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Sample records for c-n bond formation

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Efficient C-O and C-N bond forming cross-coupling reactions catalyzed by core-shell structured Cu/Cu2O nanowires

    KAUST Repository

    Elshewy, Ahmed M.

    2013-12-01

    Oxygen and Nitrogen containing compounds are of utmost importance due to their interesting and diverse biological activities. The construction of the C-O and C–N bonds is of significance as it opens avenues for the introduction of ether and amine linkages in organic molecules. Despite significant advancements in this field, the construction of C-O and C–N bonds is still a major challenge for organic chemists, due to the involvement of harsh reaction conditions or the use of expensive catalysts or ligands in many cases. Thus, it is a challenge to develop alternative, milder, cheaper and more reproducible methodologies for the construction of these types of bonds. Herein, we introduce a new efficient ligand free catalytic system for C-O and C-N bond formation reactions.

  7. A fluorescent turn-on probe for bisulfite based on hydrogen bond-inhibited C=N isomerization mechanism.

    Science.gov (United States)

    Sun, Yuan-Qiang; Wang, Pi; Liu, Jing; Zhang, Jingyu; Guo, Wei

    2012-08-07

    A fluorescence turn-on probe for bisulfite has been developed by taking advantage of the specific reaction of bisulfite and aldehyde in combination with the hydrogen bond inhibited C=N isomerization mechanism. The practical value of this selective and sensitive fluorescent probe was confirmed by its application to detection of bisulfite in granulated sugar.

  8. Degradation of Glyphosate by Mn-Oxide May Bypass Sarcosine and Form Glycine Directly after C-N Bond Cleavage.

    Science.gov (United States)

    Li, Hui; Wallace, Adam F; Sun, Mingjing; Reardon, Patrick; Jaisi, Deb P

    2018-02-06

    Glyphosate is the active ingredient of the common herbicide Roundup. The increasing presence of glyphosate and its byproducts has raised concerns about its potential impact on the environment and human health. In this research, we investigated abiotic pathways of glyphosate degradation as catalyzed by birnessite under aerobic and neutral pH conditions to determine whether certain pathways have the potential to generate less harmful intermediate products. Nuclear magnetic resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC) were utilized to identify and quantify reaction products, and density functional theory (DFT) calculations were used to investigate the bond critical point (BCP) properties of the C-N bond in glyphosate and Mn(IV)-complexed glyphosate. We found that sarcosine, the commonly recognized precursor to glycine, was not present at detectable levels in any of our experiments despite the fact that its half-life (∼13.6 h) was greater than our sampling intervals. Abiotic degradation of glyphosate largely followed the glycine pathway rather than the AMPA (aminomethylphosphonic acid) pathway. Preferential cleavage of the phosphonate adjacent C-N bond to form glycine directly was also supported by our BCP analysis, which revealed that this C-N bond was disproportionately affected by the interaction of glyphosate with Mn(IV). Overall, these results provide useful insights into the potential pathways through which glyphosate may degrade via relatively benign intermediates.

  9. 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).

  10. Unprecedented Reaction Pathway of Sterically Crowded Calcium Complexes: Sequential C-N Bond Cleavage Reactions Induced by C-H Bond Activations.

    Science.gov (United States)

    Yang, Yang; Wang, Haobing; Ma, Haiyan

    2017-01-17

    Five bis(quinolylmethyl)-(1H-indolylmethyl)amine (BQIA) compounds, that is, {(quinol-8-yl-CH2 )2 NCH2 (3-Br-1H-indol-2-yl)} (L(1) H) and {[(8-R(3) -quinol-2-yl)CH2 ]2 NCH(R(2) )[3-R(1) -1H-indol-2-yl]} (L(2-5) H) (L(2) H: R(1) =Br, R(2) =H, R(3) =H; L(3) H: R(1) =Br, R(2) =H, R(3) =iPr; L(4) H: R(1) =H, R(2) =CH3 , R(3) =iPr; L(5) H: R(1) =H, R(2) =nBu, R(3) =iPr) were synthesized and used to prepare calcium complexes. The reactions of L(1-5) H with silylamido calcium precursors (Ca[N(SiMe2 R)2 ]2 (THF)2 , R=Me or H) at room temperature gave heteroleptic products (L(1, 2) )CaN(SiMe3 )2 (1, 2), (L(3, 4) )CaN(SiHMe2 )2 (3 a, 4 a) and homoleptic complexes (L(3, 5) )2 Ca (D3, D5). NMR and X-ray analyses proved that these calcium complexes were stabilized through Ca⋅⋅⋅C-Si, Ca⋅⋅⋅H-Si or Ca⋅⋅⋅H-C agostic interactions. Unexpectedly, calcium complexes ((L(3-5) )CaN(SiMe3 )2 ) bearing more sterically encumbered ligands of the same type were extremely unstable and underwent C-N bond cleavage processes as a consequence of intramolecular C-H bond activation, leading to the exclusive formation of (E)-1,2-bis(8-isopropylquinol-2-yl)ethane. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Rhodium-Catalyzed C-H Bond Functionalization with Amides by Double C-H/C-N Bond Activation.

    Science.gov (United States)

    Meng, Guangrong; Szostak, Michal

    2016-02-19

    The first C-H bond functionalization with amides as the coupling partners via selective activation of the amide N-C bond using rhodium(I) catalysts under highly chemoselective conditions is reported. Notably, this report constitutes the first catalytic activation of the amide N-C(O) bond by rhodium. We expect that this concept will have broad implications for using amides as coupling partners for C-H activation beyond the work described herein.

  12. 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...

  13. 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.

  14. I2/TBHP Mediated C-N and C-H Bond Cleavage of Tertiary Amines toward Selective Synthesis of Sulfonamides and β-Arylsulfonyl Enamines: The Solvent Effect on Reaction.

    Science.gov (United States)

    Lai, Junyi; Chang, Liming; Yuan, Gaoqing

    2016-07-01

    A novel method toward synthesis of sulfonamides and β-arylsulfonyl enamines has been developed via I2/TBHP mediated C-N and C-H bond cleavage of tertiary amines, which features highly selective formation of two different target products depending on the reaction solvent. The experimental results reveal that H2O as the solvent could effectively achieve the C-N bond cleavage to produce sulfonamides due to H2O participating in the reaction process where H2O plays a dual role. Differing from H2O, organic solvents (such as dimethyl sulfoxide) could promote the C-H bond cleavage of tertiary amines to yield β-arylsulfonyl enamines.

  15. Shock response of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX): The C-N bond scission studied by molecular dynamics simulations

    Science.gov (United States)

    Yuan, Jiao-Nan; Wei, Yong-Kai; Zhang, Xiu-Qing; Chen, Xiang-Rong; Ji, Guang-Fu; Kotni, Meena Kumari; Wei, Dong-Qing

    2017-10-01

    The shock response has a great influence on the design, synthesis, and application of energetic materials in both industrial and military areas. Therefore, the initial decomposition mechanism of bond scission at the atomistic level of condensed-phase α-RDX under shock loading has been studied based on quantum molecular dynamics simulations in combination with a multi-scale shock technique. First, based on the frontier molecular orbital theory, our calculated result shows that the N-NO2 bond is the weakest bond in the α-RDX molecule in the ground state, which may be the initial bond for pyrolysis. Second, the changes of bonds under shock loading are investigated by the changes of structures, kinetic bond lengths, and Laplacian bond orders during the simulation. Also, the variation of thermodynamic properties with time in shocked α-RDX at 10 km/s along the lattice vector a for a timescale of up to 3.5 ps is presented. By analyzing the detailed structural changes of RDX under shock loading, we find that the shocked RDX crystal undergoes a process of compression and rotation, which leads to the C-N bond initial rupture. The time variation of dynamic bond lengths in a shocked RDX crystal is calculated, and the result indicates that the C-N bond is easier to rupture than other bonds. The Laplacian bond orders are used to predict the molecular reactivity and stability. The values of the calculated bond orders show that the C-N bonds are more sensitive than other bonds under shock loading. In a word, the C-N bond scission has been validated as the initial decomposition in a RDX crystal shocked at 10 km/s. Finally, the bond-length criterion has been used to identify individual molecules in the simulation. The distance thresholds up to which two particles are considered direct neighbors and assigned to the same cluster have been tested. The species and density numbers of the initial decomposition products are collected according to the trajectory.

  16. Centreline formation of Nb(C, N eutectic in structural steel

    Directory of Open Access Journals (Sweden)

    J. Bernetič

    2010-01-01

    Full Text Available The reduction of area in the through thickness direction is an essential mechanical property of thick steel heavy plates. By a routine control, a very small through thickness reduction of area was found for tensile specimen of a 90 mm plate. Careful investigations of the fracture and section of specimens cut from the as solidified continuously cast 250mmthick slab showed that the cause was the presence of coarse particles of niobium carbonitride as constituent of the quasi eutectic Fe-Nb(C, N that form because of the centerline segregation of niobium.

  17. 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...

  18. Conversion of amides to esters by the nickel-catalysed activation of amide C-N bonds

    Science.gov (United States)

    Hie, Liana; Fine Nathel, Noah F.; Shah, Tejas K.; Baker, Emma L.; Hong, Xin; Yang, Yun-Fang; Liu, Peng; Houk, K. N.; Garg, Neil K.

    2015-08-01

    Amides are common functional groups that have been studied for more than a century. They are the key building blocks of proteins and are present in a broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to the resonance stability of the amide bond. Although amides can readily be cleaved by enzymes such as proteases, it is difficult to selectively break the carbon-nitrogen bond of an amide using synthetic chemistry. Here we demonstrate that amide carbon-nitrogen bonds can be activated and cleaved using nickel catalysts. We use this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory calculations provide insight into the thermodynamics and catalytic cycle of the amide-to-ester transformation. Our results provide a way to harness amide functional groups as synthetic building blocks and are expected to lead to the further use of amides in the construction of carbon-heteroatom or carbon-carbon bonds using non-precious-metal catalysis.

  19. Conversion of amides to esters by the nickel-catalysed activation of amide C-N bonds.

    Science.gov (United States)

    Hie, Liana; Fine Nathel, Noah F; Shah, Tejas K; Baker, Emma L; Hong, Xin; Yang, Yun-Fang; Liu, Peng; Houk, K N; Garg, Neil K

    2015-08-06

    Amides are common functional groups that have been studied for more than a century. They are the key building blocks of proteins and are present in a broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to the resonance stability of the amide bond. Although amides can readily be cleaved by enzymes such as proteases, it is difficult to selectively break the carbon-nitrogen bond of an amide using synthetic chemistry. Here we demonstrate that amide carbon-nitrogen bonds can be activated and cleaved using nickel catalysts. We use this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory calculations provide insight into the thermodynamics and catalytic cycle of the amide-to-ester transformation. Our results provide a way to harness amide functional groups as synthetic building blocks and are expected to lead to the further use of amides in the construction of carbon-heteroatom or carbon-carbon bonds using non-precious-metal catalysis.

  20. Role of Mediator and Effects of Temperature on ortho-C-N Bond Fusion Reactions of Aniline Using Ruthenium Templates: Isolation and Characterization of New Ruthenium Complexes of the in-Situ-Generated Ligands.

    Science.gov (United States)

    Roy, Suman K; Sengupta, Debabrata; Rath, Santi Prasad; Saha, Tanushri; Samanta, Subhas; Goswami, Sreebrata

    2017-05-01

    studies of the oxidized complexes [4] + and [4] 2+ reveal that oxidations are ligand centered. DFT calculations were employed to elucidate the electronic structures as well as the redox processes associated with the above complexes. Aerial ortho-C-N bond fusion reactions of aniline using two different mediators, viz. [Ru III (terpy)Cl 3 ] and [(n-pr) 4 N] + [RuO 4 ] - , have been followed. It is found that in the case of oxidizable Ru(III) mediator complex, C-N bond fusion is limited only to dimerization reaction whereas the high-valent Ru(VII) salt mediates multiple C-N bond fusion reactions leading to the formation of a novel tetradentate N 4 -tetraamidophenylmacrocyclic ligand. Valence ambiguity in the complexes of the resultant redox-active ligands is scrutinized.

  1. 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.

  2. Renaissance of Sandmeyer-Type Reactions: Conversion of Aromatic C-N Bonds into C-X Bonds (X = B, Sn, P, or CF3).

    Science.gov (United States)

    Mo, Fanyang; Qiu, Di; Zhang, Yan; Wang, Jianbo

    2018-02-20

    The Sandmeyer reaction represents an important organic transformation that converts an arylamine to an aryl halide using Cu(I) halide via a diazonium salt intermediate. The reaction was first reported by Sandmeyer in 1884, and a number of named reactions closely related to it have been developed and widely applied in organic synthesis throughout the 20th century. These include the Pschorr reaction for the synthesis of biaryl tricycles, the Gomberg-Bachmann reaction for biaryl formations, the Balz-Schiemann reaction for C-F bond formations, and the Meerwein reaction for arylation of α,β-unsaturated carbonyl compounds. However, all these reactions were discovered before 1940. In 1977, Doyle and co-workers reported an organic phase diazotization process, and Kikukawa and Matsuda used aryldiazonium salts in transition metal-catalyzed cross-coupling reactions. However, completely new processes involving diazonium salts have been seldom reported since then, although aryldiazonium salts are widely utilized in modern organic synthesis. In the past few years, diazonium salt chemistry has been revisited and become a fast-growing research topic. Several novel transformations based on diazonium salts have been developed and have been practiced in organic synthesis. In 2010, we reported a direct conversion of arylamines to pinacol boronates through the reaction of in situ generated aryl diazonium salts with B 2 pin 2 . This new strategy is under metal-free conditions and thus completely avoids contamination by transition metals in the boron products. From readily available arylamines various functionalized arylboronates, some of which are difficult to access by other methods, can be easily obtained with this reaction. Mechanistic investigations indicate the reaction likely follows a radical mechanism, which is similar to traditional Sandmeyer-type reactions. Subsequently, modified reaction conditions for this transformation appeared in the literature, which include light

  3. 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.

  4. 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....

  5. 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.

  6. 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.

  7. Experimental and theoretical investigations of copper (I/II) complexes with triazine-pyrazole derivatives as ligands and their in situ C-N bond cleavage

    Science.gov (United States)

    Wang, Ji-Xiao; Wang, Che; Wang, Xuan; Wang, Xin-Yu; Xing, Yong-Heng; Sun, Qiao

    2015-05-01

    Two copper complexes, Cu(SCN)(Mpz∗T-(EtO)2) (1) (Mpz∗T-(EtO)2 = L3) and CuCl(H2O)(Mpz∗T-O2) (2) (Mpz∗T-O2 = L4) were synthesized by the reaction of 2,4,6-tri(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine (L1) or 2,4,6-tri(1H-pyrazol-1-yl)-1,3,5-triazine (L2) with CuCl2·2H2O in anhydrous ethanol and methanol, respectively. The complexes were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, single crystal X-ray diffraction and X-ray powder diffraction. The structural characterizations and quantum mechanical calculations of the two complexes were analyzed in detail. It was found that an in site reaction occurred during the synthesis process of complexes 1 and 2, likely due to catalytic property of copper ions which leads to the C-N bond cleavage to generate new organic species, namely, Mpz∗T-(EtO)2 (L3) and Mpz∗T-O2 (L4).

  8. Ruthenium(II) Complexes Containing Lutidine-Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of C-N bonds.

    Science.gov (United States)

    Hernández-Juárez, Martín; López-Serrano, Joaquín; Lara, Patricia; Morales-Cerón, Judith P; Vaquero, Mónica; Álvarez, Eleuterio; Salazar, Verónica; Suárez, Andrés

    2015-05-11

    A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4 ) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the C-N bond assisted either by the pincer ligand or a second coordinated H2 molecule. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. 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.

  10. 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

  11. 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.

  12. Enhanced photocatalytic degradation of Amaranth dye on mesoporous anatase TiO2: evidence of C-N, N[double bond, length as m-dash]N bond cleavage and identification of new intermediates.

    Science.gov (United States)

    Naik, Amarja P; Salkar, Akshay V; Majik, Mahesh S; Morajkar, Pranay P

    2017-07-01

    The photocatalytic degradation mechanism of Amaranth, a recalcitrant carcinogenic azo dye, was investigated using mesoporous anatase TiO 2 under sunlight. Mesoporous anatase TiO 2 of a high photocatalytic activity has been synthesized using a sol-gel method and its photocatalytic activity for the degradation of Amaranth dye has been evaluated with respect to Degussa P25. The effect of bi-dentate complexing agents like oxalic acid, ethylene glycol and urea on the surface properties of TiO 2 catalyst has been investigated using TG-DTA, FTIR, HR-TEM, SAED, PXRD, EDS, UV-DRS, PL, BET N 2 adsorption-desorption isotherm studies and BJH analysis. The influence of catalyst properties such as the mesoporous network, pore volume and surface area on the kinetics of degradation of Amaranth as a function of irradiation time under natural sunlight has been monitored using UV-Vis spectroscopy. The highest rate constant value of 0.069 min -1 was obtained for the photocatalytic degradation of Amaranth using TiO 2 synthesized via a urea assisted sol-gel synthesis method. The effect of the reaction conditions such as pH, TiO 2 concentration and Amaranth concentration on the photodegradation rate has been investigated. The enhanced photocatalytic activity of synthesized TiO 2 in comparison with P25 is attributed to the mesoporous nature of the catalyst leading to increased pore diameter, pore volume, surface area and enhanced charge carrier separation efficiency. New intermediates of photocatalytic degradation of Amaranth, namely, sodium-3-hydroxynaphthalene-2,7-disulphonate, 3-hydroxynaphthalene, sodium-4-aminonaphthalenesulphonate and sodium-4-aminobenzenesulphonate have been identified using LC-ESI-MS for the very first time, providing direct evidence for simultaneous bond cleavage pathways (-C-N-) and (-N[double bond, length as m-dash]N-). A new plausible mechanism of TiO 2 catalysed photodegradation of Amaranth along with the comparison of its toxicity to that of its degradation

  13. 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-...

  14. 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.

  15. 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.

  16. 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.

  17. Dichotomous Hydrogen Atom Transfer vs. Proton Coupled Electron Transfer During Activation of X-H Bonds (X = C, N, O) by Nonheme Iron-Oxo Complexes of Variable Basicity

    Science.gov (United States)

    Usharani, Dandamudi; Lacy, David C.; Borovik, A. S.; Shaik, Sason

    2013-01-01

    We describe herein the hydrogen-atom transfer (HAT)/ proton-coupled electron-transfer (PCET) reactivity for FeIV-oxo and FeIII-oxo complexes (1–4) that activate C-H, N-H, and O-H bonds in 9,10 dihydroanthracene (S1), dimethylformamide (S2), 1,2 diphenylhydrazine (S3), p-methoxyphenol (S4), and 1,4-cyclohexadiene (S5). In 1–3, the iron is pentacoordinated by tris[N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) or its derivatives. These complexes are basic, in the order 3 >> 1 > 2. Oxidant 4, [FeIVN4Py(O)]2+ (N4Py: N,N-bis(2-pyridylmethyl)-bis(2-pyridyl) methylamine), is the least basic oxidant. The DFT results match experimental trends and exhibit a mechanistic spectrum ranging from concerted HAT and PCET reactions to concerted-asynchronous proton transfer (PT) / electron transfer (ET) mechanisms, all the way to PT. The singly occupied orbital along the O---H---X (X= C, N, O) moiety in the TS shows clearly that in the PCET cases, the electron is transferred separately from the proton. The Bell-Evans-Polanyi principle does not account for the observed reactivity pattern, as evidenced by the scatter in the plot of calculated barrier vs. reactions driving forces. However, a plot of the deformation energy in the TS vs. the respective barrier provides a clear signature of the HAT/PCET dichotomy. Thus, in all C-H bond activations, the barrier derives from the deformation energy required to create the TS, whereas in N-H/O-H bond activations, the deformation energy is much larger than the corresponding barrier, indicating the presence of stabilizing interaction between the TS fragments. A valence bond model is used to link the observed results with the basicity/acidity of the reactants. PMID:24124906

  18. C N R Rao

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education. C N R Rao. Articles written in Resonance – Journal of Science Education. Volume 7 Issue 3 March 2002 pp 2-5 Article-in-a-Box. Tribute to Michael Faraday · C N R Rao · More Details Fulltext PDF. Volume 14 Issue 5 May 2009 pp 508-517 Reflections. Chemistry ...

  19. C N R Rao

    Indian Academy of Sciences (India)

    C N R Rao. Articles written in Journal of Chemical Sciences. Volume 112 Issue 2 April 2000 pp 83-95 Physical and Theoretical. An indigenous cluster beam apparatus with a reflectron time-of-flight mass spectrometer · G Raina G U Kulkarni R T Yadav V S Ramamurthy C N R Rao · More Details Abstract Fulltext PDF.

  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. 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...

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. "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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

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

  10. 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 ...

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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 ...

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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),.

  1. 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.

  2. 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.

  3. 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

  4. Characteristics of C-, N-DBPs formation from algal organic matter: role of molecular weight fractions and impacts of pre-ozonation.

    Science.gov (United States)

    Zhou, Shiqing; Zhu, Shumin; Shao, Yisheng; Gao, Naiyun

    2015-04-01

    Extracellular organic matter (EOM) and intracellular organic matter (IOM) of Microcystis aeruginosa have been reported to contribute to the formation of carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs). Little is known about DBPs formation from different molecular weight (MW) fractions, especially for N-nitrosodimethylamine (NDMA). This study fractionated EOM and IOM into several MW fractions using a series of ultrafiltration membranes and is the first to report on the C-DBPs and N-DBPs formation from chlorination and chloramination of different MW fractions. Results showed that EOM and IOM were mainly distributed in low-MW (100 KDa) fractions. Additionally, the low-MW and high-MW fractions of EOM and IOM generally took an important part in forming C-DBPs and N-DBPs, either in chlorination or in chloramination. Furthermore, the effects of pre-ozonation on the formation of DBPs in subsequent chlorination and chloramination were also investigated. It was found that ozone shifted the high-MW fractions of EOM and IOM into lower MW fractions and increased the C-DBPs and N-DBPs yields to different degrees. As low-MW fractions are more difficult to remove than high-MW fractions by conventional treatment processes, therefore, activated carbon adsorption, nanofiltration (NF) and biological treatment processes can be ideal to remove the low-MW fractions and minimize the formation potential of C-DBPs and N-DBPs. Moreover, the use of ozone should be carefully considered in the treatment of algal-rich water. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  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. 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.

  19. 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...

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  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. 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.

  9. 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.

  10. 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.

  11. Palladium-catalyzed one-pot three- or four-component coupling of aryl iodides, alkynes, and amines through C-N bond cleavage: efficient synthesis of indole derivatives.

    Science.gov (United States)

    Hao, Wei; Geng, Weizhi; Zhang, Wen-Xiong; Xi, Zhenfeng

    2014-02-24

    An efficient synthesis of N-substituted indole derivatives was realized by combining the Pd-catalyzed one-pot multicomponent coupling approach with cleavage of the C(sp(3))-N bonds. Three or four components of aryl iodides, alkynes, and amines were involved in this coupling process. The cyclopentadiene-phosphine ligand showed high efficiency. A variety of aryl iodides, including cyclic and acyclic tertiary amino aryl iodides, and substituted 1-bromo-2-iodobenzene derivatives could be used. Both symmetric and unsymmetric alkynes substituted with alkyl, aryl, or trimethylsilyl groups could be applied. Cyclic secondary amines such as piperidine, morpholine, 4-methylpiperidine, 1-methylpiperazine, 2-methylpiperidine, and acyclic amines including secondary and primary amines all showed good reactivity. Further application of the resulting indole derivatives was demonstrated by the synthesis of benzosilolo[2,3-b]indole. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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:

  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. 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...

  20. 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

  1. Energetic Properties and Electronic Structure of [C,N,O,P] and [C,N,S,P] Isomers.

    Science.gov (United States)

    Finney, Brian; Thanthiriwatte, K Sahan; Francisco, Joseph S; Dixon, David A

    2017-03-16

    Correlated molecular orbital theory at the coupled cluster CCSD(T) level with augmented correlation consistent basis sets including F12 explicit correlation has been used to predict the structure and energetic properties of the isomers of [C,N,O,P] and [C,N,S,P]. The predicted ground states are the species derived from a trivalent P with a P═O or P═S bond and a cyano group bonded to the P. The other low energy isomers are the isonitriles and they are 1.4 kcal/mol and 6.6 less stable than the ground state for P═O and P═S, respectively. An analysis of the bond energies is provided and the values are compared to the corresponding [N,N,C,O] isomers. Data are provided for searching for these species in interstellar regions.

  2. 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.

  3. 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...

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Plasma-deposited a-C(N) H films

    CERN Document Server

    Franceschini, D E

    2000-01-01

    The growth behaviour, film structure and mechanical properties of plasma-deposited amorphous hydrogenated carbon-nitrogen films are shortly reviewed. The effect of nitrogen-containing gas addition to the deposition to the hydrocarbon atmospheres used is discussed, considering the modifications observed in the chemical composition growth kinetics, carbon atom hybridisation and chemical bonding arrangements of a-C(N):H films. The overall structure behaviour is correlated to the variation of the mechanical properties.

  12. 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.

  13. 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.

  14. 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.

  15. 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...

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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...

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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....

  11. 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.

  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. 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.

  17. 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).

  18. 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(+).

  19. Formation of Anionic C, N-bearing Chains in the Interstellar Medium via Reactions of H‑ with HC x N for Odd-valued x from 1 to 7

    Science.gov (United States)

    Gianturco, F. A.; Satta, M.; Yurtsever, E.; Wester, R.

