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Sample records for nucleophilic ring opening

  1. Nucleophilic ring opening reactions of aziridines.

    Science.gov (United States)

    Akhtar, Rabia; Naqvi, Syed Ali Raza; Zahoor, Ameer Fawad; Saleem, Sameera

    2018-05-04

    Aziridine ring opening reactions have gained tremendous importance in the synthesis of nitrogen containing biologically active molecules. During recent years, a great effort has been put forward by scientists toward unique bond construction methodologies via ring opening of aziridines. In this regard, a wide range of chiral metal- and organo-catalyzed desymmetrization reactions of aziridines have been reported with carbon, sulfur, oxygen, nitrogen, halogen, and other nucleophiles. In this review, an outline of methodologies adopted by a number of scientists during 2013-2017 for aziridine ring opening reactions as well as their synthetic applications is described.

  2. Ring opening of epoxides with C-nucleophiles.

    Science.gov (United States)

    Faiz, Sadia; Zahoor, Ameer Fawad

    2016-11-01

    Ring opening of epoxides has been an area of interest for organic chemists, owing to their reactivity toward nucleophiles. Such reactions yield important products depending on the type of nucleophiles used. This review article covers the synthetic approaches (1991-2015) used for the ring opening of epoxides via carbon nucleophiles.

  3. Platinum Catalyzed Ring-Opening of 1,2-Cyclopropanated Sugars with O-Nucleophiles

    DEFF Research Database (Denmark)

    Beyer, Jürgen; Skaanderup, Philip Robert; Madsen, Robert

    1999-01-01

    In the presence of a catalytic amount of Zeise's dimer 1,2-cyclopropanated sugars undergo regioselective ring-opening at C-1 with O-nucleophiles including alcohols, phenols and water to produce 2-C-branched carbohydrates.......In the presence of a catalytic amount of Zeise's dimer 1,2-cyclopropanated sugars undergo regioselective ring-opening at C-1 with O-nucleophiles including alcohols, phenols and water to produce 2-C-branched carbohydrates....

  4. Ring opening of a resin-bound chiral aziridine with phenol nucleophiles

    DEFF Research Database (Denmark)

    Ottesen, Lars Korsgaard; Jaroszewski, Jerzy W; Franzyk, Henrik

    2010-01-01

    An efficient and versatile solid-phase route for the preparation of aryl-alkyl ethers is described. Regioselective ring opening of a resin-bound chiral aziridine with phenolic nucleophiles constitutes the key feature of the present protocol that allows incorporation of fluorescent moieties...

  5. Regioselective Nucleophilic Ring Opening of Epoxides and Aziridines derived from Homoallylic Alcohols

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Groth, Thomas

    1997-01-01

    The regioselectivity of nucleophilic ring opening of some 3,4-epoxy and 3,4-aziridino alcohols has been studied. The nucleophiles chosen were complex hydrides (LiAlH4, Red-Al and DIBAL) and Lipshutz- or Gilman-type organocuprate reagents. The C-4 substituent in the substrates was varied in order...... to study steric and electronic effects on the ring opening reactions. For alkyl substituents at C-4, most of the results can be explained on the basis of intramolecular delivery of the nucleophile to C-3 via a six-membered transition state, leading to 1,4-diols or 1,4-amino alcohol derivatives. In general......, the epoxy alcohols gave poorer regioselectivity than the N-tosyl aziridino alcohols, for which selectivities of >95:5 were routinely obtained. The activating effect of a phenyl group at C-4 led to a switch in regiochemistry, with the 1,3-diol or 1,3-amino alcohol derivative as the major product. (C) 1997...

  6. Highly Defined Multiblock Copolypeptoids: Pushing the Limits of Living Nucleophilic Ring-Opening Polymerization

    KAUST Repository

    Fetsch, Corinna

    2012-06-05

    Advanced macromolecular engineering requires excellent control over the polymerization reaction. Living polymerization methods are notoriously sensitive to impurities, which makes a practical realization of such control very challenging. Reversible-deactivation radical polymerization methods are typically more robust, but have other limitations. Here, we demonstrate by repeated (ge;10 times) chain extension the extraordinary robustness of the living nucleophilic ring-opening polymerization of N-substituted glycine N-carboxyanhydrides, which yields polypeptoids. We observe essentially quantitative end-group fidelity under experimental conditions that are comparatively easily managed. This is employed to synthesize a pentablock quinquiespolymer with high definition. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Highly Defined Multiblock Copolypeptoids: Pushing the Limits of Living Nucleophilic Ring-Opening Polymerization

    KAUST Repository

    Fetsch, Corinna; Luxenhofer, Robert

    2012-01-01

    Advanced macromolecular engineering requires excellent control over the polymerization reaction. Living polymerization methods are notoriously sensitive to impurities, which makes a practical realization of such control very challenging. Reversible-deactivation radical polymerization methods are typically more robust, but have other limitations. Here, we demonstrate by repeated (ge;10 times) chain extension the extraordinary robustness of the living nucleophilic ring-opening polymerization of N-substituted glycine N-carboxyanhydrides, which yields polypeptoids. We observe essentially quantitative end-group fidelity under experimental conditions that are comparatively easily managed. This is employed to synthesize a pentablock quinquiespolymer with high definition. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Chemistry of [(Perfluoroalkyl)Methyl] Oxiranes. Regioselectivity of Ring Opening with O-Nucleophiles and the Preparation of Amphiphilic Monomers

    Czech Academy of Sciences Publication Activity Database

    Církva, Vladimír; Améduri, B.; Boutevin, B.; Paleta, O.

    1997-01-01

    Roč. 84, č. 1 (1997), s. 53-61 ISSN 0022-1139 Institutional research plan: CEZ:AV0Z4072921 Keywords : fluoroalkyl thiiranes * nucleophilic oxirane ring opening Subject RIV: CC - Organic Chemistry Impact factor: 0.714, year: 1997

  9. (Salen)Ti(Ⅳ)-Catalyzed Asymmetric Ring-opening of meso Epoxides Using Dithiophosphorus Acid as the Nucleophile

    Institute of Scientific and Technical Information of China (English)

    Zheng Hong ZHOU; Zhao Ming LI; Bing LIU; Kang Ying LI; Li Xin WANG; Guo Feng ZHAO; Qi Lin ZHOU; Chu Chi TANG

    2006-01-01

    The asymmetric ring-opening of epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(Ⅳ) complex formed in situ from the reaction of Ti(OPr-i)4 and the chiral Schiff base derived from (1R,2R)-(+)-diaminocyclohexane was realized. The resulting products were obtained with low to good enantioselectivity (up to 73% ee).

  10. Ring transformation of chromone-3-carboxamide under nucleophilic conditions

    Energy Technology Data Exchange (ETDEWEB)

    Ibrahim, Magdy A., E-mail: magdy_ahmed1977@yahoo.com [Department of Chemistry, Faculty of Education, Ain Shams University, Cairo(Egypt)

    2013-11-15

    The chemical reactivity of chromone-3-carboxamide was studied towards a series of nitrogen and carbon nucleophiles. Treatment of carboxamide with some primary amines gave chromane-2,4-diones. Condensation of carboxamide with hydrazine hydrate, phenyl hydrazine and hydroxylamine hydrochloride afforded chromenopyrazoles and chromenoisoxazole, respectively. Reaction of carboxamide with guanidine hydrochloride, cyanoguanidine and thiourea resulted in ring transformation producing chromenopyridines. The chemical behavior of carboxamide was also studied towards ethylenediamine, o-phenylenediamine, 2-aminophenol and 2-aminothiophenol. A variety of products were isolated from the reaction of carboxamide with some carbon nucleophiles. (author)

  11. Microdroplets Accelerate Ring Opening of Epoxides

    Science.gov (United States)

    Lai, Yin-Hung; Sathyamoorthi, Shyam; Bain, Ryan M.; Zare, Richard N.

    2018-03-01

    The nucleophilic opening of an epoxide is a classic organic reaction that has widespread utility in both academic and industrial applications. We have studied the reaction of limonene oxide with morpholine to form 1-methyl-2-morpholino-4-(prop-1-en-2-yl) cyclohexan-1-ol in bulk solution and in electrosprayed microdroplets with a 1:1 v/v water/methanol solvent system. We find that even after 90 min at room temperature, there is no product detected by nuclear magnetic resonance spectroscopy in bulk solution whereas in room-temperature microdroplets (2-3 μm in diameter), the yield is already 0.5% in a flight time of 1 ms as observed by mass spectrometry. This constitutes a rate acceleration of 105 in the microdroplet environment, if we assume that as much as 5% of product is formed in bulk after 90 min of reaction time. We examine how the reaction rate depends on droplet size, solvent composition, sheath gas pressure, and applied voltage. These factors profoundly influence the extent of reaction. This dramatic acceleration is not limited to just one system. We have also found that the nucleophilic opening of cis-stilbene oxide by morpholine is similarly accelerated. Such large acceleration factors in reaction rates suggest the use of microdroplets for ring opening of epoxides in other systems, which may have practical significance if such a procedure could be scaled. [Figure not available: see fulltext.

  12. Microdroplets Accelerate Ring Opening of Epoxides

    Science.gov (United States)

    Lai, Yin-Hung; Sathyamoorthi, Shyam; Bain, Ryan M.; Zare, Richard N.

    2018-05-01

    The nucleophilic opening of an epoxide is a classic organic reaction that has widespread utility in both academic and industrial applications. We have studied the reaction of limonene oxide with morpholine to form 1-methyl-2-morpholino-4-(prop-1-en-2-yl) cyclohexan-1-ol in bulk solution and in electrosprayed microdroplets with a 1:1 v/ v water/methanol solvent system. We find that even after 90 min at room temperature, there is no product detected by nuclear magnetic resonance spectroscopy in bulk solution whereas in room-temperature microdroplets (2-3 μm in diameter), the yield is already 0.5% in a flight time of 1 ms as observed by mass spectrometry. This constitutes a rate acceleration of 105 in the microdroplet environment, if we assume that as much as 5% of product is formed in bulk after 90 min of reaction time. We examine how the reaction rate depends on droplet size, solvent composition, sheath gas pressure, and applied voltage. These factors profoundly influence the extent of reaction. This dramatic acceleration is not limited to just one system. We have also found that the nucleophilic opening of cis-stilbene oxide by morpholine is similarly accelerated. Such large acceleration factors in reaction rates suggest the use of microdroplets for ring opening of epoxides in other systems, which may have practical significance if such a procedure could be scaled. [Figure not available: see fulltext.

  13. Efficient, regioselective ring-opening of activated aziridine-2-carboxylates with [18F]fluoride

    DEFF Research Database (Denmark)

    Schjøth-Eskesen, Christina; Hansen, Paul Robert; Kjær, Andreas

    2015-01-01

    Aziridines can undergo a range of ring-opening reactions with nucleophiles. The regio- and stereochemistry of the products depend on the substituents on the aziridine. Aziridine ring-opening reactions have rarely been used in radiosynthesis. Herein we report the ring opening of activated aziridine...

  14. Recent trends in ring opening of epoxides with sulfur nucleophiles.

    Science.gov (United States)

    Ahmad, Sajjad; Zahoor, Ameer Fawad; Naqvi, Syed Ali Raza; Akash, Muhammad

    2018-02-01

    Thiolysis of epoxides offers an efficient and simple synthetic approach to access [Formula: see text]-hydroxy sulfides which are valuable scaffold in the synthesis of various important molecules in medicinal chemistry. This review article presents a recent compilation of the synthetic approaches developed after 2000 for the thiolysis of epoxides.

  15. Synthesis and ring openings of cinnamate-derived N-unfunctionalised aziridines

    Directory of Open Access Journals (Sweden)

    Alan Armstrong

    2012-10-01

    Full Text Available tert-Butyl cinnamates are aziridinated with high trans-selectivity by an N–N ylide generated in situ from N-methylmorpholine and O-diphenylphosphinyl hydroxylamine. The resulting N-unfunctionalised aziridines are shown to be versatile synthetic building blocks that undergo highly selective ring-opening reactions with a wide range of nucleophiles.

  16. Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

    Directory of Open Access Journals (Sweden)

    Katrina Tait

    2016-10-01

    Full Text Available Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl2(CH3CN2 in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases.

  17. Synthesis of benzamides by microwave assisted ring opening of less reactive dimethylaminobenzylidene oxazolone

    Directory of Open Access Journals (Sweden)

    Saurabh C. Khadse

    2017-02-01

    Full Text Available This paper presents the synthesis of some benzamide compounds (B1–B10 by microwave-assisted ring opening of 4-(4-dimethylaminobenzylidene-2-phenyl-5-oxazolone (AZ4. By conventional synthesis involving heating, it was found difficult to obtain ring-opened products, probably due to poor tendency of the carbonyl carbon (C5 of AZ4 to undergo nucleophilic attack by mono/or disubstituted anilines. Microwave assisted reactions were easy to perform, have reduced the reaction time and produced good yields.

  18. Plasma-ring, fast-opening switch

    International Nuclear Information System (INIS)

    Hartman, C.W.; Eddleman, J.; Hammer, J.H.

    1986-01-01

    The authors discuss a fast-opening switch concept based on magnetically confined plasma rings, PROS (for Plasma Ring Opening Switch). In PROS, the plasma ring, confined by Bθ /sub and B/poloidal /sub fields of a compact torus, provide a low mass, localized conduction path between coaxial electrodes. To operate the switch, driver current is passed across the electrodes through the ring, storing inductive energy in external inductance and between the electrodes on the driver side of the ring. The ring is accelerated away from the driver by the field of the driver current and passes over a load gap transferring the current to the load. The authors distinguish two configurations in PROS, straight PROS where the electrodes are coaxial cylinders, and cone PROS with conical electrodes. In straight PROS ring acceleration takes place during the inductive store period as in foil switches, but with the localized ring providing the current path. Increased performance is predicted for the cone PROS (see figure) which employs compression of the ring in the cone during the inductive store period. Here, the B/θ /sub field of the driver forces the ring towards the apex of the cone but the force is in near balance with the opposing component of the radial equilibrium force of the ring along the cone. As a result, the ring undergoes a slow, quasistatic compression limited only by resistive decay of the ring field. Slow compression allows inductive storage with low-power drivers (homopoloar, magneto cumulative generators, high C-low V capacitor banks, etc.). Near the apex of the cone, near peak compression, the ring is allowed to enter a straight coaxial section where, because of low-mass, it rapidly accelerates to high velocity and crosses the load gap

  19. Open-ring enhancement sign in diagnosing demyelinating pseudotumor

    International Nuclear Information System (INIS)

    Fang Liting; Wang Zhiping; Wang Linyou

    2010-01-01

    Objective: To describe open-ring enhancement sign on MRI of demyelinating pseudotumor. Methods: Contrast-enhanced MRI of histologically confirmed demyelinating pseudotumors (14 patients) and astrocytomas (21) was reviewed. Results: Of the 14 cases of demyelinating pseudotumor, open-ring enhancement pattern was observed in 6; closed ring enhancement in 2; nodular enhancement in 3; patchy enhancement in 1; slight enhancement in 1; and no enhancement in 1. Of the 21 cases of astrocytoma, there was complete ring or lace-like enhancement in 13, no contrast enhancement in 6, patchy enhancement in 2, and none with open-ring enhancement pattern. Conclusion: Open-ring enhancement is a valuable sign in differential diagnosis between demyelinating pseudotumor and astrocytoma. (authors)

  20. Ring-opening of gamma-valerolactone with amino compounds

    NARCIS (Netherlands)

    Chalid, Mochamad; Heeres, Hero J.; Broekhuis, Antonius A.

    2012-01-01

    Diols obtained by the ring-opening of biomass-based gamma-valerolactone (GVL) are potentially valuable building blocks that can be used as precursors in the manufacture of green polymers and resins. We report here a study on the ring-opening of GVL through adding amine compounds. The reactivity of

  1. Ionic Liquids: An Environmentally Friendly Media for Nucleophilic Substitution Reactions

    International Nuclear Information System (INIS)

    Jorapur, Yogesh R.; Chi, Dae Yoon

    2006-01-01

    Ionic liquids are alternative reaction media of increasing interest and are regarded as an eco-friendly alternatives, of potential use in place of the volatile organic solvents typically used in current chemical processing methods. They are emerging as the smart and excellent solvents, which are made of positive and negative ions that they are liquids near room temperature. The nucleophilic substitution reaction is one of the important method for inserting functional groups into a carbon skeleton. Many nucleophilic substitution reactions have been found with enhanced reactivity and selectivity in ionic liquid. In this review, some recent interesting results of nucleophilic substitution reactions such as hydroxylations, ether cleavages, carbon-X (X = carbon, oxygen, nitrogen, fluorine) bond forming reactions, and ring opening of epoxides in ionic liquids are discussed

  2. Synthesis of γ-hydroxypropyl P-chirogenic (±-phosphorus oxide derivatives by regioselective ring-opening of oxaphospholane 2-oxide precursors

    Directory of Open Access Journals (Sweden)

    Iris Binyamin

    2015-07-01

    Full Text Available The synthesis of P-chirogenic (±-phosphine oxides and phosphinates via selective nucleophilic ring opening of the corresponding oxaphospholanes is described. Two representative substrates: the phosphonate 2-ethoxy-1,2-oxaphospholane 2-oxide and the phosphinate 2-phenyl-1,2-oxaphospholane 2-oxide were reacted with various Grignard reagents to produce a single alkyl/aryl product. These products may possess further functionalities in addition to the phosphorus center such as the γ-hydroxypropyl group which results from the ring opening and π-donor moieties such as aryl, allyl, propargyl and allene which originates from the Grignard reagent.

  3. Effects of different reaction mediums on ring opening polymerization ...

    African Journals Online (AJOL)

    This work examined the effects of reaction conditions on ring opening ... of this study was to observe molecular weight distribution, conversion rates, and thermal ... M monomer and 0.56 M solvent), 10 mg lipase were used in the experiments.

  4. Photosonochemical catalytic ring opening of α-epoxyketones

    Directory of Open Access Journals (Sweden)

    Saffar-Teluri Ali

    2007-01-01

    Full Text Available Abstract The combination of ultrasound and photochemical methods has been used for the catalytic ring opening of α-epoxyketones by 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT as photocatalyst in methanol. Sonication of these compounds in the presence of NBTPT did not result in the opening of epoxide ring, but the use of ultrasound increased the rate of photoreaction.

  5. Synergistic dual activation catalysis by palladium nanoparticles for epoxide ring opening with phenols.

    Science.gov (United States)

    Seth, Kapileswar; Roy, Sudipta Raha; Pipaliya, Bhavin V; Chakraborti, Asit K

    2013-07-04

    Synergistic dual activation catalysis has been devised for epoxide phenolysis wherein palladium nanoparticles induce electrophilic activation via coordination with the epoxide oxygen followed by nucleophilic activation through anion-π interaction with the aromatic ring of the phenol, and water (reaction medium) also renders assistance through 'epoxide-phenol' dual activation.

  6. High pressure photoinduced ring opening of benzene

    International Nuclear Information System (INIS)

    Ciabini, Lucia; Santoro, Mario; Bini, Roberto; Schettino, Vincenzo

    2002-01-01

    The chemical transformation of crystalline benzene into an amorphous solid (a-C:H) was induced at high pressure by employing laser light of suitable wavelengths. The reaction was forced to occur at 16 GPa, well below the pressure value (23 GPa) where the reaction normally occurs. Different laser sources were used to tune the pumping wavelength into the red wing of the first excited singlet state S 1 ( 1 B 2u ) absorption edge. Here the benzene ring is distorted, presenting a greater flexibility which makes the molecule unstable at high pressure. The selective pumping of the S 1 level, in addition to structural considerations, was of paramount importance to clarify the mechanism of the reaction

  7. Aliphatic Nucleophilic Radio-fluorination

    International Nuclear Information System (INIS)

    Roeda, D.; Dolle, F.

    2010-01-01

    In this review we are looking at some aspects of nucleophilic aliphatic radio-fluorination, notably the labelled fluoride source, design aspects, the leaving group and the solvent. It should be clear that there is more to this branch of radiolabelling than one would suspect from the frequently used standard tosylate replacement with kryptofix/[ 18 F]fluoride in acetonitrile or DMSO. Competitive elimination can be a serious problem that can affect both yield and purification. De-protection of sensitive groups after radiolabelling and its possible side reactions can complicate purification. The right choice of leaving group and protecting groups may be crucial. Newer developments such as the use of tertiary alcohols or ionic liquids as solvents, long-chain poly-fluorinated sulphonate leaving groups facilitating fluorous solid phase extraction, or immobilisation of the precursor on a solid phase support may help to solve these problems, for example the longstanding problems with [ 18 F]FLT, whereas older concepts such as certain cyclic reactive entities for ring opening or even an abandoned reagent as [ 18 F]DAST should not be forgotten. (authors)

  8. Development of a single-ring OpenPET prototype

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Eiji, E-mail: rush@nirs.go.jp; Tashima, Hideaki; Wakizaka, Hidekatsu; Nishikido, Fumihiko; Hirano, Yoshiyuki; Inadama, Naoko; Murayama, Hideo; Ito, Hiroshi; Yamaya, Taiga

    2013-11-21

    One of the challenging applications of PET is implementing it for in-beam PET, which is an in situ monitoring method for charged particle therapy. For this purpose, we have previously proposed an open-type PET scanner, OpenPET. The original OpenPET had a physically opened field-of-view (FOV) between two detector rings through which irradiation beams pass. This dual-ring OpenPET (DROP) had a wide axial FOV including the gap. This geometry was not necessarily the most efficient for application to in-beam PET in which only a limited FOV around the irradiation field is required. Therefore, we have proposed a new single-ring OpenPET (SROP) geometry which can provide an accessible and observable open space with higher sensitivity and a reduced number of detectors than the DROP. The proposed geometry was a cylinder shape with its ends cut at a slant, in which the shape of each cut end became an ellipse. In this work, we developed and evaluated a small prototype of the SROP geometry for proof-of-concept. The SROP prototype was designed with 2 ellipse-shaped detector rings of 16 depth-of-interaction (DOI) detectors each. The DOI detectors consisted of 1024 GSOZ scintillator crystals which were arranged in 4 layers of 16×16 arrays, coupled to a 64-channel FP-PMT. Each ellipse-shaped detector ring had a major axis of 281.6 mm and a minor axis of 207.5 mm. For the slant mode, the rings were placed at a 45-deg slant from the axial direction and for the non-slant mode (used as a reference) they were at 90 deg from the axial direction with no gap. The system sensitivity measured from a {sup 22}Na point source was 5.0% for the slant mode. The average spatial resolutions of major and minor axis directions were calculated as 3.8 mm FWHM and 4.9 mm FWHM, respectively for the slant mode. This difference resulted from the ellipsoidal ring geometry and the spatial resolution of the minor axis direction degraded by the parallax error. Comparison between the slant mode and the non

  9. Theoretical study on the nucleophilic fluoroalkylation of propylene oxide with fluorinated sulfones

    Directory of Open Access Journals (Sweden)

    Han Ling-Li

    2013-01-01

    Full Text Available The path of nucleophilic fluoroalkylation reaction of propylene oxide with PhSO2CYF- (Y=F,H, and PhSO2, respectively in gas phase and in Et2O solvent were studied theoretically. The nucleophilic fluoroalkylation of propylene oxide with fluorinated carbanions was probed by the reactivity comparison between (benzenesulfonylmonofluoromethyl anion (PhSO2CHF-, (benzenesulfonyl difluoromethyl anion (PhSO2CF2-, and bis(benzenesul-fonyl monofluoromethyl anion ((PhSO22CF-. The nucleophilicity reactivity order of PhSO2CYF- (Y = F, H, and PhSO2 is [(PhSO22CF-] > PhSO2CHF- > PhSO2CF2-, which indicates that introducing another electron-withdrawing benzenesulfonyl group is an effective way to significantly increase the nucleophilicity of the fluorinate carbanions. For comparison, we also studied the nucleophilic addition reactions of propylene oxide with chlorine substituted carbanion PhSO2CHCl-. The calculated results show that the nucleophilicity of PhSO2CYF- is better than that of PhSO2CHCl- for the ring opening reaction with propylene oxide. The calculated results are in good agreement with the available experiments.

  10. Grafting of Ring-Opened Cyclopropylamine Thin Films on Silicon (100) Hydride via UV Photoionization.

    Science.gov (United States)

    Tung, J; Ching, J Y; Ng, Y M; Tew, L S; Khung, Y L

    2017-09-13

    The grafting of cyclopropylamine onto a silicon (100) hydride (Si-H) surface via a ring-opening mechanism using UV photoionization is described here. In brief, radicals generated from the Si-H surface upon UV irradiation were found to behave in classical hydrogen abstraction theory manner by which the distal amine group was first hydrogen abstracted and the radical propagated down to the cyclopropane moiety. This subsequently liberated the strained bonds of the cyclopropane group and initiated the surface grafting process, producing a thin film approximately 10-15 nm in height. Contact angle measurements also showed that such photoionization irradiation had yielded an extremely hydrophilic surface (∼21.3°) and X-ray photoelectron spectroscopy also confirmed the coupling was through the Si-C linkage. However, when the surface underwent high-temperature hydrosilylation (>160 °C), the reaction proceeded predominantly through the nucleophilic NH 2 group to form a Si-N linkage to the surface. This rendered the surface hydrophobic and hence suggested that the Si-H homolysis model may not be the main process. To the best of our knowledge, this was the first attempt reported in the literature to use photoionization to directly graft cyclopropylamine onto a silicon surface and in due course generate a highly rich NH-terminated surface that was found to be highly bioactive in promoting cell viability on the basis of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide studies.

  11. Catalytic ring opening of cyclic hydrocarbons in diesel fuels

    Energy Technology Data Exchange (ETDEWEB)

    Calemma, V.; Ferrari, M. [Eni S.p.A., San Donato Milanese (Italy). R and M Div.; Rabl, S.; Haas, A.; Santi, D.; Weitkamp, J. [Stuttgart Univ. (Germany). Inst. of Chemical Technology

    2013-11-01

    An approach for high-aromatic streams upgrading, allowing to meet future diesel quality standards, is saturation of the aromatic structures followed by the selective breaking of endocyclic C-C bonds of naphthenic structures so formed to produce alkanes with the same number of carbon atoms as the starting molecule ('selective ring opening, SRO'). Although theoretically, SRO is a promising route for upgrading low-value feeds to high-quality products, in practice, it continues to be a challenge owing to its complex chemistry. Product characteristics, do not only depend on the composition of the feed, but also on the operating conditions and the nature of the catalyst. Very recently, novel catalysts ('HIgh-PErformance Ring Opening Catalysts, HIPEROCs') were developed which allow a very selective ring opening of the model compound decalin to paraffins without degradation of the carbon number. The hydroconversion of dearomatized Light Cycle Oil (DeAr-LCO) over the abovementioned catalysts resulted in a remarkable change of the chemical structure of the feed with a strong decrease of naphthenic structures with two or more condensed rings and a concomitant increase of alkyl-substituted cyclohexanes and open-chain alkanes. The changes occurring in the chemical structures of feedstock during hydroconversion resulted in a remarkable increase of the Cetane Index of the products up to 11 units. In the present contribution, we examine the main factors affecting activity and selectivity of SRO catalysts in the light of the recent literature dealing with the subject and we report on the recent advances in hydroconversion of refinery cuts such as DeAr- LCO over HIPEROCs. (orig.)

  12. Opening a spiropyran ring by way of an exciplex intermediate.

    Science.gov (United States)

    Benniston, Andrew C; Harriman, Anthony; Howell, Sarah L; Li, Peiyi; Lydon, Donocadh P

    2007-02-02

    A molecular dyad has been synthesized in which the main chromophore is a 1,4-diethynylated benzene residue terminated with pyrene moieties, this latter unit acting as a single chromophore. A spiropyran group has been condensed to the central phenylene ring so as to position a weak electron donor close to the pyrene unit. Illumination of the pyrene-based chromophore leads to formation of a fluorescent exciplex in polar solvents but pyrene-like fluorescence is observed in nonpolar solvents. The exciplex has a lifetime of a few nanoseconds and undergoes intersystem crossing to the pyrene-like triplet state with low efficiency. Attaching a 4-nitrobenzene group to the open end of the spiropyran unit creates a new route for decay of the exciplex whereby the triplet state of the spiropyran is formed. Nonradiative decay of this latter species results in ring opening to form the corresponding merocyanine species. Rate constants for the various steps have been obtained from time-resolved fluorescence spectroscopy carried out over a modest temperature range. Under visible light illumination, the merocyanine form reverts to the original spiropyran geometry so that the cycle is closed. Energy transfer from the pyrene chromophore to the merocyanine unit leads to an increased rate of ring closure and serves to push the steady-state composition in favor of the spiropyran form.

  13. New transition metal complexes and their ring-opened polymers

    Science.gov (United States)

    Apodaca, Paula

    An exciting new class of metallacycle (eta5-C5 H4Fe) (CO)2CH2SiR2 that undergoes ring-opening polymerization was recently reported by Sharma et al. [1]. We are interested in further expanding this research area by synthesizing related cyclopentadienyl derivatives containing Fe, Mo, and W in combination with other elements of the group 14. We report here the synthesis and crystal structure characterization of new germa-metallacyclobutanes of Mo and W. In addition, we have successfully synthesized and characterized new ring-opening polymers of the related germanium systems [(eta5-C5 H4Fe)(CO) 2(CH2GeR2)] n. The new polymers were characterized using various spectroscopic techniques and gel permeation chromatography. The recent report on the synthesis of a new class of siloxane polymers based upon base-catalyzed ring opening of phenylene-bridged cyclic siloxanes [2] encouraged us to investigate the related ferrocenyl (Fc, (C5H 5)Fe(C5H4)) siloxane systems. The incorporation of ferrocene could provide new materials with all the interesting properties usually associated with these groups such as thermal and photochemical stability, electrochemical activity and potentially conducting materials. Thus far a new required organometallic monomer containing Fc-R, where R = disilaoxacyclopentene 5 has been synthesized and completely characterized. Based-induced ring-opening polymerizations of 5 were attempted under different reaction conditions and produced, inter alia: (C5H5)Fe(C 5H4)C(SiMe2OH)=CH(SiMe2R), R = nBu (2), tBu (3), Ph (4). The single crystal X-ray structures and full spectroscopic analysis of such products has been accomplished. Furthermore, the reactivity of the ferrocenyl silanols concerning condensation and their behavior under acidic conditions has been investigated. 1Sharma, H.; Cervantes-Lee, F.; Pannell, K. H. J. Am. Chem. Soc. 2004, 126, 1326. 2 Loy, A. D.; Rahimian, K.; Samara, M. Angew. Chem. 1999, 38, 45.

  14. Supported Catalysts Useful in Ring-Closing Metathesis, Cross Metathesis, and Ring-Opening Metathesis Polymerization

    Directory of Open Access Journals (Sweden)

    Jakkrit Suriboot

    2016-04-01

    Full Text Available Ruthenium and molybdenum catalysts are widely used in synthesis of both small molecules and macromolecules. While major developments have led to new increasingly active catalysts that have high functional group compatibility and stereoselectivity, catalyst/product separation, catalyst recycling, and/or catalyst residue/product separation remain an issue in some applications of these catalysts. This review highlights some of the history of efforts to address these problems, first discussing the problem in the context of reactions like ring-closing metathesis and cross metathesis catalysis used in the synthesis of low molecular weight compounds. It then discusses in more detail progress in dealing with these issues in ring opening metathesis polymerization chemistry. Such approaches depend on a biphasic solid/liquid or liquid separation and can use either always biphasic or sometimes biphasic systems and approaches to this problem using insoluble inorganic supports, insoluble crosslinked polymeric organic supports, soluble polymeric supports, ionic liquids and fluorous phases are discussed.

  15. Ring rearrangements and reactivity of 3-((4-oxo-4H-chromen-3-ylmethylene-4-phenyl-1H-[1,5]benzodiazepin-2(3H-one toward some nucleophiles

    Directory of Open Access Journals (Sweden)

    Hanan Salah

    2017-05-01

    Full Text Available Condensation of 4-phenyl-1H-[1,5]benzodiazepin-2(3H-one (1 with 3-formylchromone (2 afforded a mixture of 3-(chromenylmethylene[1,5]benzodiazepinone 3 and 14-chromenylbenzodiazepino[2,3:6,5]pyrano[2,3-b]benzodiazepine 4. Ring rearrangements of compound 3 with different nucleophilic reagents, such as potassium hydroxide and/or ammonium acetate led to rearrangement into pyranobenzodiazepine 5 and pyridobenzodiazepine 6, respectively. Treatment of compound 3 with hydrazine hydrate, hydroxylamine hydrochloride, malononitrile, cyanothioacetamide, 2-cyano-3,3-disufanylacrylonitrile, and/or 2-cyano-3-phenylamino-3-sufanylacrylonitrile, has been carried out at different conditions, leading to versatile heterocyclic substituted benzodiazepines at position 3, viz. pyrazole 8, isoxazole 9, pyridines 10 and 11, 1,3-dithiine 12, and 1,3-thiazine 13 derivatives.

  16. Thermodynamic Presynthetic Considerations for Ring-Opening Polymerization.

    Science.gov (United States)

    Olsén, Peter; Odelius, Karin; Albertsson, Ann-Christine

    2016-03-14

    The need for polymers for high-end applications, coupled with the desire to mimic nature's macromolecular machinery fuels the development of innovative synthetic strategies every year. The recently acquired macromolecular-synthetic tools increase the precision and enable the synthesis of polymers with high control and low dispersity. However, regardless of the specificity, the polymerization behavior is highly dependent on the monomeric structure. This is particularly true for the ring-opening polymerization of lactones, in which the ring size and degree of substitution highly influence the polymer formation properties. In other words, there are two important factors to contemplate when considering the particular polymerization behavior of a specific monomer: catalytic specificity and thermodynamic equilibrium behavior. This perspective focuses on the latter and undertakes a holistic approach among the different lactones with regard to the equilibrium thermodynamic polymerization behavior and its relation to polymer synthesis. This is summarized in a monomeric overview diagram that acts as a presynthetic directional cursor for synthesizing highly specific macromolecules; the means by which monomer equilibrium conversion relates to starting temperature, concentration, ring size, degree of substitution, and its implications for polymerization behavior are discussed. These discussions emphasize the importance of considering not only the catalytic system but also the monomer size and structure relations to thermodynamic equilibrium behavior. The thermodynamic equilibrium behavior relation with a monomer structure offers an additional layer of complexity to our molecular toolbox and, if it is harnessed accordingly, enables a powerful route to both monomer formation and intentional macromolecular design.

  17. Piranti Lunak Pengujian Struktur Matematika Grup, Ring, Field Berbasis Osp (Open Source Program

    Directory of Open Access Journals (Sweden)

    Ngarap Im Manik

    2014-06-01

    Full Text Available This design of a computer software is a development and continuation of the software made on the previous research (2009/2010. However, this further research developed and expanded the scopes of testing more on the Siclic Group, Isomorphism Group, Semi Group, Sub Group and Abelian Group, Factor Ring, Sub Ring and Polynomial Ring; developed on the OSP (Open Source Program-based. The software was developed using the OSP-based language programming, such Java, so it is open and free to use for its users. This research succeeded to develop an open source software of Java program that can be used for testing specific mathematical Groups, such Ciclic Group, Isomorphism Group, Semi Group, Sub Group and Abelian Group, and Rings, Commutative Ring, Division Ring, Ideal Sub Ring, Ring Homomorphism, Ring Epimorphism and Fields. By the results, the software developed was able to test as same as the results from manual testing.

  18. Cdt1 stabilizes an open MCM ring for helicase loading.

    Science.gov (United States)

    Frigola, Jordi; He, Jun; Kinkelin, Kerstin; Pye, Valerie E; Renault, Ludovic; Douglas, Max E; Remus, Dirk; Cherepanov, Peter; Costa, Alessandro; Diffley, John F X

    2017-06-23

    ORC, Cdc6 and Cdt1 act together to load hexameric MCM, the motor of the eukaryotic replicative helicase, into double hexamers at replication origins. Here we show that Cdt1 interacts with MCM subunits Mcm2, 4 and 6, which both destabilizes the Mcm2-5 interface and inhibits MCM ATPase activity. Using X-ray crystallography, we show that Cdt1 contains two winged-helix domains in the C-terminal half of the protein and a catalytically inactive dioxygenase-related N-terminal domain, which is important for MCM loading, but not for subsequent replication. We used these structures together with single-particle electron microscopy to generate three-dimensional models of MCM complexes. These show that Cdt1 stabilizes MCM in a left-handed spiral open at the Mcm2-5 gate. We propose that Cdt1 acts as a brace, holding MCM open for DNA entry and bound to ATP until ORC-Cdc6 triggers ATP hydrolysis by MCM, promoting both Cdt1 ejection and MCM ring closure.

  19. Structure and magnetic field of periodic permanent magnetic focusing system with open magnetic rings

    International Nuclear Information System (INIS)

    Peng Long; Li Lezhong; Yang Dingyu; Zhu Xinghua; Li Yuanxun

    2011-01-01

    The magnetic field along the central axis for an axially magnetized permanent magnetic ring was investigated by analytical and finite element methods. For open magnetic rings, both calculated and measured results show that the existence of the radial magnetic field creates a remarkable cosine distribution field along the central axis. A new structure of periodic permanent magnet focusing system with open magnetic rings is proposed. The structure provides a satisfactory magnetic field with a stable peak value of 120 mT for a traveling wave tube system. - Research highlights: → For open magnetic rings, both calculated and measured results show that the existence of the radial magnetic field creates a remarkable cosine distribution field along the central axis. → A new structure of periodic permanent magnet (PPM) focusing system with open magnetic rings is proposed. → The new PPM focusing system with open magnetic rings meets the requirements for TWT system.

  20. Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes.

    Science.gov (United States)

    Boon, Byron A; Green, Aaron G; Liu, Peng; Houk, K N; Merlic, Craig A

    2017-05-05

    Syntheses of strained cyclic dienes were accomplished via palladium(II)-catalyzed oxidative cyclizations of terminal bis(vinylboronate esters). The reactions generate strained (E,E)-1,3-dienes that undergo spontaneous 4π-electrocyclizations to form bicyclic cyclobutenes. Formation of the cyclobutenes is driven by the strain in the medium-ring (E,E)-1,3-diene intermediate. Thermal ring openings of the cyclobutenes give (Z,Z)-1,3-diene products, again for thermodynamic reasons. DFT calculations verified the thermodynamic versus kinetic control of the reactions, and kinetic studies are in excellent agreement with the calculated energy changes. An extension of the tandem coupling/4π-electrocyclization pathway was demonstrated by a palladium(II)-catalyzed oxidative homocoupling/8π-electrocyclization cascade.

  1. Novel Platinum-Catalyzed Ring-Opening of 1,2-Cyclopropanated Sugars with Alcohols

    DEFF Research Database (Denmark)

    Beyer, Jürgen; Madsen, Robert

    1998-01-01

    Reaction of 1,2-cyclopropanated sugars with a catalytic amount ofZeise's dimer [Pt(C2H4)Cl2]2 and an alcohol gives 2-C-branched glycosides by a novel platinum catalyzed ring-opening. A wide variety of alcohols can participate in this ring-opening reaction giving 2-C-branched glycosides ranging from...

  2. A Bacon Tone Ring on an Open-Back Banjo

    OpenAIRE

    Politzer, David

    2016-01-01

    Head taps on a new Goodtime banjo rim fitted with a reproduction Bacon Professional ff tone ring are contrasted with a new Goodtime, a 2002 Goodtime, and a 1999 Goodtime fitted with a 1/4′′ diameter brass ring. Conclusions: The 1/4" ring does what’s commonly imagined, the upgrades to the Goodtime over the years are not merely cosmetic, and the Bacon ring’s biggest effect is to damp head ringing and suppress high harmonics. Detailed comparisons of the new Goodtimes with and without the Bacon r...

  3. {open_quotes}O{close_quotes} ring sealed process tube, Phase II, test project

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, R.E.

    1951-04-09

    The {open_quotes}O{close_quotes} ring seal has been proposed to replace the van stone flange and the bellows thermal expansion assembly currently used on the existing Hanford piles to achieve water and gas seals, respectively. Possible advantages of the {open_quotes}O{close_quotes} ring seal are: (1) simplification of component parts and elimination of van stone corrosion; (2) simplification of maintenance; (3) lower costs of initial erection; (4) increased strength. This test supplements Test Project No. 27 (a preliminary thermal cycling test) in applying the {open_quotes}O{close_quotes} ring seal assembly to actual pile operating conditions.

  4. Computational study of hydrogen shifts and ring-opening mechanisms in α-pinene ozonolysis products

    DEFF Research Database (Denmark)

    Kurtén, Theo; Rissanen, Matti P.; Mackeprang, Kasper

    2015-01-01

    , sterically unhindered) H-shifts of all four peroxy radicals formed in the ozonolysis of α-pinene using density functional (ωB97XD) and coupled cluster [CCSD(T)-F12] theory. In contrast to the related but chemically simpler cyclohexene ozonolysis system, none of the calculated H-shifts have rate constants...... products in the α-pinene ozonolysis system, additional ring-opening reaction mechanisms breaking the cyclobutyl ring are therefore needed. We further investigate possible uni- and bimolecular pathways for opening the cyclobutyl ring in the α-pinene ozonolysis system....

  5. Conductance of closed and open long Aharonov-Bohm-Kondo rings

    Science.gov (United States)

    Shi, Zheng; Komijani, Yashar

    2017-02-01

    We calculate the finite temperature linear dc conductance of a generic single-impurity Anderson model containing an arbitrary number of Fermi liquid leads, and apply the formalism to closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected four-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T matrix of the screening channel. For closed rings we show that at temperatures high compared to the Kondo temperature, the conductance behaves differently for temperatures above and below vF/L , where vF is the Fermi velocity and L is the circumference of the ring. For open rings, when the ring arms have both a small transmission and a small reflection, we show from the microscopic model that the ring behaves like a two-path interferometer, and that the Kondo temperature is unaffected by details of the ring. Our findings confirm that ABK rings are potentially useful in the detection of the size of the Kondo screening cloud, the π /2 scattering phase shift from the Kondo singlet, and the suppression of Aharonov-Bohm oscillations due to inelastic scattering.

  6. Thermoset polymers via ring opening metathesis polymerization of functionalized oils

    Science.gov (United States)

    Larock, Richard C; Henna, Phillip H; Kessier, Michael R

    2012-11-27

    The invention provides a method for producing a thermosetting resin from renewable oils, the method comprising supplying renewable oil molecules containing strained ring alkene moieties; reacting the alkene moieties with cyclic alkenes to create a polymer; and repeating the above two steps until the resin having desired characteristics are obtained. Also provided is a thermoset resin comprising functionalized renewable oil polymerized with a co-monomer.

  7. Imaging electron wave functions inside open quantum rings.

    Science.gov (United States)

    Martins, F; Hackens, B; Pala, M G; Ouisse, T; Sellier, H; Wallart, X; Bollaert, S; Cappy, A; Chevrier, J; Bayot, V; Huant, S

    2007-09-28

    Combining scanning gate microscopy (SGM) experiments and simulations, we demonstrate low temperature imaging of the electron probability density |Psi|(2)(x,y) in embedded mesoscopic quantum rings. The tip-induced conductance modulations share the same temperature dependence as the Aharonov-Bohm effect, indicating that they originate from electron wave function interferences. Simulations of both |Psi|(2)(x,y) and SGM conductance maps reproduce the main experimental observations and link fringes in SGM images to |Psi|(2)(x,y).

  8. Current density waves in open mesoscopic rings driven by time-periodic magnetic fluxes

    International Nuclear Information System (INIS)

    Yan Conghua; Wei Lianfu

    2010-01-01

    Quantum coherent transport through open mesoscopic Aharonov-Bohm rings (driven by static fluxes) have been studied extensively. Here, by using quantum waveguide theory and the Floquet theorem we investigate the quantum transport of electrons along an open mesoscopic ring threaded by a time-periodic magnetic flux. We predicate that current density waves could be excited along such an open ring. As a consequence, a net current could be generated along the lead with only one reservoir, if the lead additionally connects to such a normal-metal loop driven by the time-dependent flux. These phenomena could be explained by photon-assisted processes, due to the interaction between the transported electrons and the applied oscillating external fields. We also discuss how the time-average currents (along the ring and the lead) depend on the amplitude and frequency of the applied oscillating fluxes.

  9. Pyrimidine-pyridine ring interconversion

    NARCIS (Netherlands)

    Plas, van der H.C.

    2003-01-01

    This chapter discusses the pyrimidine-to-pyridine ring transformation and pyridine-to-pyrimidine ring transformation. In nucleophile-induced pyrimidine-to-pyridine rearrangements, two types of reactions can be distinguished depending on the structure of the nucleophile: (1) reactions in which the

  10. Vortex ring formation at the open end of a shock tube: A particle image velocimetry study

    Science.gov (United States)

    Arakeri, J. H.; Das, D.; Krothapalli, A.; Lourenco, L.

    2004-04-01

    The vortex ring generated subsequent to the diffraction of a shock wave from the open end of a shock tube is studied using particle image velocimetry. We examine the early evolution of the compressible vortex ring for three-exit shock Mach numbers, 1.1, 1.2, and 1.3. For the three cases studied, the ring formation is complete at about tUb/D=2, where t is time, Ub is fluid velocity behind shock as it exits the tube and D is tube diameter. Unlike in the case of piston generated incompressible vortex rings where the piston velocity variation with time is usually trapezoidal, in the shock-generated vortex ring case the exit fluid velocity doubles from its initial value Ub before it slowly decays to zero. At the end of the ring formation, its translation speed is observed to be about 0.7 Ub. During initial formation and propagation, a jet-like flow exists behind the vortex ring. The vortex ring detachment from the tailing jet, commonly referred to as pinch-off, is briefly discussed.

  11. Selective Ring Opening of 1-Methylnaphthalene Over NiW-Supported Catalyst Using Dealuminated Beta Zeolite.

    Science.gov (United States)

    Kim, Eun-Sang; Lee, You-Jin; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong

    2016-02-01

    Nanoporous Beta zeolite was dealuminated by weak acid treatment for reducing the acidity. Bi-functional catalysts were prepared using commercial Beta zeolites and the dealuminated zeolites for acidic function, NiW for metallic function. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction has been investigated using the prepared bi-functional catalysts with different acidity in fixed bed reaction system. The dealuminated Beta zeolites, which crystal structure and nanoporosity were maintained, showed the higher SiO2/Al2O3 ratio and smaller acidity than their original zeolite. NiW-supported catalyst using the dealuminated Beta zeolite with SiO2/Al203 mole ratio of 55 showed the highest performance for the selective ring opening. The acidity of catalyst seemed to play an important role as active sites for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. The acidity of Beta zeolite could be controlled by the acid treatment and the catalyst with the optimum acidity for the selective ring opening could be prepared.

  12. Synthesis of Human Milk Oligosaccharides and Regioselective Ring Opening of Oxabicycles

    DEFF Research Database (Denmark)

    Jennum, Camilla Arboe

    . The tetrasaccharides were formed both by sequential and the developed one-pot method. Deprotection of the protecting group at the C-2-position on the galactose moiety liberated an acceptor for the fucosylation eventually creating the two linear pentasaccharides Lacto-N-fucopentaose I and Lacto-N-neofucopentaose I...... ligands. The ring opened iii products were similar to compounds, which had shown to be potential protein Bcl-XL antagonists, a target for future drugs in cancer treatment. The aim was to create a general asymmetric ring opening method of several enantiopure oxabicycles having different functional moieties...

  13. Catalytic ring opening of decalin. Biofunctional versus hydrogenolytic pathways

    Energy Technology Data Exchange (ETDEWEB)

    Weitkamp, J.; Rabl, S.; Haas, A.; Santi, D. [Stuttgart Univ. (Germany). Inst. of Chemical Technology; Ferrari, M.; Calemma, V. [Eni R and M Div., San Donato Milanese (Italy)

    2010-12-30

    Ir/silica, Pt/La-X and Rh/H-Beta were prepared and tested in the hydroconversion of cisdecalin at different temperatures. The catalytic tests were carried out under hydrogen in a high-pressure flow-type apparatus at 5.2 MPa. On the three catalysts open-chain decane yields up to 20 % were achieved, which is much higher than the yields reported so far in the literature. Pt/La-X and Rh/H-Beta behave as bifunctional catalysts with a high tendency for skeletal isomerization. On these catalysts the so-called paring reaction via carbenium ions occurs, leading to iso-butane and methylcyclopentane as main hydrocracked products. On Ir/SiO{sub 2}, carbon-carbon bond cleavage occurs through hydrogenolysis on the noble metal without prior isomerization. As a consequence the product spectrum is less complex than on the bifunctional catalysts which makes the system particularly amenable to mechanistic studies. (orig.)

  14. Functional polypeptides obtained by living ring opening polymerizations of N-carboxyanhydrides

    NARCIS (Netherlands)

    Habraken, G.J.M.

    2011-01-01

    N-Carboxyanhydride ring opening polymerization (NCA ROP) is a method to prepare polypeptides with a high degree of polymerization in large quantities. The living polymerization technique of NCA ROP gave the opportunity to synthesize many polymer architectures with well-defined blocks and copolymers

  15. Copper-catalyzed asymmetric ring opening of oxabicyclic alkenes with organolithium reagents

    NARCIS (Netherlands)

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

    2012-01-01

    A highly efficient method is reported for the asymmetric ring opening of oxabicyclic alkenes with organolithium reagents. Using a copper/chiral phosphoramidite complex together with a Lewis acid (BF3·OEt2), full selectivity for the anti isomer and excellent enantioselectivities were obtained for the

  16. 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...

  17. Sulfuric acid as a catalyst for ring-opening of biobased bis-epoxides

    Science.gov (United States)

    Vegetable oils can be relatively and easily transformed into bio-based epoxides. Because of this, the acid-catalyzed epoxide ring-opening has been explored for the preparation of bio-based lubricants and polymers. Detailed model studies are carried out only with mono-epoxide made from methyl oleate,...

  18. In situ ring-opening polymerization of hydroxyapatite/poly (ethylene ...

    Indian Academy of Sciences (India)

    2016-08-26

    Aug 26, 2016 ... Hydroxyapatite/poly(ethylene adipate)--poly(ethylene terephthalate) biomaterials (HAp/PEA--PET) have been prepared by ring opening polymerization (ROP) of cyclic oligo(ethylene adipate)--oligo(ethylene terephthalate) (C-OEA--C-OET) in the porous hydroxyapatite (HAp) scaffolds at 250 ...

  19. Microwave-assisted cationic ring-opening polymerization of a soy-based 2-oxazoline monomer

    NARCIS (Netherlands)

    Hoogenboom, R.; Wiesbrock, F.D.; Schubert, U.S.

    2005-01-01

    The microwave-assisted cationic ring-opening polymn. of a soy based 2-oxazoline monomer (SoyOx) is described. The microwave irradn. provides more efficient heating when compared to conventional heating and, in addn., the SoyOx was prepd. starting from a sustainable resource (soy beans). The

  20. Catalytic ring-​opening copolymerization of limonene oxide and phthalic anhydride : toward partially renewable polyesters

    NARCIS (Netherlands)

    Hosseini Nejad, E.; Pionasari, A; Melis, van C.G.W.; Koning, C.E.; Duchateau, R.

    2013-01-01

    Catalytic ring-¿opening copolymn. of limonene oxide with phthalic anhydride was performed applying metal t-¿Bu-¿salophen complexes (t-¿Bu-¿salophen)¿MX; M = Cr, X = Cl (1)¿, M = Al, X = Cl (2)¿, M = Co, X = OAc (3)¿, M = Mn, X = Cl (4)¿, t-¿Bu-¿salophen =

  1. In situ ring-opening polymerization of hydroxyapatite/poly (ethylene ...

    Indian Academy of Sciences (India)

    Hydroxyapatite/poly(ethylene adipate)--poly(ethylene terephthalate) biomaterials (HAp/PEA--PET) have been prepared by ring opening polymerization (ROP) of cyclic oligo(ethylene adipate)--oligo(ethylene terephthalate) (C-OEA--C-OET) in the porous hydroxyapatite (HAp) scaffolds at 250 °C for 24 h under ...

  2. Green chemistry: Efficient epoxides ring-opening with 1-butanol under microwave irradiation

    International Nuclear Information System (INIS)

    Garcia-Vidal, Jesus A.; Duran-Valle, Carlos J.; Ferrera-Escudero, Santiago

    2006-01-01

    Two activated carbons treated with mineral acids (HNO 3 and sulfonitric mixture) have been tested as acid catalysts in the epoxides (1,2-epoxyhexane and styrene oxide) ring-opening reaction with 1-butanol under microwave (MW) irradiation. The mayor obtained product is that resulting of the alcohol addition to the most substituted carbon in the epoxide ring. The most active catalyst is that treated with sulfonitric mixture. The use of a MW oven allows achieving to the complete conversion of styrene oxide in only 2 min

  3. Green chemistry: Efficient epoxides ring-opening with 1-butanol under microwave irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Vidal, Jesus A. [Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Extremadura, Campus Universitario, Avda. de Elvas, s/n, E-06071-Badajoz (Spain); Duran-Valle, Carlos J. [Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Extremadura, Campus Universitario, Avda. de Elvas, s/n, E-06071-Badajoz (Spain)]. E-mail: carlosdv@unex.es; Ferrera-Escudero, Santiago [Departamento de Quimica Inorganica y Quimica Tecnica, Universidad Nacional de Educacion a Distancia, C/Senda del Rey, 9, E-28040 Madrid (Spain)

    2006-06-30

    Two activated carbons treated with mineral acids (HNO{sub 3} and sulfonitric mixture) have been tested as acid catalysts in the epoxides (1,2-epoxyhexane and styrene oxide) ring-opening reaction with 1-butanol under microwave (MW) irradiation. The mayor obtained product is that resulting of the alcohol addition to the most substituted carbon in the epoxide ring. The most active catalyst is that treated with sulfonitric mixture. The use of a MW oven allows achieving to the complete conversion of styrene oxide in only 2 min.

  4. Preparation of Bottlebrush Polymers via a One-Pot Ring-Opening Polymerization (ROP) and Ring-Opening Metathesis Polymerization (ROMP) Grafting-Through Strategy.

    Science.gov (United States)

    Radzinski, Scott C; Foster, Jeffrey C; Matson, John B

    2016-04-01

    Bottlebrush polymers are synthesized using a tandem ring-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP) strategy. For the first time, ROP and ROMP are conducted sequentially in the same pot to yield well-defined bottlebrush polymers with molecular weights in excess of 10(6) Da. The first step of this process involves the synthesis of a polylactide macromonomer (MM) via ROP of d,l-lactide initiated by an alcohol-functionalized norbornene. ROMP grafting-through is then carried out in the same pot to produce the bottlebrush polymer. The applicability of this methodology is evaluated for different MM molecular weights and bottlebrush backbone degrees of polymerization. Size-exclusion chromatographic and (1)H NMR spectroscopic analyses confirm excellent control over both polymerization steps. In addition, bottlebrush polymers are imaged using atomic force microscopy and stain-free transmission electron microscopy on graphene oxide. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Ring Opening Metathesis Polymerization of Cyclopentene Using a Ruthenium Catalyst Confined by a Branched Polymer Architecture

    KAUST Repository

    Mugemana, Clement; Bukhriakov, Konstantin; Bertrand, Olivier; Vu, Khanh B.; Gohy, Jean-Francois; Hadjichristidis, Nikolaos; Rodionov, Valentin

    2016-01-01

    Multi-arm polystyrene stars functionalized with Grubbs-type catalysts in their cores were synthesized and used for the ring-opening metathesis polymerization (ROMP) of cyclopentene. The spatial confinement of the catalytic sites and the nanoscale phase separation between polystyrene and the growing polypentenamer chains lead to a dramatic inhibition of the ROMP termination and chain transfer steps. Consequently, cyclopentene polymerizations proceeded fast and with a high degree of conversion even in air. The Grubbs second generation catalyst was oxidatively inactivated under the same conditions. In contrast to conventional small-molecule catalysts, the ultimate degree of conversion of cyclopentene monomer and the polydispersity of the product polypentenamer are not affected by the temperature. This indicates that spatial confinement of the catalyst resulted in a significant change in the activation parameters for the alkene metathesis ring-opening.

