxies at redshifts 1-2 using our grating spectrometer, ZEUS on the CSO. Our first 13 galaxy survey showed that luminous star forming galaxies in this epoch have moderate intensity kpc-scale star formation likely an extension of the Schmidt-Kennicutt law to very high gas mass fractions. Our AGN dominated systems have similarly large scale, but significantly more intense star formation suggesting punctuated, collision-induced star formation. We were awarded OT1 PACS spectroscopy and PACS/SPIRE photometry of these sources to observe the oxygen [OI], [OIII], and [OIV] fine-structure lines and far-IR continuum to characterize the star formation and AGN activity in these sources. Only two of our sources have been observed to date, but with good astrophysical success. Since the OT1 submission, we have detected 11 more z ~1-2 sources in [CII] with ZEUS. Here we propose an OT2 oxygen line/far-IR continuum study for 10 of these new sources. The new source list significantly enhances our OT1 survey in that (1) we nearly double our sample greatly increasing statistical significance of the results (2) the new group includes 7 Spitzer/PAH sources. PAH emission arises from PDRs tracing the photo-electric heating, while the [CII] and [OI] lines trace the cooling. PAHS therefore trace star formation and, since the features are extremely bright, are excellent redshift indicators. Future missions (e.g. JWST and SPICA/SAFARI) will rely on PAH spectroscopy at high z. It is therefore vital to study PAH emission and its relationship to star formation. The proposed work explores this connection at redshifts 1-2, near the peak of star formation per unit co-moving volume over cosmic time. In this interval ZEUS and PACs share a great synergy with well-matched sensitivities enabling detections of [CII] and oxygen in a wide variety of systems.

  8. Oxygen reduction reaction activity on Pt{111} surface alloys.

    PubMed

    Attard, Gary A; Brew, Ashley; Ye, Jin-Yu; Morgan, David; Sun, Shi-Gang

    2014-07-21

    PtM overlayers (where M=Fe, Co or Ni) supported on Pt{111} are prepared via thermal annealing in either a nitrogen/water or hydrogen ambient of dilute aqueous droplets containing M(Z+) cations directly attached to the electrode. Two different PtM phases are detected depending on the nature of the post-annealing cooling environment. The first of these consists of small (<20 nm), closely packed microcrystals comprised of a central metallic core and a shell (several monolayers thick) of mixed metal oxides/hydroxides. The second type of PtM phase is prepared by cooling in a stream of hydrogen gas. Although this second phase also consists of numerous microcrystals covering the Pt{111} electrode surface, these are both flatter than before and moreover are entirely metallic in character. A positive shift in the onset of PtM oxide formation correlates with increased activity towards the oxygen reduction reaction (ORR), which we ascribe to the greater availability of platinum metallic sites under ORR conditions. PMID:24986646

  9. Enhanced Surfactant Adsorption on Activated Carbon through Manipulation of Surface Oxygen Groups

    NASA Astrophysics Data System (ADS)

    Collins, John; Qu, Deyang; Foster, Michelle

    2012-02-01

    Passive energy storage is a necessary component for balancing the lifecycle budget with new forms of green energy. The work presented describes how surface oxygen groups (SOG) on granulated activated carbon have been manipulated using Nitric Acid in a controlled, stepwise fashion. The structure and surface functionality of the activated carbon samples were characterized using DRIFTS, Raman Spectroscopy and Porosimetry. Total surface area was found to increase proportionally with the removal of heteroatom material, exposing previously insulated active sites responsible for SOG attachment. Broad oxide peaks were deconvoluted and analyzed, allowing for absolute identification of evolving functionality at each oxidation stage. SOGs were maximized on the third oxidation cycle with the presence of conjugated aromatic, phenol, lactone, and carboxylic acid groups. FSN Zonyl nonionic was applied to all oxidized samples at various concentrations. Total adsorbed surfactant was quantified for each concentration / oxidation scheme using attenuated total reflection. The relative quantity and polarity of chemisorbed surfactant were qualitatively assessed for each equilibrium concentration.

  10. Growth enhancement and gene expression of Arabidopsis thaliana irradiated with active oxygen species

    NASA Astrophysics Data System (ADS)

    Watanabe, Satoshi; Ono, Reoto; Hayashi, Nobuya; Shiratani, Masaharu; Tashiro, Kosuke; Kuhara, Satoru; Inoue, Asami; Yasuda, Kaori; Hagiwara, Hiroko

    2016-07-01

    The characteristics of plant growth enhancement effect and the mechanism of the enhancement induced by plasma irradiation are investigated using various active species in plasma. Active oxygen species in oxygen plasma are effective for growth enhancement of plants. DNA microarray analysis of Arabidopsis thaliana indicates that the genes coding proteins that counter oxidative stresses by eliminating active oxygen species are expressed at significantly high levels. The size of plant cells increases owing to oxygen plasma irradiation. The increases in gene expression levels and cell size suggest that the increase in the expression level of the expansin protein is essential for plant growth enhancement phenomena.

  11. Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact.

    PubMed

    Young, Edward D; Kohl, Issaku E; Warren, Paul H; Rubie, David C; Jacobson, Seth A; Morbidelli, Alessandro

    2016-01-29

    Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Δ'(17)O of -1 ± 5 parts per million (2 standard error). On the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. The results indicate that the late veneer impactors had an average Δ'(17)O within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system. PMID:26823426

  12. Carbon-Oxygen Bond Forming Mechanisms in Rhenium Oxo-Alkyl Complexes

    SciTech Connect

    Cheng, Mu-Jeng; Nielsen, Robert J.; Ahlquist, Marten; Goddard, William A.

    2010-04-07

    Three C-X bond formation mechanisms observed in the oxidation of (HBpz3)ReO(R)(OTf) [HBpz 3 = hydrotris(1-pyrazolyl)borate; R = Me, Et, and iPr; OTf = OSO2CF3] by dimethyl sulfoxide (DMSO) were investigated using quantum mechanics (M06//B3LYP DFT) combined with solvation (using the PBF Poisson-Boltzmann polarizable continuum solvent model). For R = Et we find the alkyl group is activated through α-hydrogen abstraction by external base OTf- with a free energy barrier of only 12.0 kcal/mol, leading to formation of acetaldehyde. Alternatively, ethyl migration across the M=O bond (leading to the formation of acetaldehyde and ethanol) poses a free energy barrier of 22.1 kcal/mol, and the previously proposed α-hydrogen transfer to oxo (a 2+2 forbidden reaction) poses a barrier of 44.9 kcal/mol. The rate-determining step to formation of the final product acetaldehyde is an oxygen atom transfer from DMSO to the ethylidene, with a free energy barrier of 15.3 kcal/mol. When R = iPr, the alkyl 1,2-migration pathway becomes the more favorable pathway (both kinetically and thermodynamically), with a free energy barrier (ΔG = 11.8 kcal/mol) lower than α-hydrogen abstraction by OTf- (ΔG = 13.5 kcal/mol). This suggests the feasibility of utilizing this type of migration to functionalize M-R to M-OR. We also considered the nucleophilic attack of water and ammonia on the Re-ethylidene α-carbon as a means of recovering two-electron-oxidized products from an alkane oxidation. Nucleophilic attack (with internal deprotonation of the nucleophile) is exothermic. However, the subsequent protonolysis of the Re-alkyl bond (to liberate an alcohol or amine) poses a barrier of 37.0 or 42.4 kcal/mol, respectively. Where comparisons are possible, calculated free energies agree very well with experimental measurements.

  13. The large, oxygen-rich halos of star-forming galaxies are a major reservoir of galactic metals.

    PubMed

    Tumlinson, J; Thom, C; Werk, J K; Prochaska, J X; Tripp, T M; Weinberg, D H; Peeples, M S; O'Meara, J M; Oppenheimer, B D; Meiring, J D; Katz, N S; Davé, R; Ford, A B; Sembach, K R

    2011-11-18

    The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of intergalactic gas, but its mass, heavy element enrichment, and relation to galaxy properties are poorly constrained by observations. In a survey of the outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope, we detected ubiquitous, large (150-kiloparsec) halos of ionized oxygen surrounding star-forming galaxies; we found much less ionized oxygen around galaxies with little or no star formation. This ionized CGM contains a substantial mass of heavy elements and gas, perhaps far exceeding the reservoirs of gas in the galaxies themselves. Our data indicate that it is a basic component of nearly all star-forming galaxies that is removed or transformed during the quenching of star formation and the transition to passive evolution. PMID:22096191

  14. Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

    SciTech Connect

    Christ, J. M.; Neyerlin, K. C.; Wang, H.; Richards, R.; Dinh, H. N.

    2014-10-30

    The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 – C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resulting in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Lastly, greater than a 44% loss in ORR activity at 0.9V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities.

  15. Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

    DOE PAGESBeta

    Christ, J. M.; Neyerlin, K. C.; Wang, H.; Richards, R.; Dinh, H. N.

    2014-10-30

    The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 – C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resultingmore » in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Lastly, greater than a 44% loss in ORR activity at 0.9V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities.« less

  16. Form-Focused Discovery Activities in English Classes

    ERIC Educational Resources Information Center

    Ogeyik, Muhlise Cosgun

    2011-01-01

    Form-focused discovery activities allow language learners to grasp various aspects of a target language by contributing implicit knowledge by using discovered explicit knowledge. Moreover, such activities can assist learners to perceive and discover the features of their language input. In foreign language teaching environments, they can be used…

  17. Oxide Defect Engineering Enables to Couple Solar Energy into Oxygen Activation.

    PubMed

    Zhang, Ning; Li, Xiyu; Ye, Huacheng; Chen, Shuangming; Ju, Huanxin; Liu, Daobin; Lin, Yue; Ye, Wei; Wang, Chengming; Xu, Qian; Zhu, Junfa; Song, Li; Jiang, Jun; Xiong, Yujie

    2016-07-20

    Modern development of chemical manufacturing requires a substantial reduction in energy consumption and catalyst cost. Sunlight-driven chemical transformation by metal oxides holds great promise for this goal; however, it remains a grand challenge to efficiently couple solar energy into many catalytic reactions. Here we report that defect engineering on oxide catalyst can serve as a versatile approach to bridge light harvesting with surface reactions by ensuring species chemisorption. The chemisorption not only spatially enables the transfer of photoexcited electrons to reaction species, but also alters the form of active species to lower the photon energy requirement for reactions. In a proof of concept, oxygen molecules are activated into superoxide radicals on defect-rich tungsten oxide through visible-near-infrared illumination to trigger organic aerobic couplings of amines to corresponding imines. The excellent efficiency and durability for such a highly important process in chemical transformation can otherwise be virtually impossible to attain by counterpart materials. PMID:27351805

  18. Activated carbon fibers and engineered forms from renewable resources

    DOEpatents

    Baker, Frederick S

    2013-02-19

    A method of producing activated carbon fibers (ACFs) includes the steps of providing a natural carbonaceous precursor fiber material, blending the carbonaceous precursor material with a chemical activation agent to form chemical agent-impregnated precursor fibers, spinning the chemical agent-impregnated precursor material into fibers, and thermally treating the chemical agent-impregnated precursor fibers. The carbonaceous precursor material is both carbonized and activated to form ACFs in a single step. The method produces ACFs exclusive of a step to isolate an intermediate carbon fiber.

  19. Activated carbon fibers and engineered forms from renewable resources

    DOEpatents

    Baker, Frederick S.

    2010-06-01

    A method of producing activated carbon fibers (ACFs) includes the steps of providing a natural carbonaceous precursor fiber material, blending the carbonaceous precursor material with a chemical activation agent to form chemical agent-impregnated precursor fibers, spinning the chemical agent-impregnated precursor material into fibers, and thermally treating the chemical agent-impregnated precursor fibers. The carbonaceous precursor material is both carbonized and activated to form ACFs in a single step. The method produces ACFs exclusive of a step to isolate an intermediate carbon fiber.

  20. Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact

    NASA Astrophysics Data System (ADS)

    Young, Edward D.; Kohl, Issaku E.; Warren, Paul H.; Rubie, David C.; Jacobson, Seth A.; Morbidelli, Alessandro

    2016-01-01

    Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Δ‧17O of -1 ± 5 parts per million (2 standard error). On the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. The results indicate that the late veneer impactors had an average Δ‧17O within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system.

  1. A mechanism of oxygen sensing in yeast. Multiple oxygen-responsive steps in the heme biosynthetic pathway affect Hap1 activity.

    PubMed

    Hon, Thomas; Dodd, Athena; Dirmeier, Reinhard; Gorman, Nadia; Sinclair, Peter R; Zhang, Li; Poyton, Robert O

    2003-12-12

    Heme plays central roles in oxygen sensing and utilization in many living organisms. In yeast, heme mediates the effect of oxygen on the expression of many genes involved in using or detoxifying oxygen. However, a direct link between intracellular heme level and oxygen concentration has not been vigorously established. In this report, we have examined the relationships among oxygen levels, heme levels, Hap1 activity, and HAP1 expression. We found that Hap1 activity is controlled in vivo by heme and not by its precursors and that heme activates Hap1 even in anoxic cells. We also found that Hap1 activity exhibits the same oxygen dose-response curves as Hap1-dependent aerobic genes and that these dose-response curves have a sharp break at approximately 1 microM O2. The results show that the intracellular signaling heme level, reflected as Hap1 activity, is closely correlated with oxygen concentration. Furthermore, we found that bypass of all heme synthetic steps but ferrochelatase by deuteroporphyrin IX does not circumvent the need for oxygen in Hap1 full activation by heme, suggesting that the last step of heme synthesis, catalyzed by ferrochelatase, is also subjected to oxygen control. Our results show that multiple heme synthetic steps can sense oxygen concentration and provide significant insights into the mechanism of oxygen sensing in yeast. PMID:14512429

  2. Phosphate oxygen isotopic evidence for a temperate and biologically active Archaean ocean.

    PubMed

    Blake, Ruth E; Chang, Sae Jung; Lepland, Aivo

    2010-04-15

    Oxygen and silicon isotope compositions of cherts and studies of protein evolution have been interpreted to reflect ocean temperatures of 55-85 degrees C during the early Palaeoarchaean era ( approximately 3.5 billion years ago). A recent study combining oxygen and hydrogen isotope compositions of cherts, however, makes a case for Archaean ocean temperatures being no greater than 40 degrees C (ref. 5). Ocean temperature can also be assessed using the oxygen isotope composition of phosphate. Recent studies show that (18)O:(16)O ratios of dissolved inorganic phosphate (delta(18)O(P)) reflect ambient seawater temperature as well as biological processing that dominates marine phosphorus cycling at low temperature. All forms of life require and concentrate phosphorus, and as a result of biological processing, modern marine phosphates have delta(18)O(P) values typically between 19-26 per thousand (VSMOW), highly evolved from presumed source values of approximately 6-8 per thousand that are characteristic of apatite in igneous rocks and meteorites. Here we report oxygen isotope compositions of phosphates in sediments from the 3.2-3.5-billion-year-old Barberton Greenstone Belt in South Africa. We find that delta(18)O(P) values range from 9.3 per thousand to 19.9 per thousand and include the highest values reported for Archaean rocks. The temperatures calculated from our highest delta(18)O(P) values and assuming equilibrium with sea water with delta(18)O = 0 per thousand (ref. 12) range from 26 degrees C to 35 degrees C. The higher delta(18)O(P) values are similar to those of modern marine phosphate and suggest a well-developed phosphorus cycle and evolved biologic activity on the Archaean Earth. PMID:20393560

  3. PROCESS FOR THE PRODUCTION OF AN ACTIVATED FORM OF UO$sub 2$

    DOEpatents

    Polissar, M.J.

    1957-09-24

    A process for producing a highly active form of UO/sub 2/ characterized both by rapid oxidation in air and by rapid chlorination with CCl/sub 4/ vapor at an elevated temperature is reported. In accordance with the process, commercial UO/sub 2/, is subjected to a series of oxidation-reduction operations to produce a form of UC/sub 2/ of enhanced reactivity. By treatimg commercial UO/sub 2/ at a temperature between 335 and 485 deg C with methane, then briefly with an oxygen containing gas and followimg this by a second treatment with a methane containing gas, the original relatively stable charge of UO/sub 2/ will be transformed into an active form of UO/sub 2/.

  4. Carbothermal synthesis of titanium oxycarbide as electrocatalyst support with high oxygen evolution reaction activity

    SciTech Connect

    Huang, K; Li, YF; Xing, YC

    2012-11-09

    Carbothermal reduction of semiconducting TiO2 into highly conductive titanium oxycarbide (TiOxCy) was investigated. The thermally produced uniform carbon layer on TiO2 (Degussa P25) protects the TiO2 nanoparticles from sintering and, at the same time, supplies the carbon source for doping TiO2 with carbon. At low temperatures (e. g., 700 degrees C), carbon only substitutes part of the oxide and distorts the TiO2 lattice to form TiO2-xCx with only substitutional carbon. When the carbon-doped TiO2 is annealed at a higher temperature (1100 degrees C), x-ray diffraction and x-ray photoelectron spectroscopy results showed that TiOxCy, a solid solution of TiO and TiC, was formed, which displays different diffraction peaks and binding energies. It was shown that TiOxCy has much better oxygen revolution reaction activity than TiO2 or TiO2-xCx. Further studies showed that the TiOxCy obtained can be used as a support for metal electrocatalyst, leading to a bifunctional catalyst effective for both oxygen reduction and evolution reactions.

  5. Cell death induced by direct laser activation of singlet oxygen at 1270 nm

    NASA Astrophysics Data System (ADS)

    Anquez, F.; El Yazidi Belkoura, I.; Suret, P.; Randoux, S.; Courtade, E.

    2013-02-01

    Singlet oxygen plays a major role in many chemical and biological photo-oxidation processes. It has a high chemical reactivity, which is commonly harnessed for therapeutic issues. Indeed, singlet oxygen is recognized as the major cytotoxic agent in photodynamic therapy. In this treatment of cancer, singlet oxygen is created, among other reactive species, by an indirect transfer of energy from light to molecular oxygen via excitation of a photosensitizer. In this paper, we show that the conventional singlet oxygen production scheme can be simplified. Production of singlet oxygen is achieved in living cells from photosensitizer-free 1270 nm laser excitation of the electronic ground state of molecular oxygen. The quantity of singlet oxygen produced in this way is sufficient to induce an oxidative stress leading to cell death. Other effects such as thermal stress are discriminated, and we conclude that cell death is only due to singlet oxygen creation. This new simplified scheme of singlet oxygen activation can be seen as a breakthrough for phototherapies of malignant diseases and/or as a non-invasive possibility to generate reactive oxygen species in a tightly controlled manner.

  6. Origin of Active Oxygen in a Ternary CuOx /Co3O4–CeO 2 Catalyst for CO Oxidation

    SciTech Connect

    Liu, Zhigang; Wu, Zili; Peng, Xihong; Binder, Andrew; Chai, Songhai; Dai, Sheng

    2014-11-14

    In this paper, we have studied CO oxidation over a ternary CuOx/Co3O4-CeO2 catalyst and employed the techniques of N2 adsorption/desporption, XRD, TPR, TEM, in situ DRIFTS and QMS (Quadrupole mass spectrometer) to explore the origin of active oxygen. DRIFTS-QMS results with labeled 18O2 indicate that the origin of active oxygens in CuOx/Co3O4-CeO2 obeys a model, called as queue mechanism. Namely gas-phase molecular oxygens are dissociated to atomic oxygens and then incorporate in oxygen vacancies located at the interface of Co3O4-CeO2 to form active crystalline oxygens, and these active oxygens diffuse to the CO-Cu+ sites thanks to the oxygen vacancy concentration magnitude and react with the activated CO to form CO2. This process, obeying a queue rule, provides active oxygens to form CO2 from gas-phase O2 via oxygen vacancies and crystalline oxygen at the interface of Co3O4-CeO2.

  7. Effects of dissolved oxygen level on rapamycin production by pellet-form of Streptomyces hygroscopicus.

    PubMed

    Yen, Hong-Wei; Hsiao, Hsin-Pei

    2013-09-01

    Rapamycin was known to have the functions of being an antibiotic and immunosuppressant; recently it was also recognized as being able to retard the aging process. The effects of dissolved oxygen (DO) level on rapamycin production by pellet-form of Streptomyces hygroscopicus were investigated in this study. The results suggest that a high DO level is required to enhance rapamycin production. However, the premise for getting a high rapamycin concentration by using DO control was keeping the intact of pellet-form of S. hygroscopicus. What if the high DO level achieved was coming from the increase of agitation; it might break down the morphology of pellets-form in the fermentation tank and result in the decrease of rapamycin production. The maximum rapamycin obtained in this study was about 780 mg/L in the 5 L fermentor batch with DO controlled over 30%, with the supplement of pure oxygen in the inlet gas, and the agitation speed limited to less than 200 rpm. Conclusively, a high DO level and the morphology of pellets form both were detrimental to achieving a high rapamycin production by S. hygroscopicus in the agitation fermentor. PMID:23623896

  8. Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Hu, Guangzhi; Nitze, Florian; Gracia-Espino, Eduardo; Ma, Jingyuan; Barzegar, Hamid Reza; Sharifi, Tiva; Jia, Xueen; Shchukarev, Andrey; Lu, Lu; Ma, Chuansheng; Yang, Guang; Wågberg, Thomas

    2014-10-01

    The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium:tungsten=1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are ~1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.

  9. Method of Separating Oxygen From Spacecraft Cabin Air to Enable Extravehicular Activities

    NASA Technical Reports Server (NTRS)

    Graf, John C.

    2013-01-01

    Extravehicular activities (EVAs) require high-pressure, high-purity oxygen. Shuttle EVAs use oxygen that is stored and transported as a cryogenic fluid. EVAs on the International Space Station (ISS) presently use the Shuttle cryo O2, which is transported to the ISS using a transfer hose. The fluid is compressed to elevated pressures and stored as a high-pressure gas. With the retirement of the shuttle, NASA has been searching for ways to deliver oxygen to fill the highpressure oxygen tanks on the ISS. A method was developed using low-pressure oxygen generated onboard the ISS and released into ISS cabin air, filtering the oxygen from ISS cabin air using a pressure swing absorber to generate a low-pressure (high-purity) oxygen stream, compressing the oxygen with a mechanical compressor, and transferring the high-pressure, high-purity oxygen to ISS storage tanks. The pressure swing absorber (PSA) can be either a two-stage device, or a single-stage device, depending on the type of sorbent used. The key is to produce a stream with oxygen purity greater than 99.5 percent. The separator can be a PSA device, or a VPSA device (that uses both vacuum and pressure for the gas separation). The compressor is a multi-stage mechanical compressor. If the gas flow rates are on the order of 5 to 10 lb (.2.3 to 4.6 kg) per day, the compressor can be relatively small [3 16 16 in. (.8 41 41 cm)]. Any spacecraft system, or other remote location that has a supply of lowpressure oxygen, a method of separating oxygen from cabin air, and a method of compressing the enriched oxygen stream, has the possibility of having a regenerable supply of highpressure, high-purity oxygen that is compact, simple, and safe. If cabin air is modified so there is very little argon, the separator can be smaller, simpler, and use less power.

  10. The Effect of 30% Oxygen on Visuospatial Performance and Brain Activation: An Fmri Study

    ERIC Educational Resources Information Center

    Chung, S.C.; Tack, G.R.; Lee, B.; Eom, G.M.; Lee, S.Y.; Sohn, J.H.

    2004-01-01

    This study aimed to investigate the hypothesis that administration of the air with 30% oxygen compared with normal air (21% oxygen) enhances cognitive functioning through increased activation in the brain. A visuospatial task was presented while brain images were scanned by a 3 T fMRI system. The results showed that there was an improvement in…

  11. Oxide scales formed on Fe-Cr-Al-based model alloys exposed to oxygen containing molten lead

    NASA Astrophysics Data System (ADS)

    Weisenburger, A.; Jianu, A.; Doyle, S.; Bruns, M.; Fetzer, R.; Heinzel, A.; DelGiacco, M.; An, W.; Müller, G.

    2013-06-01

    Based on the state of the art oxide maps concerning oxidation behavior of Fe-Cr-Al model alloys at 800 and 1000 °C in oxygen atmosphere, ten compositions, belonging to this alloy system, were designed in order to tap the borders of the alumina stability domain, during their exposure to oxygen (10-6 wt.%) containing lead, at 400, 500 and 600 °C. Eight alloys, Fe-6Cr-6Al, Fe-8Cr-6Al, Fe-10Cr-5Al, Fe-14Cr-4Al, Fe-16Cr-4Al, Fe-6Cr-8Al, Fe-10Cr-7Al and Fe-12Cr-5Al, were found to be protected against corrosion in oxygen containing lead, either by a duplex layer (Fe3O4 + (Fe1-x-yCrxAly)3O4) or by (Fe1-x-yCrxAly)3O4, depending on the temperature at which they were exposed. Two alloys namely Fe-12Cr-7Al and Fe-16Cr-6Al were found to form transient aluminas, κ-Al2O3 (at 400 and 500 °C) and θ-Al2O3 (at 600 °C), as protective oxide scale against corrosion in oxygen containing lead. An oxide map illustrating the stability domain of alumina, grown on Fe-Cr-Al alloys when exposed to molten, oxygen containing lead, was drawn. The map includes also additional points, extracted from literature and corresponding to alumina forming alloys, when exposed to HLMs, which fit very well with our findings. Chromium and aluminium contents of 12.5-17 wt.% and 6-7.5 wt.%, respectively, are high enough to obtain thin, stable and protective alumina scales on Fe-Cr-Al-based alloys exposed to oxygen containing lead at 400, 500 and 600 °C. For the temperature range and exposure times used during the current evaluation, the growth rate of the alumina scale was low. No area with detached scale was observed and no trace of α-Al2O3 was detected.

  12. Activation of oxygen-mediating pathway using copper ions: fine-tuning of growth kinetics in gold nanorod overgrowth.

    PubMed

    Liu, Wenqi; Zhang, Hui; Wen, Tao; Yan, Jiao; Hou, Shuai; Shi, Xiaowei; Hu, Zhijian; Ji, Yinglu; Wu, Xiaochun

    2014-10-21

    Growth kinetics plays an important role in the shape control of nanocrystals (NCs). Herein, we presented a unique way to fine-tune the growth kinetics via oxidative etching activated by copper ions. For the overgrowth of gold nanorods (Au NRs), competitive adsorption of dissolved oxygen on rod surface was found to slow down the overgrowth rate. Copper ions were able to remove the adsorbed oxygen species from the Au surface via oxidative etching, thus exposing more reaction sites for Au deposition. In this way, copper ions facilitated the overgrowth process. Furthermore, Cu(2+) rather than Cu(+) acted as the catalyst for the oxidative etching. Comparative study with Ag(+) indicated that Cu(2+) cannot regulate NC shapes via an underpotential deposition mechanism. In contrast, Ag(+) led to the formation of Au tetrahexahedra (THH) and a slight decrease of the growth rate at similar growth conditions. Combining the distinct roles of the two ions enabled elongated THH to be produced. Copper ions activating the O2 pathway suggested that dissolved oxygen has a strong affinity for the Au surface. Moreover, the results of NC-sensitized singlet oxygen ((1)O2) indicated that the absorbed oxygen species on the surface of Au NCs bounded with low-index facets mainly existed in the form of molecular O2. PMID:25244407

  13. Atmospheric oxygen plasma activation of silicon (100) surfaces

    SciTech Connect

    Habib, Sara B.; Gonzalez, Eleazar II; Hicks, Robert F.

    2010-05-15

    Silicon (100) surfaces were converted to a hydrophilic state with a water contact angle of <5 deg. by treatment with a radio frequency, atmospheric pressure helium, and oxygen plasma. A 2 in. wide plasma beam, operating at 250 W, 1.0 l/min O{sub 2}, 30 l/min He, and a source-to-sample distance of 3{+-}0.1 mm, was scanned over the sample at 100{+-}2 mm/s. Plasma oxidation of HF-etched silicon caused the dispersive component of the surface energy to decrease from 55.1 to 25.8 dyn/cm, whereas the polar component of the surface energy increased from 0.3 to 42.1 dyn/cm. X-ray photoelectron spectroscopy revealed that the treatment generated a monolayer of covalently bonded oxygen on the Si(100) surface 0.15{+-}0.10 nm thick. The surface oxidation kinetics have been measured by monitoring the change in water contact angle with treatment time, and are consistent with a process that is limited by the mass transfer of ground-state oxygen atoms to the silicon surface.

  14. Acetaminophen-induced hepatotoxicity: role of metabolic activation, reactive oxygen/nitrogen species, and mitochondrial permeability transition.

    PubMed

    Hinson, Jack A; Reid, Angela B; McCullough, Sandra S; James, Laura P

    2004-10-01

    Large doses of the analgesic acetaminophen cause centrilobular hepatic necrosis in man and in experimental animals. It has been previously shown that acetaminophen is metabolically activated by CYP enzymes to N-acetyl-p-benzoquinone imine. This species is normally detoxified by GSH, but following a toxic dose GSH is depleted and the metabolite covalently binds to a number of different proteins. Covalent binding occurs only to the cells developing necrosis. Recently we showed that these cells also contain nitrated tyrosine residues. Nitrotyrosine is mediated by peroxynitrite, a reactive nitrogen species formed by rapid reaction between nitric oxide and superoxide and is normally detoxified by GSH. Thus, acetaminophen toxicity occurs with increased oxygen/nitrogen stress. This manuscript will review current data on acetaminophen covalent binding, increased oxygen/nitrogen stress, and mitochondrial permeability transition, a toxic mechanism that is both mediated by and leads to increased oxygen/nitrogen stress. PMID:15554248

  15. Effect of surface area and chemisorbed oxygen on the SO2 adsorption capacity of activated char

    USGS Publications Warehouse

    Lizzio, A.A.; DeBarr, J.A.

    1996-01-01

    The objective of this study was to determine whether activated char produced from Illinois coal could be used effectively to remove sulfur dioxide from coal combustion flue gas. Chars were prepared from a high-volatile Illinois bituminous coal under a wide range of pyrolysis and activation conditions. A novel char preparation technique was developed to prepare chars with SO2 adsorption capacities significantly greater than that of a commercial activated carbon. In general, there was no correlation between SO2 adsorption capacity and surface area. Temperature-programmed desorption (TPD) was used to determine the nature and extent of carbon-oxygen (C-O) complexes formed on the char surface. TPD data revealed that SO2 adsorption was inversely proportional to the amount of C-O complex. The formation of a stable C-O complex during char preparation may have served only to occupy carbon sites that were otherwise reactive towards SO2 adsorption. A fleeting C(O) complex formed during SO2 adsorption is postulated to be the reaction intermediate necessary for conversion of SO2 to H2SO4. Copyright ?? 1996 Elsevier Science Ltd.

  16. Pore-forming activity of clostridial binary toxins.

    PubMed

    Knapp, O; Benz, R; Popoff, M R

    2016-03-01

    Clostridial binary toxins (Clostridium perfringens Iota toxin, Clostridium difficile transferase, Clostridium spiroforme toxin, Clostridium botulinum C2 toxin) as Bacillus binary toxins, including Bacillus anthracis toxins consist of two independent proteins, one being the binding component which mediates the internalization into cell of the intracellularly active component. Clostridial binary toxins induce actin cytoskeleton disorganization through mono-ADP-ribosylation of globular actin and are responsible for enteric diseases. Clostridial and Bacillus binary toxins share structurally and functionally related binding components which recognize specific cell receptors, oligomerize, form pores in endocytic vesicle membrane, and mediate the transport of the enzymatic component into the cytosol. Binding components retain the global structure of pore-forming toxins (PFTs) from the cholesterol-dependent cytotoxin family such as perfringolysin. However, their pore-forming activity notably that of clostridial binding components is more related to that of heptameric PFT family including aerolysin and C. perfringens epsilon toxin. This review focuses upon pore-forming activity of clostridial binary toxins compared to other related PFTs. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale. PMID:26278641

  17. Design of high pressure oxygen filter for extravehicular activity life support system, volume 1

    NASA Technical Reports Server (NTRS)

    Wilson, B. A.

    1977-01-01

    The experience of the National Aeronautics and Space Administration (NASA) with extravehicular activity life support emergency oxygen supply subsystems has shown a large number of problems associated with particulate contamination. These problems have resulted in failures of high pressure oxygen component sealing surfaces. A high pressure oxygen filter was designed which would (a) control the particulate contamination level in the oxygen system to a five-micron glass bead rating, ten-micron absolute condition (b) withstand the dynamic shock condition resulting from the sudden opening of 8000 psi oxygen system shutoff valve. Results of the following program tasks are reported: (1) contaminant source identification tests, (2) dynamic system tests, (3) high pressure oxygen filter concept evaluation, (4) design, (5) fabrication, (6) test, and (7) application demonstration.

  18. Molecular mimicry of substrate oxygen atoms by water molecules in the beta-amylase active site.

    PubMed

    Pujadas, G; Palau, J

    2001-08-01

    Soybean beta-amylase (EC 3.2.1.2) has been crystallized both free and complexed with a variety of ligands. Four water molecules in the free-enzyme catalytic cleft form a multihydrogen-bond network with eight strategic residues involved in enzyme-ligand hydrogen bonds. We show here that the positions of these four water molecules are coincident with the positions of four potential oxygen atoms of the ligands within the complex. Some of these waters are displaced from the active site when the ligands bind to the enzyme. How many are displaced depends on the shape of the ligand. This means that when one of the four positions is not occupied by a ligand oxygen atom, the corresponding water remains. We studied the functional/structural role of these four waters and conclude that their presence means that the conformation of the eight side chains is fixed in all situations (free or complexed enzyme) and preserved from unwanted or forbidden conformational changes that could hamper the catalytic mechanism. The water structure at the active pocket of beta-amylase is therefore essential for providing the ligand recognition process with plasticity. It does not affect the protein active-site geometry and preserves the overall hydrogen-bonding network, irrespective of which ligand is bound to the enzyme. We also investigated whether other enzymes showed a similar role for water. Finally, we discuss the potential use of these results for predicting whether water molecules can mimic ligand atoms in the active center. PMID:11468361

  19. Effects of carbohydrate on the internal oxygen concentration, oxygen uptake, and nitrogenase activity in detached pea nodules

    SciTech Connect

    Monroe, J.D. ); LaRue, T.A. )

    1989-10-01

    The interaction between carbon substrates and O{sub 2} and their effects on nitrogenase activity (C{sub 2}H{sub 2}) were examined in detached nodules of pea (Pisum sativum L. cv Sparkle). The internal O{sub 2} concentration was estimated from the fractional oxygenation of leghemoglobin measured by reflectance spectroscopy. Lowering the endogenous carbohydrate content of nodules by excising the shoots 16 hours before nodule harvest or by incubating detached nodules at 100 kPa O{sub 2} for 2 hours resulted in a 2- to 10-fold increase in internal O{sub 2}, and a decline in nitrogenase activity. Conversely, when detached nodules were supplied with 100 millimolar succinate, the internal O{sub 2} was lowered. Nitrogenase activity was stimulated by succinate but only at high external O{sub 2}. Oxygen uptake increased linearly with external O{sub 2} but was affected only slightly by the carbon treatments. The apparent diffusion resistance in the nodule cortex was similar in all of the treatments. Carbon substrates can thus affect nitrogenase activity indirectly by affecting the O{sub 2} concentration within detached nodules.

  20. Effects of molecular oxygen and pH on the adsorption of aniline to activated carbon

    SciTech Connect

    Fox, P.; Pinisetti, K.

    1994-12-31

    This paper examines the influence of molecular oxygen and pH on the adsorption of aniline to F-300 Calgon Carbon. Molecular oxygen increased the adsorptive capacity of GAC for anilines by 250--400 % at pH 3, 30--83% at pH 5, 17--42% at pH 9, and B-45% at pH 11 (higher than those obtained in the absence of molecular oxygen). At pH 7, some of the products formed are poorly adsorbed as evidenced by an increase in UV absorbance in the oxic isotherms as compared to the other isotherms. Oxygen uptake measurements revealed significant consumption of molecular oxygen during the adsorption of aniline compounds. It is speculated that the increase in the GAC adsorptive capacity under oxic conditions was due to the polymerization of these adsorbates on the carbon surface.

  1. Hyperstoichiometric Oxygen in Fluorite-type U3O8 Formed at Extreme Conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Fuxiang; Lang, Maik; Ewing, Rod; Department of Earth and Environmental Sciences Team

    2014-03-01

    U3O8 was obtained by annealing UO3 in a reducing atmosphere at 200 °C. Powder sample of β-U3O8 was pressurized at room temperature up to 37.5 GPa and XRD patterns clearly indicated that a phase transition occurred between 3-11 GPa. The high-pressure phase is a fluorite-like structure. The high-pressure phase was then laser heated to over 1700 K in the diamond anvil cell at high pressure conditions. No phase transition was found at high pressure/ temperature conditions, and the fluorite-like structure of U3O8 is even fully quenchable. The lattice parameter of the fluorite-like high-pressure phase is 5.425 Å at ambient conditions, which is smaller than that of the stoichiometric UO2. Previous experiments have shown that the stoichiometric uranium dioxide (UO2) is not stable at high pressure conditions and starts to transform to a cotunnite structure at ~ 30 GPa. When heating the sample at high pressure, the critical transition pressure is greatly reduced. However, the fluorite-like high-pressure phase of U3O8 is very stable at high pressure/high temperature conditions. The enhanced phase stability is believed to be related to the presence of extra oxygen (or U vacancies) in the structure.

  2. Planar and channel waveguides on Na:CBN formed by oxygen ion implantation

    NASA Astrophysics Data System (ADS)

    Guo, Sha-Sha; Zhao, Jin-Hua; Huang, Qing; Liu, Peng; Liu, Tao; Zhang, Lian; Wang, Xue-Lin

    2012-09-01

    We reported the fabrication of the planar and channel waveguides in Na-doped calcium barium niobate (CBN) with multiple-energy oxygen-ion implantation. Multiple-energy implants can broaden the barrier width to reduce light leakage from the waveguide to the substrate through the barrier wall. The guiding modes and the near-field intensity distribution of the light were measured by the prism-coupling method and the end-facing coupling arrangement separately. The refractive index profiles of planar and channel waveguides were both typical "well + barrier" distribution, and we used the finite-difference beam propagation method (FD-BPM) to simulate the light propagation. After annealing at 200 °C for 30 min, the waveguide propagation loss of the planar and channel waveguides could be reduced down to ˜3.7 dB/cm and ˜3.5 dB/cm. The calculated results were in excellent agreement with the measured waveguide modes, indicating the feasibility of designing these devices.

  3. Process for forming a homogeneous oxide solid phase of catalytically active material

    DOEpatents

    Perry, Dale L.; Russo, Richard E.; Mao, Xianglei

    1995-01-01

    A process is disclosed for forming a homogeneous oxide solid phase reaction product of catalytically active material comprising one or more alkali metals, one or more alkaline earth metals, and one or more Group VIII transition metals. The process comprises reacting together one or more alkali metal oxides and/or salts, one or more alkaline earth metal oxides and/or salts, one or more Group VIII transition metal oxides and/or salts, capable of forming a catalytically active reaction product, in the optional presence of an additional source of oxygen, using a laser beam to ablate from a target such metal compound reactants in the form of a vapor in a deposition chamber, resulting in the deposition, on a heated substrate in the chamber, of the desired oxide phase reaction product. The resulting product may be formed in variable, but reproducible, stoichiometric ratios. The homogeneous oxide solid phase product is useful as a catalyst, and can be produced in many physical forms, including thin films, particulate forms, coatings on catalyst support structures, and coatings on structures used in reaction apparatus in which the reaction product of the invention will serve as a catalyst.

  4. Study of oxygen scavenging PET-based films activated by water

    NASA Astrophysics Data System (ADS)

    Rossi, Gabriella; Scarfato, Paola; Incarnato, Loredana

    2016-05-01

    In this work an active barrier system consisting of a thin and transparent film based on polyethylene terephthalate (PET) was studied. Dynamic oxygen absorption measurements were performed at different values of relative humidity and temperature, pointing out that humidity is a key factor in activating the oxidation of the polymer sample. Moreover, the thermal and optical properties of the films were investigated and a good correlation was found between the crystallinity increase and the consequent transparency reduction occurring after the oxygen absorption.

  5. The role of beaded activated carbon's surface oxygen groups on irreversible adsorption of organic vapors.

    PubMed

    Jahandar Lashaki, Masoud; Atkinson, John D; Hashisho, Zaher; Phillips, John H; Anderson, James E; Nichols, Mark

    2016-11-01

    The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation - narrow micropores (<7Å) in the oxygen-deficient samples and midsize micropores (7-12Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials. PMID:27295065

  6. Activated human neutrophil response to perfluorocarbon nanobubbles: oxygen-dependent and -independent cytotoxic responses.

    PubMed

    Hwang, Tsong-Long; Fang, Chia-Lang; Al-Suwayeh, Saleh A; Yang, Li-Jia; Fang, Jia-You

    2011-06-10

    Nanobubbles, a type of nanoparticles with acoustically active properties, are being utilized as diagnostic and therapeutic nanoparticles to better understand, detect, and treat human diseases. The objective of this work was to prepare different nanobubble formulations and investigate their physicochemical characteristics and toxic responses to N-formyl-methionyl-leucyl-phenylalanine (fMLP)-activated human neutrophils. The nanobubbles were prepared using perfluoropentane and coconut oil as the respective core and shell, with soybean phosphatidylcholine (SPC) and/or cationic surfactants as the interfacial layers. The cytotoxic effect of the nanobubbles on neutrophils was determined by extracellular O₂(.)⁻ release, intracellular reactive oxygen species (ROS), lactate dehydrogenase (LDH), and elastase release. Particle sizes of the nanobubbles with different percentages of perfluorocarbon, oil, and surfactants in ranged 186-432 nm. The nanobubbles were demonstrated to inhibit the generation of superoxide and intracellular ROS. The cytotoxicity of nanobubbles may be mainly associated with membrane damage, as indicated by the high LDH leakage. Systems with Forestall (FE), a cationic surfactant, or higher SPC contents exhibited the greatest LDH release by 3-fold compared to the control. The further addition of an oil component reduced the cytotoxicity induced by the nanobubbles. Exposure to most of the nanobubble formulations upregulated elastase release by activated neutrophils. Contrary to this result, stearylamine (SA)-containing systems slightly but significantly suppressed elastase release. FE and SA in a free form caused stronger responses by neutrophils than when they were incorporated into nanobubbles. In summary, exposure to nanobubbles resulted in a formulation-dependent toxicity toward human neutrophils that was associated with both oxygen-dependent and -independent pathways. Clinicians should therefore exercise caution when using nanobubbles in patients

  7. Theoretical and experimental investigation of the oxidized and oxygenated forms of pyrocatechuic acid (2,3-dihydroxybenzoic acid).

    PubMed

    Petropouleas, Panayiotis; Koufopoulos, George; Hatzipanayioti, Despina

    2012-08-01

    The catecholic derivative 2,3-dihydroxybenzoic acid (2,3-DHBA or pyrocatechuic acid) represents a diversity of actions in enzymatic processes. In the present study DFT calculations (at the B3LYP/TZVP level of theory) have been performed for neutral 2,3DHBA and its dimer (models 1-1a), several semiquinone forms of 2,3-DHBA, namely the neutral (models 2-4), the monoionized (models 5-7), the di-ionized (models 8) and the dimer 7a. The more stable species in each case are those with the carboxyl group protonated. Oxygenated adducts were also constructed (models 10-15) in which the dioxygen is either H-bonded to the catecholic or carboxylic hydrogen or it is concerned to act on the intradiol or extradiol carbon atoms. The side-on placement of O(2) on C(2) facilitates the intradiol C-C cleavage. Protonation of the oxygenated on C(1) adduct leads to decarboxylation of 2,3-DHBA. Isolation in the solid state and characterization by ESMS, IR, NMR, electronic spectra of the blue-green oxidized product of 2,3-DHBA (solid 1) supports the possibility of the existence of the semiquinone form or the hydroperoxide-adduct. Experimental spectroscopic data are correlated to the calculated spectroscopic parameters. In the ESMS the decarboxylation and degradation products as well a peroxo-adduct have been detected. Oxygenated species may also account for the plethora of redox signals in the cyclic voltammograms of solid 1 (in DMSO solutions). PMID:22516121

  8. Oxygen activation with transition metal complexes in aqueous solution

    SciTech Connect

    Bakac, Andreja

    2010-04-12

    Coordination to transition-metal complexes changes both the thermodynamics and kinetics of oxygen reduction. Some of the intermediates (superoxo, hydroperoxo, and oxo species) are close analogues of organic oxygen-centered radicals and peroxides (ROO{sm_bullet}, ROOH, and RO{sm_bullet}). Metal-based intermediates are typically less reactive, but more persistent, than organic radicals, which makes the two types of intermediates similarly effective in their reactions with various substrates. The self-exchange rate constant for hydrogen-atom transfer for the couples Cr{sub aq}OO{sup 2+}/Cr{sub aq}OOH{sup 2+} and L{sup 1}(H{sub 2}O)RhOO{sup 2+}/L{sup 1}(H{sub 2}O)RhOOH{sup 2+} was estimated to be 10{sup 1 {+-} 1} M{sup -1} s{sup -1}. The use of this value in the simplified Marcus equation for the Cr{sub aq}O{sup 2+}/Cr{sub aq}OOH{sup 2+} cross reaction provided an upper limit k{sub CrO,CrOH} {le} 10{sup (-2{+-}1)} M{sup -1} s{sup -1} for Cr{sub aq}O{sup 2+}/Cr{sub aq}OH{sup 2+} self-exchange. Even though superoxo complexes react very slowly in bimolecular self-reactions, extremely fast cross reactions with organic counterparts, i.e., acylperoxyl radicals, have been observed. Many of the intermediates generated by the interaction of O{sub 2} with reduced metal complexes can also be accessed by alternative routes, both thermal and photochemical.

  9. Availability of surface boron species in improved oxygen reduction activity of Pt catalysts: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, Libo; Zhou, Gang

    2016-04-01

    The oxidation process of boron (B) species on the Pt(111) surface and the beneficial effects of boron oxides on the oxygen reduction activity are investigated by first-principles calculations. The single-atom B anchored on the Pt surface has a great attraction for the oxygen species in the immediate environment. With the dissociation of molecular oxygen, a series of boron oxides is formed in succession, both indicating exothermic oxidation reactions. After BO2 is formed, the subsequent O atom immediately participates in the oxygen reduction reaction. The calculated O adsorption energy is appreciably decreased as compared to Pt catalysts, and more approximate to the optimal value of the volcano plot, from which is clear that O hydrogenation kinetics is improved. The modulation mechanism is mainly based on the electron-deficient nature of stable boron oxides, which normally reduces available electronic states of surface Pt atoms that bind the O by facilitating more electron transfer. This modification strategy from the exterior opens the new way, different from the alloying, to efficient electrocatalyst design for PEMFCs.

  10. Availability of surface boron species in improved oxygen reduction activity of Pt catalysts: A first-principles study.

    PubMed

    Zhang, Libo; Zhou, Gang

    2016-04-14

    The oxidation process of boron (B) species on the Pt(111) surface and the beneficial effects of boron oxides on the oxygen reduction activity are investigated by first-principles calculations. The single-atom B anchored on the Pt surface has a great attraction for the oxygen species in the immediate environment. With the dissociation of molecular oxygen, a series of boron oxides is formed in succession, both indicating exothermic oxidation reactions. After BO2 is formed, the subsequent O atom immediately participates in the oxygen reduction reaction. The calculated O adsorption energy is appreciably decreased as compared to Pt catalysts, and more approximate to the optimal value of the volcano plot, from which is clear that O hydrogenation kinetics is improved. The modulation mechanism is mainly based on the electron-deficient nature of stable boron oxides, which normally reduces available electronic states of surface Pt atoms that bind the O by facilitating more electron transfer. This modification strategy from the exterior opens the new way, different from the alloying, to efficient electrocatalyst design for PEMFCs. PMID:27083744

  11. Multiple forms of soluble monophenol, dihydroxyphenylalanine: oxygen-oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum).

    PubMed

    Matheis, G; Belitz, H D

    1975-04-01

    Upon polyacrylamide gel electrophoresis, a soluble phenoloxidase from potatoes (var. Maritta) revealed 17 multiple forms with activity towards dopa and almost all other o-diphenols tested, but only 5 of the forms reacted with monophenols. Isoelectric focusing of the crude enzyme resulted in 2 main peaks with activity towards dopa, having isoelectric points at pH ranges 4.0-4.7 and 5.1-5.4: smaller amounts of the enzyme at higher pI values were also detected. When activity peaks were controlled by polyacrylamide gel electrophoresis, all bands previously detected by electrophoresis of the crude enzyme were recovered, but all peaks were electrophoretically heterogeneous. Gel chromatography of the crude enzyme showed different molecular forms. Their molecular weights indicated monomer, dimer, tetramer, octamer and polymer (at least hexadecamer) forms with a monomer molecular weight of about 36000. PMID:820122

  12. The effect of mayfly (Hexagenia spp.) burrowing activity on sediment oxygen demand in western Lake Erie

    USGS Publications Warehouse

    Edwards, William J.; Soster, Frederick M.; Matisoff, Gerald; Schloesser, Donald W.

    2009-01-01

    Previous studies support the hypothesis that large numbers of infaunal burrow-irrigating organisms in the western basin of Lake Erie may increase significantly the sediment oxygen demand, thus enhancing the rate of hypolimnetic oxygen depletion. We conducted laboratory experiments to quantify burrow oxygen dynamics and increased oxygen demand resulting from burrow irrigation using two different year classes of Hexagenia spp. nymphs from western Lake Erie during summer, 2006. Using oxygen microelectrodes and hot film anemometry, we simultaneously determined oxygen concentrations and burrow water flow velocities. Burrow oxygen depletion rates ranged from 21.7 mg/nymph/mo for 15 mm nymphs at 23 °C to 240.7 mg/nymph/mo for 23 mm nymphs at 13 °C. Sealed microcosm experiments demonstrated that mayflies increase the rate of oxygen depletion by 2-5 times that of controls, depending on size of nymph and water temperature, with colder waters having greater impact. At natural population densities, nymph pumping activity increased total sediment oxygen demand 0.3-2.5 times compared to sediments with no mayflies and accounted for 22-71% of the total sediment oxygen demand. Extrapolating laboratory results to the natural system suggest that Hexagenia spp. populations may exert a significant control on oxygen depletion during intermittent stratification. This finding may help explain some of the fluctuations in Hexagenia spp. population densities in western Lake Erie and suggests that mayflies, by causing their own population collapse irrespective of other environmental conditions, may need longer term averages when used as a bio-indicator of the success of pollution-abatement programs in western Lake Erie and possibly throughout the Great Lakes.