    2017-11-01

    We investigate the relative efficiencies of low-temperature chemical reactions in the interstellar medium with H‑ anion reacting in the gas phase with cyanopolyyne neutral molecules, leading to the formation of anionic {{{C}}}x{{{N}}}- linear chains of different lengths and of H2. All the reactions turn out to be without barriers, highly exothermic reactions that provide a chemical route to the formation of anionic chains of the same length. Some of the anions have been observed in the dark molecular clouds and in the diffuse interstellar envelopes. Quantum calculations are carried out for the corresponding reactive potential energy surfaces for all the odd-numbered members of the series (x = 1, 3, 5, 7). We employ the minimum energy paths to obtain the relevant transition state configurations and use the latter within the variational transition state model to obtain the chemical rates. The present results indicate that at typical temperatures around 100 K, a set of significantly larger rate values exists for x = 3 and x = 5, while the rate values are smaller for CN‑ and {{{C}}}7{{{N}}}-. At those temperatures, however, all the rates turn out to be larger than the estimates in the current literature for the radiative electron attachment (REA) rates, thus indicating the greater importance of the present chemical path with respect to REA processes at those temperatures. The physical reasons for our findings are discussed in detail and linked with the existing observational findings.

  20. "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.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  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. High N-content a-C:N films elaborated by femtosecond PLD with plasma assistance

    Energy Technology Data Exchange (ETDEWEB)

    Maddi, C. [Université de Lyon, F-69003, Lyon, France, Université de Saint-Étienne, Laboratoire Hubert Curien (UMR 5516 CNRS) , 42000 Saint-Étienne (France); Donnet, C., E-mail: Christophe.Donnet@univ-st-etienne.fr [Université de Lyon, F-69003, Lyon, France, Université de Saint-Étienne, Laboratoire Hubert Curien (UMR 5516 CNRS) , 42000 Saint-Étienne (France); Loir, A.-S.; Tite, T. [Université de Lyon, F-69003, Lyon, France, Université de Saint-Étienne, Laboratoire Hubert Curien (UMR 5516 CNRS) , 42000 Saint-Étienne (France); Barnier, V. [Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, 42023 Saint-Etienne (France); Rojas, T.C.; Sanchez-Lopez, J.C. [Instituto de Ciencia de Materiales de Sevilla (CSIC-US) , Avda. Américo Vespucio 49, 41092 Sevilla (Spain); Wolski, K. [Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, 42023 Saint-Etienne (France); Garrelie, F. [Université de Lyon, F-69003, Lyon, France, Université de Saint-Étienne, Laboratoire Hubert Curien (UMR 5516 CNRS) , 42000 Saint-Étienne (France)

    2015-03-30

    Graphical abstract: - Highlights: • Nitrogen doped amorphous carbon films were deposited by DC reactive plasma femtosecond (fs) -PLD and conventional fs-PLD. • High nitrogen content in plasma assisted films. • More ordered sp2 rich graphitic clusters both in terms of structural and topological order. • Correlation length La of the clusters increases with nitrogen incorporation. • Formation of CN bonds at the expense of CC bonds with N content. • At the highest nitrogen concentration, terminal C≡N groups are incorporated in the film. • Correlation between film composition and plasma process. - Abstract: Amorphous carbon nitride (a-C:N) thin films are a interesting class of carbon-based electrode materials. Therefore, synthesis and characterization of these materials have found lot of interest in environmental analytical microsystems. Herein, we report the nitrogen-doped amorphous carbon thin film elaboration by femtosecond pulsed laser deposition (fs-PLD) both with and without a plasma assistance. The chemical composition and atomic bonding configuration of the films were investigated by multi-wavelength (MW) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The highest nitrogen content, 28 at.%, was obtained with plasma assistance. The I(D)/I(G) ratio and the G peak position increased as a function of nitrogen concentration, whereas the dispersion and full width at half maximum (FWHM) of G peak decreased. This indicates more ordered graphitic like structures in the films both in terms of topological and structural, depending on the nitrogen content. EELS investigations were correlated with MW Raman results. The interpretation of XPS spectra of carbon nitride films remains a challenge. Plasma assisted PLD in the femtosecond regime led to a significant high nitrogen concentration, which is highlighted on the basis of collisional processes in the carbon plasma plume interacting with the nitrogen

  17. 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.

  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. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Extragalactic archaeology with the C, N, and O chemical abundances

    Science.gov (United States)

    Vincenzo, Fiorenzo; Kobayashi, Chiaki

    2018-03-01

    We predict how the C, N, and O abundances within the interstellar medium of galaxies evolve as functions of the galaxy star formation history (SFH). We adopt a hydrodynamical cosmological simulation, focusing on three star-forming disc galaxies with different SFHs. By assuming failed supernovae, we can predict an increasing trend of the gas-phase N/O-O/H abundance diagram, which was not produced in our previous simulations without failed supernovae. At high redshifts, contrary to the predictions of classical chemical evolution models with instantaneous mixing approximation, we find almost flat trends in the N/O-O/H diagram, which are due to the contribution of intermediate-mass stars together with an inhomogeneous chemical enrichment. Finally, we also predict that the average N/O and C/O steadily increase as functions of time, while the average C/N decreases, due to the mass and metallicity dependence of the yields of asymptotic giant branch stars; such variations are more marked during more intense star formation episodes. Our predictions on the CNO abundance evolution can be used to study the SFH of disc galaxies with the James Webb Space Telescope.

  9. 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.

  10. A New Design of In Situ Ti(C,N) Reinforced Composite Coatings and Their Microstructures, Interfaces, and Wear Resistances.

    Science.gov (United States)

    Wang, Mingliang; Cui, Hongzhi; Wei, Na; Ding, Lei; Zhang, Xinjie; Zhao, Yong; Wang, Canming; Song, Qiang

    2018-01-31

    Here, a unique combination of a novel carbon-nitrogen source (g-C 3 N 4 ) with different mole ratios of Ti/g-C 3 N 4 has been utilized to fabricate iron matrix composite coatings by a synchronized powder feeding plasma transferred arc (PTA) cladding technology. The results show that submicron Ti(C,N) particles are successfully fabricated in situ on a Q235 low carbon steel substrate to reinforce the iron matrix composite coatings and exhibit dense microstructures and good metallurgical bonding between the coating and the substrate. The microstructure of the coating consists of an α-Fe matrix and Ti(C,N) particles when the mole ratio of Ti/g-C 3 N 4 is no more than 5:1. The microhardness and wear resistance of the coating gradually improve with increasing abundance of the in-situ-synthesized Ti(C,N) particles. Interestingly, for a Ti/g-C 3 N 4 mole ratio of 6:1, a fine lamellar eutectic Laves phase (Fe 2 Ti) appears, and this phase further improves the microhardness and wear resistance of the coating. The microhardness of the coating is 3.5 times greater than that of the Q235 substrate, and the wear resistance is enhanced 7.66 times over that of the substrate. The Ti(C,N)/Fe 2 Ti and Fe 2 Ti/α-Fe interfaces are very clean, and the crystallographic orientation relationships between the phases are analyzed by high-resolution transmission electron microscopy (HRTEM) and an edge-to-edge matching model. The theoretical predictions and the experimental results are in good agreement. Furthermore, based on the present study, for the solidification process near equilibrium, smaller interatomic spacing misfits and interplanar spacing d-value mismatches contribute to the formation of crystallographic orientation relationships between phases during the PTA cladding process. The existence of orientation relationships is beneficial for improving the properties of the coatings. This work not only expands the application fields of g-C 3 N 4 but also provides a new idea for the

  11. 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.

  12. 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.

  13. 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

  14. Influence of Negative-Bias Voltage on Mechanical Properties of Quaternary Ti(Nb)C(N) Coatings

    Science.gov (United States)

    Gomez, M. E.; Caicedo, J. C.; Amaya, C.; Mendoza, G. A.; Alvarado-Rivera, J.; Munoz-Saldana, J.; Prieto, P.

    2009-03-01

    Mechanical properties of quaternary Ti-Nb-C-N films via r.f magnetron sputtering process were studied by nanoindentation. The r.f. bias voltage was systematically varied from 0, -50, -100 V, keeping all other growth parameters fixed. Active vibration modes were analyzed by using Fourier transformed infrared spectroscopy (FTIR), where bands associated to Ti-N, Nb-C-N and Ti-C-N bonds, and to Ti-Nb-C-N stretching vibrations were found. Nanoindentation results reaching the elastic-plastic behavior of the Ti-Nb-C-N films indicate that both hardness and elastic modulus increase from 22 to 30 GPa and from 220 to 306 GPa, respectively. Thus, increasing the bias-voltage from 0 to -100V a clear improvement of hardness and elastic modulus were obtained.

  15. 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.

  16. Mechanisms of Bond Cleavage during Manganese Oxide and UV Degradation of Glyphosate: Results from Phosphate Oxygen Isotopes and Molecular Simulations.

    Science.gov (United States)

    Jaisi, Deb P; Li, Hui; Wallace, Adam F; Paudel, Prajwal; Sun, Mingjing; Balakrishna, Avula; Lerch, Robert N

    2016-11-16

    Degradation of glyphosate in the presence of manganese oxide and UV light was analyzed using phosphate oxygen isotope ratios and density function theory (DFT). The preference of C-P or C-N bond cleavage was found to vary with changing glyphosate/manganese oxide ratios, indicating the potential role of sorption-induced conformational changes on the composition of intermediate degradation products. Isotope data confirmed that one oxygen atom derived solely from water was incorporated into the released phosphate during glyphosate degradation, and this might suggest similar nucleophilic substitution at P centers and C-P bond cleavage both in manganese oxide- and UV light-mediated degradation. The DFT results reveal that the C-P bond could be cleaved by water, OH(-) or (•)OH, with the energy barrier opposing bond dissociation being lowest in the presence of the radical species, and that C-N bond cleavage is favored by the formation of both nitrogen- and carbon-centered radicals. Overall, these results highlight the factors controlling the dominance of C-P or C-N bond cleavage that determines the composition of intermediate/final products and ultimately the degradation pathway.

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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

  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. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. The chemical composition and band gap of amorphous Si:C:N:H layers

    Energy Technology Data Exchange (ETDEWEB)

    Swatowska, Barbara, E-mail: swatow@agh.edu.pl [AGH University of Science and Technology, Department of Electronics, Mickiewicza Av. 30, 30-059 Krakow (Poland); Kluska, Stanislawa; Jurzecka-Szymacha, Maria [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Mickiewicza Av. 30, 30-059 Krakow (Poland); Stapinski, Tomasz [AGH University of Science and Technology, Department of Electronics, Mickiewicza Av. 30, 30-059 Krakow (Poland); Tkacz-Smiech, Katarzyna [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Mickiewicza Av. 30, 30-059 Krakow (Poland)

    2016-05-15

    Highlights: • Six type of amorphous hydrogenated films were obtained and analysed. • Investigated chemical bondings strongly influenced energy gap values. • Analysed layers could be applied as semiconductors and also as dielectrics. - Abstract: In this work we presented the correlation between the chemical composition of amorphous Si:C:N:H layers of various content of silicon, carbon and nitrogen, and their band gap. The series of amorphous Si:C:N:H layers were obtained by plasma assisted chemical vapour deposition method in which plasma was generated by RF (13.56 MHz, 300 W) and MW (2.45 GHz, 2 kW) onto monocrystalline silicon Si(001) and borosilicate glass. Structural studies were based on FTIR transmission spectrum registered within wavenumbers 400–4000 cm{sup −1}. The presence of Si−C, Si−N, C−N, C=N, C=C, C≡N, Si−H and C−H bonds was shown. The values band gap of the layers have been determined from spectrophotometric and ellipsometric measurements. The respective values are contained in the range between 1.64 eV – characteristic for typical semiconductor and 4.21 eV – for good dielectric, depending on the chemical composition and atomic structure of the layers.

  2. 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...

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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%.

  10. Nucleation-dependant chemical bonding paradigm: the effect of rare earth ions on the nucleation of urea in aqueous solution.

    Science.gov (United States)

    Chen, Xiaoyan; Sun, Congting; Wu, Sixin; Xue, Dongfeng

    2017-03-29

    Rare earth ions can be used to construct a variety of novel structures and are favorable to chemical bonding regulation and design. In this study, the chemical bonding paradigm between rare earth ions (Ln(3+)) and urea molecules in an aqueous solution can be tracked by the evolution of C[double bond, length as m-dash]O, NH2, and CN vibration bands during the urea nucleation stage. Rare earth ions such as La(3+), Gd(3+), and Lu(3+) can manipulate the nucleation time of urea via regulating the nucleation-dependant N-C[double bond, length as m-dash]OH-N hydrogen-bonding between urea molecules. Two types of chemical bondings between Ln(3+) and urea molecules have been confirmed, which are Ln(3+)O[double bond, length as m-dash]C-N and Ln(3+)NH2-C. Compared with Ln(3+)NH2-C, Ln(3+) prefers to coordinate with the O[double bond, length as m-dash]C bond in urea. With a higher concentration of rare earth ions in the solution, some N-C[double bond, length as m-dash]OH-N hydrogen bonds are broken as a consequence of the incorporation of Ln(3+) into the lattice, resulting in the decreased symmetry of local urea molecules in the crystalline nuclei and the consequent Ln(3+) concentration-dependent nucleation time of urea. Moreover, using the ionic electronegativity scale of Ln(3+), the different effects of La(3+), Gd(3+), and Lu(3+) on urea nucleation can be further distinguished. The present study provides basic data for unrevealing the chemical bonding regulation role of rare earth ions in the formation of hydrogen bonded materials, which may give insight into the design and fabrication of novel materials utilizing rare earth ions to adjust the chemical bonding process.

  11. 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.

  12. 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.

  13. 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.

  14. 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...

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Effects of extrinsic point defects in phosphorene: B, C, N, O, and F adatoms

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Gaoxue, E-mail: gaoxuew@mtu.edu, E-mail: pandey@mtu.edu, E-mail: shashi.p.karna.civ@mail.mil; Pandey, Ravindra, E-mail: gaoxuew@mtu.edu, E-mail: pandey@mtu.edu, E-mail: shashi.p.karna.civ@mail.mil [Department of Physics, Michigan Technological University, Houghton, Michigan 49931 (United States); Karna, Shashi P., E-mail: gaoxuew@mtu.edu, E-mail: pandey@mtu.edu, E-mail: shashi.p.karna.civ@mail.mil [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, ATTN: RDRL-WM, Aberdeen Proving Ground, Maryland 21005-5069 (United States)

    2015-04-27

    Phosphorene is emerging as a promising 2D semiconducting material with a direct band gap and high carrier mobility. In this paper, we examine the role of the extrinsic point defects including surface adatoms in modifying the electronic properties of phosphorene using density functional theory. The surface adatoms considered are B, C, N, O, and F with a [He] core electronic configuration. Our calculations show that B and C, with electronegativity close to P, prefer to break the sp{sup 3} bonds of phosphorene and reside at the interstitial sites in the 2D lattice by forming sp{sup 2} like bonds with the native atoms. On the other hand, N, O, and F, which are more electronegative than P, prefer the surface sites by attracting the lone pairs of phosphorene. B, N, and F adsorption will also introduce local magnetic moment to the lattice. Moreover, B, C, N, and F adatoms will modify the band gap of phosphorene, yielding metallic transverse tunneling characters. Oxygen does not modify the band gap of phosphorene, and a diode like tunneling behavior is observed. Our results therefore offer a possible route to tailor the electronic and magnetic properties of phosphorene by the adatom functionalization and provide the physical insights of the environmental sensitivity of phosphorene, which will be helpful to experimentalists in evaluating the performance and aging effects of phosphorene-based electronic devices.

  1. 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.

  2. Precise Probing of Residue Roles by Post-Translational β,γ-C,N Aza-Michael Mutagenesis in Enzyme Active Sites.

    Science.gov (United States)

    Dadová, Jitka; Wu, Kuan-Jung; Isenegger, Patrick G; Errey, James C; Bernardes, Gonçalo J L; Chalker, Justin M; Raich, Lluís; Rovira, Carme; Davis, Benjamin G

    2017-11-22

    Biomimicry valuably allows the understanding of the essential chemical components required to recapitulate biological function, yet direct strategies for evaluating the roles of amino acids in proteins can be limited by access to suitable, subtly-altered unnatural variants. Here we describe a strategy for dissecting the role of histidine residues in enzyme active sites using unprecedented, chemical, post-translational side-chain-β,γ C-N bond formation. Installation of dehydroalanine (as a "tag") allowed the testing of nitrogen conjugate nucleophiles in "aza-Michael"-1,4-additions (to "modify"). This allowed the creation of a regioisomer of His (iso-His, Hisiso) linked instead through its pros-Nπ atom rather than naturally linked via C4, as well as an aza-altered variant aza-Hisiso. The site-selective generation of these unnatural amino acids was successfully applied to probe the contributing roles (e.g., size, H-bonding) of His residues toward activity in the model enzymes subtilisin protease from Bacillus lentus and Mycobacterium tuberculosis pantothenate synthetase.

  3. 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...

  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. Preparation of bulk superhard B-C-N nanocomposite compact

    Science.gov (United States)

    Zhao, Yusheng [Los Alamos, NM; He, Duanwei [Sichuan, CN

    2011-05-10

    Bulk, superhard, B--C--N nanocomposite compacts were prepared by ball milling a mixture of graphite and hexagonal boron nitride, encapsulating the ball-milled mixture at a pressure in a range of from about 15 GPa to about 25 GPa, and sintering the pressurized encapsulated ball-milled mixture at a temperature in a range of from about 1800-2500 K. The product bulk, superhard, nanocomposite compacts were well sintered compacts with nanocrystalline grains of at least one high-pressure phase of B--C--N surrounded by amorphous diamond-like carbon grain boundaries. The bulk compacts had a measured Vicker's hardness in a range of from about 41 GPa to about 68 GPa.

  8. 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.

  9. 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

  10. Copper-Catalyzed Inter/Intramolecular N-Alkenylation of Benzimidazoles via Tandem Processes Involving Selectively Mild Iodination of sp3 C-H Bond at α-Position of Ester.

    Science.gov (United States)

    Lai, Ting-Ting; Xie, Dan; Zhou, Cheng-He; Cai, Gui-Xin

    2016-10-07

    Inter/intramolecular approaches to sp2 C-N bond formation of N-alkenyl benzimidazoles have been accomplished in the presence of an iodide anion associated with a copper catalyst. Both intermolecular and intramolecular reactions included tandem processes, in which selective iodination of sp3 C-H bond at the α-position of ester under mild conditions was demonstrated for the first time. Tandem reactions involving sp3 C-H activation via α-iodo ester intermediate under copper catalysis efficiently provided more than 20 novel azole compounds, and free radicals were not involved in this transformation.

  11. 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.

  12. 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.

  13. 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.

  14. Description of Polar Chemical Bonds from the Quantum Mechanical Interference Perspective.

    Science.gov (United States)

    Fantuzzi, Felipe; Nascimento, Marco Antonio Chaer

    2014-06-10

    The Generalized Product Function Energy Partitioning (GPF-EP) method has been applied to a set of molecules, AH (A = Li, Be, B, C, N, O, F), CO and LiF with quite different dipole moments, in order to investigate the role played by the quantum interference effect in the formation of polar chemical bonds. The calculations were carried out with GPF wave functions treating all the core electrons as a single Hartree-Fock group and the bonding electrons at the Generalized Valence Bond Perfect-Pairing (GVB-PP) level, with the cc-pVTZ basis set. The results of the energy partitioning into interference and quasi-classical contributions along the respective Potential Energy Surfaces (PES) show that the main contribution to the depth of the potential wells comes from the interference term, which is an indication that all the molecules mentioned above form typical covalent bonds. In all cases, the stabilization promoted by the interference term comes from the kinetic contribution, in agreement with previous results. The analysis of the effect of quantum interference on the electron density reveals that while polarization effects (quasi-classical) tend to displace electronic density from the most polarizable atom toward the less polarizable one, interference (quantum effects) counteracts by displacing electronic density to the bond region, giving rise to the right electronic density and dipole moment.

  15. Ab initio thermochemistry with high-level isodesmic corrections: validation of the ATOMIC protocol for a large set of compounds with first-row atoms (H, C, N, O, F).

    Science.gov (United States)

    Bakowies, Dirk

    2009-10-29

    The recently proposed ATOMIC protocol is a fully ab initio thermochemical approach designed to provide accurate atomization energies for molecules with well-defined valence structures. It makes consistent use of the concept of bond-separation reactions to supply high-level precomputed bond increments which correct for errors of lower-level models. The present work extends the approach to the calculation of standard heats of formation and validates it by comparison to experimental and benchmark level ab initio data reported in the literature. Standard heats of formation (298 K) have been compiled for a large sample of 173 neutral molecules containing hydrogen and first-row atoms (C, N, O, F), resorting to several previous compilations and to the original experimental literature. Statistical evaluation shows that the simplest implementation of the ATOMIC protocol (composite model C) achieves an accuracy comparable to the popular Gaussian-3 approach and that composite models A and B perform better. Chemical accuracy (1-2 kcal/mol) is normally achieved even for larger systems with about 10 non-hydrogen atoms and for systems with charge-separated valence structures, bearing testimony to the robustness of the bond-separation reaction model. Effects of conformational averaging have been examined in detail for the series of n-alkanes, and our most refined composite model A reproduces experimental heats of formation quantitatively, provided that conformational averaging is properly accounted for. Several cases of larger discrepancy with respect to experiment are discussed, and potential weaknesses of the approach are identified.

  16. 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…

  17. 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

  18. 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...

  19. 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...

  20. 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.

  1. 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.

  2. 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...

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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...

  11. 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...

  12. 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...

  13. 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

  14. 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....

  15. 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

  16. 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.

  17. 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.

  18. [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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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...

  8. Effects of three global change drivers on terrestrial C:N:P stoichiometry

    DEFF Research Database (Denmark)

    Yue, Kai; Fornara, Dario A; Yang, Wanqin

    2017-01-01

    more common than synergistic or antagonistic interactions, (4) C:N:P stoichiometry of soil and soil microbial biomass shows high homeostasis under global change manipulations, and (5) C:N:P responses to global change are strongly affected by ecosystem type, local climate and experimental conditions......, and elevated CO2 ) on primary productivity and on the biogeochemistry of carbon (C), N and phosphorus (P) across different terrestrial ecosystems. Here we capitalize on this large amount of information by performing a comprehensive meta-analysis (>2000 case studies worldwide) to address how C:N:P stoichiometry...

  9. 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)

  10. 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…

  11. Interaction of acetonitrile with platinum (111): more properties of the η 2(C,N) state and new species in the submonolayer

    Science.gov (United States)

    Ou, E. C.; Young, P. A.; Norton, P. R.

    1992-10-01

    The interaction of CH 3CN on Pt(111) was studied with infrared reflection absorption spectroscopy (IRRAS), temperature programmed desorption (TPD) and work function change (Δφ). Submonolayer, monolayer and multilayer states are distinguished. Measurements at submonolayer coverages are consistent with an orientation of adsorbed acetonitrile which is parallel to the surface. No infrared absorption attributable to the CN bond at around 2200 cm -1 or 1600 cm -1 could be detected by IRRAS, consistent with an η 2(C,N) state for the monolayer, as suggested by Sexton and Avery. In addition, IRRAS data showed that there was a red shift of the C-H stretches of the methyl group with the absence of methyl bends. Agostic bonding involving the β-hydrogen is proposed to explain this observation. We denote this state as η 2∗(C,N) to emphasize the involvement of the β-hydrogen in chemisorption. For monolayer coverage, IR activity for all bands present in the submonolayer spectrum decreased in intensity. The magnitude of this effect seems too large to be attributed solely to screening by neighbouring dipoles. The multilayer showed IR bands in good agreement with those in the vapour phase spectrum. When the crystal was annealed to remove the multilayer and part of the monolayer, IRRAS detected two species with the CN dipole having a component normal to the surface. These are the terminal and bridge bonded acetonitrile adsorbed via the nitrogen atom. Implications for chemical vapour deposition using cyanide containing precursors are discussed.

  12. Study on optimal production of 3-ketovalidoxylamine A C-N lyase ...

    African Journals Online (AJOL)

    3-Ketovalidoxylamine A C-N lyase and glucoside 3-dehydrogenase (G3DH), two key enzymes for valienamine synthesis, are produced by Stenotrophomonas maltrophilia. The condition of producing 3- ketovalidoxylamine A C-N lyase and G3DH was optimized. Validamycin A was showed to be suitable carbon source for ...

  13. 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...

  14. Density functional theory study of the reaction mechanism for competitive carbon-hydrogen and carbon-halogen bond activations catalyzed by transition metal complexes.

    Science.gov (United States)

    Yang, Xinzheng; Hall, Michael B

    2009-03-12

    Carbon-hydrogen and carbon-halogen bond activations between halobenzenes and metal centers were studied by density functional theory with the nonempirical meta-GGA Tao-Perdew-Staroverov-Scuseria functional and an all-electron correlation-consistent polarized valence double-zeta basis set. Our calculations demonstrate that the hydrogen on the metal center and halogen in halobenzene could exchange directly through a kite-shaped transition state. Transition states with this structure were previously predicted to have high energy barriers (J. Am. Chem. Soc. 2005, 127, 279), and this prediction misled others in proposing a mechanism for their recent experimental study (J. Am. Chem. Soc. 2006, 128, 3303). Furthermore, other halo-carbon activation pathways were found in the detailed mechanism for the competitive reactions between cationic titanium hydride complex [Cp*((t)Bu(3)P=N)TiH](+) and chlorobenzene under different pressure of H(2). These pathways include the ortho-C-H and Ti-H bond activations for the formation and release of H(2) and the indirect C-Cl bond activation via beta-halogen elimination for the movement of the C(6)H(4) ring and the formation of a C-N bond in the observed final product. A new stable isomer of the observed product with a similar total energy and an unexpected bridging between the Cp* ring and the metal center by a phenyl ring is also predicted.

  15. 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.

  16. 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.

  17. Ruthenium-Catalyzed C-H Bond Activation Approach to Azolyl Aminals and Hemiaminal Ethers, Mechanistic Evaluations, and Isomer Interconversion.