  6. Ring Opening Metathesis Polymerization of Cyclopentene Using a Ruthenium Catalyst Confined by a Branched Polymer Architecture

    KAUST Repository

    Mugemana, Clement

    2016-03-22

    Multi-arm polystyrene stars functionalized with Grubbs-type catalysts in their cores were synthesized and used for the ring-opening metathesis polymerization (ROMP) of cyclopentene. The spatial confinement of the catalytic sites and the nanoscale phase separation between polystyrene and the growing polypentenamer chains lead to a dramatic inhibition of the ROMP termination and chain transfer steps. Consequently, cyclopentene polymerizations proceeded fast and with a high degree of conversion even in air. The Grubbs second generation catalyst was oxidatively inactivated under the same conditions. In contrast to conventional small-molecule catalysts, the ultimate degree of conversion of cyclopentene monomer and the polydispersity of the product polypentenamer are not affected by the temperature. This indicates that spatial confinement of the catalyst resulted in a significant change in the activation parameters for the alkene metathesis ring-opening.

  7. Quantum Mechanics/Molecular Mechanics Simulations Identify the Ring-Opening Mechanism of Creatininase.

    Science.gov (United States)

    Jitonnom, Jitrayut; Mujika, Jon I; van der Kamp, Marc W; Mulholland, Adrian J

    2017-12-05

    Creatininase catalyzes the conversion of creatinine (a biosensor for kidney function) to creatine via a two-step mechanism: water addition followed by ring opening. Water addition is common to other known cyclic amidohydrolases, but the precise mechanism for ring opening is still under debate. The proton donor in this step is either His178 or a water molecule bound to one of the metal ions, and the roles of His178 and Glu122 are unclear. Here, the two possible reaction pathways have been fully examined by means of combined quantum mechanics/molecular mechanics simulations at the SCC-DFTB/CHARMM22 level of theory. The results indicate that His178 is the main catalytic residue for the whole reaction and explain its role as proton shuttle during the ring-opening step. In the first step, His178 provides electrostatic stabilization to the gem-diolate tetrahedral intermediate. In the second step, His178 abstracts the hydroxyl proton of the intermediate and delivers it to the cyclic amide nitrogen, leading to ring opening. The latter is the rate-limiting step with a free energy barrier of 18.5 kcal/mol, in agreement with the experiment. We find that Glu122 must be protonated during the enzyme reaction, so that it can form a stable hydrogen bond with its neighboring water molecule. Simulations of the E122Q mutant showed that this replacement disrupts the H-bond network formed by three conserved residues (Glu34, Ser78, and Glu122) and water, increasing the energy barrier. Our computational studies provide a comprehensive explanation for previous structural and kinetic observations, including why the H178A mutation causes a complete loss of activity but the E122Q mutation does not.

  8. Ring-Opening of Oxiranes using Taeniolite-Supported Tris(β-DiketonatoZirconium

    Directory of Open Access Journals (Sweden)

    Yessi Permana

    2012-11-01

    Full Text Available A series of tris(β-diketonatozirconium(IV complexes were immobilized into a synthetic clay structure of Taeniolite by an ion-exchange method to generate organic/inorganic hybrid compounds. The hybrid compound served as a good catalyst for ring-opening reactions of methyl, ethyl, and dimethyl oxiranes with various alcohols to generate primary alkoxy alcohols in appreciable selectivity. This method described a technique to immobilize cationic zirconium complexes without losing selectivity.

  9. Well-defined polyethylene molecular brushes by polyhomologation and ring opening metathesis polymerization

    KAUST Repository

    Zhang, Hefeng; Gnanou, Yves; Hadjichristidis, Nikolaos

    2014-01-01

    A novel strategy using polyhomologation and ring opening metathesis polymerization (ROMP) has been developed for the synthesis of well-defined polyethylene (PE) molecular brushes. Polyhomologation was used to afford an OH-terminated PE, which after transformation to the norbornyl PE macromonomer was subjected to ROMP. Kinetics of ROMP of the PE macromonomer was studied by in situ1H NMR monitoring. The brush structure was proved from HT-GPC, 1H NMR and DSC results.

  10. Topological optimization of opening fence brackets on ring-stiffened cylindrical shell

    Directory of Open Access Journals (Sweden)

    SONG Xiaofei

    2018-02-01

    Full Text Available [Objectives] Stress concentration is prone to take place at connections between the opening fence and ring ribs of a ring-stiffened cylindrical shell under external pressure. [Methods] In this paper, a topological optimization method for the brackets that connect the fence to the ring ribs is proposed in order to effectively reduce the local high stress in the brackets. The sub-model technique is used to analyze the stress of the connecting brackets. In the design, the connection brackets are used as design variables and the stress of the shell, fence and ribs are used as constraints. The maximum stress of the bracket is minimized as the objective function. The topology optimization results are engineered to obtain the final form of the brackets. [Results] The calculation results show that brackets of which the panel is partially widened can effectively reduce the stress concentration position of the opening fence transverse offset if the side of the bracket away from the longitudinal section is longer; the opening fence is offset relative to the brackets, and the symmetrical design of the brackets is feasible. [Conclusions] This research provides a reference for similar structural design.

  11. Preparation of nucleoside-pyridine hybrids and pyridine attached acylureas from an unexpected uracil ring-opening and pyridine ring-forming sequence

    Institute of Scientific and Technical Information of China (English)

    Xue Sen Fan; Xia Wang; Xin Ying Zhang; Dong Feng; Ying Ying Qu

    2009-01-01

    Novel pyrimidine nucleoside-3,5-dicyanopyridine hybrids (4) or pyridine attached acylureas (5) were selectively and efficiently prepared from the reaction of 2'-deoxyuridin-5-yl-methylene malonortitrile (1), malononitrile (2) and thiophenol (3) or from an unexpected uracil ring-opening and pyridine ring-forming sequence via the reaction of 1 and 3. It is the first time such a sequence has ever been reported.

  12. Liberation of methyl acrylate from metallalactone complexes via M-O ring opening (M = Ni, Pd) with methylation agents

    KAUST Repository

    Lee, S. Y Tina; Ghani, Amylia Abdul; D'Elia, Valerio; Cokoja, Mirza; Herrmann, Wolfgang A.; Basset, Jean-Marie; Kü hn, Fritz

    2013-01-01

    Ring opening of various nickela- and palladalactones induced by the cleavage of the M-O bond by methyl trifluoromethanesulfonate (MeOTf) and methyl iodide (MeI) is examined. Experimental evidence supports the mechanism of ring opening by the alkylating agent followed by β-H elimination leading to methyl acrylate and a metal-hydride species. MeOTf shows by far higher efficiency in the lactone ring opening than any other methylating agent including the previously reported methyl iodide. © 2013 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

  13. Lipase-catalyzed ring-opening polymerization of lactones to polyesters and its mechanistic aspects.

    Science.gov (United States)

    Namekawa, S; Suda, S; Uyama, H; Kobayashi, S

    1999-01-01

    Lipase catalysis induced a ring-opening polymerization of lactones with different ring-sizes. Small-size (four-membered) and medium-size lactones (six- and seven-membered) as well as macrolides (12-, 13-, 16-, and 17-membered) were subjected to lipase-catalyzed polymerization. The polymerization behaviors depended primarily on the lipase origin and the monomer structure. The macrolides showing much lower anionic polymerizability were enzymatically polymerized faster than epsilon-caprolactone. The granular immobilized lipase derived from Candida antartica showed extremely efficient catalysis in the polymerization of epsilon-caprolactone. Single-step terminal functionalization of the polyester was achieved by initiator and terminator methods. The enzymatic polymerizability of lactones was quantitatively evaluated by Michaelis-Menten kinetics.

  14. TDDFT-MD Study on Dynamics in Photoinduced Ring Opening of Benzene

    Science.gov (United States)

    Tateyama, Yoshitaka; Miyamoto, Yoshiyuki; Oyama, Norihisa; Ohno, Takahisa

    2004-03-01

    Coupled dynamics of ions and electrons in the excited states of molecular and solid benzene is investigated on the femtosecond scale by the efficient simulation scheme recently developed for the time-dependent density functional theory. Within the π arrow π excitations, any out-of-plane motion of ions is not induced in the molecular system basically. In the solid, however, we found that large swing of the C-H bonds and subsequent twist of the carbon ring takes place, leading to sp^3-like bonding of carbon ions. This swing-to-twist motion presents a plausible mechanism underlying the photoinduced ring opening in solid benzene experimentally observed under pressure. This research is partially supported by ACT-JST, and also by FSIS and Special Coordination Funds of Ministry of Education, Culture, Sports, Science and Technology of Japanese Government.

  15. Photochemical Ring-Opening Reaction in 2(1H)-Pyrimidinones: A Matrix Isolation Study

    OpenAIRE

    Lapinski, Leszek; Rostkowska, Hanna; Khvorostov, Artem; Fausto, Rui; Nowak, Maciej J.

    2003-01-01

    Photoreactions induced by UV-B (290−320 nm) irradiation were studied for 1-methyl-2(1H)-pyrimidinone and 1-methylcytosine monomers isolated in low-temperature inert gas matrixes. A Norrish type I α-cleavage reaction leading to open-ring conjugated isocyanate was observed for 1-methyl-2(1H)-pyrimidinone. The structure of the photoproduct was identified by comparison of its experimental IR spectrum with the spectrum theoretically calculated at the DFT(B3LYP)/6-31++G(d,p) level. The main indicat...

  16. Lactic Acid Yield Using Different Bacterial Strains, Its Purification, and Polymerization through Ring-Opening Reactions

    Directory of Open Access Journals (Sweden)

    F. G. Orozco

    2014-01-01

    Full Text Available Laboratory-scale anaerobic fermentation was performed to obtain lactic acid from lactose, using five lactic acid bacteria: Lactococcus lactis, Lactobacillus bulgaricus, L. delbrueckii, L. plantarum, and L. delbrueckii lactis. A yield of 0.99 g lactic acid/g lactose was obtained with L. delbrueckii, from which a final concentration of 80.95 g/L aqueous solution was obtained through microfiltration, nanofiltration, and inverse osmosis membranes. The lactic acid was polymerized by means of ring-opening reactions (ROP to obtain poly-DL-lactic acid (PDLLA, with a viscosity average molecular weight (Mv of 19,264 g/mol.

  17. Zwitterionic bis(phenolate)amine lanthanide complexes for the ring-opening polymerisation of cyclic esters

    NARCIS (Netherlands)

    Dyer, H.E.; Huijser, S.; Schwarz, A.D.; Wang, Chao; Duchateau, R.; Mountford, P.

    2008-01-01

    The reaction of Sm{N(SiMe3)2}3 with the bis(phenol)amines H2O2NR (H2O 2NR = RCH2CH2N(2-HO-3,5-C 6H2tBu2)2; R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2N R)(HO2NR). For R = OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of e-caprolactone and d,l-lactide with

  18. Synthesis and study of rare earth ortho-hydroxyphenyliminodiacetates with open lactone ring

    International Nuclear Information System (INIS)

    Martynenko, L.I.; Mitrofanova, N.D.; Muratova, N.M.; Kurbatova, S.V.

    1978-01-01

    New La, Pr, Nd, Sm, Dy, Er, and Y o-oxyphenyliminodiacetates of Ln 2 (HL) 3 xnH 2 O composition have been synthesized using the reaction of Ln chloride solutions with o-oxyphenyliminodiacetic acid previously converted into a soluble K 2 HL salt. According to the data of infrared spectra, the ligand contains an open lactone ring and ionized carboxylic groups. At the temperature of 80-190 deg the complexes undergo dehydration. The order of dehydration reaction for La, Nd, and Y complexes is equal to 2, activation energies are equal to 16.9, 12.5 and 13.2 kcal/mol, respectively

  19. Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

    Directory of Open Access Journals (Sweden)

    Nikolai V. Rostovskii

    2015-03-01

    Full Text Available Strained azirinium ylides derived from 2H-azirines and α-diazoketones under Rh(II-catalysis can undergo either irreversible ring opening across the N–C2 bond to 2-azabuta-1,3-dienes that further cyclize to 2H-1,4-oxazines or reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b]oxazoles. Dihydroazireno[2,1-b]oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methylketene generated from 3-diazoacetylacetone under Rh(II catalysis to give 4,6-dioxa-1-azabicyclo[3.2.1]oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1]deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+G(d,p, the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b]oxazole intermediate on acetyl(methylketene followed by aziridine ring opening into atropoisomeric oxazolium betaines and cyclization. Azirinium ylides generated from 2,3-di- and 2,2,3-triaryl-substituted azirines give rise to only 2-azabuta-1,3-dienes and/or 2H-1,4-oxazines.

  20. Monte Carlo simulation of second-generation open-type PET ''single-ring OpenPET'' implemented with DOI detectors

    International Nuclear Information System (INIS)

    Tashima, Hideaki; Yamaya, Taiga; Hirano, Yoshiyuki; Yoshida, Eiji; Kinouch, Shoko; Watanabe, Mitsuo; Tanaka, Eiichi

    2013-01-01

    At the National Institute of Radiological Sciences, we are developing OpenPET, an open-type positron emission tomography (PET) geometry with a physically open space, which allows easy access to the patient during PET studies. Our first-generation OpenPET system, dual-ring OpenPET, which consisted of two detector rings, could provide an extended axial field of view (FOV) including the open space. However, for applications such as in-beam PET to monitor the dose distribution in situ during particle therapy, higher sensitivity concentrated on the irradiation field is required rather than a wide FOV. In this report, we propose a second-generation OpenPET geometry, single-ring OpenPET, which can efficiently improve sensitivity while providing the required open space. When the proposed geometry was realized with block detectors, position-dependent degradation of the spatial resolution was expected because it was necessary to arrange the detector blocks in ellipsoidal rings stacked and shifted relative to one another. However, we found by Monte Carlo simulation that the use of depth-of-interaction (DOI) detectors made it feasible to achieve uniform spatial resolution in the FOV. (author)

  1. Synthesis of Polysiloxanes In Microemulsion Via ring opening of D4

    Directory of Open Access Journals (Sweden)

    Liu Jiesheng

    2016-07-01

    Full Text Available Polydimethylsiloxane (PDMS has been synthesized by ring-opening polymerization of octamethylcyclotetrasiloxane (D4 in microemulsion with acidic catalyst. The structure and properties of microemulsion were characterized by Transmission Electron Microscopy (TEM, Fourier Transform Infrared Spectroscopy (FT-IR, Photo Correlation Spectroscopy (PCS. The effect of the variation in pH value, amount of catalyst, emulsifier and monomer dropping rate on the properties of microemulsion were investigated and discussed. The results showed that the particle size of the latex becomes smaller, and the distribution size becomes wider with increasing the content of catalyst and emulsifier. When pH value changed, the reaction rate of ring-opening of D4 was faster with strong acid than that under the weak acid condition. The emulsification of 2 % OP-10 (Alkylphenol polyoxyethylene ether and 3.0% DBSA (Dodecyl benzenesulfonic acid reached to equilibrium in microemulsion. As the amount of OP-10 increases, the size of particles lowered and their corresponding  distribution widened. It is observed that emulsifier (OP-10 does not affect the transparency of the microemulsion in the case of the application of DBSA. As the monomer dropping time increased, the grain size diminished and the size distribution widened. PCS results showed that the smallest particle size was around 20nm. Taking into account of the stability of the microemulsions, the dropping time of the monomer was around 30 min.

  2. NATO Advanced Study Institute on Ring-opening Metathesis Polymerization of Olefins and Polymerization of Alkynes

    CERN Document Server

    1998-01-01

    The first NATO Advanced Study Institute on Olefin Metathesis and Polymerization Catalysts was held on September 10-22, 1989 in Akcay, Turkey. Based on the fundamental research of RRSchrock, RGrubbs and K.B.Wagener in the field of ring opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) and alkyne polymerization, these areas gained growing interest within the last years. Therefore the second NATO-ASI held on metathesis reactions was on Ring Opening Metathesis Po­ lymerization of Olefins and Polymerization of Alkynes on September 3-16, 1995 in Akcay, Turkey. The course joined inorganic, organic and polymer chemists to exchange their knowledge in this field. This volume contains the main and short lectures held in Akcay. To include ADMET reactions better into the title of this volume we changed it into: Metathesis Polymerization of Olefins and Alkyne Polymerization. This volume is addressed to research scientists, but also to those who start to work in the area of olefin metathesis and al...

  3. Modeling of lipase catalyzed ring-opening polymerization of epsilon-caprolactone.

    Science.gov (United States)

    Sivalingam, G; Madras, Giridhar

    2004-01-01

    Enzymatic ring-opening polymerization of epsilon-caprolactone by various lipases was investigated in toluene at various temperatures. The determination of molecular weight and structural identification was carried out with gel permeation chromatography and proton NMR, respectively. Among the various lipases employed, an immobilized lipase from Candida antartica B (Novozym 435) showed the highest catalytic activity. The polymerization of epsilon-caprolactone by Novozym 435 showed an optimal temperature of 65 degrees C and an optimum toluene content of 50/50 v/v of toluene and epsilon-caprolactone. As lipases can degrade polyesters, a maximum in the molecular weight with time was obtained due to the competition of ring opening polymerization and degradation by specific chain end scission. The optimum temperature, toluene content, and the variation of molecular weight with time are consistent with earlier observations. A comprehensive model based on continuous distribution kinetics was developed to model these phenomena. The model accounts for simultaneous polymerization, degradation and enzyme deactivation and provides a technique to determine the rate coefficients for these processes. The dependence of these rate coefficients with temperature and monomer concentration is also discussed.

  4. Developing new methods for the mono-end functionalization of living ring opening metathesis polymers.

    Science.gov (United States)

    Kilbinger, Andreas F M

    2012-01-01

    In this article we present a review of our recent results in one area of research we are involved in. All research efforts in our group focus on functional polymers and new ways of gaining higher levels of control with regard to the placement of functional groups within these polymers. Here, the living ring opening metathesis polymerization (ROMP) will be reviewed for which end-functionalization methods had been rare until very recently. Polymers carrying particular functional groups only at the chain-ends are, however, very interesting for a variety of industrial and academic applications. Polymeric surfactants and polymer-protein conjugates are two examples for the former and polymer-β-sheet-peptide conjugates one example for the latter. The functionalization of macroscopic or nanoscopic surfaces often relies on mono-end functional polymers. Complex macromolecular architectures are often constructed from macromolecules carrying exactly one functional group at their chain- end. The ring opening metathesis polymerization is particularly interesting in this context as it is one of the most functional group tolerant polymerization methods known. Additionally, high molecular weight polymers are readily accessible with this technique, a feature that living radical polymerizations often struggle to achieve. Finding new ways of functionalizing the polymer chain-end of ROMP polymers has therefore been a task long overdue. Here, we present our contribution to this area of research.

  5. Functionalization of multi-walled carbon nanotubes by epoxide ring-opening polymerization

    International Nuclear Information System (INIS)

    Jin Fanlong; Rhee, Kyong Yop; Park, Soo-Jin

    2011-01-01

    In this study, covalent functionalization of carbon nanotubes (CNTs) was accomplished by surface-initiated epoxide ring-opening polymerization. FT-IR spectra showed that polyether and epoxide group covalently attached to the sidewalls of CNTs. TGA results indicated that the polyether was successfully grown from the CNT surface, with the final products having a polymer weight percentage of ca. 14–74 wt%. The O/C ratio of CNTs increased significantly from 5.1% to 29.8% after surface functionalization of CNTs. SEM and TEM images of functionalized CNTs exhibited that the tubes were enwrapped by polymer chains with thickness of several nanometers, forming core–shell structures with CNTs at the center. - Graphical abstract: Functionalized CNTs were enwrapped by polymer chains with thickness of several nanometers, forming core–shell structures with CNTs at the center. Highlights: ► CNTs were functionalized by epoxide ring-opening polymerization. ► Polyether and epoxide group covalently attached to the sidewalls of CNTs. ► Functionalized CNTs have a polymer weight percentage of ca. 14–74 wt%. ► Functionalized CNTs were enwrapped by polymer chains with thickness of several nanometers.

  6. The functional outcome of surgically treated unstable pelvic ring fractures by open reduction, internal fixation

    Directory of Open Access Journals (Sweden)

    Kaykhosro Mardanpour

    2011-07-01

    Full Text Available Background:Unstable Pelvic fracture,a result of high energy antero-posterior compression injury, has been managed based on internal fixation and open reduction. The mode of fixation in Unstable Pelvic fracture has, however, been a subject of controversy and some authors have proposed a need to address the issue of partial breach of the pelvic ring elements in these injuries. This study was performed to evaluate the functional and radiological results of treatment of pelvic ring fractures by open reduction, internal fixation. Methods: Thirty eight patients with unstable pelvic fractures, treated from 2002 to2008 were retrospectively reviewed. The mean age of patients’ was 37 years old (range 20 to 67. Twenty six patients were men and 12 women. The most common cause was a road traffic accident (N=37, 97%. There were 11 type-C and 27 type-B fractures according to Tile’s classification. Thirty six patients sustained additional injuries. The most prevalent additional injuries were lower extremity fractures. Open reduction, internal fixation as a definite management was applied for all patients. Quality of reduction was graded according to the grades proposed by Matta and Majeed’s score was used to assess the clinical outcome. The mean period of follow-up was 25 months (ranged from 6 to 109 months. About 81.6% of patients had either good or excellent radiological reduction. Results: The functional outcome was excellent in 66%, good in 15%, fair in 11% and poor in 7% of the patients. There were 4 postoperative infections. No sexual function problem was reported. Nerve deficits recovered completely in 2 and partially in 3 of 11 patients with preoperative neurologic deficiency. There was no significant relation between functional outcome and the site of fracture Conclusion: Unstable pelvic ring fracture injuries should be managed surgically by rigid stabilization that must be carried out as soon as the general ndition of the patient permits, and

  7. Retention of Plasmodium falciparum ring-infected erythrocytes in the slow, open microcirculation of the human spleen.

    Science.gov (United States)

    Safeukui, Innocent; Correas, Jean-Michel; Brousse, Valentine; Hirt, Déborah; Deplaine, Guillaume; Mulé, Sébastien; Lesurtel, Mickael; Goasguen, Nicolas; Sauvanet, Alain; Couvelard, Anne; Kerneis, Sophie; Khun, Huot; Vigan-Womas, Inès; Ottone, Catherine; Molina, Thierry Jo; Tréluyer, Jean-Marc; Mercereau-Puijalon, Odile; Milon, Geneviève; David, Peter H; Buffet, Pierre A

    2008-09-15

    The current paradigm in Plasmodium falciparum malaria pathogenesis states that young, ring-infected erythrocytes (rings) circulate in peripheral blood and that mature stages are sequestered in the vasculature, avoiding clearance by the spleen. Through ex vivo perfusion of human spleens, we examined the interaction of this unique blood-filtering organ with P falciparum-infected erythrocytes. As predicted, mature stages were retained. However, more than 50% of rings were also retained and accumulated upstream from endothelial sinus wall slits of the open, slow red pulp microcirculation. Ten percent of rings were retained at each spleen passage, a rate matching the proportion of blood flowing through the slow circulatory compartment established in parallel using spleen contrast-enhanced ultrasonography in healthy volunteers. Rings displayed a mildly but significantly reduced elongation index, consistent with a retention process, due to their altered mechanical properties. This raises the new paradigm of a heterogeneous ring population, the less deformable subset being retained in the spleen, thereby reducing the parasite biomass that will sequester in vital organs, influencing the risk of severe complications, such as cerebral malaria or severe anemia. Cryptic ring retention uncovers a new role for the spleen in the control of parasite density, opening novel intervention opportunities.

  8. Zirconium(IV)-Catalyzed Ring Opening of on-DNA Epoxides in Water.

    Science.gov (United States)

    Fan, Lijun; Davie, Christopher P

    2017-05-04

    DNA-encoded library technology (ELT) has spurred wide interest in the pharmaceutical industry as a powerful tool for hit and lead generation. In recent years a number of "DNA-compatible" chemical modifications have been published and used to synthesize vastly diverse screening libraries. Herein we report a newly developed, zirconium tetrakis(dodecyl sulfate) [Zr(DS) 4 ] catalyzed ring-opening of on-DNA epoxides in water with amines, including anilines. Subsequent cyclization of the resulting on-DNA β-amino alcohols leads to a variety of biologically interesting, nonaromatic heterocycles. Under these conditions, a library of 137 million on-DNA β-amino alcohols and their cyclization products was assembled. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Ring-opening polymerization of ω-pentadecalactone catalyzed by phosphazene superbases

    KAUST Repository

    Ladelta, Viko

    2016-12-12

    A fast and living ring-opening polymerization (ROP) of ω-pentadecalactone (PDL), a representative monomer of macrolactones, was achieved using a primary alcohol as the initiator and t-BuP or t-octP as the catalyst. The use of t-BuP instead of the t-BuP superbase slows down the polymerization rate. The ROP of PDL proceeds to high conversion not only at 80 °C in bulk but also at room temperature and in dilute solution. The synthesized PDL homopolymers and block copolymers with poly(ethylene glycol) were characterized by high-temperature GPC (HT-GPC), H NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Melting temperatures, determined by differential scanning calorimetry, are also reported.

  10. Compact and Wide Stopband Lowpass Filter Using Open Complementary Split Ring Resonator and Defected Ground Structure

    Directory of Open Access Journals (Sweden)

    S. S. Karthikeyan

    2015-09-01

    Full Text Available A compact (0.16 λg x 0.08 λg and wide stop¬band lowpass filter design using open complementary split ring resonator (OCSRR and defected ground structure (DGS is presented in this paper. Low pass filter is con-structed using two cascaded stages of OCSRR. Since the rejection bandwidth of the OCSRR is narrow, tapered dumbbell shaped DGS section is placed under the OCSRR to enhance the bandwidth. The cutoff frequency (fc of the proposed lowpass filter is 1.09 GHz. The rejection band¬width of the filter covers the entire ultra wideband spec¬trum. Hence the spurious passband suppression is achieved up to 10 fc. The designed filter has been fabri¬cated and validated by experimental results

  11. Highly conductive, transparent flexible films based on open rings of multi-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Ko, Wen-Yin; Su, Jun-Wei; Guo, Chian-Hua; Fu, Shu-Juan; Hsu, Chuen-Yuan; Lin, Kuan-Jiuh

    2011-01-01

    Open rings of multi-walled carbon nanotubes were stacked to form porous networks on a poly(ethylene terephthalate) substrate to form a flexible conducting film (MWCNT-PET) with good electrical conductivity and transparency by a combination of ultrasonic atomization and spin-coating technique. To enhance the electric flexibility, we spin-coated a cast film of poly(vinyl alcohol) onto the MWCNT-PET substrate, which then underwent a thermo-compression process. Field-emission scanning electron microscopy of the cross-sectional morphology illustrates that the film has a robust network with a thickness of ∼ 175 nm, and it remarkably exhibits a sheet resistance of approximately 370 Ω/sq with ∼ 77% transmittance at 550 nm even after 500 bending cycles. This electrical conductivity is much superior to that of other MWCNT-based transparent flexible films.

  12. Nitroxide-mediated radical ring-opening copolymerization: chain-end investigation and block copolymer synthesis.

    Science.gov (United States)

    Delplace, Vianney; Harrisson, Simon; Tardy, Antoine; Gigmes, Didier; Guillaneuf, Yohann; Nicolas, Julien

    2014-02-01

    Well-defined, degradable copolymers are successfully prepared by nitroxide-mediated radical ring opening polymerization (NMrROP) of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) or methyl methacrylate (MMA), a small amount of acrylonitrile (AN) and cyclic ketene acetals (CKAs) of different structures. Phosphorous nuclear magnetic resonance allows in-depth chain-end characterization and gives crucial insights into the nature of the copoly-mer terminal sequences and the living chain fractions. By using a small library of P(OEGMA-co-AN-co-CKA) and P(MMA-co-AN-co-CKA) as macroinitiators, chain extensions with styrene are performed to furnish (amphiphilic) block copolymers comprising a degradable segment. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Ring-opening polymerization of ω-pentadecalactone catalyzed by phosphazene superbases

    KAUST Repository

    Ladelta, Viko; Bilalis, Panayiotis; Gnanou, Yves; Hadjichristidis, Nikolaos

    2016-01-01

    A fast and living ring-opening polymerization (ROP) of ω-pentadecalactone (PDL), a representative monomer of macrolactones, was achieved using a primary alcohol as the initiator and t-BuP or t-octP as the catalyst. The use of t-BuP instead of the t-BuP superbase slows down the polymerization rate. The ROP of PDL proceeds to high conversion not only at 80 °C in bulk but also at room temperature and in dilute solution. The synthesized PDL homopolymers and block copolymers with poly(ethylene glycol) were characterized by high-temperature GPC (HT-GPC), H NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Melting temperatures, determined by differential scanning calorimetry, are also reported.

  14. Recent Advances in Ring-Opening Functionalization of Cycloalkanols by C-C σ-Bond Cleavage.

    Science.gov (United States)

    Wu, Xinxin; Zhu, Chen

    2018-06-01

    Cycloalkanols prove to be privileged precursors for the synthesis of distally substituted alkyl ketones and polycyclic aromatic hydrocarbons (PAHs) by virtue of cleavage of their cyclic C-C bonds. Direct functionalization of cyclobutanols to build up other chemical bonds (e. g., C-F, C-Cl, C-Br, C-N, C-S, C-Se, C-C, etc.) has been achieved by using the ring-opening strategy. Mechanistically, the C-C cleavage of cyclobutanols can be involved in two pathways: (a) transition-metal catalyzed β-carbon elimination; (b) radical-mediated 'radical clock'-type ring opening. The recent advances of our group for the ring-opening functionalization of tertiary cycloalkanols are described in this account. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Highly Active N,O Zinc Guanidine Catalysts for the Ring-Opening Polymerization of Lactide.

    Science.gov (United States)

    Schäfer, Pascal M; Fuchs, Martin; Ohligschläger, Andreas; Rittinghaus, Ruth; McKeown, Paul; Akin, Enver; Schmidt, Maximilian; Hoffmann, Alexander; Liauw, Marcel A; Jones, Matthew D; Herres-Pawlis, Sonja

    2017-09-22

    New zinc guanidine complexes with N,O donor functionalities were prepared, characterized by X-Ray crystallography, and examined for their catalytic activity in the solvent-free ring-opening polymerization (ROP) of technical-grade rac-lactide at 150 °C. All complexes showed a high activity. The fastest complex [ZnCl 2 (DMEGasme)] (C1) produced colorless poly(lactide) (PLA) after 90 min with a conversion of 52 % and high molar masses (M w =69 100, polydispersity=1.4). The complexes were tested with different monomer-to-initiator ratios to determine the rate constant k p . Furthermore, a polymerization with the most active complex C1 was monitored by in situ Raman spectroscopy. Overall, conversion of up to 90 % can be obtained. End-group analysis was performed to clarify the mechanism. All four complexes combine robustness against impurities in the lactide with high polymerization rates, and they represent the fastest robust lactide ROP catalysts to date, opening new avenues to a sustainable ROP catalyst family for industrial use. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Cascade synthesis of chiral block copolymers combining lipase catalyzed ring opening polymerization and atom transfer radical polymerization

    NARCIS (Netherlands)

    Peeters, J.W.; Palmans, A.R.A.; Veld, M.A.J.; Scheijen, F.J.E.; Heise, A.; Meijer, E.W.

    2004-01-01

    The enantioselective polymerization of methyl-substituted -caprolactones using Novozym 435 as the catalyst was investigated. All substituted monomers could be polymerized except 6-methyl--caprolactone (6-MeCL), which failed to propagate after ring opening. Interestingly, an odd-even effect in the

  17. Phosphazene-promoted metal-free ring-opening polymerization of ethylene oxide initiated by carboxylic acid

    KAUST Repository

    Zhao, Junpeng; Pahovnik, David; Gnanou, Yves; Hadjichristidis, Nikolaos

    2014-01-01

    The effectiveness of carboxylic acid as initiator for the anionic ring-opening polymerization of ethylene oxide was investigated with a strong phosphazene base (t-BuP4) used as promoter. Kinetic study showed an induction period, i.e., transformation

  18. Lipase catalyzed HEMA initiated ring-opening polymerization: In situ formation of mixed polyester methacrylates by transesterification

    NARCIS (Netherlands)

    Takwa, M.; Xiao, Y.; Simpson, N.; Malmstrom, E.; Hult, K.; Koning, C.E.; Heise, A.; Martinelle, M.

    2008-01-01

    2-Hydroxyethyl methacrylate (HEMA) was used as initiator for the enzymatic ring-opening polymerization (ROP) of ¿-pentadecalactone (PDL) and e-caprolactone (CL). The lipase B from Candida antarctica was found to catalyze the cleavage of the ester bond in the HEMA end group of the formed polyesters,

  19. A quantitative approach to nucleophilic organocatalysis

    Directory of Open Access Journals (Sweden)

    Herbert Mayr

    2012-09-01

    Full Text Available The key steps in most organocatalytic cyclizations are the reactions of electrophiles with nucleophiles. Their rates can be calculated by the linear free-energy relationship log k(20 °C = sN(E + N, where electrophiles are characterized by one parameter (E and nucleophiles are characterized by the solvent-dependent nucleophilicity (N and sensitivity (sN parameters.Electrophilicity parameters in the range –10 E N N parameters of enamines derived from phenylacetaldehyde and MacMillan’s imidazolidinones one can rationalize why only strong electrophiles, such as stabilized carbenium ions (–8 E E = –6.75, are suitable electrophiles for enamine activated reactions with imidazolidinones. Several mechanistic controversies concerning iminium and enamine activated reactions could thus be settled by studying the reactivities of independently synthesized intermediates.Kinetic investigations of the reactions of N-heterocyclic carbenes (NHCs with benzhydrylium ions showed that they have similar nucleophilicities to common organocatalysts (e.g., PPh3, DMAP, DABCO but are much stronger (100–200 kJ mol–1 Lewis bases. While structurally analogous imidazolylidenes and imidazolidinylidenes have comparable nucleophilicities and Lewis basicities, the corresponding deoxy Breslow intermediates differ dramatically in reactivity. The thousand-fold higher nucleophilicity of 2-benzylidene-imidazoline relative to 2-benzylidene-imidazolidine is explained by the gain of aromaticity during electrophilic additions to the imidazoline derivatives. O-Methylated Breslow intermediates are a hundred-fold less nucleophilic than deoxy Breslow intermediates.

  20. Strategies to Fabricate Polypeptide-Based Structures via Ring-Opening Polymerization of N-Carboxyanhydrides

    Directory of Open Access Journals (Sweden)

    Carmen M. González-Henríquez

    2017-10-01

    Full Text Available In this review, we provide a general and clear overview about the different alternatives reported to fabricate a myriad of polypeptide architectures based on the ring-opening polymerization of N-carbonyanhydrides (ROP NCAs. First of all, the strategies for the preparation of NCA monomers directly from natural occurring or from modified amino acids are analyzed. The synthetic alternatives to prepare non-functionalized and functionalized NCAs are presented. Protection/deprotection protocols, as well as other functionalization chemistries are discussed in this section. Later on, the mechanisms involved in the ROP NCA polymerization, as well as the strategies developed to reduce the eventually occurring side reactions are presented. Finally, a general overview of the synthetic strategies described in the literature to fabricate different polypeptide architectures is provided. This part of the review is organized depending on the complexity of the macromolecular topology prepared. Therefore, linear homopolypeptides, random and block copolypeptides are described first. The next sections include cyclic and branched polymers such as star polypeptides, polymer brushes and highly branched structures including arborescent or dendrigraft structures.

  1. Novel Zinc-Catalytic Systems for Ring-Opening Polymerization of ε-Caprolactone

    Directory of Open Access Journals (Sweden)

    Karolina Żółtowska

    2015-02-01

    Full Text Available Polycaprolactone (PCL is a biodegradable synthetic polymer that is currently widely used in many pharmaceutical and medical applications. In this paper we describe the coordination ring-opening polymerization of ε-caprolactone in the presence of two newly synthesized catalytic systems: diethylzinc/gallic acid and diethylzinc/propyl gallate. The chemical structures of the obtained PCLs were characterized by 1H- or 13C-NMR, FTIR spectroscopy and MALDI TOF mass spectrometry. The average molecular weight of the resulting polyesters was analysed by gel permeation chromatography and a viscosity method. The effects of temperature, reaction time and type of catalytic system on the polymerization process were examined. Linear PCLs with defined average molecular weight were successfully obtained. Importantly, in some cases the presence of macrocyclic products was not observed during the polymerization process. This study provides an effective method for the synthesis of biodegradable polyesters for medical and pharmaceutical applications due to the fact that gallic acid/propyl gallate are commonly used in the pharmaceutical industry.

  2. A quantum dynamics study of the benzopyran ring opening guided by laser pulses

    Science.gov (United States)

    Saab, Mohamad; Doriol, Loïc Joubert; Lasorne, Benjamin; Guérin, Stéphane; Gatti, Fabien

    2014-10-01

    The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of strategies that could help experimentalists to control the photoreactivity vs. photostability ratio (selectivity). In this work we present: (i) a pump-dump technique used to control the photostability, (ii) a two-step strategy to enhance the reactivity of the system: first, a pure vibrational excitation in the electronic ground state that prepares the system and, second, an ultraviolet excitation that brings the system to the first adiabatic electronic state; (iii) finally the effect of a non-resonant pulse (Stark effect) on the dynamics.

  3. Phosphazene-catalyzed ring-opening polymerization of ε-caprolactone: Influence of solvents and initiators

    KAUST Repository

    Alamri, Haleema; Zhao, Junpeng; Pahovnik, David; Hadjichristidis, Nikolaos

    2014-01-01

    Phosphazene base (t-BuP2) catalysed metal-free ring-opening polymerization of ε-caprolactone (ε-CL) at room temperature with various protic initiators in different solvents was investigated. The polymerization proceeded, in most cases, in a controlled manner to afford poly(ε-caprolactone) with low dispersities and expected molecular weights. Kinetic studies showed that when a primary alcohol was used as an initiator the polymerization rate in different solvents followed the order of dichloromethane ≫ toluene > 1,4-dioxane ≈ tetrahydrofuran. Extremely fast polymerization of l-lactide (LLA), which was added as a second monomer, was observed in different solvents giving rise to poly(ε-caprolactone)-b- poly(l-lactide) diblock copolymers with neat PLLA blocks despite incomplete conversion of ε-CL. The dependence of polymerization rate on the concentrations of ε-CL and t-BuP2 was also revealed. In addition to primary alcohol, the feasibility of using other protic initiators, such as secondary alcohol (either on a small molecule or a polymer chain-end), (aliphatic/aromatic) amide, carboxylic acid, phenol and thiophenol, was also investigated. These studies provided important information for designing a metal-free route towards polyester-based (bio)materials. © 2014 the Partner Organisations.

  4. Comparative Theoretical Study of the Ring-Opening Polymerization of Caprolactam vs Caprolactone Using QM/MM Methods

    Energy Technology Data Exchange (ETDEWEB)

    Elsasser, Brigitta M.; Schoenen, Iris; Fels, Gregor

    2013-06-07

    Candida antarctica lipase B (CALB) efficiently catalyzes the ring-opening polymerization of lactones to high molecular weight products in good yield. In contrast, an efficient enzymatic synthesis of polyamides has so far not been described in the literature. This obvious difference in enzyme catalysis is the subject of our comparative study of the initial steps of a CALB catalyzed ring-opening polymerization of ε- caprolactone and ε-caprolactam. We have applied docking tools to generate the reactant state complex and performed quantum mechanical/molecular mechanical (QM/MM) calculations at the density functional theory (DFT) PBE0 level of theory to simulate the acylation of Ser105 by the lactone and the lactam, respectively, via the corresponding first tetrahedral intermediates. We could identify a decisive difference in the accessibility of the two substrates in the ring-opening to the respective acyl enzyme complex as the attack of ε-caprolactam is hindered because of an energetically disfavored proton transfer during this part of the catalytic reaction while ε-caprolactone is perfectly processed along the widely accepted pathway using the catalytic triade of Ser105, His224, and Asp187. Since the generation of an acylated Ser105 species is the crucial step of the polymerization procedure, our results give an explanation for the unsatisfactory enzymatic polyamide formation and opens up new possibilities for targeted rational catalyst redesign in hope of an experimentally useful CALB catalyzed polyamide synthesis.

  5. Evidence for concerted ring opening and C–Br bond breaking in UV-excited bromocyclopropane

    Energy Technology Data Exchange (ETDEWEB)

    Pandit, Shubhrangshu; Preston, Thomas J.; Orr-Ewing, Andrew J., E-mail: a.orr-ewing@bristol.ac.uk [School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS (United Kingdom); King, Simon J.; Vallance, Claire [Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA (United Kingdom)

    2016-06-28

    Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br{sup ∗}), and C{sub 3}H{sub 5} hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br{sup ∗} atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br{sup ∗} images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C{sub 3}H{sub 5} fragments have lower angular anisotropies than measured for Br and Br{sup ∗}, indicating molecular restructuring during dissociation. The high kinetic energy C{sub 3}H{sub 5} signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C–Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C{sub 3}H{sub 5} radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C{sub 3}H{sub 5}{sup +} from the photodissociation of the C{sub 3}H{sub 5}Br{sup +} molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

  6. In situ crosslinking of surface-initiated ring opening metathesis polymerization of polynorbornene for improved stability.

    Science.gov (United States)

    Fursule, Ishan A; Abtahi, Ashkan; Watkins, Charles B; Graham, Kenneth R; Berron, Brad J

    2018-01-15

    In situ crosslinking is expected to increase the solvent stability of coatings formed by surface-initiated ring opening metathesis polymerization (SI ROMP). Solvent-associated degradation limits the utility of SI ROMP coatings. SI ROMP coatings have a unique capacity for post-functionalization through reaction of the unsaturated site on the polymer backbone. Any post-reaction scheme which requires a liquid solvent has the potential to degrade the coating and lower the thickness of the resulting film. We designed a macromolecular crosslinking group based on PEG dinorbornene. The PEG length is tailored to the expected mean chain to chain distance during surface-initiated polymerization. This crosslinking macromer is randomly copolymerized with norbornene through SI ROMP on a gold coated substrate. The solvent stability of polynorbornene coatings with and without PEG dinorbornene is quantitatively determined, and the mechanism of degradation is further supported through XPS and AFM analyses. The addition of the 0.25mol% PEG dinorbornene significantly increases the solvent stability of the SI ROMP coatings. The crosslinker presence in the more stable films is supported with observable PEG absorbances by FTIR and an increase in contact angle hysteresis when compared to non-crosslinked coatings. The oxidation of the SI ROMP coatings is supported by the observation of carbonyl oxygen in the polynorbornene coatings. The rapid loss of the non-crosslinked SI ROMP coating corresponds to nanoscale pitting across the surface and micron-scale regions of widespread film loss. The crosslinked coatings have uniform nanoscale pitting, but the crosslinked films show no evidence of micron-scale film damage. In all, the incorporation of minimal crosslinking content is a simple strategy for improving the solvent stability of SI ROMP coatings. Copyright © 2017 Elsevier Inc. All rights reserved.

  7. Evidence for concerted ring opening and C-Br bond breaking in UV-excited bromocyclopropane.

    Science.gov (United States)

    Pandit, Shubhrangshu; Preston, Thomas J; King, Simon J; Vallance, Claire; Orr-Ewing, Andrew J

    2016-06-28

    Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br(∗)), and C3H5 hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br(∗) atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br(∗) images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C3H5 fragments have lower angular anisotropies than measured for Br and Br(∗), indicating molecular restructuring during dissociation. The high kinetic energy C3H5 signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C-Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C3H5 radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C3H5 (+) from the photodissociation of the C3H5Br(+) molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

  8. Chemicals from Biomass: Combining Ring-Opening Tautomerization and Hydrogenation Reactions to Produce 1,5-Pentanediol from Furfural.

    Science.gov (United States)

    Brentzel, Zachary J; Barnett, Kevin J; Huang, Kefeng; Maravelias, Christos T; Dumesic, James A; Huber, George W

    2017-04-10

    A process for the synthesis of 1,5-pentanediol (1,5-PD) with 84 % yield from furfural is developed, utilizing dehydration/hydration, ring-opening tautomerization, and hydrogenation reactions. Although this process has more reaction steps than the traditional direct hydrogenolysis of tetrahydrofurfuryl alcohol (THFA), techno-economic analyses demonstrate that this process is the economically preferred route for the synthesis of biorenewable 1,5-PD. 2-Hydroxytetrahydropyran (2-HY-THP) is the key reaction pathway intermediate that allows for a decrease in the minimum selling price of 1,5-PD. The reactivity of 2-HY-THP is 80 times greater than that of THFA over a bimetallic hydrogenolysis catalyst. This enhanced reactivity is a result of the ring-opening tautomerization to 5-hydoxyvaleraldehyde and subsequent hydrogenation to 1,5-PD. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Ring opening of azetidine cycle: First examples of 1-azetidinepropanamine molecules as a template in hybrid organic-inorganic compounds

    Science.gov (United States)

    Gurzhiy, Vladislav V.; Tyumentseva, Olga S.; Britvin, Sergey N.; Krivovichev, Sergey V.; Tananaev, Ivan G.

    2018-01-01

    Three novel uranyl selenate and sulfate oxysalts templated by protonated azetidine molecules, [AzH]+, and its ring-opened counterpart 1-azetidinepropanamine, [AzH(CH2)3NH3]2+, have been prepared and studied by X-ray structural analysis. Conformations of azetidinium cations were analysed by means of infrared vibrational assignments supported by the DFT calculations. Crystallization of [AzH]2 [(UO2)2(SeO4)3(H2O)] (I) from highly acidic solutions suggests that low pH does not necessarily result in the opening of azetidine ring. [AzH(CH2)3NH3][(UO2)2(SeO4)3(H2O)](H2O) (II) and [AzH(CH2)3NH3](H5O2)[(UO2)2(SO4)3(HSO4)] (III) are the first structurally characterized crystalline compounds bearing isolated ring-opened azetidine moiety.

  10. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321){sup S} studied by density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Franke, J.-H.; Kosov, D. S. [Department of Physics, Campus Plaine - CP 231, Universite Libre de Bruxelles, 1050 Brussels (Belgium)

    2015-01-28

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  11. Si-Imidazole-HSO4 Functionalized Magnetic Fe3O4 Nanoparticles as an Efficient and Reusable Catalyst for the Regioselective Ring Opening of Epoxides in Water

    Directory of Open Access Journals (Sweden)

    Eshagh Rezaee Nezhad

    2016-01-01

    Full Text Available An efficient and simple method for the preparation of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs and used as an efficient and reusable magnetic catalysts for the regioselective ring opening of epoxides under green conditions in water. This catalyst was used for the ring opening of epoxide corresponding to the thiocyanohydrins and azidohydrines. Compared to the classical ring opening of epoxides, this new method consistently has the advantage of excellent yields, short reaction times, and methodological simplicity.

  12. Ring transformations of heterocyclic halogeno compounds with nucleophiles. 39

    NARCIS (Netherlands)

    Geerts, J.P.; Plas, van der H.C.

    1978-01-01

    Treatment of 4-chloro-2-dimethylaminopyrimidine (1a) and its 5-phenyl derivative (1b) with potassium amide in liquid ammonia and subsequent workup of the reaction mixtures lead to the formation of 2-dimethylamino-4-methyl-s-triazine and 4-benzyl-2-dimethylamino-s-triazine, respectively. By extensive

  13. New insights into the by-product fatigue mechanism of the photo-induced ring-opening in diarylethenes.

    Science.gov (United States)

    Mendive-Tapia, David; Perrier, Aurélie; Bearpark, Michael J; Robb, Michael A; Lasorne, Benjamin; Jacquemin, Denis

    2014-09-14

    The photochromic properties of diarylethenes, some of the most studied class of molecular switches, are known to be controlled by non-adiabatic decay at a conical intersection seam. Nevertheless, as their fatigue-reaction mechanism - leading to non-photochromic products - is yet to be understood, we investigate the photo-chemical formation of the so-called by-product isomer using three complementary computational methods (MMVB, CASSCF and CASPT2) on three model systems of increasing complexity. We show that for the ring-opening reaction a transition state on S1(2A) involving bond breaking of the penta-ring leads to a low energy S1(2A)/S0(1A) conical intersection seam, which lies above one of the transition states leading to the by-product isomer on the ground state. Therefore, radiationless decay and subsequent side-product formation can take place explaining the photo-degradation responsible for the by-product generation in diarylethene-type molecules. The effect of dynamic electron correlation and the possible role of inter-system crossing along the penta-ring opening coordinate are discussed as well.

  14. Ring-Opening Polymerization of N-Carboxyanhydrides for Preparation of Polypeptides and Polypeptide-Based Hybrid Materials with Various Molecular Architectures

    KAUST Repository

    Pahovnik, David; Hadjichristidis, Nikolaos

    2015-01-01

    Different synthetic approaches utilizing ring-opening polymerization of N-carboxyanhydrides for preparation of polypeptide and polypeptide-based hybrid materials with various molecular architectures are described. An overview of polymerization

  15. Revisiting the Fully Automated Double-Ring Infiltrometer Using Open-Source Electronics

    Science.gov (United States)

    The double-ring infiltrometer (DRI) is commonly used for measuring soil hydraulic conductivity. However, constant-head DRI tests typically involve the use of Mariotte tubes, which can be problematic to set-up, and time-consuming to maintain and monitor during infiltration tests....

  16. Nucleophilic difluoromethylation and difluoromethylenation of aldehydes

    Czech Academy of Sciences Publication Activity Database

    Beier, Petr; Alexandrova, Anastasia; Zibinsky, M.; Prakash, G. K. S.

    2008-01-01

    Roč. 64, č. 49 (2008), s. 10977-10985 ISSN 0040-4020 R&D Projects: GA ČR GP203/08/P310 Institutional research plan: CEZ:AV0Z40550506 Keywords : difluoromethylation * difluoromethylenation * phosphonate * nucleophilic addition Subject RIV: CC - Organic Chemistry Impact factor: 2.897, year: 2008

  17. An Approach to Preparation of trans-DHQs via Ring-Opening of meso-N-Sulfonylaziridines

    DEFF Research Database (Denmark)

    Nolsøe, Jens Mortansson Jelstrup; Riegert, David; Müller, Paul

    2011-01-01

    As an approach to the enantioselective synthesis of trans-decahydroquinolines (DHQs), desymmetrization of meso-aziridine (5) with various carbon nucleophiles under catalytic conditions was investigated. By applying TMSCN in the presence of YbCl3 and chiral nonracemic ligands, nitrile 13 was obtai......As an approach to the enantioselective synthesis of trans-decahydroquinolines (DHQs), desymmetrization of meso-aziridine (5) with various carbon nucleophiles under catalytic conditions was investigated. By applying TMSCN in the presence of YbCl3 and chiral nonracemic ligands, nitrile 13...

  18. YCl3-Catalyzed Highly Selective Ring Opening of Epoxides by Amines at Room Temperature and under Solvent-Free Conditions

    Directory of Open Access Journals (Sweden)

    Wuttichai Natongchai

    2017-11-01

    Full Text Available A simple, efficient, and environmentally benign approach for the synthesis of β-amino alcohols is herein described. YCl3 efficiently carried out the ring opening of epoxides by amines to produce β-amino alcohols under solvent-free conditions at room temperature. This catalytic approach is very effective, with several aromatic and aliphatic oxiranes and amines. A mere 1 mol % concentration of YCl3 is enough to deliver β-amino alcohols in good to excellent yields with high regioselectivity.

  19. Synthesis and Ring-Opening Metathesis Polymerization of Second-Generation Dendronized Poly(ether Monomers Initiated by Ruthenium Carbenes

    Directory of Open Access Journals (Sweden)

    Guzmán Pablo E.

    2016-03-01

    Full Text Available The Ring-Opening Metathesis Polymerization (ROMP of second-generation dendronized monomers is described. Using the highly active and fast-initiating third-generation ruthenium complex [(H2IMes(pyr2Cl2RuCHPh], moderate to high molecular weight polymers (430-2230 kDa are efficiently synthesized with low dispersities (Ð = 1.01-1.17. This study highlights the power of the metathesis approach toward polymer synthesis in a context where monomer structure can significantly impede polymerization.

  20. Simulation studies of a new 'OpenPET' geometry based on a quad unit of detector rings

    Energy Technology Data Exchange (ETDEWEB)

    Yamaya, Taiga; Yoshida, Eiji; Nishikido, Fumihiko; Shibuya, Kengo; Inadama, Naoko; Murayama, Hideo [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan); Inaniwa, Taku [Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan)], E-mail: taiga@nirs.go.jp

    2009-03-07

    We have proposed an 'OpenPET' geometry which consists of two detector rings of axial length W each axially separated by a gap G. In order to obtain an axially continuous field-of-view (FOV) of 2W+G, the maximum limit for G must be W. However, two valleys of sensitivity appear, one on each side of the gap. In practice, the gap should be Grings obtained by dividing each right and left unit of detector rings into two units. The inner two units formed the main gap, and the outer two units were appropriately placed to improve the uniformity of sensitivity. The geometry was optimized to minimize the standard deviation of the sensitivity distribution. Numerical simulation results supported the effectiveness of the proposed method. The outer units compensated for the sensitivity valleys on both sides of the main gap. A more appropriate geometry should be designed for the desired application, such as a long axial FOV PET and in-beam PET.

  1. A novel report on Eosin Y functionalized MWCNT as an initiator for ring opening polymerization of {epsilon}-caprolactone

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Hung-Hsia; Anbarasan, R.; Kuo, Long-Sheng [MEMS Thermal Control Lab, Department of Mechanical Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Chen, Ping-Hei, E-mail: phchen@ntu.edu.tw [MEMS Thermal Control Lab, Department of Mechanical Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2011-04-15

    Research highlights: {yields} In the present investigation, first, we functionalized the MWCNT with Eosin Y dye, for the ring opening polymerization. {yields} The dye functionalized MWCNT acted as an effective initiator which was further confirmed by various analytical techniques. {yields} By this methodology we saved the number of reaction steps, reaction time and also an economically cheaper one. - Abstract: This research conducted ring opening polymerization (ROP) of {epsilon}-caprolactone (C.L.) with a novel initiator, namely; Eosin Y functionalized multiwalled carbon nanotube (MWCNT) at 140 deg. C with nitrogen sparge under different concentrations. ROP of C.L. carried out at two different experimental conditions similar to variations in [M{sub 0}/I{sub 0}] and [C.L.]. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of MWCNT-Eosin Y initiated ROP of C.L. Gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) further characterized the structure. UV-visible spectroscopy determined the binding constant (K), for samples prepared under different [C.L.].

  2. A novel report on Eosin Y functionalized MWCNT as an initiator for ring opening polymerization of ε-caprolactone

    International Nuclear Information System (INIS)

    Chen, Hung-Hsia; Anbarasan, R.; Kuo, Long-Sheng; Chen, Ping-Hei

    2011-01-01

    Research highlights: → In the present investigation, first, we functionalized the MWCNT with Eosin Y dye, for the ring opening polymerization. → The dye functionalized MWCNT acted as an effective initiator which was further confirmed by various analytical techniques. → By this methodology we saved the number of reaction steps, reaction time and also an economically cheaper one. - Abstract: This research conducted ring opening polymerization (ROP) of ε-caprolactone (C.L.) with a novel initiator, namely; Eosin Y functionalized multiwalled carbon nanotube (MWCNT) at 140 deg. C with nitrogen sparge under different concentrations. ROP of C.L. carried out at two different experimental conditions similar to variations in [M 0 /I 0 ] and [C.L.]. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of MWCNT-Eosin Y initiated ROP of C.L. Gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) further characterized the structure. UV-visible spectroscopy determined the binding constant (K), for samples prepared under different [C.L.].