  13. Mercuric ions inhibit mitogen-activated protein kinase dephosphorylation by inducing reactive oxygen species.

    PubMed

    Haase, Hajo; Engelhardt, Gabriela; Hebel, Silke; Rink, Lothar

    2011-01-01

    Mercury intoxication profoundly affects the immune system, in particular, signal transduction of immune cells. However, the mechanism of the interaction of mercury with cellular signaling pathways, such as mitogen activated protein kinases (MAPK), remains elusive. Therefore, the objective of this study is to investigate three potential ways in which Hg(2+) ions could inhibit MAPK dephosphorylation in the human T-cell line Jurkat: (1) by direct binding to phosphatases; (2) by releasing cellular zinc (Zn(2+)); and (3) by inducing reactive oxygen species (ROS). Hg(2+) causes production of ROS, measured by dihydrorhodamine 123, and triggers ROS-mediated Zn(2+) release, detected with FluoZin-3. Yet, phosphatase-inhibition is not mediated by binding of Zn(2+) or Hg(2+). Rather, phosphatases are inactivated by at least two forms of thiol oxidation; initial inhibition is reversible with reducing agents such as Tris(2-carboxyethyl)phosphine. Prolonged inhibition leads to non-reversible phosphatase oxidation, presumably oxidizing the cysteine thiol to sulfinic- or sulfonic acid. Notably, phosphatases are a particularly sensitive target for Hg(2+)-induced oxidation, because phosphatase activity is inhibited at concentrations of Hg(2+) that have only minor impact on over all thiol oxidation. This phosphatase inhibition results in augmented, ROS-dependent MAPK phosphorylation. MAPK are important regulators of T-cell function, and MAPK-activation by inhibition of phosphatases seems to be one of the molecular mechanisms by which mercury affects the immune system. PMID:20951154

  14. Activated and unactivated forms of human erythrocyte aldose reductase.

    PubMed Central

    Srivastava, S K; Hair, G A; Das, B

    1985-01-01

    Aldose reductase (alditol:NADP+ 1-oxidoreductase, EC 1.1.1.21) has been partially purified from human erythrocytes by DEAE-cellulose (DE-52) column chromatography. This enzyme is activated severalfold upon incubation with 10 microM each glucose 6-phosphate, NADPH, and glucose. The activation of the enzyme was confirmed by following the oxidation of NADPH as well as the formation of sorbitol with glucose as substrate. The activated form of aldose reductase exhibited monophasic kinetics with both glyceraldehyde and glucose (Km of glucose = 0.68 mM and Km of glyceraldehyde = 0.096 mM), whereas the native (unactivated) enzyme exhibited biphasic kinetics (Km of glucose = 9.0 and 0.9 mM and Km of glyceraldehyde = 1.1 and 0.14 mM). The unactivated enzyme was strongly inhibited by aldose reductase inhibitors such as sorbinil, alrestatin, and quercetrin, and by phosphorylated intermediates such as ADP, glycerate 3-phosphate, glycerate 1,3-bisphosphate, and glycerate 2,3-trisphosphate. The activated form of the enzyme was less susceptible to inhibition by aldose reductase inhibitors and phosphorylated intermediates. PMID:3933003

  15. Inactivation of Pathogenic Bacteria on Seeds by Active Oxygen Species Generated in Low-Pressure Plasma

    NASA Astrophysics Data System (ADS)

    Ono, Reoto; Uchida, Shohei; Hayashi, Nobuya; Kosaka, Rina; Soeda, Yasutaka

    2015-09-01

    The inactivation of bacteria on seeds by active oxygen species generated by a low-pressure oxygen plasma is investigated. Species of active oxygen contributing to the inactivation of bacteria are attempted to be identified. Cylindrical stainless chamber with the internal volume of 17 L is used and RF antenna is set inside the chamber. The oxygen gas pressure is 20-100 Pa. RF power of 13.56 MHz is supplied to RF antenna and CCP is generated. After irradiation, bacteria are extracted from seeds and cultivated on nutrient agars. The number of colonies on these agars is counted after 48 h incubation. The number of bacteria on seeds decreases to less than 10-3 after plasma irradiation for 45 min comparing with that of control. The tendency of the reduction rate of bacteria on seeds has positive correlation with that of the light emission intensity of the singlet excited oxygen molecule as the oxygen gas pressure is varied. It is supposed that the singlet excited oxygen molecule would be one of the major factors for the inactivation of bacteria on seeds.

  16. Solar Abundances of Rock Forming Elements, Extreme Oxygen and Hydrogen in a Young Polluted White Dwarf

    NASA Astrophysics Data System (ADS)

    Farihi, J.; Koester, D.; Zuckerman, B.; Vican, L.; Gänsicke, B. T.; Smith, N.; Walth, G.; Breedt, E.

    2016-09-01

    The Teff = 20 800 K white dwarf WD 1536+520 is shown to have broadly solar abundances of the major rock forming elements O, Mg, Al, Si, Ca, and Fe, together with a strong relative depletion in the volatile elements C and S. In addition to the highest metal abundances observed to date, including log (O/He) =-3.4, the helium-dominated atmosphere has an exceptional hydrogen abundance at log (H/He) =-1.7. Within the uncertainties, the metal-to-metal ratios are consistent with the accretion of an H2O-rich and rocky parent body, an interpretation supported by the anomalously high trace hydrogen. The mixed atmosphere yields unusually short diffusion timescales for a helium atmosphere white dwarf, of no more than a few hundred yr, and equivalent to those in a much cooler, hydrogen-rich star. The overall heavy element abundances of the disrupted parent body deviate modestly from a bulk Earth pattern, and suggest the deposition of some core-like material. The total inferred accretion rate is 4.2 × 109 g s-1, and at least 4 times higher than any white dwarf with a comparable diffusion timescale. Notably, when accretion is exhausted in this system, both metals and hydrogen will become undetectable within roughly 300 Myr, thus supporting a scenario where the trace hydrogen is related to the ongoing accretion of planetary debris.

  17. Activity and Stability of Nanoscale Oxygen Reduction Catalysts

    SciTech Connect

    Shao-Horn, Yang

    2015-07-28

    Design of highly active and stable nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. The amount and instability of Pt-based catalysts in the cathode limits the cost, efficiency and lifetime of proton exchange membrane fuel cells. We developed a microscopic understanding of the factors governing activity and stability in Pt and PtM alloys. Experimental efforts were focused on probing the size and shape dependence of ORR activity of Pt-based nanoparticles supported on carbon nanotubes. A microscopic understanding of the activity was achieved by correlating voltammetry and rotating ring disk electrodes to surface atomic and electronic structures, which were elucidated predominantly by high-resolution transmission electron microscopy (HRTEM), Scanning transmission electron microscopy energy dispersive X-ray Spectroscopy (STEM-EDS) and synchrotron X-ray absorption spectroscopy (XAS).

  18. SIMPLIFIED INJECTION OF OXYGEN GAS INTO AN ACTIVATED SLUDGE PROCESS

    EPA Science Inventory

    The Las Virgenes Municipal Water District conducted a pilot investigation of the Simplox process at their Tapia Water Reclamation Facility in Calabasas, California. The Simplox process, developed by the Cosmodyne Division of Cordon International, involves covering an activated sl...

  19. DESIGN PROCEDURES FOR DISSOLVED OXYGEN CONTROL OF ACTIVATED SLUDGE PROCESSES

    EPA Science Inventory

    This report presents design procedures and guidelines for the selection of aeration equipment and dissolved (DO) control systems for activated sludge treatment plants. Aeration methods, equipment and application techniques are examined and selection procedures offered. Various DO...

  20. Channel-Forming Activities in the Glycosomal Fraction from the Bloodstream Form of Trypanosoma brucei

    PubMed Central

    Miinalainen, Ilkka J.; Hiltunen, J. Kalervo; Michels, Paul A. M.; Antonenkov, Vasily D.

    2012-01-01

    Background Glycosomes are a specialized form of peroxisomes (microbodies) present in unicellular eukaryotes that belong to the Kinetoplastea order, such as Trypanosoma and Leishmania species, parasitic protists causing severe diseases of livestock and humans in subtropical and tropical countries. The organelles harbour most enzymes of the glycolytic pathway that is responsible for substrate-level ATP production in the cell. Glycolysis is essential for bloodstream-form Trypanosoma brucei and enzymes comprising this pathway have been validated as drug targets. Glycosomes are surrounded by a single membrane. How glycolytic metabolites are transported across the glycosomal membrane is unclear. Methods/Principal Findings We hypothesized that glycosomal membrane, similarly to membranes of yeast and mammalian peroxisomes, contains channel-forming proteins involved in the selective transfer of metabolites. To verify this prediction, we isolated a glycosomal fraction from bloodstream-form T.brucei and reconstituted solubilized membrane proteins into planar lipid bilayers. The electrophysiological characteristics of the channels were studied using multiple channel recording and single channel analysis. Three main channel-forming activities were detected with current amplitudes 70–80 pA, 20–25 pA, and 8–11 pA, respectively (holding potential +10 mV and 3.0 M KCl as an electrolyte). All channels were in fully open state in a range of voltages ±150 mV and showed no sub-conductance transitions. The channel with current amplitude 20–25 pA is anion-selective (PK+/PCl−∼0.31), while the other two types of channels are slightly selective for cations (PK+/PCl− ratios ∼1.15 and ∼1.27 for the high- and low-conductance channels, respectively). The anion-selective channel showed an intrinsic current rectification that may suggest a functional asymmetry of the channel's pore. Conclusions/Significance These results indicate that the membrane of glycosomes apparently

  1. Cytotoxic and Antitumor Activity of Sulforaphane: The Role of Reactive Oxygen Species

    PubMed Central

    Sestili, Piero; Fimognari, Carmela

    2015-01-01

    According to recent estimates, cancer continues to remain the second leading cause of death and is becoming the leading one in old age. Failure and high systemic toxicity of conventional cancer therapies have accelerated the identification and development of innovative preventive as well as therapeutic strategies to contrast cancer-associated morbidity and mortality. In recent years, increasing body of in vitro and in vivo studies has underscored the cancer preventive and therapeutic efficacy of the isothiocyanate sulforaphane. In this review article, we highlight that sulforaphane cytotoxicity derives from complex, concurring, and multiple mechanisms, among which the generation of reactive oxygen species has been identified as playing a central role in promoting apoptosis and autophagy of target cells. We also discuss the site and the mechanism of reactive oxygen species' formation by sulforaphane, the toxicological relevance of sulforaphane-formed reactive oxygen species, and the death pathways triggered by sulforaphane-derived reactive oxygen species. PMID:26185755

  2. Chemical forms of the fluorine, chlorine, oxygen and carbon in coal fly ash and their correlations with mercury retention.

    PubMed

    Deng, Shuang; Shu, Yun; Li, Songgeng; Tian, Gang; Huang, Jiayu; Zhang, Fan

    2016-01-15

    Fly ashes recovered from the particulate control devices at six pulverized coal boiler unites of China, are studied using an X-ray photoelectron spectroscopy (XPS) with a particular focus on the functionalities of fluorine (F), chlorine (Cl), carbon and oxygen on fly ash. It is found that the inorganic forms of F and Cl are predominant on the ash surface in comparison with their organics, and the proportion of organic Cl is relatively higher than that of organic F. Similar results are also obtained in the bulk by correlating the F and Cl contents with those of the unburnt carbon and other compositions in ash. Strong correlations of mercury retention with surface carbon-oxygen functional groups indicate that the C=O, OH/C-O and (O-C=O)-O on surface are of significant importance for mercury retention in fly ash. Their surface concentrations are related to coal type. The presence of Cl in fly ash helps with mercury retention. No obvious effect of F is observed. PMID:26410268

  3. Activity-induced tissue oxygenation changes in rat cerebellar cortex: interplay of postsynaptic activation and blood flow

    PubMed Central

    Offenhauser, Nikolas; Thomsen, Kirsten; Caesar, Kirsten; Lauritzen, Martin

    2005-01-01

    Functional neuroimaging relies on the robust coupling between neuronal activity, metabolism and cerebral blood flow (CBF), but the physiological basis of the neuroimaging signals is still poorly understood. We examined the mechanisms of activity-dependent changes in tissue oxygenation in relation to variations in CBF responses and postsynaptic activity in rat cerebellar cortex. To increase synaptic activity we stimulated the monosynaptic, glutamatergic climbing fibres that excite Purkinje cells via AMPA receptors. We used local field potentials to indicate synaptic activity, and recorded tissue oxygen partial pressure (Ptiss,O2) by polarographic microelectrodes, and CBF using laser-Doppler flowmetry. The disappearance rate of oxygen in the tissue increased linearly with synaptic activity. This indicated that, without a threshold, oxygen consumption increased as a linear function of synaptic activity. The reduction in Ptiss,O2 preceded the rise in CBF. The time integral (area) of the negative Ptiss,O2 response increased non-linearly showing saturation at high levels of synaptic activity, concomitant with a steep rise in CBF. This was accompanied by a positive change in Ptiss,O2. Neuronal nitric oxide synthase inhibition enhanced the initial negative Ptiss,O2 response (‘dip’), while attenuating the evoked CBF increase and positive Ptiss,O2 response equally. This indicates that increases in CBF counteract activity-induced reductions in Ptiss,O2, and suggests the presence of a tissue oxygen reserve. The changes in Ptiss,O2 and CBF were strongly attenuated by AMPA receptor blockade. Our findings suggest an inverse relationship between negative Ptiss,O2 and CBF responses, and provide direct in vivo evidence for a tight coupling between activity in postsynaptic AMPA receptors and cerebellar oxygen consumption. PMID:15774524

  4. NUCLEAR ACTIVITY IS MORE PREVALENT IN STAR-FORMING GALAXIES

    SciTech Connect

    Rosario, D. J.; Lutz, D.; Berta, S.; Popesso, P.; Genzel, R.; Saintonge, A.; Tacconi, L.; Wuyts, S. E-mail: lutz@mpe.mpg.de E-mail: popesso@mpe.mpg.de E-mail: amelie@mpe.mpg.de E-mail: swuyts@mpe.mpg.de; and others

    2013-07-01

    We explore the question of whether low and moderate luminosity active galactic nuclei (AGNs) are preferentially found in galaxies that are undergoing a transition from active star formation (SF) to quiescence. This notion has been suggested by studies of the UV-optical colors of AGN hosts, which find them to be common among galaxies in the so-called Green Valley, a region of galaxy color space believed to be composed mostly of galaxies undergoing SF quenching. Combining the deepest current X-ray and Herschel/PACS far-infrared (FIR) observations of the two Chandra Deep Fields with redshifts, stellar masses, and rest-frame photometry derived from the extensive and uniform multi-wavelength data in these fields, we compare the rest-frame U - V color distributions and star formation rate distributions of AGNs and carefully constructed samples of inactive control galaxies. The UV-to-optical colors of AGNs are consistent with equally massive inactive galaxies at redshifts out to z {approx} 2, but we show that such colors are poor tracers of SF. While the FIR distributions of both star-forming AGNs and star-forming inactive galaxies are statistically similar, we show that AGNs are preferentially found in star-forming host galaxies, or, in other words, AGNs are less likely to be found in weakly star-forming or quenched galaxies. We postulate that, among X-ray-selected AGNs of low and moderate accretion luminosities, the supply of cold gas primarily determines the accretion rate distribution of the nuclear black holes.

  5. Oxygen control of breathing by an olfactory receptor activated by lactate

    PubMed Central

    Chang, Andy J.; Ortega, Fabian E.; Riegler, Johannes; Madison, Daniel V.; Krasnow, Mark A.

    2015-01-01

    Summary Animals have evolved homeostatic responses to changes in oxygen availability that act on different time scales. Although the hypoxia-inducible factor (HIF) transcriptional pathway that controls long term responses to low oxygen (hypoxia) has been established1, the pathway that mediates acute responses to hypoxia in mammals is not well understood. Here we show that the olfactory receptor Olfr78 is highly and selectively expressed in oxygen-sensitive glomus cells of the carotid body, a chemosensory organ at the carotid artery bifurcation that monitors blood oxygen and stimulates breathing within seconds when oxygen declines2. Olfr78 mutants fail to increase ventilation in hypoxia but respond normally to hypercapnia. Glomus cells are present in normal numbers and appear structurally intact, but hypoxia-induced carotid body activity is diminished. Lactate, a metabolite that rapidly accumulates in hypoxia and induces hyperventilation3–6, activates Olfr78 in heterologous expression experiments, induces calcium transients in glomus cells, and stimulates carotid sinus nerve activity through Olfr78. We propose that in addition to its role in olfaction, Olfr78 acts as a hypoxia sensor in the breathing circuit by sensing lactate produced when oxygen levels decline. PMID:26560302

  6. Aerobic composting of waste activated sludge: Kinetic analysis for microbiological reaction and oxygen consumption

    SciTech Connect

    Yamada, Y.; Kawase, Y. . E-mail: bckawase@mail.eng.toyo.ac.jp

    2006-07-01

    In order to examine the optimal design and operating parameters, kinetics for microbiological reaction and oxygen consumption in composting of waste activated sludge were quantitatively examined. A series of experiments was conducted to discuss the optimal operating parameters for aerobic composting of waste activated sludge obtained from Kawagoe City Wastewater Treatment Plant (Saitama, Japan) using 4 and 20 L laboratory scale bioreactors. Aeration rate, compositions of compost mixture and height of compost pile were investigated as main design and operating parameters. The optimal aerobic composting of waste activated sludge was found at the aeration rate of 2.0 L/min/kg (initial composting mixture dry weight). A compost pile up to 0.5 m could be operated effectively. A simple model for composting of waste activated sludge in a composting reactor was developed by assuming that a solid phase of compost mixture is well mixed and the kinetics for microbiological reaction is represented by a Monod-type equation. The model predictions could fit the experimental data for decomposition of waste activated sludge with an average deviation of 2.14%. Oxygen consumption during composting was also examined using a simplified model in which the oxygen consumption was represented by a Monod-type equation and the axial distribution of oxygen concentration in the composting pile was described by a plug-flow model. The predictions could satisfactorily simulate the experiment results for the average maximum oxygen consumption rate during aerobic composting with an average deviation of 7.4%.

  7. 76 FR 25364 - Agency Information Collection Activities: Form I-864, Form I-864A, Form I-864EZ, and From I-864W...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-04

    ... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form I-864, Form I- 864A, Form I-864EZ, and From I-864W; Extension of an Existing Information Collection; Comment Request. ACTION: 60-Day Notice of Information Collection Under Review; Form I- 864, Affidavit of...

  8. Density Functional Study of the Structure, Stability and Oxygen Reduction Activity of Ultrathin Platinum Nanowires

    SciTech Connect

    Matanovic, Ivana; Kent, Paul; Garzon, Fernando; Henson, Neil J.

    2013-03-14

    We used density functional theory to study the difference in the structure, stability and catalytic reactivity between ultrathin, 0.5–1.0 nm diameter, platinum nanotubes and nanowires. Model nanowires were formed by inserting an inner chain of platinum atoms in small diameter nanotubes. In this way more stable, non-hollow structures were formed. The difference in the electronic structure of platinum nanotubes and nanowires was examined by inspecting the density of surface states and band structure. Furthermore, reactivity toward the oxygen reduction reaction of platinum nanowires was assessed by studying the change in the chemisorption energies of oxygen, hydroxyl, and hydroperoxyl groups, induced by converting the nanotube models to nanowires. Both ultrathin platinum nanotubes and nanowires show distinct properties compared to bulk platinum. Single-wall nanotubes and platinum nanowires with diameters larger than 1 nm show promise for use as oxygen reduction catalysts.

  9. Theoretical Study of the Structure, Stability and Oxygen Reduction Activity of Ultrathin Platinum Nanowires

    SciTech Connect

    Matanovic, Ivana; Kent, Paul; Garzon, Fernando; Henson, Neil J.

    2012-10-10

    We use density functional theory to study the difference in the structure, stability and catalytic reactivity between ultrathin, 0.5- 1.0 nm diameter, platinum nanotubes and nanowires. Model nanowires were formed by inserting an inner chain of platinum atoms in small diameter nanotubes. In this way more stable, nonhollow structures were formed. The difference in the electronic structure of platinum nanotubes and nanowires was examined by inspecting the density of surface states and band structure. Furthermore, reactivity towards the oxygen reduction reaction of platinum nanowires was addressed by studying the change in the chemisorption energies of oxygen and hydroxyl groups, induced by inserting the inner chain of platinum atoms into the hollow nanotubes. Both ultrathin platinum nanotubes and nanowires show distinct properties compared to bulk platinum. Nanotubes with diameters larger than 1 nm show promise for use as oxygen reduction catalysts.

  10. Processes controlling forms of phosphorus in surficial sediments from the eastern Arabian Sea impinged by varying bottom water oxygenation conditions

    NASA Astrophysics Data System (ADS)

    Babu, C. Prakash; Nath, B. Nagender

    2005-07-01

    The surficial sediments from the upper continental slope of the eastern Arabian Sea, impinged by the oxygen minimum zone (OMZ, 150-1200 m water depth), show varying concentrations of the biogenic element phosphorus (P, 0.1-0.2%) in the northern and southern areas even though total organic carbon concentrations are relatively constant (TOC, 2-5%; Prakash Babu et al., 1999). To understand this discordance, 17 surface sediment samples from shelf, slope and deep sea of the eastern Arabian Sea were investigated using a five-step sequential extraction scheme to delineate the process responsible for P enrichment in OMZ. High fractions of organic phosphorus (P org 10-26%), biogenic phosphorus (P bio 36-48%), relatively low molar C org/P org ratios (322-447), and C org/P reactive ratios close to Redfield Ratio in OMZ sediments of the SE Arabian Sea suggest accumulation under high surface production and low residence time of labile forms of P due to high sedimentation rates. Despite higher productivity in surface waters, low fractions of P org (8-13%; less than deep-sea sediments of the study area 12-13%), P bio (25-33%), relatively high molar C org/P org ratios (341-508), and C org/P reactive ratios less than Redfield Ratio in OMZ sediments from the NE Arabian Sea may indicate a higher degree of regeneration and diagenetic transformation of labile forms of P to other phases. Authigenic phosphorus (P aut) fraction varies by a factor of 2-8 in sediments from the OMZ when compared to well-oxygenated deep-sea sediments of the study area. While the P total remains constant, significant P transformation seems to occur in NE Arabian Sea, which is suggested by high P aut fraction (˜50%) compared to low P aut fraction (10-39%) in the SE Arabian Sea sediments. Supply rates of phosphorus, variable rates of P dissolution under varying dissolved oxygen contents in the bottom waters, and early diagenetic transformation of P within the sediments seem to influence P geochemistry in

  11. Active curcumin nanoparticles formed from a volatile microemulsion template.

    PubMed

    Margulis, K; Srinivasan, S; Ware, M J; Summers, H D; Godin, B; Magdassi, S

    2014-01-01

    We report on biological performance of organic nanoparticles formed by a simple method based on rapid solvent removal from a volatile microemulsion. The particular focus of the study was on testing the suitability of the method for substances soluble in partially water-miscible organic solvents as well as on evaluating the therapeutic activity of the resultant nanoparticles. Curcumin was employed as a model for hydrophobic drug, and, as it is soluble in water-miscible organic solvents, it was successfully incorporated into a new cyclopentanone-water microemulsion system. During rapid solvent removal by spray-drying, the nanometric droplets of the microemulsion were converted into nanoparticles containing amorphous curcumin with the average size of 20.2±3.4 nm, having ζ potential of -36.2 ±1.8 mV. These nanoparticles were dispersible in water and retained the high loading of the active substance. The therapeutic activity of the resulting nanoparticles was demonstrated in a pancreatic cancer cell line Panc-1. The effective concentration for reducing the metabolic activity was found to be 11.5 μM for nanoparticles compared with 19.5 μM for free curcumin. PMID:25485110

  12. NADPH Oxidase- and Mitochondria-derived Reactive Oxygen Species in Proinflammatory Microglial Activation: A Bipartisan Affair?

    PubMed Central

    Bordt, Evan A.; Polster, Brian M.

    2014-01-01

    Microglia are the resident immune cells of the brain and play major roles in central nervous system development, maintenance, and disease. Brain insults cause microglia to proliferate, migrate, and transform into one or more activated states. Classical M1 activation triggers the production of proinflammatory factors such as tumor necrosis factor- α (TNF-α), interleukin-1β (IL-1β), nitric oxide (NO), and reactive oxygen species which, in excess, can exacerbate brain injury. The mechanisms underlying microglial activation are not fully understood, yet reactive oxygen species are increasingly implicated as mediators of microglial activation. In this review, we highlight studies linking reactive oxygen species, in particular hydrogen peroxide derived from NADPH oxidase-generated superoxide, to the classical activation of microglia. In addition, we critically evaluate controversial evidence suggesting a specific role for mitochondrial reactive oxygen species in the activation of the NLRP3 inflammasome, a multiprotein complex that mediates the production of IL-1β and IL-18. Finally, the limitations of common techniques used to implicate mitochondrial ROS in microglial and inflammasome activation, such as the use of the mitochondrially-targeted ROS indicator MitoSOX and the mitochondrially-targeted antioxidant MitoTEMPO, are also discussed. PMID:25091898

  13. Novel water-resistant UV-activated oxygen indicator for intelligent food packaging.

    PubMed

    Vu, Chau Hai Thai; Won, Keehoon

    2013-09-01

    For the first time, alginate polymer has been applied to prevent dyes from leaching out of colorimetric oxygen indicator films, which enable people to notice the presence of oxygen in the package in an economic and simple manner. The dye-based oxygen indicator film suffers from dye leaching upon contact with water. In this work, UV-activated visual oxygen indicator films were fabricated using thionine, glycerol, P25 TiO2, and zein as a redox dye, a sacrificial electron donor, UV-absorbing semiconducting photocatalyst, and an encapsulation polymer, respectively. When this zein-coated film was immersed in water for 24h, the dye leakage was as high as 80.80±0.45%. However, introduction of alginate (1.25%) as the coating polymer considerably diminished the dye leaching to only 5.80±0.06%. This is because the ion-binding ability of alginate could prevent the cation dye from leaching into water. This novel water-resistant UV-activated oxygen indicator was also successfully photo-bleached and regained colour fast in the presence of oxygen. PMID:23578614

  14. Active and stable carbon nanotube/nanoparticle composite electrocatalyst for oxygen reduction

    PubMed Central

    Chung, Hoon T.; Won, Jong H.; Zelenay, Piotr

    2013-01-01

    Nanostructured carbon-based materials, such as nitrogen-doped carbon nanotube arrays, Co3O4/nitrogen-doped graphene hybrids and carbon nanotube–graphene complexes have shown respectable oxygen reduction reaction activity in alkaline media. Although certainly promising, the performance of these materials does not yet warrant implementation in the energy conversion/storage devices utilizing basic electrolytes, for example, alkaline fuel cells, metal-air batteries and certain electrolysers. Here we demonstrate a new type of nitrogen-doped carbon nanotube/nanoparticle composite oxygen reduction reaction electrocatalyst obtained from iron acetate as an iron precursor and from cyanamide as a nitrogen and carbon nanotube precursor in a simple, scalable and single-step method. The composite has the highest oxygen reduction reaction activity in alkaline media of any non-precious metal catalysts. When used at a sufficiently high loading, this catalyst also outperforms the most active platinum-based catalysts. PMID:23715281

  15. Evaluation of the Catalytic Activity and Cytotoxicity of Palladium Nanocubes. The Role of Oxygen

    PubMed Central

    Dahal, Eshan; Curtiss, Jessica; Subedi, Deepak; Chen, Gen; Houston, Jessica P.; Smirnov, Sergei

    2015-01-01

    Recently it has been reported that palladium nanocubes (PdNC) are capable of generating singlet oxygen without photo-excitation simply via chemisorption of molecular oxygen on its surface. Such a trait would make PdNC a highly versatile catalyst suitable in organic synthesis and a Reactive Oxygen Species (ROS) inducing cancer treatment reagent. Here we thoroughly investigated the catalytic activity of PdNC with respect to their ability to produce singlet oxygen and to oxidize 3,5,3′,5′-tetramethyl-benzidine (TMB), as well as, analyzed the cytotoxic properties of PdNC on HeLa cells. Our findings showed no evidence of singlet oxygen production by PdNC. The nanocubes’ activity is not necessarily linked to activation of oxygen. The oxidation of substrate on PdNC can be a first step followed by PdNC regeneration with oxygen or other oxidant. The catalytic activity of PdNC towards oxidation of TMB is very high and shows direct two-electrons oxidation when the surface of PdNC is clean and the ratio of TMB/PdNC is not very high. Sequential one electron oxidation is observed when the pristine quality of PdNC surface is compromised by serum or uncontrolled impurities and/or the ratio of TMB/PdNC is high. Clean PdNC in serum-free media efficiently induce apoptosis of HeLa cells. It is the primary route of cell death and is associated with hyperpolarization of mitochondria, contrary to a common mitochondrial depolarization initiated by ROS. Again, the effects are very sensitive to how well the pristine surface of PdNC is preserved, suggesting that PdNC can be used as an apoptosis inducing agent but only with appropriate drug delivery system. PMID:25886644

  16. Evaluation of the catalytic activity and cytotoxicity of palladium nanocubes: the role of oxygen.

    PubMed

    Dahal, Eshan; Curtiss, Jessica; Subedi, Deepak; Chen, Gen; Houston, Jessica P; Smirnov, Sergei

    2015-05-13

    Recently, it has been reported that palladium nanocubes (PdNC) are capable of generating singlet oxygen without photoexcitation simply via chemisorption of molecular oxygen on its surface. Such a trait would make PdNC a highly versatile catalyst suitable in organic synthesis and a Reactive Oxygen Species (ROS) inducing cancer treatment reagent. Here we thoroughly investigated the catalytic activity of PdNC with respect to their ability to produce singlet oxygen and to oxidize 3,3',5,5'-tetramethylbenzidine (TMB), and analyzed the cytotoxic properties of PdNC on HeLa cells. Our findings showed no evidence of singlet oxygen production by PdNC. The nanocubes' activity is not necessarily linked to activation of oxygen. The oxidation of substrate on PdNC can be a first step, followed by PdNC regeneration with oxygen or other oxidant. The catalytic activity of PdNC toward the oxidation of TMB is very high and shows direct two-electron oxidation when the surface of the PdNC is clean and the ratio of TMB/PdNC is not very high. Sequential one electron oxidation is observed when the pristine quality of PdNC surface is compromised by serum or uncontrolled impurities and/or the ratio of TMB/PdNC is high. Clean PdNC in serum-free media efficiently induce apoptosis of HeLa cells. It is the primary route of cell death and is associated with hyperpolarization of mitochondria, contrary to a common mitochondrial depolarization initiated by ROS. Again, the effects are very sensitive to how well the pristine surface of PdNC is preserved, suggesting that PdNC can be used as an apoptosis inducing agent, but only with appropriate drug delivery system. PMID:25886644

  17. Air-activated chemical warming devices: effects of oxygen and pressure.

    PubMed

    Raleigh, G; Rivard, R; Fabus, S

    2005-01-01

    Air-activated chemical warming devices use an exothermic chemical reaction of rapidly oxidizing iron to generate heat for therapeutic purposes. Placing these products in a hyperbaric oxygen environment greatly increases the supply of oxidant and thus increases the rate of reaction and maximum temperature. Testing for auto-ignition and maximum temperatures attained by ThermaCare Heat Wraps, Playtex Heat Therapy, and Heat Factory disposable warm packs under ambient conditions and under conditions similar to those encountered during hyperbaric oxygen treatments in monoplace and multiplace hyperbaric chambers (3 atm abs and > 95% oxygen) revealed a maximum temperature of 269 degrees F (132 degrees C) with no spontaneous ignition. The risk of thermal burn injury to adjacent skin may be increased significantly if these devices are used under conditions of hyperbaric oxygen. PMID:16509287

  18. Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts

    PubMed Central

    Binninger, Tobias; Mohamed, Rhiyaad; Waltar, Kay; Fabbri, Emiliana; Levecque, Pieter; Kötz, Rüdiger; Schmidt, Thomas J.

    2015-01-01

    In recent years, the oxygen evolution reaction (OER) has attracted increased research interest due to its crucial role in electrochemical energy conversion devices for renewable energy applications. The vast majority of OER catalyst materials investigated are metal oxides of various compositions. The experimental results obtained on such materials strongly suggest the existence of a fundamental and universal correlation between the oxygen evolution activity and the corrosion of metal oxides. This corrosion manifests itself in structural changes and/or dissolution of the material. We prove from basic thermodynamic considerations that any metal oxide must become unstable under oxygen evolution conditions irrespective of the pH value. The reason is the thermodynamic instability of the oxygen anion in the metal oxide lattice. Our findings explain many of the experimentally observed corrosion phenomena on different metal oxide OER catalysts. PMID:26178185

  19. Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts

    NASA Astrophysics Data System (ADS)

    Binninger, Tobias; Mohamed, Rhiyaad; Waltar, Kay; Fabbri, Emiliana; Levecque, Pieter; Kötz, Rüdiger; Schmidt, Thomas J.

    2015-07-01

    In recent years, the oxygen evolution reaction (OER) has attracted increased research interest due to its crucial role in electrochemical energy conversion devices for renewable energy applications. The vast majority of OER catalyst materials investigated are metal oxides of various compositions. The experimental results obtained on such materials strongly suggest the existence of a fundamental and universal correlation between the oxygen evolution activity and the corrosion of metal oxides. This corrosion manifests itself in structural changes and/or dissolution of the material. We prove from basic thermodynamic considerations that any metal oxide must become unstable under oxygen evolution conditions irrespective of the pH value. The reason is the thermodynamic instability of the oxygen anion in the metal oxide lattice. Our findings explain many of the experimentally observed corrosion phenomena on different metal oxide OER catalysts.

  20. Apogossypolone targets mitochondria and light enhances its anticancer activity by stimulating generation of singlet oxygen and reactive oxygen species

    PubMed Central

    Hu, Zhe-Yu; Wang, Jing; Cheng, Gang; Zhu, Xiao-Feng; Huang, Peng; Yang, Dajun; Zeng, Yi-Xin

    2011-01-01

    Apogossypolone (ApoG2), a novel derivative of gossypol, has been shown to be a potent inhibitor of antiapoptotic Bcl-2 family proteins and to have antitumor activity in multiple types of cancer cells. Recent reports suggest that gossypol stimulates the generation of cellular reactive oxygen species (ROS) in leukemia and colorectal carcinoma cells; however, gossypol-mediated cell death in leukemia cells was reported to be ROS-independent. This study was conducted to clarify the effect of ApoG2-induced ROS on mitochondria and cell viability, and to further evaluate its utility as a treatment for nasopharyngeal carcinoma (NPC). We tested the photocytotoxicity of ApoG2 to the poorly differentiated NPC cell line CNE-2 using the ROS-generating TL/10 illumination system. The rapid ApoG2-induced cell death was partially reversed by the antioxidant N-acetyl-L-cysteine (NAC), but the ApoG2-induced reduction of mitochondrial membrane potential (MMP) was not reversed by NAC. In the presence of TL/10 illumination, ApoG2 generated massive amounts of singlet oxygen and was more effective in inhibiting cell growth than in the absence of illumination. We also determined the influence of light on the anti-proliferative activity of ApoG2 using a CNE-2–xenograft mouse model. ApoG2 under TL/10 illumination healed tumor wounds and suppressed tumor growth more effectively than ApoG2 treatment alone. These results indicate that the ApoG2-induced CNE-2 cell death is partly ROS-dependent. ApoG2 may be used with photodynamic therapy (PDT) to treat NPC. PMID:21192843

  1. Antioxidative activity and growth regulation of Brassicaceae induced by oxygen radical irradiation

    NASA Astrophysics Data System (ADS)

    Hayashi, Nobuya; Ono, Reoto; Shiratani, Masaharu; Yonesu, Akira

    2015-06-01

    The growth regulation characteristics of plants are investigated when plant seeds are irradiated with atmospheric discharge plasma. Enhancement of the germination and lengths of the stem and root of plants are observed after seeding. The total length of the stem and root increases approximately 1.6 times after a cultivation period of 72 h. The growth regulation effect is found to be maintained for 80 h of cultivation after seeding. The growth regulation originates from the change in the antioxidative activity of plant cells induced by active oxygen species generated in the oxygen plasma, which leads to the production of growth factor in plants.

  2. Inclusion bodies and purification of proteins in biologically active forms.

    PubMed

    Mukhopadhyay, A

    1997-01-01

    Even though recombinant DNA technology has made possible the production of valuable therapeutic proteins, its accumulation in the host cell as inclusion body poses serious problems in the recovery of functionally active proteins. In the last twenty years, alternative techniques have been evolved to purify biologically active proteins from inclusion bodies. Most of these remain only as inventions and very few are commercially exploited. This review summarizes the developments in isolation, refolding and purification of proteins from inclusion bodies that could be used for vaccine and non-vaccine applications. The second section involves a discussion on inclusion bodies, how they are formed, and their physicochemical properties. In vivo protein folding in Escherichia coli and kinetics of in vitro protein folding are the subjects of the third and fourth sections respectively. The next section covers the recovery of bioactive protein from inclusion bodies: it includes isolation of inclusion body from host cell debris, purification in denatured state alternate refolding techniques, and final purification of active molecules. Since purity and safety are two important issues in therapeutic grade proteins, the following three sections are devoted to immunological and biological characterization of biomolecules, nature, and type of impurities normally encountered, and their detection. Lastly, two case studies are discussed to demonstrate the sequence of process steps involved. PMID:8939059

  3. Oxygen reduction and evolution at single-metal active sites: Comparison between functionalized graphitic materials and protoporphyrins

    NASA Astrophysics Data System (ADS)

    Calle-Vallejo, F.; Martínez, J. I.; García-Lastra, J. M.; Abad, E.; Koper, M. T. M.

    2013-01-01

    A worldwide spread of clean technologies such as low-temperature fuel cells and electrolyzers depends strictly on their technical reliability and economic affordability. Currently, both conditions are hardly fulfilled mainly due to the same reason: the oxygen electrode, which has large overpotentials and is made of precious materials. A possible solution is the use of non-noble electrocatalysts with single-metal active sites. Here, on the basis of DFT calculations of adsorbed intermediates and a thermodynamic analysis, we compare the oxygen reduction (ORR) and evolution (OER) activities of functionalized graphitic materials and gas-phase porphyrins with late transition metals. We find that both kinds of materials follow approximately the same activity trends, and active sites with transition metals from groups 7 to 9 may be good ORR and OER electrocatalysts. However, spin analyses show more flexibility in the possible oxidation states of the metal atoms in solid electrocatalysts, while in porphyrins they must be + 2. These observations reveal that the catalytic activity of these materials is mainly due to nearest-neighbor interactions. Based on this, we propose that this class of electrocatalysts may be improved by careful selections of the support and the ligand properties close to the active sites and/or the ramifications near them, so that charge is transferred back and forth during adsorption and selective hydrogen bonds are formed.

  4. REVIEW: Excited states in the active media of oxygen — iodine lasers

    NASA Astrophysics Data System (ADS)

    Azyazov, V. N.

    2009-11-01

    A review of investigations of kinetic processes in active media oxygen — iodine lasers (OILs) performed in the last decade is presented. The mechanisms of pumping and quenching of electronically and vibrationally excited O2 and I2 molecules are considered, and dissociation mechanisms of I2 in the active medium of the OIL are analysed. The values of kinetic constants of processes proceeding in the active media of OILs are recommended.

  5. The relationship between brain cortical activity and brain oxygenation in the prefrontal cortex during hypergravity exposure.

    PubMed

    Smith, Craig; Goswami, Nandu; Robinson, Ryan; von der Wiesche, Melanie; Schneider, Stefan

    2013-04-01

    Artificial gravity has been proposed as a method to counteract the physiological deconditioning of long-duration spaceflight; however, the effects of hypergravity on the central nervous system has had little study. The study aims to investigate whether there is a relationship between prefrontal cortex brain activity and prefrontal cortex oxygenation during exposure to hypergravity. Twelve healthy participants were selected to undergo hypergravity exposure aboard a short-arm human centrifuge. Participants were exposed to hypergravity in the +Gz axis, starting from 0.6 +Gz for women, and 0.8 +Gz for men, and gradually increasing by 0.1 +Gz until the participant showed signs of syncope. Brain cortical activity was measured using electroencephalography (EEG) and localized to the prefrontal cortex using standard low-resolution brain electromagnetic tomography (LORETA). Prefrontal cortex oxygenation was measured using near-infrared spectroscopy (NIRS). A significant increase in prefrontal cortex activity (P < 0.05) was observed during hypergravity exposure compared with baseline. Prefrontal cortex oxygenation was significantly decreased during hypergravity exposure, with a decrease in oxyhemoglobin levels (P < 0.05) compared with baseline and an increase in deoxyhemoglobin levels (P < 0.05) with increasing +Gz level. No significant correlation was found between prefrontal cortex activity and oxy-/deoxyhemoglobin. It is concluded that the increase in prefrontal cortex activity observed during hypergravity was most likely not the result of increased +Gz values resulting in a decreased oxygenation produced through hypergravity exposure. No significant relationship between prefrontal cortex activity and oxygenation measured by NIRS concludes that brain activity during exposure to hypergravity may be difficult to measure using NIRS. Instead, the increase in prefrontal cortex activity might be attributable to psychological stress, which could pose a problem for the use of a

  6. Mass spectrometric study on inactivation mechanism of spore-forming bacteria by low-pressure surface-wave excited oxygen plasma

    SciTech Connect

    Zhao Ying; Ogino, Akihisa; Nagatsu, Masaaki

    2011-05-09

    In this letter, the etching phenomena of the spore-forming bacteria by oxygen plasma were investigated by using quadrupole mass spectrometry. The etching by-products of H{sub 2}O and CO{sub 2} were obviously detected during the oxygen plasma irradiation by the multiple ion detection measurement. Inactivation of roughly 10{sup 6} spores population was achieved under almost the same reduced spore shapes for three different incident microwave powers. It is considered from the present results that the oxygen radical etching could cause damage to the germinant receptors located in the inner membrane inevitable for germination of spores, without any damage of the DNA in the cores.

  7. Mass spectrometric study on inactivation mechanism of spore-forming bacteria by low-pressure surface-wave excited oxygen plasma

    NASA Astrophysics Data System (ADS)

    Zhao, Ying; Ogino, Akihisa; Nagatsu, Masaaki

    2011-05-01

    In this letter, the etching phenomena of the spore-forming bacteria by oxygen plasma were investigated by using quadrupole mass spectrometry. The etching by-products of H2O and CO2 were obviously detected during the oxygen plasma irradiation by the multiple ion detection measurement. Inactivation of roughly 106 spores population was achieved under almost the same reduced spore shapes for three different incident microwave powers. It is considered from the present results that the oxygen radical etching could cause damage to the germinant receptors located in the inner membrane inevitable for germination of spores, without any damage of the DNA in the cores.

  8. Chemical Fingerprints of Star Forming Regions and Active Galaxies

    NASA Astrophysics Data System (ADS)

    Pérez-Beaupuits, Juan-Pablo

    2010-10-01

    This thesis is devoted to the study of the physical conditions of the interstellar medium (ISM) in active galactic nuclei (AGNs) and Galactic star-forming regions, using mostly single-dish millimeter observations. I first study the excitation conditions of dense gas in a group of Seyfert galaxies using radiative transfer models (Chapter 2). I then study the galaxy NGC 1068, and try to distinguish signatures of the contributions from the AGN and the starburst ring by incorporating observations of high-J transitions of dense gas tracers (Chapter 3). Later, I venture into the mid-infrared spectral region to study different aspects of the AGN and starburst components in the galaxy NGC 4945 (Chapter 4). In Chapter 5 I delve into theoretical aspects of the dynamical evolution of gas in an AGN torus. I use a 3D hydrodynamic simulation with chemical abundances driven by X-rays. The aim is to understand the effects of X-ray irradiation by the AGN on the temperature, formation and destruction of the molecular gas. I finally explore a Galactic star-forming region, the Omega Nebula, with high resolution single dish observations, to study the properties of the warm gas and to constrain chemical models (Chapters 6 and 7).

  9. 75 FR 16492 - Agency Information Collection Activities: Form G-28, and Form G-28I, Revision of an Existing...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-01

    ... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form G-28, and Form G- 28I, Revision of an Existing Information Collection; Comment Request ACTION: 60-Day Notice of Information Collection under Review: Form G- 28, Notice of Entry of Appearance as Attorney or...

  10. Respiratory muscle activity and oxygenation during sleep in patients with muscle weakness.

    PubMed

    White, J E; Drinnan, M J; Smithson, A J; Griffiths, C J; Gibson, G J

    1995-05-01

    Patients with respiratory muscle weakness show nocturnal hypoventilation, with oxygen desaturation particularly during rapid eye movement (REM) sleep, but evidence in individuals with isolated bilateral diaphragmatic paresis (BDP) is conflicting. The effect of sleep on relative activity of the different respiratory muscles of such patients and, consequently, the precise mechanisms causing desaturation have not been clarified. We have studied eight patients, four with generalized muscle weakness and four with isolated BDP during nocturnal sleep with measurements including oxygen saturation and surface electromyographic (EMG) activity of various respiratory muscle groups. Nocturnal oxygenation correlated inversely with postural fall in vital capacity, an index of diaphragmatic strength. During REM sleep, hypopnoea and desaturation occurred particularly during periods of rapid eye movements (phasic REM sleep). In most subjects, such events were "central" in type and associated with marked suppression of intercostal muscle activity, but two subjects had recurrent desaturation due to "obstructive" hypopnoea and/or apnoea. Expiratory activity of the external oblique muscle was present whilst awake and during non-rapid eye movement (NREM) sleep in seven of the eight subjects in the semirecumbent posture. This probably represents an "accessory inspiratory" effect, which aids passive caudal diaphragmatic motion as the abdominal muscles relax at the onset of inspiration. Expiratory abdominal muscle activity was suppressed in phasic REM sleep, suggesting that loss of this "accessory inspiratory" effect may contribute to "central" hypopnoea. We conclude that, in patients with muscle weakness, nocturnal oxygenation correlates with diaphragmatic strength.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7656954

  11. New Active Optical Technique Developed for Measuring Low-Earth-Orbit Atomic Oxygen Erosion of Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Demko, Rikako

    2003-01-01

    Polymers such as polyimide Kapton (DuPont) and Teflon FEP (DuPont, fluorinated ethylene propylene) are commonly used spacecraft materials because of desirable properties such as flexibility, low density, and in the case of FEP, a low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low-Earth-orbit (LEO) environment are exposed to energetic atomic oxygen. Atomic oxygen reaction with polymers causes erosion, which is a threat to spacecraft performance and durability. It is, therefore, important to understand the atomic oxygen erosion yield E (the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. The most common technique for determining E is a passive technique based on mass-loss measurements of samples exposed to LEO atomic oxygen during a space flight experiment. There are certain disadvantages to this technique. First, because it is passive, data are not obtained until after the flight is completed. Also, obtaining the preflight and postflight mass measurements is complicated by the fact that many polymers absorb water and, therefore, the mass change due to water absorption can affect the E data. This is particularly true for experiments that receive low atomic oxygen exposures or for samples that have a very low E. An active atomic oxygen erosion technique based on optical measurements has been developed that has certain advantages over the mass-loss technique. This in situ technique can simultaneously provide the erosion yield data on orbit and the atomic oxygen exposure fluence, which is needed for erosion yield determination. In the optical technique, either sunlight or artificial light can be used to measure the erosion of semitransparent or opaque polymers as a result of atomic oxygen attack. The technique is simple and adaptable to a rather wide range of polymers, providing that they have a sufficiently high optical absorption coefficient. If one covers a photodiode with a

  12. Benzene's metabolites alter c-MYB activity via reactive oxygen species in HD3 cells

    SciTech Connect

    Wan, Joanne; Winn, Louise M. . E-mail: winnl@queensu.ca

    2007-07-15

    Benzene is a known leukemogen that is metabolized to form reactive intermediates and reactive oxygen species (ROS). The c-Myb oncoprotein is a transcription factor that has a critical role in hematopoiesis. c-Myb transcript and protein have been overexpressed in a number of leukemias and cancers. Given c-Myb's role in hematopoiesis and leukemias, it is hypothesized that benzene interferes with the c-Myb signaling pathway and that this involves ROS. To investigate our hypothesis, we evaluated whether benzene, 1,4-benzoquinone, hydroquinone, phenol, and catechol generated ROS in chicken erythroblast HD3 cells, as measured by 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (DCFDA) and dihydrorhodamine-123 (DHR-123), and whether the addition of 100 U/ml of the antioxidating enzyme superoxide dismutase (SOD) could prevent ROS generation. Reduced to oxidized glutathione ratios (GSH:GSSG) were also assessed as well as hydroquinone and benzoquinone's effects on c-Myb protein levels and activation of a transiently transfected reporter construct. Finally we attempted to abrogate benzene metabolite mediated increases in c-Myb activity with the use of SOD. We found that benzoquinone, hydroquinone, and catechol increased DCFDA fluorescence, increased DHR-123 fluorescence, decreased GSH:GSSG ratios, and increased reporter construct expression after 24 h of exposure. SOD was able to prevent DCFDA fluorescence and c-Myb activity caused by benzoquinone and hydroquinone only. These results are consistent with other studies, which suggest metabolite differences in benzene-mediated toxicity. More importantly, this study supports the hypothesis that benzene may mediate its toxicity through ROS-mediated alterations in the c-Myb signaling pathway.

  13. Mercuric ions inhibit mitogen-activated protein kinase dephosphorylation by inducing reactive oxygen species

    SciTech Connect

    Haase, Hajo; Engelhardt, Gabriela; Hebel, Silke; Rink, Lothar

    2011-01-01

    Mercury intoxication profoundly affects the immune system, in particular, signal transduction of immune cells. However, the mechanism of the interaction of mercury with cellular signaling pathways, such as mitogen activated protein kinases (MAPK), remains elusive. Therefore, the objective of this study is to investigate three potential ways in which Hg{sup 2+} ions could inhibit MAPK dephosphorylation in the human T-cell line Jurkat: (1) by direct binding to phosphatases; (2) by releasing cellular zinc (Zn{sup 2+}); and (3) by inducing reactive oxygen species (ROS). Hg{sup 2+} causes production of ROS, measured by dihydrorhodamine 123, and triggers ROS-mediated Zn{sup 2+} release, detected with FluoZin-3. Yet, phosphatase-inhibition is not mediated by binding of Zn{sup 2+} or Hg{sup 2+}. Rather, phosphatases are inactivated by at least two forms of thiol oxidation; initial inhibition is reversible with reducing agents such as Tris(2-carboxyethyl)phosphine. Prolonged inhibition leads to non-reversible phosphatase oxidation, presumably oxidizing the cysteine thiol to sulfinic- or sulfonic acid. Notably, phosphatases are a particularly sensitive target for Hg{sup 2+}-induced oxidation, because phosphatase activity is inhibited at concentrations of Hg{sup 2+} that have only minor impact on over all thiol oxidation. This phosphatase inhibition results in augmented, ROS-dependent MAPK phosphorylation. MAPK are important regulators of T-cell function, and MAPK-activation by inhibition of phosphatases seems to be one of the molecular mechanisms by which mercury affects the immune system.

