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Sample records for carbon-carbon bond forming

  1. Rational approaches for engineering novel functionalities in carbon-carbon bond forming enzymes

    PubMed Central

    Baker, Perrin; Seah, Stephen Y. K.

    2012-01-01

    Enzymes that catalyze carbon-carbon bond formation can be exploited as biocatalyst for synthetic organic chemistry. However, natural enzymes frequently do not possess the required properties or specificities to catalyze industrially useful transformations. This mini-review describes recent work using knowledge-guided site-specific mutagenesis of key active site residues to alter substrate specificity, stereospecificity and reaction specificity of these enzymes. In addition, examples of de novo designed enzymes that catalyze C-C bond reactions not found in nature will be discussed. PMID:24688644

  2. Rational approaches for engineering novel functionalities in carbon-carbon bond forming enzymes.

    PubMed

    Baker, Perrin; Seah, Stephen Y K

    2012-01-01

    Enzymes that catalyze carbon-carbon bond formation can be exploited as biocatalyst for synthetic organic chemistry. However, natural enzymes frequently do not possess the required properties or specificities to catalyze industrially useful transformations. This mini-review describes recent work using knowledge-guided site-specific mutagenesis of key active site residues to alter substrate specificity, stereospecificity and reaction specificity of these enzymes. In addition, examples of de novo designed enzymes that catalyze C-C bond reactions not found in nature will be discussed.

  3. Acid-base bifunctional catalysis of silica-alumina-supported organic amines for carbon-carbon bond-forming reactions.

    PubMed

    Motokura, Ken; Tomita, Mitsuru; Tada, Mizuki; Iwasawa, Yasuhiro

    2008-01-01

    Acid-base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica-alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA-NR2) were characterized by solid-state 13C and 29Si NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were immobilized by acid-base interactions at the SA surface. The interactions between the surface acidic sites and the immobilized basic amines were weaker than the interactions between the SA and free amines. The catalytic performances of the SA-NR2 catalysts for various carbon-carbon bond-forming reactions, such as cyano-ethoxycarbonylation, the Michael reaction, and the nitro-aldol reaction, were investigated and compared with those of homogeneous and other heterogeneous catalysts. The SA-NR2 catalysts showed much higher catalytic activities for the carbon-carbon bond-forming reactions than heterogeneous amine catalysts using other supports, such as SiO2 and Al2O3. On the other hand, homogeneous amines hardly promoted these reactions under similar reaction conditions, and the catalytic behavior of SA-NR2 was also different from that of MgO, which was employed as a typical heterogeneous base. An acid-base dual-activation mechanism for the carbon-carbon bond-forming reactions is proposed.

  4. Method for producing bio-fuel that integrates heat from carbon-carbon bond-forming reactions to drive biomass gasification reactions

    DOEpatents

    Cortright, Randy D.; Dumesic, James A.

    2013-04-02

    A low-temperature catalytic process for converting biomass (preferably glycerol recovered from the fabrication of bio-diesel) to synthesis gas (i.e., H.sub.2/CO gas mixture) in an endothermic gasification reaction is described. The synthesis gas is used in exothermic carbon-carbon bond-forming reactions, such as Fischer-Tropsch, methanol, or dimethylether syntheses. The heat from the exothermic carbon-carbon bond-forming reaction is integrated with the endothermic gasification reaction, thus providing an energy-efficient route for producing fuels and chemicals from renewable biomass resources.

  5. Method for producing bio-fuel that integrates heat from carbon-carbon bond-forming reactions to drive biomass gasification reactions

    DOEpatents

    Cortright, Randy D [Madison, WI; Dumesic, James A [Verona, WI

    2012-04-10

    A low-temperature catalytic process for converting biomass (preferably glycerol recovered from the fabrication of bio-diesel) to synthesis gas (i.e., H.sub.2/CO gas mixture) in an endothermic gasification reaction is described. The synthesis gas is used in exothermic carbon-carbon bond-forming reactions, such as Fischer-Tropsch, methanol, or dimethylether syntheses. The heat from the exothermic carbon-carbon bond-forming reaction is integrated with the endothermic gasification reaction, thus providing an energy-efficient route for producing fuels and chemicals from renewable biomass resources.

  6. Method for producing bio-fuel that integrates heat from carbon-carbon bond-forming reactions to drive biomass gasification reactions

    DOEpatents

    Cortright, Randy D [Madison, WI; Dumesic, James A [Verona, WI

    2011-01-18

    A low-temperature catalytic process for converting biomass (preferably glycerol recovered from the fabrication of bio-diesel) to synthesis gas (i.e., H.sub.2/CO gas mixture) in an endothermic gasification reaction is described. The synthesis gas is used in exothermic carbon-carbon bond-forming reactions, such as Fischer-Tropsch, methanol, or dimethylether syntheses. The heat from the exothermic carbon-carbon bond-forming reaction is integrated with the endothermic gasification reaction, thus providing an energy-efficient route for producing fuels and chemicals from renewable biomass resources.

  7. Acetic acid promoted metal-free aerobic carbon-carbon bond forming reactions at α-position of tertiary amines.

    PubMed

    Ueda, Hirofumi; Yoshida, Kei; Tokuyama, Hidetoshi

    2014-08-15

    The oxidative functionalization of the benzylic C-H bonds in tetrahydroisoquinolines and tetrahydro-β-carboline derivatives was investigated. C-C bond forming reactions proceeded with a range of nucleophiles (nitroalkane, enol silyl ether, indole, allylstannane, and tetrabutylammonium cyanide) under metal-free conditions and an oxygen atmosphere. Acetic acid caused a significant acceleration effect.

  8. Aerobic dehydrogenative α-diarylation of benzyl ketones with aromatics through carbon-carbon bond cleavage.

    PubMed

    More, Nagnath Yadav; Jeganmohan, Masilamani

    2014-02-07

    Substituted benzyl ketones reacted with aromatics in the presence of K2S2O8 in CF3COOH at room temperature, yielding α-diaryl benzyl ketones through a carbon-carbon bond cleavage. In the reaction, two new carbon-carbon bonds were formed and one carbon-carbon bond was cleaved. It is very interesting that two different nucleophiles such as benzyl ketones and aromatics were coupled together without metal, which is unusual in organic synthesis.

  9. Aqueous-Medium Carbon-Carbon Bond-Forming Radical Reactions Catalyzed by Excited Rhodamine B as a Metal-Free Organic Dye under Visible Light Irradiation.

    PubMed

    Yoshioka, Eito; Kohtani, Shigeru; Jichu, Takahisa; Fukazawa, Takuya; Nagai, Toyokazu; Kawashima, Akira; Takemoto, Yoshiji; Miyabe, Hideto

    2016-08-19

    The utility of rhodamine B as a water-soluble organic photocatalyst was studied in the cascade radical addition-cyclization-trapping reactions under visible light irradiation. In the presence of (i-Pr)2NEt, the electron transfer from the excited rhodamine B to perfluoroalkyl iodides proceeded smoothly to promote the carbon-carbon bond-forming radical reactions in aqueous media. When i-C3F7I was employed as a radical precursor, the aqueous-medium radical reactions proceeded even in the absence of (i-Pr)2NEt. In these reactions, the direct electron transfer from the excited singlet state of rhodamine B would take place. Furthermore, the cleavage of the C-I bond in less reactive i-PrI could be achieved by the reductive electron transfer from the excited rhodamine B, which was confirmed by the fluorescence quenching of rhodamine B with the addition of i-PrI.

  10. A DFT study on the reaction pathways for carbon-carbon bond-forming reactions between propargylic alcohols and alkenes or ketones catalyzed by thiolate-bridged diruthenium complexes.

    PubMed

    Sakata, Ken; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

    2009-01-05

    The reaction pathways of two types of the carbon-carbon bond-forming reactions catalyzed by thiolate-bridged diruthenium complexes have been investigated by density-functional-theory calculations. It is clarified that both carbon-carbon bond-forming reactions proceed through a ruthenium-allenylidene complex as a common reactive intermediate. The attack of pi electrons on propene or the vinyl alcohol on the ruthenium-allenylidene complex is the first step of the reaction pathways. The reaction pathways are different after the attack of nucleophiles on the ruthenium-alkynyl complex. In the reaction with propene, the carbon-carbon bond-forming reaction proceeds through a stepwise process, whereas in the reaction with vinyl alcohol, it proceeds through a concerted process. The interactions between the ruthenium-allenylidene complex and propene or vinyl alcohol have been investigated by applying a simple way of looking at orbital interactions.

  11. Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions.

    PubMed

    Sahin, Ziya; Akkoς, Senem; İlhan, İlhan Özer; Kayser, Veysel

    2017-07-30

    Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from benzimidazolium salts. Detailed and generalized protocols are also presented for testing the catalytic activity of such complexes in arylation and Suzuki-Miyaura cross-coupling reactions. Representative results are shown for the catalytic activity of the four complexes in arylation and Suzuki-Miyaura type reactions. For each of the reactions investigated, at least one of the four complexes successfully catalyzed the reaction, qualifying them as promising candidates for catalysis of many carbon-carbon bond-forming reactions. The protocols presented are general enough to be adapted for the synthesis, purification and catalytic activity testing of new palladium N-heterocyclic carbene complexes.

  12. Monomeric metal aqua complexes in the interlayer space of montmorillonites as strong Lewis acid catalysts for heterogeneous carbon-carbon bond-forming reactions.

    PubMed

    Kawabata, Tomonori; Kato, Masaki; Mizugaki, Tomoo; Ebitani, Kohki; Kaneda, Kiyotomi

    2004-12-17

    Montmorillonite-enwrapped copper and scandium catalysts (Cu(2+)- and Sc(3+)-monts) were easily prepared by treating Na(+)-mont with the aqueous solution of the copper nitrate and scandium triflate, respectively. The resulting Cu(2+)- and Sc(3+)-monts showed outstanding catalytic activities for a variety of carbon-carbon bond-forming reactions, such as the Michael reaction, the Sakurai-Hosomi allylation, and the Diels-Alder reaction, under solvent-free or aqueous conditions. The remarkable activity of the mont catalysts is attributable to the negatively charged silicate layers that are capable of stabilizing metal cations. Furthermore, these catalysts were reusable without any appreciable loss in activity and selectivity. The Cu(2+)-mont-catalyzed Michael reaction proceeds via a ternary complex in which both the 1,3-dicarbonyl compound and the enone are coordinated to a Lewis acid Cu(2+) center.

  13. A radical process towards the development of transition-metal-free aromatic carbon-carbon bond-forming reactions.

    PubMed

    Chan, Tek Long; Wu, Yinuo; Choy, Pui Ying; Kwong, Fuk Yee

    2013-11-18

    Transition-metal-free cross-coupling reactions have been a hot topic in recent years. With the aid of a radical initiator, a number of unactivated arene C-H bonds can be directly arylated/functionalized by using aryl halides through homolytic aromatic substitution. Commercially available or specially designed promoters (e.g. diamines, diols, and amino alcohols) have been used to make this synthetically attractive method viable. This protocol offers an inexpensive, yet efficient route to aromatic C-C bond formations since transition metal catalysts and impurities can be avoided by using this reaction system. In this article, we focus on the significance of the reaction conditions (e.g. bases and promoters), which allow this type of reaction to proceed smoothly. Substrate scope limitations and challenges, as well as mechanistic discussion are also included.

  14. Transition metal-catalyzed process for addition of amines to carbon-carbon double bonds

    DOEpatents

    Hartwig, John F.; Kawatsura, Motoi; Loeber, Oliver

    2002-01-01

    The present invention is directed to a process for addition of amines to carbon-carbon double bonds in a substrate, comprising: reacting an amine with a compound containing at least one carbon-carbon double bond in the presence a transition metal catalyst under reaction conditions effective to form a product having a covalent bond between the amine and a carbon atom of the former carbon-carbon double bond. The transition metal catalyst comprises a Group 8 metal and a ligand containing one or more 2-electron donor atoms. The present invention is also directed to enantioselective reactions of amine compounds with compounds containing carbon-carbon double bonds, and a calorimetric assay to evaluate potential catalysts in these reactions.

  15. Catalytic activation of carbon-carbon bonds in cyclopentanones.

    PubMed

    Xia, Ying; Lu, Gang; Liu, Peng; Dong, Guangbin

    2016-11-24

    In the chemical industry, molecules of interest are based primarily on carbon skeletons. When synthesizing such molecules, the activation of carbon-carbon single bonds (C-C bonds) in simple substrates is strategically important: it offers a way of disconnecting such inert bonds, forming more active linkages (for example, between carbon and a transition metal) and eventually producing more versatile scaffolds. The challenge in achieving such activation is the kinetic inertness of C-C bonds and the relative weakness of newly formed carbon-metal bonds. The most common tactic starts with a three- or four-membered carbon-ring system, in which strain release provides a crucial thermodynamic driving force. However, broadly useful methods that are based on catalytic activation of unstrained C-C bonds have proven elusive, because the cleavage process is much less energetically favourable. Here we report a general approach to the catalytic activation of C-C bonds in simple cyclopentanones and some cyclohexanones. The key to our success is the combination of a rhodium pre-catalyst, an N-heterocyclic carbene ligand and an amino-pyridine co-catalyst. When an aryl group is present in the C3 position of cyclopentanone, the less strained C-C bond can be activated; this is followed by activation of a carbon-hydrogen bond in the aryl group, leading to efficient synthesis of functionalized α-tetralones-a common structural motif and versatile building block in organic synthesis. Furthermore, this method can substantially enhance the efficiency of the enantioselective synthesis of some natural products of terpenoids. Density functional theory calculations reveal a mechanism involving an intriguing rhodium-bridged bicyclic intermediate.

  16. Carbon-Carbon Bond Cleavage in Activation of the Prodrug Nabumetone

    PubMed Central

    Varfaj, Fatbardha; Zulkifli, Siti N. A.; Park, Hyoung-Goo; Challinor, Victoria L.; De Voss, James J.

    2014-01-01

    Carbon-carbon bond cleavage reactions are catalyzed by, among others, lanosterol 14-demethylase (CYP51), cholesterol side-chain cleavage enzyme (CYP11), sterol 17β-lyase (CYP17), and aromatase (CYP19). Because of the high substrate specificities of these enzymes and the complex nature of their substrates, these reactions have been difficult to characterize. A CYP1A2-catalyzed carbon-carbon bond cleavage reaction is required for conversion of the prodrug nabumetone to its active form, 6-methoxy-2-naphthylacetic acid (6-MNA). Despite worldwide use of nabumetone as an anti-inflammatory agent, the mechanism of its carbon-carbon bond cleavage reaction remains obscure. With the help of authentic synthetic standards, we report here that the reaction involves 3-hydroxylation, carbon-carbon cleavage to the aldehyde, and oxidation of the aldehyde to the acid, all catalyzed by CYP1A2 or, less effectively, by other P450 enzymes. The data indicate that the carbon-carbon bond cleavage is mediated by the ferric peroxo anion rather than the ferryl species in the P450 catalytic cycle. CYP1A2 also catalyzes O-demethylation and alcohol to ketone transformations of nabumetone and its analogs. PMID:24584631

  17. Carbon-carbon bond cleavage in activation of the prodrug nabumetone.

    PubMed

    Varfaj, Fatbardha; Zulkifli, Siti N A; Park, Hyoung-Goo; Challinor, Victoria L; De Voss, James J; Ortiz de Montellano, Paul R

    2014-05-01

    Carbon-carbon bond cleavage reactions are catalyzed by, among others, lanosterol 14-demethylase (CYP51), cholesterol side-chain cleavage enzyme (CYP11), sterol 17β-lyase (CYP17), and aromatase (CYP19). Because of the high substrate specificities of these enzymes and the complex nature of their substrates, these reactions have been difficult to characterize. A CYP1A2-catalyzed carbon-carbon bond cleavage reaction is required for conversion of the prodrug nabumetone to its active form, 6-methoxy-2-naphthylacetic acid (6-MNA). Despite worldwide use of nabumetone as an anti-inflammatory agent, the mechanism of its carbon-carbon bond cleavage reaction remains obscure. With the help of authentic synthetic standards, we report here that the reaction involves 3-hydroxylation, carbon-carbon cleavage to the aldehyde, and oxidation of the aldehyde to the acid, all catalyzed by CYP1A2 or, less effectively, by other P450 enzymes. The data indicate that the carbon-carbon bond cleavage is mediated by the ferric peroxo anion rather than the ferryl species in the P450 catalytic cycle. CYP1A2 also catalyzes O-demethylation and alcohol to ketone transformations of nabumetone and its analogs.

  18. Catalyzed hydrolytic cleavage reaction of carbon-carbon bond

    SciTech Connect

    Ioffe, I.I.; Rubinskaya, E.V.

    1986-12-01

    The authors split the carbon-carbon bond for a series of simple and complex organic compounds in neutral aqueous solutions on a heterogeneous metal-containing catalyst, palladium on carbon. The experimental results are given. In each case, the catalytic effect was controlled by a blank experiment, without a catalyst, where there was no decomposition of the substrate. The occurrence of the heterogeneous-catalytic cleavage reaction of the carbon-carbon bonds in the molecules is indicated not only by their extensive conversion, but also by the almost complete depletion of the content of organic carbon, confirmed by a similar decrease in the chemical consumption of oxygen coefficient in the system, which is possible only in the complete decomposition of the organic compounds to gaseous products or with the formation of inappreciable amounts of low-molecular-weight water-soluble compounds.

  19. Adsorption-induced scission of carbon carbon bonds

    NASA Astrophysics Data System (ADS)

    Sheiko, Sergei S.; Sun, Frank C.; Randall, Adrian; Shirvanyants, David; Rubinstein, Michael; Lee, Hyung-Il; Matyjaszewski, Krzysztof

    2006-03-01

    Covalent carbon-carbon bonds are hard to break. Their strength is evident in the hardness of diamonds and tensile strength of polymeric fibres; on the single-molecule level, it manifests itself in the need for forces of several nanonewtons to extend and mechanically rupture one bond. Such forces have been generated using extensional flow, ultrasonic irradiation, receding meniscus and by directly stretching a single molecule with nanoprobes. Here we show that simple adsorption of brush-like macromolecules with long side chains on a substrate can induce not only conformational deformations, but also spontaneous rupture of covalent bonds in the macromolecular backbone. We attribute this behaviour to the fact that the attractive interaction between the side chains and the substrate is maximized by the spreading of the side chains, which in turn induces tension along the polymer backbone. Provided the side-chain densities and substrate interaction are sufficiently high, the tension generated will be strong enough to rupture covalent carbon-carbon bonds. We expect similar adsorption-induced backbone scission to occur for all macromolecules with highly branched architectures, such as brushes and dendrimers. This behaviour needs to be considered when designing surface-targeted macromolecules of this type-either to avoid undesired degradation, or to ensure rupture at predetermined macromolecular sites.

  20. Olefin metathesis for effective polymer healing via dynamic exchange of strong carbon-carbon bonds

    DOEpatents

    Guan, Zhibin; Lu, Yixuan

    2015-09-15

    A method of preparing a malleable and/or self-healing polymeric or composite material is provided. The method includes providing a polymeric or composite material comprising at least one alkene-containing polymer, combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material, and performing an olefin metathesis reaction on the polymer so as to form reversible carbon-carbon double bonds in the polymer. Also provided is a method of healing a fractured surface of a polymeric material. The method includes bringing a fractured surface of a first polymeric material into contact with a second polymeric material, and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon-carbon double bonds with the second polymeric material. Compositions comprising malleable and/or self-healing polymeric or composite material are also provided.

  1. Catalytic asymmetric carbon-carbon bond formation via allylic alkylations with organolithium compounds.

    PubMed

    Pérez, Manuel; Fañanás-Mastral, Martín; Bos, Pieter H; Rudolph, Alena; Harutyunyan, Syuzanna R; Feringa, Ben L

    2011-05-01

    Carbon-carbon bond formation is the basis for the biogenesis of nature's essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C-C bond formation to yield single enantiomers from several organometallic reagents. Remarkably, for extremely reactive organolithium compounds, which are among the most broadly used reagents in chemical synthesis, a general catalytic methodology for enantioselective C-C formation has proven elusive, until now. Here, we report a copper-based chiral catalytic system that allows carbon-carbon bond formation via allylic alkylation with alkyllithium reagents, with extremely high enantioselectivities and able to tolerate several functional groups. We have found that both the solvent used and the structure of the active chiral catalyst are the most critical factors in achieving successful asymmetric catalysis with alkyllithium reagents. The active form of the chiral catalyst has been identified through spectroscopic studies as a diphosphine copper monoalkyl species.

  2. Structural basis for Diels-Alder ribozyme-catalyzed carbon-carbon bond formation

    PubMed Central

    Serganov, Alexander; Keiper, Sonja; Malinina, Lucy; Tereshko, Valentina; Skripkin, Eugene; Höbartner, Claudia; Polonskaia, Anna; Phan, Anh Tuân; Wombacher, Richard; Micura, Ronald; Dauter, Zbigniew; Jäschke, Andres; Patel, Dinshaw J

    2015-01-01

    The majority of structural efforts addressing RNA’s catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with a reaction product. The RNA adopts a λ-shaped nested pseudoknot architecture whose preformed hydrophobic pocket is precisely complementary in shape to the reaction product. RNA folding and product binding are dictated by extensive stacking and hydrogen bonding, whereas stereoselection is governed by the shape of the catalytic pocket. Catalysis is apparently achieved by a combination of proximity, complementarity and electronic effects. We observe structural parallels in the independently evolved catalytic pocket architectures for ribozyme- and antibody-catalyzed Diels-Alder carbon-carbon bond-forming reactions. PMID:15723077

  3. Lessons from nature: biomimetic organocatalytic carbon-carbon bond formations.

    PubMed

    Enders, Dieter; Narine, Arun A

    2008-10-17

    Nature utilizes simple C2 and C3 building blocks, such as dihydroxyacetone phosphate (DHAP), phosphoenolpyruvate (PEP), and the "active aldehyde" in various enzyme-catalyzed carbon-carbon bond formations to efficiently build up complex organic molecules. In this Perspective, we describe the transition from using enantiopure chemical synthetic equivalents of these building blocks, employing our SAMP/RAMP hydrazone methodology and metalated chiral alpha-amino nitriles, to the asymmetric organocatalytic versions developed in our laboratory. Following this biomimetic strategy, the DHAP equivalent 2,2-dimethyl-1,3-dioxan-5-one (dioxanone) has been used in the proline-catalyzed synthesis of carbohydrates, aminosugars, carbasugars, polyoxamic acid, and various sphingosines. Proline-catalyzed aldol reactions involving a PEP-like equivalent have also allowed for the asymmetric synthesis of ulosonic acid precursors. By mimicking the "active aldehyde" nucleophilic acylations in Nature catalyzed by the thiamine-dependent enzyme, transketolase, enantioselective N-heterocyclic carbene-catalyzed benzoin and Stetter reactions have been developed. Finally, based on Nature's use of domino reactions to convert simple building blocks into complex and highly functionalized molecules, we report on our development of biomimetic asymmetric multicomponent domino reactions which couple enamine and iminium catalysis.

  4. Functionalized olefin cross-coupling to construct carbon-carbon bonds

    NASA Astrophysics Data System (ADS)

    Lo, Julian C.; Gui, Jinghan; Yabe, Yuki; Pan, Chung-Mao; Baran, Phil S.

    2014-12-01

    Carbon-carbon (C-C) bonds form the backbone of many important molecules, including polymers, dyes and pharmaceutical agents. The development of new methods to create these essential connections in a rapid and practical fashion has been the focus of numerous organic chemists. This endeavour relies heavily on the ability to form C-C bonds in the presence of sensitive functional groups and congested structural environments. Here we report a chemical transformation that allows the facile construction of highly substituted and uniquely functionalized C-C bonds. Using a simple iron catalyst, an inexpensive silane and a benign solvent under ambient atmosphere, heteroatom-substituted olefins are easily reacted with electron-deficient olefins to create molecular architectures that were previously difficult or impossible to access. More than 60 examples are presented with a wide array of substrates, demonstrating the chemoselectivity and mildness of this simple reaction.

  5. Carboxymethylproline synthase (CarB), an unusual carbon-carbon bond-forming enzyme of the crotonase superfamily involved in carbapenem biosynthesis.

    PubMed

    Sleeman, Mark C; Schofield, Christopher J

    2004-02-20

    Carboxymethylproline synthase (CarB) catalyzes the committed step in the biosynthesis of (R)-1-carbapen-2-em-3-carboxylate, the simplest member of the carbapenem family of beta-lactam antibiotics, some of which are used clinically. CarB displays sequence homology with members of the crotonase family including enoyl-CoA hydratase (crotonase) and methylmalonyl-CoA decarboxylase. The CarB reaction has been proposed to comprise condensation of acetyl coenzyme A (AcCoA) and glutamate semi-aldehyde to give (2S,5S)-carboxymethylproline ((2S,5S)-CMP). (2S,5S)-CMP is then cyclized in an ATP-driven reaction catalyzed by CarA to give a carbapenam, which is subsequently epimerized and desaturated to give a carbapenem in a CarC-mediated reaction. Here we report the purification of recombinant CarB and that it exists predominantly in a trimeric form as do other members of the crotonase family. AcCoA was not found to be a substrate for CarB. Instead malonyl-CoA was found to be a substrate, efficiently producing (2S,5S)-CMP in the presence of glutamate semi-aldehyde. In the absence of glutamate semi-aldehyde, mass spectrometric analysis indicated that CarB catalyzed the decarboxylation of malonyl-CoA to AcCoA. The reactions of CarB, CarA, and CarC were coupled in vitro demonstrating the viability of malonyl-CoA as a carbapenem precursor. CarB was also shown to accept methylmalonyl CoA as a substrate to form 6-methyl-(2S,5S)CMP, which in turn is a substrate for CarA. The implications of the results for the biosynthesis of both carbapenem-3-carboxylate and C-2/C-6-substituted carbapenems, such as thienamycin, are discussed.

  6. Creating carbon-carbon bonds with samarium diiodide for the synthesis of modified amino acids and peptides.

    PubMed

    Ebran, Jean-Philippe; Jensen, Christina M; Johannesen, Sine A; Karaffa, Jakob; Lindsay, Karl B; Taaning, Rolf; Skrydstrup, Troels

    2006-10-07

    In this perspective, an overview of our experiences on the application of samarium diiodide in organic synthesis for the preparation of amino acid and peptide analogues is presented. Three different carbon-carbon bond forming reactions are discussed, including side chain introductions, gamma-amino acid synthesis and acyl-like radical additions for the construction of C-C mimics of the peptidic bonds.

  7. Micro-oxidation treatment to improve bonding strength of Sr and Na co-substituted hydroxyapatite coatings for carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Zhang, Leilei; Li, Hejun; Li, Kezhi; Zhang, Yulei; Liu, Shoujie; Guo, Qian; Li, Shaoxian

    2016-08-01

    To improve the bonding strength of Sr and Na co-substituted hydroxyapatite (SNH) coatings for carbon/carbon composites, carbon/carbon composites are surface modified by micro-oxidation treatment. The micro-oxidation treatment could generate large number of pores containing oxygenic functional groups on the surface of carbon/carbon composites. SNH is nucleated on the inwall of the pores and form a flaky shape coating with 10-50 nm in thickness and 200-900 nm in width. The bonding strength between SNH coating and carbon/carbon composites increases from 4.27 ± 0.26 MPa to 10.57 ± 0.38 MPa after the micro-oxidation treatment. The promotion of bonding strength is mainly attributed to the pinning effect caused by the pores and chemical bonding generated by the oxygenic functional groups.

  8. Biosynthesis of pyranonaphthoquinone polyketides reveals diverse strategies for enzymatic carbon-carbon bond formation.

    PubMed

    Metsä-Ketelä, Mikko; Oja, Terhi; Taguchi, Takaaki; Okamoto, Susumu; Ichinose, Koji

    2013-08-01

    Pyranonaphthoquinones synthesized by Streptomyces bacteria via type II polyketide pathways are aromatic compounds build around a common three-ring structure, which is composed of pyran, quinone and benzene rings. Over the years, actinorhodin in particular has served as a model compound for studying the biosynthesis of aromatic polyketides, while some of the other metabolites such as granaticin, medermycin, frenolicin and alnumycin A have enabled comparative studies that complement our understanding how these complex biological systems function and have evolved. In addition, despite the similarity of the aglycone units, pyranonaphthoquinones in effect display remarkable diversity in tailoring reactions, which include numerous enzymatic carbon-carbon bond forming reactions. This review focuses on the current status of molecular genetic, biochemical and structural investigations on this intriguing family of natural products.

  9. A dense and strong bonding collagen film for carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Cao, Sheng; Li, Hejun; Li, Kezhi; Lu, Jinhua; Zhang, Leilei

    2015-08-01

    A strong bonding collagen film was successfully prepared on carbon/carbon (C/C) composites. The surface conditions of the modified C/C composites were detected by contact angle measurements, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectra. The roughness, optical morphology, bonding strength and biocompatibility of collagen films at different pH values were detected by confocal laser scanning microscope (CLSM), universal test machine and cytology tests in vitro. After a 4-h modification in 30% H2O2 solution at 100 °C, the contact angle on the surface of C/C composites was decreased from 92.3° to 65.3°. Large quantities of hydroxyl, carboxyl and carbonyl functional groups were formed on the surface of the modified C/C composites. Then a dense and continuous collagen film was prepared on the modified C/C substrate. Bonding strength between collagen film and C/C substrate was reached to 8 MPa level when the pH value of this collagen film was 2.5 after the preparing process. With 2-day dehydrathermal treatment (DHT) crosslinking at 105 °C, the bonding strength was increased to 12 MPa level. At last, the results of in vitro cytological test showed that this collagen film made a great improvement on the biocompatibility on C/C composites.

  10. Carbon-Carbon Bond Cleavage Reaction: Synthesis of Multisubstituted Pyrazolo[1,5-a]pyrimidines.

    PubMed

    Saikia, Pallabi; Gogoi, Sanjib; Boruah, Romesh C

    2015-07-02

    A new carbon-carbon bond cleavage reaction was developed for the efficient synthesis of multisubstituted pyrazolo[1,5-a]pyrimidines. This base induced reaction of 1,3,5-trisubstituted pentane-1,5-diones and substituted pyrazoles afforded good yields of the pyrazolo[1,5-a]pyrimidines.

  11. Reduction of carbon-carbon double bonds using organocatalytically generated diimide.

    PubMed

    Smit, Christian; Fraaije, Marco W; Minnaard, Adriaan J

    2008-12-05

    An efficient method has been developed for the reduction of carbon-carbon double bonds with diimide, catalytically generated in situ from hydrazine hydrate. The employed catalyst is prepared in one step from riboflavin (vitamin B(2)). Reactions are carried out in air and are a valuable alternative when metal-catalyzed hydrogenations are problematic.

  12. Adhesive Bonding of Titanium to Carbon-Carbon Composites for Heat Rejection Systems

    NASA Technical Reports Server (NTRS)

    Cerny, Jennifer; Morscher, Gregory

    2006-01-01

    High temperature adhesives with good thermal conductivity, mechanical performance, and long term durability are crucial for the assembly of heat rejection system components for space exploration missions. In the present study, commercially available adhesives were used to bond high conductivity carbon-carbon composites to titanium sheets. Bonded pieces were also exposed to high (530 to 600 Kelvin for 24 hours) and low (liquid nitrogen 77K for 15 minutes) temperatures to evaluate the integrity of the bonds. Results of the microstructural characterization and tensile shear strengths of bonded specimens will be reported. The effect of titanium surface roughness on the interface microstructure will also be discussed.

  13. Carbon-CArbon bond formation by Lewis superacid catalysis.

    PubMed

    Dunach, Elisabet

    2014-11-01

    Diverse intramolecular cyclizations involving the formation of CC bonds are described using catalytic methodologies based on Lewis superacids. Examples are presented on 1,6-diene cyclizations to gem-dimethylcyclohexane structures. Tandem cyclization of trienes are described to afford bicyclic structures in reactions involving rearrangements. Hydroarylation of olefins and of allenes is developed in catalytic FriedelCrafts-type coupling processes, which can give rise to tandem reactions. The olfactory evaluation of the series of prepared compounds is also presented.

  14. Carbon-carbon double-bond reductases in nature.

    PubMed

    Huang, Minmin; Hu, Haihong; Ma, Li; Zhou, Quan; Yu, Lushan; Zeng, Su

    2014-08-01

    Reduction of C = C bonds by reductases, found in a variety of microorganisms (e.g. yeasts, bacteria, and lower fungi), animals, and plants has applications in the production of metabolites that include pharmacologically active drugs and other chemicals. Therefore, the reductase enzymes that mediate this transformation have become important therapeutic targets and biotechnological tools. These reductases are broad-spectrum, in that, they can act on isolation/conjugation C = C-bond compounds, α,β-unsaturated carbonyl compounds, carboxylic acids, acid derivatives, and nitro compounds. In addition, several mutations in the reductase gene have been identified, some associated with diseases. Several of these reductases have been cloned and/or purified, and studies to further characterize them and determine their structure in order to identify potential industrial biocatalysts are still in progress. In this study, crucial reductases for bioreduction of C = C bonds have been reviewed with emphasis on their principal substrates and effective inhibitors, their distribution, genetic polymorphisms, and implications in human disease and treatment.

  15. Is the 2,3-carbon-carbon bond of indole really inert to oxidative cleavage by Oxone?--synthesis of isatoic anhydrides from indoles.

    PubMed

    Nelson, Amber C; Kalinowski, Emily S; Czerniecki, Nikolas J; Jacobson, Taylor L; Grundt, Peter

    2013-11-21

    A recent report has indicated that the oxidizing agent Oxone does not possess the ability to cleave the 2,3-carbon-carbon bond of indole. Work in our laboratory shows that this is not the case. Indole and a variety of aryl ring substituted derivatives readily react to form synthetically important isatoic anhydrides.

  16. Carbon-Carbon Bond Formation in a Weak Ligand Field: Leveraging Open Shell First Row Transition Metal Catalysts.

    PubMed

    Chirik, Paul James

    2017-01-12

    Unique features of Earth abundant transition metal catalysts are reviewed in the context of catalytic carbon-carbon bond forming reactions. Aryl-substituted bis(imino)pyridine iron and cobalt dihalide compounds, when activated with alkyl aluminum reagents, form highly active catalysts for the polymerization of ethylene. Open shell iron and cobalt alkyl complexes have been synthesized that serve as single component olefin polymerization catalysts. Reduced bis(imino)pyridine iron- and cobalt dinitrogen compounds have also been discovered that promote the unique [2+2] cycloaddition of unactivated terminal alkenes. Electronic structure studies support open shell intermediates, a deviation from traditional strong field organometallic compounds that promote catalytic C-C bond formation.

  17. Rigid Single Carbon-Carbon Bond That Does Not Rotate in Water.

    PubMed

    Gadogbe, Manuel; Zhou, Yadong; Zou, Shengli; Zhang, Dongmao

    2016-03-10

    Carbon-carbon bond is one of the most ubiquitous molecular building blocks for natural and man-made materials. Rotational isomerization is fundamentally important for understanding the structure and reactivity of chemical and biological molecules. Reported herein is the first demonstration that a single C-C bond does not rotate in water. The two distal C-S bonds in both 1,2-ethanedithiolate ((-)S-CH2-CH2-S(-), 1,2-EDT(2-)) and 2,3-butanedithiolate (2,3-BuDT(2-)) are exclusively in the trans conformer with reference to their respective center single C-C bond. In contrast, both trans and gauche conformers are observed in neutral 1,2-ethanedithiol (1,2-EDT) and 2, 3-butanedithiol (2,3-BuDT). The insight from this work should be important for understanding the charge effect on the molecular conformation in aqueous solutions.

  18. Sequential Carbon-Carbon/Carbon-Selenium Bond Formation Mediated by Iron(III) Chloride and Diorganyl Diselenides: Synthesis and Reactivity of 2-Organoselenyl-Naphthalenes.

    PubMed

    Recchi, Ana M S; Back, Davi F; Zeni, Gilson

    2017-03-03

    In this paper, we report an intramolecular cyclization of benzylic-substituted propargyl alcohols promoted by iron(III) chloride and diorganyl diselenides to give 2-organoselenyl-naphthalenes via a sequential carbon-carbon/carbon-selenium bond formation. The present reaction tolerated a wide range of substituents in both propargyl alcohols and diorganyl diselenides to give the desired 2-organoselenyl-naphthalenes in good yields with high selectivity. In addition, O-acyl protected propargyl alcohol and propargyl bromide were also subjected to this protocol giving the corresponding 2-organoselenyl-naphthalenes. We found that dichalcogenide species affected the formation of cyclized products, whereas diorganyl diselenides gave high yields, moderate yields were obtained with diorganyl disulfides, and no product formation was found with diorganyl ditellurides. The key transformations could be attributed to the carbon-carbon triple bond activation of benzylic-substituted propargyl alcohols by a seleniranium ion, antiattack of the electron cloud from the aromatic ring at the activated triple bond, and cyclization via an exclusive 6-endo-dig process. We also found that the corresponding 2-organoselenyl-naphthalenes are suitable substrates to the selenium-lithium exchange reactions followed by trapping with aldehydes affording the corresponding secondary alcohols.

  19. Exceptionally Fast Carbon-Carbon Bond Reductive Elimination from Gold(III)

    PubMed Central

    Wolf, William J.; Winston, Matthew S.; Toste, F. Dean

    2014-01-01

    Reductive elimination of carbon-carbon (C-C) bonds occurs in numerous metal-catalyzed reactions. This process is well documented for a variety of transition metal complexes. However, C-C bond reductive elimination from a limited number of Au(III) complexes has been shown to be a slow and prohibitive process, generally requiring elevated temperature. Herein, we show that oxidation of a series of mono- and bimetallic Au(I) aryl complexes at low temperature generates observable Au(III) and Au(II) intermediates. We also show that aryl-aryl bond reductive elimination from these oxidized species is not only among the fastest observed for any transition metal, but is also mechanistically distinct from previously studied alkyl-alkyl and aryl-alkyl reductive eliminations from Au(III). PMID:24451593

  20. Carbon-carbon bond cleavage and rearrangement of benzene by a trinuclear titanium hydride

    NASA Astrophysics Data System (ADS)

    Hu, Shaowei; Shima, Takanori; Hou, Zhaomin

    2014-08-01

    The cleavage of carbon-carbon (C-C) bonds by transition metals is of great interest, especially as this transformation can be used to produce fuels and other industrially important chemicals from natural resources such as petroleum and biomass. Carbon-carbon bonds are quite stable and are consequently unreactive under many reaction conditions. In the industrial naphtha hydrocracking process, the aromatic carbon skeleton of benzene can be transformed to methylcyclopentane and acyclic saturated hydrocarbons through C-C bond cleavage and rearrangement on the surfaces of solid catalysts. However, these chemical transformations usually require high temperatures and are fairly non-selective. Microorganisms can degrade aromatic compounds under ambient conditions, but the mechanistic details are not known and are difficult to mimic. Several transition metal complexes have been reported to cleave C-C bonds in a selective fashion in special circumstances, such as relief of ring strain, formation of an aromatic system, chelation-assisted cyclometallation and β-carbon elimination. However, the cleavage of benzene by a transition metal complex has not been reported. Here we report the C-C bond cleavage and rearrangement of benzene by a trinuclear titanium polyhydride complex. The benzene ring is transformed sequentially to a methylcyclopentenyl and a 2-methylpentenyl species through the cleavage of the aromatic carbon skeleton at the multi-titanium sites. Our results suggest that multinuclear titanium hydrides could serve as a unique platform for the activation of aromatic molecules, and may facilitate the design of new catalysts for the transformation of inactive aromatics.

  1. Single Molecule Study of Force-Induced Rotation of Carbon-Carbon Double Bonds in Polymers.

    PubMed

    Huang, Wenmao; Zhu, Zhenshu; Wen, Jing; Wang, Xin; Qin, Meng; Cao, Yi; Ma, Haibo; Wang, Wei

    2017-01-24

    Carbon-carbon double bonds (C═C) are ubiquitous in natural and synthetic polymers. In bulk studies, due to limited ways to control applied force, they are thought to be mechanically inert and not to contribute to the extensibility of polymers. Here, we report a single molecule force spectroscopy study on a polymer containing C═C bonds using atomic force microscope. Surprisingly, we found that it is possible to directly observe the cis-to-trans isomerization of C═C bonds at the time scale of ∼1 ms at room temperature by applying a tensile force ∼1.7 nN. The reaction proceeds through a diradical intermediate state, as confirmed by both a free radical quenching experiment and quantum chemical modeling. The force-free activation length to convert the cis C═C bonds to the transition state is ∼0.5 Å, indicating that the reaction rate is accelerated by ∼10(9) times at the transition force. On the basis of the density functional theory optimized structure, we propose that because the pulling direction is not parallel to C═C double bonds in the polymer, stretching the polymer not only provides tension to lower the transition barrier but also provides torsion to facilitate the rotation of cis C═C bonds. This explains the apparently low transition force for such thermally "forbidden" reactions and offers an additional explanation of the "lever-arm effect" of polymer backbones on the activation force for many mechanophores. This work demonstrates the importance of precisely controlling the force direction at the nanoscale to the force-activated reactions and may have many implications on the design of stress-responsive materials.

  2. Strain-induced cleavage of carbon-carbon bonds: bridge rupture reactions of group 8 dicarba[2]metallocenophanes.

    PubMed

    Herbert, David E; Gilroy, Joe B; Staubitz, Anne; Haddow, Mairi F; Harvey, Jeremy N; Manners, Ian

    2010-02-17

    Thermal treatment of dicarba[2]ferrocenophanes [Fe(eta(5)-C(5)H(4))(2)(CMe(2))(2)] (1), rac-[Fe(eta(5)-C(5)H(4))(2)(CHiPr)(2)] (rac-5), and meso-[Fe(eta(5)-C(5)H(4))(2)(CHtBu)(2)] (meso-7) at 240-300 degrees C in the melt led to cleavage of the carbon-carbon bond in the bridge. Compounds 1 and rac-5 underwent intramolecular abstraction of H* and yielded ring-opened, vinyl-substituted 1,1'-metallocenes, while meso-7 thermally converted to the more thermodynamically stable rac isomer. The corresponding dicarba[2]ruthenocenophanes [Ru(eta(5)-C(5)H(4))(2)(CMe(2))(2)] (10), rac-[Ru(eta(5)-C(5)H(4))(2)(CHiPr)(2)] (rac-12), and meso-[Ru(eta(5)-C(5)H(4))(2)(CHtBu)(2)] (meso-15) underwent analogous thermal carbon-carbon bond cleavage but more readily, consistent with a higher degree of ring strain. In the case of 7 and 15, the stability of the rac isomers relative to the respective meso isomers was confirmed by DFT studies, despite the former species exhibiting slightly higher tilt angles (alpha/deg) between the two cyclopentadienyl (Cp) rings. Theoretical investigations were used to explore the mechanism of carbon-carbon bond cleavage in dicarba[2]metallocenophanes, confirming the validity of the proposed homolytic bond cleavage mechanism. In addition, the potential role of bis-fulvene metal(0) and 'tuck-in' complexes in the bond-cleavage mechanism was assessed. This study also provides insight into the mechanism of the thermal ring-opening polymerization of -CH(2)CH(2)- bridged dicarba[2]metallocenophanes and, for the first time, supports a homolytic carbon-carbon bond cleavage pathway.

  3. Stable gold(III) catalysts by oxidative addition of a carbon-carbon bond.

    PubMed

    Wu, Chung-Yeh; Horibe, Takahiro; Jacobsen, Christian Borch; Toste, F Dean

    2015-01-22

    Low-valent late transition-metal catalysis has become indispensable to chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of high-valent transition-metal complexes and the challenges associated with synthesizing them. Here we report a carbon-carbon bond cleavage at ambient conditions by a Au(i) complex that generates a stable Au(iii) cationic complex. In contrast to the well-established soft and carbophilic Au(i) catalyst, this Au(iii) complex exhibits hard, oxophilic Lewis acidity. For example, we observed catalytic activation of α,β-unsaturated aldehydes towards selective conjugate additions as well as activation of an unsaturated aldehyde-allene for a [2 + 2] cycloaddition reaction. The origin of the regioselectivity and catalytic activity was elucidated by X-ray crystallographic analysis of an isolated Au(iii)-activated cinnamaldehyde intermediate. The concepts revealed suggest a strategy for accessing high-valent transition-metal catalysis from readily available precursors.

  4. Stable Gold(III) Catalysts by Oxidative Addition of a Carbon-Carbon Bond

    PubMed Central

    Wu, Chung-Yeh; Horibe, Takahiro; Jacobsen, Christian Borch

    2014-01-01

    Whereas low-valent late transition metal catalysis has become indispensible for chemical synthesis, homogeneous high-valent transition metal catalysis is underdeveloped, mainly due to the reactivity of high-valent transition metal complexes and the challenges associated with synthesizing them. In this manuscript, we report a mild carbon-carbon bond cleavage reaction by a Au(I) complex that generates a stable Au(III) cationic complex. Complementary to the well-established soft and carbophilic Au(I) catalyst, this Au(III) complex exhibits hard, oxophilic Lewis acidity. This is exemplified by catalytic activation of α,β-unsaturated aldehydes towards selective conjugate additions as well as activation of an unsaturated aldehyde-allene for a [2 + 2] cycloaddition reaction. The origin of the regioselectivity and catalytic activity was elucidated by X-ray crystallographic analysis of an isolated Au(III)-activated cinnamaldehyde intermediate. The concepts revealed in this study provide a strategy for accessing high-valent transition metal catalysis from readily available precursors. PMID:25612049

  5. Stable gold(III) catalysts by oxidative addition of a carbon-carbon bond

    NASA Astrophysics Data System (ADS)

    Wu, Chung-Yeh; Horibe, Takahiro; Jacobsen, Christian Borch; Toste, F. Dean

    2015-01-01

    Low-valent late transition-metal catalysis has become indispensable to chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of high-valent transition-metal complexes and the challenges associated with synthesizing them. Here we report a carbon-carbon bond cleavage at ambient conditions by a Au(I) complex that generates a stable Au(III) cationic complex. In contrast to the well-established soft and carbophilic Au(I) catalyst, this Au(III) complex exhibits hard, oxophilic Lewis acidity. For example, we observed catalytic activation of α,β-unsaturated aldehydes towards selective conjugate additions as well as activation of an unsaturated aldehyde-allene for a [2 + 2] cycloaddition reaction. The origin of the regioselectivity and catalytic activity was elucidated by X-ray crystallographic analysis of an isolated Au(III)-activated cinnamaldehyde intermediate. The concepts revealed suggest a strategy for accessing high-valent transition-metal catalysis from readily available precursors.

  6. Nuclear magnetic resonance and molecular modeling study of exocyclic carbon-carbon double bond polarization in benzylidene barbiturates

    NASA Astrophysics Data System (ADS)

    Figueroa-Villar, J. Daniel; Vieira, Andreia A.

    2013-02-01

    Benzylidene barbiturates are important materials for the synthesis of heterocyclic compounds with potential for the development of new drugs. The reactivity of benzylidene barbiturates is mainly controlled by their exocyclic carbon-carbon double bond. In this work, the exocyclic double bond polarization was estimated experimentally by NMR and correlated with the Hammett σ values of the aromatic ring substituents and the molecular modeling calculated atomic charge difference. It is demonstrated that carbon chemical shift differences and NBO charge differences can be used to predict their reactivity.

  7. Regiocontrolled intramolecular cyclizations of carboxylic acids to carbon-carbon triple bonds promoted by acid or base catalyst.

    PubMed

    Uchiyama, Masanobu; Ozawa, Hiroki; Takuma, Kazuya; Matsumoto, Yotaro; Yonehara, Mitsuhiro; Hiroya, Kou; Sakamoto, Takao

    2006-11-23

    We systematically investigated, for the first time, the relationship between regioselectivity and acid/base effects in the cyclization reactions between carboxylic acids and carbon-carbon triple bonds. We found novel acid- and base-promoted cyclizations to selectively give isocoumarin or pyran-2(2H)-one and phthalide or furan-2(5H)-one skeletons, respectively, and established a catalytic version of regioselective heterocyclic ring synthesis. Density functional theory calculations and application to a short route to thunberginol A were also described. [reaction: see text].

  8. Synthesis, photophysical and thin-film self-assembly properties of novel fluorescent molecules with carbon-carbon triple bonds.

    PubMed

    Niu, Qingfen; Sun, Hongjian; Li, Xiaoyan

    2014-12-10

    Three novel fluorescent molecules with carbon-carbon triple bonds 2TBEA, 2TBDA and TEPEB are successfully designed and synthesized. Their thermal, photophysical, electrochemical, electronic and thin-film self-assembly properties were characterized. Three dyes showed typical photoluminescence (PL) emission behaviors, the PL intensities firstly increased and then decreased with gradually decreasing concentration. The appealing fluorescence properties indicated that three dyes could be used as good fluorescent materials. Additionally, the thin-film self-assembly behaviors of three dyes were also investigated. The microstructures of their optical microscopy (OM) images exhibited high flexibility. Furthermore, SEM and AFM surface morphology of these self-assembly nanostructures revealed that three well-defined long-range order of rod-like and tube-like self-assembly systems exhibited interesting morphology properties. Therefore, three compounds may be of great interest for the development of organic thin-film materials.

  9. Remarkably efficient synthesis of 2H-indazole 1-oxides and 2H-indazoles via tandem carbon-carbon followed by nitrogen-nitrogen bond formation.

    PubMed

    Bouillon, Isabelle; Zajícek, Jaroslav; Pudelová, Nadĕzda; Krchnák, Viktor

    2008-11-21

    Base-catalyzed tandem carbon-carbon followed by nitrogen-nitrogen bond formations quantitatively converted N-alkyl-2-nitro-N-(2-oxo-2-aryl-ethyl)-benzenesulfonamides to 2H-indazoles 1-oxides under mild conditions. Triphenylphosphine or mesyl chloride/triethylamine-mediated deoxygenation afforded 2H-indazoles.

  10. Building carbon-carbon bonds using a biocatalytic methanol condensation cycle.

    PubMed

    Bogorad, Igor W; Chen, Chang-Ting; Theisen, Matthew K; Wu, Tung-Yun; Schlenz, Alicia R; Lam, Albert T; Liao, James C

    2014-11-11

    Methanol is an important intermediate in the utilization of natural gas for synthesizing other feedstock chemicals. Typically, chemical approaches for building C-C bonds from methanol require high temperature and pressure. Biological conversion of methanol to longer carbon chain compounds is feasible; however, the natural biological pathways for methanol utilization involve carbon dioxide loss or ATP expenditure. Here we demonstrated a biocatalytic pathway, termed the methanol condensation cycle (MCC), by combining the nonoxidative glycolysis with the ribulose monophosphate pathway to convert methanol to higher-chain alcohols or other acetyl-CoA derivatives using enzymatic reactions in a carbon-conserved and ATP-independent system. We investigated the robustness of MCC and identified operational regions. We confirmed that the pathway forms a catalytic cycle through (13)C-carbon labeling. With a cell-free system, we demonstrated the conversion of methanol to ethanol or n-butanol. The high carbon efficiency and low operating temperature are attractive for transforming natural gas-derived methanol to longer-chain liquid fuels and other chemical derivatives.

  11. Catalytic carbon--carbon and carbon--silicon bond activation and functionalization by nickel complexes

    SciTech Connect

    Edelback, B.L.; Lachicotte, R.J.; Jones, W.D.

    1999-10-25

    The nickel alkyne complexes (dippe)Ni(Me{sub 3}SiC{triple{underscore}bond}CSiMe{sub 3}), 1, (dippe)Ni(Me{sub 3}CC{triple{underscore}bond}CSiMe{sub 3}), 2, and (dippe)Ni(MeC{triple{underscore}bond}CSiMe{sub 3}), 3, were synthesized (dippe = bis(diisopropylphosphino)-ethane) and characterized by {sup 1}H, {sup 31}P, and {sup 13}C{l{underscore}brace}{sup 1}H{r{underscore}brace} NMR spectroscopy. Complex 1 was characterized by X-ray crystallography. Heating complex 1, 2, or 3 with excess biphenylene and alkyne results in the catalytic formation of several novel organic compounds, several of which have been characterized by X-ray crystallography. These reactions are proposed to proceed by a competition between {Beta}-silyl migration from an acetylene insertion intermediate and elimination of phenanthrene. Mechanistic schemes are presented for these reactions.

  12. An unusual carbon-carbon bond cleavage reaction during phosphinothricin biosynthesis

    SciTech Connect

    Cicchillo, Robert M; Zhang, Houjin; Blodgett, Joshua A.V.; Whitteck, John T; Li, Gongyong; Nair, Satish K; van derDonk, Wilfred A; Metcalf, William W

    2010-01-12

    Natural products containing phosphorus-carbon bonds have found widespread use in medicine and agriculture. One such compound, phosphinothricin tripeptide, contains the unusual amino acid phosphinothricin attached to two alanine residues. Synthetic phosphinothricin (glufosinate) is a component of two top-selling herbicides (Basta and Liberty), and is widely used with resistant transgenic crops including corn, cotton and canola. Recent genetic and biochemical studies showed that during phosphinothricin tripeptide biosynthesis 2-hydroxyethylphosphonate (HEP) is converted to hydroxymethylphosphonate (HMP). Here we report the in vitro reconstitution of this unprecedented C(sp{sup 3})-C(sp{sup 3}) bond cleavage reaction and X-ray crystal structures of the enzyme. The protein is a mononuclear non-haem iron(II)-dependent dioxygenase that converts HEP to HMP and formate. In contrast to most other members of this family, the oxidative consumption of HEP does not require additional cofactors or the input of exogenous electrons. The current study expands the scope of reactions catalysed by the 2-His-1-carboxylate mononuclear non-haem iron family of enzymes.

  13. An Unusual Carbon-Carbon Bond Cleavage Reaction During Phosphinothricin Biosynthesis

    PubMed Central

    Cicchillo, Robert M.; Zhang, Houjin; Blodgett, Joshua A.V.; Whitteck, John T.; Li, Gongyong; Nair, Satish K.; van der Donk, Wilfred A.; Metcalf, William W.

    2010-01-01

    Natural products containing phosphorus-carbon bonds have found widespread use in medicine and agriculture1. One such compound, phosphinothricin tripeptide (PTT), contains the unusual amino acid phosphinothricin (PT) attached to two alanine residues (Fig. 1). Synthetic PT (glufosinate) is a component of two top-selling herbicides (Basta® and Liberty®), and is widely used with resistant transgenic crops including corn, cotton and canola. Recent genetic and biochemical studies showed that during PTT biosynthesis 2-hydroxyethylphosphonate (HEP) is converted to hydroxymethylphosphonate (HMP) (Fig. 1)2. Reported here are the in vitro reconstitution of this unprecedented C(sp3)-C(sp3) bond cleavage reaction and X-ray crystal structures of the enzyme. The protein is a mononuclear non-heme iron(II)-dependent dioxygenase that converts HEP to HMP and formate. In contrast to most other members of this family, the oxidative consumption of HEP does not require additional cofactors or the input of exogenous electrons. The current study expands the scope of reactions catalyzed by the 2-His-1-carboxylate mononuclear non-heme iron family of enzymes. PMID:19516340

  14. Three-Component Coupling of Triflyloxy-Substituted Benzocyclobutenones, Organolithium Reagents, and Arynophiles Promoted by Generation of Aryne via Carbon-Carbon Bond Cleavage.