    Science.gov (United States)

    Singh, Manish K; Akula, Hari K; Satishkumar, Sakilam; Stahl, Lothar; Lakshman, Mahesh K

    2016-03-04

    C(sp3)-N bond-forming reactions between benzotriazole and 5,6-dimethylbenzotriazole with N-methylpyrrolidinone, tetrahydrofuran, tetrahydropyran, diethyl ether, 1,4-dioxane, and isochroman have been conducted using RuCl3•3H2O/t-BuOOH in 1,2-dichloroethane. In all cases, N1 and N2 alkylation products were obtained, and these are readily separated by chromatography. One of these products, 1-(isochroman-1-yl)-5,6-dimethyl-1H-benzotriazole, was examined by X-ray crystallography. It is the first such compound to be analyzed by this method, and notably, the benzotriazolyl moiety is quasi-axially disposed, consistent with the anomeric effect. This has plausible consequences, not observed previously. In contrast to other hemiaminal ether-forming reactions, which proceed via radicals, this Ru-catalyzed process is not suppressed in the presence of a radical inhibitor. Therefore, an oxoruthenium-species-mediated rapid formation of an oxocarbenium intermediate is believed to occur. In the radical-trapping experiment, previously unknown products containing both the benzotriazole and the TEMPO unit have been identified. In these products, it is likely that the benzotriazole is introduced via a Ru-catalyzed C-N bond formation, whereas C-O bond-formation with TEMPO occurs via a radical reaction. We show that reactions of THF with TEMPO are influenced by ambient light. A competitive reaction of THF and THF-d8 with benzotriazole indicated that C-H bond cleavage occurs ca. 5 times faster than C-D cleavage. This is comparable to other metal-mediated radical reactions of THF, but lower than that observed for a reaction catalyzed by n-Bu4N+I-. Detailed mechanistic experiments and comparisons are described. The catalytic system was also evaluated for reactions of benzimidazole, imidazole, 1,2,4-triazole, and 1,2,3-triazole with THF, and successful reactions were achieved in each case. In the course of our studies, we discovered an unexpected but significant isomerization of some of the

  18. Comparative investigation of Si-C-N Films prepared by plasma enhanced chemical vapour deposition and magnetron sputtering

    Science.gov (United States)

    Kozak, A. O.; Porada, O. K.; Ivashchenko, V. I.; Ivashchenko, L. A.; Scrynskyy, P. L.; Tomila, T. V.; Manzhara, V. S.

    2017-12-01

    This paper reports on the results of comparative investigations of Si-C-N films prepared by using both plasma enhanced chemical vapor deposition (PECVD) and DC magnetron sputtering (MS) at different nitrogen flow rates (FN2). The films were characterized by an atomic force microscope, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and photoluminescence spectroscopy. All the deposited films were X-ray amorphous. For the PECVD films, nanohardness (H) and elastic module (E) increase with FN2, which can be assigned to decreasing the hydrogen content. On the contrary, for the films, deposited by magnetron sputtering, the values of H and E decrease, when FN2 increases. The latter is supposed to be due to decreasing a number of strong Si-C bonds and to increasing a number of weak Sisbnd N and Csbnd N bonds. The surface roughness of two types of the films is smaller compared to that of silicon substrates. An increase in nitrogen flow rate causes the smoothing of the film surfaces. The PECVD films deposited at high FN2 exhibit bright photoemission with the main peak at ∼440 nm. The intensity of this peak increases with increasing nitrogen content.

  19. 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

  20. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    John J. Kilbane II

    2005-10-01

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

  2. 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

  3. 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.

  4. 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.

  5. 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....

  6. Electron conjugation versus π-π repulsion in substituted benzenes: why the carbon-nitrogen bond in nitrobenzene is longer than in aniline.

    Science.gov (United States)

    Zhang, Huaiyu; Jiang, Xiaoyu; Wu, Wei; Mo, Yirong

    2016-04-28

    Gas-phase electron diffraction experiments show that the C-N bond in aniline (1.407 Å) is significantly shorter than in nitrobenzene (1.486 Å). It is known that the amino group is electron-donating and the nitro group is electron-withdrawing, and both substitution groups can effectively conjugate with benzene. Thus, it is puzzling why the C-N bond in nitrobenzene is even longer than the single C-N bond in methylamine (1.472 Å). In this work, we performed computations by strictly localizing the π electrons with the block-localized wavefunction (BLW) method, which is a variant of ab initio valence bond theory. Geometry optimizations of electron-localized states, where the conjugation over the C-N bond is quenched, show that the conjugation in nitrobenzene is only half of the conjugation in aniline. But even in optimal electron-localized states, the C-N bond in nitrobenzene is still 0.074 Å longer than in aniline. As a consequence, it is indeed not the π conjugation which is responsible for the disparity of the C-N bond distances in these systems. Instead, we demonstrated that the π-π repulsion, which is contributed by both Pauli exchange and electrostatic interaction, plays the key role in this "abnormal" behavior. Notably, the π resonance within the nitro group generates a considerable dipole, which repels the π electrons in the benzene ring. The deactivation of the resonance within the nitro group significantly shortens the C-N bond by 0.06 Å. The unfavorable π-π electrostatic repulsion is further exemplified by N2O4. In fact, the destabilizing π-π repulsion is ubiquitous but largely neglected in conjugated systems where only the stabilizing conjugation is the focus. Experimental phenomena such as the C-N bond distances in aniline and nitrobenzene result from the balance of both stabilizing and destabilizing forces.

  7. 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.

  8. Alanine check points in HNN and HN(C)N spectra

    Science.gov (United States)

    Chatterjee, Amarnath; Kumar, Ashutosh; Hosur, Ramakrishna V.

    2006-07-01

    Rapid resonance assignment is a key requirement in structural genomics research by NMR. In this context we present here two new pulse sequences, namely, HNN-A and HN(C)N-A that have been developed by simple modification of the previously described pulse sequences, HNN and HN(C)N [S.C. Panchal, N.S. Bhavesh, R.V. Hosur, Improved 3D triple resonance experiments, HNN and HN(C)N, for HN and 15N sequential correlations in (13C, 15N) labeled proteins: application to unfolded proteins, J. Biomol. NMR, 20 (2001) 135-147]. These increase the number of start/check points in HNN and/or HN(C)N spectra and hence help in pacing up resonance assignment in proteins.

  9. The heat of formation of NCO

    Science.gov (United States)

    East, Allan L. L.; Allen, Wesley D.

    1993-09-01

    The heat of formation of NCO has been determined rigorously by state-of-the-art ab initio electronic structure methods, including Møller-Plesset perturbation theory from second through fifth order (MP2-MP5) and coupled-cluster and Brueckner methods incorporating various degrees of excitation [CCSD, CCSD(T), BD, BD(T), and BD(TQ)]. Five independent reactions were investigated to establish a consistent value for ΔHf,0○(NCO): (a) HNCO(X˜ 1A')→H(2S)+NCO(2Π), (b) HNCO(X˜ 1A')→H++NCO-, (c) N(4S)+CO→NCO(2Π), (d) HCN+O(3P)→H(2S)+NCO(2Π), and (e) NH(3Σ-)+CO→H(2S)+NCO(2Π). The one-particle basis sets employed in the study were comprised of as many as 377 contracted Gaussian functions and ranged in quality from [4s2p1d] to [14s9p6d4f] on the (C,N,O) atoms and from [2s1p] to [8s6p4d] on hydrogen. After the addition of bond additivity corrections evaluated from related reactions of precisely known thermochemistry, all five approaches were found to converge on the value ΔHf,0○(NCO)=31.4(5) kcal mol-1. Appurtenant refinements were obtained for the heat of formation of isocyanic acid, ΔHf,0○(HNCO)=-27.5(5) kcal mol-1, and hydrogen cyanide, ΔHf,0○(HCN)=31.9(5) kcal mol-1. The final proposals for ΔHf,0○(NCO) and ΔHf,0○(HNCO) resolve outstanding discrepancies with experiment and provide updates for thermochemical cycles of relevance to combustion chemistry.

  10. Composite Si/C/N powder production by laser induced gas phase reactions

    Energy Technology Data Exchange (ETDEWEB)

    Borsella, E.; Botti, S.; Fantoni, R.; Alexandrescu, R.; Morjan, I.; Popescu, C.; Dikonimos-Makris, T.; Giorgi, R.; Enzo, S.

    1991-08-01

    Ultrafine amorphous Si/C/N ternary powders were prepared in a CO/sub 2/ laser assisted process. This paper demonstrates the possibility of driving the C/N ratio the powder by properly choosing the experimental conditions and the gaseous reactant ratio in the initial mixture containing silane, dimethylamine and ammonia. A kinetic model which accounts for reaching the equilibrium between the gaseous reaction intermediates and the solid products is proposed.

  11. Effect of different C/N ratios on carotenoid and lipid production by Rhodotorula glutinis.

    Science.gov (United States)

    Braunwald, Teresa; Schwemmlein, Lisa; Graeff-Hönninger, Simone; French, William Todd; Hernandez, Rafael; Holmes, William E; Claupein, Wilhelm

    2013-07-01

    Due to the increasing demand for sustainable biofuels, microbial oils as feedstock for the transesterification into biodiesel have gained scientific and commercial interest. Also, microbial carotenoids have a considerable market potential as natural colorants. The carbon to nitrogen (C/N) ratio of the respective cultivation media is one of the most important parameters that influence the production of microbial lipids and carotenoids. Thus, in the present experiment, the influence of different C/N ratios, initial glucose loadings, and ammonium concentrations of the cultivation medium on microbial cell growth and lipid and carotenoid production by the oleaginous red yeast Rhodotorula glutinis has been assessed. As a general trend, both lipid and carotenoid production increased at high C/N ratios. It was shown that not only the final C/N ratio but also the respectively applied initial carbon and nitrogen contents influenced the observed parameters. The lipid yield was not affected by different ammonium contents, while the carotenoid production significantly decreased both at low and high levels of ammonium supply. A glucose-based increase from C/N 70 to 120 did not lead to an increased lipid production, while carotenoid synthesis was positively affected. Generally, it can be asserted that lipid and carotenoid synthesis are stimulated at higher C/N ratios.

  12. 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.

  13. 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...

  14. 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.

  15. Visible light-responded C, N and S co-doped anatase TiO{sub 2} for photocatalytic reduction of Cr(VI)

    Energy Technology Data Exchange (ETDEWEB)

    Lei, X.F., E-mail: leixuefei69@163.com [School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004 (China); Institute of Metallurgical Resource and Environmental Engineering, Northeastern University, Shenyang 110819 (China); Liaoning Key Laboratory of Metallurgical Resource Recycling Science, Shenyang 110819 (China); Liaoning Engineering and Technology Research Center of Boron Resource, Comprehensive, Utilization, Shenyang 110819 (China); Liaoning Provincial Universities Key Laboratory of Boron Resource Ecological, Utilization, Technology and Boron Materials, Shenyang 110819 (China); Xue, X.X.; Yang, H. [Institute of Metallurgical Resource and Environmental Engineering, Northeastern University, Shenyang 110819 (China); Liaoning Key Laboratory of Metallurgical Resource Recycling Science, Shenyang 110819 (China); Liaoning Engineering and Technology Research Center of Boron Resource, Comprehensive, Utilization, Shenyang 110819 (China); Liaoning Provincial Universities Key Laboratory of Boron Resource Ecological, Utilization, Technology and Boron Materials, Shenyang 110819 (China); Chen, C.; Li, X.; Pei, J.X.; Niu, M.C.; Yang, Y.T.; Gao, X.Y. [School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004 (China)

    2015-10-15

    The (C, N and S) co-doped TiO{sub 2} (TH-TiO{sub 2}) samples were synthesized by a sol-gel method calcined at 500 °C, employing butyl titanate as the titanium source and thiourea as the dopant. The structures of TH-TiO{sub 2} samples were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS), photoluminescence (PL) spectroscopy, Thermo gravimetry and differential thermal analysis (TG-DTA), Scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherms. The photocatalytic activities were checked through the photocatalytic reduction of Cr(VI) as a model compound under visible light irradiation. The results showed that the thiourea content played an important role on the microstructure and photocatalytic activity of the samples. According to XPS results, (C, N and S) atoms were successfully co-doped into the nanostructures of TH-TiO{sub 2} samples. TH-TiO{sub 2} samples with thiourea: Ti molar ratio of 1.5 exhibits higher photocatalytic activity than that of the other samples under visible light irradiation, which can be attributed to the synergic effect of the pure anatase structure, the higher light absorption characteristics in visible regions, separation efficiency of electron–hole pairs, the specific surface area and the optimum (C, N and S) content. - Graphical abstract: (C, N and S) co-doped TiO{sub 2} samples show good photocatalytic activity for Cr (VI) reduction under visible light irradiation. - Highlights: • (C, N and S) co-doping in TH-TiO{sub 2} samples can promote the formation of the pure anatase structure. • (C, N and S) atoms were successfully co-doped into the nanostructures of TH-TiO{sub 2} samples. • The band gap energy of TH-TiO{sub 2} samples reduced after (C, N and S) co-doping. • (C, N and S) co-doped TiO{sub 2} samples were effective for the photocatalytic reduction of Cr(VI) under visible light

  16. 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

  17. Trends in Strong Chemical Bonding in C2, CN, CN-, CO, N2, NO, NO+, and O2

    DEFF Research Database (Denmark)

    Kepp, Kasper Planeta

    2017-01-01

    The strong chemical bonds between C, N, and O play a central role in chemistry, and their formation and cleavage are critical steps in very many catalytic processes. The close-lying molecular orbital energies and large correlation effects pose a challenge to electronic structure calculations...... and have led to different bonding interpretations, most notably for C2. One way to approach this problem is by strict benchmark comparison of related systems. This work reports reference electronic structures and computed bond dissociation enthalpies D0 for C2, CN, CN-, CO, N2, NO, NO+, O2 and related...... systems C2+ and C2- at chemical accuracy (~1 kcal/mol or 4 kJ/mol) using CCSD(T)/aug-cc-pV5Z, with additional benchmarks of HF, MP2, CCSD, explicitly correlated F12 methods, and four density functionals. Very large correlation and basis set effects are responsible for up to 93% of total D0. The order...

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. Effects of three global change drivers on terrestrial C:N:P stoichiometry: a global synthesis.

    Science.gov (United States)

    Yue, Kai; Fornara, Dario A; Yang, Wanqin; Peng, Yan; Li, Zhijie; Wu, Fuzhong; Peng, Changhui

    2017-06-01

    Over the last few decades, there has been an increasing number of controlled-manipulative experiments to investigate how plants and soils might respond to global change. These experiments typically examined the effects of each of three global change drivers [i.e., nitrogen (N) deposition, warming, and elevated CO 2 ] on primary productivity and on the biogeochemistry of carbon (C), N, and phosphorus (P) across different terrestrial ecosystems. Here, we capitalize on this large amount of information by performing a comprehensive meta-analysis (>2000 case studies worldwide) to address how C:N:P stoichiometry of plants, soils, and soil microbial biomass might respond to individual vs. combined effects of the three global change drivers. Our results show that (i) individual effects of N addition and elevated CO 2 on C:N:P stoichiometry are stronger than warming, (ii) combined effects of pairs of global change drivers (e.g., N addition + elevated CO 2 , warming + elevated CO 2 ) on C:N:P stoichiometry were generally weaker than the individual effects of each of these drivers, (iii) additive interactions (i.e., when combined effects are equal to or not significantly different from the sum of individual effects) were more common than synergistic or antagonistic interactions, (iv) C:N:P stoichiometry of soil and soil microbial biomass shows high homeostasis under global change manipulations, and (v) C:N:P responses to global change are strongly affected by ecosystem type, local climate, and experimental conditions. Our study is one of the first to compare individual vs. combined effects of the three global change drivers on terrestrial C:N:P ratios using a large set of data. To further improve our understanding of how ecosystems might respond to future global change, long-term ecosystem-scale studies testing multifactor effects on plants and soils are urgently required across different world regions. © 2017 John Wiley & Sons Ltd.

  4. Troponate/Aminotroponate Ruthenium-Arene Complexes: Synthesis, Structure, and Ligand-Tuned Mechanistic Pathway for Direct C-H Bond Arylation with Aryl Chlorides in Water.

    Science.gov (United States)

    Dwivedi, Ambikesh D; Binnani, Chinky; Tyagi, Deepika; Rawat, Kuber S; Li, Pei-Zhou; Zhao, Yanli; Mobin, Shaikh M; Pathak, Biswarup; Singh, Sanjay K

    2016-07-05

    A series of water-soluble troponate/aminotroponate ruthenium(II)-arene complexes were synthesized, where O,O and N,O chelating troponate/aminotroponate ligands stabilized the piano-stool mononuclear ruthenium-arene complexes. Structural identities for two of the representating complexes were also established by single-crystal X-ray diffraction studies. These newly synthesized troponate/aminotroponate ruthenium-arene complexes enable efficient C-H bond arylation of arylpyridine in water. The unique structure-activity relationship in these complexes is the key to achieve efficient direct C-H bond arylation of arylpyridine. Moreover, the steric bulkiness of the carboxylate additives systematically directs the selectivity toward mono- versus diarylation of arylpyridines. Detailed mechanistic studies were performed using mass-spectral studies including identification of several key cyclometalated intermediates. These studies provided strong support for an initial cycloruthenation driven by carbonate-assisted deprotonation of 2-phenylpyridine, where the relative strength of η(6)-arene and the troponate/aminotroponate ligand drives the formation of cyclometalated 2-phenylpyridine Ru-arene species, [(η(6)-arene)Ru(κ(2)-C,N-phenylpyridine) (OH2)](+) by elimination of troponate/aminotroponate ligands and retaining η(6)-arene, while cyclometalated 2-phenylpyridine Ru-troponate/aminotroponate species [(κ (2)-troponate/aminotroponate)Ru(κ(2)-C,N-phenylpyridine)(OH2)2] was generated by decoordination of η(6)-arene ring during initial C-H bond activation of 2-phenylpyridine. Along with the experimental mass-spectral evidence, density functional theory calculation also supports the formation of such species for these complexes. Subsequently, these cycloruthenated products activate aryl chloride by facile oxidative addition to generate C-H arylated products.

  5. Chemical bonding and humidity sensing properties of amorphous carbon nitride (a-CNx) by acetylene gas

    Science.gov (United States)

    Aziz, Siti Aisyah Abd; Purhanudin, Noorain; Awang, Rozidawati

    2017-05-01

    Amorphous carbon nitride (a-CNx) thin films were deposited by radio frequency plasma enhance chemical vapor deposition (RF-PECVD) using a fixed mixture of acetylene (C2H2) at 20 sccm and nitrogen (N2) gases at 50 sccm. The films were deposited at different RF power of 60, 70, 80, 90 and 100 W. The deposition pressure, deposition time and substrate temperature were kept constant at 0.8 mbar, 30 minutes and 100°C, respectively. The chemical bonding of the a-CNx thin films was characterized using Fourier transform infrared spectroscopy (FTIR) and its sensing properties was determined using a home built humidity sensor system. The increase of RF powers leads to an increment of formation of double (C=N) and triple (C≡N) bonds as compared to a-CNx deposited using methane (CH4) or ethane (C2H6) gas. This is due to a higher ratio of C to H atoms in C2H2. The humidity sensing performance show the sensitivity of the films is the highest at low deposition power in changes of relative humidity (%RH). The a-CNx thin film show good repeatability and high sensitivity as a humidity sensing materials which prepared at low RF power.

  6. 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.

  7. 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.

  8. Ecological stoichiometry of C, N and P on different time enclosed in desertification steppe soil

    Science.gov (United States)

    Yang, W. Z.; Jiao, Y.; Jia, Y. Q.

    2017-08-01

    It is the research object for the ecological stoichiometry of C, N and P on the different time of desertification grasslands enclosed and grazing grassland in Taibusi country of the Inner Mongolia, China. Through the measurement and analysis on ecological stoichiometric ratio of C, N and P in soil, the time of desertification grassland enclosed is determined. There are 13 soil of desertification grassland with different en-closure time, and 1 soil of grazing grassland. They are analyzed for the soil organic carbon, total nitro-gen, total phosphorus content and their density. The C/N of soil were increased with the extension of the time of desertification grassland enclosed. To 22 years enclosed, the C/N of grassland desertification soil enclosed is greater than the soil of grazing grassland that is 17. After the desertification grassland is en-closed, the C/N of soil is 13, and it is accumulated to maximum for C and N, and The grazing period is the best.

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

    Energy Technology Data Exchange (ETDEWEB)

    John J. Kilbane II

    2004-10-01

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

  10. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds.

    Science.gov (United States)

    Hansen, Poul Erik

    2015-01-30

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between "static" and tautomeric systems. Isotope effects on chemical shifts are particularly useful in such studies. All kinds of intramolecular hydrogen bonded systems will be treated, typical hydrogen bond donors: OH, NH, SH and NH+, typical acceptors C=O, C=N, C=S C=N-. The paper will be deal with both secondary and primary isotope effects on chemical shifts. These two types of isotope effects monitor the same hydrogen bond, but from different angles.

  11. 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.

  12. 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

  13. Binuclear Complexes and Extended Chains Featuring Pt(II)-Tl(I) Bonds: Influence of the Pyridine-2-Thiolate and Cyclometalated Ligands on the Self-Assembly and Luminescent Behavior.

    Science.gov (United States)

    Berenguer, Jesús R; Lalinde, Elena; Martín, Antonio; Moreno, M Teresa; Sánchez, Sergio; Shahsavari, Hamid R

    2016-08-15

    Platinum solvate complexes [Pt(C6F5)(C^N)(S)] [C^N = phenylpyridinyl (ppy), S = dimethyl sulfoxide (DMSO) (A); C^N = benzoquinolinyl (bzq), S = CH3COCH3 (B)] react with [Tl(Spy)] (Spy = 2-pyridinethiolate) to afford binuclear [{Pt(C6F5)(C^N)}Tl(Spy)] [C^N = ppy (1) and bzq (2)] species containing a Pt-Tl bonding interaction, supported by a μ-Spy-κN,S bridging ligand, as confirmed by X-ray diffraction. However, the related reactions with [Tl(SpyCF3-5)] [SpyCF3-5 = 5-(trifluoromethyl)-2-pyridinethiolate] give neutral extended chains [{Pt(C6F5)(C^N)}Tl(SpyCF3-5)]n [C^N = ppy (3) and bzq (4)]. 3 features a zigzag -Pt-Tl···S-Pt- chain, generated by Pt-Tl and Tl···S bonds, with the SpyCF3 acting as a μ-κN:κ(2)S bridging ligand, whereas 4 displays an unsupported ···Tl-Pt···Tl-Pt··· backbone (angle of ca. 158.7°). The lowest-energy absorption bands in the UV-vis spectra in CH2Cl2, associated with (1)L'LCT transitions with minor (1)LC/(1)MLCT (L' = Spy or SpyCF3-5; L = C^N) character, are similar for all complexes 1-4, demonstrating that for 3 and 4 the chains break down in solution to yield similar bimetallic Pt-Tl units. For 2, two different forms, 2-o (orange) and 2-y (yellow), exhibiting different colors and emissions were found depending on the isolation conditions. Slow crystallization favors formation of the thermodynamically more stable yellow form (2-y), which exhibits a high-energy (HE) structured emission band, whereas fast crystallization gives rise to the orange form (2-o), with a remarkably lower energy structureless emission. Complexes 1 and 3 exhibit dual luminescence in the solid state at 298 K: an unstructured low-energy band associated with (3)ππ* excimeric emission due to π···π (C^N) interactions and a more structured HE band, assigned, with support of density functional theory calculations, to an intraligand (3)LC (C^N) excited state mixed with some ligand (SPy)/platinum-to-ligand (C^N)(3)[(L' + M)LCT] charge transfer. Chain

  14. Bulk superhard B-C-N nanocomposite compact and method for preparing thereof

    Science.gov (United States)

    Zhao, Yusheng; He, Duanwei

    2004-07-06

    Bulk, superhard, B-C-N nanocomposite compact and method for preparing thereof. The bulk, superhard, nanocomposite compact is a well-sintered compact and includes nanocrystalline grains of at least one high-pressure phase of B-C-N surrounded by amorphous diamond-like carbon grain boundaries. The bulk compact has a Vicker's hardness of about 41-68 GPa. It is prepared by ball milling a mixture of graphite and hexagonal boron nitride, encapsulating the ball-milled mixture, and sintering the encapsulated ball-milled mixture at a pressure of about 5-25 GPa and at a temperature of about 1000-2500 K.

  15. Dynamic composting optimization through C/N ratio variation as a startup parameter

    OpenAIRE

    AZIM, Khalid; OUYIHYA, Khalid; AMELLOUK, Aomar; PERISSOL, Claude; THAMI ALAMI, Imane; Soudi, Brahim

    2014-01-01

    Different organic wastes (waste of tomato leaves and stems, sheep manure, olive mill waste and melon waste) were mixed with different proportions for different C/N ratio to make better use of tomato waste as it constitutes the majority of horticultural waste in the Souss-Massa region (south-western of Morocco). The objective of this study was to evaluate the effect of C/N ratio on the physicochemical parameters during aerobic composting process (temperature, relative humidity, pH, EC...), and...

  16. [Latitudinal Changes in Plant Stoichiometric and Soil C, N, P Stoichiometry in Loess Plateau].