  14. Absence of the cbb3 Terminal Oxidase Reveals an Active Oxygen-Dependent Cyclase Involved in Bacteriochlorophyll Biosynthesis in Rhodobacter sphaeroides

    PubMed Central

    Chen, Guangyu E.; Martin, Elizabeth C.; Hunter, C. Neil

    2016-01-01

    ABSTRACT The characteristic green color associated with chlorophyll pigments results from the formation of an isocyclic fifth ring on the tetrapyrrole macrocycle during the biosynthesis of these important molecules. This reaction is catalyzed by two unrelated cyclase enzymes employing different chemistries. Oxygenic phototrophs such as plants and cyanobacteria utilize an oxygen-dependent enzyme, the major component of which is a diiron protein named AcsF, while BchE, an oxygen-sensitive [4Fe-4S] cluster protein, dominates in phototrophs inhabiting anoxic environments, such as the purple phototrophic bacterium Rhodobacter sphaeroides. We identify a potential acsF in this organism and assay for activity of the encoded protein in a strain lacking bchE under various aeration regimes. Initially, cells lacking bchE did not demonstrate AcsF activity under any condition tested. However, on removal of a gene encoding a subunit of the cbb3-type respiratory terminal oxidase, cells cultured under regimes ranging from oxic to micro-oxic exhibited cyclase activity, confirming the activity of the oxygen-dependent enzyme in this model organism. Potential reasons for the utilization of an oxygen-dependent enzyme in anoxygenic phototrophs are discussed. IMPORTANCE The formation of the E ring of bacteriochlorophyll pigments is the least well characterized step in their biosynthesis, remaining enigmatic for over 60 years. Two unrelated enzymes catalyze this cyclization step; O2-dependent and O2-independent forms dominate in oxygenic and anoxygenic phototrophs, respectively. We uncover the activity of an O2-dependent enzyme in the anoxygenic purple phototrophic bacterium Rhodobacter sphaeroides, initially by inactivation of the high-affinity terminal respiratory oxidase, cytochrome cbb3. We propose that the O2-dependent form allows for the biosynthesis of a low level of bacteriochlorophyll under oxic conditions, so that a rapid initiation of photosynthetic processes is possible for

  15. Gold-doped graphene: A highly stable and active electrocatalysts for the oxygen reduction reaction

    SciTech Connect

    Stolbov, Sergey Alcántara Ortigoza, Marisol

    2015-04-21

    In addressing the growing need of renewable and sustainable energy resources, hydrogen-fuel-cells stand as one of the most promising routes to transform the current energy paradigm into one that integrally fulfills environmental sustainability. Nevertheless, accomplishing this technology at a large scale demands to surpass the efficiency and enhance the cost-effectiveness of platinum-based cathodes, which catalyze the oxygen reduction reaction (ORR). In this work, our first-principles calculations show that Au atoms incorporated into graphene di-vacancies form a highly stable and cost-effective electrocatalyst that is, at the same time, as or more (dependently of the dopant concentration) active toward ORR than the best-known Pt-based electrocatalysts. We reveal that partial passivation of defected-graphene by gold atoms reduces the reactivity of C dangling bonds and increases that of Au, thus optimizing them for catalyzing the ORR and yielding a system of high thermodynamic and electrochemical stabilities. We also demonstrate that the linear relation among the binding energies of the reaction intermediates assumed in computational high-throughput material screening does not hold, at least for this non-purely transition-metal material. We expect Au-doped graphene to finally overcome the cathode-related challenge hindering the realization of hydrogen-fuel cells as the leading means of powering transportation and portable devices.

  16. Reactive Oxygen Species Affect Transglutaminase Activity and Regulate Hematopoiesis in a Crustacean.

    PubMed

    Junkunlo, Kingkamon; Söderhäll, Kenneth; Söderhäll, Irene; Noonin, Chadanat

    2016-08-19

    Reactive oxygen species (ROS) serve as a prime signal in the commitment to hematopoiesis in both mammals and Drosophila In this study, the potential function of ROS during hematopoiesis in the crayfish Pacifastacus leniusculus was examined. The antioxidant N-acetylcysteine (NAC) was used to decrease ROS in both in vivo and in vitro experiments. An increase in ROS was observed in the anterior proliferation center (APC) after LPS injection. In the absence of NAC, the LPS-induced increase in ROS levels resulted in the rapid restoration of the circulating hemocyte number. In the presence of NAC, a delay in the recovery rate of the hemocyte number was observed. NAC treatment also blocked the spread of APC and other hematopoietic tissue (HPT) cells, maintaining these cells at an undifferentiated stage. Extracellular transglutaminase (TGase) has been shown previously to play a role in maintaining HPT cells in an undifferentiated form. In this study, we show that extracellular TGase activity increased when the ROS level in HPT or APC cells was reduced after NAC treatment. In addition, collagen, a major component of the extracellular matrix and a TGase substrate were co-localized on the HPT cell surface. Taken together, the results of this study show that ROS are involved in crayfish hematopoiesis, in which a low ROS level is required to maintain hematopoietic progenitor cells in the tissue and to reduce hemocyte release. The potential roles of TGase in this process are investigated and discussed. PMID:27339892

  17. Screening of catalytic oxygen reduction reaction activity of metal-doped graphene by density functional theory

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Chen, Shuangjing; Wang, Jinyu

    2016-08-01

    Graphene doping is a promising direction for developing effective oxygen reduction reaction (ORR) catalysts. In this paper, we computationally investigated the ORR performance of 10 kinds of metal-doped graphene (M-G) catalysts, namely, Al-, Si-, Mn-, Fe-, Co-, Ni-, Pd-, Ag-, Pt-, and Au-G. The results shown that the binding energies of the metal atoms incorporated into the graphene vacancy are higher than their bulk cohesive energies, indicating the formed M-G catalysts are even more stable than the corresponding bulk metal surfaces, and thus avoid the metals dissolution in the reaction environment. We demonstrated that the linear relation among the binding energies of the ORR intermediates that found on metal-based materials does not hold for the M-G catalysts, therefore a single binding energy of intermediate alone is not sufficient to evaluate the ORR activity of an arbitrary catalyst. By analysis of the detailed ORR processes, we predicted that the Au-, Co-, and Ag-G materials can be used as the ORR catalysts.

  18. Electrocatalytic activities of alkyne-functionalized copper nanoparticles in oxygen reduction in alkaline media

    NASA Astrophysics Data System (ADS)

    Liu, Ke; Song, Yang; Chen, Shaowei

    2014-12-01

    Stable alkyne-capped copper nanoparticles were prepared by chemical reduction of copper acetate with sodium borohydride in the presence of alkyne ligands. Transmission electron microscopic measurements showed that nanoparticles were well dispersed with a diameter in the range of 4-6 nm. FTIR and photoluminescence spectroscopic measurements confirmed the successful attachment of the alkyne ligands onto the nanoparticle surface most likely forming Cu-Ctbnd interfacial bonds. XPS measurements indicated the formation of a small amount of CuO in the nanoparticles with a satellite peak where the binding energy red-shifted with increasing Cu(II) concentration. Cu2O was also detected in the nanoparticles. Similar results were observed with commercial CuO nanoparticles. Electrochemical studies showed that the as-prepared alkyne-capped copper nanoparticles exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, a performance that was markedly better than those reported earlier with poly- or single-crystalline copper electrodes; and the fraction of peroxides in the final products decreased with decreasing concentration of oxide components in the nanoparticles.

  19. Abscisic Acid Structure-Activity Relationships in Barley Aleurone Layers and Protoplasts (Biological Activity of Optically Active, Oxygenated Abscisic Acid Analogs).

    PubMed

    Hill, R. D.; Liu, J. H.; Durnin, D.; Lamb, N.; Shaw, A.; Abrams, S. R.

    1995-06-01

    Optically active forms of abscisic acid (ABA) and their oxygenated metabolites were tested for their biological activity by examining the effects of the compounds on the reversal of gibberellic acid-induced [alpha]-amylase activity in barley (Hordeum vulgare cv Himalaya) aleurone layers and the induction of gene expression in barley aleurone protoplasts transformed with a chimeric construct containing the promoter region of an albumin storage protein gene. Promotion of the albumin storage protein gene response had a more strict stereochemical requirement for elicitation of an ABA response than inhibition of [alpha]-amylase gene expression. The naturally occurring stereoisomer of ABA and its metabolites were more effective at eliciting an ABA-like response. ABA showed the highest activity, followed by 7[prime]-hydroxyABA, with phaseic acid being the least active. Racemic 8[prime]-hydroxy-2[prime],3[prime]-dihydroABA, an analog of 8[prime]-hydroxyABA, was inactive, whereas racemic 2[prime],3[prime]-dihydroABA was as effective as ABA. The differences in response of the same tissue to the ABA enantiomers lead us to conclude that there exists more than one type of ABA receptor and/or multiple signal transduction pathways in barley aleurone tissue. PMID:12228494

  20. Abscisic Acid Structure-Activity Relationships in Barley Aleurone Layers and Protoplasts (Biological Activity of Optically Active, Oxygenated Abscisic Acid Analogs).

    PubMed Central

    Hill, R. D.; Liu, J. H.; Durnin, D.; Lamb, N.; Shaw, A.; Abrams, S. R.

    1995-01-01

    Optically active forms of abscisic acid (ABA) and their oxygenated metabolites were tested for their biological activity by examining the effects of the compounds on the reversal of gibberellic acid-induced [alpha]-amylase activity in barley (Hordeum vulgare cv Himalaya) aleurone layers and the induction of gene expression in barley aleurone protoplasts transformed with a chimeric construct containing the promoter region of an albumin storage protein gene. Promotion of the albumin storage protein gene response had a more strict stereochemical requirement for elicitation of an ABA response than inhibition of [alpha]-amylase gene expression. The naturally occurring stereoisomer of ABA and its metabolites were more effective at eliciting an ABA-like response. ABA showed the highest activity, followed by 7[prime]-hydroxyABA, with phaseic acid being the least active. Racemic 8[prime]-hydroxy-2[prime],3[prime]-dihydroABA, an analog of 8[prime]-hydroxyABA, was inactive, whereas racemic 2[prime],3[prime]-dihydroABA was as effective as ABA. The differences in response of the same tissue to the ABA enantiomers lead us to conclude that there exists more than one type of ABA receptor and/or multiple signal transduction pathways in barley aleurone tissue. PMID:12228494

  1. The Role of Biofilms in the Sedimentology of Actively Forming Gypsum Deposits at Guerrero Negro, Mexico

    NASA Astrophysics Data System (ADS)

    Vogel, Marilyn B.; Des Marais, David J.; Turk, Kendra A.; Parenteau, Mary N.; Jahnke, Linda L.; Kubo, Michael D. Y.

    2009-11-01

    Actively forming gypsum deposits at the Guerrero Negro sabkha and saltern system provided habitats for stratified, pigmented microbial communities that exhibited significant morphological and phylogenetic diversity. These deposits ranged from meter-thick gypsum crusts forming in saltern seawater concentration ponds to columnar microbial mats with internally crystallized gypsum granules developing in natural anchialine pools. Gypsum-depositing environments were categorized as forming precipitation surfaces, biofilm-supported surfaces, and clastic surfaces. Each surface type was described in terms of depositional environment, microbial diversity, mineralogy, and sedimentary fabrics. Precipitation surfaces developed in high-salinity subaqueous environments where rates of precipitation outpaced the accumulation of clastic, organic, and/or biofilm layers. These surfaces hosted endolithic biofilms comprised predominantly of oxygenic and anoxygenic phototrophs, sulfate-reducing bacteria, and bacteria from the phylum Bacteroidetes. Biofilm-supported deposits developed in lower-salinity subaqueous environments where light and low water-column turbulence supported dense benthic microbial communities comprised mainly of oxygenic phototrophs. In these settings, gypsum granules precipitated in the extracellular polymeric substance (EPS) matrix as individual granules exhibiting distinctive morphologies. Clastic surfaces developed in sabkha mudflats that included gypsum, carbonate, and siliclastic particles with thin gypsum/biofilm components. Clastic surfaces were influenced by subsurface brine sheets and capillary evaporation and precipitated subsedimentary gypsum discs in deeper regions. Biofilms appeared to influence both chemical and physical sedimentary processes in the various subaqueous and subaerially exposed environments studied. Biofilm interaction with chemical sedimentary processes included dissolution and granularization of precipitation surfaces, formation of

  2. The role of biofilms in the sedimentology of actively forming gypsum deposits at Guerrero Negro, Mexico.

    PubMed

    Vogel, Marilyn B; Des Marais, David J; Turk, Kendra A; Parenteau, Mary N; Jahnke, Linda L; Kubo, Michael D Y

    2009-11-01

    Actively forming gypsum deposits at the Guerrero Negro sabkha and saltern system provided habitats for stratified, pigmented microbial communities that exhibited significant morphological and phylogenetic diversity. These deposits ranged from meter-thick gypsum crusts forming in saltern seawater concentration ponds to columnar microbial mats with internally crystallized gypsum granules developing in natural anchialine pools. Gypsum-depositing environments were categorized as forming precipitation surfaces, biofilm-supported surfaces, and clastic surfaces. Each surface type was described in terms of depositional environment, microbial diversity, mineralogy, and sedimentary fabrics. Precipitation surfaces developed in high-salinity subaqueous environments where rates of precipitation outpaced the accumulation of clastic, organic, and/or biofilm layers. These surfaces hosted endolithic biofilms comprised predominantly of oxygenic and anoxygenic phototrophs, sulfate-reducing bacteria, and bacteria from the phylum Bacteroidetes. Biofilm-supported deposits developed in lower-salinity subaqueous environments where light and low water-column turbulence supported dense benthic microbial communities comprised mainly of oxygenic phototrophs. In these settings, gypsum granules precipitated in the extracellular polymeric substance (EPS) matrix as individual granules exhibiting distinctive morphologies. Clastic surfaces developed in sabkha mudflats that included gypsum, carbonate, and siliclastic particles with thin gypsum/biofilm components. Clastic surfaces were influenced by subsurface brine sheets and capillary evaporation and precipitated subsedimentary gypsum discs in deeper regions. Biofilms appeared to influence both chemical and physical sedimentary processes in the various subaqueous and subaerially exposed environments studied. Biofilm interaction with chemical sedimentary processes included dissolution and granularization of precipitation surfaces, formation of

  3. FULL-SCALE DEMONSTRATION OF OPEN TANK OXYGEN ACTIVATED SLUDGE TREATMENT

    EPA Science Inventory

    This report presents an operating summary of a full-scale demonstration of the FMC open tank pure oxygen (FMC O2) activated sludge system, conducted at the facilities of the Metropolitan Denver Sewage Disposal District No. 1 (Metro) in Denver, Colorado. The system was operated ov...

  4. In vivo imaging of brain metabolism activity using a phosphorescent oxygen-sensitive probe

    PubMed Central

    Tsytsarev, Vassiliy; Arakawa, Hiroyuki; Borisov, Sergei; Pumbo, Elena; Erzurumlu, Reha S.; Papkovsky, Dmitri B.

    2013-01-01

    Several approaches have been adopted for real-time imaging of neural activity in vivo. We tested a new cell-penetrating phosphorescent oxygen-sensitive probe, NanO2-IR, to monitor temporal and spatial dynamics of oxygen metabolism in the neocortex following peripheral sensory stimulation. Probe solution was applied to the surface of anesthetized mouse brain; optical imaging was performed using a MiCAM-02 system. Trains of whisker stimuli were delivered and associated changes in phosphorescent signal were recorded in the contralateral somatosensory (“barrel”) cortex. Sensory stimulation led to changes in oxygenation of activated areas of the barrel cortex. The oxygen imaging results were compared to those produced by the voltage-sensitive dye RH-1691. While the signals emitted by the two probes differed in shape and amplitude, they both faithfully indicated specific whisker evoked cortical activity. Thus, NanO2-IR probe can be used as a tool in visualization and realtime analysis of sensory- evoked neural activity in vivo. PMID:23624034

  5. GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN

    EPA Science Inventory

    Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen

    Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

  6. Activation of Methanogenesis in Arid Biological Soil Crusts Despite the Presence of Oxygen

    PubMed Central

    Angel, Roey; Matthies, Diethart; Conrad, Ralf

    2011-01-01

    Methanogenesis is traditionally thought to occur only in highly reduced, anoxic environments. Wetland and rice field soils are well known sources for atmospheric methane, while aerated soils are considered sinks. Although methanogens have been detected in low numbers in some aerated, and even in desert soils, it remains unclear whether they are active under natural oxic conditions, such as in biological soil crusts (BSCs) of arid regions. To answer this question we carried out a factorial experiment using microcosms under simulated natural conditions. The BSC on top of an arid soil was incubated under moist conditions in all possible combinations of flooding and drainage, light and dark, air and nitrogen headspace. In the light, oxygen was produced by photosynthesis. Methane production was detected in all microcosms, but rates were much lower when oxygen was present. In addition, the δ13C of the methane differed between the oxic/oxygenic and anoxic microcosms. While under anoxic conditions methane was mainly produced from acetate, it was almost entirely produced from H2/CO2 under oxic/oxygenic conditions. Only two genera of methanogens were identified in the BSC-Methanosarcina and Methanocella; their abundance and activity in transcribing the mcrA gene (coding for methyl-CoM reductase) was higher under anoxic than oxic/oxygenic conditions, respectively. Both methanogens also actively transcribed the oxygen detoxifying gene catalase. Since methanotrophs were not detectable in the BSC, all the methane produced was released into the atmosphere. Our findings point to a formerly unknown participation of desert soils in the global methane cycle. PMID:21655270

  7. Common catabolic enzyme patterns in a microplankton community of the Humboldt Current System off northern and central-south Chile: Malate dehydrogenase activity as an index of water-column metabolism in an oxygen minimum zone

    NASA Astrophysics Data System (ADS)

    González, R. R.; Quiñones, R. A.

    2009-07-01

    An extensive subsurface oxygen minimum zone off northern and central-south Chile, associated with the Peru-Chile undercurrent, has important effects on the metabolism of the organisms inhabiting therein. Planktonic species deal with the hypoxic and anoxic environments by relying on biochemical as well as physiological processes related to their anaerobic metabolisms. Here we characterize, for the first time, the potential enzymatic activities involved in the aerobic and anaerobic energy production pathways of microplanktonic organisms (<100 μm), their relationship, and this relationship's association with the oxygen concentration and microplanktonic biomass in the oxygen minimum zone and adjacent areas of the Humboldt Current System water column. Our results demonstrate significant potential enzymatic activity of catabolic pathways in the oxygen minimum zone. Malate dehydrogenase had the highest oxidizing activity of nicotinamide adenine dinucleotide (reduced form) in the batch of catabolic enzymatic activities assayed, including potential pyruvate oxidoreductases activity, the electron transport system, and dissimilatory nitrate reductase. Malate dehydrogenase correlated significantly with almost all the enzymes analyzed within and above the oxygen minimum zone, and also with the oxygen concentration and microplankton biomass in the water column of the Humboldt Current System, especially in the oxygen minimum zone off Iquique. These results suggest a possible specific pattern for the catabolic activity of the microplanktonic realm associated with the oxygen minimum zone spread along the Humboldt Current System off Chile. We hypothesize that malate dehydrogenase activity could be an appropriate indicator of microplankton catabolism in the oxygen minimum zone and adjacent areas.

  8. SOA Formation form the NO3 radicals Chemistry of Isoprene, Monoterpenes, Sesquiterpenes, Biogenic Oxygenated Compounds, and Aromatics

    NASA Astrophysics Data System (ADS)

    Kleindienst, T. E.; Jaoui, M.; Docherty, K.; Corse, E.; Offenberg, J. H.; Lewandowski, M.

    2011-12-01

    analysis was carried out for SOA formed from the oxidation of these hydrocarbons by OH both in the presence and absence of nitrogen oxides. Results indicate the presence of a wide range of polar oxygenated organic products in resulting SOA, including organic nitro and nitrates. For some systems, compounds previously observed only from OH reactions were also detected in SOA from NO3 reactions. SOA yields, effective enthalpy of vaporization, EC/OC ratio as well as tentative reaction schemes leading to some of the reaction products are presented. We are currently investigating whether compounds are present in both chamber SOA and ambient aerosol that could serve as indicators for nighttime reactions in atmospheric particulate matter.

  9. Oxygen vacancy ordering and magnetism in the rare earth stabilised perovskite form of "SrCoO 3- δ"

    NASA Astrophysics Data System (ADS)

    James, M.; Cassidy, D.; Wilson, K. F.; Horvat, J.; Withers, R. L.

    2004-07-01

    We have demonstrated that SrCoO 3- δ can be stabilised into phase pure perovskite forms by the introduction of small amounts ˜5% of certain rare earth ions (Sm 3+Yb 3+). At the same doping levels, La 3+ and Pr 3+ crystallise with the same isostructural trigonal structure as Sr 6Co 5O 15; while the Nd 3+ composition shows a mixture of both structure types. Powder X-ray diffraction showed only a simple cubic perovskite structure, however, a combination of electron and neutron diffraction has revealed a tetragonal ( P4/ mmm) ap× ap×2 ap superstructure. Strontium and the rare earth ions are disordered over a single site, while the oxygen vacancies are localised on the apical O2 sites. Magnetisation measurements show that these materials undergo transitions to a spin-glass state at temperatures below 150 K, and that significant coupling occurs between the rare earth ions and the mixed Co 3+/4+ ions. Magnetisation measurements as a function of applied field reveals that below the transition temperature ferromagnetic ordering takes place at relatively large fields.

  10. In Situ Observation of Active Oxygen Species in Fe-Containing Ni-Based Oxygen Evolution Catalysts: The Effect of pH on Electrochemical Activity.

    PubMed

    Trześniewski, Bartek J; Diaz-Morales, Oscar; Vermaas, David A; Longo, Alessandro; Bras, Wim; Koper, Marc T M; Smith, Wilson A

    2015-12-01

    Ni-based oxygen evolution catalysts (OECs) are cost-effective and very active materials that can be potentially used for efficient solar-to-fuel conversion process toward sustainable energy generation. We present a systematic spectroelectrochemical characterization of two Fe-containing Ni-based OECs, namely nickel borate (Ni(Fe)-B(i)) and nickel oxyhydroxide (Ni(Fe)OOH). Our Raman and X-ray absorption spectroscopy results show that both OECs are chemically similar, and that the borate anions do not play an apparent role in the catalytic process at pH 13. Furthermore, we show spectroscopic evidence for the generation of negatively charged sites in both OECs (NiOO(-)), which can be described as adsorbed "active oxygen". Our data conclusively links the OER activity of the Ni-based OECs with the generation of those sites on the surface of the OECs. The OER activity of both OECs is strongly pH dependent, which can be attributed to a deprotonation process of the Ni-based OECs, leading to the formation of the negatively charged surface sites that act as OER precursors. This work emphasizes the relevance of the electrolyte effect to obtain catalytically active phases in Ni-based OECs, in addition to the key role of the Fe impurities. This effect should be carefully considered in the development of Ni-based compounds meant to catalyze the OER at moderate pHs. Complementarily, UV-vis spectroscopy measurements show strong darkening of those catalysts in the catalytically active state. This coloration effect is directly related to the oxidation of nickel and can be an important factor limiting the efficiency of solar-driven devices utilizing Ni-based OECs. PMID:26544169

  11. Unciaphenol, an Oxygenated Analogue of the Bergman Cyclization Product of Uncialamycin Exhibits Anti-HIV Activity.

    PubMed

    Williams, David E; Bottriell, Helen; Davies, Julian; Tietjen, Ian; Brockman, Mark A; Andersen, Raymond J

    2015-11-01

    Unciaphenol (2), an oxygenated analogue of the Bergman cyclization product of the enediyne uncialamycin (1), has been isolated along with 1 from cultures of the actinomycete Streptomyces uncialis. It is proposed that the C-22 OH substituent in 2 might arise from the attack of a nucleophilic oxygen species on the p-benzyne diradical intermediate IA in the Bergman cyclization of 1. 2 shows in vitro anti-HIV activity against viral strains that are resistant to clinically utilized anti-retroviral therapies. PMID:26465962

  12. Highly oxygenated triterpenoids from the roots of Schisandra chinensis and their anti-inflammatory activities.

    PubMed

    Song, Qiu-Yan; Gao, Kun; Nan, Zhi-Biao

    2016-01-01

    A new highly oxygenated triterpenoid, schinchinenlactone D (1), and three known compounds (2-4) were isolated from the roots of Schisandra chinensis. Their structures were determined by combining the spectroscopic analysis with the theoretical computations. The anti-inflammatory activities of compounds 1-4 were evaluated, and compound 3 exhibits the most significant activity in the inhibition of NO production with an IC50 value of 10.6 μM. PMID:26313467

  13. Benthic activity in sediments of the northwestern Adriatic Sea: sediment oxygen consumption, macro- and meiofauna dynamics

    NASA Astrophysics Data System (ADS)

    Moodley, Leon; Heip, Carlo H. R.; Middelburg, Jack J.

    1998-12-01

    Benthic activity was examined at three stations (18 m water depth) in the northwestern Adriatic Sea. Carbon mineralisation rates, as based on sediment oxygen consumption rates, ranged from 54 to 89 g C m -2 y -1. The relatively high carbon mineralisation rates, large macrofaunal biomass (9 to 16 g C m -2) and macrofaunal production (11 to 19 g C m -2 y -1) provide evidence of high organic-matter input and intense benthic-pelagic coupling. This is further supported by the high dominance of the suspension-feeding bivalve Corbula gibba, which accounts for 52 to 63% of the total annual macrofaunal biomass production. Although the infaunal distribution of total macrofauna showed a sharp decline in densities and biomass with depth into the sediment, different patterns within the dominant taxa were observed. Whilst the bivalve Corbula gibba and the amphipod Ampelisca sp. were restricted to the surface layer, other species such as the dominant bivalve Mysella sp. and the gastropod Hyala sp. were not confined to a specific depth level and the majority of the populations occurred deeper than 5 cm into the sediment. Bioturbation, based on the occurrence of macrofauna, extended to at least 20 cm. Nematodes and foraminifera together formed 80 to 90% of the meiofaunal community in the upper 5 cm of the sediment. Annual mean densities ranged from 3.40 to 6.07×10 6 ind. m -2. Maximum abundance of meiofauna was not encountered at the station where maximum macrofaunal activity was recorded, and this could reflect the negative effect of biological interaction on meiofaunal densities in areas that have a high food supply.

  14. Structural and Electrochemical Impacts of Oxygen Doped and Surfactant Coated Activated Carbon Electrodes in Li-ion Batteries

    NASA Astrophysics Data System (ADS)

    Collins, John; Gourdin, Gerald; Qu, Deyang; Foster, Michelle

    2013-03-01

    Passive charge and discharge dynamics are necessary for advancing Li-ion batteries. Surfactant adsorption on activated carbon has been shown to promote advancements in the discharge capacity, time and cycle-ability of electrochemical systems--specifically by enhancing diffusion pathways for ion insertion/de-insertion and suppressing pore blockage from precipitates known to form during charge/discharge states. Enhancement of surfactant chemisorption on activated carbon is achieved through oxygen doping of the carbon surface. In addition, doping alters the degree of Faradaic processes occurring in solution, resulting in prolonged reduction at the carbon surface. The work presented describes how surface oxygen groups on a granulated activated carbon have been manipulated using nitric acid in a controlled, stepwise fashion. A nonionic surfactant was applied to oxidized and non-oxidized samples at various concentrations. The composition and structure of the activated carbon surface was characterized using DRIFTS, Raman Spectroscopy, SEM and Porosimetry. The charge/discharge Li insertion capacities along with correlating surface microstructure changes were analyzed for all treated electrodes at progressive oxidation stages.

  15. Structural and functional characterization of "laboratory evolved" cytochrome P450cam mutants showing enhanced naphthalene oxygenation activity.

    PubMed

    Matsuura, Koji; Tosha, Takehiko; Yoshioka, Shiro; Takahashi, Satoshi; Ishimori, Koichiro; Morishima, Isao

    2004-10-29

    To elucidate molecular mechanisms for the enhanced oxygenation activity in the three mutants of cytochrome P450cam screened by 'laboratory evolution' [Nature 399 (1999) 670], we purified the mutants and characterized their functional and structural properties. The electronic absorption and resonance Raman spectra revealed that the structures of heme binding site of all purified mutants were quite similar to that of the wild-type enzyme, although the fraction of the inactivated form, called "P420," was increased. In the reaction with H(2)O(2), only trace amounts of the naphthalene hydroxylation product were detected by gas chromatography. We, therefore, conclude that the three mutants do not exhibit significant changes in the structural and functional properties from those of wild-type P450cam except for the stability of the axial ligand in the reduced form. The enhanced fluorescence in the whole-cell assay would reflect enhancement in the oxygenation activity below the detectable limit of the gas chromatography and/or contributions of other reactions catalyzed by the heme iron. PMID:15451425

  16. Role of activation in alveolar macrophage-mediated suppression of the plaque-forming cell response.

    PubMed Central

    Mbawuike, I N; Herscowitz, H B

    1988-01-01

    Alveolar macrophages (AM) are highly suppressive of the in vitro plaque-forming cell (PFC) response of spleen cells obtained from mice primed with sheep erythrocytes. Comparison of macrophage populations obtained from disparate anatomical sites revealed that although in both cases there was a cell-concentration-dependent suppression of the PFC response, resident AM or AM activated as a result of intravenous injection of Mycobacterium bovis BCG were equally suppressive at the doses examined. Although there was a similar dose-dependent suppression with peritoneal macrophages, BCG-activated cells were more suppressive of the PFC response than were resident cells. In contrast, splenic macrophages at comparable concentrations were not at all suppressive. Resident AM exhibited significantly lower levels of 5'-nucleotidase activity than did resident peritoneal macrophages. Macrophage-mediated suppression of the in vitro PFC response could not be attributed to the release of toxic oxygen metabolites (H2O2, O2- ,and .OH) or prostaglandins, since the addition of catalase, superoxide dismutase, 2-mercaptoethanol, or indomethacin did not completely reverse suppression. These results suggest that the lung microenvironment may maintain AM in an activated state which contributes to their potential immunoregulatory functions. PMID:2830191

  17. Tuning the activity of Pt(111) for oxygen electroreduction by subsurface alloying.

    PubMed

    Stephens, Ifan E L; Bondarenko, Alexander S; Perez-Alonso, Francisco J; Calle-Vallejo, Federico; Bech, Lone; Johansson, Tobias P; Jepsen, Anders K; Frydendal, Rasmus; Knudsen, Brian P; Rossmeisl, Jan; Chorkendorff, Ib

    2011-04-13

    To enable the development of low temperature fuel cells, significant improvements are required to the efficiency of the Pt electrocatalysts at the cathode, where oxygen reduction takes place. Herein, we study the effect of subsurface solute metals on the reactivity of Pt, using a Cu/Pt(111) near-surface alloy. Our investigations incorporate electrochemical measurements, ultrahigh vacuum experiments, and density functional theory. Changes to the OH binding energy, ΔE(OH), were monitored in situ and adjusted continuously through the subsurface Cu coverage. The incorporation of submonolayer quantities of Cu into Pt(111) resulted in an 8-fold improvement in oxygen reduction activity. The most optimal catalyst for oxygen reduction has an ΔE(OH) ≈ 0.1 eV weaker than that of pure Pt, validating earlier theoretical predictions. PMID:21417329

  18. Effects of oxygen concentration on the nitrifying activity of an aerobic hybrid granular sludge reactor.

    PubMed

    Filali, Ahlem; Bessiere, Yolaine; Sperandio, Mathieu

    2012-01-01

    The aim of the work was to quantify the influence of the simultaneous presence of flocs and granules in the nitrifying activity in a sequencing batch airlift reactor (SBAR). The nitrification rate and oxygen limitation of flocs, granules and hybrid sludge was investigated using respirometric assays at different dissolved oxygen concentrations. The spatial distribution of Ammonium Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB) was investigated using fluorescence in situ hybridization (FISH). Results showed that the nitrification rate was much less sensitive to oxygen limitation in systems containing a fraction of flocs than in pure granular sludge. Ammonium Oxidizing Bacteria (AOB) were found to be distributed in similar quantities in flocs and granules whereas the Nitrite Oxidizing Bacteria (NOB) were located preferentially in granules. This study showed that the presence of flocs with granules could increase the robustness of the process to transitory reductions of aeration. PMID:22233907

  19. Theoretical study of the phototoxicity of naproxen and the active form of nabumetone.

    PubMed

    Musa, Klefah A K; Eriksson, Leif A

    2008-10-30

    Density functional theory using the hybrid functional B3LYP has been employed in order to study the mechanisms of photoinduced decomposition of the closely related nonsteroidal anti-inflammatory drugs naproxen (NP) and 6-methoxy-2-naphthylacetic acid (MNAA; the active form of nabumetone). The photochemical properties and computed energies of various species obtained in this study show that both drugs dominate in their deprotonated forms at physiological pH. The deprotonated acids are unable to decarboxylate from their excited singlets; instead, they decarboxylate from their first excited triplet states with high efficiency, overcoming energy barriers less than 3 and 1 kcal/mol for MNAA and NP, respectively. The ultraviolet and visible spectra of the neutral, deprotonated, and decarboxylated moieties of MNAA and NP are more-or-less similar but with higher probabilites (oscillator strength) for the latter. This fact, as well as the higher reactivity of NP, is explained in terms of the electron-donating effect of the additional methyl group present in NP. Singlet oxygen, superoxide radical anion, and corresponding peroxyl radical species are expected to be formed in different steps throughout the proposed photodegradation pathways of both drugs, which give rise to their effects on biomolecules, for example, lipid peroxidation. PMID:18834087

  20. Non-destructive measurement of carbonic anhydrase activity and the oxygen isotope composition of soil water

    NASA Astrophysics Data System (ADS)

    Jones, Sam; Sauze, Joana; Ogée, Jérôme; Wohl, Steven; Bosc, Alexandre; Wingate, Lisa

    2016-04-01

    Carbonic anhydrases are a group of metalloenzymes that catalyse the hydration of aqueous carbon dioxide (CO2). The expression of carbonic anhydrase by bacteria, archaea and eukarya has been linked to a variety of important biological processes including pH regulation, substrate supply and biomineralisation. As oxygen isotopes are exchanged between CO2 and water during hydration, the presence of carbonic anhydrase in plants and soil organisms also influences the oxygen isotope budget of atmospheric CO2. Leaf and soil water pools have distinct oxygen isotope compositions, owing to differences in pool sizes and evaporation rates, which are imparted on CO2during hydration. These differences in the isotopic signature of CO2 interacting with leaves and soil can be used to partition the contribution of photosynthesis and soil respiration to net terrestrial CO2 exchange. However, this relies on our knowledge of soil carbonic anhydrase activity and currently, the prevalence and function of these enzymes in soils is poorly understood. Isotopic approaches used to estimate soil carbonic anhydrase activity typically involve the inversion of models describing the oxygen isotope composition of CO2 fluxes to solve for the apparent, potentially catalysed, rate of oxygen exchange during hydration. This requires information about the composition of CO2 in isotopic equilibrium with soil water obtained from destructive, depth-resolved soil water sampling. This can represent a significant challenge in data collection given the considerable potential for spatial and temporal variability in the isotopic composition of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by constraining carbonic anhydrase activity and the composition of soil water in isotopic equilibrium with CO2 by solving simultaneously the mass balance for two soil CO2 steady states differing only in the

  1. Increased oxygen consumption following activation of brain: theoretical footnotes using spectroscopic data from barrel cortex.

    PubMed

    Mayhew, J; Johnston, D; Martindale, J; Jones, M; Berwick, J; Zheng, Y

    2001-06-01

    Optical imaging spectroscopy (OIS) and laser Doppler flowmetry (LDF) data sequences from anesthetized rats were used to determine the relationship between changes in oxy-and deoxygenated hemoglobin concentration and changes in blood volume and flow in the presence and absence of stimulation. The data from Jones et al. (accompanying paper) were used to explore the differences between two theoretical models of flow activation coupling. The essential difference between the two models is the extension of the model of Buxton and Frank by Hyder et al. (1998, J. Appl. Physiol. 85: 554--564) to incorporate change in capillary diffusivity coupled to flow. In both models activation-increased flow changes increase oxygen transport from the capillary; however, in Hyder et al.'s model the diffusivity of the capillary itself is increased. Hyder et al. proposed a parameter (Omega), a scaling "constant" linking increased blood flow and oxygen "diffusivity" in the capillary bed. Thus, in Buxton and Frank's theory, Omega = 0; i.e., there are no changes in diffusivity. In Hyder et al.'s theory, 0 < Omega < 1, and changes in diffusivity are assumed to be linearly related to flow changes. We elaborate the theoretical position of both models to show that, in principle, the different predictions from the two theories can be evaluated using optical imaging spectroscopy data. We find that both theoretical positions have limitations when applied to data from brief stimulation and when applied to data from mild hypercapnia. In summary, the analysis showed that although Hyder et al.'s proposal that diffusivity increased during activation did occur; it was shown to arise from an implementation of Buxton and Frank's theory under episodes of brief stimulation. The results also showed that the scaling parameter Omega is not a constant as the Hyder et al. model entails but in fact varies over the time course of the flow changes. Data from experiments in which mild hypercapnia was administered also

  2. Scavenging activity of "beta catechin" on reactive oxygen species generated by photosensitization of riboflavin.

    PubMed

    Kumari, M V; Yoneda, T; Hiramatsu, M

    1996-05-01

    "beta CATECHIN", a preparation containing green tea extract, ascorbic acid, sunflower seed extract, dunaliella carotene and natural vitamin E, has been designed as a model "universal antioxidant" that offers protection via its scavenging action on a wide range of free radicals, both water-soluble and fat-soluble. Reactive oxygen species like singlet oxygen, hydroxyl and superoxide radicals, are often generated in biological systems during photosensitized oxidation reactions. We report on the simultaneous effect of "beta CATECHIN" on active oxygen species generated during the photosensitized oxidation of riboflavin using 2,2,6,6-tetramethyl-4-piperidone (TMPD) as a "spin-trapping" agent. The intensities of the resulting stable nitroxide radical adduct, 2,2,6,6-tetramethyl-4-piperidone-1-oxyl (TEMPONE), were detected by electron spin resonance (ESR) spectroscopy. Results show simultaneous, nonspecific and complete scavenging action of reactive oxygen species generated in our in vitro model system by "beta CATECHIN". It is therefore suggested that "beta CATECHIN" could offer protection against free radical insult and in preventing cancer and other diseases that are mediated by reactive oxygen species. PMID:8739038

  3. Atrial natriuretic peptide regulates lipid mobilization and oxygen consumption in human adipocytes by activating AMPK

    SciTech Connect

    Souza, Sandra C.; Chau, Mary D.L.; Yang, Qing; Gauthier, Marie-Soleil; Clairmont, Kevin B.; Wu, Zhidan; Gromada, Jesper; Dole, William P.

    2011-07-08

    Highlights: {yields} Treatment of differentiated human adipocytes with atrial natriuretic peptide (ANP) increased lipolysis and oxygen consumption by activating AMP-activated protein kinase (AMPK). {yields} ANP stimulated lipid mobilization by selective activation of the alpha2 subunit of AMPK and increased energy utilization through activation of both the alpha1 and alpha2 subunits of AMPK. {yields} ANP enhanced adipocyte mitochondrial oxidative capacity as evidenced by induction of oxidative mitochondrial genes and increase in oxygen consumption. {yields} Exposure of human adipocytes to fatty acids and (TNF{alpha}) induced insulin resistance and decreased expression of mitochondrial genes which was restored to normal by ANP. -- Abstract: Atrial natriuretic peptide (ANP) has been shown to regulate lipid and carbohydrate metabolism providing a possible link between cardiovascular function and metabolism by mediating the switch from carbohydrate to lipid mobilization and oxidation. ANP exerts a potent lipolytic effect via cGMP-dependent protein kinase (cGK)-I mediated-stimulation of AMP-activated protein kinase (AMPK). Activation of the ANP/cGK signaling cascade also promotes muscle mitochondrial biogenesis and fat oxidation. Here we demonstrate that ANP regulates lipid metabolism and oxygen utilization in differentiated human adipocytes by activating the alpha2 subunit of AMPK. ANP treatment increased lipolysis by seven fold and oxygen consumption by two fold, both of which were attenuated by inhibition of AMPK activity. ANP-induced lipolysis was shown to be mediated by the alpha2 subunit of AMPK as introduction of dominant-negative alpha2 subunit of AMPK attenuated ANP effects on lipolysis. ANP-induced activation of AMPK enhanced mitochondrial oxidative capacity as evidenced by a two fold increase in oxygen consumption and induction of mitochondrial genes, including carnitine palmitoyltransferase 1A (CPT1a) by 1.4-fold, cytochrome C (CytC) by 1.3-fold, and

  4. MarR-type Transcriptional Regulator ChlR Activates Expression of Tetrapyrrole Biosynthesis Genes in Response to Low-oxygen Conditions in Cyanobacteria*

    PubMed Central

    Aoki, Rina; Takeda, Tomoya; Omata, Tatsuo; Ihara, Kunio; Fujita, Yuichi

    2012-01-01

    Oxygen is required for three enzyme reactions in chlorophyll and bilin biosynthesis pathways: coproporphyrinogen III oxidase (HemF), heme oxygenase (HO1), and Mg-protoporphyrin IX monomethylester cyclase (ChlAI). The cyanobacterium Synechocystis sp. PCC 6803 has alternative enzymes, HemN, HO2, and ChlAII, to supply chlorophyll/bilins even under low-oxygen environments. The three genes form an operon, chlAII-ho2-hemN, that is induced in response to low-oxygen conditions to bypass the oxygen-dependent reactions. Here we identified a transcriptional regulator for the induction of the operon in response to low-oxygen conditions. A pseudorevertant, Δho1R, was isolated from a HO1-lacking mutant Δho1 that is lethal under aerobic conditions. Δho1R grew well even under aerobic conditions. In Δho1R, HO2 that is induced only under low-oxygen conditions was anomalously expressed under aerobic conditions to complement the loss of HO1. A G-to-C transversion in sll1512 causing the amino acid change from aspartate 35 to histidine was identified as the relevant mutation by resequencing of the Δho1R genome. Sll1512 is a MarR-type transcriptional regulator. An sll1512-lacking mutant grew poorly under low-oxygen conditions with a remarked decrease in Chl content that would be caused by the suppressed induction of the chlAII and hemN genes in Chl biosynthesis under low-oxygen conditions. These results demonstrated that Sll1512 is an activator in response to low-oxygen environments and that the D35H variant becomes a constitutive activator. This hypothesis was supported by a gel shift assay showing that the Sll1512-D35H variant binds to the DNA fragment upstream of the operon. We propose to name sll1512 chlR. PMID:22375005

  5. [Oxygen consumption by the yeast-like and filamentous forms of Sporothrix schenckii as measured by polarography].

    PubMed

    Tréfouël, M J

    1976-01-01

    The study of the oxygen uptake by cultures of Sporothrix schenckii as measured with the Clark electrode has shown that when the fungus was grown in a liquid medium, the atmospheric oxygen went into solution very slowly even when the liquid was rapidly stirred. The partial oxygen pressure was very small after some days of culture (no more than 2 or 3% expressed as the saturated value). Hence, it is postulated that the linear part of the growth curve is due to the dissolved oxygen acting as a limiting factor. When the oxygen uptake by filaments, conidia, or yeasts isplotted against the time the curve variations follow the transformations of the fungus. PMID:816527

  6. [Light-induced production and consumption of oxygen by chloroplasts: activation and inhibition].

    PubMed

    Chan Van, N i; Nikandrov, V V; Brin, G P; Krasnovskii, A A

    1977-07-01

    Light-induced production and consumption of oxygen by pea chloroplasts are activated at certain concentrations of the solvents (diethyl ester, methyl alcohol, dimethylsulfoxide) and detergent Triton X-100. At higher concentrations of the compounds studied both reactions are inhibited. The uncouplers (methylamine and carbonyl cyanide-3-chlorophenylhydrazone) activate these processes. The agents studied have a similar effect on the processes of light-induced production and consumption of oxygen, which are limited by a common link bound to the phosphorylation site in photosystem I. The effects observed suggest that the inhibition may be due to inhibition of photosystem II, whereas the activation may be largely due to an action on photosystem I. PMID:907797

  7. LASERS: Efficient chemical oxygen — iodine laser with a high total pressure of the active medium

    NASA Astrophysics Data System (ADS)

    Zagidullin, M. V.; Nikolaev, V. D.; Svistun, M. I.; Khvatov, N. A.; Heiger, G. D.; Madden, T. J.

    2001-01-01

    A new concept of obtaining a high total pressure of the active medium of a chemical oxygen — iodine laser (OIL) is proposed and verified. The nozzle unit of the laser consists of the alternating vertical arrays of cylindrical nozzles to produce high-pressure nitrogen jets, plane slotted nozzles for the flow of O2(1Δ) oxygen, and vertical arrays of cylindrical nozzles to inject the N2 — I2 mixture between the first two streams. For a molar chlorine flow rate of 39.2 mmol s-1, the output power was 700 W and the chemical efficiency was 19.7 %. The combined use of the ejector nozzle unit proposed to obtain the active medium and a super-sonic diffuser allows a significant simplification of the ejection system for the exhaust active medium of the OIL.

  8. Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability.

    PubMed

    Stamenkovic, Vojislav R; Fowler, Ben; Mun, Bongjin Simon; Wang, Guofeng; Ross, Philip N; Lucas, Christopher A; Marković, Nenad M

    2007-01-26

    The slow rate of the oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cell (PEMFC) is the main limitation for automotive applications. We demonstrated that the Pt3Ni(111) surface is 10-fold more active for the ORR than the corresponding Pt(111) surface and 90-fold more active than the current state-of-the-art Pt/C catalysts for PEMFC. The Pt3Ni(111) surface has an unusual electronic structure (d-band center position) and arrangement of surface atoms in the near-surface region. Under operating conditions relevant to fuel cells, its near-surface layer exhibits a highly structured compositional oscillation in the outermost and third layers, which are Pt-rich, and in the second atomic layer, which is Ni-rich. The weak interaction between the Pt surface atoms and nonreactive oxygenated species increases the number of active sites for O2 adsorption. PMID:17218494

  9. Tuning the catalytic activity of graphene nanosheets for oxygen reduction reaction via size and thickness reduction.

    PubMed

    Benson, John; Xu, Qian; Wang, Peng; Shen, Yuting; Sun, Litao; Wang, Tanyuan; Li, Meixian; Papakonstantinou, Pagona

    2014-11-26

    Currently, the fundamental factors that control the oxygen reduction reaction (ORR) activity of graphene itself, in particular, the dependence of the ORR activity on the number of exposed edge sites remain elusive, mainly due to limited synthesis routes of achieving small size graphene. In this work, the synthesis of low oxygen content (<2.5±0.2 at. %), few layer graphene nanosheets with lateral dimensions smaller than a few hundred nanometers were achieved using a combination of ionic liquid assisted grinding of high purity graphite coupled with sequential centrifugation. We show for the first time that the graphene nanosheets possessing a plethora of edges exhibited considerably higher electron transfer numbers compared to the thicker graphene nanoplatelets. This enhanced ORR activity was accomplished by successfully exploiting the plethora of edges of the nanosized graphene as well as the efficient electron communication between the active edge sites and the electrode substrate. The graphene nanosheets were characterized by an onset potential of -0.13 V vs Ag/AgCl and a current density of -3.85 mA/cm2 at -1 V, which represent the best ORR performance ever achieved from an undoped carbon based catalyst. This work demonstrates how low oxygen content nanosized graphene synthesized by a simple route can considerably impact the ORR catalytic activity and hence it is of significance in designing and optimizing advanced metal-free ORR electrocatalysts. PMID:25334050

  10. Oxygen deficient ZnO 1-x nanosheets with high visible light photocatalytic activity.

    PubMed

    Guo, Hong-Li; Zhu, Qing; Wu, Xi-Lin; Jiang, Yi-Fan; Xie, Xiao; Xu, An-Wu

    2015-04-28

    Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO 1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO 1-x. The incorporation of oxygen defects could effectively extend the light absorption of ZnO 1-x into the visible-light region due to the fact that the energy of the localized state is located in the forbidden gap. Thus, our obtained ZnO 1-x shows a higher photodegradation of methyl orange (MO) compared to defect-free ZnO under visible light illumination. Additionally, the high content of ˙OH radicals with a strong photo-oxidation capability over the ZnO 1-x nanosheets significantly contributes to the improvement in the photocatalytic performance. Our oxygen deficient ZnO 1-x sample shows a very high photocatalytic activity for the degradation of MO even after 5 cycles without any obvious decline. The results demonstrate that defect engineering is a powerful tool to enhance the optoelectronic and photocatalytic performances of nanomaterials. PMID:25812132

  11. 76 FR 30738 - Agency Information Collection Activities: Form G-845 and Form G-845 Supplement, Revision of a...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-26

    ... the Federal Register on February 22, 2011, at 76 FR 9805, allowing for a 60-day public comment period... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form G-845 and Form G- 845 Supplement, Revision of a Currently Approved Information Collection; Comment Request...

  12. Production of Energetic Active-Oxygen Species at Atmospheric Pressure by Linear Microplasma Arrays

    NASA Astrophysics Data System (ADS)

    Rawlins, Wilson; Galbally-Kinney, Kristin; Davis, Steven; Hoskinson, Alan; Hopwood, Jeffrey

    2014-10-01

    Linear arrays of stripline resonators operated at microwave frequencies and low powers provide spatially and temporally continuous micro-discharges with high E/N at atmospheric pressure. When implemented in a discharge-flow reactor, these microplasmas excite metastable singlet molecular oxygen and dissociate oxygen molecules to produce atomic oxygen, with efficiencies comparable to conventional microwave resonant cavities at low pressures. At elevated pressure, production of atomic oxygen leads to prompt formation of ozone immediately downstream of the discharge exit. We have observed and quantified the production of O2(a 1 Δ) metastables and O3 in the effluent of linear microplasma arrays for O2/He, O2/Ar, O2/N2/He,andO2/N2/Ar mixtures as functions of pressure, gas flow rate, and species mixing ratio. We compare results for single-array microplasmas, where the discharge products are formed in a small volume and entrained into the bulk flow, and overlapping dual-array microplasmas which process larger gas flow volumes. Supported by the Air Force Research Laboratory and Department of Energy.

  13. Hyperbaric oxygen preserves neurotrophic activity of carbon monoxide-exposed astrocytes.

    PubMed

    Jurič, Damijana M; Šuput, Dušan; Brvar, Miran

    2016-06-24

    In astrocytes, carbon monoxide (CO) poisoning causes oxidative stress and mitochondrial dysfunction accompanied by caspase and calpain activation. Impairment in astrocyte function can be time-dependently reduced by hyperbaric (3bar) oxygen (HBO). Due to the central role of astrocytes in maintaining neuronal function by offering neurotrophic support we investigated the hypothesis that HBO therapy may exert beneficial effect on acute CO poisoning-induced impairment in intrinsic neurotrophic activity. Exposure to 3000ppm CO in air followed by 24-72h of normoxia caused a progressive decline of gene expression, synthesis and secretion of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) to different extent. 1h treatment with 100% oxygen disclosed a pressure- and time-dependent efficacy in preserving astrocytic neurotrophic support. The beneficial effect was most evident when the astrocytes were exposed to HBO 1-5h after exposure to CO. The results further support an active role of hyperbaric, not normobaric, oxygenation in reducing dysfunction of astrocytes after acute CO poisoning. By preserving endogenous neurotrophic activity HBO therapy might promote neuronal protection and thus prevent the occurrence of late neuropsychological sequelae. PMID:27113706

  14. The Essay: Theory and Pedagogy for an Active Form.

    ERIC Educational Resources Information Center

    Heilker, Paul

    Calling for a radical reexamination of the traditional foundation of composition instruction--the thesis/support form, this book argues that the essay, with its informality, conversational tone, meditative mood, and integration of form and content, is better suited to developmental, epistemological, ideological, and feminist rhetorical…

  15. Effect of KOH activation on the formation of oxygen structure in activated carbons synthesized from polymeric precursor.

