WorldWideScience

Sample records for bond formation catalysed

  1. Carbon–heteroatom bond formation catalysed by organometallic complexes

    OpenAIRE

    Hartwig, John F.

    2008-01-01

    At one time the synthetic chemist’s last resort, reactions catalysed by transition metals are now the preferred method for synthesizing many types of organic molecule. A recent success in this type of catalysis is the discovery of reactions that form bonds between carbon and heteroatoms (such as nitrogen, oxygen, sulphur, silicon and boron) via complexes of transition metals with amides, alkoxides, thiolates, silyl groups or boryl groups. The development of these catalytic processes has been ...

  2. The first organocatalytic carbonyl-ene reaction: isomerisation-free C-C bond formations catalysed by H-bonding thio-ureas

    Directory of Open Access Journals (Sweden)

    Jones Charlotte ES

    2007-09-01

    Full Text Available Abstract Intramolecular carbonyl ene reactions of highly activated enophiles can be catalysed by H-bonding thio-ureas to give tertiary alcohols in high yields without extensive isomerisation side products. An asymmetric variant of this reaction was realised using a chiral thiourea but was limited by low enantioselectivity (up to 33% e.e. and low turnover frequencies.

  3. Formation mechanism of diamond nanocrystal from catalysed carbon black

    International Nuclear Information System (INIS)

    Recently, our group has synthesized nanocrystal n-diamond and diamond-like carbon (DLC) from catalysed carbon black. Based on the results of XRD, TGA and DTA, a formation mechanism has been proposed to explain the phase transformation from carbon black to diamond nanocrystal. With the increase of temperature and hence the carbon diffusion in iron, the phase sequence is from Fe(OH)3 into Fe2O3, α-Fe, γ-Fe, then liquid iron. When the carbon in the liquid iron is saturated, DLC or graphite separates out of the liquid iron. With decrease of temperature, the carbon in γ-Fe is separated out, and n-diamond nuclei form and grow

  4. Formation mechanism of diamond nanocrystal from catalysed carbon black

    Science.gov (United States)

    Wen, Bin; Li, Tingju; Dong, Chuang; Zhang, Xingguo; Yao, Shan; Cao, Zhiqiang; Wang, Dehe; Ji, Shouhua; Jin, Junze

    2004-10-01

    Recently, our group has synthesized nanocrystal n-diamond and diamond-like carbon (DLC) from catalysed carbon black. Based on the results of XRD, TGA and DTA, a formation mechanism has been proposed to explain the phase transformation from carbon black to diamond nanocrystal. With the increase of temperature and hence the carbon diffusion in iron, the phase sequence is from Fe(OH)3 into Fe2O3, agr-Fe, ggr-Fe, then liquid iron. When the carbon in the liquid iron is saturated, DLC or graphite separates out of the liquid iron. With decrease of temperature, the carbon in ggr-Fe is separated out, and n-diamond nuclei form and grow.

  5. Formation mechanism of diamond nanocrystal from catalysed carbon black

    Energy Technology Data Exchange (ETDEWEB)

    Wen Bin [Department of Materials Engineering, Dalian University of Technology, Dalian 116023 (China); Li Tingju [Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023 (China); Dong Chuang [Department of Materials Engineering, Dalian University of Technology, Dalian 116023 (China); Zhang Xingguo [Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023 (China); Yao Shan [Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023 (China); Cao Zhiqiang [Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023 (China); Wang Dehe [Department of Materials Engineering, Dalian University of Technology, Dalian 116023 (China); Ji Shouhua [Department of Materials Engineering, Dalian University of Technology, Dalian 116023 (China); Jin Junze [Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023 (China)

    2004-10-06

    Recently, our group has synthesized nanocrystal n-diamond and diamond-like carbon (DLC) from catalysed carbon black. Based on the results of XRD, TGA and DTA, a formation mechanism has been proposed to explain the phase transformation from carbon black to diamond nanocrystal. With the increase of temperature and hence the carbon diffusion in iron, the phase sequence is from Fe(OH){sub 3} into Fe{sub 2}O{sub 3}, {alpha}-Fe, {gamma}-Fe, then liquid iron. When the carbon in the liquid iron is saturated, DLC or graphite separates out of the liquid iron. With decrease of temperature, the carbon in {gamma}-Fe is separated out, and n-diamond nuclei form and grow.

  6. Metal-catalysed azidation of tertiary C-H bonds suitable for late-stage functionalization

    Science.gov (United States)

    Sharma, Ankit; Hartwig, John F.

    2015-01-01

    Many enzymes oxidize unactivated aliphatic C-H bonds selectively to form alcohols; however, biological systems do not possess enzymes that catalyse the analogous aminations of C-H bonds. The absence of such enzymes limits the discovery of potential medicinal candidates because nitrogen-containing groups are crucial to the biological activity of therapeutic agents and clinically useful natural products. In one prominent example illustrating the importance of incorporating nitrogen-based functionality, the conversion of the ketone of erythromycin to the -N(Me)CH2- group in azithromycin leads to a compound that can be dosed once daily with a shorter treatment time. For such reasons, synthetic chemists have sought catalysts that directly convert C-H bonds to C-N bonds. Most currently used catalysts for C-H bond amination are ill suited to the intermolecular functionalization of complex molecules because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C-H bonds, or reagents containing specialized groups on the nitrogen atom. Among C-H bond amination reactions, those forming a C-N bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to form from ketones or alcohols that might be created in a biosynthetic pathway by oxidation. Here we report a mild, selective, iron-catalysed azidation of tertiary C-H bonds that occurs without excess of the valuable substrate. The reaction tolerates aqueous environments and is suitable for the functionalization of complex structures in the late stages of a multistep synthesis. Moreover, this azidation makes it possible to install a range of nitrogen-based functional groups, including those from Huisgen `click' cycloadditions and the Staudinger ligation. We anticipate that these reactions will create opportunities to modify natural products, their precursors and their derivatives to produce analogues that contain different polarity and charge as a

  7. Carbon-sulfur bond-forming reaction catalysed by the radical SAM enzyme HydE.

    Science.gov (United States)

    Rohac, Roman; Amara, Patricia; Benjdia, Alhosna; Martin, Lydie; Ruffié, Pauline; Favier, Adrien; Berteau, Olivier; Mouesca, Jean-Marie; Fontecilla-Camps, Juan C; Nicolet, Yvain

    2016-05-01

    Carbon-sulfur bond formation at aliphatic positions is a challenging reaction that is performed efficiently by radical S-adenosyl-L-methionine (SAM) enzymes. Here we report that 1,3-thiazolidines can act as ligands and substrates for the radical SAM enzyme HydE, which is involved in the assembly of the active site of [FeFe]-hydrogenase. Using X-ray crystallography, in vitro assays and NMR spectroscopy we identified a radical-based reaction mechanism that is best described as the formation of a C-centred radical that concomitantly attacks the sulfur atom of a thioether. To the best of our knowledge, this is the first example of a radical SAM enzyme that reacts directly on a sulfur atom instead of abstracting a hydrogen atom. Using theoretical calculations based on our high-resolution structures we followed the evolution of the electronic structure from SAM through to the formation of S-adenosyl-L-cysteine. Our results suggest that, at least in this case, the widely proposed and highly reactive 5'-deoxyadenosyl radical species that triggers the reaction in radical SAM enzymes is not an isolable intermediate. PMID:27102684

  8. Carbon–sulfur bond-forming reaction catalysed by the radical SAM enzyme HydE

    Science.gov (United States)

    Rohac, Roman; Amara, Patricia; Benjdia, Alhosna; Martin, Lydie; Ruffié, Pauline; Favier, Adrien; Berteau, Olivier; Mouesca, Jean-Marie; Fontecilla-Camps, Juan C.; Nicolet, Yvain

    2016-05-01

    Carbon–sulfur bond formation at aliphatic positions is a challenging reaction that is performed efficiently by radical S-adenosyl-L-methionine (SAM) enzymes. Here we report that 1,3-thiazolidines can act as ligands and substrates for the radical SAM enzyme HydE, which is involved in the assembly of the active site of [FeFe]-hydrogenase. Using X-ray crystallography, in vitro assays and NMR spectroscopy we identified a radical-based reaction mechanism that is best described as the formation of a C-centred radical that concomitantly attacks the sulfur atom of a thioether. To the best of our knowledge, this is the first example of a radical SAM enzyme that reacts directly on a sulfur atom instead of abstracting a hydrogen atom. Using theoretical calculations based on our high-resolution structures we followed the evolution of the electronic structure from SAM through to the formation of S-adenosyl-L-cysteine. Our results suggest that, at least in this case, the widely proposed and highly reactive 5‧-deoxyadenosyl radical species that triggers the reaction in radical SAM enzymes is not an isolable intermediate.

  9. Protein folding guides disulfide bond formation

    OpenAIRE

    Qin, Meng; Wang, Wei; Thirumalai, D.

    2015-01-01

    Anfinsen inferred the principles of protein folding by studying a protein containing four disulfide bonds in the native state. However, how protein folding drives disulfide bond formation is poorly understood despite the role such proteins play in variety of extracellular and intracellular functions. We developed a method to mimic the complex chemistry of disulfide bond formation in molecular simulations, which is used to decipher the mechanism of folding of bovine pancreatic trypsin inhibito...

  10. Halogen-bonding-triggered supramolecular gel formation.

    OpenAIRE

    Meazza, L.; Foster, J. A.; Fucke, K.; Metrangolo, P.; Resnati, G.; Steed, J. W.

    2013-01-01

    Supramolecular gels are topical soft materials involving the reversible formation of fibrous aggregates using non-covalent interactions. There is significant interest in controlling the properties of such materials by the formation of multicomponent systems, which exhibit non-additive properties emerging from interaction of the components. The use of hydrogen bonding to assemble supramolecular gels in organic solvents is well established. In contrast, the use of halogen bonding to trigger sup...

  11. Highly Enantioselective Formation of α-Allyl-α-Arylcyclopentanones via Pd-Catalysed Decarboxylative Asymmetric Allylic Alkylation.

    Science.gov (United States)

    Akula, Ramulu; Doran, Robert; Guiry, Patrick J

    2016-07-11

    A highly enantioselective Pd-catalysed decarboxylative asymmetric allylic alkylation of cyclopentanone derived α-aryl-β-keto esters employing the (R,R)-ANDEN-phenyl Trost ligand has been developed. The product (S)-α-allyl-α-arylcyclopentanones were obtained in excellent yields and enantioselectivities (up to >99.9 % ee). This represents one of the most highly enantioselective formations of an all-carbon quaternary stereogenic center reported to date. This reaction was demonstrated on a 4.0 mmol scale without any deterioration of enantioselectivity and was exploited as the key enantioselective transformation in an asymmetric formal synthesis of the natural product (+)-tanikolide. PMID:27191198

  12. 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.

  13. Orbital entanglement in bond-formation processes

    CERN Document Server

    Boguslawski, Katharina; Barcza, Gergely; Legeza, Ors; Reiher, Markus

    2013-01-01

    The accurate calculation of the (differential) correlation energy is central to the quantum chemical description of bond-formation and bond-dissociation processes. In order to estimate the quality of single- and multi-reference approaches for this purpose, various diagnostic tools have been developed. In this work, we elaborate on our previous observation [J. Phys. Chem. Lett. 3, 3129 (2012)] that one- and two-orbital-based entanglement measures provide quantitative means for the assessment and classification of electron correlation effects among molecular orbitals. The dissociation behavior of some prototypical diatomic molecules features all types of correlation effects relevant for chemical bonding. We demonstrate that our entanglement analysis is convenient to dissect these electron correlation effects and to provide a conceptual understanding of bond-forming and bond-breaking processes from the point of view of quantum information theory.

  14. Orbital entanglement in bond-formation processes

    OpenAIRE

    Boguslawski, Katharina; Tecmer, Pawel; Barcza, Gergely; Legeza, Ors; Reiher, Markus

    2013-01-01

    The accurate calculation of the (differential) correlation energy is central to the quantum chemical description of bond-formation and bond-dissociation processes. In order to estimate the quality of single- and multi-reference approaches for this purpose, various diagnostic tools have been developed. In this work, we elaborate on our previous observation [J. Phys. Chem. Lett. 3, 3129 (2012)] that one- and two-orbital-based entanglement measures provide quantitative means for the assessment a...

  15. Halogen-bonding-triggered supramolecular gel formation

    Science.gov (United States)

    Meazza, Lorenzo; Foster, Jonathan A.; Fucke, Katharina; Metrangolo, Pierangelo; Resnati, Giuseppe; Steed, Jonathan W.

    2013-01-01

    Supramolecular gels are topical soft materials involving the reversible formation of fibrous aggregates using non-covalent interactions. There is significant interest in controlling the properties of such materials by the formation of multicomponent systems, which exhibit non-additive properties emerging from interaction of the components. The use of hydrogen bonding to assemble supramolecular gels in organic solvents is well established. In contrast, the use of halogen bonding to trigger supramolecular gel formation in a two-component gel (‘co-gel’) is essentially unexplored, and forms the basis for this study. Here, we show that halogen bonding between a pyridyl substituent in a bis(pyridyl urea) and 1,4-diiodotetrafluorobenzene brings about gelation, even in polar media such as aqueous methanol and aqueous dimethylsulfoxide. This demonstrates that halogen bonding is sufficiently strong to interfere with competing gel-inhibitory interactions and create a ‘tipping point’ in gel assembly. Using this concept, we have prepared a halogen bond donor bis(urea) gelator that forms co-gels with halogen bond acceptors.

  16. Shedding light on disulfide bond formation

    DEFF Research Database (Denmark)

    Ostergaard, H; Henriksen, A; Hansen, F G;

    2001-01-01

    To visualize the formation of disulfide bonds in living cells, a pair of redox-active cysteines was introduced into the yellow fluorescent variant of green fluorescent protein. Formation of a disulfide bond between the two cysteines was fully reversible and resulted in a >2-fold decrease...... in the intrinsic fluorescence. Inter conversion between the two redox states could thus be followed in vitro as well as in vivo by non-invasive fluorimetric measurements. The 1.5 A crystal structure of the oxidized protein revealed a disulfide bond-induced distortion of the beta-barrel, as well as a structural...... reorganization of residues in the immediate chromophore environment. By combining this information with spectroscopic data, we propose a detailed mechanism accounting for the observed redox state-dependent fluorescence. The redox potential of the cysteine couple was found to be within the physiological range...

  17. Vanillin formation from ferulic acid in Vanilla planifolia is catalysed by a single enzyme

    DEFF Research Database (Denmark)

    Gallage, Nethaji Janeshawari; Hansen, Esben Halkjær; Kannangara, Rubini Maya;

    2014-01-01

    Vanillin is a popular and valuable flavour compound. It is the key constituent of the natural vanilla flavour obtained from cured vanilla pods. Here we show that a single hydratase/lyase type enzyme designated vanillin synthase (VpVAN) catalyses direct conversion of ferulic acid and its glucoside...... into vanillin and its glucoside, respectively. The enzyme shows high sequence similarity to cysteine proteinases and is specific to the substitution pattern at the aromatic ring and does not metabolize caffeic acid and p-coumaric acid as demonstrated by coupled transcription/translation assays. Vp......-glucosyltransferases result in vanillyl alcohol glucoside formation from endogenous ferulic acid. A gene encoding an enzyme showing 71% sequence identity to VpVAN was identified in another vanillin-producing plant species Glechoma hederacea and was also shown to be a vanillin synthase as demonstrated by transient expression...

  18. Antibody catalysis of peptide bond formation.

    OpenAIRE

    Jacobsen, J R; Schultz, P. G.

    1994-01-01

    An antibody generated against a neutral phosphonate diester transition-state (TS not equal to) analog catalyzes the formation of an amide bond between a phenylalanyl amino group and an acyl azide derived from L-alanine. The antibody is selective for L- vs. D-alanine and does not catalyze the hydrolysis of the acyl azide to an appreciable degree. A rate acceleration of 10,000-fold relative to the uncatalyzed reaction is observed. The antibody may achieve its catalytic efficiency both by acting...

  19. Optimisation of onion peroxidase-catalysed formation of aureusidin using 2',4',6',3,4-pentahydroxy chalcone as substrate

    Directory of Open Access Journals (Sweden)

    SONIA MOUSSOUNI

    2014-08-01

    Full Text Available Previous investigations demonstrated that crude peroxidase (POD obtained from onion solid wastes has the ability to catalyse the formation of the aurone aureusidin (ARS, using 2´,4´,6´,3,4-pentahydroxy chalcone (PHC as substrate, although this reaction under physiological conditions is mediated by a polyphenol oxidase-like enzyme, called aureusidin synthase (AS. In this study, a crude onion POD preparation was used to study the effect of some critical factors affecting the reaction, including reaction time, pH and temperature. The optimal set of conditions was identified by deploying central composite factorial design and response surface methodology. The results obtained showed that the optimum values for pH and temperature were 5 and 20°C, respectively, while time was found to exert a statistically non-significant effect. These values were the same or very close to optimal conditions found for structurally different onion POD substrates. The outcome was discussed with regard to the applicability of the onion POD as a versatile tool of biocatalysis.

  20. Alkyl Aryl Ether Bond Formation with PhenoFluor**

    OpenAIRE

    Shen, Xiao; Neumann, Constanze N.; Kleinlein, Claudia; Claudia, Nathaniel W.; Ritter, Tobias

    2015-01-01

    An alkyl aryl ether bond formation reaction between phenols and primary and secondary alcohols with PhenoFluor has been developed. The reaction features a broad substrate scope and tolerates many functional groups, and substrates that are challenging for more conventional ether bond forming processes may be coupled. A preliminary mechanistic study indicates reactivity distinct from conventional ether bond formation.

  1. Gold( i )-catalysed dehydrative formation of ethers from benzylic alcohols and phenols

    KAUST Repository

    Veenboer, Richard M. P.

    2015-01-01

    © The Royal Society of Chemistry 2015. We report the cross-dehydrative reaction of two alcohols to form unsymmetrical ethers using NHC-gold(i) complexes (NHC = N-heterocyclic carbene). Our progress in developing this reaction into a straightforward procedure is discussed in detail. The optimised methodology proceeds under mild reaction conditions and produces water as the sole by-product. The synthetic utility of this environmentally benign methodology is exemplified by the formation of a range of new ethers from readily available phenols bearing electron withdrawing substituents and secondary benzylic alcohols with various substituents. Finally, we present experimental results to account for the chemoselectivity obtained in these reactions.

  2. 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

  3. Protein nanopatterns by oxime bond formation.

    Science.gov (United States)

    Christman, Karen L; Broyer, Rebecca M; Schopf, Eric; Kolodziej, Christopher M; Chen, Yong; Maynard, Heather D

    2011-02-15

    Patterning proteins on the nanoscale is important for applications in biology and medicine. As feature sizes are reduced, it is critical that immobilization strategies provide site-specific attachment of the biomolecules. In this study, oxime chemistry was exploited to conjugate proteins onto nanometer-sized features. Poly(Boc-aminooxy tetra(ethylene glycol) methacrylate) was synthesized by free radical polymerization. The polymer was patterned onto silicon wafers using an electron beam writer. Trifluoroacetic acid removal of the Boc groups provided the desired aminooxy functionality. In this manner, patterns of concentric squares and contiguous bowtie shapes were fabricated with 150-170-nm wide features. Ubiquitin modified at the N-terminus with an α-ketoamide group and N(ε)-levulinyl lysine-modified bovine serum albumin were subsequently conjugated to the polymer nanopatterns. Protein immobilization was confirmed by fluorescence microscopy. Control studies on protected surfaces and using proteins presaturated with O-methoxyamine indicated that attachment occurred via oxime bond formation. PMID:21192671

  4. Cooperative domain type interlayer $sp^3$-bond formation in graphite

    OpenAIRE

    Nishioka, Keita; Nasu, Keiichiro

    2010-01-01

    Using the classical molecular dynamics and the semiempirical Brenner's potential, we theoretically study the interlayer sigma bond formation, as cooperative and nonlinear phenomena induced by visible light excitations of a graphite crystal. We have found several cases, wherein the excitations of certain lattice sites result in new interlayer bonds even at non-excited sites. We have also found that, a new interlayer bond is easier to be formed around a bond, if it is already existing. As many ...

  5. Vanillin formation from ferulic acid in Vanilla planifolia is catalysed by a single enzyme

    OpenAIRE

    Gallage, Nethaji Janeshawari; Hansen, Esben Halkjær; Kannangara, Rubini Maya; Olsen, Carl Erik; Motawie, Mohammed Saddik; Jørgensen, Kirsten; Holme, Inger; Hebelstrup, Kim; Grisoni, Michel; Møller, Birger Lindberg

    2014-01-01

    Vanillin is a popular and valuable flavour compound. It is the key constituent of the natural vanilla flavour obtained from cured vanilla pods. Here we show that a single hydratase/lyase type enzyme designated vanillin synthase (VpVAN) catalyses direct conversion of ferulic acid and its glucoside into vanillin and its glucoside, respectively. The enzyme shows high sequence similarity to cysteine proteinases and is specific to the substitution pattern at the aromatic ring and does not metaboli...

  6. Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds

    Directory of Open Access Journals (Sweden)

    Burkhard Koenig

    2011-01-01

    Full Text Available N-Arylated aliphatic and aromatic amines are important substituents in many biologically active compounds. In the last few years, transition-metal-mediated N-aryl bond formation has become a standard procedure for the introduction of amines into aromatic systems. While N-arylation of simple aromatic halides by simple amines works with many of the described methods in high yield, the reactions may require detailed optimization if applied to the synthesis of complex molecules with additional functional groups, such as natural products or drugs. We discuss and compare in this review the three main N-arylation methods in their application to the synthesis of biologically active compounds: Palladium-catalysed Buchwald–Hartwig-type reactions, copper-mediated Ullmann-type and Chan–Lam-type N-arylation reactions. The discussed examples show that palladium-catalysed reactions are favoured for large-scale applications and tolerate sterically demanding substituents on the coupling partners better than Chan–Lam reactions. Chan–Lam N-arylations are particularly mild and do not require additional ligands, which facilitates the work-up. However, reaction times can be very long. Ullmann- and Buchwald–Hartwig-type methods have been used in intramolecular reactions, giving access to complex ring structures. All three N-arylation methods have specific advantages and disadvantages that should be considered when selecting the reaction conditions for a desired C–N bond formation in the course of a total synthesis or drug synthesis.

  7. Enzyme mediated silicon-oxygen bond formation; the use of Rhizopus oryzae lipase, lysozyme and phytase under mild conditions.

    Science.gov (United States)

    Abbate, Vincenzo; Bassindale, Alan R; Brandstadt, Kurt F; Lawson, Rachel; Taylor, Peter G

    2010-10-21

    The potential for expanding the variety of enzymic methods for siloxane bond formation is explored. Three enzymes, Rhizopus oryzae lipase (ROL), lysozyme and phytase are reported to catalyse the condensation of the model compound, trimethylsilanol, formed in situ from trimethylethoxysilane, to produce hexamethyldisiloxane in aqueous media at 25 °C and pH 7. Thermal denaturation and reactant inhibition experiments were conducted to better understand the catalytic role of these enzyme candidates. It was found that enzyme activities were significantly reduced following thermal treatment, suggesting a potential key-role of the enzyme active sites in the catalysis. Similarly, residue-specific modification of the key-amino acids believed to participate in the ROL catalysis also had a significant effect on the silicon bio-catalysis, indicating that the catalytic triad of the lipase may be involved during the enzyme-mediated formation of the silicon-oxygen bond. E. coli phytase was found to be particularly effective at catalysing the condensation of trimethylsilanol in a predominantly organic medium consisting of 95% acetonitrile and 5% water. Whereas the use of enzymes in silicon chemistry is still very much a developing and frontier activity, the results presented herein give some grounds for optimism that the variety of enzyme mediated reactions will continue to increase and may one day become a routine element in the portfolio of the synthetic silicon chemist. PMID:20683529

  8. Formation of Embedded Microstructures by Thermal Activated Solvent Bonding

    CERN Document Server

    Ng, S H; Wang, Z F; Lu, A C W; Rodriguez, I; De Rooij, N

    2008-01-01

    We present a thermal activated solvent bonding technique for the formation of embedded microstrucutres in polymer. It is based on the temperature dependent solubility of polymer in a liquid that is not a solvent at room temperature. With thermal activation, the liquid is transformed into a solvent of the polymer, creating a bonding capability through segmental or chain interdiffusion at the bonding interface. The technique has advantages over the more commonly used thermal bonding due to its much lower operation temperature (30 degrees C lower than the material's Tg), lower load, as well as shorter time. Lap shear test indicated bonding shear strength of up to 2.9 MPa. Leak test based on the bubble emission technique showed that the bonded microfluidic device can withstand at least 6 bars (87 psi) of internal pressure (gauge) in the microchannel. This technique can be applied to other systems of polymer and solvent.

  9. Peptide catalysed prebiotic polymerization of RNA

    DEFF Research Database (Denmark)

    Wieczorek, Rafal; Luisi, Pier Luigi; Monnard, Pierre-Alain

    A short peptide composed of only two amino acid residues, serine and histidine, is here reported to enable oligomerization of RNA monomers. SerHis dipeptide was previously reported to catalyse formation of peptide bonds (Gorlero et al. 2009) as well as possessing broad hydrolytic activities...... oligomers from imidazole derivatives of mononucleotides. The thermodynamic shift towards condensation was achieved using water/ice eutectic phase environment (Monnard and Ziock 2008). To obtain such an environment, a reaction solution is cooled below its freezing point, but above the eutectic point. Under....... (2000) Dipeptide seryl-histidine and related oligopeptides cleave DNA, protein, and a carboxyl ester. Bioorg. Med. Chem. 8(12): 2675-80. Monnard PA, Ziock H. (2008) Eutectic phase in water-ice: a self-assembled environment conducive to metal-catalyzed non-enzymatic RNA polymerization. Chem Biodivers. 5...

  10. Interface formation and strength of Be/DSCu diffusion bonding

    Energy Technology Data Exchange (ETDEWEB)

    Makino, T. [NGK Insulators Ltd., Nagoya (Japan). Mater. Res. Lab.; Iwadachi, T. [NGK Insulators Ltd., Handa-city (Japan). New Metals Div.

    1998-10-01

    Beryllium has been proposed to be used as a plasma facing material of the first wall for ITER, and will be bonded by HIP process to dispersion strengthened copper (DSCu). Be/DSCu diffusion bonding tests in the range of temperature from 600 C to 850 C by hot pressing techniques have been conducted to identify the effect of bonding temperature and time on interface formation and joint strength. The bonded Be/DSCu joints were evaluated by microstructural analysis of the interface and shear strength tests at room temperature. The diffusion layer of directly bonded Be/DSCu joints and the joints with Be-Cu interlayer consisted of Be{sub 2}Cu({delta}) phase on the Be side and Cu + BeCu({gamma}) phase on the DSCu side, Cu + BeCu({gamma}) phase generated remarkably fast at 800-850 C. The thickness of the diffusion layer was linear to a square root of bonding time. Shear strength of the joints bonded at 650-750 C are all around 200 MPa. Shear strength is dominated by the formation of the layer of Be{sub 2}Cu({delta}) phase on the Be side. (orig.) 2 refs.

  11. Hydrophobic interactions and hydrogen bonds in \\beta-sheet formation

    CERN Document Server

    Narayanan, Chitra

    2013-01-01

    In this study, we investigate interactions of extended conformations of homodimeric peptides made of small (glycine or alanine) and large hydrophobic (valine or leucine) sidechains using all-atom molecular dynamics simulations to decipher driving forces for \\beta-sheet formation. We make use of a periodic boundary condition setup in which individual peptides are infinitely long and stretched. Dimers adopt \\beta-sheet conformations at short interpeptide distances (\\xi ~ 0.5 nm) and at intermediate distances (~ 0.8 nm), valine and leucine homodimers assume cross-\\beta-like conformations with side chains interpenetrating each other. These two states are identified as minima in the Potential of Mean Force (PMF). While the number of interpeptide hydrogen bonds increases with decreasing interpeptide distance, the total hydrogen bond number in the system does not change significantly, suggesting that formation of \\beta-sheet structures from extended conformations is not driven by hydrogen bonds. This is supported by...

  12. [2+2+2] cycloaddition reactions involving allenes catalysed by rhodium

    OpenAIRE

    Haraburda, Ewelina

    2015-01-01

    The development of new chemical processes for the formation of carbon-carbon bonds is an important topic in organic chemistry. In particular, the transition metal catalysed [2+2+2] cycloaddition reaction is a highly efficient synthetic tool that allows six-membered polysubstituted carbo- and heterocyclic derivatives to be obtained in an atom economy process. Allenes are versatile substrates for cycloaddition reactions that provide a good reactivity profile together with the ability to increas...

  13. Peptide Bond Formation in Water Mediated by Carbon Disulfide.

    Science.gov (United States)

    Leman, Luke J; Huang, Zheng-Zheng; Ghadiri, M Reza

    2015-09-01

    Demonstrating plausible nonenzymatic polymerization mechanisms for prebiotic monomers represents a fundamental goal in prebiotic chemistry. While a great deal is now known about the potentially prebiotic synthesis of amino acids, our understanding of abiogenic polymerization processes to form polypeptides is less well developed. Here, we show that carbon disulfide (CS2), a component of volcanic emission and sulfide mineral weathering, and a widely used synthetic reagent and solvent, promotes peptide bond formation in modest yields (up to ∼20%) from α-amino acids under mild aqueous conditions. Exposure of a variety of α-amino acids to CS2 initially yields aminoacyl dithiocarbamates, which in turn generate reactive 2-thiono-5-oxazolidone intermediates, the thio analogues of N-carboxyanhydrides. Along with peptides, thiourea and thiohydantoin species are produced. Amino acid stereochemistry was preserved in the formation of peptides. Our findings reveal that CS2 could contribute to peptide bond formation, and possibly other condensation reactions, in abiogenic settings. PMID:26308392

  14. Transition metal-catalyzed C(vinyl)-C(vinyl) bond formation via double C(vinyl)-H bond activation.

    Science.gov (United States)

    Shang, Xiaojie; Liu, Zhong-Quan

    2013-04-21

    Transition metal-catalyzed oxidative dehydrogenative coupling reactions of Caryl-H bonds with Cvinyl-H bonds to generate a Caryl-Cvinyl bonds have been well developed in recent decades. However, only a few studies have focused on the direct Cvinyl-Cvinyl bond formation via double Cvinyl-H bond activation. Recent developments in this active area have been highlighted in this tutorial review. PMID:23318664

  15. Formation of imines by selective gold-catalysed aerobic oxidative coupling of alcohols and amines under ambient conditions

    DEFF Research Database (Denmark)

    Kegnæs, Søren; Mielby, Jerrik Jørgen; Mentzel, Uffe Vie;

    2010-01-01

    The formation of imines by aerobic oxidative coupling of mixtures of alcohols and amines was studied using gold nanoparticles supported on titanium dioxide, TiO2, as a heterogeneous catalyst. The reactions were performed at ambient conditions (room temperature and atmospheric pressure) and occurr......-product represents a new green reaction protocol for imine formation....

  16. Ribosomal crystallography: peptide bond formation and its inhibition.

    Science.gov (United States)

    Bashan, Anat; Zarivach, Raz; Schluenzen, Frank; Agmon, Ilana; Harms, Joerg; Auerbach, Tamar; Baram, David; Berisio, Rita; Bartels, Heike; Hansen, Harly A S; Fucini, Paola; Wilson, Daniel; Peretz, Moshe; Kessler, Maggie; Yonath, Ada

    2003-09-01

    Ribosomes, the universal cellular organelles catalyzing the translation of genetic code into proteins, are protein/RNA assemblies, of a molecular weight 2.5 mega Daltons or higher. They are built of two subunits that associate for performing protein biosynthesis. The large subunit creates the peptide bond and provides the path for emerging proteins. The small has key roles in initiating the process and controlling its fidelity. Crystallographic studies on complexes of the small and the large eubacterial ribosomal subunits with substrate analogs, antibiotics, and inhibitors confirmed that the ribosomal RNA governs most of its activities, and indicated that the main catalytic contribution of the ribosome is the precise positioning and alignment of its substrates, the tRNA molecules. A symmetry-related region of a significant size, containing about two hundred nucleotides, was revealed in all known structures of the large ribosomal subunit, despite the asymmetric nature of the ribosome. The symmetry rotation axis, identified in the middle of the peptide-bond formation site, coincides with the bond connecting the tRNA double-helical features with its single-stranded 3' end, which is the moiety carrying the amino acids. This thus implies sovereign movements of tRNA features and suggests that tRNA translocation involves a rotatory motion within the ribosomal active site. This motion is guided and anchored by ribosomal nucleotides belonging to the active site walls, and results in geometry suitable for peptide-bond formation with no significant rearrangements. The sole geometrical requirement for this proposed mechanism is that the initial P-site tRNA adopts the flipped orientation. The rotatory motion is the major component of unified machinery for peptide-bond formation, translocation, and nascent protein progression, since its spiral nature ensures the entrance of the nascent peptide into the ribosomal exit tunnel. This tunnel, assumed to be a passive path for the

  17. Visible light induced C-C bond formation

    OpenAIRE

    Paria, Suva

    2015-01-01

    This Ph.D thesis demonstrates the development of new methodologies for C-C bond formation triggered by visible light photoredox catalysis. In Chapter 1, we have outlined a short overview on Copper in Photocatalysis. Starting from the photophysical properties of copper complexes, a comparison of main excited state aspects of prevalently used ruthenium and iridium complexes with that of copper has been shown. Several UV and visible light mediated synthetic transformation utilizing copper ca...

  18. Intermetallic compound formation at Cu-Al wire bond interface

    International Nuclear Information System (INIS)

    Intermetallic compound (IMC) formation and evolution at Cu-Al wire bond interface were studied using focused ion beam /scanning electron microscopy, transmission electron microscopy (TEM)/energy dispersive x-ray spectroscopy (EDS), nano beam electron diffraction (NBED) and structure factor (SF) calculation. It was found that discrete IMC patches were formed at the Cu/Al interface in as-packaged state and they grew toward Al pad after high temperature storage (HTS) environment at 150 °C. TEM/EDS and NBED results combined with SF calculation revealed the evidence of metastable θ′-CuAl2 IMC phase (tetragonal, space group: I4m2, a = 0.404 nm, c= 0.580 nm) formed at Cu/Al interfaces in both of the as-packaged and the post-HTS samples. Two feasible mechanisms for the formation of the metastable θ′-CuAl2 phase are discussed based on (1) non-equilibrium cooling of wire bond that is attributed to highly short bonding process time and (2) the epitaxial relationships between Cu and θ′-CuAl2, which can minimize lattice mismatch for θ′-CuAl2 to grow on Cu.

  19. Bond formation in ultrasonically welded aluminum sheet metal

    Science.gov (United States)

    Wilkosz, Daniel Edward

    Ultrasonic welding (USW), a solid state joining technology, has been used to bond aluminum alloys commonly used in the automotive industry. Bonding occurs due to USW's high frequency (˜20 kHz) in-plane vibration of sample interfaces while being held under moderate clamp pressure normal to the plane of vibration. Vibration and clamp pressure are transmitted into bond formation via contact with a weld-tip. To better understand how weld-tip geometry affected bond formation, experiments were conducted to quantify how tip geometry influenced plastic deformation characteristics between fully welded coupons of 0.9mm thick AA6111-T4 aluminum alloy. Weld-interface microstructure features were documented by optical microscopy and features quantified in a 19 point matrix. Correlation between microstructure features, such as rolling-wakes, and resulting weld bond strengths of more than 3.0kN is made. Weld zone microstructure features appear to result from deformation at and severe migration of the original weld interface during USW. To confirm this hypothesis, intrinsic and extrinsic markers were employed to monitor weld interface deformation characteristics. Various physical and analytical techniques were used in conjunction with these markers to show that joining of "like" and "dislike" aluminum samples is achieved through mechanical mixing of mating interfaces and not by elemental diffusion. It is also hypothesized that severe deformation of the original interface would result in areas of high residual strain within a formed weld zone. To investigate this and the influence that tip geometry may have on residual strain, fully welded samples were annealed at 500°C for a controlled period of time and recovery, recrystallization and grain growth characteristics were monitored. In all welds, initial recrystallization and grain growth occurred at the outer ends of weld zones and along weld interfaces where the most turbulent mixing and grain size reduction was observed

  20. Hydrogen Bond Formation between the Carotenoid Canthaxanthin and the Silanol Group on MCM-41 Surface.

    Science.gov (United States)

    Gao, Yunlong; Xu, Dayong; Kispert, Lowell D

    2015-08-20

    The formation of one or two hydrogen bonds (H-bonds) between canthaxanthin (CAN), a dye, and the silanol group(s) on the MCM-41 surface has been studied by density functional theory (DFT) calculations and calorimetric experiments. It was found that the formation of the H-bond(s) stabilized the CAN molecule more than its radical cation (CAN(•+)). The charge distribution, bond lengths, and the HOMO and LUMO energies of CAN are also affected. The formation of the H-bond(s) explains the lower photoinduced electron transfer efficiency of CAN imbedded in Cu-MCM-41 versus that for β-carotene (CAR) imbedded in Cu-MCM-41 where complex formation with Cu(2+) dominates. These calculations show that to achieve high electron transfer efficiency for a dye-sensitized solar cell, H-bonding between the dye and the host should be avoided. PMID:26230844

  1. Nickel-catalysed Suzuki-Miyaura coupling of amides

    Science.gov (United States)

    Weires, Nicholas A.; Baker, Emma L.; Garg, Neil K.

    2016-01-01

    The Suzuki-Miyaura coupling has become one of the most important and prevalent methods for the construction of C-C bonds. Although palladium catalysis has historically dominated the field, the use of nickel catalysis has become increasingly widespread because of its unique ability to cleave carbon-heteroatom bonds that are unreactive towards other transition metals. We report the first nickel-catalysed Suzuki-Miyaura coupling of amides, which proceeds by an uncommon cleavage of the amide C-N bond after N-tert-butoxycarbonyl activation. The methodology is mild, functional-group tolerant and can be strategically employed in sequential transition-metal-catalysed cross-coupling sequences to unite heterocyclic fragments. These studies demonstrate that amides, despite classically considered inert substrates, can be harnessed as synthons for use in reactions that form C-C bonds through cleavage of the C-N bond using non-precious metal catalysis.

  2. Formation of Silicon-Gold Eutectic Bond Using Localized Heating Method

    Science.gov (United States)

    Lin, Liwei; Cheng, Yu-Ting; Najafi, Khalil

    1998-11-01

    A new bonding technique is proposed by using localized heating to supplythe bonding energy.Heating is achieved by applying a dc current through micromachined heaters made of gold which serves as both the heating and bonding material.At the interface of silicon and gold, the formation of eutectic bond takes place in about 5 minutes.Assembly of two substrates in microfabrication processescan be achieved by using this method.In this paper the following important results are obtained:1) Gold diffuses into silicon to form a strong eutectic bond by means of localized heating.2) The bonding strength reaches the fracture toughness of the bulk silicon.3) This bonding technique greatly simplifies device fabrication andassembly processes.

  3. High Charge Mobility of a Perylene Bisimide Dye with Hydrogen-bond Formation Group

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    A perylene bisimide dye covalently bonded with a hydrogen-bond formation group of 1,3, 5-triazine-2, 4-diamine has been synthesized. Its casting films show a charge carrier mobility over 10-3 cm2/Vs, which is in the range of the highest values found for other promising charge transport materials suitable for solution processable technique.

  4. Mild Catalytic methods for Alkyl-Alkyl Bond Formation

    Energy Technology Data Exchange (ETDEWEB)

    Vicic, David A

    2009-08-10

    Overview of Research Goals and Accomplishments for the Period 07/01/06 – 06/30/07: Our overall research goal is to transform the rapidly emerging synthetic chemistry involving alkyl-alkyl cross-couplings into more of a mechanism-based field so that that new, rationally-designed catalysts can be performed under energy efficient conditions. Our specific objectives for the previous year were 1) to obtain a proper electronic description of an active catalyst for alkyl-alkyl cross-coupling reactions and 2) to determine the effect of ligand structure on the rate, scope, selectivity, and functional group compatibility of C(sp3)-C(sp3) cross-coupling catalysis. We have completed both of these initial objectives and established a firm base for further studies. The specific significant achievements of the current grant period include: 1) we have performed magnetic and computational studies on (terpyridine)NiMe, an active catalyst for alkyl-alkyl cross couplings, and have discovered that the unpaired electron resides heavily on the terpyridine ligand and that the proper electronic description of this nickel complex is a Ni(II)-methyl cation bound to a reduced terpyridine ligand; 2) we have for the first time shown that alkyl halide reduction by terpyridyl nickel catalysts is substantially ligand based; 3) we have shown by isotopic labeling studies that the active catalyst (terpyridine)NiMe is not produced via a mechanism that involves the formation of methyl radicals when (TMEDA)NiMe2 is used as the catalyst precursor; 4) we have performed an extensive ligand survey for the alkyl-alkyl cross-coupling reactions and have found that electronic factors only moderately influence reactivity in the terpyridine-based catalysis and that the most dramatic effects arise from steric and solubility factors; 5) we have found that the use of bis(dialkylphosphino)methanes as ligands for nickel does not produce active catalysts for cross-coupling but rather leads to bridging hydride

  5. Molecular and ionic hydrogen bond formation in fluorous solvents.

    Science.gov (United States)

    O'Neal, Kristi L; Weber, Stephen G

    2009-01-01

    There are only a few studies of noncovalent association in fluorous solvents and even fewer that are quantitative. A full understanding, particularly of stoichiometry and binding strength of noncovalent interactions in fluorous solvents could be very useful in improved molecular-receptor-based extractions, advancements in sensor technologies, crystal engineering, and supramolecular chemistry. This work investigates hydrogen bonding between heterocyclic bases and a perfluoropolyether with a terminal carboxylic acid group (Krytox 157FSH (1)), chiefly in FC-72 (a mixture of perfluorohexanes). In particular, we were interested in whether or not proton transfer occurs, and if so, under what conditions in H-bonded complexes. Continuous variations experiments show that in FC-72 weaker bases (pyrazine, pyrimidine, and quinazoline) form 1:1 complexes with 1, whereas stronger bases (quinoline, pyridine, and isoquinoline) form 1:3 complexes. Ultraviolet and infrared spectral signatures reveal that the 1:1 complexes are molecular (B.HA) whereas the 1:3 complexes are ionic (BH+.A-HAHA). Infrared spectra of 1:3 ionic complexes are discussed in detail. Literature and experimental data on complexes between N-heterocyclic bases and carboxylic acids in a range of solvents are compiled to compare solvent effects on proton transfer. Polar solvents support ionic hydrogen bonds at a 1:1 mol ratio. In nonpolar organic solvents, ionic hydrogen bonds are only observed in complexes with 1:2 (base/acid) stoichiometries. In fluorous solvents, a larger excess of acid, 1:3, is necessary to facilitate proton transfer in hydrogen bonds between carboxylic acids and the bases studied. PMID:19195102

  6. DNA Charge Transport Leading to Disulfide Bond Formation

    OpenAIRE

    Takada, Tadao; Barton, Jacqueline K.

    2005-01-01

    Here, we show that DNA-mediated charge transport (CT) can lead to the oxidation of thiols to form disulfide bonds in DNA. DNA assemblies were prepared possessing anthraquinone (AQ) as a photooxidant spatially separated on the duplex from two SH groups incorporated into the DNA backbone. Upon AQ irradiation, HPLC analysis reveals DNA ligated through a disulfide. The reaction efficiency is seen to vary in assemblies containing intervening DNA mismatches, confirming that the reaction is DNA-medi...

  7. Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

    that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific C-H bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site. A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of C-H bond functionalization reactions towards complex molecule synthesis. Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rh-catalyzed methods for C-H bond functionalization stand out, with several syntheses being described in the literature that utilize C-H bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.

  8. Covalent bonding and bandgap formation in intermetallic compounds: a case study for Al3V

    International Nuclear Information System (INIS)

    We demonstrate that a special hybridization between the Al(s, p) and V(d) orbitals which is responsible for forming of a deep pseudogap near the Fermi level in the Al3V compound is also associated with the formation of covalent bonds. We analyse the charge distribution in the elementary cell and find an enhanced charge density along the Al-V bonds and certain Al-Al bonds which is characteristic for covalent bonding. The role of the point-group symmetry and the character of the hybrid orbitals forming the covalent bonds are investigated. It is demonstrated that the deep pseudogap close to the Fermi level arises from the bonding-antibonding of the hybrid orbitals. (author)

  9. Exploring the atmospheric chemistry of O2SO3- and assessing the maximum turnover number of ion catalysed H2SO4 formation

    Directory of Open Access Journals (Sweden)

    H. Vehkamäki

    2012-11-01

    Full Text Available It has recently been demonstrated that the O2SO3− ion forms in the atmosphere as a natural consequence of ionizing radiation. Here, we present a density functional theory-based study of the reactions of O2SO3− with O3. The most important reactions are (a oxidation of O2SO3− to O3SO3− and (b cluster decomposition into SO3, O2 and O3−. The former reaction is highly exothermic and the nascent O3SO3− will rapidly decompose into SO4− and O2. If the origin of O2SO3− is SO2 oxidation by O3−, the latter reaction closes a catalytic cycle wherein SO2 is oxidized to SO3. The relative rates between the two major sinks for O2SO3− is assessed, thereby providing a measure of the maximum turnover number of ion catalysed SO2 oxidation, i.e. how many SO2 can be oxidized per free electron. The rate ratio between reactions (a and (b is significantly altered by the presence or absence of a single water molecule, but reaction (b is in general much more probable. Although we are unable to assess the overall importance of this cycle in the real atmosphere due to the unknown influence of CO2 and NOx, we roughly estimate that ion induced catalysis may contribute with several percent of H2SO4 levels in typical CO2 free and low NOx reaction chambers, e.g. the CLOUD chamber at CERN.

  10. Exploring the atmospheric chemistry of O2SO3− and assessing the maximum turnover number of ion-catalysed H2SO4 formation

    Directory of Open Access Journals (Sweden)

    N. Bork

    2013-04-01

    Full Text Available It has recently been demonstrated that the O2SO3− ion forms in the atmosphere as a natural consequence of ionizing radiation. Here, we present a density functional theory-based study of the reactions of O2SO3− with O3. The most important reactions are (a oxidation to O2SO3− and (b cluster decomposition into SO3, O2 and O3−. The former reaction is highly exothermic, and the nascent O2SO3− will rapidly decompose into SO4− and O2. If the origin of O2SO3− is SO2 oxidation by O3−, the latter reaction closes a catalytic cycle wherein SO2 is oxidized to SO3. The relative rate between the two major sinks for O2SO3− is assessed, thereby providing a measure of the maximum turnover number of ion-catalysed SO2 oxidation, i.e. how many SO2 can be oxidized per free electron. The rate ratio between reactions (a and (b is significantly altered by the presence or absence of a single water molecule, but reaction (b is in general much more probable. Although we are unable to assess the overall importance of this cycle in the real atmosphere due to the unknown influence of CO2 and NOx, we roughly estimate that ion-induced catalysis may contribute with several percent of H2SO4 levels in typical CO2-free and low NOx reaction chambers, e.g. the CLOUD chamber at CERN.

  11. "Pnicogen bonds" or "chalcogen bonds": exploiting the effect of substitution on the formation of PSe noncovalent bonds.

    Science.gov (United States)

    Shukla, Rahul; Chopra, Deepak

    2016-05-18

    In this article, we have analyzed the nature and characteristics of PSe noncovalent interactions by studying the effect of substitution on XH2PSeH2, H3PSeHX and XH2PSeHX (X= -H, -F, -CH3, -CF3, -Cl, -OH, -OCH3, -NH2, -NHCH3, and -CN) as our systems of interest at MP2/aug-cc-pVDZ level of theory. Binding energy calculations depict that binding energy increases in the order XH2PSeH2 < H3PSeHX < XH2PSeHX with the nature of the substituent having a direct effect on the strength of the interactions. PSe contacts as short as 2.52 Å were observed and analyzed in our study. The energy values for PSe contacts were found to exist in the range of -1.20 kcal mol(-1) to -7.89 kcal mol(-1). The topological analysis confirms the presence of PSe contacts in all the complexes with characteristics similar to hydrogen bonds. NBO analysis helped in categorizing these interactions into pnicogen and chalcogen bonds, depending on the strength of P(lp) to σ*(Se-X) orbitals or Se(lp) to σ*(P-X) orbitals. PMID:27145973

  12. Phase formation at bonded vanadium and stainless steel interfaces

    International Nuclear Information System (INIS)

    The interface between vanadium bonded to stainless steel was studies to determine whether a brittle phase formed during three joining operations. Inertia friction welds between V and 21-6-9 stainless steel were examined using TEM. In the as-welded condition, a continuous, polygranular intermetallic layer about 0.25 μm thick was present at the interface. This layer grew to about 50 μm thick during heat treatment at 1000 degrees C for two hours. Analysis of electron diffraction patterns confirmed that this intermetallic was the ω phase. The interface between vanadium and type 304, SANDVIK SAF 2205, and 21-6-9 stainless steel bonded by a co-extrusion process had intermetallic particles at the interface in the as-extruded condition. Heat treatment at 1000 degrees C for two hours caused these particles to grow into continuous layers in all three cases. Based on the appearance, composition and hardness of this interfacial intermetallic, it was also concluded to be ω phase. Bonding V to type 430 stainless steel by co-extrusion caused V-rich carbides to form at the interface due to the higher concentration of C in the type 430 than in the other stainless steels investigated. The carbide particles initially present grew into a continuous layer during a two-hour heat treatment at 1000 degrees C. Co-hipping 21-6-9 stainless steel tubing with V rod resulted in slightly more concentric specimens than the co-extruded ones, but a continuous layer of the ω phase formed during the hipping operation. This brittle layer could initiate failure during subsequent forming operations. The vanadium near the stainless steel interface in the co-extruded and co-hipped tubing in some cases was harder than before heat treatment. It was concluded that this hardening was due to thermal straining during cooling following heat treatment and that thermal strains might present a greater problem than seen here when longer tubes are used in actual applications

  13. Formation of RNA phosphodiester bond by histidine-containing dipeptides

    DEFF Research Database (Denmark)

    Wieczorek, Rafal; Dörr, Mark; Chotera, Agata;

    2013-01-01

    in self-organised environment, a water-ice eutectic phase, with low concentrations of reactants. Incubation periods up to 30 days resulted in the formation of short oligomers of RNA. During the oligomerisation, an active intermediate (dipeptide-mononucleotide) is produced, which is the reactive species...

  14. In vivo biofilm formation on stainless steel bonded retainers during different oral health-care regimens

    OpenAIRE

    Jongsma, Marije A.; van der Mei, Henny C.; Atema-Smit, Jelly; Busscher, Henk J.; Ren, Yijin

    2015-01-01

    Retention wires permanently bonded to the anterior teeth are used after orthodontic treatment to prevent the teeth from relapsing to pre-treatment positions. A disadvantage of bonded retainers is biofilm accumulation on the wires, which produces a higher incidence of gingival recession, increased pocket depth and bleeding on probing. This study compares in vivo biofilm formation on single-strand and multi-strand retention wires with different oral health-care regimens. Two-centimetre wires we...

  15. Monitoring Backbone Hydrogen-Bond Formation in β-Barrel Membrane Protein Folding.

    Science.gov (United States)

    Raschle, Thomas; Rios Flores, Perla; Opitz, Christian; Müller, Daniel J; Hiller, Sebastian

    2016-05-10

    β-barrel membrane proteins are key components of the outer membrane of bacteria, mitochondria and chloroplasts. Their three-dimensional structure is defined by a network of backbone hydrogen bonds between adjacent β-strands. Here, we employ hydrogen-deuterium (H/D) exchange in combination with NMR spectroscopy and mass spectrometry to monitor backbone hydrogen bond formation during folding of the outer membrane protein X (OmpX) from E. coli in detergent micelles. Residue-specific kinetics of interstrand hydrogen-bond formation were found to be uniform in the entire β-barrel and synchronized to formation of the tertiary structure. OmpX folding thus propagates via a long-lived conformational ensemble state in which all backbone amide protons exchange with the solvent and engage in hydrogen bonds only transiently. Stable formation of the entire OmpX hydrogen bond network occurs downhill of the rate-limiting transition state and thus appears cooperative on the overall folding time scale. PMID:27062600

  16. A kinetic investigation of MgH{sub 2} formation/decomposition in non-catalysed MgO–Mg thin films

    Energy Technology Data Exchange (ETDEWEB)

    Oñoro, M.; Fernández, J.F., E-mail: josefrancisco.fernandez@uam.es; Ares, J.R.; Ferrer, I.J.; Sánchez, C.

    2015-10-05

    Highlights: • A 100 nm MgO spacing layer inhibits Mg{sub 2}Si formation in Mg thin films up to 450 °C. • Formation of Mg(OH){sub 2} and Mg evaporation during thermal treatments of the layers. • Dendritic formation of MgH{sub 2} in a very low amount. - Abstract: Mg thin films without Pd-cap layer have been grown by e-beam evaporation on fused SiO{sub 2} substrates. A spacing MgO layer was grown between the substrate and the Mg with the purpose of avoiding Mg{sub 2}Si formation. Reactivity of the layers has been studied at high temperature in Ar and Ar/H{sub 2} atmospheres in order to investigate their modifications at the conditions used in hydrogenation experiments. Two processes affecting light transmission through the sample have been observed: (1) formation of Mg(OH){sub 2} or/and MgO nuclei and (2) partial evaporation of Mg crystals from the Mg layer. The MgO spacing layer effectively avoids reaction of the substrates and the Mg layer. Formation of MgH{sub 2} was done at 290 °C and 11 bar H{sub 2} for as long as 1 week. In spite of the long time passed, only small amounts of dendritic MgH{sub 2} nuclei were formed on the films. Decomposition of the MgH{sub 2} was studied by thermal desorption spectroscopy and correlated to the changes in transmitted light intensity during the hydride decomposition. The fraction of sample converted to MgH{sub 2} is only 15 ± 5% of the whole sample. The peak temperature in the H-desorption curve is higher than expected for thin films, closer to that of bulk MgH{sub 2}.

  17. Toxin-induced pore formation is hindered by intermolecular hydrogen bonding in sphingomyelin bilayers.

    Science.gov (United States)

    García-Linares, Sara; Palacios-Ortega, Juan; Yasuda, Tomokazu; Åstrand, Mia; Gavilanes, José G; Martínez-Del-Pozo, Álvaro; Slotte, J Peter

    2016-06-01

    Sticholysin I and II (StnI and StnII) are pore-forming toxins that use sphingomyelin (SM) for membrane binding. We examined how hydrogen bonding among membrane SMs affected the StnI- and StnII-induced pore formation process, resulting in bilayer permeabilization. We compared toxin-induced permeabilization in bilayers containing either SM or dihydro-SM (lacking the trans Δ(4) double bond of the long-chain base), since their hydrogen-bonding properties are known to differ greatly. We observed that whereas both StnI and StnII formed pores in unilamellar vesicles containing palmitoyl-SM or oleoyl-SM, the toxins failed to similarly form pores in vesicles prepared from dihydro-PSM or dihydro-OSM. In supported bilayers containing OSM, StnII bound efficiently, as determined by surface plasmon resonance. However, StnII binding to supported bilayers prepared from dihydro-OSM was very low under similar experimental conditions. The association of the positively charged StnII (at pH7.0) with unilamellar vesicles prepared from OSM led to a concentration-dependent increase in vesicle charge, as determined from zeta-potential measurements. With dihydro-OSM vesicles, a similar response was not observed. Benzyl alcohol, which is a small hydrogen-bonding compound with affinity to lipid bilayer interfaces, strongly facilitated StnII-induced pore formation in dihydro-OSM bilayers, suggesting that hydrogen bonding in the interfacial region originally prevented StnII from membrane binding and pore formation. We conclude that interfacial hydrogen bonding was able to affect the membrane association of StnI- and StnII, and hence their pore forming capacity. Our results suggest that other types of protein interactions in bilayers may also be affected by hydrogen-bonding origination from SMs. PMID:26975250

  18. Shedding light on disulfide bond formation: engineering a redox switch in green fluorescent protein

    DEFF Research Database (Denmark)

    Østergaard, H.; Henriksen, A.; Hansen, Flemming G.;

    2001-01-01

    To visualize the formation of disulfide bonds in living cells, a pair of redox-active cysteines was introduced into the yellow fluorescent variant of green fluorescent protein. Formation of a disulfide bond between the two cysteines was fully reversible and resulted in a >2-fold decrease...... in the intrinsic fluorescence. Inter conversion between the two redox states could thus be followed in vitro as well as in vivoby non- invasive fluorimetric measurements. The 1.5 Angstrom crystal structure of the oxidized protein revealed a disulfide bond- induced distortion of the beta -barrel, as well...... as a structural reorganization of residues in the immediate chromophore environment. By combining this information with spectroscopic data, we propose a detailed mechanism accounting for the observed redox state-dependent fluorescence. The redox potential of the cysteine couple was found to be within...

  19. The formation process of the pellet-cladding bonding layer in high burnup BWR fuels

    International Nuclear Information System (INIS)

    The bonding formation process was studied by EPMA analysis, XRD measurements, and SEM/TEM observations for the oxide layer on a cladding inner surface and the pellet-cladding bonding layer in irradiated fuel rods. Specimens were prepared from fuels which had been irradiated to the pellet average burnups of 15, 27, 42 and 49 GWd/t in BWRs. In the lower burnup specimens of 15 and 27 GWd/t, no bonding layer was found, while the higher burnup specimens of 42 and 49 GWd/t had a typical bonding layer about 10 to 20 μm thick. A bonding layer which consisted of two regions was found in the latter fuels. One region of the inner surface of the Zr liner cladding was made up mainly of ZrO2 with a small amount of dissolved UO2. The structure of this ZrO2 consisted of cubic polycrystals a few nanometers in size, while no monoclinic crystals were found. The other region, near the pellet surface, had both a cubic solid solution of (U,Zr)O2 and amorphous phase in which the concentrations of UO2 and ZrO2 changed continuously. Even in the lower burnup specimens having no bonding layer, cubic ZrO2 phase was identified in the cladding inner oxide layer. The XRD measurements were consistent with the TEM results of the absence of the monoclinic ZrO2 phase. Phase transformation and amorphization were attributed to fission damage, since such phenomena have never been observed in the cladding outer surface. Phase transformation from monoclinic to cubic ZrO2 and amorphization by irradiation damage of fission products were discussed in connection with the formation mechanism and conditions of the bonding layer. (author)

  20. Tribromobenzene on Cu(111): Temperature-dependent formation of halogen-bonded, organometallic, and covalent nanostructures

    International Nuclear Information System (INIS)

    The temperature-controlled surface-assisted synthesis of halogen bonded, organometallic, and covalent nanostructures based on 1,3,5-tribromo-benzene (TriBB) was studied with scanning tunneling microscopy and X-ray photoemission spectroscopy in ultrahigh vacuum. Vapor deposition of TriBB onto a Cu(111) surface held at 90 K leads to the formation of large domains of a honeycomb-like organic monolayer structure stabilized by triangular nodes with Br⋯Br intermolecular bonds. Upon annealing the organic monolayer to ∼140 K, a new hexagonal close-packed structure with intact TriBB molecules connected by Cu adatoms is formed. Further warming up the sample to 300 K gives rise to the scission of C–Br bonds and formation of C–Cu–C bonds between phenyl fragments such that stable dendritic organometallic networks are formed. Larger islands of organometallic networks are obtained by maintaining the temperature of Cu(111) at 420 K during deposition of TriBB. Simultaneously, large islands of Br atoms are formed around the organometallic networks. Annealing the more extended organometallic network (prepared at 420 K) to 520 K leads to the formation of a branched covalent organic framework (COF) which comprises structural elements of porous graphene and is surrounded by Br islands. These organometallic networks and COFs appear as small dendritic and branched domains, most likely due to the steric influence exerted by the Br islands

  1. Tribromobenzene on Cu(111): Temperature-dependent formation of halogen-bonded, organometallic, and covalent nanostructures

    Science.gov (United States)

    Fan, Qitang; Wang, Tao; Liu, Liming; Zhao, Jin; Zhu, Junfa; Gottfried, J. Michael

    2015-03-01

    The temperature-controlled surface-assisted synthesis of halogen bonded, organometallic, and covalent nanostructures based on 1,3,5-tribromo-benzene (TriBB) was studied with scanning tunneling microscopy and X-ray photoemission spectroscopy in ultrahigh vacuum. Vapor deposition of TriBB onto a Cu(111) surface held at 90 K leads to the formation of large domains of a honeycomb-like organic monolayer structure stabilized by triangular nodes with Br⋯Br intermolecular bonds. Upon annealing the organic monolayer to ˜140 K, a new hexagonal close-packed structure with intact TriBB molecules connected by Cu adatoms is formed. Further warming up the sample to 300 K gives rise to the scission of C-Br bonds and formation of C-Cu-C bonds between phenyl fragments such that stable dendritic organometallic networks are formed. Larger islands of organometallic networks are obtained by maintaining the temperature of Cu(111) at 420 K during deposition of TriBB. Simultaneously, large islands of Br atoms are formed around the organometallic networks. Annealing the more extended organometallic network (prepared at 420 K) to 520 K leads to the formation of a branched covalent organic framework (COF) which comprises structural elements of porous graphene and is surrounded by Br islands. These organometallic networks and COFs appear as small dendritic and branched domains, most likely due to the steric influence exerted by the Br islands.

