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Sample records for c-c bond formation

  1. C-C bond formation and cleavage in radical enzymes, a theoretical perspective.

    Science.gov (United States)

    Himo, Fahmi

    2005-02-25

    Quantum chemical methods are today a viable tool in the study of enzyme catalysis. The development of new density functional techniques and the enormous advancement in computer power have made it possible to accurately describe active sites of enzymes. This review gives a brief account of the methods and models used in this field. Three specific enzymes are discussed: pyruvate-formate lyase (PFL), spore photoproduct lyase (SPL), and benzylsuccinate synthase (BSS). What these enzymes have in common is that they use radical chemistry to catalyze C-C bond formation or cleavage reactions.

  2. 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.

  3. 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

    Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach

  4. Chiral BINOL-derived phosphoric acids: privileged Brønsted acid organocatalysts for C-C bond formation reactions.

    Science.gov (United States)

    Zamfir, Alexandru; Schenker, Sebastian; Freund, Matthias; Tsogoeva, Svetlana B

    2010-12-07

    BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Brønsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C-C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel-Crafts, aza-ene-type, Diels-Alder, as well as cascade and multi-component reactions.

  5. The mechanism of hydrocarbon oxygenate reforming: C-C bond scission, carbon formation, and noble-metal-free oxide catalysts.

    Science.gov (United States)

    Lykhach, Yaroslava; Neitzel, Armin; Ševčíková, Klára; Johánek, Viktor; Tsud, Nataliya; Skála, Tomáš; Prince, Kevin C; Matolín, Vladimír; Libuda, Jörg

    2014-01-01

    Towards a molecular understanding of the mechanism behind catalytic reforming of bioderived hydrocarbon oxygenates, we explore the C-C bond scission of C2 model compounds (acetic acid, ethanol, ethylene glycol) on ceria model catalysts of different complexity, with and without platinum. Synchrotron photoelectron spectroscopy reveals that the reaction pathway depends very specifically on both the reactant molecule and the catalyst surface. Whereas C-C bond scission on Pt sites and on oxygen vacancies involves intermittent surface carbon species, the reaction occurs without any carbon formation and deposition for ethylene glycol on CeO2(111). Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Palladium(II)-Catalyzed C-H Bond Activation/C-C and C-O Bond Formation Reaction Cascade: Direct Synthesis of Coumestans.

    Science.gov (United States)

    Neog, Kashmiri; Borah, Ashwini; Gogoi, Pranjal

    2016-12-02

    A palladium catalyzed cascade reaction of 4-hydroxycoumarins and in situ generated arynes has been developed for the direct synthesis of coumestans. This cascade strategy proceeds via C-H bond activation/C-O and C-C bond formations in a single reaction vessel. This methodology affords moderate to good yields of coumestans and is tolerant of a variety of functional groups including halide. The methodology was applied to the synthesis of natural product flemichapparin C.

  7. Low-oxidation state indium-catalyzed C-C bond formation.

    Science.gov (United States)

    Schneider, Uwe; Kobayashi, Shu

    2012-08-21

    The development of innovative metal catalysis for selective bond formation is an important task in organic chemistry. The group 13 metal indium is appealing for catalysis because indium-based reagents are minimally toxic, selective, and tolerant toward various functional groups. Among elements in this group, the most stable oxidation state is typically +3, but in molecules with larger group 13 atoms, the chemistry of the +1 oxidation state is also important. The use of indium(III) compounds in organic synthesis has been well-established as Lewis acid catalysts including asymmetric versions thereof. In contrast, only sporadic examples of the use of indium(I) as a stoichiometric reagent have been reported: to the best of our knowledge, our investigations represent the first synthetic method that uses a catalytic amount of indium(I). Depending on the nature of the ligand or the counteranion to which it is coordinated, indium(I) can act as both a Lewis acid and a Lewis base because it has both vacant p orbitals and a lone pair of electrons. This potential ambiphilicity may offer unique reactivity and unusual selectivity in synthesis and may have significant implications for catalysis, particularly for dual catalytic processes. We envisioned that indium(I) could be employed as a metallic Lewis base catalyst to activate Lewis acidic boron-based pronucleophiles for selective bond formation with suitable electrophiles. Alternatively, indium(I) could serve as an ambiphilic catalyst that activates both reagents at a single center. In this Account, we describe the development of low-oxidation state indium catalysts for carbon-carbon bond formation between boron-based pronucleophiles and various electrophiles. We discovered that indium(I) iodide was an excellent catalyst for α-selective allylations of C(sp(2)) electrophiles such as ketones and hydrazones. Using a combination of this low-oxidation state indium compound and a chiral semicorrin ligand, we developed catalytic

  8. Lewis acid mediated tandem reaction of propargylic alcohols to tetrazoles involving C-O- and C-C-bond cleavage reactions and a C-N-bond formation.

    Science.gov (United States)

    Song, Xian-Rong; Han, Ya-Ping; Qiu, Yi-Feng; Qiu, Zi-Hang; Liu, Xue-Yuan; Xu, Peng-Fei; Liang, Yong-Min

    2014-09-15

    A novel and direct synthesis of 1-aryl-5-arylvinyl-tetrazoles from easily prepared propargylic alcohols and TMSN3 is developed in the presence of TMSCl under mild conditions (TMS = trimethylsilyl). The process involves an allenylazide intermediate, followed by a C-C-bond cleavage and C-N-bond formation to afford the desired products. Moreover, this method offers a good functional-group applicability and can be scaled-up to grams (yield up to 85 %). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Sodium dichloroiodate promoted C-C bond cleavage: An efficient ...

    Indian Academy of Sciences (India)

    SAKET B BHAGAT

    2018-02-01

    Feb 1, 2018 ... benzimidazoles/benzothiazoles/benzoxazoles under mild conditions. This tandem process involved a C-C bond cleavage and C-N bond formation. Keywords. Benzimidazole/benzothiazole/benzoxazole; β-diketones; NaICl2; C-C bond cleavage. 1. Introduction. Nitrogen-containing five-member heterocyclic ...

  10. The new C-C bond formation in the reaction of o-amidophenolate indium(III) complex with alkyl iodides.

    Science.gov (United States)

    Piskunov, Alexandr V; Meshcheryakova, Irina N; Fukin, Georgy K; Shavyrin, Andrei S; Cherkasov, Vladimir K; Abakumov, Gleb A

    2013-08-07

    The reaction of bis(4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-amidophenolato)indium(III) anion with alkyl iodides is reported. This process includes oxidative addition of two RI (R = Me, Et) molecules to the non-transition metal complex and results in an alkyl transfer to ring carbon atoms with the formation of two new C-C bonds. The interaction proceeds at mild conditions and gives new indium(III) derivatives containing iminocyclohexa-1,4-dienolate type ligands.

  11. 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.

  12. A Novel Strategy for Biomass Upgrade: Cascade Approach to the Synthesis of Useful Compounds via C-C Bond Formation Using Biomass-Derived Sugars as Carbon Nucleophiles

    Directory of Open Access Journals (Sweden)

    Sho Yamaguchi

    2016-07-01

    Full Text Available Due to the depletion of fossil fuels, biomass-derived sugars have attracted increasing attention in recent years as an alternative carbon source. Although significant advances have been reported in the development of catalysts for the conversion of carbohydrates into key chemicals (e.g., degradation approaches based on the dehydration of hydroxyl groups or cleavage of C-C bonds via retro-aldol reactions, only a limited range of products can be obtained through such processes. Thus, the development of a novel and efficient strategy targeted towards the preparation of a range of compounds from biomass-derived sugars is required. We herein describe the highly-selective cascade syntheses of a range of useful compounds using biomass-derived sugars as carbon nucleophiles. We focus on the upgrade of C2 and C3 oxygenates generated from glucose to yield useful compounds via C-C bond formation. The establishment of this novel synthetic methodology to generate valuable chemical products from monosaccharides and their decomposed oxygenated materials renders carbohydrates a potential alternative carbon resource to fossil fuels.

  13. A Novel Strategy for Biomass Upgrade: Cascade Approach to the Synthesis of Useful Compounds via C-C Bond Formation Using Biomass-Derived Sugars as Carbon Nucleophiles.

    Science.gov (United States)

    Yamaguchi, Sho; Baba, Toshihide

    2016-07-20

    Due to the depletion of fossil fuels, biomass-derived sugars have attracted increasing attention in recent years as an alternative carbon source. Although significant advances have been reported in the development of catalysts for the conversion of carbohydrates into key chemicals (e.g., degradation approaches based on the dehydration of hydroxyl groups or cleavage of C-C bonds via retro-aldol reactions), only a limited range of products can be obtained through such processes. Thus, the development of a novel and efficient strategy targeted towards the preparation of a range of compounds from biomass-derived sugars is required. We herein describe the highly-selective cascade syntheses of a range of useful compounds using biomass-derived sugars as carbon nucleophiles. We focus on the upgrade of C2 and C3 oxygenates generated from glucose to yield useful compounds via C-C bond formation. The establishment of this novel synthetic methodology to generate valuable chemical products from monosaccharides and their decomposed oxygenated materials renders carbohydrates a potential alternative carbon resource to fossil fuels.

  14. Tailored synthesis of various nanomaterials by using a graphene-oxide-based gel as a nanoreactor and nanohybrid-catalyzed C-C bond formation.

    Science.gov (United States)

    Biswas, Abhijit; Banerjee, Arindam

    2014-12-01

    New graphene oxide (GO)-based hydrogels that contain vitamin B2/B12 and vitamin C (ascorbic acid) have been synthesized in water (at neutral pH value). These gel-based soft materials have been used to synthesize various metal nanoparticles, including Au, Ag, and Pd nanoparticles, as well as nanoparticle-containing reduced graphene oxide (RGO)-based nanohybrid systems. This result indicates that GO-based gels can be used as versatile reactors for the synthesis of different nanomaterials and hybrid systems on the nanoscale. Moreover, the RGO-based nanohybrid hydrogel with Pd nanoparticles was used as an efficient catalyst for C-C bond-formation reactions with good yields and showed high recyclability in Suzuki-Miyaura coupling reactions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. 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.

  16. An Electron-Poor C64 Nanographene by Palladium-Catalyzed Cascade C-C Bond Formation: One-Pot Synthesis and Single-Crystal Structure Analysis.

    Science.gov (United States)

    Seifert, Sabine; Shoyama, Kazutaka; Schmidt, David; Würthner, Frank

    2016-05-23

    Herein, we report the one-pot synthesis of an electron-poor nanographene containing dicarboximide groups at the corners. We efficiently combined palladium-catalyzed Suzuki-Miyaura cross-coupling and dehydrohalogenation to synthesize an extended two-dimensional π-scaffold of defined size in a single chemical operation starting from N-(2,6-diisopropylphenyl)-4,5-dibromo-1,8-naphthalimide and a tetrasubstituted pyrene boronic acid ester as readily accessible starting materials. The reaction of these precursors under the conditions commonly used for Suzuki-Miyaura cross-coupling afforded a C64 nanographene through the formation of ten C-C bonds in a one-pot process. Single-crystal X-ray analysis unequivocally confirmed the structure of this unique extended aromatic molecule with a planar geometry. The optical and electrochemical properties of this largest ever synthesized planar electron-poor nanographene skeleton were also analyzed. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  17. Self assembly of dialkoxo bridged dinuclear Fe(III) complex of pyridoxal Schiff base with C-C bond formation - structure, spectral and magnetic properties

    Czech Academy of Sciences Publication Activity Database

    Murašková, V.; Szabó, N.; Pižl, M.; Hoskovcová, I.; Dušek, Michal; Huber, Š.; Sedmidubský, D.

    2017-01-01

    Roč. 461, May (2017), s. 111-119 ISSN 0020-1693 R&D Projects: GA ČR(CZ) GA15-12653S; GA MŠk LO1603 EU Projects: European Commission(XE) CZ.2.16/3.1.00/24510 Institutional support: RVO:68378271 Keywords : iron (III) dinuclear complex * dialkoxo bridged pyridoxal Schiff base * C-C bond * crystal structure * magnetic properties Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.002, year: 2016

  18. Carbocyclic C-C Bond Formation: Intramolecular Radical Ring Closure to Yield Diastereomerically Pure (7'S-Me- or 7'R-Me-) Carba-LNA Nucleotide Analogs.

    Science.gov (United States)

    Plashkevych, Oleksandr; Upadhayaya, Ram Shankar; Chattopadhyaya, Jyoti

    2017-06-19

    In light of the impressive gene-silencing properties of carba-LNA modified oligo DNA and RNA, both in antisense RNA and siRNA approaches, which have been confirmed as proof-of-concept for biochemical applications in post-transcriptional gene silencing, we envision the true potential of carba-LNA modifications to be revealed soon. Herein we provide detailed protocols for synthesis of carba-LNA-A, -G, -5-Me C, and -T nucleosides on a medium/large scale (gram scale), as well as important guidelines for incorporation of these modified carba-LNAs into DNA or RNA oligonucleotides. Creation of a stereoselective C-C bond during the 5-exo radical intramolecular cyclization involves trapping of a C2' radical intermediate intramolecularly by the vicinal double bond of a C4'-tethered ─CH2 -CH═CH2 group. All diastereomers of substituted carba-LNAs are now available in pure form. The present procedure allows carba-LNA to be commercialized for medicinal or biotechnological purposes. © 2017 by John Wiley & Sons, Inc. Copyright © 2017 John Wiley & Sons, Inc.

  19. On the Michael addition of water to C = C bonds

    NARCIS (Netherlands)

    Chen, B.

    2015-01-01

    ?-Hydroxy carbonyl compounds are an important class of compounds often found as a common structural motif in natural products. Although the molecules themselves look rather simple, their synthesis can be challenging. Water addition to conjugated C = C bonds opens up a straightforward route for the

  20. Nonaqueous and halide-free route to crystalline BaTiO3, SrTiO3, and (Ba,Sr)TiO3 nanoparticles via a mechanism involving C-C bond formation.

    Science.gov (United States)

    Niederberger, Markus; Garnweitner, Georg; Pinna, Nicola; Antonietti, Markus

    2004-07-28

    A novel nonaqueous route for the preparation of nanocrystalline BaTiO(3), SrTiO(3), and (Ba,Sr)TiO(3) has been developed. In a simple one-pot reaction process, the elemental alkaline earth metals are directly dissolved in benzyl alcohol at slightly elevated temperatures. After the addition of Ti(O(i)Pr)(4), the reaction mixture is heated to 200 degrees C, resulting in the formation of a white precipitate. XRD measurements prove the exclusive presence of the perovskite phase without any other crystalline byproducts such as BaCO(3) or TiO(2). TEM investigations reveal that the BaTiO(3) nanoparticles are nearly spherical in shape with diameters ranging from 4 to 5 nm. The SrTiO(3) particles display less uniform particle shapes, and the size varies between 5 and 10 nm. Lattice fringes observed in HRTEM measurements further prove the high crystallinity of the nanoparticles. Surprisingly, GC-MS analysis of the reaction solution after hydrothermal treatment shows that hardly any ether formation occurs during the BaTiO(3) synthesis. Instead, the presence of 4-phenyl-2-butanol in stoichiometric amounts gives evidence that the formation mechanism proceeds mainly via a novel pathway involving C-C bond formation between benzyl alcohol and the isopropanolate ligand.

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

    Science.gov (United States)

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

    2016-07-04

    Unusual cleavage of P-C and C-H bonds of the P2 N2 ligand, in heteroleptic [Ni(P2 N2 )(diphosphine)](2+) complexes under mild conditions, results in the formation of an iminium formyl nickelate featuring a C,P,P-tridentate coordination mode. The structures of both the heteroleptic [Ni(P2 N2 )(diphosphine)](2+) complexes and the resulting iminium formyl nickelate have been characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were employed to investigate the mechanism of the P-C/C-H bond cleavage, which involves C-H bond cleavage, hydride rotation, Ni-C/P-H bond formation, and P-C bond cleavage. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. A new face of phenalenyl-based radicals in the transition metal-free C-H arylation of heteroarenes at room temperature: trapping the radical initiatorviaC-C σ-bond formation.

    Science.gov (United States)

    Ahmed, Jasimuddin; P, Sreejyothi; Vijaykumar, Gonela; Jose, Anex; Raj, Manthan; Mandal, Swadhin K

    2017-11-01

    The radical-mediated transition metal-free approach for the direct C-H bond functionalization of arenes is considered as a cost effective alternative to transition metal-based catalysis. An organic ligand-based radical plays a key role by generating an aryl radical which undergoes a subsequent functionalization process. The design principle of the present study takes advantage of a relatively stable odd alternant hydrocarbon-based phenalenyl (PLY) radical. In this study, the first transition metal-free catalyzed direct C-H arylation of a variety of heteroarenes such as azoles, furan, thiophene and pyridine at room temperature has been reported using a phenalenyl-based radical without employing any photoactivation step. This protocol has been successfully applied to the gram scale synthesis of core moieties of bioactive molecules. The phenalenyl-based radical initiator has been characterized crystallographically by trapping it via the formation of a C-C σ-bond between the phenalenyl radical and solvent-based radical species.

  3. Borane-catalyzed cracking of C-C bonds in coal; Boran-katalysierte C-C-Bindungungsspaltung in Steinkohle

    Energy Technology Data Exchange (ETDEWEB)

    Narangerel, J.; Haenel, M.W. [Max-Planck-Institut fuer Kohlenforschung, Muelheim an der Ruhr (Germany)

    1998-09-01

    Coal, especially coking coal, was reacted with hydrogen at comparatively mild reaction conditions (150-280 degrees centigrade, 20 MPa hydrogen pressure) in the presence of catalysts consisting of borange reagents and certain transition metal halides to obtaine more than 80 percent of pyridine-soluble products. The influence of the degree of coalification, catalyst and temperature on the borane-catalyzed hydrogenolysis of C-C bonds in coal was investigated. (orig.) [Deutsch] Steinkohlen, insbesondere im Inkohlungsbereich der Fettkohlen (Kokskohlen), werden in Gegenwart von Katalysatoren aus Boran-Reagentien und bestimmten Uebergangsmetallhalogeniden mit Wasserstoff bei vergleichsweise milden Reaktionsbedingungen (250-280 C, 20 MPa Wasserstoffdruck) in zu ueber 80% pyridinloesliche Produkte umgewandelt. Der Einfluss von Inkohlungsgrad, Katalysator und Temperatur auf die Boran-katalysierte C-C-Bindungshydrogenolyse in Kohle wurde untersucht. (orig.)

  4. Alkane Activation at Ambient Temperatures: Unusual Selectivities, C-C, C-H Bond Scission versus C-C Bond Coupling

    NARCIS (Netherlands)

    Trionfetti, C.; Agiral, A.; Gardeniers, Johannes G.E.; Lefferts, Leonardus; Seshan, Kulathuiyer

    2008-01-01

    Activating bonds: A cold plasma generated by dielectric barrier discharge in a microreactor converts alkanes (C1–C3) at atmospheric pressure. Large amounts of products with higher molecular weight than the starting hydrocarbons are observed showing that C-H activation at lower T favourably leads to

  5. Why is the linking C-C bond in tetrahedranyltetrahedrane so short?

    Science.gov (United States)

    Mo, Yirong

    2006-02-02

    [structure: see text]. The block-localized wave function (BLW) method has been employed to probe the origin of the very short linking C-C bond (1.436 A) in tetrahedranyltetrahedrane. Computations show that the vicinal hyperconjugative interactions between the two tetrahedranyl groups is stronger than the conjugation in butadiene, and if there were no hyperconjugation effect, the bond distance would be 1.491 A. Thus, both the hybridization mode and hyperconjugative interactions contribute to the shortening of the central C-C bond in tetrahedranyltetrahedrane.

  6. Direct-dynamics VTST study of hydrogen or deuterium abstraction and C-C bond formation or dissociation in the reactions of CH3 + CH4, CH3 + CD4, CH3D + CD3, CH3CH3 + H, and CH3CD3 + D

    Science.gov (United States)

    Ramazani, Shapour

    2013-05-01

    Direct-dynamics variational transition-state theory calculations are studied at the MPWB1K/6-311++G(d,p) level for the four parts of reactions. The first part is hydrogen or deuterium abstraction in the reactions of CH3 + CH4, CH3 + CD4, and CH3D + CH3. The second part involves C-C bond formation in these reactions. The third one is the reactions of CH3CH3 + H and CH3CD3 + D to form of H2, HD, and D2. The last one is the dissociation of C-C bonds in the last group of reactions. The ground-state vibrational adiabatic potential is plotted for all channels. We have carried out direct-dynamics calculations of the rate constants, including multidimensional tunneling in the temperature range T = 200-2200 K. The results of CVT/μOMT rate constants were in good agreement with the experimental data which were available for some reactions. Small-curvature tunneling and Large-curvature tunneling with the LCG4 version were used to include the quantum effects in calculation of the rate constants. To try to find the region of formation and dissociation of bounds we have also reported the variations of harmonic vibrational frequencies along the reaction path. The thermally averaged transmission probability (P(E)exp (-ΔE/RT)) and representative tunneling energy at 298 K are reported for the reactions in which tunneling is important. We have calculated kinetic isotope effect which shows tunneling and vibrational contributions are noticeable to determine the rate constant. Nonlinear least-squares fitting is used to calculate rate constant expressions in the temperature range 200-2200 K. These expressions revealed that pre-exponential factor includes two parts; the first part is a constant number which is important at low temperatures while the second part is temperature dependent which is significant at high temperatures.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shaoguang [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Li, Haixia [Texas A & M Univ., College Station, TX (United States). Dept. of Chemistry; Appel, Aaron M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Hall, Michael B. [Texas A & M Univ., College Station, TX (United States). Dept. of Chemistry; Bullock, R. Morris [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2016-06-07

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

  8. Laser photolysis studies of ω-bond dissociation in aromatic carbonyls with a C-C triple bond stimulated by triplet sensitization.

    Science.gov (United States)

    Yamaji, Minoru; Horimoto, Ami; Marciniak, Bronislaw

    2017-07-14

    We have prepared three types of carbonyl compounds, benzoylethynylmethyl phenyl sulfide (2@SPh), (p-benzoyl)phenylethynylmethyl phenyl sulfide (3@SPh) and p-(benzoylethynyl)benzyl phenyl sulfide (4@SPh) with benzoyl and phenylthiylmethyl groups, which are interconnected with a C-C triple bond and a phenyl ring. Laser flash photolysis of 3@SPh and 4@SPh in acetonitrile provided the transient absorption spectra of the corresponding triplet states where no chemical reactions were recognized. Upon laser flash photolysis of 2@SPh, the absorption band due to the phenylthiyl radical (PTR) was obtained, indicating that the C-S bond cleaved in the excited state. Triplet sensitization of these carbonyl compounds using acetone and xanthone was conducted using laser photolysis techniques. The formation of triplet 3@SPh was seen in the transient absorption, whereas the PTR formation was observed for 2@SPh and 4@SPh, indicating that the triplet states were reactive for the C-S bond dissociation. The C-S bond dissociation mechanism for 4@SPh upon triplet sensitization is discussed in comparison with those for 2@SPh and 3@SPh.

  9. The use of ultrasmall iron(0) nanoparticles as catalysts for the selective hydrogenation of unsaturated C-C bonds.

    Science.gov (United States)

    Kelsen, Vinciane; Wendt, Bianca; Werkmeister, Svenja; Junge, Kathrin; Beller, Matthias; Chaudret, Bruno

    2013-04-28

    The performance of well-defined ultrasmall iron(0) nanoparticles (NPs) as catalysts for the selective hydrogenation of unsaturated C-C and C=X bonds is reported. Monodisperse iron nanoparticles of about 2 nm size are synthesized by the decomposition of {Fe(N[Si(CH3)3]2)2}2 under dihydrogen. They are found to be active for the hydrogenation of various alkenes and alkynes under mild conditions and weakly active for C=O bond hydrogenation.

  10. Synthesis and systematic evaluation of symmetric sulfonated centrally C-C bonded cyanine near-infrared dyes for protein labelling

    NARCIS (Netherlands)

    Wal, Van Der Steffen; Kuil, Joeri; Valentijn, A.R.P.M.; Leeuwen, Van Fijs W.B.

    2016-01-01

    The most commonly used near-infrared cyanine dyes contain an aryl ether that is not fully stable towards nucleophiles. Replacement of the aryl ether by a more stable carbon-carbon bond can improve the stability. In this work we have synthesized a series of four negatively-charged symmetrical C-C

  11. Effect of the Co-C(C60(-)) bond formation on magnetic properties of the ionic complex {cryptand[2,2,2] x (Na+)} x {Co(II)TPP x (C60(-))} x (C6H4Cl2)2.

    Science.gov (United States)

    Konarev, Dmitri V; Khasanov, Salavat S; Otsuka, Akihiro; Saito, Gunzi; Lyubovskaya, Rimma N

    2009-08-28

    A new ionic complex {cryptand[2,2,2] x (Na(+))} x {Co(II)TPP x (C(60)(-))} x (C(6)H(4)Cl(2))(2) has been obtained as single crystals by a diffusion technique. It involves coordination {Co(II)TPP x u(C(60)(-))} units and bulky {cryptand[2,2,2] x (Na(+))} cations. The Co-C(C(60)(-)) coordination bond is short (2.262(2) A at 100 K) which provides ordering in the C(60)(-) anions. This is the first ordered structure of {Co(II)TPP x (C(60)(-))}. The coordination bonds weaken upon heating to be 2.316(4) A at 250 K. As a result, the C(60)(-) anions begin to rotate at 250 K about the Co-C bond between two orientations. The complex is diamagnetic from 4 up to 320 K. The Co-C bonds dissociate above 320 K only to form unbound paramagnetic Co(II)TPP and C(60)(*-) species. The process is accompanied by the reversible increase in magnetic susceptibility of the complex and the appearance of a new broad EPR signal with g = 2.1187 and a linewidth of approximately 120 mT (350 K). The signal was attributed to both paramagnetic Co(II)TPP and C(60)(*-), which showed strong exchange interaction.

  12. Direct Mechanism of the First Carbon-Carbon Bond Formation in the Methanol-to-Hydrocarbons Process.

    Science.gov (United States)

    Wu, Xinqiang; Xu, Shutao; Zhang, Wenna; Huang, Jindou; Li, Jinzhe; Yu, Bowen; Wei, Yingxu; Liu, Zhongmin

    2017-07-24

    In the past two decades, the reaction mechanism of C-C bond formation from either methanol or dimethyl ether (DME) in the methanol-to-hydrocarbons (MTH) process has been a highly controversial issue. Described here is the first observation of a surface methyleneoxy analogue, originating from the surface-activated DME, by in situ solid-state NMR spectroscopy, a species crucial to the first C-C bond formation in the MTH process. New insights into the first C-C bond formation were provided, thus suggesting DME/methanol activation and direct C-C bond formation by an interesting synergetic mechanism, involving C-H bond breakage and C-C bond coupling during the initial methanol reaction within the chemical environment of the zeolite catalyst. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    NARCIS (Netherlands)

    Perez, Manuel; Fananas Mastral, Martin; Bos, Pieter H.; Rudolph, Alena; Harutyunyan, Syuzanna R.; Feringa, Ben L.

    Carbon-carbon bond formation is the basis for the biogenesis of nature's essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C-C bond formation to yield single enantiomers from several organometallic reagents.

  14. The role of the steps in the cleavage of the C-C bond during ethanol oxidation on platinum electrodes.

    Science.gov (United States)

    Colmati, Flavio; Tremiliosi-Filho, Germano; Gonzalez, Ernesto R; Berná, Antonio; Herrero, Enrique; Feliu, Juan M

    2009-10-28

    Ethanol oxidation has been studied on stepped platinum single crystal electrodes in acid media using electrochemical and Fourier transform infrared (FTIR) techniques. The electrodes used belong to two different series of stepped surfaces: those having (111) terraces with (100) monoatomic steps and those with (111) terraces with (110) monoatomic steps. The behaviors of the two series of stepped surfaces for the oxidation of ethanol are very different. On the one hand, the presence of (100) steps on the (111) terraces provides no significant enhancement of the activity of the surfaces. On the other hand, (110) steps have a double effect on the ethanol oxidation reaction. At potentials below 0.7 V, the step catalyzes the C-C bond cleavage and also the oxidation of the adsorbed CO species formed. At higher potentials, the step is not only able to break the C-C bond, but also to catalyze the oxidation of ethanol to acetic acid and acetaldehyde. The highest catalytic activity from voltammetry for ethanol oxidation was obtained with the Pt(554) electrode.

  15. Selective C-C and C-H bond activation/cleavage of pinene derivatives: synthesis of enantiopure cyclohexenone scaffolds and mechanistic insights.

    Science.gov (United States)

    Masarwa, Ahmad; Weber, Manuel; Sarpong, Richmond

    2015-05-20

    The continued development of transition-metal-mediated C-C bond activation/cleavage methods would provide even more opportunities to implement novel synthetic strategies. We have explored the Rh(I)-catalyzed C-C activation of cyclobutanols resident in hydroxylated derivatives of pinene, which proceed in a complementary manner to the C-C bond cleavage that we have observed with many traditional electrophilic reagents. Mechanistic and computational studies have provided insight into the role of C-H bond activation in the stereochemical outcome of the Rh-catalyzed C-C bond activation process. Using this new approach, functionalized cyclohexenones that form the cores of natural products, including the spiroindicumides and phomactin A, have been accessed.

  16. Aliphatic C-C Bond Cleavage in α-Hydroxy Ketones by a Dioxygen-Derived Nucleophilic Iron-Oxygen Oxidant.

    Science.gov (United States)

    Bhattacharya, Shrabanti; Rahaman, Rubina; Chatterjee, Sayanti; Paine, Tapan K

    2017-03-17

    A nucleophilic iron-oxygen oxidant, formed in situ in the reaction between an iron(II)-benzilate complex and O2 , oxidatively cleaves the aliphatic C-C bonds of α-hydroxy ketones. In the cleavage reaction, α-hydroxy ketones without any α-C-H bond afford a 1:1 mixture of carboxylic acid and ketone. Isotope labeling studies established that one of the oxygen atoms from dioxygen is incorporated into the carboxylic acid product. Furthermore, the iron(II) complex cleaves an aliphatic C-C bond of 17-α-hydroxyprogesterone affording androstenedione and acetic acid. The O2 -dependent aliphatic C-C bond cleavage of α-hydroxy ketones containing no α-C-H bond bears similarity to the lyase activity of the heme enzyme, cytochrome P450 17A1 (CYP17A1). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Competitive C-C and C-H bond scission in the ethanol oxidation reaction on Cu(100) and the effect of an alkaline environment.

    Science.gov (United States)

    Wu, Zhipeng; Zhang, Minhua; Jiang, Haoxi; Zhong, Chuan-Jian; Chen, Yifei; Wang, Lichang

    2017-06-14

    Direct ethanol fuel cell technology is impeded by inefficient, yet expensive anode catalysts. As such, research on effective and cheap anode catalysts towards complete ethanol oxidation reaction (EOR) is greatly needed. Herein, we report the investigations of the competitive C-C and C-H bond scissions in the EOR involving CH3CO, CH2CO, and CHCO species on Cu(100) using density functional theory and transition state theory calculations. The easiest C-C bond cleavage was found in CH2CO while the most difficult C-H bond cleavage was also found in CH2CO, both with an activation energy of 1.02 eV. The feasible C-C bond scission may take place in CH2CO with a rate constant ratio of the C-C to the C-H bond scission at 100 °C of 0.32. Furthermore, in an alkaline environment, the C-H bond scission activation barrier is considerably lowered but the C-C bond cleavage activation barrier is slightly increased for both CH3CO and CH2CO species. The reaction of CH3CO species on Cu(100) under alkaline conditions produces mainly acetic acid with a barrier of 0.49 eV and a rate constant of 4.93 × 105 s-1 at 100 °C.

  18. 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 i......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...... 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...

  19. Reduction of unsaturated compounds under interstellar conditions: chemoselective reduction of C≡C and C=C bonds over C=O functional group

    Science.gov (United States)

    Jonusas, Mindaugas; Guillemin, Jean-Claude; Krim, Lahouari

    2017-07-01

    The knowledge of the H-addition reactions on unsaturated organic molecules bearing a triple or a double carbon-carbon bond such as propargyl or allyl alcohols and a CO functional group such as propynal, propenal or propanal may play an important role in the understanding of the chemical complexity of the interstellar medium. Why different aldehydes like methanal, ethanal, propynal and propanal are present in dense molecular clouds while the only alcohol detected in those cold regions is methanol? In addition, ethanol has only been detected in hot molecular cores. Are those saturated and unsaturated aldehyde and alcohol species chemically linked in molecular clouds through solid phase H-addition surface reactions or are they formed through different chemical routes? To answer such questions, we have investigated a hydrogenation study of saturated and unsaturated aldehydes and alcohols at 10 K. We prove through this experimental study that while pure unsaturated alcohol ices bombarded by H atoms lead to the formation of the corresponding fully or partially saturated alcohols, surface H-addition reactions on unsaturated aldehyde ices exclusively lead to the formation of fully saturated aldehyde. Such results show that in addition to a chemoselective reduction of C≡C and C=C bonds over the C=O group, there is no link between aldehydes and their corresponding alcohols in reactions involving H atoms in dense molecular clouds. Consequently, this could be one of the reasons why some aldehydes such as propanal are abundant in dense molecular clouds in contrast to the non-detection of alcohol species larger than methanol.

  20. 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.

  1. 4-alkyl-L-(Dehydro)proline biosynthesis in actinobacteria involves N-terminal nucleophile-hydrolase activity of γ-glutamyltranspeptidase homolog for C-C bond cleavage

    Science.gov (United States)

    Zhong, Guannan; Zhao, Qunfei; Zhang, Qinglin; Liu, Wen

    2017-07-01

    γ-Glutamyltranspeptidases (γ-GTs), ubiquitous in glutathione metabolism for γ-glutamyl transfer/hydrolysis, are N-terminal nucleophile (Ntn)-hydrolase fold proteins that share an autoproteolytic process for self-activation. γ-GT homologues are widely present in Gram-positive actinobacteria where their Ntn-hydrolase activities, however, are not involved in glutathione metabolism. Herein, we demonstrate that the formation of 4-Alkyl-L-(dehydro)proline (ALDP) residues, the non-proteinogenic α-amino acids that serve as vital components of many bioactive metabolites found in actinobacteria, involves unprecedented Ntn-hydrolase activity of γ-GT homologue for C-C bond cleavage. The related enzymes share a key Thr residue, which acts as an internal nucleophile for protein hydrolysis and then as a newly released N-terminal nucleophile for carboxylate side-chain processing likely through the generation of an oxalyl-Thr enzyme intermediate. These findings provide mechanistic insights into the biosynthesis of various ALDP residues/associated natural products, highlight the versatile functions of Ntn-hydrolase fold proteins, and particularly generate interest in thus far less-appreciated γ-GT homologues in actinobacteria.

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

    Science.gov (United States)

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

    2011-05-01

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

  3. Intramolecular hydroalkoxylation of non-activated C=C bonds catalysed by zeolites: an experimental and theoretical study.

    Science.gov (United States)

    Pérez-Mayoral, Elena; Matos, Ines; Nachtigall, Petr; Položij, Miroslav; Fonseca, Isabel; Vitvarová-Procházková, Dana; Čejka, Jiří

    2013-06-01

    The high activity and selectivity of zeolites in the cyclisation of unsaturated alcohols is reported for the first time; the details of a reaction mechanism based on quantum chemical calculations are also provided. The high efficiency of zeolites MFI, BEA and FAU in the cyclisation of unsaturated alcohols (cis-decen-1-ol, 6-methylhept-5-en-2-ol and 2-allylphenol) to afford oxygen-containing heterocyclic rings is demonstrated. The best catalytic performance is found for zeolites with the optimum concentration of Brønsted acid sites (ca. 0.2 mmol g(-1)) and the minimum number of Lewis acid sites. It is proposed that the efficiency of the catalysts is reduced by the existence of the so-called dual site, at which a molecule of unsaturated alcohol can simultaneously interact with two acid sites (an OH group with one and the double bond with the other Brønsted site), which increases the interaction strength. The formation of such adsorption complexes leads to a decrease in the catalyst activity because of (i) an increase in the reaction barrier, (ii) an unfavourable conformation and (iii) diffusion limitations. A new procedure for the preparation of tetrahydrofurans and pyrans over zeolite catalysts provides important oxygen-containing heterocycles with numerous applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Factors That Control C-C Cleavage versus C-H Bond Hydroxylation in Copper-Catalyzed Oxidations of Ketones with O2.

    Science.gov (United States)

    Tsang, Althea S-K; Kapat, Ajoy; Schoenebeck, Franziska

    2016-01-20

    The Cu-catalyzed oxidation of ketones with O2 has recently been extensively utilized to cleave the α-C-C bond. This report examines the selective aerobic hydroxylation of tertiary α-C-H bonds in ketones without C-C cleavage. We set out to understand the underlying mechanisms of these two possible reactivity modes. Using experimental, in situ IR spectroscopic, and computational studies, we investigated several mechanisms. Our data suggest that both C-C cleavage and C-H hydroxylation pathways proceed via a common key intermediate, i.e., an α-peroxo ketone. The fate of this peroxide dictates the ultimate product selectivity. Specifically, we uncovered the role of hppH [=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine] to act not only as a base in the transformation but also as a reductant of the peroxide to the corresponding α-hydroxy ketone. This reduction may also be accomplished through exogenous phosphine additives, therefore allowing the tuning of reduction efficiency toward higher driving forces, if required (e.g., for more-activated substrates). The likely competitive pathway is the cleavage of peroxide to the α-oxy radical (likely catalyzed by Cu), which is computationally predicted to spontaneously trigger C-C bond cleavage. Increasing the susceptibility of this deperoxidation step via (i) the removal of reductant (use of different base, e.g., DBU) or the modulation of (ii) the substitution pattern toward greater activation (substrate control) and (iii) the nature of Cu catalyst (counterion and solvent dependence) will favor the C-C cleavage product.

  5. Active Metal Brazing and Adhesive Bonding of Titanium to C/C Composites for Heat Rejection System

    Science.gov (United States)

    Singh, M.; Shpargel, Tarah; Cerny, Jennifer

    2006-01-01

    Robust assembly and integration technologies are critically needed for the manufacturing of heat rejection system (HRS) components for current and future space exploration missions. Active metal brazing and adhesive bonding technologies are being assessed for the bonding of titanium to high conductivity Carbon-Carbon composite sub components in various shapes and sizes. Currently a number of different silver and copper based active metal brazes and adhesive compositions are being evaluated. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Several mechanical tests have been employed to ascertain the effectiveness of different brazing and adhesive approaches in tension and in shear that are both simple and representative of the actual system and relatively straightforward in analysis. The results of these mechanical tests along with the fractographic analysis will be discussed. In addition, advantages, technical issues and concerns in using different bonding approaches will also be presented.

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

    KAUST Repository

    Yang, Wenguo

    2012-02-08

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

  7. Double-Diels-Alder Approach to Maoecrystal V. Unexpected C-C Bond-Forming Fragmentations of the [2.2.2]-Bicyclic Core.

    Science.gov (United States)

    Smith, Brandon R; Njardarson, Jon T

    2017-10-06

    Synthetic studies toward maoecrystal V are reported. An oxidative dearomatization/Diels-Alder cascade to assemble the natural product carbocyclic core in one step is proposed. A facile electrocyclization is shown to suppress the intramolecular allene Diels-Alder pathway. This obstacle is alleviated via a stepwise approach with an allene equivalent to access the key cyclopentadiene-fused [2.2.2]-bicyclic core. Upon treatment with Lewis acid, the proposed intramolecular hetero-Diels-Alder reaction is cleanly and unexpectedly diverted either via C-C bond-forming fragmentation to the spiro-indene product (when R = OMe) or via elimination (when R = H).

  8. Crystallographic snapshots of tyrosine phenol-lyase show that substrate strain plays a role in C-C bond cleavage.

    Science.gov (United States)

    Milić, Dalibor; Demidkina, Tatyana V; Faleev, Nicolai G; Phillips, Robert S; Matković-Čalogović, Dubravka; Antson, Alfred A

    2011-10-19

    The key step in the enzymatic reaction catalyzed by tyrosine phenol-lyase (TPL) is reversible cleavage of the Cβ-Cγ bond of L-tyrosine. Here, we present X-ray structures for two enzymatic states that form just before and after the cleavage of the carbon-carbon bond. As for most other pyridoxal 5'-phosphate-dependent enzymes, the first state, a quinonoid intermediate, is central for the catalysis. We captured this relatively unstable intermediate in the crystalline state by introducing substitutions Y71F or F448H in Citrobacter freundii TPL and briefly soaking crystals of the mutant enzymes with a substrate 3-fluoro-L-tyrosine followed by flash-cooling. The X-ray structures, determined at ~2.0 Å resolution, reveal two quinonoid geometries: "relaxed" in the open and "tense" in the closed state of the active site. The "tense" state is characterized by changes in enzyme contacts made with the substrate's phenolic moiety, which result in significantly strained conformation at Cβ and Cγ positions. We also captured, at 2.25 Å resolution, the X-ray structure for the state just after the substrate's Cβ-Cγ bond cleavage by preparing the ternary complex between TPL, alanine quinonoid and pyridine N-oxide, which mimics the α-aminoacrylate intermediate with bound phenol. In this state, the enzyme-ligand contacts remain almost exactly the same as in the "tense" quinonoid, indicating that the strain induced by the closure of the active site facilitates elimination of phenol. Taken together, structural observations demonstrate that the enzyme serves not only to stabilize the transition state but also to destabilize the ground state.

  9. Diphenyldiacetylene complexes of molybdenum(IV) and tungsten(IV). Crystal structures of PPh/sub 4/(WCl/sub 5/(Ph-C triple bond C-C triple bond C-Ph)) x CCl/sub 4/ and PPh/sub 4/(WCl/sub 5/(Ph-C triple bond C-C(Br)=C(Br)-Ph)) x CCl/sub 4/

    Energy Technology Data Exchange (ETDEWEB)

    Stahl, K.; Weller, F.; Dehnicke, K. (Marburg Univ. (Germany, F.R.). Fachbereich Chemie)

    1984-11-01

    Syntheses and i.r. spectra of the following diphenyldiacetylene complexes are reported: (MoCl/sub 4/(Ph-C triple bond C-C triple bond C-Ph))/sub 2/ (1), (WCl/sub 4/(Ph-C triple bond C-C triple bond C-Ph))/sub 2/ (2), PPh/sub 4/(WCl/sub 5/(Ph-C triple bond C-C triple bond C-Ph)) x CCl/sub 4/ (3). 1 is formed in the reaction of MoCl/sub 5/ with excess diphenylacetylene. 2 is prepared from WCl/sub 6/ and excess diphenylacetylene with additional C/sub 2/Cl/sub 4/ as a reducing agent. Reaction of 2 with PPh/sub 4/Cl in CH/sub 2/Cl/sub 2/ solution in the presence of CCl/sub 4/ yields 3. The complexes contain one of the acetylene functions bonded in a metallacyclopropene ring; the metal atoms are seven-coordinated. 2 reacts with bromine to form the dibromide (WCl/sub 4/(Ph-C triple bond C-C(Br)=C(Br)-Ph/sub 2/))/sub 2/ (4). In CH/sub 2/Cl/sub 2/ solution and in presence of CCl/sub 4/ 4 is turned into the ionic complex PPh/sub 4/(WCl/sub 5/(Ph-C triple bond C-C(Br)=C(Br)-Ph)) x CCl/sub 4/ (5) by PPh/sub 4/Cl. The complexes 3 and 5 are characterized by structural analyses on the basis of X-ray diffraction data. 3 crystallizes monoclinic in the space group P2/sub 1//n with four formula units per unit cell (2623 observed, independent reflexions, R = 5.4%). 5 crystallizes in the same space group, set P2/sub 1//c, the unit cell containing four formula units (2537 observed, independent reflexions, R = 5.4%).

  10. Small cycloalkane (CN)2C-C(CN)2 structures are highly directional non-covalent carbon-bond donors.

    Science.gov (United States)

    Bauzá, Antonio; Mooibroek, Tiddo J; Frontera, Antonio

    2014-08-11

    High-level calculations (RI-MP2/def2-TZVP) disclosed that the σ-hole in between two C atoms of cycloalkane X2 CCX2 structures (X=F, CN) is increasingly exposed with decreasing ring size. The interacting energy of complexes of F(-) , HO(-) , N≡C(-) , and H2 CO with cyclopropane and cyclobutane X2 CCX2 derivatives was calculated. For X=F, these energies are small to positive, while for X=CN they are all negative, ranging from -6.8 to -42.3 kcal mol(-1) . These finding are corroborated by a thorough statistical survey of the Cambridge Structural Database (CSD). No clear evidence could be found in support of non-covalent carbon bonding between electron-rich atoms (El.R.) and F2 CCF2 structures. In marked contrast, El.R.⋅⋅⋅(CN)2 CC(CN)2 interactions are abundant and highly directional. Based on these findings, the hydrophobic electrophilic bowl formed by 1,1',2,2'-tetracyano cyclopropane or cyclobutane derivatives is proposed as a new and synthetically accessible supramolecular synthon. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. New Concept of the Biosynthesis of 4-Alkyl-L-proline Precursors of Lincomycin, Hormaomycin and Pyrrolobenzodiazepines: Could a γ-Glutamyltransferase Cleave the C-C Bond?

    Directory of Open Access Journals (Sweden)

    Petra eJiraskova

    2016-03-01

    Full Text Available Structurally different and functionally diverse natural compounds – antitumour agents pyrrolo[1,4]benzodiazepines, bacterial hormone hormaomycin and lincosamide antibiotic lincomycin – share a common building unit, 4-alkyl-L-proline derivative (APD. APDs arise from L-tyrosine through a special biosynthetic pathway. Its generally accepted scheme, however, did not comply with current state of knowledge. Based on gene inactivation experiments and in vitro functional tests with recombinant enzymes, we designed a new APD biosynthetic scheme for the model of lincomycin biosynthesis. In the new scheme at least one characteristic in each of five final biosynthetic steps has been changed: the order of reactions, assignment of enzymes and/or reaction mechanisms. First, we demonstrate that LmbW methylates a different substrate than previously assumed. Second, we propose a unique reaction mechanism for the next step, in which a putative γ-glutamyltransferase LmbA indirectly cleaves off the oxalyl residue by transient attachment of glutamate to LmbW product. This unprecedented mechanism would represent the first example of the C-C bond cleavage catalyzed by a γ-glutamyltransferase, i.e., an enzyme that appears unsuitable for such activity. Finally, the inactivation experiments show that LmbX is an isomerase indicating that it transforms its substrate into a compound suitable for reduction by LmbY, thereby facilitating its subsequent complete conversion to APD 4-propyl-L-proline. Elucidation of the APD biosynthesis has long time resisted mainly due to the apparent absence of relevant C-C bond cleaving enzymatic activity. Our proposal aims to unblock this situation not only for lincomycin biosynthesis, but generally for all above mentioned groups of bioactive natural products with biotechnological potential.

  12. Organocatalytic aryl-aryl bond formation: an atroposelective [3,3]-rearrangement approach to BINAM derivatives.

    Science.gov (United States)

    Li, Gong-Qiang; Gao, Hongyin; Keene, Craig; Devonas, Michael; Ess, Daniel H; Kürti, László

    2013-05-22

    Herein we disclose an organocatalytic aryl-aryl bond-forming process for the regio- and atroposelective synthesis of 2,2'-diamino-1,1'-binaphthalenes (BINAMs). In the presence of catalytic amounts of axially chiral phosphoric acids, achiral N,N'-binaphthyl hydrazines undergo a facile [3,3]-sigmatropic rearrangement to afford enantiomerically enriched BINAM derivatives in good to excellent yield. This transformation represents the first example of a metal-free, catalytic C(sp(2))-C(sp(2)) bond formation between two aromatic rings with concomitant de novo atroposelective installation of an axis of chirality. Density functional calculations reveal that, in the transition state for C-C bond formation, the phosphoric acid proton of the catalyst is fully transferred to one of the N-atoms of the substrate, and the resulting phosphate acts as a chiral counterion.

  13. Recent advances in C-S bond formation via C-H bond functionalization and decarboxylation.

    Science.gov (United States)

    Shen, Chao; Zhang, Pengfei; Sun, Qiang; Bai, Shiqiang; Hor, T S Andy; Liu, Xiaogang

    2015-01-07

    The development of mild and general methods for C-S bond formation has received significant attention because the C-S bond is indispensable in many important biological and pharmaceutical compounds. Early examples for the synthesis of C-S bonds are generally limited to the condensation reaction between a metal thiolate and an organic halide. Recent chemical approaches for C-S bond formation, based upon direct C-H bond functionalization and decarboxylative reactions, not only provide new insights into the mechanistic understanding of C-S coupling reactions but also allow the synthesis of sulfur-containing compounds from more effective synthetic routes with high atom economy. This review intends to explore recent advances in C-S bond formation via C-H functionalization and decarboxylation, and the growing opportunities they present to the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials as well as nanotechnology.

  14. An iron-catalysed C-C bond-forming spirocyclization cascade providing sustainable access to new 3D heterocyclic frameworks

    Science.gov (United States)

    Adams, Kirsty; Ball, Anthony K.; Birkett, James; Brown, Lee; Chappell, Ben; Gill, Duncan M.; Lo, P. K. Tony; Patmore, Nathan J.; Rice, Craig. R.; Ryan, James; Raubo, Piotr; Sweeney, Joseph B.

    2017-04-01

    Heterocyclic architectures offer powerful creative possibilities to a range of chemistry end-users. This is particularly true of heterocycles containing a high proportion of sp3-carbon atoms, which confer precise spatial definition upon chemical probes, drug substances, chiral monomers and the like. Nonetheless, simple catalytic routes to new heterocyclic cores are infrequently reported, and methods making use of biomass-accessible starting materials are also rare. Here, we demonstrate a new method allowing rapid entry to spirocyclic bis-heterocycles, in which inexpensive iron(III) catalysts mediate a highly stereoselective C-C bond-forming cyclization cascade reaction using (2-halo)aryl ethers and amines constructed using feedstock chemicals readily available from plant sources. Fe(acac)3 mediates the deiodinative cyclization of (2-halo)aryloxy furfuranyl ethers, followed by capture of the intermediate metal species by Grignard reagents, to deliver spirocycles containing two asymmetric centres. The reactions offer potential entry to key structural motifs present in bioactive natural products.

  15. An iron-catalysed C-C bond-forming spirocyclization cascade providing sustainable access to new 3D heterocyclic frameworks.

    Science.gov (United States)

    Adams, Kirsty; Ball, Anthony K; Birkett, James; Brown, Lee; Chappell, Ben; Gill, Duncan M; Lo, P K Tony; Patmore, Nathan J; Rice, Craig R; Ryan, James; Raubo, Piotr; Sweeney, Joseph B

    2017-04-01

    Heterocyclic architectures offer powerful creative possibilities to a range of chemistry end-users. This is particularly true of heterocycles containing a high proportion of sp 3 -carbon atoms, which confer precise spatial definition upon chemical probes, drug substances, chiral monomers and the like. Nonetheless, simple catalytic routes to new heterocyclic cores are infrequently reported, and methods making use of biomass-accessible starting materials are also rare. Here, we demonstrate a new method allowing rapid entry to spirocyclic bis-heterocycles, in which inexpensive iron(III) catalysts mediate a highly stereoselective C-C bond-forming cyclization cascade reaction using (2-halo)aryl ethers and amines constructed using feedstock chemicals readily available from plant sources. Fe(acac) 3 mediates the deiodinative cyclization of (2-halo)aryloxy furfuranyl ethers, followed by capture of the intermediate metal species by Grignard reagents, to deliver spirocycles containing two asymmetric centres. The reactions offer potential entry to key structural motifs present in bioactive natural products.

  16. Formation of a 1D-polymeric chain of Hg building blocks through C-C coupling under ambient conditions.

    Science.gov (United States)

    Mobin, Shaikh M; Mishra, Veenu; Ram, Priti; Birla, Anil; Mathur, Pradeep

    2013-08-14

    A novel C-C coupled 1D-polymeric chain (1) is obtained by reaction of HgCl2 and hmp-H (2-(2-hydroxymethyl pyridine)) (1 : 1) in MeOH at ambient temperature. However, a new class of μ-oxo and μ-chloro bridged polymers (2) has been obtained by altering the metal : ligand ratio to 1 : 2.

  17. Long live vinylidene! A new view of the H(2)C=C: --> HC triple bond CH rearrangement from ab initio molecular dynamics.

    Science.gov (United States)

    Hayes, R L; Fattal, E; Govind, N; Carter, E A

    2001-01-31

    We present complete active space self-consistent field (CASSCF) ab initio molecular dynamics (AIMD) simulations of the preparation of the metastable species vinylidene, and its subsequent, highly exothermic isomerization to acetylene, via electron removal from vinylidene anion (D(2)C=C(-) --> D(2)C=C: --> DC triple bond CD). After equilibrating vinylidene anion-d(2) at either 600 +/- 300 K (slightly below the isomerization barrier) or 1440 K +/- 720 K (just above the isomerization barrier), we remove an electron to form a vibrationally excited singlet vinylidene-d(2) and follow its dynamical evolution for 1.0 ps. Remarkably, we find that none of the vinylidenes equilibrated at 600 K and only 20% of the vinylidenes equilibrated at 1440 K isomerized, suggesting average lifetimes >1 ps for vibrationally excited vinylidene-d(2). Since the anion and neutral vinylidene are structurally similar, and yet extremely different geometrically from the isomerization transition state (TS), neutral vinylidene is not formed near the TS so that it must live until it has sufficient instantaneous kinetic energy in the correct vibrational mode(s). The origin of the delay is explained via both orbital rearrangement and intramolecular vibrational energy redistribution (IVR) effects. Unique signatures of the isomerization dynamics are revealed in the anharmonic vibrational frequencies extracted from the AIMD, which should be observable by ultrafast vibrational spectroscopy and in fact are consistent with currently available experimental spectra. Most interestingly, of those trajectories that did isomerize, every one of them violated conventional transition-state theory by recrossing back to vinylidene multiple times, against conventional notions that expect highly exothermic reactions to be irreversible. The dynamical motion responsible for the multiple barrier recrossings involves strong mode-coupling between the vinylidene CD(2) rock and a local acetylene DCC bend mode that has been

  18. Low-molecular-weight oxidants involved in disulfide bond formation.

    Science.gov (United States)

    Ruddock, Lloyd W

    2012-05-15

    The biogenesis of most secreted and outer membrane proteins involves the formation of structure stabilizing disulfide bonds. Hence knowledge of the mechanisms for their formation is critical for understanding a myriad of cellular processes and associated disease states. Until recently it was thought that members of the Ero1 sulfhydryl oxidase family were responsible for catalyzing the majority of disulfide bond formation in the endoplasmic reticulum. However, multiple eukaryotic organisms are now known to show no or minor phenotypes when these enzymatic pathways are disrupted, suggesting that other pathways can catalyze disulfide bond formation to an extent sufficient to maintain normal physiology. This lack of a strong phenotype raises multiple questions regarding what pathways are acting and whether they themselves constitute the major route for disulfide bond formation. This review critically examines the potential low molecular oxidants that maybe involved in the catalyzed or noncatalyzed formation of disulfide bonds, with an emphasis on the mammalian endoplasmic reticulum, via an examination of their thermodynamics, kinetics, and availability and gives pointers to help guide future experimental work.

  19. Formation of Irreversible H-bonds in Cellulose Materials

    Science.gov (United States)

    Umesh P. Agarwal; Sally A. Ralph; Rick S. Reiner; Nicole M. Stark

    2015-01-01

    Understanding of formation of irreversible Hbonds in cellulose is important in a number of fields. For example, fields as diverse as pulp and paper and enzymatic saccharification of cellulose are affected. In the present investigation, the phenomenon of formation of irreversible H-bonds is studied in a variety of celluloses and under two different drying conditions....

  20. Cooperative Hydrogen Bonding in Amyloid Formation.

    Energy Technology Data Exchange (ETDEWEB)

    Tsemekhman, Kiril L.; Goldschmidt, Lukasz; Eisenberg, Dvaid; Baker, David

    2007-04-01

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Amyloid diseases, including Alzheimer's and prion diseases, are each associated with unbranched protein fibrils. Each fibril is made of a particular protein, yet they share common properties. One such property is nucleation-dependent fibril growth. Monomers of amyloid-forming proteins can remain in dissolved form for long periods, before rapidly assembly into fibrils. The lag before growth has been attributed to slow kinetics of formation of a nucleus, on which other molecules can deposit to form the fibril. We have explored the energetics of fibril formation, based on the known molecular structure of a fibril-forming peptide from the yeast prion, Sup35, using both classical and quantum (density functional theory) methods. We find that the energetics of fibril formation for the first three layers are cooperative using both methods. This cooperativity is consistent with the observation that formation of amyloid fibrils involves slow nucleation and faster growth.

  1. Creating σ-holes through the formation of beryllium bonds.

    Science.gov (United States)

    Brea, Oriana; Mó, Otilia; Yáñez, Manuel; Alkorta, Ibon; Elguero, José

    2015-09-01

    Through the use of ab initio theoretical models based on MP2/aug-cc-pVDZ-optimized geometries and CCSD(T)/aug-cc-pVTZ and CCSD(T)/aug-c-pVDZ total energies, it has been shown that the significant electron density rearrangements that follow the formation of a beryllium bond may lead to the appearance of a σ-hole in systems that previously do not exhibit this feature, such as CH3 OF, NO2 F, NO3 F, and other fluorine-containing systems. The creation of the σ-hole is another manifestation of the bond activation-reinforcement (BAR) rule. The appearance of a σ-hole on the F atoms of CH3 OF is due to the enhancement of the electronegativity of the O atom that participates in the beryllium bond. This atom recovers part of the charge transferred to Be by polarizing the valence density of the F into the bonding region. An analysis of the electron density shows that indeed this bond becomes reinforced, but the F atom becomes more electron deficient with the appearance of the σ-hole. Importantly, similar effects are also observed even when the atom participating in the beryllium bond is not directly attached to the F atom, as in NO2 F, NO3 F, or NCF. Hence, whereas the isolated CH3 OF, NO2 F, and NO3 F are unable to yield F⋅⋅⋅Base halogen bonds, their complexes with BeX2 derivatives are able to yield such bonds. Significant cooperative effects between the new halogen bond and the beryllium bond reinforce the strength of both noncovalent interactions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Initial Carbon-Carbon Bond Formation during the Early Stages of the Methanol-to-Olefin Process Proven by Zeolite-Trapped Acetate and Methyl Acetate

    NARCIS (Netherlands)

    Chowdhury, Abhishek Dutta; Houben, Klaartje; Whiting, Gareth T; Mokhtar, Mohamed; Asiri, Abdullah M; Al-Thabaiti, Shaeel A; Basahel, Suliman N; Baldus, Marc; Weckhuysen, Bert M

    2016-01-01

    Methanol-to-olefin (MTO) catalysis is a very active field of research because there is a wide variety of sometimes conflicting mechanistic proposals. An example is the ongoing discussion on the initial C-C bond formation from methanol during the induction period of the MTO process. By employing a

  3. Carenium—Calkyl Bond Making and Breaking: Key Process in the Platinum-Mediated Caryl—Calkyl Bond Formation. Analogies to Organic Electrophilic Aromatic Substitution

    OpenAIRE

    van Koten, G.; Albrecht, M.A.; Spek, A.L.

    2001-01-01

    The reaction of cationic platinum aqua complexes 2 [Pt(C6H2{CH2NMe2}2-E-4)(OH2)](X') (X' = SO3CF3, BF4) with alkyl halides RX gave various air-stable arenium complexes 3-5 containing a new C-C bond (R = Me, 3; Et, 4; Bn, 5). Electron-releasing oxo-substituents on the aromatic ligand (E = e.g., OH, b; OMe, c) enhance the reactivity of the aqua complex 2 and were essential for arenium formation from alkyl halides different from MeX. This process is initiated by oxidative addition of alkyl halid...

  4. 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

    The enantioselective allylic alkylation of (E)-1,3-diphenylallyl acetate was studied to clarify the heterogeneous or homogeneous character of the Pd/Al2O3-(R)-BINAP catalyst system. A combined approach was applied: the catalytic tests were completed with in situ XANES measurements to follow...

  5. Unraveling the Fischer-Tropsch mechanism: a combined DFT and microkinetic investigation of C-C bond formation on Ru.

    Science.gov (United States)

    Mirwald, Jens W; Inderwildi, Oliver R

    2012-05-21

    A combined modelling study on the Fischer-Tropsch Mechanism on Ru(0001). The DFT results presented herein approve the idea that the carbide mechanism is not the main reaction path in the synthesis of liquid hydrocarbons on Ru{0001}. The direct reaction of a CH(x)(s) species with a CO(s) species is kinetically and thermochemically preferred over CO dissociation and the hydrogenation of carbon monoxide can be seen as the initiation reaction of the hydrocarbon polymerisation process. Moreover, this study shows that CO dissociation is favoured over desorption on Ru{0001}, while on the analogue Co facet desorption is clearly favoured. This study therefore is an important further confirmation on new thinking in the Fischer-Tropsch synthesis. The fundamental insight gained in these studies will be of paramount importance for engineers optimising the FT process. Optimisation will not only lower the cost of FT fuels but simultaneously lower energy consumption and emissions.

