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

CERN Document Server

1998-01-01

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

Synthesis of Heterocycles through a Ruthenium‐Catalyzed Tandem Ring‐Closing Metathesis/Isomerization/N‐Acyliminium Cyclization Sequence

DEFF Research Database (Denmark)

Ascic, Erhad; Jensen, Jakob Feldthusen; Nielsen, Thomas Eiland

2011-01-01

Tandem bicycle: In the title reaction double bonds created during ring-closing metathesis isomerize to generate reactive iminium intermediates that undergo intramolecular cyclization reactions with tethered heteroatom and carbon nucleophiles. In this way, a series of biologically interesting hete...... heterocyclic compounds can be made, including a known precursor for the total synthesis of the antiparasitic natural product harmicine....

Design and synthesis of fused polycycles via Diels–Alder reaction and ring-rearrangement metathesis as key steps

Directory of Open Access Journals (Sweden)

Sambasivarao Kotha

2015-07-01

Full Text Available Atom efficient processes such as the Diels–Alder reaction (DA and the ring-rearrangement metathesis (RRM have been used to design new polycycles. In this regard, ruthenium alkylidene catalysts are effective in realizing the RRM of bis-norbornene derivatives prepared by DA reaction and Grignard addition. Here, fused polycycles are assembled which are difficult to produce by conventional synthetic routes.

Design and synthesis of fused polycycles via Diels-Alder reaction and ring-rearrangement metathesis as key steps.

Science.gov (United States)

Kotha, Sambasivarao; Ravikumar, Ongolu

2015-01-01

Atom efficient processes such as the Diels-Alder reaction (DA) and the ring-rearrangement metathesis (RRM) have been used to design new polycycles. In this regard, ruthenium alkylidene catalysts are effective in realizing the RRM of bis-norbornene derivatives prepared by DA reaction and Grignard addition. Here, fused polycycles are assembled which are difficult to produce by conventional synthetic routes.

Cyclic phosphopeptides for interference with Grb2 SH2 domain signal transduction prepared by ring-closing metathesis and phosphorylation

NARCIS (Netherlands)

Dekker, Frank J; de Mol, Nico J; Fischer, Marcel J E; Kemmink, Johan; Liskamp, Rob M J; Dekker, Frank

2003-01-01

Cyclic phosphopeptides were prepared using ring-closing metathesis followed by phosphorylation. These cyclic phosphopeptides were designed to interact with the SH2 domain of Grb2, which is a signal transduction protein of importance as a target for antiproliferative drug development. Binding of

A cross-metathesis approach to the stereocontrolled synthesis of the AB ring segment of ciguatoxin

OpenAIRE

Kadota, Isao; Abe, Takashi; Uni, Miyuki; Takamura, Hiroyoshi; Yamamoto, Yoshinori

2008-01-01

Synthesis of the AB ring segments of ciguatoxin is described. The present synthesis includes a Lewis acid mediated cyclization of allylstannane with aldehyde, cross-metathesis reaction introducing the side chain, and Grieco-Nishizawa dehydration on the A ring.

Stereoselective synthesis of functionalized cyclic amino acid derivatives via a [2,3]-Stevens rearrangement and ring-closing metathesis.

Science.gov (United States)

Nash, Aaron; Soheili, Arash; Tambar, Uttam K

2013-09-20

Unnatural cyclic amino acids are valuable tools in biomedical research and drug discovery. A two-step stereoselective strategy for converting simple glycine-derived aminoesters into unnatural cyclic amino acid derivatives has been developed. The process includes a palladium-catalyzed tandem allylic amination/[2,3]-Stevens rearrangement followed by a ruthenium-catalyzed ring-closing metathesis. The [2,3]-rearrangement proceeds with high diastereoselectivity through an exo transition state. Oppolzer's chiral auxiliary was utilized to access an enantiopure cyclic amino acid by this approach, which will enable future biological applications.

Carbohydrate carbocyclization by a zinc-mediated tandem reaction and ring-closing enyne metathesis

DEFF Research Database (Denmark)

Poulsen, Carina Storm; Madsen, Robert

2002-01-01

reaction, an amino group can be introduced in the 1,7-enyne products. Addition of 2-TMS-ethynylcerium(III) chloride after the reductive ring-opening produces the corresponding 1,6-enynes. Further annulation of the product 1,3-dienes can be achieved through a Diels-Alder reaction with good control of stereo...

Metathesis of alkanes and related reactions

KAUST Repository

Basset, Jean-Marie

2010-02-16

(Figure Presented) The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, (=SiO)2TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of aluminasupported tungsten hydride, W(H)3/Al 2O3, which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis of

Metathesis of alkanes and related reactions.

Science.gov (United States)

Basset, Jean-Marie; Copéret, Christophe; Soulivong, Daravong; Taoufik, Mostafa; Cazat, Jean Thivolle

2010-02-16

The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, ([triple bond]SiO)(2)TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of alumina-supported tungsten hydride, W(H)(3)/Al(2)O(3), which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis

Hybrid macrocycle formation and spiro annulation on cis-syn-cis-tricyclo[6.3.0.02,6]undeca-3,11-dione and its congeners via ring-closing metathesis

Directory of Open Access Journals (Sweden)

Sambasivarao Kotha

2015-07-01

Full Text Available We have developed a simple methodology to transform cis-syn-cis-triquinane derivative 2 into the diindole based macrocycle 6 involving Fischer indolization and ring-closing metathesis (RCM. Various spiro-polyquinane derivatives have been assembled via RCM as a key step.

Metathesis reactions for the synthesis of ring-fused carbazoles

CSIR Research Space (South Africa)

Pelly, SC

2005-12-09

Full Text Available stream_source_info pelly_2005.pdf.txt stream_content_type text/plain stream_size 48007 Content-Encoding ISO-8859-1 stream_name pelly_2005.pdf.txt Content-Type text/plain; charset=ISO-8859-1 Metathesis Reactions... (99). N,Nminute-Di-tert-butyldicarboxylate-2,2minute-biindolyl-3,3minute-divi- nyl 12. Into a 50-mL two-necked oven-dried flask, fitted with a dropping funnel, was placed MePPh3Br (533 mg, 1.49 mmol), and the contents of the flask were blanketed...

A tandem cross-metathesis/semipinacol rearrangement reaction.

Science.gov (United States)

Plummer, Christopher W; Soheili, Arash; Leighton, James L

2012-05-18

An efficient and (E)-selective synthesis of a 6-alkylidenebicyclo[3.2.1]octan-8-one has been developed. The key step is a tandem cross-metathesis/semipinacol rearrangement reaction, wherein the Hoveyda-Grubbs II catalyst, or more likely a derivative thereof, serves as the Lewis acid for the rearrangement. Despite the fact that both the starting alkene and the cross-metathesis product are viable rearrangement substrates, only the latter rearranges, suggesting that the Lewis acidic species is generated only after the cross-metathesis reaction is complete.

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

OpenAIRE

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

2016-01-01

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

The right computational recipe for olefin metathesis with ru-based catalysts: The whole mechanism of ring-closing olefin metathesis

KAUST Repository

Poater, Albert

2014-10-14

The initiation mechanism of ruthenium methylidene complexes was studied detailing mechanistic insights of all involved reaction steps within a classical olefin metathesis pathway. Computational studies reached a good agreement with the rarely available experimental data and even enabled to complement them. As a result, a highly accurate computational and rather cheap recipe is presented; M06/TZVP//BP86/SVP (PCM, P = 1354 atm).

The right computational recipe for olefin metathesis with ru-based catalysts: The whole mechanism of ring-closing olefin metathesis

KAUST Repository

Poater, Albert; Pump, Eva; Vummaleti, Sai V. C.; Cavallo, Luigi

2014-01-01

The initiation mechanism of ruthenium methylidene complexes was studied detailing mechanistic insights of all involved reaction steps within a classical olefin metathesis pathway. Computational studies reached a good agreement with the rarely available experimental data and even enabled to complement them. As a result, a highly accurate computational and rather cheap recipe is presented; M06/TZVP//BP86/SVP (PCM, P = 1354 atm).

Synthesis of densely functionalized enantiopure indolizidines by ring-closing metathesis (RCM of hydroxylamines from carbohydrate-derived nitrones

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Goti Andrea

2007-12-01

Full Text Available Abstract Background Indolizidine alkaloids widely occur in nature and display interesting biological activity. This is the reason for which their total synthesis as well as the synthesis of non-natural analogues still attracts the attention of many research groups. To establish new straightforward accesses to these molecules is therefore highly desirable. Results The ring closing metathesis (RCM of enantiopure hydroxylamines bearing suitable unsaturated groups cleanly afforded piperidine derivatives in good yields. Further cyclization and deprotection of the hydroxy groups gave novel highly functionalized indolizidines. The synthesis of a pyrroloazepine analogue is also described. Conclusion We have developed a new straightforward methodology for the synthesis of densely functionalized indolizidines and pyrroloazepine analogues in 6 steps and 30–60% overall yields from enantiopure hydroxylamines obtained straightforwardly from carbohydrate-derived nitrones.

Nitro-Grela-type complexes containing iodides – robust and selective catalysts for olefin metathesis under challenging conditions

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Andrzej Tracz

2015-10-01

Full Text Available Iodide-containing nitro-Grela-type catalysts have been synthesized and applied to ring closing metathesis (RCM and cross metathesis (CM reactions. These new catalysts have exhibited improved efficiency in the transformation of sterically, non-demanding alkenes. Additional steric hindrance in the vicinity of ruthenium related to the presence of iodides ensures enhanced catalyst stability. The benefits are most apparent under challenging conditions, such as very low reaction concentrations, protic solvents or with the occurrence of impurities.

Phosphate Tether-Mediated Ring-Closing Metathesis for the Generation of P-Stereogenic, Z-Configured Bicyclo[7.3.1]- and Bicyclo[8.3.1]phosphates.

Science.gov (United States)

Markley, Jana L; Maitra, Soma; Hanson, Paul R

2016-02-05

A phosphate tether-mediated ring-closing metathesis (RCM) study to the synthesis of Z-configured, P-stereogenic bicyclo[7.3.1]- and bicyclo[8.3.1]phosphates is reported. Investigations suggest that C3-substitution, olefin substitution, and proximity of the forming olefin to the bridgehead carbon of the bicyclic affect the efficiency and stereochemical outcome of the RCM event. This study demonstrates the utility of phosphate tether-mediated desymmetrization of C2-symmetric, 1,3-anti-diol-containing dienes in the generation of macrocyclic phosphates with potential synthetic and biological utility.

Ultrasound-assisted self-metathesis reactions of monounsaturated fatty acids

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Elmkaddem Mohammed Kamal

2016-09-01

Full Text Available An efficient protocol for the self-metathesis of oleic acid, using ruthenium catalysts is described. The self-metathesis reaction under ultrasonic activation allows the conversion of monoenic fatty acids such as oleic acid, elaidic acid and erucic acid into diacids and olefins with very short reaction times in the presence of Grubbs ruthenium catalysts. These yields and selectivity towards the desired products are influenced by the nature of solvents. This study demonstrated that metathesis reaction carried out in DCM or 1-butanol showed promising results, since it produced a variety of products, like n-alkenes and diacids with good yields (45–75% and high selectivities (75–95%.

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

Science.gov (United States)

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

2018-01-09

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

The metathesis of alkynes

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H. C. M. Vosloo

1991-07-01

Full Text Available The alkyne metathesis reaction is a direct result of the known and intensively studied alkene or olefin metathesis reaction. Unfortunately this reaction was never studied as intensively as the alkene metathesis reaction, mainly because of a lack of active catalytic systems. In the alkyn metathesis reaction the carbon-carbon triple bonds are broken and rearranged to give a redistribution of alkylidyne groups.

Synthetic studies on taxanes: A domino-enyne metathesis/Diels ...

Indian Academy of Sciences (India)

Abstract. A domino enyne cross-metathesis/intramolecular Diels-Alder reaction has been successfully used to synthesize a bicyclo[5.3.1] undecene, corresponding to AB-ring of taxol without the gem dimethyl group.

Asymmetric Catalytic Aza-Diels-Alder/Ring-Closing Cascade Reaction Forming Bicyclic Azaheterocycles by Trienamine Catalysis.

Science.gov (United States)

Li, Yang; Barløse, Casper; Jørgensen, Julie; Carlsen, Bjørn Dreiø; Jørgensen, Karl Anker

2017-01-01

An asymmetric catalytic aza-Diels-Alder/ring-closing cascade reaction between acylhydrazones and in situ formed trienamines is presented. The reaction proceeds through a formal aza-Diels-Alder cycloaddition, followed by a ring-closing reaction forming the hemiaminal ring leading to chiral bicyclic azaheterocycles in moderate to good yield (up to 71 %), good enantio- (up to 92 % ee) and diastereoselectivity (up to >20:1 d.r.). Furthermore, transformations are presented to show the potential application of the formed product. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Exploiting Confinement Effects to Tune Selectivity in Cyclooctane Metathesis

KAUST Repository

Pump, Eva

2017-08-24

The mechanism of cyclooctane metathesis using confinement effect strategies in mesoporous silica nanoparticles (MSNs) is discussed by catalytic experiments and density functional theory (DFT) calculations. WMe6 was immobilized inside the pores of a series of MSNs having the same structure but different pore diameters (60, 30 and 25 Å). Experiments in cyclooctane metathesis suggest that confinement effects observed in smaller pores (30 and 25 Å) improve selectivity towards the dimeric cyclohexadecane. In contrast, in larger pores (60 Å) a broad product distribution dominated by ring contracted cycloalkanes was found. The catalytic cycle and potential side reactions occurring at [(≡SiO-)WMe5] were examined with DFT calculations. Analysis of the geometries for the key reaction intermediates allowed to rationalize the impact of a confined environment on the enhanced selectivity towards the dimeric product in smaller pores, while in large pores the ring contracted products are favored.

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

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Guzmán Pablo E.

2016-03-01

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

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

KAUST Repository

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

2016-01-01

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

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

KAUST Repository

Mugemana, Clement

2016-03-22

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

Synthesis of interlocked molecules by olefin metathesis

Science.gov (United States)

Clark, Paul Gregory

A large body of work in the Grubbs group has focused on the development of functional-group tolerant ruthenium alkylidene catalysts that perform a number of olefin metathesis reactions. These catalysts have seen application in a wide range of fields, including classic total synthesis as well as polymer and materials chemistry. One particular family of compounds, interlocked molecules, has benefitted greatly from these advances in catalyst stability and activity. This thesis describes several elusive and challenging interlocked architectures whose syntheses have been realized through the utilization of different types of ruthenium-catalyzed olefin metathesis reactions. Ring-closing olefin metathesis has enabled the synthesis of a [c2]daisy-chain dimer with the ammonium binding site near the cap of the dimer. A deprotonated DCD possessing such a structural attribute will more forcefully seek to restore coordinating interactions upon reprotonation, enhancing its utility as a synthetic molecular actuator. Dimer functionalization facilitated incorporation into linear polymers, with a 48% size increase of an unbound, extended analogue of the polymer demonstrating slippage of the dimer units. Ongoing work is directed at further materials studies, in particular, exploring the synthesis of macroscopic networks containing the DCD units and analyzing the correlation between molecular-scale extension-contraction manipulations and resulting macro-scale changes. A "clipping" approach to a polycatenated cyclic polymer, a structure that resembles a molecular "charm bracelet", has been described. The use of ring-opening metathesis polymerization of a carbamate monomer in the presence of a chain transfer agent allowed for the synthesis of a linear polymer that was subsequently functionalized and cyclized to the corresponding cyclic analogue. This cyclic polymer was characterized through a variety of techniques, and subjected to further functionalization reactions, affording a cyclic

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

KAUST Repository

Zhang, Hefeng; Gnanou, Yves; Hadjichristidis, Nikolaos

2014-01-01

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

Synthesis of 7-Deoxypancratistatin from Carbohydrates by the Use of Olefin Metathesis

DEFF Research Database (Denmark)

Håkansson, Anders Eckart; Palmelund, Anders; Holm, H.

2006-01-01

from D-xylose and piperonal. The former is converted into ribofuranoside 28, which is coupled with bromide 7 in the presence of zinc, and this is followed by ring-closing olefin metathesis. Subsequent Overman rearrangement, dihydroxylation, and deprotection then affords the natural product....

Understanding the Hydro-metathesis Reaction of 1-decene by Using Well-defined Silica Supported W, Mo, Ta Carbene/Carbyne Complexes

KAUST Repository

Saidi, Aya

2017-12-21

Direct conversion of 1-decene to petroleum range alkanes was obtained using hydro-metathesis reaction. To understand this reaction we employed three different well-defined single site catalysts precursors; [(≡Si-O-)W(CH3)5] 1, [(≡Si-O-)Mo(≡CtBu)(CH2tBu)2] 2 and [(≡Si-O)Ta(=CHtBu)(CH2tBu)2] 3. We witnessed that in our conditions olefin metathesis/isomerization of 1-decene occurs much faster followed by reduction of the newly formed olefins rather than reduction of the 1-decene to decane, followed by metathesis of decane. We found that Mo-based catalyst favors 2+2 cycloaddition of 1-decene forming metallocarbene, followed by reduction of the newly formed olefins to alkanes. However, in the case of W and Ta-based catalysts, a rapid isomerization (migration) of the double bond followed by olefin metathesis and reduction of the newly formed olefins were observed. We witnessed that silica supported W catalyst precursor 1 and Mo catalyst precursor 2 are better catalysts for hydro-metathesis reaction with TONs of 818 and 808 than Ta-based catalyst 3 (TON of 334). This comparison of the catalysts provides us a better understanding that, if a catalyst is efficient in olefin metathesis reaction it would be a better catalyst for hydro-metathesis reaction.

Synthetic Strategies for Converting Carbohydrates into Carbocycles by the Use of Olefin Metathesis

DEFF Research Database (Denmark)

Madsen, Robert

2007-01-01

This microreview covers recent advances in the use of ring-closing metathesis for the synthesis of carbocycles from carbohydrates. Various strategies for the synthesis of a,w-dienes from carbohydrates are presented, which give rise to a large variety of dienes with different stereochemistry, prot...

Hydro-Metathesis of Long-Chain Olefin (1-decene) using Well-Defined Silica-Supported Tungsten (VI), Molybdenum (VI) and Tantalum (V) Catalysts

KAUST Repository

Saidi, Aya

2016-11-01

Nowadays, catalysis lies at the heart of economy growth mainly in the petroleum industry. Catalysis can offer real and potential solutions to the current challenges for a long-term sustainable energy, green chemistry, and environmental protection. In this context, one of the most important and future prosperity promising catalytic applications in the petrochemical field is hydrocarbons metathesis; it consists on the conversion of both renewable and non-petroleum fossil carbon sources to transportation fuels. Olefin metathesis has become one of the standard methodologies for constructing C-C bonds in many organic transformation reactions. This owed to the numerous types of metathesis reactions that have been developed, for example, enyne, ring-opening and closing, self and cross metathesis, etc. But the one step conversion of olefin to alkanes has not been studied much. Recently, only one such a work has been published for the hydro-metathesis of propylene by tantalum hydride supported on KCC-1 in dynamic reactor. With this knowledge, we thought to study the hydro-metathesis using liquid olefin (1-decene). Another aspect of using 1-decene comes from our previous experience on metathesis of n-decane where the first step is the conversion of decane to 1-decene and subsequently to different chain length alkanes with W-alkyl/alkylidene catalyst. In this way, it would be easy for us to use different catalysts and compare them with parent catalyst concerning TON. We found 100% conversion with TON of 1010 using supported WMe6 onto SiO2-700 [(≡Si-O-)WMe5] against the previous results for n-decane showing 20% conversion and TON of 153. In this work, we disclose the hydro-metathesis reaction of 1-decene using well-defined silica supported W(VI), Mo(VI) and Ta(V) alkyl catalysts in batch reactor condition. This work is divided into three major sections; first chapter contains an introduction to the field of catalysis and surface organometallic chemistry. In second chapter

Alkene Metathesis Catalysis: A Key for Transformations of Unsaturated Plant Oils and Renewable Derivatives

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Dixneuf Pierre H.

