WorldWideScience

Sample records for carbon-carbon bond cleavage

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

    Science.gov (United States)

    More, Nagnath Yadav; Jeganmohan, Masilamani

    2014-02-01

    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.

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

    Science.gov (United States)

    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.

  3. Enantioselective epoxidation and carbon-carbon bond cleavage catalyzed by Coprinus cinereus peroxidase and myeloperoxidase.

    Science.gov (United States)

    Tuynman, A; Spelberg, J L; Kooter, I M; Schoemaker, H E; Wever, R

    2000-02-01

    We demonstrate that myeloperoxidase (MPO) and Coprinus cinereus peroxidase (CiP) catalyze the enantioselective epoxidation of styrene and a number of substituted derivatives with a reasonable enantiomeric excess (up to 80%) and in a moderate yield. Three major differences with respect to the chloroperoxidase from Caldariomyces fumago (CPO) are observed in the reactivity of MPO and CiP toward styrene derivatives. First, in contrast to CPO, MPO and CiP produced the (S)-isomers of the epoxides in enantiomeric excess. Second, for MPO and CiP the H(2)O(2) had to be added very slowly (10 eq in 16 h) to prevent accumulation of catalytically inactive enzyme intermediates. Under these conditions, CPO hardly showed any epoxidizing activity; only with a high influx of H(2)O(2) (300 eq in 1.6 h) was epoxidation observed. Third, both MPO and CiP formed significant amounts of (substituted) benzaldehydes as side products as a consequence of C-alpha-C-beta bond cleavage of the styrene derivatives, whereas for CPO and cytochrome c peroxidase this activity is not observed. C-alpha-C-beta cleavage was the most prominent reaction catalyzed by CiP, whereas with MPO the relative amount of epoxide formed was higher. This is the first report of peroxidases catalyzing both epoxidation reactions and carbon-carbon bond cleavage. The results are discussed in terms of mechanisms involving ferryl oxygen transfer and electron transfer, respectively.

  4. Highly Efficient Oxidative Cleavage of Carbon-Carbon Double Bond over meso-Tetraphenyl Cobalt Porphyrin Catalyst in the Presence of Molecular Oxygen

    Institute of Scientific and Technical Information of China (English)

    周贤太; 纪红兵

    2012-01-01

    Highly efficient and selective carbon-carbon double bond aerobic cleavage of olefins catalyzed by metallopor- phyrins was investigated, and carbonyl compounds and epoxide were produced as the main products. CoTPP (co- balt meso-tetraphenyl porphyrin) showed excellent activity for the oxidative cleavage of carbon-carbon double bond by using styrene as model compound, in which the TOF (turnover frequency) and selectivity toward benzaldehyde was obtained with 2×10^4h-1 and 86%,respectively.

  5. Switching the Cleavage Sites in Palladium on Carbon-Catalyzed Carbon-Carbon Bond Disconnection.

    Science.gov (United States)

    Hattori, Tomohiro; Takakura, Ryoya; Ichikawa, Tomohiro; Sawama, Yoshinari; Monguchi, Yasunari; Sajiki, Hironao

    2016-04-01

    We have demonstrated a palladium on carbon-catalyzed approach to regioselectively alter the cleavage sites of the C-C bonds of cinnamaldehyde derivatives by a slight change in the reaction conditions in isopropanol under an O2 atmosphere. Styrene derivatives could be selectively formed by the addition of Na2CO3 in association with the dissociation of carbon monoxide, while benzaldehyde derivatives were generated by the addition of CuCl and morpholine instead of Na2CO3. PMID:26944077

  6. Purification, molecular cloning, and expression of 2-hydroxyphytanoyl- CoA lyase, a peroxisomal thiamine pyrophosphate-dependent enzyme that catalyzes the carbon-carbon bond cleavage during à-oxidation of 3- methyl-branched fatty acids

    CERN Document Server

    Foulon, V; Croes, K; Waelkens, E

    1999-01-01

    Purification, molecular cloning, and expression of 2-hydroxyphytanoyl- CoA lyase, a peroxisomal thiamine pyrophosphate-dependent enzyme that catalyzes the carbon-carbon bond cleavage during à-oxidation of 3- methyl-branched fatty acids

  7. Rhodium(i)-catalysed skeletal reorganisation of benzofused spiro[3.3]heptanes via consecutive carbon-carbon bond cleavage.

    Science.gov (United States)

    Matsuda, Takanori; Yuihara, Itaru; Kondo, Kazuki

    2016-08-01

    Skeletal reorganisation of benzofused spiro[3.3]heptanes has been achieved using rhodium(i) catalysts. The reaction of benzofused 2-(2-pyridylmethylene)spiro[3.3]heptanes proceeds via sequential C-C bond oxidative addition and β-carbon elimination. On the other hand, benzofused spiro[3.3]heptan-2-ols undergo two consecutive β-carbon elimination processes. In both cases, substituted naphthalenes are obtained. PMID:27357097

  8. 硅胶担载的高锰酸钾对烯烃碳碳双键的氧化%Carbon-Carbon Double Bond Cleavage by Silica-supported Potassium Permanganate under Conditions Free of Organic Solvent

    Institute of Scientific and Technical Information of China (English)

    王文军; 戴乾圜

    2002-01-01

    An improved simple method for carbon-carbon double bond cleavage by silica-supported potassium permanganate was described and a possible mechanism was proposed.%在无有机溶剂做介质的条件下,用硅胶吸附的高锰酸钾氧化6种难溶于水的液态烯烃,得到了双键发生断裂的氧化产物.该反应操作简便,反应快,收率好.此外,对硅胶的活化作用机制进行了浅析.

  9. Can laccases catalyze bond cleavage in lignin?

    DEFF Research Database (Denmark)

    Munk, Line; Sitarz, Anna Katarzyna; Kalyani, Dayanand;

    2015-01-01

    illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin...

  10. SmI(2)-mediated carbon-carbon bond fragmentation in alpha-aminomethyl malonates.

    Science.gov (United States)

    Xu, Qiongfeng; Cheng, Bin; Ye, Xinshan; Zhai, Hongbin

    2009-09-17

    A new and efficient samarium diiodide-promoted carbon-carbon bond fragmentation reaction of alpha-aminomethyl malonates, taking place normally at room temperature and generating the corresponding deaminomethylation products in 74-94% yields, is reported. The presence of the amino group is necessary for the success of the current transformation.

  11. Carbon-carbon composite and copper-composite bond damages for high flux component controlled fusion

    International Nuclear Information System (INIS)

    Plasma facing components constitute the first wall in contact with plasma in fusion machines such as Tore Supra and ITER. These components have to sustain high heat flux and consequently elevated temperatures. They are made up of an armour material, the carbon-carbon composite, a heat sink structure material, the copper chromium zirconium, and a material, the OFHC copper, which is used as a compliant layer between the carbon-carbon composite and the copper chromium zirconium. Using different materials leads to the apparition of strong residual stresses during manufacturing, because of the thermal expansion mismatch between the materials, and compromises the lasting operation of fusion machines as damage which appeared during manufacturing may propagate. The objective of this study is to understand the damage mechanisms of the carbon-carbon composite and the composite-copper bond under solicitations that plasma facing components may suffer during their life. The mechanical behaviours of carbon-carbon composite and composite-copper bond were studied in order to define the most suitable models to describe these behaviours. With these models, thermomechanical calculations were performed on plasma facing components with the finite element code Cast3M. The manufacturing of the components induces high stresses which damage the carbon-carbon composite and the composite-copper bond. The damage propagates during the cooling down to room temperature and not under heat flux. Alternative geometries for the plasma facing components were studied to reduce damage. The relation between the damage of the carbon-carbon composite and its thermal conductivity was also demonstrated. (author)

  12. Stable alkanes containing very long carbon-carbon bonds.

    Science.gov (United States)

    Fokin, Andrey A; Chernish, Lesya V; Gunchenko, Pavel A; Tikhonchuk, Evgeniya Yu; Hausmann, Heike; Serafin, Michael; Dahl, Jeremy E P; Carlson, Robert M K; Schreiner, Peter R

    2012-08-22

    The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C-C bonds of up to 1.71 Å in 2-(1-diamantyl)[121]tetramantane. Yet, these dimers are thermally very stable even at temperatures above 200 °C, which is not in line with common C-C bond length versus bond strengths correlations. We suggest that the extraordinary stabilization arises from numerous intramolecular van der Waals attractions between the neighboring H-terminated diamond-like surfaces. The C-C bond rotational dynamics of 1-(1-adamantyl)diamantane, 1-(1-diamantyl)diamantane, 2-(1-adamantyl)triamantane, 2-(1-diamantyl)triamantane, and 2-(1-diamantyl)[121]tetramantane were studied through variable-temperature (1)H- and (13)C NMR spectroscopies. The shapes of the inward (endo) CH surfaces determine the dynamic behavior, changing the central C-C bond rotation barriers from 7 to 33 kcal mol(-1). We probe the ability of popular density functional theory (DFT) approaches (including BLYP, B3LYP, B98, B3LYP-Dn, B97D, B3PW91, BHandHLYP, B3P86, PBE1PBE, wB97XD, and M06-2X) with 6-31G(d,p) and cc-pVDZ basis sets to describe such an unusual bonding situation. Only functionals accounting for dispersion are able to reproduce the experimental geometries, while most DFT functionals are able to reproduce the experimental rotational barriers due to error cancellations. Computations on larger diamondoids reveal that the interplay between the shapes and the sizes of the CH surfaces may even allow the preparation of open-shell alkyl radical dimers (and possibly polymers) that are strongly held together exclusively by dispersion forces. PMID:22835264

  13. An algorithm for predicting proton nuclear magnetic resonance deshielding over a carbon-carbon double bond.

    Science.gov (United States)

    Martin, N H; Allen, N W; Brown, J D; Ingrassia, S T; Minga, E K

    2000-02-01

    Hydrogen nuclei located over a carbon-carbon double bond in a strong magnetic field experience NMR shielding effects that result from the magnetic anisotropy of the nearby double bond and various other intramolecular shielding effects. We have used GIAO, a subroutine in Gaussian 98, to calculate isotropic shielding values and to predict the proton NMR shielding increment for a simple model system: methane held in various orientations, positions, and distances over ethene. The average proton NMR shielding increments of several orientations of methane have been plotted versus the Cartesian coordinates of the methane protons relative to the center of ethene. A single empirical equation for predicting the NMR shielding experienced by protons over a carbon-carbon double bond has been developed from these data. The predictive capability of this equation has been validated by comparing the shielding increments for several alkenes calculated using our equation to the experimentally observed shielding increments. This equation predicts the NMR shielding effects more accurately than previous models that were based on fewer geometries of methane over ethene. In fact, deshielding is predicted by this equation for protons over the center and within about 3 A of a carbon-carbon double bond. This result is in sharp contrast to predictions made by the long-held McConnell "shielding cone" model found in nearly every textbook on NMR, but is consistent with experimental observations. The algorithm for predicting the (de)shielding increment for a proton over an alkene can be used in a spreadsheet on a PC or incorporated into software that estimates chemical shifts using additive substituent constants or a database of structures. In either application its use can substantially improve the accuracy of the estimated chemical shift of a proton in the vicinity of a carbon-carbon double bond, and thus assist in spectral assignments and in correct structure determination.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. Regioselectivity in the Reductive Bond Cleavage of Diarylalkylsulfonium Salts

    DEFF Research Database (Denmark)

    Kampmeier, Jack; Mansurul Hoque, AKM; D. Saeva, Franklin;

    2009-01-01

    This investigation was stimulated by reports that one-electron reductions of monoaryldialkylsulfonium salts never give aryl bond cleavage whereas reductions of diarylmonoalkylsulfonium salts preferentially give aryl bond cleavage. We studied the product ratios from the reductive cleavage of di-4......- tolylethylsulfonium and di-4-tolyl-2-phenylethylsulfonium salts by a variety of one-electron reducing agents ranging in potential from -0.77 to +2.5 eV (vs SCE) and including thermal reductants, indirect electrolyses mediated by a series of cyanoaromatics, and excited singlet states. We report that the cleavage...... products vary from regiospecific alkyl cleavage to predominant aryl cleavage as a function of the potential of the reducing agent. We conclude that differences between the reductive cleavages of mono- and diarylsulfonium salts are direct consequences of the structures of the sulfuranyl radical...

  16. A New Paradigm for Carbon-Carbon Bond Formation: Aerobic, Copper-Templated Cross-Coupling

    OpenAIRE

    Villalobos, Janette M.; Srogl, Jiri; Liebeskind, Lanny S.

    2007-01-01

    Thiol esters and boronic acids react to produce ketones under aerobic conditions in the presence of catalytic quantities of a CuI or CuII salt. The reaction occurs at reasonable rates between room temperature and 50 °C at neutral pH using thiol esters derived from bulky 2° amides of thiosalicylamides such as those based on N-tert-butyl-2-mercaptobenzamide. In this mechanistically unprecedented reaction system the carbon-carbon bond formation occurs through templating of the thiol ester and th...

  17. Microbial cleavage of organic C-S bonds

    Science.gov (United States)

    Kilbane, II, John J.

    1994-01-01

    A microbial process for selective cleavage of organic C--S bonds which may be used for reducing the sulfur content of sulfur-containing organic carbonaceous materials, Microorganisms of Rhodococcus rhodochrous and Bacillus sphaericus have been found which have the ability of selective cleavage of organic C--S bonds. Particularly preferred microorganisms are Rhodococcus rhodochrous strain ATCC 53968 and Bacillus sphaericus strain ATCC 53969 and their derivatives.

  18. Carbon dioxide as a carbon source in organic transformation: carbon-carbon bond forming reactions by transition-metal catalysts.

    OpenAIRE

    Tsuji, Yasushi; Fujihara, Tetsuaki

    2012-01-01

    Recent carbon-carbon bond forming reactions of carbon dioxide with alkenes, alkynes, dienes, aryl zinc compounds, aryl boronic esters, aryl halides, and arenes having acidic C-H bonds are reviewed in which transition-metal catalysts play an important role.

  19. Reductive cleavage of the peptide bond

    Science.gov (United States)

    Holian, J.; Garrison, W. M.

    1973-01-01

    In many biological research efforts, long chain organic molecules are studied by breaking large molecules into smaller components. Cleavage technique of recent interest is the use of solvated electrons. These are formed when aqueous solutions are bombarded with gamma radiation. Solvated electron is very reactive and can reduce most any species present, even to form free radicals.

  20. Study of the damaging mechanisms of a carbon - carbon composite bonded to copper under thermomechanical loading

    International Nuclear Information System (INIS)

    The purpose of this work is to understand and to identify the damaging mechanisms of Carbon-Carbon composite bonded to copper under thermomechanical loading. The study of the composite allowed the development of non-linear models. These ones have been introduced in the finite elements analysis code named CASTEM 2000. They have been validated according to a correlation between simulation and mechanical tests on multi-material samples. These tests have also permitted us to better understand the behaviour of the bonding between composite and copper (damaging and fracture modes for different temperatures) under shear and tensile loadings. The damaging mechanisms of the bond under thermomechanical loading have been studied and identified according to microscopic observations on mock-ups which have sustained thermal cycling tests: some cracks appear in the composite, near the bond between the composite and the copper. The correlation between numerical and experimental results have been improved because of the reliability of the composite modelization, the use of residual stresses and the results of the bond mechanical characterisation. (author)

  1. Merging allylic carbon-hydrogen and selective carbon-carbon bond activation

    Science.gov (United States)

    Masarwa, Ahmad; Didier, Dorian; Zabrodski, Tamar; Schinkel, Marvin; Ackermann, Lutz; Marek, Ilan

    2014-01-01

    Since the nineteenth century, many synthetic organic chemists have focused on developing new strategies to regio-, diastereo- and enantioselectively build carbon-carbon and carbon-heteroatom bonds in a predictable and efficient manner. Ideal syntheses should use the least number of synthetic steps, with few or no functional group transformations and by-products, and maximum atom efficiency. One potentially attractive method for the synthesis of molecular skeletons that are difficult to prepare would be through the selective activation of C-H and C-C bonds, instead of the conventional construction of new C-C bonds. Here we present an approach that exploits the multifold reactivity of easily accessible substrates with a single organometallic species to furnish complex molecular scaffolds through the merging of otherwise difficult transformations: allylic C-H and selective C-C bond activations. The resulting bifunctional nucleophilic species, all of which have an all-carbon quaternary stereogenic centre, can then be selectively derivatized by the addition of two different electrophiles to obtain more complex molecular architecture from these easily available starting materials.

  2. Ethenolysis: A Green Catalytic Tool to Cleave Carbon-Carbon Double Bonds.

    Science.gov (United States)

    Bidange, Johan; Fischmeister, Cédric; Bruneau, Christian

    2016-08-22

    Remarkable innovations have been made in the field of olefin metathesis due to the design and preparation of new catalysts. Ethenolysis, which is cross-metathesis with ethylene, represents one catalytic transformation that has been used with the purpose of cleaving internal carbon-carbon double bonds. The objectives were either the ring opening of cyclic olefins to produce dienes or the shortening of unsaturated hydrocarbon chains to degrade polymers or generate valuable shorter terminal olefins in a controlled manner. This Review summarizes several aspects of this reaction: the catalysts, their degradation in the presence of ethylene, some parameters driving their productivity, the side reactions, and the applications of ethenolysis in organic synthesis and in potential industrial applications. PMID:27359344

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

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Sheng; Li, Hejun, E-mail: lihejun@nwpu.edu.cn; Li, Kezhi; Lu, Jinhua; Zhang, Leilei

    2015-08-30

    Graphical abstract: - Highlights: • Significantly enhancement of biocompatibility on C/C composites by preparing a collagen film. • The dense and continuous collagen film had a strong bonding strength with C/C composites after dehydrathermal treatment (DHT) crosslink. • Numerous oxygen-containing functional groups formed on the surface of C/C composites without matrix damage. - Abstract: 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% H{sub 2}O{sub 2} 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.

  4. Development and application of bond cleavage reactions in bioorthogonal chemistry.

    Science.gov (United States)

    Li, Jie; Chen, Peng R

    2016-03-01

    Bioorthogonal chemical reactions are a thriving area of chemical research in recent years as an unprecedented technique to dissect native biological processes through chemistry-enabled strategies. However, current concepts of bioorthogonal chemistry have largely centered on 'bond formation' reactions between two mutually reactive bioorthogonal handles. Recently, in a reverse strategy, a collection of 'bond cleavage' reactions has emerged with excellent biocompatibility. These reactions have expanded our bioorthogonal chemistry repertoire, enabling an array of exciting new biological applications that range from the chemically controlled spatial and temporal activation of intracellular proteins and small-molecule drugs to the direct manipulation of intact cells under physiological conditions. Here we highlight the development and applications of these bioorthogonal cleavage reactions. Furthermore, we lay out challenges and propose future directions along this appealing avenue of research.

  5. Cooperativity between Al Sites Promotes Hydrogen Transfer and Carbon-Carbon Bond Formation upon Dimethyl Ether Activation on Alumina.

    Science.gov (United States)

    Comas-Vives, Aleix; Valla, Maxence; Copéret, Christophe; Sautet, Philippe

    2015-09-23

    The methanol-to-olefin (MTO) process allows the conversion of methanol/dimethyl ether into olefins on acidic zeolites via the so-called hydrocarbon pool mechanism. However, the site and mechanism of formation of the first carbon-carbon bond are still a matter of debate. Here, we show that the Lewis acidic Al sites on the 110 facet of γ-Al2O3 can readily activate dimethyl ether to yield CH4, alkenes, and surface formate species according to spectroscopic studies combined with a computational approach. The carbon-carbon forming step as well as the formation of methane and surface formate involves a transient oxonium ion intermediate, generated by a hydrogen transfer between surface methoxy species and coordinated methanol on adjacent Al sites. These results indicate that extra framework Al centers in acidic zeolites, which are associated with alumina, can play a key role in the formation of the first carbon-carbon bond, the initiation step of the industrial MTO process. PMID:27162986

  6. Formation Mechanism of the First Carbon-Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons.

    Science.gov (United States)

    Liu, Yue; Müller, Sebastian; Berger, Daniel; Jelic, Jelena; Reuter, Karsten; Tonigold, Markus; Sanchez-Sanchez, Maricruz; Lercher, Johannes A

    2016-05-01

    The elementary reactions leading to the formation of the first carbon-carbon bond during early stages of the zeolite-catalyzed methanol conversion into hydrocarbons were identified by combining kinetics, spectroscopy, and DFT calculations. The first intermediates containing a C-C bond are acetic acid and methyl acetate, which are formed through carbonylation of methanol or dimethyl ether even in presence of water. A series of acid-catalyzed reactions including acetylation, decarboxylation, aldol condensation, and cracking convert those intermediates into a mixture of surface bounded hydrocarbons, the hydrocarbon pool, as well as into the first olefin leaving the catalyst. This carbonylation based mechanism has an energy barrier of 80 kJ mol(-1) for the formation of the first C-C bond, in line with a broad range of experiments, and significantly lower than the barriers associated with earlier proposed mechanisms. PMID:27037603

  7. Enantioselective epoxidation and carbon-carbon bond cleavage catalyzed by Coprinus cinereus peroxidase and myeloperoxidase

    NARCIS (Netherlands)

    Tuynman, A; Lutje Spelberg, Jeffrey; Kooter, IM; Schoemaker, HE; Wever, R

    2000-01-01

    We demonstrate that myeloperoxidase (MPO) and Coprinus cinereus peroxidase (CiP) catalyze the enantioselective epoxidation of styrene and a number of substituted derivatives with a reasonable enantiomeric excess (up to 80%) and in a moderate yield. Three major differences with respect to the chlorop

  8. Cleavage of an amide bond by a ribozyme

    Science.gov (United States)

    Dai, X.; De Mesmaeker, A.; Joyce, G. F.; Miller, S. L. (Principal Investigator)

    1995-01-01

    A variant form of a group I ribozyme, optimized by in vitro evolution for its ability to catalyze magnesium-dependent phosphoester transfer reactions involving DNA substrates, also catalyzes the cleavage of an unactivated alkyl amide when that linkage is presented in the context of an oligodeoxynucleotide analog. Substrates containing an amide bond that joins either two DNA oligos, or a DNA oligo and a short peptide, are cleaved in a magnesium-dependent fashion to generate the expected products. The first-order rate constant, kcat, is 0.1 x 10(-5) min-1 to 1 x 10(-5) min-1 for the DNA-flanked substrates, which corresponds to a rate acceleration of more than 10(3) as compared with the uncatalyzed reaction.

  9. C-S bond cleavage by a polyketide synthase domain.

    Science.gov (United States)

    Ma, Ming; Lohman, Jeremy R; Liu, Tao; Shen, Ben

    2015-08-18

    Leinamycin (LNM) is a sulfur-containing antitumor antibiotic featuring an unusual 1,3-dioxo-1,2-dithiolane moiety that is spiro-fused to a thiazole-containing 18-membered lactam ring. The 1,3-dioxo-1,2-dithiolane moiety is essential for LNM's antitumor activity, by virtue of its ability to generate an episulfonium ion intermediate capable of alkylating DNA. We have previously cloned and sequenced the lnm gene cluster from Streptomyces atroolivaceus S-140. In vivo and in vitro characterizations of the LNM biosynthetic machinery have since established that: (i) the 18-membered macrolactam backbone is synthesized by LnmP, LnmQ, LnmJ, LnmI, and LnmG, (ii) the alkyl branch at C-3 of LNM is installed by LnmK, LnmL, LnmM, and LnmF, and (iii) leinamycin E1 (LNM E1), bearing a thiol moiety at C-3, is the nascent product of the LNM hybrid nonribosomal peptide synthetase (NRPS)-acyltransferase (AT)-less type I polyketide synthase (PKS). Sulfur incorporation at C-3 of LNM E1, however, has not been addressed. Here we report that: (i) the bioinformatics analysis reveals a pyridoxal phosphate (PLP)-dependent domain, we termed cysteine lyase (SH) domain (LnmJ-SH), within PKS module-8 of LnmJ; (ii) the LnmJ-SH domain catalyzes C-S bond cleavage by using l-cysteine and l-cysteine S-modified analogs as substrates through a PLP-dependent β-elimination reaction, establishing l-cysteine as the origin of sulfur at C-3 of LNM; and (iii) the LnmJ-SH domain, sharing no sequence homology with any other enzymes catalyzing C-S bond cleavage, represents a new family of PKS domains that expands the chemistry and enzymology of PKSs and might be exploited to incorporate sulfur into polyketide natural products by PKS engineering.

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

    Science.gov (United States)

    Cortright, Randy D.; Dumesic, James A.

    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.

  11. Correlation between carbon-carbon bond length and the ease of retro Diels-Alder reaction

    Indian Academy of Sciences (India)

    Sambasivarao Kotha; Shaibal Banerjee; Mobin Shaikh

    2014-09-01

    The bond length between C8-C9 in (1′R,4′S,4a′R,8a′S)-6′,7′-dimethyl-1′,4′,4a′,8a′-tetrahydrospiro [cyclopropane-1,9′-[1,4]methanonaphthalene]-5′,8′-dione is 1.571 (2) Å and between C7-C12 is 1.567 (2) Å which are longer than the corresponding bond length for saturated bicyclic systems (1.531-1.535Å). This paper reports the correlation between bond length and the ease of retro Diels−Alder reaction.

  12. Carbon-Oxygen Bond Cleavage by Bis(imino)pyridine Iron Compounds : Catalyst Deactivation Pathways and Observation of Acyl C-O Bond Cleavage in Esters

    NARCIS (Netherlands)

    Trovitch, Ryan J.; Lobkovsky, Emil; Bouwkamp, Marco W.; Chirik, Paul J.

    2008-01-01

    Investigations into the substrate scope of bis(imino)pyridine iron-catalyzed hydrogenation and [2 pi + 2 pi]. diene cyclization reactions identified C-O bond cleavage as a principal deactivation pathway. Addition of diallyl or allyl ethyl ether to the bis(imino)pyridine iron dinitrogen complex, ((iP

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

    Science.gov (United States)

    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. PMID:27434380

  14. Metal Nanoparticles Catalyzed Selective Carbon-Carbon Bond Activation in the Liquid Phase.

    Science.gov (United States)

    Ye, Rong; Yuan, Bing; Zhao, Jie; Ralston, Walter T; Wu, Chung-Yeh; Unel Barin, Ebru; Toste, F Dean; Somorjai, Gabor A

    2016-07-13

    Understanding the C-C bond activation mechanism is essential for developing the selective production of hydrocarbons in the petroleum industry and for selective polymer decomposition. In this work, ring-opening reactions of cyclopropane derivatives under hydrogen catalyzed by metal nanoparticles (NPs) in the liquid phase were studied. 40-atom rhodium (Rh) NPs, encapsulated by dendrimer molecules and supported in mesoporous silica, catalyzed the ring opening of cyclopropylbenzene at room temperature under hydrogen in benzene, and the turnover frequency (TOF) was higher than other metals or the Rh homogeneous catalyst counterparts. Comparison of reactants with various substitution groups showed that electron donation on the three-membered ring boosted the TOF of ring opening. The linear products formed with 100% selectivity for ring opening of all reactants catalyzed by the Rh NP. Surface Rh(0) acted as the active site in the NP. The capping agent played an important role in the ring-opening reaction kinetics. Larger particle size tended to show higher TOF and smaller reaction activation energy for Rh NPs encapsulated in either dendrimer or poly(vinylpyrrolidone). The generation/size of dendrimer and surface group also affected the reaction rate and activation energy. PMID:27322570

  15. Cleavage enhancement of specific chemical bonds in DNA-Cisplatin complexes induced by X-rays

    International Nuclear Information System (INIS)

    The chemical bond transformation of cisplatin-DNA complexes can be probed efficiently by XPS which provides a concomitant X-ray irradiation source as well. The presence to Pt could considerably increase formation of the SE induced by X-ray and that the further interaction of these LEE with DNA leads to the enhancement of bond cleavages.

  16. Study of the damaging mechanisms of a carbon - carbon composite bonded to copper under thermomechanical loading; Etude des mecanismes d'endommagement d'un assemblage cuivre / composite carbone - carbone sous chargement thermomecanique

    Energy Technology Data Exchange (ETDEWEB)

    Moncel, L

    1999-06-15

    The purpose of this work is to understand and to identify the damaging mechanisms of Carbon-Carbon composite bonded to copper under thermomechanical loading. The study of the composite allowed the development of non-linear models. These ones have been introduced in the finite elements analysis code named CASTEM 2000. They have been validated according to a correlation between simulation and mechanical tests on multi-material samples. These tests have also permitted us to better understand the behaviour of the bonding between composite and copper (damaging and fracture modes for different temperatures) under shear and tensile loadings. The damaging mechanisms of the bond under thermomechanical loading have been studied and identified according to microscopic observations on mock-ups which have sustained thermal cycling tests: some cracks appear in the composite, near the bond between the composite and the copper. The correlation between numerical and experimental results have been improved because of the reliability of the composite modelization, the use of residual stresses and the results of the bond mechanical characterisation. (author)

  17. Reductive cleavage of dichalcogenide bonds. Communication 3. Selectivity of electron exchange in diaryldichalcogenide-bispyridinium systems

    International Nuclear Information System (INIS)

    The kinetics of reductive cleavage of the dichalcogenide bond in dimeric Schiff's bases ArEEAr (E = S, Te) induced by indirect electron transfer by the in situ generated bridged bispyridinium radical cations and biradicals was studied by cyclic voltammetry. It is found that the dependence between the apparent rate constants of intermolecular electron transfer and the electron-withdrawing properties of diaryldichalcogenides is violated. The mechanisms of homogeneous (chemical) and heterogeneous (electrochemical) reductive cleavage of diaryldichalcogenides are discussed

  18. Metabolic Engineering to Develop a Pathway for the Selective Cleavage of Carbon-Nitrogen Bonds

    Energy Technology Data Exchange (ETDEWEB)

    John J. Kilbane II

    2005-10-01

    The objective of the project is to develop a biochemical pathway for the selective cleavage of C-N bonds in molecules found in petroleum. Specifically a novel biochemical pathway will be developed for the selective cleavage of C-N bonds in carbazole. The cleavage of the first C-N bond in carbazole is accomplished by the enzyme carbazole dioxygenase, that catalyzes the conversion of carbazole to 2-aminobiphenyl-2,3-diol. The genes encoding carbazole dioxygenase were cloned from Sphingomonas sp. GTIN11 and from Pseudomonas resinovorans CA10. The selective cleavage of the second C-N bond has been challenging, and efforts to overcome that challenge have been the focus of recent research in this project. Enrichment culture experiments succeeded in isolating bacterial cultures that can metabolize 2-aminobiphenyl, but no enzyme capable of selectively cleaving the C-N bond in 2-aminobiphenyl has been identified. Aniline is very similar to the structure of 2-aminobiphenyl and aniline dioxygenase catalyzes the conversion of aniline to catechol and ammonia. For the remainder of the project the emphasis of research will be to simultaneously express the genes for carbazole dioxygenase and for aniline dioxygenase in the same bacterial host and then to select for derivative cultures capable of using carbazole as the sole source of nitrogen.

  19. Facile P-C/C-H Bond Cleavage Reactivity of Nickel Bis(diphosphine) Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shaoguang; Li, Haixia; Appel, Aaron M.; Hall, Michael B.; Bullock, R. Morris

    2016-07-04

    Unusual cleavage of P-C and C-H bonds of the P2N2 ligand in heteroleptic [Ni(P2N2)(diphosphine)]2+ complexes results in the formation of an iminium formyl nickelate featuring a C,P,P-tridentate coordination mode.

  20. Synthesis of sulfonamides via copper-catalyzed oxidative C-N bond cleavage of tertiary amines.

    Science.gov (United States)

    Ji, Jing; Liu, Zhengyi; Liu, Ping; Sun, Peipei

    2016-08-01

    A copper-catalyzed coupling reaction of sulfonyl chlorides with tertiary amines via the oxidative C-N bond cleavage of tertiary amines was developed. Sulfonamides were synthesized using this strategy in moderate to good yields. The reaction was applicable to various tertiary amines, as well as sulfonyl chlorides. PMID:27356858

  1. Thermodynamic Strategies for C-O Bond Formation and Cleavage via Tandem Catalysis.

    Science.gov (United States)

    Lohr, Tracy L; Li, Zhi; Marks, Tobin J

    2016-05-17

    To reduce global reliance on fossil fuels, new renewable sources of energy that can be used with the current infrastructure are required. Biomass represents a major source of renewable carbon based fuel; however, the high oxygen content (∼40%) limits its use as a conventional fuel. To utilize biomass as an energy source, not only with current infrastructure, but for maximum energy return, the oxygen content must be reduced. One method to achieve this is to develop selective catalytic methods to cleave C-O bonds commonly found in biomass (aliphatic and aromatic ethers and esters) for the eventual removal of oxygen in the form of volatile H2O or carboxylic acids. Once selective methods of C-O cleavage are understood and perfected, application to processing real biomass feedstocks such as lignin can be undertaken. This Laboratory previously reported that recyclable "green" lanthanide triflates are excellent catalysts for C-O bond-forming hydroalkoxylation reactions. Based on the virtues of microscopic reversibility, the same lanthanide triflate catalyst should catalyze the reverse C-O cleavage process, retrohydroalkoxylation, to yield an alcohol and an alkene. However, ether C-O bond-forming (retrohydroalkoxylation) to form an alcohol and alkene is endothermic. Guided by quantum chemical analysis, our strategy is to couple endothermic, in tandem, ether C-O bond cleavage with exothermic alkene hydrogenation, thereby leveraging the combined catalytic cycles thermodynamically to form an overall energetically favorable C-O cleavage reaction. This Account reviews recent developments on thermodynamically leveraged tandem catalysis for ether and more recently, ester C-O bond cleavage undertaken at Northwestern University. First, the fundamentals of lanthanide-catalyzed hydroelementation are reviewed, with particular focus on ether C-O bond formation (hydroalkoxylation). Next, the reverse C-O cleavage/retrohydroalkoxylation processes enabled by tandem catalysis are

  2. Thermodynamic Strategies for C-O Bond Formation and Cleavage via Tandem Catalysis.

    Science.gov (United States)

    Lohr, Tracy L; Li, Zhi; Marks, Tobin J

    2016-05-17

    To reduce global reliance on fossil fuels, new renewable sources of energy that can be used with the current infrastructure are required. Biomass represents a major source of renewable carbon based fuel; however, the high oxygen content (∼40%) limits its use as a conventional fuel. To utilize biomass as an energy source, not only with current infrastructure, but for maximum energy return, the oxygen content must be reduced. One method to achieve this is to develop selective catalytic methods to cleave C-O bonds commonly found in biomass (aliphatic and aromatic ethers and esters) for the eventual removal of oxygen in the form of volatile H2O or carboxylic acids. Once selective methods of C-O cleavage are understood and perfected, application to processing real biomass feedstocks such as lignin can be undertaken. This Laboratory previously reported that recyclable "green" lanthanide triflates are excellent catalysts for C-O bond-forming hydroalkoxylation reactions. Based on the virtues of microscopic reversibility, the same lanthanide triflate catalyst should catalyze the reverse C-O cleavage process, retrohydroalkoxylation, to yield an alcohol and an alkene. However, ether C-O bond-forming (retrohydroalkoxylation) to form an alcohol and alkene is endothermic. Guided by quantum chemical analysis, our strategy is to couple endothermic, in tandem, ether C-O bond cleavage with exothermic alkene hydrogenation, thereby leveraging the combined catalytic cycles thermodynamically to form an overall energetically favorable C-O cleavage reaction. This Account reviews recent developments on thermodynamically leveraged tandem catalysis for ether and more recently, ester C-O bond cleavage undertaken at Northwestern University. First, the fundamentals of lanthanide-catalyzed hydroelementation are reviewed, with particular focus on ether C-O bond formation (hydroalkoxylation). Next, the reverse C-O cleavage/retrohydroalkoxylation processes enabled by tandem catalysis are

  3. Achieving C-N bond cleavage in dinuclear metal cyanide complexes.

    Science.gov (United States)

    Cavigliasso, Germán; Christian, Gemma J; Stranger, Robert; Yates, Brian F

    2011-07-28

    Cleavage of cyanide is more difficult to achieve compared to dinitrogen and carbon monoxide, even though these species contain triple bonds of greater strength. In this work, we have used computational methods to investigate thermodynamic and mechanistic aspects of the C-N bond cleavage process in [L(3)M-CN-M'L(3)] systems consisting of a central cyanide unit bound in an end-on fashion to two terminal metal tris-amide complexes. In these systems, [M] is a d(3) transition metal from the 3d, 4d, 5d, or 6d series and groups 4 through 7, and [L] is either [NH(2)], [NMe(2)], [N(i)PrPh], or [N(t)BuAr]. A comparison of various models for the experimentally relevant [L(3)Mo-CN-MoL(3)] system has shown that while the C-N cleavage step appears to be an energetically favourable process, a large barrier exists for the dissociation of [L(3)Mo-CN-MoL(3)]((-)) into [L(3)Mo-C]((-)) and [N-MoL(3)], which possibly explains why C-N bond scission is not observed experimentally. The general structural, bonding, and thermochemical trends across the transition metal series investigated, indicate that the systems exhibiting the greatest degree of C-N activation, and most favourable energetics for C-N cleavage, also possess the most favourable electronic properties, namely, a close match between the relevant π-like orbitals on the metal-based and cyanide fragments. The negative charge on the cyanide fragment leads to significant destabilization of the π* level which needs to be populated through back-donation from the metal centres in order for C-N bond scission to be achieved. Therefore, metal-based systems with high-lying d(π) orbitals are best suited to C-N cleavage. In terms of chemical periodicity, these systems can be identified as the heavier members within a group and the earlier members within a period. As a consequence, Mo complexes are not well suited to cleaving the C-N bond, whereas the Ta analogues are the most favourable systems and should, in principle, be capable of

  4. Reaction Pathways and Energetics of Etheric C–O Bond Cleavage Catalyzed by Lanthanide Triflates

    Energy Technology Data Exchange (ETDEWEB)

    Assary, Rajeev S.; Atesin, Abdurrahman C.; Li, Zhi; Curtiss, Larry A.; Marks, Tobin J.

    2013-09-06

    Efficient and selective cleavage of etheric C-O bonds is crucial for converting biomass into platform chemicals and liquid transportation fuels. In this contribution, computational methods at the DFT B3LYP level of theory are employed to understand the efficacy of lanthanide triflate catalysts (Ln(OTf)3, Ln = La, Ce, Sm, Gd, Yb, and Lu) in cleaving etheric C-O bonds. In agreement with experiment, the calculations indicate that the reaction pathway for C-O cleavage occurs via a C-H → O-H proton transfer in concert with weakening of the C-O bond of the coordinated ether substrate to ultimately yield a coordinated alkenol. The activation energy for this process falls as the lanthanide ionic radius decreases, reflecting enhanced metal ion electrophilicity. Details of the reaction mechanism for Yb(OTf)3-catalyzed ring opening are explored in depth, and for 1-methyl-d3-butyl phenyl ether, the computed primary kinetic isotope effect of 2.4 is in excellent agreement with experiment (2.7), confirming that etheric ring-opening pathway involves proton transfer from the methyl group alpha to the etheric oxygen atom, which is activated by the electrophilic lanthanide ion. Calculations of the catalytic pathway using eight different ether substrates indicate that the more rapid cleavage of acyclic versus cyclic ethers is largely due to entropic effects, with the former C-O bond scission processes increasing the degrees of freedom/particles as the transition state is approached.

  5. Characterization and Modeling of the Collision Induced Dissociation Patterns of Deprotonated Glycosphingolipids: Cleavage of the Glycosidic Bond

    Science.gov (United States)

    Rožman, Marko

    2016-01-01

    Glycosphingolipid fragmentation behavior was investigated by combining results from analysis of a series of negative ion tandem mass spectra and molecular modeling. Fragmentation patterns extracted from 75 tandem mass spectra of mainly acidic glycosphingolipid species (gangliosides) suggest prominent cleavage of the glycosidic bonds with retention of the glycosidic oxygen atom by the species formed from the reducing end (B and Y ion formation). Dominant product ions arise from dissociation of sialic acids glycosidic bonds whereas product ions resulting from cleavage of other glycosidic bonds are less abundant. Potential energy surfaces and unimolecular reaction rates of several low-energy fragmentation pathways leading to cleavage of glycosidic bonds were estimated in order to explain observed dissociation patterns. Glycosidic bond cleavage in both neutral (unsubstituted glycosyl group) and acidic glycosphingolipids was the outcome of the charge-directed intramolecular nucleophilic substitution (SN2) mechanism. According to the suggested mechanism, the nucleophile in a form of carboxylate or oxyanion attacks the carbon at position one of the sugar ring, simultaneously breaking the glycosidic bond and yielding an epoxide. For gangliosides, unimolecular reaction rates suggest that dominant product ions related to the cleavage of sialic acid glycosidic bonds are formed via direct dissociation channels. On the other hand, low abundant product ions related to the dissociation of other glycosidic bonds are more likely to be the result of sequential dissociation. Although results from this study mainly contribute to the understanding of glycosphingolipid fragmentation chemistry, some mechanistic findings regarding cleavage of the glycosidic bond may be applicable to other glycoconjugates.

  6. Mercury Detoxification by Bacteria: Simulations of Transcription Activation and Mercury-Carbon Bond Cleavage

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Hao-Bo [ORNL; Parks, Jerry M [ORNL; Johs, Alexander [ORNL; Smith, Jeremy C [ORNL

    2011-01-01

    In this chapter, we summarize recent work from our laboratory and provide new perspective on two important aspects of bacterial mercury resistance: the molecular mechanism of transcriptional regulation by MerR, and the enzymatic cleavage of the Hg-C bond in methylmercury by the organomercurial lyase, MerB. Molecular dynamics (MD) simulations of MerR reveal an opening-and-closing dynamics, which may be involved in initiating transcription of mercury resistance genes upon Hg(II) binding. Density functional theory (DFT) calculations on an active-site model of the enzyme reveal how MerB catalyzes the Hg-C bond cleavage using cysteine coordination and acid-base chemistry. These studies provide insight into the detailed mechanisms of microbial gene regulation and defense against mercury toxicity.

  7. Carbon–carbon bond cleavage for Cu-mediated aromatic trifluoromethylations and pentafluoroethylations

    Directory of Open Access Journals (Sweden)

    Tsuyuka Sugiishi

    2015-12-01

    Full Text Available This short review highlights the copper-mediated fluoroalkylation using perfluoroalkylated carboxylic acid derivatives. Carbon–carbon bond cleavage of perfluoroalkylated carboxylic acid derivatives takes place in fluoroalkylation reactions at high temperature (150–200 °C or under basic conditions to generate fluoroalkyl anion sources for the formation of fluoroalkylcopper species. The fluoroalkylation reactions, which proceed through decarboxylation or tetrahedral intermediates, are useful protocols for the synthesis of fluoroalkylated aromatics.

  8. Exploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex.

    Science.gov (United States)

    Desnoyer, Addison N; Friese, Florian W; Chiu, Weiling; Drover, Marcus W; Patrick, Brian O; Love, Jennifer A

    2016-03-14

    Recently, esters have received much attention as transmetalation partners for cross-coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}2(μ-η(2):η(2)-C6H6)] (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η(2)-carbonyl complexes. In contrast, acetylthioesters underwent rapid Cacyl-S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross-coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η(2)-carbonyl complex, phenyl esters were found to predominantly undergo Caryl-O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2-naphthyl acetate was also found to undergo clean Caryl-O bond cleavage, and although stoichiometric cross-coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive.

  9. D-β-aspartyl residue exhibiting uncommon high resistance to spontaneous peptide bond cleavage

    Science.gov (United States)

    Aki, Kenzo; Okamura, Emiko

    2016-02-01

    Although L-amino acids were selected as main constituents of peptides and proteins during chemical evolution, D-aspartyl (Asp) residue is found in a variety of living tissues. In particular, D-β-Asp is thought to be stable than any other Asp isomers, and this could be a reason for gradual accumulation in abnormal proteins and peptides to modify their structures and functions. It is predicted that D-β-Asp shows high resistance to biomolecular reactions. For instance, less reactivity of D-β-Asp is expected to bond cleavage, although such information has not been provided yet. In this work, the spontaneous peptide bond cleavage was compared between Asp isomers, by applying real-time solution-state NMR to eye lens αΑ-crystallin 51-60 fragment, S51LFRTVLD58SG60 and αΒ-crystallin 61-67 analog, F61D62TGLSG67 consisting of L-α- and D-β-Asp 58 and 62, respectively. Kinetic analysis showed how tough the uncommon D-β-Asp residue was against the peptide bond cleavage as compared to natural L-α-Asp. Differences in pKa and conformation between L-α- and D-β-Asp side chains were plausible factors to determine reactivity of Asp isomers. The present study, for the first time, provides a rationale to explain less reactivity of D-β-Asp to allow abnormal accumulation.

  10. Bond cleavages of adenosine 5'-triphosphate induced by monochromatic soft X-rays

    International Nuclear Information System (INIS)

    To investigate which type of bond is likely to be cleaved by soft X-ray exposure to an adenosine 5'-triphosphate (ATP), we observed spectral changes in X-ray absorption near edge structure (XANES) around nitrogen and oxygen K-edge of an ATP film by soft X-ray irradiation. Experiments were performed at a synchrotron soft X-ray beamline at SPring-8, Japan. The XANES spectra around the nitrogen and oxygen .K-edge slightly varied by exposure to 560 eV soft X-rays. These changes are originated from the cleavage of C-N bonds between a sugar and a nucleobase site and of C-O, P-O or O-H bond of sugar and phosphate site. From the comparison between the change in XANES intensity of σ* peak at nitrogen and that at oxygen K-edges, it is inferred that the C-O, P-O or O-H bond of sugar and phosphate is much efficiently cleaved than the C-N of N-glycoside bond by the exposure of 560 eV soft X-ray to ATP film.

  11. Photoinduced C-C bond cleavage via electron-transfer reactions: visible-light-mediated scission of tertiary amines

    Energy Technology Data Exchange (ETDEWEB)

    Lee, L.Y.C.; Ci, X.; Giannotti, C.; Whitten, D.G.

    1986-01-08

    This paper reports the electron-transfer photochemistry of some substituted tertiary amines that contain potentially labile C-C bonds adjacent to the amine. Results are presented which indicate that photoinduced electron transfer can lead to reactions in which the net process involves use of visible light to mediate selective cleavage of C-C bonds to produce radicals. 34 references.

  12. METABOLIC ENGINEERING TO DEVELOP A PATHWAY FOR THE SELECTIVE CLEAVAGE OF CARBON-NITROGEN BONDS

    Energy Technology Data Exchange (ETDEWEB)

    John J. Kilbane II

    2004-10-01

    The objective of the project is to develop biochemical pathways for the selective cleavage of C-N bonds in molecules found in petroleum. The initial phase of the project was focused on the isolation or development of an enzyme capable of cleaving the C-N bond in aromatic amides, specifically 2-aminobiphenyl. The objective of the second phase of the research will be to construct a biochemical pathway for the selective removal of nitrogen from carbazole by combining the carA genes from Sphingomonas sp. GTIN11 with the gene(s) encoding an appropriate deaminase. The objective of the final phase of the project will be to develop derivative C-N bond cleaving enzymes that have broader substrate ranges and to demonstrate the use of such strains to selectively remove nitrogen from petroleum. During the first year of the project (October, 2002-September, 2003) enrichment culture experiments resulted in the isolation of microbial cultures that utilize aromatic amides as sole nitrogen sources, several amidase genes were cloned and were included in directed evolution experiments to obtain derivatives that can cleave C-N bonds in aromatic amides, and the carA genes from Sphingomonas sp. GTIN11, and Pseudomonas resinovorans CA10 were cloned in vectors capable of replicating in Escherichia coli. During the second year of the project (October, 2003-September, 2004) enrichment culture experiments succeeded in isolating a mixed bacterial culture that can utilize 2-aminobiphenyl as a sole nitrogen source, directed evolution experiments were focused on the aniline dioxygenase enzyme that is capable of deaminating aniline, and expression vectors were constructed to enable the expression of genes encoding C-N bond cleaving enzymes in Rhodococcus hosts. The construction of a new metabolic pathway to selectively remove nitrogen from carbazole and other molecules typically found in petroleum should lead to the development of a process to improve oil refinery efficiency by reducing the

  13. CO bond cleavage on supported nano-gold during low temperature oxidation.

    Science.gov (United States)

    Carley, Albert F; Morgan, David J; Song, Nianxue; Roberts, M Wyn; Taylor, Stuart H; Bartley, Jonathan K; Willock, David J; Howard, Kara L; Hutchings, Graham J

    2011-02-21

    The oxidation of CO by Au/Fe(2)O(3) and Au/ZnO catalysts is compared in the very early stages of the reaction using a temporal analysis of products (TAP) reactor. For Au/Fe(2)O(3) pre-dosing the catalyst with (18)O labelled water gives an unexpected evolution order for the labelled CO(2) product with the C(18)O(2) emerging first, whereas no temporal differentiation is found for Au/ZnO. High pressure XPS experiments are then used to show that CO bond cleavage does occur for model catalysts consisting of Au particles deposited on iron oxide films but not when deposited on ZnO films. DFT calculations, show that this observation requires carbon monoxide to dissociate in such a way that cleavage of the CO bond occurs along with dynamically co-adsorbed oxygen so that the overall process of Au oxidation and CO dissociation is energetically favourable. Our results show that for Au/Fe(2)O(3) there is a pathway for CO oxidation that involves atomic C and O surface species which operates along side the bicarbonate mechanism that is widely discussed in the literature. However, this minor pathway is absent for Au/ZnO. PMID:21152570

  14. Cleavage of thymine N3-H bonds by low-energy electrons attached to base π* orbitals

    International Nuclear Information System (INIS)

    In this work, we extend our earlier studies on single strand break (SSB) formation in DNA to consider the possibility of cleaving a thymine N3-H bond to generate a nitrogen-centered anion and a hydrogen radical which might proceed to induce further bond cleavages. In earlier studies, we considered SSBs induced by low-energy electrons that attach to DNA bases' π* orbitals or to phosphate P=O π* orbitals to cleave sugar-phosphate C-O bonds or base-sugar N1-C bonds. We also studied the effects of base π-stacking on the rates of such bond cleavages. To date, our results suggest that sugar-phosphate C-O bonds have the lowest barriers to cleavage, that attachment of electrons with energies below 2 eV most likely occurs at the base π* orbitals, that electrons with energy above 2 eV can also attach to phosphate P=O π* orbitals, and that base π stacking has a modest but slowing effect on the rates of SSB formation. However, we had not yet examined the possibility that base N3-H bonds could rupture subsequent to base π* orbital capture. In the present work, the latter possibility is considered and it is found that the barrier to cleavage of the N3-H bond in thymine is considerably higher than for cleaving sugar-phosphate C-O bonds, so our prediction that SSB formation is dominated by C-O bond cleavage remains intact

  15. METABOLIC ENGINEERING TO DEVELOP A PATHWAY FOR THE SELECTIVE CLEAVAGE OF CARBON-NITROGEN BONDS

    Energy Technology Data Exchange (ETDEWEB)

    John J. Kilbane III

    2003-12-01

    The objective of the project is to develop biochemical pathways for the selective cleavage of C-N bonds in molecules found in petroleum. The initial phase of the project will focus on the isolation or development of an enzyme capable of cleaving the C-N bond in aromatic amides, specifically 2-aminobiphenyl. The objective of the second phase of the research will be to construct a biochemical pathway for the selective removal of nitrogen from carbazole by combining the carA genes from Sphingomonas sp. GTIN11 with the gene(s) encoding an appropriate amidase. The objective of the final phase of the project will be to develop derivative CN bond cleaving enzymes that have broader substrate ranges and to demonstrate the use of such strains to selectively remove nitrogen from petroleum. The project is on schedule and no major difficulties have been encountered. During the first year of the project (October, 2002-September, 2003) enrichment culture experiments have resulted in the isolation of promising cultures that may be capable of cleaving C-N bonds in aromatic amides, several amidase genes have been cloned and are currently undergoing directed evolution to obtain derivatives that can cleave C-N bonds in aromatic amides, and the carA genes from Sphingomonas sp. GTIN11, and Pseudomonas resinovorans CA10 were cloned in vectors capable of replicating in Escherichia coli. Future research will address expression of these genes in Rhodococcus erythropolis. Enrichment culture experiments and directed evolution experiments continue to be a main focus of research activity and further work is required to obtain an appropriate amidase that will selectively cleave C-N bonds in aromatic substrates. Once an appropriate amidase gene is obtained it must be combined with genes encoding an enzyme capable of converting carbazole to 2'aminobiphenyl-2,3-diol: specifically carA genes. The carA genes from two sources have been cloned and are ready for construction of C-N bond cleavage

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

    Energy Technology Data Exchange (ETDEWEB)

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

    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. The solvent effect on the electrocatalytic cleavage of carbon-halogen bonds on Ag and Au

    International Nuclear Information System (INIS)

    In recent years it has been shown in detail how the electrocatalytic cleavage of carbon-halogen bonds is modulated by (a) the stepwise or concerted nature of the dissociative electron-transfer mechanism, which is influenced by the nature of the electrode surface, the type of halogen atom and the molecular structure of RX as a whole, and (b) the double-layer structure (as a function of the nature and bulkiness of the supporting electrolyte ions). In order to both complete and support the interpretative scheme thus developed, this work is focused on the solvent role. When one compares aprotic with protic organic solvents after appropriate intersolvental normalization, interesting peculiarities emerge, especially concerning protic media. Solvent proticity deeply affects both the reaction mechanism (on both non-catalytic and catalytic electrodes) and the extent of the catalytic effects. These items are discussed on the basis of a complete investigation carried out with a carefully controlled experimental protocol on two chloride and bromide couples, one aromatic and one aliphatic, representative of stepwise and concerted mechanisms, respectively, in four aprotic and four protic solvents, on both non−catalytic GC and catalytic Ag and Au electrodes. The results are discussed in the framework of a recently developed interpretative scheme of the carbon-halogen cleavage mechanism

  18. ATP-Dependent C–F Bond Cleavage Allows the Complete Degradation of 4-Fluoroaromatics without Oxygen

    Science.gov (United States)

    Tiedt, Oliver; Mergelsberg, Mario; Boll, Kerstin; Müller, Michael; Adrian, Lorenz; Jehmlich, Nico; von Bergen, Martin

    2016-01-01

    ABSTRACT Complete biodegradation of the abundant and persistent fluoroaromatics requires enzymatic cleavage of an arylic C–F bond, probably the most stable single bond of a biodegradable organic molecule. While in aerobic microorganisms defluorination of fluoroaromatics is initiated by oxygenases, arylic C–F bond cleavage has never been observed in the absence of oxygen. Here, an oxygen-independent enzymatic aryl fluoride bond cleavage is described during the complete degradation of 4-fluorobenzoate or 4-fluorotoluene to CO2 and HF in the denitrifying Thauera aromatica: the ATP-dependent defluorination of 4-fluorobenzoyl-coenzyme A (4-F-BzCoA) to benzoyl-coenzyme A (BzCoA) and HF, catalyzed by class I BzCoA reductase (BCR). Adaptation to growth with the fluoroaromatics was accomplished by the downregulation of a promiscuous benzoate-CoA ligase and the concomitant upregulation of 4-F-BzCoA-defluorinating/dearomatizing BCR on the transcriptional level. We propose an unprecedented mechanism for reductive arylic C–F bond cleavage via a Birch reduction-like mechanism resulting in a formal nucleophilic aromatic substitution. In the proposed anionic 4-fluorodienoyl-CoA transition state, fluoride elimination to BzCoA is favored over protonation to a fluorinated cyclic dienoyl-CoA. PMID:27507824

  19. Efficient Synthesis of Functionalized Benzimidazoles and Perimidines: Ytterbium Chloride Catalyzed CmC Bond Cleavage%Efficient Synthesis of Functionalized Benzimidazoles and Perimidines: Ytterbium Chloride Catalyzed CmC Bond Cleavage

    Institute of Scientific and Technical Information of China (English)

    Cai, Lijian; Ji, Xiaofeng; Yao, Zhigang; Xu, Fan; Shen, Qi

    2011-01-01

    An efficient method is developed for the synthesis of functionalized benzimidazoles and perimidines by the condensation of aryl diamines with β-carbonyl compounds catalyzed by ytterbium chloride. The reactions give good yields under mild conditions. A mechanism involving a lanthanide activated C--C bond cleavage is proposed.

  20. Controllable synthesis of silver and silver sulfide nanocrystals via selective cleavage of chemical bonds

    International Nuclear Information System (INIS)

    A one-step colloidal process has been adopted to prepare silver (Ag) and silver sulfide (Ag2S) nanocrystals, thus avoiding presynthesis of an organometallic precursor and the injection of a toxic phosphine agent. During the reaction, a layered intermediate compound is first formed, which then acts as a precursor, decomposing into the nanocrystals. The composition of the as-obtained products can be controlled by selective cleavage of S–C bonds or Ag–S bonds. Pure Ag2S nanocrystals can be obtained by directly heating silver acetate (Ag(OAc)) and n-dodecanethiol (DDT) at 200 ° C without any surfactant, and pure Ag nanocrystals can be synthesized successfully if the reaction temperature is reduced to 190 ° C and the amount of DDT is decreased to 1 ml in the presence of a non-coordinating organic solvent (1-octadecene, ODE). Otherwise, the mixture of Ag and Ag2S is obtained by directly heating Ag(OAc) in DDT by increasing the reaction temperature or in a mixture of DDT and ODE at 200 ° C. The formation mechanism has been discussed in detail in terms of selective S–C and Ag–S bond dissociation due to the nucleophilic attack of DDT and the lower bonding energy of Ag–S. Interestingly, some products can easily self-assemble into two- or three-dimensional (2D or 3D) highly ordered superlattice structures on a copper grid without any additional steps. The excess DDT plays a key role in the superlattice structure due to the bundling and interdigitation of the thiolate molecules adsorbed on the as-obtained nanocrystals. (paper)

  1. Dihydrogen bond interactions as a result of H2 cleavage at Cu, Ag and Au centres.

    Science.gov (United States)

    Grabowski, Sławomir J; Ruipérez, Fernando

    2016-05-14

    A quantum chemical study of H2 activation at fluorides of coinage metals, MF (M = Cu, Ag and Au), and its splitting was performed. The following reaction path was analyzed: FMH2→ FHHM → HMFH, where both the molecular complexes and the corresponding transition states have been characterized at the CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVQZ level of theory. Further single-point CASSCF/CASPT2 calculations, including spin-orbit coupling effects, were also performed to analyze the role of non-dynamic correlation. The scalar relativistic effects are included via aug-cc-pVQZ-PP basis sets used for the metals. The dihydrogen-bonded copper (FHHCu) and silver (FHHAg) complexes are observed as a result of H2 cleavage, while the corresponding FHHAu gold complex is not found but the HAuHF arrangement is observed, instead. The energetic and geometrical parameters of the complexes have been analyzed and both the Quantum Theory of Atoms in Molecules approach and the Natural Bond Orbitals method were additionally applied to analyze the intermolecular interactions. PMID:27101741

  2. Transition metal-catalyzed oxidative double bond cleavage of simple and bio-derived alkenes and unsaturated fatty acids

    NARCIS (Netherlands)

    Spannring, Peter; Bruijnincx, Pieter C. A.; Weckhuysen, Bert. M.; Klein Gebbink, Bert

    2014-01-01

    The oxidative cleavage of the C=C double bond in unsaturated fatty acids into aldehydes or carboxylic acids is a reaction of current interest in biomass valorization. The products of this reaction, which is currently being performed on an industrial scale by means of ozonolysis, can be applied for t

  3. Identification and cleavage of breakable single bonds by selective oxidation, reduction, and hydrolysis. Quarterly report No. 1, October 1-December 31, 1978

    Energy Technology Data Exchange (ETDEWEB)

    Buchanan, D.H.; Mayo, F.R.

