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Sample records for cyclic enol ethers

  1. Cycloaddition of Arynes and Cyclic Enol Ethers as a Platform for Access to Stereochemically Defined 1,2-Disubstituted Benzocyclobutenes

    PubMed Central

    Yedulla, Vijayendar R.; Pradhan, Padmanava; Yang, Lijia; Lakshman, Mahesh K.

    2015-01-01

    Benzocyclobutenes (BCBs) are important entities in a multitude of areas, such as complex organic synthesis, materials and polymer chemistry, and electronics. Whereas reactions between arynes and ketene acetals have been well studied, reactions with cyclic enol ethers are unknown. A cis olefin geometry in cyclic enol ethers makes them well suited for formal [2 + 2] cycloaddition with arynes than for competing ene reactions, making them effective reactants. Reactions of 2,3-dihydrofuran, 2,3-dihydro-3H-pyran, 5-butyl-2,3-dihydrofuran, (S)-2-((benzyloxy)methyl)-2,3-dihydrofuran, and 1,4-dioxene with various arynes were successful. An advantage of the use of cyclic enol ethers is that despite the plausible intermediacy of zwitterionic intermediates, the products are limited to a cis ring junction. This can be exploited for potential access to stereochemically-defined 1,2-disubstituted BCBs. As a demonstration, ether ring cleavage with BBr3 provided trans-functionalized BCBs and displacement with azide then provided cis derivatives. DFT computations have been utilized to understand the structures of three arynes in relation to the cycloadditions and for a predictive evaluation of product ratios in two cases. A comparative evaluation of the HOMO energies of a related series of cyclic olefins has also been performed by DFT computations. PMID:27642260

  2. A combined DFT - NMR study of cyclic 1,2-diones and methyl ethers of their enols: The power and limitations of the method based on theoretical predictions of 13C NMR chemical shifts

    NASA Astrophysics Data System (ADS)

    Kubicki, Dominik; Gryff-Keller, Adam; Szczeciński, Przemysław

    2012-08-01

    A series of cyclic 1,2-diones and methyl ethers of their enols were investigated by a combined 13C NMR/computational DFT method to establish their preferred solution structures. The optimum molecular geometries and magnetic shielding constants of carbon nuclei were calculated with GIAO DFT [PBE1PBE/6-311++G(2d,p) PCM] method for the investigated molecules allowing for enolization and dynamic conformational equilibriums occurring in the solutions. These compounds served simultaneously as model compounds for testing the effectiveness and limitations of the exploited method of investigating molecular structures based on comparison of the theoretically calculated magnetic shielding constants and experimental 13C NMR chemical shifts. Generally, a very good agreement between experimental and theoretical data was obtained for the investigated group of compounds, which proved the applied level of theory and used methodology to be adequate and should ensure a high accuracy of the 13C NMR chemical shift predictions. Some divergences between the experiment and theory could be interpreted as the results of insufficiencies of the molecular modelling and the effects of neglecting vibrational/librational molecular motions. Furthermore, we report herein an observation of an unexpected 1H NMR spectral pattern for 2,3-dimethoxycyclodeca-1,3-diene (diether of cyclodecadione dienol), which was interpreted to be caused by the slow (in NMR time scale) enantiomerization of this molecule which preferentially assumes a chiral conformation.

  3. A silver-catalyzed spirocyclization of alkynyl silyl enol ethers.

    PubMed

    Schäfer, Christian; Miesch, Michel; Miesch, Laurence

    2012-06-25

    Ring out the old: The cycloisomerization of alkynyl silyl enol ethers proceeds at ambient temperature under the mild conditions of silver catalysis. Mono- or bicyclic spiro compounds can be obtained by 5-exo-dig reactions. Trapping the vinyl silver species with an iodide source, such as N-iodosuccinimide (NIS), afforded the alkenyl iodide derivatives.

  4. Diastereo- and enantioselective iridium-catalyzed allylation of cyclic ketone enolates: synergetic effect of ligands and barium enolates.

    PubMed

    Chen, Wenyong; Chen, Ming; Hartwig, John F

    2014-11-12

    We report asymmetric allylic alkylation of barium enolates of cyclic ketones catalyzed by a metallacyclic iridium complex containing a phosphoramidite ligand derived from (R)-1-(2-naphthyl)ethylamine. The reaction products contain adjacent quaternary and tertiary stereocenters. This process demonstrates that unstabilized cyclic ketone enolates can undergo diastereo- and enantioselective Ir-catalyzed allylic substitution reactions with the proper choice of enolate countercation. The products of these reactions can be conveniently transformed to various useful polycarbocyclic structures.

  5. Diastereo- and enantioselective iridium-catalyzed allylation of cyclic ketone enolates: Synergetic effect of ligands and barium enolates

    DOE PAGES

    Chen, Wenyong; Chen, Ming; Hartwig, John F.

    2014-10-22

    Here, we report asymmetric allylic alkylation of barium enolates of cyclic ketones catalyzed by a metallacyclic iridium complex containing a phosphoramidite ligand derived from (R)-1-(2-naphthyl)ethylamine. The reaction products contain adjacent quaternary and tertiary stereocenters. This process demonstrates that unstabilized cyclic ketone enolates can undergo diastereo- and enantioselective Ir-catalyzed allylic substitution reactions with the proper choice of enolate countercation. The products of these reactions can be conveniently transformed to various useful polycarbocyclic structures.

  6. Rhodium-Catalyzed Dehydrogenative Silylation of Acetophenone Derivatives: Formation of Silyl Enol Ethers versus Silyl Ethers.

    PubMed

    Garcés, Karin; Lalrempuia, Ralte; Polo, Víctor; Fernández-Alvarez, Francisco J; García-Orduña, Pilar; Lahoz, Fernando J; Pérez-Torrente, Jesús J; Oro, Luis A

    2016-10-04

    A series of rhodium-NSiN complexes (NSiN=bis (pyridine-2-yloxy)methylsilyl fac-coordinated) is reported, including the solid-state structures of [Rh(H)(Cl)(NSiN)(PCy3 )] (Cy=cyclohexane) and [Rh(H)(CF3 SO3 )(NSiN)(coe)] (coe=cis-cyclooctene). The [Rh(H)(CF3 SO3 )(NSiN)(coe)]-catalyzed reaction of acetophenone with silanes performed in an open system was studied. Interestingly, in most of the cases the formation of the corresponding silyl enol ether as major reaction product was observed. However, when the catalytic reactions were performed in closed systems, formation of the corresponding silyl ether was favored. Moreover, theoretical calculations on the reaction of [Rh(H)(CF3 SO3 )(NSiN)(coe)] with HSiMe3 and acetophenone showed that formation of the silyl enol ether is kinetically favored, while the silyl ether is the thermodynamic product. The dehydrogenative silylation entails heterolytic cleavage of the Si-H bond by a metal-ligand cooperative mechanism as the rate-determining step. Silyl transfer from a coordinated trimethylsilyltriflate molecule to the acetophenone followed by proton transfer from the activated acetophenone to the hydride ligand results in the formation of H2 and the corresponding silyl enol ether.

  7. Rhodium-Catalyzed Enantioselective Vinylogous Addition of Enol Ethers to Vinyldiazoacetates

    PubMed Central

    Smith, Austin G.; Davies, Huw M. L.

    2012-01-01

    A highly asymmetric vinylogous addition of acyclic silyl enol ethers to siloxyvinyldiazoacetate is described. The reaction features a diastereoselective 1,4-siloxy group migration event. Products are obtained in up to 97% ee. When more sterically crowded silyl enol ethers are employed, an enantioselective formal [3 + 2] cycloaddition becomes the dominant reaction pathway. Control experiments reveal the (Z)-olefin geometry to be critical for high levels of enantiocontrol. PMID:23098215

  8. Silyl Enol Ether Prins Cyclization: Diastereoselective Formation of Substituted Tetrahydropyran-4-ones

    PubMed Central

    2015-01-01

    A diastereoselective synthesis of cis-2,6-disubstituted tetrahydropyran-4-ones was developed. The key step of this methodology, a silyl enol ether Prins cyclization, was promoted by a condensation reaction between a hydroxy silyl enol ether and an aldehyde to afford substituted tetrahydropyran-4-ones. The cyclization was tolerant of many functional groups, and the modular synthesis of the hydroxy silyl enol ether allowed for the formation of more than 30 new tetrahydropyran-4-ones with up to 97% yield and >95:5 dr. The cyclization step forms new carbon–carbon and carbon–oxygen bonds, as well as a quaternary center with good diastereoselectivity. The method provides a versatile route for the synthesis of substituted tetrahydropyrans. PMID:25200563

  9. Pd-catalyzed arylation of silyl enol ethers of substituted alpha-fluoroketones.

    PubMed

    Guo, Yong; Twamley, Brendan; Shreeve, Jean'ne M

    2009-04-21

    Alpha-fluoro-alpha-aryl-ketones were synthesized by the Pd-catalyzed cross-coupling of aryl bromides with either alpha-fluoroketones or their corresponding silyl enol ethers. The direct arylation with an alpha-fluoroketone requires a strong base, such as potassium tert-butoxide, and under these conditions the presence of a base-sensitive functional group is not compatible. However, good functional tolerance was achieved when the anionic coupling moieties were generated from the silyl enol ethers obtained by reacting alpha-fluoroketones with tetrabutylammonium (tripheny1silyl)difluorosilicate (TBAT) as the fluoride source under nearly neutral conditions. The aryl halides with a carbmethoxy, nitro, cyano or carbonyl group were used. The reaction with nonfluorinated silyl enol ether 1h gave a cross-coupling product in low yield.

  10. Synthesis of 2-substituted 7-hydroxybenzofuran-4-carboxylates via addition of silyl enol ethers to o-benzoquinone esters.

    PubMed

    Jung, Michael E; Perez, Felix

    2009-05-21

    Mukaiyama Michael addition of silyl enol ethers 13 to the 1,2-quinone-4-carboxylate 6 (formed in situ by oxidation of the catechol ester 8) afforded the 2-subsituted 7-hydroxybenzofuran-4-carboxylates 14 in fair to good yields. Alkyl and aryl systems work well, but highly electron-rich silyl enol ethers could not be used because of competing oxidation.

  11. The O- Acylation of Ketone Enolates by Allyl 1H-imidazole-1-carboxylate Mediated with Boron Trifluoride Etherate---A Convenient Procedure for the Synthesis of Substituted Allyl Enol Carbonates

    PubMed Central

    Trost, Barry M.; Xu, Jiayi

    2008-01-01

    A convenient access to substituted allyl enol carbonates was established through the reaction of ketone enolates with the complex of allyl 1H-imidazole-1-carboxylates and boron trifluoride etherate. PMID:17963405

  12. Preparation of functionalized cyclic enol phosphates by halogen-magnesium exchange and directed deprotonation reactions.

    PubMed

    Piller, Fabian M; Bresser, Tomke; Fischer, Markus K R; Knochel, Paul

    2010-07-02

    Cyclic enol phosphates were magnesiated by a halogen/magnesium exchange reaction or deprotonation using TMP-derived magnesium amide bases. The resulting magnesium reagents react readily with a wide range of electrophiles like allyl bromides and acid chlorides or can be used in Pd-catalyzed cross-coupling reactions. Several optically pure enol phosphates were prepared starting from readily available d-(+)-camphor derivatives.

  13. Palladium Catalyzed Regiocontrolled α-Arylation of Trimethylsilyl Enol Ethers with Aryl Halides

    PubMed Central

    Iwama, Tetsuo

    2008-01-01

    Inter- and intramolecular arylations of trimethylsilyl enol ethers with aryl halides are accomplished regiospecifically in the presence of a palladium catalyst and tributyltin fluoride in refluxing benzene or toluene. The optimal catalyst system called for the use of Pd2(dba)3 and tri-tert-butylphosphine in ca. 1:2 ratio. Aryl iodides, bromides and chlorides are all effective arylation partners in this reaction. PMID:17134257

  14. Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers

    NASA Astrophysics Data System (ADS)

    Sadezky, A.; Chaimbault, P.; Mellouki, A.; Römpp, A.; Winterhalter, R.; Le Bras, G.; Moortgat, G. K.

    2006-10-01

    Formation of secondary organic aerosol has been observed in the gas phase ozonolysis of a series of enol ethers, among them several alkyl vinyl ethers (AVE, ROCH=CH2), such as ethyl, propyl, n-butyl, iso-butyl, t-butyl vinyl ether, and ethyl propenyl ether (EPE, C2H5OCH=CHCH3). The ozonolysis has been studied in a 570 l spherical glass reactor at ambient pressure (730 Torr) and room temperature (296 K). Gas phase reaction products were investigated by in-situ FTIR spectroscopy, and secondary organic aerosol (SOA) formation was monitored by a scanning mobility particle sizer (SMPS). The chemical composition of the formed SOA was analysed by a hybrid mass spectrometer using electrospray ionization (ESI). The main stable gas phase reaction product is the respective alkyl formate ROC(O)H, formed with yields of 60 to 80%, implying that similar yields of the corresponding excited Criegee Intermediates (CI) CH2O2 for the AVE and CH3CHO2 for EPE are generated. Measured SOA yields are between 2 to 4% for all enol ethers. Furthermore, SOA formation is strongly reduced or suppressed by the presence of an excess of formic acid, which acts as an efficient CI scavenger. Chemical analysis of the formed SOA by ESI(+)/MS-TOF allows to identify oligomeric compounds in the mass range 200 to 800 u as its major constituents. Repetitive chain units are identified as CH2O2 (mass 46) for the AVE and C2H4O2 (mass 60) for EPE and thus have the same chemical compositions as the respective major Criegee Intermediates formed during ozonolysis of these ethers. The oligomeric structure and chain unit identity are confirmed by HPLC/ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF experiments, whereby successive and systematic loss of a fragment with mass 46 for the AVE (and mass 60 for EPE) is observed. It is proposed that the oligomer has the following basic structure of an oligoperoxide, -[CH(R)-O-O]n-, where R=H for the AVE and R=CH3 for the EPE. Oligoperoxide formation is thus suggested to be another, so

  15. Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers

    NASA Astrophysics Data System (ADS)

    Sadezky, A.; Chaimbault, P.; Mellouki, A.; Römpp, A.; Winterhalter, R.; Le Bras, G.; Moortgat, G. K.

    2006-06-01

    Formation of secondary organic aerosol has been observed in the gas phase ozonolysis of a series of enol ethers, among them several alkyl vinyl ethers (AVE, ROCH=CH2), such as ethyl, propyl, n-butyl, iso-butyl, t-butyl vinyl ether, and ethyl propenyl ether (EPE, C2H5OCH=CHCH3). The ozonolysis has been studied in a 570 l spherical glass reactor at atmospheric pressure (730 Torr) and temperature (296 K). Gas phase reaction products were investigated by in-situ FTIR spectroscopy, and secondary organic aerosol (SOA) formation was monitored by a scanning mobility particle sizer (SMPS). The chemical composition of the formed SOA was analysed by a hybrid mass spectrometer using electrospray ionization (ESI). The main stable gas phase reaction product is the respective alkyl formate ROC(O)H, formed with yields of 60 to 80%, implying that similar yields of the corresponding Criegee Intermediates (CI) CH2O2 for the AVE and CH3CHO2 for EPE are generated. Measured SOA yields are between 2 to 4% for all enol ethers. Furthermore, SOA formation is strongly reduced or suppressed by the presence of an excess of formic acid, which acts as an efficient CI scavenger. Chemical analysis of the formed SOA by ESI(+)/MS-TOF allows to identify oligomeric compounds in the mass range 200 to 800 u as its major constituents. Repetitive chain units are identified as CH2O2 (mass 46) for the AVE and C2H4O2 (mass 60) for EPE and thus have the same chemical compositions as the respective major Criegee Intermediates formed during ozonolysis of these ethers. The oligomeric structure and chain unit identity are confirmed by HPLC/ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF experiments, whereby successive and systematic loss of a fragment with mass 46 for the AVE (and mass 60 for EPE) is observed. It is proposed that the oligomer has the following basic structure of an oligoperoxide, -[CH(R)-O-O]n-, where R=H for the AVE and R=CH3 for the EPE. Oligoperoxide formation is thus suggested to be another, so far

  16. Indium-mediated one-pot three-component reaction of aromatic amines, enol ethers, and allylic bromides.

    PubMed

    Jang, Taeg-Su; Ku, Il Whea; Jang, Min Seok; Keum, Gyochang; Kang, Soon Bang; Chung, Bong Young; Kim, Youseung

    2006-01-19

    [reaction: see text] A new and efficient indium-mediated one-pot three-component reaction for the synthesis of N-aryl-substituted homoallylamines from aromatic amines, enol ethers, and allylic bromides in THF at room temperature is described.

  17. Zirconium-mediated coupling reactions of amines and enol or allyl ethers: synthesis of allyl- and homoallylamines.

    PubMed

    Barluenga, José; Rodríguez, Félix; Alvarez-Rodrigo, Lucía; Zapico, José M; Fañanás, Francisco J

    2004-01-05

    An easy and efficient zirconium-mediated synthesis of allylamines from simple amines and enol ethers is described. This strategy also allows the synthesis of amino alcohol derivatives containing a Z double bond in their structure when 2,3-dihydrofuran is used. Simple conventional modification of these amino alcohols leads to 2-substituted piperidine derivatives. By applying this approach, a formal total synthesis of the alkaloid coniine is easily achieved from a protected butylamine. Finally, the zirconium-mediated reaction of amines and allyl phenyl ether furnishes homoallylamines or amino ethers depending on the structure of the starting amine.

  18. Syntheses and GABA uptake properties of 6-ether- and 6-enol ether-substituted nipecotic acids.

    PubMed

    N'Goka, Victor; Bissantz, Caterina; Bisel, Philippe; Stenbøl, Tine B; Krogsgaard-Larsen, Povl; Schlewer, Gilbert

    2004-07-01

    6-aralkylether- and 6-arylenol-ether-substituted nipecotic acids were synthesized. These analogues are poor GABA uptake inhibitors. The electronegative region concept developed in the N-substituted nipecotic acid series cannot be transferred on the side chain of this series of 6-substituted analogues.

  19. Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

    PubMed Central

    Tarabová, Denisa; Šoralová, Stanislava; Breza, Martin; Fronc, Marek; Holzer, Wolfgang

    2014-01-01

    Summary Activated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products – pyrazoles 5 – were studied with a focus on tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits. PMID:24778729

  20. Asymmetric Electrophilic α-Amination of Silyl Enol Ether Derivatives via the Nitrosocarbonyl Hetero-ene Reaction.

    PubMed

    Sandoval, David; Samoshin, Andrey V; Read de Alaniz, Javier

    2015-09-18

    The first example of a general asymmetric nitrosocarbonyl hetero-ene reaction is described. The procedure uses a copper-catalyzed aerobic oxidation of a commercially available chiral nitrosocarbonyl precursor (EleNOr) and is operationally simple. The transformation is both high yielding and highly diastereoselective for a range of silyl enol ether derivatives. A variety of synthetically useful postfunctionalization reactions are presented along with a mechanistic rationale that can be used as a predictive model for future asymmetric reactions with nitrosocarbonyl intermediates.

  1. Organocatalyzed enantioselective protonation of silyl enol ethers: scope, limitations, and application to the preparation of enantioenriched homoisoflavones.

    PubMed

    Poisson, Thomas; Gembus, Vincent; Dalla, Vincent; Oudeyer, Sylvain; Levacher, Vincent

    2010-11-19

    In the present work, enantioselective protonation of silyl enol ethers is reported by means of a variety of chiral nitrogen bases as catalysts, mainly derived from cinchona alkaloids, in the presence of various protic nucleophiles as proton source. A detailed study of the most relevant reaction parameters is disclosed allowing high enantioselectivities of up to 92% ee with excellent yields to be achieved under mild and eco-friendly conditions. The synthetic utility of this organocatalytic protonation was demonstrated during the preparation of two homoisoflavones 4a and 4b, isolated from Chlorophytum Inornatum and Scilla Nervosa, which were obtained with 81% and 78% ee, respectively.

  2. Single step synthesis of strigolactone analogues from cyclic keto enols, germination stimulants for seeds of parasitic weeds.

    PubMed

    Mwakaboko, Alinanuswe S; Zwanenburg, Binne

    2011-08-15

    The single step synthesis of a newly designed series of strigolactones (SLs) from cyclic keto enols is described. The germinating activity of these SL analogues towards seeds of the parasitic weeds Striga and Orobanche spp. is reported. The first of these SL analogues are derived from the hydroxyl γ-pyrones kojic acid and maltol, the second type from hydroxyl α-pyrones, namely, 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxy-coumarin and the third type from 1,3-diketones, namely, 1,3-cyclohexane-dione (dimedone) and tricyclic 1,3-dione. All keto enols are coupled in a single step with the appropriate D-ring precursor in the presence of a base to give the desired SL analogues. All SL analogues are acceptably biologically active in inducing the germination of seeds of Striga hermonthica and Orobanchecernua. Most interesting are the analogues derived from 4-hydroxy coumarin and dimedone, as they have a remarkably high biological activity towards the seeds of parasitic weeds at relatively low concentrations, comparable with that of the general standard stimulant GR24.

  3. Lowering of Keto-Enol Tautomerization Barrier of Cyclic Diketones via CH\\cdotsO Interaction

    NASA Astrophysics Data System (ADS)

    Chakraborty, T.; Bandyopadhyay, B.; Banerjee, P.; Pandey, P.

    2013-06-01

    Molecular association and keto-enol tautomerization of β-cyclohexanedione (β-CHD) and analogues have been investigated in argon matrix and also in a thin solid film prepared by depositing pure β-CHD vapour on a cold (8 K) KBr window. Infrared spectra reveal that in low-pressure vapour and argon matrix, the molecules are exclusively in diketo tautomeric form. The CH\\cdotsO hydrogen bonded dimers of the diketo tautomer are produced by annealing the matrix at 28 K. No indication is found for keto-enol tautomerization of β-CHD in dimeric complexes in argon matrix within the temperature range of 8-28 K. On the other hand, in the thin film of pure diketo tautomer, the conversion initiates when the film is heated at temperatures above 165 K. The observed threshold appears to be associated with excitation of the intermolecular modes in the solid, and the IR spectra recorded at high temperatures display narrowing of vibrational bandwidths, which has been associated to re-orientations of the molecules in solid. The non-occurrence of tautomerization in the dimer is consistent with the prediction of electronic structure calculations at B3LYP/6-311++G**, M05-2X/6-311++G** and MP2/6-311++G** levels. The transition state calculation predicts that CH\\cdotsO interaction has a dramatic effect on lowering of the tautomerization barrier, from more than 60 kcal/mol of bare molecule to ˜35-40 kcal/mol in dimers. Details of the results on analogous systems will be discussed in the talk. References ``CH\\cdotsO Interaction Lowers Hydrogen Transfer Barrier to Keto-Enol Tautomerization of β-Cyclohexanedione: Combined Infrared Spectroscopic and Electronic Structure Calculation Study", B. Bandyopadhyay, P. Pandey, P. Banerjee, A. K. Samanta, and T. Chakraborty, J. Phys. Chem A. 116,3836-3845 (2012).

  4. High Resolution Rotational Spectroscopy of a Flexible Cyclic Ether

    NASA Astrophysics Data System (ADS)

    Gámez, F.; Martínez-Haya, B.; Blanco, S.; López, J. C.; Alonso, J. L.

    2011-06-01

    Crown ethers stand as one cornerstone molecular class inhost-guest Supramolecular Chemistry and constitute building blocks for a broad range of modern materials. We report here the first high resolution rotational study of a crown ether: 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5 ether,15c5). Molecular beam Fourier transform microwave spectroscopy has been employed. The liquid sample of 15c5 has been vaporized using heating methods. The considerable size of 15c5 and the broad range of conformations allowed by the flexibility of its backbone pose important challenges to spectroscopy approaches. In fact, the ab-initio computational study for isolated 15c5, yields at least six stable conformers with relative free energies within 2 kJ Mol-1 (167 Cm-1). Nevertheless, in this investigation it has been possible to identify and characterize in detail one stable rotamer of the 15c5 molecule and to challenge different quantum methods for the accurate description of this system. The results pave the ground for an extensive description of the conformational landscape of 15c5 and related cyclic ethers in the near term. J. L. Alonso, F. J. Lorenzo, J. C. López, A. Lesarri, S. Mata and H. Dreizler, Chem. Phys., 218, 267 (1997) S. Blanco, J.C López, J.L. Alonso, P. Ottaviani, W. Caminati, J. Chem. Phys. 119, 880 (2003) S.E. Hill, D. Feller, Int. J. Mass Spectrom. 201, 41 (2000)

  5. Regioselective Oxo-Amination of Alkenes and Enol Ethers with N-Bromosuccinimide-Dimethyl Sulfoxide Combination: A Facile Synthesis of α-Amino-Ketones and Esters.

    PubMed

    Prasad, Pragati K; Reddi, Rambabu N; Sudalai, Arumugam

    2016-02-05

    An unprecedented conversion of alkenes and enol ethers to the corresponding α-imido carbonyl compounds with excellent regioselectivity and yields has been developed. This oxo-amination process employs readily available N-bromosuccinimide (NBS) and secondary amines as N-sources and dimethyl sulfoxide (DMSO) as the oxidant and also leads to the production of amino alcohols in a single step on reduction, thus broadening the scope of this operationally simple reaction. For the first time, the formation of reactive Me2S(+)-O-Br species generated by the interaction of NBS with DMSO has been proven.

  6. Nucleophilic Addition of Organozinc Reagents to 2-Sulfonyl Cyclic Ethers

    PubMed Central

    Kim, Hyoungsu; Kasper, Amanda C.; Moon, Eui Jung; Park, Yongho; Wooten, Ceshea M.; Dewhirst, Mark W.; Hong, Jiyong

    2009-01-01

    A convergent route to the synthesis of manassantins A and B, potent inhibitors of HIF-1, is described. Central to the synthesis is a stereoselective addition of an organozinc reagent to a 2-benzenesulfonyl cyclic ether to achieve the 2,3-cis-3,4-trans-4,5-cis-tetrahydrofuran of the natural products. Preliminary structure—activity relationships suggested that the (R)-configuration at C-7 and C-7″′ is not critical for HIF-1 inhibition. In addition, the hydroxyl group at C-7 and C-7″′ can be replaced with carbonyl group without loss of activity. PMID:19111058

  7. A highly efficient Mukaiyama-Mannich reaction of N-Boc isatin ketimines and other active cyclic ketimines using difluoroenol silyl ethers catalyzed by Ph3PAuOTf.

    PubMed

    Yu, Jin-Sheng; Zhou, Jian

    2015-12-07

    Ph3PAuOTf is identified as a powerful catalyst for the addition of difluoroenol silyl ethers to N-Boc isatin ketimines and other two kinds of active cyclic ketimines. This represents the first Au(i)-catalyzed Mukaiyama-Mannich reaction, and the corresponding non-fluorinated enol silyl ether proves to be even much more reactive under the same conditions. This method paves the way to the total synthesis of difluoromethylated analogues of AG-041R, a gastrin/CCK-B receptor antagonist.

  8. Thermochemical properties and bond dissociation enthalpies of 3- to 5-member ring cyclic ether hydroperoxides, alcohols, and peroxy radicals: cyclic ether radical + (3)O(2) reaction thermochemistry.

    PubMed

    Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

    2014-05-01

    The formation of cyclic ethers is a major product in the oxidation of hydrocarbons, and the oxidation of biomass derived alcohols. Cyclic ethers are formed in the initial reactions of alkyl radicals with dioxygen in combustion and precombustion processes that occur at moderate temperatures. They represent a significant part of the oxygenated pollutants found in the exhaust gases of engines. Cyclic ethers can also be formed from atmospheric reactions of olefins. Additionally, cyclic ethers have been linked to the formation of the secondary organic aerosol (SOA) in the atmosphere. In combustion and thermal oxidation processes these cyclic ethers will form radicals that react with (3)O2 to form peroxy radicals. Density functional theory and higher level ab initio calculations are used to calculate thermochemical properties and bond dissociation enthalpies of 3 to 5 member ring cyclic ethers (oxirane, yC2O, oxetane, yC3O, and oxolane, yC4O), corresponding hydroperoxides, alcohols, hydroperoxy alkyl, and alkyl radicals which are formed in these oxidation reaction systems. Trends in carbon-hydrogen bond dissociation energies for the ring and hydroperoxide group relative to ring size and to distance from the ether group are determined. Bond dissociation energies are calculated for use in understanding effects of the ether oxygen in the cyclic ethers, their stability, and kinetic properties. Geometries, vibration frequencies, and enthalpies of formation, ΔH°f,298, are calculated at the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), the composite CBS-QB3, and G3MP2B3 methods. Entropy and heat capacities, S°(T) and Cp°(T) (5 K ≤ T ≤ 5000), are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations. The strong effects of ring strain on the bond dissociation energies in these peroxy systems are also of fundamental interest. Oxetane and oxolane exhibit a significant stabilization, 10 kcal mol(-1), lower ΔfH°298 when an oxygen group is on

  9. Oligomer formation during gas-phase ozonolysis of small alkenes and enol ethers: new evidence for the central role of the Criegee Intermediate as oligomer chain unit

    NASA Astrophysics Data System (ADS)

    Sadezky, A.; Winterhalter, R.; Kanawati, B.; Römpp, A.; Spengler, B.; Mellouki, A.; Le Bras, G.; Chaimbault, P.; Moortgat, G. K.

    2008-05-01

    An important fraction of secondary organic aerosol (SOA) formed by atmospheric oxidation of diverse volatile organic compounds (VOC) has recently been shown to consist of high-molecular weight oligomeric species. In our previous study (Sadezky et al., 2006), we reported the identification and characterization of oligomers as main constituents of SOA from gas-phase ozonolysis of small enol ethers. These oligomers contained repeated chain units of the same chemical composition as the main Criegee Intermediates (CI) formed during the ozonolysis reaction, which were CH2O2 (mass 46) for alkyl vinyl ethers (AVE) and C2H4O2 (mass 60) for ethyl propenyl ether (EPE). In the present work, we extend our previous study to another enol ether (ethyl butenyl ether EBE) and a variety of structurally related small alkenes (trans-3-hexene, trans-4-octene and 2,3-dimethyl-2-butene). Experiments have been carried out in a 570 l spherical glass reactor at atmospheric conditions in the absence of seed aerosol. SOA formation was measured by a scanning mobility particle sizer (SMPS). SOA filter samples were collected and chemically characterized off-line by ESI(+)/TOF MS and ESI(+)/TOF MS/MS, and elemental compositions were determined by ESI(+)/FTICR MS and ESI(+)/FTICR MS/MS. The results for all investigated unsaturated compounds are in excellent agreement with the observations of our previous study. Analysis of the collected SOA filter samples reveal the presence of oligomeric compounds in the mass range 200 to 800 u as major constituents. The repeated chain units of these oligomers are shown to systematically have the same chemical composition as the respective main Criegee Intermediate (CI) formed during ozonolysis of the unsaturated compounds, which is C3H6O2 (mass 74) for ethyl butenyl ether (EBE), trans-3-hexene, and 2,3-dimethyl-2-butene, and C4H8O2 (mass 88) for trans-4-octene. Analogous fragmentation pathways among the oligomers formed by gas-phase ozonolysis of the different

  10. Oligomer formation during gas-phase ozonolysis of small alkenes and enol ethers: new evidence for the central role of the Criegee Intermediate as oligomer chain unit

    NASA Astrophysics Data System (ADS)

    Sadezky, A.; Winterhalter, R.; Kanawati, B.; Römpp, A.; Spengler, B.; Mellouki, A.; Le Bras, G.; Chaimbault, P.; Moortgat, G. K.

    2007-10-01

    An important fraction of secondary organic aerosol (SOA) formed by atmospheric oxidation of diverse volatile organic compounds (VOC) has recently been shown to consist of high-molecular weight oligomeric species. In our previous study (Sadezky et al., 2006), we reported the identification and characterization of oligomers as main constituents of SOA from gas-phase ozonolysis of small enol ethers. These oligomers contained repeated chain units of the same chemical composition as the main Criegee Intermediates (CI) formed during the ozonolysis reaction, which were CH2O2 (mass 46) for alkyl vinyl ethers (AVE) and C2H4O2 (mass 60) for ethyl propenyl ether (EPE). In the present work, we extend our previous study (Sadezky et al., 2006) to another enol ether (ethyl butenyl ether EBE) and a variety of structurally related small alkenes (trans-3-hexene, trans-4-octene and 2,3-dimethyl-2-butene). Experiments have been carried out in a 570 l spherical glass reactor at atmospheric conditions in the absence of seed aerosol. SOA formation was measured by a scanning mobility particle sizer (SMPS). SOA filter samples were collected and chemically characterized off-line by ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF, and elemental compositions were confirmed by ESI(+)/MS/MS-FTICR. The results for all investigated unsaturated compounds are in excellent agreement with the observations of our previous study (Sadezky et al., 2006). Analysis of the collected SOA filter samples reveal the presence of oligomeric compounds in the mass range 200 to 800 u as major constituents. The repeated chain units of these oligomers are shown to systematically have the same chemical composition as the respective main Criegee Intermediate (CI) formed during ozonolysis of the unsaturated compounds, which is C3H6O2 (mass 74) for ethyl butenyl ether (EBE), trans-3-hexene, and 2,3-dimethyl-2-butene, and C4H8O2 (mass 88) for trans-4-octene. Analogous fragmentation pathways among the oligomers formed by gas

  11. Copper-catalyzed oxidative C-O bond formation of 2-acyl phenols and 1,3-dicarbonyl compounds with ethers: direct access to phenol esters and enol esters.

    PubMed

    Park, Jihye; Han, Sang Hoon; Sharma, Satyasheel; Han, Sangil; Shin, Youngmi; Mishra, Neeraj Kumar; Kwak, Jong Hwan; Lee, Cheong Hoon; Lee, Jeongmi; Kim, In Su

    2014-05-16

    A copper-catalyzed oxidative coupling of 2-carbonyl-substituted phenols and 1,3-dicarbonyl compounds with a wide range of dibenzyl or dialkyl ethers is described. This protocol provides an efficient preparation of phenol esters and enol esters in good yields with high chemoselectivity. This method represents an alternative protocol for classical esterification reactions.

  12. Synthesis of β-Keto Sulfones by a Catalyst-Free Reaction of Aryldiazonium Tetrafluoroborates, Sulfur Dioxide, and Silyl Enol Ethers.

    PubMed

    Liu, Tianshuo; Zheng, Danqing; Ding, Yechun; Fan, Xiaona; Wu, Jie

    2017-02-16

    A green approach for the generation of β-keto sulfones through a reaction of aryldiazonium tetrafluoroborates and sulfur dioxide with silyl enol ether under catalyst- and additive-free conditions has been realized. This reaction proceeds efficiently at room temperature and goes to completion in half an hour. During the reaction process, aryldiazonium tetrafluoroborate is treated with DABCO⋅(SO2 )2 (DABCO=1,4-diazabicyclo[2.2.2]octane) to provide a sulfonyl radical as the key intermediate, which then initiates the transformation. Oxidants or metal catalysts are avoided, and the presence of DABCO also plays an important role in the reaction. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Synthesis and desulfurization-decarboxylation of cyclic thionocarbonates of glycerol 1-ethers.

    PubMed

    Ramachandran, S; Panganamala, R V; Cornwell, D G

    1969-07-01

    A method is described for the synthesis of cyclic thionocarbonates of 1-O-alkyl glycerols in quantitative yield. These derivatives of glycerol ethers can be quantitated by UV absorbance, analyzed by gas-liquid chromatography, or quantitatively converted to allyl alkyl ethers for gas-chromatographic analysis.

  14. Anti-knock quality of sugar derived levulinic esters and cyclic ethers

    DOE PAGES

    Tian, Miao; McCormick, Robert L.; Luecke, Jon; ...

    2017-04-22

    Here, the objective of this paper is to investigate the anti-knock quality of sugar-derived levulinic esters (methyl levulinate (ML) and ethyl levulinate (EL)) and cyclic ethers (furfuryl ethyl ether (FEE) and ethyl tetrahydrofurfuryl ether (ETE)). To this end, combustion experiments were carried out in both an engine and a constant volume autoignition device. The results from both apparati demonstrate that ML, EL and FEE have superior anti-knock quality than the reference Euro95 gasoline. ETE, conversely, performed markedly worse than the reference fuel on both setups and might therefore be a more appropriate fuel for compression ignition engines. The main reasonmore » of the distinctions in anti-knock quality can be found in the molecular structure of the neat biofuels. ML and EL are levulinic esters, with a ketone (C=O) functionality and an ester (C(=O)-O) group on the carbon chain. They can readily produce stable intermediates during the auto-ignition process, thereby slowing down the overall reaction rate. The unsaturated cyclic ether (FEE) has very strong ring C-H bonds. However, the saturated cyclic ether (ETE) has weak ring C-H bonds, which facilitate more readily ring opening reactions. Long side chains on the cyclic ethers further accelerate the reaction rate. Importantly for future research, our results suggest that IQT and engine experiments are interchangeable setups with respect to qualitative anti-knock quality evaluation of novel compounds.« less

  15. Alkyl substituted cyclic ethers in 2,300 M yr old Transvaal algal stromatolite

    NASA Technical Reports Server (NTRS)

    Zumberge, J. E.; Nagy, B.

    1975-01-01

    Two cyclic ethers have been identified for the first time from insoluble polymer-like kerogen in a Precambrian rock by ozonolysis, gas chromatography, and mass spectrometry. The ethers are 2-n-propyl-3-methyltetrahydrofuran and 2-n-propyltetrahydropyran. These compounds could prove to be the oldest indigenous biochemical fossils. The sample was obtained 750 m stratigraphically above the base of the Transvaal Sequence from an outcrop approximately 315 km north-east of Johannesburg, South Africa.

  16. Alkyl substituted cyclic ethers in 2,300 M yr old Transvaal algal stromatolite

    NASA Technical Reports Server (NTRS)

    Zumberge, J. E.; Nagy, B.

    1975-01-01

    Two cyclic ethers have been identified for the first time from insoluble polymer-like kerogen in a Precambrian rock by ozonolysis, gas chromatography, and mass spectrometry. The ethers are 2-n-propyl-3-methyltetrahydrofuran and 2-n-propyltetrahydropyran. These compounds could prove to be the oldest indigenous biochemical fossils. The sample was obtained 750 m stratigraphically above the base of the Transvaal Sequence from an outcrop approximately 315 km north-east of Johannesburg, South Africa.

  17. Mild one-step synthesis of dibromo compounds from cyclic ethers.

    PubMed

    Billing, Peter; Brinker, Udo H

    2012-12-21

    A novel one-step method for mildly converting cyclic ethers into dibromo compounds is reported. Alcohols, oximes, aldehydes, and ketones are known to react under Appel or Corey-Fuchs reaction conditions, but apparently these have never been applied to oxetanes or larger cyclic ethers. Treatment of 3,3-dimethyloxetane (1) with tetrabromomethane and triphenylphosphine gave the corresponding dibromo compound 1,3-dibromo-2,2-dimethylpropane (2). The less-strained homologue oxolane (6) was also reacted giving 1,4-dibromobutane (7) in a 93% yield. Mechanistic interpretations are offered to explain the observed reaction rates of the conversions described.

  18. 40 CFR 721.10381 - Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether, hydroxy substituted alkane and...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether, hydroxy substituted alkane and carboxylic acid anhydride, methacrylate terminated... Specific Chemical Substances § 721.10381 Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether...

  19. 40 CFR 721.10381 - Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether, hydroxy substituted alkane and...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether, hydroxy substituted alkane and carboxylic acid anhydride, methacrylate terminated... Specific Chemical Substances § 721.10381 Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether...

  20. 40 CFR 721.10381 - Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether, hydroxy substituted alkane and...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether, hydroxy substituted alkane and carboxylic acid anhydride, methacrylate terminated... Specific Chemical Substances § 721.10381 Cyclic carboxylic acid, polymer with dihydroxy dialkyl ether...

  1. Diastereoselective Diels–Alder Reactions of N-Sulfonyl-1-aza-1,3-butadienes With Optically Active Enol Ethers: An Asymmetric Variant of the 1-Azadiene Diels–Alder Reaction

    PubMed Central

    Clark, Ryan C.; Pfeiffer, Steven S.

    2008-01-01

    The first detailed study of a room temperature asymmetric Diels–Alder reaction of N-sulfonyl-1-aza-1,3-butadienes enlisting a series of nineteen enol ethers bearing chiral auxilaries is reported with many providing highly diastereoselective (endo and facial diastereoselection) reactions largely the result of an exquisitely organized [4 + 2] cycloaddition transition state. Three new, readily accessible, and previously unexplored auxilaries (18a, 19a and 37a) rationally emerged from the studies and provide remarkable selectivities (for 19a and 37a: 49:1 endo:exo and 48:1 facial selectivity) that promise to be useful in systems beyond those detailed. PMID:16492042

  2. Organocatalytic enantioselective Michael addition of cyclic hemiacetals to nitroolefins: a facile access to chiral substituted 5- and 6-membered cyclic ethers.

    PubMed

    Zhu, Yadong; Qian, Pengfei; Yang, Jiyang; Chen, Shaohua; Hu, Yanwei; Wu, Ping; Wang, Wei; Zhang, Wei; Zhang, Shilei

    2015-04-28

    An efficient aminocatalytic enantioselective Michael addition of readily available cyclic hemiacetals to nitroolefins has been developed. The strategy serves as a powerful approach to synthetically valuable chiral 3-substituted tetrahydrofurans (THFs) and tetrahydropyrans (THPs). The synthetic utilities of the versatile Michael adducts also have been demonstrated in the synthesis of 2,3-disubstituted cyclic ethers, α-substituted lactones and venlafaxine analogues.

  3. Metabolism and Cometabolism of Cyclic Ethers by a Filamentous Fungus, a Graphium sp.▿

    PubMed Central

    Skinner, Kristin; Cuiffetti, Lynda; Hyman, Michael

    2009-01-01

    The filamentous fungus Graphium sp. (ATCC 58400) grows on gaseous n-alkanes and diethyl ether. n-Alkane-grown mycelia of this strain also cometabolically oxidize the gasoline oxygenate methyl tert-butyl ether (MTBE). In this study, we characterized the ability of this fungus to metabolize and cometabolize a range of cyclic ethers, including tetrahydrofuran (THF) and 1,4-dioxane (14D). This strain grew on THF and other cyclic ethers, including tetrahydropyran and hexamethylene oxide. However, more vigorous growth was consistently observed on the lactones and terminal diols potentially derived from these ethers. Unlike the case in all previous studies of microbial THF oxidation, a metabolite, γ-butyrolactone, was observed during growth of this fungus on THF. Growth on THF was inhibited by the same n-alkenes and n-alkynes that inhibit growth of this fungus on n-alkanes, while growth on γ-butyrolactone or succinate was unaffected by these inhibitors. Propane and THF also behaved as mutually competitive substrates, and propane-grown mycelia immediately oxidized THF, without a lag phase. Mycelia grown on propane or THF exhibited comparable high levels of hemiacetal-oxidizing activity that generated methyl formate from mixtures of formaldehyde and methanol. Collectively, these observations suggest that THF and n-alkanes may initially be oxidized by the same monooxygenase and that further transformation of THF-derived metabolites involves the activity of one or more alcohol dehydrogenases. Both propane- and THF-grown mycelia also slowly cometabolically oxidized 14D, although unlike THF oxidation, this reaction was not sustainable. Specific rates of THF, 14D, and MTBE degradation were very similar in THF- and propane-grown mycelia. PMID:19581469

  4. Copper(II)-catalyzed C-O coupling of aryl bromides with aliphatic diols: synthesis of ethers, phenols, and benzo-fused cyclic ethers.

    PubMed

    Liu, Yajun; Park, Se Kyung; Xiao, Yan; Chae, Junghyun

    2014-07-14

    A highly efficient copper-catalyzed C-O cross-coupling reaction between aryl bromides and aliphatic diols has been developed employing a cheaper, more efficient, and easily removable copper(II) catalyst. A broad range of aryl bromides were coupled with aliphatic diols of different lengths using 5 mol% CuCl2 and 3 equivalents of K2CO3 in the absence of any other ligands or solvents to afford the corresponding hydroxyalkyl aryl ethers in good to excellent yields. In this newly developed protocol, aliphatic diols have multilateral functions as coupling reactants, ligands, and solvents. The resulting hydroxyalkyl aryl ethers were further readily converted into the corresponding phenols, presenting a valuable alternative way to phenols from aryl bromides. Furthermore, it was demonstrated that they are useful intermediates for more advanced molecules such as benzofurans and benzo-fused cyclic ethers.

  5. Mass spectra of cyclic ethers formed in the low-temperature oxidation of a series of n-alkanes

    PubMed Central

    Herbinet, Olivier; Bax, Sarah; Glaude, Pierre-Alexandre; Carré, Vincent; Battin-Leclerc, Frédérique

    2013-01-01

    Cyclic ethers are important intermediate species formed during the low-temperature oxidation of hydrocarbons. Along with ketones and aldehydes, they could consequently represent a significant part of the heavy oxygenated pollutants observed in the exhaust gas of engines. Apart a few of them such as ethylene oxide and tetrahydrofuran, cyclic ethers have not been much studied and very few of them are available for calibration and identification. Electron impact mass spectra are available for very few of them, making their detection in the exhaust emissions of combustion processes very difficult. The main goal of this study was to complete the existing set of mass spectra for this class of molecules. Thus cyclic ethers have been analyzed in the exhaust gases of a jet-stirred reactor in which the low-temperature oxidation of a series of n-alkanes was taking place. Analyzes were performed by gas chromatography coupled to mass spectrometry and to MS/MS. The second goal of this study was to derive some rules for the fragmentation of cyclic ethers in electron impact mass spectrometry and allow the identification of these species when no mass spectrum is available. PMID:24092947

  6. Ambient gold-catalyzed O-vinylation of cyclic 1,3-diketone: A vinyl ether synthesis.

    PubMed

    Xi, Yumeng; Dong, Boliang; Shi, Xiaodong

    2013-01-01

    Gold-catalyzed O-vinylation of cyclic 1,3-diketones has been achieved for the first time, which provides direct access to various vinyl ethers. A catalytic amount of copper triflate was identified as the significant additive in promoting this transformation. Both aromatic and aliphatic alkynes are suitable substrates with good to excellent yields.

  7. Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation of Enol Carbonates

    PubMed Central

    Trost, Barry M.; Xu, Jiayi; Schmidt, Thomas

    2009-01-01

    Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio- and enantio-selective process for the synthesis of ketones bearing either a quaternary or a tertiary α-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic di-substituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium enolates, the DAAA reaction proceeds through an “outer sphere” SN2 type of attack on the π-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the π-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of enolates associated with the equilibrium between different enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal enolates. PMID:19928805

  8. An ether-functionalised cyclic sulfonium based ionic liquid as an electrolyte for electrochemical double layer capacitors

    NASA Astrophysics Data System (ADS)

    Neale, Alex R.; Murphy, Sinead; Goodrich, Peter; Schütter, Christoph; Hardacre, Christopher; Passerini, Stefano; Balducci, Andrea; Jacquemin, Johan

    2016-09-01

    A novel cyclic sulfonium cation-based ionic liquid (IL) with an ether-group appendage and the bis{(trifluoromethyl)sulfonyl}imide anion was synthesised and developed for electrochemical double layer capacitor (EDLC) testing. The synthesis and chemical-physical characterisation of the ether-group containing IL is reported in parallel with a similarly sized alkyl-functionalised sulfonium IL. Results of the chemical-physical measurements demonstrate how important transport properties, i.e. viscosity and conductivity, can be promoted through the introduction of the ether-functionality without impeding thermal, chemical or electrochemical stability of the IL. Although the apparent transport properties are improved relative to the alkyl-functionalised analogue, the ether-functionalised sulfonium cation-based IL exhibits moderately high viscosity, and poorer conductivity, when compared to traditional EDLC electrolytes based on organic solvents (propylene carbonate and acetonitrile). Electrochemical testing of the ether-functionalised sulfonium IL was conducted using activated carbon composite electrodes to inspect the performance of the IL as a solvent-free electrolyte for EDLC application. Good cycling stability was achieved over the studied range and the performance was comparable to other solvent-free, IL-based EDLC systems. Nevertheless, limitations of the attainable performance are primarily the result of sluggish transport properties and a restricted operative voltage of the IL, thus highlighting key aspects of this field which require further attention.

  9. Transferable potentials for phase equilibria-united atom description of five- and six-membered cyclic alkanes and ethers.

    PubMed

    Keasler, Samuel J; Charan, Sophia M; Wick, Collin D; Economou, Ioannis G; Siepmann, J Ilja

    2012-09-13

    While the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field has generally been successful at providing parameters that are highly transferable between different molecules, the polarity and polarizability of a given functional group can be significantly perturbed in small cyclic structures, which limits the transferability of parameters obtained for linear molecules. This has motivated us to develop a version of the TraPPE-UA force field specifically for five- and six-membered cyclic alkanes and ethers. The Lennard-Jones parameters for the methylene group obtained from cyclic alkanes are transferred to the ethers for each ring size, and those for the oxygen atom are common to all compounds for a given ring size. However, the partial charges are molecule specific and parametrized using liquid-phase dielectric constants. This model yields accurate saturated liquid densities and vapor pressures, critical temperatures and densities, normal boiling points, heat capacities, and isothermal compressibilities for the following molecules: cyclopentane, tetrahydrofuran, 1,3-dioxolane, cyclohexane, oxane, 1,4-dioxane, 1,3-dioxane, and 1,3,5-trioxane. The azeotropic behavior and separation factor for the binary mixtures of 1,3-dioxolane/cyclohexane and ethanol/1,4-dioxane are qualitively reproduced.

  10. Nucleophilic addition of organozinc reagents to 2-sulfonyl cyclic ethers: stereoselective synthesis of manassantins A and B.

    PubMed

    Kim, Hyoungsu; Kasper, Amanda C; Moon, Eui Jung; Park, Yongho; Wooten, Ceshea M; Dewhirst, Mark W; Hong, Jiyong

    2009-01-01

    A convergent route to the synthesis of manassantins A and B, potent inhibitors of HIF-1, is described. Central to the synthesis is a stereoselective addition of an organozinc reagent to a 2-benzenesulfonyl cyclic ether to achieve the 2,3-cis-3,4-trans-4,5-cis-tetrahydrofuran of the natural products. Preliminary structure-activity relationships suggested that the (R)-configuration at C-7 and C-7''' is not critical for HIF-1 inhibition. In addition, the hydroxyl group at C-7 and C-7''' can be replaced with a carbonyl group without loss of activity.

  11. Thermochemical properties of methyl-substituted cyclic alkyl ethers and radicals for oxiranes, oxetanes, and oxolanes: C-H bond dissociation enthalpy trends with ring size and ether site.

    PubMed

    Auzmendi-Murua, Itsaso; Charaya, Sumit; Bozzelli, Joseph W

    2013-01-17

    Cyclic ethers are an important product from the gas-phase reactions of hydrocarbon radicals with molecular oxygen in the atmospheric chemistry of diolefins and in low to moderate temperature combustion and oxidation reaction systems. They are also important in organic synthesis. Structures, and fundamental thermochemical parameters-enthalpy (ΔH°(f,298)), entropy (S°(298)), and heat capacity (C(p)(T))-have been calculated for a series of cyclic alkyl ethers and their carbon centered radicals. Enthalpies of formation (ΔH°(f,298)) are determined at the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), and CBS-QB3 levels using several work reactions for each species. Entropy (S) and heat capacity (C(p)(T)) values from vibration, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic-oscillator approximation based on the vibration frequencies and structures obtained from the density functional studies. Contributions from the internal methyl rotors are substituted for torsion frequencies. Calculated enthalpies of formation for a series of 12 cyclic ethers and methyl substituted cyclic ethers are in good agreement with available literature values. C-H bond dissociation enthalpies are reported for 28 carbon sites of 3 to 5 member ring cyclic ethers for use in understanding effects of the ring and the ether oxygen on kinetics and stability. Trends in carbon-hydrogen bond energies for the ring and methyl substituents relative to ring size and to distance from the ether group are described.

  12. Activation of Marginally Reactive Boron Enolates by MeLi for the Formation of Enol Phosphates and Synthesis of the Δ(9)-THC Intermediate.

    PubMed

    Kawada, Hiroki; Ikoma, Atsushi; Ogawa, Narihito; Kobayashi, Yuichi

    2015-09-18

    The addition of MeLi to boron enolates produced by the 1,4-addition of Ar2Cu(CN)Li2 to BF3·OEt2-activated enones was followed by the reaction with ClP(O)(OEt)2 to afford the corresponding enol phosphates in moderate to good yields. The scope of this method was examined with sterically hindered or electronically biased enones and/or reagents. This activation of boron enolates was successfully applied to the synthesis of the methyl ether of Δ(9)-tetrahydrocannabinol.

  13. Excess volumes and excess viscosities of binary mixtures of some cyclic ethers + bromocyclohexane at 298.15 and 313.15 K

    NASA Astrophysics Data System (ADS)

    Rodríguez, S.; Lafuente, C.; Carrión, J. A.; Royo, F. M.; Urieta, J. S.

    1996-11-01

    Excess Volumes, V E, and excess viscosities, η E, at 293.15 and 313.15 K are reported for binary mixtures of some cyclic ethers (tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran and 2,5-dimethyltetrahydrofuran) + bromocyclohexane. These properties were obtained from density and viscosity measurements. γ E and η E show negatives values for all the mixtures.

  14. An alternative approach to aldol reactions: gold-catalyzed formation of boron enolates from alkynes.

    PubMed

    Körner, Cindy; Starkov, Pavel; Sheppard, Tom D

    2010-05-05

    A new method for enolate generation via the gold-catalyzed addition of boronic acids to alkynes is reported. The formation of boron enolates from readily accessible ortho-alkynylbenzeneboronic acids proceeds rapidly with 2 mol % PPh(3)AuNTf(2) at ambient temperature. The enolates undergo aldol reaction with an aldehyde present in the reaction mixture to give cyclic boronate esters, which can be subsequently transformed into phenols, biaryls, or dihydrobenzofurans via oxidation, Suzuki-Miyaura, or intramolecular Chan-Lam coupling, respectively. A combined gold/boronic acid catalyzed aldol condensation reaction of an alkynyl aldehyde was also successfully achieved.

  15. Catalytic enantioselective protonation of enol trifluoroacetates by means of hydrogenocarbonates and cinchona alkaloids.

    PubMed

    Claraz, Aurélie; Leroy, Jérôme; Oudeyer, Sylvain; Levacher, Vincent

    2011-08-05

    Herein is disclosed an efficient catalytic enantioselective protonation of enol acetates by means of a readily implementable transition-metal-free chemical process. By making use of simple hygrogenocarbonates as the proton source and hydroquinine anthraquinone-1,4-diyl diether as the chiral proton shuttle, a series of cyclic enol trifluoroacetates are protonated under mild conditions to yield the corresponding ketones in up to 93% ee.

  16. Unprecedented antioxidative cyclic ether from the red seaweed Kappaphycus alvarezii with anti-cyclooxygenase and lipoxidase activities.

    PubMed

    Makkar, Fasina; Chakraborty, Kajal

    2017-05-01

    An unprecedented non-isoprenoid oxocine carboxylate cyclic ether characterised as (3S, 4R, 5S, 6Z)-3-((R)-hexan-2'-yl)-3,4,5,8-tetrahydro-4-methyl-2H-oxocin-5-yl acetate was isolated from the ethyl acetate-methanol extract of the red seaweed Kappaphycus alvarezii. The structure, as well as its relative stereochemistry, was proposed on the basis of extensive spectral data. The antioxidative activity of the isolated metabolite was found to have significantly greater as determined by 1, 1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis-3-ethylbenzothiozoline-6-sulfonic acid radical scavenging activities (IC50 ~ 0.3 mg/mL) compared to α-tocopherol (IC50 > 0.6 mg/mL) and was comparable to the synthetic antioxidants butylated hydroxytoluene and butylated hydroxyanisole (IC50 ~ 0.35-0.34 mg/mL). The compound exhibited greater activity against COX-2 (cyclooxygenase-2) than COX-1 (cyclooxygenase-1) isoform, and therefore, the selectivity index remained significantly lesser (anti-COX-1IC50: anti-COX-2IC50 0.87) than synthetic anti-inflammatory drugs (0.02-0.44). No significant difference of in vivo 5-lipoxidase activity (IC50 0.95 mg/mL) than ibuprofen (IC50 0.93 mg/mL) indicated the potential anti-inflammatory properties of the title compound.

  17. Effect of Base-Acid Properties of Mixtures of Ethanol with Water on the Enthalpy of Solution of Cyclic Ethers in these Mixtures at T = 298.15 K.

    PubMed

    Jóźwiak, Małgorzata

    2017-01-01

    The enthalpies of solution of the cyclic ethers 1,4-dioxane, 12-crown-4 and 18-crown-6 in mixtures of ethanol and water have been measured within the whole mole fraction range at T = 298.15 K. The enthalpy of solvation has been calculated. In pure ethanol and pure water, the solvation enthalpy of the investigated cyclic ethers depends linearity on the number of -CH2CH2- groups in the cyclic ether molecules. Based on the analysis of the preferential solvation model proposed by Waghorne, it can be concluded that the 1,4-dioxane, 15C5 and 18C6 molecules are preferentially solvated by water molecules in the range of low water content in these mixtures. The effect of base-acid properties of ethanol-water mixtures on the enthalpy of solution of cyclic ethers in these mixtures has been analyzed. The enthalpy of solution of cyclic ethers correlates with the acidic properties of ethanol-water mixtures in the range of high and medium water content. The results presented are compared with analogous data obtained for the methanol-water and propan-1-ol-water mixtures.