  6. Reversible Sigma C-C Bond Formation Between Phenanthroline Ligands Activated by (C5Me5)2Yb

    Energy Technology Data Exchange (ETDEWEB)

    Nocton, Gr& #233; gory; Lukens, Wayne W.; Booth, Corwin H.; Rozenel, Sergio S.; Medling, Scott A.; Maron, Laurent; Andersen, Richard A.

    2014-06-26

    The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp*2Yb are dramatically different from those of the 2,2?-bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f13, and (phen ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009, 131, 6480; J. Am. Chem. Soc 2010, 132, 17537). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy has only one 1 orbital of b1 symmetry of accessible energy, but phen has two orbitals of b1 and a2 symmetry that are energetically accessible. The carbon p-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp 2Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180190 C. When 3,8-Me2phenanthroline is used, the adduct Cp*2Yb(3,8-Me2phen) exists in the solution in a dimer monomer equilibrium in which G is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me2, and 5,6-Me2-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and LIII-edge XANES spectroscopy as a function of temperature and variable-temperature 1H NMR spectroscopy.

  7. CYP96T1 of Narcissus sp. aff. pseudonarcissus Catalyzes Formation of the Para-Para’ C-C Phenol Couple in the Amaryllidaceae Alkaloids

    Directory of Open Access Journals (Sweden)

    Matthew eKilgore

    2016-02-01

    Full Text Available The Amaryllidaceae alkaloids are a family of amino acid derived alkaloids with many biological activities; examples include haemanthamine, haemanthidine, galanthamine, lycorine, and maritidine. Central to the biosynthesis of the majority of these alkaloids is a C-C phenol-coupling reaction that can have para-para’, para-ortho’, or ortho-para’ regiospecificity. Through comparative transcriptomics of Narcissus sp. aff. pseudonarcissus, Galanthus sp., and Galanthus elwesii we have identified a para-para’ C-C phenol coupling cytochrome P450, CYP96T1, capable of forming the products (10bR,4aS-noroxomaritidine and (10bS,4aR-noroxomaritidine from 4’-O-methylnorbelladine. CYP96T1 was also shown to catalyzed formation of the para-ortho’ phenol coupled product, N-demethylnarwedine, as less than 1 % of the total product. CYP96T1 co-expresses with the previously characterized norbelladine 4’-O-methyltransferase. The discovery of CYP96T1 is of special interest because it catalyzes the first major branch in Amaryllidaceae alkaloid biosynthesis. CYP96T1 is also the first phenol-coupling enzyme characterized from a monocot.

  8. CYP96T1 of Narcissus sp. aff. pseudonarcissus Catalyzes Formation of the Para-Para' C-C Phenol Couple in the Amaryllidaceae Alkaloids.

    Science.gov (United States)

    Kilgore, Matthew B; Augustin, Megan M; May, Gregory D; Crow, John A; Kutchan, Toni M

    2016-01-01

    The Amaryllidaceae alkaloids are a family of amino acid derived alkaloids with many biological activities; examples include haemanthamine, haemanthidine, galanthamine, lycorine, and maritidine. Central to the biosynthesis of the majority of these alkaloids is a C-C phenol-coupling reaction that can have para-para', para-ortho', or ortho-para' regiospecificity. Through comparative transcriptomics of Narcissus sp. aff. pseudonarcissus, Galanthus sp., and Galanthus elwesii we have identified a para-para' C-C phenol coupling cytochrome P450, CYP96T1, capable of forming the products (10bR,4aS)-noroxomaritidine and (10bS,4aR)-noroxomaritidine from 4'-O-methylnorbelladine. CYP96T1 was also shown to catalyzed formation of the para-ortho' phenol coupled product, N-demethylnarwedine, as less than 1% of the total product. CYP96T1 co-expresses with the previously characterized norbelladine 4'-O-methyltransferase. The discovery of CYP96T1 is of special interest because it catalyzes the first major branch in Amaryllidaceae alkaloid biosynthesis. CYP96T1 is also the first phenol-coupling enzyme characterized from a monocot.

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

    Science.gov (United States)

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

    2014-02-19

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

  10. Heats of Formation and Bond Energies in Group III Compounds

    Science.gov (United States)

    Bauschlicher, Charles W., Jr.; Allendorf, Mark D.; Melius, Carl F.; Arnold, James O. (Technical Monitor)

    1999-01-01

    We present heats of formation and bond energies for Group-III compounds obtained from calculations of molecular ground-state I electronic energies. Data for compounds of the form MXn are presented, where M = B, Al, Ga, and In, X = He H, Cl, and CH3, and n = 1-3. Energies for the B, Al, and Ga compounds are obtained from G2 predictions, while those for the In compounds are obtained from CCSD(T)/CBS calculations; these are the most accurate calculations for indium-containing compounds published to date. In most cases, the calculated thermochemistry is in good agreement with published values derived from experiments for those species that have well-established heats of formation. Bond energies obtained from the heats of formation follow the expected trend (Cl much greater than CH3 approx. H). However, the CH3M-(CH3)2 bond energies obtained for trimethylgallium and trimethylindium are considerably stronger (greater than 15 kcal/mol) than currently accepted values.

  11. An easy access to α-aryl substituted γ-ketophosphonates: Lewis acid mediated reactions of 1,3-diketones with α-hydroxyphosphonates and tandem regioselective C-C bond cleavage.

    Science.gov (United States)

    Pallikonda, Gangaram; Chakravarty, Manab; Sahoo, Manoj K

    2014-09-28

    A range of α-aryl substituted γ-ketophosphonates is synthesised by Lewis acid mediated reactions of 1,3-diketones and easily accessible, inexpensive benzylic α-hydroxyphosphonates in an operationally simple method under solvent-free conditions without exclusion of air/moisture. A regioselective C-C bond cleavage for 1,3-diketones in a tandem fashion has also been demonstrated. Synthesis of a γ-ketophosphonate with phenol functionality at the α-position (structural analogue of raspberry ketone, a natural product) has also been presented.

  12. A model of hydrogen bond formation in phosphatidylethanolamine bilayers.

    Science.gov (United States)

    Pink, D A; McNeil, S; Quinn, B; Zuckermann, M J

    1998-01-19

    We have modelled hydrogen bond formation in phospholipid bilayers formed, in excess water, from lipids with phosphatidylethanolamine (PE) headgroups. The hydrogen bonds are formed between the NH3+ group and either of the PO2- or the (sn2 chain) C=O groups. We used a model that represented the conformational states accessible to a PE headgroup by 17 states and modelled lipid dipole-dipole interactions using a non-local electrostatics theory to include the effects of hydrogen bonding in the aqueous medium. We used Monte-Carlo simulation to calculate equilibrium thermodynamic properties of bilayers in the fluid (T = 340 K) or gel (T = 300 K) phases of the bilayer. We defined Eh to be the difference in free energy between a hydrogen bond formed between a pair of lipid groups, and the energy of hydrogen bonds formed between water and those two groups, and we required its average value, [Eh], to be approximately -0.3kcal/mol (approximately -0.2 X 10(-13) erg) as reported by T.-B. Shin, R. Leventis, J.R. Silvius, Biochemistry 30 (1991) 7491. We found: (i) Eh = -0.9 X 10(-13) erg gave [Eh] = -0.21 X 10(-13) erg (gel phase) and [Eh] = -0.19 X 10(-13) erg (fluid phase). (ii) The relative number of C=O groups on the sn2 chain calculated to take part in interlipid hydrogen bonding in the fluid phase compared to the gel is 1.06 which compares well with the experimental ratio of approximately 1.25 (R.N.A.H. Lewis, R.N. McElhaney, Biophys. J. 64 (1993) 1081). The ratio of such groups taking part in interlipid hydrogen bonding compared to water hydrogen bonding in each phase was calculated to lie between 0.16 and 0.17. (iii) We calculated the distribution of positions of the headgroup moieties, P, O, CH2(alpha), CH2(beta) and N, and found that, in both phases, the O lay furthest from the hydrocarbon chain layer (average approximately 5.3A) with the PO2 and NH3 groups lying at approximately 5A. This results in the P-N dipole lying nearly parallel to the bilayer plane in both phases

  13. Initial Carbon-Carbon Bond Formation during the Early Stages of the Methanol-to-Olefin Process Proven by Zeolite-Trapped Acetate and Methyl Acetate.

    Science.gov (United States)

    Chowdhury, Abhishek Dutta; Houben, Klaartje; Whiting, Gareth T; Mokhtar, Mohamed; Asiri, Abdullah M; Al-Thabaiti, Shaeel A; Basahel, Suliman N; Baldus, Marc; Weckhuysen, Bert M

    2016-12-19

    Methanol-to-olefin (MTO) catalysis is a very active field of research because there is a wide variety of sometimes conflicting mechanistic proposals. An example is the ongoing discussion on the initial C-C bond formation from methanol during the induction period of the MTO process. By employing a combination of solid-state NMR spectroscopy with UV/Vis diffuse reflectance spectroscopy and mass spectrometry on an active H-SAPO-34 catalyst, we provide spectroscopic evidence for the formation of surface acetate and methyl acetate, as well as dimethoxymethane during the MTO process. As a consequence, new insights in the formation of the first C-C bond are provided, suggesting a direct mechanism may be operative, at least in the early stages of the MTO reaction. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  14. Detection of bond formations by DNA-programmed chemical reactions and PCR amplification.

    Science.gov (United States)

    Li, Yizhou; Zhang, Mingda; Zhang, Chi; Li, Xiaoyu

    2012-10-04

    A system capable of performing both DNA-templated chemical reactions and detection of bond formations is reported. Photocleavable DNA templates direct reactions. Products from bond-forming events re-ligate original templates, amplifiable by PCR, therefore distinguishing bond formation from background. This system provides a novel approach for discovering potential new chemical reactions.

  15. Simultaneous bond degradation and bond formation during phenol-formaldehyde curing with wood

    Science.gov (United States)

    Daniel J. Yelle; John Ralph

    2016-01-01

    Bonding of wood using phenol–formaldehyde adhesive develops highly durable bonds. Phenol– formaldehyde is believed to form primary bonds with wood cell wall polymers (e.g., lignin). However, it is unclear how this adhesive interacts and bonds to lignin. Through wood solubilisation methodologies, earlywood and latewood bonded assemblies were characterized using two-...

  16. Liquid phase diffusion bonding of A1070 by using metal formate coated Zn sheet

    Science.gov (United States)

    Ozawa, K.; Koyama, S.; shohji, I.

    2017-05-01

    Aluminium alloy have high strength and easily recycle due to its low melting point. Therefore, aluminium is widely used in the manufacturing of cars and electronic devices. In recent years, the most common way for bonding aluminium alloy is brazing and friction stir welding. However, brazing requires positional accuracy and results in the formation of voids by the flax residue. Moreover, aluminium is an excellent heat radiating and electricity conducting material; therefore, it is difficult to bond together using other bonding methods. Because of these limitations, liquid phase diffusion bonding is considered to the suitable method for bonding aluminium at low temperature and low bonding pressure. In this study, the effect of metal formate coating processing of zinc surface on the bond strength of the liquid phase diffusion bonded interface of A1070 has been investigated by SEM observation of the interfacial microstructures and fractured surfaces after tensile test. Liquid phase diffusion bonding was carried out under a nitrogen gas atmosphere at a bonding temperature of 673 K and 713 K and a bonding load of 6 MPa (bonding time: 15 min). As a result of the metal formate coating processing, a joint having the ultimate tensile strength of the base aluminium was provided. It is hypothesized that this is because metallic zinc is generated as a result of thermal decomposition of formate in the bonded interface at lower bonding temperatures.

  17. Addition of Carbon-Fluorine Bonds to a Mg(I)-Mg(I) Bond: An Equivalent of Grignard Formation in Solution

    OpenAIRE

    Bakewell, C; White, AJ; Crimmin, MR

    2016-01-01

    Addition of the carbon?fluorine bond of a series of perfluorinated and polyfluorinated arenes across the Mg?Mg bond of a simple coordination complex proceeds rapidly in solution. The reaction results in the formation of a new carbon?magnesium bond and a new fluorine?magnesium bond and is analogous to Grignard formation in homogeneous solution.

  18. CYP96T1 of Narcissus sp. aff. pseudonarcissus Catalyzes Formation of the Para-Para' C-C Phenol Couple in the Amaryllidaceae Alkaloids

    National Research Council Canada - National Science Library

    Kilgore, Matthew B; Augustin, Megan M; May, Gregory D; Crow, John A; Kutchan, Toni M

    2016-01-01

    .... Through comparative transcriptomics of Narcissus sp. aff. pseudonarcissus, Galanthus sp., and Galanthus elwesii we have identified a para-para' C-C phenol coupling cytochrome P450, CYP96T1, capable of forming the products (10bR,4aS...

  19. Anti-metastatic Semi-synthetic Sulfated Maltotriose C-C Linked Dimers. Synthesis and Characterisation

    Directory of Open Access Journals (Sweden)

    Giangiacomo Torri

    2012-08-01

    Full Text Available This manuscript describes the preparation and the spectroscopic characterisation of semi-synthetic sulfated maltotriose C-C linked dimers (SMTCs where the natural C-O-C anomeric bond was substituted by one direct central C-C bond. This C-C bond induces conformation and flexibility changes with respect to the usual anomeric bond. SMTCs neutral precursors came from maltotriosyl bromide electroreduction through maltotriosyl radical intermediate dimerisation. The new C-C bond configuration, named for convenience a,a, a,b and b,b as the natural anomeric bond, dictated the statistic ratio formation of three diastereoisomers. They were separated by silica gel flash chromatography followed by semi preparative HPLC chromatography. Each diastereoisomer was exhaustively sulfated to afford the corresponding SMTCs. SMTCs were huge characterised by NMR spectroscopy which provided the sulfation degree, too. a,a and a,b were found quite homogeneous samples with a high degree of sulfation (85–95%. b,b appeared a non-homogeneous sample whose average sulfation degree was evaluated at around 78%. Mass spectroscopy experiments confirmed the sulfation degree range. Some considerations were proposed about SMTCs structure-biological properties.

  20. Preventing Disulfide Bond Formation Weakens Non-Covalent Forces among Lysozyme Aggregates

    OpenAIRE

    Vijay Kumar Ravi; Mohit Goel; Hema Chandra Kotamarthi; Sri Rama Koti Ainavarapu; Rajaram Swaminathan

    2014-01-01

    Nonnative disulfide bonds have been observed among protein aggregates in several diseases like amyotrophic lateral sclerosis, cataract and so on. The molecular mechanism by which formation of such bonds promotes protein aggregation is poorly understood. Here in this work we employ previously well characterized aggregation of hen eggwhite lysozyme (HEWL) at alkaline pH to dissect the molecular role of nonnative disulfide bonds on growth of HEWL aggregates. We employed time-resolved fluorescenc...

  1. C(arenium)-C(alkyl) bond making and breaking: key process in the platinum-mediated C(aryl)-C(alkyl) bond formation. Analogies to organic electrophilic aromatic substitution.

    Science.gov (United States)

    Albrecht, M; Spek, A L; van Koten, G

    2001-08-01

    The reaction of cationic platinum aqua complexes 2 [Pt(C(6)H(2)[CH(2)NMe(2)](2)-E-4)(OH(2))](X') (X' = SO(3)CF(3), BF(4)) with alkyl halides RX gave various air-stable arenium complexes 3-5 containing a new C-C bond (R = Me, 3; Et, 4; Bn, 5). Electron-releasing oxo-substituents on the aromatic ligand (E = e.g., OH, b; OMe, c) enhance the reactivity of the aqua complex 2 and were essential for arenium formation from alkyl halides different from MeX. This process is initiated by oxidative addition of alkyl halides to the platinum(II) center of 2, which affords (alkyl)(aryl) platinum(IV) complexes (e.g., 9, alkyl = benzyl) as intermediates. Spectroscopic analyses provided direct evidence for a subsequent reversible 1,2-sigmatropic shift of the alkyl group along the Pt-C(aryl) bond, which is identical to repetitive C(arenium)-C(alkyl) bond making and breaking and concerted metal reduction and oxidation. Temperature-dependent NMR spectroscopy revealed DeltaH degrees = -1.3 (+/- 0.1) kJ mol(-1), DeltaS degrees = +3.8 (+/- 0.2) J mol(-1) K(-1), and DeltaG degrees (298) = -2.4 (+/- 0.1) kJ mol(-1) for the formation of the arenium complex 5b from 9 involving the migration of a benzyl group. The arenium complexes were transformed to cyclohexadiene-type addition products 7 or to demetalated alkyl-substituted arenes, 8, thus completing the platinum-mediated formation of a sp(2)-sp(3) C-C bond which is analogous to the aromatic substitution of a [PtX](+) unit by an alkyl cation R(+). The formation of related trimethylsilyl arenium complexes 6 suggests arenium complexes as key intermediates, not only in (metal-mediated) sp(2)-sp(3) C-C bond making and breaking but also in silyl-directed cyclometalation.

  2. 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 i......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...... 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...

  3. 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

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

    Science.gov (United States)

    O'Neal, Kristi L; Weber, Stephen G

    2009-01-08

    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.

  5. Csbnd N bond formation in alicyclic and heterocyclic compounds by amine-modified nanoclay

    Science.gov (United States)

    Zarnegar, Zohre; Alizadeh, Roghayeh; Ahmadzadeh, Majid; Safari, Javad

    2017-09-01

    In the current protocol, amine functionalized montmorillonite K10 nanoclay (NH2-MMT) was applied to catalyze the formation of Csbnd N bonds in the synthesis of azines and 2-aminothiazoles at room temperature. In comparison with the current methods of Csbnd N bond formation, this approach displays specific advantages include atom economy, clean conversion, design for energy efficiency, the use of nontoxic and heterogeneous catalyst, higher purity and yields, safer solvent and reagents for this organic transformation.

  6. Insights into the spontaneity of hydrogen bond formation between formic acid and phthalimide derivatives.

    Science.gov (United States)

    Júnior, Rogério V A; Moura, Gustavo L C; Lima, Nathalia B D

    2016-11-01

    We evaluated a group of phthalimide derivatives, which comprise a convenient test set for the study of the multiple factors involved in the energetics of hydrogen bond formation. Accordingly, we carried out quantum chemical calculations on the hydrogen bonded complexes formed between a sample of phthalimide derivatives with formic acid with the intent of identifying the most important electronic and structural factors related to how their strength and spontaneity vary across the series. The geometries of all species considered were fully optimized at DFT B3LYP/6-31++G(d,p), RM1, RM1-DH2, and RM1-D3H4 level, followed by frequency calculations to determine their Gibbs free energies of hydrogen bond formation using Gaussian 2009 and MOPAC 2012. Our results indicate that the phthalimide derivatives that form hydrogen bond complexes most favorably, have in their structures only one C=O group and at least one NH group. On the other hand, the phthalimide derivatives predicted to form hydrogen bonds least favorably, possess in their structures two carbonyl groups, C=O, and no NH group. The ability to donate electrons and simultaneously receive one acidic hydrogen is the most important property related to the spontaneity of hydrogen bond formation. We further chose two cyclic compounds, phthalimide and isoindolin-1-one, in which to study the main changes in molecular, structural and spectroscopic properties as related to the formation of hydrogen bonds. Thus, the greatest ability of the isoindolin-1-one compound in forming hydrogen bonds is evidenced by the larger effect on the structural, vibrational, and chemical shifts properties associated with the O-H group. In summary, the electron-donating ability of the hydrogen bond acceptor emerged as the most important property differentiating the spontaneity of hydrogen bond formation in this group of complexes.

  7. Mechanisms of hydrogen bond formation between ionic liquids and cellulose and the influence of water content.

    Science.gov (United States)

    Rabideau, Brooks D; Ismail, Ahmed E

    2015-02-28

    We study the dynamics of the formation of multiple hydrogen bonds between ionic liquid anions and cellulose using molecular dynamics simulations. We examine fifteen different ionic liquids composed of 1-alkyl-3-methylimidazolium cations ([Cnmim], n = 1, 2, 3, 4, 5) paired with either chloride, acetate or dimethylphosphate. We map the transitions of anions hydrogen bonded to cellulose into different bonding states. We find that increased tail length in the ionic liquids has only a very minor effect on these transitions, tending to slow the dynamics of the transitions and increasing the hydrogen bond lifetimes. Each anion can form up to four hydrogen bonds with cellulose. We find that this hydrogen bond "redundancy" leads to multiply bonded anions having lifetimes three to four times that of singly bound anions. Such redundant hydrogen bonds account for roughly half of all anion-cellulose hydrogen bonds. Additional simulations for [C2mim]Cl, [C2mim]Ac and [C2mim]DMP were performed at different water concentrations between 70 mol% and 90 mol%. It was found that water crowds the hydrogen bond-accepting sites of the anions, preventing interactions with cellulose. The more water that is present in the system, the more crowded these sites become. Thus, if a hydrogen bond between an anion and cellulose breaks, the likelihood that it will be replaced by a nearby water molecule increases as well. We show that the formation of these "redundant" hydrogen bonding states is greatly affected by the presence of water, leading to steep drops in hydrogen bonding between the anions and cellulose.

  8. Carbon–heteroatom bond formation catalysed by organometallic complexes

    Science.gov (United States)

    Hartwig, John F.

    2010-01-01

    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 supported by the discovery of new elementary reactions that occur at metal–heteroatom bonds and by the identification of factors that control these reactions. Together, these findings have led to new synthetic processes that are in daily use and have formed a foundation for the development of processes that are likely to be central to synthetic chemistry in the future. PMID:18800130

  9. "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 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.

  10. Aeropyrum pernix membrane topology of protein VKOR promotes protein disulfide bond formation in two subcellular compartments.

    Science.gov (United States)

    Hibender, Stijntje; Landeta, Cristina; Berkmen, Mehmet; Beckwith, Jon; Boyd, Dana

    2017-11-15

    Disulfide bonds confer stability and activity to proteins. Bioinformatic approaches allow predictions of which organisms make protein disulfide bonds and in which subcellular compartments disulfide bond formation takes place. Such an analysis, along with biochemical and protein structural data, suggests that many of the extremophile Crenarachaea make protein disulfide bonds in both the cytoplasm and the cell envelope. We have sought to determine the oxidative folding pathways in the sequenced genomes of the Crenarchaea, by seeking homologues of the enzymes known to be involved in disulfide bond formation in bacteria. Some Crenarchaea have two homologues of the cytoplasmic membrane protein VKOR, a protein required in many bacteria for the oxidation of bacterial DsbAs. We show that the two VKORs of Aeropyrum pernix assume opposite orientations in the cytoplasmic membrane, when expressed in E. coli. One has its active cysteines oriented toward the E. coli periplasm (ApVKORo) and the other toward the cytoplasm (ApVKORi). Furthermore, the ApVKORo promotes disulfide bond formation in the E. coli cell envelope, while the ApVKORi promotes disulfide bond formation in the E. coli cytoplasm via a co-expressed archaeal protein ApPDO. Amongst the VKORs from different archaeal species, the pairs of VKORs in each species are much more closely related to each other than to the VKORs of the other species. The results suggest two independent occurrences of the evolution of the two topologically inverted VKORs in archaea. Our results suggest a mechanistic basis for the formation of disulfide bonds in the cytoplasm of Crenarchaea.

  11. Relationship between chemical structure and supramolecular effective molarity for formation of intramolecular H-bonds.

    Science.gov (United States)

    Sun, Hongmei; Hunter, Christopher A; Navarro, Cristina; Turega, Simon

    2013-09-04

    Effective molarity (EM) is a key parameter that determines the efficiency of a range of supramolecular phenomena from the folding of macromolecules to multivalent ligand binding. Coordination complexes formed between zinc porphyrins equipped H-bond donor sites and pyridine ligands equipped with H-bond acceptor sites have allowed systematic quantification of EM values for the formation of intramolecular H-bonds in 240 different systems. The results provide insights into the relationship of EM to supramolecular architecture, H-bond strength, and solvent. Previous studies on ligands equipped with phosphonate diester and ether H-bond acceptors were inconclusive, but the experiments described here on ligands equipped with phosphine oxide, amide, and ester H-bond acceptors resolve these ambiguities. Chemical double-mutant cycles were used to dissect the thermodynamic contributions of individual H-bond interactions to the overall stabilities of the complexes and hence determine the values of EM, which fall in the range 1-1000 mM. Solvent has little effect on EM, and the values measured in toluene and 1,1,2,2-tetrachloroethane are similar. For H-bond acceptors that have similar geometries but different H-bond strengths (amide and ester), the values of EM are very similar. For H-bond acceptors that have different geometries but similar H-bond strengths (amide and phosphonate diester), there is little correlation between the values of EM. These results imply that supramolecular EMs are independent of solvent and intrinsic H-bond strength but depend on supramolecular architecture and geometric complementarity.

  12. 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.

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

    DEFF Research Database (Denmark)

    Wieczorek, Rafal; Dörr, Mark; Chotera, Agata

    2013-01-01

    A new scenario for prebiotic formation of nucleic acid oligomers is presented. Peptide catalysis is applied to achieve condensation of activated RNA monomers into short RNA chains. As catalysts, L-dipeptides containing a histidine residue, primarily Ser-His, were used. Reactions were carried out ...

  14. Preventing disulfide bond formation weakens non-covalent forces among lysozyme aggregates.

    Directory of Open Access Journals (Sweden)

    Vijay Kumar Ravi

    Full Text Available Nonnative disulfide bonds have been observed among protein aggregates in several diseases like amyotrophic lateral sclerosis, cataract and so on. The molecular mechanism by which formation of such bonds promotes protein aggregation is poorly understood. Here in this work we employ previously well characterized aggregation of hen eggwhite lysozyme (HEWL at alkaline pH to dissect the molecular role of nonnative disulfide bonds on growth of HEWL aggregates. We employed time-resolved fluorescence anisotropy, atomic force microscopy and single-molecule force spectroscopy to quantify the size, morphology and non-covalent interaction forces among the aggregates, respectively. These measurements were performed under conditions when disulfide bond formation was allowed (control and alternatively when it was prevented by alkylation of free thiols using iodoacetamide. Blocking disulfide bond formation affected growth but not growth kinetics of aggregates which were ∼50% reduced in volume, flatter in vertical dimension and non-fibrillar in comparison to control. Interestingly, single-molecule force spectroscopy data revealed that preventing disulfide bond formation weakened the non-covalent interaction forces among monomers in the aggregate by at least ten fold, thereby stalling their growth and yielding smaller aggregates in comparison to control. We conclude that while constrained protein chain dynamics in correctly disulfide bonded amyloidogenic proteins may protect them from venturing into partial folded conformations that can trigger entry into aggregation pathways, aberrant disulfide bonds in non-amyloidogenic proteins (like HEWL on the other hand, may strengthen non-covalent intermolecular forces among monomers and promote their aggregation.

  15. Carenium—Calkyl Bond Making and Breaking: Key Process in the Platinum-Mediated Caryl—Calkyl Bond Formation. Analogies to Organic Electrophilic Aromatic Substitution

    NARCIS (Netherlands)

    Koten, G. van; Albrecht, M.A.; Spek, A.L.

    2001-01-01

    The reaction of cationic platinum aqua complexes 2 [Pt(C6H2{CH2NMe2}2-E-4)(OH2)](X') (X' = SO3CF3, BF4) with alkyl halides RX gave various air-stable arenium complexes 3-5 containing a new C-C bond (R = Me, 3; Et, 4; Bn, 5). Electron-releasing oxo-substituents on the aromatic ligand (E = e.g., OH,

  16. A novel type of catalysts for the asymmetric C-C bond formation based on chiral stereochemically inert cationic Co-III complexes

    NARCIS (Netherlands)

    Belokon, Yu. N.; Larionov, V. A.; Mkrtchyan, A. F.; Khrustalev, V. N.; Nijland, A.; Saghyan, A. S.; Godovikov, I. A.; Peregudov, A. S.; Babievsky, K. K.; Ikonnikov, N. S.; Maleev, V. I.

    2012-01-01

    Schiff bases derived from (1R,2R)-1,2-diaminocyclohexane and 1 eq. of salycylic (or substituted salycylic) aldehyde form stereochemically inert positively charged chiral octahedral Co (iii) complexes of Delta-configuration with the stereoselectivity approaching 100%. To evaluate the calatylic

  17. Evaluation of Chromane-Based Bryostatin Analogues Prepared via Hydrogen-Mediated C-C Bond Formation: Potency Does Not Confer Bryostatin-like Biology.

    Science.gov (United States)

    Ketcham, John M; Volchkov, Ivan; Chen, Te-Yu; Blumberg, Peter M; Kedei, Noemi; Lewin, Nancy E; Krische, Michael J

    2016-10-12

    The synthesis and biological evaluation of chromane-containing bryostatin analogues WN-2-WN-7 and the previously reported salicylate-based analogue WN-8 are described. Analogues WN-2-WN-7 are prepared through convergent assembly of the chromane-containing fragment B-I with the "binding domain" fragment A-I or its C26-des-methyl congener, fragment A-II. The synthesis of fragment B-I features enantioselective double C-H allylation of 1,3-propanediol to form the C2-symmetric diol 3 and Heck cyclization of bromo-diene 5 to form the chromane core. The synthesis of salicylate WN-8 is accomplished through the union of fragments A-III and B-II. The highest binding affinities for PKCα are observed for the C26-des-methyl analogues WN-3 (Ki = 63.9 nM) and WN-7 (Ki = 63.1 nM). All analogues, WN-2-WN-8, inhibited growth of Toledo cells, with the most potent analogue being WN-7. This response, however, does not distinguish between phorbol ester-like and bryostatin-like behavior. In contrast, while many of the analogues contain a conserved C-ring in the binding domain and other features common to analogues with bryostatin-like properties, all analogues evaluated in the U937 proliferation and cell attachment assays displayed phorbol ester-like and/or toxic behavior, including WN-8, for which "bryostatin-like PKC modulatory activities" previously was suggested solely on the basis of PKC binding. These results underscore the importance of considering downstream biological effects, as tumor suppression cannot be inferred from potent PKC binding.

  18. Catalyst-controlled reverse selectivity in C-C bond formation : NHC-Cu-catalyzed alpha-selective allylic alkylation with organolithium reagents

    NARCIS (Netherlands)

    Pizzolato, Stefano F.; Giannerini, Massimo; Bos, Pieter H.; Fananas-Mastral, Martin; Feringa, Ben L.

    2015-01-01

    An efficient and highly alpha-selective copper-catalyzed allylic alkylation of allylic halides with organolithium reagents is presented. The use of N-heterocyclic carbenes as ligands is key to reverse the common gamma-selectivity of this transformation and gives rise to the corresponding linear

  19. Catalyst-controlled reverse selectivity in C-C bond formation: NHC-Cu-catalyzed α-selective allylic alkylation with organolithium reagents.

    Science.gov (United States)

    Pizzolato, Stefano F; Giannerini, Massimo; Bos, Pieter H; Fañanás-Mastral, Martín; Feringa, Ben L

    2015-05-11

    An efficient and highly α-selective copper-catalyzed allylic alkylation of allylic halides with organolithium reagents is presented. The use of N-heterocyclic carbenes as ligands is key to reverse the common γ-selectivity of this transformation and gives rise to the corresponding linear products with high levels of regioselectivity.

  20. Disulfide bond formation and ToxR activity in Vibrio cholerae.

    Directory of Open Access Journals (Sweden)

    Vera H I Fengler

    Full Text Available Virulence factor production in Vibrio cholerae is complex, with ToxRS being an important part of the regulatory cascade. Additionally, ToxR is the transcriptional regulator for the genes encoding the major outer membrane porins OmpU and OmpT. ToxR is a transmembrane protein and contains two cysteine residues in the periplasmic domain. This study addresses the influence of the thiol-disulfide oxidoreductase system DsbAB, ToxR cysteine residues and ToxR/ToxS interaction on ToxR activity. The results show that porin production correlates with ToxR intrachain disulfide bond formation, which depends on DsbAB. In contrast, formation of ToxR intrachain or interchain disulfide bonds is dispensable for virulence factor production and in vivo colonization. This study further reveals that in the absence of ToxS, ToxR interchain disulfide bond formation is facilitated, whereat cysteinyl dependent homo- and oligomerization of ToxR is suppressed if ToxS is coexpressed. In summary, new insights into gene regulation by ToxR are presented, demonstrating a mechanism by which ToxR activity is linked to a DsbAB dependent intrachain disulfide bond formation.

  1. Cyclodiphosphazanes as synthetic probes: P-C/P-N bond formation ...

    Indian Academy of Sciences (India)

    Cyclodiphosphazanes as synthetic probes: P-C/P-N bond formation from the reaction with functionalized propargyl ... compounds wonderful precursors to probe organic reac- tions (chart 1). In this study, although reaction ..... 528.43, Monoclinic, Space group C2/c,a = 21.035(4), b = 10.233(2), c = 15.523(3)Å, β = 128.87(3),.

  2. Mechanism of Amide Bond Formation from Carboxylic Acids and Amines Promoted by 9-Silafluorenyl Dichloride Derivatives.

    Science.gov (United States)

    Jiang, Yuan-Ye; Zhu, Ling; Liang, Yujie; Man, Xiaoping; Bi, Siwei

    2017-09-01

    The couplings of carboxylic acids and amines promoted by dichlorosilane derivatives provide a promising tool for amide synthesis and peptide coupling, in which an unprecedented mechanism was proposed for the amide bond formation process. To investigate this mechanistic proposal and enrich the understanding of this novel reaction, a theoretical study was conducted herein. The formation and interconversion of silylamine and silyl ester intermediates were calculated to be kinetically feasible under the experiment conditions. However, the subsequent amidation via direct elimination on the AcO-Si(L)(L')-NHMe intermediate was found to involve a high energy barrier due to the formation of an unstable silanone. By contrast, the in situ generated salts can promote the amidation process by generating a silanol as the temporary product. Similarly, the anhydride formation mechanism can proceed via direct elimination or salt-assisted elimination on the AcO-Si(L)(L')-OAc intermediate but is less favorable. Finally, we found that the intermolecular nucleophilic addition on the AcO-Si(L)(L')-Cl intermediate is the most favorable mechanism among all the candidates considered. In this mechanism, carboxylic acids or bases can act as self-catalysts to promote the amide bond formation via hydrogen bonding, and the formation of the unstable silanone or anhydride is avoided.

  3. How do halogen bonds (S-O⋯I, N-O⋯I and C-O⋯I) and halogen-halogen contacts (C-I⋯I-C, C-F⋯F-C) subsist in crystal structures? A quantum chemical insight.

    Science.gov (United States)

    Pandiyan, B Vijaya; Deepa, P; Kolandaivel, P

    2017-01-01

    Thirteen X-ray crystal structures containing various non-covalent interactions such as halogen bonds, halogen-halogen contacts and hydrogen bonds (I⋯N, I⋯F, I⋯I, F⋯F, I⋯H and F⋯H) were considered and investigated using the DFT-D3 method (B97D/def2-QZVP). The interaction energies were calculated at MO62X/def2-QZVP and MP2/aug-cc-pvDZ level of theories. The higher interaction and dispersion energies (2nd crystal) of -9.58 kcal mol -1 and -7.10 kcal mol -1 observed for 1,4-di-iodotetrafluorobenzene bis [bis (2-phenylethyl) sulfoxide] structure indicates the most stable geometrical arrangement in the crystal packing. The electrostatic potential values calculated for all crystal structures have a positive σ-hole, which aids understanding of the nature of σ-hole bonds. The significance of the existence of halogen bonds in crystal packing environments was authenticated by replacing iodine atoms by bromine and chlorine atoms. Nucleus independent chemical shift analysis reported on the resonance contribution to the interaction energies of halogen bonds and halogen-halogen contacts. Hirshfeld surface analysis and topological analysis (atoms in molecules) were carried out to analyze the occurrence and strength of all non-covalent interactions. These analyses revealed that halogen bond interactions were more dominant than hydrogen bonding interactions in these crystal structures. Graphical Abstract Molecluar structure of 1,4-Di-iodotetrafluorobenzene bis(thianthrene 5-oxide) moelcule and its corresponding molecular electrostatic potential map for the view of σ-hole.

  4. Theoretical and Structural Analysis of Long C-C Bonds in the Adducts of Polycyanoethylene and Anthracene Derivatives and Their Connection to the Reversibility of Diels-Alder Reactions

    NARCIS (Netherlands)

    Hirsch, Anna K. H.; Reutenauer, Philippe; Le Moignan, Marc; Ulrich, Sebastien; Boul, Peter J.; Harrowfield, Jack M.; Jarowski, Peter D.; Lehn, Jean-Marie

    2014-01-01

    X-ray structure determinations on four Diels-Alder adducts derived from the reactions of cyano- and ester-substituted alkenes with anthracene and 9,10-dimethylanthracene have shown the bonds formed in the adduction to be particularly long. Their lengths range from 1.58 to 1.62 angstrom, some of the

  5. Catalytic-site mapping of pyruvate formate lyase. Hypophosphite reaction on the acetyl-enzyme intermediate affords carbon-phosphorus bond synthesis (1-hydroxyethylphosphonate).

    Science.gov (United States)

    Plaga, W; Frank, R; Knappe, J

    1988-12-15

    Pyruvate formate-lyase of Escherichia coli cells, a homodimeric protein of 2 x 85 kDa, is distinguished by the property of containing a stable organic free radical (g = 2.0037) in its resting state. The enzyme (E-SH) achieves pyruvate conversion to acetyl-CoA via two distinct half-reactions (E-SH + pyruvate in equilibrium E-S-acetyl + formate; E-S-acetyl + CoA in equilibrium E-SH + acetyl-CoA), the first of which has been proposed to involve reversible homolytic carbon-carbon bond cleavage [J. Knappe et al. (1984) Proc. Natl Acad. Sci. USA 81, 1332-1335]. Present studies identified Cys-419 as the covalent-catalytic cysteinyl residue via CNBr fragmentation of E-S-[14C]acetyl and radio-sequencing of the isolated peptide CB-Ac (amino acid residues 406-423). Reaction of the formate analogue hypophosphite with E-S-acetyl was investigated and found to produce 1-hydroxyethylphosphonate with a thioester linkage to the adjacent Cys-418. The structure was determined from the chymotryptic peptide CH-P (amino acid residues 415-425), using 31P-NMR spectroscopy (delta = 44 ppm) and by chemical characterisation through degradation into 1-hydroxyethylphosphonate with phosphodiesterase or bromine. This novel P-C-bond synthesis involves the enzyme-based free radical and is proposed to resemble the physiological C-C-bond synthesis (pyruvate production) from formate and E-S-acetyl. These findings are interpreted as proof of a radical mechanism for the action of pyruvate formate-lyase. The central Cys-418/Cys-419 pair of the active site shows a distinctive thiolate property even in the inactive (nonradical) form of the enzyme, as determined using an iodoacetate probe.

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

    Science.gov (United States)

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

    2015-01-01

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

  7. Corrosion Study and Intermetallics Formation in Gold and Copper Wire Bonding in Microelectronics Packaging

    Directory of Open Access Journals (Sweden)

    Christopher Breach

    2013-07-01

    Full Text Available A comparison study on the reliability of gold (Au and copper (Cu wire bonding is conducted to determine their corrosion and oxidation behavior in different environmental conditions. The corrosion and oxidation behaviors of Au and Cu wire bonding are determined through soaking in sodium chloride (NaCl solution and high temperature storage (HTS at 175 °C, 200 °C and 225 °C. Galvanic corrosion is more intense in Cu wire bonding as compared to Au wire bonding in NaCl solution due to the minimal formation of intermetallics in the former. At all three HTS annealing temperatures, the rate of Cu-Al intermetallic formation is found to be three to five times slower than Au-Al intermetallics. The faster intermetallic growth rate and lower activation energy found in this work for both Au/Al and Cu/Al as compared to literature could be due to the thicker Al pad metallization which removed the rate-determining step in previous studies due to deficit in Al material.

  8. Chemical methods and approaches to the regioselective formation of multiple disulfide bonds.

    Science.gov (United States)

    Shimamoto, Shigeru; Katayama, Hidekazu; Okumura, Masaki; Hidaka, Yuji

    2014-04-01

    Disulfide-bond formation plays an important role in the stabilization of the native conformation of peptides and proteins. In the case of multidisulfide-containing peptides and proteins, numerous folding intermediates are produced, including molecules that contain non-native and native disulfide bonds during in vitro folding. These intermediates can frequently be trapped covalently during folding and subsequently analyzed. The structural characterization of these kinetically trapped disulfide intermediates provides a clue to understanding the oxidative folding pathway. To investigate the folding of disulfide-containing peptides and proteins, in this unit, chemical methods are described for regulating regioselective disulfide formation (1) by using a combination of several types of thiol protecting groups, (2) by incorporating unique SeCys residues into a protein or peptide molecule, and (3) by combining with post-translational modification. Copyright © 2014 John Wiley & Sons, Inc.

  9. Renewable Formate from C-H Bond Formation with CO2: Using Iron Carbonyl Clusters as Electrocatalysts.

    Science.gov (United States)

    Loewen, Natalia D; Neelakantan, Taruna V; Berben, Louise A

    2017-09-19

    As a society, we are heavily dependent on nonrenewable petroleum-derived fuels and chemical feedstocks. Rapid depletion of these resources and the increasingly evident negative effects of excess atmospheric CO 2 drive our efforts to discover ways of converting excess CO 2 into energy dense chemical fuels through selective C-H bond formation and using renewable energy sources to supply electrons. In this way, a carbon-neutral fuel economy might be realized. To develop a molecular or heterogeneous catalyst for C-H bond formation with CO 2 requires a fundamental understanding of how to generate metal hydrides that selectively donate H - to CO 2 , rather than recombining with H + to liberate H 2 . Our work with a unique series of water-soluble and -stable, low-valent iron electrocatalysts offers mechanistic and thermochemical insights into formate production from CO 2 . Of particular interest are the nitride- and carbide-containing clusters: [Fe 4 N(CO) 12 ] - and its derivatives and [Fe 4 C(CO) 12 ] 2- . In both aqueous and mixed solvent conditions, [Fe 4 N(CO) 12 ] - forms a reduced hydride intermediate, [H-Fe 4 N(CO) 12 ] - , through stepwise electron and proton transfers. This hydride selectively reacts with CO 2 and generates formate with >95% efficiency. The mechanism for this transformation is supported by crystallographic, cyclic voltammetry, and spectroelectrochemical (SEC) evidence. Furthermore, installation of a proton shuttle onto [Fe 4 N(CO) 12 ] - facilitates proton transfer to the active site, successfully intercepting the hydride intermediate before it reacts with CO 2 ; only H 2 is observed in this case. In contrast, isoelectronic [Fe 4 C(CO) 12 ] 2- features a concerted proton-electron transfer mechanism to form [H-Fe 4 C(CO) 12 ] 2- , which is selective for H 2 production even in the presence of CO 2 , in both aqueous and mixed solvent systems. Higher nuclearity clusters were also studied, and all are proton reduction electrocatalysts, but none

  10. Nano-motion dynamics are determined by surface-tethered selectin mechanokinetics and bond formation.

    Directory of Open Access Journals (Sweden)

    Brian J Schmidt

    2009-12-01

    Full Text Available The interaction of proteins at cellular interfaces is critical for many biological processes, from intercellular signaling to cell adhesion. For example, the selectin family of adhesion receptors plays a critical role in trafficking during inflammation and immunosurveillance. Quantitative measurements of binding rates between surface-constrained proteins elicit insight into how molecular structural details and post-translational modifications contribute to function. However, nano-scale transport effects can obfuscate measurements in experimental assays. We constructed a biophysical simulation of the motion of a rigid microsphere coated with biomolecular adhesion receptors in shearing flow undergoing thermal motion. The simulation enabled in silico investigation of the effects of kinetic force dependence, molecular deformation, grouping adhesion receptors into clusters, surface-constrained bond formation, and nano-scale vertical transport on outputs that directly map to observable motions. Simulations recreated the jerky, discrete stop-and-go motions observed in P-selectin/PSGL-1 microbead assays with physiologic ligand densities. Motion statistics tied detailed simulated motion data to experimentally reported quantities. New deductions about biomolecular function for P-selectin/PSGL-1 interactions were made. Distributing adhesive forces among P-selectin/PSGL-1 molecules closely grouped in clusters was necessary to achieve bond lifetimes observed in microbead assays. Initial, capturing bond formation effectively occurred across the entire molecular contour length. However, subsequent rebinding events were enhanced by the reduced separation distance following the initial capture. The result demonstrates that vertical transport can contribute to an enhancement in the apparent bond formation rate. A detailed analysis of in silico motions prompted the proposition of wobble autocorrelation as an indicator of two-dimensional function. Insight into two

  11. {alpha}-Man monolayer formation via Si-C bond formation and protein recognition

    Energy Technology Data Exchange (ETDEWEB)

    Funato, Koji [School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Shirahata, Naoto [National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Miura, Yoshiko, E-mail: miuray@jaist.ac.j [School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan)

    2009-11-30

    An acetylenyl-terminated saccharide was synthesized and the thin layer formation on the hydrogen-terminated silicon was investigated. The acetylenyl-terminated saccharide was synthesized by the condensation reaction of hexynoic acid and p-aminophenyl saccharide. This was reacted with hydrogen-terminated silicon (Si-H) by a photochemical reaction. The resulting saccharide modified substrate was analyzed by ellipsometry and X-ray photoelectron spectroscopy, which showed the formation of a uniform monolayer. The surface's ability to recognize proteins was analyzed by fluorescent microscopy, and showed specific interactions with sugar recognition proteins.

  12. Formation of the market of high-bond (junk bonds in the United States in 1970–1980 years

    Directory of Open Access Journals (Sweden)

    Moshenskyi S.Z.

    2017-03-01

    Full Text Available Market of high-yield bonds (also known as «junk bonds» began to emerge in the US in the mid-1970s and was associated with the activities of «junk bond king» Michael Milken from Drexel investment company. Junk bonds emitents are small and newly established companies which cannot get a high credit rating. Emission of high-yield (8–10 % bond was their only chance to find its place in the financial market. Michael Milken realized the potential of these bonds, which, in fact, were often quite reliable securities, and started organizing their emissions by selling junk bonds to Savings and Loan Associations and other investors. In the 1980 issue of such bonds used for aggressive corporate takeovers, which supplied the capital from junk bonds market. Some of takeovers carried out in violation of laws that led to the arrest of Michael Milken, Drexel bankruptcy and the collapse of the entire junk bonds market.

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

    Directory of Open Access Journals (Sweden)

    Dennis Kühbeck

    2013-06-01

    Full Text Available 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 at 1 g scale and in good yield. A comparative kinetic study with other biocatalysts shows an increase of the first-order rate constant in the order chitosan < gelatin < bovine serum albumin (BSA < collagen. The results of this study indicate that simple edible gelatin can promote C–C bond forming reactions under physiological conditions, which may have important implications from a metabolic perspective.

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

    Science.gov (United States)

    Li, Yang; Gong, Hao; Sun, Yue; Yan, Juan; Cheng, Biao; Zhang, Xin; Huang, Jing; Yu, Mengying; Guo, Yu; Zheng, Ling; Huang, Kun

    2012-06-29

    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-A11 caused a significant cytotoxicity increase and a higher potency to form high order toxic oligomers. Copyright © 2012 Elsevier Inc. All rights reserved.

  15. Madumycin II inhibits peptide bond formation by forcing the peptidyl transferase center into an inactive state

    Energy Technology Data Exchange (ETDEWEB)

    Osterman, Ilya A.; Khabibullina, Nelli F.; Komarova, Ekaterina S.; Kasatsky, Pavel; Kartsev, Victor G.; Bogdanov, Alexey A.; Dontsova, Olga A.; Konevega, Andrey L.; Sergiev, Petr V.; Polikanov, Yury S. (InterBioScreen); (UIC); (MSU-Russia); (Kurchatov)

    2017-05-13

    The emergence of multi-drug resistant bacteria is limiting the effectiveness of commonly used antibiotics, which spurs a renewed interest in revisiting older and poorly studied drugs. Streptogramins A is a class of protein synthesis inhibitors that target the peptidyl transferase center (PTC) on the large subunit of the ribosome. In this work, we have revealed the mode of action of the PTC inhibitor madumycin II, an alanine-containing streptogramin A antibiotic, in the context of a functional 70S ribosome containing tRNA substrates. Madumycin II inhibits the ribosome prior to the first cycle of peptide bond formation. It allows binding of the tRNAs to the ribosomal A and P sites, but prevents correct positioning of their CCA-ends into the PTC thus making peptide bond formation impossible. We also revealed a previously unseen drug-induced rearrangement of nucleotides U2506 and U2585 of the 23S rRNA resulting in the formation of the U2506•G2583 wobble pair that was attributed to a catalytically inactive state of the PTC. The structural and biochemical data reported here expand our knowledge on the fundamental mechanisms by which peptidyl transferase inhibitors modulate the catalytic activity of the ribosome.

  16. 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.

  17. 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

  18. Ring-opening of cyclic ethers with carbon–carbon bond formation by Grignard reagents

    DEFF Research Database (Denmark)

    Christensen, Stig Holden; Holm, Torkil; Madsen, Robert

    2014-01-01

    The ring-opening of cyclic ethers with concomitant C–C bond formation was studied with a number of Grignard reagents. The transformation was performed in a sealed vial by heating to ∼160 °C in an aluminum block or at 180 °C in a microwave oven. Good yields of the product alcohols were obtained...... with allyl- and benzylmagnesium halides when the ether was tetrahydrofuran or 3,3-dimethyloxetane. Lower yields were obtained with substituted tetrahydrofurans while no ring-opening was observed with tetrahydropyran. Only highly reactive allyl and benzyl Grignard reagents participated in the transformation...

  19. 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

  20. Acetic Acid Can Catalyze Succinimide Formation from Aspartic Acid Residues by a Concerted Bond Reorganization Mechanism: A Computational Study

    Directory of Open Access Journals (Sweden)

    Ohgi Takahashi

    2015-01-01

    Full Text Available Succinimide formation from aspartic acid (Asp residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe as a model compound, we propose the possibility that acetic acid (AA, which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

  1. Structural analysis of SgvP involved in carbon-sulfur bond formation during griseoviridin biosynthesis.

    Science.gov (United States)

    Li, Qin; Chen, Yan; Zhang, Guiqin; Zhang, Huaidong

    2017-05-01

    Griseoviridin (GV) is a broad-spectrum antibiotic with antibacterial and antifungal activity. In the GV biosynthetic pathway, SgvP catalyzes formation of the carbon-sulfur bond in GV. Herein, we report the recombinant expression and characterization of SgvP from Streptomyces griseoviridis NRRL2427. We also present the 2.6 Å crystal structure of SgvP, which is the first structure of a cytochrome P450 involved in carbon-sulfur bond formation in GV. Structural analysis indicates that Pro237 in the I-helix of SgvP may play a critical role in dioxygen binding and proton transfer during the catalytic cycle. Of the three channels we observed in SgvP, channel 3 may be essential for substrate ingress and egress from the active site, while channels 1 and 2 may be the solvent and water pathway, respectively. Coordinate and structure factor were deposited in the Protein Data Bank database under the accession number 4MM0. © 2017 Federation of European Biochemical Societies.

  2. Efficient surface patterning of oligonucleotides inside a glass capillary through oxime bond formation.

    Science.gov (United States)

    Dendane, Nabil; Hoang, Antoine; Guillard, Ludovic; Defrancq, Eric; Vinet, Françoise; Dumy, Pascal

    2007-01-01

    The efficient surface patterning of oligonucleotides was accomplished onto the inner wall of fused-silica capillary tubes as well as on the surface of glass slides through oxime bond formation. The robustness of the method was demonstrated by achieving the surface immobilization of up to three different oligonucleotide sequences inside the same capillary tube. The method involves the preparation of surfaces grafted with reactive aminooxy functionalities masked with the photocleavable protecting group, 2-(2-nitrophenyl) propyloxycarbonyl group (NPPOC). Briefly, NPPOC-aminooxy silane 1 was prepared and used to silanize the glass surfaces. The NPPOC group was cleaved under brief irradiation to unmask the reactive aminooxy group on surfaces. These reactive aminooxy groups were allowed to react with aldehyde-containing oligonucleotides to achieve an efficient surface immobilization. The advantage associated with the present approach is that it combines the high-coupling efficiency of oxime bond formation with the convenience associated with the use of photolabile groups. The present strategy thus offers an alternative approach for the immobilization of biomolecules in the microchannels of "labs on a chip" devices.

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

    Science.gov (United States)

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

    2015-03-23

    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.

  4. Intra- and inter-subunit disulfide bond formation is nonessential in adeno-associated viral capsids.

    Directory of Open Access Journals (Sweden)

    Nagesh Pulicherla

    Full Text Available The capsid proteins of adeno-associated viruses (AAV have five conserved cysteine residues. Structural analysis of AAV serotype 2 reveals that Cys289 and Cys361 are located adjacent to each other within each monomer, while Cys230 and Cys394 are located on opposite edges of each subunit and juxtaposed at the pentamer interface. The Cys482 residue is located at the base of a surface loop within the trimer region. Although plausible based on molecular dynamics simulations, intra- or inter-subunit disulfides have not been observed in structural studies. In the current study, we generated a panel of Cys-to-Ser mutants to interrogate the potential for disulfide bond formation in AAV capsids. The C289S, C361S and C482S mutants were similar to wild type AAV with regard to titer and transduction efficiency. However, AAV capsid protein subunits with C230S or C394S mutations were prone to proteasomal degradation within the host cells. Proteasomal inhibition partially blocked degradation of mutant capsid proteins, but failed to rescue infectious virions. While these results suggest that the Cys230/394 pair is critical, a C394V mutant was found viable, but not the corresponding C230V mutant. Although the exact nature of the structural contribution(s of Cys230 and Cys394 residues to AAV capsid formation remains to be determined, these results support the notion that disulfide bond formation within the Cys289/361 or Cys230/394 pair appears to be nonessential. These studies represent an important step towards understanding the role of inter-subunit interactions that drive AAV capsid assembly.

  5. Spectroscopic Investigation of the Formation and Disruption of Hydrogen Bonds in Pharmaceutical Semicrystalline Dispersions.

    Science.gov (United States)

    Van Duong, Tu; Reekmans, Gunter; Venkatesham, Akkaladevi; Van Aerschot, Arthur; Adriaensens, Peter; Van Humbeeck, Jan; Van den Mooter, Guy

    2017-05-01

    . Screening of crystallization inhibitors of semicrystalline polymers discovers numerous candidates that exhibit the same behavior as IMC, demonstrating a general pattern of polymer crystallization inhibition rather than a particular case. Furthermore, the crystallization inhibition effect of drugs on PEG is independent of the carrier molecular weight. These mechanistic findings on the formation and disruption of hydrogen bonds in semicrystalline dispersions can be extended to amorphous dispersions and are of significant importance for preparation of solid dispersions with consistent and reproducible physicochemical properties.

  6. Disruption of reducing pathways is not essential for efficient disulfide bond formation in the cytoplasm of E. coli

    Directory of Open Access Journals (Sweden)

    Hatahet Feras

    2010-09-01

    Full Text Available Abstract Background The formation of native disulfide bonds is a complex and essential post-translational modification for many proteins. The large scale production of these proteins can be difficult and depends on targeting the protein to a compartment in which disulfide bond formation naturally occurs, usually the endoplasmic reticulum of eukaryotes or the periplasm of prokaryotes. It is currently thought to be impossible to produce large amounts of disulfide bond containing protein in the cytoplasm of wild-type bacteria such as E. coli due to the presence of multiple pathways for their reduction. Results Here we show that the introduction of Erv1p, a sulfhydryl oxidase and FAD-dependent catalyst of disulfide bond formation found in the inter membrane space of mitochondria, allows the efficient formation of native disulfide bonds in heterologously expressed proteins in the cytoplasm of E. coli even without the disruption of genes involved in disulfide bond reduction, for example trxB and/or gor. Indeed yields of active disulfide bonded proteins were higher in BL21 (DE3 pLysSRARE, an E. coli strain with the reducing pathways intact, than in the commercial Δgor ΔtrxB strain rosetta-gami upon co-expression of Erv1p. Conclusions Our results refute the current paradigm in the field that disruption of at least one of the reducing pathways is essential for the efficient production of disulfide bond containing proteins in the cytoplasm of E. coli and open up new possibilities for the use of E. coli as a microbial cell factory.

  7. Carbon-Heteroatom Bond Formation by an Ultrasonic Chemical Reaction for Energy Storage Systems.

    Science.gov (United States)

    Kim, Hyun-Tak; Shin, HyeonOh; Jeon, In-Yup; Yousaf, Masood; Baik, Jaeyoon; Cheong, Hae-Won; Park, Noejung; Baek, Jong-Beom; Kwon, Tae-Hyuk

    2017-12-01

    The direct formation of CN and CO bonds from inert gases is essential for chemical/biological processes and energy storage systems. However, its application to carbon nanomaterials for improved energy storage remains technologically challenging. A simple and very fast method to form CN and CO bonds in reduced graphene oxide (RGO) and carbon nanotubes (CNTs) by an ultrasonic chemical reaction is described. Electrodes of nitrogen- or oxygen-doped RGO (N-RGO or O-RGO, respectively) are fabricated via the fixation between N2 or O2 carrier gas molecules and ultrasonically activated RGO. The materials exhibit much higher capacitance after doping (133, 284, and 74 F g-1 for O-RGO, N-RGO, and RGO, respectively). Furthermore, the doped 2D RGO and 1D CNT materials are prepared by layer-by-layer deposition using ultrasonic spray to form 3D porous electrodes. These electrodes demonstrate very high specific capacitances (62.8 mF cm-2 and 621 F g-1 at 10 mV s-1 for N-RGO/N-CNT at 1:1, v/v), high cycling stability, and structural flexibility. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Energy Technology Data Exchange (ETDEWEB)

    Roth, Justine P. [Johns Hopkins Univ., Baltimore, MD (United States)

    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.

  9. Modular functionalized polyphosphines for supported materials: previously unobserved (31)P-NMR «through-space» ABCD spin systems and heterogeneous palladium-catalysed C-C and C-H arylation.

    Science.gov (United States)

    Beaupérin, Matthieu; Smaliy, Radomyr; Cattey, Hélène; Meunier, Philippe; Ou, Jun; Toy, Patrick H; Hierso, Jean-Cyrille

    2014-08-28

    The modular design of polyphosphines, diversely functionalized for facile immobilization on virtually any kind of support, is reported. Previously unobserved ABCD (31)P NMR spin-spin systems evidence the control exercised on the polyphosphines conformation. We illustrate the catalytic performance at low Pd loading of the recyclable immobilized polyphosphines in C-C bond formation reactions.

  10. Bane of Hydrogen-Bond Formation on the Photoinduced Charge-Transfer Process in Donor–Acceptor Systems

    KAUST Repository

    Alsam, Amani Abdu

    2017-03-14

    Controlling the ultrafast dynamical process of photoinduced charge transfer at donor acceptor interfaces remains a major challenge for physical chemistry and solar cell communities. The process is complicated by the involvement of other complex dynamical processes, including hydrogen bond formation, energy transfer, and solvation dynamics occurring on similar time scales. In this study, we explore the remarkable impact of hydrogen-bond formation on the interfacial charge transfer between a negatively charged electron donating anionic porphyrin and a positively charged electron accepting pi-conjugated polymer, as a model system in solvents with different polarities and capabilities for hydiogen bonding using femtosecond transient absorption spectroscopy. Unlike the conventional understanding of the key role of hydrogen bonding in promoting the charge-transfer process, our steadystate and time-resolved results reveal that the intervening hydrogen-bonding environment and, consequently, the probable longer spacing between the donor and acceptor molecules significantly hinders the charge-transfer process between them. These results show that site-specific hydrogen bonding and geometric considerations between donor and acceptor can be exploited to control both the charge-transfer dynamics and its efficiency not only at donor acceptor interfaces but also in complex biological systems.

  11. Paleobotany and palynology of the Bristol Hill Coal Member (Bond Formation) and Friendsville Coal Member (Mattoon Formation) of the Illinois Basin (Upper Pennsylvania)

    Energy Technology Data Exchange (ETDEWEB)

    Willard, D.A.; Phillips, T.L. [US Geological Survey, Reston, VA (United States)

    1993-12-01

    Late Pennsylvanian coal swamps of the Illinois Basin were dominated by Psaronius tree ferns with a spatially heterogeneous distribution of medullosan pteridosperms (subdominant), calamites, sigillarian lycopsids, and cordaites. Miospore and coal-ball plant assemblages from the Missourian-age Bristol Hill Coal Member (Bond Formation) and Friendsville Coal Member (Mattoon Formation) of southeastern Illinois were quantified to analyze vegetational patterns in Late Pennsylvanian peat swamps and to compare vegetational composition of the coals.

