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Sample records for acidic multimetallic catalytic

  1. Synthesis of multimetallic nanoparticles by seeded methods

    NASA Astrophysics Data System (ADS)

    Weiner, Rebecca Gayle

    This dissertation focuses on the synthesis of metal nanocrystals (NCs) by seeded methods, in which preformed seeds serve as platforms for growth. Metal NCs are of interest due to their tunable optical and catalytic properties, which arise from their composition and crystallite size and shape. Moreover, multimetallic NCs are potentially multifunctional due to the integration of the properties of each metal within one structure. However, such structures are difficult to synthesize with structural definition due to differences in precursor reduction rates and the size-dependent solubility of bimetallic phases. Seed-mediated co-reduction (SMCR) is a method developed in the Skrabalak Laboratory that couples the advantages of a seeded method with co-reduction methods to achieve multimetallic nanomaterials with defined shape and architecture. This approach was originally demonstrated in a model Au-Pd system in which Au and Pd precursors were simultaneously reduced to deposit metal onto shape-controlled Au or Pd NC seeds. Using SMCR, uniformly branched core shell Au Au-Pd and Pd Au-Pd NCs were synthesized, with the shape of the seeds directing the symmetry of the final structures. By varying the seed shape and the temperature at which metal deposition occurs, the roles of adatom diffusion and seed shape on final NC morphology were decoupled. Moreover, by selecting seeds of a composition (Ag) different than the depositing metals (Au and Pd), trimetallic nanostructures are possible, including shape-controlled Ag Au-Pd NCs and hollow Au-Pd-Ag nanoparticles (NPs). The latter architecture arises through galvanic replacement. Shape-controlled core shell NCs with trimetallic shells are also possible by co-reducing three metal precursors (Ag, Au, and Pd) with shape-controlled Au seeds; for example, convex octopods, concave cubes, and truncated octahedra were achieved in this initial demonstration and was enabled by varying the ratio of Ag to Au/Pd in the overgrowth step as well as

  2. Understanding of multimetallic cluster growth

    PubMed Central

    Mitzinger, Stefan; Broeckaert, Lies; Massa, Werner; Weigend, Florian; Dehnen, Stefanie

    2016-01-01

    The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. For (bio-)organic and organometallic compounds, this has long been realized even for very complicated molecules, whereas the formation of ligand-free inorganic molecules has widely remained a black box to date. This is due to poor structural relationships between reactants and products and the lack of structurally related intermediates—due to the comparably high coordination flexibility of involved atoms. Here we report on investigations of the stepwise formation of multimetallic clusters, based on a series of crystal structures and complementary quantum-chemical studies of (Ge2As2)2−, (Ge7As2)2−, [Ta@Ge6As4]3−, [Ta@Ge8As4]3− and [Ta@Ge8As6]3−. The study makes use of efficient quantum-chemical tools, enabling the first detailed screening of the energy hypersurface along the formation of ligand-free inorganic species for a semi-quantitative picture. The results can be generalized for an entire family of multimetallic clusters. PMID:26805602

  3. Understanding of multimetallic cluster growth.

    PubMed

    Mitzinger, Stefan; Broeckaert, Lies; Massa, Werner; Weigend, Florian; Dehnen, Stefanie

    2016-01-25

    The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. For (bio-)organic and organometallic compounds, this has long been realized even for very complicated molecules, whereas the formation of ligand-free inorganic molecules has widely remained a black box to date. This is due to poor structural relationships between reactants and products and the lack of structurally related intermediates--due to the comparably high coordination flexibility of involved atoms. Here we report on investigations of the stepwise formation of multimetallic clusters, based on a series of crystal structures and complementary quantum-chemical studies of (Ge2As2)(2-), (Ge7As2)(2-), [Ta@Ge6As4](3-), [Ta@Ge8As4](3-) and [Ta@Ge8As6](3-). The study makes use of efficient quantum-chemical tools, enabling the first detailed screening of the energy hypersurface along the formation of ligand-free inorganic species for a semi-quantitative picture. The results can be generalized for an entire family of multimetallic clusters.

  4. Advanced electron microscopy characterization of multimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Khanal, Subarna Raj

    Research in noble metal nanoparticles has led to exciting progress in a versatile array of applications. For the purpose of better tailoring of nanoparticles activities and understanding the correlation between their structures and properties, control over the composition, shape, size and architecture of bimetallic and multimetallic nanomaterials plays an important role on revealing their new or enhanced functions for potentials application. Advance electron microscopy techniques were used to provide atomic scale insights into the structure-properties of different materials: PtPd, Au-Au3Cu, Cu-Pt, AgPd/Pt and AuCu/Pt nanoparticles. The objective of this work is to understand the physical and chemical properties of nanomaterials and describe synthesis, characterization, surface properties and growth mechanism of various bimetallic and multimetallic nanoparticles. The findings have provided us with novel and significant insights into the physical and chemical properties of noble metal nanoparticles. Different synthesis routes allowed us to synthesize bimetallic: Pt-Pd, Au-Au3Cu, Cu-Pt and trimetallic: AgPd/Pt, AuCu/Pt, core-shell and alloyed nanoparticles with monodispersed sizes, controlled shapes and tunable surface properties. For example, we have synthesized the polyhedral PtPd core-shell nanoparticles with octahedral, decahedral, and triangular plates. Decahedral PtPd core-shell structures are novel morphologies for this system. For the first time we fabricated that the Au core and Au3Cu alloyed shell nanoparticles passivated with CuS2 surface layers and characterized by Cs-corrected scanning transmission electron microscopy. The analysis of the high-resolution micrographs reveals that these nanoparticles have decahedral structure with shell periodicity, and that each of the particles is composed by Au core and Au3Cu ordered superlattice alloyed shell surrounded by CuS 2 surface layer. Additionally, we have described both experimental and theoretical methods of

  5. Catalytic hydroxylation of benzoic acid by hydrogen peroxide

    SciTech Connect

    Pulippurasseril, C.R.; Filippova, T.Yu.; Dedov, A.G.

    1992-12-31

    An effective catalytic system based on Fe(III) and surfactants is proposed for the hydroxylation of benozic acid by hydrogen peroxide in an aqueous medium at a temperature of 30-80{degrees}C. 8 refs., 1 tab.

  6. Structural characterization of multimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Mukundan, Vineetha

    Bimetallic and trimetallic alloy nanoparticles have enhanced catalytic activities due to their unique structural properties. Using in situ time-resolved synchrotron based x-ray diffraction, we investigated the structural properties of nanoscale catalysts undergoing various heat treatments. Thermal treatment brings about changes in particle size, morphology, dispersion of metals on support, alloying, surface electronic properties, etc. First, the mechanisms of coalescence and grain growth in PtNiCo nanoparticles supported on planar silica on silicon were examined in detail in the temperature range 400-900°C. The sintering process in PtNiCo nanoparticles was found to be accompanied by lattice contraction and L10 chemical ordering. The mass transport involved in sintering is attributed to grain boundary diffusion and its corresponding activation energy is estimated from the data analysis. Nanoscale alloying and phase transformations in physical mixtures of Pd and Cu ultrafine nanoparticles were also investigated in real time with in situ synchrotron based x-ray diffraction complemented by ex situ high-resolution transmission electron microscopy. PdCu nanoparticles are interesting because they are found to be more efficient as catalysts in ethanol oxidation reaction (EOR) than monometallic Pd catalysts. The combination of metal support interaction and reactive/non-reactive environment was found to determine the thermal evolution and ultimate structure of this binary system. The composition of the as prepared Pd:Cu mixture in this study was 34% Pd and 66% Cu. At 300°C, the nanoparticles supported on silica and carbon black intermix to form a chemically ordered CsCl-type (B2) alloy phase. The B2 phase transforms into a disordered fcc alloy at higher temperature (>450°C). The alloy nanoparticles supported on silica and carbon black are homogeneous in volume, but evidence was found of Pd surface enrichment. In sharp contrast, when supported on alumina, the two metals

  7. Clay Minerals as Solid Acids and Their Catalytic Properties.

    ERIC Educational Resources Information Center

    Helsen, J.

    1982-01-01

    Discusses catalytic properties of clays, attributed to acidity of the clay surface. The formation of carbonium ions on montmorillonite is used as a demonstration of the presence of surface acidity, the enhanced dissociation of water molecules when polarized by cations, and the way the surface can interact with organic substances. (Author/JN)

  8. Catalytic upgrading of butyric acid towards fine chemicals and biofuels

    PubMed Central

    Sjöblom, Magnus; Matsakas, Leonidas; Christakopoulos, Paul; Rova, Ulrika

    2016-01-01

    Fermentation-based production of butyric acid is robust and efficient. Modern catalytic technologies make it possible to convert butyric acid to important fine chemicals and biofuels. Here, current chemocatalytic and biocatalytic conversion methods are reviewed with a focus on upgrading butyric acid to 1-butanol or butyl-butyrate. Supported Ruthenium- and Platinum-based catalyst and lipase exhibit important activities which can pave the way for more sustainable process concepts for the production of green fuels and chemicals. PMID:26994015

  9. Catalytic conversion of lactic acid and its derivatives

    SciTech Connect

    Kokitkar, P.B.; Langford, R.; Miller, D.J.; Jackson, J.E.

    1993-12-31

    The catalytic upgrading of lactic acid and methyl lactate is being investigated. With the commercialization of inexpensive starch fermentation technologies, US production of lactic acid is undergoing a surge. Dropping cost and increased availability offer a major opportunity to develop lactic acid as a renewable feedstock for chemicals production. IT can be catalytically converted into several important chemical intermediates currently derived from petroleum including acrylic acid, propanoic acid, and 2,3-pentanedione. The process can expand the potential of biomass as a substitute feedstock for petroleum and can benefit both the US chemical process industry and US agriculture via increased production of high-value, non-food products from crops and crop byproducts. Reaction studies of lactic acid and its ester are conducted in fixed bed reactors at 250-380{degrees}C and 0.1-0.5 MPa (1-5 atm) using salt catalysts on low surface area supports. Highest selectivities achieved are 42% to acrylic acid and 55% to 2,3-pentanedione from lactic acid over NaNO{sub 3} catalyst on low surface area silica support. High surface area (microporous) or highly acidic supports promote fragmentation to acetaldehyde and thus reduce yields of desirable products. The support acidity gives rice to lactic acid from neat methyl lactate feed but the lactic acid yield goes down after the nitrate salt is impregnated on the support. Both lactic acid and methyl lactate form 2,3-pentanedione. Methyl lactate reactions are more complex since it forms all the products obtained from lactic acid as well as many corresponding esters of the acids obtained from lactic acid (mainly methyl acrylate, methyl propionate, methyl acetate). At high temperatures, methyl acetate and acetic acid yields become significant from methyl lactate whereas lactic acid gives significant amount of acetol at high temperatures.

  10. The first catalytic asymmetric thioacetalization by chiral phosphoric acid catalysis.

    PubMed

    Yu, Jin-Sheng; Wu, Wen-Biao; Zhou, Feng

    2016-02-21

    We report here the first catalytic asymmetric thioacetalization of salicylaldehyde and dithiol. Chiral phosphoric acid STRIP C5 is identified as a powerful catalyst for this reaction to afford various chiral dithioacetals in high to excellent yields and enantioselectivities under mild conditions. PMID:26810819

  11. Characterization of a catalytically efficient acidic RNA-cleaving deoxyribozyme.

    PubMed

    Kandadai, Srinivas A; Li, Yingfu

    2005-01-01

    We previously demonstrated--through the isolation of RNA-cleaving deoxyribozymes by in vitro selection that are catalytically active in highly acidic solutions--that DNA, despite its chemical simplicity, could perform catalysis under challenging chemical conditions [Liu,Z., Mei,S.H., Brennan,J.D. and Li,Y. (2003) J. Am. Chem. Soc. 125, 7539-7545]. One remarkable DNA molecule therefrom is pH4DZ1, a self-cleaving deoxyribozyme that exhibits a k(obs) of approximately 1 min(-1) at pH 3.8. In this study, we carried out a series of experiments to examine the sequence and catalytic properties of this acidic deoxyribozyme. Extensive nucleotide truncation experiments indicated that pH4DZ1 was a considerably large deoxyribozyme, requiring approximately 80 out of the original 123 nt for the optimal catalytic activity. A reselection experiment identified ten absolutely conserved nucleotides that are distributed in three catalytically crucial sequence elements. In addition, a trans deoxyribozyme was successfully designed. Comparison of the observed rate constant of pH4DZ1 with experimentally determined rate constant for the uncatalyzed reaction revealed that pH4DZ1 achieved a rate enhancement of approximately 10(6)-fold. This study provides valuable information about this low-pH-functional deoxyribozyme and paves way for further structural and mechanistic characterization of this unique catalytic DNA. PMID:16391005

  12. Kinetics of the catalytic esterification of diglycerin with capric acid

    SciTech Connect

    Trufanova, T.N.; Nechesnyuk, G.P.; Bumina, N.A.; Kruchinin, V.A.; Slapygina, O.L.

    1988-06-10

    The object of this investigation was a further study of the rate of esterification of polyglycerins with fatty acids in the presence of acids, organometallic compounds, and metal salts. The catalytic effects of the following substances were studied (in wt. % of the reaction mixture): potassium, magnesium, copper, and zinc sulfates (analytical grade) first dried by calcination, 1%; pure grade tetrabutoxytitanate, 0.5-1%; and pure grade p-toluenesulfonic acid, recrystallized from concentrated hydrochloric acid, 1.0-3%. Samples taken after measured time intervals were analyzed by titration with an alcoholic solution of potassium hydroxide. The investigation was carried out in the kinetic regime.

  13. Catalytic Ethanol Dehydration over Different Acid-activated Montmorillonite Clays.

    PubMed

    Krutpijit, Chadaporn; Jongsomjit, Bunjerd

    2016-01-01

    In the present study, the catalytic dehydration of ethanol to obtain ethylene over montmorillonite clays (MMT) with mineral acid activation including H2SO4 (SA-MMT), HCl (HA-MMT) and HNO3 (NA-MMT) was investigated at temperature range of 200 to 400°C. It revealed that HA-MMT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. At 400°C, the HA-MMT yielded 82% of ethanol conversion having 78% of ethylene yield. At lower temperature (i.e. 200 to 300°C), diethyl ether (DEE) was a major product. The highest activity obtained from HA-MMT can be attributed to an increase of weak acid sites and acid density by the activation of MMT with HCl. It can be also proven by various characterization techniques that in most case, the main structure of MMT did not alter by acid activation (excepted for NA-MMT). Upon the stability test for 72 h during the reaction, the MMT and HA-MMT showed only slight deactivation due to carbon deposition. Hence, the acid activation of MMT by HCl is promising to enhance the catalytic dehydration of ethanol. PMID:27041515

  14. Fluorogenic, catalytic, photochemical reaction for amplified detection of nucleic acids.

    PubMed

    Dutta, Subrata; Fülöp, Annabelle; Mokhir, Andriy

    2013-09-18

    Photochemical, nucleic acid-induced reactions, which are controlled by nontoxic red light, are well-suited for detection of nucleic acids in live cells, since they do not require any additives and can be spatially and temporally regulated. We have recently described the first reaction of this type, in which a phenylselenyl derivative of thymidine (5'-PhSeT-ODNa) is cleaved in the presence of singlet oxygen (Fülöp, A., Peng, X., Greenberg, M. M., Mokhir, A. (2010) A nucleic acid directed, red light-induced chemical reaction. Chem. Commun. 46, 5659-5661). The latter reagent is produced upon exposure of a photosensitizer 3'-PS-ODNb (PS = Indium(III)-pyropheophorbide-a-chloride: InPPa) to >630 nm light. In 2012 we reported on a fluorogenic version of this reaction (Dutta, S., Flottmann, B., Heilemann, M., Mokhir, A. (2012) Hybridization and reaction-based, fluorogenic nucleic acid probes. Chem. Commun. 47, 9664-9666), which is potentially applicable for the detection of nucleic acids in cells. Unfortunately, its yield does not exceed 25% and no catalytic turnover could be observed in the presence of substrate excess. This problem occurs due to the efficient, competing oxidation of the substrate containing an electron rich carbon-carbon double bonds (SCH═CHS) in the presence of singlet oxygen with formation of a noncleavable product (SCH═CHSO). Herein we describe a related, but substantially improved photochemical, catalytic transformation of a fluorogenic, organic substrate, which consists of 9,10-dialkoxyanthracene linked to fluorescein, with formation of a bright fluorescent dye. In highly dilute solution this reaction occurs only in the presence of a nucleic acid template. We developed three types of such a reaction and demonstrated that they are high yielding and generate over 7.7 catalytic turnovers, are sensitive to single mismatches in nucleic acid targets, and can be applied for determination of both the amount of nucleic acids and potentially their

  15. Catalytic production of conjugated fatty acids and oils.

    PubMed

    Philippaerts, An; Goossens, Steven; Jacobs, Pierre A; Sels, Bert F

    2011-06-20

    The reactive double bonds in conjugated vegetable oils are of high interest in industry. Traditionally, conjugated vegetable oils are added to paints, varnishes, and inks to improve their drying properties, while recently there is an increased interest in their use in the production of bioplastics. Besides the industrial applications, also food manufactures are interested in conjugated vegetable oils due to their various positive health effects. While the isomer type is less important for their industrial purposes, the beneficial health effects are mainly associated with the c9,t11, t10,c12 and t9,t11 CLA isomers. The production of CLA-enriched oils as additives in functional foods thus requires a high CLA isomer selectivity. Currently, CLAs are produced by conjugation of oils high in linoleic acid, for example soybean and safflower oil, using homogeneous bases. Although high CLA productivities and very high isomer selectivities are obtained, this process faces many ecological drawbacks. Moreover, CLA-enriched oils can not be produced directly with the homogeneous bases. Literature reports describe many catalytic processes to conjugate linoleic acid, linoleic acid methyl ester, and vegetable oils rich in linoleic acid: biocatalysts, for example enzymes and cells; metal catalysts, for example homogeneous metal complexes and heterogeneous catalysts; and photocatalysts. This Review discusses state-of-the-art catalytic processes in comparison with some new catalytic production routes. For each category of catalytic process, the CLA productivities and the CLA isomer selectivity are compared. Heterogeneous catalysis seems the most attractive approach for CLA production due to its easy recovery process, provided that the competing hydrogenation reaction is limited and the CLA production rate competes with the current homogeneous base catalysis. The most important criteria to obtain high CLA productivity and isomer selectivity are (1) absence of a hydrogen donor, (2

  16. Catalytic production of conjugated fatty acids and oils.

    PubMed

    Philippaerts, An; Goossens, Steven; Jacobs, Pierre A; Sels, Bert F

    2011-06-20

    The reactive double bonds in conjugated vegetable oils are of high interest in industry. Traditionally, conjugated vegetable oils are added to paints, varnishes, and inks to improve their drying properties, while recently there is an increased interest in their use in the production of bioplastics. Besides the industrial applications, also food manufactures are interested in conjugated vegetable oils due to their various positive health effects. While the isomer type is less important for their industrial purposes, the beneficial health effects are mainly associated with the c9,t11, t10,c12 and t9,t11 CLA isomers. The production of CLA-enriched oils as additives in functional foods thus requires a high CLA isomer selectivity. Currently, CLAs are produced by conjugation of oils high in linoleic acid, for example soybean and safflower oil, using homogeneous bases. Although high CLA productivities and very high isomer selectivities are obtained, this process faces many ecological drawbacks. Moreover, CLA-enriched oils can not be produced directly with the homogeneous bases. Literature reports describe many catalytic processes to conjugate linoleic acid, linoleic acid methyl ester, and vegetable oils rich in linoleic acid: biocatalysts, for example enzymes and cells; metal catalysts, for example homogeneous metal complexes and heterogeneous catalysts; and photocatalysts. This Review discusses state-of-the-art catalytic processes in comparison with some new catalytic production routes. For each category of catalytic process, the CLA productivities and the CLA isomer selectivity are compared. Heterogeneous catalysis seems the most attractive approach for CLA production due to its easy recovery process, provided that the competing hydrogenation reaction is limited and the CLA production rate competes with the current homogeneous base catalysis. The most important criteria to obtain high CLA productivity and isomer selectivity are (1) absence of a hydrogen donor, (2

  17. Catalytic esterification of methacrylic acid with methyl alcohol

    SciTech Connect

    Lunin, A.F.; Zheleznaya, L.L.; Karakhanov, R.A.; Meshcheryakov, S.V.; Magadov, R.S.; Mkrtychan, V.R.; Fomin, V.A.

    1987-08-10

    The authors contend that virtually all methods for the production of methacrylic acid esters suffer from the drawbacks of low conversion, dependence on costly catalysts, low feed rates, and the need to use inhibitors in the process. To eliminate these drawbacks, they propose and test a new catalyst, sulfopolyphenyl ketone, which contains an extensive conjugated bond system together with ionic hydroxide groups. The catalytic esterification rate and yield is given for this catalyst and chromatography is performed for the resulting esters.

  18. Catalytical Conversion of Carbohydrates into Lactic Acid via Hydrothermal Reaction

    NASA Astrophysics Data System (ADS)

    Wei, Zhen; Jin, Fangming; Zhang, Guangyi; Zhang, Shiping; Yao, Guodong

    2010-11-01

    This paper focuses on catalytical conversion of carbohydrates into lactic acid, under the hydrothermal conditions, which may have a promising future for its high speediness and effectiveness. The catalysis of ZnO was investigated to improve the lactic acid yields. The results showed that the lactic acid yields increased immensely by the addition of ZnO. The effects of the reaction time and the addition amount of ZnO on the conversion of carbohydrates to lactic acid were studied. The highest lactic acid yields reached up to 28% starting from glucose after the reaction time of 60 s under the conditions of 0.2 mmol ZnO, 300° C, the filling rate of 35%, and over 30% starting from fructose at the same temperature and filling rate when the reaction time of 40 s and 2.0 mmol ZnO were employed. The collaborative effects of ZnO and NaOH used as the catalysts together at the same time were also studied. Furthermore, the catalytic mechanism of ZnO in the hydrothermal conversion of carbohydrates into lactic acid was discussed.

  19. A multimetallic piano-stool Ir-Sn3 catalyst for nucleophilic substitution reaction of γ-hydroxy lactams through N-acyliminium ions.

    PubMed

    Maity, Arnab Kumar; Roy, Sujit

    2012-03-16

    A multimetallic piano-stool complex [Cp*Ir(SnCl(3))(2){SnCl(2)(H(2)O)(2)}] (1) having Ir-Sn(3) motif has been synthesized from [Cp*IrCl(2)](2) and SnCl(2). The multimetallic complex catalytically promotes the nucleophilic substitution reaction (here after α-amidoalkylation reaction) of γ-hydroxylactams generated from phthalimidals to obtain decorated isoindolinones in excellent yields. Succinamidals, however, lead to the substituted pyrrolidinones (thermodynamic control product) via S(N)1-type path as well as eliminated pyrrolinones (kinetic control product) via an E1-type path, depending on the reaction parameters. A straightforward application of this methodology is to synthesize benzo-fused indolizidine alkaloid mimics. PMID:22364643

  20. Nonenzymatic catalytic signal amplification for nucleic acid hybridization assays

    NASA Technical Reports Server (NTRS)

    Fan, Wenhong (Inventor); Cassell, Alan M. (Inventor); Han, Jie (Inventor)

    2006-01-01

    Devices, methods, and kits for amplifying the signal from hybridization reactions between nucleic acid probes and their cognate targets are presented. The devices provide partially-duplexed, immobilized probe complexes, spatially separate from and separately addressable from immobilized docking strands. Cognate target acts catalytically to transfer probe from the site of probe complex immobilization to the site of immobilized docking strand, generating a detectable signal. The methods and kits of the present invention may be used to identify the presence of cognate target in a fluid sample.

  1. Mergers of multimetallic globular clusters: the role of dynamics

    NASA Astrophysics Data System (ADS)

    Amaro-Seoane, Pau; Konstantinidis, Symeon; Brem, Patrick; Catelan, Márcio

    2013-10-01

    Hubble Space Telescope observations of globular clusters (GCs) in the Antennae galaxy show clusters of clusters, or regions in the galaxy that span hundreds of parsec, where many of the GCs are doomed to collide, and eventually merge. Several such objects appear likely to present a significant range in ages, hence possibly metallicities, and their merger could plausibly lead to multimetallic GCs. Here we explore this process with direct-summation N-body simulations with graphics processing unit hardware. Our results reveal that colliding GCs with different metallicities and ages can produce a GC with multiplicity and occupation fractions not unlike those observed in multimetallic clusters. In our simulations, the merged clusters have a phase with a larger amount of flattening than average, as a consequence of rapid rotation - thus suggesting that relatively recent mergers may play a role in producing highly flattened, multimetallic clusters. We additionally explore the role of the King parameter of the cluster in the occupation fractions with a set of 160 direct-summation simulations and find that for equal size clusters the King parameter of the progenitor clusters determines the occupation fractions in the merger product, while in unequal size mergers the size of the clusters dominates the distribution of stars in the new GC. In particular, we find that the observed distribution of populations in ω Cen can be described to some extent with our dynamical models.

  2. Computational evaluation of factors governing catalytic 2-keto acid decarboxylation.

    PubMed

    Wu, Di; Yue, Dajun; You, Fengqi; Broadbelt, Linda J

    2014-06-01

    Recent advances in computational approaches for creating pathways for novel biochemical reactions has motivated the development of approaches for identifying enzyme-substrate pairs that are attractive candidates for effecting catalysis. We present an improved structural-based strategy to probe and study enzyme-substrate binding based on binding geometry, energy, and molecule characteristics, which allows for in silico screening of structural features that imbue higher catalytic potential with specific substrates. The strategy is demonstrated using 2-keto acid decarboxylation with various pairs of 2-keto acids and enzymes. We show that this approach fitted experimental values for a wide range of 2-keto acid decarboxylases for different 2-keto acid substrates. In addition, we show that the structure-based methods can be used to select specific enzymes that may be promising candidates to catalyze decarboxylation of certain 2-keto acids. The key features and principles of the candidate enzymes evaluated by the strategy can be used to design novel biosynthesis pathways, to guide enzymatic mutation or to guide biomimetic catalyst design.

  3. [Reductive dechlorination of trichloroacetic acid by bioelectrochemically catalytic method].

    PubMed

    Li, Yu-Ping; Cao, Hong-Bin; Zhang, Yi

    2005-07-01

    Direct electrochemical behaviors of hemoglobin (Hb) immobilized on carbon nanotube (CNT) modified carbon paste electrode with adsorption were investigated. Cyclic voltammetry of Hb-CNT-modified electrode showed a pair of well-defined and nearly reversible peaks for HbhemeFe(III) /Fe(II) redox couple in pH = 7 PBS buffers. The electrocatalytic behaviors of Hb-CNT-modified electrode for the reductive dechlorination of trichloroacetic acid (TCA) were studied by cyclic voltammmetry and fixed-potential electrolysis technique, and the reductive mechanism of TCA was discussed by analysis of reduction products. The results showed that Hb-CNT-modified electrode possessed good electro-catalytic activity for reduction of TCA and the dechlorination of TCA was stepwise, following the pathway of trichloroacetic--> dichloroacetic--> monochloroacetic--> acetic. The dechlorination of TCA in waster water was investigated using a two-compartment flow reactor with working electrode compartment packed with Hb-CNT-modified graphite electrode. The conversion of TCA was 40.13% with electrolysis for 180 min at - 0.60V (vs. SCE).

  4. Multimetallic nanoparticle catalysts with enhanced electrooxidation

    DOEpatents

    Sun, Shouheng; Zhang, Sen; Zhu, Huiyuan; Guo, Shaojun

    2015-07-28

    A new structure-control strategy to optimize nanoparticle catalysis is provided. The presence of Au in FePtAu facilitates FePt structure transformation from chemically disordered face centered cubic (fcc) structure to chemically ordered face centered tetragonal (fct) structure, and further promotes formic acid oxidation reaction (FAOR). The fct-FePtAu nanoparticles show high CO poisoning resistance, achieve mass activity as high as about 2810 mA/mg Pt, and retain greater than 90% activity after a 13 hour stability test.

  5. A Modular Approach to Redox-Active Multimetallic Hydrophobes of Discoid Topology

    PubMed Central

    Lesh, Frank D.; Shanmugam, Rama; Allard, Marco M.; Lanznaster, Maurício; Heeg, Mary Jane; Rodgers, M. T.; Shearer, Jason M.; Verani, Cláudio N.

    2011-01-01

    A new modular [FeII(FeIIIL2)3](PF6)2 species with discoid (disk-like) topology exhibits redox and surfactant properties and points to a new approach for multimetallic Langmuir film precursors. PMID:20690730

  6. Conversion of Acetic Acid from the Catalytic Pyrolysis of Xylan Over CeO2.

    PubMed

    Lee, Heejin; Ko, Jeong Huy; Kwon, Woo Hyun; Park, Young-Kwon

    2016-05-01

    CeO2 was synthesized hydrothermally in supercritical water and applied to the catalytic pyrolysis of xylan. Acetic acid, which is the main component in bio-oil produced from the non-catalytic pyrolysis of xylan, deteriorates the fuel quality of the oil. Catalysis over CeO2 effectively converted the acetic acid to ketone species, such as acetone, thereby reducing the acidity of the oil considerably. The content of aromatics in bio-oil was also increased substantially by catalysis. PMID:27483777

  7. Preparation, characterization and catalytic properties of MCM-48 supported tungstophosphoric acid mesoporous materials for green synthesis of benzoic acid

    SciTech Connect

    Wu, Hai-Yan; Zhang, Xiao-Li; Chen, Xi; Chen, Ya; Zheng, Xiu-Cheng

    2014-03-15

    MCM-48 and tungstophosphoric acid (HPW) were prepared and applied for the synthesis of HPW/MCM-48 mesoporous materials. The characterization results showed that HPW/MCM-48 obtained retained the typical mesopore structure of MCM-48, and the textural parameters decreased with the increase loading of HPW. The catalytic oxidation results of benzyl alcohol and benzaldehyde with 30% H{sub 2}O{sub 2} indicated that HPW/MCM-48 was an efficient catalyst for the green synthesis of benzoic acid. Furthermore, 35 wt% HPW/MCM-48 sample showed the highest activity under the reaction conditions. Highlights: • 5–45 wt% HPW/MCM-48 mesoporous catalysts were prepared and characterized. • Their catalytic activities for the green synthesis of benzoic acid were investigated. • HPW/MCM-48 was approved to be an efficient catalyst. • 5 wt% HPW/MCM-48 exhibited the highest catalytic activity.

  8. Highly ordered three dimensional macroporous carbon spheres and their acid catalytic properties

    NASA Astrophysics Data System (ADS)

    Huang, Hui; Zhang, Jianming; Zhang, Yuxiao; Lian, Suoyuan; Liu, Yang

    2013-10-01

    Highly ordered three dimensional macroporous carbon spheres bearing sulfonic acid groups (MPCS-SO3H) were prepared by incomplete carbonization of glucose in silica crystal bead template, followed by sulfonation and removal of the template. The composition and porous structure of the obtained carbon spheres were investigated by physical adsorption of nitrogen, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy techniques. While the Fourier-transform infrared spectroscopy was used to characterize the functional groups on the surface of carbon spheres. The catalytic properties of the MPCS-SO3H were evaluated by esterification of ethanol with acetic acid, indicating that MPCS-SO3H possess remarkable catalytic performance (high stability and acid catalytic ability) for the esterification.

  9. Catalytic air oxidation of biomass-derived carbohydrates to formic acid.

    PubMed

    Li, Jiang; Ding, Dao-Jun; Deng, Li; Guo, Qing-Xiang; Fu, Yao

    2012-07-01

    An efficient catalytic system for biomass oxidation to form formic acid was developed. The conversion of glucose to formic acid can reach up to 52% yield within 3 h when catalyzed by 5 mol% of H(5)PV(2)Mo(10)O(40) at only 373 K using air as the oxidant. Furthermore, the heteropolyacid can be used as a bifunctional catalyst in the conversion of cellulose to formic acid (yield=35%) with air as the oxidant. PMID:22499553

  10. Catalytic air oxidation of biomass-derived carbohydrates to formic acid.

    PubMed

    Li, Jiang; Ding, Dao-Jun; Deng, Li; Guo, Qing-Xiang; Fu, Yao

    2012-07-01

    An efficient catalytic system for biomass oxidation to form formic acid was developed. The conversion of glucose to formic acid can reach up to 52% yield within 3 h when catalyzed by 5 mol% of H(5)PV(2)Mo(10)O(40) at only 373 K using air as the oxidant. Furthermore, the heteropolyacid can be used as a bifunctional catalyst in the conversion of cellulose to formic acid (yield=35%) with air as the oxidant.

  11. Experimental study of humic acid degradation and theoretical modelling of catalytic ozonation.

    PubMed

    Turkay, Ozge; Inan, Hatice; Dimoglo, Anatoli

    2015-01-01

    The efficiency of TiO2 as a catalyst in the ozonation of humic acid (HA) was evaluated in a comprehensive manner. Ozonation, catalytic ozonation and adsorption experiments were conducted using both synthetic HA solution and natural water. HA degradation was evaluated in terms of DOC, VIS400 and UV254. It was shown that the addition of catalyst positively affects the mechanism of ozonation. An increase in HA degradation was observed for all these parameters. The impact of catalyst dose and initial pH value of HA on the efficacy of catalytic ozonation was investigated. The highest removal efficiencies were achieved with the dose of 1 g l(-1) of TiO2 (Degussa P-25) and in the acidic pH region. The catalytic ozonation process was efficient also on natural water component although not at the same level as it was on synthetic water. The adsorptive feature of P-25 was considered to have a clear evidence of the catalytic ozonation mechanism. The mechanism of catalysis on the surface of metal oxides was elucidated with the help of quantum-chemical calculations. In the framework of Density Function Theory (DFT), the O3 decomposition was calculated in the catalytic and non-catalytic processes. Donor-acceptor properties of the frontier (highest occupied and lowest unoccupied molecular orbitals, HOMO/LUMO) orbitals are discussed. Electron density distribution and reaction mechanism of superoxide particles formation, which participate in the process of HA ozonation are analyzed. PMID:25056748

  12. Simultaneous monitoring of multimetallic atom densities in plasma processes employing a multimicrohollow cathode lamp

    SciTech Connect

    Ohta, Takayuki; Ito, Masafumi; Tachibana, Yoshihiro; Taneda, Satoshi; Takashima, Seigo; Hori, Masaru; Kano, Hiroyuki; Den, Shoji

    2007-06-18

    The authors have developed a simultaneous measurement technique of multimetallic atom densities in process plasmas using absorption spectroscopy employing a multimicrohollow cathode plasma as a light source. The optical emissions of four metallic atoms of Cu, Zn, Fe, and Mo were simultaneously produced from the multimicrohollow cathode plasma of millimeter size. The absolute densities of Cu and Mo in the magnetron sputtering plasma were simultaneously measured using this technique. The simultaneous monitoring of multimetallic atoms is very useful for controlling the plasma processes precisely.

  13. Amino acid network for prediction of catalytic residues in enzymes: a comparison survey.

    PubMed

    Zhou, Jianhong; Yan, Wenying; Hu, Guang; Shen, Bairong

    2016-01-01

    Catalytic residues play a significant role in enzyme functions. With the recent accumulation of experimentally determined enzyme 3D structures and network theory on protein structures, the prediction of catalytic residues by amino acid network (AAN, where nodes are residues and links are residue interactions) has gained much interest. Computational methods of identifying catalytic residues are traditionally divided into two groups: sequence-based and structure-based methods. Two new structure- based methods are proposed in current advances: AAN and Elastic Network Model (ENM) of enzyme structures. By concentrating on AAN-based approach, we herein summarized network properties for predictions of catalytic residues. AAN attributes were showed responsible for performance improvement, and therefore the combination of AAN with previous sequence and structural information will be a promising direction for further improvement. Advantages and limitations of AAN-based methods, future perspectives on the application of AAN to the study of protein structure-function relationships are discussed.

  14. GABA production by glutamic acid decarboxylase is regulated by a dynamic catalytic loop.

    PubMed

    Fenalti, Gustavo; Law, Ruby H P; Buckle, Ashley M; Langendorf, Christopher; Tuck, Kellie; Rosado, Carlos J; Faux, Noel G; Mahmood, Khalid; Hampe, Christiane S; Banga, J Paul; Wilce, Matthew; Schmidberger, Jason; Rossjohn, Jamie; El-Kabbani, Ossama; Pike, Robert N; Smith, A Ian; Mackay, Ian R; Rowley, Merrill J; Whisstock, James C

    2007-04-01

    Gamma-aminobutyric acid (GABA) is synthesized by two isoforms of the pyridoxal 5'-phosphate-dependent enzyme glutamic acid decarboxylase (GAD65 and GAD67). GAD67 is constitutively active and is responsible for basal GABA production. In contrast, GAD65, an autoantigen in type I diabetes, is transiently activated in response to the demand for extra GABA in neurotransmission, and cycles between an active holo form and an inactive apo form. We have determined the crystal structures of N-terminal truncations of both GAD isoforms. The structure of GAD67 shows a tethered loop covering the active site, providing a catalytic environment that sustains GABA production. In contrast, the same catalytic loop is inherently mobile in GAD65. Kinetic studies suggest that mobility in the catalytic loop promotes a side reaction that results in cofactor release and GAD65 autoinactivation. These data reveal the molecular basis for regulation of GABA homeostasis.

  15. Catalytic Hydrogenation of Maleic Acid at Moderate Pressures: A Laboratory Demonstration

    ERIC Educational Resources Information Center

    Amoa, Kwesi

    2007-01-01

    Moderate-pressure catalytic hydrogenation is often overlooked as a classroom demonstration because of the awkwardness of the equipment and the time constraints required for the conversion of reactants to products. This article demonstrates the reduction of maleic acid in about 90 minutes. (Contains 1 table and 1 figure.)

  16. MOF-Derived Tungstated Zirconia as Strong Solid Acids toward High Catalytic Performance for Acetalization.

    PubMed

    Wang, Peng; Feng, Jian; Zhao, Yupei; Wang, Shaobin; Liu, Jian

    2016-09-14

    A strong solid acid, tungstated zirconia (WZ), has been prepared first using tungstate immobilized UiO-66 as precursors through a "double-solvent" impregnation method under mild calcination temperature. With moderate W contents, the as-synthesized WZ catalysts possess a high density of acid sites, and the proper heat treatment also has facilely led to a bunch of oligomeric tungsten clusters on stabilized tetragonal ZrO2. The resultant solid acids show an improved catalytic performance toward the benzaldehyde's acetalization in comparison with traditional zirconium hydroxide-prepared WZ. Notably, due to large surface area and additionally introduced strong acid sites, the MOF-derived WZ catalysts afforded conversion up to 86.0%. The facile method endows the WZ catalysts with superior catalytic activities and excellent recyclability, thus opening a new avenue for preparation of metal oxide-based solid superacids and superbases. PMID:27557351

  17. Catalytic asymmetric protonation of lithium enolates using amino acid derivatives as chiral proton sources.

    PubMed

    Mitsuhashi, Kaori; Ito, Rie; Arai, Takayoshi; Yanagisawa, Akira

    2006-04-13

    [reaction: see text] Asymmetric protonation of lithium enolates was examined using commercially available amino acid derivatives as chiral proton sources. Among the amino acid derivatives tested, Nbeta-l-aspartyl-l-phenylalanine methyl ester was found to cause significant asymmetric induction in the protonation of lithium enolates. The enantiomeric excess (up to 88% ee) of the products obtained in the presence of a catalytic amount of the chiral proton source was higher than those obtained in the stoichiometric reaction. PMID:16597150

  18. Catalytic asymmetric protonation of lithium enolates using amino acid derivatives as chiral proton sources.

    PubMed

    Mitsuhashi, Kaori; Ito, Rie; Arai, Takayoshi; Yanagisawa, Akira

    2006-04-13

    [reaction: see text] Asymmetric protonation of lithium enolates was examined using commercially available amino acid derivatives as chiral proton sources. Among the amino acid derivatives tested, Nbeta-l-aspartyl-l-phenylalanine methyl ester was found to cause significant asymmetric induction in the protonation of lithium enolates. The enantiomeric excess (up to 88% ee) of the products obtained in the presence of a catalytic amount of the chiral proton source was higher than those obtained in the stoichiometric reaction.

  19. Liquid-Phase Catalytic Transfer Hydrogenation of Furfural over Homogeneous Lewis Acid-Ru/C Catalysts.

    PubMed

    Panagiotopoulou, Paraskevi; Martin, Nickolas; Vlachos, Dionisios G

    2015-06-22

    The catalytic performance of homogeneous Lewis acid catalysts and their interaction with Ru/C catalyst are studied in the catalytic transfer hydrogenation of furfural by using 2-propanol as a solvent and hydrogen donor. We find that Lewis acid catalysts hydrogenate the furfural to furfuryl alcohol, which is then etherified with 2-propanol. The catalytic activity is correlated with an empirical scale of Lewis acid strength and exhibits a volcano behavior. Lanthanides are the most active, with DyCl3 giving complete furfural conversion and a 97 % yield of furfuryl alcohol at 180 °C after 3 h. The combination of Lewis acid and Ru/C catalysts results in synergy for the stronger Lewis acid catalysts, with a significant increase in the furfural conversion and methyl furan yield. Optimum results are obtained by using Ru/C combined with VCl3 , AlCl3 , SnCl4 , YbCl3 , and RuCl3 . Our results indicate that the combination of Lewis acid/metal catalysts is a general strategy for performing tandem reactions in the upgrade of furans.

  20. Tandem oxidative processes catalyzed by polymer-incarcerated multimetallic nanoclusters with molecular oxygen.

    PubMed

    Miyamura, Hiroyuki; Kobayashi, Shū

    2014-04-15

    Heterogeneous catalysis and one-pot tandem reactions are key for efficient and practical organic syntheses and for green and sustainable chemistry. Heterogeneous catalysts can be recovered and reused. These catalysts can be applied to efficient systems, such as continuous-flow systems. Tandem reactions often proceed via highly reactive but unstable intermediates. Tandem reactions do not require workup or much purification of the intermediate. This Account summarizes recent developments that we have made in the field of multifunctional heterogeneous metal nanocluster catalysts for use in tandem reactions based on aerobic oxidation reactions as key processes. We constructed our heterogeneous metal nanoclusters via two important procedures--microencapsulation and cross-linking--using polystyrene-based copolymers with cross-linking moieties. These frameworks can efficiently stabilize small metal nanoclusters to maintain high catalytic activity without aggregation and leaching of nanoclusters. Aggregation and leaching are prevented by weak but multiple interactions between metal nanocluster surfaces and benzene rings in the copolymer as well as by the physical envelopment of cross-linked polymer backbones. Small nanoclusters, including multimetallic alloy clusters (nanoalloys), can be "imprisoned" into these cross-linked polymer composites. The term we use for these processes is polymer incarceration. Direct oxidative esterifications were achieved with polymer-incarcerated (PI) Au nanocluster catalysts. Amides were synthesized from alcohols and amines under aerobic oxidative conditions with PI bimetallic nanocluster catalysts composed of Au and Fe-group metals that formed separated nanoclusters rather than alloys. Oxidative lactam formation from amino alcohols was also achieved. On the other hand, imines could be prepared selectively from alcohols and amines with PI Au-Pd bimetallic nanoclusters. We also achieved the integration of the aerobic oxidation of allylic

  1. Catalytic hydrothermal pretreatment of corncob into xylose and furfural via solid acid catalyst.

    PubMed

    Li, Huiling; Deng, Aojie; Ren, Junli; Liu, Changyu; Lu, Qi; Zhong, Linjie; Peng, Feng; Sun, Runcang

    2014-04-01

    Selectively catalytic hydrothermal pretreatment of corncob into xylose and furfural has been developed in this work using solid acid catalyst (SO4(2-)/TiO2-ZrO2/La(3+)). The effects of corncob-to-water ratio, reaction temperature and residence time on the performance of catalytic hydrothermal pretreatment were investigated. Results showed that the solid residues contained mainly lignin and cellulose, which was indicative of the efficient removal of hemicelluloses from corncob by hydrothermal method. The prepared catalyst with high thermal stability and strong acid sites originated from the acid functional groups was confirmed to contribute to the hydrolysis of polysaccharides into monosaccharides followed by dehydration into furfural. Highest furfural yield (6.18 g/100g) could be obtained at 180°C for 120 min with 6.80 g/100g xylose yield when the corncob/water ratio of was 10:100. Therefore, selectively catalytic hydrothermal pretreatment of lignocellulosic biomass into important platform chemicals by solid acids is considered to be a potential treatment for biodiesel and chemical production.

  2. Occurrence of acid rain in Baton Rouge, Louisiana, Summer 1981. The role of the catalytic converter

    SciTech Connect

    Robinson, J.W.; Ghane, H.

    1982-01-01

    Between June and October 1981, acid rain falling in Baton Rouge, LA was studied. The acidity of the rain ranged for pH 3.9 to pH 5.8. Preliminary data showed that rain associated with thermal cumulo nimbus tended to be more acidic, but rain associated with active cold fronts were less acid. This may relate to dispersion and dilution of the acid aerosols by the cold front. It is proposed that exhaust from automobiles fitted with catalytic converters is a substantial contributor to the acid rain problem, and that their net value to the abatement of pollution must be questioned, particularly in regions of the country where smog is not a problem. (JMT)

  3. [Catalytic ozonation by ceramic honeycomb for the degradation of oxalic acid in aqueous solution].

    PubMed

    Zhao, Lei; Sun, Zhi-Zhong; Ma, Jun

    2007-11-01

    Comparative experiments for the degradation of oxalic acid in aqueous solution were carried out in the three processes of ozonation alone, ceramic honeycomb-catalyzed ozonation and ceramic honeycomb adsorption. The results show that the degradation rates of oxalic acid in the ceramic honeycomb-catalyzed ozonation, ozonation alone and ceramic honeycomb adsorption systems are 37.6%, 2.2% and 0.4%, and the presence of ceramic honeycomb catalyst significantly improves the degradation rate of oxalic acid compared to the results from non-catalytic ozonation and adsorption. With the addition of tert-butanol, the degradation rates of oxalic acid in catalytic ozonation system decrease by 24.1%, 29.0% and 30.1%, respectively, at the concentration of 5, 10 and 15 mg x L(-1). This phenomenon indicates that ceramic honeycomb-catalyzed ozonation for the degradation of oxalic acid in aqueous solution follows the mechanism of *OH oxidation, namely the heterogeneous surface of catalyst enhances the initiation of *OH. The results of TOC analysis demonstrate that the process of ceramic honeycomb-catalyzed ozonation can achieve the complete mineralization level without the formation of intermediary degradation products. The experimental results suggest that the reaction temperature has positive relationship with the degradation rate of oxalic acid. The degradation rates of oxalic acid in the ceramic honeycomb-catalyzed ozonation system are 16.4%, 37.6%, 61.3% and 68.2%, at the respective reaction temperature of 10, 20, 30 and 40 degrees C.

  4. Catalytic conversion of carbohydrates to 5-hydroxymethylfurfural from the waste liquid of acid hydrolysis NCC.

    PubMed

    Sun, Yonghui; Liu, Pengtao; Liu, Zhong

    2016-05-20

    The principal goal of this work was to reuse the carbohydrates and recycle sulfuric acid in the waste liquid of acid hydrolysis nanocrystalline cellulose (NCC). Therefore, in this work, the optimizations of further hydrolysis of waste liquid of acid hydrolysis NCC and catalytic conversion of L4 to 5-hydroxymethylfurfural (5-HMF) were studied. Sulfuric acid was separated by spiral wound diffusion dialysis (SWDD). The results revealed that cellulose can be hydrolyze to glucose absolutely under the condition of temperature 35 °C, 3 h, and sulfuric acid's concentration 62 wt%. And 78.3% sulfuric acid was recovered by SWDD. The yield of 5-HMF was highest in aqueous solution under the optimal condition was as follows, temperature 160 °C, 3 h, and sulfuric acid's concentration 12 wt%. Then the effect of biphasic solvent systems catalytic conversion and inorganic salt as additives were still examined. The results showed that both of them contributed to prepare 5-HMF. The yield and selectivity of 5-HMF was up to 21.0% and 31.4%, respectively.

  5. Formic Acid Free Flowsheet Development To Eliminate Catalytic Hydrogen Generation In The Defense Waste Processing

    SciTech Connect

    Lambert, Dan P.; Stone, Michael E.; Newell, J. David; Fellinger, Terri L.; Bricker, Jonathan M.

    2012-09-14

    The Defense Waste Processing Facility (DWPF) processes legacy nuclear waste generated at the Savannah River Site (SRS) during production of plutonium and tritium demanded by the Cold War. The nuclear waste is first treated via a complex sequence of controlled chemical reactions and then vitrified into a borosilicate glass form and poured into stainless steel canisters. Converting the nuclear waste into borosilicate glass canisters is a safe, effective way to reduce the volume of the waste and stabilize the radionuclides. Testing was initiated to determine whether the elimination of formic acid from the DWPF's chemical processing flowsheet would eliminate catalytic hydrogen generation. Historically, hydrogen is generated in chemical processing of alkaline High Level Waste sludge in DWPF. In current processing, sludge is combined with nitric and formic acid to neutralize the waste, reduce mercury and manganese, destroy nitrite, and modify (thin) the slurry rheology. The noble metal catalyzed formic acid decomposition produces hydrogen and carbon dioxide. Elimination of formic acid by replacement with glycolic acid has the potential to eliminate the production of catalytic hydrogen. Flowsheet testing was performed to develop the nitric-glycolic acid flowsheet as an alternative to the nitric-formic flowsheet currently being processed at the DWPF. This new flowsheet has shown that mercury can be reduced and removed by steam stripping in DWPF with no catalytic hydrogen generation. All processing objectives were also met, including greatly reducing the Slurry Mix Evaporator (SME) product yield stress as compared to the baseline nitric/formic flowsheet. Ten DWPF tests were performed with nonradioactive simulants designed to cover a broad compositional range. No hydrogen was generated in testing without formic acid.

  6. Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate.

    PubMed

    Arimori, Sadayuki; Shibata, Norio

    2015-04-01

    Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate is described. In the presence of a catalytic amount of CuOAc and 2,4,6-collidine in ethyl acetate, the reaction proceeded in good to high yields for various substrates under mild reaction conditions at room temperature. PMID:25783441

  7. Scaleable catalytic asymmetric Strecker syntheses of unnatural α-amino acids

    PubMed Central

    Zuend, Stephan J.; Coughlin, Matthew P.; Lalonde, Mathieu P.; Jacobsen, Eric N.

    2009-01-01

    α-Amino acids are essential building blocks for protein synthesis, and are also widely useful as components of medicinally active molecules and chiral catalysts.1,2,3,4,5 Efficient chemo-enzymatic methods for the synthesis of enantioenriched α-amino acids have been devised, but the scope of these methods for the synthesis of unnatural amino acids is limited.6,7 Alkene hydrogenation is broadly useful for enantioselective catalytic synthesis of many classes of amino acids,8,9 but this approach is not applicable to the synthesis of α-amino acids bearing aryl or quaternary alkyl α-substituents. The Strecker synthesis—the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis—is an especially versatile chemical method for the synthesis of racemic α-amino acids (Fig. 1).10,11 Asymmetric Strecker syntheses using stoichiometric chiral reagents have been applied successfully on gram-to-multi-kilogram scales to the preparation of enantiomerically enriched α-amino acids.12,13,14 In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen only limited use on preparative scales (e.g., > 1 gram).15,16 The limited use of existing catalytic methodologies may be ascribed to several important practical drawbacks, including the relatively complex and precious nature of the catalysts, and the requisite use of hazardous cyanide sources. Herein we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-proteinogenic amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. Because this catalyst is robust and lacks sensitive functional groups, it is compatible with safely handled aqueous cyanide salts, and is thus adaptable to large-scale synthesis. This new methodology can be applied to the efficient syntheses of

  8. Preparation, characterization and catalytic properties of MCM-48 supported tungstophosphoric acid mesoporous materials for green synthesis of benzoic acid

    NASA Astrophysics Data System (ADS)

    Wu, Hai-Yan; Zhang, Xiao-Li; Chen, Xi; Chen, Ya; Zheng, Xiu-Cheng

    2014-03-01

    MCM-48 and tungstophosphoric acid (HPW) were prepared and applied for the synthesis of HPW/MCM-48 mesoporous materials. The characterization results showed that HPW/MCM-48 obtained retained the typical mesopore structure of MCM-48, and the textural parameters decreased with the increase loading of HPW. The catalytic oxidation results of benzyl alcohol and benzaldehyde with 30% H2O2 indicated that HPW/MCM-48 was an efficient catalyst for the green synthesis of benzoic acid. Furthermore, 35 wt% HPW/MCM-48 sample showed the highest activity under the reaction conditions.

  9. Pillared clays and pillared acid-activated clays: A comparative study of physical, acidic, and catalytic properties

    SciTech Connect

    Mokaya, R.; Jones, W.

    1995-04-15

    The preparation, characterisation, and catalytic properties of alumina-pillared materials derived from an acid-treated host clay matrix is described. Various levels of acid treatment are studied in order to ascertain the level of acid treatment which yields pillared materials with the most suitable physicochemical properties and thermal stability. The pillared acid-activated clays prepared possess basal spacing (19.3 {angstrom} after thermal treatment at 500{degrees}C) and surface areas (315-374 m{sup 2}/g) comparable to conventional pillared clays but significantly higher pore volume (0.33-0.48 cm{sup 3}/g), average pore diameter and surface acidity. The improvement in acidity is mainly of the Broensted acid type. As a result of improved acidity, the pillared acid-activated clays are better catalysts compared to conventional pillared clays and they exhibit activity indicative of the presence of strong Broensted acid sites in the temperature range 250-400{degrees}C. 36 refs., 5 figs., 6 tabs.

  10. A novel method for size uniform 200nm particles: multimetallic particles and in vitro gene delivery

    NASA Astrophysics Data System (ADS)

    Mair, Lamar; Ford, Kris; Superfine, Richard

    2008-10-01

    We report on the fabrication of arrays of mono- and multimetallic particles via metal evaporation onto lithographically patterned posts. Metal particles evaporated on cylindrical structures 0.20μm in diameter and 0.33μm tall are released via photoresist dissolution, resulting in freely suspended, shape defined particles. These Post-Particles have highly tunable composition, as demonstrated by our deposition of five different multimetallic particle blends. We calculate the susceptibility and magnetization of 200nm Fe particles in an applied 0.081T magnetic field. In order to evaluate their usefulness as magnetofection agents an antisense oligonucleotide designed to correct the aberrant splicing of enhanced green fluorescent protein mRNA was successfully attached to Fe Post-Particles via a polyethyleneimine linker and transfected into a modified HeLa cell line.

  11. Conjugate-base-stabilized Brønsted acids: catalytic enantioselective Pictet-Spengler reactions with unmodified tryptamine.

    PubMed

    Mittal, Nisha; Sun, Diana X; Seidel, Daniel

    2014-02-01

    A conjugate-base-stabilized Brønsted acid facilitates catalytic enantioselective Pictet-Spengler reactions with unmodified tryptamine. The chiral carboxylic acid catalyst is readily assembled in just two steps and enables the formation of β-carbolines with up to 92% ee. Achiral acid additives or in situ Boc-protection facilitate catalyst turnover.

  12. 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.

  13. Manganese salen complexes with acid-base catalytic auxiliary: functional mimetics of catalase.

    PubMed

    Noritake, Yukinobu; Umezawa, Naoki; Kato, Nobuki; Higuchi, Tsunehiko

    2013-04-01

    Antioxidant therapies have been considered for a wide variety of disorders associated with oxidative stress, and synthetic catalytic scavengers of reactive oxygen species would be clinically superior to stoichiometric ones. Among them, salen-manganese complexes (Mn(Salen)) seem promising, because they exhibit dual functions, i.e. superoxide dismutase- and catalase-mimetic activities. We have been developing enzyme-mimetic Mn(Salen) complexes bearing a functional group that enhances their catalytic activity. Here, we describe the design and synthesis of novel Mn(Salen) complexes with general acid-base catalytic functionality, inspired by the reaction mechanism of catalase. As expected, these Mn(Salen) complexes showed superior catalase-like activity and selectivity, while retaining moderate SOD-like activity. An unsubstituted pyridyl group worked well as a functionality to promote catalase-like activity. The introduced functionality did not alter the redox potential suggesting that the auxiliary-modified complex acted as an acid-base catalyst analogous to catalase. We believe that our approach provides a new design principle for sophisticated catalyst design. Further, the compounds described here appear to be good candidates for use in antioxidant therapy.

  14. New Insights into the Structure of Multimetallic Nanoparticles and their Advanced Characterization

    NASA Astrophysics Data System (ADS)

    Khanal, Subarna; Bhattarai, Nabraj; Velázquez-Salazar, Jesus; Guisbiers, Gregory; Jose-Yacaman, Miguel

    2015-03-01

    Noble multimetallic nanoparticles have led to exciting progress in a versatile array of applications. For the purpose of better tailoring of nanoparticles activities and understanding the correlation between their structures and properties, control over the composition, shape, size and architecture of bimetallic and multimetallic nanomaterials plays an important role on revealing their new or enhanced functions for potentials application. Advance electron microscopy techniques were used to provide atomic scale insights into the structure-properties of different materials: Pt-Pd, Au-Au3Cu, Cu-Pt, AgPd-Pt and AuCu/Pt nanoparticles. These multimetallic nanoparticles have raised interest for their various applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, and so on. The nanostructures were analyzed by transmission electron microscopy (TEM) and by aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM), in combination with high angle annular dark field (HAADF), bright field (BF), energy dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) detectors. These techniques allowed us to probe the structure at the atomic level of the nanoparticles revealing new structural information and elemental composition of the nanoparticles.

  15. Degradation of 4-hydroxybenzoic acid by combined ultrasound irradiation and catalytic wet peroxide oxidation.

    PubMed

    Nikolopoulos, Apostolos N; Igglessi-Markopoulou, Olga; Papayannakos, Nikolaos

    2004-05-01

    The aim of this study is to explore the potential benefits from the combined use of ultrasound irradiation and catalytic wet peroxide oxidation for the degradation of 4-hydroxybenzoic acid (4-HBA). The target compound degradation was studied under direct and indirect sonication, while silent conditions were employed as reference. The catalyst, a mixed (Al-Fe) pillared clay named FAZA, was in the form of powder and of extrudates. In the case of extrudates it was observed that ultrasound improves the catalyst performance due to reduction of diffusion resistance, thereby increasing the conversion after 4 h by 12-15 times. Increasing the initial concentration of 4-HBA was found to lead to lower conversion. The combined ultrasonic/catalytic process appears very promising for environmental applications. PMID:15081978

  16. Direct Catalytic Asymmetric Synthesis of β-Hydroxy Acids from Malonic Acid.

    PubMed

    Gao, Hang; Luo, Zhenli; Ge, Pingjin; He, Junqian; Zhou, Feng; Zheng, Peipei; Jiang, Jun

    2015-12-18

    A nickel(II) catalyzed asymmetric synthesis of β-hydroxy acids from malonic acid and ketones was developed, revealing for the first time the synthetic utility of malonic acid in the construction of chiral carboxyl acids; importantly, the synthetic potential of this strategy was further demonstrated by the rapid construction of cephalanthrin A, phaitanthrin B, cruciferane, and rice metabolites.

  17. Catalytic ozonation of sulfosalicylic acid over manganese oxide supported on mesoporous ceria.

    PubMed

    Xing, Shengtao; Lu, Xiaoyang; Liu, Jia; Zhu, Lin; Ma, Zichuan; Wu, Yinsu

    2016-02-01

    Manganese oxide supported on mesoporous ceria was prepared and used as catalyst for catalytic ozonation of sulfosalicylic acid (SA). Characterization results indicated that the manganese oxide was mostly incorporated into the pores of ceria. The synthesized catalyst exhibited high activity and stability for the mineralization of SA in aqueous solution by ozone, and more than 95% of total organic carbon was removed in 30 min under various conditions. Mechanism studies indicated that SA was mainly degraded by ozone molecules, and hydroxyl radical reaction played an important role for the degradation of its ozonation products (small molecular organic acids). The manganese oxide in the pores of CeO2 improved the adsorption of small molecular organic acids and the generation of hydroxyl radicals from ozone decomposition, resulting in high TOC removal efficiency.

  18. Acid-catalytic decomposition of peracetic acid in the liquid phase

    SciTech Connect

    Kharchuk, V.G.; Kolenko, I.P.; Petrov, L.A.

    1985-12-01

    This paper elucidates the kinetic relationships of peracetic acid (PAA) decomposition in the presence of mineral acids and their heterogeneous analogs, polystyrene-di-vinylbenzene cation-exchangers, differing in physicochemical and morphological parameters. It is shown that the thermal decomposition of PAA in acetic acid is an acid-catalyzed reaction. The controlling step of the reaction is protonation of the substrate with formation of an active intermediate form. Sulfonated cation-exchangers are twice as effective as sulfuric acid in this process. Polystyrene-divinylbenzene sulfonated cation-exchangers can be used with success as acid catalysts in oxidation processes involving PAA, because of their high effectiveness, stability, and availability.

  19. Catalytic biofilms on structured packing for the production of glycolic acid.

    PubMed

    Li, Xuan Zhong; Hauer, Bernhard; Rosche, Bettina

    2013-02-01

    While structured packing modules are known to be efficient for surface wetting and gas-liquid exchange in abiotic surface catalysis, this model study explores structured packing as a growth surface for catalytic biofilms. Microbial biofilms have been proposed as self-immobilized and self-regenerating catalysts for the production of chemicals. A concern is that the complex and dynamic nature of biofilms may cause fluctuations in their catalytic performance over time or may affect process reproducibility. An aerated continuous trickle-bed biofilm reactor system was designed with a 3 L structured packing, liquid recycling and pH control. Pseudomonas diminuta established a biofilm on the stainless steel structured packing with a specific surface area of 500 m2 m-3 and catalyzed the oxidation of ethylene glycol to glycolic acid for over two months of continuous operation. A steady-state productivity of up to 1.6 gl-1h-1 was achieved at a dilution rate of 0.33 h-1. Process reproducibility between three independent runs was excellent, despite process interruptions and activity variations in cultures grown from biofilm effluent cells. The results demonstrate the robustness of a catalytic biofilm on structured packing, despite its dynamic nature. Implementation is recommended for whole-cell processes that require efficient gas-liquid exchange, catalyst retention for continuous operation, or improved catalyst stability. PMID:23412062

  20. Structure and catalytic properties of magnesia-supported copper salts of molybdovanadophosphoric acid.

    PubMed

    Zhou, Guangdong; Yang, Xiaomei; Liu, Jie; Zhen, Kaiji; Wang, Haishui; Cheng, Tiexin

    2006-05-25

    The structure and stability of magnesia-supported copper salts of molybdovanadophosphoric acid (Cu(2)PMo(11)VO(40)) were characterized by different techniques. The catalyst was prepared in ethanol by impregnation because this solvent does not hurt texture of the water-sensitive MgO and Cu(2)PMo(11)VO(40). The Keggin-type structure compound may be degraded partially to form oligomerized polyoxometalate when supported on MgO. However, the oligomers can rebuild as the Keggin structure again after thermal treatment in air or during the reaction. Meanwhile, the V atoms migrate out of the Keggin structure to form a lacunary structure, as observed by Fourier transform IR spectroscopy. Moreover, the presence of Cu(2+) as a countercation showed an affirmative influence on the migration of V atoms, and the active sites derived from the lacunary species generated after release of V from the Keggin anion. The electron paramagnetic resonance data imply that V(5+) autoreduces to V(4+) in the fresh catalyst, and during the catalytic reaction a large number of V(4+) ions are produced, which enhance the formation of O(2-) vacancies around the metal atoms. These oxygen vacancies may also improve the reoxidation function of the catalyst. This behavior is correlated to higher catalytic properties of this catalyst. The oxidative dehydrogenation of hexanol to hexanal was studied over this catalyst. After reaction at 553.2 K for 50 h, catalytic properties did not decrease and exhibited higher selectivity (>96.0%) toward hexanal. PMID:16706435

  1. Multimetallic catalysed radical oxidative C(sp3)–H/C(sp)–H cross-coupling between unactivated alkanes and terminal alkynes

    PubMed Central

    Tang, Shan; Wang, Pan; Li, Haoran; Lei, Aiwen

    2016-01-01

    Radical involved transformations are now considered as extremely important processes in modern organic synthetic chemistry. According to the demand by atom-economic and sustainable chemistry, direct C(sp3)–H functionalization through radical oxidative coupling represents an appealing strategy for C–C bond formations. However, the selectivity control of reactive radical intermediates is still a great challenge in these transformations. Here we show a selective radical oxidative C(sp3)–H/C(sp)–H cross-coupling of unactivated alkanes with terminal alkynes by using a combined Cu/Ni/Ag catalytic system. It provides a new way to access substituted alkynes from readily available materials. Preliminary mechanistic studies suggest that this reaction proceeds through a radical process and the C(sp3)–H bond cleavage is the rate-limiting step. This study may have significant implications for controlling selective C–C bond formation of reactive radical intermediates by using multimetallic catalytic systems. PMID:27339161

  2. Mechanism for enhanced degradation of clofibric acid in aqueous by catalytic ozonation over MnOx/SBA-15.

    PubMed

    Sun, Qiangqiang; Wang, Yu; Li, Laisheng; Bing, Jishuai; Wang, Yingxin; Yan, Huihua

    2015-04-01

    Comparative experiments were conducted to investigate the catalytic ability of MnO(x)/SBA-15 for the ozonation of clofibric acid (CA) and its reaction mechanism. Compared with ozonation alone, the degradation of CA was barely enhanced, while the removal of TOC was significantly improved by catalytic ozonation (O3/MnO(x)/SBA-15). Adsorption of CA and its intermediates by MnO(x)/SBA-15 was proved unimportant in O3/MnO(x)/SBA-15 due to the insignificant adsorption of CA and little TOC variation after ceasing ozone in stopped-flow experiment. The more remarkably inhibition effect of sodium bisulfite (NaHSO3) on the removal of TOC in catalytic ozonation than in ozonation alone elucidated that MnO(x)/SBA-15 facilitated the generation of hydroxyl radicals (OH), which was further verified by electron spin-resonance spectroscopy (ESR). Highly dispersed MnO(x) on SBA-15 were believed to be the main active component in MnO(x)/SBA-15. Some intermediates were indentified and different degradation routes of CA were proposed in both ozonation alone and catalytic ozonation. The amounts of small molecular carboxylic acids (i.e., formic acid (FA), acetic acid (AA) and oxalic acid (OA)) generated in catalytic ozonation were lower than in ozonation alone, resulting from the generation of more OH.

  3. Catalytic wet air oxidation of carboxylic acids on TiO{sub 2}-supported ruthenium catalysts

    SciTech Connect

    Beziat, J.C.; Besson, M.; Gallezot, P.; Durecu, S.

    1999-02-15

    The total oxidation of aqueous solutions of carboxylic acids by air was studied in a slurry reactor over the temperature range 180--100 C and oxygen partial pressure of 0.3--1.8 MPa in the presence of a 2.8%Ru/TiO{sub 2} catalyst. The influence of various parameters is presented: the catalytic wet air oxidation of succinic acid is 0 order with respect to succinic acid; the order with respect to oxygen pressure is 0.4, and the activation energy is ca. 125 kJ/mol. It was found that acetic acid, which is one of the intermediates, and CO{sub 2} have no retarding effect on the total organic carbon abatement rate of succinic acid. Substitution of one hydrogen atom of the methyl group in acetic acid by Cl, OH, or NH{sub 2} gives an increase of the oxidation rate. However, it was proposed that the low activity of acetic acid oxidation is due not only to the difficulty to oxidize the methyl group, but also to the low adsorption coefficient of acetic acid on ruthenium surface. Inorganic salts, such as sodium chloride, only slightly decrease the oxidation rate of acetic acid. The absence of metal ions (Ru, Ti) in the effluents after reaction and the absence of particle sintering indicate also a high stability of the catalyst under the conditions employed. The catalyst can be recycled without loss of activity after the second run. The activity becomes stable after the attainment of a steady-state coverage of the Ru particles by oxygen. The study of the effect of reduction-oxidation treatments of the catalyst showed that the activity depends on the oxidation state of the surface.

  4. Identifying the catalytic acid/base in GH29 α-L-fucosidase subfamilies.

    PubMed

    Shaikh, F Aidha; Lammerts van Bueren, Alicia; Davies, Gideon J; Withers, Stephen G

    2013-08-27

    While the catalytic nucleophile in the configuration-retaining α-L-fucosidases from family GH29 is fully conserved with respect to sequence, there is no fully sequence-conserved acid/base residue candidate across the family. X-ray crystallographic studies and kinetic characterizations have allowed the identification of this residue in a few cases, and a recent combination of phylogenetic tree analyses with substrate specificity data has allowed the division of GH29 enzymes into two subfamilies, A and B, allowing the probable assignment of these residues. Here, we perform detailed kinetic and mechanistic characterizations of the corresponding alanine mutants and other candidates. Through comparison of kinetic parameters obtained for the hydrolysis of fucosyl substrates with activated leaving groups by these mutants with those of the corresponding wild-type enzymes, in conjunction with the demonstration of azide rescue, we largely confirm the acid/base residue predictions for the GH29 fucosidases from the two subfamilies.

  5. Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion.