  18. Flexible Cyclic Ethers/Polyethers as Novel P2-Ligands for HIV-1 Protease Inhibitors: Design, Synthesis, Biological Evaluation and Protein-ligand X-ray Studies

    PubMed Central

    Ghosh, Arun K.; Gemma, Sandra; Baldridge, Abigail; Wang, Yuan-Fang; Kovalevsky, Andrey Yu.; Koh, Yashiro; Weber, Irene T.; Mitsuya, Hiroaki

    2009-01-01

    We report the design, synthesis and biological evaluation of a series of novel HIV-1 protease inhibitors. The inhibitors incorporate stereochemically defined flexible cyclic ethers/polyethers as the high affinity P2-ligands. Inhibitors containing small ring 1,3-dioxacycloalkanes have shown potent enzyme inhibitory and antiviral activity. Inhibitors 3d and 3h are the most active inhibitors. Inhibitor 3d maintains excellent potency against a variety of multi-PI-resistant clinical strains. Our structure-activity studies indicate that the ring size, stereochemistry, and position of oxygens are important for the observed activity. Optically active synthesis of 1,3-dioxepan-5-ol along with the syntheses of various cyclic ether and polyether ligands have been described. A protein-ligand X-ray crystal structure of 3d-bound HIV-1 protease was determined. The structure revealed that the P2-ligand makes extensive interactions including hydrogen bonding with the protease backbone in the S2-site. In addition, the P2-ligand in 3d forms a unique water-mediated interaction with the NH of Gly-48. PMID:18783203

  19. Esterification of bio-oil from mallee (Eucalyptus loxophleba ssp. gratiae) leaves with a solid acid catalyst: Conversion of the cyclic ether and terpenoids into hydrocarbons.

    PubMed

    Hu, Xun; Gunawan, Richard; Mourant, Daniel; Wang, Yi; Lievens, Caroline; Chaiwat, Weerawut; Wu, Liping; Li, Chun-Zhu

    2012-11-01

    Bio-oil from pyrolysis of mallee (Eucalyptus loxophleba ssp. gratiae) leaves differs from that obtained with wood by its content of cyclic ethers, terpenoids and N-containing organic compounds. Upgrading of the leaf bio-oil in methanol with a solid acid catalyst was investigated and it was found that the N-containing organics in the bio-oil lead to deactivation of the catalyst in the initial stage of exposure and have to be removed via employing high catalyst loading to allow the occurrence of other acid-catalysed reactions. Eucalyptol, the main cyclic ether in the bio-oil, could be converted into the aromatic hydrocarbon, p-cymene, through a series of intermediates including α-terpineol, terpinolene, and α-terpinene. Various steps such as ring-opening, dehydration, isomerisation, and aromatization were involved in the conversion of eucalyptol. The terpenoids in bio-oil could also be converted into aromatic hydrocarbons that can serve as starting materials for the synthesis of fine chemicals, via the similar processes.

  20. Flexible Cyclic Ethers/Polyethers as Novel P2-Ligands for HIV-1 Protease Inhibitors: Design, Synthesis, Biological Evaluation, and Protein-Ligand X-Ray Studies

    SciTech Connect

    Ghosh, Arun; Gemma, Sandra; Baldridge, Abigal; Wang, Yuan-Fang; Kovalevsky, Andrey; Koh, Yashiro; Weber, Irene; Mitsuya, Hiroaki

    2008-12-05

    We report the design, synthesis, and biological evaluation of a series of novel HIV-1 protease inhibitors. The inhibitors incorporate stereochemically defined flexible cyclic ethers/polyethers as high affinity P2-ligands. Inhibitors containing small ring 1,3-dioxacycloalkanes have shown potent enzyme inhibitory and antiviral activity. Inhibitors 3d and 3h are the most active inhibitors. Inhibitor 3d maintains excellent potency against a variety of multi-PI-resistant clinical strains. Our structure-activity studies indicate that the ring size, stereochemistry, and position of oxygens are important for the observed activity. Optically active synthesis of 1,3-dioxepan-5-ol along with the syntheses of various cyclic ether and polyether ligands have been described. A protein-ligand X-ray crystal structure of 3d-bound HIV-1 protease was determined. The structure revealed that the P2-ligand makes extensive interactions including hydrogen bonding with the protease backbone in the S2-site. In addition, the P2-ligand in 3d forms a unique water-mediated interaction with the NH of Gly-48.

  1. Resonance stabilization effects on ketone autoxidation: Isomer-specific cyclic ether and ketohydroperoxide formation in the low-temperature (400–625 K) oxidation of diethyl ketone

    DOE PAGES

    Scheer, Adam M.; Eskola, Arkke J.; Osborn, David L.; ...

    2016-10-11

    Here, the pulsed photolytic chlorine-initiated oxidation of diethyl ketone [DEK; (CH3CH2)2C=O], 2,2,4,4-d4-DEK [d4-DEK; (CH3CD2)2C=O], and 1,1,1,5,5,5-d6-DEK [d6-DEK; (CD3CH2)2C=O] is studied at 8 torr and 1–2 atm and from 400–625 K. Cl atoms produced by laser photolysis react with diethyl ketone to form either primary (3-pentan-on-1-yl, RP) or secondary (3-pentan-on-2-yl, RS) radicals, which in turn react with O2. Multiplexed time-of-flight mass spectrometry, coupled to either a hydrogen discharge lamp or tunable synchrotron photoionizing radiation, is used to detect products as a function of mass, time, and photon energy. At 8 torr, the nature of the chain propagating cyclic ether + OHmore » channel changes as a function of temperature. At 450 K, the production of OH is mainly in conjunction with formation of 2,4-dimethyloxetan-3-one, resulting from reaction of the resonance-stabilized secondary RS with O2. In contrast, at 550 K and 8 torr, 2-methyl-tetrahydrofuran-3-one, originating from oxidation of the primary radical (RP), is observed as the dominant cyclic ether product. Formation of both of these cyclic ether production channels proceeds via a resonance-stabilized hydroperoxy alkyl (QOOH) intermediate. Little or no ketohydroperoxide (KHP) is observed under the low-pressure conditions. At higher O2 concentrations and higher pressures (1–2 atm), a strong KHP signal appears as the temperature is increased above 450 K. Definitive isomeric identification from measurements on the deuterated DEK isotopologues indicates the favored pathway produces a γ-KHP via resonance-stabilized alkyl, QOOH, and HOOPOOH radicals. Time-resolved measurements reveal the KHP formation becomes faster and signal more intense upon increasing temperature from 450 to 575 K before intensity drops significantly at 625 K. The KHP time profile also shows a peak followed by a gradual depletion for the extent of experiment. Several tertiary products exhibit a slow accumulation in

  2. Keto-Enol Thermodynamics of Breslow Intermediates.

    PubMed

    Paul, Mathias; Breugst, Martin; Neudörfl, Jörg-Martin; Sunoj, Raghavan B; Berkessel, Albrecht

    2016-04-20

    Breslow intermediates, first postulated in 1958, are pivotal intermediates in carbene-catalyzed umpolung. Attempts to isolate and characterize these fleeting amino enol species first met with success in 2012 when we found that saturated bis-Dipp/Mes imidazolidinylidenes readily form isolable, though reactive diamino enols with aldehydes and enals. In contrast, triazolylidenes, upon stoichiometric reaction with aldehydes, gave exclusively the keto tautomer, and no isolable enol. Herein, we present the synthesis of the "missing" keto tautomers of imidazolidinylidene-derived diamino enols, and computational thermodynamic data for 15 enol-ketone pairs derived from various carbenes/aldehydes. Electron-withdrawing substituents on the aldehyde favor enol formation, the same holds for N,N'-Dipp [2,6-di(2-propyl)phenyl] and N,N'-Mes [2,4,6-trimethylphenyl] substitution on the carbene component. The latter effect rests on stabilization of the diamino enol tautomer by Dipp substitution, and could be attributed to dispersive interaction of the 2-propyl groups with the enol moiety. For three enol-ketone pairs, equilibration of the thermodynamically disfavored tautomer was attempted with acids and bases but could not be effected, indicating kinetic inhibition of proton transfer.

  3. Adjustable degradation and drug release of a thermosensitive hydrogel based on a pendant cyclic ether modified poly(ε-caprolactone) and poly(ethylene glycol)co-polymer.

    PubMed

    Wang, Weiwei; Deng, Liandong; Liu, Shasha; Li, Xu; Zhao, Xiumei; Hu, Renjie; Zhang, Jianhua; Han, Haijie; Dong, Anjie

    2012-11-01

    The convenient and precise fabrication of drug-hydrogel formulations with satisfactory degradability and a well-controlled drug release profile are crucial factors for injectable hydrogel formulations in clinical applications. Here a new injectable thermosensitive hydrogel formed from poly(ε-caprolactone) (PCL)-poly(ethylene glycol)-poly(ε-caprolactone) amphiphilicco-polymers with 1,4,8-trioxa[4.6]spiro-9-undecanone (TOSUO) moieties incorporated in the poly(ε-caprolactone) (PCL)block (PECT) was constructed to provide a route to tailor the degradation and drug release behavior. The effect of hydrophilic cyclic ether moieties on the degradation of and drug release by PECT hydrogels were evaluated in vitro and in vivo. The results indicated that a freeze-dried powder of paclitaxel-loaded PECT nanoparticles rapidly dissolved in water at ambient temperature with slightly shaking and formed a stable injectable in situ drug-hydrogel formulation at body temperature, which is convenient for clinical operations because it avoids the need for pre-quenching or long-term incubation. The paclitaxel distribution was also more quantitative and homogeneous on entrapping paclitaxel in PECT nanoparticles. Further, the small number of pendant cyclic ether groups in PCL could decrease the cystallinity and hydrophobicity and, as a result, the in vitro and in vivo retention time of PECT hydrogels and the release of entrapped paclitaxel could be tuned from a few weeks to months by varying the amount of PTOSUO in the hydrophobic block. Significantly, paclitaxel-loaded PECT nanoparticles and free paclitaxel could be simultaneously released during the in vitro paclitaxel release from PECT hydrogels. A histopathological evaluation indicated that in vivo injected PECT hydrogels produced only a modest inflammatory response. Thus pendant cyclic ether modification of PCL could be an effective way to achieve the desired degradation and drug release profiles of amphiphilicco

  4. Investigation by mass spectrometry of metal complexes of new molecular hosts: cyclic oligomer of sugar amino acid and sugar-aza-crown ethers.

    PubMed

    Fournier, Françoise; Afonso, Carlos; Ménand, Mickaël; Hamon, Louis; Xie, Juan; Tabet, Jean-Claude

    2008-01-01

    The affinity of cyclic oligomers of sugar amino acid and sugar-aza-crown ether compounds towards various transition metal cations (Cu(II), Ni(II), Co(II), Fe(II) and Zn(II)) was investigated with positive-ion electrospray mass spectrometry. The binding between the receptors (M) and the different metals (Met) is evidenced mainly by the presence of the [M + Met(II)Cl](+) ion. The experimental results showed that all studied receptors present specificity to Cu(II). An attempt has been made with CuI but no complexation was obtained. The formation of these complexes can be rationalized by considering the presence of two oxygens and two nitrogens on the receptor rim. The lone electron pair can serve as the electron donor to Cu(II). Theoretical calculations were carried out in order to show the structure of the complex and, in particular, to determine if Cu(2+) is situated either on the outer surface, on the rim of the receptor or inside the cavity. Comparison of complex formation was carried out by mixing the four receptors with various amounts of Cu(II) (one equivalent and five equivalents). It appears that the best complexation was obtained with the sugar-aza-crown ethers (amine linker) for both benzylated and methylated compounds. In addition, the stereochemical effects have been investigated.

  5. Resonance stabilization effects on ketone autoxidation: Isomer-specific cyclic ether and ketohydroperoxide formation in the low-temperature (400–625 K) oxidation of diethyl ketone

    SciTech Connect

    Scheer, Adam M.; Eskola, Arkke J.; Osborn, David L.; Sheps, Leonid; Taatjes, Craig A.

    2016-10-11

    Here, the pulsed photolytic chlorine-initiated oxidation of diethyl ketone [DEK; (CH3CH2)2C=O], 2,2,4,4-d4-DEK [d4-DEK; (CH3CD2)2C=O], and 1,1,1,5,5,5-d6-DEK [d6-DEK; (CD3CH2)2C=O] is studied at 8 torr and 1–2 atm and from 400–625 K. Cl atoms produced by laser photolysis react with diethyl ketone to form either primary (3-pentan-on-1-yl, RP) or secondary (3-pentan-on-2-yl, RS) radicals, which in turn react with O2. Multiplexed time-of-flight mass spectrometry, coupled to either a hydrogen discharge lamp or tunable synchrotron photoionizing radiation, is used to detect products as a function of mass, time, and photon energy. At 8 torr, the nature of the chain propagating cyclic ether + OH channel changes as a function of temperature. At 450 K, the production of OH is mainly in conjunction with formation of 2,4-dimethyloxetan-3-one, resulting from reaction of the resonance-stabilized secondary RS with O2. In contrast, at 550 K and 8 torr, 2-methyl-tetrahydrofuran-3-one, originating from oxidation of the primary radical (RP), is observed as the dominant cyclic ether product. Formation of both of these cyclic ether production channels proceeds via a resonance-stabilized hydroperoxy alkyl (QOOH) intermediate. Little or no ketohydroperoxide (KHP) is observed under the low-pressure conditions. At higher O2 concentrations and higher pressures (1–2 atm), a strong KHP signal appears as the temperature is increased above 450 K. Definitive isomeric identification from measurements on the deuterated DEK isotopologues indicates the favored pathway produces a γ-KHP via resonance-stabilized alkyl, QOOH, and HOOPOOH radicals. Time-resolved measurements reveal the KHP formation becomes faster and signal more intense upon increasing temperature from

  6. Stereoselective construction of a beta-isopropenyl alcohol moiety at the C(2) and (3) of kallolide A and pinnatin a using a [2,3] Wittig rearrangement of cyclic furfuryl ethers.

    PubMed

    Tsubuki, Masayoshi; Takahashi, Kazunori; Honda, Toshio

    2003-12-26

    A stereocontrolled synthesis of anti- and syn-beta-isopropenyl alcohol moieties at the C(2)-C(3) positions of kallolide A and pinnatin A was accomplished employing the [2,3] Wittig rearrangement of (E)-and (Z)-cyclic furfuryl ethers 8. Enantioselective Wittig rearrangement of (E)- and (Z)-furfuryl ethers 8 using butyllithium and a chiral bis(oxazoline) was also examined to provide (2R,3R)-homoallylic alcohol anti-9 in up to 61% ee and (2R,3S)-syn-9 in up to 93% ee, respectively.

  7. Stereoselective Formation of Fully Substituted Ketone Enolates.

    PubMed

    Haimov, Elvira; Nairoukh, Zackaria; Shterenberg, Alexander; Berkovitz, Tiran; Jamison, Timothy F; Marek, Ilan

    2016-04-25

    The application of stereochemically defined acyclic fully substituted enolates of ketones to the enantioselective synthesis of quaternary carbon stereocenters would be highly valuable. Herein, we describe an approach leading to the formation of several new stereogenic centers through a combined metalation-addition of a carbonyl-carbamoyl transfer to reveal in situ stereodefined α,α-disubstituted enolates of ketone as a single stereoisomer. This approach could produce a series of aldol and Mannich products from enol carbamate with excellent diastereomeric ratios.

  8. A new reaction pathway other than the Criegee mechanism for the ozonolysis of a cyclic unsaturated ether

    NASA Astrophysics Data System (ADS)

    Tang, Shanshan; Du, Lin; Tsona, Narcisse T.; Zhao, Hailiang; Wang, Wenxing

    2017-08-01

    Biofuels are considered to be an environmental friendly alternative to fossil fuels. Furanic compounds have been considered as second generation biofuels as they can be produced from non-food biomass. However, the atmospheric behavior of such compounds is required to evaluate their potential to be used as biofuels. The matrix isolation technique combined with infrared spectroscopy has been used to study the ozonolysis mechanism of 2,5-dihydrofuran. A new reaction pathway that is different from the widely accepted Criegee mechanism has been found. Experimental and theoretical results show the evidence of the formation of a furan-H2O3 complex through a dehydrogenation process. The complex is trapped in the argon matrix and stabilized through hydrogen bonding interaction. Meanwhile, the conventional ozonolysis intermediates were also observed, including the primary ozonide, the Criegee intermediate and the secondary ozonide. The present study highlights the cases in which the Criegee mechanism is not the dominant pathway for the reactions of cyclic alkenes with ozone. The cyclic alkenes that can form an aromatic conjugated system by the dehydrogenation process may follow the new mechanism when react with ozone in the atmosphere.

  9. High-Throughput Screening of the Asymmetric Decarboxylative Alkylation Reaction of Enolate-Stabilized Enol Carbonates

    PubMed Central

    McDougal, Nolan T.; Virgil, Scott C.; Stoltz, Brian M.

    2010-01-01

    The use of high-throughput screening allowed for the optimization of reaction conditions for the palladium-catalyzed asymmetric decarboxylative alkylation reaction of enolate-stabilized enol carbonates. Changing to a non-polar reaction solvent and to an electron-deficient PHOX derivative as ligand from our standard reaction conditions improved the enantioselectivity for the alkylation of a ketal-protected,1,3-diketone-derived enol carbonate from 28% ee to 84% ee. Similar improvements in enantioselectivity were seen for a β-keto-ester derived- and an α-phenyl cyclohexanone-derived enol carbonate. PMID:21072327

  10. The evolution of the structural, vibrational and electronic properties of the cyclic ethers - on ring size. An ab initio study

    NASA Astrophysics Data System (ADS)

    Ford, Thomas A.

    2014-09-01

    The molecular structures, vibrational spectra and atomic charges of the alicyclic ethers containing from two to five carbon atoms have been determined by means of ab initio calculations, at the level of second order Møller-Plesset perturbation theory and using Dunning's augmented correlation-consistent polarized valence triple-zeta basis set. Two isomers of the oxetane, tetrahydrofuran and tetrahydropyran molecules have been identified and their relative energies determined. Structural properties, such as the COC bond angles and the CH bond lengths, are found to increase steadily with increasing ring size and with decreasing ionization energy. The mean CH2 stretching and bending wavenumbers exhibit the reverse behaviour, while the mean wavenumbers of the CH2 wagging and twisting modes follow the same trend as the structural features. The ring mode wavenumbers vary in a less regular way. The charges of the oxygen, α-carbon and axial and equatorial α- and β-hydrogen atoms also do not show systematic dependences on ring size or ionization energy. The trends in the values of these properties have been rationalized.

  11. Electroreductive dehalogenation of chlorinated aromatic ethers. Unexpected electrogenerated base catalyzed reactions

    SciTech Connect

    Kimura, Makoto; Miyahara, Hiroyoshi; Moritani, Noriyuki; Sawaki, Yasuhiko )

    1990-06-08

    The electroreductive dehalogenation of several mono- and polychlorinated aromatic ethers that serve as models of dioxins has been studied. The dechlorination was achieved by a simple constant-current electrolysis using a lead cathode in dimethylformamide. It was shown that 2,4,6-trichloroanisole undergoes successive dechlorination and the chlorine in the 2-position is selectively eliminated. Competitive reactions and cyclic voltammetric measurements suggested the increasing reactivity order of mono- < di- < trichloride for the reductive dechlorination. Use of allyl 2-chlorophenyl ether as a probe for radical cyclization indicated that free radical intermediates are of little importance. Thus, incipient radicals are immediately reduced to anionic intermediates. The electrolyses in the presence of deuterium oxide revealed proton sources for the present dechlorination. In these attempts, novel phenomena due to electrogenerated base (EGB) were found: di- and trichlorides underwent an unexpected overincorporation of deuterium in their dechlorinated products; a selective formation of Z-enol ethers from the allylic ethers was encountered. The mechanistic features of the present electroreductive dechlorination are discussed.

  12. A simple, nontoxic iron system for the allylation of zinc enolates.

    PubMed

    Jarugumilli, Gopala K; Cook, Silas P

    2011-04-15

    Diiron nonacarbonyl in combination with triphenylphosphine has been identified as a low-cost and environmentally benign catalyst system for the allylation of zinc enolates generated in situ from copper-catalyzed asymmetric conjugate addition reactions. The catalyst system provides the allylated product in modest to good yields at room temperature with unprecedented diastereoselectivity in cyclic enone systems. While triphenylphosphine was uniquely effective among the investigated ligands, the exact nature of the active catalytic species remains unknown.

  13. Marchantin A, a cyclic bis(bibenzyl ether), isolated from the liverwort Marchantia emarginata subsp. tosana induces apoptosis in human MCF-7 breast cancer cells.

    PubMed

    Huang, Wei-Jan; Wu, Chia-Li; Lin, Chia-Wei; Chi, Li-Ling; Chen, Pen-Yuan; Chiu, Chun-Jung; Huang, Chung-Yang; Chen, Chia-Nan

    2010-05-01

    Liverwort constituents have been reported to exert a broad spectrum of biological activities. In this study, we used a bioactivity-guided separation of an extract from the liverwort species Marchantia emarginata subsp. tosana to determine its anticancer activity. A high level of the active ingredient was isolated from this liverwort and its chemical structure was identified and characterized by various spectra. It was found to be identical to a well-known compound, marchantin A, a cyclic bisbibenzyl ether. However, no anticancer activities of this compound have previously been reported. We found that marchantin A efficiently induced cell growth inhibition in human MCF-7 breast cancer cells, with an IC(50) of 4.0microg/mL. Fluorescence microscopy and a Western blot analysis indicated that marchantin A actively induced apoptosis of MCF-7 cells. The levels of cleaved caspase-8, cleaved caspase-3, cleaved caspase-9, and cleaved poly (ADP ribose) polymerase (PARP) increased. However, the level of Bid markedly decreased in a dose- and time-dependent manner. We also evaluated the anticancer activities of marchantin A on the regulation of cell cycle regulators such as p21, p27, cyclin B1, and cyclin D1. The p21 and p27 gene expressions increased markedly while cyclin B1 and D1 gene expression decreased markedly by treatment with marchantin A. Many report demonstrated that liverwort was suggested to possess potent antioxidant activity. Our results indicate that marchantin A possesses free radical-scavenging activity (EC(50)=20microg/mL). Taken together, for the first time, the compound marchantin A from liverworts demonstrated to be a potent inducer of apoptosis in MCF-7 cells.

  14. Stereoselective synthesis of eight-membered cyclic ethers by tandem Nicholas reaction/ring-closing metathesis: a short synthesis of (+)-cis-Lauthisan.

    PubMed

    Ortega, Nuria; Martín, Tomás; Martín, Víctor S

    2006-03-02

    Cis-2,8-disubstituted oxocanes and the parent unsaturated precursors were prepared from the corresponding Co2(CO)6-cycloalkynic ethers. Key steps in such synthesis were the ether linkage formation by intermolecular Nicholas reaction, RCM of the suitable acyclic dienyl ether and montmorillonite K-10 induced isomerization of the complexed cycloalkyne. A short synthesis of (+)-cis-lauthisan taking advantage of the developed methodology is described.

  15. Propenyl ether monomers for photopolymerization

    DOEpatents

    Crivello, J.V.

    1996-10-22

    Propenyl ether monomers of formula A(OCH{double_bond}CHCH{sub 3}){sub n} wherein n is an integer from one to six and A is selected from cyclic ethers, polyether and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of the above formula together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

  16. Propenyl ether monomers for photopolymerization

    DOEpatents

    Crivello, James V.

    1996-01-01

    Propenyl ether monomers of formula V A(OCH.dbd.CHCH.sub.3).sub.n wherein n is an integer from one to six and A is selected from cyclic ethers, polyether and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of formula V together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

  17. Oxidative Coupling of Enolates, Enol Silanes and Enamines: Methods and Natural Product Synthesis

    PubMed Central

    Guo, Fenghai; Clift, Michael D.

    2013-01-01

    The oxidative coupling of enolates, enol silanes, and enamines provides a direct method for the construction of useful 1,4-dicarbonyl synthons. Despite being first reported in 1935, with subsequent important advances beginning in the 1970’s, the development of this powerful reaction into a reliable methodology was somewhat limited. In recent years, there have been a number of reports from several research groups demonstrating advances in several neglected areas of oxidative coupling. This microreview summarizes these new advances in methodology and provides an overview of recent natural product syntheses that showcase the power of these transformations. PMID:23471479

  18. Furanyl Cyclic Ethers: Single and Double Diastereoselectivity in the Synthesis of 2,4-di and 2,4,5-tri-substituted tetrahydropyrans.

    PubMed

    Cooper, Dennis A; Robbins, Emma; Tizzard, Graham J; Coles, Simon J; O'Brien, Matthew

    2017-02-28

    Combining the desymmetrization of a prochiral bis-hydroxymethyl group with the epimerization of a chiral furanyl ether in a single transformation, high levels of double diastereoselectivity have been achieved in a synthesis of 2,4,5-trisubstituted tetrahydropyrans which proceeds under thermodynamic control.

  19. Lactate Dehydrogenase Catalysis: Roles of Keto, Hydrated, and Enol Pyruvate

    ERIC Educational Resources Information Center

    Meany, J. E.

    2007-01-01

    Many carbonyl substrates of oxidoreductase enzymes undergo hydration and enolization so that these substrate systems are partitioned between keto, hydrated (gem-diol), and enol forms in aqueous solution. Some oxidoreductase enzymes are subject to inhibition by high concentrations of substrate. For such enzymes, two questions arise pertaining to…

  20. Lactate Dehydrogenase Catalysis: Roles of Keto, Hydrated, and Enol Pyruvate

    ERIC Educational Resources Information Center

    Meany, J. E.

    2007-01-01

    Many carbonyl substrates of oxidoreductase enzymes undergo hydration and enolization so that these substrate systems are partitioned between keto, hydrated (gem-diol), and enol forms in aqueous solution. Some oxidoreductase enzymes are subject to inhibition by high concentrations of substrate. For such enzymes, two questions arise pertaining to…

  1. Synthesis, optical and electrochemical properties of substituted 2-cinnamoyl-1, 3-indandione O-methyl ethers

    NASA Astrophysics Data System (ADS)

    Malina, Ilze; Kampars, Valdis; Turovska, Baiba

    2016-07-01

    Seven new 2-cinnamoyl-1,3-indandione (2CID) O-methyl ethers with different substituents (R = -H, -CH3, -OCH3, -N(C6H5)2, -N(CH2CH2CN)2, julolidyl, -N(CH3)2) in 4-position of the cinnamoyl moiety were synthesized. The methylation with dimethylsulfate occurred at the oxygen atom of the exocyclic enol group with high selectivity. The synthesized compounds were characterized by 1H, 13C NMR, IR, UV-Vis and luminescence spectroscopy, their electrochemical properties were investigated by cyclic voltammetry. The obtained results indicates that introducing an electron donating substituents in the 4-position of cinnamoyl moiety facilitates electrochemical oxidation, remarkably shifts absorption and emission bands to longer wavelengths, simultaneously increases extinction coefficient (ε). O-methyl ethers with strong electron donating groups (R = -N(C6H5)2, -N(CH2CH2CN)2, julolidyl, -N(CH3)2) in molecule are characterized by luminescence with maximum in range from 547 to 647 nm and absolute photoluminescence quantum yields from 0.02 to 0.32. Quantum yield (QY) of chromophore containing julolidyl fragment is solvent dependent. It was 0.32 in chloroform and decreased in other polar (ethanol, acetone) solvents.

  2. Tropospheric oxidation of cyclic unsaturated ethers in the day-time: Comparison of the reactions with Cl, OH and O3 based on the determination of their rate coefficients at 298 K

    NASA Astrophysics Data System (ADS)

    Alwe, H. D.; Walavalkar, M. P.; Sharma, A.; Dhanya, S.; Naik, P. D.

    2014-01-01

    The rate coefficients of the reactions of three unsaturated cyclic ethers, 2,5-dihydrofuran (2,5-DHF), 2,3-dihydrofuran (2,3-DHF), and 3,4-dihydropyran (3,4-DHP), with the major day-time tropospheric oxidants - OH (kOH) and O3(kO3), and that of 3,4-DHP with Cl atom (kCl) are determined using relative rate method, at 298 K. The values of kOH are (6.45 ± 1.69), (11.95 ± 2.79) and (11.38 ± 2.64) × 10-11 cm3 molecule-1 s-1 for 2,5-DHF, 2,3-DHF and 3,4-DHP, respectively and kO3 are (1.65 ± 0.31), (443.20 ± 79.0) and (31.36 ± 5.80) × 10-17 cm3 molecule-1 s-1 for 2,5-DHF, 2,3-DHF and 3,4-DHP, respectively. The value of kCl for 3,4-DHP is (6.15 ± 0.84) × 10-10 cm3 molecule-1 s-1. The dominant pathway of tropospheric degradation of 2,5-DHF is the reaction with OH, whereas that of 2,3-DHF is the reaction with O3. Reaction with both OH and O3 are equally important in the case of 3,4-DHP. Under the conditions of marine boundary layer, the reaction with Cl atom is important in the tropospheric degradation of 2,5-DHF and 3,4-DHP, but insignificant in the case of 2,3-DHF (only 1.8%). The estimated tropospheric lifetimes in the day-time are 2.0, 0.08 and 0.62 h for 2,5-DHF, 2,3-DHF and 3,4-DHP respectively. The presence of O atom, unsaturation, conjugation etc. influences the rate coefficients in a complex manner. However, there is a good correlation of kOH with HOMO energy, which further improves by treating the molecules separately, either as ethers and hydrocarbons, or as cyclic and acyclic molecules. The values of kO3 of these ethers fit very well with the straight line regression derived for simple alkenes with their HOMO energy, except 2,3-DHF, which has a high strain enthalpy. The values of kCl also show a similar trend of increase with HOMO energy, but the correlation is not as good as that of kOH.

  3. Room temperature rechargeable magnesium batteries with sulfur-containing composite cathodes prepared from elemental sulfur and bis(alkenyl) compound having a cyclic or linear ether unit

    NASA Astrophysics Data System (ADS)

    Itaoka, Kanae; Kim, In-Tae; Yamabuki, Kazuhiro; Yoshimoto, Nobuko; Tsutsumi, Hiromori

    2015-11-01

    Room temperature rechargeable magnesium (Mg) batteries are constructed from Mg as a negative material, sulfur (S)-containing composite prepared from elemental sulfur and the bis(alkenyl) compound having a crown ether unit (BUMB18C6) or linear ether unit (UOEE) as a positive material and the simple electrolyte (0.7 mol dm-3 Mg[N(SO2CF3)2]2-triglyme (G3) solution). The reaction between molten S and the bis(alkenyl) compound (BUMB18C6 or UOEE) provides the sulfur-containing composite, S-BUMB18C6 or S-UOEE. Both of the sulfur-containing composites are electrochemically active in the Mg salt-based electrolyte, acetonitrile- or G3- Mg[N(SO2CF3)2]2 electrolyte. The first discharge capacity of the test cells with the sulfur-containing composite is 460 Ah kg-1 (per the weight of sulfur in the composite) with the S-BUMB18C6 electrode and 495 Ah kg-1 with the S-UOEE electrode. According to the continuous charge-discharge cycle tests (at 10th cycle), the discharge capacity of the test cell with the S-BUMB18C6 electrode (68.1 Ah kg-1) is higher than that with the S-UOEE electrode (0.18 Ah kg-1). The crown ether units in the S-BUMB18C6 composite may create ion-conducting paths in the cathode, prevent rise in the internal resistance of the cathode, and provide better cycle performance of the test cells with the S-BUMB18C6 composite electrode than that with the S-UOEE electrode.

  4. Synthesis and Antioxidant Properties of an Unnatural Plasmalogen Analogue Bearing a trans O-Vinyl Ether Linkage

    PubMed Central

    Lankalapalli, Ravi S.; Eckelkamp, Joseph T.; Sircar, Debajit; Ford, David A.; Subbaiah, Papasani V.; Bittman, Robert

    2009-01-01

    To assess the antioxidant behavior of trans-1, we first synthesized trans-allyl ether 4 by opening an (S)-glycidol derivative with an (E)-alk-2-en-ol, and then produced the unnatural E-enol ether 1 by a stereoselective iridium(I)-catalyzed olefin isomerization. Natural cis-1 was preferentially degraded by HOCl and was more protective than trans-1 against lipid peroxidation induced by a free-radical initiator, demonstrating that the geometry of the 1’-alkenyloxy bond participates in the antioxidant defensive role of 1. PMID:19499908

  5. Marchantin M trimethyl ether.

    PubMed

    Mombrú, A W; Suescun, L; Pandolfi, E; Seoane, G; López, G; Mariezcurrena, R

    2000-11-01

    The title macrocycle, C(31)H(30)O(5), is comprised of two bibenzyl ether moieties linked cyclically by spacers which each consist of two-carbon alkyl chains. The observed conformation of the macrocycle may be partly stabilized by intramolecular C-H.O close contacts. The packing appears to be directed by van der Waals forces. This work explains the occurrence of a signal found in the (1)H NMR spectra of both marchantinquinone and marchantin M trimethyl ether at delta = 5. 49 and 5.56 p.p.m., respectively. The shift in the position of the expected peak can be explained by the proximity of an H atom belonging to one of the aromatic rings to another ring in the same molecule.

  6. A new alternative to expandable pedicle screws: Expandable poly-ether-ether-ketone shell.

    PubMed

    Demir, Teyfik

    2015-05-01

    Screw pullout is a very common problem in the fixation of sacrum with pedicle screws. The principal cause of this problem is that the cyclic micro motions in the fixation of sacrum are higher than the other regions of the vertebrae that limit the osteo-integration between bone and screw. In addition to that, the bone quality is very poor at sacrum region. This study investigated a possible solution to the pullout problem without the expandable screws' handicaps. Newly designed poly-ether-ether-ketone expandable shell and classical pedicle screws were biomechanically compared. Torsion test, pullout tests, fatigue tests, flexion/extension moment test, axial gripping capacity tests and torsional gripping capacity tests were conducted in accordance with ASTM F543, F1798 and F1717. Standard polyurethane foam and calf vertebrae were used as embedding medium for pullout tests. Classical pedicle screw pullout load on polyurethane foam was 564.8 N compared to the failure load for calf vertebrae's 1264 N. Under the same test conditions, expandable poly-ether-ether-ketone shell system's pullout loads from polyurethane foam and calf vertebrae were 1196.3 and 1890 N, respectively. The pullout values for expandable poly-ether-ether-ketone shell were 33% and 53% higher than classical pedicle screw on polyurethane foam and calf vertebrae, respectively. The expandable poly-ether-ether-ketone shell exhibited endurance on its 90% of yield load. Contrary to poly-ether-ether-ketone shell, classical pedicle screw exhibited endurance on 70% of its yield load. Expandable poly-ether-ether-ketone shell exhibited much higher pullout performance than classical pedicle screw. Fatigue performance of expandable poly-ether-ether-ketone shell is also higher than classical pedicle screw due to damping the micro motion capacity of the poly-ether-ether-ketone. Expandable poly-ether-ether-ketone shell is a safe alternative to all other expandable pedicle screw systems on mechanical perspective.

  7. Stereoelectronic, torsional, and steric effects on rates of enolization of ketones.

    PubMed

    Behnam, S M; Behnam, S E; Ando, K; Green, N S; Houk, K N

    2000-12-29

    The stereoselectivities of base-catalyzed enolizations of ketones have been studied by quantum mechanical methods. Transition structures of exo and endo deprotonation of camphor, norcamphor, and dehydronorcamphor have been located with two model bases. Stereoelectronic, torsional, and steric effects on activation energies were assessed. These calculations demonstrate the importance of torsional strain between partial bonds and vicinal bonds on the rates of deprotonation and on related reactions involving the formation of enolates or reactions of enols and enolates.

  8. Si-free enolate Claisen rearrangements of enamido substrates.

    PubMed

    Harker, Wesley R R; Carswell, Emma L; Carbery, David R

    2012-02-21

    α-Alkyl β-amino esters are available in high diastereoselectivity through a silicon-free Claisen enolate [3,3]-sigmatropic rearrangement of enamide esters. Optimisation studies have probed the crucial role of the initial enolisation and the nature of the enamide N-centre. The demonstration of chirality transfer and the formation of β-proline systems, is also presented.

  9. Substituent Effects on Keto-Enol Equilibria Using NMR Spectroscopy

    ERIC Educational Resources Information Center

    Manbeck, Kimberly A.; Boaz, Nicholas C.; Bair, Nathaniel C.; Sanders, Allix M. S.; Marsh, Anderson L.

    2011-01-01

    In this extension to a classic physical chemistry experiment, students record the proton nuclear magnetic resonance spectra of the [beta]-diketones 2,4-pentanedione, 3-methyl-2,4-pentanedione, and 3-chloro-2,4-pentanedione to investigate the effect of substituents on keto-enol tautomerization equilibria. From the integrated intensities of keto and…

  10. Lactate Dehydrogenase Catalysis: Roles of Keto, Hydrated, and Enol Pyruvate

    NASA Astrophysics Data System (ADS)

    Meany, J. E.

    2007-09-01

    Many carbonyl substrates of oxidoreductase enzymes undergo hydration and enolization so that these substrate systems are partitioned between keto, hydrated (gem-diol), and enol forms in aqueous solution. Some oxidoreductase enzymes are subject to inhibition by high concentrations of substrate. For such enzymes, two questions arise pertaining to enzyme "substrate" interactions: (i) which form of the substrate system serves as the preferential substrate and (ii) which form acts to inhibit the enzyme? Thus the relative concentrations of the forms of these substrate systems (keto, hydrated, enol) may provide a form of metabolic control. In this light, the present article considers the reduction of pyruvate by lactate dehydrogenase in the presence of NADH. This reaction is inhibited by relatively high concentrations of pyruvate and the physiological significance of this inhibition has been a subject of controversy for many years. Summarized in this article are data from the literature pertaining to the interactions of keto, hydrated, and enol pyruvate with lactate dehydrogenase. Biochemistry instructors and their students are invited to review such pertinent articles so that they also may evaluate the possibility that the "substrate" inhibition of the isoenzymes in the heart muscle may be, under certain conditions, relevant as a form of metabolic control.

  11. Substituent Effects on Keto-Enol Equilibria Using NMR Spectroscopy

    ERIC Educational Resources Information Center

    Manbeck, Kimberly A.; Boaz, Nicholas C.; Bair, Nathaniel C.; Sanders, Allix M. S.; Marsh, Anderson L.

    2011-01-01

    In this extension to a classic physical chemistry experiment, students record the proton nuclear magnetic resonance spectra of the [beta]-diketones 2,4-pentanedione, 3-methyl-2,4-pentanedione, and 3-chloro-2,4-pentanedione to investigate the effect of substituents on keto-enol tautomerization equilibria. From the integrated intensities of keto and…

  12. Keto-Enol Tautomerizations Catalyzed by Water and Carboxylic Acids

    NASA Astrophysics Data System (ADS)

    da Silva, G.

    2009-12-01

    The ability of weakly-bound complexes to influence the kinetics of gas phase reactions, particularly in atmospheric chemistry, has long been speculated. This study uses quantum chemistry and statistical reaction rate theory to identify that bound water molecules can significantly reduce barriers to intramolecular hydrogen shift reactions, via a double-hydrogen-shift mechanism. The bound water molecule directly participates in the hydrogen shift reaction, exchanging a H atom with its counterpart. For the vinyl alcohol to acetaldehyde keto-enol tautomerization this mechanism cuts the reaction barrier approximately in half, reducing it by over 30 kcal mol-1. In contrast, while a non-participatory ‘bystander’ water molecule also reduces the hydrogen shift barrier, it is only by around 3 kcal/mol. When a carboxylic acid replaces water in the double-hydrogen-shift mechanism the barrier to keto-enol tautomerization is decimated, reduced to less than 6 kcal/mol (around 15 kcal/mol in the reverse direction). This results from reduced strain in the hydrogen shift transition state, and achieves enol lifetimes in the troposphere that become short on relevant timescales. Rapid enol to ketone isomerizations are currently required to explain the oxidation products of isoprene. The wider significance of rapid hydrogen shift reactions in atmospherically relevant molecules and radicals is also explored.

  13. Enantioselective synthesis of allenylenol silyl ethers via chiral lithium amide mediated reduction of ynenoyl silanes and their Diels-Alder reactions.

    PubMed

    Sasaki, Michiko; Kondo, Yasuhiro; Moto-ishi, Ta-ichi; Kawahata, Masatoshi; Yamaguchi, Kentaro; Takeda, Kei

    2015-03-06

    An enantioselective Meerwein-Ponndorf-Verley-type reduction of ynenoylsilanes by a chiral lithium amide followed by a Brook rearrangement and anti-mode protonation across conjugated 1,3-enynes provides allene derivatives bearing a 2-siloxyvinyl moiety in high enantioselectivity. The E/Z geometry of enol silyl ethers is controlled by the geometry of the starting enyne moiety. Thus, (E)- and (Z)-enol silyl ethers are obtained from (Z)- and (E)-ynenoylsilans, respectively. The 2-siloxyvinylallene products can participate in Diels-Alder reactions with reactive dienophiles such as PTAD, which can be achieved in a one-pot operation from ynenoylsilanes.

  14. Nonabromodiphenyl ether

    Integrated Risk Information System (IRIS)

    Nonabromodiphenyl ether ; CASRN 63936 - 56 - 1 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarc

  15. Pentabromodiphenyl ether

    Integrated Risk Information System (IRIS)

    Pentabromodiphenyl ether ; CASRN 32534 - 81 - 9 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncar

  16. Octabromodiphenyl ether

    Integrated Risk Information System (IRIS)

    Octabromodiphenyl ether ; CASRN 32536 - 52 - 0 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarc

  17. Tribromodiphenyl ether

    Integrated Risk Information System (IRIS)

    Tribromodiphenyl ether ; CASRN 49690 - 94 - 0 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarci

  18. Hexabromodiphenyl ether

    Integrated Risk Information System (IRIS)

    Hexabromodiphenyl ether ; CASRN 36483 - 60 - 0 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarc

  19. Ethyl ether

    Integrated Risk Information System (IRIS)

    Ethyl ether ; CASRN 60 - 29 - 7 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic Effect

  20. Tetrabromodiphenyl ether

    Integrated Risk Information System (IRIS)

    Tetrabromodiphenyl ether ; CASRN 40088 - 47 - 9 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncar

  1. Process for making propenyl ethers and photopolymerizable compositions containing them

    DOEpatents

    Crivello, J.V.

    1996-01-23

    Propenyl ether monomers of formula A(OCH{double_bond}CHCH{sub 3}){sub n} (V) wherein n is an integer from one to six and A is selected from cyclic ethers, polyether, and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of formula V together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

  2. Process for making propenyl ethers and photopolymerizable compositions containing them

    DOEpatents

    Crivello, James V.

    1996-01-01

    Propenyl ether monomers of formula V A(OCH.dbd.CHCH.sub.3).sub.n wherein n is an integer from one to six and A is selected from cyclic ethers, polyether and alkanes are disclosed. The monomers are readily polymerized in the presence of cationic photoinitiators, when exposed to actinic radiation, to form poly(propenyl ethers) that are useful for coatings, sealants, varnishes and adhesives. Compositions for preparing polymeric coatings comprising the compounds of formula V together with particular cationic photoinitiators are also disclosed, as are processes for making the monomers from allyl halides and readily available alcohols. The process involves rearranging the resulting allyl ethers to propenyl ethers.

  3. Selectively deuterated and optically active cyclic ethers

    SciTech Connect

    Kawakami, Y.; Asai, T.; Umeyama, K.; Yamashita, Y.

    1982-08-27

    The synthesis of selectively deuterated epihalohydrins (F, Cl, Br, I) and 3,3-bis(chloromethyl)-d/sub 2/)oxetane and some observations on the stereochemistry of each transformation are reported. Further, the synthesis of optically active epihalohydrins, especially the optically active epifluorohydrin, from (S)-glycerol 1,2-acetonide ((S)-2), using mainly KX-18-CR-6 (X = F, Br, I), is reported. This is the first report on the synthesis of optically active epifluorohydrin. The direct halogenation of the presynthesized optically active epichlorohydrin with the same reagents gave the racemized products. The selectively deuterated or optically active compounds reported herein are expected to find a variety of uses in organic chemistry.

  4. Highly efficient palladium-catalyzed hydrostannation of ethyl ethynyl ether.

    PubMed

    Andrews, Ian P; Kwon, Ohyun

    2008-12-08

    The palladium-catalyzed hydrostannation of acetylenes is widely exploited in organic synthesis as a means of forming vinyl stannanes for use in palladium-catalyzed cross-coupling reactions. Application of this methodology to ethyl ethynyl ether results in an enol ether that is challenging to isolate from the crude reaction mixture because of incompatibility with typical silica gel chromatography. Reported here is a highly efficient procedure for the palladium-catalyzed hydrostannation of ethyl ethynyl ether using 0.1% palladium(0) catalyst and 1.0 equiv of tributyltin hydride. The product obtained is a mixture of regioisomers that can be carried forward with exclusive reaction of the beta-isomer. This method is highly reproducible; relative to previously reported procedures, it is more economical and involves a more facile purification procedure.

  5. Chemiexcitation induced proton transfer: enolate oxyluciferin as the firefly bioluminophore.

    PubMed

    Pinto da Silva, Luís; Esteves da Silva, Joaquim C G

    2015-02-12

    Firefly bioluminescence is a phenomenon that attracts attention from the research community because of complex challenges for fundamental investigation, as well as diverse opportunities for practical application. Here we have studied the potential deprotonation of firefly oxyluciferin by using a theoretical approach in an enzymatic-like microenvironment in chemiexcited proton transfer involving adenosine 5'-monophosphate. We have uncovered a reaction route that links the evidence that the light-emitter is an anionic molecule while it is chemiexcited in its neutral form. Moreover, the results indicated that the anionic bioluminophore is the enolate anion and not the ketonic one. Further calculations supported this identification of the light-emitter: the spectrum of resulting enolate anion covers the entire yellow-green/red bioluminescence range, which is in line with the experimental findings regarding firefly multicolor bioluminescence.

  6. A Reinvestigation of the Reactions of Enolate Anions with Cyclotriphosphazenes.

    DTIC Science & Technology

    1981-09-09

    PERFORMING ORG. REPORT NUMBER 7. AUTNOR(e) - . CONTRACT OR GRANT NUMESER(.) Christopher W. Allen, Kolikkara Ramachandran N001477C-0605 Randall P. Bright and...REACTIONS OF ENOLATE ANIONS WITH CYCLOTRIPHOSPHAZENES Christopher W. Allen, Kolikkara Ramachandran , Randall P. Bright and Jonathan C. Shaw Department...four days. The solvent was re- moved and the residue extracted with hexane. Following filtration and removal of hexane, 10.2 g of a pale yellow liquid

  7. Structural evidence for an enolate intermediate in GFP fluorophore biosynthesis.

    PubMed

    Barondeau, David P; Tainer, John A; Getzoff, Elizabeth D

    2006-03-15

    The Aequorea victoria green fluorescent protein (GFP) creates a fluorophore from its component amino acids Ser65, Tyr66, and Gly67 through a remarkable post-translational modification, involving spontaneous peptide backbone cyclization, dehydration, and oxidation reactions. Here we test and extend the understanding of fluorophore biosynthesis by coupling chemical reduction and anaerobic methodologies with kinetic analyses and protein structure determination. Two high-resolution structures of dithionite-treated GFP variants reveal a previously uncharacterized enolate intermediate form of the chromophore that is viable in generating a fluorophore (t1/2 = 39 min-1) upon exposure to air. Isolation of this enolate intermediate will now allow specific probing of the rate-limiting oxidation step for fluorophore biosynthesis in GFP and its red fluorescent protein homologues. Such targeted characterizations may lead to the design of faster maturing proteins with enhanced applications in biotechnology and cell biology. Moreover, our results reveal how the GFP protein environment mimics enzyme systems, by stabilizing an otherwise high energy enolate intermediate to achieve its post-translational modification.

  8. Rubisco Mechanism: Dissection of the Enolization Partial Reaction. Final Report

    SciTech Connect

    Hartman, F. C.

    2003-06-11

    To test experimentally, the prior theoretical deduction that active-site residue Lys166 of ribulose-bisphosphate carboxylase participates in the carboxylation step of overall catalysis, site-directed mutants and chemically rescued site-directed mutants were characterized by kinetics and product analysis. Although position-166 mutants are able to catalyze normal enolization of ribulose bisphosphate, the enediol intermediate does not undergo carboxylation but rather eliminates phosphate. Furthermore, the chemically rescued mutant (aminoethylation of the severely impaired Lys66Cys mutant) generates a highly active mimic, which displays an enhanced carboxylation/oxygenation partition ratio. These two distinct lines of experimentation document a crucial role of Lys166 in carboxylation and in discrimination between CO{sub 2} and O{sub 2}. To ascertain whether Lys166 functions as an acid or base in facilitation of enolization, the chemically rescued mutant bearing {sup 15}N was titrated by NM R. From pH 6.5-9.5, the amino group of Lys166 remains unprotonated, indicating that it promotes enolization by hydrogen bonding to the ketone group of the substrate.

  9. A transferable force field to predict phase equilibria and surface tension of ethers and glycol ethers.

    PubMed

    Ferrando, Nicolas; Lachet, Véronique; Pérez-Pellitero, Javier; Mackie, Allan D; Malfreyt, Patrice; Boutin, Anne

    2011-09-15

    We propose a new transferable force field to simulate phase equilibrium and interfacial properties of systems involving ethers and glycol ethers. On the basis of the anisotropic united-atom force field, only one new group is introduced: the ether oxygen atom. The optimized Lennard-Jones (LJ) parameters of this atom are identical whatever the molecule simulated (linear ether, branched ether, cyclic ether, aromatic ether, diether, or glycol ether). Accurate predictions are achieved for pure compound saturated properties, critical properties, and surface tensions of the liquid-vapor interface, as well as for pressure-composition binary mixture diagrams. Multifunctional molecules (1,2-dimethoxyethane, 2-methoxyethanol, diethylene glycol) have also been studied using a recently proposed methodology for the calculation of the intramolecular electrostatic energy avoiding the use of additional empirical parameters. This new force field appears transferable for a wide variety of molecules and properties. It is furthermore worth noticing that binary mixtures have been simulated without introducing empirical binary parameters, highlighting also the transferability to mixtures. Hence, this new force field gives future opportunities to simulate complex systems of industrial interest involving molecules with ether functions.

  10. Synthesis of 1,4‐Diketones from β‐Oxo Esters and Enol Acetates by ­Cerium‐Catalyzed Oxidative Umpo­lung Reaction†

    PubMed Central

    Geibel, Irina

    2016-01-01

    Abstract Cyclic β‐oxo esters are converted with enol acetates in a cerium‐catalyzed, oxidative Umpolung reaction to furnish 1,4‐diketones with up to 95 % yield. Atmospheric oxygen is the oxidant in this process, which can be regarded as ideal from economic and ecological points of view. Further advantages of this new C–C coupling reaction are its operational simplicity and the application of nontoxic and inexpensive CeCl3 ·7H2O as precatalyst.

  11. The keto/enol tautomerism of selenoformamide and telluroformamide

    NASA Astrophysics Data System (ADS)

    Dapprich, Stefan; Frenking, Gernot

    1993-04-01

    Ab initio calculations at the MP4(SDTQ) level of theory using effective core potentials for Se and Te and all-electron wave-functions for the other atoms, with inclusion of zero-point energies, predict that the keto tautomers of thioformamide, selenorformamide and telluroformamide are 10-13 kcal/mol lower in energy than the corresponding enol forms. Unlike a recent theoretical study by Leszczynski, Kwiatkowski and Leszczynska the calculations do not show that the relative energies of the tautomeric forms of selenoformamide change drastically when the core electrons are included in the correlation treatment.

  12. Method of Continuous Variation: Characterization of Alkali Metal Enolates Using 1H and 19F NMR Spectroscopies

    PubMed Central

    2015-01-01

    The method of continuous variation in conjunction with 1H and 19F NMR spectroscopies was used to characterize lithium and sodium enolates solvated by N,N,N′,N′-tetramethylethyldiamine (TMEDA) and tetrahydrofuran (THF). A strategy developed using lithium enolates was then applied to the more challenging sodium enolates. A number of sodium enolates solvated by TMEDA or THF afford exclusively tetramers. Evidence suggests that TMEDA chelates sodium on cubic tetramers. PMID:24915602

  13. Palladium-Catalyzed α-Arylation of Zinc Enolates of Esters: Reaction Conditions and Substrate Scope

    PubMed Central

    Hama, Takuo; Ge, Shaozhong; Hartwig, John F.

    2013-01-01

    The intermolecular α-arylation of esters by palladium-catalyzed coupling of aryl bromides with zinc enolates of esters is reported. Reactions of three different types of zinc enolates have been developed. α-Arylation of esters occurs in high yields with isolated Reformatsky reagents, with Reformatsky reagents generated from α-bromo esters and activated zinc, and with zinc enolates generated by quenching lithium enolates of esters with zinc chloride. The use of zinc enolates, instead of alkali metal enolates, greatly expands the scope of the arylation of esters. The reactions occur at room temperature or at 70 °C with bromoarenes containing cyano, nitro, ester, keto, fluoro, enolizable hydrogen, hydroxyl or amino functionality and with bromopyridines. The scope of esters encompasses acyclic acetates, propionates, and isobutyrates, α-alkoxyesters, and lactones. The arylation of zinc enolates of esters was conducted with catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) or the highly reactive dimeric Pd(I) complex {[P(t-Bu)3]PdBr}2. PMID:23931445

  14. Experimental and Computational Evidence of the Biradical Structure and Reactivity of Titanium(IV) Enolates.

    PubMed

    Heras, Carlos; Gómez-Palomino, Alejandro; Romea, Pedro; Urpí, Fèlix; Bofill, Josep Maria; Moreira, Ibério de P R

    2017-09-01

    Quantum chemical calculations have unveiled the unexpected biradical character of titanium(IV) enolates from N-acyl oxazolidinones and thiazolidinethiones. The electronic structure of these species therefore involves a valence tautomerism consisting of an equilibrium between a closed shell (formally Ti(IV) enolates) and an open shell, biradical, singlet (formally Ti(III) enolates) electronic states, whose origin is to be basically found in changes of the Ti-O distance. Spectroscopic studies of the intermediate species lend support to such a model, which also turns out to be crucial for a better understanding of the overall reactivity of titanium(IV) enolates. In this context, a thorough computational analysis of the radical addition of titanium(IV) enolates from N-acyl oxazolidinones to TEMPO has permitted us to suggest an entire mechanism, which accounts for the experimental details and the diastereoselectivity of the process. All together, this evidence highlights the relevance of biradical intermediates from titanium(IV) enolates and may be a useful contribution to the foundations of a more insightful comprehension of the structure and reactivity of titanium(IV) enolates.

  15. Enantioselective synthesis of alpha-terpineol and nephthenol by intramolecular acyloxazolidinone enolate alkylations.

    PubMed

    Jin, Yinghua; Coates, Robert M

    2006-07-21

    Enolate anions generated from norterpenyl bromides bearing oxazolidinone chiral auxiliaries at the chain termini underwent efficient, stereo-biased cyclizations to form 6- and 14-membered rings in novel synthetic routes to alpha-terpineol and nephthenol enantiomers.

  16. Samarium(II)-mediated linker cleavage-cyclization in fluorous synthesis: reactions of samarium enolates.

    PubMed

    James, Karen M; Willetts, Nigel; Procter, David J

    2008-03-20

    SmI2 has been used to cleave a sulfur linker and trigger cyclizations in strategies for the traceless fluorous synthesis of N-heterocycles. The studies give further insights into the reactivity of samarium enolates.

  17. Ketonization of enols in aqueous solution: is carbon protonation always rate-determining?

    PubMed

    Pelliccioli, Anna Paola; Šebej, Peter; Wirz, Jakob

    2012-06-01

    The pH-rate profiles for the ketonization of the (E)- and (Z)-photoenols of o-methylacetophenone (MA) in aqueous solution were determined by nanosecond laser flash photolysis. Carbon protonation of the enol anions of MA by solvent water is exceptionally fast, k(0)'(K)≈ 2.0 × 10(7) s(-1), too fast to permit establishment of the acid-base equilibrium on the enol oxygen prior to ketonization. Analysis of the pH-rate profile of the (E)-enol using the common assumption of rate-determining carbon protonation would lead to an erroneous value for the acidity constant of that enol, pK(a,c)(E) = 11.3, which is too high by about two pK units.

  18. Stereospecific alkylations of molybdenum(II) enolates from eta/sup 2/-aceyl complexes

    SciTech Connect

    Rusik, C.A.; Templeton, J.L.

    1986-07-23

    The authors report here spectroscopic characterization and alkylation and aldol reactions of these Mo(II) enolate complexes as well as the structure of one diastereomer of (Tp')Mo(CO)(P(OPh)/sub 3/)(C(O)CHMEBz), Tp' = hydridotris(3,5-dimethylpyrazolyl)borate). Aldol condensation reactions of transition-metal enolates have not been reported as frequently as alkylation reactions. The authors find that metal enolate reacts with benzaldehyde to yield a deep indigo eta/sup 2/-enone derivative resulting from dehydration of the initial ..beta..-hydroxy eta/sup 2/-acyl product. The formation of (Tp')CO)/sub 2/Mo(eta/sup 2/-C(O)CMe = CHPh) (9) suggests that a range of electrophiles will react with these molybdenum(II) enolate reagents.