  2. Tribromobenzene on Cu(111): Temperature-dependent formation of halogen-bonded, organometallic, and covalent nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Qitang; Wang, Tao; Zhu, Junfa, E-mail: jfzhu@ustc.edu.cn [National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei 230029 (China); Liu, Liming; Zhao, Jin [Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026,People’s Republic of China (China); Gottfried, J. Michael, E-mail: michael.gottfried@chemie.uni-marburg.de [Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg (Germany)

    2015-03-14

    The temperature-controlled surface-assisted synthesis of halogen bonded, organometallic, and covalent nanostructures based on 1,3,5-tribromo-benzene (TriBB) was studied with scanning tunneling microscopy and X-ray photoemission spectroscopy in ultrahigh vacuum. Vapor deposition of TriBB onto a Cu(111) surface held at 90 K leads to the formation of large domains of a honeycomb-like organic monolayer structure stabilized by triangular nodes with Br⋯Br intermolecular bonds. Upon annealing the organic monolayer to ∼140 K, a new hexagonal close-packed structure with intact TriBB molecules connected by Cu adatoms is formed. Further warming up the sample to 300 K gives rise to the scission of C–Br bonds and formation of C–Cu–C bonds between phenyl fragments such that stable dendritic organometallic networks are formed. Larger islands of organometallic networks are obtained by maintaining the temperature of Cu(111) at 420 K during deposition of TriBB. Simultaneously, large islands of Br atoms are formed around the organometallic networks. Annealing the more extended organometallic network (prepared at 420 K) to 520 K leads to the formation of a branched covalent organic framework (COF) which comprises structural elements of porous graphene and is surrounded by Br islands. These organometallic networks and COFs appear as small dendritic and branched domains, most likely due to the steric influence exerted by the Br islands.

  3. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay - The effect of mononucleotide structure on phosphodiester bond formation

    Science.gov (United States)

    Ferris, James P.; KAMALUDDIN

    1989-01-01

    The formation of oligomers from deoxynucleotides, catalyzed by Na(+)-montmorillonite, was investigated with special attention given to the effect of the monomer structure on the phosphodiester bond formation. It was found that adenine deoxynucleotides bind more strongly to montmorillonite than do the corresponding ribonucleotides and thymidine nucleotides. Tetramers of 2-prime-dpA were detected in the reaction of 2-prime-d-5-prime-AMP with a water-soluble carbodiimide EDAC in the presence of Na(+)-montmorillonite, illustrating the possible role of minerals in the formation of biopolymers on the primitive earth.

  4. Dipeptide catalysed prebiotic polymerization of RNA

    DEFF Research Database (Denmark)

    Wieczorek, Rafal; Luisi, Pier Luigi; Monnard, Pierre-Alain

    2011-01-01

    A very short peptide composed of only two amino acid residues; Ser and His, was reported to exhibit broad hydrolytic activities. The dipeptide SerHis can catalyse the hydrolysis of esters, proteins and nucleic acids1. The ability of such a short peptide to be an efficient catalyst could be an...... thermodynamic equilibrium towards condensation can be shifted even in this environment. For example, the reverse-proteolysis in prebiotic environment has been described for SerHis3. In this case, SerHis was able to condensate amino acids into insoluble peptides, which in turn pulled the equilibrium further...... toward more peptide synthesis. In the present work we describe a prebiotically plausible system in which the SerHis dipeptide acts as catalyst for the formation of RNA oligomers from imidazole derivatives of mononucleotides. The thermodynamic shift towards condensation was achieved using water...

  5. Practical carbon-carbon bond formation from olefins through nickel-catalyzed reductive olefin hydrocarbonation.

    Science.gov (United States)

    Lu, Xi; Xiao, Bin; Zhang, Zhenqi; Gong, Tianjun; Su, Wei; Yi, Jun; Fu, Yao; Liu, Lei

    2016-01-01

    New carbon-carbon bond formation reactions expand our horizon of retrosynthetic analysis for the synthesis of complex organic molecules. Although many methods are now available for the formation of C(sp(2))-C(sp(3)) and C(sp(3))-C(sp(3)) bonds via transition metal-catalyzed cross-coupling of alkyl organometallic reagents, direct use of readily available olefins in a formal fashion of hydrocarbonation to make C(sp(2))-C(sp(3)) and C(sp(3))-C(sp(3)) bonds remains to be developed. Here we report the discovery of a general process for the intermolecular reductive coupling of unactivated olefins with alkyl or aryl electrophiles under the promotion of a simple nickel catalyst system. This new reaction presents a conceptually unique and practical strategy for the construction of C(sp(2))-C(sp(3)) and C(sp(3))-C(sp(3)) bonds without using any organometallic reagent. The reductive olefin hydrocarbonation also exhibits excellent compatibility with varieties of synthetically important functional groups and therefore, provides a straightforward approach for modification of complex organic molecules containing olefin groups. PMID:27033405

  6. Drinking alcohol has sex-dependent effects on pair bond formation in prairie voles.

    Science.gov (United States)

    Anacker, Allison M J; Ahern, Todd H; Hostetler, Caroline M; Dufour, Brett D; Smith, Monique L; Cocking, Davelle L; Li, Ju; Young, Larry J; Loftis, Jennifer M; Ryabinin, Andrey E

    2014-04-22

    Alcohol use and abuse profoundly influences a variety of behaviors, including social interactions. In some cases, it erodes social relationships; in others, it facilitates sociality. Here, we show that voluntary alcohol consumption can inhibit male partner preference (PP) formation (a laboratory proxy for pair bonding) in socially monogamous prairie voles (Microtus ochrogaster). Conversely, female PP is not inhibited, and may be facilitated by alcohol. Behavior and neurochemical analysis suggests that the effects of alcohol on social bonding are mediated by neural mechanisms regulating pair bond formation and not alcohol's effects on mating, locomotor, or aggressive behaviors. Several neuropeptide systems involved in the regulation of social behavior (especially neuropeptide Y and corticotropin-releasing factor) are modulated by alcohol drinking during cohabitation. These findings provide the first evidence to our knowledge that alcohol has a direct impact on the neural systems involved in social bonding in a sex-specific manner, providing an opportunity to explore the mechanisms by which alcohol affects social relationships. PMID:24711424

  7. C–C Bond formation catalyzed by natural gelatin and collagen proteins

    OpenAIRE

    Dennis Kühbeck; Basab Bijayi Dhar; Eva-Maria Schön; Carlos Cativiela; Vicente Gotor-Fernández; David Díaz Díaz

    2013-01-01

    The activity of gelatin and collagen proteins towards C-C bond formation via Henry (nitroaldol) reaction between aldehydes and nitroalkanes is demonstrated for the first time. Among other variables, protein source, physical state and chemical modification influence product yield and kinetics, affording the nitroaldol products in both aqueous and organic media under mild conditions. Significantly, the scale-up of the process between 4-nitrobenzaldehyde and nitromethane is successfully achieved...

  8. Highly Shocked Polymer Bonded Explosives at a Nonplanar Interface: Hot-Spot Formation Leading to Detonation

    OpenAIRE

    An, Qi; Goddard, William A.; Zybin, Sergey V.; Jaramillo-Botero, Andres; Zhou, Tingting

    2013-01-01

    We report reactive molecular dynamics simulations using the ReaxFF reactive force field to examine shock-induced hot-spot formation followed by detonation initiation in realistic (2.7 million atoms) models of polymer bonded explosives (PBX) with nonplanar interfaces. We considered here two energetic materials (EMs) pentaerythritol tetranitrate (PETN), a common EM for PBX, and silicon pentaerythritol tetranitrate (Si-PETN), which is so extremely sensitive that it has not been possible to chara...

  9. Formation of metalsbnd F bonds during frictional sliding: Influence of water and applied load

    Science.gov (United States)

    Shen, J. T.; Pei, Y. T.; De Hosson, J. Th. M.

    2016-04-01

    Effects of water lubrication and applied load on the formation of PTFE transfer films and metalsbnd F bonds during sliding when PTFE filled composites sliding against steel and Al2O3 are investigated. In water-lubricated conditions, XPS analysis reveals that a thin layer of water molecules at the sliding interface inhibits the formation of PTFE transfer films and Alsbnd F bonds on the Al2O3 ball, leading to a detrimental effect on the tribo-performance. Under various normal loads in dry sliding condition, it is found that the smearing of PTFE onto the wear surface of the composite and the transfer of PTFE onto the surface of the steel counterpart are stimulated by a high load. During sliding, the contact pressure is found to be the driving force of the reaction between steel and PTFE. It is concluded that under various loads, the total amount of PTFE transfer films has a larger impact on the friction behavior than the formation of Fesbnd F bonds.

  10. Functionalized alkynyl-chlorogermanes: hydrometallation, Ge-Cl bond activation, Ge-H bond formation and chlorine-tert-butyl exchange via a transient germyl cation.

    Science.gov (United States)

    Honacker, Christian; Qu, Zheng-Wang; Tannert, Jens; Layh, Marcus; Hepp, Alexander; Grimme, Stefan; Uhl, Werner

    2016-04-14

    Treatment of alkynyl-arylchlorogermanes ArylnGe(Cl)(C[triple bond, length as m-dash]C-(t)Bu)3-n (n = 1, 2) with HM(t)Bu2 (M = Al, Ga) yielded mixed Al or Ga alkenyl-alkynylchlorogermanes via hydrometallation reactions. Intramolecular interactions between the Lewis-basic Cl atoms and the Lewis-acidic Al or Ga atoms afforded MCGeCl heterocycles. The endocyclic M-Cl distances were significantly lengthened compared to the starting compounds and indicated Ge-Cl bond activation. Dual hydrometallation succeeded only with HGa(t)Bu2. One Ga atom of the product was involved in a Ga-Cl bond, while the second one had an interaction to a C-H bond of a phenyl group. In two cases treatment of chlorogermanes with two equivalents of HAl(t)Bu2 resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge-H functionalized germanes, Aryl-Ge(H)(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2)[double bond, length as m-dash]C(H)-(t)Bu] (Aryl = mesityl, triisopropylphenyl). The Al atoms of these compounds interacted with the α-C atoms of the alkynyl groups. Ph(Cl)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2}[double bond, length as m-dash]C(H)-(t)Bu] reacted in an unusual Cl/(t)Bu exchange to yield the tert-butylgermane Ph((t)Bu)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C{Al((t)Bu)(Cl)}[double bond, length as m-dash]C(H)-(t)Bu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate. PMID:26610394

  11. Mechanisms of formation of chemical bonding and defect formation at the a-SiO2/BaTiO3 interfaces

    International Nuclear Information System (INIS)

    The structure and mechanisms of bonding and defect formation at the interfaces between amorphous silica (a-SiO2) and BaTiO3(0 0 1) were investigated using ab initio molecular dynamics. It was found that the nature of interfacial bonds crucially depends on the BaTiO3 surface termination. In particular, the interface between silica and TiO2-terminated BaTiO3 (BTO) slab is characterised by strong covalent Ti–O–Si bonds, while the interface between silica and BaO-terminated BTO demonstrates ionic character of interfacial bonds and exhibits bond instability. In both cases, the dynamics of oxygen species at oxide interfaces is a driving force of the formation of interfacial bonds and defects. (paper)

  12. Iron-catalysed tritiation of pharmaceuticals

    Science.gov (United States)

    Pony Yu, Renyuan; Hesk, David; Rivera, Nelo; Pelczer, István; Chirik, Paul J.

    2016-01-01

    A thorough understanding of the pharmacokinetic and pharmacodynamic properties of a drug in animal models is a critical component of drug discovery and development. Such studies are performed in vivo and in vitro at various stages of the development process—ranging from preclinical absorption, distribution, metabolism and excretion (ADME) studies to late-stage human clinical trials—to elucidate a drug molecule’s metabolic profile and to assess its toxicity. Radiolabelled compounds, typically those that contain 14C or 3H isotopes, are one of the most powerful and widely deployed diagnostics for these studies. The introduction of radiolabels using synthetic chemistry enables the direct tracing of the drug molecule without substantially altering its structure or function. The ubiquity of C-H bonds in drugs and the relative ease and low cost associated with tritium (3H) make it an ideal radioisotope with which to conduct ADME studies early in the drug development process. Here we describe an iron-catalysed method for the direct 3H labelling of pharmaceuticals by hydrogen isotope exchange, using tritium gas as the source of the radioisotope. The site selectivity of the iron catalyst is orthogonal to currently used iridium catalysts and allows isotopic labelling of complementary positions in drug molecules, providing a new diagnostic tool in drug development.

  13. Correlation of particle impact conditions with bonding, nanocrystal formation and mechanical properties in kinetic sprayed nickel

    International Nuclear Information System (INIS)

    Owing to the specific high-strain-rate thermomechanical characteristics of Ni particle impact in kinetic spraying, the rebound phenomenon of the impacting particles hinders the formation of the first layer and impedes successful build-up of the coating. Even at higher impact velocities, the deposition efficiency of the coating is quite low because of excessive kinetic energy, which induces the rebound and/or erosion of the highly flattened particles. This paper reports noticeably improved bonding and deposition characteristics of Ni particles resulting from suppressed equivalent (von Mises) flow stress and enhanced interface heat-up as a result of powder preheating. Experimental observations coupled with finite-element modeling (FEM) corroborate the fact that the thermally softened Ni particle is very effective for enhanced adhesive and cohesive bonding. Based on the FEM results, the thermal boost-up zone, increased by thermally accelerated adiabatic shear instability, is proposed as a crucial factor for enhancing bonding between the particles, which is essential in producing better coating properties. Moreover, nanocrystal formation (<100 nm) in the coating was more pronounced than cases previously reported in the literature, mainly because of the enhanced thermal activation and straining of the severely deformed particles, which was verified by transmission electron microscopy investigations and nanoindentation tests.

  14. Effect of stacking fault energy on nanostructure formation under accumulative roll bonding (ARB) process

    International Nuclear Information System (INIS)

    In this study, the effect of stacking fault energy on the formation of nanostructure in aluminum, copper, and brass fabricated via the accumulative roll bonding (ARB) process was investigated. Evolution of microstructure of the samples was investigated by transmission electron microscopy (TEM). Occurrence of the recrystallization (both continuous and discontinuous) in the copper and brass led to the formation of nano grains with mean sizes of 80, and 40 nm, respectively; while, the mean grain size of aluminum was 250 nm. Differences in microstructural evolution during processing of aluminum, copper, and brass was related to their stacking fault energies. In order to facilitate nanostructure formation in the commercial purity aluminum, the second phase particles (alumina) were added to aluminum matrix. In this case, the mean grain size of the aluminum changed down to 90 nm

  15. Thioether bond formation by SPASM domain radical SAM enzymes: Cα H-atom abstraction in subtilosin A biosynthesis.

    Science.gov (United States)

    Benjdia, Alhosna; Guillot, Alain; Lefranc, Benjamin; Vaudry, Hubert; Leprince, Jérôme; Berteau, Olivier

    2016-05-01

    AlbA is a radical SAM enzyme catalyzing the formation of three unusual thioether bonds in the antibiotic subtilosin A. We demonstrate here that AlbA catalyzes direct Cα H-atom abstraction and likely contains three essential [4Fe-4S] centers. This leads us to propose novel mechanistic perspectives for thioether bond catalysis by radical SAM enzymes. PMID:27087315

  16. Cross-dehydrogenative coupling for the intermolecular C–O bond formation

    Directory of Open Access Journals (Sweden)

    Igor B. Krylov

    2015-01-01

    Full Text Available The present review summarizes primary publications on the cross-dehydrogenative C–O coupling, with special emphasis on the studies published after 2000. The starting compound, which donates a carbon atom for the formation of a new C–O bond, is called the CH-reagent or the C-reagent, and the compound, an oxygen atom of which is involved in the new bond, is called the OH-reagent or the O-reagent. Alcohols and carboxylic acids are most commonly used as O-reagents; hydroxylamine derivatives, hydroperoxides, and sulfonic acids are employed less often. The cross-dehydrogenative C–O coupling reactions are carried out using different C-reagents, such as compounds containing directing functional groups (amide, heteroaromatic, oxime, and so on and compounds with activated C–H bonds (aldehydes, alcohols, ketones, ethers, amines, amides, compounds containing the benzyl, allyl, or propargyl moiety. An analysis of the published data showed that the principles at the basis of a particular cross-dehydrogenative C–O coupling reaction are dictated mainly by the nature of the C-reagent. Hence, in the present review the data are classified according to the structures of C-reagents, and, in the second place, according to the type of oxidative systems. Besides the typical cross-dehydrogenative coupling reactions of CH- and OH-reagents, closely related C–H activation processes involving intermolecular C–O bond formation are discussed: acyloxylation reactions with ArI(O2CR2 reagents and generation of O-reagents in situ from C-reagents (methylarenes, aldehydes, etc..

  17. Cross-dehydrogenative coupling for the intermolecular C-O bond formation.

    Science.gov (United States)

    Krylov, Igor B; Vil', Vera A; Terent'ev, Alexander O

    2015-01-01

    The present review summarizes primary publications on the cross-dehydrogenative C-O coupling, with special emphasis on the studies published after 2000. The starting compound, which donates a carbon atom for the formation of a new C-O bond, is called the CH-reagent or the C-reagent, and the compound, an oxygen atom of which is involved in the new bond, is called the OH-reagent or the O-reagent. Alcohols and carboxylic acids are most commonly used as O-reagents; hydroxylamine derivatives, hydroperoxides, and sulfonic acids are employed less often. The cross-dehydrogenative C-O coupling reactions are carried out using different C-reagents, such as compounds containing directing functional groups (amide, heteroaromatic, oxime, and so on) and compounds with activated C-H bonds (aldehydes, alcohols, ketones, ethers, amines, amides, compounds containing the benzyl, allyl, or propargyl moiety). An analysis of the published data showed that the principles at the basis of a particular cross-dehydrogenative C-O coupling reaction are dictated mainly by the nature of the C-reagent. Hence, in the present review the data are classified according to the structures of C-reagents, and, in the second place, according to the type of oxidative systems. Besides the typical cross-dehydrogenative coupling reactions of CH- and OH-reagents, closely related C-H activation processes involving intermolecular C-O bond formation are discussed: acyloxylation reactions with ArI(O2CR)2 reagents and generation of O-reagents in situ from C-reagents (methylarenes, aldehydes, etc.). PMID:25670997

  18. 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

  19. Ru-catalysed C-H silylation of unprotected gramines, tryptamines and their congeners.

    Science.gov (United States)

    Devaraj, K; Sollert, C; Juds, C; Gates, P J; Pilarski, L T

    2016-04-30

    Selective Ru-catalysed C2-H silylation of heteroarenes is presented. The transformation works with or without directing group assistance and requires no protecting groups. Gramines and tryptamines may be converted efficiently whilst avoiding deleterious elimination side-reactions. Mechanistic studies reveal an unusual activation of the indole C4-H bond by an electron-rich metal. PMID:27050747

  20. A free-standing condensation enzyme catalyzing ester bond formation in C-1027 biosynthesis.

    Science.gov (United States)

    Lin, Shuangjun; Van Lanen, Steven G; Shen, Ben

    2009-03-17

    Nonribosomal peptide synthetases (NRPSs) catalyze the biosynthesis of many biologically active peptides and typically are modular, with each extension module minimally consisting of a condensation, an adenylation, and a peptidyl carrier protein domain responsible for incorporation of an amino acid into the growing peptide chain. C-1027 is a chromoprotein antitumor antibiotic whose enediyne chromophore consists of an enediyne core, a deoxy aminosugar, a benzoxazolinate, and a beta-amino acid moiety. Bioinformatics analysis suggested that the activation and incorporation of the beta-amino acid moiety into C-1027 follows an NRPS mechanism whereby biosynthetic intermediates are tethered to the peptidyl carrier protein SgcC2. Here, we report the biochemical characterization of SgcC5, an NRPS condensation enzyme that catalyzes ester bond formation between the SgcC2-tethered (S)-3-chloro-5-hydroxy-beta-tyrosine and (R)-1-phenyl-1,2-ethanediol, a mimic of the enediyne core. SgcC5 uses (S)-3-chloro-5-hydroxy-beta-tyrosyl-SgcC2 as the donor substrate and exhibits regiospecificity for the C-2 hydroxyl group of the enediyne core mimic as the acceptor substrate. Remarkably, SgcC5 is also capable of catalyzing amide bond formation, albeit with significantly reduced efficiency, between (S)-3-chloro-5-hydroxy-beta-tyrosyl-(S)-SgcC2 and (R)-2-amino-1-phenyl-1-ethanol, an alternative enediyne core mimic bearing an amine at its C-2 position. Thus, SgcC5 is capable of catalyzing both ester and amide bond formation, providing an evolutionary link between amide- and ester-forming condensation enzymes. PMID:19246381

  1. Bridging and bonding interactions in higher education: social capital and students’ academic and professional identity formation

    Science.gov (United States)

    Jensen, Dorthe H.; Jetten, Jolanda

    2015-01-01

    It is increasingly recognized that graduates’ achievements depend in important ways on their opportunities to develop an academic and a professional identity during their studies. Previous research has shown that students’ socio-economic status (SES) and social capital prior to entering university affects their ability to obtain these identities in higher education. However, what is less well understood is whether social capital that is built during university studies shapes identity development, and if so, whether the social capital gained during university years impacts on academic and professional identity differently. In a qualitative study, we interviewed 26 Danish and 11 Australian university students about their social interaction experiences, their opportunities to develop bonding capital as well as bridging capital, and their academic and professional identity. Findings show that while bonding social capital with co-students facilitated academic identity formation, such social capital does not lead to professional identity development. We also found that the development of bridging social capital with educators facilitated students’ professional identity formation. However, bonding social capital among students stood in the way of participating in bridging interaction with educators, thereby further hindering professional identity formation. Finally, while students’ parental background did not affect the perceived difficulty of forming professional identity, there was a tendency for students from lower SES backgrounds to be more likely to make internal attributions while those from higher SES backgrounds were more likely to make external attributions for the failure to develop professional identity. Results point to the importance of creating opportunities for social interaction with educators at university because this facilitates the generation of bridging social capital, which, in turn, is essential for students’ professional identity

  2. Bridging and bonding interactions in higher education: social capital and students' academic and professional identity formation.

    Science.gov (United States)

    Jensen, Dorthe H; Jetten, Jolanda

    2015-01-01

    It is increasingly recognized that graduates' achievements depend in important ways on their opportunities to develop an academic and a professional identity during their studies. Previous research has shown that students' socio-economic status (SES) and social capital prior to entering university affects their ability to obtain these identities in higher education. However, what is less well understood is whether social capital that is built during university studies shapes identity development, and if so, whether the social capital gained during university years impacts on academic and professional identity differently. In a qualitative study, we interviewed 26 Danish and 11 Australian university students about their social interaction experiences, their opportunities to develop bonding capital as well as bridging capital, and their academic and professional identity. Findings show that while bonding social capital with co-students facilitated academic identity formation, such social capital does not lead to professional identity development. We also found that the development of bridging social capital with educators facilitated students' professional identity formation. However, bonding social capital among students stood in the way of participating in bridging interaction with educators, thereby further hindering professional identity formation. Finally, while students' parental background did not affect the perceived difficulty of forming professional identity, there was a tendency for students from lower SES backgrounds to be more likely to make internal attributions while those from higher SES backgrounds were more likely to make external attributions for the failure to develop professional identity. Results point to the importance of creating opportunities for social interaction with educators at university because this facilitates the generation of bridging social capital, which, in turn, is essential for students' professional identity development. PMID

  3. Metallaphotoredox-catalysed sp(3)-sp(3) cross-coupling of carboxylic acids with alkyl halides.

    Science.gov (United States)

    Johnston, Craig P; Smith, Russell T; Allmendinger, Simon; MacMillan, David W C

    2016-08-18

    In the past 50 years, cross-coupling reactions mediated by transition metals have changed the way in which complex organic molecules are synthesized. The predictable and chemoselective nature of these transformations has led to their widespread adoption across many areas of chemical research. However, the construction of a bond between two sp(3)-hybridized carbon atoms, a fundamental unit of organic chemistry, remains an important yet elusive objective for engineering cross-coupling reactions. In comparison to related procedures with sp(2)-hybridized species, the development of methods for sp(3)-sp(3) bond formation via transition metal catalysis has been hampered historically by deleterious side-reactions, such as β-hydride elimination with palladium catalysis or the reluctance of alkyl halides to undergo oxidative addition. To address this issue, nickel-catalysed cross-coupling processes can be used to form sp(3)-sp(3) bonds that utilize organometallic nucleophiles and alkyl electrophiles. In particular, the coupling of alkyl halides with pre-generated organozinc, Grignard and organoborane species has been used to furnish diverse molecular structures. However, the manipulations required to produce these activated structures is inefficient, leading to poor step- and atom-economies. Moreover, the operational difficulties associated with making and using these reactive coupling partners, and preserving them through a synthetic sequence, has hindered their widespread adoption. A generically useful sp(3)-sp(3) coupling technology that uses bench-stable, native organic functional groups, without the need for pre-functionalization or substrate derivatization, would therefore be valuable. Here we demonstrate that the synergistic merger of photoredox and nickel catalysis enables the direct formation of sp(3)-sp(3) bonds using only simple carboxylic acids and alkyl halides as the nucleophilic and electrophilic coupling partners, respectively. This metallaphotoredox

  4. 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...

  5. An Erbium-Based Bifuctional Heterogeneous Catalyst: A Cooperative Route Towards C-C Bond Formation

    Directory of Open Access Journals (Sweden)

    Manuela Oliverio

    2014-07-01

    Full Text Available Heterogeneous bifuctional catalysts are multifunctional synthetic catalysts enabling efficient organic transformations by exploiting two opposite functionalities without mutual destruction. In this paper we report the first Er(III-based metallorganic heterogeneous catalyst, synthesized by post-calcination MW-assisted grafting and modification of the natural aminoacid L-cysteine. The natural acid–base distance between sites was maintained to assure the cooperation. The applicability of this new bifunctional heterogeneous catalyst to C-C bond formation and the supposed mechanisms of action are discussed as well.

  6. Metalloenzyme-Like Zeolites as Lewis Acid Catalysts for C-C Bond Formation.

    Science.gov (United States)

    Van de Vyver, Stijn; Román-Leshkov, Yuriy

    2015-10-19

    The use of metalloenzyme-like zeolites as Lewis acid catalysts for C-C bond formation reactions has received increasing attention over the past few years. In particular, the observation of direct aldol condensation reactions enabled by hydrophobic zeolites with isolated framework metal sites has encouraged the development of catalytic approaches for producing chemicals from biomass-derived compounds. The discovery of new Diels-Alder cycloaddition/dehydration routes and experimental and computational studies of Lewis acid catalyzed carbonyl-ene reactions have given a further boost to this rapidly evolving field. PMID:26465652

  7. Slow peptide bond formation by proline and other N-alkylamino acids in translation

    OpenAIRE

    Pavlov, Michael Y; Watts, Richard E.; Tan, Zhongping; Cornish, Virginia W; Ehrenberg, Måns; Forster, Anthony C.

    2008-01-01

    Proteins are made from 19 aa and, curiously, one N-alkylamino acid (“imino acid”), proline (Pro). Pro is thought to be incorporated by the translation apparatus at the same rate as the 19 aa, even though the alkyl group in Pro resides directly on the nitrogen nucleophile involved in peptide bond formation. Here, by combining quench-flow kinetics and charging of tRNAs with cognate and noncognate amino acids, we find that Pro incorporates in translation significantly more slowly than Phe or Ala...

  8. Dissecting the role of disulfide bonds on the amyloid formation of insulin

    International Nuclear Information System (INIS)

    Highlights: ► We dissect how individual disulfide bond affects the amyloidogenicity of insulin. ► A controlled reduction system for insulin is established in this study. ► Disulfide breakage is associated with unfolding and increased amyloidogenicity. ► Breakage of A6-A11 is associated with significantly increased cytotoxicity. ► Analogs without A6-A11 have a higher potency to form high order toxic oligomers. -- Abstract: Disulfide bonds play a critical role in the stability and folding of proteins. Here, we used insulin as a model system, to investigate the role of its individual disulfide bond during the amyloid formation of insulin. Tris(2-carboxyethyl)phosphine (TCEP) was applied to reduce two of the three disulfide bonds in porcine insulin and the reduced disulfide bonds were then alkylated by iodoacetamide. Three disulfide bond-modified insulin analogs, INS-2 (lack of A6-A11), INS-3 (lack of A7-B7) and INS-6 (lack of both A6-A11 and A7-B7), were obtained. Far-UV circular dichroism (CD) spectroscopy results indicated that the secondary structure of INS-2 was the closest to insulin under neutral conditions, followed by INS-3 and INS-6, whereas in an acidic solution all analogs were essentially unfolded. To test how these modifications affect the amyloidogenicity of insulin, thioflavin-T (ThT) fluorescence and transmission electronic microscopy (TEM) were performed. Our results showed that all analogs were more prone to aggregation than insulin, with the order of aggregation rates being INS-6 > INS-3 > INS-2. Cross-linking of unmodified proteins (PICUP) assay results showed that analogs without A6-A11 (INS-2 and INS-6) have a higher potential for oligomerization than insulin and INS-3, which is accompanied with a higher cytotoxicity as the hemolytic assays of human erythrocytes suggested. The results indicated that breakage of A7-B7 induced more unfolding of the insulin structure and a higher amyloidogenicity than breakage of A6-A11, but breakage of A6

  9. Dissecting the role of disulfide bonds on the amyloid formation of insulin

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yang; Gong, Hao [Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan 430030 (China); Sun, Yue [College of Life Sciences, Wuhan University, Wuhan 430072 (China); Yan, Juan; Cheng, Biao; Zhang, Xin [Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan 430030 (China); Huang, Jing [College of Life Sciences, Wuhan University, Wuhan 430072 (China); Yu, Mengying; Guo, Yu [Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan 430030 (China); Zheng, Ling, E-mail: lzheng217@hotmail.com [College of Life Sciences, Wuhan University, Wuhan 430072 (China); Huang, Kun, E-mail: kunhuang2008@hotmail.com [Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan 430030 (China); Centre for Biomedicine Research, Wuhan Institutes of Biotechnology, Wuhan 430070 (China)

    2012-06-29

    Highlights: Black-Right-Pointing-Pointer We dissect how individual disulfide bond affects the amyloidogenicity of insulin. Black-Right-Pointing-Pointer A controlled reduction system for insulin is established in this study. Black-Right-Pointing-Pointer Disulfide breakage is associated with unfolding and increased amyloidogenicity. Black-Right-Pointing-Pointer Breakage of A6-A11 is associated with significantly increased cytotoxicity. Black-Right-Pointing-Pointer Analogs without A6-A11 have a higher potency to form high order toxic oligomers. -- Abstract: Disulfide bonds play a critical role in the stability and folding of proteins. Here, we used insulin as a model system, to investigate the role of its individual disulfide bond during the amyloid formation of insulin. Tris(2-carboxyethyl)phosphine (TCEP) was applied to reduce two of the three disulfide bonds in porcine insulin and the reduced disulfide bonds were then alkylated by iodoacetamide. Three disulfide bond-modified insulin analogs, INS-2 (lack of A6-A11), INS-3 (lack of A7-B7) and INS-6 (lack of both A6-A11 and A7-B7), were obtained. Far-UV circular dichroism (CD) spectroscopy results indicated that the secondary structure of INS-2 was the closest to insulin under neutral conditions, followed by INS-3 and INS-6, whereas in an acidic solution all analogs were essentially unfolded. To test how these modifications affect the amyloidogenicity of insulin, thioflavin-T (ThT) fluorescence and transmission electronic microscopy (TEM) were performed. Our results showed that all analogs were more prone to aggregation than insulin, with the order of aggregation rates being INS-6 > INS-3 > INS-2. Cross-linking of unmodified proteins (PICUP) assay results showed that analogs without A6-A11 (INS-2 and INS-6) have a higher potential for oligomerization than insulin and INS-3, which is accompanied with a higher cytotoxicity as the hemolytic assays of human erythrocytes suggested. The results indicated that breakage of A7

  10. Accelerated C-N Bond Formation in Dropcast Thin Films on Ambient Surfaces

    Science.gov (United States)

    Badu-Tawiah, Abraham K.; Campbell, Dahlia I.; Cooks, R. Graham

    2012-09-01

    The aza-Michael addition and the Mannich condensation occur in thin films deposited on ambient surfaces. The reagents for both C-N bond formation reactions were transferred onto the surface by drop-casting using a micropipette. The surface reactions were found to be much more efficient than the corresponding bulk solution-phase reactions performed on the same scale in the same acetonitrile solvent. The increase in rate of product formation in the thin film is attributed to solvent evaporation in the open air which results in reagent concentration and produces rate acceleration similar to that seen in evaporating droplets in desorption electrospray ionization. This thin film procedure has potential for the rapid synthesis of reaction products on a small scale, as well as allowing rapid derivatization of analytes to produce forms that are easily ionized by electrospray ionization. Analysis of the derivatized sample directly from the reaction surface through the use of desorption electrospray ionization is also demonstrated.

  11. Formation of III–V-on-insulator structures on Si by direct wafer bonding

    International Nuclear Information System (INIS)

    We have studied the formation of III–V-compound-semiconductors-on-insulator (III–V-OI) structures with thin buried oxide (BOX) layers on Si wafers by using developed direct wafer bonding (DWB). In order to realize III–V-OI MOSFETs with ultrathin body and extremely thin body (ETB) InGaAs-OI channel layers and ultrathin BOX layers, we have developed an electron-cyclotron resonance (ECR) O2 plasma-assisted DWB process with ECR sputtered SiO2 BOX layers and a DWB process based on atomic-layer-deposition Al2O3 (ALD-Al2O3) BOX layers. It is essential to suppress micro-void generation during wafer bonding process to achieve excellent wafer bonding. We have found that major causes of micro-void generation in DWB processes with ECR-SiO2 and ALD-Al2O3 BOX layers are desorption of Ar and H2O gas, respectively. In order to suppress micro-void generation in the ECR-SiO2 BOX layers, it is effective to introduce the outgas process before bonding wafers. On the other hand, it is a possible solution for suppressing micro-void generation in the ALD-Al2O3 BOX layers to increase the deposition temperature of the ALD-Al2O3 BOX layers. It is also another possible solution to deposit ALD-Al2O3 BOX layers on thermally oxidized SiO2 layers, which can absorb the desorption gas from ALD-Al2O3 BOX layers. (invited paper)

  12. Control of Reactivity and Regioselectivity for On-Surface Dehydrogenative Aryl-Aryl Bond Formation.

    Science.gov (United States)

    Kocić, Nemanja; Liu, Xunshan; Chen, Songjie; Decurtins, Silvio; Krejčí, Ondřej; Jelínek, Pavel; Repp, Jascha; Liu, Shi-Xia

    2016-05-01

    Regioselectivity is of fundamental importance in chemical synthesis. Although many concepts for site-selective reactions are well established for solution chemistry, it is not a priori clear whether they can easily be transferred to reactions taking place on a metal surface. A metal will fix the chemical potential of the electrons and perturb the electronic states of the reactants because of hybridization. Additionally, techniques to characterize chemical reactions in solution are generally not applicable to on-surface reactions. Only recent developments in resolving chemical structures by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) paved the way for identifying individual reaction products on surfaces. Here we exploit a combined STM/AFM technique to demonstrate the on-surface formation of complex molecular architectures built up from a heteroaromatic precursor, the tetracyclic pyrazino[2,3-f][4,7]phenanthroline (pap) molecule. Selective intermolecular aryl-aryl coupling via dehydrogenative C-H activation occurs on Au(111) upon thermal annealing under ultrahigh vacuum (UHV) conditions. A full atomistic description of the different reaction products based on an unambiguous discrimination between pyrazine and pyridine moieties is presented. Our work not only elucidates that ortho-hydrogen atoms of the pyrazine rings are preferentially activated over their pyridine equivalents, but also sheds new light onto the participation of substrate atoms in metal-organic coordination bonding during covalent C-C bond formation. PMID:27059121

  13. In vivo biofilm formation on stainless steel bonded retainers during different oral health-care regimens

    Institute of Scientific and Technical Information of China (English)

    Marije A Jongsma; Henny C van der Mei; Jelly Atema-Smit; Henk J Busscher; Yijin Ren

    2015-01-01

    Retention wires permanently bonded to the anterior teeth are used after orthodontic treatment to prevent the teeth from relapsing to pre-treatment positions. A disadvantage of bonded retainers is biofilm accumulation on the wires, which produces a higher incidence of gingival recession, increased pocket depth and bleeding on probing. This study compares in vivo biofilm formation on single-strand and multi-strand retention wires with different oral health-care regimens. Two-centimetre wires were placed in brackets that were bonded to the buccal side of the first molars and second premolars in the upper arches of 22 volunteers. Volunteers used a selected toothpaste with or without the additional use of a mouthrinse containing essential oils. Brushing was performed manually. Regimens were maintained for 1 week, after which the wires were removed and the oral biofilm was collected to quantify the number of organisms and their viability, determine the microbial composition and visualize the bacteria by electron microscopy. A 6-week washout period was employed between regimens. Biofilm formation was reduced on single-strand wires compared with multi-strand wires;bacteria were observed to adhere between the strands. The use of antibacterial toothpastes marginally reduced the amount of biofilm on both wire types, but significantly reduced the viability of the biofilm organisms. Additional use of the mouthrinse did not result in significant changes in biofilm amount or viability. However, major shifts in biofilm composition were induced by combining a stannous fluoride-or triclosan-containing toothpaste with the mouthrinse. These shifts can be tentatively attributed to small changes in bacterial cell surface hydrophobicity after the adsorption of the toothpaste components, which stimulate bacterial adhesion to the hydrophobic oil, as illustrated for a Streptococcus mutans strain.

  14. Hemicellulose hydrolysis catalysed by solid acids

    NARCIS (Netherlands)

    P.D.. Carà; M. Pagliaro; A. Elmekawy; D.R. Brown; P. Verschuren; N.R. Shiju; G. Rothenberg

    2013-01-01

    Depolymerising hemicellulose into platform sugar molecules is a key step in developing the concept of an integrated biorefinery. This reaction is traditionally catalysed by either enzymes or homogeneous mineral acids. We compared various solid catalysts for hemicellulose hydrolysis, running reaction

  15. The fascinating construction of pyridine ring systems by transition metal-catalysed [2 + 2 + 2] cycloaddition reactions.

    Science.gov (United States)

    Heller, Barbara; Hapke, Marko

    2007-07-01

    Cycloaddition reactions compose one of the most important classes of reactions when it comes to the simultaneous formation of several bonds in one reaction step. The de novo construction of carbocyclic aromatic systems from acetylenes was also found as an excellent possibility for the assembly of heteroaromatic systems. The transition metal-catalysed [2 + 2 + 2] cycloaddition reaction constitutes a fascinating tool for the synthesis of pyridines from nitriles and the most recent developments demonstrate the ability to control the substitution pattern as well as the possibility of introducing chirality by the use of achiral substrates and a chiral catalyst under mild conditions. In this tutorial review we are focusing on the de novo construction of pyridine ring systems by the transition metal-catalysed [2 + 2 + 2] cycloaddition reaction. After surveying the mechanistic features and intermediates of the reaction depending on the different metal complexes used, we depict the preparation of achiral pyridine derivatives. The last section describes the advances in the synthesis of chiral pyridines and biaryls using the cyclotrimerization method. The various possibilities of introducing chirality by catalytic means are presented and illustrated by instructive examples. This review will be of interest for people active in: Organic Chemistry, Organometallic Chemistry, Transition Metal Chemistry, Stereoselective Synthesis, Heterocyclic Chemistry. PMID:17576476

  16. The molecular mechanism of palladium-catalysed cyanoesterification of methyl cyanoformate onto norbornene.

    Science.gov (United States)

    Ishitsuka, Takuya; Okuda, Yasuhiro; Szilagyi, Robert K; Mori, Seiji; Nishihara, Yasushi

    2016-05-01

    Potential energy surface mapping was completed for the entire catalytic cycle of palladium-catalysed cyanoesterification onto norbornene (NBE) using density functional theory calculations. We found that after the oxidative addition step of the reagent methyl cyanoformate, the reaction proceeds through an insertion of olefin into a Pd(II)-COOMe bond first. Subsequently, reductive elimination occurs by transferring the cyanide group from the Pd center to NBE. This rearrangement is triggered by the rotation of the ester group into a π-interaction with the Pd(II) centre. The regioselectivity of olefin insertion is controlled by ionic and covalent interactions in the precursor π-complex formation step. Importantly, all of the intermediates and transition states along the exo pathway were found to be more stable than the corresponding structures of the endo pathway without any sign of crossing over between the two surfaces via isomerization. The rate-determining step is the reductive elimination despite the fact that the corresponding activation barrier is reduced by conformational changes via the rotation of a MeOOC-C(NBE) bond. PMID:27062989

  17. Chelation-assisted Pd-catalysed ortho-selective oxidative C-H/C-H cross-coupling of aromatic carboxylic acids with arenes and intramolecular Friedel-Crafts acylation: one-pot formation of fluorenones.

    Science.gov (United States)

    Sun, Denan; Li, Bijin; Lan, Jingbo; Huang, Quan; You, Jingsong

    2016-03-01

    Pd-Catalysed ortho-selective oxidative C-H/C-H cross-coupling of aromatic carboxylic acids with arenes and subsequent intramolecular Friedel-Crafts acylation has been accomplished for the first time through a chelation-assisted C-H activation strategy. Starting from the readily available substrates, a variety of fluorenone derivatives are obtained in one pot. The direct use of naturally occurring carboxylic acid functionalities as directing groups avoids unnecessary steps for installation and removal of an extra directing group. PMID:26861768

  18. Ag-catalysed cutting of multi-walled carbon nanotubes

    Science.gov (United States)

    La Torre, A.; Rance, G. A.; Miners, S. A.; Herreros Lucas, C.; Smith, E. F.; Fay, M. W.; Zoberbier, T.; Giménez-López, M. C.; Kaiser, U.; Brown, P. D.; Khlobystov, A. N.

    2016-04-01

    In this work, the cutting of carbon nanotubes is investigated using silver nanoparticles deposited on arc discharge multi-walled carbon nanotubes. The composite is subsequently heated in air to fabricate shortened multi-walled nanotubes. Complementary transmission electron microscopy and spectroscopy techniques shed light on the cutting mechanism. The nanotube cutting is catalysed by the fundamental mechanism based on the coordination of the silver atoms to the π-bonds of carbon nanotubes. As a result of the metal coordination, the strength of the carbon-carbon bond is reduced, promoting the oxidation of carbon at lower temperature when heated in air, or lowering the activation energy required for the removal of carbon atoms by electron beam irradiation, assuring in both cases the cutting of the nanotubes.

  19. Control of stability of polypeptide multilayer nanofilms by quantitative control of disulfide bond formation

    International Nuclear Information System (INIS)

    The crosslinking of polymers in a polymeric material will alter the mechanical properties of the material. Control over the mechanical properties of polyelectrolyte multilayer films (PEMs) could be useful for applications of the technology in medicine and other areas. Disulfide bonds are 'natural' polypeptide crosslinks found widely in wild-type proteins. Here, we have designed and synthesized three pairs of oppositely charged 32mer polypeptide to have 0, 4, or 8 cysteine (Cys) residues per molecule, and we have characterized physical properties of the peptides in a PEM context. The average linear density of free thiol in the designed peptides was 0, 0.125, or 0.25 per amino acid residue. The peptides were used to make 10-bilayer PEMs by electrostatic layer-by-layer self-assembly (LBL). Cys was included in the peptides to study specific effects of disulfide bond formation on PEM properties. Features of film assembly have been found to depend on the amino acid sequence, as in protein folding. Following polypeptide self-assembly into multilayer films, Cys residues were disulfide-crosslinked under mild oxidizing conditions. The stability of the crosslinked films at acidic pH has been found to depend on the number of Cys residues per peptide for a given crosslinking procedure. Crosslinked and non-crosslinked films have been analysed by ultraviolet spectroscopy (UVS), ellipsometry, and atomic force microscopy (AFM) to characterize film assembly, surface morphology, and disassembly. A selective etching model of the disassembly process at acidic pH is proposed on the basis of the experimental data. In this model, regions of film in which the disulfide bond density is low are etched at a higher rate than regions where the density is high

  20. Control of stability of polypeptide multilayer nanofilms by quantitative control of disulfide bond formation

    Science.gov (United States)

    Zhong, Yang; Li, Bingyun; Haynie, Donald T.

    2006-12-01

    The crosslinking of polymers in a polymeric material will alter the mechanical properties of the material. Control over the mechanical properties of polyelectrolyte multilayer films (PEMs) could be useful for applications of the technology in medicine and other areas. Disulfide bonds are 'natural' polypeptide crosslinks found widely in wild-type proteins. Here, we have designed and synthesized three pairs of oppositely charged 32mer polypeptide to have 0, 4, or 8 cysteine (Cys) residues per molecule, and we have characterized physical properties of the peptides in a PEM context. The average linear density of free thiol in the designed peptides was 0, 0.125, or 0.25 per amino acid residue. The peptides were used to make 10-bilayer PEMs by electrostatic layer-by-layer self-assembly (LBL). Cys was included in the peptides to study specific effects of disulfide bond formation on PEM properties. Features of film assembly have been found to depend on the amino acid sequence, as in protein folding. Following polypeptide self-assembly into multilayer films, Cys residues were disulfide-crosslinked under mild oxidizing conditions. The stability of the crosslinked films at acidic pH has been found to depend on the number of Cys residues per peptide for a given crosslinking procedure. Crosslinked and non-crosslinked films have been analysed by ultraviolet spectroscopy (UVS), ellipsometry, and atomic force microscopy (AFM) to characterize film assembly, surface morphology, and disassembly. A selective etching model of the disassembly process at acidic pH is proposed on the basis of the experimental data. In this model, regions of film in which the disulfide bond density is low are etched at a higher rate than regions where the density is high.

  1. Isotopic Studies of O-O Bond Formation During Water Oxidation (SISGR)

    Energy Technology Data Exchange (ETDEWEB)

    Roth, Justine P.

    2015-03-03

    Isotopic Studies of O-O Bond Formation During Water Oxidation (SISGR) Research during the project period focused primarily on mechanisms of water oxidation by structurally defined transition metal complexes. Competitive oxygen isotope fractionation of water, mediated by oxidized precursors or reduced catalysts together with ceric, Ce(IV), ammonium nitrate in aqueous media, afforded oxygen-18 kinetic isotope effects (O-18 KIEs). Measurement, calculation, and interpretation of O-18 KIEs, described in the accompanying report has important ramifications for the production of electricity and solar hydrogen (as fuel). The catalysis division of BES has acknowledged that understanding mechanisms of transition metal catalyzed water oxidation has major ramifications, potentially leading to transformation of the global economy and natural environment in years to come. Yet, because of program restructuring and decreased availability of funds, it was recommended that the Solar Photochemistry sub-division of BES would be a more appropriate parent program for support of continued research.

  2. Formation of porous surface layers in reaction bonded silicon nitride during processing

    Science.gov (United States)

    Shaw, N. J.; Glasgow, T. K.

    1979-01-01

    Microstructural examination of reaction bonded silicon nitride (RBSN) has shown that there is often a region adjacent to the as-nitrided surfaces that is even more porous than the interior of this already quite porous material. Because this layer of large porosity is considered detrimental to both the strength and oxidation resistance of RBSN, a study was undertaken to determine if its formation could be prevented during processing. All test bars studied were made from a single batch of Si powder which was milled for 4 hours in heptane in a vibratory mill using high density alumina cylinders as the grinding media. After air drying the powder, bars were compacted in a single acting die and hydropressed.

  3. Affiliation, reward, and immune biomarkers coalesce to support social synchrony during periods of bond formation in humans.

    Science.gov (United States)

    Ulmer-Yaniv, Adi; Avitsur, Ronit; Kanat-Maymon, Yaniv; Schneiderman, Inna; Zagoory-Sharon, Orna; Feldman, Ruth

    2016-08-01

    Social bonds are critical for survival and adaptation and periods of bond formation involve reorganization of neurobiological systems as mediated by social behavior. Theoretical accounts and animal studies suggest similarity between parent-infant and pair bonding, a hypothesis not yet directly tested in humans. In this study, we recruited three groups of human adults (N=189); parents who had their firstborn child in the last 4-6months, new lovers who began a romantic relationship within the past 4months, and non-attached singles. We measured plasma oxytocin (OT), beta endorphin (β-End), and interlukin-6 (IL-6), biomarkers of the affiliation, reward, and stress-response systems, and micro-coded gaze and affect synchrony between parents and infants and among new lovers during social interaction. OT significantly increased during periods of parental and romantic bonding and was highest in new lovers. In contrast, IL-6 and β-End were highest in new parents and lowest in singles. Biomarkers became more tightly coupled during periods of bond formation and inter-correlation among hormones was highest during romantic bonding. Structural equation modeling indicated that the effects of IL-6 and β-End on behavioral synchrony were mediated by their impact on OT, highlighting the integrative role of the oxytocinergic system in supporting human social affiliation. Findings suggest that periods of bond formation are accompanied by increased activity, as well as tighter cross-talk among systems underpinning affiliation, reward, and stress management and that research on the multidimensional process of bonding may shed further light on the effects of attachment on health. PMID:26902915

  4. Estimation of Abraham solvation equation coefficients for hydrogen bond formation from Abraham solvation parameters for solute acidity and basicity.

    Science.gov (United States)

    van Noort, Paul

    2013-01-01

    Abraham solvation equations find widespread use in environmental chemistry and pharmaco-chemistry. The coefficients in these equations, which are solvent (system) descriptors, are usually determined by fitting experimental data. To simplify the determination of these coefficients in Abraham solvation equations, this study derives equations, based on Abraham solvation parameters for hydrogen acidity and basicity of the solvents involved, to estimate the value of the coefficients for hydrogen bond formation. These equations were applied to calculate Abraham solvation parameters for hydrogen acidity and basicity for polyoxymethylene, polyacrylate, sodium dodecylsulfate, some ionic liquids, alkanoyl phosphatidyl cholines, and lipids for which fitted values for Abraham coefficients for hydrogen bond formation were available. PMID:22892357

  5. Exploring the atmospheric chemistry of O2SO3- and assessing the maximum turnover number of ion-catalysed H2SO4 formation

    DEFF Research Database (Denmark)

    Bork, Nicolai Christian; Kurtén, T.; Vehkamäki, H.

    2013-01-01

    two major sinks for O2SO3- is assessed, thereby providing a measure of the maximum turnover number of ion-catalysed SO2 oxidation, i.e. how many SO2 can be oxidized per free electron. The rate ratio between reactions (a) and (b) is significantly altered by the presence or absence of a single water...... decomposition into SO3, O-2 and O-3(-). The former reaction is highly exothermic, and the nascent O3SO3- will rapidly decompose into SO4- and O-2. If the origin of O2SO(3)(-) is SO2 oxidation by O-3(-), the latter reaction closes a catalytic cycle wherein SO2 is oxidized to SO3. The relative rate between the...

  6. Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model

    Science.gov (United States)

    Higa, Ryota; Asano, Kenichi

    2016-06-01

    We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.

  7. 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

  8. MICROWAVE-ASSISTED CHEMISTRY: SYNTHESIS OF AMINES AND HETEROCYCLES VIA CARBON-NITROGEN BOND FORMATION IN AQUEOUS MEDIA

    Science.gov (United States)

    Improved C-N bond formation under MW influence is demonstrated by a) solventless three-component coupling reaction to generate propargyl amines that uses only Cu (I); b) aqueous N-alkylation of amines by alkyl halides that proceeds expeditiously in the presence of NaOH to deliver...

  9. Anatomy of Bond Formation: Insights from the Analysis of Domain-Averaged Fermi Holes in Momentum Space

    Czech Academy of Sciences Publication Activity Database

    Cooper, D.L.; Ponec, Robert

    2009-01-01

    Roč. 109, č. 11 (2009), s. 2383-2392. ISSN 0020-7608 R&D Projects: GA AV ČR IAA4072403 Institutional research plan: CEZ:AV0Z40720504 Keywords : momentum space * domain averaged fermi holes * bond formation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.315, year: 2009

  10. A steric tethering approach enables palladium-catalysed C-H activation of primary amino alcohols

    Science.gov (United States)

    Calleja, Jonas; Pla, Daniel; Gorman, Timothy W.; Domingo, Victoriano; Haffemayer, Benjamin; Gaunt, Matthew J.

    2015-12-01

    Aliphatic primary amines are a class of chemical feedstock essential to the synthesis of higher-order nitrogen-containing molecules, commonly found in biologically active compounds and pharmaceutical agents. New methods for the construction of complex amines remain a continuous challenge to synthetic chemists. Here, we outline a general palladium-catalysed strategy for the functionalization of aliphatic C-H bonds within amino alcohols, an important class of small molecule. Central to this strategy is the temporary conversion of catalytically incompatible primary amino alcohols into hindered secondary amines that are capable of undergoing a sterically promoted palladium-catalysed C-H activation. Furthermore, a hydrogen bond between amine and catalyst intensifies interactions around the palladium and orients the aliphatic amine substituents in an ideal geometry for C-H activation. This catalytic method directly transforms simple, easily accessible amines into highly substituted, functionally concentrated and structurally diverse products, and can streamline the synthesis of biologically important amine-containing molecules.

  11. Ions colliding with clusters of fullerenes—Decay pathways and covalent bond formations

    International Nuclear Information System (INIS)

    We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C60 molecules following collisions with Ar2+, He2+, and Xe20+ at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C60]n+→C60++(n−1)C60 evaporation model. Excitation energies in the range of only ∼0.7 eV per C60 molecule in a [C60]13+ cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar2+ and He2+ collisions, we observe very efficient C119+ and C118+ formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C59+ or C58+ and C60 during cluster fragmentation. In the Ar2+ case, it is possible to form even smaller C120−2m+ molecules (m= 2–7), while no molecular fusion reactions are observed for the present Xe20+ collisions

  12. Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations

    Energy Technology Data Exchange (ETDEWEB)

    Seitz, F.; Zettergren, H.; Chen, T.; Gatchell, M.; Alexander, J. D.; Stockett, M. H.; Schmidt, H. T.; Cederquist, H. [Department of Physics, Stockholm University, S-106 91 Stockholm (Sweden); Rousseau, P.; Chesnel, J. Y.; Capron, M.; Poully, J. C.; Mery, A.; Maclot, S.; Adoui, L. [CIMAP, UMR 6252, CEA/CNRS/ENSICAEN/Universite de Caen Basse-Normandie, bd Henri Becquerel, BP 5133, F-14070 Caen cedex 05 (France); Universite de Caen Basse-Normandie, Esplanade de la Paix, F-14032 Caen (France); Wang, Y.; Martin, F. [Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Instituto Madrileno de Estudios Avanzados en Nanociencia (IMDEA-Nano), Cantoblanco, 28049 Madrid (Spain); Rangama, J.; Domaracka, A.; Vizcaino, V. [CIMAP, UMR 6252, CEA/CNRS/ENSICAEN/Universite de Caen Basse-Normandie, bd Henri Becquerel, BP 5133, F-14070 Caen cedex 05 (France); and others

    2013-07-21

    We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C{sub 60} molecules following collisions with Ar{sup 2+}, He{sup 2+}, and Xe{sup 20+} at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C{sub 60} monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C{sub 60}]{sub n}{sup +}{yields}C{sub 60}{sup +}+(n-1)C{sub 60} evaporation model. Excitation energies in the range of only {approx}0.7 eV per C{sub 60} molecule in a [C{sub 60}]{sub 13}{sup +} cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar{sup 2+} and He{sup 2+} collisions, we observe very efficient C{sub 119}{sup +} and C{sub 118}{sup +} formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C{sub 59}{sup +} or C{sub 58}{sup +} and C{sub 60} during cluster fragmentation. In the Ar{sup 2+} case, it is possible to form even smaller C{sub 120-2m}{sup +} molecules (m= 2-7), while no molecular fusion reactions are observed for the present Xe{sup 20+} collisions.

  13. Slow peptide bond formation by proline and other N-alkylamino acids in translation.

    Science.gov (United States)

    Pavlov, Michael Y; Watts, Richard E; Tan, Zhongping; Cornish, Virginia W; Ehrenberg, Måns; Forster, Anthony C

    2009-01-01

    Proteins are made from 19 aa and, curiously, one N-alkylamino acid ("imino acid"), proline (Pro). Pro is thought to be incorporated by the translation apparatus at the same rate as the 19 aa, even though the alkyl group in Pro resides directly on the nitrogen nucleophile involved in peptide bond formation. Here, by combining quench-flow kinetics and charging of tRNAs with cognate and noncognate amino acids, we find that Pro incorporates in translation significantly more slowly than Phe or Ala and that other N-alkylamino acids incorporate much more slowly. Our results show that the slowest step in incorporation of N-alkylamino acids is accommodation/peptidyl transfer after GTP hydrolysis on EF-Tu. The relative incorporation rates correlate with expectations from organic chemistry, suggesting that amino acid sterics and basicities affect translation rates at the peptidyl transfer step. Cognate isoacceptor tRNAs speed Pro incorporation to rates compatible with in vivo, although still 3-6 times slower than Phe incorporation from Phe-tRNA(Phe) depending on the Pro codon. Results suggest that Pro is the only N-alkylamino acid in the genetic code because it has a privileged cyclic structure that is more reactive than other N-alkylamino acids. Our data on the variation of the rate of incorporation of Pro from native Pro-tRNA(Pro) isoacceptors at 4 different Pro codons help explain codon bias not accounted for by the "tRNA abundance" hypothesis. PMID:19104062

  14. Maternal nicotine exposure leads to impaired disulfide bond formation and augmented endoplasmic reticulum stress in the rat placenta.