    PubMed

    Uchida, Keisuke; Yoshida, Suguru; Hosoya, Takamitsu

    2017-02-23

    Treatment of benzocyclobutenones bearing a triflyloxy group adjacent to the four-membered ring with organolithium reagents in the presence of arynophiles efficiently affords three-component coupled α-arylketones. Mechanistic studies indicate that the reaction is promoted by generation of the aryne via carbon-carbon bond cleavage of a benzocyclobutenoxide intermediate, which led us to find a fluoride-mediated aryne generation method from triflyloxy-substituted benzocyclobutenone silyl acetal precursors.

  15. Elucidation of an Iterative Process of Carbon-Carbon Bond Formation of Prebiotic Significance

    NASA Astrophysics Data System (ADS)

    Loison, Aurélie; Dubant, Stéphane; Adam, Pierre; Albrecht, Pierre

    2010-12-01

    Laboratory experiments carried out under plausible prebiotic conditions (under conditions that might have occurred at primitive deep-sea hydrothermal vents) in water and involving constituents that occur in the vicinity of submarine hydrothermal vents (e.g., CO, H2S, NiS) have disclosed an iterative Ni-catalyzed pathway of C-C bond formation. This pathway leads from CO to various organic molecules that comprise, notably, thiols, alkylmono- and disulfides, carboxylic acids, and related thioesters containing up to four carbon atoms. Furthermore, similar experiments with organic compounds containing various functionalities, such as thiols, carboxylic acids, thioesters, and alcohols, gave clues to the mechanisms of this novel synthetic process in which reduced metal species, in particular Ni(0), appear to be the key catalysts. Moreover, the formation of aldehydes (and ketones) as labile intermediates via a hydroformylation-related process proved to be at the core of the chain elongation process. Since this process can potentially lead to organic compounds with any chain length, it could have played a significant role in the prebiotic formation of lipidic amphiphilic molecules such as fatty acids, potential precursors of membrane constituents.

  16. Competitive Low Pressure Oxygen Plasma Interactions with Different= Carbon-Carbon Double Bonds

    NASA Astrophysics Data System (ADS)

    Patiño, P.; Sifontes, A.; Gambús, G.

    1999-10-01

    Recently we have shown advances from reactions of O(^3P) with both, l ong-chain hydrocarbons and refinery residuum. The oxidation products of t he process, a mixture of alcohols, epoxides and carbonyl compounds, might have potential properties as additives in formulating fuels. This work s hows the results of the interactions of an oxygen plasma with double bond s, both olefin and aromatic, in the same compound. The reactions have bee n carried out by making the plasma, created by a high voltage glow discha rge, reach the low vapor pressure surface of liquid 4-phenyl-1-butene. Th is (3 mL) was cooled down to -45 ^oC in a glass reactor, applied power was 24 W, at an oxygen pressure of 20 Pa. Products were analyzed by IR, N MR and mass spectroscopies. Conversions were studied as a function of the reaction time, this ranging from 5 to 120 minutes. At short times the O( ^3P) atoms produced in the discharge only reacted with the alkene fra ction of the hydrocarbon, 4-phenyl-1,2-epoxibutane (52%) and 4-phenyl-bu tanal (48%) being the products. Reactions on the benzene ring were obser ved from about 30 minutes on, the corresponding phenols having being prod uced at ratios ortho:para:meta :: 4:1:0.7. At 120 minutes, the ol efin have been completely oxidized and a low fraction of the non-equivale nt two methylene groups have reacted to produce alcohols and ketones.

  17. Carbon-carbon bond formation involving reactions of alkynes with group 9 metals (Ir, Rh, Co): preparation of conjugated olefins.

    PubMed

    Chin, Chong Shik; Won, Gyongshik; Chong, Daesung; Kim, Mieock; Lee, Hyungeui

    2002-04-01

    Stable alkynyl complexes of iridium(III) (L(n)Ir-triple bond-R) that are prepared from the reactions of terminal alkynes readily undergo the intramolecular C-C bond-forming reactions between the alkynyl and adjacent hydrocarbyl ligands to yield conjugated olefins. These reactions are initiated by electrophiles (H(+), Me(+)) that attack the beta carbon of the alkynyl ligand to increase the electrophilicity of the alpha carbon of the alkynyl ligand. The C-C bond is then formed between the alpha carbons of the alkynyl and adjacent hydrocarbyl ligands.

  18. Carbon-Carbon Bond Formation and Hydrogen Production in the Ketonization of Aldehydes.

    PubMed

    Orozco, Lina M; Renz, Michael; Corma, Avelino

    2016-09-08

    Aldehydes possess relatively high chemical energy, which is the driving force for disproportionation reactions such as Cannizzaro and Tishchenko reactions. Generally, this energy is wasted if aldehydes are transformed into carboxylic acids with a sacrificial oxidant. Here, we describe a cascade reaction in which the surplus energy of the transformation is liberated as molecular hydrogen for the oxidation of heptanal to heptanoic acid by water, and the carboxylic acid is transformed into potentially industrially relevant symmetrical ketones by ketonic decarboxylation. The cascade reaction is catalyzed by monoclinic zirconium oxide (m-ZrO2 ). The reaction mechanism has been studied through cross-coupling experiments between different aldehydes and acids, and the final symmetrical ketones are formed by a reaction pathway that involves the previously formed carboxylic acids. Isotopic studies indicate that the carboxylic acid can be formed by a hydride shift from the adsorbed aldehyde on the metal oxide surface in the absence of noble metals. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Cobryketone derived from vitamin B12 via palladium-catalyzed cleavage of the sp3-sp3 carbon-carbon bond.

    PubMed

    Kurcoń, Sylwester; Proinsias, Keith ó; Gryko, Dorota

    2013-04-19

    Heptamethyl cobyrinate was transformed into hexamethyl 8-nor-cobyrinate. The crucial step involved the synthesis of new, vitamin B12 derived cobryketone via palladium-catalyzed cleavage of the sp(3)-sp(3) carbon-carbon bond with the liberation of the ketone. The replacement of sp(3) carbon atom with sp(2) (C═O) at the 8-position produces a bathochromic shift of all absorption bands and makes α and β bands equal as a consequence of the expansion of the existing conjugated system of double bonds.

  20. Rapid carbon-carbon bond formation and cleavage revealed by carbon isotope exchange between the carboxyl carbon and inorganic carbon in hydrothermal fluids

    NASA Astrophysics Data System (ADS)

    Glein, C. R.; Cody, G. D.

    2013-12-01

    The carbon isotopic composition of organic compounds in water-rock systems (e.g., hydrothermal vents, sedimentary basins, and carbonaceous meteorites) is generally interpreted in terms of the isotopic composition of the sources of such molecules, and the kinetic isotope effects of metabolic or abiotic reactions that generate or transform such molecules. This hinges on the expectation that the carbon isotopic composition of many organic compounds is conserved under geochemical conditions. This expectation is reasonable in light of the strength of carbon-carbon bonds (ca. 81 kcal/mol); in general, environmental conditions conducive to carbon-carbon bond cleavage typically lead to transformations of organic molecules (decarboxylation is a notable example). Geochemically relevant reactions that involve isotopic exchange between carbon atoms in organic molecules and inorganic forms of carbon with no change in molecular structure appear to be rare. Notwithstanding such rarity, there have been preliminary reports of relatively rapid carbon isotope exchange between the carboxyl group in carboxylic acids and carbon dioxide in hot water [1,2]. We have performed laboratory hydrothermal experiments to gain insights into the mechanism of this surprising reaction, using phenylacetate as a model structure. By mass spectrometry, we confirm that the carboxyl carbon undergoes facile isotopic exchange with 13C-labeled bicarbonate at moderate temperatures (i.e., 230 C). Detailed kinetic analysis reveals that the reaction rate is proportional to the concentrations of both reactants. Further experiments demonstrate that the exchange reaction only occurs if the carbon atom adjacent to the carboxyl carbon is bonded to a hydrogen atom. As an example, no carbon isotope exchange was observed for benzoate in experiments lasting up to one month. The requirement of an alpha C-H bond suggests that enolization (i.e., deprotonation of the H) is a critical step in the mechanism of the exchange

  1. Filament Winding Of Carbon/Carbon Structures

    NASA Technical Reports Server (NTRS)

    Jacoy, Paul J.; Schmitigal, Wesley P.; Phillips, Wayne M.

    1991-01-01

    Improved method of winding carbon filaments for carbon/carbon composite structures less costly and labor-intensive, also produces more consistent results. Involves use of roller squeegee to ensure filaments continuously wet with resin during winding. Also involves control of spacing and resin contents of plies to obtain strong bonds between carbon filaments and carbon matrices. Lends itself to full automation and involves use of filaments and matrix-precursor resins in their simplest forms, thereby reducing costs.

  2. Development of a dye molecule-biocatalyst hybrid system with visible-light induced carbon-carbon bond formation from CO2 as a feedstock.

    PubMed

    Amao, Yutaka; Ikeyama, Shusaku; Katagiri, Takayuki; Fujita, Kohei

    2017-03-09

    Recently, CO2 utilization technology, including artificial photosynthesis, has received much attention. In this field, CO2 is used as a feedstock for fuels, polymers and in other chemical processes. Of note are malic enzymes (MEs) which catalyze the reaction of malic acid to pyruvic acid and CO2 with the co-enzyme NADP(+), and catalyze the reverse reaction of pyruvic acid and CO2 to malic acid with the co-enzyme NADPH. Thus, MEs are also an attractive biocatalyst for carbon-carbon bond formation from CO2. Studies of the visible light-induced malic acid production from pyruvic acid and CO2 using an electron donor, a photosensitizer, an electron mediator, ferredoxin-NADP(+) reductase, NADP(+), and ME have been reported. However, modification of these systems is required, as they are very complicated. In this study, the visible light-induced carbon-carbon bond formation from pyruvic acid and CO2 with ME using the photoreduction of 1,1'-diphenyl-4,4'-bipyridinium salt derivatives as a novel electron mediator with water-soluble tetraphenylporphyrin tetrasulfonate (H2TPPS) in the presence of triethanolamine (TEOA) as an electron donor was developed. When a sample solution containing TEOA, H2TPPS, 1,1'-diphenyl-4,4'-bipyridinium salt derivative, pyruvic acid, and ME in CO2-saturated bis-tris buffer was irradiated, the major product was oxaloacetic acid. Thus, a visible light-induced photoredox system for carbon-carbon bond formation from CO2 with ME using 1,1'-diphenyl-4,4'-bipyridinium salt derivative as an electron mediator was developed.

  3. Velocity Map Imaging Study of Ion-Radical Chemistry: Charge Transfer and Carbon-Carbon Bond Formation in the Reactions of Allyl Radicals with C(.).

    PubMed

    Pei, Linsen; Farrar, James M

    2016-08-11

    We present an experimental and computational study of the dynamics of collisions of ground state carbon cations with allyl radicals, C3H5, at a collision energy of 2.2 eV. Charge transfer to produce the allyl cation, C3H5(+), is exoergic by 3.08 eV and proceeds via energy resonance such that the electron transfer occurs without a significant change in nuclear velocities. The products have sufficient energy to undergo the dissociation process C3H5(+) → C3H4(+) + H. Approximately 80% of the reaction products are ascribed to charge transfer, with ∼40% of those products decaying via loss of a hydrogen atom. We also observe products arising from the formation of new carbon-carbon bonds. The experimental velocity space flux distributions for the four-carbon products are symmetric about the centroid of the reactants, providing direct evidence that the products are mediated by formation of a C4H5(+) complex living at least a few rotational periods. The primary four-carbon reaction products are formed by elimination of molecular hydrogen from the C4H5(+) complex. More than 75% of the nascent C4H3(+) products decay by C-H bond cleavage to yield a C4H2(+) species. Quantum chemical calculations at the MP2/6-311+g(d,p) level of theory support the formation of a nonplanar cyclic C4H5(+) adduct that is produced when the p-orbital containing the unpaired electron on C(+) overlaps with the unpaired spin density on the terminal carbon atoms in allyl. Product formation then occurs by 1,2-elimination of molecular hydrogen from the cyclic intermediate to form a planar cyclic C4H3(+) product. The large rearrangement in geometry as the C4H3(+) products are formed is consistent with high vibrational excitation in that product and supports the observation that the majority of those products decay to form the C4H2(+) species.

  4. Carbon-carbon bond cleavage of 1,2-hydroxy ethers b7 vanadium(V) dipicolinate complexes

    SciTech Connect

    Hanson, Susan K; Gordon, John C; Thorn, David L; Scott, Brian L; Baker, R Tom

    2009-01-01

    The development of alternatives to current petroleum-based fuels and chemicals is becoming increasingly important due to concerns over climate change, growing world energy demand, and energy security issues. Using non-food derived biomass to produce renewable feedstocks for chemicals and fuels is a particularly attractive possibility. However, the majority of biomass is in the form of lignocellulose, which is often not fully utilized due to difficulties associated with breaking down both lignin and cellulose. Recently, a number of methods have been reported to transform cellulose directly into more valuable materials such as glucose, sorbitol, 5-(chloromethyl)furfural, and ethylene glycol. Less progress has been made with selective transformations of lignin, which is typically treated in paper and forest industries by kraft pulping (sodium hydroxide/sodium sulfide) or incineration. Our group has begun investigating aerobic oxidative C-C bond cleavage catalyzed by dipicolinate vanadium complexes, with the idea that a selective C-C cleavage reaction of this type could be used to produce valuable chemicals or intermediates from cellulose or lignin. Lignin is a randomized polymer containing methoxylated phenoxy propanol units. A number of different linkages occur naturally; one of the most prevalent is the {beta}-O-4 linkage shown in Figure 1, containing a C-C bond with 1,2-hydroxy ether substituents. While the oxidative C-C bond cleavage of 1,2-diols has been reported for a number of metals, including vanadium, iron, manganese, ruthenium, and polyoxometalate complexes, C-C bond cleavage of 1,2-hydroxy ethers is much less common. We report herein vanadium-mediated cleavage of C-C bonds between alcohol and ether functionalities in several lignin model complexes. In order to explore the scope and potential of vanadium complexes to effect oxidative C-C bond cleavage in 1,2-hydroxy ethers, we examined the reactivity of the lignin model complexes pinacol monomethyl ether (A

  5. Micro-raman assessment of the ratio of carbon-carbon double bonds of two adhesive systems cured with LED or halogen light-curing units.

    PubMed

    Miletic, Vesna; Santini, Ario

    2010-12-01

    the purpose of the study was to compare the ratio of carbon-carbon double bonds (RDB) of two adhesive systems cured by five different light-curing units (LCUs) using micro-Raman spectroscopy. materials and methods: ten samples of an etch-and-rinse (Excite), a two-step self-etching adhesive system (AdheSE) - ie, primer and bond mixed - and AdheSE Bond only were prepared and cured with one of the following LEDs: Elipar Freelight2; Bluephase; SmartLite; Coltolux, each for 10 s; or a conventional halogen Prismetics Lite for 10 s or 20 s. Micro-Raman spectra were obtained from uncured and cured samples of all three groups to calculate the RDB. Data were statistically analyzed using ANOVA. the mean RDB values were 62% to 76% (Excite), 36% to 50% (AdheSE Primer+Bond) and 58% to 63% (AdheSE Bond). At 20 s, Prismetics Lite produced significantly higher RDB in Excite than the other LCUs and Prismetics Lite at 10 s (p < 0.05). Prismetics Lite at 20 s and Elipar produced comparable RDB values of AdheSE Bond and AdheSE Primer+Bond (p > 0.05). Excite showed significantly higher RDB values than AdheSE (p < 0.05) whilst AdheSE Bond showed significantly higher RDB than AdheSE Primer+Bond (p < 0.05). the etch-and-rinse adhesive cured with the halogen LCU for 20 s gave higher conversion than LED LCUs or halogen for 10 s curing time. The highest intensity LED [Elipar] produced higher or comparable conversion compared to the lower intensity LED LCUs for the same curing time. The etch-and-rinse adhesive showed higher RDB than the self-etching adhesive system. The presence of the primer in the self-etching adhesive compromised polymerisation.

  6. Transition-Metal-Catalyzed Laboratory-Scale Carbon–Carbon Bond-Forming Reactions of Ethylene

    PubMed Central

    Saini, Vaneet; Stokes, Benjamin J.; Sigman, Matthew S.

    2014-01-01

    Ethylene, the simplest alkene, is the most abundantly synthesized organic molecule by volume. It is readily incorporated into transitionmetal–catalyzed carbon-carbon bond-forming reactions through migratory insertions into alkylmetal intermediates. Because of its D2h symmetry, only one insertion outcome is possible. This limits byproduct formation and greatly simplifies analysis. As described within this Minireview, many carbon–carbon bond-forming reactions incorporate a molecule (or more) of ethylene at ambient pressure and temperature. In many cases, a useful substituted alkene is incorporated into the product. PMID:24105881

  7. Investigations of Oxidation Protection Systems for Carbon-Carbon Composites Formed by Chemical Vapor Deposition and Plasma-Assisted Chemical Vapor Deposition Techniques

    DTIC Science & Technology

    1991-01-21

    the coating oxidizes to form a protective seal. ZrO2 may react with the SiO 2 film to form zirconium silicate, which offers reasonable oxidation...oxidation behavior of coated carbon-carbon (C-C) composites is studied. Silicon carbide and zirconium diboride ceramic coating are deposited on pack...cementation process were a weight percent mixture of silicon (Si), silicon carbide (SiC), zirconium carbide (ZrC), Boron (B), and Alumina (A1203). The

  8. Biomimetic oxidation with molecular oxygen. Selective carbon-carbon bond cleavage of 1,2-diols by molecular oxygen and dihydropyridine in the presence of iron-porphyrin catalysts

    SciTech Connect

    Okamoto, T.; Sasaki, K.; Oka, S.

    1988-02-17

    The selective carbon-carbon bond cleavage of 1,2-diols in the presence of an iron-porphyrin complex, molecular oxygen, and 1-benzyl-3-carbamoyl-1,4-dihydropyridine is reported. The C-C bonds of aryl-substituted ethane-1,2-diols were cleaved exclusively to aldehydes or ketones as the oxidation products at room temperature. The reaction rates were influenced by the steric hindrance of the substituents both in the catalysts and diols, but no differences in the reactivities were observed between the two stereo isomers (meso and dl) of diols. A kinetic analysis of this bond cleavage reaction is consistent with the reaction mechanism consisting of the initial binding of diol on the active catalyst forming an intermediate complex and its subsequent breakdown in the rate-determining step of the catalytic cycle. The initial binding step is favorable for electron-deficient diols and is influenced by steric hindrance, whereas the rate-determining bond cleavage step is accelerated by electron-rich diols and unaffected by the steric effect. The mechanism of this diol cleavage reaction is discussed on the basis of these observations.

  9. Strong bonding strength between HA and (NH4)2S2O8-treated carbon/carbon composite by hydrothermal treatment and induction heating.

    PubMed

    Xiong, Xin-bo; Zeng, Xie-rong; Zou, Chun-li; Zhou, Ji-Zhao

    2009-06-01

    Carbon/carbon composite with hydroxyapatite (HA) coating is an attractive material in the dental and orthopedic fields, but the reported bonding strength between them was very poor. In this study, a compact crystalline HA coating on (NH(4))(2)S(2)O(8)-treated C/C substrate about 10 microm in width was obtained by hydrothermal treatment and induction heating. The microstructure, composition and morphologies of the as-prepared coatings were identified by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. A strong shear strength averaging 74.2 MPa between C/C substrate and HA was achieved and adhesion failures were observed more frequently than cohesion failures. The coating adhesion measured using a scratch test was 23 N and the reasons for this are discussed.

  10. Reversible carbon-carbon bond formation induced by oxidation and reduction at a redox-active cobalt complex.

    PubMed

    Atienza, Crisita Carmen Hojilla; Milsmann, Carsten; Semproni, Scott P; Turner, Zoë R; Chirik, Paul J

    2013-05-06

    The electronic structure of the diamagnetic pyridine imine enamide cobalt dinitrogen complex, ((iPr)PIEA)CoN2 ((iPr)PIEA = 2-(2,6-(i)Pr2-C6H3N═CMe)-6-(2,6-(i)Pr2-C6H3NC═CH2)C5H3N), was determined and is best described as a low-spin cobalt(II) complex antiferromagnetically coupled to an imine radical anion. Addition of potential radical sources such as NO, PhSSPh, or Ph3Cl resulted in C-C coupling at the enamide positions to form bimetallic cobalt compounds. Treatment with the smaller halocarbon, PhCH2Cl, again induced C-C coupling to form a bimetallic bis(imino)pyridine cobalt chloride product but also yielded a monomeric cobalt chloride product where the benzyl group added to the enamide carbon. Similar cooperative metal-ligand addition was observed upon treatment of ((iPr)PIEA)CoN2 with CH2═CHCH2Br, which resulted in allylation of the enamide carbon. Reduction of Coupled-((iPr)PDI)CoCl (Coupled-((iPr)PDI)CoCl = [2-(2,6-(i)Pr2-C6H3N═CMe)-C5H3N-6-(2,6-(i)Pr2-C6H3N═CCH2-)CoCl]2) with NaBEt3H led to quantitative formation of ((iPr)PIEA)CoN2, demonstrating the reversibility of the C-C bond forming reactions. The electronic structures of each of the bimetallic cobalt products were also elucidated by a combination of experimental and computational methods.

  11. Joining Carbon-Carbon Composites and High-Temperature Materials with High Energy Electron Beams

    NASA Technical Reports Server (NTRS)

    Goodman, Daniel; Singler, Robert

    1998-01-01

    1. Program goals addressed during this period. Experimental work was directed at formation of a low-stress bond between carbon- carbon and aluminum, with the objective of minimizing the heating of the aluminum substrate, thereby minimizing stresses resulting from the coefficient of thermal expansion (CTE) difference between the aluminum and carbon-carbon. A second objective was to form a bond between carbon-carbon and aluminum with good thermal conductivity for electronic thermal management (SEM-E) application. 2. Substrates and joining materials selected during this period. Carbon-Carbon Composite (CCC) to Aluminum. CCC (Cu coated) to Aluminum. Soldering compounds based on Sn/Pb and Sn/Ag/Cu/Bi compositions. 3. Soldering experiments performed. Conventional techniques. High Energy Electron Beam (HEEB) process.

  12. Chain Walking as a Strategy for Carbon-Carbon Bond Formation at Unreactive Sites in Organic Synthesis: Catalytic Cycloisomerization of Various 1,n-Dienes.

    PubMed

    Hamasaki, Taro; Aoyama, Yuka; Kawasaki, Junichi; Kakiuchi, Fumitoshi; Kochi, Takuya

    2015-12-30

    Carbon-carbon bond formation at unreactive sp(3)-carbons in small organic molecules via chain walking was achieved for the palladium-catalyzed cycloisomerization of 1,n-dienes. Various 1,n-dienes (n = 7-14) such as those containing cyclic alkenes, acyclic internal alkenes, and a trisubstituted alkene can be used for the chain-walking cycloisomerization/hydrogenation process, and five-membered ring compounds including simple cyclopentane and pyrrolidine derivatives can easily be prepared. Chain walking over a tertiary carbon was also found to be possible in the cycloisomerization. It is not necessary for the linker portion of the diene to contain a quaternary center, and diene substrates with two alkene moieties linked by a tertiary carbon or a nitrogen atom can also be used as substrates. Column chromatography using silica gel containing silver nitrate was found to be effective for isolating some of the cycloisomerization products without hydrogenation. Deuterium-labeling experiments provided direct evidence to show that the reaction proceeds via a chain-walking mechanism.

  13. Method for joining carbon-carbon composites to metals

    DOEpatents

    Lauf, R.J.; McMillan, A.D.; Moorhead, A.J.

    1997-07-15

    A method for joining carbon-carbon composites to metals by brazing. Conventional brazing of recently developed carbon-bonded carbon fiber (CBCF) material to a metal substrate is limited by the tendency of the braze alloy to ``wick`` into the CBCF composite rather than to form a strong bond. The surface of the CBCF composite that is to be bonded is first sealed with a fairly dense carbonaceous layer achieved by any of several methods. The sealed surface is then brazed to the metal substrate by vacuum brazing with a Ti-Cu-Be alloy. 1 fig.

  14. Method for joining carbon-carbon composites to metals

    DOEpatents

    Lauf, Robert J.; McMillan, April D.; Moorhead, Arthur J.

    1997-01-01

    A method for joining carbon-carbon composites to metals by brazing. Conventional brazing of recently developed carbon-bonded carbon fiber (CBCF) material to a metal substrate is limited by the tendency of the braze alloy to "wick" into the CBCF composite rather than to form a strong bond. The surface of the CBCF composite that is to be bonded is first sealed with a fairly dense carbonaceous layer achieved by any of several methods. The sealed surface is then brazed to the metal substrate by vacuum brazing with a Ti-Cu-Be alloy.

  15. Mechanism and Stereoselectivity in an Asymmetric N-Heterocyclic Carbene-Catalyzed Carbon-Carbon Bond Activation Reaction.

    PubMed

    Pareek, Monika; Sunoj, Raghavan B

    2016-11-18

    The mechanism and origin of stereoinduction in a chiral N-heterocyclic carbene (NHC) catalyzed C-C bond activation of cyclobutenone has been established using B3LYP-D3 density functional theory computations. The activation of cyclobutenone as an NHC-bound vinyl enolate and subsequent reaction with the electrophilic sulfonyl imine leads to the lactam product. The most preferred stereocontrolling transition state exhibits a number of noncovalent interactions rendering additional stabilization. The computed enantio- and diastereoselectivities are in good agreement with the previous experimental observations.

  16. The first chiral diene-based metal-organic frameworks for highly enantioselective carbon-carbon bond formation reactions

    SciTech Connect

    Sawano, Takahiro; Ji, Pengfei; McIsaac, Alexandra R.; Lin, Zekai; Abney, Carter W.; Lin, Wenbin

    2016-02-01

    We have designed the first chiral diene-based metal–organic framework (MOF), E₂-MOF, and postsynthetically metalated E₂-MOF with Rh(I) complexes to afford highly active and enantioselective single-site solid catalysts for C–C bond formation reactions. Treatment of E₂-MOF with [RhCl(C₂H₄)₂]₂ led to a highly enantioselective catalyst for 1,4-additions of arylboronic acids to α,β-unsaturated ketones, whereas treatment of E₂-MOF with Rh(acac)(C₂H₄)₂ afforded a highly efficient catalyst for the asymmetric 1,2-additions of arylboronic acids to aldimines. Interestingly, E₂-MOF·Rh(acac) showed higher activity and enantioselectivity than the homogeneous control catalyst, likely due to the formation of a true single-site catalyst in the MOF. E₂-MOF·Rh(acac) was also successfully recycled and reused at least seven times without loss of yield and enantioselectivity.

  17. Formulation of atomic positions and carbon-carbon bond length in armchair graphene nanoribbons: an ab initio study

    NASA Astrophysics Data System (ADS)

    Balarastaghi, Mehran; Ahmadi, Vahid

    2017-09-01

    In this paper, we investigate the atomic positions of single layer armchair graphene nanoribbon for two cases, with and without hydrogen-passivate edges, accurately and propose a formula which either removes the need of structural relaxation generally or decreases its time extremely (up to seven times). We also propose a general pattern (hyperbolic) for these positions. On the other hand, we show that edge effect influences several atoms near the edge not just one. These results can be used in software, which compute atomic positions and can increase their efficiency. In addition, we prove that the C-C bond distance depends on dimer number and differs in length and width directions, especially for narrow AGNRs. The maximum value of these differences is about 0.017 Å.

  18. Energetics of tert-butoxyl addition reaction to norbornadiene: a method for estimating the pi-bond strength of a carbon-carbon double bond.

    PubMed

    Nunes, Paulo M; Estácio, Sílvia G; Lopes, Gustavo T; Agapito, Filipe; Santos, Rui C; Costa Cabral, Benedito J; Borges dos Santos, Rui M; Martinho Simões, José A

    2009-06-11

    The energetics of tert-butoxyl radical addition reaction to norbornadiene was investigated by time-resolved photoacoustic calorimetry (TR-PAC). The result, together with the C-O bond dissociation enthalpy (BDE) in the addition product, allowed us to calculate the pi-bond dissociation enthalpy in norbornadiene. Quantum chemistry (QC) methods were also used to obtain several enthalpies of reaction of the addition of oxygen-centered radicals to alkenes. The pi-bond dissociation enthalpies in these molecules were calculated by a procedure similar to that used in the case of norbornadiene and were compared with the pi-BDE values obtained by the method proposed by Benson. These two different approaches yield similar values for the pi-BDEs in alkenes, indicating that the addition method proposed in the present study is a valid way to derive that quantity. The influence of strain in the pi-BDEs of cyclic alkenes was investigated and allowed us to justify the difference between the pi-BDE in norbornene and norbornadiene. Finally, the thermochemistry of the addition and abstraction reactions involving these two molecules and tert-butoxyl radical was analyzed.

  19. 45 CFR 1629.5 - Form of bonds.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 45 Public Welfare 4 2011-10-01 2011-10-01 false Form of bonds. 1629.5 Section 1629.5 Public Welfare Regulations Relating to Public Welfare (Continued) LEGAL SERVICES CORPORATION BONDING OF RECIPIENTS § 1629.5 Form of bonds. Any form of bond which may be described as individual, schedule or...

  20. 45 CFR 1629.5 - Form of bonds.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 45 Public Welfare 4 2010-10-01 2010-10-01 false Form of bonds. 1629.5 Section 1629.5 Public Welfare Regulations Relating to Public Welfare (Continued) LEGAL SERVICES CORPORATION BONDING OF RECIPIENTS § 1629.5 Form of bonds. Any form of bond which may be described as individual, schedule or...

  1. Superplastically formed diffusion bonded metallic structure

    NASA Technical Reports Server (NTRS)

    Ko, W. L. (Inventor)

    1981-01-01

    A metallic sandwich structure particularly suited for use in aerospace industries comprising a base plate, a cover plate, and an orthogonally corrugated core is described. A pair of core plates formed of a superplastic alloy are interposed between the base plate and the cover plate and bonded. Each of the core plates is characterized by a plurality of protrusions comprising square-based, truncated pyramids uniformly aligned along orthogonally related axes perpendicularly bisecting the legs of the bases of the pyramids and alternately inverted along orthogonally related planes diagonally bisecting the pyramids, whereby an orthogonally corrugated core is provided.

  2. 27 CFR 26.68 - Bond, Form 2898-Beer.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2013-04-01 2013-04-01 false Bond, Form 2898-Beer. 26... Liquors and Articles in Puerto Rico Bonds § 26.68 Bond, Form 2898—Beer. Where a brewer intends to withdraw, for purpose of shipment to the United States, beer of Puerto Rican manufacture from bonded storage...

  3. 27 CFR 26.68 - Bond, Form 2898-Beer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2014-04-01 2014-04-01 false Bond, Form 2898-Beer. 26... Liquors and Articles in Puerto Rico Bonds § 26.68 Bond, Form 2898—Beer. Where a brewer intends to withdraw, for purpose of shipment to the United States, beer of Puerto Rican manufacture from bonded storage...

  4. 27 CFR 26.68 - Bond, Form 2898-Beer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Bond, Form 2898-Beer. 26... Liquors and Articles in Puerto Rico Bonds § 26.68 Bond, Form 2898—Beer. Where a brewer intends to withdraw, for purpose of shipment to the United States, beer of Puerto Rican manufacture from bonded storage...

  5. 27 CFR 26.67 - Bond, Form 2897-Wine.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Bond, Form 2897-Wine. 26... Liquors and Articles in Puerto Rico Bonds § 26.67 Bond, Form 2897—Wine. Where a proprietor intends to withdraw, for purpose of shipment to the United States, wine of Puerto Rican manufacture from bonded...

  6. 27 CFR 26.67 - Bond, Form 2897-Wine.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2013-04-01 2013-04-01 false Bond, Form 2897-Wine. 26... Liquors and Articles in Puerto Rico Bonds § 26.67 Bond, Form 2897—Wine. Where a proprietor intends to withdraw, for purpose of shipment to the United States, wine of Puerto Rican manufacture from bonded...

  7. 27 CFR 26.67 - Bond, Form 2897-Wine.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2014-04-01 2014-04-01 false Bond, Form 2897-Wine. 26... Liquors and Articles in Puerto Rico Bonds § 26.67 Bond, Form 2897—Wine. Where a proprietor intends to withdraw, for purpose of shipment to the United States, wine of Puerto Rican manufacture from bonded...

  8. 27 CFR 26.67 - Bond, Form 2897-Wine.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2012-04-01 2012-04-01 false Bond, Form 2897-Wine. 26... Liquors and Articles in Puerto Rico Bonds § 26.67 Bond, Form 2897—Wine. Where a proprietor intends to withdraw, for purpose of shipment to the United States, wine of Puerto Rican manufacture from bonded...

  9. 27 CFR 26.67 - Bond, Form 2897-Wine.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Bond, Form 2897-Wine. 26... Liquors and Articles in Puerto Rico Bonds § 26.67 Bond, Form 2897—Wine. Where a proprietor intends to withdraw, for purpose of shipment to the United States, wine of Puerto Rican manufacture from bonded...

  10. Interfaces in carbon-carbon composites

    SciTech Connect

    Peebles, L.H.; Meyer, R.A.; Jortner, J.

    1988-01-01

    Carbon-carbon composites, consisting of a carbon matrix reinforced with carbon fibers, have complex microstructures. Several types of interfaces, microcracks, and various degress of local anisotropy were observed. This paper provides examples of microstructures seen in carbon-carbon composites, with emphasis on the interfaces. Information relating to the degree of bonding at interfaces, and its effects on composite behavior, is reviewed. The causes and effects of the various observed microstructures are beginning to be understood, but there remain many questions deserving further study.

  11. Crystal Structures of Two Bacterial 3-Hydroxy-3-methylglutaryl-CoA Lyases Suggest a Common Catalytic Mechanism among a Family of TIM Barrel Metalloenzymes Cleaving Carbon-Carbon Bonds

    SciTech Connect

    Forouhar,F.; Hussain, M.; Farid, R.; Benach, J.; Abashidze, M.; Edstrom, W.; Vorobiev, S.; Montelione, G.; Hunt, J.; et al.

    2006-01-01

    The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase catalyzes the terminal steps in ketone body generation and leucine degradation. Mutations in this enzyme cause a human autosomal recessive disorder called primary metabolic aciduria, which typically kills victims because of an inability to tolerate hypoglycemia. Here we present crystal structures of the HMG-CoA lyases from Bacillus subtilis and Brucella melitensis at 2.7 and 2.3 {angstrom} resolution, respectively. These enzymes share greater than 45% sequence identity with the human orthologue. Although the enzyme has the anticipated triose-phosphate isomerase (TIM) barrel fold, the catalytic center contains a divalent cation-binding site formed by a cluster of invariant residues that cap the core of the barrel, contrary to the predictions of homology models. Surprisingly, the residues forming this cation-binding site and most of their interaction partners are shared with three other TIM barrel enzymes that catalyze diverse carbon-carbon bond cleavage reactions believed to proceed through enolate intermediates (4-hydroxy-2-ketovalerate aldolase, 2-isopropylmalate synthase, and transcarboxylase 5S). We propose the name 'DRE-TIM metallolyases' for this newly identified enzyme family likely to employ a common catalytic reaction mechanism involving an invariant Asp-Arg-Glu (DRE) triplet. The Asp ligates the divalent cation, while the Arg probably stabilizes charge accumulation in the enolate intermediate, and the Glu maintains the precise structural alignment of the Asp and Arg. We propose a detailed model for the catalytic reaction mechanism of HMG-CoA lyase based on the examination of previously reported product complexes of other DRE-TIM metallolyases and induced fit substrate docking studies conducted using the crystal structure of human HMG-CoA lyase (reported in the accompanying paper by Fu, et al. (2006) J. Biol. Chem. 281, 7526-7532). Our model is consistent with extensive mutagenesis results and

  12. Crystal structures of two bacterial 3-hydroxy-3-methylglutaryl-CoA lyases suggest a common catalytic mechanism among a family of TIM barrel metalloenzymes cleaving carbon-carbon bonds.

    PubMed

    Forouhar, Farhad; Hussain, Munif; Farid, Ramy; Benach, Jordi; Abashidze, Mariam; Edstrom, William C; Vorobiev, Sergey M; Xiao, Rong; Acton, Thomas B; Fu, Zhuji; Kim, Jung-Ja P; Miziorko, Henry M; Montelione, Gaetano T; Hunt, John F

    2006-03-17

    The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase catalyzes the terminal steps in ketone body generation and leucine degradation. Mutations in this enzyme cause a human autosomal recessive disorder called primary metabolic aciduria, which typically kills victims because of an inability to tolerate hypoglycemia. Here we present crystal structures of the HMG-CoA lyases from Bacillus subtilis and Brucella melitensis at 2.7 and 2.3 A resolution, respectively. These enzymes share greater than 45% sequence identity with the human orthologue. Although the enzyme has the anticipated triose-phosphate isomerase (TIM) barrel fold, the catalytic center contains a divalent cation-binding site formed by a cluster of invariant residues that cap the core of the barrel, contrary to the predictions of homology models. Surprisingly, the residues forming this cation-binding site and most of their interaction partners are shared with three other TIM barrel enzymes that catalyze diverse carbon-carbon bond cleavage reactions believed to proceed through enolate intermediates (4-hydroxy-2-ketovalerate aldolase, 2-isopropylmalate synthase, and transcarboxylase 5S). We propose the name "DRE-TIM metallolyases" for this newly identified enzyme family likely to employ a common catalytic reaction mechanism involving an invariant Asp-Arg-Glu (DRE) triplet. The Asp ligates the divalent cation, while the Arg probably stabilizes charge accumulation in the enolate intermediate, and the Glu maintains the precise structural alignment of the Asp and Arg. We propose a detailed model for the catalytic reaction mechanism of HMG-CoA lyase based on the examination of previously reported product complexes of other DRE-TIM metallolyases and induced fit substrate docking studies conducted using the crystal structure of human HMG-CoA lyase (reported in the accompanying paper by Fu, et al. (2006) J. Biol. Chem. 281, 7526-7532). Our model is consistent with extensive mutagenesis results and can

  13. 8 CFR 1280.6 - Bond to obtain clearance; form.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 8 Aliens and Nationality 1 2010-01-01 2010-01-01 false Bond to obtain clearance; form. 1280.6... IMMIGRATION REGULATIONS IMPOSITION AND COLLECTION OF FINES § 1280.6 Bond to obtain clearance; form. A bond to obtain clearance of a vessel or aircraft under section 231, 237, 239, 243, 251, 253, 254, 255, 256,...

  14. 8 CFR 280.6 - Bond to obtain clearance; form.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 8 Aliens and Nationality 1 2010-01-01 2010-01-01 false Bond to obtain clearance; form. 280.6 Section 280.6 Aliens and Nationality DEPARTMENT OF HOMELAND SECURITY IMMIGRATION REGULATIONS IMPOSITION AND COLLECTION OF FINES § 280.6 Bond to obtain clearance; form. A bond to obtain clearance of a...

  15. 46 CFR Sec. 6 - Surety and form of bond.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 8 2010-10-01 2010-10-01 false Surety and form of bond. Sec. 6 Section 6 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION A-NATIONAL SHIPPING AUTHORITY BONDING OF SHIP'S... published by the U.S. Treasury Department. The form of bond required by the National Shipping Authority to...

  16. 27 CFR 28.64 - Bond, Form 2737.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... provided in § 28.51, a continuing bond on Form 2737 (5110.67). The bond shall be executed in a penal sum... wines which may remain unaccounted for at any one time: Provided, That the maximum penal sum of such bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. Distilled...

  17. Carbon-Carbon Piston Architectures

    NASA Technical Reports Server (NTRS)

    Rivers, H. Kevin (Inventor); Ransone, Philip O. (Inventor); Northam, G. Burton (Inventor); Schwind, Francis A. (Inventor)

    1999-01-01

    An improved structure for carbon-carbon composite piston architectures consists of replacing the knitted fiber, three-dimensional piston preform architecture described in U.S. Pat. No. 4.909,133 (Taylor et al.) with a two-dimensional lay-up or molding of carbon fiber fabric or tape. Initially. the carbon fabric or tape layers are prepregged with carbonaceous organic resins and/or pitches and are laid up or molded about a mandrel. to form a carbon-fiber reinforced organic-matrix composite part shaped like a "U" channel, a "T"-bar. or a combination of the two. The molded carbon-fiber reinforced organic-matrix composite part is then pyrolized in an inert atmosphere, to convert the organic matrix materials to carbon. At this point, cylindrical piston blanks are cored from the "U" channel, "T"-bar, or combination part. These blanks are then densified by reimpregnation with resins or pitches which are subsequently carbonized. Densification is also be accomplished by direct infiltration with carbon by vapor deposition processes. Once the desired density has been achieved, the piston billets are machined to final piston dimensions; coated with oxidation sealants; and/or coated with a catalyst. When compared to conventional steel or aluminum-alloy pistons, the use of carbon-carbon composite pistons reduces the overall weight of the engine; allows for operation at higher temperatures without a loss of strength; allows for quieter operation; reduces the heat loss; and reduces the level of hydrocarbon emissions.

  18. Carbon-carbon cylinder block

    NASA Technical Reports Server (NTRS)

    Ransone, Philip O. (Inventor)

    1998-01-01

    A lightweight cylinder block composed of carbon-carbon is disclosed. The use of carbon-carbon over conventional materials, such as cast iron or aluminum, reduces the weight of the cylinder block and improves thermal efficiency of the internal combustion reciprocating engine. Due to the negligible coefficient of thermal expansion and unique strength at elevated temperatures of carbon-carbon, the piston-to-cylinder wall clearance can be small, especially when the carbon-carbon cylinder block is used in conjunction with a carbon-carbon piston. Use of the carbon-carbon cylinder block has the effect of reducing the weight of other reciprocating engine components allowing the piston to run at higher speeds and improving specific engine performance.

  19. Carbon-carbon cylinder block

    NASA Technical Reports Server (NTRS)

    Ransone, Philip O. (Inventor)

    1995-01-01

    A lightweight cylinder block composed of carbon-carbon is disclosed. The use of carbon-carbon over conventional materials, such as cast iron or aluminum, reduces the weight of the cylinder block and improves thermal efficiency of the internal combustion reciprocating engine. Due to the negligible coefficient of thermal expansion and unique strength at elevated temperatures of carbon-carbon, the piston-to-cylinder wall clearance can be small, especially when the carbon-carbon cylinder block is used in conjunction with a carbon-carbon piston. Use of the carbon-carbon cylinder has the effect of reducing the weight of other reciprocating engine components allowing the piston to run at higher speeds and improving specific engine performance.

  20. Carbon-carbon piston development

    NASA Technical Reports Server (NTRS)

    Gorton, Mark P.

    1994-01-01

    A new piston concept, made of carbon-carbon refractory-composite material, has been developed that overcomes a number of the shortcomings of aluminum pistons. Carbon-carbon material, developed in the early 1960's, is lighter in weight than aluminum, has higher strength and stiffness than aluminum and maintains these properties at temperatures over 2500 F. In addition, carbon-carbon material has a low coefficient of thermal expansion and excellent resistance to thermal shock. An effort, called the Advanced Carbon-Carbon Piston Program was started in 1986 to develop and test carbon-carbon pistons for use in spark ignition engines. The carbon-carbon pistons were designed to be replacements for existing aluminum pistons, using standard piston pin assemblies and using standard rings. Carbon-carbon pistons can potentially enable engines to be more reliable, more efficient and have greater power output. By utilizing the unique characteristics of carbon-carbon material a piston can: (1) have greater resistance to structural damage caused by overheating, lean air-fuel mixture conditions and detonation; (2) be designed to be lighter than an aluminum piston thus, reducing the reciprocating mass of an engine, and (3) be operated in a higher combustion temperature environment without failure.

  1. 27 CFR 28.59 - Bond, Form 5120.36.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    .... 1379, 1380; 26 U.S.C. 5354, 5362, as amended by T.D. ATF-299, 55 FR 25033, June 19, 1990; T.D. TTB-8....36. Where the operations of a bonded wine cellar are covered by bond, Form 5120.36, as provided in...

  2. 27 CFR 26.68 - Bond, Form 2898-Beer.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ..., DEPARTMENT OF THE TREASURY LIQUORS LIQUORS AND ARTICLES FROM PUERTO RICO AND THE VIRGIN ISLANDS Taxpayment of Liquors and Articles in Puerto Rico Bonds § 26.68 Bond, Form 2898—Beer. Where a brewer intends to withdraw... Puerto Rico on computation, but before payment, of the tax imposed by 26 U.S.C. 7652(a), equal to the tax...

  3. 27 CFR 28.64 - Bond, Form 2737.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... provided in § 28.51, a continuing bond on Form 2737 (5110.67). The bond shall be executed in a penal sum sufficient to cover the tax at the rates prescribed by law on the maximum quantity of distilled spirits and wines which may remain unaccounted for at any one time: Provided, That the maximum penal sum of...

  4. 27 CFR 28.64 - Bond, Form 2737.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... provided in § 28.51, a continuing bond on Form 2737 (5110.67). The bond shall be executed in a penal sum sufficient to cover the tax at the rates prescribed by law on the maximum quantity of distilled spirits and wines which may remain unaccounted for at any one time: Provided, That the maximum penal sum of...

  5. 27 CFR 28.64 - Bond, Form 2737.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... provided in § 28.51, a continuing bond on Form 2737 (5110.67). The bond shall be executed in a penal sum sufficient to cover the tax at the rates prescribed by law on the maximum quantity of distilled spirits and wines which may remain unaccounted for at any one time: Provided, That the maximum penal sum of...

  6. 27 CFR 28.64 - Bond, Form 2737.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... provided in § 28.51, a continuing bond on Form 2737 (5110.67). The bond shall be executed in a penal sum sufficient to cover the tax at the rates prescribed by law on the maximum quantity of distilled spirits and wines which may remain unaccounted for at any one time: Provided, That the maximum penal sum of...

  7. Carbon-Carbon Piston Architectures

    NASA Technical Reports Server (NTRS)

    Rivers, H. Kevin (Inventor); Ransone, Philip O. (Inventor); Northam, G. Burton (Inventor); Schwind, Francis A. (Inventor)

    2000-01-01

    An improved structure for carbon-carbon composite piston architectures is disclosed. The improvement consists of replacing the knitted fiber, three-dimensional piston preform architecture described in U.S. Pat.No. 4,909,133 (Taylor et al.) with a two-dimensional lay-up or molding of carbon fiber fabric or tape. Initially, the carbon fabric of tape layers are prepregged with carbonaceous organic resins and/or pitches and are laid up or molded about a mandrel, to form a carbon-fiber reinforced organic-matrix composite part shaped like a "U" channel, a "T"-bar, or a combination of the two. The molded carbon-fiber reinforced organic-matrix composite part is then pyrolized in an inert atmosphere, to convert the organic matrix materials to carbon. At this point, cylindrical piston blanks are cored from the "U"-channel, "T"-bar, or combination part. These blanks are then densified by reimpregnation with resins or pitches which are subsequently carbonized. Densification is also accomplished by direct infiltration with carbon by vapor deposition processes. Once the desired density has been achieved, the piston billets are machined to final piston dimensions; coated with oxidation sealants; and/or coated with a catalyst. When compared to conventional steel or aluminum alloy pistons, the use of carbon-carbon composite pistons reduces the overall weight of the engine; allows for operation at higher temperatures without a loss of strength; allows for quieter operation; reduces the heat loss; and reduces the level of hydrocarbon emissions.

  8. Carbon K-shell electron energy loss spectra of 1- and 2-butenes, trans-1,3-butadiene, and perfluoro-2-butene. Carbon-carbon bond lengths from continuum shape resonances

    NASA Astrophysics Data System (ADS)

    Hitchcock, A. P.; Beaulieu, S.; Steel, T.; Stöhr, J.; Sette, F.

    1984-05-01

    Electron energy loss spectra of 1-butene, cis-2-butene, trans-2-butene, trans-1,3-butadiene, and perfluoro-2-butene in the region of carbon K-shell (C 1s) excitation and ionization have been recorded under dipole-dominated inelastic electron scattering conditions. The features observed below the C 1s I.P. in the spectra of the butenes and butadiene are assigned to promotions of C 1s electrons to unoccupied valence (π*) and Rydberg orbitals while broad features observed above the edge are assigned to σ(C-C) and σ(C-C) shape resonances. These spectra, along with carbon K-shell spectra of other hydrocarbons, are used to demonstrate that there is a quantitative relationship between carbon-carbon bond lengths and the location of σ shape resonances relative to the C 1s ionization threshold (I.P.). The C 1s spectrum of perfluoro-2-butene demonstrates dramatic potential barrier effects, namely suppression of Rydberg transitions and strong enhancement of σ(C-C) and σ(C-F) shape resonances in the region of the C 1s ionization threshold.

  9. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

    Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

  10. Response of carbon-carbon composites to challenging environments

    NASA Technical Reports Server (NTRS)

    Maahs, Howard G.; Ohlhorst, Craig W.; Barrett, David M.; Ransone, Philip O.; Sawyer, J. Wayne

    1988-01-01

    This paper presents results from material performance evaluations of oxidation-resistant carbon-carbon composites intended for multiuse aerospace applications, which cover the effects of the following environmental parameters: the oxidizing nature of the environments (including both high and low oxygen partial pressures), high temperatures, moisture, cyclic temperature service, and foreign-object impact. Results are presented for the carbon-carbon material currently in use as the thermal-protection-system material on Space Shuttle, as well as for newer and more advanced structural forms of carbon-carbon composites.

  11. Photoinduced, Copper-Catalyzed Carbon-Carbon Bond Formation with Alkyl Electrophiles: Cyanation of Unactivated Secondary Alkyl Chlorides at Room Temperature.

    PubMed

    Ratani, Tanvi S; Bachman, Shoshana; Fu, Gregory C; Peters, Jonas C

    2015-11-04

    We have recently reported that, in the presence of light and a copper catalyst, nitrogen nucleophiles such as carbazoles and primary amides undergo C-N coupling with alkyl halides under mild conditions. In the present study, we establish that photoinduced, copper-catalyzed alkylation can also be applied to C-C bond formation, specifically, that the cyanation of unactivated secondary alkyl chlorides can be achieved at room temperature to afford nitriles, an important class of target molecules. Thus, in the presence of an inexpensive copper catalyst (CuI; no ligand coadditive) and a readily available light source (UVC compact fluorescent light bulb), a wide array of alkyl halides undergo cyanation in good yield. Our initial mechanistic studies are consistent with the hypothesis that an excited state of [Cu(CN)2](-) may play a role, via single electron transfer, in this process. This investigation provides a rare example of a transition metal-catalyzed cyanation of an alkyl halide, as well as the first illustrations of photoinduced, copper-catalyzed alkylation with either a carbon nucleophile or a secondary alkyl chloride.

  12. Thermal bonding of polyimide to form sealed microchannels

    NASA Astrophysics Data System (ADS)

    Mekaru, Harutaka

    2017-06-01

    Polyimide has high stability, so it is attractive for use in disposable microfluidic chips. Also, it has high resistance to soft X-ray irradiation. However, its high stability makes processing polyimide difficult. In particular, sealed microchannels are difficult to fabricate; additives are usually required. Here, a technique for sealing microchannels by thermal bonding using ordinary polyimide without any special functionalities is developed. First, as a guide to form sealed microchannels in polyimide microfluidic chips, optimum bonding conditions are determined by measuring bonding strength through tensile testing. Trench structures are formed by laser ablation on the surface of a polyimide substrate, and then the polyimide substrate is bonded thermally with a polyimide film under optimal bonding conditions. The water-tightness of the resulting chip is checked by feeding a liquid into the sealed microchannels. The bonding conditions obtained in the tensile test form sealed microchannels on the polyimide microfluidic chip. Using our technique for fabricating a polyimide chip, it will be possible to easily observe microstructures in a cell containing water in a soft X-ray microscope.

  13. Scope and limitations of aliphatic Friedel-Crafts alkylations. Lewis acid catalyzed addition reactions of alkyl chlorides to carbon-carbon double bonds

    SciTech Connect

    Mayr, H.; Striepe, W.

    1983-04-22

    Lewis acid catalyzed addition reactions of alkyl halides with unsaturated hydrocarbons have been studied. 1:1 addition products are formed if the addends dissociate faster than the corresponding products; otherwise, polymerization takes place. For reaction conditions under which these compounds exist mainly undissociated, solvolysis constants of model compounds can be used to predict the outcome of any such addition reactions if systems with considerable steric hindrance are excluded.

  14. Thermographic Inspection Of Superplastically Formed Diffusion Bonded Titanium Panels

    NASA Astrophysics Data System (ADS)

    Haavig, David L.; King, Daniel C.

    1988-01-01

    Infrared thermographic nondestructive inspection of superplastically formed diffusion bonded (SPF/DB) titanium structures is discussed. Nondestructive testing (NDT) of the structures produced by this recently developed method is vital for construction of modern fighter aircraft. Forming and bonding parameters can be optimized by proper interpretation of NDT results. Currently, ultrasonic inspection is used for NDT on these parts. In an effort to reduce cost and inspection time required by ultrasonic testing, a thermographic investigation of panel response to rapid heating was undertaken. Panels were uniformly illuminated for a duration of up to four seconds by high intensity lamps. Infrared images of temperature variation due to panel thickness were observed. Correlation of thermograms with ultrasonic and destructive investigations indicate that lack of bonding and panel formations can easily be observed. We have demonstrated that thermographic inspection provides an equally sensitive and lower cost alternative to ultrasonic inspection. Finally, thermographic inspection facilities for large scale inspection are suggested.

  15. Mullite/Mo interfaces formed by Intrusion bonding

    SciTech Connect

    Bartolome, Jose F.; Diaz, Marcos; Moya, Jose S.; Saiz, Eduardo; Tomsia, Antoni P.

    2003-04-30

    The microstructure and strength of Mo/mullite interfaces formed by diffusion bonding at 1650 C has been analyzed. Interfacial metal-ceramic interlocking contributes to flexural strength of approx. 140 MPa as measured by 3 point bending. Saturation of mullite with MoO2 does not affect the interfacial strength.

  16. 19 CFR 113.14 - Approved form of bond inadequate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 1 2010-04-01 2010-04-01 false Approved form of bond inadequate. 113.14 Section 113.14 Customs Duties U.S. CUSTOMS AND BORDER PROTECTION, DEPARTMENT OF HOMELAND SECURITY; DEPARTMENT... inadequate. If the port director believes that none of the conditions contained in subpart G of this part...

  17. Liner protected carbon-carbon heat pipe concept

    NASA Astrophysics Data System (ADS)

    Rovang, Richard D.; Hunt, Maribeth E.

    1992-01-01

    A lightweight, high performance radiator concept using carbon-carbon heat pipes is being developed to support space nuclear power applications, specifically the SP-100 system. Carbon-carbon has been selected as an outer structural tube member because of its high temperature and strength characteristics; however, this material must be protected from the potassium heat pipe working fluid. A metallic liner approach is being taken to provide this fluid barrier. Feasibility issues associated with this approach include materials compatibility, fabricastion of the thin-walled liner, bonding the liner to the carbon-carbon tube, mismatch of coefficient of thermal expansion (CTE), carbon diffusion, and end cap closures. To resolve these issues, a series of test coupons have been fabricated and tested, assessing various liner materials, braze alloys, and substrate precursors. These tests will lead to a final heat pipe architecture, material selection, and component assembly.