    PubMed

    Chen, Lin; Liu, Tianzhong; Zhang, Wei; Chen, Xiaolin; Wang, Junfeng

    2012-05-01

    The effect of storage temperature and time on lipid composition of Scenedesmus sp. was studied. When stored at 4°C or higher, the free fatty acid content in the wet biomass increased from a trace to 62.0% by day 4. Using two-step catalytic conversion, algae oil with a high free fatty acid content was converted to biodiesel by pre-esterification and transesterification. The conversion rate of triacylglycerols reached 100% under the methanol to oil molar ratio of 12:1 during catalysis with 2% potassium hydroxide at 65°C for 30 min. This process was scaled up to produce biodiesel from Scenedesmus sp. and Nannochloropsis sp. oil. The crude biodiesel was purified using bleaching earth. Except for moisture content, the biodiesel conformed to Chinese National Standards. PMID:22401712

  6. Enhancing the catalytic repertoire of nucleic acids: a systematic study of linker length and rigidity

    PubMed Central

    Lee, Sarah E.; Sidorov, Alexander; Gourlain, Thierry; Mignet, Nathalie; Thorpe, Simon J.; Brazier, John A.; Dickman, Mark J.; Hornby, David P.; Grasby, Jane A.; Williams, David M.

    2001-01-01

    The incorporation of potentially catalytic groups in DNA is of interest for the in vitro selection of novel deoxyribozymes. A series of 10 C5-modified analogues of 2′-deoxyuridine triphosphate have been synthesised that possess side chains of differing flexibility and bearing a primary amino or imidazole functionality. For each series of nucleotide analogues differing degrees of flexibility of the C5 side chain was achieved through the use of alkynyl, alkenyl and alkyl moieties. The imidazole function was conjugated to these C5-amino-modified nucleotides using either imidazole 4-acetic acid or imidazole 4-acrylic acid (urocanic acid). The substrate properties of the nucleotides (fully replacing dTTP) with Taq polymerase during PCR have been investigated in order to evaluate their potential applications for in vitro selection experiments. 5-(3-Aminopropynyl)dUTP and 5-(E-3-aminopropenyl)dUTP and their imidazole 4-acetic acid- and urocanic acid-modified conjugates were found to be substrates. In contrast, C5-amino-modified dUTPs with alkane or Z-alkene linkers and their corresponding conjugates were not substrates. The incorporation of these analogues during PCR has been confirmed by inhibition of restriction enzyme digestion using XbaI and by mass spectrometry of the PCR products. PMID:11266559

  7. Catalytic activity of the two-component flavin-dependent monooxygenase from Pseudomonas aeruginosa toward cinnamic acid derivatives.

    PubMed

    Furuya, Toshiki; Kino, Kuniki

    2014-02-01

    4-Hydroxyphenylacetate 3-hydroxylases (HPAHs) of the two-component flavin-dependent monooxygenase family are attractive enzymes that possess the catalytic potential to synthesize valuable ortho-diphenol compounds from simple monophenol compounds. In this study, we investigated the catalytic activity of HPAH from Pseudomonas aeruginosa strain PAO1 toward cinnamic acid derivatives. We prepared Escherichia coli cells expressing the hpaB gene encoding the monooxygenase component and the hpaC gene encoding the oxidoreductase component. E. coli cells expressing HpaBC exhibited no or very low oxidation activity toward cinnamic acid, o-coumaric acid, and m-coumaric acid, whereas they rapidly oxidized p-coumaric acid to caffeic acid. Interestingly, after p-coumaric acid was almost completely consumed, the resulting caffeic acid was further oxidized to 3,4,5-trihydroxycinnamic acid. In addition, HpaBC exhibited oxidation activity toward 3-(4-hydroxyphenyl)propanoic acid, ferulic acid, and coniferaldehyde to produce the corresponding ortho-diphenols. We also investigated a flask-scale production of caffeic acid from p-coumaric acid as the model reaction for HpaBC-catalyzed syntheses of hydroxycinnamic acids. Since the initial concentrations of the substrate p-coumaric acid higher than 40 mM markedly inhibited its HpaBC-catalyzed oxidation, the reaction was carried out by repeatedly adding 20 mM of this substrate to the reaction mixture. Furthermore, by using the HpaBC whole-cell catalyst in the presence of glycerol, our experimental setup achieved the high-yield production of caffeic acid, i.e., 56.6 mM (10.2 g/L) within 24 h. These catalytic activities of HpaBC will provide an easy and environment-friendly synthetic approach to hydroxycinnamic acids.

  8. Multimetallic catalysed cross-coupling of aryl bromides with aryl triflates

    NASA Astrophysics Data System (ADS)

    Ackerman, Laura K. G.; Lovell, Matthew M.; Weix, Daniel J.

    2015-08-01

    The advent of transition-metal catalysed strategies for forming new carbon-carbon bonds has revolutionized the field of organic chemistry, enabling the efficient synthesis of ligands, materials, and biologically active molecules. In cases where a single metal fails to promote a selective or efficient transformation, the synergistic cooperation of two distinct catalysts--multimetallic catalysis--can be used instead. Many important reactions rely on multimetallic catalysis, such as the Wacker oxidation of olefins and the Sonogashira coupling of alkynes with aryl halides, but this approach has largely been limited to the use of metals with distinct reactivities, with only one metal catalyst undergoing oxidative addition. Here, we demonstrate that cooperativity between two group 10 metal catalysts--(bipyridine)nickel and (1,3-bis(diphenylphosphino)propane)palladium--enables a general cross-Ullmann reaction (the cross-coupling of two different aryl electrophiles). Our method couples aryl bromides with aryl triflates directly, eliminating the use of arylmetal reagents and avoiding the challenge of differentiating between multiple carbon-hydrogen bonds that is required for direct arylation methods. Selectivity can be achieved without an excess of either substrate and originates from the orthogonal reactivity of the two catalysts and the relative stability of the two arylmetal intermediates. While (1,3-bis(diphenylphosphino)propane)palladium reacts preferentially with aryl triflates to afford a persistent intermediate, (bipyridine)nickel reacts preferentially with aryl bromides to form a transient, reactive intermediate. Although each catalyst forms less than 5 per cent cross-coupled product in isolation, together they are able to achieve a yield of up to 94 per cent. Our results reveal a new method for the synthesis of biaryls, heteroaryls, and dienes, as well as a general mechanism for the selective transfer of ligands between two metal catalysts. We anticipate that this

  9. Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment

    NASA Astrophysics Data System (ADS)

    Guo, Dai-shi; Ma, Zi-feng; Yin, Chun-sheng; Jiang, Qi-zhong

    2008-02-01

    TiO2 grafted silica MCM-41 catalyst with and without sulfate treatment were prepared. The structural and acid properties of these materials were investigated by XRD, N2 adsorption-desorption, element analysis, thermal analysis, Raman and FTIR measurements. Their acid-catalytic activities were evaluated using the cyclization reaction of pseudoionone. It was found that the obtained materials possess well-ordered mesostructure, and the grafted TiO2 components were in highly dispersed amorphous form. T/MCM41 without sulfation contained only Lewis acid sites, while Brønsted and Lewis acidities were remarkably improved for the sulfated materials ST/MCM41 and d-ST/MCM41. T/MCM-41 was not active for the cyclization reaction of pseudoionone, but ST/MCM-41 and d-ST/MCM-41 possessed favorable catalytic activities. The catalytic performance of ST/MCM-41 was comparable with that of the commercial solid acid catalyst of Amberlyst-15, and better than that of d-ST/MCM-41, although the latter underwent a second TiO2 grafting process and accordingly had higher Ti and S content. The specific surface structure of Si-O-Ti-O-S=O in ST/MCM-41 and the bilateral induction effect of Si and S=O on Si-O-Ti bonds were speculated to account for its higher acid catalytic activity.

  10. Voltage-dependent motion of the catalytic region of voltage-sensing phosphatase monitored by a fluorescent amino acid

    PubMed Central

    Sakata, Souhei; Jinno, Yuka; Kawanabe, Akira; Okamura, Yasushi

    2016-01-01

    The cytoplasmic region of voltage-sensing phosphatase (VSP) derives the voltage dependence of its catalytic activity from coupling to a voltage sensor homologous to that of voltage-gated ion channels. To assess the conformational changes in the cytoplasmic region upon activation of the voltage sensor, we genetically incorporated a fluorescent unnatural amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap), into the catalytic region of Ciona intestinalis VSP (Ci-VSP). Measurements of Anap fluorescence under voltage clamp in Xenopus oocytes revealed that the catalytic region assumes distinct conformations dependent on the degree of voltage-sensor activation. FRET analysis showed that the catalytic region remains situated beneath the plasma membrane, irrespective of the voltage level. Moreover, Anap fluorescence from a membrane-facing loop in the C2 domain showed a pattern reflecting substrate turnover. These results indicate that the voltage sensor regulates Ci-VSP catalytic activity by causing conformational changes in the entire catalytic region, without changing their distance from the plasma membrane. PMID:27330112

  11. Atomistic details of the Catalytic Mechanism of Fe(III)-Zn(II) Purple Acid Phosphatase.

    PubMed

    Alberto, Marta E; Marino, Tiziana; Ramos, Maria J; Russo, Nino

    2010-08-10

    In the present work, we performed a theoretical investigation of the reaction mechanism of the Fe(III)-Zn(II) purple acid phosphatase from red kidney beans (rkbPAP), using the hybrid density functional theory and employing different exchange-correlation potentials. Characterization of the transition states and intermediates involved and the potential energy profiles for the reaction in different environments (gas phase, protein environment, and water) are reported. Our results show that the Fe(III)-Zn(II)PAP catalyzes the hydrolysis of methylphosphate via direct attack by a bridging metals-coordinated hydroxide leading to the cleavage of the ester bond. From our study emerges that the rate-limiting step of the reaction is the nucleophilic attack followed by the less energetically demanding release of the leaving group. Furthermore, we provide insights into some important points of contention concerning the precatalytic complex and the substrate coordination mode into the active site prior to hydrolysis. In particular: (i) Two models of enzyme-substrate with different orientations of the substrate into the active site were tested to evaluate the possible roles played by the conserved histidine residues (His 202 and His 296); (ii) Different protonation states of the substrate were taken into account in order to reproduce different pH values and to verify its influence on the catalytic efficiency and on the substrate binding mode; (iii) The metals role in each step of the catalytic mechanism was elucidated. We were also able to ascertain that the activation of the leaving group by the protonated His 296 is decisive to reach an optimal catalytic efficiency, while the bond scission without activation requires higher energy to occur. PMID:26613496

  12. Identification of acid-base catalytic residues of high-Mr thioredoxin reductase from Plasmodium falciparum.

    PubMed

    McMillan, Paul J; Arscott, L David; Ballou, David P; Becker, Katja; Williams, Charles H; Müller, Sylke

    2006-11-01

    High-M(r) thioredoxin reductase from the malaria parasite Plasmodium falciparum (PfTrxR) contains three redox active centers (FAD, Cys-88/Cys-93, and Cys-535/Cys-540) that are in redox communication. The catalytic mechanism of PfTrxR, which involves dithiol-disulfide interchanges requiring acid-base catalysis, was studied by steady-state kinetics, spectral analyses of anaerobic static titrations, and rapid kinetics analysis of wild-type enzyme and variants involving the His-509-Glu-514 dyad as the presumed acid-base catalyst. The dyad is conserved in all members of the enzyme family. Substitution of His-509 with glutamine and Glu-514 with alanine led to TrxR with only 0.5 and 7% of wild type activity, respectively, thus demonstrating the crucial roles of these residues for enzymatic activity. The H509Q variant had rate constants in both the reductive and oxidative half-reactions that were dramatically less than those of wild-type enzyme, and no thiolateflavin charge-transfer complex was observed. Glu-514 was shown to be involved in dithiol-disulfide interchange between the Cys-88/Cys-93 and Cys-535/Cys-540 pairs. In addition, Glu-514 appears to greatly enhance the role of His-509 in acid-base catalysis. It can be concluded that the His-509-Glu-514 dyad, in analogy to those in related oxidoreductases, acts as the acid-base catalyst in PfTrxR.

  13. [Catalytic ozonation of oxalic acid in water with Pt/graphite catalyst].

    PubMed

    Liu, Zheng-Qian; Ma, Jun; Zhao, Lei

    2007-06-01

    Pt/graphite catalyst was prepared by incipient wetness impregnation using H2PtCl6 x 6H2O as precursor substance. The removal efficiencies of oxalic acid by Pt/graphite, graphite catalyzed ozonation and ozonation alone were compared. It was found that the removal efficiency of oxalic acid in ozonation alone, graphite and Pt/graphite catalyzed ozonation was 3.0%, 47.6% and 99.3% respectively under the present experimental conditions. Results showed that loading of Pt could significantly increase the catalytic activity of graphite. Taking oxalic acid degradation efficiency as indication, the preparation conditions of Pt/graphite were optimized. The pretreatment of graphite had no favor to improve the activity of Pt/graphite catalyst. The optimal preparation conditions of Pt/graphite catalyst are as follow: impregnant, distilled water; impregnation time, 24 h; the loading amount of Pt, 1.0%; reduction temperature, 35 degrees C. The Pt/graphite catalyst was used for five times with no significant decrease of its activity and more than 90% oxalic acid removal was obtained. PMID:17674732

  14. Acid-base and catalytic properties of the products of oxidative thermolysis of double complex compounds

    NASA Astrophysics Data System (ADS)

    Pechenyuk, S. I.; Semushina, Yu. P.; Kuz'mich, L. F.; Ivanov, Yu. V.

    2016-01-01

    Acid-base properties of the products of thermal decomposition of [M(A)6] x; [M1(L)6] y (where M is Co, Cr, Cu, Ni; M1 is Fe, Cr, Co; A is NH3, 1/2 en, 1/2 pn, CO(NH2)2; and L is CN, 1/2C2O4) binary complexes in air and their catalytic properties in the oxidation reaction of ethanol with atmospheric oxygen are studied. It is found that these thermolysis products are mixed oxides of the central atoms of complexes characterized by pH values of the zero charge point in the region of 4-9, OH-group sorption limits from 1 × 10-4 to 4.5 × 10-4 g-eq/g, OH-group surface concentrations of 10-50 nm-2 in 0.1 M NaCl solutions, and S sp from 3 to 95 m2/g. Their catalytic activity is estimated from the apparent rate constant of the conversion of ethanol in CO2. The values of constants are (1-6.5) × 10-5 s-1, depending on the gas flow rate and the S sp value.

  15. Mesoporous Silica Supported Pd-MnOx Catalysts with Excellent Catalytic Activity in Room-Temperature Formic Acid Decomposition

    NASA Astrophysics Data System (ADS)

    Jin, Min-Ho; Oh, Duckkyu; Park, Ju-Hyoung; Lee, Chun-Boo; Lee, Sung-Wook; Park, Jong-Soo; Lee, Kwan-Young; Lee, Dong-Wook

    2016-09-01

    For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h‑1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance.

  16. Mesoporous Silica Supported Pd-MnOx Catalysts with Excellent Catalytic Activity in Room-Temperature Formic Acid Decomposition

    PubMed Central

    Jin, Min-Ho; Oh, Duckkyu; Park, Ju-Hyoung; Lee, Chun-Boo; Lee, Sung-Wook; Park, Jong-Soo; Lee, Kwan-Young; Lee, Dong-Wook

    2016-01-01

    For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h−1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance. PMID:27666280

  17. Acidic 1,3-propanediaminetetraacetato lanthanides with luminescent and catalytic ester hydrolysis properties

    SciTech Connect

    Chen, Mao-Long; Shi, Yan-Ru; Yang, Yu-Chen; Zhou, Zhao-Hui

    2014-11-15

    In acidic solution, a serials of water-soluble coordination polymers (CPs) were isolated as zonal 1D-CPs 1,3-propanediaminetetraacetato lanthanides [Ln(1,3-H{sub 3}pdta)(H{sub 2}O){sub 5}]{sub n}·2Cl{sub n}·3nH{sub 2}O [Ln=La, 1; Ce, 2; Pr, 3; Nd, 4; Sm, 5] (1,3-H{sub 4}pdta=1,3-propanediaminetetraacetic acid, C{sub 11}H{sub 18}N{sub 2}O{sub 8}) in high yields. When 1 eq. mol potassium hydroxide was added to the solutions of 1D-CPs, respectively, two 1D-CPs [Ln(1,3-H{sub 2}pdta)(H{sub 2}O){sub 3}]{sub n}·Cl{sub n}·2nH{sub 2}O [Ln=Sm, 6; Gd, 7] were isolated at room temperature and seven 2D-CPs [Ln(1,3-H{sub 2}pdta)(H{sub 2}O){sub 2}]{sub n}·Cl{sub n}·2nH{sub 2}O [Ln=La, 8; Ce, 9; Pr, 10; Nd, 11; Sm, 12; Eu, 13; Gd, 14] were isolated at 70 °C. When the crystals of 1–4 were hydrothermally heated at 180 °C with 1–2 eq. mol potassium hydroxide, four 3D-CPs [Ln(1,3-Hpdta)]{sub n}·nH{sub 2}O [Ln=La, 15; Ce, 16; Pr, 17; Nd, 18] were obtained. The two 2D-CPs [Ln(1,3-Hpdta)(H{sub 2}O)]{sub n}·4nH{sub 2}O (Sm, 19; Eu, 20) were isolated in similar reaction conditions. With the increments of pH value in the solution and reaction temperature, the structure becomes more complicated. 1–5 are soluble in water and 1 was traced by solution {sup 13}C({sup 1}H) NMR technique, the water-soluble lanthanides 1 and 5 show catalytic activity to ester hydrolysis reaction respectively, which indicate their important roles in the hydrolytic reaction. The europium complexes 13 and 20 show visible fluorescence at an excitation of 394 nm. The structure diversity is mainly caused by the variation of coordinated ligand in different pH values and lanthanide contraction effect. Acidic conditions are favorable for the isolations of lanthanide complexes in different structures and this may helpful to separate different lanthanides. The thermal stability investigations reveal that acidic condition is favorable to obtain the oxides at a lower temperature. - Graphical abstract: A series

  18. Inhibition of miR-21 in glioma cells using catalytic nucleic acids

    PubMed Central

    Belter, Agnieszka; Rolle, Katarzyna; Piwecka, Monika; Fedoruk-Wyszomirska, Agnieszka; Naskręt-Barciszewska, Mirosława Z.; Barciszewski, Jan

    2016-01-01

    Despite tremendous efforts worldwide, glioblastoma multiforme (GBM) remains a deadly disease for which no cure is available and prognosis is very bad. Recently, miR-21 has emerged as a key omnipotent player in carcinogenesis, including brain tumors. It is recognized as an indicator of glioma prognosis and a prosperous target for anti-tumor therapy. Here we show that rationally designed hammerhead ribozymes and DNAzymes can target miR-21 and/or its precursors. They decrease miR-21 level, and thus silence this oncomiR functions. We demonstrated that anti-miRNA catalytic nucleic acids show a novel terrific arsenal for specific and effective combat against diseases with elevated cellular miR-21 content, such as brain tumors. PMID:27079911

  19. Catalytic residues are shared between two pseudosubunits of the dehydratase domain of the animal fatty acid synthase.

    PubMed

    Pasta, Saloni; Witkowski, Andrzej; Joshi, Anil K; Smith, Stuart

    2007-12-01

    Expression, characterization, and mutagenesis of a series of N-terminal fragments of an animal fatty acid synthase, containing the beta-ketoacyl synthase, acyl transferase, and dehydratase domains, demonstrate that the dehydratase domain consists of two pseudosubunits, derived from contiguous regions of the same polypeptide, in which a single active site is formed by the cooperation of the catalytic histidine 878 residue of the first pseudosubunit with aspartate 1032 of the second pseudosubunit. Mutagenesis and modeling studies revealed an essential role for glutamine 1036 in anchoring the position of the catalytic aspartate. These findings establish that sequence elements previously assigned to a central structural core region of the type I fatty acid synthases and some modular polyketide synthase counterparts play an essential catalytic role as part of the dehydratase domain.

  20. Kinetics of Non-Catalytic Esterification of Free Fatty Acids Present in Jatropha Oil.

    PubMed

    Prasanna Rani, Karna Narayana; Ramana Neeharika, Tulasi Sri Venkata; Kumar, Thella Prathap; Satyavathi, Bankupalli; Sailu, Chintha

    2016-05-01

    Non-catalytic esterfication of free fatty acids (FFA) present in vegetable oils is an alternative pretreatment process for the biodiesel production. Biodiesel, consists of long-chain fatty acid methyl esters (FAME) and is obtained from renewable sources such as vegetable oils or animal fat. This study presents kinetics of thermal esterification of free fatty acids present in jatropha oil with methanol. The effect of process parameters like reaction time (1-5 h), temperature (170-190°C) and oil to methanol ratio (1:3-1:5) at constant pressure was investigated. The optimal conditions were found to be oil to methanol ratio of 1:4, 190°C, at 27.1 bar and 5 h which gave a maximum conversion of 95.1%. A second order kinetic model for both forward and backward reactions was proposed to study the reaction system. A good agreement was observed between the experimental data and the model values. The activation energy for forward reaction and the heat of reaction were found to be 36.364 Kcal/mol and 1.74 Kcal/mol respectively.

  1. Kinetics of Non-Catalytic Esterification of Free Fatty Acids Present in Jatropha Oil.

    PubMed

    Prasanna Rani, Karna Narayana; Ramana Neeharika, Tulasi Sri Venkata; Kumar, Thella Prathap; Satyavathi, Bankupalli; Sailu, Chintha

    2016-05-01

    Non-catalytic esterfication of free fatty acids (FFA) present in vegetable oils is an alternative pretreatment process for the biodiesel production. Biodiesel, consists of long-chain fatty acid methyl esters (FAME) and is obtained from renewable sources such as vegetable oils or animal fat. This study presents kinetics of thermal esterification of free fatty acids present in jatropha oil with methanol. The effect of process parameters like reaction time (1-5 h), temperature (170-190°C) and oil to methanol ratio (1:3-1:5) at constant pressure was investigated. The optimal conditions were found to be oil to methanol ratio of 1:4, 190°C, at 27.1 bar and 5 h which gave a maximum conversion of 95.1%. A second order kinetic model for both forward and backward reactions was proposed to study the reaction system. A good agreement was observed between the experimental data and the model values. The activation energy for forward reaction and the heat of reaction were found to be 36.364 Kcal/mol and 1.74 Kcal/mol respectively. PMID:27086997

  2. Identification of olivetolic acid cyclase from Cannabis sativa reveals a unique catalytic route to plant polyketides

    PubMed Central

    Gagne, Steve J.; Stout, Jake M.; Liu, Enwu; Boubakir, Zakia; Clark, Shawn M.; Page, Jonathan E.

    2012-01-01

    Δ9-Tetrahydrocannabinol (THC) and other cannabinoids are responsible for the psychoactive and medicinal properties of Cannabis sativa L. (marijuana). The first intermediate in the cannabinoid biosynthetic pathway is proposed to be olivetolic acid (OA), an alkylresorcinolic acid that forms the polyketide nucleus of the cannabinoids. OA has been postulated to be synthesized by a type III polyketide synthase (PKS) enzyme, but so far type III PKSs from cannabis have been shown to produce catalytic byproducts instead of OA. We analyzed the transcriptome of glandular trichomes from female cannabis flowers, which are the primary site of cannabinoid biosynthesis, and searched for polyketide cyclase-like enzymes that could assist in OA cyclization. Here, we show that a type III PKS (tetraketide synthase) from cannabis trichomes requires the presence of a polyketide cyclase enzyme, olivetolic acid cyclase (OAC), which catalyzes a C2–C7 intramolecular aldol condensation with carboxylate retention to form OA. OAC is a dimeric α+β barrel (DABB) protein that is structurally similar to polyketide cyclases from Streptomyces species. OAC transcript is present at high levels in glandular trichomes, an expression profile that parallels other cannabinoid pathway enzymes. Our identification of OAC both clarifies the cannabinoid pathway and demonstrates unexpected evolutionary parallels between polyketide biosynthesis in plants and bacteria. In addition, the widespread occurrence of DABB proteins in plants suggests that polyketide cyclases may play an overlooked role in generating plant chemical diversity. PMID:22802619

  3. Identification of olivetolic acid cyclase from Cannabis sativa reveals a unique catalytic route to plant polyketides.

    PubMed

    Gagne, Steve J; Stout, Jake M; Liu, Enwu; Boubakir, Zakia; Clark, Shawn M; Page, Jonathan E

    2012-07-31

    Δ(9)-Tetrahydrocannabinol (THC) and other cannabinoids are responsible for the psychoactive and medicinal properties of Cannabis sativa L. (marijuana). The first intermediate in the cannabinoid biosynthetic pathway is proposed to be olivetolic acid (OA), an alkylresorcinolic acid that forms the polyketide nucleus of the cannabinoids. OA has been postulated to be synthesized by a type III polyketide synthase (PKS) enzyme, but so far type III PKSs from cannabis have been shown to produce catalytic byproducts instead of OA. We analyzed the transcriptome of glandular trichomes from female cannabis flowers, which are the primary site of cannabinoid biosynthesis, and searched for polyketide cyclase-like enzymes that could assist in OA cyclization. Here, we show that a type III PKS (tetraketide synthase) from cannabis trichomes requires the presence of a polyketide cyclase enzyme, olivetolic acid cyclase (OAC), which catalyzes a C2-C7 intramolecular aldol condensation with carboxylate retention to form OA. OAC is a dimeric α+β barrel (DABB) protein that is structurally similar to polyketide cyclases from Streptomyces species. OAC transcript is present at high levels in glandular trichomes, an expression profile that parallels other cannabinoid pathway enzymes. Our identification of OAC both clarifies the cannabinoid pathway and demonstrates unexpected evolutionary parallels between polyketide biosynthesis in plants and bacteria. In addition, the widespread occurrence of DABB proteins in plants suggests that polyketide cyclases may play an overlooked role in generating plant chemical diversity.

  4. Synthesis of 4H/fcc Noble Multimetallic Nanoribbons for Electrocatalytic Hydrogen Evolution Reaction.

    PubMed

    Fan, Zhanxi; Luo, Zhimin; Huang, Xiao; Li, Bing; Chen, Ye; Wang, Jie; Hu, Yanling; Zhang, Hua

    2016-02-01

    Noble multimetallic nanomaterials, if only consisting of Au, Ag, Pt, and Pd, typically adopt the high-symmetry face-centered cubic (fcc) structure. Here for the first time, by using the 4H/fcc Au@Ag nanoribbons (NRBs) as seeds, we report the synthesis of 4H/fcc trimetallic Au@PdAg core-shell NRBs via the galvanic reaction method under ambient conditions. Moreover, this strategy can also be used to synthesize 4H/fcc trimetallic Au@PtAg and quatermetallic Au@PtPdAg core-shell NRBs. Impressively, for the first time, these alloy shells, i.e., PdAg, PtAg, and PtPdAg, epitaxially grown on the 4H/fcc Au core with novel 4H hexagonal phase were successfully synthesized. Remarkably, the obtained 4H/fcc Au@PdAg NRBs exhibit excellent electrocatalytic activity toward the hydrogen evolution reaction, which is even quite close to that of the commercial Pt black. We believe that our findings here may provide a novel strategy for the crystal-structure-controlled synthesis of advanced functional noble multimetallic nanomaterials with various promising applications.

  5. Mono- and Bis-Terpyridine-Based Dimer and Metallo-Organic Polymers as Ionic Templates for Preparation of Multi-Metallic Au Nanocluster and Nanowires.

    PubMed

    Liu, Die; Cao, Hongda; Jiang, Zhilong; Wu, Tun; Sun, Xiaoyi; Wang, Pingshan; Moorefield, Charles N; Dai, Liming; Newkome, George R

    2016-03-01

    The preparation of multi-metallic Au nanocluster and nanowires has been achieved using terpyridine-based metallo-organic polymers as multi-ionic templates through a straightforward counterion exchange with aqueous NaAuCl4 followed by a mild reduction in-situ with sodium citrate. The mild reduction of the [TpyFeTpy]2+ x 2[AuCl4]- complex, derived from [TpyFeTpy]2+ x 2Cl- 1 (tpy = 2,2':6',2"-terpyridine), led to the formation of Au nanoclusters (Au NC) with diameters ranging from 7.5-88 nm. Each Au NC alone contained multiple nanoparticles, with diameters ranging from 2.5-4.5 nm. 1,4-bis-terpyridine based metallo-oraganic polymer [-TpyFeTpy-TpyFeTpy-]n(2n+) x [Cl]2n- 2 was found to generate a multi-ionic metallo-polymer with AuCl4- as the counterion, after mild reduction with sodium citrate, resulting in irregular zigzag shaped Au nanowires (Au NW). The prepared Au NW from the di-metallic complex 3 should find applications within electronic devices. Both Au NC and NW were also found to possess excellent catalytic properties.

  6. Mono- and Bis-Terpyridine-Based Dimer and Metallo-Organic Polymers as Ionic Templates for Preparation of Multi-Metallic Au Nanocluster and Nanowires.

    PubMed

    Liu, Die; Cao, Hongda; Jiang, Zhilong; Wu, Tun; Sun, Xiaoyi; Wang, Pingshan; Moorefield, Charles N; Dai, Liming; Newkome, George R

    2016-03-01

    The preparation of multi-metallic Au nanocluster and nanowires has been achieved using terpyridine-based metallo-organic polymers as multi-ionic templates through a straightforward counterion exchange with aqueous NaAuCl4 followed by a mild reduction in-situ with sodium citrate. The mild reduction of the [TpyFeTpy]2+ x 2[AuCl4]- complex, derived from [TpyFeTpy]2+ x 2Cl- 1 (tpy = 2,2':6',2"-terpyridine), led to the formation of Au nanoclusters (Au NC) with diameters ranging from 7.5-88 nm. Each Au NC alone contained multiple nanoparticles, with diameters ranging from 2.5-4.5 nm. 1,4-bis-terpyridine based metallo-oraganic polymer [-TpyFeTpy-TpyFeTpy-]n(2n+) x [Cl]2n- 2 was found to generate a multi-ionic metallo-polymer with AuCl4- as the counterion, after mild reduction with sodium citrate, resulting in irregular zigzag shaped Au nanowires (Au NW). The prepared Au NW from the di-metallic complex 3 should find applications within electronic devices. Both Au NC and NW were also found to possess excellent catalytic properties. PMID:27455678

  7. Catalytic Hydrotreatment of Humins in Mixtures of Formic Acid/2-Propanol with Supported Ruthenium Catalysts.

    PubMed

    Wang, Yuehu; Agarwal, Shilpa; Kloekhorst, Arjan; Heeres, Hero Jan

    2016-05-10

    The catalytic hydrotreatment of humins, which are the solid byproducts from the conversion of C6 sugars (glucose, fructose) into 5-hydroxymethylfurfural (HMF) and levulinic acid (LA), by using supported ruthenium catalysts has been investigated. Reactions were carried out in a batch setup at elevated temperatures (400 °C) by using a hydrogen donor (formic acid (FA) in isopropanol (IPA) or hydrogen gas), with humins obtained from d-glucose. Humin conversions of up to 69 % were achieved with Ru/C and FA, whereas the performance for Ru on alumina was slightly poorer (59 % humin conversion). Humin oils were characterized by using a range of analytical techniques (GC, GC-MS, GCxGC, gel permeation chromatography) and were shown to consist of monomers, mainly alkyl phenolics (>45 % based on compounds detectable by GC) and higher oligomers. A reaction network for the reaction is proposed based on structural proposals for humins and the main reaction products. PMID:26836970

  8. One-step and rapid synthesis of porous Pd nanoparticles with superior catalytic activity toward ethanol/formic acid electrooxidation

    NASA Astrophysics Data System (ADS)

    Hong, Wei; Fang, Youxing; Wang, Jin; Wang, Erkang

    2014-02-01

    Porous Pd nanoparticles are successfully prepared by a rapid, one-step, and efficient route with high yield in aqueous solution. The developed method is very simple, just by mixing sodium tetrachloropalladate, polyvinylpyrrolidone and hydroquinone and heated at 70 °C for 15 min. The structure and composition are analyzed by transmission electron microscope, selected-area electron diffraction, inductively coupled plasma optical emission spectrometer, X-ray diffraction, energy dispersive X-ray spectrum and X-ray photoelectron spectroscopy. Electrochemical catalytic measurement results prove that the as synthesized porous Pd nanoparticles exhibit superior catalytic activity towards ethanol and formic acid electrooxidation.

  9. Building, characterising and catalytic activity testing of Co-C-protected amino acid complexes covalently grafted onto chloropropylated silica gel

    NASA Astrophysics Data System (ADS)

    Varga, G.; Timár, Z.; Csendes, Z.; Bajnóczi, É. G.; Carlson, S.; Canton, S. E.; Bagi, L.; Sipos, P.; Pálinkó, I.

    2015-06-01

    Co-C-protected amino acid (C-protected L-histidine, L-tyrosine, L-cysteine and L-cystine) complexes were covalently grafted onto chloropropylated silica gel, and the materials thus obtained were structurally characterised by mid/far IR and X-ray absorption spectroscopies. The superoxide dismutase-like activities of the substances were determined via the Beauchamp-Fridovich test reaction. It was found that covalent grafting and the preparation of the anchored complexes were successful in most cases. The coordinating groups varied upon changing the conditions of the syntheses. All materials displayed catalytic activity, although catalytic activities differed widely.

  10. Multimetallic Catalysis Enabled Cross-Coupling of Aryl Bromides with Aryl Triflates

    PubMed Central

    Ackerman, Laura K.G.; Lovell, Matthew M.

    2015-01-01

    Transition metal-catalyzed strategies for the formation of new C-C bonds have revolutionized the field of organic chemistry, enabling the efficient synthesis of ligands, materials, and biologically active molecules.1–3 In cases where a single metal fails to promote a selective or efficient transformation, the synergistic cooperation4 of two distinct catalysts – multimetallic catalysis – can be employed instead. Many important reactions rely on multimetallic catalysis,5 including the Wacker oxidation of olefins6–8 and the Sonogashira coupling of alkynes with aryl halides.9–10 However, the application of this strategy, even in recently developed methods11, has largely been limited to the use of metals with distinct reactivities, with only one metal catalyst undergoing an oxidative addition.12 In this manuscript, we demonstrate that cooperativity between two d10 metal catalysts, (bipyridine)nickel and (1,3-bis(diphenylphosphino)propane)palladium, enables a general cross-Ullman reaction.13–15 Our method couples aryl bromides with aryl triflates directly, eliminating the use of arylmetal reagents and avoiding the challenge of differentiating between multiple C–H bonds that is required for many C–H activation methods.16–17 The selectivity does not require an excess of either substrate and originates from the orthogonal activity of the two catalysts and the relative stability of the two arylmetal intermediates. While (dppp)Pd reacts preferentially with aryl triflates to afford a persistent intermediate, (bpy)Ni reacts preferentially with aryl bromides to form a transient, reactive intermediate. Although each catalyst forms less than 5% cross product in isolation, together they are able to achieve up to 94% yield. Our results reveal a new, general method for the synthesis of biaryls, heteroaryls, and dienes, as well as a new mechanism for selective transmetalation between two catalysts. We anticipate that this reaction will simplify the synthesis of

  11. Catalytic ozonation of 2,4-dichlorophenoxyacetic acid using alumina in the presence of a radical scavenger.

    PubMed

    Guzman-Perez, Carlos A; Soltan, Jafar; Robertson, Jared

    2012-01-01

    Using a laboratory-scale mixed reactor, the performance of alumina in degrading 2,4-Dichlorophenoxyacetic acid with ozone in the presence of tert-butyl alcohol radical scavenger was studied. The operating variables investigated were the dose of alumina catalyst and solution pH. Results showed that using ozone and alumina leads to a significant increase in 2,4-D removal in comparison to non-catalytic ozonation and adsorption processes. The observed reaction rate constants (k(obs)) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the k(obs) value increased from 19.3 to 26 M(-1) s(-1) and 67 M(-1) s(-1) when varying the alumina dose from 1 to 2 and 4 g L(-1), respectively. As pH was increased, higher reaction rates were observed for both non-catalytic ozonation and catalytic ozonation processes. Thus, at pH 3 and using a catalyst dose of 8 g L(-1), the k(obs) values for non-catalytic ozonation and catalytic ozonation processes were 3.4 and 58.9 M(-1) s(-1), respectively, whereas at pH 5 reaction rate constants of 6.5 and 128.5 M(-1) s(-1) were observed, respectively. Analysis of total organic carbon suggested that catalytic ozonation with alumina achieved a considerable level of mineralization of 2,4-D. Adsorption of 2,4-D on alumina was found to play an important role in the catalytic ozonation process.

  12. In situ generation of o-iodoxybenzoic acid (IBX) and the catalytic use of it in oxidation reactions in the presence of Oxone as a co-oxidant.

    PubMed

    Thottumkara, Arun P; Bowsher, Michael S; Vinod, Thottumkara K

    2005-07-01

    [structure: see text] Catalytic use of o-iodoxybenzoic acid (IBX) in the presence of Oxone as a co-oxidant is demonstrated for the oxidation of primary and secondary alcohols in user- and eco-friendly solvent mixtures. Also demonstrated is the in situ (re)oxidation of 2-iodosobenzoic acid (IBA) and even commercially available 2-iodobenzoic acid (2IBAcid) by Oxone to IBX allowing one to use these less hazardous reagents, in place of potentially explosive IBX, as catalytic oxidants.

  13. Efficient Diethylzinc/Gallic Acid and Diethylzinc/Gallic Acid Ester Catalytic Systems for the Ring-Opening Polymerization of rac-Lactide.

    PubMed

    Żółtowska, Karolina; Piotrowska, Urszula; Oledzka, Ewa; Sobczak, Marcin

    2015-12-08

    Polylactide (PLA) represents one of the most promising biomedical polymers due to its biodegradability, bioresorbability and good biocompatibility. This work highlights the synthesis and characterization of PLAs using novel diethylzinc/gallic acid (ZnEt₂/GAc) and diethylzinc/propyl gallate (ZnEt₂/PGAc) catalytic systems that are safe for human body. The results of the ring-opening polymerization (ROP) of rac-lactide (rac-LA) in the presence of zinc-based catalytic systems have shown that, depending on the reaction conditions, "predominantly isotactic", disyndiotactic or atactic PLA can be obtained. Therefore, the controlled and stereoselective ROP of rac-LA is discussed in detail in this paper.

  14. Generation of a chickenized catalytic anti-nucleic acid antibody by complementarity-determining region grafting.

    PubMed

    Roh, Jooho; Byun, Sung June; Seo, Youngsil; KIm, Minjae; Lee, Jae-Ho; Kim, Songmi; Lee, Yuno; Lee, Keun Woo; Kim, Jin-Kyoo; Kwon, Myung-Hee

    2015-02-01

    In contrast to a number of studies on the humanization of non-human antibodies, the reshaping of a non-human antibody into a chicken antibody has never been attempted. Therefore, nothing is known about the animal species-dependent compatibility of the framework regions (FRs) that sustain the appropriate conformation of the complementarity-determining regions (CDRs). In this study, we attempted the reshaping of the variable domains of the mouse catalytic anti-nucleic acid antibody 3D8 (m3D8) into the FRs of a chicken antibody (“chickenization”) by CDR grafting, which is a common method for the humanization of antibodies. CDRs of the acceptor chicken antibody that showed a high homology to the FRs of m3D8 were replaced with those of m3D8, resulting in the chickenized antibody (ck3D8). ck3D8 retained the biochemical properties (DNA binding, DNA hydrolysis, and cellular internalizing activities) and three-dimensional structure of m3D8 and showed reduced immunogenicity in chickens. Our study demonstrates that CDR grafting can be applied to the chickenization of a mouse antibody, probably due to the interspecies compatibility of the FRs.

  15. Enhancement of biomass conversion in catalytic fast pyrolysis by microwave-assisted formic acid pretreatment.

    PubMed

    Feng, Yu; Li, Guangyu; Li, Xiangyu; Zhu, Ning; Xiao, Bo; Li, Jian; Wang, Yujue

    2016-08-01

    This study investigated microwave-assisted formic acid (MW-FA) pretreatment as a possible way to improve aromatic production from catalytic fast pyrolysis (CFP) of lignocellulosic biomass. Results showed that short duration of MW-FA pretreatment (5-10min) could effectively disrupt the recalcitrant structure of beech wood and selectively remove its hemicellulose and lignin components. This increased the accessibility of cellulose component of biomass to subsequent thermal conversion in CFP. Consequently, the MW-FA pretreated beech wood produced 14.0-28.3% higher yields (26.4-29.8C%) for valuable aromatic products in CFP than the untreated control (23.2C%). In addition, the yields of undesired solid residue (char/coke) decreased from 33.1C% for the untreated control to 28.6-29.8C% for the MW-FA pretreated samples. These results demonstrate that MW-FA pretreatment can provide an effective way to improve the product distribution from CFP of lignocellulose. PMID:27176672

  16. Unprecedented Catalytic Wet Oxidation of Glucose to Succinic Acid Induced by the Addition of n-Butylamine to a Ru(III) Catalyst.

    PubMed

    Podolean, Iunia; Rizescu, Cristina; Bala, Camelia; Rotariu, Lucian; Parvulescu, Vasile I; Coman, Simona M; Garcia, Hermenegildo

    2016-09-01

    A new pathway for the catalytic wet oxidation (CWO) of glucose is described. Employing a cationic Ru@MNP catalyst, succinic acid is obtained in unprecedently high yield (87.5 %) for a >99.9 % conversion of glucose, most probably through a free radical mechanism combined with catalytic didehydroxylation of vicinal diols and hydrogenation of the resulted unsaturated intermediate. PMID:27511900

  17. Catalytic conversion of furfural into a 2,5-furandicarboxylic acid-based polyester with total carbon utilization.

    PubMed

    Pan, Tao; Deng, Jin; Xu, Qing; Zuo, Yong; Guo, Qing-Xiang; Fu, Yao

    2013-01-01

    One divided into two combined into one: The catalytic conversion of furfural into a 2,5-furandicarboxylic acid-based polyester, linked by the disproportionation of furoate to furan and 2,5-furandicarboxylate, is reported. In this manner, all carbons are utilized, demonstrating the success of combining a platform molecule from C(5) sugars (furfural) to one from C(6) sugars (2,5-FDCA). PMID:23239596

  18. Efficient Catalytic Ozonation over Reduced Graphene Oxide for p-Hydroxylbenzoic Acid (PHBA) Destruction: Active Site and Mechanism.

    PubMed

    Wang, Yuxian; Xie, Yongbing; Sun, Hongqi; Xiao, Jiadong; Cao, Hongbin; Wang, Shaobin

    2016-04-20

    Nanocarbons have been demonstrated as promising environmentally benign catalysts for advanced oxidation processes (AOPs) upgrading metal-based materials. In this study, reduced graphene oxide (rGO) with a low level of structural defects was synthesized via a scalable method for catalytic ozonation of p-hydroxylbenzoic acid (PHBA). Metal-free rGO materials were found to exhibit a superior activity in activating ozone for catalytic oxidation of organic phenolics. The electron-rich carbonyl groups were identified as the active sites for the catalytic reaction. Electron spin resonance (ESR) and radical competition tests revealed that superoxide radical ((•)O2(-)) and singlet oxygen ((1)O2) were the reactive oxygen species (ROS) for PHBA degradation. The intermediates and the degradation pathways were illustrated from mass spectroscopy. It was interesting to observe that addition of NaCl could enhance both ozonation and catalytic ozonation efficiencies and make ·O2(-) as the dominant ROS. Stability of the catalysts was also evaluated by the successive tests. Loss of specific surface area and changes in the surface chemistry were suggested to be responsible for catalyst deactivation. PMID:27007603

  19. Hydrolysis of biomass using a reusable solid carbon acid catalyst and fermentation of the catalytic hydrolysate to ethanol.

    PubMed

    Goswami, Mandavi; Meena, S; Navatha, S; Prasanna Rani, K N; Pandey, Ashok; Sukumaran, Rajeev Kumar; Prasad, R B N; Prabhavathi Devi, B L A

    2015-01-01

    Solid acid catalysts can hydrolyze cellulose with lower reaction times and are easy to recover and reuse. A glycerol based carbon acid catalyst developed at CSIR-IICT performed well in acid catalysis reactions and hence this study was undertaken to evaluate the catalyst for hydrolysis of biomass (alkali pretreated or native rice straw). The catalyst could release 262 mg/g total reducing sugars (TRS) in 4h at 140 °C from alkali pretreated rice straw, and more importantly it released 147 mg/g TRS from native biomass. Reusability of the catalyst was also demonstrated. Catalytic hydrolysate was used as sugar source for fermentation to produce ethanol. Results indicate the solid acid catalyst as an interesting option for biomass hydrolysis.

  20. Catalytic actions of alkaline salts in reactions between 1,2,3,4-butanetetracarboxylic acid and cellulose: II. Esterification.

    PubMed

    Ji, Bolin; Tang, Peixin; Yan, Kelu; Sun, Gang

    2015-11-01

    1,2,3,4-Butanetetracarboxylic acid (BTCA) reacts with cellulose in two steps with catalysis of alkaline salts such as sodium hypophosphite: anhydride formation and esterification of anhydride with cellulose. The alkali metal ions were found effective in catalyzing formation of BTCA anhydride in a previous report. In this work, catalytic functions of the alkaline salts in the esterification reaction between BTCA anhydride and cellulose were investigated. Results revealed that acid anions play an important role in the esterification reaction by assisting removal of protons on intermediates and completion of the esterification between cellulose and BTCA. Besides, alkaline salts with lower pKa1 values of the corresponding acids are more effective ones for the reaction since addition of these salts could lead to lower pH values and higher acid anion concentrations in finishing baths. The mechanism explains the results of FTIR and wrinkle recovery angles of the fabrics cured under different temperatures and times.

  1. Effects of novel supports on the physical and catalytic properties of tungstophosphoric acid for alcohol dehydration reactions

    SciTech Connect

    Herrera, Jose E.; Kwak, Ja Hun; Hu, Jian Zhi; Wang, Yong; Peden, Charles HF

    2008-08-17

    The catalytic behavior of tungstophosphoric acid supported on modified mesoporous silica materials for the dehydration of 2-butanol and methanol was studied. Specifically, the supports evaluated here consisted of unmodified MCM-41 and SBA-15 mesoporous silicas, and these materials coated with sub-monolayer quantities of alumina, titania, and zirconia. UV-Vis DRS and 31P-NMR spectroscopy showed that the tungstophosphoric acid species retained their chemical identity in the synthesized supported form, although the spectra were influenced by the specific support material used. In addition, their acidic properties were evaluated using temperature programmed oxidation of isopropyl amine. The differences in reaction rates between the samples reflect both the diversity in the amount of Brønsted acidic sites available for catalysis and dissimilarities in coking resistance. These two characteristics depend, in turn, on the type of support modifier used to prepare the catalyst.

  2. Stable and catalytically active iron porphyrin-based porous organic polymer: Activity as both a redox and Lewis acid catalyst

    PubMed Central

    Oveisi, Ali R.; Zhang, Kainan; Khorramabadi-zad, Ahmad; Farha, Omar K.; Hupp, Joseph T.

    2015-01-01

    A new porphyrin-based porous organic polymer (POP) with BET surface area ranging from 780 to 880 m2/g was synthesized in free-base form via the reaction of meso-tetrakis(pentafluorophenyl) porphyrin and a rigid trigonal building block, hexahydroxytriphenylene. The material was then metallated with Fe(III) imparting activity for Lewis acid catalysis (regioselective methanolysis ring-opening of styrene oxide), oxidative cyclization catalysis (conversion of bis(2-hydroxy-1-naphthyl)methanes to the corresponding spirodienone), and a tandem catalytic processes: an in situ oxidation-cyclic aminal formation-oxidation sequence, which selectively converts benzyl alcohol to 2-phenyl-quinazolin-4(3H)-one. Notably, the catalyst is readily recoverable and reusable, with little loss in catalytic activity. PMID:26177563

  3. Phosphotungstic acid encapsulated in the mesocages of amine-functionalized metal-organic frameworks for catalytic oxidative desulfurization.

    PubMed

    Wang, Xu-Sheng; Huang, Yuan-Biao; Lin, Zu-Jin; Cao, Rong

    2014-08-21

    Highly dispersed Keggin-type phosphotungstic acid (H3PW12O40, PTA) encapsulated in the mesocages of amine-functionalized metal-organic frameworks MIL-101(Cr)-NH2 has been prepared by an anion-exchange method. PTA anions (PW12O40(3-)) are stabilized in the mesocages via the electrostatic interaction with amino groups of the MIL-101(Cr)-NH2. The obtained catalyst (denoted PTA@MIL-101(Cr)-NH2) exhibits high catalytic activity in the extractive and catalytic oxidative desulfurization (ECODS) system under mild conditions. Moreover, it can be easily recovered and recycled several times without leaching and loss of activity. PMID:24967570

  4. Optimizing anti-coking abilities of zeolites by ethylene diamine tetraacetie acid modification on catalytic fast pyrolysis of corn stalk

    NASA Astrophysics Data System (ADS)

    Zhang, Bo; Zhong, Zhaoping; Song, Zuwei; Ding, Kuan; Chen, Paul; Ruan, Roger

    2015-12-01

    In order to minimize coke yield during biomass catalytic fast pyrolysis (CFP) process, ethylene diamine tetraacetie acid (EDTA) chemical modification method is carried out to selectively remove the external framework aluminum of HZSM-5 catalyst. X-ray diffraction (XRD), nitrogen (N2)-adsorption and ammonia-temperature programmed desorption (NH3-TPD) techniques are employed to investigate the porosity and acidity characteristics of original and modified HZSM-5 samples. Py-GC/MS and thermo-gravimetric analyzer (TGA) experiments are further conducted to explore the catalytic effect of modified HZSM-5 samples on biomass CFP and to verify the positive effect on coke reduction. Results show that EDTA treatment does not damage the crystal structure of HZSM-5 zeolites, but leads to a slight increase of pore volume and pore size. Meanwhile, the elimination of the strong acid peak indicates the dealumination of outer surface of HZSM-5 zeolites. Treatment time of 2 h (labeled EDTA-2H) is optimal for acid removal and hydrocarbon formation. Among all modified catalysts, EDTA-2H performs the best for deacidification and can obviously increase the yields of positive chemical compositions in pyrolysis products. Besides, EDTA modification can improve the anti-coking properties of HZSM-5 zeolites, and EDTA-2H gives rise to the lowest coke yield.

  5. Increased Biomass Yield of Lactococcus lactis by Reduced Overconsumption of Amino Acids and Increased Catalytic Activities of Enzymes

    PubMed Central

    Adamberg, Kaarel; Seiman, Andrus; Vilu, Raivo

    2012-01-01

    Steady state cultivation and multidimensional data analysis (metabolic fluxes, absolute proteome, and transcriptome) are used to identify parameters that control the increase in biomass yield of Lactococcus lactis from 0.10 to 0.12 C-mol C-mol−1 with an increase in specific growth rate by 5 times from 0.1 to 0.5 h−1. Reorganization of amino acid consumption was expressed by the inactivation of the arginine deiminase pathway at a specific growth rate of 0.35 h−1 followed by reduced over-consumption of pyruvate directed amino acids (asparagine, serine, threonine, alanine and cysteine) until almost all consumed amino acids were used only for protein synthesis at maximal specific growth rate. This balanced growth was characterized by a high glycolytic flux carrying up to 87% of the carbon flow and only amino acids that relate to nucleotide synthesis (glutamine, serine and asparagine) were consumed in higher amounts than required for cellular protein synthesis. Changes in the proteome were minor (mainly increase in the translation apparatus). Instead, the apparent catalytic activities of enzymes and ribosomes increased by 3.5 times (0.1 vs 0.5 h−1). The apparent catalytic activities of glycolytic enzymes and ribosomal proteins were seen to follow this regulation pattern while those of enzymes involved in nucleotide metabolism increased more than the specific growth rate (over 5.5 times). Nucleotide synthesis formed the most abundant biomonomer synthetic pathway in the cells with an expenditure of 6% from the total ATP required for biosynthesis. Due to the increase in apparent catalytic activity, ribosome translation was more efficient at higher growth rates as evidenced by a decrease of protein to mRNA ratios. All these effects resulted in a 30% decrease of calculated ATP spilling (0.1 vs 0.5 h−1). Our results show that bioprocesses can be made more efficient (using a balanced metabolism) by varying the growth conditions. PMID:23133574

  6. β-Amino acid catalyzed asymmetric Michael additions: design of organocatalysts with catalytic acid/base dyad inspired by serine proteases.

    PubMed

    Yang, Hui; Wong, Ming Wah

    2011-09-16

    A new type of chiral β-amino acid catalyst has been computationally designed, mimicking the enzyme catalysis of serine proteases. Our catalyst approach is based on the bioinspired catalytic acid/base dyad, namely, a carboxyl and imidazole pair. DFT calculations predict that this designed organocatalyst catalyzes Michael additions of aldehydes to nitroalkenes with excellent enantioselectivities and remarkably high anti diastereoselectivities. The unusual stacked geometry of the enamine intermediate, hydrogen bonding network, and the adoption of an exo transition state are the keys to understand the stereoselectivity.

  7. Catalytic asymmetric direct Mannich reaction: a powerful tool for the synthesis of alpha,beta-diamino acids.

    PubMed

    Arrayás, Ramón Gómez; Carretero, Juan C

    2009-07-01

    Optically active alpha,beta-diamino acids are very attractive targets in organic synthesis because of their wide-ranging biological significance and high versatility as synthetic building blocks. Efficient synthesis of such non-proteinogenic amino acid derivatives must face the challenge of generating two contiguous stereocenters with complete diastereo- and enantiocontrol in flexible, acyclic molecules. The catalytic asymmetric direct Mannich reaction has provided elegant and efficient solutions for the stereocontrolled assembly of both syn- and anti-alpha,beta-diamino acid derivatives, including those with a alpha-tetrasubstituted carbon stereocenter, with the aid of either organometallic or purely organic chiral catalysts (or the combination of both). This tutorial review highlights progress in this area, which has recently been boosted through two complementary strategies: the direct Mannich reaction of glycine ester Schiff bases with imines and the direct aza-Henry reaction between nitro compounds and imines. PMID:19551174

  8. The substrate specificity and the catalytic mechanism of N-carbamyl- D-amino acid amidohydrolase: A theoretical investigation

    NASA Astrophysics Data System (ADS)

    Han, Wei-Wei; Zhan, Dong Ling; Luo, Quan; Zhou, Yi-Han; Yao, Yuan; Li, Ze-Sheng; Feng, Yan

    2009-04-01

    N-carbamyl- D-amino acid amidohydrolasecatalyzes the hydrolysis of N-carbamyl- D-amino acids to D-amino acids, ammonia and the carbon dioxide. The docking studies validate that D-NCAase possesses of preference for D-enantiomers, predict that Gly194 and Arg174 may take part in the catalytic mechanism, and Glu136 is essential to maintain the stable conformation for catalysis. The initial step of the acylation reaction catalyzed by D-NCAase has been studied by density functional calculations. It was furthermore demonstrated that Lys126, His143, and Asn196 decrease the reaction barrier, while Asn172 raise the barrier. The structural and mechanistic insights obtained from computational study should be valuable for the mechanisms of cysteine proteases.

  9. Experimental and Mechanistic Understanding of Aldehyde Hydrogenation Using Au25 Nanoclusters with Lewis Acids: Unique Sites for Catalytic Reactions.

    PubMed

    Li, Gao; Abroshan, Hadi; Chen, Yuxiang; Jin, Rongchao; Kim, Hyung J

    2015-11-18

    The catalytic activity of Au25(SR)18 nanoclusters (R = C2H4Ph) for the aldehyde hydrogenation reaction in the presence of a base, e.g., ammonia or pyridine, and transition-metal ions M(z+), such as Cu(+), Cu(2+), Ni(2+) and Co(2+), as a Lewis acid is studied. The addition of a Lewis acid is found to significantly promote the catalytic activity of Au25(SR)18/CeO2 in the hydrogenation of benzaldehyde and a number of its derivatives. Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometry in conjunction with UV-vis spectroscopy confirm the generation of new species, Au25-n(SR)18-n (n = 1-4), in the presence of a Lewis acid. The pathways for the speciation of Au24(SR)17 from its parent Au25(SR)18 nanocluster as well as its structure are investigated via the density functional theory (DFT) method. The adsorption of M(z+) onto a thiolate ligand "-SR-" of Au25(SR)18, followed by a stepwise detachment of "-SR-" and a gold atom bonded to "-SR-" (thus an "Au-SR" unit) is found to be the most likely mechanism for the Au24(SR)17 generation. This in turn exposes the Au13-core of Au24(SR)17 to reactants, providing an active site for the catalytic hydrogenation. DFT calculations indicate that M(z+) is also capable of adsorbing onto the Au13-core surface, producing a possible active metal site of a different kind to catalyze the aldehyde hydrogenation reaction. This study suggests, for the first time, that species with an open metal site like adducts [nanoparticle-M]((z-1)+) or fragments Au25-n(SR)18-n function as the catalysts rather than the intact Au25(SR)18.

  10. Catalytic Fast Pyrolysis of Lignin over High-Surface-Area Mesoporous Aluminosilicates: Effect of Porosity and Acidity.

    PubMed

    Custodis, Victoria B F; Karakoulia, Stamatia A; Triantafyllidis, Kostas S; van Bokhoven, Jeroen A

    2016-05-23

    Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst. PMID:27079742

  11. Catalytic Fast Pyrolysis of Lignin over High-Surface-Area Mesoporous Aluminosilicates: Effect of Porosity and Acidity.

    PubMed

    Custodis, Victoria B F; Karakoulia, Stamatia A; Triantafyllidis, Kostas S; van Bokhoven, Jeroen A

    2016-05-23

    Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst.

  12. Understanding the enhanced catalytic activity of Cu1@Pd3(111) in formic acid dissociation, a theoretical perspective

    NASA Astrophysics Data System (ADS)

    He, Feng; Li, Kai; Xie, Guangyou; Wang, Ying; Jiao, Menggai; Tang, Hao; Wu, Zhijian

    2016-06-01

    The bimetallic Cu1@Pd3(111) catalyst has been synthesized recently and exhibits better catalytic activity and durability compared with pure Pd(111) as anode catalyst in direct formic acid fuel cells (DFAFCs). In this work, we studied the reaction mechanism of formic acid dissociation on both Pd(111) and Cu1@Pd3(111) by using the density functional method. Our calculations showed that the surface adsorption of the poisoning species CO on Cu1@Pd3(111) is weakened mainly by the strain effect rather than the Cusbnd Pd ligand effect. The Cu1@Pd3(111) can effectively promote the catalytic activity for formic acid dissociation by decreasing the barrier of CO2 formation from the preferential trans-COOH intermediate and increasing the barrier of CO formation from the reduction of CO2. We found that the H atom accumulation, electron accumulation and low electrode potential could accelerate the catalyst deactivation due to the contamination of the poisoning species CO. Furthermore, under low anode potential, the Cu1@Pd3(111) has better durability than pure Pd(111), which can be attributed to the unfavorable CO formation and the favorable CO desorption.

  13. Facile CO Cleavage by a Multimetallic CsU2 Nitride Complex.

    PubMed

    Falcone, Marta; Kefalidis, Christos E; Scopelliti, Rosario; Maron, Laurent; Mazzanti, Marinella

    2016-09-26

    Uranium nitrides are important materials with potential for application as fuels for nuclear power generation, and as highly active catalysts. Molecular nitride compounds could provide important insight into the nature of the uranium-nitride bond, but currently little is known about their reactivity. In this study, we found that a complex containing a nitride bridging two uranium centers and a cesium cation readily cleaved the C≡O bond (one of the strongest bonds in nature) under ambient conditions. The product formed has a [CsU2 (μ-CN)(μ-O)] core, thus indicating that the three cations cooperate to cleave CO. Moreover, the addition of MeOTf to the nitride complex led to an exceptional valence disproportionation of the CsU(IV) -N-U(IV) core to yield CsU(III) (OTf) and [MeN=U(V) ] fragments. The important role of multimetallic cooperativity in both reactions is illustrated by the computed reaction mechanisms. PMID:27596570

  14. Multimetallic Cooperativity in Activation of Dinitrogen at Iron-Potassium Sites

    PubMed Central

    Chiang, Karen P.; Bellows, Sarina M.; Brennessel, William W.; Holland, Patrick L.

    2013-01-01

    The reaction of soluble iron-oxygen-potassium assemblies with N2 gives insight into the mechanisms of multimetallic N2 coordination. We report a series of very electron-rich three-coordinate, β-diketiminate-supported iron(I) phenoxide complexes, which are metastable but have been characterized under Ar by both crystallography and solution methods. Both monomeric and dimeric Fe-OPh-K compounds have been characterized, and their iron environments are very similar in the solid and solution states. In the dimer, potassium ions hold together the phenoxide oxygens and aryl rings of the two halves, to give a flexible diiron core. The reactions of the monomeric and dimeric iron(I) compounds with N2 are surprisingly different: the mononuclear iron(I) complexes give no reaction with N2, but the dimeric Fe2K2 complex reacts rapidly to give a diiron-N2 product. Computational studies show that the key to the rapid N2 reaction of the dimer is the preorganization of the two iron atoms. Thus, cooperation between Fe (which weakens the N-N bond) and K (which orients the Fe atoms) can be used to create a low-energy pathway for N2 reactions. PMID:24379972

  15. Lewis base activation of Lewis acids: catalytic, enantioselective addition of glycolate-derived silyl ketene acetals to aldehydes.

    PubMed

    Denmark, Scott E; Chung, Won-Jin

    2008-06-20

    A catalytic system involving silicon tetrachloride and a chiral, Lewis basic bisphosphoramide catalyst is effective for the addition of glycolate-derived silyl ketene acetals to aldehydes. It was found that the sense of diastereoselectivity could be modulated by changing the size of the substituents on the silyl ketene acetals. In general, the trimethylsilyl ketene acetals derived from methyl glycolates with a large protecting group on the alpha-oxygen provide enantiomerically enriched alpha,beta-dihydroxy esters with high syn-diastereoselectivity, whereas the tert-butyldimethylsilyl ketene acetals derived from bulky esters of alpha-methoxyacetic acid provide enantiomerically enriched alpha,beta-dihydroxy esters with high anti-diastereoselecitvity.

  16. Screening acidic zeolites for catalytic fast pyrolysis of biomass and its components

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Zeolites have been shown to effectively promote cracking reactions during pyrolysis resulting in highly deoxygenated and hydrocarbon-rich compounds and stable pyrolysis oil product. Py/GC-MS was employed to study the catalytic fast pyrolysis of lignocellulosic biomass samples comprising oak, corn...

  17. Development of nitric oxide catalytic coatings by conjugating 3,3-disulfodipropionic acid and 3,3-diselenodipropionic acid for improving hemocompatibility.

    PubMed

    Yang, Ying; Li, Yalong; Li, Xiangyang; Qi, Pengkai; Tu, Qiufen; Yang, Zhilu; Huang, Nan

    2015-01-01

    Nitric oxide (NO), discovered as an endothelium-derived relaxing factor, has been found to have multiple intracellular effects in vascular diseases including vasorelaxation regulation, endothelial regeneration, inhibition of leukocyte chemotaxis, and platelet activation. In the work described here, the authors have developed a NO-catalytic bioactive coating for improving hemocompatibility. The authors first prepared a dopamine and hexamethylendiamine (PDAM/HD) amine-rich adherent copolymer coating to introduce amine groups onto 316L stainless steel, followed by covalently conjugating 3,3-disulfodipropionic acid (S-S) and 3,3-diselenodipropionic acid (Se-Se), which mimic glutathione peroxidase-like catalytic production of NO. S-S and Se-Se were immobilized on the PDAM/HD surface via carbodiimide coupling chemistry. X-ray photoelectron spectroscopy analysis revealed clear S2p and Se3d signals, confirming the immobilization of S-S and Se-Se on the PDAM/HD surface. The NO release behavior of different samples was investigated. In detail, two species of thionitrites (RSNO), S-nitrosoglutathione (GSNO, endogenous NO donors) and S-nitrosoacetylpenicillamine (SNAP) were chosen as NO donors to investigate the NO catalytic properties of S-S and Se-Se modified PDAM/HD surfaces. Not only Se-Se@PDAM/HD but also S-S@PDAM/HD coatings showed the ability to continuously catalyze RSNO to generate NO in the presence of proper thiol reducing agent. For the Se-Se@PDAM/HD coating, the NO release amount and rate were greater than S-S@PDAM/HD in both GSNO and SNAP conditions. The results showed that organosulfide species possesses NO catalytic ability as well as organoselenium species. The authors demonstrated that both S-S@PDAM/HD and Se-Se@PDAM/HD coatings exhibited outstanding inhibition effect on platelet adhesion, aggregation and activation via the cyclic guanylate monophosphate signal pathway. Thus these results suggested that NO catalytic coatings based on organoselenium and

  18. Reduction of nitrogen oxides with catalytic acid resistant aluminosilicate molecular sieves and ammonia

    DOEpatents

    Pence, Dallas T.; Thomas, Thomas R.

    1980-01-01

    Noxious nitrogen oxides in a waste gas stream such as the stack gas from a fossil-fuel-fired power generation plant or other industrial plant off-gas stream is catalytically reduced to elemental nitrogen and/or innocuous nitrogen oxides employing ammonia as reductant in the presence of a zeolite catalyst in the hydrogen or sodium form having pore openings of about 3 to 10 A.

  19. Mutational analysis of amino acid residues involved in catalytic activity of a family 18 chitinase from tulip bulbs.

    PubMed

    Suzukawa, Keisuke; Yamagami, Takeshi; Ohnuma, Takayuki; Hirakawa, Hideki; Kuhara, Satoru; Aso, Yoichi; Ishiguro, Masatsune

    2003-02-01

    We expressed chitinase-1 (TBC-1) from tulip bulbs (Tulipa bakeri) in E. coli cells and used site-directed mutagenesis to identify amino acid residues essential for catalytic activity. Mutations at Glu-125 and Trp-251 completely abolished enzyme activity, and activity decreased with mutations at Asp-123 and Trp-172 when glycolchitin was the substrate. Activity changed with the mutations of Trp-251 to one of several amino acids with side-chains of little hydrophobicity, suggesting that hydrophobic interaction of Trp-251 is important for the activity. Molecular dynamics (MD) simulation analysis with hevamine as the model compound showed that the distance between Asp-123 and Glu-125 was extended by mutation of Trp-251. Kinetic studies of Trp-251-mutated chitinases confirmed these various phenomena. The results suggested that Glu-125 and Trp-251 are essential for enzyme activity and that Trp-251 had a direct role in ligand binding.

  20. Control of product selectivity using solid acids for the catalytic addition of phenol to hydroxy fatty acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The acid catalyzed reactions of hydroxy fatty acids, such as ricinoleic and lesquerolic, in the presence of phenolics can lead to four products or product groups. These include simple dehydration to dienoic acids, cyclization to epoxides, Friedel-Crafts alkylations of the double bonds, or ether for...

  1. Direct Formation of Oxocarbenium Ions under Weakly Acidic Conditions: Catalytic Enantioselective Oxa-Pictet-Spengler Reactions.

    PubMed

    Zhao, Chenfei; Chen, Shawn B; Seidel, Daniel

    2016-07-27

    Two catalysts, an amine HCl salt and a bisthiourea, work in concert to enable the generation of oxocarbenium ions under mild conditions. The amine catalyst generates an iminium ion of sufficient electrophilicity to enable 1,2-attack by an alcohol. Catalyst turnover is achieved by amine elimination with concomitant formation of an oxocarbenium intermediate. The bisthiourea catalyst accelerates all of the steps of the reaction and controls the stereoselectivity via anion binding/ion pair formation. This new concept was applied to direct catalytic enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes. PMID:27396413

  2. Direct Formation of Oxocarbenium Ions under Weakly Acidic Conditions: Catalytic Enantioselective Oxa-Pictet-Spengler Reactions.

    PubMed

    Zhao, Chenfei; Chen, Shawn B; Seidel, Daniel

    2016-07-27

    Two catalysts, an amine HCl salt and a bisthiourea, work in concert to enable the generation of oxocarbenium ions under mild conditions. The amine catalyst generates an iminium ion of sufficient electrophilicity to enable 1,2-attack by an alcohol. Catalyst turnover is achieved by amine elimination with concomitant formation of an oxocarbenium intermediate. The bisthiourea catalyst accelerates all of the steps of the reaction and controls the stereoselectivity via anion binding/ion pair formation. This new concept was applied to direct catalytic enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes.

  3. A highly catalytic and selective conversion of carboxylic acids to 1-alkenes of one less carbon atom

    SciTech Connect

    Miller, J.A.; Nelson, J.A.; Byrne, M.P. )

    1993-01-01

    An equimolar mixture of a carboxylic acid and acetic anhydride produces a reagent combination that undergoes a highly efficient decarbonylation/dehydration at 250[degrees]C using either Pd- or Rh-based catalyst systems, affording excellent yields of the corresponding 1-alkenes and one less carbon atom. The stoichiometric and catalytic decarbonylation of aliphatic aldehydes and acid chlorides to alkanes and alkenes, respectively, by transition-metal complexes are well-known and synthetically useful transformations. Relatively little, however, has been reported concerning the analogous decarbonylation/dehydration of aliphatic carboxylic acids to olefins, with generally poor results achieved in terms of catalyst efficiency and selectivity toward terminal olefin formation in the product. For example, the decarbonylation/dehydration of stearic acid to heptadecane using a Rh-based catalyst was reported to proceed with a maximum catalyst turnover number (TON; moles of olefin product formed per mole of catalyst used) of ca. 250, with selectivities toward 1-heptadecene formation typically below 50%. Interestingly, results were presented in this work which suggested that the decarbonylation of stearic acid proceeded via intermediate formation of stearic anhydride. Use of a preformed, symmetrical anhydride is not desirable from an economic or synthetic viewpoint, particularly since its decarbonylation should result in the formation of equal amounts of olefin and carboxylic acid coproducts. The authors now report here that the use of a carboxylic acid substrate as an equimolar mixture with acetic anhydride (Ac[sub 2]O) produces a mixed anhydride system which undergoes an extremely facile decarbonylation reaction to provide a general and highly selective route to the corresponding 1-alkenes of one less carbon atom. 19 refs., 1 tab.