    Directory of Open Access Journals (Sweden)

    Michael K Wong

    Full Text Available Maternal nicotine exposure has been associated with many adverse fetal and placental outcomes. Although underlying mechanisms remain elusive, recent studies have identified that augmented endoplasmic reticulum (ER stress is linked to placental insufficiency. Moreover, ER function depends on proper disulfide bond formation--a partially oxygen-dependent process mediated by protein disulfide isomerase (PDI and ER oxidoreductases. Given that nicotine compromised placental development in the rat, and placental insufficiency has been associated with poor disulfide bond formation and ER stress, we hypothesized that maternal nicotine exposure leads to both placental ER stress and impaired disulfide bond formation. To test this hypothesis, female Wistar rats received daily subcutaneous injections of either saline (vehicle or nicotine bitartrate (1 mg/kg for 14 days prior to mating and during pregnancy. Placentas were harvested on embryonic day 15 for analysis. Protein and mRNA expression of markers involved in ER stress (e.g., phosphorylated eIF2α, Grp78, Atf4, and CHOP, disulfide bond formation (e.g., PDI, QSOX1, VKORC1, hypoxia (Hif1α, and amino acid deprivation (GCN2 were quantified via Western blot and/or Real-time PCR. Maternal nicotine exposure led to increased expression of Grp78, phosphorylated eIF2α, Atf4, and CHOP (p<0.05 in the rat placenta, demonstrating the presence of augmented ER stress. Decreased expression of PDI and QSOX1 (p<0.05 reveal an impaired disulfide bond formation pathway, which may underlie nicotine-induced ER stress. Finally, elevated expression of Hif1α and GCN2 (p<0.05 indicate hypoxia and amino acid deprivation in nicotine-exposed placentas, respectively, which may also cause impaired disulfide bond formation and augmented ER stress. This study is the first to link maternal nicotine exposure with both placental ER stress and disulfide bond impairment in vivo, providing novel insight into the mechanisms underlying

  15. Dentin bonding performance using Weibull statistics and evaluation of acid-base resistant zone formation of recently introduced adhesives.

    Science.gov (United States)

    Guan, Rui; Takagaki, Tomohiro; Matsui, Naoko; Sato, Takaaki; Burrow, Michael F; Palamara, Joseph; Nikaido, Toru; Tagami, Junji

    2016-07-30

    Dentin bonding durability of recently introduced dental adhesives: Clearfil SE Bond 2 (SE2), Optibond XTR (XTR), and Scotchbond Universal (SBU) was investigated using Weibull analysis as well as analysis of the micromorphological features of the acid-base resistant zone (ABRZ) created for the adhesives. The bonding procedures of SBU were divided into three subgroups: self-etch (SBS), phosphoric acid (PA) etching on moist (SBM) or dry dentin (SBD). All groups were thermocycled for 0, 5,000 and 10,000 cycles followed by microtensile bond strength testing. Acid-base challenge was undertaken before SEM and TEM observations of the adhesive interface. The etch-and-rinse method with SBU (SBM and SBD) created inferior interfaces on the dentin surface which resulted in reduced bond durability. ABRZ formation was detected with the self-etch adhesive systems; SE2, XTR and SBS. In the PA etching protocols of SBM and SBD, a thick hybrid layer but no ABRZ was detected, which might affect dentin bond durability. PMID:27335136

  16. Legionella pneumophila utilizes a Single Player Disulfide-Bond Oxidoreductase System to Manage Disulfide Bond Formation and Isomerization

    Science.gov (United States)

    Kpadeh, Zegbeh Z.; Day, Shandra R.; Mills, Brandy W.; Hoffman, Paul S.

    2015-01-01

    Legionella pneumophila uses a single homodimeric disulfide bond (DSB) oxidoreductase DsbA2 to catalyze extracytoplasmic protein folding and to correct DSB errors through protein-disulfide isomerase (PDI) activity. In Escherichia coli, these functions are separated to avoid futile cycling. In L. pneumophila, DsbA2 is maintained as a mixture of disulfides (S-S) and free thiols (SH), but when expressed in E. coli, only the SH form is observed. We provide evidence to suggest that structural differences in DsbB oxidases (LpDsbB1 and LpDsbB2) and DsbD reductases (LpDsbD1 and LpDsbD2) (compared to E. coli) permit bifunctional activities without creating a futile cycle. LpdsbB1 and LpdsbB2 partially complemented an EcdsbB mutant while neither LpdsbD1 nor LpdsbD2 complemented an EcdsbD mutant unless DsbA2 was also expressed. When the dsb genes of E. coli were replaced with those of L. pneumophila, motility was restored and DsbA2 was present as a mixture of redox forms. A dominant-negative approach to interfere with DsbA2 function in L. pneumophila determined that DSB oxidase activity was necessary for intracellular multiplication and assembly/function of the Dot/Icm Type IVb secretion system. Our studies show that a single-player system may escape the futile cycle trap by limiting transfer of reducing equivalents from LpDsbDs to DsbA2. PMID:25534767

  17. μ-Opioid receptors within subregions of the striatum mediate pair bond formation through parallel yet distinct reward mechanisms.

    Science.gov (United States)

    Resendez, Shanna L; Dome, Mackenzie; Gormley, Gwen; Franco, Dena; Nevárez, Natalie; Hamid, Arif A; Aragona, Brandon J

    2013-05-22

    The prairie vole is a socially monogamous rodent that is an excellent animal model for studies of the neurobiology of social attachment. Such studies have demonstrated that activation of reward circuitry during social interactions facilitates pair bond formation. Within this circuitry, μ-opioid receptors (MORs) modulate naturally rewarding behavior in an anatomically segregated manner; MORs located throughout the striatum (dorsal striatum, NAc core, and the entire NAc shell) are implicated in general motivational processes, whereas those located specifically within the dorsomedial NAc shell mediate positive hedonics (and are referred to as a "hedonic hotspot"). The purpose of the present study was to determine whether MORs within these distinct subregions differentially mediate pair bond formation. We first used receptor autoradiography to compare MOR binding densities between these regions. MOR binding was significantly higher in the NAc core and dorsomedial NAc shell compared with the ventral NAc shell. We next used partner preference testing to determine whether MORs within these subregions differentially mediate pair bonding. Blockade of MORs using 1 or 3 μg of H-d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2 within the dorsal striatum decreased mating during the cohabitation period and inhibited partner preference formation. In contrast, blockade of MORs within dorsomedial NAc shell inhibited partner preference formation without effecting mating behavior, whereas other regions were not involved. Thus, MORs within the dorsal striatum mediate partner preference formation via impairment of mating, whereas those in the dorsomedial NAc shell appear to mediate pair bond formation through the positive hedonics associated with mating. PMID:23699524

  18. In vivo biofilm formation on stainless steel bonded retainers during different oral health-care regimens

    NARCIS (Netherlands)

    Jongsma, Marije A.; van der Mei, Henny C.; Atema-Smit, Jelly; Busscher, Henk I.; Ren, Yijin

    2015-01-01

    Retention wires permanently bonded to the anterior teeth are used after orthodontic treatment to prevent the teeth from relapsing to pre-treatment positions. A disadvantage of bonded retainers is biofilm accumulation on the wires, which produces a higher incidence of gingival recession, increased po

  19. Formation process,microstructure and mechanical property of transient liquid phase bonded aluminium-based metal matrix composite joint

    Institute of Scientific and Technical Information of China (English)

    孙大谦; 刘卫红; 贾树盛; 邱小明

    2004-01-01

    The formation process, microstructure and mechanical properties of transient liquid phase (TLP) bonded aluminium-based metal matrix composite (MMC) joint with copper interlayer were investigated. The formation process of the TLP joint comprises a number of stages: plastic deformation and solid diffusion (stage 1), dissolution of interlayer and base metal (stage 2), isothermal solidification (stage 3) and homogenization (stage 4). The microstructure of the joint depends on the joint formation process (distinct stages). The plastic deformation and solid diffusion in stage 1 favoure the intimate contact at interfaces and liquid layer formation. The microstructure of joint consists of aluminium solid solution, alumina particle, Al2Cu and MgAl2O4 compounds in stage 2. The most pronounced feature of joint microstructure in stage 3 is the alumina particle segregation in the center of the joint. The increase of joint shear strength with increasing bonding temperature is mainly attributed to improving the fluidity and wettability of liquid phase and decreasing the amount of Al2Cu brittle phase in the joint. The principal reason of higher bonding temperature (>600 ℃) resulting in lowering obviously the joint shear strength is the widening of alumina particle segregation region that acts as a preferential site for failure. The increase of joint shear strength with increasing holding time is mainly associated with decreasing the amount of Al2 Cu brittle phase and promoting homogenization of joint.

  20. Regioselective carbon–carbon bond formation of 5,5,5-trifluoro-1-phenylpent-3-en-1-yne

    Directory of Open Access Journals (Sweden)

    Motoki Naka

    2013-10-01

    Full Text Available The regioselective carbon–carbon bond formation was studied using 5,5,5-trifluoro-1-phenylpent-3-en-1-yne as a model substrate, and predominant acceptance of electrophiles β to a CF3 group as well as a deuterium trap experiment of the lithiated species led to the conclusion that the obtained regioselectivity is kinetically determined for the reactions with electrophiles, under equilibration of the possible two anionic species.

  1. Investigation of biopolymer-based hydrogels as green and heterogeneous catalysts in C-C bond formation

    OpenAIRE

    Kühbeck, Dennis

    2015-01-01

    The present dissertation evaluates the efficacy of different polysaccharides (e.g. chitosan, alginate and kappa-carrageenan) and proteins (e.g. gelatin, collagen, silk fibroin) as possible catalysts for a variety of C-C bond formation reactions. These biopolymers can be obtained in different forms (e.g. hydrogels, mesoporous materials). Among different forms hydrogels are one of the most interesting since they could act as biphasic and heterogeneous systems in chemical transformations and fa...

  2. Evolution of the chemical bonding nature and electrode activity of indium selenide upon the composite formation with graphene nanosheets

    International Nuclear Information System (INIS)

    Graphical abstract: Display Omitted -- Highlights: • In4Se2.85@graphene nanocomposite is easily prepared by high energy mechanical milling process. • The bond covalency of In4Se2.85 is notably changed upon the composite formation with graphene. • In4Se2.85@graphene nanocomposite shows promising anode performance for lithium ion battery. -- Abstract: Evolution of the chemical bonding nature and electrochemical activity of indium selenide upon the composite formation with carbon species is systematically investigated. Nanocomposites of In4Se2.85@graphene and In4Se2.85@carbon-black are synthesized via a solid state reaction between In and Se elements, and the following high energy mechanical milling of In4Se2.85 with graphene and carbon-black, respectively. The high energy mechanical milling (HEMM) of In4Se2.85 with carbon species gives rise to a decrease of particle size with a significant depression of the crystallinity of In4Se2.85 phase. In contrast to the composite formation with carbon-black, that with graphene induces a notable decrease of (In−Se) bond covalency, underscoring significant chemical interaction between graphene and In4Se2.85. Both the nanocomposites of In4Se2.85@graphene and In4Se2.85@carbon-black show much better anode performance for lithium ion batteries with larger discharge capacity and better cyclability than does the pristine In4Se2.85 material, indicating the beneficial effect of composite formation on the electrochemical activity of indium selenide. Between the present nanocomposites, the electrode performance of the In4Se2.85@graphene nanocomposite is superior to that of the In4Se2.85@carbon-black nanocomposite, which is attributable to the weakening of (In−Se) bonds upon the composite formation with graphene as well as to the better mixing between In4Se2.85 and graphene. The present study clearly demonstrates that the composite formation with graphene has strong influence on the chemical bonds and electrode activity of indium

  3. Ultraclean Si/Si interface formation by surface preparation and direct bonding in ultrahigh vacuum

    DEFF Research Database (Denmark)

    Hermansson, Karin; Grey, Francois; Bengtsson, Stefan; Södervall, Ulf

    1998-01-01

    Silicon surfaces have been cleaned and bonded in ultrahigh vacuum, at a pressure in the 10(-10) Torr range. The bonded interfaces show extremely low contamination levels as measured by secondary ion mass spectroscopy. Nevertheless, a potential barrier could be detected at the interface by spreading...... resistance and current vs. temperature measurements. This suggests that the barrier is caused by inevitable dislocation networks due to wafer misorientation, as well as residual oxygen at the interface....

  4. Palladium-catalysed ortho arylation of acetanilides

    Indian Academy of Sciences (India)

    Guo-zhen zhang; Cheng-Qun Chen; Xin-Hua Feng; Guo-Sheng Huang

    2010-03-01

    The palladium-catalysed direct arylation of acetanilides by using C-H activation methodology has been demonstrated. Several acetanilides were coupled with aryl iodides in the presence of 10 mol% of Pd(OAc)2, 1.0 equiv of Cu(OTf)2, and 0.6 equiv of Ag2O to afford the corresponding products in moderate to excellent yields. The results showed that the amount of Ag2O was important for this protocol.

  5. Hemicellulose hydrolysis catalysed by solid acids

    OpenAIRE

    Carà, P.D..; Pagliaro, M.; Elmekawy, A.; Brown, D R; Verschuren, P.; Shiju, N.R.; Rothenberg, G.

    2013-01-01

    Depolymerising hemicellulose into platform sugar molecules is a key step in developing the concept of an integrated biorefinery. This reaction is traditionally catalysed by either enzymes or homogeneous mineral acids. We compared various solid catalysts for hemicellulose hydrolysis, running reactions in water, under neutral pH and relatively mild temperature and pressure (120 degrees C and 10 bar) conditions. Sulphonated resins are highly active, but they leach out sulphonic groups. Sulphonat...

  6. Dissolution kinetics of tuff rock and mechanism of chemical bond formation at the interface with cement grout

    International Nuclear Information System (INIS)

    The interaction of tuff rock and cement was studied to evaluate the effectiveness of sealing of tuff boreholes with cementitious grouts. Previous studies indicated chemical bond formation between tuff and cement. Dissolution studies were carried out on Topopah Spring member tuff and on tuff with cement. The results indicate the formation of calcium silicate and calcium aluminosilicate hydrates; phase identification is confirmed by XRD studies. The significance of the results obtained and their implications on properties of the interfacial region are included. 7 refs., 6 figs

  7. Oxidation and β-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands.

    Science.gov (United States)

    Jiménez, M Victoria; Fernández-Tornos, Javier; Modrego, F Javier; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-12-01

    The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for CC bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3 )(cod)(MeIm(2- methoxybenzyl))][BF4 ] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0 ) of 1283 h(-1) , and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new CC bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde. PMID:26493780

  8. 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

  9. Evaluation of Bonding Shear Performance of Ultra-High-Performance Concrete with Increase in Delay in Formation of Cold Joints

    Directory of Open Access Journals (Sweden)

    Han-Seung Lee

    2016-05-01

    Full Text Available This study set out to derive the optimal conditions for ensuring the monolithicity of ultra-high-performance concrete (UHPC. Direct shear tests were performed to examine the influence on the bonding shear performance. The experimental variables included tamping and delay, which were set to 0, 15, 30, and 60 min. SEM and XRD analyses of the microstructure and composition were performed. The direct shear tests showed that the bonding shear strength was enhanced by the addition of tamping. For the normal-strength concrete (NSC, it is thought that a monolithicity of around 95% can be attained with a cold joint formation delay up to 60 min. In contrast, while the normalized bonding shear strength reduction of UHPC with a delay of 15 min was the lowest at around 8%, a dramatic degradation in the bonding shear performance was observed after 15 min. XRD analyses of the middle and surface sections revealed the composition of the thin film formed at the surface of the UHPC and, as a result, the main component appeared to be SiO2, which is believed to be a result of the rising of the SiO2-based filler, used as an admixture in this study, towards the surface, due to its low specific gravity.

  10. Synthesis of Oxygen Heterocycles via Aromatic C-O Bond Formation Using Arynes

    OpenAIRE

    Hideto Miyabe

    2015-01-01

    Most of the synthetic approaches to the benzo-fused heterocycles containing an oxygen atom have involved the use of phenol derivatives as a starting material. This review highlights the new synthetic approaches involving the aromatic C-O bond-forming process using arynes. The insertion of arynes into the C=O bond gives the unstable intermediates, [2 + 2] cycloaddition-type adducts, which can be easily converted into a variety of oxygen atom-containing heterocycles in a single operation. In t...

  11. 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.

  12. Formation of Me–O–Si covalent bonds at the interface between polysilazane and stainless steel

    International Nuclear Information System (INIS)

    Highlights: • Natural metal-oxides, hydroxides are detected on the top surface of steel substrates we tested. • Polysilazane reacts with hydroxide functional groups on steel substrates to form Cr–O–Si and Fe–O–Si covalent bonds. • Covalent bonding between steel and polysilazane at the interface was probed using spectroscopic techniques. - Abstract: In earlier works, we demonstrated the potential of polysilazane (PSZ) coatings for a use as insulating layers in Cu(In,Ga)Se2 (CIGS) solar cells prepared on steels substrates and showed a good adhesion between PSZ coatings and both AISI316 and AISI430 steels. In the present paper, spectroscopic techniques are used to elucidate the reason of such adhesion. X-ray Photoelectron Spectroscopy (XPS) was used to investigate surfaces for the two steel substrates and showed the presence of metal oxides and metal hydroxides at the top surface. XPS has been also used to probe interfaces between substrates and PSZ, and metallosiloxane (Me–O–Si) covalent bonds have been detected. These results were confirmed by Infra-Red Reflection Absorption Spectroscopy (IRRAS) analyses since vibrations related to Cr–O–Si and Fe–O–Si compounds were detected. Thus, the good adhesion between steel substrates and PSZ coatings was explained by covalent bonding through chemical reactions between PSZ precursors and hydroxide functional groups present on top surface of the two types of steel. Based on these results, an adhesion mechanism between steel substrates and PSZ coatings is proposed

  13. Formation of Me–O–Si covalent bonds at the interface between polysilazane and stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Amouzou, Dodji, E-mail: adodji@gmail.com [Research Centre in Physics of Matter and Radiation (PMR), University of Namur, Rue de Bruxelles 61, 5000 Namur (Belgium); Fourdrinier, Lionel; Maseri, Fabrizio [CRM-Group, Boulevard de Colonster, B 57, 4000 Liège (Belgium); Sporken, Robert [Research Centre in Physics of Matter and Radiation (PMR), University of Namur, Rue de Bruxelles 61, 5000 Namur (Belgium)

    2014-11-30

    Highlights: • Natural metal-oxides, hydroxides are detected on the top surface of steel substrates we tested. • Polysilazane reacts with hydroxide functional groups on steel substrates to form Cr–O–Si and Fe–O–Si covalent bonds. • Covalent bonding between steel and polysilazane at the interface was probed using spectroscopic techniques. - Abstract: In earlier works, we demonstrated the potential of polysilazane (PSZ) coatings for a use as insulating layers in Cu(In,Ga)Se{sub 2} (CIGS) solar cells prepared on steels substrates and showed a good adhesion between PSZ coatings and both AISI316 and AISI430 steels. In the present paper, spectroscopic techniques are used to elucidate the reason of such adhesion. X-ray Photoelectron Spectroscopy (XPS) was used to investigate surfaces for the two steel substrates and showed the presence of metal oxides and metal hydroxides at the top surface. XPS has been also used to probe interfaces between substrates and PSZ, and metallosiloxane (Me–O–Si) covalent bonds have been detected. These results were confirmed by Infra-Red Reflection Absorption Spectroscopy (IRRAS) analyses since vibrations related to Cr–O–Si and Fe–O–Si compounds were detected. Thus, the good adhesion between steel substrates and PSZ coatings was explained by covalent bonding through chemical reactions between PSZ precursors and hydroxide functional groups present on top surface of the two types of steel. Based on these results, an adhesion mechanism between steel substrates and PSZ coatings is proposed.

  14. Anatomy of Bond Formation. Insights from the DAFH Analysis in Momentum Space

    Czech Academy of Sciences Publication Activity Database

    Ponec, Robert; Cooper, D.L.

    -: -, 2009, Poster 33. ISBN N. [Central European Symposium on Theoretical Chemistry. Dobogókö (HU), 25.09.2009-28.09.2009] R&D Projects: GA ČR GA203/09/0118 Institutional research plan: CEZ:AV0Z40720504 Keywords : chemical bond * analysis of domain averaged fermi holes * momentum space Subject RIV: CC - Organic Chemistry

  15. Ruthenium-Catalyzed Transfer Hydrogenation for C-C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs.

    Science.gov (United States)

    Perez, Felix; Oda, Susumu; Geary, Laina M; Krische, Michael J

    2016-06-01

    Merging the chemistry of transfer hydrogenation and carbonyl or imine addition, a broad new family of redox-neutral or reductive hydrohydroxyalkylations and hydroaminomethylations have been developed. In these processes, hydrogen redistribution between alcohols and π-unsaturated reactants is accompanied by C-C bond formation, enabling direct conversion of lower alcohols to higher alcohols. Similarly, hydrogen redistribution between amines to π-unsaturated reactants results in direct conversion of lower amines to higher amines. Alternatively, equivalent products of hydrohydroxyalkylation and hydroaminomethylation may be generated through the reaction of carbonyl compounds or imines with π-unsaturated reactants under the conditions of 2-propanol-mediated reductive coupling. Finally, using vicinally dioxygenated reactants, that is, diol, ketols, or diones, successive transfer hydrogenative coupling occurs to generate 2 C-C bonds, resulting in products of formal [4+2] cycloaddition. PMID:27573275

  16. Effect of hydrogen bonding and hydrophobic interaction on the formation of supramolecular hydrogels formed by L-phenylalanine derivative hydrogelator

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A new hydrogelator, pyridinium bromide salt of N-6-bromohexanoyl-L-phenylamino octadecane, was synthesized. Supramolecular hydrogels can be formed through the self-assembly of this hydrogelator in water. In this work, D2O was used instead of H2O as solvent for FT-IR measurement due to the fact that it is impossible to obtain useful FT-IR information on the hydrogen bonding in water. The investigation of FT-IR and steady-state fluorescence indicated that the driving forces for the self-assembly were mainly hydrogen bonding and hydrophobic interaction. Based on the data of XRD and molecular modeling, the possible mechanism of the formation of hydrogelator aggregates was proposed.

  17. Regularities in the formation of dislocation networks on the boundary of bonded Si(001) wafers

    International Nuclear Information System (INIS)

    The dislocation networks in structures with hydrophilically bonded Si (001) wafers are investigated by transmission electron microscopy. Networks with differing geometry and type of dominant dislocations are observed. One type of networks, which is typical of bonded structures, is formed on the basis of a square network of screw dislocations and contains a system of unidirectional 60° zigzag-shaped dislocations. It is established that such dislocation networks are flat in structures with an azimuthal misorientation of wafers exceeding 2°, whereas they are three-dimensional at smaller misorientation angles. A unique network of another type is formed only by 60° dislocations, the majority of which are extended along one direction, which does not coincide with the 〈110〉 directions in the boundary plane and has a number of specific features, the explanation of which is impossible within the framework of conventional representations.

  18. Palladium-Catalyzed C–C Bond Formations via Activation of Carboxylic Acids and Their Derivatives

    OpenAIRE

    Song, Bingrui

    2013-01-01

    Applications of carboxylic acids and their derivatives in transition metal-catalyzed cross-coupling reactions regio-selectively forming Csp3-Csp2, and Csp2-Csp2 bonds were explored in this thesis. Several important organic building blocks such as aryl acetates, diaryl acetates, imines, ketones, biaryls, styrenes and polysubstituted alkenes were successfully accessed from carboxylic acids and their derivatives by the means of C–H activation and decarboxylative cross-couplings. An efficient ...

  19. Assessment of covalent bond formation between coupling agents and wood by FTIR spectroscopy and pull strength tests

    DEFF Research Database (Denmark)

    Rasmussen, Jonas Stensgaard; Barsberg, Søren Talbro; Venås, Thomas Mark; Felby, Claus

    2014-01-01

    In the focus was the question whether metal alkoxide coupling agents – titanium, silane, and zirconium – form covalent bonds to wood and how they improve coating adhesion. In a previous work, a downshift of the lignin infrared (IR) band ∼1600 cm-1 was shown to be consistent with the formation of...... ether linkages between lignin and titanium coupling agent. In the present work, changes were found in the attenuated total reflectance-Fourier transform IR (ATR-FTIR) spectra of lignin and wood mixed with silane, and titanium coupling agents, and to a lesser extent for a zirconium coupling agent. This...

  20. Probabilistic modeling of shear-induced formation and breakage of doublets cross-linked by receptor-ligand bonds.

    OpenAIRE

    Long, M.; Goldsmith, H L; Tees, D. F.; C. Zhu

    1999-01-01

    A model was constructed to describe previously published experiments of shear-induced formation and breakage of doublets of red cells and of latexes cross-linked by receptor-ligand bonds (. Biophys. J. 65:1318-1334; Tees and Goldsmith. 1996. Biophys. J. 71:1102-1114;. Biophys. J. 71:1115-1122). The model, based on McQuarrie's master equations (1963. J. Phys. Chem. 38:433-436), provides unifying treatments for three distinctive time periods in the experiments of particles in a Couette flow in ...

  1. Concurrent Formation of Carbon-Carbon Bonds and Functionalized Graphene by Oxidative Carbon-Hydrogen Coupling Reaction.

    Science.gov (United States)

    Morioku, Kumika; Morimoto, Naoki; Takeuchi, Yasuo; Nishina, Yuta

    2016-01-01

    Oxidative C-H coupling reactions were conducted using graphene oxide (GO) as an oxidant. GO showed high selectivity compared with commonly used oxidants such as (diacetoxyiodo) benzene and 2,3-dichloro-5,6-dicyano-p-benzoquinone. A mechanistic study revealed that radical species contributed to the reaction. After the oxidative coupling reaction, GO was reduced to form a material that shows electron conductivity and high specific capacitance. Therefore, this system could concurrently achieve two important reactions: C-C bond formation via C-H transformation and production of functionalized graphene. PMID:27181191

  2. Solvent-Free Selective Condensations Based on the Formation of the Olefinic (C=C Bond Catalyzed by Organocatalyst

    Directory of Open Access Journals (Sweden)

    Heyuan Song

    2016-07-01

    Full Text Available Pyrrolidine and its derivatives were used to catalyze aldol and Knoevenagel condensations for the formation of the olefinic (C=C bond under solvent-free conditions. The 3-pyrrolidinamine showed high activity and afforded excellent yields of α,β-unsaturated compounds. The aldol condensation of aromatic/heterocyclic aldehydes with ketones affords enones in high conversion (99.5% and selectivity (92.7%. Good to excellent yields of α,β-unsaturated compounds were obtained in the Knoevenagel condensation of aldehydes with methylene-activated substrates.

  3. Assessment of covalent bond formation between coupling agents and wood by FTIR spectroscopy and pull strength tests

    OpenAIRE

    Rasmussen, Jonas Stensgaard; Barsberg, Søren Talbro; Venås, Thomas Mark; Felby, Claus

    2014-01-01

    In the focus was the question whether metal alkoxide coupling agents – titanium, silane, and zirconium – form covalent bonds to wood and how they improve coating adhesion. In a previous work, a downshift of the lignin infrared (IR) band ∼1600 cm-1 was shown to be consistent with the formation of ether linkages between lignin and titanium coupling agent. In the present work, changes were found in the attenuated total reflectance-Fourier transform IR (ATR-FTIR) spectra of lignin and wood mixed ...

  4. Characterization of Sviceucin from Streptomyces Provides Insight into Enzyme Exchangeability and Disulfide Bond Formation in Lasso Peptides.

    Science.gov (United States)

    Li, Yanyan; Ducasse, Rémi; Zirah, Séverine; Blond, Alain; Goulard, Christophe; Lescop, Ewen; Giraud, Caroline; Hartke, Axel; Guittet, Eric; Pernodet, Jean-Luc; Rebuffat, Sylvie

    2015-11-20

    Lasso peptides are bacterial ribosomally synthesized and post-translationally modified peptides. They have sparked increasing interest in peptide-based drug development because of their compact, interlocked structure, which offers superior stability and protein-binding capacity. Disulfide bond-containing lasso peptides are rare and exhibit highly sought-after activities. In an effort to expand the repertoire of such molecules, we heterologously expressed, in Streptomyces coelicolor, the gene cluster encoding sviceucin, a type I lasso peptide with two disulfide bridges originating from Streptomyces sviceus, which allowed it to be fully characterized. Sviceucin and its reduced forms were characterized by mass spectrometry and peptidase digestion. The three-dimensional structure of sviceucin was determined using NMR. Sviceucin displayed antimicrobial activity selectively against Gram-positive bacteria and inhibition of fsr quorum sensing in Enterococcus faecalis. This study adds sviceucin to the type I lasso peptide family as a new representative. Moreover, new clusters encoding disulfide-bond containing lasso peptides from Actinobacteria were identified by genome mining. Genetic and functional analyses revealed that the formation of disulfide bonds in sviceucin does not require a pathway-encoded thiol-disulfide oxidoreductase. Most importantly, we demonstrated the functional exchangeability of the sviceucin and microcin J25 (a non-disulfide-bridged lasso peptide) macrolactam synthetases in vitro, highlighting the potential of hybrid lasso synthetases in lasso peptide engineering. PMID:26343290

  5. A quantum-chemical validation about the formation of hydrogen bonds and secondary interactions in intermolecular heterocyclic systems

    Directory of Open Access Journals (Sweden)

    Boaz Galdino Oliveira

    2009-08-01

    Full Text Available We have performed a detailed theoretical study in order to understand the charge density topology of the C2H4O···C2H2 and C2H4S···C2H2 heterocyclic hydrogen-bonded complexes. Through the calculations derived from Quantum Theory of Atoms in Molecules (QTAIM, it was observed the formation of hydrogen bonds and secondary interactions. Such analysis was performed through the determination of optimized geometries at B3LYP/6-31G(d,p level of theory, by which is that QTAIM topological operators were computed, such as the electronic density ρ(r, Laplacian Ñ2ρ(r, and ellipticity ε. The examination of the hydrogen bonds has been performed through the measurement of ρ(r, Ñ2ρ(r and ε between (O···H—C and (S···H—C, whereas the secondary interaction between axial hydrogen atoms Hα and carbon of acetylene. In this insight, it was verified the existence of secondary interaction only in C2H4S···C2H2 complex because its structure is propitious to form multiple interactions.

  6. Symbiosis catalyses niche expansion and diversification.

    Science.gov (United States)

    Joy, Jeffrey B

    2013-04-01

    Interactions between species are important catalysts of the evolutionary processes that generate the remarkable diversity of life. Symbioses, conspicuous and inherently interesting forms of species interaction, are pervasive throughout the tree of life. However, nearly all studies of the impact of species interactions on diversification have concentrated on competition and predation leaving unclear the importance of symbiotic interaction. Here, I show that, as predicted by evolutionary theories of symbiosis and diversification, multiple origins of a key innovation, symbiosis between gall-inducing insects and fungi, catalysed both expansion in resource use (niche expansion) and diversification. Symbiotic lineages have undergone a more than sevenfold expansion in the range of host-plant taxa they use relative to lineages without such fungal symbionts, as defined by the genetic distance between host plants. Furthermore, symbiotic gall-inducing insects are more than 17 times as diverse as their non-symbiotic relatives. These results demonstrate that the evolution of symbiotic interaction leads to niche expansion, which in turn catalyses diversification. PMID:23390106

  7. Synthesis of 1,2,4-Triazoles via Oxidative Heterocyclization: Selective C-N Bond Over C-S Bond Formation.

    Science.gov (United States)

    Gogoi, Anupal; Guin, Srimanta; Rajamanickam, Suresh; Rout, Saroj Kumar; Patel, Bhisma K

    2015-09-18

    The higher propensity of C-N over C-S bond forming ability was demonstrated, through formal C-H functionalization during the construction of 4,5-disubstituted 1,2,4-triazole-3-thiones from arylidenearylthiosemicarbazides catalyzed by Cu(II). However, steric factors imparted by the o-disubstituted substrates tend to change the reaction path giving thiodiazole as the major or an exclusive product. Upon prolonging the reaction time, the in situ generated thiones are transformed to 4,5-disubstituted 1,2,4-triazoles via a desulfurization process. Two classes of heterocycles viz. 4,5-disubstituted 1,2,4-triazole-3-thiones and 4,5-disubstituted 1,2,4-triazoles can be synthesized from arylidenearylthiosemicarbazides by simply adjusting the reaction time. Desulfurization of 1,2,4-triazole-3-thiones is assisted by thiophilic Cu to provide 1,2,4-triazoles with concomitant formation of CuS and polynuclear sulfur anions as confirmed from scanning electron microscope and energy dispersive X-ray spectroscopy measurements. A one-pot synthesis of an antimicrobial compound has been successfully achieved following this strategy. PMID:26332253

  8. 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.

  9. Alternative pathways of disulfide bond formation yield secretion-competent, stable and functional immunoglobulins

    OpenAIRE

    Elkabetz, Yechiel; Ofir, Ayala; Argon, Yair; Bar-Nun, Shoshana

    2008-01-01

    Disulfide bonds within and between proteins are responsible for stabilizing folding and covalent assembly. They are thought to form by an obligatory pathway that leads to a single native structure compatible with secretion. We have previously demonstrated that the intradomain disulfide in the CH1 domain of the Ig γ2b heavy chains was dispensable for secretion (Elkabetz et al., 2005). Here we show that the heavy chain-light chain interchain disulfide is also dispensable. γ2b with mutated Cys12...

  10. Alcohol and group formation: a multimodal investigation of the effects of alcohol on emotion and social bonding.

    Science.gov (United States)

    Sayette, Michael A; Creswell, Kasey G; Dimoff, John D; Fairbairn, Catharine E; Cohn, Jeffrey F; Heckman, Bryan W; Kirchner, Thomas R; Levine, John M; Moreland, Richard L

    2012-08-01

    We integrated research on emotion and on small groups to address a fundamental and enduring question facing alcohol researchers: What are the specific mechanisms that underlie the reinforcing effects of drinking? In one of the largest alcohol-administration studies yet conducted, we employed a novel group-formation paradigm to evaluate the socioemotional effects of alcohol. Seven hundred twenty social drinkers (360 male, 360 female) were assembled into groups of 3 unacquainted persons each and given a moderate dose of an alcoholic, placebo, or control beverage, which they consumed over 36 min. These groups' social interactions were video recorded, and the duration and sequence of interaction partners' facial and speech behaviors were systematically coded (e.g., using the facial action coding system). Alcohol consumption enhanced individual- and group-level behaviors associated with positive affect, reduced individual-level behaviors associated with negative affect, and elevated self-reported bonding. Our results indicate that alcohol facilitates bonding during group formation. Assessing nonverbal responses in social contexts offers new directions for evaluating the effects of alcohol. PMID:22760882

  11. Emotional experiences of preservice science teachers in online learning: the formation, disruption and maintenance of social bonds

    Science.gov (United States)

    Bellocchi, Alberto; Mills, Kathy A.; Ritchie, Stephen M.

    2015-08-01

    The enactment of learning to become a science teacher in online mode is an emotionally charged experience. We attend to the formation, maintenance and disruption of social bonds experienced by online preservice science teachers as they shared their emotional online learning experiences through blogs, or e-motion diaries, in reaction to videos of face-to-face lessons. A multi-theoretic framework drawing on microsociological perspectives of emotion informed our hermeneutic interpretations of students' first-person accounts reported through an e-motion diary. These accounts were analyzed through our own database of emotion labels constructed from the synthesis of existing literature on emotion across a range of fields of inquiry. Preservice science teachers felt included in the face-to-face group as they watched videos of classroom transactions. The strength of these feelings of social solidarity were dependent on the quality of the video recording. E-motion diaries provided a resource for interactions focused on shared emotional experiences leading to formation of social bonds and the alleviation of feelings of fear, trepidation and anxiety about becoming science teachers. We offer implications to inform practitioners who wish to improve feelings of inclusion amongst their online learners in science education.

  12. A protocol for amide bond formation with electron deficient amines and sterically hindered substrates

    DEFF Research Database (Denmark)

    Due-Hansen, Maria E; Pandey, Sunil K; Christiansen, Elisabeth; Andersen, Rikke; Hansen, Steffen V F; Ulven, Trond

    2016-01-01

    A protocol for amide coupling by in situ formation of acyl fluorides and reaction with amines at elevated temperature has been developed and found to be efficient for coupling of sterically hindered substrates and electron deficient amines where standard methods failed.......A protocol for amide coupling by in situ formation of acyl fluorides and reaction with amines at elevated temperature has been developed and found to be efficient for coupling of sterically hindered substrates and electron deficient amines where standard methods failed....

  13. Formation of sulfido niobium complexes through C-S bond activation

    International Nuclear Information System (INIS)

    Upon reacting η5-C5H5)2 Nb CL2, η5-C5H5 = Cp, and (Ph)3 Sn (S Ph), in THF, (η5- C5H5)2 Nb (Cl) (μ-S) Sn (Ph)3 (Cl), 1, and (η5-C5 H5)2 Nb (S) Cl, 2, were obtained. Complexes 1 and 2 were characterized by IR, 1H-NMR, 13 C-NMR, Moessbauer spectroscopies, elemental analysis as well as by atomic absorption. Hydrolysis of 1 yielded the μ-oxo species, (η5-C5 H5)2 Nb (Cl) (μ-O) Sn (Ph)3 Cl, 3, which was characterized by IR, 1H-NMR, 13 C-NMR and Moessbauer spectroscopies, elemental analysis, atomic absorption as well as by X-ray crystallography. It crystallizes in the space group Pca21 with a= 17.282(3), b = 18.122(4), c 17.3269(2), V = 5426.2(16) angstrom3, and Z= 8. Additional studies indicated that the complexes were formed as a result of the nucleophilic displacement of the niobium-chloride bond by the thiolate ligand followed by a C-S bond cleavage. The cleavage occurs with an excess of the thiolate compound equal to or greater than 2:1. (author)

  14. Gold-catalysed facile access to indene scaffolds via sequential C-H functionalization and 5-endo-dig carbocyclization.

    Science.gov (United States)

    Ma, Ben; Wu, Ziang; Huang, Ben; Liu, Lu; Zhang, Junliang

    2016-08-01

    A concise synthesis of functionalized indene derivatives via the gold(i)-catalysed cascade C-H functionalization/conia-ene type reaction of electron-rich aromatics with o-alkynylaryl α-diazoesters has been developed. In this transformation, the gold catalyst not only catalysed the formation of the zwitterionic intermediate via intermolecular C-H functionalization but promoted the subsequent intramolecular 5-endo-dig cyclization via activation of alkynes. The reaction is characterized by high chemo- and site-selectivity, readily available starting materials, nice functional-group tolerance and mild reaction conditions. PMID:27373228

  15. Mechanistic insight into benzenethiol catalyzed amide bond formations from thioesters and primary amines

    DEFF Research Database (Denmark)

    Stuhr-Hansen, Nicolai; Bork, Nicolai; Strømgaard, Kristian

    2014-01-01

    The influence of arylthiols on cysteine-free ligation, i.e. the reaction between an alkyl thioester and a primary amine forming an amide bond, was studied in a polar aprotic solvent. We reacted the ethylthioester of hippuric acid with cyclohexylamine in the absence or presence of various quantities...... state in the aromatic thioester amidation reaction. Under similar conditions, cysteine-free ligation was achieved by coupling a fully side-chain protected 15 amino acid phosphopeptide thioester to the free N-terminal of a side-chain protected 9 amino acid peptide producing the corresponding 24 amino...... of thiophenol (PhSH) in a slurry of disodium hydrogen phosphate in dry DMF. Quantitative conversions into the resulting amide were observed within a few hours in the presence of equimolar amounts of thiophenol. Ab initio calculations showed that the reaction mechanism in DMF is similar to the well...

  16. Catalysis of peptide bond formation by histidyl-histidine in a fluctuating clay environment

    Science.gov (United States)

    White, D. H.; Erickson, J. C.

    1980-01-01

    The condensation of glycine to form oligoglycines during wet-dry fluctuations on clay surfaces was enhanced up to threefold or greater by small amounts of histidyl-histidine. In addition, higher relative yields of the longer oligomers were produced. Other specific dipeptides tested gave no enhancement, and imidazole, histidine, and N-acetylhistidine gave only slight enhancements. Histidyl-histidine apparently acts as a true catalyst (in the sense of repeatedly catalyzing the reaction), since up to 52 nmol of additional glycine were incorporated into oligoglycine for each nmol of catalyst added. This is the first known instance of a peptide or similar molecule demonstrating a catalytic turnover number greater than unity in a prebiotic oligomer synthesis reaction, and suggests that histidyl-histidine is a model for a primitive prebiotic proto-enzyme. Catalysis of peptide bond synthesis by a molecule which is itself a peptide implies that related systems may be capable of exhibiting autocatalytic growth.

  17. Splitting and/or Formation of Chemical Bonds. Insights from Momentum Space

    Czech Academy of Sciences Publication Activity Database

    Ponec, Robert; Cooper, D.L.

    Prague : IOCHB ASCR, v.v.i, 2011, s. 1. ISBN N. [JCS Symposium on Theoretical Chemistry 2011 /4./. Liblice (CZ), 18.05.2011-20.05.2011] R&D Projects: GA ČR GA203/09/0118 Institutional research plan: CEZ:AV0Z40720504 Keywords : domain averaged fermi holes * momentum space * chemical bonding Subject RIV: CF - Physical ; Theoretical Chemistry http://www. google .cz/search?q=www.jh-inst.cas.cz%2Ftchem%2Fjcs-2011&rls=com.microsoft:cs:IE-Address&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7PRFA_cs&redir_esc=&ei=wqLfTa-cFseUOomzmY8K

  18. Thermoacoustical analysis of solutions of poly(ethylene glycol) 200 through H-bond complex formation

    Energy Technology Data Exchange (ETDEWEB)

    Yasmin, Maimoona, E-mail: myasmin908@gmail.com [Department of Physics, University of Lucknow, Lucknow 226007 (India); Gupta, Manisha, E-mail: guptagm@rediffmail.com [Department of Physics, University of Lucknow, Lucknow 226007 (India)

    2011-05-10

    Research highlights: {yields} The presence of two electronegative elements viz. nitrogen and oxygen in its molecular architecture, ethanolamine has greater extent of interaction with PEG. {yields} Ethanolamine and m-cresol may be involved in a complex type of network of hydrogen bonding. {yields} Ethanolamine has greater extent of interaction with PEG than m-cresol and aniline particularly with least magnitude from aniline, where electron availability is least because of delocalization. {yields} The difference in molar volume between the components of the mixture control the mixture properties. - Abstract: Densities ({rho}) and ultrasonic velocities (u) of binary mixtures of poly(ethylene glycol) 200, PEG, with ethanolamine, m-cresol and aniline have been measured at various concentrations at 293.15, 303.15 and 313.15 K and have been fitted by third order polynomial equations at each temperature. The calculated values of isentropic compressibility (k{sub s}), free volume (V{sub f}), internal pressure ({pi}{sub i}), relaxation time ({tau}) and surface tension ({sigma}) at different mole fractions of PEG have been used to explain the hydrogen bonding and intermolecular interactions present in the mixture. Using these data, excess molar volume (V{sup E}), excess intermolecular free length (L{sub f}{sup E}), excess acoustic impedance (Z{sup E}) and excess pseudo-Grueneisen parameter ({Gamma}{sup E}) have been calculated and the results have been fitted to Redlich-Kister polynomial equation. All the results support each other and help in understanding the interactions in the mixture. Various models and mixing rules have been applied to evaluate the ultrasonic velocity data and have been compared with the experimental results.

  19. Thermoacoustical analysis of solutions of poly(ethylene glycol) 200 through H-bond complex formation

    International Nuclear Information System (INIS)

    Research highlights: → The presence of two electronegative elements viz. nitrogen and oxygen in its molecular architecture, ethanolamine has greater extent of interaction with PEG. → Ethanolamine and m-cresol may be involved in a complex type of network of hydrogen bonding. → Ethanolamine has greater extent of interaction with PEG than m-cresol and aniline particularly with least magnitude from aniline, where electron availability is least because of delocalization. → The difference in molar volume between the components of the mixture control the mixture properties. - Abstract: Densities (ρ) and ultrasonic velocities (u) of binary mixtures of poly(ethylene glycol) 200, PEG, with ethanolamine, m-cresol and aniline have been measured at various concentrations at 293.15, 303.15 and 313.15 K and have been fitted by third order polynomial equations at each temperature. The calculated values of isentropic compressibility (ks), free volume (Vf), internal pressure (πi), relaxation time (τ) and surface tension (σ) at different mole fractions of PEG have been used to explain the hydrogen bonding and intermolecular interactions present in the mixture. Using these data, excess molar volume (VE), excess intermolecular free length (LfE), excess acoustic impedance (ZE) and excess pseudo-Grueneisen parameter (ΓE) have been calculated and the results have been fitted to Redlich-Kister polynomial equation. All the results support each other and help in understanding the interactions in the mixture. Various models and mixing rules have been applied to evaluate the ultrasonic velocity data and have been compared with the experimental results.

  20. Glucose and Fructose to Platform Chemicals: Understanding the Thermodynamic Landscapes of Acid-Catalysed Reactions Using High-Level ab Initio Methods

    Energy Technology Data Exchange (ETDEWEB)

    Assary, Rajeev S.; Kim, Taijin; Low, John; Greeley, Jeffrey P.; Curtiss, Larry A.

    2012-12-28

    Molecular level understanding of acid-catalysed conversion of sugar molecules to platform chemicals such as hydroxy-methyl furfural (HMF), furfuryl alcohol (FAL), and levulinic acid (LA) is essential for efficient biomass conversion. In this paper, the high-level G4MP2 method along with the SMD solvation model is employed to understand detailed reaction energetics of the acid-catalysed decomposition of glucose and fructose to HMF. Based on protonation free energies of various hydroxyl groups of the sugar molecule, the relative reactivity of gluco-pyranose, fructo-pyranose and fructo-furanose are predicted. Calculations suggest that, in addition to the protonated intermediates, a solvent assisted dehydration of one of the fructo-furanosyl intermediates is a competing mechanism, indicating the possibility of multiple reaction pathways for fructose to HMF conversion in aqueous acidic medium. Two reaction pathways were explored to understand the thermodynamics of glucose to HMF; the first one is initiated by the protonation of a C2–OH group and the second one through an enolate intermediate involving acyclic intermediates. Additionally, a pathway is proposed for the formation of furfuryl alcohol from glucose initiated by the protonation of a C2–OH position, which includes a C–C bond cleavage, and the formation of formic acid. The detailed free energy landscapes predicted in this study can be used as benchmarks for further exploring the sugar decomposition reactions, prediction of possible intermediates, and finally designing improved catalysts for biomass conversion chemistry in the future.

  1. Revisiting the Brønsted acid catalysed hydrolysis kinetics of polymeric carbohydrates in ionic liquids by in situ ATR-FTIR spectroscopy

    DEFF Research Database (Denmark)

    Kunov-Kruse, Andreas Jonas; Riisager, Anders; Shunmugavel, Saravanamurugan;

    2013-01-01

    A new versatile method to measure rates and determine activation energies for the Brønsted acid catalysed hydrolysis of cellulose and cellobiose (and other polymeric carbohydrates) in ionic liquids is demonstrated by following the C–O stretching band of the glycoside bond with in situ ATR-FTIR. A...

  2. Enantioselective Formation of a Dynamic Hydrogen-Bonded Assembly Based on the Chiral Memory Concept

    NARCIS (Netherlands)

    Ishi-i, Tsutomu; Crego Calama, Mercedes; Timmerman, Peter; Reinhoudt, David N.; Shinkai, Seiji

    2002-01-01

    In this paper, we report the enantioselective formation of a dynamic noncovalent double rosette assembly 1a3·(CYA)6 composed of three 2-pyridylcalix[4]arene dimelamines (1a) and six butylcyanuric acid molecules (BuCYA). The six 2-pyridyl functionalities of the assembly interact stereoselectively wit

  3. Heat-induced whey protein isolate fibrils: Conversion, hydrolysis, and disulphide bond formation

    NARCIS (Netherlands)

    Bolder, S.G.; Vasbinder, A.; Sagis, L.M.C.; Linden, van der E.

    2007-01-01

    Fibril formation of individual pure whey proteins and whey protein isolate (WPI) was studied. The heat-induced conversion of WPI monomers into fibrils at pH 2 and low ionic strength increased with heating time and protein concentration. Previous studies, using a precipitation method, size-exclusion

  4. Interface microstructure and formation mechanism of diffusion-bonded joints of TiAl to steel 40Cr

    Institute of Scientific and Technical Information of China (English)

    何鹏; 冯吉才; 张炳刚; 钱乙余

    2002-01-01

    TiAl intermetallics was diffusion bonded to steel 40Cr in vacuum furnace. The results show that at the TiAl-40Cr interface the mixture reaction layer of Ti3Al+FeAl+FeAl2 is formed close to the TiAl base, TiC layer is formed in the middle and obvious decarbonized layer is formed closest to the steel 40Cr side. The whole reaction process can be divided into three stages. In the first stage, TiC layer is formed at the interface TiAl/40Cr, as well, decarbonized layer occurs on the steel 40Cr side. In the second stage, TiAl, FeAl2 and FeAl are formed adjacent to TiAl, in the mean, the continuous diffusion of Al atoms from TiAl to 40Cr gives rise to the formation of Ti3Al. In the last stage, the thickness of each reaction layer increases with bonding time according to a parabolic law. The growth energy Q and the growth velocity K0 of reaction layer Ti3Al+FeAl+FeAl2+TiC in the diffusion-bonded joints of the TiAl base alloy to steel 40Cr are 203.017kJ/mol and 6.074mm2/s, respectively, and the growth formula (thickness of reaction layer) is y2=6.074×10-6exp(-203017.48/RT)t. By virtue of this formula, the growth of reaction layer Ti3Al+FeAl+FeAl2+TiC can be presetted and controlled.

  5. Efficient Covalent Bond Formation in Gas-Phase Peptide-Peptide Ion Complexes with the Photoleucine Stapler

    Science.gov (United States)

    Shaffer, Christopher J.; Andrikopoulos, Prokopis C.; Řezáč, Jan; Rulíšek, Lubomír; Tureček, František

    2016-04-01

    Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* n L m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N2 from the L* diazirine rings underwent insertion into X-H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific 13C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)+ ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H]+ ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide-peptide ion interactions in the gas phase.

  6. Polymer GARD: computer simulation of covalent bond formation in reproducing molecular assemblies.

    Science.gov (United States)

    Shenhav, Barak; Bar-Even, Arren; Kafri, Ran; Lancet, Doron

    2005-04-01

    The basic Graded Autocatalysis Replication Domain (GARD) model consists of a repertoire of small molecules, typically amphiphiles, which join and leave a non-covalent micelle-like assembly. Its replication behavior is due to occasional fission, followed by a homeostatic growth process governed by the assembly's composition. Limitations of the basic GARD model are its small finite molecular repertoire and the lack of a clear path from a 'monomer world' towards polymer-based living entities. We have now devised an extension of the model (polymer GARD or P-GARD), where a monomer-based GARD serves as a 'scaffold' for oligomer formation, as a result of internal chemical rules. We tested this concept with computer simulations of a simple case of monovalent monomers, whereby more complex molecules (dimers) are formed internally, in a manner resembling biosynthetic metabolism. We have observed events of dimer 'take-over' - the formation of compositionally stable, replication-prone quasi stationary states (composomes) that have appreciable dimer content. The appearance of novel metabolism-like networks obeys a time-dependent power law, reminiscent of evolution under punctuated equilibrium. A simulation under constant population conditions shows the dynamics of takeover and extinction of different composomes, leading to the generation of different population distributions. The P-GARD model offers a scenario whereby biopolymer formation may be a result of rather than a prerequisite for early life-like processes. PMID:16010993

  7. Polymer Gard: Computer Simulation of Covalent Bond Formation in Reproducing Molecular Assemblies

    Science.gov (United States)

    Shenhav, Barak; Bar-Even, Arren; Kafri, Ran; Lancet, Doron

    2005-04-01

    The basic Graded Autocatalysis Replication Domain (GARD) model consists of a repertoire of small molecules, typically amphiphiles, which join and leave a non-covalent micelle-like assembly. Its replication behavior is due to occasional fission, followed by a homeostatic growth process governed by the assembly’ s composition. Limitations of the basic GARD model are its small finite molecular repertoire and the lack of a clear path from a ‘monomer world’ towards polymer-based living entities.We have now devised an extension of the model (polymer GARD or P-GARD), where a monomer-based GARD serves as a ‘scaffold’ for oligomer formation, as a result of internal chemical rules. We tested this concept with computer simulations of a simple case of monovalent monomers, whereby more complex molecules (dimers) are formed internally, in a manner resembling biosynthetic metabolism. We have observed events of dimer ‘take-over’ the formation of compositionally stable, replication-prone quasi stationary states (composomes) that have appreciable dimer content. The appearance of novel metabolism-like networks obeys a time-dependent power law, reminiscent of evolution under punctuated equilibrium. A simulation under constant population conditions shows the dynamics of takeover and extinction of different composomes, leading to the generation of different population distributions. The P-GARD model offers a scenario whereby biopolymer formation may be a result of rather than a prerequisite for early life-like processes.

  8. Interface structure and formation mechanism of diffusion-bonded joints of TiAl-based alloy to titanium alloy

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Vacuum diffusion bonding of a TiAl-based alloy (TAD) to a titanium alloy (TC2) was carried out at 1 273 K for 15~120 min under a pressure of 25 MPa. The kinds of the reaction products and the interface structures of the joints were investigated by SEM, EPMA and XRD. Based on this, a formation mechanism of the interface structure was elucidated. Experimental and analytical results show that two reaction layers have formed during the diffusion bonding of TAD to TC2. One is Al-rich α(Ti)layer adjacent to TC2,and the other is (Ti3Al+TiAl)layer adjacent to TAD,thus the interface structure of the TAD/TC2 joints is TAD/(Ti3Al+TiAl)/α(Ti)/TC2.This interface structure forms according to a three-stage mechanism,namely(a)the occurrence of a single-phase α(Ti)layer;(b)the occurrence of a duplex-phase(Ti3Al+TiAl)layer;and(c)the growth of the α(Ti)and (Ti3Al+TiAl)layers.

  9. On the formation and bonding of a surface carbonate on Ni(100)

    Science.gov (United States)

    Behm, R. J.; Brundle, C. R.

    1991-09-01

    The formation, stability, adsorption geometry and electronic structure of a surface carbonate on Ni(100) have been investigated by photoemission (XPS, UPS) and temperature-programmed reaction (TPR). The core level binding energies of 531.2 eV for 0(1s) and 289.0 eV for C(1s) are comparable to those of bulk carbonates. The He(II) spectrum of the carbonate valence levels is not well defined because of the coexisting adsorbed and oxidic oxygen. The angular dependence of the carbonate core level intensities is characteristic of the carbonate being present as an overlayer species rather than a thicker surface phase. The XPS data and isotope labelled TPR experiments indicate the oxygen atoms of the carbonate to be electronically and chemically equivalent, and on this basis we favor a structure in which the carbonate is attached to the metal via all three oxygen atoms. This is supported by comparision with the core level binding energies of HCOO ab and chemisorbed CO 2,ad, which are similarly attached to the surface. From the core level angular behavior, the close similarity of core level binding energies and available vibrational spectroscopic data, a (nearly) planar geometry of the CO 3,ad on Ni(100) is concluded, which is comparable to the planar bulk carbonate anion and the planar carbonate species on Ag(110). The activation barrier for decomposition is estimated from the observed maximum in TPR at 420 K to be 25 ± 2 kcal/mol. CO 2 does not accumulate on the clean or O ad-precovered Ni(100) surface at 130 K. The stabilized, chemisorbed CO 2,ad species often observed on other metal surfaces therefore does not play a critical role for carbonate formation on Ni(100). Also a mechanism involving the disproportionation of a CO 2… CO 2,ad- dimer anion can be ruled out from TPR data. The evidence of the experiments discussed in this paper suggests that the carbonate is predominantly formed by reaction of CO 2,ad with a less stable, defect (disordered) O ad species rather

  10. Directing Group in Decarboxylative Cross-Coupling: Copper-Catalyzed Site-Selective C-N Bond Formation from Nonactivated Aliphatic Carboxylic Acids.

    Science.gov (United States)

    Liu, Zhao-Jing; Lu, Xi; Wang, Guan; Li, Lei; Jiang, Wei-Tao; Wang, Yu-Dong; Xiao, Bin; Fu, Yao

    2016-08-01

    Copper-catalyzed directed decarboxylative amination of nonactivated aliphatic carboxylic acids is described. This intramolecular C-N bond formation reaction provides efficient access to the synthesis of pyrrolidine and piperidine derivatives as well as the modification of complex natural products. Moreover, this reaction presents excellent site-selectivity in the C-N bond formation step through the use of directing group. Our work can be considered as a big step toward controllable radical decarboxylative carbon-heteroatom cross-coupling. PMID:27439145

  11. Mineral catalysis of the formation of the phosphodiester bond in aqueous solution - The possible role of montmorillonite clays

    Science.gov (United States)

    Ferris, James P.; Ertem, Gozen; KAMALUDDIN; Agarwal, Vipin; Hua, Lu Lin

    1989-01-01

    The possible role of montmorillonite clays in the spontaneous formation on the primitive earth of the phosphodiester bond in the presence of water was investigated in experiments measuring the binding of various nucleosides and nucleotides with Na(+)-montmorillonite 22A and the reactions of these compounds with a water-soluble carbodiimide. It was found that, at neutral pH, adenine derivatives bind stronger than the corresponding uracil derivatives, consistent with the protonation of the adenine by the acidic clay surface and a cationic binding of the protonated ring to the anionic clay surface. The reaction of the 5-prime-AMP with carbodiimide resulted in the formation of 2-prime,5-prime-pApA (18.9 percent), 3-prime,5-prime-pApA (11 percent), and AppA (4.8 percent). The yields of these oligomers obtained when poly(U) was used in place of the clay were 15.5 percent, 3.7 percent, and 14.9 percent AppA, respectively.

  12. Dispersion-corrected first-principles calculation of terahertz vibration, and evidence for weak hydrogen bond formation

    Science.gov (United States)

    Takahashi, Masae; Ishikawa, Yoichi; Ito, Hiromasa

    2013-03-01

    A weak hydrogen bond (WHB) such as CH-O is very important for the structure, function, and dynamics in a chemical and biological system WHB stretching vibration is in a terahertz (THz) frequency region Very recently, the reasonable performance of dispersion-corrected first-principles to WHB has been proven. In this lecture, we report dispersion-corrected first-principles calculation of the vibrational absorption of some organic crystals, and low-temperature THz spectral measurement, in order to clarify WHB stretching vibration. The THz frequency calculation of a WHB crystal has extremely improved by dispersion correction. Moreover, the discrepancy in frequency between an experiment and calculation and is 10 1/cm or less. Dispersion correction is especially effective for intermolecular mode. The very sharp peak appearing at 4 K is assigned to the intermolecular translational mode that corresponds to WHB stretching vibration. It is difficult to detect and control the WHB formation in a crystal because the binding energy is very small. With the help of the latest intense development of experimental and theoretical technique and its careful use, we reveal solid-state WHB stretching vibration as evidence for the WHB formation that differs in respective WHB networks The research was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant No. 22550003).