  12. Hydroxyl radical formation by O-O bond homolysis in peroxynitrous acid.

    Science.gov (United States)

    Lymar, Sergei V; Khairutdinov, Rafail F; Hurst, James K

    2003-08-25

    Peroxynitrite decay in weakly alkaline media occurs by two concurrent sets of pathways which are distinguished by their reaction products. One set leads to net isomerization to NO(3)(-) and the other set to net decomposition to O(2) plus NO(2)(-). At sufficiently high peroxynitrite concentrations, the decay half-time becomes concentration-independent and approaches a limiting value predicted by a mechanism in which reaction is initiated by unimolecular homolysis of the peroxo O-O bond, i.e., the following reaction: ONOOH --> (*)OH + (*)NO(2). This dynamical behavior excludes alternative postulated mechanisms that ascribe decomposition to bond rearrangement within bimolecular adducts. Nitrate and nitrite product distributions measured at very low peroxynitrite concentrations also correspond to predictions of the homolysis model, contrary to a recent report from another laboratory. Additionally, (1) the rate constant for the reaction ONOO(-) --> (*)NO + (*)O(2)(-), which is critical to the kinetic model, has been confirmed, (2) the apparent volume of activation for ONOOH decay (DeltaV() = 9.7 +/- 1.4 cm(3)/mol) has been shown to be independent of the concentration of added nitrite and identical to most other reported values, and (3) complex patterns of inhibition of O(2) formation by radical scavengers, which are impossible to rationalize by alternative proposed reaction schemes, are shown to be quantitatively in accord with the homolysis model. These observations resolve major disputes over experimental data existing in the literature; despite extensive investigation of these reactions, no verifiable experimental evidence has been advanced that contradicts the homolysis model.

  13. 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...

  14. Intermolecular Formation of Two C−C Bonds across Olefins Enabled by Boron-Based Relay Strategies

    Czech Academy of Sciences Publication Activity Database

    Hidasová, Denisa; Jahn, Ullrich

    2017-01-01

    Roč. 56, č. 33 (2017), s. 9656-9658 ISSN 1433-7851 Institutional support: RVO:61388963 Keywords : 1,2-metalate rearrangement * C−C bond formation * radical reactions * transition metal catalysis * vinyl boronates Subject RIV: CC - Organic Chemistry Impact factor: 11.994, year: 2016

  15. Neutral copper-phosphido-borane complexes: synthesis, characterization, and use as precatalysts in C(sp)-P bond formation.

    Science.gov (United States)

    Abdellah, Ibrahim; Bernoud, Elise; Lohier, Jean-François; Alayrac, Carole; Toupet, Loïc; Lepetit, Christine; Gaumont, Annie-Claude

    2012-04-28

    Copper-phosphido-borane complexes were synthesized and isolated for the first time. Their structures were experimentally and computationally investigated. They were shown to display catalytic activity in C(sp)-P bond formation. This journal is © The Royal Society of Chemistry 2012

  16. Early biofilm formation and the effects of antimicrobial agents on orthodontic bonding materials in a parallel plate flow chamber

    NARCIS (Netherlands)

    Chin, Yeen; Busscher, HJ; Evans, R; Noar, J; Pratten, J

    Decalcification is a commonly recognized complication of orthodontic treatment with fixed appliances. A technology, based on a parallel plate flow chamber, was developed to investigate early biofilm formation of a strain of Streptococcus sanguis on the surface of four orthodontic bonding materials:

  17. Alkane activation at ambient temperature - Unusual selectivities, C-C, C-H bond scission vs C-C bond coupling

    NARCIS (Netherlands)

    Trionfetti, C.; Agiral, A.; Gardeniers, Han J G E; Lefferts, L.; Seshan, K.

    2008-01-01

    Availability and low cost of light alkanes make them interesting as feedstock for commercial fuels and chemicals. However, direct conversion of lower alkanes for such purposes is a challenging problem. A discussion covers the oxidative conversion of light alkanes in the presence of cold plasma in a

  18. Role of Hydrogen Bonding in the Formation of Adenine Chains on Cu(110 Surfaces

    Directory of Open Access Journals (Sweden)

    Lanxia Cheng

    2016-12-01

    Full Text Available Understanding the adsorption properties of DNA bases on metal surfaces is fundamental for the rational control of surface functionalization leading to the realisation of biocompatible devices for biosensing applications, such as monitoring of particular parameters within bio-organic environments and drug delivery. In this study, the effects of deposition rate and substrate temperature on the adsorption behavior of adenine on Cu(110 surfaces have been investigated using scanning tunneling microscopy (STM and density functional theory (DFT modeling, with a focus on the characterization of the morphology of the adsorbed layers. STM results revealed the formation of one-dimensional linear chains and ladder-like chains parallel to the [110] direction, when dosing at a low deposition rate at room temperature, followed by annealing to 490 K. Two mirror related, well-ordered chiral domains oriented at ±55° with respect to the [110] direction are formed upon deposition on a substrate kept at 490 K. The molecular structures observed via STM are rationalized and qualitatively described on the basis of the DFT modeling. The observation of a variety of ad-layer structures influenced by deposition rate and substrate temperature indicates that dynamic processes and hydrogen bonding play an important role in the self-assembly of adenine on the Cu(110 surface.

  19. Biofilm formation on stainless steel and gold wires for bonded retainers in vitro and in vivo and their susceptibility to oral antimicrobials

    NARCIS (Netherlands)

    Jongsma, Marije A.; Pelser, Floris D. H.; van der Mei, Henny C.; Atema-Smit, Jelly; van de Belt-Gritter, Betsy; Busscher, Henk J.; Ren, Yijin

    OBJECTIVE: Bonded retainers are used in orthodontics to maintain treatment result. Retention wires are prone to biofilm formation and cause gingival recession, bleeding on probing and increased pocket depths near bonded retainers. In this study, we compare in vitro and in vivo biofilm formation on

  20. Quantum chemical studies of a model for peptide bond formation. 3. Role of magnesium cation in formation of amide and water from ammonia and glycine

    Science.gov (United States)

    Oie, T.; Loew, G. H.; Burt, S. K.; MacElroy, R. D.

    1984-01-01

    The SN2 reaction between glycine and ammonia molecules with magnesium cation Mg2+ as a catalyst has been studied as a model reaction for Mg(2+)-catalyzed peptide bond formation using the ab initio Hartree-Fock molecular orbital method. As in previous studies of the uncatalyzed and amine-catalyzed reactions between glycine and ammonia, two reaction mechanisms have been examined, i.e., a two-step and a concerted reaction. The stationary points of each reaction including intermediate and transition states have been identified and free energies calculated for all geometry-optimized reaction species to determine the thermodynamics and kinetics of each reaction. Substantial decreases in free energies of activation were found for both reaction mechanisms in the Mg(2+)-catalyzed amide bond formation compared with those in the uncatalyzed and amine-catalyzed amide bond formation. The catalytic effect of the Mg2+ cation is to stabilize both the transition states and intermediate, and it is attributed to the neutralization of the developing negative charge on the electrophile and formation of a conformationally flexible nonplanar five-membered chelate ring structure.

  1. Sequential C-Si Bond Formations from Diphenylsilane: Application to Silanediol Peptide Isostere Precursors

    DEFF Research Database (Denmark)

    Nielsen, Lone; Skrydstrup, Troels

    2008-01-01

    and the first new carbon-silicon bond. The next step is the reduction of this hydridosilane with lithium metal providing a silyl lithium reagent, which undergoes a highly diastereoselective addition to an optically active tert-butanesulfinimine, thus generating the second C-Si bond. This method allows...

  2. 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

    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

  3. A computational study on the mechanism of ynamide-mediated amide bond formation from carboxylic acids and amines.

    Science.gov (United States)

    Zhang, Song-Lin; Wan, Hai-Xing; Deng, Zhu-Qin

    2017-08-02

    This paper reports a computational study elucidating the reaction mechanism for ynamide-mediated amide bond formation from carboxylic acids and amines. The mechanisms have been studied in detail for ynamide hydrocarboxylation and the subsequent aminolysis of the resulting adduct by an amine. Ynamide hydrocarboxylation is kinetically favorable and thermodynamically irreversible, resulting in the formation of a key low-lying intermediate CP1 featuring geminal vinylic acyloxy and sulfonamide groups. The aminolysis of CP1 by the amine is proposed to be catalyzed by the carboxylic acid itself that imparts favourable bifunctional effects. In the proposed key transition state TSaminolysis-acid-iso2, the amine undergoes direct nucleophilic substitution at the acyl of CP1 to replace the enolate group in a concerted way, which is promoted by secondary hydrogen bonding of carboxylic acid with both the amine and CP1. These secondary interactions are suggested to increase the nucleophilicity of the amine and to activate the Cacyl-O bond to be cleaved, thereby stabilizing the aminolysis transition state. The concerted aminolysis mechanism is competitive with the classic stepwise nucleophilic acyl substitution mechanism that features sequential amine addition to acyl/intramolecular proton transfer/C-O bond cleavage and a key tetrahedral intermediate. Based on the mechanistic model, the carboxylic acid substrate effect and studies of more acidic CF3SO3H as the catalyst are in good agreement with the experimental observations, lending further support for the mechanistic model. The bifunctional catalytic effect of the carboxylic acid substrate may widely play a role in related amide bond-forming reactions and peptide formation chemistry.

  4. Decreasing the Viscosity in CO2 Capture by Amino-Functionalized Ionic Liquids through the Formation of Intramolecular Hydrogen Bond.

    Science.gov (United States)

    Luo, Xiao Y; Fan, Xi; Shi, Gui L; Li, Hao R; Wang, Cong M

    2016-03-17

    A strategy for decreasing the viscosity variation in the process of CO2 capture by amino-functionalized ionic liquids (ILs) through the formation of intramolecular hydrogen bond was reported. Different with the dramatic increase in viscosity during CO2 uptake by traditional amino-functionalized ILs, slight increase or even decrease in viscosity was achieved through introducing a N or O atom as hydrogen acceptor into amino-functionalized anion, which could stabilize the active hydrogen of produced carbamic acid. Quantum chemical calculations and spectroscopic investigations demonstrated that the formation of intramolecular hydrogen bond between introduced hydrogen acceptor and carbamic acid was the key to avoid the dramatic increase in viscosity during the capture of CO2 by these amino-functionalized ILs.

  5. Activation of dinitrogen-derived hafnium nitrides for nucleophilic N-C bond formation with a terminal isocyanate.

    Science.gov (United States)

    Semproni, Scott P; Chirik, Paul J

    2013-12-02

    Better by Hf: Anion coordination to a bridging hafnocene nitride complex, prepared from CO-induced N2 cleavage, increases the nucleophilicity of the nitrogen atom, thus promoting additional NC bond formation with a typically inert terminal isocyanate ligand. This cascade sequence allows synthesis of otherwise challenging mono-substituted ureas using N2 , CO, and an appropriate electrophile. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Palladium-Catalyzed Deaminative Phenanthridinone Synthesis from Aniline via C-H Bond Activation.

    Science.gov (United States)

    Yedage, Subhash L; Bhanage, Bhalchandra M

    2016-05-20

    This work reports palladium-catalyzed phenanthridinone synthesis using the coupling of aniline and amide by formation of C-C and C-N bonds in a one-pot fashion via dual C-H bond activation. It involves simultaneous cleavage of four bonds and the formation of two new bonds. The present protocol is ligand-free, takes place under mild reaction conditions, and is environmentally benign as nitrogen gas and water are the only side products. This transformation demonstrates a broad range of aniline and amide substrates with different functional groups and has been scaled up to gram level.

  7. Exploring the Role of Substitution on the Formation of Se···O/N Noncovalent Bonds.

    Science.gov (United States)

    Shukla, Rahul; Chopra, Deepak

    2015-11-25

    In this article, we have examined the effect of substitution on the formation of neutral XHSe···O/N (X = -H, -F, -CH3, -CF3, -Cl, -OH, -OCH3, -NH2, -NHCH3, -CN) noncovalent bonds with the oxygen atom from H2O molecule and the nitrogen atom from NH3 being the electron donor atoms, respectively. In addition to this, analysis has also been performed on XMeSe···O/N complexes to study the effect of the role of hydrogen bonding with the hydrogen atoms of the methyl group on Se···O/N interactions. Binding energy calculations were performed to determine the strength of these contacts. The obtained results establish the fact that the presence of a methyl group influences the strength of the observed Se···O/N interactions. Also in some cases, the O-H···Se interaction was observed to be more preferable over the Se···O interaction. The major contribution for stabilization of such Se···O/N interactions is from an interplay among the electrostatics and the exchange energy. To obtain deeper insights and understanding of such Se···O/N contacts, a topological analysis, using the QTAIM approach were also performed. This analysis showed that although the presence of a Me group modifies the Se···O/N interaction, it does not necessitate the formation of hydrogen bonds. To obtain insights into the orbital contributions, a natural bond orbital (NBO) analysis were performed which depicts that the strength of such interactions were derived via charge transfer from the oxygen/nitrogen lone pair to the σ* orbital of the Se-X bond.

  8. Shear-bond strength between a new format of intra-buccal acrylic bioadhesive drug delivery system and adhesive systems.

    Science.gov (United States)

    Pedrazzi, V; Del Ciampo, J O; Panzeri, H; Lara, E Helena Guimarães; Issa, J P Mardegan; Do Nascimento, C

    2009-04-01

    An intra-buccal acrylic bioadhesive device designated for drug programmed release that can stay adhered to dental enamel, and also on removable prosthetic restorations, with preventive and/or therapeutic purpose for a large clinical applications based on polymethyl methacrylate/methyl methacrylate/2 hydroxyethyl methacrylate (PMMA/MMA/HEMA) was developed, using the sodium fluoride as an active principle. This bioadhesive was evaluated for its shear bond strength when bonded with different adhesive systems. Two substrates (recently extracted human teeth and acrylic prosthesis basis) were used to obtain the 96 test-specimens. Four adhesive systems (Cyanoacrylate ester, 3M Concise Enamel Bond Resin with or without previous enamel etching, MMA/HEMA or PMMA/MMA/ HEMA) were chosen for the fixation of the bioadhesives to substrate. Artificial saliva or distilled water was used as medium for maintaining the specimens until test. Statistical analysis showed that the interaction bioadhesives/acrylic prosthesis basis/cyanoacrylate ester adhesive was the most resistant to the physical removal by shearing. The newly rounded semi-convex format of acrylic device developed in this study presented satisfactory shear bond strength and might contribute to the comfort of intra-buccal use.

  9. The effects of orthodontic bonding steps on biofilm formation of Streptococcus mutans in the presence of saliva.

    Science.gov (United States)

    Ahn, Sug-Joon; Cho, Eun-Jung; Oh, Sung-Suk; Lim, Bum-Soon

    2012-12-01

    To investigate the effects of various orthodontic bonding steps on biofilm formation of Streptococcus mutans in the presence of saliva. Hydroxyapatite (HA) and orthodontic adhesive (AD) disks were prepared to a uniform size. HA disks were etched with 37% phosphoric acid gel in the etched group (HE). In the primed group (HP), Transbond XT primer was applied to the etched HA surface and light-cured. For biofilm formation, Streptococcus mutans was grown on each specimen in a biofilm medium with either glucose or sucrose in the presence of fluid-phase UWS (F-UWS) or surface adsorbed saliva (S-UWS). The adherent bacteria were quantified by enumeration of the total viable counts of bacteria. Biofilms formed on each surface were examined by scanning electron microscopy. When glucose was used, both F-UWS and S-UWS suppressed biofilm formation of S. mutans. Compared to HA and HE, biofilm formation was significantly inhibited on HP and AD in the presence of glucose. Biofilm-forming patterns that were inhibited by saliva were restored in a sucrose-containing medium. F-UWS promoted biofilm formation on HA and HE, while S-UWS significantly promoted biofilm formation on HP. S. mutans developed biofilm better on HA and HE than on AD when sucrose was used as the sole carbohydrate source. This study suggests that the biofilm development by S. mutans is significantly influenced by the orthodontic bonding procedure. Biofilm formation of S. mutans was inhibited on AD more than other surfaces, irrespective of the presence of saliva or a carbohydrate source.

  10. Reusable ionic liquid-catalyzed oxidative coupling of azoles and benzylic compounds via sp(3) C-N bond formation under metal-free conditions.

    Science.gov (United States)

    Liu, Wenbo; Liu, Chenjiang; Zhang, Yonghong; Sun, Yadong; Abdukadera, Ablimit; Wang, Bin; Li, He; Ma, Xuecheng; Zhang, Zengpeng

    2015-07-14

    The heterocyclic ionic liquid-catalyzed direct oxidative amination of benzylic sp(3) C-H bonds via intermolecular sp(3) C-N bond formation for the synthesis of N-alkylated azoles under metal-free conditions is reported for the first time. The catalyst 1-butylpyridinium iodide can be recycled and reused with similar efficacies for at least eight cycles.

  11. 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

    2014-01-01

    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 was seen as evidence for covalent bonds between lignin phenolics and the coupling agents. No spectral changes were observed when the coupling agents were mixed with the wood constituents cellulose and hemicellulose. For verification of the results, a modified EN 311 wet adhesion pull strength test......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...

  12. Hexagonal wheel formation through the hydrogen-bonded assembly of cobalt Pacman complexes.

    Science.gov (United States)

    Leeland, James W; White, Fraser J; Love, Jason B

    2011-04-14

    A cobalt aquo-hydroxo complex of a ditopic Schiff-base pyrrole-crown ether macrocycle has been prepared and forms a rigid Pacman-clefted structure that assembles through hydrogen-bonding into a hexagonal wheel motif in the solid state.

  13. Nucleophilicity and P-C bond formation reactions of a terminal phosphanido iridium complex

    NARCIS (Netherlands)

    Serrano, Á.L.; Casado, M.A.; Ciriano, M.A.; de Bruin, B.; López, J.A.; Tejel, C.

    2016-01-01

    The diiridium complex [{Ir(ABPN(2))(CO)}(2)(μ-CO)] (1; [ABPN(2)]- = [(allyl)B(Pz)(2)(CH(2)PPh(2))]-) reacts with diphenylphosphane affording [Ir(ABPN(2))(CO)(H) (PPh(2))] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the

  14. Total synthesis of feglymycin based on a linear/convergent hybrid approach using micro-flow amide bond formation

    Science.gov (United States)

    Fuse, Shinichiro; Mifune, Yuto; Nakamura, Hiroyuki; Tanaka, Hiroshi

    2016-11-01

    Feglymycin is a naturally occurring, anti-HIV and antimicrobial 13-mer peptide that includes highly racemizable 3,5-dihydroxyphenylglycines (Dpgs). Here we describe the total synthesis of feglymycin based on a linear/convergent hybrid approach. Our originally developed micro-flow amide bond formation enabled highly racemizable peptide chain elongation based on a linear approach that was previously considered impossible. Our developed approach will enable the practical preparation of biologically active oligopeptides that contain highly racemizable amino acids, which are attractive drug candidates.

  15. 2-nitroveratryl as a photocleavable thiol-protecting group for directed disulfide bond formation in the chemical synthesis of insulin.

    Science.gov (United States)

    Karas, John A; Scanlon, Denis B; Forbes, Briony E; Vetter, Irina; Lewis, Richard J; Gardiner, James; Separovic, Frances; Wade, John D; Hossain, Mohammed A

    2014-07-28

    Chemical synthesis of peptides can allow the option of sequential formation of multiple cysteines through exploitation of judiciously chosen regioselective thiol-protecting groups. We report the use of 2-nitroveratryl (oNv) as a new orthogonal group that can be cleaved by photolysis under ambient conditions. In combination with complementary S-pyridinesulfenyl activation, disulfide bonds are formed rapidly in situ. The preparation of Fmoc-Cys(oNv)-OH is described together with its use for the solid-phase synthesis of complex cystine-rich peptides, such as insulin. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Formation and Reactivity of a Molecular Magnesium Hydride with a Terminal Mg-H Bond.

    Science.gov (United States)

    Schnitzler, Silvia; Spaniol, Thomas P; Maron, Laurent; Okuda, Jun

    2015-08-03

    A complex featuring a terminal magnesium hydride bond supported by an NNNN macrocyclic ligand, [Mg{Me3 TACD⋅Al(iBu)3}H] (3), was formed from its labile Al(iBu)3 adduct. Use of Al(iBu)3 to block the amido nitrogen of the NNNN macrocyclic ligand was essential to prevent aggregation. The structurally characterized compound 3 reacted with BH3 to give the BH4 derivative, whereas Me3 SiCCH and PhSiH3 led to the corresponding acetylide and silyl derivative under H2 elimination. Pyridine is inserted into the MgH bond to give selectively the 1,4-dihydropyridinate. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. 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...... 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-known aqueous...... reaction mechanism. The energy barrier of the catalyzed amidation reaction is approximately 40 kJ mol(-1) lower than the non-catalyzed amidation reaction. At least partially this can be explained by a hydrogen bond from the amine to the π-electrons of the thiophenol, stabilizing the transition state...

  18. 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.

  19. Pair bond formation leads to a sustained increase in global cerebral glucose metabolism in monogamous male titi monkeys (Callicebus cupreus).

    Science.gov (United States)

    Maninger, Nicole; Hinde, Katie; Mendoza, Sally P; Mason, William A; Larke, Rebecca H; Ragen, Benjamin J; Jarcho, Michael R; Cherry, Simon R; Rowland, Douglas J; Ferrer, Emilio; Bales, Karen L

    2017-04-21

    Social bonds, especially attachment relationships, are crucial to our health and happiness. However, what we know about the neural substrates of these bonds is almost exclusively limited to rodent models and correlational experiments in humans. Here, we used socially monogamous non-human primates, titi monkeys (Callicebus cupreus) to experimentally examine changes in regional and global cerebral glucose metabolism (GCGM) during the formation and maintenance of pair bonds. Baseline positron emission tomography (PET) scans were taken of thirteen unpaired male titi monkeys. Seven males were then experimentally paired with females, scanned and compared, after one week, to six age-matched control males. Five of the six control males were then also paired and scanned after one week. Scans were repeated on all males after four months of pairing. PET scans were coregistered with structural magnetic resonance imaging (MRI), and region of interest (ROI) analysis was carried out. A primary finding was that paired males showed a significant increase in [18F]-fluorodeoxyglucose (FDG) uptake in whole brain following one week of pairing, which is maintained out to four months. Dopaminergic, "motivational" areas and those involved in social behavior showed the greatest change in glucose uptake. In contrast, control areas changed only marginally more than GCGM. These findings confirm the large effects of social bonds on GCGM. They also suggest that more studies should examine how social manipulations affect whole-brain FDG uptake, as opposed to assuming that it does not change across condition. Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

  20. 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.

    2016-09-01

    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.

  1. 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.

    2017-01-01

    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

  2. Formation of the First Peptide Bond: The Structure of EF-P Bound to the 70S Ribosome

    Energy Technology Data Exchange (ETDEWEB)

    Blaha, Gregor; Stanley, Robin E.; Steitz, Thomas A.; Yale

    2009-10-21

    Elongation factor P (EF-P) is an essential protein that stimulates the formation of the first peptide bond in protein synthesis. Here we report the crystal structure of EF-P bound to the Thermus thermophilus 70S ribosome along with the initiator transfer RNA N-formyl-methionyl-tRNAi (fMet-tRNA{sub i}{sup fMet}) and a short piece of messenger RNA (mRNA) at a resolution of 3.5 angstroms. EF-P binds to a site located between the binding site for the peptidyl tRNA (P site) and the exiting tRNA (E site). It spans both ribosomal subunits with its amino-terminal domain positioned adjacent to the aminoacyl acceptor stem and its carboxyl-terminal domain positioned next to the anticodon stem-loop of the P site-bound initiator tRNA. Domain II of EF-P interacts with the ribosomal protein L1, which results in the largest movement of the L1 stalk that has been observed in the absence of ratcheting of the ribosomal subunits. EF-P facilitates the proper positioning of the fMet-tRNA{sub i}{sup fMet} for the formation of the first peptide bond during translation initiation.

  3. Susceptibility towards intramolecular disulphide-bond formation affects conformational stability and folding of human basic fibroblast growth factor.

    Science.gov (United States)

    Estapé, D; van den Heuvel, J; Rinas, U

    1998-01-01

    The conformational stability and the folding properties of the all-beta-type protein human basic fibroblast growth factor (hFGF-2) were studied by means of fluorescence spectroscopy. The results show that the instability of the biological activity of hFGF-2 is also reflected in a low conformational stability of the molecule. The reversibility of the unfolding and refolding process was established under reducing conditions. Determination of the free-energy of unfolding in the presence of reducing agents revealed that the conformational stability of hFGF-2 (DeltaGH2Oapp congruent with21 kJ. mol-1, 25 degreesC) is low compared with other globular proteins under physiological conditions (20-60 kJ.mol-1). However, the conformational stability of hFGF-2 is particularly low under non-reducing conditions. This instability is attributed to intramolecular disulphide-bond formation, rendering the molecule more susceptible to denaturant-induced unfolding. In addition, denaturant-induced unfolding of hFGF-2 renders the protein more susceptible to irreversible oxidative denaturation. Experimental evidence is provided that the irreversibility of the unfolding and refolding process in the absence of reducing agents is linked to the formation of an intramolecular disulphide bond involving cysteines 96 and 101. PMID:9761733

  4. 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.

  5. Effect of copper salts on peptide bond formation using peptide thioesters.

    Science.gov (United States)

    Ingenito, Raffaele; Wenschuh, Holger

    2003-11-27

    [reaction: see text] In the present paper, systematic studies revealed that Cu(I) salts in general and Cu(II) salts under certain circumstances promote effective reaction between peptide thiol esters and the N-terminal amino function of a second peptide segment to give the native amide bond for both solution- and solid-phase syntheses. Chiral integrity was retained. Reaction conditions were optimized and applied to the synthesis of a small protein, the identity of which was confirmed by NMR analysis.

  6. Photoinduced C-C Cross-Coupling of Aryl Chlorides and Inert Arenes

    Directory of Open Access Journals (Sweden)

    Lele Wang

    2016-01-01

    Full Text Available Here we report a facile, efficient, and catalyst-free method to realize C-C cross-coupling of aryl chlorides and inert arenes under UV light irradiation. The aryl radical upon homolytic cleavage of C-Cl bond initiated the nucleophilic substitution reaction with inert arenes to give biaryl products. This mild reaction mode can also be applied to other synthetic reactions, such as the construction of C-N bonds and trifluoromethylated compounds.

  7. 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

    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....

  8. Formation of sulfido ciobium complexes through C-S bond activation

    Directory of Open Access Journals (Sweden)

    Azevedo Nélio Pires

    1998-01-01

    Full Text Available Upon reacting (eta5-C5H52NbCl2, eta5-C5H5 = Cp, and (Ph3Sn(SPh, in THF, (eta5-C5H52Nb(Cl(mu-SSn(Ph3(Cl, 1, and (eta5-C5H52Nb(SCl, 2, were obtained. Complexes 1 and 2 were characterized by IR, ¹H-NMR, 13C-NMR, Mössbauer spectroscopies, elemental analysis as well as by atomic absorption. Hydrolysis of 1 yielded the mu-oxo species, (eta5-C5H52Nb(Cl(mu-OSn(Ph3Cl, 3, which was characterized by IR, ¹H-NMR, 13C-NMR and Mössbauer spectroscopies, elemental analysis, atomic absorption as well as by X-ray crystallography. It crystallizes in the space group Pca2(1 with a = 17.282(3, b = 18.122(4, c = 17.3269(2, V = 5426.2(16 ų, 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.

  9. Mirrors fabricated with slightly oxidized C/C composites

    Science.gov (United States)

    Wang, Yongjie; Xu, Liang; Ding, Jiaoteng; Xie, Yongjie; Ma, Zhen

    2016-10-01

    Up to now, traditional materials, such as glass, metal and SiC ceramic, gradually begin to be unsatisfied development of the future mirrors. Designable carbon fiber reinforced composites became optimized material for large aperture lightweight mirrors. Carbon/carbon composites exhibit low thermal expansion and no moisture-absorption expansion problem, therefore, they get particular attention in the space reflector field. Ni was always employed as optical layer in the mirror, however, the coating behaved poor bond with substrate and often peeled off during optical processing. In order to solve this problem, slight oxidation was carried on the C/C composites before Ni plated. The Ni coating exhibited stronger coherence and better finish performance. Finally, a 100mm diameter plane mirror was successful fabricated.

  10. Recent progress in the catalytic carbene insertion reactions into the silicon-hydrogen bond.

    Science.gov (United States)

    Keipour, Hoda; Carreras, Virginie; Ollevier, Thierry

    2017-07-05

    The following review will explore the historical development of Si-H bond insertion reactions, giving an up-to-date account on the metal catalysts often employed, in addition to an assessment of their strengths and weaknesses. Diazo compounds have great synthetic potential as versatile reagents for the formation of metal carbenes, allowing the selective formation of C-C and C-heteroatom bonds and thus the introduction of functional groups into organic molecules. C-Si bond-forming methods, that introduce silicon motifs into organic molecules, rely on catalysts derived from metals such as rhodium, copper, iridium, silver, ruthenium, and iron to achieve the desired activities and selectivities.

  11. An Iron-Catalyzed Bond-Making/Bond-Breaking Cascade Merges Cycloisomerization and Cross-Coupling Chemistry.

    Science.gov (United States)

    Echeverria, Pierre-Georges; Fürstner, Alois

    2016-09-05

    Treatment of readily available enynes with alkyl-Grignard reagents in the presence of catalytic amounts of Fe(acac)3 engenders a remarkably facile and efficient reaction cascade that results in the net formation of two new C-C bonds while a C-Z bond in the substrate backbone is broken. Not only does this new manifold lend itself to the extrusion of heteroelements (Z=O, NR), but it can even be used for the cleavage of activated C-C bonds. The reaction likely proceeds via metallacyclic intermediates, the iron center of which gains ate character before reductive elimination occurs. The overall transformation represents a previously unknown merger of cycloisomerization and cross-coupling chemistry. It provides ready access to highly functionalized 1,3-dienes comprising a stereodefined tetrasubstituted alkene unit, which are difficult to make by conventional means. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Enantioselective formation of a dynamic hydrogen-bonded assembly based on the chiral memory concept

    NARCIS (Netherlands)

    Ish-i Tsutomu, T.I.; Crego Calama, Mercedes; Timmerman, P.; Reinhoudt, David; 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

  13. 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

  14. Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules

    Science.gov (United States)

    Daly, G. M.; Meot-Ner, M.; Pithawalla, Y. B.; El-Shall, M. S.

    1996-05-01

    We present a new method that applies resonant-two-photon ionization to generate reactant ions selectively in the source of a high-pressure mass spectrometer (R2PI-HPMS) for kinetic and equilibrium studies. Applications to reactions that would be obscured otherwise in a complex system are illustrated in mixtures of benzene with polar solvent molecules (S). We observe a novel type of proton transfer reactions from C6H6+• to two S molecules where S=CH3CN, CH3OH, C2H5OH and CH3COOC2H5, and from C6H5CH3+• to two S molecules where S=CH3OH and C2H5OH to form protonated solvent S2H+ dimers. The reactions are driven by the strong hydrogen bonds in the S2H+ dimers and therefore require the formation of the hydrogen bond concertedly with proton transfer, to make the process energetically feasible. The adducts (C6H6+•)S are observed with blocked solvent molecules where the subsequent switching reaction to yield S2H+ is slow, but not with alcohol reactants that can form hydrogen-bonded chains that facilitate fast subsequent proton extraction. Correspondingly, kinetic simulations suggest that the mechanism proceeds through (C6H6+•)S+S→S2H++C6H5• and C6H6+•+2S→S2H++C6H5• reactions, respectively. The rate coefficients of these reactions are in the range 10-13-10-12 cm3 s-1 for the reaction through a bimolecular switching channel and in the range 10-26-10-28 cm6 s-1 for reaction through a direct termolecular proton extraction mechanism. The relation to energetics and reactant structure is examined.

  15. Reversible Cleavage/Formation of the Chromium-Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization.

    Science.gov (United States)

    Huang, Yu-Siang; Huang, Gou-Tao; Liu, Yao-Lun; Yu, Jen-Shiang K; Tsai, Yi-Chou

    2017-11-27

    Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ(2) -HC(N-2,6-(i) Pr2 C6 H3 )(N-2,6-R2 C6 H3 )}]2 (R=iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes. During the catalysis, the ultrashort Cr-Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ-η(6) :η(6) -1,3,5-(Me3 Si)3 C6 H3 )[Cr{κ(2) -HC(N-2,6-(i) Pr2 C6 H3 )(N-2,6-R2 C6 H3 )}]2 (R=(i) Pr (5), Me (8)). In the presence of σ donors, such as THF and 2,4,6-Me3 C6 H2 CN, the bridging arene 1,3,5-(Me3 Si)3 C6 H3 in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathways of these highly regioselective [2+2+2] cylcotrimerization reactions of terminal alkynes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Carboxylic Acids as Directing Groups for C-H Bond Functionalization.

    Science.gov (United States)

    Pichette Drapeau, Martin; Gooßen, Lukas J

    2016-12-23

    The selective transformation of C-H bonds is one of the most desirable approaches to creating complexity from simple building blocks. Several directing groups are efficient in controlling the regioselectivity of catalytic C-H bond functionalizations. Among them, carboxylic acids are particularly advantageous, since they are widely available in great structural diversity and at low cost. The carboxylate directing groups can be tracelessly cleaved or may serve as the anchor point for further functionalization through decarboxylative couplings. This Minireview summarizes the substantial progress made in the last few years in the development of reactions in which carboxylate groups direct C-H bond functionalizations with formation of C-C, C-O, C-N, or C-halogen bonds at specific positions. It is divided into sections on C-C, C-O, C-N, and C-halogen bond formation, each of which is subdivided by reactions and product classes. Particular emphasis is placed on methods that enable multiple derivatizations by combining carboxylate-directed C-H functionalization with decarboxylative couplings. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Formation, structure and bonding of metalloid Al and Ga clusters. A challenge for chemical efforts in nanosciences.

    Science.gov (United States)

    Schnöckel, Hansgeorg

    2008-09-07

    The renaissance of Al and Ga cluster chemistry is presented in three steps: on the grounds of boron hydride chemistry and the Wade concept, the first step starts in the early nineties of the last century with the formation of single Al-Al and Ga-Ga bonds in molecular entities, obtained by different synthetic approaches. The special method via reaction of high-temperature molecules like AlCl and its disproportionation to Al metal and AlX(3) leads to the second step which started about 10 years ago: the formation of nanoscaled metalloid Al and Ga clusters as intermediates on the way to the metal. Based on the structure of several recent examples, bonding is discussed with respect to the structure of the elements and the generation of naked metal atom clusters. After discussion of the individual metalloid clusters including experiments of the gaseous species and discussion about the jellium model, the third step and main part of this review starts only a few years ago. This latest period hardly can be called a renaissance period as, so far, interactions of nanoscaled metal atom clusters in a perfect 1-, 2- or 3-dimensional arrangement of a crystal have never been investigated before. The most remarkable result in this perspective is the superconducting behaviour of a Ga(84) cluster compound in the crystalline state which had never been observed in metal atom clusters before. However, these experiments show that superconductivity is only observed if the clusters in the crystal are perfectly orientated: as a cluster arrangement of this type can hardly be fabricated by physical methods, these results, which have been predicted by theory, may be called a disillusionment for nanosciences; for chemistry, however, these conclusions pose a challenge.

  18. Synthesis of Reusable Silica Nanosphere-Supported Pt(IV Complex for Formation of Disulfide Bonds in Peptides

    Directory of Open Access Journals (Sweden)

    Xiaonan Hou

    2017-02-01

    Full Text Available Some peptide-based drugs, including oxytocin, vasopressin, ziconotide, pramlintide, nesiritide, and octreotide, contain one intramolecular disulfide bond. A novel and reusable monodispersed silica nanosphere-supported Pt(IV complex (SiO2@TPEA@Pt(IV; TPEA: N-[3-(trimethoxysilylpropyl]ethylenediamine was synthesized via a four-step procedure and was used for the formation of intramolecular disulfide bonds in peptides. Transmission electron microscopy (TEM and chemical mapping results for the Pt(II intermediates and for SiO2@TPEA@Pt(IV show that the silica nanospheres possess a monodisperse spherical structure and contain uniformly-distributed Si, O, C, N, Cl, and Pt. The valence state of Pt on the silica nanospheres was characterized by X-ray photoelectron spectroscopy (XPS. The Pt(IV loaded on SiO2@TPEA@Pt(IV was 0.15 mmol/g, as determined by UV-VIS spectrometry. The formation of intramolecular disulfides in six dithiol-containing peptides of variable lengths by the use of SiO2@TPEA@Pt(IV was investigated, and the relative oxidation yields were determined by high-performance liquid chromatography (HPLC. In addition, peptide 1 (Ac-CPFC-NH2 was utilized to study the reusability of SiO2@TPEA@Pt(IV. No significant decrease in the relative oxidation yield was observed after ten reaction cycles. Moreover, the structure of SiO2@TPEA@Pt(IV after being used for ten cycles was determined to be similar to its initial one, demonstrating the cycling stability of the complex.

  19. Fundamental and overtone vibrational spectroscopy, enthalpy of hydrogen bond formation and equilibrium constant determination of the methanol-dimethylamine complex.

    Science.gov (United States)

    Du, Lin; Mackeprang, Kasper; Kjaergaard, Henrik G

    2013-07-07

    We have measured gas phase vibrational spectra of the bimolecular complex formed between methanol (MeOH) and dimethylamine (DMA) up to about 9800 cm(-1). In addition to the strong fundamental OH-stretching transition we have also detected the weak second overtone NH-stretching transition. The spectra of the complex are obtained by spectral subtraction of the monomer spectra from spectra recorded for the mixture. For comparison, we also measured the fundamental OH-stretching transition in the bimolecular complex between MeOH and trimethylamine (TMA). The enthalpies of hydrogen bond formation (ΔH) for the MeOH-DMA and MeOH-TMA complexes have been determined by measurements of the fundamental OH-stretching transition in the temperature range from 298 to 358 K. The enthalpy of formation is found to be -35.8 ± 3.9 and -38.2 ± 3.3 kJ mol(-1) for MeOH-DMA and MeOH-TMA, respectively, in the 298 to 358 K region. The equilibrium constant (Kp) for the formation of the MeOH-DMA complex has been determined from the measured and calculated transition intensities of the OH-stretching fundamental transition and the NH-stretching second overtone transition. The transition intensities were calculated using an anharmonic oscillator local mode model with dipole moment and potential energy curves calculated using explicitly correlated coupled cluster methods. The equilibrium constant for formation of the MeOH-DMA complex was determined to be 0.2 ± 0.1 atm(-1), corresponding to a ΔG value of about 4.0 kJ mol(-1).

  20. σ Bond activation through tunneling: formation of the boron hydride cations BHn(+) (n = 2, 4, 6).

    Science.gov (United States)

    Qiu, Yudong; Wu, Chia-Hua; Schaefer, Henry F; Allen, Wesley D; Agarwal, Jay

    2016-02-07

    The network of H2 additions to B(+) and subsequent insertion reactions serve as a tractable model for hydrogen storage in elementary boron-containing compounds. Here, they are investigated using state-of-the-art ab initio methods (up to CCSDTQ and cc-pCV6Z basis sets). The binding energies of H2 to HBH(+) (14.9 kcal mol(-1)) and HBH(H2)(+) (18.1 kcal mol(-1)) are determined to be much higher than those for B(H2)(+) (3.8 kcal mol(-1)), B(H2)2(+) (3.0 kcal mol(-1)), and B(H2)3(+) (2.5 kcal mol(-1)) at the CCSDTQ/CBS level of theory. These predictions are in agreement with the experiments of Kemper, Bushnell, Weis, and Bowers (J. Am. Chem. Soc., 1998, 120, 7577). Molecular orbital analyses show that the enhanced binding in HBH(H2)m(+) complexes originates from the strong interaction between the 1σu HOMO of HBH(+) and the 1σu LUMO of H2. For the insertion reactions B(H2)n(+) → HBH(H2)n-1(+), activation barriers are determined to be 58.3 kcal mol(-1) [Mk-MRCCSD(T)/CBS], 12.2 kcal mol(-1) (CCSDTQ/CBS) and 4.6 kcal mol(-1) (CCSDTQ/CBS) for n = 1, 2, and 3, respectively. After using theoretical results to remove tunneling effects from the experimental rate constants, new Arrhenius fits yield activation barriers of 4.6(3) kcal mol(-1) and 3.8(1) kcal mol(-1) for the BH6(+) and BD6(+) insertion reactions, respectively, which are in near perfect agreement with converged theoretical values (4.6 kcal mol(-1) and 3.9 kcal mol(-1)). These findings demonstrate that earlier Arrhenius fits considerably underestimate these barriers, and that quantum tunneling dominates the σ bond activation mechanism witnessed in previous experiments involving BH6(+).

  1. "The cancer bond": exploring the formation of cancer risk perception in families with Lynch syndrome.

    Science.gov (United States)

    Palmquist, Aunchalee E L; Koehly, Laura M; Peterson, Susan K; Shegog, Margarette; Vernon, Sally W; Gritz, Ellen R

    2010-10-01

    This study explores the social context of hereditary cancer risk perception in three families, an African-American family, a Mexican-American family, and a Caucasian family, each with Lynch Syndrome documented by a mismatch repair gene mutation. Communication network assessments measured family communication about cancer experiences and genetic testing information among a total of 26 participants. Participant narratives were evaluated to gain insight into how family cancer experiences and genetic testing information have shaped perceptions of cancer risk. Analysis of communication networks indicated that some families discussed cancer experiences to a greater extent than genetic testing information, and vice-versa. Interviews elucidated that sharing both types of health information led participants to conceptualize linkages among a strong family history of cancer, genetic testing information, and cancer prevention strategies. Understanding how different types of family communication influence the formation of perceived hereditary disease risk may enhance efforts to tailor genetic counseling services for families.

  2. A large scale enzyme screen in the search for new methods of silicon-oxygen bond formation.

    Science.gov (United States)

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

    2011-02-01

    Biotransformations make use of biological systems to catalyze or promote specific chemical reactions. Transformations that utilize enzymes as "greener" and milder catalysts compared to traditional reaction conditions are of particular interest. Recently, organosilicon compounds have begun to be explored as non-natural enzymatic substrates for biotransformations. The aims of this study were to screen readily available (approximately eighty) enzymes for their ability to catalyze in vitro siloxane bond formation under mild reaction conditions using a model monoalkoxysilane as the substrate and to make a preliminary evaluation of potential factors that might lead to activity or inactivity of a particular enzyme. Several new hydrolase enzymes were observed to catalyze the formation of the condensation product when compared to peptide controls, or buffer solutions at the same pH, as judged from quantitative analyses by gas chromatography. Aspergillus ficuum phytase, Aspergillus niger phytase, chicken egg white lysozyme, porcine gastric mucosa pepsin, and Rhizopus oryzae lipase all catalyzed the condensation of silanols in aqueous media. Factors involved in determining the activity of an enzyme towards silanol condensation appear to include: the presence of imidazole and hydroxyl functions in the active site; solvent; the presence of water; the surface properties of the enzyme; possible covalent inhibition; and steric factors in the substrate. Copyright © 2010 Elsevier Inc. All rights reserved.

  3. 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.

  4. Controlling the Formation of Ionic-Liquid-based Aqueous Biphasic Systems by Changing the Hydrogen Bonding Ability of Polyethylene Glycol End Groups

    Science.gov (United States)

    Pereira, Jorge F. B.; Kurnia, Kiki A.; Freire, Mara G.; Coutinho, João A. P.; Rogers, Robin D.

    2017-01-01

    The formation of aqueous biphasic systems (ABS) when mixing aqueous solutions of polyethylene glycol (PEG) and an ionic liquid (IL) can be controlled by modification of the hydrogen bond ability of the polymer’s end groups. It is shown that the miscibility/immiscibility on these systems stems from both the solvation of the ether groups in the oxygen chain and the ability of the PEG terminal groups to preferably hydrogen bond with water or the salt anion. The reduction of even one hydrogen bond in PEG can noticeably affect the phase behavior, especially in those regions of the phase diagram where all the ethylene oxide (EO) units of the polymeric chain are completely solvated. In this region, removing or weakening the hydrogen bond donating ability of PEG results in greater immiscibility, i.e., in a higher ability to form ABS, as a result of the much weaker interactions between the IL anion and the PEG end groups. PMID:25943332

  5. From Molecules to Surfaces: Radical-Based Mechanisms of Si-S and Si-Se Bond Formation on Silicon.

    Science.gov (United States)

    Buriak, Jillian M; Sikder, Md Delwar H

    2015-08-05

    The derivatization of silicon surfaces can have profound effects on the underlying electronic properties of the semiconductor. In this work, we investigate the radical surface chemistry of silicon with a range of organochalcogenide reagents (comprising S and Se) on a hydride-terminated silicon surface, to cleanly and efficiently produce surface Si-S and Si-Se bonds, at ambient temperature. Using a diazonium-based radical initiator, which induces formation of surface silicon radicals, a group of organochalcogenides were screened for reactivity at room temperature, including di-n-butyl disulfide, diphenyl disulfide, diphenyl diselenide, di-n-butyl sulfide, diphenyl selenide, diphenyl sulfide, 1-octadecanethiol, t-butyl disulfide, and t-butylthiol, which comprises the disulfide, diselenide, thiol, and thioether functionalities. The surface reactions were monitored by transmission mode Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ionization mass spectrometry. Calculation of Si-Hx consumption, a semiquantitative measure of yield of production of surface-bound Si-E bonds (E = S, Se), was carried out via FTIR spectroscopy. Control experiments, sans the BBD diazonium radical initiator, were all negative for any evident incorporation, as determined by FTIR spectroscopy. The functional groups that did react with surface silicon radicals included the dialkyl/diphenyl disulfides, diphenyl diselenide, and 1-octadecanethiol, but not t-butylthiol, diphenyl sulfide/selenide, and di-n-butyl sulfide. Through a comparison with the rich body of literature regarding molecular radicals, and in particular, silyl radicals, reaction mechanisms were proposed for each. Armed with an understanding of the reaction mechanisms, much of the known chemistry within the extensive body of radical-based reactivity has the potential to be harnessed on silicon and could be extended to a range of technologically relevant semiconductor

  6. Surface treatment with methyl formate-methyl acetate increased the shear bond strength between reline resins and denture base resin.

    Science.gov (United States)

    Osathananda, Rachanee; Wiwatwarrapan, Chairat

    2016-06-01

    Chemical surface treatment increases the shear bond strength (SBS) between hard reline resins (HRRs) and denture base resin. To evaluate the effect of methyl formate-methyl acetate (MF-MA), when used as a surface treatment agent, on the SBS between denture base resin and different HRRs. One hundred and twenty specimens of heat-polymerised acrylic resin denture base (Meliodent(®) ) were divided into 12 groups. These groups comprised denture base relined with three self-polymerised HRRs [Unifast trad(®) (UT), Tokuyama(®) RebaseII Fast (TR), Ufi gel hard(®) (UG)], and treated with their respective Bonding Agent (BA) or by MF:MA solutions at ratios of 35:65, 25:75, and 15:85 for 15 s. The SBS was measured using a Universal Testing Machine. The data were analysed using two-way anova and post hoc Tukey's analysis at p < 0.05. The highest SBS was in the UT treated with MF:MA at a ratio of 25:75 group, followed by UT treated with MF:MA at ratios of 15:85, 35:65, UT treated with BA, and all UG treated with MF:MA groups. The SBS of the UT treated with MF:MA at a ratio of 25:75 group was significantly higher than those of the groups treated with BA. The SBS of the UG treated with MF:MA groups was significantly higher than control. The TR groups treated with BA or MF:MA groups showed no significant difference in SBS. Surface treatment with MF-MA significantly enhanced the SBS of denture base resin and UT and UG compared to that of the groups treated with BA. © 2014 John Wiley & Sons A/S and The Gerodontology Association. Published by John Wiley & Sons Ltd.

  7. Densification Behavior and Performances of C/C Composites Derived from Various Carbon Matrix Precursors

    Science.gov (United States)

    Shao, H. C.; Xia, H. Y.; Liu, G. W.; Qiao, G. J.; Xiao, Z. C.; Su, J. M.; Zhang, X. H.; Li, Y. J.

    2014-01-01

    Three types of carbon/carbon (C/C) composites were manufactured by densifying the needled carbon fiber preform through resin and pitch impregnation/carbonization repeatedly, as well as propylene pyrolysis by chemical vapor infiltration plus carbonization after the resin impregnation/carbonization. The densification behavior and performances (involving electric, thermal, and mechanical properties, as well as impurity) of the C/C composites were investigated systematically. The results show that besides the processing and testing conditions, the electric resistivity, thermal conductivity (TC), coefficient of thermal expansion (CTE), strength, and fracture, as well as impurity content and composition of the C/C composites were closely related to the fiber orientation, interfacial bonding between carbon fiber and carbon matrix, material characteristics of the three precursors and the resulting matrix carbons. In particular, the resin-carbon matrix C/C (RC/C) composites had the highest electric resistivity, tensile, and flexural strength, as well as impurity content. Meanwhile, the pitch-carbon matrix C/C (PC/C) composites possessed the highest TC and CTE in the parallel and vertical direction. And most of the performances of pyro-carbon/resin carbon matrix C/C composites were between those of the RC/C and PC/C composites except the impurity content.

  8. Synthetic Methods for Ester Bond Formation and Conformational Analysis of Ester-Containing Carbohydrates

    Science.gov (United States)

    Hackbusch, Sven

    This dissertation encompasses work related to synthetic methods for the formation of ester linkages in organic compounds, as well as the investigation of the conformational influence of the ester functional group on the flexibility of inter-saccharide linkages, specifically, and the solution phase structure of ester-containing carbohydrate derivatives, in general. Stereoselective reactions are an important part of the field of asymmetric synthesis and an understanding of their underlying mechanistic principles is essential for rational method development. Here, the exploration of a diastereoselective O-acylation reaction on a trans-2-substituted cyclohexanol scaffold is presented, along with possible reasons for the observed reversal of stereoselectivity dependent on the presence or absence of an achiral amine catalyst. In particular, this work establishes a structure-activity relationship with regard to the trans-2-substituent and its role as a chiral auxiliary in the reversal of diastereoselectivity. In the second part, the synthesis of various ester-linked carbohydrate derivatives, and their conformational analysis is presented. Using multidimensional NMR experiments and computational methods, the compounds' solution-phase structures were established and the effect of the ester functional group on the molecules' flexibility and three-dimensional (3D) structure was investigated and compared to ether or glycosidic linkages. To aid in this, a novel Karplus equation for the C(sp2)OCH angle in ester-linked carbohydrates was developed on the basis of a model ester-linked carbohydrate. This equation describes the sinusoidal relationship between the C(sp2)OCH dihedral angle and the corresponding 3JCH coupling constant that can be determined from a J-HMBC NMR experiment. The insights from this research will be useful in describing the 3D structure of naturally occurring and lab-made ester-linked derivatives of carbohydrates, as well as guiding the de novo-design of

  9. Remarkably Efficient Synthesis of 2H-Indazole 1-oxides and 2H-Indazoles via Tandem Carbon–Carbon Followed by Nitrogen–Nitrogen Bond Formation

    Science.gov (United States)

    Bouillon, Isabelle; Zajíček, Jaroslav; Pudelová, Naděžda; Krchňák, Viktor

    2009-01-01

    Synthesis of Indazoles Base-catalyzed tandem carbon–carbon followed by nitrogen–nitrogen bond formations quantitatively converted N-alkyl-2-nitro-N-(2-oxo-2-aryl-ethyl)-benzenesulfonamides to 2H-indazoles 1-oxides under mild conditions. Triphenylphosphine or mesyl chloride/triethylamine-mediated deoxygenation afforded 2H-indazoles. PMID:18937414

  10. Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities.

    Science.gov (United States)

    Keyvani, Zahra Alimohammadi; Shahbazian, Shant; Zahedi, Mansour

    2016-10-18

    The equivalence of the molecular graphs emerging from the comparative analysis of the optimized and the promolecule electron densities in two hundred and twenty five unsubstituted hydrocarbons was recently demonstrated [Keyvani et al. Chem. Eur. J. 2016, 22, 5003]. Thus, the molecular graph of an optimized molecular electron density is not shaped by the formation of the C-H and C-C bonds. In the present study, to trace the fingerprint of the C-H and C-C bonds in the electron densities of the same set of hydrocarbons, the amount of electron density and its Laplacian at the (3, -1) critical points associated with these bonds are derived from both optimized and promolecule densities, and compared in a newly proposed comparative analysis. The analysis not only conforms to the qualitative picture of the electron density build up between two atoms upon formation of a bond in between, but also quantifies the resulting accumulation of the electron density at the (3, -1) critical points. The comparative analysis also reveals a unified mode of density accumulation in the case of 2318 studied C-H bonds, but various modes of density accumulation are observed in the case of 1509 studied C-C bonds and they are classified into four groups. The four emerging groups do not always conform to the traditional classification based on the bond orders. Furthermore, four C-C bonds described as exotic bonds in previous studies, for example the inverted C-C bond in 1,1,1-propellane, are naturally distinguished from the analysis. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. The influence of elongational flow on hydrogen bond formation and stability of the homogeneous phase of binary hydrogen- bonded polymer blends

    NARCIS (Netherlands)

    Dormidontova, Elena E.; Brinke, Gerrit ten

    2000-01-01

    Macrophase separation tendency induced by flow in binary blends of polymers capable of single hydrogen bonding between one of the chain ends is studied analytically. To describe the conformational and orientational properties of a polymer chain a simple dumbbell model is applied. It is demonstrated

  12. Rapid preparation of branched and degradable AIE-active fluorescent organic nanoparticles via formation of dynamic phenyl borate bond.

    Science.gov (United States)

    Long, Zi; Liu, Meiying; Mao, Liucheng; Zeng, Guangjian; Wan, Qing; Xu, Dazhuang; Deng, Fengjie; Huang, Hongye; Zhang, Xiaoyong; Wei, Yen

    2017-02-01

    The fluorescent organic nanoparticles (FNPs) with aggregation-induced emission (AIE) feature have received increasing attention for their advanced optical properties. Although many efforts have been devoted to the fabrication and biomedical applications of AIE-active FNPs, the preparation of branched AIE-active FNPs with degradability through formation of dynamic bonds have rarely been reported. In this work, branched AIE-active FNPs were fabricated via dynamic linkage of hydrophobic hyperbranched and degradable Boltorn H40 (H40) with phenylboronic acid terminated AIE dye (PhB(OH)2) and mPEG (mPEG-B(OH)2), which relied on a facile one-pot strategy between phenylboronic acid and diol group of H40. The branched H40-star-mPEG-PhB(OH)2 FNPs were characterized using nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and fluorescence spectroscopy. Benefiting from their highly branched structure and amphiphilic properties, H40-star-mPEG-PhB(OH)2 could self-assemble into micelles and emit strong orange-red fluorescence. More importantly, cell viability results demonstrated that H40-star-mPEG-PhB(OH)2 FNPs showed good biocompatibility and promising candidates for bio-imaging. Taken together, we developed a one-pot strategy for preparation of branched AIE-active FNPs through the formation of dynamic phenyl borate. The resultant H40-star-mPEG-PhB(OH)2 FNPs should be promising biomaterials for different applications for biodegradability of H40 and responsiveness of phenyl borate. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Chemically fixed p-n heterojunctions for polymer electronics by means of covalent B-F bond formation.

    Science.gov (United States)

    Hoven, Corey V; Wang, Huiping; Elbing, Mark; Garner, Logan; Winkelhaus, Daniel; Bazan, Guillermo C

    2010-03-01

    Widely used solid-state devices fabricated with inorganic semiconductors, including light-emitting diodes and solar cells, derive much of their function from the p-n junction. Such junctions lead to diode characteristics and are attained when p-doped and n-doped materials come into contact with each other. Achieving bilayer p-n junctions with semiconducting polymers has been hindered by difficulties in the deposition of thin films with independent p-doped and n-doped layers. Here we report on how to achieve permanently fixed organic p-n heterojunctions by using a cationic conjugated polyelectrolyte with fluoride counteranions and an underlayer composed of a neutral conjugated polymer bearing anion-trapping functional groups. Application of a bias leads to charge injection and fluoride migration into the neutral layer, where irreversible covalent bond formation takes place. After the initial charging and doping, one obtains devices with no delay in the turn on of light-emitting electrochemical behaviour and excellent current rectification. Such devices highlight how mobile ions in organic media can open opportunities to realize device structures in ways that do not have analogies in the world of silicon and promise new opportunities for integrating organic materials within technologies now dominated by inorganic semiconductors.

  14. Catalytic C-N, C-O, and C-S Bond Formation Promoted by Organoactinide Complexes

    Science.gov (United States)

    Eisen, Moris S.

    Throughout this last decade, we have witnessed impressively how the chemistry of electrophilic d0/fn actinides has been prospering either in their new synthetic approaches reaching very interesting compounds or in their use in stoichiometric and catalytic reactions leading to high levels of complexity. The unique rich and complex features of organoactinides prompted the development of this field toward catalysis in demanding chemical transformations. In this review, we present a brief and selective survey of the recent developments in homogenous catalysis of organoactinide complexes, especially toward the formation of new C-N, C-O, and C-S bonds. We start by presenting the synthesis and characterization of the corresponding organoactinide complexes, followed by the homogeneous catalytic chemical transformations that include the hydroamination of terminal alkynes, the polymerization of ɛ-caprolactone and L-lactide, the reduction of azides and hydrazines by high-valent organouranium complexes, the hydrothiolation of terminal alkynes, and the catalytic Tishchenko reaction. For each reaction, the scope and the thermodynamic, kinetic, and mechanistic aspects are presented.

  15. Constructing safe and durable antibacterial textile surfaces using a robust graft-to strategy via covalent bond formation

    Science.gov (United States)

    He, Liang; Li, Sha; Chung, Cordelia T. W.; Gao, Chang; Xin, John H.

    2016-01-01

    Recently zwitterionic materials have been widely applied in the biomedical and bioengineering fields due to their excellent biocompatibility. Inspired by these, this study presents a graft-to strategy via covalent bond formation to fabricate safe and durable antibacterial textile surfaces. A novel zwitterionic sulfobetaine containing triazine reactive group was specifically designed and synthesized. MTT assay showed that it had no obvious cytotoxicity to human skin HaCaT cells as verified by ca. 89.9% relative viability at a rather high concentration of 0.8 mg·mL−1. In the evaluation for its skin sensitization, the maximum score for symptoms of erythema and edema in all tests were 0 in all observation periods. The sulfobetaine had a hydrophilic nature and the hydrophilicity of the textiles was enhanced by 43.9% when it was covalently grafted onto the textiles. Moreover, the textiles grafted with the reactive sulfobetaine exhibited durable antibacterial activities, which was verified by the fact that they showed antibacterial rates of 97.4% against gram-positive S. aureus and 93.2% against gram-negative E. coli even after they were laundered for 30 times. Therefore, the titled zwitterionic sulfobetaine is safe to human for healthcare and wound dressing and shows a promising prospect on antibacterial textile application. PMID:27808248

  16. 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.

  17. Long-lived transient anion of c-C4F8O

    Science.gov (United States)

    Kočišek, J.; Janečková, R.; Fedor, J.

    2018-02-01

    We report partial cross sections for electron attachment to c-C4F8O, a gas with promising technological applications in free-electron-rich environments. The dissociative electron attachment leads to a number of anionic fragments resulting from complex bond-breaking and bond-forming processes. However, the anion with the highest abundance is the non-dissociated (transient) parent anion which is formed around 0.9 eV electron energy. Its lifetime reaches tens of microseconds. We discuss the origin of this long lifetime, the anion's strong interactions with other molecules, and the consequences for electron-scavenging properties of c-C4F8O in denser environments, in particular for its use in mixtures with CO2 and N2.

  18. Physical origin of hydrogen-adsorption-induced metallization of the SiC surface: n-type doping via formation of hydrogen bridge bond.

    Science.gov (United States)

    Chang, Hao; Wu, Jian; Gu, Bing-Lin; Liu, Feng; Duan, Wenhui

    2005-11-04

    We perform first-principles calculations to explore the physical origin of hydrogen-induced semiconductor surface metallization observed in beta-SiC(001)-3 x 2 surface. We show that the surface metallization arises from a novel mechanism of n-type doping of surface band via formation of hydrogen bridge bonds (i.e., Si-H-Si complex). The hydrogen strengthens the weak Si-Si dimers in the subsurface by forming hydrogen bridge bonds, and donates electron to the surface conduction band.

  19. Density functional study of hydrogen bond formation between methanol and organic molecules containing Cl, F, NH2, OH, and COOH functional groups.