  3. Utilizing the σ-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides

    Directory of Open Access Journals (Sweden)

    Magnus Liljenberg

    2013-04-01

    Full Text Available A computational approach using density functional theory to compute the energies of the possible σ-complex reaction intermediates, the “σ-complex approach”, has been shown to be very useful in predicting regioselectivity, in electrophilic as well as nucleophilic aromatic substitution. In this article we give a short overview of the background for these investigations and the general requirements for predictive reactivity models for the pharmaceutical industry. We also present new results regarding the reaction rates and regioselectivities in nucleophilic substitution of fluorinated aromatics. They were rationalized by investigating linear correlations between experimental rate constants (k from the literature with a theoretical quantity, which we call the sigma stability (SS. The SS is the energy change associated with formation of the intermediate σ-complex by attachment of the nucleophile to the aromatic ring. The correlations, which include both neutral (NH3 and anionic (MeO− nucleophiles are quite satisfactory (r = 0.93 to r = 0.99, and SS is thus useful for quantifying both global (substrate and local (positional reactivity in SNAr reactions of fluorinated aromatic substrates. A mechanistic analysis shows that the geometric structure of the σ-complex resembles the rate-limiting transition state and that this provides a rationale for the observed correlations between the SS and the reaction rate.

  4. Monitoring conical intersections in the ring opening of furan by attosecond stimulated X-ray Raman spectroscopy

    Directory of Open Access Journals (Sweden)

    Weijie Hua

    2016-03-01

    Full Text Available Attosecond X-ray pulses are short enough to capture snapshots of molecules undergoing nonadiabatic electron and nuclear dynamics at conical intersections (CoIns. We show that a stimulated Raman probe induced by a combination of an attosecond and a femtosecond pulse has a unique temporal and spectral resolution for probing the nonadiabatic dynamics and detecting the ultrafast (∼4.5 fs passage through a CoIn. This is demonstrated by a multiconfigurational self-consistent-field study of the dynamics and spectroscopy of the furan ring-opening reaction. Trajectories generated by surface hopping simulations were used to predict Attosecond Stimulated X-ray Raman Spectroscopy signals at reactant and product structures as well as representative snapshots along the conical intersection seam. The signals are highly sensitive to the changes in nonadiabatically coupled electronic structure and geometry.

  5. Phosphazene-promoted metal-free ring-opening polymerization of ethylene oxide initiated by carboxylic acid

    KAUST Repository

    Zhao, Junpeng

    2014-03-11

    The effectiveness of carboxylic acid as initiator for the anionic ring-opening polymerization of ethylene oxide was investigated with a strong phosphazene base (t-BuP4) used as promoter. Kinetic study showed an induction period, i.e., transformation of carboxylic acid to hydroxyl ester, followed by slow chain growth together with simultaneous and fast end-group transesterification, which led to poly(ethylene oxide) (PEO) consisting of monoester (monohydroxyl), diester, and dihydroxyl species. An appropriate t-BuP4/acid ratio was proven to be essential to achieve better control over the polymerization and low dispersity of PEO. This work provides important information and enriches the toolbox for macromolecular and biomolecular engineering with protic initiating sites. © 2014 American Chemical Society.

  6. A Rectangular Ring, Open-Ended Monopole Antenna with Two Symmetric Strips for WLAN and WiMAX Applications

    Directory of Open Access Journals (Sweden)

    Joong-Han Yoon

    2013-01-01

    Full Text Available A triple-band rectangular ring, open-ended monopole antenna with symmetric L strips for wireless local area network (WLAN/Worldwide Interoperability of Microwave Access (WiMAX applications is proposed. The proposed antenna consists of two symmetric folded arms and L strips. Based on the concept, a prototype of the proposed triple antenna has been designed, fabricated, and tested. The numerical and experimental results demonstrated that the proposed antenna satisfied the −10 dB impedance bandwidth requirement while simultaneously covering the WLAN and WiMAX bands. Furthermore, this paper presented and discussed the 2D radiation patterns and 3D gains according to the results of the experiment. The proposed antenna’s peak gain varied between 2.17 and 4.93 dBi, and its average gain varied between −2.97 and −0.53 dBi.

  7. A New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Esters

    KAUST Repository

    Varghese, Jobi K.; Goncalves, Theo; Huang, Kuo-Wei; Hadjichristidis, Nikolaos; Gnanou, Yves; Feng, Xiaoshuang

    2017-01-01

    Conventional anionic ring-opening of polymerization (AROP) of cyclic esters suffers from the nonselective and concomitant attack of the monomer and of the polymer chains by the growing active species, which results in polyester samples with uncontrolled molar masses and broad polydispersity due to the competition between propagation and transesterification reactions. In this report, we describe a new AROP system mediated by a controlled amount of CO2 which prevents transesterification reactions from occurring. Using lithium monomethyl diethylene glycoxide (MEEOLi) as initiator and 1.5 equiv of CO2, ε-caprolactone could be polymerized under truly “living” conditions in dichloromethane (DCM) at 70 °C, as evidenced by the control of molar masses, the narrow polydispersity indexes (Mn up to ∼40 kg/mol, Đ < 1.16), and also successful chain extension experiments. Lithium carbonate used as initiator in the presence of 0.5 equiv of CO2 afforded similar polymerization results. Experiments carried out with other alkoxide salts and solvents demonstrate that CO2 is indispensable as well as lithium and noncoordinating solvents for the suppression of transesterifications. A similar strategy was applied for the AROP of l-lactide (LLA). At −20 °C, LLA could be polymerized under living conditions with undetectable level of transesterification as demonstrated by MALDI-ToF analysis. To account for the polymerization mechanism occurring in the presence of a slight excess of CO2, we resorted to computational studies. It appears that a fast equilibrium takes place between two tetrameric aggregates, one dormant comprising four carbonates (RCO3Li)4, and an active one involving three carbonates and one alkoxide (RCO3Li)3(ROLi). The latter is shown to selectively ring-open cyclic ester without indulging in transesterifications like (ROLi)4 precursors.

  8. A New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Esters

    KAUST Repository

    Varghese, Jobi K.

    2017-08-15

    Conventional anionic ring-opening of polymerization (AROP) of cyclic esters suffers from the nonselective and concomitant attack of the monomer and of the polymer chains by the growing active species, which results in polyester samples with uncontrolled molar masses and broad polydispersity due to the competition between propagation and transesterification reactions. In this report, we describe a new AROP system mediated by a controlled amount of CO2 which prevents transesterification reactions from occurring. Using lithium monomethyl diethylene glycoxide (MEEOLi) as initiator and 1.5 equiv of CO2, ε-caprolactone could be polymerized under truly “living” conditions in dichloromethane (DCM) at 70 °C, as evidenced by the control of molar masses, the narrow polydispersity indexes (Mn up to ∼40 kg/mol, Đ < 1.16), and also successful chain extension experiments. Lithium carbonate used as initiator in the presence of 0.5 equiv of CO2 afforded similar polymerization results. Experiments carried out with other alkoxide salts and solvents demonstrate that CO2 is indispensable as well as lithium and noncoordinating solvents for the suppression of transesterifications. A similar strategy was applied for the AROP of l-lactide (LLA). At −20 °C, LLA could be polymerized under living conditions with undetectable level of transesterification as demonstrated by MALDI-ToF analysis. To account for the polymerization mechanism occurring in the presence of a slight excess of CO2, we resorted to computational studies. It appears that a fast equilibrium takes place between two tetrameric aggregates, one dormant comprising four carbonates (RCO3Li)4, and an active one involving three carbonates and one alkoxide (RCO3Li)3(ROLi). The latter is shown to selectively ring-open cyclic ester without indulging in transesterifications like (ROLi)4 precursors.

  9. Preparation of open tubular capillary columns by in situ ring-opening polymerization and their applications in cLC-MS/MS analysis of tryptic digest.

    Science.gov (United States)

    Wang, Hongwei; Yao, Yating; Li, Ya; Ma, Shujuan; Peng, Xiaojun; Ou, Junjie; Ye, Mingliang

    2017-08-01

    An open tubular (OT) column (25 μm i.d.) was prepared by in situ ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxanes (POSS-epoxy) with 4-aminophenyl disulfide (APDS) in a binary porogenic system of ethanol/H 2 O. It was found that porogenic composition played an important role in the formation of OT stationary phases. The ratio of ethanol/H 2 O at 6/1 (v/v) would lead to the fabrication of hybrid monoliths, while the ratio of ethanol/H 2 O at 13/1 (v/v) would result in the synthesis of OT phases. In addition, the effects of precursor content and reaction duration on the thickness of OT stationary phases were investigated. Either lower precursor content or shorter reaction duration would produce thinner layer of OT column. The repeatability of OT columns was evaluated through relative standard deviation (RSD%) with benzene as the analyte. The run-to-run, column-to-column and batch-to-batch repeatabilities were 1.7%, 4.8% and 5.6%, respectively, exhibiting satisfactory repeatability of the OT column. Then tryptic digest of mouse liver proteins was used to evaluate the performance of the resulting OT columns (25 μm i.d. × 2.5 m in length) by cLC-MS/MS analysis, demonstrating their potential in proteome analysis. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. A detailed kinetic study of the direct ring opening of cyclohexane and methylcyclohexane over monofunctional Ir/Al{sub 2}O{sub 3} catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Hui; Gutierrez, O.Y.; Lercher, J.A. [Technische Univ. Muenchen (Germany). Catalysis Research Center

    2011-07-01

    The present study analyses a series of Al{sub 2}O{sub 3}-supported iridium catalysts with different pretreatments and addresses the kinetic features and structural requirements of direct ring opening of cyclohexane and methylcyclohexane catalyzed by Ir in absence of acid-catalyzed ring contraction. Mild reaction conditions and high H{sub 2}/hydrocarbon ratios (200-1000) were used to improve accuracy of kinetic measurements and to negate deactivation. Isomerization and dehydrogenation pathways were suppressed to low extents (1-5%) over the weakly acidic catalysts under the reaction conditions applied. Three main observations are shown: 1) initial selectivity to ring opening products (ROPs) increases with iridium dispersion; 2) optimal H{sub 2} pressures differ not only between primary and secondary products, but also among ROPs and fragments; 3) the air-calcination step before catalyst reduction imposes a significant impact on both activity and product distribution. (orig.)

  11. Metal-​based catalysts for controlled ring-​opening polymerization of macrolactones : high molecular weight and well-​defined copolymer architectures

    NARCIS (Netherlands)

    Bouyahyi, M.; Duchateau, R.

    2014-01-01

    This contribution describes our recent results regarding the metal-¿catalyzed ring-¿opening polymn. of pentadecalactone and its copolymn. with e-¿caprolactone involving single-¿site metal complexes based on aluminum, zinc, and calcium. Under the right conditions (i.e., monomer concn., catalyst type,

  12. Fast and Living Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides Triggered by an "Alliance" of Primary and Secondary Amines at Room Temperature

    KAUST Repository

    Zhao, Wei

    2015-04-13

    A novel highly efficient strategy, based on an "alliance" of primary and secondary amine initiators, was successfully developed allowing the fast and living ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) at room temperature. (Chemical Equation Presented). © 2015 American Chemical Society.

  13. Fast and Living Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides Triggered by an "Alliance" of Primary and Secondary Amines at Room Temperature

    KAUST Repository

    Zhao, Wei; Gnanou, Yves; Hadjichristidis, Nikolaos

    2015-01-01

    A novel highly efficient strategy, based on an "alliance" of primary and secondary amine initiators, was successfully developed allowing the fast and living ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) at room temperature. (Chemical Equation Presented). © 2015 American Chemical Society.

  14. Effects of the Amount and Type of Diol Ring Openers on the Properties of Oligolactide Acrylates for UV-Curable Printing Inks

    Directory of Open Access Journals (Sweden)

    Santi Kulsiriswad

    2017-10-01

    Full Text Available This study aimed to synthesize low viscosity oligolactide acrylates for UV-curable inks from oligolactide diols. Firstly, low molecular weight oligolactide diols were prepared by ring opening reaction of L-lactide with diols. Oligolactide acrylates were then synthesized by functionalizing the oligolactide diols with acrylic acid. In this study, three diol ring openers having short and long alkyl chain length were used to investigate the effects of the amount and type of diols on the properties of the oligolactide acrylates. The obtained oligomers were characterized, and the viscosities of oligolactide acrylates were measured. Results showed that oligolactide acrylates were successfully synthesized in all cases of ring openers, as confirmed by 1H-NMR (proton nuclear magnetic resonance spectroscopy and FTIR (Fourier transform infrared spectroscopy. An increase in the alkyl chain length of the ring openers resulted in oligomers with lower viscosity and a decrease in Tg. Following that, the obtained oligolactide acrylates were employed for the formulation of UV-curable screen printing inks and their properties were investigated. Results showed that the inks formulated from oligomers with lower molecular weight exhibited better ink flow. Additionally, all ink films cured by UV radiation were very flexible with excellent adhesion, high impact resistance, and excellent water resistance.

  15. Photophysical property of rhodamine-cored poly(amidoamine) dendrimers: Simultaneous effect of spirolactam ring-opening and PET process on sensing trivalent chromium ion

    International Nuclear Information System (INIS)

    Lei Yonglin; Su Yuanqiang; Huo Jichuan

    2011-01-01

    Two novel poly(amidoamine) (PAMAM) dendrimers, comprising rhodamine B unit in the core and 1-phenyl-3-methyl-5-pyrazolone unit at the periphery, have been synthesized and characterized. Both dendrimers displayed high selectivity and sensitivity towards Cr 3+ ion. As considering the potential of being applied as fluorescent sensors for Cr 3+ ion, we studied the complexes formed between the dendrimers and Cr 3+ ion. Different PAMAM dendrimers had different recognition mechanism towards Cr 3+ ion. For dendrimer G2, the recognition of Cr 3+ was mainly due to the ring-opening of spirolactam. However, it significantly depended on the simultaneous effect of ring-opening of spirolactam and photoinduced electron transfer (PET) in the case of dendrimer G3. - Highlights: → First synthesize two novel PAMAM simultaneously containing rhodamine and pyrazolone. → Novel dendrimer show high selectivity and sensitivity towards Cr 3+ . → Recognition Cr 3+ of dendrimer G2 is dominantly due to the ring-opening mechanism. → Sensing Cr 3+ of dendrimer G3 is dependent on simultaneous mechanisms of ring-opening and PET.

  16. Peptide block copolymers by N-carboxyanhydride ring-opening polymerization and atom transfer radical polymerization: The effect of amide macroinitiators

    NARCIS (Netherlands)

    Habraken, G.J.M.; Koning, C.E.; Heise, A.

    2009-01-01

    The synthesis of polypeptide-containing block copolymers combining N-carboxyanhydride (NCA) ring-opening polymerization and atom transfer radical polymerization (ATRP) was investigated. An amide initiator comprising an amine function for the NCA polymerization and an activated bromide for ATRP was

  17. Synthesis of poly(2-ethyl-2-oxazoline)-b-poly(styrene) copolymers via a dual initiator route combining cationic ring-opening polymerization and atom transfer radical polymerization

    NARCIS (Netherlands)

    Becer, C.R.; Paulus, R.M.; ppener, S.; Hoogenboom, R.; Fustin, C.A.; Gohy, J.M.W.; Schubert, U.S.

    2008-01-01

    Block copolymers of 2-ethyl-2-oxazoline (EtOx) and styrene were synthesized by a combination of cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP). Initially, a detailed kinetic investigation for the ?-bromoisobutyrylbromide (BrEBBr) initiated CROP of EtOx

  18. Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C2-symmetric building block: a strategy for the synthesis of decanolide natural products

    Directory of Open Access Journals (Sweden)

    Bernd Schmidt

    2013-11-01

    Full Text Available Starting from the conveniently available ex-chiral pool building block (R,R-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i a site-selective cross metathesis, (ii a highly diastereoselective extended tethered RCM to furnish a (Z,E-configured dienyl carboxylic acid and (iii a Ru–lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.

  19. Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C 2-symmetric building block: a strategy for the synthesis of decanolide natural products.

    Science.gov (United States)

    Schmidt, Bernd; Kunz, Oliver

    2013-01-01

    Starting from the conveniently available ex-chiral pool building block (R,R)-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i) a site-selective cross metathesis, (ii) a highly diastereoselective extended tethered RCM to furnish a (Z,E)-configured dienyl carboxylic acid and (iii) a Ru-lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.

  20. Controlled Synthesis of AB2 amphiphilic triarm star-shaped block copolymers by ring-opening polymerization

    OpenAIRE

    Petrova, Svetla; Riva, Raphaël; Jérôme, Christine; Lecomte, Philippe; Mateva, Rosa

    2009-01-01

    This paper describes the synthesis of a novel amphiphilic AB2 triarm star-shaped copolymer with A = non-toxic and biocompatible hydrophilic poly(ethylene oxide) (PEO) and B = biodegradable and hydrophobic poly(ε-caprolactone) (PCL). A series of AB2 triarm star-shaped copolymers with different molecular weights for the PCL block were successfully synthesized by a three-step procedure. α-methoxy-ω-epoxy-poly(ethylene oxide) (PEO-epoxide) was first synthesized by the nucleophilic substitution of...

  1. Accuracy of a new ring-opening metathesis elastomeric dental impression material with spray and immersion disinfection.

    Science.gov (United States)

    Kronström, Mats H; Johnson, Glen H; Hompesch, Richard W

    2010-01-01

    A new elastomeric impression material has been formulated with a ring-opening metathesis chemistry. In addition to other properties of clinical significance, the impression accuracy must be confirmed. The purpose of this study was to compare the accuracy of the new elastomeric impression material with vinyl polysiloxane and polyether following both spray and immersion disinfection. Impressions of a modified dentoform with a stainless steel crown preparation in the lower right quadrant were made, and type IV gypsum working casts and dies were formed. Anteroposterior (AP), cross-arch (CA), buccolingual (BL), mesiodistal (MD), occlusogingivobuccal (OGB), and occlusogingivolingual (OGL) dimensions were measured using a microscope. Working cast and die dimensions were compared to those of the master model. The impression materials were a newly formulated, ring-opening metathesis-polymerization impression material (ROMP Cartridge Tray and ROMP Volume Wash), vinyl polysiloxane (VPS, Aquasil Ultra Monophase/LV), and a polyether (PE, Impregum Penta Soft/Permadyne Garant L). Fifteen impressions with each material were made, of which 5 were disinfected by spray for 10 minutes (CaviCide), 5 were disinfected by immersion for 90 minutes (ProCide D), and 5 were not disinfected. There were significant cross-product interactions with a 2-way ANOVA, so a 1-way ANOVA and Dunnett's T3 multiple comparison test were used to compare the dimensional changes of the 3 impression materials, by disinfection status and for each location (alpha=.05). For ROMP, there were no significant differences from the master, for any dimension, when comparing the control and 2 disinfectant conditions. No significant differences were detected among the 3 impression materials for CA, BL, and MD. The working die dimensions of OGB and OGL for VPS with immersion disinfection were significantly shorter than with PE and ROMP (P<.05). Overall, the AP dimension was more accurate than CA, and the BL of working dies

  2. Addition of HO-nucleophiles to free and coordinated nitriles

    International Nuclear Information System (INIS)

    Bokach, Nadejda A; Kukushkin, Vadim Yu

    2005-01-01

    The review surveys data on the addition of HO-nucleophiles (water, oximes, hydroxylamines, hydroxamic acids, alcohols) to nitriles. Main methods for C≡N bond activation in nucleophilic addition reactions are discussed. Particular attention is given to activation of nitriles through coordination to metal centres.

  3. One-Pot Parallel Synthesis of Lipid Library via Thiolactone Ring Opening and Screening for Gene Delivery.

    Science.gov (United States)

    Molla, Mijanur R; Böser, Alexander; Rana, Akshita; Schwarz, Karina; Levkin, Pavel A

    2018-04-18

    Efficient delivery of nucleic acids into cells is of great interest in the field of cell biology and gene therapy. Despite a lot of research, transfection efficiency and structural diversity of gene-delivery vectors are still limited. A better understanding of the structure-function relationship of gene delivery vectors is also essential for the design of novel and intelligent delivery vectors, efficient in "difficult-to-transfect" cells and in vivo clinical applications. Most of the existing strategies for the synthesis of gene-delivery vectors require multiple steps and lengthy procedures. Here, we demonstrate a facile, three-component one-pot synthesis of a combinatorial library of 288 structurally diverse lipid-like molecules termed "lipidoids" via a thiolactone ring opening reaction. This strategy introduces the possibility to synthesize lipidoids with hydrophobic tails containing both unsaturated bonds and reducible disulfide groups. The whole synthesis and purification are convenient, extremely fast, and can be accomplished within a few hours. Screening of the produced lipidoids using HEK293T cells without addition of helper lipids resulted in identification of highly stable liposomes demonstrating ∼95% transfection efficiency with low toxicity.

  4. Preparation of polyhedral oligomeric silsesquioxane based hybrid monoliths by ring-opening polymerization for capillary LC and CEC.

    Science.gov (United States)

    Lin, Hui; Zhang, Zhenbin; Dong, Jing; Liu, Zhongshan; Ou, Junjie; Zou, Hanfa

    2013-09-01

    A new organic-inorganic hybrid monolith was prepared by the ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxane (POSS) with 1,4-butanediamine (BDA) using 1-propanol, 1,4-butanediol, and PEG 10,000 as a porogenic system. Benefiting from the moderate phase separation process, the resulting poly(POSS-co-BDA) hybrid monolith possessed a uniform microstructure and exhibited excellent performance in chromatographic applications. Neutral, acidic, and basic compounds were successfully separated on the hybrid monolith in capillary LC (cLC), and high column efficiencies were achieved in all of the separations. In addition, as the amino groups could generate a strong EOF, the hybrid monolith was also applied in CEC for the separation of neutral and polar compounds, and a satisfactory performance was obtained. These results demonstrate that the poly(POSS-co-BDA) hybrid monolith is a good separation media in chromatographic separations of various types of compounds by both cLC and CEC. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. An unprecedented chemospecific and stereoselective tandem nucleophilic addition/cycloaddition reaction of nucleophilic carbenes with ketenimines.

    Science.gov (United States)

    Cheng, Ying; Ma, Yang-Guang; Wang, Xiao-Rong; Mo, Jun-Ming

    2009-01-16

    The first study of the reaction between nucleophilic carbenes and ketenimines is reported. The interaction of thiazole and benzothiazole carbenes with ketenimines proceeded in a chemospecific and stereoselective manner to produce thiazole- and benzothiazole-spiro-pyrrole derivatives generally in good yields. The reaction was proposed to proceed via a tandem nucleophilic addition of carbene to the C=N bond of ketenimine followed by a stepwise [3+2] cycloaddition of the 1,3-dipolar intermediate with the C=C bond of ketenimine. This reaction provides a powerful protocol for the construction of novel polyfunctional thiazole-spiro-pyrrole or benzothiazole-spiro-pyrrole compounds that are not readily accessible by other methods.

  6. Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

    Science.gov (United States)

    Pécharman, Anne-Frédérique; Colebatch, Annie L.; Hill, Michael S.; McMullin, Claire L.; Mahon, Mary F.; Weetman, Catherine

    2017-04-01

    Organoboranes are some of the most synthetically valuable and widely used intermediates in organic and pharmaceutical chemistry. Their synthesis, however, is limited by the behaviour of common boron starting materials as archetypal Lewis acids such that common routes to organoboranes rely on the reactivity of boron as an electrophile. While the realization of convenient sources of nucleophilic boryl anions would open up a wealth of opportunity for the development of new routes to organoboranes, the synthesis of current candidates is generally limited by a need for highly reducing reaction conditions. Here, we report a simple synthesis of a magnesium boryl through the heterolytic activation of the B-B bond of bis(pinacolato)diboron, which is achieved by treatment of an easily generated magnesium diboranate complex with 4-dimethylaminopyridine. The magnesium boryl is shown to act as an unambiguous nucleophile through its reactions with iodomethane, benzophenone and N,N'-di-isopropyl carbodiimide and by density functional theory.

  7. Multiphoton control of the 1,3-cyclohexadiene ring-opening reaction in the presence of competing solvent reactions.

    Science.gov (United States)

    Carroll, Elizabeth C; White, James L; Florean, Andrei C; Bucksbaum, Philip H; Sension, Roseanne J

    2008-07-31

    Although physical chemistry has often concentrated on the observation and understanding of chemical systems, the defining characteristic of chemistry remains the direction and control of chemical reactivity. Optical control of molecular dynamics, and thus of chemical reactivity provides a path to use photon energy as a smart reagent in a chemical system. In this paper, we discuss recent research in this field in the context of our studies of the multiphoton optical control of the photo-initiated ring-opening reaction of 1,3-cyclohexadiene (CHD) to form 1,3,5- cis-hexatriene (Z-HT). Closed-loop feedback and learning algorithms are able to identify pulses that increase the desired target state by as much as a factor of two. Mechanisms for control are discussed through the influence of the intensity dependence, the nonlinear power spectrum, and the projection of the pulses onto low orders of polynomial phase. Control measurements in neat solvents demonstrate that competing solvent fragmentation reactions must also be considered. In particular, multiphoton excitation of cyclohexane alone is capable of producing hexatriene. Statistical analyses of data sets obtained in learning algorithm searches in neat cyclohexane and for CHD in hexane and cyclohexane highlight the importance of linear and quadratic chirp, while demonstrating that the control features are not so easily defined. Higher order phase components are also important. On the basis of these results the involvement of low-frequency ground-state vibrational modes is proposed. When the population is transferred to the excited state, momentum along the torsional coordinate may keep the wave packet localized as it moves toward the conical intersections controlling the yield of Z-HT.

  8. Stepwise O-Atom Transfer in Heme-Based Tryptophan Dioxygenase: Role of Substrate Ammonium in Epoxide Ring Opening.

    Science.gov (United States)

    Shin, Inchul; Ambler, Brett R; Wherritt, Daniel; Griffith, Wendell P; Maldonado, Amanda C; Altman, Ryan A; Liu, Aimin

    2018-03-28

    Heme-based tryptophan dioxygenases are established immunosuppressive metalloproteins with significant biomedical interest. Here, we synthesized two mechanistic probes to specifically test if the α-amino group of the substrate directly participates in a critical step of the O atom transfer during catalysis in human tryptophan 2,3-dioxygenase (TDO). Substitution of the nitrogen atom of the substrate to a carbon (probe 1) or oxygen (probe 2) slowed the catalytic step following the first O atom transfer such that transferring the second O atom becomes less likely to occur, although the dioxygenated products were observed with both probes. A monooxygenated product was also produced from probe 2 in a significant quantity. Analysis of this new product by HPLC coupled UV-vis spectroscopy, high-resolution mass spectrometry, 1 H NMR, 13 C NMR, HSQC, HMBC, and infrared (IR) spectroscopies concluded that this monooxygenated product is a furoindoline compound derived from an unstable epoxyindole intermediate. These results prove that small molecules can manipulate the stepwise O atom transfer reaction of TDO and provide a showcase for a tunable mechanism by synthetic compounds. The product analysis results corroborate the presence of a substrate-based epoxyindole intermediate during catalysis and provide the first substantial experimental evidence for the involvement of the substrate α-amino group in the epoxide ring-opening step during catalysis. This combined synthetic, biochemical, and biophysical study establishes the catalytic role of the α-amino group of the substrate during the O atom transfer reactions and thus represents a substantial advance to the mechanistic comprehension of the heme-based tryptophan dioxygenases.

  9. Research Update: A hafnium-based metal-organic framework as a catalyst for regioselective ring-opening of epoxides with a mild hydride source

    International Nuclear Information System (INIS)

    Stephenson, Casey J.; Hassan Beyzavi, M.; Klet, Rachel C.; Hupp, Joseph T.; Farha, Omar K.

    2014-01-01

    Reaction of styrene oxide with sodium cyanoborohydride and a catalytic amount of Hf-NU-1000 yields the anti-Markovnikov product, 2-phenylethanol, with over 98% regioselectivity. On the other hand, propylene oxide is ring opened in a Markovnikov fashion to form 2-propanol with 95% regioselectivity. Both styrene oxide and propylene oxide failed to react with sodium cyanoborohydride without the addition of Hf-NU-1000 indicative of the crucial role of Hf-NU-1000 as a catalyst in this reaction. To the best of our knowledge, this is the first report of the use of a metal-organic framework material as a catalyst for ring-opening of epoxides with hydrides

  10. Development of high-speed reactive processing system for carbon fiber-reinforced polyamide-6 composite: In-situ anionic ring-opening polymerization

    International Nuclear Information System (INIS)

    Kim, Sang-Woo; Seong, Dong Gi; Yi, Jin-Woo; Um, Moon-Kwang

    2016-01-01

    In order to manufacture carbon fiber-reinforced polyamide-6 (PA-6) composite, we optimized the reactive processing system. The in-situ anionic ring-opening polymerization of ε-caprolactam was utilized with proper catalyst and initiator for PA-6 matrix. The mechanical properties such as tensile strength, inter-laminar shear strength and compressive strength of the produced carbon fiber-reinforced PA-6 composite were measured, which were compared with the corresponding scanning electron microscope (SEM) images to investigate the polymer properties as well as the interfacial interaction between fiber and polymer matrix. Furthermore, kinetics of in-situ anionic ring-opening polymerization of ε-caprolactam will be discussed in the viewpoint of increasing manufacturing speed and interfacial bonding between PA-6 matrix and carbon fiber during polymerization.

  11. Development of high-speed reactive processing system for carbon fiber-reinforced polyamide-6 composite: In-situ anionic ring-opening polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sang-Woo; Seong, Dong Gi; Yi, Jin-Woo; Um, Moon-Kwang [Composites Research Division, Korea Institute of Materials Science (KIMS), Changwon, Gyeongnam, 642–831 (Korea, Republic of)

    2016-05-18

    In order to manufacture carbon fiber-reinforced polyamide-6 (PA-6) composite, we optimized the reactive processing system. The in-situ anionic ring-opening polymerization of ε-caprolactam was utilized with proper catalyst and initiator for PA-6 matrix. The mechanical properties such as tensile strength, inter-laminar shear strength and compressive strength of the produced carbon fiber-reinforced PA-6 composite were measured, which were compared with the corresponding scanning electron microscope (SEM) images to investigate the polymer properties as well as the interfacial interaction between fiber and polymer matrix. Furthermore, kinetics of in-situ anionic ring-opening polymerization of ε-caprolactam will be discussed in the viewpoint of increasing manufacturing speed and interfacial bonding between PA-6 matrix and carbon fiber during polymerization.

  12. Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources

    Directory of Open Access Journals (Sweden)

    Jacques Lalevée

    2015-04-01

    Full Text Available Photoinitiators (PI or photoinitiating systems (PIS usable in light induced cationic polymerization (CP and free radical promoted cationic polymerization (FRPCP reactions (more specifically for cationic ring opening polymerization (ROP together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.

  13. Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources.

    Science.gov (United States)

    Lalevée, Jacques; Mokbel, Haifaa; Fouassier, Jean-Pierre

    2015-04-20

    Photoinitiators (PI) or photoinitiating systems (PIS) usable in light induced cationic polymerization (CP) and free radical promoted cationic polymerization (FRPCP) reactions (more specifically for cationic ring opening polymerization (ROP)) together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.

  14. Probing Stereoselectivity in Ring-Opening Metathesis Polymerization Mediated by Cyclometalated Ruthenium-Based Catalysts: A Combined Experimental and Computational Study

    OpenAIRE

    Rosebrugh, L. E.; Ahmed, T. S.; Marx, V. M.; Hartung, J.; Liu, P.; López, J. G.; Houk, K. N.; Grubbs, R. H.

    2016-01-01

    The microstructures of polymers produced by ring-opening metathesis polymerization (ROMP) with cyclometalated Ru-carbene metathesis catalysts were investigated. A strong bias for a cis,syndiotactic microstructure with minimal head-to-tail bias was observed. In instances where trans errors were introduced, it was determined that these regions were also syndiotactic. Furthermore, hypothetical reaction intermediates and transition structures were analyzed computationally. Combined experimental a...

  15. Nucleophilic Aromatic Substitution Between Halogenated Benzene Dopants and Nucleophiles in Atmospheric Pressure Photoionization.

    Science.gov (United States)

    Kauppila, Tiina J; Haack, Alexander; Kroll, Kai; Kersten, Hendrik; Benter, Thorsten

    2016-03-01

    In a preceding work with dopant assisted-atmospheric pressure photoionization (DA-APPI), an abundant ion at [M + 77](+) was observed in the spectra of pyridine and quinoline with chlorobenzene dopant. This contribution aims to reveal the identity and route of formation of this species, and to systematically investigate structurally related analytes and dopants. Compounds containing N-, O-, and S-lone pairs were investigated with APPI in the presence of fluoro-, chloro-, bromo-, and iodobenzene dopants. Computational calculations on a density functional theory (DFT) level were carried out to study the reaction mechanism for pyridine and the different halobenzenes. The experimental and computational results indicated that the [M + 77](+) ion was formed by nucleophilic aromatic ipso-substitution between the halobenzene radical cation and nucleophilic analytes. The reaction was most efficient for N-heteroaromatic compounds, and it was weakened by sterical effects and enhanced by resonance stabilization. The reaction was most efficient with chloro-, bromo-, and iodobenzenes, whereas with fluorobenzene the reaction was scarcely observed. The calculated Gibbs free energies for the reaction between pyridine and the halobenzenes were shown to increase in the order I < Br < Cl < F. The reaction was found endergonic for fluorobenzene due to the strong C-F bonding, and exergonic for the other halobenzenes. For fluoro- and chlorobenzenes the reaction was shown to proceed through an intermediate state corresponding to [M + dopant](+), which was highly stable for fluorobenzene. For the bulkier bromine and iodine, this intermediate did not exist, but the halogens were shown to detach already during the approach by the nucleophile.

  16. Olefination reactions of phosphorus-stabilized carbon nucleophiles.

    Science.gov (United States)

    Gu, Yonghong; Tian, Shi-Kai

    2012-01-01

    A range of phosphorus-stabilized carbon nucleophiles have been employed for alkene synthesis with high chemo-, regio-, and stereoselectivity. The Wittig, Horner-Wadsworth-Emmons, Horner-Wittig, and Evans-Akiba reactions utilize phosphonium-, phosphonate-, phosphine oxide-, and pentacoordinated phosphorane-stabilized carbanions as nucleophiles, respectively, to undergo olefination with aldehydes or ketones, and each of these transformations has its own advantages and limitations. Modifying the structures of these nucleophiles along with optimizing reaction conditions results in the formation of a wide variety of polysubstituted alkenes in a highly stereoselective manner. The olefination of imines with phosphonium ylides has recently emerged as a useful approach to tune the stereoselectivity for alkene synthesis. This review focuses on recent advances in the stereoselective olefination of phosphorus-stabilized carbon nucleophiles.

  17. Cation Radical Accelerated Nucleophilic Aromatic Substitution via Organic Photoredox Catalysis.

    Science.gov (United States)

    Tay, Nicholas E S; Nicewicz, David A

    2017-11-15

    Nucleophilic aromatic substitution (S N Ar) is a direct method for arene functionalization; however, it can be hampered by low reactivity of arene substrates and their availability. Herein we describe a cation radical-accelerated nucleophilic aromatic substitution using methoxy- and benzyloxy-groups as nucleofuges. In particular, lignin-derived aromatics containing guaiacol and veratrole motifs were competent substrates for functionalization. We also demonstrate an example of site-selective substitutive oxygenation with trifluoroethanol to afford the desired trifluoromethylaryl ether.

  18. Optimal Hydrophobicity in Ring-Opening Metathesis Polymerization-Based Protein Mimics Required for siRNA Internalization.

    Science.gov (United States)

    deRonde, Brittany M; Posey, Nicholas D; Otter, Ronja; Caffrey, Leah M; Minter, Lisa M; Tew, Gregory N

    2016-06-13

    Exploring the role of polymer structure for the internalization of biologically relevant cargo, specifically siRNA, is of critical importance to the development of improved delivery reagents. Herein, we report guanidinium-rich protein transduction domain mimics (PTDMs) based on a ring-opening metathesis polymerization scaffold containing tunable hydrophobic moieties that promote siRNA internalization. Structure-activity relationships using Jurkat T cells and HeLa cells were explored to determine how the length of the hydrophobic block and the hydrophobic side chain compositions of these PTDMs impacted siRNA internalization. To explore the hydrophobic block length, two different series of diblock copolymers were synthesized: one series with symmetric block lengths and one with asymmetric block lengths. At similar cationic block lengths, asymmetric and symmetric PTDMs promoted siRNA internalization in the same percentages of the cell population regardless of the hydrophobic block length; however, with 20 repeat units of cationic charge, the asymmetric block length had greater siRNA internalization, highlighting the nontrivial relationships between hydrophobicity and overall cationic charge. To further probe how the hydrophobic side chains impacted siRNA internalization, an additional series of asymmetric PTDMs was synthesized that featured a fixed hydrophobic block length of five repeat units that contained either dimethyl (dMe), methyl phenyl (MePh), or diphenyl (dPh) side chains and varied cationic block lengths. This series was further expanded to incorporate hydrophobic blocks consisting of diethyl (dEt), diisobutyl (diBu), and dicyclohexyl (dCy) based repeat units to better define the hydrophobic window for which our PTDMs had optimal activity. High-performance liquid chromatography retention times quantified the relative hydrophobicities of the noncationic building blocks. PTDMs containing the MePh, diBu, and dPh hydrophobic blocks were shown to have superior

  19. Design, synthesis and biological evaluation of novel ring-opened cromakalim analogues with relaxant effects on vascular and respiratory smooth muscles and as stimulators of elastin synthesis.

    Science.gov (United States)

    Bouhedja, Mourad; Peres, Basile; Fhayli, Wassim; Ghandour, Zeinab; Boumendjel, Ahcène; Faury, Gilles; Khelili, Smail

    2018-01-20

    Two new series of ring-opened analogues of cromakalim bearing sulfonylurea moieties (series A: with N-unmethylated sulfonylureas, series B: with N-methylated sulfonylureas) were synthesized and tested as relaxants of vascular and respiratory smooth muscles (rat aorta and trachea, respectively). Ex vivo biological evaluations indicated that the most active compounds, belonging to series B, displayed a marked vasorelaxant activity on endothelium-intact aortic rings and the trachea. A majority of series B compounds exhibited a higher vasorelaxant activity (EC 50  stronger relaxant effects on the trachea than the reference compound cromakalim (EC 50  = 124 μM), in particular compounds B4, B7 and B16 (EC 50   57 μM for all, and EC 50  > 200 μM for a majority of them), but some of them showed an interesting relaxing effect on trachea (i.e. A15 and A33, EC 50  = 30 μM). The most potent compounds of both series, i.e. A15, A33 and B16, tested on aortic rings in the presence of glibenclamide or 80 mM KCl, suggested that they acted as voltage-gated Ca 2+ channel blockers, like verapamil, instead of being ATP-potassium channel activators, as is cromakalim, the parent molecule. Further investigations on cultured vascular smooth muscle cells showed a strong stimulating effect on elastin synthesis, especially compound B16, which was more active at 20 μM than diazoxide, a reference ATP-sensitive potassium channel activator. Taken together, our results show that the N-methylation of the sulfonylurea moieties of ring-opened cromakalim analogues led to new compounds blocking calcium-gated channels, which had a major impact on the arterial and tracheal activities as well as selectivity. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  20. Ring-opening polymerization of 19-electron [2]cobaltocenophanes: a route to high-molecular-weight, water-soluble polycobaltocenium polyelectrolytes.

    Science.gov (United States)

    Mayer, Ulrich F J; Gilroy, Joe B; O'Hare, Dermot; Manners, Ian

    2009-08-05

    Water-soluble, high-molecular-weight polycobaltocenium polyelectrolytes have been prepared by ring-opening polymerization (ROP) techniques. Anionic polymerization of a strained 19-electron dicarba[2]cobaltocenophane followed by oxidation in the presence of ammonium chloride resulted in the formation of oligomers with up to nine repeat units. Thermal ROP of dicarba[2]cobaltocenophane followed by oxidation in the presence of ammonium nitrate resulted in the formation of high-molecular-weight polycobaltocenium nitrate, a redox-active cobalt-containing polyelectrolyte.

  1. Enhancement of strong-field multiple ionization in the vicinity of the conical intersection in 1,3-cyclohexadiene ring opening

    International Nuclear Information System (INIS)

    Petrovic, Vladimir S.; Kim, Jaehee; Schorb, Sebastian; White, James; Cryan, James P.; Zipp, Lucas; Glownia, J. Michael; Broege, Douglas; Miyabe, Shungo; Tao, Hongli; Martinez, Todd; Bucksbaum, Philip H.

    2013-01-01

    Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser-induced double ionization in the vicinity of a conical intersection during a non-radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser-induced strong-field fragmentation during the ring-opening transition between 1,3-cyclohexadiene and 1,3,5-hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals

  2. Nucleophilic Substitution Reactions of N-Methyl α-Bromoacetanilides with Benzylamines in Dimethyl Sulfoxide

    International Nuclear Information System (INIS)

    Adhikary, Keshab Kumar; Lee, Hai Whang

    2011-01-01

    Kinetic studies of the reactions of N-methyl-Y-α-bromoacetanilides with substituted X-benzylamines have been carried out in dimethyl sulfoxide at 25.0 .deg. C. The Hammett plots for substituent X variations in the nucleophiles (log k N vs σ X ) are slightly biphasic concave upwards/downwards, while the Bronsted plots (log k N vs pK a ) are biphasic concave downwards with breakpoints at X = H. The Hammett plots for substituent Y variations in the substrates (log k N vs σ Y ) are biphasic concave upwards/downwards with breakpoints at Y = H. The cross-interaction constant ρ XY values are all negative: ρ XY = -0.32 for X = Y = electron-donating: -0.22 for X = electron-withdrawing and Y = electron-donating: -1.80 for X = electron-donating and Y = electronwithdrawing: -1.43 for X = Y = electron-withdrawing substituents. Deuterated kinetic isotope effects are primary normal (k H /k D > 1) for Y = electron-donating, while secondary inverse (k H /k D < 1) for Y = electronwithdrawing substituent. The proposed mechanisms of the benzylaminolyses of N-methyl-Y-α-bromoacetanilides are a concerted mechanism with a five membered ring TS involving hydrogen bonding between hydrogen (deuterium) atom in N-H(D) and oxygen atom in C = O for Y = electron-donating, while a concerted mechanism with an enolate-like TS in which the nucleophile attacks the α-carbon for Y = electronwithdrawing substituents

  3. Nitrile anion cyclization with epoxysilanes followed by Brook rearrangement/ring-opening of cyclopropane nitriles/alkylation.

    Science.gov (United States)

    Okugawa, Seigo; Masu, Hyuma; Yamaguchi, Kentaro; Takeda, Kei

    2005-12-09

    [reactions: see text] The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives 9-12 with a base and an alkylating agent affords (Z)-delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring. Exclusive formation of a (Z)-derivative from trans-epoxides is explained by the reaction pathway that involves a backside displacement of the epoxide by the alpha-nitrile carbanion and the O-Si bond formation followed by concerted processes involving Brook rearrangement and the anti-mode of eliminative ring fission of the cyclopropane from the rotamer 19. The fact that (E)-isomers are exclusively obtained from cis-epoxides and alpha-cyclopropyl-alpha-silylcarbinol derivative 26 provides experimental support for the proposed pathway.

  4. Translocations of Chromosome End-Segments and Facultative Heterochromatin Promote Meiotic Ring Formation in Evening Primroses[W][OPEN

    Science.gov (United States)

    Golczyk, Hieronim; Massouh, Amid; Greiner, Stephan

    2014-01-01

    Due to reciprocal chromosomal translocations, many species of Oenothera (evening primrose) form permanent multichromosomal meiotic rings. However, regular bivalent pairing is also observed. Chiasmata are restricted to chromosomal ends, which makes homologous recombination virtually undetectable. Genetic diversity is achieved by changing linkage relations of chromosomes in rings and bivalents via hybridization and reciprocal translocations. Although the structural prerequisite for this system is enigmatic, whole-arm translocations are widely assumed to be the mechanistic driving force. We demonstrate that this prerequisite is genome compartmentation into two epigenetically defined chromatin fractions. The first one facultatively condenses in cycling cells into chromocenters negative both for histone H3 dimethylated at lysine 4 and for C-banding, and forms huge condensed middle chromosome regions on prophase chromosomes. Remarkably, it decondenses in differentiating cells. The second fraction is euchromatin confined to distal chromosome segments, positive for histone H3 lysine 4 dimethylation and for histone H3 lysine 27 trimethylation. The end-segments are deprived of canonical telomeres but capped with constitutive heterochromatin. This genomic organization promotes translocation breakpoints between the two chromatin fractions, thus facilitating exchanges of end-segments. We challenge the whole-arm translocation hypothesis by demonstrating why reciprocal translocations of chromosomal end-segments should strongly promote meiotic rings and evolution toward permanent translocation heterozygosity. Reshuffled end-segments, each possessing a major crossover hot spot, can furthermore explain meiotic compatibility between genomes with different translocation histories. PMID:24681616

  5. Synthesis of a new class of fused cyclotetraphosphazene ring systems.

    Science.gov (United States)

    Beşli, Serap; Mutlu, Ceylan; İbişoğlu, Hanife; Yuksel, Fatma; Allen, Christopher W

    2015-01-05

    Octachlorocyclotetraphosphazene (1) was reacted with butylamines [n-butyl, i-butyl, sec-butyl, and t-butyl] in a 1:0.8 mol ratio in THF to obtain cyclotetraphosphazenes bearing a P-NH group, N4P4Cl7(NHR) [R = n-butyl (2a), i-butyl (2b), sec-butyl (2c), t-butyl (2d)](2a-d). The cyclotetraphosphazene derivatives 2a, 2b, and 2c were treated with sodium hydride giving rise to a new type of cyclophosphazene compounds (P8N8 ring) consisting of three fused tetramer rings (3a-c). Whereas reaction of sodium hydride with the t-butylaminocyclophosphazene derivative (2d) gave a P-O-P bridged compound (4) presumably as a result of hydrolysis reaction associated with moisture in the solvent. It is likely that the 16-membered cyclooctaphosphazene derivatives (3a-c) are formed by a proton abstraction/chloride ion elimination, intramolecular nucleophilic attack, ring opening and intermolecular condensation processes, respectively.

  6. Ring Theory

    CERN Document Server

    Jara, Pascual; Torrecillas, Blas

    1988-01-01

    The papers in this proceedings volume are selected research papers in different areas of ring theory, including graded rings, differential operator rings, K-theory of noetherian rings, torsion theory, regular rings, cohomology of algebras, local cohomology of noncommutative rings. The book will be important for mathematicians active in research in ring theory.

  7. Multi-level Quantum Mechanics and Molecular Mechanics Study of Ring Opening Process of Guanine Damage by Hydroxyl Radical in Aqueous Solution.

    Science.gov (United States)

    Liu, Peng; Wang, Qiong; Niu, Meixing; Wang, Dunyou

    2017-08-10

    Combining multi-level quantum mechanics theories and molecular mechanics with an explicit water model, we investigated the ring opening process of guanine damage by hydroxyl radical in aqueous solution. The detailed, atomic-level ring-opening mechanism along the reaction pathway was revealed in aqueous solution at the CCSD(T)/MM levels of theory. The potentials of mean force in aqueous solution were calculated at both the DFT/MM and CCSD(T)/MM levels of the theory. Our study found that the aqueous solution has a significant effect on this reaction in solution. In particular, by comparing the geometries of the stationary points between in gas phase and in aqueous solution, we found that the aqueous solution has a tremendous impact on the torsion angles much more than on the bond lengths and bending angles. Our calculated free-energy barrier height 31.6 kcal/mol at the CCSD(T)/MM level of theory agrees well with the one obtained based on gas-phase reaction profile and free energies of solvation. In addition, the reaction path in gas phase was also mapped using multi-level quantum mechanics theories, which shows a reaction barrier at 19.2 kcal/mol at the CCSD(T) level of theory, agreeing very well with a recent ab initio calculation result at 20.8 kcal/mol.

  8. Facile solvothermal synthesis of abnormal growth of one-dimensional ZnO nanostructures by ring-opening reaction of polyvinylpyrrolidone

    Energy Technology Data Exchange (ETDEWEB)

    Xu, G., E-mail: gxu@alum.imr.ac.cn; Wang, X.L.; Liu, G.Z.

    2015-02-28

    Graphical abstract: - Highlights: • Facile solvothermal synthesis of ZnO nanostructures in super high alkaline alcoholic condition. • The exact role and chemical transformations of PVP in solvothermal synthesis of ZnO nanostructures was revealed. • Mechanism of abnormal growth of ZnO nanopyramids was proposed based on ring-opening reaction of PVP. - Abstract: Abnormal growth of one-dimensional (1-D) ZnO nanostructures (NSs) have been accomplished with the assistance of polyvinylpyrrolidone (PVP) under a super high alkaline alcoholic solvothermal condition. The products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ({sup 1}H NMR) spectroscopy. The effect of synthetic conditions, such as reaction temperature and the addition of PVP, on the morphologies of ZnO products were investigated. The results show that PVP molecules had the significant role in the transformation of morphologies of ZnO NSs ranging from nanorods, nanoparticles to pyramids, as well as flower-like assembly features. The possible growth mechanism of ZnO pyramids was proposed based on ring-opening reaction of PVP.

  9. Alkoxide-induced nucleophilic trifluoromethylation using diethyl trifluoromethylphosphonate

    Czech Academy of Sciences Publication Activity Database

    Cherkupally, Prabhakar; Beier, Petr

    2010-01-01

    Roč. 51, č. 2 (2010), s. 252-255 ISSN 0040-4039 R&D Projects: GA ČR GP203/08/P310 Institutional research plan: CEZ:AV0Z40550506 Keywords : trifluoromethylation * phosphonate * nucleophilic addition Subject RIV: CC - Organic Chemistry Impact factor: 2.618, year: 2010

  10. preparation and nucleophilic substitution of the 2,4,6

    African Journals Online (AJOL)

    Mgina

    Three methods for preparation of D-amino acids by nucleophilic substitution on derivatives of ... bioactivity of the peptide (Wenger 1985, ... Acetic acid (0.29 mL, 5 mmol) was added, and the mixture was further stirred for 5 h at rt under ... methanol/dichloromethane) to yield a white ... temperature, diluted with water, extracted.

  11. Diethyl Fluoronitromethylphosphonate: Synthesis and Application in Nucleophilic Fluoroalkyl Additions

    Czech Academy of Sciences Publication Activity Database

    Opekar, Stanislav; Pohl, Radek; Beran, Pavel; Rulíšek, Lubomír; Beier, Petr

    2014-01-01

    Roč. 20, č. 5 (2014), s. 1453-1458 ISSN 0947-6539 R&D Projects: GA ČR GP203/08/P310 Institutional support: RVO:61388963 Keywords : C1 building blocks * fluorine * nucleophilic addition * phosphanes * synthetic methods Subject RIV: CC - Organic Chemistry Impact factor: 5.731, year: 2014

  12. The Quest for Converting Biorenewable Bifunctional α-Methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways

    KAUST Repository

    Tang, Xiaoyan

    2016-10-04

    α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL)VAP. Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL)ROP with Mn up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL)CLP. The formation of the three types of polymers, P(MBL)VAP, P(MBL)CLP, and P(MBL)ROP, can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La–X (X = OR, NR2, R) group. The resulting P(MBL)ROP is degradable and can be readily postfunctionalized into cross-linked or thiolated materials but, more remarkably, can also be fully recycled back to its monomer thermochemically. Computational studies provided the theoretical basis for, and a mechanistic understanding of, the three different polymerization processes and the origin of the chemoselectivity.

  13. The Quest for Converting Biorenewable Bifunctional α-Methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways

    KAUST Repository

    Tang, Xiaoyan; Hong, Miao; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y X

    2016-01-01

    α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL)VAP. Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL)ROP with Mn up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL)CLP. The formation of the three types of polymers, P(MBL)VAP, P(MBL)CLP, and P(MBL)ROP, can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La–X (X = OR, NR2, R) group. The resulting P(MBL)ROP is degradable and can be readily postfunctionalized into cross-linked or thiolated materials but, more remarkably, can also be fully recycled back to its monomer thermochemically. Computational studies provided the theoretical basis for, and a mechanistic understanding of, the three different polymerization processes and the origin of the chemoselectivity.

  14. Zn(OAc2-Catalyzing Ring-Opening Polymerization of N-Carboxyanhydrides for the Synthesis of Well-Defined Polypeptides

    Directory of Open Access Journals (Sweden)

    Yanzhao Nie

    2018-03-01

    Full Text Available Despite notable progress, the fabrication of well-defined polypeptides via controlled ring-opening polymerization (ROP of α-amino acid N-carboxyanhydrides (NCAs using convenient catalysts under mild conditions in a relatively short polymerization time is still challenging. Herein, an easily obtained catalyst system composed of zinc acetate and aniline was explored to mediate the fast ROP of γ-benzyl-l-glutamate-N-carboxyanhydride (BLG-NCA monomer, to produce poly(γ-benzyl-l-glutamates (PBLGs with controllable molecular weights and narrow dispersity. Considering the excellent cooperative action of zinc acetate and a broad scope of aniline derivatives with different functional groups to control ROP of BLG-NCA, this method may offer a useful platform enabling the rapid generation of end-functionalized PBLG and block copolymers for numerous biomedical applications.

  15. C-N Bond Activation and Ring Opening of a Saturated N-Heterocyclic Carbene by Lateral Alkali-Metal-Mediated Metalation.

    Science.gov (United States)

    Hernán-Gómez, Alberto; Kennedy, Alan R; Hevia, Eva

    2017-06-01

    Combining alkali-metal-mediated metalation (AMMM) and N-heterocyclic carbene (NHC) chemistry, a novel C-N bond activation and ring-opening process is described for these increasingly important NHC molecules, which are generally considered robust ancillary ligands. Here, mechanistic investigations on reactions of saturated NHC SIMes (SIMes=[:C{N(2,4,6-Me 3 C 6 H 2 )CH 2 } 2 ]) with Group 1 alkyl bases suggest this destructive process is triggered by lateral metalation of the carbene. Exploiting co-complexation and trans-metal-trapping strategies with lower polarity organometallic reagents (Mg(CH 2 SiMe 3 ) 2 and Al(TMP)iBu 2 ), key intermediates in this process have been isolated and structurally defined. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Efficient Diethylzinc/Gallic Acid and Diethylzinc/Gallic Acid Ester Catalytic Systems for the Ring-Opening Polymerization of rac-Lactide

    Directory of Open Access Journals (Sweden)

    Karolina Żółtowska

    2015-12-01

    Full Text Available Polylactide (PLA represents one of the most promising biomedical polymers due to its biodegradability, bioresorbability and good biocompatibility. This work highlights the synthesis and characterization of PLAs using novel diethylzinc/gallic acid (ZnEt2/GAc and diethylzinc/propyl gallate (ZnEt2/PGAc catalytic systems that are safe for human body. The results of the ring-opening polymerization (ROP of rac-lactide (rac-LA in the presence of zinc-based catalytic systems have shown that, depending on the reaction conditions, “predominantly isotactic”, disyndiotactic or atactic PLA can be obtained. Therefore, the controlled and stereoselective ROP of rac-LA is discussed in detail in this paper.

  17. Erosion of stereochemical control with increasing nucleophilicity: O-glycosylation at the diffusion limit.

    Science.gov (United States)

    Beaver, Matthew G; Woerpel, K A

    2010-02-19

    Nucleophilic substitution reactions of 2-deoxyglycosyl donors indicated that the reactivity of the oxygen nucleophile has a significant impact on stereoselectivity. Employing ethanol as the nucleophile resulted in a 1:1 (alpha:beta) ratio of diastereomers under S(N)1-like reaction conditions. Stereoselective formation of the 2-deoxy-alpha-O-glycoside was only observed when weaker nucleophiles, such as trifluoroethanol, were employed. The lack of stereoselectivity observed in reactions of common oxygen nucleophiles can be attributed to reaction rates of the stereochemistry-determining step that approach the diffusion limit. In this scenario, both faces of the prochiral oxocarbenium ion are subject to nucleophilic addition to afford a statistical mixture of diastereomeric products. Control experiments confirmed that all nucleophilic substitution reactions were performed under kinetic control.