  13. Structural Control of Nonadiabatic Photochemical Bond Formation: Photocyclization in Structurally Modified ortho-Terphenyls.

    Science.gov (United States)

    Molloy, Molly S; Snyder, Joshua A; DeFrancisco, Justin R; Bragg, Arthur E

    2016-06-16

    Understanding how molecular structure impacts the shapes of potential energy surfaces and prospects for nonadiabatic photochemical dynamics is critical for predicting and controlling the chemistry of molecular excited states. Ultrafast transient absorption spectroscopy was used to interrogate photoinduced, nonadiabatic 6π cyclization of a collection of ortho-terphenyls (OTP) modified with alkyl substituents of different sizes and electron-donating/withdrawing character positioned on its central and pendant phenyl rings. OTP alkylated at the 4,4″ and 4',5' positions of the pendant and central rings, respectively, exhibiting biphasic excited-state relaxation; this is qualitatively similar to relaxation of OTP itself, including a fast decrease in excited-state absorption (τ1 = 1-4 ps) followed by formation of metastable cyclized photoproducts (τ2 = 3-47 ps) that share common characteristic spectroscopic features for all substitutions despite variations in chemical nature of the substituents. By contrast, anomalous excited-state dynamics are observed for 3',6'dimethyl-OTP, in which the methyl substituents crowd the pendant rings sterically; time-resolved spectral dynamics and low photochemical reactivity with iodine reveal that methylation proximal to the pendant rings impedes nonadiabatic cyclization. Results from transient measurements and quantum-chemical calculations are used to decipher the nature of excited state relaxation mechanisms in these systems and how they are perturbed by mechanical, electronic, and steric interactions induced by substituents. PMID:27171560

  14. Dynamics of Radical-Mediated Enzyme Catalyses

    Science.gov (United States)

    Warncke, Kurt

    1997-11-01

    An emergent class of enzymes harnesses the extreme reactivity of electron-deficient free radical species to perform some of the most difficult reactions in biology. The regio- and stereo-selectivity achieved by these enzymes defies long-held ideas that radical reactions are non-specific. The common primary step in these catalyses is metal- or metallocenter-assisted generation of an electron-deficient organic "initiator radical". The initiator radical abstracts a hydrogen atom from the substrate, opening a new reaction channel for rearrangement to the product. Our aim is to elucidate the detailed molecular mechanisms of the radical pair separation and radical rearrangement steps. Radical pair separation and substrate radical rearrangement are tracked by using time-resolved (10-7 to 10-3 s) techniques of pulsed-electron paramagnetic resonance spectroscopy (FT-EPR, ESEEM). Synchronous time-evolution of the reactions is attained by triggering with a visible laser pulse. Transient non-Boltzmann population of the states of the spin-coupled systems, and resultant electron spin polarization, facilitates study at or near room temperature under conditions where the enzymes are operative. The systems examined include ethanolamine deaminase, a vitamin B12 coenzyme-dependent enzyme, ribonucleotide reductase and photosynthetic reaction centers. The electronic and nuclear structural and kinetic information obtained from the pulsed-EPR studies is used to address how the initiator radicals are stabilized against deleterious recombination with the metal, and to distinguish the participation of concerted versus sequential rearrangement pathways.

  15. Laccase catalysed grafting of phenolic onto xylan to improve its applicability in films

    Science.gov (United States)

    Pei, Jicheng; Wang, Bing; Zhang, Fangdong; Li, Zhongyang; Yin, Yunbei; Zhang, Dongxu

    2015-07-01

    Xylan can be tailored for various value-added applications. However, its use in aqueous systems is hampered by its complex structure, and small molecular weight. This research aimed at improving the xylan molecular weight and changing its structure. Laccase-catalysed oxidation of 4-coumaric acid (PCA), ferulic acid (FA), syringaldehyde (SD), and vanillin (VA) onto xylan was grafted to study the changes in its structure, tensile properties, and antibacterial activities. A Fourier transform infrared (FTIR) spectrum analyser was used to observe the changes in functional groups of xylan. The results showed a band at 1635 cm-1 corresponding to the stretching vibration of conjugated carbonyl carboxy hemoglobin and a benzene ring structure were strengthened; the appearance of a new band between 1200 cm-1 and 1270 cm-1 corresponding to alkyl ethers on the aryl C-O stretching vibration was due to the fact that during the grafting process, the number of benzene ring structures increased and covalent connections occurred between phenols and xylan. The reaction mechanism for the laccase-catalysed oxidation of phenol compounds onto xylan was preliminary explored by 13C-NMR. The results showed that PCA-xylan, FA-xylan graft poly onto xylan by Cγ ester bond, SD-xylan graft poly onto xylan by ether bond and an ester bond, and VD-xylan graft poly onto xylan by ether bond. The film strength of xylan derivatives has been significantly increased, especially for the PCA-xylan derivative. The increases in tensile stress at break, tensile strength, tensile yield stress, and Young's modulus were: 24.04%, 31.30%, 55.56%, and 28.21%, respectively. After laccase/phenolics were modified, xylan had a good antibacterial effect to E. coli, Corynebacterium glutamicum, and Bacillus subtilis. The SD-xylan, FA-xylan, and PCA-xylan showed a greater efficacy against E. coli, Corynebacterium glutamicum, and Bacillus subtilis, respectively.

  16. Palladium/N-heterocyclic carbene catalysed regio and diastereoselective reaction of ketones with allyl reagents via inner-sphere mechanism.

    Science.gov (United States)

    Bai, Da-Chang; Yu, Fei-Le; Wang, Wan-Ying; Chen, Di; Li, Hao; Liu, Qing-Rong; Ding, Chang-Hua; Chen, Bo; Hou, Xue-Long

    2016-01-01

    The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism-nucleophilic attack of enolate oxygen on Palladium followed by C-C bond-forming [3,3']-reductive elimination. PMID:27283477

  17. Possible evidence of amide bond formation between sinapinic acid and lysine-containing bacterial proteins by matrix-assisted laser desorption/ionization (MALDI) at 355 nm

    Science.gov (United States)

    We previously reported the apparent formation of matrix adducts of 3,5-dimethoxy-4-hydroxy-cinnamic acid (sinapinic acid or SA) via covalent attachment to disulfide bond-containing proteins (HdeA, HdeB and YbgS) from bacterial cell lysates ionized by matrix-assisted laser desorption/ionization (MALD...

  18. Palladium-catalysed transannular C-H functionalization of alicyclic amines

    Science.gov (United States)

    Topczewski, Joseph J.; Cabrera, Pablo J.; Saper, Noam I.; Sanford, Melanie S.

    2016-03-01

    Discovering pharmaceutical candidates is a resource-intensive enterprise that frequently requires the parallel synthesis of hundreds or even thousands of molecules. C-H bonds are present in almost all pharmaceutical agents. Consequently, the development of selective, rapid and efficient methods for converting these bonds into new chemical entities has the potential to streamline pharmaceutical development. Saturated nitrogen-containing heterocycles (alicyclic amines) feature prominently in pharmaceuticals, such as treatments for depression (paroxetine, amitifadine), diabetes (gliclazide), leukaemia (alvocidib), schizophrenia (risperidone, belaperidone), malaria (mefloquine) and nicotine addiction (cytisine, varenicline). However, existing methods for the C-H functionalization of saturated nitrogen heterocycles, particularly at sites remote to nitrogen, remain extremely limited. Here we report a transannular approach to selectively manipulate the C-H bonds of alicyclic amines at sites remote to nitrogen. Our reaction uses the boat conformation of the substrates to achieve palladium-catalysed amine-directed conversion of C-H bonds to C-C bonds on various alicyclic amine scaffolds. We demonstrate this approach by synthesizing new derivatives of several bioactive molecules, including varenicline.

  19. Stopped Flow Kinetics of MnII Catalysed Periodate Oxidation of 2, 3- dimethylaniline - Evaluation of Stability Constant of the Ternary Intermediate Complex

    OpenAIRE

    Rajneesh Dutt Kaushik; Richa Agarwal; Priyanka Tyagi; Om Singh; Jaspal Singh

    2015-01-01

    The formation of ternary intermediate unstable complex during the oxidation of aromatic amines by periodate ion catalysed by MnII has been proposed in case of some anilines. This paper is the first report on stopped-flow kinetic study and evaluation of stability constant of ternary complex forming in the MnII - catalysed periodate oxidation of 2, 3-dimethylaniline (D) in acetone-water medium. Stop-flow spectrophotometric method was used to study the ternary complex formation and to determine ...

  20. 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.

  1. A direct approach to amines with remote stereocentres by enantioselective CuH-catalysed reductive relay hydroamination

    Science.gov (United States)

    Zhu, Shaolin; Niljianskul, Nootaree; Buchwald, Stephen L.

    2016-02-01

    Amines with remote stereocentres (stereocentres that are three or more bonds away from the C-N bond) are important structural elements in many pharmaceutical agents and natural products. However, previously reported methods to prepare these compounds in an enantioselective manner are indirect and require multistep synthesis. Here, we report a copper-hydride-catalysed, enantioselective synthesis of γ- or δ-chiral amines from readily available allylic alcohols, esters and ethers using a reductive relay hydroamination strategy (a net reductive process in which an amino group is installed at a site remote from the original carbon-carbon double bond). The protocol was suitable for substrates containing a wide range of functional groups and provided remote chiral amine products with high levels of regio- and enantioselectivity. Sequential amination of substrates containing several carbon-carbon double bonds could be achieved, demonstrating the high chemoselectivity of this process.

  2. Bond formation and slow heterogeneous dynamics in adhesive spheres with long-ranged repulsion: quantitative test of mode coupling theory.

    Science.gov (United States)

    Henrich, O; Puertas, A M; Sperl, M; Baschnagel, J; Fuchs, M

    2007-09-01

    A colloidal system of spheres interacting with both a deep and narrow attractive potential and a shallow long-ranged barrier exhibits a prepeak in the static structure factor. This peak can be related to an additional mesoscopic length scale of clusters and/or voids in the system. Simulation studies of this system have revealed that it vitrifies upon increasing the attraction into a gel-like solid at intermediate densities. The dynamics at the mesoscopic length scale corresponding to the prepeak represents the slowest mode in the system. Using mode coupling theory with all input directly taken from simulations, we reveal the mechanism for glassy arrest in the system at 40% packing fraction. The effects of the low-q peak and of polydispersity are considered in detail. We demonstrate that the local formation of physical bonds is the process whose slowing down causes arrest. It remains largely unaffected by the large-scale heterogeneities, and sets the clock for the slow cluster mode. Results from mode-coupling theory without adjustable parameters agree semiquantitatively with the local density correlators but overestimate the lifetime of the mesoscopic structure (voids). PMID:17930244

  3. Mechanism of oxovanadium (IV)-catalysed and uncatalysed bromate oxidation of lactic acid in acid medium: evaluation of composite and individual kinetic and thermodynamic parameters

    International Nuclear Information System (INIS)

    Uncatalysed acid bromate oxidation of lactic acid (LA) exhibits fractional order (1.6) in [acid] and first order each in [Br(V)] and [LA]. Kinetic isotope effect (kH/kD=1) is absent, however an inverse solvent isotope effect (kH2O/kD2O=1.78 at 313 K) is observed. The mechanism proposed consists of a rate determining formation of bromate ester due to the nucleophilic attack by the alcoholic/hydroxyl group at the bromine atom of HOBrO2/H2O2Br+O, followed by a fast disproportionation of the ester through C-C bond cleavage to form products. Oxovanadium(IV)-catalysed LA-Br(V) reaction exhibits second order in [acid], fractional order in [lactic acid] and first order each in [VOSO4] and [oxidant]. The envisaged mechanism assumes a ternary complex formation involving a binary complex of LA and V(IV) and protonated bromate, which subsequently decomposes to the intermediate/products. The rate constants involved for each step of the reactions are evaluated along with their thermodynamic parameters. (author)

  4. On-Surface Synthesis of Two-Dimensional Covalent Organic Structures versus Halogen-Bonded Self-Assembly: Competing Formation of Organic Nanoarchitectures.

    Science.gov (United States)

    Peyrot, David; Silly, Fabien

    2016-05-24

    The competition between the on-surface synthesis of covalent nanoarchitectures and the self-assembly of star-shaped 1,3,5-Tris(4-iodophenyl)benzene molecules on Au(111) in vacuum is investigated using scanning tunneling microscopy above room temperature. The molecules form covalent polygonal nanoachitectures at the gold surface step edges and at the elbows of the gold reconstruction at low coverage. With coverage increasing two-dimensional halogen-bonded structures appear and grow on the surface terraces. Two different halogen-bonded nanoarchitectures are coexisting on the surface and hybrid covalent-halogen bonded structures are locally observed. At high coverage covalent nanoarchitectures are squeezed at the domain boundary of the halogen-bonded structures. The competitive growth between the covalent and halogen-bonded nanoarchitectures leads to formation of a two-layer film above one monolayer deposition. For this coverage, the covalent nanoarchitectures are propelled on top of the halogen-bonded first layer. These observations open up new opportunities for decoupling covalent nanoarchitectures from catalytically active and metal surfaces in vacuum. PMID:27158901

  5. Role of covalent Fe-As bonding in the magnetic moment formation and exchange mechanisms in iron-pnictide superconductors

    OpenAIRE

    Belashchenko, K. D.; Antropov, V. P.

    2008-01-01

    The electronic origin of the huge magnetostructural effect in layered Fe-As compounds is elucidated using LiFeAs as a prototype. The crucial feature of these materials is the strong covalent bonding between Fe and As, which tends to suppress the exchange splitting. The bonding-antibonding splitting is very sensitive to the distance between Fe and As nuclei. We argue that the fragile interplay between bonding and magnetism is universal for this family of compounds. The exchange interaction is ...

  6. Selenium dioxide catalysed oxidation of acetic acid hydrazide by bromate in aqueous hydrochloric acid medium

    Indian Academy of Sciences (India)

    R S Yalgudre; G S Gokavi

    2012-07-01

    Selenium dioxide catalysed acetic acid hydrazide oxidation by bromate was studied in hydrochloric acid medium. The order in oxidant concentration, substrate and catalyst were found to be unity. Increasing hydrogen ion concentration increases the rate of the reaction due to protonation equilibria of the oxidant. The mechanism of the reaction involves prior complex formation between the catalyst and substrate, hydrazide, followed by its oxidation by diprotonated bromate in a slow step. Acetic acid was found to be the oxidation product. Other kinetic data like effect of solvent polarity and ionic strength on the reaction support the proposed mechanism.

  7. A theoretical model investigation of peptide bond formation involving two water molecules in ribosome supports the two-step and eight membered ring mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Qiang [School of Chemistry & Chemical Engineering, Shandong University, Jinan 250100 (China); Gao, Jun, E-mail: gaojun@sdu.edu.cn [Agricultural Bioinformatics Key Laboratory of Hubei Province, College of Informatics, Huazhong Agricultural University, Wuhan 430070 (China); School of Chemistry & Chemical Engineering, Shandong University, Jinan 250100 (China); Zhang, Dongju; Liu, Chengbu [School of Chemistry & Chemical Engineering, Shandong University, Jinan 250100 (China)

    2015-04-01

    Highlights: • We theoretical studied peptide bond formation reaction mechanism with two water molecules. • The first water molecule can decrease the reaction barriers by forming hydrogen bonds. • The water molecule mediated three-proton transfer mechanism is the favorable mechanism. • Our calculation supports the two-step and eight membered ring mechanism. - Abstract: The ribosome is the macromolecular machine that catalyzes protein synthesis. The kinetic isotope effect analysis reported by Strobel group supports the two-step mechanism. However, the destination of the proton originating from the nucleophilic amine is uncertain. A computational simulation of different mechanisms including water molecules is carried out using the same reaction model and theoretical level. Formation the tetrahedral intermediate with proton transfer from nucleophilic nitrogen, is the rate-limiting step when two water molecules participate in peptide bond formation. The first water molecule forming hydrogen bonds with O9′ and H15′ in the A site can decrease the reaction barriers. Combined with results of the solvent isotope effects analysis, we conclude that the three-proton transfer mechanism in which water molecule mediate the proton shuttle between amino and carbon oxygen in rate-limiting step is the favorable mechanism. Our results will shield light on a better understand the reaction mechanism of ribosome.

  8. Formation of the Si-B bond: insertion reactions of silylenes into B-X(X = F, Cl, Br, O, and N) bonds.

    Science.gov (United States)

    Geng, Bing; Xu, Chongjuan; Chen, Zhonghe

    2016-06-01

    The insertion reactions of the silylene H2Si with H2BXHn-1 (X = F, Cl, Br, O, N; n = 1, 1, 1, 2, 3) have been studied by DFT and MP2 methods. The calculations show that the insertions occur in a concerted manner, forming H2Si(BH2)(XHn-1). The essences of H2Si insertions with H2BXHn-1 are the transfers of the σ electrons on the Si atom to the positive BH2 group and the electrons of X into the empty p orbital on the Si atom in H2Si. The order of reactivity in vacuum shows the barrier heights increase for the same-family element X from up to down and the same-row element X from right to left in the periodic table. The energies relating to the B-X bond in H2BXHn-1, and the bond energies of Si-X and Si-B in H2Si(BH2)(XHn-1) may determine the preference of insertions of H2Si into B-X bonds for the same-column element X or for the same-row element X. The insertion reactions in vacuum are similar to those in solvents, acetone, ether, and THF. The barriers in vacuum are lower than those in solvents and the larger polarities of solvents make the insertions more difficult to take place. Both in vacuum and in solvents, the silylene insertions are thermodynamically exothermic. Graphical Abstract The insertion process of H2Si and H2BXHn-1(X = F, Cl, Br, O, and N; n = 1, 1 , 1, 2, 3). PMID:27184004

  9. S-OO bond dissociation energies and enthalpies of formation of the thiomethyl peroxyl radicals CH3S(O)nOO (n=0,1,2)

    International Nuclear Information System (INIS)

    Optimized geometries, S-OO bond dissociation energies and enthalpies of formation for a series of thiomethyl peroxyl radicals are investigated using high level ab initio and density functional theory methods. The results show that the S-OO bond dissociation energy is largest in the methylsulfonyl peroxyl radical, CH3S(O)2OO, which contains two sulfonic type oxygen atoms followed by the methylthiyl peroxyl radical, CH3SOO. The methylsulfinyl peroxyl radical, CH3S(O)OO, which contains only one sulfonic type oxygen shows the least stability with regard to dissociation to CH3S(O)+O2. This stabilization trend is nicely reflected in the variations of the S-OO bond distance which is found to be shortest in CH3S(O)2OO and longest in CH3S(O)OO

  10. LAMMPS Framework for Directional Dynamic Bonding

    DEFF Research Database (Denmark)

    2012-01-01

    We have extended the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to support directional bonds and dynamic bonding. The framework supports stochastic formation of new bonds, breakage of existing bonds, and conversion between bond types. Bond formation can be controlled to li...

  11. Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures.

    Science.gov (United States)

    McCarthy, Michael C; Martinez, Oscar; McGuire, Brett A; Crabtree, Kyle N; Martin-Drumel, Marie-Aline; Stanton, John F

    2016-03-28

    HOCO is an important intermediate in combustion and atmospheric processes because the OH + CO → H + CO2 reaction represents the final step for the production of CO2 in hydrocarbon oxidation, and theoretical studies predict that this reaction proceeds via various intermediates, the most important being this radical. Isotopic investigations of trans- and cis-HOCO have been undertaken using Fourier transform microwave spectroscopy and millimeter-wave double resonance techniques in combination with a supersonic molecular beam discharge source to better understand the formation, chemical bonding, and molecular structures of this radical pair. We find that trans-HOCO can be produced almost equally well from either OH + CO or H + CO2 in our discharge source, but cis-HOCO appears to be roughly two times more abundant when starting from H + CO2. Using isotopically labelled precursors, the OH + C(18)O reaction predominately yields HOC(18)O for both isomers, but H(18)OCO is observed as well, typically at the level of 10%-20% that of HOC(18)O; the opposite propensity is found for the (18)OH + CO reaction. DO + C(18)O yields similar ratios between DOC(18)O and D(18)OCO as those found for OH + C(18)O, suggesting that some fraction of HOCO (or DOCO) may be formed from the back-reaction H + CO2, which, at the high pressure of our gas expansion, can readily occur. The large (13)C Fermi-contact term (aF) for trans- and cis-HO(13)CO implicates significant unpaired electronic density in a σ-type orbital at the carbon atom, in good agreement with theoretical predictions. By correcting the experimental rotational constants for zero-point vibration motion calculated theoretically using second-order vibrational perturbation theory, precise geometrical structures have been derived for both isomers. PMID:27036445

  12. Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures

    Science.gov (United States)

    McCarthy, Michael C.; Martinez, Oscar; McGuire, Brett A.; Crabtree, Kyle N.; Martin-Drumel, Marie-Aline; Stanton, John F.

    2016-03-01

    HOCO is an important intermediate in combustion and atmospheric processes because the OH + CO → H + CO2 reaction represents the final step for the production of CO2 in hydrocarbon oxidation, and theoretical studies predict that this reaction proceeds via various intermediates, the most important being this radical. Isotopic investigations of trans- and cis-HOCO have been undertaken using Fourier transform microwave spectroscopy and millimeter-wave double resonance techniques in combination with a supersonic molecular beam discharge source to better understand the formation, chemical bonding, and molecular structures of this radical pair. We find that trans-HOCO can be produced almost equally well from either OH + CO or H + CO2 in our discharge source, but cis-HOCO appears to be roughly two times more abundant when starting from H + CO2. Using isotopically labelled precursors, the OH + C18O reaction predominately yields HOC18O for both isomers, but H18OCO is observed as well, typically at the level of 10%-20% that of HOC18O; the opposite propensity is found for the 18OH + CO reaction. DO + C18O yields similar ratios between DOC18O and D18OCO as those found for OH + C18O, suggesting that some fraction of HOCO (or DOCO) may be formed from the back-reaction H + CO2, which, at the high pressure of our gas expansion, can readily occur. The large 13C Fermi-contact term (aF) for trans- and cis-HO13CO implicates significant unpaired electronic density in a σ-type orbital at the carbon atom, in good agreement with theoretical predictions. By correcting the experimental rotational constants for zero-point vibration motion calculated theoretically using second-order vibrational perturbation theory, precise geometrical structures have been derived for both isomers.

  13. Synthesis of 11C labelled methyl esters: transesterification of enol esters versus BF3 catalysed esterification-a comparative study

    International Nuclear Information System (INIS)

    C-11 labelled methyl esters have been synthesized via the transesterification of enol esters in the presence of C-11 methanol and 1,3 dichlorodibutylstannoxane as catalyst. This method leaves functional groups intact and allows access to a wider variety of C-11 labelled methyl esters compared to the BF3 catalysed ester formation, which uses carboxylic acids and C-11 methanol as starting materials

  14. Femtosecond X-ray solution scattering reveals that bond formation mechanism of a gold trimer complex is independent of excitation wavelength.

    Science.gov (United States)

    Kim, Kyung Hwan; Kim, Jong Goo; Oang, Key Young; Kim, Tae Wu; Ki, Hosung; Jo, Junbeom; Kim, Jeongho; Sato, Tokushi; Nozawa, Shunsuke; Adachi, Shin-Ichi; Ihee, Hyotcherl

    2016-07-01

    The [Au(CN)2 (-)]3 trimer in water experiences a strong van der Waals interaction between the d(10) gold atoms due to large relativistic effect and can serve as an excellent model system to study the bond formation process in real time. The trimer in the ground state (S0) exists as a bent structure without the covalent bond between the gold atoms, and upon the laser excitation, one electron in the antibonding orbital goes to the bonding orbital, thereby inducing the formation of a covalent bond between gold atoms. This process has been studied by various time-resolved techniques, and most of the interpretation on the structure and dynamics converge except that the structure of the first intermediate (S1) has been debated due to different interpretations between femtosecond optical spectroscopy and femtosecond X-ray solution scattering. Recently, the excitation wavelength of 267 nm employed in our previous scattering experiment was suggested as the culprit for misinterpretation. Here, we revisited this issue by performing femtosecond X-ray solution scattering with 310 nm excitation and compared the results with our previous study employing 267 nm excitation. The data show that a linear S1 structure is formed within 500 fs regardless of excitation wavelength and the structural dynamics observed at both excitation wavelengths are identical to each other within experimental errors. PMID:27191012

  15. Effect of interlayer configurations on joint formation in TLP bonding of Ti-6Al-4V to Mg-AZ31

    International Nuclear Information System (INIS)

    In this research work, the transient liquid phase (TLP) bonding process was utilized to fabricate joints using thin (20μm) nickel and copper foils placed between two bonding surfaces to help facilitate joint formation. Two joint configurations were investigated, first, Ti-6Al-4V/CuNi/Mg-AZ31 and second, Ti-6Al-4V/NiCu/Mg-AZ3L The effect of bonding time on microstructural developments across the joint and the changes in mechanical properties were studied as a function of bonding temperature and pressure. The bonded specimens were examined by metallographic analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD). In both cases, intermetallic phase of CuMg2 and Mg3AlNi2 was observed inside the joint region. The results show that joint shear strengths for the Ti-6Al-4V/CuNi/Mg-AZ31 setup produce joints with shear strength of 57 MPa compared to 27MPa for joints made using the Ti-6Al-4V/NiCu/Mg-AZ31 layer arrangement

  16. Appearance and distribution of regioisomers in metallo- and serine-protease-catalysed acylation of sucrose in N,N-dimethylformamide

    DEFF Research Database (Denmark)

    Lie, Aleksander; Meyer, Anne S.; Pedersen, Lars Haastrup

    2014-01-01

    -Lauroyl sucrose was the most abundant monoester regioisomer synthesised and the highest concentration observed was 23.7 mM after 24 h in the thermolysin-catalysed reaction. The highest concentration of 2-O-lauroyl sucrose detected in the reaction catalysed by ALP-901 was 19.0 mM, while it was 17.0 mM in the...... reaction without protein, both after 48 h. The detected appearance of the sucrose laurate regioisomers largely corresponded to the apparent rates of formation, and 2-O-lauroyl sucrose was among the first regioisomers to appear in all reactions. The observed sucrose laurate regioisomeric distribution after...

  17. Formation and characterization of two interconvertible side-on and end-on bonded beryllium ozonide complexes.

    Science.gov (United States)

    Zhou, Zijian; Li, Yuzhen; Zhuang, Jia; Wang, Guanjun; Chen, Mohua; Zhao, Yanying; Zheng, Xuming; Zhou, Mingfei

    2011-09-01

    The reactions of beryllium atoms with dioxygen were reinvestigated by matrix isolation infrared absorption spectroscopy. Besides the previously reported linear OBeO and cyclic Be(2)O(2) molecules, two interconvertible beryllium ozonide complexes were prepared and characterized. The BeOBe(η(2)-O(3)) complex was formed on annealing, which is characterized to be a side-on bonded ozonide complex with a planar C(2v) structure. The BeOBe(η(2)-O(3)) complex isomerized to the BeOBe(η(1)-O(3)) isomer under visible light excitation, which is an end-on bonded ozonide complex with planar C(s) symmetry. These two isomers are interconvertible; that is, visible light induces the conversion of the side-on bonded complex to the end-on bonded isomer, and vice versa on annealing. In addition, evidence is also presented for the linear BeOBeOBe cluster. PMID:21806010

  18. Covalent bonding and bandgap formation in transition-metal aluminides: di-aluminides of group VIII transition metals

    International Nuclear Information System (INIS)

    In this paper we study the electronic structure, electron density distribution and bonding mechanism in transition-metal (TM) di-aluminides Al2TM formed by metals of group VIII (TM=Fe,Ru,Os) and crystal structures of TM di-silicides C11b (MoSi2), C40 (CrSi2) and C54 (TiSi2). A peculiar feature of the electronic structure of these TM di-aluminides is the existence of a semiconducting gap at the Fermi level. A substitution of a 3d TM by 4d or 5d metal enhances the width of the gap. From the analysis of the charge-density distribution and the crystal-orbital overlap population we conclude that the bonding between atoms has strong covalent character. This is confirmed not only from the enhanced charge density halfway between atoms, but also by a clear bonding-antibonding splitting of the electronic states. Groups of bonding and antibonding states corresponding to a particular bonding configuration of atoms are separated by a gap. As such a gap is observed in all bonding configurations among atoms in the unit cell it results in a gap in the total density of states. The bandgap exists at a certain electron per atom ratio e/A∼4.67 and also occurs in TM di-aluminides of groups VII and IX. For group VIII TM di-aluminides the Fermi level falls just in the gap. (author)

  19. Chiral amides via copper-catalysed enantioselective conjugate addition

    NARCIS (Netherlands)

    Schoonen, Anne K.; Fernández-Ibáñez, M. Ángeles; Fañanás-Mastral, Martín; Teichert, Johannes F.; Feringa, Bernard

    2014-01-01

    A highly enantioselective one pot procedure for the synthesis of β-substituted amides was developed starting from the corresponding α,β-unsaturated esters. This new methodology is based on the copper-catalysed enantioselective conjugate addition of Grignard reagents to α,β-unsaturated esters and sub

  20. Acetic acid assisted cobalt methanesulfonate catalysed chemoselective diacetylation of aldehydes

    Institute of Scientific and Technical Information of China (English)

    Min Wang; Zhi Guo Song; Hong Gong; Heng Jiang

    2008-01-01

    Cobalt methanesulfonate in combination with acetic acid catalysed the chemoselective diacetylation of aldehyde with acetic anhydride at room temperature under solvent free conditions. After reaction, cobalt methanesulfonate can be easily recovered and mused many times. The reaction was mild and efficient with good to high yields.

  1. Silver-catalysed intramolecular hydroamination of alkynes with trichloroacetimidates.

    Science.gov (United States)

    Wong, Valerie H L; Hor, T S Andy; Hii, King Kuok Mimi

    2013-10-18

    Silver(I) complexes catalyse the intramolecular addition of trichloroacetimidates to alkynes. In the absence of a ligand, the selectivity of the reaction is dependent upon the nature of the counter-anion and solvent. The introduction of non-chelating nitrogeneous ligands suppresses competitive Brønsted acid catalysis, improving the yield and selectivity of the reaction. PMID:23999555

  2. Palladium-Catalysed Carbon–Carbon Coupling Reactions : Focusing on Microwave Heating, Low Catalyst Concentrations, Aqueous Conditions, Regioselectivity and Medicinal Chemistry Applications

    OpenAIRE

    Arvela, Riina K.

    2009-01-01

    It is widely accepted that palladium is one of the most useful catalysts in organic chemistry, and many palladium(0)-catalysed carbon–carbon bond-forming reactions have been developed over the years. In addition, the ever-growing need for more environmentally benign processes in the chemical industry has driven scientists to look for greener options while developing new methodologies for organic synthesis. This thesis describes a series of studies on Suzuki and Heck coupling reactions in wate...

  3. 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

  4. Silicon-Carbon Bond Formation via Nickel-Catalyzed Cross-Coupling of Silicon Nucleophiles with Unactivated Secondary and Tertiary Alkyl Electrophiles.

    Science.gov (United States)

    Chu, Crystal K; Liang, Yufan; Fu, Gregory C

    2016-05-25

    A wide array of cross-coupling methods for the formation of C-C bonds from unactivated alkyl electrophiles have been described in recent years. In contrast, progress in the development of methods for the construction of C-heteroatom bonds has lagged; for example, there have been no reports of metal-catalyzed cross-couplings of unactivated secondary or tertiary alkyl halides with silicon nucleophiles to form C-Si bonds. In this study, we address this challenge, establishing that a simple, commercially available nickel catalyst (NiBr2·diglyme) can achieve couplings of alkyl bromides with nucleophilic silicon reagents under unusually mild conditions (e.g., -20 °C); especially noteworthy is our ability to employ unactivated tertiary alkyl halides as electrophilic coupling partners, which is still relatively uncommon in the field of cross-coupling chemistry. Stereochemical, relative reactivity, and radical-trap studies are consistent with a homolytic pathway for C-X bond cleavage. PMID:27187869

  5. Use of ESR and HPLC to follow the anaerobic reaction catalysed by lipoxygenases.

    Science.gov (United States)

    Brandicourt, Stéphanie; Nicolas, Jacques; Boussard, Aline; Riquet, Anne-Marie

    2015-02-01

    The measurement of the 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) consumption by using ESR allows to follow the anaerobic reaction between linoleic acid (LH) and its 13-hydroperoxide (LOOH) catalysed by lipoxygenase. During this reaction, two types of radicals are initially obtained, alkyl (L) and alkoxyl (LO) radicals which formed two types of adducts (LT and OLT) with TEMPOL as characterised by HPLC. The stoichiometry of the adduct formation is two mole of TEMPOL consumed for one mole of LH and one mole of LOOH. Using ESR, the kinetic parameters and the mechanism of the anaerobic reaction have been determined at pH 6.5 for three different lipoxygenases, soybean, horse bean and wheat and compared to the values obtained at pH 9 for soybean lipoxygenase. Wheat lipoxygenase is very weakly active compared to the other enzymes. An uncompetitive inhibition of the anaerobic reaction catalysed by soybean and horse bean lipoxygenases was observed with 2,6-di-tert-butyl-4-methylphenol (BHT). PMID:25172715

  6. Substrate Controlled Synthesis of Benzisoxazole and Benzisothiazole Derivatives via PhI(OAc)2-Mediated Oxidation Followed by Intramolecular Oxidative O-N/S-N Bond Formation.

    Science.gov (United States)

    Anand, Devireddy; Patel, Om P S; Maurya, Rahul K; Kant, Ruchir; Yadav, Prem P

    2015-12-18

    A phenyliodine(III) diacetate (PIDA)-mediated, highly efficient and tandem approach for the synthesis of aryldiazenylisoxazolo(isothiazolo)arenes from simple 2-amino-N'-arylbenzohydrazides has been developed. The reaction proceeds via formation of (E)-(2-aminoaryl)(aryldiazenyl)methanone as the key intermediate, followed by intramolecular oxidative O-N/S-N bond formation in one pot at room temperature. The quiet different reactivity of the substrate is due to the formation of a diazo intermediate which encounters a nucleophilic attack by carbonyl oxygen on the electrophilic amine to produce isoxazole products, as compared to the previous reportsa,b,4 in which an N-acylnitrenium ion intermediate is intramolecularly trapped by an amine group. PMID:26565748

  7. An alternative synthesis of the breast cancer drug fulvestrant (Faslodex®): catalyst control over C-C bond formation.

    Science.gov (United States)

    Caprioglio, Diego; Fletcher, Stephen P

    2015-10-14

    Fulvestrant (Faslodex®) was synthesized in four steps (35% overall yield) from 6-dehydronandrolone acetate. Catalyst controlled, room temperature, diastereoselective 1,6-addition of the zirconocene derived from commercially available 9-bromonon-1-ene was used in the key C-C bond forming step. PMID:26300021

  8. Anatomy of Bond Formation. Insights from the Analysis of Domain-Averaged Fermi holes in Momentum Space

    Czech Academy of Sciences Publication Activity Database

    Ponec, Robert; Cooper, D.L.

    2010, s. 27. ISBN N. [Girona Seminar Electron Density, Density Matrices and Density Functional Theory /9./. Girona (ES), 05.07.2010-08.07.2010] R&D Projects: GA ČR GA203/09/0118 Institutional research plan: CEZ:AV0Z40720504 Keywords : chemical bonding * fermi holes * momentum space Subject RIV: CF - Physical ; Theoretical Chemistry

  9. New chromogenic and fluorogenic reagents and sensors for neutral and ionic analytes based on covalent bond formation--a review of recent developments.

    Science.gov (United States)

    Mohr, Gerhard J

    2006-11-01

    To date, hydrogen bonding and Coulomb, van der Waals and hydrophobic interactions are the major contributors to non-covalent analyte recognition using ionophores, ligands, aptamers and chemosensors. However, this article describes recent developments in the use of (reversible) covalent bond formation to detect analyte molecules, with special focus on optical signal transduction. Several new indicator dyes for analytes such as amines and diamines, amino acids, cyanide, formaldehyde, hydrogen peroxide, organophosphates, nitrogen oxide and nitrite, peptides and proteins, as well as saccharides have become available. New means of converting analyte recognition into optical signals have also been introduced, such as colour changes of chiral nematic layers. This article gives an overview of recent developments and discusses response mechanisms, selectivity and sensitivity. PMID:17039383

  10. Ruthenium-catalysed alkoxycarbonylation of alkenes with carbon dioxide.

    Science.gov (United States)

    Wu, Lipeng; Liu, Qiang; Fleischer, Ivana; Jackstell, Ralf; Beller, Matthias

    2014-01-01

    Alkene carbonylations represent a major technology for the production of value-added bulk and fine chemicals. Nowadays, all industrial carbonylation processes make use of highly toxic and flammable carbon monoxide. Here we show the application of abundantly available carbon dioxide as C1 building block for the alkoxycarbonylations of industrially important olefins in the presence of a convenient and inexpensive ruthenium catalyst system. In our system, carbon dioxide works much better than the traditional combination of carbon monoxide and alcohols. The unprecedented in situ formation of carbon monoxide from carbon dioxide and alcohols permits an efficient synthesis of carboxylic acid esters, which can be used as detergents and polymer-building blocks. Notably, this transformation allows the catalytic formation of C-C bonds with carbon dioxide as C1 source and avoids the use of sensitive and/or expensive reducing agents (for example, Grignard reagents, diethylzinc or triethylaluminum). PMID:24518431

  11. Mechanisms of the acid catalysed bridge cleavage reactions of two trinuclear ruthenium(III) complex ions (Ru3(NH3)13(SCN)X2)6+, (X=Cl-, Br-)

    International Nuclear Information System (INIS)

    Acid catalysed bridge cleavage reaction of two doubly bridged trinuclear ions [Ru3(NH3)13(SCN)X2]6+, (X=Cl-, Br-) have been investigated at 59o in perchloric and nitric acid media respectively. Both the complexes show two stages of reaction. Plots of kobs versus [acid] are linear for both the complexes in the two stages of reactions. Only the plots for first stage have intercept on rate axis. The rate constants for the chloro and the bromo complexes for acid - dependent path are as follows : first stage 5.15 x 10-4 and 2.43 x 10-4 dm3 mol-1 s-1 and second stage 7.35 x 10-3 and 4.02 x 10-4 dm3 mol-1s-1 respectively. An associative mechanism has been invoked for the reactions in which bond formation by the incoming solvent (water) molecule with the middle ruthenium atom leads to rupture of bridging bonds. (author)

  12. Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

    International Nuclear Information System (INIS)

    Combining ab initio modeling and 57Fe Mössbauer spectrometry, we characterized the nature of the chemical linkage of aminoalkyl arenediazonium salt on the surface of iron oxide nanoparticles. We established that it is built through a metal–oxygen–carbon bonding and not a metal–carbon one, as usually suggested and commonly observed in previously studied metal- or carbon-based surfaces

  13. Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Brymora, Katarzyna [LUNAM Université du Maine, IMMM UMR CNRS 6283 (France); Fouineau, Jonathan; Eddarir, Asma; Chau, François [Université Paris Diderot, Sorbonne Paris Cité, ITODYS CNRS UMR 7086 (France); Yaacoub, Nader; Grenèche, Jean-Marc [LUNAM Université du Maine, IMMM UMR CNRS 6283 (France); Pinson, Jean; Ammar, Souad [Université Paris Diderot, Sorbonne Paris Cité, ITODYS CNRS UMR 7086 (France); Calvayrac, Florent, E-mail: florent.calvayrac@univ-lemans.fr [LUNAM Université du Maine, IMMM UMR CNRS 6283 (France)

    2015-11-15

    Combining ab initio modeling and {sup 57}Fe Mössbauer spectrometry, we characterized the nature of the chemical linkage of aminoalkyl arenediazonium salt on the surface of iron oxide nanoparticles. We established that it is built through a metal–oxygen–carbon bonding and not a metal–carbon one, as usually suggested and commonly observed in previously studied metal- or carbon-based surfaces.

  14. Degradation of C-hordein by metal-catalysed oxidation.

    Science.gov (United States)

    Huang, Xin; Kanerva, Päivi; Salovaara, Hannu; Sontag-Strohm, Tuula

    2016-04-01

    C-hordein is a monomeric prolamin protein in barley. The unusual primary structure of C-hordein has highly repetitive sequences and forms a secondary structure of beta-turns. C-hordein structure is similar to that of collagen protein, whose degradation by metal-catalysed oxidation has been intensively studied. No information exists on the metal catalysed oxidation of C-hordein, however. In this study, copper-catalysed hydrogen peroxide induced oxidation of C-hordein caused substantial degradation and formed some insoluble compounds. The use of a gliadin standard in R5 ELISA determinations causes an overestimation of hordeins in a sample. A C-hordein standard was therefore directly used as a standard, thus allowing the C-hordein to be analysed as its oxidised prolamin product. After 48 h of oxidation, the prolamin concentration of oxidised C-hordein decreased to 20% of its original amount for competitive ELISA, and to 3% for sandwich ELISA methods. Carbonyl groups were formed during the oxidation. Backbone fragmentation and side-chain modification suggested structural changes of R5 epitopes in C-hordein. Oxidation is an alternative to enzymatic hydrolysis when degrading and modifying C-hordein. PMID:26593614

  15. C-C Bond Formation: Synthesis of C5 Substituted Pyrimidine and C8 Substituted Purine Nucleosides Using Water Soluble Pd-imidate Complex.

    Science.gov (United States)

    Gayakhe, Vijay; Ardhapure, Ajaykumar V; Kapdi, Anant R; Sanghvi, Yogesh S; Serrano, Jose Luis; Schulzke, Carola

    2016-01-01

    The synthesis of a highly efficient, water soluble [Pd(Sacc)2 (TPA)2 ] complex for C-C bond formation is described. Additionally, application of the [Pd(Sacc)2 (TPA)2 ] complex for Suzuki-Miyaura arylation of all four nucleosides (5-iodo-2'-deoxyuridine [5-IdU], 5-iodo-2'-deoxycytidine [5-IdC], 8-bromo-2'-deoxyadenosine, and 8-bromo-2'-deoxyguanosine) with various aryl/heteroaryl boronic acids in plain water under milder conditions is demonstrated. © 2016 by John Wiley & Sons, Inc. PMID:27248782

  16. B-N, B-O, and B-CN Bond Formation via Palladium-Catalyzed Cross-Coupling of B-Bromo-Carboranes.

    Science.gov (United States)

    Dziedzic, Rafal M; Saleh, Liban M A; Axtell, Jonathan C; Martin, Joshua L; Stevens, Simone L; Royappa, A Timothy; Rheingold, Arnold L; Spokoyny, Alexander M

    2016-07-27

    Carboranes are boron-rich molecules that can be functionalized through metal-catalyzed cross-coupling. Here, for the first time, we report the use of bromo-carboranes in palladium-catalyzed cross-coupling for efficient B-N, B-O, and unprecedented B-CN bond formation. In many cases bromo-carboranes outperform the traditionally utilized iodo-carborane species. This marked difference in reactivity is leveraged to circumvent multistep functionalization by directly coupling small nucleophiles (-OH, -NH2, and -CN) and multiple functional groups onto the boron-rich clusters. PMID:27384544

  17. Hydrogen bonding of the dissociated histidine ligand is not required for formation of a proximal NO adduct in cytochrome c'.

    Science.gov (United States)

    Ghafoor, Dlzar D; Kekilli, Demet; Abdullah, Gaylany H; Dworkowski, Florian S N; Hassan, Hamid G; Wilson, Michael T; Strange, Richard W; Hough, Michael A

    2015-09-01

    Cytochromes c', that occur in methanotrophic, denitrifying and photosynthetic bacteria, form unusual proximal penta-coordinate NO complexes via a hexa-coordinate distal NO intermediate. Their NO binding properties are similar to those of the eukaryotic NO sensor, soluble guanylate cyclase, for which they provide a valuable structural model. Previous studies suggested that hydrogen bonding between the displaced proximal histidine (His120) ligand (following its dissociation from heme due to trans effects from the distally bound NO) and a conserved aspartate residue (Asp121) could play a key role in allowing proximal NO binding to occur. We have characterized three variants of Alcaligenes xylosoxidans cytochrome c' (AXCP) where Asp121 has been replaced by Ala, Ile and Gln, respectively. In all variants, hydrogen bonding between residue 121 and His120 is abolished yet 5-coordinate proximal NO species are still formed. Our data therefore demonstrate that the His120-Asp121 bond is not essential for proximal NO binding although it likely provides an energy minimum for the displaced His ligand. All variants have altered proximal pocket structure relative to native AXCP. PMID:26100643

  18. A potential role of substrate as a base for deprotonation pathway in Rh-catalysed C-H amination of heteroArenes: DFT insights

    KAUST Repository

    Ajitha, Manjaly John

    2016-03-29

    The possibility of direct introduction of a new functionality through C–H bond activation is an attractive strategy in covalent synthesis. Here, we investigated the mechanism of Rh-catalysed C-H amination of the hetero-aryl substrate (2-phenylpyridine) using phenyl azide as nitrogen source by density functional theory (DFT). For the deprotocyclometallation and protodecyclometallation processes of the title reaction, we propose a stepwise base-assisted mechanism (pathway I) instead of previously reported concerted mechanism (pathway II). In the new mechanism proposed here, 2-phenylpyridine acts as a base in the initial deprotonation step (C-H bond cleavage) and transports the proton towards the final protonation step. In fact, the N-H bond of the strong conjugate acid (formed during initial C-H bond cleavage) considered in pathway I (via TS4) is more acidic than the C-H bond of the neutral substrate considered in pathway II (via TS5). The higher activation barrier of TS5 mainly originates from the ring strain of the four membered cyclic transition state. The vital role of base, as disclosed here, can potentially have broader mechanistic implications for the development of reaction conditions of transition metal catalysed reactions.

  19. Intramolecular electron density redistribution upon hydrogen bond formation in the anion methyl orange at the water/1,2-dichloroethane interface probed by phase interference second harmonic generation

    Science.gov (United States)

    Rinuy; Piron; Brevet; Blanchard-Desce; Girault

    2000-09-15

    Surface second harmonic generation (SSHG) studies of the azobenzene derivative p-dimethylaminoazobenzene sulfonate, often referred as Methyl Orange (MO), at the neat water/1,2-dichloroethane (DCE) interface is reported. The two forms of the anionic MO dye, which are usually observed in bulk solution, with one form being hydrogen bonded to a water molecule through the azo nitrogens (MO/H2O) and the other form not being hydrogen bonded (MO) have also been observed at the water/DCE interface. Their equilibrium constant has been compared with the corresponding bulk solution and found to be identical. The adsorption equilibrium of the two forms has been determined and the Gibbs energy of adsorption measured to be -30 kJmol(-1) for both forms. From a light polarisation analysis of the SH signal, the angle of orientation of the MO transition dipole moment was found to be 34 +/- 2 degrees for MO and 43 +/- 2 degrees for MO/H2O under the assumption of a Dirac delta function for the angle distribution, a difference explained by the different solvation properties of the two forms. Furthermore, the wavelength dependence analysis of these data revealed an interference pattern resulting from the electronic density redistribution within the hydrated anionic form occurring upon the formation of the hydrogen bond with a water molecule. This interference pattern was clearly evidenced with the use of another dye at the interface in order to define a phase reference to both forms of Methyl Orange. PMID:11039537

  20. Enhanced plasmonic properties of gold-catalysed semiconductor nanowires

    Science.gov (United States)

    Naumenko, Denys; Zannier, Valentina; Grillo, Vincenzo; Cassese, Damiano; Priante, Giacomo; Dal Zilio, Simone; Rubini, Silvia; Lazzarino, Marco

    2014-10-01

    A key challenge for the development of plasmonic nanodevices is their integration into active semiconducting structures. Gold-catalysed semiconductor nanowires are promising candidates for their bottom-up growth process that aligns a single gold nanoparticle at each nanowire apex. Unfortunately these show extremely poor plasmonic properties. In this work, we propose a way to enhance their plasmonic resonance up to those of ideal and isolated gold nanoparticles. A suitable purification protocol compatible with GaAs and ZnSe molecular beam epitaxy of nanowires is used to produce plasmonic active nanowires, which were used to enhance the Raman signal of pentacene and graphene oxide. Enhancement factors up to three orders of magnitude are demonstrated.A key challenge for the development of plasmonic nanodevices is their integration into active semiconducting structures. Gold-catalysed semiconductor nanowires are promising candidates for their bottom-up growth process that aligns a single gold nanoparticle at each nanowire apex. Unfortunately these show extremely poor plasmonic properties. In this work, we propose a way to enhance their plasmonic resonance up to those of ideal and isolated gold nanoparticles. A suitable purification protocol compatible with GaAs and ZnSe molecular beam epitaxy of nanowires is used to produce plasmonic active nanowires, which were used to enhance the Raman signal of pentacene and graphene oxide. Enhancement factors up to three orders of magnitude are demonstrated. Electronic supplementary information (ESI) available: SEM characterization of: (i) transferred ZnSe NWs onto the glass substrates, (ii) etched gold NPs of ZnSe NWs in Ar+ plasma, and (iii) self-catalysed GaAs NWs. Simulation of extinction spectra. Statistical characterization of plasmon-active sites at the focal plane with a length of NWs. Photoluminescence on ZnSe NWs. B3g Raman mode of pentacene as an indicator of molecule orientation. The dependence of graphene oxide Raman

  1. Characterisation of hydrocarbonaceous overlayers important in metal-catalysed selective hydrogenation reactions

    Energy Technology Data Exchange (ETDEWEB)

    Lennon, David; Warringham, Robbie [School of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Guidi, Tatiana [ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom); Parker, Stewart F., E-mail: stewart.parker@stfc.ac.uk [ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom)

    2013-12-12

    Highlights: • Inelastic neutron scattering spectroscopy of a commercial dehydrogenation catalyst. • The overlayer present on the catalyst is predominantly aliphatic. • A population of strongly hydrogen bonded hydroxyls is also present. - Abstract: The hydrogenation of alkynes to alkenes over supported metal catalysts is an important industrial process and it has been shown that hydrocarbonaceous overlayers are important in controlling selectivity profiles of metal-catalysed hydrogenation reactions. As a model system, we have selected propyne hydrogenation over a commercial Pd(5%)/Al{sub 2}O{sub 3} catalyst. Inelastic neutron scattering studies show that the C–H stretching mode ranges from 2850 to 3063 cm{sup −1}, indicating the mostly aliphatic nature of the overlayer and this is supported by the quantification of the carbon and hydrogen on the surface. There is also a population of strongly hydrogen-bonded hydroxyls, their presence would indicate that the overlayer probably contains some oxygen functionality. There is little evidence for any olefinic or aromatic species. This is distinctly different from the hydrogen-poor overlayers that are deposited on Ni/Al{sub 2}O{sub 3} catalysts during methane reforming.

  2. 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

  3. A Facile Method to Prepare Double-Layer Isoporous Hollow Fiber Membrane by In Situ Hydrogen Bond Formation in the Spinning Line.

    Science.gov (United States)

    Noor, Nazia; Koll, Joachim; Radjabian, Maryam; Abetz, Clarissa; Abetz, Volker

    2016-03-01

    A double-layer hollow fiber is fabricated where an isoporous surface of polystyrene-block-poly(4-vinylpyridine) is fixed on a support layer by co-extrusion. Due to the sulfonation of the support layer material, delamination of the two layers is suppressed without increasing the number of subsequent processing steps for isoporous composite membrane formation. Electron microscope-energy-dispersive X-ray spectroscopy images unveil the existence of a high sulfur concentration in the interfacial region by which in-process H-bond formation between the layers is evidenced. For the very first time, our study reports a facile method to fabricate a sturdy isoporous double-layer hollow fiber. PMID:26685710

  4. Interaction of 1,2,5-chalcogenadiazole derivatives with thiophenolate: hypercoordination with formation of interchalcogen bond versus reduction to radical anion.

    Science.gov (United States)

    Suturina, Elizaveta A; Semenov, Nikolay A; Lonchakov, Anton V; Bagryanskaya, Irina Yu; Gatilov, Yuri V; Irtegova, Irina G; Vasilieva, Nadezhda V; Lork, Enno; Mews, Rüdiger; Gritsan, Nina P; Zibarev, Andrey V

    2011-05-12

    According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 Å) is ca. 0.5 Å longer than the sum of the covalent radii of these atoms but ca. 1 Å shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9. PMID:21500829

  5. The reaction of iodoplatination of triple bond by platinum(4) complexes: formation of σ-vinyl derivatives

    International Nuclear Information System (INIS)

    According to IR and 1H NMR data, propargyl alcohol reacts with platinum(4) iodide complexes in aqueous solution at 10-15 deg C to yield the product of the addition of platinum(4) and iodine to the triple bond, which has been isolated in the form of Pt(CH=CI-CH2OH)2I2(CH3OH). The σ-vinyl ligands in the complex are situated in cis-position. The complex obtained decomposed at 80 deg C to form products of reductive elimination - E,E-2,5-diiodo-1,6-diolhexadiene-2,4 and PtI2. 3 refs

  6. Disulfide bond formation and folding of plant peroxidases expressed as inclusion body protein in Escherichia coli thioredoxin reductase negative strains

    DEFF Research Database (Denmark)

    Teilum, K; Ostergaard, L; Welinder, K G

    1999-01-01

    Escherichia coli is widely used for the production of proteins, which are of interest in structure and function studies. The folding yield of inclusion body protein is, however, generally low (a few percent) for proteins such as the plant and fungal peroxidases, which contain four disulfide bonds......, two Ca2+ ions, and a heme group. We have studied the expression yield and folding efficiency of (i) a novel Arabidopsis thaliana peroxidase, ATP N; and (ii) barley grain peroxidase, BP 1. The expression yield ranges from 0 to 60 microgram/ml of cell culture depending on the peroxidase gene and the...

  7. Scope and limitations of the dual-gold-catalysed hydrophenoxylation of alkynes

    Science.gov (United States)

    Gómez-Suárez, Adrián; Oonishi, Yoshihiro; Martin, Anthony R

    2016-01-01

    Summary Due to the synthetic advantages presented by the dual-gold-catalysed hydrophenoxylation of alkynes, a thorough study of this reaction was carried out in order to fully define the scope and limitations of the methodology. The protocol tolerates a wide range of functional groups, such as nitriles, ketones, esters, aldehydes, ketals, naphthyls, allyls or polyphenols, in a milder and more efficient manner than the previously reported methodologies. We have also identified that while we are able to use highly steric hindered phenols, small changes on the steric bulk of the alkynes have a dramatic effect on the reactivity. More importantly, we have observed that the use of substrates that facilitate the formation of diaurated species such as gem-diaurated or σ,π-digold–acetylide species, hinder the catalytic activity. Moreover, we have identified that the use of directing groups in unsymmetrical alkynes can help to achieve high regioselectivity in the hydrophenoxylation. PMID:26977176

  8. A nanosensor for in vivo selenol imaging based on the formation of AuSe bonds.

    Science.gov (United States)

    Hu, Bo; Cheng, Ranran; Liu, Xiaojun; Pan, Xiaohong; Kong, Fanpeng; Gao, Wen; Xu, Kehua; Tang, Bo

    2016-06-01

    Selenol is a key metabolite of Na2SeO3 and plays an important role in many physiological and pathological processes. The real-time monitoring of selenol is of scientific interest for understanding the anti-cancer mechanism of Na2SeO3. Based on selenol's ability to specifically break AuS bonds and form more stable AuSe bonds on the surfaces of gold nanoparticles (AuNPs), we developed a novel near-infrared fluorescent nanosensor (Cy5.5-peptide-AuNPs) for detecting selenol. The nanosensor exhibited rapid response to selenol with high selectivity and sensitivity, and it was successfully used to image changes in the selenol level in HepG2 cells during Na2SeO3-induced apoptosis. Moreover, in vivo fluorescence imaging of selenol was obtained from H22 tumor-bearing mice injected with both the nanosensor and sodium selenite. The results showed that the tumor cell apoptosis induced by Na2SeO3 is correlated with high-level of selenol under hypoxic conditions. We believe that this nanosensor could serve as a powerful tool for monitoring selenol and exploring the physiological function of selenol in a variety of physiological and pathological contexts and that the probe-designed strategy will provide a new platform for research on relevant selenium chemistry. PMID:27043769

  9. Theoretical study on the transition-metal oxoboryl complex: M-BO bonding nature, mechanism of the formation reaction, and prediction of a new oxoboryl complex.

    Science.gov (United States)

    Zeng, Guixiang; Sakaki, Shigeyoshi

    2012-04-16

    The Pt-BO bonding nature and the formation reaction of the experimentally reported platinum(II) oxoboryl complex, simplified to PtBr(BO)(PMe(3))(2), were theoretically investigated with the density functional theory method. The BO(-) ligand was quantitatively demonstrated to have extremely strong σ-donation but very weak d(π)-electron-accepting abilities. Therefore, it exhibits a strong trans influence. The formation reaction occurs through a four-center transition state, in which the B(δ+)-Br(δ-) polarization and the Br → Si and O p(π) → B p(π) charge-transfer interactions play key roles. The Gibbs activation energy (ΔG°(++)) and Gibbs reaction energy (ΔG°) of the formation reaction are 32.2 and -6.1 kcal/mol, respectively. The electron-donating bulky phosphine ligand is found to be favorable for lowering both ΔG°(++) and ΔG°. In addition, the metal effect is examined with the nickel and palladium analogues and MBrCl[BBr(OSiMe(3))](CO)(PR(3))(2) (M = Ir and Rh). By a comparison of the ΔG°(++) and ΔG° values, the M-BO (M = Ni, Pd, Ir, and Rh) bonding nature, and the interaction energy between [MBrCl(CO)(PR(3))(2)](+) and BO(-) with those of the platinum system, MBrCl(BO)(CO)(PR(3))(2) (M = Ir and Rh) is predicted to be a good candidate for a stable oxoboryl complex. PMID:22458310

  10. Alkaline-Earth-Catalysed Cross-Dehydrocoupling of Amines and Hydrosilanes: Reactivity Trends, Scope and Mechanism.

    Science.gov (United States)

    Bellini, Clément; Dorcet, Vincent; Carpentier, Jean-François; Tobisch, Sven; Sarazin, Yann

    2016-03-18

    Alkaline-earth (Ae=Ca, Sr, Ba) complexes are shown to catalyse the chemoselective cross-dehydrocoupling (CDC) of amines and hydrosilanes. Key trends were delineated in the benchmark couplings of Ph3 SiH with pyrrolidine or tBuNH2 . Ae{E(SiMe3 )2 }2 ⋅(THF)x (E=N, CH; x=2-3) are more efficient than {N^N}Ae{E(SiMe3 )2 }⋅(THF)n (E=N, CH; n=1-2) complexes (where {N^N}(-) ={ArN(o-C6 H4 )C(H)=NAr}(-) with Ar=2,6-iPr2 -C6 H3 ) bearing an iminoanilide ligand, and alkyl precatalysts are better than amido analogues. Turnover frequencies (TOFs) increase in the order Ca30 products) includes diamines and di(hydrosilane)s. Kinetic analysis of the Ba-promoted CDC of pyrrolidine and Ph3 SiH shows that 1) the kinetic law is rate=k[Ba](1) [amine](0) [hydrosilane](1) , 2) electron-withdrawing p-substituents on the arylhydrosilane improve the reaction rate and 3) a maximal kinetic isotopic effect (kSiH /kSiD =4.7) is seen for Ph3 SiX (X=H, D). DFT calculations identified the prevailing mechanism; instead of an inaccessible σ-bond-breaking metathesis pathway, the CDC appears to follow a stepwise reaction path with N-Si bond-forming nucleophilic attack of the catalytically competent Ba pyrrolide onto the incoming silane, followed by rate limiting hydrogen-atom transfer to barium. The participation of a Ba silyl species is prevented energetically. The reactivity trend Cabond strength upon descending Group 2. PMID:26864122

  11. Key processes in ruthenium-catalysed olefin metathesis

    OpenAIRE

    Nelson, David J.; Manzini, Simone; Urbina-Blanco, César A.; Nolan, Steven P.