    1979-01-25

    Bituminous coal is assumed to consist mostly of an aggregate of condensed aromatic and aliphatic rings, connected and made insoluble (but swellable) by crosslinks containing only single bonds. These connecting links consist mainly, possibly entirely, of combinations of carbon-carbon single bonds and ether (possibly ester) groups. It is at these crosslinks that the most extensive cuts can be made in the coal structure (to make it soluble or liquid) under the mildest conditions and with the least loss in fuel values. The objective of this project is to determine the proportion of the various kinds of connecting links and how they can best be broken; in other words, to determine the structure of coal with emphasis on the crosslinks. At present, our attention is directed to five kinds of connecting links: single (Ar-CH/sub 2/-Ar) and multiple methylene groups (Ar-(CH/sub 2/)/sub 2/-Ar) and three kinds of ethers, Ar-O-Ar, Ar-O-R, and R-O-R (Ar represents an aromatic aggregate and R is attached to O through at least one aliphatic carbon.) The work described in this quarterly report deals mainly with the oxidation of pyridine-extracted coal by O/sub 2/ and the cleavage by sodium in liquid ammonia of aromatic ether linkages in a pyridine-soluble, toluene-insoluble fraction of coal extract. Products from the NaOCl oxidation of pyridine-extracted coal were also studied by nuclear magnetic resonance (NMR) and acid-base titrations. 7 references, 2 figures, 6 tables.

  4. 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

    Energy Technology Data Exchange (ETDEWEB)

    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

  5. Bond cleavage reactions in the tripeptide tri-alanine upon free electron capture

    International Nuclear Information System (INIS)

    In the present study we performed dissociative electron attachment (DEA) measurements with the tripeptide tri-alanine, C9H17N3O4, utilizing a crossed electron-molecular beam experiment with high electron energy resolution (about 100 meV). Anion efficiency yields as a function of the incident electron energy are obtained for the most abundant anions up to electron energies of ∼ eV. Quantum chemical calculations are performed to determine the thermochemical thresholds for the anions observed in the measurements. There is no evidence of a molecular anion with lifetime of mass spectrometric timescales. The dehydrogenated closed shell anion (M-H)- is one of the fragment anions observed for which the calculations show that H-loss is energetically possible from carboxyl, as well as amide groups. In contrast to the dipeptide di-alanine and monomer alanine the cleavage of the N-Cα bond in the peptide chain is already possible by attachment of electrons at ∼ 0 eV. (authors)

  6. Unexpected carbon-oxygen bond cleavage of THF promoted by guanidinate titanium complex/lithium diisopropylamide: Synthesis and crystal structure

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong; WANG Mei; YAO Yingming; SHEN Qi

    2005-01-01

    An unexpected carbon-oxygen bond cleavage of THF (THF = tetrahydrofuran) promoted by guanidinate titanium complex was described. Guanidinate lithium [Pr2iNC(NCy)2]Li (Cy = cyclohexyl) formed in situ reacted with TiCl4(THF)2 in a 2:1 molar ratio to produce the guanidinate titanium chloride [Pr2iNC(NCy)2]2TiCl2 (1) in good yield. The reaction of [Pr2iNC(NCy)2]2TiCl2 with lithium diisopropylamide in THF afforded an unexpected [Pr2iNC(NCy)2]2Ti(OBun)2 (2), which was formed by the cleavage of carbon-oxygen bond of THF. Complexes 1 and 2 were fully characterized by elemental analysis, NMR and IR spectroscopies, and X-ray crystal structure determination for complex 2.

  7. Effect of trastuzumab interchain disulfide bond cleavage on Fcγ receptor binding and antibody-dependent tumour cell phagocytosis.

    Science.gov (United States)

    Suzuki, Mami; Yamanoi, Ayaka; Machino, Yusuke; Ootsubo, Michiko; Izawa, Ken-ichi; Kohroki, Junya; Masuho, Yasuhiko

    2016-01-01

    The Fc domain of human IgG1 binds to Fcγ receptors (FcγRs) to induce effector functions such as phagocytosis. There are four interchain disulfide bonds between the H and L chains. In this study, the disulfide bonds within the IgG1 trastuzumab (TRA), which is specific for HER2, were cleaved by mild S-sulfonation or by mild reduction followed by S-alkylation with three different reagents. The cleavage did not change the binding activities of TRA to HER2-bearing SK-BR-3 cells. The binding activities of TRA to FcγRIIA and FcγRIIB were greatly enhanced by modification with mild reduction and S-alkylation with ICH2CONH2 or N-(4-aminophenyl) maleimide, while the binding activities of TRA to FcγRI and FcγRIIIA were decreased by any of the four modifications. However, the interchain disulfide bond cleavage by the different modifications did not change the antibody-dependent cell-mediated phagocytosis (ADCP) of SK-BR-3 cells by activated THP-1 cells. The order of FcγR expression levels on the THP-1 cells was FcγRII > FcγRI > FcγRIII and ADCP was inhibited by blocking antibodies against FcγRI and FcγRII. These results imply that the effect of the interchain disulfide bond cleavage on FcγRs binding and ADCP is dependent on modifications of the cysteine residues and the FcγR isotypes. PMID:26254483

  8. Selective Oxidative Decarbonylative Cleavage of Unstrained C(sp(3))-C(sp(2)) Bond: Synthesis of Substituted Benzoxazinones.

    Science.gov (United States)

    Verma, Ajay; Kumar, Sangit

    2016-09-01

    A transition metal (TM)-free practical synthesis of biologically relevant benzoxazinones has been established via a selective oxidative decarbonylative cleavage of an unstrained C(sp(3))-C(sp(2)) bond employing iodine, sodium bicarbonate, and (t)butyl hydroperoxide in DMSO at 95 °C. Control experiments and Density Functional Theory (DFT) calculations suggest that the reaction involves a [1,5]H shift and extrusion of CO gas as the key steps. The extrusion of CO has also been established using PMA-PdCl2. PMID:27549986

  9. Iron catalyzed oxidation chemistry : from C-H bond activation to DNA cleavag

    NARCIS (Netherlands)

    Berg, Tieme Adriaan van den

    2008-01-01

    The synthetic iron complex Fe(N4Py) can be employed as a catalyst in the aerobic oxidation of DNA. The resulting oxidized DNA strand is rather unstable and results in cleavage of the DNA strand into two pieces. As for now, it was only possible with Fe(N4Py) or other synthetic iron complexes as catal

  10. Anaerobic DNA cleavage in red light by dicopper(II) complexes on disulphide bond activation

    Indian Academy of Sciences (India)

    Debojyoti Lahiri; Ritankar Majumdar; Ashis K Patra; Akhil R Chakravarty

    2010-05-01

    Binuclear complexes [Cu(-RSSR)]2 (1) and [M2(-PDS)(H2O)]2 (M = Cu(II), 2; Fe(II), 3), where H2RSSR is a reduced Schiff base derived from 2-(thioethyl)salicylaldimine having a disulphide moiety and H2PDS is derived from dimerization of D-penicillamine, have been prepared, structurally characterized, and their photo-induced DNA cleavage activity studied. The crystal structure of 1 shows the complex as a discrete binuclear species with each metal in a CuN2O2 square-planar geometry (Cu…Cu, 6.420 Å). The tetradentate RSSR2- acts as a bridging ligand. The sulphur atoms in the disulphide unit do not interact with the metal ions. Complexes 1-3 do not show any DNA cleavage activity in darkness. The copper(II) complexes exhibit chemical nuclease activity in the presence of 3-mercaptopropionic acid. Cleavage of supercoiled DNA has been observed in UV-A light of 365 nm for 1 and red light of 647.1 nm for both 1 and 2 in air. Mechanistic data reveal the involvement of the disulphide unit as photosensitizer generating hydroxyl radicals ($^{\\bullet}$OH) as the reactive species. Photo-induced DNA cleavage in red light seems to involve sulphide radicals in a type-I process and hydroxyl radicals. The dicopper(II) complexes show significant anaerobic photo-induced DNA cleavage activity in red light under argon following type-I pathway without involving any reactive oxygen species.

  11. Iron catalyzed oxidation chemistry: from C-H bond activation to DNA cleavag

    OpenAIRE

    Berg, Tieme Adriaan van den

    2008-01-01

    The synthetic iron complex Fe(N4Py) can be employed as a catalyst in the aerobic oxidation of DNA. The resulting oxidized DNA strand is rather unstable and results in cleavage of the DNA strand into two pieces. As for now, it was only possible with Fe(N4Py) or other synthetic iron complexes as catalyst to cut only one DNA strand at the same time. The covalent linking of two Fe(N4Py) complexes together results in a new dinuclear complex, which is capable of addressing both DNA stands at the sa...

  12. Investigations on organolead compounds V. Lead---lead bond cleavage reactions of hexaphenyldilead

    NARCIS (Netherlands)

    Willemsens, L.C.; Kerk, G.J.M. van der

    1968-01-01

    It has been shown that a number of nucleophilic and weakly electrophilic reagents (organolithium and organomagnesium compounds, metallic lithium, potassium permanganate, sodium ethoxide, diaryl disulphides, sulphur, ozone, hypochlorous acid and iodine/iodide) selectively cleave the lead---lead bond

  13. Mechanisms of Selective Cleavage of C-O Bonds in Di-aryl Ethers in Aqueous Phase

    Energy Technology Data Exchange (ETDEWEB)

    He, Jiayue; Zhao, Chen; Mei, Donghai; Lercher, Johannes A.

    2014-01-02

    A novel route for cleaving the C-O aryl ether bonds of p-substituted H-, CH3-, and OH- diphenyl ethers has been explored over Ni/SiO2 catalysts at very mild conditions. The C-O bond of diphenyl ether is cleaved by parallel hydrogenolysis and hydrolysis (hydrogenolysis combined with HO* addition) on Ni. The rates as a function of H2 pressure from 0 to 10 MPa indicate that the rate-determining step is the C-O bond cleavage on Ni. H* atoms compete with the organic reactant for adsorption leading to a maximum in the rate with increasing H2 pressure. In contrast to diphenyl ether, hydrogenolysis is the exclusive route for cleaving an ether C-O bond of di-p-tolyl ether to form p-cresol and toluene. 4,4'-dihydroxydiphenyl ether undergoes sequential surface hydrogenolysis, first to phenol and HOC6H4O* (adsorbed), which is then cleaved to phenol (C6H5O* with added H*) and H2O (O* with two added H*) in a second step. Density function theory supports the operation of this pathway. Notably, addition of H* to HOC6H4O* is less favorable than a further hydrogenolytic C-O bond cleavage. The TOFs of three aryl ethers with Ni/SiO2 in water followed the order 4,4'-dihydroxydiphenyl ether (69 h-1) > diphenyl ether (26 h-1) > di-p-tolyl ether (1.3 h-1), in line with the increasing apparent activation energies, ranging from 93 kJ∙mol-1 (4,4'-dihydroxydiphenyl ether) < diphenyl ether (98 kJ∙mol-1) to di-p-tolyl ether (105 kJ∙mol-1). D.M. thanks the support from the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the

  14. Carbon Carbon Composites: An Overview .

    Directory of Open Access Journals (Sweden)

    G. Rohini Devi

    1993-10-01

    Full Text Available Carbon carbon composites are a new class of engineering materials that are ceramic in nature but exhibit brittle to pseudoplastic behaviour. Carbon-carbon is a unique all-carbon composite with carbon fibre embeded in carbon matrix and is known as an inverse composite. Due to their excellent thermo-structural properties, carbon-carbon composites are used in specialised application like re-entry nose-tips, leading edges, rocket nozzles, and aircraft brake discs apart from several industrial and biomedical applications. The multidirectional carbon-carbon product technology is versatile and offers design flexibility. This paper describes the multidirectional preform and carbon-carbon process technology and research and development activities within the country. Carbon-carbon product experience at DRDL has also been discussed. Development of carbon-carbon brake discs process technology using the liquid impregnation process is described. Further the test results on material characterisation, thermal, mechanical and tribological properties are presented.

  15. Enzymatic Cleavage of Glycosidic Bonds: Strategies on How to Set Up and Control a QM/MM Metadynamics Simulation.

    Science.gov (United States)

    Raich, L; Nin-Hill, A; Ardèvol, A; Rovira, C

    2016-01-01

    Carbohydrates play crucial roles in many biological processes, from cell-cell adhesion to chemical signaling. Their complexity and diversity, related to α/β anomeric configuration, ring substituents, and conformational variations, require a diverse set of enzymes for their processing. Among them, glycoside hydrolases (GHs) are responsible for the hydrolysis of one of the strongest bonds in nature: the glycosidic bond. These highly specialized biological catalysts select particular conformations their carbohydrate substrates to enhance catalysis. The evolution of this conformation during the reaction of glycosidic bond cleavage, known as the conformational catalytic itinerary, is of fundamental interest in glycobiology, with impact on inhibitor and drug design. Here we review some of the aspects and the main strategies one needs to take into account when simulating a reaction in a GH enzyme using QM/MM metadynamics. Several specific aspects are highlighted, from the importance of the distortion of the substrate at the Michaelis complex to the variable control during the metadynamics simulation or the analysis of the reaction mechanism and conformational itinerary. The increasing speed of computer power and methodological advances have added a vital tool to the study of GH mechanisms, as shown here and recent reviews. It is hoped that this chapter will serve as a first guide for those attempting to perform a metadynamics simulation of these relevant and fascinating enzymes. PMID:27498638

  16. Ionic S(N)i-Si Nucleophilic Substitution in N-Methylaniline-Induced Si-Si Bond Cleavages of Si2Cl6.

    Science.gov (United States)

    Zhang, Jie; Xie, Ju; Lee, Myong Euy; Zhang, Lin; Zuo, Yujing; Feng, Shengyu

    2016-03-24

    N-Methylaniline-induced Si-Si bond cleavage of Si2Cl6 has been theoretically studied. All calculations were performed by using DFT at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) levels. An ionic SN i-Si nucleophilic substitution mechanism, which is a newly found nucleophilic substitution in silicon-containing compounds, is proposed in the N-methylaniline-induced Si-Si bond cleavage in Si2Cl6. Unlike general S(N)i-Si nucleophilic substitutions that go through a pentacoordinated silicon transition state, ionic nucleophilic substitution goes through a tetracoordinated silicon transition state, in which the Si-Si bond is broken and siliconium ions are formed. Special cleavage of the Si-Si bond is presumably due to the good bonding strength between Si and N atoms, which leads to polarization of the Si-Si bond and eventually to heterolytic cleavage. Calculation results show that, in excess N-methylaniline, the final products of the reaction, including (NMePh)(3-n) SiHCl(n) (n=0-2) and (NMePh)(4-n) SiCl(n) (n=2-3), are the Si-Si cleavage products of Si2Cl6 and the corresponding amination products of the former. The ionic S(N)i-Si nucleophilic substitution mechanism can also be employed to describe the amination of chlorosilane by N-methylaniline. The suggested mechanisms are consistent with experimental data.

  17. Characterization of carbon-sulfur bond cleavage by axenic and mixed cultures of Rhodococcus rhodochrous IGTS8

    Energy Technology Data Exchange (ETDEWEB)

    Kayser, K.J.; Bielaga, B.A.; Jackowski, K.; Oduson, O.; Kilbane, J. II

    1992-12-31

    Growth assays reveal that Rhodococcus rhodochrous IGTS8 can utilize a wide range of organosulfur compounds as the sole source of sulfur. Compounds that are utilized include thiophenes, sulfides, disulfides, mercaptans, sulfoxides, and sulfones. None of the organosulfur compounds tested can serve as a carbon source. A convenient spectrophotometric assay (Gibbs assay) based on the chromogenic reaction of 2,6-dichloroquinone-4-chloroimide with aromatic hydroxyl groups was developed and used in conjunction with GC/MS analysis to examine the kinetics of carbon-sulfur bond cleavage by axenic and mixed cell cultures of Rhodococcus rhodochrous IGTS8. The desulfurization trait is expressed at uniform levels during the mid-exponential phase, reaches a maximum during idiophase, and then declines in stationary-phase cells. Desulfurization rates for dibenzothiophene (DBT) range from 8 to 15 {mu}M of DBT/10{sup 12} cells/hour. Mixtures of genetically marked Rhodococcus rhodochrous IGTS8 and an organisms incapable of cleaning carbon-sulfur bonds in relevant test compounds, Enterobacter cloacae, were prepared in ratios that varied over six orders of magnitude. Growth studies revealed that Enterobacter cloacae was able to gain access to sulfur liberated from organosulfur compounds by IGTS8; however, cell-to-cell contact was required. These data also indicate that the desulfurization activity of IGTS8 cells in mixed cultures may be as much as 200-fold higher than in axenic cultures.

  18. Substituent-controlled selective synthesis of N-acyl 2-aminothiazoles by intramolecular Zwitterion-mediated C-N bond cleavage.

    Science.gov (United States)

    Wang, Yang; Zhao, Fei; Chi, Yue; Zhang, Wen-Xiong; Xi, Zhenfeng

    2014-11-21

    The cleavage of C-N bonds is an interesting and challenging subject in modern organic synthesis. We have achieved the first zwitterion-controlled C-N bond cleavage in the MCR reaction among lithium alkynethiolates, bulky carbodiimides, and acid chlorides to construct N-acyl 2-aminothiazoles. This is a simple, highly efficient, and general method for the preparation of N-acyl 2-aminothiazoles with a broad range of substituents. The selective synthesis of N-acyl 2-aminothiazoles significantly depends on the steric hindrance of carbodiimides. The result is in striking contrast with our previous convergent reaction giving 5-acyl-2-iminothiazolines via 1,5-acyl migration. It is indeed interesting that the slight change of the substituents on the carbodiimides can completely switch the product structure. Experimental and theoretical results demonstrate the reason why the C-N bond cleavage in the present system is prior to the acyl migration. The intramolecular hydrogen relay via unprecedented Hofmann-type elimination is essential for this totally new zwitterion-controlled C-N bond cleavage.

  19. Carbon Carbon Composites: An Overview .

    OpenAIRE

    G. Rohini Devi; K. Rama Rao

    1993-01-01

    Carbon carbon composites are a new class of engineering materials that are ceramic in nature but exhibit brittle to pseudoplastic behaviour. Carbon-carbon is a unique all-carbon composite with carbon fibre embeded in carbon matrix and is known as an inverse composite. Due to their excellent thermo-structural properties, carbon-carbon composites are used in specialised application like re-entry nose-tips, leading edges, rocket nozzles, and aircraft brake discs apart from several indust...

  20. Metal-catalyzed C-C bond cleavage in alkanes: effects of methyl substitution on transition-state structures and stability.

    Science.gov (United States)

    Flaherty, David W; Hibbitts, David D; Iglesia, Enrique

    2014-07-01

    Methyl substituents at C-C bonds influence hydrogenolysis rates and selectivities of acyclic and cyclic C2-C8 alkanes on Ir, Rh, Ru, and Pt catalysts. C-C cleavage transition states form via equilibrated dehydrogenation steps that replace several C-H bonds with C-metal bonds, desorb H atoms (H*) from saturated surfaces, and form λ H2(g) molecules. Activation enthalpies (ΔH(‡)) and entropies (ΔS(‡)) and λ values for (3)C-(x)C cleavage are larger than for (2)C-(2)C or (2)C-(1)C bonds, irrespective of the composition of metal clusters or the cyclic/acyclic structure of the reactants. (3)C-(x)C bonds cleave through α,β,γ- or α,β,γ,δ-bound transition states, as indicated by the agreement between measured activation entropies and those estimated for such structures using statistical mechanics. In contrast, less substituted C-C bonds involve α,β-bound species with each C atom bound to several surface atoms. These α,β configurations weaken C-C bonds through back-donation to antibonding orbitals, but such configurations cannot form with (3)C atoms, which have one C-H bond and thus can form only one C-M bond. (3)C-(x)C cleavage involves attachment of other C atoms, which requires endothermic C-H activation and H* desorption steps that lead to larger ΔH(‡) values but also larger ΔS(‡) values (by forming more H2(g)) than for (2)C-(2)C and (2)C-(1)C bonds, irrespective of alkane size (C2-C8) or cyclic/acyclic structure. These data and their mechanistic interpretation indicate that low temperatures and high H2 pressures favor cleavage of less substituted C-C bonds and form more highly branched products from cyclic and acyclic alkanes. Such interpretations and catalytic consequences of substitution seem also relevant to C-X cleavage (X = S, N, O) in desulfurization, denitrogenation, and deoxygenation reactions.

  1. Amide bond cleavage initiated by coordination with transition metal ions and tuned by an auxiliary ligand.

    Science.gov (United States)

    Yang, Yongpo; Lu, Chunxin; Wang, Hailong; Liu, Xiaoming

    2016-06-21

    The reaction of ligand , N,N-bis(pyridin-2-ylmethyl)acetamide, with five transition metal salts, FeCl3·6H2O, CuCl2·2H2O, Cu(ClO4)2·6H2O, ZnCl2 and K2PtCl4/KI, produced five metal complexes, [(μ-O)(FeClL')(FeCl3)] (), [CuLCl2] (), [CuBPA(ClO4)(CHCN)] ClO4 (), [ZnLCl2] () and [PtLI2] (), where = 1-(2,4,5-tri(pyridin-2-yl)-3-(pyridin-2-ylmethyl)imidazolidin-1-yl)ethanone which formed in situ, and BPA = bis(pyridin-2-ylmethyl)amine. The ligand and complexes were characterized by a variety of spectroscopic techniques including X-ray single crystal diffraction where applicable. Depending on the metal ion and auxiliary ligand of the complex, the acetyl group of the ligand could be either intact or cleaved. When ferric chloride hexahydrate was used, the deacetylation proceeded even further and a novel heterocyclic compound () was formed in situ. A possible mechanism was proposed for the formation of the heterocyclic compound found in complex . Our results indicate that to cleave effectively an amide bond, it is essential for a metal centre to bind to the amide bond and the metal centre is of sufficient Lewis acidity.

  2. Bond cleavage reactions of the bridge structure in coal in the presence of hydrogen donating compounds; Suiso kyoyosei kagobutsu sonzaika deno sekitanchu no kakyo kozo no kairetsu hanno

    Energy Technology Data Exchange (ETDEWEB)

    Bando, N.; Kidena, K.; Murata, S.; Nomura, M. [Osaka University, Osaka (Japan). Faculty of Engineering

    1996-10-28

    In this paper, bond cleavage reactions are discussed in relation to the softening and solubilization of coal. Were used 9,10-dihydroanthracene (DHA) and 9,10-dihydrophenanthrene (DHP) as models of hydrogen donating compounds in coal, and bibenzyl, 1,2-diethane, benzylphenylether, and 1,5-dibenzylnaphthalene were used as models of bridge structure compounds. They were compared mutually, as to reactivity of coal against DHA and DHP. For the homolytic cleavage of bridges, DHA with excellent radical supplement performance provided excellent hydrogen donating performance. While, for the ipso-position cleavage of bridges, it was found that DHP can act as an effective hydrogen donor. For the reaction between coal and hydrogenated aromatic compounds, cleavage of relatively weak bonds, such as ether linkage and dimethylene linkage, occurred at about 380{degree}C, and hydrogen from DHA or DHP was consumed. On the other hand, the results suggested that the cleavage reaction at ipso-position affected by hydrogen donating solvent is also important at temperature range around 420{degree}C. 2 refs., 3 figs., 1 tab.

  3. From polymer to monomer: cleavage and rearrangement of Si-O-Si bonds after oxidation yielded an ordered cyclic crystallized structure.

    Science.gov (United States)

    Zuo, Yujing; Gou, Zhiming; Cao, Jinfeng; Yang, Zhou; Lu, Haifeng; Feng, Shengyu

    2015-07-27

    Polymerization reactions are very common in the chemical industry, however, the reaction in which monomers are obtained from polymers is rarely invesitgated. This work reveals for the first time that oxone can break the Si-O-Si bond and induce further rearrangement to yield an ordered cyclic structure. The oxidation of P1, which is obtained by reaction of 2,2'-1,2-ethanediylbis(oxy)bis(ethanethiol) (DBOET) with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (MM(Vi)), with oxone yielded cyclic crystallized sulfone-siloxane dimer (P1-ox) after unexpected cleavage and rearrangement of the Si-O-Si bond.

  4. Unified view of oxidative C-H bond cleavage and sulfoxidation by a nonheme iron(IV)-oxo complex via Lewis acid-promoted electron transfer.

    Science.gov (United States)

    Park, Jiyun; Morimoto, Yuma; Lee, Yong-Min; Nam, Wonwoo; Fukuzumi, Shunichi

    2014-04-01

    Oxidative C-H bond cleavage of toluene derivatives and sulfoxidation of thioanisole derivatives by a nonheme iron(IV)-oxo complex, [(N4Py)Fe(IV)(O)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), were remarkably enhanced by the presence of triflic acid (HOTf) and Sc(OTf)3 in acetonitrile at 298 K. All the logarithms of the observed second-order rate constants of both the oxidative C-H bond cleavage and sulfoxidation reactions exhibit remarkably unified correlations with the driving forces of proton-coupled electron transfer (PCET) and metal ion-coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes between PCET and MCET were taken into account, respectively. Thus, the mechanisms of both the oxidative C-H bond cleavage of toluene derivatives and sulfoxidation of thioanisole derivatives by [(N4Py)Fe(IV)(O)](2+) in the presence of HOTf and Sc(OTf)3 have been unified as the rate-determining electron transfer, which is coupled with binding of [(N4Py)Fe(IV)(O)](2+) by proton (PCET) and Sc(OTf)3 (MCET). There was no deuterium kinetic isotope effect (KIE) on the oxidative C-H bond cleavage of toluene via the PCET pathway, whereas a large KIE value was observed with Sc(OTf)3, which exhibited no acceleration of the oxidative C-H bond cleavage of toluene. When HOTf was replaced by DOTf, an inverse KIE (0.4) was observed for PCET from both toluene and [Ru(II)(bpy)3](2+) (bpy =2,2'-bipyridine) to [(N4Py)Fe(IV)(O)](2+). The PCET and MCET reactivities of [(N4Py)Fe(IV)(O)](2+) with Brønsted acids and various metal triflates have also been unified as a single correlation with a quantitative measure of the Lewis acidity. PMID:24605985

  5. Low energy electron induced cytosine base release in 2′-deoxycytidine-3′-monophosphate via glycosidic bond cleavage: A time-dependent wavepacket study

    International Nuclear Information System (INIS)

    Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2′-deoxycytidine-3′-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3′ C–O bond cleavage from the lowest π* shape resonance in energy region * orbital of the base to the σ* orbital of the glycosidic N–C bond. In addition, the metastable state formed after impinging LEE (0–1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N–C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ∼35–55 fs. Comparison of salient features of the two dissociation events, i.e., 3′ C–O single strand break and glycosidic N–C bond cleavage in 3′-dCMPH molecule are also provided

  6. Effect of copper-sulphur bond on the DNA photo-cleavage activity of 2-(methylthio)ethylpyridine-2-carbaldimine copper(II) complexes

    Indian Academy of Sciences (India)

    Tarkeshwar Gupta; Ashis K Patra; Shanta Dhar; Munirathinam Nethaji; Akhil R Chakravarty

    2005-03-01

    The binding and photo-induced DNA cleavage activity of a binary complex [CuL2](ClO4)2 (1) and the in situ generated ternary complexes [CuLB](ClO4)2 from 1 (B: 1,10-phenanthroline, phen, 2; dipyrido[3,2-: 2',3'-]quinoxaline, dpq, 3) are studied, where L is a N2S-donor tridentate Schiff base 2-(methylthio)ethylpyridine-2-carbaldimine. Complex 1, structurally characterized by X-ray diffraction study, has six-coordinate meridional geometry showing CuN4S2 coordination. The Cu-N bond lengths are in the range of 1.968(3) to 2.158(4) Å. The Cu-S bond lengths of 2.599(2) and 2.705(2) Å are significantly long indicating weak covalent interaction between copper and sulphur atoms. The thiomethyl groups are cis to each other giving S-Cu-S angle of 75.82(5)°. The Cu-N(pyridyl) bond distances are longer than the Cu-N(imine) bonds. The complexes are redox active and display a quasi-reversible cyclic voltammetric response assignable to the Cu(II)/Cu(I) couple near 0.0 V vs SCE in DMF-Tris buffer (1 : 4 /) using 0.1 M KCl as supporting electrolyte. Electronic spectra of the complexes show a - band in the range 630 to 700 nm in DMF along with higher energy charge transfer bands. While complex 1 is a poor binder to DNA, the ternary complexes show good DNA binding propensity. The photo-nuclease activity of 1-3 is studied using UV and visible wavelengths. The DNA cleavage activity at 365 nm follows the order: 3 > 2 > 1. The cleavage reaction involves the formation of singlet oxygen as the reactive species in a type-II process.

  7. A Cobalt(I) Pincer Complex with an η(2) -C(aryl)-H Agostic Bond: Facile C-H Bond Cleavage through Deprotonation, Radical Abstraction, and Oxidative Addition.

    Science.gov (United States)

    Murugesan, Sathiyamoorthy; Stöger, Berthold; Pittenauer, Ernst; Allmaier, Günter; Veiros, Luis F; Kirchner, Karl

    2016-02-24

    The synthesis and reactivity of a Co(I) pincer complex [Co(ϰ(3) P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) featuring an η(2)-C(aryl)-H agostic bond is described. This complex was obtained by protonation of the Co(I) complex [Co(PCP(NMe) -iPr)(CO)2]. The Co(III) hydride complex [Co(PCP(NMe) -iPr)(CNtBu)2(H)](+) was obtained upon protonation of [Co(PCP(NMe) -iPr)(CNtBu)2]. Three ways to cleave the agostic C-H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C-H bond cleavage) and reformation of [Co(PCP(NMe) -iPr)(CO)2]. Second, C-H bond cleavage is achieved upon exposure of [Co(ϰ(3)P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) to oxygen or TEMPO to yield the paramagnetic Co(II) PCP complex [Co(PCP(NMe) -iPr)(CO)2](+). Finally, replacement of one CO ligand in [Co(ϰ(3) P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) by CNtBu promotes the rapid oxidative addition of the agostic η(2) -C(aryl)-H bond to give two isomeric hydride complexes of the type [Co(PCP(NMe) -iPr)(CNtBu)(CO)(H)](+).

  8. Insights into the mechanism of X-ray-induced disulfide-bond cleavage in lysozyme crystals based on EPR, optical absorption and X-ray diffraction studies

    International Nuclear Information System (INIS)

    Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage, to confirm a multi-track radiation-damage process and to develop a model of that process. Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. The observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure

  9. Metal ion-promoted cleavage of nucleoside diphosphosugars: a model for reactions of phosphodiester bonds in carbohydrates.

    Science.gov (United States)

    Dano, Meisa; Elmeranta, Marjukka; Hodgson, David R W; Jaakkola, Juho; Korhonen, Heidi; Mikkola, Satu

    2015-12-01

    Cleavage of five different nucleoside diphosphosugars has been studied in the presence of Cu(2+) and Zn(2+) complexes. The results show that metal ion catalysts promote the cleavage via intramolecular transesterification whenever a neighbouring HO group can adopt a cis-orientation with respect to the phosphate. The HO group attacks the phosphate and two monophosphate products are formed. If such a nucleophile is not available, Cu(2+) complexes are able to promote a nucleophilic attack of an external nucleophile, e.g. a water molecule or metal ion coordinated HO ligand, on phosphate. With the Zn(2+) complex, this was not observed.

  10. Formation of a Six-Coordinate fac-[Re(Co)3]+ Complex by the N-C bond cleavage of a potentially tetradentate ligand

    International Nuclear Information System (INIS)

    The rhenium(I) compound fac-[Re(CO)3(daa)]. Hpab.H2O (Hpab N,N'-(l,2-phenylene)bis(2'-aminobenzamide); Hdaa 2-amino-N-(2-aminophenyl)benzamide) was synthesized from the reaction of [Re(CO)5,Br] with two equivalent of Hpab in toluene. The monoanionic tridentate ligand daa was formed by the rhenium-mediated cleavage of an amido N-C bond of the potentially tetradentate ligand Hpab. The compound was characterized by IR spectroscopy and X-ray crystallography, and daa is coordinated as a diamino amide via three nitrogen-donor atoms

  11. Catalytic diastereoselective tandem conjugate addition-elimination reaction of Morita-Baylis-Hillman C adducts by C-C bond cleavage

    KAUST Repository

    Yang, Wenguo

    2012-02-08

    Through the cleavage of the C-C bond, the first catalytic tandem conjugate addition-elimination reaction of Morita-Baylis-Hillman C adducts has been presented. Various S N2′-like C-, S-, and P-allylic compounds could be obtained with exclusive E configuration in good to excellent yields. The Michael product could also be easily prepared by tuning the β-C-substituent group of the α-methylene ester under the same reaction conditions. Calculated relative energies of various transition states by DFT methods strongly support the observed chemoselectivity and diastereoselectivity. © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

  12. Tomato carotenoid cleavage dioxygenases 1A and 1B: Relaxed double bond specificity leads to a plenitude of dialdehydes, mono-apocarotenoids and isoprenoid volatiles

    KAUST Repository

    Ilg, Andrea

    2014-06-25

    The biosynthetic processes leading to many of the isoprenoid volatiles released by tomato fruits are still unknown, though previous reports suggested a clear correlation with the carotenoids contained within the fruit. In this study, we investigated the activity of the tomato (Solanum lycopersicum) carotenoid cleavage dioxygenase (SlCCD1B), which is highly expressed in fruits, and of its homolog SlCCD1A. Using in vitro assays performed with purified recombinant enzymes and by analyzing products formed by the two enzymes in carotene-accumulating Escherichia coli strains, we demonstrate that SlCCD1A and, to a larger extent, SlCCD1B, have a very relaxed specificity for both substrate and cleavage site, mediating the oxidative cleavage of cis- and all-. trans-carotenoids as well as of different apocarotenoids at many more double bonds than previously reported. This activity gives rise to a plenitude of volatiles, mono-apocarotenoids and dialdehyde products, including cis-pseudoionone, neral, geranial, and farnesylacetone. Our results provide a direct evidence for a carotenoid origin of these compounds and point to CCD1s as the enzymes catalyzing the formation of the vast majority of tomato isoprenoid volatiles, many of which are aroma constituents. © 2014 The Authors.

  13. Tomato carotenoid cleavage dioxygenases 1A and 1B: Relaxed double bond specificity leads to a plenitude of dialdehydes, mono-apocarotenoids and isoprenoid volatiles

    Directory of Open Access Journals (Sweden)

    Andrea Ilg

    2014-01-01

    Full Text Available The biosynthetic processes leading to many of the isoprenoid volatiles released by tomato fruits are still unknown, though previous reports suggested a clear correlation with the carotenoids contained within the fruit. In this study, we investigated the activity of the tomato (Solanum lycopersicum carotenoid cleavage dioxygenase (SlCCD1B, which is highly expressed in fruits, and of its homolog SlCCD1A. Using in vitro assays performed with purified recombinant enzymes and by analyzing products formed by the two enzymes in carotene-accumulating Escherichia coli strains, we demonstrate that SlCCD1A and, to a larger extent, SlCCD1B, have a very relaxed specificity for both substrate and cleavage site, mediating the oxidative cleavage of cis- and all-trans-carotenoids as well as of different apocarotenoids at many more double bonds than previously reported. This activity gives rise to a plenitude of volatiles, mono-apocarotenoids and dialdehyde products, including cis-pseudoionone, neral, geranial, and farnesylacetone. Our results provide a direct evidence for a carotenoid origin of these compounds and point to CCD1s as the enzymes catalyzing the formation of the vast majority of tomato isoprenoid volatiles, many of which are aroma constituents.

  14. Facile Access to Fluoroaromatic Molecules by Transition-Metal-Free C-F Bond Cleavage of Polyfluoroarenes: An Efficient, Green, and Sustainable Protocol.

    Science.gov (United States)

    Liu, Cuibo; Zhang, Bin

    2016-04-01

    The creation of new bonds via C-F bond cleavage of polyfluoroarenes has proven to be an important and powerful tool in synthetic chemistry. Using such a strategy, a myriad of valuable partially fluoroaromatic molecules and building blocks can be obtained. The transition-metal-free nucleophilic aromatic substitution (SN Ar) strategy has aroused the continuing interest of researchers due to its simple, mild, economical, and environmentally benign characteristics, which have been successfully applied to C-F bond functionalizations. In this account, we present a summary of the recent investigations of polyfluoroarenes involving SN Ar reactions and discuss some of our recent endeavors in the construction of partially fluoroaromatic molecules. Through this strategy, many new bonds including C-C, C-N, C-O, C-S, and C-H bonds can be created. Additionally, brief discussions on the transformation mechanisms are also provided. Finally, we discuss the existing limitations of the SN Ar reactions of polyfluoroarenes as well as our perspective on the future development of this chemistry.

  15. Sequence-Specific Ultrasonic Cleavage of DNA

    OpenAIRE

    Grokhovsky, Sergei L.; Il'icheva, Irina A.; Nechipurenko, Dmitry Yu.; Golovkin, Michail V.; Panchenko, Larisa A.; Polozov, Robert V.; Nechipurenko, Yury D.

    2011-01-01

    We investigated the phenomenon of ultrasonic cleavage of DNA by analyzing a large set of cleavage patterns of DNA restriction fragments using polyacrylamide gel electrophoresis. The cleavage intensity of individual phosphodiester bonds was found to depend on the nucleotide sequence and the position of the bond with respect to the ends of the fragment. The relative intensities of cleavage of the central phosphodiester bond in 16 dinucleotides and 256 tetranucleotides were determined by multiva...

  16. Resonance Raman spectroscopy reveals pH-dependent active site structural changes of lactoperoxidase compound 0 and its ferryl heme O-O bond cleavage products.

    Science.gov (United States)

    Mak, Piotr J; Thammawichai, Warut; Wiedenhoeft, Dennis; Kincaid, James R

    2015-01-14

    The first step in the enzymatic cycle of mammalian peroxidases, including lactoperoxidase (LPO), is binding of hydrogen peroxide to the ferric resting state to form a ferric-hydroperoxo intermediate designated as Compound 0, the residual proton temporarily associating with the distal pocket His109 residue. Upon delivery of this "stored" proton to the hydroperoxo fragment, it rapidly undergoes O-O bond cleavage, thereby thwarting efforts to trap it using rapid mixing methods. Fortunately, as shown herein, both the peroxo and the hydroperoxo (Compound 0) forms of LPO can be trapped by cryoradiolysis, with acquisition of their resonance Raman (rR) spectra now permitting structural characterization of their key Fe-O-O fragments. Studies were conducted under both acidic and alkaline conditions, revealing pH-dependent differences in relative populations of these intermediates. Furthermore, upon annealing, the low pH samples convert to two forms of a ferryl heme O-O bond-cleavage product, whose ν(Fe═O) frequencies reflect substantially different Fe═O bond strengths. In the process of conducting these studies, rR structural characterization of the dioxygen adduct of LPO, commonly called Compound III, has also been completed, demonstrating a substantial difference in the strengths of the Fe-O linkage of the Fe-O-O fragment under acidic and alkaline conditions, an effect most reasonably attributed to a corresponding weakening of the trans-axial histidyl imidazole linkage at lower pH. Collectively, these new results provide important insight into the impact of pH on the disposition of the key Fe-O-O and Fe═O fragments of intermediates that arise in the enzymatic cycles of LPO, other mammalian peroxidases, and related proteins.

  17. Sensitive near-infrared fluorescent probes for thiols based on Se-N bond cleavage: imaging in living cells and tissues.

    Science.gov (United States)

    Wang, Rui; Chen, Lingxin; Liu, Ping; Zhang, Qin; Wang, Yunqing

    2012-09-01

    Cy-NiSe and Cy-TfSe were designed and synthesized as sensitive near-infrared (NIR) fluorescent probes for detecting thiols on the basis of Se-N bond cleavage both in cells and in tissues. Since a donor-excited photoinduced electron transfer (d-PET) process occurs between the modulator and the fluorophore, Cy-NiSe and Cy-TfSe have weak fluorescence. On titration with glutathione, the free dye exhibits significant fluorescence enhancement. The two probes are sensitive and selective for thiols over other relevant biological species. They can function rapidly at pH 7.4, and their emission lies in the NIR region. Confocal imaging confirms that Cy-NiSe and Cy-TfSe can be used for detecting thiols in living cells and tissues. PMID:22829328

  18. {{text{C}}_{α }} - {text{C}} Bond Cleavage of the Peptide Backbone in MALDI In-Source Decay Using Salicylic Acid Derivative Matrices

    Science.gov (United States)

    Asakawa, Daiki; Takayama, Mitsuo

    2011-07-01

    The use of 5-formylsalicylic acid (5-FSA) and 5-nitrosalicylic acid (5-NSA) as novel matrices for in-source decay (ISD) of peptides in matrix-assisted laser desorption/ionization (MALDI) is described. The use of 5-FSA and 5-NSA generated a- and x-series ions accompanied by oxidized peptides [M - 2 H + H]+. The preferential formation of a- and x-series ions was found to be dependent on the hydrogen-accepting ability of matrix. The hydrogen-accepting ability estimated from the ratio of signal intensity of oxidized product [M - 2 H + H]+ to that of non-oxidized protonated molecule [M + H]+ of peptide was of the order 5-NSA > 5-FSA > 5-aminosalicylic acid (5-ASA) ≒ 2,5-dihydroxyl benzoic acid (2,5-DHB) ≒ 0. The results suggest that the hydrogen transfer reaction from peptide to 5-FSA and 5-NSA occurs during the MALDI-ISD processes. The hydrogen abstraction from peptides results in the formation of oxidized peptides containing a radical site on the amide nitrogen with subsequent radical-induced cleavage at the {{{C}}_{α }} - {{C}} bond, leading to the formation of a- and x-series ions. The most significant feature of MALDI-ISD with 5-FSA and 5-NSA is the specific cleavage of the {{{C}}_{α }} - {{C}} bond of the peptide backbone without degradation of side-chain and post-translational modifications (PTM). The matrix provides a useful complementary method to conventional MALDI-ISD for amino acid sequencing and site localization of PTMs in peptides.

  19. Effect of water on hydrolytic cleavage of non-terminal α-glycosidic bonds in cyclodextrins to generate monosaccharides and their derivatives in a dimethyl sulfoxide-water mixture.

    Science.gov (United States)

    Kimura, Hiroshi; Hirayama, Masaki; Yoshida, Ken; Uosaki, Yasuhiro; Nakahara, Masaru

    2014-02-27

    Hydrolytic cleavage of the non-terminal α-1,4-glycosidic bonds in α-, β-, and γ-cyclodextrins and the anomeric-terminal one in d-maltose was investigated to examine how the cleavage rate for α-, β-, and γ-cyclodextrins is slower than that for d-maltose. Effects of water and temperature were studied by applying in situ (13)C NMR spectroscopy and using a dimethyl sulfoxide (DMSO)-water mixture over a wide range of water mole fraction, xw = 0.004-1, at temperatures of 120-180 °C. The cleavage rate constant for the non-anomeric glycosidic bond was smaller by a factor of 6-10 than that of the anomeric-terminal one. The glycosidic-bond cleavage is significantly accelerated through the keto-enol tautomerization of the anomeric-terminal d-glucose unit into the d-fructose one. The smaller the size of the cyclodextrin, the easier the bond cleavage due to the ring strain. The remarkable enhancement in the cleavage rate with decreasing water content was observed for the cyclodextrins and d-maltose as well as d-cellobiose. This shows the important effect of the solitary water whose hydrogen bonding to other water molecules is prohibited by the presence of the organic dipolar aprotic solvent, DMSO, and which has more naked partial charges and higher reactivity. A high 5-hydroxymethyl-2-furaldehyde (5-HMF) yield of 64% was attained in a non-catalytic conversion by tuning the water content to xw = 0.30, at which the undesired polymerization by-paths can be most effectively suppressed. This study provides a step toward designing a new optimal, earth-benign generation process of 5-HMF starting from biomass.

  20. Synthesis of Biaryls through Nickel-Catalyzed Suzuki-Miyaura Coupling of Amides by Carbon-Nitrogen Bond Cleavage.

    Science.gov (United States)

    Shi, Shicheng; Meng, Guangrong; Szostak, Michal

    2016-06-01

    The first Ni-catalyzed Suzuki-Miyaura coupling of amides for the synthesis of widely occurring biaryl compounds through N-C amide bond activation is reported. The reaction tolerates a wide range of electron-withdrawing, electron-neutral, and electron-donating substituents on both coupling partners. The reaction constitutes the first example of the Ni-catalyzed generation of aryl electrophiles from bench-stable amides with potential applications for a broad range of organometallic reactions. PMID:27101428

  1. Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds. Substituent Effects in Phenethyl Phenyl Ethers

    Energy Technology Data Exchange (ETDEWEB)

    Beste, Ariana [ORNL; Buchanan III, A C [ORNL

    2009-01-01

    Lignin is an abundant natural resource that is a potential source of valuable chemicals. Improved understanding of the pyrolysis of lignin occurs through the study of model compounds for which phenethyl phenyl ether (PhCH2CH2OPh, PPE) is the simplest example representing the dominant -O-4 ether linkage. The initial step in the thermal decomposition of PPE is the homolytic cleavage of the oxygen-carbon bond. The rate of this key step will depend on the bond dissociation enthalpy, which in turn will depend on the nature and location of relevant substituents. We used modern density functional methods to calculate the oxygen-carbon bond dissociation enthalpies for PPE and several oxygen substituted derivatives. Since carbon-carbon bond cleavage in PPE could be a competitive initial reaction under high temperature pyrolysis conditions, we also calculated substituent effects on these bond dissociation enthalpies. We found that the oxygen-carbon bond dissociation enthalpy is substantially lowered by oxygen substituents situated at the phenyl ring adjacent to the ether oxygen. On the other hand, the carbon-carbon bond dissociation enthalpy shows little variation with different substitution patterns on either phenyl ring.

  2. EFFECT OF SOLVENT ON THE BETA-O-4 BOND CLEAVAGE OF A LIGNIN MODEL COMPOUND BY TERT-BUTOXIDE UNDER MILD CONDITIONS

    Directory of Open Access Journals (Sweden)

    Yuji Matsumoto

    2011-11-01

    Full Text Available The beta-O-4 bond cleavage of a non-phenolic β-O-4 type dimeric lignin model compound, 2-(2-methoxyphenoxy-1-(3,4-dimethoxyphenyl-ethanol (III, was examined in systems using potassium tert-butoxide as a base (0.5 mol/l and tert-butanol (tBuOH, dimethylsulfoxide, 1,4-dioxane, or tetrahydrofuran as a solvent. The β-O-4 bond of compound III was cleaved in any system at 30°C, and 2-methoxyphenol (II was liberated. The amount of compound II liberated was close to the quantitative yield on the basis of the amount of compound III that disappeared, except for the treatment in the t-BuOH system. The reaction rate was dependent on what solvent was used. Half-life periods for these systems were roughly about 6.0, 3.0, 0.7, and 0.2h, respectively. It seemed that the rates were very high when the polarity of the solvents was low. Two reaction products generated from the aromatic ring with two methoxyl groups of compound III, 4-acetyl-1,2-dimethoxybenzene and 3,4-dimethoxybenzoic acid, were detected in all the systems. A peculiar reaction product, 1,2-dimethoxybenzene, was detected in a fairly large quantity, only when the latter two solvents with low polarities were applied.

  3. Solvent dependent branching between C-I and C-Br bond cleavage following 266 nm excitation of CH2BrI

    International Nuclear Information System (INIS)

    It is well known that ultraviolet photoexcitation of halomethanes results in halogen-carbon bond cleavage. Each halogen-carbon bond has a dominant ultraviolet (UV) absorption that promotes an electron from a nonbonding halogen orbital (nX) to a carbon-halogen antibonding orbital (σ*C-X). UV absorption into specific transitions in the gas phase results primarily in selective cleavage of the corresponding carbon-halogen bond. In the present work, broadband ultrafast UV-visible transient absorption studies of CH2BrI reveal a more complex photochemistry in solution. Transient absorption spectra are reported spanning the range from 275 nm to 750 nm and 300 fs to 3 ns following excitation of CH2BrI at 266 nm in acetonitrile, 2-butanol, and cyclohexane. Channels involving formation of CH2Br + I radical pairs, iso-CH2Br-I, and iso-CH2I-Br are identified. The solvent environment has a significant influence on the branching ratios, and on the formation and stability of iso-CH2Br-I. Both iso-CH2Br-I and iso-CH2I-Br are observed in cyclohexane with a ratio of ∼2.8:1. In acetonitrile this ratio is 7:1 or larger. The observation of formation of iso-CH2I-Br photoproduct as well as iso-CH2Br-I following 266 nm excitation is a novel result that suggests complexity in the dissociation mechanism. We also report a solvent and concentration dependent lifetime of iso-CH2Br-I. At low concentrations the lifetime is >4 ns in acetonitrile, 1.9 ns in 2-butanol and ∼1.4 ns in cyclohexane. These lifetimes decrease with higher initial concentrations of CH2BrI. The concentration dependence highlights the role that intermolecular interactions can play in the quenching of unstable isomers of dihalomethanes

  4. Heterolytic Cleavage of Hydrogen by an Iron Hydrogenase Model: An Fe-H - - - H-N Dihydorgen Bond Characterized by Neutron Diffraction

    International Nuclear Information System (INIS)

    Use of hydrogen as a fuel by [FeFe]-hydrogenase enzymes in nature requires heterolytic cleavage of the H-H bond into a proton (H+) and hydride (H-), a reaction that is also a critical step in homogeneous catalysts for hydrogenation of C=O and C=N bonds. An understanding of the catalytic oxidation of H2 by hydrogenases provides insights into the design of synthetic catalysts that are sought as cost-effective alternatives to the use of the precious metal platinum in fuel cells. Crystallographic studies on the [FeFe]-hydrogenase enzyme were critical to understanding of its reactivity, but the key H-H cleavage step is not readily observed experimentally in natural hydrogenases. Synthetic biomimics have provided evidence for H2 cleavage leading to hydride transfer to the metal and proton transfer to an amine. Limitations on the precise location of hydrogen atoms by x-ray diffraction can be overcome by use of neutron diffraction, though its use is severely limited by the difficulty of obtaining suitable crystals and by the scarcity of neutron sources. Here we show that an iron complex with a pendant amine in the diphosphine ligand cleaves hydrogen heterolytically under mild conditions, leading to [CpC5F4NFeH(PtBu2NtBu2H)]+BArF4-, [PtBu2NtBu2 = 1,5-di(tert-butyl)-3,7-di(tert-butyl)-1,5-diaza-3,7-diphosphacyclooctane; ArF = 3,5-bis(trifluoromethyl)phenyl]. The Fe-H- - - H-N moiety has a strong dihydrogen bond, with a remarkably short H··· H distance of 1.489(10) Angstrom between the protic N-Hδ+ and hydridic Fe-Hδ-. The structural data for [CpC5F4NFeH(PtBu2NtBu2H)]+ provide a glimpse of how the H-H bond is oxidized or generated in hydrogenase enzymes, with the pendant amine playing a key role as a proton relay. The iron complex [CpC5F4NFeH(PtBu2NtBu2H)]+BArF4- is an electrocatalyst for oxidation of H2 (1 atm) at 22 °C, so the structural data are obtained on a complex that is a functional model for catalysis by [FeFe]-hydrogenase enzymes. This research was supported

  5. Cleavage of peptide bonds bearing ionizable amino acids at P1 by serine proteases with hydrophobic S1 pocket

    International Nuclear Information System (INIS)

    Research highlights: → Large pK shifts in ionizable groups when buried in the protein interior. → Substrate dependent shifts in pH optimum for serine proteases. → Lys side chain is a stronger acid in serine protease S1 pocket than Asp side chain. -- Abstract: Enzymatic hydrolysis of the synthetic substrate succinyl-Ala-Ala-Pro-Xxx-pNA (where Xxx = Leu, Asp or Lys) catalyzed by bovine chymotrypsin (CHYM) or Streptomyces griseus protease B (SGPB) has been studied at different pH values in the pH range 3-11. The pH optima for substrates having Leu, Asp, and Lys have been found to be 7.5-8.0, 5.5-6.0, and ∼10, respectively. At the normally reported pH optimum (pH 7-8) of CHYM and SGPB, the substrate with Leu at the reactive site is more than 25,000-fold more reactive than that with Asp. However, when fully protonated, Asp is nearly as good a substrate as Leu. The pK values of the side chains of Asp and Lys in the hydrophobic S1 pocket of CHYM and SGPB have been calculated from pH-dependent hydrolysis data and have been found to be about 9 for Asp and 7.4 and 9.7 for Lys for CHYM and SGPB, respectively. The results presented in this communication suggest a possible application of CHYM like enzymes in cleaving peptide bonds contributed by acidic amino acids between pH 5 and 6.

  6. The Molybdenum Active Site of Formate Dehydrogenase Is Capable of Catalyzing C-H Bond Cleavage and Oxygen Atom Transfer Reactions.

    Science.gov (United States)

    Hartmann, Tobias; Schrapers, Peer; Utesch, Tillmann; Nimtz, Manfred; Rippers, Yvonne; Dau, Holger; Mroginski, Maria Andrea; Haumann, Michael; Leimkühler, Silke

    2016-04-26

    Formate dehydrogenases (FDHs) are capable of performing the reversible oxidation of formate and are enzymes of great interest for fuel cell applications and for the production of reduced carbon compounds as energy sources from CO2. Metal-containing FDHs in general contain a highly conserved active site, comprising a molybdenum (or tungsten) center coordinated by two molybdopterin guanine dinucleotide molecules, a sulfido and a (seleno-)cysteine ligand, in addition to a histidine and arginine residue in the second coordination sphere. So far, the role of these amino acids in catalysis has not been studied in detail, because of the lack of suitable expression systems and the lability or oxygen sensitivity of the enzymes. Here, the roles of these active site residues is revealed using the Mo-containing FDH from Rhodobacter capsulatus. Our results show that the cysteine ligand at the Mo ion is displaced by the formate substrate during the reaction, the arginine has a direct role in substrate binding and stabilization, and the histidine elevates the pKa of the active site cysteine. We further found that in addition to reversible formate oxidation, the enzyme is further capable of reducing nitrate to nitrite. We propose a mechanistic scheme that combines both functionalities and provides important insights into the distinct mechanisms of C-H bond cleavage and oxygen atom transfer catalyzed by formate dehydrogenase. PMID:27054466

  7. Unusual C-C bond cleavage in the formation of amine-bis(phenoxy) group 4 benzyl complexes: Mechanism of formation and application to stereospecific polymerization

    KAUST Repository

    Gowda, Ravikumar R.

    2014-08-11

    Group 4 tetrabenzyl compounds MBn4 (M = Zr, Ti), upon protonolysis with an equimolar amount of the tetradentate amine-tris(phenol) ligand N[(2,4-tBu2C6H2(CH 2)OH]3 in toluene from -30 to 25 °C, unexpectedly lead to amine-bis(phenoxy) dibenzyl complexes, BnCH2N[(2,4- tBu2C6H2(CH2)O] 2MBn2 (M = Zr (1), Ti (2)) in 80% (1) and 75% (2) yields. This reaction involves an apparent cleavage of the >NCH2-ArOH bond (loss of the phenol in the ligand) and formation of the >NCH 2-CH2Bn bond (gain of the benzyl group in the ligand). Structural characterization of 1 by X-ray diffraction analysis confirms that the complex formed is a bis(benzyl) complex of Zr coordinated by a newly derived tridentate amine-bis(phenoxy) ligand arranged in a mer configuration in the solid state. The abstractive activation of 1 and 2 with B(C6F 5)3·THF in CD2Cl2 at room temperature generates the corresponding benzyl cations {BnCH2N[(2,4- tBu2C6H2(CH2)O] 2MBn(THF)}+[BnB(C6F5) 3]- (M = Zr (3), Ti, (4)). These cationic complexes, along with their analogues derived from (imino)phenoxy tri- and dibenzyl complexes, [(2,6-iPr2C6H3)N=C(3,5- tBu2C6H2)O]ZrBn3 (5) and [2,4-Br2C6H2(O)(6-CH2(NC 5H9))CH2N=CH(2-adamantyl-4-MeC 6H2O)]ZrBn2 (6), have been found to effectively polymerize the biomass-derived renewable β-methyl-α-methylene- γ-butyrolactone (βMMBL) at room temperature into the highly stereoregular polymer PβMMBL with an isotacticity up to 99% mm. A combined experimental and DFT study has yielded a mechanistic pathway for the observed unusual C-C bond cleavage in the present protonolysis reaction between ZrBn4 and N[(2,4-tBu2C 6H2(CH2)OH]3 for the formation of complex 1, which involves the benzyl radical and the Zr(III) species, resulting from thermal and photochemical decomposition of ZrBn4, followed by a series of reaction sequences consisting of protonolysis, tautomerization, H-transfer, oxidation, elimination, and radical coupling. © 2014 American Chemical Society.

  8. C-H Bond Activation of Bisimines by Palladium (Ⅱ) and Platinum (Ⅱ).Synthesis,Characterization of Bis (imino) aryl-palladium (Ⅱ) Pincer Complexes and Their Application in Carbon-Carbon Cross Coupling Reactions%C-H Bond Activation of Bisimines by Palladium (Ⅱ) and Platinum (Ⅱ).Synthesis, Characterization of Bis (imino) aryl-palladium (Ⅱ) Pincer Complexes and Their Application in Carbon-Carbon Cross Coupling Reactions

    Institute of Scientific and Technical Information of China (English)

    CHEN Rong; CHEN Ying; LIU Fang; LI Ping; HU Zhao-xia; WANG Hong-xing

    2013-01-01

    Abstract:The reactions of a variety of 4,6-dimethyl-1,3-bis (imino) benzenes 2a-g derived from 4,6-dimethylisophthalaldehyde and anilines or benzylamine with palladium (Ⅱ) acetate in anhydrous acetic acid under nitrogen were investigated.Experiment results demonstrate that cyclopalladations in such condition are applicable not only to the present system under study but also to the 5-substituted bis(imino)benzenes 6,7.The molecular structure of 3 b was further confirmed by X-Ray single-crystal diffraction.3b Crystallizes in orthorhombic,space groupP2 (1) 2 (1) 2 (1) with a =0.734 53 (8),b =1.683 8 (3),c =1.691 7(2) nm,α =β =γ =90°.Treatment of 2b with K2PtCl4 in anhydrous acetic acid affords the corresponding NCN-platinum pincer.Carbon-carbon cross coupling reactions catalyzed with 3b were investigated.These palladium complexes have been proved to be high effective catalysts for Suzuki coupling reaction.