  4. Acid Strength and Bifunctional Catalytic Behavior of Alloys Comprised of Noble Metals and Oxophilic Metal Promoters

    SciTech Connect

    Hibbitts, David D.; Tan, Qiaohua; Neurock, Matthew

    2014-06-01

    The promotion of metal catalysts with partially oxidized oxophilic MOx species, such as ReOx-promoted Rh, has been demonstrated to produce Brønsted acid sites that can promote hydrogenolysis of oxygenate intermediates such as those found in biomass-derived species. A wide variety of alloy compositions and structures are examined in this work to investigate strongly acidic promoters by using DFT-calculated deprotonation energies (DPE) as a measure of acid strength. Sites with the highest acid strength had DPE less than 1100 kJ mol-1, similar to DPE values of heteropolyacids or acid-containing zeolites, and were found on alloys composed of an oxophilic metal (such as Re or W) with a noble metal (such as Rh or Pt). NH3 adsorbs more strongly to sites with increasing acid strength and the activation barriers for acid-catalyzed ring opening of a furan ring decrease with increasing acid strength, which was also shown to be stronger for OH acid sites bound to multiple oxophilic metal atoms in a three-fold configuration rather than OH sites adsorbed in an atop configuration on one oxophilic metal, indicating that small MOx clusters may yield sites with the highest acid strength.

  5. Water molecule-driven reversible single-crystal to single-crystal transformation of a multi-metallic coordination polymer with controllable metal ion movement.

    PubMed

    Niu, Zheng; Ma, Jian-Gong; Shi, Wei; Cheng, Peng

    2014-02-21

    A single-crystal to single-crystal (SC-SC) transformation process driven by water molecules has been exhibited by a multi-metallic coordination polymer. The in situ heating single crystal X-ray diffraction technique was applied to study the control of metal ion movement in the reversible SC-SC transformation process.

  6. Catalytic effect of water, formic acid, or sulfuric acid on the reaction of formaldehyde with OH radicals.

    PubMed

    Zhang, Weichao; Du, Benni; Qin, Zhenglong

    2014-07-01

    In this paper, for the hydrogen abstraction reaction of HCHO by OH radicals assisted by water, formic acid, or sulfur acid, the possible reaction mechanisms and kinetics have been investigated theoretically using quantum chemistry methods and transition-state theory. The potential energy surfaces calculated at the CCSD(T)/6-311++G(df,pd)//MP2(full)/6-311++G(df,pd) levels of theory reveal that, due to the formation of strong hydrogen bond(s), the relative energies of the transition states involving catalyst are significantly reduced compared to that reaction without catalyst. However, the kinetics calculations show that the rate constants are smaller by about 3, 9, or 10 orders of magnitude for water, formic acid, or sulfur acid assisted reactions than that uncatalyzed reaction, respectively. Consequently, none of the water, formic acid, or sulfur acid can accelerate the title reaction in the atmosphere.

  7. Catalytic performance of hybrid nanocatalyst for levulinic acid production from glucose

    NASA Astrophysics Data System (ADS)

    Ya'aini, Nazlina; Amin, Nor Aishah Saidina

    2012-11-01

    Levulinic acid is one of the potential and versatile biomass-derived chemicals. Product analysis via HPLC revealed that the heterogeneous dehydration of glucose over hybrid nanocatalyst exhibited better performance compared to single catalyst. Hybrid nanocatalyst containing H-Y zeolite and CrCl3 could substitute homogenous acid catalyst for attaining high levulinic acid yield. Different CrC3 and H-Y zeolite weight ratios of 1:1, 1:2 and 2:1 were prepared according to the wetness impregnation method. The hybrid catalyst with a 1:1 weight ratio performed better compared to others with the highest levulinic acid yield reported (93.5%) at 140 °C, 180 min reaction time, 0.1 g catalyst loading and 0.1 g glucose feed. Characterization results revealed that properties such as surface area, mesoporosity and acidic strength of the catalyst have significant effects on glucose dehydration for levulinic acid production.

  8. High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone

    NASA Astrophysics Data System (ADS)

    Luo, Wenhao; Sankar, Meenakshisundaram; Beale, Andrew M.; He, Qian; Kiely, Christopher J.; Bruijnincx, Pieter C. A.; Weckhuysen, Bert M.

    2015-03-01

    The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method. Gold-palladium/titanium dioxide shows a marked,~27-fold increase in activity (that is, turnover frequency of 0.1 s-1) compared with its monometallic counterparts. Although ruthenium-palladium/titanium dioxide is not only exceptionally active (that is, turnover frequency of 0.6 s-1), it shows excellent, sustained selectivity to γ-valerolactone (99%). The dilution and isolation of ruthenium by palladium is thought to be responsible for this superior catalytic performance. Alloying, furthermore, greatly improves the stability of both supported nano-alloy catalysts.

  9. The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium-Based Catalysts.

    PubMed

    Marberger, Adrian; Ferri, Davide; Elsener, Martin; Kröcher, Oliver

    2016-09-19

    The long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH3 ) on vanadium-based catalysts rely on the involvement of Brønsted or Lewis acid sites. This issue has been clearly elucidated using a combination of transient perturbations of the catalyst environment with operando time-resolved spectroscopy to obtain unique molecular level insights. Nitric oxide reacts predominantly with NH3 coordinated to Lewis sites on vanadia on tungsta-titania (V2 O5 -WO3 -TiO2 ), while Brønsted sites are not involved in the catalytic cycle. The Lewis site is a mono-oxo vanadyl group that reduces only in the presence of both nitric oxide and NH3 . We were also able to verify the formation of the nitrosamide (NH2 NO) intermediate, which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach, demonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance.

  10. The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium-Based Catalysts.

    PubMed

    Marberger, Adrian; Ferri, Davide; Elsener, Martin; Kröcher, Oliver

    2016-09-19

    The long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH3 ) on vanadium-based catalysts rely on the involvement of Brønsted or Lewis acid sites. This issue has been clearly elucidated using a combination of transient perturbations of the catalyst environment with operando time-resolved spectroscopy to obtain unique molecular level insights. Nitric oxide reacts predominantly with NH3 coordinated to Lewis sites on vanadia on tungsta-titania (V2 O5 -WO3 -TiO2 ), while Brønsted sites are not involved in the catalytic cycle. The Lewis site is a mono-oxo vanadyl group that reduces only in the presence of both nitric oxide and NH3 . We were also able to verify the formation of the nitrosamide (NH2 NO) intermediate, which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach, demonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance. PMID:27553251

  11. High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone

    PubMed Central

    Luo, Wenhao; Sankar, Meenakshisundaram; Beale, Andrew M.; He, Qian; Kiely, Christopher J.; Bruijnincx, Pieter C. A.; Weckhuysen, Bert M.

    2015-01-01

    The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method. Gold-palladium/titanium dioxide shows a marked,~27-fold increase in activity (that is, turnover frequency of 0.1 s−1) compared with its monometallic counterparts. Although ruthenium-palladium/titanium dioxide is not only exceptionally active (that is, turnover frequency of 0.6 s−1), it shows excellent, sustained selectivity to γ-valerolactone (99%). The dilution and isolation of ruthenium by palladium is thought to be responsible for this superior catalytic performance. Alloying, furthermore, greatly improves the stability of both supported nano-alloy catalysts. PMID:25779385

  12. Characterization of AlFe-pillared Unye bentonite: A study of the surface acidity and catalytic property

    NASA Astrophysics Data System (ADS)

    Caglar, Bulent; Cubuk, Osman; Demir, Ersin; Coldur, Fatih; Catir, Mustafa; Topcu, Cihan; Tabak, Ahmet

    2015-06-01

    Aluminium-iron-pillared bentonite has been prepared by incorporation of the iron mixed aluminium-polyoxocation into bentonite layers and characterized by the powder X-ray diffraction, Fourier transform infrared, thermal analysis and surface area measurement techniques. The characteristic d001 basal spacing of raw bentonite increased with the pillaring process and reached to 18.05 Å. The siloxane layers of bentonite were perturbed and the positions of Si-O stretching vibrations were altered by pillaring process. However, these pillars in the interlayer gallery spacing enhanced the thermal stability of bentonite. The new micropores were formed by the pillaring process and the specific surface area of raw bentonite increased by ca. 2-fold for aluminium-iron-pillared bentonite. FTIR spectra and thermal analysis curves of pyridine adsorbed samples clearly show that the surface Lewis acidity of aluminium-iron-pillared bentonite is greater than that of raw bentonite. Raw and aluminium-iron-pillared bentonites have been utilized as solid catalysts for benzoylation of benzene with benzoyl chloride. The aluminium-iron-pillared bentonite catalyst showed promising catalytic activity whereas raw bentonite showed no catalytic activity in benzoylation of benzene with benzoyl chloride.

  13. Catalytic Conversion of Biomass for the Production of Hydrogen; Decomposition of Formic Acid

    NASA Astrophysics Data System (ADS)

    Azadi Manzour, Faraz

    Highly active bimetallic catalysts were synthesized and used for the decomposition of formic acid for the production of hydrogen. Ruthenium alloys were prepared and resulted in a maximum formic acid conversion of 68% (after one hour at 180 °C) and a turnover frequency of 0.7/s (at 5 wt% formic acid). The most promising catalysts were characterized by the means of X-ray diffraction and scanning electron microscopy. Kinetic studies were also carried out over these catalysts for the determination of reaction rate and turnover frequency. Promotion of Ru/C with tin, barium and cesium increased the formic acid conversion by 55%, 18% and 11% respectively.

  14. The catalytic role of aspartic acid-92 in a human dual-specific protein-tyrosine-phosphatase.

    PubMed

    Denu, J M; Zhou, G; Guo, Y; Dixon, J E

    1995-03-14

    The mechanism of catalysis for the human dual-specific (vaccinia H1-related) protein-tyrosine-phosphatase was investigated. The pH dependence of the kcat value is bell-shaped when p-nitrophenyl phosphate was employed as a model substrate. The kcat/Km pH profile rises with a slope of 2 and decreases with a slope of -1, indicating that two groups must be unprotonated and one group must be protonated for activity. An amino acid residue with an apparent pKa value of 5.5 +/- 0.2 must be unprotonated and a residue with a pKa value of 5.7 must be unprotonated for activity. The pKa value of the catalytic cysteine-124 (C124) was 5.6 +/- 0.1. The aspartic acid-92-asparagine (D92N) mutant enzyme was 100-fold less active than the native enzyme and exhibited the loss of the basic limb in the pH profiles, suggesting that in the native enzyme D92 must be protonated for activity. The D92 residue is conserved throughout the entire family of dual-specific phosphatases. Mutants glutamic acid-6-glutamine, glutamic acid-32-glutamine, aspartic acid-14-asparagine, and aspartic acid-110-asparagine had less than a 2-fold effect on the kinetic parameters when compared to native enzyme. Based upon the lack of a "burst" in rapid reaction kinetics, formation of the intermediate is rate-limiting with both native and D92N mutant enzymes. In agreement with rate-limiting formation of the intermediate, the pKa value of 5.5 for the group which must be unprotonated for activity was assigned to C124.(ABSTRACT TRUNCATED AT 250 WORDS)

  15. Catalytic Asymmetric Synthesis of anti-α,β-Diamino Acid Derivatives.

    PubMed

    Izumi, Sanae; Kobayashi, Yusuke; Takemoto, Yoshiji

    2016-02-19

    A novel approach to chiral anti-α,β-diamino acid derivatives through tandem orthogonal organocatalysis has been developed. Chiral phosphoric acid catalysts control the chemo-, regio-, and stereoselective addition of hydroxylamines to alkylideneoxazolones, while a phosphine catalyst promotes the isomerization of Z- alkylideneoxazolones to the more reactive E- alkylideneoxazolones.

  16. Analysis and properties of the decarboxylation products of oleic acid by catalytic triruthenium dodecacarbonyl

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recently, ruthenium-catalyzed isomerization-decarboxylation of fatty acids to give alkene mixtures was reported. When the substrate was oleic acid, the reaction yielded a mixture consisting of heptadecene isomers. In this work, we report the compositional analysis of the mixture obtained by triruthe...

  17. Heterogeneous catalytic esterification of omega-sulfhydryl fatty acids: Avoidance of thioethers, thioesters, and disulfides

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Two mesoporous silicas functionalized with propylsulfonic (SBA-15-PSA) and arenesulfonic (SBA-15-ASA) acid groups, and a highly acidic, functionalized styrene divinylbenzene copolymer ion exchange resin (Amberlyst-15) were examined for their ability to catalyze the ethanolic esterification of the N-...

  18. A Ta/W mixed addenda heteropolyacid with excellent acid catalytic activity and proton-conducting property

    NASA Astrophysics Data System (ADS)

    Li, Shujun; Peng, Qingpo; Chen, Xuenian; Wang, Ruoya; Zhai, Jianxin; Hu, Weihua; Ma, Fengji; Zhang, Jie; Liu, Shuxia

    2016-11-01

    A new HPAs H20[P8W60Ta12(H2O)4(OH)8O236]·125H2O (H-1) which comprises a Ta/W mixed addenda heteropolyanion, 20 protons, and 125 crystalline water molecules has been prepared through ion-exchange method. The structure and properties of H-1 have been explored in detail. AC impedance measurements indicate that H-1 is a good solid state proton conducting material at room temperature with a conductivity value of 7.2×10-3 S cm-1 (25 °C, 30% RH). Cyclic voltammograms of H-1 indicate the electrocatalytic activity towards the reduction of nitrite. Hammett acidity constant H0 of H-1 in CH3CN is -2.91, which is the strongest among the present known HPAs. Relatively, H-1 exhibits excellent catalytic activities toward acetal reaction.

  19. Catalytic Decarboxylation of Fatty Acids to Aviation Fuels over Nickel Supported on Activated Carbon

    PubMed Central

    Wu, Jianghua; Shi, Juanjuan; Fu, Jie; Leidl, Jamie A.; Hou, Zhaoyin; Lu, Xiuyang

    2016-01-01

    Decarboxylation of fatty acids over non-noble metal catalysts without added hydrogen was studied. Ni/C catalysts were prepared and exhibited excellent activity and maintenance for decarboxylation. Thereafter, the effects of nickel loading, catalyst loading, temperature, and carbon number on the decarboxylation of fatty acids were investigated. The results indicate that the products of cracking increased with high nickel loading or catalyst loading. Temperature significantly impacted the conversion of stearic acid but did not influence the selectivity. The fatty acids with large carbon numbers tend to be cracked in this reaction system. Stearic acid can be completely converted at 370 °C for 5 h, and the selectivity to heptadecane was around 80%. PMID:27292280

  20. Nitro-Assisted Brønsted Acid Catalysis: Application to a Challenging Catalytic Azidation.

    PubMed

    Dryzhakov, Marian; Hellal, Malik; Wolf, Eléna; Falk, Florian C; Moran, Joseph

    2015-08-01

    A cocatalytic effect of nitro compounds is described for the B(C6F5)3·H2O catalyzed azidation of tertiary aliphatic alcohols, enabling catalyst turnover for the first time and with a broad range of substrates. Kinetic investigations into this surprising effect reveal that nitro compounds induce a switch from first order concentration dependence in Brønsted acid to second order concentration dependence in Brønsted acid and second order dependence in the nitro compounds. Kinetic, electronic, and spectroscopic evidence suggests that higher order hydrogen-bonded aggregates of nitro compounds and acids are the kinetically competent Brønsted acid catalysts. Specific weak H-bond accepting additives may offer a new general approach to accelerating Brønsted acid catalysis in solution.

  1. Catalytic Decarboxylation of Fatty Acids to Aviation Fuels over Nickel Supported on Activated Carbon

    NASA Astrophysics Data System (ADS)

    Wu, Jianghua; Shi, Juanjuan; Fu, Jie; Leidl, Jamie A.; Hou, Zhaoyin; Lu, Xiuyang

    2016-06-01

    Decarboxylation of fatty acids over non-noble metal catalysts without added hydrogen was studied. Ni/C catalysts were prepared and exhibited excellent activity and maintenance for decarboxylation. Thereafter, the effects of nickel loading, catalyst loading, temperature, and carbon number on the decarboxylation of fatty acids were investigated. The results indicate that the products of cracking increased with high nickel loading or catalyst loading. Temperature significantly impacted the conversion of stearic acid but did not influence the selectivity. The fatty acids with large carbon numbers tend to be cracked in this reaction system. Stearic acid can be completely converted at 370 °C for 5 h, and the selectivity to heptadecane was around 80%.

  2. Catalytic Decarboxylation of Fatty Acids to Aviation Fuels over Nickel Supported on Activated Carbon.

    PubMed

    Wu, Jianghua; Shi, Juanjuan; Fu, Jie; Leidl, Jamie A; Hou, Zhaoyin; Lu, Xiuyang

    2016-01-01

    Decarboxylation of fatty acids over non-noble metal catalysts without added hydrogen was studied. Ni/C catalysts were prepared and exhibited excellent activity and maintenance for decarboxylation. Thereafter, the effects of nickel loading, catalyst loading, temperature, and carbon number on the decarboxylation of fatty acids were investigated. The results indicate that the products of cracking increased with high nickel loading or catalyst loading. Temperature significantly impacted the conversion of stearic acid but did not influence the selectivity. The fatty acids with large carbon numbers tend to be cracked in this reaction system. Stearic acid can be completely converted at 370 °C for 5 h, and the selectivity to heptadecane was around 80%. PMID:27292280

  3. Substrate Orientation and Catalytic Specificity in the Action of Xanthine Oxidase: The Sequential Hydroxylation of Hypoxanthine to Uric Acid

    SciTech Connect

    Cao, Hongnan; Pauff, James M.; Hille, Russ

    2010-11-29

    Xanthine oxidase is a molybdenum-containing enzyme catalyzing the hydroxylation of a sp{sup 2}-hybridized carbon in a broad range of aromatic heterocycles and aldehydes. Crystal structures of the bovine enzyme in complex with the physiological substrate hypoxanthine at 1.8 {angstrom} resolution and the chemotherapeutic agent 6-mercaptopurine at 2.6 {angstrom} resolution have been determined, showing in each case two alternate orientations of substrate in the two active sites of the crystallographic asymmetric unit. One orientation is such that it is expected to yield hydroxylation at C-2 of substrate, yielding xanthine. The other suggests hydroxylation at C-8 to give 6,8-dihydroxypurine, a putative product not previously thought to be generated by the enzyme. Kinetic experiments demonstrate that >98% of hypoxanthine is hydroxylated at C-2 rather than C-8, indicating that the second crystallographically observed orientation is significantly less catalytically effective than the former. Theoretical calculations suggest that enzyme selectivity for the C-2 over C-8 of hypoxanthine is largely due to differences in the intrinsic reactivity of the two sites. For the orientation of hypoxanthine with C-2 proximal to the molybdenum center, the disposition of substrate in the active site is such that Arg880 and Glu802, previous shown to be catalytically important for the conversion of xanthine to uric acid, play similar roles in hydroxylation at C-2 as at C-8. Contrary to the literature, we find that 6,8-dihydroxypurine is effectively converted to uric acid by xanthine oxidase.

  4. Spectrophotometric determination of osmium based on its catalytic effect on the oxidation of carminic acid by hydrogen peroxide.

    PubMed

    Manzoori, J L; Sorouraddin, M H; Amjadi, M

    2000-10-01

    A highly sensitive spectrophotometric method is described for the determination of trace amounts of osmium(VIII), based on its catalytic effect on the oxidation of carminic acid by hydrogen peroxide. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 540 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1x10(-4) mol l(-1) carminic acid, 0.013 mol l(-1) hydrogen peroxide and pH 10 at 25 degrees C. By using the recommended procedure, the calibration graph was linear from 0.1 to 1.5 ng ml(-1) of osmium; the detection limit was 0.02 ng ml(-1); the RSD for five replicate determinations of 0.2-1.4 ng ml(-1) was in the range of 1.8-4.7%. The influence of several foreign ions on osmium determination were studied and the effect of interfering ions were removed by extracting osmium into isobuthyl methyl ketone and back extracting into sodium hydroxide solution. PMID:18968089

  5. Ultraspecific and highly sensitive nucleic acid detection by integrating a DNA catalytic network with a label-free microcavity.

    PubMed

    Wu, Yuqiang; Zhang, David Yu; Yin, Peng; Vollmer, Frank

    2014-05-28

    Nucleic acid detection with label-free biosensors circumvents costly fluorophore functionalization steps associated with conventional assays by utilizing transducers of impressive ultimate detection limits. Despite this technological prowess, molecular recognition at a surface limits the biosensors' sensitivity, specificity, and reusability. It is therefore imperative to integrate novel molecular approaches with existing label-free transducers to overcome those limitations. Here, we demonstrate this concept by integrating a DNA strand displacement circuit with a micron-scale whispering gallery mode (WGM) microsphere biosensor. The integrated biosensor exhibits at least 25-fold improved nucleic acid sensitivity, and sets a new record for label-free microcavity biosensors by detecting 80 pM (32 fmol) of a 22nt oligomer; this improvement results from the catalytic behavior of the circuit. Furthermore, the integrated sensor exhibits extremely high specificity; single nucleotide variants yield 40- to 100-fold lower signal. Finally, the same physical sensor was demonstrated to alternatingly detect 2 different nucleic acid sequences through 5 cycles of detection, showcasing both its reusability and its versatility.

  6. Synthesis, characterization and catalytic activity of acid-base bifunctional materials through protection of amino groups

    SciTech Connect

    Shao, Yanqiu; Liu, Heng; Yu, Xiaofang; Guan, Jingqi; Kan, Qiubin

    2012-03-15

    Graphical abstract: Acid-base bifunctional mesoporous material SO{sub 3}H-SBA-15-NH{sub 2} was successfully synthesized under low acidic medium through protection of amino groups. Highlights: Black-Right-Pointing-Pointer The acid-base bifunctional material SO{sub 3}H-SBA-15-NH{sub 2} was successfully synthesized through protection of amino groups. Black-Right-Pointing-Pointer The obtained bifunctional material was tested for aldol condensation. Black-Right-Pointing-Pointer The SO{sub 3}H-SBA-15-NH{sub 2} catalyst containing amine and sulfonic acid groups exhibited excellent acid-basic properties. -- Abstract: Acid-base bifunctional mesoporous material SO{sub 3}H-SBA-15-NH{sub 2} was successfully synthesized under low acidic medium through protection of amino groups. X-ray diffraction (XRD), N{sub 2} adsorption-desorption, transmission electron micrographs (TEM), back titration, {sup 13}C magic-angle spinning (MAS) NMR and {sup 29}Si magic-angle spinning (MAS) NMR were employed to characterize the synthesized materials. The obtained bifunctional material was tested for aldol condensation reaction between acetone and 4-nitrobenzaldehyde. Compared with monofunctional catalysts of SO{sub 3}H-SBA-15 and SBA-15-NH{sub 2}, the bifunctional sample of SO{sub 3}H-SBA-15-NH{sub 2} containing amine and sulfonic acid groups exhibited excellent acid-basic properties, which make it possess high activity for the aldol condensation.

  7. Recovery of acetic acid from dilute aqueous solutions using catalytic dehydrative esterification with ethanol.

    PubMed

    Yagyu, Daisuke; Ohishi, Tetsuo; Igarashi, Takeshi; Okumura, Yoshikuni; Nakajo, Tetsuo; Mori, Yuichiro; Kobayashi, Shū

    2013-03-01

    We have developed a direct esterification of aqueous acetic acid with ethanol (molar ratio=1:1) catalyzed by polystyrene-supported or homogeneous sulfonic acids toward the recovery of acetic acid from wastewater in chemical plants. The equilibrium yield was significantly increased by the addition of toluene, which had a high ability to extract ethyl acetate from the aqueous phase. It was shown that low-loading and alkylated polystyrene-supported sulfonic acid efficiently accelerated the reaction. These results suggest that the construction of hydrophobic reaction environments in water was critical in improving the chemical yield. Addition of inorganic salts was also effective for the reaction under not only biphasic conditions (toluene-water) but also toluene-free conditions, because the mutual solubility of ethyl acetate and water was suppressed by the salting-out effect. Among the tested salts, CaCl(2) was found to be the most suitable for this reaction system. PMID:23290939

  8. Development of biomimetic catalytic oxidation methods and non-salt methods using transition metal-based acid and base ambiphilic catalysts.

    PubMed

    Murahashi, Shun-Ichi

    2011-01-01

    This review focuses on the development of ruthenium and flavin catalysts for environmentally benign oxidation reactions based on mimicking the functions of cytochrome P-450 and flavoenzymes, and low valent transition-metal catalysts that replace conventional acids and bases. Several new concepts and new types of catalytic reactions based on these concepts are described. (Communicated by Ryoji Noyori, M.J.A.).

  9. Structural aspects of catalytic mechanisms of endonucleases and their binding to nucleic acids

    SciTech Connect

    Zhukhlistova, N. E.; Balaev, V. V.; Lyashenko, A. V.; Lashkov, A. A.

    2012-05-15

    Endonucleases (EC 3.1) are enzymes of the hydrolase class that catalyze the hydrolytic cleavage of deoxyribonucleic and ribonucleic acids at any region of the polynucleotide chain. Endonucleases are widely used both in biotechnological processes and in veterinary medicine as antiviral agents. Medical applications of endonucleases in human cancer therapy hold promise. The results of X-ray diffraction studies of the spatial organization of endonucleases and their complexes and the mechanism of their action are analyzed and generalized. An analysis of the structural studies of this class of enzymes showed that the specific binding of enzymes to nucleic acids is characterized by interactions with nitrogen bases and the nucleotide backbone, whereas the nonspecific binding of enzymes is generally characterized by interactions only with the nucleic-acid backbone. It should be taken into account that the specificity can be modulated by metal ions and certain low-molecular-weight organic compounds. To test the hypotheses about specific and nonspecific nucleic-acid-binding proteins, it is necessary to perform additional studies of atomic-resolution three-dimensional structures of enzyme-nucleic-acid complexes by methods of structural biology.

  10. Structural aspects of catalytic mechanisms of endonucleases and their binding to nucleic acids

    NASA Astrophysics Data System (ADS)

    Zhukhlistova, N. E.; Balaev, V. V.; Lyashenko, A. V.; Lashkov, A. A.

    2012-05-01

    Endonucleases (EC 3.1) are enzymes of the hydrolase class that catalyze the hydrolytic cleavage of deoxyribonucleic and ribonucleic acids at any region of the polynucleotide chain. Endonucleases are widely used both in biotechnological processes and in veterinary medicine as antiviral agents. Medical applications of endonucleases in human cancer therapy hold promise. The results of X-ray diffraction studies of the spatial organization of endonucleases and their complexes and the mechanism of their action are analyzed and generalized. An analysis of the structural studies of this class of enzymes showed that the specific binding of enzymes to nucleic acids is characterized by interactions with nitrogen bases and the nucleotide backbone, whereas the nonspecific binding of enzymes is generally characterized by interactions only with the nucleic-acid backbone. It should be taken into account that the specificity can be modulated by metal ions and certain low-molecular-weight organic compounds. To test the hypotheses about specific and nonspecific nucleic-acid-binding proteins, it is necessary to perform additional studies of atomic-resolution three-dimensional structures of enzyme-nucleic-acid complexes by methods of structural biology.

  11. Tandem Catalytic Depolymerization of Lignin by Water-Tolerant Lewis Acids and Rhodium Complexes.

    PubMed

    Jastrzebski, Robin; Constant, Sandra; Lancefield, Christopher S; Westwood, Nicholas J; Weckhuysen, Bert M; Bruijnincx, Pieter C A

    2016-08-23

    Lignin is an attractive renewable feedstock for aromatic bulk and fine chemicals production, provided that suitable depolymerization procedures are developed. Here, we describe a tandem catalysis strategy for ether linkage cleavage within lignin, involving ether hydrolysis by water-tolerant Lewis acids followed by aldehyde decarbonylation by a Rh complex. In situ decarbonylation of the reactive aldehydes limits loss of monomers by recondensation, a major issue in acid-catalyzed lignin depolymerization. Rate of hydrolysis and decarbonylation were matched using lignin model compounds, allowing the method to be successfully applied to softwood, hardwood, and herbaceous dioxasolv lignins, as well as poplar sawdust, to give the anticipated decarbonylation products and, rather surprisingly, 4-(1-propenyl)phenols. Promisingly, product selectivity can be tuned by variation of the Lewis-acid strength and lignin source. PMID:27440544

  12. Surface and catalytic properties of acid metal carbons prepared by the sol gel method

    NASA Astrophysics Data System (ADS)

    Aguado-Serrano, J.; Rojas-Cervantes, M. L.; Martín-Aranda, R. M.; López-Peinado, A. J.; Gómez-Serrano, V.

    2006-06-01

    The sol-gel method has been applied for the synthesis of a series of acid metal-carbon xerogels (with M = V, Cr, Mo and Ni) by polymerisation of resorcinol with formaldehyde in the presence of metallic precursors. A blank sample was also prepared without any metal addition. The xerogels were heated in nitrogen at 1000 °C to obtain the pyrolysed products. The samples were characterised by different techniques such as thermal-mass spectrometry analysis, gas physisorption, and mercury porosimetry. In addition, the acid character of the pyrolysed products was tested by the Claisen-Schmidt condensation between benzaldehyde and acetophenone for the formation of chalcones.

  13. Catalytic Consequences of Acid Strength in the Conversion of Methanol to Dimethyl Ether

    SciTech Connect

    Carr, Robert T.; Neurock, Matthew; Iglesia, Enrique

    2011-02-14

    The effects of acid identity on CH{sub 3}OH dehydration are examined here using density functional theory (DFT) estimates of acid strength (as deprotonation energies, DPE) and reaction energies, combined with rate data on Keggin polyoxometalate (POM) clusters and zeolite H-BEA. Measured first-order (k{sub mono}) and zero-order (k{sub dimer}) CH3OH dehydration rate constants depend exponentially on DPE for POM clusters; the value of k{sub mono} depends more strongly on DPE than k{sub dimer} does. The chemical significance of these rate parameters and the basis for their dependences on acid strength were established by using DFT to estimate the energies of intermediates and transition states involved in elementary steps that are consistent with measured rate equations. We conclude from this treatment that CH{sub 3}OH dehydration proceeds via direct reactions of co-adsorbed CH{sub 3}OH molecules for relevant solid acids and reaction conditions. Methyl cations formed at ion-pair transition states in these direct routes are solvated by H{sub 2}O and CH{sub 3}OH more effectively than those in alternate sequential routes involving methoxide formation and subsequent reaction with CH{sub 3}OH. The stability of ion-pairs, prevalent as intermediates and transition states on solid acids, depends sensitively on DPE because of concomitant correlations between the stability of the conjugate anionic cluster and DPE. The chemical interpretation of k{sub mono} and k{sub dimer} from mechanism-based rate equations, together with thermochemical cycles of their respective transition state formations, show that similar charge distributions in the intermediate and transition state involved in k{sub dimer} cause its weaker dependence on DPE. Values of k{sub mono} involve uncharged reactants and the same ion-pair transition state as k{sub dimer}; these species sense acid strength differently and cause the larger effects of DPE on k{sub mono}. Confinement effects in H-BEA affect the value of

  14. Carboxylic acid-grafted mesoporous material and its high catalytic activity in one-pot three-component coupling reaction

    NASA Astrophysics Data System (ADS)

    Gomes, Ruth; Dutta, Saikat; Bhaumik, Asim

    2014-11-01

    A new carboxylic acid functionalized mesoporous organic polymer has been synthesized via in situ radical polymerization of divinylbenzene and acrylic acid using a mesoporous silica as a seed during the polymerization process under solvothermal conditions. The mesoporous material MPDVAA-1 has been thoroughly characterized employing powder XRD, solid state 13C cross polarization magic angle spinning-nuclear magnetic resonance, FT-IR spectroscopy, N2 sorption, HR-TEM, and NH3 temperature programmed desorption-thermal conductivity detector (TPD-TCD) analysis to understand its porosity, chemical environment, bonding, and surface properties. The mesoporous polymer was used as a catalyst for a three comp onent Biginelli condensation between various aldehydes, β-keto esters, and urea/thioureas to give 3,4-dihydropyrimidine-2(1H)-ones. The reactions were carried out under conventional heating as well as solvent-free microwave irradiation of solid components, and in both the cases, the mesoporous polymer MPDVAA-1 proved to be a powerful, robust, and reusable catalyst with high catalytic efficiency.

  15. Carboxylic acid-grafted mesoporous material and its high catalytic activity in one-pot three-component coupling reaction

    SciTech Connect

    Gomes, Ruth; Bhaumik, Asim; Dutta, Saikat

    2014-11-01

    A new carboxylic acid functionalized mesoporous organic polymer has been synthesized via in situ radical polymerization of divinylbenzene and acrylic acid using a mesoporous silica as a seed during the polymerization process under solvothermal conditions. The mesoporous material MPDVAA-1 has been thoroughly characterized employing powder XRD, solid state {sup 13}C cross polarization magic angle spinning-nuclear magnetic resonance, FT-IR spectroscopy, N{sub 2} sorption, HR-TEM, and NH{sub 3} temperature programmed desorption-thermal conductivity detector (TPD-TCD) analysis to understand its porosity, chemical environment, bonding, and surface properties. The mesoporous polymer was used as a catalyst for a three comp onent Biginelli condensation between various aldehydes, β-keto esters, and urea/thioureas to give 3,4-dihydropyrimidine-2(1H)-ones. The reactions were carried out under conventional heating as well as solvent-free microwave irradiation of solid components, and in both the cases, the mesoporous polymer MPDVAA-1 proved to be a powerful, robust, and reusable catalyst with high catalytic efficiency.

  16. Catalytic dechlorination of 2,4-dichlorophenol by Pd/Fe bimetallic nanoparticles in the presence of humic acid.

    PubMed

    Zhang, Zhen; Shen, Qiaohui; Cissoko, Naman; Wo, Jingjing; Xu, Xinhua

    2010-10-15

    Pd/Fe bimetallic nanoparticles were synthesized for treatment of 2,4-dichlorophenol (2,4-DCP) in the presence of humic acid (HA), in order to understand their applicability for in situ remediation of groundwater. In this case, 2,4-DCP was catalytically dechlorinated to form the final products--phenol (P) via two intermediates, namely o-chlorophenol (o-CP) and p-chlorophenol (p-CP). We demonstrated that the carbon mass balances during the dechlorination were in the range of 82-91%, and other carbons were absorbed on the surface of Pd/Fe bimetallic nanoparticles. Our results suggest the dechlorination reaction of 2,4-DCP by Pd/Fe bimetallic nanoparticles in the presence of HA followed pseudo-first-order kinetics. HA competed for reaction sites on the Pd/Fe bimetallic nanoparticles with 2,4-DCP, and thus reduced the efficiency and rate of the dechlorination of 2,4-DCP. Efficiencies of dechlorination and phenol formations increased significantly as the Pd content increased from 0.10 wt.%, 0.15 wt.% to 0.20 wt.%, the removal percentage of 2,4-DCP increased from 70.4%, 98.4% to 99.4% within 300 min, respectively, the nitrate (NO(3)(-)) content in water also has a significant impact on 2,4-DCP dechlorination efficiency. Our results show that no other intermediates were generated besides Cl(-), o-CP, p-CP and phenol during the catalytic dechlorination of 2,4-DCP.

  17. Catalytic synthesis of biodiesel from high free fatty acid-containing feedstocks

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recyclable and reusable heterogeneous diarylammonium catalysts are highly effective in catalyzing the esterification of the free fatty acid (FFA) present in greases to methyl esters to reduce the FFA content from 12-40 wt% to 0.5 – 1 wt%. The resulting ester-glyceride mixture (pretreated grease) co...

  18. Catalytic synthesis of fatty acid methyl esters from extremely low quality greases

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biodiesel (BD) is a renewable fuel for compression ignition engines that is composed of the simple alkyl esters, usually methyl-, of fatty acids (FAME). It is typically produced via base-catalyzed transesterification between refined vegetable oil or animal fat (e.g., soybean oil, tallow) and an alc...

  19. Single-crystal Au microflakes modulated by amino acids and their sensing and catalytic properties.

    PubMed

    Li, Mingjie; Wu, Xiaochen; Zhou, Jiyu; Kong, Qingshan; Li, Chaoxu

    2016-04-01

    Single-crystal Au microflakes with the planar area over 10(3)μm(2) (i.e. being accessible to the human eye resolution) were synthesized in an environment-friendly route by directing two-dimensional growth of Au nanocrystals into macroscopic scales with amino acids as both reducing agents and capping agents. Side groups of amino acids were found to be a determinant parameter to tune the dimension and size of Au single crystals. The successful synthesis of Au microflakes provides an unprecedented opportunity to bridge nanotechnology and macroscopic devices, and hereby to start a new scenario of exploring their unique properties and applications in optoelectronic devices and bio-sensing fields across multiple length scales. For example, Au microflakes respond to air humidity upon depositing on films of chitin nanofibrils, and sense various physiological molecules as electrode materials of biosensors.

  20. The Catalytic Machinery of a Key Enzyme in Amino Acid Biosynthesis

    SciTech Connect

    Viola, Ronald E.; Faehnle, Christopher R.; Blanco, Julio; Moore, Roger A.; Liu, Xuying; Arachea, Buenafe T.; Pavlovsky, Alexander G.

    2013-02-28

    The aspartate pathway of amino acid biosynthesis is essential for all microbial life but is absent in mammals. Characterizing the enzyme-catalyzed reactions in this pathway can identify new protein targets for the development of antibiotics with unique modes of action. The enzyme aspartate {beta}-semialdehyde dehydrogenase (ASADH) catalyzes an early branch point reaction in the aspartate pathway. Kinetic, mutagenic, and structural studies of ASADH from various microbial species have been used to elucidate mechanistic details and to identify essential amino acids involved in substrate binding, catalysis, and enzyme regulation. Important structural and functional differences have been found between ASADHs isolated from these bacterial and fungal organisms, opening the possibility for developing species-specific antimicrobial agents that target this family of enzymes.

  1. Catalytic conversion of cellulose to fuels and chemicals using boronic acids

    SciTech Connect

    Raines, Ronald; Caes, Benjamin; Palte, Michael

    2015-10-20

    Methods and catalyst compositions for formation of furans from carbohydrates. A carbohydrate substrate is heating in the presence of a 2-substituted phenylboronic acid (or salt or hydrate thereof) and optionally a magnesium or calcium halide salt. The reaction is carried out in a polar aprotic solvent other than an ionic liquid, an ionic liquid or a mixture thereof. Additional of a selected amount of water to the reaction can enhance the yield of furans.

  2. Development and application of versatile bis-hydroxamic acids for catalytic asymmetric oxidation

    PubMed Central

    Barlan, Allan U.; Zhang, Wei; Yamamoto, Hisashi

    2010-01-01

    In this article, we describe the development and preliminary results of our new designed C2-symmetric bis-hydroxamic acid (BHA) ligands and the application of the new ligands for vanadium-catalyzed asymmetric epoxidation of allylic alcohols as well as homoallylic alcohols. From this success we demonstrate the versatile nature of BHA in the molybdenum catalyzed asymmetric oxidation of unfunctionalized olefins and sulfides. PMID:21152351

  3. EPR characterization of the catalytic activity of clays for PCE removal by gamma-radiation induced by acid and thermal treatments.

    PubMed

    Chung, Hung-Ho; Choi, Sang-Won; Ok, Yong-Sik; Jung, Jinho

    2004-12-01

    Clays from tidal flat sediments showed efficient catalytic activity in the decomposition of PCE by gamma-radiation. The highest PCE removal of 98.6% was obtained with clays heated to 700 degrees C after acid treatment. The improved catalytic activity was identified by electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of clays were significantly changed by the acid and thermal treatments. The intensity of a narrow signal at g=2 (signal III) was decreased with increasing thermal treatment temperature and this increased the PCE removal efficiency. The acid treatment completely removed a broad signal at g=2 (signal II), decreased the intensity of signal III, and improved the gamma-radiation treatment of PCE.

  4. Catalytic nucleic acid enzymes for the study and development of therapies in the central nervous system

    PubMed Central

    Tritz, Richard; Habita, Cellia; Robbins, Joan M.; Gomez, German G.; Kruse, Carol A.

    2005-01-01

    Summary Nucleic acid enzymes have been used with great success for studying natural processes in the central nervous system (CNS). We first provide information on the structural and enzymatic differences of various ribozymes and DNAzymes. We then discuss how they have been used to explore new therapeutic approaches for treating diseases of the CNS. They have been tested in various systems modeling retinitis pigmentosum, proliferative vitreoretinopathy, Alzheimer's disease, and malignant brain tumors. For these models, effective targets for nucleic acid enzymes have been readily identified and the rules for selecting cleavage sites have been well established. The bulk of studies, including those from our laboratory, have emphasized their use for gliomas. With the availability of multiple excellent animal models to test glioma treatments, good progress has been made in the initial testing of nucleic acid enzymes for brain tumor therapy. However, opportunities still exist to significantly improve the delivery and efficacy of ribozymes to achieve effective treatment. The future holds significant potential for the molecular targeting and therapy of eye diseases, neurodegenerative disorders, and brain tumors with these unique treatment agents. PMID:16467915

  5. Identification of Amino Acid Determinants in CYP4B1 for Optimal Catalytic Processing of 4-Ipomeanol

    PubMed Central

    Wiek, Constanze; Schmidt, Eva M; Roellecke, Katharina; Freund, Marcel; Nakano, Mariko; Kelly, Edward J; Kaisers, Wolfgang; Yarov-Yarovoy, Vladimir; Kramm, Christof M; Rettie, Allan E; Hanenberg, Helmut

    2014-01-01

    Mammalian CYP4B1 enzymes are cytochrome P450 monooxygenases that are responsible for the bioactivation of several exogenous pro-toxins including 4-ipomeanol (4-IPO). In contrast to the orthologous rabbit enzyme, we show here that native human CYP4B1 with a serine at position 427 is unable to bio-activate 4-IPO and does not cause cytotoxicity in HepG2 cells and primary human T-cells that overexpress these enzymes. We also demonstrate that a proline residue in the meander region at position 427 in human CYB4B1 and 422 in rabbit CYP4B1 is important for protein stability and rescues the 4-IPO bioactivation of the human enzyme, but is not essential for the catalytic activity of the rabbit CYP4B1 protein. Systematic substitution of native and p.S427P human CYP4B1 with peptide regions from the highly active rabbit enzyme reveals that 18 amino acids in the wild-type rabbit CYP4B1 protein are key for conferring high 4-IPO metabolizing activity. Introduction of 12 of the 18 amino acids that are also present at corresponding positions in other human CYP4 family members into the p.S427P human CYP4B1 protein results in a mutant human enzyme (P+12) that is as stable and as active as the rabbit wild-type CYP4B1 protein. These 12 mutations cluster in the predicted B–C loop through F-helix regions and reveal new amino acid regions important to P450 enzyme stability. Finally, by minimally re-engineering the human CYP4B1 enzyme for efficient activation of 4-IPO, we have developed a novel human suicide gene system that is a candidate for adoptive cellular therapies in humans. PMID:25247810

  6. Origin of Kinetic Resolution of Hydroxy Esters through Catalytic Enantioselective Lactonization by Chiral Phosphoric Acids.

    PubMed

    Changotra, Avtar; Sunoj, Raghavan B

    2016-08-01

    Kinetic resolution is a widely used strategy for separation and enrichment of enantiomers. Using density functional theory computations, the origin of how a chiral BINOL-phosphoric acid catalyzes the selective lactonization of one of the enantiomers of α-methyl γ-hydroxy ester is identified. In a stepwise mechanism, the stereocontrolling transition state for the addition of the hydroxyl group to the si face of the ester carbonyl in the case of the S isomer exhibits a network of more effective noncovalent interactions between the substrate and the chiral catalyst. PMID:27463593

  7. Enhancing photo-catalytic production of organic acids in the cyanobacterium S ynechocystis sp. PCC 6803 Δ glg C , a strain incapable of glycogen storage

    DOE PAGESBeta

    Carrieri, Damian; Broadbent, Charlie; Carruth, David; Paddock, Troy; Ungerer, Justin; Maness, Pin-Ching; Ghirardi, Maria; Yu, Jianping

    2015-01-23

    We describe how a key objective in microbial biofuels strain development is to maximize carbon flux to target products while minimizing cell biomass accumulation, such that ideally the algae and bacteria would operate in a photo-catalytic state. A brief period of such a physiological state has recently been demonstrated in the cyanobacterium Synechocystis sp. PCC 6803 ΔglgC strain incapable of glycogen storage. When deprived of nitrogen, the ΔglgC excretes the organic acids alpha-ketoglutarate and pyruvate for a number of days without increasing cell biomass. This study examines the relationship between the growth state and the photo-catalytic state, and characterizes themore » metabolic adaptability of the photo-catalytic state to increasing light intensity. It is found that the culture can transition naturally from the growth state into the photo-catalytic state when provided with limited nitrogen supply during the growth phase. Photosynthetic capacity and pigments are lost over time in the photo-catalytic state. Reversal to growth state is observed with re-addition of nitrogen nutrient, accompanied by restoration of photosynthetic capacity and pigment levels in the cells. While the overall productivity increased under high light conditions, the ratio of alpha-ketoglutarate/pyruvate is altered, suggesting that carbon partition between the two products is adaptable to environmental conditions.« less

  8. Solubilizing properties of new surface-active agents, products of catalytic oxyethylation of cholic acid.

    PubMed

    Kołodziejczyk, Michał Krzysztof; Nachajski, Michal Jakub; Lukosek, Marek; Zgoda, Marian Mikołaj

    2013-01-01

    Solubilizing properties of aqueous solutions of a series of surface-active agents, products of oxyethylation of cholic acid, were examined in the present study. The content of oxyethylated segments determined by means of the 1H NMR method enabled the verification of the molecular mass of surfactants along with the calculation of the structural hydrophilic-lipophilic balance (HLB), the solubility parameter delta1/2, and the required solubility level of balance HLB(R). Viscosimetric measurements enabled the calculation of the limiting viscosity number, the content-average molecular mass, the effective volume, the hydrodynamic radius of the surfactant micelle and their equilibrium adducts with rutin, diclofenac and loratadine (BCS Class II and III). By means of the spectrophotometric method (UV) the amount of the solubilized diclofenac, loratadine and rutin (rutoside) was determined in the equilibrium system (saturated solution) in the environment of aqueous solutions of cholic acid derivatives of n(TE) = 20-70. The obtained results serve as a basis for determining the solubilization mechanism of lipophilic therapeutic products and indirectly for estimating the influence of the above process on pharmaceutical as well as biological availability of a micellar adduct from model drug forms (Lindbladt lithogenolitic index).

  9. Metal thin film growth on multimetallic surfaces: From quaternary metallic glass to binary crystal

    SciTech Connect

    Jing, Dapeng

    2010-01-01

    The work presented in this thesis mainly focuses on the nucleation and growth of metal thin films on multimetallic surfaces. First, we have investigated the Ag film growth on a bulk metallic glass surface. Next, we have examined the coarsening and decay of bilayer Ag islands on NiAl(110) surface. Third, we have investigated the Ag film growth on NiAl(110) surface using low-energy electron diffraction (LEED). At last, we have reported our investigation on the epitaxial growth of Ni on NiAl(110) surface. Some general conclusions can be drawn as follows. First, Ag, a bulk-crystalline material, initially forms a disordered wetting layer up to 4-5 monolayers on Zr-Ni-Cu-Al metallic glass. Above this coverage, crystalline 3D clusters grow, in parallel with the flatter regions. The cluster density increases with decreasing temperature, indicating that the conditions of island nucleation are far-from-equilibrium. Within a simple model where clusters nucleate whenever two mobile Ag adatoms meet, the temperature-dependence of cluster density yields a (reasonable) upper limit for the value of the Ag diffusion barrier on top of the Ag wetting layer of 0.32 eV. Overall, this prototypical study suggests that it is possible to grow films of a bulk-crystalline metal that adopt the amorphous character of a glassy metal substrate, if film thickness is sufficiently low. Next, the first study of coarsening and decay of bilayer islands has been presented. The system was Ag on NiAl(110) in the temperature range from 185 K to 250 K. The coarsening behavior, has some similarities to that seen in the Ag(110) homoepitaxial system studied by Morgenstern and co-workers. At 185 K and 205 K, coarsening of Ag islands follows a Smoluchowski ripening pathway. At 205 K and 250 K, the terrace diffusion limited Ostwald ripening dominants. The experimental observed temperature for the transition from SR to OR is 205 K. The SR exhibits anisotropic island diffusion and the OR exhibits 1D decay of island

  10. The Catalytic Scaffold fo the Haloalkanoic Acid Dehalogenase Enzyme Superfamily Acts as a Mold for the Trigonal Bipyramidal Transition State

    SciTech Connect

    Lu,Z.; Dunaway-Mariano, D.; Allen, K.

    2008-01-01

    The evolution of new catalytic activities and specificities within an enzyme superfamily requires the exploration of sequence space for adaptation to a new substrate with retention of those elements required to stabilize key intermediates/transition states. Here, we propose that core residues in the large enzyme family, the haloalkanoic acid dehalogenase enzyme superfamily (HADSF) form a 'mold' in which the trigonal bipyramidal transition states formed during phosphoryl transfer are stabilized by electrostatic forces. The vanadate complex of the hexose phosphate phosphatase BT4131 from Bacteroides thetaiotaomicron VPI-5482 (HPP) determined at 1.00 Angstroms resolution via X-ray crystallography assumes a trigonal bipyramidal coordination geometry with the nucleophilic Asp-8 and one oxygen ligand at the apical position. Remarkably, the tungstate in the complex determined to 1.03 Angstroms resolution assumes the same coordination geometry. The contribution of the general acid/base residue Asp-10 in the stabilization of the trigonal bipyramidal species via hydrogen-bond formation with the apical oxygen atom is evidenced by the 1.52 Angstroms structure of the D10A mutant bound to vanadate. This structure shows a collapse of the trigonal bipyramidal geometry with displacement of the water molecule formerly occupying the apical position. Furthermore, the 1.07 Angstroms resolution structure of the D10A mutant complexed with tungstate shows the tungstate to be in a typical 'phosphate-like' tetrahedral configuration. The analysis of 12 liganded HADSF structures deposited in the protein data bank (PDB) identified stringently conserved elements that stabilize the trigonal bipyramidal transition states by engaging in favorable electrostatic interactions with the axial and equatorial atoms of the transferring phosphoryl group.

  11. Cloning, characterization and mutagenesis of Russell's viper venom L-amino acid oxidase: Insights into its catalytic mechanism.

    PubMed

    Chen, Hong-Sen; Wang, Ying-Ming; Huang, Wan-Ting; Huang, Kai-Fa; Tsai, Inn-Ho

    2012-02-01

    To investigate the structure-function relationships and geographic variations of L-amino acid oxidase (LAAO) from Daboia venoms, a single LAAO (designated as DrLAO) was purified from eastern Indian Daboia russelii venom and characterized. The purified DrLAO showed subunit molecular mass of 60-64kDa; its N-terminal sequence (1-20) was identical to those of several true viper LAAOs. Its preferred substrates were hydrophobic l-amino acids and the kinetic specificities were ordered as follows: Phe, Tyr, Met, Leu, and Trp. Enzyme assay and Western blotting showed that the venom LAAO contents of D. russelii were higher than those of Daboia siamensis. DrLAO dose-dependently inhibited ADP- and collagen-induced platelet aggregation with IC(50) values of 0.27 and 0.82μM, respectively. Apparently, DrLAO may synergize with other venom components to prolong and enhance bleeding symptoms after Daboia envenoming. The full sequence of DrLAO was deduced from its cDNA sequence and then confirmed by peptide mass fingerprinting. Molecular phylogenetic analysis revealed that SV-LAAO family members could be differentiated not only by snake taxonomy but also by the variations at position 223, and they divided into H223, S223, N223, and D223 subclasses. We have further prepared recombinant DrLAO and mutants by the Pichia expression system. Mutagenic analyses of DrLAO His223 revealed that this residue bound substrates instead of serving as an essential base in the catalytic steps. Our results suggest a direct hydride transfer from substrate to FAD as the mechanism for SV-LAAOs. PMID:21802487

  12. Encapsulating Metal Clusters and Acid Sites within Small Voids: Synthetic Strategies and Catalytic Consequences

    NASA Astrophysics Data System (ADS)

    Goel, Sarika

    active sites. We have demonstrated the selectivity of the encapsulation processes by combining transmission electron microscopy and chemisorptive titrations with rigorous catalytic assessments of the ability of these materials to catalyze reactions of small molecules, which can access the intracrystalline voids, but not of larger molecules that cannot access the metal clusters within such voids. The selective confinement of clusters also prevented their contact with sulfur compounds (e.g., thiophene and H2S), thus allowing reactions to occur at conditions that otherwise render unconfined clusters unreactive. We have also developed synthetic protocols and guiding principles, inspired by mechanistic considerations, for the synthesis of zeolites via interzeolite transformations without the use of organic structure-directing agents (OSDA). More specifically, we have synthesized high-silica MFI (ZSM-5), CHA (chabazite), STF (SSZ-35) and MTW (ZSM-12) zeolites from FAU (faujasite) or BEA (beta) parent materials. Structures with lower framework densities (FAU or BEA) were successfully transformed into thermodynamically-favored, more stable structures with higher framework densities (MFI, CHA, STF, and MTW); to date, target materials with higher Si/Al ratios (Si/Al >10) have not been synthesized via interzeolite transformations without the aid of the OSDA species used to discover these zeolite structures and deemed essential up until now for their successful synthesis. Overcoming kinetic hurdles in such transformations required either the presence of common composite building units (CBU) between parent and target structures or, in their absence, the introduction of small amount of seeds of the daughter structures. The NaOH/SiO2 ratio, H2O/SiO2 ratio and Al content in reagents are used to enforce synchronization between the swelling and local restructuring within parent zeolite domains with the spalling of fragments or building units from seeds of the target structure. The

  13. Lewis base activation of Lewis acids: catalytic, enantioselective vinylogous aldol addition reactions.

    PubMed

    Denmark, Scott E; Heemstra, John R

    2007-07-20

    The generality of Lewis base catalyzed, Lewis acid mediated, enantioselective vinylogous aldol addition reactions has been investigated. The combination of silicon tetrachloride and chiral phosphoramides is a competent catalyst for highly selective additions of a variety of alpha,beta-unsaturated ketone-, 1,3-diketone-, and alpha,beta-unsaturated amide-derived dienolates to aldehydes. These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded high enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although alpha,beta-unsaturated ketone-derived dienolate did not react with aliphatic aldehydes, alpha,beta-unsaturated amide-derived dienolates underwent addition at reasonable rates affording high yields of vinylogous aldol product. The enantioselectivities achieved with the morpholine derived-dienolate in the addition to aliphatic aldehydes was the highest afforded to date with the silicon tetrachloride-chiral phosphoramide system. Furthermore, the ability to cleanly convert the morpholine amide to a methyl ketone was demonstrated.

  14. Ellagic Acid Directed Growth of Au-Pt Bimetallic Nanoparticles and Their Catalytic Applications

    NASA Astrophysics Data System (ADS)

    Barnaby, Stacey N.; Sarker, Nazmul H.; Banerjee, Ipsita A.

    2013-02-01

    In this work, we report the facile formation of bimetallic nanoparticles of Au-Pt in the presence of the plant polyphenol ellagic acid (EA). It was found that EA formed micro-fibrillar assemblies, which aggregated into micro-bundles under aqueous conditions. Those micro-bundles acted as templates for the growth of Au nanoparticles, as well as bimetallic Au-Pt nanoparticles biomimetically. At higher concentrations of EA, it was observed that in addition to forming fibrous micro-bundles, columnar assemblies of EA were formed in the presence of the metal nanoparticles. The formation of the assemblies was found to be concentration dependent. It appears that upon binding to metal ions and subsequent formation of the nanoparticles, morphological changes occur in the case of EA assemblies. The morphological changes observed were probed by electron microscopy. Further, the ability of the materials to degrade the toxic aromatic nitro compound 2-methoxy-4-nitroaniline was explored, where 50% degradation was observed within 15 min, indicating that such hybrid materials may have potential applications in environmental remediation.

  15. Biodiesel production from waste chicken fat with low free fatty acids by an integrated catalytic process of composite membrane and sodium methoxide.

    PubMed

    Shi, Wenying; Li, Jianxin; He, Benqiao; Yan, Feng; Cui, Zhenyu; Wu, Kaiwei; Lin, Ligang; Qian, Xiaomin; Cheng, Yu

    2013-07-01

    An integrated process of catalytic composite membranes (CCMs) and sodium methoxide was developed to produce biodiesel from waste chicken fat. The free fatty acids (FFAs) in the chicken oil were converted to methyl esters by esterification with methanol using a novel sulfonated polyethersulfone (SPES)/PES/non-woven fabric (NWF) CCMs in a flow-through catalytic membrane reactor. The CCM is that the NWF fibers were fully embedded in SPES/PES with a homogeneous and microporous structure. The oil obtained after esterification was carried out by transesterification of sodium methoxide. The results showed that the FFAs conversion obtained by CCMs with the acid capacity of 25.28 mmol (H(+)) was 92.8% at the residence time 258s. The CCMs present a good stability during the continuous running of 500 h. The conversion of transesterification was 98.1% under the optimum conditions. The quality of the biodiesel met the international standards. PMID:23665693

  16. MCM-41 supported 12-tungstophosphoric acid mesoporous materials: Preparation, characterization, and catalytic activities for benzaldehyde oxidation with H2O2

    NASA Astrophysics Data System (ADS)

    Chen, Ya; Zhang, Xiao-Li; Chen, Xi; Dong, Bei-Bei; Zheng, Xiu-Cheng

    2013-10-01

    Mesoporous molecular sieves MCM-41 and bulk 12-tungstophosphoric acid (HPW) were synthesized and employed to prepare 5-45 wt.% HPW/MCM-41 mesoporous materials. Characterization results suggested the good dispersion of HPW within MCM-41 when the loading of HPW was less than 35 wt.% and HPW/MCM-41 retained the typical mesopore structure of the supports. The results of the catalytic oxidation of benzaldehyde to benzoic acid with 30% H2O2, in the absence of any organic solvent and co-catalysts, indicated that HPW/MCM-41 was an efficient catalyst and 30 wt.% HPW/MCM-41 sample exhibited the highest catalytic activity among these materials.

  17. Biodiesel production from waste chicken fat with low free fatty acids by an integrated catalytic process of composite membrane and sodium methoxide.

    PubMed

    Shi, Wenying; Li, Jianxin; He, Benqiao; Yan, Feng; Cui, Zhenyu; Wu, Kaiwei; Lin, Ligang; Qian, Xiaomin; Cheng, Yu

    2013-07-01

    An integrated process of catalytic composite membranes (CCMs) and sodium methoxide was developed to produce biodiesel from waste chicken fat. The free fatty acids (FFAs) in the chicken oil were converted to methyl esters by esterification with methanol using a novel sulfonated polyethersulfone (SPES)/PES/non-woven fabric (NWF) CCMs in a flow-through catalytic membrane reactor. The CCM is that the NWF fibers were fully embedded in SPES/PES with a homogeneous and microporous structure. The oil obtained after esterification was carried out by transesterification of sodium methoxide. The results showed that the FFAs conversion obtained by CCMs with the acid capacity of 25.28 mmol (H(+)) was 92.8% at the residence time 258s. The CCMs present a good stability during the continuous running of 500 h. The conversion of transesterification was 98.1% under the optimum conditions. The quality of the biodiesel met the international standards.

  18. Preparation of acid-base bifunctional mesoporous KIT-6 (KIT: Korea Advanced Institute of Science and Technology) and its catalytic performance in Knoevenagel reaction

    SciTech Connect

    Xu, Ling; Wang, Chunhua; Guan, Jingqi

    2014-05-01

    Acid-base bifunctional mesoporous catalysts Al-KIT-6-NH{sub 2} containing different aluminum content have been synthesized through post synthetic grafting method. The materials were characterized by X-ray diffraction (XRD), scanning electron micrographs (SEM), transmission electron micrographs (TEM), Fourier-transform infrared spectroscopy (FTIR), IR spectra of pyridine adsorption, NH{sub 3}-TPD and TG analysis. The characterization results indicated that the pore structure of KIT-6 was well kept after the addition of aluminum and grafting of aminopropyl groups. The acid amount of Al-KIT-6 increased with enhancing aluminum content. Catalytic results showed that weak acid and weak base favor the Knoevenagel reaction, while catalysts with strong acid and weak base exhibited worse catalytic behavior. - Graphical abstract: The postulated steps of mechanism for the acid-base catalyzed process are as follows: (1) the aldehyde gets activated by the surface acidic sites which allow the amine undergoes nucleophilic to attack the carbonyl carbon of benzaldehyde. (2) Water is released in the formation of imine intermediate. (3) The ethyl cyanoacetate reacts with the intermediate. (4) The benzylidene ethyl cyanoacetate is formed and the amine is regenerated. - Highlights: • KIT-6 and Al-KIT-6-NH{sub 2} with different Si/Al ratios has been successfully prepared. • 79.4% Yield was obtained over 46-Al-KIT-6-NH{sub 2} within 20 min in Knoevenagel reaction. • Low Al-content Al-KIT-6-NH{sub 2} shows better catalytic stability than high Al-content catalysts. • There is acid-base synergistic effect in Knoevenagel reaction.

  19. Introducing deep eutectic solvents as biorenewable media for Au(I)-catalysed cycloisomerisation of γ-alkynoic acids: an unprecedented catalytic system.

    PubMed

    Rodríguez-Álvarez, María J; Vidal, Cristian; Díez, Josefina; García-Álvarez, Joaquín

    2014-11-01

    Cycloisomerisation of γ-alkynoic acids into cyclic enol-lactones was conveniently performed, for the first time, in the eutectic mixture 1ChCl/2Urea under standard bench experimental conditions (at room temperature, under air and in the absence of co-catalysts) by using a new iminophosphorane-Au(I) complex as the catalyst. Furthermore, the catalytic system could be recycled up to four runs. PMID:25215857

  20. Introducing deep eutectic solvents as biorenewable media for Au(I)-catalysed cycloisomerisation of γ-alkynoic acids: an unprecedented catalytic system.

    PubMed

    Rodríguez-Álvarez, María J; Vidal, Cristian; Díez, Josefina; García-Álvarez, Joaquín

    2014-11-01

    Cycloisomerisation of γ-alkynoic acids into cyclic enol-lactones was conveniently performed, for the first time, in the eutectic mixture 1ChCl/2Urea under standard bench experimental conditions (at room temperature, under air and in the absence of co-catalysts) by using a new iminophosphorane-Au(I) complex as the catalyst. Furthermore, the catalytic system could be recycled up to four runs.

  1. Enhancement of the catalytic activity of ferulic acid decarboxylase from Enterobacter sp. Px6-4 through random and site-directed mutagenesis.

    PubMed

    Lee, Hyunji; Park, Jiyoung; Jung, Chaewon; Han, Dongfei; Seo, Jiyoung; Ahn, Joong-Hoon; Chong, Youhoon; Hur, Hor-Gil

    2015-11-01

    The enzyme ferulic acid decarboxylase (FADase) from Enterobacter sp. Px6-4 catalyzes the decarboxylation reaction of lignin monomers and phenolic compounds such as p-coumaric acid, caffeic acid, and ferulic acid into their corresponding 4-vinyl derivatives, that is, 4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol, respectively. Among various ferulic acid decarboxylase enzymes, we chose the FADase from Enterobacter sp. Px6-4, whose crystal structure is known, and produced mutants to enhance its catalytic activity by random and site-directed mutagenesis. After three rounds of sequential mutations, FADase(F95L/D112N/V151I) showed approximately 34-fold higher catalytic activity than wild-type for the production of 4-vinylguaiacol from ferulic acid. Docking analyses suggested that the increased activity of FADase(F95L/D112N/V151I) could be due to formation of compact active site compared with that of the wild-type FADase. Considering the amount of phenolic compounds such as lignin monomers in the biomass components, successfully bioengineered FADase(F95L/D112N/V151I) from Enterobacter sp. Px6-4 could provide an ecofriendly biocatalytic tool for producing diverse styrene derivatives from biomass.

  2. Enhancement of the catalytic activity of ferulic acid decarboxylase from Enterobacter sp. Px6-4 through random and site-directed mutagenesis.

    PubMed

    Lee, Hyunji; Park, Jiyoung; Jung, Chaewon; Han, Dongfei; Seo, Jiyoung; Ahn, Joong-Hoon; Chong, Youhoon; Hur, Hor-Gil

    2015-11-01

    The enzyme ferulic acid decarboxylase (FADase) from Enterobacter sp. Px6-4 catalyzes the decarboxylation reaction of lignin monomers and phenolic compounds such as p-coumaric acid, caffeic acid, and ferulic acid into their corresponding 4-vinyl derivatives, that is, 4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol, respectively. Among various ferulic acid decarboxylase enzymes, we chose the FADase from Enterobacter sp. Px6-4, whose crystal structure is known, and produced mutants to enhance its catalytic activity by random and site-directed mutagenesis. After three rounds of sequential mutations, FADase(F95L/D112N/V151I) showed approximately 34-fold higher catalytic activity than wild-type for the production of 4-vinylguaiacol from ferulic acid. Docking analyses suggested that the increased activity of FADase(F95L/D112N/V151I) could be due to formation of compact active site compared with that of the wild-type FADase. Considering the amount of phenolic compounds such as lignin monomers in the biomass components, successfully bioengineered FADase(F95L/D112N/V151I) from Enterobacter sp. Px6-4 could provide an ecofriendly biocatalytic tool for producing diverse styrene derivatives from biomass. PMID:26059194

  3. Three-phase catalytic system of H2O, ionic liquid, and VOPO4-SiO2 solid acid for conversion of fructose to 5-hydroxymethylfurfural.

    PubMed

    Tian, Chengcheng; Zhu, Xiang; Chai, Song-Hai; Wu, Zili; Binder, Andrew; Brown, Suree; Li, Lin; Luo, Huimin; Guo, Yanglong; Dai, Sheng

    2014-06-01

    Efficient transformation of biomass-derived feedstocks to chemicals and fuels remains a daunting challenge in utilizing biomass as alternatives to fossil resources. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam (VPO-MCF), is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural (HMF). HMF is a promising, versatile building block for production of value-added chemicals and transportation fuels. The essence of this three-phase system lies in enabling the isolation of the solid-acid catalyst from the aqueous phase and regulation of its local environment by using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). This system significantly inhibits the side reactions of HMF with H2O and leads to 91 mol % selectivity to HMF at 89 % of fructose conversion. The unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled and locally regulated microenvironment near catalytically active sites by using a hydrophobic ionic liquid. PMID:24729382

  4. Three-phase catalytic system of H2O, ionic liquid, and VOPO4-SiO2 solid acid for conversion of fructose to 5-hydroxymethylfurfural.

    PubMed

    Tian, Chengcheng; Zhu, Xiang; Chai, Song-Hai; Wu, Zili; Binder, Andrew; Brown, Suree; Li, Lin; Luo, Huimin; Guo, Yanglong; Dai, Sheng

    2014-06-01

    Efficient transformation of biomass-derived feedstocks to chemicals and fuels remains a daunting challenge in utilizing biomass as alternatives to fossil resources. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam (VPO-MCF), is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural (HMF). HMF is a promising, versatile building block for production of value-added chemicals and transportation fuels. The essence of this three-phase system lies in enabling the isolation of the solid-acid catalyst from the aqueous phase and regulation of its local environment by using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). This system significantly inhibits the side reactions of HMF with H2O and leads to 91 mol % selectivity to HMF at 89 % of fructose conversion. The unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled and locally regulated microenvironment near catalytically active sites by using a hydrophobic ionic liquid.