  19. Configurational and conformational preferences in oximes and oxime carbanions. Ab initio study of the syn effect in reactions of oxyimine enolate equivalents

    SciTech Connect

    Glaser, R.; Streitwieser, A. )

    1989-09-13

    Geometries and relative energies of stationary structures of several conformers of geometrical isomers of NO s-trans-configured acetaldoxime are reported. The calculated energies and geometries agree well with comparable experimental data. Effects of the theoretical model on the NO band lengths are discussed for formaldoxime. The theoretical results suggest that the regiochemistry of enolate equivalents of oxyimines in dissociating solvents is due to the thermodynamic syn preference of the anions. Syn/anti isomerization of the anions (E{sub a} < 26 kcal mol{sup {minus}1}) is rapid even at low temperatures. In contrast, the anti preference of the radicals of acetaldoxime indicates that the formation of the syn products in oxidative coupling reactions of the anions of oxime ethers is a kinetic effect.

  20. Binding catalysis and inhibition by metal ions and protons in the enolization of phenylacetylpyrazine.

    PubMed

    Collot, Anne-Gaelle; Courtney, Michael; Coyne, Dara; Eustace, Stephen E; More O'Ferrall, Rory A

    2009-05-01

    A study of the enolization of phenylacetylpyrazine (PzCOCH(2)Ph) catalyzed by acid, base and metal ions in aqueous solution shows, unusually, that metal ions are more effective catalysts than protons, e.g., for zinc k(Zn)/k(H) = 600. Such behavior contrasts with that of the structurally related phenacylpyridine (PyCH(2)COPh) for which k(Zn)/k(H) = 0.0065. To interpret this difference, equilibrium constants for the tautomerization of phenylacetylpyrazine and for binding of protons and metal ions to its keto tautomer and enolate anion have been measured or estimated and are compared with existing measurements for phenacylpyridine. A tautomeric constant, K(E) = 1.2 x 10(-3) (pK(E) = 2.9), is derived by combining forward and reverse rate constants for enolization measured, respectively, by iodination or bromination of the keto tautomer and relaxation of the less stable enol. For the keto tautomer, NMR measurements yield a pK(a) = -0.90 for N-protonation, and spectrophotometric measurements give pK(a) = 11.90 for ionization to an enolate anion. For the enol, pK(a) values of 0.44 and -4.80 for mono- and diprotonation are obtained from the pH profile for ketonization and absorbance measurements for the transient enol reactant. Binding constants for metal ions (Cu(2+), Ni(2+), Zn(2+), Co(2+), and Cd(2+)) are derived from the saturation of their catalysis of the ketonization reaction. It is found that ketonization is efficiently catalyzed by metal ions but inhibited by acid. These findings, and the striking difference from phenacylpyridine, are ascribed to differences in thermodynamic driving force arising from stronger binding of the proton to the more basic pyridine than pyrazine nitrogen atom in both the reactant keto tautomer and in the enaminone or zwitterion product of the rate-determining (proton transfer) step of the enolization.

  1. Malonic acid half oxyesters and thioesters: solvent-free synthesis and DFT analysis of their enols.

    PubMed

    Bew, Sean P; Stephenson, G Richard; Rouden, Jacques; Martinez-Lozano, Luis A; Seylani, Haseena

    2013-08-02

    A much improved synthetic route to malonic acid half thioesters (MAHTs) and oxyesters (MAHOs), the easy incorporation of deuterium labeling expecially in MAHTs, and an unexpectedly large difference in enolization chemistry between MAHTs and MAHOs are reported. Density functional theory calculations explore the origins of this difference and identify an additional MAHT molecular orbital which increases delocalization between sulfur and the enol in both cisoid and transoid forms.

  2. Exploiting the Imidazolium Effect in Base-free Ammonium Enolate Generation: Synthetic and Mechanistic Studies.

    PubMed

    Young, Claire M; Stark, Daniel G; West, Thomas H; Taylor, James E; Smith, Andrew D

    2016-11-07

    N-Acyl imidazoles and catalytic isothiourea hydrochloride salts function as ammonium enolate precursors in the absence of base. Enantioselective Michael addition-cyclization reactions using different α,β-unsaturated Michael acceptors have been performed to form dihydropyranones and dihydropyridinones with high stereoselectivity. Detailed mechanistic studies using RPKA have revealed the importance of the "imidazolium" effect in ammonium enolate formation and have highlighted key differences with traditional base-mediated processes.

  3. Poly(arylene ether)s containing pendent ethynyl groups

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Jensen, Brian J. (Inventor)

    1996-01-01

    Poly(arylene ether)s containing pendent ethynyl and substituted ethynyl groups and poly(arylene ether) copolymers containing pendent ethynyl and substituted ethynyl groups are readily prepared from bisphenols containing ethynyl and substituted ethynyl groups. The resulting polymers are cured up to 350.degree. C. to provide crosslinked poly(arylene ether)s with good solvent resistance, high strength and modulus.

  4. Integrated catalytic and electrocatalytic conversion of substituted phenols and diaryl ethers

    SciTech Connect

    Song, Yang; Chia, Shao H.; Sanyal, Udishnu; Gutierrez, Oliver Y.; Lercher, Johannes A.

    2016-10-17

    Electrocatalytic hydrogenation and catalytic thermal hydrogenation of substituted phenols and diaryl ethers were studied on carbon-supported Rh. For electrocatalytic and catalytic thermal hydrogen addition reactions, the dominant reaction pathway is hydrogenation to cyclic alcohols and cycloalkyl ethers. The presence of substituting methyl or methoxy groups led to lower rates compared to unsubstituted phenol or diphenyl ether. Methoxy or benzyloxy groups, however, undergo C-O bond cleavage via hydrogenolysis and hydrolysis (minor pathway).

  5. A Comparative Study of Dialkylboron Chlorides and Triflates for the Enolization of Ketones. The Controlled Stereospecific Synthesis of Either (E)- or (Z)-Enol Borinates

    DTIC Science & Technology

    1988-05-12

    Wetherill Laboratories of Chemistry Purdue University, West Lafayette, Indiana 47907, U.S.A. Ketone enolates are useful intermediates in organic ... synthesis . Indeed, their nucleophilic properties are intensively applied to form carbon-carbon bonds in a number of important reactions.1 ,2 Consequently

  6. Tautomer-selective derivatives of enolate, ketone and enaminone by addition reaction of picolyl-type anions with nitriles

    NASA Astrophysics Data System (ADS)

    Bai, Jianliang; Wang, Peng; Cao, Wei; Chen, Xia

    2017-01-01

    We describe an efficient for the synthesis of compounds of tautomeric β-pyridyl/quinolyl-enol, -ketone, -enaminone, which were finally characterized by standard methods like NMR, IR or SCXRD. The addition reaction of lithiated intermediates of picoline, 2-ethylpyridine and 2-methylquinoline, respectively, with nitriles followed by acid hydrolysis afforded the corresponding tautomeric compounds of enol, ketone and emaminone. Interestingly, treatment of 2-methylpyridine or 2-ethylpyridine with nitriles, respectively, yielded mostly β-pyridyl ketone and enol tautomers without enaminones, while 2-methylquinoline with nitriles gave β-quinolyl ketone and enaminone tautomers without enols. The reaction of 2-benzylpyridine with nitriles was not available under the same conditions.

  7. Reactions of the ionized enol tautomer of acetanilide: elimination of HNCO via a novel rearrangement.

    PubMed

    Heydorn, Lisa N; Carter, Lynn M; Bowen, Richard D; Terlouw, Johan K

    2003-01-01

    The reactions of ionised acetanilide, C(6)H(5)NH(=O)CH(3)(.+), and its enol, C(6)H(5)NH(OH)=CH(2)(.+), have been studied by a combination of tandem mass spectrometric and computational methods. These two isomeric radical cations have distinct chemistries at low internal energies. The keto tautomer eliminates exclusively CH(2)=C=O to give ionised aniline. In contrast, the enol tautomer loses H-N=C=O, via an unusual skeletal rearrangement, to form predominantly ionised methylene cyclohexadiene. Hydrogen atom loss also occurs from the enol tautomer, with the formation of protonated oxindole. The mechanisms for H-N=C=O and hydrogen atom loss both involve cyclisation; the former proceeds via a spiro transition state formed by attachment of the methylene group to the ipso position, whereas the latter entails the formation of a five-membered ring by attachment to the ortho position. The behaviour of labelled analogues reveals that these two processes have different site selectivities. Hydrogen atom loss involves a reverse critical energy and is subject to an isotope effect. Surprisingly, attempts to promote the enolisation of ionised acetanilide by proton-transport catalysis were unsuccessful. In a reversal of the usual situation for ionised carbonyl compounds, ionised acetanilide is actually more stable than its enol tautomer. The enol tautomer was resistant to proton-transport catalysed ketonisation to ionised acetanilide, possibly because the favoured geometry of the encounter complex with the base molecule is inappropriate for facilitating tautomerisation.

  8. Crown ethers in graphene

    DOE PAGES

    Guo, Junjie; Lee, Jaekwang; Contescu, Cristian I.; ...

    2014-11-13

    Crown ethers, introduced by Pedersen1, are at their most basic level neutral rings constructed of oxygen atoms linked by two- or three-carbon chains. They have attracted special attention for their ability to selectively incorporate various atoms2 or molecules within the cavity formed by the ring3-6. This property has led to the use of crown ethers and their compounds in a wide range of chemical and biological applications7,8. However, crown ethers are typically highly flexible, frustrating efforts to rigidify them for many uses that demand higher binding affinity and selectivity9,10. In this Letter, we report atomic-resolution images of the same basicmore » structures of the original crown ethers embedded in graphene. This arrangement constrains the crown ethers to be rigid and planar and thus uniquely suited for the many applications that crown ethers are known for. First-principles calculations show that the close similarity of the structures seen in graphene with those of crown ether molecules also extends to their selectivity towards specific metal cations depending on the ring size. Atoms (or molecules) incorporated within the crown ethers in graphene offer a simple environment that can be easily and systematically probed and modeled. Thus, we expect that this discovery will introduce a new wave of investigations and applications of chemically functionalized graphene.« less

  9. Crown ethers in graphene

    SciTech Connect

    Guo, Junjie; Lee, Jaekwang; Contescu, Cristian I.; Gallego, Nidia C.; Pantelides, Sokrates T.; Pennycook, Stephen J.; Moyer, Bruce A.; Chisholm, Matthew F.

    2014-11-13

    Crown ethers, introduced by Pedersen1, are at their most basic level neutral rings constructed of oxygen atoms linked by two- or three-carbon chains. They have attracted special attention for their ability to selectively incorporate various atoms2 or molecules within the cavity formed by the ring3-6. This property has led to the use of crown ethers and their compounds in a wide range of chemical and biological applications7,8. However, crown ethers are typically highly flexible, frustrating efforts to rigidify them for many uses that demand higher binding affinity and selectivity9,10. In this Letter, we report atomic-resolution images of the same basic structures of the original crown ethers embedded in graphene. This arrangement constrains the crown ethers to be rigid and planar and thus uniquely suited for the many applications that crown ethers are known for. First-principles calculations show that the close similarity of the structures seen in graphene with those of crown ether molecules also extends to their selectivity towards specific metal cations depending on the ring size. Atoms (or molecules) incorporated within the crown ethers in graphene offer a simple environment that can be easily and systematically probed and modeled. Thus, we expect that this discovery will introduce a new wave of investigations and applications of chemically functionalized graphene.

  10. Cyclic Voltammetry.

    ERIC Educational Resources Information Center

    Evans, Dennis H.; And Others

    1983-01-01

    Cyclic voltammetry is a simple experiment that has become popular in chemical research because it can provide useful information about redox reactions in a form which is easily obtained and interpreted. Discusses principles of the method and illustrates its use in the study of four electrode reactions. (Author/JN)

  11. Cyclic Voltammetry.

    ERIC Educational Resources Information Center

    Evans, Dennis H.; And Others

    1983-01-01

    Cyclic voltammetry is a simple experiment that has become popular in chemical research because it can provide useful information about redox reactions in a form which is easily obtained and interpreted. Discusses principles of the method and illustrates its use in the study of four electrode reactions. (Author/JN)

  12. Crown ethers in graphene.

    PubMed

    Guo, Junjie; Lee, Jaekwang; Contescu, Cristian I; Gallego, Nidia C; Pantelides, Sokrates T; Pennycook, Stephen J; Moyer, Bruce A; Chisholm, Matthew F

    2014-11-13

    Crown ethers are at their most basic level rings constructed of oxygen atoms linked by two- or three-carbon chains. They have attracted attention for their ability to selectively incorporate various atoms or molecules within the cavity formed by the ring. However, crown ethers are typically highly flexible, frustrating efforts to rigidify them for many uses that demand higher binding affinity and selectivity. Here we present atomic-resolution images of the same basic structures of the original crown ethers embedded in graphene. This arrangement constrains the crown ethers to be rigid and planar. First-principles calculations show that the close similarity of the structures should also extend to their selectivity towards specific metal cations. Crown ethers in graphene offer a simple environment that can be systematically tested and modelled. Thus, we expect that our finding will introduce a new wave of investigations and applications of chemically functionalized graphene.

  13. Spectroscopic Evidence of Keto-enol Tautomerism in Deliquesced Malonic Acid Particles

    SciTech Connect

    Ghorai, Suman; Laskin, Alexander; Tivanski, Alexei V.

    2011-04-11

    Scanning Transmission X-ray Microscopy combined with Near Edge X-ray Absorption Fine Structure Spectroscopy (STXM/NEXAFS), and optical microscopy coupled with Fourier Transform Infrared Spectroscopy (micro-FTIR) have been applied to observe hygroscopic growth and chemical changes in malonic acid particles deposited on substrates. Extent of the hygroscopic growth of particles has been quantified in terms of the corresponding water-to-solute ratios (WSR) based on STXM/NEXAFS and micro-FTIR data sets. WSR values derived separately from two applied methods displayed a remarkable agreement with previous data reported in the literature. Comparison of NEXAFS and FTIR spectra acquired at different relative humidity (RH) shows efficient keto-enol tautomerization of malonic acid, with the enol form dominated at higher RH. The keto-enol equilibrium constants were calculated using relevant peak intensities in the carbon and oxygen K-edge NEXAFS spectra as a function of RH.

  14. Spectroscopic evidence of keto-enol tautomerism in deliquesced malonic acid particles.

    PubMed

    Ghorai, Suman; Laskin, Alexander; Tivanski, Alexei V

    2011-05-05

    Scanning transmission X-ray microscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) and optical microscopy coupled with Fourier transform infrared spectroscopy (micro-FTIR) have been applied to observe hygroscopic growth and chemical changes in malonic acid particles deposited on substrates. The extent of the hygroscopic growth of particles has been quantified in terms of the corresponding water-to-solute ratios (WSR) based on STXM/NEXAFS and micro-FTIR data sets. WSR values derived separately from two applied methods displayed a remarkable agreement with previous data reported in the literature. Comparison of NEXAFS and FTIR spectra acquired at different relative humidity (RH) shows efficient keto-enol tautomerization of malonic acid, with the enol form dominating at higher RH. The keto-enol equilibrium constants were calculated using relevant peak intensities in the carbon and oxygen K-edge NEXAFS spectra as a function of RH. We report strong dependence of the equilibrium constant on RH, with measured values of 0.18 ± 0.03, 1.11 ± 0.14, and 2.33 ± 0.37 corresponding to 2, 50, and 90% RH, respectively. Enols are important intermediates in aldol condensation reactions pertaining to formation and atmospheric aging of secondary organic aerosol (SOA). The present knowledge assumes that constituents of atmospheric deliquesced particles undergo aqueous chemistry with kinetic and equilibrium constants analogous to reactions in bulk solutions, which would estimate absolute dominance of the keto form of carboxylic acids. For instance, the keto-enol equilibrium constant of malonic acid in diluted aqueous solution is <10(-4). Our results suggest that in deliquesced micrometer-size particles, carboxylic acids may exist in predominantly enol forms that need to be explicitly considered in atmospheric aerosol chemistry.

  15. Catalytic asymmetric aldol addition reactions of 3-fluoro-indolinone derived enolates.

    PubMed

    Zhang, Lijun; Zhang, Wenzhong; Mei, Haibo; Han, Jianlin; Soloshonok, Vadim A; Pan, Yi

    2017-01-04

    Reported herein is a Cu(i)/bisoxazoline ligand-catalyzed aldol reaction of unprotected tertiary enolates generated in situ from 3-(1,1-dihydroxy-2,2,2-trifluoroethyl)-substituted derivatives of 3-fluoro-2-oxindoles. A range of α-fluoro-β-aryl/hetaryl/alkyl-β-hydroxy-indolin-2-ones containing C-F quaternary stereogenic centers of high pharmaceutical importance were furnished in good yields and satisfactory diastereo- and enantioselectivities. The reactions were conducted under operationally convenient conditions and displayed wide substrate/functional group generality including unprotected N-H on the tertiary enolates, and aromatic, hetero-aromatic and aliphatic aldehydes.

  16. Enol tautomers of Watson-Crick base pair models are metastable because of nuclear quantum effects.

    PubMed

    Pérez, Alejandro; Tuckerman, Mark E; Hjalmarson, Harold P; von Lilienfeld, O Anatole

    2010-08-25

    Intermolecular enol tautomers of Watson-Crick base pairs could emerge spontaneously via interbase double proton transfer. It has been hypothesized that their formation could be facilitated by thermal fluctuations and proton tunneling, and possibly be relevant to DNA damage. Theoretical and computational studies, assuming classical nuclei, have confirmed the dynamic stability of these rare tautomers. However, by accounting for nuclear quantum effects explicitly through Car-Parrinello path integral molecular dynamics calculations, we find the tautomeric enol form to be dynamically metastable, with lifetimes too insignificant to be implicated in DNA damage.

  17. Iridium-catalyzed enantioselective allylic substitution of unstabilized enolates derived from α,β-unsaturated ketones.

    PubMed

    Chen, Ming; Hartwig, John F

    2014-08-11

    We report Ir-catalyzed, enantioselective allylic substitution reactions of unstabilized silyl enolates derived from α,β-unsaturated ketones. Asymmetric allylic substitution of a variety of allylic carbonates with silyl enolates gave allylated products in 62-94% yield with 90-98% ee and >20:1 branched-to-linear selectivity. The synthetic utility of this method was illustrated by the short synthesis of an anticancer agent, TEI-9826. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Michael Additions of Highly Basic Enolates to ortho-Quinone Methides.

    PubMed

    Lewis, Robert S; Garza, Christopher J; Dang, Ann T; Pedro, Te Kie A; Chain, William J

    2015-05-01

    A protocol by which ketone or ester enolates and ortho-quinone methides (o-QMs) are generated in situ in a single reaction flask from silylated precursors under the action of anhydrous fluoride is reported. The reaction partners are joined to give a variety of β-(2-hydroxyphenyl)-carbonyl compounds in 32-94% yield in a single laboratory operation. The intermediacy of o-QMs is supported by control experiments utilizing enolate precursors and conventional alkyl halides as competitive alkylating agents and the isolation of 1,5-dicarbonyl products resulting from conjugate additions that do not restore the aromatic system.

  19. Michael Additions of Highly Basic Enolates to ortho-Quinone Methides

    PubMed Central

    Lewis, Robert S.; Garza, Christopher J.; Dang, Ann T.; Pedro, Te Kie A.; Chain, William J.

    2015-01-01

    A protocol by which ketone or ester enolates and ortho-quinone methides (o-QMs) are generated in situ in a single reaction flask from silylated precursors under the action of anhydrous fluoride is reported. The reaction partners are joined to give a variety of β-(2-hydroxyphenyl)-carbonyl compounds in 32–94% yield in a single laboratory operation. The intermediacy of o-QMs is supported by control experiments utilizing enolate precursors and conventional alkyl halides as competitive alkylating agents and the isolation of 1,5-dicarbonyl products resulting from conjugate additions that do not restore the aromatic system. PMID:25906358

  20. (E)- and (Z)-Stereodefined Enol Sulfate Esters Derived from α-Aryl Aldehydes: Stereocomplementary Synthesis of Styryl Sulfate Natural Products.

    PubMed

    Yu, Shuai; Li, Feng; Kim, Sanghee

    2017-07-07

    A method for the stereoselective formation of enol sulfate esters from α-aryl aldehydes is described. This method involved the stereocontrolled enolization of a carbonyl group with DBU or t-BuOK followed by trapping with a reactive sulfuryl imidazolium salt, providing the corresponding styryl enol sulfate esters in good to excellent yields and stereoselectivities. This method was applied to the first total synthesis of the enol sulfate natural products in a stereocomplementary manner.

  1. Catalytic oxidation of dimethyl ether

    SciTech Connect

    Zelenay, Piotr; Wu, Gang; Johnston, Christina M.; Li, Qing

    2016-05-10

    A composition for oxidizing dimethyl ether includes an alloy supported on carbon, the alloy being of platinum, ruthenium, and palladium. A process for oxidizing dimethyl ether involves exposing dimethyl ether to a carbon-supported alloy of platinum, ruthenium, and palladium under conditions sufficient to electrochemically oxidize the dimethyl ether.

  2. Improved method for the quantification of lysophospholipids including enol ether species by liquid chromatography-tandem mass spectrometry.

    PubMed

    Bollinger, James G; Ii, Hiromi; Sadilek, Martin; Gelb, Michael H

    2010-02-01

    LC/ESI-MS/MS has been previously demonstrated to be a powerful method to detect and quantify molecular species of glycerophospholipids including lysophospholipids. In this study, we provide an improved pre-mass spectrometry lipid extraction procedure that avoids the acid-catalyzed decomposition of plasmenyl phospholipids that is problematic with previously reported methods. We show that the use of lysophospholipid internal standards with perdeuterated fatty acyl chains avoids isobar problems associated with the use of internal standards containing odd carbon number fatty acyl chains. We also show that LC prior to MS is required to avoid numerous problems associated with isobars and with MS in-source decomposition of lysophosphatidylserine. The reported method of using normal phase chromatography/ESI-MS is used to quantify lysophospholipids in serum and to quantify lysophospholipids produced in mammalian cells by human group X secreted phospholipase A(2). The latter shows that group X phospholipase A(2) added exogenously to cells generates a different set of lysophospholipids compared with enzyme produced endogenously in cells, which supports earlier studies showing that this phospholipase A(2) can act on cell membranes prior to externalization from cells.

  3. Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto-Enol Tautomeric Equilibrium Reactions

    ERIC Educational Resources Information Center

    Nichols, Michael A.; Waner, Mark J.

    2010-01-01

    An extension of the classic keto-enol tautomerization of beta-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the alpha-methylene carbon when dissolved in methanol-d[subscript 4]. The extent of deuteration may be…

  4. Enantiopure oxazolidinones as chiral acids in the asymmetric protonation of N-Boc pyrrole derived enolates.

    PubMed

    Carbery, David R; Donohoe, Timothy J

    2004-03-21

    The first use of geminally disubstituted oxazolidinones as chiral protonating agents is described: these new acids are able to directly protonate an enolate generated by the ammonia free partial reduction of an electron deficient pyrrole and give up to 68% ee in the pyrroline product.

  5. Keto-enol tautomerization of a peptide group with proton transfer through a water bridge

    NASA Astrophysics Data System (ADS)

    Isaev, A. N.

    2015-08-01

    Calculations were performed for structures of the keto and enol forms of dipeptide N-glycylglycine and its complexes with water molecules using the quantum-chemical B3LYP/6-31+G** method. The barrier for the reactions of the dipeptide's keto-enol tautomerization that proceed by the mechanism of intramolecular proton transfer and proton transfer through water molecules connecting the oxygen and nitrogen atoms of the (-CONH-) peptide group was calculated. It was found that the barrier of the keto-enol tautomerization reaction with proton transfer by an exchange mechanism through water molecules is decreased halved compared to direct intramolecular transfer. It was shown that addition of a second water molecule in the transfer chain leads to linearization of the H-bonds bridges and increases hydrogen bonding between the peptide group and water molecules, but has virtually no influence on the calculated value of the keto-enol tautomerization barrier of about 20 kcal/mol. The structures of the transition states of the reaction indicate that the transfer of protons along the H-bonds chain is in both cases concerted but asynchronous. The order of the protons translocations along the water bridge is explained on the basis of NBO analysis of the relative strength of H-bonds in the transfer chain when the proton involved in the strongest H-bond is transferred first.

  6. Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto-Enol Tautomeric Equilibrium Reactions

    ERIC Educational Resources Information Center

    Nichols, Michael A.; Waner, Mark J.

    2010-01-01

    An extension of the classic keto-enol tautomerization of beta-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the alpha-methylene carbon when dissolved in methanol-d[subscript 4]. The extent of deuteration may be…

  7. An NMR Study of Isotope Effect on Keto-Enol Tautomerization: A Physical Organic Chemistry Experiment

    ERIC Educational Resources Information Center

    Atkinson, D.; Chechik, V.

    2004-01-01

    Isotope substitution often affects the rate of an organic reaction and can be used to reveal the underlying mechanism. A series of experiments that use (super 1)H NMR to determine primary and secondary isotope effects, activation parameters, and the regioselectivity of butanone enolization are described.

  8. An NMR Study of Isotope Effect on Keto-Enol Tautomerization: A Physical Organic Chemistry Experiment

    ERIC Educational Resources Information Center

    Atkinson, D.; Chechik, V.

    2004-01-01

    Isotope substitution often affects the rate of an organic reaction and can be used to reveal the underlying mechanism. A series of experiments that use (super 1)H NMR to determine primary and secondary isotope effects, activation parameters, and the regioselectivity of butanone enolization are described.

  9. Lewis acid/CpRu dual catalysis in the enantioselective decarboxylative allylation of ketone enolates.

    PubMed

    Linder, David; Austeri, Martina; Lacour, Jérôme

    2009-10-07

    The addition of a Lewis acidic metal triflate salt Mg(OTf)(2) as co-catalyst in the CpRu-catalyzed decarboxylative allylation of in situ-generated ketone enolates allows the reaction to proceed at lower temperature with higher regio- and enantioselectivity. Even so-far-unreactive substrates react.

  10. Cobalt-catalyzed hydrogenation of esters to alcohols: unexpected reactivity trend indicates ester enolate intermediacy.

    PubMed

    Srimani, Dipankar; Mukherjee, Arup; Goldberg, Alexander F G; Leitus, Gregory; Diskin-Posner, Yael; Shimon, Linda J W; Ben David, Yehoshoa; Milstein, David

    2015-10-12

    The atom-efficient and environmentally benign catalytic hydrogenation of carboxylic acid esters to alcohols has been accomplished in recent years mainly with precious-metal-based catalysts, with few exceptions. Presented here is the first cobalt-catalyzed hydrogenation of esters to the corresponding alcohols. Unexpectedly, the evidence indicates the unprecedented involvement of ester enolate intermediates.

  11. Lewis Acid Mediated Vinylogous Additions of Enol Nucleophiles into an α,β-Unsaturated Platinum Carbene

    PubMed Central

    Allegretti, Paul A.; Huynh, Khoi; Ozumerzifon, Tarik J.; Ferreira, Eric M.

    2016-01-01

    A variety of substituted indoles and benzofurans are accessed via a platinum catalyzed annulation and vinylogous addition of enol nucleophiles. Several β-dicarbonyl compounds participate in the reaction, as do α-nitro and α-cyano carbonyl species. Subjecting the indole products to acidic conditions results in the formation of fused heterocycles. PMID:26652926

  12. Highly efficient ligands for palladium-catalyzed asymmetric alkylation of ketone enolates.

    PubMed

    You, S L; Hou, X L; Dai, L X; Zhu, X Z

    2001-01-25

    [figure: see text] Ferrocene-modified chiral pocket ligands have been studied in the palladium-catalyzed asymmetric alkylation of simple ketone enolates, in which (R,R,Sp,Sp)-1 containing two pairs of matched chiralities, central chirality and planar chirality, behaved very efficiently in this reaction and up to 95% ee value was achieved.

  13. Cyclic multiverses

    NASA Astrophysics Data System (ADS)

    Marosek, Konrad; Dąbrowski, Mariusz P.; Balcerzak, Adam

    2016-09-01

    Using the idea of regularization of singularities due to the variability of the fundamental constants in cosmology we study the cyclic universe models. We find two models of oscillating and non-singular mass density and pressure (`non-singular' bounce) regularized by varying gravitational constant G despite the scale factor evolution is oscillating and having sharp turning points (`singular' bounce). Both violating (big-bang) and non-violating (phantom) null energy condition models appear. Then, we extend this idea on to the multiverse containing cyclic individual universes with either growing or decreasing entropy though leaving the net entropy constant. In order to get an insight into the key idea, we consider the doubleverse with the same geometrical evolution of the two `parallel' universes with their physical evolution [physical coupling constants c(t) and G(t)] being different. An interesting point is that there is a possibility to exchange the universes at the point of maximum expansion - the fact which was already noticed in quantum cosmology. Similar scenario is also possible within the framework of Brans-Dicke theory where varying G(t) is replaced by the dynamical Brans-Dicke field φ(t) though these theories are slightly different.

  14. Thermodynamic and Transport Properties of Crown-Ethers: Force Field Development and Molecular Simulations.

    PubMed

    Jamali, Seyed Hossein; Ramdin, Mahinder; Becker, Tim M; Rinwa, Shwet Kumar; Buijs, Wim; Vlugt, Thijs J H

    2017-09-07

    Crown-ethers have recently been used to assemble porous liquids (PLs), which are liquids with permanent porosity formed by mixing bulky solvent molecules (e.g., 15-crown-5 ether) with solvent-inaccessible organic cages. PLs and crown-ethers belong to a novel class of materials, which can potentially be used for gas separation and storage, but their performance for this purpose needs to be assessed thoroughly. Here, we use molecular simulations to study the gas separation performance of crown-ethers as the solvent of porous liquids. The TraPPE force field for linear ether molecules has been adjusted by fitting a new set of torsional potentials to accurately describe cyclic crown-ether molecules. Molecular dynamics (MD) simulations have been used to compute densities, shear viscosities, and self-diffusion coefficients of 12-crown-4, 15-crown-5, and 18-crown-6 ethers. In addition, Monte Carlo (MC) simulations have been used to compute the solubility of the gases CO2, CH4, and N2 in 12-crown-4 and 15-crown-5 ether. The computed properties are compared with available experimental data of crown-ethers and their linear counterparts, i.e., polyethylene glycol dimethyl ethers.

  15. Lithium Enolates in the Enantioselective Construction of Tetrasubstituted Carbon Centers with Chiral Lithium Amides as Noncovalent Stereodirecting Auxiliaries.

    PubMed

    Yu, Kai; Lu, Ping; Jackson, Jeffrey J; Nguyen, Thuy-Ai D; Alvarado, Joseph; Stivala, Craig E; Ma, Yun; Mack, Kyle A; Hayton, Trevor W; Collum, David B; Zakarian, Armen

    2017-01-11

    Lithium enolates derived from carboxylic acids are ubiquitous intermediates in organic synthesis. Asymmetric transformations with these intermediates, a central goal of organic synthesis, are typically carried out with covalently attached chiral auxiliaries. An alternative approach is to utilize chiral reagents that form discrete, well-defined aggregates with lithium enolates, providing a chiral environment conducive of asymmetric bond formation. These reagents effectively act as noncovalent, or traceless, chiral auxiliaries. Lithium amides are an obvious choice for such reagents as they are known to form mixed aggregates with lithium enolates. We demonstrate here that mixed aggregates can effect highly enantioselective transformations of lithium enolates in several classes of reactions, most notably in transformations forming tetrasubstituted and quaternary carbon centers. Easy recovery of the chiral reagent by aqueous extraction is another practical advantage of this one-step protocol. Crystallographic, spectroscopic, and computational studies of the central reactive aggregate, which provide insight into the origins of selectivity, are also reported.

  16. One-pot enantioselective formation of eight-membered rings from alkenyl Fischer carbene complexes and ketone enolates.

    PubMed

    Barluenga, José; Diéguez, Alejandro; Rodríguez, Félix; Flórez, Josefa; Fañanás, Francisco J

    2002-08-07

    Eight-membered carbocycles with up to five new stereogenic centers are enantioselectively obtained following a one-pot procedure that involves the coupling of three components: an alkenyl Fischer carbene complex, a ketone enolate, and allyl lithium.

  17. Efficient asymmetric synthesis of novel gastrin receptor antagonist AG-041R via highly stereoselective alkylation of oxindole enolates.

    PubMed

    Emura, Takashi; Esaki, Toru; Tachibana, Kazutaka; Shimizu, Makoto

    2006-10-27

    An efficient method for asymmetric synthesis of the potent Gastrin/CCK-B receptor antagonist AG-041R was developed. Core oxindole stereochemistry was established by asymmetric alkylation of oxindole enolates with bromoacetic acid esters, using l-menthol as a chiral auxiliary. The key alkylation reaction of the oxindole enolates generated tetrasubstituted chiral intermediates with high diastereoselectivity. The stereoselective alkylation reactions are described in detail.

  18. Enantioselective Synthesis of Spiroindenes by Enol-Directed Rhodium(III)-Catalyzed C–H Functionalization and Spiroannulation

    PubMed Central

    Reddy Chidipudi, Suresh; Burns, David J; Khan, Imtiaz; Lam, Hon Wai

    2015-01-01

    Chiral cyclopentadienyl rhodium complexes promote highly enantioselective enol-directed C(sp2)-H functionalization and oxidative annulation with alkynes to give spiroindenes containing all-carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O-bound rhodium enolate into the C-bound isomer, appear to be critical for high enantiomeric excesses. PMID:26404643

  19. 40 CFR 721.3440 - Haloalkyl substituted cyclic ethers.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... does not apply when a MSDS was not required under § 721.72(c). The provisions of § 721.72(g) requiring placement of specific information on a label and MSDS do not apply when a label and MSDS are not required... provided with information on the location and availability of MSDSs does not apply when a MSDS was not...

  20. Poly-amino-enolates: First examples of odd alternant conducting polymers

    NASA Astrophysics Data System (ADS)

    Tol, A. J. W.

    1997-03-01

    The molecular and electronic structure of a series of poly-amino-enolates is calculated ab initio within the density functional formalism using Car-Parinello molecular dynamics. Within this series, the bandgap is found to vary from 1 to 6.5 eV and the valence band is found to consist entirely of non-bonding orbitals. Both these features are essentially reproduced by a simple Hückel model. By variation of the Hückel parameters the important factors which determine the bandgap are identified. Hückel analysis furthermore demonstrates that the poly-amino-enolates are first examples of odd alternant conjugated polymers which allows the effects of the hetero atom substitution to be rationalised in terms of Dewar's colour rules for odd alternant systems.

  1. Fused Catechol Ethers from Gold(I)-Catalyzed Intramolecular Reaction of Propargyl Ethers with Acetals.

    PubMed

    Pati, Kamalkishore; Gomes, Gabriel dos Passos; Harris, Trevor; Alabugin, Igor V

    2016-03-04

    Selective gold(I)-catalyzed rearrangement of aromatic methoxypropynyl acetals leads to fused catechol ethers (1,2-dialkoxynapthalenes) in excellent yields. Furthermore, this process extends to the analogous heterocyclic and aliphatic substrates. Alkyne activation triggers nucleophilic addition of the acetal oxygen that leads to an equilibrating mixture of oxonium ions of similar stability. This mixture is "kinetically self-sorted" via a highly exothermic cyclization. Selective formation of 1,2-dialkoxy naphthalenes originates from chemoselective aromatization of the cyclic intermediate via 1,4-elimination of methanol.

  2. Triethylene glycol monoethyl ether

    Integrated Risk Information System (IRIS)

    Triethylene glycol monoethyl ether ; CASRN 112 - 50 - 5 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments fo

  3. Triethylene glycol monobutyl ether

    Integrated Risk Information System (IRIS)

    Triethylene glycol monobutyl ether ; CASRN 143 - 22 - 6 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments fo

  4. p-Bromodiphenyl ether

    Integrated Risk Information System (IRIS)

    p - Bromodiphenyl ether ; CASRN 101 - 55 - 3 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcin

  5. Propylene glycol monoethyl ether

    Integrated Risk Information System (IRIS)

    Propylene glycol monoethyl ether ; CASRN 52125 - 53 - 8 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments fo

  6. Chloromethyl methyl ether (CMME)

    Integrated Risk Information System (IRIS)

    Chloromethyl methyl ether ( CMME ) ; CASRN 107 - 30 - 2 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments fo

  7. Kinetics and mechanism for formation of enols in reaction of hydroxide radical with propene.

    PubMed

    Zhou, Chong-Wen; Li, Ze-Rong; Li, Xiang-Yuan

    2009-03-19

    Recently, enols have been found to be the common intermediates in hydrocarbon combustion flames (Taatjes et al. Science 2005, 308, 1887), but the knowledge of kinetic properties for such species in combustion flames is rare. Therefore in this work, particular attention is paid to the formation of enols in combustion flames. Starting with HO and propene (CH(3)CH=CH(2)), the reaction mechanism involving eight product channels has been investigated systematically. It is revealed that the electrophilic addition of OH to the double bond of CH(3)CH=CH(2) is unselective and the chemically activated adducts, CH(3)CHOH=CH(2) and CH(3)CH=CH(2)OH, may undergo dissociation in competition with H-abstractions. The kinetics and product branching ratios of the HO and propene reaction have been evaluated in the temperature range of 200-3000 K by Variflex code, based on the weak collision master equation/microcanonical variational RRKM theory. Available experimental kinetic data can be quantitatively reproduced by this study, with a minor adjustment (1.0 kcal/mol) of the OH central addition barrier. From the theoretical calculations with multiple reflection correction included, the total rate constant is fitted to k(t) = 6.07 x 10(-5)T(-2.54) exp(108/T) cm(3) x molecule(-1) x s(-1) in the range of 200-800 K and k(t) = 7.11 x 10(-23)T(3.38) exp(-1097/T) cm(3) x molecule(-1) x s(-1) in the range of 800-3000 K, which are in close agreement with experimental data. The branching ratios of enol channels are consistent with the observation in low-pressure flames and hence the reaction mechanisms presented here provide valuable descriptions of enol formations in hydrocarbon combustion chemistry.

  8. Acid-Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization.

    PubMed

    Lewis, Jennifer D; Van de Vyver, Stijn; Román-Leshkov, Yuriy

    2015-08-17

    Hf-, Sn-, and Zr-Beta zeolites catalyze the cross-aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid-base pairs in the Si-O-M framework ensemble promote soft enolization through α-proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions.

  9. Michael addition-elimination reactions of chiral enolates with ethyl 3-halopropenoates.

    PubMed

    Esteban, Jorge; Costa, Anna M; Gómez, Alex; Vilarrasa, Jaume

    2008-01-03

    Key dienoic or dienal substructures of cytotoxic macrolides amphidinolide E and dictyostatin have been prepared via a Michael addition (followed by elimination of X-) of chiral enolates on beta-halo derivatives of ethyl acrylate, with full retention of the initial E or Z configuration. Evans oxazolidin-2-ones and our related thiazolidin-2-ones, as well as a fine-tuning of the reaction conditions, have been essential. Many chiral building blocks are accessible from these adducts.

  10. Asymmetric hydroformylation of Z-enamides and enol esters with rhodium-bisdiazaphos catalysts.

    PubMed

    Abrams, M Leigh; Foarta, Floriana; Landis, Clark R

    2014-10-15

    Asymmetric hydroformylation (AHF) of Z-enamides and Z-enol esters provides chiral, alpha-functionalized aldehydes with high selectivity and atom economy. Rh-bisdiazaphospholane catalysts enable hydroformylation of these challenging disubstituted substrates under mild reaction conditions and low catalyst loadings. The synthesis of a protected analog of l-DOPA demonstrates the utility of AHF for enantioselective, atom-efficient synthesis of peptide precursors.

  11. The mechanism and thermodynamics of transesterification of acetate-ester enolates in the gas phase

    NASA Astrophysics Data System (ADS)

    Haas, George W.; Giblin, Daryl E.; Gross, Michael L.

    1998-01-01

    In solution, base-catalyzed hydrolysis and transesterification of esters are initiated by hydroxide- or alkoxide-ion attack at the carbonyl carbon. At low pressures in the gas phase, however, transesterification proceeds by an attack of the enolate anion of an acetate ester on an alcohol. Fourier transform mass spectrometry (FTMS) indicates that the reaction is the second-order process: -CH2-CO2-R + R'-OH --> - CH2-CO2-R' + R-OH and there is little to no detectable production of either alkoxide anion. Labeling studies show that the product and reactant enolate anion esters undergo exchange of hydrogens located [alpha] to the carbonyl carbon with the deuterium of R'-OD. The extent of the H/D exchange increases with reaction time, pointing to a short-lived intermediate. The alcoholysis reaction rate constants increase with increasing acidity of the primary, straight-chained alkyl alcohols, whereas steric effects associated with branched alcohols cause the rate constants to decrease. Equilibrium constants, which were determined directly from measurements at equilibrium and which were calculated from the forward and reverse rate constants, are near unity and show internal consistency. In the absence of steric effects, the larger enolate is always the favored product at equilibrium. The intermediate for the transesterification reaction, which can be generated at a few tenths of a torr in a tandem mass spectrometer, is tetrahedral, but other adducts that are collisionally stabilized under these conditions are principally loosely bound complexes.

  12. Glycol Ethers As Groundwater Contaminants

    NASA Astrophysics Data System (ADS)

    Ross, Benjamin; Johannson, Gunnar; Foster, Gregory D.; Eckel, William P.

    1992-01-01

    Ether derivatives of dihydroxy alcohols, which are formed from ethylene or propylene, comprise an important group of groundwater contaminants known as glycol ethers. Compounds in this group are used as solvents, cleaning agents, and emulsifiers in many chemical products and manufacturing operations. Glycol ethers have been associated with a variety of toxic effects, and some compounds in the group are relatively potent teratogens. The limited information available suggests that glycol ethers are contaminants in groundwater, especially in anaerobic plumes emanating from disposal of mixed industrial and household waste. Most methods used to analyze groundwater samples cannot adequately detect μg/? (ppb) concentrations of glycol ethers, and the existing methods perform worst for the most widely used and toxic species. A new method capable of analyzing μg/? concentrations of glycol ethers was recently developed, and its use is recommended for groundwater samples where glycol ethers are likely to be present.

  13. Amination of ethers using chloramine-T hydrate and a copper(I) catalyst.

    PubMed

    Albone, David P; Challenger, Stephen; Derrick, Andrew M; Fillery, Shaun M; Irwin, Jacob L; Parsons, Christopher M; Takada, Hiroya; Taylor, Paul C; Wilson, D James

    2005-01-07

    Amination of C-H bonds activated by ether oxygen atoms is facile with chloramine-T as nitrene source and copper(I) chloride in acetonitrile as catalyst. For cyclic ethers the hemiaminal products are generally stable and can be isolated pure. For acyclic ethers, the hemiaminal products, as expected, fragment with elimination of alcohol to yield imines. When activation of benzylic positions is remote through a conjugated system, stable benzylamine derivatives are isolated. Mechanistic studies are consistent with concerted insertion of an electrophilic nitrenoid into the C-H bond in the rate-determining step, though in an asynchronous manner with a more activated substrate.

  14. Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation

    PubMed Central

    Wen, Peng

    2015-01-01

    The preparation of a series of mannopyranosyl donors carrying 2-O-(2-oxoalkyl) ethers and their use in glycosylation reactions is described. The formation of cyclic products with the simple 2-O-phenacyl ether and with the 2-O-(t-butoxycarbonylmethyl) ether establishes the stereoelectronic feasibility of the participation in such systems. The high β-selectivities observed with the bis-trifluoromethyl phenacyl ether indicate that participation can be suppressed through the introduction of electron-withdrawing substituents. The high β-selectivities and absence of cyclic products observed with the 2-O-(methoxycarbonylmethyl) ether excludes the effective participation of esters through six-membered cyclic intermediates in this series. The results are discussed in terms of the conformation of cyclic dioxenium ions (E,E-, E,Z- or Z,Z,-) and in the context of “neighboring group” participation by non-vicinal esters in glycosylation. Methods for the deprotection of the 2-O-phenacyl and 2-O-(methoxycarbonylmethyl) ethers are described. PMID:26565923

  15. Palladium-catalyzed carbonylative couplings of vinylogous enolates: application to statin structures.

    PubMed

    Makarov, Ilya S; Kuwahara, Takashi; Jusseau, Xavier; Ryu, Ilhyong; Lindhardt, Anders T; Skrydstrup, Troels

    2015-11-11

    The first Pd-catalyzed carbonylative couplings of aryl and vinyl halides with vinylogous enolates are reported generating products derived from C-C bond formation exclusively at the γ-position. Good results were obtained with a dienolate derivative of acetoacetate (1,3-dioxin-4-one). These transformations occurred at room temperature and importantly with only stoichiometric carbon monoxide in a two-chamber reactor. The methodology was applied to the synthesis of two members of the statin family generating the cis-3,5-diol acid motif by a γ-selective carbonylation followed by a cis-stereoselective reduction of the 3,5-dicarbonyl acid intermediates.

  16. Diastereoselective additions of titanium enolates from N-glycolyl thiazolidinethiones to acetals.

    PubMed

    Baiget, Jessica; Caba, Marta; Gálvez, Erik; Romea, Pedro; Urpí, Fèlix; Font-Bardia, Mercè

    2012-10-05

    The stereochemical outcome of the Lewis acid-mediated glycolate addition of the titanium enolates from protected N-hydroxyacetyl-4-isopropyl-1,3-thiazolidine-2-thiones to dimethyl and dibenzyl acetals depends on the hydroxyl protecting group. Particularly, the pivaloyl protected glycolate derivative provides the reluctant anti adducts in high yields and diastereomeric ratios, which can be isolated and further converted in enantiomerically pure form to β-methoxy or β-benzyloxy α-pivaloyloxy carbonyl fragments in a straightforward manner.

  17. Regiodivergent halogenation of (E)-β-chlorovinyl ketones via soft α-vinyl enolization strategy.

    PubMed

    Kim, Hun Young; Lee, Seokwoo; Kim, Sanghee; Oh, Kyungsoo

    2015-02-06

    The soft α-vinyl enolization of (E)-β-chlorovinyl ketones was investigated in the presence of various halogen electrophiles. Depending on the nature of halogen electrophiles, the selective formation of three products, namely α,α-dichloropropargyl ketones, α,γ-dihaloallenyl ketones, and 3-halofurans, was observed. The observed regiodivergent nucleophilic pathways of (E)-β-chlorovinyl ketones demonstrate the diversity-oriented synthesis strategy in which the nucleophilic reactivity of (E)-β-chlorovinyl ketones can be selectively modulated by the choice of suitable hard and soft electrophiles.

  18. Oxyluciferin photoacidity: the missing element for solving the keto-enol mystery?

    PubMed

    da Silva, Luís Pinto; Simkovitch, Ron; Huppert, Dan; da Silva, Joaquim C G Esteves

    2013-10-21

    The oxyluciferin family of fluorophores has been receiving much attention from the research community and several systematic studies have been performed in order to gain more insight regarding their photophysical properties and photoprotolytic cycles. In this minireview, we summarize the knowledge obtained so far and define several possible lines for future research. More importantly, we analyze the impact of the discoveries on the firefly bioluminescence phenomenon made so far and explain how they re-open again the discussion regarding the identity (keto or enol species) of the bioluminophore.

  19. Poly(arylene ether)s That Resist Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Connell, John W.; Hergenrother, Paul; Smith, Joseph G., Jr.

    1994-01-01

    Novel poly(arylene ether)s containing phosphine oxide (PAEPO's) made via aromatic nucleophilic displacement reactions of activated aromatic dihalides (or, in some cases, activated aromatic dinitro compounds) with new bisphenol monomers containing phosphine oxide. Exhibited favorable combination of physical and mechanical properties and resistance to monatomic oxygen in oxygen plasma environment. Useful as adhesives, coatings, films, membranes, moldings, and composite matrices.

  20. Cyclic sulfamidates as versatile lactam precursors. An evaluation of synthetic strategies towards (-)-aphanorphine.

    PubMed

    Bower, John F; Szeto, Peter; Gallagher, Timothy

    2007-01-07

    A full account of studies which led to the efficient asymmetric synthesis of (-)-aphanorphine is reported. Two routes to the key cyclic sulfamidate intermediate are described, the first was based on a chiral auxiliary approach and the second utilised asymmetric hydrogenation methodology. A range of C(3)-substituted lactams (, and ) were synthesised and evaluated as precursors for Pd(0) catalysed entries (based on (i) alpha-arylation of a lactam enolate and (ii) reductive Heck reaction) to the 3-benzazepine core of . These approaches were less effective than an aryl radical cyclisation which allowed the completion of a synthesis of in 12 steps from anisaldehyde.

  1. InCl3/Me3SiCl-catalyzed direct Michael addition of enol acetates to α,β-unsaturated ketones.

    PubMed

    Onishi, Yoshiharu; Yoneda, Yuki; Nishimoto, Yoshihiro; Yasuda, Makoto; Baba, Akio

    2012-11-16

    The direct Michael addition of enol acetates to α,β-unsaturated ketones was achieved using a combination of Lewis acid catalysts, InCl(3) and Me(3)SiCl, which furnished stable enol-form products that could be further transformed into functionalized 1,5-diketones by reactions with various electrophiles.

  2. Formation of stable enols from 1,4-dilithio-1,3-dienes and acid chlorides by a de-aromatization/Michael addition/re-aromatization domino process.

    PubMed

    Hu, Qiaoshu; Wang, Chao; Li, Dongzhen; Xi, Zhenfeng

    2007-07-07

    Stable enols were synthesized from the reaction of (1Z,3Z)-1,4-dilithio-1,3-dienes with acid chlorides and structurally characterized by single-crystal X-ray analysis. These stable enols were formed by a novel de-aromatization/Michael addition/re-aromatization domino process.

  3. The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals.

    PubMed

    Repetto, Sonia L; Costello, James F; Butts, Craig P; Lam, Joseph K W; Ratcliffe, Norman M

    2016-01-01

    A novel approach to protecting jet fuel against the effects of water contamination is predicated upon the coupling of the rapid hydrolysis reactions of lipophilic cyclic geminal ethers, with the concomitant production of a hydrophilic acyclic hydroxyester with de-icing properties (Fuel Dehydrating Icing Inhibitors - FDII). To this end, a kinetic appraisal of the hydrolysis reactions of representative geminal ethers was undertaken using a convenient surrogate for the fuel-water interface (D2O/CD3CN 1:4). We present here a library of acyclic and five/six-membered cyclic geminal ethers arranged according to their hydroxonium catalytic coefficients for hydrolysis, providing for the first time a framework for the development of FDII. A combination of (1)H NMR, labelling and computational studies was used to assess the effects that may govern the observed relative rates of hydrolyses.

  4. The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

    PubMed Central

    Repetto, Sonia L; Butts, Craig P; Lam, Joseph K W; Ratcliffe, Norman M

    2016-01-01

    Summary A novel approach to protecting jet fuel against the effects of water contamination is predicated upon the coupling of the rapid hydrolysis reactions of lipophilic cyclic geminal ethers, with the concomitant production of a hydrophilic acyclic hydroxyester with de-icing properties (Fuel Dehydrating Icing Inhibitors - FDII). To this end, a kinetic appraisal of the hydrolysis reactions of representative geminal ethers was undertaken using a convenient surrogate for the fuel–water interface (D2O/CD3CN 1:4). We present here a library of acyclic and five/six-membered cyclic geminal ethers arranged according to their hydroxonium catalytic coefficients for hydrolysis, providing for the first time a framework for the development of FDII. A combination of 1H NMR, labelling and computational studies was used to assess the effects that may govern the observed relative rates of hydrolyses. PMID:27559399

  5. Allene ether Nazarov cyclization.

    PubMed

    Tius, Marcus A

    2014-05-07

    The ease of synthesis and the exceptional reactivity of alkoxyallenes has led to their use in a large number of highly diverse applications. This Report describes their use in various versions of the allene ether Nazarov cyclization. Following a brief introduction to the Nazarov cyclization (Section 1), the oxidative cyclization of vinyl alkoxyallenes is discussed first (Section 2). Nazarov cyclizations of α-alkoxyallenyl vinyl ketones and of α-alkoxyallenyl vinyl tertiary carbinols are covered (Section 3). The discovery and the subsequent rational design of acetals that serve as chiral auxiliaries on the allene in highly enantioselective Nazarov cyclizations is explained (Section 4). Interrupted Nazarov cyclizations of alkoxyallenes that are generated in situ from the isomerization of propargyl ethers on solid supports are discussed, including the evolution of a highly diastereoselective, chiral auxiliary controlled version of the reaction. Some applications of the methodology to natural products total synthesis have been included so as to provide the reader with benchmarks with which to judge the utility of the methodology.

  6. Solvent effect in keto-enol tautomerism for a polymerizable β-ketonitrile monomer. Spectroscopy and theoretical study

    NASA Astrophysics Data System (ADS)

    Giussi, Juan M.; Gastaca, Belén; Lavecchia, Martín J.; Schiavoni, Mercedes; Susana Cortizo, M.; Allegretti, Patricia E.

    2015-02-01

    The beta-ketonitrile 2-methyl-5-phenyl-3-oxo-4-pentenenitrile, a polymerizable monomer, exists in two important tautomeric forms, keto and enol isomers. This compound has been studied as monomer in polymerization reactions and the resulting polymers have been applied in fields of nanotechnology. Currently, these are being studied in nanomedicine. To understand the tautomeric equilibrium, we have studied this compound in solution by NMR spectrometry. Correlation with DFT calculations has been carried out in order to understand the system behavior. The results found in this work, both by experiments and calculations, show that the enol content increases with solvent polarity.

  7. Iridium Catalyzed C-C Coupling of a Simple Propargyl Ether with Primary Alcohols: Enantioselective Homoaldol Addition via Redox-Triggered (Z)-Siloxyallylation

    PubMed Central

    Liang, Tao; Zhang, Wandi; Krische, Michael J.

    2015-01-01

    A chiral iridium complex formed in situ from [Ir(cod)Cl]2 and (R)-H8-BINAP is found to catalyze the direct enantioselective C-C coupling of a simple propargyl ether, TIPSOCH2C≡CH, with primary alcohols to form γ-hydroxy (Z)-enol silanes with uniformly high enantioselectivity and complete alkene (Z)-stereoselectivity. As corroborated by deuterium labeling studies, these studies represent the first examples of 1,2-hydride shift enabled π-allyl formation in the context of iridium catalysis. PMID:26671223

  8. Iridium-Catalyzed C-C Coupling of a Simple Propargyl Ether with Primary Alcohols: Enantioselective Homoaldol Addition via Redox-Triggered (Z)-Siloxyallylation.

    PubMed

    Liang, Tao; Zhang, Wandi; Krische, Michael J

    2015-12-30

    A chiral iridium complex formed in situ from [Ir(cod)Cl]2 and (R)-H8-BINAP is found to catalyze the direct enantioselective C-C coupling of a simple propargyl ether, TIPSOCH2C≡CH, with primary alcohols to form γ-hydroxy (Z)-enol silanes with uniformly high enantioselectivity and complete alkene (Z)-stereoselectivity. As corroborated by deuterium labeling studies, these studies represent the first examples of 1,2-hydride shift-enabled π-allyl formation in the context of iridium catalysis.

  9. Oxygen vacancy-assisted coupling and enolization of acetaldehyde on CeO2(111).

    PubMed

    Calaza, Florencia C; Xu, Ye; Mullins, David R; Overbury, Steven H

    2012-10-31

    The temperature-dependent adsorption and reaction of acetaldehyde (CH(3)CHO) on a fully oxidized and a highly reduced thin-film CeO(2)(111) surface have been investigated using a combination of reflection-absorption infrared spectroscopy (RAIRS) and periodic density functional theory (DFT+U) calculations. On the fully oxidized surface, acetaldehyde adsorbs weakly through its carbonyl O interacting with a lattice Ce(4+) cation in the η(1)-O configuration. This state desorbs at 210 K without reaction. On the highly reduced surface, new vibrational signatures appear below 220 K. They are identified by RAIRS and DFT as a dimer state formed from the coupling of the carbonyl O and the acyl C of two acetaldehyde molecules. This dimer state remains up to 400 K before decomposing to produce another distinct set of vibrational signatures, which are identified as the enolate form of acetaldehyde (CH(2)CHO¯). Furthermore, the calculated activation barriers for the coupling of acetaldehyde, the decomposition of the dimer state, and the recombinative desorption of enolate and H as acetaldehyde are in good agreement with previously reported TPD results for acetaldehyde adsorbed on reduced CeO(2)(111) [Chen et al. J. Phys. Chem. C 2011, 115, 3385]. The present findings demonstrate that surface oxygen vacancies alter the reactivity of the CeO(2)(111) surface and play a crucial role in stabilizing and activating acetaldehyde for coupling reactions.

  10. Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase

    SciTech Connect

    Ghosh, Arup K.; Chatterjee, Piyali; Chakraborty, Tapas

    2014-07-28

    Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via α-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion.

  11. Enolic schiff base aluminum complexes and their catalytic stereoselective polymerization of racemic lactide.

    PubMed

    Pang, Xuan; Du, Hongzhi; Chen, Xuesi; Wang, Xianhong; Jing, Xiabin

    2008-01-01

    A series of enolic Schiff base aluminum(III) complexes LAlR (where L=NNOO-tetradentate enolic Schiff base ligand) containing ligands that differ in their steric and electronic properties were synthesized. Their single crystals showed that these complexes are five-coordinated around the aluminum center. Their coordination geometries are between square pyramidal and trigonal bipyramidal. Their catalytic properties in the solution polymerization of racemic lactide (rac-LA) were examined. The modifications in the auxiliary ligand exhibited a dramatic influence on the catalytic performance. Lengthening the backbone from C(2) alkylene to C(3) alkylene resulted in remarkable enhancement of both the stereoselectivity and the polymerization rate because of the increasing flexibility of the diimine backbone. Electron-withdrawing substituents in the diketone also highly improved the activity and the stereoselectivity. Among these complexes, 4 b had the highest activity and the stereoselectivity owing to the C(3) alkylene backbone and the two gem-methyl groups on the middle carbon atom. The value of the polymerization rate constant (k(p)) catalyzed by 4 b in 70 degrees C was 1.90 L mol(-1) min(-1), the activation energy of the polymerization (35.4 kJ mol(-1)) was calculated according to the Arrhenius equation. Other factors that influenced the polymerization, such as the polymerization time, the temperature, and the monomer concentration, are also discussed in detail.