    Science.gov (United States)

    Li, Ting; Deng, Qiang; Yuan, Zhi-you; Jiao, Feng

    2015-08-01

    Field investigations and sampling were conducted in Loess Plateau, including Fu County, Ganquan County, Ansai County, Jingbian County and Hengshan County and Yuyang District. Our objective was to examine changes of leaf and soil stoichiometry characteristics along latitudinal gradient in Loess Plateau, and to provide references for the prediction of soil nutrient status of the ecosystem and constraints of plant nutrition elements in Loess Plateau. The results showed that (1) Across the 35.95 degrees-38.36 degrees N latitude gradient, leaf C, N and P stoichiometry were ranging from 336.95 to 477.38 mg x g(-1) for C, from 18.09 to 33.173 mg x g(-1) for N and from 1.07 to 1.73 mg x g(-1) for P, the arithmetic means were 442.9 mg x g(-1), 25.79 mg x g(-1) and 1.37 mg x g(-1), separately, the variation coefficients were 11.9%, 17.4% and 13.3%. There were obvious correlation between leaf C, N, P and latitude, leaf C, C : N ratio and C: P ratio significantly decreased with the increasing latitude, while leaf N and P significantly increased with the increasing latitude. The relationship between N: P ratio and latitude was not significant. (2) The content of soil organic C and soil total N decreased with increasing latitude and soil layer. In contrast, with the increase of latitude, soil P increased and then decreased. In the 0-10 cm, 10-20 cm soil layers, soil C: N ratio did not change significantly with latitude, while in the 20-40 cm layer, C: N ratio decreased obviously, but soil C: P and N: P ratios decreased with the increasing latitude in all soil layers. (3) Leaf C, C: N and C: P ratios were correlated to soil organic C, soil total N and soil total P in all soil layers, leaf N and P were correlated to soil organic C and soil total N, while leaf N: P ratio was not correlated to soil organic C, soil total N and soil total P. There was a certain correlation between the leaf C, N, P and latitude, however, the correlations between leaf and soil C, N, P were inconsistent

  17. 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)

  18. 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.

  19. 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.

  20. 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.

  1. 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...

  2. Particulate C, N, P and Si analysis at the Bedford Institute of Oceanography, Canada

    Science.gov (United States)

    Harrison, W. G.; Head, E. J. H.

    The Biological Oceanography Division of the Bedford Institute routinely measures bioelements (C, N, P, Si) in suspended and sinking biogenic particles in support of a number of research programs focusing on primary and secondary production processes in coastal and oceanic waters of the NW Atlantic. Automated elemental analysis is conducted using commercial equipment.

  3. Classification of $n$-component Brunnian links up to $C_n$-move

    OpenAIRE

    MIYAZAWA, Haruko Aida; Yasuhara, Akira

    2004-01-01

    We give a classification of $n$-component links up to $C_n$-move. In order to prove this classification, we characterize Brunnian links, and have that a Brunnian link is ambient isotopic to a band sum of trivial link and Milnor's links.

  4. Nitrate leaching in forest ecosystems is related to forest floor C/N ratios

    NARCIS (Netherlands)

    Gundersen, P.; Callesen, I.; Vries, de W.

    1998-01-01

    Relationships between nitrogen (N) output with seepage water and forest floor C/N ratios were analysed by use of three independent datasets: (i) a compilation of input-output studies in temperate forest ecosystems in Europe; (ii) a seven-year nationalDanish survey of nitrate concentrations in forest

  5. Generation of serine/threonine check points in HN (C) N spectra

    Indian Academy of Sciences (India)

    The performance of this experiment, referred to as HN(C)N-ST, is demonstrated using two proteins, one properly folded and the other completely denatured. It is noteworthy that, even in the denatured protein, where spectral dispersions are rather poor, about 90% of the sequential connectivities through the chain could be ...

  6. Relationship between C:N/C:O stoichiometry and ecosystem services in managed production systems.

    Directory of Open Access Journals (Sweden)

    Bhim B Ghaley

    Full Text Available Land use and management intensity can influence provision of ecosystem services (ES. We argue that forest/agroforestry production systems are characterized by relatively higher C:O/C:N and ES value compared to arable production systems. Field investigations on C:N/C:O and 15 ES were determined in three diverse production systems: wheat monoculture (Cwheat, a combined food and energy system (CFE and a beech forest in Denmark. The C:N/C:O ratios were 194.1/1.68, 94.1/1.57 and 59.5/1.45 for beech forest, CFE and Cwheat, respectively. The economic value of the non-marketed ES was also highest in beech forest (US$ 1089 ha(-1 yr(-1 followed by CFE (US$ 800 ha(-1 yr(-1 and Cwheat (US$ 339 ha(-1 yr(-1. The combined economic value was highest in the CFE (US$ 3143 ha(-1 yr(-1 as compared to the Cwheat (US$ 2767 ha(-1 yr(-1 and beech forest (US$ 2365 ha(-1 yr(-1. We argue that C:N/C:O can be used as a proxy of ES, particularly for the non-marketed ES, such as regulating, supporting and cultural services. These ES play a vital role in the sustainable production of food and energy. Therefore, they should be considered in decision making and developing appropriate policy responses for land use management.

  7. Relationship between C:N/C:O stoichiometry and ecosystem services in managed production systems.

    Science.gov (United States)

    Ghaley, Bhim B; Sandhu, Harpinder S; Porter, John R

    2015-01-01

    Land use and management intensity can influence provision of ecosystem services (ES). We argue that forest/agroforestry production systems are characterized by relatively higher C:O/C:N and ES value compared to arable production systems. Field investigations on C:N/C:O and 15 ES were determined in three diverse production systems: wheat monoculture (Cwheat), a combined food and energy system (CFE) and a beech forest in Denmark. The C:N/C:O ratios were 194.1/1.68, 94.1/1.57 and 59.5/1.45 for beech forest, CFE and Cwheat, respectively. The economic value of the non-marketed ES was also highest in beech forest (US$ 1089 ha(-1) yr(-1)) followed by CFE (US$ 800 ha(-1) yr(-1)) and Cwheat (US$ 339 ha(-1) yr(-1)). The combined economic value was highest in the CFE (US$ 3143 ha(-1) yr(-1)) as compared to the Cwheat (US$ 2767 ha(-1) yr(-1)) and beech forest (US$ 2365 ha(-1) yr(-1)). We argue that C:N/C:O can be used as a proxy of ES, particularly for the non-marketed ES, such as regulating, supporting and cultural services. These ES play a vital role in the sustainable production of food and energy. Therefore, they should be considered in decision making and developing appropriate policy responses for land use management.

  8. Tree species is the major factor explaining C:N ratios in European forest soils

    DEFF Research Database (Denmark)

    Cools, Nathalie; Vesterdal, Lars; De Vos, Bruno

    2014-01-01

    .) and eucalyptus, the pine species and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) showed the highest C:N ratios in the mineral soil. The second most important explanatory variable in the forest floor and mineral topsoil was the biogeographical zoning (ecoregion). In the peat topsoil and in the deeper...

  9. 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

  10. Analisis Parameter Ber Dan C/N Dengan Lnb Combo Pada Teknologi Dvb-S2

    Directory of Open Access Journals (Sweden)

    Wahyu Pamungkas

    2013-11-01

    Full Text Available Instalasi antena parabola berfungsi untuk memudahkan pada saat pengarahan pointing antena ke satelit yang dituju. Permasalahan yang diketahui yaitu bagaimana perilaku parameter Bit Error Rate (BER dan Carrier to Noise (C/N pada LNB Combo yang menggunakan teknologi DVB-S2. Setelah instalasi antena parabola dilakukan dan sukses, maka langkah selanjutnya yaitu melakukan pointing antena. Pointing antena diarahkan pada posisi satelit yang akan dituju. Satelit yang akan dituju yaitu Palapa D menggunakan frekuensi C-Band sedangkan Ku-Band diarahkan pada satelit NSS 6. Setelah pointing selesai dilakukan maka langkah selanjutnya yaitu menghubungkan dengan Digital Video Broadcasting Satellite Second Generation (DVB-S2. DVB-S2 merupakan receiver. Parameter yang diamati yaitu parameter BER dan C/N. Parameter BER merupakan perbandingan dengan jumlah bit yang diterima secara tidak benar dengan jumlah bit informasi yang ditransmisikan pada selang waktu tertentu. Parameter C/N merupakan perbandingan nilai pada carrier yang diterima dengan nilai sinyal noise yang dihasilkan dalam suatu link. Diperlukan juga Low Noise Block (LNB Combo yang berguna untuk mentransmisikan sinyal ke receiver. LNB yang digunakan merupakan LNB Combo, dimana dua buah frekuensi yakni C-Band dan KU-Band menjadi satu dalam sebuah LNB. Setelah melakukan pengukuran dan melihat hasil pengukuran, dapat disimpulkan bahwa LNB Combo berpengaruh pada sinyal C-Band yang dihasilkan, sinyal C-Band akan mengalami penurunan kualitas, ini dibuktikan dari hasil pengukuran yang telah dilakukan bahwa nilai parameter C/N dan BER pada Ku-Band lebih baik daripada nilai parameter C/N dan BER pada CBand.

  11. 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.

  12. 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...

  13. 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 ...

  14. 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

  15. 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)

  16. 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)

  17. 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.

  18. 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.

  19. 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...

  20. 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...

  1. 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.

  2. Synthesis and characterization of a new material based on porous silica-Chemically immobilized C,N-pyridylpyrazole for heavy metals adsorption

    Energy Technology Data Exchange (ETDEWEB)

    Radi, Smaail [Laboratoire de Chimie Organique, Macromoleculaire et Produits Naturels, Departement de Chimie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco)], E-mail: radi_smaail@yahoo.fr; Attayibat, Ahmed [Laboratoire de Chimie Organique, Macromoleculaire et Produits Naturels, Departement de Chimie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco); Lekchiri, Yahya [Laboratoire de Biochimie, Departement de Biologie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco); Ramdani, Abdelkrim [Laboratoire de Chimie Organique, Macromoleculaire et Produits Naturels, Departement de Chimie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco); Bacquet, Maryse [Laboratoire de Chimie Macromoleculaire, Universite des Sciences et Technologies de Lille, 59655 Villeneuve d' Ascq (France)

    2008-10-15

    The immobilization of C,N-pyridylpyrazole on the surface of epoxy group containing silica gel phase for the formation of a newly synthesized material based on porous silica-bound C,N-pyridylpyrazole (SGPP) is described. The surface modification was characterized by {sup 13}C NMR of solid sample, elemental analysis and infrared spectra and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and BJH pore sizes, respectively. The new material exhibits good thermal stability determined by thermogravimetry curves. The synthesized material was utilised in column and batch methods for separation and trace extraction of (Hg{sup 2+}, Cd{sup 2+}, Pb{sup 2+}, Cu{sup 2+}, Zn{sup 2+}, K{sup +}, Na{sup +} and Li{sup +}) and compared to results of classical liquid-liquid extraction with the unbound C,N-pyridylpyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the material exhibits a high selectivity toward Hg(II)

  3. Nutrient recycling and the stoichiometric relationship among C, N, and P in Paleozoic anoxic sediments

    Science.gov (United States)

    Tuite, M. L., Jr.

    2016-12-01

    Remineralized organic N and P diffused into the water column from underlying anoxic sediments were important sources of macronutrients for primary production in shallow Paleozoic epicontinental seas. Ratios of total organic C to total N or P in ancient sediments that are greater than Redfield-like values are often cited as evidence for macronutrient recycling. We propose that the stoichiometric relationship among C, N, and P in anoxic Paleozoic sediments was mediated primarily by heterotrophic bacterial alkaline phosphatases. Bacterial heterotrophy in organic-rich anaerobic sediments is frequently limited by the availability of labile (low C/N) organic matter. In response, bacterial heterotrophs invest scarce C and N to produce alkaline phosphatases in order to alleviate labile organic matter limitation by hydrolysis of organophosphates. This suggests that sediment organic C/N may represent a threshold beyond which the investment of intracellular C and N in the production of alkaline phosphatase no longer results in a stoichiometrically favorable return on the investment. If this is the case, then C/P likely represents the point in the diagenesis of organic matter at which the effectiveness of alkaline phosphatase in procuring labile organic matter by remineralization of P is constrained by the lability of the organic matter itself. Because alkaline phosphatase activity is expressed in inverse proportion to the porewater concentration of phosphate, at a given distance from the terrestrial source of weathered P, an equilibrium determined by total phosphate influx results in consistent total P burial rates and consistent organic C/N values independent of the total organic content of the sediment. To account for consistent C/N in spite of variable total organic carbon at a given location, we propose that variations in the absolute abundance of organic C in organic-rich Devonian sediments were largely a function of the lipid content of algal primary producers. The

  4. 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.

  5. 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).

  6. Novel Rhodate and Iridate Complexes containing C,N Chelating Arylamine Ligand Systems

    NARCIS (Netherlands)

    Koten, G. van; Wehman-Ooyevaar, I.C.M.; Vedral, J.A.; Jastrzebski, J.T.B.H.; Grove, D.M.

    1993-01-01

    The synthesis is described of a series of new iridate and rhodate complexes Li(L-C, N){2}M(cod) (M = Rh, Ir; cod = cycloocta-1,5-diene) containing the ortho-chelating, mono-anionic, arylamine ligands L = C{6}H{4}CH{2}NR{2}-2 (R = Me, Et), C{6}H{3}CH{2}NMe{2}- 2-Me-5, C{6}H{4}CH(Me)NMe{2}-(R)-2 or

  7. 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...

  8. 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....

  9. Flexible C : N ratio enhances metabolism of large phytoplankton when resource supply is intermittent

    Directory of Open Access Journals (Sweden)

    D. Talmy

    2014-09-01

    Full Text Available Phytoplankton cell size influences particle sinking rate, food web interactions and biogeographical distributions. We present a model in which the uptake, storage and assimilation of nitrogen and carbon are explicitly resolved in different-sized phytoplankton cells. In the model, metabolism and cellular C : N ratio are influenced by the accumulation of carbon polymers such as carbohydrate and lipid, which is greatest when cells are nutrient starved, or exposed to high light. Allometric relations and empirical data sets are used to constrain the range of possible C : N, and indicate that larger cells can accumulate significantly more carbon storage compounds than smaller cells. When forced with extended periods of darkness combined with brief exposure to saturating irradiance, the model predicts organisms large enough to accumulate significant carbon reserves may on average synthesize protein and other functional apparatus up to five times faster than smaller organisms. The advantage of storage in terms of average daily protein synthesis rate is greatest when modeled organisms were previously nutrient starved, and carbon storage reservoirs saturated. Small organisms may therefore be at a disadvantage in terms of average daily growth rate in environments that involve prolonged periods of darkness and intermittent nutrient limitation. We suggest this mechanism is a significant constraint on phytoplankton C : N variability and cell size distribution in different oceanic regimes.

  10. 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....

  11. Bond lengths in organic and metal-organic compounds revisited: X-H bond lengths from neutron diffraction data.

    Science.gov (United States)

    Allen, Frank H; Bruno, Ian J

    2010-06-01

    The number of structures in the Cambridge Structural Database (CSD) has increased by an order of magnitude since the preparation of two major compilations of standard bond lengths in mid-1985. It is now of interest to examine whether this huge increase in data availability has implications for the mean bond-length values published in the late 1980s. Those compilations reported mean X-H bond lengths derived from rather sparse information and for rather few chemical environments. During the intervening years, the number of neutron studies has also increased, although only by a factor of around 2.25, permitting a new analysis of X-H bond-length distributions for (a) organic X = C, N, O, B, and (b) a variety of terminal and homometallic bridging transition metal hydrides. New mean values are reported here and are compared with earlier results. These new overall means are also complemented by an analysis of X-H distances at lower temperatures (T chemical environments for which statistically acceptable mean X-H bond lengths can be obtained, although values from individual structures are also collated to further extend the chemical range of this compilation. Updated default 'neutron-normalization' distances for use in hydrogen-bond and deformation-density studies are also proposed for C-H, N-H and O-H, and the low-temperature analysis provides specific values for certain chemical environments and hybridization states of X.

  12. 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 ...

  13. 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

  14. 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.

  15. 77 FR 62510 - C.N. Brown Electricity, LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes...

    Science.gov (United States)

    2012-10-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission C.N. Brown Electricity, LLC; Supplemental Notice That Initial Market-Based... above-referenced proceeding, of C.N. Brown Electricity, LLC's application for market-based rate...

  16. Biomass allocation and C-N-P stoichiometry in C3 and C4 crops under abiotic stress

    Science.gov (United States)

    Biomass allocation to structural, metabolic and reproductive organs as well as their carbon, nitrogen and phosphorus (C-N-P) profiles and ratios (C:N, C:P, and N:P) were estimated in C3 and C4 crop plants subjected to multiple abiotic stresses (i.e., combination of temperature and water stress level...

  17. 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

  18. Facile preparation of C, N co-modified Nb2O5 nanoneedles with enhanced visible light photocatalytic activity

    KAUST Repository

    Xue, Jiao

    2016-09-28

    C, N co-modified niobium pentoxide (Nb2O5) nanoneedles have been successfully synthesized via a facile hydrothermal method with Niobium Chloride (NbCl5) as a precursor and triethylamine as both the carbon and nitrogen source. The formation process of Nb2O5 nanoneedles has been presented in detail by investigating the effect of the crystallization temperature, the amount of triethylamine and the calcination temperature. The as-prepared Nb2O5 nanoneedles exhibit more efficient photocatalytic activity than commercial Degussa P25 and commercial Nb2O5 towards photodegradation of Rhodamine B (RhB) at a concentration of 10 mg L−1 under visible light. Special chemical species, such as carbonate species and NOX species, that exist on the surface of the as-prepared catalyst could extend the absorption into the visible region and thus enhance the photocatalytic activity of the Nb2O5 nanoneedles. At the same time, the obtained Nb2O5 nanoneedles exhibit excellent stability even after three successive cycles. A possible photodegradation mechanism was proposed and the corresponding photodecomposition process of RhB over the Nb2O5 nanoneedles was elucidated by a reactive species trapping experiment, suggesting that h+ and O2˙− play a major role in the photodegradation of RhB in aqueous solution.

  19. Mechanical and electronic properties of antiperovskite Ti-based compounds AXTi3 (X = C, N): A first-principles investigation

    Science.gov (United States)

    Wang, Ni-Na; Shao, Ding-Fu; Lu, Wen-Jian; Lu, Hong-Yan

    2016-01-01

    In this paper, we systematically studied the mechanical and electronic properties of a series of antiperovskite-type Ti-based ternary carbides and nitrides AXTi3 (A = Ba, Ca, In, Sn, Sr, Zn, Cu, Al, Ga, Cd, and La; X = C, N) from first-principles calculations. By calculating the formation energies, elastic constants, and other mechanical parameters, we predicted that 7 carbides ACTi3 and 7 nitrides ANTi3 compounds are stable among the 22 compounds. The predicted large Young's modulus and high hardness imply a good mechanical application prospect of AXTi3. Particularly, SnNTi3 was found to show ferromagnetic ground state. For the electronic structure, our results confirm that the compounds are metallic in nature, and the density of states near the Fermi energy is predominately contributed by Ti-3d states. The effect of A- and X-site atom doping on AXTi3 can be evaluated by rigid band approximation. Our prediction will be useful for the experimental exploration of the new antiperovskite compounds.

  20. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    John J. Kilbane III

    2003-12-01

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

  2. 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.

  3. 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

  4. Effects of Combined Application of Biogas Slurry and Chemical Fertilizer on Soil Aggregation and C/N Distribution in an Ultisol.

    Science.gov (United States)

    Zheng, Xuebo; Fan, Jianbo; Xu, Lei; Zhou, Jing

    2017-01-01

    Unreasonable use of chemical fertilizer (CF) on agricultural soil leads to massive losses of soil organic carbon (SOC) and total nitrogen (TN) in tropical and subtropical areas, where soil conditions are unfavorable for aggregate formation. This study evaluated the effects of combined application of biogas slurry (BS) plus CF on soil aggregation and aggregate-associated C/N concentration and storage in an Ultisol. Six treatments included: no fertilizer (T1), CF only (T2), partial (15% (T3), 30% (T4) and 45% (T5)) substitution of TN with BS and BS only (T6). Soil mechanical-stable aggregates (MSAs) formation and stability as well as MSAs-associated C/N concentration and storage were observed in different aggregate sizes (>5, 5-2, 2-1, 1.0-0.5, 0.50-0.25 and 5 mm significantly increased with BS substitution (T5), while the proportions of MSAs 1.0-0.5 mm, MSAs 0.50-0.25 mm and MSAs soil aggregation stability as well as resulted in significantly higher SOC and TN concentrations and storage in MSAs >0.5 mm that constituted 72-82% of MSAs. Stepwise regression analysis showed that MSAs >5 mm, SOC in MSAs >5 mm and TN in MSAs >5 mm were the dominant variables affecting aggregate stability. Meanwhile SOC in MSAs soils. Therefore, certain rate of combined application of BS plus CF is an effective, eco-friendly way to improve soil quality in an Ultisol.

  5. 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.

  6. 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.

  7. Nucleophilicities of Lewis Bases B and Electrophilicities of Lewis Acids A Determined from the Dissociation Energies of Complexes B⋯A Involving Hydrogen Bonds, Tetrel Bonds, Pnictogen Bonds, Chalcogen Bonds and Halogen Bonds.

    Science.gov (United States)

    Alkorta, Ibon; Legon, Anthony C

    2017-10-23

    It is shown that the dissociation energy D e for the process B⋯A = B + A for 250 complexes B⋯A composed of 11 Lewis bases B (N₂, CO, HC≡CH, CH₂=CH₂, C₃H₆, PH₃, H₂S, HCN, H₂O, H₂CO and NH₃) and 23 Lewis acids (HF, HCl, HBr, HC≡CH, HCN, H₂O, F₂, Cl₂, Br₂, ClF, BrCl, H₃SiF, H₃GeF, F₂CO, CO₂, N₂O, NO₂F, PH₂F, AsH₂F, SO₂, SeO₂, SF₂, and SeF₂) can be represented to good approximation by means of the equation D e = c ' N B E A , in which N B is a numerical nucleophilicity assigned to B, E A is a numerical electrophilicity assigned to A, and c ' is a constant, conveniently chosen to have the value 1.00 kJ mol -1 here. The 250 complexes were chosen to cover a wide range of non-covalent interaction types, namely: (1) the hydrogen bond; (2) the halogen bond; (3) the tetrel bond; (4) the pnictogen bond; and (5) the chalcogen bond. Since there is no evidence that one group of non-covalent interaction was fitted any better than the others, it appears the equation is equally valid for all the interactions considered and that the values of N B and E A so determined define properties of the individual molecules. The values of N B and E A can be used to predict the dissociation energies of a wide range of binary complexes B⋯A with reasonable accuracy.

  8. Corrosion resistance study of grey cast iron implanted with C, N, Cr and Cu ions

    Science.gov (United States)

    Usanova, O. Yu; Maryushin, L. A.; Kazantsev, A. Yu; Dyukova, A. I.

    2017-10-01

    This article deals with the corrosion resistance of gray cast iron implanted with C, N, Cr and Cu ions in sodium chloride solution and sulfuric acid solution. The potentiodynamic research was conducted in atmosphere, simulating corrosion conditions: in 3% sodium chloride solution and in 0,1 N sulfuric acid solution. Potentiodynamic curves were obtained and surfaces of samples were observed. The research proves that the implantation of ions with N and Cr leads to an increase in the corrosion resistance of cast iron in sodium chloride solution, and the implantation of ions with N and Cu leads to increased corrosion resistance in sulfuric acid solution.

  9. Romanian government bond market

    Directory of Open Access Journals (Sweden)

    Cornelia POP

    2012-12-01

    Full Text Available The present paper aims to present the level of development reached by Romanian government bond market segment, as part of the country financial market. The analysis will be descriptive (the data series available for Romania are short, based on the secondary data offered by the official bodies involved in the process of issuing and trading the Romanian government bonds (Romanian Ministry of Public Finance, Romanian National Bank and Bucharest Stock Exchange, and also on secondary data provided by the Federation of European Stock Exchanges.To enhance the market credibility as a benchmark, a various combination of measures is necessary; among these measures are mentioned: the extension of the yield curve; the issuance calendars in order to improve transparency; increasing the disclosure of information on public debt issuance and statistics; holding regular meetings with dealers, institutional investors and rating agencies; introducing a system of primary dealers; establishing a repurchase (repo market in the government bond market. These measures will be discussed based on the evolution presented inside the paper.The paper conclude with the fact that, until now, the Romanian government bond market did not provide a benchmark for the domestic financial market and that further efforts are needed in order to increase the government bond market transparency and liquidity.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Global biodiversity, stoichiometry and ecosystem function responses to human-induced C-N-P imbalances.

    Science.gov (United States)

    Carnicer, Jofre; Sardans, Jordi; Stefanescu, Constantí; Ubach, Andreu; Bartrons, Mireia; Asensio, Dolores; Peñuelas, Josep

    2015-01-01

    Global change analyses usually consider biodiversity as a global asset that needs to be preserved. Biodiversity is frequently analysed mainly as a response variable affected by diverse environmental drivers. However, recent studies highlight that gradients of biodiversity are associated with gradual changes in the distribution of key dominant functional groups characterized by distinctive traits and stoichiometry, which in turn often define the rates of ecosystem processes and nutrient cycling. Moreover, pervasive links have been reported between biodiversity, food web structure, ecosystem function and species stoichiometry. Here we review current global stoichiometric gradients and how future distributional shifts in key functional groups may in turn influence basic ecosystem functions (production, nutrient cycling, decomposition) and therefore could exert a feedback effect on stoichiometric gradients. The C-N-P stoichiometry of most primary producers (phytoplankton, algae, plants) has been linked to functional trait continua (i.e. to major axes of phenotypic variation observed in inter-specific analyses of multiple traits). In contrast, the C-N-P stoichiometry of higher-level consumers remains less precisely quantified in many taxonomic groups. We show that significant links are observed between trait continua across trophic levels. In spite of recent advances, the future reciprocal feedbacks between key functional groups, biodiversity and ecosystem functions remain largely uncertain. The reported evidence, however, highlights the key role of stoichiometric traits and suggests the need of a progressive shift towards an ecosystemic and stoichiometric perspective in global biodiversity analyses. Copyright © 2014 Elsevier GmbH. All rights reserved.