    2014-01-01

    The authors acknowledge the following sources of funding: the EPSRC, the ERC (via Advanced Investigator Grant ‘FUNCAT’ to SPN), the EC (via FP7 project ‘EUMET’) and Umicore (for gifts of materials). SPN is a Royal Society Wolfson Research Merit Award holder. While the fundamental series of [2+2]cycloadditions and retro[2+2]cycloadditions that make up the pathways of ruthenium-catalysed metathesis reactions is well-established, the exploration of mechanistic aspects of alkene metathesis con...

  12. Synthesis of New dihydropyrimidinones catalysed by dicationic ionic liquid

    Indian Academy of Sciences (India)

    Dhanaji V Jawale; Umesh R Pratap; Aparna A Mulay; Jyotirling R Mali; Ramrao A Mane

    2011-09-01

    A convenient multi step synthetic protocol for new dihydropyrimidinones bearing quinolynyl methoxy phenyl moiety has been developed from 2-chloro-3-formyl quinolines. The last step is one-pot Biginelli reaction of multicomponents, 4-((2-chloroquinolin-3-yl) methoxy) benzaldehydes, ethyl acetoacetate and urea mediated and catalysed by dicationic ionic liquid (3-methyl-1-[3-(methyl-1H-imidazolium-1-yl) propyl]-1H-imidazolium dibromide (C3 [min]2 2 [Br−] )). Simple work-up procedures and moderate to good yields of the pyrimidinones and the intermediates are the merits of the route.

  13. Asymmetric C-C Bond-Formation Reaction with Pd: How to Favor Heterogeneous or Homogeneous Catalysis?

    DEFF Research Database (Denmark)

    Reimann, S.; Grunwaldt, Jan-Dierk; Mallat, T.;

    2010-01-01

    clear deviation from the behavior of the corresponding homogeneous system. In contrast, halogenated solvents are easily dehalogenated on Pd/Al2O3 and thus they favor leaching of the metal and formation of soluble compounds, analogous to classical metal corrosion in the presence of halide ions. The...

  14. Atomic mixing and chemical bond formation in MoSx/Fe thin-film system deposited from a laser plume in a high-intensity electrostatic field

    International Nuclear Information System (INIS)

    The potential of pulsed laser deposition in an applied uniform electrostatic field was investigated. A flat, positively charged, fine-celled-grid counter electrode was used to provide bias voltage of up to +50 kV with respect to the substrate. This enabled control of the atomic mixing and made it possible to initiate chemical bond formation at the interfaces of the films formed by deposition from the laser-induced plume. As an example, the results of multilayer 56Fe/MoSx/57Fe film deposition are presented. At first, a bilayer MoSx/57Fe film was grown in the absence of the electric field. This was followed by 56Fe film deposition in an applied field. A relatively sharp interface between the MoSx and 57Fe films was observed. In contrast, after 56Fe deposition, effective atom mixing was observed and new chemical bonds between Fe, S and Mo were detected. By penetrating through the interface, accelerated 56Fe ions gave rise to the growth of an amorphous layer of up to 50 nm in thickness. It consisted of rather evenly distributed Fe, S and Mo atoms (at total ion dose of 2.5x1016 cm-2). The ion flux destroyed Mo-S chemical bonds, and the S atoms released preferably bound Fe atoms, thus forming a FeS2-type phase. The Mo atoms, as a lower-oxidation-state species (apparently together with S atoms), were localized in the vicinity of Fe atoms and affected the hyperfine magnetic fields. The technique developed has made it possible to study the ion-induced processes occurring at the interfaces of multilayer films. It can also be applied to improve the tribological functionality of thin films

  15. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay - The effect of mononucleotide structure, phosphate activation and montmorillonite composition on phosphodiester bond formation

    Science.gov (United States)

    Ferris, James P.; KAMALUDDIN; Ertem, Gozen

    1990-01-01

    The 2(prime)-d-5(prime)-GMP and 2(prime)-d-5(prime)-AMP bind 2 times more strongly to montmorillonite 22A than do 2(prime)-d-5(prime)-CMP and 5(prime)-TMP. The dinucleotide d(pG)2 forms in 9.2 percent yield and the cyclic dinucleotide c(dpG)2 in 5.4 percent yield in the reaction of 2(prime)-d-5(prime)-GMP with EDAC in the presence of montmorillonite 22A. The yield of dimers which contain the phosphodiester bond decreases as the reaction medium is changed from 0.2 M NaCl to a mixture of 0.2 M NaCl and 0.075 M MgCl2. A low yield of d(pA)2 was observed in the condensation reaction of 5(prime)-ImdpA on montmorillonite 22A. The yield of d(pA)2 obtained when EDAC is used as the condensing agent increases with increasing iron content of the Na(+)-montmorillonite used as catalyst. Evidence is presented which shows that the acidity of the Na(+)-montmorillonite is a necessary but not sufficient factor for the montmorillonite catalysis of phosphodiester bond formation.

  16. Synthesis of Bioactive 2-(Arylaminothiazolo[5,4-f]-quinazolin-9-ones via the Hügershoff Reaction or Cu- Catalyzed Intramolecular C-S Bond Formation

    Directory of Open Access Journals (Sweden)

    Damien Hédou

    2016-06-01

    Full Text Available A library of thirty eight novel thiazolo[5,4-f]quinazolin-9(8H-one derivatives (series 8, 10, 14 and 17 was prepared via the Hügershoff reaction and a Cu catalyzed intramolecular C-S bond formation, helped by microwave-assisted technology when required. The efficient multistep synthesis of the key 6-amino-3-cyclopropylquinazolin-4(3H-one (3 has been reinvestigated and performed on a multigram scale from the starting 5-nitroanthranilic acid. The inhibitory potency of the final products was evaluated against five kinases involved in Alzheimer’s disease and showed that some molecules of the 17 series described in this paper are particularly promising for the development of novel multi-target inhibitors of kinases.

  17. Palladium-catalyzed C–N and C–O bond formation of N-substituted 4-bromo-7-azaindoles with amides, amines, amino acid esters and phenols

    Directory of Open Access Journals (Sweden)

    Rajendra Surasani

    2012-11-01

    Full Text Available Simple and efficient procedures for palladium-catalyzed cross-coupling reactions of N-substituted 4-bromo-7-azaindole (1H-pyrrole[2,3-b]pyridine, with amides, amines, amino acid esters and phenols through C–N and C–O bond formation have been developed. The C–N cross-coupling reaction of amides, amines and amino acid esters takes place rapidly by using the combination of Xantphos, Cs2CO3, dioxane and palladium catalyst precursors Pd(OAc2/Pd2(dba3. The combination of Pd(OAc2, Xantphos, K2CO3 and dioxane was found to be crucial for the C–O cross-coupling reaction. This is the first report on coupling of amides, amino acid esters and phenols with N-protected 4-bromo-7-azaindole derivatives.

  18. Formation of C═C bond via knoevenagel reaction between aromatic aldehyde and barbituric acid at liquid/HOPG and vapor/HOPG interfaces.

    Science.gov (United States)

    Geng, Yanfang; Dai, Hongliang; Chang, Shaoqing; Hu, Fangyun; Zeng, Qingdao; Wang, Chen

    2015-03-01

    Controlling chemical reactions on surface is of great importance to constructing self-assembled covalent nanostructures. Herein, Knoevenagel reaction between aromatic aldehyde compound 2,5-di(5-aldehyde-2-thienyl)-1,4-dioctyloxybenzene (PT2) and barbituric acid (BA) has been successfully performed for the first time at liquid/HOPG interface and vapor/HOPG interface. The resulting surface nanostructures and the formation of C═C bond are recorded through scanning tunneling microscopy (STM), and confirmed by attenuated total reflectance Fourier-transform infrared (ATR/FT-IR) spectrometer and UV-vis absorption. The obtained results reveal that Knoevenagel condensation reaction can efficiently occur at both interfaces. This surface reaction would be an important step toward further reaction to produce innovative conjugated nanomaterial on the surface. PMID:25664650

  19. On peptide bond formation, translocation, nascent protein progression and the regulatory properties of ribosomes. Derived on 20 October 2002 at the 28th FEBS Meeting in Istanbul.

    Science.gov (United States)

    Agmon, Ilana; Auerbach, Tamar; Baram, David; Bartels, Heike; Bashan, Anat; Berisio, Rita; Fucini, Paola; Hansen, Harly A S; Harms, Joerg; Kessler, Maggie; Peretz, Moshe; Schluenzen, Frank; Yonath, Ada; Zarivach, Raz

    2003-06-01

    High-resolution crystal structures of large ribosomal subunits from Deinococcus radiodurans complexed with tRNA-mimics indicate that precise substrate positioning, mandatory for efficient protein biosynthesis with no further conformational rearrangements, is governed by remote interactions of the tRNA helical features. Based on the peptidyl transferase center (PTC) architecture, on the placement of tRNA mimics, and on the existence of a two-fold related region consisting of about 180 nucleotides of the 23S RNA, we proposed a unified mechanism integrating peptide bond formation, A-to-P site translocation, and the entrance of the nascent protein into its exit tunnel. This mechanism implies sovereign, albeit correlated, motions of the tRNA termini and includes a spiral rotation of the A-site tRNA-3' end around a local two-fold rotation axis, identified within the PTC. PTC features, ensuring the precise orientation required for the A-site nucleophilic attack on the P-site carbonyl-carbon, guide these motions. Solvent mediated hydrogen transfer appears to facilitate peptide bond formation in conjunction with the spiral rotation. The detection of similar two-fold symmetry-related regions in all known structures of the large ribosomal subunit, indicate the universality of this mechanism, and emphasizes the significance of the ribosomal template for the precise alignment of the substrates as well as for accurate and efficient translocation. The symmetry-related region may also be involved in regulatory tasks, such as signal transmission between the ribosomal features facilitating the entrance and the release of the tRNA molecules. The protein exit tunnel is an additional feature that has a role in cellular regulation. We showed by crystallographic methods that this tunnel is capable of undergoing conformational oscillations and correlated the tunnel mobility with sequence discrimination, gating and intracellular regulation. PMID:12787020

  20. Toward Design Principles for Diffusionless Transformations: The Frustrated Formation of Co-Co Bonds in a Low-Temperature Polymorph of GdCoSi2.

    Science.gov (United States)

    Vinokur, Anastasiya I; Fredrickson, Daniel C

    2016-06-20

    Diffusionless (or displacive) phase transitions allow inorganic materials to show exquisite responsiveness to external stimuli, as is illustrated vividly by the superelasticity, shape memory, and magnetocaloric effects exhibited by martensitic materials. In this Article, we present a new diffusionless transition in the compound GdCoSi2, whose origin in frustrated bonding points toward generalizable design principles for these transformations. We first describe the synthesis of GdCoSi2 and the determination of its structure using single crystal X-ray diffraction. While previous studies based on powder X-ray diffraction assigned this compound to the simple CeNi1-xSi2 structure type (space group Cmcm), our structure solution reveals a superstructure variant (space group Pbcm) in which the Co sublattice is distorted to create zigzag chains of Co atoms. DFT-calibrated Hückel calculations, coupled with a reversed approximation Molecular Orbital (raMO) analysis, trace this superstructure to the use of Co-Co isolobal bonds to complete filled 18 electron configurations on the Co atoms, in accordance with the 18-n rule. The formation of these Co-Co bonds is partially impeded, however, by a small degree of electron transfer from Si-based electronic states to those with Co-Co σ* character. The incomplete success of Co-Co bond creation suggests that these interactions are relatively weak, opening the possibility of them being overcome by thermal energy at elevated temperatures. In fact, high-temperature powder and single crystal X-ray diffraction data, as well as differential scanning calorimetry, indicate that a reversible Pbcm to Cmcm transition occurs at about 380 K. This transition is diffusionless, and the available data point toward it being first-order. We expect that similar cases of frustrated interactions could be staged in other rare earth-transition metal-main group phases, providing a potentially rich source of compounds exhibiting diffusionless transformations

  1. Solvent engineering and other reaction design methods for favouring enzyme-catalysed synthesis

    DEFF Research Database (Denmark)

    Zeuner, Birgitte

    FAE-catalysed acylation reactions was reviewed. FAE type A from Aspergillus niger and an FAE from a commercial preparation from Humicola insolens, Depol 740L, could not catalyse the esterification of arabinose or xylose with hydroxycinnamates in IL-buffer systems or in surfactantless microemulsion...

  2. 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

  3. Real-time Monitoring of Intermediates Reveals the Reaction Pathway in the Thiol-Disulfide Exchange between Disulfide Bond Formation Protein A (DsbA) and B (DsbB) on a Membrane-immobilized Quartz Crystal Microbalance (QCM) System*

    Science.gov (United States)

    Yazawa, Kenjiro; Furusawa, Hiroyuki; Okahata, Yoshio

    2013-01-01

    Disulfide bond formation protein B (DsbBS-S,S-S) is an inner membrane protein in Escherichia coli that has two disulfide bonds (S-S, S-S) that play a role in oxidization of a pair of cysteine residues (SH, SH) in disulfide bond formation protein A (DsbASH,SH). The oxidized DsbAS-S, with one disulfide bond (S-S), can oxidize proteins with SH groups for maturation of a folding preprotein. Here, we have described the transient kinetics of the oxidation reaction between DsbASH,SH and DsbBS-S,S-S. We immobilized DsbBS-S,S-S embedded in lipid bilayers on the surface of a 27-MHz quartz crystal microbalance (QCM) device to detect both formation and degradation of the reaction intermediate (DsbA-DsbB), formed via intermolecular disulfide bonds, as a mass change in real time. The obtained kinetic parameters (intermediate formation, reverse, and oxidation rate constants (kf, kr, and kcat, respectively) indicated that the two pairs of cysteine residues in DsbBS-S,S-S were more important for the stability of the DsbA-DsbB intermediate than ubiquinone, an electron acceptor for DsbBS-S,S-S. Our data suggested that the reaction pathway of almost all DsbASH,SH oxidation processes would proceed through this stable intermediate, avoiding the requirement for ubiquinone. PMID:24145032

  4. Real-time monitoring of intermediates reveals the reaction pathway in the thiol-disulfide exchange between disulfide bond formation protein A (DsbA) and B (DsbB) on a membrane-immobilized quartz crystal microbalance (QCM) system.

    Science.gov (United States)

    Yazawa, Kenjiro; Furusawa, Hiroyuki; Okahata, Yoshio

    2013-12-13

    Disulfide bond formation protein B (DsbBS-S,S-S) is an inner membrane protein in Escherichia coli that has two disulfide bonds (S-S, S-S) that play a role in oxidization of a pair of cysteine residues (SH, SH) in disulfide bond formation protein A (DsbASH,SH). The oxidized DsbAS-S, with one disulfide bond (S-S), can oxidize proteins with SH groups for maturation of a folding preprotein. Here, we have described the transient kinetics of the oxidation reaction between DsbASH,SH and DsbBS-S,S-S. We immobilized DsbBS-S,S-S embedded in lipid bilayers on the surface of a 27-MHz quartz crystal microbalance (QCM) device to detect both formation and degradation of the reaction intermediate (DsbA-DsbB), formed via intermolecular disulfide bonds, as a mass change in real time. The obtained kinetic parameters (intermediate formation, reverse, and oxidation rate constants (kf, kr, and kcat, respectively) indicated that the two pairs of cysteine residues in DsbBS-S,S-S were more important for the stability of the DsbA-DsbB intermediate than ubiquinone, an electron acceptor for DsbBS-S,S-S. Our data suggested that the reaction pathway of almost all DsbASH,SH oxidation processes would proceed through this stable intermediate, avoiding the requirement for ubiquinone. PMID:24145032

  5. Rhodium-catalysed asymmetric allylic arylation of racemic halides with arylboronic acids

    Science.gov (United States)

    Sidera, Mireia; Fletcher, Stephen P.

    2015-11-01

    Csp2-Csp2 cross-coupling reactions between arylboronic acid and aryl halides are widely used in both academia and industry and are strategically important in the development of new agrochemicals and pharmaceuticals. Csp2-Csp3 cross-coupling reactions have been developed, but enantioselective variations are rare and simply retaining the stereochemistry is a problem. Here we report a highly enantioselective Csp2-Csp3 bond-forming method that couples arylboronic acids to racemic allyl chlorides. Both enantiomers of a cyclic chloride are converted into a single enantiomer of product via a dynamic kinetic asymmetric transformation. This Rh-catalysed method uses readily available and inexpensive building blocks and is mild and broadly applicable. For electron-deficient, electron-rich or ortho-substituted boronic acids better results are obtained with racemic allyl bromides. Oxygen substitution in the allyl halide is tolerated and the products can be functionalized to provide diverse building blocks. The approach fills a significant gap in the methods for catalytic asymmetric synthesis.

  6. Suppression of Boride Formation in Transient Liquid Phase Bonding of Pairings of Parent Superalloy Materials with Different Compositions and Grain Structures and Resulting Mechanical Properties

    Science.gov (United States)

    Steuer, Susanne; Singer, Robert F.

    2014-07-01

    Two Ni-based superalloys, columnar grained Alloy 247 and single-crystal PWA1483, are joined by transient liquid phase bonding using an amorphous brazing foil containing boron as a melting point depressant. At lower brazing temperatures, two different morphologies of borides develop in both base materials: plate-like and globular ones. Their ratio to each other is temperature dependent. With very high brazing temperatures, the deleterious boride formation in Alloy 247 can be totally avoided, probably because the three-phase-field moves to higher alloying element contents. For the superalloy PWA1483, the formation of borides cannot be completely avoided at high brazing temperatures as incipient melting occurs. During subsequent solidification of these areas, Chinese-script-like borides precipitate. The mechanical properties (tensile tests at room and elevated temperatures and short-term creep rupture tests at elevated temperatures) for brazed samples without boride precipitation are very promising. Tensile strengths and creep times to 1 pct strain are comparable, respectively, higher than the ones of the weaker parent material for all tested temperatures and creep conditions (from 90 to 100 pct rsp. 175 to 250 pct).

  7. Acetaldehyde partial oxidation on the Au(111) model catalyst surface: C-C bond activation and formation of methyl acetate as an oxidative coupling product

    Science.gov (United States)

    Karatok, Mustafa; Vovk, Evgeny I.; Shah, Asad A.; Turksoy, Abdurrahman; Ozensoy, Emrah

    2015-11-01

    Partial oxidation of acetaldehyde (CH3CHO) on the oxygen pre-covered Au(111) single crystal model catalyst was investigated via Temperature Programmed Desorption (TPD) and Temperature Programmed Reaction Spectroscopy (TPRS) techniques, where ozone (O3) was utilized as the oxygen delivery agent providing atomic oxygen to the reacting surface. We show that for low exposures of O3 and small surface oxygen coverages, two partial oxidation products namely, methyl acetate (CH3COOCH3) and acetic acid (CH3COOH) can be generated without the formation of significant quantities of carbon dioxide. The formation of methyl acetate as the oxidative coupling reaction product implies that oxygen pre-covered Au(111) single crystal model catalyst surface can activate C-C bonds. In addition to the generation of these products; indications of the polymerization of acetaldehyde on the gold surface were also observed as an additional reaction route competing with the partial and total oxidation pathways. The interplay between the partial oxidation, total oxidation and polymerization pathways reveals the complex catalytic chemistry associated with the interaction between the acetaldehyde and atomic oxygen on catalytic gold surfaces.

  8. Transition metal catalysed functionalisation of c=c through boron chemistry: a tandem approach

    OpenAIRE

    Lillo García, Vanesa

    2009-01-01

    Organoboron compounds are some of the most useful reagents in organic synthesis. The carbon-boron bond, once formed, can be cleaved in a variety of ways, with or without homologation, leading to a wide range of useful functional groups. The catalytic addition of H-B or B-B across to unsaturated C-C bond is one of the catalytic processes with higher selective control in the C-B bond formation. In the first Chapter of this thesis shows the evolution through the literature of the three main cat...

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

    Science.gov (United States)

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

    2015-08-01

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

  10. Rhodium catalysed hydroformylation of alkenes using highly fluorophilic phosphines.

    Science.gov (United States)

    Adams, Dave J; Bennett, James A; Cole-Hamilton, David J; Hope, Eric G; Hopewell, Jonathan; Kight, Jo; Pogorzelec, Peter; Stuart, Alison M

    2005-12-21

    Highly fluorophilic phosphines incorporating at least one aromatic ring containing two directly attached perfluoroalkyl groups have been synthesised, their partition coefficients (organic phase : fluorous phase) measured and their electronic properties probed using (1)J(PtP) data for their trans-[PtCl(2)L(2)] complexes. These phosphines have been used as modifying ligands for the rhodium catalysed hydroformylation of 1-octene in perfluorocarbon solvents. Catalyst activity, regioselectivity and the levels of rhodium leaching to the product phase vary with the substitution patterns of the modifying ligands that do not correlate with the electronic properties or partition coefficients of these ligands, but can be interpreted in terms of differences in the resting states of the catalysts. PMID:16311639

  11. Global network cooperation catalysed by a small prosocial migrant clique

    CERN Document Server

    Miller, Steve

    2016-01-01

    Much research has been carried out to understand the emergence of cooperation in simulated social networks of competing individuals. Such research typically implements a population as a single connected network. Here we adopt a more realistic premise; namely that populations consist of multiple networks, whose members migrate from one to another. Specifically, we isolate the key elements of the scenario where a minority of members from a cooperative network migrate to a network populated by defectors. Using the public goods game to model group-wise cooperation, we find that under certain circumstances, the concerted actions of a trivial number of such migrants will catalyse widespread behavioural change throughout an entire population. Such results support a wider argument: that the general presence of some form of disruption contributes to the emergence of cooperation in social networks, and consequently that simpler models may encode a determinism that precludes the emergence of cooperation.

  12. Catalysed fusion: a very different book about CERN

    CERN Multimedia

    CERN Library

    2013-01-01

    Not many books get reviews resulting in headlines like "Steamy novel challenges CERN's serious image", "Love and death at CERN" and so on. But Francis Farley's book "Catalysed Fusion" does not leave its readers untouched.   Those of you who have been around some time will know Farley from when he worked at CERN. For "newcomers", Farley is a well-known physicist who put together the first experiment on the anomalous magnetic moment of the muon and has since taken part in all the experiments relating to this phenomenon. The back cover of his book reads: "A sizzling romance and a romp with subatomic particles at CERN. Love, discovery and adventure in the city where nations meet and beams collide. Life in a large laboratory. As always, the challenges are the same. Who leads? Who follows? Who succeeds? Who gets the credit? Who gets the women or the men? Young Jeremy arrives in CERN and joins the quest ...

  13. Proline-catalysed asymmetric ketol cyclizations: The template mechanism revisited

    Indian Academy of Sciences (India)

    R Malathi; D Rajagopal; Zoltan G Hajos; S Swaminathan

    2004-03-01

    A modified template mechanism based on modelling studies of energy minimised complexes is presented for the asymmetric proline-catalysed cyclization of triketones 1, 2 and 3 to the 2, 3-ketols 1a, 2a and 3a respectively. The template model involves a three-point contact as favoured in enzyme-substrate interactions. Our minimisation studies are in agreement with the divergent behaviour of the 6,5-, 6,6- and 6,7-bicyclic systems. They support the high 93.4% ee observed with the 6,5-bicyclic ketol and the lower 73% ee found with the 6,6-bicyclic ketol. The calculations also explain the lack of asymmetric induction with the 6,7-bicyclic system.

  14. Preferential formation of 13C- 18O bonds in carbonate minerals, estimated using first-principles lattice dynamics

    Science.gov (United States)

    Schauble, Edwin A.; Ghosh, Prosenjit; Eiler, John M.

    2006-05-01

    Equilibrium constants for internal isotopic exchange reactions of the type: Ca12C18O16O2+Ca13C16O3↔Ca13C18O16O2+Ca12C16O3 for individual CO 32- groups in the carbonate minerals calcite (CaCO 3), aragonite (CaCO 3), dolomite (CaMg(CO 3) 2), magnesite (MgCO 3), witherite (BaCO 3), and nahcolite (NaHCO 3) are calculated using first-principles lattice dynamics. Calculations rely on density functional perturbation theory (DFPT) with norm-conserving planewave pseudopotentials to determine the vibrational frequencies of isotopically substituted crystals. Our results predict an ˜0.4‰ excess of 13C18O16O22- groups in all studied carbonate minerals at room-temperature equilibrium, relative to what would be expected in a stochastic mixture of carbonate isotopologues with the same bulk 13C/ 12C, 18O/ 16O, and 17O/ 16O ratios. The amount of excess 13C18O16O22- decreases with increasing temperature of equilibration, from 0.5‰ at 0 °C to <0.1‰ at 300 °C, suggesting that measurements of multiply substituted isotopologues of carbonate could be used to infer temperatures of ancient carbonate mineral precipitation and alteration events, even where the δ 18O of coexisting fluids is uncertain. The predicted temperature sensitivity of the equilibrium constant is ˜0.003‰/°C at 25 °C. Estimated equilibrium constants for the formation of 13C18O16O22- are remarkably uniform for the variety of minerals studied, suggesting that temperature calibrations will also be applicable to carbonate minerals not studied here without greatly compromising accuracy. A related equilibrium constant for the reaction: Ca12C18O16O2+Ca12C17O16O2↔Ca12C18O17O16O+Ca12C16O3 in calcite indicates formation of 0.1‰ excess 12C 18O 17O 16O 2- at 25 °C. In a conventional phosphoric acid reaction of carbonate to form CO 2 for mass-spectrometric analysis, molecules derived from 13C18O16O22- dominate (˜96%) the mass 47 signal, and 12C 18O 17O 16O 2- contributes most of the remainder (3%). This suggests

  15. Slow rate of phosphodiester bond formation accounts for the strong bias that Taq DNA polymerase shows against 2',3'-dideoxynucleotide terminators.

    Science.gov (United States)

    Brandis, J W; Edwards, S G; Johnson, K A

    1996-02-20

    Taq and T7 DNA polymerases have become basic molecular biology "tools" for DNA sequence analysis. However, Taq, unlike T7 DNA polymerase, is strongly biased against the incorporation of 2',3'-dideoxynucleotide triphosphates (ddNTPs) indicating very different substrate selectivities. Equilibrium binding and rate constants were measured for 2',3'-ddNTPs as well as for several other 3'-substituted terminators and compared to 2'-deoxynucleotide substrates (dNTPs). In steady-state experiments, Taq Pol I was strongly biased in favor of dATP1 over ddATP incorporation by about 700 to 1, in contrast to T7 DNA polymerase which showed a preference of only about 4 to 1. Manganese reduced but did not eliminate selectivity against 2',3'-ddNTPs. Transient kinetic traces indicated different rate-limiting steps for substrate and terminator incorporation. Further mechanistic studies showed that the binding constants for substrates and terminators were equivalent. However, the rate constants for phosphodiester bond formation for 2',3'-ddNTPs were 200-3000-fold lower than for dNTPs. Alternative terminators showed only slight improvements. The data were consistent with a model in which both substrates and terminators undergo ground-state binding followed by formation of a tight-binding Enz.DNA.Nucleotide complex. Immediately after complex formation, substrates undergo a rapid nucleoside phosphoryl transfer reaction. However, the reaction rates for terminators were slower presumably due to misalignment of reactive groups in the active site. Thus, the strong bias that Taq DNA polymerase shows against terminators is due to a very slow "chemistry" step. Such a strong bias has several kinetic consequences for DNA sequence patterns. These consequences are discussed in the text. PMID:8652560

  16. 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...

  17. Palladium-catalysed cyclisation of alkenols: Synthesis of oxaheterocycles as core intermediates of natural compounds

    Directory of Open Access Journals (Sweden)

    Miroslav Palík

    2014-09-01

    Full Text Available The study of Pd-catalysed cyclisation reactions of alkenols using different catalytic systems is reported. These transformations affect the stereoselective construction of mono- and/or bicyclic oxaheterocyclic derivatives depending on a starting alkenol. The substrate scope and proposed mechanism of Pd-catalysed cyclisation reactions are also discussed. Moreover, the diastereoselective Pd-catalysed cyclisation of appropriate alkenols to tetrahydrofurans and subsequent cyclisation provided properly substituted 2,5-dioxabicyclo[2.2.1]heptane and 2,6-dioxabicyclo[3.2.1]octane, respectively. Such bicyclic ring subunits are found in many natural products including ocellenynes and aurovertines.

  18. Theoretical studies on the mechanism of palladium(II)-catalysed ortho-carboxylation of acetanilide with CO

    Indian Academy of Sciences (India)

    Xing Hui Zhang; Zhi Yuan Geng; Ke Tai Wang

    2014-01-01

    The mechanism of palladium(II)-catalysed carboxylation of acetanilide with CO has been investigated using density functional theory calculation done at the B3LYP/6-31G(d, p)(SDD for Pd) level of theory. Solvent effects on these reactions have been explored by calculation that included a polarizable continuum model (PCM) for the solvent. Two plausible pathways which led to the formation of anhydride or benzoxazinone intermediate structure were proposed. Our calculated results suggested that the steps of forming the anhydride or benzoxazinone intermediate became the rate-determining one in the whole catalytic cycle. The process of forming benzoxazinone is more favoured kinetically with a barrier of 16.6 kcal/mol versus 22.9 kcal/mol for the pathway of forming anhydride structure. Subsequent hydrolysis process of these intermediates then provide the corresponding product ortho-acetaminobenzoic acid. The computational results are consistent with the experimental observations of Yu et al. for palladium(II)-catalysed synthesis of acetanilide based on carbon monoxide.

  19. Stacked base-pair structures of adenine nucleosides stabilized by the formation of hydrogen-bonding network involving the two sugar groups

    International Nuclear Information System (INIS)

    Highlights: ► A combination of laser desorption and supersonic jet-cooling is used to produce base pairs of adenine nucleosides. ► Stacked base-pair structure of N6,N6-dimethyladnosine is identified by IR vibrational spectroscopy. ► Anharmonic vibrational calculation is employed to analyze the vibrational mode coupling in the stacked base pair. - Abstract: We have employed a laser desorption technique combined with supersonic-jet cooling for producing base pairs of adenine nucleosides, adenosine (Ado) and N6,N6-dimethyladenosine (DMAdo) under low-temperature conditions. The resulting base pairs are then ionized through resonant two-photon ionization (R2PI) and analyzed by time-of-flight mass spectrometry. It is found that dimers of these adenine nucleosides are stable, especially in the case of DMAdo, with respect to those of the corresponding bases, i.e., adenine and N6,N6-dimethyladenine. Structural analysis of the DMAdo dimer is performed based on the IR–UV double resonance measurements and theoretical calculations. The result demonstrates that the dimer possesses a stacked structure being stabilized by the formation of hydrogen-bonding network involving the two sugar groups. The occurrence of the frequency shift and broadening is explained satisfactorily based on the anharmonic coupling of the OH stretching modes with specific bending modes and low-frequency modes of base and sugar moieties

  20. Palladium(ii)-catalyzed C-C and C-O bond formation for the synthesis of C1-benzoyl isoquinolines from isoquinoline N-oxides and nitroalkenes.

    Science.gov (United States)

    Li, Jiu-Ling; Li, Wei-Ze; Wang, Ying-Chun; Ren, Qiu; Wang, Heng-Shan; Pan, Ying-Ming

    2016-08-01

    C1-Benzoyl isoquinolines can be generated via a palladium(ii)-catalyzed C-C and C-O coupling of isoquinoline N-oxides with aromatic nitroalkenes. The reaction proceeds through remote C-H bond activation and subsequent intramolecular oxygen atom transfer (OAT). In this reaction, the N-O bond was designed as a directing group in the C-H bond activation as well as the source of an oxygen atom. PMID:27443150

  1. Epoxidation of olefins catalysed by vanadium-salan complexes: a theoretical mechanistic study.

    Science.gov (United States)

    Kuznetsov, Maxim L; Pessoa, João Costa

    2009-07-28

    Plausible mechanisms of olefin epoxidation catalysed by a V-salan model complex [VIV(=O)(L)(H2O)] (1, L=(CH2NHCH2CH=CHO-)2) in the presence of H2O2 are investigated and compared by theoretical methods using density functional theory. Three main routes, i.e. the Mimoun, Sharpless and biradical mechanisms, were examined in detail, and the Sharpless pathway was found to be the most favourable one. The reaction starts from the formation of an active catalytic species [VV(=O)(OO)(LH)] (3c) upon interaction of 1 with H2O2, then concerted, highly synchronous attack of the olefin to 3c occurs yielding the epoxide and catalyst [VV(=O)2(LH)], the latter being oxidized by H2O2 to 3c. The activation barrier strongly depends on the proton location in the catalyst molecule and is the lowest when one of the oxygen atoms of the salan ligand is protonated and the vanadium atom is penta-coordinated with one vacant coordination position (complex 3c). The olefin in this reaction acts as an electron donor (nucleophile) rather than as an electron acceptor (electrophile). PMID:19587988

  2. Effects of a catalysed and an additized particle filter on the emissions of a diesel passenger car operating on low sulphur fuels

    Science.gov (United States)

    Ntziachristos, Leonidas; Samaras, Zissis; Zervas, Efthimios; Dorlhène, Pascal

    This paper presents the emission characteristics of a diesel passenger car operated on low sulphur fuels (8 and 38 ppm) when fitted with either a catalysed diesel particle filter (DPF) or a non-catalysed one combined with a fuel-borne catalyst. Measurements were conducted over the New European Driving Cycle and a higher speed driving cycle to monitor the off-cycle DPF emission behaviour. Regulated gaseous pollutants and particle mass, number and surface were recorded. Aerosol samples were collected with a dedicated sampling system, which provided identical dilution conditions, regardless of the vehicle configuration, and allowed a distinction between volatile and non-volatile particles. The results showed that DPFs have the potential of filtration efficiencies which may exceed 99.5% in all airborne particle properties measured, over the transient cycles. As a result, the cycle average particle number was reduced from 10 14 to about 10 11 particles km -1 when fitting any DPF and the particle mass was reduced from ˜40 mg km -1 to the detection limit of the current measurement procedure. The exact particle concentration depended on the filter material properties. However, the efficiency in reducing mass appears lower than the airborne number, which suggests a sampling artefact of the present particulate matter measurement procedure. A nucleation mode formed at high exhaust gas temperature with the use of the higher sulphur fuel in combination with the catalysed DPF, thus decreasing the apparent DPF filtration efficiency. This was removed when any of the contributing factors (high temperature, higher sulphur fuel, catalysed DPF) were not present, suggesting sulphate particle formation downstream of the filter. Finally, results show that the DPF soot loading has an insignificant effect on particle size distribution downstream of the filter, when operating within soot-loading limits that are typically encountered in normal on-road operation.

  3. Laccase-catalysed polymeric dye synthesis from plant-derived phenols for potential application in hair dyeing: Enzymatic colourations driven by homo- or hetero-polymer synthesis.

    Science.gov (United States)

    Jeon, Jong-Rok; Kim, Eun-Ju; Murugesan, Kumarasamy; Park, Hyo-Keun; Kim, Young-Mo; Kwon, Jung-Hee; Kim, Wang-Gi; Lee, Ji-Yeon; Chang, Yoon-Seok

    2010-05-01

    Laccase efficiently catalyses polymerization of phenolic compounds. However, knowledge on applications of polymers synthesized in this manner remains scarce. Here, the potential of laccase-catalysed polymerization of natural phenols to form products useful in hair dyeing was investigated. All 15 tested phenols yielded coloured products after laccase treatment and colour diversity was attained by using mixtures of two phenolic monomers. After exploring colour differentiation pattern of 120 different reactions with statistical regression analysis, three monomer combinations, namely gallic acid and syringic acid, catechin and catechol, and ferulic acid and syringic acid, giving rise to brown, black, and red materials, respectively, were further characterized because such colours are commercially important for grey hair dyeing. Selected polymers could strongly absorb visible light and their hydrodynamic sizes ranged from 100 to 400 nm. Analyses of enzyme kinetic constants, liquid chromatography and electrospray ionization-mass spectrometry (ESI-MS) coupled with collision-induced dissociation MS/MS indicate that both monomers in reactions involving catechin and catechol, and ferulic acid and syringic acid, are coloured by heteropolymer synthesis, but the gallic acid/syringic acid combination is based on homopolymer mixture formation. Comparison of colour parameters from these three reactions with those of corresponding artificial homopolymer mixtures also supported the idea that laccase may catalyse either hetero- or homo-polymer synthesis. We finally used selected materials to dye grey hair. Each material coloured hair appropriately and the dyeing showed excellent resistance to conventional shampooing. Our study indicates that laccase-catalysed polymerization of natural phenols is applicable to the development of new cosmetic pigments. PMID:21255331

  4. 'Impact hunters' catalyse cooperative hunting in two wild chimpanzee communities.

    Science.gov (United States)

    Gilby, Ian C; Machanda, Zarin P; Mjungu, Deus C; Rosen, Jeremiah; Muller, Martin N; Pusey, Anne E; Wrangham, Richard W

    2015-12-01

    Even when hunting in groups is mutually beneficial, it is unclear how communal hunts are initiated. If it is costly to be the only hunter, individuals should be reluctant to hunt unless others already are. We used 70 years of data from three communities to examine how male chimpanzees 'solve' this apparent collective action problem. The 'impact hunter' hypothesis proposes that group hunts are sometimes catalysed by certain individuals that hunt more readily than others. In two communities (Kasekela and Kanyawara), we identified a total of five males that exhibited high hunt participation rates for their age, and whose presence at an encounter with red colobus monkeys increased group hunting probability. Critically, these impact hunters were observed to hunt first more often than expected by chance. We argue that by hunting first, these males dilute prey defences and create opportunities for previously reluctant participants. This by-product mutualism can explain variation in group hunting rates within and between social groups. Hunting rates declined after the death of impact hunter FG in Kasekela and after impact hunter MS stopped hunting frequently in Kanyawara. There were no impact hunters in the third, smaller community (Mitumba), where, unlike the others, hunting probability increased with the number of females present at an encounter with prey. PMID:26503679

  5. Copper-catalysed enantioselective stereodivergent synthesis of amino alcohols

    Science.gov (United States)

    Shi, Shi-Liang; Wong, Zackary L.; Buchwald, Stephen L.

    2016-04-01

    The chirality, or ‘handedness’, of a biologically active molecule can alter its physiological properties. Thus it is routine procedure in the drug discovery and development process to prepare and fully characterize all possible stereoisomers of a drug candidate for biological evaluation. Despite many advances in asymmetric synthesis, developing general and practical strategies for obtaining all possible stereoisomers of an organic compound that has multiple contiguous stereocentres remains a challenge. Here, we report a stereodivergent copper-based approach for the expeditious construction of amino alcohols with high levels of chemo-, regio-, diastereo- and enantioselectivity. Specifically, we synthesized these amino-alcohol products using sequential, copper-hydride-catalysed hydrosilylation and hydroamination of readily available enals and enones. This strategy provides a route to all possible stereoisomers of the amino-alcohol products, which contain up to three contiguous stereocentres. We leveraged catalyst control and stereospecificity simultaneously to attain exceptional control of the product stereochemistry. Beyond the immediate utility of this protocol, our strategy could inspire the development of methods that provide complete sets of stereoisomers for other valuable synthetic targets.

  6. 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.

  7. Erythromycin, roxithromycin, and clarithromycin: use of slow-binding kinetics to compare their in vitro interaction with a bacterial ribosomal complex active in peptide bond formation.

    Science.gov (United States)

    Dinos, George P; Connell, Sean R; Nierhaus, Knud H; Kalpaxis, Dimitrios L

    2003-03-01

    In a cell-free system derived from Escherichia coli, it is shown that clarithromycin and roxithromycin, like their parent compound erythromycin, do not inhibit the puromycin reaction (i.e., the peptide bond formation between puromycin and AcPhe-tRNA bound at the P-site of 70S ribosomes programmed with heteropolymeric mRNA). Nevertheless, all three antibiotics compete for binding on the ribosome with tylosin, a 16-membered ring macrolide that behaves as a slow-binding, slowly reversible inhibitor of peptidyltransferase. The mutually exclusive binding of these macrolides to ribosomes is also corroborated by the fact that they protect overlapping sites in domain V of 23S rRNA from chemical modification by dimethyl sulfate. From this competition effect, detailed kinetic analysis revealed that roxithromycin or clarithromycin (A), like erythromycin, reacts rapidly with AcPhe-tRNA.MF-mRNA x 70S ribosomal complex (C) to form the encounter complex CA which is then slowly isomerized to a more tight complex, termed C*A. The value of the overall dissociation constant, K, encompassing both steps of macrolide interaction with complex C, is 36 nM for erythromycin, 20 nM for roxithromycin, and 8 nM for clarithromycin. Because the off-rate constant of C*A complex does not significantly differ among the three macrolides, the superiority of clarithromycin as an inhibitor of translation in E. coli cells and many Gram-positive bacteria may be correlated with its greater rate of association with ribosomes. PMID:12606769

  8. Stopped Flow Kinetics of MnII Catalysed Periodate Oxidation of 2, 3- dimethylaniline - Evaluation of Stability Constant of the Ternary Intermediate Complex

    Directory of Open Access Journals (Sweden)

    Rajneesh Dutt Kaushik

    2015-03-01

    Full Text Available The formation of ternary intermediate unstable complex during the oxidation of aromatic amines by periodate ion catalysed by MnII has been proposed in case of some anilines. This paper is the first report on stopped-flow kinetic study and evaluation of stability constant of ternary complex forming in the MnII - catalysed periodate oxidation of 2, 3-dimethylaniline (D in acetone-water medium. Stop-flow spectrophotometric method was used to study the ternary complex formation and to determine its stability constant. The stop-flow trace shows the reaction to occur in two steps. The first step, which is presumably the formation of ternary complex, is relatively fast while the second stage is relatively quite slow. The stability constant evaluated for D - MnII - IO4- ternary complex by determining  equilibrium absorbance is (2.2 ± 1.0 × 105. Kinetics of ternary complex formation was defined by the rate law(A  under pseudo first order conditions. ln{[C2]eq / ( [C2]eq -[C2]} = kobs . t (A where, kobs is the pseudo first order rate constant, [C2] is concentration of ternary complex at given time t, and [C2]eq is the equilibrium concentration of ternary complex. © 2015 BCREC UNDIP. All rights reservedReceived: 3rd October 2014; Revised: 4th December 2014; Accepted: 15th December 2014How to Cite: Kaushik, R.D., Agarwal, R., Tyagi, P., Singh, O., Singh, J. (2015. Stopped Flow Kinetics of MnII Catalysed Periodate Oxidation of 2,3-dimethylaniline - Evaluation of Stability Constant of the Ternary Intermediate Complex. Bulletin of Chemical Reaction Engineering & Catalysis, 10 (1: 78-87. (doi:10.9767/bcrec.10.1.7621.78-87Permalink/DOI: http://dx.doi.org/10.9767/bcrec.10.1.7621.78-87

  9. Kinetics and mechanism of iridium (III) catalysed oxidation of tellurium (IV) by cerium (IV) in sulfuric acid medium

    International Nuclear Information System (INIS)

    The kinetics and mechanism of iridium (III) catalysed oxidation of tellurium (IV) by cerium (IV) have been studied in sulfuric acid medium. The reaction is first order in [Ir (III)] as well as in [Ce (IV)] and fractional order (0.23) in [Te (IV)]. Increase in [H3O+] accelerates the rate while that in ionic strength or [HSO4-] retards. Ce (III), one of the products, inhibits while the other, Te (VI), has negligible effect on the rate. The reaction is supposed to proceed via the formation of a complex between Te (IV) and Ir (III) which in turn reacts with active Ce (IV) species in a reversible step. A rate law, consistent with the observed kinetic data, has been derived basing on the proposed mechanism. (author)

  10. Possible interstellar formation of glycine through a concerted mechanism: a computational study on the reaction of CH2[double bond, length as m-dash]NH, CO2 and H2.

    Science.gov (United States)

    Nhlabatsi, Zanele P; Bhasi, Priya; Sitha, Sanyasi

    2016-07-27

    Glycine being the simplest amino acid and also having significant astrobiological implications, has meant that intensive investigations have been carried out in the past, starting from its detection in the interstellar medium (ISM) to analysis of meteorites and cometary samples and laboratory synthesis, as well as computational studies on the possible reaction paths. In this present work quantum chemical calculations have been performed to investigate the possible interstellar formation of glycine via two different paths; (1) in a two-step process via a dihydroxy carbene intermediate and (2) through a one-step concerted mechanism, starting from reactants like CH2[double bond, length as m-dash]NH, CO, CO2, H2O and H2. For the two reactions representing the carbene route, it was observed that the formation of dihydroxy carbene from either CO + H2O or CO2 + H2 is highly endothermic with large barrier heights, whereas the subsequent step of interaction of this carbene with CH2[double bond, length as m-dash]NH to give glycine is exothermic and the barrier is below the reactants. Based on this observation it is suggested that the formation of glycine via the carbene route is a least favourable or even unfavourable path. On the other hand, the two reactions CH2[double bond, length as m-dash]NH + CO + H2O and CH2[double bond, length as m-dash]NH + CO2 + H2 representing the concerted paths were found to be favourable in leading to the formation of glycine. After an extensive study on the first concerted reaction in our previous work (Phys. Chem. Chem. Phys., 2016, 18, 375-381), in this work a detailed investigation has been carried out for the second concerted reaction, CH2[double bond, length as m-dash]NH + CO2 + H2, which can possibly lead to the interstellar formation of glycine. It was observed that this reaction proceeds through a large barrier and at the same time the transition state shows prominent hydrogen dynamics, indicating a tunnelling possibility for this

  11. Inhibition of Hotspot Formation in Polymer Bonded Explosives Using an Interface Matching Low Density Polymer Coating at the Polymer–Explosive Interface

    OpenAIRE

    An, Qi; Goddard, William A.; Zybin, Sergey V.; Luo, Sheng-Nian

    2014-01-01

    In order to elucidate how shocks in heterogeneous materials affect decomposition and reactive processes, we used the ReaxFF reactive force field in reactive molecules dynamics (RMD) simulations of the effects of strong shocks (2.5 and 3.5 km/s) on a prototype polymer bonded explosive (PBX) consisting of cyclotrimethylene trinitramine (RDX) bonded to hydroxyl-terminated polybutadiene (HTPB). We showed earlier that shock propagation from the high density RDX to the low density polymer (RDX → Po...

  12. Does the Surface Matter? Hydrogen-Bonded Chain Formation of an Oxalic Amide Derivative in a Two- and Three-Dimensional Environment

    OpenAIRE

    Klappenberger, F.; Canas-Ventura, M. E.; Clair, S.; Pons, S.; Schlickum, U.; Qu, Z. R.; Strunskus, T.; Comisso, A.; Woll, C.; Brune, H.; Kern, K.; De Vita, A; Ruben, M.; Bartha, J. V.

    2008-01-01

    We report on a multi-technique investigation of the supramolecular organisation of N,N-diphenyl oxalic amide under differently dimensioned environments, namely three-dimensional (3D) in the bulk crystal, and in two dimensions on the Ag(111) surface as well as on the reconstructed Au(111) surface. With the help of Xray structure analysis and scanning tunneling microscopy (STM) we find that the molecules organize in hydrogen-bonded chains with the bonding motif qualitatively changed by the surf...

  13. 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.

  14. 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:

  15. Taille des particules et catalyse Particle Size and Catalysis

    Directory of Open Access Journals (Sweden)

    Boitiaux J. P.

    2006-11-01

    Full Text Available Si la catalyse hétérogène et notamment la catalyse par les métaux se préoccupe de la taille des particules et donc de la surface développée, ce n'est pas seulement pour élaborer un produit efficace à moindre coût. L'étude des relations entre les caractéristiques des catalyseurs et leurs propriétés vis-à-vis des réactions a permis d'arriver dans certains cas à une description quasi atomique du site actif spécifique de chaque réaction. Les approches de ce problème qu'ont eu les différents auteurs sont différentes : l'une a consisté à prendre en considération les propriétés cristallographiques des métaux massiques, l'autre à considérer que les petites particules n'ont ni les propriétés, ni la structure du métal massif. L'approche cristallographique a d'abord conduit à prendre en compte les paramètres des cristaux et à distinguer les différents atomes situés en coins, arêtes ou faces. Mais très vite on s'est rendu compte que les particules n'avaient pas les structures attendues. On s'est donc intéressé au calcul de l'énergie des particules considérées pour imaginer comment elles pouvaient se construire à partir d'un petit noyau. Ces calculs ne tenaient compte ni de l'atmosphère en contact avec la particule, ni de la présence d'un support, ni des perturbations apportées par la réaction. En effet selon la réaction étudiée, on a pu définir des réactions facilesou insensibles à la structure et des réactions exigeantesdont la vitesse intrinsèque varie avec la structure de surface. Beaucoup de travaux ont été effectués sur des monocristaux dont les surfaces exposées avaient des indices différents et d'autres ont tenté d'étudier ces relations avec des métaux supportés, avec tous les artefacts que cela pouvait amener. Il a été difficile de trouver une unité dans tous les résultats obtenus et ceci d'autant plus que les phénomènes d'auto empoisonnement par les réactifs (hydrocarbures ou

  16. Covalent bonding and band-gap formation in ternary transition-metal di-aluminides: Al4MnCo and related compounds

    International Nuclear Information System (INIS)

    In this paper we extend our previous study of the electronic structure of and bonding mechanism in transition-metal (TM) di-aluminides to ternary systems. We have studied the character of the bonding in Al4MnCo and related TM di-aluminides in the C11b (MoSi2) and C54 (TiSi2) crystal structures. A peculiar feature of the electronic structure of these TM di-aluminides is the existence of a semiconducting gap at the Fermi level. In our previous work we predicted a gap in Al2TM compounds where the TM atoms have eight valence electrons. Here we demonstrate that the semiconducting gap does not disappear if the TM sites are occupied by two different TMs, provided that the electron-per-atom ratio is conserved. Such a replacement substantially increases the class of possibly semiconducting TM di-aluminides. Substitution for 3d TMs of 4d or 5d TMs enhances the width of the gap. From the analysis of the charge density distribution and the crystal orbital overlap population, we conclude that the bonding between atoms has dominantly covalent character. This is confirmed not only by the enhanced charge density halfway between atoms, but also by the clear bonding-antibonding splitting of the electronic states. If the gaps between split states that correspond to all bonding configurations in the crystal have a common overlap at the Fermi level, the intermetallic compound becomes a semiconductor. However, the results of the total-energy calculations suggest that the existence of a band gap does not necessarily imply a stable structure. Strong covalent bonds can exist also in Al-TM structures where no band gap is observed. (author)

  17. C-13 isotopic studies of the surface catalysed reactions of methane

    International Nuclear Information System (INIS)

    The ability of methane to methylate aromatic compounds, which are considered to be models for coal, is being studied. Related to this reaction, but at higher temperatures, is the direct formation of benzene from methane in the presence of these catalysts. Controversy exists in the literature on the former reaction, and 13C isotope studies are being used to resolve the question. The interest in this reaction arises because the utilisation of methane, in the form of natural gas, in place of hydrogen for direct coal liquefaction would have major economic advantage. For this reason Isotope studies in this area have contributed significantly to an understanding of the methylation reactions. The paper describes experiments utilising methane13C, which show that methylation of aromatics such as naphthalene by the methane13C is catalysed by microporous, Cu-exchanged SAPO-5, at elevated pressures (6.8 MPa) and temperatures around 400 degree C. The mass spectrometric analysis and n.m.r. study of the isotopic composition of the products of the methylation reaction demonstrate unequivocally that methane provides the additional carbon atom for the methylated products. Thermodynamic calculations predict that the reaction is favourable at high methane pressures under these experimental conditions. The mechanism as suggested by the isotope study is discussed. The catalysts which show activity for the activation of methane for direct methylation of organic compounds, such as naphthalene, toluene, phenol and pyrene, are substituted aluminophosphate molecular sieves, EIAPO-5 (where El=Pb, Cu, Ni and Si) and a number of metal substituted zeolites. Our earlier tritium studies had shown that these catalysts will activate alkanes, at least as far as isotope hydrogen exchange reactions are concerned

  18. A Phenomenographic Study on Chemical Bonding

    Directory of Open Access Journals (Sweden)

    Şenol Şen

    2013-12-01

    Full Text Available This study aims to reveal how students perceive and identify the concept of chemical bonding, and to identify and explain the misconceptions of students on this subject through phenomenographic research method, as well. The present study included 17 2nd grade students who enrolled to Inorganic Chemistry course in the Faculty of Education. Concept maps and lotus blossom technique were used as data collection tools in order to determine the perceptions and definitions of students about chemical bonding. Data analysis results determined the misconceptions of students about chemical bonding classified misconceptions under seven categories, which are, according to the results of the study, physical changes and bonding, ionic bond, formation of chemical bonding, the existence of chemical bonding, covalent bonds, metallic bonds and intermolecular bonding.

  19. Distinguishing Bonds.

    Science.gov (United States)

    Rahm, Martin; Hoffmann, Roald

    2016-03-23

    The energy change per electron in a chemical or physical transformation, ΔE/n, may be expressed as Δχ̅ + Δ(VNN + ω)/n, where Δχ̅ is the average electron binding energy, a generalized electronegativity, ΔVNN is the change in nuclear repulsions, and Δω is the change in multielectron interactions in the process considered. The last term can be obtained by the difference from experimental or theoretical estimates of the first terms. Previously obtained consequences of this energy partitioning are extended here to a different analysis of bonding in a great variety of diatomics, including more or less polar ones. Arguments are presented for associating the average change in electron binding energy with covalence, and the change in multielectron interactions with electron transfer, either to, out, or within a molecule. A new descriptor Q, essentially the scaled difference between the Δχ̅ and Δ(VNN + ω)/n terms, when plotted versus the bond energy, separates nicely a wide variety of bonding types, covalent, covalent but more correlated, polar and increasingly ionic, metallogenic, electrostatic, charge-shift bonds, and dispersion interactions. Also, Q itself shows a set of interesting relations with the correlation energy of a bond. PMID:26910496

  20. Features of microstructure formation of hard alloys on the base of TiC0.5N0.47 under nickel-molybdenum bond deficit

    International Nuclear Information System (INIS)

    Materials with low content of metal phase in TiCxNz-Ni-Mo system were prepared. Microstructure of solid alloys was studied. It is shown that sintering temperature should be increased in proportion to decrease of volumetric content of metallic bond when preparing low-porous solid alloys of TiC0.5N0.47-Ni-Mo system

  1. Discovery of molluscicidal and cercaricidal activities of 3-substituted quinazolinone derivatives by a scaffold hopping approach using a pseudo-ring based on the intramolecular hydrogen bond formation.

    Science.gov (United States)

    Guo, Wei; Zheng, Lv-Yin; Li, Yong-Dong; Wu, Ren-Miao; Chen, Qiang; Yang, Ding-Qiao; Fan, Xiao-Lin

    2016-06-10

    Discovery of novel topological agents against Oncomelania hupensis snails and cercariae remains a significant challenge in current Schistosomiasis control. A pseudo-ring formed from salicylanilide by an intramolecular hydrogen bond led to the discovery of 3-substituted quinazolinone derivatives which showed a potent molluscicidal and cercaricidal activities. PMID:27017555

  2. An Iterated GMM Procedure for Estimating the Campbell-Cochrane Habit Formation Model, with an Application to Danish Stock and Bond Returns

    DEFF Research Database (Denmark)

    Engsted, Tom; Møller, Stig Vinther

    2010-01-01

    We suggest an iterated GMM approach to estimate and test the consumption based habit persistence model of Campbell and Cochrane, and we apply the approach on annual and quarterly Danish stock and bond returns. For comparative purposes we also estimate and test the standard constant relative risk...

  3. Isopeptide bonds of the major pilin protein BcpA influence pilus structure and bundle formation on the surface of Bacillus cereus

    Energy Technology Data Exchange (ETDEWEB)

    Hendrickx, Antoni P.A.; Poor, Catherine B.; Jureller, Justin E.; Budzik, Jonathan M.; He, Chuan; Schneewind, Olaf (UC)

    2012-09-05

    Bacillus cereus strains elaborate pili on their surface using a mechanism of sortase-mediated cross-linking of major and minor pilus components. Here we used a combination of electron microscopy and atomic force microscopy to visualize these structures. Pili occur as single, double or higher order assemblies of filaments formed from monomers of the major pilin, BcpA, capped by the minor pilin, BcpB. Previous studies demonstrated that within assembled pili, four domains of BcpA -- CNA{sub 1}, CNA{sub 2}, XNA and CNA{sub 3} -- each acquire intramolecular lysine-asparagine isopeptide bonds formed via catalytic glutamic acid or aspartic acid residues. Here we showed that mutants unable to form the intramolecular isopeptide bonds in the CNA2 or CNA3 domains retain the ability to form pilus bundles. A mutant lacking the CNA{sub 1} isopeptide bond assembled deformed pilin subunits that failed to associate as bundles. X-ray crystallography revealed that the BcpA variant Asp{sup 312}Ala, lacking an aspartyl catalyst, did not generate the isopeptide bond within the jelly-roll structure of XNA. The Asp{sup 312}Ala mutant was also unable to form bundles and promoted the assembly of deformed pili. Thus, structural integrity of the CNA{sub 1} and XNA domains are determinants for the association of pili into higher order bundle structures and determine native pilus structure.

  4. Crystal Structure, Thermal Decomposition Behavior and the Standard Molar Enthalpy of Formation of a Novel 3D Hydrogen Bonded Supramolecular [Co(HnicO)2·(H2O)2

    Institute of Scientific and Technical Information of China (English)

    ZENG,Ming-Hua; WU,Mei-Chun; ZHU,Li-Hong; LIANG,Hong; YANG Xu-Wu

    2007-01-01

    Hydrothermal synthesis and X-ray characterized 3D supramolecular networks were constructed by [Co(HnicO)2·(H2O)2] (HnicOH=2-hydroxynicotinic acid) (1) as building block via abundant dimeric homomeric (N-H…O) and unusually cyclic tetrameric heteromeric (O-H…O) hydrogen-bonds. It is noted that there exist unusually linear metal-water chains comprised of tetrameric units linked by vertexes sharing cobalt centers through hydrogen-bonding. TG-DTG curves illustrated that thermal decomposition was completed by two steps, one is the loss of two terminal water molecules in the range of 156-234 ℃, and the other is the pyrolysis of HnicO ligand in the range of 234-730 ℃. The standard molar enthalpy of formation of the complex was determined to be (-1845.43±2.77) kJ·mol-1 by a rotary-bomb combustion calorimeter.

  5. Sensor/ROIC Integration using Oxide Bonding

    OpenAIRE

    Ye, Zhenyu; Group, for the Fermilab Pixel R&D

    2009-01-01

    We explore the Ziptronix Direct Bond Interconnect technology for the integration of sensors and readout integrated circuits (ROICs) for high energy physics. The technology utilizes an oxide bond to form a robust mechanical connection between layers which serves to assist with the formation of metallic interlayer connections. We report on testing results of sample sensors bonded to ROICs and thinned to 100 microns.