  5. Novel Dextranase Catalyzing Cycloisomaltooligosaccharide Formation and Identification of Catalytic Amino Acids and Their Functions Using Chemical Rescue Approach*

    PubMed Central

    Kim, Young-Min; Kiso, Yoshiaki; Muraki, Tomoe; Kang, Min-Sun; Nakai, Hiroyuki; Saburi, Wataru; Lang, Weeranuch; Kang, Hee-Kwon; Okuyama, Masayuki; Mori, Haruhide; Suzuki, Ryuichiro; Funane, Kazumi; Suzuki, Nobuhiro; Momma, Mitsuru; Fujimoto, Zui; Oguma, Tetsuya; Kobayashi, Mikihiko; Kim, Doman; Kimura, Atsuo

    2012-01-01

    A novel endodextranase from Paenibacillus sp. (Paenibacillus sp. dextranase; PsDex) was found to mainly produce isomaltotetraose and small amounts of cycloisomaltooligosaccharides (CIs) with a degree of polymerization of 7–14 from dextran. The 1,696-amino acid sequence belonging to the glycosyl hydrolase family 66 (GH-66) has a long insertion (632 residues; Thr451–Val1082), a portion of which shares identity (35% at Ala39–Ser1304 of PsDex) with Pro32–Ala755 of CI glucanotransferase (CITase), a GH-66 enzyme that catalyzes the formation of CIs from dextran. This homologous sequence (Val837–Met932 for PsDex and Tyr404–Tyr492 for CITase), similar to carbohydrate-binding module 35, was not found in other endodextranases (Dexs) devoid of CITase activity. These results support the classification of GH-66 enzymes into three types: (i) Dex showing only dextranolytic activity, (ii) Dex catalyzing hydrolysis with low cyclization activity, and (iii) CITase showing CI-forming activity with low dextranolytic activity. The fact that a C-terminal truncated enzyme (having Ala39–Ser1304) has 50% wild-type PsDex activity indicates that the C-terminal 392 residues are not involved in hydrolysis. GH-66 enzymes possess four conserved acidic residues (Asp189, Asp340, Glu412, and Asp1254 of PsDex) of catalytic candidates. Their amide mutants decreased activity (11,500 to 140,000 times), and D1254N had 36% activity. A chemical rescue approach was applied to D189A, D340G, and E412Q using α-isomaltotetraosyl fluoride with NaN3. D340G or E412Q formed a β- or α-isomaltotetraosyl azide, respectively, strongly indicating Asp340 and Glu412 as a nucleophile and acid/base catalyst, respectively. Interestingly, D189A synthesized small sized dextran from α-isomaltotetraosyl fluoride in the presence of NaN3. PMID:22461618

  6. Catalytic role of Cu(II) in the reduction of Cr(VI) by citric acid under an irradiation of simulated solar light.

    PubMed

    Li, Ying; Chen, Cheng; Zhang, Jing; Lan, Yeqing

    2015-05-01

    The catalytic role of Cu(II) in the reduction of Cr(VI) by citric acid with simulated solar light was investigated. The results demonstrated that Cu(II) could significantly accelerate Cr(VI) reduction and the reaction obeyed to pseudo zero-order kinetics with respect to Cr(VI). The removal of Cr(VI) was related to the initial concentrations of Cu(II), citric acid, and the types of organic acids. The optimal removal of Cr(VI) was achieved at pH 4, and the rates of Cu(II) photocatalytic reduction of Cr(VI) by organic acids were in the order: tartaric acid (two α-OH groups, two -COOH groups)>citric acid (one α-OH group, three -COOH groups)>malic acid (one α-OH group, two -COOH groups)>lactic acid (one α-OH group, one -COOH group)≫succinic acid (two -COOH groups), suggesting that the number of α-OH was the key factor for the reaction, followed by the number of -COOH. The formation of Cu(II)-citric acid complex could generate Cu(I) and radicals through a pathway of metal-ligand-electron transfer, promoting the reduction of Cr(VI). This study is helpful to fully understanding the conversion of Cr(VI) in the existence of both organic acids and Cu(II) with solar light in aquatic environments.

  7. Catalytic performance of Fe3O4-CoO/Al2O3 catalyst in ozonation of 2-(2,4-dichlorophenoxy)propionic acid, nitrobenzene and oxalic acid in water.

    PubMed

    Tong, Shaoping; Shi, Rui; Zhang, Hua; Ma, Chunan

    2010-01-01

    Fe3O4-CoO/Al2O3 catalyst was prepared by incipient wetness impregnation using Fe(NO3)3 x 9H2O and Co(NO3)2 x 6H2O as the precursors, and its catalytic performance was investigated in ozonation of 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), nitrobenzene and oxalic acid. The experimental results indicated that Fe3O4-CoO/Al2O3 catalyst enabled an interesting improvement of ozonation efficiency during the degradation of each organic pollutant, and the Fe3O4-CoO/Al2O3 catalytic ozonation system followed a radical-type mechanism. The kinetics of ozonation alone and Fe3O4-CoO/Al2O3 catalytic ozonation of three organic pollutants in aqueous solution were discussed under the mere consideration of direct ozone reaction and OH radical reaction to well investigate its performance. In the catalytic ozonation of 2,4-DP, the apparent reaction rate constants (k) were determined to be 1.456 x 10(-2) min(-1) for ozonation alone and 4.740 x 10(-2) min(-1) for O3/Fe3O4-CoO/Al203. And O3/Fe3O4-CoO/Al2O3 had a larger R(ct) (6.614 x 10(-9)) calculated by the relative method than O3 did (1.800 x 10(-9)), showing O3/Fe3O4-CoO/Al2O3 generated more hydroxyl radical. Similar results were also obtained in the catalytic ozonation of nitrobenzene and oxalic acid. The above results demonstrated that the catalytic performance of Fe3O4-CoO/Al2O3 in ozonation of studied organic substance was universal to a certain degree. PMID:21235195

  8. Green diesel production via catalytic hydrogenation/decarboxylation of triglycerides and fatty acids of vegetable oil and brown grease

    NASA Astrophysics Data System (ADS)

    Sari, Elvan

    than activated carbon itself for both decarboxylation of oleic acid and hydrogenation of alkenes. In an additional effort to reduce Pd amount in the catalyst, Pd2Co/C catalysts with various Pd content were prepared and the catalytic activity study showed that 0.5 wt% Pd2Co/C catalyst performs even better than a 5 wt% Pd/C catalyst. Pd and Co alloys were very well dispersed and formed fine clusters, which led to a higher active metal surface area and hence favored the decarboxylation of oleic acid. This study showed that an alloy of Pd on carbon with a significantly low Pd content is much more active and selective to diesel hydrocarbons production from an unsaturated fatty acid in super-critical water and may be regarded as a prospective feasible decarboxylation catalyst for the removal of oxygen from vegetable oil/animal fat without the need of additional hydrogen.

  9. Structure and catalytic activities of ferrous centers confined on the interface between carbon nanotubes and humic acid

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Zhou, Xiaoyan; Wang, Dongqi; Yin, Jun-Jie; Chen, Hanqing; Gao, Xingfa; Zhang, Jing; Ibrahim, Kurash; Chai, Zhifang; Feng, Weiyue; Zhao, Yuliang

    2015-01-01

    Preparation of heterogeneous catalysts with active ferrous centers is of great significance for industrial and environmental catalytic processes. Nanostructured carbon materials (NCM), which possess free-flowing π electrons, can coordinate with transition metals, provide a confinement environment for catalysis, and act as potential supports or ligands to construct analogous complexes. However, designing such catalysts using NCM is still seldom studied to date. Herein, we synthesized a sandwich structured ternary complex via the coordination of Fe-loaded humic acid (HA) with C&z.dbd;C bonds in the aromatic rings of carbon nanotubes (CNTs), in which the O/N-Fe-C interface configuration provides the confinement environment for the ferrous sites. The experimental and theoretical results revealed octahedrally/tetrahedrally coordinated geometry at Fe centers, and the strong hybridization between CNT C π* and Fe 3d orbitals induces discretization of the atomic charges on aromatic rings of CNTs, which facilitates O2 adsorption and electron transfer from carbon to O2, which enhances O2 activation. The O2 activation by the novel HA/Fe-CNT complex can be applied in the oxidative degradation of phenol red (PR) and bisphenol A (BPA) in aqueous media.Preparation of heterogeneous catalysts with active ferrous centers is of great significance for industrial and environmental catalytic processes. Nanostructured carbon materials (NCM), which possess free-flowing π electrons, can coordinate with transition metals, provide a confinement environment for catalysis, and act as potential supports or ligands to construct analogous complexes. However, designing such catalysts using NCM is still seldom studied to date. Herein, we synthesized a sandwich structured ternary complex via the coordination of Fe-loaded humic acid (HA) with C&z.dbd;C bonds in the aromatic rings of carbon nanotubes (CNTs), in which the O/N-Fe-C interface configuration provides the confinement environment for the

  10. Conformational Itinerary of Pseudomonas aeruginosa 1,6-Anhydro-N-acetylmuramic Acid Kinase during Its Catalytic Cycle*

    PubMed Central

    Bacik, John-Paul; Tavassoli, Marjan; Patel, Trushar R.; McKenna, Sean A.; Vocadlo, David J.; Khajehpour, Mazdak; Mark, Brian L.

    2014-01-01

    Anhydro-sugar kinases are unique from other sugar kinases in that they must cleave the 1,6-anhydro ring of their sugar substrate to phosphorylate it using ATP. Here we show that the peptidoglycan recycling enzyme 1,6-anhydro-N-acetylmuramic acid kinase (AnmK) from Pseudomonas aeruginosa undergoes large conformational changes during its catalytic cycle, with its two domains rotating apart by up to 32° around two hinge regions to expose an active site cleft into which the substrates 1,6-anhydroMurNAc and ATP can bind. X-ray structures of the open state bound to a nonhydrolyzable ATP analog (AMPPCP) and 1,6-anhydroMurNAc provide detailed insight into a ternary complex that forms preceding an operative Michaelis complex. Structural analysis of the hinge regions demonstrates a role for nucleotide binding and possible cross-talk between the bound ligands to modulate the opening and closing of AnmK. Although AnmK was found to exhibit similar binding affinities for ATP, ADP, and AMPPCP according to fluorescence spectroscopy, small angle x-ray scattering analyses revealed that AnmK adopts an open conformation in solution in the absence of ligand and that it remains in this open state after binding AMPPCP, as we had observed for our crystal structure of this complex. In contrast, the enzyme favored a closed conformation when bound to ADP in solution, consistent with a previous crystal structure of this complex. Together, our findings show that the open conformation of AnmK facilitates binding of both the sugar and nucleotide substrates and that large structural rearrangements must occur upon closure of the enzyme to correctly align the substrates and residues of the enzyme for catalysis. PMID:24362022

  11. Ultrasensitive detection of nucleic acids by template enhanced hybridization followed by rolling circle amplification and catalytic hairpin assembly.

    PubMed

    Song, Weiling; Zhang, Qiao; Sun, Wenbo

    2015-02-11

    An ultrasensitive protocol for fluorescent detection of DNA is designed by combining the template enhanced hybridization process (TEHP) with Rolling Circle Amplification (RCA) and Catalytic Hairpin Assembly (CHA), showing a remarkable amplification efficiency.

  12. Oxidative cleavage of olefins by in situ-generated catalytic 3,4,5,6-tetramethyl-2-iodoxybenzoic acid/oxone.

    PubMed

    Moorthy, Jarugu Narasimha; Parida, Keshaba Nanda

    2014-12-01

    Oxidative cleavage of a variety of olefins to the corresponding ketones/carboxylic acids is shown to occur in a facile manner with 3,4,5,6-tetramethyl-2-iodobenzoic acid (TetMe-IA)/oxone. The simple methodology involves mere stirring of the olefin and catalytic amount (10 mol %) of TetMe-IA and oxone in acetonitrile-water mixture (1:1, v/v) at rt. The reaction mechanism involves initial dihydroxylation of the olefin with oxone, oxidative cleavage by the in situ-generated 3,4,5,6-tetramethyl-2-iodoxybenzoic acid (TetMe-IBX), and oxidation of the aldehyde functionality to the corresponding acid with oxone. Differences in the reactivities of electron-rich and electron-poor double bonds have been exploited to demonstrate chemoselective oxidative cleavage in substrates containing two double bonds.

  13. A structure-based proposal for the catalytic mechanism of the bacterial acid phosphatase AphA belonging to the DDDD superfamily of phosphohydrolases.

    PubMed

    Calderone, Vito; Forleo, Costantino; Benvenuti, Manuela; Thaller, Maria Cristina; Rossolini, Gian Maria; Mangani, Stefano

    2006-01-27

    The Escherichia coli gene aphA codes for a periplasmic acid phosphatase called AphA, belonging to class B bacterial phosphatases, which is part of the DDDD superfamily of phosphohydrolases. After our first report about its crystal structure, we have started a series of crystallographic studies aimed at understanding of the catalytic mechanism of the enzyme. Here, we report three crystal structures of the AphA enzyme in complex with the hydrolysis products of nucleoside monophosphate substrates and a fourth with a proposed intermediate analogue that appears to be covalently bound to the enzyme. Comparison with the native enzyme structure and with the available X-ray structures of different phosphatases provides clues about the enzyme chemistry and allows us to propose a catalytic mechanism for AphA, and to discuss it with respect to the mechanism of other bacterial and human phosphatases.

  14. A highly selective nanogold-aptamer catalytic resonance scattering spectral assay for trace Hg(2+) using HAuCl(4)-ascorbic acid as indicator reaction.

    PubMed

    Jiang, Zhiliang; Wen, Guiqing; Fan, Yanyan; Jiang, Caina; Liu, Qingye; Huang, Zhi; Liang, Aihui

    2010-01-15

    Single strand DNA (ssDNA) was used to modify nanogold to obtain a nanogold-aptamer resonance scattering (RS) probe (NGssDNA) for Hg(2+), based on the formation of stable thymine-Hg(2+)-thymine (T-Hg(2+)-T) mismatches and aggregation of the released nanogold particles. After removing the aggregated particles by filtrate membrane, the excess NGssDNA in the filtration solution exhibit catalytic effect on the gold particle reaction between HAuCl(4) and ascorbic acid (AA) that appear as RS peak at 596nm. When Hg(2+) concentration increased, the RS intensity at 596nm decreased. The decreased intensity is linear to Hg(2+) concentration in the range of 0.00008-0.888ng/mL Hg(2+), with detection limit of 0.000034ng/mL. The nanogold-aptamer catalytic RS assay was applied to determination of Hg(2+) in water with satisfactory results.

  15. Catalytic properties of NiSO{sub 4}/ZrO{sub 2} promoted with Fe{sub 2}O{sub 3} for acid catalysis

    SciTech Connect

    Sohn, Jong Rack . E-mail: jrsohn@knu.ac.kr; Lim, Jun Seob

    2006-07-13

    A series of catalysts, NiSO{sub 4}/Fe{sub 2}O{sub 3}-ZrO{sub 2}, for acid catalysis were prepared by the impregnation method, where support, Fe{sub 2}O{sub 3}-ZrO{sub 2} was prepared by the co-precipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe{sub 2}O{sub 3}-ZrO{sub 2}. The addition of nickel sulfate (or Fe{sub 2}O{sub 3}) to ZrO{sub 2} shifted the phase transition of ZrO{sub 2} from amorphous to tetragonal to higher temperature because of the interaction between nickel sulfate (or Fe{sub 2}O{sub 3}) and ZrO{sub 2}. 15-NiSO{sub 4}/Fe{sub 2}O{sub 3}-ZrO{sub 2} containing 15 wt.% NiSO{sub 4} and 5 mol% Fe{sub 2}O{sub 3}, and calcined at 700 deg. C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe{sub 2}O{sub 3} up to 5 mol% enhanced the acidity, thermal property, and catalytic activities of NiSO{sub 4}/Fe{sub 2}O{sub 3}-ZrO{sub 2} gradually due to the interaction between Fe{sub 2}O{sub 3} and ZrO{sub 2} and consequent formation of Fe-O-Zr bond.

  16. The near-ideal catalytic property of Candida antarctica lipase A to highly concentrate n-3 polyunsaturated fatty acids in monoacylglycerols via one-step ethanolysis of triacylglycerols.

    PubMed

    He, Yongjin; Li, Jingbo; Kodali, Sitharam; Chen, Bilian; Guo, Zheng

    2016-11-01

    Declining quantity/quality of available n-3 polyunsaturated fatty acids (n-3 PUFAs) resources demand innovative technology to concentrate n-3 PUFAs from low quality oils into value-added products/health-beneficial ingredients rich in n-3 PUFAs. This work proposed the catalytic property and specificity of an ideal enzyme required to tackle this task and identified Candida antarctica lipase A (CAL-A) is such a near-ideal enzyme in practice, which concentrates n-3 PUFAs from 25% to 27% in oils to a theoretically closer value 90% in monoacylglycerols (MAGs) via one-step enzymatic ethanolysis. Non-regiospecificity and high non-n-3 PUFAs preference of CAL-A are the catalytic feature to selectively cleave non-n-3 PUFAs in all 3 positions of triacylglycerols (TAGs); while high ethanol/TAGs ratio, low operation temperature and high tolerance to polar ethanol are essential conditions beyond biocatalyst itself. C-13 Nuclear magnetic resonance ((13)C NMR) analysis and competitive factor estimation verified the hypothesis and confirmed the plausible suggestion of catalytic mechanism of CAL-A.

  17. The near-ideal catalytic property of Candida antarctica lipase A to highly concentrate n-3 polyunsaturated fatty acids in monoacylglycerols via one-step ethanolysis of triacylglycerols.

    PubMed

    He, Yongjin; Li, Jingbo; Kodali, Sitharam; Chen, Bilian; Guo, Zheng

    2016-11-01

    Declining quantity/quality of available n-3 polyunsaturated fatty acids (n-3 PUFAs) resources demand innovative technology to concentrate n-3 PUFAs from low quality oils into value-added products/health-beneficial ingredients rich in n-3 PUFAs. This work proposed the catalytic property and specificity of an ideal enzyme required to tackle this task and identified Candida antarctica lipase A (CAL-A) is such a near-ideal enzyme in practice, which concentrates n-3 PUFAs from 25% to 27% in oils to a theoretically closer value 90% in monoacylglycerols (MAGs) via one-step enzymatic ethanolysis. Non-regiospecificity and high non-n-3 PUFAs preference of CAL-A are the catalytic feature to selectively cleave non-n-3 PUFAs in all 3 positions of triacylglycerols (TAGs); while high ethanol/TAGs ratio, low operation temperature and high tolerance to polar ethanol are essential conditions beyond biocatalyst itself. C-13 Nuclear magnetic resonance ((13)C NMR) analysis and competitive factor estimation verified the hypothesis and confirmed the plausible suggestion of catalytic mechanism of CAL-A. PMID:27521783

  18. Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbons: Dilute-Acid and Enzymatic Deconstruction of Biomass to Sugars and Catalytic Conversion of Sugars to Hydrocarbons

    SciTech Connect

    Davis, R.; Tao, L.; Scarlata, C.; Tan, E. C. D.; Ross, J.; Lukas, J.; Sexton, D.

    2015-03-01

    This report describes one potential conversion process to hydrocarbon products by way of catalytic conversion of lignocellulosic-derived hydrolysate. This model leverages expertise established over time in biomass deconstruction and process integration research at NREL, while adding in new technology areas for sugar purification and catalysis. The overarching process design converts biomass to die die diesel- and naphtha-range fuels using dilute-acid pretreatment, enzymatic saccharification, purifications, and catalytic conversion focused on deoxygenating and oligomerizing biomass hydrolysates.

  19. Efficient, chemical-catalytic approach to the production of 3-hydroxypropanoic acid by oxidation of biomass-derived levulinic acid with hydrogen peroxide.

    PubMed

    Wu, Linglin; Dutta, Saikat; Mascal, Mark

    2015-04-13

    3-Hydroxypropanoic acid (HPA), a precursor to acrylic acid, can be produced in high yield by oxidation of the biomass-derived platform chemical levulinic acid. While treatment of levulinic acid with H2 O2 under acidic conditions gives predominantly succinic acid, a remarkable reversal of selectivity is observed under basic conditions, leading either directly to HPA or, under modified conditions, initially to 3-(hydroperoxy)propanoic acid, which can be quantitatively hydrogenated to HPA. PMID:25736835

  20. Catalytically Important Residues of E6AP Ubiquitin Ligase Identified Using Acid-Cleavable Photo-Cross-Linkers.

    PubMed

    Krist, David T; Statsyuk, Alexander V

    2015-07-28

    Inactivation of the E6AP E3 ubiquitin ligase (UBE3A gene) causes Angelman syndrome, while aberrant degradation of p53 by E6AP is implicated in cervical cancers. Herein, we describe the development of photo-cross-linkers to discover catalytic residues of E6AP. Using these cross-linkers, we identified covalent modifications of the E6AP catalytic cysteine and two lysines: Lys(847) and Lys(799). Lys(847) is required for the formation of Lys(48)-linked polyubiquitin chains, while the K799A E6AP mutant was more active at producing Lys(48)-linked polyubiquitin chains. Thus, opposing roles of Lys(799) and Lys(847) pave the path forward to pharmacological inhibitors or activators of E6AP for therapeutic purposes. PMID:26161728

  1. The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain

    PubMed Central

    Mysling, Simon; Kristensen, Kristian Kølby; Larsson, Mikael; Beigneux, Anne P; Gårdsvoll, Henrik; Fong, Loren G; Bensadouen, André; Jørgensen, Thomas JD; Young, Stephen G; Ploug, Michael

    2016-01-01

    GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL•GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1•LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity by mitigating the global unfolding of LPL's catalytic domain. This study provides a conceptual framework for understanding intravascular lipolysis and GPIHBP1 and LPL mutations causing familial chylomicronemia. DOI: http://dx.doi.org/10.7554/eLife.12095.001 PMID:26725083

  2. Implementing a two-layer feed-forward catalytic DNA circuit for enzyme-free and colorimetric detection of nucleic acids.

    PubMed

    Ravan, Hadi

    2016-03-01

    In the present study, a highly sensitive and specific bio-sensing platform for enzyme-free and colorimetric detection of nucleic acids has been developed. The biosensor is composed of two DNA nanostructures and two fuel strands that construct the foundation of a feed-forward catalytic DNA circuit. Upon binding the target strand to a specific DNA nanostructure, the circuit is run in order that at the end a hemin-binding aptamer, with the ability to convert a colorless substrate into a colored substance is released. Based on this strategy, 4 pM of the target DNA can be easily detected in serum samples by naked eyes after only a two-hour incubation with the circuit; meanwhile, if the incubation time is extended to 3 h, the biosensor can detect 1 pM of the target DNA. Besides the elevated sensitivity, the circuit can truly discriminate a spurious target containing one nucleotide mismatch with high specificity. Overall, the enzyme-free catalytic DNA circuit can be used as a sensitive alternative method to enzyme-based biosensors for the specific and cost-effective detection of nucleic acids.

  3. Highly catalytic hollow palladium nanoparticles derived from silver@silver-palladium core-shell nanostructures for the oxidation of formic acid

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Cui, Penglei; He, Hongyan; Liu, Hui; Yang, Jun

    2014-12-01

    Hollow Palladium (hPd) nanoparticles (NPs) are prepared via a simple and mild successive method. Firstly, core-shell NPs with silver (Ag) cores and silver-palladium (Ag-Pd) alloy shells are synthesized in aqueous phase by galvanic replacement reaction (GRR) between Ag NPs and Pd2+ ion precursors. Saturated aqueous sodium chloride (NaCl) solution was then employed to remove the Ag component from the core and shell regions of core-shell Ag@Ag-Pd NPs, resulting in the formation of hPd NPs with shrunk sizes in comparison with their core-shell parents. Specifically, the hPd NPs exhibit superior catalytic activity and durability for catalyzing the oxidation of formic acid, compared with the Pd NPs reduced by NaBH4 in aqueous solution and commercial Pd/C catalyst from Johnson Matthey, mainly due to the large electrochemically active surface areas of the hollow particles. In addition, The Ag component in core-shell Ag@Ag-Pd NPs has an unfavorable influence on catalytic activity of NPs for formic acid oxidation. However, the durability could be improved due to the electron donating effect from Ag to Pd atoms in the core-shell NPs.

  4. The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain.

    PubMed

    Mysling, Simon; Kristensen, Kristian Kølby; Larsson, Mikael; Beigneux, Anne P; Gårdsvoll, Henrik; Fong, Loren G; Bensadouen, André; Jørgensen, Thomas Jd; Young, Stephen G; Ploug, Michael

    2016-01-01

    GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL•GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1•LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity by mitigating the global unfolding of LPL's catalytic domain. This study provides a conceptual framework for understanding intravascular lipolysis and GPIHBP1 and LPL mutations causing familial chylomicronemia. PMID:26725083

  5. The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain.

    PubMed

    Mysling, Simon; Kristensen, Kristian Kølby; Larsson, Mikael; Beigneux, Anne P; Gårdsvoll, Henrik; Fong, Loren G; Bensadouen, André; Jørgensen, Thomas Jd; Young, Stephen G; Ploug, Michael

    2016-01-03

    GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL•GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1•LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity by mitigating the global unfolding of LPL's catalytic domain. This study provides a conceptual framework for understanding intravascular lipolysis and GPIHBP1 and LPL mutations causing familial chylomicronemia.

  6. Chemoselective Catalytic Oxidation of 1,2-Diols to α-Hydroxy Acids Controlled by TEMPO-ClO2 Charge-Transfer Complex.

    PubMed

    Furukawa, Keisuke; Shibuya, Masatoshi; Yamamoto, Yoshihiko

    2015-05-01

    Chemoselective catalytic oxidation from 1,2-diols to α-hydroxy acids in a cat. TEMPO/cat. NaOCl/NaClO2 system has been achieved. The use of a two-phase condition consisting of hydrophobic toluene and water suppresses the concomitant oxidative cleavage. A study of the mechanism suggests that the observed selectivity is derived from the precise solubility control of diols and hydroxy acids as well as the active species of TEMPO. Although the oxoammonium species TEMPO(+)Cl(-) is hydrophilic, the active species dissolves into the organic layer by the formation of the charge-transfer (CT) complex TEMPO-ClO2 under the reaction conditions.

  7. Chemoselective Catalytic Oxidation of 1,2-Diols to α-Hydroxy Acids Controlled by TEMPO-ClO2 Charge-Transfer Complex.

    PubMed

    Furukawa, Keisuke; Shibuya, Masatoshi; Yamamoto, Yoshihiko

    2015-05-01

    Chemoselective catalytic oxidation from 1,2-diols to α-hydroxy acids in a cat. TEMPO/cat. NaOCl/NaClO2 system has been achieved. The use of a two-phase condition consisting of hydrophobic toluene and water suppresses the concomitant oxidative cleavage. A study of the mechanism suggests that the observed selectivity is derived from the precise solubility control of diols and hydroxy acids as well as the active species of TEMPO. Although the oxoammonium species TEMPO(+)Cl(-) is hydrophilic, the active species dissolves into the organic layer by the formation of the charge-transfer (CT) complex TEMPO-ClO2 under the reaction conditions. PMID:25886211

  8. Catalytic coal liquefaction process

    DOEpatents

    Garg, D.; Sunder, S.

    1986-12-02

    An improved process for catalytic solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a solvent comprises using as catalyst a mixture of a 1,2- or 1,4-quinone and an alkaline compound, selected from ammonium, alkali metal, and alkaline earth metal oxides, hydroxides or salts of weak acids. 1 fig.

  9. Catalytic coal liquefaction process

    DOEpatents

    Garg, Diwakar; Sunder, Swaminathan

    1986-01-01

    An improved process for catalytic solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a solvent comprises using as catalyst a mixture of a 1,2- or 1,4-quinone and an alkaline compound, selected from ammonium, alkali metal, and alkaline earth metal oxides, hydroxides or salts of weak acids.

  10. Enhancement of chitosan-graphene oxide SPR sensor with a multi-metallic layers of Au-Ag-Au nanostructure for lead(II) ion detection

    NASA Astrophysics Data System (ADS)

    Kamaruddin, Nur Hasiba; Bakar, Ahmad Ashrif A.; Yaacob, Mohd Hanif; Mahdi, Mohd Adzir; Zan, Mohd Saiful Dzulkefly; Shaari, Sahbudin

    2016-01-01

    We demonstrate the enhancement of surface plasmon resonance (SPR) technique by implementing a multi-metallic layers of Au-Ag-Au nanostructure in the chitosan-graphene oxide (CS-GO) SPR sensor for lead(II) ion detection. The performance of the sensor is analyzed via SPR measurements, from which the sensitivity, signal-to-noise ratio and repeatability are determined. The nanostructure layers are characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). We showed that the proposed structure has increased the shift in the SPR angle up to 3.5° within the range of 0.1-1 ppm due to the enhanced evanescent field at the sensing layer-analyte interface. This sensor also exhibits great repeatability which benefits from the stable multi-metallic nanostructure. The SNR value of 0.92 for 5 ppm lead(II) ion solution and reasonable linearity range up to that concentration shows that the tri-metallic CS-GO SPR sensor gives a good response towards the lead(II) ion solution. The CS-GO SPR sensor is also sensitive to at least a 10-5 change in the refractive index. The results prove that our proposed tri-metallic CS-GO SPR sensor demonstrates a strong performance and reliability for lead(II) ion detection in accordance with the standardized lead safety level for wastewater.

  11. Converting Transaldolase into Aldolase through Swapping of the Multifunctional Acid-Base Catalyst: Common and Divergent Catalytic Principles in F6P Aldolase and Transaldolase.

    PubMed

    Sautner, Viktor; Friedrich, Mascha Miriam; Lehwess-Litzmann, Anja; Tittmann, Kai

    2015-07-28

    Transaldolase (TAL) and fructose-6-phosphate aldolase (FSA) both belong to the class I aldolase family and share a high degree of structural similarity and sequence identity. The molecular basis of the different reaction specificities (transferase vs aldolase) has remained enigmatic. A notable difference between the active sites is the presence of either a TAL-specific Glu (Gln in FSA) or a FSA-specific Tyr (Phe in TAL). Both residues seem to have analoguous multifunctional catalytic roles but are positioned at different faces of the substrate locale. We have engineered a TAL double variant (Glu to Gln and Phe to Tyr) with an active site resembling that of FSA. This variant indeed exhibits aldolase activity as its main activity with a catalytic efficiency even larger than that of authentic FSA, while TAL activity is greatly impaired. Structural analysis of this variant in complex with the dihydroxyacetone Schiff base formed upon substrate cleavage identifies the introduced Tyr (genuine in FSA) to catalyze protonation of the central carbanion-enamine intermediate as a key determinant of the aldolase reaction. Our studies pinpoint that the Glu in TAL and the Tyr in FSA, although located at different positions at the active site, similarly act as bona fide acid-base catalysts in numerous catalytic steps, including substrate binding, dehydration of the carbinolamine, and substrate cleavage. We propose that the different spatial positions of the multifunctional Glu in TAL and of the corresponding multifunctional Tyr in FSA relative to the substrate locale are critically controlling reaction specificity through either unfavorable (TAL) or favorable (FSA) geometry of proton transfer onto the common carbanion-enamine intermediate. The presence of both potential acid-base residues, Glu and Tyr, in the active site of TAL has deleterious effects on substrate binding and cleavage, most likely resulting from a differently organized H-bonding network. Large-scale motions of the

  12. The role of acidic sites and the catalytic reaction pathways on the Rh/ZrO2 catalysts for ethanol steam reforming.

    PubMed

    Zhong, Ziyi; Ang, Hanwee; Choong, Catherine; Chen, Luwei; Huang, Lin; Lin, Jianyi

    2009-02-01

    Rh catalysts supported on ZrO(2)-based oxides were studied for ethanol steam reforming (SR) reaction. Pure ZrO(2) as the support resulted in higher H(2) production yield compared to the ZrO(2) oxide decorated with CeO(2), Al(2)O(3), La(2)O(3) or Li(2)O at the reaction temperature of 300 degrees C. Above 450 degrees C, all the catalysts exhibited similar catalytic activity. However, at low reaction temperatures (below 400 degrees C), a significant enhancement in the catalytic activity, selectivity and stability was achieved by replacing the ZrO(2) support prepared by a precipitation method (ZrO(2)-CP) with that prepared by a hydrothermal method (ZrO(2)-HT). A deactivation was observed during the EtOH SR reaction at 300 degrees C on the two catalysts of Rh/ZrO(2)-CP and Rh/ZrO(2)-HT. NH(3)-TPD experiments confirmed that the ZrO(2)-HT support had two types of acidic sites while the ZrO(2)-CP support had only one type of weak acidic sites. DRIFTS studies showed that the absorption of EtOH molecules was strong on the Rh/ZrO(2)-HT catalyst and a number of C(2) oxygenates were accumulated on the catalyst surface. Meanwhile, the EtOH absorption on the Rh/ZrO(2)-CP catalyst was weak and the accumulation of CO, carbonate and CH(x) was observed. It is concluded that the relatively strong Lewis acidic sites in the Rh/ZrO(2)-HT catalyst is responsible for the strong absorption of EtOH molecules, and the subsequent C-H breakage step (formation of acetaldehyde or called as dehydrogenation reaction) is a fast reaction on it; on the Rh/ZrO(2)-CP catalyst, the EtOH adsorption was weak and the C-C breakage was the dominating reaction which led to the accumulation of surface CO, CH(x) and CO(2) species. Therefore, it is believed that, in order to promote the absorption of EtOH molecules and to reduce the formation of metastable carbonaceous species (C(2) oxygenates) during the reaction, the catalyst should be enhanced both with Lewis acidity and with C-C bond breakage function. Also

  13. Increased Crystalline Cellulose Activity via Combinations of Amino Acid Changes in the Family 9 Catalytic Domain and Family 3c Cellulose Binding Module of Thermobifida fusca Cel9A ▿

    PubMed Central

    Li, Yongchao; Irwin, Diana C.; Wilson, David B.

    2010-01-01

    Amino acid modifications of the Thermobifida fusca Cel9A-68 catalytic domain or carbohydrate binding module 3c (CBM3c) were combined to create enzymes with changed amino acids in both domains. Bacterial crystalline cellulose (BC) and swollen cellulose (SWC) assays of the expressed and purified enzymes showed that three combinations resulted in 150% and 200% increased activity, respectively, and also increased synergistic activity with other cellulases. Several other combinations resulted in drastically lowered activity, giving insight into the need for a balance between the binding in the catalytic cleft on either side of the cleavage site, as well as coordination between binding affinity for the catalytic domain and CBM3c. The same combinations of amino acid variants in the whole enzyme, Cel9A-90, did not increase BC or SWC activity but did have higher filter paper (FP) activity at 12% digestion. PMID:20173060

  14. Reducing NO(x) emissions from a nitric acid plant of domestic petrochemical complex: enhanced conversion in conventional radial-flow reactor of selective catalytic reduction process.

    PubMed

    Abbasfard, Hamed; Hashemi, Seyed Hamid; Rahimpour, Mohammad Reza; Jokar, Seyyed Mohammad; Ghader, Sattar

    2013-01-01

    The nitric acid plant of a domestic petrochemical complex is designed to annually produce 56,400 metric tons (based on 100% nitric acid). In the present work, radial-flow spherical bed reactor (RFSBR) for selective catalytic reduction of nitric oxides (NO(x)) from the stack of this plant was modelled and compared with the conventional radial-flow reactor (CRFR). Moreover, the proficiency of a radial-flow (water or nitrogen) membrane reactor was also compared with the CRFR which was found to be inefficient at identical process conditions. In the RFSBR, the space between the two concentric spheres is filled by a catalyst. A mathematical model, including conservation of mass has been developed to investigate the performance of the configurations. The model was checked against the CRFR in a nitric acid plant located at the domestic petrochemical complex. A good agreement was observed between the modelling results and the plant data. The effects of some important parameters such as pressure and temperature on NO(x) conversion were analysed. Results show 14% decrease in NO(x) emission annually in RFSBR compared with the CRFR, which is beneficial for the prevention of NO(x) emission, global warming and acid rain.

  15. In situ FTIR spectroscopic assessment of methylbutynol catalytic conversion products in relation to the surface acid-base properties of systematically modified aluminas

    NASA Astrophysics Data System (ADS)

    Mekhemer, Gamal A. H.; Zaki, Mohamed I.

    2016-10-01

    The present investigation was designed to assess the credibility of methylbutynol (MBOH) as an infrared (IR) reactive probe molecule for surface acid-base properties of metal oxides. Accordingly, pure alumina was systematically modified with varied amounts (0.5-10 wt.%) of K+ or SO42 - additives. Then, the influence of nature and amount of the additive on the following alumina properties were examined: (i) bulk composition and structure by X-ray powder diffractometry and ex-situ IR spectroscopy, (ii) surface area and net charge by N2 sorptiometry and pH-metry, respectively, and (iii) nature and strength of exposed surface acid sites by in-situ IR spectroscopy of adsorbed pyridine at ambient and higher temperatures. Results obtained were correlated with IR-identified product distribution of MBOH catalytic decomposition/conversion at 200 °C. It is thereby concluded that MBOH is superior to conventional IR inactive probe molecules in gauging sensitively the prevailing acid or base character, availability of base sites, relative population of Bronsted to Lewis acid sites, and strength and reactivity of the sites exposed on metal oxide surfaces. Hence, all that is needed to get this information is to handle IR spectra taken from the gas phase, a task that is experimentally much more accessible than taking spectra from adsorbed species of irreactive probe molecules.

  16. Reducing NO(x) emissions from a nitric acid plant of domestic petrochemical complex: enhanced conversion in conventional radial-flow reactor of selective catalytic reduction process.

    PubMed

    Abbasfard, Hamed; Hashemi, Seyed Hamid; Rahimpour, Mohammad Reza; Jokar, Seyyed Mohammad; Ghader, Sattar

    2013-01-01

    The nitric acid plant of a domestic petrochemical complex is designed to annually produce 56,400 metric tons (based on 100% nitric acid). In the present work, radial-flow spherical bed reactor (RFSBR) for selective catalytic reduction of nitric oxides (NO(x)) from the stack of this plant was modelled and compared with the conventional radial-flow reactor (CRFR). Moreover, the proficiency of a radial-flow (water or nitrogen) membrane reactor was also compared with the CRFR which was found to be inefficient at identical process conditions. In the RFSBR, the space between the two concentric spheres is filled by a catalyst. A mathematical model, including conservation of mass has been developed to investigate the performance of the configurations. The model was checked against the CRFR in a nitric acid plant located at the domestic petrochemical complex. A good agreement was observed between the modelling results and the plant data. The effects of some important parameters such as pressure and temperature on NO(x) conversion were analysed. Results show 14% decrease in NO(x) emission annually in RFSBR compared with the CRFR, which is beneficial for the prevention of NO(x) emission, global warming and acid rain. PMID:24527652

  17. Preparation of porous palladium nanowire arrays and their catalytic performance for hydrogen peroxide electroreduction in acid medium

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Ye, Ke; Gao, Yinyi; Zhang, Hongyu; Cheng, Kui; Xiao, Xue; Wang, Guiling; Cao, Dianxue

    2016-01-01

    Nanoporous palladium supported on the carbon coated titanium carbide (C@TiC) nanowire arrays (Pd NP/C@TiC) are successfully prepared by a facile chemical vapor deposition of three-dimensional (3D) C@TiC substrate, followed by electrochemical codeposition of Pd-Ni and removal of Ni via dealloying. The structure and morphology of the obtained Pd NP/C@TiC electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) are used to examine the catalytic performances of the electrodes for H2O2 electroreduction in H2SO4 solution. The Pd NP/C@TiC electrode exhibits a largely effective specific surface area owing to its open nanoporous structure allowing the full utilization of Pd surface active sites. At the potential of 0.2 V in 2.0 mol L-1 H2O2 and 2 mol L-1 H2SO4 solutions, the reduction current density reaches 3.47 A mg-1, which is significantly higher than the catalytic activity of H2O2 electroreduction achieved previously with precious metals as catalysts.

  18. Catalytic therapy of cancer by ascorbic acid involves redox cycling of exogenous/endogenous copper ions and generation of reactive oxygen species.

    PubMed

    Hadi, S M; Ullah, M F; Shamim, U; Bhatt, S H; Azmi, A S

    2010-01-01

    Catalytic therapy is a cancer treatment modality based on the generation of reactive oxygen species (ROS) through administration of ascorbate/medicinal herbal extracts and copper. It is known that antioxidants such as ascorbate also exhibit prooxidant activity in the presence of transition metals such as copper. Based on our work and that in the literature, in this review we propose a mechanism for the cytotoxic action of ascorbate against cancer cells. It involves redox cycling of exogenous/endogenous copper ions and the consequent generation of ROS leading to oxidative DNA breakage. Using human peripheral lymphocytes and the Comet assay, we have shown that ascorbic acid is able to cause oxidative breakage in cellular DNA. Such DNA degradation is inhibited by neocuproine (a Cu(I) sequestering agent) and scavengers of ROS indicating that the cellular DNA breakage involves the generation of Cu(I) and formation of ROS. Similar results are also obtained with plant polyphenol antioxidants that are important constituents of medicinal herbal extracts. Copper is an essential component of chromatin and can take part in redox reactions. It is well established that tissue, cellular and serum copper levels are considerably elevated in various malignancies. Therefore, cancer cells may be more subject to electron transfer between copper ions and ascorbate/plant polyphenols to generate ROS. In this review we cite evidence to indicate that in catalytic therapy cytotoxic action against cancer cells involves redox cycling of exogenous/endogenous copper ions.

  19. Molecular mechanism for H2 release from BH3NH3, including the catalytic role of the Lewis acid BH3.

    PubMed

    Nguyen, Minh Tho; Nguyen, Vinh Son; Matus, Myrna H; Gopakumar, G; Dixon, David A

    2007-02-01

    Electronic structure calculations using various methods, up to the coupled-cluster CCSD(T) level, in conjunction with the aug-cc-pVnZ basis sets with n = D, T, and Q, extrapolated to the complete basis set limit, show that the borane molecule (BH3) can act as an efficient bifunctional acid-base catalyst in the H2 elimination reactions of XHnYHn systems (X, Y = C, B, N). Such a catalyst is needed as the generation of H2 from isoelectronic ethane and borane amine compounds proceeds with an energy barrier much higher than that of the X-Y bond energy. The asymptotic energy barrier for H2 release is reduced from 36.4 kcal/mol in BH3NH3 to 6.0 kcal/mol with the presence of BH3 relative to the molecular asymptote. The NH3 molecule can also participate in a similar catalytic process but induces a smaller reduction of the energy barrier. The kinetics of these processes was analyzed by both transition-state and RRKM theory. The catalytic effect of BH3 has also been probed by an analysis of the electronic densities of the transition structures using the atom-in-molecule (AIM) and electron localization function (ELF) approaches.

  20. Multifunctional mesoporous materials with acid-base frameworks and ordered channels filled with ionic liquid: Synthesis, characterization and catalytic performance of Ti-Zr-SBA-15-IL

    NASA Astrophysics Data System (ADS)

    Zhang, Wenjuan; Wang, Hua; Han, Jinyu; Song, Zhiqiang

    2012-06-01

    A series of novel multifunctionalized SBA-15 with titanium and zirconium incorporated frameworks and ionic liquid filled ordered channels were synthesized for the first time, by combining framework doping and post-grafting. The as-prepared materials were extensively characterized to investigate the mesostructural and chemical properties. The results indicated that the products possess the periodically ordered mesoporous structure. Titanium and zirconium were efficiently introduced into the framework of the mesostructure, generating medium strong acid and basic sites. N-methylimidazole ionic liquid was covalently grafted into the channels of mesoporous materials. Moreover, a higher cooperative catalytic performance originated from the dual-metal centers and ionic liquid was shown in catalyzing the cycloaddition of carbon dioxide with epoxides. A plausible reaction mechanism was proposed based on the experimental results.

  1. Template-free synthesis of a porous organic-inorganic hybrid tin(IV) phosphonate and its high catalytic activity for esterification of free fatty acids.

    PubMed

    Dutta, Arghya; Patra, Astam K; Uyama, Hiroshi; Bhaumik, Asim

    2013-10-23

    Here we have synthesized an organic-inorganic hybrid mesoporous tin phosphonate monolith (MLSnP-1) with crystalline pore walls by a template-free sol-gel route. N2 sorption analysis shows Brunauer-Emmett-Teller (BET) surface area of 347 m2 g(-1). Wide-angle powder X-ray diffraction (PXRD) pattern shows few broad diffraction peaks indicating crystalline pore wall of the material. High-resolution transmission electron microscopic (HR TEM) image further reveals the crystal fringes on the pore wall. Framework bonding and local environment around phosphorus and carbon were examined by Fourier transform infrared (FT IR) spectroscopy and solid-state MAS NMR spectroscopy. The material exhibits remarkable catalytic activity for esterification of long chain fatty acids under mild reaction conditions at room temperature.

  2. Redox and Lewis acid relay catalysis: a titanocene/zinc catalytic platform in the development of multicomponent coupling reactions.

    PubMed

    Gianino, Joseph B; Campos, Catherine A; Lepore, Antonio J; Pinkerton, David M; Ashfeld, Brandon L

    2014-12-19

    A titanocene-catalyzed multicomponent coupling is described herein. Using catalytic titanocene, phosphine, and zinc dust, zinc acetylides can be generated from the corresponding iodoalkynes to affect sequential nucleophilic additions to aromatic aldehydes. The intermediate propargylic alkoxides are trapped in situ with acetic anhydride, which are susceptible to a second nucleophilic displacement upon treatment with a variety of electron-rich species, including acetylides, allyl silanes, electron-rich aromatics, silyl enol ethers, and silyl ketene acetals. Additionally, employing cyclopropane carboxaldehydes led to ring-opened products resulting from iodine incorporation. Taken together, these results form the basis for a new mode of three-component coupling reactions, which allows for rapid access to value added products in a single synthetic operation.

  3. Investigation of catalytic activity towards oxygen reduction reaction of Pt dispersed on boron doped graphene in acid medium.

    PubMed

    Pullamsetty, Ashok; Sundara, Ramaprabhu

    2016-10-01

    Boron doped graphene was prepared by a facile method and platinum (Pt) decoration over boron doped graphene was done in various chemical reduction methods such as sodium borohydride (NaBH4), polyol and modified polyol. X-ray diffraction analysis indicates that the synthesized catalyst particles are present in a nanocrystalline structure and transmission and scanning electron microscopy were employed to investigate the morphology and particle distribution. The electrochemical properties were investigated with the help of the rotating disk electrode (RDE) technique and cyclic voltammetry. The results show that the oxygen reduction reaction (ORR) takes place by a four-electron process. The kinetics of the ORR was evaluated using K-L and Tafel plots. The electrocatalyst obtained in modified polyol reduction method has shown the better catalytic activity compared to other two electrocatalysts. PMID:27393888

  4. CuFe2O4/activated carbon composite: a novel magnetic adsorbent for the removal of acid orange II and catalytic regeneration.

    PubMed

    Zhang, Gaosheng; Qu, Jiuhui; Liu, Huijuan; Cooper, Adrienne T; Wu, Rongcheng

    2007-06-01

    CuFe2O4/activated carbon magnetic adsorbents, which combined the adsorption features of activated carbon with the magnetic and the excellent catalytic properties of powdered CuFe2O4, were developed using a simple chemical coprecipitation procedure. The prepared magnetic composites can be used to adsorb acid orange II (AO7) in water and subsequently, easily be separated from the medium by a magnetic technique. CuFe2O4/activated carbon magnetic adsorbents with mass ratio of 1:1, 1:1.5 and 1:2 were prepared. Magnetization measurements, BET surface area measurements, powder XRD and SEM were used to characterize the prepared adsorbents. The results indicate that the magnetic phase present is spinel copper ferrite and the presence of CuFe2O4 did not significantly affect the surface area and pore structure of the activated carbon. The adsorption kinetics and adsorption isotherm of acid orange II (AO7) onto the composites at pH 5.2 also showed that the presence of CuFe2O4 did not affect the adsorption capacity of the activated carbon. The thermal decomposition of AO7 adsorbed on the activated carbon and the composite was investigated by in situ FTIR, respectively. The results suggest that the composite has much higher catalytic activity than that of activated carbon, attributed to the presence of CuFe2O4. The variation of the adsorption capacity of the composites after several adsorption-regeneration cycles has also been studied.

  5. Electrocatalytic Transformation of Carbon Dioxide into Low Carbon Compounds on Conducting Polymers Derived from Multimetallic Porphyrins.

    PubMed

    Dreyse, Paulina; Honores, Jessica; Quezada, Diego; Isaacs, Mauricio

    2015-11-01

    The electrochemical reduction of carbon dioxide is studied herein by using conducting polymers based on metallotetraruthenated porphyrins (MTRPs). The polymers on glassy carbon electrodes were obtained by electropolymerization processes of the monomeric MTRP. The linear sweep voltammetry technique resulted in polymeric films that showed electrocatalytic activity toward carbon dioxide reduction with an onset potential of -0.70 V. The reduction products obtained were hydrogen, formic acid, formaldehyde, and methanol, with a tendency for a high production of methanol with a maximum value of turnover frequency equal to 15.07 when using a zinc(II) polymeric surface. Studies of the morphology (AFM) and electrochemical impedance spectroscopy results provide an adequate background to explain that the electrochemical reduction is governed by the roughness of the polymer, for which the possible mechanism involves a series of one-electron reduction reactions.

  6. Histidine-40 of ribonuclease T1 acts as base catalyst when the true catalytic base, glutamic acid-58, is replaced by alanine.

    PubMed

    Steyaert, J; Hallenga, K; Wyns, L; Stanssens, P

    1990-09-25

    Mechanisms for the ribonuclease T1 (RNase T1; EC 3.1.27.3) catalyzed transesterification reaction generally include the proposal that Glu58 and His92 provide general base and general acid assistance, respectively [Heinemann, U., & Saenger, W. (1982) Nature (London) 299, 27-31]. This view was recently challenged by the observation that mutants substituted at position 58 retain high residual activity; a revised mechanism was proposed in which His40, and not Glu58, is engaged in catalysis as general base [Nishikawa, S., Morioka, H., Kim, H., Fuchimura, K., Tanaka, T., Uesugi, S., Hakoshima, T., Tomita, K., Ohtsuka, E., & Ikehara, M. (1987) Biochemistry 26, 8620-8624]. To clarify the functional roles of His40, Glu58, and His92, we analyzed the consequences of several amino acid substitutions (His40Ala, His40Lys, His40Asp, Glu58Ala, Glu58Gln, and His92Gln) on the kinetics of GpC transesterification. The dominant effect of all mutations is on Kcat, implicating His40, Glu58, and His92 in catalysis rather than in substrate binding. Plots of log (Kcat/Km) vs pH for wild-type, His40Lys, and Glu58Ala RNase T1, together with the NMR-determined pKa values of the histidines of these enzymes, strongly support the view that Glu58-His92 acts as the base-acid couple. The curves also show that His40 is required in its protonated form for optimal activity of wild-type enzyme. We propose that the charged His40 participates in electrostatic stabilization of the transition state; the magnitude of the catalytic defect (a factor of 2000) from the His40 to Ala replacement suggests that electrostatic catalysis contributes considerably to the overall rate acceleration. For Glu58Ala RNase T1, the pH dependence of the catalytic parameters suggests an altered mechanism in which His40 and His92 act as base and acid catalyst, respectively. The ability of His40 to adopt the function of general base must account for the significant activity remaining in Glu58-mutated enzymes.

  7. A Process for Microbial Hydrocarbon Synthesis: Overproduction of Fatty Acids in Escherichia coli and Catalytic Conversion to Alkanes

    PubMed Central

    Lennen, Rebecca M.; Braden, Drew J.; West, Ryan M.; Dumesic, James A.; Pfleger, Brian F.

    2013-01-01

    The development of renewable alternatives to diesel and jet fuels is highly desirable for the heavy transportation sector, and would offer benefits over the production and use of short-chain alcohols for personal transportation. Here, we report the development of a metabolically engineered strain of Escherichia coli that overproduces medium-chain length fatty acids via three basic modifications: elimination of β-oxidation, overexpression of the four subunits of acetyl-CoA carboxylase, and expression of a plant acyl–acyl carrier protein (ACP) thioesterase from Umbellularia californica (BTE). The expression level of BTE was optimized by comparing fatty acid production from strains harboring BTE on plasmids with four different copy numbers. Expression of BTE from low copy number plasmids resulted in the highest fatty acid production. Up to a seven-fold increase in total fatty acid production was observed in engineered strains over a negative control strain (lacking β-oxidation), with a composition dominated by C12 and C14 saturated and unsaturated fatty acids. Next, a strategy for producing undecane via a combination of biotechnology and heterogeneous catalysis is demonstrated. Fatty acids were extracted from a culture of an overproducing strain into an alkane phase and fed to a Pd/C plug flow reactor, where the extracted fatty acids were decarboxylated into saturated alkanes. The result is an enriched alkane stream that can be recycled for continuous extractions. Complete conversion of C12 fatty acids extracted from culture to alkanes has been demonstrated yielding a concentration of 0.44 g L−1 (culture volume) undecane. PMID:20073090

  8. An enantioselective strategy for the total synthesis of (S)-tylophorine via catalytic asymmetric allylation and a one-pot DMAP-promoted isocyanate formation/Lewis acid catalyzed cyclization sequence.

    PubMed

    Su, Bo; Zhang, Hui; Deng, Meng; Wang, Qingmin

    2014-06-14

    A new asymmetric total synthesis of a phenanthroindolizidine alkaloid (S)-tylophorine is reported, which features a catalytic asymmetric allylation of aldehydes and an unexpected one-pot DMAP promoted isocyanate formation and Lewis acid catalyzed intramolecular cyclization reaction. In addition, White's direct C-H oxidation catalyst system converting monosubstituted olefins to linear allylic acetates was also employed for late-stage transformation.

  9. Catalytic Upgrading of bio-oil using 1-octene and 1-butanol over sulfonic acid resin catalysts

    SciTech Connect

    Zhang, Zhijun; Wang, Qingwen; Tripathi, Prabhat; Pittman, Charles U.

    2011-02-04

    Raw bio-oil from fast pyrolysis of biomass must be refined before it can be used as a transporation fuel, a petroleum refinery feed or for many other fuel uses. Raw bio-oil was upgraded with the neat model olefin, 1-octene, and with 1-octene/1-butanol mixtures over sulfonic acid resin catalysts frin 80 to 150 degrees celisus in order to simultaneously lower water content and acidity and to increase hydrophobicity and heating value. Phase separation and coke formation were key factors limiting the reaction rate during upgrading with neat 1-octene although octanols were formed by 1-octene hydration along with small amounts of octyl acetates and ethers. GC-MS analysis confirmed that olefin hydration, carboxylic acid esterification, acetal formation from aldehydes and ketones and O- and C-alkylations of phenolic compounds occurred simultaneously during upgrading with 1-octene/1-butanol mixtures. Addition of 1-butanol increased olefin conversion dramatically be reducing mass transfer restraints and serving as a cosolvent or emulsifying agent. It also reacted with carboxylic acids and aldehydes/ketones to form esters, and acetals, respectively, while also serving to stabilize bio-oil during heating. 1-Butanol addition also protected the catalysts, increasing catalyst lifetime and reducing or eliminationg coking. Upgrading sharply increased ester content and decreased the amounts of levoglucosan, polyhydric alcohols and organic acids. Upgrading lowered acidity (pH value rise from 2.5 to >3.0), removed the uppleasant ordor and increased hydrocarbon solubility. Water content decreased from 37.2% to < 7.5% dramatically and calorific value increased from 12.6 MJ kg to about 30.0 MJ kg.

  10. Monolayer structures of niobic acids supported on SiO[sub 2] and their catalytic activities for esterification of acetic acid with ethanol

    SciTech Connect

    Shirai, Masayuki; Asakura, Kiyotaka; Iwasawa, Yasuhiro )

    1991-11-28

    New submonolayer niobic acid catalysts were prepared by the reaction of Nb(OC[sub 2]H[sub 5])[sub 5] with surface OH groups of SiO[sub 2], followed by H[sub 2]O treatment. The surface structures were characterized by means of EXAFS, XRD, XRF, and FT-IR. The niobic acids on SiO[sub 2] up to 8.0 wt % Nb loadings were found to grow in a monolayer mode. These catalysts showed activities 20 times as large as that of a niobic acid bulk catalyst for the esterification of acetic acid with ethanol. The activity was referred to Lewis acid sites in the monolayer structure, which was stable even after evacuation at high temperatures such as 873 K.

  11. The catalytic role of the water or acidic zeolite in the oxidation of BrCH2OH. A theoretical study

    NASA Astrophysics Data System (ADS)

    Papayannis, Demetrios K.; Kosmas, Agnie M.

    2016-11-01

    We present a computational investigation of the catalytic activity of the water molecules or acidic zeolite in the oxidation of bromomethanol, coming from the degradation of brominated organic compounds in the natural environment. The role of the water in this mechanism has been established using MP2(full)/6-311++G(3df, 2p) level of theory. Energetic results were further refined by CCSD(T) calculations, using optimized geometric parameters of the MP2 level. The computational investigation shows clearly the dramatic reduction of the activation energy of the oxidation to formaldehyde that occurs when explicit coordination of water molecules is taken into account. Further investigation of the degradation mechanism has been carried out by considering the oxidation reaction as taking place on acidic zeolite surface, with the help of the hybrid (QM/MM) approximation and specifically the two-layered, ONIOM2 methodology at the (MP2(full)/6-31G∗:UFF) and (M06-2X/6-311++G(3df, 2p):UFF) levels of theory.

  12. Effects of natural water ions and humic acid on catalytic nitrate reduction kinetics using an alumina supported Pd-Cu catalyst.

    PubMed

    Chaplin, Brian P; Roundy, Eric; Guy, Kathryn A; Shapley, John R; Werth, Charles J

    2006-05-01

    Catalytic nitrate reduction was evaluated for the purpose of drinking water treatment. Common anions present in natural waters and humic acid were evaluated for their effects on NO3(-) hydrogenation over a bimetallic supported catalyst (Pd-Cu/gamma-Al2O3). Groundwater samples, with and without powder activated carbon (PAC) pretreatment, were also evaluated. In the absence of inhibitors the NO3- reduction rate was 2.4 x 10(-01) L/min g cat. However, the addition of constituents (SO4(2-), SO3(2-), HS-, CI-, HCO3-, OH-, and humic acid) on the order of representative concentrations for drinking water decreased the NO3- reduction rate. Sulfite, sulfide, and elevated chloride decreased the NO3- reduction rate by over 2 orders of magnitude. Preferential adsorption of Cl- inhibited NO3- reduction to a greater extent than NO2- reduction. Partial regeneration of catalysts exposed to SO3(2-) was achieved by using a dilute hypochlorite solution, however Cu dissolution occurred. Dissolved constituents in the groundwater sample decreased the NO3- reduction rate to 3.7 x 10(-03) L/min g cat and increased ammonia production. Removal of dissolved organic matter from the groundwater using PAC increased the NO3- reduction rate to 5.06 x 10(-02) L/min g cat and decreased ammonia production. Elemental analyses of catalysts exposed to the natural groundwater suggest that mineral precipitation may also contribute to catalyst fouling. PMID:16719114

  13. Identification of amino acids related to catalytic function of Sulfolobus solfataricus P1 carboxylesterase by site-directed mutagenesis and molecular modeling

    PubMed Central

    Choi, Yun-Ho; Lee, Ye-Na; Park, Young-Jun; Yoon, Sung-Jin; Lee, Hee-Bong

    2016-01-01

    The archaeon Sulfolobus solfataricus P1 carboxylesterase is a thermostable enzyme with a molecular mass of 33.5 kDa belonging to the mammalian hormone-sensitive lipase (HSL) family. In our previous study, we purified the enzyme and suggested the expected amino acids related to its catalysis by chemical modification and a sequence homology search. For further validating these amino acids in this study, we modified them using site-directed mutagenesis and examined the activity of the mutant enzymes using spectrophotometric analysis and then estimated by homology modeling and fluorescence analysis. As a result, it was identified that Ser151, Asp244, and His274 consist of a catalytic triad, and Gly80, Gly81, and Ala152 compose an oxyanion hole of the enzyme. In addition, it was also determined that the cysteine residues are located near the active site or at the positions inducing any conformational changes of the enzyme by their replacement with serine residues. [BMB Reports 2016; 49(6): 349-354] PMID:27222124

  14. A molecular dynamics and quantum mechanics/molecular mechanics study of the catalytic reductase mechanism of methionine sulfoxide reductase A: formation and reduction of a sulfenic acid.

    PubMed

    Dokainish, Hisham M; Gauld, James W

    2013-03-12

    The catalytic mechanism of MsrA in Mycobacterium tuberculosis, in which S-methionine sulfoxide (Met-O) is reduced to methionine (Met), has been investigated using docking, molecular dynamics (MD) simulations, and ONIOM (quantum mechanics/molecular mechanics) methods. In addition, the roles of specific active site residues, including an aspartyl (Asp87) near the recycling cysteine, tyrosyls (Tyr44 and Tyr92), and glutamyl (Glu52), have been examined, as well as the general effects of the protein and active site on the nature and properties of mechanistic intermediates. The mechanism is initiated by the transfer of a proton from the catalytic cysteine's thiol (Cys13SH) via a bridging water to the R group carboxylate of Glu52. The now anionic sulfur of Cys13 nucleophilically attacks the substrate's sulfur with concomitant transfer of a proton from Glu52 to the sulfoxide oxygen, generating a sulfurane. The active site enhances the proton affinity of the sulfurane oxygen, which can readily accept a proton from the phenolic hydroxyls of Tyr44 or Tyr92 to give a sulfonium cation. Subsequently, Asp87 and the recycling cysteine (Cys154) can facilitate nucleophilic attack of a solvent water at the Cys13S center of the sulfonium to give a sulfenic acid (Cys13SOH) and Met. For the subsequent reduction of Cys13SOH with intramolecular disulfide bond formation, Asp87 can help facilitate nucleophilic attack of Cys154S at the sulfur of Cys13SOH by deprotonating its thiol. This reduction is found likely to occur readily upon suitable positioning of the active site hydrogen bond network and the sulfur centers of both Cys13 and Cys154. The calculated rate-limiting barrier is in good agreement with experiment.

  15. Mutational analysis defines the roles of conserved amino acid residues in the predicted catalytic pocket of the rRNA:m6A methyltransferase ErmC'.

    PubMed

    Maravić, Gordana; Feder, Marcin; Pongor, Sándor; Flögel, Mirna; Bujnicki, Janusz M

    2003-09-01

    Methyltransferases (MTases) from the Erm family catalyze S-adenosyl-L-methionine-dependent modification of a specific adenine residue in bacterial 23S rRNA, thereby conferring resistance to clinically important macrolide, lincosamide and streptogramin B antibiotics. Despite the available structural data and functional analyses on the level of the RNA substrate, still very little is known about the mechanism of rRNA:adenine-N(6) methylation. Only predictions regarding various aspects of this reaction have been made based on the analysis of the crystal structures of methyltransferase ErmC' (without the RNA) and their comparison with the crystallographic and biochemical data for better studied DNA:m(6)A MTases. To validate the structure-based predictions of presumably essential residues in the catalytic pocket of ErmC', we carried out the site-directed mutagenesis and studied the function of the mutants in vitro and in vivo. Our results indicate that the active site of rRNA:m(6)A MTases is much more tolerant to amino acid substitutions than the active site of DNA:m(6)A MTases. Only the Y104 residue implicated in stabilization of the target base was found to be indispensable. Remarkably, the N101 residue from the "catalytic" motif IV and two conserved residues that form the floor (F163) and one of the walls (N11) of the base-binding site are not essential for catalysis in ErmC'. This somewhat surprising result is discussed in the light of the available structural data and in the phylogenetic context of the Erm family. PMID:12946350

  16. Nd(III) and Dy(III) coordination compounds based on 1H-tetrazolate-5-acetic acid ligands: Synthesis, crystal structures and catalytic properties

    SciTech Connect

    Li Qiaoyun; Chen Dianyu; He Minghua; Yang Gaowen; Shen Lei; Zhai Chun; Shen Wei; Gu Kun; Zhao Jingjing

    2012-06-15

    Reactions of 1H-tetrazolate-5-acetic acid(H{sub 2}tza) with Nd(NO{sub 3}){sub 3}{center_dot}6H{sub 2}O or Dy(NO{sub 3}){sub 3}{center_dot}6H{sub 2}O with the presence of KOH under solvothermal conditions, produced two new coordination compounds, [M{sub 2}(tza){sub 3}(H{sub 2}O){sub 6}]{center_dot}2H{sub 2}O [M=Nd(1), Dy(2)]. Both compounds were structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Compounds 1 and 2 reveal 1D structures via bridging tza as linker. Furthermore, the compounds 1 and 2 showed a specific and good catalytic behavior for the polymerization of styrene, and the polymerization showed controlled characteristics. - Graphical Abstract: Two new coordination compounds, [M{sub 2}(tza){sub 3}(H{sub 2}O){sub 6}]{center_dot}2H{sub 2}O [M=Nd(1), Dy(2)] have been synthesis. 1 and 2 reveal 1D structures via bridging tza as linker, and showed a specific and good catalytic behavior for the polymerization of styrene. Highlights: Black-Right-Pointing-Pointer we have reported two novel compounds formed by H{sub 2}tza and Nd(III) or Dy(III). Black-Right-Pointing-Pointer Compounds 1 and 2 were found to have catalysis property for the photo-polymerization of styrene. Black-Right-Pointing-Pointer The high molecular weight polymers with narrow molecular weight distributions were obtained.

  17. Mutational analysis defines the roles of conserved amino acid residues in the predicted catalytic pocket of the rRNA:m6A methyltransferase ErmC'.

    PubMed

    Maravić, Gordana; Feder, Marcin; Pongor, Sándor; Flögel, Mirna; Bujnicki, Janusz M

    2003-09-01

    Methyltransferases (MTases) from the Erm family catalyze S-adenosyl-L-methionine-dependent modification of a specific adenine residue in bacterial 23S rRNA, thereby conferring resistance to clinically important macrolide, lincosamide and streptogramin B antibiotics. Despite the available structural data and functional analyses on the level of the RNA substrate, still very little is known about the mechanism of rRNA:adenine-N(6) methylation. Only predictions regarding various aspects of this reaction have been made based on the analysis of the crystal structures of methyltransferase ErmC' (without the RNA) and their comparison with the crystallographic and biochemical data for better studied DNA:m(6)A MTases. To validate the structure-based predictions of presumably essential residues in the catalytic pocket of ErmC', we carried out the site-directed mutagenesis and studied the function of the mutants in vitro and in vivo. Our results indicate that the active site of rRNA:m(6)A MTases is much more tolerant to amino acid substitutions than the active site of DNA:m(6)A MTases. Only the Y104 residue implicated in stabilization of the target base was found to be indispensable. Remarkably, the N101 residue from the "catalytic" motif IV and two conserved residues that form the floor (F163) and one of the walls (N11) of the base-binding site are not essential for catalysis in ErmC'. This somewhat surprising result is discussed in the light of the available structural data and in the phylogenetic context of the Erm family.

  18. Influence of amino acid replacement at position 198 on catalytic properties of zinc-bound water in human carbonic anhydrase III.

    PubMed

    LoGrasso, P V; Tu, C; Chen, X; Taoka, S; Laipis, P J; Silverman, D N

    1993-06-01

    Carbonic anhydrase III, found predominantly in skeletal muscle, is the least efficient of the mammalian carbonic anhydrases in catalyzing the hydration of CO2. Phenylalanine-198 is located on the hydrophobic side of the active-site cavity with its phenyl ring in the proximity of the catalytically active zinc-bound water. We replaced phenylalanine-198 in human carbonic anhydrase III with seven other amino acids (Ala, Asn, Asp, His, Leu, Tyr, Val) using site-directed mutagenesis. The catalytic properties of these enzymes were determined by stopped-flow spectrophotometry, and the exchange of 18O between CO2 and water was measured by mass spectrometry. All of the mutants had maximal values of kcat/Km for the hydration of CO2 enhanced, and five of the mutants had the pKa of the zinc-bound water increased compared with the wild-type enzyme. The largest effects were observed with the replacement Phe-198-->Asp which increased the maximal kcat/Km 140-fold and increased the pKa of the zinc-bound water from near 5 to 9.2. A Brønsted correlation was observed between log(kcat/Km) for hydration of CO2 and the pKa of the zinc-bound water (correlation coefficient r = 0.92); in addition, this pKa was inversely correlated with hydrophobicity of the residue at 198 (correlation coefficient r = -0.83). A direct correlation between the logarithm of the maximal kcat/Km for hydration and the logarithm of the pH-independent value of Ki for inhibition by cyanate (r = 0.95) indicated that the effect of the mutations at residue 198 occurred in large part by enhancement of the rate of dissociation of the enzyme-bicarbonate complex. PMID:8504098

  19. Hydrogenation of imines catalyzed by trisphosphine-substituted molybdenum and tungsten nitrosyl hydrides and co-catalytic acid.

    PubMed

    Chakraborty, Subrata; Blacque, Olivier; Fox, Thomas; Berke, Heinz

    2014-10-01

    Hydride complexes Mo,W(CO)(NO)H(mer-etp(i)p) (iPr2PCH2CH2)2PPh=etp(i)p) (2 a,b(syn), syn and anti of NO and Ph(etp(i)p) orientions) were prepared and probed in imine hydrogenations together with co-catalytic [H(Et2O)2][B(C6F5)4] (140 °C, 60 bar H2). 2 a,b(syn) were obtained via reduction of syn/anti-Mo,W(NO)Cl3(mer-etp(i)p) and syn,anti-Mo,W(NO)(CO)Cl(mer-etp(i)p). [H(Et2O)2][B(C6F5)4] in THF converted the hydrides into THF complexes syn-[Mo,W(NO)(CO)(etp(i)p)(THF)][B(C6F5)4]. Combinations of the p-substituents of aryl imines p-R(1)C6H4CH=N-p-C6H4R(2) (R(1),R(2)=H,F,Cl,OMe,α-Np) were hydrogenated to amines (maximum initial TOFs of 1960 h(-1) (2 a(syn)) and 740 h(-1) (2 b(syn)) for N-(4-methoxybenzylidene)aniline). An 'ionic hydrogenation' mechanism based on linear Hammett plots (ρ=-10.5, p-substitution on the C-side and ρ=0.86, p-substitution on the N-side), iminium intermediates, linear P(H2) dependence, and DKIE=1.38 is proposed. Heterolytic splitting of H2 followed by 'proton before hydride' transfers are the steps in the ionic mechanism where H2 ligand addition is rate limiting.

  20. Formation and catalytic activity of high molecular weight soluble polymers produced by heating amino acids in a modified sea medium

    NASA Astrophysics Data System (ADS)

    Okihana, Hiroyuki

    1982-06-01

    Eighteen protein amino acids with milk casein composition were heated in a modified sea medium. Marigranules were formed in the precipitates and soluble polymers were formed in the supernatant. Time course of the reaction (ultraviolet spectra, the concentration of metal ions, and the concentration of amino acids in the supernatant) were measured. The time course of the formation of the soluble polymers was also studied by Bio-Gel P-2 column. High molecular weight soluble polymers (HMWSP) were separated from low molecular weight ones by dialysis. It was shown that these polymers catalyzed the dehydrogenation of NADH. These polymers also catalyzed the coupled reaction between dehydrogenation of NADH and reduction of resazurin. This coupled reaction was accelerated by the light.