  15. Pasarela metálica sobre la C. N. III, Madrid-Valencia

    Directory of Open Access Journals (Sweden)

    Rodríguez-Borlado Olavarrieta, Ramiro

    1967-03-01

    Full Text Available The footbridge over the C. N. Ill , Madrid-Valencia road, near Madrid, enables pedestrians to cross the motor road where the latter runs between Moratalaz and Vallecas, without impeding the road traffic. The adoption of an elevated pass is convenient, since at this section the road runs along a deep trench. The structure of the footpath is a continuous metallic box girder, resting on five rectangular metal supports, and two end concrete abutments. The total length of the bridge is 100 m, and the width of the platform is 2.40 m. The project took one month to complete.La pasarela sobre la C. N. III, Madrid-Valencia, en la autopista de acceso a Madrid, permite el paso de peatones entre los barrios de Moratalaz y Vallecas sin interferir el tráfico rodado. La solución de paso superior resulta conveniente, ya que la autopista discurre en trinchera en el lugar de ubicación de esta obra. La estructura está formada por una viga metálica continua de sección en cajón, apoyada sobre cinco soportes rectangulares metálicos y dos estribos de hormigón armado. La obra tiene una longitud total de aproximadamente 100 m y el ancho de la plataforma es de 2,40 metros. El plazo de realización de la obra ha sido de un mes aproximadamente.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. [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.

  1. 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

  2. Biomolecule-controlled hydrothermal synthesis of C-N-S-tridoped TiO{sub 2} nanocrystalline photocatalysts for NO removal under simulated solar light irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Wang Yawen; Huang Yu [Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079 (China); Ho Wingkei [Department of Civil and Structural Engineering, Research Center for Environmental Technology and Management, Hong Kong Polytechnic University (Hong Kong); Zhang Lizhi, E-mail: zhanglz@mail.ccnu.edu.cn [Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079 (China); Zou Zhigang [Ecomaterials and Renewable Energy Research Center (ERERC), Department of Physics, Nanjing University, Nanjing 210093 (China); Lee Shuncheng [Department of Civil and Structural Engineering, Research Center for Environmental Technology and Management, Hong Kong Polytechnic University (Hong Kong)

    2009-09-30

    In this study, C-N-S-tridoped titanium dioxide (TiO{sub 2}) nanocrystals were synthesized by using a facile hydrothermal method in the presence of a biomolecule L-cysteine. This biomolecule could not only serve as the common source for the carbon, sulfur and nitrogen tridoping, but also could control the final crystal phases and morphology. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption and UV-vis diffuse reflectance spectroscopy. XPS analysis revealed that S was incorporated into the lattice of TiO{sub 2} through substituting oxygen atoms, N might coexist in the forms of N-Ti-O and Ti-O-N in tridoped TiO{sub 2} and most C could form a mixed layer of carbonate species deposited on the surface of TiO{sub 2} nanoparticles. The photocatalytic activities of the samples were tested on the removal of NO at typical indoor air level in a flow system under simulated solar light irradiation. The tridoped TiO{sub 2} samples showed much higher removal efficiency than commercial P25 and the undoped counterpart photocatalyst. The enhanced visible light photocatalytic activity of C-N-S-tridoped TiO{sub 2} nanocrystals was explained on the basis of characterizations. The possible formation process of the monodispersed C-N-S-tridoped anatase TiO{sub 2} nanocrystals was also proposed. This study provides a new method to prepare visible light active TiO{sub 2} photocatalyst.

  3. 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.

  4. 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

  5. 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.

  6. PERANAN BAHAN ORGANIK BERNISBAH C/N RENDAH DAN CACING TANAH UNTUK MENDEKOMPOSISI LIMBAH KUI.IT KAYU Gmelina arborea (The Roles of Low C/N Ratio Organic Matters and Earthworms to Decompose Waste Barks of Gmelina arborea

    Directory of Open Access Journals (Sweden)

    Suryo Hardiwinoto

    2005-11-01

    Full Text Available ABSTRAK Limbah kulit kayu berpotensi dapat menyebabkan dampak negatip terhadap lingkungan apabila tidak ditangani dengan baik. Sebagai bahan organik, limbah kulit kayu sebetulnya dapat dijadikan sbagai bahan baku kompos. Tujuan dari penelitian ini adalah untuk mengetahui peranan penambahan bahan organik ber-nisbah C/N rendah dan cacing tanah dalam menurunkan nisbah C/N dan meningkatkan kandungan unsur hara makro dari kompos limbah kulit kayu. Penelitian dilakukan dengan menggunakan rancangan acak lengkap yang disusun secara faktorial, terdiri dari 2 faktor dengan 5 ulangan. Faktor pertama adalah penambahan bahan organic ber-nisbah C/N rendah (daun Glyricideu maculuta and daun Gmelina arborea, dan taktor kedua adalah jenis cacing tanah, yaitu Lumbricus rubellus (Cl dan Eisenia foetida (C2. Parameter yang digunakan adalah kandungan karbon (C, dan beberapa unsur hara makro, yaitu: nitrogen (N, fosfor (P, kalium (K, kalsium (Ca and magnesium (Mg dari kompos limbah kulit kayu. Penambahan bahan organik ber-nisbah C/N rendah dan cacing tanah merupakan cara penanganan limbah kulit kayu yang ramah lingkungan. Penambahan bahan organik ber-nisbah C/N rendah secara nyata dapat menurunkan nisbah C/N dan meningkatkan kandungan unsur hara makro N, P, K, Ca dan Mg dari kompos limbah kulit kayu. Nisbah C/N kompos limbah kulit kayu dapat turun semakin rendah dan kandungan unsur hara makro N, P, K, Ca and Mg dapat naik semakin tinggi dengan adanya penambahan bahan organik ber-nisbah C/N yang semakin banyak. Cacing tanah menunjukkan peran yang sangat nyata dalam menurunkan nisbah CIN dan menaikkan kandungan unsur hara makro N, P, K, Ca dan Mg dari kompos limbah kulit kayu. Rerata nisbah C/N dari kompos limbah kulit kayu (C0 sebesar 56,17, dan dengan adanya perlakuan cacing tanah rerata nisbah C/N dapat turun secara sangat nyara menjadi 26,66 (Cl dan 22,94 (C2. Rerata kandungan N dari kompos limbah kulit kayu (C0 hanya sebesar 0,89 %, dan dengan adanya aktivitas

  7. 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.

  8. C,N-2-[(Dimethylamino)methyl]phenylplatinum Complexes Functionalized with C60 as Macromolecular Building Blocks

    NARCIS (Netherlands)

    Koten, G. van; Meijer, M.D.; Wolf, E. de; Lutz, M.H.; Spek, A.L.; Klink, G.P.M. van

    2001-01-01

    The application of platinum(II) complexes based on the N,N-dimethylbenzylamine ligand (abbreviated as H-C,N) in macromolecular synthesis was demonstrated. Two cationic C,N-platinum moieties were linked with a 4,4'-bipyridine bridge, giving [{C6H4(CH2NMe2)-2-Pt(PPh3)}2(4,4'-bpy)](BF4)2 (2), the

  9. End-of-pipe denitrification using RAS effluent waste streams: Effect of C/N-ratio and hydraulic retention time

    DEFF Research Database (Denmark)

    Suhr, Karin Isabel; Pedersen, Per Bovbjerg; Arvin, Erik

    2013-01-01

    removal rate obtained was at the intermediate treatments; 91.5–124.8 g N m−3 reactor d−1. The effect of the C/N ratio depended on the HRT. At low HRT, the variation in C/N ratio had no significant effect on NO3-N removal rate, contrary to the effect at the high HRT. The stoichiometric ratio of CODS/NO3-N...

  10. Chemical footprints of anthropogenic nitrogen deposition on recent soil C : N ratios in Europe

    Science.gov (United States)

    Mulder, C.; Hettelingh, J.-P.; Montanarella, L.; Pasimeni, M. R.; Posch, M.; Voigt, W.; Zurlini, G.

    2015-07-01

    Long-term human interactions with the natural landscape have produced a plethora of trends and patterns of environmental disturbances across time and space. Nitrogen deposition, closely tracking energy and land use, is known to be among the main drivers of pollution, affecting both freshwater and terrestrial ecosystems. We present a statistical approach for investigating the historical and geographical distribution of nitrogen deposition and the impacts of accumulation on recent soil carbon-to-nitrogen ratios in Europe. After the second Industrial Revolution, large swaths of land emerged characterized by different atmospheric deposition patterns caused by industrial activities or intensive agriculture. Nitrogen deposition affects soil C : N ratios in a still recognizable way despite the abatement of oxidized and reduced nitrogen emissions during the last 2 decades. Given a seemingly disparate land-use history, we focused on ~ 10 000 unmanaged ecosystems, providing statistical evidence for a rapid response of nature to the chronic nitrogen supply through atmospheric deposition.

  11. 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.

  12. Humic acid batteries derived from vermicomposts at different C/N ratios

    Science.gov (United States)

    Shamsuddin, R. M.; Borhan, A.; Lim, W. K.

    2017-06-01

    Humic acid is a known fertilizer derived from decomposed organic matters. Organic wastes are normally landfilled for disposal which had contributed negatively to the environment. From waste-to-wealth perspective, such wastes are potential precursors for compost fertilizers. When worms are added into a composting process, the process is termed as vermicomposting. In this work, humic acid from vermicompost derived from campus green wastes was developed into a battery. This adds value proposition to compost instead of being traditionally used solely as soil improver. This research work aimed to study the correlation between electrical potential generated by humic acid at different Carbon to Nitrogen (C/N) ratios of vermicompost at 20, 25, 30 and 35. The temperature and pH profiles of composting revealed that the compost was ready after 55 days. The humic acid was extracted from compost via alkaline extraction followed by precipitation in a strong acid. The extracted humic acid together with other additives were packed into a compartment and termed as vermibattery. Another set of battery running only on the additives was also prepared as a control. The net voltage produced by a single vermibattery cell with Zn and PbO electrodes was in the range of 0.31 to 0.44 V with compost at C/N ratio of 30 gave the highest voltage. The battery can be connected in series to increase the voltage generation. Quality assessment on the compost revealed that the final carbon content is between 16 to 23 wt%, nitrogen content of 0.4 to 0.5 wt%, humic acid yield of 0.7 to 1.5 wt% and final compost mass reduction of 10 to 35 wt%. Composting campus green wastes carries multi-fold benefits of reducing labour requirement, generating fertilizer for campus greenery and green battery construction.

  13. Elevated ozone affects C, N and P ecological stoichiometry and nutrient resorption of two poplar clones.

    Science.gov (United States)

    Shang, Bo; Feng, Zhaozhong; Li, Pin; Calatayud, Vicent

    2018-03-01

    The effects of elevated ozone on C (carbon), N (nitrogen) and P (phosphorus) ecological stoichiometry and nutrient resorption in different organs including leaves, stems and roots were investigated in poplar clones 546 (P. deltoides cv. '55/56' × P. deltoides cv. 'Imperial') and 107 (P. euramericana cv. '74/76') with a different sensitivity to ozone. Plants were exposed to two ozone treatments, NF (non-filtered ambient air) and NF60 (NF with targeted ozone addition of 60 ppb), for 96 days in open top chambers (OTCs). Significant ozone effects on most variables of C, N and P ecological stoichiometry were found except for the C concentration and the N/P in different organs. Elevated ozone increased both N and P concentrations of individual organs while for C/N and C/P ratios a reduction was observed. On these variables, ozone had a greater effect for clone 546 than for clone 107. N concentrations of different leaf positions ranked in the order upper > middle > lower, showing that N was transferred from the lower senescent leaves to the upper ones. This was also indicative of N resorption processes, which increased under elevated ozone. N resorption of clone 546 was 4 times larger than that of clone 107 under ambient air (NF). However, elevated ozone (NF60) had no significant effect on P resorption for both poplar clones, suggesting that their growth was only limited by N, while available P in the soil was enough to sustain growth. Understanding ecological stoichiometric responses under ozone stress is crucial to predict future effects on ecological processes and biogeochemical cycles. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. Effect of the C:N:P ratio on the denitrifying dephosphatation in a sequencing batch biofilm reactor (SBBR).

    Science.gov (United States)

    Mielcarek, Artur; Rodziewicz, Joanna; Janczukowicz, Wojciech; Thornton, Arthur J; Jóźwiak, Tomasz; Szymczyk, Paula

    2015-12-01

    A series of investigations were conducted using sequencing batch biofilm reactor (SBBR) to explore the influence of C:N:P ratio on biological dephosphatation including the denitrifying dephosphatation and the denitrification process. Biomass in the reactor occurred mainly in the form of a biofilm attached to completely submerged disks. Acetic acid was used as the source of organic carbon. C:N:P ratios have had a significant effect on the profiles of phosphate release and phosphate uptake and nitrogen removal. The highest rates of phosphate release and phosphate uptake were recorded at the C:N:P ratio of 140:70:7. The C:N ratio of 2.5:1 ensured complete denitrification. The highest rate of denitrification was achieved at the C:N:P ratio of 140:35:7. The increase of nitrogen load caused an increase in phosphates removal until a ratio C:N:P of 140:140:7. Bacteria of the biofilm exposed to alternate conditions of mixing and aeration exhibited enhanced intracellular accumulation of polyphosphates. Also, the structure of the biofilm encouraged anaerobic-aerobic as well as anoxic-anaerobic and absolutely anaerobic conditions in a SBBR. These heterogeneous conditions in the presence of nitrates may be a significant factor determining the promotion of denitrifying polyphosphate accumulating organism (DNPAO) development. Copyright © 2015. Published by Elsevier B.V.

  15. Increasing aridity, temperature and soil pH induce soil C-N-P imbalance in grasslands

    Science.gov (United States)

    Jiao, Feng; Shi, Xin-Rong; Han, Feng-Peng; Yuan, Zhi-You

    2016-01-01

    Due to the different degrees of controls exerted by biological and geochemical processes, climate changes are suggested to uncouple biogeochemical C, N and P cycles, influencing biomass accumulation, decomposition and storage in terrestrial ecosystems. However, the possible extent of such disruption in grassland ecosystems remains unclear, especially in China’s steppes which have undergone rapid climate changes with increasing drought and warming predicted moving forward in these dryland ecosystems. Here, we assess how soil C-N-P stoichiometry is affected by climatic change along a 3500-km temperate climate transect in Inner Mongolia, China. Our results reveal that the soil from more arid and warmer sites are associated with lower soil organic C, total N and P. The ratios of both soil C:P and N:P decrease, but soil C:N increases with increasing aridity and temperature, indicating the predicted decreases in precipitation and warming for most of the temperate grassland region could lead to a soil C-N-P decoupling that may reduce plant growth and production in arid ecosystems. Soil pH, mainly reflecting long-term climate change in our sites, also contributes to the changing soil C-N-P stoichiometry, indicating the collective influences of climate and soil type on the shape of soil C-N-P balance.

  16. 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.

  17. 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

  18. 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 ...

  19. 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.

  20. 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.

  1. 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.

  2. [C, N, P, K Stoichiometric Characteristic of Leaves, Root and Soil in Different Abandoned Years in Loess Plateau].

    Science.gov (United States)

    Zhang, Hai-dong; Ru, Hai-li; Jiao, Feng; Xue, Chao-yu; Guo, Mei-li

    2016-03-15

    The research of plant ecological stoichiometry characteristics, nutrients distribution and their changes is of great significance to explain the response and adaptation of plants to environmental change. Leaves, root and soil from eight different abandoned years in Yanhe River basin were selected to study the content, characteristic ratio and distribution of carbon ( C) , nitrogen (N) , phosphorus (P), potassium (K). The results showed that the C, N, P, K contents of plant leaves were 444.21, 22.34, 1.49, 14.66 mg · g⁻¹ respectively, the C/N, C/P, C/K, N/P ratios of plant leaves were 21.86, 424.72, 39.82, 20.27 respectively; the C, N, P, K contents of root were 285.16, 5.79, 0.27, 6.07 mg · g⁻¹ respectively, the C/N, C/P, C/K, N/P ratios of root were .60. 56, 1019.33, 46.55, 21.36 respectively; the C, N, P, K contents of soil were 2.28, 0.18, 0.28, 4.33 mg · g⁻¹ respectively, the C/N, C/P, C/K, N/P ratios of soil were 16.43, 8.40, 0.54, 0.66 respectively. During the abandoned year of 1-35, C content of leaves increased, N content increased and then declined, P content declined overall, K content declined and then increased. The C/N, C/P, C/K, N/P ratios of plant leaves showed a rising trend overall. The changing pattern of root was different from that of leaves. Along with the increasing rehabilitation age, C and N contents of soil increased, P content changed as arc-sin function, K content changed as parabola, C/N decreased, C/P, C/K, N/P increased. With the increase of Abandoned Years, the ratio of C, P, K contents in leaves and root decreased, the ratio of C, N, P contents in leaves and soil decreased, the ratio of C, N contents in root and soil decreased. Corresponding relationship and its intension between different abandoned years and plant nutrient limit status and its allocation pattern were different.

  3. 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.

  4. 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...

  5. 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...

  6. 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...

  7. 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.

  8. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds

    DEFF Research Database (Denmark)

    Hansen, Poul Erik

    2015-01-01

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between “static......” and tautomeric systems. Isotope effects on chemical shifts are particularly useful in such studies. All kinds of intramolecular hydrogen bonded systems will be treated, typical hydrogen bond donors: OH, NH, SH and NH+, typical acceptors C=O, C=N, C=S C=N−. The paper will be deal with both secondary and primary...... isotope effects on chemical shifts. These two types of isotope effects monitor the same hydrogen bond, but from different angles...

  9. Elucidating the Effect of Glycerol Concentration and C/N Ratio on Lipid Production Using Yarrowia lipolytica SKY7.

    Science.gov (United States)

    Kuttiraja, Mathiazhakan; Douha, Ayed; Valéro, Jose R; Tyagi, Rajeswar Dayal

    2016-12-01

    The high demand for renewable energy and increased biodiesel production lead to the surplus availability of crude glycerol. Due to the above reason, the bio-based value addition of crude glycerol into various bioproducts is investigated; among them, microbial lipids are attractive. The present study was dedicated to find the optimal glycerol concentration and carbon/nitrogen (C/N) ratio to produce maximum lipid using Yarrowia lipolytica SKY7. The glycerol concentration (34.4 to168.2 g/L) and C/N ratio (25 to 150) were selected to investigate to maximize the lipid production. Initial glycerol concentration 112.5 g/L, C/N molar ratio of 100, and with 5 % v/v inoculum supplementation were found to be optimum for biomass and lipid production. Based on the above optimal parameters, lipid concentration of 43.8 % w/w with a biomass concentration of 14.8 g/L was achieved. In the case of glycerol concentration, the maximum Yp/s (0.192 g/g); Yx/s (0.43 g/g) was noted when the initial glycerol concentration was 112.5 g/L with C/N molar ratio 100 and inoculum volume 5 % v/v. The glycerol uptake was also noted to increase with the increase in glycerol concentration. At low C/N ratio, the glycerol consumption was found to be high (79.43 g/L on C/N 25) whereas the glycerol consumption was observed to decrease when the C/N ratio was raised to 150 (40.8 g/L).

  10. Changes in organic matter (C, N and P) of soils under subsistence agriculture; Mudancas na materia organica (C, N e P) de solos sob agricultura de subsistencia

    Energy Technology Data Exchange (ETDEWEB)

    Fraga, Vania da Silva

    2002-10-01

    Productivities under low input or subsistence agriculture are strongly dependent on nutrient supply from soil organic matter mineralization (SOM). Few results are available and they indicate declines in soil fertility under this agricultural system, particularly in SOM levels. In an attempt to understand the nature and extent of these declines we selected ten sites having cultivated areas adjacent with areas under native vegetation at the same slope position, in the states of Pernambuco and Paraiba. Based on the management history, in situ observations and {sup 137} Cs concentrations to evaluate soil erosion, the areas were divided in four groups having different levels of soil use intensity: Undisturbed Dry Forest (UDF), Disturbed Dry Forest (DDF), Preserved-Cultivated (PC) and Degraded-Cultivated (DC). In the first part of this work we quantified total organic C, N and P, in addition to {sup 137} Cs concentrations, under the assumption that changes in organic nutrient contents among land use groups would be greater than the within group variability, thus enabling inferences at a regional scale. Concentrations of C and N in DC were 50% smaller (P<0.05) than those in UDF. Of these losses, 43% were attributed to erosion processes while 57% were related to SOM mineralization. The Po/Pi ratio under UDF was 1.47 and decreased to o.82 in PC and DC (P<0.05). The effects of changes in land use were greater when considering the 0-7.5 cm layer rather than the 0-15 cm layer. Interrelationships between C and P in the dry forest areas suggested that P availability and water controlled C accumulation in these soils. In the second part of this work two experiments were conducted. The first one included a preliminary phase, comparing four methods in their capacity to detect changes in soil organic matter quality. Eighty samples that maximized the variability in C content of the whole set (n=160), were analyzed for: C in the light SOM fraction (density < 1 kg dm{sup -3}) (C-lf); C

  11. 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.

  12. 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.

  13. 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

  14. Changes in the Coupling of C, N and P Cycles During River Transport from Source to Sea.

    Science.gov (United States)

    Cosby, B. J., Jr.; Withers, P.; Thompson, J.; Evans, C.; Fovet, O.; Bowes, M.; Gozzard, E.; Demars, B.; Stutter, M.

    2015-12-01

    The UK Turf2Surf project asks when, where and how coupling between C, N & P cycles occurs within terrestrial, freshwater and estuarine ecosystems. C-N-P cycling and fluxes are followed through two UK catchments, the Conwy and Ribble, which are Centre for Ecology and Hydrology catchment observatories for landscape scale research from source to sea. The Conwy is typical of non-industrialised areas with few discrete agricultural and industrial sources while the Ribble has a mixed urban and agricultural landscape. Both have areas of upland and moor with peats in the Conwy. Field and laboratory experiments track the incorporation of terrestrial C, N & P into the riverine ecosystems of the catchments and measure changes in C-N-P stoichiometry and cycling along the stream networks from uplands to the river-estuary transition zone (RETZ). We present results focussed on the riverine systems. Flume mesocosms at 18 sites investigated in-stream nutrient processing and algal response to increased C, N & P concentrations (singly and combined). River reach experiments at 14 sites across land use and DOC gradients examined whole ecosystem metabolic response to C, N & P additions. Pore-water sampling with DET (diffusive equilibrium in thin films) gel probes at 5 sites quantified N & P fluxes and distributions across the sediment-water interface. Laboratory mesocosm experiments with streamwater from a variety of land uses (and DOC levels) studied the fate and cycling of stream organic matter subjected to controlled light/dark treatments, and the addition of N & P and a biocide. Results indicate that the study streams are N limited in the headwaters, but become progressively N & P co-limited near the RETZ. DOC processing in streams transitions from primarily photochemical degradation in headwaters (releasing N & P) to biotic aquatic DOC production (consuming N & P) downstream. Increasing C supply leads to increasing average ecosystem respiration irrespective of N & P status

  15. 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...

  16. A systematic investigation and insight into the formation mechanism of bilayers of fatty acid/soap mixtures in aqueous solutions.

    Science.gov (United States)

    Xu, Wenlong; Song, Aixin; Dong, Shuli; Chen, Jingfei; Hao, Jingcheng

    2013-10-08

    Vesicles are the most common form of bilayer structures in fatty acid/soap mixtures in aqueous solutions; however, a peculiar bilayer structure called a "planar sheet" was found for the first time in the mixtures. In the past few decades, considerable research has focused on the formation theory of bilayers in fatty acid/soap mixtures. The hydrogen bond theory has been widely accepted by scientists to explain the formation of bilayers. However, except for the hydrogen bond, no other driving forces were proposed systematically. In this work, three kinds of weak interactions were investigated in detail, which could perfectly demonstrate the formation mechanism of bilayer structures in the fatty acid/soap mixtures in aqueous solutions. (i) The influence of hydrophobic interaction was detected by changing the chain length of fatty acid (C(n)H(2n+1)COOH), in which n = 10 to 18, the phase behavior was investigated, and the phase region was presented. With the help of cryogenic transmission electron microscopy (cryo-TEM) observations, deuterium nuclear magnetic resonance ((2)H NMR), and X-ray diffraction (XRD) measurements, the vesicles and planar sheets were determined. The chain length of C(n)H(2n+1)COOH has an important effect on the physical state of the hydrophobic chain, resulting in an obvious difference in the viscoelasticity of the solution samples. (ii) The existence of hydrogen bonds between fatty acids and their soaps in aqueous solutions was demonstrated by Fourier transform infrared (FT-IR) spectroscopy and molecule dynamical simulation. From the pH measurements, the pH ranges of the bilayer formation were at the pKa values of fatty acids, respectively. (iii) Counterions can be embedded in the stern layer of the bilayers and screen the electrostatic repulsion between the COO(-) anionic headgroups. FT-IR characterization demonstrated a bidentate bridging coordination mode between counterions and carboxylates. The conductivity measurements provided the degree

  17. Conference on Yang-Mills Gauge Field Theories : C. N. Yang's Contributions to Physics

    CERN Document Server

    Phua, K K

    2016-01-01

    During the last six decades, Yang–Mills theory has increasingly become the cornerstone of theoretical physics. It is seemingly the only fully consistent relativistic quantum many-body theory in four space-time dimensions. As such it is the underlying theoretical framework for the Standard Model of Particle Physics, which has been shown to be the correct theory at the energies we now can measure. It has been investigated also from many other perspectives, and many new and unexpected features have been uncovered from this theory. In recent decades, apart from high energy physics, the theory has been actively applied in other branches of physics, such as statistical physics, condensed matter physics, nonlinear systems, etc. This makes the theory an indispensable topic for all who are involved in physics.The conference celebrated the exceptional achievements using Yang–Mills theory over the years but also many other truly remarkable contributions to different branches of physics from Prof C N Yang. This volum...