  18. Catalytic σ-Bond Metathesis

    NASA Astrophysics Data System (ADS)

    Reznichenko, Alexander L.; Hultzsch, Kai C.

    This account summarizes information on recently reported applications of organo-rare-earth metal complexes in various catalytic transformations of small molecules. The σ-bond metathesis at d0rare-earth metal centers plays a pivotal role in carbon-carbon and carbon-heteroatom bond forming processes. Relevant mechanistic details are discussed and the focus of the review lies in practical applications of organo-rare-earth metal complexes.

  19. Vertical density profile and internal bond strength of wet-formed particleboard bonded with cellulose nanofibrils

    Treesearch

    John F. Hunt; Weiqi Leng; Mehdi Tajvidi

    2017-01-01

    In this study, the effects of cellulose nanofibrils (CNFs) ratio, press program, particle size, and density on the vertical density profile (VDP) and internal bond (IB) strength of the wet-formed particleboard were investigated. Results revealed that the VDP was significantly influenced by the press program. Pressing using a constant pressure (CP) press program...

  20. Wafer bonded virtual substrate and method for forming the same

    DOEpatents

    Atwater, Jr., Harry A.; Zahler, James M.; Morral, Anna Fontcuberta i

    2007-07-03

    A method of forming a virtual substrate comprised of an optoelectronic device substrate and handle substrate comprises the steps of initiating bonding of the device substrate to the handle substrate, improving or increasing the mechanical strength of the device and handle substrates, and thinning the device substrate to leave a single-crystal film on the virtual substrate such as by exfoliation of a device film from the device substrate. The handle substrate is typically Si or other inexpensive common substrate material, while the optoelectronic device substrate is formed of more expensive and specialized electro-optic material. Using the methodology of the invention a wide variety of thin film electro-optic materials of high quality can be bonded to inexpensive substrates which serve as the mechanical support for an optoelectronic device layer fabricated in the thin film electro-optic material.

  1. Female chacma baboons form strong, equitable, and enduring social bonds

    PubMed Central

    Beehner, Jacinta C.; Bergman, Thore J.; Crockford, Catherine; Engh, Anne L.; Moscovice, Liza R.; Wittig, Roman M.; Seyfarth, Robert M.; Cheney, Dorothy L.

    2010-01-01

    Analyses of the pattern of associations, social interactions, coalitions, and aggression among chacma baboons (Papio hamadryas ursinus) in the Okavango Delta of Botswana over a 16-year period indicate that adult females form close, equitable, supportive, and enduring social relationships. They show strong and stable preferences for close kin, particularly their own mothers and daughters. Females also form strong attachments to unrelated females who are close to their own age and who are likely to be paternal half-sisters. Although absolute rates of aggression among kin are as high as rates of aggression among nonkin, females are more tolerant of close relatives than they are of others with whom they have comparable amounts of contact. These findings complement previous work which indicates that the strength of social bonds enhances the fitness of females in this population and support findings about the structure and function of social bonds in other primate groups. PMID:20976293

  2. Wafer bonded virtual substrate and method for forming the same

    NASA Technical Reports Server (NTRS)

    Atwater, Jr., Harry A. (Inventor); Zahler, James M. (Inventor); Morral, Anna Fontcuberta i (Inventor)

    2007-01-01

    A method of forming a virtual substrate comprised of an optoelectronic device substrate and handle substrate comprises the steps of initiating bonding of the device substrate to the handle substrate, improving or increasing the mechanical strength of the device and handle substrates, and thinning the device substrate to leave a single-crystal film on the virtual substrate such as by exfoliation of a device film from the device substrate. The handle substrate is typically Si or other inexpensive common substrate material, while the optoelectronic device substrate is formed of more expensive and specialized electro-optic material. Using the methodology of the invention a wide variety of thin film electro-optic materials of high quality can be bonded to inexpensive substrates which serve as the mechanical support for an optoelectronic device layer fabricated in the thin film electro-optic material.

  3. 27 CFR 26.66 - Bond, TTB Form 5110.50-Distilled spirits.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS LIQUORS AND ARTICLES FROM PUERTO RICO AND THE VIRGIN ISLANDS Taxpayment of Liquors and Articles in Puerto Rico Bonds § 26.66 Bond, TTB Form 5110.50—Distilled... bonded warehouse and/or bonded processing room and/or rectifying plant to be covered by the bond, and the...

  4. 27 CFR 26.66 - Bond, TTB Form 5110.50-Distilled spirits.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... TRADE BUREAU, DEPARTMENT OF THE TREASURY ALCOHOL LIQUORS AND ARTICLES FROM PUERTO RICO AND THE VIRGIN ISLANDS Taxpayment of Liquors and Articles in Puerto Rico Bonds § 26.66 Bond, TTB Form 5110.50—Distilled... bonded warehouse and/or bonded processing room and/or rectifying plant to be covered by the bond, and the...

  5. 27 CFR 26.66 - Bond, TTB Form 5110.50-Distilled spirits.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... TRADE BUREAU, DEPARTMENT OF THE TREASURY ALCOHOL LIQUORS AND ARTICLES FROM PUERTO RICO AND THE VIRGIN ISLANDS Taxpayment of Liquors and Articles in Puerto Rico Bonds § 26.66 Bond, TTB Form 5110.50—Distilled... bonded warehouse and/or bonded processing room and/or rectifying plant to be covered by the bond, and the...

  6. Elastic constants for superplastically formed/diffusion-bonded sandwich structures

    NASA Technical Reports Server (NTRS)

    Ko, W. L.

    1979-01-01

    Formulae and the associated graphs are presented for contrasting the effective elastic constants for a superplastically formed/diffusion-bonded (SPF/DB) corrugated sandwich core and a honeycomb sandwich core. The results used in the comparison of the structural properties of the two types of sandwich cores are under conditions of equal sandwich density. It was found that the stiffness in the thickness direction of the optimum SPF/DB corrugated core (i.e., triangular truss core) was lower than that of the honeycomb core, and that the former had higher transverse shear stiffness than the latter.

  7. Leaching behavior of phosphate-bonded ceramic waste forms

    SciTech Connect

    Singh, D.; Wagh, A.S.; Jeong, S.Y.; Dorf, M.

    1996-04-01

    Over the last few years, Argonne National Laboratory has been developing room-temperature-setting chemically bonded phosphate ceramics for solidifying and stabilizing low-level mixed wastes. This technology is crucial for stabilizing waste streams that contain volatile species and off-gas secondary waste streams generated by high-temperature treatment of such wastes. We have developed a magnesium phosphate ceramic to treat mixed wastes such as ash, salts, and cement sludges. Waste forms of surrogate waste streams were fabricated by acid-base reactions between the mixtures of magnesium oxide powders and the wastes, and phosphoric acid or acid phosphate solutions. Dense and hard ceramic waste forms are produced in this process. The principal advantage of this technology is that the contaminants are immobilized by both chemical stabilization and subsequent microencapsulation of the reaction products. This paper reports the results of durability studies conducted on waste forms made with ash waste streams spiked with hazardous and radioactive surrogates. Standard leaching tests such as ANS 16.1 and TCLP were conducted on the final waste forms. Fates of the contaminants in the final waste forms were established by electron microscopy. In addition, stability of the waste forms in aqueous environments was evaluated with long-term water-immersion tests.

  8. 46 CFR Appendix A to Subpart C of... - Ocean Transportation Intermediary (OTI) Bond Form [Form 48

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 9 2011-10-01 2011-10-01 false Ocean Transportation Intermediary (OTI) Bond Form A Appendix A to Subpart C of Part 515 Shipping FEDERAL MARITIME COMMISSION REGULATIONS AFFECTING OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN...

  9. 46 CFR Appendix A to Subpart C of... - Ocean Transportation Intermediary (OTI) Bond Form [Form 48

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 9 2013-10-01 2013-10-01 false Ocean Transportation Intermediary (OTI) Bond Form A Appendix A to Subpart C of Part 515 Shipping FEDERAL MARITIME COMMISSION REGULATIONS AFFECTING OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN...

  10. 46 CFR Appendix A to Subpart C of... - Ocean Transportation Intermediary (OTI) Bond Form [Form 48

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 9 2012-10-01 2012-10-01 false Ocean Transportation Intermediary (OTI) Bond Form A Appendix A to Subpart C of Part 515 Shipping FEDERAL MARITIME COMMISSION REGULATIONS AFFECTING OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN...

  11. 46 CFR Appendix A to Subpart C of... - Ocean Transportation Intermediary (OTI) Bond Form [Form 48

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 9 2010-10-01 2010-10-01 false Ocean Transportation Intermediary (OTI) Bond Form A Appendix A to Subpart C of Part 515 Shipping FEDERAL MARITIME COMMISSION REGULATIONS AFFECTING OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN...

  12. 46 CFR Appendix A to Subpart C of... - Ocean Transportation Intermediary (OTI) Bond Form [Form 48

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 9 2014-10-01 2014-10-01 false Ocean Transportation Intermediary (OTI) Bond Form A Appendix A to Subpart C of Part 515 Shipping FEDERAL MARITIME COMMISSION REGULATIONS AFFECTING OCEAN... Intermediaries Pt. 515, Subpart C, App. A Appendix A to Subpart C of Part 515—Ocean Transportation...

  13. Lightweight Carbon-Carbon High-Temperature Space Radiator

    NASA Technical Reports Server (NTRS)

    Miller, W.O.; Shih, Wei

    2008-01-01

    A document summarizes the development of a carbon-carbon composite radiator for dissipating waste heat from a spacecraft nuclear reactor. The radiator is to be bonded to metal heat pipes and to operate in conjunction with them at a temperature approximately between 500 and 1,000 K. A goal of this development is to reduce the average areal mass density of a radiator to about 2 kg/m(exp 2) from the current value of approximately 10 kg/m(exp 2) characteristic of spacecraft radiators made largely of metals. Accomplishments thus far include: (1) bonding of metal tubes to carbon-carbon material by a carbonization process that includes heating to a temperature of 620 C; (2) verification of the thermal and mechanical integrity of the bonds through pressure-cycling, axial-shear, and bending tests; and (3) construction and testing of two prototype heat-pipe/carbon-carbon-radiator units having different radiator areas, numbers of heat pipes, and areal mass densities. On the basis of the results achieved thus far, it is estimated that optimization of design could yield an areal mass density of 2.2 kg/m (exp 2) close to the goal of 2 kg/m(exp 2).

  14. 31 CFR 351.4 - In what form are Series EE savings bonds issued?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 31 Money and Finance: Treasury 2 2014-07-01 2014-07-01 false In what form are Series EE savings... SAVINGS BONDS, SERIES EE General Information § 351.4 In what form are Series EE savings bonds issued? Series EE savings bonds are issued in book-entry form. Effective January 1, 2012, Treasury...

  15. 31 CFR 351.4 - In what form are Series EE savings bonds issued?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false In what form are Series EE savings... SAVINGS BONDS, SERIES EE General Information § 351.4 In what form are Series EE savings bonds issued? Series EE savings bonds are issued in either book-entry or definitive form....

  16. 31 CFR 351.4 - In what form are Series EE savings bonds issued?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 31 Money and Finance:Treasury 2 2012-07-01 2012-07-01 false In what form are Series EE savings... SAVINGS BONDS, SERIES EE General Information § 351.4 In what form are Series EE savings bonds issued? Series EE savings bonds are issued in book-entry form. Effective January 1, 2012, Treasury...

  17. 31 CFR 351.4 - In what form are Series EE savings bonds issued?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 31 Money and Finance:Treasury 2 2013-07-01 2013-07-01 false In what form are Series EE savings... SAVINGS BONDS, SERIES EE General Information § 351.4 In what form are Series EE savings bonds issued? Series EE savings bonds are issued in book-entry form. Effective January 1, 2012, Treasury...

  18. Radical-based C-C Bond-Forming Processes Enabled by the Photoexcitation of 4-Alkyl-1,4-dihydropyridines.

    PubMed

    Buzzetti, Luca; Prieto, Alexis; Raha Roy, Sudipta; Melchiorre, Paolo

    2017-10-06

    We report herein that 4-alkyl-1,4-dihydropyridines (alkyl-DHPs) can directly reach an electronically excited state upon light absorption and trigger the generation of C(sp3)-centered radicals without the need for an external photocatalyst. Selective excitation with a violet-light-emitting diode turns alkyl-DHPs into strong reducing agents that can activate reagents via single-electron transfer manifolds while undergoing a homolytic cleavage to generate radicals. We used this photochemical dual-reactivity profile to trigger radical-based carbon-carbon bond-forming processes, including nickel catalyzed cross-coupling reactions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Basic character of rare earth metal alkoxides. Utilization in catalytic C-C bond-forming reactions and catalytic asymmetric nitroaldol reactions

    SciTech Connect

    Sasai, H.; Suzuki, T.; Arai, S.

    1992-05-20

    In a recent paper, the authors reported that Zr(O-t-Bu){sub 4} was an efficient and convenient basic reagent in organic synthesis. However, all reactions examined were performed with stoichiometric quantities of the reagent. The authors envisioned that rare earth metal alkoxides would be stronger bases than group 4 metal alkoxides due to the lower ionization potential (ca. 5.4-6.4 eV) and the lower electronegativity (1.1-1.3) of rare earth elements; thus, the catalytic use of rare earth metal alkoxides in organic synthesis was expected. Although a variety of rare earth metal alkoxides have been prepared for the last three decades, to the authors knowledge, there have been few reports concerning the basicity of rare earth metal alkoxides. Herein, the authors report several carbon-carbon bond-forming reactions catalyzed by rare earth metal alkoxides and their application to a catalytic asymmetric nitroaldol reaction.

  20. Highly efficient C-C bond-forming reactions in aqueous media catalyzed by monomeric vanadate species in an apatite framework.

    PubMed

    Hara, Takayoshi; Kanai, Satoko; Mori, Kohsuke; Mizugaki, Tomoo; Ebitani, Kohki; Jitsukawa, Koichiro; Kaneda, Kiyotomi

    2006-09-15

    A calcium vanadate apatite (VAp), in which PO4(3-) of hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is completely substituted by VO4(3-) in the apatite framework, was synthesized. Physicochemical analysis of the VAp reveals the presence of isolated VO4 tetrahedron units with a pentavalent oxidation state. The VAp acts as a high-performance heterogeneous base catalyst for various carbon-carbon bond-forming reactions such as Michael and aldol reactions in aqueous media and the H-D exchange reactions using deuterium oxide. For example, a 200-mmol-scale Michael reaction under triphasic conditions proceeded rapidly, with an extremely high turnover number of up to 260 400 and an excellent turnover frequency of 48 s(-1). No vanadium leaching was detected during the above reactions, and the catalyst was readily recycled with no loss of activity.

  1. 27 CFR 26.68 - Bond, Form 2898-Beer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... subpart, on all beer so withdrawn. The bond shall be executed in a penal sum not less than the amount of unpaid tax which, at any one time, is chargeable against the bond: Provided, That the penal sum of such bond shall not exceed $500,000, but in no case shall the penal sum be less than $1,000. (Aug. 16, 1954...

  2. 29 CFR 2580.412-10 - Individual or schedule or blanket form of bonds.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... ADMINISTRATION, DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-10 Individual or schedule or blanket.... Bonding, to the extent required, of persons indirectly employed, or otherwise delegated, to...

  3. Fabrication and testing of carbon-carbon grids for ion optics

    NASA Technical Reports Server (NTRS)

    Garner, Charles E.; Brophy, John R.

    1992-01-01

    Ion optics measuring 16.5 cm in diameter and 1.0 mm in thickness were fabricated from carbon-carbon composites that were woven from a high-tensile-modulus carbon fiber. Plate flatness varied by less than 0.05 mm. Several methods were investigated for forming ion-extraction apertures in the carbon-carbon plates, including laser machining, mechanical drilling, and conventional electric discharge machining. Tests conducted using a quartz dilatometer indicated that the coefficient of thermal expansion of the carbon-carbon plates varied between -0.51 to -1.8 x 10 exp -6/degree C at plate temperatures between 173-773 K. Sputter-erosion experiments indicate that carbon-carbon erodes at a rate approximately 25 percent below molybdenum under the same conditions. These material properties indicate that carbon-carbon may be superior to molybdenum for use as ion optics electrodes for ion engines.

  4. Method of making carbon-carbon composites

    DOEpatents

    Engle, Glen B.

    1993-01-01

    A process for making 2D and 3D carbon-carbon composites having a combined high crystallinity, high strength, high modulus and high thermal and electrical conductivity. High-modulus/high-strength mesophase derived carbon fibers are woven into a suitable cloth. Layers of this easily graphitizible woven cloth are infiltrated with carbon material to form green composites. The carbonized composite is then impregnated several times with pitch by covering the composite with hot pitch under pressure. The composites are given a heat treatment between each impregnant step to crack up the infiltrated carbon and allow additional pitch to enter the microstructure during the next impregnation cycle. The impregnated composites are then given a final heat treatment in the range 2500.degree. to 3100.degree. C. to fully graphitize the fibers and the matrix carbon. The composites are then infiltrated with pyrolytic carbon by chemical vapor deposition in the range 1000.degree. C. to 1300.degree. C. at a reduced. pressure.

  5. IC Engine Applications of Carbon-Carbon

    NASA Technical Reports Server (NTRS)

    Northam, G. Burton; Rivers, H. Kevin

    2000-01-01

    Many of the properties of carbon-carbon make it an ideal material for reciprocating materials of intermittent combustion (IC) engines. Recent diesel engine tests, shown herein, indicate that the thermal and mechanical properties of carbon-carbon are adequate for piston applications, However, reducing the manufacturing costs and providing long term oxidation protection are still issues that need to be addressed.

  6. 31 CFR 359.4 - In what form are Series I savings bonds issued?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false In what form are Series I savings bonds issued? 359.4 Section 359.4 Money and Finance: Treasury Regulations Relating to Money and Finance... SAVINGS BONDS, SERIES I General Information § 359.4 In what form are Series I savings bonds issued?...

  7. 31 CFR 359.4 - In what form are Series I savings bonds issued?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 31 Money and Finance:Treasury 2 2012-07-01 2012-07-01 false In what form are Series I savings... SAVINGS BONDS, SERIES I General Information § 359.4 In what form are Series I savings bonds issued? Series... issuance of definitive Series I savings bonds....

  8. 31 CFR 359.4 - In what form are Series I savings bonds issued?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false In what form are Series I savings bonds issued? 359.4 Section 359.4 Money and Finance: Treasury Regulations Relating to Money and Finance... SAVINGS BONDS, SERIES I General Information § 359.4 In what form are Series I savings bonds issued?...

  9. 31 CFR 359.4 - In what form are Series I savings bonds issued?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 31 Money and Finance: Treasury 2 2014-07-01 2014-07-01 false In what form are Series I savings... SAVINGS BONDS, SERIES I General Information § 359.4 In what form are Series I savings bonds issued? Series... issuance of definitive Series I savings bonds....

  10. 31 CFR 359.4 - In what form are Series I savings bonds issued?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 31 Money and Finance:Treasury 2 2013-07-01 2013-07-01 false In what form are Series I savings... SAVINGS BONDS, SERIES I General Information § 359.4 In what form are Series I savings bonds issued? Series... issuance of definitive Series I savings bonds....

  11. 25 CFR 166.602 - What form of bonds will the BIA accept?

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 25 Indians 1 2011-04-01 2011-04-01 false What form of bonds will the BIA accept? 166.602 Section 166.602 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER GRAZING PERMITS Bonding and Insurance Requirements § 166.602 What form of bonds will the BIA accept? (a) We will...

  12. Torsion Testing of Diffusion Bonded LIGA Formed Nickel

    SciTech Connect

    Buchheit, T.E.; Christenson, T.R.; Schmale, D.T.

    1999-01-27

    A test technique has been devised which is suitable for the testing of the bond strength of batch diffusion bonded LIGA or DXRL defined structures. The method uses a torsion tester constructed with the aid of LIGA fabrication and distributed torsion specimens which also make use of the high aspect ratio nature of DXRL based processing. Measurements reveal achieved bond strengths of 130MPa between electroplated nickel with a bond temperature of 450 C at 7 ksi pressure which is a sufficiently low temperature to avoid mechanical strength degradation.

  13. 30 CFR 800.12 - Form of the performance bond.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 800.12 Mineral Resources OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT, DEPARTMENT OF THE INTERIOR BONDING AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS BOND AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS UNDER REGULATORY PROGRAMS §...

  14. 30 CFR 800.12 - Form of the performance bond.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 800.12 Mineral Resources OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT, DEPARTMENT OF THE INTERIOR BONDING AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS BOND AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS UNDER REGULATORY PROGRAMS §...

  15. 30 CFR 800.12 - Form of the performance bond.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 800.12 Mineral Resources OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT, DEPARTMENT OF THE INTERIOR BONDING AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS BOND AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS UNDER REGULATORY PROGRAMS §...

  16. 30 CFR 800.12 - Form of the performance bond.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 800.12 Mineral Resources OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT, DEPARTMENT OF THE INTERIOR BONDING AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS BOND AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS UNDER REGULATORY PROGRAMS §...

  17. 30 CFR 800.12 - Form of the performance bond.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 800.12 Mineral Resources OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT, DEPARTMENT OF THE INTERIOR BONDING AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS BOND AND INSURANCE REQUIREMENTS FOR SURFACE COAL MINING AND RECLAMATION OPERATIONS UNDER REGULATORY PROGRAMS §...

  18. HETERODIMERIZATION OF PROPYLENE AND VINYLARENES: FUNCTIONAL GROUP COMPATIBILITY IN A HIGHLY EFFICIENT NI-CATALYZED CARBON-CARBON BOND-FORMING REACTION. (R826120)

    EPA Science Inventory

    Abstract

    Unlike heterodimerization reactions of ethylene and vinylarenes, no such synthetically useful reactions using propylene are known. We find that propylene reacts with various vinylarenes in the presence of catalytic amounts of [(allyl)NiBr]2, triphen...

  19. 46 CFR 308.528 - Surety Bond A, Form MA-308.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.528 Surety Bond A, Form MA-308. The Standard Form of Surety Bond A, Form MA-308, which may be obtained from the American War Risk Agency...

  20. 46 CFR 308.528 - Surety Bond A, Form MA-308.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.528 Surety Bond A, Form MA-308. The Standard Form of Surety Bond A, Form MA-308, which may be obtained from the American War Risk Agency...

  1. 46 CFR 308.528 - Surety Bond A, Form MA-308.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.528 Surety Bond A, Form MA-308. The Standard Form of Surety Bond A, Form MA-308, which may be obtained from the American War Risk Agency...

  2. 46 CFR 308.528 - Surety Bond A, Form MA-308.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.528 Surety Bond A, Form MA-308. The Standard Form of Surety Bond A, Form MA-308, which may be obtained from the American War Risk Agency...

  3. 27 CFR 26.66 - Bond, TTB Form 5110.50-Distilled spirits.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS LIQUORS AND ARTICLES FROM PUERTO RICO AND THE VIRGIN ISLANDS Taxpayment of Liquors and Articles in Puerto Rico Bonds § 26.66 Bond, TTB Form 5110.50—Distilled... Puerto Rican manufacture from bonded storage in Puerto Rico on computation, but before payment, of the...

  4. 48 CFR 28.106-1 - Bonds and bond related forms.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Agreement for a Miller Act Performance Bond (see 28.202(a)(4)). (i) SF 274, Reinsurance Agreement for a Miller Act Payment Bond (see 28.202(a)(4)). (j) SF 275, Reinsurance Agreement in Favor of the United... 91, Release of Personal Property from Escrow (see 28.203-5). ...

  5. 48 CFR 28.106-1 - Bonds and bond related forms.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Agreement for a Miller Act Performance Bond (see 28.202(a)(4)). (i) SF 274, Reinsurance Agreement for a Miller Act Payment Bond (see 28.202(a)(4)). (j) SF 275, Reinsurance Agreement in Favor of the United... 91, Release of Personal Property from Escrow (see 28.203-5). ...

  6. 48 CFR 28.106-1 - Bonds and bond related forms.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Agreement for a Miller Act Performance Bond (see 28.202(a)(4)). (i) SF 274, Reinsurance Agreement for a Miller Act Payment Bond (see 28.202(a)(4)). (j) SF 275, Reinsurance Agreement in Favor of the United... 91, Release of Personal Property from Escrow (see 28.203-5). ...

  7. Integral Ring Carbon-Carbon Piston

    NASA Technical Reports Server (NTRS)

    Northam, G. Burton (Inventor)

    1999-01-01

    An improved structure for a reciprocating internal combustion engine or compressor piston fabricate from carbon-carbon composite materials is disclosed. An integral ring carbon-carbon composite piston, disclosed herein, reduces the need for piston rings and for small clearances by providing a small flexible, integral component around the piston that allows for variation in clearance due to manufacturing tolerances, distortion due to pressure and thermal loads, and variations in thermal expansion differences between the piston and cylinder liner.

  8. Disclinations in Carbon-Carbon Composites.

    DTIC Science & Technology

    1983-09-01

    carbon-carbon composite has been investigated. Shear cracks were introduced in a two-directional carbon-carbon composite by short-beam shear testing ...graphitization at 2700°C. The final bulk density was 1.95 g/cc. Specimens of this composite, oriented parallel to each fiber direction, were tested in short...symposium were as follows: - New Processing raw materials preparation mesophase control manufacturing methods m characterization and design - New

  9. Ligand-based carbon-nitrogen bond forming reactions of metal dinitrosyl complexes with alkenes and their application to C-H bond functionalization.

    PubMed

    Zhao, Chen; Crimmin, Mark R; Toste, F Dean; Bergman, Robert G

    2014-02-18

    Over the past few decades, researchers have made substantial progress in the development of transition metal complexes that activate and functionalize C-H bonds. For the most part, chemists have focused on aliphatic and aromatic C-H bonds and have put less effort into complexes that activate and functionalize vinylic C-H bonds. Our groups have recently developed a novel method to functionalize vinylic C-H bonds that takes advantage of the unique ligand-based reactivity of a rare class of metal dinitrosyl complexes. In this Account, we compare and discuss the chemistry of cobalt and ruthenium dinitrosyl complexes, emphasizing alkene binding, C-H functionalization, and catalysis. Initially discovered in the early 1970s by Brunner and studied more extensively in the 1980s by the Bergman group, the cyclopentadienylcobalt dinitrosyl complex CpCo(NO)2 reacts reversibly with alkenes to give, in many cases, stable and isolable cobalt dinitrosoalkane complexes. More recently, we found that treatment with strong bases, such as lithium hexamethyldisilazide, Verkade's base, and phosphazene bases, deprotonates these complexes and renders them nucleophilic at the carbon α to the nitroso group. This conjugate anion of metal dinitrosoalkanes can participate in conjugate addition to Michael acceptors to form new carbon-carbon bonds. These functionalized cobalt complexes can further react through alkene exchange to furnish the overall vinylic C-H functionalized organic product. This stepwise sequence of alkene binding, functionalization, and retrocycloaddition represents an overall vinylic C-H functionalization reaction of simple alkenes and does not require directing groups. We have also developed an asymmetric variant of this reaction sequence and have used this method to synthesize C1- and C2-symmetric diene ligands with high enantioinduction. Building upon these stepwise reactions, we eventually developed a simple one-pot procedure that uses stoichiometric amounts of a cobalt

  10. 46 CFR Sec. 6 - Surety and form of bond.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... authorized surety appearing on the current approved list of companies acceptable as sureties on Federal bonds... thirty (30) days prior to the completion, in a continental United States port, of the then current voyage... rata. Fourth. After discovery and report to the Agent or the Director of any loss hereunder, the...

  11. 46 CFR Sec. 6 - Surety and form of bond.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... authorized surety appearing on the current approved list of companies acceptable as sureties on Federal bonds... thirty (30) days prior to the completion, in a continental United States port, of the then current voyage... rata. Fourth. After discovery and report to the Agent or the Director of any loss hereunder, the...

  12. C-C bond-forming desulfurizations of sulfoximines.

    PubMed

    Reggelin, M; Slavik, S; Bühle, P

    2008-09-18

    Highly substituted, enantiomerically pure azaheterocyclic ring systems play an important role in medicinal chemistry as potential peptide mimetics. Metalated 2-alkenyl sulfoximines offer an efficient entry to this class of compounds. In this paper, we describe a new means to remove the sulfonimidoyl auxiliary with concomitant formation of a C-C double bond.

  13. Carbon-carbon composites: Emerging materials for hypersonic flight

    NASA Technical Reports Server (NTRS)

    Maahs, Howard G.

    1989-01-01

    An emerging class of high temperature materials called carbon-carbon composites are being developed to help make advanced aerospace flight become a reality. Because of the high temperature strength and low density of carbon-carbon composites, aerospace engineers would like to use these materials in even more advanced applications. One application of considerable interest is as the structure of the aerospace vehicle itself rather than simply as a protective heat shield as on Space Shuttle. But suitable forms of these materials have yet to be developed. If this development can be successfully accomplished, advanced aerospace vehicles such as the National Aero-Space Plane (NASP) and other hypersonic vehicles will be closer to becoming a reality. A brief definition is given of C-C composites. Fabrication problems and oxidation protection concepts are examined. Applications of C-C composites in the Space Shuttle and in advanced hypersonic vehicles as well as other applications are briefly discussed.

  14. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 3 2010-07-01 2010-07-01 true Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form...

  15. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 3 2013-07-01 2013-07-01 false Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form 4881-3-R...

  16. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 3 2014-07-01 2014-07-01 false Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form 4881-3-R...

  17. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 3 2012-07-01 2009-07-01 true Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form 4881-3-R...

  18. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 32 National Defense 3 2011-07-01 2009-07-01 true Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form 4881-3-R...

  19. 46 CFR 308.529 - Surety Bond B, Form MA-309.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 8 2014-10-01 2014-10-01 false Surety Bond B, Form MA-309. 308.529 Section 308.529 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Open Policy War Risk Cargo Insurance § 308.529 Surety Bond B, Form MA-309....

  20. 46 CFR 308.528 - Surety Bond A, Form MA-308.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 8 2014-10-01 2014-10-01 false Surety Bond A, Form MA-308. 308.528 Section 308.528 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Open Policy War Risk Cargo Insurance § 308.528 Surety Bond A, Form MA-308....

  1. Method of making carbon-carbon composites

    SciTech Connect

    Engle, G.B.

    1991-10-29

    A process is described for making a carbon-carbon composite having a combination of high crystallinity, high strength, high modulus and high thermal and electrical conductivity. High-modulus/high-strength mesophase derived carbon fibers are woven into a suitable cloth. Layers of this easily graphitizable woven cloth are covered with petroleum or coal tar pitch and pressed at a temperature a few degrees above the softening point of the pitch to form a green laminated composite. The green composite is restrained in a suitable fixture and heated slowly to carbonize the pitch binder. The carbonized composite is then impregnated several times with pitch by covering the composite with hot pitch under pressure. The composites are given a heat treatment between each impregnation step to crack up the infiltrated carbon and allow additional pitch to enter the microstructure during the next impregnation cycle. The impregnated composites are then given a final heat treatment in the range 2500 to 3000 C to fully graphitize the fibers and the matrix carbon. The composites are then infiltrated with pyrolytic carbon by chemical vapor deposition in the range 1000 to 1300 C at a reduced pressure for approximately one hundred and fifty (150) hours.

  2. Method of making carbon-carbon composites

    DOEpatents

    Engle, Glen B.

    1991-01-01

    A process for making a carbon-carbon composite having a combination of high crystallinity, high strength, high modulus and high thermal and electrical conductivity. High-modulus/high-strength mesophase derived carbon fibers are woven into a suitable cloth. Layers of this easily graphitizable woven cloth are covered with petroleum or coal tar pitch and pressed at a temperature a few degrees above the softening point of the pitch to form a green laminated composite. The green composite is restrained in a suitable fixture and heated slowly to carbonize the pitch binder. The carbonized composite is then impregnated several times with pitch by covering the composite with hot pitch under pressure. The composites are given a heat treatment between each impregnation step to crack up the infiltrated carbon and allow additional pitch to enter the microstructure during the next impregnation cycle. The impregnated composites are then given a final heat treatment in the range 2500.degree. to 3000.degree. C. to fully graphitize the fibers and the matrix carbon. The composites are then infiltrated with pyrolytic carbon by chemical vapor deposition in the range 1000.degree. to 1300.degree. C. at a reduced pressure for approximately one hundred and fifty (150) hours.

  3. Determining the Carbon-Carbon Distance in an Organic Molecule with a Ruler

    ERIC Educational Resources Information Center

    Simoni, Jose A.; Tubino, Matthieu; Ricchi, Reinaldo Alberto, Jr.

    2004-01-01

    The procedure to estimate the carbon-carbon bond distance in the naphthalene molecule is described. The procedure is easily performed and can be done either at home or in the classroom, with the restriction that the mass of the naphthalene must be determined using an analytical or a precise balance.

  4. Determining the Carbon-Carbon Distance in an Organic Molecule with a Ruler

    ERIC Educational Resources Information Center

    Simoni, Jose A.; Tubino, Matthieu; Ricchi, Reinaldo Alberto, Jr.

    2004-01-01

    The procedure to estimate the carbon-carbon bond distance in the naphthalene molecule is described. The procedure is easily performed and can be done either at home or in the classroom, with the restriction that the mass of the naphthalene must be determined using an analytical or a precise balance.

  5. Fracture morphology of 2-D carbon-carbon composition

    NASA Technical Reports Server (NTRS)

    Avery, W. B.; Herakovich, C. T.

    1985-01-01

    Out-of-plane tensile tests of a woven fabric carbon-carbon composite were performed in a scanning electron microscope equipped with a tensile stage and a videotape recording system. The composite was prepared from T-300 8-harness satin graphite fabric and a phenolic resin. The (0/90/0/90/0 sub 1/2) sub 2 laminate, with a Theta describing the orientation of the warp fibers of the fabric, was cured at 160 C and pyrolized at 871 C. This was followed by four cycles of resin impregnation, curing, and pyrolysis. A micrograph of the cross section of the composite is presented. Inspection of the specimen fracture surface revealed that the filaments had no residual matrix bonded to them. Further inspection revealed that the fracture was interlaminar in nature. Failure occurred where filaments of adjacent plies had the same orientation. Thus it is postulated that improvement in transverse tensile strength of 2-D carbon-carbon depends on the improvement of the filament-matrix bond strength.

  6. Oxidative cyclization of D-fructose thiosemicarbazones to 2-amino-5-(D-arabino-1,2,3,4-tetrahydroxybut-1-yl)-1,3,4-thiadiazoles through carbon-carbon bond cleavage of the sugar chain.

    PubMed

    Shaban, M A E; Mostafa, M A; Nasr, A Z

    2003-06-01

    Condensation of D-fructose (1) with thiosemicarbazide or 4-phenylthiosemicarbazide gave the corresponding D-fructose thiosemicarbazones (3a and 3b). The latter compounds underwent oxidative cyclization with 10% ethanolic ferric chloride to give mixtures of 2-amino-5-(D-arabino-1,2,3,4-tetrahydroxybut-1-yl)-1,3,4-thiadiazole (6a) and 2-amino-5-hydroxymethyl-1,3,4-thiadiazole (5a) from 3a and the corresponding 2-phenylamino compounds 6b and 5b from 3b. These products were formed as a result of cyclization of the thiosemicarbazone entity accompanied by C-1-C-2 or C-2-C-3 bond cleavage of the sugar chain. Structures of the 1,3,4-thiadiazole acyclo C-nucleosides 6a and 5b were confirmed by comparison with the unequivocally prepared compounds obtained by the dehydrogenative cyclization of D-arabinose thiosemicarbazones 11a and 11b with ethanolic ferric chloride. Structures of the 5-hydroxymethyl-1,3,4-thiadiazoles 5a and 5b were also confirmed by comparison with 5a and 5b unequivocally prepared by periodate cleavage of the alditolyl chain of 6a and 6b followed by reduction of the resulting aldehydes 8a and 8b with sodium borohydride. Compounds 6a and 6b were further characterized as their acetates 7a and 7b and were found to exist in the extended planar zizag conformation 13. Condensative cyclization of the D-arabinose thiosemicarbazones 11a and 11b by boiling with acetic anhydride afforded the 1,3,4-thiadiazoline acyclo C-nucleoside acetates 9a and 9b which exist in the sickle (bent) conformation 14. De-N- and de-O-acetylation with concomitant aromatization of 9a and 9b with 10% ethanolic FeCl3 gave the 1,3,4-thiadiazole acyclo C-nucleosides 6a and 6b. The assigned structures were corroborated by 2D 1H-1H HOMCOR and 2D 1H-13C HETCOR NMR spectroscopy.

  7. /sup 13/C-/sup 13/C spin-spin coupling in structural investigations. VII. Substitution effects and direct carbon-carbon constants of the triple bond in acetyline derivatives

    SciTech Connect

    Krivdin, L.B.; Proidakov, A.G.; Bazhenov, B.N.; Zinchenko, S.V.; Kalabin, G.A.

    1989-01-10

    The effects of substitution on the direct /sup 13/C-/sup 13/C spin-spin coupling constants of the triple bond were studied in 100 derivatives of acetylene. It was established that these parameters exhibit increased sensitivity to the effect of substituents compared with other types of compounds. The main factor which determines their variation is the electronegativity of the substituting groups, and in individual cases the /pi/-electronic effects are appreciable. The effect of the substituents with an element of the silicon subgroup at the /alpha/ position simultaneously at the triple bond or substituent of the above-mentioned type and a halogen atom.

  8. Metal hydrides form halogen bonds: measurement of energetics of binding.

    PubMed

    Smith, Dan A; Brammer, Lee; Hunter, Christopher A; Perutz, Robin N

    2014-01-29

    The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η(5)-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η(5)-cyclopentadienyl) is demonstrated by (1)H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = -10.9 ± 0.4 and -11.8 ± 0.3 kJ/mol; ΔS° = -38 ± 2 and -34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = -7.3 ± 0.1 kJ/mol, ΔS° = -24 ± 1 J/(mol·K)). For the more reactive complexes 2-5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M(-1), respectively.

  9. Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

    PubMed Central

    2013-01-01

    The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively. PMID:24380577

  10. Method of making carbon-carbon composites

    SciTech Connect

    Engle, G.B.

    1993-06-08

    A method for fabricating a high-strength, high-modulus and high thermal and electrical conducting 2D laminate carbon-carbon composite is described comprising the steps of: (a) forming a green laminate composite comprising: (1) graphitizible carbon cloth plies, (2) fine graphitizible pitch powder; said cloth plies comprising mesophase derived pitch fiber tow with moduli in a range of 25 to 140 Msi, and (3) thermal conductivity enhancers; (b) heating the green laminate composite to a temperature high enough to cause the pitch powder to soften and pressing the composite to form a pressed green laminate composite comprised of graphitizible carbon cloth, pitch matrix and thermal conductivity enhancers; (c) heating the pressed green composite to at least 500 C. to: (1) carbonize the pitch, (2) form a carbon matrix and (3) shrink and crack the matrix carbon; (d) impregnating the composite with additional graphitizible pitch by covering the composite with the pitch and heating the covered composite to at least 200 C. to melt the pitch and permit it to flow into the composite and then increasing the pressure to at least 15 Psi; (e) heating the composites to at least 900 C.; (f) repeating steps d and e at least once; (g) heating the composite to between 2,400 to 3,100 C to graphitize the fibers and the pitch matrix carbon in the composites to produce a graphitized composite having cracks and pores; and (h) reimpregnating the graphitized composites by infiltrating the cracks and pores of the composites with a hydrocarbon gas at a temperature in the range 982 to 1,490 C. and depositing pyrolytic carbon in the pores and cracks.

  11. Method of densifying an article formed of reaction bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Mangels, John A. (Inventor)

    1982-01-01

    A method of densifying an article formed of reaction bonded silicon nitride is disclosed. The reaction bonded silicon nitride article is packed in a packing mixture consisting of silicon nitride powder and a densification aid. The reaction bonded silicon nitride article and packing powder are sujected to a positive, low pressure nitrogen gas treatment while being heated to a treatment temperature and for a treatment time to cause any open porosity originally found in the reaction bonded silicon nitride article to be substantially closed. Thereafter, the reaction bonded silicon nitride article and packing powder are subjected to a positive high pressure nitrogen gas treatment while being heated to a treatment temperature and for a treatment time to cause a sintering of the reaction bonded silicon nitride article whereby the strength of the reaction bonded silicon nitride article is increased.

  12. Fabrication of carbon-carbon heat pipes for space nuclear power applications

    NASA Technical Reports Server (NTRS)

    Rovang, Richard D.; Palamides, Thomas R.; Hunt, Maribeth E.

    1992-01-01

    Significant advancements have been made in the development of lightweight, high performance, carbon-carbon heat pipes for space nuclear power applications. The subject program has progressed through the concept definition and feasibility analysis stages to the current test article component fabrication and assembly phase. This concept utilizes a carbon-carbon tube with integrally woven fins as the primary structural element and radiative surface, Nb-1Zr liners to contain a potassium working fluid, and welded end caps and fill tubes. Various tests have been performed in the development of suitable liner bonding techniques and in the assessment of material stability.

  13. Proposal of a new hydrogen-bonding form to maintain curdlan triple helix.

    PubMed

    Miyoshi, Kentaro; Uezu, Kazuya; Sakurai, Kazuo; Shinkai, Seiji

    2004-06-01

    Curdlan and other beta-1,3-D-glucans form right-handed triple helices, and it has been believed that the intermolecular H-bond is present at the center of the helix to maintain the structure. In this H-bond model, three secondary OH groups form an inequilateral hexagonal shape perpendicular to the helix axis. This hexagonal form seems to be characteristic for beta-1,3-D-glucans and is widely accepted. We carried out MOPAC and ab initio calculations for the curdlan helix, and we propose a new intermolecular H-bonding model. In our model, the H-bonds are formed between the O2-atoms on different x-y planes along the curdlan helix, hence the H-bonds are not perpendicular to the helix axis. The new H-bonds are connected along the helix, traversing three curdlan chains to make a left-handed helix. Therefore, the H-bonding array leads to a reverse helix of the main chain. According to our MOPAC calculation, this model is more stable than the previous one. We believe that the continuous H-bonding array is stabilized by cooperative phenomena in the polymeric system.

  14. Secondary waste form testing : ceramicrete phosphate bonded ceramics.

    SciTech Connect

    Singh, D.; Ganga, R.; Gaviria, J.; Yusufoglu, Y.

    2011-06-21

    The cleanup activities of the Hanford tank wastes require stabilization and solidification of the secondary waste streams generated from the processing of the tank wastes. The treatment of these tank wastes to produce glass waste forms will generate secondary wastes, including routine solid wastes and liquid process effluents. Liquid wastes may include process condensates and scrubber/off-gas treatment liquids from the thermal waste treatment. The current baseline for solidification of the secondary wastes is a cement-based waste form. However, alternative secondary waste forms are being considered. In this regard, Ceramicrete technology, developed at Argonne National Laboratory, is being explored as an option to solidify and stabilize the secondary wastes. The Ceramicrete process has been demonstrated on four secondary waste formulations: baseline, cluster 1, cluster 2, and mixed waste streams. Based on the recipes provided by Pacific Northwest National Laboratory, the four waste simulants were prepared in-house. Waste forms were fabricated with three filler materials: Class C fly ash, CaSiO{sub 3}, and Class C fly ash + slag. Optimum waste loadings were as high as 20 wt.% for the fly ash and CaSiO{sub 3}, and 15 wt.% for fly ash + slag filler. Waste forms for physical characterizations were fabricated with no additives, hazardous contaminants, and radionuclide surrogates. Physical property characterizations (density, compressive strength, and 90-day water immersion test) showed that the waste forms were stable and durable. Compressive strengths were >2,500 psi, and the strengths remained high after the 90-day water immersion test. Fly ash and CaSiO{sub 3} filler waste forms appeared to be superior to the waste forms with fly ash + slag as a filler. Waste form weight loss was {approx}5-14 wt.% over the 90-day immersion test. The majority of the weight loss occurred during the initial phase of the immersion test, indicative of washing off of residual unreacted

  15. Total synthesis of bryostatin 7 via C-C bond-forming hydrogenation.

    PubMed

    Lu, Yu; Woo, Sang Kook; Krische, Michael J

    2011-09-07

    The marine macrolide bryostatin 7 is prepared in 20 steps (longest linear sequence) and 36 total steps with five C-C bonds formed using hydrogenative methods. This approach represents the most concise synthesis of any bryostatin reported, to date.

  16. Recent advances in carbon-carbon materials systems

    SciTech Connect

    Rummler, D.R.

    1982-11-01

    Carbon-carbon materials and new oxidation resistant coating developments are discussed. Potential areas of application are highlighted. A short bibliography of selected references is included that describe carbon-carbon materials and related technology in detail.

  17. Translational vibrations between chains of hydrogen-bonded molecules in solid-state aspirin form I

    NASA Astrophysics Data System (ADS)

    Takahashi, Masae; Ishikawa, Yoichi

    2013-06-01

    We perform dispersion-corrected first-principles calculations, and far-infrared (terahertz) spectroscopic experiments at 4 K, to examine translational vibrations between chains of hydrogen-bonded molecules in solid-state aspirin form I. The calculated frequencies and relative intensities reproduce the observed spectrum to accuracy of 11 cm-1 or less. The stronger one of the two peaks assigned to the translational mode includes the stretching vibration of the weak hydrogen bond between the acetyl groups of a neighboring one-dimensional chain. The calculation of aspirin form II performed for comparison gives the stretching vibration of the weak hydrogen bond in one-dimensional chain.

  18. Carbon/Carbon Pistons for Internal Combustion Engines

    NASA Technical Reports Server (NTRS)

    Taylor, A. H.

    1986-01-01

    Carbon/carbon piston performs same function as aluminum pistons in reciprocating internal combustion engines while reducing weight and increasing mechanical and thermal efficiencies of engine. Carbon/carbon piston concept features low piston-to-cylinder wall clearance - so low piston rings and skirts unnecessary. Advantages possible by negligible coefficient of thermal expansion of carbon/carbon.

  19. 31 CFR 351.83 - May Public Debt issue Series EE savings bonds only in book-entry form?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... savings bonds only in book-entry form? 351.83 Section 351.83 Money and Finance: Treasury Regulations... Debt issue Series EE savings bonds only in book-entry form? We reserve the right to issue bonds only in book-entry form. ...

  20. Formation of fluorophores from the kynurenine pathway metabolite N-formylkynurenine and cyclic amines involves transamidation and carbon-carbon bond formation at the 2-position of the amine.

    PubMed

    Tomek, Petr; Palmer, Brian D; Kendall, Jackie D; Flanagan, Jack U; Ching, Lai-Ming

    2015-09-01

    Tryptophan catabolism along the kynurenine pathway is associated with a number of pathologies including cataract formation and cancer. Whilst the chemical reactions of kynurenine are well studied, less is known about the reactivity of its precursor N-formylkynurenine (NFK). We previously reported the generation of a strong fluorophore in an aqueous reaction of NFK with piperidine, and herein we describe its structure and mechanism of formation. Compounds were identified using NMR, mass and UV spectroscopic techniques. The products from the reaction of amines with amino acids were quantified using HPLC-MS. The novel fluorophore was identified as a tetrahydroquinolone adduct (PIP-THQ), where piperidine is N-formylated and attached at its 2-position to the quinolone. NFK is initially deaminated to generate an unsaturated enone, which forms an adduct with piperidine and is subsequently converted into the fluorophore. Testing of a variety of other secondary amines showed that only cyclic amines unsubstituted at both positions adjacent to nitrogen could form fluorophores efficiently. The amino acids tryptophan and kynurenine, which lack the formamide group do not form such fluorophores. NFK forms fluorophores in a not previously published reaction with cyclic amines. Our study is the first to provide evidence for concurrent transamidation and substitution at the 2-position of a cyclic amine occurring under moderately-heated aqueous conditions with no added catalysts. The high reactivity of NFK demonstrated here could result in formation of biologically relevant metabolites yet to be characterised. Copyright © 2015 Elsevier B.V. All rights reserved.

  1. Hydrogen bonding. Part 20. Infrared study of the high temperature β-form of choline chloride

    NASA Astrophysics Data System (ADS)

    Harmon, Kenneth M.; Avci, Günsel F.

    1986-02-01

    Infrared spectral studies of β-choline chloride at 95°C clearly demonstrate the presence of OH … Cl hydrogen bonding. This observation contradicts an earlier conclusion, based on X-ray structural studies, that such hydrogen bonding could not occur in this high-temperature form of choline chloride. A moderate reinterpretation of the X-ray data may reconcile these contradictory conclusions. Unlike α-choline chloride, β-choline chloride does not show CH … Cl hydrogen bonding. It is possible that loss of CH … Cl hydrogen bonding is a factor in the marked difference in radiation sensitivity of the α- and β-forms.

  2. 46 CFR 308.529 - Surety Bond B, Form MA-309.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.529 Surety Bond B, Form MA-309. An..., which may be obtained form the American War Risk Agency or MARAD....

  3. 46 CFR 308.529 - Surety Bond B, Form MA-309.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.529 Surety Bond B, Form MA-309. An..., which may be obtained form the American War Risk Agency or MARAD....

  4. 46 CFR 308.529 - Surety Bond B, Form MA-309.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.529 Surety Bond B, Form MA-309. An..., which may be obtained form the American War Risk Agency or MARAD....

  5. 46 CFR 308.529 - Surety Bond B, Form MA-309.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.529 Surety Bond B, Form MA-309. An..., which may be obtained form the American War Risk Agency or MARAD....

  6. Ab initio structures for 90 degrees -twisted s-trans-1,3-butadiene and cyclooctatetraene: the naked sp2-sp2 bond.

    PubMed

    Feller, David; Craig, Norman C; Matlin, Albert R

    2008-03-20

    The bond length of a carbon-carbon sp2-sp2 sigma-bond without the perturbing effects of pi-interactions has been estimated by high level calculations on two prototypical systems: a 90 degrees -twisted form of butadiene and the tub conformer of cyclooctatetraene. The former system yields a value of 1.4818 A, considerably longer than previous estimates. The corresponding bond length in the latter is slightly shorter due to some pi-electron delocalization.

  7. Scale-up of Carbon/Carbon Bipolar Plates

    SciTech Connect

    David P. Haack

    2009-04-08

    This project was focused upon developing a unique material technology for use in PEM fuel cell bipolar plates. The carbon/carbon composite material developed in this program is uniquely suited for use in fuel cell systems, as it is lightweight, highly conductive and corrosion resistant. The project further focused upon developing the manufacturing methodology to cost-effectively produce this material for use in commercial fuel cell systems. United Technology Fuel Cells Corp., a leading fuel cell developer was a subcontractor to the project was interested in the performance and low-cost potential of the material. The accomplishments of the program included the development and testing of a low-cost, fully molded, net-shape carbon-carbon bipolar plate. The process to cost-effectively manufacture these carbon-carbon bipolar plates was focused on extensively in this program. Key areas for cost-reduction that received attention in this program was net-shape molding of the detailed flow structures according to end-user design. Correlations between feature detail and process parameters were formed so that mold tooling could be accurately designed to meet a variety of flow field dimensions. A cost model was developed that predicted the cost of manufacture for the product in near-term volumes and long-term volumes (10+ million units per year). Because the roduct uses lowcost raw materials in quantities that are less than competitive tech, it was found that the cost of the product in high volume can be less than with other plate echnologies, and can meet the DOE goal of $4/kW for transportation applications. The excellent performance of the all-carbon plate in net shape was verified in fuel cell testing. Performance equivalent to much higher cost, fully machined graphite plates was found.

  8. Fracture Toughness of Carbon/Carbon Composites.

    DTIC Science & Technology

    1991-07-27

    during which tensile stresses develop in the matrix as a result of the thermal expansion coefficient differential between the matrix and yarns. In...thermal expansion differential . Figure 3.4 depicts the sample surface along the R-C plane. The circumferential yarns are horizontal and the radial yarns...Milieko), Elsevier, Amsterdam, (1981), pp. 109-175. 5 126 3 U 127 16). C.T. Robinson, "Damage Mechanisums and Failure of 3-D Carbon-Carbon Composites," SRI

  9. High Thermal Conductivity Carbon/Carbon Composites.

    DTIC Science & Technology

    1995-09-30

    The objective of this project was to develop a lowcost, high thermal conductivity carbon/carbon composite with a mesophase pitch -based matrix. A low...carbonization technique and heat treatment of the mesophase pitch was utilized to enhance composite properties by increasing the composite density...Three different fibers, T300 PAN-based, P55 pitch -based, and an experimental high thermal conductivity mesophase pitch -based, were incorporated as the

  10. Direct carbon-carbon coupling of furanics with acetic acid over Brønsted zeolites.

    PubMed

    Gumidyala, Abhishek; Wang, Bin; Crossley, Steven

    2016-09-01

    Effective carbon-carbon coupling of acetic acid to form larger products while minimizing CO2 emissions is critical to achieving a step change in efficiency for the production of transportation fuels from sustainable biomass. We report the direct acylation of methylfuran with acetic acid in the presence of water, all of which can be readily produced from biomass. This direct coupling limits unwanted polymerization of furanics while producing acetyl methylfuran. Reaction kinetics and density functional theory calculations illustrate that the calculated apparent barrier for the dehydration of the acid to form surface acyl species is similar to the experimentally measured barrier, implying that this step plays a significant role in determining the net reaction rate. Water inhibits the overall rate, but selectivity to acylated products is not affected. We show that furanic species effectively stabilize the charge of the transition state, therefore lowering the overall activation barrier. These results demonstrate a promising new route to C-C bond-forming reactions for the production of higher-value products from biomass.

  11. Mechanical behavior of carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Rozak, G. A.

    1984-01-01

    A general background, test plan, and some results of preliminary examinations of a carbon-carbon composite material are presented with emphasis on mechanical testing and inspection techniques. Experience with testing and evaluation was gained through tests of a low modulus carbon-carbon material, K-Karb C. The properties examined are the density - 1.55 g/cc; four point flexure strength in the warp - 137 MPa (19,800 psi) and the fill - 95.1 MPa (13,800 psi,) directions; and the warp interlaminar shear strength - 14.5 MPa (2100 psi). Radiographic evaluation revealed thickness variations and the thinner areas of the composite were scrapped. The ultrasonic C-scan showed attenuation variations, but these did not correspond to any of the physical and mechanical properties measured. Based on these initial tests and a survey of the literature, a plan has been devised to examine the effect of stress on the oxidation behavior, and the strength degradation of coated carbon-carbon composites. This plan will focus on static fatigue tests in the four point flexure mode in an elevated temperature, oxidizing environment.