    Science.gov (United States)

    Kolev, Stefan K; St Petkov, Petko; Rangelov, Miroslav A; Vayssilov, Georgi N

    2011-12-08

    Various hydrogen-bonded complexes of methanol with different proton accepting and proton donating molecules containing Cl, F, NH(2), OH, OR, and COOH functional groups have been modeled using DFT with hybrid B3LYP and M05-2X functionals. The latter functional was found to provide more accurate estimates of the structural and thermodynamic parameters of the complexes of halides, amines, and alcohols. The characteristics of these complexes are influenced not only by the principle hydrogen bond of the methanol OH with the proton acceptor heteroatom, but also by additional hydrogen bonds of a C-H moiety with methanol oxygen as a proton acceptor. The contribution of the former hydrogen bond in the total binding enthalpy increases in the order chlorides hydrogen bond increases in the reverse order. A general correlation was found between the binding enthalpy of the complex and the electrostatic potential at the hydrogen center participating in the formation of the hydrogen bond. The calculated binding enthalpies of different complexes were used to clarify which functional groups can potentially form a hydrogen bond to the 2'-OH hydroxyl group in ribose, which is strong enough to block it from participation in the intramolecular catalytic activation of the peptide bond synthesis. Such blocking could result in inhibition of the protein biosynthesis in the living cell if the corresponding group is delivered as a part of a drug molecule in the vicinity of the active site in the ribosome. According to our results, such activity can be accomplished by secondary or tertiary amines, alkoxy groups, deprotonated carboxyl groups, and aliphatic fluorides, but not by the other modeled functional groups.

  20. CS Bond formation by

    Indian Academy of Sciences (India)

    2017-02-02

    Feb 2, 2017 ... catalyzed transformation is maximized when combined with straight-forward reaction conditions and the for- mation of widely utilized synthetic building blocks. Recent work in the Chan,8 Cundy,9 and Evans10 laboratories have revealed the efficiency of copper(II) acetate in mediation of the cross-coupling ...

  1. Ester-Mediated Amide Bond Formation Driven by Wet-Dry Cycles: A Possible Path to Polypeptides on the Prebiotic Earth.

    Science.gov (United States)

    Forsythe, Jay G; Yu, Sheng-Sheng; Mamajanov, Irena; Grover, Martha A; Krishnamurthy, Ramanarayanan; Fernández, Facundo M; Hud, Nicholas V

    2015-08-17

    Although it is generally accepted that amino acids were present on the prebiotic Earth, the mechanism by which α-amino acids were condensed into polypeptides before the emergence of enzymes remains unsolved. Here, we demonstrate a prebiotically plausible mechanism for peptide (amide) bond formation that is enabled by α-hydroxy acids, which were likely present along with amino acids on the early Earth. Together, α-hydroxy acids and α-amino acids form depsipeptides-oligomers with a combination of ester and amide linkages-in model prebiotic reactions that are driven by wet-cool/dry-hot cycles. Through a combination of ester-amide bond exchange and ester bond hydrolysis, depsipeptides are enriched with amino acids over time. These results support a long-standing hypothesis that peptides might have arisen from ester-based precursors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Tomographic Evaluation of Reparative Dentin Formation after Direct Pulp Capping with Ca(OH)2, MTA, Biodentine, and Dentin Bonding System in Human Teeth.

    Science.gov (United States)

    Nowicka, Alicja; Wilk, Grażyna; Lipski, Mariusz; Kołecki, Janusz; Buczkowska-Radlińska, Jadwiga

    2015-08-01

    New materials can increase the efficiency of pulp capping through the formation of a complete reparative dentin bridge with no toxic effects. The present study involved tomographic evaluations of reparative dentin bridge formation after direct pulp capping with calcium hydroxide, mineral trioxide aggregate (MTA), Biodentine (Septodont, Saint Maur des Fossés, France), and Single Bond Universal (3M ESPE, Seefeld, Germany) in human teeth. Forty-four caries-free, intact, human third molars scheduled for extraction were subjected to mechanical pulp exposure and assigned to 1 of 4 experimental groups depending on the pulp capping agent used: calcium hydroxide, MTA, Biodentine, or Single Bond Universal. After 6 weeks, the teeth were extracted and processed for cone-beam computed tomographic imaging and histologic examination. Tomographic data, including the density and volume of formed reparative dentin bridges, were evaluated using a scoring system. The reparative dentin formed in the calcium hydroxide, MTA, and Biodentine groups was significantly superior to that formed in the Single Bond Universal group in terms of thickness and volume. The dentin bridges in the Biodentine group showed the highest average and maximum volumes. The mean density of dentin bridges was the highest in the MTA group and the lowest in the Single Bond Universal group. The volume of reparative dentin bridges formed after direct pulp capping is dependent on the material used. Biodentine and MTA resulted in the formation of bridges with a significantly higher average volume compared with Single Bond Universal, and cone-beam computed tomographic imaging allowed for the identification of the location of dentin bridges. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

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

    Directory of Open Access Journals (Sweden)

    Kyung Hwan Kim

    2016-07-01

    Full Text Available The [Au(CN2−]3 trimer in water experiences a strong van der Waals interaction between the d10 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.

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

    Science.gov (United States)

    Wang, Qiang; Gao, Jun; Zhang, Dongju; Liu, Chengbu

    2015-04-01

    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.

  5. Nickel-Catalyzed C-S Bond Formation via Decarbonylative Thioetherification of Esters, Amides and Intramolecular Recombination Fragment Coupling of Thioesters

    KAUST Repository

    Lee, Shao-Chi

    2018-01-15

    A nickel catalyzed cross-coupling protocol for the straightforward C-S bond formation has been developed. Various mercaptans and a wide range of ester and amide substrates bearing various substituents were tolerated in this process which afforded products in good to excellent yields. Furthermore, an intramolecular protocol for the synthesis of thioethers starting from thioesters has been developed. The utility of this protocol has been demonstrated in the synthesis of benzothiophene on the bench top.

  6. Monoiron hydrogenase catalysis: hydrogen activation with the formation of a dihydrogen, Fe-H(delta-)...H(delta+)-O, bond and methenyl-H4MPT+ triggered hydride transfer.

    Science.gov (United States)

    Yang, Xinzheng; Hall, Michael B

    2009-08-12

    A fully optimized resting state model with a strong Fe-H(delta-)...H(delta+)-O dihydrogen bond for the active site of the third type of hydrogenase, [Fe]-hydrogenase, is proposed from density functional theory (DFT) calculations on the reformulated active site from the recent X-ray crystal structure study of C176A (Cys176 was mutated to an alanine) mutated [Fe]-hydrogenase in the presence of dithiothreitol. The computed vibrational frequencies for this new active site model possess an average error of only +/-4.5 cm(-1) with respect to the wild-type [Fe]-hydrogenase. Based on this resting state model, a new mechanism with the following unusual aspects for hydrogen activation catalyzed by [Fe]-hydrogenase is also proposed from DFT calculations. (1) Unexpected dual pathways for H(2) cleavage with proton transfer to Cys176-sulfur or 2-pyridinol's oxygen for the formation and regeneration of the resting state with an Fe-H(delta-)...H(delta+)-O dihydrogen bond before the appearance of methenyl-H(4)MPT(+) (MPT(+)). (2) The strong dihydrogen bond in this resting state structure prevents D(2)/H(2)O exchange. (3) Only upon the arrival of MPT(+) with its strong hydride affinity can D(2)/H(2)O exchange take place as the arrival of MPT(+) triggers the breaking of the strong Fe-H(delta-)...H(delta+)-O dihydrogen bond by taking a hydride from the iron center and initiating the next H(2) (D(2)) cleavage. This new mechanism is completely different than that previously proposed (J. Am. Chem. Soc. 2008, 130, 14036) which was based on an active site model related to an earlier crystal structure. Here, Fe's role is H(2) capture and hydride formation without MPT(+) while the pyridone's special role involves the protection of the hydride by the dihydrogen bond.

  7. Controlling the Formation of Ionic-Liquid-based Aqueous Biphasic Systems by Changing the Hydrogen-Bonding Ability of Polyethylene Glycol End Groups.

    Science.gov (United States)

    Pereira, Jorge F B; Kurnia, Kiki A; Freire, Mara G; Coutinho, João A P; Rogers, Robin D

    2015-07-20

    The formation of aqueous biphasic systems (ABS) when mixing aqueous solutions of polyethylene glycol (PEG) and an ionic liquid (IL) can be controlled by modifying the hydrogen-bond-donating/-accepting ability of the polymer end groups. It is shown that the miscibility/immiscibility in these systems stems from both the solvation of the ether groups in the oxygen chain and the ability of the PEG terminal groups to preferably hydrogen bond with water or the anion of the salt. The removal of even one hydrogen bond in PEG can noticeably affect the phase behavior, especially in the region of the phase diagram in which all the ethylene oxide (EO) units of the polymeric chain are completely solvated. In this region, removing or weakening the hydrogen-bond-donating ability of PEG results in greater immiscibility, and thus, in a higher ability to form ABS, as a result of the much weaker interactions between the IL anion and the PEG end groups. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Biofilm formation on stainless steel and gold wires for bonded retainers in vitro and in vivo and their susceptibility to oral antimicrobials.

    Science.gov (United States)

    Jongsma, Marije A; Pelser, Floris D H; van der Mei, Henny C; Atema-Smit, Jelly; van de Belt-Gritter, Betsy; Busscher, Henk J; Ren, Yijin

    2013-05-01

    Bonded retainers are used in orthodontics to maintain treatment result. Retention wires are prone to biofilm formation and cause gingival recession, bleeding on probing and increased pocket depths near bonded retainers. In this study, we compare in vitro and in vivo biofilm formation on different wires used for bonded retainers and the susceptibility of in vitro biofilms to oral antimicrobials. Orthodontic wires were exposed to saliva, and in vitro biofilm formation was evaluated using plate counting and live/dead staining, together with effects of exposure to toothpaste slurry alone or followed by antimicrobial mouthrinse application. Wires were also placed intra-orally for 72 h in human volunteers and undisturbed biofilm formation was compared by plate counting and live/dead staining, as well as by denaturing gradient gel electrophoresis for compositional differences in biofilms. Single-strand wires attracted only slightly less biofilm in vitro than multi-strand wires. Biofilms on stainless steel single-strand wires however, were much more susceptible to antimicrobials from toothpaste slurries and mouthrinses than on single-strand gold wires and biofilms on multi-strand wires. Also, in vivo significantly less biofilm was found on single-strand than on multi-strand wires. Microbial composition of biofilms was more dependent on the volunteer involved than on wire type. Biofilms on single-strand stainless steel wires attract less biofilm in vitro and are more susceptible to antimicrobials than on multi-strand wires. Also in vivo, single-strand wires attract less biofilm than multi-strand ones. Use of single-strand wires is preferred over multi-strand wires, not because they attract less biofilm, but because biofilms on single-strand wires are not protected against antimicrobials as in crevices and niches as on multi-strand wires.

  9. Experimental and theoretical evaluation of the reactions leading to formation of internal double bonds in suspension PVC

    NARCIS (Netherlands)

    Purmova, Jindra; Pauwels, Kim F. D.; Agostini, Michela; Bruinsma, Maarten; Vorenkamp, Eltio J.; Schouten, Arend J.; Coote, Michelle L.

    2008-01-01

    The number of internal double bonds in poly(vinyl chloride) (PVC) samples was studied as a function of molecular weight at various monomer conversions. These defect structures were found to exhibit end-group-like characteristics: their concentration per chain was largely constant as a function of

  10. Controlling superstructural ordering in the clathrate-I Ba8M16P30 (M = Cu, Zn) through the formation of metal-metal bonds.

    Science.gov (United States)

    Dolyniuk, J; Whitfield, P S; Lee, K; Lebedev, O I; Kovnir, K

    2017-05-01

    Order-disorder-order phase transitions in the clathrate-I Ba8Cu16P30 were induced and controlled by aliovalent substitutions of Zn into the framework. Unaltered Ba8Cu16P30 crystallizes in an ordered orthorhombic (Pbcn) clathrate-I superstructure that maintains complete segregation of metal and phosphorus atoms over 23 different crystallographic positions in the clathrate framework. The driving force for the formation of this Pbcn superstructure is the avoidance of Cu-Cu bonds. This superstructure is preserved upon aliovalent substitution of Zn for Cu in Ba8Cu16-x Zn x P30 with 0 Cu-Zn bonds in the framework, leading to a collapse of the orthorhombic superstructure into the more common cubic subcell of clathrate-I (Pm3n). In the resulting cubic phases, each clathrate framework position is jointly occupied by three different elements: Cu, Zn, and P. Detailed structural characterization of the Ba-Cu-Zn-P clathrates-I via single crystal X-ray diffraction, joint synchrotron X-ray and neutron powder diffractions, pair distribution function analysis, electron diffraction and high-resolution electron microscopy, along with elemental analysis, indicates that local ordering is present in the cubic clathrate framework, suggesting the evolution of Cu-Zn bonds. For the compounds with the highest Zn content, a disorder-order transformation is detected due to the formation of another superstructure with trigonal symmetry and Cu-Zn bonds in the clathrate-I framework. It is shown that small changes in the composition, synthesis, and crystal structure have significant impacts on the structural and transport properties of Zn-substituted Ba8Cu16P30.

  11. Formation of cyclobutanones by the photolytic reaction of (CO)/sub 5/Cr/double bond/C(OMe)Me with electron-rich olefins

    Energy Technology Data Exchange (ETDEWEB)

    Sierra, M.A.; Hegedus, L.S.

    1989-03-15

    Recent research has centered on the development of useful organic synthetic methodology based on the photolytic reactions of chromium Fischer carbene complexes, particularly in regards to the development of new /beta/-lactam syntheses. In the course of these studies it became evident that photolysis of chromium-carbene complexes resulted in the reversible production of chromium-ketene complexes, by a photochemically driven CO insertion into the chromium-carbene carbon double bond and that this unstable intermediate was responsible for /beta/-lactam formation.

  12. The Stereoselective Formation of Bicyclic Enamines with Bridgehead Unsaturation via Tandem C-H Bond Activation/Alkenylation/Electrocyclization

    Energy Technology Data Exchange (ETDEWEB)

    Ellman, Jonathan A.; Yotphan, Sirilata; Bergman, Robert

    2007-12-10

    Rhodium-catalyzed intermolecular C-H activation of {alpha}, {beta}-unsaturated imines in the presence of alkynes leads to a tandem process in which coupling to the alkyne occurs at the {beta}-C-H bond of the imine, followed by electrocyclization of the resulting azatriene intermediates to give dihydropyridines (eq 1). Consideration of the intramolecular version of this overall transformation (Scheme 1) raises interesting regiochemical issues. For example in a compound such as 1, where the nitrogen and alkyne are connected by a 4-carbon tether, the presumed first-formed hydrido(vinyl)rhodium function can add to the triple bond in a 1,2-fashion, producing complex 2 with a new endocyclic double bond. Alternatively, addition might occur in a 2,1-fashion, leading to product 4 with an exocyclic double bond. We now wish to report that this intramolecular cyclization occurs smoothly at 100 C, and the exocyclic double bond route is exclusively followed. Remarkably, products such as 4 do not resist further cyclization. Even though both the transition state for this process and the resulting product are presumably strained, the overall transformation leads to good yields of unusual bridgehead doubly-bonded enamines such as 5. The unique chemistry of conjugated enamine 5 is consistent with the increased strain of this molecule as well as with inhibited conjugation between the nitrogen lone pair and the adjacent double bond (vida infra). We began our investigation into the C-H activation/cyclization of alkyne-tethered imine 1 by extensive screening of transition metal catalysts for this process. Rhodium-based catalysts were found to be the most efficient (Table 1), leading exclusively to the bridgehead dienamine; none of the catalysts that were employed in the screening led to quinolizidine 3 or to the product of intramolecular Diels-Alder reaction. The optimized reaction conditions employ the electron-rich monophosphine ligand (p-NMe{sub 2})PhPEt{sub 2} in 1:1 ratio relative

  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. Reactivity of damaged pyrimidines: formation of a Schiff base intermediate at the glycosidic bond of saturated dihydrouridine.

    Science.gov (United States)

    Jian, Yajun; Lin, Gengjie; Chomicz, Lidia; Li, Lei

    2015-03-11

    DNA glycosylases catalyze the first step of the base excision repair (BER) pathway. The chemistry used by these enzymes for deglycosylation has been largely considered as the chemistry of the oxocarbenium ion, e.g., direct rupture of the C1'-N1 bond resulting in an oxocarbenium ion intermediate. Here we present mechanistic studies revealing the 2'-deoxyribose isomerization and subsequent deglycosylation processes in two pyrimidine lesions: 5,6-dihydro-2'-deoxyuridine (dHdU) and 5,6-dihydrothymidine (dHT), formed via ionizing radiation damage to 2'-deoxycytidine and thymidine, respectively, under anoxic conditions. Acid or heat treatment of these two lesions leads to the production of two pairs of C1' epimers containing a pyranose and a furanose, respectively, indicating that both lesions favor the rupture of the C1'-O4' bond, resulting in a Schiff base intermediate at the N-glycosidic bond. Such a Schiff base intermediate was trapped and characterized by either Pd-catalyzed hydrogenation or thiol-mediated addition reaction. In contrast, in undamaged 2'-deoxyuridine and thymidine, reactions at elevated temperatures lead to the release of nucleobases most likely via the traditional oxocarbenium ion pathway. DFT calculations further support the experimental findings, suggesting that the oxocarbenium ion intermediate is responsible for the deglycosylation process if the integrity of the pyrimidine ring is maintained, while the Schiff base intermediate is preferred if the C5═C6 bond is saturated. Currently, the oxocarbenium ion pathway is indicated to be solely responsible for the deglycosylation in BER enzymes, however our results suggest an alternative Schiff base mechanism which may be responsible for the repair of saturated pyrimidine damages.

  15. Strong stacking between FH--N hydrogen-bonded foldamers and fullerenes: formation of supramolecular nano networks.

    Science.gov (United States)

    Li, Chuang; Zhu, Yuan-Yuan; Yi, Hui-Ping; Li, Chang-Zhi; Jiang, Xi-Kui; Li, Zhan-Ting; Yu, Yi-Hua

    2007-01-01

    The stacking interactions between FH--N hydrogen-bonded foldamers 1-3, bis-foldamer 4, and tris-foldamer 5 and C(60) and C(70) are described. Compound 4 contains two folded units, which are connected by an isophthalamide linker, whereas 5 has a C(3)-symmetrical discotic structure, in which three folded units are connected by a benzene-1,3,5-tricarboxamide unit. UV/Vis, fluorescence, and NMR experiments have revealed that the foldamers or folded units strongly stack with fullerenes in chloroform. The (apparent) association constants of the respective complexes have been determined by a fluorescence titration method. The strong association is tentatively attributed to intermolecular cooperative fluorophenylpi and solvophobic interactions. A similar but weaker interaction has also been observed between an MeOH--N hydrogen-bonded foldamer and fullerenes. AFM studies have revealed that the surfaces of 3 and 4 show fibrous networks, while the surface of 5 shows particles. In sharp contrast, mixtures of 3 and 4 with C(60) have been shown to generate thinner separated fibrils, whereas a mixture of 5 and C(60) produces honeycomb-like nano networks, for which a columnar cooperative stacking pattern is proposed. The results demonstrate the usefulness of FH--N hydrogen-bonded folded structures in the construction of nanoscaled materials.

  16. 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.

  17. RATIONAL APPROACHES FOR ENGINEERING NOVEL FUNCTIONALITIES IN CARBON-CARBON BOND FORMING ENZYMES

    Directory of Open Access Journals (Sweden)

    Perrin Baker

    2012-09-01

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

  18. Effect of curing modes of dual-curing core systems on microtensile bond strength to dentin and formation of an acid-base resistant zone.

    Science.gov (United States)

    Li, Na; Takagaki, Tomohiro; Sadr, Alireza; Waidyasekera, Kanchana; Ikeda, Masaomi; Chen, Jihua; Nikaido, Toru; Tagami, Junji

    2011-12-01

    To evaluate the microtensile bond strength (μTBS) and acid-base resistant zone (ABRZ) of two dualcuring core systems to dentin using four curing modes. Sixty-four caries-free human molars were randomly divided into two groups according to two dual-curing resin core systems: (1) Clearfil DC Core Automix; (2) Estelite Core Quick. For each core system, four different curing modes were applied to the adhesive and core resin: (1) dual-cured and dual-cured (DD); (2) chemically cured and dual-cured (CD); (3) dual-cured and chemically cured (DC); (4) chemically cured and chemically cured (CC). The specimens were sectioned into sticks (n = 20 for each group) for the microtensile bond test. μTBS data were analyzed using two-way ANOVA and the Dunnett T3 test. Failure patterns were examined with scanning electron microscopy (SEM) to determine the proportion of each mode. Dentin sandwiches were produced and subjected to an acid-base challenge. After argon-ion etching, the ultrastructure of ABRZ was observed using SEM. For Clearfil DC Core Automix, the μTBS values in MPa were as follows: DD: 29.1 ± 5.4, CD: 21.6 ± 5.6, DC: 17.9 ± 2.8, CC: 11.5 ± 3.2. For Estelite Core Quick, they were: DD: 48.9 ±5.7, CD: 20.5 ± 4.7, DC: 41.4 ± 8.3, CC: 19.1 ± 6.0. The bond strength was affected by both material and curing mode, and the interaction of the two factors was significant (p core systems affects bond strength to dentin, but has no significant effect on the formation of ABRZ.

  19. Vibrational mode-selected differential scattering of NH3+ methanol (d1, d3, d4): Control of product branching by hydrogen-bonded complex formation

    Science.gov (United States)

    Fu, Hungshin; Qian, Jun; Green, Richard J.; Anderson, Scott L.

    1998-02-01

    We report a study of vibrational mode effects and differential scattering in reaction of NH3+ with CD3OD, CD3OH, and CH3OD over the collision energy range from 0.1 to 5 eV. At low collision energies, abstraction of both methyl and hydroxyl D atoms is observed with roughly equal probability, even though methyl D-abstraction should be favored on both energetic and statistical grounds. Branching between the two abstraction reactions is controlled by two different hydrogen-bonded complexes. Formation of these complexes is enhanced by NH3+ umbrella bending, unaffected by the NH3+ symmetric stretch, and inhibited by collision energy. Endoergic proton transfer is mediated at low energies by a third hydrogen-bonded complex, formation of which is enhanced by both umbrella bending and the symmetric stretch. Charge transfer (CT) has a significant cross section only when the NH3+ umbrella bend excitation exceeds the endoergicity. Collision energy and symmetric stretching appear to have no effect on CT. At high collision energies all reactions become direct, with near spectator stripping dynamics. In this energy range product branching appears to be controlled by collision geometry and there are no significant vibrational effects.

  20. Large Scale Solid Phase Synthesis of Peptide Drugs: Use of Commercial Anion Exchange Resin as Quenching Agent for Removal of Iodine during Disulphide Bond Formation

    Directory of Open Access Journals (Sweden)

    K. M. Bhaskara Reddy

    2012-01-01

    Full Text Available The S-acetamidomethyl (Acm or trityl (Trt protecting groups are widely used in the chemical synthesis of peptides that contain one or more disulfide bonds. Treatment of peptides containing S-Acm protecting group with iodine results in simultaneous removal of the sulfhydryl protecting group and disulfide formation. However, the excess iodine needs to be quenched or adsorbed as quickly as possible after completion of the disulfide bond formation in order to minimize side reactions that are often associated with the iodination step. We report here a simple method for simultaneous quenching and removal of iodine and isolation of disulphide bridge peptides. The use of excess inexpensive anion exchange resin to the oxidized peptide from the aqueous acetic acid/methanol solution affords quantitative removal of iodine and other color impurities. This improves the resin life time of expensive chromatography media that is used in preparative HPLC column during the purification of peptide using preparative HPLC. Further, it is very useful for the conversion of TFA salt to acetate in situ. It was successfully applied commercially, to the large scale synthesis of various peptides including Desmopressin, Oxytocin, and Octreotide. This new approach offers significant advantages such as more simple utility, minimal side reactions, large scale synthesis of peptide drugs, and greater cost effectiveness.

  1. Large Scale Solid Phase Synthesis of Peptide Drugs: Use of Commercial Anion Exchange Resin as Quenching Agent for Removal of Iodine during Disulphide Bond Formation.

    Science.gov (United States)

    Reddy, K M Bhaskara; Kumari, Y Bharathi; Mallikharjunasarma, Dokka; Bulliraju, Kamana; Sreelatha, Vanjivaka; Ananda, Kuppanna

    2012-01-01

    The S-acetamidomethyl (Acm) or trityl (Trt) protecting groups are widely used in the chemical synthesis of peptides that contain one or more disulfide bonds. Treatment of peptides containing S-Acm protecting group with iodine results in simultaneous removal of the sulfhydryl protecting group and disulfide formation. However, the excess iodine needs to be quenched or adsorbed as quickly as possible after completion of the disulfide bond formation in order to minimize side reactions that are often associated with the iodination step. We report here a simple method for simultaneous quenching and removal of iodine and isolation of disulphide bridge peptides. The use of excess inexpensive anion exchange resin to the oxidized peptide from the aqueous acetic acid/methanol solution affords quantitative removal of iodine and other color impurities. This improves the resin life time of expensive chromatography media that is used in preparative HPLC column during the purification of peptide using preparative HPLC. Further, it is very useful for the conversion of TFA salt to acetate in situ. It was successfully applied commercially, to the large scale synthesis of various peptides including Desmopressin, Oxytocin, and Octreotide. This new approach offers significant advantages such as more simple utility, minimal side reactions, large scale synthesis of peptide drugs, and greater cost effectiveness.

  2. Effect of oxygen impurity on the efficiency of the formation of complexes with H-bond and aggregation of color centers in lithium fluoride

    Science.gov (United States)

    Nebogin, S. A.; Bryukvina, L. I.; Ivanov, N. A.; Glazunov, D. S.

    2017-06-01

    The effect of impurities on the efficiency of the formation of color centers and hydrogen-bonded molecular complexes upon exposure to various radiations in lithium fluoride crystals grown in air is studied. The results of experiments for measuring optical properties, IR vibrational spectra, luminescence, and thermally stimulated luminescence are presented. The fact that the band in the range of 1800-2300 cm-1 corresponds to stretching vibrations of a complex with strong hydrogen bond is proved based on the Fermi-resonance perturbation in the region of 2080 cm-1, shaped as the Evans hole and bands A, B, and C. It is shown that the composition of these complexes includes an OH- ion and an HF molecule. The crucial role of O2‒ V a + oxygen dipoles in the aggregation efficiency and gradient distribution of color centers and radiation resistance of hydroxyl ions is revealed. It is shown that products of radiation decomposition of OH- ions stimulate, while decay of O2‒ V a + dipoles suppress, the formation of positively charged color centers.

  3. Effect of water vapor treatment on apatite formation on precalcified titanium and bond strength of coatings to substrates.

    Science.gov (United States)

    Feng, B; Chen, Y; Zhang, X D

    2002-01-01

    In previous investigations, a simple method, precalcification, was developed for bioactivating titanium. After a titanium sample was precalcified in a boiling saturated Ca(OH)(2) solution and then immersed in a calcium phosphate supersaturated solution, an apatite coating rapidly precipitated onto its surface. In the present study, heat-treatment in water vapor was carried out prior to precalcification. Heat-treatment in water vapor stimulated the chemical reaction between titanium, calcium, and phosphate. Coating properties were improved, and the bond strength of the coating to substrate was enhanced. Copyright 2001 John Wiley & Sons, Inc.

  4. Internal friction and gas desorption of {C}/{C} composites

    Science.gov (United States)

    Serizawa, H.; Sato, S.; Kohyama, A.

    1994-09-01

    {C}/{C} composites are the most promising candidates as high heat flux component materials, where temperature dependence of mechanical properties and gas desorption behavior at elevated temperature are important properties. At the beginning, the newly developed internal friction measurement apparatus, which enables the accurate measurement of dynamic elastic properties up to 1373 K along with the measurement of gas desorption behavior, was used. The materials studied were unidirectional (UD) {C}/{C} composites reinforced with mesophase pitch-based carbon fibers, which were heat treated at temperatures ranging from 1473 to 2773 K which produced a variety of graphitized microstructures. Two-dimensional (2D) {C}/{C} composites reinfored with flat woven fabrics of PAN type carbon fibers were also studied. These materials were heat treated at 1873 K. From the temperature spectrum of internal friction of 2D {C}/{C} composites, these internal friction peaks were detected and were related to gas desorption. Also the temperature dependence of Young's modulus of UD {C}/{C} composites, negative and positive dependence of Young's modulus were observed reflecting microstructure changes resulting from the heat treatments.

  5. When friendship formation goes down the toilet: design features of shared accommodation influence interpersonal bonds and well-being.

    Science.gov (United States)

    Easterbrook, Matthew J; Vignoles, Vivian L

    2015-03-01

    Despite its omnipresence, the influence of the built environment on human psychology is not well understood. In a five-wave longitudinal study, we investigated whether physical design features within shared student accommodation predicted the frequency of coincidental meetings between new flatmates, and whether these meetings predicted the strength of their interpersonal bonds and psychological well-being. Multilevel latent growth modelling on responses from 462 new university residents supported our hypotheses: Respondents living in flats with design features that encouraged the use of communal areas--a shared common area and an absence of ensuite toilets--reported unintentionally meeting their flatmates more frequently within their flats. This in turn predicted the initial strength of their interpersonal bonds with their flatmates, which in turn positively predicted their well-being. These effects were maintained throughout the 10-week study. Our findings provide an empirical basis for the development of shared housing designed to foster positive relationships and well-being among residents. © 2014 The British Psychological Society.

  6. Unidirectional redox-stimulated movement around a C-C single bond.

    Science.gov (United States)

    Tepper, Christina; Haberhauer, Gebhard

    2011-07-11

    A remarkable challenge for the design of molecular machines is the realization of a synchronized and unidirectional movement caused by an external stimulus. Such a movement can be achieved by a unidirectionally controlled change of the conformation or the configuration. Biphenol derivatives are one possibility to realize a redox-driven unidirectional molecular switch. For this reason, a 4,4'-biphenol derivative was fixed to a chiral cyclopeptidic scaffold and stimulated by chemical oxidants and reduction agents. The conformation of the switch was determined by DFT calculations by using B3LYP and the 6-31G* basis set. The switching process was observed by UV and circular dichroism (CD) spectroscopic measurements. Several oxidation agents and various conditions were tested, among which (diacetoxy)iodobenzene (DAIB) in methanol proved to be the best. In this way it was possible to synthesize a redox-stimulated molecular switch with a movement that is part of a rotation around a biaryl binding axis. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Catalytic C-C Bond Cleavage for the Production of Chemicals from Lignin

    NARCIS (Netherlands)

    Jastrzebski, R.

    2016-01-01

    Lignin is a major component of lignocellulosic biomass and could be an important renewable feedstock in industry for the production of (aromatic) bulk and fine chemicals. To this end, the development of new catalytic processes is required; both to depolymerise the biopolymer into small aromatic

  8. C1 polymerisation and related C-C bond forming ‘carbene insertion’ reactions

    NARCIS (Netherlands)

    Jellema, E.; Jongerius, A.L.; Reek, J.N.H.; de Bruin, B.

    2010-01-01

    In this critical review we summarise the currently available ‘C1 polymerisation’ techniques as valuable alternatives for ‘C2 polymerisation’ in the preparation of saturated main-chain carbon-based polymers. C1 polymerisation involves the growth of polymers from monomers delivering only one

  9. Formation of a Three-Electron Sulfur-Sulfur Bond as a Probe for Interaction between Side Chains of Methionine Residues.

    Science.gov (United States)

    Filipiak, Piotr; Bobrowski, Krzysztof; Hug, Gordon L; Pogocki, Dariusz; Schöneich, Christian; Marciniak, Bronislaw

    2016-09-15

    The mechanism of oxidation processes of l-Met-(Pro)n-l-Met peptides that contain two Met residues located on the N- and C-terminal and separated by a defined number (n = 0-4) of proline residues was investigated in aqueous solutions using pulse radiolysis. The use of such peptides allowed for distance control between the sulfur atoms located in the side chains of the Met residues. The formation of a contact between the side chains of the Met residues was probed by the observation of transients with σ*-type 2c-3e S∴S and S∴O bonds as well as of α-(alkylthio)alkyl radicals (αS). This approach enabled the monitoring, in real time, of the efficiency and kinetics of interactions between methionine side chains. Such knowledge is important, inter alia, for long-distance electron transfer processes because methionine side chains can serve as relay stations and also for many aspects of protein folding when the formation of a contact between two amino acid residues in an unfolded polypeptide chain plays a central role in protein-folding mechanisms. The yields of these transients (measured as G-values) were found to be dependent on the number of Pro residues; however, they were not dependent in a simple way on the average distance ⟨rS-S⟩ between the sulfur atoms in Met residues. A decrease in the yield of the (S∴S)(+) species with an increase in the number of Pro residues in the bridge occurred at the expense of an increase in the yields of the intramolecular three-electron-bonded (S∴O)(+) radical cations and αS radicals. A detailed understanding of these trends in the chemical yields was developed by modeling the underlying chemical kinetics with Langevin dynamical simulations of the various oligoproline peptide chains and combining them with a simple statistical mechanical theory on the end-to-end contact rates for polymer chains. This analysis showed that the formation of a contact between terminal Met residues in the peptides with 0-2 Pro residues was

  10. Efficient C/C++ programming smaller, faster, better

    CERN Document Server

    Heller, Steve

    1994-01-01

    Efficient C/C++ Programming describes a practical, real-world approach to efficient C/C++ programming. Topics covered range from how to save storage using a restricted character set and how to speed up access to records by employing hash coding and caching. A selective mailing list system is used to illustrate rapid access to and rearrangement of information selected by criteria specified at runtime.Comprised of eight chapters, this book begins by discussing factors to consider when deciding whether a program needs optimization. In the next chapter, a supermarket price lookup system is used to

  11. Formation of Bonded Exciplex in the Excited States of Dicyanoanthracene-Pyridine System : Time Dependent Density Functional Theory Study

    NARCIS (Netherlands)

    Setiawan, D.; Sethio, D.; Martoprawiro, M.A.; Filatov, M.; Gaol, FL; Nguyen, QV

    2012-01-01

    Strong quenching of fluorescence was recently observed in pyridine solutions of 9,10-dicyanoanthracene chromophore. It was hypothesized that quenching may be attributed to the formation of bound charge transfer complexes in the excited states of the molecules. In this work, using time-dependent

  12. Helical Oligourea Foldamers as Powerful Hydrogen Bonding Catalysts for Enantioselective C-C Bond-Forming Reactions.

    Science.gov (United States)

    Bécart, Diane; Diemer, Vincent; Salaün, Arnaud; Oiarbide, Mikel; Nelli, Yella Reddy; Kauffmann, Brice; Fischer, Lucile; Palomo, Claudio; Guichard, Gilles

    2017-09-13

    Substantial progress has been made toward the development of metal-free catalysts of enantioselective transformations, yet the discovery of organic catalysts effective at low catalyst loadings remains a major challenge. Here we report a novel synergistic catalyst combination system consisting of a peptide-inspired chiral helical (thio)urea oligomer and a simple tertiary amine that is able to promote the Michael reaction between enolizable carbonyl compounds and nitroolefins with excellent enantioselectivities at exceptionally low (1/10 000) chiral catalyst/substrate molar ratios. In addition to high selectivity, which correlates strongly with helix folding, the system we report here is also highly amenable to optimization, as each of its components can be fine-tuned separately to increase reaction rates and/or selectivities. The predictability of the foldamer secondary structure coupled to the high level of control over the primary sequence results in a system with significant potential for future catalyst design.

  13. Get more control over your C/C++ service

    CERN Multimedia

    CERN. Geneva

    2015-01-01

    Are you looking for a way to better diagnose or monitor your C/C++ programs? Find out more about CMX - a neat, lightweight library (<32Kb) which targets this need. It allows to expose information from inside a process through a simple API, enabling pre-failure detection in combination with your favourite monitoring system.

  14. 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.

  15. Hydrogen Bonding-Mediated Microphase Separation during the Formation of Mesoporous Novolac-Type Phenolic Resin Templated by the Triblock Copolymer, PEO-b-PPO-b-PEO.

    Science.gov (United States)

    Chu, Wei-Cheng; Chiang, Shih-Fan; Li, Jheng-Guang; Kuo, Shiao-Wei

    2013-11-07

    After blending the triblock copolymer, poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-b-PEO) with novolac-type phenolic resin, Fourier transform infrared spectroscopy revealed that the ether groups of the PEO block were stronger hydrogen bond acceptors for the OH groups of phenolic resin than were the ether groups of the PPO block. Thermal curing with hexamethylenetetramine as the curing agent resulted in the triblock copolymer being incorporated into the phenolic resin, forming a nanostructure through a mechanism involving reaction-induced microphase separation. Mild pyrolysis conditions led to the removal of the PEO-b-PPO-b-PEO triblock copolymer and formation of mesoporous phenolic resin. This approach provided a variety of composition-dependent nanostructures, including disordered wormlike, body-centered-cubic spherical and disorder micelles. The regular mesoporous novolac-type phenolic resin was formed only at a phenolic content of 40-60 wt %, the result of an intriguing balance of hydrogen bonding interactions among the phenolic resin and the PEO and PPO segments of the triblock copolymer.

  16. Formation of intersubunit disulfide bonds and properties of the single histidine and cysteine residues in each subunit relative to the decameric structure of cyanase.

    Science.gov (United States)

    Anderson, P M; Korte, J J; Holcomb, T A; Cho, Y G; Son, C M; Sung, Y C

    1994-05-27

    Reaction of the single cysteine residue in each subunit of cyanase with certain SH reagents gives an active decameric derivative that dissociates reversibly to an inactive dimer derivative (Anderson, P. M., Johnson, W. V., Korte, J. J., Xiong, X., Sung, Y.-c., and Fuchs, J. A. (1988) J. Biol. Chem. 263, 5674-5680). Reaction of mixed disulfide dimer derivatives of cyanase with dithiothreitol at 0 degree C results in formation of a disulfide bond between the subunits in the dimer. The disulfide dimer was inactive and did not associate to a decamer; the intersubunit disulfide bond could not be formed when the dimers were associated as a decamer. The two SH groups apparently are in close proximity to each other in the dissociated dimer but not when the dimer is associated to a decamer. Substitution of glycine for the cysteine residue or of tyrosine, asparagine, glycine, valine, or leucine for the single histidine residue in each subunit gave mutant enzymes that were active. However, H113N, H113Y, and C83G were unstable at low temperature and/or ionic strength, dissociating reversibly to an inactive dimer. Efficient reassociation required the presence of bicarbonate or cyanate analog. The results are consistent with a proposed single site per subunit model explaining apparent half-site binding of substrates and the requirement of decameric structure for activity.

  17. Hydrogen Bonding-Mediated Microphase Separation during the Formation of Mesoporous Novolac-Type Phenolic Resin Templated by the Triblock Copolymer, PEO-b-PPO-b-PEO

    Directory of Open Access Journals (Sweden)

    Wei-Cheng Chu

    2013-11-01

    Full Text Available After blending the triblock copolymer, poly(ethylene oxide-b-propylene oxide-b-ethylene oxide (PEO-b-PPO-b-PEO with novolac-type phenolic resin, Fourier transform infrared spectroscopy revealed that the ether groups of the PEO block were stronger hydrogen bond acceptors for the OH groups of phenolic resin than were the ether groups of the PPO block. Thermal curing with hexamethylenetetramine as the curing agent resulted in the triblock copolymer being incorporated into the phenolic resin, forming a nanostructure through a mechanism involving reaction-induced microphase separation. Mild pyrolysis conditions led to the removal of the PEO-b-PPO-b-PEO triblock copolymer and formation of mesoporous phenolic resin. This approach provided a variety of composition-dependent nanostructures, including disordered wormlike, body-centered-cubic spherical and disorder micelles. The regular mesoporous novolac-type phenolic resin was formed only at a phenolic content of 40–60 wt %, the result of an intriguing balance of hydrogen bonding interactions among the phenolic resin and the PEO and PPO segments of the triblock copolymer.

  18. Roles of Intramolecular and Intermolecular Hydrogen Bonding in a Three-Water-Assisted Mechanism of Succinimide Formation from Aspartic Acid Residues

    Directory of Open Access Journals (Sweden)

    Ohgi Takahashi

    2014-08-01

    Full Text Available Aspartic acid (Asp residues in peptides and proteins are prone to isomerization to the β-form and racemization via a five-membered succinimide intermediate. These nonenzymatic reactions have relevance to aging and age-related diseases. In this paper, we report a three water molecule-assisted, six-step mechanism for the formation of succinimide from Asp residues found by density functional theory calculations. The first two steps constitute a stepwise iminolization of the C-terminal amide group. This iminolization involves a quintuple proton transfer along intramolecular and intermolecular hydrogen bonds formed by the C-terminal amide group, the side-chain carboxyl group, and the three water molecules. After a conformational change (which breaks the intramolecular hydrogen bond involving the iminol nitrogen and a reorganization of water molecules, the iminol nitrogen nucleophilically attacks the carboxyl carbon of the Asp side chain to form a five-membered ring. This cyclization is accompanied by a triple proton transfer involving two water molecules, so that a gem-diol tetrahedral intermediate is formed. The last step is dehydration of the gem-diol group catalyzed by one water molecule, and this is the rate-determining step. The calculated overall activation barrier (26.7 kcal mol−1 agrees well with an experimental activation energy.

  19. Alcohol and Group Formation: A Multimodal Investigation of the Effects of Alcohol on Emotion and Social Bonding

    OpenAIRE

    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.

    2012-01-01

    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 an...

  20. 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.

  1. Identification of coevolving residues and coevolution potentials emphasizing structure, bond formation and catalytic coordination in protein evolution.

    Directory of Open Access Journals (Sweden)

    Daniel Y Little

    Full Text Available The structure and function of a protein is dependent on coordinated interactions between its residues. The selective pressures associated with a mutation at one site should therefore depend on the amino acid identity of interacting sites. Mutual information has previously been applied to multiple sequence alignments as a means of detecting coevolutionary interactions. Here, we introduce a refinement of the mutual information method that: 1 removes a significant, non-coevolutionary bias and 2 accounts for heteroscedasticity. Using a large, non-overlapping database of protein alignments, we demonstrate that predicted coevolving residue-pairs tend to lie in close physical proximity. We introduce coevolution potentials as a novel measure of the propensity for the 20 amino acids to pair amongst predicted coevolutionary interactions. Ionic, hydrogen, and disulfide bond-forming pairs exhibited the highest potentials. Finally, we demonstrate that pairs of catalytic residues have a significantly increased likelihood to be identified as coevolving. These correlations to distinct protein features verify the accuracy of our algorithm and are consistent with a model of coevolution in which selective pressures towards preserving residue interactions act to shape the mutational landscape of a protein by restricting the set of admissible neutral mutations.

  2. Ion chemistry in octafluorocyclobutane, c-C 4F 8

    Science.gov (United States)

    Jiao, C. Q.; Garscadden, A.; Haaland, P. D.

    1998-11-01

    Cross-sections for electron impact ionization of octafluorocyclobutane ( c-C 4F 8) have been measured from 10 to 200 eV by Fourier transform mass spectrometry. No parent ion is observed, and over half of the dissociative ionization yields C 2F 4+ and C 3F 5+. Eleven other fluorocarbon cations are produced with smaller cross-sections, giving a total ionization cross-section of (1.6±0.2)×10 -15 cm 2 between 80 and 200 eV. Only CF 2+ and C 2F 3+ react further with the parent molecule to yield C 3F 5+ as the primary product. No evidence of cationic polymerization was found. F - and C 4F 8- are formed by electron attachment at energies below 10 eV, but neither reacts further with c-C 4F 8.

  3. Synthesis of the proteinase inhibitor LEKTI domain 6 by the fragment condensation method and regioselective disulfide bond formation.

    Science.gov (United States)

    Vasileiou, Zoe; Barlos, Kostas K; Gatos, Dimitrios; Adermann, Knut; Deraison, Celine; Barlos, Kleomenis

    2010-01-01

    Proteinase inhibitors are of high pharmaceutical interest and are drug candidates for a variety of indications. Specific kallikrein inhibitors are important for their antitumor activity and their potential application to the treatment of skin diseases. In this study we describe the synthesis of domain 6 of the kallikrein inhibitor Lympho-Epithilial Kazal-Type Inhibitor (LEKTI) by the fragment condensation method and site-directed cystine bridge formation. To obtain the linear LEKTI precursor, the condensation was best performed in solution, coupling the protected fragment 1-22 to 23-68. This method yielded LEKTI domain 6 of high purity and equipotent to the recombinantly produced peptide. (c) 2010 Wiley Periodicals, Inc.

  4. Microstructure of C/C Composites with Different Matrix Carbon

    Directory of Open Access Journals (Sweden)

    LIU Hao

    2016-07-01

    Full Text Available The microstructure of carbon/carbon(C/C composites with different matrix carbon was studied by polarized light microscopy (PLM, scanning electron microscopy (SEM, transmission electron microscopy (TEM and XRD techniques respectively. PLM results indicate that the different matrix carbon exhibits different optical reactivity, and the average optical reactivity is gradually enhanced from normal pitch carbon, smooth laminar of pyrocarbon, rough laminar of pyrocarbon to mesophase pitch carbon; SEM results show that the normal pitch carbon is mainly of grapy structure, the pyrocarbon exhibits like-crinkle lamellar structure, while the mesophase pitch carbon exhibits lamellar banded structure with different shapes. Under HRTEM, the lattice fringes of the mesophase pitch carbon are arranged regularly, is a long range ordered crystal structure, and the preferred orientation is high. The degree of the graphite and the interlayer spacing of the material B (mesophase pitch-based C/C composites are better than that of the material D (pyrocarbon-based C/C composites.

  5. Dynamic analysis of C/C composite finger seal

    Directory of Open Access Journals (Sweden)

    Chen Guoding

    2014-06-01

    Full Text Available A seal device as an important component of aeroengines has decisive influence on performance, reliability, and working life of aeroengines. With the development of aeroengines, demands on the performance characteristics of seal devices are made strictly. Finger seal as a novel kind of sealing device, recently attracts more and more attentions in academic circles and engineering fields at home and abroad. Research on finger seals has been extensively developed, especially on leakage and wear performances under dynamic conditions. However, it is a pity that the work on finger seals has been limited with a single approach that is improving the performance by structural optimization; in addition, the technology of dynamic analysis on finger seals is weak. Aiming at the problems mentioned above, a distributed mass equivalent dynamic model of finger seals considering the coupling effect of overlaid laminates is established in the present paper, the dynamic performance of 2.5 dimension C/C composite finger seal is analyzed with the model, and then the effects of fiber bundle density and fiber bundle preparation direction on finger seal’s dynamic performance are discussed, as well as compared with those of Co-based alloy finger seal. The current work is about dynamic analysis of finger seals and application of C/C composite in this paper may have much academic significance and many engineering values for improving research level of finger seal dynamics and exploring feasibility of C/C composite being used for finger seals.

  6. Mechanistic elucidation of the stepwise formation of a tetranuclear manganese pinned butterfly cluster via N-N bond cleavage, hydrogen atom transfer, and cluster rearrangement.

    Science.gov (United States)

    Hamilton, Clifton R; Gau, Michael R; Baglia, Regina A; McWilliams, Sean F; Zdilla, Michael J

    2014-12-31

    A mechanistic pathway for the formation of the structurally characterized manganese-amide-hydrazide pinned butterfly complex, Mn4(μ3-PhN-NPh-κ(3)N,N')2(μ-PhN-NPh-κ(2)-N,N')(μ-NHPh)2L4 (L = THF, py), is proposed and supported by the use of labeling studies, kinetic measurements, kinetic competition experiments, kinetic isotope effects, and hydrogen atom transfer reagent substitution, and via the isolation and characterization of intermediates using X-ray diffraction and electron paramagnetic resonance spectroscopy. The data support a formation mechanism whereby bis[bis(trimethylsilyl)amido]manganese(II) (Mn(NR2)2, where R = SiMe3) reacts with N,N'-diphenylhydrazine (PhNHNHPh) via initial proton transfer, followed by reductive N-N bond cleavage to form a long-lived Mn(IV) imido multinuclear complex. Coordinating solvents activate this cluster for abstraction of hydrogen atoms from an additional equivalent of PhNHNHPh resulting in a Mn(II)phenylamido dimer, Mn2(μ-NHPh)2(NR2)2L2. This dimeric complex further assembles in fast steps with two additional equivalents of PhNHNHPh replacing the terminal silylamido ligands with η(1)-hydrazine ligands to give a dimeric Mn2(μ-NHPh)2(PhN-NHPh)2L4 intermediate, and finally, the addition of two additional equivalents of Mn(NR2)2 and PhNHNHPh gives the pinned butterfly cluster.

  7. Spectrofluorimetric determination of total free thiols based on formation of complexes of Ce(III) with disulfide bonds

    Energy Technology Data Exchange (ETDEWEB)

    Han Guocheng; Peng Yong; Hao Yuanqiang [College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083 (China); Liu Younian, E-mail: liuyoun@mail.csu.edu.cn [College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083 (China); Zhou Feimeng, E-mail: fzhou@exchange.calstatela.edu [College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083 (China); Department of Chemistry and Biochemistry, California State University, Los Angeles, Los Angeles, CA 90032 (United States)

    2010-02-05

    A simple, rapid, and sensitive determination of total free thiol groups in biological samples using cerium (IV) as a fluorescence probe is reported. The protocol is based on the oxidation of thiols by Ce(IV) and the formation the Ce(III) disulfide complex, which gives a fluorescence enhancement of Ce(III) at 352 nm. Using glutathione (GSH) and cysteine as model compounds, incubation with Ce(IV) at 25 {sup o}C for 6 min results in fluorescence, whose intensity is proportional to the thiol concentration in the range of 1.00-160 nM. The detection limits for GSH and cysteine are 0.05 and 0.08 nM, respectively. Other common metal ions and amino acids have little interference to the thiol detection. Cu(II) was used as a fluorescence quencher to eliminate potential interference from tryptophan. The method has been successfully applied to assays of free thiol contents in pig liver tissue samples, with a RSD lower than 2.5% and recovery between 100.6% and 102.3%.

  8. C.C.D. Readout Of A Picosecond Streak Camera With An Intensified C.C.D.

    Science.gov (United States)

    Lemonier, M.; Richard, J. C.; Cavailler, C.; Mens, A.; Raze, G.

    1985-02-01

    This paper deals with a digital streak camera readout device. The device consists in a low light level television camera made of a solid state C.C.D. array coupled to an image intensifier associated to a video-digitizer coupled to a micro-computer system. The streak camera images are picked-up as a video signal, digitized and stored. This system allows the fast recording and the automatic processing of the data provided by the streak tube. Starting from the output screen of the streak camera, the constitutive elements are : - A fiber optic taper (A.O. Scientific Instruments) set in contact with the fiber optic output window of the streak tube achieves the image demagnification ; - A double proximity focused image intensifier (RTC - XX1410 SP) achieves the bright-ness amplification without any distortion ; - A second fiber optic taper achieves the dimensional matching between intensifier output and C.C.D. sensitive area ;

  9. C-C Coupling on Single-Atom-Based Heterogeneous Catalyst.

    Science.gov (United States)

    Zhang, Xiaoyan; Sun, Zaicheng; Wang, Bin; Tang, Yu; Nguyen, Luan; Li, Yuting; Tao, Franklin Feng

    2018-01-24

    Compared to homogeneous catalysis, heterogeneous catalysis allows for ready separation of products from the catalyst and thus reuse of the catalyst. C-C coupling is typically performed on a molecular catalyst which is mixed with reactants in liquid phase during catalysis. This homogeneous mixing at a molecular level in the same phase makes separation of the molecular catalyst extremely challenging and costly. Here we demonstrated that a TiO 2 -based nanoparticle catalyst anchoring singly dispersed Pd atoms (Pd 1 /TiO 2 ) is selective and highly active for more than 10 Sonogashira C-C coupling reactions (R≡CH + R'X → R≡R'; X = Br, I; R' = aryl or vinyl). The coupling between iodobenzene and phenylacetylene on Pd 1 /TiO 2 exhibits a turnover rate of 51.0 diphenylacetylene molecules per anchored Pd atom per minute at 60 °C, with a low apparent activation barrier of 28.9 kJ/mol and no cost of catalyst separation. DFT calculations suggest that the single Pd atom bonded to surface lattice oxygen atoms of TiO 2 acts as a site to dissociatively chemisorb iodobenzene to generate an intermediate phenyl, which then couples with phenylacetylenyl bound to a surface oxygen atom. This coupling of phenyl adsorbed on Pd 1 and phenylacetylenyl bound to O ad of TiO 2 forms the product molecule, diphenylacetylene.

  10. Communications: Photoinitiated bond dissociation of bromoiodomethane in solution: Comparison of one-photon and two-photon excitations and the formation of iso-CH2Br-I and iso-CH2I-Br

    Science.gov (United States)

    Tang, Kuo-Chun; Peng, Jian; Spears, Kenneth G.; Sension, Roseanne J.

    2010-04-01

    Broadband UV-visible femtosecond transient absorption spectroscopy was used to monitor the excited state photochemistry of CH2BrI following one-photon excitation at 266 or 271 nm and two-photon excitation at 395 or 405 nm in 2-butanol. The results for one-photon excitation agree with earlier studies in acetonitrile, showing clear formation of iso-CH2Br-I following cleavage of the C-I bond. In contrast, two-photon excitation at 395 nm results in the appearance of a blueshifted photoproduct absorption band assigned to formation of iso-CH2I-Br following cleavage of the C-Br bond. The results are discussed in the context of prior experimental and theoretical work and the prospects for optical control of bond cleavage.

  11. Formation of hydrogen-bonded chains through inter- and intra-molecular hydrogen bonds by a strong base of guanidine-like character and 2,2‧-biphenols

    Science.gov (United States)

    Brzezinski, B.; Wojciechowski, G.; Bartl, F.; Zundel, G.

    2000-11-01

    2,2‧-Biphenol mixtures with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) were studied by FTIR spectroscopy. In chloroform, a proton transfer from 2,2‧-biphenol to MTBD occurs. In this solution the protonated MTBD molecules are hydrogen-bonded to the 2,2‧-biphenol-2,2‧-biphenolate chains. In acetonitrile, after the proton transfer, the complexes dissociate and hence protonated MTBD molecules and hydrogen-bonded 2,2‧-biphenol-2,2‧-biphenolate chains are present. The hydrogen bonds and the hydrogen-bonded chains show large proton polarizability. In the systems intra- as well as inter-molecular hydrogen bonds are formed.

  12. Formats

    Directory of Open Access Journals (Sweden)

    Gehmann, Ulrich

    2012-03-01

    Full Text Available In the following, a new conceptual framework for investigating nowadays’ “technical” phenomena shall be introduced, that of formats. The thesis is that processes of formatting account for our recent conditions of life, and will do so in the very next future. It are processes whose foundations have been laid in modernity and which will further unfold for the time being. These processes are embedded in the format of the value chain, a circumstance making them resilient to change. In addition, they are resilient in themselves since forming interconnected systems of reciprocal causal circuits.Which leads to an overall situation that our entire “Lebenswelt” became formatted to an extent we don’t fully realize, even influencing our very percep-tion of it.

  13. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

    Asami, Hiroya [Graduate School of Bio- and Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan); Yagi, Kiyoshi [Department of Chemistry, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Ohba, Masashi [Yokohama College of Pharmacy, Yokohama 245-0066 (Japan); Urashima, Shu-hei [Graduate School of Bio- and Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan); Saigusa, Hiroyuki, E-mail: saigusa@yokohama-cu.ac.jp [Graduate School of Bio- and Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan)

    2013-06-20

    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.

  15. Phylogeny of the Vitamin K 2,3-Epoxide Reductase (VKOR) Family and Evolutionary Relationship to the Disulfide Bond Formation Protein B (DsbB) Family.

    Science.gov (United States)

    Bevans, Carville G; Krettler, Christoph; Reinhart, Christoph; Watzka, Matthias; Oldenburg, Johannes

    2015-07-29

    In humans and other vertebrate animals, vitamin K 2,3-epoxide reductase (VKOR) family enzymes are the gatekeepers between nutritionally acquired K vitamins and the vitamin K cycle responsible for posttranslational modifications that confer biological activity upon vitamin K-dependent proteins with crucial roles in hemostasis, bone development and homeostasis, hormonal carbohydrate regulation and fertility. We report a phylogenetic analysis of the VKOR family that identifies five major clades. Combined phylogenetic and site-specific conservation analyses point to clade-specific similarities and differences in structure and function. We discovered a single-site determinant uniquely identifying VKOR homologs belonging to human pathogenic, obligate intracellular prokaryotes and protists. Building on previous work by Sevier et al. (Protein Science 14:1630), we analyzed structural data from both VKOR and prokaryotic disulfide bond formation protein B (DsbB) families and hypothesize an ancient evolutionary relationship between the two families where one family arose from the other through a gene duplication/deletion event. This has resulted in circular permutation of primary sequence threading through the four-helical bundle protein folds of both families. This is the first report of circular permutation relating distant a-helical membrane protein sequences and folds. In conclusion, we suggest a chronology for the evolution of the five extant VKOR clades.

  16. Use of a temporary "solubilizing" peptide tag for the Fmoc solid-phase synthesis of human insulin glargine via use of regioselective disulfide bond formation.

    Science.gov (United States)

    Hossain, Mohammed Akhter; Belgi, Alessia; Lin, Feng; Zhang, Suode; Shabanpoor, Fazel; Chan, Linda; Belyea, Chris; Truong, Hue-Trung; Blair, Amy R; Andrikopoulos, Sof; Tregear, Geoffrey W; Wade, John D

    2009-07-01

    Solid-phase peptide synthesis has been refined to a stage where efficient preparation of long and complex peptides is now achievable. However, the postsynthesis handling of poorly soluble peptides often remains a significant hindrance to their purification and further use. Several synthetic schemes have been developed for the preparation of such peptides containing modifications to aid their solubility. However, these require the use of complex chemistry or yield non-native sequences. We describe a simple approach based on the use of penta-lysine "tags" that are linked to the C-terminus of the peptide of interest via a base-labile linker. After ready purification of the now freely solubilized peptide, the "tag" is removed by simple, brief base treatment giving the native sequence in much higher overall yield. The applicability of the method was demonstrated by the novel preparation of insulin glargine via solid-phase synthesis of each of the two chains--including the notoriously poorly soluble A-chain--followed by their combination in solution via regioselective disulfide bond formation. At the conclusion of the chain combination, the solubilizing peptide tag was removed from the A-chain to provide synthetic human glargine in nearly 10% overall yield. This approach should facilitate the development of new insulin analogues as well as be widely applicable to the improved purification and acquisition of otherwise poorly soluble synthetic peptides.

  17. Phylogeny of the Vitamin K 2,3-Epoxide Reductase (VKOR Family and Evolutionary Relationship to the Disulfide Bond Formation Protein B (DsbB Family

    Directory of Open Access Journals (Sweden)

    Carville G. Bevans

    2015-07-01

    Full Text Available In humans and other vertebrate animals, vitamin K 2,3-epoxide reductase (VKOR family enzymes are the gatekeepers between nutritionally acquired K vitamins and the vitamin K cycle responsible for posttranslational modifications that confer biological activity upon vitamin K-dependent proteins with crucial roles in hemostasis, bone development and homeostasis, hormonal carbohydrate regulation and fertility. We report a phylogenetic analysis of the VKOR family that identifies five major clades. Combined phylogenetic and site-specific conservation analyses point to clade-specific similarities and differences in structure and function. We discovered a single-site determinant uniquely identifying VKOR homologs belonging to human pathogenic, obligate intracellular prokaryotes and protists. Building on previous work by Sevier et al. (Protein Science 14:1630, we analyzed structural data from both VKOR and prokaryotic disulfide bond formation protein B (DsbB families and hypothesize an ancient evolutionary relationship between the two families where one family arose from the other through a gene duplication/deletion event. This has resulted in circular permutation of primary sequence threading through the four-helical bundle protein folds of both families. This is the first report of circular permutation relating distant a-helical membrane protein sequences and folds. In conclusion, we suggest a chronology for the evolution of the five extant VKOR clades.

  18. Tribological properties of C/C-SiC composites for brake discs

    Science.gov (United States)

    Jang, G. H.; Cho, K. H.; Park, S. B.; Lee, W. G.; Hong, U. S.; Jang, H.

    2010-02-01

    This study examines the friction and wear of ceramic matrix composites designed for use in automotive brake discs. The composites are produced by reinforcing a SiC matrix with carbon fibers using a liquid silicon infiltration method. C/C-SiC composites with two different compositions are fabricated to examine the compositional effect on the tribological properties. The tribological properties are evaluated using a scale dynamometer with a low-steel type friction material. The results show that the coefficient of friction is determined by the composition of the composite, which affects the propensity of friction film formation on the disc surface. A stable friction film on the disc surface also improves the wear resistance by diminishing the abrasive action of the disc. On the other hand, the friction film formation on the disc is affected by the applied pressure, and stable films are obtained at high pressures. This trend is prominent with discs with high Si content. However, both C/C/-SiC composites show superior performance in terms of the friction force oscillation, which is closely related to brake-induced vibration.

  19. Rapid formation of Ni3Sn4 joints for die attachment of SiC-based high temperature power devices using ultrasound-induced transient liquid phase bonding process.

    Science.gov (United States)

    Li, Z L; Dong, H J; Song, X G; Zhao, H Y; Feng, J C; Liu, J H; Tian, H; Wang, S J

    2017-05-01

    High melting point Ni3Sn4 joints for the die attachment of SiC-based high temperature power devices was successfully achieved using an ultrasound-induced transient liquid phase (TLP) bonding process within a remarkably short bonding time of 8s. The formed intermetallic joints, which are completely composed of the refined equiaxial Ni3Sn4 grains with the average diameter of 2μm, perform the average shear strength of 26.7MPa. The sonochemical effects of ultrasonic waves dominate the mechanism and kinetics of the rapid formation of Ni3Sn4 joints. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Formation of diphenylphosphanylbutadienyl complexes by insertion of two P-coordinated alkynylphosphanes into a PtbondC6F5 bond: detection of intermediate and reaction products.