  1. Improvement of catalytic activity of lipase in the presence of calix[4]arene valeric acid or hydrazine derivative.

    PubMed

    Akoz, Enise; Sayin, Serkan; Kaplan, Selcuk; Yilmaz, Mustafa

    2015-03-01

    Sol-gel encapsulation is a simple but powerful method to enhance the enantioselectivity of lipase-catalyzed transformations in an isooctane/aqueous buffer solution. Candida rugosa lipase was encapsulated according to a sol-gel procedure in the presence and absence of calix[4]arene hydrazine or carboxylic acid derivatives with Fe3O4 magnetic nanoparticles as an additive. The activity of the encapsulated lipases was evaluated for the enantioselective hydrolysis of racemic Naproxen methyl ester and the hydrolysis of p-Nitrophenylpalmitate. The results indicate that the encapsulated lipase without calix[4]arene derivative has lower conversion and enantioselectivity compared to the encapsulated lipase with calix[4]arene derivative. It was found that the calix[4]arene hydrazine and carboxylic acid-based encapsulated lipases have excellent activity and enantioselectivity (E >300) compared to encapsulated lipase without the calix[4]arene derivatives.

  2. Catalytic conversion of xylose and corn stalk into furfural over carbon solid acid catalyst in γ-valerolactone.

    PubMed

    Zhang, Tingwei; Li, Wenzhi; Xu, Zhiping; Liu, Qiyu; Ma, Qiaozhi; Jameel, Hasan; Chang, Hou-min; Ma, Longlong

    2016-06-01

    A novel carbon solid acid catalyst was synthesized by the sulfonation of carbonaceous material which was prepared by carbonization of sucrose using 4-BDS as a sulfonating agent. TEM, N2 adsorption-desorption, elemental analysis, XPS and FT-IR were used to characterize the catalyst. Then, the catalyst was applied for the conversion of xylose and corn stalk into furfural in GVL. The influence of the reaction time, temperature and dosage of catalyst on xylose dehydration were also investigated. The Brønsted acid catalyst exhibited high activity in the dehydration of xylose, with a high furfural yield of 78.5% at 170°C in 30min. What's more, a 60.6% furfural yield from corn stalk was achieved in 100min at 200°C. The recyclability of the sulfonated carbon catalyst was perfect, and it could be reused for 5times without the loss of furfural yields. PMID:26967333

  3. Catalytic conversion of xylose and corn stalk into furfural over carbon solid acid catalyst in γ-valerolactone.

    PubMed

    Zhang, Tingwei; Li, Wenzhi; Xu, Zhiping; Liu, Qiyu; Ma, Qiaozhi; Jameel, Hasan; Chang, Hou-min; Ma, Longlong

    2016-06-01

    A novel carbon solid acid catalyst was synthesized by the sulfonation of carbonaceous material which was prepared by carbonization of sucrose using 4-BDS as a sulfonating agent. TEM, N2 adsorption-desorption, elemental analysis, XPS and FT-IR were used to characterize the catalyst. Then, the catalyst was applied for the conversion of xylose and corn stalk into furfural in GVL. The influence of the reaction time, temperature and dosage of catalyst on xylose dehydration were also investigated. The Brønsted acid catalyst exhibited high activity in the dehydration of xylose, with a high furfural yield of 78.5% at 170°C in 30min. What's more, a 60.6% furfural yield from corn stalk was achieved in 100min at 200°C. The recyclability of the sulfonated carbon catalyst was perfect, and it could be reused for 5times without the loss of furfural yields.

  4. Sulfonic acid resin-catalyzed addition of phenols, carboxylic acids, and water to olefins: Model reactions for catalytic upgrading of bio-oil.

    PubMed

    Zhang, Zhi-Jun; Wang, Qing-Wen; Yang, Xu-Lai; Chatterjee, Sabornie; Pittman, Charles U

    2010-05-01

    Acid-catalyzed 1-octene reactions with phenol and mixtures of phenol with water, acetic acid and 1-butanol were studied as partial bio-oil upgrading models. Bio-oil from fast biomass pyrolysis has poor fuel properties due to the presence of substantial amounts of water, carboxylic acid, phenolic derivatives and other hydroxyl-containing compounds. Additions across olefins offer a route to simultaneously lower water content and acidity while increasing hydrophobicity, stability and heating value. Amberlyst15, Dowex50WX2 and Dowex50WX4 effectively catalyzed phenol O- and C-alkylation from 65 to 120 degrees C, giving high O-alkylation selectivities in the presence of water, acetic acid and 1-butanol. Octanols and dioctyl ethers were formed from water and octyl acetates and phenol acetates from acetic acid. Phenol alkylation slowed in the presence of water. Dowex50WX2 and Dowex50WX4 were more stable in the presence of water than Amberlyst15 and were successfully recycled. Adding 1-butanol to phenol/water/1-octene, gave emulsion-like mixtures which improved phenol conversion and olefin hydration.

  5. Characterization and catalytic performance of heteropoly acid H4SiW12O40 supported on nanoporous materials.

    PubMed

    Chen, Fengxi; Ma, Jiping; Dong, Zhibing; Liu, Rong

    2014-09-01

    Heteropoly acid H4SiW12O40 (SiW) has been supported on different nanoporous materials and characterized by powder X-ray diffraction (XRD), FTIR, HRTEM, N2 physisorption, and thermal analysis. No SiW diffraction peaks are observed after loading 33-50 wt% of SiW on various mesoporous materials (pore size: -30 Å) except for siliceous MCM-48. In contrast, the SiW diffraction peaks appear at 14 wt% loading on zeolite EMT with micropore size of ca. 7.4 x 6.5 Å. Supported SiW retains the Keggin structure on mesopore surface. The cubic mesostructure of MCM-48 is stable while MCM-41 loses its regular hexagonal mesostructure upon loading SiW. Several factors account for different behaviours of various supports, including pore size, curvature of mesopore interface and interaction between SiW and aluminium sites in the framework. The resulting 33-50 wt% SiW/MCM-48 solid acid catalysts have large surface area (- 550 m2/g), regular pore arrangement with uniform pore size (- 25 Å), finely dispersed SiW and good thermal stability. They exhibit significantly improved activity in acid-catalyzed cracking of long-chain hydrocarbons in comparison with bulk SiW and SiW/MCM-41. PMID:25924405

  6. Spectrophotometric determination of nitrite based on its catalytic effect on the oxidation of carminic acid by bromate.

    PubMed

    Manzoori, J L; Sorouraddin, M H; Haji-Shabani, A M

    1998-08-01

    A highly sensitive and selective method is described for the determination of trace amounts of nitrite based on its effect on the oxidation of carminic acid with bromate. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 490 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1.8x10(-1) mol l(-1) H(2)SO(4), 3.8x10(-3) mol l(-1) KBrO(3), and 1.2x10(-4) mol l(-1) carminic acid at 30 degrees C. By using the recommended procedure, the calibration graph was linear from 0.2 to 14 ng ml(-1) of nitrite; the detection limit was 0.04 ng ml(-1); the R.S.D. for six replicate determinations of 6 ng ml(-1) was 1.7%. The method is mostly free from interference, especially from large amounts of nitrate and ammonium ions. The proposed method was applied to the determination of nitrite in rain and river water. PMID:18967267

  7. Spectrophotometric determination of nitrite based on its catalytic effect on the oxidation of carminic acid by bromate.

    PubMed

    Manzoori, J L; Sorouraddin, M H; Haji-Shabani, A M

    1998-08-01

    A highly sensitive and selective method is described for the determination of trace amounts of nitrite based on its effect on the oxidation of carminic acid with bromate. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 490 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1.8x10(-1) mol l(-1) H(2)SO(4), 3.8x10(-3) mol l(-1) KBrO(3), and 1.2x10(-4) mol l(-1) carminic acid at 30 degrees C. By using the recommended procedure, the calibration graph was linear from 0.2 to 14 ng ml(-1) of nitrite; the detection limit was 0.04 ng ml(-1); the R.S.D. for six replicate determinations of 6 ng ml(-1) was 1.7%. The method is mostly free from interference, especially from large amounts of nitrate and ammonium ions. The proposed method was applied to the determination of nitrite in rain and river water.

  8. Correlating Acid Properties and Catalytic Function: A First-Principles Analysis of Alcohol Dehydration Pathways on Polyoxometalates

    SciTech Connect

    Janik, Michael J.; Macht, Josef; Iglesia, Enrique; Neurock, Matthew

    2009-02-05

    Density functional theory calculations and reactivity data were used to examine the mechanism of alcohol dehydration on Keggin-type polyoxometalate (POM) catalysts and the influence of the POM composition and the degree of substitution of the alcohol on kinetically relevant elimination steps. Dehydration was found to proceed through E1 pathways in which the alcohol CsO bond is cleaved heterolytically via a carbeniumion transition state. Dehydration rates were found to depend on the elimination rate constant and the equilibrium constant for the formation of unreactive alcohol dimers. E2-type elimination transition states, involving concerted CsH and CsO bond cleavage, were not found. The extent of substitution at the R-carbon on the alcohol was found to lead to marked effects on elimination barriers, because substitution increases the proton affinity of the alcohol and the stability of the carbenium-ion transition state. Changes in the central and addenda atoms of the POM cluster and the presence of n-donors, a support, vicinal POM clusters, or charge-compensating cations were found to lead to changes in the deprotonation energy (DPE) of the POM cluster, activation barriers to dehydration, and the stability of the unreactive dimer. These effects are all captured in a general linear relation between activation barriers and deprotonation energy, a rigorous measure of acid strength. The explicit dependence of the E1 activation barrier on the acid deprotonation energy is much weaker than that on reactant proton affinity. This results from the more effective compensation between the acid deprotonation energy and the interaction energy between the cationic hydrocarbon fragment and the anionic POM cluster at the transition state. The direct interactions between the POM protons and the support, other POM clusters, n-donors, base probe molecules, and charge-compensating cations increased the negative charge of the oxide shell of the W12O40 conjugate base, which increased the

  9. Green diesel production via catalytic hydrogenation/decarboxylation of triglycerides and fatty acids of vegetable oil and brown grease

    NASA Astrophysics Data System (ADS)

    Sari, Elvan

    Increase in the petroleum prices, projected increases in the world's energy demand and environmental awareness have shifted the research interest to the alternative fuel technologies. In particular, green diesel, vegetable oil/animal fat/waste oil and grease derived hydrocarbons in diesel boiling range, has become an attractive alternative to biodiesel---a mixture of fatty acid methyl esters, particularly due to its superior fuel properties that are similar to petroleum diesel. Hence, green diesel can be used as a drop-in fuel in the current diesel engines. The current technology for production of green diesel-hydrodeoxygenation of triglycerides and fatty acids over conventional hydrotreating catalysts suffers from fast catalyst deactivation in the absence of hydrogen combined with high temperatures and high fatty acid content in the feedstock. Additionally, excess hydrogen requirement for hydrodeoxygenation technique leads to high production costs. This thesis proposes a new technology-selective decarboxylation of brown grease, which is a mixture of fats and oils collected from waste water trap and rich in fatty acids, over a supported noble metal catalyst that overcomes the green diesel production challenges. In contrast to other feedstocks used for liquid biofuel production, brown grease is inexpensive and non-food competing feedstock, therefore the process finds solution to waste management issues, reduces the renewable fuel production cost and does not add to the global food shortage problems. Special catalyst formulations were developed to have a high activity and stability in the absence of hydrogen in the fatty acid decarboxylation process. The study shows how catalyst innovations can lead to a new technology that overcomes the process challenges. First, the effect of reaction parameters on the activity and the selectivity of brown grease decarboxylation with minimum hydrogen consumption over an activated carbon supported palladium catalyst were

  10. Purification of biomass-derived 5-hydroxymethylfurfural and its catalytic conversion to 2,5-furandicarboxylic Acid.

    PubMed

    Yi, Guangshun; Teong, Siew Ping; Li, Xiukai; Zhang, Yugen

    2014-08-01

    A simple and effective water extraction method is presented for the purification 5-hydroxylmethylfurfural (HMF) obtained from a biomass dehydration system. Up to 99% of the HMF can be recovered and the HMF in aqueous solution is directly converted to 2,5-furandicarboxylic acid (FDCA) as the sole product. This purification technique allows an integrated process to produce FDCA from fructose via HMF prepared in an isopropanol monophasic system, with an overall FDCA yield of 83% obtained. From Jerusalem raw artichoke biomass to FDCA via HMF prepared in a water/MIBK (methyl isobutyl ketone) biphasic system, an overall FDCA yield of 55% is obtained. PMID:24889713

  11. An efficient combination of Zr-MOF and microwave irradiation in catalytic Lewis acid Friedel-Crafts benzoylation.

    PubMed

    Doan, Tan L H; Dao, Thong Q; Tran, Hai N; Tran, Phuong H; Le, Thach N

    2016-05-01

    A zirconium-based metal-organic framework, an effective heterogeneous catalyst, has been developed for the Friedel-Crafts benzoylation of aromatic compounds under microwave irradiation. Constructed by a Zr(iv) cluster and a linker 1,4-bis(2-[4-carboxyphenyl]ethynyl)benzene (H2CPEB), the MOF, possessing large pores and high chemical stability, was appropriate for the enhancement of Lewis acid activity under microwave irradiation. The reaction studies demonstrated that the material could give high yields for a few minutes and maintain its reactivity and structure over several cycles. PMID:27064371

  12. Direct catalytic trifluoromethylthiolation of boronic acids and alkynes employing electrophilic shelf-stable N-(trifluoromethylthio)phthalimide.

    PubMed

    Pluta, Roman; Nikolaienko, Pavlo; Rueping, Magnus

    2014-02-01

    A new and safe method for the synthesis of N-(trifluoromethylthio)phthalimide, a convenient and shelf-stable reagent for the direct trifluoromethylthiolation, has been developed. N-(Trifluoromethylthio)phthalimide can be used as an electrophilic source of F3 CS(+) and reacts readily with boronic acids and alkynes under copper catalysis. The utility of CF3 S-containing molecules as biologically active agents, the mild reaction conditions employed, and the high tolerance of functional groups demonstrate the potential of this new methodology to be widely applied in organic synthesis as well as industrial pharmaceutical and agrochemical research and development. PMID:24449094

  13. Enhancing photo-catalytic production of organic acids in the cyanobacterium S ynechocystis sp. PCC 6803 Δ glg C , a strain incapable of glycogen storage

    SciTech Connect

    Carrieri, Damian; Broadbent, Charlie; Carruth, David; Paddock, Troy; Ungerer, Justin; Maness, Pin-Ching; Ghirardi, Maria; Yu, Jianping

    2015-01-23

    We describe how a key objective in microbial biofuels strain development is to maximize carbon flux to target products while minimizing cell biomass accumulation, such that ideally the algae and bacteria would operate in a photo-catalytic state. A brief period of such a physiological state has recently been demonstrated in the cyanobacterium Synechocystis sp. PCC 6803 ΔglgC strain incapable of glycogen storage. When deprived of nitrogen, the ΔglgC excretes the organic acids alpha-ketoglutarate and pyruvate for a number of days without increasing cell biomass. This study examines the relationship between the growth state and the photo-catalytic state, and characterizes the metabolic adaptability of the photo-catalytic state to increasing light intensity. It is found that the culture can transition naturally from the growth state into the photo-catalytic state when provided with limited nitrogen supply during the growth phase. Photosynthetic capacity and pigments are lost over time in the photo-catalytic state. Reversal to growth state is observed with re-addition of nitrogen nutrient, accompanied by restoration of photosynthetic capacity and pigment levels in the cells. While the overall productivity increased under high light conditions, the ratio of alpha-ketoglutarate/pyruvate is altered, suggesting that carbon partition between the two products is adaptable to environmental conditions.

  14. Catalytic activity of acid and base with different concentration on sol-gel kinetics of silica by ultrasonic method.

    PubMed

    Das, R K; Das, M

    2015-09-01

    The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol-gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln1/ΔT] vs ln(t), indicate two region - nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol-gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy.

  15. Catalytic activity of acid and base with different concentration on sol-gel kinetics of silica by ultrasonic method.

    PubMed

    Das, R K; Das, M

    2015-09-01

    The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol-gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln1/ΔT] vs ln(t), indicate two region - nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol-gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy. PMID:25600993

  16. Insights into the Role of Humic Acid on Pd-catalytic Electro-Fenton Transformation of Toluene in Groundwater

    PubMed Central

    Liao, Peng; Al-Ani, Yasir; Malik Ismael, Zainab; Wu, Xiaohui

    2015-01-01

    A recently developed Pd-based electro-Fenton (E-Fenton) process enables efficient in situ remediation of organic contaminants in groundwater. In the process, H2O2, Fe(II), and acidic conditions (~pH 3) are produced in situ to facilitate the decontamination, but the role of ubiquitous natural organic matters (NOM) remain unclear. This study investigated the effect of Aldrich humic acid (HA) on the transformation of toluene by the Pd-based E-Fenton process. At pH 3 with 50 mA current, the presence of HA promoted the efficiency of toluene transformation, with pseudo-first-order rate constants increase from 0.01 to 0.016 as the HA concentration increases from 0 to 20 mg/L. The HA-enhanced toluene transformation was attributed to the accelerated thermal reduction of Fe(III) to Fe(II), which led to production of more hydroxyl radicals. The correlation of the rate constants of toluene transformation and HA decomposition validated hydroxyl radical (·OH) as the predominant reactive species for HA decomposition. The finding of this study highlighted that application of the novel Pd-based E-Fenton process in groundwater remediation may not be concerned by the fouling from humic substances. PMID:25783864

  17. Insights into the role of humic acid on Pd-catalytic electro-Fenton transformation of toluene in groundwater.

    PubMed

    Liao, Peng; Al-Ani, Yasir; Malik Ismael, Zainab; Wu, Xiaohui

    2015-01-01

    A recently developed Pd-based electro-Fenton (E-Fenton) process enables efficient in situ remediation of organic contaminants in groundwater. In the process, H₂O₂, Fe(II), and acidic conditions (~pH 3) are produced in situ to facilitate the decontamination, but the role of ubiquitous natural organic matters (NOM) remain unclear. This study investigated the effect of Aldrich humic acid (HA) on the transformation of toluene by the Pd-based E-Fenton process. At pH 3 with 50 mA current, the presence of HA promoted the efficiency of toluene transformation, with pseudo-first-order rate constants increase from 0.01 to 0.016 as the HA concentration increases from 0 to 20 mg/L. The HA-enhanced toluene transformation was attributed to the accelerated thermal reduction of Fe(III) to Fe(II), which led to production of more hydroxyl radicals. The correlation of the rate constants of toluene transformation and HA decomposition validated hydroxyl radical (·OH) as the predominant reactive species for HA decomposition. The finding of this study highlighted that application of the novel Pd-based E-Fenton process in groundwater remediation may not be concerned by the fouling from humic substances.

  18. Molecular dynamics simulations of formamide interaction with hydrocyanic acid on a catalytic surface TiO2

    NASA Astrophysics Data System (ADS)

    Artoshina, O. V.; Vorob'eva, M. Yu.; Dushanov, E. B.; Kholmurodov, Kh. T.

    2014-06-01

    The behavior of water—formamide and hydrocyanic acid—formamide solutions on an anatase surface have been studied using molecular dynamics (MD) simulation method. The interaction activation energies have been estimated for the temperature range from 250 up to 400 K. The diffusion coefficients and structural radial distribution functions have been calculated for the formamide, water and hydrocyanic acid on an anatase surface. The calculated activation energies of the water—formamide—anatase and hydrocyanic acid—formamide—anatase systems were analyzed and compared. A comparative analysis of the systems under investigation was performed and a possible correlation between the obtained MD results and the molecular mechanism involving the formamide's interaction with dioxide titan adsorbing surface were discussed.

  19. Ellagic acid and polyhydroxylated urolithins are potent catalytic inhibitors of human topoisomerase II: an in vitro study.

    PubMed

    Furlanetto, Valentina; Zagotto, Giuseppe; Pasquale, Riccardo; Moro, Stefano; Gatto, Barbara

    2012-09-12

    Ellagic acid (EA), a natural polyphenol abundant in fruits and common in our diet, is under intense investigation for its chemopreventive activity resulting from multiple effects. EA inhibits topoisomerase II, but the effects on the human enzyme of urolithins, its monolactone metabolites, are not known. Therefore, the action of several synthetic urolithins toward topoisomerases II was evaluated, showing that polyhydroxylated urolithins, EA, and EA-related compounds are potent inhibitors of the α and β isoforms of human topoisomerase II at submicromolar concentrations. Competition tests demonstrate a dose-dependent relationship between ATP and the inhibition of the enzyme. Docking experiments show that the active compounds bind the ATP pocket of the human enzyme, thus supporting the hypothesis that EA and polyhydroxylated urolithins act as ATP-competitive inhibitors of human topoisomerase II.

  20. Comparative Modeling and Molecular Dynamics Simulation of Substrate Binding in Human Fatty Acid Synthase: Enoyl Reductase and β-Ketoacyl Reductase Catalytic Domains

    PubMed Central

    John, Arun; Krishnakumar, Subramanian

    2015-01-01

    Fatty acid synthase (FASN, EC 2.3.1.85), is a multi-enzyme dimer complex that plays a critical role in lipogenesis. This lipogenic enzyme has gained importance beyond its physiological role due to its implications in several clinical conditions-cancers, obesity, and diabetes. This has made FASN an attractive pharmacological target. Here, we have attempted to predict the theoretical models for the human enoyl reductase (ER) and β-ketoacyl reductase (KR) domains based on the porcine FASN crystal structure, which was the structurally closest template available at the time of this study. Comparative modeling methods were used for studying the structure-function relationships. Different validation studies revealed the predicted structures to be highly plausible. The respective substrates of ER and KR domains-namely, trans-butenoyl and β-ketobutyryl-were computationally docked into active sites using Glide in order to understand the probable binding mode. The molecular dynamics simulations of the apo and holo states of ER and KR showed stable backbone root mean square deviation trajectories with minimal deviation. Ramachandran plot analysis showed 96.0% of residues in the most favorable region for ER and 90.3% for the KR domain, respectively. Thus, the predicted models yielded significant insights into the substrate binding modes of the ER and KR catalytic domains and will aid in identifying novel chemical inhibitors of human FASN that target these domains. PMID:25873848

  1. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation

    NASA Astrophysics Data System (ADS)

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-05-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

  2. High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism.

    PubMed

    Zhang, Shuangshuang; Yu, Jun; Li, Huiying; Mao, Dongsen; Lu, Guanzhong

    2016-09-13

    Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg(2+)-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C-O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface.

  3. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

    PubMed

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-05-20

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

  4. High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism

    PubMed Central

    Zhang, Shuangshuang; Yu, Jun; Li, Huiying; Mao, Dongsen; Lu, Guanzhong

    2016-01-01

    Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg2+-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C–O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface. PMID:27619990

  5. High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism

    NASA Astrophysics Data System (ADS)

    Zhang, Shuangshuang; Yu, Jun; Li, Huiying; Mao, Dongsen; Lu, Guanzhong

    2016-09-01

    Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg2+-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C–O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface.

  6. High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism.

    PubMed

    Zhang, Shuangshuang; Yu, Jun; Li, Huiying; Mao, Dongsen; Lu, Guanzhong

    2016-01-01

    Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg(2+)-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C-O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface. PMID:27619990

  7. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation

    PubMed Central

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-01-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method. PMID:27198855

  8. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

    PubMed

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-01-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method. PMID:27198855

  9. A catalytic triad is responsible for acid-base chemistry in the Ascaris suum NAD-malic enzyme.

    PubMed

    Karsten, William E; Liu, Dali; Rao, G S Jagannatha; Harris, Ben G; Cook, Paul F

    2005-03-01

    The pH dependence of kinetic parameters of several active site mutants of the Ascaris suum NAD-malic enzyme was investigated to determine the role of amino acid residues likely involved in catalysis on the basis of three-dimensional structures of malic enzyme. Lysine 199 is positioned to act as the general base that accepts a proton from the 2-hydroxyl of malate during the hydride transfer step. The pH dependence of V/K(malate) for the K199R mutant enzyme reveals a pK of 5.3 for an enzymatic group required to be unprotonated for activity and a second pK of 6.3 that leads to a 10-fold loss in activity above the pK of 6.3 to a new constant value up to pH 10. The V profile for K199R is pH independent from pH 5.5 to pH 10 and decreases below a pK of 4.9. Tyrosine 126 is positioned to act as the general acid that donates a proton to the enolpyruvate intermediate to form pyruvate. The pH dependence of V/K(malate) for the Y126F mutant is qualitatively similar to K199R, with a requirement for a group to be unprotonated for activity with a pK of 5.6 and a partial activity loss of about 3-fold above a pK of 6.7 to a new constant value. The Y126F mutant enzyme is about 60000-fold less active than the wild-type enzyme. In contrast to K199R, the V rate profile for Y126F also shows a partial activity loss above pH 6.6. The wild-type pH profiles were reinvestigated in light of the discovery of the partial activity change for the mutant enzymes. The wild-type V/K(malate) pH-rate profile exhibits the requirement for a group to be unprotonated for catalysis with a pK of 5.6 and also shows the partial activity loss above a pK of 6.4. The wild-type V pH-rate profile decreases below a pK of 5.2 and is pH independent from pH 5.5 to pH 10. Aspartate 294 is within hydrogen-bonding distance to K199 in the open and closed forms of malic enzyme. D294A is about 13000-fold less active than the wild-type enzyme, and the pH-rate profile for V/K(malate) indicates the mutant is only active above p

  10. [Surface-active agents from the group of polyoxyethylated glycerol esters of fatty acids. Part II. Chromatographic analysis and basic viscosity parameters as a estimate criterion of efficiency of catalytic oxyethylation of Lard's fractions (Adeps suillus FP VII)].

    PubMed

    Piotrowska, Jowita Barbara; Nachajski, Michał Jakub; Lukosek, Marek; Kosno, Jacek; Zgoda, Marian Mikołaj

    2011-01-01

    The catalytic oxyethylation products of Lard's fractions and Tweens--as a reference products, were analised by chromatographic analysis HPLC and GPC. The above part was determination average molecular weights dispersion (Mw I Mn) and the content of polyethylene glycols (PEG), which are obtained during catalytic oxyethylation, and determination iodine value of the product (L(J2)). Viscosity measurements were carried out by Ubelohde method and enabled determination of basic viscosity and hydrodynamic parameters. The obtained results indicate that, comparing reference products--polysorbates, Tweens, products of triglycerides oxyethylation contain significantly less, in some cases very small amount of polyethylene glycols (PEG), and also maintained a high amount of unsaturated fatty acids (oleic acid), which is proven by the iodine value. Numerical value n(s) /H2O/ confirms important disparity of micells palisad structure, which are created based on oxyethylated triglycerides nTE = 40. That indicates significant solubilization possibilities of their aqueous solutions Cexp < or = Cmc.

  11. Dimension and bridging ligand effects on Mo-mediated catalytic transformation of dinitrogen to ammonia: Chain-like extended models of Nishibayashi’s catalyst

    DOE PAGESBeta

    Sheng, Xiao -Lan; Batista, Enrique Ricardo; Duan, Yi -Xiang; Tian, Yong -Hui

    2016-09-20

    Previous studies suggested that in Nishibayashi’s homogenous catalytic systems based on molybdenum (Mo) complexes, the bimetallic structure facilitated dinitrogen to ammonia conversion in comparison to the corresponding monometallic complexes, likely due to the through-bond interactions between the two Mo centers. However, more detailed model systems are necessary to support this bimetallic hypothesis, and to elucidate the multi-metallic effects on the catalytic mechanism. In this work, we computationally examined the effects of dimension as well as the types of bridging ligands on the catalytic activities of molybdenum-dinitrogen complexes by using a set of extended model systems based on Nishibayashi’s bimetallic structure.more » The polynuclear chains containing four ([Mo]4) or more Mo centers were found to drastically enhance the catalytic performance by comparing with both the monometallic and bimetallic complexes. Carbide ([:C≡C:]2–) was found to be a more effective bridging ligand than N2 in terms of electronic charges dispersion between metal centers thereby facilitating reactions in the catalytic cycle. Furthermore, the mechanistic modelling suggests that in principle, more efficient catalytic system for N2 to NH3 transformation might be obtained by extending the polynuclear chain to a proper size in combination with an effective bridging ligand for charge dispersion.« less

  12. [Preparation of Cu/ZrO2/S2O8(2-)/gamma-Al2O3 solid acid catalyst and its catalytic activity to selective reduction of NO].

    PubMed

    Guo, Xi-kun; Wang, Xiao-ming

    2008-06-01

    Cu/ZrO2/S2O8(2-)/gamma-Al2O3 solid acid catalyst was prepared by loading of (NH4)2S2O8, ZrOCl2, and Cu(NO3)2 onto gamma-Al2O3 step by step, which was obtained from calcining of pseudoboehmite. The catalytic property of Cu/ZrO2/S2O8(2-)/gamma-Al2O3 on the selective reduction of NO by C3H6 in excess oxygen was investigated. The relationship between the structure and the catalytic property of Cu/ZrO2/S2O8(2-)/gamma-Al2O3 catalyst was also explored by means of SEM, XRD, Py-IR and TPR. The experimental results of catalytic activity of the title catalyst indicated that the maximum conversion rate of NO could reach 82.9% in the absence of water and was up to 80.2% even in the presence of 10% water vapor. The results of the structural characterization toward the catalyst showed that S2O8(2-) and ZrO2 could restrain the sinteration of gamma-Al2O3 particles and the formation of CuAl2O4 spinelle, and also facilitate the formation of new acidic sites (Brönsted acid) and the enhance of the acidity on the surface of the catalyst. In addition, ZrO2 could increase the reducibility of Cu on the catalyst. Consequently, the catalytic activity and hydrothermal stability of the catalyst were improved effectively.

  13. Structural and catalytic effects of an invariant purine substitution in the hammerhead ribozyme: implications for the mechanism of acid-base catalysis.

    PubMed

    Schultz, Eric P; Vasquez, Ernesto E; Scott, William G

    2014-09-01

    The hammerhead ribozyme catalyzes RNA cleavage via acid-base catalysis. Whether it does so by general acid-base catalysis, in which the RNA itself donates and abstracts protons in the transition state, as is typically assumed, or by specific acid-base catalysis, in which the RNA plays a structural role and proton transfer is mediated by active-site water molecules, is unknown. Previous biochemical and crystallographic experiments implicate an invariant purine in the active site, G12, as the general base. However, G12 may play a structural role consistent with specific base catalysis. To better understand the role of G12 in the mechanism of hammerhead catalysis, a 2.2 Å resolution crystal structure of a hammerhead ribozyme from Schistosoma mansoni with a purine substituted for G12 in the active site of the ribozyme was obtained. Comparison of this structure (PDB entry 3zd4), in which A12 is substituted for G, with three previously determined structures that now serve as important experimental controls, allows the identification of structural perturbations that are owing to the purine substitution itself. Kinetic measurements for G12 purine-substituted schistosomal hammerheads confirm a previously observed dependence of rate on the pK(a) of the substituted purine; in both cases inosine, which is similar to G in pK(a) and hydrogen-bonding properties, is unexpectedly inactive. Structural comparisons indicate that this may primarily be owing to the lack of the exocyclic 2-amino group in the G12A and G12I substitutions and its structural effect upon both the nucleotide base and phosphate of A9. The latter involves the perturbation of a previously identified and well characterized metal ion-binding site known to be catalytically important in both minimal and full-length hammerhead ribozyme sequences. The results permit it to be suggested that G12 plays an important role in stabilizing the active-site structure. This result, although not inconsistent with the potential

  14. Two D-2-hydroxy-acid dehydrogenases in Arabidopsis thaliana with catalytic capacities to participate in the last reactions of the methylglyoxal and beta-oxidation pathways.

    PubMed

    Engqvist, Martin; Drincovich, María F; Flügge, Ulf-Ingo; Maurino, Verónica G

    2009-09-11

    The Arabidopsis thaliana locus At5g06580 encodes an ortholog to Saccharomyces cerevisiae d-lactate dehydrogenase (AtD-LDH). The recombinant protein is a homodimer of 59-kDa subunits with one FAD per monomer. A substrate screen indicated that AtD-LDH catalyzes the oxidation of d- and l-lactate, d-2-hydroxybutyrate, glycerate, and glycolate using cytochrome c as an electron acceptor. AtD-LDH shows a clear preference for d-lactate, with a catalytic efficiency 200- and 2000-fold higher than that for l-lactate and glycolate, respectively, and a K(m) value for d-lactate of approximately 160 microm. Knock-out mutants showed impaired growth in the presence of d-lactate or methylglyoxal. Collectively, the data indicated that the protein is a d-LDH that participates in planta in the methylglyoxal pathway. Web-based bioinformatic tools revealed the existence of a paralogous protein encoded by locus At4g36400. The recombinant protein is a homodimer of 61-kDa subunits with one FAD per monomer. A substrate screening revealed highly specific d-2-hydroxyglutarate (d-2HG) conversion in the presence of an organic cofactor with a K(m) value of approximately 580 microm. Thus, the enzyme was characterized as a d-2HG dehydrogenase (AtD-2HGDH). Analysis of knock-out mutants demonstrated that AtD-2HGDH is responsible for the total d-2HGDH activity present in A. thaliana. Gene coexpression analysis indicated that AtD-2HGDH is in the same network as several genes involved in beta-oxidation and degradation of branched-chain amino acids and chlorophyll. It is proposed that AtD-2HGDH participates in the catabolism of d-2HG most probably during the mobilization of alternative substrates from proteolysis and/or lipid degradation.

  15. Catalytic reactor

    SciTech Connect

    Aaron, Timothy Mark; Shah, Minish Mahendra; Jibb, Richard John

    2009-03-10

    A catalytic reactor is provided with one or more reaction zones each formed of set(s) of reaction tubes containing a catalyst to promote chemical reaction within a feed stream. The reaction tubes are of helical configuration and are arranged in a substantially coaxial relationship to form a coil-like structure. Heat exchangers and steam generators can be formed by similar tube arrangements. In such manner, the reaction zone(s) and hence, the reactor is compact and the pressure drop through components is minimized. The resultant compact form has improved heat transfer characteristics and is far easier to thermally insulate than prior art compact reactor designs. Various chemical reactions are contemplated within such coil-like structures such that as steam methane reforming followed by water-gas shift. The coil-like structures can be housed within annular chambers of a cylindrical housing that also provide flow paths for various heat exchange fluids to heat and cool components.

  16. The catalytic subunit of the system L1 amino acid transporter (slc7a5) facilitates nutrient signalling in mouse skeletal muscle.

    PubMed

    Poncet, Nadège; Mitchell, Fiona E; Ibrahim, Adel F M; McGuire, Victoria A; English, Grant; Arthur, J Simon C; Shi, Yun-Bo; Taylor, Peter M

    2014-01-01

    The System L1-type amino acid transporter mediates transport of large neutral amino acids (LNAA) in many mammalian cell-types. LNAA such as leucine are required for full activation of the mTOR-S6K signalling pathway promoting protein synthesis and cell growth. The SLC7A5 (LAT1) catalytic subunit of high-affinity System L1 functions as a glycoprotein-associated heterodimer with the multifunctional protein SLC3A2 (CD98). We generated a floxed Slc7a5 mouse strain which, when crossed with mice expressing Cre driven by a global promoter, produced Slc7a5 heterozygous knockout (Slc7a5+/-) animals with no overt phenotype, although homozygous global knockout of Slc7a5 was embryonically lethal. Muscle-specific (MCK Cre-mediated) Slc7a5 knockout (MS-Slc7a5-KO) mice were used to study the role of intracellular LNAA delivery by the SLC7A5 transporter for mTOR-S6K pathway activation in skeletal muscle. Activation of muscle mTOR-S6K (Thr389 phosphorylation) in vivo by intraperitoneal leucine injection was blunted in homozygous MS-Slc7a5-KO mice relative to wild-type animals. Dietary intake and growth rate were similar for MS-Slc7a5-KO mice and wild-type littermates fed for 10 weeks (to age 120 days) with diets containing 10%, 20% or 30% of protein. In MS-Slc7a5-KO mice, Leu and Ile concentrations in gastrocnemius muscle were reduced by ∼40% as dietary protein content was reduced from 30 to 10%. These changes were associated with >50% decrease in S6K Thr389 phosphorylation in muscles from MS-Slc7a5-KO mice, indicating reduced mTOR-S6K pathway activation, despite no significant differences in lean tissue mass between groups on the same diet. MS-Slc7a5-KO mice on 30% protein diet exhibited mild insulin resistance (e.g. reduced glucose clearance, larger gonadal adipose depots) relative to control animals. Thus, SLC7A5 modulates LNAA-dependent muscle mTOR-S6K signalling in mice, although it appears non-essential (or is sufficiently compensated by e.g. SLC7A8 (LAT2)) for maintenance

  17. Differential effects of AM fungal isolates on Medicago truncatula growth and metal uptake in a multimetallic (Cd, Zn, Pb) contaminated agricultural soil.

    PubMed

    Redon, Paul-Olivier; Béguiristain, Thierry; Leyval, Corinne

    2009-03-01

    Toxic metal accumulation in soils of agricultural interest is a serious problem needing more attention, and investigations on soil-plant metal transfer must be pursued to better understand the processes involved in metal uptake. Arbuscular mycorrhizal (AM) fungi are known to influence metal transfer in plants by increasing plant biomass and reducing metal toxicity to plants even if diverging results were reported. The effects of five AM fungi isolated from metal contaminated or non-contaminated soils on metal (Cd, Zn) uptake by plant and transfer to leachates was assessed with Medicago truncatula grown in a multimetallic contaminated agricultural soil. Fungi isolated from metal-contaminated soils were more effective to reduce shoot Cd concentration. Metal uptake capacity differed between AM fungi and depended on the origin of the isolate. Not only fungal tolerance and ability to reduce metal concentrations in plant but also interactions with rhizobacteria affected heavy metal transfer and plant growth. Indeed, thanks to association with nodulating rhizobacteria, one Glomus intraradices inoculum increased particularly plant biomass which allowed exporting twofold more Cd and Zn in shoots as compared to non-mycorrhizal treatment. Cd concentrations in leachates were variable among fungal treatments, but can be significantly influenced by AM inoculation. The differential strategies of AM fungal colonisation in metal stress conditions are also discussed. PMID:19169716

  18. Processing and synthesis of multi-metallic nano oxide ceramics via liquid-feed flame spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Azurdia, Jose Antonio

    The liquid-feed flame spray pyrolysis (LF-FSP) process aerosolizes metal-carboxylate precursors dissolved in alcohol with oxygen and combusts them at >1500°C. The products are quenched rapidly (˜10s msec) to < 400°C. By selecting the appropriate precursor mixtures, the compositions of the resulting oxide nanopowders can be tailored easily, which lends itself to combinatorial studies of systems facilitating material property optimization. The resulting nanopowders typically consist of single crystal particles with average particle sizes (APS) < 35 nm, specific surface areas (SSA) of 20-60 m2/g and spherical morphology. LF-FSP provides access to novel single phase nanopowders, known phases at compositions outside their published phase diagrams, intimate mixing at nanometer length scales in multi metallic oxide nanopowders, and control of stoichiometry to ppm levels. The materials produced may exhibit unusual properties including structural, catalytic, and photonic ones and lower sintering temperatures. Prior studies used LF-FSP to produce MgAl2O4 spinel for applications in transparent armor and IR radomes. In these studies, a stable spinel structure with a (MgO)0.1(Al2O3)0.9 composition well outside the known phase field was observed. The work reported here extends this observation to two other spinel systems: Al2O3-NiO, Al2O3-CoOx; followed by three series of transition metal binary oxides, NiO-CoO, NiO-MoO3, NiO-CuO. The impetus to study spinels derives both from the fact that a number of them are known transparent ceramics, but also others offer high SSAs coupled with unusual phases that suggest potentially novel catalytic materials. Because LF-FSP provides access to any composition, comprehensive studies of the entire tie-lines were conducted rather than just compositions of value for catalytic applications. Initial efforts established baseline properties for the nano aluminate spinels, then three binary transition metal oxide sets (Ni-Co, Ni-Mo and Ni

  19. Raney nickel catalytic device

    DOEpatents

    O'Hare, Stephen A.

    1978-01-01

    A catalytic device for use in a conventional coal gasification process which includes a tubular substrate having secured to its inside surface by expansion a catalytic material. The catalytic device is made by inserting a tubular catalytic element, such as a tubular element of a nickel-aluminum alloy, into a tubular substrate and heat-treating the resulting composite to cause the tubular catalytic element to irreversibly expand against the inside surface of the substrate.

  20. Moving to Sustainable Metals. Multifunctional Ligands in Catalytic, Outer Sphere C-H, N-H and O-H Activation

    SciTech Connect

    Crabtree, Robert

    2015-03-03

    Much of our work during this grant period has emphasized green chemistry and sustainability. For example, we were able to convert glycerine, a waste byproduct of biodiesel production, into lactic acid, a compound with numerous applications, notably in the food and cosmetics industry, as well as being a source material for a biodegradable plastic. This work required a catalyst, that ceases to work after a certain lapse of time. We were able to identify the way in which this deactivation occurs by identifying some of the metal catalyst deactivation products. These proved to be multimetallic clusters containing up to six metals and up to 14 hydrogen atoms. Both the catalytic reaction itself and the deactivation structures are novel and unexpected. We have previously proposed that nitrogen heterocycles could be good energy carriers in a low CO2 future world. In another part of our study, we found catalysts for introduction of hydrogen, an energy carrier that is hard to store, into nitrogen heterocycles. The mechanism of this process proved to be unusual in that the catalyst transfers the H2 to the heterocycle in the form of H+ and H-, first transferring the H+ and only then the H-. In a third area of study, some of our compounds, originally prepared for DOE catalysis purposes, also proved useful in hydrocarbon oxidation and in water oxidation. The latter is important in solar-to-fuel work, because, by analogy with natural photosynthesis, the goal of the Yale Solar Group of four PIs is to convert sunlight to hydrogen and oxygen, which requires water splitting catalysts. The catalysts that proved useful mediate the latter reaction: water oxidation to oxygen. In a more technical study, we developed methods for distinguishing the case where catalysis is mediated by a soluble catalyst from cases where catalysis arises from a deposit of finely divided solid. One particular application involved electrocatalysis

  1. Evidence in support of lysine 77 and histidine 96 as acid-base catalytic residues in saccharopine dehydrogenase from Saccharomyces cerevisiae.

    PubMed

    Kumar, Vidya Prasanna; Thomas, Leonard M; Bobyk, Kostyantyn D; Andi, Babak; Cook, Paul F; West, Ann H

    2012-01-31

    rate-limiting hydride transfer step. A viscosity effect of 0.8 was observed on V₂/K(Lys), indicating the solvent deuterium isotope effect resulted from stabilization of an enzyme form prior to hydride transfer. A small normal solvent isotope effect is observed on V, which decreases slightly when repeated with NADD, consistent with a contribution from product release to rate limitation. In addition, V₂/K(Lys)E(t) is pH-independent, which is consistent with the loss of an acid-base catalyst and perturbation of the pK(a) of the second catalytic group to a higher pH, likely a result of a change in the overall charge of the active site. The primary deuterium kinetic isotope effect for H96Q, measured in H₂O or D₂O, is within error equal to 1. A solvent deuterium isotope effect of 2.4 is observed with NADH or NADD as the dinucleotide substrate. Data suggest rate-limiting imine formation, consistent with the proposed role of H96 in protonating the leaving hydroxyl as the imine is formed. The pH-rate profile for V₂/K(Lys)E(t) exhibits the pK(a) for K77, perturbed to a value of ∼9, which must be unprotonated to accept a proton from the ε-amine of the substrate Lys so that it can act as a nucleophile. Overall, data are consistent with a role for K77 acting as the base that accepts a proton from the ε-amine of the substrate lysine prior to nucleophilic attack on the α-oxo group of α-ketoglutarate, and finally donating a proton to the imine nitrogen as it is reduced to give saccharopine. In addition, data indicate a role for H96 acting as a general acid-base catalyst in the formation of the imine between the ε-amine of lysine and the α-oxo group of α-ketoglutarate. PMID:22243403

  2. Evidence in support of lysine 77 and histidine 96 as acid-base catalytic residues in saccharopine dehydrogenase from Saccharomyces cerevisiae.

    PubMed

    Kumar, Vidya Prasanna; Thomas, Leonard M; Bobyk, Kostyantyn D; Andi, Babak; Cook, Paul F; West, Ann H

    2012-01-31

    rate-limiting hydride transfer step. A viscosity effect of 0.8 was observed on V₂/K(Lys), indicating the solvent deuterium isotope effect resulted from stabilization of an enzyme form prior to hydride transfer. A small normal solvent isotope effect is observed on V, which decreases slightly when repeated with NADD, consistent with a contribution from product release to rate limitation. In addition, V₂/K(Lys)E(t) is pH-independent, which is consistent with the loss of an acid-base catalyst and perturbation of the pK(a) of the second catalytic group to a higher pH, likely a result of a change in the overall charge of the active site. The primary deuterium kinetic isotope effect for H96Q, measured in H₂O or D₂O, is within error equal to 1. A solvent deuterium isotope effect of 2.4 is observed with NADH or NADD as the dinucleotide substrate. Data suggest rate-limiting imine formation, consistent with the proposed role of H96 in protonating the leaving hydroxyl as the imine is formed. The pH-rate profile for V₂/K(Lys)E(t) exhibits the pK(a) for K77, perturbed to a value of ∼9, which must be unprotonated to accept a proton from the ε-amine of the substrate Lys so that it can act as a nucleophile. Overall, data are consistent with a role for K77 acting as the base that accepts a proton from the ε-amine of the substrate lysine prior to nucleophilic attack on the α-oxo group of α-ketoglutarate, and finally donating a proton to the imine nitrogen as it is reduced to give saccharopine. In addition, data indicate a role for H96 acting as a general acid-base catalyst in the formation of the imine between the ε-amine of lysine and the α-oxo group of α-ketoglutarate.

  3. Cis-regulatory hairpin-shaped mRNA encoding a reporter protein: catalytic sensing of nucleic acid sequence at single nucleotide resolution.

    PubMed

    Narita, Atsushi; Ogawa, Kazumasa; Sando, Shinsuke; Aoyama, Yasuhiro

    2007-01-01

    DNA sensing at a single nucleotide resolution is achieved using a hairpin-shaped, unmodified (unlabeled) RNA probe or the precursor double-stranded DNA (dsDNA) in a prokaryotic cell-free translation medium. The molecular-beacon-like probe consists of a loop region that is complementary to the target sequence and a stem composed of a ribosome-binding site (RBS) and its docking domain; the RBS is followed by the gene for a reporter protein such as luciferase or beta-galactosidase. Target binding at the loop opens the hairpin to make RBS accessible by the ribosome to start translation of the reporter protein. This sensing system is signal amplifying by virtue of catalytic DNA-to-RNA transcription when using a dsDNA probe, catalytic RNA-to-protein translation, catalytic signal transduction by the enzymatic reaction of the translated reporter protein and, in the presence of RNase H, catalytic or even irreversible translation-activation of the target-probe heteroduplex. Preparation of a probe takes 1-3 d and gene sensing using the probe takes 1-3 h.

  4. Seeding a New Kind of Garden: Synthesis of Architecturally Defined Multimetallic Nanostructures by Seed-Mediated Co-Reduction.

    PubMed

    Weiner, Rebecca G; Kunz, Meredith R; Skrabalak, Sara E

    2015-10-20

    Bimetallic nanoparticles display unique optical and catalytic properties that depend on crystallite size and shape, composition, and overall architecture. They may serve as multifunctional platforms as well. Unfortunately, many routes toward shape and architecturally controlled bimetallic nanocrystals yield polydisperse samples on account of the challenges associated with homogeneously nucleating a defined bimetallic phase by co-reduction methods. Developed by the Skrabalak laboratory, seed-mediated co-reduction (SMCR) involves the simultaneous co-reduction of two metal precursors to deposit metal onto shape-controlled metal nanocrystalline seeds. The central premise is that seeds will serve as preferential and structurally defined platforms for bimetallic deposition, where the shape of the seeds can be transferred to the shells. With Au-Pd as a model system, a set of design principles has been established for the bottom-up synthesis of shape-controlled bimetallic nanocrystals by SMCR. This strategy is successful at synthesizing symmetrically stellated Au-Pd nanocrystals with a variety of symmetries and core@shell Au@Au-Pd nanocrystals. Achieving nanocrystals with high morphological control via SMCR is governed by the following parameters: seed size, shape, and composition as well as the kinetics of seeded growth (through manipulation of synthetic parameters such as pH and metal precursor ratios). For example, larger seeds yield larger nanocrystals as does increasing the amount of metal deposited relative to the number of seeds. This increase in nanocrystal size leads to red-shifts in their localized surface plasmon resonance. Additionally, seed shape directs the overgrowth process during SMCR so the resultant nanocrystals adopt related symmetries. The ability to tune structure is important due to the size-, shape- and composition-dependent optical properties of bimetallic nanocrystals. Using this toolkit, the light scattering and absorption properties of Au

  5. Kinetic method for determination of ascorbic acid on flow injection system by using its catalytic effect on the complexation reaction of an ultra sensitive colorimetric reagent of porphyrin with Cu(II)

    NASA Astrophysics Data System (ADS)

    Liu, Jianhua; Itoh, Jun-Ichi

    2007-06-01

    A kinetic method performed on a flow injection system is described for the determination of ascorbic acid by using its catalytic effect on the complexation reaction of Cu(II) with 5,10,15,20-tetrakis(4- N-trimethyl-aminophenyl)porphyrin. The characteristic spectrum of porphyrin (Soret band), which shows intense absorption around 400 nm ( ɛ > 2.0 × 10 5 cm -1 M -1), was used first time for determining ascorbic acid. By incorporating the complexation reaction into a flow injection system, ascorbic acid could be determined either over a broad dynamic range of 0.1-1000 μg/ml or at a trace level below 5 ng/ml. Good repeatability was also achieved by testing a working standard of 0.1 μg/ml with 10 injections at a throughput of 35 h -1, obtaining a relative standard deviation of 0.11%. Substances like amino acids, vitamins, sugars, organic acids and metal ions, showed no or little interference even present at high concentrations. The method was validated in the determination of ascorbic acid contents of some commercially available soft drinks by comparison with the official 2,6-dichloroindophenol method with reasonable agreement.

  6. Domain-confined catalytic soot combustion over Co3O4 anchored on a TiO2 nanotube array catalyst prepared by mercaptoacetic acid induced surface-grafting

    NASA Astrophysics Data System (ADS)

    Ren, Jiale; Yu, Yifu; Dai, Fangfang; Meng, Ming; Zhang, Jing; Zheng, Lirong; Hu, Tiandou

    2013-11-01

    Herein, we introduce a specially designed domain-confined macroporous catalyst, namely, the Co3O4 nanocrystals anchored on a TiO2 nanotube array catalyst, which was synthesized by using the mercaptoacetic acid induced surface-grafting method. This catalyst exhibits much better performance for catalytic soot combustion than the conventional TiO2 powder supported one in gravitational contact mode (GMC).Herein, we introduce a specially designed domain-confined macroporous catalyst, namely, the Co3O4 nanocrystals anchored on a TiO2 nanotube array catalyst, which was synthesized by using the mercaptoacetic acid induced surface-grafting method. This catalyst exhibits much better performance for catalytic soot combustion than the conventional TiO2 powder supported one in gravitational contact mode (GMC). Electronic supplementary information (ESI) available: The images of XRD, UV-vis, EDX and soot-TPR. The table providing information on Co/Ti-NA catalysts. See DOI: 10.1039/c3nr03757f

  7. Effect the conditions of the acid-thermal modification of clinoptilolite have on the catalytic properties of palladium-copper complexes anchored on it in the reaction of carbon monoxide oxidation

    NASA Astrophysics Data System (ADS)

    Rakitskaya, T. L.; Kiose, T. A.; Ennan, A. A.; Golubchik, K. O.; Oleksenko, L. P.; Gerasiova, V. G.

    2016-06-01

    The dependence of the physicochemical and structural-adsorption properties of natural and acid-thermal modified clinoptilolite, and of Pd(II)-Cu(II) catalysts based on them, on the duration of acid-thermal modification is investigated. The samples under study are described via XRD and thermal gravimetric (DTG and DTA) analysis, IR, DR UV-Vis, EPR spectroscopy, and water vapor adsorption. Values of both the specific surface area ( S sp) and pH of aqueous suspensions are determined. The resulting catalysts are tested in the reaction of low-temperature carbon monoxide oxidation with air oxygen. A conclusion is drawn about the nature of surface bimetallic Pd(II)-Cu(II) complexes. The greatest catalytic activity is shown by complexes based on clinoptilolite and modified with 3 M HNO3 for 0.5 and 1 h.

  8. Catalytic asymmetric alkylation of acylsilanes.

    PubMed

    Rong, Jiawei; Oost, Rik; Desmarchelier, Alaric; Minnaard, Adriaan J; Harutyunyan, Syuzanna R

    2015-03-01

    The highly enantioselective addition of Grignard reagents to acylsilanes is catalyzed by copper diphosphine complexes. This transformation affords α-silylated tertiary alcohols in up to 97% yield and 98:2 enantiomeric ratio. The competing Meerwein-Ponndorf-Verley reduction is suppressed by the use of a mixture of Lewis acid additives. The chiral catalyst can be recovered as a copper complex and used repeatedly without any loss of catalytic activity. PMID:25403641

  9. Characteristics of post-impregnated SBA-15 with 12- Tungstophosphoric acid and its correlation with catalytic activity in selective esterification of glycerol to monolaurate

    NASA Astrophysics Data System (ADS)

    Hoo, P. Y.; Abdullah, A. Z.

    2016-06-01

    Selective esterification of glycerol and lauric acid to monolaurin was conducted using 12-tungstophosphoric acid (HPW) incorporated SBA-15 as catalyst. They were synthesized with HPW loadings of 10-40 wt. % via post impregnation and characterized in terms of surficial and structural characteristic, acidity and morphology. Relatively high lauric acid conversion (up to 95%) and monolaurin yield (53%) were observed while the activity was successfully correlated to the material behaviours, i.e. highly acidic active acid sites within highly uniformed mesopores. The effects of different reaction parameters including reactant ratio (1:1-5:1), catalyst loading (1-5 wt. %) and length of fatty acid were also elucidated. Reduced fatty acid conversion was observed when longer fatty acids were used, thus further strengthen the idea of size selectivity effect provided by the synthesized catalysts.

  10. Uniquely localized intra-molecular amino acid concentrations at the glycolytic enzyme catalytic/active centers of Archaea, Bacteria and Eukaryota are associated with their proposed temporal appearances on earth.

    PubMed

    Pollack, J Dennis; Gerard, David; Pearl, Dennis K

    2013-04-01

    The distributions of amino acids at most-conserved sites nearest catalytic/active centers (C/AC) in 4,645 sequences of ten enzymes of the glycolytic Embden-Meyerhof-Parnas pathway in Archaea, Bacteria and Eukaryota are similar to the proposed temporal order of their appearance on Earth. Glycine, isoleucine, leucine, valine, glutamic acid and possibly lysine often described as prebiotic, i.e., existing or occurring before the emergence of life, were localized in positional and conservational defined aggregations in all enzymes of all Domains. The distributions of all 20 biologic amino acids in most-conserved sites nearest their C/ACs were quite different either from distributions in sites less-conserved and further from their C/ACs or from all amino acids regardless of their position or conservation. The major concentrations of glycine, e.g., perhaps the earliest prebiotic amino acid, occupies ≈ 16 % of all the most-conserved sites within a volume of ≈ 7-8 Å radius from their C/ACs and decreases linearly towards the molecule's peripheries. Spatially localized major concentrations of isoleucine, leucine and valine are in the mid-conserved and mid-distant sites from their C/ACs in protein interiors. Lysine and glutamic acid comprise ≈ 25-30 % of all amino acids within an irregular volume bounded by ≈ 24-28 Å radii from their C/ACs at the most-distant least-conserved sites. The unreported characteristics of these amino acids: their spatially and conservationally identified concentrations in Archaea, Bacteria and Eukaryota, suggest some common structural organization of glycolytic enzymes that may be relevant to their evolution and that of other proteins. We discuss our data in relation to enzyme evolution, their reported prebiotic putative temporal appearances on Earth, abundances, biological "cost", neighbor-sequence preferences or "ordering" and some thermodynamic parameters.

  11. Uniquely Localized Intra-Molecular Amino Acid Concentrations at the Glycolytic Enzyme Catalytic/Active Centers of Archaea, Bacteria and Eukaryota are Associated with Their Proposed Temporal Appearances on Earth

    NASA Astrophysics Data System (ADS)

    Pollack, J. Dennis; Gerard, David; Pearl, Dennis K.

    2013-04-01

    The distributions of amino acids at most-conserved sites nearest catalytic/active centers (C/AC) in 4,645 sequences of ten enzymes of the glycolytic Embden-Meyerhof-Parnas pathway in Archaea, Bacteria and Eukaryota are similar to the proposed temporal order of their appearance on Earth. Glycine, isoleucine, leucine, valine, glutamic acid and possibly lysine often described as prebiotic, i.e., existing or occurring before the emergence of life, were localized in positional and conservational defined aggregations in all enzymes of all Domains. The distributions of all 20 biologic amino acids in most-conserved sites nearest their C/ACs were quite different either from distributions in sites less-conserved and further from their C/ACs or from all amino acids regardless of their position or conservation. The major concentrations of glycine, e.g., perhaps the earliest prebiotic amino acid, occupies ≈16 % of all the most-conserved sites within a volume of ≈7-8 Å radius from their C/ACs and decreases linearly towards the molecule's peripheries. Spatially localized major concentrations of isoleucine, leucine and valine are in the mid-conserved and mid-distant sites from their C/ACs in protein interiors. Lysine and glutamic acid comprise ≈25-30 % of all amino acids within an irregular volume bounded by ≈24-28 Å radii from their C/ACs at the most-distant least-conserved sites. The unreported characteristics of these amino acids: their spatially and conservationally identified concentrations in Archaea, Bacteria and Eukaryota, suggest some common structural organization of glycolytic enzymes that may be relevant to their evolution and that of other proteins. We discuss our data in relation to enzyme evolution, their reported prebiotic putative temporal appearances on Earth, abundances, biological "cost", neighbor-sequence preferences or "ordering" and some thermodynamic parameters.

  12. Switchable catalytic DNA catenanes.

    PubMed

    Hu, Lianzhe; Lu, Chun-Hua; Willner, Itamar

    2015-03-11

    Two-ring interlocked DNA catenanes are synthesized and characterized. The supramolecular catenanes show switchable cyclic catalytic properties. In one system, the catenane structure is switched between a hemin/G-quadruplex catalytic structure and a catalytically inactive state. In the second catenane structure the catenane is switched between a catalytically active Mg(2+)-dependent DNAzyme-containing catenane and an inactive catenane state. In the third system, the interlocked catenane structure is switched between two distinct catalytic structures that include the Mg(2+)- and the Zn(2+)-dependent DNAzymes. PMID:25642796

  13. Comparative Study of f-Element Electronic Structure across a Series of Multimetallic Actinide, Lanthanide-Actinide and Lanthanum-Actinide Complexes Possessing Redox-Active Bridging Ligands

    SciTech Connect

    Schelter, Eric J.; Wu, Ruilian; Veauthier, Jacqueline M.; Bauer, Eric D.; Booth, Corwin H.; Thomson, Robert K.; Graves, Christopher R.; John, Kevin D.; Scott, Brian L.; Thompson, Joe D.; Morris, David E.; Kiplinger, Jaqueline L.

    2010-02-24

    A comparative examination of the electronic interactions across a series of trimetallic actinide and mixed lanthanide-actinide and lanthanum-actinide complexes is presented. Using reduced, radical terpyridyl ligands as conduits in a bridging framework to promote intramolecular metal-metal communication, studies containing structural, electrochemical, and X-ray absorption spectroscopy are presented for (C{sub 5}Me{sub 5}){sub 2}An[-N=C(Bn)(tpy-M{l_brace}C{sub 5}Me4R{r_brace}{sub 2})]{sub 2} (where An = Th{sup IV}, U{sup IV}; Bn = CH{sub 2}C{sub 6}H{sub 5}; M = La{sup III}, Sm{sup III}, Yb{sup III}, U{sup III}; R = H, Me, Et) to reveal effects dependent on the identities of the metal ions and R-groups. The electrochemical results show differences in redox energetics at the peripheral 'M' site between complexes and significant wave splitting of the metal- and ligand-based processes indicating substantial electronic interactions between multiple redox sites across the actinide-containing bridge. Most striking is the appearance of strong electronic coupling for the trimetallic Yb{sup III}-U{sup IV}-Yb{sup III}, Sm{sup III}-U{sup IV}-Sm{sup III}, and La{sup III}-U{sup IV}-La{sup III} complexes, [8]{sup -}, [9b]{sup -} and [10b]{sup -}, respectively, whose calculated comproportionation constant K{sub c} is slightly larger than that reported for the benchmark Creutz-Taube ion. X-ray absorption studies for monometallic metallocene complexes of U{sup III}, U{sup IV}, and U{sup V} reveal small but detectable energy differences in the 'white-line' feature of the uranium L{sub III}-edges consistent with these variations in nominal oxidation state. The sum of this data provides evidence of 5f/6d-orbital participation in bonding and electronic delocalization in these multimetallic f-element complexes. An improved, high-yielding synthesis of 4{prime}-cyano-2,2{prime}:6{prime},2{double_prime}-terpyridine is also reported.

  14. Identifying the Atomic-Level Effects of Metal Composition on the Structure and Catalytic Activity of Peptide-Templated Materials.

    PubMed

    Merrill, Nicholas A; McKee, Erik M; Merino, Kyle C; Drummy, Lawrence F; Lee, Sungsik; Reinhart, Benjamin; Ren, Yang; Frenkel, Anatoly I; Naik, Rajesh R; Bedford, Nicholas M; Knecht, Marc R

    2015-12-22

    Bioinspired approaches for the formation of metallic nanomaterials have been extensively employed for a diverse range of applications including diagnostics and catalysis. These materials can often be used under sustainable conditions; however, it is challenging to control the material size, morphology, and composition simultaneously. Here we have employed the R5 peptide, which forms a 3D scaffold to direct the size and linear shape of bimetallic PdAu nanomaterials for catalysis. The materials were prepared at varying Pd:Au ratios to probe optimal compositions to achieve maximal catalytic efficiency. These materials were extensively characterized at the atomic level using transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and atomic pair distribution function analysis derived from high-energy X-ray diffraction patterns to provide highly resolved structural information. The results confirmed PdAu alloy formation, but also demonstrated that significant surface structural disorder was present. The catalytic activity of the materials was studied for olefin hydrogenation, which demonstrated enhanced reactivity from the bimetallic structures. These results present a pathway to the bioinspired production of multimetallic materials with enhanced properties, which can be assessed via a suite of characterization methods to fully ascertain structure/function relationships.

  15. Concentration of Specific Amino Acids at the Catalytic/Active Centers of Highly-Conserved ``Housekeeping'' Enzymes of Central Metabolism in Archaea, Bacteria and Eukaryota: Is There a Widely Conserved Chemical Signal of Prebiotic Assembly?

    NASA Astrophysics Data System (ADS)

    Pollack, J. Dennis; Pan, Xueliang; Pearl, Dennis K.

    2010-06-01

    In alignments of 1969 protein sequences the amino acid glycine and others were found concentrated at most-conserved sites within ˜15 Å of catalytic/active centers (C/AC) of highly conserved kinases, dehydrogenases or lyases of Archaea, Bacteria and Eukaryota. Lysine and glutamic acid were concentrated at least-conserved sites furthest from their C/ACs. Logistic-regression analyses corroborated the “movement” of glycine towards and lysine away from their C/ACs: the odds of a glycine occupying a site were decreased by 19%, while the odds for a lysine were increased by 53%, for every 10 Å moving away from the C/AC. Average conservation of MSA consensus sites was highest surrounding the C/AC and directly decreased in transition toward model’s peripheries. Findings held with statistical confidence using sequences restricted to individual Domains or enzyme classes or to both. Our data describe variability in the rate of mutation and likelihoods for phylogenetic trees based on protein sequence data and endorse the extension of substitution models by incorporating data on conservation and distance to C/ACs rather than only using cumulative levels. The data support the view that in the most-conserved environment immediately surrounding the C/AC of taxonomically distant and highly conserved essential enzymes of central metabolism there are amino acids whose identity and degree of occupancy is similar to a proposed amino acid set and frequency associated with prebiotic evolution.

  16. Concentration of specific amino acids at the catalytic/active centers of highly-conserved "housekeeping" enzymes of central metabolism in archaea, bacteria and Eukaryota: is there a widely conserved chemical signal of prebiotic assembly?

    PubMed

    Pollack, J Dennis; Pan, Xueliang; Pearl, Dennis K

    2010-06-01

    In alignments of 1969 protein sequences the amino acid glycine and others were found concentrated at most-conserved sites within approximately 15 A of catalytic/active centers (C/AC) of highly conserved kinases, dehydrogenases or lyases of Archaea, Bacteria and Eukaryota. Lysine and glutamic acid were concentrated at least-conserved sites furthest from their C/ACs. Logistic-regression analyses corroborated the "movement" of glycine towards and lysine away from their C/ACs: the odds of a glycine occupying a site were decreased by 19%, while the odds for a lysine were increased by 53%, for every 10 A moving away from the C/AC. Average conservation of MSA consensus sites was highest surrounding the C/AC and directly decreased in transition toward model's peripheries. Findings held with statistical confidence using sequences restricted to individual Domains or enzyme classes or to both. Our data describe variability in the rate of mutation and likelihoods for phylogenetic trees based on protein sequence data and endorse the extension of substitution models by incorporating data on conservation and distance to C/ACs rather than only using cumulative levels. The data support the view that in the most-conserved environment immediately surrounding the C/AC of taxonomically distant and highly conserved essential enzymes of central metabolism there are amino acids whose identity and degree of occupancy is similar to a proposed amino acid set and frequency associated with prebiotic evolution.

  17. Transmetalation from B to Rh in the course of the catalytic asymmetric 1,4-addition reaction of phenylboronic acid to enones: a computational comparison of diphosphane and diene ligands.

    PubMed

    Li, You-Gui; He, Gang; Qin, Hua-Li; Kantchev, Eric Assen B

    2015-02-14

    Transmetalation is a key elementary reaction of many important catalytic reactions. Among these, 1,4-addition of arylboronic acids to organic acceptors such as α,β-unsaturated ketones has emerged as one of the most important methods for asymmetric C-C bond formation. A key intermediate for the B-to-Rh transfer arising from quaternization on a boronic acid by a Rh-bound hydroxide (the active catalyst) has been proposed. Herein, DFT calculations (IEFPCM/PBE0/DGDZVP level of theory) establish the viability of this proposal, and characterize the associated pathways. The delivery of phenylboronic acid in the orientation suited for the B-to-Rh transfer from the very beginning is energetically preferable, and occurs with expulsion of Rh-coordinated water molecules. For the bulkier binap ligand, the barriers are higher (particularly for the phenylboronic acid activation step) due to a less favourable entropy term to the free energy, in accordance with the experimentally observed slower transmetalation rate. PMID:25422851

  18. Transmetalation from B to Rh in the course of the catalytic asymmetric 1,4-addition reaction of phenylboronic acid to enones: a computational comparison of diphosphane and diene ligands.

    PubMed

    Li, You-Gui; He, Gang; Qin, Hua-Li; Kantchev, Eric Assen B

    2015-02-14

    Transmetalation is a key elementary reaction of many important catalytic reactions. Among these, 1,4-addition of arylboronic acids to organic acceptors such as α,β-unsaturated ketones has emerged as one of the most important methods for asymmetric C-C bond formation. A key intermediate for the B-to-Rh transfer arising from quaternization on a boronic acid by a Rh-bound hydroxide (the active catalyst) has been proposed. Herein, DFT calculations (IEFPCM/PBE0/DGDZVP level of theory) establish the viability of this proposal, and characterize the associated pathways. The delivery of phenylboronic acid in the orientation suited for the B-to-Rh transfer from the very beginning is energetically preferable, and occurs with expulsion of Rh-coordinated water molecules. For the bulkier binap ligand, the barriers are higher (particularly for the phenylboronic acid activation step) due to a less favourable entropy term to the free energy, in accordance with the experimentally observed slower transmetalation rate.

  19. Catalytic liquid-phase oxidation of acetaldehyde to acetic acid over a Pt/CeO2-ZrO2-SnO2/γ-alumina catalyst.

    PubMed

    Choi, Pil-Gyu; Ohno, Takanobu; Masui, Toshiyuki; Imanaka, Nobuhito

    2015-10-01

    Pt/CeO2-ZrO2-SnO2/γ-Al2O3 catalysts were prepared by co-precipitation and wet impregnation methods for catalytic oxidation of acetaldehyde to acetic acid in water. In the present catalysts, Pt and CeO2-ZrO2-SnO2 were successfully dispersed on the γ-Al2O3 support. Dependences of platinum content and reaction time on the selective oxidation of acetaldehyde to acetic acid were investigated to optimize the reaction conditions for obtaining both high acetaldehyde conversion and highest selectivity to acetic acid. Among the catalysts, a Pt(6.4wt.%)/Ce0.68Zr0.17Sn0.15O2.0(16wt.%)/γ-Al2O3 catalyst showed the highest acetaldehyde oxidation activity. On this catalyst, acetaldehyde was completely oxidized after the reaction at 0°C for 8hr, and the selectivity to acetic acid reached to 95% and higher after the reaction for 4hr and longer.