  12. Nanographene reinforced carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Bansal, Dhruv

    Carbon/Carbon Composites (CCC) are made of carbon reinforcement in carbon matrix and have high thermal stability and fatigue resistance. CCC are used in nose cones, heat shields and disc brakes of aircrafts due to their exceptional mechanical properties at high temperature. The manufacturing process of CCC involves a carbonization stage in which unwanted elements, except carbon, are eliminated from the polymer precursor. Carbonization results in the formation of voids and cracks due to the thermal mismatch between the reinforcement and the matrix and expulsion of volatiles from the polymer matrix. Thermal cracks and voids decrease the density and mechanical properties of the manufactured CCC. In this work, Nanographene Platelets (NGP) were explored as nanofillers to fill the voids/cracks and reduce thermal shrinkage in CCC. They were first compared with Vapor Grown Carbon Nanofibers (VGCNF) by dispersion of different concentrations (0.5wt%, 1.5wt%, 3wt%) in resole-type phenolic resin and were characterized to explore their effect on rheology, heat of reaction and wetting behavior. The dispersions were then cured to form nanocomposites and were characterized for morphology, flexure and thermal properties. Finally, NGP were introduced into the carbon/carboncomposites in two stages, first by spraying in different concentrations (0.5wt%, 1.5wt%, 3wt%, 5wt %) during the prepreg formation and later during densification by directly mixing in the corresponding densification mix. The manufactured NGP reinforced CCC were characterized for microstructure, porosity, bulk density and mechanical properties (Flexure and ILSS) which were further cross-checked by non-destructive techniques (vibration and ultrasonic). In this study, it was further found that at low concentration (≤ 1.5 wt%) NGP were more effective in increasing the heat of reaction and in decreasing the viscosity of the phenolic resin. The decrease in viscosity led to better wetting properties of NGP / phenolic

  13. Investigation of thermochemistry associated with the carbon-carbon coupling reactions of furan and furfural using ab initio methods.

    PubMed

    Liu, Cong; Assary, Rajeev S; Curtiss, Larry A

    2014-06-26

    Upgrading furan and small oxygenates obtained from the decomposition of cellulosic materials via formation of carbon-carbon bonds is critical to effective conversion of biomass to liquid transportation fuels. Simulation-driven molecular level understanding of carbon-carbon bond formation is required to design efficient catalysts and processes. Accurate quantum chemical methods are utilized here to predict the reaction energetics for conversion of furan (C4H4O) to C5-C8 ethers and the transformation of furfural (C5H6O2) to C13-C26 alkanes. Furan can be coupled with various C1 to C4 low molecular weight carbohydrates obtained from the pyrolysis via Diels-Alder type reactions in the gas phase to produce C5-C8 cyclic ethers. The computed reaction barriers for these reactions (∼25 kcal/mol) are lower than the cellulose activation or decomposition reactions (∼50 kcal/mol). Cycloaddition of C5-C8 cyclo ethers with furans can also occur in the gas phase, and the computed activation energy is similar to that of the first Diels-Alder reaction. Furfural, obtained from biomass, can be coupled with aldehydes or ketones with α-hydrogen atoms to form longer chain aldol products, and these aldol products can undergo vapor phase hydrocycloaddition (activation barrier of ∼20 kcal/mol) to form the precursors of C26 cyclic hydrocarbons. These thermochemical studies provide the basis for further vapor phase catalytic studies required for upgrading of furans/furfurals to longer chain hydrocarbons.

  14. Investigation of thermochemistry associated with the carbon-carbon coupling reactions of furan and furfural using ab initio methods.

    SciTech Connect

    Liu, Cong; Assary, Rajeev S.; Curtiss, Larry A.

    2014-06-26

    Upgrading of furan and small oxygenates obtained from the decomposition of cellulosic materials via formation of carbon-carbon bonds is critical to effective conversion of biomass to liquid transportation fuels. Simulation-driven molecular level understanding of carbon-carbon bond formation is required to design efficient catalysts and processes. Accurate quantum chemical methods are utilized here to predict the reaction energetics for conversion of furan (C4H4O) to C5-C8 ethers and the transformation of furfural (C5H6O2) to C13-C26 alkanes. Furan, can be coupled with various C1 to C4 lower molecular weight carbohydrates obtained from the pyrolysis via Diels-Alder type reactions in the gas phase to produce C5-C8 cyclic ethers. The computed reaction barriers for these reactions (~25 kcal/mol) are lower than the cellulose activation or decomposition reactions (~50 kcal/mol). Cycloaddition of C5-C8 cyclo-ethers with furans can also occur in the gas phase, and the computed activation energy is similar to that of the first Diels-Alder reaction. Furfural, obtained from biomass, can be coupled with aldehydes or ketones with α-hydrogen atoms to form longer chain aldol products and these aldol products can undergo vapor phase hydrocycloaddition (activation barrier of ~20 kcal/mol) to form the precursors of C26 cyclic hydrocarbons. These thermochemical studies provide the basis for further vapor phase catalytic studies required for upgrading of furans/furfurals to longer chain hydrocarbons.

  15. 46 CFR 308.531 - Endorsement of surety bond increasing or decreasing amount of coverage, Form MA-311.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 8 2010-10-01 2010-10-01 false Endorsement of surety bond increasing or decreasing... Insurance § 308.531 Endorsement of surety bond increasing or decreasing amount of coverage, Form MA-311. The Standard Form of Endorsement which shall be used in increasing or decreasing the amount of a surety bond...

  16. Bonding strength of the apatite layer formed on glass-ceramic apatite-wollastonite-polyethylene composites.

    PubMed

    Juhasz, J A; Best, S M; Kawashita, M; Miyata, N; Kokubo, T; Nakamura, T; Bonfield, W

    2003-12-01

    Bioactive glass-ceramic apatite-wollastonite (A-W) has been incorporated into polyethylene in particulate form to create new bioactive composites for potential maxillofacial applications. The effects of varying the volume fraction of glass-ceramic A-W filler and the glass-ceramic A-W particle size were investigated by measuring the bonding strength of the bonelike apatite layer formed on the surface of glass-ceramic A-W-polyethylene composites. The bonding strength was evaluated via a modified ASTM C-333 standard in which a tensile stress was applied to the substrate and the strength of the bioactive layer was compared with that formed on commercially available hydroxyapatite-polyethylene composite samples, HAPEX. The composites demonstrated greater bonding strength with increased filler content and reduced filler particle size (maximum 6.9 +/- 0.5 MPa) and a marginally greater bonding strength as compared with HAPEX (2.8 +/- 0.5 MPa), when glass-ceramic A-W-polyethylene composite samples with the same filler content were tested. The higher bonding strength of the apatite layer formed on the A-W-polyethylene composite samples suggests that, in addition to maxillofacial applications, these composites might also be utilized in applications involving higher levels of load bearing.

  17. Rigid dimers formed through strong interdigitated H-bonds yield compact 1D supramolecular helical polymers.

    PubMed

    Ciesielski, Artur; Stefankiewicz, Artur R; Hanke, Felix; Persson, Mats; Lehn, Jean-Marie; Samorì, Paolo

    2011-02-07

    Hierarchical self-assembly of small abiotic molecular modules interacting through noncovalent forces is increasingly being used to generate functional structures and materials for electronic, catalytic, and biomedical applications. The greatest control over the geometry in H-bond supramolecular architectures, especially in H-bonded supramolecular polymers, can be achieved by using conformationally rigid molecular modules undergoing self-assembly through strong H-bonds. Their binding strength depends on the multiplicity of the H-bonds, the nature of donor/acceptor pairs and their secondary attractive/repulsive interactions. Here a functionalized molecular module is described, which is capable of self-associating through self-complementary H-bonding patterns comprising four strong and two medium-strength H-bonds to form dimers. The self-association of these phenylpyrimidine-based dimers through directional H-bonding between two lateral pyridin-2(1H)-one units of neighboring molecules allows the formation of highly compact 1D supramolecular polymers by self-assembly on graphite. A concentration-dependent study by scanning tunneling microscopy at the solid-liquid interface, corroborated by dispersion-corrected density functional studies, reveals the controlled generation of either linear supramolecular 2D arrays, or long helical supramolecular polymers with a high shape persistence.

  18. Differential Sputtering Behavior of Pyrolytic Graphite and Carbon-Carbon Composite Under Xenon Bombardment

    NASA Technical Reports Server (NTRS)

    Williams, John D.; Johnson, Mark L.; Williams, Desiree D.

    2003-01-01

    A differential sputter yield measurement technique is described, which consists of a quartz crystal monitor that is swept at constant radial distance from a small target region where a high current density xenon ion beam is aimed. This apparatus has been used to characterize the sputtering behavior of various forms of carbon including polycrystalline graphite, pyrolytic graphite, and PVD-infiltrated and pyrolized carbon-carbon composites. Sputter yield data are presented for pyrolytic graphite and carbon-carbon composite over a range of xenon ion energies from 200 eV to 1 keV and angles of incidence from 0 deg (normal incidence) to 60 deg .

  19. Relating structural parameters to leachability in a glass-bonded ceramic waste form.

    SciTech Connect

    Frank, S. M.; Johnson, S. G.; Moschetti, T. L.

    1998-05-08

    Lattice parameters for a crystalline material can be obtained by several methods, notably by analyzing x-ray powder diffraction patterns. By utilizing a computer program to fit a pattern, one can follow the evolution or subtle changes in a structure of a crystalline species in different environments. This work involves such a study for an essential component of the ceramic waste form that is under development at Argonne National Laboratory. Zeolite 4A and zeolite 5A are used to produce two different types of waste forms: a glass-bonded sodalite and a glass-bonded zeolite, respectively. Changes in structure during production of the waste forms are discussed. Specific salt-loadings in the sodalite waste form are related to relative peak intensities of certain reflections in the XRD patterns. Structural parameters for the final waste forms will also be given and related to leachability under standard conditions.

  20. Characterization of high cesium containing glass-bonded ceramic waste forms.

    SciTech Connect

    Lambregts, M. J.; Frank, S. M.

    2003-10-03

    High cesium containing glass-bonded ceramic waste form samples were prepared and characterized to identify possible cesium phases present in glass-bonded ceramic waste forms developed for the containment of fission product bearing salts. Major phases of the waste forms are sodalite and glass. A combination of powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance spectroscopy (NMR) were used to study the multiphase nature of these waste forms. Cesium was found to be present in the higher loaded waste forms in a cesium aluminosilicate phase with an analcime structure and a 1:1 Si:Al ratio, a pollucite phase, and also in the glass phase. The glass phase contains the majority of the cesium at lower loadings, however some pollucite also remains. Cesium was not detected in the sodalite phase of any of the samples.

  1. 31 CFR 351.4 - In what form are Series EE savings bonds issued?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false In what form are Series EE savings bonds issued? 351.4 Section 351.4 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued) FISCAL SERVICE, DEPARTMENT OF THE TREASURY BUREAU OF THE PUBLIC DEBT OFFERING OF UNITED...

  2. 27 CFR 28.65 - Bond, Form 2738 (5110.68).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... Form 2738 (5110.68) as provided in § 28.51. The penal sum of the bond shall be sufficient to cover the... maximum penal sum shall not exceed $200,000, but in no case shall the penal sum be less than $1,000...

  3. 46 CFR 308.532 - Release of surety bond, Form MA-312.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 8 2014-10-01 2014-10-01 false Release of surety bond, Form MA-312. 308.532 Section 308.532 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Open Policy War Risk Cargo Insurance § 308.532 Release of surety...

  4. Carbon/Carbon Panels Cooled By Heat Pipes

    NASA Technical Reports Server (NTRS)

    Camarda, Charles J.; Ransone, Philip O.

    1989-01-01

    Durable and reusable high-temperature carbon/carbon heat-pipe structure operates at temperatures above 3,000 degree F (1,649 degree C) in vacuum or inert environment and up to 2,800 degree F (1,537 degree C) in oxidizing environment. New concept combines high-temperature heat-pipe and carbon/carbon technologies to extend both thermal structural capabilities of refractory-metal heat pipes and maximum heat-flux capability of carbon/carbon structures. Uses refractory-metal heat pipes embedded within carbon/carbon structure. Walls of heat pipes thin and contain working fluid (lithium or sodium) of heat pipe. Carbon/carbon acts as primary load-carrying part of structure. Heat pipes help to eliminate local hotspots and associated thermal gradients and stresses and to reduce peak surface temperatures of carbon/carbon to levels within capability of oxidation-resisting system.

  5. Method for Making a Carbon-Carbon Cylinder Block

    NASA Technical Reports Server (NTRS)

    Ransone, Phillip O. (Inventor)

    1997-01-01

    A method for making a lightweight cylinder block composed of carbon-carbon is disclosed. The use of carbon-carbon over conventional materials. such as cast iron or aluminum, reduces the weight of the cylinder block and improves thermal efficiency of the internal combustion reciprocating engine. Due to the negligible coefficient of thermal expansion and unique strength at elevated temperatures of carbon-carbon, the piston-to-cylinder wall clearance can be small, especially when the carbon-carbon cylinder block is used in conjunction with a carbon-carbon piston. Use of the carbon-carbon cylinder block has the effect of reducing the weight of other reciprocating engine components allowing the piston to run at higher speeds and improving specific engine performance.

  6. Process for biological material carbon-carbon bond formation

    DOEpatents

    Hollingsworth, R.I.; Jung, S.; Mindock, C.A.

    1998-12-22

    A process for providing vicinal dimethyl long chain between alkyl groups of organic compounds is described. The process uses intact or disrupted cells of various species of bacteria, particularly Thermoanaerobacter sp., Sarcina sp. and Butyrivibrio sp. The process can be conducted in an aqueous reaction mixture at room temperatures. 8 figs.

  7. Efficient nickel mediated carbon-carbon bond cleavage of organonitriles.

    PubMed

    Schaub, Thomas; Döring, Christian; Radius, Udo

    2007-05-28

    The reactions of the nickel complex [Ni(2)(iPr(2)Im)4(COD)] 1 with organonitriles smoothly and irreversibly proceed via intermediates with eta(2)-coordinated organonitrile ligands such as [Ni(iPr(2)Im)2(eta(2)-(CN)-PhCN)] 2 and [Ni(iPr(2)Im)2(eta(2)-(CN)-pTolCN)] 4 to yield aryl cyanide complexes of the type trans-[Ni(iPr(2)Im)2(CN)(Ar)] (Ar = Ph 3, pTol 5, 4-CF(3)C(6)H(4) 6, 2,4-(OMe)2C(6)H(3) 7, 2-C(4)H(3)O 8, 2-C(5)H(4)N 9). The compounds 3, 7, 9 and have been structurally characterized. For the conversion of 2 to 3 a free activation enthalpy DeltaG++(328 K) of 103.47 +/- 0.79 kJ mol(-1) was calculated from time dependent NMR spectroscopy. The analogous reaction of arylnitriles with electron releasing substituents or heteroaromatic organonitriles is significantly faster compared to the reaction with benzonitrile or toluonitrile. The reactions of 1 with acetonitrile or trimethylsilyl cyanide afforded [Ni(iPr(2)Im)2(CN)(Me)] 10 and structurally characterized [Ni(iPr(2)Im)2(CN)(SiMe(3))] 11. The usage of an organonitrile with a longer alkyl chain, adiponitrile, yielded [Ni(iPr(2)Im)2(eta(2)-(CN)-NCC(4)H(8)CN)] 12 as well as the C-CN activation product [Ni(iPr(2)Im)2(CN)(C(4)H(8)CN)]13 in thermal and photochemical reactions, although this pathway seems to be significantly interfered with by decomposition pathways under the formation of the dicyanide complex [Ni(iPr(2)Im)(2)(CN)(2)] 14.

  8. Process for biological material carbon-carbon bond formation

    DOEpatents

    Hollingsworth, Rawle I.; Jung, Seunho; Mindock, Carol A.

    1998-01-01

    A process for providing vicinal dimethyl long chain between alkyl groups of organic compounds is described. The process uses intact or disrupted cells of various species of bacteria, particularly Thermoanaerobacter sp., Sarcina sp. and Butyrivibrio sp. The process can be conducted in an aqueous reaction mixture at room temperatures.

  9. Hydrogen-bonded structures and interaction energies in two forms of the SGLT-2 inhibitor sotagliflozin.

    PubMed

    Gelbrich, Thomas; Adamer, Verena; Stefinovic, Marijan; Thaler, Andrea; Griesser, Ulrich J

    2017-09-01

    The sotagliflozin molecule exhibits two fundamentally different molecular conformations in form 1 {systematic name: (2S,3R,4R,5S,6R)-2-[4-chloro-3-(4-ethoxybenzyl)phenyl]-6-(methylsulfanyl)tetrahydro-2H-pyran-3,4,5-triol, C21H25ClO5S, (I)} and the monohydrate [C21H25ClO5S·H2O, (II)]. Both crystals display hydrogen-bonded layers formed by intermolecular interactions which involve the three -OH groups of the xyloside fragment of the molecule. The layer architectures of (I) and (II) contain a non-hydrogen-bonded molecule-molecule interaction along the short crystallographic axis (a axis) whose total PIXEL energy exceeds that of each hydrogen-bonded molecule-molecule pair. The hydrogen-bonded layer of (I) has the topology of the 4-connected sql net and that formed by the water and sotagliflozin molecules of (II) has the topology of a 3,7-connected net.

  10. 31 CFR 351.83 - May Public Debt issue Series EE savings bonds only in book-entry form?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false May Public Debt issue Series EE... DEBT OFFERING OF UNITED STATES SAVINGS BONDS, SERIES EE Miscellaneous Provisions § 351.83 May Public Debt issue Series EE savings bonds only in book-entry form? We reserve the right to issue bonds only...

  11. 31 CFR 359.68 - May Public Debt issue Series I savings bonds only in book-entry form?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false May Public Debt issue Series I... DEBT OFFERING OF UNITED STATES SAVINGS BONDS, SERIES I Miscellaneous Provisions § 359.68 May Public Debt issue Series I savings bonds only in book-entry form? We reserve the right to issue bonds only...

  12. Examination of superplastic forming combined with diffusion bonding for titanium: Perspective from experience

    NASA Astrophysics Data System (ADS)

    Sanders, Daniel G.; Ramulu, Mamidala

    2004-12-01

    Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised, including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past work found in the literature and forms the foundation for additional research.

  13. "Homeopathic" palladium nanoparticle catalysis of cross carbon-carbon coupling reactions.

    PubMed

    Deraedt, Christophe; Astruc, Didier

    2014-02-18

    Catalysis by palladium derivatives is now one of the most important tools in organic synthesis. Whether researchers design palladium nanoparticles (NPs) or nanoparticles occur as palladium complexes decompose, these structures can serve as central precatalysts in common carbon-carbon bond formation. Palladium NPs are also valuable alternatives to molecular catalysts because they do not require costly and toxic ligands. In this Account, we review the role of "homeopathic" palladium catalysts in carbon-carbon coupling reactions. Seminal studies from the groups of Beletskaya, Reetz, and de Vries showed that palladium NPs can catalyze Heck and Suzuki-Miyaura reactions with aryl iodides and, in some cases, aryl bromides at part per million levels. As a result, researchers coined the term "homeopathic" palladium catalysis. Industry has developed large-scale applications of these transformations. In addition, chemists have used Crooks' concept of dendrimer encapsulation to set up efficient nanofilters for Suzuki-Miyaura and selective Heck catalysis, although these transformations required high PdNP loading. With arene-centered, ferrocenyl-terminated dendrimers containing triazolyl ligands in the tethers, we designed several generations of dendrimers to compare their catalytic efficiencies, varied the numbers of Pd atoms in the PdNPs, and examined encapsulation vs stabilization. The catalytic efficiencies achieved "homeopathic" (TON = 540 000) behavior no matter the PdNP size and stabilization type. The TON increased with decreasing the Pd/substrate ratio, which suggested a leaching mechanism. Recently, we showed that water-soluble arene-centered dendrimers with tri(ethylene glycol) (TEG) tethers stabilized PdNPs involving supramolecular dendritic assemblies because of the interpenetration of the TEG branches. Such PdNPs are stable and retain their "homeopathic" catalytic activities for Suzuki-Miyaura reactions for months. (TONs can reach 2.7 × 10(6) at 80 °C for aryl

  14. Conformational flexibility and hydrogen-bonding patterns of the neotame molecule in its various solid forms.

    PubMed

    Dong, Zedong; Munson, Eric J; Schroeder, Steve A; Prakash, Indra; Grant, David J W

    2002-09-01

    The conformational flexibility and the molecular packing patterns of the neotame molecule in its various crystal forms, including neotame monohydrate, methanol solvate, ethanol solvate, benzene solvate, and anhydrate polymorph G, are analyzed in this work. The Cerius2 molecular modeling program with the Dreiding 2.21 force field was employed to calculate the most stable conformations of neotame molecules in the gaseous state and to analyze the conformations of the neotame molecule in its various crystal forms. Using graph set analysis, the hydrogen bond patterns of these crystal forms were compared. The neotame molecule takes different conformations in its crystal forms and in the free gaseous state. Cerius2 found 10 conformers with lower conformational energies than those in the actual crystal structures, which represent an energetic compromise. The relatively large differences between the energies of the conformers indicate the necessity for rewriting or customizing the force field for neotame. The hydrogen bonding patterns of the neotame methanol and ethanol solvates are identical, but different from those of the other three forms, which also differ from each other. The neotame molecule in its various crystal forms takes different conformations that differ from those in the gaseous state because of the influence of crystal packing. The intramolecular ring, S5, is present in all the crystal forms. The following hydrogen bonding patterns occur in some of the crystal forms: diad, D; intramolecular rings, S(6) and S(7); chains, C(5) and C(6); and an intermolecular ring, R2(2)(12). Copyright 2002 Wiley-Liss, Inc.

  15. Radiation damage of a glass-bonded zeolite waste form using ion irradiation.

    SciTech Connect

    Allen, T. R.; Storey, B. G.

    1997-12-05

    Glass-bonded zeolite is being considered as a candidate ceramic waste form for storing radioactive isotopes separated from spent nuclear fuel in the electrorefining process. To determine the stability of glass-bonded zeolite under irradiation, transmission electron microscope samples were irradiated using high energy helium, lead, and krypton. The major crystalline phase of the waste form, which retains alkaline and alkaline earth fission products, loses its long range order under both helium and krypton irradiation. The dose at which the long range crystalline structure is lost is about 0.4 dpa for helium and 0.1 dpa for krypton. Because the damage from lead is localized in such a small region of the sample, damage could not be recognized even at a peak damage of 50 dpa. Because the crystalline phase loses its long range structure due to irradiation, the effect on retention capacity needs to be further evaluated.

  16. Pistons and Cylinders Made of Carbon-Carbon Composite Materials

    NASA Technical Reports Server (NTRS)

    Rivers, H. Kevin (Inventor); Ransone, Philip O. (Inventor); Northam, G. Burton (Inventor); Schwind, Francis A. (Inventor)

    2000-01-01

    An improved reciprocating internal combustion engine has a plurality of engine pistons, which are fabricated from carbon---carbon composite materials, in operative association with an engine cylinder block, or an engine cylinder tube, or an engine cylinder jug, all of which are also fabricated from carbon-carbon composite materials.

  17. Smooth-Surfaced Carbon/Carbon Reflector Panels

    NASA Technical Reports Server (NTRS)

    Schmitigal, Wesley P.; Jacoy, Paul J.; Porter, Christopher C.; Hickey, Gregory S.

    1992-01-01

    Surface-densification technique integral to fabrication of reflective, lightweight, low-outgassing radio-antenna-reflector panels including carbon/carbon surface laminates supported by carbon/carbon core structures. Densification prevents "print-through" of carbon fibers on surface. When properly densified, surface polished to smooth finish.

  18. Pistons and Cylinders Made of Carbon-Carbon Composite Materials

    NASA Technical Reports Server (NTRS)

    Rivers, H. Kevin (Inventor); Ransone, Philip O. (Inventor); Northam, G. Burton (Inventor); Schwind, Francis A. (Inventor)

    2000-01-01

    An improved reciprocating internal combustion engine has a plurality of engine pistons, which are fabricated from carbon-carbon composite materials, in operative association with an engine cylinder block, or an engine cylinder tube, or an engine cylinder jug, all of which are also fabricated from carbon-carbon composite materials.

  19. 31 CFR 359.68 - May Public Debt issue Series I savings bonds only in book-entry form?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false May Public Debt issue Series I savings bonds only in book-entry form? 359.68 Section 359.68 Money and Finance: Treasury Regulations Relating to... Series I savings bonds only in book-entry form? We reserve the right to issue bonds only in book-entry...

  20. Copper(I)-catalyzed aryl bromides to form intermolecular and intramolecular carbon-oxygen bonds.

    PubMed

    Niu, Jiajia; Guo, Pengran; Kang, Juntao; Li, Zhigang; Xu, Jingwei; Hu, Shaojing

    2009-07-17

    A highly efficient Cu-catalyzed C-O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K(3)PO(4) as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.

  1. Analysis techniques for the prediction of springback in formed and bonded composite components

    NASA Technical Reports Server (NTRS)

    Gasick, Michael F.; Renieri, Gary D.

    1992-01-01

    Two finite element analysis codes are used to model the effects of cooling on the dimensional stability of formed and bonded composite parts. The two analysis routines, one h-version and one p-version, are compared for modeling time, analysis execution time, and exactness of solution as compared to actual test results. A recommended procedure for predicting temperature effects on composite parts is presented, based on the results of this study.

  2. Strong Lewis acid air-stable cationic titanocene perfluoroalkyl(aryl)sulfonate complexes as highly efficient and recyclable catalysts for C-C bond forming reactions.

    PubMed

    Li, Ningbo; Wang, Jinying; Zhang, Xiaohong; Qiu, Renhua; Wang, Xie; Chen, Jinyang; Yin, Shuang-Feng; Xu, Xinhua

    2014-08-14

    A series of strong Lewis acid air-stable titanocene perfluoroalkyl(aryl)sulfonate complexes Cp2Ti(OH2)2(OSO2X)2·THF (X = C8F17, 1·THF; X = C4F9, 2·H2O·THF; X = C6F5, 3) were successfully synthesized by the treatment of Cp2TiCl2 with C8F17SO3Ag, C4F9SO3Ag and C6F5SO3Ag, respectively. In contrast to well-known titanocene bis(triflate), these complexes showed no change in open air over three months. TG-DSC analysis showed that 1·THF, 2·H2O·THF and 3 were thermally stable at 230 °C, 220 °C and 280 °C, respectively. Conductivity measurements showed that these complexes underwent ionic dissociation in CH3CN solution. X-ray analysis results confirmed that 2·H2O·THF and 3 were cationic. ESR spectra showed that the Lewis acidity of 1·THF (1.06 eV) was higher than that of Sc(3+) (1.00 eV) and Y(3+) (0.85 eV). UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2·H2O·THF. Fluorescence spectra showed that the Lewis acidity of 2 (λ(em) = 477 nm) was higher than that of Sc(3+) (λ(em) = 474 nm). These complexes showed high catalytic ability in various carbon-carbon bond forming reactions. Moreover, they show good reusability. Compared with 1·THF, 2·H2O·THF and 3 exhibit higher solubility and better catalytic activity, and will find broad applications in organic synthesis.

  3. Glass binder development for a glass-bonded sodalite ceramic waste form

    DOE PAGES

    Riley, Brian J.; Vienna, John D.; Frank, Steven M.; ...

    2017-06-01

    This paper discusses work to develop Na2O-B2O3-SiO2 glass binders for immobilizing LiCl-KCl eutectic salt waste in a glass-bonded sodalite waste form following electrochemical reprocessing of used metallic nuclear fuel. In this paper, five new glasses with ~20 mass% Na2O were designed to generate waste forms with high sodalite. The glasses were then used to produce ceramic waste forms with a surrogate salt waste. The waste forms made using these new glasses were formulated to generate more sodalite than those made with previous baseline glasses for this type of waste. The coefficients of thermal expansion for the glass phase in themore » glass-bonded sodalite waste forms made with the new binder glasses were closer to the sodalite phase in the critical temperature region near and below the glass transition temperature than previous binder glasses used. Finally, these improvements should result in lower probability of cracking in the full-scale monolithic ceramic waste form, leading to better long-term chemical durability.« less

  4. Glass binder development for a glass-bonded sodalite ceramic waste form

    NASA Astrophysics Data System (ADS)

    Riley, Brian J.; Vienna, John D.; Frank, Steven M.; Kroll, Jared O.; Peterson, Jacob A.; Canfield, Nathan L.; Zhu, Zihua; Zhang, Jiandong; Kruska, Karen; Schreiber, Daniel K.; Crum, Jarrod V.

    2017-06-01

    This paper discusses work to develop Na2O-B2O3-SiO2 glass binders for immobilizing LiCl-KCl eutectic salt waste in a glass-bonded sodalite waste form following electrochemical reprocessing of used metallic nuclear fuel. Here, five new glasses with ∼20 mass% Na2O were designed to generate waste forms with high sodalite. The glasses were then used to produce ceramic waste forms with a surrogate salt waste. The waste forms made using these new glasses were formulated to generate more sodalite than those made with previous baseline glasses for this type of waste. The coefficients of thermal expansion for the glass phase in the glass-bonded sodalite waste forms made with the new binder glasses were closer to the sodalite phase in the critical temperature region near and below the glass transition temperature than previous binder glasses used. These improvements should result in lower probability of cracking in the full-scale monolithic ceramic waste form, leading to better long-term chemical durability.

  5. Hypervelocity technology carbon/carbon testing

    NASA Astrophysics Data System (ADS)

    Anselmo, John V.; Kretz, Lawrence O.

    The paper describes the procedures used at the Structures Test Laboratory of the Wright Laboratory's Flight Dynamics Directorate to test a carbon/carbon hot structure representing a typical hypersonic gliding body, and presents the results of tests. The forebody was heated to 1371 C over 13 test runs, using radiant quartz lamps; a vertical shear force of 5.34 kN was introduced to the nose at a stabilized temperature of 816 C. Test data were collected using prototype high-temperature strain gages, in-house-designed high-temperature extensometers, conventional strain gages, and thermocouples. Video footage was taken of all test runs. Test runs were successfully completed up to 1371 C with flight typical thermal gradients at heating rates up to 5.56 C/sec. Results showed that, overall, the termal test control systems performed as predicted and that test temperatures and thermal gradients were achieved to within about 5 percent in most cases.

  6. Randomly oriented carbon/carbon composite

    NASA Astrophysics Data System (ADS)

    Raunija, Thakur Sudesh Kumar; Babu, S.

    2013-06-01

    The main objective of this study is to develop an alternate, rapid and cost effective process for the fabrication of carbon/carbon (C/C) composite. Slurry moulding technique is adopted for the fabrication of C/C composite. Randomly oriented hybrid discrete carbon fiber (CF) reinforced and mesophase pitch (MP) derived matrix C/C composite is fabricated. Process parameters are optimized and repeatability is proved. The electrical conductivity of the composite fabricated through the developed process is found to be better than that fabricated through conventional processes. The other properties are also found to be competent. The randomly oriented C/C composite because of its mouldability is found suitable for various applications which require complex shapes.

  7. Process of making carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Withers, James C. (Inventor); Loutfy, Raouf O. (Inventor); Kowbel, Witold (Inventor); Bruce, Calvin (Inventor); Vaidyanathan, Ranji (Inventor)

    2000-01-01

    A carbon composite structure, for example, an automotive engine piston, is made by preparing a matrix including of a mixture of non crystalline carbon particulate soluble in an organic solvent and a binder that has a liquid phase. The non crystalline particulate also contains residual carbon hydrogen bonding. An uncured structure is formed by combining the matrix mixture, for example, carbon fibers such as graphite dispersed in the mixture and/or graphite cloth imbedded in the mixture. The uncured structure is cured by pyrolyzing it in an inert atmosphere such as argon. Advantageously, the graphite reinforcement material is whiskered prior to combining it with the matrix mixture by a novel method involving passing a gaseous metal suboxide over the graphite surface.

  8. Transparent Films from CO2‐Based Polyunsaturated Poly(ether carbonate)s: A Novel Synthesis Strategy and Fast Curing

    PubMed Central

    Subhani, Muhammad Afzal; Köhler, Burkhard; Gürtler, Christoph; Leitner, Walter

    2016-01-01

    Abstract Transparent films were prepared by cross‐linking polyunsaturated poly(ether carbonate)s obtained by the multicomponent polymerization of CO2, propylene oxide, maleic anhydride, and allyl glycidyl ether. Poly(ether carbonate)s with ABXBA multiblock structures were obtained by sequential addition of mixtures of propylene oxide/maleic anhydride and propylene oxide/allyl glycidyl ether during the polymerization. The simultaneous addition of both monomer mixtures provided poly(ether carbonate)s with AXA triblock structures. Both types of polyunsaturated poly(ether carbonate)s are characterized by diverse functional groups, that is, terminal hydroxy groups, maleate moieties along the polymer backbone, and pendant allyl groups that allow for versatile polymer chemistry. The combination of double bonds substituted with electron‐acceptor and electron‐donor groups enables particularly facile UV‐ or redox‐initiated free‐radical curing. The resulting materials are transparent and highly interesting for coating applications. PMID:27028458

  9. Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin.

    PubMed

    Zakeri, Bijan; Fierer, Jacob O; Celik, Emrah; Chittock, Emily C; Schwarz-Linek, Ulrich; Moy, Vincent T; Howarth, Mark

    2012-03-20

    Protein interactions with peptides generally have low thermodynamic and mechanical stability. Streptococcus pyogenes fibronectin-binding protein FbaB contains a domain with a spontaneous isopeptide bond between Lys and Asp. By splitting this domain and rational engineering of the fragments, we obtained a peptide (SpyTag) which formed an amide bond to its protein partner (SpyCatcher) in minutes. Reaction occurred in high yield simply upon mixing and amidst diverse conditions of pH, temperature, and buffer. SpyTag could be fused at either terminus or internally and reacted specifically at the mammalian cell surface. Peptide binding was not reversed by boiling or competing peptide. Single-molecule dynamic force spectroscopy showed that SpyTag did not separate from SpyCatcher until the force exceeded 1 nN, where covalent bonds snap. The robust reaction conditions and irreversible linkage of SpyTag shed light on spontaneous isopeptide bond formation and should provide a targetable lock in cells and a stable module for new protein architectures.

  10. Bond and fracture strength of metal-ceramic restorations formed by selective laser sintering

    PubMed Central

    Bae, Eun-Jeong; Kim, Woong-Chul; Kim, Hae-Young

    2014-01-01

    PURPOSE The purpose of this study was to compare the fracture strength of the metal and the bond strength in metal-ceramic restorations produced by selective laser sintering (SLS) and by conventional casting (CAST). MATERIALS AND METHODS Non-precious alloy (StarLoy C, DeguDent, Hanau, Germany) was used in CAST group and metal powder (SP2, EOS GmbH, Munich, Germany) in SLS group. Metal specimens in the form of sheets (25.0 × 3.0 × 0.5 mm) were produced in accordance with ISO 9693:1999 standards (n=30). To measure the bond strength, ceramic was fired on a metal specimen and then three-point bending test was performed. In addition, the metal fracture strength was measured by continuing the application of the load. The values were statistically analyzed by performing independent t-tests (α=.05). RESULTS The mean bond strength of the SLS group (50.60 MPa) was higher than that of the CAST group (46.29 MPa), but there was no statistically significant difference. The metal fracture strength of the SLS group (1087.2 MPa) was lower than that of the CAST group (2399.1 MPa), and this difference was statistically significant. CONCLUSION In conclusion the balling phenomenon and the gap formation of the SLS process may increase the metal-ceramic bond strength. PMID:25177469

  11. Direct evidence that two cysteines in the dopamine transporter form a disulfide bond.

    PubMed

    Chen, Rong; Wei, Hua; Hill, Erik R; Chen, Lucy; Jiang, Liying; Han, Dawn D; Gu, Howard H

    2007-04-01

    We have generated a fully functional dopamine transporter (DAT) mutant (dmDATx7) with all cysteines removed except the two cysteines in extracellular loop 2 (EL2). Random mutagenesis at either or both EL2 cysteines did not produce any functional transporter mutants, suggesting that the two cysteines cannot be replaced by any other amino acids. The cysteine-specific reagent MTSEA-biotin labeled dmDATx7 only after a DTT treatment which reduces disulfide bond. Since there are no other cysteines in dmDATx7, the MTSEA-biotin labeling must be on the EL2 cysteines made available by the DTT treatment. This result provides the first direct evidence that the EL2 cysteines form a disulfide bond. Interestingly, the DTT treatment had little effect on transport activity suggesting that the disulfide bond is not necessary for the uptake function of DAT. Our results and previous results are consistent with the notion that the disulfide bond between EL2 cysteines is required for DAT biosynthesis and/or its delivery to the cell surface.

  12. Fracture toughness measurements on a glass bonded sodalite high-level waste form.

    SciTech Connect

    DiSanto, T.; Goff, K. M.; Johnson, S. G.; O'Holleran, T. P.

    1999-05-19

    The electrometallurgical treatment of metallic spent nuclear fuel produces two high-level waste streams; cladding hulls and chloride salt. Argonne National Laboratory is developing a glass bonded sodalite waste form to immobilize the salt waste stream. The waste form consists of 75 Vol.% crystalline sodalite (containing the salt) with 25 Vol.% of an ''intergranular'' glassy phase. Microindentation fracture toughness measurements were performed on representative samples of this material using a Vickers indenter. Palmqvist cracking was confirmed by post-indentation polishing of a test sample. Young's modulus was measured by an acoustic technique. Fracture toughness, microhardness, and Young's modulus values are reported, along with results from scanning electron microscopy studies.

  13. Superplastic Forming/Adhesive Bonding of Aluminum (SPF/AB) Multi-Sheet Structures

    NASA Technical Reports Server (NTRS)

    Wagner, John A. (Technical Monitor); Will, Jeff D.; Cotton, James D.

    2003-01-01

    A significant fraction of airframe structure consists of stiffened panels that are costly and difficult to fabricate. This program explored a potentially lower-cost processing route for producing such panels. The alternative process sought to apply concurrent superplastic forming and adhesive bonding of aluminum alloy sheets. Processing conditions were chosen to balance adequate superplasticity of the alloy with thermal stability of the adhesive. As a first objective, an air-quenchable, superplastic aluminum-lithium alloy and a low-volatile content, low-viscosity adhesive with compatible forming/curing cycles were identified. A four-sheet forming pack was assembled which consisted of a welded two-sheet core separated from the face sheets by a layer of adhesive. Despite some preliminary success, of over 30 forming trials none was completely successful. The main problem was inadequate superplasticity in the heat-affected zones of the rib welds, which generally fractured prior to completion of the forming cycle. The welds are a necessary component in producing internal ribs by the 'four-sheet' process. Other challenges, such as surface preparation and adhesive bonding, were adequately solved. But without the larger issue of tearing at the weld locations, complex panel fabrication by SPF/AB does not appear viable.

  14. Preliminary studies of the disposition of cerium in a glass-bonded sodalite waste form.

    SciTech Connect

    Lambregts, M. J.; Frank, S. M.

    2001-12-18

    Argonne National Laboratory has developed an electrometallurgical treatment for DOE spent metallic nuclear fuel. Fission products are immobilized in a durable glass bonded sodalite ceramic waste form (CWF) suitable for long term storage in a geological repository. Cesium is estimated to be in the waste form at approximately 0.1 wt.%. The exact disposition of cesium was uncertain and it was believed to be uniformly distributed throughout the waste form. A correlation of X-ray diffractometry (XRD), electron microscopy (EM), and nuclear magnetic resonance spectroscopy (NMR) performed on surrogate ceramic waste forms with high cesium loadings found a high cesium content in the glass phase and in several non-sodalite aluminosilicate phases. Cesium was not detected in the sodalite phase.

  15. Fatigue characterization of advanced carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Mahfuz, Hassan; Das, Partha S.; Jeelani, Shaik; Baker, Dean M.; Johnson, Sigured A.

    1992-01-01

    Response of quasi-isotropic laminates of SiC coated Carbon-Carbon (C/C) composites under flexural fatigue are investigated at room temperature. Virgin as well as mission cycled specimens are tested to study the effects of thermal and pressure cycling on the fatigue performance of C/C. Tests were conducted in three point bending with a stress ratio of 0.2 and frequency of 1 Hz. Fatigue strength of C/C has been found to be considerably high - approximately above 85 percent of the ultimate flexural strength. The fatigue strength appears to be decreasing with the increase in the number of mission cycling of the specimens. This lower strength with the mission cycled specimens is attributed to the loss of interfacial bond strength due to thermal and pressure cycling of the material. C/C is also found to be highly sensitive to the applied stress level during cyclic loading, and this sensitivity is observed to increase with the mission cycling. Weibull characterization on the fatigue data has been performed, and the wide scatter in the Weibull distribution is discussed. Fractured as well as untested specimens were C-scanned, and the progressive damage growth during fatigue is presented.

  16. Fatigue characterization of advanced carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Mahfuz, Hassan; Das, Partha S.; Jeelani, Shaik; Baker, Dean M.; Johnson, Sigured A.

    1992-01-01

    Response of quasi-isotropic laminates of SiC coated Carbon-Carbon (C/C) composites under flexural fatigue are investigated at room temperature. Virgin as well as mission cycled specimens are tested to study the effects of thermal and pressure cycling on the fatigue performance of C/C. Tests were conducted in three point bending with a stress ratio of 0.2 and frequency of 1 Hz. Fatigue strength of C/C has been found to be considerably high - approximately above 85 percent of the ultimate flexural strength. The fatigue strength appears to be decreasing with the increase in the number of mission cycling of the specimens. This lower strength with the mission cycled specimens is attributed to the loss of interfacial bond strength due to thermal and pressure cycling of the material. C/C is also found to be highly sensitive to the applied stress level during cyclic loading, and this sensitivity is observed to increase with the mission cycling. Weibull characterization on the fatigue data has been performed, and the wide scatter in the Weibull distribution is discussed. Fractured as well as untested specimens were C-scanned, and the progressive damage growth during fatigue is presented.

  17. Nicotinamidase/pyrazinamidase of Mycobacterium tuberculosis forms homo-dimers stabilized by disulfide bonds

    PubMed Central

    Rueda, Daniel; Sheen, Patricia; Gilman, Robert H.; Bueno, Carlos; Santos, Marco; Pando-Robles, Victoria; Batista, Cesar V.; Zimic, Mirko

    2014-01-01

    Recombinant wild-pyrazinamidase from H37Rv M. tuberculosis was analyzed by gel electrophoresis under differential reducing conditions to evaluate its quaternary structure. PZAse was fractionated by size exclusion chromatography under non-reducing conditions. PZAse activity was measured and mass spectrometry analysis was performed to determine the identity of proteins by de novo sequencing and to determine the presence of disulfide bonds. This study confirmed that M. tuberculosis wild type PZAse was able to form homo-dimers in vitro. Homo-dimers showed a slightly lower specific PZAse activity compared to monomeric PZAse. PZAse dimers were dissociated into monomers in response to reducing conditions. Mass spectrometry analysis confirmed the existence of disulfide bonds (C72-C138 and C138-C138) stabilizing the quaternary structure of the PZAse homo-dimer. PMID:25199451

  18. Stresses in adhesively bonded joints: A closed form solution. [plate theory

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.; Aydinoglu, M. N.

    1980-01-01

    The plane strain of adhesively bonded structures which consist of two different orthotropic adherents is considered. Assuming that the thicknesses of the adherends are constant and are small in relation to the lateral dimensions of the bonded region, the adherends are treated as plates. The transverse shear effects in the adherends and the in-plane normal strain in the adhesive are taken into account. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form. A single lap joint and a stiffened plate under various loading conditions are considered as examples. To verify the basic trend of the solutions obtained from the plate theory a sample problem is solved by using the finite element method and by treating the adherends and the adhesive as elastic continua. The plate theory not only predicts the correct trend for the adhesive stresses but also gives rather surprisingly accurate results.

  19. Development of eclipsed and staggered forms in some hydrogen bonded complexes

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Ali; Habibi, Mostafa; Hesabi, Nahid

    Intermolecular hydrogen bonding in X3CH···NH3 (X = H, F, Cl, and Br) complexes has been studied by B3LYP, B3PW91, MP2, MP3, MP4, and CCSD methods using 6-311++G(d,p) and AUG-cc-PVTZ basis sets. These complexes could exist in both eclipsed (EC) and staggered (ST) forms. The differences between binding energies of EC and ST forms are negligible and all EC and ST shapes correspond to minimum stationary states. The order of stabilities of them is in an agreement with the results of atoms in molecules (AIM) and natural bond orbital (NBO) analyses. On the basis of low differences between binding energies, ST forms are more stable than EC forms in all complexes with the exception of Br3CH···NH3, which behaves just opposite. Although the differences between binding energies are negligible, they are consistent with the results of AIM analysis.

  20. All-carbon quaternary stereogenic centers in acyclic systems through the creation of several C-C bonds per chemical step.

    PubMed

    Marek, Ilan; Minko, Yury; Pasco, Morgane; Mejuch, Tom; Gilboa, Noga; Chechik, Helena; Das, Jaya P

    2014-02-19

    In the past few decades, it has become clear that asymmetric catalysis is one of the most powerful methods for the construction of carbon-carbon as well as carbon-heteroatom bonds in a stereoselective manner. However, when structural complexity increases (i.e., all-carbon quaternary stereogenic center), the difficulty in reaching the desired adducts through asymmetric catalytic reactions leads to a single carbon-carbon bond-forming event per chemical step between two components. Issues of efficiency and convergence should therefore be addressed to avoid extraneous chemical steps. In this Perspective, we present approaches that tackle the stimulating problem of efficiency while answering interesting synthetic challenges. Ideally, if one could create all-carbon quaternary stereogenic centers via the creation of several new carbon-carbon bonds in an acyclic system and in a single-pot operation from simple precursors, it would certainly open new horizons toward solving the synthetic problems. Even more important for any further design, the presence of polyreactive intermediates in synthesis (bismetalated, carbenoid, and oxenoids species) becomes now an indispensable tool, as it creates consecutively the same number of carbon-carbon bonds as in a multi-step process, but in a single-pot operation.

  1. Corrosion behavior of a glass-bonded sodalite ceramic waste form and its constituents.

    SciTech Connect

    Lewis, M. A.; Ebert, W. L.; Morss, L.

    1999-06-18

    A ceramic waste form (CWF) of glass bonded sodalite is being developed as a waste form for the long-term immobilization of fission products and transuranic elements from the U.S. Department of Energy's activities on spent nuclear fuel conditioning. A durable waste form was prepared by hot isostatic pressing (HIP) a mixture of salt-loaded zeolite powders and glass frit. During HIP the zeolite is converted to sodalite, and the resultant CWF is been completed for durations of up to 182 days. Four dissolution modes were identified: dissolution of free salt, dissolution of the aluminosilicate matrix of sodalite and the accompanying dissolution of occluded salt, dissolution of the boroaluminosilicate matrix of the glass, and ion exchange. Synergies inherent to the CWF were identified by comparing the results of the tests with pure glass and sodalite with those of the composite CWF.

  2. Elastic stability of superplastically formed/diffusion-bonded orthogonally corrugated core sandwich plates

    NASA Technical Reports Server (NTRS)

    Ko, W. L.

    1980-01-01

    The paper concerns the elastic buckling behavior of a newly developed superplastically formed/diffusion-bonded (SPF/DB) orthogonally corrugated core sandwich plate. Uniaxial buckling loads were calculated for this type of sandwich plate with simply supported edges by using orthotropic sandwich plate theory. The buckling behavior of this sandwich plate was then compared with that of an SPF/DB unidirectionally corrugated core sandwich plate under conditions of equal structural density. It was found that the buckling load for the former was considerably higher than that of the latter.

  3. Elastic constants for superplastically formed/diffusion-bonded corrugated sandwich core

    NASA Technical Reports Server (NTRS)

    Ko, W. L.

    1980-01-01

    Formulas and associated graphs for evaluating the effective elastic constants for a superplastically formed/diffusion bonded (SPF/DB) corrugated sandwich core, are presented. A comparison of structural stiffnesses of the sandwich core and a honeycomb core under conditions of equal sandwich core density was made. The stiffness in the thickness direction of the optimum SPF/DB corrugated core (that is, triangular truss core) is lower than that of the honeycomb core, and that the former has higher transverse shear stiffness than the latter.

  4. Structural properties of superplastically formed/diffusion-bonded orthogonally corrugated core sandwich plates

    NASA Technical Reports Server (NTRS)

    Ko, W. L.

    1980-01-01

    This paper describes a new superplastically formed/diffusion-bonded (SPF/DB) orthogonally corrugated sandwich structure, and presents formulae and the associated plots for evaluating the effective elastic constants for the core of this new sandwich structure. Comparison of structural properties of this new sandwich structure with the conventional honeycomb core sandwich structure was made under the condition of equal sandwich density. It was found that the SPF/DB orthogonally corrugated sandwich core has higher transverse shear stiffness than the conventional honeycomb sandwich core. However, the former has lower stiffness in the sandwich core thickness direction than the latter.

  5. Superplastic Formed and Diffusion Bonded Titanium Landing Gear Component Feasibility Study.

    DTIC Science & Technology

    1980-07-01

    Gear Superplastic Forming Shock Strut SPF/DB Outer Cylinder Titanium Diffusion Bonding Cylindrical Sandwich Structure Z% ABSTRACT (Continue en ro,eree...lO0 Fighter Aircraft 6 5 F-lO0 Main Landing Gear 6 6 F-lO0 Landing Gear Strut Section Selected for this Program 7 7 SPF/DB Titanium Landing Gear... Assembly with a Diaphram Seal for DB Cycle. 18 15 MLG SPF/DB Titanium Outer Cylinder Segment DB Cycle Using a Diaphram Seal 19 16 Hot Sizing Tool 20 17

  6. Electrochemically assisted co-deposition of calcium phosphate/collagen coatings on carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Zhao, Xueni; Hu, Tao; Li, Hejun; Chen, Mengdi; Cao, Sheng; Zhang, Leilei; Hou, Xianghui

    2011-02-01

    Calcium phosphate (CaP)/collagen coatings were prepared on the surface of carbon/carbon (C/C) composites by electrochemically assisted co-deposition technique. The effects of collagen concentration in the electrolyte on morphology, structure and composition of the coatings were systematically investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The adhesive strength of the coatings was also evaluated by scratch tests and tensile bond tests. It was demonstrated that the coatings of three-dimensional collagen network structure was formed on the C/C composites from the electrolyte containing collagen. The surface of the collagen network was covered by uniform CaP aggregates. The coatings were actually composites of CaP and collagen. Hydroxyapatite (HA) was a favorable composition in the coatings with the increase of the collagen concentration in the electrolyte. The formed collagen network increased the cohesive and adhesive strength of the coatings. The adhesive strength between the coatings and substrates increased as the collagen concentration in the electrolyte increased. The coatings prepared at the collagen concentration of 500 mg/L in the electrolyte were not scraped off until the applied load reached 32.0 ± 2.2 N and the average tensile adhesive strength of the coatings was 4.83 ± 0.71 MPa. After C/C coated with composite coatings (500 mg/L) being immersed in a 10-3 M Ca (OH)2 solution at 30-33 °C for 96 h, nano-structured HA/collagen coatings similar to the natural human bone were obtained on the C/C.

  7. Tensile Strength of Carbon/Carbon Composites

    NASA Astrophysics Data System (ADS)

    Hatta, Hiroshi; Aoi, Tatsuji; Kawahara, Itaru; Kogo, Yasuo; Shiota, Ichiro

    In order to identify ruling mechanisms of tensile fracture of Carbon/Carbon composites (C/Cs), tensile tests were carried out for various C/Cs as functions of the density, heat treatment temperature, and interfacial strength between fiber and matrix. Three processing routes of preformed yarn, resin char, and HIP processes were adopted to densify C/Cs. These C/Cs were finally heat-treated at temperatures from 2273K to 3300K. The interfacial strength between fiber and matrix was varied by the selection of processing routes. As a result, two ruling failure mechanisms were identified. At density lower than 1.6g/cm3, the tensile fracture was controlled by stress transfer capability from the matrix to reinforcing fibers. However, at higher density than 1.6g/cm3, tensile strength was primarily governed by the interfacial strength between the matrix and fibers. Thus the latter mechanism is nearly same as ceramic matrix composites.

  8. Effects of single bond-ion and single bond-diradical form on the stretching vibration of Cdbnd N bridging bond in 4,4‧-disubstituted benzylidene anilines

    NASA Astrophysics Data System (ADS)

    Cao, Chao-Tun; Bi, Yakun; Cao, Chenzhong

    2016-06-01

    Fifty-seven samples of model compounds, 4,4‧-disubstituted benzylidene anilines, p-X-ArCH = NAr-p-Y were synthesized. Their infrared absorption spectra were recorded, and the stretching vibration frequencies νCdbnd N of the Cdbnd N bridging bond were determined. New stretching vibration mode was proposed by means of the analysis of the factors affecting νCdbnd N, that is there are mainly three modes in the stretching vibration of Cdbnd N bond: (I) polar double bond form Cdbnd N, (II) single bond-ion form C+-N- and (III) single bond-diradical form Crad -Nrad . The contributions of the forms (I) and (II) to the change of νCdbnd N can be quantified by using Hammett substituent constant (including substituent cross-interaction effects between X and Y groups), whereas the contribution of the form (III) can be quantified by employing the excited-state substituent constant. The most contribution of these three forms is the form (III), the next is the form (II), whose contribution difference was discussed with the viewpoint of energy requirements in vibration with the form (III) and form (II).

  9. Effects of aqueous environment on long-term durability of phosphate-bonded ceramic waste forms

    SciTech Connect

    Singh, D.; Wagh, A.S.; Jeong, S.Y.

    1996-03-01

    Over the last few years, Argonne National Laboratory has been developing room-temperature-setting chemically-bonded phosphate ceramics for solidifying and stabilizing low-level mixed wastes. This technology is crucial for stabilizing waste streams that contain volatile species and off-gas secondary waste streams generated by high-temperature treatment of such wastes. Magnesium phosphate ceramic has been developed to treat mixed wastes such as ash, salts, and cement sludges. Waste forms of surrogate waste streams were fabricated by acid-base reactions between the mixtures of magnesium oxide powders and the wastes, and phosphoric acid or acid phosphate solutions. Dense and hard ceramic waste forms are produced in this process. The principal advantage of this technology is that the contaminants are immobilized by both chemical stabilization and subsequent microencapsulation of the reaction products. This paper reports the results of durability studies conducted on waste forms made with ash waste streams spiked with hazardous and radioactive surrogates. Standard leaching tests such as ANS 16.1 and TCLP were conducted on the final waste forms. Fates of the contaminants in the final waste forms were established by electron microscopy. In addition, stability of the waste forms in aqueous environments was evaluated with long-term water-immersion tests.

  10. Interstitially protected oxidation resistant carbon-carbon composite

    SciTech Connect

    Strangman, T.E.; Keiser, R.J.

    1984-02-01

    The carbon fiber bundles in a carbon-carbon composite are protected against oxidation by coating the fiber bundles with at least one protective layer consisting of an underlayer portion of boron carbide and an overlayer portion of silicon carbide.

  11. Development of carbon-carbon composites from solvent extracted pitch

    SciTech Connect

    1996-06-24

    There are several methods used to fabricate carbon-carbon composites. One used extensively in the fabrication of aerospace components such as rocket nozzles and reentry vehicle nosetips, as well as commercial components for furnace fixturing and glass manufacturing, is the densification of a woven preform with molten pitch, and the subsequent conversion of the pitch to graphite through heat treatment. Two types of pitch are used in this process; coal tar pitch and petroleum pitch. The objective of this program was to determine if a pitch produced by the direct extraction of coal could be used as a substitute for these pitches in the fabrication of carbon-carbon composites. The program involved comparing solvent extracted pitch with currently accepted pitches and rigidizing a carbon-carbon preform with solvent extracted pitch for comparison with carbon-carbon fabricated with currently available pitch.