    Science.gov (United States)

    Ara, Irene; Forniés, Juan; García, Ana; Gómez, Julio; Lalinde, Elena; Moreno, M Teresa

    2002-08-16

    The reactions between cis-[M(C(6)F(5))(2)(PPh(2)CtriplebondCR)(2)] (M=Pt, Pd; R=Ph, tBu, Tol 2, 3) or cis-[Pt(C(6)F(5))(2)(PPh(2)CtriplebondCR)(PPh(2)CtriplebondCtBu)] (R=Ph 4, Tol 5) and cis-[Pt(C(6)F(5))(2)(thf)(2)] 1 have been investigated. Whereas [M](PPh(2)CtriplebondCtBu)(2) ([M]=cis-M(C(6)F(5))(2)) is inert towards 1, the analogous reactions starting from [M](PPh(2)CtriplebondCR)(2) or [Pt](PPh(2)CtriplebondCR)(PPh(2)CtriplebondCtBu) (R=Ph, Tol) afford unusual binuclear species [Pt(C(6)F(5))(S)mu-[C(R')dbondC(PPh(2))C(PPh(2))doublebondC(R)(C(6)F(5))]M(C(6)F(5))(2)] (R=R'=Ph, Tol, M=Pt 6 a,c, M=Pd 7 a,c; M=Pt, R'=tBu, R=Ph 8, Tol 9) containing a bis(diphenylphosphanyl)butadienyl bridging ligand formed by an unprecedented sequential insertion reaction of two P-coordinated PPh(2)CtriplebondCR ligands into a PtbondC(6)F(5) bond. Although in solution the presence of coordinated solvent S (S=(thf)(x)(H(2)O)(y)) in 6, 7 is suggested by NMR spectroscopy, X-ray diffraction analyses of different crystals of the mixed complex [Pt(C(6)F(5))mu-[C(tBu)doublebondC(PPh(2))C(PPh(2))doublebondC(Tol)(C(6)F(5))]Pt(C(6)F(5))(2)] 9 unequivocally establish that in the solid state the steric crowding of the new diphenylbutadienyl ligand formed stabilizes an unusual coordinatively unsaturated T-shaped 3-coordinated platinum(II) center. Structure determinations of the mononuclear precursors cis-[Pt(C(6)F(5))(2)(PPh(2)CtriplebondCR)(2)] (R=Ph, tBu, Tol) have been carried out to evaluate the factors affecting the insertion processes. The reactions of the platinum complexes 6 towards neutral ligands (L=CO, py, PPh(2)H, CNtBu) in a 1:1 molar ratio afford related diplatinum derivatives 10-13, whereas treatment with CNtBu (1:2 molar ratio) or 2,2'-bipy (1:1 molar ratio) results in the opening of the chelating ring to give cis,cis-[Pt(C(6)F(5))(L)(2)mu-[1-kappaC(1):2-kappaPP'-C(R)doublebondC(PPh(2))C(PPh(2))doublebondC(R)(C(6)F(5))]Pt(C(6)F(5))(2)] (14, 15). The unsaturated or solvento

  1. 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...... 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....... 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...

  2. Deformation microstructure and orientation of F.C.C. crystals

    DEFF Research Database (Denmark)

    Liu, Q.; Hansen, N.

    1995-01-01

    that dependent on the crystallographic orientation of the crystal the subdividing boundaries may be nearly parallel to slip planes or they may have a non-crystallographic orientation. This difference is discussed on the basis of an analysis of potential slip planes identified by a Schmid factor analysis.......The effect of crystallographic orientation on the microstructural evolution in f.c.c. metals with medium to high stacking fault energy is analyzed. This analysis is based on a literature review of the behaviour of single crystals and polycrystals supplemented with an experimental study of cold......-rolled pure aluminium. It is generally observed that all crystallites subdivide during deformation into cell blocks and cells bounded by rotation dislocation boundaries. In general the boundaries have a macroscopic orientation with respect to the geometry of the specimen. A crystallographic analysis shows...

  3. Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry.

    Science.gov (United States)

    Ruscic, Branko

    2015-07-16

    Active Thermochemical Tables (ATcT) thermochemistry for the sequential bond dissociations of methane, ethane, and methanol systems were obtained by analyzing and solving a very large thermochemical network (TN). Values for all possible C-H, C-C, C-O, and O-H bond dissociation enthalpies at 298.15 K (BDE298) and bond dissociation energies at 0 K (D0) are presented. The corresponding ATcT standard gas-phase enthalpies of formation of the resulting CHn, n = 4-0 species (methane, methyl, methylene, methylidyne, and carbon atom), C2Hn, n = 6-0 species (ethane, ethyl, ethylene, ethylidene, vinyl, ethylidyne, acetylene, vinylidene, ethynyl, and ethynylene), and COHn, n = 4-0 species (methanol, hydroxymethyl, methoxy, formaldehyde, hydroxymethylene, formyl, isoformyl, and carbon monoxide) are also presented. The ATcT thermochemistry of carbon dioxide, water, hydroxyl, and carbon, oxygen, and hydrogen atoms is also included, together with the sequential BDEs of CO2 and H2O. The provenances of the ATcT enthalpies of formation, which are quite distributed and involve a large number of relevant determinations, are analyzed by variance decomposition and discussed in terms of principal contributions. The underlying reasons for periodic appearances of remarkably low and/or unusually high BDEs, alternating along the dissociation sequences, are analyzed and quantitatively rationalized. The present ATcT results are the most accurate thermochemical values currently available for these species.

  4. Formation of hydrogen-bonded chains through inter- and intra-molecular hydrogen bonds by a strong base of guanidine-like character and 5,5'-dibromo-2,2'-biphenols

    Science.gov (United States)

    Wojciechowski, G.; Brzezinski, B.

    2002-04-01

    5,5'-dibromo-2,2'-biphenol mixtures with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) were studied by FTIR as well as 1H NMR spectroscopy. In chloroform, a proton transfer from DBBPh to MTBD occurs and the protonated MTBD molecule is hydrogen-bonded to the chain formed between 5,5'-dibromo-2,2'-biphenol and 5,5'-dibromo-2,2'-biphenolate molecule. In acetonitrile, the complex dissociates and hence protonated MTBD molecules and hydrogen-bonded chains formed between 5,5'-dibromo-2,2'-biphenol and 5,5'-dibromo-2,2'-biphenolate are present. The hydrogen bonds of these chains show large proton polarizability.

  5. Formation of hydrogen-bonded chains through inter- and intra-molecular hydrogen bonds by 5,5'-dinitro-2,2'-biphenol with a strong base of guanidine-like character and triethylamine

    Science.gov (United States)

    Wojciechowski, Grzegorz; Brzezinski, Bogumil

    2002-04-01

    The complexes of 5,5'-dinitro-2,2'-biphenol (DNBPh) with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) and triethylamine (TEA) were studied by FTIR and 1H NMR spectroscopy. In chloroform and in acetonitrile a proton transfer from DNBPh to N-bases (MTBD, TEA) occurs. In chloroform solution the protonated N-base molecules are hydrogen-bonded to the deprotonated DNBPh molecules whereas in acetonitrile the complexes dissociate and hence protonated N-base molecules and hydrogen-bonded chains formed between DNBPh and 5,5'-dinitro-2,2'-biphenolate are present. The intra- as well as inter-molecular hydrogen bonds within the chains show large proton polarizability.

  6. 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

  7. C-C bond formation and related reactions at the CNC backbone in (smif)FeX (smif = 1,3-di-(2-pyridyl)-2-azaallyl): dimerizations, 3 + 2 cyclization, and nucleophilic attack; transfer hydrogenations and alkyne trimerization (X = N(TMS)2, dpma = (di-(2-pyridyl-methyl)-amide)).

    Science.gov (United States)

    Frazier, Brenda A; Williams, Valerie A; Wolczanski, Peter T; Bart, Suzanne C; Meyer, Karsten; Cundari, Thomas R; Lobkovsky, Emil B

    2013-03-18

    Molecular orbital analysis depicts the CNC(nb) backbone of the smif (1,3-di-(2-pyridyl)-2-azaallyl) ligand as having singlet diradical and/or ionic character where electrophilic or nucleophilic attack is plausible. Reversible dimerization of (smif)Fe{N(SiMe3)2} (1) to [{(Me3Si)2N}Fe]2(μ-κ(3),κ(3)-N,py2-smif,smif) (2) may be construed as diradical coupling. A proton transfer within the backbone-methylated, and o-pyridine-methylated smif of putative ((b)Me2(o)Me2smif)FeN(SiMe3)2 (8) provides a route to [{(Me3Si)2N}Fe]2(μ-κ(4),κ(4)-N,py2,C-((b)Me,(b)CH2,(o)Me2(smif)H))2 (9). A 3 + 2 cyclization of ditolyl-acetylene occurs with 1, leading to the dimer [{2,5-di(pyridin-2-yl)-3,4-di-(p-tolyl-2,5-dihydropyrrol-1-ide)}FeN(SiMe3)2]2 (11), and the collateral discovery of alkyne cyclotrimerization led to a brief study that identified Fe(N(SiMe3)2(THF) as an effective catalyst. Nucleophilic attack by (smif)2Fe (13) on (t)BuNCO and (2,6-(i)Pr2C6H3)NCO afforded (RNHCO-smif)2Fe (14a, R = (t)Bu; 14b, 2,6-(i)PrC6H3). Calculations suggested that (dpma)2Fe (15) would favorably lose dihydrogen to afford (smif)2Fe (13). H2-transfer to alkynes, olefins, imines, PhN═NPh, and ketones was explored, but only stoichiometric reactions were affected. Some physical properties of the compounds were examined, and X-ray structural studies on several dinuclear species were conducted.

  8. Vanadium-Catalyzed Oxidative C(CO)-C(CO) Bond Cleavage for C-N Bond Formation: One-Pot Domino Transformation of 1,2-Diketones and Amidines into Imides and Amides.

    Science.gov (United States)

    Digwal, Chander Singh; Yadav, Upasana; Ramya, P V Sri; Sana, Sravani; Swain, Baijayantimala; Kamal, Ahmed

    2017-07-21

    A novel vanadium-catalyzed one-pot domino reaction of 1,2-diketones with amidines has been identified that enables their transformation into imides and amides. The reaction proceeds by dual acylation of amidines via oxidative C(CO)-C(CO) bond cleavage of 1,2-diketones to afford N,N'-diaroyl-N-arylbenzamidine intermediates. In the reaction, these intermediates are easily hydrolyzed into imides and amides through vanadium catalysis. This method provides a practical, simple, and mild synthetic approach to access a variety of imides as well as amides in high yields. Moreover, one-step construction of imide and amide bonds with a long-chain alkyl group is an attractive feature of this protocol.

  9. Role of carbon in the formation of hard Ge1-xCx thin films by reactive magnetron sputtering

    Science.gov (United States)

    Hu, Chaoquan; Qiao, Liang; Tian, Hongwei; Lu, Xianyi; Jiang, Qing; Zheng, Weitao

    2011-07-01

    We have deposited germanium carbide (Ge1-xCx) films on Si(1 0 0) substrate via radio-frequency (RF) reactive magnetron sputtering in a CH4/Ar mixture discharge, and explored the effects of carbon content (x) on the chemical bonding and hardness for the obtained films. We find that x significantly influences the chemical bonding, which leads to a pronounced change in the hardness of the film. To reveal the relationship between the chemical bonding and hardness, first-principles calculations have been carried out. It is shown that as x increases from 0 to 0.33, the fraction of sp3 C-Ge bonds in the film increases at the expense of Ge-Ge bonds, which promotes formation of a strong covalently bonded network, and thus enhances the hardness of the film. However, as x further increases from 0.33 to 0.59, the fraction of sp3 C-Ge bonds in the film gradually reduces, while that of sp3 C-H and graphite-like sp2 C-C bonds increases, which damages the compact network structure, resulting in a sharp decrease in the hardness. This investigation suggests that the medium x (0.17formation of dominant sp3 C-Ge bonds.

  10. Synthesis of SiC decorated carbonaceous nanorods and its hierarchical composites Si@SiC@C for high-performance lithium ion batteries

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Chundong [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Li, Yi, E-mail: liyi@suda.edu.cn [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou (China); Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Ostrikov, Kostya [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland 4000 (Australia); Plasma Nanoscience, Industrial Innovation Program, CSIRO Manufacturing Flagship, Lindfield, New South Wales 2070 (Australia); Yang, Yonggang [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou (China); Zhang, Wenjun, E-mail: apwjzh@cityu.edu.hk [Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China)

    2015-10-15

    SiC- based nanomaterials possess superior electric, thermal and mechanical properties. However, due to the tricky synthesis process, which needs to be carried out under high temperature with multi-step reaction procedures, the further application is dramatically limited. Herein, a simple as well as a controllable approach is proposed for synthesis of SiC- based nanostructures under low temperature. Phenyl-bridged polysilsesquioxane was chosen as the starting material to react with magnesium at 650 °C, following which SiC@C nanocomposites were finally obtained, and it maintains the original bent rod-like architecture of polysilsesquioxanes. The possible formation process for the nanocomposites can proposed as well. The electrochemical behaviour of nanocomposites was accessed, verifying that the synthesized SiC@C nanocomposites deliver good electrochemical performance. Moreover, SiC@C also shows to be a promising scaffold in supporting Si thin film electrode in achieving stable cycling performance in lithium ion batteries. - Highlights: • SiC@C bent nanorods were synthesized with a magnesium reaction approach. • Carbon nanorod spines studded with ultrafine β-SiC nanocrystallines was realized. • The synthesized SiC@C keeps the original rod-like structure of polysilsesquioxanes. • The possible formation process for the nanocomposites was analysed and proposed. • Si@SiC@C nanocomposites reveal good electrochemical performance in LIBs.

  11. Influence of applied load on wear behavior of C/C-Cu composites under electric current

    Directory of Open Access Journals (Sweden)

    Jian Yin

    2017-04-01

    Full Text Available Using carbon fiber needled fabrics with Cu-mesh and graphite powder as the preform, Cu mesh modified carbon/carbon(C/C-Cu composites were prepared by chemical vapor deposition (CVD with C3H6 and impregnation-carbonization (I/C with furan resin. C/C composites, as a comparison, were also prepared. Their microstructures and wear morphologies were observed by optical microscopy (OM and scanning electron microscope (SEM, respectively. Wear behavior of C/C and C/C-Cu composites under different applied loads were investigated on a pin-on-disc wear tester. The results show that Cu meshes are well dispersed and pyrolytic carbon is in rough laminar structure. Both C/C and C/C-Cu composites had good wear properties. The current-carrying capacity of C/C-Cu composites increases and the arc discharge is hindered as the applied load increases from 40 N to 80 N. Both C/C and C/C-Cu composites had good wear properties. The mass wear rate of C/C-Cu composites under 80 N was only 4.2% of that under 60 N. In addition, C/C-Cu composites represent different wear behaviors because wear mechanisms of arc erosion, abrasive wear, adhesive wear, and oxidative wear are changing under different applied loads.

  12. Formation of hydrogen-bonded complexes of 3,3',5,5'-tetrabromo-2,2'-biphenol with MTBD and triethylamine

    Science.gov (United States)

    Wojciechowski, Grzegorz; Brzezinski, Bogumil

    2002-10-01

    The complexes of 3,3',5,5'-tetrabromo-2,2'-biphenol (TBBPh) with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) and triethylamine (TEA) were studied by FTIR spectroscopy. In chloroform and in acetonitrile a proton transfer from TBBPh to N-bases (MTBD, TEA) occurs. In chloroform solution the protonated N-base molecules are hydrogen-bonded to the deprotonated TBBPh molecules, whereas in acetonitrile the complexes dissociate. The intra- as well as intermolecular hydrogen bonds within the chains show large proton polarizability.

  13. Hydrogen bonded supramolecular materials

    CERN Document Server

    Li, Zhan-Ting

    2015-01-01

    This book is an up-to-date text covering topics in utilizing hydrogen bonding for constructing functional architectures and supramolecular materials. The first chapter addresses the control of photo-induced electron and energy transfer. The second chapter summarizes the formation of nano-porous materials. The following two chapters introduce self-assembled gels, many of which exhibit unique functions. Other chapters cover the advances in supramolecular liquid crystals and the versatility of hydrogen bonding in tuning/improving the properties and performance of materials. This book is designed

  14. 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.

  15. SOCIAL BONDING: REGULATION BY NEUROPEPTIDES

    Directory of Open Access Journals (Sweden)

    Claudia eLieberwirth

    2014-06-01

    Full Text Available Affiliative social relationships (e.g., among spouses, family members, and friends play an essential role in human society. These relationships affect psychological, physiological, and behavioral functions. As positive and enduring bonds are critical for the overall well-being of humans, it is not surprising that considerable effort has been made to study the neurobiological mechanisms that underlie social bonding behaviors. The present review details the involvement of the nonapeptides, oxytocin (OT and arginine vasopressin (AVP, in the regulation of social bonding in mammals including humans. In particular, we will discuss the role of OT and AVP in the formation of social bonds between partners of a mating pair as well as between parents and their offspring. Furthermore, the role of OT and AVP in the formation of interpersonal bonding involving trust is also discussed.

  16. Reductive benzylation of singly bonded 1,2,4,15-C60 dimers with an oxazoline or imidazoline heterocycle: unexpected formation of 1,2,3,16-C60 adducts and insights into the reactivity of singly bonded C60 dimers.

    Science.gov (United States)

    Li, Zong-Jun; Li, Shu-Hui; Sun, Tao; Hou, Hui-Lei; Gao, Xiang

    2015-04-03

    Upon reduction, singly bonded 1,2,4,15-C60 dimers with an oxazoline or imidazoline heterocycle dissociate into monoanionic 1,2,4-C60 intermediates, which surprisingly leads to the formation of 1,2,3,16-C60 rather than 1,2,4,15-C60 adducts of the original configuration by further benzylation, even though the analogue of dibenzylated C60 oxazoline with a 1,2,4,15-configuration is stable and has been obtained. These results are corroborated by computational calculations, which rationalize the reaction and clarify the structure of the 1,2,3,16-C60 adducts, providing new insights into the intrinsic reactivity of singly bonded C60 dimers.

  17. A Model for the Chemical Bond

    Science.gov (United States)

    Magnasco, Valerio

    2004-01-01

    Bond stereochemistry in polyatomic hydrides is explained in terms of the principle of bond energies maximization, which yields X-H straight bonds and suggests the formation of appropriate sp hybrids on the central atom. An introduction to the electron charge distribution in molecules is given, and atomic, overlap, gross and formal charges are…

  18. Measurements of psi -> K-Lambda(Xi)over-bar(+) + c.c. and psi -> gamma K-Lambda(Xi)over-bar(+) + c.c.

    NARCIS (Netherlands)

    Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; An, F. F.; An, Q.; Bai, J. Z.; Ferroli, R. Baldini; Ban, Y.; Bennett, D. W.; Bennett, J. V.; Bertani, M.; Bettoni, D.; Bian, J. M.; Bianchi, F.; Boger, E.; Bondarenko, O.; Boyko, I.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, H. Y.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Cibinetto, G.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dbeyssi, A.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; De Mori, F.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Duan, S. X.; Duan, P. F.; Fan, J. Z.; Fang, J.; Fang, S. S.; Fang, X.; Fang, Y.; Fava, L.; Feldbauer, F.; Felici, G.; Feng, C. Q.; Fioravanti, E.; Fritsch, M.; Fu, C. D.; Gao, Q.; Gao, X. Y.; Gao, Y.; Gao, Z.; Garzia, I.; Geng, C.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, Y.; Guo, Y. P.; Haddadi, Z.; Hafner, A.; Han, S.; Han, Y. L.; Hao, X. Q.; Harris, F. A.; He, K. L.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Hu, Y.; Huang, G. M.; Huang, G. S.; Huang, H. P.; Huang, J. S.; Huang, X. T.; Huang, Y.; Hussain, T.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, L. W.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Johansson, T.; Julin, A.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kang, X. S.; Kavatsyuk, M.; Ke, B. C.; Kliemt, R.; Kloss, B.; Kolcu, O. B.; Kopf, B.; Kornicer, M.; Kuehn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Leng, C.; Li, C. H.; Li, Cheng; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, Jin; Li, K.; Li, K.; Li, Lei; Li, P. R.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. M.; Li, X. N.; Li, X. Q.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, J. Y.; Liu, K.; Liu, K. Y.; Liu, L. D.; Liu, P. L.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, X. X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, H. J.; Lu, J. G.; Lu, R. Q.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Lyu, X. R.; Ma, F. C.; Ma, H. L.; Ma, L. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. N.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Marcello, S.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Mo, Y. J.; Morales, C. Morales; Moriya, K.; Muchnoi, N. Yu.; Muramatsu, H.; Nefedov, Y.; Nerling, F.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, S. L.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Patteri, P.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Pettersson, J.; Ping, J. L.; Ping, R. G.; Poling, R.; Pu, Y. N.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, N.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ren, H. L.; Ripka, M.; Rong, G.; Ruan, X. D.; Santoro, V.; Sarantsev, A.; Savrie, M.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, P. X.; Shen, X. Y.; Sheng, H. Y.; Song, W. M.; Song, X. Y.; Sosio, S.; Spataro, S.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Tiemens, M.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, B. L.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Weber, T.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Wiedner, U.; Wolke, M.; Wu, L. H.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, L.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yin, J. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Yuncu, A.; Zafar, A. A.; Zallo, A.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, K.; Zhang, L.; Zhang, S. H.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Y. T.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, H. S.; Zhao, J. W.; Zhao, J. Y.; Zhao, J. Z.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, W. J.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, S.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zotti, L.; Zou, B. S.; Zou, J. H.

    2015-01-01

    Using a sample of 1.06 x 10(8) psi(3686) events produced in e(+)e(-) collisions at root s = 3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays psi(3686) -> K-Lambda(Xi) over bar (+) + c.c. and psi(3686) -> gamma K-Lambda(Xi) over bar (+) + c.c.

  19. The thermodynamics and kinetics of phosphoester bond formation, use, and dissociation in biology, with the example of polyphosphate in platelet activation, trasience, and mineralization.

    Science.gov (United States)

    Omelon, S. J.

    2014-12-01

    Mitochondria condense orthophosphates (Pi), forming phosphoester bonds for ATP production that is important to life. This represents an exchange of energy from dissociated carbohydrate bonds to phosophoester bonds. These bonds are available to phosphorylate organic compounds or hydrolyze to Pi, driving many biochemical processes. The benthic bacteria T. namibiensis 1 and Beggiatoa 2 condense Pi into phosphate polymers in oxygenated environments. These polyphosphates (polyPs) are stored until the environment becomes anoxic, when these bacteria retrieve the energy from polyP dissociation into Pi3. Dissociated Pi is released outside of the bacteria, where it precipitates as apatite.The Gibbs free energy of polyP phosphoester bond hydrolysis is negative, however, the kinetics are slow4. Diatoms contain a polyP pool that is stable until after death, after which the polyPs hydrolyze and form apatite5. The roles of polyP in eukaryotic organism biochemistry continue to be discovered. PolyPs have a range of biochemical roles, such as bioavailable P-storage, stress adaptation, and blood clotting6. PolyP-containing granules are released from anuclear platelets to activate factor V7 and factor XII in the blood clotting process due to their polyanionic charge8. Platelets have a lifespan of approximately 8 days, after which they undergo apoptosis9. Data will be presented that demonstrate the bioactive, thermodynamically unstable polyP pool within older platelets in vitro can spontaneously hydrolyze and form phosphate minerals. This process is likely avoided by platelet digestion in the spleen and liver, possibly recycling platelet polyPs with their phosphoester bond energy for other biochemical roles. 1 Schulz HN et al. Science (2005) 307: 416-4182 Brüchert V et al. Geochim Cosmochim Acta (2003) 67: 4505-45183 Goldhammer T et al. Nat Geosci (2010) 3: 557-5614 de Jager H-J et al. J Phys Chem A (1988) 102: 2838-28415 Diaz, J et al. Science (2008) 320: 652-6556 Mason KD et al

  20. Application of C/C composites to the combustion chamber of rocket engines. Part 1: Heating tests of C/C composites with high temperature combustion gases

    Science.gov (United States)

    Tadano, Makoto; Sato, Masahiro; Kuroda, Yukio; Kusaka, Kazuo; Ueda, Shuichi; Suemitsu, Takeshi; Hasegawa, Satoshi; Kude, Yukinori

    1995-04-01

    Carbon fiber reinforced carbon composite (C/C composite) has various superior properties, such as high specific strength, specific modulus, and fracture strength at high temperatures of more than 1800 K. Therefore, C/C composite is expected to be useful for many structural applications, such as combustion chambers of rocket engines and nose-cones of space-planes, but C/C composite lacks oxidation resistivity in high temperature environments. To meet the lifespan requirement for thermal barrier coatings, a ceramic coating has been employed in the hot-gas side wall. However, the main drawback to the use of C/C composite is the tendency for delamination to occur between the coating layer on the hot-gas side and the base materials on the cooling side during repeated thermal heating loads. To improve the thermal properties of the thermal barrier coating, five different types of 30-mm diameter C/C composite specimens constructed with functionally gradient materials (FGM's) and a modified matrix coating layer were fabricated. In this test, these specimens were exposed to the combustion gases of the rocket engine using nitrogen tetroxide (NTO) / monomethyl hydrazine (MMH) to evaluate the properties of thermal and erosive resistance on the thermal barrier coating after the heating test. It was observed that modified matrix and coating with FGM's are effective in improving the thermal properties of C/C composite.

  1. DsbA2 (27-kDa Com1-Like Protein) of Legionella pneumophila Catalyses Extracytoplasmic Disulfide-Bond Formation in Proteins Including the Dot/Icm Type IV Secretion System

    OpenAIRE

    Jameson-Lee, Max; Rafael A Garduno; Hoffman, Paul S.

    2011-01-01

    In Gram negative bacteria, thiol oxidoreductases catalyze the formation of disulfide bonds (DSB) in extracytoplasmic proteins. In this study, we sought to identify DSB-forming proteins required for assembly of macromolecular structures in Legionella pneumophila. Here we describe two DSB forming proteins, one annotated as dsbA1 and the other annotated as a 27-kDa outer membrane protein similar to Com1 of Coxiella burnetii, which we designate as dsbA2. Both proteins are predicted to be periplas...

  2. A frequent, GxxxG-mediated, transmembrane association motif is optimized for the formation of interhelical Cα–H hydrogen bonds

    OpenAIRE

    Mueller, Benjamin K.; Subramaniam, Sabareesh; Senes, Alessandro

    2014-01-01

    The transmembrane helices of single-span membrane proteins are commonly engaged in oligomeric interactions that are essential for structure and function. These interactions often occur in the form of recurrent structural motifs. Here we present an analysis of one of the most important motifs (GASright), showing that its geometry is optimized to form carbon hydrogen bonds at the helix−helix interface. The analysis reveals the structural basis for its characteristic GxxxG sequence signature. We...

  3. Properties of the major non-specific endonuclease from the strict anaerobe Fibrobacter succinogenes and evidence for disulfide bond formation in vivo.

    Science.gov (United States)

    MacLellan, S R; Forsberg, C W

    2001-02-01

    DNase A is a non-specific endonuclease of Fibrobacter succinogenes. The enzyme was purified to homogeneity and its properties studied both in vitro and in vivo. Magnesium but not calcium was essential for nucleolytic activity. Manganese ions substituted for magnesium but were less stimulatory. DNase A activity was markedly inhibited by either NaCl or KCl at concentrations greater than 75 mM. The enzyme had a temperature optimum of 25 degrees C and a pH optimum of about 7.0. Values for K:(m) and K:(cat) were determined to be 61 microM and 330 s(-1) respectively, with a catalytic efficiency approximately threefold greater than bovine pancreatic DNase I, but 10-fold less than the Serratia marcescens NucA. DNase A was localized to the periplasm and probably exists as a monomeric species. The enzyme possessed one or more disulfide bonds. In the reduced form it had an apparent mass of 33 kDa, while in the oxidized form it was 29 kDa as estimated by SDS-PAGE. Reduction of the disulfide bonds by dithiothreitol with or without subsequent alkylation by iodoacetamide strongly inactivated the enzyme. DNase A accumulated in vivo had an apparent mass of 29 kDa, indicating that it was in an oxidized form. This is the first indication in a strict anaerobe of a functional periplasmic disulfide bond forming system, phenotypically similar to Dsb systems in facultative and aerobic bacteria.

  4. Investigation of chemical bonding states at interface of Zn/organic materials for analysis of early stage of inorganic/organic hybrid multi-layer formation

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Ken, E-mail: k_cho@jwri.osaka-u.ac.jp [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Japan Science and Technology Agency, CREST (Japan); Takenaka, Kosuke; Setsuhara, Yuichi [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Japan Science and Technology Agency, CREST (Japan); Shiratani, Masaharu [Department of Electronics, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan); Japan Science and Technology Agency, CREST (Japan); Sekine, Makoto; Hori, Masaru [Plasma Nanotechnology Research Center, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Japan Science and Technology Agency, CREST (Japan)

    2012-11-15

    Interactions between Ar-O{sub 2} mixture plasmas and Zn thin film on polyethylene terephthalate (PET) were investigated using the combinatorial plasma process analyzer, on the basis of nondestructive depth analyses of chemical bonding states at Zn thin film and Zn/PET interface via hard X-ray photoelectron spectroscopy (HXPES). After the Ar-O{sub 2} plasma exposure, peak-area ratio of O 1 s to Zn 2p{sub 3/2} evaluated from the HXPES spectra is found to increase with increasing the ion saturation current Multiplication-Sign time and saturated at the value obtained from ZnO. The HXPES C 1 s spectra measured at a take-off angle (TOA) of 80 Degree-Sign showed insignificant change in oxygen functionalities (O=C-O bond and C-O bond) after the deposition of Zn thin film and the plasma exposure. Whereas, the HXPES C 1 s spectra measurement at a TOA of 20 Degree-Sign suggested that the oxygen functionalities degraded in shallower regions up to about a few nanometer from the Zn/PET interface due to deposition of Zn thin film. However, after the plasma exposure, oxidation of PET substrate at the degraded layer of Zn/PET interface was caused by oxygen radicals and/or ions, which diffused through the Zn thin film.

  5. JACoW SIP4C/C++ at CERN - Status and lessons learned

    CERN Document Server

    Jensen, Steen; Dworak, Andrzej; Gourber-Pace, Marine; Hoguin, Frederic; Lauener, Joel; Locci, Frank; Sigerud, Katarina; Sliwinski, Wojciech

    2018-01-01

    After 4 years of promoting the Software Improvement Process for C/C++ (SIP4C/C++) initiative at CERN, we describe the current status for tools and procedures along with how they have been integrated into our environment. Based on feedback from four project teams, we present reasons for and against their adoption. Finally, we show how SIP4C/C++ has improved development and delivery processes as well as the first-line support of delivered products.

  6. C-C and C-N Couplings Following Hydride Addition on Isocyanide Cyclopolyenyl Dimolybdenum Complexes to Give Tethered Aldimine and Aminocarbene Derivatives.

    Science.gov (United States)

    Alvarez, Belén; Alvarez, M Angeles; García, M Esther; García-Vivó, Daniel; Ruiz, Miguel A

    2017-10-09

    Reaction of [Mo2 Cp2 (μ-κ(1) :κ(1) ,η(6) -PMes*)(CO)2 ] with S or Se followed by protonation with [H(OEt2 )2 ](BAr'4 ) gave the cationic derivatives [Mo2 Cp2 {μ-κ(2)P,E :κ(1)P ,η(5) -EP(C6 H3 tBu3 )}(CNR)(CO)2 ](BAr'4 ) (E=S; R=tBu, iPr, Ph, 4-C6 H4 OMe, Xyl; or E=Se; R=tBu; Ar'=3,5-C6 H3 (CF3 )2 ). Reaction of the latter with K[BHsBu3 ] yielded the aldimine complexes [Mo2 Cp2 {μ-κ(2)P,E :κ(2)P,N ,η(4) -SP(C6 H3 tBu3 (CHNR))}(CO)2 ] and their aminocarbene isomers [Mo2 Cp2 {μ-κ(2)P,E :κ(2)P,C ,η(4) -SP(C6 H3 tBu3 (NRCH))}(CO)2 ] (R ≠ Xyl), following C-C and C-N couplings, respectively. Monitoring of these reactions revealed that the initial H(-) attack takes place at a Cp ligand to give cyclopentadiene intermediates [Mo2 Cp{μ-κ(2)P,S :κ(1)P ,η(5) -SP(C6 H3 tBu3 )}(η(4) -C5 H6 )(CNR)(CO)2 ], which then undergo C-H oxidative addition to give the hydride isomers [Mo2 Cp2 {μ-κ(2)P,S :κ(1)P ,η(3) -SP(C6 H3 tBu3 )}(H)(CNR)(CO)2 ]. In turn, the latter rearrange to give the aldimine and aminocarbene complexes. DFT calculations revealed that the hydride intermediates first undergo migratory insertion of the isocyanide ligand into the Mo-H bond to give unobservable formimidoyl intermediates, which then evolve either by nucleophilic attack of the N atom on the C6 ring (C-N coupling) or by migratory insertion of the formimidoyl ligand into the C6 ring (C-C coupling). Our data suggest that increasing the size of the substituent R at the isocyanide ligand destabilizes the aldimine isomer to a greater extent, thus favoring formation of the aminocarbene complex. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. 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

    2011-01-01

    for the somatomedin B domain of vitronectin compared with uPAR(wt), thus recapitulating the improved affinity that accompanies uPA-uPAR(wt) complex formation. This functional mimicry is, intriguingly, operational also in a cellular setting, where it controls lamellipodia formation in uPAR-transfected HEK293 cells...

  8. Controlling superstructural ordering in the clathrate-I Ba 8 M 16 P 30 (M = Cu, Zn) through the formation of metal–metal bonds

    Energy Technology Data Exchange (ETDEWEB)

    Dolyniuk, J.; Whitfield, P. S.; Lee, K.; Lebedev, O. I.; Kovnir, K.

    2017-01-01

    Order–disorder–order phase transitions in the clathrate-I Ba8Cu16P30 were induced and controlled by aliovalent substitutions of Zn into the framework. Unaltered Ba8Cu16P30 crystallizes in an ordered orthorhombic (Pbcn) clathrate-I superstructure that maintains complete segregation of metal and phosphorus atoms over 23 different crystallographic positions in the clathrate framework. The driving force for the formation of this Pbcn superstructure is the avoidance of Cu–Cu bonds. This superstructure is preserved upon aliovalent substitution of Zn for Cu in Ba8Cu16-xZnxP30 with 0 < x < 1.6 (10% Zn/Mtotal), but vanishes at greater substitution concentrations. Higher Zn concentrations (up to 35% Zn/Mtotal) resulted in the additional substitution of Zn for P in Ba8M16+yP30-y (M = Cu, Zn) with 0 ≤ y ≤ 1. This causes the formation of Cu–Zn bonds in the framework, leading to a collapse of the orthorhombic superstructure into the more common cubic subcell of clathrate-I (Pm[3 with combining macron]n). In the resulting cubic phases, each clathrate framework position is jointly occupied by three different elements: Cu, Zn, and P. Detailed structural characterization of the Ba–Cu–Zn–P clathrates-I via single crystal X-ray diffraction, joint synchrotron X-ray and neutron powder diffractions, pair distribution function analysis, electron diffraction and high-resolution electron microscopy, along with elemental analysis, indicates that local ordering is present in the cubic clathrate framework, suggesting the evolution of Cu–Zn bonds. For the compounds with the highest Zn content, a disorder–order transformation is detected due to the formation of another superstructure with trigonal symmetry and Cu–Zn bonds in the clathrate-I framework. It is shown that small changes in the composition, synthesis, and crystal structure have significant impacts on the structural and transport properties of Zn-substituted Ba8Cu16P30.

  9. Computational Study of Low-Temperature Catalytic C-C Bond Activation of Alkanes for Portable Power

    Science.gov (United States)

    2013-06-05

    study of Rh/O2 complexes, such as spin singlet RhCl3(O2)2- and the spin doublet RhIII superoxide complex RhCl3(H2O)(O2)1-,which we consider would be...5 Figure 5. RhIII/O2 /iodine chemistry ...alcohol ionization ....................................................................................13 Figure 13. New oxidized Rh chemistry

  10. Catalytic promiscuity of 4-oxalocrotonate tautomerase : discovery and characterization of C-C bond-forming activities

    NARCIS (Netherlands)

    Zandvoort, Ellen

    2012-01-01

    Het verschijnsel katalytische promiscuïteit, waarin een enzym naast zijn natuurlijke activiteit een alternatieve reactie (of reacties) katalyseert, is een krachtig, recent opgekomen concept, dat erg relevant is voor het ontwerpen van nieuwe enzymen. Enzym promiscuïteit is een veelbelovende bron van

  11. Thermal conductivity of 2D C-C composites with pyrolytic and glass-like carbon matrices

    Energy Technology Data Exchange (ETDEWEB)

    Michalowski, J. [Institute of Nuclear Physics, Cracow (Poland); Mikociak, D. [Dept. of Biomaterials, Faculty of Materials Engineering and Ceramics, AGH University of Science and Technology, Cracow (Poland); Konsztowicz, K.J. [Dept. of Industrial Engineering, Faculty of Mechanical Engineering, and IT, University of Bielsko-Biala (Poland); Blazewicz, S., E-mail: blazew@aci.agh.edu.p [Dept. of Biomaterials, Faculty of Materials Engineering and Ceramics, AGH University of Science and Technology, Cracow (Poland)

    2009-08-15

    This study examines the relationship of thermal properties of C-C composites with structural and microstructural features resulting from specific processing steps. Samples were made with the same type of fibres, but using two distinct different methods of matrix formation: liquid impregnation with phenolic resin and the P-CVI technique. In both cases, thermal treatment after densification had decisive effect on increase of composite coefficient of thermal conductivity, due to crystallization of carbon matrix material and thus increase of its own thermal conductivity. Higher values of thermal conductivity were obtained using the pyrolytic carbon matrix processing.

  12. Effects of Preform Density on Structure and Property of C/C-SiC Composites Fabricated by Gaseous Silicon Infiltration

    Directory of Open Access Journals (Sweden)

    CAO Yu

    2016-07-01

    Full Text Available The 3-D needled C/C preforms with different densities deposited by chemical vapor infiltration (CVI method were used to fabricate C/C-SiC composites by gaseous silicon infiltration (GSI. The porosity and CVI C thickness of the preforms were studied, and the effects of preform density on the mechanical and thermal properties of C/C-SiC composites were analyzed. The results show that with the increase of preform density, the preform porosity decreases and the CVI C thickness increases from several hundred nanometers to several microns. For the C/C-SiC composites, as the preform density increases, the residual C content increases while the density and residual Si content decreases. The SiC content first keeps at a high level of about 40% (volume fraction, which then quickly reduces. Meanwhile, the mechanical properties increase to the highest values when the preform density is 1.085g/cm3, with the flexure strength up to 308.31MP and fracture toughness up to 11.36MPa·m1/2, which then decrease as the preform density further increases. The thermal conductivity and CTE of the composites, however, decrease with the increase of preform density. It is found that when the preform porosity is too high, sufficient infiltration channels lead to more residual Si, and thinner CVI C thickness results in the severe corrosion of the reinforcing fibers by Si and lower mechanical properties. When the preform porosity is relatively low, the contents of Si and SiC quickly reduce since the infiltration channels are rapidly blocked, resulting in the formation of large closed pores and not high mechanical properties.

  13. Accumulation of β-Conglycinin in Soybean Cotyledon through the Formation of Disulfide Bonds between α′- and α-Subunits1[W][OA

    Science.gov (United States)

    Wadahama, Hiroyuki; Iwasaki, Kensuke; Matsusaki, Motonori; Nishizawa, Keito; Ishimoto, Masao; Arisaka, Fumio; Takagi, Kyoko; Urade, Reiko

    2012-01-01

    β-Conglycinin, one of the major soybean (Glycine max) seed storage proteins, is folded and assembled into trimers in the endoplasmic reticulum and accumulated into protein storage vacuoles. Prior experiments have used soybean β-conglycinin extracted using a reducing buffer containing a sulfhydryl reductant such as 2-mercaptoethanol, which reduces both intermolecular and intramolecular disulfide bonds within the proteins. In this study, soybean proteins were extracted from the cotyledons of immature seeds or dry beans under nonreducing conditions to prevent the oxidation of thiol groups and the reduction or exchange of disulfide bonds. We found that approximately half of the α′- and α-subunits of β-conglycinin were disulfide linked, together or with P34, prior to amino-terminal propeptide processing. Sedimentation velocity experiments, size-exclusion chromatography, and two-dimensional polyacrylamide gel electrophoresis (PAGE) analysis, with blue native PAGE followed by sodium dodecyl sulfate-PAGE, indicated that the β-conglycinin complexes containing the disulfide-linked α′/α-subunits were complexes of more than 720 kD. The α′- and α-subunits, when disulfide linked with P34, were mostly present in approximately 480-kD complexes (hexamers) at low ionic strength. Our results suggest that disulfide bonds are formed between α′/α-subunits residing in different β-conglycinin hexamers, but the binding of P34 to α′- and α-subunits reduces the linkage between β-conglycinin hexamers. Finally, a subset of glycinin was shown to exist as noncovalently associated complexes larger than hexamers when β-conglycinin was expressed under nonreducing conditions. PMID:22218927

  14. S-glutathionylation of glyceraldehyde-3-phosphate dehydrogenase induces formation of C150-C154 intrasubunit disulfide bond in the active site of the enzyme.

    Science.gov (United States)

    Barinova, K V; Serebryakova, M V; Muronetz, V I; Schmalhausen, E V

    2017-12-01

    Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a glycolytic protein involved in numerous non-glycolytic functions. S-glutathionylated GAPDH was revealed in plant and animal tissues. The role of GAPDH S-glutathionylation is not fully understood. Rabbit muscle GAPDH was S-glutathionylated in the presence of H 2 O 2 and reduced glutathione (GSH). The modified protein was assayed by MALDI-MS analysis, differential scanning calorimetry, dynamic light scattering, and ultracentrifugation. Incubation of GAPDH in the presence of H 2 O 2 together with GSH resulted in the complete inactivation of the enzyme. In contrast to irreversible oxidation of GAPDH by H 2 O 2 , this modification could be reversed in the excess of GSH or dithiothreitol. By data of MALDI-MS analysis, the modified protein contained both mixed disulfide between Cys150 and GSH and the intrasubunit disulfide bond between Cys150 and Cys154 (different subunits of tetrameric GAPDH may contain different products). S-glutathionylation results in loosening of the tertiary structure of GAPDH, decreases its affinity to NAD + and thermal stability. The mixed disulfide between Cys150 and GSH is an intermediate product of S-glutathionylation: its subsequent reaction with Cys154 results in the intrasubunit disulfide bond in the active site of GAPDH. The mixed disulfide and the C150-C154 disulfide bond protect GAPDH from irreversible oxidation and can be reduced in the excess of thiols. Conformational changes that were observed in S-glutathionylated GAPDH may affect interactions between GAPDH and other proteins (ligands), suggesting the role of S-glutathionylation in the redox signaling. The manuscript considers one of the possible mechanisms of redox regulation of cell functions. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. QM/MM study of the C-C coupling reaction mechanism of CYP121, an essential Cytochrome p450 of Mycobacterium tuberculosis

    OpenAIRE

    Dumas, Victoria Gisel; Defelipe, Lucas Alfredo; Petruk, Ariel Alcides; Turjanski, Adrian; Marti, Marcelo Adrian

    2016-01-01

    Among 20 p450s of Mycobacterium tuberculosis (Mt), CYP121 has received an outstanding interest, not only due to its essentiality for bacterial viability but also because it catalyzes an unusual carbon-carbon coupling reaction. Based on the structure of the substrate bound enzyme, several reaction mechanisms were proposed involving first Tyr radical formation, second Tyr radical formation, and C?C coupling. Key and unknown features, being the nature of the species that generate the first and s...

  16. Thermoelectric properties of SiC/C composites from wood charcoal by pulse current sintering

    NARCIS (Netherlands)

    Fujisawa, M; Hata, T; Bronsveld, P; Castro, [No Value; Tanaka, F; Kikuchi, H; Imamura, Y

    2005-01-01

    SiC/C composites were investigated by sintering a mix of wood charcoal and SiO2 powder (32-45 mu m) at 1400, 1600 and 1800 degrees C under N-2 atmosphere with a pulse current sintering method. Thermoelectric properties of SiC/C composites were investigated by measuring the Seebeck coefficient and

  17. Observation of the decay psi -> Lambda(Sigma)over-bar(+/-) pi(-/+) + c.c

    NARCIS (Netherlands)

    Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Ambrose, D. J.; An, F. F.; An, Q.; Bai, J. Z.; Ferroli, R. Baldini; Ban, Y.; Bennett, J. V.; Bertani, M.; Bian, J. M.; Boger, E.; Bondarenko, O.; Boyko, I.; Braun, S.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Chu, Y. P.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; Ding, W. M.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Fang, J.; Fang, S. S.; Fang, Y.; Fava, L.; Feng, C. Q.; Fu, C. D.; Fu, J. L.; Fuks, O.; Gao, Q.; Gao, Y.; Geng, C.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, T.; Guo, Y. P.; Guo, Y. P.; Han, Y. L.; Harris, F. A.; He, K. L.; He, M.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Huang, G. M.; Huang, G. S.; Huang, J. S.; Huang, L.; Huang, X. T.; Hussain, T.; Ji, C. S.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Jing, F. F.; Johansson, T.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kavatsyuk, M.; Kloss, B.; Kopf, B.; Kornicer, M.; Kuehn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Leyhe, M.; Li, C. H.; Li, Cheng; Li, Cui; Li, D.; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, K.; Li, K.; Li, Lei; Li, P. R.; Li, Q. J.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. N.; Li, X. Q.; Li, X. R.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. L.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, K.; Liu, K. Y.; Liu, P. L.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, G. R.; Lu, H. J.; Lu, H. L.; Lu, J. G.; Lu, X. R.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Ma, F. C.; Ma, H. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Moeini, H.; Morales, C. Morales; Moriya, K.; Muchnoi, N. Yu.; Nefedov, Y.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Ping, J. L.; Ping, R. G.; Poling, R.; Prencipe, E.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ripka, M.; Rong, G.; Ruan, X. D.; Sarantsev, A.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, X. Y.; Sheng, H. Y.; Shepherd, M. R.; Song, W. M.; Song, X. Y.; Spataro, S.; Spruck, B.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Wiedner, U.; Wolke, M.; Wu, G. G.; Wu, L. H.; Wu, N.; Wu, W.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Xue, Z.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yu, S. P.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Zafar, A. A.; Zallo, A.; Zang, S. L.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. B.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, S. H.; Zhang, X. J.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, J. W.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, X. H.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zou, B. S.; Zou, J. H.; Werner, M.J.; Zheng, J.P.

    2013-01-01

    Using a sample of 1:06 X 10(8) psi(3686) events collected with the BESIII detector, we present the first observation of the decays of psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c. and psi(3686) -> Lambda(Sigma) over bar (-) pi(+) + c.c. The branching fractions are measured to be B(psi(3686)

  18. C. C. Li (1912–2003): his science and his spirit

    Indian Academy of Sciences (India)

    Unknown

    Ching Chun Li passed away on 20 October 2003, in Pitts- burgh. He was an outstanding population geneticist, a wonderful teacher, and above all, a great human being. Devotion to work and humility were the hallmarks of. C. C. Li, who was known as C.C. to his contemporaries and colleagues, and as Dr Li to his students.

  19. 76 FR 44800 - Election of Reduced Research Credit Under Section 280C(c)(3)

    Science.gov (United States)

    2011-07-27

    ... [TD 9539] RIN 1545-BI09 Election of Reduced Research Credit Under Section 280C(c)(3) AGENCY: Internal... dates of applicability, see Sec. 1.280C- 4(c). FOR FURTHER INFORMATION CONTACT: David Selig, (202) 622... research credit under section 280C(c)(3). On July 16, 2009, a notice of proposed rulemaking (REG-130200-08...

  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. LAMMPS Framework for Dynamic Bonding and an Application Modeling DNA

    DEFF Research Database (Denmark)

    Svaneborg, Carsten

    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...... 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....... 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...

  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......-aversion (CRRA) model. In addition, we compare the pricing errors of the different models using Hansen and Jagannathan's specification error measure. The main result is that for Denmark the Campbell-Cochrane model does not seem to perform markedly better than the CRRA model. For the long annual sample period...... covering more than 80 years there is absolutely no evidence of superior performance of the Campbell-Cochrane model. For the shorter and more recent quarterly data over a 20-30 year period, there is some evidence of counter-cyclical time-variation in the degree of risk-aversion, in accordance...

  3. 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 V.

    We suggest an iterated GMM approach to estimate and test the consumption based habit persistence model of Campbell and Cochrane (1999), and we apply the approach on annual and quarterly Danish stock and bond returns. For comparative purposes we also estimate and test the standard CRRA model....... In addition, we compare the pricing errors of the different models using Hansen and Jagannathan's (1997) specification error measure. The main result is that for Denmark the Campbell-Cochrane model does not seem to perform markedly better than the CRRA model. For the long annual sample period covering more...... than 80 years there is absolutely no evidence of superior performance of the Campbell-Cochrane model. For the shorter and more recent quarterly data over a 20-30 year period, there is some evidence of counter-cyclical time-variation in the degree of risk-aversion, in accordance with the Campbell...

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

    Science.gov (United States)

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

    2013-12-01

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

  5. Hemoglobin polymerization via disulfide bond formation in the hypoxia-tolerant turtle Trachemys scripta: implications for antioxidant defense and O2 transport

    DEFF Research Database (Denmark)

    Petersen, Asbjørn Graver; Petersen, Steen Vang; Frische, Sebastian

    2018-01-01

    The ability of many reptilian hemoglobins (Hbs) to form high-molecular weight polymers, albeit known for decades, has not been investigated in detail. Given that turtle Hbs often contain a high number of cysteine (Cys), potentially contributing to the red blood cell defense against reactive oxygen...... species, we have examined whether polymerization of Hb could occur via intermolecular disulfide bonds in red blood cells of freshwater turtle Trachemys scripta, a species that is highly tolerant of hypoxia and oxidative stress. We find that one of the two Hb isoforms of the hemolysate, HbA, is prone......A of HbA is a key element of the antioxidant capacity of turtle red blood cells....

  6. Stability and Reactivity of Cyclometallated Naphthylamine Complexes in Pd-C Bond Insertion Reactions with Coordinated Alkynylphosphanes

    KAUST Repository

    Chen, Shuli

    2013-09-17

    Phenylbis(phenylethynyl)phosphane PhP(C≡CPh)2 coordinates regiospecifically to the α-methyl-chiral ortho-platinated and -palladated naphthylamine units at the positions trans to the nitrogen donors. The P→Pt coordination bond is kinetically inert, whereas the P→Pd bond is labile. Upon heating of these phosphane complexes at 70 °C, one of the C≡C bonds in the coordinated PhP(C≡CPh)2 was activated towards an intermolecular Pd-C bond insertion reaction with an external ortho-palladated naphthylamine ring. No intramolecular insertion reaction occurred. In contrast to its palladium analogue, the ortho-platinated ring is not reactive towards coordinated PhP(C≡CPh)2, although it can promote the Pd-C bond insertion reaction. However, despite the high kinetic stability of the P→Pt coordination, the organoplatinum unit is a noticeably weaker activator than its organopalladium counterpart. The chirality of the reacting ortho-metallated naphthylamine ligand exhibited high stereochemical influence on the formation of the new stereogenic phosphorus center during the course of these C-C bond-formation reactions. The coordination chemistry and the absolute stereochemistry of the dimetallic products were determined by single-crystal X-ray crystallographic analysis. The asymmetric monoinsertion of PhP(C≡CPh)2 coordinated to a cyclometallated N,N-dimethyl naphthyl/benzylamine template into the Pd-C bonds of N,N-dimethylnaphthylamine palladacycles has been demonstrated for the synthesis of a variety of new P-stereogenic homo- or heterodimetallic complexes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Universal Bronsted-Evans-Polanyi Relations for C-C, C-O, C-N, N-O, N-N, and O-O Dissociation Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Shengguang

    2010-10-27

    It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.

  8. Examples of reductive azo cleavage and oxidative azo bond formation on Re2(CO)10 template: isolation and characterization of Re(III) complexes of new azo-aromatic ligands.

    Science.gov (United States)

    Paul, Nanda D; Samanta, Subhas; Mondal, Tapan K; Goswami, Sreebrata

    2011-08-15

    A new example of simultaneous reductive azo bond cleavage and oxidative azo bond formation in an azo-aromatic ligand is introduced. The chemical transformation is achieved by the reaction of Re(2)(CO)(10) with the ligand 2-[(2-N-Arylamino)phenylazo]pyridine (HL(1)). A new and unexpected mononuclear rhenium complex [Re(L(1))(L(3))] (1) was isolated from the above reaction. The new azo-aromatic ligand, H(2)L(3) (H(2)L(3) = 2, 2'-dianilinoazobenzene) is formed in situ from HL(1). A similar reaction of Re(2)(CO)(10) and a closely related azo-ligand, 2,4-ditert-butyl-6-(pyridin-2-ylazo)-phenol (HL(2)), resulted in a seven coordinated compound [Re(L(2)){(L(4))(•-)}(2)] (2; HL(4) = 2-amino-4,6-ditert-butyl-phenol) via reductive cleavage of the azo bond. The complexes have been characterized by using a host of physical methods: X-ray crystallography, nuclear magnetic resonance (NMR), cyclic voltammetry, ultraviolet-visible (UV-vis), electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT). The experimental structures are well reproduced by density functional theory calculations and support the overall electronic structures of the above compounds. Complex 1 is a closed shell singlet, while complex 2 exemplifies a singlet diradical complex where the two partially oxidized aminophenoleto ligands are coupled to each other, yielding the observed diamagnetic ground state. Complexes 1 and 2 showed two successive one-electron redox responses. EPR spectral studies in corroboration with DFT results indicated that all of the redox processes occur at the ligand center without affecting the trivalent state of the metal ion. © 2011 American Chemical Society

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-08-30

    Graphical abstract: - Highlights: • Significantly enhancement of biocompatibility on C/C composites by preparing a collagen film. • The dense and continuous collagen film had a strong bonding strength with C/C composites after dehydrathermal treatment (DHT) crosslink. • Numerous oxygen-containing functional groups formed on the surface of C/C composites without matrix damage. - Abstract: A strong bonding collagen film was successfully prepared on carbon/carbon (C/C) composites. The surface conditions of the modified C/C composites were detected by contact angle measurements, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectra. The roughness, optical morphology, bonding strength and biocompatibility of collagen films at different pH values were detected by confocal laser scanning microscope (CLSM), universal test machine and cytology tests in vitro. After a 4-h modification in 30% H{sub 2}O{sub 2} solution at 100 °C, the contact angle on the surface of C/C composites was decreased from 92.3° to 65.3°. Large quantities of hydroxyl, carboxyl and carbonyl functional groups were formed on the surface of the modified C/C composites. Then a dense and continuous collagen film was prepared on the modified C/C substrate. Bonding strength between collagen film and C/C substrate was reached to 8 MPa level when the pH value of this collagen film was 2.5 after the preparing process. With 2-day dehydrathermal treatment (DHT) crosslinking at 105 °C, the bonding strength was increased to 12 MPa level. At last, the results of in vitro cytological test showed that this collagen film made a great improvement on the biocompatibility on C/C composites.

  10. Stereoselective Synthesis of the C1-C9 and C11-C25 Fragments of Amphidinolides C, C2, C3, and F.

    Science.gov (United States)

    Akwaboah, Daniel C; Wu, Dimao; Forsyth, Craig J

    2017-03-03

    An efficient synthesis of the C1-C9 and the C11-C25 fragments of amphidinolides C, C2, C3, and F from a common intermediate is reported. The construction of the C1-C9 fragment involves an intramolecular hetero-Michael cyclization to form the 3,5-disubstituted trans-tetrahydrofuran moiety. The approach to prepare the C11-C25 fragment utilizes a highly stereoselective aerobic cobalt-catalyzed alkenol cyclization and a chelated Mukaiyama aldol reaction to form the C13-C14 bond and to concomitantly install the C13 hydroxyl group.

  11. Expression of hypoallergenic Der f 2 derivatives with altered intramolecular disulphide bonds induces the formation of novel ER-derived protein bodies in transgenic rice seeds.

    Science.gov (United States)

    Yang, Lijun; Hirose, Sakiko; Suzuki, Kazuya; Hiroi, Takachika; Takaiwa, Fumio

    2012-05-01

    House dust mites (HDM) are the most common source of indoor allergens and are associated with allergic diseases worldwide. To benefit allergic patients, safer and non-invasive mucosal routes of oral administration are considered to be the best alternative to conventional allergen-specific immunotherapy. In this study, transgenic rice was developed expressing derivatives of the major HDM allergen Der f 2 with reduced Der f 2-specific IgE reactivity by disrupting intramolecular disulphide bonds in Der f 2. These derivatives were produced specifically as secretory proteins in the endosperm tissue of seeds under the control of the endosperm-specific glutelin GluB-1 promoter. Notably, modified Der f 2 derivatives aggregated in the endoplasmic reticulum (ER) lumen and were deposited in a unique protein body (PB)-like structure tentatively called the Der f 2 body. Der f 2 bodies were characterized by their intracellular localization and physico-chemical properties, and were distinct from ER-derived PBs (PB-Is) and protein storage vacuoles (PB-IIs). Unlike ER-derived organelles such as PB-Is, Der f 2 bodies were rapidly digested in simulated gastric fluid in a manner similar to that of PB-IIs. Oral administration in mice of transgenic rice seeds containing Der f 2 derivatives encapsulated in Der f 2 bodies suppressed Der f 2-specific IgE and IgG production compared with that in mice fed non-transgenic rice seeds, and the effect was dependent on the type of Der f 2 derivative expressed. These results suggest that engineered hypoallergenic Der f 2 derivatives expressed in the rice seed endosperm could serve as a basis for the development of viable strategies for the oral delivery of vaccines against HDM allergy.

  12. [2 + 2]-type Reaction of Metal-Metal σ-Bond with Fullerene Forming an η1-C60 Metal Complex: Mechanistic Details of Formation Reaction and Prediction of a New η1-C60 Metal Complex.

    Science.gov (United States)

    Zheng, Hong; Zhao, Xiang; Sakaki, Shigeyoshi

    2017-06-05

    C60[CpRu(CO)2]2 is only one transition-metal fullerene complex with pure η1-coordinated bonds, which was recently synthesized through the reaction between dinuclear Ru complex [CpRu(CO)2]2 and C60. Though new properties can be expected in the η1-coordinated metal-fullerene complex, its characteristic features are unclear, and the [2 + 2]-type formation reaction is very slow with a very small yield. A density functional theory study discloses that the η1-coordinated bond is formed by a large overlap between the Ru dσ orbital and C pσ one involved in the lowest unoccupied molecular orbital (LUMO) (π*) of C60 unlike the well-known η2-coordinated metal-fullerene complex which has a π-type coordinate bond with metal dπ orbital. The binding energy per one Ru-C bond is much smaller than those of η2-coordinated Pt(PMe3)2(C60) and IrH(CO)(PH3)2(C60) because the Ru d orbital exists at low energy. The formation reaction occurs via Ru-Ru bond cleavage on the C60 surface followed by a direction change of CpRu(CO)2 to afford C60[CpRu(CO)2]2 in a stepwise manner via two asymmetrical transition states to avoid a symmetry-forbidden character. The calculated Gibbs activation energy (ΔG°‡) is very large and the Gibbs reaction energy (ΔG°) is moderately negative, which are consistent with a very slow reaction rate and very small yield. The charge transfer from CpRu(CO)2 to fullerene CT(Ru → C60) is important in the reaction, but it is small due to the presence of the Ru d orbital at low energy, which is the reason for the large ΔG°‡ and moderately negative ΔG°. The use of Li+@C60 is theoretically predicted to accelerate the reaction and increase the yield of Li+@C60[CpRu(CO)2]2, because the CT(Ru → C60) is enhanced by the low energy LUMO of Li+@C60. It is also predicted that Li+@C60[Re(CO)4(PMe3)]2 is a next promising target for the synthesis of the η1-coordinated metal-fullerene complex, but syntheses of C60[Co(CO)4]2, C60[Re(CO)5]2, Li+@C60[Co(CO)4]2, and

  13. Formation of a sandwich-structure assisted, relatively long-lived sulfur-centered three-electron bonded radical anion in the reduction of a bis(1-substituted-uracilyl) disulfide in aqueous solution.