  9. Integral Ring Carbon-Carbon Piston

    Science.gov (United States)

    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.

  10. Formation of a dinuclear copper(II) complex through the cleavage of CN bond of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole

    International Nuclear Information System (INIS)

    A simple mononuclear octahedral copper(II) complex was attempted from the reaction of three moles of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole and one mole of copper(II) perchlorate hexahydrate in methanol. However, the product of the reaction was confirmed to be a dinuclear copper(II) complex with μ-(3-(pyridin-2-yl)-pyrazolato) and 3-(pyridin-2-yl)-1H-pyrazole ligands attached to each of the Cu(II) centre atom. The copper(II) ion assisted the cleavage of the CbenzoylN bond afforded a 3-(pyridin-2-yl)-1H-pyrazole molecule. Deprotonation of the 3-(pyridin-2-yl)-1H-pyrazole gave a 3-(pyridin-2-yl)-pyrazolato, which subsequently reacted with the Cu(II) ion to give the (3-(pyridin-2-yl)-pyrazolato)(3-(pyridin-2-yl)-1H-pyrazole)Cu(II) product moiety. The structure of the dinuclear complex was confirmed by x-ray crystallography. The complex crystallized in a monoclinic crystal system with P2(1)/n space group and cell dimensions of a = 12.2029(8) Å, b = 11.4010(7) Å, c = 14.4052(9) Å and β = 102.414(2)°. The compound was further characterized by mass spectrometry, CHN elemental analysis, infrared and UV-visible spectroscopy and the results concurred with the x-ray structure. The presence of d-d transition at 671 nm (ε = 116 dm3 mol−1 cm−1) supports the presence of Cu(II) centres

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

    Science.gov (United States)

    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.

  12. New carbon-carbon linked amphiphilic carboranyl-porphyrins as boron neutron capture agents

    International Nuclear Information System (INIS)

    Novel amphiphilic carboranyl-porphyrins have been synthesized for Boron Neutron Capture Therapy (BNCT). These compounds have carbon-carbon bonds between the carborane residues and the porphyrin meso-phenyl groups, and contain 28-31% boron by weight . (author)

  13. Recent Progress in the Research of Transition-Metal-Catalyzed C-CN Bond Cleavage%过渡金属催化的C—CN键断裂的研究进展

    Institute of Scientific and Technical Information of China (English)

    寇学振; 范佳骏; 童晓峰; 沈增明

    2013-01-01

    有机氰化物是一种重要的合成中间体,在药物、农药、染料和活性物质中都有应用.使用廉价、简单、低毒的氰基化合物在过渡金属的催化下通过C-CN键断裂生成复杂的氰化物是合成有机氰化物的重要手段之一.综述了不同过渡金属(如Ni,Pd,Rh,Cu,Ru,Fe,Mo,Co等)催化不同种类的氰基化合物C-CN键断裂的最新研究进展,如含C(sp1)-CN键化合物、C(sp2)-CN键化合物以及C(sp3)-CN键化合物,并对有关的反应机理及C-CN键断裂机理的进展进行了探讨.%Nitriles are an important class of organic compounds which can be found in pharmaceuticals,agrochemicals,dyes,and bioactive compounds.Transition-metal-catalyzed C-CN bond cleavage using inexpensive,simple and less toxic nitriles is one of the most attractive modem methods for the synthesis of complicated organic cyanides.Research progress of transition-metal-catalyzed (Ni,Pd,Rh,Cu,Ru,Fe,Mo,Co) different types of C-CN bond cleavage is reviewed,which includes some organic cyanides containing C(sp1)—CN bond,C(sp2)—CN bond and C(sp3)—CN bond.The C-CN cleavage mechanisms are also discussed in this review.

  14. Formation of a dinuclear copper(II) complex through the cleavage of CBond' name='Single-Bond' value='Single-Bond'/>N bond of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole

    Energy Technology Data Exchange (ETDEWEB)

    Shardin, Rosidah; Pui, Law Kung; Yamin, Bohari M. [School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, UKM 43600 Bangi, Selangor (Malaysia); Kassim, Mohammad B. [School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, UKM 43600 Bangi, Selangor, Malaysia and Fuel Cell Institute, Universiti Kebangsaan Malaysia, UKM 43600 Bangi, Selangor (Malaysia)

    2014-09-03

    A simple mononuclear octahedral copper(II) complex was attempted from the reaction of three moles of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole and one mole of copper(II) perchlorate hexahydrate in methanol. However, the product of the reaction was confirmed to be a dinuclear copper(II) complex with μ-(3-(pyridin-2-yl)-pyrazolato) and 3-(pyridin-2-yl)-1H-pyrazole ligands attached to each of the Cu(II) centre atom. The copper(II) ion assisted the cleavage of the C{sub benzoyl}Bond' name='Single-Bond' value='Single-Bond'/>N bond afforded a 3-(pyridin-2-yl)-1H-pyrazole molecule. Deprotonation of the 3-(pyridin-2-yl)-1H-pyrazole gave a 3-(pyridin-2-yl)-pyrazolato, which subsequently reacted with the Cu(II) ion to give the (3-(pyridin-2-yl)-pyrazolato)(3-(pyridin-2-yl)-1H-pyrazole)Cu(II) product moiety. The structure of the dinuclear complex was confirmed by x-ray crystallography. The complex crystallized in a monoclinic crystal system with P2(1)/n space group and cell dimensions of a = 12.2029(8) Å, b = 11.4010(7) Å, c = 14.4052(9) Å and β = 102.414(2)°. The compound was further characterized by mass spectrometry, CHN elemental analysis, infrared and UV-visible spectroscopy and the results concurred with the x-ray structure. The presence of d-d transition at 671 nm (ε = 116 dm{sup 3} mol{sup −1} cm{sup −1}) supports the presence of Cu(II) centres.

  15. Mechanistic Insights into Ring Cleavage and Contraction of Benzene over a Titanium Hydride Cluster.

    Science.gov (United States)

    Kang, Xiaohui; Luo, Gen; Luo, Lun; Hu, Shaowei; Luo, Yi; Hou, Zhaomin

    2016-09-14

    Carbon-carbon bond cleavage of benzene by transition metals is of great fundamental interest and practical importance, as this transformation is involved in the production of fuels and other important chemicals in the industrial hydrocracking of naphtha on solid catalysts. Although this transformation is thought to rely on cooperation of multiple metal sites, molecular-level information on the reaction mechanism has remained scarce to date. Here, we report the DFT studies of the ring cleavage and contraction of benzene by a molecular trinuclear titanium hydride cluster. Our studies suggest that the reaction is initiated by benzene coordination, followed by H2 release, C6H6 hydrometalation, repeated C-C and C-H bond cleavage and formation to give a MeC5H4 unit, and insertion of a Ti atom into the MeC5H4 unit with release of H2 to give a metallacycle product. The C-C bond cleavage and ring contraction of toluene can also occur in a similar fashion, though some details are different due to the presence of the methyl substituent. Obviously, the facile release of H2 from the metal hydride cluster to provide electrons and to alter the charge population at the metal centers, in combination with the flexible metal-hydride connections and dynamic redox behavior of the trimetallic framework, has enabled this unusual transformation to occur. This work has not only provided unprecedented insights into the activation and transformation of benzene over a multimetallic framework but it may also offer help in the design of new molecular catalysts for the activation and transformation of inactive aromatics. PMID:27549745

  16. Diversification of ortho-Fused Cycloocta-2,5-dien-1-one Cores and Eight- to Six-Ring Conversion by σ Bond C-C Cleavage.

    Science.gov (United States)

    Eccleshare, Lee; Lozada-Rodríguez, Leticia; Cooper, Phillippa; Burroughs, Laurence; Ritchie, John; Lewis, William; Woodward, Simon

    2016-08-22

    Sequential treatment of 2-C6 H4 Br(CHO) with LiC≡CR(1) (R(1) =SiMe3 , tBu), nBuLi, CuBr⋅SMe2 and HC≡CCHClR(2) [R(2) =Ph, 4-CF3 Ph, 3-CNPh, 4-(MeO2 C)Ph] at -50 °C leads to formation of an intermediate carbanion (Z)-1,2-C6 H4 {CA (=O)C≡CB R(1) }{CH=CH(CH(-) )R(2) } (4). Low temperatures (-50 °C) favour attack at CB leading to kinetic formation of 6,8-bicycles containing non-classical C-carbanion enolates (5). Higher temperatures (-10 °C to ambient) and electron-deficient R(2) favour retro σ-bond C-C cleavage regenerating 4, which subsequently closes on CA providing 6,6-bicyclic alkoxides (6). Computational modelling (CBS-QB3) indicated that both pathways are viable and of similar energies. Reaction of 6 with H(+) gave 1,2-dihydronaphthalen-1-ols, or under dehydrating conditions, 2-aryl-1-alkynylnaphthlenes. Enolates 5 react in situ with: H2 O, D2 O, I2 , allylbromide, S2 Me2 , CO2 and lead to the expected C-E derivatives (E=H, D, I, allyl, SMe, CO2 H) in 49-64 % yield directly from intermediate 5. The parents (E=H; R(1) =SiMe3 , tBu; R(2) =Ph) are versatile starting materials for NaBH4 and Grignard C=O additions, desilylation (when R(1) =SiMe) and oxime formation. The latter allows formation of 6,9-bicyclics via Beckmann rearrangement. The 6,8-ring iodides are suitable Suzuki precursors for Pd-catalysed C-C coupling (81-87 %), whereas the carboxylic acids readily form amides under T3P® conditions (71-95 %). PMID:27452351

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

    Science.gov (United States)

    Subhani, Muhammad Afzal; Köhler, Burkhard; Gürtler, Christoph; Leitner, Walter; Müller, Thomas E

    2016-04-25

    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

  18. An elusive vinyl radical isolated as an appended unit in a five-coordinate Co(iii)-bis(iminobenzosemiquinone) complex formed via ligand-centered C-S bond cleavage.

    Science.gov (United States)

    Sarkar, Prasenjit; Tiwari, Archana; Sarmah, Amrit; Bhandary, Subhrajyoti; Roy, Ram Kinkar; Mukherjee, Chandan

    2016-08-23

    Redox-active ligand H4Pra(edt(AP/AP)) experienced C-S bond cleavage during complexation reaction with Co(OAc)2·2H2O in the presence of Et3N in CH3OH in air. Thus, formed complex 1 was composed of two iminobenzosemiquinone radicals in its coordination sphere and an unprecedented stable tethered-vinyl radical. The complex has been characterized by mass, X-ray single crystal, X-band EPR, variable-temperature magnetic moment measurements and DFT based computational study.

  19. Efficient and facile Ar-Si bond cleavage by montmorillonite KSF: synthetic and mechanistic aspects of solvent-free protodesilylation studied by solution and solid-state MAS NMR.

    Science.gov (United States)

    Zafrani, Yossi; Gershonov, Eytan; Columbus, Ishay

    2007-08-31

    A facile and efficient method for the cleavage of the Ar-Si bond of various aryl trimethyl silanes is described. When adsorbed on montmorillonite KSF (mont KSF), these arylsilanes readily undergo a solvent-free protodesilylation to the corresponding arenes at room temperature in excellent yields. This approach seems to be superior to the traditional mild methods (i.e., desilylation by TFA, TBAF, CsF), in terms of reaction yield, rate, and environmentally benign conditions. Some mechanistic studies using both solution and solid-state magic-angle spinning (SS MAS) (1)H NMR are also presented. PMID:17676903

  20. Carbon/Carbon Pistons for Internal Combustion Engines

    Science.gov (United States)

    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.

  1. Organometallic Methods for Forming and Cleaving Carbon-Carbon Bonds

    DEFF Research Database (Denmark)

    Christensen, Stig Holden

    The retro-Grignard addition reaction has been revisited and the benzyl addition reaction was found to be a reversible transformation by using crossover experiments. The retro benzyl addition reaction was shown by the addition of benzylmagnesium chloride to di-t-butyl ketone followed by exchange o...

  2. Method for Making a Carbon-Carbon Cylinder Block

    Science.gov (United States)

    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.

  3. PhnY and PhnZ comprise a new oxidative pathway for enzymatic cleavage of a carbon-phosphorus bond

    DEFF Research Database (Denmark)

    McSorley, Fern R.; Wyatt, Peter W.; Martinez, Ascuncion;

    2012-01-01

    The sequential activities of PhnY, an α-ketoglutarate/Fe(II)-dependent dioxygenase, and PhnZ, a Fe(II)-dependent enzyme of the histidine-aspartate motif hydrolase family, cleave the carbon-phosphorus bond of the organophosphonate natural product 2-aminoethylphosphonic acid. PhnY adds a hydroxyl g...

  4. Hydrodenitrogenation chemistry. I. Cleavage of alkylcarbon-nitrogen bonds, methane and ammonia formation in the HDN reaction of 1,2,3,4-tetrahydroquinoline with a nickel oxide catalyst supported on silica/alumina

    Energy Technology Data Exchange (ETDEWEB)

    Fish, R.H.; Thormodsen, A.D.; Moore, R.S.; Perry, D.L.; Heinemann, H.

    1986-11-01

    The hydrodenitrogenation reaction (HDN) is one of the most important industrial processes used in the refining of petroleum feedstocks and involves the removal of the nitrogen atom, as ammonia, from polynuclear heteroaromatic nitrogen compounds at high temperatures and high pressures of hydrogen gas (350-500/sup 0/C and 2000 psi). It is interesting to note that most of the reported heterogeneous catalysts require the complete hydrogenation of both the nitrogen heterocyclic ring and the aromatic ring before carbon-nitrogen bond cleavage can occur. A major breakthrough in the technical and economic aspects of the HDN reaction would take place if, in fact a catalyst could be found that would selectively cleave the C-N bond din the saturated nitrogen ring and subsequently produce ammonia, without substantial reduction of the aromatic rings, at lower temperatures as well as lower pressures of hydrogen gas. In this note, the authors report on a highly loaded nickel oxide catalyst (50% by weight Ni), supported on silica/alumina, that will effectively provide some of the criteria for an ideal HDN catalyst. 8 references.

  5. High performance carbon-carbon composites

    Indian Academy of Sciences (India)

    Lalit M Manocha

    2003-02-01

    Carbon-carbon composites rank first among ceramic composite materials with a spectrum of properties and applications in various sectors. These composites are made of fibres in various directions and carbonaceous polymers and hydrocarbons as matrix precursors. Their density and properties depend on the type and volume fraction of reinforcement, matrix precursor used and end heat treatment temperature. Composites made with thermosetting resins as matrix precursors possess low densities (1.55–1.75 g/cm3) and well-distributed microporosity whereas those made with pitch as the matrix precursor, after densification exhibit densities of 1.8–2.0 g/cm3 with some mesopores, and those made by the CVD technique with hydrocarbon gases, possess intermediate densities and matrices with close porosities. The former (resin-based) composites exhibit high flexural strength, low toughness and low thermal conductivity, whereas the latter (pitch- and CVD-based) can be made with very high thermal conductivity (400–700 W/MK) in the fibre direction. Carbon-carbon composites are used in a variety of sectors requiring high mechanical properties at elevated temperatures, good frictional properties for brake pads in high speed vehicles or high thermal conductivity for thermal management applications. However, for extended life applications, these composites need to be protected against oxidation either through matrix modification with Si, Zr, Hf etc. or by multilayer oxidation protection coatings consisting of SiC, silica, zircon etc.

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

    Science.gov (United States)

    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

  7. Temperature dependent structural variation from 2D supramolecular network to 3D interpenetrated metal–organic framework: In situ cleavage of S–S and C–S bonds

    Energy Technology Data Exchange (ETDEWEB)

    Ugale, Bharat; Singh, Divyendu; Nagaraja, C.M., E-mail: cmnraja@iitrpr.ac.in

    2015-03-15

    Two new Zn(II)–organic compounds, [Zn(muco)(dbds){sub 2}(H{sub 2}O){sub 2}] (1) and [Zn(muco)(dbs)] (2) (where, muco=trans, trans-muconate dianion, dbds=4,4′-dipyridyldisulfide and dbs=4,4′-dipyridylsulfide) have been synthesized from same precursors but at two different temperatures. Both the compounds have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, IR spectroscopy, thermal analysis and photoluminescence studies. Compound 1 prepared at room temperature possesses a molecular structure extended to 2D supramolecular network through (H–O…H) hydrogen-bonding interactions. Compound 2, obtained at high temperature (100 °C) shows a 3-fold interpenetrating 3D framework constituted by an in situ generated dbs linker by the cleavage of S–S and C–S bonds of dbds linker. Thus, the influence of reaction temperature on the formation of two structural phases has been demonstrated. Both 1 and 2 exhibit ligand based luminescence emission owing to n→π⁎ and π→π⁎ transitions and also high thermal stabilities. - Graphical abstract: The influence of temperature on the formation of two structural phases, a 2D supramolecular network and a 3D 3-fold interpenetrating framework has been demonstrated and their luminescence emission is measured. - Highlights: • Two new Zn(II)–organic compounds were synthesized by tuning reaction temperatures. • Temperature induced in situ generation of dbs linker has been observed. • The compounds exhibit high thermal stability and luminescence emission properties. • The effect of temperature on structure, dimension and topology has been presented.

  8. Temperature dependent structural variation from 2D supramolecular network to 3D interpenetrated metal–organic framework: In situ cleavage of S–S and C–S bonds

    International Nuclear Information System (INIS)

    Two new Zn(II)–organic compounds, [Zn(muco)(dbds)2(H2O)2] (1) and [Zn(muco)(dbs)] (2) (where, muco=trans, trans-muconate dianion, dbds=4,4′-dipyridyldisulfide and dbs=4,4′-dipyridylsulfide) have been synthesized from same precursors but at two different temperatures. Both the compounds have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, IR spectroscopy, thermal analysis and photoluminescence studies. Compound 1 prepared at room temperature possesses a molecular structure extended to 2D supramolecular network through (H–O…H) hydrogen-bonding interactions. Compound 2, obtained at high temperature (100 °C) shows a 3-fold interpenetrating 3D framework constituted by an in situ generated dbs linker by the cleavage of S–S and C–S bonds of dbds linker. Thus, the influence of reaction temperature on the formation of two structural phases has been demonstrated. Both 1 and 2 exhibit ligand based luminescence emission owing to n→π⁎ and π→π⁎ transitions and also high thermal stabilities. - Graphical abstract: The influence of temperature on the formation of two structural phases, a 2D supramolecular network and a 3D 3-fold interpenetrating framework has been demonstrated and their luminescence emission is measured. - Highlights: • Two new Zn(II)–organic compounds were synthesized by tuning reaction temperatures. • Temperature induced in situ generation of dbs linker has been observed. • The compounds exhibit high thermal stability and luminescence emission properties. • The effect of temperature on structure, dimension and topology has been presented

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

    Science.gov (United States)

    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.

  10. Comparison of Bond Character in Hydrocarbons and Fullerenes

    OpenAIRE

    Snoke, D. W.; Cardona, M.; Sanguinetti, S.; Benedek, G

    1996-01-01

    We present a comparison of the bond polarizabilities for carbon-carbon bonds in hydrocarbons and fullerenes, using two different models for the fullerene Raman spectrum and the results of Raman measurements on ethane and ethylene. We find that the polarizabilities for single bonds in fullerenes and hydrocarbons compare well, while the double bonds in fullerenes have greater polarizability than in ethylene.

  11. Nanographene reinforced carbon/carbon composites

    Science.gov (United States)

    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

  12. Si(111) cleavage and the (2 x 1) reconstruction process

    Science.gov (United States)

    Pearson, E. M.; Halicioglu, T.; Tiller, W. A.

    1987-01-01

    Using a computer simulation technique with a semiempirical potential, a Si crystal was cleaved along the (111) plane. The pi-bonded chain structural features of the Si(111) cleavage surface are observed and found to be a consequence of the dynamics of this cleavage process and seem not to be influenced by the final energetics.

  13. Chemical bond cleavage induced by electron heating

    International Nuclear Information System (INIS)

    Gas emissions from titanium-metalloid compounds (titanium nitride and oxide) have been investigated to understand the effects of a microwave field on chemical reactions. We employed a high vacuum system (PO2 = 10−6 Pa) to observe in situ reductions. For titanium oxides, H-field heating significantly differed from conventional one in terms of oxygen emissions. For titanium nitride, the emissions were also induced by microwave heating. These tendencies were observed at temperatures above 1000 °C. A quantum chemical interpretation is provided to explain the emissions of the gases, and the experimental data is in good agreement with results predicted using the electronic energy band structure.

  14. Catalytic graphitization of carbon/carbon composites by lanthanum oxide

    Institute of Scientific and Technical Information of China (English)

    ZHANG Can; LU Guimin; SUN Ze; YU Jianguo

    2012-01-01

    Graphitized carbon/carbon composites were prepared by the process of catalytic graphitization with the rare-earth catalyst,lanthanum oxide (La2O3),in order to increase the degree of graphitization and reduce the electrical resistivity.The modified coal tar pitch and coal-based needle coke were used as carbon source,and a small amount of La2O3 was added to catalyze the graphitization of the disordered carbon materials.The effects of La2O3 catalyst on the graphitization degree and microstructure oftbe carbon/carbon composites were investigated by X-ray diffraction,scanning electron microscopy,and Raman spectroscopy.The results showed that La2O3 promoted the formation of more perfect and larger crystallites,and improved the electrical/mechanical properties of carbon/carbon composites.Carbon/carbon composites with a lower electrical resistivity (7.0 μΩ·m) could be prepared when adding 5 wt.% La2O3 powder with heating treatment at 2800 ℃.The catalytic effect of La2O3 for the graphitization of carbon/carbon composites was analyzed.

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

    Science.gov (United States)

    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.

  16. Study of the damaging mechanisms of a copper / carbon - carbon composite under thermomechanical loading

    International Nuclear Information System (INIS)

    The purpose of this work is to understand and to identify the damaging mechanisms of Carbon-Carbon composite bonded to copper under thermomechanical loading. The study of the composite allowed the development of non-linear models. These ones have been introduced in the finite elements analysis code named CASTEM2000. They have been validated according to a correlation between simulation and mechanical tests on multi-material samples. These tests have also permitted us to better understand the behaviour of the bonding between composite and copper (damaging and fracture modes for different temperatures) under shear and tensile loadings. The damaging mechanisms of the bond under thermomechanical loading have been studied and identified according to microscopic observations on mock-ups which have sustained thermal cycling tests: some cracks appear in the composite, near the bond between the composite and the copper. The correlation between numerical and experimental results have been improved because of the reliability of the composite modelization, the use of residual stresses and the results of the bond mechanical characterization. (author)

  17. Cleavage of nucleic acids

    Science.gov (United States)

    Prudent, James R.; Hall, Jeff G.; Lyamichev, Victor I.; Brow, Mary Ann D.; Dahlberg, James E.

    2000-01-01

    The present invention relates to means for the detection and characterization of nucleic acid sequences, as well as variations in nucleic acid sequences. The present invention also relates to methods for forming a nucleic acid cleavage structure on a target sequence and cleaving the nucleic acid cleavage structure in a site-specific manner. The structure-specific nuclease activity of a variety of enzymes is used to cleave the target-dependent cleavage structure, thereby indicating the presence of specific nucleic acid sequences or specific variations thereof.

  18. Carbon-Carbon High Melt Coating for Nozzle Extensions Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The High Melt Coating system is applied to a carbon-carbon structure and embeds HfC, ZrB2 in the outer layers. ACC High Melt builds on the time tested base material...

  19. Carbon-Carbon High Melt Coating for Nozzle and Nozzle Extensions Project

    Data.gov (United States)

    National Aeronautics and Space Administration — C-CAT, which has proven carbon-carbon fabrication capabilities, will investigate use of ACC-6 High Melt oxidation protective system on carbon-carbon for use on the...

  20. Densification mechanism of chemical vapor infiltration technology for carbon/carbon composites

    Institute of Scientific and Technical Information of China (English)

    CHEN Jian-xun; XIONG Xiang; HUANG Qi-zhong; YI Mao-zhong; HUANG Bai-yun

    2007-01-01

    Carbon/carbon composites were fabricated using pressure-gradient chemical vapor infiltration(CVI) technology with propane (C3H6) as the carbon precursor gas and nitrogen (N2) as the carrier gas. The chemical process of deposition of pyrolytic carbon was deduced by analyzing the component of molecules in gas phase and observing the microstructure of deposition carbon. The results show that the process of deposition starts from the breakdown of C-C single bond of propene (C3H6), and forms two kinds of active groups in the heterogeneous gas phase reaction. Afterwards, these active groups form many stable bigger molecules and deposit on carbon fiber surface. At the same time, hydrogen atoms of the bigger molecules absorbed on carbon fiber surface are eliminated and the solid pyrolytic carbon matrix is formed in the heterogeneous reaction process.

  1. Photochemical Degradation of Lignin through αC—O Bond Cleavage of Non Phenolic Benzyl Aryl Ether Units. A Study of the Photochemistry of a(2',4',6'-Trimethyl-Phenoxy)-3,4 Dimethoxy Toluene

    International Nuclear Information System (INIS)

    The results of this study show that, even in the case of a complete chemical group protection (phenolic groups as aliphatic ethers, carbonyl groups reduced to CH2), the UV part of the sunlight near 300 nm can initiate a benzylic cleavage responsible for a subsequent yellowing of the lignin materials

  2. Intermediate Temperature Carbon - Carbon Composite Structures. CRADA Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Lara-Curzio, Edgar [ORNL

    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.

  3. AASPT Carbon/Carbon Aircraft Brake Disk Granted MPA

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    @@ Xi'an Chaoma Technology Co. Ltd. was issued Parts Manufacturer Approval (PMA) for Carbon/Carbon aircraft brake disk for Airbus 320 series by Civil Aviation Administration of China (CAAC). The company is held by Academy of Aerospace Solid Propulsion Technology (AASPT), a subsidiary of China Aerospace Science and Technology Corporation (CASC). It is the first approval given to a Chinese company to design and produce brakes for main civilian aircraft.

  4. Ratcheting of the substrate from the zymogen to proteinase conformations directs the sequential cleavage of prothrombin by prothrombinase

    OpenAIRE

    Bianchini, Elsa P.; Orcutt, Steven J.; Panizzi, Peter; Bock, Paul E.; Krishnaswamy, Sriram

    2005-01-01

    Prothrombinase catalyzes thrombin formation by the ordered cleavage of two peptide bonds in prothrombin. Although these bonds are likely ≈36 Å apart, sequential cleavage of prothrombin at Arg-320 to produce meizothrombin, followed by its cleavage at Arg-271, are both accomplished by equivalent exosite interactions that tether each substrate to the enzyme and facilitate presentation of the scissile bond to the active site of the catalyst. We show that impairing the conformational transition fr...

  5. Four advances in carbon-carbon materials technology

    Science.gov (United States)

    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.

  6. High-Melt Carbon-Carbon Coating for Nozzle Extensions

    Science.gov (United States)

    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.

  7. Selective cleavage of pepsin by molybdenum metallopeptidase

    Energy Technology Data Exchange (ETDEWEB)

    Yenjai, Sudarat; Malaikaew, Pinpinat; Liwporncharoenvong, Teerayuth [Department of Chemistry, Faculty of Science, Srinakharinwirot University, Sukhumvit 23, Bangkok 10110 (Thailand); Buranaprapuk, Apinya, E-mail: apinyac@swu.ac.th [Department of Chemistry, Faculty of Science, Srinakharinwirot University, Sukhumvit 23, Bangkok 10110 (Thailand)

    2012-03-02

    Graphical abstract: Molybdenum metallopeptidase: the Mo(VI) cluster with six molybdenum cations has the ability to cleave protein under mild conditions (37 Degree-Sign C, pH 7) without reducing agents. The reaction required only low concentration of ammonium heptamolybdatetetrahydrate ((NH{sub 4}){sub 6}Mo{sub 7}O{sub 24}{center_dot}4H{sub 2}O) (0.125 mM). The reaction undergoes possibly via a hydrolytic mechanism. This is the first demonstration of protein cleavage by a molybdenum cluster. Highlights: Black-Right-Pointing-Pointer This is the first demonstration of protein cleavage by a Mo(VI) cluster with six molybdenum cations. Black-Right-Pointing-Pointer The cleavage reaction undergoes at mild conditions. Black-Right-Pointing-Pointer No need of reducing agents. Black-Right-Pointing-Pointer Only low concentration of Mo(VI) cluster and short time of incubation are needed. -- Abstract: In this study, the cleavage of protein by molybdenum cluster is reported for the first time. The protein target used is porcine pepsin. The data presented in this study show that pepsin is cleaved to at least three fragments with molecular weights of {approx}23, {approx}19 and {approx}16 kDa when the mixture of the protein and ammonium heptamolybdate tetrahydrate ((NH{sub 4}){sub 6}Mo{sub 7}O{sub 24}{center_dot}4H{sub 2}O) was incubated at 37 Degree-Sign C for 24 h. No self cleavage of pepsin occurs at 37 Degree-Sign C, 24 h indicating that the reaction is mediated by the metal ions. N-terminal sequencing of the peptide fragments indicated three cleavage sites of pepsin between Leu 112-Tyr 113, Leu 166-Leu 167 and Leu 178-Asn 179. The cleavage reaction occurs after incubation of the mixture of pepsin and (NH{sub 4}){sub 6}Mo{sub 7}O{sub 24}{center_dot}4H{sub 2}O) only for 2 h. However, the specificity of the cleavage decreases when incubation time is longer than 48 h. The mechanism for cleavage of pepsin is expected to be hydrolytic chemistry of the amide bonds in the protein

  8. Selective cleavage of pepsin by molybdenum metallopeptidase

    International Nuclear Information System (INIS)

    Graphical abstract: Molybdenum metallopeptidase: the Mo(VI) cluster with six molybdenum cations has the ability to cleave protein under mild conditions (37 °C, pH 7) without reducing agents. The reaction required only low concentration of ammonium heptamolybdatetetrahydrate ((NH4)6Mo7O24·4H2O) (0.125 mM). The reaction undergoes possibly via a hydrolytic mechanism. This is the first demonstration of protein cleavage by a molybdenum cluster. Highlights: ► This is the first demonstration of protein cleavage by a Mo(VI) cluster with six molybdenum cations. ► The cleavage reaction undergoes at mild conditions. ► No need of reducing agents. ► Only low concentration of Mo(VI) cluster and short time of incubation are needed. -- Abstract: In this study, the cleavage of protein by molybdenum cluster is reported for the first time. The protein target used is porcine pepsin. The data presented in this study show that pepsin is cleaved to at least three fragments with molecular weights of ∼23, ∼19 and ∼16 kDa when the mixture of the protein and ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24·4H2O) was incubated at 37 °C for 24 h. No self cleavage of pepsin occurs at 37 °C, 24 h indicating that the reaction is mediated by the metal ions. N-terminal sequencing of the peptide fragments indicated three cleavage sites of pepsin between Leu 112-Tyr 113, Leu 166-Leu 167 and Leu 178-Asn 179. The cleavage reaction occurs after incubation of the mixture of pepsin and (NH4)6Mo7O24·4H2O) only for 2 h. However, the specificity of the cleavage decreases when incubation time is longer than 48 h. The mechanism for cleavage of pepsin is expected to be hydrolytic chemistry of the amide bonds in the protein backbone.

  9. Les trifluoro(organo)borates de potassium : nouvelles perspectives pour la formation de liaisons carbone-carbone à l'aide de complexes du rhodium

    OpenAIRE

    Pucheault, Mathieu

    2004-01-01

    This manuscript describes the use of potassium trifluoro(organo)borates in rhodiumcatalyzed carbon-carbon bond forming reactions. These easy to purify and very stable reagents turned out to constitute a valuable alternative to other boron reagents commonly used in transition metal catalyzed reactions. Asymmetric rhodium-catalyzed 1,4-additions of trifluoroborates were developed with the use of a chiral diphosphine which allowed a good control of the enantioselectivity. Under neutral condition...

  10. The First Example of Cation Radical Induced Ether Cleavage of Benzyl Phenyl Ether

    International Nuclear Information System (INIS)

    A thermally stable benzyl phenyl ether has been shown to cleavage under mild conditions. The new reaction described herein further expands the chemistry of the ether cleavage by cation radicals. Over the last several years, our lab has discovered cation radical-induced oxidative C-O bond cleavages such as carbonates (eq 1), carbamates (eq 2), peroxides (eq 3), and alcohols (eq 4), where R is either tert-butyl or benzyl. It was recognized from those reactions that carbocationic chemistry with C-O bond cleavages was predominant, with a 2:1 stoichiometry of Th+·:oxidized molecules

  11. Scale-up of Carbon/Carbon Bipolar Plates

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. NDE for Characterizing Oxidation Damage in Reinforced Carbon-Carbon

    Science.gov (United States)

    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.

  13. Study of the damaging mechanisms of a copper / carbon - carbon composite under thermomechanical loading; Etude des mecanismes d'endommagement d'un assemblage cuivre / composite carbone - carbone sous chargement thermomecanique

    Energy Technology Data Exchange (ETDEWEB)

    Moncel, L

    1999-06-18

    The purpose of this work is to understand and to identify the damaging mechanisms of Carbon-Carbon composite bonded to copper under thermomechanical loading. The study of the composite allowed the development of non-linear models. These ones have been introduced in the finite elements analysis code named CASTEM2000. They have been validated according to a correlation between simulation and mechanical tests on multi-material samples. These tests have also permitted us to better understand the behaviour of the bonding between composite and copper (damaging and fracture modes for different temperatures) under shear and tensile loadings. The damaging mechanisms of the bond under thermomechanical loading have been studied and identified according to microscopic observations on mock-ups which have sustained thermal cycling tests: some cracks appear in the composite, near the bond between the composite and the copper. The correlation between numerical and experimental results have been improved because of the reliability of the composite modelization, the use of residual stresses and the results of the bond mechanical characterization. (author)

  14. Inhibition of RecA-mediated cleavage in covalent dimers of UmuD.

    OpenAIRE

    Lee, M. H.; Guzzo, A; Walker, G C

    1996-01-01

    Disulfide-cross-linked UmuD2 derivatives were cleaved poorly upon incubation with activated RecA. Reducing the disulfide bonds prior to incubating the derivatives with RecA dramatically increased their extent of cleavage. These observations suggest that the UmuD monomer is a better substrate for the RecA-mediated cleavage reaction than the dimer.

  15. Prospects for using carbon-carbon composites for EMI shielding

    Science.gov (United States)

    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.

  16. NMR experiments for the measurement of proton-proton and carbon-carbon residual dipolar couplings in uniformly labelled oligosaccharides

    Energy Technology Data Exchange (ETDEWEB)

    Martin-Pastor, Manuel [Universidad de Santiago de Compostela, Laboratorio Integral de Estructura de Biomoleculas Jose. R. Carracido, Unidade de Resonancia Magnetica, RIAIDT (Spain)], E-mail: mmartin@usc.es; Canales-Mayordomo, Angeles; Jimenez-Barbero, Jesus [Departamento de Estructura y funcion de proteinas, Centro de Investigaciones Biologicas, CSIC (Spain)], E-mail: jjbarbero@cib.csic.es

    2003-08-15

    A 2D-HSQC-carbon selective/proton selective-constant time COSY, 2D-HSQC-(sel C, sel H)-CT COSY experiment, which is applicable to uniformly {sup 13}C isotopically enriched samples (U-{sup 13}C) of oligosaccharides or oligonucleotides is proposed for the measurement of proton-proton RDC in crowded regions of 2D-spectra. In addition, a heteronuclear constant time-COSY experiment, {sup 13}C-{sup 13}C CT-COSY, is proposed for the measurement of one bond carbon-carbon RDC in these molecules. These two methods provide an extension, to U-{sup 13}C molecules, of the original homonuclear constant time-COSY experiment proposed by Tian et al. (1999) for saccharides. The combination of a number of these RDC with NOE data may provide the method of choice to study oligosaccharide conformation in the free and receptor-bound state.

  17. Various Carbon to Carbon Bond Lengths Inter-related via the Golden Ratio, and their Linear Dependence on Bond Energies

    CERN Document Server

    Heyrovska, Raji

    2008-01-01

    This work presents the relations between the carbon to carbon bond lengths in the single, double and triple bonds and in graphite, butadiene and benzene. The Golden ratio, which was shown to divide the Bohr radius into two parts pertaining to the charged particles, the electron and proton, and to divide inter-atomic distances into their cationic and anionic radii, also plays a role in the carbon-carbon bonds and in the ionic/polar character of those in graphite, butadiene and benzene. Further, the bond energies of the various CC bonds are shown to vary linearly with the bond lengths.

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

    Science.gov (United States)

    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.

  19. Exploiting Catalytic Promiscuity for Biocatalysis: Carbon-Carbon Bond Formation by a Proline-Based Tautomerase

    OpenAIRE

    Miao, Yufeng

    2015-01-01

    Een belangrijk thema bij het ontwikkelen van nieuwe biokatalysatoren is katalytische promiscuïteit, waarbij een enzym alternatieve reacties katalyseert naast de reactie die biologisch relevant is. Promiscue enzymactiviteiten zijn een veelbelovende bron van synthetisch bruikbare katalytische omzettingen. Aangezien het actieve centrum van de meeste enzymen is opgebouwd uit meerdere potentiële katalytische groepen die kunnen dienen als zuren, basen of nucleofielen, zijn promiscue enzymactiviteit...

  20. Exploiting Catalytic Promiscuity for Biocatalysis : Carbon-Carbon Bond Formation by a Proline-Based Tautomerase

    NARCIS (Netherlands)

    Miao, Yufeng

    2015-01-01

    Een belangrijk thema bij het ontwikkelen van nieuwe biokatalysatoren is katalytische promiscuïteit, waarbij een enzym alternatieve reacties katalyseert naast de reactie die biologisch relevant is. Promiscue enzymactiviteiten zijn een veelbelovende bron van synthetisch bruikbare katalytische omzettin

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

    Science.gov (United States)

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

    2016-09-01

    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. PMID:27539722

  2. Continuously operated falling film microreactor for selective hydrogenation of carbon-carbon triple bonds

    OpenAIRE

    Rehm, Thomas H.; Berguerand, Charline; Ek, Satu; Zapf, Ralf; Löb, Patrick; Nikoshvili, Linda; Kiwi-Minsker, Lioubov

    2016-01-01

    Despite significant advances in the fabrication and applications of microreactors for production of chemicals, their use for catalytic reactions remains a challenge, especially in fine chemical synthesis where the selectivity towards the desired product is an issue. A falling film microstructured reactor (FFMR) was tested in the selective hydrogenation of 2-butyne-1,4-diol (1) to its olefinic derivative (2). The FFMR plates were coated with Al2O3 or ZnO followed by the deposition of Pd nanopa...

  3. Texturing Carbon-carbon Composite Radiator Surfaces Utilizing Atomic Oxygen

    Science.gov (United States)

    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. Novel apparatus for joining of carbon-carbon composites

    Science.gov (United States)

    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.

  5. Invasive cleavage of nucleic acids

    Science.gov (United States)

    Prudent, James R.; Hall, Jeff G.; Lyamichev, Victor I.; Brow, Mary Ann D.; Dahlberg, James E.

    1999-01-01

    The present invention relates to means for the detection and characterization of nucleic acid sequences, as well as variations in nucleic acid sequences. The present invention also relates to methods for forming a nucleic acid cleavage structure on a target sequence and cleaving the nucleic acid cleavage structure in a site-specific manner. The structure-specific nuclease activity of a variety of enzymes is used to cleave the target-dependent cleavage structure, thereby indicating the presence of specific nucleic acid sequences or specific variations thereof.

  6. Lyocell Based Carbon Carbon Composite for Use as a Large Exit Cone Material Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The NASA Office of the Chief Technologist (OCT) has identified a "carbon-carbon nozzle (domestic source)" as a "Top Technical Challenge" in the 2011-2016 timeframe...

  7. Alternative Fabrication Designs for Carbon-Carbon (C-C) Nozzle Extensions Project

    Data.gov (United States)

    National Aeronautics and Space Administration — In order for carbon-carbon nozzle extensions and exit cones to serve as practical, low cost components for future Earth-to-Orbit propulsion systems, it is necessary...

  8. Studies on pharmacological activation of human serum immunoglobulin G by chemical modification and active subfragments. IV. Induction of anti-inflammatory activity by chemical cleavage of interchain disulfide bonds in human immunoglobulin G and pharmacological activity of alkylated subfragments.

    Science.gov (United States)

    Mimura, T; Tsujikawa, K; Nakajima, H; Okabe, M; Kohama, Y; Iwai, M; Yokoyama, K

    1986-01-01

    Commercially available human serum immunoglobulin G (IgG, native IgG) was separated into two fractions (Fr.I and II) using a diethylaminoethyl cellulose column. Heavy and light chains containing fractions were obtained from these two fractions after carboxamide-methylation. Thus, these fractions were subjected to an anti-inflammatory screening procedure and were shown to have a potent inhibitory activity against rat carrageenin induced paw edema, while no effect was observed in native IgG, Fr.I or II. The reduction and alkylation of the interchain disulfide bonds were essential to induce the anti-inflammatory activity. The anti-inflammatory activity of alkylated heavy and light chains of Fr.I (Fr.I-H and I-L) was also noted in subacute inflammation caused by the felt pellet and croton oil granuloma methods. Moreover, strong membrane stabilizing activities of Fr.I-H and I-L were demonstrated in vitro using rat red blood cell membrane and liver lysosomal membrane. PMID:3712209

  9. Structural and Biochemical Characterization of a Copper-Binding Mutant of the Organomercurial Lyase MerB: Insight into the Key Role of the Active Site Aspartic Acid in Hg-Carbon Bond Cleavage and Metal Binding Specificity.

    Science.gov (United States)

    Wahba, Haytham M; Lecoq, Lauriane; Stevenson, Michael; Mansour, Ahmed; Cappadocia, Laurent; Lafrance-Vanasse, Julien; Wilkinson, Kevin J; Sygusch, Jurgen; Wilcox, Dean E; Omichinski, James G

    2016-02-23

    In bacterial resistance to mercury, the organomercurial lyase (MerB) plays a key role in the detoxification pathway through its ability to cleave Hg-carbon bonds. Two cysteines (C96 and C159; Escherichia coli MerB numbering) and an aspartic acid (D99) have been identified as the key catalytic residues, and these three residues are conserved in all but four known MerB variants, where the aspartic acid is replaced with a serine. To understand the role of the active site serine, we characterized the structure and metal binding properties of an E. coli MerB mutant with a serine substituted for D99 (MerB D99S) as well as one of the native MerB variants containing a serine residue in the active site (Bacillus megaterium MerB2). Surprisingly, the MerB D99S protein copurified with a bound metal that was determined to be Cu(II) from UV-vis absorption, inductively coupled plasma mass spectrometry, nuclear magnetic resonance, and electron paramagnetic resonance studies. X-ray structural studies revealed that the Cu(II) is bound to the active site cysteine residues of MerB D99S, but that it is displaced following the addition of either an organomercurial substrate or an ionic mercury product. In contrast, the B. megaterium MerB2 protein does not copurify with copper, but the structure of the B. megaterium MerB2-Hg complex is highly similar to the structure of the MerB D99S-Hg complexes. These results demonstrate that the active site aspartic acid is crucial for both the enzymatic activity and metal binding specificity of MerB proteins and suggest a possible functional relationship between MerB and its only known structural homologue, the copper-binding protein NosL.

  10. Heterolytic cleavage of ammonia N-H bond by bifunctional activation in silica-grafted single site Ta(V) imido amido surface complex. Importance of the outer sphere NH3 assistance

    KAUST Repository

    Gouré, Eric

    2011-01-01

    Ammonia N-H bond is cleaved at room temperature by the silica-supported tantalum imido amido complex [(≡SiO)2Ta(NH)(-NH2)], 2, if excess ammonia is present, but requires 150 °C to achieve the same reaction if only one equivalent NH3 is added to 2. MAS solid-state 15N NMR and in situ IR spectroscopic studies of the reaction of either 15N or 2H labeled ammonia with 2 show that initial coordination of the ammonia is followed by scrambling of either 15N or 2H among ammonia, amido and imido groups. Density functional theory (DFT) calculations with a cluster model [{(μ-O)[(H3SiO) 2SiO]2}Ta(NH)(-NH2)(NH3)], 2 q·NH3, show that the intramolecular H transfer from Ta-NH2 to TaNH is ruled out, but the H transfers from the coordinated ammonia to the amido and imido groups have accessible energy barriers. The energy barrier for the ammonia N-H activation by the Ta-amido group is energetically preferred relative to the Ta-imido group. The importance of excess NH3 for getting full isotope scrambling is rationalized by an outer sphere assistance of ammonia acting as proton transfer agent, which equalizes the energy barriers for H transfer from coordinated ammonia to the amido and imido groups. In contrast, additional coordinated ammonia does not favor significantly the H transfer. These results rationalize the experimental conditions used. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011.

  11. Irradiation-induced structure and property changes in tokamak plasma-facing, carbon-carbon composites

    International Nuclear Information System (INIS)

    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 plasma fusion reactors, such as the International Thermonuclear Experimental Reactor (ITER), will require advanced carbon-carbon composite materials possessing high thermal conductivity to manage the anticipated severe heat loads. Moreover, ignition machines such as ITER will produce large neutron fluxes. 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 (HFIR) at Oak Ridge National Laboratory (ORNL). A peak damage dose of 4.7 displacements per atom (dpa) at 600 degree C was attained. The carbon materials irradiated included uni-directional, two-directional, and three-directional carbon-carbon composites. Dimensional changes are reported for the composite materials and are related to single crystal dimensional changes through fiber and composite structural models. Moreover, the irradiation-induced dimensional changes are reported and discussed in terms of their architecture, fiber type, and graphitization temperature. The effect of neutron irradiation on thermal conductivity of two three-directional, carbon-carbon composites is reported and the recovery of thermal conductivity due to thermal annealing is discussed

  12. Site-specifically Hydrolytic Cleavage of Oxidized Insulin B Chain With Cu(II) Ion

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Electrospray mass spectrometry investigation shows that denatured oxidized insulin B chain can be selectively cleaved by simple Cu(II) ion and the site of cleavage is at Gly8-Ser9 bond which is second amide bond left from His 10 in the sequence of oxidized insulin B chain.

  13. Multielectron redox reactions involving C-C coupling and cleavage in uranium Schiff base complexes

    International Nuclear Information System (INIS)

    The reaction of U(III) with Schiff base ligands and the reduction of U(IV) Schiff base complexes both promote C-C bond formation to afford dinuclear or mononuclear U(IV) amido complexes, which can release up to four electrons to substrates through the oxidative cleavage of the C-C bond. (authors)

  14. Selective cleavage enhanced by acetylating the side chain of lysine.

    Science.gov (United States)

    Fu, Leixiaomeng; Chen, Tingting; Xue, Gaiqing; Zu, Lily; Fang, Weihai

    2013-01-01

    Selective cleavage is of great interest in mass spectrometry studies as it can help sequence identification by promoting simple fragmentation pattern of peptides and proteins. In this work, the collision-induced dissociation of peptides containing internal lysine and acetylated lysine residues were studied. The experimental and computational results revealed that multiple fragmentation pathways coexisted when the lysine residue was two amino acid residues away from N-terminal of the peptide. After acetylation of the lysine side-chain, b(n)+ ions were the most abundant primary fragment products and the Lys(Ac)-Gly amide bond became the dominant cleavage site via an oxazolone pathway. Acetylating the side-chain of lysine promoted the selective cleavage of Lys-Xxx amide bond and generated much more information of the peptide backbone sequence. The results re-evaluate the selective cleavage due to the lysine basic side-chain and provide information for studying the post-translational modification of proteins and other bio-molecules containing Lys residues. PMID:23303756

  15. Cleavage behaviors in nuclear vessel steels

    International Nuclear Information System (INIS)

    Cleavage behaviors of nuclear vessel steels in the transition temperature range are reviewed. Viewpoints are presented to assist understanding of cleavage crack speed, cleavage initiation, cleavage arrest, and the sensitivity of fracture toughness to constraint and temperature. The importance of high local stress elevations by high strain rate is emphasized. This report is designated as HSST Report No. 149

  16. Restricted Active Site Docking by Enzyme-bound Substrate Enforces the Ordered Cleavage of Prothrombin by Prothrombinase*

    OpenAIRE

    Hacisalihoglu, Ayse; Panizzi, Peter; Bock, Paul E.; Camire, Rodney M.; Krishnaswamy, Sriram

    2007-01-01

    The preferred pathway for prothrombin activation by prothrombinase involves initial cleavage at Arg320 to produce meizothrombin, which is then cleaved at Arg271 to liberate thrombin. Exosite binding drives substrate affinity and is independent of the bond being cleaved. The pathway for cleavage is determined by large differences in Vmax for cleavage at the two sites within intact prothrombin. By fluorescence binding studies in the absence of catalysis, we have assessed the ability of the indi...

  17. 4-Dimethylaminoazobenzenes: carcinogenicities and reductive cleavage by microsomal azo reductase.

    Science.gov (United States)

    Lambooy, J P; Koffman, B M

    1985-01-01

    Twenty-four 4-dimethylaminoazobenzenes (DABs) in which systematic structural modifications have been made in the prime ring have been studied for substrate specificity for microsomal azo reductase. The DABs were also evaluated for carcinogenicity and it was found that there was no correlation between carcinogenicity and extent of azo bond cleavage by azo reductase. While any substituent in the prime ring reduces the rate of cleavage of the azo bond relative to the unsubstituted dye, there is a correlation between substituent size and susceptibility to the enzyme. Substituent size was also found to be a significant factor in the induction of hepatomas by the dyes. Preliminary studies have shown that there appears to be a positive correlation between microsomal riboflavin content and the activity of the azo reductase.

  18. Intrinsic transcript cleavage activity of RNA polymerase.

    OpenAIRE

    Orlova, M; Newlands, J; Das, A; Goldfarb, A; Borukhov, S

    1995-01-01

    The GreA and GreB transcript cleavage factors of Escherichia coli suppress elongation arrest and may have a proofreading role in transcription. With the use of E. coli greA-greB- mutant, RNA polymerase is demonstrated to possess substantial intrinsic transcript cleavage activity. Mildly alkaline pH mimics the effect of the Gre proteins by inducing transcript cleavage in ternary complexes and antagonizing elongation arrest through a cleavage-and-restart reaction. Thus, transcript cleavage cons...

  19. Thermal and Mechanical Performance of a Carbon/Carbon Composite Spacecraft Radiator

    Science.gov (United States)

    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.

  20. Hydrogen cleavage by solid-phase frustrated Lewis pairs.

    Science.gov (United States)

    Xing, Jun-Yi; Buffet, Jean-Charles; Rees, Nicholas H; Nørby, Peter; O'Hare, Dermot

    2016-08-18

    We report the direct synthesis of a solid-phase frustrated Lewis pair (s-FLP) by combining a silica-supported Lewis acid ([triple bond, length as m-dash]SiOB(C6F5)2, s-BCF) with a Lewis base (tri-tert-butylphosphine, (t)Bu3P) to give [[triple bond, length as m-dash]SiOB(C6F5)2][(t)Bu3P]. Reaction of this s-FLP with H2 under mild conditions led to heterolytic H-H bond cleavage and the formation of [[triple bond, length as m-dash]SiOB(H)(C6F5)2][(t)Bu3PH].

  1. Facile scission of isonitrile carbon–nitrogen triple bond using a diborane(4) reagent

    OpenAIRE

    Asakawa, Hiroki; Lee, Ka-Ho; Lin, Zhenyang; Yamashita, Makoto

    2014-01-01

    Transition metal reagents and catalysts are generally effective to cleave all three bonds (one σ and two π) in a triple bond despite its high bonding energy. Recently, chemistry of single-bond cleavage by using main-group element compounds is rapidly being developed in the absence of transition metals. However, the cleavage of a triple bond using non-transition-metal compounds is less explored. Here we report that an unsymmetrical diborane(4) compound could react with carbon monoxide and tert...

  2. The effect of neutron irradiation on the structure and properties of carbon-carbon composite materials

    International Nuclear Information System (INIS)

    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 will 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 1.59 dpa at 600 degrees 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, thermal conductivity 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

  3. HCSE method for detection of small carbon-carbon couplings and their signs, comparison with SLAP pulse sequence.

    Science.gov (United States)

    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.

  4. Passive Hypersonic Boundary Layer Transition Control Using Ultrasonically Absorptive Carbon-Carbon Ceramic with Random Microstructure

    OpenAIRE

    Wagner, Alexander

    2014-01-01

    In the presented work ultrasonically absorptive carbon-carbon ceramic was shown for the first time to delay hypersonic laminar to turbulent boundarylayer transition. Three 7° half-angle cones with nose radii between 0.1 mm and 5.0 mm and a total length of 1100 mm were tested at zero angle of attack in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) at Mach 7.5. One model was equipped with an inhouse manufactured ultrasonically absorptive carbon-carbon ...

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

    Science.gov (United States)

    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.

  6. Regioselective Cleavage of Thioether Linkages in Microcystin Conjugates.

    Science.gov (United States)

    Zemskov, Ivan; Kropp, Heike M; Wittmann, Valentin

    2016-07-25

    Microcystins are cyanobacterial toxins that can be found in fresh and coastal waters during algal blooms. Microcystin contamination of water can cause severe poisoning of animals and humans. Quantification of these toxins in biological samples is complicated because a major proportion of microcystins is covalently linked to proteins through thioether bonds formed through a Michael-type addition of cysteine residues of proteins to an N-methyldehydroalanine residue in the microcystins. We investigated chemical methods that can be used to cleave such thioether bonds by means of an elimination reaction that leaves the microcystin backbone intact for subsequent analysis. The known reagent O-mesitylenesulfonylhydroxylamine (MSH) led to regioselective thioether cleavage, but a large excess of reagent was needed, thus making purification challenging. An unexpected side reaction observed during the investigation of the base-induced elimination inspired us to develop a new thioether-cleavage methodology based on the addition of propargylamine as a nucleophile that can trap the elimination product. This methodology could be successfully applied to the quantitative cleavage of a microcystin-LF-glutathione conjugate. The alkyne moiety introduced by this procedure offers the possibility for further reactions with azides by using click chemistry, which might be useful for the derivatization or isolation of microcystins. PMID:27346324

  7. Prediction on Carbon/Carbon Composites Ablative Performance by Artificial Neutral Net

    Institute of Scientific and Technical Information of China (English)

    Guanghui BAI; Songhe MENG; Boming ZHANG; Yang LIU

    2008-01-01

    A preliminary estimation of ablation property for carbon-carbon composites by artificial neutral net (ANN) method was presented.It was found that the carbon-carbon composites' density,degree of graphitization and the sort of matrix are the key controlling factors for its ablative performance.Then,a brief fuzzy mathe-matical relationship was established between these factors and ablative performance.Through experiments,the performance of the ANN was evaluated,which was used in the ablative performance prediction of C/C composites.When the training set,the structure and the training parameter of the net change,the best match ratio of these parameters was achieved.Based on the match ratio,this paper forecasts and evalu-ates the carbon-carbon ablation performance.Through experiences,the ablative performance prediction of carbon-carbon using ANN can achieve the line ablation rate,which satisfies the need of precision of practical engineering fields.

  8. Theoretical estimates of photoproduction cross sections for neutral subthreshold pions in carbon-carbon collisions

    Science.gov (United States)

    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 pins 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.

  9. Centralspindlin in Rappaport's cleavage signaling.

    Science.gov (United States)

    Mishima, Masanori

    2016-05-01

    Cleavage furrow in animal cell cytokinesis is formed by cortical constriction driven by contraction of an actomyosin network activated by Rho GTPase. Although the role of the mitotic apparatus in furrow induction has been well established, there remain discussions about the detailed molecular mechanisms of the cleavage signaling. While experiments in large echinoderm embryos highlighted the role of astral microtubules, data in smaller cells indicate the role of central spindle. Centralspindlin is a constitutive heterotetramer of MKLP1 kinesin and the non-motor CYK4 subunit and plays crucial roles in formation of the central spindle and recruitment of the downstream cytokinesis factors including ECT2, the major activator of Rho during cytokinesis, to the site of division. Recent reports have revealed a role of this centralspindlin-ECT2 pathway in furrow induction both by the central spindle and by the astral microtubules. Here, a unified view of the stimulation of cortical contractility by this pathway is discussed. Cytokinesis, the division of the whole cytoplasm, is an essential process for cell proliferation and embryonic development. In animal cells, cytokinesis is executed using a contractile network of actin filaments driven by a myosin-II motor that constricts the cell cortex (cleavage furrow ingression) into a narrow channel between the two daughter cells, which is resolved by scission (abscission) [1-3]. The anaphase-specific organization of the mitotic apparatus (MA, spindle with chromosomes plus asters) positions the cleavage furrow and plays a major role in spatial coupling between mitosis and cytokinesis [4-6]. The nucleus and chromosomes are dispensable for furrow specification [7-10], although they contribute to persistent furrowing and robust completion in some cell types [11,12]. Likewise, centrosomes are not essential for cytokinesis, but they contribute to the general fidelity of cell division [10,13-15]. Here, classical models of cleavage furrow

  10. Various Carbon to Carbon Bond Lengths Inter-related via the Golden Ratio, and their Linear Dependence on Bond Energies

    OpenAIRE

    Heyrovska, Raji

    2008-01-01

    This work presents the relations between the carbon to carbon bond lengths in the single, double and triple bonds and in graphite, butadiene and benzene. The Golden ratio, which was shown to divide the Bohr radius into two parts pertaining to the charged particles, the electron and proton, and to divide inter-atomic distances into their cationic and anionic radii, also plays a role in the carbon-carbon bonds and in the ionic/polar character of those in graphite, butadiene and benzene. Further...

  11. Kinetics of hairpin ribozyme cleavage in yeast.

    OpenAIRE

    Donahue, C P; Fedor, M J

    1997-01-01

    Hairpin ribozymes catalyze a self-cleavage reaction that provides a simple model for quantitative analyses of intracellular mechanisms of RNA catalysis. Decay rates of chimeric mRNAs containing self-cleaving ribozymes give a direct measure of intracellular cleavage kinetics in yeast. Intracellular ribozyme-mediated cleavage occurs at similar rates and shows similar inhibition by ribozyme mutations as ribozyme-mediated reactions in vitro, but only when ribozymes are located in a favorable mRNA...

  12. Carbon-Carbon Composites as Recuperator Material for Direct Gas Brayton Systems

    Energy Technology Data Exchange (ETDEWEB)

    RA Wolf

    2006-07-19

    Of the numerous energy conversion options available for a space nuclear power plant (SNPP), one that shows promise in attaining reliable operation and high efficiency is the direct gas Brayton (GB) system. In order to increase efficiency, the GB system incorporates a recuperator that accounts for nearly half the weight of the energy conversion system (ECS). Therefore, development of a recuperator that is lighter and provides better performance than current heat exchangers could prove to be advantageous. The feasibility of a carbon-carbon (C/C) composite recuperator core has been assessed and a mass savings of 60% and volume penalty of 20% were projected. The excellent thermal properties, high-temperature capabilities, and low density of carbon-carbon materials make them attractive in the GB system, but development issues such as material compatibility with other structural materials in the system, such as refractory metals and superalloys, permeability, corrosion, joining, and fabrication must be addressed.