  6. CuH-Catalysed Hydroamination of Styrene with Hydroxylamine Esters: A Coupled Cluster Scrutiny of Mechanistic Pathways.

    Science.gov (United States)

    Tobisch, Sven

    2016-06-01

    A detailed computational exploration of mechanistic intricacies of the copper(I) hydride (CuH)-catalysed hydroamination of styrene with a prototype hydroxylamine ester by a recently reported [(dppbz)CuH] catalyst (dppbz≡{P^P}≡1,2-bis(diphenylphosphino)-benzene) is presented. A variety of plausible mechanistic avenues have been pursued by means of a sophisticated computational methodology, from which a general understanding of the factors controlling hydroamination catalysis emerged. The catalytically competent {P^P}Cu(I) hydride, which is predominantly present as its dimer, involves in irreversible hydrocupration proceeding with complete 2,1 regioselectivity to form a secondary {P^P}Cu(I) benzyl intermediate. Its interception with benzylamine ester produces the branched tertiary amine product and {P^P}Cu(I) benzoate upon intramolecular SN 2 disruption of the amine electrophile's N-O linkage, to precede a highly rapid, strongly exergonic C-N bond-forming reductive elimination. The {P^P}Cu(I) benzoate corresponds to the catalyst resting state and its conversion back into the {P^P}Cu(I) hydride upon transmetalation with a hydrosilane is turnover limiting. The effect of electronic perturbations at the amine electrophile upon the reaction rate for productive hydroamination catalysis and also non-productive reduction of the hydroxylamine ester has been gauged, which unveiled a more fundamental insight into catalytic structure-performance relationships. PMID:27138470

  7. 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.

  8. Study in electron microscopy the formation of the hybrid layer using adhesive systems One Coat and Single Bond Universal, at the Facultad de Medicina of the Universidad de Costa Rica

    International Nuclear Information System (INIS)

    The formation of the hybrid layer is observed in dental pieces in vitro, using systems of conventional adhesives (Single Bond 2 of 3M and One Coat of Coltene), with different times of acid etching, through the use of atomic force microscopy (AFM). The images of the hybrid layer obtained from samples prepared with adhesive systems are analyzed by AFM. Samples collected have been of dental pieces (molars and premolars) recently extracted and later placed in water. The pieces used have provided more surface to be observed under the microscope, greater accessibility to the be cut for its study, and to the great pieces have facilitated their placement on the Isomet low speed saw. The differences are evaluated between hybrid layers according the adhesive system used and the mode of application of the images obtained in the atomic force microscope. The adhesive system that has allowed the formation of a hybrid layer more appropriate between the adhesive system One Coat and the adhesive system Single Bond Universal is determined. The time of acid etching as variable of procedure is determined and has interfered with the formation of a hybrid layer more stable. The images evaluated that were provided by the atomic force microscope and compared with the images of electron microscopy of other studies, have determined that the AFM is without providing detailed information, as well as the appropriate images to evaluate the hybrid layer of the adhesive systems Single Bond 2 and One Coat of Coltene, or the different times of acid etching. Therefore, for this type of study, the image of choice must be of an electron microscope

  9. Iron(III)-catalysed carbonyl-olefin metathesis.

    Science.gov (United States)

    Ludwig, Jacob R; Zimmerman, Paul M; Gianino, Joseph B; Schindler, Corinna S

    2016-05-19

    The olefin metathesis reaction of two unsaturated substrates is one of the most powerful carbon-carbon-bond-forming reactions in organic chemistry. Specifically, the catalytic olefin metathesis reaction has led to profound developments in the synthesis of molecules relevant to the petroleum, materials, agricultural and pharmaceutical industries. These reactions are characterized by their use of discrete metal alkylidene catalysts that operate via a well-established mechanism. While the corresponding carbonyl-olefin metathesis reaction can also be used to construct carbon-carbon bonds, currently available methods are scarce and severely hampered by either harsh reaction conditions or the required use of stoichiometric transition metals as reagents. To date, no general protocol for catalytic carbonyl-olefin metathesis has been reported. Here we demonstrate a catalytic carbonyl-olefin ring-closing metathesis reaction that uses iron, an Earth-abundant and environmentally benign transition metal, as a catalyst. This transformation accommodates a variety of substrates and is distinguished by its operational simplicity, mild reaction conditions, high functional-group tolerance, and amenability to gram-scale synthesis. We anticipate that these characteristics, coupled with the efficiency of this reaction, will allow for further advances in areas that have historically been enhanced by olefin metathesis. PMID:27120158

  10. Iron(III)-catalysed carbonyl–olefin metathesis

    Science.gov (United States)

    Ludwig, Jacob R.; Zimmerman, Paul M.; Gianino, Joseph B.; Schindler, Corinna S.

    2016-05-01

    The olefin metathesis reaction of two unsaturated substrates is one of the most powerful carbon–carbon-bond-forming reactions in organic chemistry. Specifically, the catalytic olefin metathesis reaction has led to profound developments in the synthesis of molecules relevant to the petroleum, materials, agricultural and pharmaceutical industries. These reactions are characterized by their use of discrete metal alkylidene catalysts that operate via a well-established mechanism. While the corresponding carbonyl–olefin metathesis reaction can also be used to construct carbon–carbon bonds, currently available methods are scarce and severely hampered by either harsh reaction conditions or the required use of stoichiometric transition metals as reagents. To date, no general protocol for catalytic carbonyl–olefin metathesis has been reported. Here we demonstrate a catalytic carbonyl–olefin ring-closing metathesis reaction that uses iron, an Earth-abundant and environmentally benign transition metal, as a catalyst. This transformation accommodates a variety of substrates and is distinguished by its operational simplicity, mild reaction conditions, high functional-group tolerance, and amenability to gram-scale synthesis. We anticipate that these characteristics, coupled with the efficiency of this reaction, will allow for further advances in areas that have historically been enhanced by olefin metathesis.

  11. Radical C-H arylations of (hetero)arenes catalysed by gallic acid.

    Science.gov (United States)

    Perretti, Marcelle D; Monzón, Diego M; Crisóstomo, Fernando P; Martín, Víctor S; Carrillo, Romen

    2016-07-12

    Gallic acid efficiently catalyses radical arylations in water-acetone at room temperature. This methodology proved to be versatile and scalable. Therefore, it constitutes a greener alternative to arylation. Moreover, considering that gallic acid is an abundant vegetable tannin, this work also unleashes an alternative method for the reutilisation of bio-wastes. PMID:26804947

  12. Solvent-free catalysed synthesis of tetrahydropyran odorants: the role of SiO

    International Nuclear Information System (INIS)

    An efficient, green and solvent-free catalysed Prins-cyclization reaction based on the simple grinding of an aldehyde and a homoallylic alcohol in the presence of catalytic amount of p-TSA on silica gel is reported. By this protocol were synthesized tetrahydropyran odorants including commercial Florol and Clarycet, in one and two steps respectively. (author)

  13. Computing the correlation between catalyst composition and its performance in the catalysed process

    Czech Academy of Sciences Publication Activity Database

    Holeňa, Martin; Steinfeldt, N.; Baerns, M.; Štefka, David

    2012-01-01

    Roč. 43, 10 August (2012), s. 55-67. ISSN 0098-1354 R&D Projects: GA ČR GA201/08/0802 Institutional support: RVO:67985807 Keywords : catalysed process * catalyst performance * correlation measures * estimating correlation value * analysis of variance * regression trees Subject RIV: IN - Informatics, Computer Science Impact factor: 2.091, year: 2012

  14. Inactivation of barley limit dextrinase inhibitor by thioredoxin-catalysed disulfide reduction

    DEFF Research Database (Denmark)

    Jensen, Johanne Mørch; Hägglund, Per; Christensen, Hans Erik Mølager; Svensson, Birte

    2012-01-01

    Barley limit dextrinase (LD) that catalyses hydrolysis of α-1,6 glucosidic linkages in starch-derived dextrins is inhibited by limit dextrinase inhibitor (LDI) found in mature seeds. LDI belongs to the chloroform/methanol soluble protein family (CM-protein family) and has four disulfide bridges and...

  15. NHC-catalysed diastereoselective synthesis of multifunctionalised piperidines via cascade reaction of enals with azalactones.

    Science.gov (United States)

    Singh, Atul K; Chawla, Ruchi; Rai, Ankita; Yadav, Lal Dhar S

    2012-04-18

    NHC-catalysed azalactone ring-opening and piperidine ring-closing cascade with α,β-unsaturated aldehydes (enals) in a one-pot operation is reported. The present reaction cascade offers a convenient method for a highly diastereoselective synthesis of multifunctionalised piperidines in excellent yields under mild conditions. PMID:22399056

  16. Amino acid-catalysed retroaldol condensation: the production of natural benzaldehyde and other flavour compounds

    NARCIS (Netherlands)

    Wolken, W.A.M.; Tramper, J.; Werf, van der M.J.

    2004-01-01

    The amino acid-catalysed retroaldol condensation previously described for citral has been extended to other alpha,beta-unsaturated aldehydes. In the presence of glycine and an elevated pH, six other alpha,beta-unsaturated aldehydes also underwent retroaldol condensation. Crotonaldehyde, as well as i

  17. Amino acid-catalysed retroaldol condensation: The production of natural benzaldehyde and other flavour compounds

    NARCIS (Netherlands)

    Wolken, W.A.M.; Tramper, J.; Werf, M.J. van der

    2004-01-01

    The amino acid-catalysed retroaldol condensation previously described for citral has been extended to other α,β -unsaturated aldehydes. In the presence of glycine and an elevated pH, six other α,β-unsaturated aldehydes also underwent retroaldol condensation. Crotonaldehyde, as well as its proposed i

  18. Amino acid-catalysed retroaldol condensation : the production of natural benzaldehyde and other flavour compounds

    NARCIS (Netherlands)

    Wolken, WAM; Tramper, J; van der Werf, MJ

    2004-01-01

    The amino acid-catalysed retroaldol condensation previously described for citral has been extended to other alpha,beta-unsaturated aldehydes. In the presence of glycine and an elevated pH, six other alpha,beta-unsaturated aldehydes also underwent retroaldol condensation. Crotonaldehyde, as well as i

  19. LES TIC DANS LA MÉTHODE CATALYSE : TRANSFERT MÉTHODOLOGIQUE ET TECHNOLOGIQUE

    OpenAIRE

    Masselot, Cyril

    2004-01-01

    The stake in the appropriation of the methods and the tools of creation, in structuralization and in mutualization of the information passes by innovative technological and methodological procedures of transfer. The example of a territorial intelligence monitoring Catalyse allows to question the current practices, and to imagine it of news.

  20. Tandem Ru-alkylidene-catalysed cross metathesis/hydrogenation: synthesis of lipophilic amino acids.

    Science.gov (United States)

    Wang, Zhen J; Spiccia, Nicolas D; Jackson, W Roy; Robinson, Andrea J

    2013-08-01

    Highly efficient synthesis of lipidic amino acids can be achieved via Ru-alkylidene-catalysed cross metathesis of long chain alkenes with commercially available allylglycine. The resultant unsaturated analogues can be then optionally hydrogenated under mild reaction conditions by using the spent metathesis catalyst. PMID:23733491

  1. p-Toluenesulphonic acid-promoted, I2-catalysed sulphenylation of pyrazolones with aryl sulphonyl hydrazides.

    Science.gov (United States)

    Zhao, Xia; Zhang, Lipeng; Li, Tianjiao; Liu, Guiyan; Wang, Haomeng; Lu, Kui

    2014-11-01

    Aryl pyrazolone thioethers were synthesized via the I2-catalysed cross-coupling of pyrazolones with aryl sulphonyl hydrazides in the presence of p-toluenesulphonic acid, which has been proposed to promote the reaction by facilitating the decomposition of sulphonyl hydrazides. PMID:25225659

  2. Selective synthesis of thiodiglycol dicarboxylic acid esters via -TsOH/C-catalysed direct esterification

    Indian Academy of Sciences (India)

    Dahong Jiang; Min Huang

    2012-09-01

    The esterification of thiodiglycol and long alkyl-chain carboxylic acids is reported. Reaction of thiodiglycol with carboxylic acid via -TsOH/C-catalysed direct esterification afforded thiodiglycol dicarboxylic acid esters in good yields and chemoselectivity. The use of immobilized -TsOH on activated carbon as catalyst is crucial for the transformation.

  3. Francis Farley presenting his novel "Catalysed Fusion" in the CERN Library

    CERN Multimedia

    Farley, Irina

    2013-01-01

    "Catalysed Fusion" is described by its author Francis Farley, 92, as a "true-to-life fantasy woven around particle physics" set in 1980s Geneva – "the city where nations meet and particles collide". Farley presented the book in the program "Literature in Focus" on Tuesday 16th April 2013.

  4. Lewis acidic metal catalysed organic transformations by designed multi-component structures and assemblies

    Indian Academy of Sciences (India)

    Afsar Ali; Amit P Singh; Rajeev Gupta

    2010-05-01

    This paper presents the recent developments in designing multi-component structures including metal-organic frameworks containing Lewis acidic metal ions. The emphasis has been given to understand the design elements adopted to synthesize such structures bearing Lewis acidic metal ion. Further, few important Lewis acidic metal catalysed organic transformation reactions have been discussed demonstrating the importance of such materials for practical purposes.

  5. Effects of growing integrated layer [GIL] formation on bonding behavior between hydroxyapatite ceramics and Ti-based bulk metallic glasses via hydrothermal hot-pressing

    International Nuclear Information System (INIS)

    The authors successfully formed a bond between bioactive hydroxyapatite (HA) ceramics and titanium (Ti)-based bulk metallic glasses (Ti40Zr10Cu36Pd14: BMG) through a growing integrated layer (GIL) to develop a new type of biomaterial. The GILs were formed on the BMG surfaces by hydrothermal-electrochemical (HE) techniques. The BMG substrates were treated in a 5 mol/L NaOH solution at 90 deg. C for 10-120 min while a constant electric current of 0.5 mA/cm2 was maintained between the electrodes. Then the BMG disks with the GIL and a powder mixture of CaHPO4.2H2O and Ca(OH)2 were simultaneously treated with an autoclave for hydrothermal hot-pressing (HHP) (150 oC, 40 MPa, 2 h). Direct bonding between the HA ceramics and the BMG disks could be achieved through the above processing method. Consequently, to the best of our knowledge, this is the first demonstration of the usefulness of a series of hydrothermal techniques (HE and HHP) for direct bonding of bulk ceramics and bulk metallic materials.

  6. Thermally activated solvent bonding of polymers

    OpenAIRE

    Ng, S H; Tjeung, R. T.; Z. F. Wang; Lu, A. C. W.; Rodriguez, I.; de Rooij, Nicolaas F.

    2010-01-01

    We present a thermally activated solvent bonding technique for the formation of embedded microstructures in polymer. It is based on the temperature dependent solubility of polymer in a liquid that is not a solvent at room temperature. With thermal activation, the liquid is transformed into a solvent of the polymer, creating a bonding capability through segmental or chain interdiffusion at the bonding interface. The technique has advantages over the more commonly used thermal bonding due to it...

  7. Recent Achievements in the Radiation-Catalysed Chlorination of Chlorinated Pentane Derivatives

    International Nuclear Information System (INIS)

    The radiation-catalysed chlorination of the so-called tetrachloro-cyclopentane, the product obtained from cyclopentadiene by addition of chlorine, has already been studied earlier by the authors with success. On maintaining an adequate dosage rate, no ring cleavage occurs, and, mainly for stereochemical reasons, octachloro-cyclopentene forms as an end product - similarly to conventional chlorination carried out at high temperature (400-500oC), but at substantially lower temperature (170oC) and without any resin formation. It is known that besides other end products, octachloro-cyclopentene forms also from perchlorinated pentane, under simultaneous cyclization. In their recent experiments presented here, the authors investigated how and to what extent the yield of octachloro-cyclopentene is affected by additional chlorination of pentane, previously chlorinated under cooling (at 10 to 30oC). The experiments were carried out with a Co60 radiation source of 330 c at a dosage rate of 8 x 103 to 8 x 104r/hr, in a heated reaction mixture, mixed with a chlorine stream for periods not exceeding 30 hr. It was found that also this type of chlorination and cyclization takes place at a temperature substantially lower than the conventional 500-600oC. According to the experiments, in this case it is advisable to raise the initial temperature of 170oC of the reaction gradually to 220oC with the progress of the reaction, in order to promote the cyclization reaction. It was found, namely, that first the paraffin chain was further chlorinated and later the perchlorinated pentane derivatives cyclize partly to octachloro-cyclopentene, under formation of other chlorinated alkane and alkene derivatives. This reaction mechanism was also supported by thermodynamical calculations. The end product contains three main components; its content of octachloro-cyclopentene ranges between 25 and 35%. The data required for the evaluation of the economy of the method will be available only on the

  8. 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.

  9. Solid acid catalysed formation of ethyl levulinate and ethyl glucopyranoside from mono- and disaccharides

    DEFF Research Database (Denmark)

    Shunmugavel, Saravanamurugan; Riisager, Anders

    2012-01-01

    Sulfonic acid functionalised SBA-15 (SO3H-SBA-15), sulfated zirconia and beta, Y, ZSM-5 and mordenite zeolite catalysts have been applied for the dehydration of sugars to ethyl levulinate and ethyl-D-glucopyranoside (EDGP) using ethanol as solvent and reactant. The SO3H-SBA-15 catalyst showed a...... high catalytic activity for the selective conversion of fructose to ethyl levulinate (57%) and glucose to EDGP (80%) at 140 °C, whereas the disaccharide sucrose yielded a significant amount of both products. The SO3H-SBA-15 catalysts were found to be highly active compared to the zeolites under...

  10. Analysis and protease-catalysed synthesis of sucrose alkanoate regioisomers

    DEFF Research Database (Denmark)

    Lie, Aleksander

    2014-01-01

    detected appearance of the sucrose laurate regioisomers largely corresponded to the apparent rates of formation, based on monoester concentration and regioisomeric distribution after 48 hours, and 2-O-lauroyl sucrose was among the first regioisomers to appear in all investigated reactions. The...

  11. Formation and Decomposition of Platinum–Thallium Bond, Kinetics and Mechanism. Structural Characterization of Some Metal Cyanides in the Solid State

    OpenAIRE

    Nagy, Péter

    2004-01-01

    The kinetic and mechanistic features of a new series ofplatinum-thallium cyano compounds containing a direct andunsupported by ligands metal-metal bond have been studied insolution, using standard mix–and–measurespectrophotometric technique and stopped–flow method.These reactions are interpreted as oxidative addition of the cspecies to the square planar Pt(CN)42-complex. Each of these processes was found to befirst-order in Pt(CN)42-, the corresponding TIIIIcomplex and a cyanide ion donating ...

  12. 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

  13. The kinetics of formation of single-stranded breaks and alkali-labile bonds in irradiated superhelical dna of PM 2 page

    International Nuclear Information System (INIS)

    The methods of neutral and alkaline agarose gel electrophoresis were used to study the dose-dependence of the concentration of different DNA species formed under the effect of X-irradiation of solutions of superhelical DNA of PM2 phage. The experimental results are described by a model in which a considerable role is attributed to conjugated lesions in both DNA strands (single-stranded breaks and alkali--labile-bonds). A study was made of the influence of metronidazole and TAN on radiation-induced changes in DNA

  14. Covalent Bond Formation of Uranium Ions in a LiCl-KCl Eutectic Melt at 450 .deg. C: Spectroscopic Evidence from Their UV-VIS Spectra

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Young Hwan; Bae, Sang Eun; Oh, Seung Yong; Kim, Jong Yun; Song, Kyu Seok; Yeon, Jei Won [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    Molten salt based electrochemical processes, so called pyroprocessing, have been proposed as a new option for the advanced spent nuclear fuel cycle. One of the important steps in the pyroprocessing of the spent nuclear fuel is the electrorefining of uranium in molten LiCl based media. The knowledge on the electronic states of uranium ions in molten salt media is essential for understanding their optical, electrochemical properties. Electronic absorption spectra may provide detailed information on the chemical state of the ions. Several studies have been reported for the past decades on the electronic absorption spectra of uranium ion species in high temperature molten salt media. However, no attempts have been made to interpret the spectra with respect to the electronic state and chemical bonding point of view. Here, report the results of insitu measurement and interpretation of the electronic spectra of the U(III) and U(IV) ion species in a LiCl- KCl eutectic melt at in terms of chemical bonding

  15. Pi Bond Orders and Bond Lengths

    Science.gov (United States)

    Herndon, William C.; Parkanyi, Cyril

    1976-01-01

    Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

  16. LAMMPS Framework for Dynamic Bonding and an Application Modeling DNA

    DEFF Research Database (Denmark)

    Svaneborg, Carsten

    2012-01-01

    and bond types. When breaking bonds, all angular and dihedral interactions involving broken bonds are removed. The framework allows chemical reactions to be modeled, and use it to simulate a simplistic, coarse-grained DNA model. The resulting DNA dynamics illustrates the power of the present framework.......We have extended the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to support directional bonds and dynamic bonding. The framework supports stochastic formation of new bonds, breakage of existing bonds, and conversion between bond types. Bond formation can be controlled to...... limit the maximal functionality of a bead with respect to various bond types. Concomitant with the bond dynamics, angular and dihedral interactions are dynamically introduced between newly connected triplets and quartets of beads, where the interaction type is determined from the local pattern of bead...

  17. Mimicry of the regulatory role of urokinase in lamellipodia formation by introduction of a non-native interdomain disulfide bond in its receptor

    DEFF Research Database (Denmark)

    Gårdsvoll, Henrik; Kjærgaard, Magnus; Jacobsen, Benedikte; Kriegbaum, Mette Camilla; Huang, Mingdong; Ploug, Michael

    2011-01-01

    adhesive function of uPAR is allosterically regulated via a "tightening" of its three-domain structure elicited by uPA binding. To challenge this proposition, we redesigned the uPAR structure to limit its inherent conformational flexibility by covalently tethering domains DI and DIII via a non......-natural interdomain disulfide bond (uPAR(H47C-N259C)). The corresponding soluble receptor has 1) a smaller hydrodynamic volume, 2) a higher content of secondary structure, and 3) unaltered binding kinetics towards uPA. Most importantly, the purified uPAR(H47C-N259C) also displays a gain in affinity for the...

  18. Access to novel fluorovinylidene ligands via exploitation of outer-sphere electrophilic fluorination: new insights into C-F bond formation and activation.

    Science.gov (United States)

    Milner, Lucy M; Hall, Lewis M; Pridmore, Natalie E; Skeats, Matthew K; Whitwood, Adrian C; Lynam, Jason M; Slattery, John M

    2016-01-19

    Metal vinylidene complexes are widely encountered, or postulated, as intermediates in a range of important metal-mediated transformations of alkynes. However, fluorovinylidene complexes have rarely been described and their reactivity is largely unexplored. By making use of the novel outer-sphere electrophilic fluorination (OSEF) strategy we have developed a rapid, robust and convenient method for the preparation of fluorovinylidene and trifluoromethylvinylidene ruthenium complexes from non-fluorinated alkynes. Spectroscopic investigations (NMR and UV/Vis), coupled with TD-DFT studies, show that fluorine incorporation results in significant changes to the electronic structure of the vinylidene ligand. The reactivity of fluorovinylidene complexes shows many similarities to non-fluorinated analogues, but also some interesting differences, including a propensity to undergo unexpected C-F bond cleavage reactions. Heating fluorovinylidene complex [Ru(η(5)-C5H5)(PPh3)2(C[double bond, length as m-dash]C{F}R)][BF4] led to C-H activation of a PPh3 ligand to form an orthometallated fluorovinylphosphonium ligand. Reaction with pyridine led to nucleophilic attack at the metal-bound carbon atom of the vinylidene to form a vinyl pyridinium species, which undergoes both C-H and C-F activation to give a novel pyridylidene complex. Addition of water, in the presence of chloride, leads to anti-Markovnikov hydration of a fluorovinylidene complex to form an α-fluoroaldehyde, which slowly rearranges to its acyl fluoride isomer. Therefore, fluorovinylidenes ligands may be viewed as synthetic equivalents of 1-fluoroalkynes providing access to reactivity not possible by other routes. PMID:26701305

  19. 3D micro-CT analysis of void formations and push-out bonding strength of resin cements used for fiber post cementation

    Science.gov (United States)

    2016-01-01

    PURPOSE To investigate the void parameters within the resin cements used for fiber post cementation by micro-CT (µCT) and regional push-out bonding strength. MATERIALS AND METHODS Twenty-one, single and round shaped roots were enlarged with a low-speed drill following by endodontic treatment. The roots were divided into three groups (n=7) and fiber posts were cemented with Maxcem Elite, Multilink N and Superbond C&B resin cements. Specimens were scanned using µCT scanner at resolution of 13.7 µm. The number, area, and volume of voids between dentin and post were evaluated. A method of analysis based on the post segmentation was used, and coronal, middle and apical thirds considered separately. After the µCT analysis, roots were embedded in epoxy resin and sectioned into 2 mm thick slices (63 sections in total). Push-out testing was performed with universal testing device at 0.5 mm/min cross-head speed. Data were analyzed with Kruskal–Wallis and Mann–Whitney U tests (α=.05). RESULTS Overall, significant differences between the resin cements and the post level were observed in the void number, area, and volume (P.05). CONCLUSION µCT proved to be a powerful non-destructive 3D analysis tool for visualizing the void parameters. Multilink N had the lowest void parameters. When efficiency of all cements was evaluated, direct relationship between the post region and push-out bonding strength was not observed. PMID:27141253

  20. Molecular Orbital and Density Functional Study of the Formation, Charge Transfer, Bonding and the Conformational Isomerism of the Boron Trifluoride (BF3 and Ammonia (NH3 Donor-Acceptor Complex

    Directory of Open Access Journals (Sweden)

    Dulal C. Ghosh

    2004-09-01

    Full Text Available The formation of the F3B–NH3 supermolecule by chemical interaction of its fragment parts, BF3 and NH3, and the dynamics of internal rotation about the ‘B–N’ bond have been studied in terms of parameters provided by the molecular orbital and density functional theories. It is found that the pairs of frontier orbitals of the interacting fragments have matching symmetry and are involved in the charge transfer interaction. The donation process stems from the HOMO of the donor into the LUMO of the acceptor and simultaneously, back donation stems from the HOMO of acceptor into the LUMO of the donor. The density functional computation of chemical activation in the donor and acceptor fragments, associated with the physical process of structural reorganization just prior to the event of chemical reaction, indicates that BF3 becomes more acidic and NH3 becomes more basic, compared to their separate equilibrium states. Theoretically it is observed that the chemical reaction event of the formation of the supermolecule from its fragment parts is in accordance with the chemical potential equalization principle of the density functional theory and the electronegativity equalization principle of Sanderson. The energetics of the chemical reaction, the magnitude of the net charge transfer and the energy of the newly formed bond are quite consistent, both internally and with the principle of maximum hardness, PMH. The dynamics of the internal rotation of one part with respect to the other part of the supermolecule about the ‘B–N’ bond mimics the pattern of the conformational isomerism of the isostructural ethane molecule. It is also observed that the dynamics and evolution of molecular conformations as a function of dihedral angles is also in accordance with the principle of maximum hardness, PMH. Quite consistent with spectroscopic predictions, the height of the molecule

  1. Enzyme catalysed production of sialylated human milk oligosaccharides and galactooligosaccharides by Trypanosoma cruzi trans-sialidase

    DEFF Research Database (Denmark)

    Holck, Jesper; Larsen, Dorte Møller; Michalak, Malwina;

    2014-01-01

    Bifidobacterium strains in single culture fermentations. The trans-sialidase also catalysed the transfer of sialic acid from CGMP to galacto-oligosaccharides (GOS) and to the human milk oligosaccharide (HMO) backbone lacto-N-tetraose (LNT) to produce 3′-sialyl-GOS, including doubly sialylated GOS products, and 3......′-sialyl-LNT, respectively. This work thus provides proof of the concept of producing 3′-sialyllactose and potentially other sialylated HMOs as well as sialylated GOS enzymatically by trans-sialidase activity, while at the same time providing valorisation of CGMP, a co-processing product from cheese....../acceptor ratio for the trans-sialidase catalysed 3′-sialyllactose production was found to be 1:4. Quantitative amounts of 3′-sialyllactose were produced from CGMP and lactose at a yield of 40mg/g CGMP. The 3′-sialyllactose obtained exerted a stimulatory effect on selected probiotic strains, including different...

  2. Alkene Cleavage Catalysed by Heme and Nonheme Enzymes: Reaction Mechanisms and Biocatalytic Applications

    Directory of Open Access Journals (Sweden)

    Francesco G. Mutti

    2012-01-01

    Full Text Available The oxidative cleavage of alkenes is classically performed by chemical methods, although they display several drawbacks. Ozonolysis requires harsh conditions (−78°C, for a safe process and reducing reagents in a molar amount, whereas the use of poisonous heavy metals such as Cr, Os, or Ru as catalysts is additionally plagued by low yield and selectivity. Conversely, heme and nonheme enzymes can catalyse the oxidative alkene cleavage at ambient temperature and atmospheric pressure in an aqueous buffer, showing excellent chemo- and regioselectivities in certain cases. This paper focuses on the alkene cleavage catalysed by iron cofactor-dependent enzymes encompassing the reaction mechanisms (in case where it is known and the application of these enzymes in biocatalysis.

  3. Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso–ene mechanism

    Science.gov (United States)

    Porter, David; Poon, Belinda M-L

    2015-01-01

    Summary Iron(II) complexes of the tetradentate amines tris(2-pyridylmethyl)amine (TPA) and N,N′-bis(2-pyridylmethyl)-N,N′-dimethylethane-1,2-diamine (BPMEN) are established catalysts of C–O bond formation, oxidising hydrocarbon substrates via hydroxylation, epoxidation and dihydroxylation pathways. Herein we report the capacity of these catalysts to promote C–N bond formation, via allylic amination of alkenes. The combination of N-Boc-hydroxylamine with either FeTPA (1 mol %) or FeBPMEN (10 mol %) converts cyclohexene to the allylic hydroxylamine (tert-butyl cyclohex-2-en-1-yl(hydroxy)carbamate) in moderate yields. Spectroscopic studies and trapping experiments suggest the reaction proceeds via a nitroso–ene mechanism, with involvement of a free N-Boc-nitroso intermediate. Asymmetric induction is not observed using the chiral tetramine ligand (+)-(2R,2′R)-1,1′-bis(2-pyridylmethyl)-2,2′-bipyrrolidine ((R,R′)-PDP). PMID:26734101

  4. Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso–ene mechanism

    Directory of Open Access Journals (Sweden)

    David Porter

    2015-12-01

    Full Text Available Iron(II complexes of the tetradentate amines tris(2-pyridylmethylamine (TPA and N,N′-bis(2-pyridylmethyl-N,N′-dimethylethane-1,2-diamine (BPMEN are established catalysts of C–O bond formation, oxidising hydrocarbon substrates via hydroxylation, epoxidation and dihydroxylation pathways. Herein we report the capacity of these catalysts to promote C–N bond formation, via allylic amination of alkenes. The combination of N-Boc-hydroxylamine with either FeTPA (1 mol % or FeBPMEN (10 mol % converts cyclohexene to the allylic hydroxylamine (tert-butyl cyclohex-2-en-1-yl(hydroxycarbamate in moderate yields. Spectroscopic studies and trapping experiments suggest the reaction proceeds via a nitroso–ene mechanism, with involvement of a free N-Boc-nitroso intermediate. Asymmetric induction is not observed using the chiral tetramine ligand (+-(2R,2′R-1,1′-bis(2-pyridylmethyl-2,2′-bipyrrolidine ((R,R′-PDP.

  5. Specific collapse followed by slow hydrogen-bond formation of β-sheet in the folding of single-chain monellin

    Science.gov (United States)

    Kimura, Tetsunari; Uzawa, Takanori; Ishimori, Koichiro; Morishima, Isao; Takahashi, Satoshi; Konno, Takashi; Akiyama, Shuji; Fujisawa, Tetsuro

    2005-01-01

    Characterization of the conformational landscapes for proteins with different secondary structures is important in elucidating the mechanism of protein folding. The folding trajectory of single-chain monellin composed of a five-stranded β-sheet and a helix was investigated by using a pH-jump from the alkaline unfolded to native state. The kinetic changes in the secondary structures and in the overall size and shape were measured by circular dichroism spectroscopy and small-angle x-ray scattering, respectively. The formation of the tertiary structure was monitored by intrinsic and extrinsic fluorescence. A significant collapse was observed within 300 μs after the pH-jump, leading to the intermediate with a small amount of secondary and tertiary structures but with an overall oblate shape. Subsequently, the stepwise formation of secondary and tertiary structures was detected. The current observation was consistent with the theoretical prediction that a more significant collapse precedes the formation of secondary structures in the folding of β-sheet proteins than that of helical proteins [Shea, J. E., Onuchic, J. N. & Brooks, C. L., III (2002) Proc. Natl. Acad. Sci. USA 99, 16064–16068]. Furthermore, it was implied that the initial collapse was promoted by the formation of some specific structural elements, such as tight turns, to form the oblate shape. PMID:15710881

  6. Specific collapse followed by slow hydrogen-bond formation of beta-sheet in the folding of single-chain monellin.

    Science.gov (United States)

    Kimura, Tetsunari; Uzawa, Takanori; Ishimori, Koichiro; Morishima, Isao; Takahashi, Satoshi; Konno, Takashi; Akiyama, Shuji; Fujisawa, Tetsuro

    2005-02-22

    Characterization of the conformational landscapes for proteins with different secondary structures is important in elucidating the mechanism of protein folding. The folding trajectory of single-chain monellin composed of a five-stranded beta-sheet and a helix was investigated by using a pH-jump from the alkaline unfolded to native state. The kinetic changes in the secondary structures and in the overall size and shape were measured by circular dichroism spectroscopy and small-angle x-ray scattering, respectively. The formation of the tertiary structure was monitored by intrinsic and extrinsic fluorescence. A significant collapse was observed within 300 micros after the pH-jump, leading to the intermediate with a small amount of secondary and tertiary structures but with an overall oblate shape. Subsequently, the stepwise formation of secondary and tertiary structures was detected. The current observation was consistent with the theoretical prediction that a more significant collapse precedes the formation of secondary structures in the folding of beta-sheet proteins than that of helical proteins [Shea, J. E., Onuchic, J. N. & Brooks, C. L., III (2002) Proc. Natl. Acad. Sci. USA 99, 16064-16068]. Furthermore, it was implied that the initial collapse was promoted by the formation of some specific structural elements, such as tight turns, to form the oblate shape. PMID:15710881

  7. The influence of non-steroidal anti-inflammatory and antithyroid agents on myeloperoxidase-catalysed activities of human leucocytes

    International Nuclear Information System (INIS)

    Viable leucocytes obtained fresh from normal human subjects were shown to be able to catalyse the in vitro iodination of bovine serum albumin (BSA) in a H2O2-generating system. The rate and degree of iodination were greatly improved by sonication of the cells. A balanced salt solution was a more favourable medium than phosphate buffer for the myeloperoxidase (MPO)-catalysed iodination of whole cells and sonicated cells. Reactions known to be catalysed by other peroxidases (e.g. thyroid peroxidase (TPO) and lactoperoxidase) such as inorganic iodide exchange for organic iodine in di-iodotyrosine (DIT) and the de-iodination of thyroxine (T4), were also catalysed by the sonicated leucocyte suspension in the system used. The non-steroidal anti-inflammatory drugs indomethacin, flufenamic acid and naproxen were far less effective inhibitors of MPO-catalysed BSA iodination of sonicated leucocytes at concentrations expected in blood with therapeutic dose levels than was observed earlier with TPO-catalysed in vitro iodination of BSA. The antithyroid drug methylmercapto-imidazole (MMI) inhibited in vitro MPO-catalysed 131I delabelling of 131I-DIT at all concentrations between 10-7 and 10-2M, whereas 131I-T4 delabelling was markedly stimulated at the same drug concentrations. On the other hand, 125I incorporation into 131I-DIT was not affected by increased concentrations of MMI up to 10-5M. At higher drug concentrations the drug caused inhibition of MPO-catalysed exchange of inorganic iodide for organic iodine in DIT

  8. Metal-catalysed organic transformations in water: From bromination to polymerisation

    Indian Academy of Sciences (India)

    Manish Bhattacharjee; Braja N Patra

    2006-11-01

    Reaction of ,-unsaturated aromatic carboxylic acids with KBr and H2O2 in the presence of Na2MoO4$\\cdot$H2O in aqueous medium affords -bromo alkenes in high yields. Metallocene dichlorides, Cp2MCl2 (M = Ti, Zr, or V) catalyse polymerisation of olefins in aqueous medium to afford high molecular weight polymers with low molecular weight distribution.

  9. Gold film-catalysed benzannulation by Microwave-Assisted, Continuous Flow Organic Synthesis (MACOS

    Directory of Open Access Journals (Sweden)

    Gjergji Shore

    2009-07-01

    Full Text Available Methodology has been developed for laying down a thin gold-on-silver film on the inner surface of glass capillaries for the purpose of catalysing benzannulation reactions. The cycloaddition precursors are flowed through these capillaries while the metal film is being heated to high temperatures using microwave irradiation. The transformation can be optimized rapidly, tolerates a wide number of functional groups, is highly regioselective, and proceeds in good to excellent conversion.

  10. Evaluating Pt-Ru/C mixtures as ethanol electro-oxidation catalysers

    OpenAIRE

    Bibian Alonso Hoyos; Javier González; Carlos Sánchez

    2010-01-01

    This work studies ethanol electro-catalytic oxidation by cyclic voltametry in sulphuric acid solutions at different temperatures and concetrations, using platinum.rutenium mixtures supported in vitreous carbon as catalysers. The results indicate that ethanol oxidation in theses electrodes is irreversible, has slow kinetics, is controlled by charge transfer and is brought about by a bi-functional reaction mechanism, this being ethanol adsorption on platinum atoms and additional oxidation of sp...

  11. Total Synthesis of (±)-Paroxetine by Diastereoconvergent Cobalt-Catalysed Arylation

    OpenAIRE

    Despiau, Carole F; Dominey, Andrew P; Harrowven, David C.; Linclau, Bruno

    2014-01-01

    A total synthesis of paroxetine is reported, with a diastereoselective and diastereoconvergent cobalt-catalysed sp3–sp2 coupling reaction involving a 3-substituted 4-bromo-N-Boc-piperidine (Boc = tert-butoxycarbonyl) substrate as a key step. A 9:1 diastereoselectivity was obtained, while a control experiment involving a conformationally locked 3-substituted 4-bromo-tert-butyl cyclohexane ring proceeded with essentially complete stereoselectivity.

  12. The role of pellet thermal stability in reactor design for heterogeneously catalysed chemical reactions

    OpenAIRE

    Wijngaarden, R.J.; Westerterp, K.R.

    1992-01-01

    For exothermic fluid-phase reactions, a reactor which is cooled at the wall can exhibit multiplicity or parametric sensitivity. Moreover, for heterogeneously catalysed exothermic fluid-phase reactions, each of the catalytically active pellets in the reactor can exhibit multiplicity. Both forms of multiplicity can lead to thermal instability and as such have to be taken into account in reactor design. Here the effect of both instabilities is quantified. To this end, simple first-order kinetics...

  13. Intramolecular Hydroalkoxylation of Non-Activated C=C Bonds Catalysed by Zeolites: An Experimental and Theoretical Study

    Czech Academy of Sciences Publication Activity Database

    Pérez-Mayoral, E.; Matos, I.; Nachtigall, P.; Položij, M.; Fonseca, I.; Vitvarová, Dana; Čejka, Jiří

    2013-01-01

    Roč. 6, č. 6 (2013), s. 1021-1030. ISSN 1864-5631 R&D Projects: GA ČR GBP106/12/G015 Institutional support: RVO:61388955 Keywords : cyclization * density functional calculations * heterogeneous catalysis Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 7.117, year: 2013

  14. Enzyme-catalysed [4+2] cycloaddition is a key step in the biosynthesis of spinosyn A.

    Science.gov (United States)

    Kim, Hak Joong; Ruszczycky, Mark W; Choi, Sei-hyun; Liu, Yung-nan; Liu, Hung-wen

    2011-05-01

    The Diels-Alder reaction is a [4+2] cycloaddition reaction in which a cyclohexene ring is formed between a 1,3-diene and an electron-deficient alkene via a single pericyclic transition state. This reaction has been proposed as a key transformation in the biosynthesis of many cyclohexene-containing secondary metabolites. However, only four purified enzymes have thus far been implicated in biotransformations that are consistent with a Diels-Alder reaction, namely solanapyrone synthase, LovB, macrophomate synthase, and riboflavin synthase. Although the stereochemical outcomes of these reactions indicate that the product formation could be enzyme-guided in each case, these enzymes typically demonstrate more than one catalytic activity, leaving their specific influence on the cycloaddition step uncertain. In our studies of the biosynthesis of spinosyn A, a tetracyclic polyketide-derived insecticide from Saccharopolyspora spinosa, we identified a cyclase, SpnF, that catalyses a transannular [4+2] cycloaddition to form the cyclohexene ring in spinosyn A. Kinetic analysis demonstrates that SpnF specifically accelerates the ring formation reaction with an estimated 500-fold rate enhancement. A second enzyme, SpnL, was also identified as responsible for the final cross-bridging step that completes the tetracyclic core of spinosyn A in a manner consistent with a Rauhut-Currier reaction. This work is significant because SpnF represents the first example characterized in vitro of a stand-alone enzyme solely committed to the catalysis of a [4+2] cycloaddition reaction. In addition, the mode of formation of the complex perhydro-as-indacene moiety in spinosyn A is now fully established. PMID:21544146

  15. The reaction mechanism of the enantioselective Tsuji allylation: inner-sphere and outer-sphere pathways, internal rearrangements, and asymmetric C–C bond formation

    OpenAIRE

    Keith, John A.; Behenna, Douglas C.; Sherden, Nathaniel; Mohr, Justin T.; Ma, Sandy; Marinescu, Smaranda C.; Nielsen, Robert J.; Oxgaard, Jonas; Stoltz, Brian M.; Goddard, William A.

    2012-01-01

    We use first principles quantum mechanics (density functional theory) to report a detailed reaction mechanism of the asymmetric Tsuji allylation involving prochiral nucleophiles and nonprochiral allyl fragments, which is consistent with experimental findings. The observed enantioselectivity is best explained with an inner-sphere mechanism involving the formation of a 5-coordinate Pd species that undergoes a ligand rearrangement, which is selective with regard to the prochiral faces of the int...

  16. 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

  17. Formation and High Reactivity of the anti-Dioxo Form of High-Spin μ-Oxodioxodiiron(IV) as the Active Species That Cleaves Strong C-H Bonds.

    Science.gov (United States)

    Kodera, Masahito; Ishiga, Shin; Tsuji, Tomokazu; Sakurai, Katsutoshi; Hitomi, Yutaka; Shiota, Yoshihito; Sajith, P K; Yoshizawa, Kazunari; Mieda, Kaoru; Ogura, Takashi

    2016-04-18

    Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is toluenebond cleavage of ethylbenzene than the most reactive diiron system reported so far. The KIE for the reaction with toluene/[D8 ]toluene is 95 at -30 °C, which the largest in diiron systems reported so far. The present diiron complex efficiently catalyzes the oxidation of various alkanes with H2 O2 . PMID:26970337

  18. Paint-Bonding Improvement for 2219 Aluminum Alloy

    Science.gov (United States)

    Daech, Alfred F.; Cibula, Audrey Y.

    1987-01-01

    Bonding of adhesives and primers to 2219 aluminum alloy improved by delaying rinse step in surface-treatment process. Delaying rinse allows formation of rougher surface for stronger bonding and greater oxide buildup.

  19. 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

  20. tri-n-butyltin hydride-mediated radical reaction of a 2-iodobenzamide: formation of an unexpected carbon-tin bond

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Marcelo T.; Alves, Rosemeire B.; Cesar, Amary [Universidade Federal de Minas Gerais, Belo Horizonte, MG (Brazil). Dept. de Quimica; Prado, Maria Auxiliadora F.; Alves, Ricardo J.; Queiroga, Carla G. [Federal de Minas Gerais, Belo Horizonte, MG (Brazil). Faculdade de Farmacia. Dept. de Produtos Farmaceuticos]. E-mail: pradora@farmacia.ufmg.br; Santos, Leonardo S. [Universidad de Talca (Chile). Inst. de Quimica de Recursos Naturales; Eberlin, Marcos N. [Universidade Estadual de Campinas, SP (Brazil). Inst. de Quimica

    2007-03-15

    The tri-n-butyltin hydride-mediated reaction of methyl 2,3-di-O-benzyl-4-O-trans-cinnamyl- 6-deoxy-6-(2-iodobenzoylamino)-{alpha}-D-galactopyranoside afforded an unexpected aryltributyltin compound. The structure of this new tetraorganotin(IV) product has been elucidated by {sup 1}H, {sup 13}C NMR spectroscopy, COSY and HMQC experiments and electrospray ionization mass spectrometry (ESI-MS). The formation of this new compound via a radical coupling reaction and a radical addition-elimination process is discussed. (author)

  1. Novel Elongated Phosphoranes by Heck-Reaction and Pd(0)-Catalysed Alkynylation and their Use in C-7 Group Functionalisation in Estrones

    OpenAIRE

    Thiemann, Thies; Umeno, Kuniharu; Inohae, Eiko; Mataka, Shuntaro

    2000-01-01

    Halobenzoylmethylidenephosphoranes 3 are reacted under C-C bond formation to give a number of novel elongated phosphoranes 5 and 6. The C-C bond formation could be achieved both under Heck conditions and by metal-catalyzed ethynylation reaction. The products, desactivated phosphoranes, can be reacted in Wittig-olefinations with aldehydes. Exemplary use of the phosphoranes is shown in the C-7 chain functionalisation in synthetic estrones, which may be valuable precursors for radioligands in ea...

  2. FORMATION OF C-I COVALENT BOND BETWEEN THE SINGLE-WALL CARBON NANOTUBES AND SODIUM IODIDE%单壁碳纳米管与碘化钠形成C-I共价键

    Institute of Scientific and Technical Information of China (English)

    黄洁华; 林治卿; 刘丽华; 刘焕亮; 胡传禄; 程文文; 袭著革

    2011-01-01

    目的 探讨单壁碳纳米管与碘化钠反应后C-I共价键的生成及其表征,为单壁碳纳米管放射性碘标记及观察其在生物体内分布提供实验参考数据.方法 采用1odogen方法制备碘化的单壁碳纳米管(I-SWCNTs),然后用透射电子显微镜(TEM)及X射线光电子能谱仪(XPS)对碳碘结合及C-I共价键的形成进行表征.结果 TEM成像和成分分析显示,与未经处理的SWCNTs 对比,处理后的产物其管壁不再光滑,有缺口,其上结合有碘.XPS检测发现,碘与SWCNTs形成C-I共价键,处理后产物的碘电子结合能与具有C-I共价键的参考物硝基碘苯基本一致,而与具有离子性质的NaI的结合能不同.结论 用Iodogen法能使SWCNTs与NaI结合生成C-I共价键.%Objective To explore the formation and characterization of C-I covalent bond between the singlewall carbon nanotubes (SWCNTs) and NaI in order to provide experimental reference data for radioiodination of SWCNTs and oberving its biodistribution. Methods IMogen method was used to synthesize iodinated SWCNTs (I-SWCNTs) in which iodine was covalently bound to SWCNTs. The formation of C-I bond was proved by transmission electron microscope(TEM) as well as X-ray photoelectron spectroscopy (XPS) . Results The image and component analyses TEM showed that the wall of the tubes of I-SWCNTs became rough, with gaps, and bound iodine, as compared to that of the tmtreated products. XPS spectra showed that the binding energy of iodine of I-SWCNTs was analogous to that of nitroiodobenzene and different from that of ionic NaI. Conclusion The C-I covalent bond between the single-wall carbon nanotubes and NaI could be formed by the Iodogen method.

  3. Intramolecular versus intermolecular hydrogen bonding in solution

    OpenAIRE

    Vliegenthart, J. F. G.; Kroon, Jan; Kroon-Batenburg, L.M.J.; Leeflang, B.R.

    1994-01-01

    The balance between intra- and intermolecular hydrogen bonding is studied for a solution of methyl beta-cellobioside in water and dimethylsulfoxide by 1H NMR and molecular dynamics simulations. In water O(3) predominantly interacts with water molecules, whereas in dimethylsulfoxide it is intramolecularly hydrogen bonded to O(5Œ). The temperature coefficient of the chemical shift of the hydroxy groups appears to be a reliable indicator of intermolecular hydrogen-bond formation, whereas the ex...

  4. Sensor/ROIC Integration using Oxide Bonding

    International Nuclear Information System (INIS)

    We explore the Ziptronix Direct Bond Interconnect (DBI) technology (2) for the integration of sensors and readout integrated circuits (ROICs) for high energy physics. The technology utilizes an oxide bond to form a robust mechanical connection between layers which serves to assist with the formation of metallic interlayer connections. We report on testing results of sample sensors bonded to ROICs and thinned to 100 (micro)m

  5. Sensor/ROIC Integration using Oxide Bonding

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Zhenyu; /Fermilab

    2009-02-01

    We explore the Ziptronix Direct Bond Interconnect (DBI) technology [2] for the integration of sensors and readout integrated circuits (ROICs) for high energy physics. The technology utilizes an oxide bond to form a robust mechanical connection between layers which serves to assist with the formation of metallic interlayer connections. We report on testing results of sample sensors bonded to ROICs and thinned to 100 {micro}m.

  6. Formation, Characterization, and O-O Bond Activation of a Peroxomanganese(III) Complex Supported by a Cross-Clamped Cyclam Ligand.

    Science.gov (United States)

    Colmer, Hannah E; Howcroft, Anthony W; Jackson, Timothy A

    2016-03-01

    Although there have been reports describing the nucleophilic reactivity of peroxomanganese(III) intermediates, as well as their conversion to high-valent oxo-bridged dimers, it remains a challenge to activate peroxomanganese(III) species for conversion to high-valent, mononuclear manganese complexes. Herein, we report the generation, characterization, and activation of a peroxomanganese(III) adduct supported by the cross-clamped, macrocyclic Me2EBC ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). This ligand is known to support high-valent, mononuclear Mn(IV) species with well-defined spectroscopic properties, which provides an opportunity to identify mononuclear Mn(IV) products from O-O bond activation of the corresponding Mn(III)-peroxo adduct. The peroxomanganese(III) intermediate, [Mn(III)(O2)(Me2EBC)](+), was prepared at low-temperature by the addition of KO2 to [Mn(II)(Cl)2(Me2EBC)] in CH2Cl2, and this complex was characterized by electronic absorption, electron paramagnetic resonance (EPR), and Mn K-edge X-ray absorption (XAS) spectroscopies. The electronic structure of the [Mn(III)(O2)(Me2EBC)](+) intermediate was examined by density functional theory (DFT) and time-dependent (TD) DFT calculations. Detailed spectroscopic investigations of the decay products of [Mn(III)(O2)(Me2EBC)](+) revealed the presence of mononuclear Mn(III)-hydroxo species or a mixture of mononuclear Mn(IV) and Mn(III)-hydroxo species. The nature of the observed decay products depended on the amount of KO2 used to generate [Mn(III)(O2)(Me2EBC)](+). The Mn(III)-hydroxo product was characterized by Mn K-edge XAS, and shifts in the pre-edge transition energies and intensities relative to [Mn(III)(O2)(Me2EBC)](+) provide a marker for differences in covalency between peroxo and nonperoxo ligands. To the best of our knowledge, this work represents the first observation of a mononuclear Mn(IV) center upon decay of a nonporphyrinoid Mn(III)-peroxo center. PMID:26908013

  7. Formation versus Hydrolysis of the Peptide Bond from a Quantum-mechanical Viewpoint: The Role of Mineral Surfaces and Implications for the Origin of Life

    Directory of Open Access Journals (Sweden)

    2009-02-01

    Full Text Available The condensation (polymerization by water elimination of molecular building blocks to yield the first active biopolymers (e.g. of amino acids to form peptides during primitive Earth is an intriguing question that nowadays still remains open since these processes are thermodynamically disfavoured in highly dilute water solutions. In the present contribution, formation and hydrolysis of glycine oligopeptides occurring on a cluster model of sanidine feldspar (001 surface have been simulated by quantum mechanical methods. Results indicate that the catalytic interplay between Lewis and Brønsted sites both present at the sanidine surface, in cooperation with the London forces acting between the biomolecules and the inorganic surface, plays a crucial role to: i favour the condensation of glycine to yield oligopeptides as reaction products; ii inhibit the hydrolysis of the newly formed oligopeptides. Both facts suggest that mineral surfaces may have helped in catalyzing, stabilizing and protecting from hydration the oligopeptides formed in the prebiotic era.

  8. Cold pressure welding - the mechanisms governing bonding

    DEFF Research Database (Denmark)

    Bay, Niels

    1979-01-01

    Investigations of the bonding surface in scanning electron microscope after fracture confirm the mechanisms of bond formation in cold pressure welding to be: fracture of work-hardened surface layer, surface expansion increasing the area of virgin surface, extrusion of virgin material through cracks...

  9. Modélisation et caractérisation des joints collés à hautes vitesses de déformation Modeling and characterization of bonded joints at high strain rates

    Directory of Open Access Journals (Sweden)

    Bourel B.

    2013-11-01

    Full Text Available Ce papier traite de la modélisation de joints collés pour les structures soumises à des sollicitations de type crash. Cette nouvelle modélisation basée sur un élément cohésif tient compte du comportement viscoplastique, de l'endommagement ainsi que de la rupture de l'adhésive. Sensible à la vitesse de déformation l'identification du critère de rupture nécessite une base expérimentale allant jusqu'à de très hautes vitesses de déformations. Un nouveau dispositif d'essais a donc été mis en place sur les barres de Hopkinson afin de solliciter des assemblages à haute vitesse et sous différents angles de chargement. This paper deals with the modeling of bonded joints for structures subjected to dynamic crash loading. This new model based on a cohesive element takes into account the viscoelastic behavior, the damage and the failure of the adhesive. Due to the strain rate sensitivity, the identification of failure criterion requires experimental tests, up to very high strain rates. A new testing device has then been set up on the Hopkinson bar in order to load the assemblies with high strain rates and with different angles.

  10. Diagraphies de cimentation : vers une analyse de la qualité du contact ciment-formation Cement Logging: Toward an Analysis of the Quality of Cement-Formation Bonding

    Directory of Open Access Journals (Sweden)

    Isambourg P.

    2006-11-01

    Full Text Available Les compagnies pétrolières ont un réel besoin d'évaluer correctement les cimentations de leurs puits : l'étanchéité entre les différentes zones est-elle assurée? Pour ce faire, les outils soniques et ultra-soniques ont été mis au point. Jusqu'à présent, la qualité du contactcasing-ciment était analysée quantitativement et celle du contactciment-formation était analysée qualitativement par les spécialistes (outil VDL. Le progrès le plus important que l'on pouvait apporter dans les logsde cimentation était de détecter les défauts à l'interface ciment-formation. C'est ce que nous avons fait dans le cadre d'un projet financé par l'ARTEP (Association de Recherche sur les Techniques d'Exploitation du Pétrole comprenant Total, Gaz de France GDF, Institut Français du Pétrole (IFP, et Elf Aquitaine Production (EAP. Les expériences laboratoires effectuées au Service Analyse FLuides de Boussens ont été conçues en injectant du ciment entre un casing et une formation-simulée avec présence, ou non, de boue d'épaisseur variable. Des formations rapides ou lentes, ainsi que des ciments, rapides ou lents, ont été utilisés. Les échos ultrasoniques, obtenus à l'aide d'une sonde CET en céramique, ont été enregistrés et analysés. La théorie, comme les expériences, ont montré que les échos ultrasoniques sont modifiés en présence de boue et/ou de gaz. Les relations entre la forme de l'onde ultrasonique et la présence de boue et de gaz entre le ciment et la formation ont été établies. Une procédure de traitement est proposée avec ses limites. Oil companies have a real need to make a correct assessment of cementing jobs in their wells. Is the seal ensured between different zones? To do this, sonic and ultrasonic logging tools have been developed. Up to now, the quality of the casing-cement contacthas been analyzed quantitatively, and that of the cement-formation contacthas been analyzed qualitatively by

  11. Bond-centered, bond-ordered stripes in doped antiferromagnets

    OpenAIRE

    Wrobel, P.; Maciag, A; Eder, R.

    2004-01-01

    Motivated by recent inelastic neutron scattering experiments on cuprates, we discuss the formation of bond order in the stripe phase. We suggest that the spin Peierls order emerges in hole-rich domain walls (DWs) formed between hole-poor regions in which long-range antiferromagnetic (AF) correlations exist. On the example of a single stripe we analyze the stability of such structures. The motion of a hole inside the DW which takes the form of a bond ordered ladder is in principle unrestricted...

  12. Frameshift Deletion by Sulfolobus solfataricus P2 DNA Polymerase Dpo4 T239W Is Selective for Purines and Involves Normal Conformational Change Followed by Slow Phosphodiester Bond Formation*

    Science.gov (United States)

    Zhang, Huidong; Beckman, Jeff W.; Guengerich, F. Peter

    2009-01-01

    The human DNA polymerase κ homolog Sulfolobus solfataricus DNA polymerase IV (Dpo4) produces “−1” frameshift deletions while copying unmodified DNA and, more frequently, when bypassing DNA adducts. As judged by steady-state kinetics and mass spectrometry, bypass of purine template bases to produce these deletions occurred rarely but with 10-fold higher frequency than with pyrimidines. The DNA adduct 1,N2-etheno-2′-deoxyguanosine, with a larger stacking surface than canonical purines, showed the highest frequency of formation of −1 frameshift deletions. Dpo4 T239W, a mutant we had previously shown to produce fluorescence changes attributed to conformational change following dNTP binding opposite cognate bases (Beckman, J. W., Wang, Q., and Guengerich, F. P. (2008) J. Biol. Chem. 283, 36711–36723), reported similar conformational changes when the incoming dNTP complemented the base following a templating purine base or bulky adduct (i.e. the “+1” base). However, in all mispairing cases, phosphodiester bond formation was inefficient. The frequency of −1 frameshift events and the associated conformational changes were not dependent on the context of the remainder of the sequence. Collectively, our results support a mechanism for −1 frameshift deletions by Dpo4 that involves formation of active complexes via a favorable conformational change that skips the templating base, without causing slippage or flipping out of the base, to incorporate a complementary residue opposite the +1 base, in a mechanism previously termed “dNTP-stabilized incorporation.” The driving force is attributed to be the stacking potential between the templating base and the incoming dNTP base. PMID:19837980

  13. Frameshift deletion by Sulfolobus solfataricus P2 DNA polymerase Dpo4 T239W is selective for purines and involves normal conformational change followed by slow phosphodiester bond formation.