2016-03-01

Full Text Available This account presents the importance of ruthenium-catalysed alkene cross-metathesis for the catalytic transformations of biomass derivatives into useful intermediates, especially those developed by the authors in the Rennes (France catalysis team in cooperation with chemical industry. The cross-metathesis of a variety of functional alkenes arising from plant oils, with acrylonitrile and fumaronitrile and followed by catalytic tandem hydrogenation, will be shown to afford linear amino acid derivatives, the precursors of polyamides. The exploration of cross-metathesis of bio-sourced unsaturated nitriles with acrylate with further catalytic hydrogenation has led to offer an excellent route to α,ω-amino acid derivatives. That of fatty aldehydes has led to bifunctional long chain aldehydes and saturated diols. Two ways of access to functional dienes by ruthenium-catalyzed ene-yne cross-metathesis of plant oil alkene derivatives with alkynes and by cross-metathesis of bio-sourced alkenes with allylic chloride followed by catalytic dehydrohalogenation, are reported. Ricinoleate derivatives offer a direct access to chiral dihydropyrans and tetrahydropyrans via ring closing metathesis. Cross-metathesis giving value to terpenes and eugenol for the straightforward synthesis of artificial terpenes and functional eugenol derivatives without C=C bond isomerization are described.

Tandem ring-closing metathesis/isomerization reactions for the total synthesis of violacein

DEFF Research Database (Denmark)

Petersen, Mette Terp; Nielsen, Thomas Eiland

2013-01-01

A series of 5-substituted 2-pyrrolidinones was synthesized through a one-pot ruthenium alkylidene-catalyzed tandem RCM/isomerization/nucleophilic addition sequence. The intermediates resulting from RCM/isomerization showed reactivity toward electrophiles in aldol condensation reactions which...

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

Directory of Open Access Journals (Sweden)

Shawna L. Balof

2015-10-01

Full Text Available Three new ruthenium alkylidene complexes (PCy3Cl2(H2ITapRu=CHSPh (9, (DMAP2Cl2(H2ITapRu=CHPh (11 and (DMAP2Cl2(H2ITapRu=CHSPh (12 have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’-dimethyl-4’-dimethylaminophenyl-4,5-dihydroimidazol-2-ylidene. Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP and ring closing metathesis (RCM reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA, however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD and mixtures of DCPD with cyclooctene (COE in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments stayed <2%. This represents an unprecedented efficiency in emulsion ROMP based on hydrophilic ruthenium alkylidene complexes.

Synthesis of Heavy Fluorous Ruthenium Metathesis Catalysts Using the Stereoselective Addition of Polyfluoroalkyllithium to Sterically Hindered Diimines

Czech Academy of Sciences Publication Activity Database

Hošek, J.; Rybáčková, M.; Čejka, J.; Cvačka, Josef; Kvíčala, J.

2015-01-01

Roč. 34, č. 13 (2015), s. 3327 -3334 ISSN 0276-7333 Institutional support: RVO:61388963 Keywords : ring-closing metathesis * form tetrasubstituted olefins * N-heterocyclic carbene Subject RIV: CC - Organic Chemistry Impact factor: 4.186, year: 2015

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

Science.gov (United States)

Kilbinger, Andreas F M

2012-01-01

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

The olefin metathesis reaction: reorganization and cyclization of organic compounds

International Nuclear Information System (INIS)

Frederico, Daniel; Brocksom, Ursula; Brocksom, Timothy John

2005-01-01

The olefin metathesis reaction allows the exchange of complex alkyl units between two olefins, with the formation of a new olefinic link and a sub-product olefin usually ethylene. This reaction has found extensive application in the last ten years with the development of the Grubbs and Schrock catalysts, in total synthesis of complex organic molecules, as opposed to the very important use in the petrochemical industry with relatively simple molecules. This review intends to trace a historical and mechanistic pathway from industry to academy, before illustrating the more recent advances. (author)

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

KAUST Repository

Wappel, Julia

2016-01-28

A straightforward synthesis utilizing the ring-opening metathesis polymerization (ROMP) reaction is described for acid-triggered N,O-chelating ruthenium-based pre-catalysts bearing one or two 8-quinolinolate ligands. The innovative pre-catalysts were tested regarding their behavior in ROMP and especially for their use in the synthesis of poly(dicyclopentadiene) (pDCPD). Bearing either the common phosphine leaving ligand in the first and second Grubbs olefin metathesis catalysts, or the Ru–O bond cleavage for the next Hoveyda-type catalysts, this work is a step forward towards the control of polymer functionalization and living or switchable polymerizations.

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

KAUST Repository

Wappel, Julia; Fischer, Roland C; Cavallo, Luigi; Slugovc, Christian; Poater, Albert

2016-01-01

A straightforward synthesis utilizing the ring-opening metathesis polymerization (ROMP) reaction is described for acid-triggered N,O-chelating ruthenium-based pre-catalysts bearing one or two 8-quinolinolate ligands. The innovative pre-catalysts were tested regarding their behavior in ROMP and especially for their use in the synthesis of poly(dicyclopentadiene) (pDCPD). Bearing either the common phosphine leaving ligand in the first and second Grubbs olefin metathesis catalysts, or the Ru–O bond cleavage for the next Hoveyda-type catalysts, this work is a step forward towards the control of polymer functionalization and living or switchable polymerizations.

Rapid synthesis of graphitic carbon nitride powders by metathesis reaction between CaCN2 and C2Cl6

International Nuclear Information System (INIS)

Pang Linlin; Bi Jianqiang; Bai Yujun; Qi Yongxin; Zhu Huiling; Wang Chengguo; Wu Jiwei; Lu Chengwei

2008-01-01

Carbon nitride powders were rapidly synthesized at low temperature via the chemical metathesis reaction between CaCN 2 and C 2 Cl 6 . X-ray diffraction results confirm the formation of crystalline graphitic carbon nitride. Besides the dominant morphology of nanoparticles, flakes, nanorods, hollow and solid spheres can be observed by transmission electron microscopy. The absorption peaks of C-N, C=N and s-triazine rings, as well as the absence of C≡N peak in the infrared spectra, further verify the formation of graphite-like sp 2 -bonded structure with planar networks. Elemental analysis gives an atomic ratio of N/C around 0.3. X-ray photoelectron spectra exhibit the existence of chemical bonding between C and N

Cationic Tungsten(VI) Penta-Methyl Complex: Synthesis, Characterization and its Application in Olefin Metathesis Reaction

KAUST Repository

Dey, Raju; Samantaray, Manoja; Callens, Emmanuel; Hamieh, Ali Imad Ali; Emwas, Abdul-Hamid M.; Abou-Hamad, Edy; Kavitake, Santosh Giridhar; Basset, Jean-Marie

2016-01-01

Tungsten-hexa-methyl readily reacts with B(C6F5)3 in dichloromethane and generates the corresponding well-defined cationic tungsten-penta-methyl complex which was identified precisely by 1H NMR, 13C NMR, 1H-13C NMR correlation spectroscopy. Unlike WMe6, this cationic complex has low energy barrier to form tungsten carbene intermediate, which was further supported by the fact that WMe6 alone has no activity in olefin metathesis reaction whereas the cationic complex shows catalytic activity for self-metathesis of 1-octene.

Cationic Tungsten(VI) Penta-Methyl Complex: Synthesis, Characterization and its Application in Olefin Metathesis Reaction

KAUST Repository

Dey, Raju

2016-04-13

Tungsten-hexa-methyl readily reacts with B(C6F5)3 in dichloromethane and generates the corresponding well-defined cationic tungsten-penta-methyl complex which was identified precisely by 1H NMR, 13C NMR, 1H-13C NMR correlation spectroscopy. Unlike WMe6, this cationic complex has low energy barrier to form tungsten carbene intermediate, which was further supported by the fact that WMe6 alone has no activity in olefin metathesis reaction whereas the cationic complex shows catalytic activity for self-metathesis of 1-octene.

Convergent synthesis of the HIJKLM ring system of ciguatoxin CTX3C.

Science.gov (United States)

Takamura, Hiroyoshi; Nishiuma, Naoki; Abe, Takashi; Kadota, Isao

2011-09-02

The HIJKLM ring system of ciguatoxin CTX3C was synthesized in a convergent manner. The key steps were a conjugate addition/alkylation sequence, spiroacetalization, intramolecular allylation, ring-closing metathesis, and hydrogenation to form the 36-α-methyl substituent.

The activation mechanism of Fe-based olefin metathesis catalysts

KAUST Repository

Poater, Albert; Pump, Eva; Vummaleti, Sai V. C.; Cavallo, Luigi

2014-01-01

Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ∼2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. © 2014 Elsevier B.V.

The activation mechanism of Fe-based olefin metathesis catalysts

KAUST Repository

Poater, Albert

2014-08-01

Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ∼2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. © 2014 Elsevier B.V.

Metathesis Polymerization Reactions Induced by the Bimetallic Complex (Ph4P2[W2(μ-Br3Br6

Directory of Open Access Journals (Sweden)

Despoina Chriti

2015-12-01

Full Text Available The reactivity of the bimetallic complex (Ph4P2[W2(μ-Br3Br6] ({W 2.5 W}7+, a′2e3 towards ring opening metathesis polymerization (ROMP of norbornene (NBE and some of its derivatives, as well as the mechanistically related metathesis polymerization of phenylacetylene (PA, is presented. Our results show that addition of a silver salt (AgBF4 is necessary for the activation of the ditungsten complex. Polymerization of PA proceeds smoothly in tetrahydrofuran (THF producing polyphenylacetylene (PPA in high yields. On the other hand, the ROMP of NBE and its derivatives is more efficient in CH2Cl2, providing high yields of polymers. 13C Cross Polarization Magic Angle Spinning (CPMAS spectra of insoluble polynorbornadiene (PNBD and polydicyclopentadiene (PDCPD revealed the operation of two mechanisms (metathetic and radical for cross-linking, with the metathesis pathway prevailing.

Synthesis of anti-tumour phosphatidylinositol analogues from glucose by the use of ring-closing olefin metathesis

DEFF Research Database (Denmark)

Andresen, Thomas Lars; Skytte, Dorthe M.; Madsen, Robert

2004-01-01

A divergent strategy is described for synthesis of the novel phosphatidylinositols 1-3. The synthetic approach commences from benzyl-protected methyl 6-iodo-6-deoxy-a-D-glucopyranoside, which undergoes zinc-mediated reductive fragmentation followed by vinyl Grignard addition and ring-closing meta...

Alkane Metathesis

KAUST Repository

Basset, Jean-Marie

2015-03-29

Catalytic activation of alkanes which directly transforms light alkanes into higher homologs is a major area in organometallic chemistry and petrochemical chemistry. This transformation is a chemical challenge considering the inertness of the sp3 carbon-hydrogen bond. It is generally accepted that this catalytic process involves the formation of olefins. This reaction is defined as alkane metathesis. To date, two catalytic systems of alkane metathesis exist: (i) a single catalytic system prepared by surface organometallic chemistry, acting as multifunctional-supported catalyst which transforms any alkanes into a mixture of their lower and higher homologs and (ii) the other catalytic systems employing a tandem strategy with two different metals, one metal for alkane (de)hydrogenation and another for olefin metathesis in which the activity of these catalysts is essentially driven by the performance of the (de)hydrogenation steps. In this book chapter, we would focus on the evolution of these two classes of catalysts by looking at their specific reactivity of the catalysts towards alkanes, comparing their performances and studying the mechanism.

Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes

DEFF Research Database (Denmark)

Poulsen, Carina Storm; Madsen, Robert

2003-01-01

Enyne metathesis combines an alkene and an alkyne into a 1,3-diene. The first enyne metathesis reaction catalyzed by a ruthenium carbene complex was reported in 1994. This review covers the advances in this transformation during the last eight years with particular emphasis on methodology...

Short syntheses of enantiopure calystegine B-2, B-3, and B-4

DEFF Research Database (Denmark)

Skaanderup, Philip Robert; Madsen, Robert

2001-01-01

Calystegine B-2 B-3, and B-4 have been prepared in 5 steps from the benzyl protected methyl 6-iodoglycopyranosides of glucose, galactose and mannose, respectively, by using a zinc-mediated domino reaction followed by ring-closing olefin metathesis as the key steps.......Calystegine B-2 B-3, and B-4 have been prepared in 5 steps from the benzyl protected methyl 6-iodoglycopyranosides of glucose, galactose and mannose, respectively, by using a zinc-mediated domino reaction followed by ring-closing olefin metathesis as the key steps....

Low-temperature synthesis of actinide tetraborides by solid-state metathesis reactions

Science.gov (United States)

Lupinetti, Anthony J [Los Alamos, NM; Garcia, Eduardo [Los Alamos, NM; Abney, Kent D [Los Alamos, NM

2004-12-14

The synthesis of actinide tetraborides including uranium tetraboride (UB.sub.4), plutonium tetraboride (PuB.sub.4) and thorium tetraboride (ThB.sub.4) by a solid-state metathesis reaction are demonstrated. The present method significantly lowers the temperature required to .ltoreq.850.degree. C. As an example, when UCl.sub.4 is reacted with an excess of MgB.sub.2, at 850.degree. C., crystalline UB.sub.4 is formed. Powder X-ray diffraction and ICP-AES data support the reduction of UCl.sub.3 as the initial step in the reaction. The UB.sub.4 product is purified by washing water and drying.

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-10-15

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

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

Science.gov (United States)

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

2016-04-01

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

Well-defined silica supported bipodal molybdenum oxo alkyl complexes: a model of the active sites of industrial olefin metathesis catalysts

KAUST Repository

Merle, Nicolas

2017-09-25

A well-defined, silica-supported molybdenum oxo alkyl species, ([triple bond, length as m-dash]SiO-)2Mo([double bond, length as m-dash]O)(CH2tBu)2, was prepared by the selective grafting of Mo([double bond, length as m-dash]O)(CH2tBu)3Cl onto a silica partially dehydroxylated at 200 °C using a rigorous surface organometallic chemistry approach. The immobilized bipodal surface species, partly resembling the active species of industrial MoO3/SiO2 olefin metathesis catalysts, exhibited excellent functional group tolerance in conjunction with its high activity in homocoupling, self and ring closing olefin metathesis.

Well-defined silica supported bipodal molybdenum oxo alkyl complexes: a model of the active sites of industrial olefin metathesis catalysts

KAUST Repository

Merle, Nicolas; Le Qué mé ner, Fré dé ric; Barman, Samir; Samantaray, Manoja; Szeto, Kai C.; De Mallmann, Aimery; Taoufik, Mostafa; Basset, Jean-Marie

2017-01-01

A well-defined, silica-supported molybdenum oxo alkyl species, ([triple bond, length as m-dash]SiO-)2Mo([double bond, length as m-dash]O)(CH2tBu)2, was prepared by the selective grafting of Mo([double bond, length as m-dash]O)(CH2tBu)3Cl onto a silica partially dehydroxylated at 200 °C using a rigorous surface organometallic chemistry approach. The immobilized bipodal surface species, partly resembling the active species of industrial MoO3/SiO2 olefin metathesis catalysts, exhibited excellent functional group tolerance in conjunction with its high activity in homocoupling, self and ring closing olefin metathesis.

Rapid synthesis of graphitic carbon nitride powders by metathesis reaction between CaCN{sub 2} and C{sub 2}Cl{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Pang Linlin [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan, 250061 (China); Carbon Fiber Engineering Research Center of Shandong Province, Shandong University, Jinan 250061 (China); Bi Jianqiang [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan, 250061 (China); Bai Yujun [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan, 250061 (China) and Carbon Fiber Engineering Research Center of Shandong Province, Shandong University, Jinan 250061 (China)], E-mail: byj97@126.com; Qi Yongxin [Carbon Fiber Engineering Research Center of Shandong Province, Shandong University, Jinan 250061 (China); Zhu Huiling [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan, 250061 (China); Carbon Fiber Engineering Research Center of Shandong Province, Shandong University, Jinan 250061 (China); Wang Chengguo; Wu Jiwei [Carbon Fiber Engineering Research Center of Shandong Province, Shandong University, Jinan 250061 (China); Lu Chengwei [Department of Equipment, Shandong University of Science and Technology, Jinan 250031 (China)

2008-12-20

Carbon nitride powders were rapidly synthesized at low temperature via the chemical metathesis reaction between CaCN{sub 2} and C{sub 2}Cl{sub 6}. X-ray diffraction results confirm the formation of crystalline graphitic carbon nitride. Besides the dominant morphology of nanoparticles, flakes, nanorods, hollow and solid spheres can be observed by transmission electron microscopy. The absorption peaks of C-N, C=N and s-triazine rings, as well as the absence of C{identical_to}N peak in the infrared spectra, further verify the formation of graphite-like sp{sup 2}-bonded structure with planar networks. Elemental analysis gives an atomic ratio of N/C around 0.3. X-ray photoelectron spectra exhibit the existence of chemical bonding between C and N.

Metathesis: A "Change-Your-Partners" Dance

Indian Academy of Sciences (India)

Organic chemistry, the chemistry of carbon compounds, is a fascinating subject. ... In general, a chemical reaction is referred to as 'metathesis' or exchange reaction, if it is of .... pounds (alcohols, ketones, aldehydes, etc.), but is stable for long.

Mo-catalyzed cross-metathesis reaction of propynylferrocene

Czech Academy of Sciences Publication Activity Database

Bobula, T.; Hudlický, J.; Novák, P.; Gyepes, R.; Císařová, I.; Štěpnička, P.; Kotora, Martin

-, č. 25 (2008), s. 3911-3920 ISSN 1434-1948 Grant - others:GA MŠk(CZ) LC06070 Program:LC Institutional research plan: CEZ:AV0Z40550506 Keywords : alkynes * metallocenes * metathesis * electrochemistry * X-ray diffraction Subject RIV: CC - Organic Chemistry Impact factor: 2.694, year: 2008

Understanding the Hydro-metathesis Reaction of 1-decene by Using Well-defined Silica Supported W, Mo, Ta Carbene/Carbyne Complexes

KAUST Repository

Saidi, Aya; Samantaray, Manoja; Tretiakov, Mykyta; Kavitake, Santosh Giridhar; Basset, Jean-Marie

2017-01-01

Direct conversion of 1-decene to petroleum range alkanes was obtained using hydro-metathesis reaction. To understand this reaction we employed three different well-defined single site catalysts precursors; [(≡Si-O-)W(CH3)5] 1, [(≡Si-O-)Mo(≡CtBu)(CH2

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

Directory of Open Access Journals (Sweden)

Thibault E. Schmid

2015-09-01

Full Text Available A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr(picolinateRuCl(indenylidene complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenylimidazolidin-2-ylidene demonstrated excellent latent behaviour in ring closing metathesis (RCM reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM and enyne metathesis reactions.