  12. Plant Cyclic Nucleotide Signalling

    PubMed Central

    Martinez-Atienza, Juliana; Van Ingelgem, Carl; Roef, Luc

    2007-01-01

    The presence of the cyclic nucleotides 3′,5′-cyclic adenyl monophosphate (cAMP) and 3′,5′-cyclic guanyl monophosphate (cGMP) in plants is now generally accepted. In addition, cAMP and cGMP have been implicated in the regulation of important plant processes such as stomatal functioning, monovalent and divalent cation fluxes, chloroplast development, gibberellic acid signalling, pathogen response and gene transcription. However, very little is known regarding the components of cyclic nucleotide signalling in plants. In this addendum, the evidence for specific mechanisms of plant cyclic nucleotide signalling is evaluated and discussed. PMID:19704553

  13. Quercetin 3,7-dimethyl ether: a vasorelaxant flavonoid isolated from Croton schiedeanus Schlecht.

    PubMed

    Guerrero, M F; Puebla, P; Carrón, R; Martín, M L; San Román, L

    2002-10-01

    The vasorelaxant profile of quercetin 3,7-dimethyl ether, a flavonoid isolated from Croton schiedeanus Schlecht (Euphorbiaceae), was assessed in aortic rings isolated from Wistar rats. To gain insight into its structure-activity relationship, we compared this substance with quercetin 3,4',7-trimethyl ether (ayanin), another flavonoid isolated from this plant, quercetin 3,3',4',7-tetramethyl ether, a flavonoid synthesized by us, and quercetin. In addition we examined the interaction of quercetin 3,7-dimethyl ether with the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway. According to their pEC50 values (concentration producing a 50% inhibition of the maximal contractile response) to phenylephrine-induced precontraction in rat isolated aorta, the potency order was quercetin 3,7-dimethyl ether > quercetin > quercetin 3,4',7-trimethyl ether > quercetin 3,3',4',7-tetramethyl ether (4.70+/-0.18; 3.96+/-0.07; 3.64+/-0.02; 3.11+/-0.16). The relaxant effect of quercetin 3,7-dimethyl ether was significantly decreased by the removal of endothelium as well as by methylene blue, an inhibitor of guanylyl cyclase, and by N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME), an NO-synthase inhibitor. Therefore, quercetin 3,7-dimethyl ether has a NO/cGMP pathway-related profile, with increased vasorelaxant activity due to hydroxylation at positions 3 and 4 of the B ring. In addition, methylation at positions 3 and 7 with respect to quercetin of the C and A rings, respectively, seems to further enhance the vasorelaxant activity of quercetin 3,7-dimethyl ether.

  14. Tautomerism, Raman, infrared and ultraviolet-visible spectra, vibrational assignments, MP2 and B3LYP calculations of dienol 3,4-dihydroxypyridine, keto-enol 3-hydroxypyridin-4-one and keto-enol dimer

    NASA Astrophysics Data System (ADS)

    Shaaban, Ibrahim A.; Mohamed, Tarek A.; Zoghaib, Wajdi M.; Wilson, Lee D.; Farag, Rabie S.; Afifi, Mahmoud S.; Badr, Yehia A.

    2013-07-01

    Raman (3500-100 cm-1) and infrared (4000-200 cm-1) spectra of 3,4-dihydroxypyridine (3,4-DHP) have been recorded in the solid phase. In addition, the UV spectrum (350-190 nm) of 3,4-DHP was measured in ethanol solution. Thirteen structures were initially proposed for 3,4-DHP as a result of keto-enol tautomerism and rotation(s) of hydroxyl group(s) around the Csbnd O bond. The conformational energies have been calculated with the methods of MP2, MP2(full) and B3LYP/DFT utilizing a variety of basis sets up to 6-311++G(d,p). Moreover, TD-DFT/B3LYP/6-311+G(d,p) computations of dienol (DHP) and keto-enol (HPO) tautomers were used to predict the electronic absorption spectra in ethanol solution utilizing a PCM. The theoretical results were compiled with infrared and Raman spectral data, favoring a mixture of dienol 3,4-dihydroxypyridine (structure 2) and keto-enol 3-hydroxypyridin-4-one (structure 9) in the solid phase. However, the keto-enol HPO tautomer is favored in solutions in agreement with the observed/calculated UV spectra. Moreover, mass spectral analysis indicates the presence of equimolar proportions of 3,4-DHP monomer and its dimer. Aided by DFT/B3LYP and ab intio/MP2(full) frequency calculations at 6-31G(d) basis set and the simulated vibrational spectra of dienol DHP and keto-enol HPO mixture, a complete vibrational assignment of the observed infrared and Raman bands has been proposed supported by normal coordinate analysis and potential energy distributions (PEDs). The results reported herein are compared with similar structural analogues whenever appropriate.

  15. Phosphine catalyzed alpha-arylation of enones and enals using hypervalent bismuth reagents: regiospecific enolate arylation via nucleophilic catalysis.

    PubMed

    Koech, Phillip K; Krische, Michael J

    2004-05-05

    Exposure of enones and enals to 20 mol % tributylphosphine in the presence of triarylbismuth(V) dichlorides results in regiospecific aryl transfer to the alpha-position of the enone or enal pronucleophile. These results represent the first examples of enolate arylation under the conditions of nucleophilic catalysis.

  16. Photochemistry of 2-diphenylmethoxyacetophenone. Direct detection of a long-lived enol from a Norrish Type II photoreaction.

    PubMed

    Sundaresan, Arun Kumar; Jockusch, Steffen; Turro, Nicholas J

    2011-09-01

    Photolysis of 2-diphenylmethoxyacetophenone (1) in deaerated acetonitrile at room temperature is expected to proceed via Norrish Type II reaction to generate benzophenone (2) and acetophenone (4) as the main isolated photoproducts. Although the acetophenone enol intermediate (3) is generally considered a putative intermediate that is a precursor of acetophenone, there are few reports of the direct spectroscopic detection of 3 when a Type II reaction is conducted in solution at room temperature. Presumably, rapid enol-ketone isomerisation under the reaction conditions causes 3 to have a very short lifetime that lowers its concentration below limits detectable by standard organic spectroscopic methods such as (1)H NMR. We report that 3 is readily observed at room temperature by (1)H NMR spectroscopy and showed a remarkably long lifetime of almost 1 h under our reaction conditions. It was found that the acetophenone enols from the classic Norrish Type II reactions of valerophenone and butyrophenone could also be readily detected by (1)H NMR in acetonitrile at room temperature, but that their lifetimes were similar (tens of minutes) from both precursors, but were considerably shorter than that of 1. The reason for the differences in the lifetime of the acetophenone enol is probably due to small amounts of adventitious catalysts that arise during the photolysis.

  17. Enantioselective Construction of Acyclic Quaternary Carbon Stereocenters: Palladium-Catalyzed Decarboxylative Allylic Alkylation of Fully Substituted Amide Enolates.

    PubMed

    Starkov, Pavel; Moore, Jared T; Duquette, Douglas C; Stoltz, Brian M; Marek, Ilan

    2017-07-19

    We report a divergent and modular protocol for the preparation of acyclic molecular frameworks containing newly created quaternary carbon stereocenters. Central to this approach is a sequence composed of a (1) regioselective and -retentive preparation of allyloxycarbonyl-trapped fully substituted stereodefined amide enolates and of a (2) enantioselective palladium-catalyzed decarboxylative allylic alkylation reaction using a novel bisphosphine ligand.

  18. Organocatalytic Lewis base functionalisation of carboxylic acids, esters and anhydrides via C1-ammonium or azolium enolates.

    PubMed

    Morrill, Louis C; Smith, Andrew D

    2014-09-07

    This tutorial review highlights the organocatalytic Lewis base functionalisation of carboxylic acids, esters and anhydrides via C1-ammonium/azolium enolates. The generation and synthetic utility of these powerful intermediates is highlighted through their application in various methodologies including aldol-lactonisations, Michael-lactonisations/lactamisations and [2,3]-rearrangements.

  19. Imide/Arylene Ether Copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Hergenrother, Paul M.; Bass, Robert G.

    1991-01-01

    New imide/arylene ether copolymers prepared by reacting anhydride-terminated poly(amic acids) with amine-terminated poly(arylene ethers) in polar aprotic solvents. Each resulting copolymer may have one glass-transition temperature or two, depending on chemical structure and/or compatibility of block units. Most of copolymers form tough, solvent-resistant films with high tensile properties. Films cast from solution tough and flexible, and exhibit useful thermal and mechanical properties. Potentially useful as moldings, adhesives, or composite matrices. Because of flexible arylene ether blocks, these copolymers easier to process than polyimides.

  20. Polyarylene Ethers with Improved Properties

    NASA Technical Reports Server (NTRS)

    Hergenrother, P. M. (Inventor); Jensen, B. J. (Inventor); Havens, S. J. (Inventor)

    1986-01-01

    This invention relates to novel polyarylene ethers which possess the combination of high strength, toughness, and high use temperature with ease of extrusion and formation into complex objects. These polyarylene ethers are suitable for use in adhesives, coatings, films, membranes, and composite matrices. The polyarylene ethers of this invention are the polycondensation products from the reaction of either 1,3-bis (4-chloro or fluorobenzoyl) benzene with any one of the following bisphenolic compounds: bis (3-hydroxyphenyl) methane; bis (4-hydroxyphenyl) methane; 1,1-dimethyl-bis (4-hydroxyphenyl)methane, or 9,9-bis (4-hydroxyphenyl) fluorene. Random and block copolymers are also comprehended.

  1. The deglaciation in Picos de Europa (area of Enol Glacier) based on geomorphological and sedimentological studies

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesus; Oliva, Marc; García, Cristina

    2013-04-01

    The chronology for the deglaciation in the Cantabrian Range is still poorly understood. Several papers have proposed a maximum advance well before the LGM (Jiménez and Farias, 2002; Moreno et al. 2010; Serrano et al. 2012). The Western massif of Picos de Europa held a ice field of 50 km2. In this communication we present two cores collected in two glacial depressions in the frontal area of Enol Glacier that allow reconstructing the environment since the deglaciation of the massif. The first core (5.6 m long) was collected in the kame terrace of Belbin. This terrace was dammed by a lateral moraine corresponding to the phase of maximum expansion of Enol Glacier. Three clear layers are observed: the basal 2.5 m consists of grey clay with small gravel limestones; the second is 2 m thick and is composed of grey clays; the upper 1.1 m shows several paleosoils with abundant organic matter and charcoals. The based was dated at 14,810 ± 70 yr BP. This age represents a minimum age for the maximum expansion of Enol Glacier. The second core was collected in the glaciokarst depression of Vega del Bricial, located within a moraine complex corresponding to LGM. The core is 8 m long and looks very homogeneous. It consists of a succession of organic layers and slope deposits. Two radiocarbon dates were performed on the sediments at 8 and 2.8 m depth, resulting in 9,690 ± 260 and 3,420 ± 95 yr BP, respectively. Based on sedimentological and geomorphological evidences, we propose a chronology for the environmental changes occurred in this massif since the last glacial period. References Jiménez, M. and Farias, P., 2002. New radiometric and geomorphologic evidences of a Last Glacial Maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains, NW Spain). Geodinamica Acta, 15, 93-101. Moreno, A., Valero, B. L., Jiménez, M., Domínguez, M. J., Mata, M. P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J. P

  2. Boryl substitution of acetaldehyde makes it an enol: inconsistency between Gn/CBS and ab initio/DFT data.

    PubMed

    Balabin, Roman M

    2010-03-18

    Tautomerism, a particular case of isomerism, plays an important role in modern organic chemistry, biochemistry, medicinal chemistry, pharmacology, and molecular biology. Inconsistency between results of complex energy computation methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio/DFT ones (CCSD(T)/CBS, MP2/CBS, and B3LYP/aug-cc-pVTZ) is found. Gn/CBS methods provide a qualitatively different description of tautomeric (keto-enol) equilibrium in 2-substituted acetaldehydes. According to valence focal point analysis (FPA) based on CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z energies, boryl substitution of acetaldehyde makes it an enol. In other words, enol was found to be the global minimum on the potential energy surface (PES) of C(2)H(5)BO. Gn/CBS methods predict the keto form to be the minimum. The relative energy of alkenol, CH(BH(2))=CH(OH), is calculated to be -1.67 +/- 0.82 kcal mol(-1) at CCSD(T)/CBS level of theory. Hydrogen shift effects are also calculated in two other 2-substituted acetaldehydes, namely, 3-oxopropanenitrile (C(3)H(3)NO) and ethanal (C(2)H(4)O), with a general formula of XH(2)C-CHO (X = BH(2), CN, and H). Electron density (charge) transfer between the C=C double bond and the free p orbital of the boron atom (B) in a boryl group (BH(2)) greatly stabilizes enol with respect to ketone, CH(2)(BH(2))-CHO. The first known stabilization of enol in an acetaldehyde derivative, without an intramolecular hydrogen bond (H-bond), questions the accuracy of complex energy computation methods for boron-containing molecules. The possible reasons and consequences of this finding are discussed.

  3. Nanomolar inhibition of type II dehydroquinase based on the enolate reaction mechanism.

    PubMed

    Toscano, Miguel D; Payne, Richard J; Chiba, Akira; Kerbarh, Olivier; Abell, Chris

    2007-01-01

    We describe the rational design of a novel, highly potent inhibitor of type II dehydroquinase, the dicarboxylate 6. The incorporation of a carboxylate at the 3-position mimics the putative enolate intermediate in the reaction mechanism, and allows a potential electrostatic binding interaction with the arginine on the active site flap. This results in a 1000-fold increase in potency, making the dicarboxylate 6 the most potent inhibitor of type II dehydroquinase reported to date, with a high ligand efficiency of -0.68 kcal mol(-1) per nonhydrogen atom. The systematic dissection of 6 in compounds 7-12, all of which show a drop in potency, confirm the synergistic importance of the two carboxylates, the C3 and C4 hydroxyl groups, and the anhydroquinate ring structure for the potency of 6.

  4. AuBr(3)-catalyzed [4 + 2] benzannulation between an enynal unit and enol.

    PubMed

    Asao, Naoki; Aikawa, Haruo; Yamamoto, Yoshinori

    2004-06-23

    The reaction of enynals 1, including o-alkynylbenzaldehydes, and carbonyl compounds 2 in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. The AuBr3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuBr3, the formation of a pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand-type Diels-Alder addition of the enols, derived from 2, to the auric ate complex, and subsequent dehydration and bond rearrangement. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds afforded the corresponding aromatic compounds in good yields.

  5. Catalytic Enantioselective Michael Addition Reactions of Tertiary Enolates Generated by Detrifluoroacetylation.

    PubMed

    Zhu, Yi; Zhang, Wenzhong; Mei, Haibo; Han, Jianlin; Soloshonok, Vadim A; Pan, Yi

    2017-08-22

    This work describes, for the first time, Michael addition reactions of tertiary fluoro-enolates in situ generated by detrifluoroacetylation with 1-(1-(phenylsulfonyl) vinylsulfonyl)benzene. Excellent enantioselectivity and chemical yields were achieved with application of catalysts (10 mol %) derived from Cu(OTf)2 and (1S,2S)-1,2-diphenylethane-1,2-diamine. These reactions show a considerable degree of structural generality and allow the preparation of new types of biologically relevant molecules that contain quaternary C-F stereogenic carbon atoms and feature five-, six-, or seven-membered rings as well as heterocyclic 3-fluoro-2,3-dihydrochromen-4-one moieties. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Catalytic, Asymmetric α-Fluorination of Acid Chlorides: Dual Metal-Ketene Enolate Activation

    PubMed Central

    Paull, Daniel H.; Scerba, Michael T.; Alden-Danforth, Ethan; Widger, Leland R.; Lectka, Thomas

    2009-01-01

    In this Communication, we disclose a catalytic, highly enantioselective (up to >99% ee) α-fluorination of acid chlorides to produce a variety of optically active carboxylic acid derivatives from readily accessible and commercially available starting materials. The reaction depends on dually activated ketene enolates generated from two discrete catalysts - a chiral nucleophile and an achiral transition metal complex working in tandem. The active, putative α-fluorobis(sulfonimide) intermediates readily transacylate in situ under mild conditions upon addition of a wide variety of nucleophiles, including complex natural products. As a consequence, the power of this method is witnessed by the broad range of α-fluorinated products that can be accessed efficiently depending on the work up conditions. PMID:19049284

  7. Imide/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor); Bass, Robert G. (Inventor)

    1992-01-01

    Imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly(arylene ethers) in polar aprotic solvents and by chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The resulting block copolymers have one glass transition temperature or two, depending upon the particular structure and/or the compatibility of the block units. Most of these block copolymers form tough, solvent resistant films with high tensile properties.

  8. Macrocyclic oligoureas with xanthene and diphenyl ether units.

    PubMed

    Meshcheryakov, Denys; Bolte, Michael; Böhmer, Volker

    2009-11-07

    Two cyclic oligoureas with 64- and 80-membered rings in which two sets of three or four rigid xanthene (X) units are connected via flexible diphenyl ether (D) units were synthesized by a stepwise fragment condensation. The compounds were characterized by (1)H NMR and ESI mass spectrometry. The structure of the cyclic octamer (XXXDXXXD) was additionally confirmed by single crystal X-ray analysis. The molecule assumes a strongly folded conformation with distorted C(2)-symmetry, stabilized by intramolecular hydrogen bonds. Surprisingly, intermolecular hydrogen bonds between the macrocycles were not observed. (1)H NMR spectra suggest a C(2) symmetrical conformation of the octamer in solution also, while its kinetically stable complex with three chloride ions has no symmetry element at all.

  9. Space, Time, Ether, and Kant

    NASA Astrophysics Data System (ADS)

    Wong, Wing-Chun Godwin

    This dissertation focused on Kant's conception of physical matter in the Opus postumum. In this work, Kant postulates the existence of an ether which fills the whole of space and time with its moving forces. Kant's arguments for the existence of an ether in the so-called Ubergang have been acutely criticized by commentators. Guyer, for instance, thinks that Kant pushes the technique of transcendental deduction too far in trying to deduce the empirical ether. In defense of Kant, I held that it is not the actual existence of the empirical ether, but the concept of the ether as a space-time filler that is subject to a transcendental deduction. I suggested that Kant is doing three things in the Ubergang: First, he deduces the pure concept of a space-time filler as a conceptual hybrid of the transcendental object and permanent substance to replace the category of substance in the Critique. Then he tries to prove the existence of such a space-time filler as a reworking of the First Analogy. Finally, he takes into consideration the empirical determinations of the ether by adding the concept of moving forces to the space -time filler. In reconstructing Kant's proofs, I pointed out that Kant is absolutely committed to the impossibility of action-at-a-distance. If we add this new principle of no-action-at-a-distance to the Third Analogy, the existence of a space-time filler follows. I argued with textual evidence that Kant's conception of ether satisfies the basic structure of a field: (1) the ether is a material continuum; (2) a physical quantity is definable on each point in the continuum; and (3) the ether provides a medium to support the continuous transmission of action. The thrust of Kant's conception of ether is to provide a holistic ontology for the transition to physics, which can best be understood from a field-theoretical point of view. This is the main thesis I attempted to establish in this dissertation.

  10. Sulfonimide-containing poly(arylene ether)s and poly(arylene ether sulfone)s, methods for producing the same, and uses thereof

    DOEpatents

    Hofmann, Michael A.

    2006-11-14

    The present invention is directed to sulfonimide-containing polymers, specifically sulfonimide-containing poly(arylene ether)s and sulfonimide-containing poly(arylene ether sulfone)s, and processes for making the sulfonimide-containing poly(arylene ether)s and sulfonimide-containing poly(arylene ether sulfone)s, for use conductive membranes and fuel cells.

  11. Affordable Cyclic Voltammetry

    ERIC Educational Resources Information Center

    Stewart, Greg; Kuntzleman, Thomas S.; Amend, John R.; Collins, Michael J.

    2009-01-01

    Cyclic voltammetry is an important component of the undergraduate chemical curriculum. Unfortunately, undergraduate students rarely have the opportunity to conduct experiments in cyclic voltammetry owing to the high cost of potentiostats, which are required to control these experiments. By using MicroLab data acquisition interfaces in conjunction…

  12. Affordable Cyclic Voltammetry

    ERIC Educational Resources Information Center

    Stewart, Greg; Kuntzleman, Thomas S.; Amend, John R.; Collins, Michael J.

    2009-01-01

    Cyclic voltammetry is an important component of the undergraduate chemical curriculum. Unfortunately, undergraduate students rarely have the opportunity to conduct experiments in cyclic voltammetry owing to the high cost of potentiostats, which are required to control these experiments. By using MicroLab data acquisition interfaces in conjunction…

  13. Designing cyclic universe models.

    PubMed

    Khoury, Justin; Steinhardt, Paul J; Turok, Neil

    2004-01-23

    The phenomenological constraints on the scalar field potential in cyclic models of the Universe are presented. We show that cyclic models require a comparable degree of tuning to that needed for inflationary models. The constraints are reduced to a set of simple design rules including "fast-roll" parameters analogous to the "slow-roll" parameters in inflation.

  14. Cyclic Hematopoiesis: animal models

    SciTech Connect

    Jones, J.B.; Lange, R.D.

    1983-08-01

    The four existing animal models of cyclic hematopoiesis are briefly described. The unusual erythropoietin (Ep) responses of the W/Wv mouse, the Sl/Sld mouse, and cyclic hematopoietic dog are reviewed. The facts reviewed indicate that the bone marrow itself is capable of influencing regulatory events of hematopoiesis.

  15. Enolate Stabilization by Anion-π Interactions: Deuterium Exchange in Malonate Dilactones on π-Acidic Surfaces.

    PubMed

    Miros, François N; Zhao, Yingjie; Sargsyan, Gevorg; Pupier, Marion; Besnard, Céline; Beuchat, César; Mareda, Jiri; Sakai, Naomi; Matile, Stefan

    2016-02-18

    Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion-π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π-acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π-acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α-protons in the (1) H NMR spectra. The reactivity of these protons on π-acidic surfaces is measured by hydrogen-deuterium (H-D) exchange for 11 different examples, excluding controls. The velocity of H-D exchange increases with π acidity (NDI core substituents: SO2 R>SOR>H>OR>OR/NR2 >SR>NR2 ). The H-D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11-13 atoms). Most importantly, H-D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure (R,R,P)-macrocycle is reported). For maximal π acidity, transition-state stabilizations up to -18.8 kJ mol(-1) are obtained for H-D exchange. The Brønsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured pKa =10.9 calculates to a ΔpKa =-5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as "impossible" in biology, the found enolate-π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven-component π-acidity gradient over almost 1 eV demonstrates quantitatively that such important anion-π activities can be expected only from

  16. Chiral N-heterocyclic carbene-catalyzed generation of ester enolate equivalents from α,β-unsaturated aldehydes for enantioselective Diels–Alder reactions

    PubMed Central

    Kaeobamrung, Juthanat; Kozlowski, Marisa C.; Bode, Jeffrey W.

    2010-01-01

    The catalytic generation of chiral ester enolate equivalents from α,β-unsaturated aldehydes with chiral N-hetereocyclic carbene catalysts makes possible highly enantioselective hetero-Diels–Alder reactions. The reactions proceed under simple, mild conditions with both aliphatic and aromatic substituted enals as substrates. Previous attempts to employ these starting materials as enolate precursors gave structurally different products via catalytically generated homoenolate equivalents. Critical to the success of the enolate generation was the strength of the catalytic base used to generate the active N-heterocyclic carbene catalyst. To complement these studies, we have investigated the enolate structure using computational methods and find that it prefers conformations perpendicular to the triazolium core. PMID:20974930

  17. Protonation-assisted conjugate addition of axially chiral enolates: asymmetric synthesis of multisubstituted β-lactams from α-amino acids.

    PubMed

    Yoshimura, Tomoyuki; Takuwa, Masatoshi; Tomohara, Keisuke; Uyama, Makoto; Hayashi, Kazuhiro; Yang, Pan; Hyakutake, Ryuichi; Sasamori, Takahiro; Tokitoh, Norihiro; Kawabata, Takeo

    2012-11-26

    β-Lactams with contiguous tetra- and trisubstituted carbon centers were prepared in a highly enantioselective manner through 4-exo-trig cyclization of axially chiral enolates generated from readily available α-amino acids. Use of a weak base (metal carbonate) in a protic solvent (EtOH) is the key to the smooth production of β-lactams. Use of the weak base is expected to generate the axially chiral enolates in a very low concentration, which undergo intramolecular conjugate addition without suffering intermolecular side reactions. Highly strained β-lactam enolates thus formed through reversible intramolecular conjugate addition (4-exo-trig cyclization) of axially chiral enolates undergo prompt protonation by EtOH in the reaction media (not during the work-up procedure) to give β-lactams in up to 97% ee. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Rotational isomers of N-methyl-N-arylacetamides and their derived enolates: implications for asymmetric Hartwig oxindole cyclizations

    PubMed Central

    Mandel, Jérémie; Pan, Xiaohong; Ben Hay, E.; Geib, Steven J.

    2013-01-01

    The rotational preferences of N-(2-bromo-4,6-dimethylphenyl)-N-methyl 2-phenyl-propanamide were studied as a model of precursors for Hartwig asymmetric oxindole cyclizations. The atropisomers of this compound were separated by flash chromatography, then the enantiomers were resolved and the interconversions of the stereocenter and the N–Ar axis were studied. Under thermal conditions, the axis is very stable. Under the basic conditions of the Hartwig cyclization, both the stere-ocenter and the chiral axis equilibrate via enolate formation. The N–Ar rotation barrier of a 2-phenylacetamide analog was reduced from 31 kcal mol−1 in the precursor to 17 kcal mol−1 in the enolate. Reasons for this dramatic barrier reduction and implications of both N–Ar and amide C–N rotations for Hartwig cyclizations are discussed. PMID:23534372

  19. Anion-π Catalysis of Enolate Chemistry: Rigidified Leonard Turns as a General Motif to Run Reactions on Aromatic Surfaces.

    PubMed

    Cotelle, Yoann; Benz, Sebastian; Avestro, Alyssa-Jennifer; Ward, Thomas R; Sakai, Naomi; Matile, Stefan

    2016-03-18

    To integrate anion-π, cation-π, and ion pair-π interactions in catalysis, the fundamental challenge is to run reactions reliably on aromatic surfaces. Addressing a specific question concerning enolate addition to nitroolefins, this study elaborates on Leonard turns to tackle this problem in a general manner. Increasingly refined turns are constructed to position malonate half thioesters as close as possible on π-acidic surfaces. The resulting preorganization of reactive intermediates is shown to support the disfavored addition to enolate acceptors to an absolutely unexpected extent. This decisive impact on anion-π catalysis increases with the rigidity of the turns. The new, rigidified Leonard turns are most effective with weak anion-π interactions, whereas stronger interactions do not require such ideal substrate positioning to operate well. The stunning simplicity of the motif and its surprisingly strong relevance for function should render the introduced approach generally useful.

  20. Flash photolytic generation of two keto tautomers of 1-naphthol in aqueous solution: kinetics and equilibria of enolization.

    PubMed

    Gut, Ivo Glynne; Scheibler, Lukas C; Wirz, Jakob

    2010-07-30

    Benzo[b]cyclohexa-2,4-dien-1-one (4) and benzo[b]cyclohexa-2,5-dien-1-one (5), the two most stable keto tautomers of 1-naphthol (1), were generated in aqueous solution by Norrish Type II fission of 4- and 2-phenacyl-1-tetralone, respectively, and the pH-rate profiles of their enolization were measured by flash photolysis. Several isotopic exchange rates of 1 were measured in aqueous acid to determine the corresponding rate constants of ketonization. The resulting equilibrium constants for enolization are pKE(4) = -7.1 and pKE(5) = -6.2. The acidity constants of the carbon acids 4 and 5, pKa(4) = 2.1 and pKa(5) = 3.0, were then obtained from a thermodynamic cycle using pKa(1) = 9.25.

  1. Enhanced degradation of spiro-insecticides and their leacher enol derivatives in soil by solarization and biosolarization techniques.

    PubMed

    Fenoll, José; Garrido, Isabel; Vela, Nuria; Ros, Caridad; Navarro, Simón

    2017-04-01

    The leaching potential of three insecticides (spirodiclofen, spiromesifen, and spirotetramat) was assessed using disturbed soil columns. Small quantities of spirodiclofen and spiromesifen were detected in leachate fraction, while spirotetramat residues were not found in the leachates. In addition, the transformation products (enol derivatives) are relatively more mobile than the parent compounds and may leach into groundwater. Moreover, the use of disinfection soil techniques (solarization and biosolarization) to enhance their degradation rates in soil was investigated. The results show that both practices achieved a reduction in the number of juvenile nematodes, enhancing in a parallel way degradation rates of the insecticides and their enol derivatives as compared with the non-disinfected soil. This behavior can be mainly attributed to the increase in soil temperature and changes in microbial activity. All insecticides showed similar behavior under solarization and biosolarization conditions. As a consequence, both agronomic techniques could be considered as suitable strategies for detoxification of soils polluted with the studied pesticides.

  2. Palladium-catalyzed arylation of ketone enolates: an expeditious entry to tamoxifen-related 1,2,2-triarylethanones.

    PubMed

    Churruca, Fátima; SanMartin, Raul; Tellitu, Imanol; Domínguez, Esther

    2002-05-02

    [reaction: see text]. After a rigorous study on the effect of several catalytic systems, a simple, high yielding procedure for the preparation of 1,2,2-triarylethanones, skeletal analogues of tamoxifen, is presented. Apart from the economic and environmental advantages involved, this palladium-catalyzed arylation of deoxybenzoin enolates features a lack of ortho-arylation side reactions. In addition, an alternative approach from acetophenones to the target triarylethanone system is also announced.

  3. Oxa-ene reaction of enols of amides with 4-phenyl-1,2,4-triazoline-3,5-dione.

    PubMed

    Basheer, Ahmad; Rappoport, Zvi

    2008-01-04

    The reaction of 16 enols of amides with 4-phenyl-1,2,4-triazoline-1,3-dione gave open chain adducts rather than the [2 + 2] cycloadducts with a hemiaminal moiety, both in solid state and in solution. This assignment is based on X-ray crystallography, (1)H and (13)C NMR data, and IR spectra. The suggested mechanism involves hydroxyl proton loss in a formal oxa-ene reaction. Mechanistic details and a possible alternative are discussed.

  4. Application of ionic liquid halide nucleophilicity for the cleavage of ethers: a green protocol for the regeneration of phenols from ethers.

    PubMed

    Boovanahalli, Shanthaveerappa K; Kim, Dong Wook; Chi, Dae Yoon

    2004-05-14

    We have used the high nucleophilicity of bromide ion in the form of the ionic liquid, 1-n-butyl-3-methylimidazolium bromide ([bmim][Br]), for the nucleophilic displacement of an alkyl group to regenerate a phenol from the corresponding aryl alkyl ether. Using 2-methoxynaphthalene (1) as a model compound, we found that the combination of ionic liquid [bmim][Br] and p-toluenesulfonic acid with warming effected demethylation in 14 h, affording the desired product 2-naphthol (2) in good yield (97%). Various other protic acids (MsOH, hydrochloric acid (35%), dilute sulfuric acid (50%)) could be used as a proton source in this demethylation reaction. Under the same conditions, cleavage of alkyl alkyl ether 2-(3-methoxypropyl)naphthalene yielded mixture of corresponding 2-(3-bromopropyl)naphthalene and 2-(3-hydroxypropyl)naphthalene. Dealkylation of various aryl alkyl ethers could also be achieved using significantly reduced (i.e., stoichiometric) amounts of concentrated hydrobromic acid (47%) in the ionic liquid. Both procedures afforded the desired products in moderate to good yield; however, cleavage of aryl alkyl cyclic ether, 2,3-dihydrobenzofuran, resulted in low yield of the desired product o-2-bromoethylphenol. The convenience of this method for ether cleavage and its effectiveness using only a moderate excess of hydrobromic acid make it attractive as a green chemical method.

  5. Microwave-Assisted Organocatalyzed Rearrangement of Propargyl Vinyl Ethers to Salicylaldehyde Derivatives: An Experimental and Theoretical Study.

    PubMed

    Tejedor, David; Cotos, Leandro; Márquez-Arce, Daniel; Odriozola-Gimeno, Mikel; Torrent-Sucarrat, Miquel; Cossío, Fernando P; García-Tellado, Fernando

    2015-12-07

    The microwave-assisted imidazole-catalyzed transformation of propargyl vinyl ethers (PVEs) into multisubstituted salicylaldehydes is described. The reaction is instrumentally simple, scalable, and tolerates a diverse degree of substitution at the propargylic position of the starting PVE. The generated salicylaldehyde motifs incorporate a broad range of topologies, spanning from simple aromatic monocycles to complex fused polycyclic systems. The reaction is highly regioselective and takes place under symmetry-breaking conditions. The preparative power of this reaction was demonstrated in the first total synthesis of morintrifolin B, a benzophenone metabolite isolated from the small tree Morinda citrifolia L. A DFT study of the reaction was performed with full agreement between calculated values and experimental results. The theoretically calculated values support a domino mechanism comprising a propargyl Claisen rearrangement, a [1,3]-H shift, a [1,7]-H shift (enolization), a 6π electrocyclization, and an aromatization reaction.

  6. Cyclic control stick

    DOEpatents

    Whitaker, Charles N.; Zimmermann, Richard E.

    1989-01-01

    A cyclic control stick of the type used in helicopters for reducing the safety hazards associated with such a mechanism in the event of a crewman being thrown violently into contact with the cyclic control stick resulting from a crash or the like. The cyclic control stick is configured to break away upon the exertion of an impact force which exceeds a predetermined value and/or is exerted for more than a momentary time duration. The cyclic control stick is also configured to be adjustable so as to locate the grip thereof as far away from the crewman as possible for safety reasons without comprising the comfort of the crewman or the use of the control stick, and a crushable pad is provided on the top of the grip for impact energy absorbing purposes.

  7. Cyclic steps on ice

    NASA Astrophysics Data System (ADS)

    Yokokawa, M.; Izumi, N.; Naito, K.; Parker, G.; Yamada, T.; Greve, R.

    2016-05-01

    Boundary waves often form at the interface between ice and fluid flowing adjacent to it, such as ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may also be formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice caps of Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic steps are relatives of upstream-migrating antidunes. Cyclic step formation on ice is not only a mechanical but also a thermodynamic process. There have been very few studies on the formation of either cyclic steps or upstream-migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclic steps on ice by flowing water, and found that trains of steps form when the Froude number is larger than unity. The features of those steps allow them to be identified as ice-bed analogs of cyclic steps in alluvial and bedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formation of upstream-migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experiments with the predictions of the analysis and found the observed steps fall in the range where the analysis predicts interfacial instability. We also found that short antidune-like undulations formed as a precursor to the appearance of well-defined steps. This fact suggests that such antidune-like undulations correspond to the instability predicted by the analysis and are precursors of cyclic steps.

  8. 21 CFR 868.5420 - Ether hook.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ether hook. 868.5420 Section 868.5420 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Therapeutic Devices § 868.5420 Ether hook. (a) Identification. An ether hook is a...

  9. 21 CFR 868.5420 - Ether hook.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Ether hook. 868.5420 Section 868.5420 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Therapeutic Devices § 868.5420 Ether hook. (a) Identification. An ether hook is a device...

  10. Cyclic polymers from alkynes.

    PubMed

    Roland, Christopher D; Li, Hong; Abboud, Khalil A; Wagener, Kenneth B; Veige, Adam S

    2016-08-01

    Cyclic polymers have dramatically different physical properties compared with those of their equivalent linear counterparts. However, the exploration of cyclic polymers is limited because of the inherent challenges associated with their synthesis. Conjugated linear polyacetylenes are important materials for electrical conductivity, paramagnetic susceptibility, optical nonlinearity, photoconductivity, gas permeability, liquid crystallinity and chain helicity. However, their cyclic analogues are unknown, and therefore the ability to examine how a cyclic topology influences their properties is currently not possible. We have solved this challenge and now report a tungsten catalyst supported by a tetraanionic pincer ligand that can rapidly polymerize alkynes to form conjugated macrocycles in high yield. The catalyst works by tethering the ends of the polymer to the metal centre to overcome the inherent entropic penalty of cyclization. Gel-permeation chromatography, dynamic and static light scattering, viscometry and chemical tests are all consistent with theoretical predictions and provide unambiguous confirmation of a cyclic topology. Access to a wide variety of new cyclic polymers is now possible by simply choosing the appropriate alkyne monomer.

  11. Cyclic polymers from alkynes

    NASA Astrophysics Data System (ADS)

    Roland, Christopher D.; Li, Hong; Abboud, Khalil A.; Wagener, Kenneth B.; Veige, Adam S.

    2016-08-01

    Cyclic polymers have dramatically different physical properties compared with those of their equivalent linear counterparts. However, the exploration of cyclic polymers is limited because of the inherent challenges associated with their synthesis. Conjugated linear polyacetylenes are important materials for electrical conductivity, paramagnetic susceptibility, optical nonlinearity, photoconductivity, gas permeability, liquid crystallinity and chain helicity. However, their cyclic analogues are unknown, and therefore the ability to examine how a cyclic topology influences their properties is currently not possible. We have solved this challenge and now report a tungsten catalyst supported by a tetraanionic pincer ligand that can rapidly polymerize alkynes to form conjugated macrocycles in high yield. The catalyst works by tethering the ends of the polymer to the metal centre to overcome the inherent entropic penalty of cyclization. Gel-permeation chromatography, dynamic and static light scattering, viscometry and chemical tests are all consistent with theoretical predictions and provide unambiguous confirmation of a cyclic topology. Access to a wide variety of new cyclic polymers is now possible by simply choosing the appropriate alkyne monomer.

  12. Keto-enol tautomerism in asymmetric Schiff bases derived from p-phenylenediamine

    NASA Astrophysics Data System (ADS)

    Užarević, Krunoslav; Rubčić, Mirta; Stilinović, Vladimir; Kaitner, Branko; Cindrić, Marina

    2010-12-01

    Reaction of dehydroacetic acid and p-phenylenediamine afforded a monosubstituted Schiff base, I, with the other amino group free. In further reactions with various salicylaldehyde derivatives, I served as a precursor for synthesis of asymmetric bis-Schiff bases. The synthesized compounds are thus comprised of two subunits, dehydroacetic ( dha) and salicylidene ( sal), which are bridged by the phenylene linker. All products were investigated by means of elemental analysis, FT-IR and NMR spectroscopy, thermal methods, powder X-ray diffraction and, when possible, by single crystal X-ray crystallography. Structural and spectroscopic studies revealed that in the bis-products, the dha subunit adopts the keto-amino tautomeric form, while the sal subunit adopts the enol-imino form. Tautomeric forms were not affected if a methoxo group was introduced on the salicylidene ring. Both tautomeric subunits are stabilized by strong resonance-assisted hydrogen bonds, RAHB. The two subunits of the prepared bis-Schiff bases predominantly retain in solution the same tautomeric forms as found in the solid state.

  13. Propylene glycol monomethyl ether (PGME)

    Integrated Risk Information System (IRIS)

    Propylene glycol monomethyl ether ( PGME ) ; CASRN 107 - 98 - 2 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assess

  14. Desoxyhemigossypol-6-methyl-ether

    USDA-ARS?s Scientific Manuscript database

    Desoxyhemigossypol-6-methyl ether is an antimicrobial compound produced by the cotton plant in response to attack by pathogens. For the first time, we now report the crystal structure of this compound. This may prove useful in studies on the interaction of the compound with pathogenic fungal cells...

  15. Lacinilene C 7-methyl ether

    USDA-ARS?s Scientific Manuscript database

    Lacinilene C 7-methyl ether is an antimicrobial compound produced by the cotton plant in response to attack by pathogens. For the first time, we now report the crystal structure of this compound. This may prove useful in studies on the interaction of the compound with pathogenic fungal cells....

  16. p,p\\'-Dibromodiphenyl ether

    Integrated Risk Information System (IRIS)

    p , p ' - Dibromodiphenyl ether ; CASRN 2050 - 47 - 7 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for

  17. Bis(chloroethyl)ether (BCEE)

    Integrated Risk Information System (IRIS)

    Bis ( chloroethyl ) ether ( BCEE ) ; CASRN 111 - 44 - 4 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments fo

  18. Bis(chloromethyl)ether (BCME)

    Integrated Risk Information System (IRIS)

    Bis ( chloromethyl ) ether ( BCME ) ; CASRN 542 - 88 - 1 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments f

  19. The continuous acid-catalyzed dehydration of alcohols in supercritical fluids: A new approach to the cleaner synthesis of acetals, ketals, and ethers with high selectivity

    SciTech Connect

    Gray, W.K.; Smail, F.R.; Hitzler, M.G.; Ross, S.K.; Poliakoff, M.

    1999-11-24

    This report describes a new a continuous method for forming ethers, acetals and ketals using solid acid catalysts, DELOXAN ASP or AMBERLYST 15, and supercritical fluid solvents. In the case of ether formation, the authors observe a high selectivity for linear alkyl ethers with little rearrangement to give branches ethers. Such rearrangement is common in conventional synthesis. The approach is effective for a range of n-alcohols up to n-octanol and also for the secondary alcohol 2-propanol. In the reaction of phenol with an alkylating agent, the continuous reaction can be tuned to give preferential O- or C-alkylation with up to 49% O-alkylation with supercritical propene. The authors also investigate the synthesis of a range of cyclic ethers and show an improved method for the synthesis of THF from 1,4-butandiol under very mild conditions.

  20. The cyclic reduction algorithm

    NASA Astrophysics Data System (ADS)

    Bini, Dario; Meini, Beatrice

    2009-05-01

    Cyclic reduction is an algorithm invented by G.H. Golub and R. W. Hockney in the mid 1960s for solving linear systems related to the finite differences discretization of the Poisson equation over a rectangle. Among the algorithms of Gene Golub, it is one of the most versatile and powerful ever created. Recently, it has been applied to solve different problems from different applicative areas. In this paper we survey the main features of cyclic reduction, relate it to properties of analytic functions, recall its extension to solving more general finite and infinite linear systems, and different kinds of nonlinear matrix equations, including algebraic Riccati equations, with applications to Markov chains, queueing models and transport theory. Some new results concerning the convergence properties of cyclic reduction and its applicability are proved under very weak assumptions. New formulae for overcoming breakdown are provided.

  1. The keto-enol equilibrium in substituted acetaldehydes: focal-point analysis and ab initio limit

    NASA Astrophysics Data System (ADS)

    Balabin, Roman M.

    2011-10-01

    High-level ab initio electronic structure calculations up to the CCSD(T) theory level, including extrapolations to the complete basis set (CBS) limit, resulted in high precision energetics of the tautomeric equilibrium in 2-substituted acetaldehydes (XH2C-CHO). The CCSD(T)/CBS relative energies of the tautomers were estimated using CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z calculations with MP2/aug-cc-pVTZ geometries. The relative enol (XHC = CHOH) stabilities (ΔE e,CCSD(T)/CBS) were found to be 5.98 ± 0.17, -1.67 ± 0.82, 7.64 ± 0.21, 8.39 ± 0.31, 2.82 ± 0.52, 10.27 ± 0.39, 9.12 ± 0.18, 5.47 ± 0.53, 7.50 ± 0.43, 10.12 ± 0.51, 8.49 ± 0.33, and 6.19 ± 0.18 kcal mol-1 for X = BeH, BH2, CH3, Cl, CN, F, H, NC, NH2, OCH3, OH, and SH, respectively. Inconsistencies between the results of complex/composite energy computations methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio methods (CCSD(T)/CBS and MP2/CBS) were found. DFT/aug-cc-pVTZ results with B3LYP, PBE0 (PBE1PBE), TPSS, and BMK density functionals were close to the CCSD(T)/CBS levels (MAD = 1.04 kcal mol-1).

  2. Cyclic membrane separation process

    DOEpatents

    Bowser, John

    2004-04-13

    A cyclic process for controlling environmental emissions of volatile organic compounds (VOC) from vapor recovery in storage and dispensing operations of liquids maintains a vacuum in the storage tank ullage. In one of a two-part cyclic process ullage vapor is discharged through a vapor recovery system in which VOC are stripped from vented gas with a selectively gas permeable membrane. In the other part, the membrane is inoperative while gas pressure rises in the ullage. Ambient air is charged to the membrane separation unit during the latter part of the cycle.

  3. Cyclic membrane separation process

    DOEpatents

    Nemser, Stuart M.

    2005-05-03

    A cyclic process for controlling environmental emissions of volatile organic compounds (VOC) from vapor recovery in storage and dispensing operations of liquids maintains a vacuum in the storage tank ullage. In the first part of a two-part cyclic process ullage vapor is discharged through a vapor recovery system in which VOC are stripped from vented gas with a selectively gas permeable membrane. In the second part, the membrane is inoperative while gas pressure rises in the ullage. In one aspect of this invention, a vacuum is drawn in the membrane separation unit thus reducing overall VOC emissions.

  4. Ether and siloxane functionalized ionic liquids and their mixtures as electrolyte for lithium-ion batteries.

    PubMed

    Chavan, Santosh N; Tiwari, Aarti; Nagaiah, Tharamani C; Mandal, Debaprasad

    2016-06-28

    The present study deals with an investigation of two novel imidazolium ionic liquids bearing ether-ether (1O2O2-Im-2O1) or ether-siloxane (1O2O2-Im-1SiOSi) functionalities with TFSI anion and their mixtures with propylene carbonate as electrolytes in lithium-ion batteries. The electrochemical stability and conductivity of these novel ILs were analyzed by electrochemical studies, such as cyclic voltammetry, linear sweep voltammetry and impedance measurements. The applicability of these ILs as electrolytes in Li-ion batteries was studied in the presence of a high concentration of LiTFSI (1 mol kg(-1) electrolyte) and the ether-ether IL was shown to possess a high electrochemical stability window (ESW) of 5.9 V and good conductivity of 2.2 mS cm(-1). The electrochemical stability and conductivity were further complimented by self-diffusion of different ions using pulsed gradient spin-echo (PGSE) NMR, viscosity and thermal properties like TGA and DSC analysis. More importantly, we explored the effect of temperature on the electrochemical stability and conductivity of these ILs by electrochemical impedance spectroscopy.

  5. Theoretical and vibrational spectroscopic approach to keto-enol tautomerism in methyl-2-(4-methoxybenzoyl)-3-(4-methoxyphenyl)-3-oxopropanoylcarbamate

    NASA Astrophysics Data System (ADS)

    Arı, Hatice; Özpozan, Talat; Büyükmumcu, Zeki; Kabacalı, Yiğit; Saçmaci, Mustafa

    2016-10-01

    A carbamate compound having tricarbonyl groups, methyl-2-(4-methoxybenzoyl)-3-(4-methoxyphenyl)-3-oxopropanoylcarbamate (BPOC) was investigated from theoretical and vibrational spectroscopic point of view employing quantum chemical methods. Hybrid Density Functionals (B3LYP, X3LYP and B3PW91) with 6-311 G(d,p) basis set were used for the calculations. Rotational barrier and conformational analyses were performed to find the most stable conformers of keto and enol forms of the molecule. Three transition states for keto-enol tautomerism in gas phase were determined. The results of the calculations show that enol-1 form of BPOC is more stable than keto and enol-2 forms. Hydrogen bonding investigation including Natural bond orbital analysis (NBO) for all the tautomeric structures was employed to compare intra-molecular interactions. The energies of HOMO and LUMO molecular orbitals for all tautomeric forms of BPOC were predicted. Normal Coordinate Analysis (NCA) was carried out for the enol-1 to assign vibrational bands of IR and Raman spectra. The scaling factors were calculated as 0.9721, 0.9697 and 0.9685 for B3LYP, X3LYP and B3PW91 methods, respectively. The correlation graphs of experimental versus calculated vibrational wavenumbers were plotted and X3LYP method gave better frequency agreement than the others.

  6. Wholly Aromatic Ether-imides. Potential Materials for n-Type Semiconductors

    NASA Technical Reports Server (NTRS)

    Dingemans, Theo J.; St.Clair, Terry L.; Samulski, Edward T.; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    We report on the synthesis and characterization of a novel series low-molar-mass ether-imide rod-shaped model compounds. All ether-imides were obtained by terminating the appropriate rigid core dianhydride, i.e. pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3,4,4'-oxydiphthalic dianhydride (ODPA) with three flexible aryl-ether tails of different chain length. The mono-functional aryl-ether amines, i.e. 4-(3-phenoxy-phenoxy)-phenylamine (2) and 4-(3-phenoxy-3-phenoxy-phenoxy)-phenylamine (4), were synthesized using standard fluoro-displacement and Ullmann condensation techniques. The corresponding ether-imide model compounds were obtained in high yields using a one-step solution imidization procedure. Increasing the number of meta-substituted aryl-ether units reduces the melt transition temperatures and at the same time it increases the solubility of the model compounds. Most model compounds are crystalline solids and form isotropic melts upon heating. 2,7-Bis-(-4-phenoxy-phenyl)-benzo[Imn][3,8]phenanthroline1,3,6,8-tetraone (NDA-n0), however, displays a smectic A (SA) when cooled from the isotropic phase, followed by what appears to be either a highly ordered smectic phase or a, columnar phase. This is the first example, known to date, in which a mesophase is detected in a wholly aromatic ether-imide compound. For all compounds we present spectroscopic data and X-ray diffraction data. Cyclic voltammetry was used to determine the redox behavior and pertinent energy levels of the model compounds.

  7. Measuring exposures to glycol ethers.

    PubMed

    Clapp, D E; Zaebst, D D; Herrick, R F

    1984-08-01

    In 1981, NIOSH began investigating the potential reproductive health effects resulting from exposures to a class of organic solvents known generically as glycol ethers (GE). This research was begun as a result of the NIOSH criteria document development program which revealed little data available on the health effects of glycol ether exposure. Toxicologic research was begun by NIOSH and other researchers which suggested substantial reproductive effects in animals. These animal data motivated a study of human exposures in the occupational setting. In 1981 and 1982 NIOSH conducted several walk-through surveys which included preliminary measurements of exposures in a variety of industries including painting trades, coal mining, production blending and distribution facilities, aircraft fueling, and communications equipment repair facilities. The human exposure data from these surveys is summarized in this paper with most results well below 1 parts per million (ppm) and only a few values approaching 10 ppm. Blood samples were collected at one site resulting in GE concentrations below the limit of detection. Exposures to airborne glycol ethers, in the industries investigated during the collection of this data, revealed several problems in reliably sampling GE at low concentrations. It became apparent, from the data and observations of work practices, that air monitoring alone provided an inadequate index of GE exposure. Further field studies of exposure to GE are anticipated, pending location of additional groups of exposed workers and development of more reliable methods for characterizing exposure, especially biological monitoring.

  8. Residue evaluation of imidacloprid, spirotetramat, and spirotetramat-enol in/on grapes (Vitis vinifera L.) and soil.

    PubMed

    Mohapatra, Soudamini; Kumar, Sampath; Prakash, G S

    2015-10-01

    A combination of imidacloprid and spirotetramat effectively controls sucking pests on grapevines. Residues of these insecticides on grapes were evaluated after treatment with spirotetramat 12% + imidacloprid 12% (240 SC) three times at 90 and 180 g a.i. ha(-1). The samples were extracted and purified by QuEChERS method and analyzed by high-performance liquid chromatography with a photodiode array detector (imidacloprid) and gas chromatography mass spectrometry (spirotetramat and its metabolite spirotetramat-enol). Satisfactory results were obtained with ranges of 80.6-98.6% for the recovery, 3.1-10% for the relative standard deviation range, and 9.8-15.6% for the uncertainty. The limits of detection and quantification were 0.015 μg mL(-1) and 0.05 mg kg(-1), respectively. Initial residue concentrations of imidacloprid after the 90 and 180 g a.i. ha(-1) treatments were 0.912 (half-life 11 days) and 1.681 mg kg(-1) (half-life 12.4 days), respectively. For spirotetramat + spirotetramat-enol, the residue concentrations were 1.337 (half-life 5.6 days) and 2.0 mg kg(-1) (half-life 7.6 days) for the 90 and 180 g a.i. ha(-1) treatments, respectively. Spirotetramat degraded faster than spirotetramat-enol. After treatment at 90 g a.i. ha(-1), the initial residues of both insecticides were within European Union maximum residue limits and a 1-day pre-harvest interval (PHI) was adequate for safe consumption of grapes. After treatment at 180 g a.i. ha(-1), the required PHI was 7 day. Therefore, a PHI of 7 day should be used after treatment with imidacloprid and spirotetramat.

  9. Cyclic Opioid Peptides.

    PubMed

    Remesic, Michael; Lee, Yeon Sun; Hruby, Victor J

    2016-01-01

    For decades the opioid receptors have been an attractive therapeutic target for the treatment of pain. Since the first discovery of enkephalin, approximately a dozen endogenous opioid peptides have been known to produce opioid activity and analgesia, but their therapeutics have been limited mainly due to low blood brain barrier penetration and poor resistance to proteolytic degradation. One versatile approach to overcome these drawbacks is the cyclization of linear peptides to cyclic peptides with constrained topographical structure. Compared to their linear parents, cyclic analogs exhibit better metabolic stability, lower offtarget toxicity, and improved bioavailability. Extensive structure-activity relationship studies have uncovered promising compounds for the treatment of pain as well as further elucidate structural elements required for selective opioid receptor activity. The benefits that come with employing cyclization can be further enhanced through the generation of polycyclic derivatives. Opioid ligands generally have a short peptide chain and thus the realm of polycyclic peptides has yet to be explored. In this review, a brief history of designing ligands for the opioid receptors, including classic linear and cyclic ligands, is discussed along with recent approaches and successes of cyclic peptide ligands for the receptors. Various scaffolds and approaches to improve bioavailability are elaborated and concluded with a discourse towards polycyclic peptides.

  10. Cyclic Voltammetry Experiment.

    ERIC Educational Resources Information Center

    Van Benschoten, James J.; And Others

    1983-01-01

    Describes a three-part experiment designed to introduce cyclic voltammetry to graduate/undergraduate students. Part 1 demonstrates formal reduction potential, redox electron transfer, diffusion coefficient, and electrochemical reversibility. Part 2 investigates electrochemical behavior of acetaminophen. Part 3 examines such experimental variables…

  11. Cyclic Voltammetry Experiment.

    ERIC Educational Resources Information Center

    Van Benschoten, James J.; And Others

    1983-01-01

    Describes a three-part experiment designed to introduce cyclic voltammetry to graduate/undergraduate students. Part 1 demonstrates formal reduction potential, redox electron transfer, diffusion coefficient, and electrochemical reversibility. Part 2 investigates electrochemical behavior of acetaminophen. Part 3 examines such experimental variables…

  12. 13²,17³-Cyclopheophorbide b enol as a catabolite of chlorophyll b in phycophagy by protists.

    PubMed

    Kashiyama, Yuichiro; Yokoyama, Akiko; Shiratori, Takashi; Inouye, Isao; Kinoshita, Yusuke; Mizoguchi, Tadashi; Tamiaki, Hitoshi

    2013-08-19

    Both 13(2),17(3)-cyclopheophorbide a and b enols were produced along with ingestion of green microalgae containing chlorophylls a and b by a centrohelid protist (phycophagy). The results suggest that chlorophyll b as well as chlorophyll a were directly degraded to colored yet non-phototoxic catabolites in the protistan phycophagic process. Such a simple process by the predators makes a contrast to the much sophisticated chlorophyll degradation process of land plants and some algae, where phototoxicity of chlorophylls was cancelled through the multiple enzymatic steps resulting in colorless and non-phototoxic catabolites.

  13. (E)- and (Z)-stereodefined enol phosphonates derived from β-ketoesters: stereocomplementary synthesis of fully-substituted α,β-unsaturated esters.

    PubMed

    Nakatsuji, Hidefumi; Ashida, Yuichiro; Hori, Hiroshi; Sato, Yuka; Honda, Atsushi; Taira, Mayu; Tanabe, Yoo

    2015-08-14

    A versatile, robust, and stereocomplementary synthesis of fully-substituted (E)- and (Z)-stereodefined α,β-unsaturated esters 3 from accessible α-substituted β-ketoesters 1via (E)- and (Z)-enol phosphonates was achieved. The present method involves two accessible reaction sequences: (i) (E)- and (Z)-stereocomplementary enol phosphorylations of a wide variety of β-ketoesters 1 (24 examples; 71–99% yield, each >95: 5 ds), and (ii) (E)- and (Z)-stereoretentive Suzuki–Miyaura cross-coupling (16 examples; 71–91% yield, >81/19 ds) and Negishi cross-coupling (32 examples; 65–96% yield, >95 : 5 ds) using (E)- and (Z)-enol phosphonates 2. 1H-NMR monitoring for a key reactive N-phosphorylammonium (imidazolium) intermediate I and an application in the synthesis of both (E)- and (Z)-tamoxifen precursors 6 are described.

  14. Cyclic networks of quantum gates

    NASA Astrophysics Data System (ADS)

    Cabauy, Peter

    In this thesis we first give an introduction to the basic aspects of quantum computation followed by an analysis of networks of quantum logic gates where the qubit lines are loops (cyclic). Thus far, investigations into cyclic networks of quantum logic gates have not been examined (as far as we know) by the quantum information community. In our investigations of cyclic quantum networks we have studied simple, one and two qubit systems. The analysis includes: classifying networks into groups, the dynamics of the qubits in a cyclic quantum network, and the perturbation effects of an external qubit acting on a cyclic quantum network. The analysis will be followed by a discussion on quantum algorithms and quantum information processing with cyclic quantum networks, a novel implementation of a cyclic network quantum memory and a discussion of quantum sensors via cyclic quantum networks.