  13. Carbon-carbon composites for orthopedic prosthesis and implants. CRADA final report

    Energy Technology Data Exchange (ETDEWEB)

    Burchell, T D; Klett, J W; Strizak, J P [Oak Ridge National Lab., TN (United States); Baker, C [FMI, Biddeford, ME (United States)

    1998-01-21

    The prosthetic implant market is extensive. For example, because of arthritic degeneration of hip and knee cartilage and osteoporotic fractures of the hip, over 200,000 total joint replacements (TJRs) are performed in the United States each year. Current TJR devices are typically metallic (stainless steel, cobalt, or titanium alloy) and are fixed in the bone with polymethylacrylate (PMMA) cement. Carbon-carbon composite materials offer several distinct advantages over metals for TJR prosthesis. Their mechanical properties can be tailored to match more closely the mechanical properties of human bone, and the composite may have up to 25% porosity, the size and distribution of which may be controlled through processing. The porous nature of carbon-carbon composites will allow for the ingrowth of bone, achieving biological fixation, and eliminating the need for PMMA cement fixation.

  14. Multi-physical field coupling simulation of TCVI process for preparing carbon/carbon composites

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    To prepare Carbon/Carbon (C/C) composites with advanced performance, the thermal gradient chemical vapor infiltration (TCVI) process has been optimized by simulation. A 2D axisymmetric unstable model was built, which included convection, conduction, diffusion, densification reactions in the pores and the evolution of the porous medium. The multi-physical field coupling model was solved by finite element method (FEM) and iterative calculation. The time evolution of the fluid, temperature and preform density field were obtained by the calculation. It is indicated that convection strongly affects the temperature field. For the preform of carbon/carbon composites infiltrated for 100 h by TCVI, the radial average densities from simulation agrees well with those from experiment. The model is validated to be reliable and the simulation has capability of forecasting the process.

  15. Si-Al-Ir Oxidation Resistant Coating for Carbon/Carbon Composites by Slurry Dipping

    Institute of Scientific and Technical Information of China (English)

    Min Huang; Kezhi Li; Hejun Li; Qiangang Fu; Yu Wang

    2009-01-01

    A Si-Al-Ir oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping.The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-Ir coating were studied by XRD (X-ray diffraction), SEM (scanning electron microscopy), and isothermal oxidation test at 1773 K in air, respectively.The surface of the as-prepared Si-Al-Ir coating was dense and the thickness was approximately 100/μm.Its anti-oxidation property was superior to that of the inner SiC coating.The weight loss of SiC/Si-Al-Ir coated carbon/carbon composites was less than 5 wt.pct after oxidation at 1773 K in air for 79 h.The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

  16. Erosion of carbon/carbon by solar wind charged particle radiation during a solar probe mission

    Science.gov (United States)

    Sokolowski, Witold; O'Donnell, Tim; Millard, Jerry

    1991-01-01

    The possible erosion of a carbon/carbon thermal shield by solar wind-charged particle radiation is reviewed. The present knowledge of erosion data for carbon and/or graphite is surveyed, and an explanation of erosion mechanisms under different charged particle environments is discussed. The highest erosion is expected at four solar radii. Erosion rates are analytically estimated under several conservative assumptions for a normal quiet and worst case solar wind storm conditions. Mass loss analyses and comparison studies surprisingly indicate that the predicted erosion rate by solar wind could be greater than by nominal free sublimation during solar wind storm conditions at four solar radii. The predicted overall mass loss of a carbon/carbon shield material during the critical four solar radii flyby can still meet the mass loss mission requirement of less than 0.0025 g/sec.

  17. Carbon-Carbon Cross Coupling Reactions in Ionic Liquids Catalysed by Palladium Metal Nanoparticles

    OpenAIRE

    Martin H. G. Prechtl; Scholten, Jackson D.; Jairton Dupont

    2010-01-01

    A brief summary of selected pioneering and mechanistic contributions in the field of carbon-carbon cross-coupling reactions with palladium nanoparticles (Pd-NPs) in ionic liquids (ILs) is presented. Five exemplary model systems using the Pd-NPs/ILs approach are presented: Heck, Suzuki, Stille, Sonogashira and Ullmann reactions which all have in common the use of ionic liquids as reaction media and the use of palladium nanoparticles as reservoir for the catalytically active palladium species.

  18. Effect of Oxidation on Fracture Toughness of a Carbon/Carbon Composite

    Institute of Scientific and Technical Information of China (English)

    ZHANG Chengyun; YAN Kefei; QIAO Shengru; LI Mei; HAN Dong; GUO Yong

    2012-01-01

    The fracture toughness of a carbon/carbon composites oxidized at different temperature for 1 h was measured.The fracture surfaces were examined by scanning electron microscopy (SEM).The results indicate that oxidation temperature has significant effects on the fracture toughness.Fracture toughness decreases with the increase of the weight loss.The SEM images reveal that the decrease of fracture toughness was mainly attributed to the oxidation of the interface in the composite.

  19. Cleavage speed and implantation potential of early-cleavage embryos in IVF or ICSI cycles

    OpenAIRE

    Lee, Meng-Ju; Lee, Robert Kuo-Kuang; Lin, Ming-Huei; Hwu, Yuh-Ming

    2012-01-01

    We examined whether there is a correlation among early embryo cleavage, speed of cleavage, and implantation potential for in-vitro fertilization (IVF) treatment and intracytoplasmic sperm injection (ICSI). This retrospective study examined 112 cycles of IVF and 82 cycles of ICSI in patients less than 40 years of age. Early cleavage was defined as embryonic mitosis occurring 25–27 h after insemination. These day-3 embryos were then grouped according to cleavage speed (rapid, normal, and slow) ...

  20. Pre-mRNA 3’ Cleavage is Reversibly Inhibited In Vitro by Cleavage Factor Dephosphorylation

    OpenAIRE

    Ryan, Kevin

    2007-01-01

    During 3' end formation most pre-mRNAs undergo endonucleolytic cleavage and polyadenylation in the 3' untranslated region. Very little is known concerning the role that post-translational modifications play in the function and regulation of the factors required for 3' cleavage. Using the reconstituted pre-mRNA cleavage reaction, we find that non-specific dephosphorylation of HeLa cell nuclear extract leads to the loss of 3' cleavage activity. A variety of serine/threonine phosphatases inhibit...

  1. Lightweight, Ultra-High-Temperature, CMC-Lined Carbon/Carbon Structures

    Science.gov (United States)

    Wright, Matthew J.; Ramachandran, Gautham; Williams, Brian E.

    2011-01-01

    Carbon/carbon (C/C) is an established engineering material used extensively in aerospace. The beneficial properties of C/C include high strength, low density, and toughness. Its shortcoming is its limited usability at temperatures higher than the oxidation temperature of carbon . approximately 400 C. Ceramic matrix composites (CMCs) are used instead, but carry a weight penalty. Combining a thin laminate of CMC to a bulk structure of C/C retains all of the benefits of C/C with the high temperature oxidizing environment usability of CMCs. Ultramet demonstrated the feasibility of combining the light weight of C/C composites with the oxidation resistance of zirconium carbide (ZrC) and zirconium- silicon carbide (Zr-Si-C) CMCs in a unique system composed of a C/C primary structure with an integral CMC liner with temperature capability up to 4,200 F (.2,315 C). The system effectively bridged the gap in weight and performance between coated C/C and bulk CMCs. Fabrication was demonstrated through an innovative variant of Ultramet fs rapid, pressureless melt infiltration processing technology. The fully developed material system has strength that is comparable with that of C/C, lower density than Cf/SiC, and ultra-high-temperature oxidation stability. Application of the reinforced ceramic casing to a predominantly C/C structure creates a highly innovative material with the potential to achieve the long-sought goal of long-term, cyclic high-temperature use of C/C in an oxidizing environment. The C/C substructure provided most of the mechanical integrity, and the CMC strengths achieved appeared to be sufficient to allow the CMC to perform its primary function of protecting the C/C. Nozzle extension components were fabricated and successfully hot-fire tested. Test results showed good thermochemical and thermomechanical stability of the CMC, as well as excellent interfacial bonding between the CMC liner and the underlying C/C structure. In particular, hafnium-containing CMCs on

  2. Fracto—emissions in Catastrophic Cleavage Process

    Institute of Scientific and Technical Information of China (English)

    HonglaiTAN; WeiYANG

    1996-01-01

    Fracto-emissions accompanying crack propagation are observed in the recent experiments.The energy impulses during and after fracture stimulate the fracto-emissions.Model concerning atomic scale cleavage processes is proposed to formulate a catastrophic fracure theory relevant to these phenomena.A criterion for catastrophic jump of the cleavage potential is applied to representative crystals.

  3. Microstructure and cleavage in lath martensitic steels

    Directory of Open Access Journals (Sweden)

    John W Morris Jr, Chris Kinney, Ken Pytlewski and Y Adachi

    2013-01-01

    Full Text Available In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified 'classic' lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov–Sachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage.

  4. Microstructure and cleavage in lath martensitic steels

    International Nuclear Information System (INIS)

    In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified ‘classic’ lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov–Sachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage. (paper)

  5. Pistol ribozyme adopts a pseudoknot fold facilitating site-specific in-line cleavage.

    Science.gov (United States)

    Ren, Aiming; Vušurović, Nikola; Gebetsberger, Jennifer; Gao, Pu; Juen, Michael; Kreutz, Christoph; Micura, Ronald; Patel, Dinshaw J

    2016-09-01

    The field of small self-cleaving nucleolytic ribozymes has been invigorated by the recent discovery of the twister, twister-sister, pistol and hatchet ribozymes. We report the crystal structure of a pistol ribozyme termed env25, which adopts a compact tertiary architecture stabilized by an embedded pseudoknot fold. The G-U cleavage site adopts a splayed-apart conformation with in-line alignment of the modeled 2'-O of G for attack on the adjacent to-be-cleaved P-O5' bond. Highly conserved residues G40 (N1 position) and A32 (N3 and 2'-OH positions) are aligned to act as a general base and a general acid, respectively, to accelerate cleavage chemistry, with their roles confirmed by cleavage assays on variants, and an increased pKa of 4.7 for A32. Our structure of the pistol ribozyme defined how the overall and local topologies dictate the in-line alignment at the G-U cleavage site, with cleavage assays on variants revealing key residues that participate in acid-base-catalyzed cleavage chemistry. PMID:27398999

  6. Experiments on schistosity and slaty cleavage

    Science.gov (United States)

    Becker, George Ferdinand

    1904-01-01

    Schistosity as a structure is important, and it is a part of the business of geologists to explain its origin. Slaty cleavage has further and greater importance as a possible tectonic feature. Scarcely a great mountain range exists, or has existed, along the course of which belts of slaty rock are not found, the dip of the cleavage usually approaching verticality. Are these slate belts equivalent to minutely distributed step faults of great total throw, or do they indicate compression perpendicular to the cleavage without attendant relative dislocation? Evidently the answer to this question is of first importance in the interpretation of orogenic phenomena.

  7. [Recent knowledge about intestinal absorption and cleavage of carotenoids].

    Science.gov (United States)

    Borel, P; Drai, J; Faure, H; Fayol, V; Galabert, C; Laromiguière, M; Le Moël, G

    2005-01-01

    Our knowledge about intestinal absorption and cleavage of carotenoids has rapidly grown during the last years. New facts about carotenoid absorption have emerged while some controversies about cleavage are close to end. The knowledge of the absorption and conversion processes is indispensable to understand and interpret the perturbations that can occur in the metabolism of carotenoids and vitamin A. Recently, it has been shown that the absorption of certain carotenoids is not passive - as believed for a long time - but is a facilitated process that requires, at least for lutein, the class B-type 1 scavenger receptor (SR-B1). Various epidemiological and clinical studies have shown wide variations in carotenoid absorption from one subject to another, such differences are now explained by the structure of the concerned carotenoid, by the nature of the food that is absorbed with the carotenoid, by diverse exogenous factors like the intake of medicines or interfering components, by diet factors, by genetic factors, and by the nutritional status of the subject. Recently, the precise mechanism of beta-carotene cleavage by betabeta-carotene 15,15' monooxygenase (EC 1.14.99.36) - formerly called beta-carotene 15,15' dioxygenase (ex EC 1.13.11.21) - has been discovered, and a second enzyme which cleaves asymmetrically the beta-carotene molecule has been found. beta-carotene 15,15' monooxygenase only acts on the 15,15' bond, thus forming two molecules of retinal from one molecule of beta-carotene by central cleavage. Even though the betabeta-carotene 15,15' monooxygenase is much more active on the beta-carotene molecule, a study has shown that it can act on all carotenoids. Searchers now agree that other enzymes that can catalyse an eccentric cleavage of carotenoids probably exist, but under physiological conditions the betabeta-carotene 15,15' monooxygenase is by far the most active, and it is mainly effective in the small bowel mucosa and in the liver. However the

  8. ABLATION PROPERTY OF SiC-TaSi2 COATED CARBON/CARBON COMPOSITES

    OpenAIRE

    SHUPING LI; KEZHI LI; HEJUN LI

    2010-01-01

    To prevent the carbon/carbon (C/C) composites from ablation, a new type of ablation protective coating was prepared on the surface of the C/C composites by a step pack cementation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis show, the coatings obtained by pack cementation were silicon carbide/tantalum silicide (SiC-TaSi2). The ablation behavior of the coated samples were evaluated by the oxyacetylene flame. The results show that, the SiC-TaSi2 coating can...

  9. Model for the Effect of Fiber Bridging on the Fracture Resistance of Reinforced-Carbon-Carbon

    Science.gov (United States)

    Chan, Kwai S.; Lee, Yi-Der; Hudak, Stephen J., Jr.

    2009-01-01

    A micromechanical methodology has been developed for analyzing fiber bridging and resistance-curve behavior in reinforced-carbon-carbon (RCC) panels with a three-dimensional (3D) composite architecture and a silicon carbide (SiC) surface coating. The methodology involves treating fiber bridging traction on the crack surfaces in terms of a weight function approach and a bridging law that relates the bridging stress to the crack opening displacement. A procedure has been developed to deduce material constants in the bridging law from the linear portion of the K-resistance curve. This report contains information on the application of procedures and outcomes.

  10. Metalloradical-Catalyzed Selective 1,2-Rh-H Insertion into the Aliphatic Carbon-Carbon Bond of Cyclooctane

    NARCIS (Netherlands)

    Y.W. Chan; B. de Bruin; K.S. Chan

    2015-01-01

    The selective aliphatic carboncarbon activation of cyclo-octane (c-octane) was achieved via the Rh-II(ttp)-catalyzed 1,2-addition of Rh(ttp)H to give Rh(ttp)(n-octyl) (ttp = tetratolylporphyrinato dianion) in good yield under mild reaction conditions. This mechanism is further supported by DFT calcu

  11. Bond Issues.

    Science.gov (United States)

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of…

  12. Nondestructive Evaluation (NDE) for Characterizing Oxidation Damage in Cracked Reinforced Carbon-Carbon (RCC)

    Science.gov (United States)

    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 nondestructive evaluation (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.

  13. Nondestructive Evaluation (NDE) for Characterizing Oxidation Damage in Cracked Reinforced Carbon-Carbon

    Science.gov (United States)

    Roth, Don J.; Jacobson, Nathan S.; Rauser, Richard W.; Wincheski, Russell A.; Walker, James L.; Cosgriff, Laura A.

    2010-01-01

    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 nondestructive evaluation (NDE) methods. These specimens were heat treated in air at 1143 C 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 3mm. Single-sided NDE methods were used because 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.

  14. Improvement of capacitive performances of symmetric carbon/carbon supercapacitors by addition of nanostructured polypyrrole powder

    Science.gov (United States)

    Benhaddad, L.; Gamby, J.; Makhloufi, L.; Pailleret, A.; Pillier, F.; Takenouti, H.

    2016-03-01

    A nanostructured polypyrrole powder was synthesized in a previous work from the oxidation of pyrrole by a nanostructured MnO2 powder used simultaneously as an oxidizing agent and a sacrificial template in a redox heterogeneous mechanism. In this study, this original PPy powder was used as an active additive material with different ratio in carbon/carbon symmetrical supercapacitors whose performances were studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) using a Swagelok-type cell. From the EIS spectra, the complex capacitance was extracted using a model involving two Cole-Cole type complex capacitances linked in series. The specific capacitance values evaluated by EIS and cyclic voltammetry are in a good agreement between them. The results show that the addition of nanostructured polypyrrole powder improves significantly the specific capacitance of the carbon electrode and consequently the performances of carbon/carbon supercapacitors. The original and versatile synthesis method used to produce this polypyrrole powder appears to be attractive for large scale production of promising additives for electrode materials of supercapacitors.

  15. Mechanical testing and modelling of carbon-carbon composites for aircraft disc brakes

    Science.gov (United States)

    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. Numerical simulation of isothermal chemical vapor infiltration process in fabrication of carbon-carbon composites by finite element method

    Institute of Scientific and Technical Information of China (English)

    李克智; 李贺军; 姜开宇

    2000-01-01

    The chemical vapor infiltration process in fabrication of carbon-carbon composites is highly inefficient and requires long processing time. These limitations add considerably to the cost of fabrication and restrict the application of this material. Efforts have been made to study the CVI process in fabrication of carbon-carbon composites by computer simulation and predict the process parameters, density, porosity, etc. According to the characteristics of CVI process, the basic principle of FEM and mass transport, the finite element model has been established. Incremental finite element equations and the elemental stiffness matrices have been derived for the first time. The finite element program developed by the authors has been used to simulate the ICVI process in fabrication of carbon-carbon composites. Computer color display of simulated results can express the densification and distributions of density and porosity in preform clearly. The influence of process parameters on the densification of prefo

  17. Cleavage of resveratrol in fungi: characterization of the enzyme Rco1 from Ustilago maydis.

    Science.gov (United States)

    Brefort, Thomas; Scherzinger, Daniel; Limón, M Carmen; Estrada, Alejandro F; Trautmann, Danika; Mengel, Carina; Avalos, Javier; Al-Babili, Salim

    2011-02-01

    Ustilago maydis, the causative agent of corn smut disease, contains two genes encoding members of the carotenoid cleavage oxygenase family, a group of enzymes that cleave double bonds in different substrates. One of them, Cco1, was formerly identified as a β-carotene cleaving enzyme. Here we elucidate the function of the protein encoded by the second gene, termed here as Ustilago maydis Resveratrol cleavage oxygenase 1 (Um Rco1). In vitro incubations of heterologously expressed and purified UM Rco1 with different carotenoid and stilbene substrates demonstrate that it cleaves the interphenyl Cα-Cβ double bond of the phytoalexin resveratrol and its derivative piceatannol. Um Rco1 exhibits a high degree of substrate specificity, as suggested by the lack of activity on carotenoids and the other resveratrol-related compounds tested. The activity of Um Rco1 was confirmed by incubation of U. maydis rco1 deletion and over-expression strains with resveratrol. Furthermore, treatment with resveratrol resulted in striking alterations of cell morphology. However, pathogenicity assays indicated that Um rco1 is largely dispensable for biotrophic development. Our work reveals Um Rco1 as the first eukaryotic resveratrol cleavage enzyme identified so far. Moreover, Um Rco1 represents a subfamily of fungal enzymes likely involved in the degradation of stilbene compounds, as suggested by the cleavage of resveratrol by homologs from Aspergillus fumigatus, Chaetomium globosum and Botryotinia fuckeliana.

  18. Cleavage kinetics and anchor linked intermediates in solid phase peptide amide synthesis.

    Science.gov (United States)

    Dürr, H; Beck-Sickinger, A G; Schnorrenberg, G; Rapp, W; Jung, G

    1991-08-01

    Kinetics and cleavage conditions of peptide amide synthesis were studied using the anchor molecules 5-(4'-aminomethyl-3',5'-dimethoxyphenoxy)valeric acid (4-ADPV-OH) and 5-(2'-aminomethyl-3'-5'-dimethoxyphenoxy) valeric acid (2-ADPV-OH). Unexpectedly the anchor amide alanyl-4-ADPV-NH2 was isolated and characterized as an intermediate during the cleavage with trifluoroacetic acid (TFA) of alanyl-4-ADPV-alanyl-aminomethyl-polystyrene to yield the alanine amide. As a matter of fact the NH--CH alpha bond of the alanyl spacer has to be cleaved to form this intermediate. Using TFA-dichloromethane (1:9) alanyl-4-ADPV-NH2 was obtained as a cleavage product in 50% yield within 60 min, whereas the isomeric alanyl-2-ADPV-NH2 was formed more slowly under these mild conditions. At high TFA concentration no difference between the 2- and 4-ADPV anchor was observed in the rate of formation of the free alanine amide. The presence of tryptophan amide in the cleavage mixture resulted in an anchor alkylated tryptophan amide, which remains stable in acidic solution but disappears rapidly in the presence of the resin. A low TFA/high TFA cleavage procedure is recommended for peptide amid synthesis applying the ADPV anchor.

  19. Distinct mechanisms for DNA cleavage by myoglobin with a designed heme active center.

    Science.gov (United States)

    Zhao, Yuan; Du, Ke-Jie; Gao, Shu-Qin; He, Bo; Wen, Ge-Bo; Tan, Xiangshi; Lin, Ying-Wu

    2016-03-01

    Heme proteins perform diverse biological functions, of which myoglobin (Mb) is a representative protein. In this study, the O2 carrier Mb was shown to cleave double stranded DNA upon aerobic dithiothreitol-induced reduction, which is fine-tuned by an additional distal histidine, His29 or His43, engineered in the heme active center. Spectroscopic (UV-vis and EPR) and inhibition studies suggested that free radicals including singlet oxygen and hydroxyl radical are responsible for efficient DNA cleavage via an oxidative cleavage mechanism. On the other hand, L29E Mb, with a distinct heme active center involving three water molecules in the met form, was found to exhibit an excellent DNA cleavage activity that was not depending on O2. Inhibition and ligation studies demonstrated for the first time that L29E Mb cleaves double stranded DNA into both the nicked circular and linear forms via a hydrolytic cleavage mechanism, which resembles native endonucleases. This study provides valuable insights into the distinct mechanisms for DNA cleavage by heme proteins, and lays down a base for creating artificial DNA endonucleases by rational design of heme proteins. Moreover, this study suggests that the diverse functions of heme proteins can be fine-tuned by rational design of the heme active center with a hydrogen-bonding network.

  20. Does Cleavage Work at Work? Men, but Not Women, Falsely Believe Cleavage Sells a Weak Product

    Science.gov (United States)

    Glick, Peter; Chrislock, Karyna; Petersik, Korinne; Vijay, Madhuri; Turek, Aleksandra

    2008-01-01

    We examined whether men, but not women, would be distracted by a female sales representative's exposed cleavage, leading to greater perceived efficacy for a weak, but not for a strong product. A community sample of 88 men and 97 women viewed a video of a female pharmaceutical sales representative who (a) had exposed cleavage or dressed modestly…

  1. Parental Bonding

    Directory of Open Access Journals (Sweden)

    T. Paul de Cock

    2014-08-01

    Full Text Available Estimating the early parent–child bonding relationship can be valuable in research and practice. Retrospective dimensional measures of parental bonding provide a means for assessing the experience of the early parent–child relationship. However, combinations of dimensional scores may provide information that is not readily captured with a dimensional approach. This study was designed to assess the presence of homogeneous groups in the population with similar profiles on parental bonding dimensions. Using a short version of the Parental Bonding Instrument (PBI, three parental bonding dimensions (care, authoritarianism, and overprotection were used to assess the presence of unobserved groups in the population using latent profile analysis. The class solutions were regressed on 23 covariates (demographics, parental psychopathology, loss events, and childhood contextual factors to assess the validity of the class solution. The results indicated four distinct profiles of parental bonding for fathers as well as mothers. Parental bonding profiles were significantly associated with a broad range of covariates. This person-centered approach to parental bonding has broad utility in future research which takes into account the effect of parent–child bonding, especially with regard to “affectionless control” style parenting.

  2. The potato carotenoid cleavage dioxygenase 4 catalyzes a single cleavage of β-ionone ring-containing carotenes and non-epoxidated xanthophylls

    KAUST Repository

    Bruno, Mark

    2015-04-01

    Down-regulation of the potato carotenoid cleavage dioxygenase 4 (StCCD4) transcript level led to tubers with altered morphology and sprouting activity, which also accumulated higher levels of violaxanthin and lutein leading to elevated carotenoid amounts. This phenotype indicates a role of this enzyme in tuber development, which may be exerted by a cleavage product. In this work, we investigated the enzymatic activity of StCCD4, by expressing the corresponding cDNA in carotenoid accumulating Escherichia coli strains and by performing in vitro assays with heterologously expressed enzyme. StCCD4 catalyzed the cleavage of all-. trans-β-carotene at the C9\\'-C10\\' double bond, leading to β-ionone and all-. trans-β-apo-10\\'-carotenal, both in vivo and in vitro. The enzyme also cleaved β,β-cryptoxanthin, zeaxanthin and lutein either at the C9\\'-C10\\' or the C9-C10 double bond in vitro. In contrast, we did not observe any conversion of violaxanthin and only traces of activity with 9-. cis-β-carotene, which led to 9-. cis-β-apo-10\\'-carotenal. Our data indicate that all-. trans-β-carotene is the likely substrate of StCCD4 in planta, and that this carotene may be precursor of an unknown compound involved in tuber development.

  3. The potato carotenoid cleavage dioxygenase 4 catalyzes a single cleavage of β-ionone ring-containing carotenes and non-epoxidated xanthophylls.

    Science.gov (United States)

    Bruno, Mark; Beyer, Peter; Al-Babili, Salim

    2015-04-15

    Down-regulation of the potato carotenoid cleavage dioxygenase 4 (StCCD4) transcript level led to tubers with altered morphology and sprouting activity, which also accumulated higher levels of violaxanthin and lutein leading to elevated carotenoid amounts. This phenotype indicates a role of this enzyme in tuber development, which may be exerted by a cleavage product. In this work, we investigated the enzymatic activity of StCCD4, by expressing the corresponding cDNA in carotenoid accumulating Escherichia coli strains and by performing in vitro assays with heterologously expressed enzyme. StCCD4 catalyzed the cleavage of all-trans-β-carotene at the C9'-C10' double bond, leading to β-ionone and all-trans-β-apo-10'-carotenal, both in vivo and in vitro. The enzyme also cleaved β,β-cryptoxanthin, zeaxanthin and lutein either at the C9'-C10' or the C9-C10 double bond in vitro. In contrast, we did not observe any conversion of violaxanthin and only traces of activity with 9-cis-β-carotene, which led to 9-cis-β-apo-10'-carotenal. Our data indicate that all-trans-β-carotene is the likely substrate of StCCD4 in planta, and that this carotene may be precursor of an unknown compound involved in tuber development. PMID:25703194

  4. C-Terminally modified peptides via cleavage of the HMBA linker by O-, i>N>- or S-nucleophiles

    DEFF Research Database (Denmark)

    Hansen, Jonas; Diness, Frederik; Meldal, Morten Peter

    2016-01-01

    A large variety of C-terminally modified peptides was obtained by nucleophilic cleavage of the ester bond in solid phase linked peptide esters of 4-hydroxymethyl benzamide (HMBA). The developed methods provided peptides, C-terminally functionalized as esters, amides and thioesters, with high puri...

  5. THE BIOCHEMICAL CHARACTERIZATION OF FERRET CAROTENE-9', 10'-MONOOXYGENASE CATALYZING CLEAVAGE OF CAROTENOIDS IN VITRO AND IN VIVO

    Science.gov (United States)

    Previous studies have shown that beta -carotene 15,15'-monooxygenase (CMO1) catalyzes the cleavage of beta -carotene at the central carbon 15, 15’-double bond, but cleaves lycopene with much lower activity. However, expressing the mouse carotene-9’,10’-monooxygenase (CMO2) in beta-carotene/lycopene...

  6. Dataset of cocoa aspartic protease cleavage sites.

    Science.gov (United States)

    Janek, Katharina; Niewienda, Agathe; Wöstemeyer, Johannes; Voigt, Jürgen

    2016-09-01

    The data provide information in support of the research article, "The cleavage specificity of the aspartic protease of cocoa beans involved in the generation of the cocoa-specific aroma precursors" (Janek et al., 2016) [1]. Three different protein substrates were partially digested with the aspartic protease isolated from cocoa beans and commercial pepsin, respectively. The obtained peptide fragments were analyzed by matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/TOF-MS/MS) and identified using the MASCOT server. The N- and C-terminal ends of the peptide fragments were used to identify the corresponding in-vitro cleavage sites by comparison with the amino acid sequences of the substrate proteins. The same procedure was applied to identify the cleavage sites used by the cocoa aspartic protease during cocoa fermentation starting from the published amino acid sequences of oligopeptides isolated from fermented cocoa beans. PMID:27508221

  7. Eurosceptism: the Birth of a New Cleavage?

    Directory of Open Access Journals (Sweden)

    Lorenzo Viviani

    2010-05-01

    Full Text Available Euroscepticism is an ambivalent and polysemic concept, consisting of the theme of the European identity, the construction of European Union as new polity, the development of an opposition as expression of new social cleavage, and finally the perspective of an ideological politicization of the european integration by national and supranational political actors. The article attempts to make light on the nature and on the dynamics of development of the euroscepticism through a sequence of analysis that starts from the identity of Europe (what we mean by euroscepticism, then addresses the social dimension of Europe (what we mean by the new european cleavage, and it finally examines the political dimension (the risks and opportunities of politicization by political parties of the european cleavage.

  8. Dataset of cocoa aspartic protease cleavage sites

    Directory of Open Access Journals (Sweden)

    Katharina Janek

    2016-09-01

    Full Text Available The data provide information in support of the research article, “The cleavage specificity of the aspartic protease of cocoa beans involved in the generation of the cocoa-specific aroma precursors” (Janek et al., 2016 [1]. Three different protein substrates were partially digested with the aspartic protease isolated from cocoa beans and commercial pepsin, respectively. The obtained peptide fragments were analyzed by matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/TOF-MS/MS and identified using the MASCOT server. The N- and C-terminal ends of the peptide fragments were used to identify the corresponding in-vitro cleavage sites by comparison with the amino acid sequences of the substrate proteins. The same procedure was applied to identify the cleavage sites used by the cocoa aspartic protease during cocoa fermentation starting from the published amino acid sequences of oligopeptides isolated from fermented cocoa beans.

  9. Activation of the C−N Bond in Nitromethane by Palladium α-Diimine Complexes

    OpenAIRE

    Golisz, Suzanne R.; Hazari, Nilay; Labinger, Jay A.; Bercaw, John E.

    2009-01-01

    The reaction of glyoxal-derived α-diimines with palladium acetates in nitromethane leads to cleavage of the C−N bond in nitromethane, to give palladium nitro complexes in which the α-diimine ligand has been methylated.

  10. Characterization and Damage Evaluation of Coal Tar Pitch Carbon Matrix Used in Carbon/Carbon Composites

    Science.gov (United States)

    Bhagat, Atul Ramesh; Mahajan, Puneet

    2016-09-01

    Flexure, compressive, and shear properties of the carbon matrix in carbon/carbon (C/C) composites made via a pitch impregnation method have been determined. The pitch carbon matrix was made using the same densification cycle used in making the C/C composite. Cyclic compression tests were performed on the matrix specimens. While unloading, a reduction in modulus was observed and residual strains were observed on complete unloading. These features were attributed to the presence of damage and plasticity in the densified matrix. A J 2 plasticity model with damage was used to simulate this behavior numerically. The parameters required for plasticity and damage model were evaluated iteratively by comparing the results in experiments with simulation.

  11. W-Mo-Si/SiC Oxidation Protective Coating for Carbon/Carbon Composites

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A W-Mo-Si/SiC double-layer oxidation protective coating for carbon/carbon (C/C) composites was prepared by a two-step pack cementation technique. XRD (X-ray diffraction) and SEM (scanning electron microscopy)results show that the coating obtained by the first step pack cementation was a thin inner buffer layer of SiC with some cracks and pores, and a new phase of (WxMo1-x)Si2 appeared after the second step pack cementation. Oxidation test shows that, after oxidation in air at 1773 K for 175 h and thermal cycling between 1773 K and room temperature for 18 times, the weight loss of the W-Mo-Si/SiC coated C/C composites was only 2.06%. The oxidation protective failure of the W-Mo-Si/SiC coating was attributed to the formation of some penetrable cracks in the coating.

  12. Fractal characterization of pore microstructure evolution in carbon/carbon composites

    Institute of Scientific and Technical Information of China (English)

    LI MiaoLing; QI LeHua; LI HeJun; XU GuoZhong

    2009-01-01

    A fractal characterization approach was proposed to research pore microstructure evolution in carbon/carbon (C/C) composites during the chemical vapor infiltration process. The data obtained from mercury porosimetry determinations were analyzed using the sponge fractal model and the thermodynamics relation fractal model, respectively. The fractal dimensions of C/C composites at different densification stages were evaluated. The pore microstructure evolution with densification time was studied by fractal dimension analysis. The results showed that ClC composites belong to porous fractal structure. The fractal dimensions increase on the whole with decreasing porosity as the densification proceeds. The fractal dimensions are influenced by the texture of pyrocarbon and decrease with increasing anisotropy from isotropic pyrocarbon to high textural one. Both the complicacy of pore structure and the textural morphology of pyrocarbon can be represented simultaneously by the fractal dimension. The pore evolution of C/C composites in the densification process can be monitored using fractal dimension.

  13. Sodium VCHP with Carbon-Carbon Radiator for Radioisotope Stirling Systems

    Science.gov (United States)

    Tarau, Calin; Anderson, William G.; Miller, William O.; Ramirez, Rogelio

    2010-01-01

    In a Stirling radioisotope system, heat must continually be removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. The Stirling converter normally provides this cooling. If the Stirling convertor stops in the current system the insulation is designed to spoil, preventing damage to the GPHS at the cost of an earlier termination of the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) can be used to allow multiple stops and restarts of the Stirling convertor. A sodium VCHP with a Haynes 230 envelope was designed and fabricated for the Advanced Stirling Radioisotope Generator (ASRG), with a baseline 850° C heater head temperature. When the Stirling convertor is stopped, the heat from the GPHS is rejected to the Cold Side Adapter Flange using a low-mass, carbon-carbon radiator. The VCHP is designed to activate with a AT of 30° C. The 880° C temperature when the Stirling convertor is stopped is high enough to avoid risking standard ASRG operation, but low enough to save most of the heater head life. The VCHP has low mass and low thermal losses for normal operation. The design has been modified from an earlier, stainless steel prototype with a nickel radiator. In addition to replacing the nickel radiator with a low mass carbon-carbon radiator, the radiator location has been moved from the ASRG case to the cold side adapter flange. This flange already removes two-thirds of the heat during normal operation, so it is optimized to transfer heat to the case. The VCHP was successfully tested with a turn-on ΔT of 30° C in three orientations: horizontal, gravity-aided, and against gravity.

  14. Comparison of methods for the quantification of carbonate carbon in atmospheric PM10 aerosol samples

    Science.gov (United States)

    Jankowski, Nicole; Schmidl, Christoph; Marr, Iain L.; Bauer, Heidi; Puxbaum, Hans

    Carbonate carbon (CC) represents an important fraction of atmospheric PM10 along with organic carbon (OC) and elemental carbon (EC), if specific sources (e.g. street abrasion, construction sites, desert dust) contribute to its composition. However, analytical methods for an easy and unambiguous determination of CC in atmospheric aerosols collected on filter matrices are scarce. We propose here a method for the determination of CC based on a heating pretreatment of the sample to remove OC and EC, followed by a total carbon determination to measure CC. This procedure is used for the correction of EC also determined by a heating pretreatment (Cachier, H., Bremond, M.P., Buat-Ménard, P., 1989. Determination of atmospheric soot carbon with a simple thermal method. Tellus 41B, 379-390) but without previous HCl fumigation, as proposed. Comparison of the carbon remaining after the proposed thermal treatment at 460 °C for 60 min in an oxygen stream showed good correlation for the carbonate carbon derived by calculation from the ionic balance for ambient air and street dust samples. Using the "three step" combustion technique it is now possible to determine OC, EC and CC by the use of a TC analyser in the concentration range of 2-200 μg carbon per sample aliquot, with good precision (3-5% RSD for TC and 5-10% for CC) and accuracy. In ambient air samples from a sampling site in Vienna with elevated PM10 levels ("Liesing") CC values as high as 25% of TC and 27% CO 32-; for street dust samples 32% of TC and 25% CO 32- of total PM10 mass were observed.

  15. Cleavage site analysis in picornaviral polyproteins

    DEFF Research Database (Denmark)

    Blom, Nikolaj; Hansen, Jan; Blaas, Dieter;

    1996-01-01

    are indeed cleaved awaits experimental verification. Additionally, we report several errors detected in the protein databases. A computer server for prediction of cleavage sites by picornaviral proteinases is publicly available at the e-mail address NetPicoRNA@cbs.dtu.dk or via WWW at http://www.cbs.dtu.dk/services/NetPicoRNA...

  16. Bond Boom

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Ministry of Finance recently kick-started a pilot program allowing local governments of Shanghai and Shenzhen, and Zhejiang and Guangdong provinces to issue bonds for the first time. How will the new policy affect fiscal capacities of local governments and the broader economy? What else should the country do to build a healthy bond market? Economists and experts discussed these issues in an interview with the ShanghaiSecuritiesJournal. Edited excerpts follow:

  17. Bond Boom

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Ministry of Finance recently kick-started a pilot program allowing local governments of Shanghai and Shenzhen,and Zhejiang and Guangdong provinces to issue bonds for the first time.How will the new policy affect fiscal capacities of local governments and the broader economy? What else should the country do to build a healthy bond market? Economists and experts discussed these issues in an interview with the Shanghai Securities Journal.Edited excerpts follow.

  18. Cross talk between the +73/294 interaction and the cleavage site in RNase P RNA mediated cleavage

    OpenAIRE

    Brännvall, Mathias; Kikovska, Ema; Kirsebom, Leif A.

    2004-01-01

    To monitor functionally important metal ions and possible cross talk in RNase P RNA mediated cleavage we studied cleavage of substrates, where the 2′OH at the RNase P cleavage site (at −1) and/or at position +73 had been replaced with a 2′ amino group (or 2′H). Our data showed that the presence of 2′ modifications at these positions affected cleavage site recognition, ground state binding of substrate and/or rate of cleavage. Cleavage of 2′ amino substituted substrates at different pH showed ...

  19. Autoproteolytic Cleavage and Activation of Human Acid Ceramidase*

    OpenAIRE

    Shtraizent, Nataly; Eliyahu, Efrat; Park, Jae-Ho; He, Xingxuan; Shalgi, Ruth; Schuchman, Edward H.

    2008-01-01

    Herein we report the mechanism of human acid ceramidase (AC; N-acylsphingosine deacylase) cleavage and activation. A highly purified, recombinant human AC precursor underwent self-cleavage into α and β subunits, similar to other members of the N-terminal nucleophile hydrolase superfamily. This reaction proceeded with first order kinetics, characteristic of self-cleavage. AC self-cleavage occurred most rapidly at acidic pH, but also at neutral pH. Site-directed mutagene...

  20. Cleavage specificity analysis of six type II transmembrane serine proteases (TTSPs using PICS with proteome-derived peptide libraries.

    Directory of Open Access Journals (Sweden)

    Olivier Barré

    Full Text Available BACKGROUND: Type II transmembrane serine proteases (TTSPs are a family of cell membrane tethered serine proteases with unclear roles as their cleavage site specificities and substrate degradomes have not been fully elucidated. Indeed just 52 cleavage sites are annotated in MEROPS, the database of proteases, their substrates and inhibitors. METHODOLOGY/PRINCIPAL FINDING: To profile the active site specificities of the TTSPs, we applied Proteomic Identification of protease Cleavage Sites (PICS. Human proteome-derived database searchable peptide libraries were assayed with six human TTSPs (matriptase, matriptase-2, matriptase-3, HAT, DESC and hepsin to simultaneously determine sequence preferences on the N-terminal non-prime (P and C-terminal prime (P' sides of the scissile bond. Prime-side cleavage products were isolated following biotinylation and identified by tandem mass spectrometry. The corresponding non-prime side sequences were derived from human proteome databases using bioinformatics. Sequencing of 2,405 individual cleaved peptides allowed for the development of the family consensus protease cleavage site specificity revealing a strong specificity for arginine in the P1 position and surprisingly a lysine in P1' position. TTSP cleavage between R↓K was confirmed using synthetic peptides. By parsing through known substrates and known structures of TTSP catalytic domains, and by modeling the remainder, structural explanations for this strong specificity were derived. CONCLUSIONS: Degradomics analysis of 2,405 cleavage sites revealed a similar and characteristic TTSP family specificity at the P1 and P1' positions for arginine and lysine in unfolded peptides. The prime side is important for cleavage specificity, thus making these proteases unusual within the tryptic-enzyme class that generally has overriding non-prime side specificity.

  1. Reaction kinetics of bond rotations in graphene

    KAUST Repository

    Skowron, Stephen T.

    2016-04-12

    The formation and healing processes of the fundamental topological defect in graphitic materials, the Stone-Wales (SW) defect, are brought into a chemical context by considering the rotation of a carbon-carbon bond as chemical reaction. We investigate the rates and mechanisms of these SW transformations in graphene at the atomic scale using transmission electron microscopy. We develop a statistical atomic kinetics formalism, using direct observations obtained under different conditions to determine key kinetic parameters of the reactions. Based on the obtained statistics we quantify thermally and irradiation induced routes, identifying a thermal process of healing with an activation energy consistent with predicted adatom catalysed mechanisms. We discover exceptionally high rates for irradiation induced SW healing, incompatible with the previously assumed mechanism of direct knock-on damage and indicating the presence of an efficient nonadiabatic coupling healing mechanism involving beam induced electronic excitations of the SW defect.

  2. Calcium waves along the cleavage furrows in cleavage-stage Xenopus embryos and its inhibition by heparin

    OpenAIRE

    1996-01-01

    Calcium signaling is known to be associated with cytokinesis; however, the detailed spatio-temporal pattern of calcium dynamics has remained unclear. We have studied changes of intracellular free calcium in cleavage-stage Xenopus embryos using fluorescent calcium indicator dyes, mainly Calcium Green-1. Cleavage formation was followed by calcium transients that localized to cleavage furrows and propagated along the furrows as calcium waves. The calcium transients at the cleavage furrows were o...

  3. Direct measurement of acylenzyme hydrolysis demonstrates rate-limiting deacylation in cleavage of physiological sequences by the processing protease Kex2.

    Science.gov (United States)

    Rockwell, N C; Fuller, R S

    2001-03-27

    Saccharomyces cerevisiae Kex2 protease is the prototype for the family of eukaryotic proprotein convertases that includes furin, PC1/3, and PC2. These enzymes belong to the subtilase superfamily of serine proteases and are distinguished from degradative subtilisins by structural features and by their much more stringent substrate specificity. Pre-steady-state studies have shown that both Kex2 and furin exhibit an initial burst of 7-amino-4-methylcoumarin release in cleavage of peptidyl methylcoumarinamide substrates that are based on physiological cleavage sites. Thus, in cleavage of such substrates, formation of the acylenzyme intermediate is fast relative to some later step (deacylation or N-terminal product release). This behavior is significant, because Kex2 also exhibits burst kinetics in cleavage of peptide bonds. k(cat) for cleavage of a tetrapeptidyl methylcoumarinamide substrate based on the physiological yeast substrate pro-alpha-factor exhibits a weak solvent isotope effect, but neither this isotope effect nor temperature dependence studies with this substrate conclusively identify the rate-limiting step for Kex2 cleavage of this substrate. We therefore developed an assay to measure deacylation directly by pulse-chase incorporation of H(2)(18)O in a rapid-quenched-flow mixer followed by mass spectrometric quantitation. The results given by this assay rule out rate-limiting product release for cleavage of this substrate by Kex2. These experiments demonstrate that cleavage of the acylenzyme ester bond, as opposed to either the initial attack on the amide bond or product release, is rate-limiting for the action of Kex2 at physiological sequences. This work demonstrates a fundamental difference in the catalytic strategy of proprotein processing enzymes and degradative subtilisins. PMID:11297433

  4. First-wall tile attachment using carbon-carbon composite fittings

    International Nuclear Information System (INIS)

    As the reality of a tokamak device capable of achieving sustained burn missions approaches, the need for a reliable and maintainable plasma-interfacing first wall becomes more evident. This is especially true of compact ignition tokamaks such as LITE, ISP, and Ignitor. Current studies indicate that the compact ignition tokamak may be designed for inertial cooling using a cryogen such as liquid nitrogen, for active cooling using water, or for a combination of inertial (LN2) and active (H2O) cooling. In none of these cases it is anticipated that the first wall proper will be actively cooled. Based on limiter development for operating tokamaks such as the Tokamak Fusion Test Reactor and on supporting engineering studies, an array of monolithic graphite blocks or tiles of appropriate thickness, size, and shape appears to be the most effective approach for a first-wall design. The entire internal wetted surface of the vacuum vessel, exclusive of penetrations and minimal clearance (∼ 1.5 mm) between tiles, will be covered by the monolithic graphite tiles. One of the major challenges of this first-wall approach will be the physical attachment of the tiles to the vacuum vessel inner surface. This paper presents unique first-wall tile attachment concepts that use structural attachment of the graphite tiles to an Inconel 625 vacuum vessel with carbon-carbon composite structural/mechanical elements

  5. Influence of Temperature and Time Shifts on the Densification of Randomly Oriented Carbon/Carbon Composite

    Directory of Open Access Journals (Sweden)

    Thakur Sudesh Kumar Raunija

    2015-09-01

    Full Text Available The efforts were made to improve the hot-pressing method of carbon/carbon (C/C composite fabrication. The C/C composite was fabricated by hot-pressing the slurry moulded compact followed by carbonisation. The temperature and time shifts during hot-pressing were made in order to see their effect on the densification. Their effect was checked through visual inspection, density measurement, scanning electron microscope (SEM analysis, and mechanical properties evaluation. The results showed that the temperature shift yielded in significant increase in the density after hot-pressing. Further, the density pick up instead of fall after carbonisation was noticed. The results further showed that the time shift too yielded in significant enhancement of density after hot-pressing and showed the pattern after carbonisation similar to the temperature shift. And also showed that the shifts of both temperature and time yielded in significant increase in density and moderate increase in mechanical properties.

  6. Modeling of CVI process in fabrication of carbon/carbon composites by an artificial neural network

    Institute of Scientific and Technical Information of China (English)

    李爱军; 李贺军; 李克智; 顾正彬

    2003-01-01

    The chemical vapor infiltration(CVI) process in fabrication of carbon-carbon composites is very complex and highly inefficient, which adds considerably to the cost of fabrication and limits the application of the material. This paper tries to use a supervised artificial neural network(ANN) to model the nonlinear relationship between parameters of isothermal CVI(ICVI) processes and physical properties of C/C composites. A model for preprocessing dataset and selecting its topology is developed using the Levenberg-Marquardt training algorithm and trained with comprehensive dataset of tubal C/C components collected from experimental data and abundant simulated data obtained by the finite element method. A basic repository on the domain knowledge of CVI processes is established via sufficient data mining by the network. With the help of the repository stored in the trained network, not only the time-dependent effects of parameters in CVI processes but also their coupling effects can be analyzed and predicted. The results show that the ANN system is effective and successful for optimizing CVI processes in fabrication of C/C composites.

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

    Science.gov (United States)

    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

  8. Infrared On-Orbit Inspection of Shuttle Orbiter Reinforced Carbon-Carbon Using Solar Heating

    Science.gov (United States)

    Howell, P. A.; Winfree, W. P.; Cramer, K. Elliott

    2005-01-01

    Thermographic nondestructive inspection techniques have been shown to provide quantitative, large area damage detection capabilities for the ground inspection of the reinforced carbon-carbon (RCC) used for the wing leading edge of the Shuttle orbiter. The method is non-contacting and able to inspect large areas in a relatively short inspection time. Thermal nondestructive evaluation (NDE) inspections have been shown to be applicable for several applications to the Shuttle in preparation for return to flight, including for inspection of RCC panels during impact testing, and for between-flight orbiter inspections. The focus of this work is to expand the capabilities of the thermal NDE methodology to enable inspection by an astronaut during orbital conditions. The significant limitations of available resources, such as weight and power, and the impact of these limitations on the inspection technique are discussed, as well as the resultant impact on data analysis and processing algorithms. Of particular interest is the impact to the inspection technique resulting from the use of solar energy as a heat source, the effect on the measurements due to working in the vacuum of space, and the effect of changes in boundary conditions, such as radiation losses seen by the material, on the response of the RCC. The resultant effects on detectability limits are discussed. Keywords: Nondestructive Evaluation, Shuttle, on-orbit inspection, thermography, infrared

  9. Structural analysis of an NDE-inspected carbon-carbon component

    Science.gov (United States)

    Striz, A. G.; Cruse, G.; Kline, R. A.; Madaras, E. I.

    1992-01-01

    In this research, it is demonstrated that the integration of nondestructive evaluation with the finite element method (a quantitative NDE/FEM approach) can be used for analysis and behavior prediction of advanced materials, such as fiber composites, after processing and during in-service testing. First, stress, strain, and energy data were calculated by the finite element method for square plates with a 10 percent difference in the material properties between specified segments, i.e., between the center and the outside section or between two halves of the plate. This demonstrated the efficiency of the method in predicting variations in the structural behavior based on small material property differences. Then, finite element analyses and actual axial compression tests were performed on a Space Shuttle brake stator made from woven carbon-carbon composites. The material properties used in the numerical modeling of the stator were previously characterized at a large number of points on the component by quantitative NDE-procedures, i.e., ultrasonics and radiography. The results from the experimental compressive loading tests were used to verify the NDE/FEM results. Good agreement was found for most parameters.

  10. Friction and wear studies of graphite and a carbon-carbon composite in air and in helium

    Energy Technology Data Exchange (ETDEWEB)

    Li, C.C.; Sheehan, J.E.

    1980-10-01

    Sliding friction and wear tests were conducted on a commercial isotropic graphite and a carbon-carbon composite in air, purified helium, and a helium environment containing controlled amounts of impurities simulating the primary coolant chemistry of a high-temperature gas-cooled reactor (HTGR). The friction and wear characteristics of the materials investigated were stable and were found to be very sensitive to the testing temperature. In general, friction and wear decreased with increasing temperature in the range from ambient to 950/sup 0/C. This temperature dependence is concluded to be due to chemisorption of impurities to form lubricating films and oxidation at higher temperatures, which reduce friction and wear. Graphite and carbon-carbon composites are concluded to be favorable candidate materials for high-temperature sliding service in helium-cooled reactors.

  11. VAMP/synaptobrevin cleavage by tetanus and botulinum neurotoxins is strongly enhanced by acidic liposomes.

    Science.gov (United States)

    Caccin, Paola; Rossetto, Ornella; Rigoni, Michela; Johnson, Eric; Schiavo, Giampietro; Montecucco, Cesare

    2003-05-01

    Tetanus and botulinum neurotoxins (TeNT and BoNTs) block neuroexocytosis via specific cleavage and inactivation of SNARE proteins. Such activity is exerted by the N-terminal 50 kDa light chain (L) domain, which is a zinc-dependent endopeptidase. TeNT, BoNT/B, /D, /F and /G cleave vesicle associated membrane protein (VAMP), a protein of the neurotransmitter-containing small synaptic vesicles, at different single peptide bonds. Since the proteolytic activity of these metalloproteases is higher on native VAMP inserted in synaptic vesicles than on recombinant VAMP, we have investigated the influence of liposomes of different lipid composition on this activity. We found that the rate of VAMP cleavage with all neurotoxins tested here is strongly enhanced by negatively charged lipid mixtures. This effect is at least partially due to the binding of the metalloprotease to the lipid membranes, with electrostatic interactions playing an important role.

  12. Experiments on passive hypersonic boundary layer control using ultrasonically absorptive carbon-carbon material with random microstructure

    Science.gov (United States)

    Wagner, Alexander; Kuhn, Markus; Martinez Schramm, Jan; Hannemann, Klaus

    2013-10-01

    For the first time, the influence of ultrasonically absorptive carbon-carbon material on hypersonic laminar to turbulent boundary layer transition was investigated experimentally. A 7° half-angle blunted cone with a nose radius of 2.5 mm and a total length of 1,077 mm was tested at zero angle of attack in the High Enthalpy Shock Tunnel Göttingen of the German Aerospace Center (DLR) at Mach 7.5. One-third of the metallic model surface in circumferential direction was replaced by DLR in-house manufactured ultrasonically absorptive carbon-carbon material with random microstructure for passive transition control. The remaining model surface consisted of polished steel and served as reference surface. The model was equipped with coaxial thermocouples to determine the transition location by means of surface heat flux distribution. Flush-mounted piezoelectric fast-response pressure transducers were used to measure the pressure fluctuations in the boundary layer associated with second-mode instabilities. The free-stream unit Reynolds number was varied over a range of Re m = 1.5 × 106 m-1 to Re m = 6.4 × 106 m-1 at a stagnation enthalpy of h 0 ≈ 3.2 MJ/kg and a wall temperature ratio of T w/ T 0 ≈ 0.1. The present study revealed a clear damping of the second-mode instabilities and a delay of boundary layer transition along the ultrasonically absorptive carbon-carbon insert.

  13. Numerical simulation of isothermal chemical vapor infiltration process in fabrication of carbon-carbon composites by finite element method

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The chemical vapor infiltration process in fabrication of carbon-carbon composites is highly inefficient and requires long processing time. These limitations add considerably to the cost of fabrication and restrict the application of this material. Efforts have been made to study the CVI process in fabrication of carbon-carbon composites by computer simulation and predict the process parameters, density, porosity, etc. According to the characteristics of CVI process, the basic principle of FEM and mass transport, the finite element model has been established. Incremental finite element equations and the elemental stiffness matrices have been derived for the first time. The finite element program developed by the authors has been used to simulate the ICVI process in fabrication of carbon-carbon composites. Computer color display of simulated results can express the densification and distributions of density and porosity in preform clearly. The influence of process parameters on the densification of preform has been analyzed. The numerically simulated and experimental results give a good agreement.

  14. Cleavage crystallography of liquid metal embrittled aluminum alloys

    Science.gov (United States)

    Reynolds, A. P.; Stoner, G. E.

    1991-01-01

    The crystallography of liquid metal-induced transgranular cleavage in six aluminum alloys having a variety of microstructures has been determined via Laue X-ray back reflection. The cleavage crystallography was independent of alloy microstructure, and the cleavage plane was 100-plane oriented in all cases. It was further determined that the cleavage crystallography was not influenced by alloy texture. Examination of the fracture surface indicated that there was not a unique direction of crack propagation. In addition, the existence of 100-plane cleavage on alloy 2024 fracture surfaces was inferred by comparison of secondary cleavage crack intersection geometry on the 2024 surfaces with the geometry of secondary cleavage crack intersections on the test alloys.

  15. Effect of mutations in the human immunoglobulin A1 (IgA1) hinge on its susceptibility to cleavage by diverse bacterial IgA1 proteases.

    Science.gov (United States)

    Senior, Bernard W; Woof, Jenny M

    2005-03-01

    Components of the human immunoglobulin A1 (IgA1) hinge governing sensitivity to cleavage by bacterial IgA1 proteases were investigated. Recombinant antibodies with distinct hinge mutations were constructed from a hybrid comprised of human IgA2 bearing half of the human IgA1 hinge region. This hybrid antibody and all the mutant antibodies derived from it were resistant to cleavage by the IgA1 proteases from Streptococcus oralis and Streptococcus mitis biovar 1 strains but were cleaved to various degrees by those of Streptococcus pneumoniae, some Streptococcus sanguis strains, and the type 1 and 2 IgA1 proteases of Haemophilus influenzae, Neisseria meningitidis, and Neisseria gonorrhoeae. Remarkably, those proteases that cleave a Pro-Ser peptide bond in the wild-type IgA1 hinge were able to cleave mutant antibodies lacking a Pro-Ser peptide bond in the hinge, and those that cleave a Pro-Thr peptide bond in the wild-type IgA1 hinge were able to cleave mutant antibodies devoid of a Pro-Thr peptide bond in the hinge. Thus, the enzymes can cleave alternatives to their preferred postproline peptide bond when such a bond is unavailable. Peptide sequence analysis of a representative antibody digestion product confirmed this conclusion. The presence of a cleavable peptide bond near the CH2 end of the hinge appeared to result in greater cleavage than if the scissile bond was at the CH1 end of the hinge. Proline-to-serine substitution at residue 230 in a hinge containing potentially cleavable Pro-Ser and Pro-Thr peptide bonds increased the resistance of the antibody to cleavage by many IgA1 proteases. PMID:15731049

  16. Dynamical Binding of Hydrogen Bond Surrogate-Derived Bak Helices to Anti-apoptotic Protein Bcl-xL

    OpenAIRE

    Bao, Ju; Dong, Xiao Y.; John Z. H. Zhang; Arora, Paramjit S.

    2009-01-01

    A new peptide modification strategy was recently developed to replace the i to i+4 hydrogen bond of the main chain of an a-helix with a carbon-carbon covalent bond to afford highly stable constrained α-helices, termed Hydrogen Bond Surrogate (HBS) helices. HBS helices that mimic the Bak BH3 domains were experimentally demonstrated to target protein Bcl-xL with high affinity. In this study, molecular dynamics (MD) simulation is used to understand how the covalent modification of the natural Ba...

  17. Regulated Cleavage of Prothrombin by Prothrombinase: REPOSITIONING A CLEAVAGE SITE REVEALS THE UNIQUE KINETIC BEHAVIOR OF THE ACTION OF PROTHROMBINASE ON ITS COMPOUND SUBSTRATE*♦

    OpenAIRE

    Bradford, Harlan N.; Micucci, Joseph A.; Krishnaswamy, Sriram

    2009-01-01

    Prothrombinase converts prothrombin to thrombin via cleavage at Arg320 followed by cleavage at Arg271. Exosite-dependent binding of prothrombin to prothrombinase facilitates active site docking by Arg320 and initial cleavage at this site. Precise positioning of the Arg320 site for cleavage is implied by essentially normal cleavage at Arg320 in recombinant prothrombin variants...

  18. On the quantification of atmospheric carbonate carbon by thermal/optical analysis protocols

    Directory of Open Access Journals (Sweden)

    A. Karanasiou

    2010-11-01

    Full Text Available Carbonaceous species, usually classified into two categories, organic carbon (OC and elemental carbon (EC, constitute an important component of the atmospheric aerosol. Carbonate carbon (CC, or inorganic carbon, another constituent of carbonaceous material, is often not considered in many atmospheric chemistry studies. The reason for this may be its low contribution to fine particle mass in most areas studied, along with the difficulties in its analytical determination in atmospheric aerosols. The objective of this study was the quantification of atmospheric carbonate concentrations using the thermal optical transmittance method (Sunset Laboratory, Inc.. Three different temperature protocols (two modified NIOSH protocols and the EUSAAR-2 protocol were tested on filter samples containing known amounts of CC. Moreover, the performance of the two most widely used protocols across European countries (NIOSH and EUSAAR-2 was also checked on two different instruments namely the semi-continuous OCEC analyzer and the laboratory OCEC analyzer. NIOSH-840 thermal protocol (NIOSH protocol with a maximum temperature of 840 °C in the He-mode can be used for the detection and quantification of atmospheric carbonate concentrations. CC was determined in ambient PM10 and PM2.5 samples From Athens and Barcelona by using the NIOSH-840 thermal protocol. The results confirm that in South European countries CC may constitute a significant fraction of carbonaceous aerosols (~15%, thus it should not be neglected. However, the NIOSH-840 protocol seems to overestimate the OC concentrations when compared to the EUSAAR-2 protocol. The results suggest that during dust episodes, common for the Southern Europe, the analytical laboratories could use the NIOSH-840 protocol as a suitable method for the carbonate determination and manually integrate the sharp peak that appears in the maximum temperature step in the inert mode. Afterwards, carbonate should be

  19. Diffusion bonding

    Science.gov (United States)

    Anderson, Robert C.