    PubMed

    Park, Soo-Jin; Jung, Woo-Young

    2002-06-01

    In this work, the influence of KOH activation on the surface chemistry of activated carbons (ACs) synthesized from polystyrene-based cation exchangeable resin (PSI) has been investigated. The surface chemistry of ACs has been characterized by using Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), pH measurement, and Boehm's titration method. As a result, PSI can be successfully converted into ACs with high porosities. The total oxygen content on the ACs studied increases with increasing the KOH-to-PSI ratio. FT-IR and XPS analyses show that the resulting carbons possess a number of oxygen surface functional groups, such as carbonyl, quinone, phenol, ether, and carboxylic acid groups. The highest oxygen content and acid value are observed at a KOH-to-PSI ratio of 4 (KPS-4). However, its pH and surface basicity are higher than those of a KOH-to-PSI ratio of 2 (KPS-2), indicating the formation of basic species, such as quinone and pyrone groups. Although the oxygen-containing groups with basic character exist in the resulting carbons, all the samples are still acidic in character. PMID:16290638

  16. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    NASA Astrophysics Data System (ADS)

    Holby, Edward F.; Taylor, Christopher D.

    2015-03-01

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

  17. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    PubMed Central

    Holby, Edward F.; Taylor, Christopher D.

    2015-01-01

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date. PMID:25788358

  18. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: role of *OH ligands.

    PubMed

    Holby, Edward F; Taylor, Christopher D

    2015-01-01

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date. PMID:25788358

  19. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    DOE PAGESBeta

    Holby, Edward F.; Taylor, Christopher D.

    2015-03-19

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O₂ bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H₂O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH boundmore » structures have the highest calculated activity to date.« less

  20. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    SciTech Connect

    Holby, Edward F.; Taylor, Christopher D.

    2015-03-19

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O₂ bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H₂O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

  1. Reactive Oxygen Species Production by Potato Tuber Mitochondria Is Modulated by Mitochondrially Bound Hexokinase Activity1

    PubMed Central

    Camacho-Pereira, Juliana; Meyer, Laudiene Evangelista; Machado, Lilia Bender; Oliveira, Marcus Fernandes; Galina, Antonio

    2009-01-01

    Potato tuber (Solanum tuberosum) mitochondria (PTM) have a mitochondrially bound hexokinase (HK) activity that exhibits a pronounced sensitivity to ADP inhibition. Here we investigated the role of mitochondrial HK activity in PTM reactive oxygen species generation. Mitochondrial HK has a 10-fold higher affinity for glucose (Glc) than for fructose (KMGlc = 140 μm versus KMFrc = 1,375 μm). Activation of PTM respiration by succinate led to an increase in hydrogen peroxide (H2O2) release that was abrogated by mitochondrial HK activation. Mitochondrial HK activity caused a decrease in the mitochondrial membrane potential and an increase in oxygen consumption by PTM. Inhibition of Glc phosphorylation by mannoheptulose or GlcNAc induced a rapid increase in H2O2 release. The blockage of H2O2 release sustained by Glc was reverted by oligomycin and atractyloside, indicating that ADP recycles through the adenine nucleotide translocator and F0F1ATP synthase is operative during the mitochondrial HK reaction. Inhibition of mitochondrial HK activity by 60% to 70% caused an increase of 50% in the maximal rate of H2O2 release. Inhibition in H2O2 release by mitochondrial HK activity was comparable to, or even more potent, than that observed for StUCP (S. tuberosum uncoupling protein) activity. The inhibition of H2O2 release in PTM was two orders of magnitude more selective for the ADP produced from the mitochondrial HK reaction than for that derived from soluble yeast (Saccharomyces cerevisiae) HK. Modulation of H2O2 release and oxygen consumption by Glc and mitochondrial HK inhibitors in potato tuber slices shows that hexoses and mitochondrial HK may act as a potent preventive antioxidant mechanism in potato tubers. PMID:19109413

  2. Selective nitrogen doping in graphene: Enhanced catalytic activity for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Wang, Xianlong; Hou, Zhufeng; Ikeda, Takashi; Huang, Sheng-Feng; Terakura, Kiyoyuki; Boero, Mauro; Oshima, Masaharu; Kakimoto, Masa-Aki; Miyata, Seizo

    2011-12-01

    The structural and electronic properties of N-doped zigzag graphene ribbons with various ratios of dihydrogenated to monohydrogenated edge carbons are investigated within the density functional theory framework. We find that the stability of graphitic N next to the edge, which is claimed to play important roles in the catalytic activity in our previous work, will be enhanced with increasing the concentration of dihydrogenated carbons. Furthermore, the dihydrogenated edge carbons turn out to be easily converted into monohydrogenated ones in the presence of oxygen molecules at room temperature. Based on our results, we propose a possible way to enhance the oxygen reduction catalytic activity of N-doped graphene by controlling the degrees of hydrogenation of edge carbons. The characteristic features in the x-ray absorption and emission spectra for each specific N site considered here will also be given.

  3. Structural Characterization of Mutations at the Oxygen Activation Site in Monomeric Sarcosine Oxidase

    SciTech Connect

    Schuman Jorns, Marilyn; Chen, Zhi-wei; Mathews, F. Scott

    2010-04-30

    Oxygen reduction and sarcosine oxidation in monomeric sarcosine oxidase (MSOX) occur at separate sites above the si- and re-faces, respectively, of the flavin ring. Mutagenesis studies implicate Lys265 as the oxygen activation site. Substitution of Lys265 with a neutral (Met, Gln, or Ala) or basic (Arg) residue results in an {approx}10{sup 4}- or 250-fold decrease, respectively, in the reaction rate. The overall structure of MSOX and residue conformation in the sarcosine binding cavity are unaffected by replacement of Lys265 with Met or Arg. The side chain of Met265 exhibits the same configuration in each molecule of Lys265Met crystals and is nearly congruent with Lys265 in wild-type MSOX. The side chain of Arg265 is, however, dramatically shifted (4-5 {angstrom}) compared with Lys265, points in the opposite direction, and exhibits significant conformational variability between molecules of the same crystal. The major species in solutions of Lys265Arg is likely to contain a 'flipped-out' Arg265 and exhibit negligible oxygen activation, similar to Lys265Met. The 400-fold higher oxygen reactivity observed with Lys265Arg is attributed to a minor (<1%) 'flipped-in' Arg265 conformer whose oxygen reactivity is similar to that of wild-type MSOX. A structural water (WAT1), found above the si-face of the flavin ring in all previously determined MSOX structures, is part of an apparent proton relay system that extends from FAD N(5) to bulk solvent. WAT1 is strikingly absent in Lys265Met and Lys265Arg, a feature that may account for the apparent kinetic stabilization of a reductive half-reaction intermediate that is detectable with the mutants but not wild-type MSOX.

  4. Reactive Oxygen and Nitrogen Species in Defense/Stress Responses Activated by Chitosan in Sycamore Cultured Cells

    PubMed Central

    Malerba, Massimo; Cerana, Raffaella

    2015-01-01

    Chitosan (CHT) is a non-toxic and inexpensive compound obtained by deacetylation of chitin, the main component of the exoskeleton of arthropods as well as of the cell walls of many fungi. In agriculture CHT is used to control numerous diseases on various horticultural commodities but, although different mechanisms have been proposed, the exact mode of action of CHT is still unknown. In sycamore (Acer pseudoplatanus L.) cultured cells, CHT induces a set of defense/stress responses that includes production of H2O2 and nitric oxide (NO). We investigated the possible signaling role of these reactive molecules in some CHT-induced responses by means of inhibitors of production and/or scavengers. The results show that both reactive nitrogen and oxygen species are not only a mere symptom of stress conditions but are involved in the responses induced by CHT in sycamore cells. In particular, NO appears to be involved in a cell death form induced by CHT that shows apoptotic features like DNA fragmentation, increase in caspase-3-like activity and release of cytochrome c from the mitochondrion. On the contrary, reactive oxygen species (ROS) appear involved in a cell death form induced by CHT that does not show these apoptotic features but presents increase in lipid peroxidation. PMID:25642757

  5. Reactive oxygen and nitrogen species in defense/stress responses activated by chitosan in sycamore cultured cells.

    PubMed

    Malerba, Massimo; Cerana, Raffaella

    2015-01-01

    Chitosan (CHT) is a non-toxic and inexpensive compound obtained by deacetylation of chitin, the main component of the exoskeleton of arthropods as well as of the cell walls of many fungi. In agriculture CHT is used to control numerous diseases on various horticultural commodities but, although different mechanisms have been proposed, the exact mode of action of CHT is still unknown. In sycamore (Acer pseudoplatanus L.) cultured cells, CHT induces a set of defense/stress responses that includes production of H2O2 and nitric oxide (NO). We investigated the possible signaling role of these reactive molecules in some CHT-induced responses by means of inhibitors of production and/or scavengers. The results show that both reactive nitrogen and oxygen species are not only a mere symptom of stress conditions but are involved in the responses induced by CHT in sycamore cells. In particular, NO appears to be involved in a cell death form induced by CHT that shows apoptotic features like DNA fragmentation, increase in caspase-3-like activity and release of cytochrome c from the mitochondrion. On the contrary, reactive oxygen species (ROS) appear involved in a cell death form induced by CHT that does not show these apoptotic features but presents increase in lipid peroxidation. PMID:25642757

  6. Highly branched PtCu bimetallic alloy nanodendrites with superior electrocatalytic activities for oxygen reduction reactions

    NASA Astrophysics Data System (ADS)

    Fu, Shaofang; Zhu, Chengzhou; Shi, Qiurong; Xia, Haibing; Du, Dan; Lin, Yuehe

    2016-02-01

    Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst.Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07682j

  7. A General Method for Multimetallic Platinum Alloy Nanowires as Highly Active and Stable Oxygen Reduction Catalysts.

    PubMed

    Bu, Lingzheng; Ding, Jiabao; Guo, Shaojun; Zhang, Xu; Su, Dong; Zhu, Xing; Yao, Jianlin; Guo, Jun; Lu, Gang; Huang, Xiaoqing

    2015-11-25

    An unconventional class of high-performance Pt alloy multimetallic nanowires (NWs) is produced by a general method. The obtained PtNi NWs exhibit amazingly specific and mass oxygen reduction reaction (ORR) activities with improvement factors of 51.1 and 34.6 over commercial Pt/C catalysts, respectively, and are also stable in ORR conditions, making them among the most efficient electrocatalysts for ORR. PMID:26459261

  8. The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and Aspergillus niger phytase

    NASA Astrophysics Data System (ADS)

    von Sperber, C.; Tamburini, F.; Brunner, B.; Bernasconi, S. M.; Frossard, E.

    2015-07-01

    Phosphorus (P) is an essential nutrient for living organisms. Under P-limiting conditions plants and microorganisms can exude extracellular phosphatases that release inorganic phosphate (Pi) from organic phosphorus compounds (Porg). Phytic acid (myo-inositol hexakisphosphate, IP6) is an important form of Porg in many soils. The enzymatic hydrolysis of IP6 by phytase yields available Pi and less phosphorylated inositol derivates as products. The hydrolysis of organic P compounds by phosphatases leaves an isotopic imprint on the oxygen isotope composition (δ18O) of released Pi, which might be used to trace P in the environment. This study aims at determining the effect of phytase on the oxygen isotope composition of released Pi. For this purpose, enzymatic assays with histidine acid phytases from wheat and Aspergillus niger were prepared using IP6, adenosine 5'-monophosphate (AMP) and glycerophosphate (GPO4) as substrates. For a comparison to the δ18O of Pi released by other extracellular enzymes, enzymatic assays with acid phosphatases from potato and wheat germ with IP6 as a substrate were prepared. During the hydrolysis of IP6 by phytase, four of the six Pi were released, and one oxygen atom from water was incorporated into each Pi. This incorporation of oxygen from water into Pi was subject to an apparent inverse isotopic fractionation (ϵ ~ 6 to 10 ‰), which was similar to that imparted by acid phosphatase from potato during the hydrolysis of IP6 (ϵ ~ 7 ‰), where less than three Pi were released. The incorporation of oxygen from water into Pi during the hydrolysis of AMP and GPO4 by phytase yielded a normal isotopic fractionation (ϵ ~ -12 ‰), similar to values reported for acid phosphatases from potato and wheat germ. We attribute this similarity in ϵ to the same amino acid sequence motif (RHGXRXP) at the active site of these enzymes, which leads to similar reaction mechanisms. We suggest that the striking

  9. The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and Aspergillus niger phytase

    NASA Astrophysics Data System (ADS)

    Sperber, C. v.; Tamburini, F.; Brunner, B.; Bernasconi, S. M.; Frossard, E.

    2015-03-01

    Phosphorus (P) is an essential nutrient for living organisms. Under P-limiting conditions plants and microorganisms can exude extracellular phosphatases that release inorganic phosphate (Pi) from organic phosphorus compounds (Porg). Phytic acid (IP6) is an important form of Porg in many soils. The enzymatic hydrolysis of IP6 by phytase yields plant available inorganic phosphate (Pi) and less phosphorylated inositol derivates as products. The hydrolysis of organic P-compounds by phosphatases leaves an isotopic imprint on the oxygen isotope composition (δ18O) of released Pi, which might be used to trace P in the environment. This study aims at determining the effect of phytase on the oxygen isotope composition of released Pi. For this purpose, enzymatic assays with histidine acid phytases from wheat and Aspergillus niger were prepared using IP6, adenosine 5'monophosphate (AMP) and glycerophosphate (GPO4) as substrates. For a comparison to the δ18O of Pi released by other extracellular enzymes, enzymatic assays with acid phosphatases from potato and wheat germ with IP6 as substrate were prepared. During the hydrolysis of IP6 by phytase, four Pi are released, and one oxygen atom from water is incorporated into each Pi. This incorporation of oxygen from water into Pi is subject to an apparent inverse isotopic fractionation (ϵ ∼ 6 to 10‰), which is similar to that imparted by acid phosphatase from potato during the hydrolysis of IP6 (ϵ ∼ 7‰) where less than three Pi are released. The incorporation of oxygen from water into Pi during the hydrolysis of AMP and GPO4 by phytase yielded a normal isotopic fractionation (ϵ ∼ -12‰), again similar to values reported for acid phosphatases from potato and wheat germ. We attribute this similarity in ɛ to the same amino acid sequence motif (RHGXRXP) at the active site of these enzymes, which leads to similar reaction mechanisms. We suggest that the striking substrate-dependency of

  10. Enhanced oxygen evolution activity of IrO2 and RuO2 (100) surfaces

    SciTech Connect

    Stoerzinger, Kelsey; Qiao, Liang; Biegalski, Michael D; Christen, Hans M; Shao-Horn, Yang

    2014-01-01

    The activities of the oxygen evolution reaction (OER) on IrO2 and RuO2 catalysts are among the highest known to date. However, the intrinsic OER activities of surfaces with defined crystallographic orientations are not well established experimentally. Here we report that the (100) surface of IrO2 and RuO2 is more active than the (110) surface that has been traditionally explored by density functional theory studies. The relation between the OER activity and density of coordinatively undersaturated metal sites exposed on each rutile crystallographic facet is discussed. The surface-orientation dependent activities can guide the design of high-surface-area catalysts with increased activity for electrolyzers, metal-air batteries, and photoelectrochemical water splitting applications.

  11. Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts.

    PubMed

    Sahraie, Nastaran Ranjbar; Kramm, Ulrike I; Steinberg, Julian; Zhang, Yuanjian; Thomas, Arne; Reier, Tobias; Paraknowitsch, Jens-Peter; Strasser, Peter

    2015-01-01

    Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and (57)Fe Mössbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity. PMID:26486465

  12. Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

    NASA Astrophysics Data System (ADS)

    Sahraie, Nastaran Ranjbar; Kramm, Ulrike I.; Steinberg, Julian; Zhang, Yuanjian; Thomas, Arne; Reier, Tobias; Paraknowitsch, Jens-Peter; Strasser, Peter

    2015-10-01

    Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mössbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity.

  13. Suppression of oxygen reduction reaction activity on Pt-based electrocatalysts from ionomer incorporation

    NASA Astrophysics Data System (ADS)

    Shinozaki, Kazuma; Morimoto, Yu; Pivovar, Bryan S.; Kocha, Shyam S.

    2016-09-01

    The impact of Nafion on the oxygen reduction reaction (ORR) activity is studied for Pt/C and Pt-alloy/C catalysts using thin-film rotating disk electrode (TF-RDE) methods in 0.1 M HClO4. Ultrathin uniform catalyst layers and standardized activity measurement protocols are employed to obtain accurate and reproducible ORR activity. Nafion lowers the ORR activity which plateaus with increasing loading on Pt catalysts. Pt particle size is found not to have significant influence on the extent of the SA decrease upon Nafion incorporation. Catalysts using high surface area carbon (HSC) support exhibit attenuated activity loss resulting from lower ionomer coverage on catalyst particles located within the deep pores. The impact of metallic composition on the activity loss due to Nafion incorporation is also discussed.

  14. Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

    PubMed Central

    Sahraie, Nastaran Ranjbar; Kramm, Ulrike I.; Steinberg, Julian; Zhang, Yuanjian; Thomas, Arne; Reier, Tobias; Paraknowitsch, Jens-Peter; Strasser, Peter

    2015-01-01

    Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mössbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity. PMID:26486465

  15. Extensive sugar modification improves triple helix forming oligonucleotide activity in vitro but reduces activity in vivo.

    PubMed

    Alam, Md Rowshon; Majumdar, Alokes; Thazhathveetil, Arun Kalliat; Liu, Su-Ting; Liu, Ji-Lan; Puri, Nitin; Cuenoud, Bernard; Sasaki, Shigeki; Miller, Paul S; Seidman, Michael M

    2007-09-01

    We are developing triple helix forming oligonucleotides (TFOs) for gene targeting. Previously, we synthesized bioactive TFOs containing 2'-O-methylribose (2'-OMe) and 2'-O-aminoethylribose (2'-AE) residues. Active TFOs contained four contiguous 2'-AE residues and formed triplexes with high thermal stability and rapid association kinetics. In an effort to further improve bioactivity, we synthesized three series of TFOs containing the 2'-AE patch and additional ribose modifications distributed throughout the remainder of the oligonucleotide. These were either additional 2'-AE residues, the conformationally locked BNA/LNA ribose with a 2'-O,4'-C-methylene bridge, or the 2'-O,4'-C-ethylene analogue (ENA). The additionally modified TFOs formed triplexes with greater thermal stability than the reference TFO, and some had improved association kinetics. However, the most active TFOs in the biochemical and biophysical assays were the least active in the bioassay. We measured the thermal stability of triplexes formed by the TFOs in each series on duplex targets containing a change in sequence at a single position. The Tm value of the variant sequence triplexes increased as the number of all additional modifications increased. A simple explanation for the failure of the improved TFOs in the bioassay was that the increased affinity for nonspecific targets lowered the effective nuclear concentration. Enhancement of TFO bioactivity will require chemical modifications that improve interaction with the specific targets while retaining selectivity against mismatched sequences. PMID:17691818

  16. Synthesis, Characterization, and Catalytic Oxygen Electroreduction Activities of Carbon-Supported PtW Nanoparticle Catalysts

    SciTech Connect

    Xiong, Liufeng; More, Karren Leslie; He, Ting

    2010-01-01

    Carbon-supported PtW (PtW/C) alloy nanoparticle catalysts with well-controlled particle size, dispersion, and composition uniformity, have been synthesized by wet chemical methods of decomposition of carbonyl cluster complexes, hydrolysis of metal salts, and chemical reactions within a reverse microemulsion. The synthesized PtW/C catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, and energy-dispersive spectroscopy. The catalytic oxygen electroreduction activities were measured by the hydrodynamic rotating disk electrode technique in an acidic electrolyte. The influence of the synthesis method on PtW particle size, size distribution, composition uniformity, and catalytic oxygen electroreduction activity, have been investigated. Among the synthesis methods studied, PtW/C catalysts prepared by the decomposition of carbonyl cluster complexes displayed the best platinum mass activity for oxygen reduction reaction under the current small scale production; a 3.4-fold catalytic enhancement was achieved in comparison to a benchmark Pt/C standard.

  17. Phenol degradation in heterogeneous system generating singlet oxygen employing light activated electropolymerized phenothiazines

    NASA Astrophysics Data System (ADS)

    Piwowar, Katarzyna; Blacha-Grzechnik, Agata; Bernas, Paulina; Zak, Jerzy

    2015-12-01

    Five selected amine-derivatives of phenothiazine were electropolymerized on an ITO/glass substrate and then used in the daylight-activated process to produce in situ singlet oxygen which degrades phenol in a solution. The phenothiazines were immobilized in a simple electrochemical procedure in an acidic solution which led to the formation of an ultrathin transparent polymeric film. All films obtained on the ITO substrate including azure A (AA), azure C (AC), methylene blue (MB), toluidine blue (TBO), and thionine (Th) had a comparable surface coverage at the level of picomoles/cm2. The activity of these materials was then compared and presented in terms of an efficiency of the phenol degradation process in an aqueous solution by photogenerated singlet oxygen. That efficiency was determined by the UV-vis spectroscopy employing a phenol/4-aminoantipyrine complex. All the phenothiazine ultrathin polymeric films were capable of generating the singlet oxygen in the aqueous solution under daylight activation, which was used in the consecutive process of phenol degradation. The highest efficiency at a level of 51.4% and 45.4% was found for the AC/ITO and MB/ITO layers, respectively.

  18. Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Liang, Hai-Wei; Zhuang, Xiaodong; Brüller, Sebastian; Feng, Xinliang; Müllen, Klaus

    2014-09-01

    Development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the oxygen reduction reaction is of significance for many important electrochemical devices, such as fuel cells, metal-air batteries and chlor-alkali electrolysers. Here we report a highly active nitrogen-doped, carbon-based, metal-free oxygen reduction reaction electrocatalyst, prepared by a hard-templating synthesis, for which nitrogen-enriched aromatic polymers and colloidal silica are used as precursor and template, respectively, followed by ammonia activation. Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of nitrogen-doped carbons. Accordingly, the prepared catalysts show the highest oxygen reduction reaction activity (half-wave potential of 0.85 V versus reversible hydrogen electrode with a low loading of 0.1 mg cm-2) in alkaline media among all reported metal-free catalysts. Significantly, when used for constructing the air electrode of zinc-air battery, our metal-free catalyst outperforms the state-of the-art platinum-based catalyst.

  19. Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction.

    PubMed

    Liang, Hai-Wei; Zhuang, Xiaodong; Brüller, Sebastian; Feng, Xinliang; Müllen, Klaus

    2014-01-01

    Development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the oxygen reduction reaction is of significance for many important electrochemical devices, such as fuel cells, metal-air batteries and chlor-alkali electrolysers. Here we report a highly active nitrogen-doped, carbon-based, metal-free oxygen reduction reaction electrocatalyst, prepared by a hard-templating synthesis, for which nitrogen-enriched aromatic polymers and colloidal silica are used as precursor and template, respectively, followed by ammonia activation. Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of nitrogen-doped carbons. Accordingly, the prepared catalysts show the highest oxygen reduction reaction activity (half-wave potential of 0.85 V versus reversible hydrogen electrode with a low loading of 0.1 mg cm(-2)) in alkaline media among all reported metal-free catalysts. Significantly, when used for constructing the air electrode of zinc-air battery, our metal-free catalyst outperforms the state-of the-art platinum-based catalyst. PMID:25229121

  20. Stable platinum nanoclusters on genomic DNA–graphene oxide with a high oxygen reduction reaction activity

    PubMed Central

    Tiwari, Jitendra N.; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N.; Kemp, K. Christian; Le, Nhien H.; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S.

    2013-01-01

    Nanosize platinum clusters with small diameters of 2–4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA–graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA–graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA–graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456

  1. Oxygen activation in NO synthases: evidence for a direct role of the substrate.

    PubMed

    Brunel, Albane; Lang, Jérôme; Couture, Manon; Boucher, Jean-Luc; Dorlet, Pierre; Santolini, Jérôme

    2016-05-01

    Nitric oxide (NO) and the other reactive nitrogen species (RNOS) play crucial patho-physiological roles at the interface of oxidative stress and signalling processes. In mammals, the NO synthases (NOSs) are the source of these reactive nitrogen species, and so to understand the precise biological role of RNOS and NO requires elucidation of the molecular functioning of NOS. Oxygen activation, which is at the core of NOS catalysis, involves a sophisticated sequence of electron and proton transfers. While electron transfer in NOS has received much attention, the proton transfer processes has been scarcely investigated. Here, we report an original approach that combines fast-kinetic techniques coupled to resonance Raman spectroscopy with the use of synthetic analogues of NOS substrate. We characterise Fe(II)-O2 reaction intermediates in the presence of L-arginine (Arg), alkyl- and aryl-guanidines. The presence of new reaction intermediates, such as ferric haem-peroxide, that was formerly postulated, was tracked by analysing the oxygen activation reaction at different times and with different excitation wavelengths. Our results suggest that Arg is not a proton donor, but indirectly intervenes in oxygen activation mechanism by modulating the distal H-bond network and, in particular, by tuning the position and the role of the distal water molecule. This report supports a catalytic model with two proton transfers in step 1 (Arg hydroxylation) but only one proton transfer in step 2 (N(ω)-hydroxy-L-arginine oxidation). PMID:27419044

  2. Inhibitory activities of soluble and bound millet seed phenolics on free radicals and reactive oxygen species.

    PubMed

    Chandrasekara, Anoma; Shahidi, Fereidoon

    2011-01-12

    Oxidative stress, caused by reactive oxygen species (ROS), is responsible for modulating several pathological conditions and aging. Soluble and bound phenolic extracts of commonly consumed millets, namely, kodo, finger (Ravi), finger (local), foxtail, proso, little, and pearl, were investigated for their phenolic content and inhibition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and ROS, namely, hydroxyl radical, peroxyl radical, hydrogen peroxide (H(2)O(2)), hypochlorous acid (HOCl), and singlet oxygen ((1)O(2)). Inhibition of DPPH and hydroxyl radicals was detrmined using electron paramagnetic resonance (EPR) spectroscopy. The peroxyl radical inhibitory activity was measured using the oxygen radical absorbance capacity (ORAC) assay. The scavenging of H(2)O(2), HOCl, and (1)O(2) was evaluated using colorimetric methods. The results were expressed as micromoles of ferulic acid equivalents (FAE) per gram of grain on a dry weight basis. In addition, major hydroxycinnamic acids were identified and quantified using high-performance liquid chromatography (HPLC) and HPLC-mass spectrometry (MS). All millet varieties displayed effective radical and ROS inhibition activities, which generally positively correlated with phenolic contents, except for hydroxyl radical. HPLC analysis revealed the presence of ferulic and p-coumaric acids as major hydroxycinnamic acids in phenolic extract and responsible for the observed effects. Bound extracts of millet contributed 38-99% to ROS scavenging, depending on the variety and the test system employed. Hence, bound phenolics must be included in the evaluation of the antioxidant activity of millets and other cereals. PMID:21133411

  3. A mathematical model relating cortical oxygenated and deoxygenated hemoglobin flows and volumes to neural activity

    NASA Astrophysics Data System (ADS)

    Cornelius, Nathan R.; Nishimura, Nozomi; Suh, Minah; Schwartz, Theodore H.; Doerschuk, Peter C.

    2015-08-01

    Objective. To describe a toolkit of components for mathematical models of the relationship between cortical neural activity and space-resolved and time-resolved flows and volumes of oxygenated and deoxygenated hemoglobin motivated by optical intrinsic signal imaging (OISI). Approach. Both blood flow and blood volume and both oxygenated and deoxygenated hemoglobin and their interconversion are accounted for. Flow and volume are described by including analogies to both resistive and capacitive electrical circuit elements. Oxygenated and deoxygenated hemoglobin and their interconversion are described by generalization of Kirchhoff's laws based on well-mixed compartments. Main results. Mathematical models built from this toolkit are able to reproduce experimental single-stimulus OISI results that are described in papers from other research groups and are able to describe the response to multiple-stimuli experiments as a sublinear superposition of responses to the individual stimuli. Significance. The same assembly of tools from the toolkit but with different parameter values is able to describe effects that are considered distinctive, such as the presence or absence of an initial decrease in oxygenated hemoglobin concentration, indicating that the differences might be due to unique parameter values in a subject rather than different fundamental mechanisms.

  4. Adair-based hemoglobin equilibrium with oxygen, carbon dioxide and hydrogen ion activity.

    PubMed

    Mateják, Marek; Kulhánek, Tomáš; Matoušek, Stanislav

    2015-04-01

    As has been known for over a century, oxygen binding onto hemoglobin is influenced by the activity of hydrogen ions (H⁺), as well as the concentration of carbon dioxide (CO₂). As is also known, the binding of both CO₂and H⁺ on terminal valine-1 residues is competitive. One-parametric situations of these hemoglobin equilibria at specific levels of H⁺, O₂or CO₂are also well described. However, we think interpolating or extrapolating this knowledge into an 'empirical' function of three independent variables has not yet been completely satisfactory. We present a model that integrates three orthogonal views of hemoglobin oxygenation, titration, and carbamination at different temperatures. The model is based only on chemical principles, Adair's oxygenation steps and Van't Hoff equation of temperature dependences. Our model fits the measurements of the Haldane coefficient and CO₂hemoglobin saturation. It also fits the oxygen dissociation curve influenced by simultaneous changes in H⁺, CO₂and O₂, which makes it a strong candidate for integration into more complex models of blood acid-base with gas transport, where any combination of mentioned substances can appear. PMID:25594800

  5. Adsorption of cadmium ions on oxygen surface sites in activated carbon

    SciTech Connect

    Jia, Y.F.; Thomas, K.M.

    2000-02-08

    Various types of oxygen functional groups were introduced onto the surface of coconut shell derived activated carbon by oxidation using nitric acid. Fourier-transform infrared spectroscopy (FTIR), temperature-programmed desorption (TPD), and selective neutralization were used to characterize the surface oxygen functional groups. The oxidized carbons were also heat treated to provide a suite of carbons where the oxygen functional groups of various thermal stabilities were varied progressively. The adsorption of cadmium ions was enhanced dramatically by oxidation of the carbon. The ratio of released protons to adsorbed cadmium ions on oxidized carbon was approximately 2, indicating cation exchange was involved in the process of adsorption. Na{sup +} exchange studies with the oxidized carbon gave a similar ratio. After heat treatment of the oxidized carbons to remove oxygen functional groups, the ratio of H{sup +} released to Cd{sup 2+} adsorbed and the adsorption capacity decreased significantly. Both reversible and irreversible processes were involved in cadmium ion adsorption with reversible adsorption having higher enthalpy. The irreversible adsorption resulted from cation exchange with carboxylic acid groups, whereas the reversible adsorption probably involved physisorption of the partially hydrated cadmium ion.

  6. Oxygen activation and intramolecular C-H bond activation by an amidate-bridged diiron(II) complex.

    PubMed

    Jones, Matthew B; Hardcastle, Kenneth I; Hagen, Karl S; MacBeth, Cora E

    2011-07-18

    A diiron(II) complex containing two μ-1,3-(κN:κO)-amidate linkages has been synthesized using the 2,2',2''-tris(isobutyrylamido)triphenylamine (H(3)L(iPr)) ligand. The resulting diiron complex, 1, reacts with dioxygen (or iodosylbenzene) to effect intramolecular C-H bond activation at the methine position of the ligand isopropyl group. The ligand-activated product, 2, has been isolated and characterized by a variety of methods including X-ray crystallography. Electrospray ionization mass spectroscopy of 2 prepared from(18)O(2) was used to confirm that the oxygen atom incorporated into the ligand framework is derived from molecular oxygen. PMID:21667986

  7. Microbial activities and phosphorus cycling: An application of oxygen isotope ratios in phosphate

    NASA Astrophysics Data System (ADS)

    Stout, Lisa M.; Joshi, Sunendra R.; Kana, Todd M.; Jaisi, Deb P.

    2014-08-01

    Microorganisms carry out biochemical transformations of nutrients that make up their cells. Therefore, understanding how these nutrients are transformed or cycled in natural environments requires knowledge of microbial activity. Commonly used indicators for microbial activity typically include determining microbial respiration by O2/CO2 measurements, cell counts, and measurement of enzyme activities. However, coupled studies on nutrient cycling and microbial activity are not given enough emphasis. Here we apply phosphate oxygen isotope ratios (δ18OP) as a tool for measurement of microbial activity and compare the rate of isotope exchange with methods of measuring microbial activities that are more commonly applied in environmental studies including respiration, dehydrogenase activity, alkaline phosphatase activity, and cell counts. Our results show that different bacteria may have different strategies for P uptake, storage and release, their respiration and consequently expression of DHA and APase activities, but in general the trend of their enzyme activities are comparable. Phosphate δ18OP values correlated well with these other parameters used to measure microbial activity with the strongest linear relationships between δ18OP and CO2 evolution (r = -0.99). Even though the rate of isotope exchange for each microorganism used in this study is different, the rate per unit CO2 respiration showed one general trend, where δ18OP values move towards equilibrium while CO2 is generated. While this suggests that P cycling among microorganisms used in this study can be generalized, further research is needed to determine whether the microorganism-specific isotope exchange trend may occur in natural environments. In summary, phosphate oxygen isotope measurements may offer an alternative for use as a tracer to measure microbial activity in soils, sediments, and many other natural environments.

  8. Reactive oxygen species scavenging activity of Jixueteng evaluated by electron spin resonance (ESR) and photon emission.

    PubMed

    Toyama, Toshizo; Wada-Takahashi, Satoko; Takamichi, Maomi; Watanabe, Kiyoko; Yoshida, Ayaka; Yoshino, Fumihiko; Miyamoto, Chihiro; Maehata, Yojiro; Sugiyama, Shuta; Takahashi, Shun-Suke; Todoki, Kazuo; Lee, Masaichi-Chang-Il; Hamada, Nobushiro

    2014-12-01

    Jixueteng, the dried stem of Spatholobus suberectus Dunn (Leguminosae), is a traditional Chinese herbal medicine that is commonly classified as a herb that promotes blood circulation and can be used to treat blood stasis. The aim of this study was to examine the reactive oxygen species (ROS) scavenging activity of Jixueteng and other herbal medicines. The ROS scavenging activities of the water extracts of Jixueteng, Cnidium officinale and Salvia miltiorrhiza were examined using an electron spin resonance (ESR) technique and faint luminescence measurement. The ESR signal intensities of the superoxide anion (O2·) and hydroxyl radical (HO·) were reduced more by Jixueteng than the other herbal medicines we tested. High photon emission intensity to hydrogen peroxide (H202) and HO· was observed in Jixueteng using the XYZ chemiluminescence system that was used as faint luminescence measurement and analysis. The results of the present study revealed that the ROS scavenging activity of 8% Jixueteng was the strongest among the herbal medicines we tested. It has been reported that Jixueteng includes various polyphenols. In the ROS scavenging activity by Jixueteng, it is supposed that the antioxidant activity caused by these polyphenols would contribute greatly. In conclusion, a water extract component of Jixueteng had potent free radical scavenging activity and an antioxidative effect that inhibited the oxidative actions of O2·⁻, H2O2 and HO·. Therefore, Jixueteng represents a promising therapeutic drug for reactive oxygen-associated pathologies. PMID:25632478

  9. Protection of active aroma compound against moisture and oxygen by encapsulation in biopolymeric emulsion-based edible films.

    PubMed

    Hambleton, Alicia; Debeaufort, Frédéric; Beney, Laurent; Karbowiak, Thomas; Voilley, Andrée

    2008-03-01

    Edible films made of iota-carrageenans display interesting advantages: good mechanical properties, stabilization of emulsions, and reduction of oxygen transfers. Moreover, the addition of lipids to iota-carrageenan-based films to form emulsified films decreases the transfer of water vapor and can be considered to encapsulate active molecules as flavors. The aim of this study was to better understand the influence of the composition and the structure of the carrageenan-based film matrices on its barrier properties and thus on its capacity to encapsulate and to protect active substances encapsulated. Granulometry, differential scanning calorimetry, and Fourier transform infrared spectroscopy characterizations of films with or without flavor and/or fat showed that the flavor compound modifies the film structure because of interactions with the iota-carrageenan chains. The study of the water vapor permeability (WVP), realized at 25 and 35 degrees C and for three relative humidity differentials (30-100%, 30-84%, 30-75%), showed that the flavor compound increases significantly the WVP, especially for the weaker gradients, but has no effect on the oxygen permeability. This study brings new understanding of the role of carrageenan as a film matrix and on its capacity to protect encapsulated flavors. PMID:18257554

  10. STYPu fuel form activities, March 1-September 30, 1985

    SciTech Connect

    Not Available

    1986-01-01

    The SRP portion of this report summarizes production STYPuO2 fuel forms for use in radioisotopic thermoelectric generators (RTG's) in the Plutonium Fuel Form (PuFF) Facility at the Savannah River Plant. The PuFF Facility began producing iridium-encapsulated, 62.5-watt STYPuO2 right circular cylinders for GPHS (General Purpose Heat Source) RTG's in June 1980; this program was completed in December 1983. The PuFF Facility has been placed in a production readiness mode of operation pending funding of additional heat source programs.

  11. Pt5Gd as a highly active and stable catalyst for oxygen electroreduction.

    PubMed

    Escudero-Escribano, María; Verdaguer-Casadevall, Arnau; Malacrida, Paolo; Grønbjerg, Ulrik; Knudsen, Brian P; Jepsen, Anders K; Rossmeisl, Jan; Stephens, Ifan E L; Chorkendorff, Ib

    2012-10-10

    The activity and stability of Pt(5)Gd for the oxygen reduction reaction (ORR) have been studied, using a combination of electrochemical measurements, angle-resolved X-ray photoelectron spectroscopy (AR-XPS), and density functional theory calculations. Sputter-cleaned, polycrystalline Pt(5)Gd shows a 5-fold increase in ORR activity, relative to pure Pt at 0.9 V, approaching the most active in the literature for catalysts prepared in this way. AR-XPS profiles after electrochemical measurements in 0.1 M HClO(4) show the formation of a thick Pt overlayer on the bulk Pt(5)Gd, and the enhanced ORR activity can be explained by means of compressive strain effects. Furthermore, these novel bimetallic electrocatalysts are highly stable, which, in combination with their enhanced activity, makes them very promising for the development of new cathode catalysts for fuel cells. PMID:22998588

  12. Evidence that reactive oxygen species do not mediate NF-κB activation

    PubMed Central

    Hayakawa, Makio; Miyashita, Hiroshi; Sakamoto, Isao; Kitagawa, Masatoshi; Tanaka, Hirofumi; Yasuda, Hideyo; Karin, Michael; Kikugawa, Kiyomi

    2003-01-01

    It has been postulated that reactive oxygen species (ROS) may act as second messengers leading to nuclear factor (NF)-κB activation. This hypothesis is mainly based on the findings that N-acetyl-l-cysteine (NAC) and pyrrolidine dithiocarbamate (PDTC), compounds recognized as potential antioxidants, can inhibit NF-κB activation in a wide variety of cell types. Here we reveal that both NAC and PDTC inhibit NF-κB activation independently of antioxidative function. NAC selectively blocks tumor necrosis factor (TNF)-induced signaling by lowering the affinity of receptor to TNF. PDTC inhibits the IκB–ubiquitin ligase activity in the cell-free system where extracellular stimuli-regulated ROS production does not occur. Furthermore, we present evidence that endogenous ROS produced through Rac/NADPH oxidase do not mediate NF-κB signaling, but instead lower the magnitude of its activation. PMID:12839997

  13. Coupling of total hemoglobin concentration, oxygenation, and neural activity in rat somatosensory cortex.

    PubMed

    Devor, Anna; Dunn, Andrew K; Andermann, Mark L; Ulbert, Istvan; Boas, David A; Dale, Anders M

    2003-07-17

    Recent advances in brain imaging techniques, including functional magnetic resonance imaging (fMRI), offer great promise for noninvasive mapping of brain function. However, the indirect nature of the imaging signals to the underlying neural activity limits the interpretation of the resulting maps. The present report represents the first systematic study with sufficient statistical power to quantitatively characterize the relationship between changes in blood oxygen content and the neural spiking and synaptic activity. Using two-dimensional optical measurements of hemodynamic signals, simultaneous recordings of neural activity, and an event-related stimulus paradigm, we demonstrate that (1) there is a strongly nonlinear relationship between electrophysiological measures of neuronal activity and the hemodynamic response, (2) the hemodynamic response continues to grow beyond the saturation of electrical activity, and (3) the initial increase in deoxyhemoglobin that precedes an increase in blood volume is counterbalanced by an equal initial decrease in oxyhemoglobin. PMID:12873390

  14. A Strategy to Promote the Electrocatalytic Activity of Spinels for Oxygen Reduction by Structure Reversal.

    PubMed

    Wu, Guangping; Wang, Jun; Ding, Wei; Nie, Yao; Li, Li; Qi, Xueqiang; Chen, Siguo; Wei, Zidong

    2016-01-22

    The electrocatalytic performance of a spinel for the oxygen reduction reaction (ORR) can be significantly promoted by reversing its crystalline structure from the normal to the inverse. As the spinel structure reversed, the activation and cleavage of O-O bonds are accelerated owing to a dissimilarity effect of the distinct metal atoms co-occupying octahedral sites. The Co(II)Fe(III)Co(III)O4 spinel with the Fe and Co co-occupying inverse structure exhibits an excellent ORR activity, which even exceeds that of the state-of-the-art commercial Pt/C by 42 mV in alkaline medium. PMID:26663768

  15. Structure-activity relationship in high-performance iron-based electrocatalysts for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Song, Ping; Wang, Ying; Pan, Jing; Xu, Weilin; Zhuang, Lin

    2015-12-01

    A sustainable Iron (Fe), Nitrogen (N) co-doped high performance Fe-Nx/C electrocatalyst for oxygen reduction reaction (ORR) is synthesized simply based on nitric acid oxidation of cheap carbon black. The obtained optimal nonprecious metal electrocatalyst shows high ORR performance in both alkaline and acidic conditions and possesses appreciable performance/price ratio due to its low cost. Furthermore, the structure-activity relationship of different active sites on Fe-Nx/C is revealed systematically: Fe-N4/2-C > Fe4-N-C > N-C >> Fe4-C ≥ C, from both experimental and theoretical points of view.

  16. Transcript levels of antioxidative genes and oxygen radical scavenging enzyme activities in chilled zucchini squash in response to superatmospheric oxygen

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The transcript levels of antioxidative genes including Mn-superoxide dismutase (Mn-SOD), Cu/Zn SOD, ascorbate peroxidise (APX), and catalase (CAT) do not vary significantly during storage at 5 °C with high oxygen treatment in freshly harvested zucchini squash (Cucurbita pepo L. cv. Elite). However, ...

  17. Design Insights for Tuning the Electrocatalytic Activity of Perovskite Oxides for the Oxygen Evolution Reaction

    SciTech Connect

    Malkhandi, S; Trinh, P; Manohar, AK; Manivannan, A; Balasubramanian, M; Prakash, GKS; Narayanan, SR

    2015-04-16

    Rechargeable metal-air batteries and water electrolyzers based on aqueous alkaline electrolytes hold the potential to be sustainable solutions to address the challenge of storing large amounts of electrical energy generated from solar and wind resources. For these batteries and electrolyzers to be economically viable, it is essential to have efficient, durable, and inexpensive electrocatalysts for the oxygen evolution reaction. In this article, we describe new insights for predicting and tuning the activity of inexpensive transition metal oxides for designing efficient and inexpensive electrocatalysts. We have focused on understanding the factors determining the electrocatalytic activity for oxygen evolution in a strong alkaline medium. To this end, we have conducted a systematic investigation of nanophase calcium-doped lanthanum cobalt manganese oxide, an example of a mixed metal oxide that can be tuned for its electrocatalytic activity by varying the transition metal composition. Using X-ray absorption spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS), electrochemical polarization experiments, and analysis of mechanisms, we have identified the key determinants of electrocatalytic activity. We have found that the Tafel slopes are determined by the oxidation states and the bond energy of the surface intermediates of Mn-OH and Co-OH bonds while the catalytic activity increased with the average d-electron occupancy of the sigma* orbital of the M-OH bond. We anticipate that such understanding will be very useful in predicting the behavior of other transition metal oxide catalysts.

  18. Khat (Catha edulis) generates reactive oxygen species and promotes hepatic cell apoptosis via MAPK activation.

    PubMed

    Abid, Morad Dirhem Naji; Chen, Juan; Xiang, Min; Zhou, Jie; Chen, Xiaoping; Gong, Feili

    2013-08-01

    A number of studies have suggested an association between khat (Catha edulis) chewing and acute liver lesions or chronic liver disease. However, little is known about the effects of khat on hepatic cells. In the current study, we investigated the mechanism behind khat-induced apoptosis in the L02 human hepatic cell line. We used cell growth inhibition assay, flow cytometry and Hoechst 33258 staining to measure hepatocyte apoptosis induced by khat. Western blot analysis was used to detect the expression levels of caspase-8 and -9, as well as those of Bax and Bcl-2. We also measured reactive oxygen species production. The results indicated that khat induced significant hepatocyte apoptosis in L02 cells. We found that khat activated caspase-8 and -9, upregulated Bax protein expression and downregulated Bcl-2 expression levels, which resulted in the coordination of apoptotic signals. Khat-induced hepatocyte apoptosis is primarily regulated through the sustained activation of the c-Jun NH2-terminal kinase (JNK) pathway and only partially via the extracellular signal-regulated kinase (ERK) cascade. Furthermore, the khat-induced reactive oxygen species (ROS) production and the activation of the ROS scavenger, N-acetyl-L-cysteine (NAC), attenuated the khat-induced activation of JNK and ERK. Our results demonstrate that khat triggers the generation of intracellular ROS and sequentially induces the sustainable activation of JNK, which in turn results in a decrease in cell viability and an increase in cell apoptosis. PMID:23708648

  19. Enhancing Electrocatalytic Oxygen Reduction on Nitrogen-Doped Graphene by Active Sites Implantation

    NASA Astrophysics Data System (ADS)

    Feng, Leiyu; Yang, Lanqin; Huang, Zujing; Luo, Jingyang; Li, Mu; Wang, Dongbo; Chen, Yinguang

    2013-11-01

    The shortage of nitrogen active sites and relatively low nitrogen content result in unsatisfying eletrocatalytic activity and durability of nitrogen-doped graphene (NG) for oxygen reduction reaction (ORR). Here we report a novel approach to substantially enhance electrocatalytic oxygen reduction on NG electrode by the implantation of nitrogen active sites with mesoporous graphitic carbon nitride (mpg-C3N4). Electrochemical characterization revealed that in neutral electrolyte the resulting NG (I-NG) exhibited super electrocatalytic activity (completely 100% of four-electron ORR pathway) and durability (nearly no activity change after 100000 potential cyclings). When I-NG was used as cathode catalyst in microbial fuel cells (MFCs), power density and its drop percentage were also much better than the NG and Pt/C ones, demonstrating that the current I-NG was a perfect alternative to Pt/C and offered a new potential for constructing high-performance and less expensive cathode which is crucial for large-scale application of MFC technology.

  20. Enhancing Electrocatalytic Oxygen Reduction on Nitrogen-Doped Graphene by Active Sites Implantation

    PubMed Central

    Feng, Leiyu; Yang, Lanqin; Huang, Zujing; Luo, Jingyang; Li, Mu; Wang, Dongbo; Chen, Yinguang

    2013-01-01

    The shortage of nitrogen active sites and relatively low nitrogen content result in unsatisfying eletrocatalytic activity and durability of nitrogen-doped graphene (NG) for oxygen reduction reaction (ORR). Here we report a novel approach to substantially enhance electrocatalytic oxygen reduction on NG electrode by the implantation of nitrogen active sites with mesoporous graphitic carbon nitride (mpg-C3N4). Electrochemical characterization revealed that in neutral electrolyte the resulting NG (I-NG) exhibited super electrocatalytic activity (completely 100% of four-electron ORR pathway) and durability (nearly no activity change after 100000 potential cyclings). When I-NG was used as cathode catalyst in microbial fuel cells (MFCs), power density and its drop percentage were also much better than the NG and Pt/C ones, demonstrating that the current I-NG was a perfect alternative to Pt/C and offered a new potential for constructing high-performance and less expensive cathode which is crucial for large-scale application of MFC technology. PMID:24264379

  1. Developing mononuclear copper-active-oxygen complexes relevant to reactive intermediates of biological oxidation reactions.