  15. Aza crown ether compounds as anion receptors

    DOEpatents

    Lee, H.S.; Yang, X.O.; McBreen, J.

    1998-08-04

    A family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the new family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of LI{sup +} ion in alkali metal batteries. 3 figs.

  16. Aza crown ether compounds as anion receptors

    DOEpatents

    Lee, Hung Sui; Yang, Xiao-Oing; McBreen, James

    1998-08-04

    A family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the new family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of LI.sup.+ ion in alkali metal batteries.

  17. Crystalline Imide/Arylene Ether Copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Hergenrother, Paul M.; Bass, Robert G.

    1991-01-01

    Series of imide/arylene ether block copolymers prepared by using arylene ether blocks to impart low melt viscosity, and imide blocks to provide high strength and other desirable mechanical properties. Work represents extension of LAR-14159 on imide/arylene ether copolymers in form of films, moldings, adhesives, and composite matrices. Copolymers potentially useful in variety of high-temperature aerospace and microelectronic applications.

  18. Polyphenylene ethers with imide linking groups

    NASA Technical Reports Server (NTRS)

    St.clair, T. L.; Burks, H. D. (Inventor)

    1984-01-01

    Novel polyphenylene ethers with imide linking units are disclosed. These polymers incorporate the solvent and thermal resistance of polyimides and the processability of polyphenylene ethers. Improved physical properties over those of the prior art are obtained by incorporating meta linked ethers and/or polyphenylene oxides into the polymer backbone. A novel process for making polymers of this type is also disclosed. The process is unique in that the expected need of high process temperatures and/or special atmospheres are eliminated.

  19. Is the ether group hydrophilic or hydrophobic?

    PubMed

    Menger, Fredric M; Chlebowski, Mary E

    2005-03-29

    A series of six surfactants, each with two ether oxygens within otherwise all-hydrocarbon chains, were synthesized and examined for their colloidal properties. Since an ether oxygen is sterically and conformationally similar to the methylene group it has replaced, the ether effect on micellization should stem mainly from solvation of the oxygen and, possibly, disrupted hydrophobicity of its adjacent carbons. It was found that critical aggregation values among the surfactants differ only modestly despite the total length of the ether-separated carbon segments ranging from 12 to 18. Shorter ether surfactants with only 12 or 14 total carbons appear to form small, loose aggregates owing, presumably, to a mild hydrophilicity of the ether groups. A surfactant with 18 chain carbons has a greater tendency to associate hydrophobically, but this is counterbalanced by a relatively water-free environment encountered by the ether groups within a more conventional micelle interior. The result is a leveling effect in which the critical aggregation concentration (cac) loses it sensitivity to chain length. Above their cac's, none of the ether surfactants is a good solubilizer of tetramethysilane or mesitylene. This is not necessarily a predictable finding since it was conceivable that the presence of interior ether groups might actually enhance solubilization (much as ether is a better solvent than hexane). Foamability and solid adsorption studies also indicate that the ethers impair surface activity. In response to the question posed in the paper's title, two ether groups are not sufficiently hydrophilic to prevent aggregation, but they do manage to alter the micelles' morphology and properties considerably.

  20. LaRC-ITPI/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Working, Dennis C.

    1991-01-01

    As part of an effort to develop high performance structural resins for aerospace applications, work has continued on block copolymers containing imide and arylene ether segments. The arylene ether block used in this study contains a bulky fluorene group in the polymer backbone while the imide block contains an arylene ketone segment similar to that in the arylene ether block and has been named LaRC-ITPI. A series of imide/arylene ether block and segmented copolymers were prepared and characterized. Films were prepared from these copolymers and mechanical properties were measured.

  1. Catalytic Enantioselective Synthesis of C 1‐ and C 2‐Symmetric Spirobiindanones through Counterion‐Directed Enolate C‐Acylation

    PubMed Central

    Rahemtulla, Benjamin F.; Clark, Hugh F.

    2016-01-01

    Abstract A catalytic enantioselective route to C1‐ and C2‐symmetric 2,2′‐spirobiindanones has been realized through an intramolecular enolate C‐acylation. This reaction employs a chiral ammonium counterion to direct the acylation of an in situ generated ketone enolate with a pentafluorophenyl ester. This reaction constitutes the first example of a direct catalytic enantioselective C‐acylation of a ketone and provides an efficient and highly enantioselective route to axially chiral spirobiindanediones. These products can be diastereoselectively derivatized, offering access to a range of functionalized spirocyclic architectures. PMID:27628946

  2. A Metallacycle Fragmentation Strategy for Vinyl Transfer from Enol Carboxylates to Secondary Alcohol C-H Bonds via Osmium- or Ruthenium-Catalyzed Transfer Hydrogenation.

    PubMed

    Park, Boyoung Y; Luong, Tom; Sato, Hiroki; Krische, Michael J

    2015-06-24

    A strategy for catalytic vinyl transfer from enol carboxylates to activated secondary alcohol C-H bonds is described. Using XPhos-modified ruthenium(0) or osmium(0) complexes, enol carboxylate-carbonyl oxidative coupling forms transient β-acyloxy-oxametallacycles, which eliminate carboxylate to deliver allylic ruthenium(II) or osmium(II) alkoxides. Reduction of the metal(II) salt via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-H vinylation and regenerates ketone and zero-valent catalyst.

  3. Effect of structural modification of enol-carboxamide-type nonsteroidal antiinflammatory drugs on COX-2/COX-1 selectivity.

    PubMed

    Lazer, E S; Miao, C K; Cywin, C L; Sorcek, R; Wong, H C; Meng, Z; Potocki, I; Hoermann, M; Snow, R J; Tschantz, M A; Kelly, T A; McNeil, D W; Coutts, S J; Churchill, L; Graham, A G; David, E; Grob, P M; Engel, W; Meier, H; Trummlitz, G

    1997-03-14

    Meloxicam (5), an NSAID in the enol-carboxamide class, was developed on the basis of its antiinflammatory activity and relative safety in animal models. In subsequent screening in microsomal assays using human COX-1 and COX-2, we discovered that it possessed a selectivity profile for COX-2 superior to piroxicam and other marketed NSAIDs. We therefore embarked on a study of enol-carboxamide type compounds to determine if COX-2 selectivity and potency could be dramatically improved by structural modification. Substitution at the 6- and 7-positions of the 4-oxo-1,2-benzothiazine-3-carboxamide, alteration of the N-methyl substituent, and amide modification were all examined. In addition we explored several related systems including the isomeric 3-oxo-1,2-benzothiazine-4-carboxamides, thienothiazines, indolothizines, benzothienothiazines, naphthothiazines, and 1,3- and 1,4-dioxoisoquinolines. While a few examples were found with greater potency in the COX-2 assay, no compound tested had a better COX-2/COX-1 selectivity profile than that of 5.

  4. Gold-catalyzed annulations of 2-alkynyl benzaldehydes with vinyl ethers: synthesis of dihydronaphthalene, isochromene, and bicyclo[2.2.2]octane derivatives.

    PubMed

    Malhotra, Deepika; Liu, Le-Ping; Mashuta, Mark S; Hammond, G B

    2013-03-18

    With the suitable selection of a gold catalyst as well as the appropriate control of the reaction conditions, various new gold-catalyzed cyclizations of 2-alkynyl benzaldehyde with acyclic or cyclic vinyl ethers have been developed. Acetal-tethered dihydronaphthalene and isochromenes were obtained from the reactions of 2-alkynyl benzaldehydes with acyclic vinyl ethers under mild conditions. And, more interestingly, the gold-catalyzed reactions of 2-alkynyl benzaldehyde with a cyclic vinyl ether afforded the bicyclo[2.2.2]octane derivative involving two molecules of cyclic vinyl ethers. These products contain interesting substructures that have been found in many biologically active molecules and natural products. In addition, a gold-catalyzed homo-dimerization of 2-phenylethynyl benzaldehyde 1a was observed when the reaction was carried out in the absence of vinyl ether, affording a set of separable diastereomeric products. Plausible mechanisms for these transformations are discussed; a gold-containing benzopyrylium was regarded as the crucial intermediate by which a number of these new transformations took place.

  5. Cyclic quantum teleportation

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Xuan; Du, Jing; Liu, Si-Yuan; Wang, Xiao-Hui

    2017-08-01

    We propose a scheme of cyclic quantum teleportation for three unknown qubits using six-qubit maximally entangled state as the quantum channel. Suppose there are three observers Alice, Bob and Charlie, each of them has been given a quantum system such as a photon or spin-1/2 particle, prepared in state unknown to them. We show how to implement the cyclic quantum teleportation where Alice can transfer her single-qubit state of qubit a to Bob, Bob can transfer his single-qubit state of qubit b to Charlie and Charlie can also transfer his single-qubit state of qubit c to Alice. We can also implement the cyclic quantum teleportation with N≥slant 3 observers by constructing a 2 N-qubit maximally entangled state as the quantum channel. By changing the quantum channel, we can change the direction of teleportation. Therefore, our scheme can realize teleportation in quantum information networks with N observers in different directions, and the security of our scheme is also investigated at the end of the paper.

  6. Metallo-supramolecular cyclic polymers.

    PubMed

    Zhang, Ke; Zha, Yongping; Peng, Bo; Chen, Yongming; Tew, Gregory N

    2013-10-30

    Cyclic brush polymers represent an exciting new macromolecular topology. For the first time, this new topology has been combined with metallo-supramolecular interactions to construct novel cyclic brush polymers. Here, ring-expansion metathesis polymerization was used to synthesize a universal cyclic template with a polynorbornene backbone, which was further modified with the metal-chelating synthon terpyridine. The terpyridine side chains served as the key supramolecular unit for the creation of cyclic polymer brushes and gels. This metallo-supramolecular functionality allowed direct visualization of the cyclic brush polymers by transmission electron microscopy for the first time. This demonstration should open a new area in which supramolecular interactions are used to build an array of novel cyclic brush copolymers as well as other cyclic-polymer-based architectures generating new materials.

  7. Conformational Study of Dibenzyl Ether

    NASA Astrophysics Data System (ADS)

    Hernandez-Castillo, Alicia O.; Abeysekera, Chamara; Hewett, Daniel M.; Zwier, Timothy S.

    2017-06-01

    Understanding the initial stages of polycyclic aromatic hydrocarbon (PAH) aggregation, the onset of soot formation, is an important goal on the pathway to cleaner combustion processes. PAHs with short alkyl chains, present in fuel-rich combustion environments, can undergo reactions that will chemically link aromatic rings together. One such example of a linked diaryl compound is dibenzyl ether, C_{6}H_{5}-CH_{2}-O-CH_{2}-C_{6}H_{5}. The -CH_{2}-O-CH_{2}- linkage has a length and flexibility well-suited to forming a π-stacked conformation between the two phenyl rings. In this talk, we will explore the single-conformation spectroscopy of dibenzyl ether under jet-cooled conditions in the gas phase. Laser-induced fluorescence, chirped pulse Fourier transform microwave (8-18 GHz region), and single-conformation infrared spectroscopy in the alkyl CH stretch region were all carried out on the molecule, thereby interrogating its full array of electronic, vibrational and rotational degrees of freedom. This work is the first step in a broader study to determine the extent of π-stacking in linked aryl compounds as a function of linkage and PAH size.

  8. Purification of aqueous cellulose ethers

    SciTech Connect

    Bartscherer, K.A.; de Pablo, J.J.; Bonnin, M.C.; Prausnitz, J.M.

    1990-07-01

    Manufacture of cellulose ethers usually involves high amounts of salt by-products. For application of the product, salt must be removed. In this work, we have studied the injection of high-pressure CO{sub 2} into an aqueous polymer-salt solution; we find that upon addition of isopropanol in addition to CO{sub 2}, the solution separates into two phases. One phase is rich in polymer and water, and the other phase contains mostly isopropanol, water and CO{sub 2}. The salt distributes between the two phases, thereby offering interesting possibilities for development of a new purification process for water-soluble polymers. This work presents experimental phase-equilibrium data for hydroxyethyl cellulose and sodium carboxymethyl cellulose with sodium acetate and potassium sulfate, respectively, in the region 40{degree}C and 30 to 80 bar. Based on these data, we suggest a process for the manufacture and purification of water-soluble cellulose ethers. 15 refs., 14 figs., 9 tabs.

  9. Bacterial Utilization of Ether Glycols

    PubMed Central

    Fincher, Edward L.; Payne, W. J.

    1962-01-01

    A soil bacterium capable of using oligo- and polyethylene glycols and ether alcohols as sole sources of carbon for aerobic growth was isolated. The effects of substituent groups added to the ether bonds on the acceptability of the compounds as substrates were studied. Mechanisms for the incorporation of two-carbon compounds were demonstrated by the observation that acetate, glyoxylate, ethylene glycol, and a number of the tricarboxylic acid cycle intermediates served as growth substrates in minimal media. The rate of oxidation of the short-chained ethylene glycols by adapted resting cells varied directly with increasing numbers of two-carbon units in the chains from one to four. The amount of oxygen consumed per carbon atom of oligo- and polyethylene glycols was 100% of theoretical, but only 67% of theoretical for ethylene glycol. Resting cells oxidized oligo- and polyethylene glycols with 2 to 600 two-carbon units in the chains. Longer chained polyethylene glycols (up to 6,000) were oxidized at a very slow rate by these cells. Dehydrogenation of triethylene glycol by adapted cells was observed, coupling the reaction with methylene blue reduction. PMID:13945208

  10. 27 CFR 21.108 - Ethyl ether.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Ethyl ether. 21.108 Section 21.108 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT....108 Ethyl ether. (a) Odor. Characteristic odor. (b) Specific gravity at 15.56 °/15.56 °C. Not...

  11. Polymeric Electrolyte Containing 12-Crown-4 Ether

    NASA Technical Reports Server (NTRS)

    Nagasubramanian, Ganesa; Distefano, Salvador

    1992-01-01

    Experiments show incorporation of 12-crown-4 ether into solid electrolytes based on polyethylene oxide enhances their electrochemical properties. More specifically, 12-crown-4 ether increases Faradaic efficiency for Li+ ions in low-power secondary Li cells and enables operation of these cells at lower temperatures with higher efficiencies.

  12. A Rational Entry to Cyclic Polymers via Selective Cyclization by Self-Assembly and Topology Transformation of Linear Polymers.

    PubMed

    Aoki, Daisuke; Aibara, Gouta; Uchida, Satoshi; Takata, Toshikazu

    2017-05-24

    A simple and effective synthetic route to cyclic polymers has been developed based on the following sequence: (i) selective cyclization of two self-complementary sec-ammonium-containing crown ether monomers to afford [c2] daisy-chain bifunctional initiators, (ii) living polymerization to afford the corresponding linear polymers, and (iii) a topology transformation of these linear polymers to furnish cyclic polymers. The key step in this sequence is the quantitative cyclization via self-assembly of two crown ether molecules with hydroxyl and sec-ammonium moieties. After the living polymerization, the linear polymers release the daisy-chain assembly to generate a cyclic topology. The specific advantages of the present synthetic protocol, i.e., procedural simplicity and concentration independence, are demonstrated by a gram-scale synthesis.

  13. An expedient synthesis of linden ether.

    PubMed

    Serra, Stefano; Cominetti, Alessandra A

    2014-03-01

    We here describe a comprehensive study on the preparation of the intensive flavor 3,9-epoxy-p-mentha-1,4(8)-diene (1). Key steps of the presented synthesis are the selective addition of MeLi to the keto-ester 7, the regioselective cyclization of the obtained triol to give the ethers 4 and 8 and the selective dehydration of ether 4 through the use of POCI3 and pyridine. It is worth noting that the presented synthesis represents the first expedient and reliable entry to ether 1. Being present in linden honey, 1 is also known as linden ether and it has been regarded as a potential marker for the authentication of the linden honey origin. Therefore, ether 1 can be used as a useful reference standard for the analysis of the natural flavors, as we demonstrated by means of its identification in a sample ofunifloral linden honey.

  14. Thermodynamic properties (enthalpy, bond energy, entropy, and heat capacity) and internal rotor potentials of vinyl alcohol, methyl vinyl ether, and their corresponding radicals.

    PubMed

    da Silva, Gabriel; Kim, Chol-Han; Bozzelli, Joseph W

    2006-06-29

    Vinyl alcohols (enols) have been discovered as important intermediates and products in the oxidation and combustion of hydrocarbons, while methyl vinyl ethers are also thought to occur as important combustion intermediates. Vinyl alcohol has been detected in interstellar media, while poly(vinyl alcohol) and poly(methyl vinyl ether) are common polymers. The thermochemical property data on these vinyl alcohols and methyl vinyl ethers is important for understanding their stability, reaction paths, and kinetics in atmospheric and thermal hydrocarbon-oxygen systems. Enthalpies , entropies , and heat capacities (C(p)()(T)) are determined for CH(2)=CHOH, C(*)H=CHOH, CH(2)=C(*)OH, CH(2)=CHOCH(3), C(*)H=CHOCH(3), CH(2)=C(*)OCH(3), and CH(2)=CHOC(*)H(2). Molecular structures, vibrational frequencies, , and C(p)(T) are calculated at the B3LYP/6-31G(d,p) density functional calculation level. Enthalpies are also determined using the composite CBS-Q, CBS-APNO, and G3 methods using isodesmic work reactions to minimize calculation errors. Potential barriers for internal rotors are calculated at the B3LYP/6-31G(d,p) level and used to determine the hindered internal rotational contributions to entropy and heat capacity. The recommended ideal gas phase values calculated in this study are the following (in kcal mol(-1)): -30.0, -28.9 (syn, anti) for CH(2)=CHOH; -25.6, -23.9 for CH(2)=CHOCH(3); 31.3, 33.5 for C(*)H=CHOH; 27.1 for anti-CH(2)=C(*)OH; 35.6, 39.3 for C(*)H=CHOCH(3); 33.5, 32.2 for CH(2)=C(*)OCH(3); 21.3, 22.0 for CH(2)=CHOC(*)H(2). Bond dissociation energies (BDEs) and group additivity contributions are also determined. The BDEs reveal that the O-H, O-CH(3), C-OH, and C-OCH(3) bonds in vinyl alcohol and methyl vinyl ether are similar in energy to those in the aromatic molecules phenol and methyl phenyl ether, being on average around 3 kcal mol(-1) weaker in the vinyl systems. The keto-enol tautomerization enthalpy for the interconversion of vinyl alcohol to acetaldehyde is

  15. Quantum mechanical transition-state analysis reveals the precise origin of stereoselectivity in chiral quaternary cinchonidinium phase-transfer catalyzed enolate allylation.

    PubMed

    Cook, Thomas C; Andrus, Merritt B; Ess, Daniel H

    2012-12-07

    Density functional theory was used to model glycinate enolate binding and enantiomeric allylation transition states mediated by the cinchonidinium phase-transfer catalyst 2. Transition states show oxy-anion-ammonium interactions in contrast to π-face interactions in the ground states. The details of stereoselectivity are described within the quaternary ammonium-tetrahedron face model.

  16. Chiral N-phosphonyl imine chemistry: asymmetric synthesis of alpha-alkyl beta-amino ketones by reacting phosphonyl imines with ketone-derived enolates.

    PubMed

    Ai, Teng; Han, Jianlin; Chen, Zhong-Xiu; Li, Guigen

    2009-02-01

    A series of new chiral syn-alpha-branched beta-amino ketones has been synthesized by reacting chiral phosphonyl imines with ketone-derived enolates. The N-protection group on imine auxiliary was found to be crucial to the asymmetric induction. The absolute stereochemistry has been unambiguously determined by converting a product to a known sample.

  17. Generation, Isolation, and Characterization of a Stable Enol from Grignard Addition to a Bis-Ester: A Microscale Experiment for the Undergraduate Organic Chemistry Laboratory

    ERIC Educational Resources Information Center

    Nicaise, Olivier J. C.; Ostrom, Kyle F.; Dalke, Brent J.

    2005-01-01

    An experiment is described that introduces students to the concept of temperature-dependent stability of the tetrahedral intermediate in an acyl-transfer reaction. The process involves the determination of the structure of an alpha-ketoester and its corresponding remarkably stable enol ester to suggest a mechanism for the formation of the products.

  18. Generation, Isolation, and Characterization of a Stable Enol from Grignard Addition to a Bis-Ester: A Microscale Experiment for the Undergraduate Organic Chemistry Laboratory

    ERIC Educational Resources Information Center

    Nicaise, Olivier J. C.; Ostrom, Kyle F.; Dalke, Brent J.

    2005-01-01

    An experiment is described that introduces students to the concept of temperature-dependent stability of the tetrahedral intermediate in an acyl-transfer reaction. The process involves the determination of the structure of an alpha-ketoester and its corresponding remarkably stable enol ester to suggest a mechanism for the formation of the products.

  19. Cyclic torsion testing

    NASA Technical Reports Server (NTRS)

    Leese, G. E.

    1984-01-01

    Torsional fatigue testing and data analysis procedures are described. Since there are no standards governing cyclic torsion testing that are generally accepted on a widespread basis by the technical community, the different approaches that dominate current experimental activity, and the ramifications of each are discussed. Particular attention is given to the theoretical and experimental difficulties that have paced refinement and general acceptance of test procedures. Finally, specific quantities and nomenclature modelled after analagous axial fatigue properties are suggested as an effective way to communicate torsional fatigue results until accepted standards are established.

  20. An Early Cyclic Universe

    NASA Astrophysics Data System (ADS)

    Duhe, William; Biswas, Tirthibir

    2014-03-01

    We provide a comprehensive numerical study of the Emergent Cyclic Inflation scenario. This is a scenario where instead of traditional monotonic slow roll inflation, the universe expands over numerous short asymmetric cycles due to the production of entropy via interactions among different species. This is one of the very few scenarios of inflation which provides a nonsingular geodesically complete space-time and does not require any ``reheating'' mechanism. A special thanks to Loyola University for an excellent community to help this project grow.

  1. Emergence of symmetry and chirality in crown ether complexes with alkali metal cations.

    PubMed

    Martínez-Haya, Bruno; Hurtado, Paola; Hortal, Ana R; Hamad, Said; Steill, Jeffrey D; Oomens, Jos

    2010-07-08

    Crown ethers provide a valuable benchmark for the comprehension of molecular recognition mediated by inclusion complexes. One of the most relevant crown ethers, 18-crown-6 (18c6), features a flexible six-oxygen cyclic backbone that is well-known for its selective cation binding. This study employs infrared spectroscopy and quantum mechanical calculations to elucidate the structure of the gas-phase complexes formed by the 18c6 ether with the alkali metal cations. It is shown that symmetric and chiral arrangements play a dominant role in the conformational landscape of the 18c6-alkali system. Most stable 18c6-M(+) conformers are found to have symmetries C(3v) and C(2) for Cs(+), D(3d) for K(+), C(1) and D(3d) for Na(+), and D(2) for Li(+). Remarkably, whereas the bare 18c6 ether is achiral, chirality emerges in the C(2) and D(2) 18c6-M(+) conformations, both of which involve pairs of stable atropoisomers capable of acting as enantiomeric selective substrates.

  2. [Asthma and cyclic neutropenia].

    PubMed

    Salazar Cabrera, A N; Berrón Pérez, R; Ortega Martell, J A; Onuma Takane, E

    1996-01-01

    We report a male with history of recurrent infections (recurrent oral aphtous disease [ROAD], middle ear infections and pharyngo amigdalitis) every 3 weeks since he was 7 months old. At the age of 3 years cyclic neutropenia was diagnosed with cyclic fall in the total neutrophil count in blood smear every 21 days and prophylactic antimicrobial therapy was indicated. Episodic events every 3 weeks of acute asthma and allergic rhinitis were detected at the age of 6 years old and specific immunotherapy to Bermuda grass was given during 3 years with markedly improvement in his allergic condition but not in the ROAD. He came back until the age of 16 with episodic acute asthma and ROAD. The total neutrophil count failed to 0 every 21 days and surprisingly the total eosinophil count increased up to 2,000 at the same time, with elevation of serum IgE (412 Ul/mL). Specific immunotherapy to D.pt. and Aller.a. and therapy with timomodulin was indicated. After 3 months we observed clinical improvement in the asthmatic condition and the ROAD disappeared, but the total neutrophil count did not improve. We present this case as a rare association between 2 diseases with probably no etiological relationship but may be physiopatological that could help to understand more the pathogenesis of asthma.

  3. Ekpyrotic and cyclic cosmology

    NASA Astrophysics Data System (ADS)

    Lehners, Jean-Luc

    2008-09-01

    Ekpyrotic and cyclic cosmologies provide theories of the very early and of the very late universe. In these models, the big bang is described as a collision of branes — and thus the big bang is not the beginning of time. Before the big bang, there is an ekpyrotic phase with equation of state w=Pρ≫1 (where P is the average pressure and ρ the average energy density) during which the universe slowly contracts. This phase resolves the standard cosmological puzzles and generates a nearly scale-invariant spectrum of cosmological perturbations containing a significant non-Gaussian component. At the same time it produces small-amplitude gravitational waves with a blue spectrum. The dark energy dominating the present-day cosmological evolution is reinterpreted as a small attractive force between our brane and a parallel one. This force eventually induces a new ekpyrotic phase and a new brane collision, leading to the idea of a cyclic universe. This review discusses the detailed properties of these models, their embedding in M-theory and their viability, with an emphasis on open issues and observational signatures.

  4. Cyclic generalized projection MRI.

    PubMed

    Sarty, Gordon E

    2015-04-01

    Progress in the development of portable MRI hinges on the ability to use lightweight magnets that have non-uniform magnetic fields. An image encoding method and mathematical procedure for recovering the image from the NMR signal from non-uniform magnets with closed isomagnetic contours is given. Individual frequencies in an NMR signal from an object in a non-uniform magnetic field give rise to integrals of the object along contours of constant magnetic field: generalized projections. With closed isomagnetic field contours a simple, cyclic, direct reconstruction of the image from the generalized projections is possible when the magnet and RF transmit coil are held fixed relative to the imaged object while the RF receive coil moves. Numerical simulations, using the Shepp and Logan mathematical phantom, were completed to show that the mathematical method works and to illustrate numerical limitations. The method is numerically verified and exact reconstruction demonstrated for discrete mathematical image phantoms. Correct knowledge of the RF receive field is necessary or severe image distortions will result. The cyclic mathematical reconstruction method presented here will be useful for portable MRI schemes that use non-uniform magnets with closed isomagnetic contours along with mechanically or electronically moving the RF receive coils.

  5. A study of the direct dimethyl ether fuel cell using alkaline anolyte

    NASA Astrophysics Data System (ADS)

    Xu, Kan; Lao, Shao Jiang; Qin, Hai Ying; Liu, Bin Hong; Li, Zhou Peng

    The electrooxidation behavior of dimethyl ether (DME) dissolved in acidic, neutral or alkaline anolyte has been studied. The cyclic voltammetry measurements reveal that DME in alkaline anolyte demonstrates higher electrooxidation reactivity than that in acidic or neutral anolyte. With increasing the NaOH concentration in the anolyte, the electrooxidation reactivity of DME can be further improved. Direct dimethyl ether fuel cells (DDFCs) are assembled by using Nafion membrane as the electrolyte, Pt/C as the cathode catalyst, and Pt-Ru/C as the anode catalyst. It is found that the use of alkaline anolyte can significantly improve the performance of DDFCs. A maximum power density of 60 mW cm -2 has been achieved when operating the DDFC at 80 °C under ambient pressure.

  6. "False" thymine-1H-Enol guanine base pair. low misinsertion rate by DNA polymerase explained by computational chemistry consideration.

    PubMed

    Seclaman, E; Kurunczi, L; Simon, Z

    2007-03-01

    Formation of correct TA and GC and "false" thymine-1H-enol guanine (TGenol) base pairs is here considered to control nucleotide insertion into DNA via low substrate concentration Michaelis-Menten controlled kinetics. Contributions of base pairing to formation of Gibbs free energies in water solution, DeltaDeltaG, are calculated for the correct and false base pairs with the semi-empiric MNDO/PM3 method for base pairing energies in vacuum and the BEM method for hydration effects. The results for DeltaDeltaG indicate equal insertion rates for correct base pairing and a 10(-3)-10(-4) error probability for false insertion controlled by the TGenol false pair.

  7. Quantum chemical investigation of the electronic spectra of the keto, enol, and keto-imine tautomers of cytosine.

    PubMed

    Tomić, Katarina; Tatchen, Jörg; Marian, Christel M

    2005-09-22

    The low-lying excited singlet states of the keto, enol, and keto-imine tautomers of cytosine have been investigated employing a combined density functional/multireference configuration interaction (DFT/MRCI) method. Unconstrained geometry optimizations have yielded out-of-plain distorted structures of the pi --> pi and n --> pi excited states of all cytosine forms. For the keto tautomer, the DFT/MRCI adiabatic excitation energy of the pi --> pi state (4.06 eV including zero-point vibrational energy corrections) supports the resonant two-photon ionization (R2PI) spectrum (Nir et al. Phys. Chem. Chem. Phys. 2002, 5, 4780). On its S1 potential energy surface, a conical intersection between the 1pipi state and the electronic ground state has been identified. The barrier height of the reaction along a constrained minimum energy path amounts to merely 0.2 eV above the origin and explains the break-off of the R2PI spectrum. The 1pipi minimum of the enol tautomer is found at considerably higher excitation energies (4.50 eV). Because of significant geometry shifts with respect to the ground state, long vibrational progressions are expected, in accord with experimental observations. For the keto-imine tautomer, a crossing of the 1pipi potential energy surface with the ground-state surface has been found, too. Its n --> pi minimum (3.27 eV) is located well below the conical intersection between the pi --> pi and S0 states, but it will be difficult to observe because of its small transition moment. The identified conical intersections of the pi --> pi excited states of the keto cytosine tautomers are made responsible for the ultrafast decay to the electronic ground states and thus may explain their subpicoseconds lifetimes.

  8. Role of added chloride ions in alteration of reaction pathway in the oxidation of cyclic ketones by dichloroisocyanuric acid—A kinetic study

    NASA Astrophysics Data System (ADS)

    Lakshman Kumar, Y.; Venkata Nadh, R.; Radhakrishnamurti, P. S.

    2015-03-01

    Effect of added chloride ions on kinetics and pathway of reaction between cyclic ketones (five to eight membered rings) and dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Formation of aliphatic dicarboxylic acids as the end products demonstrates the ring cleavage oxidation. Positive effect of acid and negative effect of dielectric constant on the reaction rate reveals a interaction between positive ion (oxidant in the form of H2OCl+) and dipolar substrate molecule. Zero and first orders by oxidant in absence and presence of added chloride ions illustrates the participation of substrate as enolic form of ketone and protonated ketone, respectively, in the rate determining steps. The observed order of reactivity of cyclic ketones (cyclohexanone > cyclooctanone > cyclopentanone > cycloheptanone) was explained on the bases of ring strain, change of hybridization and conformational considerations. The envisaged plausible mechanism based on order of reactants in presence and absence of added chloride ions was substantiated by the order of Arrhenius parameters.

  9. Cyclic GMP transporters.

    PubMed

    Sager, Georg

    2004-11-01

    The biokinetics of guanosine 3',5'-cyclic monophosphate (cGMP) is characterized by three distinct processes: synthesis by guanylate cyclases (GCs), conversion of cGMP to GMP by cyclic nucleotide phosphodiesterases (PDEs) and the excretion of unchanged cGMP by transport proteins in the cell membrane. Efflux is observed in virtually all cell types including cells which originate from brain. Studies of intact cells, in which metabolic inhibitors and probenecid reduced extrusion of cGMP and wherein cGMP was extruded against concentration gradients, indicated the existence of ATP requiring organic anion transport system(s). Functional studies of inside-out vesicles have revealed cGMP transport systems wherein translocation is coupled to hydrolysis of ATP. The extrusion of cGMP is inhibited by a number of unrelated compounds and this indicates that cGMP is substrate for multispecific transporters. Recent transfection studies suggest that members of the MRP (multidrug resistance protein) family; MRP4, MRP5 and MRP8 translocate cGMP across the cell membrane. Many of the MRPs have been detected in brain. In addition tertiary active transport by the organic anion transporter family has also been identified. At least one member (OAT1) shows relative high affinity for cGMP and is also expressed in brain. The biological significance of cGMP transporters has to be clarified. Their role in cGMP biokinetics, being responsible for one of the cellular elimination pathways, is well established. However, there is growing evidence that extracellular cGMP has effects on cell physiology and pathophysiology by an auto- or paracrine mechanism.

  10. Polybrominated Diphenyl Ethers (PBDEs) Action Plan

    EPA Pesticide Factsheets

    Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants in a number of applications. EPA is concerned that some of the component congeners are persistent, bioaccumulative and toxic.

  11. Triethylene Glycol Monomethyl Ether; Final Test Rule

    EPA Pesticide Factsheets

    EPA is issuing a final test rule under section 4 of the Toxic Substances Control Act (TSCA) requiring manufacturers and processors of triethylene glycol monomethyl ether (TGME, CAS No. 112-35-6) to perform developmental neurotoxicity tasting.

  12. Improved Li/TiS2 cell cycling in ether-based electrolytes with synergistic additives

    NASA Technical Reports Server (NTRS)

    Dominey, L. A.; Goldman, J. L.; Koch, V. R.; Shen, D.; Subbarao, S.; Huang, C.-K.; Halpert, G.; Deligiannis, F.

    1991-01-01

    Based on an extensive series of normalized full cell Li/TiS2 cycling studies, open-circuit storage tests, microcalorimetry and AC impedance studies, and chemical precedent, we propose an integrated chemical model consistent with experimental observations concerning the behavior of numerous LiAsF6/cyclic ether electrolytes. The particularly striking potency of certain additives such as 2-methylfuran and the hydroxide action resides in their ability to intercept several different adverse catalytic processes concurrently in the bulk electrolyte as well as the Li anode and TiS2 cathode.

  13. Cyclic imines: chemistry and mechanism of action: a review.

    PubMed

    Otero, Alberto; Chapela, María-José; Atanassova, Miroslava; Vieites, Juan M; Cabado, Ana G

    2011-11-21

    In recent years, there has been an increase in the production of shellfish and in global demand for seafood as nutritious and healthy food. Unfortunately, a significant number of incidences of shellfish poisoning occur worldwide, and microalgae that produce phycotoxins are responsible for most of these. Phycotoxins include several groups of small to medium sized natural products with molecular masses ranging from 300 to over 3000 Da. Cyclic imines (CIs) are a recently discovered group of marine biotoxins characterized by their fast acting toxicity, inducing a characteristic rapid death in the intraperitoneal mouse bioassay. These toxins are macrocyclic compounds with imine (carbon-nitrogen double bond) and spiro-linked ether moieties. They are grouped together due to the imino group functioning as their common pharmacore and due to the similarities in their intraperitoneal toxicity in mice. Spirolides (SPXs) are the largest group of CIs cyclic imines that together with gymnodimines (GYMs) are best characterized. Although the amount of cyclic imines in shellfish is not regulated and these substances have not been categorically linked to human intoxication, they trigger high intraperitoneal toxicity in rodents. In this review, the corresponding chemical structures of each member of the CIs and their derivatives are reviewed as well as all the data accumulated on their mechanism of action at cellular level.

  14. Crosslinkage of collagen by polyglycidyl ethers.

    PubMed

    Tang, Z; Yue, Y

    1995-01-01

    Calcification is the principal cause of failure of glutaraldehyde treated bioprosthetic heart valves. This article reports the crosslinkage of several polyglycidyl ethers. Calcification of yak pericardium with polyglycidyl ethers was significantly decreased compared with that crosslinked with glutaraldehyde. The process of calcification of crosslinked yak pericardium was studied using 21 day subdermal implants in rats. The uptake of calcium with ethane diglycidyl ether was reduced (0.57 +/- 0.19 vs 4.28 +/- 1.62 micrograms/mg) over that with glutaraldehyde. Four polyglycidyl ethers were developed and compared. The best compound for raising the shrinkage temperature was the shortest chain compound without steric hindrance. In the polyglycidyl ether process, a suitable amount of alcohol was necessary to promote crosslinking; the catalyst, 2, 4, 6 -tris (dimethyl aminomethyl) phenol (TDAMP) and salicylic acid, were not favorable for long-term treatment of tissues because of the unnecessarily deep dyeing of the tissue, in addition to raising the shrinkage temperature. Unlike glutaraldehyde treatment, which reacts with lysine, polyglycidyl ether treated tissues maintained flexibility of the pericardial tissue, while binding amino acids such as lysine, methionine, tyrosine, aspartic acid and glutamic acid. The authors conclude that the ethane diglycidyl ether process combined with formaldehyde would further raise the shrinkage temperature from 78 degrees C to 87.5 degrees C and sustain it above 80 degrees C. Reverse treatment was not as effective. Compared with glutaraldehyde, polyglycidyl ether treatment renders tissue more flexible, increases the thermal stability of collagen, and decreases the incidence of calcification in vivo.

  15. Anaerobic biodegradation of ether compounds by ether bond-cleaving bacteria and methanogenic consortia

    SciTech Connect

    Dwyer, D.F.

    1989-01-01

    Ether compounds are manufactured for use in nonionic detergents, plastics, pesticides and other products and occur as toxic organic compounds, the most famous being tetrachlorodibenzo-p-dioxin. Ether compounds were considered recalcitrant to anaerobic biodegradation due to the lack of an appropriate oxidant for ether bond-cleavage in reducing environments. Many of these compounds reside in anaerobic environments or are exposed to anaerobic waste treatment processes. Thus, it is of interest to identify: (i) whether ether compounds are anaerobically biodegradable, (ii) the anaerobic microorganisms able to degrade these compounds, and (iii) the mechanism(s) of anaerobic ether bond-cleavage. The ether bonds of polyethylene glycol (PEG; HO-(CH{sub 2}CH{sub 2}-O-){sub n}H), phenyl ether ((C{sub 6}H{sub 5}){sub 2}O), and dibenzo-p-dioxin ((C{sub 6}H{sub 4}){sub 2}O{sub 2}) were shown to be degraded in methanogenic consortia enriched with these compounds and polyethoxylate (nonionic) surfactants as substrates. Two anaerobic microorganisms which used PEGs as sole substrates were isolated and characterized. Desulfovibrio desulfuricans strain DG2 degraded the monomer ethylene glycol and oligomers up to tetraethylene glycol (HO-(CH{sub 2}CH{sub 2}-O-){sub 4}H) in length. Bacteroides sp. strain PG1 degraded diethylene glycol and all other polymer lengths of PEG. PEGs were degraded by Bacteroides sp. strain PG1 via an external depolymerization which was either a hydrolytic or a reductive cleavage of the ether bond. The ether bond of diaryl ethers was apparently cleaved by a reductive mechanism which produced benzene and phenol as products from phenyl ether degradation and benzene and, by indirect analysis, catechol from dibenzo-dioxin.

  16. Cyclic AMP in prokaryotes.

    PubMed Central

    Botsford, J L; Harman, J G

    1992-01-01

    Cyclic AMP (cAMP) is found in a variety of prokaryotes including both eubacteria and archaebacteria. cAMP plays a role in regulating gene expression, not only for the classic inducible catabolic operons, but also for other categories. In the enteric coliforms, the effects of cAMP on gene expression are mediated through its interaction with and allosteric modification of a cAMP-binding protein (CRP). The CRP-cAMP complex subsequently binds specific DNA sequences and either activates or inhibits transcription depending upon the positioning of the complex relative to the promoter. Enteric coliforms have provided a model to explore the mechanisms involved in controlling adenylate cyclase activity, in regulating adenylate cyclase synthesis, and in performing detailed examinations of CRP-cAMP complex-regulated gene expression. This review summarizes recent work focused on elucidating the molecular mechanisms of CRP-cAMP complex-mediated processes. For other bacteria, less detail is known. cAMP has been implicated in regulating antibiotic production, phototrophic growth, and pathogenesis. A role for cAMP has been suggested in nitrogen fixation. Often the only data that support cAMP involvement in these processes includes cAMP measurement, detection of the enzymes involved in cAMP metabolism, or observed effects of high concentrations of the nucleotide on cell growth. PMID:1315922

  17. Conformations and Barriers to Methyl Group Internal Rotation in Two Asymmetric Ethers: Propyl Methyl Ether and Butyl Methyl Ether

    NASA Astrophysics Data System (ADS)

    Long, B. E.; Dechirico, F.; Cooke, S. A.

    2012-06-01

    The conformational preferences of the O-C-C-C unit are important in many biological systems with the unit generally preferring a gauche configuration compared to an anti configuration. Butyl methyl ether and propyl methyl ether provide very simple systems for this phenomenom to manifest. Pure rotational spectra of the title molecules have been recorded using chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). In the case of butyl methyl ether, only one conformer has been observed. This conformer has torsional angles of COCC = 180°, OCCC = 62° and CCCC = 180° (anti-gauche-anti) and rotational constants of A = 10259.4591(33) MHz, B = 1445.6470(13) MHz, and C = 1356.2944(14) MHz. The rotational spectrum was doubled and has been analyzed to produce an effective barrier to methyl group internal rotation of 780(35) cm-1. A prior rotational spectroscopic study on propyl methyl ether had focused only on the high energy anti-anti conformer. We have analyzed spectra from the lowest energy anti-gauche conformer and the spectroscopic constants will be presented. A summary of the differences in conformational energies and methyl group internal rotation barriers for the class of aliphatic asymmetric ethers will be presented. K. N. Houk, J. E. Eksterowicz, Y.-D. Wu, C. D. Fuglesang, D. B. Mitchell. J. Am. Chem. Soc. 115 (4170), 1993. Hiroshi Kato, Jun Nakagawa, Michiro Hayashi. J. Mol. Spectrosc. 80 (272), 1980.

  18. Stereocontrolled Cyanohydrin Ether Synthesis through Chiral Brønsted Acid-Mediated Vinyl Ether Hydrocyanation

    PubMed Central

    Lu, Chunliang; Su, Xiaoge; Floreancig, Paul E.

    2013-01-01

    Vinyl ethers can be protonated to generate oxocarbenium ions that react with Me3SiCN to form cyanohydrin alkyl ethers. Reactions that form racemic products proceed efficiently upon converting the vinyl ether to an α-chloro ether prior to cyanide addition in a pathway that proceeds through Brønsted acid-mediated chloride ionization. Enantiomerically enriched products can be accessed by directly protonating the vinyl ether with a chiral Brønsted acid to form a chiral ion pair. Me3SiCN acts as the nucleophile and PhOH serves as a stoichiometric proton source in a rare example of an asymmetric bimolecular nucleophilic addition reaction into an oxocarbenium ion. Computational studies provide a model for the interaction between the catalyst and the oxocarbenium ion. PMID:23968162

  19. Asymmetric total synthesis of (+)-bermudenynol, a C15 Laurencia metabolite with a vinyl chloride containing oxocene skeleton, through intramolecular amide enolate alkylation.

    PubMed

    Kim, Gyudong; Sohn, Te-Ik; Kim, Deukjoon; Paton, Robert S

    2014-01-03

    A substrate-controlled asymmetric total synthesis of (+)-bermudenynol, a compact and synthetically challenging C15 Laurencia metabolite that contains several halogen atoms, is reported. The oxocene core, which contains a vinyl chloride, was constructed by an efficient and highly stereoselective intramolecular amide enolate alkylation (IAEA). This result showcases the broad utility of the IAEA methodology as a useful alternative for cases in which the ring-closing metathesis is inefficient.

  20. Chiral N-phosphonyl imine chemistry: asymmetric synthesis of alpha,beta-diamino esters by reacting phosphonyl imines with glycine enolates.

    PubMed

    Ai, Teng; Li, Guigen

    2009-07-15

    Chiral phosphonyl imines attached with N-isopropyl protection group were found to react with lithium glycine enolates under convenient conditions to give alpha,beta-diamino esters. Thirteen examples have been examined in good to excellent chemical yields (85-97%) diastereoselectivity (up to 99% de). By treating with HBr at room temperature, the chiral auxiliary can be readily removed and recycled. The absolute structure has been unambiguously determined by converting a product to a known sample.

  1. Thermodynamic equilibrium calculations of dimethyl ether steam reforming and dimethyl ether hydrolysis

    NASA Astrophysics Data System (ADS)

    Semelsberger, Troy A.; Borup, Rodney L.

    The production of a hydrogen-rich fuel-cell feed by dimethyl ether (DME) steam reforming was investigated using calculations of thermodynamic equilibrium as a function of steam-to-carbon ratio (0.00-4.00), temperature (100-600 °C), pressure (1-5 atm), and product species. Species considered were acetone, acetylene, carbon dioxide, carbon monoxide, dimethyl ether, ethane, ethanol, ethylene, formaldehyde, formic acid, hydrogen, isopropanol, methane, methanol, methyl-ethyl ether, n-propanol and water. Thermodynamic equilibrium calculations of DME steam reforming indicate complete conversion of dimethyl ether to hydrogen, carbon monoxide and carbon dioxide at temperatures greater than 200 °C and steam-to-carbon ratios greater than 1.25 at atmospheric pressure ( P = 1 atm). Increasing the operating pressure shifts the equilibrium toward the reactants; increasing the pressure from 1 to 5 atm decreases the conversion of dimethyl ether from 99.5 to 76.2%. The trend of thermodynamically stable products in decreasing mole fraction is methane, ethane, isopropyl alcohol, acetone, n-propanol, ethylene, ethanol, methyl-ethyl ether and methanol-formaldehyde, formic acid, and acetylene were not observed. Based on the equilibrium calculations, the optimal processing conditions for dimethyl ether steam reforming occur at a steam-to-carbon ratio of 1.50, a pressure of 1 atm, and a temperature of 200 °C. These thermodynamic equilibrium calculations show dimethyl ether processed with steam will produce hydrogen-rich fuel-cell feeds—with hydrogen concentrations exceeding 70%. The conversion of dimethyl ether via hydrolysis (considering methanol as the only product) is limited by thermodynamic equilibrium. Equilibrium conversion increases with temperature and steam-to-carbon ratio. A maximum dimethyl ether conversion of 62% is achieved at a steam-to-carbon ratio of 5.00 and a processing temperature of 600 °C.

  2. Why Do Enolate Anions Favor O-Alkylation over C-Alkylation in the Gas Phase? The Roles of Resonance and Inductive Effects in the Gas-Phase SN2 Reaction between the Acetaldehyde Enolate Anion and Methyl Fluoride.

    PubMed

    Seitz, Christian G; Zhang, Huaiyu; Mo, Yirong; Karty, Joel M

    2016-05-06

    Contributions by resonance and inductive effects toward the net activation barrier were determined computationally for the gas-phase SN2 reaction between the acetaldehyde enolate anion and methyl fluoride, for both O-methylation and C-methylation, in order to understand why this reaction favors O-methylation. With the use of the vinylogue extrapolation methodology, resonance effects were determined to contribute toward increasing the size of the barrier by about 9.5 kcal/mol for O-methylation and by about 21.2 kcal/mol for C-methylation. Inductive effects were determined to contribute toward increasing the size of the barrier by about 1.7 kcal/mol for O-methylation and 4.2 kcal/mol for C-methylation. Employing our block-localized wave function methodology, we determined the contributions by resonance to be 12.8 kcal/mol for O-methylation and 22.3 kcal/mol for C-methylation. Thus, whereas inductive effects have significant contributions, resonance is the dominant factor that leads to O-methylation being favored. More specifically, resonance serves to increase the size the barrier for C-methylation significantly more than it does for O-methylation.

  3. Erratum to "The mechanism and thermodynamics of transesterification of acetate-ester enolates in the gas phase" : [Int. J. Mass Spectrom. Ion Process. 172 (1998) 25

    NASA Astrophysics Data System (ADS)

    Haas, George W.; Giblin, Daryl E.; Gross, Michael L.

    1998-02-01

    In solution, base-catalyzed hydrolysis and transesterification of esters are initiated by hydroxide- or alkoxide-ion attack at the carbonyl carbon. At low pressures in the gas phase, however, transesterification proceeds by an attack of the enolate anion of an acetate ester on an alcohol. Fourier transform mass spectrometry (FTMS) indicates that the reaction is the second-order process: -CH2-CO2-R+R'-OH-->-CH2-CO2-R'+R-OH and there is little to no detectable production of either alkoxide anion. Labeling studies show that the product and reactant enolate anion esters undergo exchange of hydrogens located [alpha] to the carbonyl carbon with the deuterium of R'--OD. The extent of the H/D exchange increases with reaction time, pointing to a short-lived intermediate. The alcoholysis reaction rate constants increase with increasing acidity of the primary, straight-chained alkyl alcohols, whereas steric effects associated with branched alcohols cause the rate constants to decrease. Equilibrium constants, which were determined directly from measurements at equilibrium and which were calculated from the forward and reverse rate constants, are near unity and show internal consistency. In the absence of steric effects, the larger enolate is always the favored product at equilibrium. The intermediate for the transesterification reaction, which can be generated at a few tenths of a torr in a tandem mass spectrometer, is tetrahedral, but other adducts that are collisionally stabilized under these conditions are principally loosely bound complexes.

  4. Ether and the atmospheric chemistry data assimilation

    NASA Astrophysics Data System (ADS)

    Ricaud, P.; Phulpin, T.; Girod, F.; Boonne, C.

    The French atmospheric chemistry data base Ether has been developed and funded by the French Space Agency (CNES) and the Institut National des Sciences de l'Univers (INSU/CNRS) for about 6 years. The role of Ether is to assist French atmospheric researchers, European scientists, as long as they are involved in co-operation agreements with French scientists, to locate, access and interpret atmospheric data. This centre gathers data from satellite, balloon campaigns linked to satellite validation, aircraft and model results for stratospheric and tropospheric purposes and from different levels of production (raw data, physical data, interpolated or assimilated data). All Ether data are available on-line through a World Web interface (http://ether.ipsl.jussieu.fr). Software and added-value services are provided to assist in the manipulation of the data or to generate higher levels standard data products. Extensive information is also provided on the data collection procedures, formats, contact names and references to scientific papers. In addition to data support activities, a major goal of Ether is to promote the creation of different expertise networks on varying atmospheric chemistry topics. The first working group has been created on data assimilation. It consists in gathering expertises in different themes (satellites, assimilation techniques, modelling, real-time processing) in order to optimally develop a tool able to answer different scientific questions relative to the evolution of the Earth atmosphere in terms of chemistry and dynamics. Based on the PALM tool able to interconnect different codes, it will be able to process different satellite data using two atmospheric models and assimilation schemes within the French Ether data base. Ether will focus on the handling and on the development of added-value services of data for which the French community is directly or indirectly involved. For these projects Ether will provide all the data needed, and will

  5. Genetics Home Reference: cyclic neutropenia

    MedlinePlus

    ... infection, neutrophils release neutrophil elastase. This protein then modifies the function of certain cells and proteins to help fight the infection. ELANE gene mutations that cause cyclic neutropenia lead to an ...

  6. Cyclic Cushing's syndrome: an overview.

    PubMed

    Mantero, Franco; Scaroni, Carla M; Albiger, Nora M E

    2004-01-01

    Cyclic Cushing's syndrome (CS) involves rhythmic fluctuations in ACTH secretion resulting in a cyclic variation of adrenal steroid production. In the majority of cases, cyclic CS is caused by an ACTH-secreting pituitary adenoma, but it can also be due to ectopic ACTH production or an adrenal adenoma. This condition should be strongly suspected in patients with symptoms or signs of hypercortisolism but normal cortisol levels and paradoxical responses to the dexamethasone test, that may reflect an increasing or decreasing endogenous hormone activity. Dynamic tests are best interpreted if they are performed during a sustained period of hypercortisolism. Sometimes, it is necessary to confirm the diagnosis over lengthy periods of observation. Responses to treatment must be closely monitored, interpreted and evaluated with caution because of the potential variations in steroidogenesis. An original case report of a cyclic Cushing's syndrome is presented in this review.

  7. Development of the scope of a co-mediated O-->C rearrangement reaction.

    PubMed

    Meek, Simon J; Pradaux, Fabienne; Carbery, David R; Demont, Emmanuel H; Harrity, Joseph P A

    2005-11-25

    [reaction: see text] In this paper we describe an Al-promoted, Co-mediated O-->C rearrangement reaction of cyclic enol ethers. This process delivers functionalized cyclohexanones with good to excellent levels of diastereocontrol, whereby the product stereochemistry is dependent on the E/Z-stereochemistry of the starting enol ether. The rearrangement process also permits access to highly substituted alpha-spirocyclic cyclohexanones as well as cyclopentanones. The latter rearrangement appears to proceed via an unusual 5-(enolendo)-exo-trig cyclization process.

  8. Cyclic mixmaster universes

    NASA Astrophysics Data System (ADS)

    Barrow, John D.; Ganguly, Chandrima

    2017-04-01

    We investigate the behavior of bouncing Bianchi type IX "mixmaster" universes in general relativity. This generalizes all previous studies of the cyclic behavior of closed spatially homogeneous universes with and without an entropy increase. We determine the behavior of models containing radiation by analytic and numerical integration and show that an increase of radiation entropy leads to an increasing cycle size and duration. We introduce a null energy condition violating ghost field to create a smooth, nonsingular bounce of finite size at the end of each cycle and compute the evolution through many cycles with and without an entropy increase injected at the start of each cycle. In the presence of increasing entropy, we find that the cycles grow larger and longer and the dynamics approach flatness, as in the isotropic case. However, successive cycles become increasingly anisotropic at the expansion maxima which is dominated by the general-relativistic effects of anisotropic 3-curvature. When the dynamics are significantly anisotropic, the 3-curvature is negative. However, it becomes positive after continued expansion drives the dynamics close enough to isotropy for the curvature to become positive and for gravitational collapse to ensue. In the presence of a positive cosmological constant, radiation, and a ghost field, we show that, for a very wide range of cosmological constant values, the growing oscillations always cease and the dynamics subsequently approach those of the isotropic de Sitter universe at late times. This model is not included in the scope of earlier cosmic no-hair theorems because the 3-curvature can be positive. In the case of a negative cosmological constant, radiation, and an ultrastiff field (to create nonsingular bounces), we show that a sequence of chaotic oscillations also occurs, with sensitive dependence on initial conditions. In all cases, we follow the oscillatory evolution of the scale factors, the shear, and the 3-curvature from

  9. Atmospheric degradation of 2-chloroethyl vinyl ether, allyl ether and allyl ethyl ether: Kinetics with OH radicals and UV photochemistry.

    PubMed

    Antiñolo, M; Ocaña, A J; Aranguren, J P; Lane, S I; Albaladejo, J; Jiménez, E

    2017-08-01

    Unsaturated ethers are oxygenated volatile organic compounds (OVOCs) emitted by anthropogenic sources. Potential removal processes in the troposphere are initiated by hydroxyl (OH) radicals and photochemistry. In this work, we report for the first time the rate coefficients of the gas-phase reaction with OH radicals (kOH) of 2-chloroethyl vinyl ether (2ClEVE), allyl ether (AE), and allyl ethyl ether (AEE) as a function of temperature in the 263-358 K range, measured by the pulsed laser photolysis-laser induced fluorescence technique. No pressure dependence of kOH was observed in the 50-500 Torr range in He as bath gas, while a slightly negative T-dependence was observed. The temperature dependent expressions for the rate coefficients determined in this work are: The estimated atmospheric lifetimes (τOH) assuming kOH at 288 K were 3, 2, and 4 h for 2ClEVE, AE and AEE, respectively. The kinetic results are discussed in terms of the chemical structure of the unsaturated ethers by comparison with similar compounds. We also report ultraviolet (UV) and infrared (IR) absorption cross sections (σλ and σ(ν˜), respectively). We estimate the photolysis rate coefficients in the solar UV actinic region to be less than 10(-7) s(-1), implying that these compounds are not removed from the atmosphere by this process. In addition, from σ(ν˜) and τOH, the global warming potential of each unsaturated ether was calculated to be almost zero. A discussion on the atmospheric implications of the titled compounds is presented. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Computer Simulation Of Cyclic Oxidation

    NASA Technical Reports Server (NTRS)

    Probst, H. B.; Lowell, C. E.

    1990-01-01

    Computer model developed to simulate cyclic oxidation of metals. With relatively few input parameters, kinetics of cyclic oxidation simulated for wide variety of temperatures, durations of cycles, and total numbers of cycles. Program written in BASICA and run on any IBM-compatible microcomputer. Used in variety of ways to aid experimental research. In minutes, effects of duration of cycle and/or number of cycles on oxidation kinetics of material surveyed.

  11. Cyclic Cushing's syndrome: an overview.

    PubMed

    Albiger, Nora Maria Elvira; Scaroni, Carla M; Mantero, Franco

    2007-11-01

    Cyclic Cushing's syndrome (CS) is a disorder in which glucocorticoid levels are alternately normal and high, the latter occurring in episodes that can last from a few days to several months. It is more common in children than in adults. Cyclic CS may be either of the two different forms of CS (ACTH-dependent or -independent CS). Clinically, it may present with one or many symptoms, depending on the duration of disease activity and the timing of the fluctuations. A serotoninergic influence, cyclic changes in central dopaminergic tone, spontaneous episodic hemorrhage in the tumor, and the action of inflammatory cytokines with antitumor properties are some of the mechanisms suggested to explain the physiopathology of this phenomenon but the exact mechanism remains to be clarified. The cyclic pattern of hypercortisolism can delay the final diagnosis of CS and make it difficult to interpret the results of dynamic tests. Patients may have paradoxical responses to dexamethasone that can reflect increasing or decreasing levels of endogenous activity. Hormone assessments have to be repeated periodically when a diagnosis of CS is suspected. The cyclic pattern can also interfere with medical treatment because patients may show unexpected clinical and biochemical signs of hypocortisolism when cortisol secretion cyclically returns to normal, so an accurate follow-up is mandatory in these patients.