    Science.gov (United States)

    Wenska, Grazyna; Filipiak, Piotr; Asmus, Klaus-Dieter; Bobrowski, Krzysztof; Koput, Jacek; Marciniak, Bronislaw

    2008-08-14

    The one-electron reduction of bis[1-(2',3',5'-tri-O-acetylribosyl)uracil-4-yl] disulfide, initiated by hydrated electrons in a radiation chemical study, has been shown to yield 1-(2',3',5'-tri-O-acetylribosyl)-4-thiouracil as a stable molecular product. The reduction reaction leads, in the first instance, to a transient, albeit remarkably stable disulfide radical anion. This is characterized by a 2-center-3-electron bond with two bonding sigma-electrons and an antibonding sigma*-electron in the sulfur-sulfur bridge, (-S therefore S-)(-). It receives its stability from a sandwich-structure with the two uracilyl moieties facing each other (possibly further assisted by the 2',3',5'-tri-O-acetylribosyl substituents). A considerable lengthening of the original disulfide bridge from 2.02 to 2.73 A in the radical anion seems to facilitate the interaction of the heterocycles and leads to a gain in stabilization energy of 24 and 33 kcal/mol (100 and 140 kJ/mol) as evaluated by UMP2/cc-pVTZ and UMP2/cc-pVDZ calculations, respectively. The (-S therefore S-)(-) bonded radical anion shows a broad optical absorption band with lambdamax=450 nm, epsilonmax=6000 M(-1) cm(-1), and a half-width of 1.0 eV. It exists in equilibrium with the conjugated 1-(2',3',5'-tri- O-acetylribosyl)uracil-4-yl thiyl radical -S(*), and the corresponding thiolate, -S(-). The rate determining step for the disappearance of the disulfide radical anion appears to be protonation of both the radical anion and the free thiolate by reaction with H(+)aq. Absolute rate constants have been measured for these protonation processes, for the formation of the stable thiouridine product, and for the electron transfer from the disulfide radical anion to molecular oxygen. With the (-S therefore S-)(-) -S(*) + -S(-) equilibrium lying very much on the left-hand side, the reduced disulfide system exhibits predominantly reducing properties whereas any oxidizing property of the conjugated thiyl radical has only little if any

  14. Carbon-carbon bond formation and pyrrole synthesis via the [3,3] sigmatropic rearrangement of O-vinyl oxime ethers.

    Science.gov (United States)

    Wang, Heng-Yen; Mueller, Daniel S; Sachwani, Rachna M; Londino, Hannah N; Anderson, Laura L

    2010-05-21

    A new method for the synthesis of 2,4- and 2,3,4-substituted pyrroles in two or three steps from commercially available ketones and allyl hydroxylamine is described. An iridium-catalyzed isomerization reaction has been developed to convert O-allyl oximes to O-vinyl oximes, which undergo a facile [3,3] rearrangement to form 1,4-imino aldehyde Paal-Knorr intermediates that cyclize to afford the corresponding pyrroles. Optimization and examples of the isomerization and pyrrole formation are discussed.

  15. Thermal response experiments of {SiC}/{C} and {TiC}/{C} functionally gradient materials as plasma facing materials for fusion application

    Science.gov (United States)

    Araki, M.; Sasaki, M.; Kim, S.; Suzuki, S.; Nakamura, K.; Akiba, M.

    1994-09-01

    To evaluate the applicability of a functionally gradient technique for the fabrication of the armor tile or the interface of the divertor plate element for next fusion machines such as ITER/FER, {SiC}/{C} and {TiC}/{C} functionally gradient materials (FGMs) were prepared and tested using an electron and ion beams test facilities. FGM layer with a thickness of 1.0 mm was produced by CVD process on fine grain graphite. Their thermal resistivities were evaluated under a condition for surface heat fluxes up to 70 MW/m 2 for durations up to several seconds. As the results, we confirmed that FGMs are clearly better than non-FGMs from a view point of the reduction of thermal stress. Both FGM layers on the graphite bulk material could withstand a temperature difference as high as 1500 K without cracking or melting, leading us to conceive a promising prospect for the application of the divertor plate.

  16. The Complaint before the Judge against the Prosecutor’s Resolutions or Writs for not Proceeding to Trial – Article278 (8, Letter c C.C.P

    Directory of Open Access Journals (Sweden)

    Dragu Cretu

    2010-06-01

    Full Text Available It has been noticed in the doctrine a more pronounced current trend of “privatizing” the trial, this aspect concerning a significant part of the foreign doctrine. It was proved that its most insidious form, and undoubtedly the most dangerous, is not the traditional one, of the injured person’s prior complaint, but that which is incident to the public prosecution itself. Romanian legislator gave up the prior complaint formulated in the article 279. par. 2 letter A, C.C.P., repealing these provisions through the Law no. 356/2006, thuseliminating the procedure of direct criminal proceedings. The complaint registered in the article 278 C.C.P. arousing lots of controversies, which allow almost unlimited access from the crime victim to public proceeding. Generally, the complaint governed by the provisions of the article 275 and the next C.C.P. is, in terms of legal nature, an appeal against criminal acts and measures of prosecution and a way to control their legality. According to the law, any person whose legitimate rights were affected can lodge a complaint. The law without prescribing a limitation period, the complaint can be lodged by any natural or legal person, if there is evidence of harm of her legitimate interests.

  17. 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

    2016-03-07

    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.

  18. 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.

  19. 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

  20. Tribological Property of C/C-SiC Composites Fabricated by Isothermal Chemical Vapor Infiltration

    Directory of Open Access Journals (Sweden)

    WANG Yueming

    2017-08-01

    Full Text Available Four kinds of C/C-SiC composites were fabricated by isothermal chemical vapor infiltration (ICVI, and the 2.5D needle-punching carbon felt was taken as the preform. The volume fraction of carbon fiber in felt is 30%. The density of C/C-SiC composites is similar (1.87-1.91 g/cm3, while the weight ratio of SiC is decreased from 56% to 15%. The microstructure and phase composition of C/C-SiC composites were observed by SEM and XRD respectively. Friction and wear behavior of the C/C-SiC composites were investigated with the MM-1000 friction machine. The results show that the average macro hardness of matrix is decreased from 98.2HRA to 65.1HRA with the decrease of SiC content from 56% to 15%, and uniformity of hardness distribution is significantly decreased. Finally, by the analysis of microtopography of friction surface and wear debris, it is found that the superficial hardness has an obvious influence on mechanism of wear during braking process. The wear mechanism of the C/C-SiC composites transforms from grain wear to the combination of grain wear and adherent wear with the decrease of surface hardness. At the same time, the average friction coefficient and mass wear rate is increased obviously during breaking process.

  1. Active Metal Brazing and Characterization of Brazed Joints in C-C and C-SiC Composites to Copper-Clad-Molybdenum System

    Science.gov (United States)

    Singh, M.; Asthana, R.

    2008-01-01

    Carbon/carbon composites with CVI and resin-derived matrices, and C/SiC composites reinforced with T-300 carbon fibers in a CVI SiC matrix were joined to Cu-clad Mo using two Ag-Cu braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward delamination in resin-derived C/C composite. Extensive braze penetration of the inter-fiber channels in the CVI C/C composites was observed. The Knoop microhardness (HK) distribution across the C/C joints indicated sharp gradients at the interface, and a higher hardness in Ticusil than in Cusil-ABA. For the C/SiC composite to Cu-clad-Mo joints, the effect of composite surface preparation revealed that ground samples did not crack whereas unground samples cracked. Calculated strain energy in brazed joints in both systems is comparable to the strain energy in a number of other ceramic/metal systems. Theoretical predictions of the effective thermal resistance suggest that such joined systems may be promising for thermal management applications.

  2. Chemical stabilization and improved thermal resilience of molecular arrangements: possible formation of a surface network of bonds by multiple pulse atomic layer deposition.

    Science.gov (United States)

    de Pauli, Muriel; Matos, Matheus J S; Siles, Pablo F; Prado, Mariana C; Neves, Bernardo R A; Ferreira, Sukarno O; Mazzoni, Mário S C; Malachias, Angelo

    2014-08-14

    In this work, we make use of an atomic layer deposition (ALD) surface reaction based on trimethyl-aluminum (TMA) and water to modify O-H terminated self-assembled layers of octadecylphosphonic acid (OPA). The structural modifications were investigated by X-ray reflectivity, X-ray diffraction, and atomic force microscopy. We observed a significant improvement in the thermal stability of ALD-modified molecules, with the existence of a supramolecular packing structure up to 500 °C. Following the experimental observations, density functional theory (DFT) calculations indicate the possibility of formation of a covalent network with aluminum atoms connecting OPA molecules at terrace surfaces. Chemical stability is also achieved on top of such a composite surface, inhibiting further ALD oxide deposition. On the other hand, in the terrace edges, where the covalent array is discontinued, the chemical conditions allow for oxide growth. Analysis of the DFT results on band structure and density of states of modified OPA molecules suggests that besides the observed thermal resilience, the dielectric character of OPA layers is preserved. This new ALD-modified OPA composite is potentially suitable for applications such as dielectric layers in organic devices, where better thermal performance is required.

  3. Understanding Bonds - Denmark

    DEFF Research Database (Denmark)

    Rimmer, Nina Røhr

    2016-01-01

    a specified rate of interest during the life of the bond and to repay the face value of the bond (the principal) when it “matures,” or comes due. Among the types of bonds you can choose from are: Government securities, municipal bonds, corporate bonds, mortgage and asset-backed securities, federal agency...

  4. Pd/Norbornene: A Winning Combination for Selective Aromatic Functionalization via C-H Bond Activation.

    Science.gov (United States)

    Della Ca', Nicola; Fontana, Marco; Motti, Elena; Catellani, Marta

    2016-07-19

    Direct C-H bond activation is an important reaction in synthetic organic chemistry. This methodology has the potential to simplify reactions by avoiding the use of prefunctionalized reagents. However, selectivity, especially site selectivity, remains challenging. Sequential reactions, in which different molecules or groups are combined in an ordered sequence, represent a powerful tool for the construction of complex molecules in a single operation. We have discovered and developed a synthetic methodology that combines selective C-H bond activation with sequential reactions. This procedure, which is now known as the "Catellani reaction", enables the selective functionalization of both the ortho and ipso positions of aryl halides. The desired molecules are obtained with high selectivity from a pool of simple precursors. These molecules are assembled under the control of a palladacycle, which is formed through the joint action of a metal (Pd) and an olefin such as norbornene. These two species act cooperatively with an aryl halide to construct the palladacycle, which is formed through ortho-C-H activation of the original aryl halide. The resulting complex acts as a scaffold to direct the reaction (via Pd(IV)) of other species, such as alkyl or aryl halides and amination or acylation agents, toward the sp(2) C-Pd bond. At the end of this process, because of steric hindrance, the scaffold is dismantled by norbornene extrusion. Pd(0) is cleaved from the organic product through C-C, C-H, C-N, C-O, or C-B coupling, in agreement with the well-known reactivity of aryl-Pd complexes. The cycle involves Pd(0), Pd(II), and Pd(IV) species. In particular, our discovery relates to alkylation and arylation reactions. Recently, remarkable progress has been made in the following areas: (a) the installation of an amino or an acyl group at the ortho position of aryl halides, (b) the formation of a C-B bond at the ipso position, (c) the achievement of meta-C-H bond activation of aryl

  5. The chemical bonds effect of Amaranthus hybridus L. and Dracaena Angustifolia on TiO2 as photo-sensitizer for dye-sensitized solar Cells (DSSC)

    Science.gov (United States)

    Ahliha, A. H.; Nurosyid, F.; Supriyanto, A.

    2017-08-01

    Dye-Sensitized Solar Cells (DSSC) consists of a working electrode, dye, electrolyte, and a counter electrode. The paper showed the effect of chemical bonds Dracaena Angustifolia (suji leaves) and Amaranthus Hybridus L. (spinach leaves) on TiO2 for application in DSSC. Dracaena Angustifolia (suji leaves) and Amaranthus Hybridus L. (spinach leaves) were extracted using acetone solvent as a dye containing chlorophyll, the absorbance spectrum of the dye and TiO2 were characterized using Uv-visible spectrophotometer 1601 PC, the chemical bonds contained in TiO2-dye was characterized using FT-IR spectrophotometer Shimadzu Prestige 21. The efficiency of DSSC was calculated using I-V Keithley 2602A. Absorbance characterization of dye Dracaena Angustifolia showed two peaks at the wavelength of 665,5 nm and 412 nm. The absorbance peaks of dye Amaranthus Hybridus L. at the wavelength of 664 nm and 412,5 nm. FT-IR characterization of TiO2 founded the functional groups C=C-C, C=C-H, C-O, C-H, C=C, C-H aliphatic, and O-H. Dye Amaranthus Hybridus L. obtained functional groups C=C-C, C=C-H, C-O, C-H, C=C, C=O, C-H aliphatic, and O-H. Dye Dracaena Angustifolia obtained functional groups were identified as C=C-C, C=C-H, C-O, C-H, C=C, C-H aliphatic, and O-H. DSSC efficiency with Amaranthus Hybridus L. and Dracaena Angustifolia dyes of 0,063% and 0,058% respectively

  6. Characterization of C/C composites porosity for the fusion; Caracterisation de la porosite de composites C/C d'interet pour la fusion

    Energy Technology Data Exchange (ETDEWEB)

    Martin, C.; Ballet, A.C.; Pardanaud, C.; Roubin, P. [Universite de Provence, Centre St-Jerome, Laboratoire PIIM, 13 - Marseille (France); Beurroies, I.; Richou, M. [Universite de Provence, Centre St-Jerome, Laboratoire Madirel, 13 - Marseille (France); Brosset, C.; Pegourie, B. [Association EURATOM-CEA sur la Fusion Controlee, CE Cadarache, 13 - St-Paul-lez-Durance (France)

    2008-07-01

    In tokamaks, the composites C/C are used as components facing the plasma because of their excellent thermo-mechanical properties. In Tore Supra tokamak, analysis of particles of graphite erosion showed a big deuterium retention by the machine wall. This fuel retention will lead in ITER to a non acceptable level of tritium. As the diffusion in materials is bound to the porosity, the authors realized a study of two composites porosity: N11 and NB31. Different analysis methods have been performed and the temperature or grain size dependence studied. (A.L.B.)

  7. Efficient detection of dangling pointer error for C/C++ programs

    Science.gov (United States)

    Zhang, Wenzhe

    2017-08-01

    Dangling pointer error is pervasive in C/C++ programs and it is very hard to detect. This paper introduces an efficient detector to detect dangling pointer error in C/C++ programs. By selectively leave some memory accesses unmonitored, our method could reduce the memory monitoring overhead and thus achieves better performance over previous methods. Experiments show that our method could achieve an average speed up of 9% over previous compiler instrumentation based method and more than 50% over previous page protection based method.

  8. Monitoring and Diagnostics for C/C++ Real-Time Applications

    CERN Document Server

    Fischer, Yves

    Knowledge about the internal state of computational processes is essential for problem diagnostics as well as for constant monitoring and pre-failure recognition. The CMX li- brary provides monitoring capabilities similiar to the Java Management Extensions (JMX) for C and C++ applications. This thesis provides a detailed analysis of the requirements for monitoring and diagnos- tics of the C/C++ processes at CERN. The developed CMX library enables real-time C/C++ processes to expose values with- out harming their normal execution. CMX is portable and can be integrated in different monitoring architectures.

  9. Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM).

    Science.gov (United States)

    Netzel, Jeanette; van Smaalen, Sander

    2009-10-01

    Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T approximately 20 K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (l(max) = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent C-C, C-N and C-O bonds, and for hydrogen bonds together with covalent C-H and N-H bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H...O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997). An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds.

  10. Chemical Bonds II

    Science.gov (United States)

    Sanderson, R. T.

    1972-01-01

    The continuation of a paper discussing chemical bonding from a bond energy viewpoint, with a number of examples of single and multiple bonds. (Part I appeared in volume 1 number 3, pages 16-23, February 1972.) (AL)

  11. Trifunctional fluorescent unnatural nucleoside: Label free detection of T-T/C-C base mismatches, abasic site and bulge DNA.

    Science.gov (United States)

    Bag, Subhendu Sekhar; Pradhan, Manoj Kumar; Talukdar, Sangita

    2017-08-01

    The detection and targeting of both the mismatched and abasic DNA is highly important which would ultimately help in designing new diagnostics and chemotherapeutics. Furthermore, sensing and targeting the bulge sequence with a fluorescent probe would be useful to study the role of bulges in nucleic acid function or could have significant therapeutic potential. Thus, detection of specific bulges by small fluorescent molecules is an attractive research area since the past several years. Many attempts have been made to prepare such compounds. We report herein a label free strategy for the detection of pyrimidine base mismatches (T/T and C/C), sensing of abasic site, and pyrimidine base bulge DNA using an unnatural tetrazolylpyrene nucleoside ( TPy B Do ) as a bare fluorescent probe. The H-bonding/hydrophobic force mediated interactions allow the sensing of all three deformed DNA via an enhancement of fluorescence signal using our simple "Just-Mix and Read" strategy. The binding of the probe to all the three deformed DNA duplexes is accompanied by an increase in the thermal melting stability of the deformed DNAs. That the probe binds efficiently to the minor groove near the deformed site was evident from spectroscopic studies. All the spectral evidences open up a multitude of possibilities for using our probe, tetrazolylpyrene nucleoside, as an efficient fluorescent light-up bio-probe for label free DNA detection. Copyright © 2017. Published by Elsevier B.V.

  12. What Determines Bond Costs. Municipal Bonds Series.

    Science.gov (United States)

    Young, Douglas; And Others

    Public officials in small towns who participate infrequently in the bond market need information about bond financing. This publication, one in a series of booklets published by the Western Rural Development Center using research gathered between 1967-77, discusses factors influencing the marketability and cost of bond financing for towns and…

  13. Development of a Class for Multiple Precision Arithmetic in C/C++ Language

    OpenAIRE

    福田, 宏

    1998-01-01

    We have defined a floating-point variable of arbitrary length for a calculation of high precision and have developed a set of mathematical functions of it in C/C++ language. The variable and the functions are combined into a class in C++ language. In addition, the functions can be easily converted to those in FORTRAN language.

  14. Admission chemokine (C-C motif) ligand 4 levels predict survival in pediatric septic shock.

    Science.gov (United States)

    Nowak, Jeffrey E; Wheeler, Derek S; Harmon, Kelli K; Wong, Hector R

    2010-03-01

    Stratification with an effective outcome biomarker could improve the design of interventional trials in pediatric septic shock. The objective of this study was to test the usefulness of chemokine (C-C motif) ligand 4 as an outcome biomarker for mortality in pediatric septic shock. A cross-sectional, observational study. Eighteen pediatric intensive care units in the United States. One hundred fifty-six pediatric patients with septic shock. Serum samples were obtained within 24 hrs of admission to the pediatric intensive care unit. Serum levels of chemokine (C-C motif) ligand 4 were measured by enzyme-linked immunosorbent assay and compared with mortality in a training set of 34 patients. These data were used to generate a cutoff value whose usefulness was evaluated through prospective application-without post hoc modification-to a larger validation set of 122 patients. On inspection of the training set data, a cutoff value of 140 pg/mL was chosen. When applied to the validation set, serum chemokine (C-C motif) ligand 4 levels >140 pg/mL yielded a sensitivity of 92% and a specificity of 40% for mortality. A serum level of pediatric septic shock. Exclusion of patients with a chemokine (C-C motif) ligand 4 level of pediatric septic shock could create a study population in which survival benefit from the study agent could be more readily demonstrated.

  15. 77 FR 10004 - C$ cMoney, Inc.; Order of Suspension of Trading

    Science.gov (United States)

    2012-02-21

    ... COMMISSION C$ cMoney, Inc.; Order of Suspension of Trading February 16, 2012. It appears to the Securities... the opinion that the public interest and the protection of investors require a suspension of trading... the Securities Exchange Act of 1934, that trading in the securities of the above-listed company is...

  16. Botnet C&C Traffic and Flow Lifespans Using Survival Analysis

    Directory of Open Access Journals (Sweden)

    Vaclav Oujezsky

    2017-03-01

    Based on our research we have figured out a possibility to distinguish the individual lifespans of C&C communications that are identical to each other by using survival projection curves, although it occurred in a different time course.

  17. B-N as a C-C substitute in aromatic systems

    National Research Council Canada - National Science Library

    Bosdet, Michael J.D; Piers, Warren E

    2009-01-01

    ... electronic properties and chemistry. Since the pioneering work of Dewar some 50 years ago, the relationship between B-N and C-C and the wealth of parent all-carbon aromatics has captured the imagination of organic, inorganic, materials...

  18. 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...

  19. DETECTING DOMAIN BOUNDARIES IN PROTEINS THROUGH PLOTTING OF THE ENERGY OF NON-BONDED INTERACTIONS (ENBI AS A FUNCTION OF PROGRESSIVE IN SILICO TRUNCATION OF CHAINS IN NATIVE STRUCTURAL FORMAT

    Directory of Open Access Journals (Sweden)

    Purnananda Guptasarma

    2012-12-01

    Full Text Available Several methods exist for the detection of domain boundaries in proteins. Different methods exploit different structural-biochemical characteristics distinguishing, and defining, protein domains. However, perhaps because ‘domains’ remain poorly defined, no single method has proved to be entirely satisfactory. Here, a new approach to defining and detecting domains is presented, along with some preliminary data from three proteins, in the form of a proof-of-concept. It is argued from first principles that protein domain boundaries may be identified through plotting of variations in the energy of non-bonded interactions of a naturally-occurring protein as a function of varying chain length (in native structural format. Such plots may be expected to show a broadly descending trend as a function of increasing chain length, marked by slope changes at domain boundaries. The approach is demonstrated with three multi-domain, single-subunit proteins, porcine pepsin (4PEP, thymidylate synthase (4TMS and aconitase (5ACN.

  20. A new reaction mode of germanium-silicon bond formation: insertion reactions of H₂GeLiF with SiH₃X (X = F, Cl, Br).

    Science.gov (United States)

    Yan, Bingfei; Li, Wenzuo; Xiao, Cuiping; Li, Qingzhong; Cheng, Jianbo

    2013-10-01

    A combined density functional and ab initio quantum chemical study of the insertion reactions of the germylenoid H2GeLiF with SiH3X (X = F, Cl, Br) was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connected the reactants and the products. The calculated barrier heights relative to the respective precursors are 102.26 (X = F), 95.28 (X = Cl), and 84.42 (X = Br) kJ mol(-1) for the three different insertion reactions, respectively, indicating the insertion reactions should occur easily according to the following order: SiH3-Br > SiH3-Cl > SiH3-F under the same situation. The solvent effects on the insertion reactions were also calculated and it was found that the larger the dielectric constant, the easier the insertion reactions. The elucidations of the mechanism of these insertion reactions provided a new reaction model of germanium-silicon bond formation.

  1. Van Der Waals heterogeneous layer-layer carbon nanostructures involving π···H-C-C-H···π···H-C-C-H stacking based on graphene and graphane sheets.

    Science.gov (United States)

    Yuan, Kun; Zhao, Rui-Sheng; Zheng, Jia-Jia; Zheng, Hong; Nagase, Shigeru; Zhao, Sheng-Dun; Liu, Yan-Zhi; Zhao, Xiang

    2017-04-15

    Noncovalent interactions involving aromatic rings, such as π···π stacking, CH···π are very essential for supramolecular carbon nanostructures. Graphite is a typical homogenous carbon matter based on π···π stacking of graphene sheets. Even in systems not involving aromatic groups, the stability of diamondoid dimer and layer-layer graphane dimer originates from C - H···H - C noncovalent interaction. In this article, the structures and properties of novel heterogeneous layer-layer carbon-nanostructures involving π···H-C-C-H···π···H-C-C-H stacking based on [n]-graphane and [n]-graphene and their derivatives are theoretically investigated for n = 16-54 using dispersion corrected density functional theory B3LYP-D3 method. Energy decomposition analysis shows that dispersion interaction is the most important for the stabilization of both double- and multi-layer-layer [n]-graphane@graphene. Binding energy between graphane and graphene sheets shows that there is a distinct additive nature of CH···π interaction. For comparison and simplicity, the concept of H-H bond energy equivalent number of carbon atoms (noted as NHEQ), is used to describe the strength of these noncovalent interactions. The NHEQ of the graphene dimers, graphane dimers, and double-layered graphane@graphene are 103, 143, and 110, indicating that the strength of C-H···π interaction is close to that of π···π and much stronger than that of C-H···H-C in large size systems. Additionally, frontier molecular orbital, electron density difference and visualized noncovalent interaction regions are discussed for deeply understanding the nature of the C-H···π stacking interaction in construction of heterogeneous layer-layer graphane@graphene structures. We hope that the present study would be helpful for creations of new functional supramolecular materials based on graphane and graphene carbon nano-structures. © 2017 Wiley Periodicals, Inc. © 2017 Wiley

  2. 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

  3. Revisiting Hydrogen Bond Thermodynamics in Molecular Simulations.

    Science.gov (United States)

    Sapir, Liel; Harries, Daniel

    2017-06-13

    In processes involving aqueous solutions and in almost every biomolecular interaction, hydrogen bonds play important roles. Though weak compared to the covalent bond, hydrogen bonds modify the stability and conformation of numerous small and large molecules and modulate their intermolecular interactions. We propose a simple methodology for extracting hydrogen bond strength from atomistic level simulations. The free energy associated with hydrogen bond formation is conveniently calculated as the reversible work required to reshape a completely random pair probability distribution reference state into the one found in simulations where hydrogen bonds are formed. Requiring only the probability density distribution of donor-acceptor pairs in the first solvation shell of an electronegative atom, the method uniquely defines the free energy, entropy, and enthalpy of the hydrogen bond. The method can be easily extended to molecules other than water and to multiple component mixtures. We demonstrate and apply this methodology to hydrogen bonds that form in molecular dynamics simulations between water molecules in pure water, as well as to bonds formed between different molecules in a binary mixture of a sugar (trehalose) and water. Finally, we comment on how the method should be useful in assessing the role of hydrogen bonds in different molecular mechanisms.

  4. Log ASCII Standard (LAS) Files for Geophysical (Gamma Ray) Wireline Well Logs and Their Application to Geologic Cross Section C-C' Through the Central Appalachian Basin

    Science.gov (United States)

    Trippi, Michael H.; Crangle, Robert D.

    2009-01-01

    U.S. Geological Survey (USGS) regional geologic cross section C-C' (Ryder and others, 2008) displays key stratigraphic intervals in the central Appalachian basin. For this cross section, strata were correlated by using descriptions of well cuttings and gamma ray well log traces. This report summarizes the procedures used to convert gamma ray curves on paper well logs to the digital Log ASCII (American Standard Code for Information Interchange) Standard (LAS) format using the third-party software application Neuralog. The procedures could be used with other geophysical wireline logs also. The creation of digital LAS files from paper well logs by using Neuralog is very helpful, especially when dealing with older logs with limited or nonexistent digital data. The LAS files from the gamma ray logs of 11 wells used to construct cross section C-C' are included in this report. They may be downloaded from the index page as a single ZIP file.

  5. Methane Formation by Flame-Generated Hydrogen Atoms in the Flame Ionization Detector

    DEFF Research Database (Denmark)

    Holm, Torkil; Madsen, Jørgen Øgaard

    1996-01-01

    The precombustion degradation of organic compounds in the flame ionization detector has been studied (1) by heating the additives in hydrogen in a quartz capillary and analyzing the reaction products by GC and (2) by following the degradation of the additives in a hydrogen flame, by means of a thin......, and conceivably all hydrocarbons are quantitatively converted into methane at temperatures below 600 C, that is, before the proper combustion has started. The splitting of the C-C bonds is preceded by hydrogenation of double and triple bonds and aromatic rings. The reactions, no doubt, are caused by hydrogen...... atoms, which are formed in the burning hydrogen and which diffuse into the inner core of the flame. The quantitative formation of methane appears to explain the "equal per carbon" rule for the detector response of hydrocarbons, since all carbons are "exchanged" for methane molecules....

  6. Bond strengthening in oral bacterial adhesion to salivary conditioning films

    NARCIS (Netherlands)

    van der Mei, Henderina; Rustema-Abbing, Mina; de Vries, Jacob; Busscher, Hendrik

    Transition from reversible to irreversible bacterial adhesion is a highly relevant but poorly understood step in initial biofilm formation. We hypothesize that in oral biofilm formation, irreversible adhesion is caused by bond strengthening due to specific bacterial interactions with salivary

  7. Peptide Bond Formations through Flow Chemistry.

    Science.gov (United States)

    Ahmed, N

    2017-10-04

    Peptides and proteins play important roles in body functions(1) ,(2) and are used exclusively in drug discoveries, having advantages because of their high biological activity, high specificity, and low toxicity. For peptide synthesis, researchers mostly use the solid-phase peptide synthesis (SPPS)(3) with modern modifications.(4) However, scientists failed to overcome two main factors; the concentration and time required for peptide coupling. The flow-based technology may help in the rapid production of peptides due to having advantages over batch reactions(5-7) in terms of productivity, heat and mixing efficiency, safety, and reproducibility. Herein, we discussed both solution and solid phase synthesis of peptides in flow.(8-12) This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

  8. Enhancing the Acylation Activity of Acetic Acid by Formation of an Intermediate Aromatic Ester.

    Science.gov (United States)

    Duong, Nhung N; Wang, Bin; Sooknoi, Tawan; Crossley, Steven P; Resasco, Daniel E

    2017-07-10

    Acylation is an effective C-C bond-forming reaction to condense acetic acid and lignin-derived aromatic compounds into acetophenones, valuable precursors to fuels and chemicals. However, acetic acid is intrinsically an ineffective acylating agent. Here, we report that its acylation activity can be greatly enhanced by forming intermediate aromatic esters directly derived from acetic acid and phenolic compounds. Additionally, the acylation reaction was studied in the liquid phase over acid zeolites and was found to happen in two steps: 1) formation of an acylium ion and 2) C-C bond formation between the acylium ion and the aromatic substrate. Each of these steps may be rate-limiting, depending on the type of acylating agent and the aromatic substrate. Oxygen-containing substituents, such as -OH and -OCH3 , can activate aromatic substrates for step 2, with -OH> -OCH3 , whereas alkyl substituent -R cannot. At the same time, aromatic esters can rearrange to acetophenones by both an intramolecular pathway and, preferentially, an intermolecular one. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Quick Way to Port Existing C/C++ Chemoinformatics Toolkits to the Web Using Emscripten.

    Science.gov (United States)

    Jiang, Chen; Jin, Xi

    2017-10-23

    Emscripten is a special open source compiler that compiles C and C++ code into JavaScript. By utilizing this compiler, some typical C/C++ chemoinformatics toolkits and libraries are quickly ported to to web. The compiled JavaScript files have sizes similar to native programs, and from a series of constructed benchmarks, the performance of the compiled JavaScript codes is also close to that of the native codes and is better than the handwritten JavaScript codes. Therefore, we believe that Emscripten is a feasible and practical tool for reusing existing C/C++ codes on the web, and many other chemoinformatics or molecular calculation software tools can also be easily ported by Emscripten.

  10. Thermo-mechanical and tribological properties of phenolic polymers composites and C-C composites

    Directory of Open Access Journals (Sweden)

    Virgil MARINESCU

    2010-12-01

    Full Text Available Formaldehyde resin-based composites have been an inaugural step in obtaining and usingcomposite materials and they have grown rapidly because of their multiple uses, especially inelectrical and aeronautical field.Phenolic matrix composites represent a preliminary study to obtain mezophase carbon-carboncomposites for advanced materials as potential solutions for reentry shields of cosmic vehicles andlaunch subsystems, as elements of modern braking systems in aircraft or as potential solutions for thecomponents of the combustion chamber of rockets and also as hypersonic transport solutions for thefuture. Both phenolic matrix laminated composites and C-C mezophase matrix C-C composites wereobtained.This paper presents an evaluation of the mechanical and tribological behavior of the obtainedcomposites.

  11. A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

    Energy Technology Data Exchange (ETDEWEB)

    Legesse, Merid; Nolan, Michael, E-mail: Michael.nolan@tyndall.ie; Fagas, Giorgos, E-mail: Georgios.fagas@tyndall.ie [Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork (Ireland)

    2014-05-28

    In this paper, we use a model of hydrogenated amorphous silicon generated from molecular dynamics with density functional theory calculations to examine how the atomic geometry and the optical and mobility gaps are influenced by mild hydrogen oversaturation. The optical and mobility gaps show a volcano curve as the hydrogen content varies from undersaturation to mild oversaturation, with largest gaps obtained at the saturation hydrogen concentration. At the same time, mid-gap states associated with dangling bonds and strained Si-Si bonds disappear at saturation but reappear at mild oversaturation, which is consistent with the evolution of optical gap. The distribution of Si-Si bond distances provides the key to the change in electronic properties. In the undersaturation regime, the new electronic states in the gap arise from the presence of dangling bonds and strained Si-Si bonds, which are longer than the equilibrium Si-Si distance. Increasing hydrogen concentration up to saturation reduces the strained bonds and removes dangling bonds. In the case of mild oversaturation, the mid-gap states arise exclusively from an increase in the density of strained Si-Si bonds. Analysis of our structure shows that the extra hydrogen atoms form a bridge between neighbouring silicon atoms, thus increasing the Si-Si distance and increasing disorder in the sample.

  12. Formation of an Ion-Pair Molecule with a Single NH+...Cl- Hydrogen Bond: Raman spectra of 1,1,3,3-Tetramethylguanidinium chloride in the solid state, in solution and in the vapor phase

    DEFF Research Database (Denmark)

    Berg, Rolf W.; Riisager, Anders; Fehrmann, Rasmus

    2008-01-01

    scattering spectra are presented and assigned, by comparing to the quantum mechanical calculations. It is concluded that dimeric molecular ion pairs with four N-H+ · · · Cl- hydrogen bonds probably exist in the solutions and are responsible for the relatively high solubility of the “salt” in ethanol......- hydrogen bond, the stretching band of which is causing the band....

  13. Determination of material properties for short fibre reinforced C/C-SiC

    Directory of Open Access Journals (Sweden)

    Hausherr J.-M.

    2015-01-01

    Full Text Available Determining the mechanical properties of short fibre reinforced CMC using standard sized coupons has always been a challenge due to a high statistical scattering of the measured values. Although the random orientation of short fibres results in a quasi-isotropic material behavior of 2D-structures with a sufficiently large volume, the small volume typical for test coupons usually results in a non-isotropic fibre orientation in the tested volume. This paper describes a method for manufacturing unidirectional oriented short fibre reinforced CMC materials and presents material properties of UD-C/C-SiC. After verifying the fibre orientation of the CMC using micro-computed tomography, coupons were extracted to determine the orthotropic material properties. These orthotropic material properties were then used to predict the properties of C/C-SiC with randomly distributed short fibres. To validate the method, micro-computed tomography is used to quantitatively determine the fibre orientation within coupons extracted from randomly distributed short fibre C/C-SiC. After mechanical three-point-bending tests, the measured stiffness and bending strength is compared with the predicted properties. Finally, the data are used to devise a method suited for reducing the inherent large spread of material properties associated with the measurement of CMC materials with randomly distributed short fibres.

  14. A C/C++ Build System Based On Maven for the LHC Controls System

    CERN Document Server

    Nguyen Xuan, J; Dönszelmann, M

    2011-01-01

    The CERN accelerator controls system, mainly written in Java and C/C++, consists nowadays of 50 projects and 150 active developers. The controls group has decided to unify the development process and standards (e.g. project layout) using Apache Maven and Sonatype Nexus. Maven is the de-facto build tool for Java, it deals with versioning and dependency management, whereas Nexus is a repository manager. C/C++ developers were struggling to keep their dependencies on other CERN projects, as no versioning was applied, the libraries have to be compiled and available for several platforms and architectures, and finally there was no dependency management mechanism. This results in very complex Makefiles which were difficult to maintain. Even if Maven is primarily designed for Java, a plugin (Maven NAR) adapts the build process for native programming languages for different operating systems and platforms. However C/C++ developers were not keen to abandon their current Makefiles. Hence our approach was to combine the ...

  15. C/C-SiC Composites for Nozzle of Solid Propellant Ramjet

    Directory of Open Access Journals (Sweden)

    WANG Lingling

    2017-01-01

    Full Text Available Carbon fiber reinforced carbon and silicon carbide matrix composites for nozzle inner of solid propellant ramjet were prepared by using the hybrid process of "chemical vapor infiltration + precursor impregnation pyrolysis (CVI+PIP". The microstructure, flexural and anti-ablation properties of the C/C-SiC composites and hydraulic test and rocket motor hot firing test for nozzle inner of solid propellant ramjet were comprehensively investigated. The results show that when the flexural strength of the composite reachs 197 MPa, the fracture damage behavior of the composites presents typical toughness mode.Also the composites has excellent anti-ablative property, i.e., linear ablation rate is only 0.0063 mm·s-1 after 200 s ablation. The C/C-SiC component have excellent integral bearing performance with the hydraulic bursting pressure of 6.5 MPa, and the high temperature combination property of the C/C-SiC composite nozzle inner is verified through motor hot firing of solid propellant ramjet.

  16. Energy decomposition analysis of single bonds within Kohn-Sham density functional theory.

    Science.gov (United States)

    Levine, Daniel S; Head-Gordon, Martin

    2017-11-28

    An energy decomposition analysis (EDA) for single chemical bonds is presented within the framework of Kohn-Sham density functional theory based on spin projection equations that are exact within wave function theory. Chemical bond energies can then be understood in terms of stabilization caused by spin-coupling augmented by dispersion, polarization, and charge transfer in competition with destabilizing Pauli repulsions. The EDA reveals distinguishing features of chemical bonds ranging across nonpolar, polar, ionic, and charge-shift bonds. The effect of electron correlation is assessed by comparison with Hartree-Fock results. Substituent effects are illustrated by comparing the C-C bond in ethane against that in bis(diamantane), and dispersion stabilization in the latter is quantified. Finally, three metal-metal bonds in experimentally characterized compounds are examined: a [Formula: see text]-[Formula: see text] dimer, the [Formula: see text]-[Formula: see text] bond in dizincocene, and the Mn-Mn bond in dimanganese decacarbonyl.

  17. Evolution of C-H Bond Functionalization from Methane to Methodology.

    Science.gov (United States)

    Hartwig, John F

    2016-01-13

    This Perspective presents the fundamental principles, the elementary reactions, the initial catalytic systems, and the contemporary catalysts that have converted C-H bond functionalization from a curiosity to a reality for synthetic chemists. Many classes of elementary reactions involving transition-metal complexes cleave C-H bonds at typically unreactive positions. These reactions, coupled with a separate or simultaneous functionalization process lead to products containing new C-C, C-N, and C-O bonds. Such reactions were initially studied for the conversion of light alkanes to liquid products, but they have been used (and commercialized in some cases) most often for the synthesis of the more complex structures of natural products, medicinally active compounds, and aromatic materials. Such a change in direction of research in C-H bond functionalization is remarkable because the reactions must occur at an unactivated C-H bond over functional groups that are more reactive than the C-H bond toward classical reagents. The scope of reactions that form C-C bonds or install functionality at an unactivated C-H bond will be presented, and the potential future utility of these reactions will be discussed.

  18. Chemical bonding in electron-deficient boron oxide clusters: core boronyl groups, dual 3c-4e hypervalent bonds, and rhombic 4c-4e bonds.

    Science.gov (United States)

    Chen, Qiang; Lu, Haigang; Zhai, Hua-Jin; Li, Si-Dian

    2014-04-28

    We explore the structural and bonding properties of the electron-deficient boron oxide clusters, using a series of B3On(-/0/+) (n = 2-4) clusters as examples. Global-minimum structures of these boron oxide clusters are identified via unbiased Coalescence Kick and Basin Hopping searches, which show a remarkable size and charge-state dependence. An array of new bonding elements are revealed: core boronyl groups, dual 3c-4e hypervalent bonds (ω-bonds), and rhombic 4c-4e bonds (o-bonds). In favorable cases, oxygen can exhaust all its 2s/2p electrons to facilitate the formation of B-O bonds. The current findings should help understand the bonding nature of low-dimensional boron oxide nanomaterials and bulk boron oxides.

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

    Science.gov (United States)

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

    2014-12-01

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

  20. Redox-controlled hydrogen bonding: turning a superbase into a strong hydrogen-bond donor.

    Science.gov (United States)

    Wild, Ute; Neuhäuser, Christiane; Wiesner, Sven; Kaifer, Elisabeth; Wadepohl, Hubert; Himmel, Hans-Jörg

    2014-05-12

    Herein the synthesis, structures and properties of hydrogen-bonded aggregates involving redox-active guanidine superbases are reported. Reversible hydrogen bonding is switched on by oxidation of the hydrogen-donor unit, and leads to formation of aggregates in which the hydrogen-bond donor unit is sandwiched by two hydrogen-bond acceptor units. Further oxidation (of the acceptor units) leads again to deaggregation. Aggregate formation is associated with a distinct color change, and the electronic situation could be described as a frozen stage on the way to hydrogen transfer. A further increase in the basicity of the hydrogen-bond acceptor leads to deprotonation reactions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. 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 in a specially...... developed equipment allowing independent variation of normal pressure and surface expansion confirm this. Based upon a slip-line analysis of the extrusion through cracks of the surface layer and upon the establishment of real contact between virgin material, a theory for the bond strength as a function...

  2. CYP719B1 is salutaridine synthase, the C-C phenol-coupling enzyme of morphine biosynthesis in opium poppy.

    Science.gov (United States)

    Gesell, Andreas; Rolf, Megan; Ziegler, Jörg; Díaz Chávez, María Luisa; Huang, Fong-Chin; Kutchan, Toni M

    2009-09-04

    Morphine is a powerful analgesic natural product produced by the opium poppy Papaver somniferum. Although formal syntheses of this alkaloid have been reported, the morphine molecule contains five stereocenters and a C-C phenol linkage that to date render a total synthesis of morphine commercially unfeasible. The C-C phenol-coupling reaction along the biosynthetic pathway to morphine in opium poppy is catalyzed by the cytochrome P450-dependent oxygenase salutaridine synthase. We report herein on the identification of salutaridine synthase as a member of the CYP719 family of cytochromes P450 during a screen of recombinant cytochromes P450 of opium poppy functionally expressed in Spodoptera frugiperda Sf9 cells. Recombinant CYP719B1 is a highly stereo- and regioselective enzyme; of forty-one compounds tested as potential substrates, only (R)-reticuline and (R)-norreticuline resulted in formation of a product (salutaridine and norsalutaridine, respectively). To date, CYP719s have been characterized catalyzing only the formation of a methylenedioxy bridge in berberine biosynthesis (canadine synthase, CYP719A1) and in benzo[c]phenanthridine biosynthesis (stylopine synthase, CYP719A14). Previously identified phenol-coupling enzymes of plant alkaloid biosynthesis belong only to the CYP80 family of cytochromes. CYP719B1 therefore is the prototype for a new family of plant cytochromes P450 that catalyze formation of a phenol-couple.

  3. Disulfide Bonds: A Key Modification in Bacterial Extracytoplasmic Proteins.

    Science.gov (United States)

    Lee, S F; Davey, L

    2017-12-01

    Disulfide bonds are a common posttranslational modification that contributes to the folding and stability of extracytoplasmic proteins. Almost all organisms, from eukaryotes to prokaryotes, have evolved enzymes to make and break these bonds. Accurate and efficient disulfide bond formation can be vital for protein function; therefore, the enzymes that catalyze disulfide bond formation are involved in multiple biological processes. Recent advances clearly show that oral bacteria also have the ability to from disulfide bonds, and this ability has an effect on a range of dental plaque-related phenotypes. In the gram-positive Streptococcus gordonii, the ability to form disulfide bonds affected autolysis, extracellular DNA release, biofilm formation, genetic competence, and bacteriocin production. In Actinomyces oris, disulfide bond formation is needed for pilus assembly, coaggregation, and biofilm formation. In other gram-positive bacteria, such as Enterococcus faecalis, disulfide bonds are formed in secreted bacteriocins and required for activity. In these oral bacteria, the enzymes that catalyze the disulfide bonds are quite diverse and share little sequence homology, but all contain a CXXC catalytic active site motif and a conserved C-terminal cis-proline, signature features of a thiol-disulfide oxidoreductase. Emerging evidence also indicates that gram-negative oral bacteria, such as Porphyromonas gingivalis and Tannerella forsythia, use disulfide bonds to stabilize their outer membrane porin proteins. Bioinformatic screens reveal that these gram-negative bacteria carry genes coding for thiol-disulfide oxidoreductases in their genomes. In conclusion, disulfide bond formation in oral bacteria is an emerging field, and the ability to form disulfide bonds plays an important role in dental plaque formation and fitness for the bacteria.

  4. Core-level photoabsorption study of defects and metastable bonding configurations in boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez, I.; Jankowski, A.F.; Terminello, L.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Boron nitride is an interesting material for technological applications and for fundamental solid state physics investigations. It is a compound isoelectronic with carbon and, like carbon can possess sp{sup 2} and sp{sup 3} bonded phases resembling graphite and diamond. BN crystallizes in the sp{sup 2}-bonded hexagonal (h-BN), rhombohedral (r-BN) and turbostratic phases, and in the sp{sup 3}-bonded cubic (c-BN) and wurtzite (w-BN) phases. A new family of materials is obtained when replacing C-C pairs in graphite with isoelectronic B-N pairs, resulting in C{sub 2}BN compounds. Regarding other boron compounds, BN is exceptional in the sense that it has standard two-center bonds with conventional coordination numbers, while other boron compounds (e.g. B{sub 4}C) are based on the boron icosahedron unit with three-center bonds and high coordination numbers. The existence of several allotropic forms and fullerene-like structures for BN suggests a rich variety of local bonding and poses the questions of how this affects the local electronic structure and how the material accommodates the stress induced in the transition regions between different phases. One would expect point defects to play a crucial role in stress accommodation, but these must also have a strong influence in the electronic structure, since the B-N bond is polar and a point defect will thus be a charged structure. The study of point defects in relationship to the electronic structure is of fundamental interest in these materials. Recently, the authors have shown that Near-Edge X-ray Absorption Fine Structure (NEXAFS) is sensitive to point defects in h-BN, and to the formation of metastable phases even in amorphous materials. This is significant since other phase identification techniques like vibrational spectroscopies or x-ray diffraction yield ambiguous results for nanocrystalline and amorphous samples. Serendipitously, NEXAFS also combines chemical selectivity with point defect sensitivity.

  5. Insights into the Diels-Alder Reaction between 3-Vinylindoles and Methyleneindolinone without and with the Assistance of Hydrogen-Bonding Catalyst Bisthiourea: Mechanism, Origin of Stereoselectivity, and Role of Catalyst.

    Science.gov (United States)

    Yan, Chao-Xian; Yang, Fan; Yang, Xing; Zhou, Da-Gang; Zhou, Pan-Pan

    2017-03-17

    The Diels-Alder reaction between 3-vinylindoles and methyleneindolinone can proceed both under catalyst-free conditions and with bisthiourea as the catalyst. The reaction with bisthiourea is much faster and results in higher stereoselectivity of the product. The reaction mechanism, origin of stereoselectivity, and role of the catalyst were elaborated based on quantum mechanical calculations and theoretical methods of reactivity indices, NCI, QTAIM, and distortion/interaction models. In the uncatalyzed reaction, the two C-C bonds that are formed undergo conversion from noncovalent to covalent bonding via a concerted asynchronous mechanism. The weak intermolecular interactions formed in the transition state play important roles. The difference between the interaction and distortion energies is responsible for the stereoselectivity. In the catalyzed reaction, bisthiourea induces both the diene and dienophile to approach it via weak intermolecular interactions, which greatly lowers the energy barrier of the reaction and leads to the product with excellent stereoselectivity. The possible pathways of this reaction were explored, which suggested that the formation of the two C-C bonds goes through either a stepwise or concerted asynchronous mechanism. These results detail the reaction mechanism and shed light on both the significant role of the bisthiourea catalyst and the origin of stereoselectivity for this type of Diels-Alder reaction and related ones.

  6. 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

  7. Dielectron Production in C + C and p + p Collisions with Hades

    Science.gov (United States)

    Pietraszko, J.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Durán, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P. J. R.; Friese, J.; Frhölich, I.; Galatyuk, T.; Garzón, J. A.; Gernhóuser, R.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Hadjivasiliou, Ch.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kugler, A.; Kühn, W.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, S.; Lopez, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Pechenov, V.; Pérez, T.; Pleskac, R.; Pospísil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Senger, P.; Shileev, K.; Simon, R.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Teilab, K.; Tlusty, P.; Traxler, M.; Trȩbacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wiśniowski, M.; Wójcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

    The High Acceptance Di-Electron Spectrometer HADES1 has been constructed at the SIS accelerator (GSI Darmstadt) to investigate electron-positron pairs produced in proton, pion and heavy ion induced reactions. The main goal of these studies is to explore properties of hadrons in nuclear matter. The apparatus and the experimental results from C+C at 2.0 AGeV and 1.0 AGeV and p+p at 2.2 GeV compared with Monte-Carlo events from a generator based on known cross-sections and branching ratios are presented.

  8. Study of dielectron production in C+C collisions at 1A GeV

    Science.gov (United States)

    Hades Collaboration; Agakishiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bassini, R.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Bortolotti, A.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kajetanowicz, M.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Maier, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Morinière, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pérez Cavalcanti, T.; Pietraszko, J.; Pleskac, R.; Pospísil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schroeder, C.; Schwab, E.; Simon, R. S.; Sobolev, Yu. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Toia, A.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Weber, M.; Wen, H.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.

    2008-05-01

    The emission of ee pairs from C+C collisions at an incident energy of 1 GeV per nucleon has been investigated. The measured production probabilities, spanning from the π-Dalitz to the ρ/ω invariant-mass region, display a strong excess above the cocktail of standard hadronic sources. The bombarding-energy dependence of this excess is found to scale like pion production, rather than like eta production. The data are in good agreement with results obtained in the former DLS experiment.

  9. Dynamics of the chemical bond: inter- and intra-molecular hydrogen bond.

    Science.gov (United States)

    Arunan, Elangannan; Mani, Devendra

    2015-01-01

    In this discussion, we show that a static definition of a 'bond' is not viable by looking at a few examples for both inter- and intra-molecular hydrogen bonding. This follows from our earlier work (Goswami and Arunan, Phys. Chem. Chem. Phys. 2009, 11, 8974) which showed a practical way to differentiate 'hydrogen bonding' from 'van der Waals interaction'. We report results from ab initio and atoms in molecules theoretical calculations for a series of Rg∙∙∙HX complexes (Rg=He/Ne/Ar and X=F/Cl/Br) and ethane-1,2-diol. Results for the Rg∙∙∙HX/DX complexes show that Rg∙∙∙DX could have a 'deuterium bond' even when Rg∙∙∙HX is not 'hydrogen bonded', according to the practical criterion given by Goswami and Arunan. Results for ethane-1,2-diol show that an 'intra-molecular hydrogen bond' can appear during a normal mode vibration which is dominated by the OO stretching, though a 'bond' is not found in the equilibrium structure. This dynamical 'bond' formation may nevertheless be important in ensuring the continuity of electron density across a molecule. In the former case, a vibration 'breaks' an existing bond and in the later case, a vibration leads to 'bond' formation. In both cases, the molecule/complex stays bound irrespective of what happens to this 'hydrogen bond'. Both these cases push the borders on the recent IUPAC recommendation on hydrogen bonding (Arunan et al. Pure. Appl. Chem. 2011, 83 1637) and justify the inclusive nature of the definition.

  10. Regioselectivity of enzymatic and photochemical single electron transfer promoted carbon-carbon bond fragmentation reactions of tetrameric lignin model compounds.

    Science.gov (United States)

    Cho, Dae Won; Latham, John A; Park, Hea Jung; Yoon, Ung Chan; Langan, Paul; Dunaway-Mariano, Debra; Mariano, Patrick S

    2011-04-15

    New types of tetrameric lignin model compounds, which contain the common β-O-4 and β-1 structural subunits found in natural lignins, have been prepared and carbon-carbon bond fragmentation reactions of their cation radicals, formed by photochemical (9,10-dicyanoanthracene) and enzymatic (lignin peroxidase) SET-promoted methods, have been explored. The results show that cation radical intermediates generated from the tetrameric model compounds undergo highly regioselective C-C bond cleavage in their β-1 subunits. The outcomes of these processes suggest that, independent of positive charge and odd-electron distributions, cation radicals of lignins formed by SET to excited states of sensitizers or heme-iron centers in enzymes degrade selectively through bond cleavage reactions in β-1 vs β-O-4 moieties. In addition, the findings made in the enzymatic studies demonstrate that the sterically large tetrameric lignin model compounds undergo lignin peroxidase-catalyzed cleavage via a mechanism involving preliminary formation of an enzyme-substrate complex.

  11. Acrylic mechanical bond tests

    Energy Technology Data Exchange (ETDEWEB)

    Wouters, J.M.; Doe, P.J.

    1991-02-01

    The tensile strength of bonded acrylic is tested as a function of bond joint thickness. 0.125 in. thick bond joints were found to posses the maximum strength while the acceptable range of joints varied from 0.063 in. to almost 0.25 in. Such joints are used in the Sudbury Neutrino Observatory.

  12. Phenylacetylene and H bond

    Indian Academy of Sciences (India)

    ... all resembling H bonds. Non-linear H bonds due to secondary interactions. C-H stretching frequency shows blue shift. Heavy atom distances are longer than the sum of van der Waals radii. Formed a task group through IUPAC to come up with a modern definition of H bond. 15 international experts including Desiraju.

  13. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of cobalt carbide (CoC) and its cation (CoC+).

    Science.gov (United States)

    Lau, Kai-Chung; Pan, Yi; Lam, Chow-Shing; Huang, Huang; Chang, Yih-Chung; Luo, Zhihong; Shi, Xiaoyu; Ng, C Y

    2013-03-07

    The ionization energy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (ΔH°f0) and 298 K (ΔH°f298) for CoC and CoC(+) are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ∕CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, (1)Σ(+), for the ground state of CoC(+). The CCSDTQ∕CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 ± 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ∕CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ωe (ωe (+)) = 956 (992) and 976 (1004) cm(-1) and the bond lengths re (re (+)) = 1.560 (1.528) and 1.550 (1.522) Å, respectively, for CoC (CoC(+)) in comparison with the experimental values. The CCSDTQ∕CBS calculations give the prediction of D0(Co(+)-C) - D0(Co-C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 ± 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of CoC∕CoC(+). For

  14. Chemical bond fundamental aspects of chemical bonding

    CERN Document Server

    Frenking, Gernot

    2014-01-01

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

  15. Prospective bonding applications

    Science.gov (United States)

    Ancenay, H.; Benazet, D.

    1981-07-01

    Adhesive bonding in industry and in the laboratory is surveyed and prospects for its wider utilization are assessed. The economic impact of bonding technology on industry is discussed. Research is reviewed, centering on the development of nondestructive testing and inspection techniques. Traditional (wood) as well as new materials susceptible to bonding are considered. Applications in construction and civil engineering, in aeronautics, and in the automobile industry are covered. The use of glues in mechanical constructions, in assembling cylindrical parts, and in metal-metal bonding are examined. Hybrid assembling and bonding of composite materials are included.

  16. Electron attachment, ionization and drift in c-C4F8

    Science.gov (United States)

    de Urquijo, J.; Basurto, E.

    2001-05-01

    The pulsed Townsend method has been used to measure the drift velocity ve and the density-normalized effective ionization coefficient (α-η)/N, (α and η are the ionization and attachment coefficients, respectively) in c-C4F8 over the density-normalized electric field strength E/N, 12 Td≤E/N≤43 Td and 330 Td≤E/N≤600 Td (1 Td = 10-17 V cm2), at pressures between 1 and 7.5 Torr (1 Torr = 133.3 Pa). For 12 Td≤E/N≤43 Td, the above parameters were found to be pressure independent, while for the range 330 Td≤E/N≤600 Td an inverse dependence of the above coefficients was found for gas pressures less than 2 Torr. Such dependence is believed to be due to the autodetachment of the originally formed, unstable parent negative ion c-C4F8-*. At low E/N, no previous data for ve or (α-η)/N were found for comparison with the present data. A critical field strength of E/Ncrit = 439.5 Td, for which α = η, was found to be in good agreement with previous data.

  17. A two-dimensional conjugated aromatic polymer via C-C coupling reaction

    Science.gov (United States)

    Liu, Wei; Luo, Xin; Bao, Yang; Liu, Yan Peng; Ning, Guo-Hong; Abdelwahab, Ibrahim; Li, Linjun; Nai, Chang Tai; Hu, Zhi Gang; Zhao, Dan; Liu, Bin; Quek, Su Ying; Loh, Kian Ping

    2017-06-01

    The fabrication of crystalline 2D conjugated polymers with well-defined repeating units and in-built porosity presents a significant challenge to synthetic chemists. Yet they present an appealing target because of their desirable physical and electronic properties. Here we report the preparation of a 2D conjugated aromatic polymer synthesized via C-C coupling reactions between tetrabromopolyaromatic monomers. Pre-arranged monomers in the bulk crystal undergo C-C coupling driven by endogenous solid-state polymerization to produce a crystalline polymer, which can be mechanically exfoliated into micrometre-sized lamellar sheets with a thickness of 1 nm. Isothermal gas-sorption measurements of the bulk material reveal a dominant pore size of ~0.6 nm, which indicates uniform open channels from the eclipsed stacking of the sheets. When employed as an organic anode in an ambient-temperature sodium cell, the material allows a fast charge/discharge of sodium ions, with impressive reversible capacity, rate capability and stability metrics.

  18. Would be the photon a composed particle? / Sobre a possibilidade da quantiza\\c{c}\\~ao dos fluxos de campo na radia\\c{c}\\~ao eletromagn\\'etica

    CERN Document Server

    Duarte, Celso de Araujo

    2013-01-01

    Here it is made a comparative analysis between the classical and the quantum expressions for the energy of electromagnetic radiation (ER). The comparison points to the possibility of the quantization of the magnetic and the electric field fluxes in the ER. ----- Apresenta-se uma an\\'alise comparativa entre as express\\~oes cl\\'assica e qu\\^antica para a energia da radia\\c{c}\\~ao eletromagn\\'etica (RE). A compara\\c{c}\\~ao nos aponta para a possibilidade de haver uma quantiza\\c{c}\\~ao dos fluxos dos campos magn\\'etico e el\\'etrico na RE.

  19. 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.

  20. Architectural Visualization of C/C++ Source Code for Program Comprehension

    Energy Technology Data Exchange (ETDEWEB)

    Panas, T; Epperly, T W; Quinlan, D; Saebjornsen, A; Vuduc, R

    2006-09-01

    Structural and behavioral visualization of large-scale legacy systems to aid program comprehension is still a major challenge. The challenge is even greater when applications are implemented in flexible and expressive languages such as C and C++. In this paper, we consider visualization of static and dynamic aspects of large-scale scientific C/C++ applications. For our investigation, we reuse and integrate specialized analysis and visualization tools. Furthermore, we present a novel layout algorithm that permits a compressive architectural view of a large-scale software system. Our layout is unique in that it allows traditional program visualizations, i.e., graph structures, to be seen in relation to the application's file structure.

  1. The 3D Lima\\c{c}on: Properties and Applications

    CERN Document Server

    Kreismann, Jakob; Sinzinger, Stefan

    2016-01-01

    We perform electromagnetic wave simulations of fully three-dimensional optical Lima\\c{c}on-microcavities, one basis for their future applications in microlasers and photonic devices. The analysis of the three-dimensional modes and far-fields reveals an increase of the quality factors as compared to the two-dimensional case. The structure of the far-field in the third dimension shows pronounced maxima in the emission directionality inclined to the resonator plane which may be exploited for coupling the resonator modes to the environment. This triggers ideas for technical applications, like the suggested sensor that can detect small changes in the environment based on changes in the emission profile.

  2. Dilepton analysis in the HADES spectrometer for C+C at 2 A GeV

    Science.gov (United States)

    Bielcik, J.; Agakishiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Djeridi, R.; Dohrmann, F.; Durán, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Garzón, J. A.; Gernhäuser, R.; Golubeva, M.; González-Daz, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kottel, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lehnert, J.; Maiolino, C.; Markert, J.; Metag, V.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Novotny, J.; Otwinowski, J.; Pachmayer, Y. C.; Pant, L. M.; Pechenov, V.; Pérez, T.; Pietraszko, J.; Pleskac, R.; Pospísil, V.; Przygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sánchez, M.; Sapienza, P.; Schmah, A.; Simon, R.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.

    2005-04-01

    The high-acceptance dielectron spectrometer (HADES) has become operational at GSI Darmstadt. The primary physics programme is to study in-medium changes of light vector mesons via their e+e- decays. The methods of dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 A GeV are presented. In the signal reconstruction, particularly important is the reduction of the huge combinatorial background arising from e+e- combinations of leptons from gamma conversion in materials with other leptons in the collision. The purity of the dilepton signal is determined by using GEANT simulations with the full HADES geometry and a realistic detector response.