  20. Ionizable Side Chains at Catalytic Active Sites of Enzymes

    PubMed Central

    Jimenez-Morales, David; Liang, Jie

    2012-01-01

    Catalytic active sites of enzymes of known structure can be well defined by a modern program of computational geometry. The CASTp program was used to define and measure the volume of the catalytic active sites of 573 enzymes in the Catalytic Site Atlas database. The active sites are identified as catalytic because the amino acids they contain are known to participate in the chemical reaction catalyzed by the enzyme. Acid and base side chains are reliable markers of catalytic active sites. The catalytic active sites have 4 acid and 5 base side chains, in an average volume of 1072 Å3. The number density of acid side chains is 8.3 M (in chemical units); the number density of basic side chains is 10.6 M. The catalytic active site of these enzymes is an unusual electrostatic and steric environment in which side chains and reactants are crowded together in a mixture more like an ionic liquid than an ideal infinitely dilute solution. The electrostatics and crowding of reactants and side chains seems likely to be important for catalytic function. In three types of analogous ion channels, simulation of crowded charges accounts for the main properties of selectivity measured in a wide range of solutions and concentrations. It seems wise to use mathematics designed to study interacting complex fluids when making models of the catalytic active sites of enzymes. PMID:22484856

  1. Temperature Independent Catalytic Two-Electron Reduction of Dioxygen by Ferrocenes with a Tris[2-(2-pyridyl)ethyl]amine-Copper(II) Catalyst in the Presence of Perchloric Acid

    PubMed Central

    Das, Dipanwita; Lee, Yong-Min; Ohkubo, Kei; Nam, Wonwoo; Karlin, Kenneth D.; Fukuzumi, Shunichi

    2013-01-01

    Selective two-electron plus two-proton (2e−/2H+) reduction of O2 to hydrogen peroxide by ferrocene (Fc) or 1,1′-dimethylferrocene (Me2Fc) in the presence of perchloric acid is catalyzed efficiently by a mononuclear copper(II) complex, [CuII(tepa)]2+ {tepa = tris[2-(2-pyridyl)ethyl]amine} (1) in acetone. The E1/2 value for [CuII(tepa)]2+ as measured by cyclic voltammetry is 0.07 V vs Fc/Fc+ in acetone, being significantly positive, which makes it possible to use relatively weak one-electron reductants such as Fc and Me2Fc for the overall two-electron reduction of O2. Fast electron transfer from Fc or Me2Fc to 1 affords the corresponding CuI complex, [CuI(tepa)]+ (2), which reacts at low temperature (193 K) with O2, however only in presence of HClO4 to afford the hydroperoxo complex, [CuII(tepa)(OOH)]2+ (3). The detailed kinetic study on the homogeneous catalytic system reveals the rate-determining step to be the O2-binding process in the presence of HClO4 at lower temperature as well as at room temperature. The O2-binding kinetics in the presence of HClO4 were studied, demonstrating that the rate of formation of the hydroperoxo complex (3) as well as the overall catalytic reaction remained virtually the same with changing temperature. The apparent lack of an activation energy for the catalytic two-electron reduction of O2 is shown to result from the existence of a pre-equilibrium between 2 and O2 prior to the formation of the hydroperoxo complex 3. No further reduction of [CuII(tepa)(OOH)]2+ (3) by Fc or Me2Fc occurred, and instead 3 is protonated by HClO4 to yield H2O2 accompanied by regeneration of 1, thus completing the catalytic cycle for the two-electron reduction of O2 by Fc or Me2Fc. PMID:23394287

  2. Temperature-independent catalytic two-electron reduction of dioxygen by ferrocenes with a copper(II) tris[2-(2-pyridyl)ethyl]amine catalyst in the presence of perchloric acid.

    PubMed

    Das, Dipanwita; Lee, Yong-Min; Ohkubo, Kei; Nam, Wonwoo; Karlin, Kenneth D; Fukuzumi, Shunichi

    2013-02-20

    Selective two-electron plus two-proton (2e(-)/2H(+)) reduction of O(2) to hydrogen peroxide by ferrocene (Fc) or 1,1'-dimethylferrocene (Me(2)Fc) in the presence of perchloric acid is catalyzed efficiently by a mononuclear copper(II) complex, [Cu(II)(tepa)](2+) (1; tepa = tris[2-(2-pyridyl)ethyl]amine) in acetone. The E(1/2) value for [Cu(II)(tepa)](2+) as measured by cyclic voltammetry is 0.07 V vs Fc/Fc(+) in acetone, being significantly positive, which makes it possible to use relatively weak one-electron reductants such as Fc and Me(2)Fc for the overall two-electron reduction of O(2). Fast electron transfer from Fc or Me(2)Fc to 1 affords the corresponding Cu(I) complex [Cu(I)(tepa)](+) (2), which reacts at low temperature (193 K) with O(2), however only in the presence of HClO(4), to afford the hydroperoxo complex [Cu(II)(tepa)(OOH)](+) (3). A detailed kinetic study on the homogeneous catalytic system reveals the rate-determining step to be the O(2)-binding process in the presence of HClO(4) at lower temperature as well as at room temperature. The O(2)-binding kinetics in the presence of HClO(4) were studied, demonstrating that the rate of formation of the hydroperoxo complex 3 as well as the overall catalytic reaction remained virtually the same with changing temperature. The apparent lack of activation energy for the catalytic two-electron reduction of O(2) is shown to result from the existence of a pre-equilibrium between 2 and O(2) prior to the formation of the hydroperoxo complex 3. No further reduction of [Cu(II)(tepa)(OOH)](+) (3) by Fc or Me(2)Fc occurred, and instead 3 is protonated by HClO(4) to yield H(2)O(2) accompanied by regeneration of 1, thus completing the catalytic cycle for the two-electron reduction of O(2) by Fc or Me(2)Fc.

  3. Risk-based assessment of multimetallic soil pollution in the industrialized peri-urban area of Huelva, Spain.

    PubMed

    Fernández-Caliani, J C

    2012-02-01

    The peri-urban soils of Huelva, one of the first industrial cities in Spain, are subject to severe pollution problems primarily due to past poor management of industrial wastes and effluents. In this study, soil cores were collected in seven sites potentially contaminated with toxic chemicals arising from multiple anthropogenic sources, in order to identify trace elements of concern and to assess human health risks associated with them. In most soil core samples, total concentrations of As (up to 4,390 mg kg(-1)), Cd (up to 12.9 mg kg(-1)), Cu (up to 3,162 mg kg(-1)), Pb (up to 6,385 mg kg(-1)), Sb (up to 589 mg kg(-1)) and Zn (up to 4,874 mg kg(-1)) were by more than one order of magnitude greater than the site-specific reference levels calculated on the basis of regional soil geochemical baselines. These chemicals are transferred from the hazardous wastes, mainly crude pyrite and roasted pyrite cinders, to the surrounding soils by acid drainage and atmospheric deposition of wind-blown dust. Locally, elevated concentrations of U (up to 96.3 mg kg(-1)) were detected in soils affected by releases of radionuclides from phosphogypsum wastes. The results of the human health risk-based assessment for the hypothetical exposure of an industrial worker to the surface soils indicate that, in four of the seven sites monitored, cancer risk due to As (up to 4.4 × 10(-5)) is slightly above the target health risk limit adopted by the Spanish legislation (1 × 10(-5)). The cumulative non-carcinogenic hazard index ranged from 2.0 to 12.2 indicating that there is also a concern for chronic toxic effects from dermal contact with soil.

  4. Rich catalytic injection

    DOEpatents

    Veninger, Albert

    2008-12-30

    A gas turbine engine includes a compressor, a rich catalytic injector, a combustor, and a turbine. The rich catalytic injector includes a rich catalytic device, a mixing zone, and an injection assembly. The injection assembly provides an interface between the mixing zone and the combustor. The injection assembly can inject diffusion fuel into the combustor, provides flame aerodynamic stabilization in the combustor, and may include an ignition device.

  5. Two stage catalytic combustor

    NASA Technical Reports Server (NTRS)

    Alvin, Mary Anne (Inventor); Bachovchin, Dennis (Inventor); Smeltzer, Eugene E. (Inventor); Lippert, Thomas E. (Inventor); Bruck, Gerald J. (Inventor)

    2010-01-01

    A catalytic combustor (14) includes a first catalytic stage (30), a second catalytic stage (40), and an oxidation completion stage (49). The first catalytic stage receives an oxidizer (e.g., 20) and a fuel (26) and discharges a partially oxidized fuel/oxidizer mixture (36). The second catalytic stage receives the partially oxidized fuel/oxidizer mixture and further oxidizes the mixture. The second catalytic stage may include a passageway (47) for conducting a bypass portion (46) of the mixture past a catalyst (e.g., 41) disposed therein. The second catalytic stage may have an outlet temperature elevated sufficiently to complete oxidation of the mixture without using a separate ignition source. The oxidation completion stage is disposed downstream of the second catalytic stage and may recombine the bypass portion with a catalyst exposed portion (48) of the mixture and complete oxidation of the mixture. The second catalytic stage may also include a reticulated foam support (50), a honeycomb support, a tube support or a plate support.

  6. Single step synthesis of gold-amino acid composite, with the evidence of the catalytic hydrogen atom transfer (HAT) reaction, for the electrochemical recognition of Serotonin

    NASA Astrophysics Data System (ADS)

    Choudhary, Meenakshi; Siwal, Samarjeet; Nandi, Debkumar; Mallick, Kaushik

    2016-03-01

    A composite architecture of amino acid and gold nanoparticles has been synthesized using a generic route of 'in-situ polymerization and composite formation (IPCF)' [1,2]. The formation mechanism of the composite has been supported by a model hydrogen atom (H•≡H++e-) transfer (HAT) type of reaction which belongs to the proton coupled electron transfer (PCET) mechanism. The 'gold-amino acid composite' was used as a catalyst for the electrochemical recognition of Serotonin.

  7. The Translocation Domain of Botulinum Neurotoxin A Moderates the Propensity of the Catalytic Domain to Interact with Membranes at Acidic pH

    PubMed Central

    Araye, Anne; Goudet, Amélie; Barbier, Julien; Pichard, Sylvain; Baron, Bruno; England, Patrick; Pérez, Javier; Zinn-Justin, Sophie; Chenal, Alexandre; Gillet, Daniel

    2016-01-01

    Botulinum neurotoxin A (BoNT/A) is composed of three domains: a catalytic domain (LC), a translocation domain (HN) and a receptor-binding domain (HC). Like most bacterial toxins BoNT/A is an amphitropic protein, produced in a soluble form that is able to interact, penetrate and/or cross a membrane to achieve its toxic function. During intoxication BoNT/A is internalized by the cell by receptor-mediated endocytosis. Then, LC crosses the membrane of the endocytic compartment and reaches the cytosol. This translocation is initiated by the low pH found in this compartment. It has been suggested that LC passes in an unfolded state through a transmembrane passage formed by HN. We report here that acidification induces no major conformational change in either secondary or tertiary structures of LC and HN of BoNT/A in solution. GdnHCl-induced denaturation experiments showed that the stability of LC and HN increases as pH drops, and that HN further stabilizes LC. Unexpectedly we found that LC has a high propensity to interact with and permeabilize anionic lipid bilayers upon acidification without the help of HN. This property is downplayed when LC is linked to HN. HN thus acts as a chaperone for LC by enhancing its stability but also as a moderator of the membrane interaction of LC. PMID:27070312

  8. Catalytic distillation structure

    DOEpatents

    Smith, Jr., Lawrence A.

    1984-01-01

    Catalytic distillation structure for use in reaction distillation columns, a providing reaction sites and distillation structure and consisting of a catalyst component and a resilient component intimately associated therewith. The resilient component has at least about 70 volume % open space and being present with the catalyst component in an amount such that the catalytic distillation structure consist of at least 10 volume % open space.

  9. Catalytic cyclometallation in steroid chemistry III: Synthesis of steroidal derivatives of 5Z,9Z-dienoic acid and investigation of its human topoisomerase I inhibitory activity.

    PubMed

    D'yakonov, Vladimir A; Dzhemileva, Lilya U; Tuktarova, Regina A; Makarov, Aleksey A; Islamov, Ilgiz I; Mulyukova, Alfiya R; Dzhemilev, Usein M

    2015-10-01

    Two approaches to stereoselective synthesis of steroid 5Z,9Z-dienoic acids were developed, the first one being based on the cross-cyclomagnesiation of 2-(hepta-5,6-dien-1-yloxy)tetrahydro-2H-pyran and 1,2-diene cholesterol derivatives on treatment with EtMgBr catalyzed by Cp2TiCl2, while the other involving the synthesis of esters of hydroxy steroids with (5Z,9Z)-tetradeca-5,9-dienedioic acid, prepared in two steps using homo-cyclomagnesiation of 2-(hepta-5,6-dien-1-yloxy)tetrahydro-2H-pyran as the key step. High inhibitory activity of the synthesized acids against human topoisomerase I (hTop1) was found.

  10. Acetic Acid Reforming over Rh Supported on La2O3/CeO2-ZrO2: Catalytic Performance and Reaction Pathway Analysis

    SciTech Connect

    Lemonidou, Angeliki A.; Vagia, Ekaterini C.; Lercher, Johannes A.

    2013-07-11

    Reforming of acetic acid was investigated on Rh supported on CeO2-ZrO2 modified with 3 wt % La. The active catalyst converted acetic acid to H-2-rich gas and hardly formed coke. The low rate of coke formation is concluded to be related to the presence of redox-active oxygen limiting the concentration of coke precursors. Temperature-programmed O-18(2)) isotope exchange measurements showed that the La2O3 and Rh enhanced the mobility of lattice oxygen compared with that of the parent CeO2-ZrO2. Ketonization and decarboxylation of acetic acid are the dominating reactions over the latter up to 600 degrees C, whereas above 600 degrees C, steam reforming and water gas shift also contribute. Over 0.5 wt % Rh on La2O3/CeO2-ZrO2, reforming and water gas shift reactions dominate, even below 300 degrees C, producing mostly H-2 and CO2. Using isotope labeling, it is shown that acetic acid adsorbs dissociatively on Rh, forming acetates, which sequentially decarboxylate and form surface methyl groups. The latter are in turn converted to CO, CO2, and H-2.

  11. Determination of the structure and catalytic mechanism of Sorghum bicolor caffeic acid O-methyltransferase and the structural impact of three brown midrib12 mutations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    With S-adenosylmethionine (SAM) acting as the methyl donor, caffeic acid O-methyltransferase from Sorghum bicolor (SbCOMT) methylates the 5-hydroxyl group of its preferred substrate, 5-hydroxyconiferaldehyde, to form sinapaldehyde. In order to determine the mechanism of SbCOMT and understand the red...

  12. Catalytic C-H bond activation at nanoscale Lewis acidic aluminium fluorides: H/D exchange reactions at aromatic and aliphatic hydrocarbons.

    PubMed

    Prechtl, Martin H G; Teltewskoi, Michael; Dimitrov, Anton; Kemnitz, Erhard; Braun, Thomas

    2011-12-16

    Nanoscopic amorphous Lewis acidic aluminium fluorides, such as aluminium chlorofluoride (ACF) and high-surface aluminium fluoride (HS-AlF(3)), are capable of activating C-H bonds of aliphatic hydrocarbons. H/D exchange reactions are catalysed under mild conditions (40 °C).

  13. Multimetallic Electrodeposition on Carbon Fibers

    NASA Astrophysics Data System (ADS)

    Böttger-Hiller, F.; Kleiber, J.; Böttger, T.; Lampke, T.

    2016-03-01

    Efficient lightweight design requires intelligent materials that meet versatile functions. One approach is to extend the range of properties of carbon fiber reinforced plastics (CFRP) by plating the fiber component. Electroplating leads to metalized layers on carbon fibers. Herein only cyanide-free electrolytes where used. Until now dendrite-free layers were only obtained using current densities below 1.0 A dm-2. In this work, dendrite-free tin and copper coatings were achieved by pre-metalizing the carbon fiber substrates. Furthermore, applying a combination of two metals with different sized thermal expansion coefficient lead to a bimetallic coating on carbon fiber rovings, which show an actuatory effect.

  14. Determination of Catalytic Coefficient for a First-Order Reaction

    ERIC Educational Resources Information Center

    Fraga, E. R.; And Others

    1975-01-01

    Describes an undergraduate physical chemistry experiment in which the acid catalyzed hydrolysis of sucrose is used to determine the catalytic coefficient of the hydronium ion, the catalyst in this reaction. (MLH)

  15. Probing the Lewis acidity and catalytic activity of the metal-organic framework [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate).

    PubMed

    Alaerts, Luc; Séguin, Etienne; Poelman, Hilde; Thibault-Starzyk, Frédéric; Jacobs, Pierre A; De Vos, Dirk E

    2006-09-25

    An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework. [Cu3(btc)2] is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of alpha-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, it was demonstrated that the active sites in [Cu3(btc)2] are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed. PMID:16881030

  16. Dual catalytic activity of hydroxycinnamoyl-coenzyme A quinate transferase from tomato allows it to moonlight in the synthesis of both mono- and dicaffeoylquinic acids.

    PubMed

    Moglia, Andrea; Lanteri, Sergio; Comino, Cinzia; Hill, Lionel; Knevitt, Daniel; Cagliero, Cecilia; Rubiolo, Patrizia; Bornemann, Stephen; Martin, Cathie

    2014-12-01

    Tomato (Solanum lycopersicum), like other Solanaceous species, accumulates high levels of antioxidant caffeoylquinic acids, which are strong bioactive molecules and protect plants against biotic and abiotic stresses. Among these compounds, the monocaffeoylquinic acids (e.g. chlorogenic acid [CGA]) and the dicaffeoylquinic acids (diCQAs) have been found to possess marked antioxidative properties. Thus, they are of therapeutic interest both as phytonutrients in foods and as pharmaceuticals. Strategies to increase diCQA content in plants have been hampered by the modest understanding of their biosynthesis and whether the same pathway exists in different plant species. Incubation of CGA with crude extracts of tomato fruits led to the formation of two new products, which were identified by liquid chromatography-mass spectrometry as diCQAs. This chlorogenate:chlorogenate transferase activity was partially purified from ripe fruit. The final protein fraction resulted in 388-fold enrichment of activity and was subjected to trypsin digestion and mass spectrometric sequencing: a hydroxycinnamoyl-Coenzyme A:quinate hydroxycinnamoyl transferase (HQT) was selected as a candidate protein. Assay of recombinant HQT protein expressed in Escherichia coli confirmed its ability to synthesize diCQAs in vitro. This second activity (chlorogenate:chlorogenate transferase) of HQT had a low pH optimum and a high Km for its substrate, CGA. High concentrations of CGA and relatively low pH occur in the vacuoles of plant cells. Transient assays demonstrated that tomato HQT localizes to the vacuole as well as to the cytoplasm of plant cells, supporting the idea that in this species, the enzyme catalyzes different reactions in two subcellular compartments.

  17. Brønsted Acid-Promoted Formation of Stabilized Silylium Ions for Catalytic Friedel-Crafts C-H Silylation.

    PubMed

    Chen, Qing-An; Klare, Hendrik F T; Oestreich, Martin

    2016-06-29

    A counterintuitive approach to electrophilic aromatic substitution with silicon electrophiles is disclosed. A strong Brønsted acid that would usually promote the reverse reaction, i.e., protodesilylation, was found to initiate the C-H silylation of electron-rich (hetero)arenes with hydrosilanes. Protonation of the hydrosilane followed by liberation of dihydrogen is key to success, fulfilling two purposes: to generate the stabilized silylium ion and to remove the proton released from the Wheland intermediate. PMID:27303857

  18. ECUT: Energy Conversion and utilization Technologies program biocatalysis research activity. Generation of chemical intermediates by catalytic oxidative decarboxylation of dilute organic acids

    NASA Technical Reports Server (NTRS)

    Distefano, S.; Gupta, A.; Ingham, J. D.

    1983-01-01

    A rhodium-based catalyst was prepared and preliminary experiments were completed where the catalyst appeared to decarboxylate dilute acids at concentrations of 1 to 10 vol%. Electron spin resonance spectroscoy was used to characterize the catalyst as a first step leading toward modeling and optimization of rhodium catalysts. Also, a hybrid chemical/biological process for the production of hydrocarbons has been assessed. These types of catalysts could greatly increase energy efficiency of this process.

  19. Correlation of zeolite ZSM-5 acid strength with catalytic activity and selectivity. Final report. [Cobalt and cobalt/thorium impregnated H-ZSM-5

    SciTech Connect

    Hayhurst, D.T.

    1984-04-01

    Isosteric heats of ammonia adsorption were determined for several cobalt and cobalt/thorium impregnated H-ZSM-5. Samples were impregnated to the 3, 6 and 9 wt % levels using an incipient wetness technique and either acetone or water for dissolving the metal nitrate salt. The metal impregnation resulted in a lowering of the maximum heat of ammonia adsorption and in a corresponding lowering of the maximum acid site strength. The ammonia adsorption capacity and adsorption heat was unaltered by a reduction of the metal-impregnated samples in hydrogen, indicating that the incipient wetness method leads to cobalt which was most likely ion-exchanged into the zeolite rather than impregnated into the sieve in a reducable form. In addition, the impregnated cobalt caused a slight steric hinderance to the diffusion of n-butane into the metal-loaded zeolite. The use of either water or acetone for dissolving the metal nitrate salt altered the acid-strength distribution. Water was found to lower the acid-site strength to a greater degree than the acetone. 11 references, 8 figures.

  20. Inhibition of Mycobacterium tuberculosis PknG by non-catalytic rubredoxin domain specific modification: reaction of an electrophilic nitro-fatty acid with the Fe-S center.

    PubMed

    Gil, Magdalena; Graña, Martín; Schopfer, Francisco J; Wagner, Tristan; Denicola, Ana; Freeman, Bruce A; Alzari, Pedro M; Batthyány, Carlos; Durán, Rosario

    2013-12-01

    PknG from Mycobacterium tuberculosis is a Ser/Thr protein kinase that regulates key metabolic processes within the bacterial cell as well as signaling pathways from the infected host cell. This multidomain protein has a conserved canonical kinase domain with N- and C-terminal flanking regions of unclear functional roles. The N-terminus harbors a rubredoxin-like domain (Rbx), a bacterial protein module characterized by an iron ion coordinated by four cysteine residues. Disruption of the Rbx-metal binding site by simultaneous mutations of all the key cysteine residues significantly impairs PknG activity. This encouraged us to evaluate the effect of a nitro-fatty acid (9- and 10-nitro-octadeca-9-cis-enoic acid; OA-NO2) on PknG activity. Fatty acid nitroalkenes are electrophilic species produced during inflammation and metabolism that react with nucleophilic residues of target proteins (i.e., Cys and His), modulating protein function and subcellular distribution in a reversible manner. Here, we show that OA-NO2 inhibits kinase activity by covalently adducting PknG remote from the catalytic domain. Mass spectrometry-based analysis established that cysteines located at Rbx are the specific targets of the nitroalkene. Cys-nitroalkylation is a Michael addition reaction typically reverted by thiols. However, the reversible OA-NO2-mediated nitroalkylation of the kinase results in an irreversible inhibition of PknG. Cys adduction by OA-NO2 induced iron release from the Rbx domain, revealing a new strategy for the specific inhibition of PknG. These results affirm the relevance of the Rbx domain as a target for PknG inhibition and support that electrophilic lipid reactions of Rbx-Cys may represent a new drug strategy for specific PknG inhibition.

  1. Central-metal exchange, improved catalytic activity, photoluminescence properties of a new family of d(10) coordination polymers based on the 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid ligand.

    PubMed

    Wang, Huarui; Huang, Chao; Han, Yanbing; Shao, Zhichao; Hou, Hongwei; Fan, Yaoting

    2016-05-01

    The rigid and planar tetracarboxylic acid 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid (H4L), incorporating a triazole group, has been used with no or different pyridine-based linkers to construct a family of d(10) coordination polymers, namely, {[H2N(CH3)2]3[Cd3(L)2(HCOO)]}n (), {[Cd2(L)(py)6]·H2O}n (), {[H2N(CH3)2] [Cd2(L)(HCOO)(H2O)4]}n (), {[Zn(H2L)]·H2O}n (), and {[Zn(H2L)(4,4'-bipy)0.5]·C2H5OH·H2O}n () (py = pyridine, 4,4'-bipy = 4,4'-bipyridine). constructs a 3D porous network containing two kinds of channels: one is filled with coordinated HCOO(-) anions, and the other with [H2N(CH3)2](+) cations. The framework of can be described as a rare (5,6,7)-connected net with the Schläfli symbol of (4(12)·5·6(2))(4(5)·5(3)·6(2))2(4(8)·5(3)·6(8)·8(2))2. The Cd(ii) ions in are connected through the carboxylate ligands to form a 2D layer, with aperture dimensions of ∼15.1 Å × 16.2 Å. The network of features a 3D (3,4)-connected (6·8·10)2(6·8(3)·10(2)) topology. A 3D network with the (4(2)·6·8(3)) topology of possesses an open 1D channel with the free volume of 29.2%. is a 2D layer structure with the (4(2)·6(3)·8)(4(2)·6) topology. The fluorescence lifetime τ values of are on the nanosecond timescale at room temperature. In particular, central-metal exchange in leads to a series of isostructural M(ii)-Cd frameworks [M = Cu (), Co (), Ni ()] showing improved catalytic activity for the synthesis of 1,4,5,6-tetrahydropyrimidine derivatives. Based on this, a plausible mechanism for the catalytic reaction has been proposed and the reactivity-structure relationship has been further clarified. PMID:27063339

  2. Determination of the Structure and Catalytic Mechanism of Sorghum bicolor Caffeic Acid O-Methyltransferase and the Structural Impact of Three brown midrib12 Mutations1[W

    PubMed Central

    Green, Abigail R.; Lewis, Kevin M.; Barr, John T.; Jones, Jeffrey P.; Lu, Fachuang; Ralph, John; Vermerris, Wilfred; Sattler, Scott E.; Kang, ChulHee

    2014-01-01

    Using S-adenosyl-methionine as the methyl donor, caffeic acid O-methyltransferase from sorghum (Sorghum bicolor; SbCOMT) methylates the 5-hydroxyl group of its preferred substrate, 5-hydroxyconiferaldehyde. In order to determine the mechanism of SbCOMT and understand the observed reduction in the lignin syringyl-to-guaiacyl ratio of three brown midrib12 mutants that carry COMT gene missense mutations, we determined the apo-form and S-adenosyl-methionine binary complex SbCOMT crystal structures and established the ternary complex structure with 5-hydroxyconiferaldehyde by molecular modeling. These structures revealed many features shared with monocot ryegrass (Lolium perenne) and dicot alfalfa (Medicago sativa) COMTs. SbCOMT steady-state kinetic and calorimetric data suggest a random bi-bi mechanism. Based on our structural, kinetic, and thermodynamic results, we propose that the observed reactivity hierarchy among 4,5-dihydroxy-3-methoxycinnamyl (and 3,4-dihydroxycinnamyl) aldehyde, alcohol, and acid substrates arises from the ability of the aldehyde to stabilize the anionic intermediate that results from deprotonation of the 5-hydroxyl group by histidine-267. Additionally, despite the presence of other phenylpropanoid substrates in vivo, sinapaldehyde is the preferential product, as demonstrated by its low Km for 5-hydroxyconiferaldehyde. Unlike its acid and alcohol substrates, the aldehydes exhibit product inhibition, and we propose that this is due to nonproductive binding of the S-cis-form of the aldehydes inhibiting productive binding of the S-trans-form. The S-cis-aldehydes most likely act only as inhibitors, because the high rotational energy barrier around the 2-propenyl bond prevents S-trans-conversion, unlike alcohol substrates, whose low 2-propenyl bond rotational energy barrier enables rapid S-cis/S-trans-interconversion. PMID:24948836

  3. Silver(I) as a widely applicable, homogeneous catalyst for aerobic oxidation of aldehydes toward carboxylic acids in water—“silver mirror”: From stoichiometric to catalytic

    PubMed Central

    Liu, Mingxin; Wang, Haining; Zeng, Huiying; Li, Chao-Jun

    2015-01-01

    The first example of a homogeneous silver(I)-catalyzed aerobic oxidation of aldehydes in water is reported. More than 50 examples of different aliphatic and aromatic aldehydes, including natural products, were tested, and all of them successfully underwent aerobic oxidation to give the corresponding carboxylic acids in extremely high yields. The reaction conditions are very mild and greener, requiring only a very low silver(I) catalyst loading, using atmospheric oxygen as the oxidant and water as the solvent, and allowing gram-scale oxidation with only 2 mg of our catalyst. Chromatography is completely unnecessary for purification in most cases. PMID:26601150

  4. Catalytic distillation process

    DOEpatents

    Smith, Jr., Lawrence A.

    1982-01-01

    A method for conducting chemical reactions and fractionation of the reaction mixture comprising feeding reactants to a distillation column reactor into a feed zone and concurrently contacting the reactants with a fixed bed catalytic packing to concurrently carry out the reaction and fractionate the reaction mixture. For example, a method for preparing methyl tertiary butyl ether in high purity from a mixed feed stream of isobutene and normal butene comprising feeding the mixed feed stream to a distillation column reactor into a feed zone at the lower end of a distillation reaction zone, and methanol into the upper end of said distillation reaction zone, which is packed with a properly supported cationic ion exchange resin, contacting the C.sub.4 feed and methanol with the catalytic distillation packing to react methanol and isobutene, and concurrently fractionating the ether from the column below the catalytic zone and removing normal butene overhead above the catalytic zone.

  5. Catalytic distillation process

    DOEpatents

    Smith, L.A. Jr.

    1982-06-22

    A method is described for conducting chemical reactions and fractionation of the reaction mixture comprising feeding reactants to a distillation column reactor into a feed zone and concurrently contacting the reactants with a fixed bed catalytic packing to concurrently carry out the reaction and fractionate the reaction mixture. For example, a method for preparing methyl tertiary butyl ether in high purity from a mixed feed stream of isobutene and normal butene comprising feeding the mixed feed stream to a distillation column reactor into a feed zone at the lower end of a distillation reaction zone, and methanol into the upper end of said distillation reaction zone, which is packed with a properly supported cationic ion exchange resin, contacting the C[sub 4] feed and methanol with the catalytic distillation packing to react methanol and isobutene, and concurrently fractionating the ether from the column below the catalytic zone and removing normal butene overhead above the catalytic zone.

  6. Evolution of catalytic function

    NASA Technical Reports Server (NTRS)

    Joyce, G. F.

    1993-01-01

    An RNA-based evolution system was constructed in the laboratory and used to develop RNA enzymes with novel catalytic function. By controlling the nature of the catalytic task that the molecules must perform in order to survive, it is possible to direct the evolving population toward the expression of some desired catalytic behavior. More recently, this system has been coupled to an in vitro translation procedure, raising the possibility of evolving protein enzymes in the laboratory to produce novel proteins with desired catalytic properties. The aim of this line of research is to reduce darwinian evolution, the fundamental process of biology, to a laboratory procedure that can be made to operate in the service of organic synthesis.

  7. A series of hybrid P450 BM3 enzymes with different catalytic activity in the light-initiated hydroxylation of lauric acid

    PubMed Central

    Tran, Ngoc-Han; Huynh, Ngoc; Chavez, Garrett; Nguyen, Angelina; Dwaraknath, Sudharsan; Nguyen, Thien-Anh; Nguyen, Maxine; Cheruzel, Lionel

    2012-01-01

    We have developed a series of hybrid P450 BM3 enzymes to perform the light-activated hydroxylation of lauric acid. These enzymes contain a Ru(II)-diimine photosensitizer covalently attached to single cysteine residues of mutant P450 BM3 heme domains. The library of hybrid enzymes includes four non-native single cysteine mutants (K97C, Q397C, Q109C and L407C). In addition, mutations around the heme active site, F87A and I401P, were inserted in the Q397C mutant. Two heteroleptic Ru(II) complexes, Ru(bpy)2phenA (1) and Ru(phen)2phenA (2) (bpy=bipyridine, phen=1,10-phenanthroline, and phenA=5-acetamido-1,10-phenanthroline), are used as photosensitizers. Upon visible light irradiation, the hybrid enzymes display various total turnover numbers in the hydroxylation of lauric acid, up to 140 for the L407C-1 mutant, a 16-fold increase compared to the F87A/Q397C-1 mutant. CO binding studies confirm the ability of the photogenerated Ru(I) compound to reduce the fraction of ferric high spin species present in the mutants upon substrate binding. PMID:22922311

  8. Catalytic performance comparison of shape-dependent nanocrystals and oriented ultra thin films of Pt4Cu alloy in the formic acid oxidation process

    NASA Astrophysics Data System (ADS)

    Bromberg, Lori Ana

    Research efforts continue to focus on the development of viable and cost effective fuel cell catalysts with minimized Pt content. This work presents a comparison study between Pt4Cu nanocubes and nano-octahedra as well as Pt4Cu (100) and (111) thin films used as catalysts for formic acid oxidation. The paper introduces a novel synthetic method for Pt 4Cu nano-octahedra and it also demonstrates for the first time the use of surface limited redox replacement of Pb underpotentially deposited layer for epitaxial growth of thin alloy films. Overall, the nanoparticle catalysts exhibit superior performance in terms of durability when compared to their thin film counterparts, but feature nearly five-fold lower activity. As a result it was determined that both types of catalysts accumulate nearly equal charge density in their lifespan. In terms of crystallographic orientation, the results indicate that the nanocubes and Pt4Cu (100) thin films outperform the nano-octahedra and Pt4Cu (111) thin films in terms of durability but feature equal to slightly lower activity. This significant difference in durability of catalysts with different crystallographic orientation is attributed to interplay of passivation (from CO poisoning and Pt oxidation) and dissolution of Pt. When compared to pure Pt catalysts (nanoparticles and thin films), all of the Pt4Cu catalysts in this work exhibit superior performance towards formic acid oxidation in terms of activity and durability.

  9. Catalytic distillation structure

    DOEpatents

    Smith, L.A. Jr.

    1984-04-17

    Catalytic distillation structure is described for use in reaction distillation columns, and provides reaction sites and distillation structure consisting of a catalyst component and a resilient component intimately associated therewith. The resilient component has at least about 70 volume % open space and is present with the catalyst component in an amount such that the catalytic distillation structure consists of at least 10 volume % open space. 10 figs.

  10. Clean catalytic combustor program

    NASA Technical Reports Server (NTRS)

    Ekstedt, E. E.; Lyon, T. F.; Sabla, P. E.; Dodds, W. J.

    1983-01-01

    A combustor program was conducted to evolve and to identify the technology needed for, and to establish the credibility of, using combustors with catalytic reactors in modern high-pressure-ratio aircraft turbine engines. Two selected catalytic combustor concepts were designed, fabricated, and evaluated. The combustors were sized for use in the NASA/General Electric Energy Efficient Engine (E3). One of the combustor designs was a basic parallel-staged double-annular combustor. The second design was also a parallel-staged combustor but employed reverse flow cannular catalytic reactors. Subcomponent tests of fuel injection systems and of catalytic reactors for use in the combustion system were also conducted. Very low-level pollutant emissions and excellent combustor performance were achieved. However, it was obvious from these tests that extensive development of fuel/air preparation systems and considerable advancement in the steady-state operating temperature capability of catalytic reactor materials will be required prior to the consideration of catalytic combustion systems for use in high-pressure-ratio aircraft turbine engines.

  11. Size-controlled synthesis of NiFe2O4 nanospheres via a PEG assisted hydrothermal route and their catalytic properties in oxidation of alcohols by periodic acid

    NASA Astrophysics Data System (ADS)

    Paul, Bappi; Purkayastha, Debraj Dhar; Dhar, Siddhartha Sankar

    2016-05-01

    A novel and facile approach for synthesis of spinel nickel ferrites (NiFe2O4) nanoparticles (NPs) employing homogeneous chemical precipitation followed by hydrothermal heating is reported. The synthesis involves use of tributylamine (TBA) as a hydroxylating agent in synthesis of nickel ferrites. Polyethylene glycol (PEG) 4000 was used as surfactant. As-synthesized NiFe2O4 NPs were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption isotherm (BET) and vibrating sample magnetometry (VSM). The XRD pattern revealed formation of cubic face-centered NiFe2O4 and TEM image showed spherical particles of sizes 2-10 nm. These NiFe2O4 NPs were used as magnetically recoverable catalyst in oxidation of cyclic alcohols to their corresponding aldehydes by periodic acid. This eco-friendly procedure affords products in very high yield and selectivity. The reusability of the catalyst is proved to be noteworthy as the material exhibits no significant changes in its catalytic activity even after five cycles of reuse.

  12. Enhanced bromate formation during chlorination of bromide-containing waters in the presence of CuO: catalytic disproportionation of hypobromous acid.

    PubMed

    Liu, Chao; von Gunten, Urs; Croué, Jean-Philippe

    2012-10-16

    Bromate (BrO(3)(-)) in drinking water is traditionally seen as an ozonation byproduct from the oxidation of bromide (Br(-)), and its formation during chlorination is usually not significant. This study shows enhanced bromate formation during chlorination of bromide-containing waters in the presence of cupric oxide (CuO). CuO was effective to catalyze hypochlorous acid (HOCl) or hypobromous acid (HOBr) decay (e.g., at least 10(4) times enhancement for HOBr at pH 8.6 by 0.2 g L(-1) CuO). Significant halate concentrations were formed from a CuO-catalyzed hypohalite disproportionation pathway. For example, the chlorate concentration was 2.7 ± 0.2 μM (225.5 ± 16.7 μg L(-1)) after 90 min for HOCl (C(o) = 37 μM, 2.6 mg L(-1) Cl(2)) in the presence of 0.2 g L(-1) CuO at pH 7.6, and the bromate concentration was 6.6 ± 0.5 μM (844.8 ± 64 μg L(-1)) after 180 min for HOBr (C(o) = 35 μM) in the presence of 0.2 g L(-1) CuO at pH 8.6. The maximum halate formation was at pHs 7.6 and 8.6 for HOCl or HOBr, respectively, which are close to their corresponding pK(a) values. In a HOCl-Br(-)-CuO system, BrO(3)(-) formation increases with increasing CuO doses and initial HOCl and Br(-) concentrations. A molar conversion (Br(-) to BrO(3)(-)) of up to (90 ± 1)% could be achieved in the HOCl-Br(-)-CuO system because of recycling of Br(-) to HOBr by HOCl, whereas the maximum BrO(3)(-) yield in HOBr-CuO is only 26%. Bromate formation is initiated by the formation of a complex between CuO and HOBr/OBr(-), which then reacts with HOBr to generate bromite. Bromite is further oxidized to BrO(3)(-) by a second CuO-catalyzed process. These novel findings may have implications for bromate formation during chlorination of bromide-containing drinking waters in copper pipes.

  13. Catalytic combustion over hexaaluminates

    SciTech Connect

    Ramesh, K.S.; Kingsley, J.J.; Hubler, T.L.; McCready, D.E.; Cox, J.L.

    1997-12-31

    Combustion is the oldest and most extensively used process for the production of light, heat, and energy utilization. Mankind has sought to control combustion since prehistoric times to more effectively utilize the combustible material, control the products of combustion, and harness the energy released during combustion. Catalysts provide the means to control the reactions of combustion beyond what can be achieved in the homogeneous gas phase (1). Catalysts also enable operation outside the range of flammability limits and control atmospheric pollutants of combustion, mainly NO{sub x}, carbon monoxide, and particles of incomplete combustion (soot). The major technical difficulty that has hindered widespread application of catalytic combustion devices is their poor performance, particularly durability of their ceramic substrates and catalytically active phases in the high temperature environment. Catalytic combustion of hydrocarbons over metals and metal oxide catalysts has been explored extensively. Recent reviews of materials for high temperature catalytic combustion have been provided by Marcus et al. (2) and Trim (3). Hexaaluminates which show good thermal stability above 1200{degrees}C are one class of metal oxides receiving consideration for application in high temperature combustion devices. Matsuda et al. (4) have developed thermally stable La-hexaaluminates with the same layer structure as Ba-hexaaluminate and have investigated their catalytic application. Machida et al. (5-7) have investigated the catalytic properties of a number of hexaaluminates of BaMAl{sub 11}O{sub 19-{alpha}}(M=Cr, Mn,Fe,Co,Ni). Here we report the synthesis, properties and catalytic combustion of some new hexaaluminates.

  14. Evidence for catalytic intermediates involved in generating the chromopyrrolic acid scaffold of rebeccamycin by RebO and RebD.

    PubMed

    Spolitak, Tatyana; Ballou, David P

    2015-05-01

    We provide the first experimental evidence for intermediates being involved in catalysis by RebD in generating the chromopyrrolic acid (CPA) scaffold of rebeccamycin. In the presence of its substrates (indole pyruvate imine - IPAI - and H2O2 both produced by the flavoprotein oxidase RebO that oxidizes tryptophan), RebD reacts as a peroxidase forming two IPAI radicals that recombine as a C-C bond in the CPA. When catalase is included to remove H2O2, CPA can still be formed because the IPAI rapidly reduces RebD, which reacts with O2, utilizing oxidase-peroxidase chemistry to produce CPA. Reduced RebD can also react with H2O2 forming Cpd II directly, which can oxidize IPAI. Stopped-flow spectrophotometric studies demonstrated that during the reaction of RebO and RebD with Trp and oxygen, a species with a red-shifted Soret band at 424.5 nm appeared. This species can react with either guaiacol or ABTS to form ferric RebD, suggesting that it is Cpd II of RebD involved in the formation of CPA. In summary, the studies reveal new and unusual aspects peroxidase and peroxygenase chemistry used by RebD in catalyzing carbon-carbon oxidative coupling reactions that are involved in biosynthesis of indolocarbazoles. PMID:25837855

  15. Computational insight into the catalytic implication of head/tail-first orientation of arachidonic acid in human 5-lipoxygenase: consequences for the positional specificity of oxygenation.

    PubMed

    Saura, Patricia; Maréchal, Jean-Didier; Masgrau, Laura; Lluch, José M; González-Lafont, Àngels

    2016-08-17

    In the present work we have combined homology modeling, protein-ligand dockings, quantum mechanics/molecular mechanics calculations and molecular dynamics simulations to generate human 5-lipoxygenase (5-LOX):arachidonic acid (AA) complexes consistent with the 5-lipoxygenating activity (which implies hydrogen abstraction at the C7 position). Our results suggest that both the holo and the apo forms of human Stable 5-LOX could accommodate AA in a productive form for 5-lipoxygenation. The former, in a tail-first orientation, with the AA carboxylate end interacting with Lys409, gives the desired structures with C7 close to the Fe-OH(-) cofactor and suitable barrier heights for H7 abstraction. Only when using the apo form structure, a head-first orientation with the AA carboxylate close to His600 (a residue recently proposed as essential for AA positioning) is obtained in the docking calculations. However, the calculated barrier heights for this head-first orientation are in principle consistent with 5-LOX specificity, but also with 12/8 regioselectivity. Finally, long MD simulations give support to the recent hypothesis that the Phe177 + Tyr181 pair needs to close the active site access during the chemical reaction, and suggest that in the case of a head-first orientation Phe177 may be the residue interacting with the AA carboxylate. PMID:27489112

  16. Catalytically Increased Prebiotic Peptide Formation: Ditryptophan, Dilysine, and Diserine

    NASA Astrophysics Data System (ADS)

    Plankensteiner, Kristof; Reiner, Hannes; Rode, Bernd M.

    2005-10-01

    “Mutual” amino acid catalysis of glycine on the formation of ditryptophan, dilysine, and diserine in the prebiotically relevant Salt-Induced Peptide Formation (SIPF) Reaction was investigated varying the starting concentration and chirality of the educt amino acid, and analyzing the increase of yield resulting from this catalytic effect. Our results show the possibility of an amplified diverse pool of peptides being available for chemical evolution of larger peptides and proteins using also these more complicated amino acids for the evolution of more complex functions in future biochemical cycles and thus for the emergence of life. Catalytic effects are especially high in the case of serine, the most basic amino acid of the three, but are also significant for the other two examples investigated in the present work. Besides that, especially for serine, but also in the case of tryptophan, differences in catalytic yield increase according to the chiral form of the amino acid used could be observed.

  17. Transient catalytic combustor model

    NASA Technical Reports Server (NTRS)

    Tien, J. S.

    1981-01-01

    A quasi-steady gas phase and thermally thin substrate model is used to analyze the transient behavior of catalytic monolith combustors in fuel lean operation. The combustor response delay is due to the substrate thermal inertia. Fast response is favored by thin substrate, short catalytic bed length, high combustor inlet and final temperatures, and small gas channel diameters. The calculated gas and substrate temperature time history at different axial positions provides an understanding of how the catalytic combustor responds to an upstream condition change. The computed results also suggest that the gas residence times in the catalytic bed in the after bed space are correlatable with the nondimensional combustor response time. The model also performs steady state combustion calculations; and the computed steady state emission characteristics show agreement with available experimental data in the range of parameters covered. A catalytic combustor design for automotive gas turbine engine which has reasonably fast response ( 1 second) and can satisfy the emission goals in an acceptable total combustor length is possible.

  18. Catalytic nanoporous membranes

    DOEpatents

    Pellin, Michael J; Hryn, John N; Elam, Jeffrey W

    2013-08-27

    A nanoporous catalytic membrane which displays several unique features Including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity. Also provided is a method for producing a catalytic membrane having flow-through pores and discreet catalytic clusters adhering to the inside surfaces of the pores.

  19. Catalytic coherence transformations

    NASA Astrophysics Data System (ADS)

    Bu, Kaifeng; Singh, Uttam; Wu, Junde

    2016-04-01

    Catalytic coherence transformations allow the otherwise impossible state transformations using only incoherent operations with the aid of an auxiliary system with finite coherence that is not being consumed in any way. Here we find the necessary and sufficient conditions for the deterministic and stochastic catalytic coherence transformations between a pair of pure quantum states. In particular, we show that the simultaneous decrease of a family of Rényi entropies of the diagonal parts of the states under consideration is a necessary and sufficient condition for the deterministic catalytic coherence transformations. Similarly, for stochastic catalytic coherence transformations we find the necessary and sufficient conditions for achieving a higher optimal probability of conversion. We thus completely characterize the coherence transformations among pure quantum states under incoherent operations. We give numerous examples to elaborate our results. We also explore the possibility of the same system acting as a catalyst for itself and find that indeed self-catalysis is possible. Further, for the cases where no catalytic coherence transformation is possible we provide entanglement-assisted coherence transformations and find the necessary and sufficient conditions for such transformations.

  20. Catalytic hydrotreating process

    DOEpatents

    Karr, Jr., Clarence; McCaskill, Kenneth B.

    1978-01-01

    Carbonaceous liquids boiling above about 300.degree. C such as tars, petroleum residuals, shale oils and coal-derived liquids are catalytically hydrotreated by introducing the carbonaceous liquid into a reaction zone at a temperature in the range of 300.degree. to 450.degree. C and a pressure in the range of 300 to 4000 psig for effecting contact between the carbonaceous liquid and a catalytic transition metal sulfide in the reaction zone as a layer on a hydrogen permeable transition metal substrate and then introducing hydrogen into the reaction zone by diffusing the hydrogen through the substrate to effect the hydrogenation of the carbonaceous liquid in the presence of the catalytic sulfide layer.

  1. Catalytic membranes beckon

    SciTech Connect

    Caruana, C.M.

    1994-11-01

    Chemical engineers here and abroad are finding that the marriage of catalysts and membranes holds promise for faster and more specific reactions, although commercialization of this technology is several years away. Catalytic membrane reactors (CMRs) combine a heterogeneous catalyst and a permselective membrane. Reactions performed by CMRs provide higher yields--sometimes as much as 50% higher--because of better reaction selectivity--as opposed to separation selectivity. CMRs also can work at very high temperatures, using ceramic materials that would not be possible with organic membranes. Although the use of CMRs is not widespread presently, the development of new membranes--particularly porous ceramic and zeolite membranes--will increase the potential to improve yields of many catalytic processes. The paper discusses ongoing studies, metal and advanced materials for membranes, the need for continued research, hydrogen recovery from coal-derived gases, catalytic oxidation of sulfides, CMRs for water purification, and oxidative coupling of methane.

  2. Catalytic molecular beacons.

    PubMed

    Stojanovic, M N; de Prada, P; Landry, D W

    2001-06-01

    We have constructed catalytic molecular beacons from a hammerhead-type deoxyribozyme by a modular design. The deoxyribozyme was engineered to contain a molecular beacon stem-loop module that, when closed, inhibits the deoxyribozyme module and is complementary to a target oligonucleotide. Binding of target oligonucleotides opens the beacon stem-loop and allosterically activates the deoxyribozyme module, which amplifies the recognition event through cleavage of a doubly labeled fluorescent substrate. The customized modular design of catalytic molecular beacons allows for any two single-stranded oligonucleotide sequences to be distinguished in homogenous solution in a single step. Our constructs demonstrate that antisense conformational triggers based on molecular beacons can be used to initiate catalytic events. The selectivity of the system is sufficient for analytical applications and has potential for the construction of deoxyribozyme-based drug delivery tools specifically activated in cells containing somatic mutations.

  3. Fluid catalytic cracking

    SciTech Connect

    Bartley, B.H.; Petty, R.H.

    1982-08-17

    Gaseous sulfur compounds are removed from a sulfur-containing gas mixture by reacting sulfur oxides in the gas mixture with alumina in association with bismuth. The process is particularly useful in fluid catalytic cracking of sulfur-containing petroleum charge stocks wherein sulfur is contained in coke deposited on the fluidized cracking catalyst. By the process of this invention, sulfur oxides may be removed from regenerator off-gases from a fluidized catalytic cracking unit by incorporating particulate alumina impregnated with bismuth in particulate cracking catalyst whereby sulfur oxides generated in the regeneration of the catalyst are reacted with bismuth-impregnated alumina. Sulfur oxides produced during regeneration of the catalyst by burning the coke with air are captured and converted to hydrogen sulfide in the cracking reactor. The hydrogen sulfide so produced is readily separated from petroleum products of the catalytic cracking reaction process.

  4. Structural insights into the recovery of aldolase activity in N-acetylneuraminic acid lyase by replacement of the catalytically active lysine with γ-thialysine by using a chemical mutagenesis strategy.

    PubMed

    Timms, Nicole; Windle, Claire L; Polyakova, Anna; Ault, James R; Trinh, Chi H; Pearson, Arwen R; Nelson, Adam; Berry, Alan

    2013-03-01

    Chemical modification has been used to introduce the unnatural amino acid γ-thialysine in place of the catalytically important Lys165 in the enzyme N-acetylneuraminic acid lyase (NAL). The Staphylococcus aureus nanA gene, encoding NAL, was cloned and expressed in E. coli. The protein, purified in high yield, has all the properties expected of a class I NAL. The S. aureus NAL which contains no natural cysteine residues was subjected to site-directed mutagenesis to introduce a cysteine in place of Lys165 in the enzyme active site. Subsequently chemical mutagenesis completely converted the cysteine into γ-thialysine through dehydroalanine (Dha) as demonstrated by ESI-MS. Initial kinetic characterisation showed that the protein containing γ-thialysine regained 17 % of the wild-type activity. To understand the reason for this lower activity, we solved X-ray crystal structures of the wild-type S. aureus NAL, both in the absence of, and in complex with, pyruvate. We also report the structures of the K165C variant, and the K165-γ-thialysine enzyme in the presence, or absence, of pyruvate. These structures reveal that γ-thialysine in NAL is an excellent structural mimic of lysine. Measurement of the pH-activity profile of the thialysine modified enzyme revealed that its pH optimum is shifted from 7.4 to 6.8. At its optimum pH, the thialysine-containing enzyme showed almost 30 % of the activity of the wild-type enzyme at its pH optimum. The lowered activity and altered pH profile of the unnatural amino acid-containing enzyme can be rationalised by imbalances of the ionisation states of residues within the active site when the pK(a) of the residue at position 165 is perturbed by replacement with γ-thialysine. The results reveal the utility of chemical mutagenesis for the modification of enzyme active sites and the exquisite sensitivity of catalysis to the local structural and electrostatic environment in NAL.

  5. Steam reformer with catalytic combustor

    DOEpatents

    Voecks, Gerald E.

    1990-03-20

    A steam reformer is disclosed having an annular steam reforming catalyst bed formed by concentric cylinders and having a catalytic combustor located at the center of the innermost cylinder. Fuel is fed into the interior of the catalytic combustor and air is directed at the top of the combustor, creating a catalytic reaction which provides sufficient heat so as to maintain the catalytic reaction in the steam reforming catalyst bed. Alternatively, air is fed into the interior of the catalytic combustor and a fuel mixture is directed at the top. The catalytic combustor provides enhanced radiant and convective heat transfer to the reformer catalyst bed.

  6. Steam reformer with catalytic combustor

    NASA Technical Reports Server (NTRS)

    Voecks, Gerald E. (Inventor)

    1990-01-01

    A steam reformer is disclosed having an annular steam reforming catalyst bed formed by concentric cylinders and having a catalytic combustor located at the center of the innermost cylinder. Fuel is fed into the interior of the catalytic combustor and air is directed at the top of the combustor, creating a catalytic reaction which provides sufficient heat so as to maintain the catalytic reaction in the steam reforming catalyst bed. Alternatively, air is fed into the interior of the catalytic combustor and a fuel mixture is directed at the top. The catalytic combustor provides enhanced radiant and convective heat transfer to the reformer catalyst bed.

  7. Fluid catalytic cracking

    SciTech Connect

    Petty, R.H.; Bartley, B.H.

    1984-05-01

    A fluid catalytic cracking process is disclosed for sulfur-containing petroleum charge stocks. Sulfur contained in coke deposited on the fluidized cracking catalyst in the reactor is converted to sulfur oxides in the regenerator and removed from regenerator off-gases by incorporating a composite of alumina and bismuth oxides in a particulate cracking catalyst. Sulfur oxides produced during regeneration of the catalyst by burning the coke with air in the regenerator are captured by the alumina-bismuth oxides composite and converted to hydrogen sulfide in the cracking reactor. The hydrogen sulfide so produced is readily separated from petroleum products of the catalytic cracking reaction process.

  8. An integrated process for the production of platform chemicals and diesel miscible fuels by acid-catalyzed hydrolysis and downstream upgrading of the acid hydrolysis residues with thermal and catalytic pyrolysis.

    PubMed

    Girisuta, Buana; Kalogiannis, Konstantinos G; Dussan, Karla; Leahy, James J; Hayes, Michael H B; Stefanidis, Stylianos D; Michailof, Chrysa M; Lappas, Angelos A

    2012-12-01

    This study evaluates an integrated process for the production of platform chemicals and diesel miscible biofuels. An energy crop (Miscanthus) was treated hydrothermally to produce levulinic acid (LA). Temperatures ranging between 150 and 200 °C, sulfuric acid concentrations 1-5 wt.% and treatment times 1-12 h were applied to give different combined severity factors. Temperatures of 175 and 200 °C and acid concentration of 5 wt.% were found to be necessary to achieve good yield (17 wt.%) and selectivities of LA while treatment time did not have an effect. The acid hydrolysis residues were characterized for their elemental, cellulose, hemicellulose and lignin contents, and then tested in a small-scale pyrolyzer using silica sand and a commercial ZSM-5 catalyst. Milder pretreatment yielded more oil (43 wt.%) and oil O(2) (37%) while harsher pretreatment and catalysis led to more coke production (up to 58 wt.%), less oil (12 wt.%) and less oil O(2) (18 wt.%).

  9. Thermal and sonochemical synthesis of porous (Ce,Zr)O2 mixed oxides from metal β-diketonate precursors and their catalytic activity in wet air oxidation process of formic acid.

    PubMed

    Cau, Camille; Guari, Yannick; Chave, Tony; Larionova, Joulia; Nikitenko, Sergey I

    2014-07-01

    Porous (Ce0.5Zr0.5)O2 solid solutions were prepared by thermolysis (T=285 °C) or sonolysis (20 kHz, I=32 W cm(-2), Pac=0.46 W mL(-1), T=200 °C) of Ce(III) and Zr(IV) acetylacetonates in oleylamine or hexadecylamine under argon followed by heat treatment of the precipitates obtained in air at 450 °C. Transmission Electron Microscopy images of the samples show nanoparticles of ca. 4-6 nm for the two synthetic approaches. The powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and μ-Raman spectroscopy of solids obtained after heat treatment indicate the formation of (Ce0.5Zr0.5)O2 solid solutions with a metastable tetragonal crystal structure for the two synthetic routes. The specific surface area of the samples varies between 78 and 149 m(2) g(-1) depending on synthesis conditions. The use of Barrett-Joyner-Halenda and t-plot methods reveal the formation of mixed oxides with a hybrid morphology that combines mesoporosity and microporosity regardless of the method of preparation. Platinum nanoparticles were deposited on the surface of the mixed oxides by sonochemical reduction of Pt(IV). It was found that the materials prepared by sonochemistry exhibit better resistance to dissolution during the deposition process of platinum. X-ray photoelectron spectroscopy analysis shows the presence of Pt(0) and Pt(II) on the surface of mixed oxides. Porous (Ce0.5Zr0.5)O2 mixed oxides loaded with 1.5%wt. platinum exhibit high activity in catalytic wet air oxidation of formic acid at 40 °C.

  10. The antitumor mechanism of di-2-pyridylketone 2-pyridine carboxylic acid hydrazone and its copper complex in ROS generation and topoisomerase inhibition, and hydrazone involvement in oxygen-catalytic iron mobilization.

    PubMed

    Huang, Tengfei; Li, Cuiping; Sun, Xingzhi; Zhu, Zhenfu; Fu, Yun; Liu, Youxun; Yuan, Yanbin; Li, Shaoshan; Li, Changzheng

    2015-11-01

    Iron depletion and stimulation of iron-dependent free radical damage is a rapidly developing field for chelation therapy, but the iron mobilization from ferritin by chelators has received less attention. In this study, the di-2-pyridylketone 2-pyridine carboxylic acid hydrazone (DPPCAH) and its copper complex was prepared and characterized by NMR and MS spectra. The proliferation inhibition assay showed that both DPPCAH and its copper complex exhibited selectively proliferation inhibition for HepG2 (IC50, 4.6 ± 0.2 µM for DPPACH and 1.3 ± 0.2 µM for its copper complex), but less inhibition for HCT-116 cell line (IC50, >100 µM for DPPACH and 7.8 ± 0.4 µM for its copper complex). The mechanistic studies revealed that DPPACH could remove iron from ferritin in a oxygen-catalytic manner, and contributed to redox activity of labile iron pool (LIP), that is less reported for the chelators that possess significant biological activity. The reactive oxygen species (ROS) generation and DNA cleavage assay in vitro and in vivo showed that both DPPACH-Fe(II) and DPPACH-Cu were redox-active species, indicating that ROS may mediate their antitumor activity. Further study revealed that both DPPACH and its copper complex displayed certain degree of inhibition of type II topoisomerase (Top) which contributed to their antitumor activity. Thus, the mechanism that iron mobilization by DPPACH from ferritin contributed to LIP was proposed, and both DPPACH and its copper complex were involved in ROS generation and Top II inhibition for their antitumor activities.

  11. Catalytic anomeric aminoalkynylation of unprotected aldoses.

    PubMed

    Kimura, Yasuaki; Ito, Soichi; Shimizu, Yohei; Kanai, Motomu

    2013-08-16

    A copper(I)-catalyzed anomeric aminoalkynylation reaction of unprotected aldoses was realized. Use of an electron-deficient phosphine ligand, boric acid to stabilize the iminium intermediate, and a protic additive (IPA) to presumably enhance reversible carbohydrate-boron complexation were all essential for efficient conversion. The reaction proceeded well even with a natural disaccharide substrate, suggesting that the developed catalytic reaction could be useful for the synthesis of glycoconjugates with minimum use of protecting groups. PMID:23901780

  12. Catalytic efficiency of designed catalytic proteins

    PubMed Central

    Korendovych, Ivan V; DeGrado, William F

    2014-01-01

    The de novo design of catalysts that mimic the affinity and specificity of natural enzymes remains one of the Holy Grails of chemistry. Despite decades of concerted effort we are still unable to design catalysts as efficient as enzymes. Here we critically evaluate approaches to (re)design of novel catalytic function in proteins using two test cases: Kemp elimination and ester hydrolysis. We show that the degree of success thus far has been modest when the rate enhancements seen for the designed proteins are compared with the rate enhancements by small molecule catalysts in solvents with properties similar to the active site. Nevertheless, there are reasons for optimism: the design methods are ever improving and the resulting catalyst can be efficiently improved using directed evolution. PMID:25048695

  13. Catalytic efficiency of designed catalytic proteins.

    PubMed

    Korendovych, Ivan V; DeGrado, William F

    2014-08-01

    The de novo design of catalysts that mimic the affinity and specificity of natural enzymes remains one of the Holy Grails of chemistry. Despite decades of concerted effort we are still unable to design catalysts as efficient as enzymes. Here we critically evaluate approaches to (re)design of novel catalytic function in proteins using two test cases: Kemp elimination and ester hydrolysis. We show that the degree of success thus far has been modest when the rate enhancements seen for the designed proteins are compared with the rate enhancements by small molecule catalysts in solvents with properties similar to the active site. Nevertheless, there are reasons for optimism: the design methods are ever improving and the resulting catalyst can be efficiently improved using directed evolution.

  14. Architecture and function of metallopeptidase catalytic domains

    PubMed Central

    Cerdà-Costa, Núria; Gomis-Rüth, Francesc Xavier

    2014-01-01

    The cleavage of peptide bonds by metallopeptidases (MPs) is essential for life. These ubiquitous enzymes participate in all major physiological processes, and so their deregulation leads to diseases ranging from cancer and metastasis, inflammation, and microbial infection to neurological insults and cardiovascular disorders. MPs cleave their substrates without a covalent intermediate in a single-step reaction involving a solvent molecule, a general base/acid, and a mono-or dinuclear catalytic metal site. Most monometallic MPs comprise a short metal-binding motif (HEXXH), which includes two metal-binding histidines and a general base/acid glutamate, and they are grouped into the zincin tribe of MPs. The latter divides mainly into the gluzincin and metzincin clans. Metzincins consist of globular ∼130–270-residue catalytic domains, which are usually preceded by N-terminal pro-segments, typically required for folding and latency maintenance. The catalytic domains are often followed by C-terminal domains for substrate recognition and other protein–protein interactions, anchoring to membranes, oligomerization, and compartmentalization. Metzincin catalytic domains consist of a structurally conserved N-terminal subdomain spanning a five-stranded β-sheet, a backing helix, and an active-site helix. The latter contains most of the metal-binding motif, which is here characteristically extended to HEXXHXXGXX(H,D). Downstream C-terminal subdomains are generally shorter, differ more among metzincins, and mainly share a conserved loop—the Met-turn—and a C-terminal helix. The accumulated structural data from more than 300 deposited structures of the 12 currently characterized metzincin families reviewed here provide detailed knowledge of the molecular features of their catalytic domains, help in our understanding of their working mechanisms, and form the basis for the design of novel drugs. PMID:24596965

  15. Dinuclear complexes of copper and zinc with m-xylene/cyclohexane-linked bis-aspartic acids: synthesis, characterization, dioxygen activation, and catalytic oxidation of nitrobenzene in pure aqueous solution.

    PubMed

    Zhu, Shourong; Qiu, Zhixiang; Ni, Tianjun; Zhao, Xiujuan; Yan, Shikai; Xing, Feifei; Zhao, Yongmei; Bai, Yueling; Li, Mingxing

    2013-08-14

    Two new m-xylene/cyclohexane-linked bis-aspartic acid ligands, L(b) and L(c), were synthesized via Michael addition in basic aqueous solution. Their structures were characterized by elemental analysis, NMR and MS spectrometry. Both ligands react with Cu(II) and Zn(II) to form dinuclear complexes, with M2L(OH)(-) the major species in neutral/weak basic aqueous solution. To quantify the relative interaction strength between a Lewis acid and base, a new parameter σ = log K/14 was proposed which compares the stability constant with the binding constant between H(+) and OH(-). The dinuclear copper complexes (L(b)-2Cu and L(c)-2Cu) react with H2O2 in aqueous solution. The reaction in 0.020 M phosphate buffer at pH 7.5 is first-order for [L(c)-2Cu], but second-order for [L(b)-2Cu]. The oxidation products are oxygenated and/or dehydrogenated species. Radical trapping tests indicate that both complexes slightly scavenge the OH˙ radical, but generate the H˙ radical. L(c)-2Cu generates the H˙ radical much more effectively than that of L(b)-2Cu when reacted with H2O2. Both complexes are excellent catalysts for the oxidation of nitrobenzene in the presence of H2O2 in weakly basic aqueous solution. The oxidation follows the rate-law v = k[complex][nitrobenzene][H2O2]. The k values in pH 8.0 phosphate buffer at 25 °C are 211.2 ± 0.3 and 607.9 ± 1.7 mol(-2) L(2) s(-1) for L(b)-2Cu and L(c)-2Cu, respectively. The Arrhenius activation energies are 69.4 ± 2.2 and 70.0 ± 4.3 kJ mol(-1) for L(b)-2Cu and L(c)-2Cu, respectively, while the Arrhenius pre-exponential factors are 2.62 × 10(14) and 1.06 × 10(15), respectively. The larger pre-exponential factor makes L(c)-2Cu more catalytically active than L(b)-2Cu. These complexes are some of the most effective oxidation catalysts known for the oxidation of nitrobenzene.

  16. Method for recovering catalytic elements from fuel cell membrane electrode assemblies

    DOEpatents

    Shore, Lawrence; Matlin, Ramail; Heinz, Robert

    2012-06-26

    A method for recovering catalytic elements from a fuel cell membrane electrode assembly is provided. The method includes converting the membrane electrode assembly into a particulate material, wetting the particulate material, forming a slurry comprising the wetted particulate material and an acid leachate adapted to dissolve at least one of the catalytic elements into a soluble catalytic element salt, separating the slurry into a depleted particulate material and a supernatant containing the catalytic element salt, and washing the depleted particulate material to remove any catalytic element salt retained within pores in the depleted particulate material.

  17. A graphene-based smart catalytic system with superior catalytic performances and temperature responsive catalytic behaviors.

    PubMed

    Qi, Junjie; Lv, Weipeng; Zhang, Guanghui; Li, Yang; Zhang, Guoliang; Zhang, Fengbao; Fan, Xiaobin

    2013-07-21

    We have successfully developed a unique graphene-based smart catalytic system which consists of the graphene supported Au-Pt bimetallic nanocatalyst with a well-defined core-shell structure and a dextran-based temperature-responsive polymer. The unique catalytic system possesses excellent catalytic performances and the catalytic activities could be readily switched on or off at different temperature windows. PMID:23740038

  18. Purification of reformer streams by catalytic hydrogenation

    SciTech Connect

    Polanek, P.J.; Hooper, H.M.; Mueller, J.; Walter, M.; Emmrich, G.

    1996-12-01

    Catalytic Reforming is one of the most important processes to produce high grade motor gasolines. Feedstocks are mainly gasoline and naphtha streams from the crude oil distillation boiling in the range of 212 F to 350 F. By catalytic reforming the octane number of these gasoline components is increased from 40--60 RON to 95--100 RON. Besides isomerization and dehydrocyclization reactions mainly formation of aromatics by dehydrogenation of naphthenes occur. Thus, catalytic reformers within refineries are an important source of BTX--aromatics (benzene, toluene, xylenes). Frequently, high purity aromatics are recovered from these streams using modern extractive distillation or liquid extraction processes, e.g. the Krupp-Koppers MORPHYLANE{reg_sign} process. Aromatics product specifications, notably bromine index and acid wash color, have obligated producers to utilize clay treatment to remove trace impurities of diolefins and/or olefins. The conventional clay treatment is a multiple vessel batch process which periodically requires disposal of the spent clay in a suitable environmental manner. BASF, in close cooperation with Krupp-Koppers, has developed a continuous Selective Catalytic Hydrogenation Process (SCHP) as an alternative to clay treatment which is very efficient, cost effective and environmentally compatible. In the following the main process aspects including the process scheme catalyst and operating conditions is described.

  19. Catalytic thermal barrier coatings

    DOEpatents

    Kulkarni, Anand A.; Campbell, Christian X.; Subramanian, Ramesh

    2009-06-02

    A catalyst element (30) for high temperature applications such as a gas turbine engine. The catalyst element includes a metal substrate such as a tube (32) having a layer of ceramic thermal barrier coating material (34) disposed on the substrate for thermally insulating the metal substrate from a high temperature fuel/air mixture. The ceramic thermal barrier coating material is formed of a crystal structure populated with base elements but with selected sites of the crystal structure being populated by substitute ions selected to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a higher rate than would the base compound without the ionic substitutions. Precious metal crystallites may be disposed within the crystal structure to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a lower light-off temperature than would the ceramic thermal barrier coating material without the precious metal crystallites.

  20. Catalytic, hollow, refractory spheres

    NASA Technical Reports Server (NTRS)

    Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)

    1987-01-01

    Improved, heterogeneous, refractory catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitable formed of a shell (12) of refractory such as alumina having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be itself catalytic or a catalytically active material coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.

  1. Catalytic nanoporous membranes

    DOEpatents

    Pellin, Michael J.; Hryn, John N.; Elam, Jeffrey W.

    2009-12-01

    A nanoporous catalytic membrane which displays several unique features including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity.

  2. Catalytic pyrolysis of palm kernel shell waste in a fluidized bed.

    PubMed

    Kim, Sung Won; Koo, Bon Seok; Lee, Dong Hyun

    2014-09-01

    The catalytic pyrolysis of palm kernel shell was investigated in a fluidized bed with zsm-5 and equilibrium FCC (Ecat) catalysts. Catalytic pyrolysis oil yields were remarkably reduced and gas yields were increased due to the higher catalytic reaction of primary volatiles compared to non-catalytic pyrolysis. Char yields were affected by temperature and the pore structure of the catalysts. The pyrolysis oil was characterized by lower H/C and O/C molar ratios due to aromatization and deoxygenation of volatiles by the catalysts. The catalytic pyrolysis oils contained more oxygen and nitrogen and less sulfur than petroleum oils. The oils had a high concentration of nitriles, with a carbon number distribution similar to fatty acids. The catalytic pyrolysis oils featured high nitriles yield with Ecat and high aromatics yield in the light fraction with zsm-5, due to characteristics of the catalyst. The catalytic pyrolysis oils showed potentials as feedstocks for bio-diesel and chemicals.