Influence of alkene substituent in dictating the reaction course to ...

Indian Academy of Sciences (India)

RITABRATA DATTA

2017-11-06

Nov 6, 2017 ... form carbocycles or oxacycles during ring closing metathesis of ... Electronic supplementary material: The online version of this article (https:// doi.org/ ...... tific and Industrial Research for a Senior Research Fellowship.

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

Science.gov (United States)

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

2017-05-05

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

Nicholas reactions in the construction of cyclohepta[de]naphthalenes and cyclohepta[de]naphthalenones. The total synthesis of microstegiol.

Science.gov (United States)

Taj, Rafiq A; Green, James R

2010-12-03

The application of the Nicholas reaction chemistry of 2,7-dioxygenated naphthalenes in the synthesis of cyclohepta[de]napthalenes and in the synthesis of (±)-microstegiol (1) is presented. The substitution profile of Nicholas monosubstitution (predominantly C-1) and disubstitution reactions (predominantly 1,6-) on 2,7-dioxygenated napthalenes is reported. Application of a 1,8-dicondensation product and selected C-1 monocondensation products to the construction of cyclohepta[de]naphthalenes by way of ring closing metathesis and intramolecular Friedel-Crafts reactions, respectively, is described. Deprotection of the C-7 oxygen function to the corresponding naphthol allows tautomerization to cyclohepta[de]naphthalene-1-ones upon seven-membered-ring closure in most cases, and replacement of the C-2 oxygen function in the naphthalene by a methyl group ultimately allows the synthesis of (±)-microstegiol.

Rapid synthesis of the A-E fragment of ciguatoxin CTX3C.

Science.gov (United States)

Clark, J Stephen; Conroy, Joanne; Blake, Alexander J

2007-05-24

The A-E fragment of the marine natural product CTX3C has been prepared in an efficient manner by using a strategy in which two-directional and iterative ring-closing metathesis (RCM) reactions were employed for ring construction.

Revisiting the metathesis of 13C-monolabeled ethane

KAUST Repository

Maury, Olivier; Lefort, Laurent; Vidal, Vé ronique; Thivolle-Cazat, Jean; Basset, Jean-Marie

2010-01-01

The metathesis of 13C-monolabeled ethane leads to the parallel occurrence of degenerate and productive reactions, affording the statistical distribution of the various product isotopomers, which can be rationalized in terms of a mechanistic reaction

Comparing Ru and Fe-catalyzed olefin metathesis

KAUST Repository

Poater, Albert; Chaitanya Vummaleti, Sai Vikrama; Pump, Eva; Cavallo, Luigi

2014-01-01

Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (≈ 2 kcal mol -1) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Fe-based catalysts have the potential to be very effective olefin metathesis catalysts. This journal is © the Partner Organisations 2014.

Iron based superconductors and related compounds synthesized by solid state metathesis and high temperature reactions

International Nuclear Information System (INIS)

Frankovsky, Rainer

2013-01-01

The results of this thesis can be divided into three major topics, which can also be seen as different approaches of solid state chemistry to reveal interesting features of known and unknown compounds and to develop alternative synthesis routes. Firstly, known compounds with related structural motifs to the superconducting iron-arsenides were investigated regarding their structural and physical properties. In case of La 3 Pd 4 Ge 4 the influence of Fe doping on the properties was studied, whereas in the series ZrMAs (M=Ti,V) the physical properties have not yet been reported at all and were investigated for the first time. Secondly, an alternative synthesis route has been developed for the synthesis of superconducting LaFeAsO 1-x F x . This solid state metathesis reaction distinctly increased the quality of the samples compared to conventionally prepared products. Furthermore, the reaction pathway was investigated and clarified, which helps to understand the processes during high temperature solid state metathesis reactions in general. Thirdly, this alternative synthesis route was expanded to other systems and new compounds like co-substituted LaFe 1-x Mn x AsO 1-y F y were prepared and thoroughly investigated. This led to a complex study of the interplay of magnetism, electronic and structural conditions and the occurrence of superconducting properties. The investigation and understanding of such complex coherences will probably be decisive for the further understanding of the superconducting mechanism in iron based superconductors.

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

Science.gov (United States)

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

2018-01-15

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

Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

Science.gov (United States)

Schrodi, Yann [Agoura Hills, CA

2011-11-29

This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

Well-defined silica-supported zirconium–imido complexes mediated heterogeneous imine metathesis

KAUST Repository

Hamzaoui, Bilel

2016-02-15

Upon prolonged thermal exposure under vacuum, a well-defined single-site surface species [(≡Si-O-)Zr(NEt2)3] (1) evolves into an ethylimido complex [(≡Si-O-)Zr(=NEt)NEt2] (2). Reactions of 2 with an imine substrate result in imido/imine (=NRi, R: Et, Ph) exchange (metathesis) with the formation of [(≡Si-O-)Zr(=NPh)NEt2] (3). Compounds 2 and 3 effectively catalyze imine/imine cross-metathesis and are thus considered as the first heterogeneous catalysts active for imine metathesis. © The Royal Society of Chemistry 2016.

Well-defined silica-supported zirconium–imido complexes mediated heterogeneous imine metathesis

KAUST Repository

Hamzaoui, Bilel; Pelletier, Jeremie; Abou-Hamad, Edy; Basset, Jean-Marie

2016-01-01

Upon prolonged thermal exposure under vacuum, a well-defined single-site surface species [(≡Si-O-)Zr(NEt2)3] (1) evolves into an ethylimido complex [(≡Si-O-)Zr(=NEt)NEt2] (2). Reactions of 2 with an imine substrate result in imido/imine (=NRi, R: Et, Ph) exchange (metathesis) with the formation of [(≡Si-O-)Zr(=NPh)NEt2] (3). Compounds 2 and 3 effectively catalyze imine/imine cross-metathesis and are thus considered as the first heterogeneous catalysts active for imine metathesis. © The Royal Society of Chemistry 2016.

Revisiting the metathesis of 13C-monolabeled ethane

KAUST Repository

Maury, Olivier

2010-12-13

The metathesis of 13C-monolabeled ethane leads to the parallel occurrence of degenerate and productive reactions, affording the statistical distribution of the various product isotopomers, which can be rationalized in terms of a mechanistic reaction scheme combining both processes. © 2010 American Chemical Society.

SOMC-Designed Silica Supported Tungsten Oxo Imidazolin-2-iminato Methyl Precatalyst for Olefin Metathesis Reactions

KAUST Repository

Qureshi, Ziyauddin

2017-01-05

Synthesis, structure, and olefin metathesis activity of a surface complex [(≡Si-O-)W(═O)(CH3)2-ImDippN] (4) (ImDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) supported on silica by a surface organometallic chemistry (SOMC) approach are reported. The reaction of N-silylated 2-iminoimidazoline with tungsten(VI) oxytetrachloride generated the tungsten oxo imidazolin-2-iminato chloride complex [ImDippNW(═O)Cl3] (2). This was grafted on partially dehydroxylated silica pretreated at 700 °C (SiO2-700) to afford a well-defined monopodal surface complex [(≡Si-O-)W(═O)Cl2-ImDippN] (3). 3 underwent alkylation by ZnMe2 to produce [(≡Si-O-)W(═O)(CH3)2-ImDippN] (4). The alkylated surface complex was thoroughly characterized by solid-state NMR, elemental microanalysis, Raman, FT-IR spectroscopies, and XAS analysis. 4 proved to be an active precatalyst for self-metathesis of terminal olefins such as propylene and 1-hexene.

SOMC-Designed Silica Supported Tungsten Oxo Imidazolin-2-iminato Methyl Precatalyst for Olefin Metathesis Reactions

KAUST Repository

Qureshi, Ziyauddin; Hamieh, Ali Imad Ali; Barman, Samir; Maity, Niladri; Samantaray, Manoja; Ould-Chikh, Samy; Abou-Hamad, Edy; Falivene, Laura; D’ Elia, Valerio; Rothenberger, Alexander; Llorens, Isabelle; Hazemann, Jean-Louis; Basset, Jean-Marie

2017-01-01

Synthesis, structure, and olefin metathesis activity of a surface complex [(≡Si-O-)W(═O)(CH3)2-ImDippN] (4) (ImDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) supported on silica by a surface organometallic chemistry (SOMC) approach are reported. The reaction of N-silylated 2-iminoimidazoline with tungsten(VI) oxytetrachloride generated the tungsten oxo imidazolin-2-iminato chloride complex [ImDippNW(═O)Cl3] (2). This was grafted on partially dehydroxylated silica pretreated at 700 °C (SiO2-700) to afford a well-defined monopodal surface complex [(≡Si-O-)W(═O)Cl2-ImDippN] (3). 3 underwent alkylation by ZnMe2 to produce [(≡Si-O-)W(═O)(CH3)2-ImDippN] (4). The alkylated surface complex was thoroughly characterized by solid-state NMR, elemental microanalysis, Raman, FT-IR spectroscopies, and XAS analysis. 4 proved to be an active precatalyst for self-metathesis of terminal olefins such as propylene and 1-hexene.

A latent ruthenium based olefin metathesis catalyst with a sterically demanding NHC ligand

KAUST Repository

Leitgeb, Anita; Abbas, Mudassar E.; Fischer, Roland C.; Poater, Albert; Cavallo, Luigi; Slugovc, Christian

2012-01-01

An olefin metathesis catalyst featuring a SIPr NHC and an ester chelating carbene ligand is introduced. In contrast to its previously published SIMes analogue, only the trans dichloro configurated isomer was obtained. The two counterparts are tested in various olefin metathesis reactions, revealing a striking superiority of the new complex in the cross metathesis of olefins with methyl vinyl ketone allowing for full conversion with only 500 ppm catalyst loading. © 2012 The Royal Society of Chemistry.

Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: Structure and application as latent catalyst in olefin metathesis

KAUST Repository

Rouen, Mathieu

2014-09-11

An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions.

Metallacyclobutane substitution and its effect on alkene metathesis for propylene production over W-H/Al2O3: Case of isobutene/2-butene cross-metathesis

KAUST Repository

Szeto, Kaï Chung; Mazoyer, Etienne; Merle, Nicolas; Norsic, Sé bastien; Basset, Jean-Marie; Nicholas, Christopher P.; Taoufik, Mostafa

2013-01-01

Cross metathesis between 2-butenes and isobutene yielding the valuable products propylene and 2-methyl-2-butene has been investigated at low pressure and temperature using WH3/Al2O3, a highly active and selective catalyst. Two parallel catalytic cycles for this reaction have been proposed where the cycle involving the less sterically hindered tungstacyclobutane intermediates is most likely favored. Moreover, it has been found that the arrangement of substituents on the least thermodynamically favored tungstacyclobutane governs the conversion rate of the cross metathesis reaction for propylene production from butenes and/or ethylene. © 2013 American Chemical Society.

Metallacyclobutane substitution and its effect on alkene metathesis for propylene production over W-H/Al2O3: Case of isobutene/2-butene cross-metathesis

KAUST Repository

Szeto, Kaï Chung

2013-09-06

Cross metathesis between 2-butenes and isobutene yielding the valuable products propylene and 2-methyl-2-butene has been investigated at low pressure and temperature using WH3/Al2O3, a highly active and selective catalyst. Two parallel catalytic cycles for this reaction have been proposed where the cycle involving the less sterically hindered tungstacyclobutane intermediates is most likely favored. Moreover, it has been found that the arrangement of substituents on the least thermodynamically favored tungstacyclobutane governs the conversion rate of the cross metathesis reaction for propylene production from butenes and/or ethylene. © 2013 American Chemical Society.

Well-Defined Silica Grafted Molybdenum Bis(imido) Catalysts for Imine Metathesis Reactions

KAUST Repository

Barman, Samir

2017-04-06

Novel site-isolated tetracoordinated molybdenum complexes possessing bis(imido) ligands, [(≡Si–O)2Mo(═NR)2] (R = t-Bu, 2,6-C6H3-i-Pr2), were immobilized on partially dehydroxylated silica (SiO2-200) by a rigorous surface organometallic chemistry protocol. The newly developed materials adorned with bis(imido) functional units, which were previously exploited mainly as spectator ligands on silica-supported olefin metathesis molybdenum catalysts, are found to be efficient heterogeneous catalytic systems for imine cross metathesis under mild conditions.

Well-Defined Silica Grafted Molybdenum Bis(imido) Catalysts for Imine Metathesis Reactions

KAUST Repository

Barman, Samir; Merle, Nicolas; Minenkov, Yury; De Mallmann, Aimery; Samantaray, Manoja; Le Qué mé ner, Fré dé ric; Szeto, Kai C.; Abou-Hamad, Edy; Cavallo, Luigi; Taoufik, Mostafa; Basset, Jean-Marie

2017-01-01

Novel site-isolated tetracoordinated molybdenum complexes possessing bis(imido) ligands, [(≡Si–O)2Mo(═NR)2] (R = t-Bu, 2,6-C6H3-i-Pr2), were immobilized on partially dehydroxylated silica (SiO2-200) by a rigorous surface organometallic chemistry protocol. The newly developed materials adorned with bis(imido) functional units, which were previously exploited mainly as spectator ligands on silica-supported olefin metathesis molybdenum catalysts, are found to be efficient heterogeneous catalytic systems for imine cross metathesis under mild conditions.

South African Journal of Chemistry - Vol 60 (2007)

African Journals Online (AJOL)

The Synthesis of 5-, 6-, 7- and 8-Membered Oxygen-containing Benzo-fused Rings using Alkene Isomerization and Ring-closing Metathesis Reactions · EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT. R Pathak, J Panayides, TD Jeftic, CB de Koning, WAL van Otterlo ...

Synthesis of E- and Z-trisubstituted alkenes by catalytic cross-metathesis

Science.gov (United States)

Nguyen, Thach T.; Koh, Ming Joo; Mann, Tyler J.; Schrock, Richard R.; Hoveyda, Amir H.

2017-12-01

Catalytic cross-metathesis is a central transformation in chemistry, yet corresponding methods for the stereoselective generation of acyclic trisubstituted alkenes in either the E or the Z isomeric forms are not known. The key problems are a lack of chemoselectivity—namely, the preponderance of side reactions involving only the less hindered starting alkene, resulting in homo-metathesis by-products—and the formation of short-lived methylidene complexes. By contrast, in catalytic cross-coupling, substrates are more distinct and homocoupling is less of a problem. Here we show that through cross-metathesis reactions involving E- or Z-trisubstituted alkenes, which are easily prepared from commercially available starting materials by cross-coupling reactions, many desirable and otherwise difficult-to-access linear E- or Z-trisubstituted alkenes can be synthesized efficiently and in exceptional stereoisomeric purity (up to 98 per cent E or 95 per cent Z). The utility of the strategy is demonstrated by the concise stereoselective syntheses of biologically active compounds, such as the antifungal indiacen B and the anti-inflammatory coibacin D.

Synthesis of LaO1-xFxFeAs (x=0-0.15) via solid state metathesis reaction

Science.gov (United States)

Frankovsky, Rainer; Marchuk, Alexey; Pobel, Roman; Johrendt, Dirk

2012-04-01

LaOFeAs and superconducting LaO1-xFxFeAs have been synthesized via salt metathesis reactions and characterized by X-ray powder diffraction and magnetic susceptibility measurements. The process uses LaOCl and NaFeAs as precursors and yielded very pure samples. Superconductivity was confirmed in samples with x=0.05, 0.10 and 0.15 at critical temperatures of 11 K, 26 K and 9 K, respectively. According to temperature-dependent X-ray diffraction data, the reaction pathway is not topotactic in contrast to earlier suggestions.

Tandem cross enyne metathesis (CEYM)-intramolecular Diels-Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds.

Science.gov (United States)

Miró, Javier; Sánchez-Roselló, María; Sanz, Álvaro; Rabasa, Fernando; Del Pozo, Carlos; Fustero, Santos

2015-01-01

A new tandem cross enyne metathesis (CEYM)-intramolecular Diels-Alder reaction (IMDAR) has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM-IMDAR protocols.

The activation mechanism of Ru-indenylidene complexes in olefin metathesis

KAUST Repository

Urbina-Blanco, Cé sar A.; Poater, Albert; Lé bl, Tomá š; Manzini, Simone; Slawin, Alexandra M. Z.; Cavallo, Luigi; Nolan, Steven P.

2013-01-01

Olefin metathesis is a powerful tool for the formation of carbon-carbon double bonds. Several families of well-defined ruthenium (Ru) catalysts have been developed during the past 20 years; however, the reaction mechanism for all such complexes was assumed to be the same. In the present study, the initiation mechanism of Ru-indenylidene complexes was examined and compared with that of benzylidene counterparts. It was discovered that not all indenylidene complexes followed the same mechanism, highlighting the importance of steric and electronic properties of so-called spectator ligands, and that there is no single mechanism for the Ru-based olefin metathesis reaction. The experimental findings are supported quantitatively by DFT calculations. © 2013 American Chemical Society.

The activation mechanism of Ru-indenylidene complexes in olefin metathesis

KAUST Repository

Urbina-Blanco, César A.

2013-05-08

Olefin metathesis is a powerful tool for the formation of carbon-carbon double bonds. Several families of well-defined ruthenium (Ru) catalysts have been developed during the past 20 years; however, the reaction mechanism for all such complexes was assumed to be the same. In the present study, the initiation mechanism of Ru-indenylidene complexes was examined and compared with that of benzylidene counterparts. It was discovered that not all indenylidene complexes followed the same mechanism, highlighting the importance of steric and electronic properties of so-called spectator ligands, and that there is no single mechanism for the Ru-based olefin metathesis reaction. The experimental findings are supported quantitatively by DFT calculations. © 2013 American Chemical Society.

Tandem cross enyne metathesis (CEYM–intramolecular Diels–Alder reaction (IMDAR. An easy entry to linear bicyclic scaffolds

Directory of Open Access Journals (Sweden)

Javier Miró

2015-08-01

Full Text Available A new tandem cross enyne metathesis (CEYM–intramolecular Diels–Alder reaction (IMDAR has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM–IMDAR protocols.

Build/Couple/Pair Strategy Combining the Petasis 3-Component Reaction with Ru-Catalyzed Ring-Closing Metathesis and Isomerization

DEFF Research Database (Denmark)

Ascic, Erhad; Le Quement, Sebastian Thordal; Ishøy, Mette

2012-01-01

A “build/couple/pair” pathway for the systematic synthesis of structurally diverse small molecules is presented. The Petasis 3-component reaction was used to synthesize anti-amino alcohols displaying pairwise reactive combinations of alkene moieties. Upon treatment with a ruthenium alkylidene...