  3. C-C Coupling Reactions between Benzofurazan Derivatives and 1,3-Diaminobenzenes

    Directory of Open Access Journals (Sweden)

    Gabriele Micheletti

    2017-04-01

    Full Text Available Aromatic substitution reactions between 1,3-diaminobenzene and chloronitrobenzofurazan derivatives have never been reported so far. The aim of the current study was to synthesize novel electron-donor and -acceptor architectures of interest in applied fields and to provide new insights on the nucleophilic behavior of 1,3-diaminobenzenes. The reaction of 1,3-dipiperidinyl-, 1,3-dimorpholinyl-, 1,3-dipyrrolidinyl-, or 1,3-dimethylamino-benzene with 7-chloro-4,6-dinitrobenzofuroxan or with a series of chloro-nitrobenzofurazans has been carried out in mild conditions. The partners reactivity has been investigated by monitoring the reaction course through 1H-NMR spectroscopy. The reaction occurred in a regioselective way, providing in good yields the novel C-C coupling compounds. Indications on the reactivity behavior for the studied nucleophiles have been relieved.

  4. Analytical modeling of the steady state ablation of a 3D C/C composite

    Energy Technology Data Exchange (ETDEWEB)

    Lachaud, J.; Aspa, Y.; Vignoles, G.L. [Universite Bordeaux 1, Laboratoire des Composites ThermoStructuraux (LCTS), 33 - Pessac (France); Aspa, Y. [Institut de Mecanique des Fluides de Toulouse (IMFT), 31 - Toulouse (France)

    2008-05-15

    Following an analysis of surface roughness features that develop on a 3D C/C composite during ablation, i.e. wall recession by oxidation and/or sublimation, a modeling strategy is set up in order to predict the composite behavior from that of its components. It relies on two changes of scale: (i) microscopic scale (fiber, matrix) to mesoscopic scale (bundle) and (ii) mesoscopic scale (bundle, matrix) to macroscopic scale (composite). The physical basis is a general model for receding surfaces under a gasification process coupled to mass transfer. At each scale, the 3D surface equation is analytically solved in steady state considering a 1-D mass transfer perpendicular to the overall surface. The models are validated by comparison to experimental data. (authors)

  5. Continuous Casting of Single Crystal Ingots by the O.C.C. Process

    Science.gov (United States)

    Ohno, A.

    1986-01-01

    To prevent the nucleation of crystals on the mold wall in the continuous casting of metals, a heated mold that maintained that temperature above the solidification temperature of the cast metal was used instead of the conventional cold mold. The cooling of the ingot was conducted outside of the mold. Heat was conducted axially along the ingot from the mold zone to the cooling zone. The principle of the O.C.C. (Ohno Continuous Casting) Process® was applied to the horizontal casting and vertical (upward) casting of wire and platelike ingots of Sn and Al. The ingots consisted of a completely unidirectionally solidified structure. It was possible to obtain a long single crystal ingot as a result of the growth competition of crystals.

  6. Overview of C/C-SiC Composite Development for the Orion Launch Abort System

    Science.gov (United States)

    Allen, Lee R.; Valentine, Peter G.; Schofield, Elizabeth S.; Beshears, Ronald D.; Coston, James E.

    2012-01-01

    Past and present efforts by the authors to further understanding of the ceramic matrix composite (CMC) material used in the valve components of the Orion Launch Abort System (LAS) Attitude Control Motor (ACM) will be presented. The LAS is designed to quickly lift the Orion Crew Exploration Vehicle (CEV) away from its launch vehicle in emergency abort scenarios. The ACM is a solid rocket motor which utilizes eight throttleable nozzles to maintain proper orientation of the CEV during abort operations. Launch abort systems have not been available for use by NASA on manned launches since the last Apollo ]Saturn launch in 1975. The CMC material, carbon-carbon/silicon-carbide (C/C-SiC), is manufactured by Fiber Materials, Inc. and consists of a rigid 4-directional carbon-fiber tow weave reinforced with a mixed carbon plus SiC matrix. Several valve and full system (8-valve) static motor tests have been conducted by the motor vendor. The culmination of these tests was the successful flight test of the Orion LAS Pad Abort One (PA ]1) vehicle on May 6, 2010. Due to the fast pace of the LAS development program, NASA Marshall Space Flight Center assisted the LAS community by performing a series of material and component evaluations using fired hardware from valve and full ]system development motor tests, and from the PA-1 flight ACM motor. Information will be presented on the structure of the C/C-SiC material, as well as the efficacy of various non ]destructive evaluation (NDE) techniques, including but not limited to: radiography, computed tomography, nanofocus computed tomography, and X-ray transmission microscopy. Examinations of the microstructure of the material via scanning electron microscopy and energy dispersive spectroscopy will also be discussed. The findings resulting from the subject effort are assisting the LAS Project in risk assessments and in possible modifications to the final ACM operational design.

  7. The United States Congress Can Tax Interest on State Bonds: "South Carolina v. Baker".

    Science.gov (United States)

    Wyatt, Terrence M.; Sparkman, William E.

    1988-01-01

    The United States Supreme Court has made it clear that Congress can tax state bonds. All public purpose bonds issued by school districts must be issued in a registered format in order to continue their tax-exempt status. (MLF)

  8. Complexes between hypohalous acids and phosphine derivatives. Pnicogen bond versus halogen bond versus hydrogen bond.

    Science.gov (United States)

    Li, Qingzhong; Zhu, Hongjie; Zhuo, Hongying; Yang, Xin; Li, Wenzuo; Cheng, Jianbo

    2014-11-11

    The complexes of HOBr:PH2Y (Y=H, F, Cl, Br, CH3, NH2, OH, and NO2), HOCl:PH2F, and HOI:PH2F have been investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Four types of structures (1, 2, 3a, and 3b) were observed for these complexes. 1 is stabilized by an O⋯P pnicogen bond, 2 by a P⋯X halogen bond, 3a by a H⋯P hydrogen bond and a P⋯X pnicogen bond, and 3b by H⋯P and H⋯Br hydrogen bonds. Their relative stability is related to the halogen X of HOX and the substituent Y of PH2Y. These structures can compete with interaction energy of -10.22∼-29.40 kJ/mol. The HO stretch vibration shows a small red shift in 1, a small irregular shift in 2, but a prominent red shift in 3a and 3b. The XO stretch vibration exhibits a smaller red shift in 1, a larger red shift in 2, but an insignificant blue shift in 3a and 3b. The PY stretch vibration displays a red shift in 1 but a blue shift in 2, 3a, and 3b. The formation mechanism, stability, and properties of these structures have been analyzed with molecular electrostatic potentials, orbital interactions, and non-covalent interaction index. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Chemical bonding technology

    Science.gov (United States)

    Plueddemann, E.

    1986-01-01

    Primers employed in bonding together the various material interfaces in a photovoltaic module are being developed. The approach develops interfacial adhesion by generating actual chemical bonds between the various materials bonded together. The current status of the program is described along with the progress toward developing two general purpose primers for ethylene vinyl acetate (EVA), one for glass and metals, and another for plastic films.

  10. Hydrogen bonding penalty upon ligand binding.

    Directory of Open Access Journals (Sweden)

    Hongtao Zhao

    Full Text Available Ligand binding involves breakage of hydrogen bonds with water molecules and formation of new hydrogen bonds between protein and ligand. In this work, the change of hydrogen bonding energy in the binding process, namely hydrogen bonding penalty, is evaluated with a new method. The hydrogen bonding penalty can not only be used to filter unrealistic poses in docking, but also improve the accuracy of binding energy calculation. A new model integrated with hydrogen bonding penalty for free energy calculation gives a root mean square error of 0.7 kcal/mol on 74 inhibitors in the training set and of 1.1 kcal/mol on 64 inhibitors in the test set. Moreover, an application of hydrogen bonding penalty into a high throughput docking campaign for EphB4 inhibitors is presented, and remarkably, three novel scaffolds are discovered out of seven tested. The binding affinity and ligand efficiency of the most potent compound is about 300 nM and 0.35 kcal/mol per non-hydrogen atom, respectively.

  11. Mechanical and Chemical Characterization of a TiC/C System Synthesized Using a Focus Plasma Arc

    National Research Council Canada - National Science Library

    Mahmoodian, Reza; Hamdi, M; Hassan, M A; Akbari, Abolghasem

    2015-01-01

    Titanium carbide-graphite (TiC/C) composite was successfully synthesized from Ti and C starting elemental powders using self-propagating high-temperature synthesis technique in an ultra-high plasma inert medium in a single stage...

  12. Prediction of cutting forces in ball-end milling of 2.5D C/C composites

    Directory of Open Access Journals (Sweden)

    Shan Chenwei

    2016-06-01

    Full Text Available Machining of carbon/carbon (C/C composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, burr, poor surface quality and rapid wear of cutters. Accurate and fast prediction of cutting forces is important for milling C/C composite materials with high quality. This paper presents an alternative cutting force model involving the influences of the directions of fiber. Based on the calculated and experimental results, the cutting forces’ coefficients of 2.5D C/C composites are evaluated using multiple linear regression method. Verification experiment has been carried out through a group of orthogonal tests. Results indicate that the proposed model is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.

  13. 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...

  14. Direct conversion of cellulose using carbon monoxide and water on a Pt-Mo2C/C catalyst

    KAUST Repository

    Li, Jing

    2014-01-01

    CO and H2O were employed as the hydrogen source for cellulose conversion to polyols. Pt-Mo2C/C tandem catalyst with the Pt-Mo 2C domain responsible for H2 and/or H production and the Pt-C domain for cellulose conversion was fabricated. Considerable polyols were obtained over this tandem Pt-Mo2C/C catalyst. This journal is © 2014 The Royal Society of Chemistry.

  15. Electrochemical Polymerization of Iron(III) Polypyridyl Complexes through C-C Coupling of Redox Non-innocent Phenolato Ligands.

    Science.gov (United States)

    Unjaroen, Duenpen; Swart, Marcel; Browne, Wesley R

    2017-01-03

    Phenolato moieties impart redox flexibility to metal complexes due their accessible (oxidative) redox chemistry and have been proposed as functional ligand moieties in redox non-innocent ligand based transition metal catalysis. Here, the electro- and spectroelectrochemistry of phenolato based μ-oxo-diiron(III) complexes [(L 1 )Fe(μ-O)Fe(L 1 )] 2+ (1) and [(L 2 )Fe(μ-O)Fe(L 2 )] 2+ (2), where L 1 = 2-(((di(pyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenol and L 2 = 3,5-di-tert-butyl-2-(((di(pyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenol, is described. The electrochemical oxidation of 1 in dichloromethane results in aryl C-C coupling of phenoxyl radical ligand moieties to form tetra nuclear complexes, which undergo subsequent oxidation to form iron(III) phenolato based polymers (poly-1). The coupling is blocked by placing tert-butyl groups at para and ortho positions of phenol units (i.e., 2). Poly-1 shows two fully reversible redox processes in monomer free solution. Assignment of species observed during the electrochemical and chemical {(NH 4 ) 2 [Ce IV (NO 3 ) 6 ]} oxidation of 1 in acetonitrile is made by comparison with the UV-vis-NIR absorption and resonance micro-Raman spectroelectrochemistry of poly-1, and by DFT calculations, which confirms that oxidative coupling occurs in acetonitrile also. However, in contrast to that observed in dichloromethane, in acetonitrile, the oligomers formed are degraded in terms of a loss of the Fe(III)-O-Fe(III) bridge by protonation. The oxidative redox behavior of 1 and 2 is, therefore, dominated by the formation and reactivity of Fe(III) bound phenoxyl radicals, which considerably holds implications in regard to the design of phenolato based complexes for oxidation catalysis.

  16. High Levels of Chemokine C-C Motif Ligand 20 in Human Milk and Its Production by Oral Keratinocytes.

    Science.gov (United States)

    Lourenço, Alan G; Komesu, Marilena C; Duarte, Geraldo; Del Ciampo, Luiz A; Mussi-Pinhata, Marisa M; Yamamoto, Aparecida Y

    2017-03-01

    Chemokine C-C motif ligand 20 (CCL20) is implicated in the formation and function of mucosal lymphoid tissues. Although CCL20 is secreted by many normal human tissues, no studies have evaluated the presence of CCL20 in human milk or its production by oral keratinocytes stimulated by human milk. To evaluate the presence of CCL20 in breast milk and verify CCL20 secretion in vitro by oral keratinocytes stimulated with human and bovine milk, as well as its possible association with breast milk lactoferrin levels. The levels of CCL20 and lactoferrin were measured by enzyme-linked immunosorbent assay in human milk at three different stages of maturation from 74 healthy breastfeeding mothers. In vitro, oral keratinocytes were stimulated with human and bovine milk, and CCL20 was measured in their supernatant. High concentrations of CCL20 were detected in the human breast milk samples obtained during the first week (1,777.07 pg/mL) and second week postpartum (1,523.44 pg/mL), with a significantly low concentration in samples at 3-6 weeks postpartum (238.42 pg/mL; p milk at different weeks postpartum stimulated higher CCL20 secretion by oral keratinocytes compared with bovine milk (p milk lactoferrin concentration. CCl20 is present at high levels in human milk, predominantly in the first and second week postpartum, but at significantly lower levels at 3-6 weeks postpartum. Human milk is capable of stimulating CCL20 secretion by oral keratinocytes, and this induction had no association with breast milk lactoferrin concentration.

  17. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of nickel carbide (NiC) and its cation (NiC+).

    Science.gov (United States)

    Lau, Kai-Chung; Chang, Yih Chung; Shi, Xiaoyu; Ng, C Y

    2010-09-21

    The ionization energy (IE) of NiC and the 0 K bond dissociation energies (D(0)) and heats of formation at 0 K (ΔH(o)(f0)) and 298 K (ΔH(o)(f298)) for NiC and NiC(+) are predicted by the wavefunction based CCSDTQ(Full)/CBS approach and the multireference configuration interaction (MRCI) method with Davidson correction (MRCI+Q). The CCSDTQ(Full)/CBS calculations presented here involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation, core-valence electronic (CV), spin-orbit coupling (SO), and scalar relativistic effect (SR) corrections. The present calculations provide the correct symmetry predictions for the ground states of NiC and NiC(+) to be (1)∑(+) and (2)∑(+), respectively. The CCSDTQ(Full)/CBS IE(NiC)=8.356 eV is found to compare favorably with the experimental IE value of 8.372 05±0.000 06 eV. The predicted IE(NiC) value at the MRCI+Q/cc-pwCV5Z level, including the ZPVE, SO, and SR effects is 8.00 eV, which is 0.37 eV lower than the experimental value. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ(Full)/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC and NiC. Furthermore, the CCSDTQ(Full)/CBS calculations give the prediction of D(0)(Ni-C)-D(0)(Ni(+)-C)=0.688 eV, which is also consistent with the experimental determination of 0.732 21±0.000 06 eV, whereas the MRCI+Q calculations (with relativistic and CV effects) predict a significantly lower value of 0.39 eV for D(0)(Ni-C)-D(0)(Ni(+)-C). The analysis of the correction terms shows that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of NiC/NiC(+). For the experimental D(0) and ΔH(o)(f0) values of

  18. Hydrogen Bond Nanoscale Networks Showing Switchable Transport Performance

    Science.gov (United States)

    Long, Yong; Hui, Jun-Feng; Wang, Peng-Peng; Xiang, Guo-Lei; Xu, Biao; Hu, Shi; Zhu, Wan-Cheng; Lü, Xing-Qiang; Zhuang, Jing; Wang, Xun

    2012-08-01

    Hydrogen bond is a typical noncovalent bond with its strength only one-tenth of a general covalent bond. Because of its easiness to fracture and re-formation, materials based on hydrogen bonds can enable a reversible behavior in their assembly and other properties, which supplies advantages in fabrication and recyclability. In this paper, hydrogen bond nanoscale networks have been utilized to separate water and oil in macroscale. This is realized upon using nanowire macro-membranes with pore sizes ~tens of nanometers, which can form hydrogen bonds with the water molecules on the surfaces. It is also found that the gradual replacement of the water by ethanol molecules can endow this film tunable transport properties. It is proposed that a hydrogen bond network in the membrane is responsible for this switching effect. Significant application potential is demonstrated by the successful separation of oil and water, especially in the emulsion forms.

  19. 27 CFR 24.147 - Operations bond or unit bond.

    Science.gov (United States)

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Operations bond or unit... § 24.147 Operations bond or unit bond. Notwithstanding the provisions of § 24.146, each person... amended, give an operations bond or unit bond in accordance with the applicable provisions of 27 CFR part...

  20. Structural, intramolecular hydrogen bonding and vibrational studies ...

    Indian Academy of Sciences (India)

    An extensive theoretical study on the molecular structure and vibrational analysis of 3-amino-4- methoxy benzamide (3A4MBA) was undertaken using density functional theoretical (DFT) method. The possibility of formation of intramolecular hydrogen bonding was identified from structural parameter analysis and confirmed ...

  1. 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

  2. Mother-Child Bonding.

    Science.gov (United States)

    Pearce, Joseph Chilton

    1994-01-01

    Examines the nature of mother-child bonding from the prenatal stage through early infancy, discussing how the mother's actions, even before birth, stimulate her child's senses. Explains the crucial role that physical contact, breastfeeding, and visual stimuli have on mother-child bonding in human and animal newborns. (MDM)

  3. Chemical Bonds I

    Science.gov (United States)

    Sanderson, R. T.

    1972-01-01

    Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

  4. Halogen-bond and hydrogen-bond interactions between three benzene derivatives and dimethyl sulphoxide.

    Science.gov (United States)

    Zheng, Yan-Zhen; Wang, Nan-Nan; Zhou, Yu; Yu, Zhi-Wu

    2014-04-21

    Halogen-bonds, like hydrogen-bonds, are a kind of noncovalent interaction and play an important role in diverse fields including chemistry, biology and crystal engineering. In this work, a comparative study was carried out to examine the halogen/hydrogen-bonding interactions between three fluoro-benzene derivatives and dimethyl sulphoxide (DMSO). A number of conclusions were obtained by using attenuated total reflection infrared spectroscopy (ATR-IR), nuclear magnetic resonance (NMR) and ab initio calculations. Electrostatic surface potential, geometry, energy, vibrational frequency, intensity and the natural population analysis (NPA) of the monomers and complexes are studied at the MP2 level of theory with the aug-cc-pVDZ basis set. First, the interaction strength decreases in the order C6F5H-DMSO ∼ ClC6F4H-DMSO > C6F5Cl-DMSO, implying that the hydrogen-bond is stronger than the halogen-bond in the systems and, when interacting with ClC6F4H, DMSO favors the formation of a hydrogen-bond rather than a halogen-bond. Second, attractive energy dependences on 1/r(3.3) and 1/r(3.1) were established for the hydrogen-bond and halogen-bond, respectively. Third, upon the formation of a hydrogen-bond and halogen-bond, there is charge transfer from DMSO to the hydrogen-bond and halogen-bond donor. The back-group CH3 was found to contribute positively to the stabilization of the complexes. Fourth, an isosbestic point was detected in the ν(C-Cl) absorption band in the C6F5Cl-DMSO-d6 system, indicating that there exist only two dominating forms of C6F5Cl in binary mixtures; the non-complexed and halogen-bond-complexed forms. The presence of stable complexes in C6F5H-DMSO and ClC6F4H-DMSO systems are evidenced by the appearance of new peaks with fixed positions.

  5. Crack propagation studies and bond coat properties in thermal ...

    Indian Academy of Sciences (India)

    Unknown

    high temperatures with the formation of an intermediate ... The ramp rate for loading was maintained as 2⋅5 N s–1 and the deflection ... The strain energy released at the interface of the ceramic coating and the bond coat and within the bond coat are shown in table. 2. From the load deflection curves of the bent composite.

  6. Corporate Bonds in Denmark

    DEFF Research Database (Denmark)

    Tell, Michael

    2015-01-01

    to think in alternative ways such as issuing corporate bonds. A market for corporate bonds exists in countries such as Norway, Germany, France, the United Kingdom and the United States, while Denmark is still behind in this trend. Some large Danish corporations have instead used foreign corporate bonds...... markets. However, NASDAQ OMX has introduced the First North Bond Market in December 2012 and new regulatory framework came into place in 2014, which may contribute to a Danish based corporate bond market. The purpose of this article is to present the regulatory changes in Denmark in relation to corporate......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...

  7. 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...

  8. Effect of moist bonding on composite/enamel bond strength.

    Science.gov (United States)

    Moll, Karlheinz; Gärtner, Thomas; Haller, Bernd

    2002-04-01

    To evaluate the effect of moist bonding on shear bond strength of resin-based composite to enamel using different adhesive systems. Six restorative systems were selected for this study: OptiBond FL/Prodigy, Solid Bond/Charisma F, Syntac Single Component/Tetric, Prime&Bond 2.1/Spectrum TPH, Single Bond/Z100, Etch&Prime 3.0/Degufill Mineral. Flat enamel surfaces were ground on the buccal and lingual aspects of 80 extracted human molars. OptiBond FL and Solid Bond were tested with and without primer application. Prior to application of the adhesives, the enamel was either carefully dried with compressed air (dry bonding) or blot dried with a cotton pellet (moist bonding). Shear bond strength was determined with a universal testing machine after 24-hour storage in 0.9% NaCl at 37 degrees C. Moist bonding did not significantly affect shear bond strength to enamel of the adhesives tested except for Solid Bond without primer application. Primer contamination of the etched enamel did not significantly influence bond strength, neither in the dry bonding nor in the moist bonding group. Of all adhesives tested in both groups, the highest mean bond strength was observed with Prime&Bond 2.1 and the lowest with Etch&Prime 3.0.

  9. Microstructure and Mechanical Properties of Two Kinds of Dual-matrix C/C Composites

    Directory of Open Access Journals (Sweden)

    LIU Hao

    2017-08-01

    Full Text Available The microstructure and mechanical properties of two kinds of dual-matrix C/C composites were studied by polarized light microscopy (PLM, scanning electron microscopy (SEM and mechanical properties tests techniques respectively. PLM results indicate that the matrix carbon exhibits the smooth laminar structure of the pyrocarbon, the isotropic, mosaics and flow domains of the pitch carbon. The TEM results show the normal pitch carbon is the grape structure; the mesophase pitch carbon is the lamellar banded structure. Materials with multi-interface structure can improve the flexural strength and fracture toughness, the load-displacement curve shows the load drop is decreased for step type, the composites show a pseudo-plastic fracture characteristics. The flexural strengths of the material A and material B are 206.68MPa and 243.66MPa, the fracture toughness are 8.06MPa·m1/2 and 9.66MPa·m1/2, respectively. The flexural strength and fracture toughness of material B are both superior than that of material A.

  10. Relationships Between Metformin, Paraoxonase-1 and the Chemokine (C-C Motif) Ligand 2.

    Science.gov (United States)

    Camps, Jordi; Hernandez-Aguilera, Anna; Garcia-Heredia, Anabel; Cabre, Noemi; Luciano-Mateo, Fedra; Arenas, Meritxell; Joven, Jorge

    2016-01-01

    Metformin is a biguanide used in the treatment of type 2 diabetes mellitus and obesity. The main mechanism of action is to decrease the intestinal glucose absorption and the hepatic glucose production, however, it does not influence insulin secretion. Metformin also increases the affinity of the insulin receptor, reduces high insulin levels and improves insulin resistance. Additionally, it promotes weight loss. Metformin is a pleiotropic compound but acts, largely, by activating 5 adenosine monophosphate (AMP)-activated protein kinase (AMPK). Data suggest that the therapeutic effects of this compound are mediated, at least in part, through an upregulation of paraoxonase-1 (PON1) synthesis. PON1 is a thiolactonase that degrades lipid peroxides, and downregulates the chemokine (C-C motif) ligand 2 (CCL2) which is a pro-inflammatory chemokine that stimulates the migration of monocytes to areas of inflammation where they differentiate into macrophages. However, the prescription of metformin in patients with liver disease is controversial since, in some cases, this drug causes worsening of liver function. Patients with chronic liver disease have decreased hepatic PON1 activity. A study in mice deficient in PON1 showed that in this experimental model, metformin administration increased the severity of steatosis, increased CCL2 expression, did not activate AMPK, and increased the expression of the apoptosis marker caspase-9. These results suggest that PON1 is essential for the successful activation of AMPK in the liver, and for metformin to demonstrate its therapeutic function.

  11. Migrating C/C++ Software to Mobile Platforms in the ADM Context

    Directory of Open Access Journals (Sweden)

    Liliana Martinez

    2017-03-01

    Full Text Available Software technology is constantly evolving and therefore the development of applications requires adapting software components and applications in order to be aligned to new paradigms such as Pervasive Computing, Cloud Computing and Internet of Things. In particular, many desktop software components need to be migrated to mobile technologies. This migration faces many challenges due to the proliferation of different mobile platforms. Developers usually make applications tailored for each type of device expending time and effort. As a result, new programming languages are emerging to integrate the native behaviors of the different platforms targeted in development projects. In this direction, the Haxe language allows writing mobile applications that target all major mobile platforms. Novel technical frameworks for information integration and tool interoperability such as Architecture-Driven Modernization (ADM proposed by the Object Management Group (OMG can help to manage a huge diversity of mobile technologies. The Architecture-Driven Modernization Task Force (ADMTF was formed to create specifications and promote industry consensus on the modernization of existing applications. In this work, we propose a migration process from C/C++ software to different mobile platforms that integrates ADM standards with Haxe. We exemplify the different steps of the process with a simple case study, the migration of “the Set of Mandelbrot” C++ application. The proposal was validated in Eclipse Modeling Framework considering that some of its tools and run-time environments are aligned with ADM standards.

  12. Te(II)/Te(IV) Mediated C-N Bond Formation on 2,5-Diphenyltellurophene and a Reassignment of the Product from the Reaction of PhI(OAc)2 with 2 TMS-OTf.

    Science.gov (United States)

    Aprile, Antonino; Iversen, Kalon J; Wilson, David J D; Dutton, Jason L

    2015-05-18

    We report a novel C-H to C-N bond metathesis at the 3-position of 1,2-diphenyltellurophene via oxidation of the Te(II) center to Te(IV) using the I(III) oxidant [PhI(4-DMAP)2](2+). Spontaneous reduction of a transient Te(IV) coordination compound to Te(II) generates an electrophilic equivalent of 4-DMAP that substitutes at a C-H bond at the 3-position of the tellurophene. Theoretical and synthetic reaction pathway studies confirm that a Te(IV) coordination complex with 4-DMAP is an intermediate. In the course of these pathway studies, it was also found that the identity of the I(III) oxidant generated from PhI(OAc)2 and 2 TMS-OTf is PhI(OAc)(OTf) and not PhI(OTf)2, as had been previously thought.

  13. Effectiveness of several solutions to prevent the formation of precipitate due to the interaction between sodium hypochlorite and chlorhexidine and its effect on bond strength of an epoxy-based sealer.

    Science.gov (United States)

    Magro, M G; Kuga, M C; Aranda-Garcia, A J; Victorino, K R; Chávez-Andrade, G M; Faria, G; Keine, K C; Só, M V R

    2015-05-01

    To evaluate the effectiveness of isopropyl alcohol, saline or distilled water to prevent the precipitate formed between sodium hypochlorite (NaOCl) and chlorhexidine (CHX) and its effect on the bond strength of an epoxy-based sealer in radicular dentine. The root canals of 50 extracted human canines (n = 10) were instrumented. In G1, root canals were irrigated with 17% EDTA and 2.5% NaOCl; G2, as G1, except that 2% CHX was used as the final irrigant. In the other groups, intermediate flushes with isopropyl alcohol (G3), saline (G4) or distilled water (G5) were used between NaOCl and CHX. The specimens were submitted to SEM analysis to evaluate the presence of debris and smear layer, in the apical and cervical segments. In sequence, fifty extracted human canines were distributed into five groups (n = 10), similar to the SEM study. After root filling, the roots were sectioned transversally to obtain dentine slices, in the cervical, middle and apical thirds. The root filling was submitted to a push-out bond strength test using an electromechanical testing machine. Statistical analysis was performed using Kruskal-Wallis and Dunn's tests (α = 5%). All groups had similar amounts of residue precipitated on the canal walls (P > 0.05). The push-out bond strength values were similar for all groups, independently of the root third evaluated (P > 0.05). Isopropyl alcohol, saline and distilled water failed to prevent the precipitation of residues on canal walls following the use of NaOCl and CHX. The residues did not interfere with the push-out bond strength of the root filling. © 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd.

  14. Bipodal surface organometallic complexes with surface N-donor ligands and application to the catalytic cleavage of C-H and C-C bonds in n -Butane

    KAUST Repository

    Bendjeriou-Sedjerari, Anissa

    2013-11-27

    We present a new generation of "true vicinal" functions well-distributed on the inner surface of SBA15: [(Sî - Si-NH 2)(≡Si-OH)] (1) and [(≡Si-NH2)2] (2). From these amine-modified SBA15s, two new well-defined surface organometallic species [(≡Si-NH-)(≡Si-O-)]Zr(CH2tBu) 2 (3) and [(≡Si-NH-)2]Zr(CH2tBu) 2 (4) have been obtained by reaction with Zr(CH2tBu) 4. The surfaces were characterized with 2D multiple-quantum 1H-1H NMR and infrared spectroscopies. Energy-filtered transmission electron microscopy (EFTEM), mass balance, and elemental analysis unambiguously proved that Zr(CH2tBu)4 reacts with these vicinal amine-modified surfaces to give mainly bipodal bis(neopentyl)zirconium complexes (3) and (4), uniformly distributed in the channels of SBA15. (3) and (4) react with hydrogen to give the homologous hydrides (5) and (6). Hydrogenolysis of n-butane catalyzed by these hydrides was carried out at low temperature (100 C) and low pressure (1 atm). While (6) exhibits a bis(silylamido)zirconium bishydride, [(≡Si-NH-)2]Zr(H) 2 (6a) (60%), and a bis(silylamido)silyloxozirconium monohydride, [(≡Si-NH-)2(≡Si-O-)]ZrH (6b) (40%), (5) displays a new surface organometallic complex characterized by an 1H NMR signal at 14.46 ppm. The latter is assigned to a (silylimido)(silyloxo)zirconium monohydride, [(≡Si-Nî)(≡Si-O-)]ZrH (5b) (30%), coexistent with a (silylamido)(silyloxo)zirconium bishydride, [(≡Si-NH-)(≡Si-O-)] Zr(H)2 (5a) (45%), and a silylamidobis(silyloxo)zirconium monohydride, [(≡Si-NH-)(≡Si-O-)2]ZrH (5c) (25%). Surprisingly, nitrogen surface ligands possess catalytic properties already encountered with silicon oxide surfaces, but interestingly, catalyst (5) with chelating [N,O] shows better activity than (6) with chelating [N,N]. © 2013 American Chemical Society.

  15. Post-synthetic modification of metal-organic framework thin films using click chemistry: the importance of strained C-C triple bonds.

    Science.gov (United States)

    Wang, Zhengbang; Liu, Jinxuan; Arslan, Hasan K; Grosjean, Sylvain; Hagendorn, Tobias; Gliemann, Hartmut; Bräse, Stefan; Wöll, Christof

    2013-12-23

    In this work, we demonstrate that strain-promoted azide-alkyne cycloaddition (SPAAC) yields virtually complete conversion in the context of the post-synthetic modification (PSM) of metal-organic frameworks (MOFs). We use surface-anchored MOF (SURMOF) thin films, [Zn2(N3-bdc)2(dabco)], grown on modified Au substrates using liquid-phase epitaxy (LPE) as a model system to first show that, with standard click chemistry, presently, the most popular method for rendering additional functionality to MOFs via PSM, quantitative conversion yields, cannot be reached. In addition, it is virtually impossible to avoid contaminations of the product by the cytotoxic Cu(I) ions used as a catalyst, a substantial problem for applications in life sciences. Both problems could be overcome by SPAAC, where a metal catalyst is not needed. After optimization of reaction conditions, conversion yields of nearly 100% could be achieved. The consequences of these results for various applications of PSM-modified SURMOFs in the fields of membranes, optical coatings, catalysis, selective gas separation, and chemical sensing are briefly discussed.

  16. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths.

    Science.gov (United States)

    Chen, Liang; Suh, Byoung In; Brown, Douglas; Chen, Xinqi

    2012-04-01

    To investigate changes of zirconia surface hydrophobicity (contact angle) following the application of a zirconia primer as a function of post-priming storage period and after exposure to harsh conditions and to analyze whether there is a chemical bond formation between a zirconia primer and zirconia ceramics. Zirconia ceramics were treated with a zirconia primer (ZPrime Plus, Bisco), left undisturbed for specific times (reaction time), followed by ultrasonic cleansing in ethanol or acetone bath, and then contact angles were measured (n = 10). The primed zirconia ceramics were also subjected to harsh conditions (strong acid or boiling water) prior to contact angle testing. The chemical change of zirconia surface with and without being primed was analyzed by time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Shear bond strength (Ultradent jig method) on zirconia surface was tested using different zirconia primers. The data were statistically analyzed using one-way ANOVA and Tukey's post-hoc test with 95% confidence level. The contact angle on the primed zirconia surface (from 56 degrees to 72 degrees for different primers) was significantly higher than that of unprimed zirconia (15 degrees) (P reaction time increased within 5 minutes (increased from 58 degree at 10 seconds, to 72 degrees at 5 minutes). Exposure to harsh conditions (i.e. strong acid or boiling water) exhibited no significant change in contact angle values (P > 0.05). The TOF-SIMS detected fragmentations with mass of 549 and 411, indicating that a chemical group of phosphate monomer(P)-O-Zr existed, which indicated a chemical bond was formed between zirconia and ZPrime Plus. All of the zirconia primers tested in the study significantly improved zirconia bond strengths (4 MPa for unprimed zirconia, and 17-23 MPa for primed zirconia, P < 0.05).

  17. Indirect bonding technique in orthodontics

    National Research Council Canada - National Science Library

    Kübra Yıldırım; Banu Sağlam Aydınatay

    2016-01-01

    ‘Direct Bonding Technique’ which allows the fixed orthodontic appliances to be directly bonded to teeth without using bands decreased the clinic time for bracket bonding and increased esthetics and oral hygiene during orthodontic treatment...

  18. 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....

  19. Effects of chemokine (C-C motif) ligand 1 on microglial function.

    Science.gov (United States)

    Akimoto, Nozomi; Ifuku, Masataka; Mori, Yuki; Noda, Mami

    2013-07-05

    Microglia, which constitute the resident macrophages of the central nervous system (CNS), are generally considered as the primary immune cells in the brain and spinal cord. Microglial cells respond to various factors which are produced following nerve injury of multiple aetiologies and contribute to the development of neuronal disease. Chemokine (C-C motif) ligand 1 (CCL-1), a well-characterized chemokine secreted by activated T cells, has been shown to play an important role in neuropathic pain induced by nerve injury and is also produced in various cell types in the CNS, especially in dorsal root ganglia (DRG). However, the role of CCL-1 in the CNS and the effects on microglia remains unclear. Here we showed the multiple effects of CCL-1 on microglia. We first showed that CCR-8, a specific receptor for CCL-1, was expressed on primary cultured microglia, as well as on astrocytes and neurons, and was upregulated in the presence of CCL-1. CCL-1 at concentration of 1 ng/ml induced chemotaxis, increased motility at a higher concentration (100 ng/ml), and increased proliferation and phagocytosis of cultured microglia. CCL-1 also activated microglia morphologically, promoted mRNA levels for brain-derived neurotrophic factor (BDNF) and IL-6, and increased the release of nitrite from microglia. These indicate that CCL-1 has a role as a mediator in neuron-glia interaction, which may contribute to the development of neurological diseases, especially in neuropathic pain. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

  20. C-C Motif Chemokine Receptor 9 Exacerbates Pressure Overload-Induced Cardiac Hypertrophy and Dysfunction.

    Science.gov (United States)

    Xu, Zhengxi; Mei, Fanghua; Liu, Hanning; Sun, Cheng; Zheng, Zhe

    2016-05-04

    Maladaptive cardiac hypertrophy is a major risk factor for heart failure, which is the leading cause of death worldwide. C-C motif chemokine receptor 9 (CCR9), a subfamily of the G protein-coupled receptor supergene family, has been highlighted as an immunologic regulator in the development and homing of immune cells and in immune-related diseases. Recently, CCR9 was found to be involved in the pathogenesis of other diseases such as cardiovascular diseases; however, the effects that CCR9 exerts in cardiac hypertrophy remain elusive. We observed significantly increased CCR9 protein levels in failing human hearts and in a mouse or cardiomyocyte hypertrophy model. In loss- and gain-of-function experiments, we found that pressure overload-induced hypertrophy was greatly attenuated by CCR9 deficiency in cardiac-specific CCR9 knockout mice, whereas CCR9 overexpression in cardiac-specific transgenic mice strikingly enhanced cardiac hypertrophy. The prohypertrophic effects of CCR9 were also tested in vitro, and a similar phenomenon was observed. Consequently, we identified a causal role for CCR9 in pathological cardiac hypertrophy. Mechanistically, we revealed a lack of difference in the expression levels of mitogen-activated protein kinases between groups, whereas the phosphorylation of AKT/protein kinase B and downstream effectors significantly decreased in CCR9 knockout mice and increased in CCR9 transgenic mice after aortic binding surgery. The prohypertrophic effects of CCR9 were not attributable to the mitogen-activated protein kinase signaling pathway but rather to the AKT-mammalian target of rapamycin-glycogen synthase kinase 3β signaling cascade. © 2016 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.

  1. C-C chemokine receptor-7 mediated endocytosis of antibody cargoes into intact cells

    Directory of Open Access Journals (Sweden)

    Xavier eCharest-Morin

    2013-09-01

    Full Text Available The C-C chemokine receptor-7 (CCR7 is a G protein coupled receptor that has a role in leukocyte homing, but that is also expressed in aggressive tumor cells. Preclinical research supports that CCR7 is a valid target in oncology. In view of the increasing availability of therapeutic monoclonal antibodies that carry cytotoxic cargoes, we studied the feasibility of forcing intact cells to internalize known monoclonal antibodies by exploiting the cycle of endocytosis and recycling triggered by the CCR7 agonist CCL19. Firstly, an anti-CCR7 antibody (CD197; clone 150503 labeled surface recombinant CCR7 expressed in intact HEK 293a cells and the fluorescent antibody was internalized following CCL19 treatment. Secondly, a recombinant myc-tagged CCL19 construction was exploited along the anti-myc monoclonal antibody 4A6. The myc-tagged ligand was produced as a conditioned medium of transfected HEK 293a cells that contained the equivalent of 430 ng/ml of immunoreactive CCL19 (average value, ELISA determination. CCL19-myc, but not authentic CCL19, carried the fluorophore-labeled antibody 4A6 into other recipient cells that expressed recombinant CCR7 (microscopy, cytofluorometry. The immune complexes were apparent in endosomal structures, colocalized well with the small GTPase Rab5 and progressed toward Rab7-positive endosomes. A dominant negative form of Rab5 (GDP-locked inhibited this endocytosis. Further, endosomes in CCL19-myc- or CCL19-stimulated cells were positive for β-arrestin2, but rarely for β-arrestin1. Following treatment with CCL19-myc and the 4A6 antibody, the melanoma cell line A375 that expresses endogenous CCR7 was specifically stained using a secondary peroxidase-conjugated antibody. Agonist-stimulated CCR7 can transport antibody-based cargoes, with possible therapeutic applications in oncology.

  2. Safe and Liquid Mortgage Bonds

    DEFF Research Database (Denmark)

    Dick-Nielsen, Jens; Gyntelberg, Jacob; Lund, Jesper

    eliminates credit risk from the investor's perspective. Similar to other safe bonds, funding liquidity becomes the main driver of mortgage bond liquidity and this creates commonality in liquidity across markets and countries. These findings have implications for how to design a robust mortgage bond system......This paper shows that strict match pass-through funding of covered bonds provides safe and liquid mortgage bonds. Despite a 30% drop in house prices during the 2008 global crisis Danish mortgage bonds remained as liquid as most European government bonds. The Danish pass-through system effectively...... and for the treatment of covered bonds in capital regulation....

  3. Metal-Ion- and Hydrogen-Bond-Mediated Interstellar Prebiotic Chemistry: The First Step in the Formose Reaction.

    Science.gov (United States)

    Thripati, Sorakayala; Ramabhadran, Raghunath O

    2017-11-16

    The formose reaction, which offers a feasible chemical pathway for the prebiotic synthesis of sugars, is a well-studied reaction for over two hundred and 50 years. Yet huge knowledge gaps exist even in the very first step of the formose reaction. In this work, we provide a new and otherwise unintuitive reaction pathway for the gas-phase conversion of formaldehyde to glycolaldehyde (the first step in the formose reaction) occurring in the interstellar medium (ISM). Employing electronic structure calculations (CCSD(T) and DFT methods), we exhaustively probe the role of various metal ions and small molecules detected in the ISM to propose a new mechanism wherein metal-oxygen interactions and hydrogen bonds cooperatively facilitate an otherwise implausible chemical reaction. The reactions involving Mg2+ are throughout found to be barrierless, and those featuring Al+ ions are noted to only have a small barrier. The proton affinities of the small molecules, metal-oxygen interactions, and the extent of C-C-bond formation are found to be the significant factors that influence the barrier heights. The mechanism is also shown to be consistent with well-known experimental details in the terrestrial formose reaction (which could, however, proceed through a different mechanism). Future experimental and theoretical scope arising out of this paper are subsequently discussed.

  4. Bonding with Your Baby

    Science.gov (United States)

    ... in infant massage in your area. Breastfeeding and bottle-feeding are both natural times for bonding. Infants respond ... milk you've pumped, the staff, including a lactation consultant, can help you make the transition to ...

  5. Page 1 92 C C Desai and A N Hanchinal (130) U an C Figure 2 ...

    Indian Academy of Sciences (India)

    from the gel (tartaric acid). This is called 'syneresis which is one of the important properties of gels. Syneresis is also considered as an internal dehydration. It produces shrinking of the gel thereby changing its pore size. The formation of this type of crystals is believed to be due to lack of place to grow further. At the top of the ...

  6. Formation and reactivity of a porphyrin iridium hydride in water: acid dissociation constants and equilibrium thermodynamics relevant to Ir-H, Ir-OH, and Ir-CH2- bond dissociation energetics.

    Science.gov (United States)

    Bhagan, Salome; Wayland, Bradford B

    2011-11-07

    Aqueous solutions of group nine metal(III) (M = Co, Rh, Ir) complexes of tetra(3,5-disulfonatomesityl)porphyrin [(TMPS)M(III)] form an equilibrium distribution of aquo and hydroxo complexes ([(TMPS)M(III)(D(2)O)(2-n)(OD)(n)]((7+n)-)). Evaluation of acid dissociation constants for coordinated water show that the extent of proton dissociation from water increases regularly on moving down the group from cobalt to iridium, which is consistent with the expected order of increasing metal-ligand bond strengths. Aqueous (D(2)O) solutions of [(TMPS)Ir(III)(D(2)O)(2)](7-) react with dihydrogen to form an iridium hydride complex ([(TMPS)Ir-D(D(2)O)](8-)) with an acid dissociation constant of 1.8(0.5) × 10(-12) (298 K), which is much smaller than the Rh-D derivative (4.3 (0.4) × 10(-8)), reflecting a stronger Ir-D bond. The iridium hydride complex adds with ethene and acetaldehyde to form organometallic derivatives [(TMPS)Ir-CH(2)CH(2)D(D(2)O)](8-) and [(TMPS)Ir-CH(OD)CH(3)(D(2)O)](8-). Only a six-coordinate carbonyl complex [(TMPS)Ir-D(CO)](8-) is observed for reaction of the Ir-D with CO (P(CO) = 0.2-2.0 atm), which contrasts with the (TMPS)Rh-D analog which reacts with CO to produce an equilibrium with a rhodium formyl complex ([(TMPS)Rh-CDO(D(2)O)](8-)). Reactivity studies and equilibrium thermodynamic measurements were used to discuss the relative M-X bond energetics (M = Rh, Ir; X = H, OH, and CH(2)-) and the thermodynamically favorable oxidative addition of water with the (TMPS)Ir(II) derivatives. © 2011 American Chemical Society

  7. 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.

  8. Validity of bond strength tests: A critical review: Part I

    Science.gov (United States)

    Sirisha, Kantheti; Rambabu, Tankonda; Shankar, Yalavarthi Ravi; Ravikumar, Pabbati

    2014-01-01

    Adhesive systems are selected based on their bond strengths achieved while testing in laboratories. These bond strengths can predict the longevity of a restoration to some extent. There were several discrepancies in the reported bond strengths. To critically review the reliability of macro-bond strength tests used to evaluate resin-tooth interface. Relevant literature published between January 1983 and May 2013 was collected from PubMed database, Google scholar, and hand-searched journals of Conservative Dentistry, Endodontics and Dental materials. Variables that influence the test outcome are categorized into substrate-related factors, factors related to specimen properties, preparation of specimens, and test methodology. Impact of these variables on the test outcome is critically analyzed. There is lack of a standard format for reporting the bond strength tests, which could lead to misinterpretation of the data and bonding abilities of adhesives. PMID:25125840

  9. On the formation of smaller p-block endohedral fullerenes: Bonding analysis in the E@C20 (E = Si, Ge, Sn, Pb) series from relativistic DFT calculations.

    Science.gov (United States)

    Muñoz-Castro, Alvaro; King, R Bruce

    2017-07-15

    Experimentally characterized endohedral metallofullerenes are of current interest in expanding the range of viable fullerenic structures and their applications. Smaller metallofullerenes, such as M@C28 , show that several d- and f-block elements can be efficiently confined in relatively small carbon cages. This article explores the potential capabilities of the smallest fullerene cage, that is, C20 , to encapsulate p-block elements from group 14, that is, E = Si, Ge, Sn, and Pb. Our interest relates to the bonding features and optical properties related to E@C20 . The results indicate both s- and p-type concentric bonds, in contrast to the well explored endohedral structures encapsulating f-block elements. Our results suggest the E@C20 series to be a new family of viable endohedral fullerenes. In addition spectroscopic properties related to electron affinity, optical, and vibrational were modeled to gain further information useful for characterization. Characteristic optical patterns were studied predicting a distinctive first peak located between 400 and 250 nm, which is red-shifted going to the heavier encapsulated Group 14 atoms. Electron affinity properties expose different patterns useful to differentiate the hollow C20 fullerene to the proposed p-block endohedral counterparts. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  10. Effect of double-hyperconjugation on the apparent donor ability of sigma-bonds: insights from the relative stability of delta-substituted cyclohexyl cations.

    Science.gov (United States)

    Alabugin, Igor V; Manoharan, Mariappan

    2004-12-24

    A combination of electronic, structural, and energetic analyses shows that a somewhat larger intrinsic donor ability of the C-H bonds compared to that of C-C bonds can be overshadowed by cooperative hyperconjugative interactions with participation of remote substituents (double hyperconjugation or through-bond interaction). The importance of double hyperconjugation was investigated computationally using two independent criteria: (a) relative total energies and geometries of two conformers ("hyperconjomers") of delta-substituted cyclohexyl cations (b) and natural bond orbital (NBO) analysis of electronic structure and orbital interactions in these molecules. Both criteria clearly show that the apparent donor ability of C-C bonds can vary over a wide range, and the relative order of donor ability of C-H and C-C bonds can be easily inverted depending on molecular connectivity and environment. In general, relative donor abilities of sigma bonds can be changed by their through-bond communication with remote substituents and by greater polarizability of C-X bonds toward heavier elements. These computational results can be confirmed by experimental studies of conformational equilibrium of delta-substituted cyclohexyl cations.

  11. Hydrogen bond dynamics at the water/hydrocarbon interface.

    Science.gov (United States)

    Chowdhary, Janamejaya; Ladanyi, Branka M

    2009-04-02

    The dynamics of hydrogen bond formation and breakage for water in the vicinity of water/hydrocarbon liquid interfaces is studied using molecular dynamics simulations. Several liquid alkanes are considered as the hydrocarbon phase in order to determine the effects of their chain length and extent of branching on the properties of the adjacent water phase. In addition to defining the interface location in terms of the laboratory-frame density profiles, the effects of interfacial fluctuations are considered by locating the interface in terms of the proximity of the molecules of the other phase. We find that the hydrogen bond dynamics of interfacial water is weakly influenced by the identity of the hydrocarbon phase and by capillary waves. In addition to calculating hydrogen bond time correlations, we examine how the hydrogen bond dynamics depend on local coordination and determine the extent of cooperativity in the population relaxation of the hydrogen bonds that a given molecule participates in. The contributions of translational diffusion and reorientation of molecular O-H bonds to the mechanism of hydrogen bond breakage and reformation are investigated. In previous work, we have shown that rotation of the principal axes of water is anisotropic at the interface and depends on the initial orientation of the molecule relative to the interface. Here, we extend this analysis to the reorientation of the O-H vector and to hydrogen bond time correlation. We find that hydrogen bond dynamics are also sensitive to the initial orientation of the molecules participating in the hydrogen bond.

  12. Fundamentals of fiber bonding in thermally point-bonded nonwovens

    Science.gov (United States)

    Chidambaram, Aparna

    Thermal point bonding (TPB) uses heat and pressure to bond a web of fibers at discrete points imparting strength to the manufactured fabric. This process significantly reduces the strength and elongation of the bridging fibers between bond points while strengthening the web. Single fiber experiments were performed with four structurally different polypropylene fibers to analyze the inter-relationships between fiber structure, fiber properties and bonding process. Two fiber types had a low birefringence sheath or surface layer while the remaining had uniform birefringence profiles through their thickness. Bonds were formed between isolated pairs of fibers by subjecting the fibers to a calendering process and simulating TPB process conditions. The dependence of bond strength on bonding temperature and on the type of fiber used was evaluated. Fiber strengths before and after bonding were measured and compared to understand the effect of bonding on fiber strength. Additionally, bonded fiber strength was compared to the strength of single fibers which had experienced the same process conditions as the bonded pairs. This comparison estimated the effect of mechanical damage from pressing fibers together with steel rolls while creating bonds in TPB. Interfiber bond strength increased with bonding temperature for all fiber types. Fiber strength decreased with increasing bonding temperature for all fiber types except for one type of low birefringent sheath fibers. Fiber strength degradation was unavoidable at temperatures required for successful bonding. Mechanical damage from compression of fibers between rolls was an insignificant factor in this strength loss. Thermal damage during bonding was the sole significant contributor to fiber strength degradation. Fibers with low birefringence skins formed strong bonds with minimal fiber strength loss and were superior to fibers without such surface layers in TPB performance. A simple model to predict the behavior of a two-bond

  13. C atom endohedral doping effect on the bond lengths in the crystal structure of fcc-C60

    Directory of Open Access Journals (Sweden)

    S Javanbakht

    2011-03-01

    Full Text Available Single and double equilibrium bond lengths of the fcc-C60 crystal were calculated in the absence and presence of the endohedral C atom as an impurity doped into each C60 cluster, i.e., fcc-C@C60, by means of fully-relaxed self-consistent calculations within the density functtional theory (DFT employing the full potential-augmented plane waves plus local orbital (FP-APW+lo method. The result shows that the single and double bond lengths were decreased for the doped case of fcc-C@C60 when compared with the pure fcc-C60. The reduction in the bond lengths by the carbon impurity doping is attributed to the bond alternation effect and reduction of the symmetry in the C60 molecule. The result shows that the impurity injection gives rise to change in the electron charge distribution and as a result to change in electronic properties.

  14. Controllable Fabricating Dielectric-Dielectric SiC@C Core-Shell Nanowires for High-Performance Electromagnetic Wave Attenuation.

    Science.gov (United States)

    Liang, Caiyun; Wang, Zhijiang

    2017-11-22

    Heterostructured dielectric-dielectric nanowires of SiC core and carbon shell (SiC@C) with high-performance electromagnetic wave absorption were synthesized by combining an interfacial in situ polymer encapsulation and carbonization process. This approach overcomes the shortcomings of previous reported methods to prepare carbon shell that both carbon shell and free carbon particles are formed simultaneously. In our developed approach, the core of SiC nanowires are first positively charged. Then the negative resorcinol-formaldehyde polymers as the carbon source are anchored on SiC nanowires under the attraction of electrostatic force, which well suppresses the nucleation of free carbon particles. The thickness of the carbon shell could be modulated from 4 to 20 nm by simply adjusting the moral ratio of resorcinol to SiC nanowires. The resulting SiC@C core-shell nanostructures without free carbon particles offer synergism among the SiC nanowires and the carbon shells, generating multiple dipolar polarization, surfaced polarization, and associated relaxations, which endow SiC@C hybrid nanowires with a minimum reflection loss (RL) value of -50 dB at the frequency of 12 GHz and an effective absorption bandwidth of 8 GHz with RL value under -10 dB at the optimized state. Our results demonstrate that SiC@C hybrid nanowires are promising candidates for electromagnetic wave absorption applications.

  15. Highly Conductive, Mechanically Robust, and Electrochemically Inactive TiC/C Nanofiber Scaffold for High-Performance Silicon Anode Batteries

    KAUST Repository

    Yao, Yan

    2011-10-25

    Silicon has a high specific capacity of 4200 mAh/g as lithium-ion battery anodes, but its rapid capacity fading due to >300% volume expansion and pulverization presents a significant challenge for practical applications. Here we report a core-shell TiC/C/Si inactive/active nanocomposite for Si anodes demonstrating high specific capacity and excellent electrochemical cycling. The amorphous silicon layer serves as the active material to store Li+, while the inactive TiC/C nanofibers act as a conductive and mechanically robust scaffold for electron transport during the Li-Si alloying process. The core-shell TiC/C/Si nanocomposite anode shows ∼3000 mAh g-1 discharge capacity and 92% capacity retention after 100 charge/discharge cycles. The excellent cycling stability and high rate performance could be attributed to the tapering of the nanofibers and the open structure that allows facile Li ion transport and the high conductivity and mechanical stability of the TiC/C scaffold. © 2011 American Chemical Society.

  16. Computer Simulation of the E.C.C.S. Buckling Curve using a Monte-Carlo Method

    NARCIS (Netherlands)

    Strating, J.; Vos, H.

    1973-01-01

    The application of a Monte-Carlo simulation procedure to obtain the distribution function of the maximum load of a hinged column with imperfections is discussed. Buckling tests carried out by the E.C.C.S. on IPE 160 sections have been simulated. Information concerning the column variables is

  17. [Detection of HBV DNA by sensitive techniques and definition of chronic VHB infection by pre-C-C mutants].

    Science.gov (United States)

    Lebarbier, C; Williams, V; Garandeau, C; Bellaiche, G; Deny, P; Maisonneuve, L; Gordien, E

    2004-11-01

    Our purpose is to assess the question of the definition of hepatitis B virus pre-C-C mutant-chronic infection, according to the level of the viral load at the era of very sensitive techniques of quantification of HBV DNA.

  18. Page 1 Chromones—IV - 35 acetic acid (10.0 c.c.) and nitric acid (d ...

    Indian Academy of Sciences (India)

    methylchromone (I, R = R1 = Me) at 0° : 5-Methoxy-2-methyl-8-nitrochromone (III, R = R1 = Me). 5-Methoxy-2-methylchromone (1-0 g.) was cooled externally to 0°, and a cooled mixture of concentrated Sulphuric acid (5.0 c.c.) and nitric acid (d. 1.42 ...

  19. Interaction between lattice dislocations and grain boundaries in f.c.c. and ordered compounds : a computer simulation

    NARCIS (Netherlands)

    Pestman, B.J.; Hosson, J.Th.M. De; Vitek, V.; Schapink, F.W.

    1991-01-01

    The interaction of 1/2<110> screw- and 60° dislocations with symmetric [110] tilt boundaries was investigated by atomistic simulations using many-body potentials representing a pure f.c.c. metal and ordered intermetallic compounds. The calculations were performed with and without an applied shear

  20. Are One-Electron Bonds Any Different from Standard Two-Electron Covalent Bonds?

    Science.gov (United States)

    Sousa, David Wilian Oliveira de; Nascimento, Marco Antonio Chaer

    2017-09-19

    molecules H 2 + , H 3 C·CH 3 + , B 2 H 4 - , [Cu·BH 3 (PH 3 ) 3 ], and an alkali-metal cation dimer, and we evaluated the components of the electronic energy and density, which account for the formation of the bond, and compared the results with those for the respective analogous molecules exhibiting the "conventional" two-electron bond. In all cases, it was verified that interference is the dominant effect for the one-electron bonds. The GPF-EP results clearly indicate that molecules exhibiting (2c1e) bonds should not be considered as special systems, since one- and two-electron bonds result from quantum interference and therefore there is no conceptual difference between them. Moreover, these results show that quantum interference provides a way to unify the chemical bond concept.

  1. Dynamic covalent bond from first principles: Diarylbibenzofuranone structural, electronic, and oxidation studies.

    Science.gov (United States)

    Schleder, Gabriel R; Fazzio, Adalberto; Arantes, Jeverson T

    2017-12-05

    A structure that can self-heal under standard conditions is a challenge faced nowadays and is one of the most promising areas in smart materials science. This can be achieved by dynamic bonds, of which diarylbibenzofuranone (DABBF) dynamic covalent bond is an appealing solution. In this report, we studied the DABBF bond formation against arylbenzofuranone (ABF) and O 2 reaction (autoxidation). Our results show that the barrierless DABBF bond formation is preferred over autoxidation due to the charge transfer process that results in the weakly bonded superoxide. We calculated the electronic and structural properties using total energy density functional theory. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  2. Bond Energies and Thermochemical Properties of Ring-Opened Diradicals and Carbenes of exo-Tricyclo[5.2.1.0(2,6)]decane.

    Science.gov (United States)

    Hudzik, Jason M; Castillo, Álvaro; Bozzelli, Joseph W

    2015-09-24

    Exo-tricyclo[5.2.1.0(2,6)]decane (TCD) or exo-tetrahydrodicyclopentadiene is an interesting strained ring compound and the single-component high-energy density hydrocarbon fuel known as JP-10. Important initial reactions of TCD at high temperatures could cleave a strained carbon-carbon (C-C) bond in the ring system creating diradicals also constrained by the remaining ring system. This study determines the thermochemical properties of these diradicals (TCD-H2 mJ-nJ where m and n correspond to the cleaved carbons sites) including the carbon-carbon bond dissociation energy (C-C BDE) corresponding to the cleaved TCD site. Thermochemical properties including enthalpies (ΔH°f298), entropies (S(T)), heat capacities (Cp(T)), and C-H and C-C BDEs for the parent (TCD-H2 m-n), radical (TCD-H2 mJ-n and m-nJ), diradical (TCD-H2 mJ-nJ), and carbene (TCD-H2 mJJ-n and m-nJJ) species are determined. Structures, vibrational frequencies, moments of inertia, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level of theory. Standard enthalpies of formation in the gas phase for the TCD-H2 m-n parent and radical species are determined using the B3LYP density functional theory and the higher level G3MP2B3 and CBS-QB3 composite methods. For singlet and triplet TCD diradicals and carbenes, M06-2X, ωB97X-D, and CCSD(T) methods are included in the analysis to determine ΔH°f298 values. The C-C BDEs are further calculated using CASMP2(2,2)/aug-cc-pvtz//CASSCF(2,2)/cc-pvtz and with the CASMP2 energies extrapolated to the complete basis set limit. The bond energies calculated with these methods are shown to be comparable to the other calculation methods. Isodesmic work reactions are used for enthalpy analysis of these compounds for effective cancelation of systematic errors arising from ring strain. C-C BDEs range from 77.4 to 84.6 kcal mol(-1) for TCD diradical singlet species. C-H BDEs for the parent TCD-H2 m-n carbon sites range from 93 to 101 kcal mol(-1) with a

  3. 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.

  4. Asymmetric bifurcated halogen bonds.

    Science.gov (United States)

    Novák, Martin; Foroutan-Nejad, Cina; Marek, Radek

    2015-03-07

    Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as 'σ-hole - lone pair' or 'σ-hole - π' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction.

  5. Strength of Chemical Bonds

    Science.gov (United States)

    Christian, Jerry D.

    1973-01-01

    Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

  6. Evidence of amino acid precursors: C-N bond coupling in simulated interstellar CO2/NH3 ices

    Science.gov (United States)

    Esmaili, Sasan

    2015-08-01

    Low energy secondary electrons are abundantly produced in astrophysical or planetary ices by the numerous ionizing radiation fields typically encountered in space environments and may thus play a role in the radiation processing of such ices [1]. One approach to determine their chemical effect is to irradiate nanometer thick molecular solids of simple molecular constituents, with energy selected electron beams and to monitor changes in film chemistry with the surface analytical techniques [2].Of particular interest is the formation of HCN, which is a signature of dense gases in interstellar clouds, and is ubiquitous in the ISM. Moreover, the chemistry of HCN radiolysis products such as CN- may be essential to understand of the formation of amino acids [3] and purine DNA bases. Here we present new results on the irradiation of multilayer films of CO2 and NH3 with 70 eV electrons, leading to CN bond formations. The electron stimulated desorption (ESD) yields of cations and anions are recorded as a function of electron fluence. The prompt desorption of cationic reaction/scattering products [4], is observed at low fluence (~4x1013 electrons/cm2). Detected ions include C2+, C2O2+, C2O+, CO3+, C2O3+ or CO4+ from pure CO2, and N+, NH+, NH2+, NH3+, NH4+, N2+, N2H+ from pure NH3, and NO+, NOH+ from CO2/NH3 mixtures. Most saliently, increasing signals of negative ion products desorbing during prolonged irradiation of CO2/NH3 films included C2-, C2H-, C2H2-, as well as CN-, HCN- and H2CN-. The identification of particular product ions was accomplished by using 13CO2 and 15NH3 isotopes. The chemistry induced by electrons in pure films of CO2 and NH3 and mixtures with composition ratios (3:1), (1:1), and (1:3), was also studied by X-ray photoelectron spectroscopy (XPS). Irradiation of CO2/NH3 mixed films at 22 K produces species containing the following bonds/functional groups identified by XPS: C=O, O-H, C-C, C-O, C=N and N=O. (This work has been funded by NSERC).