  18. Optimization studies concerning the direct nucleophilic fluorination of butyrophenone neuroleptics

    Energy Technology Data Exchange (ETDEWEB)

    Katsifis, A; Hamacher, K; Schnitter, J; Stoecklin, G [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Chemie 1 - Nuklearchemie

    1993-07-01

    Based on the direct nucleophilic aromatic substitution described previously for [[sup 18]F]N-methylspiperone the butyrophenone neuroleptics benperidol, droperidol, fluanisone and haloperidol were labelled with fluorine-18. The n.c.a. aromatic nucleophilic NO[sub 2] [yields] [sup 18]F substitution takes place in the presence of the moderately basic cryptate system consisting of Kryptofix 2.2.2., potassium oxalate and potassium carbonate. The one step labeling reaction was performed in different solvents and is equally successful in dimethylsulfoxide, dimethylformamide or dimethylacetamide yielding 25-35% (EOS) within a reaction time of 5-30 min in the range of 140-160[sup o]C at analytical activity levels. (author).

  19. Nucleophilic tetrafluoroethylation of carbonyl compounds with fluorinated sulfones

    Czech Academy of Sciences Publication Activity Database

    Václavík, Jiří; Chernykh, Yana; Jurásek, Bronislav; Beier, Petr

    2015-01-01

    Roč. 169, Jan (2015), s. 24-31 ISSN 0022-1139 R&D Projects: GA ČR GAP207/11/0421 Grant - others:GA MŠk(CZ) ED3.2.00/08.0144; GA MŠk(CZ) LM2010005 Institutional support: RVO:61388963 Keywords : fluorine * tetrafluoroethylation * sulfones * nucleophilic addition * carbonyl compounds Subject RIV: CC - Organic Chemistry Impact factor: 2.213, year: 2015

  20. General Allylic C–H Alkylation with Tertiary Nucleophiles

    Science.gov (United States)

    2015-01-01

    A general method for intermolecular allylic C–H alkylation of terminal olefins with tertiary nucleophiles has been accomplished employing palladium(II)/bis(sulfoxide) catalysis. Allylic C–H alkylation furnishes products in good yields (avg. 64%) with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z). For the first time, the olefin scope encompasses unactivated aliphatic olefins as well as activated aromatic/heteroaromatic olefins and 1,4-dienes. The ease of appending allyl moieties onto complex scaffolds is leveraged to enable this mild and selective allylic C–H alkylation to rapidly diversify phenolic natural products. The tertiary nucleophile scope is broad and includes latent functionality for further elaboration (e.g., aliphatic alcohols, α,β-unsaturated esters). The opportunities to effect synthetic streamlining with such general C–H reactivity are illustrated in an allylic C–H alkylation/Diels–Alder reaction cascade: a reactive diene is generated via intermolecular allylic C–H alkylation and approximated to a dienophile contained within the tertiary nucleophile to furnish a common tricyclic core found in the class I galbulimima alkaloids. PMID:24641574

  1. General allylic C-H alkylation with tertiary nucleophiles.

    Science.gov (United States)

    Howell, Jennifer M; Liu, Wei; Young, Andrew J; White, M Christina

    2014-04-16

    A general method for intermolecular allylic C-H alkylation of terminal olefins with tertiary nucleophiles has been accomplished employing palladium(II)/bis(sulfoxide) catalysis. Allylic C-H alkylation furnishes products in good yields (avg. 64%) with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z). For the first time, the olefin scope encompasses unactivated aliphatic olefins as well as activated aromatic/heteroaromatic olefins and 1,4-dienes. The ease of appending allyl moieties onto complex scaffolds is leveraged to enable this mild and selective allylic C-H alkylation to rapidly diversify phenolic natural products. The tertiary nucleophile scope is broad and includes latent functionality for further elaboration (e.g., aliphatic alcohols, α,β-unsaturated esters). The opportunities to effect synthetic streamlining with such general C-H reactivity are illustrated in an allylic C-H alkylation/Diels-Alder reaction cascade: a reactive diene is generated via intermolecular allylic C-H alkylation and approximated to a dienophile contained within the tertiary nucleophile to furnish a common tricyclic core found in the class I galbulimima alkaloids.

  2. Black rings

    International Nuclear Information System (INIS)

    Emparan, Roberto; Reall, Harvey S

    2006-01-01

    A black ring is a five-dimensional black hole with an event horizon of topology S 1 x S 2 . We provide an introduction to the description of black rings in general relativity and string theory. Novel aspects of the presentation include a new approach to constructing black ring coordinates and a critical review of black ring microscopics. (topical review)

  3. Enzymatic catalysis of anti-Baldwin ring closure in polyether biosynthesis.

    Science.gov (United States)

    Hotta, Kinya; Chen, Xi; Paton, Robert S; Minami, Atsushi; Li, Hao; Swaminathan, Kunchithapadam; Mathews, Irimpan I; Watanabe, Kenji; Oikawa, Hideaki; Houk, Kendall N; Kim, Chu-Young

    2012-03-04

    Polycyclic polyether natural products have fascinated chemists and biologists alike owing to their useful biological activity, highly complex structure and intriguing biosynthetic mechanisms. Following the original proposal for the polyepoxide origin of lasalocid and isolasalocid and the experimental determination of the origins of the oxygen and carbon atoms of both lasalocid and monensin, a unified stereochemical model for the biosynthesis of polyether ionophore antibiotics was proposed. The model was based on a cascade of nucleophilic ring closures of postulated polyepoxide substrates generated by stereospecific oxidation of all-trans polyene polyketide intermediates. Shortly thereafter, a related model was proposed for the biogenesis of marine ladder toxins, involving a series of nominally disfavoured anti-Baldwin, endo-tet epoxide-ring-opening reactions. Recently, we identified Lsd19 from the Streptomyces lasaliensis gene cluster as the epoxide hydrolase responsible for the epoxide-opening cyclization of bisepoxyprelasalocid A to form lasalocid A. Here we report the X-ray crystal structure of Lsd19 in complex with its substrate and product analogue to provide the first atomic structure-to our knowledge-of a natural enzyme capable of catalysing the disfavoured epoxide-opening cyclic ether formation. On the basis of our structural and computational studies, we propose a general mechanism for the enzymatic catalysis of polyether natural product biosynthesis. © 2012 Macmillan Publishers Limited. All rights reserved

  4. White Ring; White ring

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, H.; Yuzawa, H. [Nikken Sekkei Ltd., Osaka (Japan)

    1998-01-05

    White Ring is a citizen`s gymnasium used for figure skating and short track speed skating games of 18th Winter Olympic Games in 1998. White Ring is composed of a main-arena and a sub-arena. For the main-arena with an area 41mtimes66m, an ice link can be made by disengaging the potable floor and by flowing brine in the bridged polystyrene pipes embedded in the concrete floor. Due to the fortunate groundwater in this site, well water is used for the outside air treatment energy in 63% during heating and in 35% during cooling. Ammonia is used as a cooling medium for refrigerating facility. For the heating of audience area in the large space, heat load from the outside is reduced by enhancing the heat insulation performance of the roof of arena. The audience seats are locally heated using heaters. For the White Ring, high quality environment is realized for games through various functions of the large-scale roof of the large space. Success of the big event was expected. 15 figs., 4 tabs.

  5. Random Poly(Amino Acids Synthesized by Ring Opening Polymerization as Additives in the Biomimetic Mineralization of CaCO3

    Directory of Open Access Journals (Sweden)

    Vladimir Dmitrovic

    2012-05-01

    Full Text Available Biominerals such as bones, teeth and seashells, very often have advanced material properties and are a source of inspiration for material chemists. As in biological systems acidic proteins play an important role in regulating the formation of CaCO3 biominerals, we employ poly(amino acids to mimic the processes involved in the laboratory. Here we report on the synthesis of random aminoacid copolymers of glutamic acid (Glu, lysine (Lys and alanine (Ala using the ring opening polymerization (ROP of their respective N-carboxy anhydrides (NCA. The synthetic approach yields a series of polymers with different monomer composition but with similar degrees of polymerization (DP 45–56 and comparable polydispersities (PDI 1.2–1.6. Using random copolymers we can investigate the influence of composition on the activity of the polymers without having to take into account the effects of secondary structure or specific sequences. We show that variation of the Glu content of the polymer chains affects the nucleation and thereby also the particle size. Moreover, it is shown that the polymers with the highest Glu content affect the kinetics of mineral formation such that the first precipitate is more soluble than in the case of the control.

  6. Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties.

    Science.gov (United States)

    Roumeli, Eleftheria; Papageorgiou, Dimitrios G; Tsanaktsis, Vasilios; Terzopoulou, Zoe; Chrissafis, Konstantinos; Avgeropoulos, Apostolos; Bikiaris, Dimitrios N

    2015-06-03

    In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (f-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % f-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. f-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30-40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy.

  7. Synthesis of Aluminum Complexes Bearing 8-Anilide-5,6,7-trihydroquinoline Ligands: Highly Active Catalyst Precursors for Ring-Opening Polymerization of Cyclic Esters

    Directory of Open Access Journals (Sweden)

    Shaofeng Liu

    2017-03-01

    Full Text Available The stoichiometric reactions of 8-(2,6-R1-4-R2-anilide-5,6,7-trihydroquinoline (LH with AlR3 (R = Me or Et afforded the aluminum complexes LAlR2 (Al1–Al5,Al1: R1 = iPr, R2 = H, R = Me; Al2: R1 = Me, R2 = H, R = Me; Al3: R1 = H, R2 = H, R = Me; Al4: R1 = Me, R2 = Me, R = Me; Al5: R1 = Me, R2 = Me, R = Et in high yields. All aluminum complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complexes Al4 and Al5 were determined by single-crystal X-ray diffractions and revealed a distorted tetrahedral geometry at aluminum. In the presence of BnOH, complexes Al1–Al5 efficiently initiated the ring-opening homopolymerization of ε-caprolactone (ε-CL and rac-lactide (rac-LA, respectively, in a living/controlled manner.

  8. Factors influencing catalytic behavior of titanium complexes bearing bisphenolate ligands toward ring-opening polymerization of L-lactide and ε-caprolactone

    Directory of Open Access Journals (Sweden)

    M-T. Jiang

    2018-02-01

    Full Text Available A series of titanium complexes bearing substituted diphenolate ligands (RCH(phenolate2, where R = H, CH3, o-OTs-phenyl, o-F-phenyl, o-OMe-phenyl, 2,4-OMe-phenyl was synthesized and studied as catalysts for the ring opening polymerization of L-lactide and ε-caprolactone. Ligands were designed to probe the role of chelate effect and steric effect in the catalytic performance. From the structure of triphenolate (with one extra coordination site than diphenolate ligand Ti complex, TriOTiOiPr2, we found no additional chelation to influence the catalytic activity of Ti complexes. It was found that bulky aryl groups in the diphenolate ligands decreased the rate of polymerization most. We conclude that steric effect is the most controlling factor in these polymerization reactions by using Ti complexes bearing diphenolate ligands as catalysts since it is responsible for the exclusion of needed space for incoming monomer by the bulky substituents on the catalyst.

  9. In Situ Generated Ruthenium-Arene Catalyst for Photoactivated Ring-Opening Metathesis Polymerization through Photolatent N-Heterocyclic Carbene Ligand.

    Science.gov (United States)

    Pinaud, Julien; Trinh, Thi Kim Hoang; Sauvanier, David; Placet, Emeline; Songsee, Sriprapai; Lacroix-Desmazes, Patrick; Becht, Jean-Michel; Tarablsi, Bassam; Lalevée, Jacques; Pichavant, Loïc; Héroguez, Valérie; Chemtob, Abraham

    2018-01-09

    1,3-Bis(mesityl)imidazolium tetraphenylborate (IMesH + BPh 4 - ) can be synthesized in one step by anion metathesis between the corresponding imidazolium chloride and sodium tetraphenylborate. In the presence of 2-isopropylthioxanthone (sensitizer), an IMes N-heterocyclic carbene (NHC) ligand can be photogenerated under irradiation at 365 nm through coupled electron/proton transfer reactions. By combining this tandem NHC photogenerator system with metathesis inactive [RuCl 2 (p-cymene)] 2 precatalyst, the highly active RuCl 2 (p-cymene)(IMes) complex can be formed in situ, enabling a complete ring-opening metathesis polymerization (ROMP) of norbornene in the matter of minutes at room temperature. To the best of our knowledge, this is the first example of a photogenerated NHC. Its exploitation in photoROMP has resulted in a simplified process compared to current photocatalysts, because only stable commercial or easily synthesized reagents are required. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Vatansever, Fatma, E-mail: vatansever.fatma@mgh.harvard.edu; Hamblin, Michael R., E-mail: hamblin@helix.mgh.harvard.edu [Massachusetts General Hospital, Wellman Center for Photomedicine (United States)

    2016-10-15

    Core–shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original tri-octylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48–53 nm.

  11. Green Polymer Chemistry: Investigating the Mechanism of Radical Ring-Opening Redox Polymerization (R3P of 3,6-Dioxa-1,8-octanedithiol (DODT

    Directory of Open Access Journals (Sweden)

    Emily Q. Rosenthal-Kim

    2015-04-01

    Full Text Available The mechanism of the new Radical Ring-opening Redox Polymerization (R3P of 3,6-dioxa-1,8-octanedithiol (DODT by triethylamine (TEA and dilute H2O2 was investigated. Scouting studies showed that the formation of high molecular weight polymers required a 1:2 molar ratio of DODT to TEA and of DODT to H2O2. Further investigation into the chemical composition of the organic and aqueous phases by 1H-NMR spectroscopy and mass spectrometry demonstrated that DODT is ionized by two TEA molecules (one for each thiol group and thus transferred into the aqueous phase. The organic phase was found to have cyclic disulfide dimers, trimers and tetramers. Dissolving DODT and TEA in water before the addition of H2O2 yielded a polymer with Mn = 55,000 g/mol, in comparison with Mn = 92,000 g/mol when aqueous H2O2 was added to a DODT/TEA mixture. After polymer removal, MALDI-ToF MS analysis of the residual reaction mixtures showed only cyclic oligomers remaining. Below the LCST for TEA in water, 18.7 °C, the system yielded a stable emulsion, and only cyclic oligomers were found. Below DODT/TEA and H2O2 1:2 molar ratio mostly linear oligomers were formed, with <20% cyclic oligomers. The findings support the proposed mechanism of R3P.

  12. Mechanochemical Ring-Opening Polymerization of Lactide: Liquid-Assisted Grinding for the Green Synthesis of Poly(lactic acid) with High Molecular Weight.

    Science.gov (United States)

    Ohn, Nuri; Shin, Jihoon; Kim, Sung Sik; Kim, Jeung Gon

    2017-09-22

    Mechanochemical polymerization of lactide is carried out by using ball milling. Mechanical energy from collisions between the balls and the vessel efficiently promotes an organic-base-mediated metal- and solvent-free solid-state polymerization. Investigation of the parameters of the ball-milling synthesis revealed that the degree of lactide ring-opening polymerization could be modulated by the ball-milling time, vibration frequency, mass of the ball media, and liquid-assisted grinding. Liquid-assisted grinding was found to be an especially important factor for achieving a high degree of mechanochemical polymerization. Although polymer-chain scission from the strong collision energy prevented mechanical-force-driven high-molecular-weight polymer synthesis, the addition of only a small amount of liquid enabled sufficient energy dissipation and poly(lactic acid) was thereby obtained with a molecular weight of over 1×10 5  g mol -1 . © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Ring-Opening Polymerization of N-Carboxyanhydrides for Preparation of Polypeptides and Polypeptide-Based Hybrid Materials with Various Molecular Architectures

    KAUST Repository

    Pahovnik, David

    2015-09-01

    Different synthetic approaches utilizing ring-opening polymerization of N-carboxyanhydrides for preparation of polypeptide and polypeptide-based hybrid materials with various molecular architectures are described. An overview of polymerization mechanisms using conventional (various amines) as well as some recently developed initiators (hexamethyldisilazane, N-heterocyclic persistent carbenes, etc.) is presented, and their benefits and drawbacks for preparation of polypeptides with well-defined chain lengths and chain-end functionality are discussed. Recent examples from literature are used to illustrate different possibilities for synthesis of pure polypeptide materials with different molecular architectures bearing various functional groups, which are introduced either by modification of amino acids, before they are transformed into corresponding Ncarboxyanhydrides, or by post-polymerization modifications using protective groups and/or orthogonal functional groups. Different approaches for preparation of polypeptide-based hybrid materials are discussed as well using examples from recent literature. Syntheses of simple block copolymers or copolymers with more complex molecular architectures (graft and star copolymers) as well as modifications of nanoparticles and other surfaces with polypeptides are described.

  14. Enhanced thermal and mechanical properties of PLA/MoS2 nanocomposites synthesized via the in-situ ring-opening polymerization

    Science.gov (United States)

    Chen, Pengpeng; Liang, Xiao; Xu, Ying; Zhou, Yifeng; Nie, Wangyan

    2018-05-01

    In this work, MoS2 nanosheets were employed to reinforce PLA. In order to promote the homogeneous dispersion of MoS2 in PLA and form a strong interface between MoS2 and PLA, the MoS2 nanosheets were firstly modified by mercapto-ethylamine, and then functionalized with PLA chains through ring-opening polymerization of poly(L-lactide). The XRD, XPS, TGA and 1H NMR characterizations confirmed the successful amino and PLA functionalization of MoS2 nanosheets. The obtained MoS2-g-PLA nanosheets were then introduced to reinforce PLA. SEM images displayed that the MoS2-g-PLA nanosheets were dispersed in PLA matrix uniformly. TGA results showed that initial decomposition temperature was improved from 275.6 °C to 334.8 °C with 0.5 wt% of MoS2-g-PLA nanosheets. The storage modulus of PLA/MoS2-g-PLA-0.5 wt% in the glass state and rubber state were both greatly enhanced compared with neat PLA.

  15. Azabicycles construction : the transannular ring contraction with N-protected nucleophiles

    NARCIS (Netherlands)

    Rizzo, Antonio; Harutyunyan, Syuzanna R.

    2014-01-01

    Synthetic strategies are one of the most critical factors for the success of a synthetic campaign, but most importantly they are crucial for the economy and the efficiency of the sequence. Within this perspective, the synthesis of azabicyclic scaffolds, constituents of many bioactive alkaloids, can

  16. Vortex rings

    CERN Document Server

    Akhmetov, D G

    2009-01-01

    This text on vortex rings covers their theoretical foundation, systematic investigations, and practical applications such as the extinction of fires at gushing oil wells. It pays special attention to the formation and motion of turbulent vortex rings.

  17. Multiple C-H Bond Activations and Ring-Opening C-S Bond Cleavage of Thiophene by Dirhenium Carbonyl Complexes.

    Science.gov (United States)

    Adams, Richard D; Dhull, Poonam; Tedder, Jonathan D

    2018-06-14

    The reaction of Re 2 (CO) 8 (μ-C 6 H 5 )(μ-H) (1) with thiophene in CH 2 Cl 2 at 40 °C yielded the new compound Re 2 (CO) 8 (μ-η 2 -SC 4 H 3 )(μ-H) (2), which contains a bridging σ-π-coordinated thienyl ligand formed by the activation of the C-H bond at the 2 position of the thiophene. Compound 2 exhibits dynamical activity on the NMR time scale involving rearrangements of the bridging thienyl ligand. The reaction of compound 2 with a second 1 equiv of 1 at 45 °C yielded the doubly metalated product [Re 2 (CO) 8 (μ-H)] 2 (μ-η 2 -2,3-μ-η 2 -4,5-C 4 H 2 S) (3), formed by the activation of the C-H bond at the 5 position of the thienyl ligand in 2. Heating 3 in a hexane solvent to reflux transformed it into the ring-opened compound Re(CO) 4 [μ-η 5 -η 2 -SCC(H)C(H)C(H)][Re(CO) 3 ][Re 2 (CO) 8 (μ-H)] (4) by the loss of one CO ligand. Compound 4 contains a doubly metalated 1-thiapentadienyl ligand formed by the cleavage of one of the C-S bonds. When heated to reflux (125 °C) in an octane solvent in the presence of H 2 O, the new compound Re(CO) 4 [η 5 -μ-η 2 -SC(H)C(H)C(H)C(H)]Re(CO) 3 (5) was obtained by cleavage of the Re 2 (CO) 8 (μ-H) group from 4 with formation of the known coproduct [Re(CO) 3 (μ 3 -OH)] 4 . All new products were characterized by single-crystal X-ray diffraction analyses.

  18. Effects of thermal history in the ring opening polymerization of CBT and its mixtures with montmorillonite on the crystallization of the resulting poly(butylene terephthalate)

    Energy Technology Data Exchange (ETDEWEB)

    Lanciano, Giuseppina [Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce (Italy); Greco, Antonio, E-mail: antonio.greco@unile.it [Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce (Italy); Maffezzoli, Alfonso [Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce (Italy); Mascia, Leno [Department of Materials, Loughborough University, Loughborough, LE 11 3TU (United Kingdom)

    2009-09-10

    Differential scanning calorimetry was used to study the thermal characteristics and morphological structure of species produced during the ring opening polymerization of cyclic butylene terephthalate (CBT). Thermal programs consisting of a first ramp heating scan and an isothermal step, followed by cooling and a second ramp heating step, were used to study the effects of thermal history, catalyst (butyl chlorotin dihydroxide) at concentrations between 0.1 and 1.3% (w/w), and the presence of a layered silicate nanofiller (montmorillonite at 4.0%, w/w) on the structure of the resulting polymer (poly(butylene terephthalate), pCBT). Wide angle X-ray diffraction was used to monitor the degree of exfoliation of the nanocomposites. It was found that pCBT is formed in the amorphous state, and crystallizes during the heating step or during the isothermal step at temperatures lower than the equilibrium melting temperature of the polymer (T{sub m}{sup 0}). When premixed with the nanofiller, irrespective of whether this was previously intercalated with a tallow surfactant or used in its pristine form, polymerization took place at higher temperatures and most of the crystallization was found to occur during the cooling stage. In those cases where crystallization took place during either the first heating scan, or during a prolonged isothermal step below the T{sub m}{sup 0} of the polymer, the resulting crystals were found to have a higher lamellar thickness, as compared with the same polymer crystallized from the melt during the cooling step from temperatures above the polymer T{sub m}{sup 0}.

  19. Effects of thermal history in the ring opening polymerization of CBT and its mixtures with montmorillonite on the crystallization of the resulting poly(butylene terephthalate)

    International Nuclear Information System (INIS)

    Lanciano, Giuseppina; Greco, Antonio; Maffezzoli, Alfonso; Mascia, Leno

    2009-01-01

    Differential scanning calorimetry was used to study the thermal characteristics and morphological structure of species produced during the ring opening polymerization of cyclic butylene terephthalate (CBT). Thermal programs consisting of a first ramp heating scan and an isothermal step, followed by cooling and a second ramp heating step, were used to study the effects of thermal history, catalyst (butyl chlorotin dihydroxide) at concentrations between 0.1 and 1.3% (w/w), and the presence of a layered silicate nanofiller (montmorillonite at 4.0%, w/w) on the structure of the resulting polymer (poly(butylene terephthalate), pCBT). Wide angle X-ray diffraction was used to monitor the degree of exfoliation of the nanocomposites. It was found that pCBT is formed in the amorphous state, and crystallizes during the heating step or during the isothermal step at temperatures lower than the equilibrium melting temperature of the polymer (T m 0 ). When premixed with the nanofiller, irrespective of whether this was previously intercalated with a tallow surfactant or used in its pristine form, polymerization took place at higher temperatures and most of the crystallization was found to occur during the cooling stage. In those cases where crystallization took place during either the first heating scan, or during a prolonged isothermal step below the T m 0 of the polymer, the resulting crystals were found to have a higher lamellar thickness, as compared with the same polymer crystallized from the melt during the cooling step from temperatures above the polymer T m 0 .

  20. The synthesis of no-carrier-added DL-4-[18F]fluorodeprenyl via the nucleophilic aromatic substitution reaction

    International Nuclear Information System (INIS)

    Plenevaux, Alain; Guillaume, Marcel

    1991-01-01

    No-carrier-added DL-α-methyl-β-4-[ 18 F]fluorophenyl-N-methyl-N-propynylethylamine (DL-4-[ 18 F]fluorodeprenyl) was synthesized via a 3-step procedure. The overall yield was 11%, the synthesis time was 90 min and the specific activity >0.57 Ci/μmol (end of synthesis). This synthesis approach, the conversion of an aromatic aldehyde to a homologous methyl ketone, extends the flexibility of the nucleophilic aromatic substitution reaction by applying it to the synthesis of radiotracers which do not bear electron-withdrawing activating groups on the aromatic ring. The tissue distribution of DL-4-[ 18 F]fluorodeprenyl in mice at 1, 10 and 50 min was also measured and showed that metabolic defluorination was not significant. Clearance or radioactivity from brain after injection of DL-4-[ 18 F]fluorodeprenyl was more rapid than that previously observed for [ 11 C]L-deprenyl. (author)

  1. Experimental Determination of Activation Energy of Nucleophilic Aromatic Substitution on Porphyrins

    Science.gov (United States)

    Rizvi, Waqar; Khwaja, Emaad; Siddiqui, Saim; Bhupathiraju, N. V. S. Dinesh K.; Drain, Charles Michael

    2018-01-01

    A physical organic chemistry experiment is described for second-year college students. Students performed nucleophilic aromatic substitution (NAS) reactions on 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin (TPPF[subscript 20]) using three different nucleophiles. Substitution occurs preferentially at the 4-position ("para")…

  2. General-base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions

    NARCIS (Netherlands)

    Buurma, NJ; Blandamer, MJ; Engberts, JBFN; Buurma, Niklaas J.

    The reactivity of 1-benzoyl-3-phenyl-1,2,4-triazole (1a) was studied in the presence of a range of weak bases in aqueous solution. A change in mechanism is observed from general-base catalysed hydrolysis to nucleophilic substitution and general-base catalysed nucleophilic substitution. A slight

  3. Multiple nucleophilic elbows leading to multiple active sites in a single module esterase from Sorangium cellulosum

    DEFF Research Database (Denmark)

    Udatha, D.B.R.K. Gupta; Madsen, Karina Marie; Panagiotou, Gianni

    2015-01-01

    The catalytic residues in carbohydrate esterase enzyme families constitute a highly conserved triad: serine, histidine and aspartic acid. This catalytic triad is generally located in a very sharp turn of the protein backbone structure, called the nucleophilic elbow and identified by the consensus...... sequence GXSXG. An esterase from Sorangium cellulosum Soce56 that contains five nucleophilic elbows was cloned and expressed in Escherichia coli and the function of each nucleophilic elbowed site was characterized. In order to elucidate the function of each nucleophilic elbow, site directed mutagenesis....... To our knowledge, this is the first report presenting the role of multiple nucleophilic elbows in the catalytic promiscuity of an esterase. Further structural analysis at protein unit level indicates the new evolutionary trajectories in emerging promiscuous esterases....

  4. Nucleophilic addition of nitriles to secondary terpene alcohols

    International Nuclear Information System (INIS)

    Kozlov, N.G.; Popova, L.A.; Nesterov, G.V.

    1987-01-01

    The addition of nitriles of varying nucleophilicity to isocamphanol and exo-1,5,5-trimethyl-bicyclo[2.2.1]heptan-2-ol (isofenchol) was investigated. The authors examined the effect of the reaction conditions on the yield and structure of the target products of the reaction: N-substituted amides. As a result of the study, it was shown that in the reaction with chloroacetonitrile, propionitrile, methoxypropionitrile, isovaleronitrile, and phenylacetonitrile under the conditions of the Ritter reaction, isocamphanol is transformed into the corresponding substituted exo-N-acyl-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylamines, as in the reaction with aceto- and benzonitriles, due to 2,6-hydride displacement accompanied by Wagner-Meerwein rearrangement. The structures of these amides were demonstrated by PMR spectroscopy

  5. Antioxidant activity of selenenamide-based mimic as a function of the aromatic thiols nucleophilicity, a DFT-SAPE model.

    Science.gov (United States)

    Kheirabadi, Ramesh; Izadyar, Mohammad

    2018-05-18

    The mechanism of action of the selenenamide 1 as a mimic of the glutathione peroxidase (GPx) was investigated by the density functional theory. The solvent-assisted proton exchange procedure was applied to model the catalytic behavior and antioxidant activity of this mimic. To have an insight into the charge transfer effect, different aromatic thiols, including electron donating substituents on the phenyl ring were considered. The catalytic behavior of the selenenamide was modeled in a four-step mechanism, described by the oxidation of the mimic, the reduction of the obtained product, selenoxide, the reduction of the selenenylsulfide and dehydration of selenenic acid. On the basis of the activation parameters, the final step of the proposed mechanism is the rate determining states of the catalytic cycle. Turnover frequency (TOF) analysis showed that the electron donating groups at the para-position of the phenyl ring of the PhSH do not affect the catalytic activity of the selenenamide in contrast to p-methyl thiophenol which indicates the highest nucleophilicity. The evaluation of the electronic contribution of the various donating groups on the phenyl ring of the aromatic thiols shows that the antioxidant activity of the selenenamide sufficiently increases in the presence of the electron-donating substitutions. Finally, the charge transfer process at the rate-determining state was investigated based on the natural bond orbital analysis. Copyright © 2018 Elsevier Ltd. All rights reserved.

  6. Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

    Directory of Open Access Journals (Sweden)

    Holger F. Bettinger

    2013-04-01

    Full Text Available The ring opening of the Dewar form of 1,2-dihydro-1,2-azaborine, 2-aza-3-borabicyclo[2.2.0]hex-5-ene (3 is investigated by theoretical methods by using multiconfiguration SCF (CASSCF and coupled cluster theory [CCSD(T] with basis sets up to polarised quadruple-zeta quality. The title compound was previously reported to form photochemically in cryogenic noble gas matrices from 1,2-dihydro-1,2-azaborine (4. Four reaction paths for the thermal ring opening of 3 to 4 could be identified. These are the conventional disrotatory and conrotatory electrocyclic ring-opening pathways where the BN unit is only a bystander. Two more favourable paths are stepwise and involve 1,3-boron–carbon interactions. The lowest energy barrier for the isomerisation reaction, 22 kcal mol−1, should be high enough for an experimental observation in solution. However, in solution the dimerisation of 3 is computed to have a very low barrier (3 kcal mol−1, and thus 3 is expected to be a short-lived reactive intermediate.

  7. In situ nucleophilic substitutional growth of methylammonium lead iodide polycrystals.

    Energy Technology Data Exchange (ETDEWEB)

    Acik, Muge [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials and Nanoscience and Technology Division; Alam, Todd M. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Dept. of Organic Materials Science; Guo, Fangmin [Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS) and X-ray Science Division; Ren, Yang [Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS) and X-ray Science Division; Lee, Byeongdu [Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS) and X-ray Science Division; Rosenberg, Richard A. [Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS) and X-ray Science Division; Mitchell, JF [Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division; Kinaci, Alper [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials and Nanoscience and Technology Division; Chan, Maria [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials and Nanoscience and Technology Division; Darling, Seth B. [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials and Nanoscience and Technology Division; Univ. of Chicago, IL (United States). Inst. for Molecular Engineering

    2017-01-01

    Methylammonium lead iodide (MAPbIx) perovskites are organic-inorganic semiconductors that serve as the light-harvesting component of the photovoltaics, and are desirable with their long diffusion length yielding power conversion efficiencies of ≥22%. Conventional techniques grow perovskites by spin coating precursors on an oxide or a polymer substrate followed by annealing, however, use of high boiling point solvents and high temperatures hinder device stability and performance. Through a one-step, acid-catalyzed nucleophilic-substitutional crystal growth in polar protic solvents, we show evidence for the substrate- and annealing- free production of MAPbIx polycrystals that are metallic-lead-free with negligibly small amount of PbI2 precipitation (<10%). On the basis of this chemical composition, we have devised an in situ growth of highly air (upto ~1.5 months) and thermally-stable (≤300°C), tetragonal-phased, variable-sized polycrystals (~100 nm-10 μm) amendable for large-area deposition, and ultimately, large-scale manufacturing. This method is encouraging for stable optoelectronic devices, and leads to energy-efficient and low-cost processing.

  8. Reactivity of polychlorinated biphenyls in nucleophilic and electrophilic substitutions

    Energy Technology Data Exchange (ETDEWEB)

    Gorbunova, Tatyana I., E-mail: gorbunova@ios.uran.ru [I. Ya. Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Kovalevskoy St., 22, Ekaterinburg 620990 (Russian Federation); Subbotina, Julia O. [Ural Federal University named after the first President of Russia B.N. Yeltsin, Mira St., 19, Ekaterinburg 620002 (Russian Federation); Saloutin, Viktor I.; Chupakhin, Oleg N. [I. Ya. Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Kovalevskoy St., 22, Ekaterinburg 620990 (Russian Federation)

    2014-08-15

    Graphical abstract: - Highlights: • Quantum chemical calculations were carried out for PCBs congeners. • Calculated descriptors were used to explain the PCBs reactivity in S{sub N} and S{sub E} substitutions. • Obtained data were used to estimate the PCBs reactivity in the S{sub N} reactions. • Calculated descriptors were insufficient to explain the PCBs reactivity in the S{sub E} reactions. • New neutralization methods of the large-capacity PCBs were discussed. - Abstract: To explain the chemical reactivity of polychlorinated biphenyls in nucleophilic (S{sub N}) and electrophilic (S{sub E}) substitutions, quantum chemical calculations were carried out at the B3LYP/6-31G(d) level of the Density Functional Theory in gas phase. Carbon atomic charges in biphenyl structure were calculated by the Atoms-in-Molecules method. Chemical hardness and global electrophilicity index parameters were determined for congeners. A comparison of calculated descriptors and experimental data for congener reactivity in the S{sub N} and S{sub E} reactions was made. It is shown that interactions in the S{sub N} mechanism are reactions of the hard acid–hard base type, these are the most effective in case of highly chlorinated substrates. To explain the congener reactivity in the S{sub E} reactions, correct descriptors were not established. The obtained results can be used to carry out chemical transformations of the polychlorinated biphenyls in order to prepare them for microbiological destruction or preservation.

  9. Energy landscapes of nucleophilic substitution reactions: a comparison of density functional theory and coupled cluster methods

    NARCIS (Netherlands)

    Swart, M.; Sola, M.; Bickelhaupt, F.M.

    2007-01-01

    We have carried out a detailed evaluation of the performance of all classes of density functional theory (DFT) for describing the potential energy surface (PES) of a wide range of nucleophilic substitution (S

  10. Reactions of aromatic diazonium salts with unsaturated compounds in the presence of nucleophiles

    Science.gov (United States)

    Grishchuk, B. D.; Gorbovoi, P. M.; Ganushchak, N. I.; Dombrovskii, A. V.

    1994-03-01

    The review surveys the reactions of aromatic diazonium salts with diene and monounsaturated compounds in the presence of nucleophiles. Certain further reactions of the reaction products and their application are considered. The bibliography includes 63 references.

  11. Chemoselective reductive nucleophilic addition to tertiary amides, secondary amides, and N-methoxyamides.

    Science.gov (United States)

    Nakajima, Minami; Oda, Yukiko; Wada, Takamasa; Minamikawa, Ryo; Shirokane, Kenji; Sato, Takaaki; Chida, Noritaka

    2014-12-22

    As the complexity of targeted molecules increases in modern organic synthesis, chemoselectivity is recognized as an important factor in the development of new methodologies. Chemoselective nucleophilic addition to amide carbonyl centers is a challenge because classical methods require harsh reaction conditions to overcome the poor electrophilicity of the amide carbonyl group. We have successfully developed a reductive nucleophilic addition of mild nucleophiles to tertiary amides, secondary amides, and N-methoxyamides that uses the Schwartz reagent [Cp2 ZrHCl]. The reaction took place in a highly chemoselective fashion in the presence of a variety of sensitive functional groups, such as methyl esters, which conventionally require protection prior to nucleophilic addition. The reaction will be applicable to the concise synthesis of complex natural alkaloids from readily available amide groups. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Water promoted allylic nucleophilic substitution reactions of (E)-1,3 diphenylallyl acetate

    KAUST Repository

    Ghorpade, Seema Arun; Sawant, Dinesh N; Makki, Arwa; Sekar, N; Eppinger, Jö rg

    2017-01-01

    Transition metal free, water based, greener protocol for allylic alkylation, allylic amination, O-allylation of (E)-1,3-diphenylallyl acetate is described. The developed methodology is applicable for a wide range of nucleophiles furnishing excellent yields of corresponding products up to 87% under mild reaction conditions. A Distinct effect of water and base is explored for allylic nucleophilic substitution reactions of (E)-1,3-diphenylallyl acetate.

  13. Synthesis and nucleophilic aromatic substitution of 3-fluoro-5-nitro-1-(pentafluorosulfanyl)benzene

    Czech Academy of Sciences Publication Activity Database

    Ajenjo, Javier; Greenhall, M.; Zarantonello, C.; Beier, Petr

    2016-01-01

    Roč. 12, Feb 3 (2016), s. 192-197 ISSN 1860-5397 EU Projects: European Commission(XE) 607787 - FLUOR21 Institutional support: RVO:61388963 Keywords : direct fluorination * fluorine * nucleophilic aromatic substitution * pentafluorosulfanyl group * vicarious nucleophilic substitution Subject RIV: CC - Organic Chemistry Impact factor: 2.337, year: 2016 http://www.beilstein-journals.org/bjoc/single/articleFullText.htm?publicId=1860-5397-12-21

  14. Continuous Flow Nucleophilic Aromatic Substitution with Dimethylamine Generated in Situ by Decomposition of DMF

    DEFF Research Database (Denmark)

    Petersen, Trine P; Larsen, Anders Foller; Ritzén, Andreas

    2013-01-01

    A safe, practical, and scalable continuous flow protocol for the in situ generation of dimethylamine from DMF followed by nucleophilic aromatic substitution of a broad range of aromatic and heteroaromatic halides is reported.......A safe, practical, and scalable continuous flow protocol for the in situ generation of dimethylamine from DMF followed by nucleophilic aromatic substitution of a broad range of aromatic and heteroaromatic halides is reported....

  15. Water promoted allylic nucleophilic substitution reactions of (E)-1,3 diphenylallyl acetate

    KAUST Repository

    Ghorpade, Seema Arun

    2017-11-30

    Transition metal free, water based, greener protocol for allylic alkylation, allylic amination, O-allylation of (E)-1,3-diphenylallyl acetate is described. The developed methodology is applicable for a wide range of nucleophiles furnishing excellent yields of corresponding products up to 87% under mild reaction conditions. A Distinct effect of water and base is explored for allylic nucleophilic substitution reactions of (E)-1,3-diphenylallyl acetate.

  16. Conjugate Addition of Nucleophiles to the Vinyl Function of 2-Chloro-4-vinylpyrimidine Derivatives

    Directory of Open Access Journals (Sweden)

    Lucjan Strekowski

    2010-03-01

    Full Text Available Conjugate addition reaction of various nucleophiles across the vinyl group of 2-chloro-4-vinylpyrimidine, 2-chloro-4-(1-phenylvinylpyrimidine and 2-chloro-4-vinylquinazoline provides the corresponding 2-chloro-4-(2-substituted ethylpyrimidines and 2-chloro-4-(2-substituted ethylquinazolines. Treatment of these products, without isolation, with N-methylpiperazine results in nucleophilic displacement of chloride and yields the corresponding 2,4-disubstituted pyrimidines and quinazolines.

  17. ring system

    African Journals Online (AJOL)

    1,3,2-DIAZABORACYCLOALKANE. RING SYSTEM. Negussie Retta" and Robert H. Neilson. 'Department of Chemistry, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia. Department of Chemistry, Texas Christian University.

  18. Planetary Rings

    Science.gov (United States)

    Nicholson, P. D.

    2001-11-01

    A revolution in the studies in planetary rings studies occurred in the period 1977--1981, with the serendipitous discovery of the narrow, dark rings of Uranus, the first Voyager images of the tenuous jovian ring system, and the many spectacular images returned during the twin Voyager flybys of Saturn. In subsequent years, ground-based stellar occultations, HST observations, and the Voyager flybys of Uranus (1986) and Neptune (1989), as well as a handful of Galileo images, provided much additional information. Along with the completely unsuspected wealth of detail these observations revealed came an unwelcome problem: are the rings ancient or are we privileged to live at a special time in history? The answer to this still-vexing question may lie in the complex gravitational interactions recent studies have revealed between the rings and their retinues of attendant satellites. Among the four known ring systems, we see elegant examples of Lindblad and corotation resonances (first invoked in the context of galactic disks), electromagnetic resonances, spiral density waves and bending waves, narrow ringlets which exhibit internal modes due to collective instabilities, sharp-edged gaps maintained via tidal torques from embedded moonlets, and tenuous dust belts created by meteoroid impact onto parent bodies. Perhaps most puzzling is Saturn's multi-stranded, clumpy F ring, which continues to defy a simple explanation 20 years after it was first glimpsed in grainy images taken by Pioneer 11. Voyager and HST images reveal a complex, probably chaotic, dynamical interaction between unseen parent bodies within this ring and its two shepherd satellites, Pandora and Prometheus. The work described here reflects contributions by Joe Burns, Jeff Cuzzi, Luke Dones, Dick French, Peter Goldreich, Colleen McGhee, Carolyn Porco, Mark Showalter, and Bruno Sicardy, as well as those of the author. This research has been supported by NASA's Planetary Geology and Geophysics program and the

  19. α-deuterium isotope effects in benzyl halides. 2. Reaction of nucleophiles with substituted benzyl bromides. Evidence for a change in transition-state structure with electron-donating substituents

    International Nuclear Information System (INIS)

    Vitullo, V.P.; Grabowski, J.; Sridharan, S.

    1980-01-01

    Rates and α-D isotope effects have been determined for the following substrates and nucleophiles: p-methoxybenzyl bromide (Et 3 N, SCN - , N 3 - , OH - , S 2 O 3 2- ), benzyl bromide (Et 3 N, SCN - , N 3 - , OH - , S 2 O 3 2- ), and p-nitrobenzyl bromide (Et 3 N, SCN - , N 3 - , S 2 O 3 2- ). In nearly all cases the second-order rate constant for each nucleophile goes through a minimum for the unsubstituted compound while the α-D isotope increases monotonically in the squence p-NO 2 > p-H > p-OCH 3 . These results are consistent with an increasing looseness of the S/sub N/2 transition state as the substituent on the aromatic ring becomes more electron donating. 4 figures, 3 tables

  20. Radar imaging of Saturn's rings

    Science.gov (United States)

    Nicholson, Philip D.; French, Richard G.; Campbell, Donald B.; Margot, Jean-Luc; Nolan, Michael C.; Black, Gregory J.; Salo, Heikki J.

    2005-09-01

    We present delay-Doppler images of Saturn's rings based on radar observations made at Arecibo Observatory between 1999 and 2003, at a wavelength of 12.6 cm and at ring opening angles of 20.1°⩽|B|⩽26.7°. The average radar cross-section of the A ring is ˜77% relative to that of the B ring, while a stringent upper limit of 3% is placed on the cross-section of the C ring and 9% on that of the Cassini Division. These results are consistent with those obtained by Ostro et al. [1982, Icarus 49, 367-381] from radar observations at |B|=21.4°, but provide higher resolution maps of the rings' reflectivity profile. The average cross-section of the A and B rings, normalized by their projected unblocked area, is found to have decreased from 1.25±0.31 to 0.74±0.19 as the rings have opened up, while the circular polarization ratio has increased from 0.64±0.06 to 0.77±0.06. The steep decrease in cross-section is at variance with previous radar measurements [Ostro et al., 1980, Icarus 41, 381-388], and neither this nor the polarization variations are easily understood within the framework of either classical, many-particle-thick or monolayer ring models. One possible explanation involves vertical size segregation in the rings, whereby observations at larger elevation angles which see deeper into the rings preferentially see the larger particles concentrated near the rings' mid-plane. These larger particles may be less reflective and/or rougher and thus more depolarizing than the smaller ones. Images from all four years show a strong m=2 azimuthal asymmetry in the reflectivity of the A ring, with an amplitude of ±20% and minima at longitudes of 67±4° and 247±4° from the sub-Earth point. We attribute the asymmetry to the presence of gravitational wakes in the A ring as invoked by Colombo et al. [1976, Nature 264, 344-345] to explain the similar asymmetry long seen at optical wavelengths. A simple radiative transfer model suggests that the enhancement of the azimuthal

  1. Storage Rings

    International Nuclear Information System (INIS)

    Fischer, W.

    2010-01-01

    Storage rings are circular machines that store particle beams at a constant energy. Beams are stored in rings without acceleration for a number of reasons (Tab. 1). Storage rings are used in high-energy, nuclear, atomic, and molecular physics, as well as for experiments in chemistry, material and life sciences. Parameters for storage rings such as particle species, energy, beam intensity, beam size, and store time vary widely depending on the application. The beam must be injected into a storage ring but may not be extracted (Fig. 1). Accelerator rings such as synchrotrons are used as storage rings before and after acceleration. Particles stored in rings include electrons and positrons; muons; protons and anti-protons; neutrons; light and heavy, positive and negative, atomic ions of various charge states; molecular and cluster ions, and neutral polar molecules. Spin polarized beams of electrons, positrons, and protons were stored. The kinetic energy of the stored particles ranges from 10 -6 eV to 3.5 x 10 12 eV (LHC, 7 x 10 12 eV planned), the number of stored particles from one (ESR) to 1015 (ISR). To store beam in rings requires bending (dipoles) and transverse focusing (quadrupoles). Higher order multipoles are used to correct chromatic aberrations, to suppress instabilities, and to compensate for nonlinear field errors of dipoles and quadrupoles. Magnetic multipole functions can be combined in magnets. Beams are stored bunched with radio frequency systems, and unbunched. The magnetic lattice and radio frequency system are designed to ensure the stability of transverse and longitudinal motion. New technologies allow for better storage rings. With strong focusing the beam pipe dimensions became much smaller than previously possible. For a given circumference superconducting magnets make higher energies possible, and superconducting radio frequency systems allow for efficient replenishment of synchrotron radiation losses of large current electron or positron beams

  2. Topological rings

    CERN Document Server

    Warner, S

    1993-01-01

    This text brings the reader to the frontiers of current research in topological rings. The exercises illustrate many results and theorems while a comprehensive bibliography is also included. The book is aimed at those readers acquainted with some very basic point-set topology and algebra, as normally presented in semester courses at the beginning graduate level or even at the advanced undergraduate level. Familiarity with Hausdorff, metric, compact and locally compact spaces and basic properties of continuous functions, also with groups, rings, fields, vector spaces and modules, and with Zorn''s Lemma, is also expected.

  3. Ring accelerators

    International Nuclear Information System (INIS)

    Gisler, G.; Faehl, R.

    1983-01-01

    We present two-dimensional simulations in (r-z) and r-theta) cylinderical geometries of imploding-liner-driven accelerators of rings of charged particles. We address issues of azimuthal and longitudinal stability of the rings. We discuss self-trapping designs in which beam injection and extraction is aided by means of external cusp fields. Our simulations are done with the 2-1/2-D particle-in-cell plasma simulation code CLINER, which combines collisionless, electromagnetic PIC capabilities with a quasi-MHD finite element package

  4. Ring interferometry

    CERN Document Server

    Malykin, Grigorii B; Zhurov, Alexei

    2013-01-01

    This monograph is devoted to the creation of a comprehensive formalism for quantitative description of polarized modes' linear interaction in modern single-mode optic fibers. The theory of random connections between polarized modes, developed in the monograph, allows calculations of the zero shift deviations for a fiber ring interferometer. The monograph addresses also the

  5. Collector ring project at FAIR

    International Nuclear Information System (INIS)

    Dolinskii, A; Blell, U; Dimopoulou, C; Gorda, O; Leibrock, H; Litvinov, S; Laier, U; Schurig, I; Weinrich, U; Berkaev, D; Koop, I; Starostenko, A; Shatunov, P

    2015-01-01

    The collector ring is a dedicated ring for fast cooling of ions coming from separators at the FAIR project. To accommodate optimal technical solutions, a structure of a magnet lattice was recently reviewed and modified. Consequently, more appropriate technical solutions for the main magnets could be adopted. A general layout and design of the present machine is shown. The demanding extraction schemes have been detailed and open design issues were completed. (paper)

  6. Bond Energies and Thermochemical Properties of Ring-Opened Diradicals and Carbenes of exo-Tricyclo[5.2.1.0(2,6)]decane.

    Science.gov (United States)

    Hudzik, Jason M; Castillo, Álvaro; Bozzelli, Joseph W

    2015-09-24

    Exo-tricyclo[5.2.1.0(2,6)]decane (TCD) or exo-tetrahydrodicyclopentadiene is an interesting strained ring compound and the single-component high-energy density hydrocarbon fuel known as JP-10. Important initial reactions of TCD at high temperatures could cleave a strained carbon-carbon (C-C) bond in the ring system creating diradicals also constrained by the remaining ring system. This study determines the thermochemical properties of these diradicals (TCD-H2 mJ-nJ where m and n correspond to the cleaved carbons sites) including the carbon-carbon bond dissociation energy (C-C BDE) corresponding to the cleaved TCD site. Thermochemical properties including enthalpies (ΔH°f298), entropies (S(T)), heat capacities (Cp(T)), and C-H and C-C BDEs for the parent (TCD-H2 m-n), radical (TCD-H2 mJ-n and m-nJ), diradical (TCD-H2 mJ-nJ), and carbene (TCD-H2 mJJ-n and m-nJJ) species are determined. Structures, vibrational frequencies, moments of inertia, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level of theory. Standard enthalpies of formation in the gas phase for the TCD-H2 m-n parent and radical species are determined using the B3LYP density functional theory and the higher level G3MP2B3 and CBS-QB3 composite methods. For singlet and triplet TCD diradicals and carbenes, M06-2X, ωB97X-D, and CCSD(T) methods are included in the analysis to determine ΔH°f298 values. The C-C BDEs are further calculated using CASMP2(2,2)/aug-cc-pvtz//CASSCF(2,2)/cc-pvtz and with the CASMP2 energies extrapolated to the complete basis set limit. The bond energies calculated with these methods are shown to be comparable to the other calculation methods. Isodesmic work reactions are used for enthalpy analysis of these compounds for effective cancelation of systematic errors arising from ring strain. C-C BDEs range from 77.4 to 84.6 kcal mol(-1) for TCD diradical singlet species. C-H BDEs for the parent TCD-H2 m-n carbon sites range from 93 to 101 kcal mol(-1) with a

  7. Effects of a One Year Reusable Contraceptive Vaginal Ring on Vaginal Microflora and the Risk of Vaginal Infection: An Open-Label Prospective Evaluation.

    Science.gov (United States)

    Huang, Yongmei; Merkatz, Ruth B; Hillier, Sharon L; Roberts, Kevin; Blithe, Diana L; Sitruk-Ware, Régine; Creinin, Mitchell D

    2015-01-01

    A contraceptive vaginal ring (CVR) containing Nestorone® (NES) and ethinyl estradiol (EE) that is reusable for 1- year (13 cycles) is under development. This study assessed effects of this investigational CVR on the incidence of vaginal infections and change in vaginal microflora. There were 120 women enrolled into a NES/EE CVR Phase III trial and a microbiology sub-study for up to 1- year of cyclic product use. Gynecological examinations were conducted at baseline, the first week of cycle 6 and last week of cycle 13 (or during early discontinuation visits). Vaginal swabs were obtained for wet mount microscopy, Gram stain and culture. The CVR was removed from the vagina at the last study visit and cultured. Semi-quantitative cultures for Lactobacillus, Gardnerella vaginalis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, anaerobic gram negative rods (GNRs), Candida albicans and other yeasts were performed on vaginal and CVR samples. Vaginal infections were documented throughout the study. Over 1- year of use, 3.3% of subjects were clinically diagnosed with bacterial vaginosis, 15.0% with vulvovaginal candidiasis, and 0.8% with trichomoniasis. The detection rate of these three infections did not change significantly from baseline to either Cycle 6 or 13. Nugent scores remained stable. H2O2-positive Lactobacillus dominated vaginal flora with a non-significant prevalence increase from 76.7% at baseline to 82.7% at cycle 6 and 90.2% at cycle 13, and a median concentration of 107 colony forming units (cfu) per gram. Although anaerobic GNRs prevalence increased significantly, the median concentration decreased slightly (104 to 103cfu per gram). There were no significant changes in frequency or concentrations of other pathogens. High levels of agreement between vaginal and ring surface microbiota were observed. Sustained use of the NES/EE CVR did not increase the risk of vaginal infection and was not disruptive to the vaginal ecosystem. Clinical

  8. Energy spectra of quantum rings.

    Science.gov (United States)

    Fuhrer, A; Lüscher, S; Ihn, T; Heinzel, T; Ensslin, K; Wegscheider, W; Bichler, M

    2001-10-25

    Quantum mechanical experiments in ring geometries have long fascinated physicists. Open rings connected to leads, for example, allow the observation of the Aharonov-Bohm effect, one of the best examples of quantum mechanical phase coherence. The phase coherence of electrons travelling through a quantum dot embedded in one arm of an open ring has also been demonstrated. The energy spectra of closed rings have only recently been studied by optical spectroscopy. The prediction that they allow persistent current has been explored in various experiments. Here we report magnetotransport experiments on closed rings in the Coulomb blockade regime. Our experiments show that a microscopic understanding of energy levels, so far limited to few-electron quantum dots, can be extended to a many-electron system. A semiclassical interpretation of our results indicates that electron motion in the rings is governed by regular rather than chaotic motion, an unexplored regime in many-electron quantum dots. This opens a way to experiments where even more complex structures can be investigated at a quantum mechanical level.

  9. Effects of a One Year Reusable Contraceptive Vaginal Ring on Vaginal Microflora and the Risk of Vaginal Infection: An Open-Label Prospective Evaluation.

    Directory of Open Access Journals (Sweden)

    Yongmei Huang

    Full Text Available A contraceptive vaginal ring (CVR containing Nestorone® (NES and ethinyl estradiol (EE that is reusable for 1- year (13 cycles is under development. This study assessed effects of this investigational CVR on the incidence of vaginal infections and change in vaginal microflora.There were 120 women enrolled into a NES/EE CVR Phase III trial and a microbiology sub-study for up to 1- year of cyclic product use. Gynecological examinations were conducted at baseline, the first week of cycle 6 and last week of cycle 13 (or during early discontinuation visits. Vaginal swabs were obtained for wet mount microscopy, Gram stain and culture. The CVR was removed from the vagina at the last study visit and cultured. Semi-quantitative cultures for Lactobacillus, Gardnerella vaginalis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, anaerobic gram negative rods (GNRs, Candida albicans and other yeasts were performed on vaginal and CVR samples. Vaginal infections were documented throughout the study.Over 1- year of use, 3.3% of subjects were clinically diagnosed with bacterial vaginosis, 15.0% with vulvovaginal candidiasis, and 0.8% with trichomoniasis. The detection rate of these three infections did not change significantly from baseline to either Cycle 6 or 13. Nugent scores remained stable. H2O2-positive Lactobacillus dominated vaginal flora with a non-significant prevalence increase from 76.7% at baseline to 82.7% at cycle 6 and 90.2% at cycle 13, and a median concentration of 107 colony forming units (cfu per gram. Although anaerobic GNRs prevalence increased significantly, the median concentration decreased slightly (104 to 103cfu per gram. There were no significant changes in frequency or concentrations of other pathogens. High levels of agreement between vaginal and ring surface microbiota were observed.Sustained use of the NES/EE CVR did not increase the risk of vaginal infection and was not disruptive to the vaginal ecosystem

  10. Effects of a One Year Reusable Contraceptive Vaginal Ring on Vaginal Microflora and the Risk of Vaginal Infection: An Open-Label Prospective Evaluation

    Science.gov (United States)

    Huang, Yongmei; Merkatz, Ruth B.; Hillier, Sharon L.; Roberts, Kevin; Blithe, Diana L.; Sitruk-Ware, Régine; Creinin, Mitchell D.