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

Science.gov (United States)

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

2010-01-01

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

Efforts toward rapid construction of the cortistatin A carbocyclic core via enyne-ene metathesis

KAUST Repository

Baumgartner, Corinne; Ma, Sandy; Liu, Qi; Stoltz, Brian M.

2010-01-01

Our efforts toward the construction of the carbocylic core of cortistatin A via an enyne-ene metathesis are disclosed. Interestingly, an attempted S N2 inversion of a secondary mesylate in our five-membered D-ring piece gave a product with retention

Benzoylureas as removable cis amide inducers: synthesis of cyclic amides via ring closing metathesis (RCM).

Science.gov (United States)

Brady, Ryan M; Khakham, Yelena; Lessene, Guillaume; Baell, Jonathan B

2011-02-07

Rapid and high yielding synthesis of medium ring lactams was made possible through the use of a benzoylurea auxiliary that serves to stabilize a cisoid amide conformation, facilitating cyclization. The auxiliary is released after activation under the mild conditions required to deprotect a primary amine, such as acidolysis of a Boc group in the examples given here. This methodology is a promising tool for the synthesis of medium ring lactams, macrocyclic natural products and peptides.

Nucleophilic ring opening reactions of aziridines.

Science.gov (United States)

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

2018-05-04

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

Efficient Homodifunctional Bimolecular Ring-Closure Method for Cyclic Polymers by Combining RAFT and Self-Accelerating Click Reaction.

Science.gov (United States)

Qu, Lin; Sun, Peng; Wu, Ying; Zhang, Ke; Liu, Zhengping

2017-08-01

An efficient metal-free homodifunctional bimolecular ring-closure method is developed for the formation of cyclic polymers by combining reversible addition-fragmentation chain transfer (RAFT) polymerization and self-accelerating click reaction. In this approach, α,ω-homodifunctional linear polymers with azide terminals are prepared by RAFT polymerization and postmodification of polymer chain end groups. By virtue of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DBA) as small linkers, well-defined cyclic polymers are then prepared using the self-accelerating double strain-promoted azide-alkyne click (DSPAAC) reaction to ring-close the azide end-functionalized homodifunctional linear polymer precursors. Due to the self-accelerating property of DSPAAC ring-closing reaction, this novel method eliminates the requirement of equimolar amounts of telechelic polymers and small linkers in traditional bimolecular ring-closure methods. It facilitates this method to efficiently and conveniently produce varied pure cyclic polymers by employing an excess molar amount of DBA small linkers. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metathesis synthesis and characterization of complex metal fluoride ...

Indian Academy of Sciences (India)

Administrator

Sivakumar et al 2004; Mandal and Gopalakrishnan 2005). Although metathesis reactions may initiate spontane- ously .... cal lithography are needed (Sahnoun et al 2005). KMF3 materials with perovskite structures are ... (Knox 1961; Machin et al 1963; Pari et al 1994) and shown in figure 5. The KMF3 compounds are anti-.

The asymmetric Schrock olefin metathesis catalysts. A computational study

NARCIS (Netherlands)

Goumans, T.P.M.; Ehlers, A.W.; Lammertsma, K.

2005-01-01

The mechanism of the transition metal catalyzed olefin metathesis reaction with the Schrock catalyst is investigated with pure (BP86) and hybrid (B3LYP) density functional theory. On the free-energy surface there is no adduct between ethylene and model catalyst (MeO)

Efforts toward rapid construction of the cortistatin A carbocyclic core via enyne-ene metathesis

KAUST Repository

Baumgartner, Corinne

2010-01-01

Our efforts toward the construction of the carbocylic core of cortistatin A via an enyne-ene metathesis are disclosed. Interestingly, an attempted S N2 inversion of a secondary mesylate in our five-membered D-ring piece gave a product with retention of stereochemistry. © 2010 The Royal Society of Chemistry.

Evaluation of an olefin metathesis pre-catalyst with a bulky and electron-rich N-heterocyclic carbene

KAUST Repository

Manzini, Simone

2015-03-01

The commercially-available metathesis pre-catalyst M23 has been evaluated alongside new complex [RuCl2((3-phenyl)indenylidene)(PPh3)(SIPrOMe)] (1), which bears a para-methoxy-substituted N-heterocyclic carbene ligand. Several model metathesis reactions could be conducted using only parts-per-million levels of ruthenium catalyst. The effects of the different NHC ligands on reactivity have been explored.

Evaluation of an olefin metathesis pre-catalyst with a bulky and electron-rich N-heterocyclic carbene

KAUST Repository

Manzini, Simone; Urbina Blanco, Cé sar A.; Nelson, David J.; Poater, Albert; Lebl, Tomas; Meiries, Sé bastien; Slawin, Alexandra M.Z.; Falivene, Laura; Cavallo, Luigi; Nolan, Steven P.

2015-01-01

The commercially-available metathesis pre-catalyst M23 has been evaluated alongside new complex [RuCl2((3-phenyl)indenylidene)(PPh3)(SIPrOMe)] (1), which bears a para-methoxy-substituted N-heterocyclic carbene ligand. Several model metathesis reactions could be conducted using only parts-per-million levels of ruthenium catalyst. The effects of the different NHC ligands on reactivity have been explored.

Recent advances in the development of alkyne metathesis catalysts

Directory of Open Access Journals (Sweden)

Matthias Tamm

2011-01-01

Full Text Available The number of well-defined molybdenum and tungsten alkylidyne complexes that are able to catalyze alkyne metathesis reactions efficiently has been significantly expanded in recent years.The latest developments in this field featuring highly active imidazolin-2-iminato- and silanolate–alkylidyne complexes are outlined in this review.

Preparation and Reaction Chemistry of Novel Silicon-Substituted 1,3-Dienes

Directory of Open Access Journals (Sweden)

Partha P. Choudhury

2015-09-01

Full Text Available 2-Silicon-substituted 1,3-dienes containing non transferrable groups known to promote transmetallation were prepared by Grignard chemistry and enyne metathesis. These dienes participated in one pot metathesis/Diels-Alder reactions in regio- and diastereoselective fashions. Electron-rich alkenes showed the fastest rates in metathesis reactions, and ethylene, a commonly used metathesis promoter slowed enyne metathesis. 2-Pyridyldimethylsilyl and 2-thienyldimethylsilyl substituted Diels-Alder cycloadducts participated in cross-coupling chemistry and the 2-thienyldimethylsilyl substituted cycloadducts underwent cross-coupling under very mild reaction conditions.

Omega-functionalized fatty acids, alcohols, and ethers via olefin metathesis

Science.gov (United States)

Methyl 17-hydroxy stearate was converted to methyl octadec-16-enoate using copper sulfate adsorbed on silica gel. This compound, possessing unsaturation at the opposite end of the chain from the carboxylate, served as a useful substrate for the olefin metathesis reaction. As a result, several fatt...

Selective conversion of butane into liquid hydrocarbon fuels on alkane metathesis catalysts

KAUST Repository

Szeto, Kaï Chung; Hardou, Lucie; Merle, Nicolas; Basset, Jean-Marie; Thivolle-Cazat, Jean; Papaioannou, Charalambos; Taoufik, Mostafa

2012-01-01

We report a selective direct conversion of n-butane into higher molecular weight alkanes (C 5+) by alkane metathesis reaction catalysed by silica-alumina supported tungsten or tantalum hydrides at moderate temperature and pressure. The product

Ruthenium-catalyzed intramolecular metathesis of dienes and its application in the synthesis of bridged and spiro azabicycles

Science.gov (United States)

Kuznetsov, N. Yu; Bubnov, Yu N.

2015-07-01

The review presents a historical excursion into catalytic alkene metathesis, covering the problems of history of the discovery of this process, as well as investigations on the properties, structure and reactivity of the most popular ruthenium catalysts for metathesis, mechanism of their action and decomposition. The main part covers studies devoted to the syntheses of bridged azabicyclic and 1-azaspirocyclic compounds comprising the intramolecular metathesis of dienes as the key step. The formation of a bicyclic skeleton of a series of natural bridged (cocaine, ferruginine, calystegines, and anatoxin-a) and spiro (pinnaic acids, halichlorine, hystrionicotoxin, and cephalotaxine) azabicycles, as well as their analogues and compounds with larger rings is demonstrated. The methods for the synthesis of diene precursors and the conditions for final assembling of the bicyclic compounds are considered in detail. The generalization of the literature data allows one to efficiently carry out the mentioned process taking into account the most important features. The bibliography includes 129 references.

Ruthenium-catalyzed intramolecular metathesis of dienes and its application in the synthesis of bridged and spiro azabicycles

International Nuclear Information System (INIS)

Kuznetsov, N Yu; Bubnov, Yu N

2015-01-01

The review presents a historical excursion into catalytic alkene metathesis, covering the problems of history of the discovery of this process, as well as investigations on the properties, structure and reactivity of the most popular ruthenium catalysts for metathesis, mechanism of their action and decomposition. The main part covers studies devoted to the syntheses of bridged azabicyclic and 1-azaspirocyclic compounds comprising the intramolecular metathesis of dienes as the key step. The formation of a bicyclic skeleton of a series of natural bridged (cocaine, ferruginine, calystegines, and anatoxin-a) and spiro (pinnaic acids, halichlorine, hystrionicotoxin, and cephalotaxine) azabicycles, as well as their analogues and compounds with larger rings is demonstrated. The methods for the synthesis of diene precursors and the conditions for final assembling of the bicyclic compounds are considered in detail. The generalization of the literature data allows one to efficiently carry out the mentioned process taking into account the most important features. The bibliography includes 129 references

THE RINGS OF CHARIKLO UNDER CLOSE ENCOUNTERS WITH THE GIANT PLANETS

Energy Technology Data Exchange (ETDEWEB)

Araujo, R. A. N.; Sfair, R.; Winter, O. C., E-mail: ran.araujo@gmail.com, E-mail: rsfair@feg.unesp.br, E-mail: ocwinter@gmail.com [UNESP - Univ. Estadual Paulista, Grupo de Dinâmica Orbital e Planetologia, CEP 12516-410, Guaratingueta, SP (Brazil)

2016-06-20

The Centaur population is composed of minor bodies wandering between the giant planets that frequently perform close gravitational encounters with these planets, leading to a chaotic orbital evolution. Recently, the discovery of two well-defined narrow rings was announced around the Centaur 10199 Chariklo. The rings are assumed to be in the equatorial plane of Chariklo and to have circular orbits. The existence of a well-defined system of rings around a body in such a perturbed orbital region poses an interesting new problem. Are the rings of Chariklo stable when perturbed by close gravitational encounters with the giant planets? Our approach to address this question consisted of forward and backward numerical simulations of 729 clones of Chariklo, with similar initial orbits, for a period of 100 Myr. We found, on average, that each clone experiences during its lifetime more than 150 close encounters with the giant planets within one Hill radius of the planet in question. We identified some extreme close encounters that were able to significantly disrupt or disturb the rings of Chariklo. About 3% of the clones lose their rings and about 4% of the clones have their rings significantly disturbed. Therefore, our results show that in most cases (more than 90%), the close encounters with the giant planets do not affect the stability of the rings in Chariklo-like systems. Thus, if there is an efficient mechanism that creates the rings, then these structures may be common among these kinds of Centaurs.

Unsaturated Fatty Acid Esters Metathesis Catalyzed by Silica Supported WMe5

KAUST Repository

Riache, Nassima

2015-11-14

Metathesis of unsaturated fatty acid esters (FAEs) by silica supported multifunctional W-based catalyst is disclosed. This transformation represents a novel route towards unsaturated di-esters. Especially, the self-metathesis of ethyl undecylenate results almost exclusively on the homo-coupling product whereas with such catalyst, 1-decene gives ISOMET (isomerization and metathesis olefin) products. The olefin metathesis in the presence of esters is very selective without any secondary cross-metathesis products demonstrating that a high selective olefin metathesis could operate at 150 °C. Additionally, a cross-metathesis of unsaturated FAEs and α-olefins allowed the synthesis of the corresponding ester with longer hydrocarbon skeleton without isomerisation.

Zinc Mediated Tandem Fragmentation-Allylation of Methyl 5-Iodopentofuranosides

DEFF Research Database (Denmark)

Hyldtoft, Lene; Madsen, Robert

1999-01-01

In the presence of zinc and allyl bromide methyl 5-iodopentofuranosides undergo a tandem fragmentation alkylation to give functionalized dienes. These can undergo ring-closing olefin metathesis to produce cyclohexenes which on dihydroxylation give quercitols.......In the presence of zinc and allyl bromide methyl 5-iodopentofuranosides undergo a tandem fragmentation alkylation to give functionalized dienes. These can undergo ring-closing olefin metathesis to produce cyclohexenes which on dihydroxylation give quercitols....

Olefin metathesis in air

Directory of Open Access Journals (Sweden)

Lorenzo Piola

2015-10-01

Full Text Available Since the discovery and now widespread use of olefin metathesis, the evolution of metathesis catalysts towards air stability has become an area of significant interest. In this fascinating area of study, beginning with early systems making use of high oxidation state early transition metal centers that required strict exclusion of water and air, advances have been made to render catalysts more stable and yet more functional group tolerant. This review summarizes the major developments concerning catalytic systems directed towards water and air tolerance.

Alkane Metathesis

KAUST Repository

Basset, Jean-Marie; Callens, Emmanuel; Riache, Nassima

2015-01-01

metal for alkane (de)hydrogenation and another for olefin metathesis in which the activity of these catalysts is essentially driven by the performance of the (de)hydrogenation steps. In this book chapter, we would focus on the evolution of these two

Cyclooctane metathesis catalyzed by silica-supported tungsten pentamethyl [(ΞSiO)W(Me)5]: Distribution of macrocyclic alkanes

KAUST Repository

Riache, Nassima

2014-10-03

Metathesis of cyclic alkanes catalyzed by the new surface complex [(ΞSiO)W(Me)5] affords a wide distribution of cyclic and macrocyclic alkanes. The major products with the formula CnH2n are the result of either a ring contraction or ring expansion of cyclooctane leading to lower unsubstituted cyclic alkanes (5≤n≤7) and to an unprecedented distribution of unsubstituted macrocyclic alkanes (12≤n≤40), respectively, identified by GC/MS and by NMR spectroscopies.

A Concise Synthesis of Castanospermine by the Use of a Transannular Cyclization

DEFF Research Database (Denmark)

Jensen, Thomas; Mikkelsen, Mette; Lauritsen, Anne

2009-01-01

A nine-step synthesis of (+)-castanospermine has been accomplished in 22% overall yield from methyl alpha-D-glucopyranoside. The key transformations involve a zinc-mediated fragmentation of benzyl-protected methyl 6-iodoglucopyranoside, ring-closing olefin metathesis, and strain-release transannu......A nine-step synthesis of (+)-castanospermine has been accomplished in 22% overall yield from methyl alpha-D-glucopyranoside. The key transformations involve a zinc-mediated fragmentation of benzyl-protected methyl 6-iodoglucopyranoside, ring-closing olefin metathesis, and strain...

A Modular Approach to Aryl-C-ribonucleosides via the Allylic Substitution and Ring-Closing Metathesis Sequence. A Stereocontrolled Synthesis of All Four alpha-/beta- and D-/L-C-Nucleoside Stereoisomers

Czech Academy of Sciences Publication Activity Database

Štambaský, J.; Kapras, V.; Štefko, Martin; Kysilka, O.; Hocek, Michal; Malkov, A. V.; Kočovský, P.

2011-01-01

Roč. 76, č. 19 (2011), s. 7781-7803 ISSN 0022-3263 R&D Projects: GA MŠk LC512; GA AV ČR IAA400550902 Institutional research plan: CEZ:AV0Z40550506 Keywords : C-nucleosides * allylic substitution * metathesis * dihydroxylation Subject RIV: CC - Organic Chemistry Impact factor: 4.450, year: 2011

Striking difference between alkane and olefin metathesis using the well-defined precursor [≡Si-O-WMe5]: Indirect evidence in favour of a bifunctional catalyst W alkylidene-hydride

KAUST Repository

Riache, Nassima; Callens, Emmanuel; Espinas, Jeff; Dé ry, Alexandre; Samantaray, Manoja; Dey, Raju; Basset, Jean-Marie

2015-01-01

Metathesis of linear alkanes catalyzed by the well-defined precursor (≡Si-O-WMe5) affords a wide distribution of linear alkanes from methane up to triacontane. Olefin metathesis using the same catalyst and under the same reaction conditions gives a very striking different distribution of linear α-olefins and internal olefins. This shows that olefin and alkane metathesis processes occur via very different pathways.

Ene-yne Cross-Metathesis for the Preparation of 2,3-Diaryl-1,3-dienes

Directory of Open Access Journals (Sweden)

Meriem K. Abderrezak

2017-11-01

Full Text Available Ene-yne cross-metathesis from alkynes and ethylene is a useful method to produce substituted conjugated butadiene derivatives. If this method has been used with aliphatic alkynes, it has however never been used starting from diarylacetylenes as internal alkynes. We show that the ene-yne cross-metathesis catalyzed by the second generation Hoveyda ruthenium catalyst provides the 2,3-diarylbuta-1,3-dienes under 3 atm of ethylene at 100 °C. The scope and limitations of the reaction have been evaluated starting from unsymmetrical functionalized diarylacetylene derivatives hence leading to unsymmetrical 2,3-diarylbuta-1,3-dienes in a straightforward and environmentally acceptable manner.

Selective conversion of butane into liquid hydrocarbon fuels on alkane metathesis catalysts

KAUST Repository

Szeto, Kaï Chung

2012-01-01

We report a selective direct conversion of n-butane into higher molecular weight alkanes (C 5+) by alkane metathesis reaction catalysed by silica-alumina supported tungsten or tantalum hydrides at moderate temperature and pressure. The product is unprecedented, asymmetrically distributed towards heavier alkanes. This journal is © 2012 The Royal Society of Chemistry.

Ring-Expansion/Contraction Radical Crossover Reactions of Cyclic Alkoxyamines: A Mechanism for Ring Expansion-Controlled Radical Polymerization

Directory of Open Access Journals (Sweden)

Atsushi Narumi

2018-06-01

Full Text Available Macrocyclic polymers present an important class of macromolecules, displaying the reduced radius of gyration or impossibility to entangle. A rare approach for their synthesis is the ring expansion-controlled radical “vinyl” polymerization, starting from a cyclic alkoxyamine. We here describe ring-expansion radical crossover reactions of cyclic alkoxyamines which run in parallel to chain-propagation reactions in the polymerization system. The radical crossover reactions extensively occurred at 105–125 °C, eventually producing high molecular weight polymers with multiple inherent dynamic covalent bonds (NOC bonds. A subsequent ring-contraction radical crossover reaction and the second ring-expansion radical crossover reaction are also described. The major products for the respective three stages were shown to possess cyclic morphologies by the molecular weight profiles and the residual ratios for the NOC bonds (φ in %. In particular, the high φ values ranging from ca. 80% to 98% were achieved for this cyclic alkoxyamine system. This result verifies the high availability of this system as a tool demonstrating the ring-expansion “vinyl” polymerization that allows them to produce macrocyclic polymers via a one-step vinyl polymerization.