  12. A general strategy for the evolution of bond-forming enzymes using yeast display

    PubMed Central

    Chen, Irwin; Dorr, Brent M.; Liu, David R.

    2011-01-01

    The ability to routinely generate efficient protein catalysts of bond-forming reactions chosen by researchers, rather than nature, is a long-standing goal of the molecular life sciences. Here, we describe a directed evolution strategy for enzymes that catalyze, in principle, any bond-forming reaction. The system integrates yeast display, enzyme-mediated bioconjugation, and fluorescence-activated cell sorting to isolate cells expressing proteins that catalyze the coupling of two substrates chosen by the researcher. We validated the system using model screens for Staphylococcus aureus sortase A–catalyzed transpeptidation activity, resulting in enrichment factors of 6,000-fold after a single round of screening. We applied the system to evolve sortase A for improved catalytic activity. After eight rounds of screening, we isolated variants of sortase A with up to a 140-fold increase in LPETG-coupling activity compared with the starting wild-type enzyme. An evolved sortase variant enabled much more efficient labeling of LPETG-tagged human CD154 expressed on the surface of HeLa cells compared with wild-type sortase. Because the method developed here does not rely on any particular screenable or selectable property of the substrates or product, it represents a powerful alternative to existing enzyme evolution methods. PMID:21697512

  13. Palladium-catalyzed 1,4-difunctionalization of butadiene to form skipped polyenes.

    PubMed

    McCammant, Matthew S; Liao, Longyan; Sigman, Matthew S

    2013-03-20

    A palladium-catalyzed 1,4-addition across the commodity chemical 1,3-butadiene to afford skipped polyene products is reported. Through a palladium σ → π → σ allyl isomerization, two new carbon-carbon bonds are formed with high regioselectivity and trans stereoselectivity of the newly formed alkene. The utility of this method is highlighted by the successful synthesis of the ripostatin A skipped triene core.

  14. Effectiveness of bonded and vacuum-formed retainers: A prospective randomized controlled clinical trial.

    PubMed

    O'Rourke, Niamh; Albeedh, Hussein; Sharma, Pratik; Johal, Ama

    2016-09-01

    The objective of this prospective trial was to compare the clinical effectiveness of bonded retainers with vacuum-formed retainers, in terms of maintaining the results of orthodontic treatment in the lower arch up to 18 months post debond. This was a hospital-based, prospective randomized controlled clinical trial in which a total of 82 subjects were randomly allocated using a computer-generated number sequence to 1 of 2 groups, receiving either a vacuum-formed retainer (Essix Ace plastic (120 mm; DENTSPLY Raintree Essix, Sarasota, Fla) or a bonded retainer (0.0175 coaxial archwire (Ortho-Care, UK, Shipley, United Kingdom) bonded in place with Transbond LR (3M United Kingdom, Brachnell, United Kingdom) for the mandibular arch. Each number was placed in an opaque, concealed envelope and chosen randomly by the study subject; this determined the allocation group. Eligibility criteria included patients nearing debond after treatment with 0.022 × 0.028-in slot size preadjusted edgewise fixed orthodontic appliances whose pretreatment records and study models were available to confirm pretreatment labial segment crowding or spacing and who had clinically acceptable alignment at the end of treatment. The main outcome was to investigate the clinical effectiveness of the 2 types of retainers in terms of changes in incisor irregularity at 6 months of retention. The following measurements were recorded at each time point (6, 12, and 18 months) with a digital caliper: Little's irregularity index, intercanine width, intermolar width, arch length, and extraction site opening. Blinding was applicable only at debond because of the permanence of 1 intervention. The 2 groups were well matched with respect to age, sex, clinical characteristics, and treatment plans. There was a statistically significant difference between the groups for changes in Little's irregularity index at 6 months, with the vacuum-formed retainer group showing greater changes than the bonded retainer

  15. Effect of Test Specimen Shape and Size on Interlaminar Tensile Properties of Advanced Carbon-Carbon Composites

    NASA Technical Reports Server (NTRS)

    Vaughn, Wallace L.

    2015-01-01

    The interlaminar tensile strength of 1000-tow T-300 fiber ACC-6 carbon-carbon composites was measured using the method of bonding the coupons to adherends at room temperature. The size, 0.70 to 1.963 inches maximum width or radius, and shape, round or square, of the test coupons were varied to determine if the test method was sensitive to these variables. Sixteen total variations were investigated and the results modeled.

  16. Comparison of σ-Hole and π-Hole Tetrel Bonds Formed by Pyrazine and 1,4-Dicyanobenzene: The Interplay between Anion-π and Tetrel Bonds.

    PubMed

    Xu, Huili; Cheng, Jianbo; Yang, Xin; Liu, Zhenbo; Li, Wenzuo; Li, Qingzhong

    2017-07-14

    The σ-hole tetrel bond in pyrazine/1,4-dicyanobenzene⋅⋅⋅TH3 F (T=C and Si) and the π-hole tetrel bond in pyrazine/1,4-dicyanobenzene⋅⋅⋅F2 TO have been compared. The π-hole tetrel bond is stronger than the corresponding σ-hole tetrel bond, with a larger interaction energy, shorter binding contact, greater electron density, and bigger charge transfer. Pyrazine forms a more stable tetrel-bonded complex than 1,4-dicyanobenzene even though the nitrogen atom in the former has a smaller negative electrostatic potential than the latter. An interesting cooperative effect was found when anion-π and tetrel-bond interactions coexisted in the same multicomponent complex of X(-) ⋅⋅⋅pyrazine/1,4-dicyanobenzene⋅⋅⋅TH3 F/F2 TO (X=F, Cl, and Br). Both interactions displayed a positive cooperative effect, as shown by the larger interaction energies, shorter binding separations, and greater electron densities. The enhancement in the tetrel bond is dependent on the strength of the anion-π interaction and it becomes larger in the order Br(-) bond changes its nature from a purely closed-shell interaction to a partially covalent interaction. Conversely, the anion-π interaction shows a prominent strengthening of up to -38 kcal mol(-1) . This effect has been analyzed in terms of electrostatic potentials and charge transfer. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Fluorescence detection of cytosine/guanine transversion based on a hydrogen bond forming ligand.

    PubMed

    Nishizawa, Seiichi; Yoshimoto, Keitaro; Seino, Takehiro; Xu, Chun-Yan; Minagawa, Masakazu; Satake, Hiroyuki; Tong, Aijun; Teramae, Norio

    2004-05-10

    In combination with abasic site (AP site)-containing oligodeoxynucleotides (ODNs), we demonstrate potential use of a hydrogen bond forming ligand, 2-amino-7-methyl-1,8-naphthyridine (AMND), for the fluorescence detection of the cytosine (C)/guanine (G) mutation sequence of the cancer repression gene p53. Our method is based on construction of the AP site in ODN duplexes, which allows small synthetic ligands to bind to target nucleobases accompanied by fluorescence signaling: an AP site-containing ODN is hybridized with a target ODN so as to place the AP site toward a target nucleobase, by which hydrophobic microenvironments are provided for ligands to recognize target nucleobases through hydrogen-bonding. In 10mM sodium cacodylate buffer solutions (pH, 7.0) containing 100mM NaCl and 1.0mM EDTA, AMND is found to strongly bind to C (K(d)=1.5x10(-6)M) in the target ODN while the binding affinity for G is relatively moderate (K(d)=50x10(-6)M). Significant fluorescence quenching of AMND is observed only when binding to C, making it possible to judge the C/G transversion with the naked eye.

  18. Comparison of mechanical properties of glass-bonded sodalite and borosilicate glass high-level waste forms

    SciTech Connect

    O'Holleran, T. P.; DiSanto, T.; Johnson, S. G.; Goff, K. M.

    2000-05-09

    Argonne National Laboratory has developed a glass-bonded sodalite waste form to immobilize the salt waste stream from electrometallurgical treatment of spent nuclear fuel. The waste form consists of 75 vol.% crystalline sodalite and 25 vol.% glass. Microindentation fracture toughness measurements were performed on this material and borosilicate glass from the Defense Waste Processing Facility using a Vickers indenter. Palmqvist cracking was confined for the glass-bonded sodalite waste form, while median-radial cracking occurred in the borosilicate glass. The elastic modulus was measured by an acoustic technique. Fracture toughness, microhardness, and elastic modulus values are reported for both waste forms.

  19. Stereochemistry of enzymatic water addition to C=C bonds.

    PubMed

    Chen, Bi-Shuang; Otten, Linda G; Hanefeld, Ulf

    2015-01-01

    Water addition to carbon-carbon double bonds using hydratases is attracting great interest in biochemistry. Most of the known hydratases are involved in primary metabolism and to a lesser extent in secondary metabolism. New hydratases have recently been added to the toolbox, both from natural sources or artificial metalloenzymes. In order to comprehensively understand how the hydratases are able to catalyse the water addition to carbon-carbon double bonds, this review will highlight the mechanistic and stereochemical studies of the enzymatic water addition to carbon-carbon double bonds, focusing on the syn/anti-addition and stereochemistry of the reaction.

  20. Urea destabilizes RNA by forming stacking interactions and multiple hydrogen bonds with nucleic acid bases.

    PubMed

    Priyakumar, U Deva; Hyeon, Changbong; Thirumalai, D; Mackerell, Alexander D

    2009-12-16

    Urea titration of RNA by urea is an effective approach to investigate the forces stabilizing this biologically important molecule. We used all atom molecular dynamics simulations using two urea force fields and two RNA constructs to elucidate in atomic detail the destabilization mechanism of folded RNA in aqueous urea solutions. Urea denatures RNA by forming multiple hydrogen bonds with the RNA bases and has little influence on the phosphodiester backbone. Most significantly we discovered that urea engages in stacking interactions with the bases. We also estimate, for the first time, the m-value for RNA, which is a measure of the strength of urea-RNA interactions. Our work provides a conceptual understanding of the mechanism by which urea enhances RNA folding rates.

  1. Application of superplastically formed and diffusion bonded aluminum to a laminar flow control leading edge

    NASA Technical Reports Server (NTRS)

    Goodyear, M. D.

    1987-01-01

    NASA sponsored the Aircraft Energy Efficiency (ACEE) program in 1976 to develop technologies to improve fuel efficiency. Laminar flow control was one such technology. Two approaches for achieving laminar flow were designed and manufactured under NASA sponsored programs: the perforated skin concept used at McDonnell Douglas and the slotted design used at Lockheed-Georgia. Both achieved laminar flow, with the slotted design to a lesser degree (JetStar flight test program). The latter design had several fabrication problems concerning springback and adhesive flow clogging the air flow passages. The Lockheed-Georgia Company accomplishments is documented in designing and fabricating a small section of a leading edge article addressing a simpler fabrication method to overcome the previous program's manufacturing problems, i.e., design and fabrication using advanced technologies such as diffusion bonding of aluminum, which has not been used on aerospace structures to date, and the superplastic forming of aluminum.

  2. Halogen bonds form the basis for selective P-TEFb inhibition by DRB.

    PubMed

    Baumli, Sonja; Endicott, Jane A; Johnson, Louise N

    2010-09-24

    Cdk9, the kinase of the positive transcription elongation factor b, is required for processive transcription elongation by RNA polymerase II. Cdk9 inhibition contributes to the anticancer activity of many Cdk inhibitors under clinical investigation and hence there is interest in selective Cdk9 inhibitors. DRB (5,6-dichlorobenzimidazone-1-β-D-ribofuranoside) is a commonly used reagent for Cdk9 inhibition in cell biology studies. The crystal structures of Cdk9 and Cdk2 in complex with DRB reported here describe the molecular basis for the DRB selectivity toward Cdk9. The DRB chlorine atoms form halogen bonds that are specific for the Cdk9 kinase hinge region. Kinetic and thermodynamic experiments validate the structural findings and implicate the C-terminal residues of Cdk9 in contributing to the affinity for DRB. These results open the possibility to exploit halogen atoms in inhibitor design to specifically target Cdk9. Copyright © 2010 Elsevier Ltd. All rights reserved.

  3. STABILIZING GLASS BONDED WASTE FORMS CONTAINING FISSION PRODUCTS SEPARATED FROM SPENT NUCLEAR FUEL

    SciTech Connect

    Kenneth J. Bateman; Charles W. Solbrig

    2008-07-01

    A model has been developed to represent the stresses developed when a molten, glass-bonded brittle cylinder (used to store nuclear material) is cooled from high temperature to working temperature. Large diameter solid cylinders are formed by heating glass or glass-bonded mixtures (mixed with nuclear waste) to high temperature (915°C). These cylinders must be cooled as the final step in preparing them for storage. Fast cooling time is desirable for production; however, if cooling is too fast, the cylinder can crack into many pieces. To demonstrate the capability of the model, cooling rate cracking data were obtained on small diameter (7.8 cm diameter) glass-only cylinders. The model and experimental data were combined to determine the critical cooling rate which separates the non-cracking stable glass region from the cracked, non-stable glass regime. Although the data have been obtained so far only on small glass-only cylinders, the data and model were used to extrapolate the critical-cooling rates for large diameter ceramic waste form (CWF) cylinders. The extrapolation estimates long term cooling requirements. While a 52-cm diameter cylinder (EBR-II-waste size) can be cooled to 100°C in 70 hours without cracking, a 181.5-cm diameter cylinder (LWR waste size) requires 35 days to cool to 100°C. These cooling times are long enough that verification of these estimates are required so additional experiments are planned on both glass only and CWF material.

  4. Oxidation Microstructure Studies of Reinforced Carbon/Carbon

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Curry, Donald M.

    2006-01-01

    Laboratory oxidation studies of reinforced carbon/carbon (RCC) are discussed with particular emphasis on the resulting microstructures. This study involves laboratory furnace (500-1500 C deg) and arc-jet exposures (1538 C deg) on various forms of RCC. RCC without oxidation protection oxidized at 800 and 1100 C deg exhibits pointed and reduced diameter fibers, due to preferential attack along the fiber edges. RCC with a SiC conversion coating exhibits limited attack of the carbon substrate at 500, 700 and 1500 C deg. However samples oxidized at 900, 1100, and 1300 C deg show small oxidation cavities at the SiC/carbon interface below through-thickness cracks in the SiC coating. These cavities have rough edges with denuded fibers and can be easily distinguished from cavities created in processing. Arc-jet tests at 1538 C deg show limited oxidation attack when the SiC coating and glass sealants are intact. When the SiC/sealant protection system is damaged, attack is extensive and proceeds through matrix cracks, creating denuded fibers on the edges of the cracks. Even at 1538 C deg, where diffusion control dominates, attack is non-uniform with fiber edges oxidizing in preference to the bulk fiber and matrix.

  5. Resistivity of Carbon-Carbon Composites Halved

    NASA Technical Reports Server (NTRS)

    Gaier, James R.

    2004-01-01

    Carbon-carbon composites have become the material of choice for applications requiring strength and stiffness at very high temperatures (above 2000 C). These composites comprise carbon or graphite fibers embedded in a carbonized or graphitized matrix. In some applications, such as shielding sensitive electronics in very high temperature environments, the performance of these materials would be improved by lowering their electrical resistivity. One method to lower the resistivity of the composites is to lower the resistivity of the graphite fibers, and a proven method to accomplish that is intercalation. Intercalation is the insertion of guest atoms or molecules into a host lattice. In this study the host fibers were highly graphitic pitch-based graphite fibers, or vapor-grown carbon fibers (VGCF), and the intercalate was bromine. Intercalation compounds of graphite are generally thought of as being only metastable, but it has been shown that the residual bromine graphite fiber intercalation compound is remarkably stable, resisting decomposition even at temperatures at least as high as 1000 C. The focus of this work was to fabricate composite preforms, determine whether the fibers they were made from were still intercalated with bromine after processing, and determine the effect on composite resistivity. It was not expected that the resistivity would be lowered as dramatically as with graphite polymer composites because the matrix itself would be much more conductive, but it was hoped that the gains would be substantial enough to warrant its use in high-performance applications. In a collaborative effort supporting a Space Act Agreement between the NASA Glenn Research Center and Applied Sciences, Inc. (Cedarville, OH), laminar preforms were fabricated with pristine and bromine-intercalated pitch-based fibers (P100 and P100-Br) and VGCF (Pyro I and Pyro I-Br). The green preforms were carbonized at 1000 C and then heat treated to 3000 C. To determine whether the

  6. Indirect Versus Direct Heating of Sheet Materials: Superplastic Forming and Diffusion Bonding Using Lasers

    NASA Astrophysics Data System (ADS)

    Jocelyn, Alan; Kar, Aravinda; Fanourakis, Alexander; Flower, Terence; Ackerman, Mike; Keevil, Allen; Way, Jerome

    2010-06-01

    Many from within manufacturing industry consider superplastic forming (SPF) to be ‘high tech’, but it is often criticized as too complicated, expensive, slow and, in general, an unstable process when compared to other methods of manipulating sheet materials. Perhaps, the fundamental cause of this negative perception of SPF, and also of diffusion bonding (DB), is the fact that the current process of SPF/DB relies on indirect sources of heating to produce the conditions necessary for the material to be formed. Thus, heat is usually derived from the electrically heated platens of hydraulic presses, to a lesser extent from within furnaces and, sometimes, from heaters imbedded in ceramic moulds. Recent evaluations of these isothermal methods suggest they are slow, thermally inefficient and inappropriate for the process. In contrast, direct heating of only the material to be formed by modern, electrically efficient, lasers could transform SPF/DB into the first choice of designers in aerospace, automotive, marine, medical, architecture and leisure industries. Furthermore, ‘variable temperature’ direct heating which, in theory, is possible with a laser beam(s) may provide a means to control material thickness distribution, a goal of enormous importance as fuel efficient, lightweight structures for transportation systems are universally sought. This paper compares, and contrasts, the two systems and suggests how a change to laser heating might be achieved.

  7. Microstructure and Mechanical Properties of Reaction-Formed Joints in Reaction Bonded Silicon Carbide Ceramics

    NASA Technical Reports Server (NTRS)

    Singh, M.

    1998-01-01

    A reaction-bonded silicon carbide (RB-SiC) ceramic material (Carborundum's Cerastar RB-SIC) has been joined using a reaction forming approach. Microstructure and mechanical properties of three types of reaction-formed joints (350 micron, 50-55 micron, and 20-25 micron thick) have been evaluated. Thick (approximately 350 micron) joints consist mainly of silicon with a small amount of silicon carbide. The flexural strength of thick joints is about 44 plus or minus 2 MPa, and fracture always occurs at the joints. The microscopic examination of fracture surfaces of specimens with thick joints tested at room temperature revealed the failure mode to be typically brittle. Thin joints (<50-55 micron) consist of silicon carbide and silicon phases. The room and high temperature flexural strengths of thin (<50-55 micron) reaction-formed joints have been found to be at least equal to that of the bulk Cerastar RB-SIC materials because the flexure bars fracture away from the joint regions. In this case, the fracture origins appear to be inhomogeneities inside the parent material. This was always found to be the case for thin joints tested at temperatures up to 1350C in air. This observation suggests that the strength of Cerastar RB-SIC material containing a thin joint is not limited by the joint strength but by the strength of the bulk (parent) materials.

  8. 27 CFR 28.62 - Bond, Form 2735 (5100.30).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...), as provided in § 28.51. (b) Penal sum of bond. The penal sum of the bond shall be sufficient to cover... one time. However, the maximum penal sum of the bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. Distilled spirits and wine withdrawn for exportation, use on...

  9. 27 CFR 26.66 - Bond, TTB Form 5110.50-Distilled spirits.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... this subpart, on all distilled spirits products shipped. The bond shall be executed in a penal sum not less than the amount of unpaid tax which, at any one time, is chargeable against the bond. The penal sum of such bond shall not exceed $1,000,000, but in no case shall the penal sum be less than $1,000...

  10. Oxidation of Carbon/Carbon through Coating Cracks

    NASA Technical Reports Server (NTRS)

    Jacobson, N. S.; Roth, d. J.; Rauser, R. W.; Cawley, J. D.; Curry, D. M.

    2008-01-01

    Reinforced carbon/carbon (RCC) is used to protect the wing leading edge and nose cap of the Space Shuttle Orbiter on re-entry. It is composed of a lay-up of carbon/carbon fabric protected by a SiC conversion coating. Due to the thermal expansion mismatch of the carbon/carbon and the SiC, the SiC cracks on cool-down from the processing temperature. The cracks act as pathways for oxidation of the carbon/carbon. A model for the diffusion controlled oxidation of carbon/carbon through machined slots and cracks is developed and compared to laboratory experiments. A symmetric cylindrical oxidation cavity develops under the slots, confirming diffusion control. Comparison of cross sectional dimensions as a function of oxidation time shows good agreement with the model. A second set of oxidation experiments was done with samples with only the natural craze cracks, using weight loss as an index of oxidation. The agreement of these rates with the model is quite reasonab

  11. [Study on implant material of carbon/carbon composites].

    PubMed

    Wang, Guohui; Yu, Shu; Zhu, Shaihong; Liu, Yong; Miu, Yunliang; Huang, Boyun

    2010-12-01

    This study was aimed to evaluate the biocompatibility and mechanical property of carbon/carbon composites. At first, carbon/carbon composites were prepared by chemical vapor deposition, and the mechanical property of carbon/carbon composites was tested. The biocompatibility of carbon/carbon composites was evaluated by cytotoxicity test, sensitization test, micronucleus test and implantation test. Mechanical property test showed such carbon/carbon composites are of good compression property and tension property. Cytotoxicity test showed that the leaching liquor of samples has no effect on the growth and proliferation of L-929 cells. The medullary micronucleus frequency of mouse was 2.3 per thousand +/- 0.7 per thousand in experiment group. The sensitization test showed that the skin of the subjects of experiment group had slight erythema and edema, which was 0.188 +/- 0.40 according to Magnusson and Kligman classification. Implantation test revealed that there was slight inflammation around the tissue after the implantation of sample. At 12 weeks, scanning electron microscopy and histopathological exam indicated that the samples of experiment group were of good histocompatibility; and in comparison with control group, there was no significant differences (P > 0.05). So these kinds of samples have good biocompatibility, mechanical property and prospects of clinical application.

  12. Coefficients of thermal expansion for a carbon-carbon composite

    SciTech Connect

    Feng, W.W.; Hoheisel, T.H.

    1989-11-17

    From the published data, carbon-carbon composites possess many unique properties at high temperature. They retain their room temperature strength in excess of 2200{degrees}C. The low coefficients of thermal expansion (CTE) and the property of non-wetting by molten metals make carbon-carbon composites excellent candidates for applications in the LIS program. Among these unique properties, CTE is the most important factor for the LIS program. In seeking to evaluate typical CTE's we obtained complementary samples of selected carbon-carbon specimens. These samples were laminates with (0{sub 2}){sub s}, (0{sub 2}90{sub 2}){sub s} and ({plus minus}45){sub s} orientations. These results indicated that the selected carbon-carbon composites are almost isotropic in thermal expansion. The CTE's are slightly negative at low temperature and become positive at high temperature. The exact values are shown in the figures. In order to determine the outgassing of carbon-carbon composites, two samples were tested in vacuum. The results have shown that the outgassing can not be neglected. 8 figs.

  13. Direct Observation of a Cytosine Analogue that Forms Five Hydrogen Bonds to Guanosine: Guanyl G-Clamp

    SciTech Connect

    Wilds, C.J.; Maier, M.A.; Tereshko, V.; Manoharan, M.; Egli, M.

    2010-03-08

    A novel heterocyclic base modification, the guanidino G-clamp, is designed to allow two Hoogsteen-type hydrogen bonds to form between the amino and imino nitrogen atoms of a tethered guanidinium group to O6 and N7 of guanosine, which results in a total of five hydrogen bonds (broken lines, see picture). Details of a crystal structure at 1.0-{angstrom} resolution of a modified DNA decamer containing this guanidino G-clamp analogue demonstrate its mechanism of binding.

  14. Cross-dehydrogenative coupling (CDC): exploring C-C bond formations beyond functional group transformations.

    PubMed

    Li, Chao-Jun

    2009-02-17

    Synthetic chemists aspire both to develop novel chemical reactions and to improve reaction conditions to maximize resource efficiency, energy efficiency, product selectivity, operational simplicity, and environmental health and safety. Carbon-carbon bond formation is a central part of many chemical syntheses, and innovations in these types of reactions will profoundly improve overall synthetic efficiency. This Account describes our work over the past several years to form carbon-carbon bonds directly from two different C-H bonds under oxidative conditions, cross-dehydrogenative coupling (CDC). We have focused most of our efforts on carbon-carbon bonds formed via the functionalization of sp(3) C-H bonds with other C-H bonds. In the presence of simple and cheap catalysts such as copper and iron salts and oxidants such as hydrogen peroxide, dioxygen, tert-butylhydroperoxide, and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), we can directly functionalize various sp(3) C-H bonds by other C-H bonds without requiring preactivation. We demonstrate (1) reaction of alpha-C-H bonds of nitrogen in amines, (2) reaction of alpha-C-H bonds of oxygen in ethers, (3) reaction of allylic and benzylic C-H bonds, and (4) reaction of alkane C-H bonds. These CDC reactions can tolerate a variety of functional groups, and some can occur under aqueous conditions. Depending on the specific transformation, we propose the in situ generation of different intermediates. These methods provide an alternative to the separate steps of prefunctionalization and defunctionalization that have traditionally been part of synthetic design. As a result, these methods will increase synthetic efficiencies at the most fundamental level. On an intellectual level, the development of C-C bond formations based on the reaction of only C-H bonds (possibly in water) challenges us to rethink some of the most fundamental concepts and theories regarding chemical reactivities. A successful reaction requires the

  15. Energetics and chemical bonding of the 1,3,5-tridehydrobenzene triradical and its protonated form

    NASA Astrophysics Data System (ADS)

    Nguyen, Hue Minh Thi; Höltzl, Tibor; Gopakumar, G.; Veszprémi, Tamás; Peeters, Jozef; Nguyen, Minh Tho

    2005-09-01

    Quantum chemical calculations were applied to investigate the electronic structure of the parent 1,3,5-tridehydrobenzene triradical (C 6H 3, TDB) and its anion (C6H3-), cation (C6H3+) and protonated form (C6H4+). Our results obtained using the state-averaged complete active space self-consistent-field (CASSCF) followed by second-order multi-state multi-configuration perturbation theory, MS-CASPT2, and MRMP2 in conjunction with the large ANO-L and 6-311++G(3df,2p) basis set, confirm and reveal the followings: (i) TDB has a doublet 2A 1 ground state with a 4B 2- 2A 1 energy gap of 29 kcal/mol, (ii) the ground state of the C6H3- anion in the triplet 3B 2 being 4 kcal/mol below the 1A 1 state. (iii) the electron affinity (EA), ionization energy (IE) and proton affinity (PA) are computed to be: EA = 1.6 eV, IE = 7.2 eV, PA = 227 kcal/mol using UB3LYP/6-311++G(3df,2p) + ZPE; standard heat of formation Δ Hf(298 K, 1 atm) (TDB) = 179 ± 2 kcal/mol was calculated with CBS-QB3 method. An atoms-in-molecules (AIM) analysis of the structure reveals that the topology of the electron density is similar in all compounds: hydrogens connect to a six-membered ring, except for the case of the 2A 2 state of C6H4+ (MBZ +) which is bicyclic with fused five- and three-membered rings. Properties of the chemical bonds were characterized with Electron Localization Function (ELF) analysis, as well as Wiberg indices, Laplacian and spin density maps. We found that the radicals form separate monosynaptic basins on the ELF space, however its pair character remains high. In the 2A 1 state of TDB, the radical center is mainly localized on the C1 atom, while in the 2B 2 state it is equally distributed between the C3 and C5 atoms and, due to the symmetry, in the 4B 2 state the C1, C2 and C3 atoms have the same radical character. There is no C3-C5 bond in the 2A 1 state of TDB, but the interaction between these atoms is strong. The ground state of cation C6H3+ (DHP), 1A 1, is not a diradical and has

  16. Stability of Criegee intermediates formed by ozonolysis of different double bonds.

    PubMed

    Kalinowski, Jaroslaw; Heinonen, Petri; Kilpeläinen, Ilkka; Räsänen, Markku; Gerber, R Benny

    2015-03-19

    The formation of Criegee intermediates by ozonolysis of different species containing C═N and C═P bonds is studied computationally. Electronic structure calculations are carried out for the energetics of ozonolysis, and the lifetime of the Criegee intermediate formed is computed by transition state theory. All calculations are carried out for formation of CH2OO, the simplest Criegee intermediate. Extremely large differences are found for the lifetime of CH2OO depending on the specific C═N, C═P, and C═C precursor, due to the great variations in the exoergicity of the ozonolysis. The largest lifetimes of CH2OO are found to be up to a millisecond range for a Schiff base precursor, being orders of magnitude greater than for C═C and C═P precursors at the same conditions. The results provide insights into the role of the precursor in determining the stability of the Criegee species formed and suggest an approach for preparing Criegee intermediates of relatively long lifetimes.

  17. Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

    PubMed Central

    Jouffroy, Matthieu; Gramage-Doria, Rafael; Sémeril, David; Oberhauser, Werner; Toupet, Loïc

    2014-01-01

    Summary The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki–Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon–carbon bond forming reactions both in terms of activity and selectivity. For example, when used as ligands in the rhodium-catalysed hydroformylation of styrene, they lead to both high isoselectivity and high enantioselectivity. In the study dealing with the Mizoroki–Heck reactions, comparative tests were carried out with WIDEPHOS, a diphosphine analogue of HUGPHOS-2. PMID:25383109

  18. Nitric oxide in star-forming regions: further evidence for interstellar N-O bonds.

    PubMed

    Ziurys, L M; McGonagle, D; Minh, Y; Irvine, W M

    1991-06-01

    Nitric oxide has been newly detected towards several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2 --> 1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both lambda-doubling components of NO were observed towards all sources. Column densities derived for nitric oxide in these clouds are N approximately 10(15)-10(16) cm-2, corresponding to fractional abundances of f approximately 0.5-1.0 x 10(-8), relative to H2. Towards Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude. The abundance of NO, unlike other simple interstellar nitrogen compounds, does appear to be reproduced by chemical models, at least to a good approximation. Regardless of the nature of formation of NO, it appears to be a common constituent of warm, dense molecular clouds. N-O bonds may therefore be more prevalent than previously thought.

  19. (abstract) Unidirectional Carbon/Carbon for Ion Engine Optics

    NASA Technical Reports Server (NTRS)

    Brown, D. Kyle

    1995-01-01

    Conventional ion engine optical grids are made from hydroformed molybdenum. Carbon/carbon has been utilized in place of molybdenum because of its lower sputter yield, which contributes a greatly increased engine life, and for its low cte, which allows more efficient engine operation. The requirements for this material are that it must have high stiffness, very tight dimensional tolerances, and can be optimized for an hexagonal hole pattern with a very high open area friction. The carbon/carbon for this application was fabricated from unidirectional tape prepreg, using pitch fiber, and was processed to a very high temperature. The use of unidirectional tape allowed for a sufficient number of plies to be used to generate a balanced three directional layup within the thickness constraints of the material, as well as providing strength and stiffness over that normally seen with fabric based carbon/carbons.

  20. Oxidative Attack of Carbon/Carbon Substrates through Coating Pinholes

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Leonhardt, Todd; Curry, Donald; Rapp, Robert A.

    1998-01-01

    A critical issue with oxidation protected carbon/carbon composites used for spacecraft thermal protection is the formation of coating pinholes. In laboratory experiments, artificial pinholes were drilled through SiC-coatings on a carbon/carbon material and the material was oxidized at 600, 1000, and 1400 C at reduced pressures of air. The attack of the carbon/carbon was quantified by both weight loss and a novel cross-sectioning technique. A two-zone, one dimensional diffusion control model was adapted to analyze this problem. Agreement of the model with experiment was reasonable at 1000 and 1400 C; however results at lower temperatures show clear deviations from the theory suggesting that surface reaction control plays a role.

  1. Dual hydrogen-bonding motifs in complexes formed between tropolone and formic acid

    NASA Astrophysics Data System (ADS)

    Nemchick, Deacon J.; Cohen, Michael K.; Vaccaro, Patrick H.

    2016-11-01

    The near-ultraviolet π*←π absorption system of weakly bound complexes formed between tropolone (TrOH) and formic acid (FA) under cryogenic free-jet expansion conditions has been interrogated by exploiting a variety of fluorescence-based laser-spectroscopic probes, with synergistic quantum-chemical calculations built upon diverse model chemistries being enlisted to unravel the structural and dynamical properties of the pertinent ground [X˜ 1A'] and excited [A˜ 1A'(" separators="π*π )] electronic states. For binary TrOH ṡ FA adducts, the presence of dual hydrogen-bond linkages gives rise to three low-lying isomers designated (in relative energy order) as INT, EXT1, and EXT2 depending on whether docking of the FA ligand to the TrOH substrate takes place internal or external to the five-membered reaction cleft of tropolone. While the symmetric double-minimum topography predicted for the INT potential surface mediates an intermolecular double proton-transfer event, the EXT1 and EXT2 structures are interconverted by an asymmetric single proton-transfer process that is TrOH-centric in nature. The A ˜ -X ˜ origin of TrOH ṡ FA at ν˜ 00=27 484 .45 cm-1 is displaced by δ ν˜ 00=+466 .76 cm-1 with respect to the analogous feature for bare tropolone and displays a hybrid type - a/b rotational contour that reflects the configuration of binding. A comprehensive analysis of vibrational landscapes supported by the optically connected X˜ 1A' and A˜ 1A'(" separators="π*π ) manifolds, including the characteristic isotopic shifts incurred by partial deuteration of the labile TrOH and FA protons, has been performed leading to the uniform assignment of numerous intermolecular (viz., modulating hydrogen-bond linkages) and intramolecular (viz., localized on monomer subunits) degrees of freedom. The holistic interpretation of all experimental and computational findings affords compelling evidence that an external-binding motif (attributed to EXT1), rather than the

  2. Alkali metal mediated C–C bond coupling reaction

    SciTech Connect

    Tachikawa, Hiroto

    2015-02-14

    Metal catalyzed carbon-carbon (C–C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz){sub 2}, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz){sub 2}, the structure of [Li(Bz){sub 2}]{sup −} was drastically changed: Bz–Bz parallel form was rapidly fluctuated as a function of time, and a new C–C single bond was formed in the C{sub 1}–C{sub 1}′ position of Bz–Bz interaction system. In the hole capture, the intermolecular vibration between Bz–Bz rings was only enhanced. The mechanism of C–C bond formation in the electron capture was discussed on the basis of theoretical results.

  3. Alkali metal mediated C-C bond coupling reaction

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto

    2015-02-01

    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2]- was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C1-C1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results.

  4. Alkali metal mediated C-C bond coupling reaction.

    PubMed

    Tachikawa, Hiroto

    2015-02-14

    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2](-) was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C1-C1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results.

  5. Carbon-Carbon Turbocharger Housing Unit for Intermittent Combustion Engines

    NASA Technical Reports Server (NTRS)

    Northam, G. Burton (Inventor); Ransone, Philip O. (Inventor); Rivers, H. Kevin (Inventor)

    1998-01-01

    An improved, lightweight, turbine housing unit for an intermittent combustion reciprocating internal combustion engine turbocharger is prepared from a lay-up or molding of carbon-carbon composite materials in a single-piece or two-piece process. When compared to conventional steel or cast iron, the use of carbon-carbon composite materials in a turbine housing unit reduces the overall weight of the engine and reduces the heat energy loss used in the turbocharging process. This reduction in heat energy loss and weight reduction provides for more efficient engine operation.

  6. Transition-metal-free C-C bond forming reactions of aryl, alkenyl and alkynylboronic acids and their derivatives.

    PubMed

    Roscales, S; Csákÿ, A G

    2014-12-21

    Investigation of new methods for the synthesis of C-C bonds is fundamental for the development of new organic drugs and materials. Aryl-, alkenyl- and alkynylboronic acids and their derivatives constitute attractive reagents towards this end, due to their stability, low toxicity and ease of handling. However, these compounds are only moderately nucleophilic. Consequently, the most popular C-C bond forming reactions of these boronic acids, such as the Suzuki-Miyaura, Heck, and Hayashi-Miyaura reactions, or additions to C=O and C=N bonds, require catalysis by transition metals. However, due to the toxicity and cost of transition metals, some new methods for C-C bond formation using aryl-, alkenyl- and alkynylboronic acids under transition-metal-free conditions are beginning to emerge. In this tutorial review, the recent synthetic advances in this field are highlighted and discussed.

  7. Microsolvation of anions by molecules forming CH··X- hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Nepal, Binod; Scheiner, Steve

    2015-12-01

    Various anions were surrounded by n molecules of CF3H, which was used as a prototype CH donor solvent, and the structures and energies studied by M06-2X calculations with a 6-31+G∗∗ basis set. Anions considered included the halides F-, Cl-, Br- and I-, as well as those with multiple proton acceptor sites: CN-, NO3-, HCOO-, CH3COO-, HSO4-, H2PO4-, and anions with higher charges SO42-, HPO42- and PO43-. Well structured cages were formed and the average H-bond energy decreases steadily as the number of surrounding solvent molecules rises, even when n exceeds 6 and the CF3H molecules begin to interact with one another rather than with the central anion. Total binding energies are very nearly proportional to the magnitude of the negative charge on the anion. The free energy of complexation becomes more negative for larger n initially, but then reaches a minimum and begins to rise for larger values of n.

  8. Properties of Plutonium-Containing Colloids Released from Glass-Bonded Sodalite Nuclear Waste Form

    SciTech Connect

    Morss, L.R.; Mertz, C.J.; Kropf, A.J.; Holly, J.L.

    2004-10-11

    In glass-bonded sodalite, which is the ceramic waste form (CWF) to immobilize radioactive electrorefiner salt from spent metallic reactor fuel, uranium and plutonium are found as 20-50 nm (U,Pu)O{sub 2} particles encapsulated in glass near glass-sodalite phase boundaries. In order to determine whether the (U,Pu)O{sub 2} affects the durability of the CWF, and to determine release behavior of uranium and plutonium during CWF corrosion, tests were conducted to measure the release of matrix and radioactive elements from crushed CWF samples into water and the properties of released plutonium. Released colloids have been characterized by sequential filtration of test solutions followed by elemental analysis, dynamic light scattering, transmission electron microscopy (TEM), and X-ray absorption spectroscopy. This paper reports the composition, size, and agglomeration of these colloids. Significant amounts of colloidal, amorphous aluminosilicates and smaller amounts of colloidal crystalline (U,Pu)O{sub 2} were identified in test solutions. The normalized releases of uranium and plutonium were significantly less than the normalized releases of matrix elements.

  9. 27 CFR 28.63 - Bond, Form 2736 (5100.12).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... penal sum of such bond shall be not less than the tax prescribed by law on the quantity of distilled spirits or wines to be withdrawn: Provided, That the maximum penal sum of such bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. (Sec. 201, Pub. L. 85-859, 72 Stat....

  10. 27 CFR 28.63 - Bond, Form 2736 (5100.12).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... penal sum of such bond shall be not less than the tax prescribed by law on the quantity of distilled spirits or wines to be withdrawn: Provided, That the maximum penal sum of such bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. (Sec. 201, Pub. L. 85-859, 72 Stat....

  11. 27 CFR 28.63 - Bond, Form 2736 (5100.12).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... penal sum of such bond shall be not less than the tax prescribed by law on the quantity of distilled spirits or wines to be withdrawn: Provided, That the maximum penal sum of such bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. (Sec. 201, Pub. L. 85-859, 72 Stat....

  12. 27 CFR 28.63 - Bond, Form 2736 (5100.12).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... penal sum of such bond shall be not less than the tax prescribed by law on the quantity of distilled spirits or wines to be withdrawn: Provided, That the maximum penal sum of such bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. (Sec. 201, Pub. L. 85-859, 72 Stat....

  13. Iterative reactions of transient boronic acids enable sequential C-C bond formation.

    PubMed

    Battilocchio, Claudio; Feist, Florian; Hafner, Andreas; Simon, Meike; Tran, Duc N; Allwood, Daniel M; Blakemore, David C; Ley, Steven V

    2016-04-01

    The ability to form multiple carbon-carbon bonds in a controlled sequence and thus rapidly build molecular complexity in an iterative fashion is an important goal in modern chemical synthesis. In recent times, transition-metal-catalysed coupling reactions have dominated in the development of C-C bond forming processes. A desire to reduce the reliance on precious metals and a need to obtain products with very low levels of metal impurities has brought a renewed focus on metal-free coupling processes. Here, we report the in situ preparation of reactive allylic and benzylic boronic acids, obtained by reacting flow-generated diazo compounds with boronic acids, and their application in controlled iterative C-C bond forming reactions is described. Thus far we have shown the formation of up to three C-C bonds in a sequence including the final trapping of a reactive boronic acid species with an aldehyde to generate a range of new chemical structures.

  14. Hydrogen bonds between short polar side chains and peptide backbone: prevalence in proteins and effects on helix-forming propensities.

    PubMed

    Vijayakumar, M; Qian, H; Zhou, H X

    1999-03-01

    A survey of 322 proteins showed that the short polar (SP) side chains of four residues, Thr, Ser, Asp, and Asn, have a very strong tendency to form hydrogen bonds with neighboring backbone amides. Specifically, 32% of Thr, 29% of Ser, 26% of Asp, and 19% of Asn engage in such hydrogen bonds. When an SP residue caps the N terminal of a helix, the contribution to helix stability by a hydrogen bond with the amide of the N3 or N2 residue is well established. When an SP residue is in the middle of a helix, the side chain is unlikely to form hydrogen bonds with neighboring backbone amides for steric and geometric reasons. In essence the SP side chain competes with the backbone carbonyl for the same hydrogen-bonding partner (i.e., the backbone amide) and thus SP residues tend to break backbone carbonyl-amide hydrogen bonds. The proposition that this is the origin for the low propensities of SP residues in the middle of alpha helices (relative to those of nonpolar residues) was tested. The combined effects of restricting side-chain rotamer conformations (documented by Creamer and Rose, Proc Acad Sci USA, 1992;89:5937-5941; Proteins, 1994;19:85-97) and excluding side- chain to backbone hydrogen bonds by the helix were quantitatively analyzed. These were found to correlate strongly with four experimentally determined scales of helix-forming propensities. The correlation coefficients ranged from 0.72 to 0.87, which are comparable to those found for nonpolar residues (for which only the loss of side-chain conformational entropy needs to be considered).

  15. In vivo study of the early bone-bonding ability of Ti meshes formed with calcium titanate via chemical treatments.

    PubMed

    Tian, Yi; Fujibayashi, Shunsuke; Yamaguchi, Seiji; Matsushita, Tomiharu; Kokubo, Tadashi; Matsuda, Shuichi

    2015-12-01

    Alkali and heat (AH) treatment forming sodium titanate has been shown to connect bioinert Ti metal and bone tissue. Artificial joints treated with this method have achieved extensive clinical application. Recently a new chemical treatment of Alkali-Calcium-Heat-Water (ACaHW) treatment forming calcium titanate was proposed. Notably, the apatite-forming ability of this treatment is greater than that of AH treatment, as verified in vitro. However, the early bone-bonding abilities of the two treatments have not been compared in vivo. To simulate clinical application, we treated a commercially pure Ti (Cp-Ti) mesh implant with AH or ACaHW. Then, using mechanical and histological methods, we compared the bone-bonding abilities of the two treatments early during the implantation process (2-4 weeks); untreated Cp-Ti mesh was used as a control. Because the mesh structure might influence bone-bonding ability, we compared these bonding abilities with values obtained at 4 and 8 weeks using a Cp-Ti implant with a plate structure. In the mesh group, histological comparisons at 2 and 3 weeks indicated that ACaHW treatment resulted in a bone-bonding ability similar to that of AH treatment; ACaHW exhibited a greater bonding ability than AH at 4 weeks. However, in tests of the plate group at later time points, such differences were not apparent. The results obtained here indicate that during the early stage of embedment, ACaHW treatment of Cp-Ti mesh implants yields a higher bone-bonding ability than AH treatment, thus providing a positive reference for future clinical applications.

  16. Finned Carbon-Carbon Heat Pipe with Potassium Working Fluid

    NASA Technical Reports Server (NTRS)

    Juhasz, Albert J.

    2010-01-01

    This elemental space radiator heat pipe is designed to operate in the 700 to 875 K temperature range. It consists of a C-C (carbon-carbon) shell made from poly-acrylonitride fibers that are woven in an angle interlock pattern and densified with pitch at high process temperature with integrally woven fins. The fins are 2.5 cm long and 1 mm thick, and provide an extended radiating surface at the colder condenser section of the heat pipe. The weave pattern features a continuous fiber bath from the inner tube surface to the outside edges of the fins to maximize the thermal conductance, and to thus minimize the temperature drop at the condenser end. The heat pipe and radiator element together are less than one-third the mass of conventional heat pipes of the same heat rejection surface area. To prevent the molten potassium working fluid from eroding the C C heat pipe wall, the shell is lined with a thin-walled, metallic tube liner (Nb-1 wt.% Zr), which is an integral part of a hermetic metal subassembly which is furnace-brazed to the inner surface of the C-C tube. The hermetic metal liner subassembly includes end caps and fill tubes fabricated from the same Nb-1Zr alloy. A combination of laser and electron beam methods is used to weld the end caps and fill tubes. A tungsten/inert gas weld seals the fill tubes after cleaning and charging the heat pipes with potassium. The external section of this liner, which was formed by a "Uniscan" rolling process, transitions to a larger wall thickness. This section, which protrudes beyond the C-C shell, constitutes the "evaporator" part of the heat pipe, while the section inside the shell constitutes the condenser of the heat pipe (see figure).

  17. Aromatic Cations from Oxidative Carbon–Hydrogen Bond Cleavage in Bimolecular Carbon–Carbon Bond Forming Reactions

    PubMed Central

    Clausen, Dane J.

    2012-01-01

    Chromenes and isochromenes react quickly with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form persistent aromatic oxocarbenium ions through oxidative carbon–hydrogen cleavage. This process is tolerant of electron-donating and electron-withdrawing groups on the benzene ring and additional substitution on the pyran ring. A variety of nucleophiles can be added to these cations to generate a diverse set of structures. PMID:22780559

  18. Determination of carbonate carbon in geological materials by coulometric titration

    USGS Publications Warehouse

    Engleman, E.E.; Jackson, L.L.; Norton, D.R.

    1985-01-01

    A coulometric titration is used for the determination of carbonate carbon in geological materials. Carbon dioxide is evolved from the sample by the addition of 2 M perchloric acid, with heating, and is determined by automated coulometric titration. The coulometric titration showed improved speed and precision with comparable accuracy to gravimetric and gasometric techniques. ?? 1985.

  19. Some Observations on Stress Graphitization in Carbon-Carbon Composites

    DTIC Science & Technology

    1992-09-15

    expansion ( CTE ) versus heat-treatment temperature for T-50/PAA carbon-carbon com posites...are derived from asphaltic precursors such as coal -tar and petroleum pitches. These materials are unique in passing through a liquid-crystalline...at a lower tem- perature and, for a given temperature, proceeded more extensively in the hard carbon than in a graphitizing polyvinylchloride coke

  20. In-Space Repair of Reinforced Carbon-Carbon Thermal Protection System Structures

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay

    2006-01-01

    Advanced repair and refurbishment technologies are critically needed for the thermal protection system of current space transportation system as well as for future Crew Exploration Vehicles (CEV). The damage to these components could be caused by impact during ground handling or due to falling of ice or other objects during launch. In addition, in-orbit damage includes micrometeoroid and orbital debris impact as well as different factors (weather, launch acoustics, shearing, etc.) during launch and re-entry. The GRC developed GRABER (Glenn Refractory Adhesive for Bonding and Exterior Repair) material has shown multiuse capability for repair of small cracks and damage in reinforced carbon-carbon (RCC) material. The concept consists of preparing an adhesive paste of desired ceramic with appropriate additives and then applying the paste to the damaged/cracked area of the RCC composites with adhesive delivery system. The adhesive paste cures at 100-120 C and transforms into a high temperature ceramic during simulated entry conditions. A number of plasma torch and ArcJet tests were carried out to evaluate the crack repair capability of GRABER materials for Reinforced Carbon-Carbon (RCC) composites. For the large area repair applications, integrated system for tile and leading edge repair (InSTALER) have been developed. In this presentation, critical in-space repair needs and technical challenges as well as various issues and complexities will be discussed along with the plasma performance and post test characterization of repaired RCC materials.

  1. Joining and Integration of Advanced Carbon-Carbon Composites to Metallic Systems for Thermal Management Applications

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.

    2008-01-01

    Recent research and development activities in joining and integration of carbon-carbon (C/C) composites to metals such as Ti and Cu-clad-Mo for thermal management applications are presented with focus on advanced brazing techniques. A wide variety of carbon-carbon composites with CVI and resin-derived matrices were joined to Ti and Cu-clad Mo using a number of active braze alloys. The brazed joints revealed good interfacial bonding, preferential precipitation of active elements (e.g., Ti) at the composite/braze interface. Extensive braze penetration of the inter-fiber channels in the CVI C/C composites was observed. The chemical and thermomechanical compatibility between C/C and metals at elevated temperatures is assessed. The role of residual stresses and thermal conduction in brazed C/C joints is discussed. Theoretical predictions of the effective thermal resistance suggest that composite-to-metal brazed joints may be promising for lightweight thermal management applications.

  2. In-Space Repair of Reinforced Carbon-Carbon (RCC) Thermal Protection System Structures

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay

    2005-01-01

    Advanced repair and refurbishment technologies are critically needed for the RCC-based thermal protection system of current space transportation system as well as for future Crew Exploration Vehicles (CEV). The damage to these components could be caused by impact during ground handling or due to falling of ice or other objects during launch. In addition, in-orbit damage includes micrometeoroid and orbital debris impact as well as different factors (weather, launch acoustics, shearing, etc.) during launch and re-entry. The GRC developed GRABER (Glenn Refractory Adhesive for Bonding and Exterior Repair) material has shown multiuse capability for repair of small cracks and damage in reinforced carbon-carbon (RCC) material. The concept consists of preparing an adhesive paste of desired ceramic with appropriate adhesives and then applying the paste to the damaged/cracked area of the RCC composites with adhesive delivery system. The adhesive paste cures at 100-120 C and transforms into a high temperature ceramic during simulated entry conditions. A number of plasma torch and ArcJet tests were carried out to evaluate the crack repair capability of GRABER materials for Reinforced Carbon-Carbon (RCC) composites. For the large area repair applications, PLASTER (Patch Laminates and Sealant Technology for Exterior Repair) based systems have been developed. In this presentation, critical in-space repair needs and technical challenges as well as various issues and complexities will be discussed along with the plasma performance and post test characterization of repaired RCC materials.

  3. Self-Protecting Bactericidal Titanium Alloy Surface Formed by Covalent Bonding of Daptomycin Bisphosphonates

    PubMed Central

    Chen, Chang-Po; Wickstrom, Eric

    2010-01-01

    Infections are a devastating complication of titanium alloy orthopedic implants. Current therapy includes antibiotic-impregnated bone cement, and antibiotic-containing coatings. We hypothesized that daptomycin, a Gram-positive peptide antibiotic, could prevent bacterial colonization on titanium alloy surfaces if covalently bonded via a flexible, hydrophilic spacer. We designed and synthesized a series of daptomycin conjugates for bonding to the surface of 1.0 cm2 Ti6Al4V foils through bisphosphonate groups, reaching a maximum yield of 180 pmol /cm2. Daptomycin-bonded foils killed 53±5% of a high challenge dose of 3×105 cfu Staphylococcus aureus ATCC 29213. PMID:20949909

  4. 46 CFR Appendix D to Subpart C of... - Ocean Transportation Intermediary (OTI) Group Bond Form [FMC-69

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 9 2010-10-01 2010-10-01 false Ocean Transportation Intermediary (OTI) Group Bond Form... OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN TRANSPORTATION INTERMEDIARIES Financial Responsibility Requirements; Claims Against Ocean...

  5. 46 CFR Appendix D to Subpart C of... - Ocean Transportation Intermediary (OTI) Group Bond Form [FMC-69

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 9 2013-10-01 2013-10-01 false Ocean Transportation Intermediary (OTI) Group Bond Form... OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN TRANSPORTATION INTERMEDIARIES Financial Responsibility Requirements; Claims Against Ocean...

  6. 46 CFR Appendix D to Subpart C of... - Ocean Transportation Intermediary (OTI) Group Bond Form [FMC-69

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 9 2014-10-01 2014-10-01 false Ocean Transportation Intermediary (OTI) Group Bond Form... OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN TRANSPORTATION INTERMEDIARIES Financial Responsibility Requirements; Claims Against Ocean...

  7. 46 CFR Appendix D to Subpart C of... - Ocean Transportation Intermediary (OTI) Group Bond Form [FMC-69

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 9 2011-10-01 2011-10-01 false Ocean Transportation Intermediary (OTI) Group Bond Form... OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN TRANSPORTATION INTERMEDIARIES Financial Responsibility Requirements; Claims Against Ocean...

  8. 46 CFR Appendix D to Subpart C of... - Ocean Transportation Intermediary (OTI) Group Bond Form [FMC-69

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 9 2012-10-01 2012-10-01 false Ocean Transportation Intermediary (OTI) Group Bond Form... OCEAN SHIPPING IN FOREIGN COMMERCE LICENSING, FINANCIAL RESPONSIBILITY REQUIREMENTS, AND GENERAL DUTIES FOR OCEAN TRANSPORTATION INTERMEDIARIES Financial Responsibility Requirements; Claims Against Ocean...

  9. Evaluation of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Seok; Lee, Sangmok; Lee, Jong-Sup; Kim, Yong-Bae; Lee, Geun-An; Lee, Sang-Pill; Bae, Dong-Su

    2016-09-01

    The aim of the present study is to identify the properties of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials by transmission electron microscopy and nano-indentation analyses. Cu/Al clad materials were fabricated by hot pressing under 200 MPa at 250 °C for 1 h and then heat treated at 400 °C for 1 h. Nano-indentation measurement was conducted to evaluate the nanohardness and modulus of the intermediate phases formed between the Cu/Al interfaces. A 3-tier diffusion layer was observed at the Cu/Al interfaces. Knoop microhardness values at the bonding interface were 7 to 11 times that of the Cu and Al matrix metals. The intermediate phases formed at the bonding interface were Al4Cu9, AlCu, and Al2Cu. A mapping analysis confirmed that the Al and Cu particles moved via mutual diffusion toward the intermediate phases formed at the bonding interface. The nanohardness values of η2-AlCu and γ1-Al4Cu9 were 4 to 7 times that of the Cu and Al matrix metals. Nanohardness and Knoop microhardness measurement curves exhibited similar tendencies. The rigidity values of the respective intermediate phases can be arranged in descending order as follows: γ1-Al4Cu9 > η2-AlCu > θ-Al2Cu.

  10. 46 CFR 308.531 - Endorsement of surety bond increasing or decreasing amount of coverage, Form MA-311.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 8 2014-10-01 2014-10-01 false Endorsement of surety bond increasing or decreasing amount of coverage, Form MA-311. 308.531 Section 308.531 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Open Policy War Risk...

  11. 46 CFR 308.530 - Letter requesting increase or decrease in amount of surety bond, Form MA-310.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 8 2014-10-01 2014-10-01 false Letter requesting increase or decrease in amount of surety bond, Form MA-310. 308.530 Section 308.530 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Open Policy War Risk...