    2015-01-01

    Background A contraceptive vaginal ring (CVR) containing Nestorone® (NES) and ethinyl estradiol (EE) that is reusable for 1- year (13 cycles) is under development. This study assessed effects of this investigational CVR on the incidence of vaginal infections and change in vaginal microflora. Methods There were 120 women enrolled into a NES/EE CVR Phase III trial and a microbiology sub-study for up to 1- year of cyclic product use. Gynecological examinations were conducted at baseline, the first week of cycle 6 and last week of cycle 13 (or during early discontinuation visits). Vaginal swabs were obtained for wet mount microscopy, Gram stain and culture. The CVR was removed from the vagina at the last study visit and cultured. Semi-quantitative cultures for Lactobacillus, Gardnerella vaginalis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, anaerobic gram negative rods (GNRs), Candida albicans and other yeasts were performed on vaginal and CVR samples. Vaginal infections were documented throughout the study. Results Over 1- year of use, 3.3% of subjects were clinically diagnosed with bacterial vaginosis, 15.0% with vulvovaginal candidiasis, and 0.8% with trichomoniasis. The detection rate of these three infections did not change significantly from baseline to either Cycle 6 or 13. Nugent scores remained stable. H2O2-positive Lactobacillus dominated vaginal flora with a non-significant prevalence increase from 76.7% at baseline to 82.7% at cycle 6 and 90.2% at cycle 13, and a median concentration of 107 colony forming units (cfu) per gram. Although anaerobic GNRs prevalence increased significantly, the median concentration decreased slightly (104 to 103cfu per gram). There were no significant changes in frequency or concentrations of other pathogens. High levels of agreement between vaginal and ring surface microbiota were observed. Conclusion Sustained use of the NES/EE CVR did not increase the risk of vaginal infection and was not disruptive to

  11. Direct Amination of Nitro(pentafluorosulfanyl)benzenes through Vicarious Nucleophilic Substitution of Hydrogen

    Czech Academy of Sciences Publication Activity Database

    Pastýříková, Tereza; Iakobson, George; Vida, Norbert; Pohl, Radek; Beier, Petr

    -, č. 11 (2012), s. 2123-2126 ISSN 1434-193X R&D Projects: GA ČR GAP207/12/0072 Institutional research plan: CEZ:AV0Z40550506 Keywords : sulfur * amination * nucleophilic substitution * nitrogen heterocycles Subject RIV: CC - Organic Chemistry Impact factor: 3.344, year: 2012

  12. Hydroxylation of nitro-(pentafluorosulfanyl)benzenes via vicarious nucleophilic substitution of hydrogen

    Czech Academy of Sciences Publication Activity Database

    Beier, Petr; Pastýříková, Tereza

    2011-01-01

    Roč. 52, č. 34 (2011), s. 4392-4394 ISSN 0040-4039 R&D Projects: GA ČR GAP207/11/0344 Institutional research plan: CEZ:AV0Z40550506 Keywords : pentafluorosulfanyl group * vicarious nucleophilic substitution * hydroxylation Subject RIV: CC - Organic Chemistry Impact factor: 2.683, year: 2011

  13. Copper-Catalyzed Electrophilic Amination of Organoaluminum Nucleophiles with O-Benzoyl Hydroxylamines.

    Science.gov (United States)

    Zhou, Shuangliu; Yang, Zhiyong; Chen, Xu; Li, Yimei; Zhang, Lijun; Fang, Hong; Wang, Wei; Zhu, Xiancui; Wang, Shaowu

    2015-06-19

    A copper-catalyzed electrophilic amination of aryl and heteroaryl aluminums with N,N-dialkyl-O-benzoyl hydroxylamines that affords the corresponding anilines in good yields has been developed. The catalytic reaction proceeds very smoothly under mild conditions and exhibits good substrate scope. Moreover, the developed catalytic system is also well suited for heteroaryl aluminum nucleophiles, providing facile access to heteroaryl amines.

  14. Nucleophilic additions of [(diethoxyphosphoryl)difluoromethyl]lithium to a,b-unsaturated compounds

    Czech Academy of Sciences Publication Activity Database

    Cherkupally, Prabhakar; Beier, Petr

    2012-01-01

    Roč. 137, May (2012), s. 34-43 ISSN 0022-1139 R&D Projects: GA ČR GP203/08/P310 Institutional research plan: CEZ:AV0Z40550506 Keywords : 1,4-Addition * nucleophilic addition * difluoromethylphosphonate Subject RIV: CC - Organic Chemistry Impact factor: 1.939, year: 2012

  15. Kinetic secondary deuterium isotope effect in addition of nucleophile to m-bromobenzaldehyde

    International Nuclear Information System (INIS)

    Amaral, L. do; Rossi, M.H.

    1985-01-01

    The kinetic secondary deuterium isotope effects, KD/KH for hydrated proton catalyzed addition of semicarbazide, methoxyamine and hydroxylamine to m-bromobenzaldehyde is studied. The nature of the nucleophile, addition of the carbonyl group and the chemical reactions are evaluated. (M.J.C.) [pt

  16. Oxidative nucleophilic substitution of hydrogen in nitro(pentafluorosulfanyl)benzenes with alkyl Grignard and lithium reagents

    Czech Academy of Sciences Publication Activity Database

    Vida, Norbert; Beier, Petr

    2012-01-01

    Roč. 143, SI (2012), s. 130-134 ISSN 0022-1139 R&D Projects: GA ČR GAP207/12/0072 Institutional support: RVO:61388963 Keywords : pentafluorosulfanyl group * nucleophilic aromatic substitutions * oxidations Subject RIV: CC - Organic Chemistry Impact factor: 1.939, year: 2012

  17. Synthesis of a Fluorescent Acridone Using a Grignard Addition, Oxidation, and Nucleophilic Aromatic Substitution Reaction Sequence

    Science.gov (United States)

    Goodrich, Samuel; Patel, Miloni; Woydziak, Zachary R.

    2015-01-01

    A three-pot synthesis oriented for an undergraduate organic chemistry laboratory was developed to construct a fluorescent acridone molecule. This laboratory experiment utilizes Grignard addition to an aldehyde, alcohol oxidation, and iterative nucleophilic aromatic substitution steps to produce the final product. Each of the intermediates and the…

  18. Benzimidazoles and benzoxazoles via the nucleophilic addition of anilines to nitroalkanes.

    Science.gov (United States)

    Aksenov, Alexander V; Smirnov, Alexander N; Aksenov, Nicolai A; Bijieva, Asiyat S; Aksenova, Inna V; Rubin, Michael

    2015-04-14

    PPA-induced umpolung triggers efficient nucleophilic addition of unactivated anilines to nitroalkanes to produce N-hydroxyimidamides. The latter undergo sequential acid-promoted cyclocondensation with ortho-OH or ortho-NHR moieties to afford benzoxazoles and benzimidazoles, respectively.

  19. Organic Chemistry Students' Ideas about Nucleophiles and Electrophiles: The Role of Charges and Mechanisms

    Science.gov (United States)

    Anzovino, Mary E.; Bretz, Stacey Lowery

    2015-01-01

    Organic chemistry students struggle with reaction mechanisms and the electron-pushing formalism (EPF) used by practicing organic chemists. Faculty have identified an understanding of nucleophiles and electrophiles as one conceptual prerequisite to mastery of the EPF, but little is known about organic chemistry students' knowledge of nucleophiles…

  20. Nucleophilic difluoromethylenation of aldehydes and ketones using diethyl difluoro(trimethylsilyl)methylphosphonate

    Czech Academy of Sciences Publication Activity Database

    Alexandrova, Anastasia; Beier, Petr

    2009-01-01

    Roč. 130, č. 5 (2009), s. 493-500 ISSN 0022-1139 R&D Projects: GA ČR GP203/08/P310 Institutional research plan: CEZ:AV0Z40550506 Keywords : phosphonates * phosphates * nucleophilic additions * difluoromethylene Subject RIV: CC - Organic Chemistry Impact factor: 1.730, year: 2009

  1. Cavity Ring-Down Absorption of O2 in Air as a Temperature Sensor for an Open and a Cryogenic Optical Cavity.

    Science.gov (United States)

    Nyaupane, Parashu R; Perez-Delgado, Yasnahir; Camejo, David; Wright, Lesley M; Manzanares, Carlos E

    2017-05-01

    The A-band of oxygen has been measured at low resolution at temperatures between 90 K and 373 K using the phase shift cavity ring down (PS-CRD) technique. For temperatures between 90 K and 295 K, the PS-CRD technique presented here involves an optical cavity attached to a cryostat. The static cell and mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of the cell can be changed between 77 K and 295 K. For temperatures above 295 K, a hollow glass cylindrical tube without windows has been inserted inside an optical cavity to measure the temperature of air flowing through the tube. The cavity consists of two highly reflective mirrors which are mounted parallel to each other and separated by a distance of 93 cm. In this experiment, air is passed through a heated tube. The temperature of the air flowing through the tube is determined by measuring the intensity of the oxygen absorption as a function of the wavenumber. The A-band of oxygen is measured between 298 K and 373 K, with several air flow rates. To obtain the temperature, the energy of the lower rotational state for seven selected rotational transitions is linearly fitted to a logarithmic function that contains the relative intensity of the rotational transition, the initial and final rotational quantum numbers, and the energy of the transition. Accuracy of the temperature measurement is determined by comparing the calculated temperature from the spectra with the temperature obtained from a calibrated thermocouple inserted at the center of the tube. This flowing air temperature sensor will be used to measure the temperatures of cooling air at the input (cold air) and output (hot air) after cooling the blades of a laboratory gas turbine. The results could contribute to improvements in turbine blade cooling design.

  2. Propellers in Saturn's rings

    Science.gov (United States)

    Sremcevic, M.; Stewart, G. R.; Albers, N.; Esposito, L. W.

    2013-12-01

    Theoretical studies and simulations have demonstrated the effects caused by objects embedded in planetary rings. Even if the objects are too small to be directly observed, each creates a much larger gravitational imprint on the surrounding ring material. These strongly depend on the mass of the object and range from "S" like propeller-shaped structures for about 100m-sized icy bodies to the opening of circumferential gaps as in the case of the embedded moons Pan and Daphnis and their corresponding Encke and Keeler Gaps. Since the beginning of the Cassini mission many of these smaller objects (~data from Cassini Ultraviolet Imaging Spectrograph (UVIS) and Imaging Science Subsystem (ISS) experiments. We show evidence that B ring seems to harbor two distinct populations of propellers: "big" propellers covering tens of degrees in azimuth situated in the densest part of B ring, and "small" propellers in less dense inner B ring that are similar in size and shape to known A ring propellers. The population of "big" propellers is exemplified with a single object which is observed for 5 years of Cassini data. The object is seen as a very elongated bright stripe (40 degrees wide) in unlit Cassini images, and dark stripe in lit geometries. In total we report observing the feature in images at 18 different epochs between 2005 and 2010. In UVIS occultations we observe this feature as an optical depth depletion in 14 out of 93 occultation cuts at corrotating longitudes compatible with imaging data. Combining the available Cassini data we infer that the object is a partial gap located at r=112,921km embedded in the high optical depth region of the B ring. The gap moves at Kepler speed appropriate for its radial location. Radial offsets of the gap locations in UVIS occultations are consistent with an asymmetric propeller shape. The asymmetry of the observed shape is most likely a consequence of the strong surface mass density gradient, as the feature is located at an edge between

  3. Common pass decentered annular ring resonator

    Energy Technology Data Exchange (ETDEWEB)

    Holmes, D. A.; Waite, T. R.

    1985-04-30

    An optical resonator having an annular cylindrical gain region for use in a chemical laser or the like in which two ring-shaped mirrors having substantially conical reflecting surfaces are spaced apart along a common axis of revolution of the respective conical surfaces. A central conical mirror reflects incident light directed along said axis radially outwardly to the reflecting surface of a first one of the ring-shaped mirrors. The radial light rays are reflected by the first ring mirror to the second ring mirror within an annular cylindrical volume concentric with said common axis and forming a gain region. Light rays impinging on the second ring mirror are reflected to diametrically opposite points on the same conical mirror surfaces and back to the first ring mirror through the same annular cylindrical volume. The return rays are then reflected by the conical mirror surface of the first ring mirror back to the central conical mirror. The mirror surfaces are angled such that the return rays are reflected back along the common axis by the central mirror in a concentric annular cylindrical volume. A scraper mirror having a central opening centered on said axis and an offset opening reflects all but the rays passing through the two openings in an output beam. The rays passing through the second opening are reflected back through the first opening to provide feedback.

  4. Breaking the Dogma of Aldolase Specificity: Simple Aliphatic Ketones and Aldehydes are Nucleophiles for Fructose-6-phosphate Aldolase.

    Science.gov (United States)

    Roldán, Raquel; Sanchez-Moreno, Israel; Scheidt, Thomas; Hélaine, Virgil; Lemaire, Marielle; Parella, Teodor; Clapés, Pere; Fessner, Wolf-Dieter; Guérard-Hélaine, Christine

    2017-04-11

    d-Fructose-6-phosphate aldolase (FSA) was probed for extended nucleophile promiscuity by using a series of fluorogenic substrates to reveal retro-aldol activity. Four nucleophiles ethanal, propanone, butanone, and cyclopentanone were subsequently confirmed to be non-natural substrates in the synthesis direction using the wild-type enzyme and its D6H variant. This exceptional widening of the nucleophile substrate scope offers a rapid entry, in good yields and high stereoselectivity, to less oxygenated alkyl ketones and aldehydes, which was hitherto impossible. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Synthesis and Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 5. Influence of Mesogenic Group and Interconnecting Group on the Thermotropic Behavior of the Resulting Polymers

    Science.gov (United States)

    1992-07-22

    Scheme I. The first nucleophilic displacement of halide of an n-haloalkan-l-ol with 4-cyano-4’-hydroxybiphenyl employed potassium carbonate in...21 𔃼 polysiloxanes, 23.24 and polyacrylates . 2- All these polymers exhibit an odd-even effect. If one considers the total number of atoms between the...0.019 mol) and 4’-methoxy-4-hydroxybiphenyl (4.0g, 0.020 tool) were heated at 100°C in 40 mL of dimethylformamide in the presence of potassium carbonate

  6. Chromatographic assessment of two hybrid monoliths prepared via epoxy-amine ring-opening polymerization and methacrylate-based free radical polymerization using methacrylate epoxy cyclosiloxane as functional monomer.

    Science.gov (United States)

    Wang, Hongwei; Ou, Junjie; Lin, Hui; Liu, Zhongshan; Huang, Guang; Dong, Jing; Zou, Hanfa

    2014-11-07

    Two kinds of hybrid monolithic columns were prepared by using methacrylate epoxy cyclosiloxane (epoxy-MA) as functional monomer, containing three epoxy moieties and one methacrylate group. One column was in situ fabricated by ring-opening polymerization of epoxy-MA and 1,10-diaminodecane (DAD) using a porogenic system consisting of isopropanol (IPA), H2O and ethanol at 65°C for 12h. The other was prepared by free radical polymerization of epoxy-MA and ethylene dimethacrylate (EDMA) using 1-propanol and 1,4-butanediol as the porogenic solvents at 60°C for 12h. Two hybrid monoliths were investigated on the morphology and chromatographic assessment. Although two kinds of monolithic columns were prepared with epoxy-MA, their morphologies looked rather different. It could be found that the epoxy-MA-DAD monolith possessed higher column efficiencies (25,000-34,000plates/m) for the separation of alkylbenzenes than the epoxy-MA-EDMA monolith (12,000-13,000plates/m) in reversed-phase nano-liquid chromatography (nano-LC). Depending on the remaining epoxy or methacrylate groups on the surface of two pristine monoliths, the epoxy-MA-EDMA monolith could be easily modified with 1-octadecylamine (ODA) via ring-opening reaction, while the epoxy-MA-DAD monolith could be modified with stearyl methacrylate (SMA) via free radical reaction. The chromatographic performance for the separation of alkylbenzenes on SMA-modified epoxy-MA-DAD monolith was remarkably improved (42,000-54,000 plates/m) when compared with that on pristine epoxy-MA-DAD monolith, while it was not obviously enhanced on ODA-modified epoxy-MA-EDMA monolith when compared with that on pristine epoxy-MA-EDMA monolith. The enhancement of the column efficiency of epoxy-MA-DAD monolith after modification might be ascribed to the decreased mass-transfer resistence. The two kinds of hybrid monoliths were also applied for separations of six phenols and seven basic compounds in nano-LC. Copyright © 2014 Elsevier B.V. All

  7. Report of the eRHIC Ring-Ring Working Group

    Energy Technology Data Exchange (ETDEWEB)

    Aschenauer, E. C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Berg, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Blaskiewicz, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Brennan, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Fedotov, A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Fischer, W. [Brookhaven National Lab. (BNL), Upton, NY (United States); Litvinenko, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Montag, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Palmer, R. [Brookhaven National Lab. (BNL), Upton, NY (United States); Parker, B. [Brookhaven National Lab. (BNL), Upton, NY (United States); Peggs, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Ptitsyn, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Ranjbar, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Tepikian, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Trbojevic, D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Willeke, F. [Brookhaven National Lab. (BNL), Upton, NY (United States)

    2015-10-13

    This report evaluates the ring-ring option for eRHIC as a lower risk alternative to the linac-ring option. The reduced risk goes along with a reduced initial luminosity performance. However, a luminosity upgrade path is kept open. This upgrade path consists of two branches, with the ultimate upgrade being either a ring-ring or a linac-ring scheme. The linac-ring upgrade could be almost identical to the proposed linac-ring scheme, which is based on an ERL in the RHIC tunnel. This linac-ring version has been studied in great detail over the past ten years, and its significant risks are known. On the other hand, no detailed work on an ultimate performance ring-ring scenario has been performed yet, other than the development of a consistent parameter set. Pursuing the ring-ring upgrade path introduces high risks and requires significant design work that is beyond the scope of this report.

  8. A General Ligand Design for Gold Catalysis allowing Ligand-Directed Anti Nucleophilic Attack of Alkynes

    Science.gov (United States)

    Wang, Yanzhao; Wang, Zhixun; Li, Yuxue; Wu, Gongde; Cao, Zheng; Zhang, Liming

    2014-01-01

    Most homogenous gold catalyses demand ≥0.5 mol % catalyst loading. Due to the high cost of gold, these reactions are unlikely to be applicable in medium or large scale applications. Here we disclose a novel ligand design based on the privileged biphenyl-2-phosphine framework that offers a potentially general approach to dramatically lowering catalyst loading. In this design, an amide group at the 3’ position of the ligand framework directs and promotes nucleophilic attack at the ligand gold complex-activated alkyne, which is unprecedented in homogeneous gold catalysis considering the spatial challenge of using ligand to reach antiapproaching nucleophile in a linear P-Au-alkyne centroid structure. With such a ligand, the gold(I) complex becomes highly efficient in catalyzing acid addition to alkynes, with a turnover number up to 99,000. Density functional theory calculations support the role of the amide moiety in directing the attack of carboxylic acid via hydrogen bonding. PMID:24704803

  9. Nucleophilic reactions of hydrazido(2-) complexes of molybdenum and tungsten with succinyl dichloride and phenyl isocyanate

    International Nuclear Information System (INIS)

    Iwanami, Kiyotaka; Mizobe, Yasushi; Takahashi, Tamotsu; Kodama, Teruyuki; Uchida, Yasuzo

    1981-01-01

    Nucleophilic attack of the WNNH 2 group in the hydrazido(2-) complex [WF(NNH 2 )(dpe) 2 ][BF 4 ] (dpe = Ph 2 PCH 2 CH 2 PPh 2 ) on succinyl dichloride gives a novel ethanedioylhydrazido(2-) complex, [WF(NNCOCH 2 CH 2 CO)(dpe) 2 ][BF 4 ]. X-Ray structural analysis shows that the carbon, nitrogen, and oxygen atoms of the ethanedioylhydrazido(2-) ligand lie nearly in the same plane, indicating sp 2 character of the nitrogen atom bearing the two carbonyl groups. Phenyl isocyanate also undergoes nucleophilic attack by the hydrazido(2-) complex [MBr(NNH 2 )(dpe) 2 ]Br (M = Mo or W) to yield the phenylsemicarbazido(2-) type complex, [MBr(NNHCONHPh)(dpe) 2 ]Br. Treatment of the semicarbazido(2-) complex with triethylamine gives a new diazenido complex [MBr(NNCONHPh)(dpe) 2 ]. (author)

  10. Homologation chemistry with nucleophilic α-substituted organometallic reagents: chemocontrol, new concepts and (solved) challenges.

    Science.gov (United States)

    Castoldi, Laura; Monticelli, Serena; Senatore, Raffaele; Ielo, Laura; Pace, Vittorio

    2018-05-31

    The transfer of a reactive nucleophilic CH2X unit into a preformed bond enables the introduction of a fragment featuring the exact and desired degree of functionalization through a single synthetic operation. The instability of metallated α-organometallic species often poses serious questions regarding the practicability of using this conceptually intuitive and simple approach for forming C-C or C-heteroatom bonds. A deep understanding of processes regulating the formation of these nucleophiles is a precious source of inspiration not only for successfully applying theoretically feasible transformations (i.e. determining how to employ a given reagent), but also for designing new reactions which ultimately lead to the introduction of molecular complexity via short experimental sequences.

  11. Kayser-Fleischer Rings

    Science.gov (United States)

    ... Support Contacts Lab Tracker/Copper Calculator Stories Programs & Research ... About Everything you need to know about Wilson Disease Kayser-Fleischer Rings Definition Kayser-Fleischer Ring: Clinical sign. Brownish-yellow ring visible around the corneo- ...

  12. Barbier Continuous Flow Preparation and Reactions of Carbamoyllithiums for Nucleophilic Amidation.

    Science.gov (United States)

    Ganiek, Maximilian A; Becker, Matthias R; Berionni, Guillaume; Zipse, Hendrik; Knochel, Paul

    2017-08-01

    An ambient temperature continuous flow method for nucleophilic amidation and thioamidation is described. Deprotonation of formamides by lithium diisopropylamine (LDA) affords carbamoyllithium intermediates that are quenched in situ with various electrophiles such as ketones, allyl bromides, Weinreb and morpholino amides. The nature of the reactive lithium intermediates and the thermodynamics of the metalation were further investigated by ab initio calculations and kinetic experiments. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Enabling nucleophilic substitution reactions of activated alkyl fluorides through hydrogen bonding.

    Science.gov (United States)

    Champagne, Pier Alexandre; Pomarole, Julien; Thérien, Marie-Ève; Benhassine, Yasmine; Beaulieu, Samuel; Legault, Claude Y; Paquin, Jean-François

    2013-05-03

    It was discovered that the presence of water as a cosolvent enables the reaction of activated alkyl fluorides for bimolecular nucleophilic substitution reactions. DFT calculations show that activation proceeds through stabilization of the transition structure by a stronger F···H2O interaction and diminishing C-F bond elongation, and not simple transition state electrostatic stabilization. Overall, the findings put forward a distinct strategy for C-F bond activation through H-bonding.

  14. Synthesis and structure of a ferric complex of 2,6-di(1H-pyrazol-3-yl)pyridine and its excellent performance in the redox-controlled living ring-opening polymerization of ε-caprolactone.

    Science.gov (United States)

    Fang, Yang-Yang; Gong, Wei-Jie; Shang, Xiu-Juan; Li, Hong-Xi; Gao, Jun; Lang, Jian-Ping

    2014-06-14

    The reaction of FeCl3 with a pincer ligand, 2,6-di(1H-pyrazol-3-yl)pyridine (bppyH2), produced a mononuclear Fe(III) complex [Fe(bppyH2)Cl3] (1), which could be reduced to the corresponding Fe(II) dichloride complex [Fe(bppyH2)Cl2] (2) by suitable reducing agents such as Cp2Co or Fe powder. 1 and 2 exhibited a reversible transformation from each other with appropriate redox reagents. 1 could be utilized as a pre-catalyst to initiate the ring-opening polymerization of ε-caprolactone in the presence of alcohol but did not work. The 1/alcohol system displayed characteristics of a well-controlled polymerization with the resulting poly(ε-caprolactone) having low molecular weight distributions, a linear tendency of molecular weight evolution with conversion, and polymer growth observed for the sequential additions of ε-caprolactone monomer to the polymerization reaction. The polymerization was completely turned off by the in situ reduction of the catalytic Fe center via Cp2Co and then turned back upon the addition of [Cp2Fe]PF6. The rate of polymerization was modified by switching in situ between the Fe(III) and Fe(II) species.

  15. Electrophilic properties of patulin. Adduct structures and reaction pathways with 4-bromothiophenol and other model nucleophiles.

    Science.gov (United States)

    Fliege, R; Metzler, M

    2000-05-01

    The mycotoxin patulin (PAT) is believed to exert its cytotoxic and chromosome-damaging effects by forming covalent adducts with essential cellular thiols. Since the chemical structures of such adducts are unknown to date, we have studied the reaction of PAT and its O-acetylated derivative with the monofunctional thiol model compound 4-bromothiophenol (BTP), which was chosen due to analytical advantages. By means of analytical and preparative high-performance liquid chromatography, 16 adducts of PAT and 3 adducts of acetyl-PAT were isolated and their chemical structures elucidated by (1)H and (13)C NMR, IR, and UV spectroscopy. Time course studies and analysis of daughter product formation from isolated intermediate adducts led to a detailed scheme for the reaction of PAT with BTP. The structures of adducts of PAT formed with other model nucleophiles, e. g., the aliphatic thiol 2-mercaptoethanol and the aromatic amine 4-bromoaniline, were also elucidated and found to corroborate the reaction scheme. In addition, one further reaction pathway was observed with 2-mercaptoethanol, which appears to be independent from those found for BTP. Our study with model nucleophiles provides insights into the electrophilic reactivity of PAT and proved to be useful for the structure elucidation of PAT adducts with biological nucleophiles of toxicological relevance, as will be reported by Fliege and Metzler [(2000) Chem. Res. Toxicol. 13, 373-381].

  16. Electronic forces as descriptors of nucleophilic and electrophilic regioselectivity and stereoselectivity.

    Science.gov (United States)

    Liu, Shubin; Rong, Chunying; Lu, Tian

    2017-01-04

    One of the main tasks of theoretical chemistry is to rationalize computational results with chemical insights. Key concepts of such nature include nucleophilicity, electrophilicity, regioselectivity, and stereoselectivity. While computational tools are available to predict barrier heights and other reactivity properties with acceptable accuracy, a conceptual framework to appreciate above quantities is still lacking. In this work, we introduce the electronic force as the fundamental driving force of chemical processes to understand and predict molecular reactivity. It has three components but only two are independent. These forces, electrostatic and steric, can be employed as reliable descriptors for nucleophilic and electrophilic regioselectivity and stereoselectivity. The advantages of using these forces to evaluate molecular reactivity are that electrophilic and nucleophilic attacks are featured by distinct characteristics in the electrostatic force and no knowledge of quantum effects included in the kinetic and exchange-correlation energies is required. Examples are provided to highlight the validity and general applicability of these reactivity descriptors. Possible applications in ambident reactivity, σ and π holes, frustrated Lewis pairs, and stereoselective reactions are also included in this work.

  17. ASSOCIATIVE RINGS SOLVED AS LIE RINGS

    Directory of Open Access Journals (Sweden)

    M. B. Smirnov

    2011-01-01

    Full Text Available The paper has proved that an associative ring which is solvable of a n- class as a Lie ring has a nilpotent ideal of the nilpotent class not more than 3×10n–2  and a corresponding quotient ring satisfies an identity [[x1, x2, [x3, x4

  18. Stirling engine piston ring

    Science.gov (United States)

    Howarth, Roy B.

    1983-01-01

    A piston ring design for a Stirling engine wherein the contact pressure between the piston and the cylinder is maintained at a uniform level, independent of engine conditions through a balancing of the pressure exerted upon the ring's surface and thereby allowing the contact pressure on the ring to be predetermined through the use of a preloaded expander ring.

  19. Alternative loop rings

    CERN Document Server

    Goodaire, EG; Polcino Milies, C

    1996-01-01

    For the past ten years, alternative loop rings have intrigued mathematicians from a wide cross-section of modern algebra. As a consequence, the theory of alternative loop rings has grown tremendously. One of the main developments is the complete characterization of loops which have an alternative but not associative, loop ring. Furthermore, there is a very close relationship between the algebraic structures of loop rings and of group rings over 2-groups. Another major topic of research is the study of the unit loop of the integral loop ring. Here the interaction between loop rings and group ri

  20. Tyrosyl-DNA Phosphodiesterase I Catalytic Mutants Reveal an Alternative Nucleophile That Can Catalyze Substrate Cleavage*

    Science.gov (United States)

    Comeaux, Evan Q.; Cuya, Selma M.; Kojima, Kyoko; Jafari, Nauzanene; Wanzeck, Keith C.; Mobley, James A.; Bjornsti, Mary-Ann; van Waardenburg, Robert C. A. M.

    2015-01-01

    Tyrosyl-DNA phosphodiesterase I (Tdp1) catalyzes the repair of 3′-DNA adducts, such as the 3′-phosphotyrosyl linkage of DNA topoisomerase I to DNA. Tdp1 contains two conserved catalytic histidines: a nucleophilic His (Hisnuc) that attacks DNA adducts to form a covalent 3′-phosphohistidyl intermediate and a general acid/base His (Hisgab), which resolves the Tdp1-DNA linkage. A Hisnuc to Ala mutant protein is reportedly inactive, whereas the autosomal recessive neurodegenerative disease SCAN1 has been attributed to the enhanced stability of the Tdp1-DNA intermediate induced by mutation of Hisgab to Arg. However, here we report that expression of the yeast HisnucAla (H182A) mutant actually induced topoisomerase I-dependent cytotoxicity and further enhanced the cytotoxicity of Tdp1 Hisgab mutants, including H432N and the SCAN1-related H432R. Moreover, the HisnucAla mutant was catalytically active in vitro, albeit at levels 85-fold less than that observed with wild type Tdp1. In contrast, the HisnucPhe mutant was catalytically inactive and suppressed Hisgab mutant-induced toxicity. These data suggest that the activity of another nucleophile when Hisnuc is replaced with residues containing a small side chain (Ala, Asn, and Gln), but not with a bulky side chain. Indeed, genetic, biochemical, and mass spectrometry analyses show that a highly conserved His, immediately N-terminal to Hisnuc, can act as a nucleophile to catalyze the formation of a covalent Tdp1-DNA intermediate. These findings suggest that the flexibility of Tdp1 active site residues may impair the resolution of mutant Tdp1 covalent phosphohistidyl intermediates and provide the rationale for developing chemotherapeutics that stabilize the covalent Tdp1-DNA intermediate. PMID:25609251

  1. Nucleophilic Fluorination Reactions in Novel Reaction Media for 18F-Fluorine Labeling Method

    International Nuclear Information System (INIS)

    Kim, Dong Wook; Jeong, Hwan Jeong; Lim, Seok Tae; Sohn, Myung Hee

    2009-01-01

    Noninvasive imaging of molecular and biological processes in living subjects with positron emission tomography (PET) provides exciting opportunities to monitor metabolism and detect diseases in humans. Measuring these processes with PET requires the preparation of specific molecular imaging probes labeled with 18F-fluorine. In this review we describe recent methods and novel trends for the introduction of 18 F-fluorine into molecules which in turn are intended to serve as imaging agents for PET study. Nucleophilic 18 F-fluorination of some halo- and mesyloxyalkanes to the corresponding 18 F-fluoroalkanes with 18 F-fluoride obtained from an 18 O(p,n) 18 F reaction, using novel reaction media system such as an ionic liquidor tert-alcohol, has been studied as a new method for 18 F-fluorine labeling. Ionic liquid method is rapid and particularly convenient because 18 F-fluoride in H 2 O can be added directly to the reaction media, obviating the careful drying that is typically required for currently used radiofluorination methods. The nonpolar protic tert-alcohol enhances the nucleophilicity of the fluoride ion dramatically in the absence of any kind of catalyst, greatly increasing the rate of the nucleophilic fluorination and reducing formation of byproducts compared with conventional methods using dipolar aprotic solvents. The great efficacy of this method is a particular advantage in labeling radiopharmaceuticals with 18 F-fluorine for PET imaging, and it is illustrated by the synthesis of 18 F-fluoride radiolabeled molecular imaging probes, such as 18 F-FDG, 18 F-FLT, 18 F-FP-CIT, and 18 F-FMISO, in high yield and purity and in shorter times compared to conventional syntheses

  2. Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: final results from the Guinea ring vaccination, open-label, cluster-randomised trial (Ebola Ça Suffit!).

    Science.gov (United States)

    Henao-Restrepo, Ana Maria; Camacho, Anton; Longini, Ira M; Watson, Conall H; Edmunds, W John; Egger, Matthias; Carroll, Miles W; Dean, Natalie E; Diatta, Ibrahima; Doumbia, Moussa; Draguez, Bertrand; Duraffour, Sophie; Enwere, Godwin; Grais, Rebecca; Gunther, Stephan; Gsell, Pierre-Stéphane; Hossmann, Stefanie; Watle, Sara Viksmoen; Kondé, Mandy Kader; Kéïta, Sakoba; Kone, Souleymane; Kuisma, Eewa; Levine, Myron M; Mandal, Sema; Mauget, Thomas; Norheim, Gunnstein; Riveros, Ximena; Soumah, Aboubacar; Trelle, Sven; Vicari, Andrea S; Røttingen, John-Arne; Kieny, Marie-Paule

    2017-02-04

    rVSV-ZEBOV is a recombinant, replication competent vesicular stomatitis virus-based candidate vaccine expressing a surface glycoprotein of Zaire Ebolavirus. We tested the effect of rVSV-ZEBOV in preventing Ebola virus disease in contacts and contacts of contacts of recently confirmed cases in Guinea, west Africa. We did an open-label, cluster-randomised ring vaccination trial (Ebola ça Suffit!) in the communities of Conakry and eight surrounding prefectures in the Basse-Guinée region of Guinea, and in Tomkolili and Bombali in Sierra Leone. We assessed the efficacy of a single intramuscular dose of rVSV-ZEBOV (2×10 7 plaque-forming units administered in the deltoid muscle) in the prevention of laboratory confirmed Ebola virus disease. After confirmation of a case of Ebola virus disease, we definitively enumerated on a list a ring (cluster) of all their contacts and contacts of contacts including named contacts and contacts of contacts who were absent at the time of the trial team visit. The list was archived, then we randomly assigned clusters (1:1) to either immediate vaccination or delayed vaccination (21 days later) of all eligible individuals (eg, those aged ≥18 years and not pregnant, breastfeeding, or severely ill). An independent statistician generated the assignment sequence using block randomisation with randomly varying blocks, stratified by location (urban vs rural) and size of rings (≤20 individuals vs >20 individuals). Ebola response teams and laboratory workers were unaware of assignments. After a recommendation by an independent data and safety monitoring board, randomisation was stopped and immediate vaccination was also offered to children aged 6-17 years and all identified rings. The prespecified primary outcome was a laboratory confirmed case of Ebola virus disease with onset 10 days or more from randomisation. The primary analysis compared the incidence of Ebola virus disease in eligible and vaccinated individuals assigned to immediate

  3. Laparoscopic appendicectomy using endo-ring applicator and fallope rings

    International Nuclear Information System (INIS)

    Ali, Iyoob V; Maliekkal, Joji I

    2009-01-01

    Wider adoption of laparoscopic appendicectomy (LA) is limited by problems in securing the appendiceal base as well as the cost and the duration compared with the open procedure. The objective of this study was to assess the feasibility and efficacy of a new method for securing the appendiceal base in LA, so as to make the entire procedure simpler and cheaper, and hence, more popular. Twenty-five patients who were candidates for appendicectomy (emergency as well as elective) and willing for the laparoscopic procedure were selected for this study. Ports used were 10 mm at the umbilicus, 5 mm at the lower right iliac fossa, and 10 mm at the left iliac fossa. Extremely friable, ruptured, or turgid organs of diameters larger than 8 mm were excluded from the study. The mesoappendix was divided close to the appendix by diathermy. Fallope rings were applied to the appendiceal base using a special ring applicator, and the appendix was divided and extracted through the lumen of the applicator. The procedure was successful in 23 (92%) cases, and the mean duration of the procedure was 20 minutes (15-32 minutes). There were no procedural complications seen during a median follow-up of two weeks. The equipment and rings were cheaper when compared with that of the standard methods of securing the base of the appendix. LA using fallope rings is a safe, simple, easy-to-learn, and economically viable method. (author)

  4. Transcatheter Mitral Valve-in-Ring Implantation

    LENUS (Irish Health Repository)

    Tanner, RE

    2018-05-01

    Failed surgical mitral valve repair using an annuloplasty ring has traditionally been treated with surgical valve replacement or repair1. For patients at high risk for repeat open heart surgery, placement of a trans-catheter aortic valve (i.e., TAVI valve) within the mitral ring (i.e., Mitral-Valve-in-Ring, MViR) has emerged as a novel alternative treatment strategy2-5 . We describe our experience of a failed mitral valve repair that was successfully treated with a TAVI valve delivered via the trans-septal approach, and summarise the data relating to this emerging treatment strategy.

  5. Nucleophilic addition of amines to the activated ethylene bond in non-aqueous media

    International Nuclear Information System (INIS)

    Perepichka, Igor F.; Popov, Anatolii F.

    1995-01-01

    The kinetics of addition of a number of primary and secondary aliphatic amines to trans-(2-furyl) nitro ethylene (1) has been studied in solvents of various polarities (from acetonitrile, ε 37.5, to heptane, ε 1.89). It has been shown that the reaction is catalysed both by the amine reagent and by tertiary amines. On the basis of analyzing the observed kinetic regularities a stepwise reaction mechanism has been proposed which involves formation of zwitterionic intermediate (3) at the first equilibrium step (k 1 , K 1 ) which is then converted into the reaction product by means of proton transfer in parallel routes, the non-catalytic one (k 2 ) and that catalysed by the initial (K 3 ) or tertiary (K 4 ) amine. The observed high values of the deuterium isotope effects in the reaction (K H /K D ∼ 2.3 - 8.9) confirm that proton transfer occurs in the rate-limiting step of the reaction (primary kinetic isotope effect). The third order by amine kinetic route is observed in low polar media which is due to participation of amine dimers (R 2 NH HNR 2 ) in the reaction. The observed kinetic regularities are compared with those for the nucleophilic aromatic substitution reactions in low-polar media, and the conclusion has been made that the reaction route of the third order by amine proceeds as reversible nucleophilic attack by amine dimer and following base-catalysed transformation of the intermediate into the product. (author)

  6. Abstraction of methyl from neutral Fischer-type carbene complexes: A new site for nucleophilic attack

    Energy Technology Data Exchange (ETDEWEB)

    Toomey, L.M.; Atwood, J.D. [State Univ. of New York, Buffalo, NY (United States)

    1997-02-04

    Reactions of Fischer-type carbene complexes, M(CO){sub 5}(C(OMe)pH) (M = Cr, W), with metal carbonyl anions (M`{sup -} = CpFe(CO){sub 2}{sup -@}, Re(CO){sub 5}{sup -}, Mn(CO){sub 4}PPh{sub 3}{sup -}, Co(CO){sub 3}PPh{sub 3}{sup -}, Cp{sup *}Cr(CO){sub 3}{sup -}, CpMo(CO){sub 3}{sup -}) result in demethylation of the carbene complexes. The products are M(CO){sub 5}C(O)Ph{sup -} and M`-Me, characterized by infrared and NMR spectroscopy. A slower rate for reaction with W(CO){sub 5}(C(OEt)Ph) in comparison to the methyl analogue is consistent with nucleophilic attack of the metal carbonyl anion on the methyl of the methoxy group of the carbene. This is a new type of nucleophilic attack of a Fischer-type carbene. 22 refs., 1 fig., 1 tab.

  7. Development of selective colorimetric probes for hydrogen sulfide based on nucleophilic aromatic substitution.

    Science.gov (United States)

    Montoya, Leticia A; Pearce, Taylor F; Hansen, Ryan J; Zakharov, Lev N; Pluth, Michael D

    2013-07-05

    Hydrogen sulfide is an important biological signaling molecule and an important environmental target for detection. A major challenge in developing H2S detection methods is separating the often similar reactivity of thiols and other nucleophiles from H2S. To address this need, the nucleophilic aromatic substitution (SNAr) reaction of H2S with electron-poor aromatic electrophiles was developed as a strategy to separate H2S and thiol reactivity. Treatment of aqueous solutions of nitrobenzofurazan (7-nitro-1,2,3-benzoxadiazole, NBD) thioethers with H2S resulted in thiol extrusion and formation of nitrobenzofurazan thiol (λmax = 534 nm). This reactivity allows for unwanted thioether products to be converted to the desired nitrobenzofurazan thiol upon reaction with H2S. The scope of the reaction was investigated using a Hammett linear free energy relationship study, and the determined ρ = +0.34 is consistent with the proposed SN2Ar reaction mechanism. The efficacy of the developed probes was demonstrated in buffer and in serum with associated submicromolar detection limits as low as 190 nM (buffer) and 380 nM (serum). Furthermore, the sigmoidal response of nitrobenzofurazan electrophiles with H2S can be fit to accurately quantify H2S. The developed detection strategy offers a manifold for H2S detection that we foresee being applied in various future applications.

  8. Reduced Reactivity of Amines against Nucleophilic Substitution via Reversible Reaction with Carbon Dioxide

    Directory of Open Access Journals (Sweden)

    Fiaz S. Mohammed

    2015-12-01

    Full Text Available The reversible reaction of carbon dioxide (CO2 with primary amines to form alkyl-ammonium carbamates is demonstrated in this work to reduce amine reactivity against nucleophilic substitution reactions with benzophenone and phenyl isocyanate. The reversible formation of carbamates has been recently exploited for a number of unique applications including the formation of reversible ionic liquids and surfactants. For these applications, reduced reactivity of the carbamate is imperative, particularly for applications in reactions and separations. In this work, carbamate formation resulted in a 67% reduction in yield for urea synthesis and 55% reduction for imine synthesis. Furthermore, the amine reactivity can be recovered upon reversal of the carbamate reaction, demonstrating reversibility. The strong nucleophilic properties of amines often require protection/de-protection schemes during bi-functional coupling reactions. This typically requires three separate reaction steps to achieve a single transformation, which is the motivation behind Green Chemistry Principle #8: Reduce Derivatives. Based upon the reduced reactivity, there is potential to employ the reversible carbamate reaction as an alternative method for amine protection in the presence of competing reactions. For the context of this work, CO2 is envisioned as a green protecting agent to suppress formation of n-phenyl benzophenoneimine and various n-phenyl–n-alky ureas.

  9. Rings in drugs.

    Science.gov (United States)

    Taylor, Richard D; MacCoss, Malcolm; Lawson, Alastair D G

    2014-07-24

    We have analyzed the rings, ring systems, and frameworks in drugs listed in the FDA Orange Book to understand the frequency, timelines, molecular property space, and the application of these rings in different therapeutic areas and target classes. This analysis shows that there are only 351 ring systems and 1197 frameworks in drugs that came onto the market before 2013. Furthermore, on average six new ring systems enter drug space each year and approximately 28% of new drugs contain a new ring system. Moreover, it is very unusual for a drug to contain more than one new ring system and the majority of the most frequently used ring systems (83%) were first used in drugs developed prior to 1983. These observations give insight into the chemical novelty of drugs and potentially efficient ways to assess compound libraries and develop compounds from hit identification to lead optimization and beyond.

  10. Birth Control Ring

    Science.gov (United States)

    ... Health Food & Fitness Diseases & Conditions Infections Drugs & Alcohol School & Jobs Sports Expert Answers (Q&A) Staying Safe Videos for Educators Search English Español Birth Control Ring KidsHealth / For Teens / Birth Control Ring What's ...

  11. Groups, rings, modules

    CERN Document Server

    Auslander, Maurice

    2014-01-01

    This classic monograph is geared toward advanced undergraduates and graduate students. The treatment presupposes some familiarity with sets, groups, rings, and vector spaces. The four-part approach begins with examinations of sets and maps, monoids and groups, categories, and rings. The second part explores unique factorization domains, general module theory, semisimple rings and modules, and Artinian rings. Part three's topics include localization and tensor products, principal ideal domains, and applications of fundamental theorem. The fourth and final part covers algebraic field extensions

  12. Mechanism of Oxidative Amidation of Nitroalkanes with Oxygen and Amine Nucleophiles by Using Electrophilic Iodine.

    Science.gov (United States)

    Li, Jing; Lear, Martin J; Kwon, Eunsang; Hayashi, Yujiro

    2016-04-11

    Recently, we developed a direct method to oxidatively convert primary nitroalkanes into amides that entailed mixing an iodonium source with an amine, base, and oxygen. Herein, we systematically investigated the mechanism and likely intermediates of such methods. We conclude that an amine-iodonium complex first forms through N-halogen bonding. This complex reacts with aci-nitronates to give both α-iodo- and α,α-diiodonitroalkanes, which can act as alternative sources of electrophilic iodine and also generate an extra equimolar amount of I(+) under O2. In particular, evidence supports α,α-diiodonitroalkane intermediates reacting with molecular oxygen to form a peroxy adduct; alternatively, these tetrahedral intermediates rearrange anaerobically to form a cleavable nitrite ester. In either case, activated esters are proposed to form that eventually reacts with nucleophilic amines in a traditional fashion. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Nucleophilic radioiodination of 6-bromocholesterol via non-isotopic exchange reaction in molten state

    International Nuclear Information System (INIS)

    El-Shaboury, G.; Farah, K.; El-Tawoosy, M.

    2001-01-01

    A synthetic method for preparing radioiodinated 6-[ 125 I]iodocholesterol [CL-6- 125 I] for adrenal evaluation is described. The radioiodine atom was incorporated onto the cholesterol molecule via non-isotopic exchange between 6-bromocholesterol [CL-6-Br] and radioiodine as iodide ion [ 125 I - ] in a molten state. The different parameters affecting the yield of exchange were investigated using 125 I (T 1/2 ≅ 60 d) to centralize the different physical and chemical reaction conditions and purification of the final product as pure as 6-[ 125 I]iodocholesterol. The method was suitable to either 131 I (T 1/2 ≅ 8 d) nucleophilic radioiodination which facilitates the scanning of the adrenal for a few days after administration or the use of 124 I (T 1/2 ≅ 4.16 d) nucleophilic radioiodination for PET evaluation of the adrenal. TLC as well as HPLC chromatographic analysis is used to determine the efficiency of the exchange reactions under different chemical reaction conditions and to monitor the stability of the final product as pure as CL-6- 125 I with radiochemical purity of ≅99%. This no-carrier-added method improved the speed of the reaction and affords high radiochemical yield of 90% and suitable specific activity due to the use of CL-6-Br rather than CL-6-I as substrate. Kinetic studies revealed second order iodine-bromine exchange reaction. The activation energy for the exchange reaction in ammonium acetate (m.p. 114 deg C) was calculated to be 4.576 kcal/mole. (author)

  14. Theoretical studies of the nucleophilic substitution of halides and amine at a sulfonyl center.

    Science.gov (United States)

    Sung, Dae Dong; Kim, Tae Joon; Lee, Ikchoon

    2009-06-25

    Gas-phase nucleophilic substitution reactions, F(-) + CH(3)SO(2)F, Cl(-) + CH(3)SO(2)Cl, Cl(-) + CH(3)SO(2)F, and NH(3) + CH(3)SO(2)Cl, have been investigated at the B3LYP/6-311+G** and MP2/6-31+G* levels of theory. A very shallow well for the reaction intermediate in a triple-well potential energy surface (PES) was observed for the identity fluoride exchange, but double well PESs were obtained for the other three reactions with three different PES profiles. NBO analyses of the transition states showed substantial charge transfer interactions in all cases which provided a much larger amount of stabilization energy compared with the corresponding species at the carbon center of methyl halides. This difference is primarily caused by the strong electropositive nature of the sulfur center. The F-S-F axial linkage in the distorted TBP type intermediate in the identity fluoride exchange reaction exhibited a weak three-center, four-electron omega-bonding, which is considered to provide stability of the intermediate. All the reactant (RC) and product complexes (PC) have Cs symmetry. The symmetry plane bisects angles HCH (of methyl group), OSO (of sulfonyl group), and HNH (of ammonia). Vicinal charge transfer interactions between the two out-of-plane C-H, S-O, and N-H bonds provide extra stabilization to the ion-dipole complexes together with H-bond formation of in-plane H atom with the nucleophile and/or leaving group.

  15. The development of catalytic nucleophilic additions of terminal alkynes in water.

    Science.gov (United States)

    Li, Chao-Jun

    2010-04-20

    One of the major research endeavors in synthetic chemistry over the past two decades is the exploration of synthetic methods that work under ambient atmosphere with benign solvents, that maximize atom utilization, and that directly transform natural resources, such as renewable biomass, from their native states into useful chemical products, thus avoiding the need for protecting groups. The nucleophilic addition of terminal alkynes to various unsaturated electrophiles is a classical (textbook) reaction in organic chemistry, allowing the formation of a C-C bond while simultaneously introducing the alkyne functionality. A prerequisite of this classical reaction is the stoichiometric generation of highly reactive metal acetylides. Over the past decade, our laboratory and others have been exploring an alternative, the catalytic and direct nucleophilic addition of terminal alkynes to unsaturated electrophiles in water. We found that various terminal alkynes can react efficiently with a wide range of such electrophiles in water (or organic solvent) in the presence of simple and readily available catalysts, such as copper, silver, gold, iron, palladium, and others. In this Account, we describe the development of these synthetic methods, focusing primarily on results from our laboratory. Our studies include the following: (i) catalytic reaction of terminal alkynes with acid chloride, (ii) catalytic addition of terminal alkynes to aldehydes and ketones, (iii) catalytic addition of alkynes to C=N bonds, and (iv) catalytic conjugate additions. Most importantly, these reactions can tolerate various functional groups and, in many cases, perform better in water than in organic solvents, clearly defying classical reactivities predicated on the relative acidities of water, alcohols, and terminal alkynes. We further discuss multicomponent and enantioselective reactions that were developed. These methods provide an alternative to the traditional requirement of separate steps in

  16. Nucleophilic 18F-Labeling of Spirocyclic Iodonium Ylide or Boronic Pinacol Ester Precursors - Advantages and Disadvantages

    DEFF Research Database (Denmark)

    Petersen, Ida Nymann; Kristensen, Jesper Langgaard; Herth, Matthias Manfred

    2017-01-01

    The field of labeling electron-rich aryl compounds with nucleophilic [18F]fluoride has recently expanded with radiofluorination strategies that apply boronic esters or spirocyclic iodonium ylides as precursors. Herein, we present a direct comparison of these strategies by using nine chemically di...

  17. Citrus Peel Additives for One-Pot Triazole Formation by Decarboxylation, Nucleophilic Substitution, and Azide-Alkyne Cycloaddition Reactions

    Science.gov (United States)

    Mendes, Desiree E.; Schoffstall, Allen M.

    2011-01-01

    This undergraduate organic laboratory experiment consists of three different reactions occurring in the same flask: a cycloaddition reaction, preceded by decarboxylation and nucleophilic substitution reactions. The decarboxylation and cycloaddition reactions occur using identical Cu(I) catalyst and conditions. Orange, lemon, and other citrus fruit…

  18. Organic Chemistry Students' Fragmented Ideas about the Structure and Function of Nucleophiles and Electrophiles: A Concept Map Analysis

    Science.gov (United States)

    Anzovino, Mary E.; Bretz, Stacey Lowery

    2016-01-01

    Organic chemistry students struggle with multiple aspects of reaction mechanisms and the curved arrow notation used by organic chemists. Many faculty believe that an understanding of nucleophiles and electrophiles, among other concepts, is required before students can develop fluency with the electronpushing formalism (EPF). An expert concept map…

  19. Recent applications of ring-rearrangement metathesis in organic synthesis

    Directory of Open Access Journals (Sweden)

    Sambasivarao Kotha

    2015-10-01

    Full Text Available Ring-rearrangement metathesis (RRM involves multiple metathesis processes such as ring-opening metathesis (ROM/ring-closing metathesis (RCM in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008–2014.

  20. Token Ring Project

    Directory of Open Access Journals (Sweden)

    Adela Ionescu

    2007-01-01

    Full Text Available Ring topology is a simple configuration used to connect processes that communicate among themselves. A number of network standards such as token ring, token bus, and FDDI are based on the ring connectivity. This article will develop an implementation of a ring of processes that communicate among themselves via pipe links. The processes are nodes in the ring. Each process reads from its standard input and writes in its standard output. N-1 process redirects the its standard output to a standard input of the process through a pipe. When the ring-structure is designed, the project can be extended to simulate networks or to implement algorithms for mutual exclusion

  1. Token ring technology report

    CERN Document Server

    2013-01-01

    Please note this is a Short Discount publication. This report provides an overview of the IBM Token-Ring technology and products built by IBM and compatible vendors. It consists of two sections: 1. A summary of the design trade-offs for the IBM Token-Ring. 2. A summary of the products of the major token-ring compatible vendors broken down by adapters and components, wiring systems, testing, and new chip technology.

  2. Radioactive gold ring dermatitis

    International Nuclear Information System (INIS)

    Miller, R.A.; Aldrich, J.E.

    1990-01-01

    A superficial squamous cell carcinoma developed in a woman who wore a radioactive gold ring for more than 30 years. Only part of the ring was radioactive. Radiation dose measurements indicated that the dose to basal skin layer was 2.4 Gy (240 rad) per week. If it is assumed that the woman continually wore her wedding ring for 37 years since purchase, she would have received a maximum dose of approximately 4600 Gy

  3. Physics of quantum rings

    International Nuclear Information System (INIS)

    Fomin, Vladimir M.

    2014-01-01

    Presents the new class of materials of quantum rings. Provides an elemental basis for low-cost high-performance devices promising for electronics, optoelectronics, spintronics and quantum information processing. Explains the physical properties of quantum rings to cover a gap in scientific literature. Presents the application of most advanced nanoengineering and nanocharacterization techniques. This book deals with a new class of materials, quantum rings. Innovative recent advances in experimental and theoretical physics of quantum rings are based on the most advanced state-of-the-art fabrication and characterization techniques as well as theoretical methods. The experimental efforts allow to obtain a new class of semiconductor quantum rings formed by capping self-organized quantum dots grown by molecular beam epitaxy. Novel optical and magnetic properties of quantum rings are associated with non-trivial topologies at the nanoscale. An adequate characterization of quantum rings is possible on the basis of modern characterization methods of nanostructures, such as Scanning Tunneling Microscopy. A high level of complexity is demonstrated to be needed for a dedicated theoretical model to adequately represent the specific features of quantum rings. The findings presented in this book contribute to develop low-cost high-performance electronic, spintronic, optoelectronic and information processing devices based on quantum rings.

  4. EBT ring physics

    International Nuclear Information System (INIS)

    Uckan, N.A.

    1980-04-01

    This workshop attempted to evaluate the status of the current experimental and theoretical understanding of hot electron ring properties. The dominant physical processes that influence ring formation, scaling, and their optimal behavior are also studied. Separate abstracts were prepared for each of the 27 included papers

  5. Analysis of reforming process of large distorted ring in final enlarging forging

    International Nuclear Information System (INIS)

    Miyazawa, Takeshi; Murai, Etsuo

    2002-01-01

    In the construction of reactors or pressure vessels for oil chemical plants and nuclear power stations, mono block open-die forging rings are often utilized. Generally, a large forged ring is manufactured by means of enlarging forging with reductions of the wall thickness. During the enlarging process the circular ring is often distorted and becomes an ellipse in shape. However the shape control of the ring is a complicated work. This phenomenon makes the matter still worse in forging of larger rings. In order to make precision forging of large rings, we have developed the forging method using a v-shape anvil. The v-shape anvil is geometrically adjusted to fit the distorted ring in the final circle and reform automatically the shape of the ring during enlarging forging. This paper has analyzed the reforming process of distorted ring by computer program based on F.E.M. and examined the effect on the precision of ring forging. (author)

  6. On the Laurent polynomial rings

    International Nuclear Information System (INIS)

    Stefanescu, D.

    1985-02-01

    We describe some properties of the Laurent polynomial rings in a finite number of indeterminates over a commutative unitary ring. We study some subrings of the Laurent polynomial rings. We finally obtain two cancellation properties. (author)

  7. Probing the reactivity of nucleophile residues in human 2,3-diphosphoglycerate/deoxy-hemoglobin complex by aspecific chemical modifications.