Exceptionally Stable and Efficient Solid Supported Hoveyda-Type Catalyst

Czech Academy of Sciences Publication Activity Database

Skowerski, K.; Pastva, J.; Czarnocki, S. J.; Janošcová, Jana

2015-01-01

Roč. 19, č. 7 (2015), s. 872-877 ISSN 1083-6160 Institutional support: RVO:61388955 Keywords : OLEFIN-METATHESIS CATALYSTS * RING-CLOSING METATHESIS * N-HETEROCYCLIC CARBENES Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.922, year: 2015

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

Science.gov (United States)

Shi, Zheng; Komijani, Yashar

2017-02-01

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

In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60Fullerenes

KAUST Repository

Martínez, Juan Pablo

2016-04-10

Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60Fullerenes

KAUST Repository

Martí nez, Juan Pablo; Vummaleti, Sai V. C.; Falivene, Laura; Nolan, Steven P.; Cavallo, Luigi; Solà , Miquel; Poater, Albert

2016-01-01

Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Total synthesis of ciguatoxin and 51-hydroxyCTX3C.

Science.gov (United States)

Inoue, Masayuki; Miyazaki, Keisuke; Ishihara, Yuuki; Tatami, Atsushi; Ohnuma, Yuyu; Kawada, Yuuya; Komano, Kazuo; Yamashita, Shuji; Lee, Nayoung; Hirama, Masahiro

2006-07-26

Ciguatoxins, the principal causative toxins of ciguatera seafood poisoning, are large ladder-like polycyclic ethers with the 13 ether rings ranging from five- to nine-membered. In this paper, we describe the total synthesis of the two most toxic members of the ciguatoxin family, ciguatoxin 1 and 51-hydroxyCTX3C 2, based on a unified synthetic strategy. The key features in our syntheses were (i) direct construction of the O,S-acetal from the corresponding left and right wing fragments (3, 4, 14); (ii) stereo- and chemoselective radical reaction of the alpha-oxyradical with pentafluorophenyl acrylate to achieve cyclization of the seven-membered G-ring; (iii) ring-closing metathesis reaction to build the nine-membered F-ring; and (iv) an efficient protective group strategy using the oxidatively removable 2-naphthylmethyl groups.

A Sociolinguistic Analysis of Metathesis in Azeri Language

Directory of Open Access Journals (Sweden)

Biook Behnam

2012-07-01

Full Text Available This study tries to investigate the correlation between sociolinguistic parameters such as sex, age, and social class and the use of metathesis in Azeri. There have been few studies from a sociolinguistic perspective on the use of metathesis. Through studying the stigmatized forms of speech in Azeri, the present study indicates that a significant relationship exists between extralinguistic variables and metathesis as a phonological process. The subjects of the study were Azeri speakers living in different districts of Tabriz categorized by three socioeconomically different groups. The statistical analyses of data indicate that there is an intimate and reciprocal relationship between linguistic behavior and social structure.

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

Energy Technology Data Exchange (ETDEWEB)

Johnson, R.E.

1951-04-09

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

Divergent Synthesis of Diastereomeric Sphingosines from a Chiral Aziridine

Energy Technology Data Exchange (ETDEWEB)

Kang, On-Yu; Shin, Mi-Ri; Kang, Han-Young [Chungbuk National University, Gongju (Korea, Republic of)

2016-07-15

All four stereoisomers of sphingosines were synthesized starting from a single intermediate, chiral aziridine (2), which was efficiently prepared by enzymatic desymmetrization in an enatiopure form. Aziridine (2) was converted to 3, which was used for the synthesis of 4. Both the advanced key intermediates, vinylaziridines 3 and 4, were successfully converted to threo-sphingosines 1a and 1b, respectively. Ring-closing metathesis (RCM) using the Grubbs II catalyst was the key reaction in the synthesis. Two erythro-sphingosines 1c and 1d were synthesized by the ring-expansion reactions of vinylaziridines 3 and 4, followed by RCM reactions. The successful divergent synthesis confirmed that chiral vinylaziridine 2 can be used as a key intermediate for the synthesis of sphingosine-related natural products.

Synthesis of Calystegine A(3) from Glucose by the Use of Ring-Closing Metathesis

DEFF Research Database (Denmark)

Monrad, Rune Nygaard; Pipper, Charlotte Bressen; Madsen, Robert

2009-01-01

A synthesis of the nortropane alkaloid calystegine A(3) is described from D-glucose. The key step employs a zinc-mediated tandem reaction where a benzyl-protected methyl 6-iodo glucoside is fragmented to give an unsaturated aldehyde, which is then transformed into the corresponding benzylimine...... affords calystegine A(3). The synthesis uses a total of 13 steps from glucose and confirms the absolute configuration of the natural product....

Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

Energy Technology Data Exchange (ETDEWEB)

Zhu, Z.; Espenson, H. [Iowa State Univ., Ames, IA (United States)

1995-11-03

Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) has found wise use in catalysis, including the epoxidation and metathesis of olefins, aldehyde olefination, and oxygen transfer. Extensive reports have now appeared in the area of MTO-catalyzed substrate oxidations with hydrogen peroxide. Certain catalytic applications of MTO for organic reactions that do not utilize peroxide have now been realized. In particular, a catalytic amount of MTO with ethyl diazoacetate (EDA) will convert aromatic imines to aziridines and convert aldehydes and ketones to epoxides. The aziridine preparation proceeds in high yields under anaerobic conditions more conveniently than with existing methods. Compounds with a three-membered heterocyclic ring can be obtained with the EDA/MTO catalytic system. Aromatic imines undergo cycloaddition reactions to give aziridines under mild conditions.

Single Turnover at Molecular Polymerization Catalysts Reveals Spatiotemporally Resolved Reactions.

Science.gov (United States)

Easter, Quinn T; Blum, Suzanne A

2017-10-23

Multiple active individual molecular ruthenium catalysts have been pinpointed within growing polynorbornene, thereby revealing information on the reaction dynamics and location that is unavailable through traditional ensemble experiments. This is the first single-turnover imaging of a molecular catalyst by fluorescence microscopy and allows detection of individual monomer reactions at an industrially important molecular ruthenium ring-opening metathesis polymerization (ROMP) catalyst under synthetically relevant conditions (e.g. unmodified industrial catalyst, ambient pressure, condensed phase, ca. 0.03 m monomer). These results further establish the key fundamentals of this imaging technique for characterizing the reactivity and location of active molecular catalysts even when they are the minor components. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

New ROMP Synthesis of Ferrocenyl Dendronized Polymers.

Science.gov (United States)

Liu, Xiong; Ling, Qiangjun; Zhao, Li; Qiu, Guirong; Wang, Yinghong; Song, Lianxiang; Zhang, Ying; Ruiz, Jaime; Astruc, Didier; Gu, Haibin

2017-10-01

First- and second-generation Percec-type dendronized ferrocenyl norbornene macromonomers containing, respectively, three and nine ferrocenyl termini are synthesized and polymerized by ring-opening metathesis polymerization using Grubbs' third-generation olefin metathesis catalyst with several monomer/catalyst feed ratios between 10 and 50. The rate of polymerization is highly dependent on the generation of the dendronized macromonomers, but all these ring-opening metathesis polymerization reactions are controlled, and near-quantitative monomer conversions are achieved. The numbers of ferrocenyl groups obtained are in agreement with the theoretical ones according to the cyclic voltammetry studies as determined using the Bard-Anson method. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Regioselective Wacker Oxidation of Internal Alkenes: Rapid Access to Functionalized Ketones Facilitated by Cross-Metathesis

KAUST Repository

Morandi, Bill

2013-07-26

Wacka wacka: The title reaction makes use of a wide range of directing groups (DG) to enable the highly regioselective oxidation of alkenes, and occurs predictably at the distal position. Both E and Z alkenes afford valuable functionalized ketones and cross-metathesis was shown to facilitate the preparation of the starting materials. BQ=benzoquinone.

Regioselective Wacker Oxidation of Internal Alkenes: Rapid Access to Functionalized Ketones Facilitated by Cross-Metathesis

KAUST Repository

Morandi, Bill; Wickens, Zachary K.; Grubbs, Robert H.

2013-01-01

Wacka wacka: The title reaction makes use of a wide range of directing groups (DG) to enable the highly regioselective oxidation of alkenes, and occurs predictably at the distal position. Both E and Z alkenes afford valuable functionalized ketones and cross-metathesis was shown to facilitate the preparation of the starting materials. BQ=benzoquinone.

Development of neutron shielding material using metathesis-polymer matrix

Energy Technology Data Exchange (ETDEWEB)

Sakurai, Yoshinori E-mail: ysakurai@rri.kyoto-u.ac.jp; Sasaki, Akira; Kobayashi, Tooru

2004-04-21

A neutron shielding material using a metathesis-polymer matrix, which is a thermosetting resin, was developed. This shielding material has characteristics that can be controlled for different mixing ratios of neutron absorbers and for formation in the laboratory. Additionally, the elastic modulus can be changed at the hardening process, from a flexible elastoma to a mechanically tough solid. Experiments were performed at the Kyoto University Research Reactor in order to determine the important characteristics of this metathesis-polymer shielding material, such as neutron shielding performance, secondary gamma-ray generation and activation. The metathesis-polymer shielding material was shown to be practical and as effective as the other available shielding materials, which mainly consist of thermoplastic resin.

Unsaturated Fatty Acid Esters Metathesis Catalyzed by Silica Supported WMe5

KAUST Repository

Riache, Nassima; Callens, Emmanuel; Talbi, Karima; Basset, Jean-Marie

2015-01-01

Metathesis of unsaturated fatty acid esters (FAEs) by silica supported multifunctional W-based catalyst is disclosed. This transformation represents a novel route towards unsaturated di-esters. Especially, the self-metathesis of ethyl undecylenate

RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

KAUST Repository

Suleimanov, Yu.V.

2013-03-01

We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH 4, OH+CH4 and H+C2H6 reactions. © 2012 Elsevier B.V. All rights reserved.

RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

KAUST Repository

Suleimanov, Yu.V.; Allen, J.W.; Green, W.H.

2013-01-01

We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH 4, OH+CH4 and H+C2H6 reactions. © 2012 Elsevier B.V. All rights reserved.

Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

Directory of Open Access Journals (Sweden)

Patrick Claude

2011-12-01

Full Text Available Phenyl 3,4,6-tri-O-benzyl-2-O-(3-carboxypropionyl-1-thio-β-D-galactopyranoside (1 was condensed via its pentafluorophenyl ester 2 with 5-aminopentyl (4a, 4-aminobutyl (4b, 3-aminopropyl (4c and 2-aminoethyl 4,6-O-benzylidene-β-D-glucopyranoside (4d, prepared from the corresponding N-Cbz protected glucosides 3a–d, to give the corresponding 2-[3-(alkylcarbamoylpropionyl] tethered saccharides 5a–d. Intramolecular, ring closing glycosylation of the saccharides with NIS and TMSOTf afforded the tethered β(1→3 linked disaccharides 6a–c, the α(1→3 linked disaccharides 7a–d and the α(1→2 linked disaccharide 8d in ratios depending upon the ring size formed during glycosylation. No β(1→2 linked disaccharides were formed. Molecular modeling of saccharides 6–8 revealed that a strong aromatic stacking interaction between the aromatic parts of the benzyl and benzylidene protecting groups in the galactosyl and glucosyl moieties was mainly responsible for the observed regioselectivity and anomeric selectivity of the ring-closing glycosylation step.

Synergy between Two Metal Catalysts: A Highly Active Silica Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane

KAUST Repository

Samantaray, Manoja

2016-06-01

A well-defined, silica supported, bimetallic precatalyst [≡Si-O-W(Me)5 ≡Si-O-Zr(Np)3](4) has been synthesized for the first time via successively grafting two organometallic complexes [W(CH3)6 (1) followed by ZrNp4 (2)] on a single silica support. Surprisingly, multiple quantum NMR characterization demonstrates that W and Zr species are in close proximity to each other. Hydrogenation of this bimetallic catalyst at room temperature showed the easy formation of Zirconium hydride, probably facilitated by tungsten hydride which was formed at this temperature. This bimetallic W/Zr hydride precatalyst proved to be more efficient (TON: 1436) than the monometallic W hydride (TON: 650) in metathesis of n-decane at 150 0C. This synergy between Zr and W suggests that the slow step of alkane metathesis is the C-H bond activation which occurs on Zr. The produced olefin resulting from a ß–H elimination undergoes easy metathesis on W.

Methods for treating a metathesis feedstock with metal alkoxides

Science.gov (United States)

Cohen, Steven A.; Anderson, Donde R.; Wang, Zhe; Champagne, Timothy M.; Ung, Thay A.

2018-04-17

Various methods are provided for treating and reacting a metathesis feedstock. In one embodiment, the method includes providing a feedstock comprising a natural oil, chemically treating the feedstock with a metal alkoxide under conditions sufficient to diminish catalyst poisons in the feedstock, and, following the treating, combining a metathesis catalyst with the feedstock under conditions sufficient to metathesize the feedstock.

Metathesis in the generation of low-temperature gas in marine shales

Directory of Open Access Journals (Sweden)

Jarvie Daniel M

2010-01-01

Full Text Available Abstract The recent report of low-temperature catalytic gas from marine shales took on additional significance with the subsequent disclosure of natural gas and low-temperature gas at or near thermodynamic equilibrium in methane, ethane, and propane. It is important because thermal cracking, the presumed source of natural gas, cannot generate these hydrocarbons at equilibrium nor can it bring them to equilibrium over geologic time. The source of equilibrium and the source of natural gas are either the same (generation under equilibrium control or closely associated. Here we report the catalytic interconversion of hydrocarbons (metathesis as the source of equilibrium in experiments with Cretaceous Mowry shale at 100°C. Focus was on two metathetic equilibria: methane, ethane, and propane, reported earlier, Q (K = [(C1*(C3]/[(C22], and between these hydrocarbons and n-butane, Q* (K = [(C1*(n-C4]/[(C2*(C3], reported here for the first time. Two observations stand out. Initial hydrocarbon products are near equilibrium and have maximum average molecular weights (AMW. Over time, products fall from equilibrium and AMW in concert. It is consistent with metathesis splitting olefin intermediates [Cn] to smaller intermediates (fission as gas generation creates open catalytic sites ([ ]: [Cn] + [ ] → [Cn-m] + [Cm]. Fission rates increasing exponentially with olefin molecular weight could contribute to these effects. AMW would fall over time, and selective fission of [C3] and [n-C4] would draw Q and Q* from equilibrium. The results support metathesis as the source of thermodynamic equilibrium in natural gas.

A tandem Mannich addition–palladium catalyzed ring-closing route toward 4-substituted-3(2H-furanones

Directory of Open Access Journals (Sweden)

Jubi John

2014-06-01

Full Text Available A facile route towards highly functionalized 3(2H-furanones via a sequential Mannich addition–palladium catalyzed ring closing has been elaborated. The reaction of 4-chloroacetoacetate esters with imines derived from aliphatic and aromatic aldehydes under palladium catalysis afforded 4-substituted furanones in good to excellent yields. 4-Hydrazino-3(2H-furanones could also be synthesized from diazo esters in excellent yields by utilising the developed strategy. We could also efficiently transform the substituted furanones to aza-prostaglandin analogues.

A general enantioselective route to the chamigrene natural product family

KAUST Repository

White, David E.; Stewart, Ian C.; Seashore-Ludlow, Brinton A.; Grubbs, Robert H.; Stoltz, Brian M.

2010-01-01

Described in this report is an enantioselective route toward the chamigrene natural product family. The key disconnections in our synthetic approach include sequential enantioselective decarboxylative allylation and ring-closing olefin metathesis to form the all-carbon quaternary stereocenter and spirocyclic core present in all members of this class of compounds. The generality of this strategy is demonstrated by the first total syntheses of elatol and the proposed structure of laurencenone B, as well as the first enantioselective total syntheses of laurencenone C and α-chamigrene. A brief exploration of the substrate scope of the enantioselective decarboxylative allylation/ring-closing metathesis sequence with fully substituted vinyl chlorides is also presented.

A general enantioselective route to the chamigrene natural product family

KAUST Repository

White, David E.

2010-06-01

Described in this report is an enantioselective route toward the chamigrene natural product family. The key disconnections in our synthetic approach include sequential enantioselective decarboxylative allylation and ring-closing olefin metathesis to form the all-carbon quaternary stereocenter and spirocyclic core present in all members of this class of compounds. The generality of this strategy is demonstrated by the first total syntheses of elatol and the proposed structure of laurencenone B, as well as the first enantioselective total syntheses of laurencenone C and α-chamigrene. A brief exploration of the substrate scope of the enantioselective decarboxylative allylation/ring-closing metathesis sequence with fully substituted vinyl chlorides is also presented.

Dynamic behaviour of tantalum hydride supported on silica or MCM-41 in the metathesis of alkanes

KAUST Repository

Soignier, Sophie

2014-01-01

The metathesis of ethane and propane catalysed by tantalum hydride supported on silica or MCM-41 was studied under static and dynamic conditions. During the reaction, the rate decreased over time, indicating deactivation of the catalyst. The evolution of the catalytic system and surface species over time was monitored by various physico-chemical methods: FTIR, 13C NMR spectroscopy, elemental analysis and chemical reactivity. A carbonaceous deposit composed of unsaturated hydrocarbyl species was observed by 13C NMR. This deposit was responsible for poisoning of the catalyst. The deactivation of the catalyst proved more severe at higher temperatures and under static rather than dynamic conditions. A partial regeneration of the catalyst could be achieved during a series of repeated runs. Mechanistically, the deconvolution of the products\\' distribution over time indicated the occurrence of hydrogenolysis in the early stages of the reaction, while pure metathesis dominated later on. The hydrogen was supplied by the dehydrogenation of hydrocarbyl surface species involved in the deactivation process. © 2014 The Royal Society of Chemistry.

Dynamic behaviour of tantalum hydride supported on silica or MCM-41 in the metathesis of alkanes

KAUST Repository

Soignier, Sophie; Saggio, Guillaume; Taoufik, Mostafa; Basset, Jean-Marie; Thivolle-Cazat, Jean

2014-01-01

The metathesis of ethane and propane catalysed by tantalum hydride supported on silica or MCM-41 was studied under static and dynamic conditions. During the reaction, the rate decreased over time, indicating deactivation of the catalyst. The evolution of the catalytic system and surface species over time was monitored by various physico-chemical methods: FTIR, 13C NMR spectroscopy, elemental analysis and chemical reactivity. A carbonaceous deposit composed of unsaturated hydrocarbyl species was observed by 13C NMR. This deposit was responsible for poisoning of the catalyst. The deactivation of the catalyst proved more severe at higher temperatures and under static rather than dynamic conditions. A partial regeneration of the catalyst could be achieved during a series of repeated runs. Mechanistically, the deconvolution of the products' distribution over time indicated the occurrence of hydrogenolysis in the early stages of the reaction, while pure metathesis dominated later on. The hydrogen was supplied by the dehydrogenation of hydrocarbyl surface species involved in the deactivation process. © 2014 The Royal Society of Chemistry.