  18. Extraterrestrial flux of potentially prebiotic C, N, and P to the early Earth.

    Science.gov (United States)

    Pasek, Matthew; Lauretta, Dante

    2008-02-01

    With growing evidence for a heavy bombardment period ending 4-3.8 billion years ago, meteorites and comets may have been an important source of prebiotic carbon, nitrogen, and phosphorus on the early Earth. Life may have originated shortly after the late-heavy bombardment, when concentrations of organic compounds and reactive phosphorus were enough to "kick life into gear". This work quantifies the sources of potentially prebiotic, extraterrestrial C, N, and P and correlates these fluxes with a comparison to total Ir fluxes, and estimates the effect of atmosphere on the survival of material. We find (1) that carbonaceous chondrites were not a good source of organic compounds, but interplanetary dust particles provided a constant, steady flux of organic compounds to the surface of the Earth, (2) extraterrestrial metallic material was much more abundant on the early Earth, and delivered reactive P in the form of phosphide minerals to the Earth's surface, and (3) large impacts provided substantial local enrichments of potentially prebiotic reagents. These results help elucidate the potential role of extraterrestrial matter in the origin of life.

  19. 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.

  20. 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.

  1. Upper limits to the reaction rate coefficients of C(n)(-) and C(n)H(-) (n = 2, 4, 6) with molecular hydrogen.

    Science.gov (United States)

    Endres, Eric S; Lakhmanskaya, Olga; Hauser, Daniel; Huber, Stefan E; Best, Thorsten; Kumar, Sunil S; Probst, Michael; Wester, Roland

    2014-08-21

    In the interstellar medium (ISM) ion–molecule reactions play a key role in forming complex molecules. Since 2006, after the radioastronomical discovery of the first of by now six interstellar anions, interest has grown in understanding the formation and destruction pathways of negative ions in the ISM. Experiments have focused on reactions and photodetachment of the identified negatively charged ions. Hints were found that the reactions of CnH(–) with H2 may proceed with a low (rate [Eichelberger, B.; et al. Astrophys. J. 2007, 667, 1283]. Because of the high abundance of molecular hydrogen in the ISM, a precise knowledge of the reaction rate is needed for a better understanding of the low-temperature chemistry in the ISM. A suitable tool to analyze rare reactions is the 22-pole radiofrequency ion trap. Here, we report on reaction rates for Cn(–) and CnH(–) (n = 2, 4, 6) with buffer gas temperatures of H2 at 12 and 300 K. Our experiments show the absence of these reactions with an upper limit to the rate coefficients between 4 × 10(–16) and 5 × 10(–15) cm(3) s(–1), except for the case of C2(–), which does react with a finite rate with H2 at low temperatures. For the cases of C2H(–) and C4H(–), the experimental results were confirmed with quantum chemical calculations. In addition, the possible influence of a residual reactivity on the abundance of C4H(–) and C6H(–) in the ISM were estimated on the basis of a gas-phase chemical model based on the KIDA database. We found that the simulated ion abundances are already unaffected if reaction rate coefficients with H2 were below 10(–14) cm(3) s(–1).

  2. 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.

  3. 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...

  4. Utilising Sodium-Mediated Ferration for Regioselective Functionalisation of Fluoroarenes via C-H and C-F Bond Activations.

    Science.gov (United States)

    Hevia, Eva; Maddock, Lewis C H; Nixon, Tracy; Kennedy, Alan R; Probert, Michael R; Clegg, William

    2017-10-25

    While Fe(II) complexes have shown little promise in deprotonative metallation chemistry, pairing iron bis(amide) Fe(HMDS)2 with Na(HMDS) to form new sodium ferrate base [(dioxane)0.5·NaFe(HMDS)3] (1) enables regioselective mono and di-ferration (via direct Fe-H exchange) of a wide range of fluoroaromatic substrates under mild reaction conditions. Trapping of several ferrated intermediates has provided key insight into how synchronised Na/Fe cooperation operates in these transformations. Furthermore using excess 1 at 80oC switches on a remarkable cascade process inducing the collective 2-fold C-H/3-fold C-F bond activation, where each C-H bond is transformed to C-Fe bonds whereas each C-F bond is transformed into a C-N bond. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. 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.

  6. Volatiles (H, C, N, O, noble gases) in comets as tracers of early solar system events (Invited)

    Science.gov (United States)

    Marty, B.

    2013-12-01

    Volatiles (H, C, N, O, noble gases) present the largest variations in their relative abundances and, importantly, in their isotopic ratios, among solar system elements. The original composition of the protosolar nebula has been investigated through the measurements of primitive meteorites and of in-situ (e.g. Galileo probe analysis of the Jupiter's atmosphere) and sample-return (Genesis, recovery and analysis of solar wind) missions. The protosolar gas was poor in deuterium, in 15N and in 17,18O. Variations among solar system reservoir reach several hundreds of percents for the D/H and 15N/14N ratios. These variations are possibly : (i) due to interactions between XUV photons of the proto-Sun and the-dust, (ii) result from low temperature ion-molecule reactions, or (iii) constitute an heritage on interstellar volatiles trapped in dust (e.g., organics). Likewise, noble gases are elementally and isotopically (1% per amu for xenon) fractionated with respect to the composition of the solar wind (our best proxy for the protosolar nebula composition). Cometary matter directly measured on coma, or in Stardust material, or in IDPs, seems to present among the largest heterogeneities in their stable isotope compositions but knowledge on their precise compositions of the different phases and species is partial and mosty lacking. Among the several important issues requiring a better knowledge of cometary volatiles are the origin(s) of volatile elements on Earth and Moon, on Mars and on Venus, understanding large scale circulation of matter between hot and frozen zones, and the possibility of interstellar heritage for organics. Critical measurements to be made by the next cometary missions include the value of the D/H ratio in water ice, in NH3 and organics. Nitrogen is particularly interesting as cometary HCN and CN are rich in 15N, but an isotoppe mass balance will require to measure the main host species (N2 ?). Noble gases are excellent tracers of physical processes

  7. 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.

  8. 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.

  9. Multifunctional Ti-(Ca,Zr)-(C,N,O,P) films for load-bearing implants.

    Science.gov (United States)

    Shtansky, D V; Gloushankova, N A; Bashkova, I A; Kharitonova, M A; Moizhess, T G; Sheveiko, A N; Kiryukhantsev-Korneev, F V; Petrzhik, M I; Levashov, E A

    2006-07-01

    Films of Ti-Ca-P-C-O-(N), Ti-Ca-C-O-(N) and Ti-Zr-C-O-(N) were deposited by DC magnetron sputtering or ion implantation-assisted magnetron sputtering of composite targets TiC0.5 + 10%Ca10(PO4)6(OH)2, TiC0.5 + 20%(CaO + TiO2) and TiC0.5 + 10%ZrO2 in an Ar atmosphere or reactively in a gaseous mixture of Ar + 14%N2. The microstructure, elemental and phase composition of films were studied by means of X-ray diffraction, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The films were characterized in terms of their hardness, Young's modulus, elastic recovery, adhesion strength, and friction and wear both in air and under physiological solution. Particular attention was paid to the analysis of deformation and fracture for various film/substrate systems during scratch testing. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of adhesion, spreading, and proliferation of MC3T3-E1 osteoblasts and IAR-2 epithelial cells, morphometric analysis, actin cytoskeleton, focal contacts staining, alkaline phosphatase activity and von Kossa staining of osteoblastic culture. Cell culture experiments demonstrated an increase of osteoblastic proliferation on Ca- and P-incorporated films. In vivo studies were fulfilled by subcutaneous implantation of Teflon plates coated with the tested films in mice and analysis of the population of adherent cells on their surfaces. The results obtained show that multicomponent nanostructured Ti-(Ca, Zr)-(C, N, O, P) films possess a combination of high hardness, wear resistance and adhesion strength, reduced Young's modulus, low friction coefficient and high biocompatibility.

  10. Towards a unified description of the hydrogen bond network of liquid water: a dynamics based approach.

    Science.gov (United States)

    Ozkanlar, Abdullah; Zhou, Tiecheng; Clark, Aurora E

    2014-12-07

    The definition of a hydrogen bond (H-bond) is intimately related to the topological and dynamic properties of the hydrogen bond network within liquid water. The development of a universal H-bond definition for water is an active area of research as it would remove many ambiguities in the network properties that derive from the fixed definition employed to assign whether a water dimer is hydrogen bonded. This work investigates the impact that an electronic-structure based definition, an energetic, and a geometric definition of the H-bond has upon both topological and dynamic network behavior of simulated water. In each definition, the use of a cutoff (either geometric or energetic) to assign the presence of a H-bond leads to the formation of transiently bonded or broken dimers, which have been quantified within the simulation data. The relative concentration of transient species, and their duration, results in two of the three definitions sharing similarities in either topological or dynamic features (H-bond distribution, H-bond lifetime, etc.), however no two definitions exhibit similar behavior for both classes of network properties. In fact, two networks with similar local network topology (as indicated by similar average H-bonds) can have dramatically different global network topology (as indicated by the defect state distributions) and altered H-bond lifetimes. A dynamics based correction scheme is then used to remove artificially transient H-bonds and to repair artificially broken bonds within the network such that the corrected network exhibits the same structural and dynamic properties for two H-bond definitions (the properties of the third definition being significantly improved). The algorithm described represents a significant step forward in the development of a unified hydrogen bond network whose properties are independent of the original hydrogen bond definition that is employed.

  11. Comparative study of halogen- and hydrogen-bond interactions between benzene derivatives and dimethyl sulfoxide.

    Science.gov (United States)

    Zheng, Yan-Zhen; Deng, Geng; Zhou, Yu; Sun, Hai-Yuan; Yu, Zhi-Wu

    2015-08-24

    The halogen bond, similar to the hydrogen bond, is an important noncovalent interaction and plays important roles in diverse chemistry-related fields. Herein, bromine- and iodine-based halogen-bonding interactions between two benzene derivatives (C6 F5 Br and C6 F5 I) and dimethyl sulfoxide (DMSO) are investigated by using IR and NMR spectroscopy and ab initio calculations. The results are compared with those of interactions between C6 F5 Cl/C6 F5 H and DMSO. First, the interaction energy of the hydrogen bond is stronger than those of bromine- and chlorine-based halogen bonds, but weaker than iodine-based halogen bond. Second, attractive energies depend on 1/r(n) , in which n is between three and four for both hydrogen and halogen bonds, whereas all repulsive energies are found to depend on 1/r(8.5) . Third, the directionality of halogen bonds is greater than that of the hydrogen bond. The bromine- and iodine-based halogen bonds are strict in this regard and the chlorine-based halogen bond only slightly deviates from 180°. The directional order is iodine-based halogen bond>bromine-based halogen bond>chlorine-based halogen bond>hydrogen bond. Fourth, upon the formation of hydrogen and halogen bonds, charge transfers from DMSO to the hydrogen- and halogen-bond donors. The CH3 group contributes positively to stabilization of the complexes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Better Bonded Ethernet Load Balancing

    Energy Technology Data Exchange (ETDEWEB)

    Gabler, Jason

    2006-09-29

    When a High Performance Storage System's mover shuttles large amounts of data to storage over a single Ethernet device that single channel can rapidly become saturated. Using Linux Ethernet channel bonding to address this and similar situations was not, until now, a viable solution. The various modes in which channel bonding could be configured always offered some benefit but only under strict conditions or at a system resource cost that was greater than the benefit gained by using channel bonding. Newer bonding modes designed by various networking hardware companies, helpful in such networking scenarios, were already present in their own switches. However, Linux-based systems were unable to take advantage of those new modes as they had not yet been implemented in the Linux kernel bonding driver. So, except for basic fault tolerance, Linux channel bonding could not positively combine separate Ethernet devices to provide the necessary bandwidth.

  13. Bonding by Hydroxide-Catalyzed Hydration and Dehydration

    Science.gov (United States)

    Gwo, Dz-Hung

    2008-01-01

    A simple, inexpensive method for bonding solid objects exploits hydroxide-catalyzed hydration and dehydration to form silicate-like networks in thin surface and interfacial layers between the objects. The method can be practiced at room temperature or over a wide range of temperatures. The method was developed especially to enable the formation of precise, reliable bonds between precise optical components. The bonds thus formed exhibit the precision and transparency of bonds formed by the conventional optical-contact method and the strength and reliability of high-temperature frit bonds. The method also lends itself to numerous non-optical applications in which there are requirements for precise bonds and/or requirements for bonds, whether precise or imprecise, that can reliably withstand severe environmental conditions. Categories of such non-optical applications include forming composite materials, coating substrates, forming laminate structures, and preparing objects of defined geometry and composition. The method is applicable to materials that either (1) can form silicate-like networks in the sense that they have silicate-like molecular structures that are extensible into silicate-like networks or (2) can be chemically linked to silicate-like networks by means of hydroxide-catalyzed hydration and dehydration. When hydrated, a material of either type features surface hydroxyl (-OH) groups. In this method, a silicate-like network that bonds two substrates can be formed either by a bonding material alone or by the bonding material together with material from either or both of the substrates. Typically, an aqueous hydroxide bonding solution is dispensed and allowed to flow between the mating surfaces by capillary action. If the surface figures of the substrates do not match precisely, bonding could be improved by including a filling material in the bonding solution. Preferably, the filling material should include at least one ingredient that can be hydrated to

  14. Why Should Governments Issue Bonds?

    OpenAIRE

    Romer, David

    1993-01-01

    This paper has three purposes. First, it shows that several recent arguments that the optimal nominal interest rate on government bonds is zero even when second best considerations are accounted for rest on perfect substitutes assumptions. Second, it characterizes the conditions under which the issue of interest-bearing bonds is desirable once these assumptions are relaxed. And third, it shows that these potential microeconomic benefits of bond issue are closely related to traditional macroec...

  15. Adhesives for orthodontic bracket bonding

    OpenAIRE

    Déborah Daniella Diniz Fonseca; Daene Patrícia Tenório Salvador da Costa; Renata Cimões; Lúcia Carneiro de Souza Beatrice; Ana Cláudia da Silva Araújo

    2010-01-01

    The advent of acid etching, introduced by Buonocore in 1955, brought the possibility of bonding between the bracket base and enamel, contributing to more esthetic and conservative orthodontics. This direct bracket bonding technique has brought benefits such as reduced cost and time in performing the treatment, as well as making it easier to perform oral hygiene. The aim of this study was to conduct a survey of published studies on orthodontic bracket bonding to dental enamel. It was verified ...

  16. Butterflyfishes as a System for Investigating Pair Bonding

    KAUST Repository

    Nowicki, Jessica

    2017-11-14

    For many animals, affiliative relationships such as pair bonds form the foundation of society, and are highly adaptive. Animal systems amenable for comparatively studying pair bonding are important for identifying underlying biological mechanisms, but mostly exist in mammals. Better establishing fish systems will enable comparison of pair bonding mechanisms across taxonomically distant lineages that may reveal general underlying principles. We examined the utility of wild butterflyfishes (f: Chaetodontidae; g: Chaetodon) for comparatively studying pair bonding. Stochastic character mapping inferred that within the family, pairing is ancestral, with at least seven independent transitions to group formation and seven transition to solitary behavior from the late Miocene to recent. In six sympatric and wide-spread species representing a clade with one ancestrally reconstructed transition from paired to solitary grouping, we then verified social systems at Lizard Island, Australia. In situ observations confirmed that Chaetodon baronessa, C. lunulatus, and C. vagabundus are predominantly pair bonding, whereas C. rainfordi, C. plebeius, and C. trifascialis are predominantly solitary. Even in the predominantly pair bonding species, C. lunulatus, a proportion of adults (15 %) are solitary. Importantly, inter- and intra-specific differences in social systems do not co-vary with other previously established attributes (geographic occurrence, parental care, diet, or territoriality). Hence, the proposed butterflyfish populations are promising for comparative analyses of pair bonding and its mechanistic underpinnings. Avenues for further developing the system are proposed, including determining whether the utility of these species applies across their geographic disruptions.

  17. Comparison of shear bond strength and micro-leakage of three commercially available seventh generation bonding agents in primary anterior teeth: An in vitro study

    Directory of Open Access Journals (Sweden)

    Mahesh K Duddu

    2015-01-01

    Full Text Available Purpose: The study was conducted with the aim of comparing the shear bond strength (SBS and microleakage of Tetric N-Bond, G-bond, and Xeno V (seventh generation dentin adhesives in primary anterior teeth. Materials and Methods: For the shear bond strength, 45 teeth were randomly divided in to three groups namely group A, B, C (n = 15. Samples were mounted horizontally on acrylic block exposing the facial surface and bonded with different adhesives according to manufacturer instructions. A split Teflon mold was used to build the composite resin cylinder and light cured. Shear bond strength was tested using a universal testing machine. The values were statistically analysed. For microleakage, another 45 teeth were similarly grouped. Two class V cavities were prepared on the labial surface and treated with different dentine bonding agents and restored with resin composite (Ivoclar vivadent A2 shade. The restorations were subsequently thermally stressed for 200 cycles and were subjected to dye penetration test, followed by sectioning through the center of the restoration labiolingually. Each section was examined using stereomicroscope at × 40 magnification to asses dye penetration at the margins of the restoration. Results: The SBS varied between 22.12-23.77 N/mm 2 (P-value = 0.231. The microleakage scores varied between 0.6-1.2 (P-value = 0.03; Post-hoc test A vs B (0.007.There was a statistically higher degree of microleakage observed in group A when compared to group B. Conclusion: Among the three commercially available bonding agents, there were no statistically significant differences in SBS. G bond had higher microleakage when compared to the others.

  18. Roll bonding of strained aluminium

    DEFF Research Database (Denmark)

    Staun, Jakob M.

    2003-01-01

    This report investigates roll bonding of pre-strained (å ~ 4) aluminium sheets to produce high strain material from high purity aluminium (99.996%) and commercial pure aluminium (99.6%). The degree of bonding is investigated by optical microscopy and ultrasonic scanning. Under the right...... circumstances both materials show good bonding, but the high purity material is excluded because of recrystallisation and the resulting loss of mechanical properties. The effect of cross stacking and roll bonding pre-strained sheets of the commercial purity material is investigated and some dependence...

  19. Wafer bonding applications and technology

    CERN Document Server

    Gösele, Ulrich

    2004-01-01

    During the past decade direct wafer bonding has developed into a mature materials integration technology. This book presents state-of-the-art reviews of the most important applications of wafer bonding written by experts from industry and academia. The topics include bonding-based fabrication methods of silicon-on-insulator, photonic crystals, VCSELs, SiGe-based FETs, MEMS together with hybrid integration and laser lift-off. The non-specialist will learn about the basics of wafer bonding and its various application areas, while the researcher in the field will find up-to-date information about this fast-moving area, including relevant patent information.

  20. A simplified indirect bonding technique

    Directory of Open Access Journals (Sweden)

    Radha Katiyar

    2014-01-01

    Full Text Available With the advent of lingual orthodontics, indirect bonding technique has become an integral part of practice. It involves placement of brackets initially on the models and then their transfer to teeth with the help of transfer trays. Problems encountered with current indirect bonding techniques used are (1 the possibility of adhesive flash remaining around the base of the brackets which requires removal (2 longer time required for the adhesive to gain enough bond strength for secure tray removal. The new simplified indirect bonding technique presented here overcomes both these problems.

  1. Morphology, topography, and hardness of diffusion bonded sialon to AISI 420 at different bonding time

    Science.gov (United States)

    Ibrahim, Nor Nurulhuda Md.; Hussain, Patthi; Awang, Mokhtar

    2015-07-01

    Sialon and AISI 420 martensitic stainless steel were diffusion bonded in order to study the effect of bonding time on reaction layer's growth. Joining of these materials was conducted at 1200°C under a uniaxial pressure of 17 MPa in a vacuum ranging from 5.0 to 8.0×10-6 Torr with bonding time varied for 0.5, 2, and 3 h. Thicker reaction layer was formed in longer bonded sample since the elements from sialon could diffuse further into the steel. Sialon retained its microstructure but it was affected at the initial contact with the steel to form the new interface layer. Diffusion layer grew toward the steel and it was segregated with the parent steel as a result of the difference in properties between these regions. The segregation formed a stream-like structure and its depth decreased when the bonding time was increased. The microstructure of the steel transformed into large grain size with precipitates. Prolonging the bonding time produced more precipitates in the steel and reduced the steel thickness as well. Interdiffusions of elements occurred between the joined materials and the concentrations were decreasing toward the steel and vice versa. Silicon easily diffused into the steel because it possessed lower ionization potential compared to nitrogen. Formation of silicide and other compounds such as carbides were detected in the interface layer and steel grain boundary, respectively. These compounds were harmful due to silicide brittleness and precipitation of carbides in the grain boundary might cause intergranular corrosion cracking. Sialon retained its hardness but it dropped very low at the interface layer. The absence of crack at the joint in all samples could be contributed from the ductility characteristic of the reaction layer which compensated the residual stress that was formed upon the cooling process.

  2. Human Bond Communication

    DEFF Research Database (Denmark)

    Prasad, Ramjee

    2016-01-01

    Modern dexterous communication technology is progressively enabling humans to communicate their information through them with speech (aural) and media (optical) as underpinning essence. Humans realize this kind of aural and optical information by their optical and auditory senses. However, due...... to certain constraints, the ability to incorporate the other three sensory features namely, olfactory, gustatory, and tactile are still far from reality. Human bond communication is a novel concept that incorporates olfactory, gustatory, and tactile that will allow more expressive and holistic sensory...... information exchange through communication techniques for more human sentiment centric communication. This concept endorses the need of inclusion of other three senses and proposes an innovative approach of holistic communication for future communication network....

  3. Analyses of antibacterial activity and cell compatibility of titanium coated with a Zr-C-N film.

    Directory of Open Access Journals (Sweden)

    Yin-Yu Chang

    Full Text Available OBJECTIVE: The purpose of this study was to verify the antibacterial performance and cell proliferation activity of zirconium (Zr-carbon (C-nitride (N coatings on commercially pure titanium (Ti with different C contents. MATERIALS AND METHODS: Reactive nitrogen gas (N(2 with and without acetylene (C(2H(2 was activated by Zr plasma in a cathodic-arc evaporation system to deposit either a zirconium nitride (ZrN or a Zr-C-N coating onto Ti plates. The bacterial activity of the coatings was evaluated against Staphylococcus aureus with the aid of SYTO9 nucleic acid staining and scanning electron microscopy (SEM. Cell compatibility, mRNA expression, and morphology related to human gingival fibroblasts (HGFs on the coated samples were also determined by using the MTT assay, reverse transcriptase-polymerase chain reaction, and SEM. RESULTS: The Zr-C-N coating with the highest C content (21.7 at% exhibited the lowest bacterial preservation (P<0.001. Biological responses including proliferation, gene expression, and attachment of HGF cells to ZrN and Zr-C-N coatings were comparable to those of the uncoated Ti plate. CONCLUSIONS: High-C-content Zr-C-N coatings not only provide short-term antibacterial activity against S. aureus but are also biocompatible with HGF cells.

  4. Effects of C/N controlled periphyton based organic farming of freshwater prawn on water quality parameters and biotic factors

    Directory of Open Access Journals (Sweden)

    Md. Rezoanul Haque

    2014-08-01

    Full Text Available The effects of C:N controlled periphyton based organic farming of freshwater prawn on water quality parameters and biotic factors were investigated. The experiment had two treatments: T1 and T2 each with three replications. Stocking density was maintained at 20,000 juveniles ha-1. In T1, only commercially available prawn feed was applied and in T2, a locally formulated and prepared feed containing 24% crude protein with C:N ratio close to 20 was used, and maize flour and bamboo side shoots were provided for maintaining C:N ratio 20.Mean values of water quality parameters did not vary significantly (P>0.05 between treatments. Periphytic biomass in terms of dry matter, ash free dry matter (AFDM and chlorophyll a showed significant difference (P<0.05 among different sampling months. Individual harvesting weight, individual weight gain, specific growth rates, gross and net yields of prawn were significantly higher (P<0.05 in T2 than T1. Therefore, it was concluded that freshwater prawn might consume periphyton biomass in C:N controlled periphyton based organic farming practices resulted a significantly (P<0.05 higher production of freshwater prawn than traditional farming.

  5. Early History of Acapulco and Lodran Constrained by the Nanostructure and C, N Isotopic Composition of Their Carbons

    Science.gov (United States)

    Charon, E.; Aléon, J.; Rouzaud, J. N.

    2012-03-01

    New results of structure and C, N isotopes of carbons on A-L meteorites allows us to defend an original history of A-L parent body benefiting of previous interpretations implying shock after the peak temperature and seeding by an exogenous carbons.

  6. Differential NtcA Responsiveness to 2-Oxoglutarate Underlies the Diversity of C/N Balance Regulation in Prochlorococcus

    Directory of Open Access Journals (Sweden)

    María A. Domínguez-Martín

    2018-01-01

    Full Text Available Previous studies showed differences in the regulatory response to C/N balance in Prochlorococcus with respect to other cyanobacteria, but no information was available about its causes, or the ecological advantages conferred to thrive in oligotrophic environments. We addressed the changes in key enzymes (glutamine synthetase, isocitrate dehydrogenase and the ntcA gene (the global nitrogen regulator involved in C/N metabolism and its regulation, in three model Prochlorococcus strains: MED4, SS120, and MIT9313. We observed a remarkable level of diversity in their response to azaserine, a glutamate synthase inhibitor which increases the concentration of the key metabolite 2-oxoglutarate, used to sense the C/N balance by cyanobacteria. Besides, we studied the binding between the global nitrogen regulator (NtcA and the promoter of the glnA gene in the same Prochlorococcus strains, and its dependence on the 2-oxoglutarate concentration, by using isothermal titration calorimetry, surface plasmon resonance, and electrophoretic mobility shift. Our results show a reduction in the responsiveness of NtcA to 2-oxoglutarate in Prochlorococcus, especially in the MED4 and SS120 strains. This suggests a trend to streamline the regulation of C/N metabolism in late-branching Prochlorococcus strains (MED4 and SS120, in adaptation to the rather stable conditions found in the oligotrophic ocean gyres where this microorganism is most abundant.