    Science.gov (United States)

    Scaloni, A; Ferranti, P; De Simone, G; Mamone, G; Sannolo, N; Malorni, A

    1999-06-11

    The use of aspecific methylation reaction in combination with MS procedures has been employed for the characterization of the nucleophilic residues present on the molecular surface of the human 2,3-diphosphoglycerate/deoxy-hemoglobin complex. In particular, direct molecular weight determinations by ESMS allowed to control the reaction conditions, limiting the number of methyl groups introduced in the modified globin chains. A combined LCESMS-Edman degradation approach for the analysis of the tryptic peptide mixtures yielded to the exact identification of methylation sites together with the quantitative estimation of their degree of modification. The reactivities observed were directly correlated with the pKa and the relative surface accessibility of the nucleophilic residues, calculated from the X-ray crystallographic structure of the protein. The results here described indicate that this methodology can be efficiently used in aspecific modification experiments directed to the molecular characterization of the surface topology in proteins and protein complexes.

  8. Diastereomerically and enantiomerically pure 2,3-disubstituted pyrrolidines from 2,3-aziridin-1-ols using a sulfoxonium ylide: a one-carbon homologative relay ring expansion.

    Science.gov (United States)

    Schomaker, Jennifer M; Bhattacharjee, Somnath; Yan, Jun; Borhan, Babak

    2007-02-21

    An ylide-based aza-Payne rearrangement of 2,3-aziridin-1-ols leads to an efficient process for the preparation of pyrrolidines. The aza-Payne rearrangement under basic reaction conditions favors the formation of epoxy amines. Subsequent nucleophilic attack of the epoxide by the ylide yields a bis-anion, which upon a 5-exo-tet ring-closure yields the desired pyrrolidine, thus completing the relay of the three-membered to the five-membered nitrogen-containing ring system. This process takes place with complete transfer of stereochemical fidelity and can be applied to sterically hindered aziridinols.

  9. Nucleophile-directed selectivity towards linear carbonates in the niobium pentaethoxide-catalysed cycloaddition of CO2 and propylene oxide

    KAUST Repository

    Dutta, Barnali

    2014-01-01

    Homoleptic Nb-complexes combined with selected organic nucleophiles generate very active catalytic systems for the cycloaddition of propylene oxide and CO2 under ambient conditions. An unprecedented reaction pathway towards an acyclic organic carbonate is observed when extending the study to [Nb(OEt)5] in combination with 4-dimethylamino-pyridine (DMAP) or tetra-n-butylammonium bromide (TBAB). Mechanistic insights of the reaction are provided based on experimental and spectroscopic evidences. This journal is © the Partner Organisations 2014.

  10. Heavy ion storage rings

    International Nuclear Information System (INIS)

    Schuch, R.

    1987-01-01

    A brief overview of synchrotron storage rings for heavy ions, which are presently under construction in different accelerator laboratories is given. Ions ranging from protons up to uranium ions at MeV/nucleon energies will be injected into these rings using multiturn injection from the accelerators available or being built in these laboratories. After injection, it is planned to cool the phase space distribution of the ions by merging them with cold electron beams or laser beams, or by using stochastic cooling. Some atomic physics experiments planned for these rings are presented. 35 refs

  11. Faithfully quadratic rings

    CERN Document Server

    Dickmann, M

    2015-01-01

    In this monograph the authors extend the classical algebraic theory of quadratic forms over fields to diagonal quadratic forms with invertible entries over broad classes of commutative, unitary rings where -1 is not a sum of squares and 2 is invertible. They accomplish this by: (1) Extending the classical notion of matrix isometry of forms to a suitable notion of T-isometry, where T is a preorder of the given ring, A, or T = A^2. (2) Introducing in this context three axioms expressing simple properties of (value) representation of elements of the ring by quadratic forms, well-known to hold in

  12. PREFACE: Special section on vortex rings Special section on vortex rings

    Science.gov (United States)

    Fukumoto, Yasuhide

    2009-10-01

    This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill

  13. On arbitrarily graded rings

    Indian Academy of Sciences (India)

    58

    paper is devoted to the study of arbitrary rings graded through arbitrary sets. .... which recover certain multiplicative relations among the homogeneous components ... instance the case in which the grading set A is an Abelian group, where the ...

  14. The g-2 ring

    CERN Multimedia

    1974-01-01

    The precise measurement of "g-2", the anomalous magnetic moment of the muon, required a special muon storage ring with electrostatic focussing and very accurate knowledge of the magnetic bending field. For more details see under photo 7405430.

  15. Minimal open strings

    International Nuclear Information System (INIS)

    Hosomichi, Kazuo

    2008-01-01

    We study FZZT-branes and open string amplitudes in (p, q) minimal string theory. We focus on the simplest boundary changing operators in two-matrix models, and identify the corresponding operators in worldsheet theory through the comparison of amplitudes. Along the way, we find a novel linear relation among FZZT boundary states in minimal string theory. We also show that the boundary ground ring is realized on physical open string operators in a very simple manner, and discuss its use for perturbative computation of higher open string amplitudes.

  16. Experimental Study of Shock Generated Compressible Vortex Ring

    Science.gov (United States)

    Das, Debopam; Arakeri, Jaywant H.; Krothapalli, Anjaneyulu

    2000-11-01

    Formation of a compressible vortex ring and generation of sound associated with it is studied experimentally. Impulse of a shock wave is used to generate a vortex ring from the open end of a shock-tube. Vortex ring formation process has been studied in details using particle image Velocimetry (PIV). As the shock wave exits the tube it diffracts and expands. A circular vortex sheet forms at the edge and rolls up into a vortex ring. Far field microphone measurement shows that the acoustic pressure consists of a spike due to shock wave followed by a low frequency pressure wave of decaying nature, superimposed with high frequency pressure wave. Acoustic waves consist of waves due to expansion, waves formed in the tube during diaphragm breakage and waves associated with the vortex ring and shear-layer vortices. Unsteady evolution of the vortex ring and shear-layer vortices in the jet behind the ring is studied by measuring the velocity field using PIV. Corresponding vorticity field, circulation around the vortex core and growth rate of the vortex core is calculated from the measured velocity field. The velocity field in a compressible vortex ring differs from that of an incompressible ring due to the contribution from both shock and vortex ring.

  17. [Liesegang's rings resembling helminthiasis].

    Science.gov (United States)

    Zámecník, M; Riedl, I

    1996-12-01

    So called Liesegang's rings are lamellar corpuscles which develop after periodical precipitation of oversaturated solutions in gel medium. They can occur in cysts, closed cavities, inflammatory exudates and necroses. They resemble parasitic eggs, larvae or adult forms. A case of 28-year-old woman is presented with many Liesegang's rings in a stuff from dilated renal calyx. Their preliminary evaluation considered helminths, especially Dioctophyma renale.

  18. Storage ring group summary

    International Nuclear Information System (INIS)

    King, N.M.

    1980-01-01

    The Storage Ring Group set out to identify and pursue salient problems in accelerator physics for heavy ion fusion, divorced from any particular reference design concept. However, it became apparent that some basic parameter framework was required to correlate the different study topics. As the Workshop progressed, ring parameters were modified and updated. Consequently, the accompanying papers on individual topics will be found to refer to slightly varied parameters, according to the stage at which the different problems were tackled

  19. The rings of Uranus

    Science.gov (United States)

    Elliot, J. L.; Dunham, E.; Mink, D.

    1977-01-01

    A description is given of the observation of five brief occultations of the star SAO 158687 which occurred both before and after its occultation by Uranus on March 10, 1977. The events were observed with a three-channel occultation photometer, attached to a 91-cm telescope. The observations indicate that at least five rings encircle the planet Uranus. Possible reasons for the narrowness of the Uranus rings are discussed.

  20. Robust gap repair in the contractile ring ensures timely completion of cytokinesis.

    OpenAIRE

    Silva, AM; Osório, DS; Pereira, AJ; Maiato, H; Pinto, IM; Rubinstein, B; Gassmann, R; Telley, IA; Carvalho, AX

    2016-01-01

    Cytokinesis in animal cells requires the constriction of an actomyosin contractile ring, whose architecture and mechanism remain poorly understood. We use laser microsurgery to explore the biophysical properties of constricting rings in Caenorhabditis elegans embryos. Laser cutting causes rings to snap open. However, instead of disintegrating, ring topology recovers and constriction proceeds. In response to severing, a finite gap forms and is repaired by recruitment of new material in an acti...

  1. Some Aspects of Ring Theory

    CERN Document Server

    Herstein, IN

    2011-01-01

    S. Amitsur: Associative rings with identities.- I.N. Herstein: Topics in ring theory.- N. Jacobson: Representation theory of Jordan algebras.- I. Kaplansky: The theory of homological dimension.- D. Buchsbaum: Complexes in local ring theory.- P.H. Cohn: Two topics in ring theory.- A.W. Goldie: Non-commutative localisation.

  2. Ring correlations in random networks.

    Science.gov (United States)

    Sadjadi, Mahdi; Thorpe, M F

    2016-12-01

    We examine the correlations between rings in random network glasses in two dimensions as a function of their separation. Initially, we use the topological separation (measured by the number of intervening rings), but this leads to pseudo-long-range correlations due to a lack of topological charge neutrality in the shells surrounding a central ring. This effect is associated with the noncircular nature of the shells. It is, therefore, necessary to use the geometrical distance between ring centers. Hence we find a generalization of the Aboav-Weaire law out to larger distances, with the correlations between rings decaying away when two rings are more than about three rings apart.

  3. Direct evidence for the ring opening of monosaccharide anions in the gas phase: photodissociation of aldohexoses and aldohexoses derived from disaccharides using variable-wavelength infrared irradiation in the carbonyl stretch region

    NARCIS (Netherlands)

    Brown, D. J.; Stefan, S. E.; Berden, G.; Steill, J.D.; Oomens, J.; Eyler, J.R.; Bendiak, B.

    2011-01-01

    All eight d-aldohexoses and aldohexoses derived from the non-reducing end of disaccharides were investigated by variable-wavelength infrared multiple-photon dissociation (IRMPD) as anions in the negative-ion mode. Spectroscopic evidence supports the existence of a relatively abundant open-chain

  4. Direct evidence for the ring opening of monosaccharide anions in the gas phase: photodissociation of aldohexoses and aldohexoses derived from disaccharides using variable-wavelength infrared irradiation in the carbonyl stretch region

    NARCIS (Netherlands)

    Brown, D. J.; Stefan, S. E.; G. Berden,; Steill, J. D.; Oomens, J.; Eyler, J. R.; Bendiak, B.

    2011-01-01

    All eight D-aldohexoses and aldohexoses derived from the non-reducing end of disaccharides were investigated by variable-wavelength infrared multiple-photon dissociation (IRMPD) as anions in the negative-ion mode. Spectroscopic evidence supports the existence of a relatively abundant open-chain

  5. Mapping Ring Particle Cooling across Saturn's Rings with Cassini CIRS

    Science.gov (United States)

    Brooks, Shawn M.; Spilker, L. J.; Edgington, S. G.; Pilorz, S. H.; Deau, E.

    2010-10-01

    Previous studies have shown that the rings' thermal inertia, a measure of their response to changes in the thermal environment, varies from ring to ring. Thermal inertia can provide insight into the physical structure of Saturn's ring particles and their regoliths. Low thermal inertia and quick temperature responses are suggestive of ring particles that have more porous or fluffy regoliths or that are riddled with cracks. Solid, coherent particles can be expected to have higher thermal inertias (Ferrari et al. 2005). Cassini's Composite Infrared Spectrometer has recorded millions of spectra of Saturn's rings since its arrival at Saturn in 2004 (personal communication, M. Segura). CIRS records far infrared radiation between 10 and 600 cm-1 (16.7 and 1000 µm) at focal plane 1 (FP1), which has a field of view of 3.9 mrad. Thermal emission from Saturn's rings peaks in this wavelength range. FP1 spectra can be used to infer ring temperatures. By tracking how ring temperatures vary, we can determine the thermal inertia of the rings. In this work we focus on CIRS observations of the shadowed portion of Saturn's rings. The thermal budget of the rings is dominated by the solar radiation absorbed by its constituent particles. When ring particles enter Saturn's shadow this source of energy is abruptly cut off. As a result, ring particles cool as they traverse Saturn's shadow. From these shadow observations we can create cooling curves at specific locations across the rings. We will show that the rings' cooling curves and thus their thermal inertia vary not only from ring to ring, but by location within the individual rings. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2010 California Institute of Technology. Government sponsorship acknowledged.

  6. The Rings of Saturn

    Science.gov (United States)

    Cuzzi, J. N.; Filacchione, G.; Marouf, E. A.

    2018-03-01

    One could become an expert on Saturn's iconic rings pretty easily in the early 1970s, as very little was known about them beyond the distinction between the A, B, and C rings, and the Cassini Division or "gap" between rings A and B (Alexander, 1962; Bobrov, 1970). Water ice was discovered spectroscopically on the ring particle surfaces, and radar and microwave emission observations proved that the particles must be centimeters to meters in size, consisting primarily, not just superficially, of water ice (Pollack, 1975). While a 2:1 orbital resonance with Mimas had long been suspected of having something to do with the Cassini Division, computers of the time were unable to model the subtle dynamical effects that we now know to dominate ring structure. This innocent state of affairs was exploded by the Voyager 1 and 2 encounters in 1980 and 1981. Spectacular images revealed filigree structure and odd regional color variations, and exquisitely detailed radial profiles of fluctuating particle abundance were obtained from the first stellar and radio occultations, having resolution almost at the scale of single particles. Voyager-era understanding was reviewed by Cuzzi et al. (1984) and Esposito et al. (1984). While the Voyager data kept ring scientists busy for decades, planning which led to the monumentally successful NASA-ESA-ASI Cassini mission, which arrived in 2004, had been under way even before Voyager got to Saturn. A review of pre-Cassini knowledge of Saturn's Rings can be found in Orton et al. (2009). This chapter will build on recent topical and process-specific reviews that treat the gamut of ring phenomena and its underlying physics in considerable detail (Colwell et al., 2009; Cuzzi et al., 2009; Horányi et al., 2009; Schmidt et al., 2009; Esposito, 2010; Tiscareno, 2013b; Esposito, 2014). We will follow and extend the general organization of Cuzzi et al. (2010), the most recent general discussion of Saturn's rings. For brevity and the benefit of the

  7. BERKELEY: ALS ring

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1993-06-15

    Everybody at Lawrence Berkeley Laboratory's Center for Beam Physics is pleased with the rapid progress in commissioning LBL's Advanced Light Source (ALS) electron storage ring, the foundation for this third-generation synchrotron radiation facility. Designed for a maximum current of 400 mA, the ALS storage ring reached 407 mA just 24 days after storing the first beam on 16 March. ALS construction as a US Department of Energy (DOE) national user facility to provide high-brightness vacuum ultra-violet and soft x-ray radiation began in October 1987. One technical requirement marking project completion was to accumulate a 50-mA current in the storage ring. The ALS passed this milestone on 24 March, a week ahead of the official deadline. Once injected, the electron beam decays quasi-exponentially primarily because of interactions with residual gas molecules in the storage-ring vacuum chamber. Eventually, when the pressure in the vacuum chamber with beam decreases toward the expected operating level of 1 nano Torr, it will only be necessary to refill the storage ring at intervals of four to eight hours. At present the vacuum is improving rapidly as surfaces are irradiated (scrubbed) by the synchrotron radiation itself. At 100 mA, beam lifetime was about one hour (9 April)

  8. Compressible Vortex Ring

    Science.gov (United States)

    Elavarasan, Ramasamy; Arakeri, Jayawant; Krothapalli, Anjaneyulu

    1999-11-01

    The interaction of a high-speed vortex ring with a shock wave is one of the fundamental issues as it is a source of sound in supersonic jets. The complex flow field induced by the vortex alters the propagation of the shock wave greatly. In order to understand the process, a compressible vortex ring is studied in detail using Particle Image Velocimetry (PIV) and shadowgraphic techniques. The high-speed vortex ring is generated from a shock tube and the shock wave, which precedes the vortex, is reflected back by a plate and made to interact with the vortex. The shadowgraph images indicate that the reflected shock front is influenced by the non-uniform flow induced by the vortex and is decelerated while passing through the vortex. It appears that after the interaction the shock is "split" into two. The PIV measurements provided clear picture about the evolution of the vortex at different time interval. The centerline velocity traces show the maximum velocity to be around 350 m/s. The velocity field, unlike in incompressible rings, contains contributions from both the shock and the vortex ring. The velocity distribution across the vortex core, core diameter and circulation are also calculated from the PIV data.

  9. BERKELEY: ALS ring

    International Nuclear Information System (INIS)

    Anon.

    1993-01-01

    Everybody at Lawrence Berkeley Laboratory's Center for Beam Physics is pleased with the rapid progress in commissioning LBL's Advanced Light Source (ALS) electron storage ring, the foundation for this third-generation synchrotron radiation facility. Designed for a maximum current of 400 mA, the ALS storage ring reached 407 mA just 24 days after storing the first beam on 16 March. ALS construction as a US Department of Energy (DOE) national user facility to provide high-brightness vacuum ultra-violet and soft x-ray radiation began in October 1987. One technical requirement marking project completion was to accumulate a 50-mA current in the storage ring. The ALS passed this milestone on 24 March, a week ahead of the official deadline. Once injected, the electron beam decays quasi-exponentially primarily because of interactions with residual gas molecules in the storage-ring vacuum chamber. Eventually, when the pressure in the vacuum chamber with beam decreases toward the expected operating level of 1 nano Torr, it will only be necessary to refill the storage ring at intervals of four to eight hours. At present the vacuum is improving rapidly as surfaces are irradiated (scrubbed) by the synchrotron radiation itself. At 100 mA, beam lifetime was about one hour (9 April)

  10. Tripodal polyphosphine ligands as inductors of chelate ring-opening processes in mononuclear palladium(II) and platinum(II) compounds. The X-ray crystal structure of two derivatives containing dangling phosphorus.

    Science.gov (United States)

    Fernández-Anca, Damián; García-Seijo, M Inés; García-Fernández, M Esther

    2010-03-07

    The reaction of NP(3) (tris[2-(diphenylphosphino)ethyl]amine and PP(3) (tris[2-(diphenylphosphino)ethyl]phosphine) with the five-coordinate complexes [PdCl(NP(3))]Cl (1) and [MX(PP(3))]X [M = Pd: X = Cl(2), Br(3), I(4); M = Pt: X = Cl(5), Br(6), I(7)], respectively, followed by (31)P{(1)H}NMR when X = Cl, led to the formation of unprecedented four-coordinate halides in a 1 : 2 metal to ligand ratio, [M(AP(3))(2)]X(2) [A = N, M = Pd: X = Cl(8); A = P, M = Pd: X = Cl(9), Br(10), I(11); A = P, M = Pt: X = Cl(12), Br(13), I (14)], containing reactive dangling phosphorus. Given the non characterised precursors [M(ONO(2))(PP(3))](NO(3))], the interaction between the heteronuclear species [MAg(NO(3))(3)(PP(3))] [M = Pd(15), Pt(16)] and PP(3) was explored. It was found that the addition of 1 equivalent of phosphine afforded [MAg(NO(3))(PP(3))(2)](NO(3))(2) [M = Pd(15*), Pt(16*)] containing Ag(I) bound to two dangling phosphorus while the reaction with 2 equivalents led to the complexes [M(PP(3))(2)](NO(3))(2) [M = Pd (17), Pt (18)] in coexistence with [Ag(2)(mu-PP(3))(2)](NO(3))(2). The fate of Ag(I) on the reaction of the mixed metal compounds with excess PP(3) consisted of preventing dissociation, observed in solution for halides, and acting as an assistant for crystallization. Colourless single crystals of 18 and 10, studied by X-ray diffraction, were afforded by reaction of 16 with 4 equivalents of PP(3) and from solutions of 10 in chloroform coexisting with red crystals of 3, respectively. The structures revealed the presence of dications [M(PP(3))(2)](2+) that show two five-membered chelate rings to M(II) in a square-planar arrangement and four uncoordinated phosphine arms with the counter anions being symmetrically placed at 4.431 (Br(-)) and 13.823 (NO(3)(-)) A from M(II) above and below its coordination, MP(4), plane. Complexes 9 and 12 were shown to undergo an interesting reactivity in solution versus group 11 monocations. The reactions consisted of conversions

  11. Almost ring theory

    CERN Document Server

    2003-01-01

    This book develops thorough and complete foundations for the method of almost etale extensions, which is at the basis of Faltings' approach to p-adic Hodge theory. The central notion is that of an "almost ring". Almost rings are the commutative unitary monoids in a tensor category obtained as a quotient V-Mod/S of the category V-Mod of modules over a fixed ring V; the subcategory S consists of all modules annihilated by a fixed ideal m of V, satisfying certain natural conditions. The reader is assumed to be familiar with general categorical notions, some basic commutative algebra and some advanced homological algebra (derived categories, simplicial methods). Apart from these general prerequisites, the text is as self-contained as possible. One novel feature of the book - compared with Faltings' earlier treatment - is the systematic exploitation of the cotangent complex, especially for the study of deformations of almost algebras.

  12. Direct no-carrier-added 18F-labelling of arenes via nucleophilic substitution on aryl(2-thienyl)iodonium salts

    International Nuclear Information System (INIS)

    Ross, T.L.

    2006-01-01

    For in vivo imaging of molecular processes via positron emission tomography (PET) radiotracers of high specific activity are demanded. In case of the most commonly used positron emitter fluorine-18, this is only achievable with no-carrier-added [ 18 F]fluoride, which implies nucleophilic methods of 18 F-substitution. Whereas electron deficient aromatic groups can be labelled in one step using no-carrier-added [ 18 F]fluoride, electron rich 18 F-labelled aromatic molecules are only available by multi-step radiosyntheses or carrier-added electrophilic reactions. Here, diaryliodonium salts represent an alternative, since they have been proven as potent precursor for a direct nucleophilic 18 F-introduction into aromatic molecules. Furthermore, as known from non-radioactive studies, the highly electron rich 2-thienyliodonium leaving group leads to a high regioselectivity in nucleophilic substitution reactions. Consequently, a direct nucleophilic no-carrier-added 18 F-labelling of electron rich arenes via aryl(2-thienyl)iodonium precursors was developed in this work. The applicability of direct nucleophilic 18 F-labelling was examined in a systematic study on eighteen aryl(2-thienyl)iodonium salts. As electron rich precursors the ortho-, meta- and para-methoxyphenyl(2-thienyl)iodonium bromides, iodides, tosylates and triflates were synthesised. In addition, para-substituted (R=BnO, CH 3 , H, Cl, Br, I) aryl(2-thienyl)iodonium bromides were prepared as precursors with a systematically varying electron density. As first approach, the general reaction conditions of the nucleophilic 18 F-substitution procedure were optimised. The best conditions for direct nucleophilic no-carrier-added 18 F-labelling via aryl(2-thienyl)iodonium salts were found with dimethylformamide as solvent, a reaction temperature of 130±3 C and 25 mmol/l as concentration of the precursor. (orig.)

  13. Direct no-carrier-added {sup 18}F-labelling of arenes via nucleophilic substitution on aryl(2-thienyl)iodonium salts

    Energy Technology Data Exchange (ETDEWEB)

    Ross, T L

    2006-01-15

    For in vivo imaging of molecular processes via positron emission tomography (PET) radiotracers of high specific activity are demanded. In case of the most commonly used positron emitter fluorine-18, this is only achievable with no-carrier-added [{sup 18}F]fluoride, which implies nucleophilic methods of {sup 18}F-substitution. Whereas electron deficient aromatic groups can be labelled in one step using no-carrier-added [{sup 18}F]fluoride, electron rich {sup 18}F-labelled aromatic molecules are only available by multi-step radiosyntheses or carrier-added electrophilic reactions. Here, diaryliodonium salts represent an alternative, since they have been proven as potent precursor for a direct nucleophilic {sup 18}F-introduction into aromatic molecules. Furthermore, as known from non-radioactive studies, the highly electron rich 2-thienyliodonium leaving group leads to a high regioselectivity in nucleophilic substitution reactions. Consequently, a direct nucleophilic no-carrier-added {sup 18}F-labelling of electron rich arenes via aryl(2-thienyl)iodonium precursors was developed in this work. The applicability of direct nucleophilic {sup 18}F-labelling was examined in a systematic study on eighteen aryl(2-thienyl)iodonium salts. As electron rich precursors the ortho-, meta- and para-methoxyphenyl(2-thienyl)iodonium bromides, iodides, tosylates and triflates were synthesised. In addition, para-substituted (R=BnO, CH{sub 3}, H, Cl, Br, I) aryl(2-thienyl)iodonium bromides were prepared as precursors with a systematically varying electron density. As first approach, the general reaction conditions of the nucleophilic {sup 18}F-substitution procedure were optimised. The best conditions for direct nucleophilic no-carrier-added {sup 18}F-labelling via aryl(2-thienyl)iodonium salts were found with dimethylformamide as solvent, a reaction temperature of 130{+-}3 C and 25 mmol/l as concentration of the precursor. (orig.)

  14. Compact electron storage rings

    International Nuclear Information System (INIS)

    Williams, G.P.

    1987-01-01

    There have been many recent developments in the area of compact storage rings. Such rings would have critical wavelengths of typically 10 A, achieved with beam energies of several hundreds of MeV and superconducting dipole fields of around 5 Tesla. Although the primary motivation for progress in this area is that of commercial x-ray lithography, such sources might be an attractive source for college campuses to operate. They would be useful for many programs in materials science, solid state, x-ray microscopy and other biological areas. We discuss the properties of such sources and review developments around the world, primarily in the USA, japan and W. Germany

  15. The covariant chiral ring

    Energy Technology Data Exchange (ETDEWEB)

    Bourget, Antoine; Troost, Jan [Laboratoire de Physique Théorique, École Normale Supérieure, 24 rue Lhomond, 75005 Paris (France)

    2016-03-23

    We construct a covariant generating function for the spectrum of chiral primaries of symmetric orbifold conformal field theories with N=(4,4) supersymmetry in two dimensions. For seed target spaces K3 and T{sup 4}, the generating functions capture the SO(21) and SO(5) representation theoretic content of the chiral ring respectively. Via string dualities, we relate the transformation properties of the chiral ring under these isometries of the moduli space to the Lorentz covariance of perturbative string partition functions in flat space.

  16. Vortex and source rings

    DEFF Research Database (Denmark)

    Branlard, Emmanuel Simon Pierre

    2017-01-01

    The velocity field, vector potential and velocity gradient of a vortex ring is derived in this chapter. The Biot-Savart law for the vector potential and velocity is expressed in a first section. Then, the flow is derived at specific locations: on the axis, near the axis and in the far field where...... the analogy to a doublet field is made. The following section derive the value of the vector potential and velocity field in the full domain. The expression for the velocity gradient is also provided since it may be relevant in a simulation with vortex particles and vortex rings. Most of this chapter...

  17. The Saturnian rings

    International Nuclear Information System (INIS)

    Alfven, H.

    1975-09-01

    The structure of the Saturnian rings is traditionally believed to be due to resonances caused by Mimas (and possibly other satellites). It is shown that both theoretical and observational evidence rule out this interpretation. The increased observational accuracy on one hand and the increased understanding of the cosmogonic processes on the other makes it possible to explain the structure of the ring system as a product of condensation from a partially corotating plasma. In certain respects the agreement between theory and observations is about 1%. (Auth.)

  18. RINGED ACCRETION DISKS: INSTABILITIES

    Energy Technology Data Exchange (ETDEWEB)

    Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

    2016-04-01

    We analyze the possibility that several instability points may be formed, due to the Paczyński mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.

  19. The ring plus project: safety and acceptability of vaginal rings that protect women from unintended pregnancy.

    Science.gov (United States)

    Schurmans, Céline; De Baetselier, Irith; Kestelyn, Evelyne; Jespers, Vicky; Delvaux, Thérèse; Agaba, Stephen K; van Loen, Harry; Menten, Joris; van de Wijgert, Janneke; Crucitti, Tania

    2015-04-10

    Research is ongoing to develop multipurpose vaginal rings to be used continuously for contraception and to prevent Human Immunodeficiency Virus (HIV) infection. Contraceptive vaginal rings (CVRs) are available in a number of countries and are most of the time used intermittently i.e. three weeks out of a 4-week cycle. Efficacy trials with a dapivirine-containing vaginal ring for HIV prevention are ongoing and plans to develop multi-purpose vaginal rings for prevention of both HIV and pregnancy have been elaborated. In contrast with the CVRs, multi-purpose vaginal rings will have to be used continuously. Women who continuously use a CVR will no longer have menses. Furthermore, some safety aspects of CVR use have never been studied in-depth in the past, such as the impact of the vaginal ring on the vaginal microbiota, biofilm formation and induction of inflammation. We studied acceptability and these novel aspects of safety in Rwandan women. Although significant progress has been made over the past decade, Rwanda still has a high unmet need for contraception (with 47% unplanned births) and a generalized HIV epidemic, and CVRs are not yet available. We will conduct an open label, single centre, randomized controlled trial. A total of 120 HIV-negative women will be randomized to intermittent CVR use (to allow menstruation) or continuous CVR use. Women will be followed for a maximum of 14 weeks. In parallel, we will conduct a qualitative study using in-depth interview and focus group discussion methodology. In addition to evaluating the safety and acceptability of intermittent and continuous CVR use in Rwandan women, we hope that our findings will inform the development of future multipurpose vaginal rings, will prepare Rwandan study populations for future clinical trials of multipurpose vaginal rings, and will pave the way for introduction of CVRs on African markets. Clinicaltrials.gov NCT01796613 . Registered 14 February 2013.

  20. Fusion rings and fusion ideals

    DEFF Research Database (Denmark)

    Andersen, Troels Bak

    by the so-called fusion ideals. The fusion rings of Wess-Zumino-Witten models have been widely studied and are well understood in terms of precise combinatorial descriptions and explicit generating sets of the fusion ideals. They also appear in another, more general, setting via tilting modules for quantum......This dissertation investigates fusion rings, which are Grothendieck groups of rigid, monoidal, semisimple, abelian categories. Special interest is in rational fusion rings, i.e., fusion rings which admit a finite basis, for as commutative rings they may be presented as quotients of polynomial rings...

  1. Flushing Ring for EDM

    Science.gov (United States)

    Earwood, L.

    1985-01-01

    Removing debris more quickly lowers cutting time. Operation, cutting oil and pressurized air supplied to ring placed around workpiece. Air forces oil through small holes and agitates oil as it flows over workpiece. High flow rate and agitation dislodge and remove debris. Electrical discharge removes material from workpiece faster.

  2. Sector ring accelerator ''RESATRON''

    International Nuclear Information System (INIS)

    Schwabe, E.

    1980-01-01

    Project of sector ring accelerator RESATRON is described. The curiosity of this accelerator is the second cycle of acceleration of the beam after stripping it on the foil. In such an accelerator heavy ions with a different ratio Z to A can be accelerated. (S.B.)

  3. Ring chromosome 13

    DEFF Research Database (Denmark)

    Brandt, C A; Hertz, Jens Michael; Petersen, M B

    1992-01-01

    A stillborn male child with anencephaly and multiple malformations was found to have the karyotype 46,XY,r(13) (p11q21.1). The breakpoint at 13q21.1, determined by high resolution banding, is the most proximal breakpoint ever reported in patients with ring chromosome 13. In situ hybridisation...

  4. SXLS storage ring design

    International Nuclear Information System (INIS)

    Anon.

    1991-01-01

    X-ray lithography has emerged as a strong candidate to meet the demands of ever finer linewidths on integrated circuits, particularly for linewidths less than .25 microns. Proximity printing X-ray lithography makes use of soft X-rays to shadow print an image of a mask onto a semiconductor wafer to produce integrated circuits. To generate the required X-rays in sufficient quantities to make commercial production viable, electron storage rings have been proposed as the soft X-ray sources. Existing storage rings have been used to do the initial development work and the success of these efforts has led the lithographers to request that new rings be constructed that are dedicated to X-ray lithography. As a result of a series of workshops held at BNL [10.3] which were attended by both semiconductor and accelerator scientists, the following set of zeroth order specifications' on the light and electron beam of a storage ring for X-ray lithography were developed: critical wavelength of light: λ c = 6 to 10 angstroms, white light power: P = 0.25 to 2.5 watts/mrad, horizontal collection angle per port: θ = 10 to 50 mrad, electron beam sizes: σ x ∼ σ y y ' < 1 mrad

  5. Ring magnetron ionizer

    International Nuclear Information System (INIS)

    Alessi, J.G.

    1986-01-01

    A ring magnetron D - charge exchange ionizer has been built and tested. An H - current of 500 μA was extracted with an estimated H 0 density in the ionizer of 10 12 cm -3 . This exceeds the performance of ionizers presently in use on polarized H - sources. The ionizer will soon be tested with a polarized atomic beam

  6. Algebras, rings and modules

    CERN Document Server

    Hazewinkel, Michiel; Kirichenko, V V

    Provides both the classical aspects of the theory of groups and their representations as well as a general introduction to the modern theory of representations, including the representations of quivers and finite partially ordered sets. This volume provides the theory of semiprime Noetherian semiperfect and semidistributive rings.

  7. Lattices for antiproton rings

    International Nuclear Information System (INIS)

    Autin, B.

    1984-01-01

    After a description of the constraints imposed by the cooling of Antiprotons on the lattice of the rings, the reasons which motivate the shape and the structure of these machines are surveyed. Linear and non-linear beam optics properties are treated with a special amplification to the Antiproton Accumulator. (orig.)

  8. One molecule of ionic liquid and tert-alcohol on a polystyrene-support as catalysts for efficient nucleophilic substitution including fluorination.

    Science.gov (United States)

    Shinde, Sandip S; Patil, Sunil N

    2014-12-07

    The tert-alcohol and ionic liquid solvents in one molecule [mim-(t)OH][OMs] was immobilized on polystyrene and reported to be a highly efficient catalyst in aliphatic nucleophilic substitution using alkali metal salts. Herein, we investigated the catalytic activity of a new structurally modified polymer-supported tert-alcohol functionalized imidazolium salt catalyst in nucleophilic substitution of 2-(3-methanesulfonyloxypropyoxy)naphthalene as a model substrate with various metal nucleophiles. The tert-alcohol moiety of the ionic liquid with a hexyl chain distance from polystyrene had a better catalytic activity compared to the other resin which lacked an alkyl linker and tert-alcohol moiety. We found that the maximum [mim-(t)OH][OMs] loading had the best catalytic efficacy among the tested polystyrene-based ionic liquids (PSILs) in nucleophilic fluorination. The catalytic efficiency of the PS[him-(t)OH][OMs] as a phase transfer catalyst (PTC) was determined by carrying out various nucleophilic substitutions using the corresponding alkali metal salts from the third to sixth periodic in CH3CN or tert-BuOH media. The scope of this protocol with primary and secondary polar substrates containing many heteroatoms is also reported. This PS[him-(t)OH][OMs] catalyst not only enhances the reactivity of alkali metal salts and reduces the formation of by-products but also affords high yield with easy isolation.

  9. Synthesis and application of aryl-ferrocenyl(pseudo-biarylic) complexes. Part 5. Design and synthesis of a new type of ferrocene-based planar chiral DMAP analogues. A new catalyst system for asymmetric nucleophilic catalysis

    DEFF Research Database (Denmark)

    Seitzberg, J.G; Dissing, C; Søtofte, Inger

    2005-01-01

    A new first-generation catalyst system for nucleophilic catalysis has been developed. It is based on a planar chiral ferrocene skeleton with either the potent nucleophile 4-(dimethylamino)pyridine (DMAP) or the related 4-nitropyridine N-oxide attached in either the 2- or the 3-position. The synth......A new first-generation catalyst system for nucleophilic catalysis has been developed. It is based on a planar chiral ferrocene skeleton with either the potent nucleophile 4-(dimethylamino)pyridine (DMAP) or the related 4-nitropyridine N-oxide attached in either the 2- or the 3-position...

  10. FUZZY RINGS AND ITS PROPERTIES

    Directory of Open Access Journals (Sweden)

    Karyati Karyati

    2017-01-01

      One of algebraic structure that involves a binary operation is a group that is defined  an un empty set (classical with an associative binary operation, it has identity elements and each element has an inverse. In the structure of the group known as the term subgroup, normal subgroup, subgroup and factor group homomorphism and its properties. Classical algebraic structure is developed to algebraic structure fuzzy by the researchers as an example semi group fuzzy and fuzzy group after fuzzy sets is introduced by L. A. Zadeh at 1965. It is inspired of writing about semi group fuzzy and group of fuzzy, a research on the algebraic structure of the ring is held with reviewing ring fuzzy, ideal ring fuzzy, homomorphism ring fuzzy and quotient ring fuzzy with its properties. The results of this study are obtained fuzzy properties of the ring, ring ideal properties fuzzy, properties of fuzzy ring homomorphism and properties of fuzzy quotient ring by utilizing a subset of a subset level  and strong level  as well as image and pre-image homomorphism fuzzy ring.   Keywords: fuzzy ring, subset level, homomorphism fuzzy ring, fuzzy quotient ring

  11. Ring-shaped lesions in the CT scan

    International Nuclear Information System (INIS)

    Kazner, E.; Steinhoff, H.; Wende, S.; Mauersberger, W.

    1978-01-01

    Computerised tomography has really opened new dimensions for the diagnosis of various intracranial space-occupying lesions. However, during the last years we had to learn how difficult it can be to evaluate a certain CT finding correctly. Especially the group of ring-type lesions still pose some unsolved problems even if clinical information available in the individual case is considered. The ring blush is a nonspecific finding which occurs in primary and metastatic neoplasms, abscess, infarction, certain stages of intracerebral hematomas and even after neurosurgical operations. The ring blush is caused partly by breakdown of the blood brain barrier, partly by hypervascular pathologic tissue or by both factors. (orig.) [de

  12. Inorganic glass ceramic slip rings

    Science.gov (United States)

    Glossbrenner, E. W.; Cole, S. R.

    1972-01-01

    Prototypes of slip rings have been fabricated from ceramic glass, a material which is highly resistant to deterioration due to high temperature. Slip ring assemblies were not structurally damaged by mechanical tests and performed statisfactorily for 200 hours.

  13. Uniquely Strongly Clean Group Rings

    Institute of Scientific and Technical Information of China (English)

    WANG XIU-LAN

    2012-01-01

    A ring R is called clean if every element is the sum of an idempotent and a unit,and R is called uniquely strongly clean (USC for short) if every element is uniquely the sum of an idempotent and a unit that commute.In this article,some conditions on a ring R and a group G such that RG is clean are given.It is also shown that if G is a locally finite group,then the group ring RG is USC if and only if R is USC,and G is a 2-group.The left uniquely exchange group ring,as a middle ring of the uniquely clean ring and the USC ring,does not possess this property,and so does the uniquely exchange group ring.

  14. Conference on Recent Advances in Commutative Ring and Module Theory & Conference on Rings and Polynomials

    CERN Document Server

    Frisch, Sophie; Glaz, Sarah; Tartarone, Francesca; Zanardo, Paolo

    2017-01-01

    This volume presents a collection of articles highlighting recent developments in commutative algebra and related non-commutative generalizations. It also includes an extensive bibliography and lists a substantial number of open problems that point to future directions of research in the represented subfields. The contributions cover areas in commutative algebra that have flourished in the last few decades and are not yet well represented in book form. Highlighted topics and research methods include Noetherian and non-Noetherian ring theory, module theory and integer-valued polynomials along with connections to algebraic number theory, algebraic geometry, topology and homological algebra. Most of the eighteen contributions are authored by attendees of the two conferences in commutative algebra that were held in the summer of 2016: “Recent Advances in Commutative Ring and Module Theory,” Bressanone, Italy; “Conference on Rings and Polynomials”  Graz, Austria. There is also a small collection of invite...

  15. Fine-tuning the nucleophilic reactivities of boron ate complexes derived from aryl and heteroaryl boronic esters.

    Science.gov (United States)

    Berionni, Guillaume; Leonov, Artem I; Mayer, Peter; Ofial, Armin R; Mayr, Herbert

    2015-02-23

    Boron ate complexes derived from thienyl and furyl boronic esters and aryllithium compounds have been isolated and characterized by X-ray crystallography. Products and mechanisms of their reactions with carbenium and iminium ions have been analyzed. Kinetics of these reactions were monitored by UV/Vis spectroscopy, and the influence of the aryl substituents, the diol ligands (pinacol, ethylene glycol, neopentyl glycol, catechol), and the counterions on the nucleophilic reactivity of the boron ate complexes were examined. A Hammett correlation confirmed the polar nature of their reactions with benzhydrylium ions, and the correlation lg k(20 °C)=sN (E+N) was employed to determine the nucleophilicities of the boron ate complexes and to compare them with those of other borates and boronates. The neopentyl and ethylene glycol derivatives were found to be 10(4) times more reactive than the pinacol and catechol derivatives. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Ring closure in actin polymers

    Energy Technology Data Exchange (ETDEWEB)

    Sinha, Supurna, E-mail: supurna@rri.res.in [Raman Research Institute, Bangalore 560080 (India); Chattopadhyay, Sebanti [Doon University, Dehradun 248001 (India)

    2017-03-18

    We present an analysis for the ring closure probability of semiflexible polymers within the pure bend Worm Like Chain (WLC) model. The ring closure probability predicted from our analysis can be tested against fluorescent actin cyclization experiments. We also discuss the effect of ring closure on bend angle fluctuations in actin polymers. - Highlights: • Ring closure of biopolymers. • Worm like chain model. • Predictions for experiments.

  17. Acid dissociation constant and apparent nucleophilicity of lysine-501 of the alpha-polypeptide of sodium and potassium ion activated adenosinetriphosphatase

    International Nuclear Information System (INIS)

    Xu, K.Y.

    1989-01-01

    A combination of competitive labeling with [ 3 H]acetic anhydride and immunoaffinity chromatography is described that permits the assignment of the acid dissociation constant and the absolute nucleophilicity of individual lysines in a native enzyme. The acid dissociation constant of lysine-501 of the alpha-polypeptide in native (Na+ + K+)-ATPase was determined. This lysine had a normal pKa of 10.4. The rate constant for the reaction of the free base of lysine-501 with acetic anhydride at 10 degrees C is 400 M-1 s-1. This value is only 30% that for a fully accessible lysine in a protein. The lower than normal apparent nucleophilicity suggests that lysine-501 is hindered from reacting with its intrinsic nucleophilicity by the tertiary structure of the enzyme and is consistent with its location within a pocket that forms the active site upon the surface of the native protein

  18. Inversion of Configuration at the Phosphorus Nucleophile in the Diastereoselective and Enantioselective Synthesis of P-Stereogenic syn-Phosphiranes from Chiral Epoxides.

    Science.gov (United States)

    Muldoon, Jake A; Varga, Balázs R; Deegan, Meaghan M; Chapp, Timothy W; Eördögh, Ádám M; Hughes, Russell P; Glueck, David S; Moore, Curtis E; Rheingold, Arnold L

    2018-04-23

    Nucleophilic substitution results in inversion of configuration at the electrophilic carbon center (S N 2) or racemization (S N 1). The stereochemistry of the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P-stereogenic syn-phosphiranes. DFT studies suggested that the novel stereochemistry results from acid-promoted tosylate dissociation to yield an intermediate phosphenium-bridged cation, which undergoes syn-selective cyclization. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Design of low energy ring(s)

    CERN Document Server

    Lachaize, Antoine

    During the last two years, several upgrades of the initial baseline scenario were studied with the aim of increasing the average intensity of ion beams in the accelerator chain of the Beta Beam complex. This is the reason why the Rapid Cycling Synchrotron (RCS) specifications were reconsidered many times [1], [2], [3].General considerations on the optical design were presented at the Beta Beam Task Meetings held at CERN and at Saclay in 2005 [4]. More detailed beam optics studies were performed during the next months. Lattices, RF system parameters, multi-turn injection scheme, fast extraction, closed orbit correction and chromaticity correction systems were proposed for different versions of the RCS [5], [6], [7].Finally, the RCS specifications have stabilized in November 2006 after the fourth Beta Beam Task Meeting when it was decided to fix the maximum magnetic rigidity of ion beams to 14.47 T.m (3.5 GeV equivalent proton energy) and to adopt a ring physical radius of 40 m in order to facilitate injectio...

  20. Fusion Rings for Quantum Groups

    DEFF Research Database (Denmark)

    Andersen, Henning Haahr; Stroppel, Catharina

    2012-01-01

    We study the fusion rings of tilting modules for a quantum group at a root of unity modulo the tensor ideal of negligible tilting modules. We identify them in type A with the combinatorial rings from [12] and give a similar description of the sp2n-fusion ring in terms of noncommutative symmetric...

  1. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

    2015-12-15

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  2. Ring Confidential Transactions

    Directory of Open Access Journals (Sweden)

    Shen Noether

    2016-12-01

    Full Text Available This article introduces a method of hiding transaction amounts in the strongly decentralized anonymous cryptocurrency Monero. Similar to Bitcoin, Monero is a cryptocurrency which is distributed through a proof-of-work “mining” process having no central party or trusted setup. The original Monero protocol was based on CryptoNote, which uses ring signatures and one-time keys to hide the destination and origin of transactions. Recently the technique of using a commitment scheme to hide the amount of a transaction has been discussed and implemented by Bitcoin Core developer Gregory Maxwell. In this article, a new type of ring signature, A Multilayered Linkable Spontaneous Anonymous Group signature is described which allows one to include a Pedersen Commitment in a ring signature. This construction results in a digital currency with hidden amounts, origins and destinations of transactions with reasonable efficiency and verifiable, trustless coin generation. The author would like to note that early drafts of this were publicized in the Monero Community and on the #bitcoin-wizards IRC channel. Blockchain hashed drafts are available showing that this work was started in Summer 2015, and completed in early October 2015. An eprint is also available at http://eprint.iacr.org/2015/1098.

  3. Confinement and stability of crystalline beams in storage rings

    International Nuclear Information System (INIS)

    Haffmans, A.F.

    1995-01-01

    We present a fully analytical approach to the study of the confinement and stability of open-quote open-quote Crystalline Beams close-quote close-quote in storage rings, in terms of such fundamental accelerator concepts as tune shift and stopband. We consider a open-quote open-quote Crystalline Beam close-quote close-quote consisting of substrings, arranged symmetrically around the reference trajectory, and we examine the motion of a slightly perturbed test particle on one of them. Our approach quite naturally leads to the conclusion, that (a) storage rings need to be operated below the transition energy, and (b) the open-quote open-quote Crystalline Beam close-quote close-quote has the same periodicity as the storage ring. Each open-quote open-quote Crystalline Beam close-quote close-quote has an upper and lower limit of the spacing between the ions. The upper limit is determined by condition (b), and the lower limit is set by the stability of the test particle motion around the equilibrium. copyright 1995 American Institute of Physics

  4. Fusion Rings for Quantum Groups

    DEFF Research Database (Denmark)

    Andersen, Henning Haahr; Stroppel, Catharina

    2014-01-01

    We study the fusion rings of tilting modules for a quantum group at a root of unity modulo the tensor ideal of negligible tilting modules. We identify them in type A with the combinatorial rings from Korff, C., Stroppel, C.: The sl(ˆn)k-WZNW fusion ring: a combinato-rial construction...... and a realisation as quotient of quantum cohomology. Adv. Math. 225(1), 200–268, (2010) and give a similar description of the sp2n-fusion ring in terms of non-commutative symmetric functions. Moreover we give a presentation of all fusion rings in classical types as quotients of polynomial rings. Finally we also...... compute the fusion rings for type G2....

  5. Glycosyl Cross-Coupling of Anomeric Nucleophiles: Scope, Mechanism, and Applications in the Synthesis of Aryl C-Glycosides.

    Science.gov (United States)

    Zhu, Feng; Rodriguez, Jacob; Yang, Tianyi; Kevlishvili, Ilia; Miller, Eric; Yi, Duk; O'Neill, Sloane; Rourke, Michael J; Liu, Peng; Walczak, Maciej A

    2017-12-13

    Stereoselective manipulations at the C1 anomeric position of saccharides are one of the central goals of preparative carbohydrate chemistry. Historically, the majority of reactions forming a bond with anomeric carbon has focused on reactions of nucleophiles with saccharide donors equipped with a leaving group. Here, we describe a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles. First, methods for the preparation of anomeric stannanes have been developed and optimized to afford both anomers of common saccharides in high anomeric selectivities. We established that oligosaccharide stannanes could be prepared from monosaccharide stannanes via O-glycosylation with Schmidt-type donors, glycal epoxides, or under dehydrative conditions with C1 alcohols. Second, we identified a general set of catalytic conditions with Pd 2 (dba) 3 (2.5 mol%) and a bulky ligand (JackiePhos, 10 mol%) controlling the β-elimination pathway. We demonstrated that the glycosyl cross-coupling resulted in consistently high anomeric selectivities for both anomers with mono- and oligosaccharides, deoxysugars, saccharides with free hydroxyl groups, pyranose, and furanose substrates. The versatility of the glycosyl cross-coupling reaction was probed in the total synthesis of salmochelins (siderophores) and commercial anti-diabetic drugs (gliflozins). Combined experimental and computational studies revealed that the β-elimination pathway is suppressed for biphenyl-type ligands due to the shielding of Pd(II) by sterically demanding JackiePhos, whereas smaller ligands, which allow for the formation of a Pd-F complex, predominantly result in a glycal product. Similar steric effects account for the diminished rates of cross-couplings of 1,2-cis C1-stannanes with aryl halides. DFT calculations also revealed that the transmetalation occurs via a cyclic transition state with retention of configuration at the anomeric

  6. Tree Rings: Timekeepers of the Past.

    Science.gov (United States)

    Phipps, R. L.; McGowan, J.

    One of a series of general interest publications on science issues, this booklet describes the uses of tree rings in historical and biological recordkeeping. Separate sections cover the following topics: dating of tree rings, dating with tree rings, tree ring formation, tree ring identification, sample collections, tree ring cross dating, tree…

  7. SOR-ring failure

    International Nuclear Information System (INIS)

    Kitamura, Hideo

    1981-01-01

    It was in the autumn of 1976 that the SOR-ring (synchrotron radiation storage ring) has commenced the regular operation. Since then, the period when the operation was interrupted due to the failures of SOR-ring itself is in total about 8 weeks. Failures and accidents have occurred most in the vacuum system. Those failure experiences are described on the vacuum, electromagnet, radio-frequency acceleration and beam transport systems with their interrupted periods. The eleven failures in the vacuum system have been reported, such as bellows breakage in a heating-evacuating period, leakage from the bellows of straight-through valves (made in U.S.A. and Japan), and leakage from the joint flange of the vacuum system. The longest interruption was 5 weeks due to the failure of a domestically manufactured straight-through valve. The failures of the electromagnet system involve the breakage in a cooling water system, short circuit of a winding in the Q magnet power transformer, blow of a fuse protecting the deflection magnet power source by the current less than the rating, and others. The failures of the RF acceleration system include the breakage of an output electronic tube the breakage of a cavity ceramic, RF voltage fluctuation due to the contact deterioration at a cavity electrode, and the failure of grid bias power source. It is necessary to select the highly reliable components for the vacuum system because the vacuum system failures require longer time for recovery, and very likely to induce secondary and tertiary failures. (Wakatsuki, Y.)

  8. Proton storage rings

    International Nuclear Information System (INIS)

    Rau, R.R.

    1978-04-01

    A discussion is given of proton storage ring beam dynamic characteristics. Topics considered include: (1) beam energy; (2) beam luminosity; (3) limits on beam current; (4) beam site; (5) crossing angle; (6) beam--beam interaction; (7) longitudinal instability; (8) effects of scattering processes; (9) beam production; and (10) high magnetic fields. Much of the discussion is related to the design parameters of ISABELLE, a 400 x 400 GeV proton---proton intersecting storage accelerator to be built at Brookhaven National Laboratory

  9. Ring-constrained Join

    DEFF Research Database (Denmark)

    Yiu, Man Lung; Karras, Panagiotis; Mamoulis, Nikos

    2008-01-01

    . This new operation has important applications in decision support, e.g., placing recycling stations at fair locations between restaurants and residential complexes. Clearly, RCJ is defined based on a geometric constraint but not on distances between points. Thus, our operation is fundamentally different......We introduce a novel spatial join operator, the ring-constrained join (RCJ). Given two sets P and Q of spatial points, the result of RCJ consists of pairs (p, q) (where p ε P, q ε Q) satisfying an intuitive geometric constraint: the smallest circle enclosing p and q contains no other points in P, Q...

  10. Femtoslicing in Storage Rings

    CERN Document Server

    Khan, Shaukat

    2005-01-01

    The generation of ultrashort synchrotron radiation pulses by laser-induced energy modulation of electrons and their subsequent transverse displacement, now dubbed "femtoslicing," was demonstrated at the Advanced Light Source in Berkeley. More recently, a femtoslicing user facility was commissioned at the BESSY storage ring in Berlin, and another project is in progress at the Swiss Light Source. The paper reviews the principle of femtoslicing, its merits and shortcomings, as well as the variations of its technical implementation. Various diagnostics techniques to detect successful laser-electron interaction are discussed and experimental results are presented.

  11. Viscosity of ring polymer melts

    KAUST Repository

    Pasquino, Rossana

    2013-10-15

    We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as a function of the number of entanglements Z. In the unentangled regime η0,linear/η 0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/ η0,ring = 2. In the entanglement regime, the Z-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < Z < 20, η0,linear/η0,ring ∼ Z 1.2±0.3, is weaker than the scaling prediction (η0,linear/η0,ring ∼ Z 1.6±0.3) and the simulations (η0,linear/ η0,ring ∼ Z2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem. © 2013 American Chemical Society.

  12. Viscosity of ring polymer melts

    KAUST Repository

    Pasquino, Rossana; Vasilakopoulos, Thodoris C.; Jeong, Youncheol; Lee, Hyojoon; Rogers, Simon A.; Sakellariou, Georgios; Allgaier, Jü rgen B.; Takano, Atsushi; Brá s, Ana Rita E; Chang, Taihyun; Gooß en, Sebastian; Pyckhout-Hintzen, Wim; Wischnewski, Andreas; Hadjichristidis, Nikolaos; Richter, Dieter R.; Rubinstein, Michael H.; Vlassopoulos, Dimitris

    2013-01-01

    We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as a function of the number of entanglements Z. In the unentangled regime η0,linear/η 0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/ η0,ring = 2. In the entanglement regime, the Z-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < Z < 20, η0,linear/η0,ring ∼ Z 1.2±0.3, is weaker than the scaling prediction (η0,linear/η0,ring ∼ Z 1.6±0.3) and the simulations (η0,linear/ η0,ring ∼ Z2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem. © 2013 American Chemical Society.

  13. Alpha - Skew Pi - Armendariz Rings

    Directory of Open Access Journals (Sweden)

    Areej M Abduldaim

    2018-03-01

    Full Text Available In this article we introduce a new concept called Alpha-skew Pi-Armendariz rings (Alpha - S Pi - ARas a generalization of the notion of Alpha-skew Armendariz rings.Another important goal behind studying this class of rings is to employ it in order to design a modern algorithm of an identification scheme according to the evolution of using modern algebra in the applications of the field of cryptography.We investigate general properties of this concept and give examples for illustration. Furthermore, this paperstudy the relationship between this concept and some previous notions related to Alpha-skew Armendariz rings. It clearly presents that every weak Alpha-skew Armendariz ring is Alpha-skew Pi-Armendariz (Alpha-S Pi-AR. Also, thisarticle showsthat the concepts of Alpha-skew Armendariz rings and Alpha-skew Pi- Armendariz rings are equivalent in case R is 2-primal and semiprime ring.Moreover, this paper proves for a semicommutative Alpha-compatible ringR that if R[x;Alpha] is nil-Armendariz, thenR is an Alpha-S Pi-AR. In addition, if R is an Alpha - S Pi -AR, 2-primal and semiprime ring, then N(R[x;Alpha]=N(R[x;Alpha]. Finally, we look forwardthat Alpha-skew Pi-Armendariz rings (Alpha-S Pi-ARbe more effect (due to their properties in the field of cryptography than Pi-Armendariz rings, weak Armendariz rings and others.For these properties and characterizations of the introduced concept Alpha-S Pi-AR, we aspire to design a novel algorithm of an identification scheme.