    Science.gov (United States)

    Zhang, Huidong; Beckman, Jeff W; Guengerich, F Peter

    2009-12-11

    The human DNA polymerase kappa homolog Sulfolobus solfataricus DNA polymerase IV (Dpo4) produces "-1" frameshift deletions while copying unmodified DNA and, more frequently, when bypassing DNA adducts. As judged by steady-state kinetics and mass spectrometry, bypass of purine template bases to produce these deletions occurred rarely but with 10-fold higher frequency than with pyrimidines. The DNA adduct 1,N(2)-etheno-2'-deoxyguanosine, with a larger stacking surface than canonical purines, showed the highest frequency of formation of -1 frameshift deletions. Dpo4 T239W, a mutant we had previously shown to produce fluorescence changes attributed to conformational change following dNTP binding opposite cognate bases (Beckman, J. W., Wang, Q., and Guengerich, F. P. (2008) J. Biol. Chem. 283, 36711-36723), reported similar conformational changes when the incoming dNTP complemented the base following a templating purine base or bulky adduct (i.e. the "+1" base). However, in all mispairing cases, phosphodiester bond formation was inefficient. The frequency of -1 frameshift events and the associated conformational changes were not dependent on the context of the remainder of the sequence. Collectively, our results support a mechanism for -1 frameshift deletions by Dpo4 that involves formation of active complexes via a favorable conformational change that skips the templating base, without causing slippage or flipping out of the base, to incorporate a complementary residue opposite the +1 base, in a mechanism previously termed "dNTP-stabilized incorporation." The driving force is attributed to be the stacking potential between the templating base and the incoming dNTP base. PMID:19837980

  14. 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....

  15. An on-line communication system as an international catalysator for initiating storage projects

    International Nuclear Information System (INIS)

    The presented internet platform realizes an international contact stock of the companies and institutes being interested in storage technologies and cooperation and will take over the function of a catalysator for the planning of future storage use. In this regard the system creates an information and marketing device that will help, in the shape of an international, virtual exhibition hall, to find new markets, that are interesting for producers and suppliers of electrical energy storage technologies. In this virtual exhibition hall, need and offer regarding the electrical energy storage technologies are shown in order to support the main aim of the works regarding Annex IX, the starting of concrete projects. (author)

  16. Kinetics of bromide catalysed oxidation of dextrose by cerium (IV) in aqueous sulphuric acid solution

    International Nuclear Information System (INIS)

    Kinetics of bromide catalysed oxidation of dextrose by CeIV in aqueous sulphuric acid medium show first order dependence each in dextrose and cerium(IV). The reaction rate decreases on increasing the concentration of hydrogen ion. The increase in [HSO4-] or [SO42-] decreases the rate. The bromide ion shows positive catalytic effect on the reaction rate. The value of activation energy has been calculated and a suitable mechanism confirming to the kinetic data is proposed. (author). 3 refs., 3 tabs

  17. Identification of the human cytochromes P450 catalysing the rate-limiting pathways of gliclazide elimination

    OpenAIRE

    Elliot, David J.; Suharjono,; Lewis, Benjamin C; Gillam, Elizabeth M. J.; Birkett, Donald J; Gross, Annette S.; Miners, John O

    2007-01-01

    What is already known about this subjectGliclazide is a widely used oral hypoglycaemic agent.The major metabolites of gliclazide formed in vivo have been identified.However, the cytochrome P450 enzymes catalysing the rate-limiting pathways of gliclazide elimination are unknown.What this study addsCYP2C9 is the major enzyme involved in the various hydroxylation pathways of gliclazide, although a contribution of CYP2C19 to tolymethylhydroxylation, the major metabolic route, cannot be discounted...

  18. Evaluating Pt-Ru/C mixtures as ethanol electro-oxidation catalysers

    Directory of Open Access Journals (Sweden)

    Bibian Alonso Hoyos

    2010-04-01

    Full Text Available This work studies ethanol electro-catalytic oxidation by cyclic voltametry in sulphuric acid solutions at different temperatures and concetrations, using platinum.rutenium mixtures supported in vitreous carbon as catalysers. The results indicate that ethanol oxidation in theses electrodes is irreversible, has slow kinetics, is controlled by charge transfer and is brought about by a bi-functional reaction mechanism, this being ethanol adsorption on platinum atoms and additional oxidation of specties adsorbed in the presence of platinum and retenium oxides. Experimental results show increased catalytic activity with electrodes, followed by reduced activity for electrodes having a greater quantity of rutenium.

  19. Synthesis of asymmetric supramolecular compounds using a Ni(0) catalysed homo-coupling approach

    OpenAIRE

    Cassidy, Lynda; Horn, Sabine; Cleary, Laura; Halpin, Yvonne; Browne, Wesley R.; Vos, Johannes G.

    2009-01-01

    The synthesis and characterisation of a series of dinuclear ruthenium and osmium polypyridyl metal complexes based on the bridging ligands [5-(5'-bipyridin-2',2 ''-yl)-3-(pyridin-2-yl)]-1,2,4-triazole (Hpytr-bipy), 2,2 ''-bis(pyridin-2 '' yl)-5,5 ''-bis(pyridin-3 ''-yl) (bipy-bipy) and 5,5'-bis(pyridin-2 ''-yl)-3,3'-bis(1,2,4-triazole) (Hpytr-Hpytr) are reported. The dinuclear complexes have been synthesised via a Ni(0) catalysed cross-coupling reaction from brominated precursors. With this a...

  20. Cold pressure welding - the mechanisms governing bonding

    DEFF Research Database (Denmark)

    Bay, Niels

    1979-01-01

    Investigations of the bonding surface in scanning electron microscope after fracture confirm the mechanisms of bond formation in cold pressure welding to be: fracture of work-hardened surface layer, surface expansion increasing the area of virgin surface, extrusion of virgin material through cracks...... of the original surface layer, and establishment of real contact and bonding between virgin material. This implies that normal pressure as well as surface expansion are basic parameters governing the bond strength. Experimental investigations of pressure welding Al-Al under plane strain compression...

  1. 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...

  2. A cooperative hydrogen bonding system with a Csbnd H⋯O hydrogen bond in ofloxacin

    Science.gov (United States)

    Gao, Xiuxiang; Liu, Yufeng; Li, Huizhen; Bian, Jiang; Zhao, Ying; Cao, Ye; Mao, Yuezhi; Li, Xin; Xu, Yizhuang; Ozaki, Yukihiro; Wu, Jinguang

    2013-05-01

    We have investigated a cooperative hydrogen bonding system with a Csbnd H⋯O hydrogen bond in ofloxacin by using NMR, UV-Vis spectra together with quantum chemistry calculation. Both pH-dependent NMR experiments and DFT calculation indicate that the intra-molecular Csbnd H⋯O hydrogen bond between an aromatic proton and an oxygen atom from the carboxyl group is formed. Notably, the Csbnd H⋯O hydrogen bond forms a cooperative hydrogen bonding system with a neighboring Osbnd H⋯O hydrogen bond between the carboxyl group and the keto oxygen. The cooperative hydrogen bonding system makes the formation and disruption of the Osbnd H⋯O and Csbnd H⋯O hydrogen bonds in a synergistic manner. Comparison on the pKa value of the carboxylic group in different fluoroquinolones compounds indicates that the Csbnd H⋯O hydrogen bond plays a significant role in stabilizing the Osbnd H⋯O hydrogen bond. In addition, the formation and disruption of the cooperative hydrogen bonding system could regulate the conformation of the carboxyl group, which affects the size of the conjugated system and spectral behavior of π-π transition of ofloxacin.

  3. Catalysed fusion

    CERN Document Server

    Farley, Francis

    2012-01-01

    A sizzling romance and a romp with subatomic particles at CERN. Love, discovery and adventure in the city where nations meet and beams collide. Life in a large laboratory. As always, the challenges are the same. Who leads? Who follows? Who succeeds? Who gets the credit? Who gets the women or the men? Young Jeremy arrives in CERN and joins the quest for green energy. Coping with baffling jargon and manifold dangers, he is distracted by radioactive rats, lovely ladies and an unscrupulous rival. Full of doubts and hesitations, he falls for a dazzling Danish girl, who leads him astray. His brilliant idea leads to a discovery and a new route to cold fusion. But his personal life is scrambled. Does it bring fame or failure? Tragedy or triumph?

  4. Implementation of steady state approximation for modelling of reaction kinetic of UV catalysed hydrogen peroxide oxidation of starch

    Science.gov (United States)

    Kumoro, Andri Cahyo; Retnowati, Diah Susetyo; Ratnawati, Budiyati, Catarina Sri

    2015-12-01

    With regard to its low viscosity, high stability, clarity, film forming and binding properties, oxidised starch has been widely used in various applications specifically in the food, paper, textile, laundry finishing and binding materials industries. A number of methods have been used to produce oxidised starch through reactions with various oxidizing agents, such as hydrogen peroxide, air oxygen, ozone, bromine, chromic acid, permanganate, nitrogen dioxide and hypochlorite. Unfortunately, most of previous works reported in the literatures were focused on the study of reaction mechanism and physicochemical properties characterization of the oxidised starches produced without investigation of the reaction kinetics of the oxidation process. This work aimed to develop a simple kinetic model for UV catalysed hydrogen peroxide oxidation of starch through implementation of steady state approximation for the radical reaction rates. The model was then verified using experimental data available in the literature. The model verification revealed that the proposed model shows its good agreement with the experimental data as indicated by an average absolute relative error of only 2.45%. The model also confirmed that carboxyl groups are oxidised further by hydroxyl radical. The carbonyl production rate was found to follow first order reaction with respect to carbonyl concentration. Similarly, carboxyl production rate also followed first order reaction with respect to carbonyl concentration. The apparent reaction rate constant for carbonyl formation and oxidation were 6.24 × 104 s-1 and 1.01 × 104 M-1.s-1, respectively. While apparent reaction rate constant for carboxyl oxidation was 4.86 × 104 M-1.s-1.

  5. Palladium-catalysed norbornene-mediated C-H functionalization of arenes

    Science.gov (United States)

    Ye, Juntao; Lautens, Mark

    2015-11-01

    The Catellani reaction -- a palladium-catalysed C-H functionalization reaction mediated by norbornene -- was first reported in 1997. The capacity to functionalize both the ortho and ipso positions of aryl halides in a single transformation held great appeal. We reported an annulative Catellani reaction in 2000. Since then, our two groups have explored the synthetic utility of this reaction and dramatic progress has been made by a number of groups in the past five years. Whereas the original Catellani reaction uses Pd(0) catalysts, recent studies have shown that Pd(II) catalysts can be used in combination with norbornene to effect (1) direct 2-alkylation of indoles and pyrroles and (2) selective meta-C-H functionalization of arenes bearing commonly used ortho-directing groups, thereby opening new avenues for future research. We describe the most recent developments concerning the Pd-catalysed norbornene-mediated C-H functionalization of arenes, including applications in natural products synthesis. We outline challenges and future opportunities.

  6. Atomic scale observation of oxygen delivery during silver-oxygen nanoparticle catalysed oxidation of carbon nanotubes

    Science.gov (United States)

    Yue, Yonghai; Yuchi, Datong; Guan, Pengfei; Xu, Jia; Guo, Lin; Liu, Jingyue

    2016-07-01

    To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars-van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes.

  7. Challenging nickel-catalysed amine arylations enabled by tailored ancillary ligand design.

    Science.gov (United States)

    Lavoie, Christopher M; MacQueen, Preston M; Rotta-Loria, Nicolas L; Sawatzky, Ryan S; Borzenko, Andrey; Chisholm, Alicia J; Hargreaves, Breanna K V; McDonald, Robert; Ferguson, Michael J; Stradiotto, Mark

    2016-01-01

    Palladium-catalysed C(sp(2))-N cross-coupling (that is, Buchwald-Hartwig amination) is employed widely in synthetic chemistry, including in the pharmaceutical industry, for the synthesis of (hetero)aniline derivatives. However, the cost and relative scarcity of palladium provides motivation for the development of alternative, more Earth-abundant catalysts for such transformations. Here we disclose an operationally simple and air-stable ligand/nickel(II) pre-catalyst that accommodates the broadest combination of C(sp(2))-N coupling partners reported to date for any single nickel catalyst, without the need for a precious-metal co-catalyst. Key to the unprecedented performance of this pre-catalyst is the application of the new, sterically demanding yet electron-poor bisphosphine PAd-DalPhos. Featured are the first reports of nickel-catalysed room temperature reactions involving challenging primary alkylamine and ammonia reaction partners employing an unprecedented scope of electrophiles, including transformations involving sought-after (hetero)aryl mesylates for which no capable catalyst system is known. PMID:27004442

  8. 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.

  9. Multicenter bonds, bond valence and bond charge apportion

    International Nuclear Information System (INIS)

    In the same way that the valence of an atom issues from the definition of bond index, we shoe here that the three-center bond index lends itself to the definition of a bond valence. Within the charge of a bond, we show that its self-charge (i.e., the amount of electron kept by the atoms involved in the bond) is parted in a such a way that the more electronegative atom tends to allot more electronic charge than the other atom. We give examples of these quantities and discuss the results for different kinds of chemical systems. We also show some results for four-center indices and report six-center indices for hexagonal rings. (author). 54 refs., 4 figs., 8 tabs

  10. Direct evidence for a coordination-insertion mechanism of ethylene oligomerization catalysed by neutral 2,6-bisiminopyridine iron monoalkyl complexes

    OpenAIRE

    Cartes, M. Ángeles; Rodríguez-Delgado, Antonio; Palma, Pilar; Sánchez, Luis J.; Cámpora, Juan; CSIC - Unidad de Recursos de Información Científica para la Investigación (URICI)

    2014-01-01

    1H NMR studies on ethylene oligomerization catalysed by the neutral monoalkyl complex [Fe(Me)(iPrBIP)] allow direct observation of alkyl iron intermediates as well as reversible ethylene coordination to the metal center, providing for the first time experimental evidence for a coordination-insertion mechanism of iron-catalysed ethylene upgrade reactions. © 2014 the Partner Organisations.

  11. EDITORIAL: Catalysing progress Catalysing progress

    Science.gov (United States)

    Demming, Anna

    2010-01-01

    Examples of the merits of blue-sky research in the history of science are legion. The invention of the laser, celebrating its 50th anniversary this year, is an excellent example. When it was invented it was considered to be 'a solution waiting for a problem', and yet the level to which it has now infiltrated our day-to-day technological landscape speaks volumes. At the same time it is also true to say that the direction of research is also at times rightly influenced by the needs and concerns of the general public. Over recent years, growing concerns about the environment have had a noticeable effect on research in nanotechnology, motivating work on a range of topics from green nanomaterial synthesis [1] to high-efficiency solar cells [2] and hydrogen storage [3]. The impact of the world's energy consumption on the welfare of the planet is now an enduring and well founded concern. In the face of an instinctive reluctance to curtail habits of comfort and convenience and the appendages of culture and consumerism, research into renewable and more efficient energy sources seem an encouraging approach to alleviating an impending energy crisis. Fuel cells present one alternative to traditional combustion cells that have huge benefits in terms of the efficiency of energy conversion and the limited harmful emissions. In last week's issue of Nanotechnology, Chuan-Jian Zhong and colleagues at the State University of New York at Binghamton in the USA presented an overview of research on nanostructured catalysts in fuel cells [4]. The topical review includes insights into the interactions between nanoparticles and between nanoparticles and their substrate as well as control over the composition and nanostructure of catalysts. The review also serves to highlight how the flourishing of nanotechnology research has heralded great progress in the exploitation of catalysts with nanostructures ingeniously controlled to maximize surface area and optimize energetics for synthesis procedures. One man who was well aware of the role of nanostructured catalysts in the progress of material science research was the late Ulrich Gösele, director at the Max-Planck-Institut für Mikrostrukturphysik Halle, who passed away at the age of 60 on 8 November, 2009. Ulrich Gösele published over 750 papers of premium calibre research that have collectively been cited over 20,000 times. His research output includes a cornucopia of excellent work published in Nanotechnology, amongst which are a number of papers detailing the deft manipulation of nanocatalysts to control the quality and structure of nanomaterials [5-8]. Ulrich Gösele was a pioneer in nanoscience. In 1991, when the nanotechnology revolution was little more than a portentous rumble, he published a seminal report examining the effect of quantum confinement on the optical properties of silicon nanowires [9]. While we lament the loss to the community, we have much to celebrate in the insights his legacy has provided for the progress of materials science. It would be unwise to assume that science will or can ultimately advance in such a way as to allow ample means to indulge an unrestrained appetite for consumerism and energy consumption. As with most things, a balanced approach, considering solutions to the problem from many angles, seems sensible. Nonetheless, a browse through the latest literature leaves much cause for optimism for the positive role science can play in improving and sustaining our lifestyle. References [1] Mukherjee P, Roy M, Mandal B P, Dey G K, Mukherjee P K, Ghatak J, Tyagi A K and Kale S P 2008 Nanotechnology 19 075103 [2] Greenham N C and Grätzel M 2008 Nanotechnology 19 420201 [3] Vajo J, Pinkerton F and Stetson N 2009 Nanotechnology 20 200201 [4] Zhong C-J, Luo J, Fang B, Wanjala B N, Njoki P N, Loukrakpam R and Yin J 2010 Nanotechnology 21 062001 [5] Sivakov V A, Scholz A, Syrowatka F, Falk F, Gösele U and Christiansen S H 2009 Nanotechnology 20 405607 [6] Liu L, Lee W, Huang Z, Scholz R and Gösele U 2008 Nanotechnology 19 335604 [7] Fan H J et al 2006 Nanotechnology 17 S231-9 [8] Stelzner Th et al 2006 Nanotechnology 17 2895-8 [9] Lehmann V and Gösele U 1991 Appl. Phys. Lett. 58 856-8

  12. EDITORIAL: Catalysing progress Catalysing progress

    Science.gov (United States)

    Demming, Anna

    2010-01-01

    Examples of the merits of blue-sky research in the history of science are legion. The invention of the laser, celebrating its 50th anniversary this year, is an excellent example. When it was invented it was considered to be 'a solution waiting for a problem', and yet the level to which it has now infiltrated our day-to-day technological landscape speaks volumes. At the same time it is also true to say that the direction of research is also at times rightly influenced by the needs and concerns of the general public. Over recent years, growing concerns about the environment have had a noticeable effect on research in nanotechnology, motivating work on a range of topics from green nanomaterial synthesis [1] to high-efficiency solar cells [2] and hydrogen storage [3]. The impact of the world's energy consumption on the welfare of the planet is now an enduring and well founded concern. In the face of an instinctive reluctance to curtail habits of comfort and convenience and the appendages of culture and consumerism, research into renewable and more efficient energy sources seem an encouraging approach to alleviating an impending energy crisis. Fuel cells present one alternative to traditional combustion cells that have huge benefits in terms of the efficiency of energy conversion and the limited harmful emissions. In last week's issue of Nanotechnology, Chuan-Jian Zhong and colleagues at the State University of New York at Binghamton in the USA presented an overview of research on nanostructured catalysts in fuel cells [4]. The topical review includes insights into the interactions between nanoparticles and between nanoparticles and their substrate as well as control over the composition and nanostructure of catalysts. The review also serves to highlight how the flourishing of nanotechnology research has heralded great progress in the exploitation of catalysts with nanostructures ingeniously controlled to maximize surface area and optimize energetics for synthesis procedures. One man who was well aware of the role of nanostructured catalysts in the progress of material science research was the late Ulrich Gösele, director at the Max-Planck-Institut für Mikrostrukturphysik Halle, who passed away at the age of 60 on 8 November, 2009. Ulrich Gösele published over 750 papers of premium calibre research that have collectively been cited over 20,000 times. His research output includes a cornucopia of excellent work published in Nanotechnology, amongst which are a number of papers detailing the deft manipulation of nanocatalysts to control the quality and structure of nanomaterials [5-8]. Ulrich Gösele was a pioneer in nanoscience. In 1991, when the nanotechnology revolution was little more than a portentous rumble, he published a seminal report examining the effect of quantum confinement on the optical properties of silicon nanowires [9]. While we lament the loss to the community, we have much to celebrate in the insights his legacy has provided for the progress of materials science. It would be unwise to assume that science will or can ultimately advance in such a way as to allow ample means to indulge an unrestrained appetite for consumerism and energy consumption. As with most things, a balanced approach, considering solutions to the problem from many angles, seems sensible. Nonetheless, a browse through the latest literature leaves much cause for optimism for the positive role science can play in improving and sustaining our lifestyle. References [1] Mukherjee P, Roy M, Mandal B P, Dey G K, Mukherjee P K, Ghatak J, Tyagi A K and Kale S P 2008 Nanotechnology 19 075103 [2] Greenham N C and Grätzel M 2008 Nanotechnology 19 420201 [3] Vajo J, Pinkerton F and Stetson N 2009 Nanotechnology 20 200201 [4] Zhong C-J, Luo J, Fang B, Wanjala B N, Njoki P N, Loukrakpam R and Yin J 2010 Nanotechnology 21 062001 [5] Sivakov V A, Scholz A, Syrowatka F, Falk F, Gösele U and Christiansen S H 2009 Nanotechnology 20 405607 [6] Liu L, Lee W, Huang Z, Scholz R and Gösele U 2008 Nanotechnology 19 335604 [7] Fan H J et al 2006 Nanotechnology 1

  13. A γ-lactamase from cereal infecting Fusarium spp. catalyses the first step in the degradation of the benzoxazolinone class of phytoalexins.

    Science.gov (United States)

    Kettle, Andrew J; Carere, Jason; Batley, Jacqueline; Benfield, Aurelie H; Manners, John M; Kazan, Kemal; Gardiner, Donald M

    2015-10-01

    The benzoxazolinone class of phytoalexins are released by wheat, maize, rye and other agriculturally important species in the Poaceae family upon pathogen attack. Benzoxazolinones show antimicrobial effects on plant pathogens, but certain fungi have evolved mechanisms to actively detoxify these compounds which may contribute to the virulence of the pathogens. In many Fusarium spp. a cluster of genes is thought to be involved in the detoxification of benzoxazolinones. However, only one enzyme encoded in the cluster has been unequivocally assigned a role in this process. The first step in the detoxification of benzoxazolinones in Fusarium spp. involves the hydrolysis of a cyclic ester bond. This reaction is encoded by the FDB1 locus in F. verticillioides but the underlying gene is yet to be cloned. We previously proposed that FDB1 encodes a γ-lactamase, and here direct evidence for this is presented. Expression analyses in the important wheat pathogen F. pseudograminearum demonstrated that amongst the three predicted γ-lactamase genes only the one designated as FDB1, part of the proposed benzoxazolinone cluster in F. pseudograminearum, was strongly responsive to exogenous benzoxazolinone application. Analysis of independent F. pseudograminearum and F. graminearum FDB1 gene deletion mutants, as well as biochemical assays, demonstrated that the γ-lactamase enzyme, encoded by FDB1, catalyses the first step in detoxification of benzoxazolinones. Overall, our results support the notion that Fusarium pathogens that cause crown rot and head blight on wheat have adopted strategies to overcome host-derived chemical defences. PMID:26296598

  14. IMPACT OF PHYSICAL AND CHEMICAL MUD CONTAMINATION ON WELLBORE CEMENT- FORMATION SHEAR BOND STRENGTH Authors: Arome Oyibo1 and Mileva Radonjic1 * 1. Craft and Hawkins Department of Petroleum Engineering, 2131 Patrick F. Taylor Hall, Louisiana State University, Baton Rouge, LA 70803, aoyibo1@tigers.lsu.edu, mileva@lsu.edu

    Science.gov (United States)

    Oyibo, A. E.

    2013-12-01

    Wellbore cement has been used to provide well integrity through zonal isolation in oil & gas wells and geothermal wells. Cementing is also used to provide mechanical support for the casing and protect the casing from corrosive fluids. Failure of cement could be caused by several factors ranging from poor cementing, failure to completely displace the drilling fluids to failure on the path of the casing. A failed cement job could result in creation of cracks and micro annulus through which produced fluids could migrate to the surface which could lead to sustained casing pressure, contamination of fresh water aquifer and blow out in some cases. In addition, cement failures could risk the release of chemicals substances from hydraulic fracturing into fresh water aquifer during the injection process. To achieve proper cementing, the drilling fluid should be completely displaced by the cement slurry. However, this is hard to achieve in practice, some mud is usually left on the wellbore which ends up contaminating the cement afterwards. The purpose of this experimental study is to investigate the impact of both physical and chemical mud contaminations on cement-formation bond strength for different types of formations. Physical contamination occurs when drilling fluids (mud) dries on the surface of the formation forming a mud cake. Chemical contamination on the other hand occurs when the drilling fluids which is still in the liquid form interacts chemically with the cement during a cementing job. We investigated the impact of the contamination on the shear bond strength and the changes in the mineralogy of the cement at the cement-formation interface to ascertain the impact of the contamination on the cement-formation bond strength. Berea sandstone and clay rich shale cores were bonded with cement cores with the cement-formation contaminated either physically or chemically. For the physically contaminated composite cores, we have 3 different sample designs: clean

  15. Bond excitations in the pseudogap phase of the Hubbard Model

    OpenAIRE

    Macridin, Alexandru; Jarrell, Mark (Eds. )

    2008-01-01

    Using the dynamical cluster approximation, we calculate the correlation functions associated with the nearest neighbor bond operator which measure the z component of the spin exchange in the two-dimensional Hubbard model with $U$ equal to the bandwidth. We find that in the pseudogap region, the local bond susceptibility diverges at T=0. This shows the existence of degenerate bond spin excitation and implies quantum criticality and bond order formation when long range correlations are consider...

  16. Multicomponent click synthesis of potentially biologically active triazoles catalysed by copper nanoparticles on activated carbon in water

    OpenAIRE

    Alonso Valdés, Francisco; Moglie, Yanina; Radivoy, Gabriel; Yus Astiz, Miguel

    2011-01-01

    A variety of potentially biologically active 1,2,3-triazoles, derived from (–)-menthol, lactic acid, D-glucose, oestrone, cholesterol, and phenacetin, have been synthesised through the multicomponent alkyne-azide 1,3-dipolar cycloaddition catalysed by copper nanoparticles on activated carbon in neat water.

  17. One-pot three-component synthesis of quinazolines via a copper-catalysed oxidative amination reaction.

    Science.gov (United States)

    Duan, Tiantian; Zhai, Tianran; Liu, Huanhuan; Yan, Zilong; Zhao, Yue; Feng, Lei; Ma, Chen

    2016-07-01

    A copper-catalysed three-component reaction for constructing a series of quinazoline derivatives has been developed. In this system, solvents act as the reactants and different functional groups are well tolerated to obtain corresponding products in moderate to good yields. PMID:27304252

  18. Potash alum [KAl(SO4)2.12H2O] catalysed esterification of formylphenoxyaliphatic acids

    Indian Academy of Sciences (India)

    Ganesan Shunmugadhas Suresh Kumar; Sudalaiandi Kumaresan

    2012-07-01

    A convenient and clean procedure for esterification is reported. Direct condensation of formylphenoxyaliphatic acids with low to high boiling alcohols catalysed by potash alum gave moderate to good yields. This catalyst could be recovered and reused without substantial loss in its catalytic activity and the methodology could be used for a range of closely related substrates.

  19. Mg(ClO4)2 catalysed preparation of 1-amidoalkyl-2-naphthols under solvent-free conditions

    Indian Academy of Sciences (India)

    Mohammad Ali Amrollahi; Bi Bi Fatemeh Mirjalili; Hamideh Emtiazi

    2013-05-01

    A simple, efficient, and practical procedure for the synthesis of amidoalkyl naphthols via multicomponent one-pot reaction of 2-naphthol, aldehydes and amides catalysed by Mg(ClO4)2 is described in high yields. The present work offers several advantages such as high

  20. Selective preparation of terminal alkenes from aliphatic carboxylic acids by a palladium-catalysed decarbonylation-eliminiation reaction

    NARCIS (Netherlands)

    Notre, le J.E.L.; Scott, E.L.; Franssen, M.C.R.; Sanders, J.P.M.

    2010-01-01

    Trialkylamines were used as additives in the decarbonylation–elimination reaction catalysed by the combination of palladium(II) chloride and DPE-Phos. Aliphatic carboxylic acids were transformed at relatively low temperature into terminal alkenes in high yield and high selectivity, without the need

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

    Directory of Open Access Journals (Sweden)

    Matthieu Jouffroy

    2014-10-01

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

  2. Neural mechanisms of mother-infant bonding and pair bonding: Similarities, differences, and broader implications.

    Science.gov (United States)

    Numan, Michael; Young, Larry J

    2016-01-01

    This article is part of a Special Issue "Parental Care". Mother-infant bonding is a characteristic of virtually all mammals. The maternal neural system may have provided the scaffold upon which other types of social bonds in mammals have been built. For example, most mammals exhibit a polygamous mating system, but monogamy and pair bonding between mating partners occur in ~5% of mammalian species. In mammals, it is plausible that the neural mechanisms that promote mother-infant bonding have been modified by natural selection to establish the capacity to develop a selective bond with a mate during the evolution of monogamous mating strategies. Here we compare the details of the neural mechanisms that promote mother-infant bonding in rats and other mammals with those that underpin pair bond formation in the monogamous prairie vole. Although details remain to be resolved, remarkable similarities and a few differences between the mechanisms underlying these two types of bond formation are revealed. For example, amygdala and nucleus accumbens-ventral pallidum (NA-VP) circuits are involved in both types of bond formation, and dopamine and oxytocin actions within NA appear to promote the synaptic plasticity that allows either infant or mating partner stimuli to persistently activate NA-VP attraction circuits, leading to an enduring social attraction and bonding. Further, although the medial preoptic area is essential for maternal behavior, its role in pair bonding remains to be determined. Our review concludes by examining the broader implications of this comparative analysis, and evidence is provided that the maternal care system may have also provided the basic neural foundation for other types of strong social relationships, beyond pair bonding, in mammals, including humans. PMID:26062432

  3. Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams

    KAUST Repository

    Behenna, Douglas C.

    2011-12-18

    The enantioselective synthesis of nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines, including the total synthesis of natural products and medicinal chemistry. In this Article, we describe the highly enantioselective palladium-catalysed decarboxylative allylic alkylation of readily available lactams to form 3,3-disubstituted pyrrolidinones, piperidinones, caprolactams and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envisage that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously used in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures. © 2012 Macmillan Publishers Limited. All rights reserved.

  4. RNA with iron(II) as a cofactor catalyses electron transfer

    Science.gov (United States)

    Hsiao, Chiaolong; Chou, I.-Chun; Okafor, C. Denise; Bowman, Jessica C.; O'Neill, Eric B.; Athavale, Shreyas S.; Petrov, Anton S.; Hud, Nicholas V.; Wartell, Roger M.; Harvey, Stephen C.; Williams, Loren Dean

    2013-06-01

    Mg2+ is essential for RNA folding and catalysis. However, for the first 1.5 billion years of life on Earth RNA inhabited an anoxic Earth with abundant and benign Fe2+. We hypothesize that Fe2+ was an RNA cofactor when iron was abundant, and was substantially replaced by Mg2+ during a period known as the ‘great oxidation’, brought on by photosynthesis. Here, we demonstrate that reversing this putative metal substitution in an anoxic environment, by removing Mg2+ and replacing it with Fe2+, expands the catalytic repertoire of RNA. Fe2+ can confer on some RNAs a previously uncharacterized ability to catalyse single-electron transfer. We propose that RNA function, in analogy with protein function, can be understood fully only in the context of association with a range of possible metals. The catalysis of electron transfer, requisite for metabolic activity, may have been attenuated in RNA by photosynthesis and the rise of O2.

  5. Production de biohydrogène par électro-catalyse microbienne

    OpenAIRE

    Rousseau, Raphaël

    2013-01-01

    La cellule d’électrolyse microbienne (CEM) permet la conversion de la biomasse en dihydrogène via un apport théorique en énergie électrique 10 fois moindre que celui de l’électrolyse de l’eau. Un tel procédé fonctionne via la technologie des bioanodes, qui permet la catalyse de l’oxydation de la biomasse en CO2 par l’intermédiaire d’un biofilm électro-actif. Les travaux exposés dans ce manuscrit de thèse ont pour but l’optimisation des performances de la bioanode, la compréhension des mécanis...

  6. Chlorophyll catalyse the photo-transformation of carcinogenic benzo[a]pyrene in water

    Science.gov (United States)

    Luo, Lijuan; Lai, Xueying; Chen, Baowei; Lin, Li; Fang, Ling; Tam, Nora F. Y.; Luan, Tiangang

    2015-08-01

    Algal blooms cause great damage to water quality and aquaculture. However, this study showed that dead algal cells and chlorophyll could accelerate the photo-transformation of benzo[a]pyrene (BaP), a ubiquitous and persistent pollutant with potently mutagenic and carcinogenic toxicities, under visible light irradiation. Chlorophyll was found to be the major active substance in dead algal cells, and generated a high level of singlet oxygen to catalyse the photo-transformation of BaP. According to various BaP metabolites formed, the degradation mechanism was proposed as that chlorophyll in dead algal cells photo-oxidized BaP to quinones via photocatalytic generation of singlet oxygen. The results provided a good insight into the role of chlorophyll in the photo-transformation of organic contaminants and could be a possible remediation strategy of organic pollutants in natural environment.

  7. Synthesis of asymmetric supramolecular compounds using a Ni(0) catalysed homo-coupling approach.

    Science.gov (United States)

    Cassidy, Lynda; Horn, Sabine; Cleary, Laura; Halpin, Yvonne; Browne, Wesley R; Vos, Johannes G

    2009-05-28

    The synthesis and characterisation of a series of dinuclear ruthenium and osmium polypyridyl metal complexes based on the bridging ligands [5-(5'-bipyridin-2',2''-yl)-3-(pyridin-2-yl)]-1,2,4-triazole (Hpytr-bipy), 2,2'-bis(pyridin-2''yl)-5,5'-bis(pyridin-3''-yl) (bipy-bipy) and 5,5'-bis(pyridin-2''-yl)-3,3'-bis(1,2,4-triazole) (Hpytr-Hpytr) are reported. The dinuclear complexes have been synthesised via a Ni(0) catalysed cross-coupling reaction from brominated precursors. With this approach a mixture of three products is obtained, which are separated by chromatographic methods. The compounds obtained are characterised by elemental analysis, (1)H NMR, absorption and emission spectroscopy. The synthetic approach developed offers a new route to asymmetric multinuclear supramolecular structures that is complimentary to the complexes as ligands/complexes as metal approaches. PMID:19440590

  8. Bonding silicones with epoxies

    Energy Technology Data Exchange (ETDEWEB)

    Tira, J.S.

    1980-01-01

    It is shown that silicones, both room temperature vulcanizing (RTV) and millable rubber (press cured) can be successfully bonded to other materials using plasma treatment and epoxy adhesives. The plasma treatment using dry air atmosphere increases the surface energy of the silicone and thus provides a lower water contact angle. This phenomenon allows the epoxy adhesive to wet the silicone surface and ultimately bond. Bond strengths are sufficiently high to result in failures in the silicone materials rather than the adhesive bond.

  9. 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 ...

  10. Malaysia : Bond Market Development

    OpenAIRE

    International Monetary Fund; World Bank

    2013-01-01

    This paper pertains to the bond market development in Malaysia, and provides an overview of the market scenario in the country. Malaysia has been successful in developing the capital markets, particularly bond markets, in the recent past. Now, it faces the challenge of how to improve broader access and efficiency of the bond market. A high degree of investor concentration, dominated by gov...

  11. 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

  12. Credit unions and the common bond

    OpenAIRE

    William R. Emmons; Frank A. Schmid

    1998-01-01

    A distinguishing feature of credit unions is the legal requirement that members share a common bond. This organizing principle recently became the focus of national attention when the Supreme Court and the U.S. Congress took opposite sides in a controversy regarding the number of common bonds (fields of membership) that could coexist within a single credit union. In this article, Emmons and Schmid develop and simulate a model of credit-union formation and consolidation to examine the effects ...

  13. Copper-catalysed asymmetric allylic alkylation of alkylzirconocenes to racemic 3,6-dihydro-2H-pyrans

    Science.gov (United States)

    Rideau, Emeline

    2015-01-01

    Summary Asymmetric allylic alkylation is a powerful reaction that allows the enantioselective formation of C–C bonds. Here we describe the asymmetric alkylation of alkylzirconium species to racemic 3,6-dihydro-2H-pyrans. Two systems were examined: 3-chloro-3,6-dihydro-2H-pyran using linear optimization (45–93% ee, up to 33% yield, 5 examples) and 3,6-dihydro-2H-pyran-3-yl diethyl phosphate with the assistance of a design of experiments statistical approach (83% ee, 12% yield). 1H NMR spectroscopy was used to gain insight into the reaction mechanisms. PMID:26734091

  14. Body of Knowledge (BOK) for Copper Wire Bonds

    Science.gov (United States)

    Rutkowski, E.; Sampson, M. J.

    2015-01-01

    Copper wire bonds have replaced gold wire bonds in the majority of commercial semiconductor devices for the latest technology nodes. Although economics has been the driving mechanism to lower semiconductor packaging costs for a savings of about 20% by replacing gold wire bonds with copper, copper also has materials property advantages over gold. When compared to gold, copper has approximately: 25% lower electrical resistivity, 30% higher thermal conductivity, 75% higher tensile strength and 45% higher modulus of elasticity. Copper wire bonds on aluminum bond pads are also more mechanically robust over time and elevated temperature due to the slower intermetallic formation rate - approximately 1/100th that of the gold to aluminum intermetallic formation rate. However, there are significant tradeoffs with copper wire bonding - copper has twice the hardness of gold which results in a narrower bonding manufacturing process window and requires that the semiconductor companies design more mechanically rigid bonding pads to prevent cratering to both the bond pad and underlying chip structure. Furthermore, copper is significantly more prone to corrosion issues. The semiconductor packaging industry has responded to this corrosion concern by creating a palladium coated copper bonding wire, which is more corrosion resistant than pure copper bonding wire. Also, the selection of the device molding compound is critical because use of environmentally friendly green compounds can result in internal CTE (Coefficient of Thermal Expansion) mismatches with the copper wire bonds that can eventually lead to device failures during thermal cycling. Despite the difficult problems associated with the changeover to copper bonding wire, there are billions of copper wire bonded devices delivered annually to customers. It is noteworthy that Texas Instruments announced in October of 2014 that they are shipping microcircuits containing copper wire bonds for safety critical automotive applications

  15. Hydrogen bonds in PC61BM solids

    Directory of Open Access Journals (Sweden)

    Chun-Qi Sheng

    2015-09-01

    Full Text Available We have studied the hydrogen bonds in PC61BM solids. Inter-molecular interaction is analyzed theoretically for the well-defined monoclinic (P21/n structure. The results indicate that PC61BM combines into C–H⋯Od bonded molecular chains, where Od denotes the doubly-bonded O atom of PC61BM. The molecular chains are linked together by C–H⋯Os bonds, where Os denotes the singly-bonded O atom of PC61BM. To reveal the consequences of hydrogen bond formation on the structural properties of PC61BM solids (not limited to the monoclinic structure, we design and perform some experiments for annealed samples with the monoclinic (P21/n PC61BM as starting material. The experiments include differential scanning calorimetry, X-ray diffraction and infrared absorption measurements. Structural phase transitions are observed below the melting point. The C–H⋯Od bonds seem persisting in the altered structures. The inter-molecular hydrogen bonds can help to understand the phase separation in polymer/PC61BM blends and may be responsible for the existence of liquid PC61BM.

  16. Hydrogen bonds in PC61BM solids

    International Nuclear Information System (INIS)

    We have studied the hydrogen bonds in PC61BM solids. Inter-molecular interaction is analyzed theoretically for the well-defined monoclinic (P21/n) structure. The results indicate that PC61BM combines into C–H⋯Od bonded molecular chains, where Od denotes the doubly-bonded O atom of PC61BM. The molecular chains are linked together by C–H⋯Os bonds, where Os denotes the singly-bonded O atom of PC61BM. To reveal the consequences of hydrogen bond formation on the structural properties of PC61BM solids (not limited to the monoclinic structure), we design and perform some experiments for annealed samples with the monoclinic (P21/n) PC61BM as starting material. The experiments include differential scanning calorimetry, X-ray diffraction and infrared absorption measurements. Structural phase transitions are observed below the melting point. The C–H⋯Od bonds seem persisting in the altered structures. The inter-molecular hydrogen bonds can help to understand the phase separation in polymer/PC61BM blends and may be responsible for the existence of liquid PC61BM

  17. Towards understanding a mechanism for reversible hydrogen storage: theoretical study of transition metal catalysed dehydrogenation of sodium alanate.

    Science.gov (United States)

    Ljubić, Ivan; Clary, David C

    2010-04-28

    On the basis of density functional theory and coupled-cluster CCSD(T) calculations we propose a mechanism of the dehydrogenation of transition metal doped sodium alanate. Insertion of two early 3d-transition metals, scandium and titanium, both of which are promising catalysts for reversible hydrogen storage in light metal hydrides, is compared. The mechanism is deduced from studies on the decomposition of a model system consisting of one transition metal atom and two NaAlH(4) units. Subsequently, the significance of such minimal cluster model systems to the real materials is tested by embedding the systems into the surface of the NaAlH(4) crystal. It is found that the dehydrogenation proceeds via breaking of the bridge H-Al bond and consequent formation of intermediate coordination compounds in which the H(2) molecule is side-on (eta(2)-) bonded to the transition metal centre. The total barrier to the H(2) release is thus dependent upon both the strength of the Al-H bond to be broken and the depth of the coordinative potential. The analogous mechanism applies for the recognized three successive dehydrogenation steps. The gas-phase model structures embedded into the surface of the NaAlH(4) crystal exhibit an unambiguous kinetic stability and their general geometric features remain largely unchanged. PMID:20379493

  18. 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.

  19. A Coupled Thermal-Mechanical Analysis of Ultrasonic Bonding Mechanism

    Science.gov (United States)

    Zhang, Chunbo (Sam); Li, Leijun

    2009-04-01

    A three-dimensional (3-D) finite element model has been developed to simulate the coupled thermal-mechanical fields in ultrasonic welding of aluminum foils. Transient distributions and evolution of the in-process variables, including normal stress, shear stress, slide distance, heat generation, temperature, and plastic deformation on the contact interface, and their interactions have been studied in detail. The von Mises plastic strain from the simulation has been correlated with the measured bonded area of ultrasonic joints. A possible mechanism for ultrasonic bond formation is proposed. The severe, localized, plastic deformation at the bond region is believed to be the major phenomenon causing bond formation in ultrasonic welding.

  20. Laccase‐catalysed oxidations of naturally occurring phenols: from in vivo biosynthetic pathways to green synthetic applications

    OpenAIRE

    Jeon, Jong‐Rok; Baldrian, Petr; Murugesan, Kumarasamy; Chang, Yoon‐Seok

    2012-01-01

    Summary Laccases are oxidases that contain several copper atoms, and catalyse single‐electron oxidations of phenolic compounds with concomitant reduction of oxygen to water. The enzymes are particularly widespread in ligninolytic basidiomycetes, but also occur in certain prokaryotes, insects and plants. Depending on the species, laccases are involved in various biosynthetic processes contributing to carbon recycling in land ecosystems and the morphogenesis of biomatrices, wherein low‐molecula...

  1. Laccase-catalysed oxidations of naturally occurring phenols: from in vivo biosynthetic pathways to green synthetic applications.

    Science.gov (United States)

    Jeon, Jong-Rok; Baldrian, Petr; Murugesan, Kumarasamy; Chang, Yoon-Seok

    2012-05-01

    Laccases are oxidases that contain several copper atoms, and catalyse single-electron oxidations of phenolic compounds with concomitant reduction of oxygen to water. The enzymes are particularly widespread in ligninolytic basidiomycetes, but also occur in certain prokaryotes, insects and plants. Depending on the species, laccases are involved in various biosynthetic processes contributing to carbon recycling in land ecosystems and the morphogenesis of biomatrices, wherein low-molecular-weight naturally occurring phenols serve as key enzyme substrates. Studies of these in vivo synthetic pathways have afforded new insights into fungal laccase applicability in green synthetic chemistry. Thus, we here review fungal laccase-catalysed oxidations of naturally occurring phenols that are particularly relevant to the synthesis of fine organic chemicals, and we discuss how the discovered synthetic strategies mimic laccase-involved in vivo pathways, thus enhancing the green nature of such reactions. Laccase-catalysed in vivo processes yield several types of biopolymers, including those of cuticles, lignin, polyflavonoids, humus and the melanin pigments, using natural mono- or poly-phenols as building blocks. The in vivo synthetic pathways involve either phenoxyl radical-mediated coupling or cross-linking reactions, and can be adapted to the design of in vitro oxidative processes involving fungal laccases in organic synthesis; the laccase substrates and the synthetic mechanisms reflect in vivo processes. Notably, such in vitro synthetic pathways can also reproduce physicochemical properties (e.g. those of chromophores, and radical-scavenging, hydration and antimicrobial activities) found in natural biomaterials. Careful study of laccase-associated in vivo metabolic pathways has been rewarded by the discovery of novel green applications for fungal laccases. This review comprehensively summarizes the available data on laccase-catalysed biosynthetic pathways and associated

  2. Experimental and kinetic modelling studies on the acid-catalysed hydrolysis of the water hyacinth plant to levulinic acid

    OpenAIRE

    Girisuta, B.; Danon, B.; Manurung, R.; Janssen, L. P. B. M.; Heeres, H. J.

    2008-01-01

    A comprehensive experimental and modelling study on the acid-catalysed hydrolysis of the water hyacinth plant (Eichhornia crassipes) to optimise the yield of levulinic acid (LA) is reported (T = 150-175 degrees C, C-H2SO4 - 0.1-1 M, water hyacinth intake = 1-5 wt%). At high acid concentrations (> 0.5 M), LA was the major organic acid whereas at low acid concentrations (

  3. Employing fly ash and FCC catalyser waste in recovering chrome (III) from liquid effluent emitted by tanneries

    OpenAIRE

    Jeceny Amaya; Andrés Tristancho; Francisco José Sánchez Castellanos

    2010-01-01

    The present work studies the possibility of using two solid industrial wastes TERMOPAIPA's fly ash and ECOPETROL's alkaline hydrothermal treatments for obtaining zeolytic structures having better propierties; waste catalyser was calcined for eliminatin surface coke. Solids were characterised following treatment including DRX, BET area and CEC. A colorimetric method was standardised for determining chrome in solution; a response surface experimental design was implemented for finding optimum r...

  4. Bond Markets in Africa

    OpenAIRE

    Yibin Mu; Peter Phelps; Janet Gale Stotsky

    2013-01-01

    African bond markets have been steadily growing in recent years, but nonetheless remain undeveloped. African countries would benefit from greater access to financing and deeper financial markets. This paper compiles a unique set of data on corporate bond markets in Africa. It then applies an econometric model to analyze the key determinants of African government securities market and corporate bond market capitalization. Government securities market capitalization is directly related to bette...

  5. Build America Bonds

    OpenAIRE

    Andrew Ang; Vineer Bhansali; Yuhang Xing

    2010-01-01

    Build America Bonds (BABs) are a new form of municipal financing introduced in 2009. Investors in BAB municipal bonds receive interest payments that are taxable, but issuers receive a subsidy from the U.S. Treasury. The BAB program has succeeded in lowering the cost of funding for state and local governments with BAB issuers obtaining finance 54 basis points lower, on average, compared to issuing regular municipal bonds. For institutional investors, BAB issue yields are 116 basis points highe...

  6. 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...

  7. Hydrogen bonding and anaesthesia

    Science.gov (United States)

    Sándorfy, C.

    2004-12-01

    General anaesthetics act by perturbing intermolecular associations without breaking or forming covalent bonds. These associations might be due to a variety of van der Waals interactions or hydrogen bonding. Neurotransmitters all contain OH or NH groups, which are prone to form hydrogen bonds with those of the neurotransmitter receptors. These could be perturbed by anaesthetics. Aromatic rings in amino acids can act as weak hydrogen bond acceptors. On the other hand the acidic hydrogen in halothane type anaesthetics are weak proton donors. These two facts together lead to a probable mechanism of action for all general anaesthetics.

  8. Substrate-water exchange in photosystem II is arrested before dioxygen formation

    Science.gov (United States)

    Nilsson, Håkan; Rappaport, Fabrice; Boussac, Alain; Messinger, Johannes

    2014-07-01

    Light-driven oxidation of water into dioxygen, catalysed by the oxygen-evolving complex (OEC) in photosystem II, is essential for life on Earth and provides the blueprint for devices for producing fuel from sunlight. Although the structure of the OEC is known at atomic level for its dark-stable state, the mechanism by which water is oxidized remains unsettled. Important mechanistic information was gained in the past two decades by mass spectrometric studies of the H218O/H216O substrate-water exchange in the four (semi) stable redox states of the OEC. However, until now such data were not attainable in the transient states formed immediately before the O-O bond formation. Using modified photosystem II complexes displaying up to 40-fold slower O2 production rates, we show here that in the transient state the substrate-water exchange is dramatically slowed as compared with the earlier S states. This further constrains the possible sites for substrate-water binding in photosystem II.

  9. Natural spectroscopic hydrogen isotope transfer in alcohol dehydrogenase-catalysed reduction

    International Nuclear Information System (INIS)

    The enantiomeric purity of natural α-mono deuterated enantiomers, (R) and (S)ethanol-1-d1, in the alcohol produced by sugar fermentation with yeast was studied by 2H NMR using their esters derived from optical mandelic acid. The results of isotope tracing experiments show that the transfer pathways of the two eantiotopic hydrogens of the methylene group are different. It was observed that (S)-deuterium comes only from the medium water. The (R)-deuterium transferred by NADH in alcohol dehydrogenase reduction of the acetaldehyde is complex origin. Some of them originates from carbon bound hydrogen of the sugar, especially from C(4) position of glucose and most of them comes from water. Only a small portion of the NADH deuterium is incorporated indirectly from water through enzyme catalysed exchange between the pro-S site of NADH and flavin. When a carbonyl compound (ethyl acetoacetate) was reduced under the same conditions during the alcoholic fermentation, among the NADH-transferred deuterium, only a small portion comes from water while most comes from the unexchangeable positions of the glucose. (author)

  10. Sequence-defined bioactive macrocycles via an acid-catalysed cascade reaction

    Science.gov (United States)

    Porel, Mintu; Thornlow, Dana N.; Phan, Ngoc N.; Alabi, Christopher A.

    2016-06-01

    Synthetic macrocycles derived from sequence-defined oligomers are a unique structural class whose ring size, sequence and structure can be tuned via precise organization of the primary sequence. Similar to peptides and other peptidomimetics, these well-defined synthetic macromolecules become pharmacologically relevant when bioactive side chains are incorporated into their primary sequence. In this article, we report the synthesis of oligothioetheramide (oligoTEA) macrocycles via a one-pot acid-catalysed cascade reaction. The versatility of the cyclization chemistry and modularity of the assembly process was demonstrated via the synthesis of >20 diverse oligoTEA macrocycles. Structural characterization via NMR spectroscopy revealed the presence of conformational isomers, which enabled the determination of local chain dynamics within the macromolecular structure. Finally, we demonstrate the biological activity of oligoTEA macrocycles designed to mimic facially amphiphilic antimicrobial peptides. The preliminary results indicate that macrocyclic oligoTEAs with just two-to-three cationic charge centres can elicit potent antibacterial activity against Gram-positive and Gram-negative bacteria.

  11. Estimation of Kinetic Parameters for Enzyme Catalysed Batch Bioreactor for the Production of Ethanol from Corn

    Directory of Open Access Journals (Sweden)

    Z. R. Yelebe

    2014-03-01

    Full Text Available This paper addresses the challenge of estimating various kinetic parameters for the design of an optimized enzyme catalysed batch bioreactor of high efficiency and yield. Mathematical models were developed to describe the batch reaction time in relation to the substrate, enzyme and product concentration. The results obtained from the plots generated were: 35.50gmol/l.hr for the velocity of reaction of the enzymes (Vmax, 0.10049hr-1 for the maximum specific growth rate (µmax 826.45gmol/l for the Michaelis-Menten constant (Km, 0.005402577 for maintenance coefficient (Ms, 10.104kgCx/kgCs for yield of cell weight per unit weight of substrate (Ycx/CS, 0.05436kgCp/kgCs for yield of product weight per unit weight of substrate utilized (Ycp/CS and 0.01416 for endogenous decay coefficient (Kd for the design of the batch biochemical reactor. Hence, they are useful parameters for predicting the most appropriate batch reaction conditions and the efficiency of the bioreactor. The mathematical model predictions showed that it can be considered as a good complimentary tool to real system since the simulation results of the mathematical model agrees with experimental data reported in literature.

  12. Glycolysis of carbon fiber-epoxy unidirectional mat catalysed by sodium hydroxide

    Energy Technology Data Exchange (ETDEWEB)

    Zaini, Mariana Binti Mohd [School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia); Badri, Khairiah Haji [School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia and Polymer Research Center, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43 (Malaysia)

    2014-09-03

    This study was conducted to recycle carbon fibre-epoxy (CFRP) composite in woven sheet/ mat form. The CFRP was recycled through glycolysis with polyethlyene glycol (PEG 200) as the solvent. The CFRP was loaded into the solvent at a ratio of 4:1 (w/w). PEG200 was diluted with water to a ratio of 80:20 (v/v). This reaction was catalysed by sodium hydroxide (NaOH) solution with varying concentrations at 1.5, 1.7 and 1.9% (w/v). The glycolysis was conducted at 180-190 °C. The recovered CF (rCF) was analysed using Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray (EDX) while the degraded solution was analysed using FTIR and the epoxy content was determined. The FTIR spectrum of the rCF exhibited the disappearance of the COC peak belonged to epoxy and supported by the SEM micrographs that showed clear rCF. On the other hand, the analysed filtrate detected the disappearance of oxygen peak element in the EDX spectrum for all rCF samples. This gave an indication that the epoxy resin has been removed from the surface of the carbon fiber.

  13. Coordinence en catalyse hétèrogène appliquée Coordination in Applied Heterogeneous Catalysis

    Directory of Open Access Journals (Sweden)

    Montarnal R.

    2006-11-01

    Full Text Available L'exposé concerne l'activation des paraffines et des oléfines en présence d'hydrogène sur les métaux du groupe VIII. L'activation des paraffines fait intervenir les voies d'hydrogénolyse, d'isomérisation et de cyclisation. La profondeur d'hydrogénolyse permet de proposer un classement des métaux selon l'ordre croissant de la force de la liaison, paraffine chimisorbée-métal Pd-Pt-Ir-Rh-Ru-Os-Ni-Co-Fe L'activité spécifique d'hydrogénolyse, portée alors en fonction de la force de cette liaison, passe par un maximum autour de la position de Rh - Ru - Os. Les activités d'isomérisation et de cyclisation passent, par un maximum, pour la position de Pt. On retrouve ainsi la notion de force optimale de chimisorption pour catalyser une transformation précise. Sur la base des notions développées par Pearson, on peut alors considérer que la paraffine chimisorbée intervient plutôt en qualité de base «dure» de telle façon que la force de la liaison paraffine métal, augmente avec le caractère «dur» du métal. L'effet des ligands dans la sphère de coordination du site catalytique est ensuite analysé, en distinguant les ligands introduits lors de la préparation du catalyseur et ceux amenés par la phase réactionnelle. Les modifications ainsi apportées au caractère « dur ou mou » du site catalytique, conduisent à prévoir le sens de variation de l'activité d'hdrogénolyse ou de cyclisation. L'expérience confirme en gros les prévisions. L'étude de l'activation des oléfines est limitée au cas de l'éthylène, pour lequel on examine l'activité de l'hydrogénation et de l'échange éthylène-deutérium. La valeur de la multiplicité de cet échange permet de proposer un classement des métaux selon l'ordre croissant de la force de la liaison oléfine-métal Fe - Co-Ni-Ru-Rh-Os-Ir-Pt L'activité d'hydrogénation portée alors en fonction de la force de cette liaison, passe par un maximum autour (également de la position

  14. Bonding Description of the Harpoon Mechanism

    CERN Document Server

    Rodriguez-Mayorga, Mauricio; Salvador, Pedro; Sola, Miquel; Matito, Eduard

    2015-01-01

    The lowest-lying states of LiH have been widely used to develop and calibrate many different methods in quantum mechanics. In this paper we show that the charge-transfer processes occurring in these two states are a difficult test for chemical bonding descriptors and can be used to assess new bonding descriptors on its ability to recognize the harpoon mechanism. To this aim, we study the bond formation mechanism in a series of diatomic molecules. In all studied charge-transfer mechanisms, the maximal charge-transfer variation point along the bond formation path occurs when about half electron has been transferred from one atom to another. If the process takes places through a harpoon mechanism, this point of the reaction path coincides with the avoided crossing. The electron sharing indices and one-dimensional plots of the electron localization function and the Laplacian of the electron density along the molecular axis can be used to monitor the bond formation in diatomics and provide a distinction between th...

  15. Aspergillus nidulans α-galactosidase of glycoside hydrolase family 36 catalyses the formation of α-galacto-oligosaccharides by transglycosylation

    DEFF Research Database (Denmark)

    Nakai, Hiroyuki; Baumann, Martin; Petersen, B. O.;

    2010-01-01

    transglycosylate monosaccharides without the 6-hydroxymethyl group, i.e. xylose, l-arabinose, l-fucose and l-rhamnose, or with axial 3-OH, i.e. gulose, allose, altrose and l-rhamnose. Structural modelling using Thermotoga maritima GH36 α-galactosidase as the template and superimposition of melibiose from the...

  16. 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

  17. Negligible Isotopic Effect on Dissociation of Hydrogen Bonds.

    Science.gov (United States)

    Ge, Chuanqi; Shen, Yuneng; Deng, Gang-Hua; Tian, Yuhuan; Yu, Dongqi; Yang, Xueming; Yuan, Kaijun; Zheng, Junrong

    2016-03-31

    Isotopic effects on the formation and dissociation kinetics of hydrogen bonds are studied in real time with ultrafast chemical exchange spectroscopy. The dissociation time of hydrogen bond between phenol-OH and p-xylene (or mesitylene) is found to be identical to that between phenol-OD and p-xylene (or mesitylene) in the same solvents. The experimental results demonstrate that the isotope substitution (D for H) has negligible effects on the hydrogen bond kinetics. DFT calculations show that the isotope substitution does not significantly change the frequencies of vibrational modes that may be along the hydrogen bond formation and dissociation coordinate. The zero point energy differences of these modes between hydrogen bonds with OH and OD are too small to affect the activation energy of the hydrogen bond dissociation in a detectible way at room temperature. PMID:26967376

  18. 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

  19. 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.

  20. 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.

  1. Money and Nominal Bonds

    OpenAIRE

    Marchesiani, Alessandro; Senesi, Pietro

    2007-01-01

    This paper studies an economy with trading frictions, ex post heterogeneity and nominal bonds in a model à la Lagos and Wright (2005). It is shown that a strictly positive interest rate is a sufficient condition for the allocation with nominal bonds to be welfare improving. This result comes from the protection against the inflation tax.

  2. 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.))