  12. Synthesis of analogues of Eunicea gamma-cembranolides containing cyclic ethers via saponification.

    PubMed

    Rodríguez, A D; Piña, I C; Acosta, A L; Ramírez, C; Soto, J J

    2001-02-09

    A method for the synthesis of derivatives of the lead structures euniolide (1), 12,13-bisepieupalmerin (2), and eupalmerin acetate (3) containing tetrahydrofuran and tetrahydropyran ring systems was developed on the basis of alkali-induced intramolecular oxacyclizations. Representatives of the new analogues were submitted to the in vitro antitumor cell-line-screening program of the National Cancer Institute (NCI). While it was shown that a variety of structural modifications are possible, these transformations led typically to nontoxic synthetic cembranoids.

  13. Conformations and "nictinic" activites of cyclic analogues of choline aryl ether.

    PubMed

    Clark, E R; Hughes, I E; Smith, C F

    1976-05-01

    The synthesis of cis and trans isomers of N,N-N-trimethyl-2-phenoxycyclohexylammonium bromide, cis-N,N,-N-trimethyl-2(2',6'-xylyloxy)cyclohexylammonium bromide, and N,N-dimethyl-3-phenoxypiperidinium bromide is described. Their structures and conformations were determined by NMR and uv absorption spectroscopy, the minimum torsional angles about the aryl-oxygen gond geing 20, 20, 80, and 27 degrees, respectively. Since the piperidinium compound stimulates ganglia, it is concluded the either planarity of the aryl--O--C system is not essential for this type of activity or receptor interaction can involve appreciable bond distortion. The absence of ganglion-stimulant activity in the remaining compounds indicates the need for a transoid arrangement of the O--C--C--N+ system.

  14. Statistical analysis of fragmentation patterns of electron ionization mass spectra of enolized-trimethylsilylated anabolic androgenic steroids

    NASA Astrophysics Data System (ADS)

    Fragkaki, A. G.; Angelis, Y. S.; Tsantili-Kakoulidou, A.; Koupparis, M.; Georgakopoulos, C.

    2009-08-01

    Anabolic androgenic steroids (AAS) are included in the List of prohibited substances of the World Anti-Doping Agency (WADA) as substances abused to enhance athletic performance. Gas chromatography coupled to mass spectrometry (GC-MS) plays an important role in doping control analyses identifying AAS as their enolized-trimethylsilyl (TMS)-derivatives using the electron ionization (EI) mode. This paper explores the suitability of complementary GC-MS mass spectra and statistical analysis (principal component analysis, PCA and partial least squares-discriminant analysis, PLS-DA) to differentiate AAS as a function of their structural and conformational features expressed by their fragment ions. The results obtained showed that the application of PCA yielded a classification among the AAS molecules which became more apparent after applying PLS-DA to the dataset. The application of PLS-DA yielded a clear separation among the AAS molecules which were, thus, classified as: 1-ene-3-keto, 3-hydroxyl with saturated A-ring, 1-ene-3-hydroxyl, 4-ene-3-keto, 1,4-diene-3-keto and 3-keto with saturated A-ring anabolic steroids. The study of this paper also presents structurally diagnostic fragment ions and dissociation routes providing evidence for the presence of unknown AAS or chemically modified molecules known as designer steroids.

  15. Ring-opening reactions of cyclic acetals and 1,3-oxazolidines with halosilane equivalents.

    PubMed

    Iwata, Arihiro; Tang, Heqing; Kunai, Atsutaka; Ohshita, Joji; Yamamoto, Yasushi; Matui, Chinami

    2002-07-26

    Reactions of acetal and 1,3-oxazolidine rings were examined using two kinds of iodosilane equivalent reagents, a 1:2 mixture of Me3SiNEt2 and MeI (reagent 1a) and a 1:1 mixture of Et3SiH and MeI containing a catalytic amount of PdCl2 (reagent 1b). In the reactions of alkanone ethylene acetals with reagent 1a, a C-O bond in the acetal ring readily cleaved to give 2-(trimethylsiloxy)ethyl enol ethers. Similarly, the C-O bond of 1,3-oxazolidine rings cleaved to give ring-opened imine or enamine derivatives. The reactions of aromatic ketone ethylene acetals and cyclohexanone trimethylene acetal led to deprotection of the acetal unit to liberate free ketones. With reagent 1b, cycloalkanone ethylene acetal afforded a dimeric product with 2-iodoethyl alkenoate moieties, while aromatic ketone ethylene or trimethylene acetals produced deprotected ketones.

  16. Inhalation anaesthesia: from diethyl ether to xenon.

    PubMed

    Bovill, J G

    2008-01-01

    Modern anaesthesia is said to have began with the successful demonstration of ether anaesthesia by William Morton in October 1846, even though anaesthesia with nitrous oxide had been used in dentistry 2 years before. Anaesthesia with ether, nitrous oxide and chloroform (introduced in 1847) rapidly became commonplace for surgery. Of these, only nitrous oxide remains in use today. All modern volatile anaesthetics, with the exception of halothane (a fluorinated alkane), are halogenated methyl ethyl ethers. Methyl ethyl ethers are more potent, stable and better anaesthetics than diethyl ethers. They all cause myocardial depression, most markedly halothane, while isoflurane and sevoflurane cause minimal cardiovascular depression. The halogenated ethers also depress the normal respiratory response to carbon dioxide and to hypoxia. Other adverse effects include hepatic and renal damage. Hepatitis occurs most frequently with halothane, although rare cases have been reported with the other agents. Liver damage is not caused by the anaesthetics themselves, but by reactive metabolites. Type I hepatitis occurs fairly commonly and takes the form of a minor disturbance of liver enzymes, which usually resolves without treatment. Type II, thought to be immune-mediated, is rare, unpredictable and results in a severe fulminant hepatitis with a high mortality. Renal damage is rare, and was most often associated with methoxyflurane because of excessive plasma fluoride concentrations resulting from its metabolism. Methoxyflurane was withdrawn from the market because of the high incidence of nephrotoxicity. Among the contemporary anaesthetics, the highest fluoride concentrations have been reported with sevoflurane, but there are no reports of renal dysfunction associated with its use. Recently there has been a renewed interest in xenon, one of the noble gases. Xenon has many of the properties of an ideal anaesthetic. The major factor limiting its more widespread is the high cost, about

  17. Crystalline imide/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor); Bass, Robert G. (Inventor)

    1995-01-01

    Crystalline imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly)arylene ethers) in polar aprotic solvents and chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The block copolymers of the invention have one glass transition temperature or two, depending on the particular structure and/or the compatibility of the block units. Most of these crystalline block copolymers for tough, solvent resistant films with high tensile properties. While all of the copolymers produced by the present invention are crystalline, testing reveals that copolymers with longer imide blocks or higher imide content have increased crystallinity.

  18. 41. LOOKING WEST AT BUILDING NO. 519, ETHER AND ALCOHOL ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    41. LOOKING WEST AT BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, (LEFT) AND BUILDING NO. 521, ETHER VAULT, (RIGHT) IN FOREGROUND - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  19. 37. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, NORTHWEST ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    37. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, NORTHWEST CORNER OF BUILDING. BUILDING NO. 521 (ETHER VAULT) IN BACKGROUND LEFT. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  20. Calculations for the properties and reactions of the NH, PH, and AsH counterparts of dimethyl ether and acetone.

    PubMed

    Wiberg, Kenneth B

    2014-11-21

    The properties and reactions of compounds in which the O of dimethyl ether or acetone has been replaced by NH, PH, or AsH have been studied computationally using CBS-QB3, CBS-APNO, G4, and W1BD. The properties include the bond dissociation energies and ionization potentials, and the reactions include those with with protons, methyl cations, and lithium cations. The effect on keto-enol equilibria also was examined. In all cases there was good agreement with the available experimental data. The agreement between these methods suggests that the least computationally costly model (CBS-QB3) should be of general use in studying organic compounds. The double-bond dissociation enthalpies of CH2═XHn were linearly related to those of the corresponding CH3-XHn+1 single bonds with a slope of 2.5. With the exception of C-C, the order corresponded to the electronegativity of X, suggesting that the differences are largely determined by internal Coulombic interactions. The differences in the electronegativities of the heteroatoms are largely responsible for the differences in the properties and reactions. Oxygen has a significantly higher electronegativity than the others, and as a result, the oxygen-substituted compounds are often different than the others.

  1. High octane ethers from synthesis gas-derived alcohols

    SciTech Connect

    Klier, K.; Herman, R.G.; Johansson, M.; Feeley, O.C.

    1992-01-01

    The objective of the proposed research is to synthesize high octane ethers, primarily methyl isobutyl ether (MIBE) and methyl tertiary butyl ether (MTBE), directly from H{sub 2}/CO/CO{sub 2} coal-derived synthesis gas via alcohol mixtures that are rich in methanol and 2-methyl-1-propanol (isobutanol). The overall scheme involves gasification of coal, purification and shifting of the synthesis gas, higher alcohol synthesis, and direct synthesis of ethers.

  2. High octane ethers from synthesis gas-derived alcohols

    SciTech Connect

    Klier, K.; Herman, R.G.; Johansson, M.A.; Feeley, O.C.

    1992-04-01

    The objective of the proposal research is to synthesize high octane ethers, primarily methyl isobutyl ether (MIBE) and methyl tertiary butyl ether (MTBE), directly from H{sub 2}/CO/CO{sub 2} coal-derived synthesis gas via alcohol mixtures that are rich in methanol and 2-methyl-1-propanol (isobutanol). The overall scheme involves gasification of coal, purification and shifting of the synthesis gas, higher alcohol synthesis, and direct synthesis of ethers.

  3. Comparison of oxygen and sulfur effects on keto-enol chemistry in benzolactone systems: benzo[b]-2,3-dihydrofuran-2-one and -2-thione and benzo[b]-2,3-dihydrothiophene-2-one and -2-thione.

    PubMed

    Kresge, A J; Meng, Q

    2002-08-07

    Carbon-acid ionization constants, Q(K)(a)(concentration quotient at ionic strength = 0.10 M), were determined by spectrophotometric titration in aqueous solution for benzo[b]-2,3-dihydrofuran-2-one (3, pQ(K)(a) = 11.87), benzo[b]-2,3-dihydrothiophene-2-one (2, pQ(K)(a) = 8.85), and benzo[b]-2,3-dihydrofuran-2-thione (1, pQ(K)(a) = 2.81). Rates of approach to keto-enol equilibrium were also measured for the latter two substrates in perchloric acid, sodium hydroxide, and buffer solutions, and the rate profiles constructed from these data gave the ionization constants of the enols ionizing as oxygen or sulfur acids pQ(E)(a) = 5.23 for 2 and pQ(E)(a) = 2.69 for 1. Combination of these acidity constants with the carbon-acid ionization constants according to the relationship Q(K)(a)/Q(E)(a) = K(E) then gave the keto-enol equilibrium constants pK(E) = 3.62 for 2 and pK(E) = 0.12 for 1. The fourth, all-sulfur, member of this series, benzo[b]-2,3-dihydrothiophene-2-thione (4), proved to exist solely as the enol in aqueous solution, and only the enol ionization constant pQ(E)(a) = 3.44 could be determined for this substance; the limits pK(E) < 1.3 and pQ(K)(a) < 2.1, however, could be set. The unusually high acidities and enol contents of these substances are discussed, as are also the relative values of the ketonization and enolization rate constants measured; in the latter cases, Marcus rate theory is used to determine intrinsic kinetic reactivities, free of thermodynamic effects.

  4. 40 CFR 721.3435 - Butoxy-substituted ether alkane.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Butoxy-substituted ether alkane. 721... Substances § 721.3435 Butoxy-substituted ether alkane. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as butoxy-substituted ether...

  5. 40 CFR 721.3465 - Stilbene diglycidyl ether.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Stilbene diglycidyl ether. 721.3465... Substances § 721.3465 Stilbene diglycidyl ether. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as stilbene diglycidyl ether (PMN P-96-1427) is subject...

  6. 39. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, LOOKING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    39. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, LOOKING AT SOUTHWEST CORNER WITH BUILDING NO. 521, ETHER VAULT, AND BUILDING NO. 519-A, ETHER & ALOCOHL STORAGE TANKS, IN BACKGROUND RIGHT. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  7. Alkyl Aryl Ether Bond Formation with PhenoFluor**

    PubMed Central

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

    2015-01-01

    An alkyl aryl ether bond formation reaction between phenols and primary and secondary alcohols with PhenoFluor has been developed. The reaction features a broad substrate scope and tolerates many functional groups, and substrates that are challenging for more conventional ether bond forming processes may be coupled. A preliminary mechanistic study indicates reactivity distinct from conventional ether bond formation. PMID:25800679

  8. Gels based on cyclic polymers.

    PubMed

    Zhang, Ke; Lackey, Melissa A; Cui, Jun; Tew, Gregory N

    2011-03-23

    Cyclic poly(5-hydroxy-1-cyclooctene) (PACOE) was synthesized by ring-expansion metathesis polymerization (REMP), and thiol-ene chemistry was used to cross-link the internal double bonds in the PACOE backbone. This created a novel network material (gels formed from cyclic polymers) with unique structural units, where the cyclic PACOE main chains, which serve as secondary topological cross-linkages, were connected by primary intermolecular chemical cross-linkages. The resulting properties were notably different from those of traditional chemically cross-linked linear PACOE gels, whose gel fraction (GF) and modulus (G) increased while the swelling ratio (Q) decreased with increasing initial polymer concentration in the gel precursor solution (C(0)). For the gels formed from cyclic polymers, however, the GF, Q, and G all simultaneously increased as C(0) increased at the higher range. Furthermore, at the same preparation state (same C(0)), the swelling ability and the maximum strain at break of the gels formed from cyclic polymers were always greater than those of the gels formed from linear polymers, and these differences became more pronounced as C(0) increased.

  9. Synthesis and characterizations of electrospun sulfonated poly (ether ether ketone) SPEEK nanofiber membrane

    NASA Astrophysics Data System (ADS)

    Hasbullah, N.; Sekak, K. A.; Ibrahim, I.

    2016-07-01

    A novel electrospun polymer electrolyte membrane (PEM) based on Sulfonated Poly (ether ether ketone) were prepared and characterized. The poly (ether ether ketone) PEEK was sulfonated using concentrated sulfuric acid at room temperature for 60 hours reaction time. The degree sulfonation (DS) of the SPEEK are 58% was determined by H1 NMR using area under the peak of the hydrogen shielding at aromatic ring of the SPEEK. Then, the functional group of the SPEEK was determined using Fourier transfer infrared (FTIR) showed O-H vibration at 3433 cm-1 of the sulfonated group (SO2-OH). The effect of the solvent and polymer concentration toward the electrospinning process was investigated which, the DMAc has electrospun ability compared to the DMSO. While, at 20 wt.% of the polymer concentration able to form a fine and uniform nanofiber, this was confirmed by FESEM that shown electrospun fiber mat SPEEK surface at nano scale diameter.

  10. Review of glycol ether and glycol ether ester solvents used in the coating industry.

    PubMed Central

    Smith, R L

    1984-01-01

    Ethylene oxide-based glycol ether and glycol ether ester solvents have been used in the coatings industry for the past fifty years. Because of their excellent performance properties (evaporation rate, blush resistance, flow-out and leveling properties, solubility for coating resins, solvent activity, mild odor, good coupling ability, good solvent release) a complete line of ethylene oxide-based solvents of various molecular weights has been developed. These glycol ether and glycol ether ester solvents have better solvent activity for coating resin than ester or ketone solvents in their evaporation rate range. The gloss, flow and leveling, and general performance properties of many coating systems are dependent on the use of these products in the coating formula. Because of the concern about the toxicity of certain ethylene oxide-based solvents, other products are being evaluated as replacements in coating formulas. PMID:6499793

  11. POLYBROMINATED DIPHENYL ETHERS IN US SOILS

    EPA Science Inventory

    Chemical analysis of thirty-three soil samples from 15 US states reveals Polybrominated Diphenyl Ethers (PBDEs), in every sample.PBDE concentrations rangefrom 0.09 to 1200 parts per billion by mass. These data are the first analysis of soil concentrations of PBDEs in soils from a...

  12. Methyl tert-butyl ether (MTBE)

    Integrated Risk Information System (IRIS)

    Methyl tert - butyl ether ( MTBE ) ; CASRN 1634 - 04 - 4 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments f

  13. Orphan enzymes in ether lipid metabolism.

    PubMed

    Watschinger, Katrin; Werner, Ernst R

    2013-01-01

    Ether lipids are an emerging class of lipids which have so far not been investigated and understood in every detail. They have important roles as membrane components of e.g. lens, brain and testis, and as mediators such as platelet-activating factor. The metabolic enzymes for biosynthesis and degradation have been investigated to some extent. As most involved enzymes are integral membrane proteins they are tricky to handle in biochemical protocols. The sequence of some ether lipid metabolising enzymes has only recently been reported and other sequences still remain obscure. Defined enzymes without assigned sequence are known as orphan enzymes. One of these enzymes with uncharacterised sequence is plasmanylethanolamine desaturase, a key enzyme for the biosynthesis of one of the most abundant phospholipids in our body, the plasmalogens. This review aims to briefly summarise known functions of ether lipids, give an overview on their metabolism including the most prominent members, platelet-activating factor and the plasmalogens. A special focus is set on the description of orphan enzymes in ether lipid metabolism and on the successful strategies how four previous orphans have recently been assigned a sequence. Only one of these four was characterised by classical protein purification and sequencing, whereas the other three required alternative strategies such as bioinformatic candidate gene selection and recombinant expression or development of an inhibitor and multidimensional metabolic profiling. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

  14. POLYBROMINATED DIPHENYL ETHERS IN SOUTHERN MISSISSIPPI CATFISH

    EPA Science Inventory

    Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a wide variety of consumer products. Concerns surrounding these compounds are primarily due do their ubiquitous presence in the environment as well as in human tissue, such as milk, coupled with evidence indi...

  15. Ethylene glycol monobutyl ether (EGBE) (2-Butoxyethanol)

    Integrated Risk Information System (IRIS)

    EPA / 635 / R - 08 / 006F www.epa.gov / iris TOXICOLOGICAL REVIEW OF ETHYLENE GLYCOL MONOBUTYL ETHER ( EGBE ) ( CAS No . 111 - 76 - 2 ) In Support of Summary Information on the Integrated Risk Information System ( IRIS ) March 2010 U.S . Environmental Protection Agency Washington , DC DISCLAIMER Thi

  16. Dimensionally Stable Ether-Containing Polyimide Copolymers

    NASA Technical Reports Server (NTRS)

    Fay, Catharine C. (Inventor); St.Clair, Anne K. (Inventor)

    1999-01-01

    Novel polyimide copolymers containing ether linkages were prepared by the reaction of an equimolar amount of dianhydride and a combination of diamines. The polyimide copolymers described herein possess the unique features of low moisture uptake, dimensional stability, good mechanical properties, and moderate glass transition temperatures. These materials have potential application as encapsulants and interlayer dielectrics.

  17. Bis(2-chloro-1-methylethyl) ether

    Integrated Risk Information System (IRIS)

    Bis ( 2 - chloro - 1 - methylethyl ) ether ; CASRN 108 - 60 - 1 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assess

  18. 40 CFR 721.3380 - Anilino ether.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.3380 Anilino ether. Link to an amendment published at 79 FR 34637, June 18, 2014. (a) Chemical substances and significant new uses subject to reporting. (1) The chemical substance identified generically as anilino...

  19. Biomonitoring Polybrominated Diphenyl Ethers in Lactating Women

    USDA-ARS?s Scientific Manuscript database

    Breast milk is a valuable biological specimen for biomonitoring lipid-soluble polybrominated diphenyl ethers (PBDEs). The goal of this project was to determine the levels of PBDEs in breast milk of lactating women from the Seacoast region of New Hampshire and to examine potential relationships betw...

  20. 21 CFR 868.5420 - Ether hook.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES... that fits inside a patient's mouth and that is intended to deliver vaporized ether. (b) Classification... the quality system regulation in part 820 of this chapter, with the exception of § 820.180,...

  1. POLYBROMINATED DIPHENYL ETHERS IN SOUTHERN MISSISSIPPI CATFISH

    EPA Science Inventory

    Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a wide variety of consumer products. Concerns surrounding these compounds are primarily due do their ubiquitous presence in the environment as well as in human tissue, such as milk, coupled with evidence indi...

  2. Imide/arylene ether block copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Hergenrother, P. M.; Bass, R. G.

    1991-01-01

    Two series of imide/arylene either block copolymers were prepared using an arylene ether block and either an amorphous or semi-crystalline imide block. The resulting copolymers were characterized and selected physical and mechanical properties were determined. These results, as well as comparisons to the homopolymer properties, are discussed.

  3. Ruthenium(II) bipyridine complexes bearing new keto-enol azoimine ligands: Synthesis, structure, electrochemistry and DFT calculations

    NASA Astrophysics Data System (ADS)

    Al-Noaimi, Mousa; Awwadi, Firas F.; Mansi, Ahmad; Abdel-Rahman, Obadah S.; Hammoudeh, Ayman; Warad, Ismail

    2015-01-01

    The novel azoimine ligand, Phsbnd NHsbnd Ndbnd C(COCH3)sbnd NHPh(Ctbnd CH) (H2L), was synthesized and its molecular structure was determined by X-ray crystallography. Catalytic hydration of the terminal acetylene of H2L in the presence of RuCl3·3H2O in ethanol at reflux temperature yielded a ketone (L1 = Phsbnd Ndbnd Nsbnd C(COCH3)dbnd Nsbnd Ph(COCH3) and an enol (L2 = Phsbnd Ndbnd Nsbnd C(COCH3)dbnd Nsbnd PhC(OH)dbnd CH2) by Markovnikov addition of water. Two mixed-ligand ruthenium complexes having general formula, trans-[Ru(bpy)(Y)Cl2] (1-2) (where Y = L1 (1) and Y = L2 (2), bpy is 2.2‧-bipyrdine) were achieved by the stepwise addition of equimolar amounts of (H2L) and bpy ligands to RuCl3·3H2O in absolute ethanol. Theses complexes were characterized by elemental analyses and spectroscopic (IR, UV-Vis, and NMR (1D 1H NMR, 13C NMR, (DEPT-135), (DEPT-90), 2D 1H-1H and 13C-1H correlation (HMQC) spectroscopy)). The two complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple at 604 mV vs. ferrocene/ferrocenium (Cp2Fe0/+) couple along with one electron ligand reduction at -1010 mV. The crystal structure of complex 1 showed that the bidentate ligand L1 coordinates to Ru(II) by the azo- and imine-nitrogen donor atoms. The complex adopts a distorted trans octahedral coordination geometry of chloride ligands. The electronic spectra of 1 and 1+ in dichloromethane have been modeled by time-dependent density functional theory (TD-DFT).

  4. Ruthenium(II) bipyridine complexes bearing new keto-enol azoimine ligands: synthesis, structure, electrochemistry and DFT calculations.

    PubMed

    Al-Noaimi, Mousa; Awwadi, Firas F; Mansi, Ahmad; Abdel-Rahman, Obadah S; Hammoudeh, Ayman; Warad, Ismail

    2015-01-25

    The novel azoimine ligand, Ph-NH-N=C(COCH3)-NHPh(C≡CH) (H2L), was synthesized and its molecular structure was determined by X-ray crystallography. Catalytic hydration of the terminal acetylene of H2L in the presence of RuCl3·3H2O in ethanol at reflux temperature yielded a ketone (L1=Ph-N=N-C(COCH3)=N-Ph(COCH3) and an enol (L2=Ph-N=N-C(COCH3)=N-PhC(OH)=CH2) by Markovnikov addition of water. Two mixed-ligand ruthenium complexes having general formula, trans-[Ru(bpy)(Y)Cl2] (1-2) (where Y=L1 (1) and Y=L2 (2), bpy is 2.2'-bipyrdine) were achieved by the stepwise addition of equimolar amounts of (H2L) and bpy ligands to RuCl3·3H2O in absolute ethanol. Theses complexes were characterized by elemental analyses and spectroscopic (IR, UV-Vis, and NMR (1D (1)H NMR, (13)C NMR, (DEPT-135), (DEPT-90), 2D (1)H-(1)H and (13)C-(1)H correlation (HMQC) spectroscopy)). The two complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple at 604 mV vs. ferrocene/ferrocenium (Cp2Fe(0/+)) couple along with one electron ligand reduction at -1010 mV. The crystal structure of complex 1 showed that the bidentate ligand L1 coordinates to Ru(II) by the azo- and imine-nitrogen donor atoms. The complex adopts a distorted trans octahedral coordination geometry of chloride ligands. The electronic spectra of 1 and 1+ in dichloromethane have been modeled by time-dependent density functional theory (TD-DFT). Copyright © 2014 Elsevier B.V. All rights reserved.

  5. Cyclopropane pipecolic acids as templates for linear and cyclic peptidomimetics: application in the synthesis of an Arg-Gly-Asp (RGD)-containing peptide as an αvβ3 integrin ligand.

    PubMed

    Sernissi, Lorenzo; Petrović, Martina; Scarpi, Dina; Guarna, Antonio; Trabocchi, Andrea; Bianchini, Francesca; Occhiato, Ernesto G

    2014-08-25

    The synthesis and evaluation of substituted cyclopropane pipecolic acids (CPA) as conformationally restricted templates for linear and cyclic peptidomimetics is reported. A variety of differently substituted (poly)hydroxy- and amino-2-azabicyclo[4.1.0]heptane-1-carboxylic acids were prepared by means of the Pd-catalyzed methoxycarbonylation of suitably functionalized lactam-derived enol phosphates, followed by OH-directed cyclopropanation. CPAs were successfully introduced into a linear peptide sequence to assess the cis/trans isomerism about the pipecolic acid peptide bond, and in a cyclic peptidomimetic that bore the Arg-Gly-Asp (RGD) sequence, which displayed nanomolar activity as antagonist of the αvβ3 integrin in M21 human melanoma cells. Thus, CPAs appear to be suitable for the generation of novel peptidomimetics for drug discovery.

  6. Secondary H/T and D/T isotope effects in enzymatic enolization reactions. Coupled motion and tunneling in the triosephosphate isomerase reaction.

    PubMed

    Alston, W C; Kanska, M; Murray, C J

    1996-10-01

    Secondary kH/kT kinetic isotope effects in H2O and kH/kT or kD/kT isotope effects in D2O have been measured for the triosephosphate isomerase-catalyzed conversion of dihydroxyacetone 3-phosphate (DHAP) to D-glyceraldehyde 3-phosphate. The proton transfer steps are made rate-limiting using [1(R)-2H]-labeled substrate in D2O to slow the chemical steps, relative to product release. After a small correction for the beta-equilibrium isotope effect for dehydration of DHAP, the H/T kinetic isotope effect kH/kT = 1.27 +/- 0.03 for [1(R)-2H,(S)-3H]-labeled substrate in D2O is subtantially larger than the equilibrium isotope effect for enolization of DHAP, KH/KT = 1.12. The H/T isotope effect is related to the D/T isotope effect with a Swain-Schaad exponent y = 4.4 +/- 1.3. These results are consistent with coupled motion of the C-1 primary and secondary hydrogens of DHAP and tunneling. Large secondary kinetic isotope effects are a general feature of enzymatic enolization reactions while nonenzymatic enolization reactions show secondary kinetic isotope effects that are substantially smaller than equilibrium effects [Alston, W. A., II, Haley, K., Kanski, R., Murray, C.J., & Pranata, J. (1996) J. Am. Chem Soc., 118, 6562-6569]. Possible origins for these differences in transition state structure are discussed.

  7. A Rh(II)-catalyzed multicomponent reaction by trapping an α-amino enol intermediate in a traditional two-component reaction pathway

    PubMed Central

    Liu, Shunying; Yao, Wenfeng; Liu, Yuan; Wei, Qinghua; Chen, Jianghui; Wu, Xiang; Xia, Fei; Hu, Wenhao

    2017-01-01

    Multicomponent reactions (MCRs) represent an ideal organic synthesis tool for the rapid construction of complex molecules due to their step and atom economy. Compared to two-component reactions, the development of new MCRs has been greatly limited during the 170 years since the first MCR was reported. Theoretically, the trapping of an active intermediate generated from two components by a third component could change the traditional two-component reaction pathway, leading to the discovery of MCRs. We report an example of the trapping of α-imino enols generated in situ from 1-sulfonyl-1,2,3-triazoles via α-imino metal carbene species by vinylimine ions using C(2)-substituted indoles and paraformaldehyde as precursors in the presence of a rhodium(II) catalyst. The traditional enol-ketone transformation pathway was suspended by the trapping procedure and efficiently switched to an MCR pathway to produce α-amino-β-indole ketones in moderate to good yields. Unexpectedly, the resulting products and the theoretical density functional theory (DFT) calculation results indicated that the enolic carbon had a stronger nucleophilicity than the well-known traditional enamic carbon in the trapping process. The reaction mechanism was investigated using control experiments and detailed DFT calculations, and the synthetic application of the products was also illustrated. The developed strategy provides a mild and rapid access to α-amino-β-indole ketones and suggests a rationale for the discovery of MCRs by trapping an active intermediate with a third component in a traditional two-component reaction pathway. PMID:28345053

  8. Color visualization of cyclic magnitudes

    NASA Astrophysics Data System (ADS)

    Restrepo, Alfredo; Estupiñán, Viviana

    2014-02-01

    We exploit the perceptual, circular ordering of the hues in a technique for the visualization of cyclic variables. The hue is thus meaningfully used for the indication of variables such as the azimuth and the units of the measurement of time. The cyclic (or circular) variables may be both of the continuous type or the discrete type; among the first there is azimuth and among the last you find the musical notes and the days of the week. A correspondence between the values of a cyclic variable and the chromatic hues, where the natural circular ordering of the variable is respected, is called a color code for the variable. We base such a choice of hues on an assignment of of the unique hues red, yellow, green and blue, or one of the 8 even permutations of this ordered list, to 4 cardinal values of the cyclic variable, suitably ordered; color codes based on only 3 cardinal points are also possible. Color codes, being intuitive, are easy to remember. A possible low accuracy when reading instruments that use this technique is compensated by fast, ludic and intuitive readings; also, the use of a referential frame makes readings precise. An achromatic version of the technique, that can be used by dichromatic people, is proposed.

  9. Buffering in cyclic gene networks

    NASA Astrophysics Data System (ADS)

    Glyzin, S. D.; Kolesov, A. Yu.; Rozov, N. Kh.

    2016-06-01

    We consider cyclic chains of unidirectionally coupled delay differential-difference equations that are mathematical models of artificial oscillating gene networks. We establish that the buffering phenomenon is realized in these system for an appropriate choice of the parameters: any given finite number of stable periodic motions of a special type, the so-called traveling waves, coexist.

  10. An enolate-mediated organocatalytic azide-ketone [3+2]-cycloaddition reaction: regioselective high-yielding synthesis of fully decorated 1,2,3-triazoles.

    PubMed

    Shashank, Adluri B; Karthik, S; Madhavachary, R; Ramachary, Dhevalapally B

    2014-12-15

    An enolate-mediated organocatalytic azide-ketone [3+2]-cycloaddition (OrgAKC) reaction of a variety of enolizable arylacetones and deoxybenzoins with aryl azides was developed for the synthesis of fully decorated 1,4-diaryl-5-methyl(alkyl)-1,2,3-triazoles in excellent yields with high regioselectivity at 25 °C for 0.5-6 h. This reaction has an excellent outcome with reference to reaction rate, yield, regioselectivity, operation simplicity, and availability of substrates and catalyst. This reaction has advantages over the previously known metal-mediated reactions.

  11. Development of (trimethylsilyl)ethyl ester protected enolates and applications in palladium-catalyzed enantioselective allylic alkylation: intermolecular cross-coupling of functionalized electrophiles.

    PubMed

    Reeves, Corey M; Behenna, Douglas C; Stoltz, Brian M

    2014-05-02

    The development of (trimethylsilyl)ethyl ester protected enolates is reported. The application of this class of compounds in palladium-catalyzed asymmetric allylic alkylation is explored, yielding a variety of α-quaternary six- and seven-membered ketones and lactams. Independent coupling partner synthesis engenders enhanced allyl substrate scope relative to traditional β-ketoester substrates; highly functionalized α-quaternary ketones generated by the union of (trimethylsilyl)ethyl β-ketoesters and sensitive allylic alkylation coupling partners serve to demonstrate the utility of this method for complex fragment coupling.

  12. One-Pot Domino Aldol Reaction of Indium Enolates Affording 6-Deoxy-α-D,L-altropyranose Derivatives: Synthesis, Mechanism, and Computational Results.

    PubMed

    Cinar, M Emin; Schmittel, Michael

    2015-08-21

    The domino-aldol-aldol-hemiacetal-reaction cascade of indium and other group 13 metal enolates furnished 6-deoxy-α-D,L-altropyranose derivatives in up to 99% yield under thermodynamic control. At lower temperature and thus under kinetic control, the reaction proceeded in a much less diastereoselective manner. The changeover from kinetic to thermodynamic control operating in this multistep domino-aldol-aldol-hemiacetal protocol was used for probing the efficiency of DFT computations. Calculations at the B3LYP/6-31G(d)/LANL2DZ level provided a mechanistic picture in full agreement with the experimental outcome.

  13. Inhibition of diethyl ether degradation in Rhodococcus sp. strain DEE5151 by glutaraldehyde and ethyl vinyl ether.

    PubMed

    Kim, Yong-Hak; Engesser, Karl-Heinrich

    2005-02-15

    Alkyl ether-degrading Rhodococcus sp. strain DEE5151, isolated from activated sewage sludge, has an activity for the oxidation of a variety of alkyl ethers, aralkyl ethers and dibenzyl ether. The whole cell activity for diethyl ether oxidation was effectively inhibited by 2,3-dihydrofurane, ethyl vinyl ether and glutaraldehyde. Glutaraldehyde of less than 30 microM inhibited the activity by a competitive manner with the inhibition constant, K(I) of 7.07+/-1.36 microM. The inhibition type became mixed at higher glutaraldehyde concentrations >30 microM, probably due to the inactivation of the cell activity by the Schiff-base formation. Structurally analogous ethyl vinyl ether inhibited the diethyl ether oxidation activity in a mixed manner with decreasing the apparent maximum oxidation rate, v(max)(app), and increasing the apparent Michaelis-Menten constant, K(M)(app). The mixed type inhibition by ethyl vinyl ether seemed to be introduced not only by the structure similarity with diethyl ether, but also by the reactivity of the vinyl ether with cellular components in the whole cell system.

  14. Poly(aryl-ether-ether-ketone) as a Possible Metalized Film Capacitor Dielectric: Accurate Description of the Band Gap Through Ab Initio Calculation

    DTIC Science & Technology

    2014-12-01

    Poly(aryl-ether-ether- ketone ) as a Possible Metalized Film Capacitor Dielectric: Accurate Description of the Band Gap Through Ab Initio...the originator. Army Research Laboratory Adelphi, MD 20783-1138 ARL-TR-7160 December 2014 Poly(aryl-ether-ether- ketone ) as a...REPORT DATE (DD-MM-YYYY) December 2014 2. REPORT TYPE Final 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Poly(aryl-ether-ether- ketone ) as

  15. Cyclic peptide therapeutics: past, present and future.

    PubMed

    Zorzi, Alessandro; Deyle, Kaycie; Heinis, Christian

    2017-02-26

    Cyclic peptides combine several favorable properties such as good binding affinity, target selectivity and low toxicity that make them an attractive modality for the development of therapeutics. Over 40 cyclic peptide drugs are currently in clinical use and around one new cyclic peptide drug enters the market every year on average. The vast majority of clinically approved cyclic peptides are derived from natural products, such as antimicrobials or human peptide hormones. New powerful techniques based on rational design and in vitro evolution have enabled the de novo development of cyclic peptide ligands to targets for which nature does not offer solutions. A look at the cyclic peptides currently under clinical evaluation shows that several have been developed using such techniques. This new source for cyclic peptide ligands introduces a freshness to the field, and it is likely that de novo developed cyclic peptides will be in clinical use in the near future.

  16. Formation of δ-Lactones with anti-Baeyer-Villiger Regiochemistry - Investigations into the Mechanism of the Cerium-Catalyzed Aerobic Coupling of β-Oxoesters with Enol Acetates.

    PubMed

    Christoffers, Jens; Geibel, Irina; Dierks, Anna; Müller, Thomas

    2017-02-23

    The cerium-catalyzed, aerobic coupling of β-oxoesters with enol acetates and dioxygen yields δ-lactones with a 1,4-diketone moiety. In contrast to the Baeyer-Villiger oxidation (BVO), where the higher substituted residue migrates, in this case of an oxidative C-C coupling reaction the less substituted alkyl residue undergoes a 1,2-shift. An endoperoxidic oxycarbenium ion comparable to the Criegee intermediate in the BVO is proposed as a reaction intermediate and submitted to conformational analysis by computational methods. As a result, the inverse regiochemistry is explained by a primary stereoelectronic effect. A Hammett analysis using different donor and acceptor substituted enol esters provides support for the oxycarbenium ion being the crucial intermediate in the rate determining step of the conversion. An overall mechanism is suggested with a radical chain reaction for the formation of endoperoxides from β-oxoesters, enol acetates and dioxygen with a cerium(IV) species as initiating reagent.

  17. Solvent-controlled diastereoselective synthesis of cyclopentane derivatives by a [3 + 2] cyclization reaction of alpha,beta-disubstituted (alkenyl)(methoxy)carbene complexes with methyl ketone lithium enolates.

    PubMed

    Barluenga, José; Alonso, Jorge; Fañanás, Francisco J

    2003-03-05

    Reaction of alpha,beta-unsaturated methoxycarbene complexes 1 and 11 with methyl ketone lithium enolates 2 leads to the corresponding five-membered carbocyclic compounds 4 or diast-4 and 12. The influence of the solvent and/or cosolvent (PMDTA), which turned out to be crucial to direct the reaction to 4 or diast-4, is studied, and a tentative mechanism according to these facts is proposed. In addition, the reaction of carbene complex 1a with alkynyl methyl ketone lithium enolates can be directed to the formal [3 + 2] or [4 + 1] cyclization products by a slight variation of the reaction conditions. Finally, consecutive three-component coupling reactions with carbene complex 1a, lithium enolates 2, and aldehydes 18 to give, in a diastereoselective way, hydroxy carbonyl compounds 19 and tricyclic polyethers 20 are presented.

  18. Ether bridge formation in loline alkaloid biosynthesis

    PubMed Central

    Pan, Juan; Bhardwaj, Minakshi; Faulkner, Jerome R.; Nagabhyru, Padmaja; Charlton, Nikki D.; Higashi, Richard M.; Miller, Anne-Frances; Young, Carolyn A.; Grossman, Robert B.; Schardl, Christopher L.

    2014-01-01

    Lolines are potent insecticidal agents produced by endophytic fungi of cool-season grasses. These alkaloids are composed of a pyrrolizidine ring system and an uncommon ether bridge linking carbons 2 and 7. Previous results indicated that 1-aminopyrrolizidine was a pathway intermediate. We used RNA interference to knock down expression of lolO, resulting in the accumulation of a novel alkaloid identified as exo-1-acetamidopyrrolizidine based on high-resolution MS and NMR. Genomes of endophytes differing in alkaloid profiles were sequenced, revealing that those with mutated lolO accumulated exo-1-acetamidopyrrolizidine but no lolines. Heterologous expression of wild-type lolO complemented a lolO mutant, resulting in the production of N-acetylnorloline. These results indicated that the non-heme iron oxygenase, LolO, is required for ether bridge formation, probably through oxidation of exo-1-acetamidopyrrolizidine. PMID:24374065

  19. Thrust measurement of dimethyl ether arcjet thruster

    NASA Astrophysics Data System (ADS)

    Kakami, Akira; Beppu, Shinji; Maiguma, Muneyuki; Tachibana, Takeshi

    2011-04-01

    The present paper describes thrust measurement results for an arcjet thruster using Dimethyl ether (DME) as the propellant. DME is an ether compound and can be stored as a liquid due to its relatively low freezing point and preferable vapor pressure. The thruster successfully produced high-voltage mode at DME mass flow rates above 30 mg/s, whereas it yielded low-voltage mode below 30 mg/s. Thrust measurements yielded a thrust of 0.15 N and a specific impulse of 270 s at a mass flow rate of 60 mg/s with a discharge power of 1300 W. The DME arcjet thruster was comparable to a conventional one for thrust and discharge power.

  20. Results on Cyclic Signal Processing Systems,

    DTIC Science & Technology

    1998-01-01

    8] Vaidyanathan, P. P. Multirate systems and filter banks , Prentice Hall, 1993. [9] Vaidyanathan, P. P., and Kirac, A. "Theory of cyclic filter ...91125 Abstract We present a state space description for cyclic LTI sys- tems which find applications in cyclic filter banks and wavelets. We also...in a unified way by using the realization matrix defined by the state space description. 1. INTRODUCTION Cyclic digital filters and filter banks

  1. Promoting environmentally sound management of polybrominated diphenyl ethers in Asia.

    PubMed

    Li, Jinhui; Zhao, Nana; Liu, Xue; Wu, Xiaoyang

    2014-06-01

    Polybrominated diphenyl ethers with persistent organic pollutant properties are required to be controlled by the Stockholm Convention. Recently, polybrominated diphenyl ether contamination has become widespread in Asia, mainly because of the disposal and recycling processes of polybrominated diphenyl ether-containing wastes. The management status, production, usage, import/export, treatment, and disposal, as well as implementation deficiencies for the environmentally sound management of polybrominated diphenyl ethers and polybrominated diphenyl ether-containing materials in ten Asian countries were investigated and assessed in this study. This information could help the participating countries implement the Stockholm Convention and could promote the regional environmentally sound management of polybrominated diphenyl ether-containing articles and products. The results obtained were as follows. (1) Most of the countries studied lacked environmental policies and regulations, or even standards of polybrominated diphenyl ether pollution management and emission control actions. Accurate data on the consumption and importation of polybrominated diphenyl ether-containing materials, however, were not available for all the participating countries. In addition, there were no special treatment or disposal systems for polybrominated diphenyl ether-containing materials, or emission-cutting measures for the treatment of waste in these countries, owing to the lack of sufficient funding or technologies. (2) The improper dismantling of e-waste is a major source of polybrominated diphenyl ether emissions in these countries. (3) Proper e-waste management could result in a breakthrough in the environmentally sound management of this major polybrominated diphenyl ether-containing material flow, and could significantly reduce polybrominated diphenyl ether emissions. Finally, based on the study results, this article puts forward some recommendations for improving the environmentally

  2. Nikola Tesla, the Ether and his Telautomaton

    NASA Astrophysics Data System (ADS)

    Milar, Kendall

    2014-03-01

    In the nineteenth century physicists' understanding of the ether changed dramatically. New developments in thermodynamics, energy physics, and electricity and magnetism dictated new properties of the ether. These have traditionally been examined from the perspective of the scientists re-conceptualizing the ether. However Nikola Tesla, a prolific inventor and writer, presents a different picture of nineteenth century physics. Alongside the displays that showcased his inventions he presented alternative interpretations of physical, physiological and even psychical research. This is particularly evident in his telautomaton, a radio remote controlled boat. This invention and Tesla's descriptions of it showcase some of his novel interpretations of physical theories. He offered a perspective on nineteenth century physics that focused on practical application instead of experiment. Sometimes the understanding of physical theories that Tesla reached was counterproductive to his own inventive work; other times he offered new insights. Tesla's utilitarian interpretation of physical theories suggests a more scientifically curious and invested inventor than previously described and a connection between the scientific and inventive communities.

  3. Biodegradation of glycol ethers in soil

    SciTech Connect

    Gonsior, S.J.; West, R.J.

    1995-08-01

    Because of the widespread use of glycol ethers in applications ranging from consumer products to use as chemical intermediates, there is a need to better understand the fate of these compounds in the environment. Soil biodegradation studies were conducted for three propylene glycol ethers: 1-methoxy-2-propanol, 1-phenoxy-2-propanol, and 1-methoxy-2-propanol acetate. The test compounds were labeled with carbon-14 at either the methoxy or phenoxy substituents. Biodegradation of the three compounds was observed in two sandy loam soils. The time required for disappearance of 50% of the test compounds ranged from < 1 d at 0.2 ppm (w/w) to <7 d at 107 ppm. Degradation rates were slower in a sandy soil, reflecting the lower concentration of microorganisms present. No significant accumulation of intermediate products was observed, and ultimate yields of {sup 14}CO{sub 2} were in the range of 40 to 65% of the initial concentration. Results indicated that the glycol ethers were degraded in a variety of soils under aerobic conditions.

  4. Determination of the pKa of cyclobutanone: Brønsted correlation of the general base-catalyzed enolization in aqueous solution and the effect of ring strain.

    PubMed

    Cope, Steven M; Tailor, Dishant; Nagorski, Richard W

    2011-01-21

    The induction of strain in carbocycles, thereby increasing the amount of s-character in the C-H bonds and the acidity of these protons, has been probed with regard to its effect on the rate constants for the enolization of cyclobutanone. The second-order rate constants for the general base-catalyzed enolization of cyclobutanone have been determined for a series of 3-substituted quinuclidine buffers in D(2)O at 25 °C, I = 1.0 M (KCl). The rate constants for enolization were determined by following the extent of deuterium incorporation (up to ∼30% of the first α-proton) into the α-position, as a function of time. The observed pseudo-first-order rate constants correlated to the [basic form] of the buffer and yielded the second-order rate constants for the general base-catalyzed enolization of cyclobutanone for four tertiary amine buffers. A Brønsted β-value of 0.59 was determined from the second-order rate constants determined. Comparison of the results for cyclobutanone to those previously reported for acetone and a 1-phenylacetone derivative, under similar conditions, indicated that the ring strain of the carbocycle appeared to have only a small effect on the general base-catalyzed rate constants for enolization. The similarity of the rate constants for the general base-catalyzed enolization of cyclobutanone to those determined for acetone allowed for an estimation of the limits of the rate constant for protonation of the enolate intermediate of cyclobutanone by the conjugate acid of 3-quinuclidinone (k(BH) = 5 × 10(8) - 2 × 10(9) M(-1) s(-1)). Combining the rate constants for deprotonation of cyclobutanone (k(B)) and protonation of the enolate of cyclobutanone (k(BH)) by 3-quinuclidinone and its conjugate acid, the pK(a) of the α-protons of cyclobutanone has been estimated to be pK(a) = 19.7-20.2.

  5. Isoelectronic caesium compounds: the triphosphenide Cs[tBu3SiPPPSitBu3] and the enolate Cs[OCH=CH2].

    PubMed

    Lerner, Hans-Wolfram; Sänger, Inge; Schödel, Frauke; Lorbach, Andreas; Bolte, Michael; Wagner, Matthias

    2008-02-14

    The caesium triphosphenide Cs[tBu3SiPPPSitBu3] was accessible from the reaction of CsF with the sodium triphosphenide Na[tBu3SiPPPSitBu3] in tetrahydrofuran at room temperature. In contrast to the preparation of tetrahydrofuran-solvated silanides M[SitBu3] (M = Li, Na, K), our efforts to synthesize the caesium silanide Cs[SitBu3] as a tetrahydrofuran complex failed. When tBu3SiBr was treated with an excess of caesium metal in tetrahydrofuran at room temperature, the caesium enolate Cs[OCH=CH2] and the supersilane tBu3SiH formed rather than the silanide Cs[SitBu3]. X-Ray quality crystals of the enolate Cs[OCH=CH2] (orthorhombic, Pnma) were obtained from tetrahydrofuran at ambient temperature. In contrast to the structures of its homologues M[tBu3SiPPPSitBu3] (M = Na, K), the caesium triphosphenide Cs[tBu3SiPPPSitBu3] features a polymer in the solid state (orthorhombic, Cmcm).

  6. Solvent effects on the absorption spectrum and first hyperpolarizability of keto-enol tautomeric forms of anil derivatives: A Monte Carlo/quantum mechanics study.

    PubMed

    Adriano Junior, L; Fonseca, T L; Castro, M A

    2016-06-21

    Theoretical results for the absorption spectrum and electric properties of the enol and keto tautomeric forms of anil derivatives in the gas-phase and in solution are presented. The electronic properties in chloroform, acetonitrile, methanol, and water were determined by carrying out sequential Monte Carlo simulations and quantum mechanics calculations based on the time dependent density functional theory and on the second-order Møller-Plesset perturbation theory method. The results illustrate the role played by electrostatic interactions in the electronic properties of anil derivatives in a liquid environment. There is a significant increase of the dipole moment in solution (20%-100%) relative to the gas-phase value. Solvent effects are mild for the absorption spectrum and linear polarizability but they can be particularly important for first hyperpolarizability. A large first hyperpolarizability contrast between the enol and keto forms is observed when absorption spectra present intense lowest-energy absorption bands. Dynamic results for the first hyperpolarizability are in qualitative agreement with the available experimental results.

  7. Solvent effects on the absorption spectrum and first hyperpolarizability of keto-enol tautomeric forms of anil derivatives: A Monte Carlo/quantum mechanics study

    NASA Astrophysics Data System (ADS)

    Adriano Junior, L.; Fonseca, T. L.; Castro, M. A.

    2016-06-01

    Theoretical results for the absorption spectrum and electric properties of the enol and keto tautomeric forms of anil derivatives in the gas-phase and in solution are presented. The electronic properties in chloroform, acetonitrile, methanol, and water were determined by carrying out sequential Monte Carlo simulations and quantum mechanics calculations based on the time dependent density functional theory and on the second-order Møller-Plesset perturbation theory method. The results illustrate the role played by electrostatic interactions in the electronic properties of anil derivatives in a liquid environment. There is a significant increase of the dipole moment in solution (20%-100%) relative to the gas-phase value. Solvent effects are mild for the absorption spectrum and linear polarizability but they can be particularly important for first hyperpolarizability. A large first hyperpolarizability contrast between the enol and keto forms is observed when absorption spectra present intense lowest-energy absorption bands. Dynamic results for the first hyperpolarizability are in qualitative agreement with the available experimental results.

  8. Safety evaluation of the double mutant 5-enol pyruvylshikimate-3-phosphate synthase (2mEPSPS) from maize that confers tolerance to glyphosate herbicide in transgenic plants.

    PubMed

    Herouet-Guicheney, Corinne; Rouquié, David; Freyssinet, Martine; Currier, Thomas; Martone, Aris; Zhou, Junguo; Bates, Elizabeth E M; Ferullo, Jean-Marc; Hendrickx, Koen; Rouan, Dominique

    2009-07-01

    Glyphosate tolerance can be conferred by decreasing the herbicide's ability to inhibit the enzyme 5-enol pyruvylshikimate-3-phosphate synthase, which is essential for the biosynthesis of aromatic amino acids in all plants, fungi, and bacteria. Glyphosate tolerance is based upon the expression of the double mutant 5-enol pyruvylshikimate-3-phosphate synthase (2mEPSPS) protein. The 2mEPSPS protein, with a lower binding affinity for glyphosate, is highly resistant to the inhibition by glyphosate and thus allows sufficient enzyme activity for the plants to grow in the presence of herbicides that contain glyphosate. Based on both a review of published literature and experimental studies, the potential safety concerns related to the transgenic 2mEPSPS protein were assessed. The safety evaluation supports that the expressed protein is innocuous. The 2mEPSPS enzyme does not possess any of the properties associated with known toxins or allergens, including a lack of amino acid sequence similarity to known toxins and allergens, a rapid degradation in simulated gastric and intestinal fluids, and no adverse effects in mice after intravenous or oral administration (at 10 or 2000 mg/kg body weight, respectively). In conclusion, there is a reasonable certainty of no harm resulting from the inclusion of the 2mEPSPS protein in human food or in animal feed.

  9. From ether theory to ether theology: Oliver Lodge and the physics of immortality.

    PubMed

    Raia, Courtenay Grean

    2007-01-01

    This article follows the development of physicist Oliver Lodge's religio-scientific worldview, beginning with his reticent attraction to metaphysics in the early 1880s to the full formulation of his "ether theology" in the late 1890s. Lodge undertook the study of psychical phenomena such as telepathy, telekinesis, and "ectoplasm" to further his scientific investigations of the ether, speculating that electrical and psychical manifestations were linked phenomena that described the deeper underlying structures of the universe, beneath and beyond matter. For Lodge, to fully understand the ether was to force from the universe an ultimate Revelation, and psychical research, as the most modern and probatory science, was poised to replace religion as the means of that disclosure. (c) 2007 Wiley Periodicals, Inc.

  10. Chemistry and adhesive properties of poly(arylene ether)s containing heterocyclic units

    NASA Technical Reports Server (NTRS)

    Connell, John W.

    1991-01-01

    Novel poly(arylene ether)s containing heterocyclic units were prepared, characterized, and evaluated as adhesives and composite matrices. The polymers were prepared by reacting a heterocyclic bisphenol with an activated aromatic dihalide in a polar aprotic solvent, using potassium carbonate. The polymerizations were generally carried out in N,N-dimethylacetamide at 155 C. In some cases, where the polymers were semicrystalline, higher temperatures and thus higher boiling solvents were necessary to keep the polymers in solution. Heterocyclic rings incorporated into the poly(arylene ether) backbone include phenylquinoxaline, phenylimidazole, benzimidazole, benzoxazole, 1,3,4-oxadiazole, and 1,2,4-triazole. The polymers were characterized by differential scanning calorimetry, solution viscosity, X-ray diffraction, thin film, and adhesive and (in some cases) composite properties. The glass transition temperatures, crystalline melt temperature, solubility, and mechanical properties varied depending upon the heterocyclic ring. The chemistry and properties of these materials are discussed.

  11. Cyclic Pursuit in Three Dimensions

    DTIC Science & Technology

    2010-12-17

    A three-dimensional version of the motion camouflage pursuit 49th IEEE Conference on Decision and Control December 15-17, 2010 Hilton Atlanta Hotel ...show that Θ is a constant value on MCB(a). Proposition 4: Consider a two-particle system operating on MCB(a) according to the closed-loop mutual CB...illustrate various types of trajectories in terms of initial conditions (` and Θ) and parameter values (a+ and a−). In our planar discussion of cyclic

  12. Comparison of Properties among Dendritic and Hyperbranched Poly(ether ether ketone)s and Linear Poly(ether ketone)s.

    PubMed

    Morikawa, Atsushi

    2016-02-16

    Poly(ether ether ketone) dendrimers and hyperbranched polymers were prepared from 3,5-dimethoxy-4'-(4-fluorobenzoyl)diphenyl ether and 3,5-dihydroxy-4'-(4-fluorobenzoyl)diphenyl ether through aromatic nucleophilic substitution reactions. 1-(tert-Butyldimethylsiloxy)-3,5-bis(4-fluorobenzoyl)benzene was polycondensed with bisphenols, followed by cleavage of the protective group to form linear poly(ether ketone)s having the same hydroxyl groups in the side chains as the chain ends of the dendrimer and hyperbranched polymers. Their properties, such as solubilities, reduced viscosities, and thermal properties, were compared with one another. Similar comparisons were also carried out among the corresponding methoxy group polymers, and the size of the molecules was shown to affect the properties.

  13. Plant cyclic nucleotide signalling: facts and fiction.

    PubMed

    Martinez-Atienza, Juliana; Van Ingelgem, Carl; Roef, Luc; Maathuis, Frans Jm

    2007-11-01

    The presence of the cyclic nucleotides 3',5'-cyclic adenyl monophosphate (cAMP) and 3',5'-cyclic guanyl monophosphate (cGMP) in plants is now generally accepted. In addition, cAMP and cGMP have been implicated in the regulation of important plant processes such as stomatal functioning, monovalent and divalent cation fluxes, chloroplast development, gibberellic acid signalling, pathogen response and gene transcription. However, very little is known regarding the components of cyclic nucleotide signalling in plants. In this addendum, the evidence for specific mechanisms of plant cyclic nucleotide signalling is evaluated and discussed.

  14. Supramolecular nesting of cyclic polymers.

    PubMed

    Kondratuk, Dmitry V; Perdigão, Luís M A; Esmail, Ayad M S; O'Shea, James N; Beton, Peter H; Anderson, Harry L

    2015-04-01

    Advances in template-directed synthesis make it possible to create artificial molecules with protein-like dimensions, directly from simple components. These synthetic macromolecules have a proclivity for self-organization that is reminiscent of biopolymers. Here, we report the synthesis of monodisperse cyclic porphyrin polymers, with diameters of up to 21 nm (750 C–C bonds). The ratio of the intrinsic viscosities for cyclic and linear topologies is 0.72, indicating that these polymers behave as almost ideal flexible chains in solution. When deposited on gold surfaces, the cyclic polymers display a new mode of two-dimensional supramolecular organization, combining encapsulation and nesting; one nanoring adopts a near-circular conformation, thus allowing a second nanoring to be captured within its perimeter, in a tightly folded conformation. Scanning tunnelling microscopy reveals that nesting occurs in combination with stacking when nanorings are deposited under vacuum, whereas when they are deposited directly from solution under ambient conditions there is stacking or nesting, but not a combination of both.