  14. The effect of varying the anion of an ionic liquid on the solvent effects on a nucleophilic aromatic substitution reaction.

    Science.gov (United States)

    Hawker, Rebecca R; Haines, Ronald S; Harper, Jason B

    2018-05-09

    A variety of ionic liquids, each containing the same cation but a different anion, were examined as solvents for a nucleophilic aromatic substitution reaction. Varying the proportion of ionic liquid was found to increase the rate constant as the mole fraction of ionic liquid increased demonstrating that the reaction outcome could be controlled through varying the ionic liquid. The solvent effects were correlated with the hydrogen bond accepting ability (β) of the ionic liquid anion allowing for qualitative prediction of the effect of changing this component of the solute. To determine the microscopic origins of the solvent effects, activation parameters were determined through temperature-dependent kinetic analyses and shown to be consistent with previous studies. With the knowledge of the microscopic interactions in solution, an ionic liquid was rationally chosen to maximise rate enhancement demonstrating that an ionic solvent can be selected to control reaction outcome for this reaction type.

  15. NCA nucleophilic radiofluorination on substituted benzaldehydes for the preparation of [18F]fluorinated aromatic amino acids

    International Nuclear Information System (INIS)

    Wadsak, Wolfgang; Wirl-Sagadin, Barbara; Mitterhauser, Markus; Mien, Leonhard-Key; Ettlinger, Dagmar E.; Keppler, Bernhard K.; Dudczak, Robert; Kletter, Kurt

    2006-01-01

    Nucleophilic aromatic substitution is a challenging task in radiochemistry. Therefore, a thorough evaluation and optimisation of this step is needed to provide a satisfactory tool for the routine preparation of [ 18 F]fluorinated aromatic amino acids. Two methods, already proposed elsewhere, were evaluated and improved. The yields for the radiofluorination were increased whereas activity loss during solid phase extraction was observed. Radiochemical yields for the two methods were 92.7±5.5% (method 1) and 92.1±12.3% (method 2) for conversion and 11.1±2.8% (method 1) and 34.8±0.6% (method 2) for purification, respectively. In total, we demonstrate an optimised method for the preparation of this important class of [ 18 F]fluorinated synthons for PET

  16. Iminoboronate Formation Leads to Fast and Reversible Conjugation Chemistry of α-Nucleophiles at Neutral pH.

    Science.gov (United States)

    Bandyopadhyay, Anupam; Gao, Jianmin

    2015-10-12

    Bioorthogonal reactions that are fast and reversible under physiological conditions are in high demand for biological applications. Herein, it is shown that an ortho boronic acid substituent makes aryl ketones rapidly conjugate with α-nucleophiles at neutral pH. Specifically, 2-acetylphenylboronic acid and derivatives were found to conjugate with phenylhydrazine with rate constants of 10(2) to 10(3) M(-1) s(-1) , comparable to the fastest bioorthogonal conjugations known to date. (11) B NMR analysis revealed the varied extent of iminoboronate formation of the conjugates, in which the imine nitrogen forms a dative bond with boron. The iminoboronate formation activates the imines for hydrolysis and exchange, rendering these oxime/hydrazone conjugations reversible and dynamic under physiological conditions. The fast and dynamic nature of the iminoboronate chemistry should find wide applications in biology. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Dechlorination of chloropicrin and 1,3-dichloropropene by hydrogen sulfide species: redox and nucleophilic substitution reactions.

    Science.gov (United States)

    Zheng, Wei; Yates, Scott R; Papiernik, Sharon K; Guo, Mingxin; Gan, Jianying

    2006-03-22

    The chlorinated fumigants chloropicrin (trichloronitromethane) and 1,3-dichloropropene (1,3-D) are extensively used in agricultural production for the control of soilborne pests. The reaction of these two fumigants with hydrogen sulfide species (H2S and HS-) was examined in well-defined anoxic aqueous solutions. Chloropicrin underwent an extremely rapid redox reaction in the hydrogen sulfide solution. Transformation products indicated reductive dechlorination of chloropicrin by hydrogen sulfide species to produce dichloro- and chloronitromethane. The transformation of chloropicrin in hydrogen sulfide solution significantly increased with increasing pH, indicating that H2S is less reactive toward chloropicrin than HS- is. For both 1,3-D isomers, kinetics and transformation products analysis revealed that the reaction between 1,3-D and hydrogen sulfide species is an S(N)2 nucleophilic substitution process, in which the chlorine at C3 of 1,3-D is substituted by the sulfur nucleophile to form corresponding mercaptans. The 50% disappearance time (DT50) of 1,3-D decreased with increasing hydrogen sulfide species concentration at a constant pH. Transformation of 1,3-D was more rapid at high pH, suggesting that the reactivity of hydrogen sulfide species in the experimental system stems primarily from HS-. Because of the relatively low smell threshold values and potential environmental persistence of organic sulfur products yielded by the reaction of 1,3-D and HS-, the effects of reduced sulfide species should be considered in the development of alternative fumigation practices, especially in the integrated application of sulfur-containing fertilizers.

  18. A theoretical quantum study on the distribution of electrophilic and nucleophilic active sites on Cu(100) surfaces modeled as finite clusters

    International Nuclear Information System (INIS)

    Rios R, C.H.; Romero R, M.; Ponce R, A.; Mendoza H, L.H.

    2008-01-01

    In this work, it is shown a theoretical quantum study of the active sites distribution on a monocrystalline surface of Cu(100). The copper surface was modeled as finite clusters of 14, 23, 38 and 53 atoms. We performed Hartree-Fock and Density Functional Theory (B3LYP) ab initio calculations employing the pseudopotentials of Hay and Wadt (LANLlMB y LANL2DZ). From calculations, we found a work function value of 4.1 eV. The mapping of the HOMO and LUMO in the frozen core approximation, allowed us finding the electrophilic and nucleophilic active sites distribution, respectively. The results indicated that electrophilic sites on the Cu(100) surface were located on hollow position and its numerical density was 8.6 x 10 16 sites cm -2 . From the nucleophilic local softness study, it was found that the nucleophilic sites were formed by a group of atoms and it had a numerical density of 2.4x 10 16 sitescm -2 . Last results indicated that adsorptions with 2 x 2 and 3 x 3 distributions can be favored onto a Cu(100) surface for the electrophilic and nucleophilic cases, respectively. (Author)

  19. Synthesis and reactivity of novel sulfur pentafluorides-Effect of the SF5 group on reactivity of nitrobenzenes in nucleophilic substitution

    Czech Academy of Sciences Publication Activity Database

    Beier, Petr

    2017-01-01

    Roč. 192, č. 2 (2017), s. 212-215 ISSN 1042-6507. [International Symposium on the Organic Chemistry of Sulfur (ISOCS) /27./. Jena, 26.07.2016-29.07.2016] Institutional support: RVO:61388963 Keywords : nucleophilic substitution * sulfur * fluorine * reaction rate Subject RIV: CC - Organic Chemistry OBOR OECD: Organic chemistry Impact factor: 0.809, year: 2016

  20. Stereocontrolled generation of nucleophilic (Z)- or (E)-α-fluoroalkenylchromium reagents via carbon-fluorine bond activation: highly stereoselective synthesis of (E)- or (Z)-β-fluoroallylic alcohols.

    Science.gov (United States)

    Nihei, Takashi; Yokotani, Saya; Ishihara, Takashi; Konno, Tsutomu

    2014-02-14

    Highly nucleophilic (Z)- or (E)-α-fluoroalkenylchromium species could be generated in a stereoselective manner via C-F bond activation of CBrF2-containing molecules, and they reacted smoothly with various aldehydes to give (E)- or (Z)-β-fluoroallylic alcohol derivatives in high yields, respectively.

  1. Origin of Enhanced Reactivity of a Microsolvated Nucleophile in Ion Pair SN2 Reactions: The Cases of Sodium p-Nitrophenoxide with Halomethanes in Acetone.

    Science.gov (United States)

    Li, Qiang-Gen; Xu, Ke; Ren, Yi

    2015-04-30

    In a kinetic experiment on the SN2 reaction of sodium p-nitrophenoxide with iodomethane in acetone-water mixed solvent, Humeres et al. (J. Org. Chem. 2001, 66, 1163) found that the reaction depends strongly on the medium, and the fastest rate constant was observed in pure acetone. The present work tries to explore why acetone can enhance the reactivity of the title reactions. Accordingly, we make a mechanistic study on the reactions of sodium p-nitrophenoxide with halomethanes (CH3X, X = Cl, Br, I) in acetone by using a supramolecular/continuum model at the PCM-MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level, in which the ion pair nucleophile is microsolvated by one to three acetone molecules. We compared the reactivity of the microsolvated ion pair nucleophiles with solvent-free ion pair and anionic ones. Our results clearly reveal that the microsolvated ion pair nucleophile is favorable for the SN2 reactions; meanwhile, the origin of the enhanced reactivity induced by microsolvation of the nucleophile is discussed in terms of the geometries of transition state (TS) structures and activation strain model, suggesting that lower deformation energies and stronger interaction energies between the deformed reactants in the TS lead to the lower overall reaction barriers for the SN2 reaction of microsolvated sodium p-nitrophenoxide toward halomethanes in acetone.

  2. New type of transformation of a 1,2,4-triazine ring to pyrazine derivatives

    International Nuclear Information System (INIS)

    Alekseev, S.G.; Charushin, V.N.; Chupakhin, O.N.

    1987-01-01

    We have discovered a new type of transformation of a triazine ring in which the l-ethyl-1,2,4-triazine cation participates. It has been established that the cation reacts at 20 0 C with ortho-phenylenediamine (in methylene chloride) and 5,6-diaminopyrimidin-4-one (in 9:1 ethanol-DMF) with the formation of quinoxaline (yield 43%) and pteridin-4-one (yield 23%). This transformation is based on the susceptibility of the cation to bi-addition of nucleophiles and proceeds via cyclic adducts which are then aromatized on account of separation of 3-morpholinoamidrazone. The reaction products were identified by comparison of their melting points and spectroscopic characteristics (NMR, mass-spectra) with those of samples whose structure is definitely known

  3. NRL ion ring program

    International Nuclear Information System (INIS)

    Kapetanakos, C.A.; Golden, J.; Drobot, A.; Mahaffey, R.A.; Marsh, S.J.; Pasour, J.A.

    1977-01-01

    An experiment is under way to form a storng proton ring using the 200 ka, 1.2 MeV, 50 nsec hollow proton beam recently generated at NRL. The 5 m long magnetic field configuration consists of a magnetic cusp, a compressing magnetic field, a gate field and a magnetic mirror. The midplane value of the magnetic mirror is such that the major radius of the ring will be about 10 cm. The degree of field reversal that will be achieved with 5 x 10 16 protons per pulse from the existing beam depends upon the field reversal is possible with the 600 kA proton beam that would be generated from the low inductance coaxial triode coupled to the upgraded Gamble II generator. The propagation and trapping of an intense proton beam in the experimental magnetic field configuration is investigated numerically. The results show that the self magnetic has a very pronounced effect on the dynamics of the gyrating protons

  4. Flexible ring seal

    International Nuclear Information System (INIS)

    Abbes, Claude; Gournier, Andre; Rouaud, Christian; Villepoix, Raymond de.

    1976-01-01

    The invention concerns a flexible metal ring seal, able to ensure a perfect seal between two bearings due to the crushing and elastic deformation properties akin to similar properties in elastomers. Various designs of seal of this kind are already known, particularly a seal made of a core formed by a helical wire spring with close-wound turns and with high axial compression ratio, closed on itself and having the shape of an annulus. This wire ring is surrounded by at least one envelope having at rest the shape of a toroidal surface of which the generating circle does not close on itself. In a particular design mode, the seal in question can include, around the internal spring, two envelopes of which one in contact with the spring is composed of a low ductility elastic metal, such as mild steel or stainless steel and the other is, on the contrary, made of a malleable metal, such as copper or nickel. The first envelope evenly distributes the partial crushing of the spring, when the seal is tightened, on the second envelope which closely fits the two surfaces between which the seal operates. The stress-crushing curve characteristic of the seal comprises two separate parts, the first with a relatively sharp slope corresponds to the start of the seal compression phase, enabling at least some of these curves to reach the requisite seal threshold very quickly, then, beyond this, a second part, practically flat, where the stress is appreciably constant for a wide operating bracket [fr

  5. Magnetization of two coupled rings

    International Nuclear Information System (INIS)

    Avishai, Y; Luck, J M

    2009-01-01

    We investigate the persistent currents and magnetization of a mesoscopic system consisting of two clean metallic rings sharing a single contact point in a magnetic field. Many novel features with respect to the single-ring geometry are underlined, including the explicit dependence of wavefunctions on the Aharonov-Bohm fluxes, the complex pattern of two-fold and three-fold degeneracies, the key role of length and flux commensurability, and in the case of commensurate ring lengths the occurrence of idle levels which do not carry any current. Spin-orbit interactions, induced by the electric fields of charged wires threading the rings, give rise to a peculiar version of the Aharonov-Casher effect where, unlike for a single ring, spin is not conserved. Remarkably enough, this can only be realized when the Aharonov-Bohm fluxes in both rings are neither integer nor half-integer multiples of the flux quantum

  6. Multiple-Ring Digital Communication Network

    Science.gov (United States)

    Kirkham, Harold

    1992-01-01

    Optical-fiber digital communication network to support data-acquisition and control functions of electric-power-distribution networks. Optical-fiber links of communication network follow power-distribution routes. Since fiber crosses open power switches, communication network includes multiple interconnected loops with occasional spurs. At each intersection node is needed. Nodes of communication network include power-distribution substations and power-controlling units. In addition to serving data acquisition and control functions, each node acts as repeater, passing on messages to next node(s). Multiple-ring communication network operates on new AbNET protocol and features fiber-optic communication.

  7. Straightforward Entry toward Highly Substituted 2,3-Dihydrobenz[ b]oxepines by Ring Expansion of Benzopyryliums with Donor-Acceptor Diazo Compounds.

    Science.gov (United States)

    Courant, Thibaut; Pasco, Morgane; Lecourt, Thomas

    2018-05-04

    Ylide-type reactivity of diazo compounds is exploited in a new way to prepare benzo[ b]oxepines thanks to the formation of three chemical bonds and two contiguous and highly substituted stereocenters in a single pot. This cationic reaction cascade first involves addition of a donor-acceptor-substituted diazo compound to a benzopyrylium. Selective 1,2 migration of the endocyclic C-C bond then results in a ring-expansion and generates a second oxocarbenium that is trapped by a nucleophile added sequentially.

  8. Probing the reactivation process of sarin-inhibited acetylcholinesterase with α-nucleophiles: hydroxylamine anion is predicted to be a better antidote with DFT calculations.

    Science.gov (United States)

    Khan, Md Abdul Shafeeuulla; Lo, Rabindranath; Bandyopadhyay, Tusar; Ganguly, Bishwajit

    2011-08-01

    Inactivation of acetylcholinesterase (AChE) due to inhibition by organophosphorus (OP) compounds is a major threat to human since AChE is a key enzyme in neurotransmission process. Oximes are used as potential reactivators of OP-inhibited AChE due to their α-effect nucleophilic reactivity. In search of more effective reactivating agents, model studies have shown that α-effect is not so important for dephosphylation reactions. We report the importance of α-effect of nucleophilic reactivity towards the reactivation of OP-inhibited AChE with hydroxylamine anion. We have demonstrated with DFT [B3LYP/6-311G(d,p)] calculations that the reactivation process of sarin-serine adduct 2 with hydroxylamine anion is more efficient than the other nucleophiles reported. The superiority of hydroxylamine anion to reactivate the sarin-inhibited AChE with sarin-serine adducts 3 and 4 compared to formoximate anion was observed in the presence and absence of hydrogen bonding interactions of Gly121 and Gly122. The calculated results show that the rates of reactivation process of adduct 4 with hydroxylamine anion are 261 and 223 times faster than the formoximate anion in the absence and presence of such hydrogen bonding interactions. The DFT calculated results shed light on the importance of the adjacent carbonyl group of Glu202 for the reactivation of sarin-serine adduct, in particular with formoximate anion. The reverse reactivation reaction between hydroxylamine anion and sarin-serine adduct was found to be higher in energy compared to the other nucleophiles, which suggests that this α-nucleophile can be a good antidote agent for the reactivation process. Copyright © 2011 Elsevier Inc. All rights reserved.

  9. Split ring containment attachment device

    International Nuclear Information System (INIS)

    Sammel, A.G.

    1996-01-01

    A containment attachment device is described for operatively connecting a glovebag to plastic sheeting covering hazardous material. The device includes an inner split ring member connected on one end to a middle ring member wherein the free end of the split ring member is inserted through a slit in the plastic sheeting to captively engage a generally circular portion of the plastic sheeting. A collar potion having an outer ring portion is provided with fastening means for securing the device together wherein the glovebag is operatively connected to the collar portion. 5 figs

  10. Magnetic ring for stripping enhancement

    International Nuclear Information System (INIS)

    Selph, F.

    1992-10-01

    A ring designed to recycle ions through a stripping medium offers the possibility for increasing output of the desired charge state by up to 4x. This could be a very important component of a Radioactive Nuclear Beam Facility. In order for such a ring to work effectively it must satisfy certain design conditions. These include achromaticity at the stripper, a dispersed region for an extraction magnet, and a number of first and higher order optics constraints which are necessary to insure that the beam emittance is not degraded unduly by the ring. An example is given of a candidate design of a stripping ring

  11. Saturn's Rings Edge-on

    Science.gov (United States)

    1995-01-01

    In one of nature's most dramatic examples of 'now-you see-them, now-you-don't', NASA's Hubble Space Telescope captured Saturn on May 22, 1995 as the planet's magnificent ring system turned edge-on. This ring-plane crossing occurs approximately every 15 years when the Earth passes through Saturn's ring plane.For comparison, the top picture was taken by Hubble on December 1, 1994 and shows the rings in a more familiar configuration for Earth observers.The bottom picture was taken shortly before the ring plane crossing. The rings do not disappear completely because the edge of the rings reflects sunlight. The dark band across the middle of Saturn is the shadow of the rings cast on the planet (the Sun is almost 3 degrees above the ring plane.) The bright stripe directly above the ring shadow is caused by sunlight reflected off the rings onto Saturn's atmosphere. Two of Saturn's icy moons are visible as tiny starlike objects in or near the ring plane. They are, from left to right, Tethys (slightly above the ring plane) and Dione.This observation will be used to determine the time of ring-plane crossing and the thickness of the main rings and to search for as yet undiscovered satellites. Knowledge of the exact time of ring-plane crossing will lead to an improved determination of the rate at which Saturn 'wobbles' about its axis (polar precession).Both pictures were taken with Hubble's Wide Field Planetary Camera 2. The top image was taken in visible light. Saturn's disk appears different in the bottom image because a narrowband filter (which only lets through light that is not absorbed by methane gas in Saturn's atmosphere) was used to reduce the bright glare of the planet. Though Saturn is approximately 900 million miles away, Hubble can see details as small as 450 miles across.The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Spaced Flight Center for NASA's Office of Space Science.This image and other images and

  12. Acceleration of magnetized plasma rings

    International Nuclear Information System (INIS)

    Hartman, D.; Eddleman, J.; Hammer, J.H.

    1982-01-01

    One scheme is considered, acceleration of a ring between coaxial electrodes by a B/sub theta/ field as in a coaxial rail-gun. If the electrodes are conical, a ring accelerated towards the apex of the cone undergoes self-similar compression (focussing) during acceleration. Because the allowable acceleration force F/sub a/ = kappa U/sub m//R (kappa - 2 , the accelerating distance for conical electrodes is considerably shortened over that required for coaxial electrodes. In either case however, since the accelerating flux can expand as the ring moves, most of the accelerating field energy can be converted into kinetic energy of the ring leading to high efficiency

  13. Ground Movement in SSRL Ring

    International Nuclear Information System (INIS)

    Sunikumar, Nikita

    2011-01-01

    Users of the Stanford Synchrotron Radiation Lightsource (SSRL) are being affected by diurnal motion of the synchrotron's storage ring, which undergoes structural changes due to outdoor temperature fluctuations. In order to minimize the effects of diurnal temperature fluctuations, especially on the vertical motion of the ring floor, scientists at SSRL tried three approaches: painting the storage ring white, covering the asphalt in the middle of the ring with highly reflective Mylar and installing Mylar on a portion of the ring roof and walls. Vertical motion in the storage ring is measured by a Hydrostatic Leveling System (HLS), which calculates the relative height of water in a pipe that extends around the ring. The 24-hr amplitude of the floor motion was determined using spectral analysis of HLS data, and the ratio of this amplitude before and after each experiment was used to quantitatively determine the efficacy of each approach. The results of this analysis showed that the Mylar did not have any significant effect on floor motion, although the whitewash project did yield a reduction in overall HLS variation of 15 percent. However, further analysis showed that the reduction can largely be attributed to a few local changes rather than an overall reduction in floor motion around the ring. Future work will consist of identifying and selectively insulating these local regions in order to find the driving force behind diurnal floor motion in the storage ring.

  14. ring og refleksion

    DEFF Research Database (Denmark)

    Wahlgren, B.; Rattleff, Pernille; Høyrup, S.

    State of the art inden for forskning om læring på arbejdspladsen samt gennemgang af læringsteori og refleksionsbegrebet hos Dewey, Dreyfus, Schön, Argyris, Kolb, Jarvis, Mezirow og Brookfield. Afsluttes med diskussion af syntetiseret model for læring på arbejdspladsen.......State of the art inden for forskning om læring på arbejdspladsen samt gennemgang af læringsteori og refleksionsbegrebet hos Dewey, Dreyfus, Schön, Argyris, Kolb, Jarvis, Mezirow og Brookfield. Afsluttes med diskussion af syntetiseret model for læring på arbejdspladsen....

  15. Synthesis of first row transition metal carboxylate complexes by ring ...

    Indian Academy of Sciences (India)

    tion of pyromellitic dianhydride with methanol and ring opening of pyromellitic dianhydride takes place. The corresponding carboxylate complex formed dur- ing the process can be crystallised by adding biden- tate nitrogen donor ligands such as 1,10-phenanthroline or 2,2 - bipyridine.20 From the reaction with 1,10-.

  16. Competitive and Cooperative Torquoselectivity in the thermal ring ...

    Indian Academy of Sciences (India)

    All the stationary points and TSs were optimized at. B3LYP23/6-31G (d) level using Gaussian 98 software.24. The stationary geometries of reactants and products were characterized with real frequencies and TSs have one imaginary frequency with animation corresponding to conrotatory ring opening. Thermochemical and ...

  17. Control of the rings of exceptional points in photonic crystal slabs

    DEFF Research Database (Denmark)

    Kaminski, Piotr Marek; Breinbjerg, Olav; Mørk, Jesper

    2017-01-01

    shown that when the system becomes non-Hermitian, e.g. it is an open system exhibiting radiation losses, Dirac cones can be deformed spawning rings of exceptional points [2]. Within the ring, the dispersion follows the two-dimensional flat band which provides a high density of states and therefore high...

  18. Rotating ring-ring electrode theory and experiment

    NARCIS (Netherlands)

    Kuiken, H.K.; Bakkers, E.P.A.M.; Ligthart, H.; Kellyb, J.J.

    2000-01-01

    A model is presented for the rotating ring-ring electrode. Although the electrode is defined by four characteristic lengths, it is shown that the collection efficiency depends on only two dimensionless parameters. A simple relationship between these and the corresponding parameters for the rotating

  19. The Rotating Ring-Ring Electrode. Theory and Experiment

    NARCIS (Netherlands)

    Kuiken, H.K.; Bakkers, E.P.A.M.; Ligthart, H.; Kelly, J.J.

    2000-01-01

    A model is presented for the rotating ring-ring electrode. Although the electrode is defined by four characteristic lengths, it is shown that the collection efficiency depends on only two dimensionless parameters. A simple relationship between these and the corresponding parameters for the rotating

  20. Damping rings for CLIC

    CERN Document Server

    Jowett, John M; Zimmermann, Frank; Owen, H

    2001-01-01

    The Compact Linear Colider (CLIC) is designed to operate at 3 TeV centre-of-mass energy with a total luminosity of 10^35 cm^-2 s^-1. The overall system design leads to extremely demanding requirements on the bunch trains injected into the main libac at frequency of 100 Hz. In particular, the emittances of the intense bunches have to be about an order of magnitude smaller than presently achieved. We describe our approach to finding a damping ring design capable of meeting these requirements. Besides lattice design, emittance and damping rate considerations, a number of scattering and instability effects have to be incorporated into the optimisation of parameters. Among these, intra-bem scattering and the electron cloud effect are two of the most significant.

  1. Does the sun ring

    International Nuclear Information System (INIS)

    Isaak, G.R.

    1978-01-01

    The work of various groups, which have been investigating the possibility of measuring the periodicities of solar oscillations in an attempt to test theoretical models of the sun, is reported. In particular the observation of small velocity oscillations of the surface layers of the sun that permits the measurement of the sound waves (or phonons) in the solar atmosphere, is discussed. Oscillations with periods of 2.65 h, 58 and 40 min and amplitudes of 2.7, 0.8 and 0.7 ms -1 respectively are reported. Support for a periodicity at about 2.65 h from a number of other groups using other measuring techniques are considered. It is felt that the most probable interpretation of the observed solar oscillations is that the sun is a resonator which is ringing. (UK)

  2. Undulator tunability and synchrotron ring-energy

    International Nuclear Information System (INIS)

    Viccaro, P.J.; Sheony, G.K.

    1992-01-01

    An undulator has two properties which make it an extremely attractive source of electromagnetic radiation. The first is that the radiation is concentrated in a number of narrow energy bands known as harmonics of the device. The second characteristic is that under favorable operating conditions, the energy of these harmonics can be shifted or open-quote tunedclose quotes over an energy interval which can be as large as two or three times the value of the lowest energy harmonic. Both the photon energy of an undulator as well as its tunability are determined by the period, λ, of the device, the magnetic gap, G (which is larger than the minimum aperture required for injection and operation of the storage ring) and the storage ring energy E R . Given the photon energy, E p , the above parameters ultimately define the limits of operation or tunability of the undulator. In general, the larger the tunability range, the more useful the device. Therefore, for a given required maximum photon energy, it is desirable to find the operating conditions and device parameters which result in the largest tunability interval possible. With this in mind, we have investigated the question of undulator tunability with emphasis on the role of the ring energy in order to find the smallest E R consistent with the desired tunability interval and photon energy. As a guideline, we have included a preliminary criteria, concerning the tunability requirements for the Advanced Photon Source (APS) to be built at Argonne. The analysis is aimed at X-ray undulator sources on the APS but is applicable to any storage ring

  3. How Jupiter's Ring Was Discovered.

    Science.gov (United States)

    Elliot, James; Kerr, Richard

    1985-01-01

    "Rings" (by astronomer James Elliot and science writer Richard Kerr) is a nontechnical book about the discovery and exploration of ring systems from the time of Galileo to the era of the Voyager spacecraft. One of this book's chapters is presented. (JN)

  4. Binomial Rings: Axiomatisation, Transfer and Classification

    OpenAIRE

    Xantcha, Qimh Richey

    2011-01-01

    Hall's binomial rings, rings with binomial coefficients, are given an axiomatisation and proved identical to the numerical rings studied by Ekedahl. The Binomial Transfer Principle is established, enabling combinatorial proofs of algebraical identities. The finitely generated binomial rings are completely classified. An application to modules over binomial rings is given.

  5. Ring-Opening Cycloaddition of Aziridines to Ketenimines.

    Science.gov (United States)

    Maas, Heiko; Bensimon, Corinne; Alper, Howard

    1998-01-09

    The Lewis acid-catalyzed addition of aziridines to ketenimines gave substituted pyrrolidonimines in 47-87% yields. The hard Lewis acid LiClO(4) proved to be superior to the soft [(PhCN)(2)PdCl(2)], affording higher yields under milder conditions. The reaction is regioselective and occurs with complete stereoselectivity using [(PhCN)(2)PdCl(2)] and with a small amount of racemization in the case of LiClO(4).

  6. Catalysts and methods for ring opening metathesis polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Schrock, Richard Royce; Autenrieth, Benjamin

    2018-04-03

    The present invention, among other things, provides highly syndiotactic poly(dicyclopentadiene) and/or hydrogenated poly(dicyclopentadiene), compositions thereof, and compounds and methods for preparing the same. In some embodiments, a provided compound is a compound of formula I, II or III. In some embodiments, a provided method comprises providing a compound of formula I, II or III.

  7. Ring-Opening Polymerization of Lactides by (Pyrazol-1-ylmethyl ...

    African Journals Online (AJOL)

    NICO

    2014-09-03

    Sep 3, 2014 ... An excellent example of such a biodegradable polymer is polylactide ... 2.1. Materials. All air-sensitive manipulations were performed under argon ... lated by filtration and dried to constant weight prior to analy- ses by NMR ...

  8. Ionization cooling ring for muons

    Directory of Open Access Journals (Sweden)

    R. Palmer

    2005-06-01

    Full Text Available Practical ionization cooling rings could lead to lower cost or improved performance in neutrino factory or muon collider designs. The ring modeled here uses realistic three-dimensional fields. The performance of the ring compares favorably with the linear cooling channel used in the second U.S. Neutrino Factory Study. The normalized 6D emittance of an ideal ring is decreased by a factor of approximately 240, compared with a factor of only 15 for the linear channel. We also examine such real-world effects as windows on the absorbers and rf cavities and leaving empty lattice cells for injection and extraction. For realistic conditions the ring decreases the normalized 6D emittance by a factor of 49.

  9. Application of combinatorial biocatalysis for a unique ring expansion of dihydroxymethylzearalenone.

    Science.gov (United States)

    Rich, Joseph O; Budde, Cheryl L; McConeghey, Luke D; Cotterill, Ian C; Mozhaev, Vadim V; Singh, Sheo B; Goetz, Michael A; Zhao, Annie; Michels, Peter C; Khmelnitsky, Yuri L

    2009-06-01

    Combinatorial biocatalysis was applied to generate a diverse set of dihydroxymethylzearalenone analogs with modified ring structure. In one representative chemoenzymatic reaction sequence, dihydroxymethylzearalenone was first subjected to a unique enzyme-catalyzed oxidative ring opening reaction that creates two new carboxylic groups on the molecule. These groups served as reaction sites for further derivatization involving biocatalytic ring closure reactions with structurally diverse bifunctional reagents, including different diols and diamines. As a result, a library of cyclic bislactones and bislactams was created, with modified ring structures covering chemical space and structure activity relationships unattainable by conventional synthetic means.

  10. Containing Ebola at the Source with Ring Vaccination.

    Directory of Open Access Journals (Sweden)

    Stefano Merler

    2016-11-01

    Full Text Available Interim results from the Guinea Ebola ring vaccination trial suggest high efficacy of the rVSV-ZEBOV vaccine. These findings open the door to the use of ring vaccination strategies in which the contacts and contacts of contacts of each index case are promptly vaccinated to contain future Ebola virus disease outbreaks. To provide a numerical estimate of the effectiveness of ring vaccination strategies we introduce a spatially explicit agent-based model to simulate Ebola outbreaks in the Pujehun district, Sierra Leone, structurally similar to previous modelling approaches. We find that ring vaccination can successfully contain an outbreak for values of the effective reproduction number up to 1.6. Through an extensive sensitivity analysis of parameters characterising the readiness and capacity of the health care system, we identify interventions that, alongside ring vaccination, could increase the likelihood of containment. In particular, shortening the time from symptoms onset to hospitalisation to 2-3 days on average through improved contact tracing procedures, adding a 2km spatial component to the vaccination ring, and decreasing human mobility by quarantining affected areas might contribute increase our ability to contain outbreaks with effective reproduction number up to 2.6. These results have implications for future control of Ebola and other emerging infectious disease threats.

  11. Evaluation of ring impedance of the Photon Factory storage ring

    International Nuclear Information System (INIS)

    Kiuchi, T.; Izawa, M.; Tokumoto, S.; Hori, Y.; Sakanaka, S.; Kobayashi, M.; Kobayakawa, H.

    1992-05-01

    The loss parameters of the ducts in the Photon Factory (PF) storage ring were evaluated using the wire method and the code TBCI. Both the measurement and the calculation were done for a different bunch length (σ) ranging from 23 to 80 ps. The PF ring impedance was estimated to be |Z/n|=3.2 Ω using the broadband impedance model. The major contribution to the impedance comes from the bellows and the gate valve sections. Improvements of these components will lower the ring impedance by half. (author)

  12. Ring-Opening Reactions of Aziridines Fused to a Conformationally Locked Tetrahydropyran Ring

    Czech Academy of Sciences Publication Activity Database

    Karban, Jindřich; Kroutil, J.; Buděšínský, Miloš; Sýkora, Jan; Císařová, I.

    2009-01-01

    Roč. 2009, č. 36 (2009), s. 6399-6406 ISSN 1434-193X R&D Projects: GA AV ČR IAA400720703; GA AV ČR IAA400720706 Institutional research plan: CEZ:AV0Z40720504; CEZ:AV0Z40550506 Keywords : aziridines * carbohydrates * regioselectivity Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.096, year: 2009

  13. Tinkering at the main-ring lattice

    Energy Technology Data Exchange (ETDEWEB)

    Ohnuma, S.

    1982-08-23

    To improve production of usable antiprotons using the proton beam from the main ring and the lossless injection of cooled antiprotons into the main ring, modifications of the main ring lattice are recommended.

  14. Is the bell ringing?

    CERN Multimedia

    Francesco Poppi

    2010-01-01

    During the Nobel prize-winning UA1 experiment, scientists in the control room used to ring a bell if a particularly interesting event had occurred. Today, the “CMS Exotica hotline” routine produces a daily report that lists the exotic events that were recorded the day before.   Display of an event selected by the Exotica routine. Take just a very small fraction of the available data (max. 5%); define the events that you want to keep and set the parameters accordingly; run the Exotica routine and only look at the very few images that the system has selected for you. This is the recipe that a small team of CMS researchers has developed to identify the signals coming from possible new physics processes. “This approach does not replace the accurate data analysis on the whole set of data. However, it is a very fast and effective way to focus on just a few events that are potentially very interesting”, explains Maurizio Pierini (CERN), who developed the...

  15. Esophagectomy - open

    Science.gov (United States)

    ... Lewis esophagectomy, Blunt esophagectomy; Esophageal cancer - esophagectomy - open; Cancer of the esophagus - esophagectomy - open ... lining of the esophagus that can lead to cancer ( Barrett esophagus ) Severe trauma Destroyed esophagus Severely damaged stomach

  16. Moving ring reactor 'Karin-1'

    International Nuclear Information System (INIS)

    1983-12-01

    The conceptual design of a moving ring reactor ''Karin-1'' has been carried out to advance fusion system design, to clarify the research and development problems, and to decide their priority. In order to attain these objectives, a D-T reactor with tritium breeding blanket is designed, a commercial reactor with net power output of 500 MWe is designed, the compatibility of plasma physics with fusion engineering is demonstrated, and some other guideline is indicated. A moving ring reactor is composed mainly of three parts. In the first formation section, a plasma ring is formed and heated up to ignition temperature. The plasma ring of compact torus is transported from the formation section through the next burning section to generate fusion power. Then the plasma ring moves into the last recovery section, and the energy and particles of the plasma ring are recovered. The outline of a moving ring reactor ''Karin-1'' is described. As a candidate material for the first wall, SiC was adopted to reduce the MHD effect and to minimize the interaction with neutrons and charged particles. The thin metal lining was applied to the SiC surface to solve the problem of the compatibility with lithium blanket. Plasma physics, the engineering aspect and the items of research and development are described. (Kako, I.)

  17. Quantum Fourier Transform Over Galois Rings

    OpenAIRE

    Zhang, Yong

    2009-01-01

    Galois rings are regarded as "building blocks" of a finite commutative ring with identity. There have been many papers on classical error correction codes over Galois rings published. As an important warm-up before exploring quantum algorithms and quantum error correction codes over Galois rings, we study the quantum Fourier transform (QFT) over Galois rings and prove it can be efficiently preformed on a quantum computer. The properties of the QFT over Galois rings lead to the quantum algorit...

  18. Open access

    NARCIS (Netherlands)

    Valkenburg, P.M.

    2015-01-01

    Open access week Van 19 tot en met 25 oktober 2015 vond wereldwijd de Open Access Week plaats. Tijdens deze week werden er over de hele wereld evenementen georganiseerd waar open access een rol speelt. Ook in Nederland zijn er diverse symposia, workshops en debatten georganiseerd zoals het debat in

  19. Polarized particles in storage rings

    International Nuclear Information System (INIS)

    Derbenev, Ya.S.; Kondratenko, A.M.; Serednyakov, S.I.; Skrinskij, A.N.; Tumajkin, G.M.; Shatunov, Yu.M.

    1977-01-01

    Experiments with polarized beams on the VEPP-2M and SPEAK storage rings are described. Possible methods of producing polarized particle beams in storage rings as well as method of polarization monitoring are counted. Considered are the processes of radiation polarization of electrons and positrons. It is shown, that to preserve radiation polarization the introduction of regions with a strong sign-variable magnetic field is recommended. Methods of polarization measurement are counted. It is suggested for high energies to use dependence of synchrotron radiation power on transverse polarization of electrons and positrons. Examples of using polarizability of colliding beams in storage rings are presented

  20. Researches on the Piston Ring

    Science.gov (United States)

    Ehihara, Keikiti

    1944-01-01

    In internal combustion engines, steam engines, air compressors, and so forth, the piston ring plays an important role. Especially, the recent development of Diesel engines which require a high compression pressure for their working, makes, nowadays, the packing action of the piston ring far more important than ever. Though a number of papers have been published in regard to researches on the problem of the piston ring, none has yet dealt with an exact measurement of pressure exerted on the cylinder wall at any given point of the ring. The only paper that can be traced on this subject so far is Mr. Nakagawa's report on the determination of the relative distribution of pressure on the cylinder wall, but the measuring method adopted therein appears to need further consideration. No exact idea has yet been obtained as to how the obturation of gas between the piston and cylinder, the frictional resistance of the piston, and the wear of the cylinder wall are affected by the intensity and the distribution of the radial pressure of the piston ring. Consequently, the author has endeavored, by employing an apparatus of his own invention, to get an exact determination of the pressure distribution of the piston ring. By means of a newly devised ring tester, to which piezoelectricity of quartz was applied, the distribution of the radial pressure of many sample rings on the market was accurately determined. Since many famous piston rings show very irregular pressure distribution, the author investigated and achieved a manufacturing process of the piston ring which will exert uniform pressure on the cylinder wall. Temperature effects on the configuration and on the mean spring power have also been studied. Further, the tests were performed to ascertain how the gas tightness of the piston ring may be affected by the number or spring power. The researches as to the frictional resistance between the piston ring and the cylinder wall were carried out, too. The procedure of study, and

  1. Soft Congruence Relations over Rings

    Science.gov (United States)

    Xin, Xiaolong; Li, Wenting

    2014-01-01

    Molodtsov introduced the concept of soft sets, which can be seen as a new mathematical tool for dealing with uncertainty. In this paper, we initiate the study of soft congruence relations by using the soft set theory. The notions of soft quotient rings, generalized soft ideals and generalized soft quotient rings, are introduced, and several related properties are investigated. Also, we obtain a one-to-one correspondence between soft congruence relations and idealistic soft rings and a one-to-one correspondence between soft congruence relations and soft ideals. In particular, the first, second, and third soft isomorphism theorems are established, respectively. PMID:24949493

  2. Distributively generated matrix near rings

    International Nuclear Information System (INIS)

    Abbasi, S.J.

    1993-04-01

    It is known that if R is a near ring with identity then (I,+) is abelian if (I + ,+) is abelian and (I,+) is abelian if (I*,+) is abelian [S.J. Abbasi, J.D.P. Meldrum, 1991]. This paper extends these results. We show that if R is a distributively generated near ring with identity then (I,+) is included in Z(R), the center of R, if (I + ,+) is included in Z(M n (R)), the center of matrix near ring M n (R). Furthermore (I,+) is included in Z(R) if (I*,+) is included in Z(M n (R)). (author). 5 refs

  3. SMARANDACHE NON-ASSOCIATIVE RINGS

    OpenAIRE

    Vasantha, Kandasamy

    2002-01-01

    An associative ring is just realized or built using reals or complex; finite or infinite by defining two binary operations on it. But on the contrary when we want to define or study or even introduce a non-associative ring we need two separate algebraic structures say a commutative ring with 1 (or a field) together with a loop or a groupoid or a vector space or a linear algebra. The two non-associative well-known algebras viz. Lie algebras and Jordan algebras are mainly built using a vecto...

  4. The features of nucleophilic substitution of the nitro group in 4-alkyl-6-nitro-1,2,4-triazolo[5,1-c][1,2,4]triazines

    Directory of Open Access Journals (Sweden)

    E. N. Ulomsky

    2017-05-01

    Full Text Available The nucleophilic substitution of the nitro group of 4-alkyl-6-nitro-4,7-dihydro-1,2,4-triazolo[5,1-c][1,2,4]triazine-7-ones on the example of interactionwith morpholine was studied. It is established that under the action of excess cycloalkylimine at room temperature the unusual easy disclosure of triazine cycle with the formation of sterically hindered hydrazones occurs which are the key intermediates for further transformations. The carrying of reaction at elevated temperatures leads to the formation of products of substitution of the nitro group with the amine and also with morpholyl hydrazones which are the products of hydrolysis of amides of hydrazones and subsequent decarboxylation. Thus, the nucleophilic substitution of the nitro group in the described triazolotriazines flows through the ANRORC mechanism.

  5. Additional Nucleophile-Free FeCl3-Catalyzed Green Deprotection of 2,4-Dimethoxyphenylmethyl-Protected Alcohols and Carboxylic Acids.

    Science.gov (United States)

    Sawama, Yoshinari; Masuda, Masahiro; Honda, Akie; Yokoyama, Hiroki; Park, Kwihwan; Yasukawa, Naoki; Monguchi, Yasunari; Sajiki, Hironao

    2016-01-01

    The deprotection of the methoxyphenylmethyl (MPM) ether and ester derivatives can be generally achieved by the combinatorial use of a catalytic Lewis acid and stoichiometric nucleophile. The deprotections of 2,4-dimethoxyphenylmethyl (DMPM)-protected alcohols and carboxylic acids were found to be effectively catalyzed by iron(III) chloride without any additional nucleophile to form the deprotected mother alcohols and carboxylic acids in excellent yields. Since the present deprotection proceeds via the self-assembling mechanism of the 2,4-DMPM protective group itself to give the hardly-soluble resorcinarene derivative as a precipitate, the rigorous purification process by silica-gel column chromatography was unnecessary and the sufficiently-pure alcohols and carboxylic acids were easily obtained in satisfactory yields after simple filtration.

  6. Novel organophosphorus scaffolds of urease inhibitors obtained by substitution of Morita-Baylis-Hillman adducts with phosphorus nucleophiles.

    Science.gov (United States)

    Ntatsopoulos, Vassilis; Vassiliou, Stamatia; Macegoniuk, Katarzyna; Berlicki, Łukasz; Mucha, Artur

    2017-06-16

    The reactivity of Morita-Baylis-Hillman allyl acetates was employed to introduce phosphorus-containing functionalities to the side chain of the cinnamic acid conjugated system by nucleophilic displacement. The proximity of two acidic groups, the carboxylate and phosphonate/phosphinate groups, was necessary to form interactions in the active site of urease by recently described inhibitor frameworks. Several organophosphorus scaffolds were obtained and screened for inhibition of the bacterial urease, an enzyme that is essential for survival of urinary and gastrointestinal tract pathogens. α-Substituted phosphonomethyl- and 2-phosphonoethyl-cinnamate appeared to be the most potent and were further optimized. As a result, one of the most potent organophosphorus inhibitors of urease, α-phosphonomethyl-p-methylcinnamic acid, was identified, with K i  = 0.6 μM for Sporosarcina pasteurii urease. High complementarity to the enzyme active site was achieved with this structure, as any further modifications significantly decreased its affinity. Finally, this work describes the challenges faced in developing ligands for urease. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  7. Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine

    Directory of Open Access Journals (Sweden)

    Katja Hofmann

    2010-07-01

    Full Text Available Novel chromophoric and fluorescent carbonitrile-functionalized poly(vinyl amine (PVAm and PVAm/silica particles were synthesized by means of nucleophilic aromatic substitution of 8-oxo-8H-acenaphtho[1,2-b]pyrrol-9-carbonitrile (1 with PVAm in water. The water solubility of 1 has been mediated by 2,6-O-β-dimethylcyclodextrin or by pre-adsorption onto silica particles. Furthermore, 1 was converted with isopropylamine into the model compound 1-M. All new compounds were characterized by NMR, FTIR, UV–vis and fluorescence spectroscopy. The solvent-dependent UV–vis absorption and fluorescence emission band positions of the model compound and the carbonitrile-functionalized PVAm were studied and interpreted using the empirical Kamlet–Taft solvent parameters π* (dipolarity/polarizability, α (hydrogen-bond donating capacity and β (hydrogen-accepting ability in terms of the linear solvation energy relationship (LSER. The solvent-independent regression coefficients a, b and s were determined using multiple linear correlation analysis. It is shown, that the chains of the polymer have a significant influence on the solvatochromic behavior of 1-P. The structure of the carbonitrile 1-Si bound to polymer-modified silica particles was studied by means of X-ray photoelectron spectroscopy (XPS and Brunauer–Emmett–Teller (BET measurements. Fluorescent silica particles were obtained as shown by fluorescence spectroscopy with a diffuse reflectance technique.

  8. Energetic ion injection and formation of the storm-time symmetric ring current

    Directory of Open Access Journals (Sweden)

    L. Xie

    2006-12-01

    Full Text Available An extensive study of ring current injection and intensification of the storm-time ring current is conducted with three-dimensional (3-D test particle trajectory calculations (TPTCs. The TPTCs reveal more accurately the process of ring current injection, with the main results being the following: (1 an intense convection electric field can effectively energize and inject plasma sheet particles into the ring current region within 1–3 h. (2 Injected ions often follow chaotic trajectories in non-adiabatic regions, which may have implications in storm and ring current physics. (3 The shielding electric field, which arises as a consequence of enhanced convection and co-exists with the injection and convection electric field, may cause the original open trajectories of injected ions with higher energy to change into closed ones, thus playing a role in the formation of the symmetric ring current.

  9. Tandem Cu-catalyzed ketenimine formation and intramolecular nucleophile capture: Synthesis of 1,2-dihydro-2-iminoquinolines from 1-(o-acetamidophenyl)propargyl alcohols

    Science.gov (United States)

    Kant, Ruchir

    2014-01-01

    Summary The copper-catalyzed ketenimine formation reaction of 1-(o-acetamidophenyl)propargyl alcohols with various sulfonyl azides is found to undergo a concomitant intramolecular nucleophile attack to generate 1,2-dihydro-2-iminoquinolines after aromatization (via elimination of acetyl and hydroxy groups) and tautomerization. The reaction produces 4-substituted and 3,4-unsubstituted title compounds in moderate to good yields under mild reaction conditions. PMID:24991276

  10. Glassy carbon electrode modified with horse radish peroxidase/organic nucleophilic-functionalized carbon nanotube composite for enhanced electrocatalytic oxidation and efficient voltammetric sensing of levodopa

    Energy Technology Data Exchange (ETDEWEB)

    Shoja, Yalda; Rafati, Amir Abbas, E-mail: aa_rafati@basu.ac.ir; Ghodsi, Javad

    2016-01-01

    A novel and selective enzymatic biosensor was designed and constructed for voltammetric determination of levodopa (L-Dopa) in aqueous media (phosphate buffer solution, pH = 7). Biosensor development was on the basis of to physically immobilizing of horse radish peroxidase (HRP) as electrochemical catalyst by sol–gel on glassy carbon electrode modified with organic nucleophilic carbon nanotube composite which in this composite p-phenylenediamine (pPDA) as organic nucleophile chemically bonded with functionalized MWCNT (MWCNT-COOH). The results of this study suggest that prepared bioorganic nucleophilic carbon nanotube composite (HRP/MWCNT-pPDA) shows fast electron transfer rate for electro oxidation of L-Dopa because of its high electrochemical catalytic activity toward the oxidation of L-Dopa, more −NH{sub 2} reactive sites and large effective surface area. Also in this work we measured L-Dopa in the presence of folic acid and uric acid as interferences. The proposed biosensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), FT-IR spectroscopy and cyclic voltammetry (CV). The differential pulse voltammetry (DPV) was used for determination of L-Dopa from 0.1 μM to 1.9 μM with a low detection limit of 40 nM (for S/N = 3) and sensitivity was about 35.5 μA/μM. Also this biosensor has several advantages such as rapid response, high stability and reproducibility. - Highlights: • Glassy carbon electrode modified by a novel composite in which pPDA as nucleophile is chemically attached to MWCNTs. • The developed biosensor exhibited excellent electrocatalytic activity in electrochemically determination of L-Dopa. • The biosensor showed acceptable sensitivity, reproducibility, detection limit, selectivity and stability. • MWCNT-pPDA provides a good electrical conductivity and large effective surface area for enzyme immobilization.

  11. 4-alkyl-L-(Dehydro)proline biosynthesis in actinobacteria involves N-terminal nucleophile-hydrolase activity of γ-glutamyltranspeptidase homolog for C-C bond cleavage

    Science.gov (United States)

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

    2017-07-01

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

  12. Prototype moving-ring reactor

    International Nuclear Information System (INIS)

    Smith, A.C. Jr.; Ashworth, C.P.; Abreu, K.E.

    1982-01-01

    We have completed a design of the Prototype Moving-Ring Reactor. The fusion fuel is confined in current-carrying rings of magnetically-field-reversed plasma (Compact Toroids). The plasma rings, formed by a coaxial plasma gun, undergo adiabatic magnetic compression to ignition temperature while they are being injected into the reactor's burner section. The cylindrical burner chamber is divided into three burn stations. Separator coils and a slight axial guide field gradient are used to shuttle the ignited toroids rapidly from one burn station to the next, pausing for 1/3 of the total burn time at each station. D-T- 3 He ice pellets refuel the rings at a rate which maintains constant radiated power

  13. Autumn study on storage rings

    CERN Multimedia

    1974-01-01

    The first two weeks of October have seen storage ring people from accelerator Laboratories throughout the world at CERN to study the fundamental problems of very high energy protonproton colliding beam machines.

  14. Minimal Gromov-Witten rings

    International Nuclear Information System (INIS)

    Przyjalkowski, V V

    2008-01-01

    We construct an abstract theory of Gromov-Witten invariants of genus 0 for quantum minimal Fano varieties (a minimal class of varieties which is natural from the quantum cohomological viewpoint). Namely, we consider the minimal Gromov-Witten ring: a commutative algebra whose generators and relations are of the form used in the Gromov-Witten theory of Fano varieties (of unspecified dimension). The Gromov-Witten theory of any quantum minimal variety is a homomorphism from this ring to C. We prove an abstract reconstruction theorem which says that this ring is isomorphic to the free commutative ring generated by 'prime two-pointed invariants'. We also find solutions of the differential equation of type DN for a Fano variety of dimension N in terms of the generating series of one-pointed Gromov-Witten invariants

  15. Cosmic rings from colliding galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Mitton, S

    1976-11-18

    Research on two ring galaxies has led to the proposal of an interaction model to account for the rings. It is envisaged that this class of galaxy is created when a compact galaxy crashes through the disc of a spiral galaxy. The results of a spectroscopic investigation of the galaxy known as the Cartwheel and of another ring galaxy 11 NZ 4 are discussed. The general picture of ring galaxies which emerges from these studies of a massive starry nucleus with a necklace of emitting gas and some spokes and along the spin axis of the wheel a small companion galaxy that is devoid of interstellar gas. An explanation of these properties is considered.

  16. Ring lasers - a brief history

    Science.gov (United States)

    Klein, Tony

    2017-10-01

    Used these days in inertial navigation, ring lasers are also used in recording the tiniest variations in the Earth's spin, as well in detecting earthquakes and even the drift of continents. How did it all begin?

  17. Open Content in Open Context

    Science.gov (United States)

    Kansa, Sarah Whitcher; Kansa, Eric C.

    2007-01-01

    This article presents the challenges and rewards of sharing research content through a discussion of Open Context, a new open access data publication system for field sciences and museum collections. Open Context is the first data repository of its kind, allowing self-publication of research data, community commentary through tagging, and clear…

  18. Finite element modelling of process-integrated powder coating by radial axial rolling of rings

    International Nuclear Information System (INIS)

    Frischkorn, J.; Kebriaei, R.; Reese, S.; Moll, H.; Theisen, W.; Husmann, T.; Meier, H.

    2011-01-01

    The process-integrated powder coating by radial axial rolling of rings represents a new hybrid production technique applied in the manufacturing of large ring-shaped work pieces with functional layers. It is thought to break some limitations that come along with the hot isostatic pressing (HIP) which is used nowadays to apply the powdery layer material onto the rolled substrate ring. Within the new process the compaction of the layer material is integrated into the ring rolling and HIP becomes dispensable. Following this approach the rolling of such compound rings brings up some new challenges. The volume of a solid ring stays nearly constant during the rolling. This behaviour can be exploited to determine the infeed of the rollers needed to reach the desired ring shape. Since volume consistency cannot be guaranteed for the rolling of a compound ring the choice of appropriate infeed of the rollers is still an open question. This paper deals with the finite element (FE) simulation of this new process. First, the material model that is used to describe the compaction of the layer material is shortly reviewed. The main focus of the paper is then put on a parameterized FE ring rolling model that incorporates a control system in order to stabilize the process. Also the differences in the behaviour during the rolling stage between a compound and a solid ring will be discussed by means of simulation results.

  19. Ring insertions as light sources

    International Nuclear Information System (INIS)

    Green, G.K.

    1975-01-01

    Bending magnets can be inserted in the long straight sections of electron storage rings to produce synchrotron radiation. If the design is carefully proportioned, the bending magnets create only a small perturbation of the properties of the ring. The resulting spectra have favorable optical properties as sources for spectroscopy and diffraction studies. The characteristics of the source are discussed, and the geometrical requirements of the magnets are presented

  20. Synlig læring

    DEFF Research Database (Denmark)

    Brandsen, Mads

    2017-01-01

    Introduktionen af John Hatties synlig læring i den danske skoleverden møder stadig meget kritik. Mange lærere og pædagoger oplever synlig læring som en tornado, der vil opsuge og ødelægge deres særlige danske udgave af den kontinentale dannelsestænkning, didaktik og pædagogik. Spørgsmålet er om...

  1. The circular RFQ storage ring

    International Nuclear Information System (INIS)

    Ruggiero, A.G.

    1998-01-01

    This paper presents a novel idea of storage ring for the accumulation of intense beams of light and heavy ions at low energy. The new concept is a natural development of the combined features used in a conventional storage ring and an ion trap, and is basically a linear RFQ bend on itself. In summary the advantages are: smaller beam dimensions, higher beam intensity, and a more compact storage device

  2. The Circular RFQ Storage Ring

    International Nuclear Information System (INIS)

    Ruggiero, A. G.

    1999-01-01

    This paper presents a novel idea of storage ring for the accumulation of intense beams of light and heavy ions at low energy. The new concept is a natural development of the combined features of conventional storage rings and ion traps, and is basically a linear RFQ bent on itself. The advantages are: smaller beam dimensions, higher beam intensity, and a more compact storage device

  3. Electrically charged dilatonic black rings

    International Nuclear Information System (INIS)

    Kunduri, Hari K.; Lucietti, James

    2005-01-01

    In this Letter we present (electrically) charged dilatonic black ring solutions of the Einstein-Maxwell-dilaton theory in five dimensions and we consider their physical properties. These solutions are static and as in the neutral case possess a conical singularity. We show how one may remove the conical singularity by application of a Harrison transformation, which physically corresponds to supporting the charged ring with an electric field. Finally, we discuss the slowly rotating case for arbitrary dilaton coupling

  4. Low emittance electron storage rings

    Science.gov (United States)

    Levichev, E. B.