    1976-06-22

    1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

  20. Stereoelectronic Control of Cleavage of Dioxolane Five-membered Ring on Carbohydrates

    Institute of Scientific and Technical Information of China (English)

    PAN Xiao-liang; ZHOU Yi-xuan; LIU Wei; LIU Jing-yao; DONG Hai

    2013-01-01

    A mechanism about the origin of the selectivities for the cleavage of dioxolane five-membered rings on pyranoside rings was suggested.Quantum chemical studies were performed to testify the rationality of the mechanism.It is thus suggested that the selectivities should be dependent on the differences of the free energy at the transition states when the five-membered ring cleaves.Natural bond orbital(NBO) analysis was further made to assess the influence of stereoelectronic effects on the selectivities.

  1. DNA Cleavage Promoted by Cu2+ Complex of N,N'-Bis(2-aminoethyl)-2,6-pyridinedicarboxamide

    Institute of Scientific and Technical Information of China (English)

    LI, Ying; SHENG, Xin; SHAO, Ying; LU, Guo-Yuan

    2007-01-01

    The interaction of Cu2+ complex of N,N'-bis(2-aminoethyl)-2,6-pyridinedicarboxamide (BAP) with DNA was studied by agarose gel electrophoresis analysis. The results indicate that the BAP-Cu2+ complex can promote the cleavage of phosphodiester bond of supercoiled DNA at physiological condition, which is 3.2×106 times higher than DNA natural degradation. A hydrolytic cleaving mechanism through the cooperation of copper ions and functional amino groups was proposed.

  2. A Historical Trend of Ethnic Cleavages in Contemporary Iran

    Directory of Open Access Journals (Sweden)

    Hussein Mohammadzadeh

    2013-10-01

    Full Text Available The goal of this study is evaluation social and historical content of social cleavage in contemporary Iran. Analytical framework rooted in Rokan theory. Rokan believed that social cleavage appearance post of revolutions. Method of study was historical comparatives.The method of this research is comparative historical in which we used of historical documents and data. In this field, I have compared data of indexes of socio-economic of ethnic states.Assessment of data and documents show that social cleavages and particularly ethnic cleavages rise after Reza shah revolution. He established centralized and dictated government and divided society of Iran and institutionalization the inequality in social structure. Sense of deprivation about inequality and suited circumstance activated ethnic cleavage in Iran. Decrease of inequality and justice could decrease of social deprivation and deactivated social cleavages.

  3. Effects of Atomic-Scale Structure on the Fracture Properties of Amorphous Carbon - Carbon Nanotube Composites

    Science.gov (United States)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    The fracture of carbon materials is a complex process, the understanding of which is critical to the development of next generation high performance materials. While quantum mechanical (QM) calculations are the most accurate way to model fracture, the fracture behavior of many carbon-based composite engineering materials, such as carbon nanotube (CNT) composites, is a multi-scale process that occurs on time and length scales beyond the practical limitations of QM methods. The Reax Force Field (ReaxFF) is capable of predicting mechanical properties involving strong deformation, bond breaking and bond formation in the classical molecular dynamics framework. This has been achieved by adding to the potential energy function a bond-order term that varies continuously with distance. The use of an empirical bond order potential, such as ReaxFF, enables the simulation of failure in molecular systems that are several orders of magnitude larger than would be possible in QM techniques. In this work, the fracture behavior of an amorphous carbon (AC) matrix reinforced with CNTs was modeled using molecular dynamics with the ReaxFF reactive forcefield. Care was taken to select the appropriate simulation parameters, which can be different from those required when using traditional fixed-bond force fields. The effect of CNT arrangement was investigated with three systems: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. For each arrangement, covalent bonds are added between the CNTs and AC, with crosslink fractions ranging from 0-25% of the interfacial CNT atoms. The SWNT and MWNT array systems represent ideal cases with evenly spaced CNTs; the SWNT bundle system represents a more realistic case because, in practice, van der Waals interactions lead to the agglomeration of CNTs into bundles. The simulation results will serve as guidance in setting experimental processing conditions to optimize the mechanical properties of CNT

  4. SVM-based prediction of caspase substrate cleavage sites

    OpenAIRE

    Wee, Lawrence JK; Tan, Tin Wee; Ranganathan, Shoba

    2006-01-01

    Background Caspases belong to a class of cysteine proteases which function as critical effectors in apoptosis and inflammation by cleaving substrates immediately after unique sites. Prediction of such cleavage sites will complement structural and functional studies on substrates cleavage as well as discovery of new substrates. Recently, different computational methods have been developed to predict the cleavage sites of caspase substrates with varying degrees of success. As the support vector...

  5. Modeling and Inferring Cleavage Patterns in Proliferating Epithelia

    OpenAIRE

    Patel, Ankit B.; Gibson, William T.; Gibson, Matthew C; Radhika Nagpal

    2009-01-01

    The regulation of cleavage plane orientation is one of the key mechanisms driving epithelial morphogenesis. Still, many aspects of the relationship between local cleavage patterns and tissue-level properties remain poorly understood. Here we develop a topological model that simulates the dynamics of a 2D proliferating epithelium from generation to generation, enabling the exploration of a wide variety of biologically plausible cleavage patterns. We investigate a spectrum of models that incorp...

  6. Amino acid sequence requirements in the human IgA1 hinge for cleavage by streptococcal IgA1 proteases

    DEFF Research Database (Denmark)

    Senior, BW; Batten, MR; Kilian, Mogens;

    2002-01-01

    All the IgA1 proteases of the different pathogenic species of Streptococcus cleave the hinge of the alpha chain of human IgA1 only at one proline-threonine peptide bond. In order to study the importance of these amino acids for cleavage, several hinge mutant recombinant IgA1 antibodies were...

  7. Dilepton spectroscopy at intermediate energies; the carbon - carbon reaction at 1 GeV/A

    International Nuclear Information System (INIS)

    The Physics context of this work is heavy ion collisions at relativistic energies where di-electron provide informations on the produced hot and dense nuclear matter. The experiment is performed by the DiLepton Spectrometer (DLS) Collaboration at the Lawrence Berkeley's Bevalac. After a description of the apparatus, we review the whole program and the main results so far obtained: first evidence of a significant di-electron signal at energies above 1 GeV/A; improvement of the understanding of di-electron production (electromagnetic decays of hadrons, π+π- annihilation and hadronic Bremsstrahlung). The results of p-p, p-d reactions from 1 to 4.9 GeV/A show that hadronic Bremsstrahlung (pp, pn) should be reformulated. Our analysis, optimized on the reaction Carbon-Carbon at 1 GeV/A, has been applied to α-Ca and d-Ca. We have developed two main aspects: improvement of the time resolution (500 ps) in order to eliminate all of the protons. Improvement of the space resolution (300 μ) for better mass resolution, in particular in the ρ region. We obtain the cross section of di-electron production as a function of mass, transverse momentum and rapidity from the C-C, α-Ca and d-Ca reactions at 1 GeV/A. We also compare the cross section for all of the measured systems at 1 GeV/A, including Ca-Ca, and we show a (ApAt)α dependence with α ≅ 1.1. A study of the associated multiplicity has also been performed. Nevertheless, the limited acceptance of the DLS and its poor mass resolution to identify the ρ, ω vector mesons, do not allow to conclude on hadron behaviour in nuclear matter. This point is one of the main goal of the HADES project at GSI (Darmstadt), which we give a brief description of the main features. (authors). 60 refs

  8. Structural Basis for Accelerated Cleavage of Bovine Pancreatic Trypsin Inhibitor (BPTI) by Human Mesotrypsin

    Energy Technology Data Exchange (ETDEWEB)

    Salameh,M.; Soares, A.; Hockla, A.; Radisky, E.

    2008-01-01

    Human mesotrypsin is an isoform of trypsin that displays unusual resistance to polypeptide trypsin inhibitors and has been observed to cleave several such inhibitors as substrates. Whereas substitution of arginine for the highly conserved glycine 193 in the trypsin active site has been implicated as a critical factor in the inhibitor resistance of mesotrypsin, how this substitution leads to accelerated inhibitor cleavage is not clear. Bovine pancreatic trypsin inhibitor (BPTI) forms an extremely stable and cleavage-resistant complex with trypsin, and thus provides a rigorous challenge of mesotrypsin catalytic activity toward polypeptide inhibitors. Here, we report kinetic constants for mesotrypsin and the highly homologous (but inhibitor sensitive) human cationic trypsin, describing inhibition by, and cleavage of BPTI, as well as crystal structures of the mesotrypsin-BPTI and human cationic trypsin-BPTI complexes. We find that mesotrypsin cleaves BPTI with a rate constant accelerated 350-fold over that of human cationic trypsin and 150,000-fold over that of bovine trypsin. From the crystal structures, we see that small conformational adjustments limited to several side chains enable mesotrypsin-BPTI complex formation, surmounting the predicted steric clash introduced by Arg-193. Our results show that the mesotrypsin-BPTI interface favors catalysis through (a) electrostatic repulsion between the closely spaced mesotrypsin Arg-193 and BPTI Arg-17, and (b) elimination of two hydrogen bonds between the enzyme and the amine leaving group portion of BPTI. Our model predicts that these deleterious interactions accelerate leaving group dissociation and deacylation.

  9. Active site specificity profiling of the matrix metalloproteinase family: Proteomic identification of 4300 cleavage sites by nine MMPs explored with structural and synthetic peptide cleavage analyses.

    Science.gov (United States)

    Eckhard, Ulrich; Huesgen, Pitter F; Schilling, Oliver; Bellac, Caroline L; Butler, Georgina S; Cox, Jennifer H; Dufour, Antoine; Goebeler, Verena; Kappelhoff, Reinhild; Keller, Ulrich Auf dem; Klein, Theo; Lange, Philipp F; Marino, Giada; Morrison, Charlotte J; Prudova, Anna; Rodriguez, David; Starr, Amanda E; Wang, Yili; Overall, Christopher M

    2016-01-01

    leucine locked in S1'. Similar negative cooperativity between P3 proline and the novel preference for asparagine in P1 cements our conclusion that non-prime side flexibility greatly impacts MMP binding affinity and cleavage efficiency. Thus, unexpected sequence cooperativity consequences were revealed by PICS that uniquely encompasses both the non-prime and prime sides flanking the proteomic-pinpointed scissile bond.

  10. Densification and microstructure of carbon/carbon composites prepared by chemical vapor infiltration using ethanol as precursor

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Chemical vapor infiltration of carbon fiber felts with uniform initial bulk density of 0.47 g·cm-3 was investigated at the ethanol partial pressures of 5-20 kPa,as well as the temperatures of 1050,1100,1150 and 1200°C.Ethanol,diluted by nitrogen,was employed as the precursor of pyrolytic carbon.Polarized light microscopy(PLM),scanning electron microscopy and X-ray diffraction were adopted to study the texture of pyrolytic carbon deposited at various temperatures.A change from medium-to high-textured pyrolytic carbon was observed in the sample infiltrated at 1050°C.Whereas,homogeneous high-textured pyrolytic carbons were deposited at the temperatures of 1100,1150 and 1200°C.Extinction angles of 19°-21° were determined for different regions in the samples densified at the temperatures ranging from 1100 to 1200°C.Scanning electron microscopy of the fracture surface after bending test indicated that the prepared carbon/carbon composite samples exhibited a pseudo-plastic fracture behavior.In addition,fracture behavior of the carbon/carbon samples was obviously effected by their infiltration temperature.The fracture mode of C/C composites was transformed from shearing failure to tensile breakage with increasing infiltration temperature. Results of this study show that ethanol is a promising carbon source to synthesize carbon/carbon composites with homogeneously high-textured pyrolytic carbon over a wide range of temperatures(from 1100 to 1200°C).

  11. Analysis of the cleavage site of the human immunodeficiency virus type 1 glycoprotein: requirement of precursor cleavage for glycoprotein incorporation.

    OpenAIRE

    Dubay, J W; Dubay, S R; Shin, H. J.; Hunter, E

    1995-01-01

    Endoproteolytic cleavage of the glycoprotein precursor to the mature SU and TM proteins is an essential step in the maturation of retroviral glycoproteins. Cleavage of the precursor polyprotein occurs at a conserved, basic tetrapeptide sequence and is carried out by a cellular protease. The glycoprotein of the human immunodeficiency virus type 1 contains two potential cleavage sequences immediately preceding the N terminus of the TM protein. To determine the functional significance of these t...

  12. Cleavage of nicotinamide adenine dinucleotide by the ribosome-inactivating protein from Momordica charantia.

    Science.gov (United States)

    Vinkovic, M; Dunn, G; Wood, G E; Husain, J; Wood, S P; Gill, R

    2015-09-01

    The interaction of momordin, a type 1 ribosome-inactivating protein from Momordica charantia, with NADP(+) and NADPH has been investigated by X-ray diffraction analysis of complexes generated by co-crystallization and crystal soaking. It is known that the proteins of this family readily cleave the adenine-ribose bond of adenosine and related nucleotides in the crystal, leaving the product, adenine, bound to the enzyme active site. Surprisingly, the nicotinamide-ribose bond of oxidized NADP(+) is cleaved, leaving nicotinamide bound in the active site in the same position but in a slightly different orientation to that of the five-membered ring of adenine. No binding or cleavage of NADPH was observed at pH 7.4 in these experiments. These observations are in accord with current views of the enzyme mechanism and may contribute to ongoing searches for effective inhibitors. PMID:26323301

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

    Science.gov (United States)

    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. The Oxygenase CAO-1 of Neurospora crassa Is a Resveratrol Cleavage Enzyme

    KAUST Repository

    Diaz-Sanchez, V.

    2013-07-26

    The genome of the ascomycete Neurospora crassa encodes CAO-1 and CAO-2, two members of the carotenoid cleavage oxygenase family that target double bonds in different substrates. Previous studies demonstrated the role of CAO-2 in cleaving the C40 carotene torulene, a key step in the synthesis of the C35 apocarotenoid pigment neurosporaxanthin. In this work, we investigated the activity of CAO-1, assuming that it may provide retinal, the chromophore of the NOP-1 rhodopsin, by cleaving β-carotene. For this purpose, we tested CAO-1 activity with carotenoid substrates that were, however, not converted. In contrast and consistent with its sequence similarity to family members that act on stilbenes, CAO-1 cleaved the interphenyl Cα-Cβ double bond of resveratrol and its derivative piceatannol. CAO-1 did not convert five other similar stilbenes, indicating a requirement for a minimal number of unmodified hydroxyl groups in the stilbene background. Confirming its biological function in converting stilbenes, adding resveratrol led to a pronounced increase in cao-1 mRNA levels, while light, a key regulator of carotenoid metabolism, did not alter them. Targeted Δcao-1 mutants were not impaired by the presence of resveratrol, a phytoalexin active against different fungi, which did not significantly affect the growth and development of wild-type Neurospora. However, under partial sorbose toxicity, the Δcao-1 colonies exhibited faster radial growth than control strains in the presence of resveratrol, suggesting a moderate toxic effect of resveratrol cleavage products.

  15. Presence of Meiotic Spindles Indicates Early Cleavage of Embryos

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Objective To assess whether the detection of the meiotic spindle could anticipate the appearance of early cleavage.Methods Oocytes were obtained from stimulated ovaries of consenting patients undergoing oocytes retrieval for ICSI.Spindles were imaged with the Polscope.After ICSI,oocytes with or without spindles were cultured for examination of early cleavage and embryo development.A total of 328 oocytes from 50 cycles were examined with the Polscope and inseminated by ICSI.Results Spindles were imaged in 81.7% of oocytes.After ICSI,more oocytes with spindles (78.4%) fertilized normally than oocytes without spindles (53.3%)(P<0.001).At 25-27 h post ICSI.more fertilized oocytes developed from oocytes with spindles (81.9%) were detected early cleavage than those from oocytes without spindles(28.1%)(P<0.001).Significantly more embryos with early cleavage (82.2%) developed to high quality embryos at d 3 compared with the embryos without early cleavage(48.3%)(P=0.001).The value of rs related to the relationship between spindles and early cleavage was 0.420(P<0.0001).Conclusion The existing of the early cleavage may have a predictive value on the opportunity of high quality embryos and the existing of the spindle may have a predictive value in the appearance of early cleavage.

  16. Deletion Mapping of the Encephalomyocarditis Virus Primary Cleavage Site

    OpenAIRE

    Hahn, Harry; Palmenberg, Ann C.

    2001-01-01

    The cotranslational, primary self-cleavage reaction of cardiovirus polyprotein relies on a highly conserved, short segment of amino acids at the 2A-2B protein boundary. The amino terminus of the required element for encephalomyocarditis virus has now been mapped to include Tyr126 of the 2A protein, the 18th amino acid before the cleavage site.

  17. A photoinduced cleavage of DNA useful for determining T residues.

    OpenAIRE

    Simoncsits, A; Török, I

    1982-01-01

    Irradiation of 5'-[32P]-phosphate labeled DNA fragments with ultraviolet light in the presence of primary amines followed by piperidine treatment resulted in base-specific cleavage of the DNA chain at T residues, accompanied by a less intensive G reaction. This simple, T greater than G cleavage offers an alternative method for determining T residues in chemical DNA sequencing.

  18. Semiconductor Surface Structure Determination via Low Energy Positron Diffraction: Cleavage Faces of Cadmium-Selenide

    Science.gov (United States)

    Horsky, Thomas Neil

    Low energy positron diffraction (LEPD) is used to determine the surface structure of the wurtzite CdSe(1010) and CdSe(1120) cleavage faces. Low energy electron diffraction (LEED) is also performed, utilizing a beam optical system which produces both a e^+ and e ^- beam with the same phase-space characteristics, i.e. 1 mm-deg. Both e^+ and e^- measurements were collected from the same sample surface of each cleavage face, removing systematic errors from the comparison. Dynamical calculations were performed for both the LEPD and LEED using the R-factor methodology of Duke et al. For the (1010) surface, the calculations and analyses were performed at Brandeis via link to the John Von Neumann Supercomputer Center at Princeton, NJ. For the (1120) surface, the LEPD calculations and analysis was performed by Battelle Pacific Northwest Laboratories, while the LEED calculations were performed by Princeton University. Resulting surface structures for CdSe(1010) are in accord with the proposed reconstruction model of Wang and Duke, indicating a bond-length-conserving rotation of the surface dimer. The best-fit values of the bond-rotation angle omega are 15^circ +/- 5^circ as determined by LEPD and omega = 21.5^ circ +/- 4^ circ as determined by LEED. These values are in agreement with the predicted value of omega = 17^circ. For CdSe(1120), the best-fit LEPD results indicate an omega of 27^circ +/- 7^circ while preliminary LEED results indicate an omega of 35^circ +/- 5^circ. Both values for this previously undetermined surface are also in agreement with the theoretically predicted value of omega = 32^circ . These results serve to confirm a universal model of reconstruction which describes the surface structures of both the zincblende and wurtzite compound semiconductor cleavage faces.

  19. A novel carotenoid cleavage activity involved in the biosynthesis of Citrus fruit-specific apocarotenoid pigments

    KAUST Repository

    Rodrigo, María J.

    2013-09-04

    Citrus is the first tree crop in terms of fruit production. The colour of Citrus fruit is one of the main quality attributes, caused by the accumulation of carotenoids and their derivative C30 apocarotenoids, mainly ?-citraurin (3-hydroxy-?-apo-8?-carotenal), which provide an attractive orange-reddish tint to the peel of oranges and mandarins. Though carotenoid biosynthesis and its regulation have been extensively studied in Citrus fruits, little is known about the formation of C30 apocarotenoids. The aim of this study was to the identify carotenoid cleavage enzyme(s) [CCD(s)] involved in the peel-specific C30 apocarotenoids. In silico data mining revealed a new family of five CCD4-type genes in Citrus. One gene of this family, CCD4b1, was expressed in reproductive and vegetative tissues of different Citrus species in a pattern correlating with the accumulation of C30 apocarotenoids. Moreover, developmental processes and treatments which alter Citrus fruit peel pigmentation led to changes of ?-citraurin content and CCD4b1 transcript levels. These results point to the involvement of CCD4b1 in ?-citraurin formation and indicate that the accumulation of this compound is determined by the availability of the presumed precursors zeaxanthin and ?-cryptoxanthin. Functional analysis of CCD4b1 by in vitro assays unequivocally demonstrated the asymmetric cleavage activity at the 7?,8? double bond in zeaxanthin and ?-cryptoxanthin, confrming its role in C30 apocarotenoid biosynthesis. Thus, a novel plant carotenoid cleavage activity targeting the 7?,8? double bond of cyclic C40 carotenoids has been identified. These results suggest that the presented enzyme is responsible for the biosynthesis of C30 apocarotenoids in Citrus which are key pigments in fruit coloration. The Author 2013.

  20. SiC-Si-ZrSiO4 Multiphase Oxidation Protective Coating for Carbon/Carbon Composites

    Institute of Scientific and Technical Information of China (English)

    Yulei ZHANG; Hejun LI; Qiangang FU; Kezhi LI; Dangshe HOU

    2008-01-01

    In order to improve the anti-oxidation property of carbon/carbon (C/C) composites,a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compos-ites by a pack cementation technique.The phase composition and microstructure of the as-prepared coatings were characterized by XRD (X-ray diffraction),SEM (scanning electron microscopy) and EDS (energy dis-persive spectroscopy).Oxidation behavior of the multiphase coated C/C composites was also investigated.It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock re-sistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times,whereas the corresponding weight loss is only 1.47%.The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.

  1. Metallic Concepts for Repair of Reinforced Carbon-Carbon Space Shuttle Leading Edges

    Science.gov (United States)

    Ritzert, Frank; Nesbitt, James

    2007-01-01

    The Columbia accident has focused attention on the critical need for on-orbit repair concepts for wing leading edges in the event that potentially catastrophic damage is incurred during Space Shuttle Orbiter flight. The leading edge of the space shuttle wings consists of a series of eleven panels on each side of the orbiter. These panels are fabricated from reinforced carbon-carbon (RCC) which is a light weight composite with attractive strength at very high temperatures. The damage that was responsible for the loss of the Colombia space shuttle was deemed due to formation of a large hole in one these RCC leading edge panels produced by the impact of a large piece of foam. However, even small cracks in the RCC are considered as potentially catastrophic because of the high temperature re-entry environment. After the Columbia accident, NASA has explored various means to perform on-orbit repairs in the event that damage is sustained in future shuttle flights. Although large areas of damage, such as that which doomed Columbia, are not anticipated to re-occur due to various improvements to the shuttle, especially the foam attachment, NASA has also explored various options for both small and large area repair. This paper reports one large area repair concept referred to as the "metallic over-wrap." Environmental conditions during re-entry of the orbiter impose extreme requirements on the RCC leading edges as well as on any repair concepts. These requirements include temperatures up to 3000 F (1650 C) for up to 15 minutes in the presence of an extremely oxidizing plasma environment. Figure 1 shows the temperature profile across one panel (#9) which is subject to the highest temperatures during re-entry. Although the RCC possesses adequate mechanical strength at these temperatures, it lacks oxidation resistance. Oxidation protection is afforded by converting the outer layers of the RCC to SiC by chemical vapor deposition (CVD). At high temperatures in an oxidizing

  2. Cleavage factor Im (CFIm) as a regulator of alternative polyadenylation.

    Science.gov (United States)

    Hardy, Jessica G; Norbury, Chris J

    2016-08-15

    Most mammalian protein coding genes are subject to alternative cleavage and polyadenylation (APA), which can generate distinct mRNA 3'UTRs with differing regulatory potential. Although this process has been intensely studied in recent years, it remains unclear how and to what extent cleavage site selection is regulated under different physiological conditions. The cleavage factor Im (CFIm) complex is a core component of the mammalian cleavage machinery, and the observation that its depletion causes transcriptome-wide changes in cleavage site use makes it a key candidate regulator of APA. This review aims to summarize current knowledge of the CFIm complex, and explores the evidence surrounding its potential contribution to regulation of APA. PMID:27528751

  3. Amino acid sequence requirements in the human IgA1 hinge for cleavage by streptococcal IgA1 proteases.

    Science.gov (United States)

    Senior, B W; Batten, M R; Kilian, M; Woof, J M

    2002-08-01

    All the IgA1 proteases of the different pathogenic species of Streptococcus cleave the hinge of the alpha chain of human IgA1 only at one proline-threonine peptide bond. In order to study the importance of these amino acids for cleavage, several hinge mutant recombinant IgA1 antibodies were constructed. The mutations were found to be without major effect upon the structure or functional abilities of the antibodies. However, they had a major effect upon their sensitivity to cleavage by some of the IgA1 proteases. PMID:12196126

  4. Silver(I) NHC mediated C-C bond activation of alkyl nitriles and catalytic efficiency in oxazoline synthesis.

    Science.gov (United States)

    Heath, Rachael; Müller-Bunz, Helge; Albrecht, Martin

    2015-05-21

    Preparation of silver triazolylidene (trz) species from triazolium salts and Ag2O in refluxing MeCN leads to a selective C-C bond cleavage and the formation of complexes of general formula [(trz)Ag(CN)] from Calkyl-CN bond activation. Moreover, these silver carbene complexes are precursors of highly active catalysts for oxazoline formation via aldol condensation. PMID:25913007

  5. Use of Cleavage as an Aid in the Optical Determination of Minerals.

    Science.gov (United States)

    Ehlers, Ernest G.

    1980-01-01

    Described is the use of cleavage as an aid to microscopic determination of unknown minerals by immersion methods. Cleavages are examined in relation to fragment shapes, types of extinction, and cleavage-optical relationships. (Author/DS)

  6. A cleavage toughness master curve model

    International Nuclear Information System (INIS)

    Development of fusion power will require a fracture toughness database, derived largely from small specimen tests, closely integrated with methods to assess first wall and blanket structural integrities. A master curve-shift (MC-ΔT) method has been proposed as an engineering expedient to treat the effects of structural geometry, irradiation, loading rates and safety margins. However, a number of issues related to the MC-ΔT method remain to be resolved, including the universality of MC shapes. A new micromechanical model of fracture toughness in the cleavage transition regime is proposed that combines analytical representations of finite element analysis simulations of crack-tip stress fields with a local critical stress-critical stressed area (σ*-A*) fracture criterion. This model, has been successful in predicting geometry effects, as well as high loading rate and irradiation hardening-induced Charpy shifts. By incorporating a modest temperature dependence in σ*(T), an inconsistency between model predictions and an observed universal-type MC shape is resolved

  7. Development of early composite cleavage in pelites from West Donegal

    Science.gov (United States)

    Meneilly, A. W.

    In the Portnoo-Rosbeg area of west Donegal the main penetrative cleavage, S2, generally dips to the south with F2 folds facing up to the north. In places the S2 cleavage is cut by a gently SW-dipping crenulation cleavage ( S3) verging and facing south on the long limbs of F2 folds. A series of structural domains have been mapped in which the relationship of S2 and S3 changes from cross-cutting at a large angle (Rosbeg domain) to the development of a composite S {2}/{3} cleavage (Portnoo domain). The relationship between the two phases and the composite cleavage was investigated by mapping out cleavages (megascopic scale), detailed mesoscopic field observations and on a microscopic scale using textural relationships to widespread post D2-pre D3 garnet porphyroblasts. In addition to demonstrating the composite nature of the cleavage, the examples of D2/ D3 interference and the rotation of, and drag patterns around, the garnet porphyroblasts allow discussion of the kinematics of D3. D3 appears to have involved either bulk pure shear or north-directed bulk simple shear, or any intermediate type of deformation history, and was promoted by southerly directed active slip parallel to S2.

  8. [On the classification of the cleavage patterns in amphibian embryos].

    Science.gov (United States)

    Desnitskiĭ, A G

    2014-01-01

    This paper presents a brief survey and preliminary classification of embryonic cleavage patterns in the class Amphibia. We use published data on 41 anuran and 22 urodele species concerning the character of the third cleavage furrow (latitudinal or longitudinal) and the stage of transition from synchronous to asynchronous blastomere divisions in the animal hemisphere (4-8-celled stage, 8-16-celled stage or later). Based on this, four patterns of amphibian embryonic cleavage are recognized, and an attempt to elucidate the evolutionary relationships among these patterns is undertaken. The so-called "standard" cleavage pattern (the extensive series of synchronous blastomere divisions including latitudinal furrows of the third cleavage) with the typical model species Ambystoma mexicanum and Xenopus laevis seems to be derived and probably originated independently in the orders Anura and Caudata. The ancestral amphibian cleavage pattern seems to be represented by species with longitudinal furrows of the third cleavage and the loss ofsynchrony as early as the 8-celled stage (such as in primitive urodele species from the family Cryptobranchidae). PMID:25720261

  9. Quantification of DNA cleavage specificity in Hi-C experiments.

    Science.gov (United States)

    Meluzzi, Dario; Arya, Gaurav

    2016-01-01

    Hi-C experiments produce large numbers of DNA sequence read pairs that are typically analyzed to deduce genomewide interactions between arbitrary loci. A key step in these experiments is the cleavage of cross-linked chromatin with a restriction endonuclease. Although this cleavage should happen specifically at the enzyme's recognition sequence, an unknown proportion of cleavage events may involve other sequences, owing to the enzyme's star activity or to random DNA breakage. A quantitative estimation of these non-specific cleavages may enable simulating realistic Hi-C read pairs for validation of downstream analyses, monitoring the reproducibility of experimental conditions and investigating biophysical properties that correlate with DNA cleavage patterns. Here we describe a computational method for analyzing Hi-C read pairs to estimate the fractions of cleavages at different possible targets. The method relies on expressing an observed local target distribution downstream of aligned reads as a linear combination of known conditional local target distributions. We validated this method using Hi-C read pairs obtained by computer simulation. Application of the method to experimental Hi-C datasets from murine cells revealed interesting similarities and differences in patterns of cleavage across the various experiments considered.

  10. Bundled slaty cleavage in laminated argillite, north-central minnesota

    Science.gov (United States)

    Southwick, D.L.

    1987-01-01

    Exceptional bundled slaty cleavage (defined herein) has been found in drill cores of laminated, folded, weakly metamorphosed argillite at several localities in the early Proterozoic Animikie basin of north-central Minnesota. The cleavage domains are more closely spaced within the cleavage bundles than outside them, the mean tectosilicate grain size of siltstone layers, measured normal to cleavage, is less in the cleavage bundles than outside them, and the cleavage bundles are enriched in opaque phases and phyllosilicates relative to extra-bundle segments. These facts suggest that pressure solution was a major factor in bundle development. If it is assumed that opaque phases have been conserved during pressure solution, the modal differences in composition between intra-bundle and extra-bundle segments of beds provide a means for estimating bulk material shortening normal to cleavage. Argillite samples from the central part of the Animikie basin have been shortened a minimum of about 22%, as estimated by this method. These estimates are similar to the shortening values derived from other strain markers in other rock types interbedded with the argillite, and are also consistent with the regional pattern of deformation. ?? 1987.

  11. Metal compound-mediated hydrolytic cleavage of oxidized insulin B chain: Regioselectivity and influence of peptide secondary structure

    Institute of Scientific and Technical Information of China (English)

    罗雪梅; 何卫江; 张宇; 郭子建; 朱龙根

    2000-01-01

    The interaction of oxidized insulin B chain (B) with cis-[Pd-(en) Cl2] (en= ethylendiamine), cis-[Pd-(dtco-3-OH)Cl2](dtc o-3-OH= dithiacyclooctan-3-ol) and CuCl2 was studied by electrospray mass spectrometry. It is discovered that the binding of Pd(Ⅱ) complexes and the sites of cleavage are highly dependent on the secondary structure and local e nvironment of B. The hydrolytic cleavage of denatured B by Pd (Ⅱ) complexes was monitored by HPLC. The reaction is regioselective and follows first order kinetics with half-life of 4.8 days at 40°C. Two a mide bonds, i.e. at Leu6-Cys7 and at Gly8-Ser9, which are close to the two potential Pd(Ⅱ) binding sites His5 and His10, are selectively cleaved. In the case of Cu(Ⅱ) ion as promoter, only one cleavage site was observed which is located at Gly8-Ser9 bond. These results provide improved understanding on the deign of artificial metallopeptidase.

  12. Active Metal Brazing and Characterization of Brazed Joints in Titanium to Carbon-Carbon Composites

    Science.gov (United States)

    Singh, M.; Shpargel, T. P.; Morscher, G. N.; Asthana, R.

    2006-01-01

    The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSiI. 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. A tube-on-plate tensile test was used to evaluate joint strength of Ti-tube/ C-C composite joints. The load-carrying ability was greatest for the Cu-ABA braze joint structures. This system appeared to have the best braze spreading which resulted in a larger braze/C-C composite bonded area compared to the other two braze materials. Also, joint loadcarrying ability was found to be higher for joint structures where the fiber tows in the outer ply of the C-C composite were aligned perpendicular to the tube axis when compared to the case where fiber tows were aligned parallel to the tube axis.

  13. Detection of nucleic acid sequences by invader-directed cleavage

    Science.gov (United States)

    Brow, Mary Ann D.; Hall, Jeff Steven Grotelueschen; Lyamichev, Victor; Olive, David Michael; Prudent, James Robert

    1999-01-01

    The present invention relates to means for the detection and characterization of nucleic acid sequences, as well as variations in nucleic acid sequences. The present invention also relates to methods for forming a nucleic acid cleavage structure on a target sequence and cleaving the nucleic acid cleavage structure in a site-specific manner. The 5' nuclease activity of a variety of enzymes is used to cleave the target-dependent cleavage structure, thereby indicating the presence of specific nucleic acid sequences or specific variations thereof. The present invention further relates to methods and devices for the separation of nucleic acid molecules based by charge.

  14. Prediction of proteasome cleavage motifs by neural networks

    DEFF Research Database (Denmark)

    Kesimir, C.; Nussbaum, A.K.; Schild, H.;

    2002-01-01

    We present a predictive method that can simulate an essential step in the antigen presentation in higher vertebrates, namely the step involving the proteasomal degradation of polypeptides into fragments which have the potential to bind to MHC Class I molecules. Proteasomal cleavage prediction...... the prediction of MHC Class I ligand boundaries more accurate: 65% of the cleavage sites and 85% of the non-cleavage sites are correctly determined. Moreover, we show that the neural networks trained on the constitutive proteasome data learns a specificity that differs from that of the networks...

  15. Localized Calcium Signals along the Cleavage Furrow of the Xenopus Egg Are Not Involved in Cytokinesis

    OpenAIRE

    Noguchi, Tatsuhiko; Mabuchi, Issei

    2002-01-01

    It has been proposed that a localized calcium (Ca) signal at the growing end of the cleavage furrow triggers cleavage furrow formation in large eggs. We have examined the possible role of a Ca signal in cleavage furrow formation in the Xenopus laevis egg during the first cleavage. We were able to detect two kinds of Ca waves along the cleavage furrow. However, the Ca waves appeared after cleavage furrow formation in late stages of the first cleavage. In addition, cleavage was not affected by ...

  16. Cross Shear Roll Bonding

    DEFF Research Database (Denmark)

    Bay, Niels; Bjerregaard, Henrik; Petersen, Søren. B;

    1994-01-01

    The present paper describes an investigation of roll bonding an AlZn alloy to mild steel. Application of cross shear roll bonding, where the two equal sized rolls run with different peripheral speed, is shown to give better bond strength than conventional roll bonding. Improvements of up to 20......-23% in bond strength are found and full bond strength is obtained at a reduction of 50% whereas 65% is required in case of conventional roll bonding. Pseudo cross shear roll bonding, where the cross shear effect is obtained by running two equal sized rolls with different speed, gives the same results....

  17. Strontium and magnesium substituted dicalcium phosphate dehydrate coating for carbon/carbon composites prepared by pulsed electrodeposition

    Science.gov (United States)

    Liu, Shou-jie; Li, He-jun; Zhang, Lei-lei; Feng, Lei; Yao, Pei

    2015-12-01

    Trace elements substituted apatite coatings have received a lot of interest recently as they have many benefits. In this work, strontium and magnesium substituted DCPD (SM-DCPD) coatings were deposited on carbon/carbon (C/C) composites by pulsed electrodeposition method. The morphology, microstructure, corrosion resistance and in vitro bioactivity of the SM-DCPD coatings are analyzed. The results show that the SM-DCPD coatings exhibit a flake-like morphology with dense and uniform structure. The SM-DCPD coatings could induce the formation of apatite layers on their surface in simulated body fluid. The electrochemical test indicates that the SM-DCPD coatings can evidently decrease the corrosion rate of the C/C composites in simulated body fluid. The SM-DCPD has potential application as the bioactive coatings.

  18. Measurement of In-Plane Shear Strength of Carbon/Carbon Composites by Compression of Double-Notched Specimens

    Science.gov (United States)

    Yan, K. F.; Zhang, C. Y.; Qiao, S. R.; Song, C. Z.; Han, D.; Li, M.

    2012-01-01

    The compression of a double-notched specimen was used to determine the in-plane shear strength (IPSS) of a carbon/carbon composite in the paper. The effects of the notch distance ( L), thickness ( T), and notch width ( W) and supporting jig on the IPSS of the double-notched specimens were investigated numerically and experimentally. The fracture surfaces were examined by a scanning electron microscope. It was found that the IPSS varied with L. Thin specimen yielded low strength. W has little effect on IPSS. The main failure modes include the matrix shear cracking, delamination, fracture and pullout of fibers or fiber bundles. Meanwhile, a supporting jig can provide lateral support and prevent buckling, therefore lead to the failure in a shear mode.

  19. Preparation and Microstructure of a Si-Mo Fused Slurry Coating on Carbon/Carbon Composites for Oxidation Protection

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure Si slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370°C.

  20. Carbide Coatings for Nickel Alloys, Graphite and Carbon/Carbon Composites to be used in Fluoride Salt Valves

    Energy Technology Data Exchange (ETDEWEB)

    Nagle, Denis [Johns Hopkins Univ., Baltimore, MD (United States); Zhang, Dajie [Johns Hopkins Univ., Baltimore, MD (United States)

    2015-10-22

    The focus of this research was concerned with developing materials technology that supports the evolution of Generation IV Advanced High Temperature Reactor (AHTR) concepts. Specifically, we investigate refractory carbide coatings for 1) nickel alloys, and 2) commercial carbon-carbon composites (CCCs). Numerous compelling reasons have driven us to focus on carbon and carbide materials. First, unlike metals, the strength and modulus of CCCs increase with rising temperature. Secondly, graphite and carbon composites have been proven effective for resisting highly corrosive fluoride melts such as molten cryolite [Na₃AlF₆] at ~1000°C in aluminum reduction cells. Thirdly, graphite and carbide materials exhibit extraordinary radiation damage tolerance and stability up to 2000°C. Finally, carbides are thermodynamically more stable in liquid fluoride salt than the corresponding metals (i.e. Cr and Zr) found in nickel based alloys.

  1. Theoretical spectral distributions and total cross sections for neutral subthreshold pion production in carbon-carbon collisions

    Science.gov (United States)

    Norbury, J. W.; Cucinotta, F. A.; Deutchman, P. A.; Townsend, L. W.

    1985-01-01

    A coherent isobar formalism is employed to model subthreshold production of neutral pions in carbon-carbon collisions at energies below 100 MeV/nucleon. No arbitrary scale factors or adjustable free parameters are used in calculation of the Lorentz-invariant cross sections for pion production in the projectile, which produces an excited state that goes to M1 resonance in the target by conservation of spin and isospin. Pion production is also modeled for the projectile, which also reaches M1 resonance. The overall pion spectral distribution in the center of mass system is then integrated over the energy range 35-84 MeV/nucleon. The results expose an energy loss in the incident ions, as observed experimentally, and indicate that an isobar mechanism is responsible for higher energy pion production. Lower energy pions are a result of thermal processes.

  2. Increasing the Tensile Property of Unidirectional Carbon/Carbon Composites by Grafting Carbon Nanotubes onto Carbon Fibers by Electrophoretic Deposition

    Institute of Scientific and Technical Information of China (English)

    Qiang Song; Kezhi Li; Hejun Li; Qiangang Fu

    2013-01-01

    Although in-situ growing carbon nanotubes (CNTs) on carbon fibers could greatly increase the matrix-dominated mechanical properties of carbon/carbon composites (C/Cs),it always decreased the tensile strength of carbon fibers.In this work,CNTs were introduced into unidirectional carbon fiber (CF) preforms by electrophoretic deposition (EPD) and they were used to reinforce C/Cs.Effects of the content of CNTs introduced by EPD on tensile property of unidirectional C/Cs were investigated.Results demonstrated that EPD could be used as a simple and efficient method to fabricate carbon nanotube reinforced C/Cs (CNT-C/Cs) with excellent tensile strength,which pays a meaningful way to maximize the global performance of CNT-C/Cs.

  3. Influence of Thermal Shock on the Mechanical Behavior of Si-SiC Coated Carbon/Carbon Composites

    Institute of Scientific and Technical Information of China (English)

    Qiangang Fu; Hejun Li; Yongjie Wang; Kezhi Li; Lu Wei

    2009-01-01

    Si-SiC coating was prepared on the surface of carbon/carbon (C/C) composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechanical property and fracture behavior of the coated C/C were studied. The results show that, after thermal shock between 1773 K and room temperature for 5, 10 and 15 times, the flexural strength of coated composites increases by 4.29%, 15.00% and 24.20%, respectively. The toughness of the coated C/C enhances gradually during the thermal shock test. The improvement of the mechanical property after the thermal shock test is primarily caused by the weakening of the fiber-matrix interface and the reduction of residual thermal stresses by thermal shock.

  4. Investigation of test methods for measuring compressive strength and modulus of two-dimensional carbon-carbon composites

    Science.gov (United States)

    Ohlhorst, Craig W.; Sawyer, James Wayne; Yamaki, Y. Robert

    1989-01-01

    An experimental evaluation has been conducted to ascertain the the usefulness of two techniques for measuring in-plane compressive failure strength and modulus in coated and uncoated carbon-carbon composites. The techniques involved testing specimens with potted ends as well as testing them in a novel clamping fixture; specimen shape, length, gage width, and thickness were the test parameters investigated for both coated and uncoated 0/90 deg and +/-45 deg laminates. It is found that specimen shape does not have a significant effect on the measured compressive properties. The potting of specimen ends results in slightly higher measured compressive strengths than those obtained with the new clamping fixture. Comparable modulus values are obtained by both techniques.

  5. Chemistry of zerumbone. 2. Regulation of ring bond cleavage and unique antibacterial activities of zerumbone derivatives.

    Science.gov (United States)

    Kitayama, T; Yamamoto, K; Utsumi, R; Takatani, M; Hill, R K; Kawai, Y; Sawada, S; Okamoto, T

    2001-10-01

    Further investigation of the chemistry of the eleven-membered cyclic sesquiterpene, zerumbone, the major component of the wild ginger, Zingiber zerumbet Smith, has revealed a new selective epoxidation process, a further example of a novel Favorskii-initiated double ring contraction, and a regiospecific fragmentation of zerumbone dibromide derivatives. Several zerumbone derivatives were found to be selective inhibitors of the growth of gram-positive bacteria. PMID:11758909

  6. Homolytic cleavage C-C bond in the electrooxidation of ethanol and bioethanol

    Science.gov (United States)

    Barroso, J.; Pierna, A. R.; Blanco, T. C.; Morallón, E.; Huerta, F.

    Nowadays, the studies are focused on the search of better electrocatalysts that promote the complete oxidation of ethanol/bioethanol to CO 2. To that end, amorphous bi-catalytic catalysts of composition Ni 59Nb 40Pt 1- xY x (Y = Cu, Ru, x = 0.4% at.) have been developed, obtained by mechanical alloying, resulting in higher current densities and an improvement in tolerance to adsorbed CO vs. Ni 59Nb 40Pt 1 catalyst. By using voltammetric techniques, the appearance of three oxidation peaks can be observed. The first peak could be associated with the electrooxidative process of ethanol/bioethanol to acetaldehyde, the second peak could be the oxidation of acetaldehyde to acetic acid, and the last peak might be the final oxidation to CO 2. Chrono-amperometric experiments show qualitative poisoning of catalytic surfaces. However, the in situ Fourier Transformed Infrared Spectroscopy, FTIR, is used for the quasi-quantitative determination with which can be observed the appearance and evolution of different vibrational bands of carbonyl and carboxylic groups of different species, as it moves towards anodic potential in the electrooxidative process.

  7. Probing Electron-Induced Bond Cleavage at the Single-Molecule Level Using DNA Origami Templates

    DEFF Research Database (Denmark)

    Keller, Adrian Clemens; Bald, Ilko; Rotaru, Alexandru;

    2012-01-01

    sequence. This novel technique enables the fast and parallel determination of DNA strand break yields with unprecedented control over the DNA’s primary and secondary structure. Thus the detailed investigation of DNA radiation damage in its most natural environment, e.g., DNA nucleosomes constituting...

  8. Synthesis and Cleavage Activity of Artifical Minic Polypeptides

    Institute of Scientific and Technical Information of China (English)

    Yong YE; Xiao Lian HU; Ping LI; Ming Yu NIU; Li Feng CAO; Yu Fen ZHAO

    2006-01-01

    Two artificial minic polypeptides which are synthetic analogues of natural products with DNA affinity were synthesized, and theirs cleavage activity with DNA were examined. The structures of these compounds was confirmed by 1H NMR, MS and IR.

  9. Detection of nucleic acids by multiple sequential invasive cleavages 02

    Energy Technology Data Exchange (ETDEWEB)

    Hall, Jeff G. (Madison, WI); Lyamichev, Victor I. (Madison, WI); Mast, Andrea L. (Madison, WI); Brow, Mary Ann D. (Madison, WI)

    2002-01-01

    The present invention relates to means for the detection and characterization of nucleic acid sequences, as well as variations in nucleic acid sequences. The present invention also relates to methods for forming a nucleic acid cleavage structure on a target sequence and cleaving the nucleic acid cleavage structure in a site-specific manner. The structure-specific nuclease activity of a variety of enzymes is used to cleave the target-dependent cleavage structure, thereby indicating the presence of specific nucleic acid sequences or specific variations thereof. The present invention further relates to methods and devices for the separation of nucleic acid molecules based on charge. The present invention also provides methods for the detection of non-target cleavage products via the formation of a complete and activated protein binding region. The invention further provides sensitive and specific methods for the detection of human cytomegalovirus nucleic acid in a sample.

  10. Implementation of a combinatorial cleavage and deprotection scheme

    DEFF Research Database (Denmark)

    Nielsen, John; Rasmussen, Palle H.

    1996-01-01

    Phthalhydrazide libraries are synthesized in solution from substituted hydrazines and phthalimides in several different library formats including single compounds, indexed sub-libraries and a full library. When carried out during solid-phase synthesis, this combinatorial cleavage and deprotection...

  11. Detection of nucleic acids by multiple sequential invasive cleavages

    Energy Technology Data Exchange (ETDEWEB)

    Hall, Jeff G; Lyamichev, Victor I; Mast, Andrea L; Brow, Mary Ann D

    2012-10-16

    The present invention relates to means for the detection and characterization of nucleic acid sequences, as well as variations in nucleic acid sequences. The present invention also relates to methods for forming a nucleic acid cleavage structure on a target sequence and cleaving the nucleic acid cleavage structure in a site-specific manner. The structure-specific nuclease activity of a variety of enzymes is used to cleave the target-dependent cleavage structure, thereby indicating the presence of specific nucleic acid sequences or specific variations thereof. The present invention further relates to methods and devices for the separation of nucleic acid molecules based on charge. The present invention also provides methods for the detection of non-target cleavage products via the formation of a complete and activated protein binding region. The invention further provides sensitive and specific methods for the detection of human cytomegalovirus nucleic acid in a sample.

  12. 1,4-Diketones from Cross-Conjugated Dienones: Potassium Permanganate-Interrupted Nazarov Reaction.

    Science.gov (United States)

    Kwon, Yonghoon; Schatz, Devon J; West, Frederick G

    2015-08-17

    A domino potassium permanganate-interrupted Nazarov reaction to yield syn-2,3-disubstituted 1,4-diketones via a decarbonylative cleavage of the Nazarov oxyallyl intermediate, believed to be without precedent, is presented. This process allows syn substituents to be established stereospecifically on the 2-carbon bridge connecting the ketone carbonyl carbons, and the formation of one carbon-carbon and two carbon-oxygen bonds. Two carbon-carbon bonds are cleaved in this process. PMID:26138361

  13. Microstructural study of the ablation behaviors of 3D fine weave pierced Carbon/Carbon composites using plasma torch at ultra-high temperature

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A simple and effective method of testing ablation behaviors of carbon/carbon composites at high temperature was provided, which used plasma torch as the heater. The ablation resistance of 3D fine weave pierced carbon/carbon composites at high temperature was also studied. The results show that temperature of the plasma flame is very high which is much closer to the real work environment of carbon/carbon composites. The factors that affect the ablation characters of carbon/carbon composites depend on both the properties of their components and the environmental conditions in which the material is placed. The ablation behaviors of C/C composites change from the center flame region predominantly influenced by sublimation of graphite to the region close to the outer flame influenced mainly by oxidization of graphite. The sublimation ability of carbon matrix is equal to that of carbon fibers but the oxidization ability of carbon fibers is significantly enhanced compared to that of carbon matrix.

  14. Wire bonding in microelectronics

    CERN Document Server

    Harman, George G

    2010-01-01

    Wire Bonding in Microelectronics, Third Edition, has been thoroughly revised to help you meet the challenges of today's small-scale and fine-pitch microelectronics. This authoritative guide covers every aspect of designing, manufacturing, and evaluating wire bonds engineered with cutting-edge techniques. In addition to gaining a full grasp of bonding technology, you'll learn how to create reliable bonds at exceedingly high yields, test wire bonds, solve common bonding problems, implement molecular cleaning methods, and much more. Coverage includes: Ultrasonic bonding systems and technologies, including high-frequency systems Bonding wire metallurgy and characteristics, including copper wire Wire bond testing Gold-aluminum intermetallic compounds and other interface reactions Gold and nickel-based bond pad plating materials and problems Cleaning to improve bondability and reliability Mechanical problems in wire bonding High-yield, fine-pitch, specialized-looping, soft-substrate, and extreme-temperature wire bo...

  15. Mechanisms for ribotoxin-induced ribosomal RNA cleavage

    Energy Technology Data Exchange (ETDEWEB)

    He, Kaiyu [Department of Microbiology and Molecular Genetics (United States); Center for Integrative Toxicology, Michigan State University, East Lansing, MI 48824 (United States); Zhou, Hui-Ren [Food Science and Human Nutrition (United States); Pestka, James J., E-mail: pestka@msu.edu [Department of Microbiology and Molecular Genetics (United States); Food Science and Human Nutrition (United States); Center for Integrative Toxicology, Michigan State University, East Lansing, MI 48824 (United States)

    2012-11-15

    The Type B trichothecene deoxynivalenol (DON), a ribotoxic mycotoxin known to contaminate cereal-based foods, induces ribosomal RNA (rRNA) cleavage in the macrophage via p38-directed activation of caspases. Here we employed the RAW 264.7 murine macrophage model to test the hypothesis that this rRNA cleavage pathway is similarly induced by other ribotoxins. Capillary electrophoresis confirmed that the antibiotic anisomycin (≥ 25 ng/ml), the macrocylic trichothecene satratoxin G (SG) (≥ 10 ng/ml) and ribosome-inactivating protein ricin (≥ 300 ng/ml) induced 18s and 28s rRNA fragmentation patterns identical to that observed for DON. Also, as found for DON, inhibition of p38, double-stranded RNA-activated kinase (PKR) and hematopoietic cell kinase (Hck) suppressed MAPK anisomycin-induced rRNA cleavage, while, in contrast, their inhibition did not affect SG- and ricin-induced rRNA fragmentation. The p53 inhibitor pifithrin-μ and pan caspase inhibitor Z-VAD-FMK suppressed rRNA cleavage induced by anisomycin, SG and ricin, indicating that these ribotoxins shared with DON a conserved downstream pathway. Activation of caspases 8, 9 and 3 concurrently with apoptosis further suggested that rRNA cleavage occurred in parallel with both extrinsic and intrinsic pathways of programmed cell death. When specific inhibitors of cathepsins L and B (lysosomal cysteine cathepsins active at cytosolic neutral pH) were tested, only the former impaired anisomycin-, SG-, ricin- and DON-induced rRNA cleavage. Taken together, the data suggest that (1) all four ribotoxins induced p53-dependent rRNA cleavage via activation of cathepsin L and caspase 3, and (2) activation of p53 by DON and anisomycin involved p38 whereas SG and ricin activated p53 by an alternative mechanism. Highlights: ► Deoxynivalenol (DON) anisomycin, satratoxin G (SG) and ricin are ribotoxins. ► Ribotoxins induce 18s and 28s rRNA cleavage in the RAW 264.7 macrophage model. ► Ribotoxins induce rRNA cleavage via

  16. Mechanisms for ribotoxin-induced ribosomal RNA cleavage

    International Nuclear Information System (INIS)

    The Type B trichothecene deoxynivalenol (DON), a ribotoxic mycotoxin known to contaminate cereal-based foods, induces ribosomal RNA (rRNA) cleavage in the macrophage via p38-directed activation of caspases. Here we employed the RAW 264.7 murine macrophage model to test the hypothesis that this rRNA cleavage pathway is similarly induced by other ribotoxins. Capillary electrophoresis confirmed that the antibiotic anisomycin (≥ 25 ng/ml), the macrocylic trichothecene satratoxin G (SG) (≥ 10 ng/ml) and ribosome-inactivating protein ricin (≥ 300 ng/ml) induced 18s and 28s rRNA fragmentation patterns identical to that observed for DON. Also, as found for DON, inhibition of p38, double-stranded RNA-activated kinase (PKR) and hematopoietic cell kinase (Hck) suppressed MAPK anisomycin-induced rRNA cleavage, while, in contrast, their inhibition did not affect SG- and ricin-induced rRNA fragmentation. The p53 inhibitor pifithrin-μ and pan caspase inhibitor Z-VAD-FMK suppressed rRNA cleavage induced by anisomycin, SG and ricin, indicating that these ribotoxins shared with DON a conserved downstream pathway. Activation of caspases 8, 9 and 3 concurrently with apoptosis further suggested that rRNA cleavage occurred in parallel with both extrinsic and intrinsic pathways of programmed cell death. When specific inhibitors of cathepsins L and B (lysosomal cysteine cathepsins active at cytosolic neutral pH) were tested, only the former impaired anisomycin-, SG-, ricin- and DON-induced rRNA cleavage. Taken together, the data suggest that (1) all four ribotoxins induced p53-dependent rRNA cleavage via activation of cathepsin L and caspase 3, and (2) activation of p53 by DON and anisomycin involved p38 whereas SG and ricin activated p53 by an alternative mechanism. Highlights: ► Deoxynivalenol (DON) anisomycin, satratoxin G (SG) and ricin are ribotoxins. ► Ribotoxins induce 18s and 28s rRNA cleavage in the RAW 264.7 macrophage model. ► Ribotoxins induce rRNA cleavage via

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

    Science.gov (United States)

    Williams, B S; Goldberg, K I

    2001-03-21

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

  18. A Historical Trend of Ethnic Cleavages in Contemporary Iran

    OpenAIRE

    Hussein Mohammadzadeh

    2013-01-01

    The goal of this study is evaluation social and historical content of social cleavage in contemporary Iran. Analytical framework rooted in Rokan theory. Rokan believed that social cleavage appearance post of revolutions. Method of study was historical comparatives.The method of this research is comparative historical in which we used of historical documents and data. In this field, I have compared data of indexes of socio-economic of ethnic states.Assessment of data and documents show that so...

  19. Mutational analysis of the encephalomyocarditis virus primary cleavage.

    OpenAIRE

    Hahn, H.; Palmenberg, A C

    1996-01-01

    Sixteen substitution mutations of the conserved DvExNPGP sequence, implicated in cardiovirus and aphthovirus primary polyprotein cleavage, were created in encephalomyocarditis virus cDNA, expressed, and characterized for processing activity. Nearly all the mutations severely decreased the efficiency of the primary cleavage reaction during cell-free synthesis of viral precursors, indicating a stringent requirement for the natural sequence in this processing event. When representative mutations...

  20. Cleavage of a viral polyprotein by a cellular proteolytic activity.

    OpenAIRE

    Tian, Y. C.; Shih, D S

    1986-01-01

    The 200,000-dalton polyprotein encoded by the bottom component RNA of cowpea mosaic virus was synthesized in rabbit reticulocyte lysates, and this in vitro-synthesized protein was isolated from the lysate reaction mixture by sucrose density gradient centrifugation. Incubation of the isolated polyprotein with buffer caused no change in the protein, but incubation with reticulocyte lysates or with fractionated lysate proteins resulted in cleavage of the protein into the expected cleavage produc...

  1. Evidence for intramolecular self-cleavage of picornaviral replicase precursors.

    OpenAIRE

    Palmenberg, A C; Rueckert, R R

    1982-01-01

    It has previously been shown that when encephalomyocarditis viral RNA is translated in cell-free extracts of rabbit reticulocytes, it synthesizes a virus-coded protease, p22, which is derived by cleavage of a precursor protein, C. Protein C is shown here to be cleaved by two different mechanisms, which were distinguished by their sensitivity to dilution. One mechanism was sensitive to dilution; the other was not. The biphasic cleavage behavior was unchanged by diluting incubation mixtures wit...

  2. Internal guide RNA interactions interfere with Cas9-mediated cleavage.

    Science.gov (United States)

    Thyme, Summer B; Akhmetova, Laila; Montague, Tessa G; Valen, Eivind; Schier, Alexander F

    2016-01-01

    The CRISPR/Cas system uses guide RNAs (gRNAs) to direct sequence-specific DNA cleavage. Not every gRNA elicits cleavage and the mechanisms that govern gRNA activity have not been resolved. Low activity could result from either failure to form a functional Cas9-gRNA complex or inability to recognize targets in vivo. Here we show that both phenomena influence Cas9 activity by comparing mutagenesis rates in zebrafish embryos with in vitro cleavage assays. In vivo, our results suggest that genomic factors such as CTCF inhibit mutagenesis. Comparing near-identical gRNA sequences with different in vitro activities reveals that internal gRNA interactions reduce cleavage. Even though gRNAs containing these structures do not yield cleavage-competent complexes, they can compete with active gRNAs for binding to Cas9. These results reveal that both genomic context and internal gRNA interactions can interfere with Cas9-mediated cleavage and illuminate previously uncharacterized features of Cas9-gRNA complex formation. PMID:27282953

  3. Internal guide RNA interactions interfere with Cas9-mediated cleavage

    Science.gov (United States)

    Thyme, Summer B.; Akhmetova, Laila; Montague, Tessa G.; Valen, Eivind; Schier, Alexander F.