  12. Multilayered thermal insulation formed of zirconia bonded layers of zirconia fibers and metal oxide fibers and method for making same

    DOEpatents

    Wrenn, G.E. Jr.; Holcombe, C.E. Jr.

    1988-09-13

    A multilayered thermal insulating composite is formed of a first layer of zirconia-bonded zirconia fibers for utilization near the hot phase or surface of a furnace or the like. A second layer of zirconia-bonded metal oxide fibers is attached to the zirconia fiber layer by a transition layer formed of intermingled zirconia fibers and metal oxide fibers. The thermal insulation is fabricated by vacuum molding with the layers being sequentially applied from aqueous solutions containing the fibers to a configured mandrel. A portion of the solution containing the fibers forming the first layer is intermixed with the solution containing the fibers of the second layer for forming the layer of mixed fibers. The two layers of fibers joined together by the transition layer are saturated with a solution of zirconium oxynitrate which provides a zirconia matrix for the composite when the fibers are sintered together at their nexi.

  13. Multilayered thermal insulation formed of zirconia bonded layers of zirconia fibers and metal oxide fibers and method for making same

    DOEpatents

    Wrenn, Jr., George E.; Holcombe, Jr., Cressie E.

    1988-01-01

    A multilayered thermal insulating composite is formed of a first layer of zirconia-bonded zirconia fibers for utilization near the hot phase or surface of a furnace or the like. A second layer of zirconia-bonded metal oxide fibers is attached to the zirconia fiber layer by a transition layer formed of intermingled zirconia fibers and metal oxide fibers. The thermal insulation is fabricated by vacuum molding with the layers being sequentially applied from aqueous solutions containing the fibers to a configured mandrel. A portion of the solution containing the fibers forming the first layer is intermixed with the solution containing the fibers of the second layer for forming the layer of mixed fibers. The two layers of fibers joined together by the transition layer are saturated with a solution of zirconium oxynitrate which provides a zirconia matrix for the composite when the fibers are sintered together at their nexi.

  14. 46 CFR 308.532 - Release of surety bond, Form MA-312.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ....532 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.532 Release of surety bond... American War Risk Agency or MARAD....

  15. Dinuclear complexes formed by hydrogen bonds: synthesis, structure and magnetic and electrochemical properties.

    PubMed

    Williams, Alan Francis; Granelli, Matteo; Downward, Alan M; Huber, Robin; Guenée, Laure; Besnard, Céline; Krämer, Karl W; Decurtins, Silvio; Liu, Shi-Xia; Thompson, Laurence K

    2017-03-20

    The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent M(II)M(II), mixed valent M(II)M(III) and heteronuclear M(II)M'(III) species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O…O distances for the hydrogen bonds. Magnetic measurements show the hydrogen bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen bonded structure.

  16. 46 CFR 308.532 - Release of surety bond, Form MA-312.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ....532 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.532 Release of surety bond... American War Risk Agency or MARAD....

  17. 46 CFR 308.532 - Release of surety bond, Form MA-312.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ....532 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.532 Release of surety bond... American War Risk Agency or MARAD....

  18. 46 CFR 308.532 - Release of surety bond, Form MA-312.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ....532 Shipping MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION EMERGENCY OPERATIONS WAR RISK INSURANCE War Risk Cargo Insurance Ii-Open Policy War Risk Cargo Insurance § 308.532 Release of surety bond... American War Risk Agency or MARAD....

  19. Enantioselective Allylation, Crotylation and Reverse Prenylation of Substituted Isatins via Iridium Catalyzed C-C Bond Forming Transfer Hydrogenation**

    PubMed Central

    Itoh, Junji; Han, Soo Bong; Krische, Michael J.

    2010-01-01

    Oxindoles with a Twist Transfer hydrogenation of substituted isatins in the presence of allyl acetate, α-methyl allyl acetate or 1,1,-dimethylallene employing an ortho-cyclometallated iridium catalyst modified by CTH-(R)-P-PHOS provides products of carbonyl allylation, crotylation and reverse prenylation, respectively, in highly enantiomerically enriched form. These studies represent the first use of activated ketones as electrophilic partners in asymmetric C-C bond forming transfer hydrogenation. PMID:19606435

  20. 27 CFR 28.61 - Bond, Form 2734 (5100.25).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... filed by the exporter, as provided in § 28.51. The penal sum of the bond shall not be less than the tax prescribed by law on the quantity of spirits or wine to be withdrawn. However, the maximum penal sum of the bond shall not exceed $200,000 but in no case shall the penal sum be less than $1,000. (Sec. 201, Pub...

  1. 27 CFR 28.63 - Bond, Form 2736 (5100.12).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... penal sum of such bond shall be not less than the tax prescribed by law on the quantity of distilled spirits or wines to be withdrawn: Provided, That the maximum penal sum of such bond shall not exceed $200,000, but in no case shall the penal sum be less than $1,000. (Sec. 201, Pub. L. 85-859, 72 Stat. 1352...

  2. 27 CFR 28.61 - Bond, Form 2734 (5100.25).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... filed by the exporter, as provided in § 28.51. The penal sum of the bond shall not be less than the tax prescribed by law on the quantity of spirits or wine to be withdrawn. However, the maximum penal sum of the bond shall not exceed $200,000 but in no case shall the penal sum be less than $1,000. (Sec. 201,...

  3. 27 CFR 28.61 - Bond, Form 2734 (5100.25).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... filed by the exporter, as provided in § 28.51. The penal sum of the bond shall not be less than the tax prescribed by law on the quantity of spirits or wine to be withdrawn. However, the maximum penal sum of the bond shall not exceed $200,000 but in no case shall the penal sum be less than $1,000. (Sec. 201,...

  4. 27 CFR 28.61 - Bond, Form 2734 (5100.25).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... filed by the exporter, as provided in § 28.51. The penal sum of the bond shall not be less than the tax prescribed by law on the quantity of spirits or wine to be withdrawn. However, the maximum penal sum of the bond shall not exceed $200,000 but in no case shall the penal sum be less than $1,000. (Sec. 201,...

  5. 27 CFR 28.61 - Bond, Form 2734 (5100.25).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... filed by the exporter, as provided in § 28.51. The penal sum of the bond shall not be less than the tax prescribed by law on the quantity of spirits or wine to be withdrawn. However, the maximum penal sum of the bond shall not exceed $200,000 but in no case shall the penal sum be less than $1,000. (Sec. 201,...

  6. Born-Oppenheimer Molecular Dynamics Study on Proton Dynamics of Strong Hydrogen Bonds in Aspirin Crystals, with Emphasis on Differences between Two Crystal Forms.

    PubMed

    Brela, Mateusz Z; Wójcik, Marek J; Witek, Łukasz J; Boczar, Marek; Wrona, Ewa; Hashim, Rauzah; Ozaki, Yukihiro

    2016-04-28

    In this study, the proton dynamics of hydrogen bonds for two forms of crystalline aspirin was investigated by the Born-Oppenheimer molecular dynamics (BOMD) method. Analysis of the geometrical parameters of hydrogen bonds using BOMD reveals significant differences in hydrogen bonding between the two crystalline forms of aspirin, Form I and Form II. Analysis of the trajectory for Form I shows spontaneous proton transfer in cyclic dimers, which is absent in Form II. Quantization of the O-H stretching modes allows a detailed discussion on the strength of hydrogen-bonding interactions. The focal point of our study is examination of the hydrogen bond characteristics in the crystal structure and clarification of the influence of hydrogen bonding on the presence of the two crystalline forms of aspirin. In the BOMD method, thermal motions were taken into account. Solving the Schrödinger equation for the snapshots of 2D proton potentials, extracted from MD, gives the best agreement with IR spectra. The character of medium-strong hydrogen bonds in Form I of aspirin was compared with that of weaker hydrogen bonds in aspirin Form II. Two proton minima are present in the potential function for the hydrogen bonds in Form I. The band contours, calculated by using one- and two-dimensional O-H quantization, reflect the differences in the hydrogen bond strengths between the two crystalline forms of aspirin, as well as the strong hydrogen bonding in the cyclic dimers of Form I and the medium-strong hydrogen bonding in Form II.

  7. Titanium metals form direct bonding to bone after alkali and heat treatments.

    PubMed

    Nishiguchi, S; Kato, H; Fujita, H; Oka, M; Kim, H M; Kokubo, T; Nakamura, T

    2001-09-01

    In this article we evaluated the bone-bonding strengths of titanium and titanium alloy implants with and without alkali and heat treatments using the conventional canine femur push-out model. Four kinds of smooth cylindrical implants, made of pure titanium or three titanium alloys, were prepared with and without alkali and heat treatments. The implants were inserted hemitranscortically into canine femora. The bone-bonding shear strengths of the implants were measured using push-out test. At 4 weeks all types of the alkali- and heat-treated implants showed significantly higher bonding strength (2.4-4.5 MPa) than their untreated counterparts (0.3-0.6 MPa). At 12 weeks the bonding strengths of the treated implants showed no further increase, while those of the untreated implants had increased to 0.6-1.2MPa. Histologically, alkali- and heat-treated implants showed direct bonding to bony tissue without intervening fibrous tissue. On the other hand, untreated implants usually had intervening fibrous tissue at the interface between bone and the implant. The early and strong bonding to bone of alkali- and heat-treated titanium and its alloys without intervening fibrous tissue may be useful in establishing cementless stable fixation of orthopedic implants.

  8. Ultra low friction carbon/carbon composites for extreme temperature applications

    DOEpatents

    Erdemir, Ali; Busch, Donald E.; Fenske, George R.; Lee, Sam; Shepherd, Gary; Pruett, Gary J.

    2001-01-01

    A carbon/carbon composite in which a carbon matrix containing a controlled amount of boron or a boron compound is reinforced with carbon fiber exhibits a low coefficient of friction, i.e., on the order of 0.04 to 0.1 at temperatures up to 600.degree. C., which is one of the lowest frictional coefficients for any type of carbonaceous material, including graphite, glassy carbon, diamond, diamond-like carbon and other forms of carbon material. The high degree of slipperiness of the carbon composite renders it particularly adapted for limiting friction and wear at elevated temperatures such as in seals, bearings, shafts, and flexible joints

  9. Do polyamines contribute to plant cell wall assembly by forming amide bonds with pectins?

    PubMed

    Lenucci, Marcello; Piro, Gabriella; Miller, Janice G; Dalessandro, Giuseppe; Fry, Stephen C

    2005-11-01

    Two new reducing glycoconjugates [N-D-galacturonoyl-putrescinamide (GalA-Put) and N,N'-di-D-galacturonoyl-putrescinamide (GalA-Put-GalA)] and homogalacturonan-putrescine (GalAn-Put) conjugates were synthesised as model compounds representing possible amide (isopeptide) linkage points between a polyamine and either one or two pectic galacturonate residues. The amide bond(s) were stable to cold acid and alkali (2M TFA and 0.1M NaOH at 25 degrees C) but rapidly hydrolysed by these agents at 100 degrees C. The amide bond(s) were resistant to Driselase and to all proteinases tested, although Driselase digested GalAn-Put, releasing fragments such as GalA3-Put-GalA3. To trace the possible formation of GalA-polyamine amide bonds in vivo, we fed Arabidopsis and rose cell-cultures and chickpea internodes with [14C]Put. About 20% of the 14C taken up was released as 14CO2, indicating some catabolism. An additional approximately 73% of the 14C taken up (in Arabidopsis), or approximately 21% (in rose), became ethanol-insoluble, superficially suggestive of polysaccharide-Put covalent bonding. However, much of the ethanol-inextractable 14C was subsequently extractable by acidified phenol or by cold 1M TFA. The small proportion of radioactive material that stayed insoluble in both phenol and TFA was hydrolysable by Driselase or hot 6M HCl, yielding 14C-oligopeptides and/or amino acids (including Asp, Glu, Gly, Ala and Val); no free 14C-polyamines were released by hot HCl. We conclude that if pectin-polyamine amide bonds are present, they are a very minor component of the cell walls of cultured rose and Arabidopsis cells and chickpea internodes.

  10. KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons prepares to electroweld a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

    NASA Image and Video Library

    2003-09-16

    KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons prepares to electroweld a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

  11. KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons electrowelds a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

    NASA Image and Video Library

    2003-09-16

    KENNEDY SPACE CENTER, FLA. - United Space Alliance employee Anthony Simmons electrowelds a crack formed in the insulator inside a Reinforced Carbon Carbon panel. The gray carbon composite RCC panels are attached to the leading edge of the wing of the orbiters to withstand the aerodynamic forces experienced during launch and reentry, which can reach as high as 800 pounds per square foot. The operating range of RCC is from minus 250º F to about 3,000º F, the temperature produced by friction with the atmosphere during reentry.

  12. Peroxidasin Forms Sulfilimine Chemical Bonds Using Hypohalous Acids In Tissue Genesis

    PubMed Central

    Bhave, G.; Cummings, C.F.; Vanacore, R.M.; Kumagai-Cresse, C.; Ero-Tolliver, I.A.; Rafi, M.; Kang, J.-S.; Pedchenko, V.P.; Fessler, L.I.; Fessler, J.H.; Hudson, B.G.

    2014-01-01

    Collagen IV is the predominant protein network of basement membranes, a specialized extracellular matrix, which underlie epithelia and endothelia. These networks assemble through oligomerization and covalent cross-linking to endow mechanical strength and shape cell behavior through interactions with cell surface receptors. A novel sulfilimine (S=N) bond between a methionine sulfur and hydroxylysine nitrogen reinforces the collagen IV network. We demonstrate that peroxidasin, an enzyme found in basement membranes, catalyzes formation of the sulfilimine bond. Drosophila peroxidasin mutants exhibit disorganized collagen IV networks and torn visceral muscle basement membranes pointing to a critical role for the enzyme in tissue biogenesis. Peroxidasin generates hypohalous acids as reaction intermediates suggesting a paradoxically anabolic role for these usually destructive oxidants. This work highlights sulfilimine bond formation as the first known physiologic function for peroxidasin, a role for hypohalous oxidants in tissue biogenesis, and a possible role for peroxidasin in inflammatory diseases. PMID:22842973

  13. Selenoprotein K form an intermolecular diselenide bond with unusually high redox potential.

    PubMed

    Liu, Jun; Zhang, Zhengqi; Rozovsky, Sharon

    2014-09-17

    Selenoprotein K (SelK) is a membrane protein involved in antioxidant defense, calcium regulation and the ER-associated protein degradation pathway. We found that SelK exhibits a peroxidase activity with a rate that is low but within the range of other peroxidases. Notably, SelK reduced hydrophobic substrates, such as phospholipid hydroperoxides, which damage membranes. Thus, SelK might be involved in membrane repair or related pathways. SelK was also found to contain a diselenide bond-the first intramolecular bond of that kind reported for a selenoprotein. The redox potential of SelK was -257 mV, significantly higher than that of diselenide bonds in small molecules or proteins. Consequently, SelK can be reduced by thioredoxin reductase. These finding are essential for understanding SelK activity and function. Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  14. Fluorous oxime palladacycle: a precatalyst for carbon-carbon coupling reactions in aqueous and organic medium.

    PubMed

    Susanto, Woen; Chu, Chi-Yuan; Ang, Wei Jie; Chou, Tzyy-Chao; Lo, Lee-Chiang; Lam, Yulin

    2012-03-16

    To facilitate precatalyst recovery and reuse, we have developed a fluorous, oxime-based palladacycle 1 and demonstrated that it is a very efficient and versatile precatalyst for a wide range of carbon-carbon bond formation reactions (Suzuki-Miyaura, Sonogashira, Stille, Heck, Glaser-type, and Kumada) in either aqueous or organic medium under microwave irradiation. Palladacycle 1 could be recovered through F-SPE in various coupling reactions with recovery ranging from 84 to 95% for the first cycle. Inductively coupled plasma optical emission spectrometry (ICP-OES) analyses of the Pd content in the crude product from each class of transformation indicated extremely low levels of leaching and the palladacycle could be reused four to five times without significant loss of activity.

  15. [Progress of researches on carbon/carbon composites used in human loaded bones].

    PubMed

    Sui, Jinling; Li, Musen; Lü, Yupeng

    2004-08-01

    Carbon/carbon composites have excellent biocompatibility with human hard tissue and elasticity modulus similar with that of human bones, which endow them great potential applications in substitution for human loaded bones. The current research situations and applications of carbon/carbon composites in human loaded bones are reviewed. The coating technologies of bioactive layers on carbon/carbon composites are discussed. The problems to be solved and the prospects of carbon/carbon composites in human loaded bones are analyzed and predicted. It is believed that bioactive layers coating on carbon/carbon composites should play an important role in human loaded bones.

  16. A triclinic polymorph of benzanilide: disordered molecules form hydrogen-bonded chains.

    PubMed

    Bowes, Katharine F; Glidewell, Christopher; Low, John N; Skakle, Janet M S; Wardell, James L

    2003-01-01

    In the P-1 polymorph of benzanilide or N-phenylbenzamide, C(13)H(11)NO, the molecules are linked into simple C(4) chains by N-H...O hydrogen bonds. The molecules exhibit orientational disorder, but the donor and acceptor in a given hydrogen bond may occur, independently, in either the major or the minor orientation, such that all four possible N-H.O combinations have very similar geometries. The structure of this P-1 polymorph can be related to that of a previously reported C2/c polymorph.

  17. Intermediate Temperature Carbon - Carbon Composite Structures. CRADA Final Report

    SciTech Connect

    Lara-Curzio, Edgar

    2007-06-01

    The objective of this Cooperative Research and Development Agreement (CRADA) between UT-Battelle, LLC (the "Contractor") and Synterials, Inc. (the "Participant") was to demonstrate promising processing methods, which can lead to producing Carbon-Carbon Composites (CCC), with tensile and interlaminar properties comparable to those of organic matrix composites and environmental stability at 1200 F for long periods of time. The participant synthesized carbon-carbon composites with two different fiber coatings and three different matrices. Both parties evaluated the tensile and interlaminar properties of these materials and characterized the microstructure of the matrices and interfaces. It was found that fiber coatings of carbon and boron carbide provided the best environmental protection and resulted in composites with high tensile strength.

  18. Acoustic fatigue characterization of carbon/carbon panels

    NASA Technical Reports Server (NTRS)

    Rizzi, S. A.; Clevenson, S. A.; Daniels, E. F.

    1992-01-01

    Data from a sonic fatigue test of a blade-stiffened carbon/carbon panel is analyzed to determine the progression of damage to failure. The reduction in stiffness, as observed from acceleration measurements taken during the test, is correlated with the physical damage. Damage was measured through visual inspection, thermographic measurements, and through the novel use of vibration data collected using a scanning laser vibrometer.

  19. Carbon/Carbon Fasteners For Use At High Temperatures

    NASA Technical Reports Server (NTRS)

    Bohlmann, Frank J.

    1992-01-01

    Fasteners made of advanced carbon/carbon material perform well at ambient and high temperatures. Exhibit shear strengths of more than 10 kpsi at room temperature and 13 kpsi at temperature of 2,700 degrees F. However, fasteners exhibited poor tensile strength at room temperature. Best suited to applications in which exposed to shear loads with minimal tension loads. Parts reused after thermal cycling.

  20. As-Fabricated Reinforced Carbon/Carbon Characterized

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Calomino, Anthony M.; Webster, Neal

    2004-01-01

    Reinforced carbon/carbon (RCC) is a critical material for the space shuttle orbiter. It is used on the wing leading edge and the nose cap, where maximum temperatures are reached on reentry. The existing leading-edge system is a single-plate RCC composite construction with a wall thickness of approximately 1/4 in., making it a prime reliant protection scheme for vehicle operation.

  1. Reactive Brazing of Carbon-Carbon Composites to Titanium

    NASA Technical Reports Server (NTRS)

    Shpargel, Tarah; Singh, M.; Morscher, Gregory; Asthana, Rajiv

    2004-01-01

    The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSil. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The results of the microstructure analysis indicate solute redistribution across the joint and possible metallurgical bond formation via interdiffusion, which led to good wetting and spreading.

  2. Active Metal Brazing of Carbon-Carbon Composites to Titanium

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, T. P.; Morscher, G.; Asthana, R.

    2004-01-01

    The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSil. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The results of the microstructure analysis indicate solute redistribution across the joint which led to good wetting, spreading, and metallurgical bond formation via interdiffusion.

  3. High-Melt Carbon-Carbon Coating for Nozzle Extensions

    NASA Technical Reports Server (NTRS)

    Thompson, James

    2015-01-01

    Carbon-Carbon Advanced Technologies, Inc. (C-CAT), has developed a high-melt coating for use in nozzle extensions in next-generation spacecraft. The coating is composed primarily of carbon-carbon, a carbon-fiber and carbon-matrix composite material that has gained a spaceworthy reputation due to its ability to withstand ultrahigh temperatures. C-CAT's high-melt coating embeds hafnium carbide (HfC) and zirconium diboride (ZrB2) within the outer layers of a carbon-carbon structure. The coating demonstrated enhanced high-temperature durability and suffered no erosion during a test in NASA's Arc Jet Complex. (Test parameters: stagnation heat flux=198 BTD/sq ft-sec; pressure=.265 atm; temperature=3,100 F; four cycles totaling 28 minutes) In Phase I of the project, C-CAT successfully demonstrated large-scale manufacturability with a 40-inch cylinder representing the end of a nozzle extension and a 16-inch flanged cylinder representing the attach flange of a nozzle extension. These demonstrators were manufactured without spalling or delaminations. In Phase II, C-CAT worked with engine designers to develop a nozzle extension stub skirt interfaced with an Aerojet Rocketdyne RL10 engine. All objectives for Phase II were successfully met. Additional nonengine applications for the coating include thermal protection systems (TPS) for next-generation spacecraft and hypersonic aircraft.

  4. Four advances in carbon-carbon materials technology

    NASA Technical Reports Server (NTRS)

    Maahs, Howard G.; Vaughn, Wallace L.; Kowbel, Witold

    1994-01-01

    Carbon-carbon composites are a specialty class of materials having many unique properties making these composites attractive for a variety of demanding engineering applications. Chief among these properties are exceptional retention of mechanical properties at temperatures as high as 4000 F, excellent creep resistance, and low density (1.6 to 1.8 g/cu cm). Although carbon-carbon composites are currently in service in a variety of applications, much development work remains to be accomplished before these materials can be considered to be fully mature, realizing their full potential. Four recent technology advances holding particular promise for overcoming current barriers to the wide-spread commercialization of carbon-carbon composites are described. These advances are: markedly improved interlaminar strengths (more than doubled) of two dimensional composites achieved by whiskerization of the fabric reinforcing plies, simultaneously improved oxidation resistance and mechanical properties achieved by the incorporation of matrix-phase oxidation inhibitors based on carborane chemistry, improved oxidation resistance achieved by compositionally graded oxidation protective coatings, and markedly reduced processing times (hours as opposed to weeks or months) accomplished through a novel process of carbon infiltration and coatings deposition based on the use of liquid-phase precursor materials.

  5. Carbon-carbon turbopump concept for Space Nuclear Thermal Propulsion

    NASA Astrophysics Data System (ADS)

    Overholt, David M.

    1993-06-01

    The U.S. Air Force Space Nuclear Thermal Propulsion (SNTP) program is placing high priority on maximizing specific impulse (ISP) and thrust-to-weight ratio in the development of a practical high-performance nuclear rocket. The turbopump design is driven by these goals. The liquid hydrogen propellant is pressurized and pumped to the reactor inlet by the turbopump assembly (TPA). Rocket propulsion is from rapid heating of the propellant from 180 R to thousands of degrees in the particle bed reactor (PBR). The exhausted propellant is then expanded through a high-temperature nozzle. A high-performance approach is to use an uncooled carbon-carbon nozzle and duct turbine inlet. Carbon-carbon components are used throughout the TPA hot section to obtain the high-temperature capability. Several carbon-carbon components are in development including structural parts, turbine nozzles/stators, and turbine rotors. The technology spinoff is applicable to conventional liquid propulsion engines and many other turbomachinery applications.

  6. Water for Carbon, Carbon for Water

    NASA Astrophysics Data System (ADS)

    Carminati, Andrea; Kroener, Eva; Ahmed, Mutez A. A.; Zarebanadkouki, Mohsen; Holz, Maire; Ghezzehei, Teamrat

    2015-04-01

    Plant roots exude approximately 10% of the carbon assimilated through photosynthesis into the soil, a process referred to as rhizodeposition. Although this may look like a waste of energy, it has been shown that the carbon exuded into the soil helps roots to take up nutrients and promote positive interactions with microorganisms. Here, we show that the mucilaginous fraction of the rhizodeposits, referred to as mucilage, plays also a crucial role on soil-plant water relations and triggers positive feedbacks between the water and carbon cycles. Mucilage is a gel that can absorb large volumes of water, altering the physical properties of the rhizosphere and maintaining the rhizosphere wet and conductive when the soil dries. Acting as a hydraulic bridge between roots and the soil, mucilage facilitates root water uptake and maintains transpiration and photosynthesis in dry soils. By employing a simplified model of root water uptake coupled with mucilage dynamics, we found that indeed the carbon exuded in form of mucilage maintains photosynthesis in dry soils resulting a in a net gain of carbon. In summary, by exuding mucilage, plants modify the physical soil environment, have a better access to water when water is scarce, and maintain photosynthesis for a prolonged time during drought. We propose that mucilage exudation is a plant trait conferring drought resistance. In other words: water for carbon, but also carbon for water.

  7. 25 CFR 162.436 - What is the release process for a performance bond or alternative form of security under a...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... What is the release process for a performance bond or alternative form of security under a business... 25 Indians 1 2013-04-01 2013-04-01 false What is the release process for a performance bond or alternative form of security under a business lease? 162.436 Section 162.436 Indians BUREAU OF INDIAN...

  8. 25 CFR 162.436 - What is the release process for a performance bond or alternative form of security under a...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... What is the release process for a performance bond or alternative form of security under a business... 25 Indians 1 2014-04-01 2014-04-01 false What is the release process for a performance bond or alternative form of security under a business lease? 162.436 Section 162.436 Indians BUREAU OF INDIAN...

  9. The biologically active form of the sea urchin egg receptor for sperm is a disulfide-bonded homo-multimer

    PubMed Central

    1994-01-01

    Since many cell surface receptors exist in their active form as oligomeric complexes, we have investigated the subunit composition of the biologically active sperm receptor in egg plasma membranes from Strongylocentrotus purpuratus. Electrophoretic analysis of the receptor without prior reduction of disulfide bonds revealed that the surface receptor exists in the form of a disulfide-bonded multimer, estimated to be a tetramer. These findings are in excellent agreement with the fact that the NH2-terminus of the extracellular domain of the sperm receptor is rich in cysteine residues. Studies with cross-linking agents of various length and hydrophobicity suggest that no other major protein is tightly associated with the receptor. Given the multimeric structure of the receptor, we investigated the effect of disulfide bond reduction on its biological activity. Because in quantitative bioassays fertilization was found to be inhibited by treatment of eggs with 5 mM dithiothreitol, we undertook more direct studies of the effect of reduction on properties of the receptor. First, we studied the effect of addition of isolated, pure receptor on fertilization. Whereas the non-reduced, native receptor complex inhibited fertilization in a dose- dependent manner, the reduced and alkylated receptor was inactive. Second, we tested the ability of the isolated receptor to mediate binding of acrosome-reacted sperm to polystyrene beads. Whereas beads coated with native receptor bound sperm, those containing reduced and alkylated receptor did not. Thus, these results demonstrate that the biologically active form of the sea urchin sperm receptor consists only of 350 kD subunits and that these must be linked as a multimer via disulfide bonds to produce a complex that is functional in sperm recognition and binding. PMID:8188748

  10. Theory of relaxation dynamics in glass-forming hydrogen-bonded liquids

    NASA Astrophysics Data System (ADS)

    Hentschel, H. G. E.; Procaccia, Itamar

    2008-03-01

    We address the relaxation dynamics in hydrogen-bonded supercooled liquids near (but above) the glass transition, measured via broadband dielectric spectroscopy (BDS). We propose a theory based on decomposing the relaxation of the macroscopic dipole moment into contributions from hydrogen-bonded clusters of s molecules, with smin≤s≤smax . The existence of smax is translated into a sum rule on the concentrations of clusters of size s . We construct the statistical mechanics of the supercooled liquid subject to this sum rule as a constraint, to estimate the temperature-dependent density of clusters of size s . With a theoretical estimate of the relaxation time of each cluster, we provide predictions for the real and imaginary parts of the frequency-dependent dielectric response. The predicted spectra and their temperature dependence are in accord with measurements, explaining a host of phenomenological fits like the Vogel-Fulcher fit and the stretched exponential fit. Using glycerol as a particular example, we demonstrate quantitative correspondence between theory and experiments. The theory also demonstrates that the α peak and the “excess wing” stem from the same physics in this material. The theory also shows that in other hydrogen-bonded glass formers the excess wing can develop into a β peak, depending on the molecular material parameters (predominantly the surface energy of the clusters). We thus argue that α and β peaks can stem from the same physics. We address the BDS in constrained geometries (pores) and explain why recent experiments on glycerol did not show a deviation from bulk spectra. Finally, we discuss the dc part of the BDS spectrum and argue why it scales with the frequency of the α peak, providing an explanation for the remarkable data collapse observed in experiments.

  11. Modification of the PTCDA-Ag bond by forming a heteromolecular bilayer film

    NASA Astrophysics Data System (ADS)

    Stadtmüller, Benjamin; Willenbockel, Martin; Schröder, Sonja; Kleimann, Christoph; Reinisch, Eva M.; Ules, Thomas; Soubatch, Sergey; Ramsey, Michael G.; Tautz, F. Stefan; Kumpf, Christian

    2015-04-01

    The understanding of the fundamental physical properties of metal-organic and organic-organic interfaces is crucial for improving the performance of organic electronic devices. This is particularly true for (multilayer) systems containing several molecular species due to their relevance for donor-acceptor systems. A prototypical heteromolecular bilayer system is copper-II-phthalocyanine (CuPc) on 3,4,9,10-perylene-tetra-carboxylic-dianhydride (PTCDA) on Ag(111). In an earlier work we have reported a commensurate registry between both organic layers and an enhanced charge transfer from the Ag substrate into the organic bilayer film [Phys. Rev. Lett. 108, 106103 (2012), 10.1103/PhysRevLett.108.106103], which both indicate an unexpectedly strong intermolecular interaction across the organic-organic interface. Here we present new details regarding electronic and geometric structure for the same system. In particular, we provide evidence that the enhanced charge transfer from the substrate into the organic bilayer does not involve CuPc electronic states, hence, there is no significant charge transfer into the second organic layer. Furthermore, we report vertical bonding distances revealing a shortening of the PTCDA-Ag(111) distance upon CuPc adsorption. Thus, electronic and geometric properties (charge transfer and bonding distance, respectively) both indicate a strengthening of the PTCDA-Ag(111) bond upon CuPc adsorption. We explain these findings—in particular the correlation between CuPc adsorption and increased charge transfer into PTCDA—in a model involving an intermolecular screening mechanism.

  12. Stress-strain and thermal expansion characteristics of a phosphate-bonded investment mould material for dental super plastic forming.

    PubMed

    Curtis, R V

    1998-03-01

    The stress-strain and thermal expansion characteristics of a phosphate-bonded investment material were measured to determine its suitability as a die material for superplastic forming of dental appliances. Titanium alloy denture bases and implant superstructures have been fabricated successfully using this investment material, but a greater understanding of its properties was sought to optimize the forming technique before exploitation could proceed. The effect of a boron nitride powder on the properties of phosphate-bonded investment was also investigated. Three-point bend test specimens were cast in the phosphate-bonded investment material. Four groups of test samples were produced at specified water-to-powder ratios (w/p ratios). For one group 5 wt.% boron nitride powder was added to the investment powder before mixing with water. For stress-strain measurements specimens were heated to 920 degrees C and held for 30 min prior to the application of load. For thermal expansion measurements specimen length was measured for the entire heating and cooling cycle. Curves of stress versus strain and thermal expansion were recorded for all four test groups. For increasing initial w/p ratio failure stress decreased with lowest failure stresses for specimens containing boron nitride. Strain to failure also decreased with increasing initial w/p ratio, except for the group containing boron nitride which showed relatively large elongations to fracture. Specimen surfaces with higher initial w/p ratios were observed to have larger surface porosity. Thermal expansion curves for three groups were very similar, but differed considerably from the group containing boron nitride. The lowest initial w/p ratio should be used for highest hot strength. Hot deformation of phosphate-bonded investment dies for superplastic forming is an issue that requires further investigation because of potential die deformation and the resulting loss of fit between the superplastic superstructure and

  13. Halogen-bonded network of trinuclear copper(II) 4-iodo­pyrazolate complexes formed by mutual breakdown of chloro­form and nanojars

    PubMed Central

    Surmann, Stuart A.; Mezei, Gellert

    2016-01-01

    Crystals of bis­(tetra­butyl­ammonium) di-μ3-chlorido-­tris­(μ2-4-iodo­pyrazolato-κ2 N:N′)tris­[chlorido­cuprate(II)] 1,4-dioxane hemisolvate, (C16H36N)2[Cu3(C3H2IN2)3Cl5]·0.5C4H8O or (Bu4N)2[CuII 3(μ 3-Cl)2(μ-4-I-pz)3Cl3]·0.5C4H8O, were obtained by evaporating a solution of (Bu4N)2[{CuII(μ-OH)(μ-4-I-pz)}nCO3] (n = 27–31) nanojars in chloro­form/1,4-dioxane. The decomposition of chloro­form in the presence of oxygen and moisture provides HCl, which leads to the breakdown of nanojars to the title trinuclear copper(II) pyrazolate complex, and possibly CuII ions and free 4-iodo­pyrazole. CuII ions, in turn, act as catalyst for the accelerated decomposition of chloro­form, ultimately leading to the complete breakdown of nanojars. The crystal structure presented here provides the first structural description of a trinuclear copper(II) pyrazolate complex with iodine-substituted pyrazoles. In contrast to related trinuclear complexes based on differently substituted 4-R-pyrazoles (R = H, Cl, Br, Me), the [Cu3(μ-4-I-pz)3Cl3] core in the title complex is nearly planar. This difference is likely a result of the presence of the iodine substituent, which provides a unique, novel feature in copper pyrazolate chemistry. Thus, the iodine atoms form halogen bonds with the terminal chlorido ligands of the surrounding complexes [mean length of I⋯Cl contacts = 3.48 (1) Å], leading to an extended two-dimensional, halogen-bonded network along (-110). The cavities within this framework are filled by centrosymmetric 1,4-dioxane solvent mol­ecules, which create further bridges via C—H⋯Cl hydrogen bonds with terminal chlorido ligands of the trinuclear complex not involved in halogen bonding. PMID:27840698

  14. Carbon-Carbon Composite Radiator Development for the EO-1 Spacecraft

    NASA Technical Reports Server (NTRS)

    Vaughn, Wallace; Shinn, Elizabeth; Rawal, Suraj; Wright, Joe

    2004-01-01

    The Carbon-Carbon Space Radiator Partnership (CSRP), an informal partnership of Government and industrial personnel, was formed to promote the use of Carbon-carbon composites (C-C) as engineering materials for spacecraft thermal management applications . As a part of this effort the partnership has built a structural radiator for the Earth Orbiter - 1 (EO-1) spacecraft. This radiator, using C-C face-sheets with an aluminum honeycomb core, will demonstrate both the thermal and structural properties of C-C under actual service conditions as well as provide performance data from space flight. This paper will present results from the design of the radiator, the thermal/mechanical tests of the facesheet materials, and sub-component test results on the C-C/Al honeycomb sandwich material. The 29- by 28-inch radiator was designed to support two electronics boxes with a combined heat output of 60 watts maximum and a weight of 58 lbs. The analysis of the radiator design shows that the radiator constructed with 20-mil-thick facesheets of a P30-fiber-reinforced C-C from BFGoodrich is able to meet or exceed all the required thermal and mechanical requirements.

  15. Nickel-Catalyzed Carbon–Carbon Bond-Forming Reactions of Unactivated Tertiary Alkyl Halides: Suzuki Arylations

    PubMed Central

    Zultanski, Susan L.; Fu, Gregory C.

    2013-01-01

    The first Suzuki cross-couplings of unactivated tertiary alkyl electrophiles are described, employing a readily accessible catalyst (NiBr2·-diglyme/4,4′-di-t-butyl-2,2′-bipyridine, both commercially available); this also represents the initial example of the use of a Group 10 catalyst to cross-couple unactivated tertiary electrophiles to form carbon–carbon bonds. This approach to the synthesis of all-carbon quaternary carbon centers does not suffer from isomerization of the alkyl group, in contrast with the umpolung strategy for this bond construction (cross-coupling a tertiary alkylmetal with an aryl electrophile). Preliminary mechanistic studies are consistent with the generation of a radical intermediate along the reaction pathway. PMID:23281960

  16. Methyl group dynamics in paracetamol and acetanilide: probing the static properties of intermolecular hydrogen bonds formed by peptide groups

    NASA Astrophysics Data System (ADS)

    Johnson, M. R.; Prager, M.; Grimm, H.; Neumann, M. A.; Kearley, G. J.; Wilson, C. C.

    1999-06-01

    Measurements of tunnelling and librational excitations for the methyl group in paracetamol and tunnelling excitations for the methyl group in acetanilide are reported. In both cases, results are compared with molecular mechanics calculations, based on the measured low temperature crystal structures, which follow an established recipe. Agreement between calculated and measured methyl group observables is not as good as expected and this is attributed to the presence of comprehensive hydrogen bond networks formed by the peptide groups. Good agreement is obtained with a periodic quantum chemistry calculation which uses density functional methods, these calculations confirming the validity of the one-dimensional rotational model used and the crystal structures. A correction to the Coulomb contribution to the rotational potential in the established recipe using semi-emipircal quantum chemistry methods, which accommodates the modified charge distribution due to the hydrogen bonds, is investigated.

  17. Bonding Lexan and sapphire to form high-pressure, flame-resistant window

    NASA Astrophysics Data System (ADS)

    Richardson, William R.; Walker, Ernie D.

    Flammable materials have been studied in normal gravity and microgravity for many years. Photography plays a major role in the study of the combustion process giving a permanent visual record that can be analyzed. When these studies are extended to manned spacecraft, safety becomes a primary concern. The need for a high-pressure, flame-resistant, shatter-resistant window permitting photographic recording of combustion experiments in manned spacecraft prompted the development of a method for bonding Lexan and sapphire. Materials that resist shattering (e.g., Lexan) are not compatible with combustion experiments; the material loses strength at combustion temperatures. Sapphire is compatible with combustion temperatures in oxygen-enriched atmospheres but is subject to shattering. Combining the two materials results in a shatter-resistant, flame-resistant window. Combustion in microgravity produces a low-visibility flame; however, flame propagation and flame characteristics are readily visible as long as there is no deterioration of the image. Since an air gap between the Lexan and the sapphire would reduce transmission, a method was developed for bonding these unlike materials to minimize light loss.

  18. Bonding Lexan and sapphire to form high-pressure, flame-resistant window

    NASA Technical Reports Server (NTRS)

    Richardson, William R.; Walker, Ernie D.

    1987-01-01

    Flammable materials have been studied in normal gravity and microgravity for many years. Photography plays a major role in the study of the combustion process giving a permanent visual record that can be analyzed. When these studies are extended to manned spacecraft, safety becomes a primary concern. The need for a high-pressure, flame-resistant, shatter-resistant window permitting photographic recording of combustion experiments in manned spacecraft prompted the development of a method for bonding Lexan and sapphire. Materials that resist shattering (e.g., Lexan) are not compatible with combustion experiments; the material loses strength at combustion temperatures. Sapphire is compatible with combustion temperatures in oxygen-enriched atmospheres but is subject to shattering. Combining the two materials results in a shatter-resistant, flame-resistant window. Combustion in microgravity produces a low-visibility flame; however, flame propagation and flame characteristics are readily visible as long as there is no deterioration of the image. Since an air gap between the Lexan and the sapphire would reduce transmission, a method was developed for bonding these unlike materials to minimize light loss.

  19. GeSn-on-insulator substrate formed by direct wafer bonding

    SciTech Connect

    Lei, Dian; Wang, Wei; Gong, Xiao E-mail: yeo@ieee.org; Yeo, Yee-Chia E-mail: yeo@ieee.org; Lee, Kwang Hong; Wang, Bing; Bao, Shuyu; Tan, Chuan Seng

    2016-07-11

    GeSn-on-insulator (GeSnOI) on Silicon (Si) substrate was realized using direct wafer bonding technique. This process involves the growth of Ge{sub 1-x}Sn{sub x} layer on a first Si (001) substrate (donor wafer) followed by the deposition of SiO{sub 2} on Ge{sub 1-x}Sn{sub x}, the bonding of the donor wafer to a second Si (001) substrate (handle wafer), and removal of the Si donor wafer. The GeSnOI material quality is investigated using high-resolution transmission electron microscopy, high-resolution X-ray diffraction (HRXRD), atomic-force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. The Ge{sub 1-x}Sn{sub x} layer on GeSnOI substrate has a surface roughness of 1.90 nm, which is higher than that of the original Ge{sub 1-x}Sn{sub x} epilayer before transfer (surface roughness is 0.528 nm). The compressive strain of the Ge{sub 1-x}Sn{sub x} film in the GeSnOI is as low as 0.10% as confirmed using HRXRD and Raman spectroscopy.

  20. Structural and biochemical characterization of the essential DsbA-like disulfide bond forming protein from Mycobacterium tuberculosis

    PubMed Central

    2013-01-01

    Background Bacterial Disulfide bond forming (Dsb) proteins facilitate proper folding and disulfide bond formation of periplasmic and secreted proteins. Previously, we have shown that Mycobacterium tuberculosis Mt-DsbE and Mt-DsbF aid in vitro oxidative folding of proteins. The M. tuberculosis proteome contains another predicted membrane-tethered Dsb protein, Mt-DsbA, which is encoded by an essential gene. Results Herein, we present structural and biochemical analyses of Mt-DsbA. The X-ray crystal structure of Mt-DsbA reveals a two-domain structure, comprising a canonical thioredoxin domain with the conserved CXXC active site cysteines in their reduced form, and an inserted α-helical domain containing a structural disulfide bond. The overall fold of Mt-DsbA resembles that of other DsbA-like proteins and not Mt-DsbE or Mt-DsbF. Biochemical characterization demonstrates that, unlike Mt-DsbE and Mt-DsbF, Mt-DsbA is unable to oxidatively fold reduced, denatured hirudin. Moreover, on the substrates tested in this study, Mt-DsbA has disulfide bond isomerase activity contrary to Mt-DsbE and Mt-DsbF. Conclusion These results suggest that Mt-DsbA acts upon a distinct subset of substrates as compared to Mt-DsbE and Mt-DsbF. One could speculate that Mt-DsbE and Mt-DsbF are functionally redundant whereas Mt-DsbA is not, offering an explanation for the essentiality of Mt-DsbA in M. tuberculosis. PMID:24134223

  1. Orthogonal natural atomic orbitals form an appropriate one-electron basis for expanding CASSCF wave functions into localized bonding schemes and their weights.

    PubMed

    Bachler, Vinzenz

    2007-09-01

    Localized bonding schemes and their weights have been obtained for the pi-electron system of nitrone by expanding complete active space self-consistent field wave functions into a set of Slater determinants composed of orthogonal natural atomic orbitals (NAOs) of Weinhold and Landis (Valency and Bonding: A Natural Bond Orbital Donor-Acceptor Perspective, 2005). Thus, the derived bonding schemes are close to orthogonal valence bond structures. The calculated sequence of bonding scheme weights accords with the sequence of genuine resonance structure weights derived previously by Ohanessian and Hiberty (Chem Phys Lett 1987, 137, 437), who employed nonorthogonal atomic orbitals. This accord supports the notion that NAOs form an appropriate orthogonal one-electron basis for expanding complete active space self-consistent field wave functions into meaningful bonding schemes and their weights.

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

    SciTech Connect

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

    2010-04-07

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

  3. The hydrogen bond stabilizing effect in enammonium salts of captodative aminoalkenes containing a carbonyl group

    NASA Astrophysics Data System (ADS)

    Fedorov, S. V.; Rulev, A. Yu; Chipanina, N. N.; Sherstyannikova, L. V.; Turchaninov, V. K.

    2004-03-01

    Enhanced stability of enammonium salts of captodative carbonyl-containing aminoalkenes as compared to the salts of simple enamines is discussed on the basis of 1H and 13C NMR, IR, UV spectroscopy and the results quantum chemical calculations. Stabilization of the N-protonated form of captodative aminoalkenes is due to either intramolecular (NH +⋯OC) or intermolecular (NH +⋯Solv or NH +⋯X -) hydrogen bonding, whereas the C-protonated form is destabilized due to umpolung of the carbon-carbon double bond. The formation of bifurcated (three-centered) hydrogen bond between the enammonium cation and the solvent is demonstrated. The three-centered solvate complex is characterized by nonclassical dependence of the chemical shift of the bridging hydrogen atom from the proton-acceptor power of the solvent.

  4. Oxidation of Reinforced Carbon-Carbon Subjected to Hypervelocity Impact

    NASA Technical Reports Server (NTRS)

    Curry, Donald M.; Pham, Vuong T.; Norman, Ignacio; Chao, Dennis C.; Nicholson, Leonard S. (Technical Monitor)

    1999-01-01

    Results of arc-jet tests conducted at the NASA Johnson Space Center (JSC) on Reinforced Carbon-Carbon (RCC) samples subjected to hypervelocity impact are presented. The RCC test specimens are representative of RCC component used on the Space Shuttle Orbiter. The objective of the arc jet testing was to establish the oxidation characteristics of RCC when hypervelocity projectiles, simulating meteoroid/orbital debris (MOD), impact the RCC material. In addition, analytical modeling of the increased material oxidation in the impacted area, using measured hole growth data, to develop correlations for use in trajectory simulations is also discussed.

  5. Hydroburst test of a carbon-carbon involute exit cone

    NASA Technical Reports Server (NTRS)

    Sullivan, Roy M.

    1986-01-01

    A hydroburst test of the aft portion of the PAM-D exit cone and the test procedure are described in detail. The hydrostatic pressure required to buckle the cone was 9.75 psi. Meanwhile, the PAM-D exit cone was modeled using the finite element method and a theoretical bucking pressure (8.76 psi) was predicted using the SPAR finite element code. The modeling technique employed is discussed. By comparing the theoretical to predicted critical pressures, this report verifies the modeling technique and calculates a material knockdown factor for the carbon-carbon exit cone.

  6. Failure mechanisms in laminated carbon/carbon composites under biaxial compression

    SciTech Connect

    Grape, J.A.; Gupta, V.

    1995-07-01

    The failure mechanisms of 2D carbon/carbon (C/C) woven laminates have been determined under inplane biaxial compression loads, and the associated failure envelopes that account for the effect of matrix-type and loading directions were also obtained. The failure was in the form of micro-kinking of fiber bundles, interspersed with localized interply delaminations to form an overall shear fault. The shear fault was aligned with the major axis of loading except at above 75% of balanced biaxial compressive stress where failure occurred along both axes. Although the biaxial strength varied significantly with the ratio of in-plane principal stresses, R, there was no variation in the local failure mechanisms. Accordingly, it was found that the samples fail upon achieving a critical strain along the primary axis of loading.

  7. The use of carboranes as oxidation inhibitors for carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Petty, John T.

    1991-01-01

    Carbon-carbon composites have many beneficial properties for use in aerospace applications, including their high specific strength and modulus at elevated temperatures. However, they share with all carbon based substances a strong tendency to burn when heated in air. In order to exploit their good qualities, it is necessary to slow or prevent their oxidation during use. Molecular inhibiters offer protection with the advantage of being able to form a homogeneous solution with the resin. Since boron oxides are known to provide the desired kind of protection, molecular compounds based on boron seem reasonable candidates to test as inhibitors. Performance tests indicated that carboranes are excellent materials for obtaining high uniform loadings of boron inhibitors in glassy carbon materials and thus reducing their rates of oxidation. Further, there is evidence that the use of substituted derivatives could provide more complete and thorough forms of protection.

  8. Effect of Cementation Technique of Individually Formed Fiber-Reinforced Composite Post on Bond Strength and Microleakage

    PubMed Central

    Makarewicz, Dominika; Le Bell-Rönnlöf, Anna-Maria B; Lassila, Lippo V.J.; Vallittu, Pekka K.

    2013-01-01

    Objectives: The aim of this study was to evaluate the effect of two different cementation techniques of individually formed E-glass fiber-reinforced composite (FRC) post on bond strength and microleakage. Methods: The crowns of extracted third molars were removed and post preparation was carried out with parapost drills (diameter 1.5 mm). After application of bonding agents individually formed FRC posts (everStick POST, diameter 1.5 mm) were cemented into the post spaces with either ParaCem®Universal or self-adhesive RelyX™Unicem, using two different cementation techniques: 1) an “indirect (traditional) technique” where the post was prepolymerized prior application of luting cement and insertion into the post space or 2) a “direct technique” where the uncured post was inserted to the post space with luting cement and light-polymerized in situ at the same time. After water storage of 48 hours, the roots (n = 10/group) were cut into discs of thickness of 2 mm. A push-out force was applied until specimen fracture or loosening of the post. A microleakage test was carried out on roots which were not subjected to the loading test (n= 32) to evaluate the sealing capacity of the post-canal interface. The microleakage was measured using dye penetration depth under a stereomicroscope. Results: Higher bond strength values (p<0.05) and less microleakage (p<0.05) were obtained with the “direct technique” compared to the “indirect technique”. None of the FRC posts revealed any dye penetration between the post and the cement. Conclusions: The “direct technique” seems to be beneficial when cementing individually formed FRC posts. PMID:23986792

  9. Characterization of an alternative low energy fold for bovine α-lactalbumin formed by disulfide bond shuffling.

    PubMed

    Lewney, Sarah; Smith, Lorna J

    2012-03-01

    Bovine α-lactalbumin (αLA) forms a misfolded disulfide bond shuffled isomer, X-αLA. This X-αLA isomer contains two native disulfide bridges (Cys 6-Cys 120 and Cys 28-Cys 111) and two non-native disulfide bridges (Cys 61-Cys 73 and Cys 77-Cys 91). MD simulations have been used to characterize the X-αLA isomer and its formation via disulfide bond shuffling and to compare it with the native fold of αLA. In the simulations of the X-αLA isomer the structure of the α-domain of native αLA is largely retained in agreement with experimental data. However, there are significant rearrangements in the β-domain, including the loss of the native β-sheet and calcium binding site. Interestingly, the energies of X-αLA and native αLA in simulations in the absence of calcium are closely similar. Thus, the X-αLA isomer represents a different low energy fold for the protein. Calcium binding to native αLA is shown to help preserve the structure of the β-domain of the protein limiting possibilities for disulfide bond shuffling. Hence, binding calcium plays an important role in both maintaining the native structure of αLA and providing a mechanism for distinguishing between folded and misfolded species.

  10. Connection between fragility, mean-squared displacement, and shear modulus in two van der Waals bonded glass-forming liquids

    NASA Astrophysics Data System (ADS)

    Hansen, Henriette W.; Frick, Bernhard; Hecksher, Tina; Dyre, Jeppe C.; Niss, Kristine

    2017-03-01

    The temperature dependence of the high-frequency shear modulus measured in the kHz range is compared with the mean-squared displacement measured in the nanosecond range for the two van der Waals bonded glass-forming liquids cumene and 5-polyphenyl ether. This provides an experimental test for the assumption connecting two versions of the shoving model for the non-Arrhenius temperature dependence of the relaxation time in glass formers. The two versions of the model are also tested directly and both are shown to work well for these liquids.

  11. Comparison of structural behavior of superplastically formed/diffusion-bonded sandwich structures and honeycomb core sandwich structures

    NASA Technical Reports Server (NTRS)

    Ko, W. L.

    1980-01-01

    A superplasticity formed/diffusion-bonded (SPF/DB) orthogonally corrugated core sandwich structure is discussed and its structural behavior is compared to that of a conventional honeycomb core sandwich structure. The stiffness and buckling characteristics of the two types of sandwich structures are compared under conditions of equal structural density. It is shown that under certain conditions, the SPF/DB orthogonally corrugated core sandwich structure is slightly more efficient than the optimum honeycomb core (square-cell core) sandwich structure. However, under different conditions, this effect can be reversed.

  12. Integrative Pericyclic Cascade: An Atom Economic, Multi C-C Bond-Forming Strategy for the Construction of Molecular Complexity.

    PubMed

    Tejedor, David; Delgado-Hernández, Samuel; Peyrac, Jesús; González-Platas, Javier; García-Tellado, Fernando

    2017-07-26

    An all-pericyclic manifold is developed for the construction of topologically diverse, structurally complex and natural product-like polycyclic chemotypes. The manifold uses readily accessible tertiary propargyl vinyl ethers as substrates and imidazole as a catalyst to form up to two new rings, three new C-C bonds, six stereogenic centers and one transannular oxo-bridge. The manifold is efficient, scalable and instrumentally simple to perform and entails a propargyl Claisen rearrangement-[1,3]H shift, an oxa-6π-electrocyclization, and an intramolecular Diels-Alder reaction. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Method and apparatus for forming a carbon-silicon bond in a silane

    DOEpatents

    Schattenmann, Florian Johannes

    2002-01-01

    A method for forming at least one product silane, comprising reacting a transition metal hydride with a starting silane in a presence of a catalyst and at a temperature that exceeds a threshold temperature associated with said reacting.

  14. Topological description of the bond-breaking and bond-forming processes of the alkene protonation reaction in zeolite chemistry: an AIM study.

    PubMed

    Zalazar, María Fernanda; Peruchena, Nélida Maria

    2011-10-01

    Density functional theory and atoms in molecules theory were used to study bond breakage and bond formation in the trans-2-butene protonation reaction in an acidic zeolitic cluster. The progress of this reaction along the intrinsic reaction coordinate, in terms of several topological properties of relevant bond critical points and atomic properties of the key atoms involved in these concerted mechanisms, were analyzed in depth. At B3LYP/6-31++G(d,p)//B3LYP/6-31G(d,p) level, the results explained the electron density redistributions associated with the progressive bond breakage and bond formation of the reaction under study, as well as the profiles of the electronic flow between the different atomic basins involved in these electron reorganization processes. In addition, we found a useful set of topological indicators that are useful to show what is happening in each bond/atom involved in the reaction site as the reaction progresses.

  15. Mechanical testing and modelling of carbon-carbon composites for aircraft disc brakes

    NASA Astrophysics Data System (ADS)

    Bradley, Luke R.