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

Science.gov (United States)

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

2016-06-13

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

Effect of support on hydro-metathesis of propene: A comparative study of W(CH 3 ) 6 anchored to silica vs. silica-alumina

KAUST Repository

Tretiakov, Mykyta

2018-03-27

Hydro-metathesis of propene was carried out by using well-defined W(CH3)6 supported on silica and silica-alumina. It was observed that W(CH3)6 supported silica-alumina catalyst is much better (TON 4577) than the silica supported catalyst (TON 2104). We demonstrated that the present catalysts are much better than the previously reported (tantalum hydride/KCC-1, TON 786) catalyst. For the first time, we observed the formation of n-decane from propene, which enables us to think of using cheaper raw materials and converting them to petroleum range alkanes using hydro-metathesis reaction.

Condensation reactions of glucose and aromatic ring; Glucose to hokokan tono shukugo hanno

Energy Technology Data Exchange (ETDEWEB)

Komano, T.; Mashimo, K.; Wainai, T.; Tanaka, C.; Yoshioka, T. [Nihon University, Tokyo (Japan). College of Science and Technology; Sugimoto, Y.; Miki, Y. [National Institute of Materials and Chemical Research, Tsukuba (Japan)

1996-10-28

For artificial coalification, condensation reactions of aromatic ring and activated compounds produced by dehydrating reaction of glucose were studied experimentally. In heat treatment experiment in water, three reaction specimens such as glucose, glucose and phenol, and glucose and benzaldehyde were fed into an autoclave together with distilled water, and subjected to reaction at 180{degree}C under spontaneous pressure for 50 hours. In hydrogenation experiment, the specimens were fed into an autoclave together with tetradecane and sulfurization catalyst, and subjected to reaction at 350{degree}C under initial pressure of 9.8MPa for 2 hours for gas chromatography (GC) analysis of products. As the experimental result, the reaction between glucose and aromatic ring in heat treatment in water occurred between aromatic ring and active fragment with a mean carbon number of 4-5 produced by decomposition of glucose. The reactivity was higher in benzaldehyde addition than phenol addition. 3 refs., 4 figs., 1 tab.

by a solid-state metathesis approach

Indian Academy of Sciences (India)

Wintec

Department of Mechanical Engineering,. † ... A solid-state metathesis approach initiated by microwave energy has been successfully applied for ... and chemical properties of synthesized powders are determined by powder X-ray diffraction, ...

Microwave-Assisted Syntheses of Bioactive Seven-Membered, Macro-Sized Heterocycles and Their Fused Derivatives

Directory of Open Access Journals (Sweden)

Mohsine Driowya

2016-08-01

Full Text Available This review describes the recent advances in the microwave-assisted synthesis of 7-membered and larger heterocyclic compounds. Several types of reaction for the cyclization step are discussed: Ring Closing Metathesis (RCM, Heck and Sonogashira reactions, Suzuki-Miyaura cross-coupling, dipolar cycloadditions, multi-component reactions (Ugi, Passerini, etc. Green syntheses and solvent-free procedures have been introduced whenever possible. The syntheses discussed herein have been selected to illustrate the huge potential of microwave in the synthesis of highly functionalized molecules with potential therapeutic applications, in high yields, enhanced reaction rates and increased chemoselectivity, compared to conventional methods. More than 100 references from the recent literature are listed in this review.

Truncated borrelidin analogues: synthesis by sequential cross metathesis/olefination for the southern fragment and biological evaluation.

Science.gov (United States)

Gündemir-Durmaz, Tülay; Schmid, Fabian; El Baz, Yana; Häusser, Annette; Schneider, Carmen; Bilitewski, Ursula; Rauhut, Guntram; Garnier, Delphine; Baro, Angelika; Laschat, Sabine

2016-09-21

The construction of novel borrelidin analogues is reported in which the northern fragment is truncated to a simple hydroxyundecanecarboxylate and the original cyclopentanecarboxylic acid in the southern fragment is replaced with different six-membered rings. The required precursors were prepared by cross metathesis of the appropriate carbocycle-based homoallylic alcohol with crotonaldehyde followed by HWE olefination of the resulting enal with bromocyanophosphonate. The key aldehyde for intramolecular cross coupling was accessible by oxidation of the hydroxy group of the linked undecanecarboxylate unit. Grignard mediated macrocyclization finally yielded the borrelidin related products. The investigation is complemented by SAR studies and quantum-chemical calculations.

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

African Journals Online (AJOL)

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

Synthesis of amide-functionalized cellulose esters by olefin cross-metathesis.

Science.gov (United States)

Meng, Xiangtao; Edgar, Kevin J

2015-11-05

Cellulose esters with amide functionalities were synthesized by cross-metathesis (CM) reaction of terminally olefinic esters with different acrylamides, catalyzed by Hoveyda-Grubbs 2nd generation catalyst. Chelation by amides of the catalyst ruthenium center caused low conversions using conventional solvents. The effects of both solvent and structure of acrylamide on reaction conversion were investigated. While the inherent tendency of acrylamides to chelate Ru is governed by the acrylamide N-substituents, employing acetic acid as a solvent significantly improved the conversion of certain acrylamides, from 50% to up to 99%. Homogeneous hydrogenation using p-toluenesulfonyl hydrazide successfully eliminated the α,β-unsaturation of the CM products to give stable amide-functionalized cellulose esters. The amide-functionalized product showed higher Tg than its starting terminally olefinic counterpart, which may have resulted from strong hydrogen bonding interactions of the amide functional groups. Copyright © 2015 Elsevier Ltd. All rights reserved.

Liposomal Drug Delivery of Anticancer Agents

DEFF Research Database (Denmark)

Pedersen, Palle Jacob

and retention (EPR) effect. The liposomes consists of sPLA2 IIA sensitive phospholipids having anticancer drugs covalently attached to the sn-2 position of the glycerol backbone in the phospholipids, hence drug leakage is avoided from the carrier system. Various known anticancer agents, like chlorambucil, all......) based strategy using a limited number of reaction types. Upon coupling of unsaturated building blocks ring closing metathesis cascades were used to “reprogram” the molecular scaffold and highly diverse structures were obtained. In total 20 novel compounds with a broad structural diversity were prepared...

Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane

KAUST Repository

Samantaray, Manoja; Kavitake, Santosh Giridhar; Morlanes, Natalia Sanchez; Abou-Hamad, Edy; Hamieh, Ali Imad Ali; Dey, Raju; Basset, Jean-Marie

2017-01-01

Two compatible organometallic complexes, W(Me)(6) (1) and TiNp4 (2), were successively anchored on a highly dehydroxylated single silica support (SiO2-700) to synthesize the well-defined bimetallic precatalyst [(equivalent to Si-O-)W(Me)(5)(equivalent to Si-O-)Ti(Np)(3)] (4). Precatalyst 4 was characterized at the molecular level using advanced surface organometallic chemistry (SOMC) characterization techniques. The strong autocorrelation observed between methyl of W and Ti in H-1-H-1 multiple-quantum NMR spectra demonstrates that W and Ti species are in close proximity to each other. The bimetallic precatalyst 4, with a turnover number (TON) of 9784, proved to be significantly more efficient than the silica-supported monometallic catalyst [(equivalent to Si-O-)W(Me)(5)] (3), with a TON of 98, for propane metathesis at 150 degrees C in a flow reactor. The dramatic improvement in the activity signifies the cooperativity between Ti and W and indicates that the key step of alkane metathesis (C-H bond activation followed by beta-H elimination) occurs on Ti, followed by olefin metathesis, which occurs on W. We have demonstrated the influence and importance of proximity of Ti to W for achieving such a significantly high activity. This is the first report demonstrating the considerably high activity (TON = 9784) in propane metathesis at moderate temperature (150 degrees C) using a well-defined bimetallic system prepared via the SOMC approach.

Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane

KAUST Repository

Samantaray, Manoja

2017-02-10

Two compatible organometallic complexes, W(Me)(6) (1) and TiNp4 (2), were successively anchored on a highly dehydroxylated single silica support (SiO2-700) to synthesize the well-defined bimetallic precatalyst [(equivalent to Si-O-)W(Me)(5)(equivalent to Si-O-)Ti(Np)(3)] (4). Precatalyst 4 was characterized at the molecular level using advanced surface organometallic chemistry (SOMC) characterization techniques. The strong autocorrelation observed between methyl of W and Ti in H-1-H-1 multiple-quantum NMR spectra demonstrates that W and Ti species are in close proximity to each other. The bimetallic precatalyst 4, with a turnover number (TON) of 9784, proved to be significantly more efficient than the silica-supported monometallic catalyst [(equivalent to Si-O-)W(Me)(5)] (3), with a TON of 98, for propane metathesis at 150 degrees C in a flow reactor. The dramatic improvement in the activity signifies the cooperativity between Ti and W and indicates that the key step of alkane metathesis (C-H bond activation followed by beta-H elimination) occurs on Ti, followed by olefin metathesis, which occurs on W. We have demonstrated the influence and importance of proximity of Ti to W for achieving such a significantly high activity. This is the first report demonstrating the considerably high activity (TON = 9784) in propane metathesis at moderate temperature (150 degrees C) using a well-defined bimetallic system prepared via the SOMC approach.

Constraining astrophysical reaction rates: using the storage rings at FAIR/GSI

Science.gov (United States)

Langer, Christoph; Glorius, Jan; Slavkovská, Zuzana; Litvinov, Sergey; Litvinov, Yuri A.; Reifarth, René

2018-01-01

Ion optical calculations for a storage ring at the present GSI facility for direct proton-induced reactions relevant for different astrophysical processes are presented. As an example case, the 59Cu(p,γ) and 59Cu(p,α) reactions are shown. The branching of these two reactions is important in X-ray burst scenarios, since it determines the breakout out of the major 56Ni waiting point.

Transforming n=1 members of the Ruddlesden-Popper phases to a n=3 member through metathesis: synthesis of a new layered perovskite, Ca2La2CuTi2O10

International Nuclear Information System (INIS)

Sivakumar, T.; Lofland, S.E.; Ramanujachary, K.V.; Ramesha, K.; Subbanna, G.N.; Gopalakrishnan, J.

2004-01-01

We report the formation of a new n=3 Ruddlesden-Popper (R-P) layered perovskite oxide, Ca 2 La 2 CuTi 2 O 10 (I), in the metathesis reaction between NaLaTiO 4 and Ca 2 CuO 2 Cl 2 (n=1 R-P phases) at 700 deg. C in air. Rietveld refinement of powder XRD data shows that I is isostructural with Sr 4 Ti 3 O 10 (space group I4/mmm; a=3.8837(5), c=27.727(6) A), consisting of triple perovskite CuTi 2 O 10 sheets wherein Cu and Ti are ordered at the central and terminal octahedral sites, respectively. Magnetization data provide support for the presence of strong antiferromagnetically coupled CuO 2 sheets in the structure. I is metastable decomposing at higher temperatures (∼950 deg. C) to a mixture of perovskite-like CaLa 2 CuTi 2 O 9 and CaO. Interestingly, the reaction between NaLaTiO 4 and Sr 2 CuO 2 Cl 2 follows a different metathesis route, 2NaLaTiO 4 +Sr 2 CuO 2 Cl 2 →La 2 CuO 4 +2SrTiO 3 +2NaCl, revealing multiplicity of reaction pathways for solid-state metathesis reactions

Build/Couple/Pair and Multifunctional Catalysis Strategies for the Synthesis of Heterocycles from Simple Starting Materials

DEFF Research Database (Denmark)

Ascic, Erhad

. Multifunctional Catalysis: Synthesis of Heterocycles from Simple Starting Materials A multifunctional catalysis approach, involving a ruthenium-catalyzed tandem ringclosing metathesis/isomerization/N-acyliminium cyclization sequence, is described. Double bonds created during ring-closing metathesis isomerize......, a series of interesting indolizidinones are formed in good yields with excellent diastereoselectivities, including a formal total synthesis of the antiparasitic natural product harmicine and the first total synthesis of mescalotam. Furthermore, preliminary asymmetric variants of the tandem process have...

Combination of in situ metathesis reaction with a novel "magnetic effervescent tablet-assisted ionic liquid dispersive microextraction" for the determination of endogenous steroids in human fluids.

Science.gov (United States)

Wu, Jia; Xu, Zilin; Pan, Yixuan; Shi, Yi; Bao, Xiujie; Li, Jun; Tong, Yu; Tang, Han; Ma, Shuyan; Wang, Xuedong; Lyu, Jianxin

2018-05-01

Herein, a novel magnetic effervescence tablet-assisted microextraction coupled to in situ metathesis reaction of ionic liquid (IS-META-ILDM) is presented for the determination of four endogenous steroids in human urine, pregnant women's blood, and fetal umbilical cord blood. The magnetic effervescent tablets, which were composed of Fe 3 O 4 nanoparticles, sodium carbonate (alkaline source), and tartaric acid (acidic source), were used to disperse the extractant and for convenient magnetic separation. After the effervescent reaction, in situ reaction between NH 4 PF 6 and [C 6 MIM]BF 4 was adopted to change hydrophilic ionic liquid to hydrophobic liquid, which could be separated from the aqueous phase. The newly developed method has three obvious advantages: (1) combination of effervescent dispersion and magnetic nanoparticles' retrieval is cost-effective and the dispersion and collection of the extractant can be completed almost simultaneously; (2) as compared to temperature-controlled ionic liquid dispersive microextraction and cold-induced solidified microextraction, this method avoids a heating and cooling process which significantly reduces the extraction time and energy cost; and (3) the combination of adsorption by magnetic nanoparticles with extraction by in situ metathesis reaction easily produces high recoveries for target analytes. The optimized composition of effervescent tablet and experimental parameters are as follows: 0.64 g mixture of sodium carbonate and tartaric acid, 7 mg of Fe 3 O 4 (20 nm) as magnetic sorbents, 40 μL of [C 6 MIM]BF 4 as the extraction solvent, 0.15 g NH 4 PF 6 , and 300 μL of elution solvent. Under the optimized conditions, the newly developed method provided high extraction recoveries (90.0-118.5%) and low LODs (0.14-0.17 μg L -1 ) in urine and blood samples. In total, this IS-META-ILDM method provided high extraction efficiency, fast and convenient separation, and underutilization of any organic solvent, and thus

First- and second-generation total synthesis of ciguatoxin CTX3C.

Science.gov (United States)

Inoue, Masayuki; Miyazaki, Keisuke; Uehara, Hisatoshi; Maruyama, Megumi; Hirama, Masahiro

2004-08-17

More than 20,000 people suffer annually from ciguatera seafood poisoning in subtropical and tropical regions. The extremely low content of the causative neurotoxins, designated as ciguatoxins, in fish has hampered isolation, detailed biological studies, and preparation of anti-ciguatoxin antibodies for detecting these toxins. Furthermore, the large (3 nm in length) and complex molecular structure of ciguatoxins has impeded chemists from completing their total synthesis. In this article, the full details of studies leading to the total synthesis of ciguatoxin CTX3C are provided. The key elements of the first-generation approach include O,O-acetal formation from the right and left wing fragments, conversion from O,O-acetal to O,S-acetal, a radical reaction to cyclize the G ring, a ring-closing metathesis reaction to close the F ring, and final removal of the 2-naphtylmethyl protective groups. Subsequent studies provided a second-generation total synthesis, which is more concise and results in a higher yield. Second-generation synthesis was accomplished by using a direct method of constructing the key intermediate O,S-acetal from alpha-chlorosulfide and a secondary alcohol. These syntheses ensure a practical supply of ciguatoxin for biological applications.

Mechanism of the Ru–Allenylidene to Ru–Indenylidene Rearrangement in Ruthenium Precatalysts for Olefin Metathesis

KAUST Repository

Pump, Eva

2015-06-30

The intramolecular allenylidene RuCl2(PR3)2(C═C═CPh2) to indenylidene RuCl2(PR3)2(Ind) rearrangement that occurs during the synthesis of Ru-based precatalysts for olefin metathesis is presented. In the absence of acid, the ring closure via C–H activation was shown to be unfavored for energy barriers up to 70 kcal/mol. Thus, it turned out to be HCl (or other acid) that plays a crucial role during formation of the indenylidene, as the upper energy barrier decreases to a reasonable 35 kcal/mol. Moreover, we proved computationally that depending on the nature of the phosphine the intramolecular rearrangement is either facilitated (PPh3) or slightly hampered (PCy3), which is in line with experimental results.

Mechanism of the Ru–Allenylidene to Ru–Indenylidene Rearrangement in Ruthenium Precatalysts for Olefin Metathesis

KAUST Repository

Pump, Eva; Slugovc, Christian; Cavallo, Luigi; Poater, Albert

2015-01-01

The intramolecular allenylidene RuCl2(PR3)2(C═C═CPh2) to indenylidene RuCl2(PR3)2(Ind) rearrangement that occurs during the synthesis of Ru-based precatalysts for olefin metathesis is presented. In the absence of acid, the ring closure via C–H activation was shown to be unfavored for energy barriers up to 70 kcal/mol. Thus, it turned out to be HCl (or other acid) that plays a crucial role during formation of the indenylidene, as the upper energy barrier decreases to a reasonable 35 kcal/mol. Moreover, we proved computationally that depending on the nature of the phosphine the intramolecular rearrangement is either facilitated (PPh3) or slightly hampered (PCy3), which is in line with experimental results.

Synthesis of (+)-dumetorine and congeners by using flow chemistry technologies.

Science.gov (United States)

Riva, Elena; Rencurosi, Anna; Gagliardi, Stefania; Passarella, Daniele; Martinelli, Marisa

2011-05-23

An efficient total synthesis of the natural alkaloid (+)-dumetorine by using flow technology is described. The process entailed five separate steps starting from the enantiopure (S)-2-(piperidin-2-yl)ethanol 4 with 29% overall yield. Most of the reactions were carried out by exploiting solvent superheating and by using packed columns of immobilized reagents or scavengers to minimize handling. New protocols for performing classical reactions under continuous flow are disclosed: the ring-closing metathesis reaction with a novel polyethylene glycol-supported Hoveyda catalyst and the unprecedented flow deprotection/Eschweiler-Clarke methylation sequence. The new protocols developed for the synthesis of (+)-dumetorine were applied to the synthesis of its simplified natural congeners (-)-sedamine and (+)-sedridine. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thiol-ene reaction as tool for crosslinking of polynorbornene micelles in the nanoscale

Science.gov (United States)

Rupp, Barbara; Bauer, Thomas; Slugovc, Christian

2009-08-01

The thiol-ene reaction is a established photoreaction of multifunctional thiols and enes. Virtually any type of ene will participate in a free radical polymerisation process with a thiol. An advantage over many other photochemical reactions is that the reaction proceeds almost as rapidly in ambient conditions as in inert atmosphere. In this work we introduce the UV-crosslinking of polynorbornenes made by ring opening metathesis polymerization making use of the residual double bond in the polymer backbone. The crosslinking experiments were done in thin films and were followed by FTIR measurements, to proof the accessibility of double-bonds in the polymers for the addition of the thiols. As a result of these pre-experiments we created flexible and light transmitting films. To further increase the scope of this reaction, amphiphilic block copolymers were prepared and used to form block copolymer micelles in a selective solvent, which were subsequently crosslinked with pentaerythritol tetra(3-mercaptopropionate) (PETMP). FT-IR, DLS and SEM-measurements were used to prove the successful crosslinking and thus nanoparticle formation.