    PubMed

    Itoh, Shinobu

    2015-07-21

    Active-oxygen species generated on a copper complex play vital roles in several biological and chemical oxidation reactions. Recent attention has been focused on the reactive intermediates generated at the mononuclear copper active sites of copper monooxygenases such as dopamine β-monooxygenase (DβM), tyramine β-monooxygenase (TβM), peptidylglycine-α-hydroxylating monooxygenase (PHM), and polysaccharide monooxygenases (PMO). In a simple model system, reaction of O2 and a reduced copper(I) complex affords a mononuclear copper(II)-superoxide complex or a copper(III)-peroxide complex, and subsequent H(•) or e(-)/H(+) transfer, which gives a copper(II)-hydroperoxide complex. A more reactive species such as a copper(II)-oxyl radical type species could be generated via O-O bond cleavage of the peroxide complex. However, little had been explored about the chemical properties and reactivity of the mononuclear copper-active-oxygen complexes due to the lack of appropriate model compounds. Thus, a great deal of effort has recently been made to develop efficient ligands that can stabilize such reactive active-oxygen complexes in synthetic modeling studies. In this Account, I describe our recent achievements of the development of a mononuclear copper(II)-(end-on)superoxide complex using a simple tridentate ligand consisting of an eight-membered cyclic diamine with a pyridylethyl donor group. The superoxide complex exhibits a similar structure (four-coordinate tetrahedral geometry) and reactivity (aliphatic hydroxylation) to those of a proposed reactive intermediate of copper monooxygenases. Systematic studies based on the crystal structures of copper(I) and copper(II) complexes of the related tridentate supporting ligands have indicated that the rigid eight-membered cyclic diamine framework is crucial for controlling the geometry and the redox potential, which are prerequisites for the generation of such a unique mononuclear copper(II)-(end-on)superoxide complex

  2. Reactive oxygen species in signalling the transcriptional activation of WIPK expression in tobacco.

    PubMed

    Xu, Juan; Yang, Kwang-Yeol; Yoo, Seung Jin; Liu, Yidong; Ren, Dongtao; Zhang, Shuqun

    2014-07-01

    Plant mitogen-activated protein kinases represented by tobacco WIPK (wounding-induced protein kinase) and its orthologs in other species are unique in their regulation at transcriptional level in response to stress and pathogen infection. We previously demonstrated that transcriptional activation of WIPK is essential for induced WIPK activity, and activation of salicylic acid-induced protein kinase (SIPK) by the constitutively active NtMEK2(DD) is sufficient to induce WIPK gene expression. Here, we report that the effect of SIPK on WIPK gene expression is mediated by reactive oxygen species (ROS). Using a combination of pharmacological and gain-of-function transgenic approaches, we studied the relationship among SIPK activation, WIPK gene activation in response to fungal cryptogein, light-dependent ROS generation in chloroplasts, and ROS generated via NADPH oxidase. In the conditional gain-of-function GVG-NtMEK2(DD) transgenic tobacco, induction of WIPK expression is dependent on the ROS generation in chloroplasts. Consistently, methyl viologen, an inducer of ROS generation in chloroplasts, highly activated WIPK expression. In addition to chloroplast-originated ROS, H(2)O(2) generated from the cell-surface NADPH oxidase could also activate WIPK gene expression, and inhibition of cryptogein-induced ROS generation also abolished WIPK gene activation. Our data demonstrate that WIPK gene activation is mediated by ROS, which provides a mechanism by which ROS influence cellular signalling processes in plant stress/defence response. PMID:24392654

  3. Tuning the surface oxygen concentration of {111} surrounded ceria nanocrystals for enhanced photocatalytic activities

    NASA Astrophysics Data System (ADS)

    Younis, Adnan; Chu, Dewei; Kaneti, Yusuf Valentino; Li, Sean

    2015-12-01

    For oxide semiconductors, the morphology, particle size and oxygen vacancies are usually considered as key influential parameters for photocatalytic degradation of organic pollutants/dyes. It is widely accepted that cation doping not only modifies their phase and microstructures but also introduces variations in oxygen vacancy concentration. Herein, we report the fabrication of sub-10 nm sized pure and indium doped CeO2 nanocrystals (NCs) via a facile, green hydrothermal method for the investigation of photocatalytic activities. X-ray diffraction and transmission electron microscopy were employed to examine the crystal phase and morphology of the as-prepared nanocrystals. Raman and X-ray photoelectron spectroscopy techniques were implemented to investigate the presence and variations in oxygen vacancy concentration in un-doped and indium doped CeO2 nanocrystals. The photocatalytic activity results revealed that 10 at% doping is the optimal indium doping level to demonstrate superior dye removal efficiency (~40%) over un-doped and doped CeO2 NCs. Moreover, the 10% In-doped CeO2 nanocrystals expressed excellent cycling stability and superior photocatalytic performance toward other dye pollutants. Finally, on the basis of our findings, a possible photocatalytic mechanism in which indium doping can generate more surface oxygen vacancies in the ceria lattice which delay the electron-hole recombination rates, thus increasing the lifetime of electron-hole separation for enhanced photocatalytic performances was proposed.For oxide semiconductors, the morphology, particle size and oxygen vacancies are usually considered as key influential parameters for photocatalytic degradation of organic pollutants/dyes. It is widely accepted that cation doping not only modifies their phase and microstructures but also introduces variations in oxygen vacancy concentration. Herein, we report the fabrication of sub-10 nm sized pure and indium doped CeO2 nanocrystals (NCs) via a facile

  4. High performance electrodes in vanadium redox flow batteries through oxygen-enriched thermal activation

    NASA Astrophysics Data System (ADS)

    Pezeshki, Alan M.; Clement, Jason T.; Veith, Gabriel M.; Zawodzinski, Thomas A.; Mench, Matthew M.

    2015-10-01

    The roundtrip electrochemical energy efficiency is improved from 63% to 76% at a current density of 200 mA cm-2 in an all-vanadium redox flow battery (VRFB) by utilizing modified carbon paper electrodes in the high-performance no-gap design. Heat treatment of the carbon paper electrodes in a 42% oxygen/58% nitrogen atmosphere increases the electrochemically wetted surface area from 0.24 to 51.22 m2 g-1, resulting in a 100-140 mV decrease in activation overpotential at operationally relevant current densities. An enriched oxygen environment decreases the amount of treatment time required to achieve high surface area. The increased efficiency and greater depth of discharge doubles the total usable energy stored in a fixed amount of electrolyte during operation at 200 mA cm-2.

  5. EFFECT OF MOLECULAR OXYGEN ON THE ACTIVATED CARBON ADSORPTION OF NATURAL ORGANIC MATTER IN OHIO RIVER WATER

    EPA Science Inventory

    Recently published data show that the adsorptive capacity of granular activated carbon for phenois increases significantly in the presence of molecular oxygen (Vidic, Suidan,Traegner and Nakhla, 1990). in this study, the effect of molecular oxygen on the adsorptive capacity of a...

  6. The MOSDEF Survey: Detection of [O III]λ4363 and the Direct-method Oxygen Abundance of a Star-forming Galaxy at z = 3.08

    NASA Astrophysics Data System (ADS)

    Sanders, Ryan L.; Shapley, Alice E.; Kriek, Mariska; Reddy, Naveen A.; Freeman, William R.; Coil, Alison L.; Siana, Brian; Mobasher, Bahram; Shivaei, Irene; Price, Sedona H.; de Groot, Laura

    2016-07-01

    We present measurements of the electron-temperature-based oxygen abundance for a highly star-forming galaxy at z = 3.08, COSMOS-1908. This is the highest redshift at which [O iii]λ4363 has been detected and the first time that this line has been measured at z\\gt 2. We estimate an oxygen abundance of 12+{log}({{O}}/{{H}})={8.00}-0.14+0.13. This galaxy is a low-mass ({10}9.3 {M}ȯ ), highly star-forming (∼50 {M}ȯ yr‑1) system that hosts a young stellar population (∼160 Myr). We investigate the physical conditions of the ionized gas in COSMOS-1908 and find that this galaxy has a high ionization parameter, little nebular reddening (E{(B-V)}{{gas}}\\lt 0.14), and a high electron density ({n}e∼ 500 cm‑3). We compare the ratios of strong oxygen, neon, and hydrogen lines to the direct-method oxygen abundance for COSMOS-1908 and additional star-forming galaxies at z=0-1.8 with [O iii]λ4363 measurements and show that galaxies at z∼ 1{--}3 follow the same strong-line correlations as galaxies in the local universe. This agreement suggests that the relationship between ionization parameter and O/H is similar for z∼ 0 and high-redshift galaxies. These results imply that metallicity calibrations based on lines of oxygen, neon, and hydrogen do not strongly evolve with redshift and can reliably estimate abundances out to z∼ 3, paving the way for robust measurements of the evolution of the mass–metallicity relation to high redshift. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

  7. Formation of Nano-Bacteria-Like Flow Textures Formed at Oxygen-Rich Air Condition of Shock Wave Reaction

    NASA Astrophysics Data System (ADS)

    Miura, Y.; Tanosaki, T.

    2011-03-01

    Nano-flow textures with irregular shapes are obtained by shock impact on carbon-fibers with oxygen-rich air condition (not at vacuum condition), which are different with nano-bacteria texture of the martian meteorite with regular nano-flow textures.

  8. Mechanically driven activation of polyaniline into its conductive form.

    PubMed

    Baytekin, Bilge; Baytekin, H Tarik; Grzybowski, Bartosz A

    2014-07-01

    Mechanical treatment of polymers produces surface cations and anions which, as demonstrated here for the first time, can drive chemical reactions. In particular, it is shown that such a mechanical treatment transforms nonconductive polyaniline into its conductive form. These results provide a mechanical means of patterning conductive polymers and also coating small polymer objects with conductive polyaniline films preventing accumulation of static electricity. PMID:24824971

  9. Submaximal oxygen uptake kinetics, functional mobility, and physical activity in older adults with heart failure and reduced ejection fraction

    PubMed Central

    Hummel, Scott L; Herald, John; Alpert, Craig; Gretebeck, Kimberlee A; Champoux, Wendy S; Dengel, Donald R; Vaitkevicius, Peter V; Alexander, Neil B

    2016-01-01

    Background Submaximal oxygen uptake measures are more feasible and may better predict clinical cardiac outcomes than maximal tests in older adults with heart failure (HF). We examined relationships between maximal oxygen uptake, submaximal oxygen kinetics, functional mobility, and physical activity in older adults with HF and reduced ejection fraction. Methods Older adults with HF and reduced ejection fraction (n = 25, age 75 ± 7 years) were compared to 25 healthy age- and gender-matched controls. Assessments included a maximal treadmill test for peak oxygen uptake (VO2peak), oxygen uptake kinetics at onset of and on recovery from a submaximal treadmill test, functional mobility testing [Get Up and Go (GUG), Comfortable Gait Speed (CGS), Unipedal Stance (US)], and self-reported physical activity (PA). Results Compared to controls, HF had worse performance on GUG, CGS, and US, greater delays in submaximal oxygen uptake kinetics, and lower PA. In controls, VO2peak was more strongly associated with functional mobility and PA than submaximal oxygen uptake kinetics. In HF patients, submaximal oxygen uptake kinetics were similarly associated with GUG and CGS as VO2peak, but weakly associated with PA. Conclusions Based on their mobility performance, older HF patients with reduced ejection fraction are at risk for adverse functional outcomes. In this population, submaximal oxygen uptake measures may be equivalent to VO2 peak in predicting functional mobility, and in addition to being more feasible, may provide better insight into how aerobic function relates to mobility in older adults with HF. PMID:27594875

  10. Breakpoints in ventilation, cerebral and muscle oxygenation, and muscle activity during an incremental cycling exercise

    PubMed Central

    Racinais, Sebastien; Buchheit, Martin; Girard, Olivier

    2014-01-01

    The aim of this study was to locate the breakpoints of cerebral and muscle oxygenation and muscle electrical activity during a ramp exercise in reference to the first and second ventilatory thresholds. Twenty-five cyclists completed a maximal ramp test on an electromagnetically braked cycle-ergometer with a rate of increment of 25 W/min. Expired gazes (breath-by-breath), prefrontal cortex and vastus lateralis (VL) oxygenation [Near-infrared spectroscopy (NIRS)] together with electromyographic (EMG) Root Mean Square (RMS) activity for the VL, rectus femoris (RF), and biceps femoris (BF) muscles were continuously assessed. There was a non-linear increase in both cerebral deoxyhemoglobin (at 56 ± 13% of the exercise) and oxyhemoglobin (56 ± 8% of exercise) concomitantly to the first ventilatory threshold (57 ± 6% of exercise, p > 0.86, Cohen's d < 0.1). Cerebral deoxyhemoglobin further increased (87 ± 10% of exercise) while oxyhemoglobin reached a plateau/decreased (86 ± 8% of exercise) after the second ventilatory threshold (81 ± 6% of exercise, p < 0.05, d > 0.8). We identified one threshold only for muscle parameters with a non-linear decrease in muscle oxyhemoglobin (78 ± 9% of exercise), attenuation in muscle deoxyhemoglobin (80 ± 8% of exercise), and increase in EMG activity of VL (89 ± 5% of exercise), RF (82 ± 14% of exercise), and BF (85 ± 9% of exercise). The thresholds in BF and VL EMG activity occurred after the second ventilatory threshold (p < 0.05, d > 0.6). Our results suggest that the metabolic and ventilatory events characterizing this latter cardiopulmonary threshold may affect both cerebral and muscle oxygenation levels, and in turn, muscle recruitment responses. PMID:24782786

  11. Reconstructing ecosystem functions of the active microbial community of the Baltic Sea oxygen depleted sediments.

    PubMed

    Thureborn, Petter; Franzetti, Andrea; Lundin, Daniel; Sjöling, Sara

    2016-01-01

    Baltic Sea deep water and sediments hold one of the largest anthropogenically induced hypoxic areas in the world. High nutrient input and low water exchange result in eutrophication and oxygen depletion below the halocline. As a consequence at Landsort Deep, the deepest point of the Baltic Sea, anoxia in the sediments has been a persistent condition over the past decades. Given that microbial communities are drivers of essential ecosystem functions we investigated the microbial community metabolisms and functions of oxygen depleted Landsort Deep sediments by metatranscriptomics. Results show substantial expression of genes involved in protein metabolism demonstrating that the Landsort Deep sediment microbial community is active. Identified expressed gene suites of metabolic pathways with importance for carbon transformation including fermentation, dissimilatory sulphate reduction and methanogenesis were identified. The presence of transcripts for these metabolic processes suggests a potential for heterotrophic-autotrophic community synergism and indicates active mineralisation of the organic matter deposited at the sediment as a consequence of the eutrophication process. Furthermore, cyanobacteria, probably deposited from the water column, are transcriptionally active in the anoxic sediment at this depth. Results also reveal high abundance of transcripts encoding integron integrases. These results provide insight into the activity of the microbial community of the anoxic sediment at the deepest point of the Baltic Sea and its possible role in ecosystem functioning. PMID:26823996

  12. Involvement of Activated Oxygen in Nitrate-Induced Senescence of Pea Root Nodules.

    PubMed Central

    Escuredo, P. R.; Minchin, F. R.; Gogorcena, Y.; Iturbe-Ormaetxe, I.; Klucas, R. V.; Becana, M.

    1996-01-01

    The effect of short-term nitrate application (10 mM, 0-4 d) on nitrogenase (N2ase) activity, antioxidant defenses, and related parameters was investigated in pea (Pisum sativum L. cv Frilene) nodules. The response of nodules to nitrate comprised two stages. In the first stage (0-2 d), there were major decreases in N2ase activity and N2ase-linked respiration and concomitant increases in carbon cost of N2ase and oxygen diffusion resistance of nodules. There was no apparent oxidative damage, and the decline in N2ase activity was, to a certain extent, reversible. The second stage (>2 d) was typical of a senescent, essentially irreversible process. It was characterized by moderate increases in oxidized proteins and catalytic Fe and by major decreases in antioxidant enzymes and metabolites. The restriction in oxygen supply to bacteroids may explain the initial decline in N2ase activity. The decrease in antioxidant protection is not involved in this process and is not specifically caused by nitrate, since it also occurs with drought stress. However, comparison of nitrate- and drought-induced senescence shows an important difference: there is no lipid degradation or lipid peroxide accumulation with nitrate, indicating that lipid peroxidation is not necessarily involved in nodule senescence. PMID:12226252

  13. Reactive Oxygen Species in the Paraventricular Nucleus of the Hypothalamus Alter Sympathetic Activity During Metabolic Syndrome

    PubMed Central

    Cruz, Josiane C.; Flôr, Atalia F. L.; França-Silva, Maria S.; Balarini, Camille M.; Braga, Valdir A.

    2015-01-01

    The paraventricular nucleus of the hypothalamus (PVN) contains heterogeneous populations of neurons involved in autonomic and neuroendocrine regulation. The PVN plays an important role in the sympathoexcitatory response to increasing circulating levels of angiotensin II (Ang-II), which activates AT1 receptors in the circumventricular organs (OCVs), mainly in the subfornical organ (SFO). Circulating Ang-II induces a de novo synthesis of Ang-II in SFO neurons projecting to pre-autonomic PVN neurons. Activation of AT1 receptors induces intracellular increases in reactive oxygen species (ROS), leading to increases in sympathetic nerve activity (SNA). Chronic sympathetic nerve activation promotes a series of metabolic disorders that characterizes the metabolic syndrome (MetS): dyslipidemia, hyperinsulinemia, glucose intolerance, hyperleptinemia and elevated plasma hormone levels, such as noradrenaline, glucocorticoids, leptin, insulin, and Ang-II. This review will discuss the contribution of our laboratory and others regarding the sympathoexcitation caused by peripheral Ang-II-induced reactive oxygen species along the subfornical organ and paraventricular nucleus of the hypothalamus. We hypothesize that this mechanism could be involved in metabolic disorders underlying MetS. PMID:26779026

  14. Reconstructing ecosystem functions of the active microbial community of the Baltic Sea oxygen depleted sediments

    PubMed Central

    Franzetti, Andrea; Lundin, Daniel; Sjöling, Sara

    2016-01-01

    Baltic Sea deep water and sediments hold one of the largest anthropogenically induced hypoxic areas in the world. High nutrient input and low water exchange result in eutrophication and oxygen depletion below the halocline. As a consequence at Landsort Deep, the deepest point of the Baltic Sea, anoxia in the sediments has been a persistent condition over the past decades. Given that microbial communities are drivers of essential ecosystem functions we investigated the microbial community metabolisms and functions of oxygen depleted Landsort Deep sediments by metatranscriptomics. Results show substantial expression of genes involved in protein metabolism demonstrating that the Landsort Deep sediment microbial community is active. Identified expressed gene suites of metabolic pathways with importance for carbon transformation including fermentation, dissimilatory sulphate reduction and methanogenesis were identified. The presence of transcripts for these metabolic processes suggests a potential for heterotrophic-autotrophic community synergism and indicates active mineralisation of the organic matter deposited at the sediment as a consequence of the eutrophication process. Furthermore, cyanobacteria, probably deposited from the water column, are transcriptionally active in the anoxic sediment at this depth. Results also reveal high abundance of transcripts encoding integron integrases. These results provide insight into the activity of the microbial community of the anoxic sediment at the deepest point of the Baltic Sea and its possible role in ecosystem functioning. PMID:26823996

  15. Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution.

    PubMed

    Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

    2015-01-01

    Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co(3+/4+) ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions. PMID:26456525

  16. Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution

    NASA Astrophysics Data System (ADS)

    Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

    2015-10-01

    Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions.

  17. Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution

    PubMed Central

    Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

    2015-01-01

    Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions. PMID:26456525

  18. Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

    DOEpatents

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2010-08-03

    A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

  19. Cellular Metabolic Activity and the Oxygen and Hydrogen Stable Isotope Composition of Intracellular Water and Metabolites

    NASA Astrophysics Data System (ADS)

    Kreuzer-Martin, H. W.; Hegg, E. L.

    2008-12-01

    Intracellular water is an important pool of oxygen and hydrogen atoms for biosynthesis. Intracellular water is usually assumed to be isotopically identical to extracellular water, but an unexpected experimental result caused us to question this assumption. Heme O isolated from Escherichia coli cells grown in 95% H218O contained only a fraction of the theoretical value of labeled oxygen at a position where the O atom was known to be derived from water. In fact, fewer than half of the oxygen atoms were labeled. In an effort to explain this surprising result, we developed a method to determine the isotope ratios of intracellular water in cultured cells. The results of our experiments showed that during active growth, up to 70% of the oxygen atoms and 50% of the hydrogen atoms in the intracellular water of E. coli are generated during metabolism and can be isotopically distinct from extracellular water. The fraction of isotopically distinct atoms was substantially less in stationary phase and chilled cells, consistent with our hypothesis that less metabolically-generated water would be present in cells with lower metabolic activity. Our results were consistent with and explained the result of the heme O labeling experiment. Only about 40% of the O atoms on the heme O molecule were labeled because, presumably, only about 40% of the water inside the cells was 18O water that had diffused in from the culture medium. The rest of the intracellular water contained 16O atoms derived from either nutrients or atmospheric oxygen. To test whether we could also detect metabolically-derived hydrogen atoms in cellular constituents, we isolated fatty acids from log-phase and stationary phase E. coli and determined the H isotope ratios of individual fatty acids. The results of these experiments showed that environmental water contributed more H atoms to fatty acids isolated in stationary phase than to the same fatty acids isolated from log-phase cells. Stable isotope analyses of

  20. Thrombomodulin Binding Selects the Catalytically Active Form of Thrombin.

    PubMed

    Handley, Lindsey D; Treuheit, Nicholas A; Venkatesh, Varun J; Komives, Elizabeth A

    2015-11-01

    Human α-thrombin is a serine protease with dual functions. Thrombin acts as a procoagulant, cleaving fibrinogen to make the fibrin clot, but when bound to thrombomodulin (TM), it acts as an anticoagulant, cleaving protein C. A minimal TM fragment consisting of the fourth, fifth, and most of the sixth EGF-like domain (TM456m) that has been prepared has much improved solubility, thrombin binding capacity, and anticoagulant activity versus those of previous TM456 constructs. In this work, we compare backbone amide exchange of human α-thrombin in three states: apo, D-Phe-Pro-Arg-chloromethylketone (PPACK)-bound, and TM456m-bound. Beyond causing a decreased level of amide exchange at their binding sites, TM and PPACK both cause a decreased level of amide exchange in other regions including the γ-loop and the adjacent N-terminus of the heavy chain. The decreased level of amide exchange in the N-terminus of the heavy chain is consistent with the historic model of activation of serine proteases, which involves insertion of this region into the β-barrel promoting the correct conformation of the catalytic residues. Contrary to crystal structures of thrombin, hydrogen-deuterium exchange mass spectrometry results suggest that the conformation of apo-thrombin does not yet have the N-terminus of the heavy chain properly inserted for optimal catalytic activity, and that binding of TM allosterically promotes the catalytically active conformation. PMID:26468766

  1. Forming a Learning Culture to Promote Fracture Prevention Activities

    ERIC Educational Resources Information Center

    Hjalmarson, Helene V.; Strandmark, Margaretha

    2012-01-01

    Purpose: The purpose of this paper is to explore interprofessional experiences of incorporating fracture prevention activities in clinical practice inspired by an empowerment approach. Design/methodology/approach: Data collection consisted primarily of focus groups interviews, systematized and analyzed by the grounded theory method. The study took…

  2. Comparative studies of singlet oxygen generation by fullerenes and single- and multilayer carbon nanotubes in the form of solid-phase film coatings

    NASA Astrophysics Data System (ADS)

    Bagrov, I. V.; Kiselev, V. M.; Kislyakov, I. M.; Starodubtsev, A. M.; Burchinov, A. N.

    2015-03-01

    Four types of carbon nanoparticles: C60 fullerene (crystalline and amorphized) and single- and multilayer carbon nanotubes were studied in the form of solid-phase film coatings for the purpose of obtaining singlet oxygen generation in the process of irradiation of these materials by continuous-wave broadband light-emitting diodes in the visible region spectra and by a monopulse 532-nm neodymium laser.

  3. Polydopamine-Coated Manganese Complex/Graphene Nanocomposite for Enhanced Electrocatalytic Activity Towards Oxygen Reduction

    PubMed Central

    Parnell, Charlette M.; Chhetri, Bijay; Brandt, Andrew; Watanabe, Fumiya; Nima, Zeid A.; Mudalige, Thilak K.; Biris, Alexandru S.; Ghosh, Anindya

    2016-01-01

    Platinum electrodes are commonly used electrocatalysts for oxygen reduction reactions (ORR) in fuel cells. However, this material is not economical due to its high cost and scarcity. We prepared an Mn(III) catalyst supported on graphene and further coated with polydopamine, resulting in superior ORR activity compared to the uncoated PDA structures. During ORR, a peak potential at 0.433 V was recorded, which is a significant shift compared to the uncoated material’s −0.303 V (both versus SHE). All the materials reduced oxygen in a wide pH range via a four-electron pathway. Rotating disk electrode and rotating ring disk electrode studies of the polydopamine-coated material revealed ORR occurring via 4.14 and 4.00 electrons, respectively. A rate constant of 6.33 × 106 mol−1s−1 was observed for the polydopamine-coated material–over 4.5 times greater than the uncoated nanocomposite and superior to those reported for similar carbon-supported metal catalysts. Simply integrating an inexpensive bioinspired polymer coating onto the Mn-graphene nanocomposite increased ORR performance significantly, with a peak potential shift of over +730 mV. This indicates that the material can reduce oxygen at a higher rate but with lower energy usage, revealing its excellent potential as an ORR electrocatalyst in fuel cells. PMID:27528439

  4. Singlet molecular oxygen-quenching activity of carotenoids: relevance to protection of the skin from photoaging

    PubMed Central

    Terao, Junji; Minami, Yuko; Bando, Noriko

    2011-01-01

    Carotenoids are known to be potent quenchers of singlet molecular oxygen [O2 (1Δg)]. Solar light-induced photooxidative stress causes skin photoaging by accelerating the generation of reactive oxygen species via photodynamic actions in which O2 (1Δg) can be generated by energy transfer from excited sensitizers. Thus, dietary carotenoids seem to participate in the prevention of photooxidative stress by accumulating as antioxidants in the skin. An in vivo study using hairless mice clarified that a O2 (1Δg) oxygenation-specific peroxidation product of cholesterol, cholesterol 5α-hydroperoxide, accumulates in skin lipids due to ultraviolet-A exposure. Matrix metalloproteinase-9, a metalloproteinase family enzyme responsible for the formation of wrinkles and sagging, was enhanced in the skin of ultraviolet-A -irradiated hairless mice. The activation of metalloproteinase-9 and the accumulation of 5α-hydroperoxide, as well as formation of wrinkles and sagging, were lowered in mice fed a β-carotene diet. These results strongly suggest that dietary β-carotene prevents the expression of metalloproteinase-9 (at least in part), by inhibiting the photodynamic action involving the formation of 5α-hydroperoxide in the skin. Intake of β-Carotene therefore appears to be helpful in slowing down ultraviolet-A -induced photoaging in human skin by acting as a O2 (1Δg) quencher. PMID:21297913

  5. Polydopamine-Coated Manganese Complex/Graphene Nanocomposite for Enhanced Electrocatalytic Activity Towards Oxygen Reduction.

    PubMed

    Parnell, Charlette M; Chhetri, Bijay; Brandt, Andrew; Watanabe, Fumiya; Nima, Zeid A; Mudalige, Thilak K; Biris, Alexandru S; Ghosh, Anindya

    2016-01-01

    Platinum electrodes are commonly used electrocatalysts for oxygen reduction reactions (ORR) in fuel cells. However, this material is not economical due to its high cost and scarcity. We prepared an Mn(III) catalyst supported on graphene and further coated with polydopamine, resulting in superior ORR activity compared to the uncoated PDA structures. During ORR, a peak potential at 0.433 V was recorded, which is a significant shift compared to the uncoated material's -0.303 V (both versus SHE). All the materials reduced oxygen in a wide pH range via a four-electron pathway. Rotating disk electrode and rotating ring disk electrode studies of the polydopamine-coated material revealed ORR occurring via 4.14 and 4.00 electrons, respectively. A rate constant of 6.33 × 10(6) mol(-1)s(-1) was observed for the polydopamine-coated material-over 4.5 times greater than the uncoated nanocomposite and superior to those reported for similar carbon-supported metal catalysts. Simply integrating an inexpensive bioinspired polymer coating onto the Mn-graphene nanocomposite increased ORR performance significantly, with a peak potential shift of over +730 mV. This indicates that the material can reduce oxygen at a higher rate but with lower energy usage, revealing its excellent potential as an ORR electrocatalyst in fuel cells. PMID:27528439

  6. Investigation of a sterilization system using active oxygen species generated by ultraviolet irradiation.

    PubMed

    Yoshino, Kiyoshi; Matsumoto, Hiroyuki; Iwasaki, Tatsuyuki; Kinoshita, Shinobu; Noda, Kazutoshi; Oya, Kei; Iwamori, Satoru

    2015-01-01

    We have been investigating an advanced sterilization system that employs active oxygen species (AOS). We designed the sterilization equipment, including an evacuation system, which generates AOS from pure oxygen gas using ultraviolet irradiation, in order to study the conditions necessary for sterilization in the system's chamber. Using Geobachillus stearothermophilus spores (10(6) CFU) in a sterile bag as a biological indicator (BI) in the chamber of the AOS sterilization apparatus, we examined the viability of the BI as a function of exposure time, assessing the role of the decompression level in the sterilization performance. We found that the survival curves showed exponential reduction, and that the decompression level did not exert a significant influence on the survival curve. Subsequently, we investigated the sterilization effect as influenced by the spatial and environmental temperature variation throughout the chamber, and found that the sterilization effect varied with position, due to the varying environmental temperature in the respective areas. We confirmed that temperature is one of the most important factors influencing sterilization in the chamber, and estimated the temperature effect on the distribution of atomic oxygen concentration, using the quartz crystal microbalance (QCM) method with fluorocarbon thin film prepared by radio frequency sputtering. PMID:25817808

  7. In situ x-ray, electrochemical, and modeling investigation of the oxygen electrode activation.

    SciTech Connect

    Yildiz, B.; Chang, K.-C.; Meyers, D.; Carter, J. D.; You, H.

    2006-01-01

    Oxygen electrodes of solid oxide electrochemical cells have been shown to improve under strong cathodic and anodic polarization. Our study investigates the mechanism causing such improvement, using in situ x-ray and electrochemical characterization and electrochemical impedance modeling of the oxygen electrodes. Several porous and dense thin-film model electrodes of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSM) and La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LCM) on single crystal yttria-stabilized zirconia (YSZ) electrolytes have been analyzed in situ at the Advanced Photon Source (APS) using x-ray reflectivity and x-ray absorption near edge spectroscopy (XANES) at the Mn K-edge and La LII-edge. In situ x-ray reflectivity analysis show that no clear correlation between the polarization of the electrode and any further changes in the roughness of the LSM/YSZ interface exist. XANES measurements illustrate that the cathodic or anodic dc polarization at high temperature induces no detectable changes in Mn chemical state either in the bulk or at the surface of the LCM and LSM electrodes on YSZ, while the La chemical state changes reversibly at the electrode surface. This field-induced chemical change of La at the surface of electrodes is assumed to be a cause of the electrochemical activation through enhanced surface exchange of oxygen on the doped lanthanum manganite electrodes.

  8. How Lipid Membranes Affect Pore Forming Toxin Activity.

    PubMed

    Rojko, Nejc; Anderluh, Gregor

    2015-12-15

    Pore forming toxins (PFTs) evolved to permeate the plasma membrane of target cells. This is achieved in a multistep mechanism that usually involves binding of soluble protein monomer to the lipid membrane, oligomerization at the plane of the membrane, and insertion of part of the polypeptide chain across the lipid membrane to form a conductive channel. Introduced pores allow uncontrolled transport of solutes across the membrane, inflicting damage to the target cell. PFTs are usually studied from the perspective of structure-function relationships, often neglecting the important role of the bulk membrane properties on the PFT mechanism of action. In this Account, we discuss how membrane lateral heterogeneity, thickness, and fluidity influence the pore forming process of PFTs. In general, lipid molecules are more accessible for binding in fluid membranes due to steric reasons. When PFT specifically binds ordered domains, it usually recognizes a specific lipid distribution pattern, like sphingomyelin (SM) clusters or SM/cholesterol complexes, and not individual lipid species. Lipid domains were also suggested to act as an additional concentration platform facilitating PFT oligomerization, but this is yet to be shown. The last stage in PFT action is the insertion of the transmembrane segment across the membranes to build the transmembrane pore walls. Conformational changes are a spontaneous process, and sufficient free energy has to be available for efficient membrane penetration. Therefore, fluid bilayers are permeabilized more readily in comparison to highly ordered and thicker liquid ordered lipid phase (Lo). Energetically more costly insertion into the Lo phase can be driven by the hydrophobic mismatch between the thinner liquid disordered phase (Ld) and large protein complexes, which are unable to tilt like single transmembrane segments. In the case of proteolipid pores, membrane properties can directly modulate pore size, stability, and even selectivity. Finally

  9. Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal-nitrogen coordination

    NASA Astrophysics Data System (ADS)

    Strickland, Kara; Miner, Elise; Jia, Qingying; Tylus, Urszula; Ramaswamy, Nagappan; Liang, Wentao; Sougrati, Moulay-Tahar; Jaouen, Frédéric; Mukerjee, Sanjeev

    2015-06-01

    Replacement of noble metals in catalysts for cathodic oxygen reduction reaction with transition metals mostly create active sites based on a composite of nitrogen-coordinated transition metal in close concert with non-nitrogen-coordinated carbon-embedded metal atom clusters. Here we report a non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media. In situ X-ray absorption spectroscopy in conjunction with ex situ microscopy clearly shows nitrided carbon fibres with embedded iron particles that are not directly involved in the oxygen reduction pathway. Instead, the reaction occurs primarily on the carbon-nitrogen structure in the outer skin of the nitrided carbon fibres. Implications include the potential of creating greater active site density and the potential elimination of any Fenton-type process involving exposed iron ions culminating in peroxide initiated free-radical formation.

  10. Antioxidant Activity of Oxygen Evolving Enhancer Protein 1 Purified from Capsosiphon fulvescens.

    PubMed

    Kim, Eun-Young; Choi, Youn Hee; Lee, Jung Im; Kim, In-Hye; Nam, Taek-Jeong

    2015-06-01

    This study was conducted to determine the antioxidant activity of a protein purified from Capsosiphon fulvescens. The purification steps included sodium acetate (pH 6) extraction and diethylaminoethyl-cellulose, reversed phase Shodex C4P-50 column chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that the molecular weight of the purified protein was 33 kDa. The N-terminus and partial peptide amino acid sequence of this protein was identical to the sequence of oxygen evolving enhancer (OEE) 1 protein. The antioxidant activity of the OEE 1 was determined in vitro using a scavenging test with 4 types of reactive oxygen species (ROS), including the 2,2-diphenyl-1-picrylhydrazyl radical, hydroxyl radical, superoxide anion, and hydrogen peroxide (H2 O2 ). OEE 1 had higher H2 O2 scavenging activity, which proved to be the result of enzymatic antioxidants rather than nonenzymatic antioxidants. In addition, OEE 1 showed less H2 O2 -mediated ROS formation in HepG2 cells. In conclusion, this study demonstrates that OEE 1 purified from C. fulvescens is an excellent antioxidant. PMID:25944160

  11. Activity-stability relationship in the surface electrochemistry of the oxygen evolution reaction.

    PubMed

    Chang, Seo Hyoung; Connell, Justin G; Danilovic, Nemanja; Subbaraman, Ram; Chang, Kee-Chul; Stamenkovic, Vojislav R; Markovic, Nenad M

    2014-01-01

    Understanding the functional links between the stability and reactivity of oxide materials during the oxygen evolution reaction (OER) is one key to enabling a vibrant hydrogen economy capable of competing with fossil fuel-based technologies. In this work, by focusing on the surface chemistry of monometallic Ru oxide in acidic and alkaline environments, we found that the kinetics of the OER are almost entirely controlled by the stability of the Ru surface atoms. The same activity-stability relationship was found for more complex, polycrystalline and single-crystalline SrRuO(3) thin films in alkaline solutions. We propose that the electrochemical transformation of either water (acidic solutions) or hydroxyl ions (alkaline solutions) to di-oxygen molecules takes place at defect sites that are inherently present on every electrode surface. During the OER, surface defects are also created by the corrosion of the Ru ions. The dissolution is triggered by the potential-dependent change in the valence state (n) of Ru: from stable but inactive Ru(4+) to unstable but active Ru(n>4+). We conclude that if the oxide is stable then it is completely inactive for the OER. A practical consequence is that the best materials for the OER should balance stability and activity in such a way that the dissolution rate of the oxide is neither too fast nor too slow. PMID:25490237

  12. Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination

    PubMed Central

    Strickland, Kara; Miner, Elise; Jia, Qingying; Tylus, Urszula; Ramaswamy, Nagappan; Liang, Wentao; Sougrati, Moulay-Tahar; Jaouen, Frédéric; Mukerjee, Sanjeev

    2015-01-01

    Replacement of noble metals in catalysts for cathodic oxygen reduction reaction with transition metals mostly create active sites based on a composite of nitrogen-coordinated transition metal in close concert with non-nitrogen-coordinated carbon-embedded metal atom clusters. Here we report a non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media. In situ X-ray absorption spectroscopy in conjunction with ex situ microscopy clearly shows nitrided carbon fibres with embedded iron particles that are not directly involved in the oxygen reduction pathway. Instead, the reaction occurs primarily on the carbon–nitrogen structure in the outer skin of the nitrided carbon fibres. Implications include the potential of creating greater active site density and the potential elimination of any Fenton-type process involving exposed iron ions culminating in peroxide initiated free-radical formation. PMID:26059552

  13. Electrochemical activation of commercial polyacrylonitrile-based carbon fiber for the oxygen reduction reaction.

    PubMed

    Xu, Haibo; Xia, Guangsen; Liu, Haining; Xia, Shuwei; Lu, Yonghong

    2015-03-28

    Nitrogen (N)-doped carbon and its non-noble metal composite replacing platinum-based oxygen reduction reaction (ORR) electrocatalysts still have some fundamental problems that remain. Here the micron-sized commercial polyacrylonitrile-based carbon fiber (PAN-CF) electrode was modified using an electrochemical method, converting its inherent pyridinic-N into 2-pyridone (or 2-hydroxyl pyridine) functional group existing in three-dimensional active layers with remarkable ORR catalytic activity and stability. The carbon atom adjacent to the nitrogen and oxygen atoms is prone to act as an active site to efficiently catalyze a two-electron ORR process. However, after coordinating pyridone to the Cu(2+) ion, together with the electrochemical reaction, the chemical redox between Cu(+) and ORR intermediates synergistically tends towards a four-electron pathway in alkaline solution. In different medium, the complexation and dissociation can induce the charge transfer and reconstruction among proton, metal ion and pyridone functionalities, eventually leading to the changes of ORR performance. PMID:25712410

  14. Testing and Oxygen Assessment Results for a Next Generation Extravehicular Activity Portable Life Support System Fan

    NASA Technical Reports Server (NTRS)

    Paul, Heather L.; Jennings, Mallory A.; Rivera, Fatonia L.; Martin, Devin

    2011-01-01

    NASA is designing a next generation Extravehicular Activity (EVA) Portable Life Support System (PLSS) for use in future surface exploration endeavors. To meet the new requirements for ventilation flow at nominal and buddy modes, a fan has been developed and tested. This paper summarizes the results of the performance and life cycle testing efforts conducted at the NASA Johnson Space Center. Additionally, oxygen compatibility assessment results from an evaluation conducted at White Sands Test Facility (WSTF) are provided, and lessons learned and future recommendations are outlined.

  15. Evaluation of the persistence of micropollutants through pure-oxygen activated sludge nitrification and denitrification

    USGS Publications Warehouse

    Levine, A.D.; Meyer, M.T.; Kish, G.

    2006-01-01

    The persistence of pharmaceuticals, hormones, and household and industrial chemicals through a pure-oxygen activated sludge, nitrification, denitrification wastewater treatment facility was evaluated. Of the 125 micropollutants that were tested in this study, 55 compounds were detected in the untreated wastewater, and 27 compounds were detected in the disinfected effluent. The persistent compounds included surfactants, fire-retardant chemicals, pesticides, fragrance compounds, hormones, and one pharmaceutical. Physical-chemical properties of micropollutants that affected partitioning onto wastewater solids included vapor pressure and octanol-water partition coefficients.

  16. Catalytic activity of metal oxides in hydrogen sulfide oxidation by oxygen and sulfur dioxide

    SciTech Connect

    Marshneva, V.I.; Mokrinskii, V.V.

    1989-02-01

    Separate investigations have been made of the catalytic activities of a wide range of oxides by groups I-VIII metals in the Claus reaction and oxidation of H/sub 2/S by oxygen. Only 9 of 21 oxides used in the Claus reaction exhibit stable activity. The remaining oxides are deactivated, mainly by absorbing H/sub 2/S and being converted into sulfides. There are similar tendencies in the changes of sulfur formation specific velocities in both processes in the series of stable oxides V/sub 2/O/sub 5/, TiO/sub 2/, Mn/sub 2/O/sub 3/, Al/sub 2/O/sub 3/, MgO, Cr/sub 2/O/sub 3/. Vanadium pentoxide is the most active catalyst in the total and partial oxidations of H/sub 2/S and the Claus reaction.

  17. Elucidating the activity of stepped Pt single crystals for oxygen reduction.

    PubMed

    Bandarenka, Aliaksandr S; Hansen, Heine A; Rossmeisl, Jan; Stephens, Ifan E L

    2014-07-21

    The unexpectedly high measured activity of Pt[n(111) × (111)] and Pt[n(111) × (100)] stepped single crystal surfaces towards the oxygen reduction reaction (ORR) is explained utilizing the hydroxyl binding energy as the activity descriptor. Using this descriptor (estimated using experimental data obtained by different groups), a well-defined Sabatier-type volcano is observed for the activities measured for the Pt[n(111) × (111)] and Pt[n(111) × (100)] stepped single crystals, in remarkable agreement with earlier theoretical studies. We propose that the observed destabilisation of *OH species at these surfaces is due to the decreased solvation of the adsorbed hydroxyl intermediates on adjacent terrace sites. PMID:24643715

  18. Reactive oxygen species production and antioxidant enzyme activity during epididymal sperm maturation in Corynorhinus mexicanus bats.

    PubMed

    Arenas-Ríos, Edith; Rosado García, Adolfo; Cortés-Barberena, Edith; Königsberg, Mina; Arteaga-Silva, Marcela; Rodríguez-Tobón, Ahiezer; Fuentes-Mascorro, Gisela; León-Galván, Miguel Angel

    2016-03-01

    Prolonged sperm storage in the epididymis of Corynorhinus mexicanus bats after testicular regression has been associated with epididymal sperm maturation in the caudal region, although the precise factors linked with this phenomenon are unknown. The aim of this work is to determine the role of reactive oxygen species (ROS) and changes in antioxidant enzymatic activity occurring in the spermatozoa and epididymal fluid over time, in sperm maturation and storage in the caput, corpus and cauda of the bat epididymis. Our data showed that an increment in ROS production coincided with an increase in superoxide dismutase (SOD) activity in epididymal fluid and with a decrease in glutathione peroxidase (GPX) activity in the spermatozoa in at different time points and epididymal regions. The increase in ROS production was not associated with oxidative damage measured by lipid peroxidation. The results of the current study suggest the existence of a shift in the redox balance, which might be associated with sperm maturation and storage. PMID:26952757

  19. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    SciTech Connect

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; Mavrikakis, Manos; Xia, Younan

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.

  20. Palladium-platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    NASA Astrophysics Data System (ADS)

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; Mavrikakis, Manos; Xia, Younan

    2015-07-01

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. These results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.

  1. Active Oxygen Metabolites and Thromboxane in Phorbol Myristate Acetate Toxicity to the Isolated, Perfused Rat Lung.

    NASA Astrophysics Data System (ADS)

    Carpenter, Laurie Jean

    When administered intravenously or intratracheally to rats, rabbits and sheep, phorbol myristate acetate (PMA) produces changes in lung morphology and function are similar to those seen in humans with the adult respiratory distress syndrome (ARDS). Therefore, it is thought that information about the mechanism of ARDS development can be gained from experiments using PMA-treated animals. Currently, the mechanisms by which PMA causes pneumotoxicity are unknown. Results from other studies in rabbits and in isolated, perfused rabbit lungs suggest that PMA-induced lung injury is mediated by active oxygen species from neutrophils (PMN), whereas studies in sheep and rats suggest that PMN are not required for the toxic response. The role of PMN, active oxygen metabolites and thromboxane (TxA_2) in PMA-induced injury to isolated, perfused rat lungs (IPLs) was examined in this thesis. To determine whether PMN were required for PMA to produce toxicity to the IPL, lungs were perfused for 30 min with buffer containing various concentrations of PMA (in the presence or absence of PMN). When concentrations >=q57 ng/ml were added to medium devoid of added PMN, perfusion pressure and lung weight increased. When a concentration of PMA (14-28 ng/ml) that did not by itself cause lungs to accumulate fluid was added to the perfusion medium containing PMN (1 x 10 ^8), perfusion pressure increased, and lungs accumulated fluid. These results indicate that high concentrations of PMA produce lung injury which is independent of PMN, whereas injury induced by lower concentrations is PMN-dependent. To examine whether active oxygen species were involved in mediating lung injury induced by PMA and PMN, lungs were coperfused with the oxygen radical scavengers SOD and/or catalase. Coperfusion with either or both of these enzymes totally protected lungs against injury caused by PMN and PMA. These results suggest that active oxygen species (the hydroxyl radical in particular), mediate lung injury in

  2. Oxygenator Is the Main Responsible for Leukocyte Activation in Experimental Model of Extracorporeal Circulation: A Cautionary Tale

    PubMed Central

    Rungatscher, Alessio; Tessari, Maddalena; Stranieri, Chiara; Solani, Erika; Linardi, Daniele; Milani, Elisabetta; Montresor, Alessio; Merigo, Flavia; Salvetti, Beatrice; Menon, Tiziano

    2015-01-01

    In order to assess mechanisms underlying inflammatory activation during extracorporeal circulation (ECC), several small animal models of ECC have been proposed recently. The majority of them are based on home-made, nonstandardized, and hardly reproducible oxygenators. The present study has generated fundamental information on the role of oxygenator of ECC in activating inflammatory signaling pathways on leukocytes, leading to systemic inflammatory response, and organ dysfunction. The present results suggest that experimental animal models of ECC used in translational research on inflammatory response should be based on standardized, reproducible oxygenators with clinical characteristics. PMID:26063972

  3. Active Curved Polymers Form Vortex Patterns on Membranes

    NASA Astrophysics Data System (ADS)

    Denk, Jonas; Huber, Lorenz; Reithmann, Emanuel; Frey, Erwin

    2016-04-01

    Recent in vitro experiments with FtsZ polymers show self-organization into different dynamic patterns, including structures reminiscent of the bacterial Z ring. We model FtsZ polymers as active particles moving along chiral, circular paths by Brownian dynamics simulations and a Boltzmann approach. Our two conceptually different methods point to a generic phase behavior. At intermediate particle densities, we find self-organization into vortex structures including closed rings. Moreover, we show that the dynamics at the onset of pattern formation is described by a generalized complex Ginzburg-Landau equation.

  4. Active Curved Polymers Form Vortex Patterns on Membranes.

    PubMed

    Denk, Jonas; Huber, Lorenz; Reithmann, Emanuel; Frey, Erwin

    2016-04-29

    Recent in vitro experiments with FtsZ polymers show self-organization into different dynamic patterns, including structures reminiscent of the bacterial Z ring. We model FtsZ polymers as active particles moving along chiral, circular paths by Brownian dynamics simulations and a Boltzmann approach. Our two conceptually different methods point to a generic phase behavior. At intermediate particle densities, we find self-organization into vortex structures including closed rings. Moreover, we show that the dynamics at the onset of pattern formation is described by a generalized complex Ginzburg-Landau equation. PMID:27176542

  5. Catalytic Activity of Platinum Monolayer on Iridium and Rhenium Alloy Nanoparticles for the Oxygen Reduction Reaction

    SciTech Connect

    Karan, Hiroko I.; Sasaki, Kotaro; Kuttiyiel, Kurian; Farberow, Carrie A.; Mavrikakis, Manos; Adzic, Radoslav R.

    2012-05-04

    A new type of electrocatalyst with a core–shell structure that consists of a platinum monolayer shell placed on an iridium–rhenium nanoparticle core or platinum and palladium bilayer shell deposited on that core has been prepared and tested for electrocatalytic activity for the oxygen reduction reaction. Carbon-supported iridium–rhenium alloy nanoparticles with several different molar ratios of Ir to Re were prepared by reducing metal chlorides dispersed on Vulcan carbon with hydrogen gas at 400 °C for 1 h. These catalysts showed specific electrocatalytic activity for oxygen reduction reaction comparable to that of platinum. The activities of PtML/PdML/Ir2Re1, PtML/Pd2layers/Ir2Re1, and PtML/Pd2layers/Ir7Re3 catalysts were, in fact, better than that of conventional platinum electrocatalysts, and their mass activities exceeded the 2015 DOE target. Our density functional theory calculations revealed that the molar ratio of Ir to Re affects the binding strength of adsorbed OH and, thereby, the O2 reduction activity of the catalysts. The maximum specific activity was found for an intermediate OH binding energy with the corresponding catalyst on the top of the volcano plot. The monolayer concept facilitates the use of much less platinum than in other approaches. Finally, the results with the PtML/PdML/Ir2Re electrocatalyst indicate that it is a promising alternative to conventional Pt electrocatalysts in low-temperature fuel cells.

  6. Tuning oxygen reduction reaction activity via controllable dealloying: a model study of ordered Cu3Pt/C intermetallic nanocatalysts.

    PubMed

    Wang, Deli; Yu, Yingchao; Xin, Huolin L; Hovden, Robert; Ercius, Peter; Mundy, Julia A; Chen, Hao; Richard, Jonah H; Muller, David A; DiSalvo, Francis J; Abruña, Héctor D

    2012-10-10

    A promising electrocatalyst prototype of low Pt mole fraction, intermetallic nanoparticles of Cu(3)Pt, has been prepared using a simple impregnation-reduction method, followed by a post heat-treatment. Two dealloying methods (electrochemical and chemical) were implemented to control the atomic-level morphology and improve performance for the oxygen reduction reaction (ORR). The morphology and elemental composition of the dealloyed nanoparticles were characterized at angstrom resolution using an aberration-corrected scanning transmission electron microscope equipped with an electron energy loss spectrometer. We found that the electrochemical dealloying method led to the formation of a thin Pt skin of ca. 1 nm in thickness with an ordered Cu(3)Pt core structure, while chemical leaching gave rise to a "spongy" structure with no ordered structure being preserved. A three-dimensional tomographic reconstruction indicated that numerous voids were formed in the chemically dealloyed nanoparticles. Both dealloying methods yielded enhanced specific and mass activities toward the ORR and higher stability relative to Pt/C. The spongy nanoparticles exhibited better mass activity with a slightly lower specific activity than the electrochemically dealloyed nanoparticles after 50 potential cycles. In both cases, the mass activity was still enhanced after 5000 potential cycles. PMID:22954373

  7. Elucidating Oxygen Reduction Active Sites in Pyrolyzed Metal–Nitrogen Coordinated Non-Precious-Metal Electrocatalyst Systems

    PubMed Central

    2015-01-01

    Detailed understanding of the nature of the active centers in non-precious-metal-based electrocatalyst, and their role in oxygen reduction reaction (ORR) mechanistic pathways will have a profound effect on successful commercialization of emission-free energy devices such as fuel cells. Recently, using pyrolyzed model structures of iron porphyrins, we have demonstrated that a covalent integration of the Fe–Nx sites into π-conjugated carbon basal plane modifies electron donating/withdrawing capability of the carbonaceous ligand, consequently improving ORR activity. Here, we employ a combination of in situ X-ray spectroscopy and electrochemical methods to identify the various structural and functional forms of the active centers in non-heme Fe/N/C catalysts. Both methods corroboratively confirm the single site 2e– × 2e– mechanism in alkaline media on the primary Fe2+–N4 centers and the dual-site 2e– × 2e– mechanism in acid media with the significant role of the surface bound coexisting Fe/FexOy nanoparticles (NPs) as the secondary active sites. PMID:24817921

  8. Inhibition of histone deacetylase activity in reduced oxygen environment enhances the osteogenesis of mouse adipose-derived stromal cells.