  3. Catalytic pyrolysis of waste rice husk over mesoporous materials

    PubMed Central

    2012-01-01

    Catalytic fast pyrolysis of waste rice husk was carried out using pyrolysis-gas chromatography/mass spectrometry [Py-GC/MS]. Meso-MFI zeolite [Meso-MFI] was used as the catalyst. In addition, a 0.5-wt.% platinum [Pt] was ion-exchanged into Meso-MFI to examine the effect of Pt addition. Using a catalytic upgrading method, the activities of the catalysts were evaluated in terms of product composition and deoxygenation. The structure and acid site characteristics of the catalysts were analyzed by Brunauer-Emmett-Teller surface area measurement and NH3 temperature-programmed desorption analysis. Catalytic upgrading reduced the amount of oxygenates in the product vapor due to the cracking reaction of the catalysts. Levoglucosan, a polymeric oxygenate species, was completely decomposed without being detected. While the amount of heavy phenols was reduced by catalytic upgrading, the amount of light phenols was increased because of the catalytic cracking of heavy phenols into light phenols and aromatics. The amount of aromatics increased remarkably as a result of catalytic upgrading, which is attributed to the strong Brönsted acid sites and the shape selectivity of the Meso-MFI catalyst. The addition of Pt made the Meso-MFI catalyst even more active in deoxygenation and in the production of aromatics. PMID:22221540

  4. Catalytic reforming methods

    DOEpatents

    Tadd, Andrew R; Schwank, Johannes

    2013-05-14

    A catalytic reforming method is disclosed herein. The method includes sequentially supplying a plurality of feedstocks of variable compositions to a reformer. The method further includes adding a respective predetermined co-reactant to each of the plurality of feedstocks to obtain a substantially constant output from the reformer for the plurality of feedstocks. The respective predetermined co-reactant is based on a C/H/O atomic composition for a respective one of the plurality of feedstocks and a predetermined C/H/O atomic composition for the substantially constant output.

  5. Catalysis by multimetallics. Catalyzed homogeneous oxidation of alcohols, ketones, and triphenylphosphine with molecular oxygen in the presence of hexarhodium dodecacarbonyl and dirhenium decacarbonyl

    SciTech Connect

    Roundhill, D.M.; Dickson, M.K.; Dixit, N.S.; Sudha-dixit, B.P.

    1980-01-01

    The conversion, mechanism, and solvent effects were studied for the oxidation of cyclohexanone and cyclohexanol to adipic acid catalyzed by Rh/sub 6/(CO)/sub 16/ and Re/sub 2/(CO)/sub 10/. The oxidation reactions of cyclopentanone, cycloheptanone, acetone, ethanol, diethylcarbinol, and isopropanol, and the decomposition of hydrogen peroxide with these catalysts were also investigated.

  6. Novel Catalytic Membrane Reactors

    SciTech Connect

    Stuart Nemser, PhD

    2010-10-01

    There are many industrial catalytic organic reversible reactions with amines or alcohols that have water as one of the products. Many of these reactions are homogeneously catalyzed. In all cases removal of water facilitates the reaction and produces more of the desired chemical product. By shifting the reaction to right we produce more chemical product with little or no additional capital investment. Many of these reactions can also relate to bioprocesses. Given the large number of water-organic compound separations achievable and the ability of the Compact Membrane Systems, Inc. (CMS) perfluoro membranes to withstand these harsh operating conditions, this is an ideal demonstration system for the water-of-reaction removal using a membrane reactor. Enhanced reaction synthesis is consistent with the DOE objective to lower the energy intensity of U.S. industry 25% by 2017 in accord with the Energy Policy Act of 2005 and to improve the United States manufacturing competitiveness. The objective of this program is to develop the platform technology for enhancing homogeneous catalytic chemical syntheses.

  7. Catalytic Activities Of [GADV]-Peptides

    NASA Astrophysics Data System (ADS)

    Oba, Takae; Fukushima, Jun; Maruyama, Masako; Iwamoto, Ryoko; Ikehara, Kenji

    2005-10-01

    We have previously postulated a novel hypothesis for the origin of life, assuming that life on the earth originated from “[GADV]-protein world”, not from the “RNA world” (see Ikehara's review, 2002). The [GADV]-protein world is constituted from peptides and proteins with random sequences of four amino acids (glycine [G], alanine [A], aspartic acid [D] and valine [V]), which accumulated by pseudo-replication of the [GADV]-proteins. To obtain evidence for the hypothesis, we produced [GADV]-peptides by repeated heat-drying of the amino acids for 30 cycles ([GADV]-P30) and examined whether the peptides have some catalytic activities or not. From the results, it was found that the [GADV]-P30 can hydrolyze several kinds of chemical bonds in molecules, such as umbelliferyl-β-D-galactoside, glycine-p-nitroanilide and bovine serum albumin. This suggests that [GADV]-P30 could play an important role in the accumulation of [GADV]-proteins through pseudo-replication, leading to the emergence of life. We further show that [GADV]-octapaptides with random sequences, but containing no cyclic compounds as diketepiperazines, have catalytic activity, hydrolyzing peptide bonds in a natural protein, bovine serum albumin. The catalytic activity of the octapeptides was much higher than the [GADV]-P30 produced through repeated heat-drying treatments. These results also support the [GADV]-protein-world hypothesis of the origin of life (see Ikehara's review, 2002). Possible steps for the emergence of life on the primitive earth are presented.

  8. Catalytic pyrolysis of olive mill wastewater sludge

    NASA Astrophysics Data System (ADS)

    Abdellaoui, Hamza

    From 2008 to 2013, an average of 2,821.4 kilotons/year of olive oil were produced around the world. The waste product of the olive mill industry consists of solid residue (pomace) and wastewater (OMW). Annually, around 30 million m3 of OMW are produced in the Mediterranean area, 700,000 m3 year?1 in Tunisia alone. OMW is an aqueous effluent characterized by an offensive smell and high organic matter content, including high molecular weight phenolic compounds and long-chain fatty acids. These compounds are highly toxic to micro-organisms and plants, which makes the OMW a serious threat to the environment if not managed properly. The OMW is disposed of in open air evaporation ponds. After evaporation of most of the water, OMWS is left in the bottom of the ponds. In this thesis, the effort has been made to evaluate the catalytic pyrolysis process as a technology to valorize the OMWS. The first section of this research showed that 41.12 wt. % of the OMWS is mostly lipids, which are a good source of energy. The second section proved that catalytic pyrolysis of the OMWS over red mud and HZSM-5 can produce green diesel, and 450 °C is the optimal reaction temperature to maximize the organic yields. The last section revealed that the HSF was behind the good fuel-like properties of the OMWS catalytic oils, whereas the SR hindered the bio-oil yields and quality.

  9. Investigating the Synthesis, Structure, and Catalytic Properties of Versatile Gold-Based Nanocatalvsts

    NASA Astrophysics Data System (ADS)

    Pretzer, Lori A.

    thermophilic-enzyme complexes responsive to near infrared electromagnetic radiation, which is absorbed minimally by biological tissues. When enzyme-Au nanorod complexes are illuminated with a near-infrared laser, thermal energy is generated which activates the thermophilic enzyme. Enzyme-Au nanorod complexes encapsulated in calcium alginate are reusable and stable for several days, making them viable for industrial applications. Lastly, highly versatile Au nanoparticles with diameters of ~3-12 nm were prepared using carbon monoxide (CO) to reduce a Au salt precursor onto preformed catalytic Au particles. Compared to other reducing agents used to generate metallic NPs, CO can be used at room temperature and its oxidized form does not interfere with the colloidal stability of NPs suspended in water. Controlled synthesis of different sized particles was verified through detailed ultraviolet-visible spectroscopy, small angle X-ray scattering, and transmission electron microscopy measurements. This synthesis method should be extendable to other monometallic and multimetallic compositions and shapes, and can be improved by using preformed particles with a narrower size distribution.

  10. ``OPTICAL Catalytic Nanomotors''

    NASA Astrophysics Data System (ADS)

    Rosary-Oyong, Se, Glory

    D. Kagan, et.al, 2009:'' a motion-based chemical sensing involving fuel-driven nanomotors is demonstrated. The new protocol relies on the use of an optical microscope for tracking charge in the speed of nanowire motors in the presence of target analyte''. Synthetic nanomotors are propelled by catalytic decomposition of .. they do not require external electric, magnetic or optical fields as energy... Accompanying Fig 2.6(a) of optical micrograph of a partial monolayer of silica microbeads [J.Gibbs, 2011 ] retrieves WF Paxton:''rods were characterized by transmission electron & dark-field optical microscopy..'' & LF Valadares:''dimer due to the limited resolution of optical microscopy, however the result..'. Acknowledged to HE. Mr. Prof. SEDIONO M.P. TJONDRONEGORO.

  11. Bifunctional catalytic electrode

    NASA Technical Reports Server (NTRS)

    Cisar, Alan (Inventor); Murphy, Oliver J. (Inventor); Clarke, Eric (Inventor)

    2005-01-01

    The present invention relates to an oxygen electrode for a unitized regenerative hydrogen-oxygen fuel cell and the unitized regenerative fuel cell having the oxygen electrode. The oxygen electrode contains components electrocatalytically active for the evolution of oxygen from water and the reduction of oxygen to water, and has a structure that supports the flow of both water and gases between the catalytically active surface and a flow field or electrode chamber for bulk flow of the fluids. The electrode has an electrocatalyst layer and a diffusion backing layer interspersed with hydrophilic and hydrophobic regions. The diffusion backing layer consists of a metal core having gas diffusion structures bonded to the metal core.

  12. Catalytic hollow spheres

    NASA Technical Reports Server (NTRS)

    Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)

    1989-01-01

    The improved, heterogeneous catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitably formed of a shell (12) of metal such as aluminum having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be, itself, catalytic or the catalyst can be coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.

  13. Catalytic enantioselective intramolecular aza-diels-alder reactions.

    PubMed

    Min, Chang; Lin, Chih-Tsung; Seidel, Daniel

    2015-05-26

    A readily available chiral Brønsted acid was identified as an efficient catalyst for intramolecular Povarov reactions. Polycyclic amines containing three contiguous stereogenic centers were obtained with excellent stereocontrol in a single step from secondary anilines and aldehydes possessing a pendent dienophile. These transformations constitute the first examples of catalytic enantioselective intramolecular aza-Diels-Alder reactions.

  14. Catalytic activities of zeolite compounds for decomposing aqueous ozone.

    PubMed

    Kusuda, Ai; Kitayama, Mikito; Ohta, Yoshio

    2013-12-01

    The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Using the commercial zeolite powders with various Si/Al ratios and crystal structures, their catalytic activities for decomposing aqueous ozone were evaluated by continuously flowing ozone to water containing the zeolite powders. The hydrophilic zeolites (low Si/Al ratio) with alkali cations in the crystal structures were found to possess high catalytic activity for decomposing aqueous ozone. The hydrophobic zeolite compounds (high Si/Al ratio) were found to absorb ozone very well, but to have no catalytic activity for decomposing aqueous ozone. Their catalytic activities were also evaluated by using the fixed bed column method. When alkali cations were removed by acid rinsing or substituted by alkali-earth cations, the catalytic activities was significantly deteriorated. These results suggest that the metal cations on the crystal surface of the hydrophilic zeolite would play a key role for catalytic activity for decomposing aqueous ozone.

  15. Molecular self-assembly strategy for generating catalytic hybrid polypeptides

    DOE PAGESBeta

    Maeda, Yoshiaki; Fang, Justin; Ikezoe, Yasuhiro; Pike, Douglas H.; Nanda, Vikas; Matsui, Hiroshi

    2016-04-26

    Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β- sheets and amyloidmore » fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. Furthermore, the enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality.« less

  16. Catalytic activities of zeolite compounds for decomposing aqueous ozone.

    PubMed

    Kusuda, Ai; Kitayama, Mikito; Ohta, Yoshio

    2013-12-01

    The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Using the commercial zeolite powders with various Si/Al ratios and crystal structures, their catalytic activities for decomposing aqueous ozone were evaluated by continuously flowing ozone to water containing the zeolite powders. The hydrophilic zeolites (low Si/Al ratio) with alkali cations in the crystal structures were found to possess high catalytic activity for decomposing aqueous ozone. The hydrophobic zeolite compounds (high Si/Al ratio) were found to absorb ozone very well, but to have no catalytic activity for decomposing aqueous ozone. Their catalytic activities were also evaluated by using the fixed bed column method. When alkali cations were removed by acid rinsing or substituted by alkali-earth cations, the catalytic activities was significantly deteriorated. These results suggest that the metal cations on the crystal surface of the hydrophilic zeolite would play a key role for catalytic activity for decomposing aqueous ozone. PMID:25078817

  17. Molecular Self-Assembly Strategy for Generating Catalytic Hybrid Polypeptides

    PubMed Central

    Ikezoe, Yasuhiro; Pike, Douglas H.; Nanda, Vikas; Matsui, Hiroshi

    2016-01-01

    Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β-sheets and amyloid fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. The enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality. PMID:27116246

  18. Unsteady catalytic processes and sorption-catalytic technologies

    NASA Astrophysics Data System (ADS)

    Zagoruiko, A. N.

    2007-07-01

    Catalytic processes that occur under conditions of the targeted unsteady state of the catalyst are considered. The highest efficiency of catalytic processes was found to be ensured by a controlled combination of thermal non-stationarity and unsteady composition of the catalyst surface. The processes based on this principle are analysed, in particular, catalytic selective reduction of nitrogen oxides, deep oxidation of volatile organic impurities, production of sulfur by the Claus process and by hydrogen sulfide decomposition, oxidation of sulfur dioxide, methane steam reforming and anaerobic combustion, selective oxidation of hydrocarbons, etc.

  19. Enhancement of CO2 Adsorption and Catalytic Properties by Fe-Doping of [Ga2(OH)2(L)] (H4L = Biphenyl-3,3′,5,5′-tetracarboxylic Acid), MFM-300(Ga2)

    PubMed Central

    2016-01-01

    Metal–organic frameworks (MOFs) are usually synthesized using a single type of metal ion, and MOFs containing mixtures of different metal ions are of great interest and represent a methodology to enhance and tune materials properties. We report the synthesis of [Ga2(OH)2(L)] (H4L = biphenyl-3,3′,5,5′-tetracarboxylic acid), designated as MFM-300(Ga2), (MFM = Manchester Framework Material replacing NOTT designation), by solvothermal reaction of Ga(NO3)3 and H4L in a mixture of DMF, THF, and water containing HCl for 3 days. MFM-300(Ga2) crystallizes in the tetragonal space group I4122, a = b = 15.0174(7) Å and c = 11.9111(11) Å and is isostructural with the Al(III) analogue MFM-300(Al2) with pores decorated with −OH groups bridging Ga(III) centers. The isostructural Fe-doped material [Ga1.87Fe0.13(OH)2(L)], MFM-300(Ga1.87Fe0.13), can be prepared under similar conditions to MFM-300(Ga2) via reaction of a homogeneous mixture of Fe(NO3)3 and Ga(NO3)3 with biphenyl-3,3′,5,5′-tetracarboxylic acid. An Fe(III)-based material [Fe3O1.5(OH)(HL)(L)0.5(H2O)3.5], MFM-310(Fe), was synthesized with Fe(NO3)3 and the same ligand via hydrothermal methods. [MFM-310(Fe)] crystallizes in the orthorhombic space group Pmn21 with a = 10.560(4) Å, b = 19.451(8) Å, and c = 11.773(5) Å and incorporates μ3-oxo-centered trinuclear iron cluster nodes connected by ligands to give a 3D nonporous framework that has a different structure to the MFM-300 series. Thus, Fe-doping can be used to monitor the effects of the heteroatom center within a parent Ga(III) framework without the requirement of synthesizing the isostructural Fe(III) analogue [Fe2(OH)2(L)], MFM-300(Fe2), which we have thus far been unable to prepare. Fe-doping of MFM-300(Ga2) affords positive effects on gas adsorption capacities, particularly for CO2 adsorption, whereby MFM-300(Ga1.87Fe0.13) shows a 49% enhancement of CO2 adsorption capacity in comparison to the homometallic parent material. We thus report herein the

  20. Enhancement of CO2 Adsorption and Catalytic Properties by Fe-Doping of [Ga2(OH)2(L)] (H4L = Biphenyl-3,3',5,5'-tetracarboxylic Acid), MFM-300(Ga2).

    PubMed

    Krap, Cristina P; Newby, Ruth; Dhakshinamoorthy, Amarajothi; García, Hermenegildo; Cebula, Izabela; Easun, Timothy L; Savage, Mathew; Eyley, Jennifer E; Gao, Shan; Blake, Alexander J; Lewis, William; Beton, Peter H; Warren, Mark R; Allan, David R; Frogley, Mark D; Tang, Chiu C; Cinque, Gianfelice; Yang, Sihai; Schröder, Martin

    2016-02-01

    Metal-organic frameworks (MOFs) are usually synthesized using a single type of metal ion, and MOFs containing mixtures of different metal ions are of great interest and represent a methodology to enhance and tune materials properties. We report the synthesis of [Ga2(OH)2(L)] (H4L = biphenyl-3,3',5,5'-tetracarboxylic acid), designated as MFM-300(Ga2), (MFM = Manchester Framework Material replacing NOTT designation), by solvothermal reaction of Ga(NO3)3 and H4L in a mixture of DMF, THF, and water containing HCl for 3 days. MFM-300(Ga2) crystallizes in the tetragonal space group I4122, a = b = 15.0174(7) Å and c = 11.9111(11) Å and is isostructural with the Al(III) analogue MFM-300(Al2) with pores decorated with -OH groups bridging Ga(III) centers. The isostructural Fe-doped material [Ga(1.87)Fe(0.13)(OH)2(L)], MFM-300(Ga(1.87)Fe(0.13)), can be prepared under similar conditions to MFM-300(Ga2) via reaction of a homogeneous mixture of Fe(NO3)3 and Ga(NO3)3 with biphenyl-3,3',5,5'-tetracarboxylic acid. An Fe(III)-based material [Fe3O(1.5)(OH)(HL)(L)(0.5)(H2O)(3.5)], MFM-310(Fe), was synthesized with Fe(NO3)3 and the same ligand via hydrothermal methods. [MFM-310(Fe)] crystallizes in the orthorhombic space group Pmn21 with a = 10.560(4) Å, b = 19.451(8) Å, and c = 11.773(5) Å and incorporates μ3-oxo-centered trinuclear iron cluster nodes connected by ligands to give a 3D nonporous framework that has a different structure to the MFM-300 series. Thus, Fe-doping can be used to monitor the effects of the heteroatom center within a parent Ga(III) framework without the requirement of synthesizing the isostructural Fe(III) analogue [Fe2(OH)2(L)], MFM-300(Fe2), which we have thus far been unable to prepare. Fe-doping of MFM-300(Ga2) affords positive effects on gas adsorption capacities, particularly for CO2 adsorption, whereby MFM-300(Ga(1.87)Fe(0.13)) shows a 49% enhancement of CO2 adsorption capacity in comparison to the homometallic parent material. We thus report

  1. Catalytic poly(vinyl alcohol) functionalized membranes obtained by gamma irradiation

    NASA Astrophysics Data System (ADS)

    Casimiro, M. H.; Silva, A. G.; Pinto, J. V.; Ramos, A. M.; Vital, J.; Ferreira, L. M.

    2012-09-01

    Polymeric catalytic membranes bearing sulfonic acid functions have been prepared by mutual gamma irradiation at a 60Co source, of poly(vinyl alcohol) (PVA) membranes and methanesulfonic acid. The effect of various synthesis conditions on membranes' physical-chemical properties and catalytic activity in the esterification reaction between acetic acid and isoamyl alcohol to obtain isoamyl acetate (banana flavor), was evaluated. The membranes were characterized by ATR-FTIR, TPP, AFM and SEM. Water contact angle determinations were also performed. The obtained results showed that within the range of conditions studied the increase in sulfonic acid groups' content is accompanied by an enhancement in the membranes catalytic activity, while the increase in absorbed dose leads to a decrease in catalytic activity.

  2. Catalytic Stereoinversion of L-Alanine to Deuterated D-Alanine.

    PubMed

    Moozeh, Kimia; So, Soon Mog; Chin, Jik

    2015-08-01

    A combination of an achiral pyridoxal analogue and a chiral base has been developed for catalytic deuteration of L-alanine with inversion of stereochemistry to give deuterated D-alanine under mild conditions (neutral pD and 25 °C) without the use of any protecting groups. This system can also be used for catalytic deuteration of D-alanine with retention of stereochemistry to give deuterated D-alanine. Thus a racemic mixture of alanine can be catalytically deuterated to give an enantiomeric excess of deuterated D-alanine. While catalytic deracemization of alanine is forbidden by the second law of thermodynamics, this system can be used for catalytic deracemization of alanine with deuteration. Such green and biomimetic approach to catalytic stereocontrol provides insights into efficient amino acid transformations.

  3. Catalytic Microtube Rocket Igniter

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.; Deans, Matthew C.

    2011-01-01

    Devices that generate both high energy and high temperature are required to ignite reliably the propellant mixtures in combustion chambers like those present in rockets and other combustion systems. This catalytic microtube rocket igniter generates these conditions with a small, catalysis-based torch. While traditional spark plug systems can require anywhere from 50 W to multiple kW of power in different applications, this system has demonstrated ignition at less than 25 W. Reactants are fed to the igniter from the same tanks that feed the reactants to the rest of the rocket or combustion system. While this specific igniter was originally designed for liquid methane and liquid oxygen rockets, it can be easily operated with gaseous propellants or modified for hydrogen use in commercial combustion devices. For the present cryogenic propellant rocket case, the main propellant tanks liquid oxygen and liquid methane, respectively are regulated and split into different systems for the individual stages of the rocket and igniter. As the catalyst requires a gas phase for reaction, either the stored boil-off of the tanks can be used directly or one stream each of fuel and oxidizer can go through a heat exchanger/vaporizer that turns the liquid propellants into a gaseous form. For commercial applications, where the reactants are stored as gases, the system is simplified. The resulting gas-phase streams of fuel and oxidizer are then further divided for the individual components of the igniter. One stream each of the fuel and oxidizer is introduced to a mixing bottle/apparatus where they are mixed to a fuel-rich composition with an O/F mass-based mixture ratio of under 1.0. This premixed flow then feeds into the catalytic microtube device. The total flow is on the order of 0.01 g/s. The microtube device is composed of a pair of sub-millimeter diameter platinum tubes connected only at the outlet so that the two outlet flows are parallel to each other. The tubes are each

  4. Catalytic glucose isomerization by porous coordination polymers with open metal sites.

    PubMed

    Akiyama, George; Matsuda, Ryotaro; Sato, Hiroshi; Kitagawa, Susumu

    2014-10-01

    Highly efficient catalytic isomerization reactions from glucose to fructose in aqueous media using porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) is reported for the first time. The catalytic activity of PCPs functionalized with -NH2, -(CH3)2, -NO2, and -SO3H groups on the pore surface is systematically tested. The catalytic activity can be tuned by the acidity of open metal sites (OMSs) by modifying the organic linkers with the functional groups. As a result, it is demonstrated that MIL-101 functionalized with -SO3H not only shows high conversion of glucose but also selectively produces fructose. Further, catalytic one-pot conversion of amylose to fructose is achieved, thanks to the high stability of the framework in an acidic solution. These results show that MOF/PCP compounds having OMSs are promising materials for various useful heterogeneous catalytic reactions, in particular in the biomass field. PMID:25080129

  5. Catalytic Membrane Sensors

    SciTech Connect

    Boyle, T.J.; Brinker, C.J.; Gardner, T.J.; Hughes, R.C.; Sault, A.G.

    1998-12-01

    The proposed "catalytic membrane sensor" (CMS) was developed to generate a device which would selectively identify a specific reagent in a complex mixture of gases. This was to be accomplished by modifying an existing Hz sensor with a series of thin films. Through selectively sieving the desired component from a complex mixture and identifying it by decomposing it into Hz (and other by-products), a Hz sensor could then be used to detect the presence of the select component. The proposed "sandwich-type" modifications involved the deposition of a catalyst layered between two size selective sol-gel layers on a Pd/Ni resistive Hz sensor. The role of the catalyst was to convert organic materials to Hz and organic by-products. The role of the membraneo was to impart both chemical specificity by molecukir sieving of the analyte and converted product streams, as well as controlling access to the underlying Pd/Ni sensor. Ultimately, an array of these CMS elements encompassing different catalysts and membranes were to be developed which would enable improved selectivity and specificity from a compiex mixture of organic gases via pattern recognition methodologies. We have successfully generated a CMS device by a series of spin-coat deposited methods; however, it was determined that the high temperature required to activate the catalyst, destroys the sensor.

  6. Catalytic gasification of biomass

    NASA Astrophysics Data System (ADS)

    Robertus, R. J.; Mudge, L. K.; Sealock, L. J., Jr.; Mitchell, D. H.; Weber, S. L.

    1981-12-01

    Methane and methanol synthesis gas can be produced by steam gasification of biomass in the presence of appropriate catalysts. This concept is to use catalysts in a fluidized bed reactor which is heated indirectly. The objective is to determine the technical and economic feasibility of the concept. Technically the concept has been demonstrated on a 50 lb per hr scale. Potential advantages over conventional processes include: no oxygen plant is needed, little tar is produced so gas and water treatment are simplified, and yields and efficiencies are greater than obtained by conventional gasification. Economic studies for a plant processing 2000 T/per day dry wood show that the cost of methanol from wood by catalytic gasification is competitive with the current price of methanol. Similar studies show the cost of methane from wood is competitive with projected future costs of synthetic natural gas. When the plant capacity is decreased to 200 T per day dry wood, neither product is very attractive in today's market.

  7. Fuel-Rich Catalytic Combustion

    NASA Technical Reports Server (NTRS)

    Brabbs, Theodore A.; Olson, Sandra L.

    1987-01-01

    Two-stage combustion system reduces particulate emissions. Program on catalytic oxidation of iso-octane demonstrates feasibility of two-stage combustion system for reducing particulate emissions. With fuel-rich (fuel/air equivalence ratios of 4.8 to 7.8) catalytic-combustion preburner as first stage, combustion process free of soot at reactor-outlet temperatures of 1,200 K or less.

  8. A critical view on catalytic pyrolysis of biomass.

    PubMed

    Venderbosch, R H

    2015-04-24

    The rapid heating of biomass in an oxygen-free environment optimizes the yield of fast-pyrolysis liquids. This liquid comprises a mix of acids, (dehydrated) carbohydrates, aldehydes, ketones, lignin fragments, aromatics, and alcohols, limiting its use. Deoxygenation of these liquids to replace hydrocarbons represents significant challenges. Catalytic pyrolysis is seen as a promising route to yield liquids with a higher quality. In this paper, literature data on catalytic fast pyrolysis of biomass are reviewed and deoxygenation results correlated with the overall carbon yield. Evidence is given that in an initial stage of the catalytic process reactive components are converted to coke, gas, and water, and only to a limited extent to a liquid product. Catalysts are not yet good enough, and an appropriate combination of pyrolysis conditions, reactive products formed, and different reactions to take place to yield improved quality liquids may be practically impossible.

  9. Catalytic conversion of cellulose over mesoporous Y zeolite.

    PubMed

    Park, Young-Kwon; Jun, Bo Ram; Park, Sung Hoon; Jeon, Jong-Ki; Lee, See Hoon; Kim, Seong-Soo; Jeong, Kwang-Eun

    2014-07-01

    Mesoporous Y zeolite (Meso-Y) was applied, for the first time, to the catalytic pyrolysis of cellulose which is a major constituent of lignocellulosic biomass, to produce high-quality bio-oil. A representative mesoporous catalyst Al-MCM-41 was also used to compare its catalytic activity with that of Meso-Y. Pyrolysis-gas chromatography/mass spectrometry was used for the experiments. Meso-Y, with higher acidity, led to larger yields of aromatics and furans with high value-added than Al-MCM-41, resulting in the production of bio-oil with higher quality. The effect of temperature on the catalytic pyrolysis was not significant within the range of 400-500 degrees C. When the Meso-Y to cellulose ratio was increased from 1/1 via 2/1 to 3/1, the deoxygenation efficiency increased, leading to increased yield of aromatics. PMID:24757989

  10. Catalytic ammonia decomposition over industrial-waste-supported Ru catalysts

    SciTech Connect

    Pei Fang Ng; Li Li; Shaobin Wang; Zhonghua Zhu; Gaoqing Lu; Zifeng Yan

    2007-05-15

    Industrial solid wastes (fly ash and red mud, a by-product of the aluminium industry) have been employed as supports for preparation of Ru-based catalysts. Physical and chemical treatments on red mud were conducted and these modified supports were also used for preparation of Ru-based catalysts. Those Ru catalysts were characterized by various techniques such as N2 adsorption, H{sub 2} adsorption, XRD, XPS, and temperature-programmed reduction (TPR), and were then tested for catalytic ammonia decomposition to hydrogen. It was found that red-mud-supported Ru catalyst exhibits higher ammonia conversion and hydrogen production than fly-ash-supported catalyst. Heat and chemical treatments of the red mud greatly improve the catalytic activity. Moreover, a combination of acid and heat treatments produces the highest catalytic conversion of ammonia. 35 refs., 4 figs., 4 tabs.

  11. Simultaneous realization of high catalytic activity and stability for catalytic cracking of n-heptane on highly exposed (010) crystal planes of nanosheet ZSM-5 zeolite.

    PubMed

    Xiao, Xia; Zhang, Yaoyuan; Jiang, Guiyuan; Liu, Jia; Han, Shanlei; Zhao, Zhen; Wang, Ruipu; Li, Cong; Xu, Chunming; Duan, Aijun; Wang, Yajun; Liu, Jian; Wei, Yuechang

    2016-08-01

    Nanosheet ZSM-5 zeolite with highly exposed (010) crystal planes demonstrates high reactivity and good anti-coking stability for the catalytic cracking of n-heptane, which is attributed to the synergy of high external surface area and acid sites, fully accessible channel intersection acid sites, and hierarchical porosity caused by the unique morphology.

  12. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue. PMID:25302630

  13. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue.

  14. Effect of hierarchical porosity and phosphorus modification on the catalytic properties of zeolite Y

    NASA Astrophysics Data System (ADS)

    Li, Wenlin; Zheng, Jinyu; Luo, Yibin; Da, Zhijian

    2016-09-01

    The zeolite Y is considered as a leading catalyst for FCC industry. The acidity and porosity modification play important roles in determining the final catalytic properties of zeolite Y. The alkaline treatment of zeolite Y by dealumination and alkaline treatment with NaOH and NaOH&TBPH was investigated. The zeolites were characterized by X-ray diffraction, low-temperature adsorption of nitrogen, transmission electron microscope, NMR, NH3-TPD and IR study of acidity. Accordingly, the hierarchical porosity and acidity property were discussed systematically. Finally, the catalytic performance of the zeolites Y was evaluated in the cracking of 1,3,5-TIPB. It was found that desilication with NaOH&TBPH ensured the more uniform intracrystalline mesoporosity with higher microporosity, while preserving higher B/L ratio and moderate Brønsted acidities resulting in catalysts with the most appropriated acidity and then with better catalytic performance.

  15. Catalytic combustion with steam injection

    NASA Astrophysics Data System (ADS)

    Anderson, D. N.; Tacina, R. R.

    The effects of steam injection on (1) catalytic combustion performance, and (2) the tendency of residual fuel to burn in the premixing duct upstream of the catalytic reactor were determined. A petroleum residual, no. 2 diesel, and a blend of middle and heavy distillate coal derived fuels were tested. Fuel and steam were injected together into the preheated airflow entering a 12 cm diameter catalytic combustion test section. The inlet air velocity and pressure were constant at 10 m/s and 600 kPa, respectively. Steam flow rates were varied from 24 percent to 52 percent of the air flow rate. The resulting steam air mixture temperatures varied from 630 to 740 K. Combustion temperatures were in the range of 1200 to 1400 K. The steam had little effect on combustion efficiency or emissions. It was concluded that the steam acts as a diluent which has no adverse effect on catalytic combustion performance for no. 2 diesel and coal derived liquid fuels. Tests with the residual fuel showed that upstream burning could be eliminated with steam injection rates greater than 30 percent of the air flow rate, but inlet mixture temperatures were too low to permit stable catalytic combustion of this fuel.

  16. Catalytic combustion with steam injection

    NASA Technical Reports Server (NTRS)

    Anderson, D. N.; Tacina, R. R.

    1982-01-01

    The effects of steam injection on (1) catalytic combustion performance, and (2) the tendency of residual fuel to burn in the premixing duct upstream of the catalytic reactor were determined. A petroleum residual, no. 2 diesel, and a blend of middle and heavy distillate coal derived fuels were tested. Fuel and steam were injected together into the preheated airflow entering a 12 cm diameter catalytic combustion test section. The inlet air velocity and pressure were constant at 10 m/s and 600 kPa, respectively. Steam flow rates were varied from 24 percent to 52 percent of the air flow rate. The resulting steam air mixture temperatures varied from 630 to 740 K. Combustion temperatures were in the range of 1200 to 1400 K. The steam had little effect on combustion efficiency or emissions. It was concluded that the steam acts as a diluent which has no adverse effect on catalytic combustion performance for no. 2 diesel and coal derived liquid fuels. Tests with the residual fuel showed that upstream burning could be eliminated with steam injection rates greater than 30 percent of the air flow rate, but inlet mixture temperatures were too low to permit stable catalytic combustion of this fuel.

  17. A Bio-Catalytic Approach to Aliphatic Ketones

    PubMed Central

    Xiong, Mingyong; Deng, Jin; Woodruff, Adam P.; Zhu, Minshan; Zhou, Jun; Park, Sun Wook; Li, Hui; Fu, Yao; Zhang, Kechun

    2012-01-01

    Depleting oil reserves and growing environmental concerns have necessitated the development of sustainable processes to fuels and chemicals. Here we have developed a general metabolic platform in E. coli to biosynthesize carboxylic acids. By engineering selectivity of 2-ketoacid decarboxylases and screening for promiscuous aldehyde dehydrogenases, synthetic pathways were constructed to produce both C5 and C6 acids. In particular, the production of isovaleric acid reached 32 g/L (0.22 g/g glucose yield), which is 58% of the theoretical yield. Furthermore, we have developed solid base catalysts to efficiently ketonize the bio-derived carboxylic acids such as isovaleric acid and isocaproic acid into high volume industrial ketones: methyl isobutyl ketone (MIBK, yield 84%), diisobutyl ketone (DIBK, yield 66%) and methyl isoamyl ketone (MIAK, yield 81%). This hybrid “Bio-Catalytic conversion” approach provides a general strategy to manufacture aliphatic ketones, and represents an alternate route to expanding the repertoire of renewable chemicals. PMID:22416247

  18. Cutoff lensing: predicting catalytic sites in enzymes

    NASA Astrophysics Data System (ADS)

    Aubailly, Simon; Piazza, Francesco

    2015-10-01

    Predicting function-related amino acids in proteins with unknown function or unknown allosteric binding sites in drug-targeted proteins is a task of paramount importance in molecular biomedicine. In this paper we introduce a simple, light and computationally inexpensive structure-based method to identify catalytic sites in enzymes. Our method, termed cutoff lensing, is a general procedure consisting in letting the cutoff used to build an elastic network model increase to large values. A validation of our method against a large database of annotated enzymes shows that optimal values of the cutoff exist such that three different structure-based indicators allow one to recover a maximum of the known catalytic sites. Interestingly, we find that the larger the structures the greater the predictive power afforded by our method. Possible ways to combine the three indicators into a single figure of merit and into a specific sequential analysis are suggested and discussed with reference to the classic case of HIV-protease. Our method could be used as a complement to other sequence- and/or structure-based methods to narrow the results of large-scale screenings.

  19. Lube catalytic dewaxing-hydrotreating process

    SciTech Connect

    Harandi, M.N.

    1989-08-01

    This patent describes a method of producing a catalytically dewaxed, hydrotreated lubricating oil of improved quality. It comprises: catalytically dewaxing a hydrocarbon lubricating oil fraction by contacting the fraction during a dewaxing/hydrotreating cycle with a zeolitic dewaxing catalyst in the presence of hydrogen under dewaxing conditions, to produce a dewaxed effluent, hydrotreating the dewaxed effluent by contacting the effluent during the dewaxing/hydrotreating cycle with a hydrotreating catalyst. The catalyst comprising a metal hydrogen component on a porous non-acidic support in the presence of hydrogen under hydrotreating conditions, to produce a hydrotreated, dewaxed effluent, reactivating the dewaxing catalyst at the end of the dewaxing/hydrotreating cycle contacting the dewaxing catalyst with hydrogen at an elevated temperature to restore dewaxing activity to the catalyst, oxidatively regenerating the hydrotreating catalyst at the end of the dewaxing/hydrotreating cycle by contacting the hydrotreating catalyst with an oxygen containing gas at an elevated temperature to restore hydrotreating activity to the catalyst, repeating the first two steps with the reactivated dewaxing and regenerated hydrotreating catalyst in a new dewaxing/hydrotreating cycle in which aromatic components formed by the hydrogenative reactivation of the dewaxing catalyst in the third step and sorbed on the dewaxing catalyst pass with the dewaxed effluent form the dewaxing catalyst to the hydrotreating catalyst on which they are sorbed during the initial stages of the dewaxing/hydrotreating cycle.

  20. Catalytic distillation water recovery subsystem

    NASA Technical Reports Server (NTRS)

    Budininkas, P.; Rasouli, F.

    1985-01-01

    An integrated engineering breadboard subsystem for the recovery of potable water from untreated urine based on the vapor phase catalytic ammonia removal was designed, fabricated and tested. Unlike other evaporative methods, this process catalytically oxidizes ammonia and volatile hydrocarbons vaporizing with water to innocuous products; therefore, no pretreatment of urine is required. Since the subsystem is fabricated from commercially available components, its volume, weight and power requirements are not optimized; however, it is suitable for zero-g operation. The testing program consists of parametric tests, one month of daily tests and a continuous test of 168 hours duration. The recovered water is clear, odorless, low in ammonia and organic carbon, and requires only an adjustment of its pH to meet potable water standards. The obtained data indicate that the vapor phase catalytic ammonia removal process, if further developed, would also be competitive with other water recovery systems in weight, volume and power requirements.

  1. Catalytic Enantioselective Carboannulation with Allylsilanes

    PubMed Central

    Ball-Jones, Nicolas R.; Badillo, Joseph J.; Tran, Ngon T.; Franz, Annaliese K.

    2015-01-01

    The first catalytic asymmetric carboannulation with allylsilanes is presented. The enantioselective [3+2] annulation is catalyzed using a Sc(III)-indapybox complex with tetrakis-[3,5-bis(trifluoromethyl)phenyl]-borate (BArF) to enhance catalytic activity and control stereoselectivity. Functionalized cyclopentanes containing a quaternary carbon are derived from alkylidene oxindole, coumarin, and malonate substrates with high stereoselectivity. The enantioselective 1,4-conjugate addition and enantioselective lactone formation (via trapping of the β-silyl carbocation) is also described. PMID:25045133

  2. Catalytic enantioselective carboannulation with allylsilanes.

    PubMed

    Ball-Jones, Nicolas R; Badillo, Joseph J; Tran, Ngon T; Franz, Annaliese K

    2014-09-01

    The first catalytic asymmetric carboannulation with allylsilanes is presented. The enantioselective [3+2] annulation is catalyzed using a scandium(III)/indapybox complex with tetrakis-[3,5-bis(trifluoromethyl)phenyl]-borate (BArF) to enhance catalytic activity and control stereoselectivity. Functionalized cyclopentanes containing a quaternary carbon center are derived from alkylidene oxindole, coumarin, and malonate substrates with high stereoselectivity. The enantioselective 1,4-conjugate addition and enantioselective lactone formation (by trapping of the β-silyl carbocation) is also described. PMID:25045133

  3. Perfluoropolyalkylether decomposition on catalytic aluminas

    NASA Technical Reports Server (NTRS)

    Morales, Wilfredo

    1994-01-01

    The decomposition of Fomblin Z25, a commercial perfluoropolyalkylether liquid lubricant, was studied using the Penn State Micro-oxidation Test, and a thermal gravimetric/differential scanning calorimetry unit. The micro-oxidation test was conducted using 440C stainless steel and pure iron metal catalyst specimens, whereas the thermal gravimetric/differential scanning calorimetry tests were conducted using catalytic alumina pellets. Analysis of the thermal data, high pressure liquid chromatography data, and x-ray photoelectron spectroscopy data support evidence that there are two different decomposition mechanisms for Fomblin Z25, and that reductive sites on the catalytic surfaces are responsible for the decomposition of Fomblin Z25.

  4. Maximizing the catalytic function of hydrogen spillover in platinum-encapsulated aluminosilicates with controlled nanostructures.

    PubMed

    Im, Juhwan; Shin, Hyeyoung; Jang, Haeyoun; Kim, Hyungjun; Choi, Minkee

    2014-02-25

    Hydrogen spillover has been studied for several decades, but its nature, catalytic functions and even its existence remain topics of vigorous debate. This is a consequence of the lack of model catalysts that can provide direct evidences of the existence of hydrogen spillover and simplify the catalytic interpretation. Here we use platinum encapsulated in a dense aluminosilicate matrix with controlled diffusional properties and surface hydroxyl concentrations to elucidate the catalytic functions of hydrogen spillover. The catalytic investigation and theoretical modelling show that surface hydroxyls, presumably Brønsted acids, are crucial for utilizing the catalytic functions of hydrogen spillover on the aluminosilicate surface. The catalysts with optimized nanostructure show remarkable activities in hydro-/dehydrogenation, but virtually no activity for hydrogenolysis. This distinct chemoselectivity may be beneficial in industrially important hydroconversions such as propane dehydrogenation to propylene because the undesired hydrogenolysis pathway producing light hydrocarbons of low value (methane and ethane) is greatly suppressed.

  5. Pyridoxal-5'-phosphate-dependent catalytic antibodies.

    PubMed

    Gramatikova, Svetlana; Mouratou, Barbara; Stetefeld, Jörg; Mehta, Perdeep K; Christen, Philipp

    2002-11-01

    Strategies for expanding the catalytic scope of antibodies include the incorporation of inorganic or organic cofactors into their binding sites. An obvious choice is pyridoxal-5'-phosphate (PLP), which is probably the most versatile organic cofactor of enzymes. Monoclonal antibodies against the hapten N(alpha)-(5'-phosphopyridoxyl)-L-lysine, a stable analog of the covalent coenzyme-substrate adducts were screened by a competition ELISA for binding of the PLP-amino acid Schiff base adduct. The Schiff base with its C4'-N alpha double bond is, in contrast to the hapten, a planar compound and is an obligatory intermediate in all PLP-dependent reactions of amino acids. This highly discriminating screening step eliminated all but 5 of 24 hapten-binding antibodies. The five remaining antibodies were tested for catalysis of the PLP-dependent alpha,beta-elimination reaction of beta-chloroalanine. Antibody 15A9 complied with this selection criterion and catalyzed in addition the cofactor-dependent transamination reaction of hydrophobic D-amino acids and oxo acids (k(cat)'=0.42 min(-1) with D-alanine at 25 degrees C). Homology modeling together with alanine scanning yielded a 3D model of Fab 15A9. The striking analogy between antibody 15A9 and PLP-dependent enzymes includes the following features: (1) The binding sites accommodate the planar coenzyme-amino acid adduct. (2) The bond at C alpha to be broken lies together with the C alpha-N bond in a plane orthogonal to the plane of coenzyme and imine bond. (3) The alpha-carboxylate group of the substrate is bound by an arginine residue. (4) The coenzyme-substrate adduct assumes a cisoid conformation. (5) PLP markedly contributes to catalytic efficiency, being a 10(4) times more efficient amino group acceptor than pyruvate. The protein moiety, however, ensures reaction as well as substrate specificity, and further accelerates the reaction (in 15A9 k(cat (Ab x PLP))'/k(cat (PLP))'=5 x 10(3)). The analogies of antibody 15A9 with

  6. Catalytic control over supramolecular gel formation

    NASA Astrophysics Data System (ADS)

    Boekhoven, Job; Poolman, Jos M.; Maity, Chandan; Li, Feng; van der Mee, Lars; Minkenberg, Christophe B.; Mendes, Eduardo; van Esch, Jan H.; Eelkema, Rienk

    2013-05-01

    Low-molecular-weight gels show great potential for application in fields ranging from the petrochemical industry to healthcare and tissue engineering. These supramolecular gels are often metastable materials, which implies that their properties are, at least partially, kinetically controlled. Here we show how the mechanical properties and structure of these materials can be controlled directly by catalytic action. We show how in situ catalysis of the formation of gelator molecules can be used to accelerate the formation of supramolecular hydrogels, which drastically enhances their resulting mechanical properties. Using acid or nucleophilic aniline catalysis, it is possible to make supramolecular hydrogels with tunable gel-strength in a matter of minutes, under ambient conditions, starting from simple soluble building blocks. By changing the rate of formation of the gelator molecules using a catalyst, the overall rate of gelation and the resulting gel morphology are affected, which provides access to metastable gel states with improved mechanical strength and appearance despite an identical gelator composition.

  7. Basicity, Catalytic and Adsorptive Properties of Hydrotalcites

    NASA Astrophysics Data System (ADS)

    Figueras, Francois

    Solid bases have numerous potential applications, not only as catalyst for the manufacture of fine chemicals, in refining and petrochemistry, but also for adsorption and anion exchange. The present processes use liquid bases, typically alcoholic potash, and require neutralisation of the reaction medium at the end of the reaction, with production of salts. The substitution of these liquid bases by solids would provide cleaner and safer processes, due to the reduction of salts, and facilitate separation of the products and recycling of the catalyst. This chapter reviews the recent ideas on the modification of the basic properties of hydrotalcites by anion exchange and on the catalytic properties of solid bases as catalysts. Many examples of successful applications are given, with emphasis to industrial processes recently presented such as isomerisation of olefins. The basic properties of hydrotalcites can also be used to carry the exchange of toxic anions, humic acids or dyes, and have driven recent developments proposing HDT as drug carriers.

  8. Catalytical Properties of Free and Immobilized Aspergillus niger Tannase

    PubMed Central

    Flores-Maltos, Abril; Rodríguez-Durán, Luis V.; Renovato, Jacqueline; Contreras, Juan C.; Rodríguez, Raúl; Aguilar, Cristóbal N.

    2011-01-01

    A fungal tannase was produced, recovered, and immobilized by entrapment in calcium alginate beads. Catalytical properties of the immobilized enzyme were compared with those of the free one. Tannase was produced intracellularly by the xerophilic fungus Aspergillus niger GH1 in a submerged fermentation system. Enzyme was recovered by cell disruption and the crude extract was partially purified. The catalytical properties of free and immobilized tannase were evaluated using tannic acid and methyl gallate as substrates. KM and Vmax values for free enzyme were very similar for both substrates. But, after immobilization, KM and Vmax values increased drastically using tannic acid as substrate. These results indicated that immobilized tannase is a better biocatalyst than free enzyme for applications on liquid systems with high tannin content, such as bioremediation of tannery or olive-mill wastewater. PMID:21918717

  9. Catalytic determination of vanadium in water

    USGS Publications Warehouse

    Fishman, M. J.; Skougstad, M.W.

    1964-01-01

    A rapid, accurate, and sensitive spectrophotometric method for the quantitative determination of trace amounts of vanadium in water is based on the catalytic effect of vanadium on the rate of oxidation of gallic acid by persulfate in acid solution. Under given conditions of concentrations of reactants, temperature, and reaction time, the extent of oxidation of gallic acid is proportional to the concentration of vanadium present. Vanadium is determined by measuring the absorbance of the sample at 415 m?? and comparison with standard solutions treated in an identical manner. Concentrations in the range of from 0.1 to 8.0 ??g. per liter may be determined with a standard deviation of 0.2 or less. By reducing the reaction time, the method may be extended to cover the range from 1 to 100 ??g. with a standard deviation of 0.8 or less. Several substances interfere, including chloride above 100 p.p.m., and bromide and iodide in much lower concentrations. Interference from the halides is eliminated or minimized by the addition of mercuric nitrate solution. Most other substances do not interfere at the concentration levels at which they commonly occur in natural waters.

  10. Catalytic Synthesis of Oxygenates: Mechanisms, Catalysts and Controlling Characteristics

    SciTech Connect

    Klier, Kamil; Herman, Richard G

    2005-11-30

    This research focused on catalytic synthesis of unsymmetrical ethers as a part of a larger program involving oxygenated products in general, including alcohols, ethers, esters, carboxylic acids and their derivatives that link together environmentally compliant fuels, monomers, and high-value chemicals. The catalysts studied here were solid acids possessing strong Brnsted acid functionalities. The design of these catalysts involved anchoring the acid groups onto inorganic oxides, e.g. surface-grafted acid groups on zirconia, and a new class of mesoporous solid acids, i.e. propylsulfonic acid-derivatized SBA-15. The former catalysts consisted of a high surface concentration of sulfate groups on stable zirconia catalysts. The latter catalyst consists of high surface area, large pore propylsulfonic acid-derivatized silicas, specifically SBA-15. In both cases, the catalyst design and synthesis yielded high concentrations of acid sites in close proximity to one another. These materials have been well-characterization in terms of physical and chemical properties, as well as in regard to surface and bulk characteristics. Both types of catalysts were shown to exhibit high catalytic performance with respect to both activity and selectivity for the bifunctional coupling of alcohols to form ethers, which proceeds via an efficient SN2 reaction mechanism on the proximal acid sites. This commonality of the dual-site SN2 reaction mechanism over acid catalysts provides for maximum reaction rates and control of selectivity by reaction conditions, i.e. pressure, temperature, and reactant concentrations. This research provides the scientific groundwork for synthesis of ethers for energy applications. The synthesized environmentally acceptable ethers, in part derived from natural gas via alcohol intermediates, exhibit high cetane properties, e.g. methylisobutylether with cetane No. of 53 and dimethylether with cetane No. of 55-60, or high octane properties, e.g. diisopropylether with

  11. Kinetics of catalytic transfer hydrogenation of soybean lecithin

    SciTech Connect

    Naglic, M.; Smidovnik, A.; Koloini, T.

    1997-12-01

    Catalytic transfer hydrogenation of soybean lecithin has been studied using aqueous sodium formate solution as hydrogen donor and palladium on carbon as catalyst. Kinetic constants and selectivity have been determined at intensive stirring. Hydrogenation reactions followed the first-order kinetics with respect to fatty acids. In addition to short reaction time, this method offers safe and easy handling. Hydrogenated soybean lecithin provides products with increased stability with respect to oxidation.

  12. Catalytic efficiency of expressed aromatase following site-directed mutagenesis.

    PubMed

    Kadohama, N; Zhou, D; Chen, S; Osawa, Y

    1993-05-13

    Mutant aromatase cytochrome P-450s, expressed in CHO cells after transfection with cDNAs, have been characterized in terms of their catalytic efficiencies. After solubilization from microsomes, specific aromatase P-450 content of wild-type and mutants Pro308Phe, Asp309Asn, Asp309Ala and Phe406Arg was quantitated by a sandwich enzyme-linked immunosorbent assay (ELISA). Microsomal aromatase activity was determined by the 3H-water method using [1 beta-3H]androstenedione as substrate. Estimations of the actual turnover rate (catalytic efficiency) were derived from the combined data. The P-450 content in the mutants varied but was always less than that in the wild type. Hence, the decreases in the Vmax observed in the mutant enzymes did not correlate completely with reductions in catalytic effectiveness. In recent studies on the structure-function relationship of aromatase cytochrome P-450, the observed reduction of enzyme activity in terms of Vmax following site-directed mutagenesis led to the assumption that there was a corresponding loss of catalytic effectiveness. The present study reveals that a lower P-450 content can contribute significantly to decreasing catalytic activity in the mutants. In fact, in mutant Phe406Arg which exhibited virtually no catalytically active aromatase, the specific P-450 content was below the detectable level. Because of its location, the result of this latter mutation could be a major structural perturbation of the heme-binding property. Thus, interpretation of losses and reductions in aromatase activity resulting from single amino-acid replacement should take into account changes in the specific content of aromatase cytochrome P-450.

  13. Catalytic oxidation of waste materials

    NASA Technical Reports Server (NTRS)

    Jagow, R. B.

    1977-01-01

    Aqueous stream of human waste is mixed with soluble ruthenium salts and is introduced into reactor at temperature where ruthenium black catalyst forms on internal surfaces of reactor. This provides catalytically active surface to convert oxidizable wastes into breakdown products such as water and carbon dioxide.

  14. Heterogeneous catalytic alcoholysis of benzonitrile

    SciTech Connect

    Kagarlitskii, A.D.; Dmumakaev, K.Kh.; Bekova, N.S.

    1986-04-01

    The authors investigate the possibility of the direct heterogeneous catalytic synthesis of ethylbenzoate from benzonitrile. The catalysts tested were oxides of aluminium, titanium, and vanadium. The main conversion product detected chromatographically was ethylbenzoate; benzaldehyde, benzamide, and benzanilide were also identified. Aluminium oxide was found to be the most effective catalyst.

  15. High temperature catalytic membrane reactors

    SciTech Connect

    Not Available

    1990-03-01

    Current state-of-the-art inorganic oxide membranes offer the potential of being modified to yield catalytic properties. The resulting modules may be configured to simultaneously induce catalytic reactions with product concentration and separation in a single processing step. Processes utilizing such catalytically active membrane reactors have the potential for dramatically increasing yield reactions which are currently limited by either thermodynamic equilibria, product inhibition, or kinetic selectivity. Examples of commercial interest include hydrogenation, dehydrogenation, partial and selective oxidation, hydrations, hydrocarbon cracking, olefin metathesis, hydroformylation, and olefin polymerization. A large portion of the most significant reactions fall into the category of high temperature, gas phase chemical and petrochemical processes. Microporous oxide membranes are well suited for these applications. A program is proposed to investigate selected model reactions of commercial interest (i.e. dehydrogenation of ethylbenzene to styrene and dehydrogenation of butane to butadiene) using a high temperature catalytic membrane reactor. Membranes will be developed, reaction dynamics characterized, and production processes developed, culminating in laboratory-scale demonstration of technical and economic feasibility. As a result, the anticipated increased yield per reactor pass economic incentives are envisioned. First, a large decrease in the temperature required to obtain high yield should be possible because of the reduced driving force requirement. Significantly higher conversion per pass implies a reduced recycle ratio, as well as reduced reactor size. Both factors result in reduced capital costs, as well as savings in cost of reactants and energy.

  16. Simple, chemoselective, catalytic olefin isomerization.

    PubMed

    Crossley, Steven W M; Barabé, Francis; Shenvi, Ryan A

    2014-12-01

    Catalytic amounts of Co(Sal(tBu,tBu))Cl and organosilane irreversibly isomerize terminal alkenes by one position. The same catalysts effect cycloisomerization of dienes and retrocycloisomerization of strained rings. Strong Lewis bases like amines and imidazoles, and labile functionalities like epoxides, are tolerated.

  17. Social Entrepreneurs and Catalytic Change.

    ERIC Educational Resources Information Center

    Waddock, Sandra A.; Post, James E.

    1991-01-01

    Social entrepreneurs are private citizens who play critical roles in bringing about catalytic changes in the public sector agenda and the perception of social issues. Factors that make their projects--such as the Partnership for a Drug-Free America and Earth Day--successful include problem complexity, credibility, and a commitment to a collective…

  18. Process for Coating Substrates with Catalytic Materials

    NASA Technical Reports Server (NTRS)

    Klelin, Ric J. (Inventor); Upchurch, Billy T. (Inventor); Schryer, David R. (Inventor)

    2004-01-01

    A process for forming catalysts by coating substrates with two or more catalytic components, which comprises the following sequence of steps. First, the substrate is infused with an adequate amount of solution having a starting material comprising a catalytic component precursor, wherein the thermal decomposition product of the catalytic component precursor is a catalytic component. Second, the excess of the solution is removed from the substrate. thereby leaving a coating of the catalytic component precursor on the surface of the substrate. Third, the coating of the catalytic component precursor is converted to the catalytic component by thermal decomposition. Finally, the coated substance is etched to increase the surface area. The list three steps are then repeated for at least a second catalytic component. This process is ideally suited for application in producing efficient low temperature oxidation catalysts.

  19. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    PubMed

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-01

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid.

  20. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    PubMed

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-01

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid. PMID:21268603

  1. Catalytic pyrolysis of Laminaria japonica over nanoporous catalysts using Py-GC/MS

    PubMed Central

    2011-01-01

    The catalytic pyrolysis of Laminaria japonica was carried out over a hierarchical meso-MFI zeolite (Meso-MFI) and nanoporous Al-MCM-48 using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The effect of the catalyst type on the product distribution and chemical composition of the bio-oil was examined using Py-GC/MS. The Meso-MFI exhibited a higher activity in deoxygenation and aromatization during the catalytic pyrolysis of L. japonica. Meanwhile, the catalytic activity of Al-MCM-48 was lower than that of Meso-MFI due to its weak acidity. PMID:21851599

  2. Catalytic [3 + 2] Cycloaddition through Ring Cleavage of Simple Cyclopropanes with Isocyanates.

    PubMed

    Tsunoi, Shinji; Maruoka, Yoshiaki; Suzuki, Itaru; Shibata, Ikuya

    2015-08-21

    The catalytic synthesis of γ-butyrolactams was established via [3 + 2]-cycloaddition of cyclopropanes with isocyanates. An organotin iodide ate complex, MgBr(+)[Bu2SnBrI2](-), was employed as an effective catalyst. Simple cyclopropanes that lack aryl or vinyl substituents were useful precursors. Even acyl cyclopropanes were applicable. The hybrid characteristics of a tin complex, acidic MgBr(+) with nucleophilic tin iodide, was responsible for the catalytic reaction.

  3. Catalytic [3 + 2] Cycloaddition through Ring Cleavage of Simple Cyclopropanes with Isocyanates.

    PubMed

    Tsunoi, Shinji; Maruoka, Yoshiaki; Suzuki, Itaru; Shibata, Ikuya

    2015-08-21

    The catalytic synthesis of γ-butyrolactams was established via [3 + 2]-cycloaddition of cyclopropanes with isocyanates. An organotin iodide ate complex, MgBr(+)[Bu2SnBrI2](-), was employed as an effective catalyst. Simple cyclopropanes that lack aryl or vinyl substituents were useful precursors. Even acyl cyclopropanes were applicable. The hybrid characteristics of a tin complex, acidic MgBr(+) with nucleophilic tin iodide, was responsible for the catalytic reaction. PMID:26247349

  4. Catalytically active nanomaterials: a promising candidate for artificial enzymes.

    PubMed

    Lin, Youhui; Ren, Jinsong; Qu, Xiaogang

    2014-04-15

    cancer cells, nucleic acids, proteins, metal ions, and other small molecules. In addition, we also introduce three exciting advances in the use of efficient modulators on artificial enzyme systems to improve the catalytic performance of existing nanozymes. For example, we report that graphene oxide could serve as a modulator to greatly improve the catalytic activity of lysozyme-stabilized gold nanoclusters at neutral pH, which will have great potential for applications in biological systems. We show that, through the incorporation of modulator into artificial enzymes, we can offer a facile but highly effective way to improve their overall catalytic performance or realize the catalytic reactions that were not possible in the past. We expect that nanozymes with unique properties and functions will attract increasing research interest and lead to new opportunities in various fields of research.

  5. Mechanism of Ribonuclease III Catalytic Regulation by Serine Phosphorylation

    NASA Astrophysics Data System (ADS)

    Gone, Swapna; Alfonso-Prieto, Mercedes; Paudyal, Samridhdi; Nicholson, Allen W.

    2016-05-01

    Ribonuclease III (RNase III) is a conserved, gene-regulatory bacterial endonuclease that cleaves double-helical structures in diverse coding and noncoding RNAs. RNase III is subject to multiple levels of control, reflective of its global regulatory functions. Escherichia coli (Ec) RNase III catalytic activity is known to increase during bacteriophage T7 infection, reflecting the expression of the phage-encoded protein kinase, T7PK. However, the mechanism of catalytic enhancement is unknown. This study shows that Ec-RNase III is phosphorylated on serine in vitro by purified T7PK, and identifies the targets as Ser33 and Ser34 in the N-terminal catalytic domain. Kinetic experiments reveal a 5-fold increase in kcat and a 1.4-fold decrease in Km following phosphorylation, providing a 7.4–fold increase in catalytic efficiency. Phosphorylation does not change the rate of substrate cleavage under single-turnover conditions, indicating that phosphorylation enhances product release, which also is the rate-limiting step in the steady-state. Molecular dynamics simulations provide a mechanism for facilitated product release, in which the Ser33 phosphomonoester forms a salt bridge with the Arg95 guanidinium group, thereby weakening RNase III engagement of product. The simulations also show why glutamic acid substitution at either serine does not confer enhancement, thus underscoring the specific requirement for a phosphomonoester.

  6. Mechanism of Ribonuclease III Catalytic Regulation by Serine Phosphorylation

    PubMed Central

    Gone, Swapna; Alfonso-Prieto, Mercedes; Paudyal, Samridhdi; Nicholson, Allen W.

    2016-01-01

    Ribonuclease III (RNase III) is a conserved, gene-regulatory bacterial endonuclease that cleaves double-helical structures in diverse coding and noncoding RNAs. RNase III is subject to multiple levels of control, reflective of its global regulatory functions. Escherichia coli (Ec) RNase III catalytic activity is known to increase during bacteriophage T7 infection, reflecting the expression of the phage-encoded protein kinase, T7PK. However, the mechanism of catalytic enhancement is unknown. This study shows that Ec-RNase III is phosphorylated on serine in vitro by purified T7PK, and identifies the targets as Ser33 and Ser34 in the N-terminal catalytic domain. Kinetic experiments reveal a 5-fold increase in kcat and a 1.4-fold decrease in Km following phosphorylation, providing a 7.4–fold increase in catalytic efficiency. Phosphorylation does not change the rate of substrate cleavage under single-turnover conditions, indicating that phosphorylation enhances product release, which also is the rate-limiting step in the steady-state. Molecular dynamics simulations provide a mechanism for facilitated product release, in which the Ser33 phosphomonoester forms a salt bridge with the Arg95 guanidinium group, thereby weakening RNase III engagement of product. The simulations also show why glutamic acid substitution at either serine does not confer enhancement, thus underscoring the specific requirement for a phosphomonoester. PMID:27150669

  7. Dual Catalytic Activity of Hydroxycinnamoyl-Coenzyme A Quinate Transferase from Tomato Allows It to Moonlight in the Synthesis of Both Mono- and Dicaffeoylquinic Acids1[W][OPEN

    PubMed Central

    Moglia, Andrea; Lanteri, Sergio; Comino, Cinzia; Hill, Lionel; Knevitt, Daniel; Cagliero, Cecilia; Rubiolo, Patrizia; Bornemann, Stephen

    2014-01-01

    Tomato (Solanum lycopersicum), like other Solanaceous species, accumulates high levels of antioxidant caffeoylquinic acids, which are strong bioactive molecules and protect plants against biotic and abiotic stresses. Among these compounds, the monocaffeoylquinic acids (e.g. chlorogenic acid [CGA]) and the dicaffeoylquinic acids (diCQAs) have been found to possess marked antioxidative properties. Thus, they are of therapeutic interest both as phytonutrients in foods and as pharmaceuticals. Strategies to increase diCQA content in plants have been hampered by the modest understanding of their biosynthesis and whether the same pathway exists in different plant species. Incubation of CGA with crude extracts of tomato fruits led to the formation of two new products, which were identified by liquid chromatography-mass spectrometry as diCQAs. This chlorogenate:chlorogenate transferase activity was partially purified from ripe fruit. The final protein fraction resulted in 388-fold enrichment of activity and was subjected to trypsin digestion and mass spectrometric sequencing: a hydroxycinnamoyl-Coenzyme A:quinate hydroxycinnamoyl transferase (HQT) was selected as a candidate protein. Assay of recombinant HQT protein expressed in Escherichia coli confirmed its ability to synthesize diCQAs in vitro. This second activity (chlorogenate:chlorogenate transferase) of HQT had a low pH optimum and a high Km for its substrate, CGA. High concentrations of CGA and relatively low pH occur in the vacuoles of plant cells. Transient assays demonstrated that tomato HQT localizes to the vacuole as well as to the cytoplasm of plant cells, supporting the idea that in this species, the enzyme catalyzes different reactions in two subcellular compartments. PMID:25301886

  8. Vapor Phase Catalytic Ammonia Reduction

    NASA Technical Reports Server (NTRS)

    Flynn, Michael T.; Harper, Lynn D. (Technical Monitor)

    1994-01-01

    This paper discusses the development of a Vapor Phase Catalytic Ammonia Reduction (VPCAR) teststand and the results of an experimental program designed to evaluate the potential of the technology as a water purification process. In the experimental program the technology is evaluated based upon product water purity, water recovery rate, and power consumption. The experimental work demonstrates that the technology produces high purity product water and attains high water recovery rates at a relatively high specific power consumption. The experimental program was conducted in 3 phases. In phase I an Igepon(TM) soap and water mixture was used to evaluate the performance of an innovative Wiped-Film Rotating-Disk evaporator and associated demister. In phase II a phenol-water solution was used to evaluate the performance of the high temperature catalytic oxidation reactor. In phase III a urine analog was used to evaluate the performance of the combined distillation/oxidation functions of the processor.

  9. Catalytic combustion of residual fuels

    NASA Technical Reports Server (NTRS)

    Bulzan, D. L.; Tacina, R. R.

    1981-01-01

    A noble metal catalytic reactor was tested using two grades of petroleum derived residual fuels at specified inlet air temperatures, pressures, and reference velocities. Combustion efficiencies greater than 99.5 percent were obtained. Steady state operation of the catalytic reactor required inlet air temperatures of at least 800 K. At lower inlet air temperatures, upstream burning in the premixing zone occurred which was probably caused by fuel deposition and accumulation on the premixing zone walls. Increasing the inlet air temperature prevented this occurrence. Both residual fuels contained about 0.5 percent nitrogen by weight. NO sub x emissions ranged from 50 to 110 ppm by volume at 15 percent excess O2. Conversion of fuel-bound nitrogen to NO sub x ranged from 25 to 50 percent.

  10. Effective function annotation through catalytic residue conservation.

    PubMed

    George, Richard A; Spriggs, Ruth V; Bartlett, Gail J; Gutteridge, Alex; MacArthur, Malcolm W; Porter, Craig T; Al-Lazikani, Bissan; Thornton, Janet M; Swindells, Mark B

    2005-08-30

    Because of the extreme impact of genome sequencing projects, protein sequences without accompanying experimental data now dominate public databases. Homology searches, by providing an opportunity to transfer functional information between related proteins, have become the de facto way to address this. Although a single, well annotated, close relationship will often facilitate sufficient annotation, this situation is not always the case, particularly if mutations are present in important functional residues. When only distant relationships are available, the transfer of function information is more tenuous, and the likelihood of encountering several well annotated proteins with different functions is increased. The consequence for a researcher is a range of candidate functions with little way of knowing which, if any, are correct. Here, we address the problem directly by introducing a computational approach to accurately identify and segregate related proteins into those with a functional similarity and those where function differs. This approach should find a wide range of applications, including the interpretation of genomics/proteomics data and the prioritization of targets for high-throughput structure determination. The method is generic, but here we concentrate on enzymes and apply high-quality catalytic site data. In addition to providing a series of comprehensive benchmarks to show the overall performance of our approach, we illustrate its utility with specific examples that include the correct identification of haptoglobin as a nonenzymatic relative of trypsin, discrimination of acid-d-amino acid ligases from a much larger ligase pool, and the successful annotation of BioH, a structural genomics target.

  11. Catalytic partial oxidation of pyrolysis oils

    NASA Astrophysics Data System (ADS)

    Rennard, David Carl

    2009-12-01

    This thesis explores the catalytic partial oxidation (CPO) of pyrolysis oils to syngas and chemicals. First, an exploration of model compounds and their chemistries under CPO conditions is considered. Then CPO experiments of raw pyrolysis oils are detailed. Finally, plans for future development in this field are discussed. In Chapter 2, organic acids such as propionic acid and lactic acid are oxidized to syngas over Pt catalysts. Equilibrium production of syngas can be achieved over Rh-Ce catalysts; alternatively mechanistic evidence is derived using Pt catalysts in a fuel rich mixture. These experiments show that organic acids, present in pyrolysis oils up to 25%, can undergo CPO to syngas or for the production of chemicals. As the fossil fuels industry also provides organic chemicals such as monomers for plastics, the possibility of deriving such species from pyrolysis oils allows for a greater application of the CPO of biomass. However, chemical production is highly dependent on the originating molecular species. As bio oil comprises up to 400 chemicals, it is essential to understand how difficult it would be to develop a pure product stream. Chapter 3 continues the experimentation from Chapter 2, exploring the CPO of another organic functionality: the ester group. These experiments demonstrate that equilibrium syngas production is possible for esters as well as acids in autothermal operation with contact times as low as tau = 10 ms over Rh-based catalysts. Conversion for these experiments and those with organic acids is >98%, demonstrating the high reactivity of oxygenated compounds on noble metal catalysts. Under CPO conditions, esters decompose in a predictable manner: over Pt and with high fuel to oxygen, non-equilibrium products show a similarity to those from related acids. A mechanism is proposed in which ethyl esters thermally decompose to ethylene and an acid, which decarbonylates homogeneously, driven by heat produced at the catalyst surface. Chapter 4

  12. Thermodynamics of catalytic nanoparticle morphology

    NASA Astrophysics Data System (ADS)

    Zwolak, Michael; Sharma, Renu; Lin, Pin Ann

    Metallic nanoparticles are an important class of industrial catalysts. The variability of their properties and the environment in which they act, from their chemical nature & surface modification to their dispersion and support, allows their performance to be optimized for many chemical processes useful in, e.g., energy applications and other areas. Their large surface area to volume ratio, as well as varying sizes and faceting, in particular, makes them an efficient source for catalytically active sites. These characteristics of nanoparticles - i.e., their morphology - can often display intriguing behavior as a catalytic process progresses. We develop a thermodynamic model of nanoparticle morphology, one that captures the competition of surface energy with other interactions, to predict structural changes during catalytic processes. Comparing the model to environmental transmission electron microscope images of nickel nanoparticles during carbon nanotube (and other product) growth demonstrates that nickel deformation in response to the nanotube growth is due to a favorable interaction with carbon. Moreover, this deformation is halted due to insufficient volume of the particles. We will discuss the factors that influence morphology and also how the model can be used to extract interaction strengths from experimental observations.