Model-independent and fast determination of optical functions in storage rings via multiturn and closed-orbit data

Directory of Open Access Journals (Sweden)

Bernard Riemann

2011-06-01

Full Text Available Multiturn (or turn-by-turn data acquisition has proven to be a new source of direct measurements for Twiss parameters in storage rings. On the other hand, closed-orbit measurements are a long-known tool for analyzing closed-orbit perturbations with conventional beam position monitor (BPM systems and are necessarily available at every storage ring. This paper aims at combining the advantages of multiturn measurements and closed-orbit data. We show that only two multiturn BPMs and four correctors in one localized drift space in the storage ring (diagnostic drift are sufficient for model-independent and absolute measuring of β and φ functions at all BPMs, including the conventional ones, instead of requiring all BPMs being equipped with multiturn electronics.

Model-independent and fast determination of optical functions in storage rings via multiturn and closed-orbit data

Science.gov (United States)

Riemann, Bernard; Grete, Patrick; Weis, Thomas

2011-06-01

Multiturn (or turn-by-turn) data acquisition has proven to be a new source of direct measurements for Twiss parameters in storage rings. On the other hand, closed-orbit measurements are a long-known tool for analyzing closed-orbit perturbations with conventional beam position monitor (BPM) systems and are necessarily available at every storage ring. This paper aims at combining the advantages of multiturn measurements and closed-orbit data. We show that only two multiturn BPMs and four correctors in one localized drift space in the storage ring (diagnostic drift) are sufficient for model-independent and absolute measuring of β and φ functions at all BPMs, including the conventional ones, instead of requiring all BPMs being equipped with multiturn electronics.

About the activity and selectivity of less well-known metathesis catalysts during ADMET polymerizations

Directory of Open Access Journals (Sweden)

Hatice Mutlu

2010-12-01

Full Text Available We report on the catalytic activity of commercially available Ru-indenylidene and “boomerang” complexes C1, C2 and C3 in acyclic diene metathesis (ADMET polymerization of a fully renewable α,ω-diene. A high activity of these catalysts was observed for the synthesis of the desired renewable polyesters with molecular weights of up to 17000 Da, which is considerably higher than molecular weights obtained using the same monomer with previously studied catalysts. Moreover, olefin isomerization side reactions that occur during the ADMET polymerizations were studied in detail. The isomerization reactions were investigated by degradation of the prepared polyesters via transesterification with methanol, yielding diesters. These diesters, representing the repeat units of the polyesters, were then quantified by GC-MS.

Efficient synthetic methods for the installation of boron-nitrogen bonds in conjugated organic molecules.

Science.gov (United States)

Morgan, Matthew M; Piers, Warren E

2016-04-14

Polycyclic aromatic hydrocarbons in which one or more CC units have been replaced by isoelectronic BN units have attracted interest as potentially improved organic materials in various devices. This promise has been hampered by a lack of access to gram quantities of these materials. However, the exploitation of keystone reactions such as ring closing metathesis, borylative cyclization of amino styrenes and electrophilic borylation has lead to strategies for access to workable amounts of material. These strategies can be augmented by judicious postfunctionalization reactions to diversify the library of materials available. This Frontier article highlights some of the recent successes and shows that the long promised applications of BN-doped PAHs are beginning to be explored in a meaningful way.

The Effect of Nitrogen Surface Ligands on Propane Metathesis: Design and Characterizations of N-modified SBA15-Supported Schrock-type Tungsten Alkylidyne

KAUST Repository

Eid, Ahmed A.

2014-04-01

Catalysis, which is primarily a molecular phenomenon, is an important field of chemistry because it requires the chemical conversion of molecules into other molecules. It also has an effect on many fields, including, but not limited to, industry, environment and life Science[1]. Surface Organometallic Chemistry is an effective methodology for Catalysis as it imports the concept and mechanism of organometallic chemistry, to surface science and heterogeneous catalysis. So, it bridges the gap between homogenous and heterogeneous catalysis[1]. The aim of the present research work is to study the effect of Nitrogen surface ligands on the activity of Alkane, Propane in particular, metathesis. Our approach is based on the preparation of selectively well-defined group (VI) transition metal complexes supported onto mesoporous materials, SBA15 and bearing amido and/or imido ligands. We choose nitrogen ligands because, according to the literature, they showed in some cases better catalytic properties in homogenous catalysis in comparison with their oxygen counterparts[2]. The first section covers the modification of a highly dehydroxylated SBA15 surface using a controlled ammonia treatment. These will result in the preparation of two kind of Nitrogen surface ligands: -\\tOne with vicinal silylamine/silanol, (≡SiNH2)(≡SiOH), noted [N,O]SBA15 and, -\\tAnother\\tone\\twith\\tvicinal\\tbis-silylamine moieties (≡SiNH2)2, noted [N,N]SBA15[3]. The second section covers the reaction of Schrock type Tungsten Carbyne [W(≡C- tBu)(CH2-tBu)3] with those N-surface ligands and their characterizations by FT-IR, multiple quantum solid state NMR (1H, 13C), elemental analysis and gas phase analysis. The third section covers the generation of the active site, tungsten hydride species. Their performance toward propane metathesis reaction using the dynamic reactor technique PID compared toward previous well-known catalysts supported on silica oxide or mesoporous materials[4]. A fairly good

Study of ethylene/2-butene cross-metathesis over W-H/Al2O 3 for propylene production: Effect of the temperature and reactant ratios on the productivity and deactivation

KAUST Repository

Mazoyer, Etienne

2013-05-01

A highly active and selective catalyst based on supported tungsten hydride for the cross-metathesis between ethylene and 2-butenes yielding propylene has been investigated at low pressure with various temperatures and feed ratios. At low temperature (120 °C), the catalyst deactivates notably with time on stream. This phenomenon was extensively examined by DRIFTS, TGA, DSC, and solid-state NMR techniques. It was found that a large amount of carbonaceous species were formed due to a side-reaction such as olefin polymerization which took place simultaneously with the metathesis reaction. However, at 150 °C, the catalyst was stable with time and thereby gave a high productivity in propylene. Importantly, the slight increase in temperature clearly disfavored the side reaction. The ratio of ethylene to trans-2-butene was also studied, and surprisingly, the W-H/Al2O3 catalyst is stable and highly selective to propylene even at substoichiometric ethylene ratios. © 2013 Elsevier Inc. All rights reserved.

Medium-Ring Effects on the Endo/Exo Selectivity of the Organocatalytic Intramolecular Diels-Alder Reaction.

Science.gov (United States)

Hooper, Joel F; James, Natalie C; Bozkurt, Esra; Aviyente, Viktorya; White, Jonathan M; Holland, Mareike C; Gilmour, Ryan; Holmes, Andrew B; Houk, K N

2015-12-18

The intramolecular Diels-Alder reaction has been used as a powerful method to access the tricyclic core of the eunicellin natural products from a number of 9-membered-ring precursors. The endo/exo selectivity of this reaction can be controlled through a remarkable organocatalytic approach, employing MacMillan's imidazolidinone catalysts, although the mechanistic origin of this selectivity remains unclear. We present a combined experimental and density functional theory investigation, providing insight into the effects of medium-ring constraints on the organocatalyzed intramolecular Diels-Alder reaction to form the isobenzofuran core of the eunicellins.

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

Directory of Open Access Journals (Sweden)

Katrina Tait

2016-10-01

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

Metathesis synthesis and characterization of complex metal fluoride ...

Indian Academy of Sciences (India)

Administrator

V MANIVANNAN*, P PARHI and JONATHAN W KRAMER. Department of Mechanical Engineering, Campus Delivery 1374, Colorado State University, Fort Collins,. CO 80523, USA. MS received 30 April 2008. Abstract. Metathesis synthesis of complex metal fluorides using mechanochemical activation has been reported.

A Silica-Supported Monoalkylated Tungsten Dioxo Complex Catalyst for Olefin Metathesis

KAUST Repository

Maity, Niladri

2018-02-15

A well-defined silica-supported monoalkylated tungsten dioxo complex [(Si-O-)W(=O)(CH-Bu)] was prepared by treatment of highly dehydroxylated silica (SiO: silica treated at 700 °C under high vacuum) with an ionic precursor complex [NEt][W(=O)(CH-Bu)]. The identity of the resulting neutral monoalkylated tungsten dioxo surface complex was established by means of elemental microanalysis and spectroscopic studies (IR, solid-state NMR, Raman, and X-ray absorption spectroscopies). The supported tungsten complex was found to act as a precatalyst for the self-metathesis of 1-octene in a batch reactor. The mechanistic implications of this reaction are discussed with the support of DFT calculations highlighting the potential occurrence of thus-far unexplored mechanistic pathways.

A Silica-Supported Monoalkylated Tungsten Dioxo Complex Catalyst for Olefin Metathesis

KAUST Repository

Maity, Niladri; Barman, Samir; Minenkov, Yury; Ould-Chikh, Samy; Abou-Hamad, Edy; Ma, Tao; Qureshi, Ziyauddin; Cavallo, Luigi; D'Elia, Valerio; Gates, Bruce C.; Basset, Jean-Marie

2018-01-01

A well-defined silica-supported monoalkylated tungsten dioxo complex [(Si-O-)W(=O)(CH-Bu)] was prepared by treatment of highly dehydroxylated silica (SiO: silica treated at 700 °C under high vacuum) with an ionic precursor complex [NEt][W(=O)(CH-Bu)]. The identity of the resulting neutral monoalkylated tungsten dioxo surface complex was established by means of elemental microanalysis and spectroscopic studies (IR, solid-state NMR, Raman, and X-ray absorption spectroscopies). The supported tungsten complex was found to act as a precatalyst for the self-metathesis of 1-octene in a batch reactor. The mechanistic implications of this reaction are discussed with the support of DFT calculations highlighting the potential occurrence of thus-far unexplored mechanistic pathways.

Thermoset polymers via ring opening metathesis polymerization of functionalized oils

Science.gov (United States)

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

2012-11-27

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

Synthesis of Mono(perfluoroalkyl) Cyclodextrins via Cross Metathesis

Czech Academy of Sciences Publication Activity Database

Řezanka, M.; Eignerová, Barbara; Jindřich, J.; Kotora, M.

-, č. 32 (2010), s. 6256-6262 ISSN 1434-193X R&D Projects: GA AV ČR KAN200200651 Institutional research plan: CEZ:AV0Z40550506 Keywords : metathesis * cyclodextrins * fluorine * alkylation * amphiphiles Subject RIV: CC - Organic Chemistry Impact factor: 3.206, year: 2010

Model-Based, Closed-Loop Control of PZT Creep for Cavity Ring-Down Spectroscopy.

Science.gov (United States)

McCartt, A D; Ognibene, T J; Bench, G; Turteltaub, K W

2014-09-01

Cavity ring-down spectrometers typically employ a PZT stack to modulate the cavity transmission spectrum. While PZTs ease instrument complexity and aid measurement sensitivity, PZT hysteresis hinders the implementation of cavity-length-stabilized, data-acquisition routines. Once the cavity length is stabilized, the cavity's free spectral range imparts extreme linearity and precision to the measured spectrum's wavelength axis. Methods such as frequency-stabilized cavity ring-down spectroscopy have successfully mitigated PZT hysteresis, but their complexity limits commercial applications. Described herein is a single-laser, model-based, closed-loop method for cavity length control.

Structural diversification of the aminobicyclo[4.3.0]nonane skeleton using alkynylsilyl-derived allylic trichloroacetimidates.

Science.gov (United States)

Mostafa, Mohamed A B; McMillan, Angus E; Sutherland, Andrew

2017-04-05

The amino substituted bicyclo[4.3.0]nonane is a molecular scaffold found in a wide range of natural products and medicinal agents. Despite this, synthetic methods for the general preparation of this structural motif are sparse. Here we evaluate a diastereoselective approach for the preparation of vinylsilyl derived aminobicyclo[4.3.0]nonanes using a one-pot multi-bond forming process involving a Pd(ii)-catalysed Overman rearrangement, a Ru(ii)-catalysed ring closing enyne metathesis reaction, followed by a hydrogen bonding directed Diels-Alder reaction. We show that a benzyldimethylsilyl-substituted alkene analogue is amenable to further functionalisation and the late stage generation of diverse sp 3 -rich, drug-like aminobicyclo[4.3.0]nonane scaffolds with up to six stereogenic centres.

A Simple and Novel Approach to Delineating Stereochemistry of Electrocyclic Reactions

Science.gov (United States)

Mandal, Dipak K.

2012-01-01

The dynamic stereochemistry of electrocyclic reactions (a class of pericyclic reactions) stems from the operation of either conrotatory (con) or disrotatory (dis) mode of ring-closing and ring-opening processes. Difficulty is often encountered in depicting product stereochemistry resulting from such movements of substituents. A novel, simple,…

Metathesis of alkanes and related reactions

KAUST Repository

Basset, Jean-Marie; Copé ret, Christophe; Soulivong, Daravong; Taoufik, Mostafa; Thivolle-Cazat, Jean

2010-01-01

, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, (=SiO)2TaH, a multifunctional catalyst with a single site of action. This reaction completes the story

Rare-earth-metal nitridophosphates through high-pressure metathesis

International Nuclear Information System (INIS)

Kloss, Simon David; Schnick, Wolfgang

2015-01-01

Developing a synthetic method to target an broad spectrum of unknown phases can lead to fascinating discoveries. The preparation of the first rare-earth-metal nitridophosphate LiNdP_4N_8 is reported. High-pressure solid-state metathesis between LiPN_2 and NdF_3 was employed to yield a highly crystalline product. The in situ formed LiF is believed to act both as the thermodynamic driving force and as a flux to aiding single-crystal formation in dimensions suitable for crystal structure analysis. Magnetic properties stemming from Nd"3"+ ions were measured by SQUID magnetometry. LiNdP_4N_8 serves as a model system for the exploration of rare-earth-metal nitridophosphates that may even be expanded to transition metals. High-pressure metathesis enables the systematic study of these uncharted regions of nitride-based materials with unprecedented properties. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Olefin Metathesis in Peptidomimetics, Dynamic Combinatorial Chemistry, and Molecular Imprinting

National Research Council Canada - National Science Library

Low, Tammy K

2006-01-01

.... Our research goals consisted of employing olefin metathesis in the synthesis of peptidomimetics, and studying the feasibility of this method in dynamic combinatorial chemistry and molecular imprinting of nerve agents...

Convergent Synthesis of Pancratistatin from Piperonal and Xylose

DEFF Research Database (Denmark)

Dam, Johan Hygum; Madsen, Robert

2009-01-01

to afford a highly functionalised 1,7-diene, which is then converted into the corresponding cyclohexene by ring-closing olefin metathesis. Subsequent Overman rearrangement, dihydroxylation and deprotection afford the natural product in a total of 25 steps from the two starting materials. The longest linear...

Total Syntheses of Cyanthiwigins B, F, and G

KAUST Repository

Enquist, John A.

2011-07-18

A concise and versatile approach toward the preparation of the cyanthiwigin family of cyathane natural products is described. By leveraging a unique double asymmetric catalytic alkylation procedure it is possible to quickly establish two of the most critical stereocenters of the cyanthiwigin framework with high levels of selectivity and expediency. The synthetic route additionally employs both a tandem ring-closing cross-metathesis reaction, and an aldehyde-olefin radical cyclization process, in order to rapidly arrive at the tricyclic cyathane core of the cyanthiwigin molecules. From this unifying intermediate, the preparations of cyanthiwigins B, F, and G are attained swiftly and without the need for protecting groups.

Total Syntheses of Cyanthiwigins B, F, and G

KAUST Repository

Enquist, John A.; Virgil, Scott C.; Stoltz, Brian M.

2011-01-01

A concise and versatile approach toward the preparation of the cyanthiwigin family of cyathane natural products is described. By leveraging a unique double asymmetric catalytic alkylation procedure it is possible to quickly establish two of the most critical stereocenters of the cyanthiwigin framework with high levels of selectivity and expediency. The synthetic route additionally employs both a tandem ring-closing cross-metathesis reaction, and an aldehyde-olefin radical cyclization process, in order to rapidly arrive at the tricyclic cyathane core of the cyanthiwigin molecules. From this unifying intermediate, the preparations of cyanthiwigins B, F, and G are attained swiftly and without the need for protecting groups.

Posterior pelvic ring fractures: Closed reduction and percutaneous CT-guided sacroiliac screw fixation

International Nuclear Information System (INIS)

Jacob, Augustinus Ludwig; Messmer, Peter; Stock, Klaus-Wilhelm; Suhm, Norbert; Baumann, Bernard; Regazzoni, Pietro; Steinbrich, Wolfgang

1997-01-01

Purpose. To assess the midterm results of closed reduction and percutaneous fixation (CRPF) with computed tomography (CT)-guided sacroiliac screw fixation in longitudinal posterior pelvic ring fractures. Methods. Thirteen patients with 15 fractures were treated. Eleven patients received a unilateral, two a bilateral, screw fixation. Twenty-seven screws were implanted. Continuous on-table traction was used in six cases. Mean radiological follow-up was 13 months. Results. Twenty-five (93%) screws were placed correctly. There was no impingement of screws on neurovascular structures. Union occurred in 12 (80%), delayed union in 2 (13%), and nonunion in 1 of 15 (7%) fractures. There was one screw breakage and two axial dislocations. Conclusion. Sacroiliac CRPF of longitudinal fractures of the posterior pelvic ring is technically simple, minimally invasive, well localized, and stable. It should be done by an interventional/surgical team. CT is an excellent guiding modality. Closed reduction may be a problem and succeeds best when performed as early as possible

A Stereoselective [3+1] Ring Expansion for the Synthesis of Highly Substituted Methylene Azetidines.

Science.gov (United States)

Schmid, Steven C; Guzei, Ilia A; Schomaker, Jennifer M

2017-09-25

The reaction of rhodium-bound carbenes with strained bicyclic methylene aziridines results in a formal [3+1] ring expansion to yield highly substituted methylene azetidines with excellent regio- and stereoselectivity. The reaction appears to proceed through an ylide-type mechanism, where the unique strain and structure of the methylene aziridine promotes a ring-opening/ring-closing cascade that efficiently transfers chirality from substrate to product. The resultant products can be elaborated into new azetidine scaffolds containing vicinal tertiary-quaternary and even quaternary-quaternary stereocenters. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Synthesis of cis- and trans-Fused Bicyclic Sugar Amino Acids

NARCIS (Netherlands)

Risseeuw, Martijn D.P.; Grotenbreg, Gijsbert M.; Witte, Martin D.; Tuin, Adriaan W.; Leeuwenburgh, Michiel A.; Marel, Gijsbert A. van der; Overkleeft, Herman S.; Overhand, Mark

2006-01-01

Four isomeric bicyclic sugar amino acids (SAAs) were prepared from an α-acetylenic-C-glucoside by employing a Petasis olefination and a ring-closing metathesis (RCM) as key steps. The applicability of the resulting SAAs in solid-phase peptide synthesis was demonstrated by the synthesis of a

The enantioselective total synthesis of (+)-clusianone.