    PubMed

    Xu, Yue; Hammerick, Kyle E; James, Aaron W; Carre, Antoine L; Leucht, Philipp; Giaccia, Amato J; Longaker, Michael T

    2009-12-01

    Recent studies suggest that oxygen tension has a great impact on the osteogenic differentiation capacity of mesenchymal cells derived from adipose tissue: reduced oxygen impedes osteogenesis. We have found that expansion of mouse adipose-derived stromal cells (mASCs) in reduced oxygen tension (10%) results in increased cell proliferation along with induction of histone deacetylase (HDAC) activity. In this study, we utilized two HDAC inhibitors (HDACi), sodium butyrate (NaB) and valproic acid (VPA), and studied their effects on mASCs expanded in various oxygen tensions (21%, 10%, and 1% O(2)). Significant growth inhibition was observed with NaB or VPA treatment in each oxygen tension. Osteogenesis was enhanced by treatment with NaB or VPA, particularly in reduced oxygen tensions (10% and 1% O(2)). Conversely, adipogenesis was decreased with treatments of NaB or VPA at all oxygen tensions. Finally, NaB- or VPA-treated, reduced oxygen tension-exposed (1% O(2)) ASCs were grafted into surgically created mouse tibial defects and resulted in significantly increased bone regeneration. In conclusion, HDACi significantly promote the osteogenic differentiation of mASCs exposed to reduced oxygen tension; HDACi may hold promise for future clinical applications of ASCs for skeletal regeneration. PMID:19505250

  9. Inhibition of Histone Deacetylase Activity in Reduced Oxygen Environment Enhances the Osteogenesis of Mouse Adipose-Derived Stromal Cells

    PubMed Central

    Xu, Yue; Hammerick, Kyle E.; James, Aaron W.; Carre, Antoine L.; Leucht, Philipp; Giaccia, Amato J.

    2009-01-01

    Recent studies suggest that oxygen tension has a great impact on the osteogenic differentiation capacity of mesenchymal cells derived from adipose tissue: reduced oxygen impedes osteogenesis. We have found that expansion of mouse adipose-derived stromal cells (mASCs) in reduced oxygen tension (10%) results in increased cell proliferation along with induction of histone deacetylase (HDAC) activity. In this study, we utilized two HDAC inhibitors (HDACi), sodium butyrate (NaB) and valproic acid (VPA), and studied their effects on mASCs expanded in various oxygen tensions (21%, 10%, and 1% O2). Significant growth inhibition was observed with NaB or VPA treatment in each oxygen tension. Osteogenesis was enhanced by treatment with NaB or VPA, particularly in reduced oxygen tensions (10% and 1% O2). Conversely, adipogenesis was decreased with treatments of NaB or VPA at all oxygen tensions. Finally, NaB- or VPA-treated, reduced oxygen tension–exposed (1% O2) ASCs were grafted into surgically created mouse tibial defects and resulted in significantly increased bone regeneration. In conclusion, HDACi significantly promote the osteogenic differentiation of mASCs exposed to reduced oxygen tension; HDACi may hold promise for future clinical applications of ASCs for skeletal regeneration. PMID:19505250

  10. Hypolyminetic Oxygen Depletion And Dynamics of P Binding Forms: Insights From Modeling Sediment Early Diagenesis Coupled With Automatic Parameter Estimation

    NASA Astrophysics Data System (ADS)

    Shafei, Babak; Schmid, Martin; Müller, Beat; Chwalek, Thomas

    2014-05-01

    Sediment diagenesis can significantly impact on lake water quality through depleting hypolimnion oxygen and acting as a sink or source of nutrients and contaminants. In this study, we apply MATsedLAB, a sediment diagenesis module developed in MATLAB [1, 2] to quantify benthic oxygen consumption and biogeochemical cycling of phosphate (P) in lacustrine sediments of Lake Baldegg, located in central Switzerland. MATsedLAB provides an access to the advanced computational and visualization capabilities of the interactive programming environment of MATLAB. It allows for a flexible definition of non steady-state boundary conditions at the sediment-water interface (SWI), the model parameters as well as transport and biogeochemical reactions. The model has been extended to facilitate the model-independent parameter estimation and uncertainty analysis using the software package, PEST. Lake Baldegg represents an interesting case where sediment-water interactions control P loading in an eutrophic lake. It is of 5.2 km2 surface area and has been artificially aerated since 1982. Between 1960 and 1980, low oxygen concentrations and meromictic condition were established as a result of high productivity. Here, we use the cores for the measurements of anions and cations which were collected in April and June 2012 respectively from the deepest location (66 m), by Torres et al. (2013) to calibrate the developed model [3]. Depth profiles of thirty three species were simulated by including thirty mixed kinetic-equilibrium biogeochemical processes as well as imposing the fluxes of organic and inorganic matters along with solute concentrations at the SWI as dynamic boundary conditions. The diffusive transport in the boundary layer (DBL) above the SWI was included as the supply of O2 to the sediment surface can be diffusion-limited, and applying a constant O2 concentration at the sediment surface may overestimate O2 consumption. Benthic oxygen consumption was calculated as a function of

  11. 75 FR 21013 - Agency Information Collection Activities: Form N-644; Extension of an Existing Information...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-22

    ... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form N-644... Collection Under Review; Form N- 644, Application for Posthumous Citizenship; OMB Control No. 1615-0059. The..., USCIS will be evaluating whether to revise the Form N-644. Should USCIS decide to revise Form N-644...

  12. 76 FR 21913 - Agency Information Collection Activities: Form N-644; Extension of an Existing Information...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-19

    ... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form N-644... Collection Under Review: Form N- 644, Application for Posthumous Citizenship; OMB Control No. 1615-0059. The..., USCIS will be evaluating whether to revise the Form N-644. Should USCIS decide to revise Form N-644...

  13. 75 FR 51095 - Agency Information Collection Activities: Form N-336; Extension of an Existing Information...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-18

    ... SECURITY U.S. Citizenship and Immigration Services Agency Information Collection Activities: Form N-336... Collection under Review; Form N- 336, Request for Hearing on a Decision in Naturalization Proceedings Under... the Form N-336. Should USCIS decide to revise Form N-336 we will advise the public when we publish...

  14. Measuring the activities of higher organisms in activated sludge by means of mechanical shearing pretreatment and oxygen uptake rate.

    PubMed

    Hao, Xiaodi; Wang, Qilin; Cao, Yali; van Loosdrecht, Mark C M

    2010-07-01

    A pretreatment method was developed to assess the activities of higher organisms. The method is based on mechanical shearing to damage the large cells of the protozoan and metazoan community in activated sludge. The procedure was confirmed through experimentation to be effective in determining the activities of higher organisms by comparing oxygen uptake rates (OURs) before and after the higher organisms were eradicated. Shearing led to disintegration of flocs, which could be effectively reconstituted by centrifugation. The reconstitution of the sludge flocs was essential since otherwise the activity of the floc mass would be too high due to lack of diffusion limitation. Mechanical shearing had no influence on the morphology, quantity and specific activity of yeasts, and it was inferred that bacteria smaller than yeasts in size would also not be influenced by the applied shearing procedure. Moreover, the effect of filamentous organisms on the measured activities of higher organisms was experimentally demonstrated and analyzed, and determined to be so weak that it could be ignored. Based on these tests, five typical activated sludge processes were selected to measure the contribution of higher organisms to the original OUR. The measured activities of higher organisms ranged from 9.4 to 25.0% of the original OURs. PMID:20605188

  15. Maximal Oxygen Intake and Maximal Work Performance of Active College Women.

    ERIC Educational Resources Information Center

    Higgs, Susanne L.

    Maximal oxygen intake and associated physiological variables were measured during strenuous exercise on women subjects (N=20 physical education majors). Following assessment of maximal oxygen intake, all subjects underwent a performance test at the work level which had elicited their maximal oxygen intake. Mean maximal oxygen intake was 41.32…

  16. Heat of Hydration of Low Activity Cementitious Waste Forms

    SciTech Connect

    Nasol, D.

    2015-07-23

    During the curing of secondary waste grout, the hydraulic materials in the dry mix react exothermally with the water in the secondary low-activity waste (LAW). The heat released, called the heat of hydration, can be measured using a TAM Air Isothermal Calorimeter. By holding temperature constant in the instrument, the heat of hydration during the curing process can be determined. This will provide information that can be used in the design of a waste solidification facility. At the Savannah River National Laboratory (SRNL), the heat of hydration and other physical properties are being collected on grout prepared using three simulants of liquid secondary waste generated at the Hanford Site. From this study it was found that both the simulant and dry mix each had an effect on the heat of hydration. It was also concluded that the higher the cement content in the dry materials mix, the greater the heat of hydration during the curing of grout.

  17. Non-hypoxic activation of the negative regulatory feedback loop of prolyl-hydroxylase oxygen sensors.

    PubMed

    Tug, Suzan; Delos Reyes, Buena; Fandrey, Joachim; Berchner-Pfannschmidt, Utta

    2009-07-10

    Hypoxia inducible factors (HIF) coordinate cellular responses towards hypoxia. HIFs are mainly regulated by a group of prolyl-hydroxylases (PHDs) that in the presence of oxygen, target the HIFalpha subunit for degradation. Herein, we studied the role of nitric oxide (NO) in regulating PHD activities under normoxic conditions. In the present study we show that different NO-donors initially inhibited endogenous PHD2 activity which led to accumulation of HIF-1alpha subsequently to enhance HIF-1 dependent increased PHD2 promoter activity. Consequently PHD2 abundance and activity were strongly induced which caused downregulation of HIF-1alpha. Interestingly, upregulation of endogenous PHD2 activity by NO was not found in cells that lack an intact pVHL dependent degradation pathway. Recovery of PHD activity required intact cells and was not observed in cell extracts or recombinant PHD2. In conclusion induction of endogenous PHD2 activity by NO is dependent on a feedback loop initiated despite normoxic conditions. PMID:19427832

  18. Oxygenation, EMG and position sense during computer mouse work. Impact of active versus passive pauses.

    PubMed

    Crenshaw, A G; Djupsjöbacka, M; Svedmark, A

    2006-05-01

    We investigated the effects of active versus passive pauses implemented during computer mouse work on muscle oxygenation and EMG of the forearm extensor carpi radialis muscle, and on wrist position sense. Fifteen healthy female subjects (age: 19-24 years) performed a 60-min mouse-operated computer task, divided into three 20 min periods, on two occasions separated by 3-6 days. On one occasion a passive pause (subjects resting) was implemented at the end of each 20-min period, and on another occasion an active pause (subjects performed a number of high intensity extensions of the forearm) was implemented. Also at the end of each 20-min period, test contractions were conducted and subjective ratings of fatigue and stress were obtained. Another parameter of interest was total haemoglobin calculated as the summation of oxy-and deoxy-haemoglobin, since it reflects blood volume changes. The most interesting findings were an overall increasing trend in total haemoglobin throughout the mouse work (P<0.001), and that this trend was greater for the active pause as compared to the passive pause (P<0.01). These data were accompanied by an overall increase in oxygen saturation (P<0.001), with a tendency, albeit not significant, toward a higher increase for the active pause (P=0.13). EMG amplitude and median frequency tended to decrease (P=0.08 and 0.05, respectively) during the mouse work but was not different between pause types. Borg ratings of forearm fatigue showed an overall increase during the activity (P<0.001), but the perceptions of stress did not change. Position sense did not change due to the mouse work for either pause type. While increasing trends were found for both pause types, the present study lends support to the hypothesis of an enhancement in oxygenation and blood volume for computer mouse work implemented with active pauses. However, a presumption of an association between this enhancement and attenuated fatigue during the mouse work was not supported

  19. Identification of biotransformation products of citalopram formed in activated sludge.

    PubMed

    Beretsou, Vasiliki G; Psoma, Aikaterini K; Gago-Ferrero, Pablo; Aalizadeh, Reza; Fenner, Kathrin; Thomaidis, Nikolaos S

    2016-10-15

    Citalopram (CTR) is a worldwide highly consumed antidepressant which has demonstrated incomplete removal by conventional wastewater treatment. Despite its global ubiquitous presence in different environmental compartments, little is known about its behaviour and transformation processes during wastewater treatment. The present study aims to expand the knowledge on fate and transformation of CTR during the biological treatment process. For this purpose, batch reactors were set up to assess biotic, abiotic and sorption losses of this compound. One of the main objectives of the study was the identification of the formed transformation products (TPs) by applying suspect and non-target strategies based on liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS). The complementary use of reversed phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) for the identification of polar TPs, and the application of in-house developed quantitative structure-retention relationship (QSRR) prediction models, in addition to the comprehensive evaluation of the obtained MS/MS spectra, provided valuable information to support identification. In total, fourteen TPs were detected and thirteen of them were tentatively identified. Four compounds were confirmed (N-desmethylCTR, CTR amide, CTR carboxylic acid and 3-oxo-CTR) through the purchase of the corresponding reference standard. Probable structures based on diagnostic evidence were proposed for the additional nine TPs. Eleven TPs are reported for the first time. A transformation pathway for the biotransformation of CTR was proposed. The presence of the identified TPs was assessed in real wastewater samples through retrospective analysis, resulting in the detection of five compounds. Finally, the potential ecotoxicological risk posed by CTR and its TPs to different trophic levels of aquatic organisms was evaluated by means of risk quotients. PMID:27459150

  20. Effects of hydrogen sulfide on the heme coordination structure and catalytic activity of the globin-coupled oxygen sensor AfGcHK.

    PubMed

    Fojtikova, Veronika; Bartosova, Martina; Man, Petr; Stranava, Martin; Shimizu, Toru; Martinkova, Marketa

    2016-08-01

    AfGcHK is a globin-coupled histidine kinase that is one component of a two-component signal transduction system. The catalytic activity of this heme-based oxygen sensor is due to its C-terminal kinase domain and is strongly stimulated by the binding of O2 or CO to the heme Fe(II) complex in the N-terminal oxygen sensing domain. Hydrogen sulfide (H2S) is an important gaseous signaling molecule and can serve as a heme axial ligand, but its interactions with heme-based oxygen sensors have not been studied as extensively as those of O2, CO, and NO. To address this knowledge gap, we investigated the effects of H2S binding on the heme coordination structure and catalytic activity of wild-type AfGcHK and mutants in which residues at the putative O2-binding site (Tyr45) or the heme distal side (Leu68) were substituted. Adding Na2S to the initial OH-bound 6-coordinate Fe(III) low-spin complexes transformed them into SH-bound 6-coordinate Fe(III) low-spin complexes. The Leu68 mutants also formed a small proportion of verdoheme under these conditions. Conversely, when the heme-based oxygen sensor EcDOS was treated with Na2S, the initially formed Fe(III)-SH heme complex was quickly converted into Fe(II) and Fe(II)-O2 complexes. Interestingly, the autophosphorylation activity of the heme Fe(III)-SH complex was not significantly different from the maximal enzyme activity of AfGcHK (containing the heme Fe(III)-OH complex), whereas in the case of EcDOS the changes in coordination caused by Na2S treatment led to remarkable increases in catalytic activity. PMID:27395436

  1. Atomic Ordering Enhanced Electrocatalytic Activity of Nanoalloys for Oxygen Reduction Reaction

    SciTech Connect

    Loukrakpam, Rameshwori; Shan, Shiyao; Petkov, Valeri; Yang, Lefu; Luo, Jin; Zhong, Chuan-Jian

    2013-10-01

    For oxygen reduction reaction (ORR) over alloy electrocatalysts, the understanding of how the atomic arrangement of the metal species in the nanocatalysts is responsible for the catalytic enhancement is challenging for achieving better design and tailoring of nanoalloy catalysts. This paper reports results of an investigation of the atomic structures and the electrocatalytic activities of ternary and binary nanoalloys, aiming at revealing a fundamental insight into the unique atomic-scale structure-electrocatalytic activity relationship. PtIrCo catalyst and its binary counterparts (PtCo and PtIr) are chosen as a model system for this study. The effect of thermochemical treatment temperature on the atomic-scale structure of the catalysts was examined as a useful probe to the structure-activity correlation. The structural characterization of the binary and ternary nanoalloy catalysts was performed by combining surface sensitive techniques such as XPS and 3D atomic ordering sensitive techniques such as high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis (HE-XRD/PDFs) and computer simulations. The results show that the thermal treatment temperature tunes the nanoalloy’s atomic and chemical ordering in a different way depending on the chemical composition, leading to differences in the nanoalloy’s mass and specific activities. A unique structural tunability of the atomic ordering in a platinum-iridium-cobalt nanoalloy has been revealed for enhancing greatly the electrocatalytic activity toward oxygen reduction reaction, which has significant implication for rational design and nanoengineering of advanced catalysts for electrochemical energy conversion and storage.

  2. Biomass Oxidation: Formyl C-H Bond Activation by the Surface Lattice Oxygen of Regenerative CuO Nanoleaves.

    PubMed

    Amaniampong, Prince N; Trinh, Quang Thang; Wang, Bo; Borgna, Armando; Yang, Yanhui; Mushrif, Samir H

    2015-07-27

    An integrated experimental and computational investigation reveals that surface lattice oxygen of copper oxide (CuO) nanoleaves activates the formyl C-H bond in glucose and incorporates itself into the glucose molecule to oxidize it to gluconic acid. The reduced CuO catalyst regains its structure, morphology, and activity upon reoxidation. The activity of lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface and the hydrogen abstraction ability of the catalyst is correlated with the adsorption energy. Based on the present investigation, it is suggested that surface lattice oxygen is critical for the oxidation of glucose to gluconic acid, without further breaking down the glucose molecule into smaller fragments, because of C-C cleavage. Using CuO nanoleaves as catalyst, an excellent yield of gluconic acid is also obtained for the direct oxidation of cellobiose and polymeric cellulose, as biomass substrates. PMID:26119659

  3. Enhanced oxygen dissociation in a propagating constricted discharge formed in a self-pulsing atmospheric pressure microplasma jet

    NASA Astrophysics Data System (ADS)

    Schröder, Daniel; Burhenn, Sebastian; Kirchheim, Dennis; Schulz-von der Gathen, Volker

    2013-11-01

    We report on the propagation of a constricted discharge feature in a repetitively self-pulsing microplasma jet operated in helium with a 0.075 vol% molecular oxygen admixture in ambient air environment. The constricted discharge is about 1 mm in width and repetitively ignites at the point of smallest electrode distance in a wedge-shaped electrode configuration, propagates through the discharge channel towards the nozzle, extinguishes, and re-ignites at the inlet at frequencies in the kHz range. It co-exists with a homogeneous, volume-dominated low temperature (T ⋍ 300 K) α-mode glow. Time-resolved measurements of nitrogen molecule C-state and nitrogen molecule ion B-state emission bands reveal an increase of the rotational temperature within the constricted discharge to about 600 K within 50 µs. Its propagation velocity was determined by phase-resolved diagnostics to be similar to the gas velocity, in the order of 40 m s-1. Two-photon absorption laser-induced fluorescence spectroscopy synchronized to the self-pulsing reveals spatial regions of increased oxygen atom densities co-propagating with the constricted discharge feature. The generated oxygen pulse density is about ten times higher than in the co-existing homogeneous α-mode. Densities reach about 1.5 × 1016 cm-3 at average temperatures of 450 K at the nozzle. This enhanced dissociation of about 80% is attributed to the continuous interaction of the constricted discharge to the co-propagating gas volume.

  4. Wound healing activity of topical application forms based on ayurveda.

    PubMed

    Datta, Hema Sharma; Mitra, Shankar Kumar; Patwardhan, Bhushan

    2011-01-01

    The traditional Indian medicine-Ayurveda, describes various herbs, fats, oils and minerals with anti-aging as well as wound healing properties. With aging, numerous changes occur in skin, including decrease in tissue cell regeneration, decrease in collagen content, loss of skin elasticity and mechanical strength. We prepared five topical anti-aging formulations using cow ghee, flax seed oil, Phyllanthus emblica fruits, Shorea robusta resin, Yashada bhasma as study materials. For preliminary efficacy evaluation of the anti-aging activity we chose excision and incision wound healing animal models and studied the parameters including wound contraction, collagen content and skin breaking strength which in turn is indicative of the tissue cell regeneration capacity, collagenation capacity and mechanical strength of skin. The group treated with the formulations containing Yashada bhasma along with Shorea robusta resin and flax seed oil showed significantly better wound contraction (P < .01), higher collagen content (P < .05) and better skin breaking strength (P < .01) as compared to control group; thus proposing them to be effective prospective anti-aging formulations. PMID:19252191

  5. Wound Healing Activity of Topical Application Forms Based on Ayurveda

    PubMed Central

    Datta, Hema Sharma; Mitra, Shankar Kumar; Patwardhan, Bhushan

    2011-01-01

    The traditional Indian medicine—Ayurveda, describes various herbs, fats, oils and minerals with anti-aging as well as wound healing properties. With aging, numerous changes occur in skin, including decrease in tissue cell regeneration, decrease in collagen content, loss of skin elasticity and mechanical strength. We prepared five topical anti-aging formulations using cow ghee, flax seed oil, Phyllanthus emblica fruits, Shorea robusta resin, Yashada bhasma as study materials. For preliminary efficacy evaluation of the anti-aging activity we chose excision and incision wound healing animal models and studied the parameters including wound contraction, collagen content and skin breaking strength which in turn is indicative of the tissue cell regeneration capacity, collagenation capacity and mechanical strength of skin. The group treated with the formulations containing Yashada bhasma along with Shorea robusta resin and flax seed oil showed significantly better wound contraction (P < .01), higher collagen content (P < .05) and better skin breaking strength (P < .01) as compared to control group; thus proposing them to be effective prospective anti-aging formulations. PMID:19252191

  6. [L forms of Staphylococcus aureus. Behavior of coagulase, hemolytic and desoxyribonuclease activities and antibiotic sensitivity].

    PubMed

    Loschiavo, F; Giarrizzo, S

    1977-01-01

    L Forms derived from strains of coagulase positive Staphylococcus aureus, have, on the whole, preserved their DNAsic, haemolitic and coagulastic activities. L. forms showed high resistence to antibiotics acting on the bacterial cell-wall. The sensibility to other antibiotics was, roughly, analogous for the L forms as well as for the bacterial strains ones, with the exception of the clortetraciclin and the diidrostreptomicin, ehich proved to be comparatively more active on the L forms. PMID:614141

  7. Metal-Oxygen Bond Ionicity as an Efficient Descriptor for Doped NiOOH Photocatalytic Activity.

    PubMed

    Zaffran, Jeremie; Toroker, Maytal Caspary

    2016-06-01

    The computational design of solid catalysts has become a very "hot" field during the last decades, especially with the recent increase in computational tool performance. However, theoretical techniques are still very time demanding because they require the consideration of many adsorption configurations of the reaction intermediates on the surface. Herein, we propose to use the metal-oxygen (M-O) bond ionicity as a descriptor for the photocatalytic activity of one of the best catalysts for the oxygen evolution reaction (OER). Ionicity is a bulk property and thus carries the advantage of being easily obtainable from a simple Bader charge analysis by using density functional theory (DFT). We will show that this criterion can be used successfully to design efficient dopants for NiOOH material. This catalyst is known to exhibit interesting photoelectrochemical properties for OER if it is doped with specific transition metals. Finally, we demonstrate that other electronic properties that relate to bulk calculation, such as oxidation states and density of states, are not alone sufficient to explain the photocatalytic activity of the material. Thus, M-O bond ionicity attracts significant interest compared with other bulk observables obtained by using DFT computations. PMID:26945687

  8. Ordered mesoporous porphyrinic carbons with very high electrocatalytic activity for the oxygen reduction reaction

    PubMed Central

    Cheon, Jae Yeong; Kim, Taeyoung; Choi, YongMan; Jeong, Hu Young; Kim, Min Gyu; Sa, Young Jin; Kim, Jaesik; Lee, Zonghoon; Yang, Tae-Hyun; Kwon, Kyungjung; Terasaki, Osamu; Park, Gu-Gon; Adzic, Radoslav R.; Joo, Sang Hoon

    2013-01-01

    The high cost of the platinum-based cathode catalysts for the oxygen reduction reaction (ORR) has impeded the widespread application of polymer electrolyte fuel cells. We report on a new family of non-precious metal catalysts based on ordered mesoporous porphyrinic carbons (M-OMPC; M = Fe, Co, or FeCo) with high surface areas and tunable pore structures, which were prepared by nanocasting mesoporous silica templates with metalloporphyrin precursors. The FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9 V than Pt/C catalysts, as well as superior long-term durability and MeOH-tolerance. Density functional theory calculations in combination with extended X-ray absorption fine structure analysis revealed a weakening of the interaction between oxygen atom and FeCo-OMPC compared to Pt/C. This effect and high surface area of FeCo-OMPC appear responsible for its significantly high ORR activity. PMID:24056308

  9. Ni- and Mn-Promoted Mesoporous Co3O4: A Stable Bifunctional Catalyst with Surface-Structure-Dependent Activity for Oxygen Reduction Reaction and Oxygen Evolution Reaction.

    PubMed

    Song, Wenqiao; Ren, Zheng; Chen, Sheng-Yu; Meng, Yongtao; Biswas, Sourav; Nandi, Partha; Elsen, Heather A; Gao, Pu-Xian; Suib, Steven L

    2016-08-17

    Efficient bifunctional catalysts for electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable due to their wide applications in fuel cells and rechargeable metal air batteries. However, the development of nonprecious metal catalysts with comparable activities to noble metals is still challenging. Here we report a one-step wet-chemical synthesis of Ni-/Mn-promoted mesoporous cobalt oxides through an inverse micelle process. Various characterization techniques including powder X-ray diffraction (PXRD), N2 sorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) confirm the successful incorporation of Ni and Mn leading to the formation of Co-Ni(Mn)-O solid solutions with retained mesoporosity. Among these catalysts, cobalt oxide with 5% Ni doping demonstrates promising activities for both ORR and OER, with an overpotential of 399 mV for ORR (at -3 mA/cm(2)) and 381 mV (at 10 mA/cm(2)) for OER. Furthermore, it shows better durability than precious metals featuring little activity decay throughout 24 h continuous operation. Analyses of cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman, and O2-temperature-programmed desorption (O2-TPD) reveal that redox activity of Co(3+) to Co(4+) is crucial for OER performance, while the population of surface oxygen vacancies and surface area determine ORR activities. The comprehensive investigation of the intrinsic active sites for ORR and OER by correlating different physicochemical properties to the electrochemical activities is believed to provide important insight toward the rational design of high-performance electrocatalysts for ORR and OER reactions. PMID:27458646

  10. NQO1-induced activation of AMPK contributes to cancer cell death by oxygen-glucose deprivation

    PubMed Central

    Lee, Hyemi; Oh, Eun-Taex; Choi, Bo-Hwa; Park, Moon-Taek; Lee, Ja-Kyeong; Lee, Jae-Seon; Park, Heon Joo

    2015-01-01

    Oxygen and glucose deprivation (OGD) due to insufficient blood circulation can decrease cancer cell survival and proliferation in solid tumors. OGD increases the intracellular [AMP]/[ATP] ratio, thereby activating the AMPK. In this study, we have investigated the involvement of NQO1 in OGD-mediated AMPK activation and cancer cell death. We found that OGD activates AMPK in an NQO1-dependent manner, suppressing the mTOR/S6K/4E-BP1 pathway, which is known to control cell survival. Thus, the depletion of NQO1 prevents AMPK-induced cancer cell death in OGD. When we blocked OGD-induced Ca2+/CaMKII signaling, the NQO1-induced activation of AMPK was attenuated. In addition, when we blocked the RyR signaling, the accumulation of intracellular Ca2+ and subsequent activation of CaMKII/AMPK signaling was decreased in NQO1-expressing cells under OGD. Finally, siRNA-mediated knockdown of CD38 abrogated the OGD-induced activation of Ca2+/CaMKII/AMPK signaling. Taken together, we conclude that NQO1 plays a key role in the AMPK-induced cancer cell death in OGD through the CD38/cADPR/RyR/Ca2+/CaMKII signaling pathway. PMID:25586669

  11. Semi-synthesis of oxygenated dolabellane diterpenes with highly in vitro anti-HIV-1 activity.

    PubMed

    Pardo-Vargas, Alonso; Ramos, Freddy A; Cirne-Santos, Claudio Cesar; Stephens, Paulo Roberto; Paixão, Izabel Christina Palmer; Teixeira, Valeria Laneuville; Castellanos, Leonardo

    2014-09-15

    Research on dolabellane diterpenes of brown algae Dictyota spp. has shown that these diterpenoids have strong anti-HIV-1 activity, but there are not data about antiviral activity of dolabellane diterpenes isolated from octocorals, which are antipodes of those isolated from the brown algae. Dolabellanes 13-keto-1(R),11(S)-dolabella-3(E),7(E),12(18)-triene (1) and β-Araneosene (2) were isolated from the Caribbean octocoral Eunicea laciniata, and both showed low anti-HIV-1 activity and low toxicity. Since it was shown that oxygenated dolabellanes from algae have better anti-HIV-1 activity, in this work some derivatives of the main dolabellane of E. laciniata1 were obtained by epoxidation (3), epoxide opening (4), and allylic oxidation (5). The derivatives showed significant improvement in the anti-HIV-1potency (100-fold), being compounds 3 and 5 the most active ones. Their high antiviral activities, along with their low cytotoxicity, make them promissory antiviral compounds; and it is worth noting that the absolute configuration at the ring junction in the dolabellane skeleton does not seem to be determinant in the antiviral potency of these diterpeneoids. PMID:25176328

  12. Segregated Pt on Pd nanotubes for enhanced oxygen reduction activity in alkaline electrolyte.

    PubMed

    St John, Samuel; Atkinson, Robert W; Dyck, Ondrej; Sun, Cheng-Jun; Zawodzinski, Thomas A; Papandrew, Alexander B

    2015-12-01

    Nanoscaled Pt domains were integrated with Pd nanotubes via vapor deposition to yield a highly active electrocatalyst for the oxygen reduction reaction (ORR) in alkaline media. The surface-area-normalized ORR activity of these bi-metallic Pt-on-Pd nanotubes (PtPdNTs) was nearly 6× the corresponding carbon-supported Pt nanoparticle (Pt/C) activity at 0.9 V vs. RHE (1.5 vs. 0.24 mA cmmetal(-2), respectively). Furthermore, the high specific activity of the PtPdNTs was achieved without sacrificing mass-normalized activity, which is more than twice that of Pt/C (0.333 A mgPtPdNT(-1)vs. 0.141 A mgPt/C(-1)) and also greater than that of Pd/C (0.221 A mgPd/C(-1)). We attribute the enhancements in specific and mass activity to modifications of the segregated Pt electronic structure and to nanoscale porosity, respectively. PMID:26553367

  13. Enhanced electrocatalytic activity of nitrogen-doped olympicene/graphene hybrids for the oxygen reduction reaction.

    PubMed

    Hou, Xiuli; Zhang, Peng; Li, Shuang; Liu, Wei

    2016-08-17

    Developing inexpensive and non-precious metal electrocatalysts for the oxygen reduction reaction (ORR) is among the major goals in fuel cells. Herein, by using density-functional theory calculations, we show that N-doped olympicene/graphene hybrids exhibit unexpectedly high ORR catalytic activity-even comparable to that of the Pt(111) surface. Both graphitic-type and pyridine-type N-doped olympicene/graphene hybrids are highly active for the ORR and have good CO tolerance. The formation of the second H2O molecule is the rate-determining step for the ORR with the graphitic-type hybrid, whereas on the pyridine-type hybrid, it is the formation of OOH. Note that N-doped olympicene/graphene hybrid materials combine the high reactivity of olympicene and the high electrical conductivity of graphene, which allows them to be potentially used as low-cost and non-precious-metal ORR catalysts. PMID:27499058

  14. Enhanced oxygen reduction activity and solid oxide fuel cell performance with a nanoparticles-loaded cathode.

    PubMed

    Zhang, Xiaomin; Liu, Li; Zhao, Zhe; Tu, Baofeng; Ou, Dingrong; Cui, Daan; Wei, Xuming; Chen, Xiaobo; Cheng, Mojie

    2015-03-11

    Reluctant oxygen-reduction-reaction (ORR) activity has been a long-standing challenge limiting cell performance for solid oxide fuel cells (SOFCs) in both centralized and distributed power applications. We report here that this challenge has been tackled with coloading of (La,Sr)MnO3 (LSM) and Y2O3 stabilized zirconia (YSZ) nanoparticles within a porous YSZ framework. This design dramatically improves ORR activity, enhances fuel cell output (200-300% power improvement), and enables superior stability (no observed degradation within 500 h of operation) from 600 to 800 °C. The improved performance is attributed to the intimate contacts between nanoparticulate YSZ and LSM particles in the three-phase boundaries in the cathode. PMID:25686380

  15. Porous Dendritic Platinum Nanotubes with Extremely High Activity and Stability for Oxygen Reduction Reaction

    PubMed Central

    Zhang, Gaixia; Sun, Shuhui; Cai, Mei; Zhang, Yong; Li, Ruying; Sun, Xueliang

    2013-01-01

    Controlling the morphology of Pt nanostructures can provide opportunities to greatly increase their activity and stability. Porous dendritic Pt nanotubes were successfully synthesized by a facile, cost-effective aqueous solution method at room temperature in large scale. These unique structures are porous, hollow, hierarchical, and single crystalline, which not only gives them a large surface area with high catalyst utilization, but also improves mass transport and gas diffusion. These novel Pt structures exhibited significantly improved catalytic activity (4.4 fold) for oxygen reduction reaction (ORR) and greatly enhanced durability (6.1 fold) over that of the state-of-the-art commercial Pt/C catalyst. This work provides a promising approach to the design of highly efficient next-generation electrocatalysts. PMID:23524665

  16. Rationalizing the Hydrogen and Oxygen Evolution Reaction Activity of Two-Dimensional Hydrogenated Silicene and Germanene.

    PubMed

    Rupp, Caroline J; Chakraborty, Sudip; Anversa, Jonas; Baierle, Rogério J; Ahuja, Rajeev

    2016-01-20

    We have undertaken first-principles electronic structure calculations to show that the chemical functionalization of two-dimensional hydrogenated silicene (silicane) and germanene (germanane) can become a powerful tool to increase the photocatalytic water-splitting activity. Spin-polarized density functional theory within the GGA-PBE and HSE06 types of exchange correlation functionals has been used to obtain the structural, electronic, and optical properties of silicane and germanane functionalized with a series of nonmetals (N, P, and S), alkali metals (Li, Na, and K) and alkaline-earth metals (Mg and Ca). The surface-adsorbate interaction between the functionalized systems with H2 and O2 molecules that leads to envisaged hydrogen and oxygen evolution reaction activity has been determined. PMID:26704530

  17. Understanding Iron-based catalysts with efficient Oxygen reduction activity from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Hafiz, Hasnain; Barbiellini, B.; Jia, Q.; Tylus, U.; Strickland, K.; Bansil, A.; Mukerjee, S.

    2015-03-01

    Catalysts based on Fe/N/C clusters can support the oxygen-reduction reaction (ORR) without the use of expensive metals such as platinum. These systems can also prevent some poisonous species to block the active sites from the reactant. We have performed spin-polarized calculations on various Fe/N/C fragments using the Vienna Ab initio Simulation Package (VASP) code. Some results are compared to similar calculations obtained with the Gaussian code. We investigate the partial density of states (PDOS) of the 3d orbitals near the Fermi level and calculate the binding energies of several ligands. Correlations of the binding energies with the 3d electronic PDOS's are used to propose electronic descriptors of the ORR associated with the 3d states of Fe. We also suggest a structural model for the most active site with a ferrous ion (Fe2+) in the high spin state or the so-called Doublet 3 (D3).

  18. The oxygen fugacity at which graphite or diamond forms from carbonate-bearing melts in eclogitic rocks

    NASA Astrophysics Data System (ADS)

    Stagno, V.; Frost, D. J.; McCammon, C. A.; Mohseni, H.; Fei, Y.

    2015-02-01

    The oxygen fugacity ( fO2) at which carbonate-bearing melts are reduced to either graphite or diamond in synthetic eclogite compositions has been measured in multi-anvil experiments performed at pressures between 3 and 7 GPa and temperatures between 800 and 1,300 °C using iron-iridium and iron-platinum alloys as sliding redox sensors. The determined oxygen fugacities buffered by the coexistence of elemental carbon and carbonate-bearing melt are approximately 1 log unit below thermodynamic calculations for a similar redox buffering equilibrium involving only solid phases. The measured oxygen fugacities normalized to the fayalite-magnetite-quartz oxygen buffer decrease with temperature from ~-0.8 to ~-1.7 log units at 3 GPa, most likely as a result of increasing dilution of the carbonate liquid with silicate. The normalized fO2 values also decrease with pressure and show a similar decrease with temperature at 6 GPa from ~-1.5 log units at 1,100 °C to ~-2.4 log units at 1,300 °C. In contrast to previous arguments, the stability field of the carbonate-bearing melt extends to lower oxygen fugacity in eclogite rocks than in peridotite rocks, which implies a wider range of conditions over which carbon remains mobile in natural eclogites. The raised prevalence of diamonds in eclogites compared to peridotites may, therefore, reflect more effective scavenging of carbon by melts in these rocks. The ferric iron contents of monomineralic layers of clinopyroxene and garnet contained in the same experiments were also measured using Mössbauer spectroscopy. A preliminary model was derived for determining the fO2 of eclogitic rocks from the compositions of garnet and clinopyroxene, including the Fe3+/ΣFe ratio of garnet, using the equilibrium, The model, which reproduces the independently determined fO2 of the experimental data to within 0.5 log units, can be used to estimate the fO2 of ultrahigh-pressure metamorphic eclogites and cratonic eclogitic xenoliths. Although there

  19. Oxidative DNA adducts after Cu(2+)-mediated activation of dihydroxy PCBs: role of reactive oxygen species.

    PubMed

    Spencer, Wendy A; Lehmler, Hans-Joachim; Robertson, Larry W; Gupta, Ramesh C

    2009-05-15

    Polychlorinated biphenyls (PCBs) are toxic industrial chemicals, complete carcinogens, and efficacious tumor promoters. However, the mechanism(s) of PCB-mediated carcinogenicity remains largely undefined. One likely pathway by which these agents may play a role in carcinogenesis is the generation of oxidative DNA damage by redox cycling of dihydroxylated PCB metabolites. We have now employed a new (32)P-postlabeling system to examine novel oxidative DNA lesions induced by Cu(2+)-mediated activation of PCB metabolites. (32)P postlabeling of DNA incubated with various PCB metabolites resulted in over a dozen novel polar oxidative DNA adducts that were chromatographically similar for all active agents. The most potent metabolites tested were the hydroquinones (hydroxyl groups arranged para to each other), yielding polar oxidative adduct levels ranging from 55 to 142 adducts/10(6) nucleotides. PCB catechols, or ortho-dihydroxy metabolites, were up to 40% less active than their corresponding hydroquinone congeners, whereas monohydroxylated and quinone metabolites did not produce detectable oxidative damage over that of vehicle. With the exception of 2,4,5-Cl-2',5'-dihydroxybiphenyl, this oxidative DNA damage seemed to be inversely related to chlorine content: no chlorine approximately mono->di->trichlorinated metabolites. Importantly, copper, but not iron, was essential for activation of the PCB metabolites to these polar oxidative DNA adducts, because in its absence or in the presence of the Cu(+)-specific scavenger bathocuproine, no adducts were detected. Intervention studies with known reactive oxygen species (ROS) modifiers suggested that H(2)O(2), singlet oxygen, hydroxyl radical, and superoxide may also be involved in this PCB-mediated oxidative DNA damage. These data indicate a mechanistic role for several ROS, in addition to copper, in PCB-induced DNA damage and provide further support for oxidative DNA damage in PCB-mediated carcinogenesis. PMID:19233261

  20. Intensity of daily physical activity is associated with central hemodynamic and leg muscle oxygen availability in COPD.

    PubMed

    Louvaris, Zafeiris; Kortianou, Eleni A; Spetsioti, Stavroula; Vasilopoulou, Maroula; Nasis, Ioannis; Asimakos, Andreas; Zakynthinos, Spyros; Vogiatzis, Ioannis

    2013-09-01

    In chronic obstructive pulmonary disease (COPD), daily physical activity is reported to be adversely associated with the magnitude of exercise-induced dynamic hyperinflation and peripheral muscle weakness. There is limited evidence whether central hemodynamic, oxygen transport, and peripheral muscle oxygenation capacities also contribute to reduced daily physical activity. Nineteen patients with COPD (FEV1, 48 ± 14% predicted) underwent a treadmill walking test at a speed corresponding to the individual patient's mean walking intensity, captured by a triaxial accelerometer during a preceding 7-day period. During the indoor treadmill test, the individual patient mean walking intensity (range, 1.5 to 2.3 m/s2) was significantly correlated with changes from baseline in cardiac output recorded by impedance cardiography (range, 1.2 to 4.2 L/min; r = 0.73), systemic vascular conductance (range, 7.9 to 33.7 ml·min(-1)·mmHg(-1); r = 0.77), systemic oxygen delivery estimated from cardiac output and arterial pulse-oxymetry saturation (range, 0.15 to 0.99 L/min; r = 0.70), arterio-venous oxygen content difference calculated from oxygen uptake and cardiac output (range, 3.7 to 11.8 mlO2/100 ml; r = -0.73), and quadriceps muscle fractional oxygen saturation assessed by near-infrared spectrometry (range, -6 to 23%; r = 0.77). In addition, mean walking intensity significantly correlated with the quadriceps muscle force adjusted for body weight (range, 0.28 to 0.60; r = 0.74) and the ratio of minute ventilation over maximal voluntary ventilation (range, 38 to 89%, r = -0.58). In COPD, in addition to ventilatory limitations and peripheral muscle weakness, intensity of daily physical activity is associated with both central hemodynamic and peripheral muscle oxygenation capacities regulating the adequacy of matching peripheral muscle oxygen availability by systemic oxygen transport. PMID:23845982

  1. Metal Ion Adsorption by Activated Carbons Made from Pecan Shells: Effect of Oxygen Level During Activation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Agricultural by-products represent a considerable quantity of harvested commodity crops. The use of by-products as precursors for the production of widely used adsorbents, such as activated carbons, may impart a value-added component of the overall biomass harvested. Our objective in this presenta...

  2. Mitochondria are required for antigen-specific T cell activation through reactive oxygen species signaling

    PubMed Central

    Sena, Laura A.; Li, Sha; Jairaman, Amit; Prakriya, Murali; Ezponda, Teresa; Hildeman, David A.; Wang, Chyung-Ru; Schumacker, Paul T.; Licht, Jonathan D.; Perlman, Harris; Bryce, Paul J.; Chandel, Navdeep S.

    2013-01-01

    SUMMARY It is widely appreciated that T cells increase glycolytic flux during activation, however the role of mitochondrial flux is unclear. Here we have shown that mitochondrial metabolism, in the absence of glucose metabolism, was sufficient to support interleukin-2 (IL-2) induction. Furthermore, we used mice with reduced mitochondrial reactive oxygen species (mROS) production in T cells (T-Uqcrfs−/− mice) to show that mitochondria are required for T cell activation to produce mROS for activation of nuclear factor of activated T cells (NFAT) and subsequent IL-2 induction. These mice could not induce antigen-specific expansion of T cells in vivo, however Uqcrfs1−/− T cells retained the ability to proliferate in vivo under lymphopenic conditions. This suggests that Uqcrfs1−/− T cells were not lacking bioenergetically, but rather lacked specific ROS-dependent signaling events needed for antigen-specific expansion. Thus, mitochondrial metabolism is a critical component of T cell activation through production of complex III ROS. PMID:23415911

  3. Activity and stability trends of perovskite oxides for oxygen evolution catalysis at neutral pH.

    PubMed

    Han, Binghong; Risch, Marcel; Lee, Yueh-Lin; Ling, Chen; Jia, Hongfei; Shao-Horn, Yang

    2015-09-21

    Perovskite oxides (ABO3) have been studied extensively to promote the kinetics of the oxygen evolution reaction (OER) in alkaline electrolytes. However, developing highly active catalysts for OER at near-neutral pH is desirable for many photoelectrochemical/electrochemical devices. In this paper, we systematically studied the activity and stability of well-known perovskite oxides for OER at pH 7. Previous activity descriptors established for perovskite oxides at pH 13, such as having an eg occupancy close to unity or having an O p-band center close to Fermi level, were shown to scale with OER activity at pH 7. Stability was a greater challenge at pH 7 than at pH 13, where two different modes of instability were identified from combined transmission electron microscopy and density functional theory analyses. Perovskites with O p-band close to Fermi level showed leaching of A-site atoms and surface amorphization under all overpotentials examined at pH 7, while those with O p-band far from Fermi level were stable under low OER current/potential but became unstable at high current/potential accompanied by leaching of B-site atoms. Therefore, efforts are needed to enhance the activity and stability of perovskites against A-site or B-site loss if used at neutral pH. PMID:26271910

  4. Activity and stability of the oxygen evolution reaction on electrodeposited Ru and its thermal oxides

    NASA Astrophysics Data System (ADS)

    Kim, Jin Yeong; Choi, Jihui; Kim, Ho Young; Hwang, Eunkyoung; Kim, Hyoung-Juhn; Ahn, Sang Hyun; Kim, Soo-Kil

    2015-12-01

    The activity and stability of Ru metal and its thermal oxide films for the oxygen evolution reaction (OER) were investigated. The metallic Ru films were prepared by electrodeposition on a Ti substrate and then thermally oxidized at various temperatures under atmospheric conditions. During long-term operation of the OER with cyclic voltammetry (CV) in H2SO4 electrolyte, changes in the properties of the Ru and its thermal oxides were monitored in terms of their morphology, crystal structure, and electronic structure. In the initial stages of the OER, all of the Ru thermal oxide films underwent an activation process that was related to the continuous removal of low-activity Ru oxides from the surface. With further cycling, the OER activity decreased. The rate of decrease was different for each Ru film and was related to the annealing temperatures. Monitoring of material properties indicates that the amount of stable anhydrous RuO2 is important for OER stability because it prevents both the severe dissolution of metallic Ru beneath the oxide surface and the formation of a less active hydrous RuO2 at the surface.

  5. Enhancement of oxygen reduction reaction activities by Pt nanoclusters decorated on ordered mesoporous porphyrinic carbons

    DOE PAGESBeta

    Sun-Mi Hwang; Choi, YongMan; Kim, Min Gyu; Sohn, Young-Jun; Cheon, Jae Yeong; Joo, Sang Hoon; Yim, Sung-Dae; Kuttiyiel, Kurian A.; Sasaki, Kotaro; Adzic, Radoslav R.; et al

    2016-03-08

    The high cost of Pt-based membrane electrode assemblies (MEAs) is a critical hurdle for the commercialization of polymer electrolyte fuel cells (PEFCs). Recently, non-precious metal-based catalysts (NPMCs) have demonstrated much enhanced activity but their oxygen reduction reaction (ORR) activity is still inferior to that of Pt-based catalysts resulting in a much thicker electrode in the MEA. For the reduction of mass transport and ohmic overpotential we adopted a new concept of catalyst that combines an ultra-low amount of Pt nanoclusters with metal–nitrogen (M–Nx) doped ordered mesoporous porphyrinic carbon (FeCo–OMPC(L)). The 5 wt% Pt/FeCo–OMPC(L) showed a 2-fold enhancement in activities comparedmore » to a higher loading of Pt. Our experimental results supported by first-principles calculations indicate that a trace amount of Pt nanoclusters on FeCo–OMPC(L) significantly enhances the ORR activity due to their electronic effect as well as geometric effect from the reduced active sites. Finally, in terms of fuel cell commercialization, this class of catalysts is a promising candidate due to the limited use of Pt in the MEA.« less

  6. A Clark-type oxygen chip for in situ estimation of the respiratory activity of adhering cells.

    PubMed

    Wu, Ching-Chou; Luk, Hsiang-Ning; Lin, Yen-Ting Tsai; Yuan, Chia-Yin

    2010-04-15

    A Clark-type oxygen chip consisting of a polydimethylsiloxane (PDMS) reservoir containing an amino group-modified PDMS oxygen-permeable membrane (OPM) and a glass substrate containing a three-electrode detector has been constructed by using microfabrication techniques, and it is utilized for in situ measurement of the respiration activity of adhering cells. Use of the alginate sol electrolyte and the electroplating Ag/AgCl pseudo-reference electrode can effectively diminish the crosstalk between the electrochemical electrodes and supply a stable potential for the detection of dissolved oxygen, respectively. The Clark-type oxygen chips possess only 1.00% residual current, response time of 13.4s and good linearity with a correlation coefficient of 0.9933. The modification of amino groups for the OPM obviously facilitates the adhesion of HeLa cells onto the PDMS OPM surface and allows the cells to spread after 2h of incubation. The oxygen consumption of the cells in the cell-adhesion process increases with the adhesion time, and the increment of cellular oxygen consumption per minute reaches a maximum after 30 min of incubation. Moreover, the change in the respiration activity of adhering HeLa cells stimulated by the high concentration of glucose or propofol anaesthetic can be monitored in real time with the Clark-type oxygen chip. PMID:20188913

  7. The MOSDEF Survey: Detection of [O III]λ4363 and the Direct-method Oxygen Abundance of a Star-forming Galaxy at z = 3.08

    NASA Astrophysics Data System (ADS)

    Sanders, Ryan L.; Shapley, Alice E.; Kriek, Mariska; Reddy, Naveen A.; Freeman, William R.; Coil, Alison L.; Siana, Brian; Mobasher, Bahram; Shivaei, Irene; Price, Sedona H.; de Groot, Laura

    2016-07-01

    We present measurements of the electron-temperature-based oxygen abundance for a highly star-forming galaxy at z = 3.08, COSMOS-1908. This is the highest redshift at which [O iii]λ4363 has been detected and the first time that this line has been measured at z\\gt 2. We estimate an oxygen abundance of 12+{log}({{O}}/{{H}})={8.00}-0.14+0.13. This galaxy is a low-mass ({10}9.3 {M}ȯ ), highly star-forming (˜50 {M}ȯ yr‑1) system that hosts a young stellar population (˜160 Myr). We investigate the physical conditions of the ionized gas in COSMOS-1908 and find that this galaxy has a high ionization parameter, little nebular reddening (E{(B-V)}{{gas}}\\lt 0.14), and a high electron density ({n}e˜ 500 cm‑3). We compare the ratios of strong oxygen, neon, and hydrogen lines to the direct-method oxygen abundance for COSMOS-1908 and additional star-forming galaxies at z=0-1.8 with [O iii]λ4363 measurements and show that galaxies at z˜ 1{--}3 follow the same strong-line correlations as galaxies in the local universe. This agreement suggests that the relationship between ionization parameter and O/H is similar for z˜ 0 and high-redshift galaxies. These results imply that metallicity calibrations based on lines of oxygen, neon, and hydrogen do not strongly evolve with redshift and can reliably estimate abundances out to z˜ 3, paving the way for robust measurements of the evolution of the mass–metallicity relation to high redshift. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

  8. A method to determine photosynthetic activity from oxygen microsensor data in biofilms subjected to evaporation.

    PubMed

    Li, Tong; Podola, Björn; de Beer, Dirk; Melkonian, Michael

    2015-10-01

    Phototrophic biofilms are widely distributed in nature and their ecological importance is well recognized. More recently, there has been a growing interest in using artificial phototrophic biofilms in innovative photobioreactors for production of microalgal biomass in biotechnological applications. To study physiological processes within these biofilms, microsensors have been applied in several studies. Here, the 'light-dark shift method' relies on measurement of photosynthetic activity in terms of light-induced oxygen production. However, when applied to non-submerged biofilms that can be found in numerous locations in nature, as well as in some types of photobioreactors, limitations of this approach are obvious due to rapid removal of gaseous species at the biofilm surface. Here, we introduce a mathematical correction to recover the distribution of the actual photosynthetic activity along the depth gradient in the biofilm, based on a numerical solution of the inversed diffusion equation of oxygen. This method considers changes in mass transport during the measurement period as can found on biofilms possessing a thin flow/mass transfer boundary layer (e. g., non-submerged biofilms). Using both simulated and real microsensor data, the proposed method was shown to be much more accurate than the classical method, which leads to underestimations of rates near the biofilm surface. All test profiles could be recovered with a high fit. According to our simulated microsensor measurements, a depth resolution of ≤20 μm is recommended near the surface. We conclude that our method strongly improves the quality of data acquired from light-dark measurements of photosynthetic activity in biofilms. PMID:26232709

  9. Human autonomic activity and its response to acute oxygen supplement after high altitude acclimatization.

    PubMed

    Bao, Xuping; Kennedy, Brian P; Hopkins, Susan R; Bogaard, Harm J; Wagner, Peter D; Ziegler, Michael G

    2002-11-29

    It is well established that after acclimatization at high altitude, many sympathetic pathways are hyperactive yet heart rate (HR) remains unchanged. In this study, we attempted to determine if this unchanged heart rate is due to compensatory mechanisms such as changes in parasympathetic activity or levels of receptors for autonomic neurotransmitters. We also examined the role played by hypoxia in these autonomic adaptations to high altitude. Three experiments were carried out on five healthy lowlanders both at sea level (SL) and after 2 weeks of acclimatization at 3800 m (Post-Ac) with: (a) placebo (control); (b) acute beta-adrenergic receptor blockade by propranolol (PRO), or (c) acute parasympathetic receptor blockade by glycopyrrolate (GLY). Compared with SL control values, post-Ac venous norepinephrine (NE) and dopamine increased by 96% (p < 0.001) and 55% (p < 0.05), but epinephrine and HR did not change. PRO resulted in a smaller decrease in HR (bpm) Post-Ac than at SL (15 +/- 6 vs. 21 +/- 6, p < 0.05), while GLY caused a greater increase in HR Post-Ac than at SL (59 +/- 8 vs. 45 +/- 6, p < 0.05). Breathing oxygen at SL concentration while at altitude did not decrease NE, or alter the effect of PRO on HR, but reduced the chronotropic effect of GLY by 14% (p < 0.05). These results suggest that after acclimatization to altitude, increased parasympathetic neurotransmitter release and decreased beta-adenoreceptor activity account for the unchanged HR despite enhanced sympathetic activity. Acute oxygen replacement rapidly counteracted the parasympathetic, but not sympathetic hyperactivity that occurs at high altitude. PMID:12492136

  10. Abundance ratios of oxygen, neon, and magnesium in solar active regions and flares: The FIP effect

    NASA Technical Reports Server (NTRS)

    Widing, K. G.; Feldman, U.