  7. Short-term changes in soil C, N, and biota following harvesting and regeneration of loblolly pine (Pinus taeda L.)

    Science.gov (United States)

    Mason C. Carter; Thomas J. Dean; Minyi Zhou; Michael G. Messina; Ziyin Wang

    2002-01-01

    In affiliation with the USDA-FS long-term soil productivity program, a series of studies have been established in the US gulf coast region to monitor the effects of intensive silviculture on site productivity. This report presents early results of a study of the interactive effects of harvest intensity and cultural treatments on soil C, N, and biological processes...

  8. Accumulation, release and turnover of nutrients (C-N-P-Si) by the blue mussel Mytilus edulis under oligotrophic conditions

    NARCIS (Netherlands)

    Jansen, H.M.; Strand, O.; Verdegem, M.C.J.; Smaal, A.C.

    2012-01-01

    To evaluate the potential role of mussels in nutrient cycling in oligotrophic fjord ecosystems, we applied a multiple-element (C-N-P-Si) approach considering several physiological processes (excretion, tissue composition, biodeposition) simultaneously. The study covered one annual cycle, reflecting

  9. Charge-Shift Corrected Electronegativities and the Effect of Bond Polarity and Substituents on Covalent-Ionic Resonance Energy.

    Science.gov (United States)

    James, Andrew M; Laconsay, Croix J; Galbraith, John Morrison

    2017-07-13

    Bond dissociation energies and resonance energies for HnA-BHm molecules (A, B = H, C, N, O, F, Cl, Li, and Na) have been determined in order to re-evaluate the concept of electronegativity in the context of modern valence bond theory. Following Pauling's original scheme and using the rigorous definition of the covalent-ionic resonance energy provided by the breathing orbital valence bond method, we have derived a charge-shift corrected electronegativity scale for H, C, N, O, F, Cl, Li, and Na. Atomic charge shift character is defined using a similar approach resulting in values of 0.42, 1.06, 1.43, 1.62, 1.64, 1.44, 0.46, and 0.34 for H, C, N, O, F, Cl, Li, and Na, respectively. The charge-shift corrected electronegativity values presented herein follow the same general trends as Pauling's original values with the exception of Li having a smaller value than Na (1.57 and 1.91 for Li and Na respectively). The resonance energy is then broken down into components derived from the atomic charge shift character and polarization effects. It is then shown that most of the resonance energy in the charge-shift bonds H-F, H3C-F, and Li-CH3 and borderline charge-shift H-OH is associated with polarity rather than the intrinsic atomic charge-shift character of the bonding species. This suggests a rebranding of these bonds as "polar charge-shift" rather than simply "charge-shift". Lastly, using a similar breakdown method, it is shown that the small effect the substituents -CH3, -NH2, -OH, and -F have on the resonance energy (bonding atom.

  10. Positively charged phosphorus as a hydrogen bond acceptor

    DEFF Research Database (Denmark)

    Hansen, Anne Schou; Du, Lin; Kjærgaard, Henrik Grum

    2014-01-01

    Phosphorus (P) is an element that is essential to the life of all organisms, and the atmospheric detection of phosphine suggests the existence of a volatile biogeochemical P cycle. Here, we investigate the ability of P to participate in the formation of OH···P hydrogen bonds. Three bimolecular......-stretching frequency red shifts and quantum chemical calculations, we find that P is an acceptor atom similar in strength to O and S and that all three P, O, and S atoms are weaker acceptors than N. The quantum chemical calculations show that both H and P in the OH···P hydrogen bond have partial positive charges......, as expected from their electronegativities. However, the electrostatic potentials show a negative potential area on the electron density surface around P that facilitates formation of hydrogen bonds....

  11. The Influence of Small Monovalent Cations on Neighbouring Hydrogen Bonds of Aquo-Protein Complexes

    Science.gov (United States)

    Sagarik, Kritsana P.; Rode, Bernd M.

    1981-12-01

    The influence of small monovalent metal ions on hydrogen bonds of aquo-protein complexes is studied on Li+/HCONH2-OH2 as an example. Using results obtained from ab initio calculations with minimal GLO basis sets, the remarkable changes in the hydrogen bond energy and charge distribution, due to metal ion complex formation, are discussed. The metal ion seems to enhance strongly the donor-acceptor interaction of the O ... H-N-C=0 hydrogen-bonded system.

  12. The Significance of Multivalent Bonding Motifs and “Bond Order” in DNA-Directed Nanoparticle Crystallization

    Energy Technology Data Exchange (ETDEWEB)

    Thaner, Ryan V.; Eryazici, Ibrahim; Macfarlane, Robert J.; Brown, Keith A.; Lee, Byeongdu; Nguyen, SonBinh T.; Mirkin, Chad A.

    2016-05-18

    Multivalent oligonucleotide-based bonding elements have been synthesized and studied for the assembly and crystallization of gold nanoparticles. Through the use of organic branching points, divalent and trivalent DNA linkers were readily incorporated into the oligonucleotide shells that define DNA-nanoparticles and compared to monovalent linker systems. These multivalent bonding motifs enable the change of "bond strength" between particles and therefore modulate the effective "bond order." In addition, the improved accessibility of strands between neighboring particles, either due to multivalency or modifications to increase strand flexibility, gives rise to superlattices with less strain in the crystallites compared to traditional designs. Furthermore, the increased availability and number of binding modes also provide a new variable that allows previously unobserved crystal structures to be synthesized, as evidenced by the formation of a thorium phosphide superlattice.

  13. Chain formation of metal atoms

    DEFF Research Database (Denmark)

    Bahn, Sune Rastad; Jacobsen, Karsten Wedel

    2001-01-01

    The possibility of formation of single-atomic chains by manipulation of nanocontacts is studied for a selection of metals (Ni, Pd, Pt, Cu, Ag, Au). Molecular dynamics simulations show that the tendency for chain formation is strongest for Au and Pt. Density functional theory calculations indicate...... that the metals which form chains exhibit pronounced many-atom interactions with strong bonding in low coordinated systems....

  14. Redshift or adduct stabilization -- a computational study of hydrogen bonding in adducts of protonated carboxylic acids

    DEFF Research Database (Denmark)

    Olesen, Solveig Gaarn; Hammerum, Steen

    2009-01-01

    changes and the redshift favor the Z OH group, matching the results of NBO and AIM calculations. This reflects that the thermochemistry of adduct formation is not a good measure of the hydrogen bond strength in charged adducts, and that the ionic interactions in the E and Z adducts of protonated......It is generally expected that the hydrogen bond strength in a D-H-A adduct is predicted by the difference between the proton affinities of D and A, measured by the adduct stabilization, and demonstrated by the IR redshift of the D-H bond stretching vibrational frequency. These criteria do...... not always yield consistent predictions, as illustrated by the hydrogen bonds formed by the E and Z OH groups of protonated carboxylic acids. The delta-PA and the stabilization of a series of hydrogen bonded adducts indicate that the E OH group forms the stronger hydrogen bonds, whereas the bond length...

  15. Push-out bond strengths of two fiber post types bonded with different dentin bonding agents.

    Science.gov (United States)

    Topcu, Fulya Toksoy; Erdemir, Ugur; Sahinkesen, Gunes; Mumcu, Emre; Yildiz, Esra; Uslan, Ibrahim

    2010-05-01

    The aim of this study was to evaluate the regional push-out bond strengths for two fiber-reinforced post types using three different dentin bonding agents. Sixty single-rooted extracted human first premolar teeth were sectioned below the cemento-enamel junction, and the roots were endodontically treated. Following standardized post space preparations, the roots were divided into two fiber-post groups (Glassix and Carbopost), and further divided into three subgroups of 10 specimens each for the bonding systems self-etching dentin bonding agents (Clearfil SE Bond and Optibond all-in-one), and total-etching dentin bonding agent (XP Bond). A dual-cure resin luting cement (Maxcem) was then placed in the post spaces and posts were then seated into the root canals polymerized through the cervical portion. The roots were then cut into 3-mm thick sections. Push-out tests were performed at a crosshead speed of 0.5 mm/min. The data were analyzed with multivariate ANOVA (alpha = 0.05). The morphology of interface between different dentin bonding agents from the cervical sections were analyzed with SEM. Glass fiber-reinforced posts demonstrated significantly higher push-out bond strengths than carbon fiber-reinforced posts (p dentin adhesive Clearfil SE Bond and total-etching dentin adhesive XP Bond demonstrated similar bond strengths values and this was significantly higher compared with the Optibond all-in-one in cervical root canal region. In conclusion, in all root segments, the glass fiber-reinforced posts provided significantly increased post retention than the carbon fiber-reinforced posts, regardless of the adhesive used. (c) 2010 Wiley Periodicals, Inc.

  16. How to bond to root canal dentin

    Science.gov (United States)

    Nica, Luminita; Todea, Carmen; Furtos, Gabriel; Baldea, Bogdan

    2014-01-01

    Bonding to root canal dentin may be difficult due to various factors: the structural characteristic of the root canal dentin, which is different from that of the coronal dentin; the presence of the organic tissue of the dental pulp inside the root canal, which has to be removed during the cleaning-shaping of the root canal system; the smear-layer resulted after mechanical instrumentation, which may interfere with the adhesion of the filling materials; the type of the irrigants used in the cleaning protocol; the type of the sealer and core material used in the obturation of the endodontic space; the type of the materials used for the restoration of the endodontically treated teeth. The influence of the cleaning protocol, of the root canal filling material, of the type of the adhesive system used in the restoration of the treated teeth and of the region of the root canal, on the adhesion of several filling and restorative materials to root canal dentin was evaluated in the push-out bond strength test on 1-mm thick slices of endodontically treated human teeth. The results showed that all these factors have a statistically significant influence on the push-out bond strength. Formation of resin tags between radicular dentin and the investigated materials was observed in some of the samples at SEM analysis.

  17. Red emitting [Ir(C^N)2(N^N)]+ complexes employing bidentate 2,2':6',2''-terpyridine ligands for light-emitting electrochemical cells.

    Science.gov (United States)

    Constable, Edwin C; Housecroft, Catherine E; Schneider, Gabriel E; Zampese, Jennifer A; Bolink, Henk J; Pertegás, Antonio; Roldan-Carmona, Cristina

    2014-03-28

    2,2':6',2''-Terpyridine (tpy), 4'-(4-HOC6H4)-2,2':6',2''-terpyridine (1), 4'-(4-MeOC6H4)-2,2':6',2''-terpyridine (2), 4'-(4-MeSC6H4)-2,2':6',2''-terpyridine (3), 4'-(4-H2NC6H4)-2,2':6',2''-terpyridine (4) and 4'-(4-pyridyl)-2,2':6',2''-terpyridine (4) act as N^N chelates in complexes of the type [Ir(C^N)2(N^N)][PF6] in which the cyclometallating ligand, C^N, is derived from 2-phenylpyridine (Hppy) or 3,5-dimethyl-1-phenyl-1H-pyrazole (Hdmppz). The single crystal structures of eight complexes have been determined, and in each iridium(III) complex cation, the non-coordinated pyridine ring of the tpy unit is involved in a face-to-face π-stacking interaction with the cyclometallated ring of an adjacent ligand. Solution NMR spectra of the [Ir(ppy)2(N^N)](+) complexes are consistent with the presence of a non-classical hydrogen bond between the non-coordinated N-donor of the tpy domain and a CH unit of one pyridine ring of an adjacent ppy(-) ligand; the presence of the N···HC interaction was confirmed in one of the solid-state structures. The pendant pyridine ring of the coordinated tpy undergoes hindered rotation on the NMR timescale at 295 K. In CH2Cl2, the complexes are orange or red emitters, with λ(max)(em) in the range 580 to 642 nm; photoluminescence quantum yields (PLQY) are complex in thin film configuration. For the device incorporating [Ir(ppy)2(pytpy)][PF6], the PL to EL red-shift is extremely large and this is indicative of a different emitting state being involved. The most efficient devices used [Ir(ppy)2(1)][PF6], [Ir(ppy)2(2)][PF6] or [Ir(ppy)2(3)][PF6] in the emissive layer; the devices exhibited rapid turn-on times, but showed relatively low efficiencies in accordance with the solid state photoluminescence quantum yields.

  18. Low litter N constrained earthworm-induced soil carbon pools loss across differing C:N litters

    Science.gov (United States)

    Zheng, Yong; Liu, Manqiang; Wang, Shuai; Bonkowski, Michael; Chen, Xiaoyun; Griffiths, Bryan; Hu, Feng

    2017-04-01

    Earthworms regulate soil carbon (C) and nitrogen (N) pools via modifying soil microbial biomass and extracellular enzyme activities. However, previous studies on earthworm-driven C and N cycling considered only C or N, reflecting single-element limitation. Understanding the stoichiometric variation of microbial biomass and extracellular enzyme activities would help to reveal the mechanisms of how earthworms affect the coupled soil C and N dynamics. A microcosm experiment was conducted to access how earthworms influenced microbial stoichiometry and different fractions of soil C and N pools in the presence of six different litters with contrasting C:N ratio ranging from 22 to 150. A treatment without litter was used as control. Earthworm biomass increased with the decreasing of litter C:N ratio except clover litter, indicating earthworms was constrained by N availability. Earthworms reduced particulate organic nitrogen (PON) and soil total nitrogen (TN), but the extent was less than the C content in the corresponding fractions, leading to a decline in soil C to N ratio. Extracellular enzyme allocation was commonly regarded as a proxy of the microbial biomass requirements, however, earthworms altered C- and N-degrading extracellular enzyme activities but have no effects on soil microbial biomass C:N ratio. Earthworms efficiently stimulated C- rather than N-degrading related enzymes in the presence of rich N litters, accelerating C metabolism and resulting in soil C pools loss and decline in soil C:N. In conclusion, earthworms significantly decreased soil C:N ratio when earthworms was unconstrained by soil N availability. Earthworm-driven reduction on soil C pools and relative N retention was linked to changes in the soil enzyme activities, highlighting the pivotal roles of soil microbial stoichiometry in regulating soil C and N dynamics.

  19. Effects of Nitrogen Sources and C/N Ratios on the Lipid-Producing Potential of Chlorella sp. HQ.

    Science.gov (United States)

    Zhan, Jingjing; Hong, Yu; Hu, Hongying

    2016-07-28

    Microalgae are being researched for their potential as attractive biofuel feedstock, particularly for their lipid production. For maximizing biofuel production, it is necessary to explore the effects of environmental factors on algal lipid-producing potential. In this study, the effects of nitrogen (N) sources (NO2-N, NO3-N, urea-N, NH4-N, and N-deficiency) and carbon-to-nitrogen ratios (C/N= 0, 1.0, 3.0, and 5.0) on algal lipid-producing potential of Chlorella sp. HQ were investigated. The results showed that for Chlorella growth and lipid accumulation potential, NO2-N was the best amongst the nitrogen sources, and NO3-N and urea-N also contributed to algal growth and lipid accumulation potential, but NH4-N and N-deficiency instead caused inhibitory effects. Moreover, the results indicated that algal lipid-producing potential was related to C/N ratios. With NO2-N treatment and carbon addition (C/N = 1.0, 3.0, and 5.0), total lipid yield was enhanced by 12.96-20.37%, but triacylglycerol (TAG) yields decreased by 25.52-94.31%. As for NO3-N treatment, carbon addition led to a 17.82-57.43%/ 25.86-82.67% reduction of total lipid/TAG yields. When NH4-N was used as the nitrogen source, total lipid/TAG yields were increased by 46.67-113.33%/28.99-74.76% with carbon addition. The total lipid/TAG yields of urea-N treatment varied with C/N ratios. Overall, the highest TAG yield (TAG yield: 38.75 ± 5.21 mg/l; TAG content: 44.16 ± 4.35%) was achieved under NO2-N treatment without carbon addition (C/N = 0), the condition that had merit for biofuel production.

  20. Temporal changes in soil C-N-P stoichiometry over the past 60 years across subtropical China.

    Science.gov (United States)

    Yu, Zaipeng; Wang, Minhuang; Huang, Zhiqun; Lin, Teng-Chiu; Vadeboncoeur, Matthew A; Searle, Eric B; Chen, Han Y H

    2018-03-01

    Controlled experiments have shown that global changes decouple the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), resulting in shifting stoichiometry that lies at the core of ecosystem functioning. However, the response of soil stoichiometry to global changes in natural ecosystems with different soil depths, vegetation types, and climate gradients remains poorly understood. Based on 2,736 observations along soil profiles of 0-150 cm depth from 1955 to 2016, we evaluated the temporal changes in soil C-N-P stoichiometry across subtropical China, where soils are P-impoverished, with diverse vegetation, soil, and parent material types and a wide range of climate gradients. We found a significant overall increase in soil total C concentration and a decrease in soil total P concentration, resulting in increasing soil C:P and N:P ratios during the past 60 years across all soil depths. Although average soil N concentration did not change, soil C:N increased in topsoil while decreasing in deeper soil. The temporal trends in soil C-N-P stoichiometry differed among vegetation, soil, parent material types, and spatial climate variations, with significantly increased C:P and N:P ratios for evergreen broadleaf forest and highly weathered Ultisols, and more pronounced temporal changes in soil C:N, N:P, and C:P ratios at low elevations. Our sensitivity analysis suggests that the temporal changes in soil stoichiometry resulted from elevated N deposition, rising atmospheric CO 2 concentration and regional warming. Our findings revealed that the responses of soil C-N-P and stoichiometry to long-term global changes have occurred across the whole soil depth in subtropical China and the magnitudes of the changes in soil stoichiometry are dependent on vegetation types, soil types, and spatial climate variations. © 2017 John Wiley & Sons Ltd.

  1. Quantitative effects of composting state variables on C/N ratio through GA-aided multivariate analysis.

    Science.gov (United States)

    Sun, Wei; Huang, Guo H; Zeng, Guangming; Qin, Xiaosheng; Yu, Hui

    2011-03-01

    It is widely known that variation of the C/N ratio is dependent on many state variables during composting processes. This study attempted to develop a genetic algorithm aided stepwise cluster analysis (GASCA) method to describe the nonlinear relationships between the selected state variables and the C/N ratio in food waste composting. The experimental data from six bench-scale composting reactors were used to demonstrate the applicability of GASCA. Within the GASCA framework, GA searched optimal sets of both specified state variables and SCA's internal parameters; SCA established statistical nonlinear relationships between state variables and the C/N ratio; to avoid unnecessary and time-consuming calculation, a proxy table was introduced to save around 70% computational efforts. The obtained GASCA cluster trees had smaller sizes and higher prediction accuracy than the conventional SCA trees. Based on the optimal GASCA tree, the effects of the GA-selected state variables on the C/N ratio were ranged in a descending order as: NH₄+-N concentration>Moisture content>Ash Content>Mean Temperature>Mesophilic bacteria biomass. Such a rank implied that the variation of ammonium nitrogen concentration, the associated temperature and the moisture conditions, the total loss of both organic matters and available mineral constituents, and the mesophilic bacteria activity, were critical factors affecting the C/N ratio during the investigated food waste composting. This first application of GASCA to composting modelling indicated that more direct search algorithms could be coupled with SCA or other multivariate analysis methods to analyze complicated relationships during composting and many other environmental processes. Copyright © 2010 Elsevier B.V. All rights reserved.

  2. Binding of reactive organophosphate by oximes via hydrogen bond

    Indian Academy of Sciences (India)

    In this contribution, the ability of simple oximes to bind a well-known nerve agent simulant (dimethylmethylphosphonate, DMMP) via hydrogen bond is reported. UV/Vis measurements indicate the formation of 1:1 complexes. 1H-, 31P-NMR titrations and T-ROESY experiments confirm that oximes bind the organophosphate ...

  3. Self-Healing of Polymer Networks with Reversible Bonds

    Science.gov (United States)

    Rubinstein, Michael

    2015-03-01

    Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very low) density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess nonequilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface (formation of bridges) occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk. The model is extended to describe enhanced toughness of dual networks with both permanent and reversible cross-links. This work was done in collaboration with Drs. Ludwik Leibler, Li-Heng Cai, Evgeny B. Stukalin, N. Arun Kumar and supported by the National Science Foundation.

  4. Plasmachemical Synthesis of Nanopowders in the System Ti(O,C,N for Material Structure Modification

    Directory of Open Access Journals (Sweden)

    Michael Filkov

    2016-01-01

    Full Text Available Refractory nanoparticles are finding broad application in manufacturing of materials with enhanced physical properties. Production of carbide, nitride, and carbonitride nanopowders in high volumes is possible in the multijet plasmachemical reactor, where temperature and velocity distributions in reaction zone can be controlled by plasma jet collision angle and mixing chamber geometry. A chemical reactor with three Direct Current (DC arc plasma jets intersecting at one point was applied for titanium carbonitride synthesis from titanium dioxide, propane-butane mixture, and nitrogen. The influence of process operational parameters on the product chemical and phase composition was investigated. Mixing conditions in the plasma jet collision zone, particles residence time, and temperatures were evaluated with the help of Computational Fluid Dynamics (CFD simulations. The synthesized nanoparticles have predominantly cubic shape and dimensions in the range 10–200 nm. Phase compositions were represented by oxycarbonitride phases. The amount of free (not chemically bonded carbon in the product varied in the range 3–12% mass, depending on synthesis conditions.

  5. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

    2012-01-01

    of the article is to provide possible explanations for the puzzle of why small retail investors hold structured bonds. The investment universe consists of a stock index, a risk-free bank account, and a structured bond containing an option written on another index. We apply expected utility maximization...

  6. Distance criterion for hydrogen bond

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Distance criterion for hydrogen bond. In a D-H ...A contact, the D...A distance must be less than the sum of van der Waals Radii of the D and A atoms, for it to be a hydrogen bond.

  7. Fusion-bonded fluidic interconnects

    NARCIS (Netherlands)

    Fazal, I.; Elwenspoek, Michael Curt

    2008-01-01

    A new approach to realize fluidic interconnects based on the fusion bonding of glass tubes with silicon is presented. Fusion bond strength analyses have been carried out. Experiments with plain silicon wafers and coated with silicon oxide and silicon nitride are performed. The obtained results are

  8. Why are Hydrogen Bonds Directional?

    Indian Academy of Sciences (India)

    for an interaction to be characterized as a hydro- gen bond but does not provide any rationale for the same. This article reports a rationale for limiting the angle, based on the electron density topology using the quantum theory of atoms in molecules. Electron density topol- ogy for common hydrogen bond donors HF, HCl, ...

  9. Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Bo, Maolin [Yangtze Normal University, College of Mechanical and Electrical Engineering, Chongqing 408100 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Liu, Yonghui [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q. [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China)

    2017-02-28

    Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O{sup 2−} lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta{sup +} electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta{sup +}; the sp{sup 3}-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent

  10. Unfolding Ubiquitin by force: water mediated H-bond destabilization

    Directory of Open Access Journals (Sweden)

    Germán Pabón

    2012-12-01

    Full Text Available Using the “pull and wait” (PNW simulation protocol at 300 K, we studied the unfolding by force of an ubiquitin molecule. PNW was implemented in the CHARMM program using an integration time step of 1 fs and a uniform dielectric constant of 1. The ubiquitin molecule, initially solvated, was put under mechanical stress, exerting forces from different directions. The rupture of five hydrogen bonds between parallel strands β1 and β5 takes place during the extension from 13 to 15 Å, defines a mechanical barrier for unfolding and dominates the point of maximum unfolding force. The simulations described here show that given adequate time, a small applied force can destabilize those five H-bonds relative to the bonds that can be created to water molecules; allowing the formation of stable H-bonds between a single water molecule and the donor and acceptor groups of the interstrand H-bonds. Thus, simulations run with PNW show that the force is not responsible for “ripping apart” the backbone H-bonds; it merely destabilizes them making them less stable than the H-bonds they can make with water. Additional simulations show that the force necessary to destabilize the H-bonds and allow them to be replaced by H-bonds to water molecules depends strongly on the pulling direction. By using a simulation protocol that allows equilibration at each extension we have been able to observe the details of the events leading to the unfolding of ubiquitin by mechanical force.

  11. Subtle differences in the hydrogen bonding of alcohol to divalent oxygen and sulfur

    DEFF Research Database (Denmark)

    Du, Lin; Tang, Shanshan; Hansen, Anne Schou

    2017-01-01

    complexes are more stable and form stronger hydrogen bonds compared to complexes with MeOH and EtOH, which are comparable, and only for the stronger hydrogen bond donor (TFE) are the small differences in acceptor molecules highlighted. The equilibrium constant for complex formation was determined from...

  12. Studies in Group IV organometallic chemistry XXIII. Mechanism of the hydrostannolysis of tin---element bonds

    NARCIS (Netherlands)

    Creemers, H.M.J.C.; Verbeek, F.; Noltes, J.G.

    The mechanism of the reaction of organotin hydrides with compounds containing a tin---element bond (Sn---N, Sn---P, Sn---As, Sn---O, Sn---S) has been investigated using IR spectroscopic techniques. In reactions involving formation of a tin---tin bond (hydrostannolysis reactions) a polar mechanism is

  13. Nanostructures via noncovalent synthesis: 144 hydrogen bonds bring together 27 components

    NARCIS (Netherlands)

    Paraschiv, V.; Crego Calama, Mercedes; Fokkens, R.H.; Padberg, Clemens J.; Timmerman, P.; Reinhoudt, David

    2001-01-01

    This paper describes the spontaneous and reversible assembly of 20 kDa synthetic hydrogen-bonded assemblies via the formation of 144 cooperative hydrogen bonds. These nanostructures (3.0 × 5.5 nm), consisting of 27 different components, have been carefully characterized using a combination of 1H NMR

  14. High-Strength, Tough, and Self-Healing Nanocomposite Physical Hydrogels Based on the Synergistic Effects of Dynamic Hydrogen Bond and Dual Coordination Bonds.