  15. Cyclic Deformation in Metallic Glasses.

    PubMed

    Sha, Z D; Qu, S X; Liu, Z S; Wang, T J; Gao, H

    2015-10-14

    Despite the utmost importance and decades of experimental studies on fatigue in metallic glasses (MGs), there has been so far little or no atomic-level understanding of the mechanisms involved. Here we perform molecular dynamics simulations of tension-compression fatigue in Cu50Zr50 MGs under strain-controlled cyclic loading. It is shown that the shear band (SB) initiation under cyclic loading is distinctly different from that under monotonic loading. Under cyclic loading, SB initiation takes place when aggregates of shear transformation zones (STZs) accumulating at the MG surface reach a critical size comparable to the SB width, and the accumulation of STZs follows a power law with rate depending on the applied strain. It is further shown that almost the entire fatigue life of nanoscale MGs under low cycle fatigue is spent in the SB-initiation stage, similar to that of crystalline materials. Furthermore, a qualitative investigation of the effect of cycling frequency on the fatigue behavior of MGs suggests that higher cycling frequency leads to more cycles to failure. The present study sheds light on the fundamental fatigue mechanisms of MGs that could be useful in developing strategies for their engineering applications.

  16. 40 CFR 721.10067 - Ether amine phosphonate salt (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Ether amine phosphonate salt (generic... Specific Chemical Substances § 721.10067 Ether amine phosphonate salt (generic). (a) Chemical substances... ether amine phosphonate salt (PMNs P-05-57, P-05-58, P-05-59, P-05-61, P-05-62, P-05-63, P-05-64, and...

  17. 40 CFR 721.10067 - Ether amine phosphonate salt (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Ether amine phosphonate salt (generic... Specific Chemical Substances § 721.10067 Ether amine phosphonate salt (generic). (a) Chemical substances... ether amine phosphonate salt (PMNs P-05-57, P-05-58, P-05-59, P-05-61, P-05-62, P-05-63, P-05-64, and...

  18. 40 CFR 721.10067 - Ether amine phosphonate salt (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Ether amine phosphonate salt (generic... Specific Chemical Substances § 721.10067 Ether amine phosphonate salt (generic). (a) Chemical substances... ether amine phosphonate salt (PMNs P-05-57, P-05-58, P-05-59, P-05-61, P-05-62, P-05-63, P-05-64, and...

  19. 40 CFR 721.10067 - Ether amine phosphonate salt (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Ether amine phosphonate salt (generic... Specific Chemical Substances § 721.10067 Ether amine phosphonate salt (generic). (a) Chemical substances... ether amine phosphonate salt (PMNs P-05-57, P-05-58, P-05-59, P-05-61, P-05-62, P-05-63, P-05-64, and...

  20. 40 CFR 721.10067 - Ether amine phosphonate salt (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Ether amine phosphonate salt (generic... Specific Chemical Substances § 721.10067 Ether amine phosphonate salt (generic). (a) Chemical substances... ether amine phosphonate salt (PMNs P-05-57, P-05-58, P-05-59, P-05-61, P-05-62, P-05-63, P-05-64, and...

  1. Poly (Aryl Ether Ketones) Bearing Alkylated Side Chains

    NASA Technical Reports Server (NTRS)

    Cassidy, Patrick E. (Inventor); Fitch, John W., III (Inventor); Gronewald, Scott D. (Inventor); St.Clair, Ann K. (Inventor); Stoakley, Diane M. (Inventor)

    2002-01-01

    This invention relates generally to poly(aryl ether ketones) bearing alkylated side chains. It relates particularly to soluble, thermally stable. low dielectric poly(aryl ether ketones) with alkylated side chains and especially to films and coatings thereof. These poly(aryl ether ketones) have a structural formula wherein Y is selected from the group consisting of CF3 and CH3; and wherein R is C(sub n)H(sub (2n+1)) and n = 11-18.

  2. IRIS Toxicological Review of Ethyl Tertiary Butyl Ether (Etbe) ...

    EPA Pesticide Factsheets

    EPA is conducting a peer review and public comment of the scientific basis supporting the human health hazard and dose-response assessment of ethyl tertiary butyl ether (ETBE) that when finalized will appear on the Integrated Risk Information System (IRIS) database. The draft Toxicological Review of Ethyl Tertiary Butyl Ether provides scientific support and rationale for the hazard and dose-response assessment pertaining to chronic exposure to ethyl tertiary butyl ether.

  3. Glycol ether/siloxane polymer penetrating and lubricating composition

    SciTech Connect

    MacIntosh, D.H.

    1981-02-03

    A penetrating and lubricating composition consists of a silicone lubricant dissolved in a glycol ether carrier having a very low surface tension. The glycol ether gives the composition the ability to penetrate into the cracks between two seized or corroded elements and dissolve any rust or corrosion present. The glycol ether then volitalizes leaving a coating of silicone on the parts to serve as a lubricant and prevent further corrosion.

  4. Temperature, Molecular Weight, and Concentration Dependences of Thermal Diffusion for Ethylene Glycol Oligomers and Crown Ethers

    NASA Astrophysics Data System (ADS)

    Maeda, Kousaku; Kita, Rio; Shinyashiki, Naoki; Yagihara, Shin

    The Soret coefficient ST of ethylene glycol oligomers (EGOs) and crown ethers (CEs) in water were obtained by thermal diffusion forced Rayleigh scattering by changing the temperature, molecular weight, and concentration. The effect of a hydroxyl group on the EGOs and the effect of the cyclic structure of CEs on the thermal diffusion were determined systematically by changing the molecular weights of the EGOs and CEs. For dilute aqueous solutions, EGOs and CEs, except EG, show positive ST values that decrease with increasing temperature, which is similar to the results of previous studies on mixtures of water and organic solvents. The temperature dependence of ST changes its behavior from negative to positive with decreasing number of repeating units of EGOs. This behavior is related to the increase in the number density of the hydroxyl group. The ST values of EG show two different concentration regions, namely, the low concentration (0-2 wt %) and high concentration (2-100 wt %) regions.

  5. Comparative Study of Ether-Based Electrolytes for Application in Lithium-Sulfur Battery.

    PubMed

    Carbone, Lorenzo; Gobet, Mallory; Peng, Jing; Devany, Matthew; Scrosati, Bruno; Greenbaum, Steve; Hassoun, Jusef

    2015-07-01

    Herein, we report the characteristics of electrolytes using various ether-solvents with molecular composition CH3O[CH2CH2O]nCH3, differing by chain length, and LiCF3SO3 as the lithium salt. The electrolytes, considered as suitable media for lithium-sulfur batteries, are characterized in terms of thermal properties (TGA, DSC), lithium ion conductivity, lithium interface stability, cyclic voltammetry, self-diffusion properties of the various components, and lithium transference number measured by NMR. Furthermore, the electrolytes are characterized in lithium cells using a sulfur-carbon composite cathode by galvanostatic charge-discharge tests. The results clearly evidence the influence of the solvent chain length on the species mobility within the electrolytes that directly affects the behavior in lithium sulfur cell. The results may effectively contribute to the progress of an efficient, high-energy lithium-sulfur battery.

  6. Novel polymer electrolyte from poly(carbonate-ether) and lithium tetrafluoroborate for lithium-oxygen battery

    NASA Astrophysics Data System (ADS)

    Lu, Qi; Gao, Yonggang; Zhao, Qiang; Li, Ji; Wang, Xianhong; Wang, Fosong

    2013-11-01

    Novel polymer electrolyte based on low-molecular weight poly(carbonate-ether) and lithium tetrafluoroborate has been prepared and used in lithium-oxygen battery for the first time, the electrolyte with approximate 17% of LiBF4 showed ionic conductivity of 1.57 mS cm-1. Infrared spectra analysis indicates that obvious interaction between the lithium ions and partial oxygen atoms in the host polymer exists, and the lithium salt and the host polymer have good miscibility. The lithium-oxygen battery from this polymer electrolyte shows similar cyclic stability to traditional liquid electrolyte observed by FT-IR, AFM and electrochemical measurements, which may provide a new choice for fabrication of all-solid-state high-capacity rechargeable lithium-oxygen battery with better safety.

  7. Cyclic modular beta-sheets.

    PubMed

    Woods, R Jeremy; Brower, Justin O; Castellanos, Elena; Hashemzadeh, Mehrnoosh; Khakshoor, Omid; Russu, Wade A; Nowick, James S

    2007-03-07

    The development of peptide beta-hairpins is problematic, because folding depends on the amino acid sequence and changes to the sequence can significantly decrease folding. Robust beta-hairpins that can tolerate such changes are attractive tools for studying interactions involving protein beta-sheets and developing inhibitors of these interactions. This paper introduces a new class of peptide models of protein beta-sheets that addresses the problem of separating folding from the sequence. These model beta-sheets are macrocyclic peptides that fold in water to present a pentapeptide beta-strand along one edge; the other edge contains the tripeptide beta-strand mimic Hao [JACS 2000, 122, 7654] and two additional amino acids. The pentapeptide and Hao-containing peptide strands are connected by two delta-linked ornithine (deltaOrn) turns [JACS 2003, 125, 876]. Each deltaOrn turn contains a free alpha-amino group that permits the linking of individual modules to form divalent beta-sheets. These "cyclic modular beta-sheets" are synthesized by standard solid-phase peptide synthesis of a linear precursor followed by solution-phase cyclization. Eight cyclic modular beta-sheets 1a-1h containing sequences based on beta-amyloid and macrophage inflammatory protein 2 were synthesized and characterized by 1H NMR. Linked cyclic modular beta-sheet 2, which contains two modules of 1b, was also synthesized and characterized. 1H NMR studies show downfield alpha-proton chemical shifts, deltaOrn delta-proton magnetic anisotropy, and NOE cross-peaks that establish all compounds but 1c and 1g to be moderately or well folded into a conformation that resembles a beta-sheet. Pulsed-field gradient NMR diffusion experiments show little or no self-association at low (

  8. Divinyl ether synthase gene, and protein and uses thereof

    DOEpatents

    Howe, Gregg A.; Itoh, Aya

    2006-12-26

    The present invention relates to divinyl ether synthase genes, proteins, and methods of their use. The present invention encompasses both native and recombinant wild-type forms of the synthase, as well as mutants and variant forms, some of which possess altered characteristics relative to the wild-type synthase. The present invention also relates to methods of using divinyl ether synthase genes and proteins, including in their expression in transgenic organisms and in the production of divinyl ether fatty acids, and to methods of suing divinyl ether fatty acids, including in the protection of plants from pathogens.

  9. Divinyl ether synthase gene and protein, and uses thereof

    DOEpatents

    Howe, Gregg A [East Lansing, MI; Itoh, Aya [Tsuruoka, JP

    2011-09-13

    The present invention relates to divinyl ether synthase genes, proteins, and methods of their use. The present invention encompasses both native and recombinant wild-type forms of the synthase, as well as mutants and variant forms, some of which possess altered characteristics relative to the wild-type synthase. The present invention also relates to methods of using divinyl ether synthase genes and proteins, including in their expression in transgenic organisms and in the production of divinyl ether fatty acids, and to methods of suing divinyl ether fatty acids, including in the protection of plants from pathogens.

  10. Ether Cleavage Re-Investigated: Elucidating the Mechanism of BBr3-Facilitated Demethylation of Aryl Methyl Ethers

    PubMed Central

    Kosak, Talon M; Conrad, Heidi A; Korich, Andrew L; Lord, Richard L

    2015-01-01

    One of the most well-known, highly utilized reagents for ether cleavage is boron tribromide (BBr3), and this reagent is frequently employed in a 1:1 stoichiometric ratio with ethers. Density functional theory calculations predict a new mechanistic pathway involving charged intermediates for ether cleavage in aryl methyl ethers. Moreover, these calculations predict that one equivalent of BBr3 can cleave up to three equivalents of anisole, producing triphenoxyborane [B(OPh)3] prior to hydrolysis. These predictions were validated by gas chromatography analysis of reactions where the BBr3:anisole ratio was varied. Not only do we confirm that sub-stoichiometric equivalents may be used for ether demethylation, but the findings also support our newly proposed three cycle mechanism for cleavage of aryl methyl ethers. PMID:26693209

  11. Computational Study of Nanosized Drug Delivery from Cyclodextrins, Crown Ethers and Hyaluronan in Pharmaceutical Formulations.

    PubMed

    Torrens, Francisco; Castellano, Gloria

    2015-01-01

    The problem in this work is the computational characterization of cyclodextrins, crown ethers and hyaluronan (HA) as hosts of inclusion complexes for nanosized drug delivery vehicles in pharmaceutical formulations. The difficulty is addressed through a computational study of some thermodynamic, geometric and topological properties of the hosts. The calculated properties of oligosaccharides of D-glucopyranoses allow these to act as co-solvents of polyanions in water. In crown ethers, the central channel is computed. Mucoadhesive polymer HA in formulations releases drugs in mucosas. Geometric, topological and fractal analyses are carried out with code TOPO. Reference calculations are performed with code GEPOL. From HA to HA·3Ca and hydrate, the hydrophilic solvent-accessible surface varies with the count of H-bonds. The fractal dimension rises. The dimension of external atoms rises resulting 1.725 for HA. It rises going to HA·3Ca and hydrate. Nonburied minus molecular dimension rises and decays. Hydrate globularity is lower than O(water), Ca(2+) and O(HA). Ca(2+) rugosity is smaller than for hydrate, O(HA) and O(water). Ca(2+) and O(water) accessibilities are greater than hydrate. Conclusions are drawn on: (1) the relative stability of linear/cyclic and shorter/larger polymers; (2) the atomic analysis of properties allows determining the atoms with maximum reactivity.

  12. Unprecedented reactions: from epichlorohydrin to epoxyglycidyl substituted divinyl ether and its conversion into epoxyglycidyl propargyl ether.

    PubMed

    Yao, Yiwu; Li, Zheng; Qiu, Yatao; Bai, Jinhong; Su, Jinyue; Zhang, Dayong; Jiang, Sheng

    2015-09-18

    The reaction of epichlorohydrin with concentrated sodium hydroxide in hexane under phase transfer conditions has surprisingly led to the formation of the symmetrical di(3-epoxyglycidyl-1-propenyl) ether 1 which contains both nucleophilic and electrophilic moieties. When it was reacted with n-butyllithium, intermediate 1 once again surprisingly generated epoxyglycidyl propargyl ether, which was further reacted in situ with a variety of benzaldehydes to furnish the corresponding substituted propargylic alcohols in good yields. While the reaction is operationally simple, it provides a powerful method for the synthesis of the important products from commodity materials such as epichlorohydrin. Moreover, these reactions may have revealed that some fundamental properties of the hydroxide anion in those once thought straightforward reactions are not well understood. A careful analysis of the experimental data suggests that an unprecedented concerted elimination of the epoxyglycidyl ether with sodium hydroxide may be operative and an alpha deprotonation followed by alpha elimination of the di(3-epoxyglycidyl-1-propenyl) ether with alkyllithium may have been involved.

  13. Unprecedented reactions: from epichlorohydrin to epoxyglycidyl substituted divinyl ether and its conversion into epoxyglycidyl propargyl ether

    PubMed Central

    Yao, Yiwu; Li, Zheng; Qiu, Yatao; Bai, Jinhong; Su, Jinyue; Zhang, Dayong; Jiang, Sheng

    2015-01-01

    The reaction of epichlorohydrin with concentrated sodium hydroxide in hexane under phase transfer conditions has surprisingly led to the formation of the symmetrical di(3-epoxyglycidyl-1-propenyl) ether 1 which contains both nucleophilic and electrophilic moieties. When it was reacted with n-butyllithium, intermediate 1 once again surprisingly generated epoxyglycidyl propargyl ether, which was further reacted in situ with a variety of benzaldehydes to furnish the corresponding substituted propargylic alcohols in good yields. While the reaction is operationally simple, it provides a powerful method for the synthesis of the important products from commodity materials such as epichlorohydrin. Moreover, these reactions may have revealed that some fundamental properties of the hydroxide anion in those once thought straightforward reactions are not well understood. A careful analysis of the experimental data suggests that an unprecedented concerted elimination of the epoxyglycidyl ether with sodium hydroxide may be operative and an alpha deprotonation followed by alpha elimination of the di(3-epoxyglycidyl-1-propenyl) ether with alkyllithium may have been involved. PMID:26383123

  14. Unprecedented reactions: from epichlorohydrin to epoxyglycidyl substituted divinyl ether and its conversion into epoxyglycidyl propargyl ether

    NASA Astrophysics Data System (ADS)

    Yao, Yiwu; Li, Zheng; Qiu, Yatao; Bai, Jinhong; Su, Jinyue; Zhang, Dayong; Jiang, Sheng

    2015-09-01

    The reaction of epichlorohydrin with concentrated sodium hydroxide in hexane under phase transfer conditions has surprisingly led to the formation of the symmetrical di(3-epoxyglycidyl-1-propenyl) ether 1 which contains both nucleophilic and electrophilic moieties. When it was reacted with n-butyllithium, intermediate 1 once again surprisingly generated epoxyglycidyl propargyl ether, which was further reacted in situ with a variety of benzaldehydes to furnish the corresponding substituted propargylic alcohols in good yields. While the reaction is operationally simple, it provides a powerful method for the synthesis of the important products from commodity materials such as epichlorohydrin. Moreover, these reactions may have revealed that some fundamental properties of the hydroxide anion in those once thought straightforward reactions are not well understood. A careful analysis of the experimental data suggests that an unprecedented concerted elimination of the epoxyglycidyl ether with sodium hydroxide may be operative and an alpha deprotonation followed by alpha elimination of the di(3-epoxyglycidyl-1-propenyl) ether with alkyllithium may have been involved.

  15. Novel high T[sub g] high-strength poly(aryl ether)s

    SciTech Connect

    Banerjee, S.; Maier, G. . Lehrstuhl fuer Makromolekulare Stoffe)

    1999-08-01

    A novel 2-perfluoroalkyl-activated bisfluoro monomer has been synthesized successfully using a Pd(0)-catalyzed cross-coupling reaction of 4-fluoro-3-trifluoromethyl phenyl boronic acid with 4,4[prime]-dibromodiphenylbenzene. This monomer was converted to novel poly(aryl ether)s by nucleophilic displacement of the fluorine atoms on the benzene ring with several bisphenols. The products obtained by displacement of the fluorine atoms exhibit weight average molar masses up to 1.06 [times] 10[sup 5] g/mol in GPC. These poly(aryl ether)s showed outstanding thermooxidative stability up to 534 C for 5% weight loss in TGA under synthetic air and high glass transition temperatures (T[sub g]) even up to 300 C in DSC and DMTA. These polymers are soluble in a wide range of organic solvents, e.g., CHCl[sub 3], THF, NMP, DMF, toluene, etc., and are insoluble in DMSO and acetone. Transparent thin films of these polymers cast from DMF exhibited tensile strengths up to 115 MPa, moduli up to 2.59 GPa, and elongations up to 120% depending on their exact repeating unit structures. These values are comparable to those of high performance thermoplastic materials such as PEEK or Ultem PEI.

  16. Novel high T{sub g} high-strength poly(aryl ether)s

    SciTech Connect

    Banerjee, S.; Maier, G.

    1999-08-01

    A novel 2-perfluoroalkyl-activated bisfluoro monomer has been synthesized successfully using a Pd(0)-catalyzed cross-coupling reaction of 4-fluoro-3-trifluoromethyl phenyl boronic acid with 4,4{prime}-dibromodiphenylbenzene. This monomer was converted to novel poly(aryl ether)s by nucleophilic displacement of the fluorine atoms on the benzene ring with several bisphenols. The products obtained by displacement of the fluorine atoms exhibit weight average molar masses up to 1.06 {times} 10{sup 5} g/mol in GPC. These poly(aryl ether)s showed outstanding thermooxidative stability up to 534 C for 5% weight loss in TGA under synthetic air and high glass transition temperatures (T{sub g}) even up to 300 C in DSC and DMTA. These polymers are soluble in a wide range of organic solvents, e.g., CHCl{sub 3}, THF, NMP, DMF, toluene, etc., and are insoluble in DMSO and acetone. Transparent thin films of these polymers cast from DMF exhibited tensile strengths up to 115 MPa, moduli up to 2.59 GPa, and elongations up to 120% depending on their exact repeating unit structures. These values are comparable to those of high performance thermoplastic materials such as PEEK or Ultem PEI.

  17. Phenylethynyl-Terminated Poly(Arylene Ethers)

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Bryant, Robert G.; Hergenrother, Paul M.

    1994-01-01

    Phenylethynyl-terminated poly(arylene ethers) synthesized in wide range of molecular weights by adjusting monomer ratios and adding appropriate amounts of 4-phenylethynyl-4'-fluorobenzophenone to monomers to end-cap oligomers during polymerization. Have low molecular weights and low melt viscosities, and are easily processed as adhesives, composites, and moldings. Thermally cured to provide materials that are crosslinked and insoluble in common organic solvents. Exhibit increased resistance to solvents, greater tensile moduli, and better high-temperature properties. Useful as adhesives, composite matrices, and moldings, especially in applications in which combination of toughness and resistance to solvents needed.

  18. Epoxy resin cure. [Phenyl glycidyl ether

    SciTech Connect

    Smith, R.E.; Woodburn, G.L.

    1986-07-01

    The reactions that occur between the model epoxy, phenyl glycidyl ether, and the cure agent dicyandiamide (DICY) have been investigated using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), gel permeation chromatography (GPC), and high-performance liquid chromatography (HPLC) techniques. It is shown that the reaction at 130/sup 0/C requires 90 min for completion when catalyzed by boron trifluoride monoethyl amine (BF/sub 3/-MEA). At least three major products are formed. The identity of these products is based on previously published spectroscopic data. 3 refs., 5 figs.

  19. Fluorinated Poly(Phenylene Ether Ketones)

    NASA Technical Reports Server (NTRS)

    St. Clair, Anne K.; Cassidy, Patrick E.; Tullos, Gordon L.

    1994-01-01

    Fluorinated poly(phenylene ether ketones) are colorless, transparent, low-dielectric-constant, highly thermally stable polymers. Particularly suitable for use as film and coating materials in electronic and thermal-control applications such as; passivant insulating coats and interlevel dielectrics in microelectronic circuits, or as protective transparent coats on solar cells or mirrors. Solubility and transparency of 12F-PEK along with its lower dielectric constant and other properties make it more useful as dielectric film and coating material in many applications.

  20. An Exposure Assessment of Polybrominated Diphenyl Ethers ...

    EPA Pesticide Factsheets

    EPA announced the availability of the final report, An Exposure Assessment of Polybrominated Diphenyl Ethers. This report provides a comprehensive assessment of the exposure of Americans to this class of persistent organic pollutants. Individual chapters in this document address: the production, use, and lifecycle of PBDEs; environmental fate; environmental levels; and human exposure. This final report addresses the exposure assessment needs identified in the OPBDE Workgroup project plan. It provides a comprehensive assessment of the exposure of Americans to this class of persistent organic pollutants. Individual chapters in this document address: the production, use, and lifecycle of PBDEs; environmental fate; environmental levels; and human exposure.

  1. Obstetric and Other Uses of Ether Before Ether Day, According to the Boston Medical and Surgical Journal of 1828-1846.

    PubMed

    Stoller, Sundrayah N; Minehart, Rebecca D; Alston, Theodore A

    2016-04-01

    From the inception of the Boston Medical and Surgical Journal in 1828 until the prominent public demonstration of surgical anesthesia on Ether Day of 1846, ether was often mentioned in the journal. Many of the examples were related to obstetrics. Because molecular structures were not available in the early 1800s, diverse volatile liquids were termed ethers. In addition to sulphuric ether, so-called ethers included cyanide-releasing propionitrile and ethanolic solutions of chloroform and of the potent vasodilator ethyl nitrite. Familiarity with anesthetically unsuitable ethers may have long deterred consideration of inhaled sulphuric ether for analgesia and anesthesia.

  2. Advances in targeting cyclic nucleotide phosphodiesterases

    PubMed Central

    Maurice, Donald H.; Ke, Hengming; Ahmad, Faiyaz; Wang, Yousheng; Chung, Jay; Manganiello, Vincent C.

    2014-01-01

    Cyclic nucleotide phosphodiesterases (PDEs) catalyse the hydrolysis of cyclic AMP and cyclic GMP, thereby regulating the intracellular concentrations of these cyclic nucleotides, their signalling pathways and, consequently, myriad biological responses in health and disease. Currently, a small number of PDE inhibitors are used clinically for treating the pathophysiological dysregulation of cyclic nucleotide signalling in several disorders, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication and chronic obstructive pulmonary disease. However, pharmaceutical interest in PDEs has been reignited by the increasing understanding of the roles of individual PDEs in regulating the subcellular compartmentalization of specific cyclic nucleotide signalling pathways, by the structure-based design of novel specific inhibitors and by the development of more sophisticated strategies to target individual PDE variants. PMID:24687066

  3. Biosynthesis of archaeal membrane ether lipids

    PubMed Central

    Jain, Samta; Caforio, Antonella; Driessen, Arnold J. M.

    2014-01-01

    A vital function of the cell membrane in all living organism is to maintain the membrane permeability barrier and fluidity. The composition of the phospholipid bilayer is distinct in archaea when compared to bacteria and eukarya. In archaea, isoprenoid hydrocarbon side chains are linked via an ether bond to the sn-glycerol-1-phosphate backbone. In bacteria and eukarya on the other hand, fatty acid side chains are linked via an ester bond to the sn-glycerol-3-phosphate backbone. The polar head groups are globally shared in the three domains of life. The unique membrane lipids of archaea have been implicated not only in the survival and adaptation of the organisms to extreme environments but also to form the basis of the membrane composition of the last universal common ancestor (LUCA). In nature, a diverse range of archaeal lipids is found, the most common are the diether (or archaeol) and the tetraether (or caldarchaeol) lipids that form a monolayer. Variations in chain length, cyclization and other modifications lead to diversification of these lipids. The biosynthesis of these lipids is not yet well understood however progress in the last decade has led to a comprehensive understanding of the biosynthesis of archaeol. This review describes the current knowledge of the biosynthetic pathway of archaeal ether lipids; insights on the stability and robustness of archaeal lipid membranes; and evolutionary aspects of the lipid divide and the LUCA. It examines recent advances made in the field of pathway reconstruction in bacteria. PMID:25505460

  4. Biosynthesis of archaeal membrane ether lipids.

    PubMed

    Jain, Samta; Caforio, Antonella; Driessen, Arnold J M

    2014-01-01

    A vital function of the cell membrane in all living organism is to maintain the membrane permeability barrier and fluidity. The composition of the phospholipid bilayer is distinct in archaea when compared to bacteria and eukarya. In archaea, isoprenoid hydrocarbon side chains are linked via an ether bond to the sn-glycerol-1-phosphate backbone. In bacteria and eukarya on the other hand, fatty acid side chains are linked via an ester bond to the sn-glycerol-3-phosphate backbone. The polar head groups are globally shared in the three domains of life. The unique membrane lipids of archaea have been implicated not only in the survival and adaptation of the organisms to extreme environments but also to form the basis of the membrane composition of the last universal common ancestor (LUCA). In nature, a diverse range of archaeal lipids is found, the most common are the diether (or archaeol) and the tetraether (or caldarchaeol) lipids that form a monolayer. Variations in chain length, cyclization and other modifications lead to diversification of these lipids. The biosynthesis of these lipids is not yet well understood however progress in the last decade has led to a comprehensive understanding of the biosynthesis of archaeol. This review describes the current knowledge of the biosynthetic pathway of archaeal ether lipids; insights on the stability and robustness of archaeal lipid membranes; and evolutionary aspects of the lipid divide and the LUCA. It examines recent advances made in the field of pathway reconstruction in bacteria.

  5. [Aerobic microbial degradation of polybrominated diphenyl ethers].

    PubMed

    Ding, Juan; Zhou, Juan; Jiang, Wei-Ying; Gao, Shi-Xiang

    2008-11-01

    The biodegradation of 4, 4'-dibromodipheny ether (BDE15) and decabromodiphenyl ether (BDE209) by white rot fungi under aerobic conditions was studied. Effects of non-ionic surfactant Tween 80 and beta-cyclodextrin as solubilizers on the apparent solubilities and biodegradation rates of BDE15 and BDE209 were also evaluated. The results showed that both BDE15 and BDE209 were efficiently degraded by white rot fungi. The degradation rates were 43.0% and 62.5% for BDE209 and BDE15, respectively, after 10 d incubation. The degradation of BDE209 was greatly enhanced by addition of Tween 80 (< or = 700 mg/L) and beta-cyclodextrin, which may own to their solubilization effects on BDE209. However, Tween 80 at a high concentration (900 mg/L) would restrain the fungal growth, thereby decrease the degradation of BDE209. Addition of Tween 80 and beta-cyclodextrin exhibited some negative effects on the degradation of BDE15, which may due to decreased concentration of free BDE15 in water solution resulted from inclusion function of Tween 80 micelles and beta-cyclodextrin cavity, although the apparent solubility of BDE15 was drastically increased by both of them.

  6. Process for producing dimethyl ether from synthesis gas

    DOEpatents

    Pierantozzi, R.

    1985-06-04

    This invention pertains to a Fischer Tropsch process for converting synthesis gas to an oxygenated hydrocarbon with particular emphasis on dimethyl ether. Synthesis gas comprising carbon monoxide and hydrogen are converted to dimethyl ether by carrying out the reaction in the presence of an alkali metal-manganese-iron carbonyl cluster incorporated onto a zirconia-alumina support.

  7. Process for producing dimethyl ether form synthesis gas

    DOEpatents

    Pierantozzi, Ronald

    1985-01-01

    This invention pertains to a Fischer Tropsch process for converting synthesis gas to an oxygenated hydrocarbon with particular emphasis on dimethyl ether. Synthesis gas comprising carbon monoxide and hydrogen are converted to dimethyl ether by carrying out the reaction in the presence of an alkali metal-manganese-iron carbonyl cluster incorporated onto a zirconia-alumina support.

  8. IRIS Toxicological Review of Decabromodiphenyl Ether (Final Report)

    EPA Science Inventory

    EPA announced the release of the final report, Toxicological Review of Decabromodiphenyl Ether: in support of the Integrated Risk Information System (IRIS). The updated Summary for Decabromodiphenyl Ether and accompanying toxicological review have been added to the IRIS Da...

  9. IRIS Toxicological Review of Decabromodiphenyl Ether (Final Report)

    EPA Science Inventory

    EPA is announcing the release of the final report, Toxicological Review of Decabromodiphenyl Ether: in support of the Integrated Risk Information System (IRIS). The updated Summary for Decabromodiphenyl Ether and accompanying Quickview have also been added to the IRIS Data...

  10. 48. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    48. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, 5TH LEVEL, LOOKING NORTH AT ETHER AND ALCOHOL CONDENSERS AT TOP OF TOWER. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  11. 46. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    46. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, CONTROL PANEL LEVEL (2ND DECK) OF ETHER AND ALCOHOL STILL BUILDING, LOOKING NORTH, SHOWING TWO ALCOHOL DISTILLATION TOWERS BEHIND 'MIXED SOLVENT UNIT' CONTROL PANEL. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  12. 47. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    47. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, 4TH LEVEL, LOOKING NORTH AT TOPS OF ALCOHOL AND ETHER DISTILLATION TOWERS. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  13. The Ether Wind and the Global Positioning System.

    ERIC Educational Resources Information Center

    Muller, Rainer

    2000-01-01

    Explains how students can perform a refutation of the ether theory using information from the Global Positioning System (GPS). Discusses the functioning of the GPS, qualitatively describes how position determination would be affected by an ether wind, and illustrates the pertinent ideas with a simple quantitative model. (WRM)

  14. 40 CFR 721.3550 - Dipropylene glycol dimethyl ether.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... SUBSTANCES CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.3550 Dipropylene glycol dimethyl ether. (a) Chemical substances and significant new uses subject to reporting. (1) The chemical substance identified as dipropylene glycol dimethyl ether (PMN...

  15. The Ether Wind and the Global Positioning System.

    ERIC Educational Resources Information Center

    Muller, Rainer

    2000-01-01

    Explains how students can perform a refutation of the ether theory using information from the Global Positioning System (GPS). Discusses the functioning of the GPS, qualitatively describes how position determination would be affected by an ether wind, and illustrates the pertinent ideas with a simple quantitative model. (WRM)

  16. IRIS Toxicological Review of Decabromodiphenyl Ether (Final Report)

    EPA Science Inventory

    EPA announced the release of the final report, Toxicological Review of Decabromodiphenyl Ether: in support of the Integrated Risk Information System (IRIS). The updated Summary for Decabromodiphenyl Ether and accompanying toxicological review have been added to the IRIS Da...

  17. [Cyclic Cushing's Syndrome - rare or rarely recognized].

    PubMed

    Kiałka, Marta; Doroszewska, Katarzyna; Mrozińska, Sandra; Milewicz, Tomasz; Stochmal, Ewa

    2015-01-01

    Cyclic Cushing's syndrome is a type of Cushing's disease which is characterized by alternating periods of increasing and decreasing levels of cortisol in the blood. The diagnostic criteria for cyclic Cushing's syndrome are at least three periods of hypercortisolism alternating with at least two episodes of normal levels of serum cortisol concentration. The epidemiology, signs, symptoms, pathogenesis and treatment of cyclic Cushing's syndrome have been discussed.

  18. Cyclic Imide Dioxime: Formation and Hydrolytic Stability

    SciTech Connect

    Kang, S.O.; Vukovic, Sinisa; Custelcean, Radu; Hay, Benjamin

    2012-01-01

    Poly(acrylamidoximes) play an important role in the uranium extraction from seawater. The present work reports solution studies of simple analogs to address the formation and stability of two binding sites present in these polymers, open-chain amidoximes and cyclic imide dioximes, including: 1) conditions that maximize the formation of the cyclic form, 2) existence of a base-induced conversion from open-chain to cyclic form, and 3) degradation under acid and base conditions.

  19. A study of interstellar aldehydes and enols as tracers of a cosmic ray-driven nonequilibrium synthesis of complex organic molecules

    PubMed Central

    Abplanalp, Matthew J.; Gozem, Samer; Krylov, Anna I.; Shingledecker, Christopher N.; Herbst, Eric; Kaiser, Ralf I.

    2016-01-01

    Complex organic molecules such as sugars and amides are ubiquitous in star- and planet-forming regions, but their formation mechanisms have remained largely elusive until now. Here we show in a combined experimental, computational, and astrochemical modeling study that interstellar aldehydes and enols like acetaldehyde (CH3CHO) and vinyl alcohol (C2H3OH) act as key tracers of a cosmic-ray-driven nonequilibrium chemistry leading to complex organics even deep within low-temperature interstellar ices at 10 K. Our findings challenge conventional wisdom and define a hitherto poorly characterized reaction class forming complex organic molecules inside interstellar ices before their sublimation in star-forming regions such as SgrB2(N). These processes are of vital importance in initiating a chain of chemical reactions leading eventually to the molecular precursors of biorelevant molecules as planets form in their interstellar nurseries. PMID:27382172

  20. Practical asymmetric synthesis of a potent PDE4 inhibitor via stereoselective enolate alkylation of a chiral aryl-heteroaryl secondary tosylate.

    PubMed

    O'Shea, Paul D; Chen, Cheng-yi; Chen, Weirong; Dagneau, Philippe; Frey, Lisa F; Grabowski, Edward J J; Marcantonio, Karen M; Reamer, Robert A; Tan, Lushi; Tillyer, Richard D; Roy, Amélie; Wang, Xin; Zhao, Dalian

    2005-04-15

    A practical, chromatography-free catalytic asymmetric synthesis of a potent and selective PDE4 inhibitor (L-869,298, 1) is described. Catalytic asymmetric hydrogenation of thiazole ketone 5a afforded the corresponding alcohol 3b in excellent enantioselectivity (up to 99.4% ee). Activation of alcohol 3b via formation of the corresponding p-toluenesulfonate followed by an unprecedented displacement with the lithium enolate of ethyl 3-pyridylacetate N-oxide 4a generated the required chiral trisubstituted methane. The displacement reaction proceeded with inversion of configuration and without loss of optical purity. Conversion of esters 2b to 1 was accomplished via a one-pot deprotection, saponification, and decarboxylation sequence in excellent overall yield.

  1. Synthesis and characterization of two new hydroxamic acids derivatives and their metal complexes. An investigation on the keto/enol, E/Z and hydroxamate/hydroximate forms

    NASA Astrophysics Data System (ADS)

    Adiguzel, Ekrem; Yilmaz, Fatih; Emirik, Mustafa; Ozil, Musa

    2017-01-01

    2-phenylbenzimidazole-N-acetohydroxamic acid (HL1), 2-phenylbenzimidazole-N-butanohydroxamic acid (HL2) and Ni(II), Cu(II), Zn(II) and Cd(II) metal complexes have been synthesized and characterized by elemental analyses, 1H NMR, 13C NMR, FT-IR spectrometry, LC-MS (ESI+) and thermal analyses. The results of NMR spectra and theoretical calculations showed that the hydroxamic acids were in the keto-E and keto-Z conformations. The elemental analysis and thermal analysis indicated that M:L ratio of the complexes are 1:1 and the spectral analysis confirmed that hydroxamate groups are keto form in the Ni(II) and Zn(II) complexes of 2-phenylbenzimidazole-N-butanohydroxamic acid and enol form in the other complexes.

  2. Determination of thermodynamic parameters of tautomerization in gas phase by mass spectrometry and DFT calculations: Keto-enol versus nitrile-ketenimine equilibria.

    PubMed

    Giussi, Juan M; Gastaca, Belen; Albesa, Alberto; Cortizo, M Susana; Allegretti, Patricia E

    2011-02-01

    The study of tautomerics equilibria is really important because the reactivity of each compound with tautomeric capacity can be determined from the proportion of each tautomer. In the present work the tautomeric equilibria in some γ,δ-unsaturated β-hydroxynitriles and γ,δ-unsaturated β-ketonitriles were studied. The first family of compounds presents two possible theoretical tautomers, nitrile and ketenimine, while the second one presents four possible theoretical tautomers, keto-nitrile, enol (E and Z)-nitrile and keto-ketenimine. The equilibrium in gas phase was studied by gas chromatography-mass spectrometry (GC-MS). Tautomerization enthalpies were calculated by this methodology, and results were compared with those obtained by density functional theory (DFT) calculations, observing a good agreement between them. Nitrile tautomers were favored within the first family of compounds, while keto-nitrile tautomers were favored in the second family. Copyright © 2010 Elsevier B.V. All rights reserved.

  3. Double-Mutated 5-Enol Pyruvylshikimate-3-phosphate Synthase Protein Expressed in MZHG0JG Corn (Zea mays L.) Has No Impact on Toxicological Safety and Nutritional Composition.

    PubMed

    Matthews, Bethany A; Launis, Karen L; Bauman, Patricia A; Juba, Nicole C

    2017-09-27

    MZHG0JG corn will offer growers the flexibility to alternate between herbicides with two different modes of action in their weed-management programs, helping to mitigate and manage the evolution of herbicide resistance in weed populations. The proteins conferring herbicide tolerence in MZHG0JG corn, double-mutated 5-enol pyruvylshikimate-3-phosphate synthase protein (mEPSPS) and phosphinothricin acetyltransferase (PAT), as well as the MZHG0JG corn event, have been assessed by regulatory authorities globally and have been determined to be safe for humans, animals, and the environment. In addition to the safety data available for these proteins, further studies were conducted on MZHG0JG corn to assess levels of mEPSPS as compared to previously registered genetically modified (GM) corn. The results support the conclusion of no impact on toxicological safety or nutritional composition.

  4. A ratiometric fluorescent pH probe based on keto-enol tautomerization for imaging of living cells in extreme acidity.

    PubMed

    Tong, Zong-Xuan; Liu, Wei; Huang, Hui; Chen, Hong-Zong; Liu, Xian-Jun; Kuang, Yong-Qing; Jiang, Jian-Hui

    2017-09-18

    6-(Diethylamino)-2,3-dihydro-1H-xanthene-4-carbaldehyde (DDXC), a reported synthetic intermediate for near-infrared fluorescent dyes, was developed into a fluorescent pH probe for extreme acidity. The unique sensing mechanism of DDXC for pH is based on the reversible protonation of the carbonyl oxygen followed by keto-enol tautomerization. The probe displays a linear ratiometric fluorescence response (I512/I580) to H(+) over the extremely acidic range of pH 2.0-4.0 with a pKa of 3.11, and features high fluorescence quantum yield (Φ = 0.60) and excellent selectivity. More importantly, the probe can be applied to ratiometric fluorescence imaging of pH changes in living cells, making it a potential molecular tool for pH-related cell biology study.

  5. Subtle trade-off existing between (anti)aromaticity, push-pull interaction, keto-enol tautomerism, and steric hindrance when defining the electronic properties of conjugated structures.

    PubMed

    Kleinpeter, Erich; Bölke, Ute; Koch, Andreas

    2010-07-22

    The spatial magnetic properties (through space NMR shieldings, TSNMRS) of conjugated structures (benzenoid/quinonoid keto/enol tautomers, 1,3-dihydroxyaryl-2-aldehydes, Don-pi-Acc chromophores with trade-off existing push-pull vs aromatic behavior) have been calculated by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept, and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values, thus obtained, can be successfully employed to quantify and visualize (anti)aromaticity and to identify readily hereby zwitterionic structures due to push-pull behavior of the compounds studied. In addition, the push-pull behavior was quantified by the quotient (pi*/pi) approach of the central partial C=C double bond.

  6. Ether in the developing world: rethinking an abandoned agent.

    PubMed

    Chang, Connie Y; Goldstein, Elisabeth; Agarwal, Nitin; Swan, Kenneth G

    2015-10-16

    The first true demonstration of ether as an inhalation anesthetic was on October 16, 1846 by William T.G. Morton, a Boston dentist. Ether has been replaced completely by newer inhalation agents and open drop delivery systems have been exchanged for complicated vaporizers and monitoring systems. Anesthesia in the developing world, however, where lack of financial stability has halted the development of the field, still closely resembles primitive anesthetics. In areas where resources are scarce, patients are often not given supplemental intraoperative analgesia. While halothane provides little analgesia, ether provides excellent intra-operative pain control that can extend for several hours into the postoperative period. An important barrier to the widespread use of ether is availability. With decreasing demand, production of the inexpensive inhalation agent has fallen. Ether is inexpensive to manufacture, and encouraging increased production at a local level would help developing nations to cut costs and become more self-sufficient.

  7. Synthesis of (+/-)-clusianone: high-yielding bridgehead and diketone substitutions by regioselective lithiation of enol ether derivatives of bicyclo[3.3.1]nonane-2,4,9-triones.

    PubMed

    Rodeschini, Vincent; Ahmad, Nadia M; Simpkins, Nigel S

    2006-11-09

    [Structure: see text] A concise synthesis of the polyprenylated acylphloroglucinol natural product, clusianone, in racemic form, is described. An Effenburger cyclization generated a core bicyclo[3.3.1]nonane-trione structure, which was then elaborated by means of regioselective lithiation reactions.

  8. 2-Acetylcyclopentanone, an Enolate-Forming 1,3-Dicarbonyl Compound, Is Cytoprotective in Warm Ischemia-Reperfusion Injury of Rat Liver

    PubMed Central

    Kosharskyy, Boleslav; Vydyanathan, Amaresh; Zhang, Lihai; Shaparin, Naum; Geohagen, Brian C.; Bivin, William; Liu, Qiang; Gavin, Terrence

    2015-01-01

    We have previously shown that 2-acetylcyclopentanone (2-ACP), an enolate-forming 1,3-dicarbonyl compound, provides protection in cell culture and animal models of oxidative stress. The pathophysiology of ischemia-reperfusion injury (IRI) involves oxidative stress, and, therefore, we determined the ability of 2-ACP to prevent this injury in a rat liver model. IRI was induced by clamping the portal vasculature for 45 minutes (ischemia phase), followed by recirculation for 180 minutes (reperfusion phase). This sequence was associated with substantial derangement of plasma liver enzyme activities, histopathological indices, and markers of oxidative stress. The 2-ACP (0.80–2.40 mmol/kg), administered by intraperitoneal injection 10 minutes prior to reperfusion, provided dose-dependent cytoprotection, as indicated by normalization of the IRI-altered liver histologic and biochemical parameters. The 2-ACP (2.40 mmol/kg) was also hepatoprotective when injected before clamping the circulation (ischemia phase). In contrast, an equimolar dose of N-acetylcysteine (2.40 mmol/kg) was not hepatoprotective when administered prior to reperfusion. Our studies to date suggest that during reperfusion the enolate nucleophile of 2-ACP limits the consequences of mitochondrial-based oxidative stress through scavenging unsaturated aldehyde electrophiles (e.g., acrolein) and chelation of metal ions that catalyze the free radical-generating Fenton reaction. The ability of 2-ACP to reduce IRI when injected prior to ischemia most likely reflects the short duration of this experimental phase (45 minutes) and favorable pharmacokinetics that maintain effective 2-ACP liver concentrations during subsequent reperfusion. These results provide evidence that 2-ACP or an analog might be useful in treating IRI and other conditions that have oxidative stress as a common molecular etiology. PMID:25659651

  9. Synthesis and characterization of poly(silyl ether)s and modified poly(siloxane)s

    NASA Astrophysics Data System (ADS)

    Mabry, Joseph Mark

    Activated dihydridocarbonyltris(triphenylphosphine)ruthenium ( Ru) catalyzes the dehydrogenative silylation condensation copolymerization of ortho-quinones with alpha,o-dihydrido-oligodimethylsiloxanes to give high molecular weight copoly(arylene-1,2-dioxy/oligodimethylsiloxanylene)s in good chemical yield. The hydrosilylation polymerization of aliphatic o-dimethylsilyloxy ketones is also catalyzed by activated Ru to yield unsymmetrical poly(silyl ether)s. Likewise, Ru catalyzes the copolymerization of alpha,o-diketones with alpha,o-dihydrido-oligodimethylsiloxanes to yield symmetrical poly(silyl ether)s. A mechanism of the copolymerizations is proposed, in which beta-hydride elimination is favored over reductive elimination in the reaction of the ortho-quinones. Chiral centers affect the NMR spectra of the poly(silyl ether)s produced by hydrosilylation. The photoluminescence properties of the polymers were studied along with those of model compounds. The decrease in Tgs with increase in siloxane chain length as well as fluorescence spectra is discussed. RuH2(CO)(PPh3)3 (Ru), activated with a stoichiometric amount of styrene, catalyzes the anti-Markovnikov addition of an ortho C-H bond of benzophenone across the C-C double bonds of alpha,o-bis(trimethylsilyloxy)copoly(dimethylsiloxane/vinylmethylsiloxane), alpha,o-bis(vinyldimethsilyloxy)poly(dimethylsiloxane)s, and 1,3-divinyltetramethyldisiloxane to yield alpha,o-bis(trimethylsilyloxy)copoly[dimethylsiloxane/2-(2 '-benzophenonyl)ethylmethylsiloxane]s, alpha,o-bis[2-(2 '-benzophenonyl)ethyldimethylsilyloxy]poly(dimethylsiloxane)s, and 1,3-bis[2-(2'-benzophenonyl)ethyl]tetramethyldisiloxane, respectively. While the Mw/Mn and Tgs of the modified polysiloxanes are similar to those of the precursor polymers, an increase in molecular weight is observed upon heating. 1,3-bis[2-(2 '-Benzophenonyl)ethyl]tetramethyldisiloxane, a model compound, was utilized to test a mechanism for the increase in molecular weight. A

  10. Synthesis of chiral cyclic amines via Ir-catalyzed enantioselective hydrogenation of cyclic imines.

    PubMed

    Zhang, Ying; Kong, Duanyang; Wang, Rui; Hou, Guohua

    2017-04-05

    A highly enantioselective hydrogenation of cyclic imines for synthesis of chiral cyclic amines has been realized. With the complex of iridium and (R,R)-f-spiroPhos as the catalyst, a range of cyclic 2-aryl imines were smoothly hydrogenated under mild conditions without any additive to provide the corresponding chiral cyclic amines with excellent enantioselectivities of up to 98% ee. Moreover, this method could be successfully applied to the synthesis of (+)-(6S,10bR)-McN-4612-Z.

  11. Low temperature (550-700 K) oxidation pathways of cyclic ketones: Dominance of HO2-elimination channels yielding conjugated cyclic coproducts

    DOE PAGES

    Scheer, Adam M.; Welz, Oliver; Vasu, Subith S.; ...

    2015-04-13

    The low-temperature oxidation of three cyclic ketones, cyclopentanone (CPO; C5H8O), cyclohexanone (CHO; C6H10 O), and 2-methyl-cyclopentanone (2-Me-CPO; CH3–C5H7 O), is studied between 550 and 700 K and at 4 or 8 Torr total pressure. Initial fuel radicals R are formedvia fast H-abstraction from the ketones by laser-photolytically generated chlorine atoms. Intermediates and products from the subsequent reactions of these radicals in the presence of excess O2 are probed with time and isomeric resolution using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. For CPO and CHO the dominant product channel in the R + O2 reactions is chain-terminating HO2-eliminationmore » yielding the conjugated cyclic coproducts 2-cyclopentenone and 2-cyclohexenone, respectively. Results on oxidation of 2-Me-CPO also show a dominant contribution from HO2-elimination. Moreover, the photoionization spectrum of the co-product suggests formation of 2-methyl-2-cyclopentenone and/or 2-cyclohexenone, resulting from a rapid Dowd–Beckwith rearrangement, preceding addition to O2, of the initial (2-oxocyclopentyl)methyl radical to 3-oxocyclohexyl. Cyclic ethers, markers for hydroperoxyalkyl radicals (QOOH), key intermediates in chain-propagating and chain-branching low-temperature combustion pathways, are only minor products. The interpretation of the experimental results is supported by stationary point calculations on the potential energy surfaces of the associated R + O2 reactions at the CBS-QB3 level. Furthermore, the calculations indicate that HO2-elimination channels are energetically favored and product formation via QOOH is disfavored. Lastly, the prominence of chain-terminating pathways linked with HO2 formation in low-temperature oxidation of cyclic ketones suggests little low-temperature reactivity of these species as fuels in internal combustion engines.« less

  12. Low temperature (550-700 K) oxidation pathways of cyclic ketones: dominance of HO2-elimination channels yielding conjugated cyclic coproducts.

    PubMed

    Scheer, Adam M; Welz, Oliver; Vasu, Subith S; Osborn, David L; Taatjes, Craig A

    2015-05-14

    The low-temperature oxidation of three cyclic ketones, cyclopentanone (CPO; C5H8=O), cyclohexanone (CHO; C6H10=O), and 2-methyl-cyclopentanone (2-Me-CPO; CH3-C5H7=O), is studied between 550 and 700 K and at 4 or 8 Torr total pressure. Initial fuel radicals R are formed via fast H-abstraction from the ketones by laser-photolytically generated chlorine atoms. Intermediates and products from the subsequent reactions of these radicals in the presence of excess O2 are probed with time and isomeric resolution using multiplexed photoionization mass spectrometry with tunable synchrotron ionizing radiation. For CPO and CHO the dominant product channel in the R + O2 reactions is chain-terminating HO2-elimination yielding the conjugated cyclic coproducts 2-cyclopentenone and 2-cyclohexenone, respectively. Results on oxidation of 2-Me-CPO also show a dominant contribution from HO2-elimination. The photoionization spectrum of the co-product suggests formation of 2-methyl-2-cyclopentenone and/or 2-cyclohexenone, resulting from a rapid Dowd-Beckwith rearrangement, preceding addition to O2, of the initial (2-oxocyclopentyl)methyl radical to 3-oxocyclohexyl. Cyclic ethers, markers for hydroperoxyalkyl radicals (QOOH), key intermediates in chain-propagating and chain-branching low-temperature combustion pathways, are only minor products. The interpretation of the experimental results is supported by stationary point calculations on the potential energy surfaces of the associated R + O2 reactions at the CBS-QB3 level. The calculations indicate that HO2-elimination channels are energetically favored and product formation via QOOH is disfavored. The prominence of chain-terminating pathways linked with HO2 formation in low-temperature oxidation of cyclic ketones suggests little low-temperature reactivity of these species as fuels in internal combustion engines.

  13. Investigating cyclic nucleotide and cyclic dinucleotide binding to HCN channels by surface plasmon resonance.

    PubMed

    Hayoz, Sebastien; Tiwari, Purushottam B; Piszczek, Grzegorz; Üren, Aykut; Brelidze, Tinatin I

    2017-01-01

    Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels control cardiac and neuronal rhythmicity. HCN channels contain cyclic nucleotide-binding domain (CNBD) in their C-terminal region linked to the pore-forming transmembrane segment with a C-linker. The C-linker couples the conformational changes caused by the direct binding of cyclic nucleotides to the HCN pore opening. Recently, cyclic dinucleotides were shown to antagonize the effect of cyclic nucleotides in HCN4 but not in HCN2 channels. Based on the structural analysis and mutational studies it has been proposed that cyclic dinucleotides affect HCN4 channels by binding to the C-linker pocket (CLP). Here, we first show that surface plasmon resonance (SPR) can be used to accurately measure cyclic nucleotide binding affinity to the C-linker/CNBD of HCN2 and HCN4 channels. We then used SPR to investigate cyclic dinucleotide binding in HCN channels. To our surprise, we detected no binding of cyclic dinucleotides to the isolated monomeric C-linker/CNBDs of HCN4 channels with SPR. The binding of cyclic dinucleotides was further examined with isothermal calorimetry (ITC), which indicated no binding of cyclic dinucleotides to both monomeric and tetrameric C-linker/CNBDs of HCN4 channels. Taken together, our results suggest that interaction of the C-linker/CNBD with other parts of the channel is necessary for cyclic-dinucleotide binding in HCN4 channels.

  14. Sulfonated poly(tetramethydiphenyl ether ether ketone) membranes for vanadium redox flow battery application

    NASA Astrophysics Data System (ADS)

    Mai, Zhensheng; Zhang, Huamin; Li, Xianfeng; Bi, Cheng; Dai, Hua

    Sulfonated poly(tetramethydiphenyl ether ether ketone) (SPEEK) with various degree of sulfonation is prepared and first used as ion exchange membrane for vanadium redox flow battery (VRB) application. The vanadium ion permeability of SPEEK40 membrane is one order of magnitude lower than that of Nafion 115 membrane. The low cost SPEEK membranes exhibit a better performance than Nafion at the same operating condition. VRB single cells with SPEEK membranes show very high energy efficiency (>84%), comparable to that of the Nafion, but at much higher columbic efficiency (>97%). In the self-discharge test, the duration of the cell with the SPEEK membrane is two times longer than that with Nafion 115. The membrane keeps a stable performance after 80-cycles charge-discharge test.

  15. Wear of ceramic-on-carbon fiber-reinforced poly-ether ether ketone hip replacements.

    PubMed

    Brockett, Claire L; John, Gemma; Williams, Sophie; Jin, Zhongmin; Isaac, Graham H; Fisher, John

    2012-08-01

    Total hip replacement has been a successful surgical intervention for over 50 years, with the majority of bearings using a polyethylene cup. Long-term failure due to osteolysis and loosening has been widely documented and alternative bearings have been sought. A novel carbon fiber-reinforced poly-ether ether ketone (CFR-PEEK) cup was investigated through experimental friction and wear studies. Friction studies demonstrated the bearings operated in a boundary lubrication condition, with friction factors higher than those for other hip replacement bearings. The wear study was conducted with 36 mm diameter bearings tested against Biolox Delta heads for a period of 10 million cycles. The mean volumetric wear rate was 0.3 mm(3)/Mc, indicating the ceramic-on-CFR-PEEK bearing to be a very low wearing option for total hip replacement.

  16. A sulfonated poly (aryl ether ether ketone ketone) isomer: synthesis and DMFC performance

    SciTech Connect

    Kim, Yu Seung; Liu, Baijun; Hu, Wei; Jiang, Zhenhua; Robertson, Gilles; Guiver, Michael

    2009-01-01

    A sulfonated poly(aryl ether ether ketone ketone) (PEEKK) having a well-defined rigid homopolymer-like chemical structure was synthesized from a readily-prepared PEEKK post-sulfonation with concentrated sulfuric acid at room temperature within several hours. The polymer electrolyte membrane (PEM) cast from the resulting polymer exhibited an excellent combination of thermal resistance, oxidative and dimensional stability, low methanol fuel permeability and high proton conductivity. Furthermore, membrane electrode assemblies (MEAs) were successfully fabricated and good direct methanol fuel cell (DMFC) performance was observed. At 2 M MeOH feed, the current density at 0.5 V reached 165 mA/cm, which outperformed our reported analogues and eveluated Nafion membranes.

  17. Enhanced osteogenic activity of poly ether ether ketone using calcium plasma immersion ion implantation.

    PubMed

    Lu, Tao; Qian, Shi; Meng, Fanhao; Ning, Congqin; Liu, Xuanyong

    2016-06-01

    As a promising implantable material, poly ether ether ketone (PEEK) possesses similar elastic modulus to that of cortical bones yet suffers from bio-inertness and poor osteogenic properties, which limits its application as orthopedic implants. In this work, calcium is introduced onto PEEK surface using calcium plasma immersion ion implantation (Ca-PIII). The results obtained from scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) confirm the modified layer with varying contents of calcium are formed on PEEK surfaces. Water contact angle measurements reveal the increasing hydrophobicity of both Ca-PIII treated surfaces. In vitro cell adhesion, viability assay, alkaline phosphatase activity and collagen secretion analyses disclose improved the adhesion, proliferation, and osteo-differentiation of rat bone mesenchymal stem cells (bMSCs) on Ca-PIII treated surfaces. The obtained results indicate that PEEK surface with enhanced osteogenic activity can be produced by calcium incorporation. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Origin of mechanical modifications in poly (ether ether ketone)/carbon nanotube composite

    SciTech Connect

    Pavlenko, Ekaterina; Puech, Pascal; Bacsa, Wolfgang; Boyer, François; Olivier, Philippe; Sapelkin, Andrei; King, Stephen; Heenan, Richard; Pons, François; Gauthier, Bénédicte; Cadaux, Pierre-Henri

    2014-06-21

    Variations in the hardness of a poly (ether ether ketone) beam electrically modified with multi-walled carbon nanotubes (MWCNT, 0.5%-3%) are investigated. It is shown that both rupture and hardness variations correlate with the changes in carbon nanotube concentration when using micro indentation and extended Raman imaging. Statistical analysis of the relative spectral intensities in the Raman image is used to estimate local tube concentration and polymer crystallinity. We show that the histogram of the Raman D band across the image provides information about the amount of MWCNTs and the dispersion of MWCNTs in the composite. We speculate that we have observed a local modification of the ordering between pure and modified polymer. This is partially supported by small angle neutron scattering measurements, which indicate that the agglomeration state of the MWCNTs is the same at the concentrations studied.