    1995-01-01

    Relative abundances of oxygen, neon, and magnesium have been derived for a sample of nine solar active regions, flares, and an erupting prominance by combining plots of the ion differential emission measures. The observations were photographed in the 300-600 A range by the Naval Research Laboratory (NRL) spectroheliograph on Skylab. Methods for deriving the Mg/Ne abundance ratio-which measures the separation between the low- first ionization potential (FIP) and high-FIP abundnace plateaus-have been described in previous papers. In this paper we describe the spectroscopic methods for deriving the O/Ne abundance ratio, which gives the ratio between two high-FIP elements. The plot of the O/Ne ratio versus the Mg/Ne ratio in the sample of nine Skylab events is shown. The variation in the Mg/Ne ratio by a factor of 6 is associated with a much smaller range in the O/Ne ratio. This is broadly consistent with the presence of the standard FIP pattern of abundances in the outer atmosphere of the Sun. However, a real change in the relative abundances of oxygen and neon by a factor of 1.5 cannot be excluded.

  11. Oxygen-activated growth and bandgap tunability of large single-crystal bilayer graphene.

    PubMed

    Hao, Yufeng; Wang, Lei; Liu, Yuanyue; Chen, Hua; Wang, Xiaohan; Tan, Cheng; Nie, Shu; Suk, Ji Won; Jiang, Tengfei; Liang, Tengfei; Xiao, Junfeng; Ye, Wenjing; Dean, Cory R; Yakobson, Boris I; McCarty, Kevin F; Kim, Philip; Hone, James; Colombo, Luigi; Ruoff, Rodney S

    2016-05-01

    Bernal (AB)-stacked bilayer graphene (BLG) is a semiconductor whose bandgap can be tuned by a transverse electric field, making it a unique material for a number of electronic and photonic devices. A scalable approach to synthesize high-quality BLG is therefore critical, which requires minimal crystalline defects in both graphene layers and maximal area of Bernal stacking, which is necessary for bandgap tunability. Here we demonstrate that in an oxygen-activated chemical vapour deposition (CVD) process, half-millimetre size, Bernal-stacked BLG single crystals can be synthesized on Cu. Besides the traditional 'surface-limited' growth mechanism for SLG (1st layer), we discovered new microscopic steps governing the growth of the 2nd graphene layer below the 1st layer as the diffusion of carbon atoms through the Cu bulk after complete dehydrogenation of hydrocarbon molecules on the Cu surface, which does not occur in the absence of oxygen. Moreover, we found that the efficient diffusion of the carbon atoms present at the interface between Cu and the 1st graphene layer further facilitates growth of large domains of the 2nd layer. The CVD BLG has superior electrical quality, with a device on/off ratio greater than 10(4), and a tunable bandgap up to ∼100 meV at a displacement field of 0.9 V nm(-1). PMID:26828845

  12. Adsorption of volatile sulphur compounds onto modified activated carbons: effect of oxygen functional groups.

    PubMed

    Vega, Esther; Lemus, Jesús; Anfruns, Alba; Gonzalez-Olmos, Rafael; Palomar, José; Martin, María J

    2013-08-15

    The effect of physical and chemical properties of activated carbon (AC) on the adsorption of ethyl mercaptan, dimethyl sulphide and dimethyl disulphide was investigated by treating a commercial AC with nitric acid and ozone. The chemical properties of ACs were characterised by temperature programme desorption and X-ray photoelectron spectroscopy. AC treated with nitric acid presented a larger amount of oxygen functional groups than materials oxidised with ozone. This enrichment allowed a significant improvement on adsorption capacities for ethyl mercaptan and dimethyl sulphide but not for dimethyl disulphide. In order to gain a deeper knowledge on the effect of the surface chemistry of AC on the adsorption of volatile sulphur compounds, the quantum-chemical COSMO-RS method was used to simulate the interactions between AC surface groups and the studied volatile sulphur compounds. In agreement with experimental data, this model predicted a greater affinity of dimethyl disulphide towards AC, unaffected by the incorporation of oxygen functional groups in the surface. Moreover, the model pointed out to an increase of the adsorption capacity of AC by the incorporation of hydroxyl functional groups in the case of ethyl mercaptan and dimethyl sulphide due to the hydrogen bond interactions. PMID:23708449

  13. Surface structure of α-Cr2O3(0001) after activated oxygen exposure

    SciTech Connect

    Kaspar, Tiffany C.; Chamberlin, Sara E.; Chambers, Scott A.

    2013-09-13

    The surface structure of a-Cr2O3(0001) before and after exposure to activated oxygen from an ECR plasma source was investigated by x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD). Epitaxial Cr2O3(0001) thin films were deposited on Al2O3(0001) substrates by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE). When cooled or annealed in vacuum, strong evidence for a Cr-Cr-O3- termination was obtained by comparing the Cr3+ XPD azimuthal scan to single scattering simulations. However, after plasma exposure, a high binding energy feature was observed in the Cr 2p XPS spectrum that possesses an ordered structure distinct from the underlying Cr3+ of Cr2O3, which remains Cr-Cr-O3-like. Investigation of this new surface structure with simulations of various candidate structures tentatively rules out CrO2-like configurations. The high binding energy feature likely arises from a higher oxidation state of Cr. One possibility is the oxidation of the surface layer of Cr to Cr6- with a double chromyl structure (O=Cr=O).

  14. Surface structure of α-Cr2O3(0001) after activated oxygen exposure

    NASA Astrophysics Data System (ADS)

    Kaspar, Tiffany C.; Chamberlin, Sara E.; Chambers, Scott A.

    2013-12-01

    The surface structure of α-Cr2O3(0001) before and after exposure to activated oxygen from an ECR plasma source was investigated by x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD). Epitaxial Cr2O3(0001) thin films were deposited on Al2O3(0001) substrates by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE). When cooled or annealed in vacuum, strong evidence for a Crsbnd Crsbnd O3sbnd termination was obtained by comparing the Cr3 + XPD azimuthal scan to single scattering simulations. However, after plasma exposure, a high binding energy feature was observed in the Cr 2p XPS spectrum that possesses an ordered structure distinct from the underlying Cr3 + of Cr2O3, which remains Cr-Cr-O3-like. Investigation of this new surface structure with simulations of various candidate structures tentatively rules out CrO2-like configurations. The high binding energy feature likely arises from a higher oxidation state of Cr. One possibility is the oxidation of the surface layer of Cr to Cr6 - δ with a double chromyl structure (Odbnd Crdbnd O).

  15. Oxygen-activated growth and bandgap tunability of large single-crystal bilayer graphene

    NASA Astrophysics Data System (ADS)

    Hao, Yufeng; Wang, Lei; Liu, Yuanyue; Chen, Hua; Wang, Xiaohan; Tan, Cheng; Nie, Shu; Suk, Ji Won; Jiang, Tengfei; Liang, Tengfei; Xiao, Junfeng; Ye, Wenjing; Dean, Cory R.; Yakobson, Boris I.; McCarty, Kevin F.; Kim, Philip; Hone, James; Colombo, Luigi; Ruoff, Rodney S.

    2016-05-01

    Bernal (AB)-stacked bilayer graphene (BLG) is a semiconductor whose bandgap can be tuned by a transverse electric field, making it a unique material for a number of electronic and photonic devices. A scalable approach to synthesize high-quality BLG is therefore critical, which requires minimal crystalline defects in both graphene layers and maximal area of Bernal stacking, which is necessary for bandgap tunability. Here we demonstrate that in an oxygen-activated chemical vapour deposition (CVD) process, half-millimetre size, Bernal-stacked BLG single crystals can be synthesized on Cu. Besides the traditional ‘surface-limited’ growth mechanism for SLG (1st layer), we discovered new microscopic steps governing the growth of the 2nd graphene layer below the 1st layer as the diffusion of carbon atoms through the Cu bulk after complete dehydrogenation of hydrocarbon molecules on the Cu surface, which does not occur in the absence of oxygen. Moreover, we found that the efficient diffusion of the carbon atoms present at the interface between Cu and the 1st graphene layer further facilitates growth of large domains of the 2nd layer. The CVD BLG has superior electrical quality, with a device on/off ratio greater than 104, and a tunable bandgap up to ∼100 meV at a displacement field of 0.9 V nm‑1.

  16. Effect of glutaphen on generation of active oxygen species, photosynthetic electron transport, and the functional activity of photosystem 2 in Chlorella cells

    NASA Astrophysics Data System (ADS)

    Samovich, T. V.; Pshibytko, N. L.; Averina, N. G.

    2006-11-01

    Treatment of chlorella green algae (Chlorella sp.) for 2 h in the dark with the photodynamic herbicide glutaphen (GTP), consisting of 0.3 mM 1,10-phenanthroline and 0.6 mM glutamic acid, followed by illumination leads to efficient generation of active oxygen species (AOS). After 15 min of illumination, AOS accumulation reaches 200% compared with the level in cells of the control culture, then it decreases down to 130% and 115% after 1 day and 3 days of illumination. During the first few days after treatment, we observe inhibition of synthesis of a specific precursor of chlorophyll (Chl): 5-aminolevulinic acid molecules, and then we observe stimulation of the synthesis. The effect of GTP on the photosynthetic activity of chlorella does not depend on the AOS level but rather remains uniform, in contrast to its effect on the Chl biosynthesis system. GTP does not change the efficiency of light harvesting and charge separation at the reaction centers of photosystem (PS) 2, but significantly lowers the functional efficiency of the electron transport chain: the photochemical quenching constants for Chl a fluorescence and the effective quantum yield of photochemical reactions in photosystem 2 decrease. The major mechanism of action for GTP is probably displacement of the secondary quinone acceptor QB from its binding site on the D1 protein by the 1,10-phenanthroline, consequent inhibition of electron efflux from Q{A/-} and increase in the fraction of QB-nonreducing centers of PS 2. The active oxygen species generated in the cells have a photodegradative effect on the Chl biosynthesis system, in particular on its initial steps, and do not involve already formed pigment-protein complexes of PS 2.

  17. Low Oxygen Tension Enhances Expression of Myogenic Genes When Human Myoblasts Are Activated from G0 Arrest

    PubMed Central

    Sellathurai, Jeeva; Nielsen, Joachim; Hejbøl, Eva Kildall; Jørgensen, Louise Helskov; Dhawan, Jyotsna; Nielsen, Michael Friberg Bruun; Schrøder, Henrik Daa

    2016-01-01

    Objectives Most cell culture studies have been performed at atmospheric oxygen tension of 21%, however the physiological oxygen tension is much lower and is a factor that may affect skeletal muscle myoblasts. In this study we have compared activation of G0 arrested myoblasts in 21% O2 and in 1% O2 in order to see how oxygen tension affects activation and proliferation of human myoblasts. Materials and Methods Human myoblasts were isolated from skeletal muscle tissue and G0 arrested in vitro followed by reactivation at 21% O2 and 1% O2. The effect was assesses by Real-time RT-PCR, immunocytochemistry and western blot. Results and Conclusions We found an increase in proliferation rate of myoblasts when activated at a low oxygen tension (1% O2) compared to 21% O2. In addition, the gene expression studies showed up regulation of the myogenesis related genes PAX3, PAX7, MYOD, MYOG (myogenin), MET, NCAM, DES (desmin), MEF2A, MEF2C and CDH15 (M-cadherin), however, the fraction of DES and MYOD positive cells was not increased by low oxygen tension, indicating that 1% O2 may not have a functional effect on the myogenic response. Furthermore, the expression of genes involved in the TGFβ, Notch and Wnt signaling pathways were also up regulated in low oxygen tension. The differences in gene expression were most pronounced at day one after activation from G0-arrest, thus the initial activation of myoblasts seemed most sensitive to changes in oxygen tension. Protein expression of HES1 and β-catenin indicated that notch signaling may be induced in 21% O2, while the canonical Wnt signaling may be induced in 1% O2 during activation and proliferation of myoblasts. PMID:27442119

  18. Composition and topology of activity cliff clusters formed by bioactive compounds.

    PubMed

    Stumpfe, Dagmar; Dimova, Dilyana; Bajorath, Jürgen

    2014-02-24

    The assessment of activity cliffs has thus far mostly focused on compound pairs, although the majority of activity cliffs are not formed in isolation but in a coordinated manner involving multiple active compounds and cliffs. However, the composition of coordinated activity cliff configurations and their topologies are unknown. Therefore, we have identified all activity cliff configurations formed by currently available bioactive compounds and analyzed them in network representations where activity cliff configurations occur as clusters. The composition, topology, frequency of occurrence, and target distribution of activity cliff clusters have been determined. A limited number of large cliff clusters with unique topologies were identified that were centers of activity cliff formation. These clusters originated from a small number of target sets. However, most clusters were of small to moderate size. Three basic topologies were sufficient to describe recurrent activity cliff cluster motifs/topologies. For example, frequently occurring clusters with star topology determined the scale-free character of the global activity cliff network and represented a characteristic activity cliff configuration. Large clusters with complex topology were often found to contain different combinations of basic topologies. Our study provides a first view of activity cliff configurations formed by currently available bioactive compounds and of the recurrent topologies of activity cliff clusters. Activity cliff clusters of defined topology can be selected, and from compounds forming the clusters, SAR information can be obtained. The SAR information of activity cliff clusters sharing a/one specific activity and topology can be compared. PMID:24437577

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  6. ACROLEIN ACTIVATES MATRIX METALLOPROTEINASES BY INCREASING REACTIVE OXYGEN SPECIES IN MACROPHAGES

    PubMed Central

    O’Toole, Timothy E.; Zheng, Yu-Ting; Hellmann, Jason; Conklin, Daniel J.; Barski, Oleg; Bhatnagar, Aruni

    2009-01-01

    Acrolein is a ubiquitous component of environmental pollutants such as automobile exhaust, cigarette, wood, and coal smoke. It is also a natural constituent of several foods and is generated endogenously during inflammation or oxidation of unsaturated lipids. Because increased inflammation and episodic exposure to acrolein-rich pollutants such as traffic emissions or cigarette smoke have been linked to acute myocardial infarction, we examined the effects of acrolein on matrix metalloproteinases (MMPs), which destabilize atherosclerotic plaques. Our studies show that exposure to acrolein resulted in the secretion of MMP-9 from differentiated THP-1 macrophages. Acrolein-treatment of macrophages also led to an increase in reactive oxygen species (ROS), free intracellular calcium ([Ca2+]i), and xanthine oxidase (XO) activity. ROS production was prevented by allopurinol, but not by rotenone or apocynin and by buffering changes in [Ca2+]I with BAPTA-AM. The increase in MMP production was abolished by pre-treatment with the antioxidants Tiron and N-acetyl cysteine (NAC) or with the xanthine oxidase inhibitors allopurinol or oxypurinol. Finally, MMP activity was significantly stimulated in aortic sections from apoE-null mice containing advanced atherosclerotic lesions after exposure to acrolein ex vivo. These observations suggest that acrolein exposure results in MMP secretion from macrophages via a mechanism that involves an increase in [Ca2+]I, leading to xanthine oxidase activation and an increase in ROS production. ROS-dependent activation of MMPs by acrolein could destabilize atherosclerotic lesions during brief episodes of inflammation or pollutant exposure. PMID:19371603

  7. Acrolein activates matrix metalloproteinases by increasing reactive oxygen species in macrophages.

    PubMed

    O'Toole, Timothy E; Zheng, Yu-Ting; Hellmann, Jason; Conklin, Daniel J; Barski, Oleg; Bhatnagar, Aruni

    2009-04-15

    Acrolein is a ubiquitous component of environmental pollutants such as automobile exhaust, cigarette, wood, and coal smoke. It is also a natural constituent of several foods and is generated endogenously during inflammation or oxidation of unsaturated lipids. Because increased inflammation and episodic exposure to acrolein-rich pollutants such as traffic emissions or cigarette smoke have been linked to acute myocardial infarction, we examined the effects of acrolein on matrix metalloproteinases (MMPs), which destabilize atherosclerotic plaques. Our studies show that exposure to acrolein resulted in the secretion of MMP-9 from differentiated THP-1 macrophages. Acrolein-treatment of macrophages also led to an increase in reactive oxygen species (ROS), free intracellular calcium ([Ca2+](i)), and xanthine oxidase (XO) activity. ROS production was prevented by allopurinol, but not by rotenone or apocynin and by buffering changes in [Ca2+](I) with BAPTA-AM. The increase in MMP production was abolished by pre-treatment with the antioxidants Tiron and N-acetyl cysteine (NAC) or with the xanthine oxidase inhibitors allopurinol or oxypurinol. Finally, MMP activity was significantly stimulated in aortic sections from apoE-null mice containing advanced atherosclerotic lesions after exposure to acrolein ex vivo. These observations suggest that acrolein exposure results in MMP secretion from macrophages via a mechanism that involves an increase in [Ca2+](I), leading to xanthine oxidase activation and an increase in ROS production. ROS-dependent activation of MMPs by acrolein could destabilize atherosclerotic lesions during brief episodes of inflammation or pollutant exposure. PMID:19371603

  8. A unique platinum-graphene hybrid structure for high activity and durability in oxygen reduction reaction

    PubMed Central

    Wang, Chengming; Ma, Liang; Liao, Lingwen; Bai, Song; Long, Ran; Zuo, Ming; Xiong, Yujie

    2013-01-01

    It remains a grand challenge to achieve both high activity and durability in Pt electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Here we develop a class of Pt highly concave cubic (HCC) nanocrystals, which are enriched with high-index facets, to enable high ORR activity. The durability of HCC nanocrystals can be significantly improved via assembly with graphene. Meanwhile, the unique hybrid structure displays further enhanced specific activity, which is 7-fold greater than the state-of-the-art Pt/C catalysts. Strikingly, it exhibits impressive performance in terms of half-wave potential (E1/2). The E1/2 of 0.967 V at the Pt loading as low as 46 μg cm−2, which stands as 63 mV higher than that of the Pt/C catalysts, is slightly superior to the record observed for the most active porous Pt-Ni catalyst in literature. This work paves the way to designing high-performance electrocatalysts by modulating their surface and interface with loading substrates. PMID:23999570

  9. Role of Oxygen as Surface-Active Element in Linear GTA Welding Process

    NASA Astrophysics Data System (ADS)

    Yadaiah, Nirsanametla; Bag, Swarup

    2013-11-01

    Although the surface-active elements such as oxygen and sulfur have an adverse effect on momentum transport in liquid metals during fusion welding, such elements can be used beneficially up to a certain limit to increase the weld penetration in the gas tungsten arc (GTA) welding process. The fluid flow pattern and consequently the weld penetration and width change due to a change in coefficient of surface tension from a negative value to a positive value. The present work is focused on the analysis of possible effects of surface-active elements to change the weld pool dimensions in linear GTA welding. A 3D finite element-based heat transfer and fluid flow model is developed to study the effect of surface-active elements on stainless steel plates. A velocity in the order of 180 mm/s due to surface tension force is estimated at an optimum concentration of surface-active elements. Further, the differential evolution-based global optimization algorithm is integrated with the numerical model to estimate uncertain model parameters such as arc efficiency, effective arc radius, and effective values of material properties at high temperatures. The effective values of thermal conductivity and viscosity are estimated to be enhanced nine and seven times, respectively, over corresponding room temperature values. An error analysis is also performed to find out the overall reliability of the computed results, and a maximum reliability of 0.94 is achieved.

  10. Blood Oxygen Level-Dependent Activation of the Primary Visual Cortex Predicts Size Adaptation Illusion

    PubMed Central

    Pooresmaeili, Arezoo; Arrighi, Roberto; Biagi, Laura; Morrone, Maria Concetta

    2016-01-01

    In natural scenes, objects rarely occur in isolation but appear within a spatiotemporal context. Here, we show that the perceived size of a stimulus is significantly affected by the context of the scene: brief previous presentation of larger or smaller adapting stimuli at the same region of space changes the perceived size of a test stimulus, with larger adapting stimuli causing the test to appear smaller than veridical and vice versa. In a human fMRI study, we measured the blood oxygen level-dependent activation (BOLD) responses of the primary visual cortex (V1) to the contours of large-diameter stimuli and found that activation closely matched the perceptual rather than the retinal stimulus size: the activated area of V1 increased or decreased, depending on the size of the preceding stimulus. A model based on local inhibitory V1 mechanisms simulated the inward or outward shifts of the stimulus contours and hence the perceptual effects. Our findings suggest that area V1 is actively involved in reshaping our perception to match the short-term statistics of the visual scene. PMID:24089504

  11. Platinum multicubes prepared by ni(2+) -mediated shape evolution exhibit high electrocatalytic activity for oxygen reduction.

    PubMed

    Ma, Liang; Wang, Chengming; Xia, Bao Yu; Mao, Keke; He, Jiawei; Wu, Xiaojun; Xiong, Yujie; Lou, Xiong Wen David

    2015-05-01

    Pt(100) facets are generally considered less active for the oxygen reduction reaction (ORR). Reported herein is a unique Pt-branched structure, a multicube, whose surface is mostly enclosed by {100} facets but contains high-index facets at the small junction area between the adjacent cubic components. The synthesis is accomplished by a Ni(2+) -mediated facet evolution from high-index {311} to {100} facets on the frameworks of multipods. Despite the high {100} facet coverage, the Pt multicubes exhibit impressive ORR activity in terms of half-wave potential and current density nearly to the level of the most active Pt-based catalysts, while the durability of catalysts is well retained. The facet evolution creates a set of samples with tunable ratios of high-index to low-index facets. The results reveal that the excellent ORR performance of Pt multicubes is a combined result of active sites by high-index facets and low resistance by flat surface. It is anticipated that this work will offer a new approach to facet-controlled synthesis and ORR catalysts design. PMID:25756931

  12. Ultrathin Icosahedral Pt-Enriched Nanocage with Excellent Oxygen Reduction Reaction Activity.

    PubMed

    He, Dong Sheng; He, Daping; Wang, Jing; Lin, Yue; Yin, Peiqun; Hong, Xun; Wu, Yuen; Li, Yadong

    2016-02-10

    Cost-efficient utilization of Pt in the oxygen reduction reaction (ORR) is of great importance for the potential industrial scale demand of proton-exchange membrane fuel cells. Designing a hollow structure of a Pt catalyst offers a great opportunity to enhance the electrocatalytic performance and maximize the use of precious Pt. Herein we report a routine to synthesize ultrathin icosahedral Pt-enriched nanocages. In detail, the Pt atoms were conformally deposited on the surface of Pd icosahedral seeds, followed by selective removal of the Pd core by a concentrated HNO3 solution. The icosahedral Pt-enriched nanocage that is a few atomic layers thick includes the merits of abundant twin defects, an ultrahigh surface/volume ratio, and an ORR-favored Pt{111} facet, all of which have been demonstrated to be promoting factors for ORR. With a 10 times higher specific activity and 7 times higher mass activity, this catalyst shows more extraordinary ORR activity than the commercial Pt/C. The ORR activity of icosahedral Pt-enriched nanocages outperforms the cubic and octahedral nanocages reported in the literature, demonstrating the superiority of the icosahedral nanocage structure. PMID:26808073

  13. Nrf2 activation in astrocytes contributes to spinal cord ischemic tolerance induced by hyperbaric oxygen preconditioning.

    PubMed

    Xu, Jiajun; Huang, Guoyang; Zhang, Kun; Sun, Jinchuan; Xu, Tao; Li, Runping; Tao, Hengyi; Xu, Weigang

    2014-08-01

    In this study, we investigated whether nuclear factor erythroid 2-related factor 2 (Nrf2) activation in astrocytes contributes to the neuroprotection induced by a single hyperbaric oxygen preconditioning (HBO-PC) against spinal cord ischemia/reperfusion (SCIR) injury. In vivo: At 24 h after a single HBO-PC at 2.5 atmospheres absolute for 90 min, the male ICR mice underwent SCIR injury by aortic cross-clamping surgery and observed for 48 h. HBO-PC significantly improved hindlimb motor function, reduced secondary spinal cord edema, ameliorated the reactivity of spinal motor-evoked potentials, and slowed down the process of apoptosis to exert neuroprotective effects against SCIR injury. At 12 h or 24 h after HBO-PC without aortic cross-clamping surgery, Western blot, enzyme-linked immunosorbent assay, realtime-polymerase chain reaction and double-immunofluorescence staining were used to detect the Nrf2 activity of spinal cord tissue, such as mRNA level, protein content, DNA binding activity, and the expression of downstream gene, such as glutamate-cysteine ligase, γ-glutamyltransferase, multidrug resistance protein 1, which are key proteins for intracellular glutathione synthesis and transit. The Nrf2 activity and downstream genes expression were all enhanced in normal spinal cord with HBO-PC. Glutathione content of spinal cord tissue with HBO-PC significantly increased at all time points after SCIR injury. Moreover, Nrf2 overexpression mainly occurs in astrocytes. In vitro: At 24 h after HBO-PC, the primary spinal astrocyte-neuron co-cultures from ICR mouse pups were subjected to oxygen-glucose deprivation (OGD) for 90 min to simulate the ischemia-reperfusion injury. HBO-PC significantly increased the survival rate of neurons and the glutathione content in culture medium, which was mainly released from asctrocytes. Moreover, the Nrf2 activity and downstream genes expression induced by HBO-PC were mainly enhanced in astrocytes, but not in neurons. In

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  15. Dance as a Fitness Activity: The Impact of Teaching Style and Dance Form.

    ERIC Educational Resources Information Center

    Fromel, Karel; Vasendova, Jana; Stratton, Gareth; Pangrazi, Robert P.

    2002-01-01

    Analyzed the amount of activity, intensity of activity, and attitudes of participants in Czech high school physical education classes taught using different teaching styles and dance forms. Measurements of heart rate and dance intensity and student surveys indicated that teaching style and dance form significantly impacted the intensity and volume…

  16. Structure of RdxA: an oxygen insensitive nitroreductase essential for metronidazole activation in Helicobacter pylori

    PubMed Central

    Martínez-Júlvez, Marta; Rojas, Adriana L.; Olekhnovich, Igor; Angarica, Vladimir Espinosa; Hoffman, Paul S.; Sancho, Javier

    2012-01-01

    The RdxA oxygen insensitive nitroreductase of the human gastric pathogen Helicobacter pylori is responsible for the susceptibility of this organism to the redox active prodrug metronidazole (MTZ). Loss-of-function mutations in rdxA are primarily responsible for resistance to this therapeutic. RdxA exhibits potent NADPH oxidase activity under aerobic conditions and metronidazole reductase activity under strictly anaerobic conditions. Here we report the crystal structure of RdxA, which is a homodimer exhibiting domain swapping and containing two molecules of FMN bound at the dimer interface. We have found a gap between the side chain of Tyr47 and the isoalloxazine ring of FMN that seems appropriate for substrate binding. The structure does not include residues 97–128, which corresponds to a locally unstable part of the NTR from E. coli, and might be involved in cofactor binding. Comparison of H pylori RdxA to other oxidoreductases of known structure suggests RdxA may belong to a new subgroup of oxidoreductases in which a cysteine sidechain close to the FMN cofactor could be involved in the reductive activity. In this respect, mutation of C159 to A or S (C159A/S) has resulted in loss of MTZ reductase activity, but not NADPH oxidase activity. The RdxA structure allows interpretation of the many loss-of-function mutations previously described, including those affecting C159, a residue whose interaction with FMN is required for nitroreduction of MTZ. Our studies provide unique insights into the redox behavior of the flavin in this key enzyme for metronidazole activation, and with potential use in gene therapy. PMID:23039228

  17. Concentration Effects of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Activity for Three Platinum Catalysts

    DOE PAGESBeta

    Christ, J. M.; Neyerlin, K. C.; Richards, R.; Dinh, H. N.

    2014-10-04

    A rotating disk electrode (RDE) along with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were used to investigate the impact of two model compounds representing degradation products of Nafion and 3M perfluorinated sulfonic acid membranes on the electrochemical surface area (ECA) and oxygen reduction reaction (ORR) activity of polycrystalline Pt, nano-structured thin film (NSTF) Pt (3M), and Pt/Vulcan carbon (Pt/Vu) (TKK) electrodes. ORR kinetic currents (measured at 0.9 V and transport corrected) were found to decrease linearly with the log of concentration for both model compounds on all Pt surfaces studied. Ultimately, model compound adsorption effects on ECA weremore » more abstruse due to competitive organic anion adsorption on Pt surfaces superimposing with the hydrogen underpotential deposition (HUPD) region.« less

  18. Highly active cobalt phosphate and borate based oxygen evolving catalysts operating in neutral and natural waters

    SciTech Connect

    Esswein, AJ; Surendranath, Y; Reece, SY; Nocera, DG

    2011-02-01

    A high surface area electrode is functionalized with cobalt-based oxygen evolving catalysts (Co-OEC = electrodeposited from pH 7 phosphate, Pi, pH 8.5 methylphosphonate, MePi, and pH 9.2 borate electrolyte, Bi). Co-OEC prepared from MePi and operated in Pi and Bi achieves a current density of 100 mA cm(-2) for water oxidation at 442 and 363 mV overpotential, respectively. The catalyst retains activity in near-neutral pH buffered electrolyte in natural waters such as those from the Charles River (Cambridge, MA) and seawater (Woods Hole, MA). The efficacy and ease of operation of anodes functionalized with Co-OEC at appreciable current density together with its ability to operate in near neutral pH buffered natural water sources bodes well for the translation of this catalyst to a viable renewable energy storage technology.

  19. Singlet oxygen scavenging activity of tocopherol and plastochromanol in Arabidopsis thaliana: relevance to photooxidative stress.

    PubMed

    Rastogi, Anshu; Yadav, Deepak Kumar; Szymańska, Renata; Kruk, Jerzy; Sedlářová, Michaela; Pospíšil, Pavel

    2014-02-01

    In the present study, singlet oxygen (¹O₂) scavenging activity of tocopherol and plastochromanol was examined in tocopherol cyclase-deficient mutant (vte1) of Arabidopsis thaliana lacking both tocopherol and plastochromanol. It is demonstrated here that suppression of tocopherol and plastochromanol synthesis in chloroplasts isolated from vte1 Arabidopsis plants enhanced ¹O₂ formation under high light illumination as monitored by electron paramagnetic resonance spin-trapping spectroscopy. The exposure of vte1 Arabidopsis plants to high light resulted in the formation of secondary lipid peroxidation product malondialdehyde as determined by high-pressure liquid chromatography. Furthermore, it is shown here that the imaging of ultra-weak photon emission known to reflect oxidation of lipids was unambiguously higher in vte1 Arabidopsis plants. Our results indicate that tocopherol and plastochromanol act as efficient ¹O₂ scavengers and protect effectively lipids against photooxidative damage in Arabidopsis plants. PMID:23848570

  20. Genetic damage in CHO cells exposed to enzymically generated active oxygen species.

    PubMed

    Phillips, B J; James, T E; Anderson, D

    1984-05-01

    The genetic toxicity of active oxygen species produced during the enzymic oxidation of xanthine has been investigated using Chinese hamster ovary (CHO) cells. Incubation of cells with xanthine plus xanthine oxidase resulted in extensive chromosome breakage and sister-chromatid exchange and gave a small increase in frequency of thioguanine-resistant cells (HGPRT test). Inclusion of superoxide dismutase or catalase in the xanthine/xanthine oxidase system inhibited chromosome breakage, whereas only catalase prevented SCE and mutant induction. It is concluded that hydrogen peroxide is responsible for most of the genetic effects observed in CHO cells exposed to xanthine/xanthine oxidase but that superoxide plays a key role in chromosome breakage. PMID:6325900

  1. Nitride stabilized PtNi core-shell nanocatalyst for high oxygen reduction activity.

    PubMed

    Kuttiyiel, Kurian A; Sasaki, Kotaro; Choi, Yongman; Su, Dong; Liu, Ping; Adzic, Radoslav R

    2012-12-12

    We describe a route to the development of novel PtNiN core-shell catalysts with low Pt content shell and inexpensive NiN core having high activity and stability for the oxygen reduction reaction (ORR). The PtNiN synthesis involves nitriding Ni nanoparticles and simultaneously encapsulating it by 2-4 monolayer-thick Pt shell. The experimental data and the density functional theory calculations indicate nitride has the bifunctional effect that facilitates formation of the core-shell structures and improves the performance of the Pt shell by inducing both geometric and electronic effects. Synthesis of inexpensive NiN cores opens up possibilities for designing of various transition metal nitride based core-shell nanoparticles for a wide range of applications in energy conversion processes. PMID:23194259

  2. Short Self-Assembling Peptides Are Able to Bind to Copper and Activate Oxygen.

    PubMed

    Makhlynets, Olga V; Gosavi, Pallavi M; Korendovych, Ivan V

    2016-07-25

    We have shown that de novo designed peptides self-assemble in the presence of copper to create supramolecular assemblies capable of carrying out the oxidation of dimethoxyphenol in the presence of dioxygen. Formation of the supramolecular assembly, which is akin to a protein fold, is critical for productive catalysis since peptides possessing the same functional groups but lacking the ability to self-assemble do not catalyze substrate oxidation. The ease with which we have discovered robust and productive oxygen activation catalysts suggests that these prion-like assemblies might have served as intermediates in the evolution of enzymatic function and opens the path for the development of new catalyst nanomaterials. PMID:27276534

  3. Concentration Effects of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Activity for Three Platinum Catalysts

    SciTech Connect

    Christ, J. M.; Neyerlin, K. C.; Richards, R.; Dinh, H. N.

    2014-10-04

    A rotating disk electrode (RDE) along with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were used to investigate the impact of two model compounds representing degradation products of Nafion and 3M perfluorinated sulfonic acid membranes on the electrochemical surface area (ECA) and oxygen reduction reaction (ORR) activity of polycrystalline Pt, nano-structured thin film (NSTF) Pt (3M), and Pt/Vulcan carbon (Pt/Vu) (TKK) electrodes. ORR kinetic currents (measured at 0.9 V and transport corrected) were found to decrease linearly with the log of concentration for both model compounds on all Pt surfaces studied. Ultimately, model compound adsorption effects on ECA were more abstruse due to competitive organic anion adsorption on Pt surfaces superimposing with the hydrogen underpotential deposition (HUPD) region.

  4. EFFECT OF MOLECULAR OXYGEN ON ADSORPTIVE CAPACITY AND EXTRACTION EFFICIENCY OF GRANULATED ACTIVATED CARBON FOR THREE ORTHO-SUBSTITUTED PHENOLS

    EPA Science Inventory

    Adsorptive capacity of activated carbon for several organic compounds was found to be strongly influenced by the presence of molecular oxygen. This influence is manifested by the polymerization of adsorbate on the surface of activated carbon. As a result, GAC exhibits much high...

  5. Student Responses to a Hands-On Kinesthetic Lecture Activity for Learning about the Oxygen Carrying Capacity of Blood

    ERIC Educational Resources Information Center

    Breckler, Jennifer; Yu, Justin R.

    2011-01-01

    This article describes a new hands-on, or "kinesthetic," activity for use in a physiology lecture hall to help students comprehend an important concept in cardiopulmonary physiology known as oxygen carrying capacity. One impetus for designing this activity was to address the needs of students who have a preference for kinesthetic learning and to…

  6. Theoretical insights on the catalytic activity and mechanism for oxygen reduction reaction at Fe and P codoped graphene.

    PubMed

    He, Feng; Li, Kai; Xie, Guangyou; Wang, Ying; Jiao, Menggai; Tang, Hao; Wu, Zhijian

    2016-05-14

    The non-precious metal graphene catalyst doped with Fe-Px are recently proposed as a promising candidate in substituting Pt for catalyzing oxygen reduction reaction (ORR) in fuel cells. Systematic DFT calculations are performed to investigate the catalytic activity and the ORR mechanism on the Fe-Px (x = 1-4) system in acid medium in this work. Our results indicated that the configuration with one Fe and two P atoms codoped at zigzag edge site (Fe-P2-zig-G) is the most stable, in excellent agreement with the experimental observation that the ratio of Fe and P is nearly 1 : 2. The four-electron reduction mechanism for ORR on the Fe-P2-zig-G is via the competing OOH hydrogenation pathways (to form either OH + OH or O + H2O). The rate determining step is the O2 hydrogenation with an energy barrier of 0.43 eV, much smaller that of calculated 0.80 eV for pure Pt. In addition, the highest energy barrier of the studied ORR mechanism is the O2 dissociation with an energy barrier of 0.70 eV, a value also smaller than that of pure Pt. This demonstrated that the zigzag edge site of the Fe-P2 codoped graphene should be active for the ORR. PMID:27094325

  7. In vitro activity of Rutaceae species against the trypomastigote form of Trypanosoma cruzi.

    PubMed

    Mafezoli, J; Vieira, P C; Fernandes, J B; da Silva, M F; de Albuquerque, S

    2000-11-01

    The activity of crude plant extracts of nine species of Rutaceae against the trypomastigote form of Trypanosoma cruzi was evaluated at 4 mg/ml. Thirty-two crude extracts were tested and eight of them showed significant activity (>80%). The most active extract was obtained from the stems of Pilocarpus spicatus (97.3%). Fractionation of the active crude extracts provided 25 fractions which were tested against the trypomastigote form of T. cruzi at 2 mg/ml. Of these six showed significant activity (>80%). The most active fractions (100%) were obtained from the leaves of Almeidea coerulea (butanol fraction) and Conchocarpus inopinatus (dichloromethane fraction). PMID:11025175

  8. Probenecid protects against oxygen-glucose deprivation injury in primary astrocytes by regulating inflammasome activity.

    PubMed

    Jian, Zhihong; Ding, Shuai; Deng, Hongping; Wang, Jun; Yi, Wei; Wang, Lei; Zhu, Shengmei; Gu, Lijuan; Xiong, Xiaoxing

    2016-07-15

    Inflammation is extremely important in the development of cerebral ischemia/reperfusion injury. Pannexin 1 (Panx1) channel has been reported to activate inflammasome in astrocytes and be involved in ischemic injury, but this damage effect is reversed by a Panx1 inhibitor-probenecid. However, the mechanism of probenecid protects against cerebral ischemia/reperfusion injury remains unclear. In present study, we hypothesized that probenecid protected astrocytes from ischemia/reperfusion injury in vitro by modulating the inflammasome. Primary cultured neocortical astrocytes were exposed to oxygen-glucose deprivation/reoxygenation (OGD/RX) and probenecid was added in this model. Viability and nuclear morphology of astrocytes, production of reactive oxygen species (ROS), protein expressions of NLRP3 (NOD-like receptor protein 3), caspase-1, and AQP4 (Aquaporins 4), as well as release of cellular HMGB1 and IL-1β were observed to evaluate the effect and mechanisms of probenecid on OGD/reoxygenated astrocytes. Probenecid did not affect cell viability at concentrations of 1, 5, 10, and 100μM but induced significant astrocytes death at 500μM. Probenecid inhibited cell death and ROS generation in astrocytes subjected to 6h of OGD and 24h of reoxygenation. The expression levels of NLRP3, caspase-1, and AQP4 increased after 6h of OGD, but probenecid treatment attenuated this increase. Moreover, the extracellular release of IL-1β and HMGB1 from OGD/reoxygenated astrocytes increased significantly. However, treatment by probenecid resulted in substantial reduction of these proteins levels in extracellular space. In conclusion, The Panx1 inhibitor, probenecid, which was administered before OGD, provided protective effects on the OGD/reoxygenation model of cultured astrocytes by modulating inflammasome activity and downregulating AQP4 expression. PMID:27154322

  9. Labor Contractions Enhance Oxygenation and Behavioral Activity of Newborn Rat Pups

    NASA Technical Reports Server (NTRS)

    Mills, N. A.; Baer, L. A.; Ronca, A. E.; Balton, Bonnie (Technical Monitor)

    2002-01-01

    Labor contractions help instigate behavioral responses at birth (viz., breathing and suckling) that are vital for the newborn's adaptation to the extrauterine world (Ronca et al., 1996). In the present study, we analyzed the role of labor contractions in postpartum oxygenation and behavioral activity of newborn rat pups. Newborns were observed following either vaginal (V) or cesarean delivery. For cesarean delivery, day 21 pregnant dams' were administered a spinal transaction to eliminate lower body sensation, a laparotomy was performed and the uterus was maintained in a heated (37.5 C) bath. Four rat fetuses in one of the dams' paired uterine horn were compressed (C) to Simulate labor contractions (20 sec/min for 10 min) while four fetuses in the opposite horn were not compressed (NC). Fetuses were surgically removed from the uterus, stroked with a soft brush to mimic postnatal licking by the dam, the umbilical cord occluded. Pups were exposed to room temperature (22 C) for one hr, then nest temperature (33 C) for one hr. PO2, CO2, and O2, saturation were determined at 0, 30, 60, or 120 min post delivery using a blood gas analyzer. V and C delivered neonates showed comparable rates of PO2, CO2 and O2 saturation whereas NC neonates showed depressed levels at all time points (p<0.05). Respiratory rates of V, C and NC neonates increased significantly (p<0.05) over the first two postpartum hrs and did not differ across groups. Postpartum behavioral activity was significantly greater in V and C conditions and positively correlated with postnatal oxygenation. These findings provide further evidence for importance of labor contractions in early postpartum adaptation.

  10. Regulation of IDO activity by oxygen supply: inhibitory effects on antimicrobial and immunoregulatory functions.

    PubMed

    Schmidt, Silvia K; Ebel, Sebastian; Keil, Eric; Woite, Claudia; Ernst, Joachim F; Benzin, Anika E; Rupp, Jan; Däubener, Walter

    2013-01-01

    Tryptophan is an essential amino acid for human beings as well as for some microorganisms. In human cells the interferon-γ (IFN-γ) inducible enzyme indoleamine 2,3-dioxygenase (IDO) reduces local tryptophan levels and is therefore able to mediate broad-spectrum effector functions: IDO activity restricts the growth of various clinically relevant pathogens such as bacteria, parasites and viruses. On the other hand, it has been observed that IDO has immunoregulatory functions as it efficiently controls the activation and survival of T-cells. Although these important effects have been analysed in much detail, they have been observed in vitro using cells cultured in the presence of 20% O₂ (normoxia). Such high oxygen concentrations are not present in vivo especially within infected and inflamed tissues. We therefore analysed IDO-mediated effects under lower oxygen concentrations in vitro and observed that the function of IDO is substantially impaired in tumour cells as well as in native cells. Hypoxia led to reduced IDO expression and as a result to reduced production of kynurenine, the downstream product of tryptophan degradation. Consequently, effector functions of IDO were abrogated under hypoxic conditions: in different human cell lines such as tumour cells (glioblastoma, HeLa) but also in native cells (human foreskin fibroblasts; HFF) IDO lost the capacity to inhibit the growth of bacteria (Staphylococcus aureus), parasites (Toxoplasma gondii) or viruses (herpes simplex virus type 1). Additionally, IDO could no longer efficiently control the proliferation of T-cells that have been co-cultured with IDO expressing HFF cells in vitro. In conclusion, the potent antimicrobial as well as immunoregulatory functions of IDO were substantially impaired under hypoxic conditions that pathophysiologically occurs in vivo. PMID:23675474

  11. Regulation of IDO Activity by Oxygen Supply: Inhibitory Effects on Antimicrobial and Immunoregulatory Functions

    PubMed Central

    Keil, Eric; Woite, Claudia; Ernst, Joachim F.; Benzin, Anika E.; Rupp, Jan; Däubener, Walter

    2013-01-01

    Tryptophan is an essential amino acid for human beings as well as for some microorganisms. In human cells the interferon-γ (IFN-γ) inducible enzyme indoleamine 2,3-dioxygenase (IDO) reduces local tryptophan levels and is therefore able to mediate broad-spectrum effector functions: IDO activity restricts the growth of various clinically relevant pathogens such as bacteria, parasites and viruses. On the other hand, it has been observed that IDO has immunoregulatory functions as it efficiently controls the activation and survival of T-cells. Although these important effects have been analysed in much detail, they have been observed in vitro using cells cultured in the presence of 20% O2 (normoxia). Such high oxygen concentrations are not present in vivo especially within infected and inflamed tissues. We therefore analysed IDO-mediated effects under lower oxygen concentrations in vitro and observed that the function of IDO is substantially impaired in tumour cells as well as in native cells. Hypoxia led to reduced IDO expression and as a result to reduced production of kynurenine, the downstream product of tryptophan degradation. Consequently, effector functions of IDO were abrogated under hypoxic conditions: in different human cell lines such as tumour cells (glioblastoma, HeLa) but also in native cells (human foreskin fibroblasts; HFF) IDO lost the capacity to inhibit the growth of bacteria (Staphylococcus aureus), parasites (Toxoplasma gondii) or viruses (herpes simplex virus type 1). Additionally, IDO could no longer efficiently control the proliferation of T-cells that have been co-cultured with IDO expressing HFF cells in vitro. In conclusion, the potent antimicrobial as well as immunoregulatory functions of IDO were substantially impaired under hypoxic conditions that pathophysiologically occurs in vivo. PMID:23675474

  12. Shoulder and forearm oxygenation and myoelectric activity in patients with work-related muscle pain and healthy subjects.