    The objective of this study is to improve the understanding of the stress distributions and failure mechanisms experienced by carbon-carbon composite aircraft brake discs using finite element (FE) analyses. The project has been carried out in association with Dunlop Aerospace as an EPSRC CASE studentship. It therefore focuses on the carbon-carbon composite brake disc material produced by Dunlop Aerospace, although it is envisaged that the approach will have broader applications for modelling and mechanical testing of carbon-carbon composites in general. The disc brake material is a laminated carbon-carbon composite comprised of poly(acrylonitrile) (PAN) derived carbon fibres in a chemical vapour infiltration (CVI) deposited matrix, in which the reinforcement is present in both continuous fibre and chopped fibre forms. To pave the way for the finite element analysis, a comprehensive study of the mechanical properties of the carbon-carbon composite material was carried out. This focused largely, but not entirely, on model composite materials formulated using structural elements of the disc brake material. The strengths and moduli of these materials were measured in tension, compression and shear in several orientations. It was found that the stress-strain behaviour of the materials were linear in directions where there was some continuous fibre reinforcement, but non-linear when this was not the case. In all orientations, some degree of non-linearity was observed in the shear stress-strain response of the materials. However, this non-linearity was generally not large enough to pose a problem for the estimation of elastic moduli. Evidence was found for negative Poisson's ratio behaviour in some orientations of the material in tension. Additionally, the through-thickness properties of the composite, including interlaminar shear strength, were shown to be positively related to bulk density. The in-plane properties were mostly unrelated to bulk density over the range of

  16. Inhibition of catalytic oxidation of carbon/carbon composite materials

    NASA Astrophysics Data System (ADS)

    Wu, Xianxian

    An investigation coupling experimental efforts with computational chemistry analysis was conducted to study the inhibition effects of phosphorous or boron on the oxidation of carbon/carbon composite materials catalyzed by potassium or calcium acetate (KAC or CaAC). Commercial aircraft brakes were used, which are exposed during use to K- or Ca-containing runway deicing agents. The reactivity of inhibitor-doped carbon materials was determined by temperature programmed oxidation (TPO) and isothermal oxidation in 1 atm O2. The structure and surface chemistry of inhibitor-doped samples were characterized, and the inhibition mechanisms were explored with the help of ab initio molecular orbital calculations. The catalytic effects of KAC or CaAC were found to be dependent on catalyst loading, pretreatment procedure, temperature and O2 partial pressure. Experimental observations showed that K is a more effective catalyst for carbon composite oxidation than Ca as expected from prior studies of catalyzed carbon gasification. This was attributed to its ability to form and maintain good interfacial contact with carbon, as well as to its insensitivity to carbon structure because of its excellent wetting ability and mobility. The experimental results suggested that the interfacial catalyst/carbon contact is the critical factor determining the catalytic effectiveness. Thermally deposited phosphorus, upon heat treatment of P-containing compounds such as CH3OP(OH)2 and POCl3 at around 600°C in the presence of inert gas, exhibited a good inhibition effect in the oxidation of C/C composites used in aircraft brake systems. These P compounds were also effective inhibitors for Ca- or K-catalyzed oxidation. The P loading up to a certain amount (ca. 4.0 wt%) was found to suppress Ca-catalyzed oxidation completely. It also improved the resistance of carbon to K-catalyzed oxidation, but the effect was much less significant than in the case of Ca-catalyzed reaction. The characterization of P

  17. Carbon-sulfur bond-forming reaction catalysed by the radical SAM enzyme HydE

    NASA Astrophysics Data System (ADS)

    Rohac, Roman; Amara, Patricia; Benjdia, Alhosna; Martin, Lydie; Ruffié, Pauline; Favier, Adrien; Berteau, Olivier; Mouesca, Jean-Marie; Fontecilla-Camps, Juan C.; Nicolet, Yvain

    2016-05-01

    Carbon-sulfur bond formation at aliphatic positions is a challenging reaction that is performed efficiently by radical S-adenosyl-L-methionine (SAM) enzymes. Here we report that 1,3-thiazolidines can act as ligands and substrates for the radical SAM enzyme HydE, which is involved in the assembly of the active site of [FeFe]-hydrogenase. Using X-ray crystallography, in vitro assays and NMR spectroscopy we identified a radical-based reaction mechanism that is best described as the formation of a C-centred radical that concomitantly attacks the sulfur atom of a thioether. To the best of our knowledge, this is the first example of a radical SAM enzyme that reacts directly on a sulfur atom instead of abstracting a hydrogen atom. Using theoretical calculations based on our high-resolution structures we followed the evolution of the electronic structure from SAM through to the formation of S-adenosyl-L-cysteine. Our results suggest that, at least in this case, the widely proposed and highly reactive 5‧-deoxyadenosyl radical species that triggers the reaction in radical SAM enzymes is not an isolable intermediate.

  18. Self-Assembled Liquid-Crystalline Membranes Form Supramolecular Hydrogels via Hydrogen Bonding.

    PubMed

    Yue, Youfeng

    2017-04-01

    Developing simple methods to organize nanoscale building blocks into ordered superstructures is a crucial step toward the practical development of nanotechnology. Bottom-up nanotechnology using self-assembly bridges the molecular and macroscopic, and can provide unique material properties, different from the isotropic characteristics of common substances. In this study, a new class of supramolecular hydrogels comprising 40 nm thick linear polymer layers sandwiched between nanolayers of self-assembled amphiphilic molecules are prepared and studied by nuclear magnetic resonance spectroscopy, scanning electronic microscopy, small angle X-ray diffraction, and rheometry. The amphiphilic molecules spontaneously self-assemble into bilayer membranes when they are in liquid-crystal state. The hydrogen bonds at the interface of the nanolayers and linear polymers serve as junctions to stabilize the network. These hydrogels with layered structure are facile to prepare, mechanically stable, and with unique temperature-dependent optical transparency, which makes it interesting in applications, such as soft biological membranes, drug release, and optical filters. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Cyclodipeptide synthases are a family of tRNA-dependent peptide bond-forming enzymes.

    PubMed

    Gondry, Muriel; Sauguet, Ludovic; Belin, Pascal; Thai, Robert; Amouroux, Rachel; Tellier, Carine; Tuphile, Karine; Jacquet, Mickaël; Braud, Sandrine; Courçon, Marie; Masson, Cédric; Dubois, Steven; Lautru, Sylvie; Lecoq, Alain; Hashimoto, Shin-ichi; Genet, Roger; Pernodet, Jean-Luc

    2009-06-01

    Cyclodipeptides and their derivatives belong to the diketopiperazine (DKP) family, which is comprised of a broad array of natural products that exhibit useful biological properties. In the few known DKP biosynthetic pathways, nonribosomal peptide synthetases (NRPSs) are involved in the synthesis of cyclodipeptides that constitute the DKP scaffold, except in the albonoursin (1) pathway. Albonoursin, or cyclo(alpha,beta-dehydroPhe-alpha,beta-dehydroLeu), is an antibacterial DKP produced by Streptomyces noursei. In this pathway, the formation of the cyclo(Phe-Leu) (2) intermediate is catalyzed by AlbC, a small protein unrelated to NRPSs. We demonstrated that AlbC uses aminoacyl-tRNAs as substrates to catalyze the formation of the DKP peptide bonds. Moreover, several other bacterial proteins, presenting moderate similarity to AlbC, also use aminoacyl-tRNAs to synthesize various cyclodipeptides. Therefore, AlbC and these related proteins belong to a newly defined family of enzymes that we have named cyclodipeptide synthases (CDPSs).

  20. Carbon-sulfur bond-forming reaction catalysed by the radical SAM enzyme HydE.

    PubMed

    Rohac, Roman; Amara, Patricia; Benjdia, Alhosna; Martin, Lydie; Ruffié, Pauline; Favier, Adrien; Berteau, Olivier; Mouesca, Jean-Marie; Fontecilla-Camps, Juan C; Nicolet, Yvain

    2016-05-01

    Carbon-sulfur bond formation at aliphatic positions is a challenging reaction that is performed efficiently by radical S-adenosyl-L-methionine (SAM) enzymes. Here we report that 1,3-thiazolidines can act as ligands and substrates for the radical SAM enzyme HydE, which is involved in the assembly of the active site of [FeFe]-hydrogenase. Using X-ray crystallography, in vitro assays and NMR spectroscopy we identified a radical-based reaction mechanism that is best described as the formation of a C-centred radical that concomitantly attacks the sulfur atom of a thioether. To the best of our knowledge, this is the first example of a radical SAM enzyme that reacts directly on a sulfur atom instead of abstracting a hydrogen atom. Using theoretical calculations based on our high-resolution structures we followed the evolution of the electronic structure from SAM through to the formation of S-adenosyl-L-cysteine. Our results suggest that, at least in this case, the widely proposed and highly reactive 5'-deoxyadenosyl radical species that triggers the reaction in radical SAM enzymes is not an isolable intermediate.

  1. Orbiter Reinforced Carbon-Carbon Advanced Sealant Systems: Screening Tests

    NASA Technical Reports Server (NTRS)

    Curry, Donald M.; Lewis, Ronad K.; Norman, Ignacio; Chao, Dennis; Nicholson, Leonard S. (Technical Monitor)

    2000-01-01

    Oxidation protection for the Orbiter reinforced carbon-carbon (RCC consists of three components: silicon carbide coating, tetraethyl orthosilicate (TEOS) impregnated into the carbon substrate and a silicon based surface sealant (designated Type A). The Orbiter Type A sealant is being consumed each mission, which results in increased carbon-carbon substrate mass loss, which adversely impacts the mission life of the RCC components. In addition, the sealant loss in combination with launch pad contamination (salt deposit and zinc oxide) results in RCC pinholes. A sealant refurbishment schedule to maintain mission life and minimize affects of pin hole formation has been implemented in the Orbiter maintenance schedule. The objective of this investigation is to develop an advanced sealant system for the RCC that extends the refurbishment schedule by reducing sealant loss/pin hole formation and that can be applied to existing Orbiter RCC components. This paper presents the results of arc jet screening tests conducted on several sealants that are being considered for application to the Orbiter RCC.

  2. NDE for Characterizing Oxidation Damage in Reinforced Carbon-Carbon

    NASA Technical Reports Server (NTRS)

    Roth, Don J.; Rauser, Richard W.; Jacobson, nathan S.; Wincheski, Russell A.; Walker, James L.; Cosgriff, Laura A.

    2009-01-01

    In this study, coated reinforced carbon-carbon (RCC) samples of similar structure and composition as that from the NASA space shuttle orbiter s thermal protection system were fabricated with slots in their coating simulating craze cracks. These specimens were used to study oxidation damage detection and characterization using NDE methods. These specimens were heat treated in air at 1143 and 1200 C to create cavities in the carbon substrate underneath the coating as oxygen reacted with the carbon and resulted in its consumption. The cavities varied in diameter from approximately 1 to 3 mm. Single-sided NDE methods were used since they might be practical for on-wing inspection, while x-ray micro-computed tomography (CT) was used to measure cavity sizes in order to validate oxidation models under development for carbon-carbon materials. An RCC sample having a naturally-cracked coating and subsequent oxidation damage was also studied with x-ray micro-CT. This effort is a follow-on study to one that characterized NDE methods for assessing oxidation damage in an RCC sample with drilled holes in the coating. The results of that study are briefly reviewed in this article as well. Additionally, a short discussion on the future role of simulation to aid in these studies is provided.

  3. Orbiter Reinforced Carbon-Carbon Advanced Sealant Systems: Screening Tests

    NASA Technical Reports Server (NTRS)

    Curry, Donald M.; Lewis, Ronad K.; Norman, Ignacio; Chao, Dennis; Nicholson, Leonard S. (Technical Monitor)

    2000-01-01

    Oxidation protection for the Orbiter reinforced carbon-carbon (RCC consists of three components: silicon carbide coating, tetraethyl orthosilicate (TEOS) impregnated into the carbon substrate and a silicon based surface sealant (designated Type A). The Orbiter Type A sealant is being consumed each mission, which results in increased carbon-carbon substrate mass loss, which adversely impacts the mission life of the RCC components. In addition, the sealant loss in combination with launch pad contamination (salt deposit and zinc oxide) results in RCC pinholes. A sealant refurbishment schedule to maintain mission life and minimize affects of pin hole formation has been implemented in the Orbiter maintenance schedule. The objective of this investigation is to develop an advanced sealant system for the RCC that extends the refurbishment schedule by reducing sealant loss/pin hole formation and that can be applied to existing Orbiter RCC components. This paper presents the results of arc jet screening tests conducted on several sealants that are being considered for application to the Orbiter RCC.

  4. Enhancement of gene delivery using novel homodimeric tat peptide formed by disulfide bond.

    PubMed

    Lee, Soo-Jin; Yoon, Sung-Hwa; Doh, Kyung-Oh

    2011-08-01

    Cationic liposomes have been actively used as gene delivery vehicle because of their minimal toxicity, but their relatively low efficiency of gene delivery is the major disadvantage of these vectors. Recently, cysteine residue incorporation to HIV-1 Tat peptide increased liposomemediated transfection compared with unmodified Tat peptide. Therefore, we designed a novel modified Tat peptide having a homodimeric (Tat-CTHD, Tat-NTHD) and closed structure (cyclic Tat) simply by using the disulfide bond between cysteines to develop a more efficient and safe nonviral gene delivery system. The mixing of Tat-CTHD and Tat-NTHD with DNA before mixing with lipofectamine increased the transfection efficiency compared with unmodified Tat peptide and lipofectamine only in MCF-7 breast cancer cells and rat vascular smooth muscle cells. However, cyclic Tat did not show any improvement in the transfection efficiency. In the gel retardation assay, Tat-CTHD and Tat-NTHD showed more strong binding with DNA than unmodified Tat and cyclic Tat peptide. This enhancement was only shown when Tat-CTHD and Tat-NTHD were mixed with DNA before mixing with lipofectamine. The effects of Tat- CTHD and Tat-NTHD were also valid in the experiment using DOTAP and DMRIE instead of lipofectamine. We could not find any significant cytotoxicity in the working concentration and more usage of these peptides. In conclusion, we have designed a novel transfection-enhancing peptide by easy homodimerization of Tat peptide, and the simple mix of these novel peptides with DNA increased the gene transfer of cationic lipids more efficiently with no additional cytotoxicity.

  5. Bonding and Electronic Properties of Linear Diethynyl Oligothienoacene-Bridged Diruthenium Complexes and Their Oxidized Forms.

    PubMed

    Ou, Ya-Ping; Zhang, Jing; Zhang, Ming-Xing; Zhang, Fuxing; Kuang, Daizhi; Hartl, František; Liu, Sheng Hua

    2017-08-29

    A series of five diruthenium diethynyl complexes based on α,β-fused oligothienoacenes in the core of the bridging ligands [{Ru(dppe)Cp*}2(μ-C≡C-L-C≡C)] [dppe = 1,2-bis(diphenylphosphino)ethane, Cp* = η(5)-C5Me5; L = thieno[3,2-b]thiophene (4), thieno[2,3-b]thiophene (5), 3,4-dimethylthieno[2,3-b]thiophene (6), dithieno[3,2-b:2',3'-d]thiophene (7), and thieno[3,2-b]thieno[2',3':4,5]thieno[2,3-d]thiophene (8)] have been synthesized and fully characterized electrochemically and spectroscopically. Elongation of the redox noninnocent oligothienoacene bridge core causes a smaller potential difference between the initial two anodic steps, not seen for free dialkyl oligothienoacenes, and increased positive charge delocalization over the conjugated bridge backbone. The highest occupied molecular orbital of the parent complexes resides predominantly on the oligothienoacene core, with strong participation of the ethynyl linkers and slightly smaller contribution from the metallic termini. This bonding character makes the initial one-electron oxidation symmetrical, as revealed by combined voltammetric and spectroscopic (IR, UV-vis-near-IR, and electron paramagnetic resonance) methods as well as density functional theory (DFT) and time-dependent DFT calculations of truncated and selected nontruncated models of the studied series. The remarkable gradual appearance of two C≡C stretching absorptions in the IR spectra of the monocationic diethynyl complexes is ascribed to increasing vibronic coupling of the IR-forbidden νs(C≡C) mode of the oxidized -[C≡C-core-C≡C](+)- bridge with a low-lying π-π*(intrabridge)/metal-to-ligand charge-transfer electronic transition in the near-to-mid-IR spectral region.

  6. Effect of cooking conditions on fiber bonding in dry-formed binderless hardboard

    Treesearch

    Otto Suchsland; George E. Woodson; Charles W. McMillin

    1987-01-01

    Binderless dry-formed hardboards were manufactured in the laboratory from refined Masonite pulp cooked for 2.5 minutes at steam pressures varying from 200 to 500 psi. Increasing steam pressure caused a general improvement in mechanical and physical properties except that linear expanaion increased with increasing steam pressures and that bending strength and stiffness...

  7. Metallomacrocycles as anion receptors: combining hydrogen bonding and ion pair based hosts formed from Ag(I) salts and flexible bis- and tris-pyrimidine ligands.

    PubMed

    Tasada, Andres; Albertí, Francisca M; Bauzá, Antonio; Barceló-Oliver, Miquel; García-Raso, Angel; Fiol, Juan J; Molins, Elies; Caubet, Amparo; Frontera, Antonio

    2013-05-28

    Two self-assembled hosts are formed from Ag(I) salts and bis-pyrimidyl ligands and X-ray characterized. Both are able to incorporate two anions into the structure combining hydrogen bonding and electrostatic interactions.

  8. Brazing of Carbon Carbon Composites to Cu-clad Molybdenum for Thermal Management Applications

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.; Shpargel, T> P.

    2007-01-01

    Advanced carbon carbon composites were joined to copper-clad molybdenum (Cu/Mo) using four active metal brazes containing Ti (Cu ABA, Cusin-1 ABA, Ticuni, and Ticusil) for potential use in thermal management applications. The brazed joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Knoop microhardness measurements across the joint region. Metallurgically sound C-C/Cu/Mo joints, devoid of interfacial cracks formed in all cases. The joint interfaces were preferentially enriched in Ti, with Cu ABA joints exhibiting the largest interfacial Ti concentrations. The microhardness measurements revealed hardness gradients across the joint region, with a peak hardness of 300-350 KHN in Cusin-1 ABA and Ticusil joints and 200-250 KHN in Cu ABA and Ticuni joints, respectively.

  9. Brazing of Carbon Carbon Composites to Cu-clad Molybdenum for Thermal Management Applications

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.; Shpargel, T> P.

    2007-01-01

    Advanced carbon carbon composites were joined to copper-clad molybdenum (Cu/Mo) using four active metal brazes containing Ti (Cu ABA, Cusin-1 ABA, Ticuni, and Ticusil) for potential use in thermal management applications. The brazed joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Knoop microhardness measurements across the joint region. Metallurgically sound C-C/Cu/Mo joints, devoid of interfacial cracks formed in all cases. The joint interfaces were preferentially enriched in Ti, with Cu ABA joints exhibiting the largest interfacial Ti concentrations. The microhardness measurements revealed hardness gradients across the joint region, with a peak hardness of 300-350 KHN in Cusin-1 ABA and Ticusil joints and 200-250 KHN in Cu ABA and Ticuni joints, respectively.

  10. Formation mechanism of a silicon carbide coating for a reinforced carbon-carbon composite

    NASA Technical Reports Server (NTRS)

    Rogers, D. C.; Shuford, D. M.; Mueller, J. I.

    1975-01-01

    Results are presented for a study to determine the mechanisms involved in a high-temperature pack cementation process which provides a silicon carbide coating on a carbon-carbon composite. The process and materials used are physically and chemically analyzed. Possible reactions are evaluated using the results of these analytical data. The coating is believed to develop in two stages. The first is a liquid controlled phase process in which silicon carbide is formed due to reactions between molten silicon metal and the carbon. The second stage is a vapor transport controlled reaction in which silicon vapors react with the carbon. There is very little volume change associated with the coating process. The original thickness changes by less than 0.7%. This indicates that the coating process is one of reactive penetration. The coating thickness can be increased or decreased by varying the furnace cycle process time and/or temperature to provide a wide range of coating thicknesses.

  11. Nitric oxide in star-forming regions - Further evidence for interstellar N-O bonds

    NASA Technical Reports Server (NTRS)

    Ziurys, L. M.; Mcgonagle, D.; Minh, Y.; Irvine, W. M.

    1991-01-01

    Nitric oxide has been newly detected toward several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2-1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both lambda-doubling components of NO were observed toward all sources. Column densities derived for nitric oxide in these clouds are 10 to the 15th-10 to the 16th/sq cm, corresponding to fractional abundances of 0.5-1.0 x 10 to the -8th, relative to H2. Toward Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude.

  12. Nitric oxide in star-forming regions - Further evidence for interstellar N-O bonds

    NASA Technical Reports Server (NTRS)

    Ziurys, L. M.; Mcgonagle, D.; Minh, Y.; Irvine, W. M.

    1991-01-01

    Nitric oxide has been newly detected toward several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2-1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both lambda-doubling components of NO were observed toward all sources. Column densities derived for nitric oxide in these clouds are 10 to the 15th-10 to the 16th/sq cm, corresponding to fractional abundances of 0.5-1.0 x 10 to the -8th, relative to H2. Toward Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude.

  13. Stilbene Boronic Acids Form a Covalent Bond with Human Transthyretin and Inhibit Its Aggregation.

    PubMed

    Smith, Thomas P; Windsor, Ian W; Forest, Katrina T; Raines, Ronald T

    2017-09-28

    Transthyretin (TTR) is a homotetrameric protein. Its dissociation into monomers leads to the formation of fibrils that underlie human amyloidogenic diseases. The binding of small molecules to the thyroxin-binding sites in TTR stabilizes the homotetramer and attenuates TTR amyloidosis. Herein, we report on boronic acid-substituted stilbenes that limit TTR amyloidosis in vitro. Assays of affinity for TTR and inhibition of its tendency to form fibrils were coupled with X-ray crystallographic analysis of nine TTR·ligand complexes. The ensuing structure-function data led to a symmetrical diboronic acid that forms a boronic ester reversibly with serine 117. This diboronic acid inhibits fibril formation by both wild-type TTR and a common disease-related variant, V30M TTR, as effectively as does tafamidis, a small-molecule drug used to treat TTR-related amyloidosis in the clinic. These findings establish a new modality for covalent inhibition of fibril formation and illuminate a path for future optimization.

  14. Stress rupture behavior of silicon carbide coated, low modulus carbon/carbon composites

    SciTech Connect

    Rozak, G.A.; Wallace, J.F.

    1988-01-01

    The disadvantages of carbon-carbon composites, in addition to the oxidation problem, are low thermal expansion, expensive fabrication procedures, and poor off axis properties. The background of carbon-carbon composites, their fabrication, oxidation, oxidation protection and mechanical testing in flexure are discussed.

  15. Molecular bond selective x-ray scattering for nanoscale analysisof soft matter

    SciTech Connect

    Mitchell, G.E.; Koprinarov, I.; Landes, B.G.; Lyons, J.; Kern,B.J.; Devon, M.J.; Gullikson, E.M.; Kortright, J.B.

    2005-05-26

    We introduce a new technique using resonant soft x-ray scattering for characterizing heterogeneous chemical structure at nanometer length scales in polymers, biological material, and other soft matter. Resonant enhancements bring new contrast mechanisms and increased sensitivity to bridge a gap between bond-specific contrast in chemical sensitive imaging and the higher spatial resolution of traditional small-angle scattering techniques. We illustrate sensitivity to chemical bonding with the resonant scattering near the carbon K edge from latex spheres of differing chemistry and sizes. By tuning to x-ray absorption resonances associated with particular carbon-carbon or carbon-oxygen bonds we can isolate the scattering from different phases in a 2-phase mixture. We then illustrate this increased scattering contrast with a study of the templating process to form nanometer scale pores in 100 nm thick polymer films.

  16. Double C-H bond activation of acetylene by atomic boron in forming aromatic cyclic-HBC2BH in solid neon.

    PubMed

    Jian, Jiwen; Li, Wei; Wu, Xuan; Zhou, Mingfei

    2017-06-01

    The organo-boron species formed from the reactions of boron atoms with acetylene in solid neon are investigated using matrix isolation infrared spectroscopy with isotopic substitutions as well as quantum chemical calculations. Besides the previously reported single C-H bond activation species, a cyclic-HBC2BH diboron species is formed via double C-H bond activation of acetylene. It is characterized to have a closed-shell singlet ground state with planar D2h symmetry. Bonding analysis indicates that it is a doubly aromatic species involving two delocalized σ electrons and two delocalized π electrons. This finding reveals the very first example of double C-H bond activation of acetylene in forming new organo-boron compounds.

  17. Mass-analyzed threshold ionization spectroscopy of lanthanum-hydrocarbon radicals formed by C—H bond activation of propene

    NASA Astrophysics Data System (ADS)

    Kumari, Sudesh; Cao, Wenjin; Hewage, Dilrukshi; Silva, Ruchira; Yang, Dong-Sheng

    2017-02-01

    La(C3H4) and La(C3H6) are observed from the reaction of laser-vaporized La atoms with propene by photoionization time-of-flight mass spectrometry and characterized by mass-analyzed threshold ionization spectroscopy. Two isomers of La(C3H4) are identified as methyl-lanthanacyclopropene [La(CHCCH3)] (Cs) and lanthanacyclobutene [La(CHCHCH2)] (C1); La(C3H6) is determined to be H—La(η3-allyl) (Cs), a C—H bond inserted species. All three metal-hydrocarbon radicals prefer a doublet ground state with a La 6s-based electron configuration. Ionization of the neutral doublet state of each of these radicals produces a singlet ion state by removing the La-based 6s electron. The threshold ionization allows accurate measurements of the adiabatic ionization energy of the neutral doublet state and metal-ligand and ligand-based vibrational frequencies of the neutral and ionic states. The formation of the three radicals is investigated by density functional theory computations. The inserted species is formed by La inserting into an allylic C—H bond and lanthanacyclopropene by concerted vinylic H2 elimination, whereas lanthanacyclobutene involves both allylic and vinylic dehydrogenations. The inserted species is identified as an intermediate for the formation of lanthanacyclobutene.

  18. Statistical analysis of protein structures suggests that buried ionizable residues in proteins are hydrogen bonded or form salt bridges.

    PubMed

    Bush, Jeffrey; Makhatadze, George I

    2011-07-01

    It is well known that nonpolar residues are largely buried in the interior of proteins, whereas polar and ionizable residues tend to be more localized on the protein surface where they are solvent exposed. Such a distribution of residues between surface and interior is well understood from a thermodynamic point: nonpolar side chains are excluded from the contact with the solvent water, whereas polar and ionizable groups have favorable interactions with the water and thus are preferred at the protein surface. However, there is an increasing amount of information suggesting that polar and ionizable residues do occur in the protein core, including at positions that have no known functional importance. This is inconsistent with the observations that dehydration of polar and in particular ionizable groups is very energetically unfavorable. To resolve this, we performed a detailed analysis of the distribution of fractional burial of polar and ionizable residues using a large set of ˜2600 nonhomologous protein structures. We show that when ionizable residues are fully buried, the vast majority of them form hydrogen bonds and/or salt bridges with other polar/ionizable groups. This observation resolves an apparent contradiction: the energetic penalty of dehydration of polar/ionizable groups is paid off by favorable energy of hydrogen bonding and/or salt bridge formation in the protein interior. Our conclusion agrees well with the previous findings based on the continuum models for electrostatic interactions in proteins.

  19. The oxidation behavior of carbon-carbon composites and their coatings

    SciTech Connect

    Schaeffer, J.C.

    1989-01-01

    The oxidation of carbon-carbon composites and coatings in oxygen at temperatures between 300 and 1400 C was investigated. State-of-the-art systems were characterized prior to the oxidation studies using optical and scanning electron microscopy. It was determined that uncoated carbon-carbon composites cannot be used at temperatures above about 400 C for extended periods of time because of oxidation. Oxidation does occur at temperatures below 400 C but at very low rates. Boron was found to be an ineffective inhibitor for carbon-carbon oxidation. Coatings were useful in protecting carbon-carbon composites from oxidation under isothermal test conditions but these coatings failed under cyclic conditions. The factors leading to the failure of coatings on carbon-carbon composites are described.

  20. [Hydroxyapatite bioactive coating on carbon/carbon composites].

    PubMed

    Sui, Jinling; Li, Musen; Lü, Yupeng; Bai, Yunqiang

    2005-04-01

    A simple plasma spraying method was employed in coating hydroxyapaptite (HA) on to carbon/carbon composites (C/C composites). The morphology of the coating was examined under scanning electron microscope (SEM). The phase constitutions of the HA coating were determined by X-ray diffractometer (XRD). The shear strength of the HA coating-C/C composite substrates was detected. A hydroxyapatite coating with rough surface was observed. A considerable amount of amorphous phase appeared as a result from the coating process, which could be transformed into the morphous phase crystalline HA after subsequent heat treatment. The shear strength between the HA coating and C/C composite substrates was 7.15 MPa.

  1. Structural investigation of carbon/carbon composites by neutron scattering

    NASA Astrophysics Data System (ADS)

    Prem, Manfred; Krexner, Gerhard; Peterlik, Herwig

    2006-11-01

    Carbon/carbon (C/C) composite material was investigated by means of small-angle as well as wide-angle elastic neutron scattering. The C/C-composites were built up from bi-directionally woven fabrics from PAN-based carbon fibers. Pre-impregnation with phenolic resin was followed by pressure curing and carbonization at 1000 °C and a final heat treatment at either 1800 or 2400 °C. Measurements of the samples were performed in orientations arranging the carbon fibers, respectively, parallel and perpendicular to the incoming beam. Structural features of the fibers as well as the inherently existing pores are presented and the influence of the heat treatment is discussed. The results are compared to earlier X-ray investigations of carbon fibers and C/C-composites.

  2. Mathematical models of carbon-carbon composite deformation

    NASA Astrophysics Data System (ADS)

    Golovin, N. N.; Kuvyrkin, G. N.

    2016-09-01

    Mathematical models of carbon-carbon composites (CCC) intended for describing the processes of deformation of structures produced by using CCC under high-temperature loading are considered. A phenomenological theory of CCC inelastic deformation is proposed, where such materials are considered as homogeneous ones with effective characteristics and where their high anisotropy of mechanical characteristics and different ways of resistance to extension and compression are taken into account. Micromechanical models are proposed for spatially reinforced CCC, where the difference between mechanical characteristics of components and the reinforcement scheme are taken into account. Themodel parameters are determined from the results of experiments of composite macrospecimens in the directions typical of the material. A version of endochronictype theory with several internal times "launched" for each composite component and related to some damage accumulation mechanisms is proposed for describing the inelastic deformation. Some practical examples are considered.

  3. Joining of carbon-carbon composites for thermonuclear fusion applications

    SciTech Connect

    Salvo, M.; Lemoine, P.; Ferraris, M.; Montorsi, M.; Merola, M.

    1997-01-01

    Carbon-fiber-reinforced carbon (CfC) composites have been joined by using different joining agents: metals (silicon, aluminum, and titanium), an intermetallic compound (magnesium silicide, Mg{sub 2}Si), and glasses (borosilicates and zinc borates). These joining agents have been chosen by considering their possible use in a thermonuclear fusion reactor, as suggested by their low-activation properties, reasonably high working temperature, industrial feasibility, and potential scale-up of the joined carbon-carbon structures using pressureless-processing techniques. Each joined structure (CfC composite-joining material-CfC composite) has been first morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. Then, single-lap shear tests have been performed on the most-promising joined structures, i.e., silicon- and aluminum-joined CfC-composite samples, which have shown an average shear strength of 22 and 10 MPa, respectively.

  4. Emittance measurements of Space Shuttle orbiter reinforced carbon-carbon

    NASA Technical Reports Server (NTRS)

    Caram, Jose M.; Bouslog, Stanley A.; Cunnington, George R., Jr.

    1992-01-01

    The spectral and total normal emittance of the Reinforced Carbon-Carbon (RCC) used on Space Shuttle nose cap and wing leading edges has been measured at room temperature and at surface temperatures of 1200 to 2100 K. These measurements were made on virgin and two flown RCC samples. Room temperature directional emittance data were also obtained and were used to determine the total hemispherical emittance of RCC as a function of temperature. Results of the total normal emittance for the virgin samples showed good agreement with the current RCC emittance design curve; however, the data from the flown samples showed an increase in the emittance at high temperature possibly due to exposure from flight environments.

  5. Prospects for using carbon-carbon composites for EMI shielding

    NASA Technical Reports Server (NTRS)

    Gaier, James R.

    1990-01-01

    Since pyrolyzed carbon has a higher electrical conductivity than most polymers, carbon-carbon composites would be expected to have higher electromagnetic interference (EMI) shielding ability than polymeric resin composites. A rule of mixtures model of composite conductivity was used to calculate the effect on EMI shielding of substituting a pyrolyzed carbon matrix for a polymeric matrix. It was found that the improvements were small, no more than about 2 percent for the lowest conductivity fibers (ex-rayon) and less than 0.2 percent for the highest conductivity fibers (vapor grown carbon fibers). The structure of the rule of mixtures is such that the matrix conductivity would only be important in those cases where it is much higher than the fiber conductivity, as in metal matrix composites.

  6. Carbon-Carbon Heat Pipe Testing and Evaluation

    NASA Technical Reports Server (NTRS)

    Juhasz, Albert J.; Rovang, Richard D.

    1994-01-01

    This report discusses development and proof-of-concept testing of a new lightweight carbon-carbon (C-C) space radiator heat pipe developed under the NASA Civil Space Technology Initiative (CSTI) High Capacity Power Program. The heat pipe was filled with potassium working fluid and tested for 11 hours including startup from ambient temperature with the working fluid initially in the frozen state to near 700 K condenser temperature. Steady-state heat pipe input power during testing was facility limited to about 300 watts, representing about 50 percent of the design input power. Post test inspection showed the heat pipe to be in excellent condition after eight thermal cycles from ambient to steady-state operating temperature. Potential applications, ranging from small spacecraft heat rejection to aircraft and terrestrial uses, are discussed.

  7. Oxidation of Reinforced Carbon-Carbon Subjected to Hypervelocity Impact

    NASA Technical Reports Server (NTRS)

    Curry, Donald M.; Pham, Vuong T.; Norman, Ignacio; Chao, Dennis C.

    2000-01-01

    This paper presents results from arc jet tests conducted at the NASA Johnson Space Center on reinforced carbon-carbon (RCC) samples subjected to hypervelocity impact. The RCC test specimens are representative of RCC components used on the Space Shuttle Orbiter. The arc jet testing established the oxidation characteristics of RCC when hypervelocity projectiles, simulating meteoroid/orbital debris, impact the RCC material. In addition to developing correlations for use in trajectory simulations, we discuss analytical modeling of the increased material oxidation in the impacted area using measured hole growth data. Entry flight simulations are useful in assessing the increased Space Shuttle RCC component degradation as a result of impact damage and the hot gas flow through an enlarging hole into the wing leading-edge cavity.

  8. Analysis of Carbon/Carbon Fragments From the Columbia Tragedy

    NASA Technical Reports Server (NTRS)

    Tallant, David R.; Simpson, Regina L.; Jacobson, Nathan S.

    2005-01-01

    The extensive investigation following the Space Shuttle Orbiter Columbia accident of February 1, 2003 determined that hot gases entered the wing through a breach in the protective reinforced carbon/carbon (RCC) leading edge. In the current study, the exposed edges of the recovered RCC from the vicinity of the breach are examined with scanning electron microscopy and Raman spectroscopy. Electron microscopy of the exposed edges revealed regions of pointed carbon fibers, characteristic of exposure to high temperature oxidizing gases. The Raman technique relates the observed 1350 and 1580 to 1600 cm(-1) bands to graphitic dom ains and their corresponding temperatures of formation. Some of the regions showed evidence of exposure temperatures beyond 2700 ?C during the accident.

  9. Effect of surface roughening of aluminum plates on the strength of bonds formed between aluminum and polyphenylene sulfide by thermosonic bonding

    NASA Astrophysics Data System (ADS)

    Yasuda, Kiyokazu; Saito, Ryo

    2014-08-01

    Thermosonic bonding of aluminum on polyphenylene sulfide was carried out in order to examine the effect of surface roughening of aluminum on the joint strength. Repeated chemical treatment of aluminum by immersion in aqueous sodium hydroxide and hydrochloric acid solutions increased its surface roughness (Ra ~25 μm) and surface area (~445% increase). Consequently, the bonding strength (~1.8N in average) was enhanced through anchoring effects.

  10. Superstrong nature of covalently bonded glass-forming liquids at select compositions

    NASA Astrophysics Data System (ADS)

    Gunasekera, K.; Bhosle, S.; Boolchand, P.; Micoulaut, M.

    2013-10-01

    Variation of fragility (m) of specially homogenized GexSe100-x melts is established from complex specific heat measurements and shows that m(x) has a global minimum at an extremely low value (m = 14.8(0.5)) in the 21.5% < x < 23% range of Ge. Outside of that compositional range, m(x) then increases first rapidly and then slowly to about m = 25-30. By directly mapping melt stoichiometry as a function of reaction time at a fixed temperature T > Tg, we observe a slowdown of melt-homogenization by the super-strong melt compositions, 21.5% < x < 23%. This range furthermore appears to be correlated to the one observed between the flexible and stressed rigid phase in network glasses. These spectacular features underscore the crucial role played by topology and rigidity in the properties of network-forming liquids and glasses which are highlighted when fragility is represented as a function of variables tracking the effect of rigidity. Finally, we investigate the fragility-glass transition temperature relationship, and find that reported scaling laws do not apply in the flexible phase, while being valid for intermediate and stressed rigid compositions.

  11. Peptide bond-forming reagents HOAt and HATU are not mutagenic in the bacterial reverse mutation test.

    PubMed

    Nicolette, John; Neft, Robin E; Vanosdol, Jessica; Murray, Joel

    2016-04-01

    The peptide bond-forming reagents 1-hydroxy-7-azabenzotriazole (HOAt, CAS 39968-33-7) and O-(7-Azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU, CAS 148893-10-1) either have structural alerts, unclassified features or are considered out of domain when evaluated for potential mutagenicity with in silico programs DEREK and CaseUltra. Since they are commonly used reagents in pharmaceutical drug syntheses, they may become drug substance or drug product impurities and would need to be either controlled to appropriately safe levels or tested for mutagenicity. Both reagents were tested in the bacterial reverse mutation (Ames) test at Covance, under GLP conditions, following the OECD test guideline and ICH S2(R1) recommendations and found to be negative. Our data show that HOAt and HATU-common pharmaceutical synthesis reagents-are not mutagenic, and can be treated as ordinary drug impurities.

  12. Evaluation of superplastic forming and co-diffusion bonding of Ti-6Al-4V titanium alloy expanded sandwich structures

    NASA Technical Reports Server (NTRS)

    Arvin, G. H.; Israeli, L.; Stolpestad, J. H.; Stacher, G. W.

    1981-01-01

    The application of the superplastic forming/diffusion bonding (SPF/DB) process to supersonic cruise research is investigated. The capability of an SPF/DB titanium structure to meet the structural requirements of the inner wing area of the NASA arrow-wing advanced supersonic transport design is evaluated. Selection of structural concepts and their optimization for minimum weight, SPF/DB process optimization, fabrication of representative specimens, and specimen testing and evaluation are described. The structural area used includes both upper and lower wing panels, where the upper wing panel is used for static compression strength evaluation and the lower panel, in tension, is used for fracture mechanics evaluations. The individual test specimens, cut from six large panels, consist of 39 static specimens, 10 fracture mechanics specimens, and one each full size panel for compression stability and fracture mechanics testing. Tests are performed at temperatures of -54 C (-65 F), room temperature, and 260 C (500 F).

  13. {alpha}' Subunit of soybean {beta}-conglycinin forms complex with rice glutelin via a disulphide bond in transgenic rice seeds.

    PubMed

    Motoyama, Takayasu; Maruyama, Nobuyuki; Amari, Yoshiki; Kobayashi, Kanna; Washida, Haruhiko; Higasa, Takahiko; Takaiwa, Fumio; Utsumi, Shigeru

    2009-01-01

    The alpha' and beta subunits of soybean beta-conglycinin were expressed in rice seeds in order to improve the nutritional and physiological properties of rice as a food. The alpha' subunit accumulated in rice seeds at a higher level than the beta subunit, but no detectable difference in mRNA transcription level between subunits was observed. Sequential extraction results indicate that the alpha' subunit formed one or more disulphide bonds with glutelin. Electron microscopic analysis showed that the alpha' subunit and the beta subunit were transported to PB-II together with glutelin. In mature transgenic seeds, the beta subunit accumulated in low electron density regions in the periphery of PB-II, whereas the alpha' subunit accumulated together with glutelin in high-density regions of the periphery. The subcellular localization of mutated alpha' subunits lacking one cysteine residue in the N-terminal mature region (alpha'DeltaCys1) or five cysteine residues in the pro and N-terminal mature regions (alpha'DeltaCys5) were also examined. Low-density regions were formed in PB-II in mature seeds of transgenic rice expressing alpha'DeltaCys 5 and alpha'DeltaCys1. alpha'DeltaCys5 was localized only in the low-density regions, whereas alpha'DeltaCys1 was found in both low- and high-density regions. These results suggest that the alpha' subunit could make a complex via one or more disulphide bonds with glutelin and accumulate together in PB-II of transgenic rice seeds.

  14. Effect of mission cycling on the fatigue performance of SiC-coated carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Mahfuz, H.; Das, P. S.; Jeelani, S.; Baker, D. M.; Johnson, S. A.

    1993-01-01

    The effects of thermal and pressure cycling on the fatigue performance of carbon-carbon composites, and the influence of mission cycling on these effects, were investigated by subjecting both virgin and mission-cycled two-dimensional specimens of SiC-coated carbon-carbon composites to fatigue tests, conducted at room temperature in three-point bending, with a stress ratio of 0.2 and a frequency of 1 Hz. It was found that the fatigue strength of C-C composites is high (about 90 percent of the ultimate flexural strength), but decreased with the mission cycling. The lowering of the fatigue strength with mission cycling is attributed to the increase in interfacial bond strength due to thermal and pressure cycling of the material. The already high sensitivity of C-C composites to stress during cyclic loading increases further with the amount of mission cycling. Results of NDE suggest that the damage growth in virgin C-C, in the high-cycle range, is slow at the initial stage of the cyclic life, but propagates rapidly after certain threshold cycles of the fatigue life.

  15. STUDY ON ELASTO-PLASTIC BEHAVIOR OF DIFFERENT CARBON TYPES IN CARBON/CARBON COMPOSITES

    SciTech Connect

    Ozcan, Soydan; Tezcan, Jale; Howe, Jane Y; Filip, Peter

    2008-01-01

    Indentation tests combined with the knowledge of corresponding microstructure of carbonaceous materials offer valuable information that cannot be extracted from the conventional indentation tests alone. Since mechanical properties of carbon are sensitive to the crystal orientation, inelastic mechanisms can be detected by studying the stress-strain behavior of carbon/carbon composites. The aim of this paper is to investigate the elasto-plastic behavior and related microstructure of pan-fiber reinforced carbon matrix composites heat-treated at 2100 C. The microstructure was characterized using polarized light microscopy and high-resolution electron microscopy. Elastic modulus of each constituent of the composites was measured. Nanoindentation tests were carried out to obtain loading-unloading cycles at different indentation depths using a berkovich-type diamond indenter tip. The residual displacement at complete unloading was correlated with the microstructure data to reveal the extent of the deformation mechanisms of crystallites and graphene sheets. The pitch fiber and rough laminar pyrocarbon exhibited plastic behavior, which can be attributed to the low shear resistance due to weak bonding between the well-organized graphene sheets. On the other hand, the PAN fiber, charred resin and isotropic pyrocarbon, exhibited almost full elasticity within applied displacement limits.

  16. Processing and thermal properties of filament wound carbon-carbon composites for impact shell application

    NASA Astrophysics Data System (ADS)

    Zee, Ralph; Romanoski, Glenn; Gale, H. Shyam; Wang, Hsin

    2001-02-01

    The performance and safety of the radioisotope power source depend in part on the thermal and impact properties of the materials used in the general purpose heat source (GPHS) through the use of an impact shell, thermal insulation and an aeroshell. Results from an earlier study indicate the importance of circumferential fibers to the mechanical properties of cylindrical filament wound carbon-carbon composites for the impact shell application. Based on this study, an investigation was initiated to determine the processing characteristics and the mechanical and thermal response of three filament wound configurations with different percentages of circumferential fibers: 50%, 66% and 80%. The performs were fabricated using a 3-D filament winding machine followed by five cycles of resin impregnation and carbonization. In this paper, the processing sequence and the resulting microstructures of the composites will be described. The thermal conductivity values of the composites as a function of fiber configuration and density will be discussed. These results will be compared with the fine-weave pierced-fabric (FWPF) material and carbon-bonded carbon-fiber insulation. Finally, the relevance of the new configurations for applications in the general purpose heat source (GPHS) will also be inferred. .

  17. Preparation and structure analysis of carbon/carbon composite made from phenolic resin impregnation into exfoliated graphite

    NASA Astrophysics Data System (ADS)

    Chen, X.; Zheng, Y. P.; Kang, F.; Shen, W. C.

    2006-05-01

    Exfoliated graphite-based carbon/carbon composites were prepared using sequence processes of phenolic resin alcohol solution impregnation, carbonization and carbon dioxide (or steam) activation. The textural/structural characteristics of the composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption and mercury porosimetry. The results indicated that the composites were composed of graphite and amorphous carbon. On the surface, the worm-like particles were covered by pyrolytic carbon, which also penetrated into parts of the interior pores of the particles. Macropores still remained in the composite, whereas micropores which were formed by the activation of pyrolytic carbon contributed to most of the pore volume.

  18. Carbon-Carbon Recuperators in Closed-Brayton-Cycle Nuclear Space Power Systems: A Feasibility Assessment

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.

    2004-01-01

    The feasibility of using carbon-carbon recuperators in closed-Brayton-cycle (CBC) nuclear space power conversion systems (PCS) was assessed. Recuperator performance expectations were forecast based on projected thermodynamic cycle state values for a planetary mission. Resulting thermal performance, mass and volume for a plate-fin carbon-carbon recuperator were estimated and quantitatively compared with values for a conventional offset-strip-fin metallic design. Material compatibility issues regarding carbon-carbon surfaces exposed to the working fluid in the CBC PCS were also discussed.

  19. Development of carbon-carbon nozzle extension for liquid fuel rocket motors

    NASA Astrophysics Data System (ADS)

    Sokolovsky, M. I.; Petukhov, S. N.; Semyonov, Yu. P.; Sokolov, B. A.

    2008-12-01

    Successful experience of RSC “Energy” and SPA “Iskra” in the development of carbon-carbon extension for oxygen-kerosene liquid fuel rocket motor has been summarized. Methodological approach that served to completion of carbon-carbon extension development in full and at comparatively small expenses has been described. Results of practical application of carbon-carbon extension for liquid fuel rocket motor 11D58M have been presented within the framework of International Space Program “Sea Launch”.

  20. Directed evolution of rubisco in Escherichia coli reveals a specificity-determining hydrogen bond in the form II enzyme.

    PubMed

    Mueller-Cajar, Oliver; Morell, Matthew; Whitney, Spencer M

    2007-12-11

    Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) occupies a critical position in photosynthetic CO2-fixation and consequently has been the focus of intense study. Crystal-structure-guided site-directed mutagenesis studies have met with limited success in engineering kinetic improvements to Rubisco, highlighting our inadequate understanding of structural constraints at the atomic level that dictate the enzyme's catalytic chemistry. Bioselection provides an alternative random mutagenic approach that is useful for identifying and elucidating imperceptible structure-function relationships. Using the dimeric Form II Rubisco from Rhodospirillum rubrum, its gene (rbcM) was randomly mutated and introduced under positive selection into Escherichia coli cells metabolically engineered to be dependent on Rubisco to detoxify its substrate ribulose 1,5-bisphosphate. Thirteen colonies displaying improved fitness were isolated, and all were found to harbor mutations in rbcM at one of two codons, histidine-44 or aspartate-117, that are structurally adjacent amino acids located about 10 A from the active site. Biochemical characterization of the mutant enzymes showed the mutations reduced their CO2/O2 specificity by 40% and decreased their carboxylation turnover rate by 20-40%. Structural analyses showed histidine-44 and aspartate-117 form a hydrogen bond in R. rubrum Rubisco and that the residues are conserved among other Form II Rubiscos. This study demonstrated the utility of directed evolution in E. coli for identifying catalytically relevant residues (in particular nonobvious residues disconnected from active site residues) and their potential molecular interactions that influence Rubisco's catalytic chemistry.

  1. A statistical model of carbon/carbon composite failure

    NASA Technical Reports Server (NTRS)

    Slattery, Kerry T.

    1991-01-01

    A failure model which considers the stochastic nature of the damage accumulation process is essential to assess reliability and to accurately scale the results from standard test specimens to composite structures. A superior filamentary composite for high temperature applications is composed of carbon fibers in a carbon matrix. Carbon-carbon composites are the strongest known material at very high temperatures. Since there appears to be a significant randomness in C-C material strength which cannot be controlled or detected with current technology, a better model of the material failure based upon statistical principles should be used. Simple applications of the model based upon the limited data provide encouraging results that indicate that better design of test specimens would provide a substantially higher prediction for the design strength of C-C composites. An A-basis strength for the C-C tensile rings from a first stage D-5 billets was estimated. A statistical failure model was developed for these rings which indicates that this strength may be very conservative for larger C-C parts. The analysis may be improved by use of a heterogeneous/noncontinuum finite element approach on the minimechanical level.

  2. Novel low Wigner energy amorphous carbon-carbon composite

    NASA Astrophysics Data System (ADS)

    Dasgupta, Kinshuk; Prakash, Jyoti; Tripathi, B. M.

    2014-02-01

    A novel amorphous carbon-carbon composite has been developed using carbon black dispersed in carbonized phenolic resin matrix in order to avoid Wigner energy problem associated with graphite. The as prepared sample showed a density of 1320 kg m-3. This has been further densified by resin impregnation and chemical vapour infiltration. The effect of processing parameters on final density (1517 kg m-3) has been investigated. This composite possesses the compressive strength of 65 Mpa, coefficient of thermal expansion of 3 × 10-6 K-1 and the specific heat of 1.2 J g-1 K-1. This novel composite was subjected to 145 MeV Ne+6 heavy ion irradiation at different doses. The highest dose was kept at 3 × 10-4 dpa. The stored energy in the composite was found to be 212 J g-1 at the highest dose of irradiation, which is much below than that of graphite. The composite remained amorphous after irradiation as confirmed by X-ray diffraction.

  3. Texturing Carbon-carbon Composite Radiator Surfaces Utilizing Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Raack, Taylor

    2004-01-01

    Future space nuclear power systems will require radiator technology to dissipate excess heat created by a nuclear reactor. Large radiator fins with circulating coolant are in development for this purpose and an investigation of how to make them most efficient is underway. Maximizing the surface area while minimizing the mass of such radiator fins is critical for obtaining the highest efficiency in dissipating heat. Processes to develop surface roughness are under investigation to maximize the effective surface area of a radiator fin. Surface roughness is created through several methods including oxidation and texturing. The effects of atomic oxygen impingement on carbon-carbon surfaces are currently being investigated for texturing a radiator surface. Early studies of atomic oxygen impingement in low Earth orbit indicate significant texturing due to ram atomic oxygen. The surface morphology of the affected surfaces shows many microscopic cones and valleys which have been experimentally shown to increase radiation emittance. Further study of this morphology proceeded in the Long Duration Exposure Facility (LDEF). Atomic oxygen experiments on the LDEF successfully duplicated the results obtained from materials in spaceflight by subjecting samples to 4.5 eV atomic oxygen from a fixed ram angle. These experiments replicated the conical valley morphology that was seen on samples subjected to low Earth orbit.

  4. Airborne ultrasonic inspection in carbon/carbon composite materials

    NASA Astrophysics Data System (ADS)

    Yang, In-Young; Kim, Young-Hun; Park, Je-Woong; Hsu, David K.; Song, Song-Jin; Cho, Hyun-Jun; Kim, Sun-Kyu; Im, Kwang-Hee

    2007-07-01

    In this work, a carbon/carbon (C/C) composite material was nondestructively characterized with non-contact ultrasonic methods using automated acquisition scanner as well as contact ultrasonic measurement because (C/C) composite materials have obvious high price over conventional materials. Because of permeation of coupling medium such as water, it is desirable to perform contact-less nondestructive evaluation to assess material properties and part homogeneity. Also through transmission mode was performed because of the main limitation for air-coupled transducers, which is the acoustic impedance mismatch between most materials and air. Especially ultrasonic images and velocities for C/C composite disk brake was measured and found to be consistent to some degree with the non-contact and contact ultrasonic measurement methods. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Measured results were compared with those obtained by the motorized system with using dry-coupling ultrasonics and through transmission method in immersion. Finally, results using a proposed peak-delay measurement method well corresponded to ultrasonic velocities of the pulse overlap method.

  5. Novel apparatus for joining of carbon-carbon composites

    NASA Astrophysics Data System (ADS)

    White, Jeremiah D. E.; Mukasyan, Alexander S.; La Forest, Mark L.; Simpson, Allen H.

    2007-01-01

    A novel apparatus for joining carbon-carbon (C-C) composites is presented. This device was designed and built based on the concept of self-sustained oxygen-free high-temperature reactions. A layer of reactive mixture is contained between two disks of C-C composite that are to be joined. The stack is held in place between two electrodes, which are connected to a dc power supply. dc current is used to uniformly initiate the reaction in the reactive layer. The electrodes are also part of the pneumatic system, which applies a load to the stack. The designed hydraulic system is effective, lending to low cost and simplified, rapid, accurate operation. It provides a very short response time (˜10ms), which is important for the considered applications. All operational parameters such as initial and final loads, applied current, delay time between ignition and final load application, duration of Joule heating, and safety interlocks are controlled by a programable logic controller system. These features make it an efficient, user-friendly and safe machine to join refractory materials. The entire joining process takes place on the order of seconds, rather than hours as required for solid-state joining methods. The mechanical properties of the obtained joints are higher than those for the C-C composites.

  6. Direct carbon-carbon coupling of furanics with acetic acid over Brønsted zeolites

    PubMed Central

    Gumidyala, Abhishek; Wang, Bin; Crossley, Steven

    2016-01-01

    Effective carbon-carbon coupling of acetic acid to form larger products while minimizing CO2 emissions is critical to achieving a step change in efficiency for the production of transportation fuels from sustainable biomass. We report the direct acylation of methylfuran with acetic acid in the presence of water, all of which can be readily produced from biomass. This direct coupling limits unwanted polymerization of furanics while producing acetyl methylfuran. Reaction kinetics and density functional theory calculations illustrate that the calculated apparent barrier for the dehydration of the acid to form surface acyl species is similar to the experimentally measured barrier, implying that this step plays a significant role in determining the net reaction rate. Water inhibits the overall rate, but selectivity to acylated products is not affected. We show that furanic species effectively stabilize the charge of the transition state, therefore lowering the overall activation barrier. These results demonstrate a promising new route to C–C bond–forming reactions for the production of higher-value products from biomass. PMID:27652345

  7. Bonding energetics in clusters formed by cesium salts: a study by collision-induced dissociation and density functional theory.