    2016-01-01

    The CRISPR/Cas system uses guide RNAs (gRNAs) to direct sequence-specific DNA cleavage. Not every gRNA elicits cleavage and the mechanisms that govern gRNA activity have not been resolved. Low activity could result from either failure to form a functional Cas9–gRNA complex or inability to recognize targets in vivo. Here we show that both phenomena influence Cas9 activity by comparing mutagenesis rates in zebrafish embryos with in vitro cleavage assays. In vivo, our results suggest that genomic factors such as CTCF inhibit mutagenesis. Comparing near-identical gRNA sequences with different in vitro activities reveals that internal gRNA interactions reduce cleavage. Even though gRNAs containing these structures do not yield cleavage-competent complexes, they can compete with active gRNAs for binding to Cas9. These results reveal that both genomic context and internal gRNA interactions can interfere with Cas9-mediated cleavage and illuminate previously uncharacterized features of Cas9–gRNA complex formation. PMID:27282953

  4. On Bond Portfolio Management

    OpenAIRE

    Vladislav Kargin

    2002-01-01

    This paper describes a new method of bond portfolio optimization based on stochastic string models of correlation structure in bond returns. The paper shows how to approximate correlation function of bond returns, compute the optimal portfolio allocation using Wiener-Hopf factorization, and check whether a collection of bonds presents arbitrage opportunities.

  5. Novel carotenoid cleavage dioxygenase catalyzes the first dedicated step in saffron crocin biosynthesis

    KAUST Repository

    Frusciante, Sarah

    2014-08-05

    Crocus sativus stigmas are the source of the saffron spice and accumulate the apocarotenoids crocetin, crocins, picrocrocin, and safranal, responsible for its color, taste, and aroma. Through deep transcriptome sequencing, we identified a novel dioxygenase, carotenoid cleavage dioxygenase 2 (CCD2), expressed early during stigma development and closely related to, but distinct from, the CCD1 dioxygenase family. CCD2 is the only identified member of a novel CCD clade, presents the structural features of a bona fide CCD, and is able to cleave zeaxanthin, the presumed precursor of saffron apocarotenoids, both in Escherichia coli and in maize endosperm. The cleavage products, identified through high-resolution mass spectrometry and comigration with authentic standards, are crocetin dialdehyde and crocetin, respectively. In vitro assays show that CCD2 cleaves sequentially the 7,8 and 7′,8′ double bonds adjacent to a 3-OH-β-ionone ring and that the conversion of zeaxanthin to crocetin dialdehyde proceeds via the C30 intermediate 3-OH-β-apo-8′-carotenal. In contrast, zeaxanthin cleavage dioxygenase (ZCD), an enzyme previously claimed to mediate crocetin formation, did not cleave zeaxanthin or 3-OH-β-apo-8′-carotenal in the test systems used. Sequence comparison and structure prediction suggest that ZCD is an N-truncated CCD4 form, lacking one blade of the β-propeller structure conserved in all CCDs. These results constitute strong evidence that CCD2 catalyzes the first dedicated step in crocin biosynthesis. Similar to CCD1, CCD2 has a cytoplasmic localization, suggesting that it may cleave carotenoids localized in the chromoplast outer envelope.

  6. A highly efficient ADH-coupled NADH-recycling system for the asymmetric bioreduction of carbon-carbon double bonds using enoate reductases.

    Science.gov (United States)

    Tauber, Katharina; Hall, Melanie; Kroutil, Wolfgang; Fabian, Walter M F; Faber, Kurt; Glueck, Silvia M

    2011-06-01

    The asymmetric bioreduction of activated alkenes catalyzed by flavin-dependent enoate reductases from the OYE-family represents a powerful method for the production of optically active compounds. For its preparative-scale application, efficient and economic NADH-recycling is crucial. A novel enzyme-coupled NADH-recycling system is proposed based on the concurrent oxidation of a sacrificial sec-alcohol catalyzed by an alcohol dehydrogenase (ADH-A). Due to the highly favorable position of the equilibrium of ene-reduction versus alcohol-oxidation, the cosubstrate is only required in slight excess.

  7. Direct carbon-carbon bond formation via reductive soft enolization: a syn-selective Mannich addition of α-iodo thioesters.

    Science.gov (United States)

    Truong, Ngoc; Sauer, Scott J; Seraphin-Hatcher, Cyndie; Coltart, Don M

    2016-08-16

    The β-amino carboxylic acid moiety is a key feature of numerous important biologically active compounds. We describe a syn-selective direct Mannich addition reaction that uses α-iodo thioesters and sulfonyl imines and produces β-amino thioesters. Enolate formation is achieved by reductive soft enolization. The products of the reaction provide straightforward access to biologically important β-lactams through a variety of known reactions. PMID:27492274

  8. Intramolecular coupling of eta/sup 2/-iminoacyl groups at group 4 metal centers: a kinetic study of the carbon-carbon double-bond-forming reaction

    Energy Technology Data Exchange (ETDEWEB)

    Durfee, L.D.; McMullen, A.K.; Rothwell, I.P.

    1988-03-02

    The series of bis(eta/sup 2/-iminoacyl) compounds of general formula M(OAr)/sub 2/(eta/sup 2/-R'NCR)/sub 2/ (M = Ti, Zr, Hf; OAr = 2,6-diisopropyl- and 2,6-di-tert-butylphenoxide; R = CH/sub 3/, CH/sub 2/Ph; R' = various substituted phenyls) undergo intramolecular coupling on thermolysis to produce the corresponding enediamide derivatives M(OAr)/sub 2/(R'NC(R) = C(R)NR'). A kinetic study of the reaction in hydrocarbon solvents has shown it to be first order. The reaction is metal dependent with the rate decreasing in the order Ti > Zr > Hf. The rate of the reaction is also dependent on the steric and electronic nature of the nitrogen substituent (R'). The use of the bulky aryl group 2,6-dimethylphenyl retards the reaction, while the use of various 3- and 4-substituted phenyls (3-F, 3-OMe, 4-OMe, 4-Cl, 4-NMe/sub 2/) shows the reaction to be accelerated by electron-withdrawing substituents. A sigma plot based on kinetic data obtained at 67/sup 0/C and 77/sup 0/C yielded rho values of 0.83 (R = 0.97) and 0.84 (R = 0.95), respectively. Both the steric and electronic dependence of the reactivity on the nitrogen substituents is discussed mechanistically and used to rationalize the much more facile intramolecular coupling observed for the related eta/sup 2/-acyl (eta/sup 2/-OCR) functionalities.

  9. Identification and expression pattern of a new carotenoid cleavage dioxygenase gene member from Bixa orellana.

    Science.gov (United States)

    Rodríguez-Ávila, N L; Narváez-Zapata, J A; Ramírez-Benítez, J E; Aguilar-Espinosa, M L; Rivera-Madrid, R

    2011-11-01

    Carotenoid cleavage dioxygenases (CCDs) are a class of enzymes involved in the biosynthesis of a broad diversity of secondary metabolites known as apocarotenoids. In plants, CCDs are part of a genetic family with members which cleave specific double bonds of carotenoid molecules. CCDs are involved in the production of diverse and important metabolites such as vitamin A and abscisic acid (ABA). Bixa orellana L. is the main source of the natural pigment annatto or bixin, an apocarotenoid accumulated in large quantities in its seeds. Bixin biosynthesis has been studied and the involvement of a CCD has been confirmed in vitro. However, the CCD genes involved in the biosynthesis of the wide variety of apocarotenoids found in this plant have not been well documented. In this study, a new CCD1 gene member (BoCCD1) was identified and its expression was charaterized in different plant tissues of B. orellana plantlets and adult plants. The BoCCD1 sequence showed high homology with plant CCD1s involved mainly in the cleavage of carotenoids in several sites to generate multiple apocarotenoid products. Here, the expression profiles of the BoCCD1 gene were analysed and discussed in relation to total carotenoids and other important apocarotenoids such as bixin. PMID:21813796

  10. Optimization schemes for selective molecular cleavage with tailored ultrashort laser pulses

    International Nuclear Information System (INIS)

    Graphical abstract: Isosurface plot of the electronic density, and positions of the nuclei, during the irradiation of a formaldiminium ion with an optimized laser pulse, leading to the selective cleavage of a proton. Display Omitted Highlights: ► We use QOCT in combination with mixed quantum-classical molecular models. ► TDDFT models the electrons coupled to the nuclei through Ehrenfest equations. ► Both gradient-free and gradient-based algorithms are explored for the optimization. ► We explore different options for the definition of the target functional. - Abstract: We present some approaches to the computation of ultra-fast laser pulses capable of selectively breaking molecular bonds. The calculations are based on a mixed quantum-classical description: The electrons are treated quantum mechanically (making use of time-dependent density-functional theory), whereas the nuclei are treated classically. The temporal shape of the pulses is tailored to maximize a control target functional which is designed to produce the desired molecular cleavage. The precise definition of this functional is a crucial ingredient: we explore expressions based on the forces, on the momenta and on the velocities of the nuclei. The algorithm used to find the optimum pulse is also relevant; we test both direct gradient-free algorithms, as well as schemes based on formal optimal control theory. The tests are performed both on one dimensional models of atomic chains, and on first-principles descriptions of molecules.

  11. Molecular Basis of Catalytic Chamber-assisted Unfolding and Cleavage of Human Insulin by Human Insulin-degrading Enzyme

    Energy Technology Data Exchange (ETDEWEB)

    Manolopoulou, Marika; Guo, Qing; Malito, Enrico; Schilling, Alexander B.; Tang, Wei-Jen; (UC); (UIC)

    2009-06-02

    Insulin is a hormone vital for glucose homeostasis, and insulin-degrading enzyme (IDE) plays a key role in its clearance. IDE exhibits a remarkable specificity to degrade insulin without breaking the disulfide bonds that hold the insulin A and B chains together. Using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry to obtain high mass accuracy, and electron capture dissociation (ECD) to selectively break the disulfide bonds in gas phase fragmentation, we determined the cleavage sites and composition of human insulin fragments generated by human IDE. Our time-dependent analysis of IDE-digested insulin fragments reveals that IDE is highly processive in its initial cleavage at the middle of both the insulin A and B chains. This ensures that IDE effectively splits insulin into inactive N- and C-terminal halves without breaking the disulfide bonds. To understand the molecular basis of the recognition and unfolding of insulin by IDE, we determined a 2.6-A resolution insulin-bound IDE structure. Our structure reveals that IDE forms an enclosed catalytic chamber that completely engulfs and intimately interacts with a partially unfolded insulin molecule. This structure also highlights how the unique size, shape, charge distribution, and exosite of the IDE catalytic chamber contribute to its high affinity ( approximately 100 nm) for insulin. In addition, this structure shows how IDE utilizes the interaction of its exosite with the N terminus of the insulin A chain as well as other properties of the catalytic chamber to guide the unfolding of insulin and allowing for the processive cleavages.

  12. Size effects and strain localization in atomic-scale cleavage modeling.

    Science.gov (United States)

    Elsner, B A M; Müller, S

    2015-09-01

    In this work, we study the adhesion and decohesion of Cu(1 0 0) surfaces using density functional theory (DFT) calculations. An upper stress to surface decohesion is obtained via the universal binding energy relation (UBER), but the model is limited to rigid separation of bulk-terminated surfaces. When structural relaxations are included, an unphysical size effect arises if decohesion is considered to occur as soon as the strain energy equals the energy of the newly formed surfaces. We employ the nudged elastic band (NEB) method to show that this size effect is opposed by a size-dependency of the energy barriers involved in the transition. Further, we find that the transition occurs via a localization of bond strain in the vicinity of the cleavage plane, which resembles the strain localization at the tip of a sharp crack that is predicted by linear elastic fracture mechanics. PMID:26219654

  13. Size effects and strain localization in atomic-scale cleavage modeling

    International Nuclear Information System (INIS)

    In this work, we study the adhesion and decohesion of Cu(1 0 0) surfaces using density functional theory (DFT) calculations. An upper stress to surface decohesion is obtained via the universal binding energy relation (UBER), but the model is limited to rigid separation of bulk-terminated surfaces. When structural relaxations are included, an unphysical size effect arises if decohesion is considered to occur as soon as the strain energy equals the energy of the newly formed surfaces. We employ the nudged elastic band (NEB) method to show that this size effect is opposed by a size-dependency of the energy barriers involved in the transition. Further, we find that the transition occurs via a localization of bond strain in the vicinity of the cleavage plane, which resembles the strain localization at the tip of a sharp crack that is predicted by linear elastic fracture mechanics. (paper)

  14. Optimization Schemes for Selective Molecular Cleavage with Tailored Ultrashort Laser Pulses

    CERN Document Server

    Krieger, Kevin; Gross, E K U

    2011-01-01

    We present some approaches to the computation of ultra-fast laser pulses capable of selectively breaking molecular bonds. The calculations are based on a mixed quantum-classical description: The electrons are treated quantum mechanically (making use of time-dependent density-functional theory), whereas the nuclei are treated classically. The temporal shape of the pulses is tailored to maximise a control target functional which is designed to produce the desired molecular cleavage. The precise definition of this functional is a crucial ingredient: we explore expressions based on the forces, on the momenta and on the velocities of the nuclei. The algorithm used to find the optimum pulse is also relevant; we test both direct gradient-free algorithms, as well as schemes based on formal optimal control theory. The tests are performed both on one dimensional models of atomic chains, and on first-principles descriptions of molecules.

  15. Synthesis and Integration of Nanostructured Carbon: Carbon Nanotube-Polymer Nanocomposites and Graphene

    Science.gov (United States)

    Gulotty, Richard Stephen

    Nanostructured carbon, in the form of tubes or sheets, exhibits exceptional thermal and electrical properties. Graphene, a single atomic sheet of hexagonal sp2 bonded carbon, posesses a thermal conductivity higher than diamond, with an extremely high electron mobility. Carbon nanotubes (CNT), which are tubes composed of one or more graphene sheets, also posess high thermal conductivity and electron mobility. One of the major problems facing the application of nanomaterials is integration into already existing material systems. A second challenge is controlled synthesis of nanomaterials. In this dissertation research novel methods were investigated for coupling carbon nanotubes to polymer matrices, as well as new approaches for controlling the synthesis of graphene and reduced graphene oxide like carbon (R-GOC) on copper (Cu) foils via chemical vapor deposition. It was determined that carboxylic functionalization of carbon nanotubes was effective in improving the coupling of CNTs to polymer matrices, affecting the thermal transport of the resulting CNT-polymer nanocomposites. From the CVD studies it was established that the cooling phase gases flowed after deposition influence the growth mechanics of graphene on Cu foil. Further CVD studies showed that methane may be decomposed directly onto quartz to form reduced graphene oxide like carbon thin films. The obtained thermal characterization results are important for development of CNTs as fillers for composite pastes with high thermal conductivity, and the results of the CVD studies are important for developing further understanding of growth mechanics of bilayer graphene and other nanostructured carbon. In addition to the fundamental study of CVD synthesis of graphene and R-GOC, this dissertation work includes engineering of graphene and R-GOC to various applications, including the development of the thinnest flexible transistor with active materials made from all-2D materials, as well as large-scale electron

  16. Small molecule activators of pre-mRNA 3′ cleavage

    OpenAIRE

    Ryan, Kevin; Khleborodova, Asya; Pan, Jingyi; Ryan, Xiaozhou P.

    2009-01-01

    3′ Cleavage and polyadenylation are obligatory steps in the biogenesis of most mammalian pre-mRNAs. In vitro reconstitution of the 3′ cleavage reaction from human cleavage factors requires high concentrations of creatine phosphate (CP), though how CP activates cleavage is not known. Previously, we proposed that CP might work by competitively inhibiting a cleavage-suppressing serine/threonine (S/T) phosphatase. Here we show that fluoride/EDTA, a general S/T phosphatase inhibitor, activates in ...

  17. Cleavage entropy as quantitative measure of protease specificity.

    Directory of Open Access Journals (Sweden)

    Julian E Fuchs

    2013-04-01

    Full Text Available A purely information theory-guided approach to quantitatively characterize protease specificity is established. We calculate an entropy value for each protease subpocket based on sequences of cleaved substrates extracted from the MEROPS database. We compare our results with known subpocket specificity profiles for individual proteases and protease groups (e.g. serine proteases, metallo proteases and reflect them quantitatively. Summation of subpocket-wise cleavage entropy contributions yields a measure for overall protease substrate specificity. This total cleavage entropy allows ranking of different proteases with respect to their specificity, separating unspecific digestive enzymes showing high total cleavage entropy from specific proteases involved in signaling cascades. The development of a quantitative cleavage entropy score allows an unbiased comparison of subpocket-wise and overall protease specificity. Thus, it enables assessment of relative importance of physicochemical and structural descriptors in protease recognition. We present an exemplary application of cleavage entropy in tracing substrate specificity in protease evolution. This highlights the wide range of substrate promiscuity within homologue proteases and hence the heavy impact of a limited number of mutations on individual substrate specificity.

  18. Preparation of fluorescence quenched libraries containing interchain disulphide bonds for studies of protein disulphide isomerases

    DEFF Research Database (Denmark)

    Spetzler, J C; Westphal, V; Winther, Jakob R.;

    1998-01-01

    the quenching chromophore (Tyr(NO2)) and Cys(pNpys) activated for reaction with a second thiol. The formation and cleavage of the interchain disulphide bonds in the library were monitored under a fluorescence microscope. Substrates to investigate the properties of protein disulphide isomerase in solution were...

  19. Hydrogen bonded supramolecular structures

    CERN Document Server

    Li, Zhanting

    2015-01-01

    This book covers the advances in the studies of hydrogen-bonding-driven supramolecular systems  made over the past decade. It is divided into four parts, with the first introducing the basics of hydrogen bonding and important hydrogen bonding patterns in solution as well as in the solid state. The second part covers molecular recognition and supramolecular structures driven by hydrogen bonding. The third part introduces the formation of hollow and giant macrocycles directed by hydrogen bonding, while the last part summarizes hydrogen bonded supramolecular polymers. This book is designed to b

  20. A comparative of quantum mechanical Calculations on adsorption of CCl2O by Carbon-Carbon & Aluminum -Nitride Nanotubes

    Directory of Open Access Journals (Sweden)

    A. Kazemi Babaheydari

    2015-06-01

    Full Text Available In this paper, is calculated structural optimization and interactions on surface nanotubes (AlN,CNT and phosgene. Based on the optimized ground state geometries using B3LYP/6-31G* method, the NBO analysis of donor-acceptor (bond- anti bond interactions revealed that the stabilizationenergies associated with the electronic delocalization.

  1. A new cultural cleavage in post-modern society

    Directory of Open Access Journals (Sweden)

    Jan-Erik Lane

    2007-09-01

    Full Text Available The attitudes towards gender and homosexuality tend to be linked at the micro level (individuals, which explains the political saliency of this newly emerging cleavage. At the macro level (country, the main finding is that the value orientations towards gender and homosexuality are strongly embedded in the basic cultural or civilisation differences among countries. As developing countries modernise and enter post-modernity, they will also experience the gender cleavage, especially when they adhere to an individualistic culture. Cultural cleavages in the post-modern society, whether in rich or developing countries, can only be properly researched by the survey method. It opens up a large area for both micro and macro analyses in the social sciences.

  2. Short RNA guides cleavage by eukaryotic RNase III.

    Directory of Open Access Journals (Sweden)

    Bruno Lamontagne

    Full Text Available In eukaryotes, short RNAs guide a variety of enzymatic activities that range from RNA editing to translation repression. It is hypothesized that pre-existing proteins evolved to bind and use guide RNA during evolution. However, the capacity of modern proteins to adopt new RNA guides has never been demonstrated. Here we show that Rnt1p, the yeast orthologue of the bacterial dsRNA-specific RNase III, can bind short RNA transcripts and use them as guides for sequence-specific cleavage. Target cleavage occurred at a constant distance from the Rnt1p binding site, leaving the guide RNA intact for subsequent cleavage. Our results indicate that RNase III may trigger sequence-specific RNA degradation independent of the RNAi machinery, and they open the road for a new generation of precise RNA silencing tools that do not trigger a dsRNA-mediated immune response.

  3. Analytical model for intergrain expansion and cleavage: random grain boundaries

    International Nuclear Information System (INIS)

    A description of rigid-body grain boundary relaxation and cleavage in tungsten is performed using a pair-wise Morse interatomic potential in real and reciprocal spaces. Cleavage energies and grain boundary dilatation of random grain boundaries were formulated and computed using atomic layer interaction energies. These values were determined using a model for a relaxed random grain boundary that consists of rigid grains on either side of the boundary plane that are allowed to float to reach the equilibrium position. Expressions are given that describe in real space the energy of interatomic interaction on random grain boundaries with twist orientation. It was shown that grain-boundary expansion and cleavage energies of the most widespread random grain boundaries are mainly determined by grain boundary atomic density

  4. Three-dimensional interpretation of cleavage fracture tests of cladded specimens with local approach to cleavage fracture

    International Nuclear Information System (INIS)

    Electricite de France has conducted during these last years an experimental and numerical research programme in order to evaluate fracture mechanics analyses used in nuclear reactor pressure vessels integrity assessment, regarding the risk of brittle fracture. Two cladded specimens made of ferritic steel A508 Cl3 with stainless steel cladding, and containing shallow subclad flaws, have been tested in four point bending at very low temperature to obtain cleavage failure. The crack instability was obtained in base metal by cleavage fracture, without crack arrest. The tests have been interpreted by local approach to cleavage fracture (Beremin model) using three-dimensional finite element computations. After the elastic-plastic computation of stress intensity factor KJ along the crack front, the probability of cleavage failure of each specimen is evaluated using m, σu Beremin model parameters identified on the same material. The failure of two specimens is conservatively predicted by both analyses. The elastic-plastic stress intensity factor KJ in base metal is always greater than base metal fracture toughness K1c. The calculated probabilities of cleavage failure are in agreement with experimental results. The sensitivity of Beremin model to numerical aspects is finally exposed. (orig.)

  5. Fabrication method and microstructural characteristics of coal-tar-pitch-based 2D carbon/carbon composites

    Science.gov (United States)

    Esmaeeli, Mohammad; Khosravi, Hamed; Mirhabibi, Alireza

    2015-02-01

    The lignin-cellulosic texture of wood was used to produce two-dimensional (2D) carbon/carbon (C/C) composites using coal tar pitch. Ash content tests were conducted to select two samples among the different kinds of woods present in Iran, including walnut, white poplar, cherry, willow, buttonwood, apricots, berry, and blue wood. Walnut and white poplar with ash contents of 1.994wt% and 0.351wt%, respectively, were selected. The behavior of these woods during pyrolysis was investigated by differential thermal analysis (DTA) and thermo gravimetric (TG) analysis. The bulk density and open porosity were measured after carbonization and densification. The microstructural characteristics of samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy. The results indicate that the density of both the walnut and white poplar is increased, and the open porosity is decreased with the increasing number of carbonization cycles. The XRD patterns of the wood charcoal change gradually with increasing pyrolysis temperature, possibly as a result of the ultra-structural changes in the charcoal or the presence of carbonized coal tar pitch in the composite's body.

  6. Al current collector surface treatment and carbon nano tubes influences on Carbon / Carbon super-capacitors performances

    Energy Technology Data Exchange (ETDEWEB)

    Portet, C.; Taberna, P.L.; Simon, P. [Universite Paul Sabatier, CIRIMAT-LCMIE, 31 - Toulouse (France)

    2004-07-01

    Performances of 4 cm{sup 2} carbon/carbon super-capacitors cells using Al current collectors foils in organic electrolyte are presented; the improvement of electrode material has been investigated. In a first part, a surface treatment of the Al current collector is proposed in order to improve contact surface between the current collector and the active material leading to an internal resistance decrease. The process consists in an etching of the Al foil and is followed by a carbonaceous sol-gel deposit. Galvano-static cycling and Electrochemical Impedance Spectroscopy measurements of super-capacitors all assembled with treated Al foil were tested over 10,000 cycles: an ESR of 0.5 {omega} cm{sup 2} and a capacitance of 95 F g{sup -1} of activated carbon are obtained and performances remain stable during cycling. The second part is devoted to the study of Carbon Nano Tubes (CNTs) adding into the active material on the performances of super-capacitors. A content of 15% of CNTs appears to be the best composition; the ESR is 0.4 {omega} cm{sup 2} (20% lowered as compared to a cell using activated carbon based electrode) and the capacitance remain high 93 F g{sup -1} of carbonaceous active material. (authors)

  7. Prospects in using carbon-carbon composite materials based on viscose carbon fibers for the space technology needs

    International Nuclear Information System (INIS)

    Due to the unique combination of low density, high mechanical strength under elevated temperatures, high resistance to thermal shock loads and ablation resistance, carbon-carbon composite materials (CCCM) are widely used for manufacturing of highly thermally loaded structural components. The important scientific and technical difficulty is to increase and stabilize CCCM properties, reduce cost and leads to searching for new raw materials and engineering solutions. The article describes the prospects of replacing carbon fiber fills based on PAN-precursors which are traditionally used for producing CCCM by carbon fillers on the basis of viscose raw material; shows the advantages of using viscose-based carbon fibers when forming products of complex shape as well as the possibility of obtaining products with high functional characteristics. The creation of CCCM of layered reinforcement structure, in which carbon fabric layers interleave with layers of discontinuous carbon fibers, enabled to increase the overall density of carbon composites, to ensure sufficiently high level of mechanical characteristics and resistance to ablation

  8. Oxidation protection and behavior of in-situ zirconium diboride–silicon carbide coating for carbon/carbon composites

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lu; Li, Hejun, E-mail: lihejun@nwpu.edu.cn; Yin, Xuemin; Chu, Yanhui; Chen, Xi; Fu, Qiangang, E-mail: fuqiangang@nwpu.edu.cn

    2015-10-05

    Highlights: • ZrB{sub 2}–SiC coating was prepared on C/C composite by in-situ reaction. • A two-layered structure was obtained when the coating was oxidized at 1500 °C. • The formation and collapse of bubbles influenced the coating oxidation greatly. • The morphology evolution of oxide scale during oxidation was illuminated. - Abstract: To protect carbon/carbon (C/C) composites against oxidation, zirconium diboride–silicon carbide (ZrB{sub 2}–SiC) coating was prepared by in-situ reaction using ZrC, B{sub 4}C and Si as raw materials. The in-situ ZrB{sub 2}–SiC coated C/C presented good oxidation resistance, whose weight loss was only 0.15% after isothermal oxidation at 1500 °C for 216 h. Microstructure evolution of coating at 1500 °C was studied, revealing a two-layered structure: (1) ZrO{sub 2} (ZrSiO{sub 4}) embedded in SiO{sub 2}-rich glass, and (2) unaffected ZrB{sub 2}–SiC. The formation and collapse of bubbles influenced the coating oxidation greatly. A model based on the evolution of oxide scale was proposed to explain the failure mechanism of coating.

  9. Sensitive and fast mutation detection by solid phase chemical cleavage

    DEFF Research Database (Denmark)

    Hansen, Lise Lotte; Justesen, Just; Kruse, Torben A

    1996-01-01

    We have developed a solid phase chemical cleavage method (SpCCM) for screening large DNA fragments for mutations. All reactions can be carried out in microtiterwells from the first amplification of the patient (or test) DNA through the search for mutations. The reaction time is significantly...... reduced compared to the conventional chemical cleavage method (CCM), and even by using a uniformly labelled probe, the exact position and nature of the mutation can be revealed. The SpCCM is suitable for automatization using a workstation to carry out the reactions and a fluorescent detection-based DNA...

  10. Study of 16O(12C,α20Ne)α for the investigation of carbon-carbon fusion reaction via the Trojan Horse Method

    Science.gov (United States)

    Rapisarda, G. G.; Spitaleri, C.; Bordeanu, C.; Hons, Z.; Kiss, G. G.; La Cognata, M.; Mrazek, J.; Nita, C.; Pantelica, D.; Petrascu, H.; Pizzone, R. G.; Romano, S.; Szücs, T.; Trache, L.; Tumino, A.; Velisa, G.

    2016-04-01

    Carbon-carbon fusion reaction represents a nuclear process of great interest in astrophysics, since the carbon burning is connected with the third phase of massive stars (M > 8 M⊙) evolution. In spite of several experimental works, carbon-carbon cross section has been measured at energy still above the Gamow window moreover data at low energy present big uncertainty. In this paper we report the results about the study of the 16O(12C,α 20Ne)α reaction as a possible three-body process to investigate 12C(12C,α)20Ne at astrophysical energy via Trojan Horse Method (THM). This study represents the first step of a program of experiments aimed to measure the 12C+12C cross section at astrophysical energy using the THM.

  11. Australia's Bond Home Bias

    OpenAIRE

    Mishra, Anil V; Umaru B. Conteh

    2014-01-01

    This paper constructs the float adjusted measure of home bias and explores the determinants of bond home bias by employing the International Monetary Fund's high quality dataset (2001 to 2009) on cross-border bond investment. The paper finds that Australian investors' prefer investing in countries with higher economic development and more developed bond markets. Exchange rate volatility appears to be an impediment for cross-border bond investment. Investors prefer investing in countries with ...

  12. Bond percolation in films

    Science.gov (United States)

    Korneta, W.; Pytel, Z.

    1988-04-01

    Bond percolation in films with simple cubic structure is considered. It is assumed that the probability of a bond being present between nearest-neighbor sites depends on the distances to surfaces. Based on the relation between the Potts model and the bond percolation model, and using the mean-field approximation, the phase diagram and profiles of the percolation probability have been obtained.

  13. Corporate Bonds in Denmark

    DEFF Research Database (Denmark)

    Tell, Michael

    2015-01-01

    to think in alternative ways such as issuing corporate bonds. A market for corporate bonds exists in countries such as Norway, Germany, France, the United Kingdom and the United States, while Denmark is still behind in this trend. Some large Danish corporations have instead used foreign corporate bonds...

  14. Chemical bond fundamental aspects of chemical bonding

    CERN Document Server

    Frenking, Gernot

    2014-01-01

    This is the perfect complement to ""Chemical Bonding - Across the Periodic Table"" by the same editors, who are two of the top scientists working on this topic, each with extensive experience and important connections within the community. The resulting book is a unique overview of the different approaches used for describing a chemical bond, including molecular-orbital based, valence-bond based, ELF, AIM and density-functional based methods. It takes into account the many developments that have taken place in the field over the past few decades due to the rapid advances in quantum chemica

  15. Tandem Bond-Forming Reactions of 1-Alkynyl Ethers.

    Science.gov (United States)

    Minehan, Thomas G

    2016-06-21

    Electron-rich alkynes, such as ynamines, ynamides, and ynol ethers, are functional groups that possess significant potential in organic chemistry for the formation of carbon-carbon bonds. While the synthetic utility of ynamides has recently been expanded considerably, 1-alkynyl ethers, which possess many of the reactivity features of ynamides, have traditionally been far less investigated because of concerns about their stability. Like ynamides, ynol ethers are relatively unhindered to approach by functional groups present in the same or different molecules because of their linear geometry, and they can potentially form up to four new bonds in a single transformation. Ynol ethers also possess unique reactivity features that make them complementary to ynamides. Research over the past decade has shown that ynol ethers formed in situ from stable precursors engage in a variety of useful carbon-carbon bond-forming processes. Upon formation at -78 °C, allyl alkynyl ethers undergo a rapid [3,3]-sigmatropic rearrangement to form allyl ketene intermediates, which may be trapped with alcohol or amine nucleophiles to form γ,δ-unsaturated carboxylic acid derivatives. The process is stereospecific, takes place in minutes at cryogenic temperatures, and affords products containing (quaternary) stereogenic carbon atoms. Trapping of the intermediate allyl ketene with carbonyl compounds, epoxides, or oxetanes instead leads to complex α-functionalized β-, γ-, or δ-lactones, respectively. [3,3]-Sigmatropic rearrangement of benzyl alkynyl ethers also takes place at temperatures ranging from -78 to 60 °C to afford substituted 2-indanones via intramolecular carbocyclization of the ketene intermediate. tert-Butyl alkynyl ethers containing pendant di- and trisubstituted alkenes and enol ethers are stable to chromatographic isolation and undergo a retro-ene/[2 + 2] cycloaddition reaction upon mild thermolysis (90 °C) to afford cis-fused cyclobutanones and donor

  16. Bonding thermoplastic polymers

    Science.gov (United States)

    Wallow, Thomas I.; Hunter, Marion C.; Krafcik, Karen Lee; Morales, Alfredo M.; Simmons, Blake A.; Domeier, Linda A.

    2008-06-24

    We demonstrate a new method for joining patterned thermoplastic parts into layered structures. The method takes advantage of case-II permeant diffusion to generate dimensionally controlled, activated bonding layers at the surfaces being joined. It is capable of producing bonds characterized by cohesive failure while preserving the fidelity of patterned features in the bonding surfaces. This approach is uniquely suited to production of microfluidic multilayer structures, as it allows the bond-forming interface between plastic parts to be precisely manipulated at micrometer length scales. The bond enhancing procedure is easily integrated in standard process flows and requires no specialized equipment.

  17. Fe-Catalyzed Oxidative Cleavage of Unsaturated Fatty Acids

    NARCIS (Netherlands)

    Spannring, P.

    2013-01-01

    The oxidative cleavage of unsaturated fatty acids into aldehydes or carboxylic acids gives access to valuable products. The products can be used as chemical building blocks, as emulsifiers or in the paint or polymer industry. Ozonolysis is applied industrially to cleave the fatty acid oleic acid int

  18. The pattern of DNA cleavage intensity around indels.

    Science.gov (United States)

    Chen, Wei; Zhang, Liqing

    2015-01-01

    Indels (insertions and deletions) are the second most common form of genetic variations in the eukaryotic genomes and are responsible for a multitude of genetic diseases. Despite its significance, detailed molecular mechanisms for indel generation are still unclear. Here we examined 2,656,597 small human and mouse germline indels, 16,742 human somatic indels, 10,599 large human insertions, and 5,822 large chimpanzee insertions and systematically analyzed the patterns of DNA cleavage intensities in the 200 base pair regions surrounding these indels. Our results show that DNA cleavage intensities close to the start and end points of indels are significantly lower than other regions, for both small human germline and somatic indels and also for mouse small indels. Compared to small indels, the patterns of DNA cleavage intensity around large indels are more complex, and there are two low intensity regions near each end of the indels that are approximately 13 bp apart from each other. Detailed analyses of a subset of indels show that there is slight difference in cleavage intensity distribution between insertion indels and deletion indels that could be contributed by their respective enrichment of different repetitive elements. These results will provide new insight into indel generation mechanisms. PMID:25660536

  19. Perceiving Social Cleavages and Inequalities: The Case of Israeli Adolescents.

    Science.gov (United States)

    Dar, Yechezkel; Erhard, Rachel; Resh, Nura

    1998-01-01

    An analysis of perceptions of social cleavage and inequality among approximately 9000 Israeli eighth and ninth graders showed students accurately comprehended a multifaceted society with major social divisions. A social map with inequality was revealed in which ethnicity played the least prominent role. Personal and social traits influenced…

  20. Modeling Radial Holoblastic Cleavage: A Laboratory Activity for Developmental Biology.

    Science.gov (United States)

    Ellis, Linda K.

    2000-01-01

    Introduces a laboratory activity designed for an undergraduate developmental biology course. Uses Play-Doh (plastic modeling clay) to build a multicellular embryo in order to provide a 3-D demonstration of cleavage. Includes notes for the instructor and student directions. (YDS)

  1. Bond strength of individual carbon nanotubes grown directly on carbon fibers

    Science.gov (United States)

    Kim, Kyoung Ju; Lee, Geunsung; Kim, Sung-Dae; Kim, Seong-Il; Youk, Ji Ho; Lee, Jinyong; Kim, Young-Woon; Yu, Woong-Ryeol

    2016-10-01

    The performance of carbon nanotube (CNT)-based devices strongly depends on the adhesion of CNTs to the substrate on which they were directly grown. We report on the bond strength of CNTs grown on a carbon fiber (T700SC Toray), measured via in situ pulling of individual CNTs inside a transmission electron microscope. The bond strength of an individual CNT, obtained from the measured pulling force and CNT cross-section, was very high (˜200 MPa), 8-10 times higher than that of an adhesion model assuming only van der Waals interactions (25 MPa), presumably due to carbon-carbon interactions between the CNT (its bottom atoms) and the carbon substrate.

  2. C-H bond activation by f-block complexes.

    Science.gov (United States)

    Arnold, Polly L; McMullon, Max W; Rieb, Julia; Kühn, Fritz E

    2015-01-01

    Most homogeneous catalysis relies on the design of metal complexes to trap and convert substrates or small molecules to value-added products. Organometallic lanthanide compounds first gave a tantalizing glimpse of their potential for catalytic C-H bond transformations with the selective cleavage of one C-H bond in methane by bis(permethylcyclopentadienyl)lanthanide methyl [(η(5) -C5 Me5 )2 Ln(CH3 )] complexes some 25 years ago. Since then, numerous metal complexes from across the periodic table have been shown to selectively activate hydrocarbon C-H bonds, but the challenges of closing catalytic cycles still remain; many f-block complexes show great potential in this important area of chemistry. PMID:25384554

  3. Application of the linear/exponential hybrid force field scaling scheme to the bond length alternation modes of polyacetylene

    Science.gov (United States)

    Yang, Shujiang; Kertesz, Miklos

    2006-12-01

    The two bond length alternation related backbone carbon-carbon stretching Raman active normal modes of polyacetylene are notoriously difficulty to predict theoretically. We apply our new linear/exponential scaled quantum mechanical force field scheme to tackle this problem by exponentially adjusting the decay of the coupling force constants between backbone stretchings based on their distance which extends over many neighbors. With transferable scaling parameters optimized by least squares fitting to the experimental vibrational frequencies of short oligoenes, the scaled frequencies of trans-polyacetylene and its isotopic analogs agree very well with experiments. The linear/exponential scaling scheme is also applicable to the cis-polyacetylene case.

  4. Crack tip blunting and cleavage under dynamic conditions

    Science.gov (United States)

    Rajan, V. P.; Curtin, W. A.

    2016-05-01

    In structural materials with both brittle and ductile phases, cracks often initiate within the brittle phase and propagate dynamically towards the ductile phase. The macroscale, quasistatic toughness of the material thus depends on the outcome of this microscale, dynamic process. Indeed, dynamics has been hypothesized to suppress dislocation emission, which may explain the occurrence of brittle transgranular fracture in mild steels at low temperatures (Lin et al., 1987). Here, crack tip blunting and cleavage under dynamic conditions are explored using continuum mechanics and molecular dynamics simulations. The focus is on two questions: (1) whether dynamics can affect the energy barriers for dislocation emission and cleavage, and (2) what happens in the dynamic "overloaded" situation, in which both processes are energetically possible. In either case, dynamics may shift the balance between brittle cleavage and ductile blunting, thereby affecting the intrinsic ductility of the material. To explore these effects in simulation, a novel interatomic potential is used for which the intrinsic ductility is tunable, and a novel simulation technique is employed, termed as a "dynamic cleavage test", in which cracks can be run dynamically at a prescribed energy release rate into a material. Both theory and simulation reveal, however, that the intrinsic ductility of a material is unaffected by dynamics. The energy barrier to dislocation emission appears to be identical in quasi-static and dynamic conditions, and, in the overloaded situation, ductile crack tip behavior ultimately prevails since a single emission event can blunt and arrest the crack, preventing further cleavage. Thus, dynamics cannot embrittle a ductile material, and the origin of brittle failure in certain alloys (e.g., mild steels) appears unrelated to dynamic effects at the crack tip.

  5. SiC nanowires reinforced MAS joint of SiC coated carbon/carbon composites to LAS glass ceramics

    International Nuclear Information System (INIS)

    Graphical abstract: Schematic cross-section images of the samples with SiC nanowires and assembly sequence for the raw materials through the process of the hot-pressing method. Highlights: ► The SiC nanowires were firstly used as porous layer in the middle of the joint. ► The shear strength of the joint with SiC nanowires was largely improved. ► A new mode of fracture was proposed. - Abstract: In order to improve the shear strength of the joints of carbon/carbon (C/C) composites to lithium aluminum silicate (LAS) glass ceramics, SiC coating and magnesium aluminum silicate (MAS) glass ceramics were used as transition layer and middle layer, respectively, and high quality SiC nanowires were applied as the reinforcement materials in MAS. The SiC nanowires reinforced MAS joint of SiC coated C/C composites to LAS glass ceramics was prepared by a three-step technique of pack cementation, CVD and hot-pressing. The microstructures of the as-prepared joints were characterized by SEM and EDS, and the shear strength of the joints was also examined. The shear strength of the SiC–MAS joint increased from 24.0 ± 2.0 MPa to 35.5 ± 5.5 MPa after adding SiC nanowires in MAS. The load decreases in step-style but not perpendicularly after the maximum value, which demonstrates good toughness of the joint with SiC nanowire porous layer.

  6. Weak bond screening system

    Science.gov (United States)

    Chuang, S. Y.; Chang, F. H.; Bell, J. R.

    Consideration is given to the development of a weak bond screening system which is based on the utilization of a high power ultrasonic (HPU) technique. The instrumentation of the prototype bond strength screening system is described, and the adhesively bonded specimens used in the system developmental effort are detailed. Test results obtained from these specimens are presented in terms of bond strength and level of high power ultrasound irradiation. The following observations were made: (1) for Al/Al specimens, 2.6 sec of HPU irradiation will screen weak bond conditions due to improper preparation of bonding surfaces; (2) for composite/composite specimens, 2.0 sec of HPU irradiation will disrupt weak bonds due to under-cured conditions; (3) for Al honeycomb core with composite skin structure, 3.5 sec of HPU irradiation will disrupt weak bonds due to bad adhesive or oils contamination of bonding surfaces; and (4) for Nomex honeycomb with Al skin structure, 1.3 sec of HPU irradiation will disrupt weak bonds due to bad adhesive.

  7. School Desegregation and Racial Cleavage, 1954-1970: A Review of the Literature

    Science.gov (United States)

    Carithers, Martha W.

    1970-01-01

    Reviews the empirical studies dealing with school desegregation and racial cleavage which have appeared since the 1954 Supreme Court decision. Focuses on patterns and consequences of interracial association, and attitude change relevant to racial cleavage. (DM)

  8. The effect of structure in a long target RNA on ribozyme cleavage efficiency.

    OpenAIRE

    Campbell, T B; McDonald, C K; Hagen, M.

    1997-01-01

    Inhibition of gene expression by catalytic RNA (ribozymes) requires that ribozymes efficiently cleave specific sites within large target RNAs. However, the cleavage of long target RNAs by ribozymes is much less efficient than cleavage of short oligonucleotide substrates because of higher order structure in the long target RNA. To further study the effects of long target RNA structure on ribozyme cleavage efficiency, we determined the accessibility of seven hammerhead ribozyme cleavage sites i...

  9. Mutational analysis of a type II topoisomerase cleavage site: distinct requirements for enzyme and inhibitors.

    OpenAIRE

    Freudenreich, C H; Kreuzer, K. N.

    1993-01-01

    We have analyzed the DNA sequence requirements for cleavage of a 30 bp oligonucleotide that contains a strong bacteriophage T4 type II topoisomerase site. A novel method was used to generate substrates with each of the four nucleotides at 10 positions surrounding the cleavage site, and mutant substrates were also prepared for the four internal positions of the staggered cleavage site. The substrates were tested for cleavage in the presence of several inhibitors that induce enzyme-mediated cle...

  10. Cleavage patterns and the topology of the metazoan tree of life

    OpenAIRE

    Valentine, James W.

    1997-01-01

    Several major alliances of metazoan phyla have been identified by small subunit rRNA sequence comparisons. It is possible to arrange the phyla to produce a parsimonious distribution of cleavage types, requiring only one change from a radial ancestral condition to spiral cleavage and one other to “idiosyncratic” cleavage; this arrangement is consistent with most of the recent molecular phylogenies. The cleavage shifts are correlated with changes in many of the features that once were used to d...

  11. Dilepton spectroscopy at intermediate energies; the carbon - carbon reaction at 1 GeV/A; Spectroscopie des dileptons aux energies intermediaires; la reaction carbone - carbone A 1 GeV/A

    Energy Technology Data Exchange (ETDEWEB)

    Prunet, M.

    1995-06-01

    The Physics context of this work is heavy ion collisions at relativistic energies where di-electron provide informations on the produced hot and dense nuclear matter. The experiment is performed by the DiLepton Spectrometer (DLS) Collaboration at the Lawrence Berkeley`s Bevalac. After a description of the apparatus, we review the whole program and the main results so far obtained: first evidence of a significant di-electron signal at energies above 1 GeV/A; improvement of the understanding of di-electron production (electromagnetic decays of hadrons, {pi}{sup +}{pi}{sup -} annihilation and hadronic Bremsstrahlung). The results of p-p, p-d reactions from 1 to 4.9 GeV/A show that hadronic Bremsstrahlung (pp, pn) should be reformulated. Our analysis, optimized on the reaction Carbon-Carbon at 1 GeV/A, has been applied to {alpha}-Ca and d-Ca. We have developed two main aspects: improvement of the time resolution (500 ps) in order to eliminate all of the protons. Improvement of the space resolution (300 {mu}) for better mass resolution, in particular in the {rho} region. We obtain the cross section of di-electron production as a function of mass, transverse momentum and rapidity from the C-C, {alpha}-Ca and d-Ca reactions at 1 GeV/A. We also compare the cross section for all of the measured systems at 1 GeV/A, including Ca-Ca, and we show a (ApAt){sup {alpha}} dependence with {alpha} {approx_equal} 1.1. A study of the associated multiplicity has also been performed. Nevertheless, the limited acceptance of the DLS and its poor mass resolution to identify the {rho}, {omega} vector mesons, do not allow to conclude on hadron behaviour in nuclear matter. This point is one of the main goal of the HADES project at GSI (Darmstadt), which we give a brief description of the main features. (authors). 60 refs.

  12. Copper wire bonding

    CERN Document Server

    Chauhan, Preeti S; Zhong, ZhaoWei; Pecht, Michael G

    2014-01-01

    This critical volume provides an in-depth presentation of copper wire bonding technologies, processes and equipment, along with the economic benefits and risks.  Due to the increasing cost of materials used to make electronic components, the electronics industry has been rapidly moving from high cost gold to significantly lower cost copper as a wire bonding material.  However, copper wire bonding has several process and reliability concerns due to its material properties.  Copper Wire Bonding book lays out the challenges involved in replacing gold with copper as a wire bond material, and includes the bonding process changes—bond force, electric flame off, current and ultrasonic energy optimization, and bonding tools and equipment changes for first and second bond formation.  In addition, the bond–pad metallurgies and the use of bare and palladium-coated copper wires on aluminum are presented, and gold, nickel and palladium surface finishes are discussed.  The book also discusses best practices and re...

  13. Equilibrium CO bond lengths

    Science.gov (United States)

    Demaison, Jean; Császár, Attila G.

    2012-09-01

    Based on a sample of 38 molecules, 47 accurate equilibrium CO bond lengths have been collected and analyzed. These ultimate experimental (reEX), semiexperimental (reSE), and Born-Oppenheimer (reBO) equilibrium structures are compared to reBO estimates from two lower-level techniques of electronic structure theory, MP2(FC)/cc-pVQZ and B3LYP/6-311+G(3df,2pd). A linear relationship is found between the best equilibrium bond lengths and their MP2 or B3LYP estimates. These (and similar) linear relationships permit to estimate the CO bond length with an accuracy of 0.002 Å within the full range of 1.10-1.43 Å, corresponding to single, double, and triple CO bonds, for a large number of molecules. The variation of the CO bond length is qualitatively explained using the Atoms in Molecules method. In particular, a nice correlation is found between the CO bond length and the bond critical point density and it appears that the CO bond is at the same time covalent and ionic. Conditions which permit the computation of an accurate ab initio Born-Oppenheimer equilibrium structure are discussed. In particular, the core-core and core-valence correlation is investigated and it is shown to roughly increase with the bond length.

  14. The Bond Market's q

    OpenAIRE

    Thomas Philippon

    2006-01-01

    I propose an implementation of the q-theory of investment using bond prices instead of equity prices. Credit risk makes corporate bond prices sensitive to future asset values, and q can be inferred from bond prices. The bond market's q performs much better than the usual measure in standard investment equations. With aggregate data, the fit is three times better, cash flows are driven out and the implied adjustment costs are reduced by more than an order of magnitude. The new measure also imp...

  15. Kinetics of phycocyanobilin cleavage from C-phycocyanin by methanolysis

    DEFF Research Database (Denmark)

    Malwade, Chandrakant Ramkrishna; Roda Serrat, Maria Cinta; Christensen, Knud Villy;

    2016-01-01

    Phycocyanobilin (PCB) is an important linear tetrapyrrolic molecule for food as well as pharmaceutical industry. It is obtained from blue-green algae, where it is attached covalently to phycobiliproteins (C-PC and APC) present in the light harvesting complexes. In this work, cleavage of PCB from...... phycobiliproteins present in the extract of Arthrospira platensis by methanolysis is investigated. Different initial concentrations (25 mg/mL, 10 mg/mL, and 5 mg/mL) of proteins are used in order to investigate the effect of protein aggregation on process yield. A kinetic model is developed by fitting...... the experimental data for methanolysis. Results show that the kinetics follows a pseudo first order kinetics and remains unaffected due to the different initial concentration of phycobiliproteins. Moreover, yield of PCB in the cleavage process is found to be proportional to the initial concentration...

  16. Sequence specific inhibition of DNA restriction enzyme cleavage by PNA

    DEFF Research Database (Denmark)

    Nielsen, P.E.; Egholm, M.; Berg, R.H.;

    1993-01-01

    Plasmids containing double-stranded 10-mer PNA (peptide nucleic acid chimera) targets proximally flanked by two restriction enzyme sites were challenged with the complementary PNA or PNAs having one or two mismatches, and the effect on the restriction enzyme cleavage of the flanking sites...... was assayed. The following PNAs were used: T10-LysNH2, T5CT4-LysNH2 and T2CT2CT4-LysNH2 and the corresponding targets cloned into pUC 19 were flanked by BamH1, Sal1 or Pstl sites, respectively. In all cases it was found that complete inhibition of restriction enzyme cleavage was obtained...

  17. Fe-Catalyzed Oxidative Cleavage of Unsaturated Fatty Acids

    OpenAIRE

    Spannring, P.

    2013-01-01

    The oxidative cleavage of unsaturated fatty acids into aldehydes or carboxylic acids gives access to valuable products. The products can be used as chemical building blocks, as emulsifiers or in the paint or polymer industry. Ozonolysis is applied industrially to cleave the fatty acid oleic acid into the aldehydes nonanal and 9-oxo-nonanoic acid or into pelargonic and azelaic acid. Considerable hazards, including explosion risks, are associated with the use of ozone, and alternative processes...

  18. Embryo apoptosis identification: Oocyte grade or cleavage stage?

    OpenAIRE

    Bakri, Noraina Mohd; Ibrahim, Siti Fatimah; Osman, Nurul Atikah; Hasan, Nurhaslina; Jaffar, Farah Hanan Fathihah; Rahman, Zulaiha Abdul; Osman, Khairul

    2015-01-01

    Apoptosis is a programed cell death that is vital for tissue homeostasis. However, embryo apoptosis had been known to be related to embryo fragmentation which should be avoided in in vitro fertilization (IVF). The purpose of this study was to evaluate the relationship of embryo apoptosis with the grade of immature oocytes and cleavage stage of in vitro produced (IVP) cattle embryos. This study consisted of 345 oocytes collected through ovary slicing. Immature oocytes were graded as A, B and C...

  19. Developing a programmed restriction endonuclease for highly specific DNA cleavage

    OpenAIRE

    Eisenschmidt, Kristin; Lanio, Thomas; Simoncsits, András; Jeltsch, Albert; Pingoud, Vera; Wende, Wolfgang; Pingoud, Alfred

    2005-01-01

    Specific cleavage of large DNA molecules at few sites, necessary for the analysis of genomic DNA or for targeting individual genes in complex genomes, requires endonucleases of extremely high specificity. Restriction endonucleases (REase) that recognize DNA sequences of 4–8 bp are not sufficiently specific for this purpose. In principle, the specificity of REases can be extended by fusion to sequence recognition modules, e.g. specific DNA-binding domains or triple-helix forming oligonucleotid...

  20. The pattern of DNA cleavage intensity around indels

    OpenAIRE

    Wei Chen; Liqing Zhang

    2015-01-01

    Indels (insertions and deletions) are the second most common form of genetic variations in the eukaryotic genomes and are responsible for a multitude of genetic diseases. Despite its significance, detailed molecular mechanisms for indel generation are still unclear. Here we examined 2,656,597 small human and mouse germline indels, 16,742 human somatic indels, 10,599 large human insertions, and 5,822 large chimpanzee insertions and systematically analyzed the patterns of DNA cleavage intensiti...

  1. Effects of Cysteamine on Sheep Embryo Cleavage Rates

    Directory of Open Access Journals (Sweden)

    Sinem Ö. ENGİNLER

    2015-01-01

    Full Text Available Oxidative stress during in vitro culture leads to defects in development of gametes and embryos. Several antioxidants such as cysteamine, L-ascorbic acid, beta mercaptoethanol, cysteine, glutathione, proteins, vitamins have been used to supplement culture media to counter the oxidative stress. This study was conducted to detect the effect of adding cysteamine to the maturation medium to subsequent cleavage rates of sheep embryos. Totally 604 ovaries were obtained by ten replica and 2060 oocytes were collected. The cumulus oocyte complexes were recovered by the slicing method. A total of 1818 selected oocytes were divided into two groups and used for maturation (88.25%. The first group was created as supplemented with cysteamine (Group A and second group (Group B, control without cysteamine in TCM-199. The two groups were incubated for 24 h at 38.8 °C in an atmosphere of 5% CO2 in humidified air for in vitro maturation (IVM. After IVM, oocytes were fertilized with 50 x 107 / mL fresh ram semen in BSOF medium for 18 h. After fertilization, maturation groups were divided into two subgroups with different culture media: Group AI-SOF (Synthetic Oviduct Fluid medium, Group AII-CR1aa (Charles Rosencrans medium, Group BI-SOF and Group BII-CR1aa were achieved. Cleavage rates were evaluated at day 2. post insemination. The rates of cleavage were detected as 59.54% (184/309, 55.44% (173/312, 65.34% (215/329, 59.34% (200/337 respectively, with showing no statistically significant difference between the groups at the level of P>0.05. In conclusion, supplementing cysteamine to maturation media in TCM-199 did not affect the cleavage rates of sheep embryos in SOF and CR1aa culture media.

  2. Mutagenesis of the yellow fever virus NS2B/3 cleavage site: determinants of cleavage site specificity and effects on polyprotein processing and viral replication.

    OpenAIRE

    Chambers, T J; Nestorowicz, A.; Rice, C.M.

    1995-01-01

    The determinants of cleavage site specificity of the yellow fever virus (YF) NS3 proteinase for its 2B/3 cleavage site have been studied by using site-directed mutagenesis. Mutations at residues within the GARR decreases S sequence were tested for effects on cis cleavage of an NS2B-3(181) polyprotein during cell-free translation. At the P1 position, only the conservative substitution R-->K exhibited significant levels of cleavage. Conservative and nonconservative substitutions were tolerated ...

  3. Comparison of Gold Bonding with Mercury Bonding

    NARCIS (Netherlands)

    Kraka, Elfi; Filatov, Michael; Cremer, Dieter

    2009-01-01

    Nine AuX molecules (X = H, O, S, Se, Te, F, Cl, Br, I), their isoelectronic HgX(+) analogues, and the corresponding neutral HgX diatomics have been investigated using NESC (Normalized Elimination of the Small Component) and B3LYP theory to determine relativistic effects for bond dissociation energie

  4. Precocious (pre-anaphase) cleavage furrows in Mesostoma spermatocytes.

    Science.gov (United States)

    Forer, Arthur; Pickett-Heaps, Jeremy

    2010-08-01

    It generally is assumed that cleavage furrows start ingression at anaphase, but this is not always true. Cleavage furrows are initiated during prometaphase in spermatocytes of the flatworm Mesostoma, becoming detectable soon after the spindles achieve bipolarity. The furrows deepen during prometaphase, but ingression soon arrests. After anaphase the pre-existing furrow recommences its ingression and rapidly cleaves the cell. Such "precocious" furrowing also commonly occurs in diatoms and other algae. The position of the "precocious" cleavage furrow changes when there are changes in the distribution of chromosomes. Each of the 4 unipolarly-oriented univalent chromosomes moves to a pole at the start of prometaphase but later in prometaphase may move to the opposite pole. The furrow position adjusts during prometaphase according to the numbers of univalents at the two poles: when there are two univalent chromosomes at each pole the furrow is symmetrical at the spindle equator, but when there are unequal numbers at the poles the furrow shifts 2-3 microm toward the half-spindle with fewer univalents. Nocodazole causes spindle microtubules to disappear. After addition of nocodazole, bivalents become detached from one pole and move toward the other, which causes the furrow to shift 2-3 microm toward the pole with fewer chromosomes. Furrow positioning thus is sensitive to the positioning of chromosomes in the spindle and furrow positions change in the absence of spindle microtubules. PMID:20434231

  5. Cell-surface acceleration of urokinase-catalyzed receptor cleavage

    DEFF Research Database (Denmark)

    Høyer-Hansen, G; Ploug, M; Behrendt, N;

    1997-01-01

    The urokinase-type plasminogen activator (uPA) binds to a specific cell-surface receptor, uPAR. On several cell types uPAR is present both in the full-length form and a cleaved form, uPAR(2+3), which is devoid of binding activity. The formation of uPAR(2+3) on cultured U937 cells is either directly...... by a prior incubation of the cells with uPA inactivated by diisopropyl fluorophosphate, demonstrating a requirement for specific receptor binding of the active uPA to obtain the high-efficiency cleavage of cell-bound uPAR. Furthermore, amino-terminal sequence analysis revealed that uPAR(2+3), purified from U......937 cell lysates, had the same amino termini as uPAR(2+3), generated by uPA in a purified system. In both cases cleavage had occurred at two positions in the hinge region connecting domain 1 and 2, between Arg83-Ala84 and Arg89-Ser90, respectively. The uPA-catalyzed cleavage of uPAR is a new negative...

  6. Cleavage mechanoluminescence in elemental and III-V semiconductors

    CERN Document Server

    Chandra, B P; Gour, A S; Chandra, V K; Gupta, R K

    2003-01-01

    The present paper reports the theory of mechanoluminescence (ML) produced during cleavage of elemental and III-V semiconductors. It seems that the formation of crack-induced localized states is responsible for the ML excitation produced during the cleavage of elemental and III-V semiconductors. According to this mechanism, as the atoms are drawn away from each other in an advancing crack tip, the decreasing wave function overlap across the crack may result in localized states which is associated with increasing electron energy. If the energy of these localized states approach that of the conduction band, transition to the conduction band via tunnelling would be possible, creating minority carriers, and consequently the electron-hole recombination may give rise to mechanoluminescence. When an elemental or III-V semiconductor is cleaved, initially the ML intensity increases with time, attains a peak value I sub m at the time t sub m corresponding to completion of the cleavage of the semiconductor, and then it d...