    PubMed

    Elcadi, Guilherme H; Forsman, Mikael; Aasa, Ulrika; Fahlstrom, Martin; Crenshaw, Albert G

    2013-05-01

    We tested hypotheses of (a) reduced oxygen usage, oxygen recovery, blood flow and oxygen consumption; and (b) increased muscle activity for patients diagnosed with work-related muscle pain (WRMP) in comparison to healthy controls. Oxygenation was measured with near infrared spectroscopy (NIRS), and muscle activity with EMG for the extensor carpi radialis (ECR) and trapezius descendens (TD) muscles. Eighteen patients with diffuse neck-shoulder-arm pain and 17 controls (matched in age and sex) were equipped with NIRS and EMG probes. After determining an individual's maximum voluntary contraction (MVC) force, short-term (20 s) isometric contractions for the ECR and TD of 10, 30, 50 and 70 % MVC generated ∆StO₂ and StO₂% recovery (Rslope) from NIRS, and RMS%max from EMG signals. In addition, upper arm venous (VO) and arterial (AO) occlusions generated slopes of total hemoglobin (HbTslope) and deoxyhemoglobin (HHbslope) for the resting ECR as surrogates of blood flow and oxygen consumption, respectively. Mixed model analyses, t tests, and Mann-Whitney test were used to assess differences between groups. There was no significant difference in MVC between groups for either muscle. Also, ∆StO₂%, Rslope for either muscle, and ECR-HbTslope were not different between groups, thus our hypotheses of reduced oxygen use, recovery, and blood flow for patients were not confirmed. However, patients had a significantly lower ECR-HHbslope confirming our hypothesis of reduced consumption. Further, there was no difference in RMS%max during contractions meaning that the hypothesis of increased activity for patients was not confirmed. When taking into account the number of NIRS variables studied, differences we found between our patient group and healthy controls (i.e., in forearm oxygen consumption and shoulder oxygen saturation level) may be considered modest. Overall our findings may have been impacted by the fact that our patients and controls were similar in muscle strength

  13. Reactive oxygen species mediate TNFR1 increase after TRPV1 activation in mouse DRG neurons

    PubMed Central

    Ma, Fei; Zhang, Liping; Westlund, Karin N

    2009-01-01

    Background Transient receptor potential vanilloid subtype 1 (TRPV1) is activated by low pH/protons and is well known to be involved in hyperalgesia during inflammation. Tumor necrosis factor α (TNF-α), a proinflammatory cytokine, is involved in nociceptive responses causing hyperalgesia through TNF receptor type 1 (TNFR1) activation. Reactive oxygen species (ROS) production is also prominently increased in inflamed tissue. The present study investigated TNFR1 receptors in primary cultured mouse dorsal root ganglion (DRG) neurons after TRPV1 activation and the involvement of ROS. C57BL/6 mice, both TRPV1 knockout and wild type, were used for immunofluorescent and live cell imaging. The L4 and L5 DRGs were dissected bilaterally and cultured overnight. TRPV1 was stimulated with capsaicin or its potent analog, resiniferatoxin. ROS production was measured with live cell imaging and TNFR1 was detected with immunofluorescence in DRG primary cultures. The TRPV1 knockout mice, TRPV1 antagonist, capsazepine, and ROS scavenger, N-tert-Butyl-α-phenylnitrone (PBN), were employed to explore the functional relationship among TRPV1, ROS and TNFR1 in these studies. Results The results demonstrate that TRPV1 activation increases TNFR1 receptors and ROS generation in primary cultures of mouse DRG neurons. Activated increases in TNFR1 receptors and ROS production are absent in TRPV1 deficient mice. The PBN blocks increases in TNFR1 and ROS production induced by capsaicin/resiniferatoxin. Conclusion TRPV1 activation increases TNFR1 in cultured mouse DRG neurons through a ROS signaling pathway, a novel sensitization mechanism in DRG neurons. PMID:19531269

  14. Effects of oxygen functional groups on the enhancement of the hydrogen spillover of Pd-doped activated carbon.

    PubMed

    Chung, Tsui-Yun; Tsao, Cheng-Si; Tseng, Hui-Ping; Chen, Chien-Hung; Yu, Ming-Sheng

    2015-03-01

    The hydrogen storage performance of Pd-doped oxidized activated carbon (Pd/AC-ox) with various oxygen contents or functional groups was investigated. The surface chemistry of the Pd/AC-ox sample was modified by treatment with hydrogen gas. Temperature-programmed desorption was performed to characterize the oxygen functional groups in each sample. In this study, low- and high-pressure hydrogen adsorption isotherm experiments were conducted using a static volumetric measurement at room temperature (RT) and pressures of up to 8 MPa. The results showed that increasing the oxygen content and functional groups on the surface of the Pd/AC-ox significantly improved the reversible RT hydrogen storage capacity due to the spillover effect. The hydrogen spillover enhancement factors at 0.12 MPa were greater than 100% for all samples. The hydrogen uptake of Pd/AC-ox1 at RT and 8 MPa with an oxygen content of 8.94 wt.% was 0.37 wt.%, which was 48% greater than that of Pd-free AC-ox (0.25 wt.%). In addition, the hydrogen uptake of Pd/AC-ox3 with lower oxygen contents demonstrates that the hydrogen spillover enhancement gradually disappears when the pressure is increased to more than 2 MPa (i.e., a transition from spillover to physisorption). The surface diffusion, or reversible adsorption, of the spiltover H atoms, which is enhanced by oxygen functional groups, was affected by a threshold amount of oxygen groups (such as hydroxyl groups). PMID:25490569

  15. In situ probing of the active site geometry of ultrathin nanowires for the oxygen reduction reaction

    DOE PAGESBeta

    Liu, Haiqing; Wong, Stanislaus S.; An, Wei; Li, Yuanyuan; Frenkel, Anatoly I.; Sasaki, Kotaro; Koenigsmann, Christopher; Su, Dong; Anderson, Rachel M.; Crooks, Richard M.; et al

    2015-09-24

    To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (~2 nm) core–shell Pt~Pd9Au nanowires, which have been previously shownmore » to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu~Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Thus, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.« less

  16. Iridium-Tin oxide solid-solution nanocatalysts with enhanced activity and stability for oxygen evolution

    NASA Astrophysics Data System (ADS)

    Li, Guangfu; Yu, Hongmei; Yang, Donglei; Chi, Jun; Wang, Xunying; Sun, Shucheng; Shao, Zhigang; Yi, Baolian

    2016-09-01

    Addressing major challenges from the material cost, efficiency and stability, it is highly desirable to develop high-performance catalysts for oxygen evolution reaction (OER). Herein we explore a facile surfactant-assisted approach for fabricating Irsbnd Sn (Ir/Sn = 0.6/0.4, by mol.) nano-oxide catalysts with good morphology control. Direct proofs from XRD and X-ray photoelectron spectra indicate hydrophilic triblock polymer (TBP, like Pluronic® F108) surfactant can boost the formation of stable solid-solution structure. With the TBP hydrophilic and block-length increase, the fabricated Irsbnd Sn oxides undergoing the rod-to-sphere transition obtain the relatively lower crystallization, decreased crystallite size, Ir-enriched surface and incremental available active sites, all of which can bolster the OER activity and stability. Meanwhile, it is observed that the coupled Ir oxidative etching takes a crucial role in determining the material structure and performance. Compared with commercial Ir black, half-cell tests confirm F108-assistant catalysts with over 40 wt% Ir loading reduction show 2-fold activity enhancement as well as significant stability improvement. The lowest cell voltage using 0.88 mg cm-2 Ir loading is only 1.621 V at 1000 mA cm-2 and 80 °C with a concomitant energy efficiency of 75.8% which is beyond the DOE 2017 efficiency target of 74%.

  17. In situ probing of the active site geometry of ultrathin nanowires for the oxygen reduction reaction

    SciTech Connect

    Liu, Haiqing; Wong, Stanislaus S.; An, Wei; Li, Yuanyuan; Frenkel, Anatoly I.; Sasaki, Kotaro; Koenigsmann, Christopher; Su, Dong; Anderson, Rachel M.; Crooks, Richard M.; Adzic, Radoslav R.; Liu, Ping

    2015-09-24

    To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (~2 nm) core–shell Pt~Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu~Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Thus, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.

  18. Synthesis of highly active and dual-functional electrocatalysts for methanol oxidation and oxygen reduction reactions

    NASA Astrophysics Data System (ADS)

    Zhao, Qi; Zhang, Geng; Xu, Guangran; Li, Yingjun; Liu, Baocang; Gong, Xia; Zheng, Dafang; Zhang, Jun; Wang, Qin

    2016-12-01

    The promising Pt-based ternary catalyst is crucial for polymer electrolyte membrane fuel cells (PEMFCs) due to improving catalytic activity and durability for both methanol oxidation reaction and oxygen reduction reaction. In this work, a facile strategy is used for the synthesis ternary RuMPt (M = Fe, Co, Ni, and Cu) nanodendrities catalysts. The ternary RuMPt alloys exhibit enhanced specific and mass activity, positive half-wave potential, and long-term stability, compared with binary Pt-based alloy and the commercial Pt/C catalyst, which is attributed to the high electron density and upshifting of the d-band center for Pt atoms, and synergistic catalytic effects among Pt, M, and Ru atoms by introducing a transition metal. Impressively, the ternary RuCoPt catalyst exhibits superior mass activity (801.59 mA mg-1) and positive half-wave potential (0.857 V vs. RHE) towards MOR and ORR, respectively. Thus, the RuMPt nanocomposite is a very promising material to be used as dual electrocatalyst in the application of PEMFCs.

  19. In Situ Probing of the Active Site Geometry of Ultrathin Nanowires for the Oxygen Reduction Reaction.

    PubMed

    Liu, Haiqing; An, Wei; Li, Yuanyuan; Frenkel, Anatoly I; Sasaki, Kotaro; Koenigsmann, Christopher; Su, Dong; Anderson, Rachel M; Crooks, Richard M; Adzic, Radoslav R; Liu, Ping; Wong, Stanislaus S

    2015-10-01

    To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (∼2 nm) core-shell Pt∼Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu∼Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Hence, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general. PMID:26402364

  20. Palladium-platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction.

    PubMed

    Wang, Xue; Choi, Sang-Il; Roling, Luke T; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A; Mavrikakis, Manos; Xia, Younan

    2015-01-01

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. These results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability. PMID:26133469

  1. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    DOE PAGESBeta

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; et al

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can bemore » attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.« less

  2. A key parameter on the adsorption of diluted aniline solutions with activated carbons: The surface oxygen content.

    PubMed

    Pardo, Beatrice; Ferrer, Nabí; Sempere, Julià; Gonzalez-Olmos, Rafael

    2016-11-01

    A total of 11 different commercial activated carbons (AC) with well characterized textural properties and oxygen surface content were tested as adsorbents for the removal of aniline as a target water pollutant. The maximum adsorption capacity of aniline for the studied AC was from 138.9 to 257.9 mg g(-1) at 296.15 K and it was observed to be strongly related to the textural properties of the AC, mainly with the BET surface area and the micropore volume. It was not observed any influence of the oxygen surface content of the AC on the maximum adsorption capacity. However, it was found that at low aniline aqueous concentration, the presence of oxygen surface groups plays a dominant role during the adsorption. A high concentration of oxygen surface groups, mainly carboxylic and phenolic groups, decreases the aniline adsorption regardless of the surface area of the AC. PMID:27497348

  3. Reactive Oxygene Species and Thioredoxin Activity in Plants at Development of Hypergravity and Oxidative Stresses

    NASA Astrophysics Data System (ADS)

    Jadko, Sergiy

    Early increasing of reactive oxygen species (ROS) content, including H2O2, occurs in plant cells under various impacts and than these ROS can function as signaling molecules in starting of cell stress responses. At the same time thioredoxins (TR) are significant ROS and H2O2 sensors and transmitters to activation of various redox sensitive proteins, transcription factors and MAP kinases. This study was aimed to investigate early increasing of ROS and H2O2 contents and TR activity in the pea roots and in tissue culture under hypergravity and oxidative stresses. Pea roots of 3-5 days old seedlings and 12-14 days old tissue culture of Arabidopsis thaliana were studied. The pea seedlings were grown on wet filter paper and the tissue culture was grown on MS medium in dark conditions under 24oC. Hypergravity stress was induced by centrifugation at 10 and 15 g. Chemiluminescence (ChL) intensity for ROS concentration, H2O2 content and TR activity were determined. All experiments were repeated by 3-5 times. Early and reliable increasing of ChL intensity and H2O2 contents in the pea roots and in the tissue culture took place under hypergravity and oxidative stresses to 30, 60 and 90 min. At the same time TR activity increased on 11 and 19 percents only to 60 and 90 min. Thus under hypergravity and oxidative stresses in both investigated plants take place early increasing of ROS and H2O2 contents which as second messengers lead to increasing of TR activity with creating of ROS-TR stress signaling pathway.

  4. Density Functional Theory Study of Oxygen Reduction Activity on Ultrathin Platinum Nanotubes

    SciTech Connect

    Matanovic, Ivana; Kent, Paul; Garzon, Fernando; Henson, Neil J.

    2012-07-13

    The structure, stability, and catalytic activity of a number of single- and double-wall platinum (n,m) nanotubes ranging in diameter from 0.3 to 2.0 nm were studied using plane-wave based density functional theory in the gas phase and water environment. The change in the catalytic activity toward the oxygen reduction reaction (ORR) with the size and chirality of the nanotube was studied by calculating equilibrium adsorption potentials for ORR intermediates and by constructing free energy diagrams in the ORR dissociative mechanism network. In addition, the stability of the platinum nanotubes is investigated in terms of electrochemical dissolution potentials and by determining the most stable state of the material as a function of pH and potential, as represented in Pourbaix diagrams. Our results show that the catalytic activity and the stability toward electrochemical dissolution depend greatly on the diameter and chirality of the nanotube. On the basis of the estimated overpotentials for ORR, we conclude that smaller, approximately 0.5 nm in diameter single-wall platinum nanotubes consistently show a huge, up to 400 mV larger overpotential than platinum, indicating very poor catalytic activity toward ORR. This is the result of substantial structural changes induced by the adsorption of any chemical species on these tubes. Single-wall n = m platinum nanotubes with a diameter larger than 1 nm have smaller ORR overpotentials than bulk platinum for up to 180 mV and thus show improved catalytic activity relative to bulk. We also predict that these nanotubes can endure the highest cell potentials but dissolution potentials are still for 110 mV lower than for the bulk, indicating a possible corrosion problem.

  5. Lewis Acid Pairs for the Activation of Biomass-derived Oxygenates in Aqueous Media

    SciTech Connect

    Roman, Yuriy

    2015-09-14

    The objective of this project is to understand the mechanistic aspects behind the cooperative activation of oxygenates by catalytic pairs in aqueous media. Specifically, we will investigate how the reactivity of a solid Lewis acid can be modulated by pairing the active site with other catalytic sites at the molecular level, with the ultimate goal of enhancing activation of targeted functional groups. Although unusual catalytic properties have been attributed to the cooperative effects promoted by such catalytic pairs, virtually no studies exist detailing the use heterogeneous water-tolerant Lewis pairs. A main goal of this work is to devise rational pathways for the synthesis of porous heterogeneous catalysts featuring isolated Lewis pairs that are active in the transformation of biomass-derived oxygenates in the presence of bulk water. Achieving this technical goal will require closely linking advanced synthesis techniques; detailed kinetic and mechanistic investigations; strict thermodynamic arguments; and comprehensive characterization studies of both materials and reaction intermediates. For the last performance period (2014-2015), two technical aims were pursued: 1) C-C coupling using Lewis acid and base pairs in Lewis acidic zeolites. Tin-, zirconium-, and hafnium containing zeolites (e.g., Sn-, Zr-, and Hf-Beta) are versatile solid Lewis acids that selectively activate carbonyl functional groups. In this aim, we demonstrate that these zeolites catalyze the cross-aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid-base pairs in the Si-O-M framework ensemble promote soft enolization through α-proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions. 2) One-pot synthesis of MWW zeolite nanosheets for activation of bulky substrates. Through

  6. Low effective activation energies for oxygen release from metal oxides: evidence for mass-transfer limits at high heating rates.

    PubMed

    Jian, Guoqiang; Zhou, Lei; Piekiel, Nicholas W; Zachariah, Michael R

    2014-06-01

    Oxygen release from metal oxides at high temperatures is relevant to many thermally activated chemical processes, including chemical-looping combustion, solar thermochemical cycles and energetic thermite reactions. In this study, we evaluated the thermal decomposition of nanosized metal oxides under rapid heating (~10(5) K s(-1)) with time-resolved mass spectrometry. We found that the effective activation-energy values that were obtained using the Flynn-Wall-Ozawa isoconversional method are much lower than the values found at low heating rates, indicating that oxygen transport might be rate-determining at a high heating rate. PMID:24619858

  7. The characteristics of alumina scales formed on HVOF-sprayed MCrAlY coatings[High Velocity Oxygen Fuel

    SciTech Connect

    Toma, D.; Brandl, W.; Koester, U.

    2000-02-01

    HVOF MCrAlY (M = Ni, Co) coatings were isothermally oxidized in synthetic air between 850 and 1050 C for times up to 167 hr. During thermal spraying, aluminum and yttrium oxidized to form a fine oxide dispersion. The HVOF MCrAlY coatings exhibited a microstructure similar to ODS alloys. The fine dispersion consisted of Al{sub 2}O{sub 3} and aluminum-yttrium oxides. The oxidation experiments showed that the oxidation rate of HVOF coatings was two times slower than the oxidation rate of VPS MCrAlY coatings. The oxidation mechanism changed mainly in the transient-stage (no metastable modification of Al{sub 2}O{sub 3} formed) and it was assumed that the oxide dispersion hindered diffusion of various elements from the bulk material during oxidation. The formation of the fine oxide dispersion also influenced the adherence of the oxide scale. The microstructures of the transient oxide scales were examined by X-ray diffraction (XRD) scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

  8. Enhancement of activity of RuSex electrocatalyst by modification with nanostructured iridium towards more efficient reduction of oxygen

    NASA Astrophysics Data System (ADS)

    Dembinska, Beata; Kiliszek, Malgorzata; Elzanowska, Hanna; Pisarek, Marcin; Kulesza, Pawel J.

    2013-12-01

    Electrocatalytic activity of carbon (Vulcan XC-72) supported selenium-modified ruthenium, RuSex/C, nanoparticles for reduction of oxygen was enhanced through intentional decoration with iridium nanostructures (dimensions, 2-3 nm). The catalytic materials were characterized in oxygenated 0.5 mol dm-3 H2SO4 using cyclic and rotating ring disk voltammetric techniques as well as using transmission electron microscopy and scanning electron microscopy equipped with X-ray dispersive analyzer. Experiments utilizing gas diffusion electrode aimed at mimicking conditions existing in the low-temperature fuel cell. Upon application of our composite catalytic system, the reduction of oxygen proceeded at more positive potentials, and higher current densities were observed when compared to the behavior of the simple iridium-free system (RuSex/C) investigated under the analogous conditions. The enhancement effect was more pronounced than that one would expect from simple superposition of voltammetric responses for the oxygen reduction at RuSex/C and iridium nanostructures studied separately. Nanostructured iridium acted here as an example of a powerful catalyst for the reduction of H2O2 (rather than O2) and, when combined with such a moderate catalyst as ruthenium-selenium (for O2 reduction), it produced an integrated system of increased electrocatalytic activity in the oxygen reduction process. The proposed system retained its activity in the presence of methanol that could appear in a cathode compartment of alcohol fuel cell.

  9. Kinetics of an oxygen - iodine active medium with iodine atoms optically pumped on the 2P1/2 - 2P3/2 transition

    NASA Astrophysics Data System (ADS)

    Zagidullin, M. V.; Malyshev, M. S.; Azyazov, V. N.

    2015-08-01

    The kinetics of the processes occurring in an O2 - I2 - He - H2O gas flow in which photodissociation of molecular iodine at a wavelength close to 500 nm and excitation of atomic iodine on the 2P1/2 - 2P3/2 transition by narrow-band radiation near 1315 nm are implemented successively has been analysed. It is shown that implementation of these processes allows one to form an oxygen - iodine medium with a high degree of dissociation of molecular iodine and a relative content of singlet oxygen O2(a1Δ) exceeding 10%. Having formed a supersonic gas flow with a temperature ~100 K from this medium, one can reach a small-signal gain of about 10-2 cm-1 on the 2P1/2 - 2P3/2 transition in iodine atoms. The specific power per unit flow cross section in the oxygen - iodine laser with this active medium may reach ~100 W cm-2.

  10. Multiple forms of soluble monophenol, dihydroxyphenylalamine: oxygen-oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum). II. Partial characterization of the enzyme forms with different molecular weights.

    PubMed

    Matheis, G; Belitz, H D

    1977-04-28

    Gel chromatography on Sephadex G-200 was used to separate a soluble phenoloxidase from potatoes (var. Maritta) into at least six active fractions with dopa (dihydroxyphenylalanine) as substrate. Only high-molecular-weight-enzyme forms exhibited monophenoloxidase activity. Re-chromatography of the highest-molecular-weight form gave the same molecular weight distribution as with the crude enzyme. The molecular weights indicate association phenomena of subunits with a molecular weight of about 36000 daltons. According to polyacrylamide-gel electrophoresis, several monomeric forms with differnt isoelectric points seem to be present. This suggests that the large number of multiple forms of the enzyme arises from various combinations of identical and/or different subunits. SDS polyacrylamide gel electrophoresis failed to show the monomeric forms; the dimer and higher oligomers were obtained. PMID:404778

  11. Acrolein activates matrix metalloproteinases by increasing reactive oxygen species in macrophages

    SciTech Connect

    O'Toole, Timothy E. Zheng Yuting; Hellmann, Jason; Conklin, Daniel J.; Barski, Oleg; Bhatnagar, Aruni

    2009-04-15

    Acrolein is a ubiquitous component of environmental pollutants such as automobile exhaust, cigarette, wood, and coal smoke. It is also a natural constituent of several foods and is generated endogenously during inflammation or oxidation of unsaturated lipids. Because increased inflammation and episodic exposure to acrolein-rich pollutants such as traffic emissions or cigarette smoke have been linked to acute myocardial infarction, we examined the effects of acrolein on matrix metalloproteinases (MMPs), which destabilize atherosclerotic plaques. Our studies show that exposure to acrolein resulted in the secretion of MMP-9 from differentiated THP-1 macrophages. Acrolein-treatment of macrophages also led to an increase in reactive oxygen species (ROS), free intracellular calcium ([Ca{sup 2+}]{sub i}), and xanthine oxidase (XO) activity. ROS production was prevented by allopurinol, but not by rotenone or apocynin and by buffering changes in [Ca{sup 2+}]{sub I} with BAPTA-AM. The increase in MMP production was abolished by pre-treatment with the antioxidants Tiron and N-acetyl cysteine (NAC) or with the xanthine oxidase inhibitors allopurinol or oxypurinol. Finally, MMP activity was significantly stimulated in aortic sections from apoE-null mice containing advanced atherosclerotic lesions after exposure to acrolein ex vivo. These observations suggest that acrolein exposure results in MMP secretion from macrophages via a mechanism that involves an increase in [Ca{sup 2+}]{sub I}, leading to xanthine oxidase activation and an increase in ROS production. ROS-dependent activation of MMPs by acrolein could destabilize atherosclerotic lesions during brief episodes of inflammation or pollutant exposure.

  12. Identification of oxygen-19 during in vivo neutron activation analysis of water phantoms.

    PubMed

    Tahir, Syed N A; Chettle, David R

    2015-12-01

    Hand bone equivalent phantoms (250 ml) carrying selenium in various amounts were irradiated and counted for in vivo neutron activation analysis (IVNAA) by employing a 4π NaI(TI) based detection system. During the analysis of counting data, a feature at a higher energy than the gamma ray peak from (77m)Se (0.162 MeV) was observed at 0.197 MeV. Further investigations were made by preparing water phantoms containing only de-ionized water in 250 ml and 1034 ml quantities. Neutrons were produced by the (7)Li(p,n)(7)Be reaction using the high beam current Tandetron accelerator. Phantoms were irradiated at a fixed proton energy of 2.3 MeV and proton currents of 400 μA and 550 μA for 30 s and 22 s respectively. The counting data saved using the 4π NaI(TI) detection system for 10 s intervals in anticoincidence, coincidence and singles modes of detection were analyzed. Areas under gamma peaks at energies 0.197 MeV and 1.357 MeV were computed and half-lives from the number of counts for the two peaks were established. It was concluded that during neutron activation of water phantoms, oxygen-18 is activated, producing short-lived radioactive (19)O having T1/2  =  26.9 s. Induced activity from (19)O may contribute spectral interference in the gamma ray spectrum. This effect may need to be taken into account by researchers while carrying out IVNAA of biological subjects. PMID:26502270

  13. The ancestral activation promiscuity of ADP-glucose pyrophosphorylases from oxygenic photosynthetic organisms

    PubMed Central

    2013-01-01

    Background ADP-glucose pyrophosphorylase (ADP-Glc PPase) catalyzes the first committed step in the synthesis of glycogen in bacteria and starch in algae and plants. In oxygenic photosynthetic organisms, ADP-Glc PPase is mainly activated by 3-phosphoglycerate (3-PGA) and to a lesser extent by other metabolites. In this work, we analyzed the activation promiscuity of ADP-Glc PPase subunits from the cyanobacterium Anabaena PCC 7120, the green alga Ostreococcus tauri, and potato (Solanum tuberosum) tuber by comparing a specificity constant for 3-PGA, fructose-1,6-bisphosphate (FBP), fructose-6-phosphate, and glucose-6-phosphate. Results The 3-PGA specificity constant for the enzymes from Anabaena (homotetramer), O. tauri, and potato tuber was considerably higher than for other activators. O. tauri and potato tuber enzymes were heterotetramers comprising homologous small and large subunits. Conversely, the O. tauri small subunit (OtaS) homotetramer was more promiscuous because its FBP specificity constant was similar to that for 3-PGA. To explore the role of both OtaS and OtaL (O. tauri large subunit) in determining the specificity of the heterotetramer, we knocked out the catalytic activity of each subunit individually by site-directed mutagenesis. Interestingly, the mutants OtaSD148A/OtaL and OtaS/OtaLD171A had higher specificity constants for 3-PGA than for FBP. Conclusions After gene duplication, OtaS seemed to have lost specificity for 3-PGA compared to FBP. This was physiologically and evolutionarily feasible because co-expression of both subunits restored the specificity for 3-PGA of the resulting heterotetrameric wild type enzyme. This widespread promiscuity seems to be ancestral and intrinsic to the enzyme family. Its presence could constitute an efficient evolutionary mechanism to accommodate the ADP-Glc PPase regulation to different metabolic needs. PMID:23433303

  14. Catalytic Activity of Human Indoleamine 2,3-Dioxygenase (hIDO1) at Low Oxygen

    PubMed Central

    Kolawole, Ayodele O.; Hixon, Brian P.; Dameron, Laura S.; Chrisman, Ian M.; Smirnov, Valeriy V.

    2015-01-01

    A cytokine-inducible extrahepatic human indoleamine 2,3-dioxygenase (hIDO1) catalyzes the first step of the kynurenine pathway. Immunosuppressive activity of hIDO1 in tumor cells weakens host T-cell immunity, contributing to the progression of cancer. Here we report on enzyme kinetics and catalytic mechanism of hIDO1, studied at varied levels of dioxygen (O2) and L-tryptophan (L-Trp). Using a cytochrome b5-based activating system, we measured the initial rates of O2 decay with a Clark-type oxygen electrode at physiologically-relevant levels of both substrates. Kinetics was also studied in the presence of two substrate analogs: 1-methyl-L-tryptophan and norharmane. Quantitative analysis supports a steady-state rather than a rapid equilibrium kinetic mechanism, where the rates of individual pathways, leading to a ternary complex, are significantly different, and the overall rate of catalysis depends on contributions of both routes. One path, where O2 binds to ferrous hIDO1 first, is faster than the second route, which starts with the binding of L-Trp. However, L-Trp complexation with free ferrous hIDO1 is more rapid than that of O2. As the level of L-Trp increases, the slower route becomes a significant contributor to the overall rate, resulting in observed substrate inhibition. PMID:25712221

  15. p53 activation contributes to patulin-induced nephrotoxicity via modulation of reactive oxygen species generation

    PubMed Central

    Jin, Huan; Yin, Shutao; Song, Xinhua; Zhang, Enxiang; Fan, Lihong; Hu, Hongbo

    2016-01-01

    Patulin is a major mycotoxin found in fungal contaminated fruits and their derivative products. Previous studies showed that patulin was able to induce increase of reactive oxygen species (ROS) generation and oxidative stress was suggested to play a pivotal role in patulin-induced multiple toxic signaling. The objective of the present study was to investigate the functional role of p53 in patulin-induced oxidative stress. Our study demonstrated that higher levels of ROS generation and DNA damage were induced in wild-type p53 cell lines than that found in either knockdown or knockout p53 cell lines in response to patulin exposure, suggesting p53 activation contributed to patulin-induced ROS generation. Mechanistically, we revealed that the pro-oxidant role of p53 in response to patulin was attributed to its ability to suppress catalase activity through up-regulation of PIG3. Moreover, these in vitro findings were further validated in the p53 wild-type/knockout mouse model. To the best of our knowledge, this is the first report addressing the functional role of p53 in patulin-induced oxidative stress. The findings of the present study provided novel insights into understanding mechanisms behind oxidative stress in response to patulin exposure. PMID:27071452

  16. Oxygen uptake and energy expenditure for children during rock climbing activity.

    PubMed

    Watts, Phillip Baxter; Ostrowski, Megan L

    2014-02-01

    The purpose of this study was to measure oxygen uptake and energy expenditure in children during rock climbing activity. 29 children (age = 10.9 ± 1.7 yr) participated in the study. A commercially available rock climbing structure with ample features for submaximal effort climbing provided continuous terrain. Participants were instructed to climb at a comfortable pace. Following an initial 5-min rest, each child climbed one sustained 5-min bout followed by 5-min sitting recovery for a total of 10 min (SUS). This was immediately followed by five 1-min climbing + 1-min recovery intervals for a second total of 10 min (INT). Expired air was analyzed continuously. Energy expenditure (EE) was determined via the Weir method for 10-s intervals throughout the full protocol. The total energy expenditure in kilocalories during the 10-min SUS period was 34.3 ± 11.3 kcal. Energy expenditure during the 10-min INT period averaged 39.3 ± 13.1 kcal and was significantly higher than during SUS (p < .05). The mean total EE for SUS + INT was 73.7 ± 24.2 kcal. EE was correlated with body mass; r = .86. The rock climbing tasks employed in this study produced EE levels similar to what have been reported in children for stair climbing, sports/games activities, and easy jogging. PMID:24018310

  17. Caveolin-1 is involved in reactive oxygen species-induced SHP-2 activation in astrocytes

    PubMed Central

    Yun, Ji Hee; Park, Soo Jung; Jo, Ara; Jou, Ilo; Park, Jung Soo

    2011-01-01

    Recent evidence supports a neuroprotective role of Src homology 2-containing protein tyrosine phosphatase 2 (SHP-2) against ischemic brain injury. However, the molecular mechanisms of SHP-2 activation and those governing how SHP-2 exerts its function under oxidative stress conditions are not well understood. Recently we have reported that reactive oxygen species (ROS)-mediated oxidative stress promotes the phosphorylation of endogenous SHP-2 through lipid rafts, and that this phosphorylation strongly occurs in astrocytes, but not in microglia. To investigate the molecules involved in events leading to phosphorylation of SHP-2, raft proteins were analyzed using astrocytes and microglia. Interestingly, caveolin-1 and -2 were detected only in astrocytes but not in microglia, whereas flotillin-1 was expressed in both cell types. To examine whether the H2O2-dependent phosphorylation of SHP-2 is mediated by caveolin-1, we used specific small interfering RNA (siRNA) to downregulate caveolin-1 expression. In the presence of caveolin-1 siRNA, the level of SHP-2 phosphorylation induced by H2O2 was significantly decreased, compared with in the presence of control siRNA. Overexpression of caveolin-1 effectively increased H2O2-induced SHP-2 phosphorylation in microglia. Lastly, H2O2 induced extracellular signal-regulated kinase (ERK) activation in astrocytes through caveolin-1. Our results suggest that caveolin-1 is involved in astrocyte-specific intracellular responses linked to the SHP-2-mediated signaling cascade following ROS-induced oxidative stress. PMID:21918362

  18. Relationship between Active Oxygen Species, Lipid Peroxidation, Necrosis, and Phytoalexin Production Induced by Elicitins in Nicotiana.

    PubMed Central

    Rusterucci, C.; Stallaert, V.; Milat, M. L.; Pugin, A.; Ricci, P.; Blein, J. P.

    1996-01-01

    Excised leaves of Nicotiana tabacum var Xanthi and Nicotiana rustica were treated with cryptogein and capsicein, basic and acidic elicitins, respectively. Both compounds induced leaf necrosis, the intensity of which depended on concentration and duration of treatment. N. tabacum var Xanthi was the most sensitive species and cryptogein was the most active elicitin. Lipid peroxidation in elicitin-treated Nicotiana leaves was closely correlated with the appearance of necrosis. Elicitin treatments induced a rapid and transient burst of active oxygen species (AOS) in cell cultures of both Nicotiana species, with the production by Xanthi cells being 6-fold greater than that by N. rustica. Similar maximum AOS production levels were observed with both elicitins, but capsicein required 10-fold higher concentrations than those of cryptogein. Phytoalexin production was lower in response to both elicitins in N. tabacum var Xanthi cells than in N. rustica cells, and capsicein was the most efficient elicitor of this response. In cryptogein-treated cell suspensions, phytoalexin synthesis was unaffected by diphenyleneiodonium, which inhibited AOS generation, nor was it affected by tiron or catalase, which suppressed AOS accumulation in the extracellular medium. These results suggest that AOS production, lipid peroxidation, and necrosis are directly related, whereas phytoalexin production depends on neither the presence nor the intensity of these responses. PMID:12226334

  19. Mineralization of naphtenic acids with thermally-activated persulfate: The important role of oxygen.

    PubMed

    Xu, Xiyan; Pliego, Gema; Zazo, Juan A; Casas, Jose A; Rodriguez, Juan J

    2016-11-15

    This study reports on the mineralization of model naphtenic acids (NAs) in aqueous solution by catalyst-free thermally-activated persulfate (PS) oxidation. These species are found to be pollutants in oil sands process-affected waters. The NAs tested include saturated-ring (cyclohexanecarboxylic and cyclohexanebutyric acids) and aromatic (2-naphthoic and 1,2,3,4-tetrahydro-2-naphthoic acids) structures, at 50mgL(-1)starting concentration. The effect of PS dose within a wide range (10-100% of the theoretical stoichiometric) and working temperature (40-97°C) was investigated. At 80°C and intitial pH=8 complete mineralization of the four NAs was achieved with 40-60% of the stoichiometric PS dose. This is explained because of the important contribution of oxygen, which was experimentally verified and was found to be more effective toward the NAs with a single cyclohexane ring than for the bicyclic aromatic-ring-bearing ones. The effect of chloride and bicarbonate was also checked. The former showed negative effect on the degradation rate of NAs whereas it was negligible or even positive for bicarbonate. The rate of mineralization was well described by simple pseudo-first order kinetics with values of the rate constants normalized to the PS dose within the range of 0.062-0.099h(-1). Apparent activation energy values between 93.7-105.3kJmol(-1) were obtained. PMID:27442986

  20. Production and evolution of light elements in active star-forming regions.

    PubMed

    Cassé, M; Lehoucq, R; Vangioni-Flam, E

    1995-01-26

    Collisions between cosmic rays (energetic protons and alpha-particles) and carbon, nitrogen and oxygen in the interstellar medium have been considered to be the main source of lithium, beryllium and boron, through fragmentation of the larger nuclei. But this mechanism is unable to account for the observed Solar System abundances of the isotopes 7Li and 11B. The recent detection of an excess of gamma-rays in the direction of the star-forming region in the Orion cloud has been interpreted as arising from the excitation of carbon and oxygen nuclei ejected from supernovae when they collide with the surrounding gas, which is primarily molecular and atomic hydrogen. Here we investigate the consequences of the two-body interactions of the ejected carbon and oxygen nuclei (and the alpha-particles ejected with them) with the hydrogen and helium in the surrounding gas, using a model developed previously. We show that these interactions offer a way to make lithium, beryllium and boron that is independent of the abundance of heavy elements in the surrounding medium. Such supernova-driven interactions, combined with the effect of galactic cosmic rays, can explain the observed Solar System abundances of these light elements. PMID:7830765

  1. Mechanism of dark decomposition of iodine donor in the active medium of a pulsed chemical oxygen - iodine laser

    SciTech Connect

    Andreeva, Tamara L; Kuznetsova, S V; Maslov, A I; Sorokin, Vadim N

    2002-06-30

    A scheme is proposed that describes the dark decomposition of iodide - the donor of iodine - and the relaxation of singlet oxygen in the chlorine-containing active medium of a pulsed chemical oxygen - iodine laser (COIL). For typical compositions of the active media of pulsed COILs utilising CH{sub 3}I molecules as iodine donors, a branching chain reaction of the CH{sub 3}I decomposition accompanied by the efficient dissipation of singlet oxygen is shown to develop even at the stage of filling the active volume. In the active media with CF{sub 3}I as the donor, a similar chain reaction is retarded due to the decay of CF{sub 3} radicals upon recombination with oxygen. The validity of this mechanism is confirmed by a rather good agreement between the results of calculations and the available experimental data. The chain decomposition of alkyliodides accompanied by an avalanche production of iodine atoms represents a new way of efficient chemical production of iodine for a COIL. (active media)

  2. Effects of nitrogen- and oxygen-containing functional groups of activated carbon nanotubes on the electrochemical performance in supercapacitors

    NASA Astrophysics Data System (ADS)

    Liu, Haiyan; Song, Huaihe; Chen, Xiaohong; Zhang, Su; Zhou, Jisheng; Ma, Zhaokun

    2015-07-01

    A kind of nitrogen- and oxygen-containing activated carbon nanotubes (ACNTs) has been prepared by carbonization and activation of polyaniline nanotubes obtained by rapidly mixed reaction. The ACNTs show oxygen content of 15.7% and nitrogen content of 2.97% (atomic ratio). The ACNTs perform high capacitance and good rate capability (327 F g-1 at the current density of 10 A g-1) when used as the electrode materials for supercapacitors. Hydrogen reduction has been further used to investigate the effects of surface functional groups on the electrochemical performance. The changes for both structural component and electrochemical performance reveal that the quinone oxygen, pyridinic nitrogen, and pyrrolic nitrogen of carbon have the most obvious influence on the capacitive property because of their pseudocapacitive contributions.

  3. Comparison of dissolved-organic-carbon residuals from air- and pure-oxygen-activated-sludge sequencing-batch reactors.

    PubMed

    Esparza-Soto, Mario; Fox, Peter; Westerhoff, Paul

    2006-03-01

    Literature shows that full-scale pure-oxygen activated sludge (O2-AS) wastewater treatment plants (WWTPs) generate effluents with higher dissolved-organic carbon (DOC) concentrations and larger high-molecular-weight fractions compared to air-activated-sludge (Air-AS) WWTP effluents. The purpose of this paper was to evaluate how gas supplied (air vs. pure oxygen) to sequencing-batch reactors affected DOC transformations. The main conclusions of this paper are (a) O2-AS effluent DOC is more refractory than air-AS effluent DOC; and (b) O2-AS systems may have higher five-day biochemical oxygen demand removals than air-AS systems; however, in terms of COD and DOC removal, air-AS systems are better than O2-AS systems. Analysis of a database from side-by-side O2- and air-AS pilot tests from literature supported these observations. PMID:16629273

  4. Highly-active oxygen evolution electrocatalyzed by a Fe-doped NiSe nanoflake array electrode.

    PubMed

    Tang, Chun; Asiri, Abdullah M; Sun, Xuping

    2016-03-25

    Alkaline water electrolysis offers a simple method for mass production of hydrogen but suffers from the sluggish kinetics of the anodic oxygen evolution reaction (OER), calling for the development of low-cost and durable oxygen evolution electrocatalysts with high activity. In this communication, we report a highly-active robust oxygen evolution electrode, developed by in situ hydrothermal growth of an Fe-doped NiSe nanoflake array directly on a macroporous FeNi foam (Fe-NiSe/FeNi foam). This electrode catalyzes the OER with an onset overpotential as low as 200 mV and needs overpotentials of 245 and 264 mV to achieve 50 and 100 mA cm(-2), respectively, in 1.0 M KOH. Remarkably, it is also highly robust to drive 500 and 1000 mA cm(-2) at overpotentials of 246 and 263 mV, respectively, in 30 wt% KOH. PMID:26935420

  5. Study on the killing of oceanic harmful micro-organisms in ship's ballast water using oxygen active particles

    NASA Astrophysics Data System (ADS)

    Chen, C.; Meng, X. Y.; Bai, M. D.; Tian, Y. P.; Jing, Y.

    2013-03-01

    Global Environment Facility has identified that the spread of marine invasive alien species is one of the four major risk factors threatening the safety of global marine environments. Ballast water discharge is the main cause of biological invasion. With physical methods of strong electric field ionization discharge at atmospheric pressure, O2 and sea water (gaseous) were ionized, and then dissociated to a number of oxygen active particles (ROS) such as ·OH, O2+, H2O+, etc. ROS was injected into 0.6 t h-1 ballast water treatment system to form high concentration ROS solution in order to kill the harmful micro-organisms in ballast water. According to the land-based test standard of International Maritime Organization (IMO) Guidelines for Approval of Ballast Water Management Systems (G8), this paper concludes that single-cell algae of 3.0 × 104 cell ml-1 and bacteria of 2.0 × 104 cfu ml-1 were killed by ROS solution of 2.0 ppm. Death rate could reach almost 100%. The results meet the requirements of Regulation D-2 of International Convention for the Control and Management of Ships' Ballast Water and Sediments completely.

  6. Arylhydrocarbon receptor (AhR) activation in airway epithelial cells induces MUC5AC via reactive oxygen species (ROS) production.

    PubMed

    Chiba, Takahito; Uchi, Hiroshi; Tsuji, Gaku; Gondo, Hisaki; Moroi, Yoichi; Furue, Masutaka

    2011-02-01

    The dioxins and dioxin-like compounds in cigarette smoke regulate various immunological responses via the arylhydrocarbon receptor (AhR). These environmental toxicants are known to cause bronchitis, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. Recent studies have demonstrated that AhR activation upregulates the expression of mucin 5AC, oligomeric mucus/gel-forming (MUC5AC) in the airway epithelial cell line. However, the mechanism for the production of mucin has not been clarified. In this study, we investigated the role and pathway of AhR in airway epithelial cells by using selective agonists and antagonists. After stimulation with or without benzopyrene (B[a]P), an AhR agonist, MUC5AC expression was measured by real-time RT-PCR. The mechanism of AhR-induced MUC5AC expression in airway epithelial cells was studied in terms of the production of cytokine and reactive oxygen species (ROS). Treatment with B[a]P increased ROS generation in NCI-H₂₉₂ cells. Furthermore, B[a]P-induced MUC5AC upregulation and mucin production were inhibited by AhR siRNA or the use of an antioxidative agent. These results suggest that the AhR-induced increase of mucin production is partially mediated by ROS generation. An antioxidant therapy approach may help to cure AhR-induced mucus hypersecretory diseases. PMID:20709182

  7. Activity of Co-N multi walled carbon nanotubes electrocatalysts for oxygen reduction reaction in acid conditions

    NASA Astrophysics Data System (ADS)

    Osmieri, Luigi; Monteverde Videla, Alessandro H. A.; Specchia, Stefania

    2015-03-01

    Two catalysts are synthesized by wet impregnation of multi walled carbon nanotubes (MWCNT) with a complex formed between Co(II) ions and the nitrogen-containing molecule 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), followed by one or two identical heat treatments in N2 atmosphere at 800 °C for 3 h. Catalysts are fully characterized by FESEM, EDX, BET, XRD, FTIR, TGA, XPS analyses, and electrochemical techniques. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalysts in acid conditions is assessed by means of a rotating disk electrode (RDE) apparatus and a specific type of cell equipped with a gas diffusion working electrode (GDE). In both testing approaches, the catalyst heat-treated twice (Co-N/MWCNT-2) exhibits higher electroactivity than the catalyst heat-treated once (Co-N/MWCNT-1). Chronoamperometries both in RDE and GDE cell are also performed, showing less electroactivity decay and better current performance for the catalyst heat-treated twice.

  8. Microspheres assembled by KMn8O16 nanorods and their catalytic oxygen reduction activity in direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Fang, Yuan; Yang, Xiaodong; Wang, Li; Liu, Yongning

    2014-12-01

    Microspheres assembled using cryptomelane-type KMn8O16 nanorods are synthesized via a facile template-free, single-step hydrothermal technique. The synthesized KMn8O16 generates nanorods 10-20 nm in diameter and approximately 300-1000 nm long. The rods self-assemble to form microspheres of 2-6 μm in diameters. The electron transfer number for KMn8O16 during the ORR is approximately 3.98 at 0.5 V vs. Hg/HgO, and the H2O2 percentage is 0.66%. Moreover, a direct methanol fuel cell (DMFC) is built using KMn8O16 as cathodic catalyst, PtRu/C alloy as the anodic catalyst and a polymer fiber membrane (PFM) instead of a conventional polymer electrolyte membrane (PEM). The peak power densities (43.3 mW cm-2 and 153.9 mW cm-2) have been achieved at 25 °C and 70 °C, respectively. KMn8O16 shows good electrocatalytic activity and stability during oxygen reduction in alkaline solutions and demonstrates tolerance toward methanol poisoning.

  9. 75 FR 30098 - Reports, Forms and RecordKeeping Requirements; Agency Information Collection Activity Under OMB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-28

    ... to help States enhance motorcyclist safety training and motorcyclist awareness programs. To qualify... National Highway Traffic Safety Administration Reports, Forms and RecordKeeping Requirements; Agency Information Collection Activity Under OMB Review AGENCY: National Highway Traffic Safety Administration,...

  10. 78 FR 26766 - Commission Information Collection Activities (FERC Form 580); Comment Request; Revision

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-08

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Commission Information Collection Activities (FERC Form 580); Comment Request; Revision AGENCY: Federal Energy Regulatory Commission. ACTION: Notice of information...

  11. 76 FR 52014 - Agency Information Collection Activities: Applicant Information Form (1-783)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-19

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF JUSTICE Federal Bureau of Investigation Agency Information Collection Activities: Applicant Information Form (1-783) ACTION: 30-Day Notice of Information Collection. The Department of Justice (DOJ), Federal...

  12. Chemistry of the catalytic conversion of phthalate into its cis-dihydrodiol during the reaction of oxygen with the reduced form of phthalate dioxygenase.

    PubMed

    Tarasev, Michael; Ballou, David P

    2005-04-26

    The phthalate dioxygenase system, a Rieske non-heme iron dioxygenase, catalyzes the dihydroxylation of phthalate to form the 4,5-dihydro-cis-dihydrodiol of phthalate (DHD). It has two components: phthalate dioxygenase (PDO), a multimer with one Rieske-type [2Fe-2S] and one mononuclear Fe(II) center per monomer, and a reductase (PDR) that contains flavin mononucleotide (FMN) and a plant-type ferredoxin [2Fe-2S] center. This work shows that product formation in steady-state reactions is tightly coupled to electron delivery, with 1 dihydrodiol (DHD) of phthalate formed for every 2 electrons delivered from NADH. However, in reactions of reduced PDO with O(2), only about 0.5 DHD is formed per Rieske center that becomes oxidized. Although the product forms rapidly, its release from PDO is slow in these reactions with oxygen that do not include reductase and NADH. EPR data show that, at the completion of the oxidation, iron in the mononuclear center remains in the ferrous state. In contrast, naphthalene dioxygenase (NDO) [Wolfe, M. D., Parales, J. V., Gibson, D. T., and Lipscomb, J. D. (2001) J. Biol. Chem. 276, 1945-1953] and benzoate dioxygenase (BZDO) [Wolfe, M. D., Altier, D. J., Stubna, A., Popescu, C. V., Munck, E., and Lipscomb, J. D. (2002) Biochemistry, 41, 9611-9626], related Rieske non-heme iron dioxygenases, form 1 DHD per Rieske center oxidized, and the mononuclear center iron ends up ferric. Thus, both electrons from reduced NDO and BZDO monomers are used to form the product, whereas only the reduced Rieske centers in PDO become oxidized during production of DHD. This emphasizes the importance of PDO subunit interaction in catalysis. Electron redistribution was practically unaffected by the presence of oxidized PDR. A scheme is presented that emphasizes some of the differences in the mechanisms involved in substrate hydroxylation employed by PDO and either NDO or BZDO. PMID:15835907

  13. Role of Reactive Oxygen Species in the Abrogation of Oxaliplatin Activity by Cetuximab in Colorectal Cancer

    PubMed Central

    Santoro, Valeria; Jia, Ruochen; Thompson, Hannah; Nijhuis, Anke; Jeffery, Rosemary; Kiakos, Konstantinos; Silver, Andrew R.; Hartley, John A.

    2016-01-01

    Background: The antibody cetuximab, targeting epidermal growth factor receptor (EGFR), is used to treat metastatic colorectal cancer (mCRC). Clinical trials suggest reduced benefit from the combination of cetuximab with oxaliplatin. The aim of this study was to investigate potential negative interactions between cetuximab and oxaliplatin. Methods: Thiazolyl blue tetrazolium bromide (MTT) assay and Calcusyn software were used to characterize drug interactions. Reactive oxygen species (ROS) were measured by flow cytometry and real-time polymerase chain reaction oxidative stress arrays identified genes regulating ROS production. Chromatin immunoprecipitation (ChIP) measured signal transducer and activator of transcription 1 (STAT-1) binding to dual oxidase 2 (DUOX2) promoter. SW48, DLD-1 KRAS wild-type cell lines and DLD-1 xenograft models exposed to cetuximab, oxaliplatin, or oxaliplatin + cetuximab (control [saline]; n = 3 mice per treatment group) were used. Statistical tests were two-sided. Results: Cetuximab and oxaliplatin exhibited antagonistic effects on cellular proliferation and apoptosis (caspase 3/7 activity reduced by 1.4-fold, 95% confidence interval [CI] = 0.78 to 2.11, P = .003) as opposed to synergistic effects observed with the irinotecan metabolite 7-Ethyl-10-hydroxycamptothecin (SN-38). Although both oxaliplatin and SN-38 produced ROS, only oxaliplatin-mediated apoptosis was ROS dependent. Production of ROS by oxaliplatin was secondary to STAT1-mediated transcriptional upregulation of DUOX2 (3.1-fold, 95% CI = 1.75 to 2.41, P < .001). Inhibition of DUOX2 induction and p38 activation by cetuximab reduced oxaliplatin cytotoxicity. Conclusions: Inhibition of STAT1 and DUOX2-mediated ROS generation by cetuximab impairs p38-dependent apoptosis by oxaliplatin in preclinical models and may contribute to reduced efficacy in clinical settings. Understanding the rationale for unexpected trial results will inform improved rationales for combining EGFR

  14. Electro-catalytic activity of Ni–Co-based catalysts for oxygen evolution reaction

    SciTech Connect

    Ju, Hua; Li, Zhihu; Xu, Yanhui

    2015-04-15

    Graphical abstract: The electro-catalytic activity of different electro-catalysts with a porous electrode structure was compared considering the real electrode area that was evaluated by cyclic measurement. - Highlights: • Ni–Co-based electro-catalysts for OER have been studied and compared. • The real electrode area is calculated and used for assessing the electro-catalysts. • Exchange current and reaction rate constant are estimated. • Ni is more useful for OER reaction than Co. - Abstract: In the present work, Ni–Co-based electrocatalysts (Ni/Co = 0:6, 1:5, 2:4, 3:3, 4:2, 5:1 and 6:0) have been studied for oxygen evolution reaction. The phase structure has been analyzed by X-ray diffraction technique. Based on the XRD and SEM results, it is believed that the synthesized products are poorly crystallized. To exclude the disturbance of electrode preparation technology on the evaluation of electro-catalytic activity, the real electrode surface area is calculated based on the cyclic voltammetry data, assumed that the specific surface capacitance is 60 μF cm{sup −2} for metal oxide electrode. The real electrode area data are used to calculate the current density. The reaction rate constant of OER at different electrodes is also estimated based on basic reaction kinetic equations. It is found that the exchange current is 0.05–0.47 mA cm{sup −2} (the real surface area), and the reaction rate constant has an order of magnitude of 10{sup −7}–10{sup −6} cm s{sup −1}. The influence of the electrode potential on OER rate has been also studied by electrochemical impedance spectroscopy (EIS) technique. Our investigation has shown that the nickel element has more contribution than the cobalt; the nickel oxide has the best electro-catalytic activity toward OER.

  15. Structure-composition-activity relationships in transition-metal oxide and oxyhydroxide oxygen-evolution electrocatalysts

    NASA Astrophysics Data System (ADS)

    Trotochaud, Lena

    Solar water-splitting is a potentially transformative renewable energy technology. Slow kinetics of the oxygen evolution reaction (OER) limit the efficiency of solar-watersplitting devices, thus constituting a hurdle to widespread implementation of this technology. Catalysts must be stable under highly oxidizing conditions in aqueous electrolyte and minimally absorb light. A grand goal of OER catalysis research is the design of new materials with higher efficiencies enabled by comprehensive understanding of the fundamental chemistry behind catalyst activity. However, little progress has been made towards this goal to date. This dissertation details work addressing major challenges in the field of OER catalysis. Chapter I introduces the current state-of-the-art and challenges in the field. Chapter II highlights work using ultra-thin films as a platform for fundamental study and comparison of catalyst activity. Key results of this work are (1) the identification of a Ni0.9Fe0.1OOH catalyst displaying the highest OER activity in base to date and (2) that in base, many transition-metal oxides transform to layered oxyhydroxide materials which are the active catalysts. The latter result is critical in the context of understanding structure-activity relationships in OER catalysts. Chapter III explores the optical properties of these catalysts, using in situ spectroelectrochemistry to quantify their optical absorption. A new figure-of-merit for catalyst performance is developed which considers both optical and kinetic losses due to the catalyst and describes how these factors together affect the efficiency of composite semiconductor/catalyst photoanodes. In Chapter IV, the fundamental structure-composition-activity relationships in Ni1--xFexOOH catalysts are systematically investigated. This work shows that nearly all previous studies of Ni-based catalysts were likely affected by the presence of Fe impurities, a realization which holds significant weight for future study

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