  7. Ordinary and partial differential equation routines in C, C++, Fortran, Java, Maple, and Matlab

    CERN Document Server

    Lee, HJ

    2003-01-01

    This book provides a set of ODE/PDE integration routines in the six most widely used computer languages, enabling scientists and engineers to apply ODE/PDE analysis toward solving complex problems. This text concisely reviews integration algorithms and then analyzes the widely used Runge-Kutta method. It first presents a complete code before discussing its components in detail, focusing on integration concepts such as error monitoring and control. The format allows readers to understand the basics of ODE/PDE integration, and then calculate sample numerical solutions within the targeted program

  8. C–H bond halogenation catalyzed or mediated by copper: an overview

    Directory of Open Access Journals (Sweden)

    Wenyan Hao

    2015-11-01

    Full Text Available 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.

  9. A Study in Drag Reduction of Close Formation Flight Accounting for Flight Control Trim Positions and Dissimilar Formations

    Science.gov (United States)

    2005-03-21

    rewind(92) read(92,*) aoa,cl1,cl2,cd2,cm2,cy2,cll2, cln2 c c compute increments for sim table look-up c c dcy2=cy2-cy2s c...dcll2=cll2-cll2s c dcln2= cln2 - cln2s c c print output files c write(102,925) (delx-130.)/span,dely/span,(delz-202...span, 1 aoa,cl1,cl2,cd2,cm2,cy2,cll2, cln2 c rewind(15) c 1000 continue c 900 format(a80) 910 format(5(f9.2,1x

  10. 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.

  11. Microstructure of plastic bonded nickel electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Kulcsar, S.; Agh, J.; Fazekas, A.; Vigh, J.; Bujdoso, Z.

    1982-07-01

    Structure is of great importance in the characteristics of plastic bonded nickel electrodes. On the basis of SEM tests it has been established that in pressed Ni electrodes some tenth of a millimetre-long PTFE fibres can be found with a diameter smaller than 500 nm. These form a net-like structure in the electrode which holds the active material together without any decrease in the conductivity. The formation and arrangement of this structure can be influenced by technological parameters.

  12. Optimization of Roll Bonding by Hot Rolling in Experimental and Industrial Use

    Directory of Open Access Journals (Sweden)

    Szabó G.

    2017-06-01

    Full Text Available In this study the major topic were the bonding properties of the layer-clad aluminum sheets. The bonding was performed between AlMn1Si0.8 and AlSi10 alloys using hot rolling (a VON ROLL experimental duo mill. The experimental temperatures were 460, 480 and 500°C. The goodness of bonding was tested by tensile test and T-peel test. T-peel test provided a good description about the quality of bonding. Structure analysis was also performed by light microscopy to detect typical bonding faults. The aim of this investigation is modelling the bonding conformation in experimental conditions. Further aim of this investigation is to produce some typical bonding faults and find the cause of formation. The influence of the rolling temperature and surface roughness on the bonding was also analyzed. Rolling schedule and the role of first pass on the development of perfect bonding were experimentally determined.

  13. Potential Hazards Relating to Pyrolysis of c-C{sub 4}F{sub 8} in Selected Gaseous Diffusion Plant Operations

    Energy Technology Data Exchange (ETDEWEB)

    Trowbridge, L.D.

    1999-03-01

    As part of a program intended to replace the present evaporative coolant at the gaseous diffusion plants (GDPs) with a non-ozone-depleting alternate, a series of investigations of the suitability of candidate substitutes in under way. One issue concerning a primary candidate, c-C4F8, is the possibility that it might produce the highly toxic perfluoroisobutylene (PFIB) in high temperature environments. This study was commissioned to determine the likelihood and severity of decomposition under two specific high temperature thermal environments, namely the use of a flame test for the presence of coolant vapors and welding in the presence of coolant vapors. The purpose of the study was to develop and evaluate available data to provide information that will allow the technical and industrial hygiene staff at the GDPs to perform appropriate safety evaluations and to determine the need for field testing or experimental work. The scope of this study included a literature search and an evaluation of the information developed therefrom. Part of that evaluation consists of chemical kinetics modeling of coolant decomposition in the two operational environments. The general conclusions are that PFIB formation is unlikely in either situation but that it cannot be ruled out completely under extreme conditions. The presence of oxygen, moisture, and combustion products will tend to lead to formation of oxidation products (COF2, CO, CO2, and HF) rather than PFIB.

  14. Bond strength comparison of color change adhesives for orthodontic bonding.

    Science.gov (United States)

    Duers, Michael W; English, Jeryl D; Ontiveros, Joe C; Powers, John M; Bussa, Harry I; Frey, Gary N; Gallerano, Ronald L; Paige, Sebastian Z

    2011-03-01

    This study investigated whether three different color change light-cured orthodontic bonding adhesives have comparable shear bond strengths to a conventional light-cured orthodontic bonding adhesive. The sample of 240 bovine incisors was divided into four groups of 60 each. Each group tested one of four orthodontic bonding adhesives: 3M Unitek Transbond PLUS, Ormco Gréngloo, Ormco Blúgloo, and 3M Unitek Transbond XT (control). The four groups were further divided into two subgroups of 30 with shear bond strength tested at two different times (15 minutes and 24 hours) post-bond. The shear bond strength was measured on a universal testing machine. The data were analyzed by two-way analysis of variance and post-hoc comparisons (Fisher's PLSD) at the 0.05 level of significance. The average shear bond strength was greater at 24 hours than at 15 minutes for Transbond PLUS, Blúgloo, and Transbond XT. For Gréngloo, the average shear bond strength was greater at 15 minutes than at 24 hours. Gréngloo tested at 15 minutes had the highest average shear bond strength. Gréngloo tested at 24 hours had the lowest average shear bond strength. All four orthodontic bonding adhesives demonstrated bond strengths considered to be clinically acceptable for orthodontic purposes.

  15. Social bonds and rank acquisition in raven nonbreeder aggregations

    Science.gov (United States)

    Braun, Anna; Bugnyar, Thomas

    2012-01-01

    Complex social life has been characterized as cognitively challenging and recently, social relationships such as long-term social bonds and alliances have been identified as key elements for brain evolution. Whereas good evidence is available to support the link between social relations and cognition in mammals, it remains unsatisfying for birds. Here we investigated the role of avian social bonds in a nonbreeder aggregation of ravens, Corvus corax, in the Austrian Alps. We individually marked 138 wild ravens, representing approximately half of a population that uses the area of a local zoo for foraging. For 2 years, we observed the dynamics of group composition and the birds' agonistic and affiliative interactions. We identified two levels of organization: the formation of an unrelated local group and the individuals' engagement in social bonds of different length and reciprocity pattern. Whereas belonging to the local group had no significant effect on conflicts won during foraging, the individual bonding type did. Birds that engaged in affiliative relationships were more successful when competing for food than those without such bonds. Bonded birds did suffer from aggression by other bonded birds and, probably as a consequence, most of the ravens' social relations were not stable over time. These results support the idea that social bonding and selective cooperation and competition are prominent features in nonbreeding ravens. Proximately, bonding may qualify as a social manoeuvre that facilitates access to resources; ultimately it might function to assess the quality of a partner in these long-term monogamous birds. PMID:23264693

  16. [Direct bonding in orthodontics].

    Science.gov (United States)

    Hablützel, W

    1976-03-01

    Composite materials have been used to attach orthodontic brackets on the conditioned enamel surface. A method of direct bonding with Enamelite of metal brackets with a mechanical retention on the basis is described. Clinical experience with the adhesive technique, its range of indication and possible failures are discussed in several case reports.

  17. Use of N-Methylformamide as a Solvent in Indium-Promoted Barbier Reactions en Route to Enediyne and Epoxy Diyne Formation: Comparison of Rate and Stereoselectivity in C−C Bond-Forming Reactions with Water

    Science.gov (United States)

    2009-01-01

    Indium-promoted coupling reactions between propargyl aldehydes (1) and α-chloropropargylphenyl sulfide are reported. Although water has been shown to accelerate indium metal promoted reactions, the reverse pattern was observed in this series. Use of N-methylformamide (NMF), which has not previously been a solvent known for use in indium-promoted reactions, afforded an acceleration of these Barbier-style reactions compared to water. Indium-promoted reactions in this study also showed excellent regiocontrol and good stereocontrol, allowing for easy entry into the formation of epoxydiyne and enediyne skeletal structures. This paper also describes use of the Barbier Coupled product (2) as a new, and easy, entry into the formation of enediyne and epoxydiyne skeletal structures. PMID:19634900

  18. Initial dissolution of D2O at the gas-liquid interface of the ionic liquid [C4min][NTf2] associated with hydrogen-bond network formation.

    Science.gov (United States)

    Ohoyama, H; Teramoto, T

    2016-10-12

    We have studied the initial dissolution of D2O at the interfacial surface of the flowing jet sheet beam of the ionic liquid (IL) [C4min][NTf2] using the King and Wells method as a function of both the temperature and collision energy of the IL. The initial dissolution probability of D2O into the IL [C4min][NTf2] was found to follow the general propensity that the solubility of gases into a liquid decreases with temperature. However, a large partial molar enthalpy and entropy for the initial dissolution of D2O in the IL [C4min][NTf2] were observed from the temperature dependence of the initial dissolution probability: ΔHl = -53 ± 8 kJ mol-1, ΔSl = -210 ± 30 J mol-1 K-1. In addition, it was found that the collision energy significantly reduced the initial dissolution probability. We propose that the associated D2O molecules at the interface of the IL [C4min][NTf2] make a hydrogen-bond network around the [NTf2]- anion before dissolution into the deeper portion of the interface layer.

  19. Impedance spectroscopy of heterojunction solar cell a-SiC/c-Si with ITO antireflection film investigated at different temperatures

    Science.gov (United States)

    Šály, V.; Perný, M.; Janíček, F.; Huran, J.; Mikolášek, M.; Packa, J.

    2017-04-01

    Progressive smart photovoltaic technologies including heterostructures a-SiC/c-Si with ITO antireflection film are one of the prospective replacements of conventional photovoltaic silicon technology. Our paper is focused on the investigation of heterostructures a-SiC/c-Si provided with a layer of ITO (indium oxide/tin oxide 90/10 wt.%) which acts as a passivating and antireflection coating. Prepared photovoltaic cell structure was investigated at various temperatures and the influence of temperature on its operation was searched. The investigation of the dynamic properties of heterojunction PV cells was carried out using impedance spectroscopy. The equivalent AC circuit which approximates the measured impedance data was proposed. Assessment of the influence of the temperature on the operation of prepared heterostructure was carried out by analysis of the temperature dependence of AC equivalent circuit elements.

  20. Impact of Intragranular Substructure Parameters on the Forming Limit Diagrams of Single-Phase B.C.C. Steels

    Directory of Open Access Journals (Sweden)

    Gérald Franz

    2013-11-01

    Full Text Available An advanced elastic-plastic self-consistent polycrystalline model, accounting for intragranular microstructure development and evolution, is coupled with a bifurcation-based localization criterion and applied to the numerical investigation of the impact of microstructural patterns on ductility of single-phase steels. The proposed multiscale model, taking into account essential microstructural aspects, such as initial and induced textures, dislocation densities, and softening mechanisms, allows us to emphasize the relationship between intragranular microstructure of B.C.C. steels and their ductility. A qualitative study in terms of forming limit diagrams for various dislocation networks, during monotonic loading tests, is conducted in order to analyze the impact of intragranular substructure parameters on the formability of single-phase B.C.C. steels.

  1. Interferon alpha and Tat involvement in the immunosuppression of uninfected T cells and C-C chemokine decline in AIDS.

    Science.gov (United States)

    Zagury, D; Lachgar, A; Chams, V; Fall, L S; Bernard, J; Zagury, J F; Bizzini, B; Gringeri, A; Santagostino, E; Rappaport, J; Feldman, M; Burny, A; Gallo, R C

    1998-03-31

    HIV type 1 (HIV-1) not only directly kills infected CD4(+) T cells but also induces immunosuppression of uninfected T cells. Two immunosuppressive proteins, interferon alpha (IFNalpha) and extracellular Tat, mediate this process because specific antibodies against these proteins prevent generation of suppressor cells in HIV-1-infected peripheral blood mononuclear cell cultures. Furthermore, the production of C-C chemokines in response to immune cell activation, initially enhanced by IFNalpha and Tat, ultimately is inhibited by these proteins in parallel with their induction of immunosuppression. The clinical corollary is the immunosuppression of uninfected T cells and the decline in C-C chemokine release found at advanced stages of HIV-1 infection paralleling rising levels of IFNalpha and extracellular Tat. We, therefore, suggest that IFNalpha and Tat may be critical targets for anti-AIDS strategies.

  2. Microstructure of C/C composites prepared by chemical vapor infiltration method with vaporized kerosene as a precursor

    Energy Technology Data Exchange (ETDEWEB)

    Wang Jiping [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)]. E-mail: jipingwang@gmail.com; Qian Junmin [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Jin Zhihao [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Qiao Guanjun [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)

    2006-03-15

    The microstructures of two types of C/C composites prepared from different carbon felts by a rapid densification method, thermal gradient chemical vapor infiltration with vaporized kerosene as a precursor, at 1080-1120 deg. C for 6 h were characterized by polarized light microscopy (PLM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman micro-spectrometry techniques. The experimental results show that the fibers in the two composites are both surrounded by ring-shaped pyrocarbons with rough laminar texture, but the thickness, the surface morphology of the pyrocarbons and the graphitizability of the composites depend much on the configurations of carbon felts. The C/C composite fabricated from a higher porosity carbon felt possesses larger thickness and rougher surface of pyrocarbon, and has a lower graphitizability after heat treatment at 2300 deg. C for 2 h.

  3. LAMMPS framework for dynamic bonding and an application modeling DNA

    Science.gov (United States)

    Svaneborg, Carsten

    2012-08-01

    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 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 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. Catalogue identifier: AEME_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEME_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence No. of lines in distributed program, including test data, etc.: 2 243 491 No. of bytes in distributed program, including test data, etc.: 771 Distribution format: tar.gz Programming language: C++ Computer: Single and multiple core servers Operating system: Linux/Unix/Windows Has the code been vectorized or parallelized?: Yes. The code has been parallelized by the use of MPI directives. RAM: 1 Gb Classification: 16.11, 16.12 Nature of problem: Simulating coarse-grain models capable of chemistry e.g. DNA hybridization dynamics. Solution method: Extending LAMMPS to handle dynamic bonding and directional bonds. Unusual features: Allows bonds to be created and broken while angular and dihedral interactions are kept consistent. Additional comments: The distribution file for this program is approximately 36 Mbytes and therefore is not delivered directly

  4. Hydrogen bonds, and σ-hole and π-hole bonds - mechanisms protecting doublet and octet electron structures.

    Science.gov (United States)

    Grabowski, Sławomir J

    2017-11-15

    The hydrogen bond interaction and σ-hole and π-hole bonds are steered by the same mechanisms. There is electron charge transfer from the Lewis base to the Lewis acid unit, and further, for various interactions the same mechanisms try to protect the former electronic structure of the Lewis acid centre. The increase of the polarization of bonds to this centre seems to be the common effect. In the case of the A-HB hydrogen bond it is the increase of the polarization of the A-H bond connected with the outflow of the electron charge from the H-atom to the A-centre. For other interactions the outflow of electron charge from the Lewis acid centre is also observed. These electron charge shifts try to protect the doublet/octet structure of the acidic centre. The extremely strong interaction is often equivalent to the formation of new covalent bonds or it may lead to chemical reactions. Numerous interactions may be treated as the preliminary stages of chemical reactions: hydrogen bond - proton transfer, dihydrogen bond - molecular hydrogen release, tetrel bond - S N 2 reaction, etc.

  5. A method of quantitative characterization for the component of C/C composites based on the PLM video

    Science.gov (United States)

    Li, Y. X.; Qi, L. H.; Song, Y. S.; Li, H. J.

    2016-07-01

    PLM video is used for studying the microstructure of C/C composites, because it contains the structure and motion information at the same time. It means that PLM video could provide more comprehensive microstructure features of C/C composites, and then the microstructure could be quantitatively characterized by image processing. However, several unavoidable displacements still exist in the PLM video, which could occur during the process of image acquisition. Therefore, an image registration method was put forward to correct the displacements by the phase correlation, and further to achieve the quantitative characterization of component combined with image fusion and threshold segmentation based on the PLM video of C/C composites. Specifically, PLM video was decomposed to a frame sequence firstly. Then a series of processes was carried out on this basis, including selecting the frame as equal interval, segmenting the static and dynamic regions and correcting the relative displacements between the adjacent frames. Meanwhile, the result of image registration was verified through image fusion, and it indicates that the proposed method could eliminate the displacements effectively. Finally, some operations of image processing were used to segment the components and calculate their fractions, thus the quantitative calculation was achieved successfully.

  6. Finite Element Modeling of 3D Orthogonal Woven C/C Composite Based on Micro-Computed Tomography Experiment

    Science.gov (United States)

    Shigang, Ai; Xiaolei, Zhu; Yiqi, Mao; Yongmao, Pei; Daining, Fang

    2014-08-01

    Two-dimensional images of C/C 3D orthogonal woven composite were captured by X-ray micro-computed tomography (μCT). The μCT data reveal comprehensive meso-geometrical information about the carbon fiber tows, carbon matrix, and void defects etc. The fibers tows are characterized consisting of the cancroids of a tow, the area and aspect ratio of its cross-section. A statistical analysis of the volume fraction and positioning of the void defects in the 3D orthogonal woven architecture is performed based on 2-D micro tomography images. The tabulated statistics are sufficient to generate the virtual specimen, which shares the same statistical characteristics of the C/C composite and the void defects are included. Three-point bending experiment and simulation are carried out and the results show that the finite element model including the void defects gives more accurate results. The finite element model will give some highlights to the numerical simulation approach of the C/C textile composite under thermal, mechanical and oxygen coupled service environment. And the numerical techniques for modelling such kind materials with woven architecture and void defects are recommended.

  7. SnTe-TiC-C composites as high-performance anodes for Li-ion batteries

    Science.gov (United States)

    Son, Seung Yeon; Hur, Jaehyun; Kim, Kwang Ho; Son, Hyung Bin; Lee, Seung Geol; Kim, Il Tae

    2017-10-01

    Intermetallic SnTe composites dispersed in a conductive TiC/C hybrid matrix are synthesized by high-energy ball milling (HEBM). The electrochemical performances of the composites as potential anodes for Li-ion batteries are evaluated. The structural and morphological characteristics of the SnTe-TiC-C composites with various TiC contents are investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy, which reveal that SnTe and TiC are uniformly dispersed in a carbon matrix. The electrochemical performance is significantly improved by introducing TiC to the SnTe-C composite; higher TiC contents result in better performances. Among the prepared composites, the SnTe-TiC (30%)-C and SnTe-TiC (40%)-C electrodes exhibit the best electrochemical performance, showing the reversible capacities of, respectively, 652 mAh cm-3 and 588 mAh cm-3 after 400 cycles and high rate capabilities with the capacity retentions of 75.4% for SnTe-TiC (30%)-C and 82.2% for SnTe-TiC (40%)-C at 10 A g-1. Furthermore, the Li storage reaction mechanisms of Te or Sn in the SnTe-TiC-C electrodes are confirmed by ex situ XRD.

  8. Indirect bonding technique in orthodontics

    Directory of Open Access Journals (Sweden)

    Kübra Yıldırım

    2016-08-01

    Full Text Available ‘Direct Bonding Technique’ which allows the fixed orthodontic appliances to be directly bonded to teeth without using bands decreased the clinic time for bracket bonding and increased esthetics and oral hygiene during orthodontic treatment. However, mistakes in bracket positioning were observed due to decreased direct visual sight and access to posterior teeth. ‘Indirect Bonding Technique’ was developed for eliminating these problems. Initially, decreased bond strength, higher bond failure rate, periodontal tissue irritation, compromised oral hygiene and increased laboratory time were the main disadvantages of this technique when compared to direct bonding. The newly developed materials and modified techniques help to eliminate these negative consequences. Today, the brackets bonded with indirect technique have similar bond strength with brackets bonded directly. Moreover, indirect and direct bonding techniques have similar effects on periodontal tissues. However, indirect bonding technique requires more attention and precision in laboratory and clinical stage, and has higher cost. Orthodontist's preference between these two bonding techniques may differ according to time spent in laboratory and clinic, cost, patient comfort and personal opinion.

  9. Comparison of shear bond strength of the stainless steel metallic brackets bonded by three bonding systems

    Directory of Open Access Journals (Sweden)

    Mehdi Ravadgar

    2013-09-01

    Full Text Available Introduction: In orthodontic treatment, it is essential to establish a satisfactory bond between enamel and bracket. After the self-etch primers (SEPs were introduced for the facilitation of bracket bonding in comparison to the conventional etch-and-bond system, multiple studies have been carried out on their shear bond strengths which have yielded different results. This study was aimed at comparing shear bond strengths of the stainless steel metallic brackets bonded by three bonding systems. Methods: In this experimental in vitro study, 60 extracted human maxillary premolar teeth were randomly divided into three equal groups: in the first group, Transbond XT (TBXT light cured composite was bonded with Transbond plus self-etching primer (TPSEP; in the second group, TBXT composite was bonded with the conventional method of acid etching; and in the third group, the self cured composite Unite TM bonding adhesive was bonded with the conventional method of acid etching. In all the groups, Standard edgewise-022 metallic brackets (American Orthodontics, Sheboygan, USA were used. Twenty-four hours after the completion of thermocycling, shear bond strength of brackets was measured by Universal Testing Machine (Zwick. In order to compare the shear bond strengths of the groups, the variance analysis test (ANOVA was adopted and p≤0.05 was considered as a significant level. Results: Based on megapascal, the average shear bond strength for the first, second, and third groups was 8.27±1.9, 9.78±2, and 8.92±2.5, respectively. There was no significant difference in the shear bond strength of the groups. Conclusions: Since TPSEP shear bond strength is approximately at the level of the conventional method of acid etching and within the desirable range for orthodontic brackets shear bond strength, applying TPSEP can serve as a substitute for the conventional method of etch and bond, particularly in orthodontic operations.

  10. Wafer bonding using Cu-Sn intermetallic bonding layers

    NARCIS (Netherlands)

    Flötgen, C.; Pawlak, M.; Pabo, E.; Wiel, H.J. van de; Hayes, G.R.; Dragoi, V.

    2014-01-01

    Wafer-level Cu-Sn intermetallic bonding is an interesting process for advanced applications in the area of MEMS and 3D interconnects. The existence of two intermetallic phases for Cu-Sn system makes the wafer bonding process challenging. The impact of process parameters on final bonding layer

  11. Making Weak Bonds (cooling) and Breaking Strong Bonds (heating ...

    Indian Academy of Sciences (India)

    Making Weak Bonds (cooling) and Breaking Strong Bonds (heating) with Supersonic Techniques · Acknowledgements · Outline · Slide 4 · A comparison of the two techniques · What is a hydrogen bond? Phenylacetylene and its complexes · Slide 8 · Phenylacetylene and PAH · phenylacetylene · Complexes in the interstellar ...

  12. Glutamic Acid Selective Chemical Cleavage of Peptide Bonds.

    Science.gov (United States)

    Nalbone, Joseph M; Lahankar, Neelam; Buissereth, Lyssa; Raj, Monika

    2016-03-04

    Site-specific hydrolysis of peptide bonds at glutamic acid under neutral aqueous conditions is reported. The method relies on the activation of the backbone amide chain at glutamic acid by the formation of a pyroglutamyl (pGlu) imide moiety. This activation increases the susceptibility of a peptide bond toward hydrolysis. The method is highly specific and demonstrates broad substrate scope including cleavage of various bioactive peptides with unnatural amino acid residues, which are unsuitable substrates for enzymatic hydrolysis.

  13. Revisiting the beryllium bonding interactions from energetic and wavefunction perspectives

    Science.gov (United States)

    Zhong, Aiguo; Chen, Dan; Li, Rongrong

    2015-07-01

    Not too much is known about the beryllium bonding interactions. Here, the total energy partition schemes as well as DFT-SAPT are used to explore the origin and nature of the beryllium bonds from an energetic point of view. In addition, Shannon entropy and Fisher information, which are based upon the electron probability density, rather than the shape function, are adopted to dissect the impact resulted from a wavefunction perspective. Results reveal that the electrostatic potential largely causes the formation of beryllium bonds. Moreover, there are strong linear relationships between atomic Shannon entropy and Fisher information of Be atoms, which can aid to distinguish the different sources of noncovalent weak interactions.

  14. 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.

  15. Bond yield curve construction

    Directory of Open Access Journals (Sweden)

    Kožul Nataša

    2014-01-01

    Full Text Available In the broadest sense, yield curve indicates the market's view of the evolution of interest rates over time. However, given that cost of borrowing it closely linked to creditworthiness (ability to repay, different yield curves will apply to different currencies, market sectors, or even individual issuers. As government borrowing is indicative of interest rate levels available to other market players in a particular country, and considering that bond issuance still remains the dominant form of sovereign debt, this paper describes yield curve construction using bonds. The relationship between zero-coupon yield, par yield and yield to maturity is given and their usage in determining curve discount factors is described. Their usage in deriving forward rates and pricing related derivative instruments is also discussed.

  16. Formation of unsaturated hydrocarbons in interstellar ice analogues by cosmic rays

    Science.gov (United States)

    Pilling, S.; Andrade, D. P. P.; da Silveira, E. F.; Rothard, H.; Domaracka, A.; Boduch, P.

    2012-07-01

    The formation of C=C and C≡C bonds from the processing of pure c-C6H12 (cyclohexane) and mixed H2O:NH3:c-C6H12 (1:0.3:0.7) ices by highly charged and energetic ions (219-MeV 16O7 + and 632-MeV 58Ni24 +) is studied. The experiments simulate the physical chemistry induced by medium-mass and heavy-ion cosmic rays in interstellar ice analogues. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator Grand Accelératéur National d'Ions Lourds (GANIL) in Caen, France. The gas samples were deposited on to a polished CsI substrate previously cooled to 13 K. In situ analysis was performed by a Fourier transform infrared spectrometry at different ion fluences. Dissociation cross-section of cyclohexane and its half-life in astrophysical environments were determined. A comparison between spectra of bombarded ices and young stellar sources indicates that the initial composition of grains in these environments should contain a mixture of H2O, NH3, CO (or CO2), simple alkanes and CH3OH. Several species containing double or triple bounds were identified in the radiochemical products, such as hexene, cyclohexene, benzene, OCN-, CO, CO2, as well as several aliphatic and aromatic alkenes and alkynes. The results suggest an alternative scenario for the production of unsaturated hydrocarbons and possibly aromatic rings (via dehydrogenation processes) in interstellar ices induced by cosmic ray bombardment.

  17. 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...

  18. Integration of European Bond Markets

    DEFF Research Database (Denmark)

    Christiansen, Charlotte

    2014-01-01

    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...

  19. 46 CFR Sec. 10 - Bonds.

    Science.gov (United States)

    2010-10-01

    ...) shall be used. (b) In compliance with the perform- ance bond and payment bond requirements of Article 14... November 1950) respectively, shall be used. Such bonds (in the respective penal sums of 50 percent of the... penal sum of 40 percent of such job order contract price) shall guarantee the Contractor's performance...

  20. The chemical bond in inorganic chemistry the bond valence model

    CERN Document Server

    Brown, I David

    2016-01-01

    The bond valence model is a version of the ionic model in which the chemical constraints are expressed in terms of localized chemical bonds formed by the valence charge of the atoms. Theorems derived from the properties of the electrostatic flux predict the rules obeyed by both ionic and covalent bonds. They make quantitative predictions of coordination number, crystal structure, bond lengths and bond angles. Bond stability depends on the matching of the bonding strengths of the atoms, while the conflicting requirements of chemistry and space lead to the structural instabilities responsible for the unusual physical properties displayed by some materials. The model has applications in many fields ranging from mineralogy to molecular biology.

  1. Thermal fatigue behavior of C/C composites modified by SiC-MoSi{sub 2}-CrSi{sub 2} coating

    Energy Technology Data Exchange (ETDEWEB)

    Chu Yanhui [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi' an 710072 (China); Fu Qiangang, E-mail: fuqiangang@nwpu.edu.cn [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi' an 710072 (China); Li Hejun; Li Kezhi [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi' an 710072 (China)

    2011-08-04

    Highlights: > The low-density C/C composites were modified by SiC-MoSi{sub 2}-CrSi{sub 2} multiphase coating by pack cementation. > The thermal fatigue behavior of the modified C/C composites was studied after undergoing thermal cycling for 20 times under the different environments. > The decrease of the flexural strength of the modified C/C composites during thermal cycle in air was primarily attributed to the partial oxidation of the modified C/C samples. - Abstract: Carbon/carbon (C/C) composites were modified by SiC-MoSi{sub 2}-CrSi{sub 2} multiphase coating by pack cementation, and their thermal fatigue behavior under thermal cycling in Ar and air environments was investigated. The modified C/C composites were characterized by scanning electron microscopy and X-ray diffraction. Results of tests show that, after 20-time thermal cycles between 1773 K and room temperature in Ar environment, the flexural strength of modified C/C samples decreased lightly and the percentage of remaining strength was 94.92%. While, after thermal cycling between 1773 K and room temperature in air for 20 times, the weight loss of modified C/C samples was 5.1%, and the flexural strength of the modified C/C samples reduced obviously and the percentage of remaining strength was only 75.22%. The fracture mode of modified C/C samples changed from a brittle behavior to a pseudo-plastic one as the service environment transformed from Ar to air. The decrease of the flexural strength during thermal cycle in air was primarily attributed to the partial oxidation of modified C/C samples.

  2. Hydrogen Bonding and Vibrational Spectroscopy: A Theoretical Study

    Science.gov (United States)

    Chaban, Galina M.

    2005-01-01

    Effects of hydrogen bonding on vibrational spectra are studied for several hydrogen-bonded complexes, in which hydrogen bonding ranges from weak (25 kcal/mol). The systems studied include complexes of inorganic acids and salts with water and ammonia, as well as complexes of several organic molecules (nitriles and amino acids) with water. Since anharmonic effects are very strong in hydrogen-bonded systems, anharmonic vibrational frequencies and infrared intensities are computed using the correlation-corrected vibrational self-consistent field (CC-VSCF) method with ab initio potential surfaces at the MP2 and CCSD(T) levels. The most common spectral effects induced by hydrogen bonding are red shifts of stretching vibrational frequencies ranging from approx.200/cm to over 2000/cm and significant increases of infrared intensities for those bonds that participate in hydrogen bonding. However, some systems (e.g. nitrile-water complexes) exhibit shifts in the opposite direction (to the blue) upon formation of hydrogen bonds.

  3. Hydrogen bonding in ionic liquids.

    Science.gov (United States)

    Hunt, Patricia A; Ashworth, Claire R; Matthews, Richard P

    2015-03-07

    Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (ρBCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X-H σ* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak

  4. Iron-catalyzed aerobic oxidation of allylic alcohols: the issue of C═C bond isomerization.

    Science.gov (United States)

    Liu, Jinxian; Ma, Shengming

    2013-10-18

    An aerobic oxidation of allylic alcohols using Fe(NO3)3·9H2O/TEMPO/NaCl as catalysts under atmospheric pressure of oxygen at room temperature was developed. This eco-friendly and mild protocol provides a convenient pathway to the synthesis of stereodefined α,β-unsaturated enals or enones with the retention of the C-C double-bond configuration.

  5. Additional disulfide bonds in insulin

    DEFF Research Database (Denmark)

    Vinther, Tine N; Pettersson, Ingrid; Huus, Kasper

    2015-01-01

    The structure of insulin, a glucose homeostasis-controlling hormone, is highly conserved in all vertebrates and stabilized by three disulfide bonds. Recently, we designed a novel insulin analogue containing a fourth disulfide bond located between positions A10-B4. The N-terminus of insulin's B......-chain is flexible and can adapt multiple conformations. We examined how well disulfide bond predictions algorithms could identify disulfide bonds in this region of insulin. In order to identify stable insulin analogues with additional disulfide bonds, which could be expressed, the Cβ cut-off distance had...... in comparison to analogues with additional disulfide bonds that were more difficult to predict. In contrast, addition of the fourth disulfide bond rendered all analogues resistant to fibrillation under stress conditions and all stable analogues bound to the insulin receptor with picomolar affinities. Thus...

  6. Method 446.0: In Vitro Determination of Chlorophylls a, b, c + c and Pheopigments in 1 2Marine And Freshwater Algae by Visible Spectrophotometry

    Science.gov (United States)

    This method provides a procedure for determination of chlorophylls a (chl a), b (chl b), c + c 1 2 (chl c + c ) and pheopigments of chlorophyll a (pheo a) 1 2 found in marine and freshwater phytoplankton. Chlorophyllide a is determined as chl a. Visible wavelength spectrophotomet...

  7. Numerical modelling of micro-machining of f.c.c. single crystal: Influence of strain gradients

    KAUST Repository

    Demiral, Murat

    2014-11-01

    A micro-machining process becomes increasingly important with the continuous miniaturization of components used in various fields from military to civilian applications. To characterise underlying micromechanics, a 3D finite-element model of orthogonal micro-machining of f.c.c. single crystal copper was developed. The model was implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine VUMAT. Strain-gradient crystal-plasticity and conventional crystal-plasticity theories were used to demonstrate the influence of pre-existing and evolved strain gradients on the cutting process for different combinations of crystal orientations and cutting directions. Crown Copyright © 2014.

  8. Ligand versus Complex: C-F and C-H Bond Activation of Polyfluoroaromatics at a Cyclic (Alkyl)(Amino)Carbene.

    Science.gov (United States)

    Paul, Ursula S D; Radius, Udo

    2017-03-17

    C-F and C-H bond activation reactions of polyfluoroaromatics at the cyclic (alkyl)(amino)carbene (cAAC) cAACmethyl (1) are reported. Studies on the C-F bond activation using the cAAC-stabilized nickel(0) complex [Ni(cAACmethyl )2 ] (2) have shown that 2 does not react with fluorinated arenes. However, these investigations led to the observation of C-F bond cleavage of perfluorinated arenes by the carbene ligand cAACmethyl (1) itself. The reaction of 1 with C6 F6 , C6 F5 -C6 F5 , C6 F5 -CF3 , and C5 F5 N afforded the insertion products of cAAC into one of the C-F bonds of the substrate, that is, the C-F bond activation products (cAACmethyl )F(Arf ) (Arf =C6 F5 4 a, C6 F4 -C6 F5 4 b, C6 F4 -CF3 4 c, C5 F4 N 4 d). These products decompose readily upon heating to 80 °C within a few hours in solution with formation of ionic iminium salts [(cAACmethyl )(Arf )][X] 6 a-d or neutral alkenyl perfluoroaryl imine compounds 7 a-d. The compounds (cAACmethyl )F(Arf ) 4 a-d readily transfer fluoride, which has been exemplified by the fluoride transfer of all compounds using BF3 etherate as fluoride acceptor. Fluoride transfer has also been achieved starting from (cAACmethyl )F(C6 F4 -CF3 ) (4 c) or (cAACmethyl )F(C5 F4 N) (4 d) to other selected substrates such as trimethylchlorosilane, benzoyl chloride and tosyl chloride. Instead of C-F bond activation, insertion of the cAAC into the C-H bond was observed if 1 was treated with the partially fluorinated arenes C6 F5 H, 1,2,4,5-C6 F4 H2 , 1,3,5-C6 F3 H3 , and 1,3-C6 F2 H4 . The compounds (cAACmethyl )H(Arf ) (Arf =C6 F5 12 e, 2,3,5,6-C6 F4 H 12 f, 2,4,6-C6 F3 H2 12 g and 2,6-C6 F2 H3 12 h) have been isolated in good yields and have been characterized including X-ray analysis. Fluorobenzene C6 FH5 (pKa ≈37), the least C-H acidic fluoroarene used in this study, does not react. In order to investigate the scope and limitations of this type of cAAC C-H bond activation reaction, cAACmethyl (1) was treated

  9. Metal-metal bonds in biology.

    Science.gov (United States)

    Lindahl, Paul A

    2012-01-01

    Nickel-containing carbon monoxide dehydrogenases, acetyl-CoA synthases, nickel-iron hydrogenases, and diron hydrogenases are distinct metalloenzymes yet they share a number of important characteristics. All are O(2)-sensitive, with active-sites composed of iron and/or nickel ions coordinated primarily by sulfur ligands. In each case, two metals are juxtaposed at the "heart" of the active site, within range of forming metal-metal bonds. These active-site clusters exhibit multielectron redox abilities and must be reductively activated for catalysis. Reduction potentials are milder than expected based on formal oxidation state changes. When reductively activated, each cluster attacks an electrophilic substrate via an oxidative addition reaction. This affords a two-electron-reduced substrate bound to one or both metals of an oxidized cluster. M-M bonds have been established in hydrogenases where they serve to initiate the oxidative addition of protons and perhaps stabilize active sites in multiple redox states. The same may be true of the CODH and ACS active sites-Ni-Fe and Ni-Ni bonds in these sites may play critical roles in catalysis, stabilizing low-valence states and initiating oxidative addition of CO(2) and methyl group cations, respectively. In this article, the structural and functional commonalities of these metalloenzyme active sites are described, and the case is made for the formation and use of metal-metal bonds in each enzyme mentioned. As a post-script, the importance of Fe-Fe bonds in the nitrogenase FeMoco active site is discussed. Copyright © 2011 Elsevier Inc. All rights reserved.

  10. NMR and Raman spectroscopy monitoring of proton/deuteron exchange in aqueous solutions of ionic liquids forming hydrogen bond: a role of anions, self-aggregation, and mesophase formation.

    Science.gov (United States)

    Klimavicius, Vytautas; Gdaniec, Zofia; Kausteklis, Jonas; Aleksa, Valdemaras; Aidas, Kestutis; Balevicius, Vytautas

    2013-09-05

    The H/D exchange process in the imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride ([C10mim][Br] and [C10mim][Cl]) in D2O solutions of various concentrations was studied applying (1)H, (13)C NMR, and Raman spectroscopy. The time dependencies of integral intensities in NMR spectra indicate that the H/D exchange in [C10mim][Br] at very high dilution (10(-4) mole fraction of RTIL) runs only slightly faster than in [C10mim][Cl]. The kinetics of this process drastically changes above critical aggregation concentration (CAC). The time required to reach the apparent reaction saturation regime in the solutions of 0.01 mole fraction of RTIL was less 10 h for [C10mim][Br], whereas no such features were seen for [C10mim][Cl] even tens of days after the sample was prepared. The H/D exchange was not observed in the liquid crystalline gel mesophase. The role of anions, self-aggregation (micellization), and mesophase formation has been discussed. Crucial influence of Br(-) and Cl(-) anions on the H/D exchange rates above CAC could be related to the short-range ordering and molecular microdynamics, in particular that of water molecules. The concept of the conformational changes coupled with the H/D exchange in imidazolium-based ionic liquids with longer hydrocarbon chains can be rejected in the light of (13)C NMR experiment. The revealed changes in (13)C NMR spectra are caused by the secondary ((13)C) isotope effects not being the signal shifts due to the conformational trans-gauche transition.

  11. A discrete event simulation model for evaluating the performances of an m/g/c/c state dependent queuing system.

    Directory of Open Access Journals (Sweden)

    Ruzelan Khalid

    Full Text Available M/G/C/C state dependent queuing networks consider service rates as a function of the number of residing entities (e.g., pedestrians, vehicles, and products. However, modeling such dynamic rates is not supported in modern Discrete Simulation System (DES software. We designed an approach to cater this limitation and used it to construct the M/G/C/C state-dependent queuing model in Arena software. Using the model, we have evaluated and analyzed the impacts of various arrival rates to the throughput, the blocking probability, the expected service time and the expected number of entities in a complex network topology. Results indicated that there is a range of arrival rates for each network where the simulation results fluctuate drastically across replications and this causes the simulation results and analytical results exhibit discrepancies. Detail results that show how tally the simulation results and the analytical results in both abstract and graphical forms and some scientific justifications for these have been documented and discussed.

  12. The C-C Chemokines CCL17 and CCL22 and Their Receptor CCR4 in CNS Autoimmunity

    Directory of Open Access Journals (Sweden)

    Stefanie Scheu

    2017-11-01

    Full Text Available Multiple sclerosis (MS is a chronic inflammatory demyelinating disease of the central nervous system (CNS. It affects more than two million people worldwide, mainly young adults, and may lead to progressive neurological disability. Chemokines and their receptors have been shown to play critical roles in the pathogenesis of experimental autoimmune encephalomyelitis (EAE, a murine disease model induced by active immunization with myelin proteins or transfer of encephalitogenic CD4+ T cells that recapitulates clinical and neuropathological features of MS. Chemokine ligand-receptor interactions orchestrate leukocyte trafficking and influence multiple pathophysiological cellular processes, including antigen presentation and cytokine production by dendritic cells (DCs. The C-C class chemokines 17 (CCL17 and 22 (CCL22 and their C-C chemokine receptor 4 (CCR4 have been shown to play an important role in homeostasis and inflammatory responses. Here, we provide an overview of the involvement of CCR4 and its ligands in CNS autoimmunity. We review key clinical studies of MS together with experimental studies in animals that have demonstrated functional roles of CCR4, CCL17, and CCL22 in EAE pathogenesis. Finally, we discuss the therapeutic potential of newly developed CCR4 antagonists and a humanized anti-CCR4 antibody for treatment of MS.

  13. First observation of the isospin violating decay $J/\\psi\\rightarrow \\Lambda\\bar{\\Sigma}^{0}+c.c.$

    CERN Document Server

    Ablikim, M; Ambrose, D J; An, F F; An, Q; An, Z H; Bai, J Z; Ban, Y; Becker, J; Berger, N; Bertani, M; Bian, J M; Boger, E; Bondarenko, O; Boyko, I; Briere, R A; Bytev, V; Cai, X; Cakir, O; Calcaterra, A; Cao, G F; Cetin, S A; Chang, J F; Chelkov, G; Chen, G; Chen, H S; Chen, J C; Chen, M L; Chen, S J; Chen, Y; Chen, Y B; Cheng, H P; Chu, Y P; Cronin-Hennessy, D; Dai, H L; Dai, J P; Dedovich, D; Deng, Z Y; Denig, A; Denysenko, I; Destefanis, M; Ding, W M; Ding, Y; Dong, L Y; Dong, M Y; Du, S X; Fang, J; Fang, S S; Fava, L; Feldbauer, F; Feng, C Q; Ferroli, R B; Fu, C D; Fu, J L; Gao, Y; Geng, C; Goetzen, K; Gong, W X; Gradl, W; Greco, M; Gu, M H; Gu, Y T; Guan, Y H; Guo, A Q; Guo, L B; Guo, Y P; Han, Y L; Hao, X Q; Harris, F A; He, K L; He, M; He, Z Y; Held, T; Heng, Y K; Hou, Z L; Hu, H M; Hu, J F; Hu, T; Huang, B; Huang, G M; Huang, J S; Huang, X T; Huang, Y P; Hussain, T; Ji, C S; Ji, Q; Ji, X B; Ji, X L; Jia, L K; Jiang, L L; Jiang, X S; Jiao, J B; Jiao, Z; Jin, D P; Jin, S; Jing, F F; Kalantar-Nayestanaki, N; Kavatsyuk, M; Kuehn, W; Lai, W; Lange, J S; Li, C H; Li, Cheng; Li, Cui; Li, D M; Li, F; Li, G; Li, H B; Li, J C; Li, K; Li, Lei; Li, N B; Li, Q J; Li, S L; Li, W D; Li, W G; Li, X L; Li, X N; Li, X Q; Li, X R; Li, Z B; Liang, H; Liang, Y F; Liang, Y T; Liao, G R; Liao, X T; Liu, B J; Liu, C L; Liu, C X; Liu, C Y; Liu, F H; Liu, Fang; Liu, Feng; Liu, H; Liu, H B; Liu, H H; Liu, H M; Liu, H W; Liu, J P; Liu, K Y; Liu, Kai; Liu, Kun; Liu, P L; Liu, S B; Liu, X; Liu, X H; Liu, Y; Liu, Y B; Liu, Z A; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H; Lu, G R; Lu, H J; Lu, J G; Lu, Q W; Lu, X R; Lu, Y P; Luo, C L; Luo, M X; Luo, T; Luo, X L; Lv, M; Ma, C L; Ma, F C; Ma, H L; Ma, Q M; Ma, S; Ma, T; Ma, X Y; Ma, Y; Maas, F E; Maggiora, M; Malik, Q A; Mao, H; Mao, Y J; Mao, Z P; Messchendorp, J G; Min, J; Min, T J; Mitchell, R E; Mo, X H; Morales, C Morales; Motzko, C; Muchnoi, N Yu; Muramatsu, H; Nefedov, Y; Nicholson, C; Nikolaev, I B; Ning, Z; Olsen, S L; Ouyang, Q; Pacetti, S; Park, J W; Pelizaeus, M; Peng, H P; Peters, K; Ping, J L; Ping, R G; Poling, R; Prencipe, E; Qi, M; Qian, S; Qiao, C F; Qin, X S; Qin, Y; Qin, Z H; Qiu, J F; Rashid, K H; Rong, G; Ruan, X D; Sarantsev, A; Schaefer, B D; Schulze, J; Shao, M; Shen, C P; Shen, X Y; Sheng, H Y; Shepherd, M R; Song, X Y; Spataro, S; Spruck, B; Sun, D H; Sun, G X; Sun, J F; Sun, S S; Sun, X D; Sun, Y J; Sun, Y Z; Sun, Z J; Sun, Z T; Tang, C J; Tang, X; Tapan, X F Tang I; Thorndike, E H; Tian, H L; Toth, D; Ullrich, M; Varner, G S; Wang, B; Wang, B Q; Wang, K; Wang, L L; Wang, L S; Wang, M; Wang, P; Wang, P L; Wang, Q; Wang, Q J; Wang, S G; Wang, X L; Wang, Y D; Wang, Y F; Wang, Y Q; Wang, Z; Wang, Z G; Wang, Z Y; Wei, D H; Weidenkaff, P; Wen, Q G; Wen, S P; Werner, M; Wiedner, U; Wu, L H; Wu, N; Wu, S X; Wu, W; Wu, Z; Xia, L G; Xiao, Z J; Xie, Y G; Xiu, Q L; Xu, G F; Xu, G M; Xu, H; Xu, Q J; Xu, X P; Xu, Z R; Xue, F; Xue, Z; Yan, L; Yan, W B; Yan, Y H; Yang, H X; Yang, Y; Yang, Y X; Ye, H; Ye, M; Ye, M H; Yu, B X; Yu, C X; Yu, J S; Yu, S P; Yuan, C Z; Yuan, W L; Yuan, Y; Zafar, A A; Zallo, A; Zeng, Y; Zhang, B X; Zhang, B Y; Zhang, C C; Zhang, D H; Zhang, H H; Zhang, H Y; Zhang, J; Zhang, J Q; Zhang, J W; Zhang, J Y; Zhang, J Z; Zhang, S H; Zhang, T R; Zhang, X J; Zhang, X Y; Zhang, Y; Zhang, Y H; Zhang, Y S; Zhang, Z P; Zhang, Z Y; Zhao, G; Zhao, H S; Zhao, J W; Zhao, K X; Zhao, Lei; Zhao, Ling; Zhao, M G; Zhao, Q; Zhao, S J; Zhao, T C; Zhao, X H; Zhao, Y B; Zhao, Z G; Zhemchugov, A; Zheng, B; Zheng, J P; Zheng, Y H; Zheng, Z P; Zhong, B; Zhong, J; Zhou, L; Zhou, X K; Zhou, X R; Zhu, C; Zhu, K; Zhu, K J; Zhu, S H; Zhu, X L; Zhu, X W; Zhu, Y C; Zhu, Y M; Zhu, Y S; Zhu, Z A; Zhuang, J; Zou, B S; Zou, J H; Zuo, J X

    2012-01-01

    Using a sample of $(225.2\\pm 2.8)\\times 10^6$ $J/\\psi$ events collected with the BESIII detector, we present results of a study of $J/\\psi\\rightarrow \\gamma\\Lambda\\bar{\\Lambda}$ and report the first observation of the isospin violating decay $J/\\psi\\rightarrow\\Lambda\\bar{\\Sigma}^{0}+c.c.$, in which $\\bar{\\Sigma}^{0}$ decays to $\\gamma \\bar{\\Lambda}$. The measured branching fractions are $\\mathcal{B}(J/\\psi\\rightarrow\\bar{\\Lambda}\\Sigma^{0}$) = $(1.46\\pm0.11\\pm0.12) \\times10^{-5}$ and $\\mathcal{B}(J/\\psi\\rightarrow\\Lambda\\bar{\\Sigma^{0}}$) = $(1.37\\pm0.12\\pm0.11) \\times10^{-5}$. We search for $\\Lambda(1520) \\rightarrow \\gamma \\Lambda$ decay, and find no evident signal, and an upper limit for the product branching fraction $\\mathcal{B}(J/\\psi\\rightarrow\\Lambda\\bar{\\Lambda}(1520)+c.c.)\\times \\mathcal{B}(\\Lambda(1520)\\rightarrow\\gamma\\Lambda)<4.1 \\times10^{-6}$ is set at the 90% confidence level. We also report the observation of $\\eta_{c}\\rightarrow\\Lambda\\bar{\\Lambda}$ in $J/\\psi \\rightarrow \\gamma \\eta_{c}$...

  14. Vibrationally Excited c-C_3H_2 Re-Visited New Laboratory Measurements and Theoretical Calculations

    Science.gov (United States)

    Gupta, Harshal; Westerfield, J. H.; Baraban, Joshua H.; Changala, Bryan; Thorwirth, Sven; Stanton, John F.; Martin-Drumel, Marie-Aline; Pirali, Olivier; Gottlieb, Carl A.; McCarthy, Michael C.

    2017-06-01

    Cyclopropenylidene, c-C_3H_2, is one of the more abundant organic molecules in the interstellar medium, as evidenced from astronomical detection of its single ^{13}C and both its singly- and doubly-deuterated isotopic species. For this reason, vibrational satellites are of considerable astronomical interest, and were the primary motivation for the earlier laboratory work by Mollaaghababa and co-workers [1]. The recent detection of intense unidentified lines near 18 GHz in a hydrocarbon discharge by FT microwave spectroscopy has spurred a renewed search for the vibrational satellite transitions of c-C_3H_2. Several strong lines have been definitively assigned to the v_6 progression on the basis of follow-up measurements at 3 mm, double resonance and millimeter-wave absorption spectroscopy, and new theoretical calculations using a rovibrational VMP2 method [2] and a high-quality ab initio potential energy surface. The treatment was applied to several excited states as well as the ground state, and included deperturbation of Coriolis interactions. [1] R. Mollaaghababa, C.A. Gottlieb, J. M. Vrtilek, and P. Thaddeus, J. Chem. Phys., 99, 890-896 (1992). [2] P. B. Changala and J. H. Baraban. J. Chem. Phys., 145, 174106 (2016).

  15. The Influence of the Position of the Double Bond and Ring Size on the Stability of Hydrogen Bonded Complexes.

    Science.gov (United States)

    Cheng, Shumin; Tang, Shanshan; Tsona, Narcisse T; Du, Lin

    2017-09-12

    To study the influence of the position of the double bond and ring size on the stability of hydrogen bonded complexes, the 1:1 complexes formed between 2,2,2-trifluoroethanol (TFE) and three heterocyclic compounds including 2,3-dihydrofuran (2,3-DHF), 2,5-dihydrofuran (2,5-DHF) and 3,4-dihydropyran (3,4-DHP) were investigated systematically. The formation of hydrogen bonded TFE-2,3-DHF, TFE-2,5-DHF and TFE-3,4-DHP complexes were identified by gas phase FTIR spectroscopy at room temperature, and the OH-stretching fundamental transition of TFE was red shifted upon complexation. The competition between the O atom and π-electrons bonding sites within the complexes was studied, and the O-H···π type hydrogen bond was found to be less stable than the O-H···O in all three cases. The observed red shifts of the OH-stretching fundamental transitions in the complexes were attributed to the formation of O-H···O hydrogen bond. Equilibrium constants of the complexation reactions were determined from measured and calculated OH-stretching fundamental intensities. Both theoretical calculations and experimental results reveal that the hydrogen bond strengths in the complexes follow the sequence: TFE-2,5-DHF > TFE-2,3-DHF ≈ TFE-3,4-DHP, thus the position of the double bond exerts significantly larger influence than ring size on the stability of the selected hydrogen bonded complexes.

  16. Developing Foreign Bond Markets: The Arirang Bond Experience in Korea

    OpenAIRE

    Jonathan A. Batten; Peter G. Szilagyi

    2006-01-01

    This study investigates the development of Korea’s foreign bond (Arirang) market for won-denominated foreign bonds. We provide an institutional perspective and discuss the problems, concerns and key issues related to the development of this market. We find no evidence that Arirang issuance either crowded out local debt or had exchange rate implications. Overall, the Korean experience provides valuable lessons for other emerging nations seeking to build bond markets for local and foreign issue...

  17. The methylenetetrahydrofolate reductase c.c.677 C>T and c.c.1298 A>C polymorphisms in reproductive failures: Experience from an RSA and RIF study on a Polish population.

    Science.gov (United States)

    Nowak, Izabela; Bylińska, Aleksandra; Wilczyńska, Karolina; Wiśniewski, Andrzej; Malinowski, Andrzej; Wilczyński, Jacek R; Radwan, Paweł; Radwan, Michał; Barcz, Ewa; Płoski, Rafał; Motak-Pochrzęst, Hanna; Banasik, Małgorzata; Sobczyński, Maciej; Kuśnierczyk, Piotr

    2017-01-01

    Almost 1600 individuals from the Polish population were recruited to this study. Among them 319 were fertile couples, 289 were recurrent spontaneous abortion (RSA) couples, and 131 were in the group of recurrent implantation failure (RIF) following in vitro fertilization. The aim of this study was to evaluate the MTHFR c.c.677 C>T and c.c.1298 A>C polymorphisms' association with RSA and RIF. We used PCR-RFLP with HinfI (677 C>T) and MboII (1298 A>C) digestion. We observed a protective effect of the female AC genotype (OR = 0.64, p = 0.01) and the C allele (AC+CC genotypes; OR = 0.65, p = 0.009) against RSA. Moreover, 1298 AA/677 CT women were more frequent in RSA (31.14%) and RIF (25.20%) groups in comparison to fertile women (22.88%), although this difference was significant only in the case of RSA (p = 0.022, OR = 1.52). Male combined genotype analysis revealed no association with reproductive failure of their partners. Nevertheless, the female/male combination AA/AC of the 1298 polymorphism was more frequent in RSA couples (p = 0.049, OR = 1.49). However, the significant results became insignificant after Bonferroni correction. In addition, analysis of haplotypes showed significantly higher frequency of the C/C haplotype (1298 C/677 C) in the female control group than in the female RSA group (p = 0.03, OR = 0.77). Moreover, the association between elevated homocysteine (Hcy) level in plasma of RSA and RIF women and MTHFR polymorphisms was investigated but did not reveal significant differences. In conclusion, for clinical practice, it is better to check the homocysteine level in plasma and, if the Hcy level is increased, to recommend patients to take folic acid supplements rather than undergo screening of MTHFR for 1298 A>C and 677 C>T polymorphisms.

  18. Formation of [Cu 2 O 2 ] 2+ and [Cu 2 O] 2+ toward C–H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39

    Energy Technology Data Exchange (ETDEWEB)

    Ipek, Bahar; Wulfers, Matthew J.; Kim, Hacksung [Department; Chemical; Göltl, Florian; Hermans, Ive; Smith, Joseph P.; Booksh, Karl S.; Brown, Craig M. [Center; Lobo, Raul F.

    2017-05-26

    Cu-exchanged small-pore zeolites (CHA and AEI) form methanol from methane (>95% selectivity) using a 3-step cyclic procedure (Wulfers et al. Chem. Commun. 2015, 51, 4447-4450) with methanol amounts higher than Cu-ZSM-5 and Cu-mordenite on a per gram and per Cu basis. Here, the CuxOy species formed on Cu-SSZ-13 and Cu-SSZ-39 following O2 or He activation at 450 °C are identified as trans-μ-1,2-peroxo dicopper(II) ([Cu2O2]2+) and mono-(μ-oxo) dicopper(II) ([Cu2O]2+) using synchrotron X-ray diffraction, in situ UV–vis, and Raman spectroscopy and theory. [Cu2O2]2+ and [Cu2O]2+ formed on Cu-SSZ-13 showed ligand-to-metal charge transfer (LMCT) energies between 22,200 and 35,000 cm–1, Cu–O vibrations at 360, 510, 580, and 617 cm–1 and an O–O vibration at 837 cm–1. The vibrations at 360, 510, 580, and 837 cm–1 are assigned to the trans-μ-1,2-peroxo dicopper(II) species, whereas the Cu–O vibration at 617 cm–1 (Δ18O = 24 cm–1) is assigned to a stretching vibration of a thermodynamically favored mono-(μ-oxo) dicopper(II) with a Cu–O–Cu angle of 95°. On the basis of the intensity loss of the broad LMCT band between 22,200 and 35,000 cm–1 and Raman intensity loss at 571 cm–1 upon reaction, both the trans-μ-1,2-peroxo dicopper(II) and mono-(μ-oxo) dicopper(II) species are suggested to take part in methane activation at 200 °C with the trans-μ-1,2-peroxo dicopper(II) core playing a dominant role. A relationship between the [Cu2Oy]2+ concentration and Cu(II) at the eight-membered ring is observed and related to the concentration of [CuOH]+ suggested as an intermediate in [Cu2Oy]2+ formation.

  19. Characterization of Dentine to Assess Bond Strength of Dental Composites

    Science.gov (United States)

    Liaqat, Saad; Aljabo, Anas; Khan, Muhammad Adnan; Ben Nuba, Hesham; Bozec, Laurent; Ashley, Paul; Young, Anne

    2015-01-01

    This study was performed to develop alternating dentine adhesion models that could help in the evaluation of a self-bonding dental composite. For this purpose dentine from human and ivory was characterized chemically and microscopically before and after acid etching using Raman and SEM. Mechanical properties of dentine were determined using 3 point bend test. Composite bonding to dentine, with and without use of acid pre-treatment and/or the adhesive, were assessed using a shear bond test. Furthermore, micro gap formation after restoration of 3 mm diameter cavities in dentine was assessed by SEM. Initial hydroxyapatite level in ivory was half that in human dentine. Surface hydroxyapatites decreased by approximately half with every 23 s of acid etch. The human dentine strength (56 MPa) was approximately double that of ivory, while the modulus was almost comparable to that of ivory. With adhesive use, average shear bond strengths were 30 and 26 MPa with and without acid etching. With no adhesive, average bond strength was 6 MPa for conventional composites. This, however, increased to 14 MPa with a commercial flowable “self–bonding” composite or upon addition of low levels of an acidic monomer to the experimental composite. The acidic monomer additionally reduced micro-gap formation with the experimental composite. Improved bonding and mechanical properties should reduce composite failures due to recurrent caries or fracture respectively.

  20. Characterization of Dentine to Assess Bond Strength of Dental Composites

    Directory of Open Access Journals (Sweden)

    Saad Liaqat

    2015-04-01

    Full Text Available This study was performed to develop alternating dentine adhesion models that could help in the evaluation of a self-bonding dental composite. For this purpose dentine from human and ivory was characterized chemically and microscopically before and after acid etching using Raman and SEM. Mechanical properties of dentine were determined using 3 point bend test. Composite bonding to dentine, with and without use of acid pre-treatment and/or the adhesive, were assessed using a shear bond test. Furthermore, micro gap formation after restoration of 3 mm diameter cavities in dentine was assessed by SEM. Initial hydroxyapatite level in ivory was half that in human dentine. Surface hydroxyapatites decreased by approximately half with every 23 s of acid etch. The human dentine strength (56 MPa was approximately double that of ivory, while the modulus was almost comparable to that of ivory. With adhesive use, average shear bond strengths were 30 and 26 MPa with and without acid etching. With no adhesive, average bond strength was 6 MPa for conventional composites. This, however, increased to 14 MPa with a commercial flowable “self–bonding” composite or upon addition of low levels of an acidic monomer to the experimental composite. The acidic monomer additionally reduced micro-gap formation with the experimental composite. Improved bonding and mechanical properties should reduce composite failures due to recurrent caries or fracture respectively.