    Science.gov (United States)

    Shao, Changyou; Chang, Huanliang; Wang, Meng; Xu, Feng; Yang, Jun

    2017-08-30

    Dynamic noncovalent interactions with reversible nature are critical for the integral synthesis of self-healing biological materials. In this work, we developed a simple one-pot strategy to prepare a fully physically cross-linked nanocomposite hydrogel through the formation of the hydrogen bonds and dual metal-carboxylate coordination bonds within supramolecular networks, in which iron ions (Fe3+) and TEMPO oxidized cellulose nanofibrils (CNFs) acted as cross-linkers and led to the improved mechanical strength, toughness, time-dependent self-recovery capability and self-healing property. The spectroscopic analysis and rheological measurements corroborated the existence of hydrogen bonds and dual coordination bonds. The mechanical tests and microscopic morphology were explored to elucidate the recovery properties and toughening mechanisms. The hydrogen bonds tend to preferentially break prior to the coordination bonds associated complexes that act as skeleton to maintain primary structure integrity, and the survived coordination bonds with dynamic feature also serve as sacrificial bonds to dissipate another amount of energy after the rupture of hydrogen bonds, which collectively maximize the contribution of sacrificial bonds to energy dissipation while affording elasticity. Additionally, the multiple noncovalent interactions in diverse types synergistically serve as dynamic but highly stable associations, leading to the effective self-healing efficiency over 90% after damage. We expect that this facile strategy of incorporating the biocompatible and biodegradable CNFs as building blocks may enrich the avenue in exploration of dynamic and tunable cellulosic hydrogels to expand their potential applications in the biomedical field.

  15. The Stepwise Reaction of Rhodium and Iridium Complexes of Formula [MCl2 (κ4 C,N,N',P-L)] with Silver Cations: A Case of trans-Influence and Chiral Self-Recognition.

    Science.gov (United States)

    Carmona, María; Tejedor, Leyre; Rodríguez, Ricardo; Passarelli, Vincenzo; Lahoz, Fernando J; García-Orduña, Pilar; Carmona, Daniel

    2017-10-17

    Acetonitrile suspensions of the dichlorido complexes [MCl2 (κ4 C,N,N',P-L)] [M=Rh (1), Ir (2)] react with AgSbF6 in a 1:2 molar ratio affording the bis-acetonitrile complexes [M(κ4 C,N,N',P-L)(NCMe)2 ][SbF6 ]2 (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido-bridged compounds [{MCl(κ4 C,N,N',P-L)}2 (μ-Cl)][SbF6 ] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato-complexes [MCl(κ4 C,N,N',P-L)(Solv)][SbF6 ] (Solv=H2 O, MeCN, 7-10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ4 C,N,N',P-L)(NCMe)(μ-Cl)}2 Ag][SbF6 ]3 in which a silver cation joints two cationic monosubstituted acetonitrile-complexes [MCl(κ4 C,N,N',P-L)(NCMe)]+ through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh2 group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self-recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X-ray diffraction methods. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Synthesis of (Cr,V){sub 2}(C,N) solid solution powders by thermal processing precursors

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Anrui [School of Materials Science & Engineering, Sichuan University, Chengdu, 610065 (China); Liu, Ying [School of Materials Science & Engineering, Sichuan University, Chengdu, 610065 (China); Key Laboratory of Advanced Special Material & Technology, Ministry of Education, Chengdu, 610065 (China); Ma, Shiqing; Qiu, Yuchong; Rong, Pengcheng; Ye, Jinwen [School of Materials Science & Engineering, Sichuan University, Chengdu, 610065 (China)

    2017-06-01

    The single-phase (Cr,V){sub 2}(C,N) solid solution powders were fabricated via carbothermal reduction-nitridation (CRN) processing technique. The effects of heat treatment temperature, nitrogen pressure and carbon proportion were experimentally studied in detail by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and thermal analysis. The chemical transformations of vanadium and chromium compounds were as follows: precursors → V{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} → Cr{sub 3}C{sub 2}, Cr{sub 2}O{sub 3}, (Cr,V){sub 2}(C,N) → (Cr,V){sub 2}(C,N). When the heat-treated temperature was below 1200 °C, chromium oxides didn’t completely react. However, higher temperature ∼1300 °C could not only lead to the segregation of some nitrides and carbon black, but also to the occurrence of fiber-bridged particles. The system nitrogen pressure over 0.03 MPa would cause a subtle transformation of (Cr,V){sub 2}(C,N) to VCrN{sub 2}. When the carbon proportion was below 15 wt%, the oxides could not be completely reduced, while when the carbon proportion was above 15.5 wt%, some undesired carbides, like Cr{sub 23}C{sub 6} and Cr{sub 3}C{sub 2}, would form. Ultimately, the homogeneously distributed pure-phase (Cr,V){sub 2}(C,N) spherical particles with the average size of ∼1.5 μm were obtained at the optimal conditions of the treatment of precursors at 1200 °C for 1 h with the nitrogen pressure of 0.03 MPa and carbon content of 15.5 wt%. The chemical composition of the solid solution with the optimal process could be drawn as (Cr{sub 0.85}V{sub 0.15}){sub 2}(C{sub 0.57}N{sub 0.43}). Thermal processing precursors method shows the advantages of lower synthesis temperature, shorter period and finer particles when comparing with the conventional preparations. - Highlights: • Single phase of (Cr,V){sub 2}(C,N) powders were synthesized for the first time. • Precursors were used to prepared the powders by carbothermal

  17. Dentin-bonding agents

    Directory of Open Access Journals (Sweden)

    João Carlos Gomes

    2008-01-01

    Full Text Available New dental restorative materials have been developed to meet not only the functional demands, but esthetics as well, and in the last few years an enormous range of new materials has appeared for use in dentistry. Among them, several adhesive systems, and different operative techniques for each group materials. Therefore, is indispensable for the professional to know about the properties, characteristics, and association of these materials with the dental structures, in order to select and use them correctly. Should conventional self-etching adhesive systems be used? This question encouraged this literature review to be conducted, with the aim of comparing the conventional adhesive systems with the self-etching systems and to look for scientific data that would help professionals to choose which adhesive system to use. When compared to conventional systems, it was noted that the self-etching systems show less sensitivity to technique, especially as regards errors the operator could commit. The self-etching systems, particularly the 2-step type, have shown equivalent values of bond strength, marginal microleakage and performance, therefore, will be an option for direct composite resin restorations in posterior teeth.

  18. Laboratoire de Chimie Bactérienne C.N.R.S., Marsielle, France.

    Science.gov (United States)

    Chippaux, M; Giudici, D; Abou-Jaoudé, A; Casse, F; Pascal, M C

    1978-04-06

    Mutants of E. coli, completely devoid of nitrite reductase activity with glucose or formate as donor were studied. Biochemical analysis indicates that they are simultaneously affected in nitrate reductase, nitrite reductase, fumarate reductase and hydrogenase activities as well as in cytochrome C552 biosynthesis. The use of an antiserum specific for nitrate reductase shows that the nitrate reductase protein is probably missing. A single mutation is responsible for this phenotype: the gene affected, nir R, is located close to tyr R i.e. at 29 min on the chromosomal map.

  19. Chemistry of aminoacylation and peptide bond formation on the 3 ...

    Indian Academy of Sciences (India)

    Madhu

    2006-10-04

    deoxy' tRNAs by aminoacyl-tRNA synthetases of different specificity, mostly performed in the research groups of F Cramer (Sprinzl and Cramer 1975) and S Hecht (Chinault et al 1977) resulted in following. Figure 1. P Zamecnik ...

  20. Platinum-Catalyzed Selective Tin-Carbon Bond Formation

    NARCIS (Netherlands)

    Thoonen, Sander Hendrikus Lambertus

    2003-01-01

    In conclusion, two improved methods for the selective synthesis of monoorganotin trihalides were developed. The platinum-catalyzed Kocheshkov redistribution reaction of dialkyltin dichlorides with tin tetrachloride is the most interesting. Contrary to the other two methods described (the direct

  1. Covalent-Bond Formation via On-Surface Chemistry.

    Science.gov (United States)

    Held, Philipp Alexander; Fuchs, Harald; Studer, Armido

    2017-05-02

    In this Review article pioneering work and recent achievements in the emerging research area of on-surface chemistry is discussed. On-surface chemistry, sometimes also called two-dimensional chemistry, shows great potential for bottom-up preparation of defined nanostructures. In contrast to traditional organic synthesis, where reactions are generally conducted in well-defined reaction flasks in solution, on-surface chemistry is performed in the cavity of a scanning probe microscope on a metal crystal under ultrahigh vacuum conditions. The metal first acts as a platform for self-assembly of the organic building blocks and in many cases it also acts as a catalyst for the given chemical transformation. Products and hence success of the reaction are directly analyzed by scanning probe microscopy. This Review provides a general overview of this chemistry highlighting advantages and disadvantages as compared to traditional reaction setups. The second part of the Review then focuses on reactions that have been successfully conducted as on-surface processes. On-surface Ullmann and Glaser couplings are addressed. In addition, cyclodehydrogenation reactions and cycloadditions are discussed and reactions involving the carbonyl functionality are highlighted. Finally, the first examples of sequential on-surface chemistry are considered in which two different functionalities are chemoselectively addressed. The Review gives an overview for experts working in the area but also offers a starting point to non-experts to enter into this exciting new interdisciplinary research field. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Formation of chemically bonded ceramics with magnesium dihydrogen phosphate binder

    Science.gov (United States)

    Wagh, Arun S.; Jeong, Seung-Young

    2004-08-17

    A new method for combining magnesium oxide, MgO, and magnesium dihydrogen phosphate to form an inexpensive compactible ceramic to stabilize very low solubility metal oxides, ashes, swarfs, and other iron or metal-based additives, to create products and waste forms which can be poured or dye cast, and to reinforce and strengthen the ceramics formed by the addition of fibers to the initial ceramic mixture.

  3. Protein evolution: intrinsic preferences in peptide bond formation: a ...

    Indian Academy of Sciences (India)

    Unknown

    position of early proteins (Kolaskar and Ramabrahmam. 1982), mapping of evolutionary trees (Doolittle 1989) and classification of organisms (Erhan 1978). X-ray stud- ... the spectra were recorded at room temperature with m-nitrobenzyl alcohol as the matrix. Elemental analysis was carried out in automatic C, H, N analyser.

  4. Investigations of Reactive Carbohydrates in Glycosidic Bond Formation and Degradation

    DEFF Research Database (Denmark)

    Heuckendorff, Mads

    was to develop new synthetic methods to evolve the field of synthetic carbohydrate chemistry. In addition, easy methods for obtaining complex oligosaccharides are needed to accommodate biochemical research and drug development. Furthermore, the aim was to shed light on the complex mechanisms of glycosylation...... and hy rolysis of glycosides. This mechanistic insight can then be used to develop new synthetic methods and obtain a better understanding of already existing methods. In Chapter 1 general aspects of synthetic carbohydrate chemistry is described with an emphasis on elements that affects reactivity...

  5. Carbon-Carbon and Carbon-Heteroatom Bonds Formation and ...

    Indian Academy of Sciences (India)

    IAS Admin

    Guru, M. M.; Ali, M. A.; Punniyamurthy, T. Org. Lett. 2011, 13, 1194; J. Org. Chem. 2011, 76, 5295. Highlights: Synfacts 2011, 479; Org. Process Res. Dev. 2011, 15, 950. Benzimidazoles and Benzoxazoles. 6 ...

  6. Investigations of Reactive Carbohydrates in Glycosidic Bond Formation and Degradation

    DEFF Research Database (Denmark)

    Heuckendorff, Mads

    was to develop new synthetic methods to evolve the field of synthetic carbohydrate chemistry. In addition, easy methods for obtaining complex oligosaccharides are needed to accommodate biochemical research and drug development. Furthermore, the aim was to shed light on the complex mechanisms of glycosylation...... and hy rolysis of glycosides. This mechanistic insight can then be used to develop new synthetic methods and obtain a better understanding of already existing methods. In Chapter 1 general aspects of synthetic carbohydrate chemistry is described with an emphasis on elements that affects reactivity...... and their properties in glycosylations were carefully examined. The physical chemistry aspects of conformationally changed donors were investigated with emphasis on the anomeric effect. Finally, neighboring group effects in glycosylations and hydrolysis of glycosides were investigated. The goal of this research...

  7. Monitoring disulfide bond formation in the eukaryotic cytosol

    DEFF Research Database (Denmark)

    Østergaard, Henrik; Tachibana, Christine; Winther, Jakob R.

    2004-01-01

    Glutathione is the most abundant low molecular weight thiol in the eukaryotic cytosol. The compartment-specific ratio and absolute concentrations of reduced and oxidized glutathione (GSH and GSSG, respectively) are, however, not easily determined. Here, we present a glutathione-specific green flu...

  8. Interface structure of Be/DSCu diffusion bonding

    Energy Technology Data Exchange (ETDEWEB)

    Makino, T.; Iwadachi, T. [NGK Insulators Ltd., Nagoya (Japan)

    1998-01-01

    Beryllium is used as plasma facing components of the first wall on ITER. Dispersion-Strengthened Copper (DSCu) is used as heat sink material by joining to Be because DSCu has high thermal conductivity and strength. In this study, Be/DSCu diffusion bonding tests using the interlayer of Al, Ni, Nb, Ti, Zr and Be-Cu alloy have been conducted to choose the suitable interlayer materials. As a result of the shear strength tests, Be/DSCu joints by using Be-Cu alloy interlayer showed the strength of about 200 MPa. Diffusion bonding tests using Be-Cu alloy interlayer or no interlayer (direct bonding) at the range of temperature from 600degC to 850degC have been conducted to identify the effect of bonding temperature and time on interface formation and strength. The thickness of diffusion layer was proportional to a square root of bonding time by diffusion controlled process. The shear strength is controlled by the formation of intermetallic layer at Be side. (author)

  9. Elemental (C/N ratios) and Isotope (δ13CTOC, δ15NTN) Compositions of Surface Sediments from the Barrier Islands in the Nakdong River Estuary, South Korea

    Science.gov (United States)

    Lee, Jun-Ho; Woo, Han Jun; Jeong, Kap-Sik; Kang, Jeongwon; Choi, Jae Ung; Lee, Dong-Hun

    2017-04-01

    The Nakdong River Estuary (NRE) in South Korea is a typical, artificially-manipulated estuary and blocked by two large dam. The Noksan Dam, built in 1934, blocks the flow of the West Nakdong River, and the NRE Dam was completed between 1983 and 1987 to regulate the flow of the East Nakdong River (called the Eulsuk River locally). For the past half century, several huge industrial complexes have been developed in the reclaimed land near the NRE. In the estuary, the hydraulic circulation has been markedly modified caused by the changes in the river discharge and geomorphic configuration of such as the formation of a series of barrier islands, the two large dams resulting from the artificial control of the natural river flow and upstream intrusion of saltwater by the operation of the two large dams. Consequently, the saltwater wedge that once reached approximately 40 km upstream is now blocked at the dam, considerably reducing the tidal prism. The estuary is typified by barrier-lagoon system with various subenvironments and microtidal with a 1.5 m tidal range. We investigated the elemental (C/N ratios) and isotopic (δ13CTOC, δ15NTN) compositions of organic matters in various composition in the surface sediments in the NRE. In May 2015, 90 surface sediment samples were collected on and around three islands in the NRE. The mean grain size of the barrier island system in the NRE ranged from 1.1 to 8.9 Φ (average 3.9 Φ) in mean grain size, and they were composed of various sediment types, including muddy Sand (S), sandy Mud (sM), and Mud (M). A useful application of the C/N ratios is as a proxy for assessment of organic matter source change, related to the sediment origins terrestrial or marine. The C/N ratios (average, 5.88) imply that the organic matter in the study area was of marine origins, as indicated by the lower ratios between 4 and 10. The isotope composition of sedimentary organic matter (δ13CTOC, δ15NTN) indicated the deposition of algae-derived organic

  10. Prof C. N. Yang (Physics Nobel Prize 1957) from Tsinghua University (Beijing) during his CERN Colloquium: "Thematic Melodies of Twentieth Century Theoretical Physics: Quantization, Symmetry and Phase Factor".

    CERN Multimedia

    Maximilien Brice

    2006-01-01

    Prof C. N. Yang (Physics Nobel Prize 1957) from Tsinghua University (Beijing) during his CERN Colloquium: "Thematic Melodies of Twentieth Century Theoretical Physics: Quantization, Symmetry and Phase Factor".

  11. Bonding over Dentin Replacement Materials.

    Science.gov (United States)

    Meraji, Naghmeh; Camilleri, Josette

    2017-08-01

    Dentin replacement materials are necessary in large cavities to protect the pulp and reduce the bulk of filling material. These materials are layered with a composite resin restorative material. Microleakage caused by poor bonding of composite resin to underlying dentin replacement material will result in pulp damage. The aim of this study was to characterize the interface between dentin replacement materials and composite resin and to measure the shear bond strength after dynamic aging. Biodentine (Septodont, Saint Maur-des-Fosses, France), Theracal LC (Bisco, Schaumburg, IL), and Fuji IX (GC, Tokyo, Japan) were used as dentin replacement materials. They were then overlaid with a total-etch and bonding agent or a self-etch primer and composite resin or a glass ionomer cement. All combinations were thermocycled for 3000 cycles. The interface was characterized using scanning electron microscopy and elemental mapping. Furthermore, the shear bond strength was assessed. The Biodentine surface was modified by etching. The Theracal LC and Fuji IX microstructure was unchanged upon the application of acid etch. The Biodentine and glass ionomer interface showed an evident wide open space, and glass particles from the glass ionomer adhered to the Biodentine surface. Elemental migration was shown with aluminum, barium, fluorine, and ytterbium present in Biodentine from the overlying composite resin. Calcium was more stable. The bond strength between Theracal LC and composite using a total-etch technique followed by self-etch primer achieved the best bond strength values. Biodentine exhibited the weakest bond with complete failure of bonding shown after demolding and thermocycling. Dynamic aging is necessary to have clinically valid data. Bonding composite resin to water-based dentin replacement materials is still challenging, and further alternatives for restoration of teeth using such materials need to be developed. Copyright © 2017 American Association of Endodontists

  12. Unusual Ligand Isomerization Dictated by Coordination Requirements of the Metal Ion: A Double-Bond Shift in Cu(II)-Assisted Template Condensation between Diacetylpyridine and a Tripodal Tetramine.

    Science.gov (United States)

    Rybak-Akimova, Elena V.; Nazarenko, Alexander Y.; Silchenko, Svetlana S.

    1999-06-14

    This paper reports a new effect in template-directed Schiff base condensation, a "fine-tuning" of the macrocyclic structure in accordance with the precise coordination requirements of the metal ion. The nature of the metal template determines the outcome of Schiff base condensation between a difunctional carbonyl component (2,6-diacetylpyridine) and a trifunctional amine component (tris(3-aminopropyl)amine, trpn). Both Cu(II) and Ni(II) facilitate [1 + 1] condensation with the formation of macrocyclic products in 50-60% yield, but single-crystal X-ray diffraction reveals that the chemical structure of the major product is metal-ion dependent. In the nickel(II) complex [Ni(L(sym))](2+), the C=N double bonds are conjugated with the pyridine ring, as expected from the structure of the starting diacetylpyridine. In contrast, the copper(II) ion caused isomerization of the macrocyclic ligand, with one of the C=N double bonds migrating into the initially saturated six-membered chelate ring forming [Cu(L(asym))](2+). The second product isolated, in small quantities, from the copper(II)-templated condensation has been characterized as an isomeric symmetric macrocycle [Cu(L(sym))](2+). In the case of the zinc(II) template, no macrocyclic product has been isolated; instead, a zinc(II) complex of the starting tetramine, Zn(trpn)Cl(2).2H(2)O, was recovered and structurally characterized. An unusual double-bond migration in the course of Cu(II)-directed template condensation is governed by the coordination requirements of the central metal ion. The asymmetric ligand isomer is more flexible than its symmetric counterpart and can therefore better accommodate the five-coordinate central metal ion. This effect is more pronounced for the copper(II) complex than for the nickel(II) complex, because of shorter in-plane M-N distances in the former, as follows from the X-ray structure determination. The position of the double bond in the macrocyclic ring influences the spectral properties

  13. Mechanism of generation of large (Ti,Nb,V)(C,N)-type precipitates in H13 + Nb tool steel

    Science.gov (United States)

    Xie, You; Cheng, Guo-guang; Chen, Lie; Zhang, Yan-dong; Yan, Qing-zhong

    2016-11-01

    The characteristics and generation mechanism of (Ti,Nb,V)(C,N) precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of (Ti,Nb,V)(C,N) phases exist—a Ti-V-rich one and an Nb-rich one—in the form of single or complex precipitates. The sizes of the single Ti-V-rich (Ti,Nb,V)(C,N) precipitates are mostly within 5 to 10 μm, whereas the sizes of the single Nb-rich precipitates are mostly 2-5 μm. The complex precipitates are larger and contain an inner Ti-V-rich layer and an outer Nb-rich layer. The compositional distribution of (Ti,Nb,V)(C,N) is concentrated. The average composition of the single Ti-V-rich phase is (Ti0.511V0.356Nb0.133)(C x N y ), whereas that for the single Nb-rich phase is (Ti0.061V0.263Nb0.676)(C x N y ). The calculation results based on the Scheil-Gulliver model in the Thermo-Calc software combining with the thermal stability experiments show that the large phases precipitate during the solidification process. With the development of solidification, the Ti-V-rich phase precipitates first and becomes homogeneous during the subsequent temperature reduction and heat treatment processes. The Nb-rich phase appears later.

  14. Compton energy-absorption scattering cross-sections for H, C, N, O, P, Ca and assessment of doppler broadening

    CERN Document Server

    Rao, D V; Brunetti, A; Gigante, G E

    2003-01-01

    Total Compton, individual shell and Compton energy-absorption scattering cross-sections are evaluated in the energy region 0.005 to 10 MeV for H, C. N, O. P and Ca. Compton energy absorption cross-sections deviate numerically with available values. The cause of the numerical discrepancies are not fully understood but can be attributed to Doppler broadening of the Compton scattered photons through a given angle. (authors)

  15. A new route to multifunctionalized p-terphenyls and heteroaryl analogues via [5C + 1C(N)] annulation strategy.

    Science.gov (United States)

    Zhang, Lei; Liang, Fushun; Cheng, Xin; Liu, Qun

    2009-01-16

    p-Terphenyls and heteroaryl analogues including bipyridines were prepared via [5C + 1C(N)] annulation of alpha-aryl-alpha-alkenoyl ketene-(S,S)-acetals (five carbon 1,5-bielectrophilic species) with nitroethane or ammonium acetate. The reaction features mild conditions, multisubstitution, and functional group tolerance and is metal catalyst free. The present protocol provides a new alternative to the conventional methodologies for the synthesis of teraryls.

  16. Direct Bonded Pontic (Laporan Kasus

    Directory of Open Access Journals (Sweden)

    Suhandi Sidjaja

    2015-10-01

    Full Text Available Advanced science and technology in dentistry enable dental practitioners to modified she bonding techniques in tooth replacement. A pontic made of composite resin bonded to etched enamel of the adjacent teeth can be used in the replacement of one missing anterior tooth with a virgin or sowed adpicent tooth. The advantages of this technique include a one visit treatment, cow cost, good esthetics, less side effects and easy repair or rebounding. Clinical evaluation showed a high success rate therefore with a proper diagnosis and a perfect skill of the direct bonded technique this treatment can be used as an alternative restoration.

  17. The chemisorptive bond basic concepts

    CERN Document Server

    Clark, Alfred

    1974-01-01

    The Chemisorptive Bond: Basic Concepts describes the basic concepts of the chemisorptive bond on solid surfaces from the simple analogies with ordinary chemical bonds to the quantum-mechanical approaches.This book is composed of 10 chapters and begins with discussions of simple formulas for correlating measurable quantities in chemisorptions and catalysis. The succeeding chapters deal with theories based on quantum-mechanical principles that describe the mutual interactions of atoms of the solid and foreign atoms on the surface. The remaining chapters consider the possible arrangements

  18. Corporate Bonds : Analyzing the availability of the Swedish bond market

    OpenAIRE

    Peterson, Rickard; Höglund, Linn; Jarnegren, Carl

    2006-01-01

    In the past, the Swedish bond market has been distinguished for its illiquidity and difficulties with retrieving information. This is the starting point of our thesis and the purpose is to analyze and describe the availability of the present corporate bond market for manufacturing firms in Sweden. In order to fulfill the purpose, a qualitative method was used and interviews with different operators of the market were conducted. Our respondents were sampled from large issuing companies, the ma...

  19. 77 FR 553 - Surety Companies Acceptable on Federal Bonds: Termination; Western Bonding Company

    Science.gov (United States)

    2012-01-05

    ... Fiscal Service Surety Companies Acceptable on Federal Bonds: Termination; Western Bonding Company AGENCY... Company (NAIC 13191) under 31 U.S.C. 9305 to qualify as an acceptable surety on Federal bonds is... bonds, including continuous bonds, currently in force with above listed Company, bond-approving officers...

  20. C-heteroatom bond-formation via ni-catalyzed c-o bond cleavage

    OpenAIRE

    Zárate Sáez, Cayetana

    2017-01-01

    A pesar de que el campo del acoplamiento cruzado ha desarrollado increíbles avances, la gran mayoría de procesos todavía se basa en el uso de halogenuros de arilo. Sin embargo, este tipo de electrófilos presentan una toxicidad intrínseca y, a su vez, su síntesis resulta tediosa, especialmente cuando se trata de halogenuros de arilo altamente funcionalizados. Debido a ello, la comunidad sintética se ha volcado en la búsqueda de alternativas al uso de halogenuros de arilo en química de acoplami...