  7. Hyperphosphorylation and cleavage at D421 enhance tau secretion.

    Directory of Open Access Journals (Sweden)

    Vanessa Plouffe

    Full Text Available It is well established that tau pathology propagates in a predictable manner in Alzheimer's disease (AD. Moreover, tau accumulates in the cerebrospinal fluid (CSF of AD's patients. The mechanisms underlying the propagation of tau pathology and its accumulation in the CSF remain to be elucidated. Recent studies have reported that human tau was secreted by neurons and non-neuronal cells when it was overexpressed indicating that tau secretion could contribute to the spreading of tau pathology in the brain and could lead to its accumulation in the CSF. In the present study, we showed that the overexpression of human tau resulted in its secretion by Hela cells. The main form of tau secreted by these cells was cleaved at the C-terminal. Surprisingly, secreted tau was dephosphorylated at several sites in comparison to intracellular tau which presented a strong immunoreactivity to all phospho-dependent antibodies tested. Our data also revealed that phosphorylation and cleavage of tau favored its secretion by Hela cells. Indeed, the mimicking of phosphorylation at 12 sites known to be phosphorylated in AD enhanced tau secretion. A mutant form of tau truncated at D421, the preferential cleavage site of caspase-3, was also significantly more secreted than wild-type tau. Taken together, our results indicate that hyperphosphorylation and cleavage of tau by favoring its secretion could contribute to the propagation of tau pathology in the brain and its accumulation in the CSF.

  8. Examination of Early Cleavage an its Importance in IVF Treatment

    Directory of Open Access Journals (Sweden)

    Fancsovits P

    2006-01-01

    Full Text Available Since the introduction of assisted reproduction, the number of multiple pregnancies has increased due to the high number of transferred embryos. There is an urgent need for IVF specialists to reduce the number of embryos transferred without the risk of decreasing pregnancy rates. Embryos are selected for transfer on the basis of their developmental stage and morphology. The number of blastomeres of the embryo indicates the speed of early embryo development which correlates to the viability of the embryo. Examination of early embryo development, especially the timing of the first cleavage, can be recommended as a tool for predicting embryo viability. Observation of timing of the first cleavage and its different stages helps us to identify fast- and slow-developing embryos. Early pronuclear breakdown and early cleavage of the zygote are indicators of fast embryo development and good embryo viability. Thereby, they can lead to high implantation and pregnancy rates. The aim of this paper is to provide an overview of the timing of early embryo development and to show its significance in IVF treatment.

  9. Cleavage mechanoluminescence in elemental and III-V semiconductors

    International Nuclear Information System (INIS)

    The present paper reports the theory of mechanoluminescence (ML) produced during cleavage of elemental and III-V semiconductors. It seems that the formation of crack-induced localized states is responsible for the ML excitation produced during the cleavage of elemental and III-V semiconductors. According to this mechanism, as the atoms are drawn away from each other in an advancing crack tip, the decreasing wave function overlap across the crack may result in localized states which is associated with increasing electron energy. If the energy of these localized states approach that of the conduction band, transition to the conduction band via tunnelling would be possible, creating minority carriers, and consequently the electron-hole recombination may give rise to mechanoluminescence. When an elemental or III-V semiconductor is cleaved, initially the ML intensity increases with time, attains a peak value Im at the time tm corresponding to completion of the cleavage of the semiconductor, and then it decreases following power law decay. Expressions are derived for the ML intensity Im corresponding to the peak of the ML intensity versus time curve and for the total ML intensity IT. It is shown that both Im and IT should increase directly with the area of the newly created surfaces of the crystals. From the measurements of the ML intensity, the velocity of crack propagation in material can be determined by using the relation v=H/tm

  10. Demethylation and cleavage of dimethylsulfoniopropionate in marine intertidal sediments

    Science.gov (United States)

    Visscher, P.T.; Kiene, R.P.; Taylor, B.F.

    1994-01-01

    Demethylation and cleavage of dimethylsulfoniopropionate (DMSP) was measured in three different types of,intertidal marine sediments: a cyanobacterial mat, a diatom-covered tidal flat and a carbonate sediment. Consumption rates of added DMSP were highest in cyanobacterial mat slurries (59 ?? mol DMSP l-1 slurry h-1) and lower in slurries from a diatom mat and a carbonate tidal sediment (24 and 9 ??mol DMSP l-1 h-1, respectively). Dimethyl sulfide (DMS) and 3-mercaptopropionate (MPA) were produced simultaneously during DMSP consumption, indicating that cleavage and demethylation occurred at the same time. Viable counts of DMSP-utilizing bacteria revealed a population of 2 x 107 cells cm-3 sediment (90% of these cleaved DMSP to DMS, 10% demethylated DMSP to MPA) in the cyanobacterial mat, 7 x 105 cells cm-3 in the diatom mat (23% cleavers, 77% demethylators), and 9 x 104 cells cm-3 (20% cleavers and 80% demethylators) in the carbonate sediment. In slurries of the diatom mat, the rate of MPA production from added 3-methiolpropionate (MMPA) was 50% of the rate of MPA formation from DMSP. The presence of a large population of demethylating bacteria and the production of MPA from DMSP suggest that the demethylation pathway, in addition to cleavage, contributes significantly to DMSP consumption in coastal sediments.

  11. Coupled valence bond theory

    NARCIS (Netherlands)

    Havenith, R.W.A.

    2005-01-01

    In this Letter, the formulation and implementation of a parallel response property code for non-orthogonal, valence bond wave-functions are described. Test calculations on benzene and cyclobutadiene show that the polarisability and magnetisability tensors obtained using valence bond theory are compa

  12. Bonded labour in Pakistan

    OpenAIRE

    Ercelawn, Aly; Nauman, Muhammad

    2001-01-01

    Examines the continuing prevalence of debt bondage in the 1990s despite the introduction of national legislation banning the practice. Makes recommendations to the Government and the international community for actions to be taken to eliminate bonded labour and provide rehabilitation for freed workers. Includes texts of Land Reforms Regulations, 1972, the Sindh Tenancy Act, 1950 and the Bonded Labour System (Abolition) Act, 1992.

  13. Hydrogen bonding in polyanilines

    Energy Technology Data Exchange (ETDEWEB)

    Bahceci, S. (Department of Chemistry, Middle East Technical University, Ankara 06531 (Turkey)); Toppare, L. (Department of Chemistry, Middle East Technical University, Ankara 06531 (Turkey)); Yurtsever, E. (Department of Chemistry, Middle East Technical University, Ankara 06531 (Turkey))

    1994-11-29

    Hydrogen bonding between poly(bisphenol A carbonate) (PC) and polyaniline (PAn) is analyzed using semi-empirical quantum methodology. Fully optimized AM1 molecular orbital calculations are reported for various aniline structures (monomer, dimer and trimer), the monomer of the PC and the hydrogen-bonded model of PAn-PC oligomer. ((orig.))

  14. The dissociative bond.

    Science.gov (United States)

    Gordon, Nirit

    2013-01-01

    Dissociation leaves a psychic void and a lingering sense of psychic absence. How do 2 people bond while they are both suffering from dissociation? The author explores the notion of a dissociative bond that occurs in the aftermath of trauma--a bond that holds at its core an understanding and shared detachment from the self. Such a bond is confined to unspoken terms that are established in the relational unconscious. The author proposes understanding the dissociative bond as a transitional space that may not lead to full integration of dissociated knowledge yet offers some healing. This is exemplified by R. Prince's (2009) clinical case study. A relational perspective is adopted, focusing on the intersubjective aspects of a dyadic relationship. In the dissociative bond, recognition of the need to experience mutual dissociation can accommodate a psychic state that yearns for relationship when the psyche cannot fully confront past wounds. Such a bond speaks to the need to reestablish a sense of human relatedness and connection when both parties in the relationship suffer from disconnection. This bond is bound to a silence that becomes both a means of protection against the horror of traumatic memory and a way to convey unspoken gestures toward the other.

  15. The samurai bond market

    OpenAIRE

    Frank Packer; Elizabeth Reynolds

    1997-01-01

    Issuance in the samurai bond market has more than tripled over the past several years. Some observers have attributed this growth to a systematic underestimation of credit risk in the market. A detailed review of credit quality, ratings differences, and initial issue pricing in the samurai bond market, however, turns up little evidence to support this concern.

  16. Wood Bond Testing

    Science.gov (United States)

    1989-01-01

    A joint development program between Hartford Steam Boiler Inspection Technologies and The Weyerhaeuser Company resulted in an internal bond analyzer (IBA), a device which combines ultrasonics with acoustic emission testing techniques. It is actually a spinoff from a spinoff, stemming from a NASA Lewis invented acousto-ultrasonic technique that became a system for testing bond strength of composite materials. Hartford's parent company, Acoustic Emission Technology Corporation (AET) refined and commercialized the technology. The IBA builds on the original system and incorporates on-line process control systems. The IBA determines bond strength by measuring changes in pulsar ultrasonic waves injected into a board. Analysis of the wave determines the average internal bond strength for the panel. Results are displayed immediately. Using the system, a mill operator can adjust resin/wood proportion, reduce setup time and waste, produce internal bonds of a consistent quality and automatically mark deficient products.

  17. Water's Hydrogen Bond Strength

    CERN Document Server

    Chaplin, Martin

    2007-01-01

    Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for life-giving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy. These hydrogen bonds are roughly tetrahedrally arranged such that when strongly formed the local clustering expands, decreasing the density. Such low density structuring naturally occurs at low and supercooled temperatures and gives rise to many physical and chemical properties that evidence the particular uniqueness of liquid water. If aqueous hydrogen bonds were actually somewhat stronger then water would behave similar to a glass, whereas if they were weaker then water would be a gas and only exist as a liquid at sub-zero temperature...

  18. Altered cleavage patterns in human tripronuclear embryos and their association to fertilization method

    DEFF Research Database (Denmark)

    Joergensen, Mette Warming; Agerholm, Inge; Hindkjaer, Johnny;

    2014-01-01

    PURPOSE: To analyze the cleavage patterns in dipronuclear (2PN) and tripronuclear (3PN) embryos in relation to fertilization method. METHOD: Time-lapse analysis. RESULTS: Compared to 2PN, more 3PN IVF embryos displayed early cleavage into 3 cells (p ... stage (p time frame. However, timing of the cell divisions within the cleavage cycles differed between the two groups. In contrast.......001). More 3PN IVF than ICSI embryos displayed early cleavage into 3 cells (p time demonstrates differences in the cleavage pattern between 3PN IVF and ICSI embryos....

  19. The influences of hinge length and composition on the susceptibility of human IgA to cleavage by diverse bacterial IgA1 proteases.

    Science.gov (United States)

    Senior, Bernard W; Woof, Jenny M

    2005-06-15

    The influences of IgA hinge length and composition on its susceptibility to cleavage by bacterial IgA1 proteases were examined using a panel of IgA hinge mutants. The IgA1 proteases of Streptococcus pneumoniae, Streptococcus sanguis strains SK4 and SK49, Neisseria meningitidis, Neisseria gonorrhoeae, and Haemophilus influenzae cleaved IgA2-IgA1 half hinge, an Ab featuring half of the IgA1 hinge incorporated into the equivalent site in IgA1 protease-resistant IgA2, whereas those of Streptococcus mitis, Streptococcus oralis, and S. sanguis strain SK1 did not. Hinge length reduction by removal of two of the four C-terminal proline residues rendered IgA2-IgA1 half hinge resistant to all streptococcal IgA1 metalloproteinases but it remained sensitive to cleavage by the serine-type IgA1 proteases of Neisseria and Haemophilus spp. The four C-terminal proline residues could be substituted by alanine residues or transferred to the N-terminal extremity of the hinge without affect on the susceptibility of the Ab to cleavage by serine-type IgA1 proteases. However, their removal rendered the Ab resistant to cleavage by all the IgA1 proteases. We conclude that the serine-type IgA1 proteases of Neisseria and Haemophilus require the Fab and Fc regions to be separated by at least ten (or in the case of N. gonorrhoeae type I protease, nine) amino acids between Val(222) and Cys(241) (IgA1 numbering) for efficient access and cleavage. By contrast, the streptococcal IgA1 metalloproteinases require 12 or more appropriate amino acids between the Fab and Fc to maintain a minimum critical distance between the scissile bond and the start of the Fc. PMID:15944283

  20. Transversely Compressed Bonded Joints

    DEFF Research Database (Denmark)

    Hansen, Christian Skodborg; Schmidt, Jacob Wittrup; Stang, Henrik

    2012-01-01

    The load capacity of bonded joints can be increased if transverse pressure is applied at the interface. The transverse pressure is assumed to introduce a Coulomb-friction contribution to the cohesive law for the interface. Response and load capacity for a bonded single-lap joint was derived using...... non-linear fracture mechanics. The results indicated a good correlation between theory and tests. Furthermore, the model is suggested as theoretical base for determining load capacity of bonded anchorages with transverse pressure, in externally reinforced concrete structures....

  1. Peptide backbone cleavage by α-amidation is enhanced at methionine residues.

    Science.gov (United States)

    Hellwig, Michael; Löbmann, Katja; Orywol, Tom

    2015-01-01

    Cleavage reactions at backbone loci are one of the consequences of oxidation of proteins and peptides. During α-amidation, the Cα -N bond in the backbone is cleaved under formation of an N-terminal peptide amide and a C-terminal keto acyl peptide. On the basis of earlier works, a facilitation of α-amidation by the thioether group of adjacent methionine side chains was proposed. This reaction was characterized by using benzoyl methionine and benzoyl alanyl methionine as peptide models. The decomposition of benzoylated amino acids (benzoyl-methionine, benzoyl-alanine, and benzoyl-methionine sulfoxide) to benzamide in the presence of different carbohydrate compounds (reducing sugars, Amadori products, and reductones) was studied during incubation for up to 48 h at 80 °C in acetate-buffered solution (pH 6.0). Small amounts of benzamide (0.3-1.5 mol%) were formed in the presence of all sugars and from all benzoylated species. However, benzamide formation was strongly enhanced, when benzoyl methionine was incubated in the presence of reductones and Amadori compounds (3.5-4.2 mol%). The reaction was found to be intramolecular, because α-amidation of a similar 4-methylbenzoylated amino acid was not enhanced in the presence of benzoyl-methionine and carbohydrate compounds. In the peptide benzoyl-alanyl-methionine, α-amidation at the methionine residue is preferred over α-amidation at the benzoyl peptide bond. We propose here a mechanism for the enhancement of α-amidation at methionine residues.

  2. Synthesis and enzymatic cleavage of dual-ligand quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Sewell, Sarah L. [Department of Biomedical Engineering, Vanderbilt University, Nashville, TN (United States); Giorgio, Todd D., E-mail: todd.d.giorgio@vanderbilt.edu [Department of Biomedical Engineering, Vanderbilt University, Nashville, TN (United States); Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN (United States)

    2009-05-05

    Site directed therapy promises to minimize treatment-limiting systemic effects associated with cytotoxic agents that have no specificity for pathologic tissues. One general strategy is to target cell surface receptors uniquely presented on particular tissues. Highly specific in vivo targeting of an emerging neoplasm through a single molecular recognition mechanism has not generally been successful. Nonspecific binding and specific binding to non-target cells compromise the therapeutic index of small molecule, ubiquitous cancer targeting ligands. In this work, we have designed and fabricated a nanoparticle (NP) construct that could potentially overcome the current limitations of targeted in vivo delivery. Quantum dots (QDs) were functionalized with a poly(ethylene glycol) (PEG) modified to enable specific cleavage by matrix metalloprotease-7 (MMP-7). The QDs were further functionalized with folic acid, a ligand for a cell surface receptor that is overexpressed in many tumors, but also expressed in some normal tissues. The nanomolecular construct is designed so that the PEG initially conceals the folate ligand and construct binding to cells is inhibited. MMP-7 activated peptide cleavage and subsequent unmasking of the folate ligand occurs only near tumor tissue, resulting in a proximity activated (PA) targeting system. QDs functionalized with both the MMP-7 cleavable substrate and folic acid were successfully synthesized and characterized. The proteolytic capability of the dual ligand QD construct was quantitatively assessed by fluorometric analysis and compared to a QD construct functionalized with only the PA ligand. The dual ligand PA nanoparticles studied here exhibit significant susceptibility to cleavage by MMP-7 at physiologically relevant conditions. The capacity to autonomously convert a biopassivated nanostructure to a tissue-specific targeted delivery agent in vivo represents a paradigm change for site-directed therapies.

  3. Embryo apoptosis identification: Oocyte grade or cleavage stage?

    Science.gov (United States)

    Bakri, Noraina Mohd; Ibrahim, Siti Fatimah; Osman, Nurul Atikah; Hasan, Nurhaslina; Jaffar, Farah Hanan Fathihah; Rahman, Zulaiha Abdul; Osman, Khairul

    2016-01-01

    Apoptosis is a programed cell death that is vital for tissue homeostasis. However, embryo apoptosis had been known to be related to embryo fragmentation which should be avoided in in vitro fertilization (IVF). The purpose of this study was to evaluate the relationship of embryo apoptosis with the grade of immature oocytes and cleavage stage of in vitro produced (IVP) cattle embryos. This study consisted of 345 oocytes collected through ovary slicing. Immature oocytes were graded as A, B and C. This grading was based on cumulus cell thickness and compactness. All oocytes then underwent an in vitro maturation (IVM) procedure. An IVF was done 24 h after IVM culture. Prior to staining, stage of cleaved embryos was determined and classified as either 2, 4, 8 or >8-cell embryo stage. Apoptosis status of cleaved IVP embryos was determined by using annexin V-FITC staining technique at 48 and 72 h post insemination (hpi). Apoptosis status for each embryo was classified as either early or late. The result showed that there was no significant difference (p > 0.05) of apoptosis status among grade A, B and C embryos. All grades of oocytes showed embryo apoptosis where 1.5% late apoptosis for grade A, 4.5% and 10.4% of early and late apoptosis for grade B and grade C. Early apoptosis was not seen in grade A embryo. We also noted no significant difference (p > 0.05) of apoptosis status between 2, 4, 8 and >8-cell embryo stage. Early apoptosis was also not seen in >8-cell stage. Even though there were no differences in apoptosis expression between the three classes, the cleavage rate of grade A oocytes was significantly higher (p quality and the cleavage stage of the embryo produced. PMID:26858565

  4. Carotenoid-cleavage activities of crude enzymes from Pandanous amryllifolius.

    Science.gov (United States)

    Ningrum, Andriati; Schreiner, Matthias

    2014-11-01

    Carotenoid degradation products, known as norisoprenoids, are aroma-impact compounds in several plants. Pandan wangi is a common name of the shrub Pandanus amaryllifolius. The genus name 'Pandanus' is derived from the Indonesian name of the tree, pandan. In Indonesia, the leaves from the plant are used for several purposes, e.g., as natural colorants and flavor, and as traditional treatments. The aim of this study was to determine the cleavage of β-carotene and β-apo-8'-carotenal by carotenoid-cleavage enzymes isolated from pandan leaves, to investigate dependencies of the enzymatic activities on temperature and pH, to determine the enzymatic reaction products by using Headspace Solid Phase Microextraction Gas Chromatography/Mass Spectrophotometry (HS-SPME GC/MS), and to investigate the influence of heat treatment and addition of crude enzyme on formation of norisoprenoids. Crude enzymes from pandan leaves showed higher activity against β-carotene than β-apo-8'-carotenal. The optimum temperature of crude enzymes was 70°, while the optimum pH value was 6. We identified β-ionone as the major volatile reaction product from the incubations of two different carotenoid substrates, β-carotene and β-apo-8'-carotenal. Several treatments, e.g., heat treatment and addition of crude enzymes in pandan leaves contributed to the norisoprenoid content. Our findings revealed that the crude enzymes from pandan leaves with carotenoid-cleavage activity might provide a potential application, especially for biocatalysis, in natural-flavor industry.

  5. Synthesis and enzymatic cleavage of dual-ligand quantum dots

    International Nuclear Information System (INIS)

    Site directed therapy promises to minimize treatment-limiting systemic effects associated with cytotoxic agents that have no specificity for pathologic tissues. One general strategy is to target cell surface receptors uniquely presented on particular tissues. Highly specific in vivo targeting of an emerging neoplasm through a single molecular recognition mechanism has not generally been successful. Nonspecific binding and specific binding to non-target cells compromise the therapeutic index of small molecule, ubiquitous cancer targeting ligands. In this work, we have designed and fabricated a nanoparticle (NP) construct that could potentially overcome the current limitations of targeted in vivo delivery. Quantum dots (QDs) were functionalized with a poly(ethylene glycol) (PEG) modified to enable specific cleavage by matrix metalloprotease-7 (MMP-7). The QDs were further functionalized with folic acid, a ligand for a cell surface receptor that is overexpressed in many tumors, but also expressed in some normal tissues. The nanomolecular construct is designed so that the PEG initially conceals the folate ligand and construct binding to cells is inhibited. MMP-7 activated peptide cleavage and subsequent unmasking of the folate ligand occurs only near tumor tissue, resulting in a proximity activated (PA) targeting system. QDs functionalized with both the MMP-7 cleavable substrate and folic acid were successfully synthesized and characterized. The proteolytic capability of the dual ligand QD construct was quantitatively assessed by fluorometric analysis and compared to a QD construct functionalized with only the PA ligand. The dual ligand PA nanoparticles studied here exhibit significant susceptibility to cleavage by MMP-7 at physiologically relevant conditions. The capacity to autonomously convert a biopassivated nanostructure to a tissue-specific targeted delivery agent in vivo represents a paradigm change for site-directed therapies.

  6. The Structural Basis of [beta]-Peptide-Specific Cleavage by the Serine Protease Cyanophycinase

    Energy Technology Data Exchange (ETDEWEB)

    Law, Adrienne M.; Lai, Sandy W.S.; Tavares, John; Kimber, Matthew S.; (Guelph)

    2010-10-01

    Cyanophycin, or poly-L-Asp-multi-L-Arg, is a non-ribosomally synthesized peptidic polymer that is used for nitrogen storage by cyanobacteria and other select eubacteria. Upon synthesis, it self-associates to form insoluble granules, the degradation of which is uniquely catalyzed by a carboxy-terminal-specific protease, cyanophycinase. We have determined the structure of cyanophycinase from the freshwater cyanobacterium Synechocystis sp. PCC6803 at 1.5-{angstrom} resolution, showing that the structure is dimeric, with individual protomers resembling aspartyl dipeptidase. Kinetic characterization of the enzyme demonstrates that the enzyme displays Michaelis-Menten kinetics with a k{sub cat} of 16.5 s{sup -1} and a k{sub cat}/K{sub M} of 7.5 x 10{sup -6} M{sup -1} s{sup -1}. Site-directed mutagenesis experiments confirm that cyanophycinase is a serine protease and that Gln101, Asp172, Gln173, Arg178, Arg180 and Arg183, which form a conserved pocket adjacent to the catalytic Ser132, are functionally critical residues. Modeling indicates that cyanophycinase binds the {beta}-Asp-Arg dipeptide residue immediately N-terminal to the scissile bond in an extended conformation in this pocket, primarily recognizing this penultimate {beta}-Asp-Arg residue of the polymeric chain. Because binding and catalysis depend on substrate features unique to {beta}-linked aspartyl peptides, cyanophycinase is able to act within the cytosol without non-specific cleavage events disrupting essential cellular processes.

  7. Micelle-Vesicle Transition by Cleavage of Disulfide Spacer Chain for Gemini Surfactant in Didodecyldimethylammonium Chloride Aqueous Solutions.

    Science.gov (United States)

    Mizuhashi, Toshinari; Asakawa, Tsuyoshi; Ohta, Akio

    2015-01-01

    We examined the "micelle-vesicle transition" through the mixing effect of single-tailed thiol surfactants produced by the cleavage of gemini surfactants, [C12H25N(CH3)2CH2CH2SSCH2CH2N(CH3)2C12H25] 2Cl (C12SSC12), which have a disulfide bond in the spacer chain. Phase diagrams of C12H25N(CH3)2CH2CH2SHCl-didodecyldimethylammonium chloride (C12SH-DDAC) and C12SSC12-DDAC were determined by conductivity and pyrene fluorescence probe methods. The aggregate diameters were evaluated by dynamic light scattering (DLS). The critical vesicle concentration (CVC) was confirmed by the abrupt increase in the intensity of light scattering with excitation at 335 nm. Vesicle formation was confined to the DDAC-rich region of the C12SSC12-DDAC system, while the vesicle formation region for the C12SH-DDAC system spread out with the addition of dithiothreitol (DTT) to C12SSC12-DDAC. This implies that single-tailed surfactants can induce a more favorable environment for molecular packing of the vesicular surface. The micelle-vesicle transition occurs with disulfide spacer chain cleavage of gemini surfactants at a particular specific concentration range. PMID:26250426

  8. Handbook of wafer bonding

    CERN Document Server

    Ramm, Peter; Taklo, Maaike M V

    2011-01-01

    Written by an author and editor team from microsystems companies and industry-near research organizations, this handbook and reference presents dependable, first-hand information on bonding technologies.In the first part, researchers from companies and institutions around the world discuss the most reliable and reproducible technologies for the production of bonded wafers. The second part is devoted to current and emerging applications, including microresonators, biosensors and precise measuring devices.

  9. Programmable RNA recognition and cleavage by CRISPR/Cas9

    OpenAIRE

    O’Connell, Mitchell R.; Oakes, Benjamin L.; Sternberg, Samuel H.; East-Seletsky, Alexandra; Kaplan, Matias; Doudna, Jennifer A.

    2014-01-01

    The CRISPR-associated protein Cas9 is an RNA-guided DNA endonuclease that uses RNA:DNA complementarity to identify target sites for sequence-specific doublestranded DNA (dsDNA) cleavage 1-5 . In its native context, Cas9 acts on DNA substrates exclusively because both binding and catalysis require recognition of a short DNA sequence, the protospacer adjacent motif (PAM), next to and on the strand opposite the 20-nucleotide target site in dsDNA 4-7 . Cas9 has proven to be a versatile tool for g...

  10. Features of Controlled Laser Thermal Cleavage of Crystalline Silicon

    International Nuclear Information System (INIS)

    Controlled laser thermal cleavage of crystalline silicon has been numerically simulated. A 3D analysis of the thermoelastic fields formed in a single-crystal silicon wafer as a result of successive laser heating and exposure to a coolant was performed for three different versions of anisotropy. The simulation was performed for laser irradiation with different wavelengths: 1.06 and 0.808 μm. The calculation results have been experimentally verified using a YAG laser. The results can be used in the electronics industry to optimize the precise separation of silicon wafers into crystals.

  11. Thimet oligopeptidase specificity: evidence of preferential cleavage near the C-terminus and product inhibition from kinetic analysis of peptide hydrolysis.

    Science.gov (United States)

    Knight, C G; Dando, P M; Barrett, A J

    1995-01-01

    The substrate-size specificity of human thimet oligopeptidase (EC 3.4.24.15) was investigated with oligomers of glycyl-prolyl-leucine (GPL)n where n = 2, 3, 4 and 5. These peptides were cleaved only at Leu-Gly bonds to give GPL as the single final product. Hydrolysis was most rapid with (GPL)3 and slowest with (GPL)5. The more water-soluble oligomers of Gly-Hyp-Leu showed the same trend. (Gly-Hyp-Leu)6 was not hydrolysed, consistent with the previous finding that substrates larger than 17 amino acids are not cleaved by thimet oligopeptidase. The cleavage of (GPL)3 to GPL fitted a sequential first-order model. First-order kinetics were unexpected as the initial substrate concentration was greater than Km. The anomaly was also seen during the cleavage of bradykinin and neurotensin, and in these cases first-order behaviour was due to potent competitive inhibition by the C-terminal product. The sequential mechanism for (GPL)3 breakdown by thimet oligopeptidase does not discriminate between initial cleavages towards the N- or C-terminus. As isoleucine is an unfavourable residue in P1, substrates were made in which selected leucine residues were replaced by isoleucine. GPL--GPI--GPL (where--represents the bond between the tripeptide units) was resistant to hydrolysis and GPI--GPL--GPL was cleaved only at the -Leu-Gly- bond. Experiments with isoleucine-containing analogues of (Gly-Hyp-Leu)4 showed that thimet oligopeptidase preferred to cleave these peptides near the C-terminus. PMID:7755557

  12. Molecular Basis of Catalytic Chamber-assisted Unfolding and Cleavage of Human Insulin by Human Insulin-degrading Enzyme*S⃞

    Science.gov (United States)

    Manolopoulou, Marika; Guo, Qing; Malito, Enrico; Schilling, Alexander B.; Tang, Wei-Jen

    2009-01-01

    Insulin is a hormone vital for glucose homeostasis, and insulin-degrading enzyme (IDE) plays a key role in its clearance. IDE exhibits a remarkable specificity to degrade insulin without breaking the disulfide bonds that hold the insulin A and B chains together. Using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry to obtain high mass accuracy, and electron capture dissociation (ECD) to selectively break the disulfide bonds in gas phase fragmentation, we determined the cleavage sites and composition of human insulin fragments generated by human IDE. Our time-dependent analysis of IDE-digested insulin fragments reveals that IDE is highly processive in its initial cleavage at the middle of both the insulin A and B chains. This ensures that IDE effectively splits insulin into inactive N- and C-terminal halves without breaking the disulfide bonds. To understand the molecular basis of the recognition and unfolding of insulin by IDE, we determined a 2.6-Å resolution insulin-bound IDE structure. Our structure reveals that IDE forms an enclosed catalytic chamber that completely engulfs and intimately interacts with a partially unfolded insulin molecule. This structure also highlights how the unique size, shape, charge distribution, and exosite of the IDE catalytic chamber contribute to its high affinity (∼100 nm) for insulin. In addition, this structure shows how IDE utilizes the interaction of its exosite with the N terminus of the insulin A chain as well as other properties of the catalytic chamber to guide the unfolding of insulin and allowing for the processive cleavages. PMID:19321446

  13. Drosha regulates gene expression independently of RNA cleavage function

    DEFF Research Database (Denmark)

    Gromak, Natalia; Dienstbier, Martin; Macias, Sara;

    2013-01-01

    Drosha is the main RNase III-like enzyme involved in the process of microRNA (miRNA) biogenesis in the nucleus. Using whole-genome ChIP-on-chip analysis, we demonstrate that, in addition to miRNA sequences, Drosha specifically binds promoter-proximal regions of many human genes in a transcription......-terminal protein-interaction domain, which associates with the RNA-binding protein CBP80 and RNA Polymerase II. Consequently, we uncover a previously unsuspected RNA cleavage-independent function of Drosha in the regulation of human gene expression.......Drosha is the main RNase III-like enzyme involved in the process of microRNA (miRNA) biogenesis in the nucleus. Using whole-genome ChIP-on-chip analysis, we demonstrate that, in addition to miRNA sequences, Drosha specifically binds promoter-proximal regions of many human genes in a transcription......-dependent manner. This binding is not associated with miRNA production or RNA cleavage. Drosha knockdown in HeLa cells downregulated nascent gene transcription, resulting in a reduction of polyadenylated mRNA produced from these gene regions. Furthermore, we show that this function of Drosha is dependent on its N...

  14. K3[Fe(CN)6].3H2O supported on silica gel: An efficient and selective reagent for the cleavage of oximes to their corresponding carbonyl compounds in aqueous medium

    Indian Academy of Sciences (India)

    Abbas Amini Manesh; Behzad Shirmardi Shaghasemi

    2015-03-01

    K3[Fe(CN)6].3H2O supported on silica gel, a new oxidant, for efficient, simple and selective cleavage of ketoximes and aldoximes to their corresponding carbonyl compounds in aqueous medium is described. Further oxidation of aldehydes to carboxylic acid and formation of by-products were not observed. − unsaturated oxime was deoximated smoothly without oxidation of the double bond.

  15. Synthesis of Novel High Energy Polyaniline Derivative Containing S-S Bond in Six-membered Cycle

    Institute of Scientific and Technical Information of China (English)

    ZHOU Lei; DENG Shi-Ren; LI Zao-Ying

    2003-01-01

    @@ A novel conducting polymer as new class of high energy storage material, [1,2] which has one six-membered cycle containing S-S bond in the moiety of aniline was synthesized. The polymer had enhanced redox progress due to an intramolecular electrocatalytic effect of polyaniline on S-S bond. The polymer has some advantages because of its high theoretical specific energy and fast kinetics when used in lithium batteries. The most promised advantage of it is that the intramolecular cleavage and recombination of the S-S bond improve the cyclicability greatly.

  16. Cleavage of silicon by laser-based shock waves: Interpretation by nanoscopic length scales

    International Nuclear Information System (INIS)

    Cleavage along the weakest Si{1 1 1} cleavage plane is measured by impulsive fracture using surface acoustic waves (SAWs) with steep shock fronts, generated by pulsed laser irradiation and recorded with a laser probe–beam-deflection setup. The theoretical cleavage strength, obtained by ab initio calculations for perfect single-crystal silicon lattices is compared with the strength resulting from an improved Polanyi–Orowan cleavage model. The critical strength of a real silicon crystal, measured by using calibrated elastic surface pulses with shocks, was employed to extract the corresponding critical length scale characterizing the cleavage process on the basis of the modified cleavage model. The extracted length scale of 7 nm can be connected with the size of the microstructural defect initiating failure. Usually stress generating surface defects are responsible for the nucleation of brittle fracture, especially in nanoscale systems with large surface areas.

  17. Microscopic investigation of cleavage initiation in modified A508B pressure vessel steel

    International Nuclear Information System (INIS)

    A microscopic study on ductile-brittle crack growth in a modified version of the A508B pressure vessel steel has been performed. Small SEN(B)-specimens tested at different temperatures in and above the transition region have been thoroughly examined with a scanning electron microscope. Focus was directed towards: amount of ductile crack growth prior to cleavage, distance from the crack front to cleavage initiation sites, and type of defect that caused the cleavage initiation. The results show, among other things, that cleavage facets are present in specimens tested at all temperatures, even on the upper shelf where no global failure by cleavage was observed. These preliminary results give an indication that the ability of the matrix material to arrest and sustain small cleavage cracks can be crucial in explaining why ferritic steels show a transition behaviour. (orig.)

  18. Intracellular ribozyme-catalyzed trans-cleavage of RNA monitored by fluorescence resonance energy transfer.

    OpenAIRE

    Vitiello, D; Pecchia, D B; Burke, J M

    2000-01-01

    Small catalytic RNAs like the hairpin ribozyme are proving to be useful intracellular tools; however, most attempts to demonstrate trans-cleavage of RNA by ribozymes in cells have been frustrated by rapid cellular degradation of the cleavage products. Here, we describe a fluorescence resonance energy transfer (FRET) assay that directly monitors cleavage of target RNA in tissue-culture cells. An oligoribonucleotide substrate was modified to inhibit cellular ribonuclease degradation without int...

  19. A pathway sensor for genome-wide screens of intracellular proteolytic cleavage

    OpenAIRE

    Ketteler, Robin; Sun, Zairen; Kovacs, Karl F; He, Wei-Wu; Seed, Brian

    2008-01-01

    Protein cleavage is a central event in many regulated biological processes. We describe a system for detecting intracellular proteolysis based on non-conventional secretion of Gaussia luciferase (GLUC). GLUC exits the cell without benefit of a secretory leader peptide, but can be anchored in the cell by fusion to \\(\\beta\\)-actin. By including protease cleavage sites between GLUC and \\(\\beta\\)-actin, proteolytic cleavage can be detected. Using this assay, we have identified regulators of autop...

  20. A real-time assay for monitoring nucleic acid cleavage by quadruplex formation

    OpenAIRE

    Kankia, Besik I.

    2006-01-01

    Direct and straightforward methods to follow nucleic acid cleavage are needed. A spectrophotometric quadruplex formation assay (QFA) was developed, which allows real-time monitoring of site-specific cleavage of nucleic acids. QFA was applied to study both protein and nucleic acid restriction enzymes, and was demonstrated to accurately determine Michaelis–Menten parameters for the cleavage reaction catalyzed by EcoRI. QFA can be used to study the mechanisms of protein–nucleic acid recognition....

  1. Romanian government bond market

    Directory of Open Access Journals (Sweden)

    Cornelia POP

    2012-12-01

    Full Text Available The present paper aims to present the level of development reached by Romanian government bond market segment, as part of the country financial market. The analysis will be descriptive (the data series available for Romania are short, based on the secondary data offered by the official bodies involved in the process of issuing and trading the Romanian government bonds (Romanian Ministry of Public Finance, Romanian National Bank and Bucharest Stock Exchange, and also on secondary data provided by the Federation of European Stock Exchanges.To enhance the market credibility as a benchmark, a various combination of measures is necessary; among these measures are mentioned: the extension of the yield curve; the issuance calendars in order to improve transparency; increasing the disclosure of information on public debt issuance and statistics; holding regular meetings with dealers, institutional investors and rating agencies; introducing a system of primary dealers; establishing a repurchase (repo market in the government bond market. These measures will be discussed based on the evolution presented inside the paper.The paper conclude with the fact that, until now, the Romanian government bond market did not provide a benchmark for the domestic financial market and that further efforts are needed in order to increase the government bond market transparency and liquidity.

  2. Formation of H3+ due to Intramolecular Bond Rearrangement in Doubly Charged Methanol

    Science.gov (United States)

    de, Sankar; Rajput, Jyoti; Roy, A.; Ghosh, P. N.; Safvan, C. P.

    2006-11-01

    We report the formation of H3+ by proton coagulation in methanol under the impact of low energy Ar8+ projectiles. Our time-of-flight coincidence measurements with CH3OD establish that the H3+ formation arises from intramolecular bond rearrangement of the methyl group. We have performed ab initio quantum chemical calculations that show the preferred pathway for C-H3 bond cleavage. Fragmentation of organic molecules like methanol under impact of highly charged ions is suggested as an alternative mechanism of H3+ formation in outer space.

  3. Cleavage of RseA by RseP requires a carboxyl-terminal hydrophobic amino acid following DegS cleavage

    OpenAIRE

    Li, Xiaochun; Wang, Boyuan; Feng, Lihui; Kang, Hui; Qi, Yang; Wang, Jiawei; Shi, Yigong

    2009-01-01

    Regulated intramembrane proteolysis (RIP) by the Site-2 protease (S2P) results in the release of a transmembrane signaling protein. Curiously, however, S2P cleavage must be preceded by the action of the Site-1 protease (S1P). To decipher the underlying mechanism, we reconstituted sequential, in vitro cleavages of the Escherichia coli transmembrane protein RseA by DegS (S1P) and RseP (S2P). After DegS cleavage, the newly exposed carboxyl-terminal residue Val-148 of RseA plays an essential role...

  4. Specific pre-cleavage and post-cleavage complexes involved in the formation of SV40 late mRNA 3' termini in vitro.

    OpenAIRE

    Zarkower, D; Wickens, M

    1987-01-01

    Complexes form between processing factors present in a crude nuclear extract from HeLa cells and a simian virus 40 (SV40) late pre-mRNA which spans the polyadenylation [poly(A)] site. A specific 'pre-cleavage complex' forms on the pre-mRNA before cleavage. Formation of this complex requires the highly conserved sequence AAUAAA: it is prevented by mutations in AAUAAA, and by annealing DNA oligonucleotides to that sequence. After cleavage, the 5' half-molecule is found in a distinct 'post-cleav...

  5. RNase II is important for A-site mRNA cleavage during ribosome pausing

    OpenAIRE

    Garza-Sánchez, Fernando; Shoji, Shinichiro; Fredrick, Kurt; Hayes, Christopher S.

    2009-01-01

    In Escherichia coli, translational arrest can elicit cleavage of codons within the ribosomal A site. This A-site mRNA cleavage is independent of RelE, and has been proposed to be an endonucleolytic activity of the ribosome. Here, we show that the 3′→5′ exonuclease RNase II plays an important role in RelE-independent A-site cleavage. Instead of A-site cleavage, translational pausing in ΔRNase II cells produces transcripts that are truncated +12 and +28 nucleotides downstream of the A-site codo...

  6. Coronavirus 3CL(pro) proteinase cleavage sites: Possible relevance to SARS virus pathology

    DEFF Research Database (Denmark)

    Kiemer, Lars; Lund, Ole; Brunak, Søren;

    2004-01-01

    . Prompted by this, we set out to analyse and predict cleavage by the coronavirus main proteinase using computational methods. Results: We retrieved sequence data on seven fully sequenced coronaviruses and identified the main 3CL proteinase cleavage sites in polyproteins using alignments. A neural network...... was trained to recognise the cleavage sites in the genomes obtaining a sensitivity of 87.0% and a specificity of 99.0%. Several proteins known to be cleaved by other viruses were submitted to prediction as well as proteins suspected relevant in coronavirus pathology. Cleavage sites were predicted in proteins...

  7. Hairpin DNA Sequences Bound Strongly by Bleomycin Exhibit Enhanced Double-Strand Cleavage

    OpenAIRE

    Roy, Basab; Hecht, Sidney M.

    2014-01-01

    Clinically used bleomycin A5 has been employed in a study of double-strand cleavage of a library of 10 hairpin DNAs originally selected on the basis of their strong binding to bleomycin. Each of the DNAs underwent double-strand cleavage at more than one site, and all of the cleavage sites were within, or in close proximity to, an eight-base-pair region of the duplex that had been randomized to create the original library. A total of 31 double-strand cleavage sites were identified on the 10 DN...

  8. A single molecule assay for measuring site-specific DNA cleavage.

    Science.gov (United States)

    Gambino, Stefano; Mousley, Briana; Cathcart, Lindsay; Winship, Janelle; Loparo, Joseph J; Price, Allen C

    2016-02-15

    Sequence-specific DNA cleavage is a key step in a number of genomic transactions. Here, we report a single-molecule technique that allows the simultaneous measurement of hundreds of DNAs, thereby collecting significant statistics in a single experiment. Microbeads are tethered with single DNA molecules in a microfluidic channel. After the DNA cleavage reaction is initiated, the time of cleavage of each DNA is recorded using video microscopy. We demonstrate the utility of our method by measuring the cleavage kinetics of NdeI, a type II restriction endonuclease.

  9. Insulation bonding test system

    Science.gov (United States)

    Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (Inventor)

    1984-01-01

    A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

  10. The Illiquidity of Corporate Bonds

    OpenAIRE

    Bao, Jack; Pan, Jun; Wang, Jiang

    2011-01-01

    This paper examines the illiquidity of corporate bonds and its asset-pricing implications. Using transactions data from 2003 to 2009, we show that the illiquidity in corporate bonds is substantial, significantly greater than what can be explained by bid–ask spreads. We establish a strong link between bond illiquidity and bond prices. In aggregate, changes in market-level illiquidity explain a substantial part of the time variation in yield spreads of high-rated (AAA through A) bonds, overshad...

  11. Embryo apoptosis identification: Oocyte grade or cleavage stage?

    Science.gov (United States)

    Bakri, Noraina Mohd; Ibrahim, Siti Fatimah; Osman, Nurul Atikah; Hasan, Nurhaslina; Jaffar, Farah Hanan Fathihah; Rahman, Zulaiha Abdul; Osman, Khairul

    2015-01-01

    Apoptosis is a programed cell death that is vital for tissue homeostasis. However, embryo apoptosis had been known to be related to embryo fragmentation which should be avoided in in vitro fertilization (IVF). The purpose of this study was to evaluate the relationship of embryo apoptosis with the grade of immature oocytes and cleavage stage of in vitro produced (IVP) cattle embryos. This study consisted of 345 oocytes collected through ovary slicing. Immature oocytes were graded as A, B and C. This grading was based on cumulus cell thickness and compactness. All oocytes then underwent an in vitro maturation (IVM) procedure. An IVF was done 24 h after IVM culture. Prior to staining, stage of cleaved embryos was determined and classified as either 2, 4, 8 or >8-cell embryo stage. Apoptosis status of cleaved IVP embryos was determined by using annexin V-FITC staining technique at 48 and 72 h post insemination (hpi). Apoptosis status for each embryo was classified as either early or late. The result showed that there was no significant difference (p > 0.05) of apoptosis status among grade A, B and C embryos. All grades of oocytes showed embryo apoptosis where 1.5% late apoptosis for grade A, 4.5% and 10.4% of early and late apoptosis for grade B and grade C. Early apoptosis was not seen in grade A embryo. We also noted no significant difference (p > 0.05) of apoptosis status between 2, 4, 8 and >8-cell embryo stage. Early apoptosis was also not seen in >8-cell stage. Even though there were no differences in apoptosis expression between the three classes, the cleavage rate of grade A oocytes was significantly higher (p < 0.01) than grade B and grade C. In conclusion, the apoptosis expression in the embryo can occur regardless of the oocyte quality and the cleavage stage of the embryo produced. PMID:26858565

  12. The Trouble With Bonds

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    @@ In early June,global financial markets gyrated downwards in the wake of central banks'tough language on inflation.At one point bond prices reflected expectations of four rate hikes by the US Federal Reserve (Fed) in the next 12 months.As a result,the dollar firmed,oil prices stabilized,and yield curves flattened around the world.If all these inflation-fighting measures are real,the situation bodes well for bonds.But,I think otherwise.

  13. Effect of SiC whiskers on the oxidation protective properties of SiC coatings for carbon/carbon composites

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.

  14. Preparation and characterization of carbon/SiC nanowire/Na-doped carbonated hydroxyapatite multilayer coating for carbon/carbon composites

    Energy Technology Data Exchange (ETDEWEB)

    Leilei, Zhang, E-mail: zhangleilei1121@aliyun.com; Hejun, Li; Kezhi, Li; Shouyang, Zhang; Qiangang, Fu; Yulei, Zhang; Jinhua, Lu; Wei, Li

    2014-09-15

    Highlights: • CSH coatings were prepared by combination of magnetron sputter ion plating, CVD and UECD. • Na{sup +} and CO{sub 3}{sup 2−} were developed to co-substitute hydroxyapatite. • SiC nanowires were introduced into Na-doped carbonated hydroxyapatite. • CSH coatings showed excellent cell activity and cell proliferation behavior. - Abstract: A carbon/SiC nanowire/Na-doped carbonated hydroxyapatite multilayer coating (CSH coating) was prepared on carbon/carbon composites using a combination method of magnetron sputter ion plating, chemical vapor deposition and ultrasound-assisted electrochemical deposition procedure. The morphology, microstructure and chemical composition of the coating were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed that the CSH coating was consisted of three components: carbon layer, SiC nanowires and Na-doped carbonated hydroxyapatite. The carbon layer provided a dense and uniform surface structure for the growth of SiC nanowires. The SiC nanowires exhibited a porous structure, favoring the infiltration of Na-doped carbonated hydroxyapatite crystals. The Na-doped carbonated hydroxyapatite could infiltrate into the pores of SiC nanowires and finally cover the SiC nanowires entirely with a needle shape. The osteoblast-like MG63 cells were employed to assess the in vitro biocompatibility of the CSH coating. The MG63 cells favorably spread and grew well across the CSH coating surface with plenty of filopods and microvilli, exhibiting excellent cell activity. Moreover, the CSH coating elicited higher cell proliferation as compared to bare carbon/carbon composites. In conclusion, the CSH offers great potential as a coating material for future medical application in hard tissue replacement.

  15. A designer bleomycin with significantly improved DNA cleavage activity.

    Science.gov (United States)

    Huang, Sheng-Xiong; Feng, Zhiyang; Wang, Liyan; Galm, Ute; Wendt-Pienkowski, Evelyn; Yang, Dong; Tao, Meifeng; Coughlin, Jane M; Duan, Yanwen; Shen, Ben

    2012-08-15

    The bleomycins (BLMs) are used clinically in combination with a number of other agents for the treatment of several types of tumors, and the BLM, etoposide, and cisplatin treatment regimen cures 90-95% of metastatic testicular cancer patients. BLM-induced pneumonitis is the most feared, dose-limiting side effect of BLM in chemotherapy, which can progress into lung fibrosis and affect up to 46% of the total patient population. There have been continued efforts to develop new BLM analogues in the search for anticancer drugs with better clinical efficacy and lower lung toxicity. We have previously cloned and characterized the biosynthetic gene clusters for BLMs from Streptomyces verticillus ATCC15003, tallysomycins from Streptoalloteichus hindustanus E465-94 ATCC31158, and zorbamycin (ZBM) from Streptomyces flavoviridis SB9001. Comparative analysis of the three biosynthetic machineries provided the molecular basis for the formulation of hypotheses to engineer novel analogues. We now report engineered production of three new analogues, 6'-hydroxy-ZBM, BLM Z, and 6'-deoxy-BLM Z and the evaluation of their DNA cleavage activities as a measurement for their potential anticancer activity. Our findings unveiled: (i) the disaccharide moiety plays an important role in the DNA cleavage activity of BLMs and ZBMs, (ii) the ZBM disaccharide significantly enhances the potency of BLM, and (iii) 6'-deoxy-BLM Z represents the most potent BLM analogue known to date. The fact that 6'-deoxy-BLM Z can be produced in reasonable quantities by microbial fermentation should greatly facilitate follow-up mechanistic and preclinical studies to potentially advance this analogue into a clinical drug.

  16. Ultrarapid mutation detection by multiplex, solid-phase chemical cleavage

    Energy Technology Data Exchange (ETDEWEB)

    Rowley, G.; Saad, S.; Giannelli, F.; Green, P.M. [Guy`s & St. Thomas`s Hospitals, London (United Kingdom)

    1995-12-10

    The chemical cleavage of mismatches in heteroduplexes formed by probe and test DNA detects and locates any sequence change in long DNA segments ({approximately}1.8 kb), and its efficiency has been well tested in the analysis of both average (e.g., coagulation factor IX) and large, complex genes (e.g., coagulation factor VIII and dystrophin). In the latter application RT/PCR products allow the examination of all essential sequences of the gene in a minimum number of reactions. We use two specific chemical reactants (hydroxylamine and osmium tetroxide) and piperidine cleavage of the above procedure to develop a very fast mutation screening method. This is based on: (1) 5{prime} or internal fluorescent labeling to allow concurrent screening of three to four DNA fragments and (2) solid-phase chemistry to use a microliter format and reduce the time required for the procedure, from amplification of sequence to gel loading inclusive, to one person-working-day. We test the two variations of the method, one entailing 5{prime} labeling of probe DNA and the other uniform labeling of both probe and target DNA, by detecting 114 known hemophilia B (coagulation factor IX) mutations and by analyzing 129 new patients. Uniform labeling of both probe and target DNA prior to formation of the heteroduplexes leads to almost twofold redundancy in the ability to detect mutations. Alternatively, the latter procedure may offer very efficient though less than 100% screening for sequence changes with only hydroxylamine. The full method with two chemical reactions (hydroxylamine and osmium tetroxide) should allow one person to screen with virtually 100% accuracy more than 300 kb of sequence in three ABI 373 gels in 1 day. 26 refs., 7 figs., 1 tab.

  17. Role of carbon-carbon phenyl migration in the pyrolysis mechanism of β-O-4 lignin model compounds: phenethyl phenyl ether and α-hydroxy phenethyl phenyl ether.

    Science.gov (United States)

    Beste, Ariana; Buchanan, A C

    2012-12-20

    We investigate phenyl shift and subsequent β-scission reactions for PhCHXCH·OPh [X = H, OH], which are part of the pyrolysis mechanism of phenethyl phenyl ether (PPE) and α-hydroxy PPE. PPE and its derivatives are model compounds for the most common linkage in lignin, the β-O-4 linkage. We use density functional theory to locate transition states and equilibrium structures and kinetic Monte Carlo in combination with transition-state theory for kinetic simulations. Oxygen-carbon and carbon-carbon phenyl shift reactions proceed through cyclic intermediates with similar barriers. However, while subsequent β-scission of the oxygen-carbon shift products proceeds with virtually no barrier, the activation energy for β-scission of the carbon-carbon shift products exceeds 15 kcal/mol. We found that about 15% of β-radical conversion can be attributed to carbon-carbon shift for PPE and α-hydroxy PPE at 618 K. Whereas the oxygen-carbon shift reaction has been established as an integral part of the pyrolysis mechanism of PPE and its derivatives, participation of the carbon-carbon shift reaction has not been shown previously.

  18. OZONE REACTION WITH N-ALDEHYDES (N=4-10), BENZALDEHYDE, ETHANOL, ISOPROPANOL, AND N-PROPANOL ADSORBED ON A DUAL-BED GRAPHITIZED CARBON/CARBON MOLECULAR SIEVE ADSORBENT CARTRIDGE

    Science.gov (United States)

    Ozone reacts with n-aldehydes (n = 4 - 10), benzaldehyde, ethanol, isopropanol, and n-propanol adsorbed on a dual-bed graphitized carbon/carbon molecular sieve adsorbent cartridge. Destruction of n-aldehydes increases with n number and with ozone concentration. In some samp...

  19. Photochemical tissue bonding

    Science.gov (United States)

    Redmond, Robert W.; Kochevar, Irene E.

    2012-01-10

    Photochemical tissue bonding methods include the application of a photosensitizer to a tissue and/or tissue graft, followed by irradiation with electromagnetic energy to produce a tissue seal. The methods are useful for tissue adhesion, such as in wound closure, tissue grafting, skin grafting, musculoskeletal tissue repair, ligament or tendon repair and corneal repair.

  20. Thread bonds in molecules

    CERN Document Server

    Ivlev, B

    2015-01-01

    Unusual chemical bonds are proposed. Each bond is almost covalent but is characterized by the thread of a small radius $\\sim 0.6\\times 10^{-11}$cm, between two nuclei in a molecule. The main electron density is concentrated outside the thread as in a covalent bond. The thread is formed by the electron wave function which has a tendency to be singular on it. The singularity along the thread is cut off by electron "vibrations" due to the interaction with zero point electromagnetic oscillations. The electron energy has its typical value of (1-10)eV. Due to the small tread radius the uncertainty of the electron momentum inside the thread is large resulting in a large electron kinetic energy $\\sim 1 MeV$. This energy is compensated by formation of a potential well due to the reduction of the energy of electromagnetic zero point oscillations. This is similar to formation of a negative van der Waals potential. Thread bonds are stable and cannot be created or destructed in chemical or optical processes.

  1. Bonds Between Atoms.

    Science.gov (United States)

    Holden, Alan

    The field of inquiry into how atoms are bonded together to form molecules and solids crosses the borderlines between physics and chemistry encompassing methods characteristic of both sciences. At one extreme, the inquiry is pursued with care and rigor into the simplest cases; at the other extreme, suggestions derived from the more careful inquiry…

  2. Delay of HeLa cell cleavage into interphase using dihydrocytochalasin B: retention of a postmitotic spindle and telophase disc correlates with synchronous cleavage recovery

    OpenAIRE

    1995-01-01

    The molecular signals that determine the position and timing of the cleavage furrow during mammalian cell cytokinesis are presently unknown. We have studied in detail the effect of dihydrocytochalasin B (DCB), a drug that interferes with actin assembly, on specific late mitotic events in synchronous HeLa cells. When cleavage furrow formation is blocked at 10 microM DCB, cells return to interphase by the criteria of reformation of nuclei with lamin borders, degradation of the cyclin B componen...

  3. SARS coronavirus nsp1 protein induces template-dependent endonucleolytic cleavage of mRNAs: viral mRNAs are resistant to nsp1-induced RNA cleavage.

    Directory of Open Access Journals (Sweden)

    Cheng Huang

    2011-12-01

    Full Text Available SARS coronavirus (SCoV nonstructural protein (nsp 1, a potent inhibitor of host gene expression, possesses a unique mode of action: it binds to 40S ribosomes to inactivate their translation functions and induces host mRNA degradation. Our previous study demonstrated that nsp1 induces RNA modification near the 5'-end of a reporter mRNA having a short 5' untranslated region and RNA cleavage in the encephalomyocarditis virus internal ribosome entry site (IRES region of a dicistronic RNA template, but not in those IRES elements from hepatitis C or cricket paralysis viruses. By using primarily cell-free, in vitro translation systems, the present study revealed that the nsp1 induced endonucleolytic RNA cleavage mainly near the 5' untranslated region of capped mRNA templates. Experiments using dicistronic mRNAs carrying different IRESes showed that nsp1 induced endonucleolytic RNA cleavage within the ribosome loading region of type I and type II picornavirus IRES elements, but not that of classical swine fever virus IRES, which is characterized as a hepatitis C virus-like IRES. The nsp1-induced RNA cleavage of template mRNAs exhibited no apparent preference for a specific nucleotide sequence at the RNA cleavage sites. Remarkably, SCoV mRNAs, which have a 5' cap structure and 3' poly A tail like those of typical host mRNAs, were not susceptible to nsp1-mediated RNA cleavage and importantly, the presence of the 5'-end leader sequence protected the SCoV mRNAs from nsp1-induced endonucleolytic RNA cleavage. The escape of viral mRNAs from nsp1-induced RNA cleavage may be an important strategy by which the virus circumvents the action of nsp1 leading to the efficient accumulation of viral mRNAs and viral proteins during infection.

  4. Molecular Basis for the Recognition and Cleavages of IGF-II, TGF-[alpha], and Amylin by Human Insulin-Degrading Enzyme

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Qing; Manolopoulou, Marika; Bian, Yao; Schilling, Alexander B.; Tang, Wei-Jen (UC); (UIC)

    2010-02-11

    Insulin-degrading enzyme (IDE) is involved in the clearance of many bioactive peptide substrates, including insulin and amyloid-{beta}, peptides vital to the development of diabetes and Alzheimer's disease, respectively. IDE can also rapidly degrade hormones that are held together by intramolecular disulfide bond(s) without their reduction. Furthermore, IDE exhibits a remarkable ability to preferentially degrade structurally similar peptides such as the selective degradation of insulin-like growth factor (IGF)-II and transforming growth factor-{alpha} (TGF-{alpha}) over IGF-I and epidermal growth factor, respectively. Here, we used high-accuracy mass spectrometry to identify the cleavage sites of human IGF-II, TGF-{alpha}, amylin, reduced amylin, and amyloid-{beta} by human IDE. We also determined the structures of human IDE-IGF-II and IDE-TGF-{alpha} at 2.3 {angstrom} and IDE-amylin at 2.9 {angstrom}. We found that IDE cleaves its substrates at multiple sites in a biased stochastic manner. Furthermore, the presence of a disulfide bond in amylin allows IDE to cut at an additional site in the middle of the peptide (amino acids 18-19). Our amylin-bound IDE structure offers insight into how the structural constraint from a disulfide bond in amylin can alter IDE cleavage sites. Together with NMR structures of amylin and the IGF and epidermal growth factor families, our work also reveals the structural basis of how the high dipole moment of substrates complements the charge distribution of the IDE catalytic chamber for the substrate selectivity. In addition, we show how the ability of substrates to properly anchor their N-terminus to the exosite of IDE and undergo a conformational switch upon binding to the catalytic chamber of IDE can also contribute to the selective degradation of structurally related growth factors.