    2018-01-01

    Low-emittance electron (positron) beams are essential for synchrotron light sources, linear collider damping rings, and circular Crab Waist colliders. In this review, the principles and methods of emittance minimization are discussed, prospects for developing relativistic electron storage rings with small beam phase volume are assessed, and problems related to emittance minimization are examined together with their possible solutions. The special features and engineering implementation aspects of various facilities are briefly reviewed.

  5. Resonance capture and Saturn's rings

    International Nuclear Information System (INIS)

    Patterson, C.W.

    1986-05-01

    We have assigned the resonances apparently responsible for the stabilization of the Saturn's shepherd satellites and for the substructure seen in the F-ring and the ringlets in the C-ring. We show that Saturn's narrow ringlets have a substructure determined by three-body resonances with Saturn's ringmoons and the sun. We believe such resonances have important implications to satellite formation. 17 refs., 1 fig., 1 tab

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    A large variety of C-terminally modified peptides was obtained by nucleophilic cleavage of the ester bond in solid phase linked peptide esters of 4-hydroxymethyl benzamide (HMBA). The developed methods provided peptides, C-terminally functionalized as esters, amides and thioesters, with high purity...... directly from the resin in a single reaction step. A comprehensive screening of the reaction conditions and scope for nucleophilic cleavage of peptides from the HMBA linker was performed....

  7. Optimal control of quantum rings by terahertz laser pulses.

    Science.gov (United States)

    Räsänen, E; Castro, A; Werschnik, J; Rubio, A; Gross, E K U

    2007-04-13

    Complete control of single-electron states in a two-dimensional semiconductor quantum-ring model is established, opening a path into coherent laser-driven single-gate qubits. The control scheme is developed in the framework of optimal-control theory for laser pulses of two-component polarization. In terms of pulse lengths and target-state occupations, the scheme is shown to be superior to conventional control methods that exploit Rabi oscillations generated by uniform circularly polarized pulses. Current-carrying states in a quantum ring can be used to manipulate a two-level subsystem at the ring center. Combining our results, we propose a realistic approach to construct a laser-driven single-gate qubit that has switching times in the terahertz regime.

  8. Weak openness and almost openness

    Directory of Open Access Journals (Sweden)

    David A. Rose

    1984-01-01

    Full Text Available Weak openness and almost openness for arbitrary functions between topological spaces are defined as duals to the weak continuity of Levine and the almost continuity of Husain respectively. Independence of these two openness conditions is noted and comparison is made between these and the almost openness of Singal and Singal. Some results dual to those known for weak continuity and almost continuity are obtained. Nearly almost openness is defined and used to obtain an improved link from weak continuity to almost continuity.

  9. Accretion in Saturn's F Ring

    Science.gov (United States)

    Meinke, B. K.; Esposito, L. W.; Stewart, G.

    2012-12-01

    Saturn's F ring is the solar system's principal natural laboratory for direct observation of accretion and disruption processes. The ring resides in the Roche zone, where tidal disruption competes with self-gravity, which allows us to observe the lifecycle of moonlets. Just as nearby moons create structure at the B ring edge (Esposito et al. 2012) and the Keeler gap (Murray 2007), the F ring "shepherding" moons Prometheus and Pandora stir up ring material and create observably changing structures on timescales of days to decades. In fact, Beurle et al (2010) show that Prometheus makes it possible for "distended, yet gravitationally coherent clumps" to form in the F ring, and Barbara and Esposito (2002) predicted a population of ~1 km bodies in the ring. In addition to the observations over the last three decades, the Cassini Ultraviolet Imaging Spectrograph (UVIS) has detected 27 statistically significant features in 101 occultations by Saturn's F ring since July 2004. Seventeen of those 27 features are associated with clumps of ring material. Two features are opaque in occultation, which makes them candidates for solid objects, which we refer to as Moonlets. The 15 other features partially block stellar signal for 22 m to just over 3.7 km along the radial expanse of the occultation. Upon visual inspection of the occultation profile, these features resemble Icicles, thus we will refer to them as such here. The density enhancements responsible for such signal attenuations are likely due to transient clumping of material, evidence that aggregations of material are ubiquitous in the F ring. Our lengthy observing campaign reveals that Icicles are likely transient clumps, while Moonlets are possible solid objects. Optical depth is an indicator of clumping because more-densely aggregated material blocks more light; therefore, it is natural to imagine moonlets as later evolutionary stage of icicle, when looser clumps of material compact to form a feature that appears

  10. Double acting stirling engine piston ring

    Science.gov (United States)

    Howarth, Roy B.

    1986-01-01

    A piston ring design for a Stirling engine wherein the contact pressure between the piston and the cylinder is maintained at a uniform level, independent of engine conditions through a balancing of the pressure exerted upon the ring's surface and thereby allowing the contact pressure on the ring to be predetermined through the use of a preloaded expander ring.

  11. Study for ILC Damping Ring at KEKB

    Energy Technology Data Exchange (ETDEWEB)

    Flanagan, J.W.; Fukuma, H.; Kanazawa, K.I.; Koiso, H.; Masuzawa, M.; Ohmi, Kazuhito; Ohnishi, Y.; Oide, Katsunobu; Suetsugu, Y.; Tobiyama, M.; /KEK, Tsukuba; Pivi, M.; /SLAC

    2011-11-04

    ILC damping ring consists of very low emittance electron and positron storage rings. It is necessary for ILC damping ring to study electron cloud effects in such low emittance positron ring. We propose a low emittance operation of KEKB to study the effects.

  12. MR imaging findings of ring apophyseal fractures in lumbar vertebrae

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Yong Soo; Kwon, Soon Tae; Song, Chang Joon; Lee, Young Hwan; Kim, Hyoung Seob; Lee, Hwan Do; Cho, June Sik; Ahn, Jae Sung; Lee, June Kyu [Chungnam National Univ. College of Medicine, Taejon (Korea, Republic of)

    1997-07-01

    To assess the location and associated findings of fractures of the posterior lumbar vertebral ring apophysis as seen on MRI We retrospectively evaluated MR findings in 77 patients (86 lesions) with lumbar apophyseal ring fractures. Their age ranged from ten to 67 (mean 33-1) years. To confirm the presence of verterbral ring fractures, CT was performed in 29 patients (31 lesions) within two weeks of MR imaging. Open laminectomy was performed in ten patients, percutaneous automated nucleotomy in three, and LASER operation in four. The most common location of fractures was the superior margin of L5 (36 lesions 41.9%), next was superior margin of S1 (21 lesions, 24.4%). On CT, a bony fragment was seen in 28 patients (30 lesions); the positive predictive value of MR was 99.7%. Multiple lesions were seen in nine patients. Associated disc herniation and bulging were noted in 64 (74.4%) and 15 lesions (17.4%), respectively, and a high signal intensity rim aound the bony fragment on T1 weighted image was noted in 33 (38.4%). Other associated findings were spondylolysis in eight patients, retrolisthesis in five, and spondylolisthesis in three. Operative outcomes were variable. The results of open laminectomy were better than those of percutaneous automated laminectomy or LASER operation. In patients with lumbar apophyseal ring fractures, their exact location and associated findings could be evalvated by MRI, which was therefore useful in the planning of appropriate surgery.

  13. MR imaging findings of ring apophyseal fractures in lumbar vertebrae

    International Nuclear Information System (INIS)

    Kang, Yong Soo; Kwon, Soon Tae; Song, Chang Joon; Lee, Young Hwan; Kim, Hyoung Seob; Lee, Hwan Do; Cho, June Sik; Ahn, Jae Sung; Lee, June Kyu

    1997-01-01

    To assess the location and associated findings of fractures of the posterior lumbar vertebral ring apophysis as seen on MRI We retrospectively evaluated MR findings in 77 patients (86 lesions) with lumbar apophyseal ring fractures. Their age ranged from ten to 67 (mean 33-1) years. To confirm the presence of verterbral ring fractures, CT was performed in 29 patients (31 lesions) within two weeks of MR imaging. Open laminectomy was performed in ten patients, percutaneous automated nucleotomy in three, and LASER operation in four. The most common location of fractures was the superior margin of L5 (36 lesions 41.9%), next was superior margin of S1 (21 lesions, 24.4%). On CT, a bony fragment was seen in 28 patients (30 lesions); the positive predictive value of MR was 99.7%. Multiple lesions were seen in nine patients. Associated disc herniation and bulging were noted in 64 (74.4%) and 15 lesions (17.4%), respectively, and a high signal intensity rim aound the bony fragment on T1 weighted image was noted in 33 (38.4%). Other associated findings were spondylolysis in eight patients, retrolisthesis in five, and spondylolisthesis in three. Operative outcomes were variable. The results of open laminectomy were better than those of percutaneous automated laminectomy or LASER operation. In patients with lumbar apophyseal ring fractures, their exact location and associated findings could be evalvated by MRI, which was therefore useful in the planning of appropriate surgery

  14. Manipulation of vortex rings for flow control

    International Nuclear Information System (INIS)

    Toyoda, Kuniaki; Hiramoto, Riho

    2009-01-01

    This paper reviews the dynamics of vortex rings and the control of flow by the manipulation of vortex rings. Vortex rings play key roles in many flows; hence, the understanding of the dynamics of vortex rings is crucial for scientists and engineers dealing with flow phenomena. We describe the structures and motions of vortex rings in circular and noncircular jets, which are typical examples of flows evolving into vortex rings. For circular jets the mechanism of evolving, merging and breakdown of vortex rings is described, and for noncircular jets the dynamics of three-dimensional deformation and interaction of noncircular vortex rings under the effect of self- and mutual induction is discussed. The application of vortex-ring manipulation to the control of various flows is reviewed with successful examples, based on the relationship between the vortex ring dynamics and the flow properties. (invited paper)

  15. Structure and dynamics of ringed galaxies

    International Nuclear Information System (INIS)

    Buta, R.J.

    1984-01-01

    In many spiral and SO galaxies, single or multiple ring structures are visible in the disk. These inner rings (r), outer rings (R), and nuclear rings (nr) were investigated by means of morphology, photometry, and spectroscopy in order to provide basic data on a long neglected phenomenon. The metric properties of each ring are investigated and found to correlate with the structure of the parent galaxy. When properly calibrated, inner rings in barred (SB) systems can be used as geometric extragalactic distance indicators to distances in excess of 100 Mpc. Other statistics are presented that confirm previous indications that the rings have preferred shapes, relative sizes, and orientations with respect to bars. A survey is made of the less homogeneous non-barred (SA) ringed systems, and the causes of the inhomogeneity are isolated. It is shown that rings can be identified in multiple-ring SA systems that are exactly analogous to those in barred spirals

  16. Robust gap repair in the contractile ring ensures timely completion of cytokinesis.

    Science.gov (United States)

    Silva, Ana M; Osório, Daniel S; Pereira, Antonio J; Maiato, Helder; Pinto, Inês Mendes; Rubinstein, Boris; Gassmann, Reto; Telley, Ivo Andreas; Carvalho, Ana Xavier

    2016-12-19

    Cytokinesis in animal cells requires the constriction of an actomyosin contractile ring, whose architecture and mechanism remain poorly understood. We use laser microsurgery to explore the biophysical properties of constricting rings in Caenorhabditis elegans embryos. Laser cutting causes rings to snap open. However, instead of disintegrating, ring topology recovers and constriction proceeds. In response to severing, a finite gap forms and is repaired by recruitment of new material in an actin polymerization-dependent manner. An open ring is able to constrict, and rings repair from successive cuts. After gap repair, an increase in constriction velocity allows cytokinesis to complete at the same time as controls. Our analysis demonstrates that tension in the ring increases while net cortical tension at the site of ingression decreases throughout constriction and suggests that cytokinesis is accomplished by contractile modules that assemble and contract autonomously, enabling local repair of the actomyosin network. Consequently, cytokinesis is a highly robust process impervious to discontinuities in contractile ring structure. © 2016 Silva et al.

  17. Convergent synthesis of 6-substituted phenanthridines via anionic ring closure

    DEFF Research Database (Denmark)

    Lysén, M.; Kristensen, Jesper Langgaard; Vedsø, P.

    2002-01-01

    Chemical equation presented The addition of organometallic derivatives to the cyano group of 2-(2-fluorophenyl)benzonitrile followed by intramolecular nucleophilic substitution produces 6-substituted phenanthridines. Alkyllithiums, aryllithiums, and sterically nondemanding lithium amides reacted ...

  18. Open hardware for open science

    CERN Multimedia

    CERN Bulletin

    2011-01-01

    Inspired by the open source software movement, the Open Hardware Repository was created to enable hardware developers to share the results of their R&D activities. The recently published CERN Open Hardware Licence offers the legal framework to support this knowledge and technology exchange.   Two years ago, a group of electronics designers led by Javier Serrano, a CERN engineer, working in experimental physics laboratories created the Open Hardware Repository (OHR). This project was initiated in order to facilitate the exchange of hardware designs across the community in line with the ideals of “open science”. The main objectives include avoiding duplication of effort by sharing results across different teams that might be working on the same need. “For hardware developers, the advantages of open hardware are numerous. For example, it is a great learning tool for technologies some developers would not otherwise master, and it avoids unnecessary work if someone ha...

  19. Pure subrings of the rings

    International Nuclear Information System (INIS)

    Tsarev, Andrei V

    2009-01-01

    Pure subrings of finite rank in the Z-adic completion of the ring of integers and in its homomorphic images are considered. Certain properties of these rings are studied (existence of an identity element, decomposability into a direct sum of essentially indecomposable ideals, condition for embeddability into a csp-ring, etc.). Additive groups of these rings and conditions under which these rings are subrings of algebraic number fields are described. Bibliography: 12 titles.

  20. Open Access

    Science.gov (United States)

    Suber, Peter

    2012-01-01

    The Internet lets us share perfect copies of our work with a worldwide audience at virtually no cost. We take advantage of this revolutionary opportunity when we make our work "open access": digital, online, free of charge, and free of most copyright and licensing restrictions. Open access is made possible by the Internet and copyright-holder…

  1. Open innovation

    DEFF Research Database (Denmark)

    Bogers, Marcel; Chesbrough, Henry; Moedas, Carlos

    2018-01-01

    Open innovation is now a widely used concept in academia, business, and policy making. This article describes the state of open innovation at the intersection of research, practice, and policy. It discusses some key trends (e.g., digital transformation), challenges (e.g., uncertainty...

  2. Primitivity and weak distributivity in near rings and matrix near rings

    International Nuclear Information System (INIS)

    Abbasi, S.J.

    1993-08-01

    This paper shows the structure of matrix near ring constructed over a weakly distributive and primative near ring. It is proved that a weakly distributive primitive near ring is a ring and the matrix near rings constructed over it is also a bag. (author). 14 refs

  3. Ring wormholes via duality rotations

    Directory of Open Access Journals (Sweden)

    Gary W. Gibbons

    2016-09-01

    Full Text Available We apply duality rotations and complex transformations to the Schwarzschild metric to obtain wormhole geometries with two asymptotically flat regions connected by a throat. In the simplest case these are the well-known wormholes supported by phantom scalar field. Further duality rotations remove the scalar field to yield less well known vacuum metrics of the oblate Zipoy–Voorhees–Weyl class, which describe ring wormholes. The ring encircles the wormhole throat and can have any radius, whereas its tension is always negative and should be less than −c4/4G. If the tension reaches the maximal value, the geometry becomes exactly flat, but the topology remains non-trivial and corresponds to two copies of Minkowski space glued together along the disk encircled by the ring. The geodesics are straight lines, and those which traverse the ring get to the other universe. The ring therefore literally produces a hole in space. Such wormholes could perhaps be created by negative energies concentrated in toroidal volumes, for example by vacuum fluctuations.

  4. HYPERAUTOFLUORESCENT RING IN AUTOIMMUNE RETINOPATHY

    Science.gov (United States)

    LIMA, LUIZ H.; GREENBERG, JONATHAN P.; GREENSTEIN, VIVIENNE C.; SMITH, R. THEODORE; SALLUM, JULIANA M. F.; THIRKILL, CHARLES; YANNUZZI, LAWRENCE A.; TSANG, STEPHEN H.

    2015-01-01

    Purpose To report the presence of a hyperautofluorescent ring and corresponding spectral-domain optical coherence tomography (SD-OCT) features seen in patients with autoimmune retinopathy. Methods All eyes were evaluated by funduscopic examination, full-fleld electroretinography, fundus autofluorescence, and SD-OCT. Further confirmation of the diagnosis was obtained with immunoblot and immunohistochemistry testing of the patient’s serum. Humphrey visual fields and microperimetry were also performed. Results Funduscopic examination showed atrophic retinal pigment epithelium (RPE) associated with retinal artery narrowing but without pigment deposits. The scotopic and photopic full-field electroretinograms were nondetectable in three patients and showed a cone–rod pattern of dysfunction in one patient. Fundus autofluorescence revealed a hyperautofluorescent ring in the parafoveal region, and the corresponding SD-OCT demonstrated loss of the photoreceptor inner segment–outer segment junction with thinning of the outer nuclear layer from the region of the hyperautofluorescent ring toward the retinal periphery. The retinal layers were generally intact within the hyperautofluorescent ring, although the inner segment–outer segment junction was disrupted, and the outer nuclear layer and photoreceptor outer segment layer were thinned. Conclusion This case series revealed the structure of the hyperautofluorescent ring in autoimmune retinopathy using SD-OCT. Fundus autofluorescence and SD-OCT may aid in the diagnosis of autoimmune retinopathy and may serve as a tool to monitor its progression. PMID:22218149

  5. A correlation for safety valve blowdown and ring settings

    International Nuclear Information System (INIS)

    Singh, A.; Shak, D.

    1982-01-01

    The blowdown of a spring loaded safety valve is defined as the difference between the pressure at which the valve opens and the pressure at which the valve fully closes under certain fluid flow conditions. Generally, the blowdown is expressed in terms of percentage of the opening pressure. An extensive series of tests carried out in the EPRI/PWR Utilities Valve Test Program has shown that the blowdown of safety valves can in general be strongly dependent upon the valve geometry and other parameters such as ring adjustments, spring stiffness, backpressure etc. In the present study, correlations have been developed using the EPRI safety valve test data to predict the expected blowdown as a function of adjustment ring settings for geometrically similar valves under steam discharge conditions. The correlation is validated against two different size Dresser valves

  6. Superconducting analogs of quantum optical phenomena: Macroscopic quantum superpositions and squeezing in a superconducting quantum-interference device ring

    International Nuclear Information System (INIS)

    Everitt, M.J.; Clark, T.D.; Stiffell, P.B.; Prance, R.J.; Prance, H.; Vourdas, A.; Ralph, J.F.

    2004-01-01

    In this paper we explore the quantum behavior of a superconducting quantum-interference device (SQUID) ring which has a significant Josephson coupling energy. We show that the eigenfunctions of the Hamiltonian for the ring can be used to create macroscopic quantum superposition states of the ring. We also show that the ring potential may be utilized to squeeze coherent states. With the SQUID ring as a strong contender as a device for manipulating quantum information, such properties may be of great utility in the future. However, as with all candidate systems for quantum technologies, decoherence is a fundamental problem. In this paper we apply an open systems approach to model the effect of coupling a quantum-mechanical SQUID ring to a thermal bath. We use this model to demonstrate the manner in which decoherence affects the quantum states of the ring

  7. Golden half ring sign for identification of pseudophacocele

    Directory of Open Access Journals (Sweden)

    Shivcharan Lal Chandravanshi

    2015-01-01

    Full Text Available Dislocation of intraocular lens (IOL is a serious complication of blunt ocular trauma in pseudophakic eyes. Here, a 72-year-old male patient with subconjunctival dislocation of an IOL (pseudophacocele secondary to bull horn injury was reported. In this case report, a new sign named as "golden half ring sign" was described for easy identification and localization of subconjunctival dislocation of IOL in patient with open globe injury (surgical wound dehiscence associated dense subconjunctival hemorrhage.

  8. A proposal of an open PET geometry

    Energy Technology Data Exchange (ETDEWEB)

    Yamaya, Taiga [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan); Inaniwa, Taku [Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan); Minohara, Shinichi [Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan); Yoshida, Eiji [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan); Inadama, Naoko [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan); Nishikido, Fumihiko [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan); Shibuya, Kengo [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan); Lam, Chih Fung [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan); Murayama, Hideo [Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan)

    2008-02-07

    The long patient port of a PET scanner tends to put stress on patients, especially patients with claustrophobia. It also prevents doctors and technicians from taking care of patients during scanning. In this paper, we proposed an 'open PET' geometry, which consists of two axially separated detector rings. A long and continuous field-of-view (FOV) including a 360 deg. opened gap between two detector rings can be imaged enabling a fully 3D image reconstruction of all the possible lines-of-response. The open PET will become practical if iterative image reconstruction methods are applied even though image reconstruction of the open PET is analytically an incomplete problem. First we implemented a 'masked' 3D ordered subset expectation maximization (OS-EM) in which the system matrix was obtained from a long 'gapless' scanner by applying a mask to detectors corresponding to the open space. Next, in order to evaluate imaging performance of the proposed open PET geometry, we simulated a dual HR+ scanner (ring diameter of D = 827 mm, axial length of W = 154 mm x 2) separated by a variable gap. The gap W was the maximum limit to have axially continuous FOV of 3W though the maximum diameter of FOV at the central slice was limited to D/2. Artifacts, observed on both sides of the open space when the gap exceeded W, were effectively reduced by inserting detectors partially into unnecessary open spaces. We also tested the open PET geometry using experimental data obtained by the jPET-D4. The jPET-D4 is a prototype brain scanner, which has 5 rings of 24 detector blocks. We simulated the open jPET-D4 with a gap of 66 mm by eliminating 1 block-ring from experimental data. Although some artifacts were seen at both ends of the opened gap, very similar images were obtained with and without the gap. The proposed open PET geometry is expected to lead to realization of in-beam PET, which is a method for an in situ monitoring of charged particle therapy, by

  9. CMB lensing and giant rings

    Energy Technology Data Exchange (ETDEWEB)

    Rathaus, Ben; Itzhaki, Nissan, E-mail: nitzhaki@post.tau.ac.il, E-mail: ben.rathaus@gmail.com [Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv, 69978 (Israel)

    2012-05-01

    We study the CMB lensing signature of a pre-inationary particle (PIP), assuming it is responsible for the giant rings anomaly that was found recently in the WMAP data. Simulating Planck-like data we find that generically the CMB lensing signal to noise ratio associated with such a PIP is quite small and it would be difficult to cross correlate the temperature giant rings with the CMB lensing signal. However, if the pre-inationary particle is also responsible for the bulk flow measured from the local large scale structure, which happens to point roughly at the same direction as the giant rings, then the CMB lensing signal to noise ratio is fairly significant.

  10. Proton storage ring summer workshop

    International Nuclear Information System (INIS)

    Lawrence, G.P.; Cooper, R.K.

    1977-10-01

    During the week of August 16, 1976 a Workshop was held at the Los Alamos Scientific Laboratory (LASL) on the Proton Storage Ring (PSR) for the Weapons Neutron Research Facility (WNRF). Written contributions were solicited from each of the participants in the Workshop, and the contributions that were received are presented. The papers do not represent polished or necessarily complete work, but rather represent ''first cuts'' at their respective areas. Topics covered include: (1) background information on the storage ring; (2) WNRF design; (3) rf transient during filling; (4) rf capture; (5) beam bunch compression; (6) transverse space charge limits; (7) transverse resistive instability in the PSR; (8) longitudinal resistive instability; (9) synchrotron frequency splitting; (10) E Quintus Unum--off resonance; (11) first harmonic bunching in the storage ring; (12) kicker considerations; (13) beam extraction; (14) ferrite kicker magnets; and (15) E Quintus Unum: a possible ejection scheme

  11. New Main Ring control system

    International Nuclear Information System (INIS)

    Seino, K.; Anderson, L.; Ducar, R.; Franck, A.; Gomilar, J.; Hendricks, B.; Smedinghoff, J.

    1990-03-01

    The Fermilab Main Ring control system has been operational for over sixteen years. Aging and obsolescence of the equipment make the maintenance difficult. Since the advent of the Tevatron, considerable upgrades have been made to the controls of all the Fermilab accelerators except the Main Ring. Modernization of the equipment and standardization of the hardware and software have thus become inevitable. The Tevatron CAMAC serial system has been chosen as a basic foundation in order to make the Main Ring control system compatible with the rest of the accelerator complex. New hardware pieces including intelligent CAMAC modules have been designed to satisfy unique requirements. Fiber optic cable and repeaters have been installed in order to accommodate new channel requirements onto the already saturated communication medium system. 8 refs., 2 figs

  12. Tree rings and radiocarbon calibration

    International Nuclear Information System (INIS)

    Barbetti, M.

    1999-01-01

    Only a few kinds of trees in Australia and Southeast Asia are known to have growth rings that are both distinct and annual. Those that do are therefore extremely important to climatic and isotope studies. In western Tasmania, extensive work with Huon pine (Lagarostrobos franklinii) has shown that many living trees are more than 1,000 years old, and that their ring widths are sensitive to temperature, rainfall and cloud cover (Buckley et al. 1997). At the Stanley River there is a forest of living (and recently felled) trees which we have sampled and measured. There are also thousands of subfossil Huon pine logs, buried at depths less than 5 metres in an area of floodplain extending over a distance of more than a kilometre with a width of tens of metres. Some of these logs have been buried for 50,000 years or more, but most of them belong to the period between 15,000 years and the present. In previous expeditions in the 1980s and 1990s, we excavated and sampled about 350 logs (Barbetti et al. 1995; Nanson et al. 1995). By measuring the ring-width patterns, and matching them between logs and living trees, we have constructed a tree-ring dated chronology from 571 BC to AD 1992. We have also built a 4254-ring floating chronology (placed by radiocarbon at ca. 3580 to 7830 years ago), and an earlier 1268-ring chronology (ca. 7,580 to 8,850 years ago). There are many individuals, or pairs of logs which match and together span several centuries, at 9,000 years ago and beyond

  13. Adiabatic compression of ion rings

    International Nuclear Information System (INIS)

    Larrabee, D.A.; Lovelace, R.V.

    1982-01-01

    A study has been made of the compression of collisionless ion rings in an increasing external magnetic field, B/sub e/ = zB/sub e/(t), by numerically implementing a previously developed kinetic theory of ring compression. The theory is general in that there is no limitation on the ring geometry or the compression ratio, lambdaequivalentB/sub e/ (final)/B/sub e/ (initial)> or =1. However, the motion of a single particle in an equilibrium is assumed to be completely characterized by its energy H and canonical angular momentum P/sub theta/ with the absence of a third constant of the motion. The present computational work assumes that plasma currents are negligible, as is appropriate for a low-temperature collisional plasma. For a variety of initial ring geometries and initial distribution functions (having a single value of P/sub theta/), it is found that the parameters for ''fat'', small aspect ratio rings follow general scaling laws over a large range of compression ratios, 1 3 : The ring radius varies as lambda/sup -1/2/; the average single particle energy as lambda/sup 0.72/; the root mean square energy spread as lambda/sup 1.1/; and the total current as lambda/sup 0.79/. The field reversal parameter is found to saturate at values typically between 2 and 3. For large compression ratios the current density is found to ''hollow out''. This hollowing tends to improve the interchange stability of an embedded low β plasma. The implications of these scaling laws for fusion reactor systems are discussed

  14. Superconducting proton ring for PETRA

    International Nuclear Information System (INIS)

    Baynham, E.

    1979-01-01

    A powerful new facility for colliding beam physics could be provided by adding a proton storage ring in the range of several hundred GeV to the electron-positron storage ring PETRA at DESY. This can be achieved in an economic way utilizing the PETRA tunnel and taking advantage of the higher magnetic fields of superconducting magnets which would be placed above or below the PETRA magnets. A central field of 4 Tesla in the bending magnets corresponds to a proton energy of 225 GeV. (orig.)

  15. The Cryogenic Storage Ring CSR

    OpenAIRE

    von Hahn, Robert; Becker, Arno; Berg, Felix; Blaum, Klaus; Breitenfeldt, Christian; Fadil, Hisham; Fellenberger, Florian; Froese, Michael; George, Sebastian; Göck, Jürgen; Grieser, Manfred; Grussie, Florian; Guerin, Elisabeth A.; Heber, Oded; Herwig, Philipp

    2016-01-01

    An electrostatic cryogenic storage ring, CSR, for beams of anions and cations with up to 300 keV kinetic energy per unit charge has been designed, constructed, and put into operation. With a circumference of 35 m, the ion-beam vacuum chambers and all beam optics are in a cryostat and cooled by a closed-cycle liquid helium system. At temperatures as low as (5.5 ± 1) K inside the ring, storage time constants of several minutes up to almost an hour were observed for atomic and molecular, anion a...

  16. Supersymmetric rings in field theory

    International Nuclear Information System (INIS)

    Blanco-Pillado, Jose J.; Redi, Michele

    2006-01-01

    We study the dynamics of BPS string-like objects obtained by lifting monopole and dyon solutions of N = 2 Super-Yang-Mills theory to five dimensions. We present exact traveling wave solutions which preserve half of the supersymmetries. Upon compactification this leads to macroscopic BPS rings in four dimensions in field theory. Due to the fact that the strings effectively move in six dimensions the same procedure can also be used to obtain rings in five dimensions by using the hidden dimension

  17. Damping ring designs and issues

    International Nuclear Information System (INIS)

    Wolski, Andrzej; Decking, Winfried

    2003-01-01

    The luminosity performance of a future linear collider (LC) will depend critically on the performance of the damping rings. The design luminosities of the current LC proposals require rings with very short damping times, large acceptance, low equilibrium emittance and high beam intensity. We discuss the design strategies for lattices achieving the goals of dynamical stability, examine the challenges for alignment and coupling correction, and consider a variety of collective effects that threaten to limit beam quality. We put the design goals in context by referring to the experience of operating facilities, and outline the further research and development that is needed

  18. Uranium nucleophilic carbene complexes

    International Nuclear Information System (INIS)

    Tourneux, Jean-Christophe

    2012-01-01

    The only stable f-metal carbene complexes (excluding NHC) metals f present R 2 C 2- groups having one or two phosphorus atoms in the central carbon in alpha position. The objective of this work was to develop the chemistry of carbenes for uranium (metal 5f) with the di-anion C{Ph 2 P(=S)} 2 2- (SCS 2- ) to extend the organometallic chemistry of this element in its various oxidation states (+3-+6), and to reveal the influence of the 5f orbitals on the nature and reactivity of the double bond C=U. We first isolated the reactants M(SCHS) (M = Li and K) and demonstrated the role of the cation M + on the evolution of the di-anion M 2 SCS (M = Li, K, Tl) which is transformed into LiSCHS in THF or into product of intramolecular cyclization K 2 [C(PhPS) 2 (C 6 H 4 )]. We have developed the necessary conditions mono-, bis- and tris-carbene directly from the di-anion SCS 2- and UCl 4 , as the precursor used in uranium chemistry. The protonolysis reactions of amides compounds (U-NEt 2 ) by the neutral ligand SCH 2 S were also studied. The compounds [Li(THF)] 2 [U(SCS)Cl 3 ] and [U(SCS)Cl 2 (THF) 2 ] were then used to prepare a variety of cyclopentadienyl and mono-cyclo-octa-tetra-enyliques uranium(IV) carbene compounds of the DFT analysis of compounds [M(SCS)Cl 2 (py) 2 ] and [M(Cp) 2 (SCS)] (M = U, Zr) reveals the strong polarization of the M=C double bond, provides information on the nature of the σ and π interactions in this binding, and shows the important role of f orbitals. The influence of ancillary ligands on the M=C bond is revealed by examining the effects of replacing Cl - ligands and pyridine by C 5 H 5 - groups. Mulliken and NBO analyzes show that U=C bond, unlike the Zr=C bond, is not affected by the change in environment of the metal center. While the oxidation tests of carbene complexes of U(IV) were disappointing, the first carbene complex of uranium (VI), [UO 2 (SCS)(THF) 2 ], was isolated with the uranyl ion UO 2 2+ . The reactions of compounds UO 2 X 2 (X = I, OTf) with anions SCS 2- and SCHS - provide the first notable developments in the organometallic chemistry of the uranyl ion. DFT studies show the essentially ionic binding U(VI)-R and U(VI)=C and the small contribution of 5f orbitals covalently. (author) [fr

  19. Open Bibliography

    OpenAIRE

    Murray-Rust, Peter; Pollock, Rufus; MacGillivray, Mark; O'Steen, Ben; Waites, William

    2011-01-01

    Poster presented at the VSMF Symposium held at the Unilever Centre on 2011-01-17. More research is published currently than can be understood or followed by a researcher without the aid of a computer. We need Open shareable information on research publications, an Open Bibliography, to build the services that enable researchers to explore their field and discover the research they need. Producers of bibliographic data such as libraries, publishers, universities, scholars or social referenc...

  20. Open IS

    DEFF Research Database (Denmark)

    Germonprez, Matt; Crowston, Kevin; Avital, Michel

    2013-01-01

    The collective intelligence and collective action of “open” communities have produced a variety of complex knowledge goods and radical social change. The Information Systems (IS) community has invested significant effort into researching open communities and the ecosystems in which they operate...... therefore seeks to stimulate a thoughtful and dynamic discussion around the proposition that becoming a more open community will enhance the IS discipline’s scholarly inquiry and global impact....

  1. Type II GaSb quantum ring solar cells under concentrated sunlight.

    Science.gov (United States)

    Tsai, Che-Pin; Hsu, Shun-Chieh; Lin, Shih-Yen; Chang, Ching-Wen; Tu, Li-Wei; Chen, Kun-Cheng; Lay, Tsong-Sheng; Lin, Chien-Chung

    2014-03-10

    A type II GaSb quantum ring solar cell is fabricated and measured under the concentrated sunlight. The external quantum efficiency confirms the extended absorption from the quantum rings at long wavelength coinciding with the photoluminescence results. The short-circuit current of the quantum ring devices is 5.1% to 9.9% more than the GaAs reference's under various concentrations. While the quantum ring solar cell does not exceed its GaAs counterpart in efficiency under one-sun, the recovery of the open-circuit voltages at higher concentration helps to reverse the situation. A slightly higher efficiency (10.31% vs. 10.29%) is reported for the quantum ring device against the GaAs one.

  2. Commissioning of the Cryogenic Plant for the Cryogenic Storage Ring (CSR) at Heidelberg

    CERN Document Server

    von Hahn, R; Grieser, M; Haberstroh, C; Kaiser, D; Lange, M; Laux, F; Menk, S; Orlov, D A; Repnow, R; Sieber, T; Quack, H; Varju, J; Wolf A

    2009-01-01

    At the Max-Planck-Institute for Nuclear Physics in Heidelberg a next generation electrostatic storage ring for low velocity atomic and molecular ion beams is under construction. In contrast to existing electrostatic storage rings, the Cryogenic Storage Ring CSR will be cooled down to temperatures below 2 K. Thus acting as a large cryopump it will provide long storage times and, in addition, open a new field of quantum state controlled molecular physics due to a low heat radiation background from space-like environment. A concept for cooling the storage ring has been developed and is presently tested by means of a linear trap as a prototype with a length of 1/10 of the planned ring. A commercial refrigerator with 21 W at 2 K has been successfully commissioned and was connected to the prototype. This paper presents the status of the cryogenic plant after the commissioning and one year of operation.

  3. Gallbladder removal - open

    Science.gov (United States)

    Cholecystectomy - open; Gallbladder - open cholecystectomy; Cholecystitis - open cholecystectomy; Gallstones - open cholecystectomy ... a medical instrument called a laparoscope ( laparoscopic ... Open gallbladder surgery is used when laparoscopic surgery cannot ...

  4. Examination techniques for non-magnetic rings

    International Nuclear Information System (INIS)

    Metala, M.J.; Kilpatrick, N.L.; Frank, W.W.

    1990-01-01

    Until the introduction of 18Mn18Cr rings a few years ago, most non-magnetic steel rings for generator rotors were made from 18Mn5Cr alloy steel, which is highly susceptible to stress corrosion cracking in the presence of water. This, the latest in a series of papers on the subject of non-magnetic rings by the authors' company, provides a discussion of nondestructive examination of 18Mn5Cr rings for stress corrosion distress. With rings on the rotor, fluorescent penetrant, ultrasonic and special visual techniques are applied. With rings off the rotor, the fluorescent penetrant technique is used, with and without stress enhancement

  5. Ring diagrams and phase transitions

    International Nuclear Information System (INIS)

    Takahashi, K.

    1986-01-01

    Ring diagrams at finite temperatures carry most infrared-singular parts among Feynman diagrams. Their effect to effective potentials are in general so significant that one must incorporate them as well as 1-loop diagrams. The author expresses these circumstances in some examples of supercooled phase transitions

  6. WR stars with ring nebulae

    International Nuclear Information System (INIS)

    Tutukov, A.

    1982-01-01

    It is shown that most of usually apparently single nitrogen WR stars with ring emission nebulae around them (WN + Neb) are a probable product of the evolution of a massive close binary with initial masses of components exceeding approximately 20 solar masses. (Auth.)

  7. Alignment for new Subaru ring

    International Nuclear Information System (INIS)

    Zhang, Ch.; Matsui, S.; Hashimoto, S.

    1999-01-01

    The New SUBARU is a synchrotron light source being constructed at the SPring-8 site. The main facility is a 1.5 GeV electron storage ring that provides light beam in the region from VUV to soft X-ray using SPring-8's 1 GeV linac as an injector. The ring, with a circumference of about 119 meters, is composed of six bending cells. Each bending cell has two normal dipoles of 34 degree and one inverse dipole of -8 degree. The ring has six straight sections: two very long straight sections for a 11-m long undulator and an optical klystron, four short straight sections for a 2.3-m undulator, a super-conducting wiggler, rf cavity and injection, etc. The magnets of the storage ring are composed of 12 dipoles (BMs), 6 invert dipoles (BIs), 56 quadrupoles and 44 sextupoles, etc. For the magnet alignment, positions of the dipoles (the BMs and BIs) are determined by network survey method. The multipoles, which are mounted on girders between the dipoles, are aligned with a laser-CCD camera system. This article presents the methodology used to position the different components and particularly to assure the precise alignment of the multipoles. (authors)

  8. Characteristic of Rings. Prime Fields

    Directory of Open Access Journals (Sweden)

    Schwarzweller Christoph

    2015-12-01

    Full Text Available The notion of the characteristic of rings and its basic properties are formalized [14], [39], [20]. Classification of prime fields in terms of isomorphisms with appropriate fields (ℚ or ℤ/p are presented. To facilitate reasonings within the field of rational numbers, values of numerators and denominators of basic operations over rationals are computed.

  9. Ring laser frequency biasing mechanism

    International Nuclear Information System (INIS)

    McClure, R.E.

    1975-01-01

    A ring laser cavity including a magnetically saturable member for differentially phase shifting the contradirectional waves propagating in the laser cavity, the phase shift being produced by the magneto-optic interaction occurring between the light waves and the magnetization in the cavity forming component as the light waves are reflected therefrom is described

  10. Counting problems for number rings

    NARCIS (Netherlands)

    Brakenhoff, Johannes Franciscus

    2009-01-01

    In this thesis we look at three counting problems connected to orders in number fields. First we study the probability that for a random polynomial f in Z[X] the ring Z[X]/f is the maximal order in Q[X]/f. Connected to this is the probability that a random polynomial has a squarefree

  11. Progressiv læring

    DEFF Research Database (Denmark)

    Wahlgren, Bjarne

    2017-01-01

    SAMMENFATNING I denne evalueringsrapport præsenterer Nationalt Center for Kompetenceudvikling ved Aarhus Universitet (herefter NCK) og Rambøll Management Consulting (herefter Rambøll) den værktøjsspecifikke evaluering af Progressiv Læring som pædagogisk værktøj for de ni implementeringsskoler i s...

  12. Wands of the Black Ring

    Czech Academy of Sciences Publication Activity Database

    Pravda, Vojtěch; Pravdová, Alena

    2005-01-01

    Roč. 37, č. 7 (2005), s. 1277-1287 ISSN 0001-7701 R&D Projects: GA ČR GP202/03/P017; GA AV ČR KJB1019403 Institutional research plan: CEZ:AV0Z10190503 Keywords : algebraic classification * Petrov classification * black ring Subject RIV: BA - General Mathematics Impact factor: 1.550, year: 2005

  13. Substitution of matrices over rings

    NARCIS (Netherlands)

    Hautus, M.L.J.

    1995-01-01

    For a given commutative ring with an identity element, we define and study the substitution of a matrix with entries in into a matrix polynomial or rational function over . A Bezout-type remainder theorem and a "partial-substitution rule" are derived and used to obtain a number of results. The

  14. Exercises in modules and rings

    CERN Document Server

    Lam, TY

    2009-01-01

    This volume offers a compendium of exercises of varying degree of difficulty in the theory of modules and rings. All exercises are solved in full detail. Each section begins with an introduction giving the general background and the theoretical basis for the problems that follow.

  15. On commutativity theorems for rings

    Directory of Open Access Journals (Sweden)

    H. A. S. Abujabal

    1990-01-01

    Full Text Available Let R be an associative ring with unity. It is proved that if R satisfies the polynomial identity [xny−ymxn,x]=0(m>1,n≥1, then R is commutative. Two or more related results are also obtained.

  16. One-pot regioselective synthesis of nitrophenyloxazolinyl styrene oxides by the Darzens reaction of vicarious nucleophilic substitution-formed carbanions of 2-dichloromethyl-4,4-dimethyloxazoline.

    Science.gov (United States)

    Florio, Saverio; Lorusso, Patrizia; Granito, Catia; Luisi, Renzo; Troisi, Luigino

    2004-07-23

    The vicarious nucleophilic substitution reaction of dichloromethyloxazoline 2 with nitrobenzene has been investigated. Treatment of 2 with t-BuOK followed by the addition of nitrobenzene leads to benzylic carbanions 4 or 9 depending upon the solvent used (DMSO, DMF, or THF). Subsequent treatment of 4 or 9 with aldehydes, in a Darzens-like reaction, furnishes very good yields of nitrophenyl oxazolinyloxiranes 8 and 11. 1,2-Dioxazolinyl-1,2-dinitrophenylethene 7 forms quantitatively when carbanion 4 is allowed to warm to room temperature in the absence of external electrophiles.

  17. Dynamics of the NbCl5-catalyzed cycloaddition of propylene oxide and CO2: Assessing the dual role of the nucleophilic co-catalysts

    KAUST Repository

    D'Elia, Valerio

    2014-07-23

    A mechanistic study on the synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO) catalyzed by NbCl5 and organic nucleophiles such as 4-dimethylaminopyridine (DMAP) or tetra-n-butylammonium bromide (NBu4Br) is reported. A combination of in situ spectroscopic techniques and kinetic studies has been used to provide detailed insight into the reaction mechanism, the formation of intermediates, and interactions between the reaction partners. The results of DFT calculations support the experimental observations and allow us to propose a mechanism for this reaction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Use of fluorine-18 free of carrier for the synthesis of 2-[18 F]-fluoro-2-deoxy-d-glucose by nucleophilic substitution

    International Nuclear Information System (INIS)

    Garcia S, I.; Ramirez, F.M.

    1990-11-01

    Preliminary studies on the synthesis of 2 - [ 18 F]-fluoro-2-deoxy-d-glucose (2 - [ 18 F]-FDG) were carried out by means of the nucleophilic method proposed by K. Hamacher and the 18 F obtained in the Nuclear Reactor TRIGA Mark III of the Nuclear Center of Mexico. For the control of radiochemical quality it was used the chromatography technique in paper and silica gel with 4 solvent systems. The identification of the marked species with 18 F was carried out by means of comparison of its Rf with the Rf of the obtained not radioactive species, using the same synthesis method. (Author)

  19. A Stereoselective [3+1] Ring Expansion for the Synthesis of Highly Substituted Methylene Azetidines.

    Science.gov (United States)

    Schmid, Steven C; Guzei, Ilia A; Schomaker, Jennifer M

    2017-09-25

    The reaction of rhodium-bound carbenes with strained bicyclic methylene aziridines results in a formal [3+1] ring expansion to yield highly substituted methylene azetidines with excellent regio- and stereoselectivity. The reaction appears to proceed through an ylide-type mechanism, where the unique strain and structure of the methylene aziridine promotes a ring-opening/ring-closing cascade that efficiently transfers chirality from substrate to product. The resultant products can be elaborated into new azetidine scaffolds containing vicinal tertiary-quaternary and even quaternary-quaternary stereocenters. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Open access

    CERN Document Server

    Suber, Peter

    2012-01-01

    The Internet lets us share perfect copies of our work with a worldwide audience at virtually no cost. We take advantage of this revolutionary opportunity when we make our work "open access": digital, online, free of charge, and free of most copyright and licensing restrictions. Open access is made possible by the Internet and copyright-holder consent, and many authors, musicians, filmmakers, and other creators who depend on royalties are understandably unwilling to give their consent. But for 350 years, scholars have written peer-reviewed journal articles for impact, not for money, and are free to consent to open access without losing revenue. In this concise introduction, Peter Suber tells us what open access is and isn't, how it benefits authors and readers of research, how we pay for it, how it avoids copyright problems, how it has moved from the periphery to the mainstream, and what its future may hold. Distilling a decade of Suber's influential writing and thinking about open access, this is the indispe...

  1. 21 CFR 870.3800 - Annuloplasty ring.

    Science.gov (United States)

    2010-04-01

    ...) Identification. An annuloplasty ring is a rigid or flexible ring implanted around the mitral or tricuspid heart valve for reconstructive treatment of valvular insufficiency. (b) Classification. Class II (special...

  2. International Tree Ring Data Bank (ITRDB)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Tree ring data from the International Tree Ring Data Bank and World Data Center for Paleoclimatology archives. Data include raw treering measurements (most are...

  3. Planetary ring systems properties, structures, and evolution

    CERN Document Server

    Murray, Carl D

    2018-01-01

    Planetary rings are among the most intriguing structures of our solar system and have fascinated generations of astronomers. Collating emerging knowledge in the field, this volume reviews our current understanding of ring systems with reference to the rings of Saturn, Uranus, Neptune, and more. Written by leading experts, the history of ring research and the basics of ring–particle orbits is followed by a review of the known planetary ring systems. All aspects of ring system science are described in detail, including specific dynamical processes, types of structures, thermal properties and their origins, and investigations using computer simulations and laboratory experiments. The concluding chapters discuss the prospects of future missions to planetary rings, the ways in which ring science informs and is informed by the study of other astrophysical disks, and a perspective on the field's future. Researchers of all levels will benefit from this thorough and engaging presentation.

  4. Vortex rings in classical and quantum systems

    International Nuclear Information System (INIS)

    Barenghi, C F; Donnelly, R J

    2009-01-01

    The study of vortex rings has been pursued for decades and is a particularly difficult subject. However, the discovery of quantized vortex rings in superfluid helium has greatly increased interest in vortex rings with very thin cores. While rapid progress has been made in the simulation of quantized vortex rings, there has not been comparable progress in laboratory studies of vortex rings in a viscous fluid such as water. This article overviews the history and current frontiers of classical and quantum vortex rings. After introducing the classical results, this review discusses thin-cored vortex rings in superfluid helium in section 2, and recent progress in understanding vortex rings of very thin cores propagating in water in section 3. (invited paper)

  5. Mathematical simulation of bearing ring grinding process

    Science.gov (United States)

    Koltunov, I. I.; Gorbunova, T. N.; Tumanova, M. B.

    2018-03-01

    The paper suggests the method of forming a solid finite element model of the bearing ring. Implementation of the model allowed one to evaluate the influence of the inner cylindrical surface grinding scheme on the ring shape error.

  6. Dynamics of long ring Raman fiber laser

    Science.gov (United States)

    Sukhanov, Sergey V.; Melnikov, Leonid A.; Mazhirina, Yulia A.

    2016-04-01

    The numerical model for dynamics of long fiber ring Raman laser is proposed. The model is based on the transport equations and Courant-Isaacson-Rees numerical method. Different regimes of a long ring fiber Raman laser are investigated.

  7. Genetics Home Reference: ring chromosome 20 syndrome

    Science.gov (United States)

    ... drugs. Prolonged seizure episodes known as non-convulsive status epilepticus also appear to be characteristic of ring chromosome ... K, Takahashi Y. Ring chromosome 20 and nonconvulsive status epilepticus. A new epileptic syndrome. Brain. 1997 Jun;120 ( ...

  8. Open innovation

    DEFF Research Database (Denmark)

    West, Joel; Bogers, Marcel

    2017-01-01

    Interest in open innovation (OI) as a field of research has grown exponentially since the phrase was coined by Chesbrough in his 2003 book, with numerous articles, special issues, books, and conference sessions. Various reviews of the literature have summarized prior work, offered new frameworks......, and identified opportunities for future research. Here we summarize these opportunities, which include more research on outbound OI, the role of open innovation in services, and network forms of collaboration such as consortia, communities, ecosystems, and platforms. Research should also examine the use of OI...... by small, new, and not-for-profit organizations, as well as the linkage of individual actions and motivations to open innovation. Other opportunities include better measuring the costs, benefits, antecedents, mediators and moderators of the effects of OI on performance, and understanding why and how OI...

  9. The Hi-Ring DCN Architecture

    DEFF Research Database (Denmark)

    Galili, Michael; Kamchevska, Valerija; Ding, Yunhong

    2016-01-01

    We will review recent work on the proposed hierarchical ring-based architecture (HiRing) proposed for data center networks. We will discuss the architecture and initial demonstrations of optical switching performance and time-domain synchronization......We will review recent work on the proposed hierarchical ring-based architecture (HiRing) proposed for data center networks. We will discuss the architecture and initial demonstrations of optical switching performance and time-domain synchronization...

  10. Nonlinear analysis of ring oscillator circuits

    KAUST Repository

    Ge, Xiaoqing

    2010-06-01

    Using nonlinear systems techniques, we analyze the stability properties and synchronization conditions for ring oscillator circuits, which are essential building blocks in digital systems. By making use of its cyclic structure, we investigate local and global stability properties of an n-stage ring oscillator. We present a sufficient condition for global asymptotic stability of the origin and obtain necessity if the ring oscillator consists of identical inverter elements. We then give a synchronization condition for identical interconnected ring oscillators.

  11. On P-coherent endomorphism rings

    Indian Academy of Sciences (India)

    A ring is called right -coherent if every principal right ideal is finitely presented. Let M R be a right -module. We study the -coherence of the endomorphism ring of M R . It is shown that is a right -coherent ring if and only if every endomorphism of M R has a pseudokernel in add M R ; S is a left -coherent ring if and ...

  12. Nonlinear analysis of ring oscillator circuits

    KAUST Repository

    Ge, Xiaoqing; Arcak, Murat; Salama, Khaled N.

    2010-01-01

    Using nonlinear systems techniques, we analyze the stability properties and synchronization conditions for ring oscillator circuits, which are essential building blocks in digital systems. By making use of its cyclic structure, we investigate local and global stability properties of an n-stage ring oscillator. We present a sufficient condition for global asymptotic stability of the origin and obtain necessity if the ring oscillator consists of identical inverter elements. We then give a synchronization condition for identical interconnected ring oscillators.

  13. On the compressor ring for the JAERI neutron science project

    Energy Technology Data Exchange (ETDEWEB)

    Yamane, Isao [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan)

    1997-11-01

    (1), As long as a 1.5 GeV-8 MW linear accelerator is constructed in the JAERI neutron science center, it is quite reasonable to construct a 5 MW compressor ring as a driver of a high intensity spallation neutron source to generate pulsed neutron beams. (2), Suppression of beam loss around the compressor ring to an acceptable level is the most crucial subject to be coped with in designing a MW-class compressor ring. This subject should be successfully cleared by carefully studying and designing the overall system of accelerator and tunnel. (3), The `PSR instability` was comprehensively discussed in the NSNS workshop held at Santa Fe in March, 1997, as a remaining problem of a high intensity proton compressor ring. People of Los Alamos attributed it to an e-p instability. But some questions like the cause that makes some part of protons leak away from a beam bunch to a bunch gap are yet left open. (4), A new scheme of two step H{sup 0} injection is proposed to remove defects of the conventional one of Los Alamos PSR. (author)

  14. Hydrolyses of 2- and 4-fluoro N-heterocycles. 3. Nucleophilic catalysis by buffer bases in the general acid catalyzed hydrolysis of 4-fluoroquinaldine

    International Nuclear Information System (INIS)

    Muscio, O.J. Jr.; Theobald, P.G.; Rutherford, D.R.

    1989-01-01

    Pseudo-first-order rate constants and catalytic rate constants are reported for the buffer-catalyzed hydrolysis of 4-fluoroquinaldine (1) in carboxylic acid and phosphoric acid buffers. The buffer catalysis is consistent with specific acid, general base catalysis. Hydrolyses in 99% 18 O-labeled acetate, indicate that the predominant catalytic mode for the acetic acid/acetate buffer system is nucleophilic catalysis by the acetate anion coupled with specific acid catalysis. The other buffers presumably react in a similar manner. A Broensted-type plot of the catalytic rate constants for hydrolysis of protonated 1 has a slope of 0.57, with formate deviating positively from the line determined by acetate, chloroacetate, monohydrogen phosphate, and water. This Broensted slope is less than that found for hydrolysis of the 2-fluoro-1-methylpyridinium ion, 2, but is still within the range expected for aromatic nucleophilic substitution. Rate constants and 18 O-labeling results for hydrolysis in acetate buffer are also reported for 4-acetoxyquinaldine (3), the proposed intermediate in the acetate-catalyzed hydrolysis of 1. 15 references, 5 figures, 3 tables

  15. Beam dynamic issues in TESLA damping ring

    International Nuclear Information System (INIS)

    Shiltsev, V.

    1996-05-01

    In this paper we study general requirements on impedances of the linear collider TESLA damping ring design. Quantitative consideration is performed for 17-km long ''dog-bone'' ring. Beam dynamics in alternative options of 6.3 and 2.3-km long damping rings is briefly discussed. 5 refs., 2 tabs

  16. IAG ring test animal proteins 2014

    NARCIS (Netherlands)

    Raamsdonk, van L.W.D.; Pinckaers, V.G.Z.; Scholtens-Toma, I.M.J.; Prins, T.W.; Voet, van der H.; Vliege, J.J.M.

    2014-01-01

    A ring test was organized for the detection of animal proteins in animal feed by microscopy in the framework of the annual ring tests of the IAG – International Association for Feeding stuff Analysis, Section Feeding stuff Microscopy. The aim of the ring study was to provide the participants

  17. IAG ring test animal proteins 2015

    NARCIS (Netherlands)

    Raamsdonk, van L.W.D.; Rhee, van de N.E.; Scholtens-Toma, I.M.J.; Prins, T.W.; Vliege, J.J.M.; Pinckaers, V.G.Z.

    2015-01-01

    A ring test was organized for the detection of animal proteins in animal feed by microscopy in the framework of the annual ring tests of the IAG - International Association for Feeding stuff Analysis, Section Feeding stuff Microscopy. The organizer of the ring test was RIKILT - Wageningen UR, The

  18. IAG ring test animal proteins 2013

    NARCIS (Netherlands)

    Raamsdonk, van L.W.D.; Pinckaers, V.G.Z.; Scholtens-Toma, I.M.J.; Prins, T.W.; Vliege, J.J.M.

    2013-01-01

    A ring test was organized for the detection of animal proteins in animal feed by microscopy in the framework of the annual ring tests of the IAG - International Association for Feeding stuff Analysis, Section Feeding stuff Microscopy. The organizer of the the ring study was to provide the

  19. Self-gravitation in Saturn's rings

    International Nuclear Information System (INIS)

    Salo, H.; Lukkari, J.

    1982-01-01

    In a ring-shaped collisional system self-gravitation reduces the equilibrium values of the geometric and optical thickness. In Saturn's rings both effects are appreciable. The previously found discrepancy between the calculated profile and the observed profile of the rings is chiefly caused by the omission of self-gravitation. (Auth.)

  20. Open Education and the Open Science Economy

    Science.gov (United States)

    Peters, Michael A.

    2009-01-01

    Openness as a complex code word for a variety of digital trends and movements has emerged as an alternative mode of "social production" based on the growing and overlapping complexities of open source, open access, open archiving, open publishing, and open science. This paper argues that the openness movement with its reinforcing structure of…