  19. [Recent development of research on the biotribology of carbon fiber reinforced poly ether ether ketone composites].

    PubMed

    Chen, Yan; Pan, Yusong

    2014-12-01

    Carbon fiber reinforced poly ether ether ketone (CF/PEEK) composite possesses excellent biocompatible, biomechanical and bioribological properties. It is one of the most promising implant materials for artificial joint. Many factors influence the bioribological properties of CF/PEEK composites. In this paper, the authors reviewed on the biotribology research progress of CF/PEEK composites. The influences of various factors such as lubricant, reinforcement surface modification, functional particles, friction counterpart and friction motion modes on the bio-tribological properties of CF/PEEK composites are discussed. Based on the recent research, the authors suggest that the further research should be focused on the synergistic effect of multiple factors on the wear and lubrication mechanism of CF/PEEK.

  20. Ethylene glycol monomethyl ether and propylene glycol monomethyl ether: metabolism, disposition, and subchronic inhalation toxicity studies

    SciTech Connect

    Miller, R.R.; Hermann, E.A.; Young, J.T.; Landry, T.D.; Calhoun, L.L.

    1984-08-01

    Short-term and subchronic vapor inhalation studies have shown that there are pronounced differences in the toxicological properties of ethylene glycol monomethyl ether (EGME) and propylene glycol monomethyl ether (PGME). Overexposure to EGME has resulted in adverse effects on testes, bone marrow and lymphoid tissues in laboratory animals. PGME does not affect these tissues, and instead, overexposure to PGME has been associated with increases in liver weight and central nervous system depression. EGME is primarily oxidized to methoxyacetic acid in male rats, while PGME apparently undergoes O-demethylation to form propylene glycol. Since methoxyacetic acid has been shown to have the same spectrum of toxicity as EGME in male rats, the observed differences in the toxicological properties of EGME and PGME are thought to be due to the fact that the two materials are biotransformed via different routes to different types of metabolites. 6 references, 3 figures, 12 tables.

  1. Nonlinear, nonbinary cyclic group codes

    NASA Technical Reports Server (NTRS)

    Solomon, G.

    1992-01-01

    New cyclic group codes of length 2(exp m) - 1 over (m - j)-bit symbols are introduced. These codes can be systematically encoded and decoded algebraically. The code rates are very close to Reed-Solomon (RS) codes and are much better than Bose-Chaudhuri-Hocquenghem (BCH) codes (a former alternative). The binary (m - j)-tuples are identified with a subgroup of the binary m-tuples which represents the field GF(2 exp m). Encoding is systematic and involves a two-stage procedure consisting of the usual linear feedback register (using the division or check polynomial) and a small table lookup. For low rates, a second shift-register encoding operation may be invoked. Decoding uses the RS error-correcting procedures for the m-tuple codes for m = 4, 5, and 6.

  2. Cell reorientation under cyclic stretching

    PubMed Central

    Livne, Ariel; Bouchbinder, Eran; Geiger, Benjamin

    2014-01-01

    Mechanical cues from the extracellular microenvironment play a central role in regulating the structure, function and fate of living cells. Nevertheless, the precise nature of the mechanisms and processes underlying this crucial cellular mechanosensitivity remains a fundamental open problem. Here we provide a novel framework for addressing cellular sensitivity and response to external forces by experimentally and theoretically studying one of its most striking manifestations – cell reorientation to a uniform angle in response to cyclic stretching of the underlying substrate. We first show that existing approaches are incompatible with our extensive measurements of cell reorientation. We then propose a fundamentally new theory that shows that dissipative relaxation of the cell’s passively-stored, two-dimensional, elastic energy to its minimum actively drives the reorientation process. Our theory is in excellent quantitative agreement with the complete temporal reorientation dynamics of individual cells, measured over a wide range of experimental conditions, thus elucidating a basic aspect of mechanosensitivity. PMID:24875391

  3. Metal dihalide photodissociation cyclic laser

    SciTech Connect

    Celto, J.E.; Schimitschek, E.J.; Trias, J.A.

    1980-10-21

    A pulsed laser produces emitted laser energy by photodissociation of metal dihalide and cyclic recombination. A metal dihalide selected from sub-group ii-b of the periodic table of elements is contained within an elongated sealed enclosure. Ultraviolet photons supplied from another laser employed as an excitation pump causes dissociation of the metal dihalide for achieving the ultimate laser action. An inert buffer gas is included within the enclosure for aiding photon energy transfer uniformity and to provide vibrational relaxation of the lasing medium in its electronic states. Two reflective surfaces, one of which is only partially reflective, are aligned with the principal axis of the laser assembly for producing an optical resonator for the emitted laser energy.

  4. A Cyclic Universe Numerically Realized

    NASA Astrophysics Data System (ADS)

    Duhe, William; Biswas, Tirthbar

    2013-04-01

    A unique way of realizing inflation has been proposed recently in the context of cyclic cosmology where the universe grows by a constant factor in each cycle. This leads to an overall exponential growth over many cycles. In a given cycle such a growth is possible if, for instance, ``heavy particles'' can decay into radiation (photons) leading to an increase in entropy. However, to sustain this mechanism over successive cycles, it is crucial to reproduce the heavy particles back through quantum scattering processes and re-establish thermal equilibrium between all the species. We attempt to prove the viability of a ``multiple bang'' scenario to produce known cosmological data as well as use it to predict fluctuations in the upcoming higher resolution plank telescope data. This paradigm opens doors for new investigations into the principles surrounding the content and origin of the universe.

  5. Development of specialty chemicals from dimethyl ether

    SciTech Connect

    Tartamella, T.L.; Lee, S.

    1996-12-31

    Dimethyl ether (DME) may be efficiently produced from coal-bases syngas in a high pressure, mechanically agitated slurry reactor. DME synthesis occurs in the liquid phase using a dual catalyst. By operating in a dual catalyst mode, DME may be converted from in-situ produced methanol resulting in higher methyl productivities and syngas conversions over methanol conversion alone. The feasibility of utilizing DME as a building block for more valuable specialty chemicals has been examined. A wide variety of petrochemicals may be produced from DME including light olefins, gasoline range hydrocarbons, oxygenates, and glycol precursors. These chemicals represent an important part of petroleum industries inventory of fine chemicals. Carbonylation, hydrocarbonylation, and oxidative dimerization are but a few of the reactions in which DME may undergo conversion. DME provides an additional route for the production of industrially important petrochemicals.

  6. Acyclic archaebacterial ether lipids in swamp sediments

    NASA Astrophysics Data System (ADS)

    Pauly, George G.; Van Vleet, Edward S.

    1986-06-01

    Acyclic phytanyl diether glycerol and biphytanyl ether lipids have been quantified in two modern swamp sediment cores in concentrations ranging up to 360 μg/ml porewater. Methanogenic bacteria are the only known source organisms which can inhabit the swamp sediments. Variations in relative abundance between these lipids may reflect taxonomic changes in methanogen populations or the stage of growth. Maxima in methanogen lipid concentrations coincide with local maxima of 13C of organic matter, possibly the result of a pool effect on CO 2 or acetate. Methane production estimates calculated from lipid concentrations in swamp sediments range from 0.1 to 1.3 mmol cm -2 yr -1, values which are consistent with published methane fluxes.

  7. High temperature fuel cell membranes based on poly(arylene ether)s containing benzimidazole groups

    SciTech Connect

    Kim, Dae Sik; Kim, Yu Seung; Lee, Kwan - Soo; Boncella, James M; Kuiper, David; Guiver, Michael D

    2009-01-01

    Development of new high-performance polymer membranes that retain their proton conductivity under low humidity conditions is one of the most critical requirements to commercialize PEMFC systems. Current sulfonated proton exchange membranes acquire proton conductivity by water that solvates ion and carries proton. Consequently, a loss of water under low RH conditions immediately results in a loss of proton conductivity. One approach to maintain proton conductivity under low RH conditions is to replace water with a less volatile proton solvent. Kreuer has pointed out the possibility to develop fully polymeric proton-conducting membranes based on nitrogen-containing heterocycles such as imidazole, benzimidazole, and pyrazole. We have attempted to blend those less volatile proton solvent with sulfonated copolymers such as polystyrene sulfonic acid, Nafion, poly(arylene ether sulfone, BPSH-xx). [Ref. DOE review meeting 2007 and 2008] However, we observed that imidazole was slowly sublimated out as temperature and humidity increases which could cause poisoning of electro-catalyst, corrosion and losing conductivity. In this presentation, we report the synthesis of novel poly(arylene ether sulfone)s containing benzimidazole groups These benzimidazole containing polymer was blended with sulfonated poly(arylene ether sulfone). In the blend system, benzimidazole group attached to the polysulfone acts as a medium through the basic nitrogen for transfer of protons between the sulfonic acid groups. Proton conductivity of the blend membranes was investigated as a function of water content at 80 C and compared the performance with water based proton conduction system.

  8. Cationic Poly(benzyl ether)s as Self-Immolative Antimicrobial Polymers.

    PubMed

    Ergene, Cansu; Palermo, Edmund F

    2017-10-09

    Self-immolative polymers (SIMPs) are macromolecules that spontaneously undergo depolymerization into small molecules when triggered by specific external stimuli. We report here the first examples of antimicrobial SIMPs with potent, rapid, and broad-spectrum bactericidal activity. Their antibacterial and hemolytic activities were examined as a function of cationic functionality. Polymers bearing primary ammonium cationic groups showed more potent bactericidal activity against Escherichia coli, relative to tertiary and quaternary ammonium counterparts, whereas the quaternary ammonium polymers showed the lowest hemolytic toxicity. These antibacterial polycations undergo end-to-end depolymerization when triggered by an externally applied stimulus. Specifically, poly(benzyl ether)s end-capped with a silyl ether group and bearing pendant allyl side chains were converted to polycations by photoinitiated thiol-ene radical addition using cysteamine HCl. The intact polycations are stable in solution, but they spontaneously unzip into their component monomers upon exposure to fluoride ions, with excellent sensitivity and selectivity. Upon triggered depolymerization, the antibacterial potency was largely retained but the hemolytic toxicity was substantially reduced. Thus, we reveal the first example of a self-immolative antibacterial polymer platform that will enable antibacterial materials to spontaneously unzip into biologically active small molecules upon the introduction of a specifically designed stimulus.

  9. Cyclic metabolites: chemical and biological considerations.

    PubMed

    Erve, John C L

    2008-02-01

    Metabolism of xenobiotics can sometimes generate cyclic metabolites. Such metabolites are usually the result of intramolecular reactions occurring within a primary or secondary metabolite and this chemistry may lead to unexpected structures. Intramolecular chemistry is often driven by nucleophilic groups reacting with electrophilic atoms, often carbon, although radical processes also occur. Conjugation of xenobiotics or their metabolites with endogenous thiols, such as glutathione or cysteine, introduce a reactive amino group that can lead to the formation of cyclic structures. Less common than chemically driven cyclizations are enzymatically mediated ring-closures, although this may reflect our incomplete recognition of enzymatic involvement in this step of cyclic metabolite formation. While some cyclic metabolites are biologically inactive, others are biologically active. Thus, a cyclic metabolite may display desirable pharmacology, or, contribute to toxicology. When a cyclic metabolite is identified, it is important to consider the possibility that it is an artifact, i.e. metabonate, that was formed during processing of the sample, for example, through degradation or by chemical reactions with other components present in the matrix. From a medicinal chemistry perspective, a cyclic metabolite with a different chemical scaffold from the parent structure may lead to a new series of structurally novel, biologically active molecules with the same, or different, pharmacology from the parent. This review will cover a selection of cyclic metabolites from a mechanistic point of view, and when possible, discuss their biological relevance.

  10. Enantioselective Conjugate Allylation of Cyclic Enones

    PubMed Central

    Taber, Douglass F.; Gerstenhaber, David A.; Berry, James F.

    2011-01-01

    Enantioselective organocatalytic 1,2-allylation of a cyclic enone followed by anionic oxy-Cope rearrangement delivered the ketone as a mixture of diastereomers. This appears to be a general method for the net enantioselective conjugate allylation of cyclic enones. PMID:21830779

  11. Cyclic Linearization and Island Repair in Sluicing

    ERIC Educational Resources Information Center

    Qiu, Chunan

    2009-01-01

    Cyclic Linearization is adopted to account for the island repair of Sluicing in English. The extraction of wh-phrase out of certain islands undergoes non-successive-cyclic movement, which yields conflicting ordering statements. The derivation can be rescued by deleting all ordering statements in IP, including those conflicting ones. Two arguments…

  12. Cyclic homology for Hom-associative algebras

    NASA Astrophysics Data System (ADS)

    Hassanzadeh, Mohammad; Shapiro, Ilya; Sütlü, Serkan

    2015-12-01

    In the present paper we investigate the noncommutative geometry of a class of algebras, called the Hom-associative algebras, whose associativity is twisted by a homomorphism. We define the Hochschild, cyclic, and periodic cyclic homology and cohomology for this class of algebras generalizing these theories from the associative to the Hom-associative setting.

  13. Modular arithmetic weight and cyclic shifting.

    NASA Technical Reports Server (NTRS)

    Hartman, W. F.

    1972-01-01

    This note shows that the modular arithmetic weight of an integer is invariant to the cyclic shifts of its radix-2 form. This result leads to a reduced search for the minimum weight codeword in a cyclic AN-code as well as to a better understanding of previous work.

  14. Cyclic malyl anthocyanins in Dianthus caryophyllus.

    PubMed

    Nakayama, M; Koshioka, M; Yoshida, H; Kan, Y; Fukui, Y; Koike, A; Yamaguchi, M

    2000-12-01

    3,5-Di-O-(beta-glucopyranosyl) pelargonidin 6''-O-4,6'''-O-1-cyclic malate and a previously reported cyanidin equivalent, 3,5-di-O-(beta-glucopyranosyl) cyanidin 6''-O-4,6'''-O-1-cyclic malate were identified from petals of deep pink and red-purple flower cultivars of Dianthus caryophyllus, respectively.

  15. Formulating liquid ethers for microtubular SOFCs

    NASA Astrophysics Data System (ADS)

    Kendall, Kevin; Slinn, Matthew; Preece, John

    One of the key problems of applying solid oxide fuel cells (SOFCs) in transportation is that conventional fuels like kerosene and diesel do not operate directly in SOFCs without prereforming to hydrogen and carbon monoxide which can be handled by the nickel cermet anode. SOFCs can internally reform certain hydrocarbon molecules such as methanol and methane. However, other liquid fuels usable in petrol or diesel internal combustion engines (ICEs) have not easily been reformable directly on the anode. This paper describes a search for liquid fuels which can be mixed with petrol or diesel and also injected directly into an SOFC without destroying the nickel anode. When fuel molecules such as octane are injected onto the conventional nickel/yttria stabilised zirconia (Ni/YSZ) SOFC fuel electrode, the anode rapidly becomes blocked by carbon deposition and the cell power drops to near zero in minutes. This degeneration of the anode can be inhibited by injection of air or water into the anode or by some upstream reforming just before entry to the SOFC. Some smaller molecules such as methane, methanol and methanoic acid produce a slight tendency to carbon deposition but not sufficient to prevent long term operation. In this project we have investigated a large number of molecules and now found that some liquid ethers do not significantly damage the anode when directly injected. These molecules and formulations with other components have been evaluated in this study. The theory put forward in this paper is that carbon-carbon bonds in the fuel are the main reason for anode damage. By testing a number of fuels without such bonds, particularly liquid ethers such as methyl formate and dimethoxy methane, it has been shown that SOFCs can run without substantial carbon formation. The proposal is that conventional fuels can be doped with these molecules to allow hybrid operation of an ICE/SOFC device.

  16. A Chitosan Derivative Containing Both Carboxylic Acid and Quaternary Ammonium Moieties for the Synthesis of Cyclic Carbonates.

    PubMed

    Besse, Vincent; Illy, Nicolas; David, Ghislain; Caillol, Sylvain; Boutevin, Bernard

    2016-08-23

    Chitosan, a renewable feedstock, is modified and used as a catalytic support in the presence of potassium iodide. The system is highly efficient towards the incorporation of carbon dioxide (CO2 ) into epoxides. It demonstrates very good thermal stability and is recyclable more than five times without loss of activity. The optimal reaction conditions were determined using allylglycidyl ether as a model and extended to a wide range of other epoxides. Cyclic carbonates were obtained with very high yield in a few hours under mild conditions (2-7 bar≈0.2-0.7 MPa, 80 °C) and no solvent.

  17. Development of Stereocontrolled Palladium(II)-Catalyzed Domino Heck/Suzuki β,α-Diarylation Reactions with Chelating Vinyl Ethers and Arylboronic Acids.

    PubMed

    Trejos, Alejandro; Odell, Luke R; Larhed, Mats

    2012-02-01

    A stereoselective and 1,4-benzoquinone-mediated palladium(II)-catalyzed Heck/Suzuki domino reaction involving metal coordinating cyclic methylamino vinyl ethers and a number of electronically diverse arylboronic acids has been developed and studied. Diastereomeric ratios up to 39:1 and 78 % isolated yields were obtained. The stereoselectivity of the reaction was found to be highly dependent on the nature of the arylboronic acid and the amount of water present in the reaction mixture. Thus, a domino β,α-diarylation-reduction of chelating vinyl ethers can now be accomplished and stereochemically controlled, given that optimized conditions and an appropriate chiral auxiliary are used. To the best of our knowledge, this represents the first example of a stereoselective, oxidative Heck/Suzuki domino reaction in the literature.

  18. Prenyl Ethers: Novel Fungal Volatiles Formed by Penicillium digitatum.

    PubMed

    Amrein, Thomas M; Frey, Peter; Meier, Roberto; Baumann, Heidi; Tanner, Miriam; Gassenmeier, Klaus F

    2014-10-01

    Prenyl ethyl ether (PEE) was previously described as the cause for a solvent-like off-note in ground hazelnuts, but its origin remained unclear. Investigations were carried out by analytical groups of Coop and Givaudan over four years to elucidate this phenomenon. From mouldy citrus fruits a strain of Penicillium digitatum was isolated and found to form PEE. Formation on citrus and other fruits was prominent and contributed to the particular smell of decayed fruits. Several strains of P. digitatum formed PEE, while other fungal species did not. In contrast to citrus fruit, prenyl methyl ether (PME) was formed as dominant prenyl ether on hazelnuts while only small amounts of PEE were found. PME has not been previously described as volatile metabolite of fungi or as a food-taint. Spiking experiments with deuterated ethanol showed that the ethyl group is likely incorporated into PEE via the aldehyde form. On hazelnuts strongly decayed by P. digitatum yet another prenyl ether was tentatively identified: Prenyl isopropyl ether. Prenyl ethers present a novel group of volatile metabolites of P. digitatum. They are likely typical for this species and have not been described before. Prenyl ethers seem to play a significant role in the smell of food decayed by P. digitatum and should be considered in cases of off-notes and taints.

  19. Vapor intrusion risk of fuel ether oxygenates methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME) and ethyl tert-butyl ether (ETBE): A modeling study.

    PubMed

    Ma, Jie; Xiong, Desen; Li, Haiyan; Ding, Yi; Xia, Xiangcheng; Yang, Yongqi

    2017-06-15

    Vapor intrusion of synthetic fuel additives represents a critical yet still neglected problem at sites contaminated by petroleum fuel releases. This study used an advanced numerical model to investigate the vapor intrusion potential of fuel ether oxygenates methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME), and ethyl tert-butyl ether (ETBE). Simulated indoor air concentration of these compounds can exceed USEPA indoor air screening level for MTBE (110μg/m(3)). Our results also reveal that MTBE has much higher chance to cause vapor intrusion problems than TAME and ETBE. This study supports the statements made by USEPA in the Petroleum Vapor Intrusion (PVI) Guidance that the vertical screening criteria for petroleum hydrocarbons may not provide sufficient protectiveness for fuel additives, and ether oxygenates in particular. In addition to adverse impacts on human health, ether oxygenate vapor intrusion may also cause aesthetic problems (i.e., odour and flavour). Overall, this study points out that ether oxygenates can cause vapor intrusion problems. We recommend that USEPA consider including the field measurement data of synthetic fuel additives in the existing PVI database and possibly revising the PVI Guidance as necessary.

  20. Toward structure prediction of cyclic peptides.

    PubMed

    Yu, Hongtao; Lin, Yu-Shan

    2015-02-14

    Cyclic peptides are a promising class of molecules that can be used to target specific protein-protein interactions. A computational method to accurately predict their structures would substantially advance the development of cyclic peptides as modulators of protein-protein interactions. Here, we develop a computational method that integrates bias-exchange metadynamics simulations, a Boltzmann reweighting scheme, dihedral principal component analysis and a modified density peak-based cluster analysis to provide a converged structural description for cyclic peptides. Using this method, we evaluate the performance of a number of popular protein force fields on a model cyclic peptide. All the tested force fields seem to over-stabilize the α-helix and PPII/β regions in the Ramachandran plot, commonly populated by linear peptides and proteins. Our findings suggest that re-parameterization of a force field that well describes the full Ramachandran plot is necessary to accurately model cyclic peptides.

  1. Ribosomally encoded cyclic peptide toxins from mushrooms.

    PubMed

    Walton, Jonathan D; Luo, Hong; Hallen-Adams, Heather

    2012-01-01

    The cyclic peptide toxins of poisonous Amanita mushrooms are chemically unique among known natural products. Furthermore, they differ from other fungal cyclic peptides in being synthesized on ribosomes instead of by nonribosomal peptide synthetases. Because of their novel structures and biogenic origins, elucidation of the biosynthetic pathway of the Amanita cyclic peptides presents both challenges and opportunities. In particular, a full understanding of the pathway should lead to the ability to direct synthesis of a large number of novel cyclic peptides based on the Amanita toxin scaffold by genetic engineering of the encoding genes. Here, we highlight some of the principal methods for working with the Amanita cyclic peptides and the known steps in their biosynthesis.

  2. Characterization of Microsolvated Crown Ethers from Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Perez, Cristobal; Schnell, Melanie; Blanco, Susana; Lopez, Juan Carlos

    2016-06-01

    Since they were first synthetized, crown ethers have been extensively used in organometallic chemistry due to their unparalleled binding selectivity with alkali metal cations. From a structural point of view, crown ethers are heterocycles containing oxygen and/or other heteroatoms, although the most common ones are formed from ethylene oxide unit. Crown ethers are conventionally seen as being hydrophilic inside and hydrophobic outside when the structures found for the metal cation complexes are considered. However, crown ethers are extremely flexible and in isolation may present a variety of stable conformations so that their structure may be easily adapted in presence of a strong ligand as an alkali metal cation minimize the energy of the resulting complex. Water can be considered a soft ligand which interacts with crown ethers through moderate hydrogen bonds. It is thus interesting to investigate which conformers are selected by water to form complexes, the preferred interaction sites and the possible conformational changes due to the presence of one or more water molecules. Previous studies identified microsolvated crown ethers but in all cases with a chromophore group attached to the structure. Here we present a broadband rotational spectroscopy study of microsolvated crown ethers produced in a pulsed molecular jet expansion. Several 1:1 and 1:2 crown ether:water aggregates are presented for 12-crown-4, 15-crown-5 and 18-crown-6. Unambiguous identification of the structures has been achieved using isotopic substitution within the water unit. The subtle changes induced in the structures of the crown ether monomer upon complexation and the hydrogen-bonding network that hold them together will be also discussed. F. Gámez, B. Martínez-Haya, S. Blanco,J. C. López and J. L. Alonso, Phys. Chem. Chem. Phys. 2014, 14 12912-12918 V. A. Shubert, C.W. Müller and T. Zwier, J. Phys. Chem. A 2009, 113 8067-8079

  3. Synthesis and biological activity of gem-dichlorocyclopropyl ethers

    SciTech Connect

    Shostakovskii, S.M.; Mochalov, V.N.; Larionov, G.M.

    1986-09-01

    In order to examine the antimicrobial activity of oxygenated cyclopropanes, the authors have synthesized the bis-gem-dichlorocyclopropyl ether of ethylene glycol, the meso- and dl- forms of bis-gem-dichlorocyclopropyl ether, and the gem-dichlorocyclopropyl alkyl ethers. The physiocochemical properties of compounds obtained are presented. The authors conclude that in the case of gem-dichlorocyclopropane compounds, decontamination of microorganisms occurs at the pre-metabolic stage, and results in the denaturation of the protein components of the cell wall and external membranes and of the specific peptides of the peptide-glycan layer.

  4. Synthesis of a novel ether-bridged GM3-lactone analogue as a target for an antibody-based cancer therapy.

    PubMed

    Tietze, L F; Keim, H; Janssen, C O; Tappertzhofen, C; Olschimke, J

    2000-08-04

    We describe herein the synthesis of a new analogue of the GM3-lactone containing a cyclic ether moiety. The ether moiety was chosen as a replacement for the regular lactone group since it shows high resemblance with the lactone and is completely stable under biological conditions. The cyclic ether moiety was formed by reduction of the corresponding lactone to give the lactol followed by formation of the S,O-hemiacetal and hydrogenation. In addition, we have prepared haptens with a hexanoic acid moiety, which can be used for the preparation of poly- and monoclonal antibodies after binding to BSA or KLH. This is the first example of an analogue of the GM3-lactone which is stable under hydrolytic conditions in vitro and probably also in vivo. Reaction of lactone 18 with a Red/Al derivative led to the lactol 19 which was transformed into the S,O-hemiacetal 20 using 2,2'-bis(pyridinium) disulfide in quantitative yield. Hydrogenation with Raney Nickel gave 21 from which after removal of the protecting group at C-1a the trichloroacetimidate 25 was prepared. Reaction with azidosphingosine to give 26 followed by reduction of the azido group with NHEt3+[(PhS)3Sn], acylation with stearic acid using EDC and removal of the protecting groups led to the desired ether analogue of GM3 lactone 4. In addition the trichloroacetimidate 25 was glycosidated with 6-hydroxyhexanoic acid methyl ester, which was deprotected to give 29. The compound will be used for the preparation of poly- and monoclonal antibodies after coupling with BSA and KLH.

  5. 40 CFR 63.62 - Redefinition of glycol ethers listed as hazardous air pollutants.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... in 42 U.S.C. 7412(b)(1), footnote 2: Glycol ethers include mono- and di-ethers of ethylene glycol... 40 Protection of Environment 9 2010-07-01 2010-07-01 false Redefinition of glycol ethers listed as... List § 63.62 Redefinition of glycol ethers listed as hazardous air pollutants. The following definition...

  6. Selective sorption of alkali-metal cations by carboxylic acid resins containing acyclic or cyclic polyether units

    SciTech Connect

    Hayashita, Takashi; Goo, Mija; Lee, Jong Chan; Kim, Jong Seung; Krzykawski, J.; Bartsch, R.A. )

    1990-11-01

    Novel ion-exchange resins have been prepared by condensation polymerization with formaldehyde in formic acid of three polyether carboxylic acids which possess two benzo group substituents. The selectivities and efficiencies of competitive alkali-metal cation sorption from aqueous solutions by these polyether carboxylic acid resins are strongly influenced by (1) the pH of the aqueous solution, (2) the acyclic or cyclic nature of the polyether unit, and (3) the conformational positioning of the carboxylic acid group in the resins derived from cyclic polyether (crown ether) compounds. Good sorption selectivity for Na{sup +} was observed for dibenzo-16-crown-5 resin 3 in which the pendant carboxylic acid group is oriented over the polyether cavity. Resin 3 was utilized as a stationary phase for selective column concentration of Na{sup +} from dilute aqueous solution.

  7. Dependence of the optical absorption and Na+ binding energies of coumarin-crown ethers on the size and attachment position of ether ring: density functional investigation.

    PubMed

    Kasapbasi, Esra; Yurtsever, Mine

    2013-01-01

    The crowned coumarin complexes are well known compounds for their ion recognition abilities. They undergo photophysical changes upon cation binding. On the basis of density functional theory calculations, we examined the sodium cation (Na+) binding energies of coumarin-crown ethers based on 15-Crown-5 (15 C5) and 18-Crown-6 (18 C6) as well as the optical absorptions of coumarin-crown ethers based on 12-Crown-4 (12 C4), 15 C5 and 18 C6. We explored why the attachment of crown ether ring to coumarin affects the Na+ binding energies of coumarin-crown ethers and also why the optical absorption of coumarin is modified by the crown ethers. Our study reveals that the Na+ ion binding energies of coumarin-crown ethers depend strongly on the size of the crown ether ring and also on the attachment position of the ether ring on coumarin. These factors affect the intramolecular charge transfer and overall stability of the complexes. The absorptions of the coumarin and ether ring parts of coumarin-crown ether are red shifted from those of isolated coumarin and crown ether, respectively. The red-shift of the coumarin ester group absorption is much stronger depending on the attachment position of the ether ring to coumarin. The absorption intensity of the coumarin part in coumarin-crown ethers is reduced for the benzene group absorption, but is enhanced for the ester group absorption.

  8. A New Analogue of Echinomycin and a New Cyclic Dipeptide from a Marine-Derived Streptomyces sp. LS298.

    PubMed

    Zhen, Xin; Gong, Ting; Liu, Fu; Zhang, Pei-Cheng; Zhou, Wan-Qi; Li, Yan; Zhu, Ping

    2015-11-18

    Quinomycin G (1), a new analogue of echinomycin, together with a new cyclic dipeptide, cyclo-(l-Pro-4-OH-l-Leu) (2), as well as three known antibiotic compounds tirandamycin A (3), tirandamycin B (4) and staurosporine (5), were isolated from Streptomyces sp. LS298 obtained from a marine sponge Gelliodes carnosa. The planar and absolute configurations of compounds 1 and 2 were established by MS, NMR spectral data analysis and Marfey's method. Furthermore, the differences in NMR data of keto-enol tautomers in tirandamycins were discussed for the first time. Antibacterial and anti-tumor activities of compound 1 were measured against 15 drug-sensitive/resistant strains and 12 tumor cell lines. Compound 1 exhibited moderate antibacterial activities against Staphylococcuse pidermidis, S. aureus, Enterococcus faecium, and E. faecalis with the minimum inhibitory concentration (MIC) values ranged from 16 to 64 μg/mL. Moreover, it displayed remarkable anti-tumor activities; the highest activity was observed against the Jurkat cell line (human T-cell leukemia) with an IC50 value of 0.414 μM.

  9. Enolboration. 5. An Examination of the Effects of Amine, Solvent, and Other Reaction Parameters on the Stereoselective Enolboration of Ketones with Various Chx sub 2 BX Reagents. An Optimized Procedure to Achieve the Stereoselective Synthesis of E Enol Borinates from Representative Ketones Using Chx sub 2 BC1/Et sub 3 N

    DTIC Science & Technology

    1993-10-13

    to warm slowly to room temperature overnight unless otherwise stated. dDetermined by IH NMR. eAldolization at 0 OC for 2 h. fEnolization at -78 °C...PhCHO at -78 OC for 2 h unless otherwise stated. eRefer to footnotesf and g of Table I. fEnolization at 25 oC for 48 h.

  10. POLYBROMINATED DIPHENYL ETHERS (PBDES) CONTAMINATION OF UNITED STATES FOOD

    EPA Science Inventory

    Elevated levels of polybrominated diphenyl ethers (PBDEs), a type of brominated flame retardant, were recently detected in United States (U.S.) nursing mothers' milk. These halogenated compounds chemically and toxicologically resemble others such as polychlorinated biphenyls (PC...

  11. Fluorinated Alkyl Ether Epoxy Resin Compositions and Applications Thereof

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J. (Inventor); Connell, John W. (Inventor); Smith, Joseph G. (Inventor); Siochi, Emilie J. (Inventor); Gardner, John M. (Inventor); Palmieri, Frank M. (Inventor)

    2017-01-01

    Epoxy resin compositions prepared using amino terminated fluoro alkyl ethers. The epoxy resin compositions exhibit low surface adhesion properties making them useful as coatings, paints, moldings, adhesives, and fiber reinforced composites.

  12. 46 CFR 151.50-42 - Ethyl ether.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... shall be designed and tested to meet the rules of the American Bureau of Shipping for a head of water at... liquid. (g) Precautions shall be taken to prevent the contamination of ethyl ether by strong...

  13. POLYBROMINATED DIPHENYL ETHERS (PBDES) CONTAMINATION OF UNITED STATES FOOD

    EPA Science Inventory

    Elevated levels of polybrominated diphenyl ethers (PBDEs), a type of brominated flame retardant, were recently detected in United States (U.S.) nursing mothers' milk. These halogenated compounds chemically and toxicologically resemble others such as polychlorinated biphenyls (PC...

  14. Aquatic Life Criteria - Methyl Tertiary-Butyl Ether (MTBE)

    EPA Pesticide Factsheets

    Information pertaining to the 1999 Acute and Chronic Ambient Aquatic Life Water Quality Criteria for Methyl Tertiary-Butyl Ether (MTBE) for freshwater and salt water. Information includes the safe levels of MTBE that should protect the majority of species.

  15. POLYBROMINATED DIPHENYL ETHERS IN HOUSE DUST AND CLOTHES DRYER LINT

    EPA Science Inventory

    Polybrominated diphenyl ether (PBDE) flame retardants are now considered ubiquitous and persistent pollutants. Few studies have examined the concentrations of these chemicals in the home and here we report measurements of PBDEs in house dust samples collected from the Washington...

  16. 36. BUILDINGS NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    36. BUILDINGS NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, AND NO. 523, REFRIGERATION PLANT BUILDING, LOOKING EAST. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  17. Improved boundary lubrication with formulated C-ethers

    NASA Technical Reports Server (NTRS)

    Loomis, W. R.

    1982-01-01

    A comparison of five recently developed C-ether-formulated fluids with an advanced formulated MIL-L-27502 candidate ester is described. Steady state wear and friction measurements were made with a sliding pin on disk friction apparatus. Conditions included disk temperatures up to 260 C, dry air test atmosphere, 1 kilogram load, 50 rpm disk speed, and test times to 130 minutes. Based on wear rates and coefficients of friction, three of the C-ether formulations as well as the C-ether base fluid gave better boundary lubrication than the ester fluid under all test conditions. The susceptibility of C-ethers to selective additive treatment (phosphinic esters or acids and other antiwear additives) was demonstrated when two of the formulations gave somewhat improved lubrication over the base fluid. The increased operating potential for this fluid was shown in relationship to bulk oil temperature limits for MIL-L-23699 and MIL-L-27502 type esters.

  18. 44. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    44. BUILDING NO. 519, ETHER AND ALCOHOL RECOVERY HOUSE, INTERIOR, LOOKING UP DISTILLATION TOWER FROM 2ND LEVEL. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

  19. The zeolite mediated isomerization of allyl phenyl ether

    NASA Astrophysics Data System (ADS)

    Pebriana, R.; Mujahidin, D.; Syah, Y. M.

    2017-04-01

    Allyl phenyl ether is an important starting material in organic synthesis that has several applications in agrochemical industry. The green transformation of allyl phenyl ether assisted by heterogeneous catalyst is an attractive topic for an industrial process. In this report, we investigated the isomerization of allyl phenyl ether by heating it in zeolite H-ZSM-5 and Na-ZSM-5. The conversion of allyl phenyl ether (neat) in H-ZSM-5 was 67% which produced 40% of 2-allylphenol, 17% of 2-methyldihydrobenzofuran, and other product (4:1.7:1), while in Na-ZSM-5 produced exclusively 2-allylphenol with 52% conversion. These results showed that zeolite properties can be tuned to give a selective transformation by substitution of metal ion into the zeolite interior.

  20. POLYBROMINATED DIPHENYL ETHERS IN HOUSE DUST AND CLOTHES DRYER LINT

    EPA Science Inventory

    Polybrominated diphenyl ether (PBDE) flame retardants are now considered ubiquitous and persistent pollutants. Few studies have examined the concentrations of these chemicals in the home and here we report measurements of PBDEs in house dust samples collected from the Washington...

  1. Syngas to olefins via dimethyl ether over zeolite catalysts

    SciTech Connect

    Lee, B.G.; Sardesai, A.; Lee, S.

    1998-12-31

    Coal or natural gas-based syngas can be converted to dimethyl ether (DME) in a dual catalytic, single-stage liquid phase process. The process described here converts dimethyl ether to lower olefins, such as ethylene, propylene, and butenes. Thus, a novel process of producing olefins from syngas via dimethyl ether has been introduced. The process feasibility of dimethyl ether conversion has been evaluated and the range of products of this process has also been identified. The effect of operating parameters and catalyst characteristics on product selectivity has been studied. The superior process advantages as well as its competitive economics quite clearly identify this process to be quite promising when conducted on an industrial scale.

  2. Mixed Strategies in cyclic competition

    NASA Astrophysics Data System (ADS)

    Intoy, Ben; Pleimling, Michel

    2015-03-01

    Physicists have been using evolutionary game theory to model and simulate cyclically competing species, with applications to lizard mating strategies and competing bacterial strains. However these models assume that each agent plays the same strategy, which is called a pure strategy in game theory, until they are beaten by a better strategy which they immediately adopt. We relax this constraint of an agent playing a single strategy by instead letting the agent pick its strategy randomly from a probability distribution, which is called a mixed strategy in game theory. This scheme is very similar to multiple occupancy models seen in the literature, the major difference being that interactions happen between sites rather than within them. Choosing strategies out of a distribution also has applications to economic/social systems such as the public goods game. We simulate a model of mixed strategy and cylic competition on a one-dimensional lattice with three and four strategies and find interesting spatial and stability properties depending on how discretized the choice of strategy is for the agents. This work is supported by the US National Science Foundation through Grant DMR-1205309.

  3. Asymmetric cyclic evolution in polymerised cosmology

    SciTech Connect

    Hrycyna, Orest; Mielczarek, Jakub; Szydłowski, Marek E-mail: jakub.mielczarek@uj.edu.pl

    2009-12-01

    The dynamical systems methods are used to study evolution of the polymerised scalar field cosmologies with the cosmological constant. We have found all evolutional paths admissible for all initial conditions on the two-dimensional phase space. We have shown that the cyclic solutions are generic. The exact solution for polymerised cosmology is also obtained. Two basic cases are investigated, the polymerised scalar field and the polymerised gravitational and scalar field part. In the former the division on the cyclic and non-cyclic behaviour is established following the sign of the cosmological constant. The value of the cosmological constant is upper bounded purely from the dynamical setting.

  4. Advanced hybrid fluoropolymers from the cycloaddition of aryl trifluorovinyl ethers

    NASA Astrophysics Data System (ADS)

    Ligon, S. Clark, Jr.

    This dissertation discusses the synthesis of aryl trifluorovinyl ethers and their cycloaddition polymerization to give perfluorocyclobutyl (PFCB) polymers. To explore the stereochemistry of these polymers, simple monomfunctional aryl trifluorovinyl ethers were dimerized and the resultant cis and trans isomers were separated. Differences in structure help to improve understanding of the amorphous nature of the bulk PFCB polymeric material. To apply this knowledge, crown ether containing perfluorocyclobutyl (PFCB) polymers were synthesized for use in lithium ion battery applications. While poor solubility has hindered further development of these materials, slight modifications to structure may provide a solution. Also described is a fluorinated aryl vinyl ether and its attempted copolymerization with chlorotrifluoroethylene. While this copolymerization did not yield the desired materials, novel semifluorinated phenol precursors have been utilized in reactions with carboxylic acids to give polyesters and most recently with phosgene like species to give polycarbonates. Next, PFCB polymers were post functionalized with fluoroalkyl tethers to improve oleophobicity and hydrophobicity without decreasing thermal stability or optical clarity. In addition, various silica nanostructures were functionalized with aryl trifluorovinyl ethers. This includes the reaction of aryl silanes to give trifluorovinyl ether functional POSS and their polymerization to provide PFCB hybrid materials. Silane coupling agents were also used to functionalize colloidal silica and fumed silica nanoparticles. These procedures allow excellent dispersion of the silica nanoparticles throughout the fluoropolymer matrix. Finally, the reaction of aryl trifluorovinyl ether with nonfluorinated alkenes and alkynes was explored. In these reactions, the fluorinated olefin adds with the hydrocarbon olefin to give semifluorinated cyclobutanes (SFCB) and with the alkyne to give semifluorinated cyclobutene. The

  5. Imide/Arylene Ether Copolymers Containing Phosphine Oxide

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Partos, Richard D.

    1993-01-01

    Phosphine oxide groups react with oxygen to form protective phosphate surface layers. Series of imide/arylene ether block copolymers containing phosphine oxide units in backbone synthesized and characterized. In comparison with commercial polyimide, these copolymers display better resistance to etching by oxygen plasma. Tensile strengths and tensile moduli greater than those of polyarylene ether homopolymer. Combination of properties makes copolymers attractive for films, coatings, adhesives, and composite matrices where resistance to atomic oxygen needed.

  6. The thiolase reaction mechanism: the importance of Asn316 and His348 for stabilizing the enolate intermediate of the Claisen condensation.

    PubMed

    Meriläinen, Gitte; Poikela, Visa; Kursula, Petri; Wierenga, Rik K

    2009-11-24

    The biosynthetic thiolase catalyzes a Claisen condensation reaction between acetyl-CoA and the enzyme acetylated at Cys89. Two oxyanion holes facilitate this catalysis: oxyanion hole I stabilizes the enolate intermediate generated from acetyl-CoA, whereas oxyanion hole II stabilizes the tetrahedral intermediate of the acetylated enzyme. The latter intermediate is formed when the alpha-carbanion of acetyl-CoA enolate reacts with the carbonyl carbon of acetyl-Cys89, after which C-C bond formation is completed. Oxyanion hole II is made of two main chain peptide NH groups, whereas oxyanion hole I is formed by a water molecule (Wat82) and NE2(His348). Wat82 is anchored in the active site by an optimal set of hydrogen bonding interactions, including a hydrogen bond to ND2(Asn316). Here, the importance of Asn316 and His348 for catalysis has been studied; in particular, the properties of the N316D, N316A, N316H, H348A, and H348N variants have been determined. For the N316D variant, no activity could be detected. For each of the remaining variants, the k(cat)/K(m) value for the Claisen condensation catalysis is reduced by a factor of several hundred, whereas the thiolytic degradation catalysis is much less affected. The crystal structures of the variants show that the structural changes in the active site are minimal. Our studies confirm that oxyanion hole I is critically important for the condensation catalysis. Removing either one of the hydrogen bond donors causes the loss of at least 3.4 kcal/mol of transition state stabilization. It appears that in the thiolytic degradation direction, oxyanion hole I is not involved in stabilizing the transition state of its rate limiting step. However, His348 has a dual role in the catalytic cycle, contributing to oxyanion hole I and activating Cys89. The analysis of the hydrogen bonding interactions in the very polar catalytic cavity shows the importance of two conserved water molecules, Wat82 and Wat49, for the formation of oxyanion

  7. Explosion and detonation characteristics of dimethyl ether.

    PubMed

    Mogi, Toshio; Horiguchi, Sadashige

    2009-05-15

    In this study, the explosion and detonation characteristics of dimethyl ether (DME) were experimentally investigated. A spherical pressure vessel with an internal volume of 180L was used as the explosion vessel. Therefore, tubes 10m in length with internal diameters of 25mm and 50mm were used as detonation tubes. In addition, we compared the characteristics of DME with those of propane since DME is considered as a substitute fuel for liquid petroleum gas (LPG). At room temperature and atmospheric pressure, the maximum explosive pressure increased tenfold. The explosion index (K(G) values), an indicator of the intensity of an explosion, was larger than that of propane, indicating that the explosion was intense. No experimental study has been conducted on the detonation behavior of DME so far, but this research confirmed a transition to detonation. The detonation characteristics were similar to the characteristics of the Chapman-Jouguet detonation, and the concentration range for detonation was from 5.5% to 9.0%.

  8. Atmospheric and combustion chemistry of dimethyl ether

    SciTech Connect

    Nielsen, O.J.; Egsgaard, H.; Larsen, E.; Sehested, J.; Wallington, T.J.

    1997-12-31

    It has been demonstrated that dimethyl ether (DME) is an ideal diesel fuel alternative. DME, CH{sub 3}OCH{sub 3}, combines good fuel properties with low exhaust emissions and low combustion noise. Large scale production of this fuel can take place using a single step catalytic process converting CH{sub 4} to DME. The fate of DME in the atmosphere has previously been studied. The atmospheric degradation is initiated by the reaction with hydroxyl radicals, which is also a common feature of combustion processes. Spectrokinetic investigations and product analysis were used to demonstrate that the intermediate oxy radical, CH{sub 3}OCH{sub 2}O, exhibits a novel reaction pathway of hydrogen atom ejection. The application of tandem mass spectrometry to chemi-ions based on supersonic molecular beam sampling has recently been demonstrated. The highly reactive ionic intermediates are sampled directly from the flame and identified by collision activation mass spectrometry and ion-molecule reactions. The mass spectrum reflects the distribution of the intermediates in the flame. The atmospheric degradation of DME as well as the unique fuel properties of a oxygen containing compound will be discussed.

  9. Nonlinear dielectric effect in supercritical diethyl ether

    NASA Astrophysics Data System (ADS)

    Drozd-Rzoska, Aleksandra; Rzoska, Sylwester J.; Martinez-Garcia, Julio Cesar

    2014-09-01

    Nonlinear dielectric effect (NDE) describes changes of dielectric permittivity induced by a strong electric field in a liquid dielectric. The most classical finding related to this magnitude is the negative sign of NDE in liquid diethyl ether (DEE), recalled by Peter Debye in his Nobel Prize lecture. This article shows that the positive sign of NDE in DEE is also possible, in the supercritical domain. Moreover, NDE on approaching the gas-liquid critical point exhibits a unique critical effect described by the critical exponent ψ ≈ 0.4 close to critical temperature (TC) and ψ ≈ 0.6 remote from TC. This can be linked to the emergence of the mean-field behavior in the immediate vicinity of TC, contrary to the typical pattern observed for critical phenomena. The multi-frequency mode of NDE measurements made it possible to estimate the evolution of lifetime of critical fluctuations. The new way of data analysis made it possible to describe the critical effect without a knowledge of the non-critical background contribution in prior.

  10. Dimethyl ether (DME) as an alternative fuel

    NASA Astrophysics Data System (ADS)

    Semelsberger, Troy A.; Borup, Rodney L.; Greene, Howard L.

    With ever growing concerns on environmental pollution, energy security, and future oil supplies, the global community is seeking non-petroleum based alternative fuels, along with more advanced energy technologies (e.g., fuel cells) to increase the efficiency of energy use. The most promising alternative fuel will be the fuel that has the greatest impact on society. The major impact areas include well-to-wheel greenhouse gas emissions, non-petroleum feed stocks, well-to-wheel efficiencies, fuel versatility, infrastructure, availability, economics, and safety. Compared to some of the other leading alternative fuel candidates (i.e., methane, methanol, ethanol, and Fischer-Tropsch fuels), dimethyl ether appears to have the largest potential impact on society, and should be considered as the fuel of choice for eliminating the dependency on petroleum. DME can be used as a clean high-efficiency compression ignition fuel with reduced NO x, SO x, and particulate matter, it can be efficiently reformed to hydrogen at low temperatures, and does not have large issues with toxicity, production, infrastructure, and transportation as do various other fuels. The literature relevant to DME use is reviewed and summarized to demonstrate the viability of DME as an alternative fuel.

  11. Polybrominated diphenyl ethers in California wastestreams.

    PubMed

    Petreas, Myrto; Oros, Daniel

    2009-02-01

    Polybrominated diphenyl ethers (PBDEs) are used in consumer products, including electronics, fabrics, and polyurethane foam. Exposures may occur during the products' useful lifetime and also after the products' disposal. A survey of California wastestreams (e-wastes, autoshredder waste and wastewater sewage sludge) attempted to assess the relative importance of these wastestreams as repositories of PBDEs. Based on measurements of PBDEs in samples of such wastestreams and on assumptions regarding use patterns, e-wastes appeared to be by far the predominant wastestream with 1200 metric tons (MT) of PBDEs year(-1), followed by autoshredder waste (31 MT of PBDEs year(-1)) and sewage sludge (2.3 MT of PBDEs year(-1)). When these estimates were compared with the reported use of PBDEs in California, about half of the PBDEs could not be accounted for in the wastestreams examined. This suggests that additional wastestreams, such as household wastes should be evaluated for their PBDE content. Information on the presence and fate of PBDEs in all wastestreams needs to be included in decision making practices for waste management to avoid public health and ecologic catastrophes.

  12. Dimethyl ether chemical ionization of arylalkylamines.

    PubMed

    Ramos, L E; Cardoso, A M; Correia, A J; Nibbering, N M

    2000-01-01

    The gas-phase reactions of dimethyl ether (DME) ions with a number of biologically active arylalkylamines of the general formula R(1)R(2)C(6)H(3)CHR(3)(CH(2))(n)NR(4)R(5), where R(1) = H or OH, R(2) = H, F, NO(2), OH or OCH(3), R(3) = H or OH, R(4) and R(5) = H or CH(3), have been studied by means of chemical ionization mass spectrometry. Under the experimental conditions used, the most abundant DME ion is the methoxymethyl cation (CH(3)OCH(2)(+), m/z 45). The unimolecular metastable decompositions of the [M + 45](+), [M + 13](+) and [M + 15](+) adducts formed have been interpreted in terms of the initial site of reaction with the amines and the presence of different functional groups in the molecule. This has permitted establishment of general fragmentation patterns for the adducts, and their correlation with structural features of the molecules. The main site of reaction of the ion CH(3)OCH(2)(+) with the amines seems to be the amino group, particularly if the amine is primary, although a competition with attack on the aromatic ring and especially on the benzylic hydroxy group is observed. In a few cases the reaction mechanisms have been elucidated through the use of deuterated amines obtained by H/D exchange with D(2)O. Copyright 2000 John Wiley & Sons, Ltd.

  13. Molecular structure, vibrational and electronic properties of 4-Phenyl-3H-1,3-thiazol-2-ol using density functional theory and comparison of drug efficacy of keto and enol forms by QSAR analysis.

    PubMed

    Sachan, Alok K; Pathak, Shilendra K; Chand, Satish; Srivastava, Ruchi; Prasad, Onkar; Belaidi, Salah; Sinha, Leena

    2014-11-11

    4-Phenyl-3H-1,3-thiazol-2-ol can exist in two tautomeric forms - keto and enol. Comprehensive investigation of molecular geometry and electronic structure in ground as well as in the first excited state of 4-Phenyl-3H-1,3-thiazol-2-ol (enol) has been carried out. To determine lowest-energy molecular conformation of the title molecule, the selected torsion angles were varied in steps of 10° and molecular energy profile was calculated from -180° to +180°. Experimental FT-IR and FT-Raman spectra of title compound were compared with the spectral data obtained by DFT/B3LYP method. Dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface map have been calculated to get a better insight of the properties of title molecule. Natural bond orbital (NBO) analysis has been done to study the stability of the molecule arising from charge delocalization. UV-Vis spectrum of the title compound was also recorded and electronic properties such as frontier orbitals and band gap energies were calculated by TD-DFT approach. To compare the drug efficacy of enolic and keto forms, QSAR properties of both forms have also been computed and discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

  14. Influence of Solvent Polarizability on the Keto-Enol Equilibrium in 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol.

    PubMed

    Matwijczuk, Arkadiusz; Górecki, Andrzej; Kamiński, Daniel; Myśliwa-Kurdziel, Beata; Fiedor, Leszek; Niewiadomy, Andrzej; Karwasz, Grzegorz P; Gagoś, Mariusz

    2015-11-01

    This work presents spectroscopic studies of the keto-enol equilibrium induced by solvent polarizability in 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol a strong antiproliferative and anticancer thiadiazol derivative. Electronic absorption, steady state and time resolved fluorescence, and infrared spectroscopies were applied to investigate the keto and enol forms of this compound in a series of polar and non-polar solvents. The enol form dominates in polar solvents while, surprisingly, the keto form dominates in non-polar solvents with high average electric dipole polarizability e.g. n-alkenes. The electronic absorption spectrum of this derivative is more dependent on spatially averaged electric dipole polarizability of the solvent than on Kirkwood's correlation or on Lorenz-Lorenz electric polarizability. By analogy of n-alkanes to the alkyl parts of lipids, one can expect that the transformation of 1,3,4-thiadiazoles to the keto form may be facilitated in the hydrophobic core of the lipid membrane. Such a transition may be of great practical importance for the design of biologically active pharmaceutics, which are able to interact with the hydrophobic regions of cell membranes in a specific manner.

  15. Cyclic hardening in bundled actin networks.

    PubMed

    Schmoller, K M; Fernández, P; Arevalo, R C; Blair, D L; Bausch, A R

    2010-01-01

    Nonlinear deformations can irreversibly alter the mechanical properties of materials. Most soft materials, such as rubber and living tissues, display pronounced softening when cyclically deformed. Here we show that, in contrast, reconstituted networks of crosslinked, bundled actin filaments harden when subject to cyclical shear. As a consequence, they exhibit a mechano-memory where a significant stress barrier is generated at the maximum of the cyclic shear strain. This unique response is crucially determined by the network architecture: at lower crosslinker concentrations networks do not harden, but soften showing the classic Mullins effect known from rubber-like materials. By simultaneously performing macrorheology and confocal microscopy, we show that cyclic shearing results in structural reorganization of the network constituents such that the maximum applied strain is encoded into the network architecture.

  16. Parallel architectures for computing cyclic convolutions

    NASA Technical Reports Server (NTRS)

    Yeh, C.-S.; Reed, I. S.; Truong, T. K.

    1983-01-01

    In the paper two parallel architectural structures are developed to compute one-dimensional cyclic convolutions. The first structure is based on the Chinese remainder theorem and Kung's pipelined array. The second structure is a direct mapping from the mathematical definition of a cyclic convolution to a computational architecture. To compute a d-point cyclic convolution the first structure needs d/2 inner product cells, while the second structure and Kung's linear array require d cells. However, to compute a cyclic convolution, the second structure requires less time than both the first structure and Kung's linear array. Another application of the second structure is to multiply a Toeplitz matrix by a vector. A table is listed to compare these two structures and Kung's linear array. Both structures are simple and regular and are therefore suitable for VLSI implementation.

  17. Parallel architectures for computing cyclic convolutions

    NASA Technical Reports Server (NTRS)

    Yeh, C.-S.; Reed, I. S.; Truong, T. K.

    1983-01-01

    In the paper two parallel architectural structures are developed to compute one-dimensional cyclic convolutions. The first structure is based on the Chinese remainder theorem and Kung's pipelined array. The second structure is a direct mapping from the mathematical definition of a cyclic convolution to a computational architecture. To compute a d-point cyclic convolution the first structure needs d/2 inner product cells, while the second structure and Kung's linear array require d cells. However, to compute a cyclic convolution, the second structure requires less time than both the first structure and Kung's linear array. Another application of the second structure is to multiply a Toeplitz matrix by a vector. A table is listed to compare these two structures and Kung's linear array. Both structures are simple and regular and are therefore suitable for VLSI implementation.

  18. Colour cyclic code for Brillouin distributed sensors

    NASA Astrophysics Data System (ADS)

    Le Floch, Sébastien; Sauser, Florian; Llera, Miguel; Rochat, Etienne

    2015-09-01

    For the first time, a colour cyclic coding (CCC) is theoretically and experimentally demonstrated for Brillouin optical time-domain analysis (BOTDA) distributed sensors. Compared to traditional intensity-modulated cyclic codes, the code presents an additional gain of √2 while keeping the same number of sequences as for a colour coding. A comparison with a standard BOTDA sensor is realized and validates the theoretical coding gain.

  19. Cyclic period in the CBE model

    NASA Astrophysics Data System (ADS)

    Frampton, Paul H.

    2017-08-01

    In a cyclic entropy model in which the extroverse is jettisoned at turnaround with a Come Back Empty (CBE) assumption, we address the matching of the contaction scale factor â(t) = f(tT)a(t) to the expansion scale factor a(t), where f(tT) is the ratio at turnaround of the introverse to the extroverse radii. Such matching is necessary for infinite cyclicity and fixes the CBE period at ˜ 2.6 Ty.

  20. Cyclic behaviors of amorphous shape memory polymers.

    PubMed

    Yu, Kai; Li, Hao; McClung, Amber J W; Tandon, Gyaneshwar P; Baur, Jeffery W; Qi, H Jerry

    2016-04-07

    Cyclic loading conditions are commonly encountered in the applications of shape memory polymers (SMPs), where the cyclic characteristics of the materials determine their performance during the service life, such as deformation resistance, shape recovery speed and shape recovery ratio. Recent studies indicate that in addition to the physical damage or some other irreversible softening effects, the viscoelastic nature could also be another possible reason for the degraded cyclic behavior of SMPs. In this paper, we explore in detail the influence of the viscoelastic properties on the cyclic tension and shape memory (SM) behavior of an epoxy based amorphous thermosetting polymer. Cyclic experiments were conducted first, which show that although the epoxy material does not have any visible damage or irreversible softening effect during deformation, it still exhibits obvious degradation in the cyclic tension and SM behaviors. A linear multi-branched model is utilized to assist in the prediction and understanding of the mechanical responses of amorphous SMPs. Parametric studies based on the applied model suggest that the shape memory performance can be improved by adjusting programming and recovery conditions, such as lowering the loading rate, increasing the programming temperature, and reducing the holding time.