    PubMed

    Maria, Pierre-Charles; Massi, Lionel; Box, Natzaret Sindreu; Gal, Jean-François; Burk, Peeter; Tammiku-Taul, Jaana; Kutsar, Martin

    2006-01-01

    In relation to the interaction between (137)Cs and soil organic matter, electrospray mass spectrometry experiments and density functional theory (DFT) calculations were carried out on the dissociation of positively charged adducts formed by cesium nitrate and cesium organic salts attached to a cesium cation [Cs(CsNO(3))(CsA)](+) (A = benzoate, salicylate, hydrogen phthalate, hydrogen maleate, hydrogen fumarate, hydrogen oxalate, and hydrogen malonate ion). These mixed clusters were generated by electrospray from methanol solutions containing cesium nitrate and an organic acid. Collision-induced dissociation of [Cs(CsNO(3))(CsA)](+) in a quadrupole ion trap gave [Cs(CsNO(3))](+) and [Cs(CsA)](+) as major product ions. Loss of HNO(3) was observed, and also CO(2) loss in the case of A = hydrogen malonate. Branching ratios for the dissociation into [Cs(CsNO(3))](+) and [Cs(CsA)](+) were treated by the Cooks' kinetic method to obtain a quantitative order of bonding energetics (enthalpies and Gibbs free energies) between Cs(+) and the molecular salt (ion pair) CsA, and were correlated with the corresponding values calculated using DFT. The kinetic method leads to relative scales of Cs(+) affinities and basicities that are consistent with the DFT-calculated values. This study brings new data on the strong interaction between the cesium cation and molecular salts CsA.

  8. Minuteman 3/Mark 12A reentry vehicle carbon-carbon nosetip production program

    NASA Astrophysics Data System (ADS)

    1980-05-01

    The purpose of this document is to provide SAMSO with Avco's current plan for critical item control and subsequent monitoring of the manufacturing processes in production of the Mark 12A Carbon/Carbon nosetip.

  9. Superplastic Forming/Diffusion Bonding Without Interlayer of 5A90 Al-Li Alloy Hollow Double-Layer Structure

    NASA Astrophysics Data System (ADS)

    Jiang, Shaosong; Jia, Yong; Lu, Zhen; Shi, Chengcheng; Zhang, Kaifeng

    2017-09-01

    The hollow double-layer structure of 5A90 Al-Li alloy was fabricated by SPF/DB process in this study. The characteristics and mechanism of 5A90 Al-Li alloy with respect to superplasticity and diffusion bonding were investigated. Tensile tests showed that the optimal elongation of tensile specimens was 243.97% at the temperature of 400 °C and the strain rate of 0.001 s-1. Effect of the surface roughness, bonding temperature and bonding time to determine the microstructure and mechanical properties of diffusion bonding joints was investigated, and the optimum bonding parameters were 540 °C/2.5 h/Ra18. Through the finite element simulation, it could be found that the SPF/DB process of hollow double-layer structure was feasible. The hollow double-layer structure of 5A90 Al-Li alloy was manufactured, showing that the thickness distribution of the bonding area was uniform and the thinnest part was the round corner. The SEM images of diffusion bonding joints showed that sound bonding interfaces were obtained in which no discontinuity existed.

  10. A slow-forming isopeptide bond in the structure of the major pilin SpaD from Corynebacterium diphtheriae has implications for pilus assembly

    SciTech Connect

    Kang, Hae Joo; Paterson, Neil G.; Kim, Chae Un; Middleditch, Martin; Chang, Chungyu; Ton-That, Hung; Baker, Edward N.

    2014-05-01

    Two crystal structures of the major pilin SpaD from C. diphtheriae have been determined at 1.87 and 2.5 Å resolution. The N-terminal domain is found to contain an isopeptide bond that forms slowly over time in the recombinant protein. Given its structural context, this provides insight into the relationship between internal isopeptide-bond formation and pilus assembly. The Gram-positive organism Corynebacterium diphtheriae, the cause of diphtheria in humans, expresses pili on its surface which it uses for adhesion and colonization of its host. These pili are covalent protein polymers composed of three types of pilin subunit that are assembled by specific sortase enzymes. A structural analysis of the major pilin SpaD, which forms the polymeric backbone of one of the three types of pilus expressed by C. diphtheriae, is reported. Mass-spectral and crystallographic analysis shows that SpaD contains three internal Lys–Asn isopeptide bonds. One of these, shown by mass spectrometry to be located in the N-terminal D1 domain of the protein, only forms slowly, implying an energy barrier to bond formation. Two crystal structures, of the full-length three-domain protein at 2.5 Å resolution and of a two-domain (D2-D3) construct at 1.87 Å resolution, show that each of the three Ig-like domains contains a single Lys–Asn isopeptide-bond cross-link, assumed to give mechanical stability as in other such pili. Additional stabilizing features include a disulfide bond in the D3 domain and a calcium-binding loop in D2. The N-terminal D1 domain is more flexible than the others and, by analogy with other major pilins of this type, the slow formation of its isopeptide bond can be attributed to its location adjacent to the lysine used in sortase-mediated polymerization during pilus assembly.

  11. The bond-forming reactions of atomic dications with neutral molecules: formation of ArNH+ and ArN+ from collisions of Ar2+ with NH3.

    PubMed

    Lambert, Natalie; Kearney, Dominic; Kaltsoyannis, Nikolas; Price, Stephen D

    2004-03-24

    An experimental and computational study has been performed to investigate the bond-forming reactivity between Ar(2+) and NH(3). Experimentally, we detect two previously unobserved bond-forming reactions between Ar(2+) and NH(3) forming ArN(+) and ArNH(+). This is the first experimental observation of a triatomic product ion (ArNH(+)) following a chemical reaction of a rare gas dication with a neutral. The intensity of ArNH(+) was found to decrease with increasing collision energy, with a corresponding increase in the intensity of ArN(+), indicating that ArN(+) is formed by the dissociation of ArNH(+). Key features on the potential energy surface for the reaction were calculated quantum chemically using CASSCF and MRCI methods. The calculated reaction mechanism, which takes place on a singlet surface, involves the initial formation of an Ar-N bond to give Ar-NH(3)(2+). This complexation is followed by proton loss via a transition state, and then loss of the two remaining hydrogen atoms in two subsequent activationless steps to give the products (3)ArN(+) + H(+) + 2H. This calculated pathway supports the sequential formation of ArN(+) from ArNH(+), as suggested by the experimental data. The calculations also indicate that no bond-forming pathway exists on the ground triplet surface for this system.

  12. Radiation damage in carbon-carbon composites: Structure and property effects

    SciTech Connect

    Burchell, T.D.

    1995-12-31

    Carbon-carbon composites are an attractive choice for fusion reactor plasma facing components because of their low atomic number, superior thermal shock resistance, and low neutron activation. Next generation tokamak reactors such as the International Thermonuclear Experimental Reactor (ITER), will require high thermal conductivity carbon-carbon composites and other materials, such as beryllium, to protect their plasma facing components from the anticipated high heat fluxes. Moreover, ignition machines such as ITER will produce a large neutron flux. Consequently, the influence of neutron damage on the structure and properties of carbon-carbon composite materials must be evaluated. Data from two irradiation experiments are reported and discussed here. Carbon-carbon composite materials were irradiated in target capsules in the High Flux Isotope Reactor (HAIR) at Oak Ridge National Laboratory (ORAL). A peak damage dose of 4.7 displacements per atom (da) at an irradiation temperature of {approximately}600{degrees}C was attained. The carbon materials irradiated here included unidirectional, two- directional, and three-directional carbon-carbon composites. Irradiation induced dimensional changes are reported for the materials and related to single crystal dimensional changes through fiber and composite structural models. Moreover, carbon-carbon composite material dimensional changes are discussed in terms of their architecture, fiber type, and graphitization temperature. Neutron irradiation induced reductions in the thermal conductivity of two, three-directional carbon-carbon composites are reported, and the recovery of thermal conductivity due to thermal annealing is demonstrated. Irradiation induced strength changes are reported for several carbon-carbon composite materials and are explained in terms of in-crystal and composite structural effects.

  13. Oxidative coupling of sp (2) and sp (3) carbon-hydrogen bonds to construct dihydrobenzofurans.

    PubMed

    Shi, Jiang-Ling; Wang, Ding; Zhang, Xi-Sha; Li, Xiao-Lei; Chen, Yu-Qin; Li, Yu-Xue; Shi, Zhang-Jie

    2017-08-10

    Metal-catalyzed cross-couplings provide powerful, concise, and accurate methods to construct carbon-carbon bonds from organohalides and organometallic reagents. Recent developments extended cross-couplings to reactions where one of the two partners connects with an aryl or alkyl carbon-hydrogen bond. From an economic and environmental point of view, oxidative couplings between two carbon-hydrogen bonds would be ideal. Oxidative coupling between phenyl and "inert" alkyl carbon-hydrogen bonds still awaits realization. It is very difficult to develop successful strategies for oxidative coupling of two carbon-hydrogen bonds owning different chemical properties. This article provides a solution to this challenge in a convenient preparation of dihydrobenzofurans from substituted phenyl alkyl ethers. For the phenyl carbon-hydrogen bond activation, our choice falls on the carboxylic acid fragment to form the palladacycle as a key intermediate. Through careful manipulation of an additional ligand, the second "inert" alkyl carbon-hydrogen bond activation takes place to facilitate the formation of structurally diversified dihydrobenzofurans.Cross-dehydrogenative coupling is finding increasing application in synthesis, but coupling two chemically distinct sites remains a challenge. Here, the authors report an oxidative coupling between sp (2) and sp (3) carbons by sequentially activating the more active aryl site followed by the alkyl position.

  14. Recent advances in carbon-carbon substrate technology at NASA. Langley Research Center

    NASA Technical Reports Server (NTRS)

    Ransone, Philip O.; Yamaki, Y. Robert; Maahs, Howard G.

    1992-01-01

    A comparison of specific strengths of candidate high-temperature materials as a function of temperature is shown. From this comparison, it is apparent why there is an interest in carbon-carbon composites for applications as a strong, light-weight thermal protection system (TPS), or as hot structure, for applications above 2500 F. The lower bound of the carbon-carbon band is representative of the tensile strength of cross-ply Advanced Carbon-Carbon (ACC). The upper bound represents capabilities of various experimental carbon-carbon composites. Thin carbon-carbon composites, such as would be used as TPS panels or hot aero-structure, are usually constructed of layups of 2-D fabrics of carbon-fiber yarns (tows). Although the in-plane strengths of these composites can be very attractive, a major problem area is low interlaminar strength. The low interlaminar strength is the result of a relatively weak carbon matrix and poor interaction between the fibers and matrix. The purpose of this paper is to discuss strategies being employed to improve the interlaminar strengths of the materials at the upper bound of the carbon-carbon band, and to present some recent encouraging results. The emphasis of these strategies is to improve interlaminar shear and tensile strengths while maintaining, or even improving, the inplane properties.

  15. Demonstration That the Radical S-Adenosylmethionine (SAM) Enzyme PqqE Catalyzes de Novo Carbon-Carbon Cross-linking within a Peptide Substrate PqqA in the Presence of the Peptide Chaperone PqqD.

    PubMed

    Barr, Ian; Latham, John A; Iavarone, Anthony T; Chantarojsiri, Teera; Hwang, Jennifer D; Klinman, Judith P

    2016-04-22

    The radical S-adenosylmethionine (SAM) protein PqqE is predicted to function in the pyrroloquinoline quinone (PQQ) biosynthetic pathway via catalysis of carbon-carbon bond formation between a glutamate and tyrosine side chain within the small peptide substrate PqqA. We report here that PqqE activity is dependent on the accessory protein PqqD, which was recently shown to bind PqqA tightly. In addition, PqqE activity in vitro requires the presence of a flavodoxin- and flavodoxin reductase-based reduction system, with other reductants leading to an uncoupled cleavage of the co-substrate SAM. These results indicate that PqqE, in conjunction with PqqD, carries out the first step in PQQ biosynthesis: a radical-mediated formation of a new carbon-carbon bond between two amino acid side chains on PqqA. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  16. Toward efficient asymmetric carbon-carbon bond formation: continuous flow with chiral heterogeneous catalysts.

    PubMed

    Tsubogo, Tetsu; Yamashita, Yasuhiro; Kobayashi, Shū

    2012-10-22

    A chiral Ca catalyst based on CaCl(2) with a chiral ligand was developed and applied to the asymmetric 1,4-addition of 1,3-dicarbonyl compounds to nitroalkenes as a model system. To address product inhibition issues, the Ca catalyst was applied to continuous flow with a chiral heterogeneous catalyst. The continuous flow system using a newly synthesized, polymer-supported Pybox was successfully employed, and the TON was improved 25-fold compared with those of the previous Ca(OR)(2) catalysts.

  17. Nitrososynthase triggered oxidative carbon-carbon bond cleavage in baumycin biosynthesis

    PubMed Central

    Al-Mestarihi, Ahmad; Romo, Anthony; Liu, Hung-wen; Bachmann, Brian O.

    2013-01-01

    Baumycins are coproduced with clinically important anticancer secondary metabolites daunorubicin and doxorubicin, which are glycosylated anthracyclines isolated from Streptomyces peucetius. The distinguishing feature of baumycins is the presence of an unusual acetal moiety appended to daunosamine, which is hydrolyzed during acidic extraction of daunorubicin from fermentation broth. The structure of the baumycin acetal suggests that it is likely derived from an unknown C-3” methyl deoxysugar cleaved between the C-3” and C-4” positions. This is supported by analysis of the baumycin/daunorubicin biosynthetic gene cluster (dox), which also encodes putative proteins consistent with production of an anthracycline dissacharide containing a branched sugar. Notably, the dnmZ gene in the dox gene cluster possesses high translated sequence similarity to nitrososynthases, which are flavin-dependent amine monooxygenases involved in the four electron oxidation of aminosugars to nitrososugars. Herein we demonstrate that DnmZ is an amino sugar nitrososynthase initiating the conversion of thymidine-5’-diphosphate-l-epi-vancosamine to a ring opened product via a previously uncharacterized retro oxime-aldol reaction. PMID:23885759

  18. Reversible Carbon-Carbon Bond Breaking and Spin Equilibria in Bis(pyrimidinenorcorrole).

    PubMed

    Liu, Bin; Yoshida, Takuya; Li, Xiaofang; Stępień, Marcin; Shinokubo, Hiroshi; Chmielewski, Piotr J

    2016-10-10

    Reversible homolytic dissociation of the bis(pyrimidinenorcorrole) σ-dimer was elucidated by means of variable temperature ESR and (1) H NMR spectroscopy, mass spectrometry, and optical spectrocopy. Dehydrogenation of the σ-dimer yielded another dimer displaying a singlet-triplet equilibrium in solution, strong NIR absorption (1570 nm), and a narrow electrochemical HOMO-LUMO gap (0.74 V). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. 25 CFR 162.561 - What is the release process for a performance bond or alternative form of security under a WSR...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 25 Indians 1 2014-04-01 2014-04-01 false What is the release process for a performance bond or alternative form of security under a WSR lease? 162.561 Section 162.561 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER LEASES AND PERMITS Wind and Solar Resource Leases Wsr Lease...

  20. 25 CFR 162.561 - What is the release process for a performance bond or alternative form of security under a WSR...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 25 Indians 1 2013-04-01 2013-04-01 false What is the release process for a performance bond or alternative form of security under a WSR lease? 162.561 Section 162.561 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER LEASES AND PERMITS Wind and Solar Resource Leases Wsr Lease...

  1. Light-mediated heterogeneous cross dehydrogenative coupling reactions: metal oxides as efficient, recyclable, photoredox catalysts in C-C bond-forming reactions.

    PubMed

    Rueping, Magnus; Zoller, Jochen; Fabry, David C; Poscharny, Konstantin; Koenigs, René M; Weirich, Thomas E; Mayer, Joachim

    2012-03-19

    Let there be light: A heterogeneous photocatalytic system based on easily recyclable TiO(2) or ZnO allows cross dehydrogenative coupling reactions of tertiary amines. The newly developed protocols have successfully been applied to various C-C and C-P bond-forming reactions to provide nitro amines as well as amino ketones, nitriles and phosphonates.

  2. MEMS packaging with etching and thinning of lid wafer to form lids and expose device wafer bond pads

    DOEpatents

    Chanchani, Rajen; Nordquist, Christopher; Olsson, Roy H; Peterson, Tracy C; Shul, Randy J; Ahlers, Catalina; Plut, Thomas A; Patrizi, Gary A

    2013-12-03

    In wafer-level packaging of microelectromechanical (MEMS) devices a lid wafer is bonded to a MEMS wafer in a predermined aligned relationship. Portions of the lid wafer are removed to separate the lid wafer into lid portions that respectively correspond in alignment with MEMS devices on the MEMS wafer, and to expose areas of the MEMS wafer that respectively contain sets of bond pads respectively coupled to the MEMS devices.

  3. Synthesis of 1,1-Disubstituted Indenes and Dihydronaphthalenes through C-C/C-C Bond-Forming Pd-Catalyzed Autotandem Reactions.

    PubMed

    Barroso, Raquel; Paraja, Miguel; Cabal, María-Paz; Valdés, Carlos

    2017-08-04

    A novel synthesis of 1,1-disubstituted 1H-indenes is described involving the Pd-catalyzed cascade reaction between o-bromophenyl-β-bromostyrenes and N-tosylhydrazones in a process comprising the consecutive formation of two Csp(3)-C bonds on the same carbon atom: the cross-coupling of the N-tosylhydrazone with the alkenyl bromide and the intramolecular Heck reaction on the newly formed double bond. A similar approach has been applied to the preparation of 1,1-disubstituted naphthalenes.

  4. Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

    PubMed

    Cemin, F; Bim, L T; Leidens, L M; Morales, M; Baumvol, I J R; Alvarez, F; Figueroa, C A

    2015-07-29

    Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer.

  5. A carbon-carbon composite materials development program for fusion energy applications

    SciTech Connect

    Burchell, T.D.; Eatherly, W.P. ); Engle, G.B. ); Hollenberg, G.W. )

    1992-10-01

    Carbon-carbon composites increasingly are being used for plasma-facing component (PFC) applications in magnetic-confinement plasma-fusion devices. They offer substantial advantages such as enhanced physical and mechanical properties and superior thermal shock resistance compared to the previously favored bulk graphite. Next-generation plasma-fusion reactors, such as the International Thermonuclear Experimental Reactor (ITER) and the Burning Plasma Experiment (BPX), will require advanced carbon-carbon composites possessing extremely high thermal conductivity to manage the anticipated extreme thermal heat loads. This report outlines a program that will facilitate the development of advanced carbon-carbon composites specifically tailored to meet the requirements of ITER and BPX. A strategy for developing the necessary associated design data base is described. Materials property needs, i.e., high thermal conductivity, radiation stability, tritium retention, etc., are assessed and prioritized through a systems analysis of the functional, operational, and component requirements for plasma-facing applications. The current Department of Energy (DOE) Office of Fusion Energy Program on carbon-carbon composites is summarized. Realistic property goals are set based upon our current understanding. The architectures of candidate PFC carbon-carbon composite materials are outlined, and architectural features considered desirable for maximum irradiation stability are described. The European and Japanese carbon-carbon composite development and irradiation programs are described. The Working Group conclusions and recommendations are listed. It is recommended that developmental carbon-carbon composite materials from the commercial sector be procured via request for proposal/request for quotation (RFP/RFQ) as soon as possible.

  6. Thermal and Mechanical Performance of a Carbon/Carbon Composite Spacecraft Radiator

    NASA Technical Reports Server (NTRS)

    Kuhn, Jonathan; Benner, Steve; Butler, Dan; Silk, Eric

    1999-01-01

    Carbon-carbon composite materials offer greater thermal efficiency, stiffness to weight ratio, tailorability, and dimensional stability than aluminum. These lightweight thermal materials could significantly reduce the overall costs associated with satellite thermal control and weight. However, the high cost and long lead-time for carbon-carbon manufacture have limited their widespread usage. Consequently, an informal partnership between government and industrial personnel called the Carbon-Carbon Spacecraft Radiator Partnership (CSRP) was created to foster carbon-carbon composite use for thermally and structurally demanding space radiator applications. The first CSRP flight opportunity is on the New Millennium Program (NMP) Earth Orbiter-1 (EO-1) spacecraft, scheduled for launch in late 1999. For EO-1, the CSRP designed and fabricated a Carbon-Carbon Radiator (CCR) with carbon-carbon facesheets and aluminum honeycomb core, which will also serve as a structural shear panel. While carbon-carbon is an ideal thermal candidate for spacecraft radiators, in practice there are technical challenges that may compromise performance. In this work, the thermal and mechanical performance of the EO-1 CCR is assessed by analysis and testing. Both then-nal and mechanical analyses were conducted to predict the radiator response to anticipated launch and on-orbit loads. The thermal model developed was based on thermal balance test conditions. The thermal analysis was performed using SINDA version 4.0. Structural finite element modeling and analysis were performed using SDRC/1-DEAS and UAI/NASTRAN, respectively. In addition, the CCR was subjected to flight qualification thermal/vacuum and vibration tests. The panel meets or exceeds the requirements for space flight and demonstrates promise for future satellite missions.

  7. Thermochemical Degradation Mechanisms for the Reinforced Carbon/Carbon Panels on the Space Shuttle

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Rapp, Robert A.

    1995-01-01

    The wing leading edge and nose cone of the Space Shuttle are fabricated from a reinforced carbon/carbon material (RCC). The material attains its oxidation resistance from a diffusion coating of SiC and a glass sealant. During re-entry, the RCC material is subjected to an oxidizing high temperature environment, which leads to degradation via several mechanisms. These mechanisms include oxidation to form a silica scale, reaction of the SiO2 with the SiC to evolve gaseous products, viscous flow of the glass, and vaporization of the glass. Each of these is discussed in detail. Following extended service and many missions, the leading-edge wing surfaces have exhibited small pinholes. A chloridation/oxidation mechanism is proposed to arise from the NaCl deposited on the wings from the sea-salt laden air in Florida. This involves a local chloridation reaction of the SiC and subsequent re-oxidation at the external surface. Thermodynamic calculations indicate the feasibility of these reactions at active pits. Kinetic calculations predict pore depths close to those observed.

  8. Development of a Simple Adjustable Zinc Acid/Base Hybrid Catalyst for C-C and C-O Bond-Forming and C-C Bond-Cleavage Reactions.

    PubMed

    Yamashita, Yasuhiro; Minami, Kodai; Saito, Yuki; Kobayashi, Shū

    2016-09-06

    A newly designed zinc Lewis acid/base hybrid catalyst was developed. By adjusting the Lewis acidity of the zinc center, aldol-type additions of 2-picolylamine Schiff base to aldehydes proceeded smoothly to afford syn-aldol adduct equivalents, trans-N,O-acetal adducts, in high yields with high selectivities. NMR experiments, including microchanneled cell for synthesis monitoring (MICCS) NMR analysis, revealed that anti-aldol adducts were formed at the initial stage of the reactions under kinetic control, but the final products were the trans-(syn)-N,O-acetal adducts that were produced through a retro-aldol process under thermodynamic control. In the whole reaction process, the zinc catalyst played three important roles: i) promotion of the aldol process (C-C bond formation), ii) cyclization process to the N,O-acetal product (C-O bond formation), and iii) retro-aldol process from the anti-aldol adduct to the syn-aldol adduct (C-C bond cleavage and C-C bond formation).

  9. Emotional stocks and bonds: a metaphorical model for conceptualizing and treating codependency and other forms of emotional overinvesting.

    PubMed

    Daire, Andrew P; Jacobson, Lamerial; Carlson, Ryan G

    2012-01-01

    Codependent behaviors are associated with an unhealthy reliance on others for meeting emotional needs. This over-reliance on others often leads to dysfunctional interpersonal relationships. This article presents emotional stocks and bonds (ESB), a metaphorical model for use with clients who display codependent behaviors. Emotional stocks and bonds incorporates theoretical tenets from Bowen family systems and attachment theory and aids clients in understanding and changing unhealthy relationship behavior patterns. In addition to an overview of the model's key concepts and its use in clinical practice, we provide a case illustration and a discussion of practice implications and limitations.

  10. The effect of neutron irradiation on the structure and properties of carbon-carbon composite materials

    NASA Astrophysics Data System (ADS)

    Burchell, T. D.; Eatherly, W. P.; Robbins, J. M.; Strizak, J. P.

    1992-09-01

    Carbon-based materials are an attractive choice for fusion reactor plasma facing components (PFCs) because of their low atomic number, superior thermal shock resistance, and low neutron activation. Next generation plasma fusion reactors, such as the international thermonuclear experimental reactor (ITER), will require advanced carbon-carbon composite materials possessing extremely high thermal conductivity to manage the anticipated severe heat loads. Moreover, ignition machines such as ITER wilt produce high neutron fluxes. Consequently, the influence of neutron damage on the structure and properties of carbon-carbon composite materials must be evaluated. Data from an irradiation experiment are reported and discussed here. Fusion relevant graphite and carbon-carbon composites were irradiated in a target capsule in the high flux isotope reactor (HFIR) at Oak Ridge National Laboratory (ORNL). A peak damage dose of 1.58 dpa (displacements per atom) at 600°C was attained. The carbon materials irradiated included nuclear graphite grade H-451 and one-, two-, and three-directional carbon-carbon composite materials. Dimensional changes and strength are reported for the materials examined. The influence of fiber type, architecture, and heat treatment temperature on properties and irradiation behavior are reported. Carbon-carbon composite dimensional changes are interpreted in terms of simple microstructural models.

  11. HCSE method for detection of small carbon-carbon couplings and their signs, comparison with SLAP pulse sequence.

    PubMed

    Blechta, Vratislav; Schraml, Jan

    2013-11-01

    Performance of homonuclear coupling sign edited (HCSE) experiment applied to detection of signed carbon-carbon couplings is discussed using a set of already measured samples of nine monosubstituted benzenes. It is shown that coupling sign detection is insensitive to the settings of carbon-carbon polarization transfer delays. The HCSE spectra of ten from the total of 43 measured carbon-carbon couplings were considerably influenced by relaxations and proton-proton strong couplings. These effects are quantitatively discussed. The results of HCSE and SLAP experiments are compared. It is shown that the two methods may complement each other in detection of signed carbon-carbon couplings.

  12. Superplastic forming and diffusion bonding of rapidly solidified, dispersion strengthened aluminum alloys for elevated temperature structural applications

    NASA Technical Reports Server (NTRS)

    Ting, E. Y.; Kennedy, J. R.

    1989-01-01

    Rapidly solidified alloys, based upon the Al-Fe-V-Si system and designed for elevated temperature applications, were evaluated for superplasticity and diffusion bonding behavior. Alloys with 8, 16, 27, and 36 volume percent silicide dispersoids were produced; dispersoid condition was varied by rolling at 300, 400, and 500 C (572, 752, and 932 F). Superplastic behavior was evaluated at strain rates from 1 x 10(exp -6)/s to 8.5/s at elevated temperatures. The results indicate that there was a significant increase in elongation at higher strain rates and at temperatures above 600 C (1112 F). However, the exposure of the alloys to temperatures greater than 600 C (1112 F) resulted in the coarsening of the strengthening dispersoid and the degradation of mechanical properties. Diffusion bonding was possible using low gas pressure at temperatures greater than 600 C (1112 F) which also resulted in degraded properties. The bonding of Al-Fe-V-Si alloys to 7475 aluminum alloy was performed at 516 C (960 F) without significant degradation in microstructure. Bond strengths equal to 90 percent that of the base metal shear strength were achieved. The mechanical properties and microstructural characteristics of the alloys were investigated.

  13. Plasma-sprayed hydroxyapatite coating on carbon/carbon composite scaffolds for bone tissue engineering and related tests in vivo.

    PubMed

    Cao, Ning; Dong, Jianwen; Wang, Qiangxiu; Ma, Quansheng; Wang, Feng; Chen, Huaying; Xue, Chengqian; Li, Musen

    2010-03-01

    The bioactive hydroxyapatite (HA) coatings were successfully prepared on carbon/carbon composites (C/C) by means of sand-blasting pretreatment and plasma-spraying technology. X-ray diffraction was employed to analyze the phase constitute of the coatings. Meanwhile, the bond strength between the HA coatings and C/C substrates was determined via shear test. Experimental results show that the coatings constitute HA, CaO, and other amorphous phosphates. The post heat treatment could effectively increase crystallization and purity of the coatings. Through observation and analysis by electron microprobe and scanning electron microscopy, it is concluded that the bond strength of the plasma-sprayed HA coatings on C/C is mainly determined by the interface structure and can be further improved by the post heat treatment. Meanwhile, the implantation in vivo was carried out in hybrid goats. The histological observation revealed that the osteoplaque gradually grew on the surface of the HA coatings and the pure C/C surface was covered by the fibrous tissues. No inflammation symptoms were found in the bone tissue around the implants.

  14. Morphology and microtensile bond strength of adhesive systems to in situ-formed caries-affected dentin after the use of a papain-based chemomechanical gel method.

    PubMed

    Botelho Amaral, Flavia Lucisano; Martão Florio, Flávia; Bovi Ambrosano, Glaucia Maria; Basting, Roberta Tarkany

    2011-02-01

    To evaluate the microtensile bond strength of adhesive systems to caries-affected dentin formed in situ after the use of a papain-based chemomechanical removal method. 84 human dentin specimens (5 x 5 x 3 mm) were sterilized and randomly distributed on palatal devices of 14 volunteers. Each palatal device, containing six dentin slabs, was used for 14 days according to a caries induction design involving plaque accumulation and sucrose use. After this, fragments were removed from devices and randomly assigned to two groups according to the caries removal method: (1) Chemomechanical (papain-based gel followed by curette), or (2) Mechanical (curette--control group). Specimens were subdivided into three subgroups according to the adhesive system tested: (SB) a two-step etch-and-rinse (Adper Single Bond 2); (SE) a two-step self-etching adhesive (Clearfil SE Bond) and (TriS) a one-step self-etching adhesive (Clearfil Tri-S Bond) and subsequently restored with microhybrid composite resin. After 24 hours, resin-tooth blocks were sectioned into 0.9 mm thick slabs, with one slab of each block being prepared for adhesive interface analysis by scanning electron microscopy, and the remaining blocks were sectioned into 0.8-mm2 sticks that were subjected to tensile stress (0.5 mm/minute). Data were subjected to two-way ANOVA and Tukey's test at a 5% level of significance. The application of the chemomechanical and mechanical methods to demineralized dentin did not affect the bond strength values. SB and SE adhesives promoted statistically similar and significantly higher bond strength values than the TriS. SEM analysis showed no interference of papain-based gel in the formation of hybrid layer; SB showed the thickest hybrid layer with presence of numerous tags; SE showed an intermediate hybrid layer thickness and quantity of tags and the TriS showed no evidence of tag formation.

  15. Meaning and consequence of the coexistence of competitive hydrogen bond/salt forms on the dissociation orientation of non-covalent complexes.

    PubMed

    Darii, Ekaterina; Alves, Sandra; Gimbert, Yves; Perret, Alain; Tabet, Jean-Claude

    2017-03-15

    Non-covalent complexes (NCC) between hexose monophosphates (HexP) and arginine (R) were analyzed using ESI MS and MS/MS in negative mode under different (hard, HC and soft, SC) desolvation conditions. High resolution mass spectrometry (HRMS) revealed the presence of different ionic species, namely, homo- and heteromultimers of R and HexP. Deprotonated heterodimers and corresponding sodiated species were enhanced under HC likely due to a decrease in available charge number associated with the reduction of H(+)/Na(+) exchange. The quantum calculations showed that the formation of covalent systems is very little exothermic, therefore, such systems are disfavored. Desolvation dependent CID spectra of deprotonated [(HexP+R)‒H](-) complexes demonstrated that they can exist within the hydrogen bond (HB) and salt bridge (SB) forms, yielding either NCC separation or covalent bond cleavages, respectively. Although HB forms are the main species, they cannot survive under HC; therefore, the minor SB forms became detectable. Energy-resolved mass spectrometry (ERMS) experiments revealed diagnostic fragment ions from both SB and HB forms, providing evidence that these isomeric forms are inconvertible. SB formation should result from the ionic interactions of highly acidic group of HexP with strongly basic guanidine group of arginine and thus requires an arginine zwitterion (ZW) form. This was confirmed by quantum calculations. Ion-ion interactions are significantly affected by the presence of sodium cation as demonstrated by the fragmentation patterns of sodiated complex species. Regarding CID data, only SB between protonated amino group of R and deprotonated phosphate group of HexP could be suggested, but the primary amine is not enough basic then, the SB must be fleeting. Nevertheless, the observation of the covalent bond cleavages suggests the presence of structures with a free negative charge able to induce fragmentations. Indeed, according to quantum calculations, solvated

  16. Electron Beam Exposure of Thermal Control Paints on Carbon-Carbon and Carbon-Polyimide Composites

    NASA Astrophysics Data System (ADS)

    Jaworske, Donald A.

    2006-01-01

    Carbon-carbon and carbon-polyimide composites are being considered for use as radiator face sheets or fins for space radiator applications. Several traditional white thermal control paints are being considered for the surface of the composite face sheets or fins. One threat to radiator performance is high energy electrons. The durability of the thermal control paints applied to the carbon-carbon and carbon-polyimide composites was evaluated after extended exposure to 4.5 MeV electrons. Electron exposure was conducted under argon utilizing a Mylar™ bag enclosure. Solar absorptance and infrared emittance was evaluated before and after exposure to identify optical properties degradation. Adhesion of the paints to the carbon-carbon and carbon-polyimide composite substrates was also of interest. Adhesion was evaluated on pristine and electron beam exposed coupons using a variation of the ASTM D-3359 tape test. Results of the optical properties evaluation and the adhesion tape tests are summarized.

  17. Emission intensity in the visible and IR spectral ranges from Si-based structures formed by direct bonding with simultaneous doping with erbium (Er) and europium (Eu)

    SciTech Connect

    Mezdrogina, M. M. Kostina, L. S.; Beliakova, E. I.; Kuzmin, R. V.

    2013-09-15

    The photo- and electroluminescence spectra of silicon-based structures formed by direct bonding with simultaneous doping with rare-earth metals are studied. It is shown that emission in the visible and IR spectral ranges can be obtained from n-Si:Er/p-Si and n-Si:Eu/p-Si structures fabricated by the method suggested in the study. The results obtained make this method promising for the fabrication of optoelectronic devices.

  18. A slow-forming isopeptide bond in the structure of the major pilin SpaD from Corynebacterium diphtheriae has implications for pilus assembly.

    PubMed

    Kang, Hae Joo; Paterson, Neil G; Kim, Chae Un; Middleditch, Martin; Chang, Chungyu; Ton-That, Hung; Baker, Edward N

    2014-05-01

    The Gram-positive organism Corynebacterium diphtheriae, the cause of diphtheria in humans, expresses pili on its surface which it uses for adhesion and colonization of its host. These pili are covalent protein polymers composed of three types of pilin subunit that are assembled by specific sortase enzymes. A structural analysis of the major pilin SpaD, which forms the polymeric backbone of one of the three types of pilus expressed by C. diphtheriae, is reported. Mass-spectral and crystallographic analysis shows that SpaD contains three internal Lys-Asn isopeptide bonds. One of these, shown by mass spectrometry to be located in the N-terminal D1 domain of the protein, only forms slowly, implying an energy barrier to bond formation. Two crystal structures, of the full-length three-domain protein at 2.5 Å resolution and of a two-domain (D2-D3) construct at 1.87 Å resolution, show that each of the three Ig-like domains contains a single Lys-Asn isopeptide-bond cross-link, assumed to give mechanical stability as in other such pili. Additional stabilizing features include a disulfide bond in the D3 domain and a calcium-binding loop in D2. The N-terminal D1 domain is more flexible than the others and, by analogy with other major pilins of this type, the slow formation of its isopeptide bond can be attributed to its location adjacent to the lysine used in sortase-mediated polymerization during pilus assembly.

  19. Process for Making Carbon-Carbon Turbocharger Housing Unit for Intermittent Combustion Engines

    NASA Technical Reports Server (NTRS)

    Northam, G. Burton (Inventor); Ransone, Philip O. (Inventor); Rivers, H. Kevin (Inventor)

    1999-01-01

    An improved. lightweight, turbine housing unit for an intermittent combustion reciprocating internal combustion engine turbocharger is prepared from a lay-up or molding of carbon-carbon composite materials in a single-piece or two-piece process. When compared to conventional steel or cast iron, the use of carbon-carbon composite materials in a turbine housing unit reduces the overall weight of the engine and reduces the heat energy loss used in the turbo-charging process. This reduction in heat energy loss and weight reduction provides for more efficient engine operation.

  20. Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Roth, Don J.; Rauser, Richard W.; Curry, Donald M.

    2007-01-01

    The oxidation of SiC-protected carbon/carbon through machined slots and naturally occurring craze cracks in the SiC was studied. The slot and crack geometries were characterized, and the subsurface oxidation of the carbon/carbon substrate at temperatures of 1000 to 1300 C in air was assessed using weight change, x-ray computed tomography, and optical microscopy of sections. Rate constants were derived from these measurements and compared with a two-step diffusion control model of carbon oxidation. Oxidation kinetic measurements on both the specimens with machined slots and with naturally occurring craze cracks showed good agreement with the model.

  1. Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Roth, Don J.; Rauser, Richard W.; Cawley, James D.; Curry, Donald M.

    2008-01-01

    The oxidation of SiC-protected carbon/carbon through machined slots and naturally occurring craze cracks in the SiC was studied. The slot and crack geometries were characterized, and the subsurface oxidation of the carbon/carbon substrate at temperatures of 1000 to 1300 C in air was assessed using weight change, x-ray computed tomography, and optical microscopy of sections. Rate constants were derived from these measurements and compared with a two-step diffusion control model of carbon oxidation. Oxidation kinetic measurements on both the specimens with machined slots and with naturally occurring craze cracks showed good agreement with the model.

  2. Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Roth, Don J.; Rauser, Richard W.; Curry, Donald M.

    2007-01-01

    The oxidation of SiC-protected carbon/carbon through machined slots and naturally occurring craze cracks in the SiC was studied. The slot and crack geometries were characterized, and the subsurface oxidation of the carbon/carbon substrate at temperatures of 1000 to 1300 C in air was assessed using weight change, x-ray computed tomography, and optical microscopy of sections. Rate constants were derived from these measurements and compared with a two-step diffusion control model of carbon oxidation. Oxidation kinetic measurements on both the specimens with machined slots and with naturally occurring craze cracks showed good agreement with the model.

  3. Concerted O atom-proton transfer in the O-O bond forming step in water oxidation.

    PubMed

    Chen, Zuofeng; Concepcion, Javier J; Hu, Xiangqian; Yang, Weitao; Hoertz, Paul G; Meyer, Thomas J

    2010-04-20

    As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H(2)O --> O(2) + 4e(-) + 4H(+)) is key, but it imposes a significant mechanistic challenge with requirements for both 4e(-)/4H(+) loss and O-O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as [Ru(Mebimpy)(bpy)(OH(2))](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine]. When oxidized from to Ru(V) = O(3+), these complexes undergo O-O bond formation by O-atom attack on a H(2)O molecule, which is often the rate-limiting step. Microscopic details of O-O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom-proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation.

  4. Presence of interchain disulfide bonds between two gene products that compose the secreted form of an antigen-specific suppressor factor

    PubMed Central

    1981-01-01

    The secreted form of the suppressor T cell factor specific for keyhole limpet hemocyanin derived from the hybridoma 34S-704 was found to consist of the two distinct polypeptide chains, i.e., the antigen- binding and the I-J-encoded chains. They were linked in covalent association with disulfide bonds. The two chains were cleaved by the reduction with dithiothreitol and were easy to reconstitute the active form of TsF. The association of the two distinct chains was suggested to be essential for the expression of the TsF activity. PMID:6166720

  5. Influence of Laser Activated Irrigation with two Erbium Lasers on Bond Strength of Inidividually Formed Fiber Reinforced Composite Posts to Root Canal Dentin.

    PubMed

    Parčina, Ivana; Amižić; Miletić, Ivana; Ionescu, Andrei C; Brambilla, Eugenio; Gabrić, Dragana; Baraba, Anja

    2016-12-01

    The aim of this in vitro study was to investigate the effect of laser activated irrigation (LAI) using two erbium lasers on bond strength of individually formed fiber-reinforced composite (FRC) posts to root canal dentin. Twenty-seven single-rooted human teeth were endodontically treated and after post space preparation divided into three groups (n=9 per group), according to the pre-treatment of post space preparation: 1) Conventional syringe irrigation (CSI) and saline; 2) Er.YAG photon-induced photoacoustic streaming (PIPS) technique and saline; 3) Er,Cr:YSGG activated irrigation with RFT2 tip. Two specimens from each group were used for SEM analysis. The remaining specimens (n=7 per group) received individually formed FRC post, everStick POST, luted with self-adhesive cement, G-CEM LinkAce. After cementation, the roots were perpendicularly sectioned into 1 mm thin sections and a push-out test was carried out (0.5 mm/min). The data were calculated as megapascals and were log transformed and statistically analysed using one-way ANOVA at the level of significance set at 5%. In the control group, the smear layer was still present. In the Er:YAG group, the smear layer was removed. In the Er,Cr:YSGG group, the smear layer was partially removed. The Er,Cr:YSGG group achieved the highest bond strength values, followed by the control group and then the Er:YAG group, but no statistically significant difference was found in bond strength values in the tested group of post space pretreatment (p=0.564). LAI using two erbium lasers, with PIPS or RFT2 tip, did not affect the bond strength of individually formed FRC posts to root canal dentin.

  6. Influence of Laser Activated Irrigation with two Erbium Lasers on Bond Strength of Inidividually Formed Fiber Reinforced Composite Posts to Root Canal Dentin

    PubMed Central

    Parčina, Ivana; Miletić, Ivana; Ionescu, Andrei C.; Brambilla, Eugenio; Gabrić, Dragana; Baraba, Anja

    2016-01-01

    Objective The aim of this in vitro study was to investigate the effect of laser activated irrigation (LAI) using two erbium lasers on bond strength of individually formed fiber-reinforced composite (FRC) posts to root canal dentin. Materials and methods Twenty-seven single-rooted human teeth were endodontically treated and after post space preparation divided into three groups (n=9 per group), according to the pre-treatment of post space preparation: 1) Conventional syringe irrigation (CSI) and saline; 2) Er.YAG photon-induced photoacoustic streaming (PIPS) technique and saline; 3) Er,Cr:YSGG activated irrigation with RFT2 tip. Two specimens from each group were used for SEM analysis. The remaining specimens (n=7 per group) received individually formed FRC post, everStick POST, luted with self-adhesive cement, G-CEM LinkAce. After cementation, the roots were perpendicularly sectioned into 1 mm thin sections and a push-out test was carried out (0.5 mm/min). The data were calculated as megapascals and were log transformed and statistically analysed using one-way ANOVA at the level of significance set at 5%. Results In the control group, the smear layer was still present. In the Er:YAG group, the smear layer was removed. In the Er,Cr:YSGG group, the smear layer was partially removed. The Er,Cr:YSGG group achieved the highest bond strength values, followed by the control group and then the Er:YAG group, but no statistically significant difference was found in bond strength values in the tested group of post space pretreatment (p=0.564). Conclusions LAI using two erbium lasers, with PIPS or RFT2 tip, did not affect the bond strength of individually formed FRC posts to root canal dentin. PMID:28275279

  7. Stress Rupture Behavior of Silicon Carbide Coated, Low Modulus Carbon/Carbon Composites. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Rozak, Gary A.; Wallace, John F.

    1988-01-01

    The disadvantages of carbon-carbon composites, in addition to the oxidation problem, are low thermal expansion, expensive fabrication procedures, and poor off axis properties. The background of carbon-carbon composites, their fabrication, oxidation, oxidation protection and mechanical testing in flexure are discussed.

  8. Concerted O atom–proton transfer in the O—O bond forming step in water oxidation

    PubMed Central

    Chen, Zuofeng; Concepcion, Javier J.; Hu, Xiangqian; Yang, Weitao; Hoertz, Paul G.; Meyer, Thomas J.

    2010-01-01

    As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H2O → O2 + 4e- + 4H+) is key, but it imposes a significant mechanistic challenge with requirements for both 4e-/4H+ loss and O—O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as [Ru(Mebimpy)(bpy)(OH2)]2+ [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2′-bipyridine]. When oxidized from to RuV = O3+, these complexes undergo O—O bond formation by O-atom attack on a H2O molecule, which is often the rate-limiting step. Microscopic details of O—O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom–proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation. PMID:20360565

  9. Concerted O atom-proton transfer in the O—O bond forming step in water oxidation

    SciTech Connect

    Chen, Zuofeng; Concepcion, Javier C.; Hu, Xiangqian; Yang, Weitao; Hoertz, Paul G.; Meyer, Thomas J

    2010-04-20

    As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H2O → O2 + 4e- + 4H+) is key, but it imposes a significant mechanistic challenge with requirements for both 4e-/4H- loss and O—O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as [Ru(Mebimpy)(bpy)(OH2)]2+ [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine]. When oxidized from RuII-OH22+ to RuV = O3+, these complexes undergo O—O bond formation by O-atom attack on a H2O molecule, which is often the rate-limiting step. Microscopic details of O—O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom–proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation.

  10. Organic salts formed by 2,4,6-triaminopyrimidine and selected carboxylic acids via a variety of hydrogen bonds: Synthons cooperation, and crystal structures

    NASA Astrophysics Data System (ADS)

    Xing, Peiqi; Li, Qingyun; Li, Yingying; Wang, Kunpeng; Zhang, Qi; Wang, Lei

    2017-05-01

    By using solvent evaporation method, 2,4,6-triaminopyrimidine (TAPI) is employed to crystallize with a variety of acids, including 3,5-dihydroxybenzoic acid (HDHBA), 3-nitrophthalic acid (H2NPA), 5-amino-2,4,6-triiodoisophthalic acid (H2ATIPIA), 2,5-dibromoterephthalic acid (H2DBTPA), 1,5-naphthalenedisulfonic acid (H2NDSA), sebacic acid (H2SA), 1,2,4-benzenetricarboxylic acid (H3BTA), and biphenyl-2,2‧,5,5'-tetracarboxylic acid (H4BPTA). In all eight complexes, protons are completely exchanged from O atom of acid to nitrogen of TAPI in 1, 3, 4, and, 5, partly transferred in 2, 6, 7, and 8. The crystal structure of all eight complexes exhibit that classical robust hydrogen bonds X-H⋯X (X = O/N) direct the molecular crystals to bind together in a stacking modes. Classical hydrogen bond Nsbnd H⋯O is participated in forming all eight organic salts, while hydrogen bonding Osbnd H⋯O are found in constructing the diversity structures in salts 1, 2, 3, 4, 6, and 7. The analysis shows that some classical supramolecular synthons, such as I R22(8), V R24(12), and VI S(6), are observed again in the construction of hydrogen-bonding networks. In the formation of layered and reticular structure, strong hydrogen bonds between water molecules and ligands having well-refined hydrogen atoms have been considered. Water molecules play an important role in building supramolecular structures of 1, 2, 3, 4, 7, and 8. Moreover, salts 1-8 are further characterized and analyzed by element analysis, infrared radiation, thermogravimetric analysis, proton nuclear magnetic resonance spectra, and mass spectra.

  11. Effects of precursor thermal aging and fiber arrangement on the properties of carbon/carbon (C/C) composites

    SciTech Connect

    Ma, C.C.M.; Chang, W.C.; Tai, N.H.

    1993-12-31

    Carbon/carbon composites fabricated by the pyrolysis of high strength carbon fiber fabrics reinforced phenolic resin were investigated. A liquid impregnation process has been used to fabricate composite precursor for 2-D carbon/carbon composite and an unique pultrusion process also used to fabricate the 1-D carbon/carbon composite precursor. Effects of thermal aging of the precursor on flexural strength of the resulted carbon/carbon composites are studied. Results shows that suitable thermal aging improves the flexural properties of carbon/carbon composites in this study. And based on the SEM examination and flexural tests, they show that the 2-D plain woven fiber arrangement results the significant degradation of the carbon fiber and the decreasing of composites flexural properties.

  12. Thermal Conductivity Database of Various Structural Carbon-Carbon Composite Materials

    NASA Technical Reports Server (NTRS)

    Ohlhorst, Craig W.; Vaughn, Wallace L.; Ransone, Philip O.; Tsou, Hwa-Tsu

    1997-01-01

    Advanced thermal protection materials envisioned for use on future hypersonic vehicles will likely be subjected to temperatures in excess of 1811 K (2800 F) and, therefore, will require the rapid conduction of heat away from the stagnation regions of wing leading edges, the nose cap area, and from engine inlet and exhaust areas. Carbon-carbon composite materials are candidates for use in advanced thermal protection systems. For design purposes, high temperature thermophysical property data are required, but a search of the literature found little thermal conductivity data for carbon-carbon materials above 1255 K (1800 F). Because a need was recognized for in-plane and through-the-thickness thermal conductivity data for carbon-carbon composite materials over a wide temperature range, Langley Research Center (LaRC) embarked on an effort to compile a consistent set of thermal conductivity values from room temperature to 1922 K (3000 F) for carbon-carbon composite materials on hand at LaRC for which the precursor materials and thermal processing history were known. This report documents the thermal conductivity data generated for these materials. In-plane thermal conductivity values range from 10 to 233 W/m-K, whereas through-the-thickness values range from 2 to 21 W/m-K.

  13. Exploration of Multilayer Concepts for Oxidation Protection of Carbon- Carbon Composites

    DTIC Science & Technology

    1993-02-01

    Microstructural Evaluations 14 Compliant Layer Properties 18 Oxidation Results 19 CONCLUSIONS 21I SUMMARY AND RECOMMENDATIONS 23 REFERENCES 25 I APPENDIX \\ 26...ABSTRACT The development of multilayer coating concepts for oxidation protection of carbon-carbon composites is the subject of this work. Property ...components. Since elevated temperature properties were lacking for many components, the study was relegated to fabrication and assessment rather than

  14. Thermal Cycling of Thermal Control Paints on Carbon-Carbon and Carbon-Polyimide Composites

    NASA Technical Reports Server (NTRS)

    Jaworske, Donald A.

    2006-01-01

    Carbon-carbon composites and carbon-polyimide composites are being considered for space radiator applications owing to their light weight and high thermal conductivity. For those radiator applications where sunlight will impinge on the surface, it will be necessary to apply a white thermal control paint to minimize solar absorptance and enhance infrared emittance. Several currently available white thermal control paints were applied to candidate carbon-carbon and carbon-polyimide composites and were subjected to vacuum thermal cycling in the range of -100 C to +277 C. The optical properties of solar absorptance and infrared emittance were evaluated before and after thermal cycling. In addition, adhesion of the paints was evaluated utilizing a tape test. The test matrix included three composites: resin-derived carbon-carbon and vapor infiltrated carbon-carbon, both reinforced with pitch-based P-120 graphite fibers, and a polyimide composite reinforced with T-650 carbon fibers, and three commercially available white thermal control paints: AZ-93, Z-93-C55, and YB-71P.

  15. Theoretical estimates of photoproduction cross sections for neutral subthreshold pions in carbon-carbon collisions.

    PubMed

    Norbury, J W; Townsend, L W

    1986-01-01

    Using the Weizsacher-Williams method of virtual quanta, total cross section estimates for the photoproduction of neutral subthreshold pions in carbon-carbon collisions at incident energies below 300 MeV/nucleon are made. Comparisons with recent experimental data indicate that the photoproduction mechanism makes an insignificant contribution to these measured cross sections.

  16. Micromechanics of crenulated fibers in carbon/carbon composites. M.S. Thesis Interim Report, 1 Jan. 1990 - 31 Dec. 1992

    NASA Technical Reports Server (NTRS)

    Carapella, E. E.; Hyer, M. W.; Griffin, O. H., Jr.; Maahs, H. G.

    1993-01-01

    The influence of crenulated noncircular fibers on the micromechanical stress states due to a transverse strain and to a temperature change in carbon/carbon composites is examined using the finite element method. Stresses at the interface of both fully bonded and fully disbonded fibers having two crenulation amplitudes and with two fiber volume fractions are presented. In each case, these interface stresses are compared to stresses at the interface of circular fibers which have the same degree of disbond and fiber volume fraction and are under the same loading conditions. For the disbonded cases, deformed meshes showing locations of fiber/matrix contact are also included. In addition to the interface stress states, selected composite properties are also computed and compared in each case examined. Interest in studying noncircular fibers stems from a desire to increase the transverse properties of carbon/carbon by introducing a mechanical interlocking between the fiber and the matrix. Results presented here indicate that this interlocking does in fact occur. Evidence from the interface stress data suggests, however, that any possible advantage of this interlocking may be outweighed by the disadvantage of stress concentrations which arise at the interface due to the crenulated geometry of the fibers.

  17. Hydrogen-bonded clusters of 1, 1'-ferrocenedicarboxylic acid on Au(111) are initially formed in solution.

    PubMed

    Quardokus, Rebecca C; Wasio, Natalie A; Brown, Ryan D; Christie, John A; Henderson, Kenneth W; Forrest, Ryan P; Lent, Craig S; Corcelli, Steven A; Kandel, S Alex

    2015-03-14

    Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

  18. Energy transport mechanism in the form of proton soliton in a one-dimensional hydrogen-bonded polypeptide chain.

    PubMed

    Kavitha, L; Priya, R; Ayyappan, N; Gopi, D; Jayanthi, S

    2016-01-01

    The dynamics of protons in a one-dimensional hydrogen-bonded (HB) polypeptide chain (PC) is investigated theoretically. A new Hamiltonian is formulated with the inclusion of higher-order molecular interactions between peptide groups (PGs). The wave function of the excitation state of a single particle is replaced by a new wave function of a two-quanta quasi-coherent state. The dynamics is governed by a higher-order nonlinear Schrödinger equation and the energy transport is performed by the proton soliton. A nonlinear multiple-scale perturbation analysis has been performed and the evolution of soliton parameters such as velocity and amplitude is explored numerically. The proton soliton is thermally stable and very robust against these perturbations. The energy transport by the proton soliton is more appropriate to understand the mechanism of energy transfer in biological processes such as muscle contraction, DNA replication, and neuro-electric pulse transfer on biomembranes.

  19. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

    A method of bonding substrates by hydroxide-catalyzed hydration/dehydration involves applying a bonding material to at least one surface to be bonded, and placing the at least one surface sufficiently close to another surface such that a bonding interface is formed between them. A bonding material of the invention comprises a source of hydroxide ions, and may optionally include a silicate component, a particulate filling material, and a property-modifying component. Bonding methods of the invention reliably and reproducibly provide bonds which are strong and precise, and which may be tailored according to a wide range of possible applications. Possible applications for bonding materials of the invention include: forming composite materials, coating substrates, forming laminate structures, assembly of precision optical components, and preparing objects of defined geometry and composition. Bonding materials and methods of preparing the same are also disclosed.

  20. Preparation of Ag-Ni-Cu Composite Material by Ultrasonic Arc Spray Forming and Accumulative Roll Bonding and the Evolution of Its Microstructure

    NASA Astrophysics Data System (ADS)

    Zhang, Ke; Qin, Guo-Yi; Xu, Si-Yong; Guo, Jin-Xin; Ma, Guang

    2015-02-01

    We prepared a layered composite material by subjecting a deposition billet of AgNiCu15-5 formed by ultrasonic arc spray forming (UASF) to extrusion at 773 K (500 °C), rolling at 673 K (400 °C), and accumulative roll bonding (ARB). The evolution of the microstructure of the formed AgNiCu15-5 strips was analyzed through X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectrometry. The deposition billet had a rapid solidification microstructure consisting of β-Ni particles dispersed in α-Ag matrix. ARB significantly refined the microstructure of the AgNiCu15-5 samples. There was no further decrease in the grain size after the 9th ARB cycle. Thus, UASF combined with extrusion and ARB is suitable for producing high-performance AgNiCu15-5-based electrical contact materials efficiently and economically.