  5. Molecular basis for the recognition and cleavages of IGF-II, TGF-α, and amylin by human insulin degrading enzyme

    Science.gov (United States)

    Guo, Qing; Manolopoulou, Marika; Bian, Yao; Schilling, Alexander B.; Tang, Wei-Jen

    2009-01-01

    Insulin-degrading enzyme (IDE) is involved in the clearance of many bioactive peptide substrates, including insulin and amyloid-β (Aβ), peptides vital to the development of diabetes and Alzheimer's disease, respectively. IDE can also rapidly degrade hormones that are held together by intra-molecular disulfide bond(s) without their reduction. Furthermore, IDE exhibits a remarkable ability to preferentially degrade structurally similar peptides such as the selective degradation of insulin-growth factor-II (IGF-II) and transforming growth factor-α (TGF-α) over IGF-I and epidermal growth factor (EGF), respectively. Here, we used high accuracy mass spectrometry to identify the cleavage sites of human IGF-II, TGF-α, amylin, reduced amylin, and Aβ by human IDE. We also determined the structures of human IDE-IGF-II and IDE-TGF-α at 2.3 Å and IDE-amylin at 2.9 Å. We found that IDE cleaves its substrates at multiple sites in a biased stochastic manner. Furthermore, the presence of a disulfide bond in amylin allows IDE to cut at an additional site in the middle of the peptide (aa 18-19). Our amylin-bound IDE structure offers insight into how the structural constraint from a disulfide bond in amylin can alter IDE cleavage sites. Together with NMR structures of amylin and the IGF and EGF families, our work also reveals the structural basis of how the high dipole moment of substrates complements the charge distribution of the IDE catalytic chamber for the substrate selectivity. In addition, we show how the ability of substrates to properly anchor their N-terminus to the exosite of IDE and undergo a conformational switch upon binding to the catalytic chamber of IDE can also contribute to the selective degradation of structurally related growth factors. PMID:19896952

  6. Amino acid sequence requirements in the hinge of human immunoglobulin A1 (IgA1) for cleavage by streptococcal IgA1 proteases.

    Science.gov (United States)

    Batten, Margaret R; Senior, Bernard W; Kilian, Mogens; Woof, Jenny M

    2003-03-01

    The amino acid sequence requirements in the hinge of human immunoglobulin A1 (IgA1) for cleavage by IgA1 proteases of different species of Streptococcus were investigated. Recombinant IgA1 antibodies were generated with point mutations at proline 227 and threonine 228, the residues lying on either side of the peptide bond at which all streptococcal IgA1 proteases cleave wild-type human IgA1. The amino acid substitutions produced no major effect upon the structure of the mutant IgA1 antibodies or their functional ability to bind to Fcalpha receptors. However, the substitutions had a substantial effect upon sensitivity to cleavage with some streptococcal IgA1 proteases, with, in some cases, a single point mutation rendering the antibody resistant to a particular IgA1 protease. This effect was least marked with the IgA1 protease from Streptococcus pneumoniae, which showed no absolute requirement for either proline or threonine at residues 227 to 228. By contrast, the IgA1 proteases of Streptococcus oralis, Streptococcus sanguis, and Streptococcus mitis had an absolute requirement for proline at 227 but not for threonine at 228, which could be replaced by valine. There was evidence in S. mitis that proteases from different strains may have different amino acid requirements for cleavage. Remarkably, some streptococcal proteases appeared able to cleave the hinge at a distant alternative site if substitution prevented efficient cleavage of the original site. Hence, this study has identified key residues required for the recognition of the IgA1 hinge as a substrate by streptococcal IgA1 proteases, and it marks a preliminary step towards development of specific enzyme inhibitors. PMID:12595464

  7. Localization of double bonds in wax esters by high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry utilizing the fragmentation of acetonitrile-related adducts.

    Science.gov (United States)

    Vrkoslav, Vladimír; Háková, Martina; Pecková, Karolina; Urbanová, Klára; Cvačka, Josef

    2011-04-15

    Unsaturated wax esters (WEs) provided molecular adducts with C(3)H(5)N ([M + 55](+•)) in APCI sources in the presence of acetonitrile. CID MS/MS of [M + 55](+•) yielded fragments allowing the localization of double bond(s) in the hydrocarbon chains of the WEs. These fragments were formed by a cleavage on each side of the double bond. In methylene-interrupted polyunsaturated WEs, diagnostic fragments related to each double bond were detected; the most abundant were those corresponding to the cleavage of the C-C bond next to the first and the last double bond. To differentiate between those fragments differing in their structure or origin, a simple nomenclature based on α and ω ions has been introduced. Fragmentation of the α-type ions (fragments containing an ester bond) provided information on the occurrence of a double bond in the acid or alcohol part of the WEs. While no significant differences between the spectra of the WEs differing by cis/trans isomerism were found, the isomers were separated chromatographically. A data-dependent HPLC/APCI-MS(2) method for the comprehensive characterization of WEs in their complex mixtures has been developed and applied to natural mixtures of WEs isolated from jojoba oil and beeswax. More than 50 WE molecular species were completely identified, including the information on the acid and alcohol chain length and the position of the double bonds.

  8. The cleavage of the aryl-O-CH/sub 3/ bond using anisole as a model compound

    Energy Technology Data Exchange (ETDEWEB)

    Afifi, A.I.; Hindermann, J.P.; Chornet, E.; Overend, R.P.

    1989-04-01

    The thermal decomposition of anisole as a prototype of the aryl-methyl-ether linkage of lignin and coals has been studied under supercritical conditions using tetralin as hydrogen donor solvent. The effect of homogenous Lewis acid catalysts have also been studied under the same conditions. The main reaction products are phenol, benzene, toluene and cresols. At high tetralin to anisole ratios the selectivity to phenol is almost 80% with little or no cresol production. This selective conversion can be carried out rapidly and cleanly at high temperature (>450 degrees C). Kinetic studies were undertaken using pyrolytic, donor solvent hydrogenolytic and Lewis acid catalysed regimes in the temperature range 400-500 degrees C. The kinetics of anisole decomposition in a large excess of tetralin have been found to be in good agreement with those published in the literature. The Lewis acid catalysts lower the activation energy relative to the pyrolytic and hydrogenolytic cases. The kinetic studies and their mechanistic interpretation lead to a mechanism involving surprisingly few radical species: methyl, phenoxy, phenoxymethyl and phenyl radicals. In the presence of FeCl/sub 3/, the selectivity towards phenols and cresols is enhanced, though a side reaction leads to polymerization at low (400-420 degrees C) temperatures. It is concluded that the aryl-O-methyl ether linkage in anisole can easily be broken at high temperatures, 450-500 degrees C, in supercritical hydrogen donor solvent to give phenol in high yield and selectivity. 23 refs., 4 figs., 5 tabs.

  9. Processive pectin methylesterases: the role of electrostatic potential, breathing motions and bond cleavage in the rectification of Brownian motions.

    Directory of Open Access Journals (Sweden)

    Davide Mercadante

    Full Text Available Pectin methylesterases (PMEs hydrolyze the methylester groups that are found on the homogalacturonan (HG chains of pectic polysaccharides in the plant cell wall. Plant and bacterial PMEs are especially interesting as the resulting de-methylesterified (carboxylated sugar residues are found to be arranged contiguously, indicating a so-called processive nature of these enzymes. Here we report the results of continuum electrostatics calculations performed along the molecular dynamics trajectory of a PME-HG-decasaccharide complex. In particular it was observed that, when the methylester groups of the decasaccharide were arranged in order to mimic the just-formed carboxylate product of de-methylesterification, a net unidirectional sliding of the model decasaccharide was subsequently observed along the enzyme's binding groove. The changes that occurred in the electrostatic binding energy and protein dynamics during this translocation provide insights into the mechanism by which the enzyme rectifies Brownian motions to achieve processivity. The free energy that drives these molecular motors is thus demonstrated to be incorporated endogenously in the methylesterified groups of the HG chains and is not supplied exogenously.

  10. The mechanism and kinetics of the electrochemical cleavage of azo bond of 2-hydroxy-5-sulfophenyl-azo-benzoic acids

    Energy Technology Data Exchange (ETDEWEB)

    Mandic, Zoran; Nigovic, Biljana; Simunic, Branimir

    2004-02-15

    The electrochemical reduction of 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(3-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(2-sulfophenyl)azo]benzoic acid and 2-hydroxy-5-azo-benzoic acid has been carried out in aqueous solutions at glassy carbon electrode using cyclic voltammetry and chronoamperometry. The position of sulfo substituent relative to azo bridge as well as pH of the solution have significant impact on the electrochemical behavior of these compounds. It has been proposed that these compounds are reduced predominantly as hydrazone tautomers resulting in corresponding hydrazo compounds. The overall electrochemical reduction follows DISP2 mechanism, ultimately leading to the 5-amino salicylic acid and sulfanilic acid. The rate determining step is the homogenous redox reaction between intermediate hydrazo compound and 5-amino salicylic acid quinoneimine. The mechanism is proposed in which activated complex of 5-amino salicylic acid quinoneimine and intermediate hydrazo compound is formed with the simultaneous loss of one proton.

  11. Heterogeneous Catalysis of C–O Bond Cleavage for Cellulose Deconstruction: A Potential Pathway for Ethanol Production

    OpenAIRE

    Crews, Kristy; Reeves, Crystal; Thomas, Porsha; Abugri, Daniel; Russell, Albert; Michael L. Curry

    2014-01-01

    Due to difficulty deconstructing the linkages between lignin, hemicellulose and cellulose during the conversion of cellulose to sugar, the commercial production of cellulosic ethanol is limited. This can be overcome by using a high surface-area metal catalyst. In this study, high surface-area metal NPs were synthesized using 20 mM of chloroplatinic acid and cobalt chloride prepared in THF with 0.1 mM of generation four poly(amido)amine (PAMAM) terminated dendrimer (G4-NH2) prepared in methano...

  12. Comparative and phylogenetic perspectives of the cleavage process in tailed amphibians.

    Science.gov (United States)

    Desnitskiy, Alexey G; Litvinchuk, Spartak N

    2015-10-01

    The order Caudata includes about 660 species and displays a variety of important developmental traits such as cleavage pattern and egg size. However, the cleavage process of tailed amphibians has never been analyzed within a phylogenetic framework. We use published data on the embryos of 36 species concerning the character of the third cleavage furrow (latitudinal, longitudinal or variable) and the magnitude of synchronous cleavage period (up to 3-4 synchronous cell divisions in the animal hemisphere or a considerably longer series of synchronous divisions followed by midblastula transition). Several species from basal caudate families Cryptobranchidae (Andrias davidianus and Cryptobranchus alleganiensis) and Hynobiidae (Onychodactylus japonicus) as well as several representatives from derived families Plethodontidae (Desmognathus fuscus and Ensatina eschscholtzii) and Proteidae (Necturus maculosus) are characterized by longitudinal furrows of the third cleavage and the loss of synchrony as early as the 8-cell stage. By contrast, many representatives of derived families Ambystomatidae and Salamandridae have latitudinal furrows of the third cleavage and extensive period of synchronous divisions. Our analysis of these ontogenetic characters mapped onto a phylogenetic tree shows that the cleavage pattern of large, yolky eggs with short series of synchronous divisions is an ancestral trait for the tailed amphibians, while the data on the orientation of third cleavage furrows seem to be ambiguous with respect to phylogeny. Nevertheless, the midblastula transition, which is characteristic of the model species Ambystoma mexicanum (Caudata) and Xenopus laevis (Anura), might have evolved convergently in these two amphibian orders. PMID:25180466

  13. Comparative and phylogenetic perspectives of the cleavage process in tailed amphibians.

    Science.gov (United States)

    Desnitskiy, Alexey G; Litvinchuk, Spartak N

    2015-10-01

    The order Caudata includes about 660 species and displays a variety of important developmental traits such as cleavage pattern and egg size. However, the cleavage process of tailed amphibians has never been analyzed within a phylogenetic framework. We use published data on the embryos of 36 species concerning the character of the third cleavage furrow (latitudinal, longitudinal or variable) and the magnitude of synchronous cleavage period (up to 3-4 synchronous cell divisions in the animal hemisphere or a considerably longer series of synchronous divisions followed by midblastula transition). Several species from basal caudate families Cryptobranchidae (Andrias davidianus and Cryptobranchus alleganiensis) and Hynobiidae (Onychodactylus japonicus) as well as several representatives from derived families Plethodontidae (Desmognathus fuscus and Ensatina eschscholtzii) and Proteidae (Necturus maculosus) are characterized by longitudinal furrows of the third cleavage and the loss of synchrony as early as the 8-cell stage. By contrast, many representatives of derived families Ambystomatidae and Salamandridae have latitudinal furrows of the third cleavage and extensive period of synchronous divisions. Our analysis of these ontogenetic characters mapped onto a phylogenetic tree shows that the cleavage pattern of large, yolky eggs with short series of synchronous divisions is an ancestral trait for the tailed amphibians, while the data on the orientation of third cleavage furrows seem to be ambiguous with respect to phylogeny. Nevertheless, the midblastula transition, which is characteristic of the model species Ambystoma mexicanum (Caudata) and Xenopus laevis (Anura), might have evolved convergently in these two amphibian orders.

  14. Low-temperature side-chain cleavage and decarboxylation of polythiophene esters by acid catalysis

    DEFF Research Database (Denmark)

    Søndergaard, Roar; Norrman, Kion; Krebs, Frederik C

    2012-01-01

    substituents have been examined by TGA‐MS using different sulphonic acids. A substantial lowering of the cleavage temperature is observed, and the ester cleavage can even be performed in situ on roll‐to‐roll‐coated films on polyethylene terephthalate (PET). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A...

  15. Unexpected tolerance of alpha-cleavage of the prion protein to sequence variations.

    Directory of Open Access Journals (Sweden)

    José B Oliveira-Martins

    Full Text Available The cellular form of the prion protein, PrP(C, undergoes extensive proteolysis at the alpha site (109K [see text]H110. Expression of non-cleavable PrP(C mutants in transgenic mice correlates with neurotoxicity, suggesting that alpha-cleavage is important for PrP(C physiology. To gain insights into the mechanisms of alpha-cleavage, we generated a library of PrP(C mutants with mutations in the region neighbouring the alpha-cleavage site. The prevalence of C1, the carboxy adduct of alpha-cleavage, was determined for each mutant. In cell lines of disparate origin, C1 prevalence was unaffected by variations in charge and hydrophobicity of the region neighbouring the alpha-cleavage site, and by substitutions of the residues in the palindrome that flanks this site. Instead, alpha-cleavage was size-dependently impaired by deletions within the domain 106-119. Almost no cleavage was observed upon full deletion of this domain. These results suggest that alpha-cleavage is executed by an alpha-PrPase whose activity, despite surprisingly limited sequence specificity, is dependent on the size of the central region of PrP(C.

  16. Cleavage-based voting behavior in cross-national perspective : Evidence from six postwar democracies

    NARCIS (Netherlands)

    Brooks, Clem; Nieuwbeerta, Paul; Manza, Jeff

    2006-01-01

    We investigate trends and cross-national variation in the impact of class, religious, and gender cleavages on voting behavior in six advanced capitalist democracies in the postwar period. Earlier research on cleavage voting has been criticized for utilizing outdated ‘‘two-class’’ models of class str

  17. Cleavage-based voting behavior in cross-national perspective: evidence from six postwar democracies

    NARCIS (Netherlands)

    Brooks, Clem; Nieuwbeerta, Paul; Manza, Jeff

    2006-01-01

    We investigate trends and cross-national variation in the impact of class, religious, and gender cleavages on voting behavior in six advanced capitalist democracies in the postwar period. Earlier research on cleavage voting has been criticized for utilizing outdated “two-class” models of class struc

  18. Role of Austenite in Brittle Fracture of Bond Region of Super Duplex Stainless Steel

    Science.gov (United States)

    Kitagawa, Yoshihiko; Ikeuchi, Kenji; Kuroda, Toshio

    Weld simulation of heat-affected zone (HAZ) was performed to investigate the mechanism by which austenite affects the toughness of super duplex stainless steel. Thermal cycles of various peak temperatures in the range from 1373 K to 1673 K corresponding to the HAZ were applied to SAF2507 super duplex stainless steel specimens. Charpy impact test was carried out using the specimens after the weld simulation, and the fracture surfaces were observed by SEM using three-dimensionally reconstruction technique. Austenite content decreased with increasing the peak temperature when the peak temperature exceeded 1473 K and the impact value decreased with increasing the peak temperature and decreasing the austenite content. The thermal cycle of the peak temperature of 1673 K corresponding to weld bond region caused decreasing of austenite content which was 22% lower than that of the base metal. The ductile-brittle transition temperature was measured. As a result the temperature increased rapidly in the weld bond region, the peak temperature of which exceeded 1623 K by the grain growth of ferrite matrix occurring subsequently to the completely dissolution of austenite. The morphology of the fracture surfaces after impact testing at 77 K showed cleavage fracture of ferrite. The {100} orientations of cleavage fracture facets were measured using three-dimensional images of the fracture surfaces and the results were visualized as the orientation color maps. The results showed that there were cleavage fractures consisting of a few facets parallel to each other. It was considered that a few facets existed in one ferrite grain. It was concluded that Widmanstätten austenite divided the large fracture into smaller cleavage facets in a ferrite grain and then suppressed the degradation of bond toughness of duplex stainless steel.

  19. Convertible bond valuation focusing on Chinese convertible bond market

    OpenAIRE

    Yang, Ke

    2010-01-01

    This paper mainly discusses the methods of valuation of convertible bonds in Chinese market. Different from common convertible bonds in European market, considering the complicate features of Chinese convertible bond, this paper represents specific pricing approaches for pricing convertible bonds with different provisions along with the increment of complexity of these provisions. More specifically, this paper represents the decomposing method and binomial tree method for pricing both of Non-...

  20. Real-time monitoring of DNAzyme cleavage process using fluorescent assay

    Institute of Scientific and Technical Information of China (English)

    Xiang Xian Meng; Xiao Hai Yang; Ke Min Wang; Wei Hong Tan; Qiu Ping Guo

    2009-01-01

    Detection of deoxyribozyme (DNAzyme) cleavage process usually needs complex and time-consuming radial labeling, gel electrophoresis and autoradiography. This paper reported an approach to detect DNAzyme cleavage process in real time using a fluorescence probe. The probe was employed as DNAzyme substrate to convert directly the cleavage information into fluorescence signal in real time. Compared with traditional approach, this non-isotope method not only brought a convenient means to monitor the DNAzyme cleavage reaction, but also offered abundant dynamic data for choosing potential gene therapeutic agents. It provides a new tool for DNAzyme research, as well as a new insight into research on human disease diagnosis. Based on this method, 8-17deoxyribozyme (8-17DNAzyme) against hepatitis C virus RNA (HCV-RNA) was designed and the cleavage process was studied in real time.

  1. Ultrasensitive monitoring of ribozyme cleavage product using molecular-beacon-ligation system

    Institute of Scientific and Technical Information of China (English)

    MENG XiangXian; TANG ZhiWen; WANG KeMin; TAN WeiHong; YANG XiaoHai; LI Jun; GUO QiuPing

    2007-01-01

    This paper reports a new approach to detect ribozyme cleavage product based on the molecular- beacon-ligation system. The molecular beacon, designed in such a way that one-half of its loop is complementary to ribozyme cleavage product, is used to monitor ligation process of RNA/DNA complex in a homogeneous solution and to convert directly cleavage product information into fluorescence signal. The method need not label ribozyme and ribozyme substrate, which is fast, simple and ultrasensitive for detection of cleavage product. Detection limit of the assay is 0.05 nmol/L. The cleavage product of hammerhead ribozyme against hepatitis C virus RNA (HCV-RNA) was detected perfectly based on this assay. Owing to its ultrasensitivity, excellent specificity, convenience and fidelity, this method might hold out great promise in ribozyme reaction and ribozyme gene therapy.

  2. Indirect bonding technique in orthodontics

    Directory of Open Access Journals (Sweden)

    Kübra Yıldırım

    2016-08-01

    Full Text Available ‘Direct Bonding Technique’ which allows the fixed orthodontic appliances to be directly bonded to teeth without using bands decreased the clinic time for bracket bonding and increased esthetics and oral hygiene during orthodontic treatment. However, mistakes in bracket positioning were observed due to decreased direct visual sight and access to posterior teeth. ‘Indirect Bonding Technique’ was developed for eliminating these problems. Initially, decreased bond strength, higher bond failure rate, periodontal tissue irritation, compromised oral hygiene and increased laboratory time were the main disadvantages of this technique when compared to direct bonding. The newly developed materials and modified techniques help to eliminate these negative consequences. Today, the brackets bonded with indirect technique have similar bond strength with brackets bonded directly. Moreover, indirect and direct bonding techniques have similar effects on periodontal tissues. However, indirect bonding technique requires more attention and precision in laboratory and clinical stage, and has higher cost. Orthodontist's preference between these two bonding techniques may differ according to time spent in laboratory and clinic, cost, patient comfort and personal opinion.

  3. Atomistic Details of the Associative Phosphodiester Cleavage in Human Ribonuclease H

    Energy Technology Data Exchange (ETDEWEB)

    Elsasser, Brigitta M.; Fels, Gregor

    2010-07-30

    During translation of the genetic information of DNA into proteins, mRNA is synthesized by RNA polymerase and after the transcription process degraded by RNase H. The endoribonuclease RNase H is a member of the nucleotidyl-transferase (NT) superfamily and is known to hydrolyze the phosphodiester bonds of RNA which is hybridized to DNA. Retroviral RNase H is part of the viral reverse transcriptase enzyme that is indispensable for the proliferation of retroviruses, such as HIV. Inhibitors of this enzyme could therefore provide new drugs against diseases like AIDS. In our study we investigated the molecular mechanism of RNA cleavage by human RNase H using a comprehensive high level DFT/B3LYP QM/MM theoretical method for the calculation of the stationary points and nudged elastic band (NEB) and free energy calculations to identify the transition state structures, the rate limiting step and the reaction barrier. Our calculations reveal that the catalytic mechanism proceeds in two steps and that the nature of the nucleophile is a water molecule. In the first step, the water attack on the scissile phosphorous is followed by a proton transfer from the water to the O2P oxygen and a trigonal bipyramidal pentacoordinated phosphorane is formed. Subsequently, in the second step the proton is shuttled to the O30 oxygen to generate the product state. During the reaction mechanism two Mg2+ ions support the formation of a stable associated in-line SN2-type phosphorane intermediate. Our calculated energy barrier of 19.3 kcal mol*1 is in excellent agreement with experimental findings (20.5 kcal mol*1). These results may contribute to the clarification and understanding of the RNase H reaction mechanism and of further enzymes from the RNase family.

  4. China-Russia Bond

    Institute of Scientific and Technical Information of China (English)

    Ji Zhiye; Ma Zongshi

    2007-01-01

    @@ Thanks to China's successful launching of the Year of Russia, 2006 will surely go down as a milestone in the history of the China-Russia bond. Furthermore, a still-warmer climate will continue to prevail in 2007 when Moscow, in its turn, hosts the Year of China, trying to outshine its next-door neighbor in this regard, as Russian President Vladimir Putin promised in the exchange of new year greetings with his Chinese counterpart, President Hu Jintao.

  5. Direct bonded space maintainers.

    Science.gov (United States)

    Santos, V L; Almeida, M A; Mello, H S; Keith, O

    1993-01-01

    The aim of this study was to evaluate clinically a bonded space maintainer, which would reduce chair-side time and cost. Sixty appliances were fabricated from 0.7 mm stainless steel round wire and bonded using light-cured composite to the two teeth adjacent to the site of extraction of a posterior primary tooth. Twenty males and sixteen females (age range 5-9-years-old) were selected from the Pedodontic clinic of the State University of Rio de Janeiro. The sixty space maintainers were divided into two groups according to the site in which they were placed: a) absent first primary molar and b) absent second primary molar. Impressions and study models were obtained prior to and 6 months after bonding the appliances. During this period only 8.3% of failures were observed, most of them from occlusal or facial trauma. Student t-test did not show statistically significant alterations in the sizes of the maintained spaces during the trial period.

  6. Structural and functional basis for RNA cleavage by Ire1

    Directory of Open Access Journals (Sweden)

    Stroud Robert M

    2011-07-01

    Full Text Available Abstract Background The unfolded protein response (UPR controls the protein folding capacity of the endoplasmic reticulum (ER. Central to this signaling pathway is the ER-resident bifunctional transmembrane kinase/endoribonuclease Ire1. The endoribonuclease (RNase domain of Ire1 initiates a non-conventional mRNA splicing reaction, leading to the production of a transcription factor that controls UPR target genes. The mRNA splicing reaction is an obligatory step of Ire1 signaling, yet its mechanism has remained poorly understood due to the absence of substrate-bound crystal structures of Ire1, the lack of structural similarity between Ire1 and other RNases, and a scarcity of quantitative enzymological data. Here, we experimentally define the active site of Ire1 RNase and quantitatively evaluate the contribution of the key active site residues to catalysis. Results This analysis and two new crystal structures suggest that Ire1 RNase uses histidine H1061 and tyrosine Y1043 as the general acid-general base pair contributing ≥ 7.6 kcal/mol and 1.4 kcal/mol to transition state stabilization, respectively, and asparagine N1057 and arginine R1056 for coordination of the scissile phosphate. Investigation of the stem-loop recognition revealed that additionally to the stem-loops derived from the classic Ire1 substrates HAC1 and Xbp1 mRNA, Ire1 can site-specifically and rapidly cleave anticodon stem-loop (ASL of unmodified tRNAPhe, extending known substrate specificity of Ire1 RNase. Conclusions Our data define the catalytic center of Ire1 RNase and suggest a mechanism of RNA cleavage: each RNase monomer apparently contains a separate catalytic apparatus for RNA cleavage, whereas two RNase subunits contribute to RNA stem-loop docking. Conservation of the key residues among Ire1 homologues suggests that the mechanism elucidated here for yeast Ire1 applies to Ire1 in metazoan cells, and to the only known Ire1 homologue RNase L.

  7. Preparation and Performances of Room Molten Salt as Electrolyte in Carbon-carbon Capacitor Based on LiPFe and Trifluoroacetamide%LiPF6/三氟乙酰胺室温熔盐的制备及在碳-碳电容器中的性能

    Institute of Scientific and Technical Information of China (English)

    左晓希; 李奇; 刘建生; 肖信; 范成杰; 南俊民

    2012-01-01

    利用LiPF6和三氟乙酰胺为前驱物,制备了低共熔温度约为-62℃的室温熔盐,并测试了该熔盐作为碳-碳电化学电容器(EDLCs)电解液时的性能。其中,使用差示扫描量热法(DSC)和红外光谱法(FTIR)分析了不同LiPF6和三氟乙酰胺配比熔盐的热稳定性,拟制了该二元组分的共熔相图,认为LiPF6和三氟乙酰胺极性基团间的氢键作用促成了室温熔盐的形成。循环伏安(CV)、交流阻抗(EIS)和电导等测定结果表明,所制备的LiPF6/三氟乙酰胺电解液的室温电导率为1.30mS/cm,电化学窗口大于5.6V,大于60℃的使用温度,作为电解液可满足碳-碳EDLCs的使用要求。%A novel room molten salt with an eutectic temperature of about -62℃ is prepared using LiPF6 and trifluoroacetamide as precursors. And then its performances are evaluated in carbon-carbon electrochemical double layer capacitor (EDLC) as electrolyte. The thermal properties of the complex electrolyte with different molar ratios are characterized and then the liquid-solid phase diagram is presented by using differential scanning calorimeter (DSC) and Fourier transform infrared spectroscopy (FTIR). The hydrogen bonding interaction between LiPF6 and trifluoroacetamide molecules is attributed to the formation of the as-prepared molten salt. In addition, the results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and conductance tests show that the as-prepared LiPF6/trifluoroacetamide electrolyte has a maximum conductance at room temperature, i.e. 1.30 mS/cm, a stable electrochemical window of ca. 5.6 V, an applicable temperature of more than 60℃, suggesting it is a promising electrolyte candidate for carbon-carbon EDLCs.

  8. Coulombic Models in Chemical Bonding.

    Science.gov (United States)

    Sacks, Lawrence J.

    1986-01-01

    Compares the coulumbic point charge model for hydrogen chloride with the valence bond model. It is not possible to assign either a nonpolar or ionic canonical form of the valence bond model, while the covalent-ionic bond distribution does conform to the point charge model. (JM)

  9. Mittal bonded tongue thrusting appliance

    Directory of Open Access Journals (Sweden)

    Rekha Mittal

    2014-01-01

    Full Text Available These days majority of orthodontist includes bonded molar attachment in their inventory to eliminate the discomfort of molar separation during initial appointment and band spaces left at the end of treatment. This article describes a innovative and economical method of attachment of bonded tongue crib if required during the initial or later stages of treatment along with bonded molar tubes.

  10. Hamiltonian formulation of bond graphs

    NARCIS (Netherlands)

    Golo, Goran; Schaft, van der Arjan; Breedveld, Peter C.; Maschke, Bernhard M.; Johansson, R.; Rantzer, A.

    2003-01-01

    This paper deals with the mathematical formulation of bond graphs. It is proven that the power continuous part of bond graphs, the junction structure, can be associated with a Dirac structure and that the equations describing a bond graph model correspond to a port Hamiltonian system. The conditions

  11. Not all social cleavages are the same: On the relationship between religious diversity and party system fragmentation

    OpenAIRE

    Raymond, Christopher D.

    2016-01-01

    Most studies examining the relationship between social cleavages and party system fragmentation maintain that higher levels of social diversity lead to greater party system fragmentation. However, most aggregate-level studies focus on one type of social cleavage:ethnic diversity. In order to develop a better understanding of how different cleavages impact electoral competition, this paper considers another type of social cleavage: religious diversity.Contrary to previous literature, higher le...

  12. Party agency and the religious-secular cleavage in post-Communist countries: The case of Romania

    OpenAIRE

    Raymond, Christopher

    2014-01-01

    Research focusing on several post-communist countries has found evidence of social cleavage effects on political behaviour similar to those found in Western Europe. In some post-communist countries, however, social cleavage effects appear far weaker (if at all). To understand why this is the case, I perform a case study of Romania, focusing on the religious–secular cleavage. Drawing upon research that emphasises the role of parties in forming cleavages, I argue that the reason for the absence...

  13. Fusion function of the Semliki Forest virus spike is activated by proteolytic cleavage of the envelope glycoprotein precursor p62.

    OpenAIRE

    Lobigs, M; Garoff, H

    1990-01-01

    The precursor protein p62 of the prototype alphavirus Semliki Forest virus (SFV) undergoes during transport to the cell surface a proteolytic cleavage to form the mature envelope glycoprotein E2. To investigate the biological significance of this cleavage event, single amino acid substitutions were introduced at the cleavages site through mutagenesis of cDNA corresponding to the structural region of the SFV genome. The phenotypes of the cleavage site mutants were studied in BHK cells by using...

  14. Modulation of enteroviral proteinase cleavage of poly(A)-binding protein (PABP) by conformation and PABP-associated factors

    OpenAIRE

    Rivera, Carlos I.; Lloyd, Richard E.

    2008-01-01

    Poliovirus (PV) causes a drastic inhibition of cellular cap-dependant protein synthesis due to the cleavage of translation factors eukaryotic initiation factor 4G (eIF4G) and poly (A) binding protein (PABP). Only about half of cellular PABP is cleaved by viral 2A and 3C proteinases during infection. We have investigated PABP cleavage determinants that regulate this partial cleavage. PABP cleavage kinetics analyses indicate that PABP exists in multiple conformations, some of which are resistan...

  15. Diaphanous gene mutation affects spiral cleavage and chirality in snails

    Science.gov (United States)

    Kuroda, Reiko; Fujikura, Kohei; Abe, Masanori; Hosoiri, Yuji; Asakawa, Shuichi; Shimizu, Miho; Umeda, Shin; Ichikawa, Futaba; Takahashi, Hiromi

    2016-01-01

    L-R (left and right) symmetry breaking during embryogenesis and the establishment of asymmetric body plan are key issues in developmental biology, but the onset including the handedness-determining gene locus still remains unknown. Using pure dextral (DD) and sinistral (dd) strains of the pond snail Lymnaea stagnalis as well as its F2 through to F10 backcrossed lines, the single handedness-determining-gene locus was mapped by genetic linkage analysis, BAC cloning and chromosome walking. We have identified the actin-related diaphanous gene Lsdia1 as the strongest candidate. Although the cDNA and derived amino acid sequences of the tandemly duplicated Lsdia1 and Lsdia2 genes are very similar, we could discriminate the two genes/proteins in our molecular biology experiments. The Lsdia1 gene of the sinistral strain carries a frameshift mutation that abrogates full-length LsDia1 protein expression. In the dextral strain, it is already translated prior to oviposition. Expression of Lsdia1 (only in the dextral strain) and Lsdia2 (in both chirality) decreases after the 1-cell stage, with no asymmetric localization throughout. The evolutionary relationships among body handedness, SD/SI (spiral deformation/spindle inclination) at the third cleavage, and expression of diaphanous proteins are discussed in comparison with three other pond snails (L. peregra, Physa acuta and Indoplanorbis exustus). PMID:27708420

  16. Computational redesign of endonuclease DNA binding and cleavage specificity

    Science.gov (United States)

    Ashworth, Justin; Havranek, James J.; Duarte, Carlos M.; Sussman, Django; Monnat, Raymond J.; Stoddard, Barry L.; Baker, David

    2006-06-01

    The reprogramming of DNA-binding specificity is an important challenge for computational protein design that tests current understanding of protein-DNA recognition, and has considerable practical relevance for biotechnology and medicine. Here we describe the computational redesign of the cleavage specificity of the intron-encoded homing endonuclease I-MsoI using a physically realistic atomic-level forcefield. Using an in silico screen, we identified single base-pair substitutions predicted to disrupt binding by the wild-type enzyme, and then optimized the identities and conformations of clusters of amino acids around each of these unfavourable substitutions using Monte Carlo sampling. A redesigned enzyme that was predicted to display altered target site specificity, while maintaining wild-type binding affinity, was experimentally characterized. The redesigned enzyme binds and cleaves the redesigned recognition site ~10,000 times more effectively than does the wild-type enzyme, with a level of target discrimination comparable to the original endonuclease. Determination of the structure of the redesigned nuclease-recognition site complex by X-ray crystallography confirms the accuracy of the computationally predicted interface. These results suggest that computational protein design methods can have an important role in the creation of novel highly specific endonucleases for gene therapy and other applications.

  17. DNA targeting and cleavage by an engineered metalloprotein dimer.

    Science.gov (United States)

    Wong-Deyrup, Siu Wah; Prasannan, Charulata; Dupureur, Cynthia M; Franklin, Sonya J

    2012-03-01

    Nature has illustrated through numerous examples that protein dimerization has structural and functional advantages. We previously reported the design and characterization of an engineered "metallohomeodomain" protein (C2) based on a chimera of the EF-hand Ca-binding motif and the helix-turn-helix motif of homeodomains (Lim and Franklin in Protein Sci. 15:2159-2165, 2004). This small metalloprotein binds the hard metal ions Ca(II) and Ln(III) and interacts with DNA with modest sequence preference and affinity, yet exhibits only residual DNA cleavage activity. Here we have achieved substantial improvement in function by constructing a covalent dimer of this C2 module (F2) to create a larger multidomain protein. As assayed via fluorescence spectroscopy, this F2 protein binds Ca(II) more avidly (25-fold) than C2 on a per-domain basis; in gel shift selection experiments, metallated F2 exhibits a specificity toward 5'-TAATTA-3' sequences. Finally, Ca(2)F2 cleaves plasmid DNA and generates a linear product in a Ca(II)-dependent way, unlike the CaC2 monomer. To the best of our knowledge this activation of Ca(II) in the context of an EF-hand binding motif is unique and represents a significant step forward in the design of artificial metallonucleases by utilizing biologically significant metal ions.

  18. Sox11 Reduces Caspase-6 Cleavage and Activity.

    Directory of Open Access Journals (Sweden)

    Elaine Waldron-Roby

    Full Text Available The apoptotic cascade is an orchestrated event, whose final stages are mediated by effector caspases. Regulatory binding proteins have been identified for caspases such as caspase-3, -7, -8, and -9. Many of these proteins belong to the inhibitor of apoptosis (IAP family. By contrast, caspase-6 is not believed to be influenced by IAPs, and little is known about its regulation. We therefore performed a yeast-two-hybrid screen using a constitutively inactive form of caspase-6 for bait in order to identify novel regulators of caspase-6 activity. Sox11 was identified as a potential caspase-6 interacting protein. Sox11 was capable of dramatically reducing caspase-6 activity, as well as preventing caspase-6 self- cleavage. Several regions, including amino acids 117-214 and 362-395 within sox11 as well as a nuclear localization signal (NLS all contributed to the reduction in caspase-6 activity. Furthermore, sox11 was also capable of decreasing other effector caspase activity but not initiator caspases -8 and -9. The ability of sox11 to reduce effector caspase activity was also reflected in its capacity to reduce cell death following toxic insult. Interestingly, other sox proteins also had the ability to reduce caspase-6 activity but to a lesser extent than sox11.

  19. Large volume loss during cleavage formation, Hamburg sequence, Pennsylvania

    Science.gov (United States)

    Beutner, Edward C.; Charles, Emmanuel G.

    1985-11-01

    Green reduction spots in red slate of the Hamburg sequence exposed near Shartlesville, Pennsylvania, have axial ratios of 1.42:1.0:0.28 on the limbs of near-isoclinal folds and 1.0:0.79:0.41 in fold hinge zones. Conodont cusps and denticles within the reduction spots have been brittlely pulled apart and give independent measures of extension in various directions. Comparison of conodont extensions with reduction spot shapes on limbs and hinges indicates that sedimentary compaction of 44% preceded the tectonic strain associated with cleavage formation. This strain, having identical maximum extensions but greater shortening in fold hinges as compared to limbs, was characterized by 41% extension in X, no change in Y, 50% to 59% shortening in Z, and 29% to 42% tectonic volume loss. The general lack of directed overgrowths on grains reflects the large volume loss and contrasts with other slates, where deformation was an almost constant volume process and extension in X compensated for shortening in Z. *Present address: Department of Geology, Miami University, Oxford, Ohio 45056

  20. Irreversible and reversible topoisomerase II DNA cleavage stimulated by clerocidin: sequence specificity and structural drug determinants.

    Science.gov (United States)

    Binaschi, M; Zagotto, G; Palumbo, M; Zunino, F; Farinosi, R; Capranico, G

    1997-05-01

    In contrast to other topoisomerase II poisons, the microbial terpenoid clerocidin was shown to stimulate irreversible topoisomerase II-mediated DNA cleavage. To establish the structural determinants for drug activity, in this study we have investigated intensity patterns and sequence specificity of clerocidin-stimulated DNA cleavage using 5'-end 32P-labeled DNA fragments. At a majority of the sites, clerocidin-stimulated cleavage did not revert upon NaCl addition; nevertheless, at some sites, cleavage completely reverted. Statistical analyses showed that drug-preferred bases were different in the two cases: guanine and cytosine were highly preferred at position -1 at irreversible and reversible sites, respectively. These results demonstrated that cleavage irreversibility was site selective and required a guanine at the 3' end of the cut. Further experiments revealed that some irreversible sites showed an abnormal electrophoretic mobility in sequencing gels with respect to cleaved bands generated by 4-(9-acridinylamino)methanesulfon-m-anisidide, suggesting a chemical alteration of the DNA strand. Interestingly, the ability to stimulate irreversible cleavage progressively decreased over time when clerocidin was stored in ethanol. Under these conditions, nuclear magnetic resonance measurements demonstrated that the drug underwent structural modifications that involved the C-12-C-15 side chain. Thus, the results indicate that a specific moiety of clerocidin may react with the DNA (guanine at -1) in the ternary complex, resulting in cleavage irreversibility and in altered DNA mobility in sequencing gels. PMID:9135013

  1. ASEAN+3 Bond Market Guides

    OpenAIRE

    Asian Development Bank (ADB)

    2012-01-01

    The ASEAN+3 Bond Market Guide contains the comprehensive reports of the ASEAN+3 Bond Market Forum Sub-Forum 1 (SF1) and Sub-Forum 2 (SF2). The SF1 report (Volume 1) analyzes the harmonization and standardization of the existing bond markets in the ASEAN+3. It also contains the individual market guides of 11 economies under the ASEAN+3 Bond Market Forum (ABMF). The SF2 report (Volume 2) provides an overview of the ASEAN+3 bond markets and their infrastructures, as well as issues confronted by ...

  2. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

    The paper examines the role of structured bonds in the optimal portfolio of a small retail investor. We consider the typical structured bond essentially repacking an exotic option and a zero coupon bond, i.e. an investment with portfolio insurance. The optimal portfolio is found when the investment...... opportunities consist of a risky reference fund, a risk-free asset and a structured bond. Key model elements are the trading strategy and utility function of the investor. Our numerical results indicate structured bonds do have basis for consideration in the optimal portfolio. The product holdings...

  3. Hydrogen bonding in ionic liquids.

    Science.gov (United States)

    Hunt, Patricia A; Ashworth, Claire R; Matthews, Richard P

    2015-03-01

    Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (ρBCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X-H σ* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak

  4. Transcriptome-Wide Cleavage Site Mapping on Cellular mRNAs Reveals Features Underlying Sequence-Specific Cleavage by the Viral Ribonuclease SOX.

    Directory of Open Access Journals (Sweden)

    Marta Maria Gaglia

    2015-12-01

    Full Text Available Many viruses express factors that reduce host gene expression through widespread degradation of cellular mRNA. An example of this class of proteins is the mRNA-targeting endoribonuclease SOX from the gamma-herpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV. Previous studies indicated that cleavage of messenger RNAs (mRNA by SOX occurs at specific locations defined by the sequence of the target RNA, which is at odds with the down-regulation of a large portion of cellular transcripts. In this study, we address this paradox by using high-throughput sequencing of cleavage intermediates combined with a custom bioinformatics-based analysis pipeline to identify SOX cleavage sites across the mRNA transcriptome. These data, coupled with targeted mutagenesis, reveal that while cleavage sites are specific and reproducible, they are defined by a degenerate sequence motif containing a small number of conserved residues rather than a strong consensus sequence. This degenerate element is well represented in both human and KSHV mRNA, and its presence correlates with RNA destabilization by SOX. This represents a new endonuclease targeting strategy, in which use of a degenerate targeting element enables RNA cleavage at specific locations without restricting the range of targets. Furthermore, it shows that strong target selectivity can be achieved without a high degree of sequence specificity.

  5. Intracellular ribozyme-catalyzed trans-cleavage of RNA monitored by fluorescence resonance energy transfer.

    Science.gov (United States)

    Vitiello, D; Pecchia, D B; Burke, J M

    2000-04-01

    Small catalytic RNAs like the hairpin ribozyme are proving to be useful intracellular tools; however, most attempts to demonstrate trans-cleavage of RNA by ribozymes in cells have been frustrated by rapid cellular degradation of the cleavage products. Here, we describe a fluorescence resonance energy transfer (FRET) assay that directly monitors cleavage of target RNA in tissue-culture cells. An oligoribonucleotide substrate was modified to inhibit cellular ribonuclease degradation without interfering with ribozyme cleavage, and donor (fluorescein) and acceptor (tetramethylrhodamine) fluorophores were introduced at positions flanking the cleavage site. In simple buffers, the intact substrate produces a strong FRET signal that is lost upon cleavage, resulting in a red-to-green shift in dominant fluorescence emission. Hairpin ribozyme and fluorescent substrate were microinjected into murine fibroblasts under conditions in which substrate cleavage can occur only inside the cell. A strong FRET signal was observed by fluorescence microscopy when substrate was injected, but rapid decay of the FRET signal occurred when an active, cognate ribozyme was introduced with the substrate. No acceleration in cleavage rates was observed in control experiments utilizing a noncleavable substrate, inactive ribozyme, or an active ribozyme with altered substrate specificity. Subsequently, the fluorescent substrates were injected into clonal cell lines that expressed cognate or noncognate ribozymes. A decrease in FRET signal was observed only when substrate was microinjected into cells expressing its cognate ribozyme. These results demonstrate trans-cleavage of RNA within mammalian cells, and provide an experimental basis for quantitative analysis of ribozyme activity and specificity within the cell. PMID:10786853

  6. Additional disulfide bonds in insulin

    DEFF Research Database (Denmark)

    Vinther, Tine N; Pettersson, Ingrid; Huus, Kasper;

    2015-01-01

    The structure of insulin, a glucose homeostasis-controlling hormone, is highly conserved in all vertebrates and stabilized by three disulfide bonds. Recently, we designed a novel insulin analogue containing a fourth disulfide bond located between positions A10-B4. The N-terminus of insulin's B......-chain is flexible and can adapt multiple conformations. We examined how well disulfide bond predictions algorithms could identify disulfide bonds in this region of insulin. In order to identify stable insulin analogues with additional disulfide bonds, which could be expressed, the Cβ cut-off distance had...... in comparison to analogues with additional disulfide bonds that were more difficult to predict. In contrast, addition of the fourth disulfide bond rendered all analogues resistant to fibrillation under stress conditions and all stable analogues bound to the insulin receptor with picomolar affinities. Thus...

  7. Synthesis of a Novel Organic Molecule for DNA Cleavage%新型有机小分子DNA切割试剂的合成

    Institute of Scientific and Technical Information of China (English)

    安东; 赵晓辉; 周密; 叶志文

    2014-01-01

    The artificial nucleic acid cleaving agents have attracted extensive attention due to their potential applications in molecular biological technology and drug development. Metal-free cleaving reagents have been considered safer for their hydrolytic pathway of cleaving the P-O bond of phosphodiester in nucleic acids and have shown clinical potential. It is known that guanidinium is the arginine residue and the key functionality at the active site in staphylococcal nuclease( SNase) for DNA hydrolysis. Some small organic molecules as guani-dinium derivatives have been used to cleave phosphodiester for DNA hydrolysis. We report here, according to active groups synergetic catalysis principle, the design and synthsis of a novel phosphodiester receptor 1-( N-guanidinoethyl)-4-( N-hydroxyethyl)-piperazidine hydrochloride ( 4 ) and the preliminary studies of its DNA cleavage activity. In the compound, the guanidinium group serves to recognize, bind, and electrophili-cally activate the anionic phosphodiester through hydrogen bonding and electrostatic interaction. The hydroxyl group works as a nucleophilic group in the transphosphorylation reaction, which is expected to be highly effi-cient because of the proximity effect. A “couple hardness with softness” piperazidine is designed to connect these two groups. Compound 4 was synthesized via a three-step reaction( nucleophilic substitution, hydrazinol-ysis and guanylation) . Its structure was confirmed by 1 H NMR, 13 C NMR and LC-MS. The influence of pH on the cleaving of pUC 19 DNA was studied by sugar gel electrophoresis. The mechanism of cleaving DNA by the compound was proved through the free radicals quenches experiments. The way of DNA cleavage was dis-cussed through density functional theory and theoretical investigation by Gaussian. The results indicate that with pH value of 7.2 is the optimal pH for DNA cleavage in the presence of compound 4 , the phosphodiester bond of DNA would be cleaved by compound 4 via a

  8. The short transcript of Leishmania RNA virus is generated by RNA cleavage.

    OpenAIRE

    MacBeth, K J; Patterson, J. L.

    1995-01-01

    Leishmania RNA virus 1 produces a short viral RNA transcript corresponding to the 5' end of positive-sense single-stranded RNAs both in virally infected cells and in in vitro polymerase assays. We hypothesized that this short transcript was generated via cleavage of full-length positive-sense single-stranded RNA. A putative cleavage site was mapped by primer extension analysis to nucleotide 320 of the viral genome. To address the hypothesis that the short transcript is generated via cleavage ...

  9. Guest-host interactions in the cleavage of phenylphenyl acetates by -cyclodextrin in alkaline medium

    Indian Academy of Sciences (India)

    V Raj; T Chandrakala; K Rajasekaran

    2008-05-01

    Kinetics of cleavage of phenylphenyl acetates (PPA) and several para-substituted PPAs in basic aqueous sodium carbonate-bicarbonate buffer containing -cyclodextrin (CD) have been studied. The reaction exhibits saturation type kinetics and CD accelerates the rate of cleavage by the formation of 1G : 1H inclusion complex. The kinetic results indicate that aryloxy moiety of PPA is included in the hydrophobic cavity of CD. The overall rate constants for the cleavage of the [CD-ester] complex correlate with the Hammett -constants and Hansch hydrophobicity parameters . At higher concentrations of CD, there is an additional catalysis due to the formation of weak 1G : 2H complex.

  10. Enhanced cleavage of type II collagen by collagenases in osteoarthritic articular cartilage.

    OpenAIRE

    Billinghurst, R.C.; Dahlberg, L; Ionescu, M.; Reiner, A; Bourne, R; Rorabeck, C; Mitchell, P; Hambor, J; Diekmann, O.; Tschesche, H; Chen, J; Van Wart, H; Poole, A. R.

    1997-01-01

    We demonstrate the direct involvement of increased collagenase activity in the cleavage of type II collagen in osteoarthritic human femoral condylar cartilage by developing and using antibodies reactive to carboxy-terminal (COL2-3/4C(short)) and amino-terminal (COL2-1/4N1) neoepitopes generated by cleavage of native human type II collagen by collagenase matrix metalloproteinase (MMP)-1 (collagenase-1), MMP-8 (collagenase-2), and MMP-13 (collagenase-3). A secondary cleavage followed the initia...

  11. Processing of pestivirus polyprotein: cleavage site between autoprotease and nucleocapsid protein of classical swine fever virus.

    OpenAIRE

    Stark, R; Meyers, G; Rümenapf, T.; Thiel, H J

    1993-01-01

    The polyprotein of classical swine fever virus starts with the nonstructural protein p23, which is followed by the nucleocapsid protein p14. Proteolytic cleavage between p23 and p14 was demonstrated in a cell-free transcription-translation system. Successive truncation of the cDNA used for the transcription indicated that the proteolytic activity responsible for the cleavage between p23 and p14 resides within p23. In order to determine the cleavage site between these two proteins, the respect...

  12. Preferential DNA Cleavage under Anaerobic Conditions by a DNA Binding Ruthenium Dimer

    OpenAIRE

    Janaratne, Thamara K.; Ongeri, Fiona; Yadav, Abishek; MacDonnell, Frederick M.

    2007-01-01

    In the absence of O2, the cationic complex, [(phen)2Ru(tatpp)Ru(phen)2]4+ (P4+), undergoes in situ reduction by glutathione (GSH) to form a species that induces DNA cleavage. Exposure to air strongly attenuates the cleavage activity, even in the presence of a large excess of reducing agent (e.g., 40 equiv GSH per P4+) suggesting the complex may be useful in targeting cells with a low oxygen microenvironment (hypoxia) for destruction via DNA cleavage. The active species is identified as the do...

  13. Mechanisms of RNAi: mRNA cleavage fragments may indicate stalled RISC

    OpenAIRE

    Holen, Torgeir

    2005-01-01

    The molecular mechanism of RNA interference (RNAi) is under intense investigation. We previously demonstrated the existence of inactive siRNAs and also of mRNA cleavage in vivo in human cells. Here it is shown that some siRNAs with low activity leave mRNA cleavage fragments while an siRNA with higher activity does not. The pattern is consistent with both short-term (4-24 hours) and long-term (1-4 days) time-series. Analysis of the putative 3′ mRNA cleavage product showed high GC content immed...

  14. C-H bond activation by metal-superoxo species: what drives high reactivity?

    Science.gov (United States)

    Ansari, Azaj; Jayapal, Prabha; Rajaraman, Gopalan

    2015-01-01

    Metal-superoxo species are ubiquitous in metalloenzymes and bioinorganic chemistry and are known for their high reactivity and their ability to activate inert C-H bonds. The comparative oxidative abilities of M-O2(.-) species (M = Cr(III), Mn(III), Fe(III), and Cu(II)) towards C-H bond activation reaction are presented. These superoxo species generated by oxygen activation are found to be aggressive oxidants compared to their high-valent metal-oxo counterparts generated by O⋅⋅⋅O bond cleavage. Our calculations illustrate the superior oxidative abilities of Fe(III)- and Mn(III)-superoxo species compared to the others and suggest that the reactivity may be correlated to the magnetic exchange parameter.

  15. Degradation of β-Aryl Ether Bonds in Transgenic Plants

    DEFF Research Database (Denmark)

    Mnich, Ewelina

    system to degrade lignin. An important step in this degradation is cleavage of the most abundant lignin linkage type, β-aryl ether. It is cleaved in a three step reaction catalyzed by a dehydrogenase, a glutathione S-transferase and a glutathione lyase. Due to the nature of the enzymatic reactions...... of the cell wall. The aim of the study was to alter lignin structure by expression in plants of the enzymes from S. paucimobilis involved in ether bond degradation (LigDFG). Arabidopsis thaliana and Brachypodium distachyon transgenic lines were generated and characterized with respect to lignin structure...... be degraded by LigDFG, which can presumably cause loosening of the lignin-ferulate-polysaccharide matrix. In a xylanase hydrolysis of Brachypodium transgenic stems, the release of arabinose and xylose was increased compared to wild type. The data presented demonstrate that introduction of lignin degrading...

  16. A Cytochrome P450-Mediated Intramolecular Carbon-Carbon Ring Closure in the Biosynthesis of Multidrug-Resistance-Reversing Lathyrane Diterpenoids.

    Science.gov (United States)

    King, Andrew J; Brown, Geoffrey D; Gilday, Alison D; Forestier, Edith; Larson, Tony R; Graham, Ian A

    2016-09-01

    The Euphorbiaceae produce a wide variety of bioactive diterpenoids. These include the lathyranes, which have received much interest due to their ability to inhibit the ABC transporters responsible for the loss of efficacy of many chemotherapy drugs. The lathyranes are also intermediates in the biosynthesis of range of other bioactive diterpenoids with potential applications in the treatment of pain, HIV and cancer. We report here a gene cluster from Jatropha curcas that contains the genes required to convert geranylgeranyl pyrophosphate into a number of diterpenoids, including the lathyranes jolkinol C and epi-jolkinol C. The conversion of casbene to the lathyranes involves an intramolecular carbon-carbon ring closure. This requires the activity of two cytochrome P450s that we propose form a 6-hydroxy-5,9-diketocasbene intermediate, which then undergoes an aldol reaction. The discovery of the P450 genes required to convert casbene to lathyranes will allow the scalable heterologous production of these potential anticancer drugs, which can often only be sourced in limited quantities from their native plant. PMID:27272333

  17. Structural characteristics and formation mechanisms of crack-free multilayer TaC/SiC coatings on carbon-carbon composites

    Institute of Scientific and Technical Information of China (English)

    LI Guo-dong; XIONG Xiang; HUANG Bai-yun; HUANG Ke-long

    2008-01-01

    In order to improve high temperature (over 2 273 K) ablation resistance, TaC and TaC/SiC composite coatings were deposited on carbon-carbon composites by CVD method utilizing reactive TaCl5-C3H6-H2-Ar and TaCl5-C3H6-CH3SiCl3-H2-Ar systems respectively. The structure and morphology of these coatings were analyzed by XRD and SEM. The results show that the double carbide coatings have good chemical compatibility during preparation. Two distinctive composition gradients are developed and used to produce multilayer TaC/SiC coatings with low internal stress, free crack and good resistant to thermal shock. A transition layer consisting of either C-TaC or C-SiC formed between the coating and the C/C matrix can reduce the residual stress effectively. The processing parameters were optimized and the possible growth mechanisms for these coatings were proposed. A designing methodology to prepare high performance multilayer TaC/SiC composite coatings was developed.

  18. High energy flux thermo-mechanical test of 1D-carbon-carbon fibre composite prototypes for the SPIDER diagnostic calorimeter

    Energy Technology Data Exchange (ETDEWEB)

    De Muri, M., E-mail: michela.demuri@igi.cnr.it; Pasqualotto, R.; Dalla Palma, M.; Cervaro, V.; Fasolo, D.; Franchin, L.; Tollin, M.; Serianni, G. [Consorzio RFX, Euratom-ENEA association, Corso Stati Uniti 4, 35127 Padova (Italy); Cavallin, T. [Istituto per l’Energetica e le Interfasi, Corso Stati Uniti 4, 35127 Padova (Italy); Greuner, H.; Böswirth, B. [Max-Planck-Institut für Plasmaphysik, D-85748 Garching bei München (Germany)

    2014-02-15

    Operation of the thermonuclear fusion experiment ITER requires additional heating via injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction in Padova, the production of negative ions will be studied and optimised. STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) is a diagnostic used to characterise the SPIDER beam during short pulse operation (several seconds) to verify if the beam meets the ITER requirements about the maximum allowed beam non-uniformity (below ±10%). The major components of STRIKE are 16 1D-CFC (Carbon-Carbon Fibre Composite) tiles, observed at the rear side by a thermal camera. This contribution gives an overview of some tests under high energy particle flux, aimed at verifying the thermo-mechanical behaviour of several CFC prototype tiles. The tests were performed in the GLADIS facility at IPP (Max-Plank-Institut für Plasmaphysik), Garching. Dedicated linear and nonlinear simulations were carried out to interpret the experiments and a comparison of the experimental data with the simulation results is presented. The results of some morphological and structural studies on the material after exposure to the GLADIS beam are also given.

  19. High energy flux thermo-mechanical test of 1D-carbon-carbon fibre composite prototypes for the SPIDER diagnostic calorimeter.

    Science.gov (United States)

    De Muri, M; Cavallin, T; Pasqualotto, R; Dalla Palma, M; Cervaro, V; Fasolo, D; Franchin, L; Tollin, M; Greuner, H; Böswirth, B; Serianni, G

    2014-02-01

    Operation of the thermonuclear fusion experiment ITER requires additional heating via injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction in Padova, the production of negative ions will be studied and optimised. STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) is a diagnostic used to characterise the SPIDER beam during short pulse operation (several seconds) to verify if the beam meets the ITER requirements about the maximum allowed beam non-uniformity (below ±10%). The major components of STRIKE are 16 1D-CFC (Carbon-Carbon Fibre Composite) tiles, observed at the rear side by a thermal camera. This contribution gives an overview of some tests under high energy particle flux, aimed at verifying the thermo-mechanical behaviour of several CFC prototype tiles. The tests were performed in the GLADIS facility at IPP (Max-Plank-Institut für Plasmaphysik), Garching. Dedicated linear and nonlinear simulations were carried out to interpret the experiments and a comparison of the experimental data with the simulation results is presented. The results of some morphological and structural studies on the material after exposure to the GLADIS beam are also given.

  20. Synthesis and Characterization of Graphene and Graphene Oxide Based Palladium Nanocomposites and Their Catalytic Applications in Carbon-Carbon Cross-Coupling Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Minjae [Kunsan National Univ., Gunsan (Korea, Republic of); Kim, Bohyun; Lee, Yuna; Kim, Beomtae; Park, Joon B. [Chonbuk National Univ., Jeonju (Korea, Republic of)

    2014-07-15

    We have developed an efficient method to generate highly active Pd and PdO nanoparticles (NPs) dispersed on graphene and graphene oxide (GO) by an impregnation method combined with thermal treatments in H{sub 2} and O{sub 2} gas flows, respectively. The Pd NPs supported on graphene (Pd/G) and the PdO NPs supported on GO (PdO/GO) demonstrated excellent carbon-carbon cross-coupling reactions under a solvent-free, environmentally-friendly condition. The morphological and chemical structures of PdO/GO and Pd/G were fully characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). We found that the remarkable reactivity of the Pd/G and PdO/GO catalysts toward the cross-coupling reaction is attributed to the high degree of dispersion of the Pd and PdO NPs while the oxidative states of Pd and the oxygen functionalities of graphene oxide are not critical for their catalytic performance.