  13. Catalytic conversion of cellulose to chemicals in ionic liquid.

    PubMed

    Tao, Furong; Song, Huanling; Chou, Lingjun

    2011-01-01

    A simple and effective route for the production of 5-hydroxymethyl furfural (HMF) and furfural from microcrystalline cellulose (MCC) has been developed. CoSO(4) in an ionic liquid, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1), was found to be an efficient catalyst for the hydrolysis of cellulose at 150°C, which led to 84% conversion of MCC after 300min reaction time. In the presence of a catalytic amount of CoSO(4), the yields of HMF and furfural were up to 24% and 17%, respectively; a small amount of levulinic acid (LA) and reducing sugars (8% and 4%, respectively) were also generated. Dimers of furan compounds were detected as the main by-products through HPLC-MS, and with the help of mass spectrometric analysis, the components of gas products were methane, ethane, CO, CO(2,) and H(2). A mechanism for the CoSO(4)-IL-1 hydrolysis system was proposed and IL-1 was recycled for the first time, which exhibited favorable catalytic activity over five repeated runs. This catalytic system may be valuable to facilitate energy-efficient and cost-effective conversion of biomass into biofuels and platform chemicals. PMID:21092940

  14. One-step catalytic asymmetric synthesis of all-syn deoxypropionate motif from propylene: Total synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid

    PubMed Central

    Ota, Yusuke; Murayama, Toshiki; Nozaki, Kyoko

    2016-01-01

    In nature, many complex structures are assembled from simple molecules by a series of tailored enzyme-catalyzed reactions. One representative example is the deoxypropionate motif, an alternately methylated alkyl chain containing multiple stereogenic centers, which is biosynthesized by a series of enzymatic reactions from simple building blocks. In organic synthesis, however, the majority of the reported routes require the syntheses of complex building blocks. Furthermore, multistep reactions with individual purifications are required at each elongation. Here we show the construction of the deoxypropionate structure from propylene in a single step to achieve a three-step synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid, a major acid component of a preen-gland wax of the graylag goose. To realize this strategy, we focused on the coordinative chain transfer polymerization and optimized the reaction condition to afford a stereo-controlled oligomer, which is contrastive to the other synthetic strategies developed to date that require 3–6 steps per unit, with unavoidable byproduct generation. Furthermore, multiple oligomers with different number of deoxypropionate units were isolated from one batch, showing application to the construction of library. Our strategy opens the door for facile synthetic routes toward other natural products that share the deoxypropionate motif. PMID:26908873

  15. Selenium utilization in thioredoxin and catalytic advantage provided by selenocysteine

    SciTech Connect

    Kim, Moon-Jung; Lee, Byung Cheon; Hwang, Kwang Yeon; Gladyshev, Vadim N.; Kim, Hwa-Young

    2015-06-12

    Thioredoxin (Trx) is a major thiol-disulfide reductase that plays a role in many biological processes, including DNA replication and redox signaling. Although selenocysteine (Sec)-containing Trxs have been identified in certain bacteria, their enzymatic properties have not been characterized. In this study, we expressed a selenoprotein Trx from Treponema denticola, an oral spirochete, in Escherichia coli and characterized this selenoenzyme and its natural cysteine (Cys) homologue using E. coli Trx1 as a positive control. {sup 75}Se metabolic labeling and mutation analyses showed that the SECIS (Sec insertion sequence) of T. denticola selenoprotein Trx is functional in the E. coli Sec insertion system with specific selenium incorporation into the Sec residue. The selenoprotein Trx exhibited approximately 10-fold higher catalytic activity than the Sec-to-Cys version and natural Cys homologue and E. coli Trx1, suggesting that Sec confers higher catalytic activity on this thiol-disulfide reductase. Kinetic analysis also showed that the selenoprotein Trx had a 30-fold higher K{sub m} than Cys-containing homologues, suggesting that this selenoenzyme is adapted to work efficiently with high concentrations of substrate. Collectively, the results of this study support the hypothesis that selenium utilization in oxidoreductase systems is primarily due to the catalytic advantage provided by the rare amino acid, Sec. - Highlights: • The first characterization of a selenoprotein Trx is presented. • The selenoenzyme Trx exhibits 10-fold higher catalytic activity than Cys homologues. • Se utilization in Trx is primarily due to the catalytic advantage provided by Sec residue.

  16. Crystallography captures catalytic steps in human methionine adenosyltransferase enzymes.

    PubMed

    Murray, Ben; Antonyuk, Svetlana V; Marina, Alberto; Lu, Shelly C; Mato, Jose M; Hasnain, S Samar; Rojas, Adriana L

    2016-02-23

    The principal methyl donor of the cell, S-adenosylmethionine (SAMe), is produced by the highly conserved family of methionine adenosyltranferases (MATs) via an ATP-driven process. These enzymes play an important role in the preservation of life, and their dysregulation has been tightly linked to liver and colon cancers. We present crystal structures of human MATα2 containing various bound ligands, providing a "structural movie" of the catalytic steps. High- to atomic-resolution structures reveal the structural elements of the enzyme involved in utilization of the substrates methionine and adenosine and in formation of the product SAMe. MAT enzymes are also able to produce S-adenosylethionine (SAE) from substrate ethionine. Ethionine, an S-ethyl analog of the amino acid methionine, is known to induce steatosis and pancreatitis. We show that SAE occupies the active site in a manner similar to SAMe, confirming that ethionine also uses the same catalytic site to form the product SAE.

  17. Hollow mesoporous aluminosilica spheres with perpendicular pore channels as catalytic nanoreactors.

    PubMed

    Fang, Xiaoliang; Liu, Zhaohui; Hsieh, Ming-Feng; Chen, Mei; Liu, Pengxin; Chen, Cheng; Zheng, Nanfeng

    2012-05-22

    The design and synthesis of hollow/yolk-shell mesoporous structures with catalytically active ordered mesoporous shells can infuse new vitality into the applications of these attractive structures. In this study, we report that hollow/yolk-shell structures with catalytically active ordered mesoporous aluminosilica shells can be easily prepared by using silica spheres as the silica precursors. By simply treating with a hot alkaline solution in the presence of sodium aluminate (NaAlO(2)) and cetyltrimethylammonium bromide (CTAB), solid silica spheres can be directly converted into high-quality hollow mesoporous aluminosilica spheres with perpendicular pore channels. On the basis of the proposed formation mechanism of etching followed by co-assembly, the synthesis strategy developed in this work can be extended as a general strategy to prepare ordered mesoporous yolk-shell structures with diverse compositions and morphologies simply by replacing solid silica spheres with silica-coated nanocomposites. The reduction of 4-nitrophenol with yolk-shell structured Au@ordered mesoporous aluminosilica as the catalyst has clearly demonstrated that the highly permeable perpendicular pore channels of mesoporous aluminosilica can effectively prevent the catalytically active yolk from aggregating. Furthermore, with accessible acidity, the yolk-shell structured ordered mesoporous aluminosilica spheres containing Pd yolk exhibit high catalytic activity and recyclability in a one-pot two-step synthesis involving an acid catalysis and subsequent catalytic hydrogenation for desired benzimidazole derivative, which makes the proposed hollow ordered aluminosilica spheres a versatile and practicable scaffold for advanced catalytic nanoreactor systems.

  18. Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels.

    PubMed

    Zhou, Chun-Hui; Xia, Xi; Lin, Chun-Xiang; Tong, Dong-Shen; Beltramini, Jorge

    2011-11-01

    Lignocellulosic biomass is the most abundant and bio-renewable resource with great potential for sustainable production of chemicals and fuels. This critical review provides insights into the state-of the-art accomplishments in the chemocatalytic technologies to generate fuels and value-added chemicals from lignocellulosic biomass, with an emphasis on its major component, cellulose. Catalytic hydrolysis, solvolysis, liquefaction, pyrolysis, gasification, hydrogenolysis and hydrogenation are the major processes presently studied. Regarding catalytic hydrolysis, the acid catalysts cover inorganic or organic acids and various solid acids such as sulfonated carbon, zeolites, heteropolyacids and oxides. Liquefaction and fast pyrolysis of cellulose are primarily conducted over catalysts with proper acidity/basicity. Gasification is typically conducted over supported noble metal catalysts. Reaction conditions, solvents and catalysts are the prime factors that affect the yield and composition of the target products. Most of processes yield a complex mixture, leading to problematic upgrading and separation. An emerging technique is to integrate hydrolysis, liquefaction or pyrolysis with hydrogenation over multifunctional solid catalysts to convert lignocellulosic biomass to value-added fine chemicals and bio-hydrocarbon fuels. And the promising catalysts might be supported transition metal catalysts and zeolite-related materials. There still exist technological barriers that need to be overcome (229 references). PMID:21863197

  19. Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels.

    PubMed

    Zhou, Chun-Hui; Xia, Xi; Lin, Chun-Xiang; Tong, Dong-Shen; Beltramini, Jorge

    2011-11-01

    Lignocellulosic biomass is the most abundant and bio-renewable resource with great potential for sustainable production of chemicals and fuels. This critical review provides insights into the state-of the-art accomplishments in the chemocatalytic technologies to generate fuels and value-added chemicals from lignocellulosic biomass, with an emphasis on its major component, cellulose. Catalytic hydrolysis, solvolysis, liquefaction, pyrolysis, gasification, hydrogenolysis and hydrogenation are the major processes presently studied. Regarding catalytic hydrolysis, the acid catalysts cover inorganic or organic acids and various solid acids such as sulfonated carbon, zeolites, heteropolyacids and oxides. Liquefaction and fast pyrolysis of cellulose are primarily conducted over catalysts with proper acidity/basicity. Gasification is typically conducted over supported noble metal catalysts. Reaction conditions, solvents and catalysts are the prime factors that affect the yield and composition of the target products. Most of processes yield a complex mixture, leading to problematic upgrading and separation. An emerging technique is to integrate hydrolysis, liquefaction or pyrolysis with hydrogenation over multifunctional solid catalysts to convert lignocellulosic biomass to value-added fine chemicals and bio-hydrocarbon fuels. And the promising catalysts might be supported transition metal catalysts and zeolite-related materials. There still exist technological barriers that need to be overcome (229 references).

  20. Treatment of activated carbon to enhance catalytic activity for reduction of nitric oxide with ammonia

    SciTech Connect

    Ku, B.J.; Rhee, H.K. . Dept. of Chemical Engineering); Lee, J.K.; Park, D. )

    1994-11-01

    Catalytic activity of activated carbon treated with various techniques was examined in a fixed bed reactor for the reduction of nitric oxide with ammonia at 150 C. Activated carbon derived from coconut shell impregnated with an aqueous solution of ammonium sulfate, further treated with sulfuric acid, dried at 120 C, and then heated in an inert gas stream at 400 C, showed the highest catalytic activity within the range of experimental conditions. The enhancement of catalytic activity of modified activated carbon could be attributed to the increase in the amount of oxygen function groups which increased the adsorption site for ammonia. Catalytic activity of activated carbons depended on the surface area and the oxygen content as well.

  1. Modeling a Transient Catalytic Combustor

    NASA Technical Reports Server (NTRS)

    Tien, J. S.

    1985-01-01

    Transient model of monolith catalytic combustor presented in report done under NASA/DOE contract. Model assumes quasi-steady gas phase and thermally "thin" solid. In gas-phase treatment, several quasi-global chemical reactions assumed capable of describing CO and unburnt hydrocarbon emissions in fuel-lean operations. In steady-state computation presented, influence of selected operating and design parameters on minimum combustor length studied. When fast transient responses required, both steady and unsteady studies made to achieve meaningful compromise in design.

  2. Catalytic Organometallic Reactions of Ammonia

    PubMed Central

    Klinkenberg, Jessica L.

    2012-01-01

    Until recently, ammonia had rarely succumbed to catalytic transformations with homogeneous catalysts, and the development of such reactions that are selective for the formation of single products under mild conditions has encountered numerous challenges. However, recently developed catalysts have allowed several classes of reactions to create products with nitrogen-containing functional groups from ammonia. These reactions include hydroaminomethylation, reductive amination, alkylation, allylic substitution, hydroamination, and cross-coupling. This Minireview describes examples of these processes and the factors that control catalyst activity and selectivity. PMID:20857466

  3. Molecular catalytic coal liquid conversion

    SciTech Connect

    Stock, L.M.; Yang, Shiyong

    1995-12-31

    This research, which is relevant to the development of new catalytic systems for the improvement of the quality of coal liquids by the addition of dihydrogen, is divided into two tasks. Task 1 centers on the activation of dihydrogen by molecular basic reagents such as hydroxide ion to convert it into a reactive adduct (OH{center_dot}H{sub 2}){sup {minus}} that can reduce organic molecules. Such species should be robust withstanding severe conditions and chemical poisons. Task 2 is focused on an entirely different approach that exploits molecular catalysts, derived from organometallic compounds that are capable of reducing monocyclic aromatic compounds under very mild conditions. Accomplishments and conclusions are discussed.

  4. Catalytic membranes for fuel cells

    DOEpatents

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

    2011-04-19

    A fuel cell of the present invention comprises a cathode and an anode, one or both of the anode and the cathode including a catalyst comprising a bundle of longitudinally aligned graphitic carbon nanotubes including a catalytically active transition metal incorporated longitudinally and atomically distributed throughout the graphitic carbon walls of said nanotubes. The nanotubes also include nitrogen atoms and/or ions chemically bonded to the graphitic carbon and to the transition metal. Preferably, the transition metal comprises at least one metal selected from the group consisting of Fe, Co, Ni, Mn, and Cr.

  5. Computational Introduction of Catalytic Activity into Proteins.

    PubMed

    Bertolani, Steve J; Carlin, Dylan Alexander; Siegel, Justin B

    2016-01-01

    Recently, there have been several successful cases of introducing catalytic activity into proteins. One method that has been used successfully to achieve this is the theozyme placement and enzyme design algorithms implemented in Rosetta Molecular Modeling Suite. Here, we illustrate how to use this software to recapitulate the placement of catalytic residues and ligand into a protein using a theozyme, protein scaffold, and catalytic constraints as input. PMID:27094294

  6. 3-Nitropropionic Acid is a Suicide Inhibitor of MitochondrialRespiration that, Upon Oxidation by Complex II, Forms a Covalent AdductWith a Catalytic Base Arginine in the Active Site of the Enzyme

    SciTech Connect

    Huang, Li-shar; Sun, Gang; Cobessi, David; Wang, Andy C.; Shen,John T.; Tung, Eric Y.; Anderson, Vernon E.; Berry, Edward A.

    2005-12-01

    We report three new structures of mitochondrial respiratory Complex II (succinate ubiquinone oxidoreductase, E.C. 1.3.5.1) at up to 2.1 {angstrom} resolution, with various inhibitors. The structures define the conformation of the bound inhibitors and suggest the residues involved in substrate binding and catalysis at the dicarboxylate site. In particular they support the role of Arg297 as a general base catalyst accepting a proton in the dehydrogenation of succinate. The dicarboxylate ligand in oxaloacetate-containing crystals appears to be the same as that reported for Shewanella flavocytochrome c treated with fumarate. The plant and fungal toxin 3-nitropropionic acid, an irreversible inactivator of succinate dehydrogenase, forms a covalent adduct with the side chain of Arg297. The modification eliminates a trypsin cleavage site in the flavoprotein, and tandem mass spectroscopic analysis of the new fragment shows the mass of Arg 297 to be increased by 83 Da and to have potential of losing 44 Da, consistent with decarboxylation, during fragmentation.

  7. Catalytic oxidizers and Title V requirements

    SciTech Connect

    Uberoi, M.; Rach, S.E.

    1999-07-01

    Catalytic oxidizers have been used to reduce VOC emissions from various industries including printing, chemical, paint, coatings, etc. A catalytic oxidizer uses a catalyst to reduce the operating temperature for combustion to approximately 600 F, which is substantially lower than thermal oxidation unit. Title V requirements have renewed the debate on the best methods to assure compliance of catalytic oxidizers, with some suggesting the need for continuous emission monitoring equipment. This paper will discuss the various aspects of catalytic oxidation and consider options such as monitoring inlet/outlet temperatures, delta T across the catalyst, periodic laboratory testing of catalyst samples, and preventive maintenance procedures as means of assuring continuous compliance.

  8. Techno-economics of carbon preserving butanol production using a combined fermentative and catalytic approach.

    PubMed

    Nilsson, Robert; Bauer, Fredric; Mesfun, Sennai; Hulteberg, Christian; Lundgren, Joakim; Wännström, Sune; Rova, Ulrika; Berglund, Kris Arvid

    2014-06-01

    This paper presents a novel process for n-butanol production which combines a fermentation consuming carbon dioxide (succinic acid fermentation) with subsequent catalytic reduction steps to add hydrogen to form butanol. Process simulations in Aspen Plus have been the basis for the techno-economic analyses performed. The overall economy for the novel process cannot be justified, as production of succinic acid by fermentation is too costly. Though, succinic acid price is expected to drop drastically in a near future. By fully integrating the succinic acid fermentation with the catalytic conversion the need for costly recovery operations could be reduced. The hybrid process would need 22% less raw material than the butanol fermentation at a succinic acid fermentation yield of 0.7g/g substrate. Additionally, a carbon dioxide fixation of up to 13ktonnes could be achieved at a plant with an annual butanol production of 10ktonnes.

  9. Design of a Brønsted acid with two different acidic sites: synthesis and application of aryl phosphinic acid-phosphoric acid as a Brønsted acid catalyst.

    PubMed

    Momiyama, N; Narumi, T; Terada, M

    2015-12-11

    A Brønsted acid with two different acidic sites, aryl phosphinic acid-phosphoric acid, has been synthesized. Its catalytic performance was assessed in the hetero-Diels-Alder reaction of aldehyde hydrates with Danishefsky's diene, achieving high reaction efficiency. PMID:26445921

  10. Catalytic conversion of light alkanes

    SciTech Connect

    Lyons, J.E.

    1992-06-30

    The second Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between April 1, 1992 and June 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products that can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon uwspomdon fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE I).

  11. Role of Charged Residues in the Catalytic Sites of Escherichia coli ATP Synthase

    PubMed Central

    Ahmad, Zulfiqar; Okafor, Florence; Laughlin, Thomas F.

    2011-01-01

    Here we describe the role of charged amino acids at the catalytic sites of Escherichia coli ATP synthase. There are four positively charged and four negatively charged residues in the vicinity of of E. coli ATP synthase catalytic sites. Positive charges are contributed by three arginine and one lysine, while negative charges are contributed by two aspartic acid and two glutamic acid residues. Replacement of arginine with a neutral amino acid has been shown to abrogate phosphate binding, while restoration of phosphate binding has been accomplished by insertion of arginine at the same or a nearby location. The number and position of positive charges plays a critical role in the proper and efficient binding of phosphate. However, a cluster of many positive charges inhibits phosphate binding. Moreover, the presence of negatively charged residues seems a requisite for the proper orientation and functioning of positively charged residues in the catalytic sites. This implies that electrostatic interactions between amino acids are an important constituent of initial phosphate binding in the catalytic sites. Significant loss of function in growth and ATPase activity assays in mutants generated through charge modulations has demonstrated that precise location and stereochemical interactions are of paramount importance. PMID:22312470

  12. Catalytic cracking of C5 raffinate to light olefins over phosphorous-modified microporous and mesoporous ZSM-5.

    PubMed

    Lee, Joongwon; Hong, Ung Gi; Hwang, Sunhwan; Youn, Min Hye; Song, In Kyu

    2013-11-01

    Phosphorous-modified microporous and mesoporous ZSM-5 catalysts (XP/C-ZSM5) were prepared with a variation of phosphorous content (X = 0.17, 0.3, 0.7, 1.4, and 2.7 wt%), and they were applied to the production of light olefins (ethylene and propylene) through catalytic cracking of C5 raffinate. The effect of phosphorous content on the physicochemical properties and catalytic activities of XP/C-ZSM5 catalysts was investigated. It was revealed that physicochemical properties of XP/C-ZSM5 catalysts were strongly influenced by phosphorous content. Strong acidity of XP/C-ZSM5 catalysts decreased with increasing phosphorous content. In the catalytic cracking of C5 raffinate, both conversion of C5 raffinate and yield for light olefins (ethylene and propylene) showed volcano-shaped curves with respect to strong acidity. This result indicates that strong acidity of XP/C-ZSM5 catalysts played an important role in determining the catalytic performance in the catalytic cracking of C5 raffinate. Among the catalysts tested, 0.3P/C-ZSM5 catalyst with moderate strong acidity showed the best catalytic performance.

  13. Catalytic, Enantioselective, Intramolecular Carbosulfenylation of Olefins. Preparative and Stereochemical Aspects

    PubMed Central

    Denmark, Scott E.; Jaunet, Alex

    2014-01-01

    The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a co-catalytic Brønsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50–92%) and high enantioselectivities (71:29 – 97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with mono-activated arene nucleophiles. PMID:24328051

  14. Gas phase catalytic hydrodechlorination of chlorobenzene over cobalt phosphide catalysts with different P contents.

    PubMed

    Cecilia, J A; Infantes-Molina, A; Rodríguez-Castellón, E; Jiménez-López, A

    2013-09-15

    The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene (CB) at atmospheric pressure was investigated over silica-supported cobalt and cobalt phosphide catalysts containing different P loading and a fixed amount of cobalt (5 wt.%). The effect of the initial P/Co molar ratio on the stoichiometry of the cobalt phosphide phase, the acidity and the hydrogen activation capability were discussed and these properties correlated with the catalytic activity. Catalytic results indicated that the cobalt phosphide phase is much more active than the monometallic cobalt one. The activity raised with the P content present in the sample due to the formation of the CoP phase instead of the Co₂P one, which favored the formation of hydrogen spillover species, increased the amount of weak acid sites and the number of exposed superficial cobalt atoms probably related to a better dispersion of the active phase. All the catalysts gave rise benzene as the main reaction product.

  15. Liquid-phase chemical hydrogen storage: catalytic hydrogen generation under ambient conditions.

    PubMed

    Jiang, Hai-Long; Singh, Sanjay Kumar; Yan, Jun-Min; Zhang, Xin-Bo; Xu, Qiang

    2010-05-25

    There is a demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. Lithium and sodium borohydride, ammonia borane, hydrazine, and formic acid have been extensively investigated as promising hydrogen storage materials based on their relatively high hydrogen content. Significant advances, such as hydrogen generation temperatures and reaction kinetics, have been made in the catalytic hydrolysis of aqueous lithium and sodium borohydride and ammonia borane as well as in the catalytic decomposition of hydrous hydrazine and formic acid. In this Minireview we briefly survey the research progresses in catalytic hydrogen generation from these liquid-phase chemical hydrogen storage materials.

  16. Glycine and Diglycine as Possible Catalytic Factors in the Prebiotic Evolution of Peptides

    NASA Astrophysics Data System (ADS)

    Plankensteiner, Kristof; Righi, Alessandro; Rode, Bernd M.

    2002-06-01

    Mutual catalytic effects within the Salt-Induced Peptide Formation (SIPF) Reaction might be one little puzzle piece in the complicated process of the formation of complex peptidic systems and their chemical evolution on the prebiotic earth. The catalytic effects of glycine and diglycine on the formation of dipeptides from mixed amino acid systems in the SIPF Reaction was investigated for systems with leucine, proline, valine and aspartic acid and showed to result in a significant increase of the yield of the majority of the produced dipeptides. The results of the experiments strongly confirm previous theories on the catalytic mechanism and show the ability of the SIPF Reaction to produce a very diverse set of peptide products with relevance to the formation of a biosphere.

  17. Direct catalytic reduction of sulfur dioxide to elemental sulfur

    SciTech Connect

    Loftus, P.J.; Benedek, K.R.; Lunt, R.R.; Flytzani-Stephanopoulos, M.

    1996-12-31

    More than 170 wet scrubber systems applied to 72,000 MW of US, coal-fired, utility boilers are in operation or under construction. A small fraction of these systems produce a useable byproduct (gypsum): the remainder generate approximately 20 million tons per annum of disposable flue gas desulfurization (FGD) byproduct, which are transported and disposed of in landfills. The use of regenerable sorbent technologies has the potential to reduce or eliminate this solid waste production, transportation and disposal. All regenerable FGD systems produce an off-gas stream from the regenerator that must be processed further in order to obtain a saleable byproduct, such as elemental sulfur, sulfuric acid or liquid SO{sub 2}. This off-gas has only a fraction of the flue gas volume, and contains no oxygen. Recovery of sulfur from this stream in a single-stage catalytic converter, avoiding a multi-stage Claus plant, could decrease the cost and accelerate the commercialization of many regenerable FGD processes. The paper describes the plan to develop and scale-up an advanced byproduct recovery technology that is based on a direct, single-stage, catalytic process for converting sulfur dioxide to elemental sulfur. This catalytic process reduces SO{sub 2} over a fluorite-type oxide such as ceria and zirconia.

  18. Selenium utilization in thioredoxin and catalytic advantage provided by selenocysteine

    PubMed Central

    Kim, Moon-Jung; Lee, Byung Cheon; Hwang, Kwang Yeon; Gladyshev, Vadim N.; Kim, Hwa-Young

    2016-01-01

    Thioredoxin (Trx) is a major thiol-disulfide reductase that plays a role in many biological processes, including DNA replication and redox signaling. Although selenocysteine (Sec)-containing Trxs have been identified in certain bacteria, their enzymatic properties have not been characterized. In this study, we expressed a selenoprotein Trx from Treponema denticola, an oral spirochete, in Escherichia coli and characterized this selenoenzyme and its natural cysteine (Cys) homologue using E. coli Trx1 as a positive control. 75Se metabolic labeling and mutation analyses showed that the SECIS (Sec insertion sequence) of T. denticola selenoprotein Trx is functional in the E. coli Sec insertion system with specific selenium incorporation into the Sec residue. The selenoprotein Trx exhibited approximately 10-fold higher catalytic activity than the Sec-to-Cys version and natural Cys homologue and E. coli Trx1, suggesting that Sec confers higher catalytic activity on this thiol-disulfide reductase. Kinetic analysis also showed that the selenoprotein Trx had a 10-fold higher Km than Cys-containing homologues, suggesting that this selenoenzyme is adapted to work efficiently with high concentrations of substrate. Collectively, the results of this study support the hypothesis that selenium utilization in oxidoreductase systems is primarily due to the catalytic advantage provided by the rare amino acid, Sec. PMID:25912135

  19. Catalytic Isomerization of Biomass‐Derived Aldoses: A Review

    PubMed Central

    Delidovich, Irina

    2016-01-01

    Abstract Selected aldohexoses (d‐glucose, d‐mannose, and d‐galactose) and aldopentoses (d‐xylose, l‐arabinose, and d‐ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon‐efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations. PMID:26948404

  20. Catalytic Isomerization of Biomass-Derived Aldoses: A Review.

    PubMed

    Delidovich, Irina; Palkovits, Regina

    2016-03-21

    Selected aldohexoses (D-glucose, D-mannose, and D-galactose) and aldopentoses (D-xylose, L-arabinose, and D-ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon-efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations.

  1. Catalytic peptide hydrolysis by mineral surface: Implications for prebiotic chemistry

    NASA Astrophysics Data System (ADS)

    Marshall-Bowman, Karina; Ohara, Shohei; Sverjensky, Dimitri A.; Hazen, Robert M.; Cleaves, H. James

    2010-10-01

    The abiotic polymerization of amino acids may have been important for the origin of life, as peptides may have been components of the first self-replicating systems. Though amino acid concentrations in the primitive oceans may have been too dilute for significant oligomerization to occur, mineral surface adsorption may have provided a concentration mechanism. As unactivated amino acid polymerization is thermodynamically unfavorable and kinetically slow in aqueous solution, we studied mainly the reverse reaction of polymer degradation to measure the impact of mineral surface catalysis on peptide bonds. Aqueous glycine (G), diglycine (GG), diketopiperazine (DKP), and triglycine (GGG) were reacted with minerals (calcite, hematite, montmorillonite, pyrite, rutile, or amorphous silica) in the presence of 0.05 M, pH 8.1, KHCO 3 buffer and 0.1 M NaCl as background electrolyte in a thermostatted oven at 25, 50 or 70 °C. Below 70 °C, reaction kinetics were too sluggish to detect catalytic activity over amenable laboratory time-scales. Minerals were not found to have measurable effects on the degradation or elongation of G, GG or DKP at 70 °C in solution. At 70 °C pyrite was the most catalytic mineral with detectible effects on the degradation of GGG, although several others also displayed catalytic behavior. GGG degraded ˜1.5-4 times faster in the presence of pyrite than in control reactions, depending on the ratio of solution concentration to mineral surface area. The rate of pyrite catalysis of GGG hydrolysis was found to be saturable, suggesting the presence of discrete catalytic sites on the mineral surface. The mineral-catalyzed degradation of GGG appears to occur via a GGG → DKP + G mechanism, rather than via GGG → GG + G, as in solution-phase reactions. These results are compatible with many previous findings and suggest that minerals may have assisted in peptide synthesis in certain geological settings, specifically by speeding the approach to equilibrium

  2. Diesel engine catalytic combustor system. [aircraft engines

    NASA Technical Reports Server (NTRS)

    Ream, L. W. (Inventor)

    1984-01-01

    A low compression turbocharged diesel engine is provided in which the turbocharger can be operated independently of the engine to power auxiliary equipment. Fuel and air are burned in a catalytic combustor to drive the turbine wheel of turbine section which is initially caused to rotate by starter motor. By opening a flapper value, compressed air from the blower section is directed to catalytic combustor when it is heated and expanded, serving to drive the turbine wheel and also to heat the catalytic element. To start, engine valve is closed, combustion is terminated in catalytic combustor, and the valve is then opened to utilize air from the blower for the air driven motor. When the engine starts, the constituents in its exhaust gas react in the catalytic element and the heat generated provides additional energy for the turbine section.

  3. Catalytic ignition of hydrogen and oxygen propellants

    NASA Technical Reports Server (NTRS)

    Zurawski, Robert L.; Green, James M.

    1988-01-01

    An experimental program was conducted to evaluate the catalytic ignition of gaseous hydrogen and oxygen propellants. Shell 405 granular catalyst and a monolithic sponge catalyst were tested. Mixture ratio, mass flow rate, propellant temperature, and back pressure were varied parametrically in testing to determine the operational limits of the catalytic igniter. The test results show that the gaseous hydrogen and oxygen propellant combination can be ignited catalytically using Shell 405 catalyst over a wide range of mixture ratios, mass flow rates, and propellant injection temperatures. These operating conditions must be optimized to ensure reliable ignition for an extended period of time. A cyclic life of nearly 2000, 2 sec pulses at nominal operating conditions was demonstrated with the catalytic igniter. The results of the experimental program and the established operational limits for a catalytic igniter using the Shell 405 catalysts are presented.

  4. Method of fabricating a catalytic structure

    DOEpatents

    Rollins, Harry W.; Petkovic, Lucia M.; Ginosar, Daniel M.

    2009-09-22

    A precursor to a catalytic structure comprising zinc oxide and copper oxide. The zinc oxide has a sheet-like morphology or a spherical morphology and the copper oxide comprises particles of copper oxide. The copper oxide is reduced to copper, producing the catalytic structure. The catalytic structure is fabricated by a hydrothermal process. A reaction mixture comprising a zinc salt, a copper salt, a hydroxyl ion source, and a structure-directing agent is formed. The reaction mixture is heated under confined volume conditions to produce the precursor. The copper oxide in the precursor is reduced to copper. A method of hydrogenating a carbon oxide using the catalytic structure is also disclosed, as is a system that includes the catalytic structure.

  5. Catalytic ignition of hydrogen and oxygen propellants

    NASA Technical Reports Server (NTRS)

    Zurawski, Robert L.; Green, James M.

    1988-01-01

    An experimental program was conducted to evaluate the catalytic ignition of gaseous hydrogen and oxygen propellants. Shell 405 granular catalyst and a monolithic sponge catalyst were tested. Mixture ratio, mass flow rate, propellant temperature, and back pressure were varied parametrically in testing to determine the operational limits of the catalytic igniter. The test results show that the gaseous hydrogen and oxygen propellant combination can be ignited catalytically using Shell 405 catalyst over a wide range of mixture ratios, mass flow rates, and propellant injection temperatures. These operating conditions must be optimized to ensure reliable ignition for an extended period of time. A cyclic life of nearly 2000, 2 sec pulses at nominal operating conditions was demonstrated with the catalytic igniter. The results of the experimental program and the established operational limits for a catalytic igniter using the Shell 405 catalyst are presented.

  6. Catalytic ignition of hydrogen/oxygen

    NASA Technical Reports Server (NTRS)

    Green, James M.; Zurawski, Robert L.

    1988-01-01

    An experimental program was conducted to evaluate the catalytic ignition of gaseous hydrogen and oxygen. Shell 405 granular catalyst and a unique monolithic sponge catalyst were tested. Mixture ratio, mass flow rate, propellant inlet temperature, and back pressure were varied parametrically in testing to determine the operational limits of a catalytic igniter. The test results showed that the gaseous hydrogen/oxygen propellant combination can be ignited catalytically using Shell 405 catalyst over a wide range of mixture ratios, mass flow rates, and propellant injection temperatures. These operating conditions must be optimized to ensure reliable ignition for an extended period of time. The results of the experimental program and the established operational limits for a catalytic igniter using both the granular and monolithic catalysts are presented. The capabilities of a facility constructed to conduct the igniter testing and the advantages of a catalytic igniter over other ignition systems for gaseous hydrogen and oxygen are also discussed.

  7. Silver nanocluster catalytic microreactors for water purification

    NASA Astrophysics Data System (ADS)

    Da Silva, B.; Habibi, M.; Ognier, S.; Schelcher, G.; Mostafavi-Amjad, J.; Khalesifard, H. R. M.; Tatoulian, M.; Bonn, D.

    2016-07-01

    A new method for the elaboration of a novel type of catalytic microsystem with a high specific area catalyst is developed. A silver nanocluster catalytic microreactor was elaborated by doping a soda-lime glass with a silver salt. By applying a high power laser beam to the glass, silver nanoclusters are obtained at one of the surfaces which were characterized by BET measurements and AFM. A microfluidic chip was obtained by sealing the silver coated glass with a NOA 81 microchannel. The catalytic activity of the silver nanoclusters was then tested for the efficiency of water purification by using catalytic ozonation to oxidize an organic pollutant. The silver nanoclusters were found to be very stable in the microreactor and efficiently oxidized the pollutant, in spite of the very short residence times in the microchannel. This opens the way to study catalytic reactions in microchannels without the need of introducing the catalyst as a powder or manufacturing complex packed bed microreactors.

  8. Catalytic decarbonylation of biosourced substrates.

    PubMed

    Ternel, Jérémy; Lebarbé, Thomas; Monflier, Eric; Hapiot, Frédéric

    2015-05-11

    Linear α-olefins (LAO) are one of the main targets in the field of surfactants, lubricants, and polymers. With the depletion of petroleum resources, the production of LAO from renewable feedstocks has gained increasing interest in recent years. In the present study, we demonstrated that Ir catalysts were suitable to decarbonylate a wide range of biosourced substrates under rather mild conditions (160 °C, 5 h reaction time) in the presence of potassium iodide and acetic anhydride. The resulting LAO were obtained with good conversion and selectivity provided that the purity of the substrate, the nature of the ligand, and the amounts of the additives were controlled accurately. The catalytic system could be recovered efficiently by using a Kugelrohr distillation apparatus and recycled.

  9. Non-catalytic recuperative reformer

    SciTech Connect

    Khinkis, Mark J.; Kozlov, Aleksandr P.; Kurek, Harry

    2015-12-22

    A non-catalytic recuperative reformer has a flue gas flow path for conducting hot flue gas from a thermal process and a reforming mixture flow path for conducting a reforming mixture. At least a portion of the reforming mixture flow path is embedded in the flue gas flow path to permit heat transfer from the hot flue gas to the reforming mixture. The reforming mixture flow path contains substantially no material commonly used as a catalyst for reforming hydrocarbon fuel (e.g., nickel oxide, platinum group elements or rhenium), but instead the reforming mixture is reformed into a higher calorific fuel via reactions due to the heat transfer and residence time. In a preferred embodiment, extended surfaces of metal material such as stainless steel or metal alloy that are high in nickel content are included within at least a portion of the reforming mixture flow path.

  10. Catalytic Carbonylative Spirolactonization of Hydroxycyclopropanols.

    PubMed

    Davis, Dexter C; Walker, Katherine L; Hu, Chunhua; Zare, Richard N; Waymouth, Robert M; Dai, Mingji

    2016-08-24

    A palladium-catalyzed cascade carbonylative spirolactonization of hydroxycyclopropanols has been developed to efficiently synthesize oxaspirolactones common to many complex natural products of important therapeutic value. The mild reaction conditions, high atom economy, broad substrate scope, and scalability of this new method were highlighted in expedient total syntheses of the Turkish tobacco natural products α-levantanolide and α-levantenolide in two and four steps, respectively. The hydroxycyclopropanol substrates are readily available in one step via a Kulinkovich reaction of the corresponding lactones. Mechanistic studies utilizing high-resolution electrospray ionization mass spectrometry (ESI-MS) identified several key intermediates in the catalytic cycle, as well as those related to catalyst decomposition and competitive pathways. PMID:27459274

  11. APPARATUS FOR CATALYTICALLY COMBINING GASES

    DOEpatents

    Busey, H.M.

    1958-08-12

    A convection type recombiner is described for catalytically recombining hydrogen and oxygen which have been radiolytically decomposed in an aqueous homogeneous nuclear reactor. The device is so designed that the energy of recombination is used to circulate the gas mixture over the catalyst. The device consists of a vertical cylinder having baffles at its lower enda above these coarse screens having platinum and alumina pellets cemented thereon, and an annular passage for the return of recombined, condensed water to the reactor moderator system. This devicea having no moving parts, provides a simple and efficient means of removing the danger of accumulated hot radioactive, explosive gases, and restoring them to the moderator system for reuse.

  12. Wood stove having catalytic converter

    SciTech Connect

    Willson, A.C.

    1982-12-14

    A wood burning stove is formed with double front and rear side walls of heat conductive metal spaced apart by heat conductive spacer fins and providing air passageways by which room air is heated by conduction from the walls which are heated by the burning of wood deposited on a firebox floor supported in heat conducting relationship with the inner side walls. A catalytic converter is disposed over the fire area in the upper portion of the stove, and is arranged to receive preheated fresh secondary air which mixes with hot, incompletely combusted compounds from the fire and, in the presence of the catalyst, induces a secondary combustion of the substances. This mixture is channeled into a heat extraction chamber where the secondary combustion is completed and the resultant heat is transferred to the metal body of the stove. An exhaust passageway is provided for releasing the products of complete combustion into the atmosphere.

  13. Catalytic reactor with improved burner

    DOEpatents

    Faitani, Joseph J.; Austin, George W.; Chase, Terry J.; Suljak, George T.; Misage, Robert J.

    1981-01-01

    To more uniformly distribute heat to the plurality of catalyst tubes in a catalytic reaction furnace, the burner disposed in the furnace above the tops of the tubes includes concentric primary and secondary annular fuel and air outlets. The fuel-air mixture from the primary outlet is directed towards the tubes adjacent the furnace wall, and the burning secondary fuel-air mixture is directed horizontally from the secondary outlet and a portion thereof is deflected downwardly by a slotted baffle toward the tubes in the center of the furnace while the remaining portion passes through the slotted baffle to another baffle disposed radially outwardly therefrom which deflects it downwardly in the vicinity of the tubes between those in the center and those near the wall of the furnace.

  14. Catalytic converter with thermoelectric generator

    SciTech Connect

    Parise, R.J.

    1998-07-01

    The unique design of an electrically heated catalyst (EHC) and the inclusion of an ECO valve in the exhaust of an internal combustion engine will meet the strict new emission requirements, especially at vehicle cold start, adopted by several states in this country as well as in Europe and Japan. The catalytic converter (CC) has been a most useful tool in pollution abatement for the automobile. But the emission requirements are becoming more stringent and, along with other improvements, the CC must be improved to meet these new standards. Coupled with the ECO valve, the EHC can meet these new emission limits. In an internal combustion engine vehicle (ICEV), approximately 80% of the energy consumed leaves the vehicle as waste heat: out the tail pipe, through the radiator, or convected/radiated off the engine. Included with the waste heat out the tail pipe are the products of combustion which must meet strict emission requirements. The design of a new CC is presented here. This is an automobile CC that has the capability of producing electrical power and reducing the quantity of emissions at vehicle cold start, the Thermoelectric Catalytic Power Generator. The CC utilizes the energy of the exothermic reactions that take place in the catalysis substrate to produce electrical energy with a thermoelectric generator. On vehicle cold start, the thermoelectric generator is used as a heat pump to heat the catalyst substrate to reduce the time to catalyst light-off. Thus an electrically heated catalyst (EHC) will be used to augment the abatement of tail pipe emissions. Included with the EHC in the exhaust stream of the automobile is the ECO valve. This valve restricts the flow of pollutants out the tail pipe of the vehicle for a specified amount of time until the EHC comes up to operating temperature. Then the ECO valve opens and allows the full exhaust, now treated by the EHC, to leave the vehicle.

  15. The evolution of catalytic function

    NASA Astrophysics Data System (ADS)

    Maurel, Marie-Christine; Ricard, Jacques

    2006-03-01

    It is very likely that the main driving force of enzyme evolution is the requirement to improve catalytic and regulatory efficiency which results from the intrinsic performance as well as from the spatial and functional organization of enzymes in living cells. Kinetic co-operativity may occur in simple monomeric proteins if they display “slow” conformational transitions, at the cost of catalytic efficiency. Oligomeric enzymes on the other hand can be both efficient and co-operative. We speculate that the main reason for the emergence of co-operative oligomeric enzymes is the need for catalysts that are both cooperative and efficient. As it is not useful for an enzyme to respond to a change of substrate concentration in a complex kinetic way, the emergence of symmetry has its probable origin in a requirement for “functional simplicity”. In a living cell, enzyme are associated with other macromolecules and membranes. The fine tuning of their activity may also be reached through mutations of the microenvironment. Our hypothesis is that these mutations are related to the vectorial transport of molecules, to achieve the hysteresis loops of enzyme reactions generated by the coupling of reaction and diffusion, through the co-operativity brought about by electric interactions between a charged substrate and a membrane, and last but not least, through oscillations. As the physical origins of these effects are very simple and do not require complex molecular devices, it is very likely that the functional advantage generated by the spatial and functional organization of enzyme molecules within the cell have appeared in prebiotic catalysis or very early during the primeval stages of biological evolution. We shall began this paper by presenting the nature of the probable earliest catalysts in the RNA world.

  16. High-resolution single-molecule fluorescence imaging of zeolite aggregates within real-life fluid catalytic cracking particles.

    PubMed

    Ristanović, Zoran; Kerssens, Marleen M; Kubarev, Alexey V; Hendriks, Frank C; Dedecker, Peter; Hofkens, Johan; Roeffaers, Maarten B J; Weckhuysen, Bert M

    2015-02-01

    Fluid catalytic cracking (FCC) is a major process in oil refineries to produce gasoline and base chemicals from crude oil fractions. The spatial distribution and acidity of zeolite aggregates embedded within the 50-150 μm-sized FCC spheres heavily influence their catalytic performance. Single-molecule fluorescence-based imaging methods, namely nanometer accuracy by stochastic chemical reactions (NASCA) and super-resolution optical fluctuation imaging (SOFI) were used to study the catalytic activity of sub-micrometer zeolite ZSM-5 domains within real-life FCC catalyst particles. The formation of fluorescent product molecules taking place at Brønsted acid sites was monitored with single turnover sensitivity and high spatiotemporal resolution, providing detailed insight in dispersion and catalytic activity of zeolite ZSM-5 aggregates. The results point towards substantial differences in turnover frequencies between the zeolite aggregates, revealing significant intraparticle heterogeneities in Brønsted reactivity.

  17. Selective conversion of bio-oil to light olefins: controlling catalytic cracking for maximum olefins.

    PubMed

    Gong, Feiyan; Yang, Zhi; Hong, Chenggui; Huang, Weiwei; Ning, Shen; Zhang, Zhaoxia; Xu, Yong; Li, Quanxin

    2011-10-01

    Light olefins are the basic building blocks for the petrochemical industry. In this work, selective production of light olefins from catalytic cracking of bio-oil was performed by using the La/HZSM-5 catalyst. With a nearly complete conversion of bio-oil, the maximum yield reached 0.28±0.02 kg olefins/(kg bio-oil), which was close to that from methanol. Addition of La into zeolite efficiently changed the total acid amount of HZSM-5, especially the acid distribution among the strong, medium and weak acid sites. A moderate increase of the number of the medium acid sites effectively enhanced the olefins selectivity and improved the catalyst stability. The comparison between the catalytic cracking and pyrolysis of bio-oil was studied. The mechanism of the conversion of bio-oil to light olefins was also discussed. PMID:21807503

  18. Influence of alumina binder content on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone.

    PubMed

    Kong, Xiangjin; Liu, Junhai

    2014-01-01

    The influence of the amount of alumina binders on the catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone was investigated in a fixed-bed reactor. N2 sorption, X-ray diffraction, H2-chemisorption and temperature-programmed desorption of ammonia were used to characterize the catalysts. It can be observed that the Ni/HZSM-5 catalyst bound with 30 wt.% alumina binder exhibited the best catalytic performance. The high catalytic performance may be due to relatively good Ni metal dispersion, moderate mesoporosity, and proper acidity of the catalyst.

  19. Revolutionary systems for catalytic combustion and diesel catalytic particulate traps.

    SciTech Connect

    Stuecker, John Nicholas; Witze, Peter O.; Ferrizz, Robert Matthew; Cesarano, Joseph, III; Miller, James Edward

    2004-12-01

    This report is a summary of an LDRD project completed for the development of materials and structures conducive to advancing the state of the art for catalyst supports and diesel particulate traps. An ancillary development for bio-medical bone scaffolding was also realized. Traditionally, a low-pressure drop catalyst support, such as a ceramic honeycomb monolith, is used for catalytic reactions that require high flow rates of gases at high-temperatures. A drawback to the traditional honeycomb monoliths under these operating conditions is poor mass transfer to the catalyst surface in the straight-through channels. ''Robocasting'' is a unique process developed at Sandia National Laboratories that can be used to manufacture ceramic monoliths with alternative 3-dimensional geometries, providing tortuous pathways to increase mass transfer while maintaining low-pressure drops. These alternative 3-dimensional geometries may also provide a foundation for the development of self-regenerating supports capable of trapping and combusting soot particles from a diesel engine exhaust stream. This report describes the structures developed and characterizes the improved catalytic performance that can result. The results show that, relative to honeycomb monolith supports, considerable improvement in mass transfer efficiency is observed for robocast samples synthesized using an FCC-like geometry of alternating rods. Also, there is clearly a trade-off between enhanced mass transfer and increased pressure drop, which can be optimized depending on the particular demands of a given application. Practical applications include the combustion of natural gas for power generation, production of syngas, and hydrogen reforming reactions. The robocast lattice structures also show practicality for diesel particulate trapping. Preliminary results for trapping efficiency are reported as well as the development of electrically resistive lattices that can regenerate the structure by combusting the

  20. Evaluation of the Catalytic Contribution from a Positioned General Base in Ketosteroid Isomerase.

    PubMed

    Lamba, Vandana; Yabukarski, Filip; Pinney, Margaux; Herschlag, Daniel

    2016-08-10

    Proton transfer reactions are ubiquitous in enzymes and utilize active site residues as general acids and bases. Crystal structures and site-directed mutagenesis are routinely used to identify these residues, but assessment of their catalytic contribution remains a major challenge. In principle, effective molarity measurements, in which exogenous acids/bases rescue the reaction in mutants lacking these residues, can estimate these catalytic contributions. However, these exogenous moieties can be restricted in reactivity by steric hindrance or enhanced by binding interactions with nearby residues, thereby resulting in over- or underestimation of the catalytic contribution, respectively. With these challenges in mind, we investigated the catalytic contribution of an aspartate general base in ketosteroid isomerase (KSI) by exogenous rescue. In addition to removing the general base, we systematically mutated nearby residues and probed each mutant with a series of carboxylate bases of similar pKa but varying size. Our results underscore the need for extensive and multifaceted variation to assess and minimize steric and positioning effects and determine effective molarities that estimate catalytic contributions. We obtained consensus effective molarities of ∼5 × 10(4) M for KSI from Comamonas testosteroni (tKSI) and ∼10(3) M for KSI from Pseudomonas putida (pKSI). An X-ray crystal structure of a tKSI general base mutant showed no additional structural rearrangements, and double mutant cycles revealed similar contributions from an oxyanion hole mutation in the wild-type and base-rescued reactions, providing no indication of mutational effects extending beyond the general base site. Thus, the high effective molarities suggest a large catalytic contribution associated with the general base. A significant portion of this effect presumably arises from positioning of the base, but its large magnitude suggests the involvement of additional catalytic mechanisms as well

  1. Evaluation of the Catalytic Contribution from a Positioned General Base in Ketosteroid Isomerase.

    PubMed

    Lamba, Vandana; Yabukarski, Filip; Pinney, Margaux; Herschlag, Daniel

    2016-08-10

    Proton transfer reactions are ubiquitous in enzymes and utilize active site residues as general acids and bases. Crystal structures and site-directed mutagenesis are routinely used to identify these residues, but assessment of their catalytic contribution remains a major challenge. In principle, effective molarity measurements, in which exogenous acids/bases rescue the reaction in mutants lacking these residues, can estimate these catalytic contributions. However, these exogenous moieties can be restricted in reactivity by steric hindrance or enhanced by binding interactions with nearby residues, thereby resulting in over- or underestimation of the catalytic contribution, respectively. With these challenges in mind, we investigated the catalytic contribution of an aspartate general base in ketosteroid isomerase (KSI) by exogenous rescue. In addition to removing the general base, we systematically mutated nearby residues and probed each mutant with a series of carboxylate bases of similar pKa but varying size. Our results underscore the need for extensive and multifaceted variation to assess and minimize steric and positioning effects and determine effective molarities that estimate catalytic contributions. We obtained consensus effective molarities of ∼5 × 10(4) M for KSI from Comamonas testosteroni (tKSI) and ∼10(3) M for KSI from Pseudomonas putida (pKSI). An X-ray crystal structure of a tKSI general base mutant showed no additional structural rearrangements, and double mutant cycles revealed similar contributions from an oxyanion hole mutation in the wild-type and base-rescued reactions, providing no indication of mutational effects extending beyond the general base site. Thus, the high effective molarities suggest a large catalytic contribution associated with the general base. A significant portion of this effect presumably arises from positioning of the base, but its large magnitude suggests the involvement of additional catalytic mechanisms as well.

  2. Topological entropy of catalytic sets: Hypercycles revisited

    NASA Astrophysics Data System (ADS)

    Sardanyés, Josep; Duarte, Jorge; Januário, Cristina; Martins, Nuno

    2012-02-01

    The dynamics of catalytic networks have been widely studied over the last decades because of their implications in several fields like prebiotic evolution, virology, neural networks, immunology or ecology. One of the most studied mathematical bodies for catalytic networks was initially formulated in the context of prebiotic evolution, by means of the hypercycle theory. The hypercycle is a set of self-replicating species able to catalyze other replicator species within a cyclic architecture. Hypercyclic organization might arise from a quasispecies as a way to increase the informational containt surpassing the so-called error threshold. The catalytic coupling between replicators makes all the species to behave like a single and coherent evolutionary multimolecular unit. The inherent nonlinearities of catalytic interactions are responsible for the emergence of several types of dynamics, among them, chaos. In this article we begin with a brief review of the hypercycle theory focusing on its evolutionary implications as well as on different dynamics associated to different types of small catalytic networks. Then we study the properties of chaotic hypercycles with error-prone replication with symbolic dynamics theory, characterizing, by means of the theory of topological Markov chains, the topological entropy and the periods of the orbits of unimodal-like iterated maps obtained from the strange attractor. We will focus our study on some key parameters responsible for the structure of the catalytic network: mutation rates, autocatalytic and cross-catalytic interactions.

  3. Structure-based identification of catalytic residues.

    PubMed

    Yahalom, Ran; Reshef, Dan; Wiener, Ayana; Frankel, Sagiv; Kalisman, Nir; Lerner, Boaz; Keasar, Chen

    2011-06-01

    The identification of catalytic residues is an essential step in functional characterization of enzymes. We present a purely structural approach to this problem, which is motivated by the difficulty of evolution-based methods to annotate structural genomics targets that have few or no homologs in the databases. Our approach combines a state-of-the-art support vector machine (SVM) classifier with novel structural features that augment structural clues by spatial averaging and Z scoring. Special attention is paid to the class imbalance problem that stems from the overwhelming number of non-catalytic residues in enzymes compared to catalytic residues. This problem is tackled by: (1) optimizing the classifier to maximize a performance criterion that considers both Type I and Type II errors in the classification of catalytic and non-catalytic residues; (2) under-sampling non-catalytic residues before SVM training; and (3) during SVM training, penalizing errors in learning catalytic residues more than errors in learning non-catalytic residues. Tested on four enzyme datasets, one specifically designed by us to mimic the structural genomics scenario and three previously evaluated datasets, our structure-based classifier is never inferior to similar structure-based classifiers and comparable to classifiers that use both structural and evolutionary features. In addition to the evaluation of the performance of catalytic residue identification, we also present detailed case studies on three proteins. This analysis suggests that many false positive predictions may correspond to binding sites and other functional residues. A web server that implements the method, our own-designed database, and the source code of the programs are publicly available at http://www.cs.bgu.ac.il/∼meshi/functionPrediction.

  4. Effect of Porosity on Surface Catalytic Efficiency

    NASA Technical Reports Server (NTRS)

    Stewart, David A.; Pallix, Joan; Rasky, Daniel J. (Technical Monitor)

    1994-01-01

    This paper describes the effect of surface porosity of thermal protection materials on surface catalytic efficiency using test data taken from both arc-jet and side-arm reactor facilities. Relative surface porosity of the samples varied from 6% to 50%. Surface porosity was measured using a flow apparatus and Bernoulli equation. The surface catalytic efficiency of the materials was calculated using aerothermodynamic, and kinetic theories. The catalytic efficiency of the materials are compared at surface temperatures between room temperature and 2500 F. The data are presented in the form of graphs and tables.

  5. Catalytic reaction in confined flow channel

    DOEpatents

    Van Hassel, Bart A.

    2016-03-29

    A chemical reactor comprises a flow channel, a source, and a destination. The flow channel is configured to house at least one catalytic reaction converting at least a portion of a first nanofluid entering the channel into a second nanofluid exiting the channel. The flow channel includes at least one turbulating flow channel element disposed axially along at least a portion of the flow channel. A plurality of catalytic nanoparticles is dispersed in the first nanofluid and configured to catalytically react the at least one first chemical reactant into the at least one second chemical reaction product in the flow channel.

  6. Sulfuric acid as autocatalyst in the formation of sulfuric acid.

    PubMed

    Torrent-Sucarrat, Miquel; Francisco, Joseph S; Anglada, Josep M

    2012-12-26

    Sulfuric acid can act as a catalyst of its own formation. We have carried out a computational investigation on the gas-phase formation of H(2)SO(4) by hydrolysis of SO(3) involving one and two water molecules, and also in the presence of sulfuric acid and its complexes with one and two water molecules. The hydrolysis of SO(3) requires the concurrence of two water molecules, one of them acting as a catalyzer, and our results predict an important catalytic effect, ranging between 3 and 11 kcal·mol(-1) when the catalytic water molecule is substituted by a sulfuric acid molecule or one of its hydrates. In these cases, the reaction products are either bare sulfuric acid dimer or sulfuric acid dimer complexed with a water molecule. There are broad implications from these new findings. The results of the present investigation show that the catalytic effect of sulfuric acid in the SO(3) hydrolysis can be important in the Earth's stratosphere, in the heterogeneous formation of sulfuric acid and in the formation of aerosols, in H(2)SO(4) formation by aircraft engines, and also in understanding the formation of sulfuric acid in the atmosphere of Venus.

  7. Piezoelectrically induced mechano-catalytic effect for degradation of dye wastewater through vibrating Pb(Zr0.52Ti0.48)O3 fibers

    NASA Astrophysics Data System (ADS)

    Lin, He; Wu, Zheng; Jia, Yanmin; Li, Weijian; Zheng, Ren-Kui; Luo, Haosu

    2014-04-01

    Hydrothermally synthesized piezoelectric Pb(Zr0.52Ti0.48)O3 fibers were used as a mechano-catalyzer to degrade acid orange 7 dye wastewater via the mechano-catalytic effect, which was achieved as a product of the piezoelectric effect and the electro-catalytic effect. When subjected to mechanical vibration, the Pb(Zr0.52Ti0.48)O3 fibers bend, which in turn induces electric charges on the surfaces of the fibers via the piezoelectric effect. The piezoelectrically induced electric charges induce chemical degradation reactions in the dye wastewater through the electro-catalytic effect. A high mechano-catalytic degradation ratio of ˜80% was achieved for the acid orange 7 solutions (˜30 μmol/l). The piezoelectrically induced mechano-catalytic effect thus provides a highly efficient and reusable technology for dye wastewater degradation applications.

  8. Catalytic hydrogen evolution from a covalently linked dicobaloxime

    PubMed Central

    Valdez, Carolyn N.; Dempsey, Jillian L.; Brunschwig, Bruce S.; Winkler, Jay R.; Gray, Harry B.

    2012-01-01

    A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at -0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (kapp = 1100 ± 70 M-1 s-1). Electrochemical experiments reveal no significant enhancement in the rate of H2 evolution from that of a monomeric analogue: The experimental rate law is first order in catalyst and acid consistent with previous findings for similar mononuclear cobaloximes. Our work suggests that H2 evolution likely occurs by protonation of reductively generated CoIIH rather than homolysis of two CoIIIH units. PMID:22786932

  9. Two Molecular Information Processing Systems Based on Catalytic Nucleic Acids

    NASA Astrophysics Data System (ADS)

    Stojanovic, Milan

    Mixtures of molecules are capable of powerful information processing [1]. This statement is in the following way self-evident: it is a hierarchically organized complex mixture of molecules that is formulating it to other similarly organized mixtures of molecules. By making such a statement I am not endorsing the extreme forms of reductionism; rather, I am making what I think is a small first step towards harnessing information processing prowess of molecules and, hopefully, overcoming some limitations of more traditional computing paradigms. There are different ideas on how to understand and use molecular information processing abilities and I will list some below. My list is far from inclusive, and delineations are far from clear-cut; whenever available, I will provide examples from our research efforts. I should stress, for a computer science audience that I am a chemist. Thus, my approach may have much different focus and mathematical rigor, then if it would be taken by a computer scientist.

  10. Vacuum-insulated catalytic converter

    DOEpatents

    Benson, David K.

    2001-01-01

    A catalytic converter has an inner canister that contains catalyst-coated substrates and an outer canister that encloses an annular, variable vacuum insulation chamber surrounding the inner canister. An annular tank containing phase-change material for heat storage and release is positioned in the variable vacuum insulation chamber a distance spaced part from the inner canister. A reversible hydrogen getter in the variable vacuum insulation chamber, preferably on a surface of the heat storage tank, releases hydrogen into the variable vacuum insulation chamber to conduct heat when the phase-change material is hot and absorbs the hydrogen to limit heat transfer to radiation when the phase-change material is cool. A porous zeolite trap in the inner canister absorbs and retains hydrocarbons from the exhaust gases when the catalyst-coated substrates and zeolite trap are cold and releases the hydrocarbons for reaction on the catalyst-coated substrate when the zeolite trap and catalyst-coated substrate get hot.

  11. Fundamental studies of catalytic gasification

    SciTech Connect

    Heinemann, H.; Somorjai, G.A.

    1990-06-01

    Previous work has shown that chars and coal can be gasified with steam in the presence of alkali-transition metal oxide catalysts or alkali-earth alkali catalysts at relatively low temperatures. These studies are to be extended to the investigation of the amounts of catalysts required and whether a throw away catalyst can be used. Fresh versus stored char will be gasified to determine the role of oxidation of the char on gasification rates. Less expensive catalyst materials such as sodium instead of potassium and iron instead of nickel will be explored. Reaction rates will be determined in the presence of nitrogen, Co and CO{sub 2}. Reactions of methane and carbon solids in the presence of an oxidizing agent such as water, oxygen, and/or carbon dioxide will be explored in the presence of similar catalyst. This quarter, additional experiments on catalytic gasification of coal were carried out. Major emphasis, however, was on the production of C{sub 2} and higher hydrocarbons from methane at very high selectivities. Catalysts studied include KCaNiO. 6 figs., 1 tab.

  12. Halogen Chemistry on Catalytic Surfaces.

    PubMed

    Moser, Maximilian; Pérez-Ramírez, Javier

    2016-01-01

    Halogens are key building blocks for the manufacture of high-value products such as chemicals, plastics, and pharmaceuticals. The catalytic oxidation of HCl and HBr is an attractive route to recover chlorine and bromine in order to ensure the sustainability of the production processes. Very few materials withstand the high corrosiveness and the strong exothermicity of the reactions and among them RuO2 and CeO2-based catalysts have been successfully applied in HCl oxidation. The search for efficient systems for HBr oxidation was initiated by extrapolating the results of HCl oxidation based on the chemical similarity of these reactions. Interestingly, despite its inactivity in HCl oxidation, TiO2 was found to be an outstanding HBr oxidation catalyst, which highlighted that the latter reaction is more complex than previously assumed. Herein, we discuss the results of recent comparative studies of HCl and HBr oxidation on both rutile-type (RuO2, IrO2, and TiO2) and ceria-based catalysts using a combination of advanced experimental and theoretical methods to provide deeper molecular-level understanding of the reactions. This knowledge aids the design of the next-generation catalysts for halogen recycling. PMID:27131113

  13. Catalytic and reactive polypeptides and methods for their preparation and use

    DOEpatents

    Schultz, Peter

    1994-01-01

    Catalytic and reactive polypeptides include a binding site specific for a reactant or reactive intermediate involved in a chemical reaction of interest. The polypeptides further include at least one active functionality proximate the binding site, where the active functionality is capable of catalyzing or chemically participating in the chemical reaction in such a way that the reaction rate is enhanced. Methods for preparing the catalytic peptides include chemical synthesis, site-directed mutagenesis of antibody and enzyme genes, covalent attachment of the functionalities through particular amino acid side chains, and the like.

  14. Catalytic decomposition of trilon B on the nickel-ferricyanide catalyst

    NASA Astrophysics Data System (ADS)

    A, Apalkov G.

    2014-10-01

    The method of nickel-ferricyanide catalyst preparation is elaborated. The results of catalytic decomposition of trilon B on the prepared catalyst are presented. The developed method allows performing the efficient decomposition of trilon B (>99,9%) either in acid or in alkaline medium in temperature interval of 37-80°C. Technologically-fit dynamic conditions of the process, providing the intensity of a heterogeneous interaction, are selected and explored, and the nickel-ferricyanide catalyst resistance is achieved. The instrument flowchart of the developed method of catalytic decomposition is introduced for industrial application during the reprocessing of low- and medium-activity effluent, containing complexons.

  15. Catalytic Carbocation Generation Enabled by the Mesolytic Cleavage of Alkoxyamine Radical Cations.

    PubMed

    Zhu, Qilei; Gentry, Emily C; Knowles, Robert R

    2016-08-16

    A new catalytic method is described to access carbocation intermediates via the mesolytic cleavage of alkoxyamine radical cations. In this process, electron transfer between an excited state oxidant and a TEMPO-derived alkoxyamine substrate gives rise to a radical cation with a remarkably weak C-O bond. Spontaneous scission results in the formation of the stable nitroxyl radical TEMPO(.) as well as a reactive carbocation intermediate that can be intercepted by a wide range of nucleophiles. Notably, this process occurs under neutral conditions and at comparatively mild potentials, enabling catalytic cation generation in the presence of both acid sensitive and easily oxidized nucleophilic partners. PMID:27403637

  16. Structural, textural and catalytic properties of Al-, Ti-pillared clays

    SciTech Connect

    Ramos-Galvan, C.E.; Dominguez, J.M.; Sandoval-Robles, G.; Castillo-Mares, A.; Nava E, N.

    1996-12-31

    Al-, Ti- and Zr-pillared clays were characterized and NiMo/Pilc`s were tested in HDS reactions. The combination of activity measurements with Moessbauer Spectroscopy and x-ray microanalysis at microscopical scale give insight in the metal phases migration during pillaring, reaction and regeneration steps. {Alpha}-Fe phase in free Fe{sub 2}O{sub 3} islands predominate together with structural Fe{sup 3+} phase, but during the catalytic reaction Fe{sup 2+} forms. Delamination of the Ti- and Zr-Clay supports, together with high Lewis acidity might enhance their catalytic properties.

  17. A review of tin oxide-based catalytic systems: Preparation, characterization and catalytic behavior

    NASA Technical Reports Server (NTRS)

    Hoflund, Gar B.

    1987-01-01

    This paper reviews the important aspects of the preparation, characterization and catalytic behavior of tin oxide-based catalytic systems including doped tin oxide, mixed oxides which contain tin oxide, Pt supported on tin oxide and Pt/Sn supported on alumina. These systems have a broad range of applications and are continually increasing in importance. However, due to their complex nature, much remains to be understood concerning how they function catalytically.

  18. Catalytic microwave pyrolysis of biomass for renewable phenols and fuels

    NASA Astrophysics Data System (ADS)

    Bu, Quan

    Bio-oil is an unstable intermediate and needs to be upgraded before its use. This study focused on improving the selectivity of bio-oilby catalytic pyrolysis of biomass using activated carbon (AC) catalysts. Firstly, the effects of process conditions on product quality and product yield were investigated by catalytic microwave pyrolysis of biomass using AC as a catalyst. The optimized reaction condition for bio-oil and volatile was determined. Chemical composition analysis by GC/MS showed that phenols rich bio-oils were obtained. Furthermore, the effects of different carbon sources based AC catalysts on products yield and chemical composition selectivity of obtained bio-oils were investigated during microwave pyrolysis of Douglas fir pellet. The catalysts recycling test of the selected catalysts indicated that the AC catalysts can be used for 3-4 times with high concentration of phenolic compounds. The individual surface polar/acidic oxygen functional groups analysis suggested the changes of functional groups in ACs explained the reaction mechanism of this process. In addition, the potential for production of renewable phenols and fuels by catalytic pyrolysis of biomass using lignin as a model compound was explored. The main chemical compounds of the obtained bio-oils were phenols, guaiacols, hydrocarbons and esters. The thermal decomposition behaviors of lignin and kinetics study were investigated by TGA. The change of functional groups of AC catalyst indicated the bio-oil reduction was related to the reaction mechanism of this process. Finally, the effects of Fe-modified AC catalyst on bio-oil upgrading and kintic study of biomass pyrolysis were investigated. The catalytic pyrolysis of biomass using the Fe-modified AC catalyst may promote the occurrence of the fragmentation of cellulose, rather than repolymerization as in the non-catalytic pyrolysis which leads to partial of guaiacols derived from furans. Results showed that the main chemical compounds of bio

  19. Catalytic Fast Pyrolysis of Wild Reed Over Nanoporous SBA-15 Catalysts.

    PubMed

    Park, Y K; Yoo, Myung Lang; Park, Sung Hoon

    2016-05-01

    Wild reed was pyrolyzed over two nanoporous SBA-15 catalysts with different acid characteristics: Si-SBA-15 and Al-SBA-15. Al was grafted on Si-SBA-15 to increase the acidity and enhance the catalytic activity. Fast pyrolysis was carried out using a pyrolysis-gas chromatography/mass spectrometry system at 550 degrees C for real-time analysis of the products. Significant improvement of the product bio-oil quality was attained by catalytic reforming over nanoporous Al-SBA-15. The fraction of total oxygenates was reduced because of the decrease in. the fraction of ketones, aldehydes, and carboxylates, which deteriorate the fuel quality of bio-oil. On the other hand, the fractions of furans and aromatics, which are the chemicals with high value-added, were increased by the catalytic reforming. The catalytic activity of Al-SBA-15 was considerably higher than that of Si-SBA-15 because the incorporation of Al increased the catalyst acidity. PMID:27483790

  20. Chemical and catalytic properties of elemental carbon

    SciTech Connect

    Chang, S.G.; Brodzinsky, R.; Gundel, L.A.; Novakov, T.

    1980-10-01

    Elemental carbon particles resulting from incomplete combustion of fossil fuel are one of the major constituents of airborne particulate matter. These particles are a chemically and catalytically active material and can be an effective carrier for other toxic air pollutants through their adsorptive capability. The chemical, adsorptive, and catalytic behaviors of carbon particles depend very much on their crystalline structure, surface composition, and electronic properties. This paper discusses these properties and examines their relevance to atmospheric chemistry.