  3. Nucleophilic addition of amines to the activated ethylene bond in non-aqueous media

    International Nuclear Information System (INIS)

    The kinetics of addition of a number of primary and secondary aliphatic amines to trans-(2-furyl) nitro ethylene (1) has been studied in solvents of various polarities (from acetonitrile, ε 37.5, to heptane, ε 1.89). It has been shown that the reaction is catalysed both by the amine reagent and by tertiary amines. On the basis of analyzing the observed kinetic regularities a stepwise reaction mechanism has been proposed which involves formation of zwitterionic intermediate (3) at the first equilibrium step (k1, K1) which is then converted into the reaction product by means of proton transfer in parallel routes, the non-catalytic one (k2) and that catalysed by the initial (K3) or tertiary (K4) amine. The observed high values of the deuterium isotope effects in the reaction (KH/KD ∼ 2.3 - 8.9) confirm that proton transfer occurs in the rate-limiting step of the reaction (primary kinetic isotope effect). The third order by amine kinetic route is observed in low polar media which is due to participation of amine dimers (R2 NH HNR2) in the reaction. The observed kinetic regularities are compared with those for the nucleophilic aromatic substitution reactions in low-polar media, and the conclusion has been made that the reaction route of the third order by amine proceeds as reversible nucleophilic attack by amine dimer and following base-catalysed transformation of the intermediate into the product. (author)

  4. Shape Bonding method

    Science.gov (United States)

    Pontius, James T. (Inventor)

    2010-01-01

    The present invention is directed to a method of bonding at least two surfaces together. The methods step of the present invention include applying a strip of adhesive to a first surface along a predefined outer boundary of a bond area and thereby defining a remaining open area there within. A second surface, or gusset plate, is affixed onto the adhesive before the adhesive cures. The strip of adhesive is allowed to cure and then a second amount of adhesive is applied to cover the remaining open area and substantially fill a void between said first and second surfaces about said bond area. A stencil may be used to precisely apply the strip of adhesive. When the strip cures, it acts as a dam to prevent overflow of the subsequent application of adhesive to undesired areas. The method results in a precise bond area free of undesired shapes and of a preferred profile which eliminate the drawbacks of the prior art bonds.

  5. 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...

  6. Solvent effects on hydrogen bonding between primary alcohols and esters

    Institute of Scientific and Technical Information of China (English)

    DHARMALINGAM K.; RAMACHANDRAN K.; SIVAGURUNATHAN P.

    2006-01-01

    The interaction by hydrogen bond formation of some primary alcohols (1-heptanol, 1-octanol and 1-decanol) with esters (methyl methacrylate, ethyl methacrylate and butyl methacrylate) was investigated in non-polar solvents viz., n-heptane,CCh and benzene by means of FTIR spectroscopy. Formation constants and free energy changes of complex formation were determined. The dependence of the equilibrium constants and free energy changes of complex formation on the alkyl chain length of both the alcohols and esters are discussed. The solvent effect on the hydrogen bond formation is discussed in terms of specific interaction between the solute and solvent.

  7. 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.; Meldal, M

    1998-01-01

    Protein disulphide isomerase is an enzyme that catalyses disulphide redox reactions in proteins. In this paper, fluorogenic and interchain disulphide bond containing peptide libraries and suitable substrates, useful in the study of protein disulphide isomerase, are described. In order to establish...... the chemistry required for the generation of a split-synthesis library, two substrates containing an interchain disulphide bond, a fluorescent probe and a quencher were synthesized. The library consists of a Cys residue flanked by randomized amino acid residues at both sides and the fluorescent Abz...... group at the amino terminal. All the 20 natural amino acids except Cys were employed. The library was linked to PEGA-beads via methionine so that the peptides could be selectively removed from the resin by cleavage with CNBr. A disulphide bridge was formed between the bead-linked library and a peptide...

  8. Interpretation of hydrogen bonding in the weak and strong regions using conceptual DFT descriptors

    OpenAIRE

    Özen, Alimet Sema; Ozen, Alimet Sema; De Proft, Frank; Aviyente , Viktorya; Geerlings, Paul

    2006-01-01

    Hydrogen bonding is among the most fundamental interactions in biology and chemistry, providing an extra stabilization of 1-40 kcal/mol to the molecular systems involved. This wide range of stabilization energy underlines the need for a general and comprehensive theory that will explain the formation of hydrogen bonds. While a simple electrostatic model is adequate to describe the bonding patterns in the weak and moderate hydrogen bond regimes, strong hydrogen bonds, on the other hand, requir...

  9. Significantly shorter Fe-S bond in cytochrome P450-I is consistent with greater reactivity relative to chloroperoxidase

    Science.gov (United States)

    Krest, Courtney M.; Silakov, Alexey; Rittle, Jonathan; Yosca, Timothy H.; Onderko, Elizabeth L.; Calixto, Julio C.; Green, Michael T.

    2015-09-01

    Cytochrome P450 (P450) and chloroperoxidase (CPO) are thiolate-ligated haem proteins that catalyse the activation of carbon hydrogen bonds. The principal intermediate in these reactions is a ferryl radical species called compound I. P450 compound I (P450-I) is significantly more reactive than CPO-I, which only cleaves activated C-H bonds. To provide insight into the differing reactivities of these intermediates, we examined CPO-I and P450-I using variable-temperature Mössbauer and X-ray absorption spectroscopies. These measurements indicate that the Fe-S bond is significantly shorter in P450-I than in CPO-I. This difference in Fe-S bond lengths can be understood in terms of variations in the hydrogen-bonding patterns within the ‘cys-pocket’ (a portion of the proximal helix that encircles the thiolate ligand). Weaker hydrogen bonding in P450-I results in a shorter Fe-S bond, which enables greater electron donation from the axial thiolate ligand. This observation may in part explain P450's greater propensity for C-H bond activation.

  10. Defective Cytochrome P450-Catalysed Drug Metabolism in Niemann-Pick Type C Disease

    Science.gov (United States)

    Wassif, Christopher A.; Gray, James; Burkert, Kathryn R.; Smith, David A.; Morris, Lauren; Cologna, Stephanie M.; Peer, Cody J.; Sissung, Tristan M.; Uscatu, Constantin-Daniel; Figg, William D.; Pavan, William J.; Vite, Charles H.; Porter, Forbes D.; Platt, Frances M.

    2016-01-01

    Niemann-Pick type C (NPC) disease is a neurodegenerative lysosomal storage disease caused by mutations in either the NPC1 or NPC2 gene. NPC is characterised by storage of multiple lipids in the late endosomal/lysosomal compartment, resulting in cellular and organ system dysfunction. The underlying molecular mechanisms that lead to the range of clinical presentations in NPC are not fully understood. While evaluating potential small molecule therapies in Npc1-/- mice, we observed a consistent pattern of toxicity associated with drugs metabolised by the cytochrome P450 system, suggesting a potential drug metabolism defect in NPC1 disease. Investigation of the P450 system in the context of NPC1 dysfunction revealed significant changes in the gene expression of many P450 associated genes across the full lifespan of Npc1-/- mice, decreased activity of cytochrome P450 reductase, and a global decrease of multiple cytochrome P450 catalysed dealkylation reactions. In vivo drug metabolism studies using a prototypic P450 metabolised drug, midazolam, confirmed dysfunction in drug clearance in the Npc1-/- mouse. Expression of the Phase II enzyme uridinediphosphate-glucuronosyltransferase (UGT) was also significantly reduced in Npc1-/- mice. Interestingly, reduced activity within the P450 system was also observed in heterozygous Npc1+/- mice. The reduced activity of P450 enzymes may be the result of bile acid deficiency/imbalance in Npc1-/- mice, as bile acid treatment significantly rescued P450 enzyme activity in Npc1-/- mice and has the potential to be an adjunctive therapy for NPC disease patients. The dysfunction in the cytochrome P450 system were recapitulated in the NPC1 feline model. Additionally, we present the first evidence that there are alterations in the P450 system in NPC1 patients. PMID:27019000

  11. Kinetics of acyl transfer reactions in organic media catalysed by Candida antarctica lipase B.

    Science.gov (United States)

    Martinelle, M; Hult, K

    1995-09-01

    The acyl transfer reactions catalysed by Candida antartica lipase B in organic media followed a bi-bi ping-pong mechanism, with competitive substrate inhibition by the alcohols used as acyl acceptors. The effect of organic solvents on Vm and Km was investigated. The Vm values in acetonitrile was 40-50% of those in heptane. High Km values in acetonitrile compared to those in heptane could partly be explained by an increased solvation of the substrates in acetonitrile. Substrate solvation caused a 10-fold change in substrate specificity, defined as (Vm/Km)ethyl octanoate/(Vm/Km)octanoic acid, going from heptane to acetonitrile. Deacylation was the rate determining step for the acyl transfer in heptane with vinyl- and ethyl octanoate as acyl donors and (R)-2-octanol as acyl acceptor. With 1-octanol, a rate determining deacylation step in heptane was indicated using the same acyl donors. Using 1-octanol as acceptor in heptane, S-ethyl thiooctanoate had a 25- to 30-fold lower Vm/Km value and vinyl octanoate a 4-fold higher Vm/Km value than that for ethyl octanoate. The difference showed to be a Km effect for vinyl octanoate and mainly a Km effect for S-ethyl thiooctanoate. The Vm values of the esterification of octanoic acid with different alcohols was 10-30-times lower than those for the corresponding transesterification of ethyl octanoate. The low activity could be explained by a low pH around the enzyme caused by the acid or a withdrawing of active enzyme by nonproductive binding by the acid. PMID:7669809

  12. Defective Cytochrome P450-Catalysed Drug Metabolism in Niemann-Pick Type C Disease.

    Science.gov (United States)

    Nicoli, Elena-Raluca; Al Eisa, Nada; Cluzeau, Celine V M; Wassif, Christopher A; Gray, James; Burkert, Kathryn R; Smith, David A; Morris, Lauren; Cologna, Stephanie M; Peer, Cody J; Sissung, Tristan M; Uscatu, Constantin-Daniel; Figg, William D; Pavan, William J; Vite, Charles H; Porter, Forbes D; Platt, Frances M

    2016-01-01

    Niemann-Pick type C (NPC) disease is a neurodegenerative lysosomal storage disease caused by mutations in either the NPC1 or NPC2 gene. NPC is characterised by storage of multiple lipids in the late endosomal/lysosomal compartment, resulting in cellular and organ system dysfunction. The underlying molecular mechanisms that lead to the range of clinical presentations in NPC are not fully understood. While evaluating potential small molecule therapies in Npc1-/- mice, we observed a consistent pattern of toxicity associated with drugs metabolised by the cytochrome P450 system, suggesting a potential drug metabolism defect in NPC1 disease. Investigation of the P450 system in the context of NPC1 dysfunction revealed significant changes in the gene expression of many P450 associated genes across the full lifespan of Npc1-/- mice, decreased activity of cytochrome P450 reductase, and a global decrease of multiple cytochrome P450 catalysed dealkylation reactions. In vivo drug metabolism studies using a prototypic P450 metabolised drug, midazolam, confirmed dysfunction in drug clearance in the Npc1-/- mouse. Expression of the Phase II enzyme uridinediphosphate-glucuronosyltransferase (UGT) was also significantly reduced in Npc1-/- mice. Interestingly, reduced activity within the P450 system was also observed in heterozygous Npc1+/- mice. The reduced activity of P450 enzymes may be the result of bile acid deficiency/imbalance in Npc1-/- mice, as bile acid treatment significantly rescued P450 enzyme activity in Npc1-/- mice and has the potential to be an adjunctive therapy for NPC disease patients. The dysfunction in the cytochrome P450 system were recapitulated in the NPC1 feline model. Additionally, we present the first evidence that there are alterations in the P450 system in NPC1 patients. PMID:27019000

  13. Defective Cytochrome P450-Catalysed Drug Metabolism in Niemann-Pick Type C Disease.

    Directory of Open Access Journals (Sweden)

    Elena-Raluca Nicoli

    Full Text Available Niemann-Pick type C (NPC disease is a neurodegenerative lysosomal storage disease caused by mutations in either the NPC1 or NPC2 gene. NPC is characterised by storage of multiple lipids in the late endosomal/lysosomal compartment, resulting in cellular and organ system dysfunction. The underlying molecular mechanisms that lead to the range of clinical presentations in NPC are not fully understood. While evaluating potential small molecule therapies in Npc1-/- mice, we observed a consistent pattern of toxicity associated with drugs metabolised by the cytochrome P450 system, suggesting a potential drug metabolism defect in NPC1 disease. Investigation of the P450 system in the context of NPC1 dysfunction revealed significant changes in the gene expression of many P450 associated genes across the full lifespan of Npc1-/- mice, decreased activity of cytochrome P450 reductase, and a global decrease of multiple cytochrome P450 catalysed dealkylation reactions. In vivo drug metabolism studies using a prototypic P450 metabolised drug, midazolam, confirmed dysfunction in drug clearance in the Npc1-/- mouse. Expression of the Phase II enzyme uridinediphosphate-glucuronosyltransferase (UGT was also significantly reduced in Npc1-/- mice. Interestingly, reduced activity within the P450 system was also observed in heterozygous Npc1+/- mice. The reduced activity of P450 enzymes may be the result of bile acid deficiency/imbalance in Npc1-/- mice, as bile acid treatment significantly rescued P450 enzyme activity in Npc1-/- mice and has the potential to be an adjunctive therapy for NPC disease patients. The dysfunction in the cytochrome P450 system were recapitulated in the NPC1 feline model. Additionally, we present the first evidence that there are alterations in the P450 system in NPC1 patients.

  14. Binding of reactive organophosphate by oximes via hydrogen bond

    Indian Academy of Sciences (India)

    Andrea Pappalardo; Maria E Amato; Francesco P Ballistreri; Valentina La Paglia Fragola; Gaetano A Tomaselli; Rosa Maria Toscano; Giuseppe Trusso Sfrazzetto

    2013-07-01

    In this contribution, the ability of simple oximes to bind a well-known nerve agent simulant (dimethylmethylphosphonate, DMMP) via hydrogen bond is reported. UV/Vis measurements indicate the formation of 1:1 complexes. 1H-, 31P-NMR titrations and T-ROESY experiments confirm that oximes bind the organophosphate via hydrogen bond.

  15. Corporate Bonds in Denmark

    DEFF Research Database (Denmark)

    Tell, Michael

    2015-01-01

    Corporate financing is the choice between capital generated by the corporation and capital from external investors. However, since the financial crisis shook the markets in 2007–2008, financing opportunities through the classical means of financing have decreased. As a result, corporations have...... 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...

  16. 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....

  17. The Halogen Bond

    Science.gov (United States)

    2016-01-01

    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design. PMID:26812185

  18. Tetra-substituted olefin synthesis using palladium-catalysed C-H activation

    OpenAIRE

    Lopez Suarez, Laura; Suarez, Laura Lopez

    2012-01-01

    In an effort to obtain more efficient and greener chemical transformations, a substantial amount of research interest has been directed towards the use of arene C-H bonds as functional groups. Hydroarylation of alkynes through direct functionalisation of C-H bonds has been studied in recent years leading to the development of high-yielding metal-mediated processes. The main aim of the current work is the addition of a third component in the hydroarylation of alkynes trough C-H activation, in ...

  19. Formation of Benzimidazoisoquinolinium and Benzimidazoisoindolinum Cyclic Systems by the Reaction of 2-(2-Alkynylphenyl)benzimidazoles with Iodine and Iodine-Iodine Interaction Including Halogen Bonding in Their Crystal Structures.

    Science.gov (United States)

    Matsumoto, Shoji; Kikuchi, Shu; Norita, Naoto; Masu, Hyuma; Akazome, Motohiro

    2016-07-01

    The reaction of 2-(2-alkynylphenyl)benz[d]imidazoles with molecular iodine constructed 5- and 6-membered rings as novel organic salts in high yield. The constituted number of ring systems was influenced by the substituent at the triple bond: 6-membered rings were formed from compounds bearing aryl substituents, whereas 5-membered ones were obtained from compounds with hydrogen or alkyl substituents. The products were obtained with triiodide as a counteranion; however, compounds with iodide were also obtainable under certain conditions. We also revealed that they had an iodine-iodine interaction included in halogen bonding between an iodo moiety of the cation and a triiodide or iodide of the counteranion. The iodine-iodine interaction was formed with greater preference than the electrostatic interaction between the cationic atom and triiodide or iodide. PMID:27258839

  20. Bond dissociation & electronegativity equalization

    OpenAIRE

    Verstraelen, Toon; Ayers, Paul W.; Van Speybroeck, Veronique; Waroquier, Michel

    2012-01-01

    It is well known that the Electrongativity Equalization Mtehod (EEM) fails to describe the charge distribution upon bond dissocation. In this presentation, the bond dissocation is studied with the Atom-Condensed Kohn-Sham DFT approximated to second order (ACKS2). After reviewing the basic equations, a two-fragment system is studied in the dissociation limit. The limiting behavior of the Coulomb interaction (1/r) and the Kohn-Sham matrix elements (exponentially decaying) are plugged into the e...

  1. Anodic bonded graphene

    OpenAIRE

    Balan, Adrian; Kumar, Rakesh; Boukhicha, Mohamed; Beyssac, Olivier; Bouillard, Jean-Claude; Taverna, Dario; Sacks, William; Marangolo, Massimiliano; Lacaze, Emmanuelle; Escoffier, Walter; Poumirol, Jean-Marie; Shukla, Abhay

    2010-01-01

    Abstract We show how to prepare graphene samples on a glass substrate with the anodic bonding method. In this method, a graphite precursor in flake form is bonded to a glass substrate with the help of an electrostatic field and then cleaved off to leave few layer graphene on the substrate. Now that several methods are available for producing graphene, the relevance of our method is in its simplicity and practicality for producing graphene samples of about 100 ?m lateral dimensions. This me...

  2. 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.

  3. Accumulation and reactions of H2O2 during the copper ion catalysed autoxidation of cysteine in alkaline medium

    OpenAIRE

    Koningsberger, D.C.; De Zwart, J.; Wolput, J.H.M.C. van; Cammen, J.C.J.M. van der

    1981-01-01

    The stoichiometry of the copper catalysed alkaline autoxidation of cysteine has been investigated. Products of this oxidation reaction are cystine, H{2}O{2} and H{2}O. No oxygen containing sulfur acids are produced as long as cysteine is present in the reaction liquid.The H{2}O{2} generated reacts with cysteine selectively to form cystine and H{2}O with r{H}{2}{O}{2} = k{H}{2}{O}{2} [CyS][H{2}O{2}] (k{H}{2}{O}{2} = 0.17 1 mol}-{}1{ s}-{}1{).The reaction between H{2}O{2} and cysteine is not ca...

  4. N-Heterocyclic Carbene-Catalysed Diastereoselective Vinylogous Michael Addition Reaction of gamma-Substituted deconjugated Butenolides

    KAUST Repository

    Guo, Hao

    2015-11-16

    An efficient N-heterocyclic carbene (NHC)-catalysed vinylogous Michael addition of deconjugated butenolides was developed. In the presence of 5 mol% of the NHC catalyst, both γ-alkyl and aryl-substituted deconjugated butenolides undergo vinylogous Michael addition with various α, β-unsaturated ketones, esters, or nitriles to afford γ,γ-disubstituted butenolides containing adjacent quaternary and tertiary carbon centers in good to excellent yields with excellent diastereoselectivities. In this process, the free carbene is assumed to act as a strong Brønsted base to promote the conjugate addition.

  5. Rh-catalysed [5 + 1] cycloaddition of allenylcyclopropanes and CO: reaction development and application to the formal synthesis of (-)-galanthamine.

    Science.gov (United States)

    Liu, Cheng-Hang; Yu, Zhi-Xiang

    2016-07-01

    A Rh-catalysed [5 + 1] cycloaddition of allenylcyclopropanes and CO has been developed to synthesize functionalized 2-methylidene-3,4-cyclohexenones. The scope of this methodology has been investigated, showing that various functional groups can be tolerated. Both di- and tri-substituted allenylcyclopropanes can be applied to this cycloaddition and the [5 + 1] cycloadducts with the E configuration were obtained as the major products. In addition, the present [5 + 1] cycloaddition reaction has been utilized as a key step in the formal synthesis of the natural product (-)-galanthamine. PMID:27253492

  6. Ru-Catalysed C–H Arylation of Indoles and Pyrroles with Boronic Acids: Scope and Mechanistic Studies

    Science.gov (United States)

    Sollert, Carina; Devaraj, Karthik; Orthaber, Andreas; Gates, Paul J; Pilarski, Lukasz T

    2015-01-01

    The Ru-catalysed C2–H arylation of indoles and pyrroles by using boronic acids under oxidative conditions is reported. This reaction can be applied to tryptophan derivatives and tolerates a wide range of functional groups on both coupling partners, including bromides and iodides, which can be further derivatised selectively. New indole-based ruthenacyclic complexes are described and investigated as possible intermediates in the reaction. Mechanistic studies suggest the on-cycle intermediates do not possess a para-cymene ligand and that the on-cycle metalation occurs through an electrophilic attack by the Ru centre. PMID:25689052

  7. Bond Length and Bond Order in One of the Shortest Cr-Cr Bonds

    OpenAIRE

    La Macchia, Giovanni; Aquilante, Francesco; Veryazov, Valera; Roos, Bjorn O.; Gagliardi, Laura

    2008-01-01

    Multiconfigurational quantum chemical calculations on the R-diimines dichromium compound confirm that the Cr-Cr bond, 1.80 A, is among the shortest Cr (I)-Cr (I) bonds. However, the bond between the two Cr atoms is only a quadruple bond rather than a quintuple bond. The reason why the bond is so short has to be attributed to the strain in the NCCN ligand moieties.

  8. Minimal model for dynamic bonding in colloidal transient networks

    Science.gov (United States)

    Krinninger, Philip; Fortini, Andrea; Schmidt, Matthias

    2016-04-01

    We investigate a model for colloidal network formation using Brownian dynamics computer simulations. Hysteretic springs establish transient bonds between particles with repulsive cores. If a bonded pair of particles is separated by a cutoff distance, the spring vanishes and reappears only if the two particles contact each other. We present results for the bond lifetime distribution and investigate the properties of the van Hove dynamical two-body correlation function. The model displays crossover from fluidlike dynamics, via transient network formation, to arrested quasistatic network behavior.

  9. 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.

  10. Benzyne in synthesis: a search for palladium catalysed three-component couplings

    OpenAIRE

    Henderson, Jaclyn

    2008-01-01

    It is over 100 years since scientists first postulated the existence of arynes as reactive intermediates. Their use in organic synthesis is now well-established and investigations into novel methods for their generation and utility in carbon-carbon bond forming reactions continue to this day. In 1983 Kobayashi and co-workers introduced a novel method of generating benzyne under mild conditions, using a fluoride induced decomposition of 2-(trimethylsilyl)phenyl triflate 1. This ...

  11. Production of uranium hexafluoride by the catalysed fluorox process: pilot plant and supporting bench-scale studies

    International Nuclear Information System (INIS)

    The feasibility of producing UF6 by the catalysed reaction of UF4 with oxygen (the Fluorox process) was investigated in a 150 mm diameter fluidised bed reactor and in supporting bench-scale experiments. The rate of the Fluorox reaction in batch experiments was increased by an order of magnitude with 1 to 5 per cent catalyst (containing 3 to 4 per cent platinum on alumina). The maximum UF6 production rate at 650 deg. C was 0.9 kg h-1. However, the platinum catalyst was completely poisoned after production of only 1 and 20 kg UF6 per kg of catalyst when using respectively French and British UF4. Regeneration of the catalyst was demonstrated to be technically feasible by washing with water or ammonium oxalate solution or treating with hydrogen and hydrogen fluoride at 350-650 deg. C. However, since the very fast rate of poisoning would necessitate higher catalyst concentrations and/or frequent regeneration, the catalysed Fluorox process in unlikely to be economically competitive with the direct fluorination of UF4

  12. Employing fly ash and FCC catalyser waste in recovering chrome (III from liquid effluent emitted by tanneries

    Directory of Open Access Journals (Sweden)

    Jeceny Amaya

    2010-04-01

    Full Text Available The present work studies the possibility of using two solid industrial wastes TERMOPAIPA's fly ash and ECOPETROL's alkaline hydrothermal treatments for obtaining zeolytic structures having better propierties; waste catalyser was calcined for eliminatin surface coke. Solids were characterised following treatment including DRX, BET area and CEC. A colorimetric method was standardised for determining chrome in solution; a response surface experimental design was implemented for finding optimum removal conditions. The most efficient adsorbent was fly ash treated with increased NaOH concentration; optimum condictions for removing chrome were: 58 minutes at 36ºC, 5.9 pH and 31% w/v solid removal. When reused, it was found that the two batches of treated fly ash became saturated following 6 cycles of use, whilst original ash and FCC Catalyser became saturated the second time they were used. Four de-absorbent agents were used for recovering chrome from adsorbent product H2SO4 0.6M being the best. Field trials showed that removal efficiency became reduced by the effect of other contaminantsm depending on the solution's initial concentration.

  13. TEXT tf coil bonding system

    International Nuclear Information System (INIS)

    An extensive bond test program was conducted prior to manufacturing and bonding the toroidal field (TF) coils for the Texas Experimental Tokamak (TEXT). The bonding materials consisted of fiberglass cloth with pre-impregnated, 'B' staged Hexcel F-159 resin. Approximately 100 double lap bond samples were constructed to test quality, strength, and repeatability of the bonds. The variables investigated included surface machining methods, surface preparations, bond sample size (planform area), bonding pressure, bonding temperature, and the number of laminations bonded simultaneously. Double lap shear tests conducted at room temperature resulted in ultimate shear strengths for all variables in the range of 3000 to 7000 psi with an average value of 5650 psi. Fatigue tests were also conducted to demonstrate bond integrity over the anticipated cycle lifetime of the TEXT machine (10/sup 6/ cycles) under simulated worst case conditions. 2 refs

  14. 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.

  15. 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.

  16. 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...

  17. Anodic bonded graphene

    Energy Technology Data Exchange (ETDEWEB)

    Balan, Adrian; Kumar, Rakesh; Boukhicha, Mohamed; Beyssac, Olivier; Bouillard, Jean-Claude; Taverna, Dario; Sacks, William; Shukla, Abhay [Universite Pierre et Marie Curie-Paris 6, CNRS-UMR7590, Institut de Mineralogie et de Physique des Milieux Condenses, 140 rue de Lourmel, Paris, F-75015 France (France); Marangolo, Massimiliano; Lacaze, Emanuelle; Gohler, Roger [Universite Pierre et Marie Curie-Paris 6, CNRS-UMR7588, Institut des Nanosciences de Paris, 140 rue de Lourmel, Paris, F-75015 France (France); Escoffier, Walter; Poumirol, Jean-Marie, E-mail: abhay.shukla@upmc.f [Laboratoire National des Champs Magnetiques Intenses, INSA UPS CNRS, UPR 3228, Universite de Toulouse, 143 avenue de Rangueil, 31400 Toulouse (France)

    2010-09-22

    We show how to prepare graphene samples on a glass substrate with the anodic bonding method. In this method, a graphite precursor in flake form is bonded to a glass substrate with the help of an electrostatic field and then cleaved off to leave few layer graphene on the substrate. Now that several methods are available for producing graphene, the relevance of our method is in its simplicity and practicality for producing graphene samples of about 100 {mu}m lateral dimensions. This method is also extensible to other layered materials. We discuss some detailed aspects of the fabrication and results from Raman spectroscopy, local probe microscopy and transport measurements on these samples.

  18. 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.

  19. Solvent deuterium isotope effect in the acid catalysed decarboxylation of phenylpropiolic acid in 85% D3PO4 in D2O

    International Nuclear Information System (INIS)

    A comparative study of the solvent deuterium isotope effect in the decarboxylation of phenylpropiolic acid (PPA) in 85% perdeuterated orthophosphoric acid, D3PO4/D2O, has been carried out and the ratio of the decarboxylation rate constants, k(H2O/k(D2O) equal 1.88±0.07, interpreted as caused by different dissociation constants Kh/Kd, of normal and perdeuterated phosphoric acids in H2O and D2O respectively, and by the deuterium discriminations in the subsequent steps of hydrogen transfer from π-complex to nearest Cα-carbon and sp2 (Cα-H) covalent bond formation. The detachment of carbon dioxide from PPA (decarboxylation step) is the fast process taking place or directly after the rate determining T.S. formation or stepwise by hydration of the vinyl cation and formation of the benzylacetic acid intermediate compound, which then decarboxylates in the kinetically insignificant step. The discussion is supplemented by calculating the k(H2O/k(D2O) ratios for decarboxylation scheme involving protonation of the triple bond in the rate determining step and for the reaction scheme involving fast isotope equilibrium between protonated water and protonated triple bond, followed by the rate determining transfer of proton from π-complex to the usual sP2 (CH) covalent bond. A good agreement between experimental solvent D2O I.E. and values calculated for reaction scheme involving proton transfer in the r.d.s. (what follows also from the 13C K.I.E. determinations in decarboxylation of PPA in H3PO4/H2O and D3PO4/D2O solvents) was found. (author)

  20. Flax Fiber - Interfacial Bonding

    Science.gov (United States)

    Measured flax fiber physical and chemical properties potentially impact bonding and thus stress transfer between the matrix and fiber within composites. These first attempts at correlating flax fiber quality and biofiber composites contain the initial steps towards identifying key flax fiber charac...

  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. Metallic Re-Re bond formation in different MRe2O6 (M=Fe, Co, Ni) rutile-like polymorphs: The role of temperature in high-pressure synthesis

    International Nuclear Information System (INIS)

    Different polymorphs of MRe2O6 (M=Fe, Co, Ni) with rutile-like structures were prepared using high-pressure high-temperature synthesis. For syntheses temperatures higher than ∼1573 K, tetragonal rutile-type structures (P42/mnm) with a statistical distribution of M- and Re-atoms on the metal position in the structure were observed for all three compounds, whereas rutile-like structures with orthorhombic or monoclinic symmetry, partially ordered M- and Re-ions on different sites and metallic Re-Re-bonds within Re2O10-pairs were found for CoRe2O6 and NiRe2O6 at a synthesis temperature of 1473 K. According to the XPS measurements, a mixture of Re+4/Re+6 and M2+/M3+ is present in both structural modifications of CoRe2O6 and NiRe2O6. The low-temperature forms contain more Re+4 and M3+ than the high-temperature forms. Tetragonal and monoclinic modifications of NiRe2O6 order with a ferromagnetic component at ∼24 K, whereas tetragonal and orthorhombic CoRe2O6 show two magnetic transitions: below ∼17.5 and 27 K for the tetragonal and below 18 and 67 K for the orthorhombic phase. Tetragonal FeRe2O6 is antiferromagnetic below 123 K. - Graphical abstract: Complex rhenium oxides MRe2O6 crystallize in different rutile-like polymorphs depending on synthesis temperature. Low temperature modifications contain chains of edge-sharing ReO6-octahedra with Re-Re bonds

  3. Oxytocin and mutual communication in mother-infant bonding

    Directory of Open Access Journals (Sweden)

    Miho eNagasawa

    2012-02-01

    Full Text Available Mother-infant bonding is universal to all mammalian species. In this review, we describe the manner in which reciprocal communication between the mother and infant leads to mother-infant bonding in rodents. In rats and mice, mother-infant bond formation is reinforced by various social stimuli, such as tactile stimuli and ultrasonic vocalizations from the pups to the mother, and feeding and tactile stimulation from the mother to the pups. Some evidence suggests that mother and infant can develop a cross-modal sensory recognition of their counterpart during this bonding process. Neurochemically, oxytocin in the neural system plays a pivotal role in each side of the mother-infant bonding process, although the mechanisms underlying bond formation in the brains of infants has not yet been clarified. Impairment of mother-infant bonding, that is, deprivation of social stimuli from the mother, strongly influences offspring sociality, including maternal behavior toward their own offspring in their adulthood, implying a non-genomic transmission of maternal environment, even in rodents. The comparative understanding of cognitive functions between mother and infants, and the biological mechanisms involved in mother-infant bonding may help us understand psychiatric disorders associated with mother-infant relationships.

  4. Tetra-bonding of C, N and O at solid surface

    OpenAIRE

    Sun, Chang Q.

    2008-01-01

    In order to gain advanced understanding of the kinetics and dynamics of C, N, and O reacting with a solid surface, it is necessary to consider the reaction from the perspectives of bond formation, bond dissociation, bond relaxation, bond vibration, and the associated charge redistribution and polarization and the energetic response of the involved atoms and valence electrons. The sp-orbital hybridization is found necessary for these concerned reactions associated with strongly anisotropic bon...

  5. C-H bond halogenation catalyzed or mediated by copper: an overview.

    Science.gov (United States)

    Hao, Wenyan; Liu, Yunyun

    2015-01-01

    Carbon-halogen (C-X) bonds are amongst the most fundamental groups in organic synthesis, they are frequently and widely employed in the synthesis of numerous organic products. The generation of a C-X bond, therefore, constitutes an issue of universal interest. Herein, the research advances on the copper-catalyzed and mediated C-X (X = F, Cl, Br, I) bond formation via direct C-H bond transformation is reviewed. PMID:26664634

  6. Development of HIP bonding procedure and mechanical properties of HIP bonded joints for reduced activation ferritic steel F-82H

    International Nuclear Information System (INIS)

    Structural materials of blanket components in fusion DEMO reactors will receive a neutron wall load more than 3-5MW/m2 as well as exposed by surface heat flux more than 0.5MW/m2. A reduced activation ferritic steel F-82H has been developed by JAERI in collaboration with NKK from viewpoints of resistance for high temperature and neutron loads and lower radioactivity. This study intends to obtain basic performance of F-82H to establish the fabrication procedure of the first wall and blanket box by using Hot Isostatic Pressing (HIP) bonding. Before HIP bonding tests, effects of heat treatment temperature and surface roughness on mechanical properties of joints were investigated in the heat treatment tests and diffusion bonding tests, respectively. From these results, the optimum HIP bonding conditions and the post heat treatment were selected. Using these conditions, the HIP bonding tests were carried out to evaluate HIP bondability and to obtain mechanical properties of the joints. Sufficient HIP bonding performance was obtained under the temperature of 1040degC, the compressive stress of 150MPa, the holding time of 2h, and the surface roughness ∼μ m. Mechanical properties of HIP bonded joints with these conditions were similar to those of as-received base metal. An oxide formation on the surface to be bonded would need to be avoided for sufficient bonding. The bonding ratio, Charpy impact value and fatigue performance of the joints strongly depended on the HIP conditions, especially temperature, while micro-structure, Vickers hardness and tensile properties had little dependence on the HIP temperature. The surface roughness strongly affected the bonding ratio and would be required to be in the level of a few μ m. In the HIP bonding test of the welded material, the once-melted surface could be jointed by the HIP bonding under the above-mentioned procedure. (J.P.N.)

  7. The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation

    Directory of Open Access Journals (Sweden)

    Abas Mohsenzadeh

    2013-11-01

    Full Text Available The effect of carbon monoxide (CO co-adsorption on the dissociation of water on the Ni(111 surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction.

  8. 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-...

  9. Void-free wafer-level adhesive bonding utilizing modified poly (diallyl phthalate)

    Science.gov (United States)

    Zhong, Fang; Dong, Tao; Yong, He; Yan, Su; Wang, Kaiying

    2013-12-01

    A new thermosetting polymer, modified poly (diallyl phthalate) (PDAP), is used as intermediate layer to realize a void-free wafer-level transfer bonding, in which the bonding interface contains patterned metal. Through glass-silicon bonding experiments, bonding defects are easily recognized with light microscopy. Three typical defect types are identified as: uneven flow defect, particle defect and bubble defect. The processing parameters, such as bonding pressure, pre-baking temperature, polymer thickness and coating conditions, have been optimized based on analysis of the defect formation. The optimized conditions have yielded a void-free wafer-level adhesive bonding. Then, the die shearing test indicates a good bonding strength. Additionally, the transfer bonding process is applied in SOI-silicon bonding as a practical example of MEMS fabrication.

  10. Palladium-Catalysed Enantioselective Conjugate Addition of Aromatic Amines to α,β-Unsaturated N-Imides. Effect of the Chelating Moiety

    NARCIS (Netherlands)

    Phua, Pim Huat; Vries, Johannes G. de; Hii, King Kuok

    2005-01-01

    Palladium-catalysed enantioselective additions of aromatic amines to α,β-unsaturated N-imides are reported. The N-substituent of the Michael acceptor appears to have an unusual modulating effect on the amine activity. The effects of introducing different substituents are examined. Overall, the yield

  11. Zn(OTf)2-catalysed indolylation and pyrrolylation of isatins: Efficient synthesis and biochemical assay of 3,3-di(heteroaryl)oxindoles

    Indian Academy of Sciences (India)

    C Praveen; S Narendiran; P Dheenkumar; P T Perumal

    2013-11-01

    An efficient and cheap synthetic approach to 3,3-di(indolyl)oxindoles and 3,3-di(pyrrolyl) oxindoles has been developed via Zn(OTf)2 catalysed indolylation and pyrrolylation of isatins. A preliminary biochemical assay of the synthesized molecules in rodent models were performed to estimate the serum glutamate oxaloacetate transaminase and malondialdehyde levels.

  12. Is There a Quadruple Bond in C2?

    Science.gov (United States)

    de Sousa, David Wilian Oliveira; Nascimento, Marco Antonio Chaer

    2016-05-10

    The chemical structure of the ground state of C2 has been the subject of intense debate after the suggestion that the molecule could exhibit a "fourth" covalent bond. In this paper, we investigate this problem explicitly avoiding all the points of conflict from the previous papers to show that there is no quadruple bond in C2. The generalized product function energy partitioning (GPF-EP) method has been applied to calculate the interference energy (IE) that accounts for the formation of covalent bonds for each bond of the molecule. The IE analysis shows that for the standard σ and π bonds interference exhibits the expected behavior, while for the "fourth" bond interference is a destabilizing factor. To make sure this could not be attributed to a new kind of bond, we performed an equivalent analysis for the (3)Σ(-) excited state of C3 molecule in which similar "bonding" occurs between the two ending carbon atoms. We also show that the difference in force constants of C2 and acetylene can be rationalized in terms of the amount of charge density in the internuclear region by looking at the changes in the overlaps between orbitals along the bond axis. PMID:27045682

  13. Localized CO2 laser bonding process for MEMS packaging

    Institute of Scientific and Technical Information of China (English)

    SUN Li; A. P. MALSHE; S. CUNNINGHAM; A. MORRIS

    2006-01-01

    The packaging poses a critical challenge for commercialization of MEMS products. Major problems with the packaging process include degraded reliability caused by the excess stress due to thermal mismatch and altered performance of the MEMS device after packaging caused by thermal exposure. The localized laser bonding technique for ceramic MEMS packaging to address above-mentioned challenges was investigated. A continuous wave CO2 laser was used to locally heat sealing material for ceramic MEMS package lid to substrate bonding. To determine the laser power density and scanning speed,finite element analysis thermal models were constructed to simulate the localized laser bonding process. Further,the effect of external pressure at sealing ring on the bonding formation was studied. Pull testing results show that the scanning speed and external pressure have significant influence on the pull strength at the bonding interface. Cross-sectional microscopy of the bonding interface indicates that the packages bonded with relatively low scanning speed and external pressure conditions have higher bonding quality. This research demonstrates the potential of localized laser bonding process for ceramic MEMS packaging.

  14. A 19F NMR study of C-I....pi- halogen bonding

    DEFF Research Database (Denmark)

    Hauchecorne, Dieter; vand er Veken, Benjamin J.; Herrebout, Wouter A.; Hansen, Poul Erik

    The formation of halogen bonded complexes between toluene-d8 and the perfluoroiodopropanes 1-C3F7I and 2-C3F7I has been investigated using 19F NMR spectroscopy. For both Lewis acids, evidence was found for the formation of a C–I⋯π halogen bonded complex. The complex formed is a 1:1 type. Using...

  15. The electrochemical oxidation of toluene catalysed by Co(II) in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide.

    Science.gov (United States)

    Balaji, S; Kannan, K; Moon, I S

    2015-12-14

    The electrochemical oxidation of toluene in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([bmpyr](+)[Ntf2](-)) was investigated by using cyclic voltammetry and galvanostatic electrolysis in the presence of Co(II) at a Pt disc working electrode. Cyclic voltammetry (CV) investigations revealed that Co(II)-Co(III) oxidation is a diffusion controlled electron transfer process. The diffusion coefficient values of Co(II) were found to increase from 0.38 × 10(-7) to 1.9 × 10(-7) cm(2) s(-1) as the temperature was increased from 25 °C to 80 °C. The CV peak current for toluene electro-oxidation increased by nearly 7 fold in the presence of Co(II) demonstrating a good catalytic effect. Co(II) catalysed galvanostatic electrolysis of toluene at room temperature has shown that benzaldehyde was formed along with a small quantity of 3-methyl-1-hexanol. PMID:26538114

  16. N-H∙∙∙O, O-H∙∙∙O hydrogen-bonded supramolecular sheet formation in the bis(2-aminoanilinium) fumarate, 3-methylanilinium hydrogen fumarate and 4-chloroanilinium hydrogen fumarate salts.

    Science.gov (United States)

    Sathya, D; Jagan, R; Padmavathy, R; Kumar, R Mohan; Sivakumar, K

    2013-08-01

    In bis(2-aminoanilinum) fumarate, 2C₆H₉N₂⁺·C₄H₂O₄²⁻, (I), the asymmetric unit consists of two aminoanilinium cations and one fumarate dianion, whereas in 3-methylanilinium hydrogen fumarate, C₇H₁₀N⁺·C₄H3O₄⁻, (II), and 4-chloroanilinium hydrogen fumarate, C₆H₇ClN⁺·C₄H3O₄⁻, (III), the asymmetric unit contains two symmetry-independent hydrogen fumate anions and anilinium cations with a slight difference in their geometric parameters; the two salts are isostructural. In (II) and (III), the carboxylic acid H atoms of the anions are disordered across both ends of the anion, with equal site occupancies of 0.50. Both the 4-chloroanilinium cations of (III) are disordered over two orientations with major occupancies fixed at 0.60 in each case. The hydrogen fumarate anions of (II) and (III) form one-dimensional anionic chains linked through O-H∙∙∙O hydrogen bonds. Salts (II) and (III) form two-dimensional supramolecular sheets built from R₄⁴16), R₄⁴(18), R₅⁵(25) and C₂²(14) motifs extending parallel to the (010) plane, whereas in (I), an (010) sheet is formed built from two R₄³(13) motifs, two R₂²(9) motifs and an R₄⁴(18) motif. PMID:23907887

  17. Domestic Bond Market Development

    OpenAIRE

    Jonathan A. Batten; Szilagyi, Peter G.

    2007-01-01

    A two-tiered approach to financial market development aimed at both bank and bond market reform would also be complementary to longer term economic development, provided services could be delivered through efficient financial and legal institutions (Chakraborty and Ray 2006) and there was strong protection for investors and sound fiscal and monetary policy management by government (Burger and Warnock 2006b). Historically, local issuers tend to issue in the major currencies (U.S. dollars, yen,...

  18. Disulfide bonds of acetylcholinesterase

    International Nuclear Information System (INIS)

    The positions of the inter- and intrasubunit disulfide bridges were established for the 11S form of acetylcholinesterase (AChE) isolated from Torpedo californica. A major form of AChE localized within the basal lamina of the synapse is a dimensionally asymmetric molecule which contains either two (13S) or three (17S) sets of catalytic subunits linked to collagenous and non-collagenous structural subunits. Limited proteolysis yields a tetramer of catalytic subunits which sediments at 11S. Each catalytic subunit contains 8 cysteine residues. Initially, these Cys residues were identified following trypsin digestion of the reduced protein alkylated with [14C]-iodoacetate. Peptides were resolved by gel filtration followed by reverse phase HPLC. To determine the disulfide bonding profile, native non-reduced 11S AChE was treated with a fluorescent, sulfhydryl-specific reagent, monobromobimane, prior to proteolytic digestion. One fluorescent Cys peptide was identified indicating that a single sulfhydryl residue was present in its reduced form. Three pairs of disulfide bonded peptides were identified, sequenced, and localized in the polypeptide chain. The Cys residue that is located in the C-terminal tryptic peptide was disulfide bonded to an identical peptide and thus forms the intersubunit crosslink. Finally, the cysteine positions have been compared with the sequence of the homologous protein, thyroglobulin. Both likely share a common pattern of folding

  19. Integration of European Bond Markets

    OpenAIRE

    Christiansen, Charlotte

    2012-01-01

    I investigate the time variation in the integration of EU government bond markets. The integration is measured by the explanatory power of European factor portfolios for the individual bond markets for each year. The integration of the government bond markets is stronger for EMU than non-EMU members and stronger for old than new EU members. The integration is weaker for the sovereign debt crisis countries than for other countries. The integration of the EU bond markets is decreasing over time...

  20. Doseringsutrustningen SafeBond Electronic

    OpenAIRE

    Bodegren, Patrik

    2003-01-01

    This thesis for the Master of Science degree was performed at Oppunda Electronics AB. The assignment was to further develop an existing prototype of a dispensing equipment. The dispensing equipment doses a kind of glue, bonding which dentist use to mend teeth. The dispensing equipment is adjusted to dose 12 micro litres of bonding. With the dispensing equipment SafeBond Electronic the user can reduce the bonding consumption with approximately 50 percent. Furthermore will the handling of the b...

  1. Enantioselective synthesis of aziridines using asymmetric transfer hydrogenation as a precursor for chiral derivatives used as bonding agent for rocket solid propellants

    Directory of Open Access Journals (Sweden)

    Aparecida M. Kawamoto

    2002-11-01

    Full Text Available A rapid, expedient and enantioselective method for the synthesis of beta-hydroxy amines and monosubstituted aziridines in up to 99% e.e., via asymmetric transfer hydrogenation of a-amino ketones and cyclisation through treatment with tosyl chloride and base, is described. (1R,2R-N-(para-toluenesulfonyl-1,2-ethylenediamine with formic acid has been utilised as a ligand for the Ruthenium (II catalysed enantioselective transfer hydrogenation of the ketones.The chiral 2-methyl aziridine, which is a potentially more efficient bonding agent for Rocket Solid Propellant has been successfully achieved.

  2. Chemical bonding and electronic structure of fullerene-based compounds

    International Nuclear Information System (INIS)

    This talk will focus on the nature of bonding of fullerenes with other materials as demonstrated by synchrotron radiation and x-ray photoemission. Adsorption of C60 on metallic and semiconducting substrates occurs via charge transfer from the substrate to a LUMO-derived resonance, resulting in Fermi level alignment and dipole formation. Bonding of metal atoms to C60 depends on the metal work function and bulk cohesive energy. Evaporation of high cohesive energy materials onto a fullerene substrate results in metal cluster nucleation and limited C60 disruption for transition metals. Low cohesive energy metals form compounds with a degree of ionic character related to the metal work function. Photoemission results show the formation of ionic K-fulleride compounds while greater hybridization is observed for Ca-rich fullerides. Finally the electronic structure of fluorinated and hydrogenated fullerenes demonstrate changes in states derived from C60 π bonds due to reaction of dangling bonds

  3. Diffusion Bonding of Silicon Carbide for MEMS-LDI Applications

    Science.gov (United States)

    Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, J. Douglas

    2007-01-01

    A robust joining approach is critically needed for a Micro-Electro-Mechanical Systems-Lean Direct Injector (MEMS-LDI) application which requires leak free joints with high temperature mechanical capability. Diffusion bonding is well suited for the MEMS-LDI application. Diffusion bonds were fabricated using titanium interlayers between silicon carbide substrates during hot pressing. The interlayers consisted of either alloyed titanium foil or physically vapor deposited (PVD) titanium coatings. Microscopy shows that well adhered, crack free diffusion bonds are formed under optimal conditions. Under less than optimal conditions, microcracks are present in the bond layer due to the formation of intermetallic phases. Electron microprobe analysis was used to identify the reaction formed phases in the diffusion bond. Various compatibility issues among the phases in the interlayer and substrate are discussed. Also, the effects of temperature, pressure, time, silicon carbide substrate type, and type of titanium interlayer and thickness on the microstructure and composition of joints are discussed.

  4. Bonding in Molecular Crystals from the Local Electronic Pressure Viewpoint

    CERN Document Server

    Tsirelson, Vladimir G; Tokatly, Ilya V

    2015-01-01

    The spatial distribution of the internal pressure of an electron fluid, which spontaneously arises at the formation of a molecule or a crystal, is linked to the main features of chemical bonding in molecular crystals. The local pressure is approximately expressed in terms of the experimental electron density and its derivatives using the density functional formalism and is applied to identify the bonding features in benzene, formamide and chromium hexacarbonyl. We established how the spatial regions of compression and stretching of the electron fluid in these solids reflect the typical features of chemical bonds of different types. Thus, the internal electronic pressure can serve as a bonding descriptor, which has a clear physical meaning and reveals the specific features of variety of the chemical bonds expressing them in terms of the electron density.

  5. 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

  6. Iron(III) porphyrin-catalysed oxidation reactions by -chloroperbenzoic acid: Nature of reactive intermediates

    Indian Academy of Sciences (India)

    A Agarwala; V Bagchi; D Bandyopadhyay

    2005-03-01

    The reaction of -chloroperbenzoic (-CPBA) acid with meso-tetrakis (pentafluorophenyl) porphynatoiron(III) chloride (F20TPPFe(III)Cl) has been studied in dichloromethane and acetonitrile medium at 25 ± 1° C. The reactive intermediates formed in this reaction have been quantitatively trapped by 2,4,6-tri -butylphenol (TTBP) in both the solvents. It has been observed that the kinetic plots of the formation of TTBP$^{\\bullet}$ radical in dichloromethane are all multiexponential, supporting the formation of more than one reactive intermediate in this solvent. In acetonitrile solvent the formation of TTBP$^{\\bullet}$ radical was however observed to be distinctly single exponential. Different kinds of reactive intermediates are proposed in these two solvents.

  7. 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

  8. Molecular orbital analysis of the hydrogen bonded water dimer

    OpenAIRE

    Bo Wang; Wanrun Jiang; Xin Dai; Yang Gao; Zhigang Wang; Rui-Qin Zhang

    2016-01-01

    As an essential interaction in nature, hydrogen bonding plays a crucial role in many material formations and biological processes, requiring deeper understanding. Here, using density functional theory and post-Hartree-Fock methods, we reveal two hydrogen bonding molecular orbitals crossing the hydrogen-bond’s O and H atoms in the water dimer. Energy decomposition analysis also shows a non-negligible contribution of the induction term. Our finding sheds light on the essential understanding of ...

  9. From an insulating to a superfluid pair-bond liquid

    OpenAIRE

    Cuoco, Mario; Ranninger, Julius

    2006-01-01

    We study an exchange coupled system of itinerant electrons and localized fermion pairs resulting in a resonant pairing formation. This system inherently contains resonating fermion pairs on bonds which lead to a superconducting phase provided that long range phase coherence between their constituents can be established. The prerequisite is that the resonating fermion pairs can become itinerant. This is rendered possible through the emergence of two kinds of bond-fermions: individual and compo...

  10. FTIR adsorption studies of H2O and CH3OH in the isostructural H-SSZ-13 and H-SAPO-34: formation of H-bonded adducts and protonated clusters.

    Science.gov (United States)

    Bordiga, Silvia; Regli, Laura; Lamberti, Carlo; Zecchina, Adriano; Bjørgen, Morten; Lillerud, Karl Petter

    2005-04-28

    The acidity of the isostructural H-SSZ-13 and H-SAPO-34 has been investigated by transmission FTIR spectroscopy using H2O and CH3OH as molecular probes. Interactions between the zeolitic samples and the probe molecules led to perturbations and proton transfers directly related to the acidity of the materials. The entire set of acidic sites in H-SSZ-13 interacts with H2O and CH3OH to give H-bonded adducts or protonated species. H3O+ is not formed in appreciable amounts upon H2O adsorption on H-SSZ-13, but at high coverages H2O generates clusters that have a proton affinity sufficiently high to abstract protons from the zeolite framework. Parallel experiments carried out for H-SAPO-34 showed that the H2O clusters abstract protons from Brønsted sites only to a minor extent. Moving to CH3OH, even if it has a higher proton affinity than H2O and should expectingly experience an easier protonation, proton transfer is totally absent in H-SAPO-34 under our set of conditions. The clear evidence of methanol protonation in H-SSZ-13 definitely states the strong acidic character of this material. When irreversibly adsorbed CH3OH is present in H-SSZ-13, an appreciable amount of (CH3)2O is formed upon heating to 573 K. Compared to its SAPO analogue, the present set of data indisputably points to H-SSZ-13 as the strongest Brønsted acidic material. PMID:16851897

  11. Terahertz Vibrations and Hydrogen-Bonded Networks in Crystals

    Directory of Open Access Journals (Sweden)

    Masae Takahashi

    2014-03-01

    Full Text Available The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating noncovalent interactions has established the position of THz spectroscopy as a powerful tool for detecting the weak bonding in crystals. In this review, we are going to introduce, briefly, the contribution of weak bonds in the construction of molecular crystals first, and then, we will review THz spectroscopy as a powerful tool for detecting the formation of weak bonds and will show the significant contribution of advanced computational codes in treating noncovalent interactions. From the second section, following the Introduction, to the seventh section, before the conclusions, we describe: (1 the crystal packing forces, the hydrogen-bonded networks and their contribution to the construction of organic crystals; (2 the THz vibrations observed in hydrogen-bonded molecules; (3 the computational methods for analyzing the THz vibrations of hydrogen-bonded molecules; (4 the dispersion correction and anharmonicity incorporated into the first-principles calculations and their effect on the peak assignment of the THz spectrum (5 the temperature dependence; and (6 the polarization dependence of the THz spectrum.

  12. 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 ...

  13. 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 are...

  14. Hydrogen bonds in PC{sub 61}BM solids

    Energy Technology Data Exchange (ETDEWEB)

    Sheng, Chun-Qi [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 311121 (China); Li, Wen-Jie; Du, Ying-Ying; Chen, Guang-Hua; Chen, Zheng; Li, Hai-Yang; Li, Hong-Nian, E-mail: phylihn@mail.zju.edu.cn [Department of Physics, Zhejiang University, Hangzhou 310027 (China)

    2015-09-15

    We have studied the hydrogen bonds in PC{sub 61}BM solids. Inter-molecular interaction is analyzed theoretically for the well-defined monoclinic (P2{sub 1}/n) structure. The results indicate that PC{sub 61}BM combines into C–H⋯O{sub d} bonded molecular chains, where O{sub d} denotes the doubly-bonded O atom of PC{sub 61}BM. The molecular chains are linked together by C–H⋯O{sub s} bonds, where O{sub s} denotes the singly-bonded O atom of PC{sub 61}BM. To reveal the consequences of hydrogen bond formation on the structural properties of PC{sub 61}BM solids (not limited to the monoclinic structure), we design and perform some experiments for annealed samples with the monoclinic (P2{sub 1}/n) PC{sub 61}BM as starting material. The experiments include differential scanning calorimetry, X-ray diffraction and infrared absorption measurements. Structural phase transitions are observed below the melting point. The C–H⋯O{sub d} bonds seem persisting in the altered structures. The inter-molecular hydrogen bonds can help to understand the phase separation in polymer/PC{sub 61}BM blends and may be responsible for the existence of liquid PC{sub 61}BM.

  15. Non-stabilized nucleophiles in Cu-catalysed dynamic kinetic asymmetric allylic alkylation

    Science.gov (United States)

    You, Hengzhi; Rideau, Emeline; Sidera, Mireia; Fletcher, Stephen P.

    2015-01-01

    The development of new reactions forming asymmetric carbon-carbon bonds has enabled chemists to synthesize a broad range of important carbon-containing molecules, including pharmaceutical agents, fragrances and polymers. Most strategies to obtain enantiomerically enriched molecules rely on either generating new stereogenic centres from prochiral substrates or resolving racemic mixtures of enantiomers. An alternative strategy--dynamic kinetic asymmetric transformation--involves the transformation of a racemic starting material into a single enantiomer product, with greater than 50 per cent maximum yield. The use of stabilized nucleophiles (pKa =50, more than 25 orders of magnitude more basic than the nucleophiles that are typically used in such transformations. Organometallic reagents are generated in situ from alkenes by hydrometallation and give highly enantioenriched products under mild reaction conditions. The method is used to synthesize natural products that possess activity against tuberculosis and leprosy, and an inhibitor of para-aminobenzoate biosynthesis. Mechanistic studies indicate that the reaction proceeds through a rapidly isomerizing intermediate. We anticipate that this approach will be a valuable complement to existing asymmetric catalytic methods.

  16. Silicon carbide wafer bonding by modified surface activated bonding method

    Science.gov (United States)

    Suga, Tadatomo; Mu, Fengwen; Fujino, Masahisa; Takahashi, Yoshikazu; Nakazawa, Haruo; Iguchi, Kenichi

    2015-03-01

    4H-SiC wafer bonding has been achieved by the modified surface activated bonding (SAB) method without any chemical-clean treatment and high temperature annealing. Strong bonding between the SiC wafers with tensile strength greater than 32 MPa was demonstrated at room temperature under 5 kN force for 300 s. Almost the entire wafer has been bonded very well except a small peripheral region and few voids. The interface structure was analyzed to verify the bonding mechanism. It was found an amorphous layer existed as an intermediate layer at the interface. After annealing at 1273 K in vacuum for 1 h, the bonding tensile strength was still higher than 32 MPa. The interface changes after annealing were also studied. The results show that the thickness of the amorphous layer was reduced to half after annealing.

  17. Fluxless eutectic bonding of GaAs-on-Si by using Ag/Sn solder

    Science.gov (United States)

    Eo, Sung-Hwa; Kim, Dae-Seon; Jeong, Ho-Jung; Jang, Jae-Hyung

    2013-11-01

    Fluxless GaAs-on-Si wafer bonding using Ag/Sn solder was investigated to realize uniform and void-free heterogeneous material integration. The effects of the diffusion barrier, Ag/Sn thickness, and Ar plasma treatment were studied to achieve the optimal fluxless bonding process. Pt on a GaAs wafer and Mo on a Si wafer act as diffusion barriers by preventing the flow of Ag/Sn solder into both the wafers. The bonding strength is closely related to the Ag/Sn thickness and Ar plasma treatment. A shear strength test was carried out to investigate the bonding strength. Under identical bonding conditions, the Ag/Sn thickness was optimized to achieve higher bonding strength and to avoid the formation of voids due to thermal stress. An Ar plasma pretreatment process improved the bonding strength because the Ar plasma removed carbon contaminants and metal-oxide bonds from the metal surface.

  18. Credit default swaps, bond spreads and the bond market

    OpenAIRE

    Zhu, Meicheng

    2014-01-01

    With the rapid development of the credit default swap (CDS) market, the issue of how the introduction of CDSs affects the corporate bond market has been of particular interest to researchers and policy makers. This has been investigated in the literature from two perspectives. One is to examine the relationship between the CDS and the bond markets in price discovery, and the other is concerned with researching the CDS trading effects on bond spreads. Referring to the former approach, most rel...

  19. Solder extrusion pressure bonding process and bonded products produced thereby

    Science.gov (United States)

    Beavis, Leonard C.; Karnowsky, Maurice M.; Yost, Frederick G.

    1992-01-01

    Production of soldered joints which are highly reliable and capable of surviving 10,000 thermal cycles between about -40.degree. C. and 110.degree. C. Process involves interposing a thin layer of a metal solder composition between the metal surfaces of members to be bonded and applying heat and up to about 1000 psi compression pressure to the superposed members, in the presence of a reducing atmosphere, to extrude the major amount of the solder composition, contaminants including fluxing gases and air, from between the members being bonded, to form a very thin, strong intermetallic bonding layer having a thermal expansion tolerant with that of the bonded members.

  20. Avoiding silicon/glass bonding damage with fusion bonding method

    Institute of Scientific and Technical Information of China (English)

    Daohong Yang(杨道虹); Chen Xu(徐晨); Guangdi Shen(沈光地)

    2004-01-01

    A novel fusion bonding method between silicon and glass with Nd:YAG laser is described.This method overcomes the movable mechanical parts damage caused by the electrostatics force in micro-electronic machine-system(MEMS)device during the anodic bonding. The diameter of laser spot is 300 μm,the power of laser is 100 W,the laser velocity for bonding is 0.05 m/s,the average bonding tension is 6.3 MPa.It could distinctly reduce and eliminate the defects and damage,especially in movable sensitive mechanical parts of MEMS device.