Science.gov (United States)

Horeischi, Fiene; Guttroff, Claudia; Plietker, Bernd

2015-02-11

(+)-Clusianone, an exo-type B PPAP with reported anti-HIV and chemoprotective activities, was synthesized in eleven steps with 97% ee starting from acetylacetone. An enantioselective decarboxylative Tsuji-Trost-allylation and a Ru-catalyzed ring-closing metathesis-decarboxylative allylation were used to control both diastereo- and enantioselectivity.

A simple approach to the construction of the core structure present

Indian Academy of Sciences (India)

A convenient route for the synthesis of oxacyclobutapentalene, the tricyclic bridged core structure present in bioactive marine diterpene bielschowskysin and the polyketide hippolachnin A, is reported. The key steps involve ring closing metathesis of a triene derived from D-mannitol to produce selectively the dihydrofuran ...

Exploring new generations of ruthenium olefin metathesis catalysts: The reactivity of a bis-ylidene ruthenium complex by DFT

KAUST Repository

Poater, Albert; Credendino, Raffaele; Slugovc, Christian; Cavallo, Luigi

2013-01-01

Density functional theory calculations were used to predict the behaviour of a potential novel architecture of olefin metathesis catalysts, in which one of the neutral ligands of classical Ru-based catalysts, e.g. a phosphine or an N-heterocyclic carbene, is replaced by an alkylidene group. Introduction of a second alkylidene ligand favors dissociation of the remaining phosphine and the overall energy profile for the metathesis using ethylene as the probe substrate reveals that the proposed bis-alkylidene complexes might match the requirements of a good performing olefin metathesis catalyst. © 2013 The Royal Society of Chemistry.

Explicitly-correlated ring-coupled-cluster-doubles theory: Including exchange for computations on closed-shell systems

Energy Technology Data Exchange (ETDEWEB)

Hehn, Anna-Sophia; Holzer, Christof; Klopper, Wim, E-mail: klopper@kit.edu

2016-11-10

Highlights: • Ring-coupled-cluster-doubles approach now implemented with exchange terms. • Ring-coupled-cluster-doubles approach now implemented with F12 functions. • Szabo–Ostlund scheme (SO2) implemented for use in SAPT. • Fast convergence to the limit of a complete basis. • Implementation in the TURBOMOLE program system. - Abstract: Random-phase-approximation (RPA) methods have proven to be powerful tools in electronic-structure theory, being non-empirical, computationally efficient and broadly applicable to a variety of molecular systems including small-gap systems, transition-metal compounds and dispersion-dominated complexes. Applications are however hindered due to the slow basis-set convergence of the electron-correlation energy with the one-electron basis. As a remedy, we present approximate explicitly-correlated RPA approaches based on the ring-coupled-cluster-doubles formulation including exchange contributions. Test calculations demonstrate that the basis-set convergence of correlation energies is drastically accelerated through the explicitly-correlated approach, reaching 99% of the basis-set limit with triple-zeta basis sets. When implemented in close analogy to early work by Szabo and Ostlund [36], the new explicitly-correlated ring-coupled-cluster-doubles approach including exchange has the perspective to become a valuable tool in the framework of symmetry-adapted perturbation theory (SAPT) for the computation of dispersion energies of molecular complexes of weakly interacting closed-shell systems.

Impact of electronic modification of the chelating benzylidene ligand in cis-dichloro-configured second-generation olefin metathesis catalysts on their activity

KAUST Repository

Pump, Eva; Poater, Albert; Zirngast, Michaela; Torvisco, Ana; Fischer, Roland C.; Cavallo, Luigi; Slugovc, Christian

2014-01-01

A series of electronically modified second-generation cis-dichloro ruthenium ester chelating benzylidene complexes was prepared, characterized, and benchmarked in a typical ring-opening metathesis polymerization (ROMP) experiment. The electronic tuning of the parent chelating benzylidene ligand (2-ethyl ester benzylidene) was achieved by substitution at the 4- and 5-positions with electron-withdrawing nitro or electron-donating methoxy groups. The effect of the electronic tuning on the cis-trans isomerization process was studied experimentally and theoretically. Density functional theory calculations clearly revealed the influence of electronic modification on the relative stability between the cis and trans isomers, which is decisive for the activity of the studied compounds as initiators in ROMP. © 2014 American Chemical Society.

Impact of electronic modification of the chelating benzylidene ligand in cis-dichloro-configured second-generation olefin metathesis catalysts on their activity

KAUST Repository

Pump, Eva

2014-06-09

A series of electronically modified second-generation cis-dichloro ruthenium ester chelating benzylidene complexes was prepared, characterized, and benchmarked in a typical ring-opening metathesis polymerization (ROMP) experiment. The electronic tuning of the parent chelating benzylidene ligand (2-ethyl ester benzylidene) was achieved by substitution at the 4- and 5-positions with electron-withdrawing nitro or electron-donating methoxy groups. The effect of the electronic tuning on the cis-trans isomerization process was studied experimentally and theoretically. Density functional theory calculations clearly revealed the influence of electronic modification on the relative stability between the cis and trans isomers, which is decisive for the activity of the studied compounds as initiators in ROMP. © 2014 American Chemical Society.

New regioselective multicomponent reaction: one pot synthesis of spiro heterobicyclic aliphatic rings.

Science.gov (United States)

Byk, G; Gottlieb, H E; Herscovici, J; Mirkin, F

2000-01-01

In the context of our high-throughput organic synthesis program, we have studied the reactivity of special beta-keto esters toward the Biginelli reaction. We have found that a cyclic beta-keto ester reacts with one molecule of urea and two molecules of aldehyde to give a new family of spiro heterobicyclic aliphatic rings in good yields. Interestingly, the Biginelli product was not detected. After analysis of products using HPLC, 1H NMR, and 13C NMR, we have found that the reaction is driven by a regio-specific condensation of two molecules of aldehyde with the other reagents to afford only products harboring substituents exclusively in cis configuration. Monte Carlo minimization studies using MM2 force field suggest that cis products are energetically more stable than the trans counterparts. Together with previously reported data, these results suggest that the trans products were not obtained as result of steric hindrance produced by the equatorial position of one of the ring substituents. This new reaction is useful for high-throughput organic synthesis. Indeed, the new scaffold can be used to introduce additional groups in the molecules through remaining functional groups by a "domino strategy".

Characterization and reactions of a Salix extractive with a unique ring system

Science.gov (United States)

Lawrence Landucci; Sally Ralph; Kolby Hirth

2003-01-01

An extractive compound with a novel ring system was isolated from the wood of Salix alba and was given the name Salucci. The compound was primarily identified from the 1D NMR, 2D NMR and LC-MSMS data and the structure investigated through reactions and derivatizations.

Extrudate versus Powder Silica Alumina as Support for Re2O7 Catalyst in the Metathesis of Seed Oil-Derivatives – A Comparison

Directory of Open Access Journals (Sweden)

Bassie B. Marvey

2009-01-01

Full Text Available Self- and cross-metathesis of fatty acid methyl esters (FAMEs was investigated using a silica alumina supported Re2O7 catalyst. Although a 3 wt% Re2O7/SiO2-Al2O3/SnBu4 is already active for the metathesis of unsaturated FAMEs, the results have shown that particle size of silica alumina support has a profound influence on its activity and selectivity. Consequently, high substrate conversions coupled with improved product yields (for mono- and diesters and reaction rates were obtained upon using powder, as opposed to extrudate silica alumina as the support material. Diesters are platform compounds for the synthesis of polymers and fragrances. In this paper a comparative outline of the influence of particle size of silica alumina (extrudate versus powder on catalytic performance of a 3 wt% Re2O7/SiO2-Al2O3/SnBu4 for self- and cross-metathesis of FAMEs is made. Low surface area and diffusion constraints associated with extrudates were identified as some of the factors leading to low catalytic activity and selectivity.

Control of alpha/beta Anomer Formation by a 2',5' Bridge: Toward Nucleoside Derivatives Locked in the South Conformation

Czech Academy of Sciences Publication Activity Database

Hřebabecký, Hubert; Dračínský, Martin; Procházková, Eliška; Šála, Michal; Mackman, R.; Nencka, Radim

2017-01-01

Roč. 82, č. 21 (2017), s. 11337-11347 ISSN 0022-3263 R&D Projects: GA ČR(CZ) GA16-20054S Institutional support: RVO:61388963 Keywords : borne encephalitis virus * ring closing metathesis * nucleotide analogs Subject RIV: CC - Organic Chemistry OBOR OECD: Organic chemistry Impact factor: 4.849, year: 2016

Carbon Dioxide Utilization by the Five-Membered Ring Products of Cyclometalation Reactions

Science.gov (United States)

Omae, Iwao

2016-01-01

In carbon dioxide utilization by cyclometalated five-membered ring products, the following compounds are used in four types of applications: 1. 2-Phenylpyrazole iridium compounds, pincer phosphine iridium compounds and 2-phenylimidazoline iridium compounds are used as catalysts for both formic acid production from CO2 and H2, and hydrogen production from the formic acid. This formic acid can be a useful agent for H2 production and storage for fuel cell electric vehicles. 2. Other chemicals, e.g., dimethyl carbonate, methane, methanol and CO, are produced with dimethylaminomethylphenyltin compounds, pincer phosphine iridium compounds, pincer phosphine nickel compound and ruthenium carbene compound or 2-phenylpyridine iridium compounds, and phenylbenzothiazole iridium compounds as the catalysts for the reactions with CO2. 3. The five-membered ring intermediates of cyclometalation reactions with the conventional substrates react with carbon dioxide to afford their many types of carboxylic acid derivatives. 4. Carbon dioxide is easily immobilized at room temperature with immobilizing agents such as pincer phosphine nickel compounds, pincer phosphine palladium compounds, pincer N,N-dimethylaminomethyltin compounds and tris(2-pyridylthio)methane zinc compounds. PMID:28503084

Synthesis of 5/7-, 5/8- and 5/9-bicyclic lactam templates as constraints for external beta-turns.

Science.gov (United States)

Duggan, Heather M E; Hitchcock, Peter B; Young, Douglas W

2005-06-21

The 5/7-, 5/8- and 5/9-bicyclic lactams 3, 17, 5 and 6 have been synthesised as single diastereoisomers by a route involving ring closing olefin metathesis. The X-ray crystal structure of the amino acid hydrochloride has been carried out and compared to that of the saturated external beta-turn constraint 18.

Alkane metathesis with the tantalum methylidene [(≡SiO)Ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)Me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4

KAUST Repository

Chen, Yin; Abou-Hamad, Edy; Hamieh, Ali Imad Ali; Hamzaoui, Bilel; Emsley, Lyndon; Basset, Jean-Marie

2015-01-01

By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(≡SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(≡SiO)2Ta(=CH2)Me] and [(≡SiO)Ta(=CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(≡SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction.

Alkane metathesis with the tantalum methylidene [(≡SiO)Ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)Me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4

KAUST Repository

Chen, Yin

2015-01-21

By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(≡SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(≡SiO)2Ta(=CH2)Me] and [(≡SiO)Ta(=CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(≡SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction.

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

Science.gov (United States)

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

2008-07-31

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

Synthesis of naturally occurring iminosugars from D-fructose by the use of a zinc-mediated fragmentation reaction

DEFF Research Database (Denmark)

Lauritsen, Anne; Madsen, Robert

2006-01-01

A short synthesis of 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) and a formal synthesis of australine are described. In both cases, D-fructose is employed as the starting material and converted into a protected methyl 6-deoxy-6-iodo-furanoside. Zinc-mediated fragmentation produces an unsaturated...... ketone which serves as a key building block for both syntheses. Ozonolysis, reductive amination with benzylamine and deprotection affordfs 1,4-dideoxy-1,4-imino-D-arabinitol in only 7 steps and 11% overall yield from D-fructose. Alternatively, reductive amination with homoallylamine, ring......-closing metathesis and protecting group manipulations give rise to an intermediate which can be converted into australine in 3 steps. The intermediate is prepared by two different strategies both of which use a total of 9 steps. The first strategy utilizes benzyl ethers for protection of fructose while the second...

Digital closed orbit feedback system for the Advanced Photon Source storage ring

International Nuclear Information System (INIS)

Chung, Y.; Barr, D.; Decker, G.; Galayda, J.; Lenkszus, F.; Lumpkin, A.; Votaw, A.J.

1995-01-01

Closed orbit feedback for the Advanced Photon Source (APS) storage ring employs unified global an local feedback systems for stabilization of particle and photon beams based on digital signal processing (DSP). Hardware and software aspects of the system will be described. In particular, we will discuss global and local orbit feedback algorithms, PID (proportional, integral, and derivative) control algorithm. application of digital signal processing to compensate for vacuum chamber eddy current effects, resolution of the interaction between global and local systems through decoupling, self-correction of the local bump closure error, user interface through the APS control system, and system performance in the frequency and time domains. The system hardware, including the DSPS, is distributed in 20 VNE crates around the ring, and the entire feedback system runs synchronously at 4-kHz sampling frequency in order to achieve a correction bandwidth exceeding 100 Hz. The required data sharing between the global and local feedback systems is facilitated via the use of fiber-optically-networked reflective memories

Mesoporous molecular sieves as advanced supports for olefin metathesis catalysts

Czech Academy of Sciences Publication Activity Database

Balcar, Hynek; Čejka, Jiří

2013-01-01

Roč. 257, 21-22 (2013), s. 3107-3124 ISSN 0010-8545 R&D Projects: GA AV ČR IAA400400805; GA ČR GBP106/12/G015 Institutional support: RVO:61388955 Keywords : Olefin metathesis * mesoporous molecular sieves * Heterogeneous catalysts Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 12.098, year: 2013

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

Energy Technology Data Exchange (ETDEWEB)

Soorkia, Satchin; Taatjes, Craig A.; Osborn, David L.; Selby, Talitha M.; Trevitt, Adam J.; Wilson, Kevin R.; Leone, Stephen R.

2010-03-16

The reaction of the ground state methylidyne radical CH (X2Pi) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 90 oC (363 K), at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by Helimination. The Photoionization Efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (dpyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as in gas-phase combustion processes, are discussed.

Global DC closed orbit correction experiments on the NSLS X-ray ring and SPEAR

International Nuclear Information System (INIS)

Chung, Y.; Decker, G.; Evans, K. Jr.; Safranek, J.; So, I.; Tang, Y.; Corbett, W.J.; Hettel, R.

1993-01-01

The global closed orbit correction experiments conducted on the NSLS X-ray ring and the SPEAR using the technique of singular value decomposition (SVD) are presented. The beam response matrix, defined as beam motion at beam position monitor (BPM) locations per unit kick by corrector magnets, was measured and then analyzed using SVD. The BPMs and correctors are reconfigured into open-quotes transformedclose quotes BPMs (t-BPMs) and open-quotes transformedclose quotes correctors (t-correctors), with each T-BPM coupled to at most one t-corrector and vice versa for orbit correction. The decoupled t-BPMs are used to estimate the limit on orbit correction, while the decoupled t-correctors are used to optimize the corrector strengths. As a result the vertical r.m.s. orbit error at the BPM locations was reduced from 208 μm to 61 μm about an arbitrary reference orbit in the NSLS X-ray ring. In SPEAR, the vertical closed orbit was brought to the BPM centers at the selected BPM locations with an r.m.s. error of 215 μm reduced from the initial 780 μm

Efficient Synthesis of Spirobarbiturates and Spirothiobarbiturates Bearing Cyclopropane Rings by Rhodium(II)-Catalyzed Reactions of Cyclic Diazo Compounds

International Nuclear Information System (INIS)

Wang, Xue; Lee, Yong Rok

2013-01-01

Rhodium(II)-catalyzed reactions of cyclic diazo compounds derived from barbituric acid and thiobarbituric acid with a variety of styrene moieties were examined. These reactions provide rapid synthetic routes to the preparations of spirobarbiturates and spirothiobarbiturates bearing cyclopropane rings

Efficient Synthesis of Spirobarbiturates and Spirothiobarbiturates Bearing Cyclopropane Rings by Rhodium(II)-Catalyzed Reactions of Cyclic Diazo Compounds

Energy Technology Data Exchange (ETDEWEB)

Wang, Xue; Lee, Yong Rok [Yeungnam Univ., Gyeongsan (Korea, Republic of)

2013-06-15

Rhodium(II)-catalyzed reactions of cyclic diazo compounds derived from barbituric acid and thiobarbituric acid with a variety of styrene moieties were examined. These reactions provide rapid synthetic routes to the preparations of spirobarbiturates and spirothiobarbiturates bearing cyclopropane rings.

Domino Wittig Diels-Alder reaction: An expeditious entry into the AB ring system of furanosesquiterpenes

Digital Repository Service at National Institute of Oceanography (India)

Patre, R.E.; Gawas, S.; Sen, S.; Parameswaran, P.S.; Tilve, S.G.

A domino Wittig Diels - Alder reaction has been employed in delineating a short and flexible synthetic stratagem for ready access to the AB ring system and the tricyclic framework of furanosesquiterpenes, such as the bioactive natural products...

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

Science.gov (United States)

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

2017-04-10

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

Moving from Classical Ru-NHC to Neutral or Charged Rh-NHC Based Catalysts in Olefin Metathesis

Directory of Open Access Journals (Sweden)

Albert Poater

2016-01-01

Full Text Available Considering the versatility of oxidation states of rhodium together with the successful background of ruthenium-N-heterocyclic carbene based catalysts in olefin metathesis, it is envisaged the exchange of the ruthenium of the latter catalysts by rhodium, bearing an open-shell neutral rhodium center, or a +1 charged one. In the framework of in silico experiments, density functional theory (DFT calculations have been used to plot the first catalytic cycle that as a first step includes the release of the phosphine. DFT is, in this case, the tool that allows the discovery of the less endergonic reaction profile from the precatalytic species for the neutral catalyst with respect to the corresponding ruthenium one; increasing the endergonic character when dealing with the charged system.

Exploiting Confinement Effects to Tune Selectivity in Cyclooctane Metathesis

KAUST Repository

Pump, Eva; Cao, Zhen; Samantaray, Manoja K; Bendjeriou-Sedjerari, Anissa; Cavallo, Luigi; Basset, Jean-Marie

2017-01-01

. In contrast, in larger pores (60 Å) a broad product distribution dominated by ring contracted cycloalkanes was found. The catalytic cycle and potential side reactions occurring at [(≡SiO-)WMe5] were examined with DFT calculations. Analysis of the geometries

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

KAUST Repository

Żukowska, Karolina; Pump, Eva; Pazio, Aleksandra E; Woźniak, Krzysztof; Cavallo, Luigi; Slugovc, Christian

2015-01-01

Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted compound. The studied complexes are very stable at high temperatures up to 140 °C. The placement of an electron-withdrawing functionality translates into an enhanced activity in RCM. While electronically modified precatalysts, which exist predominantly in the trans-dichloro configuration, gave mostly the RCM and a minor amount of the cycloisomerization product, the unmodified congener, which preferentially exists as its cis-dichloro isomer, shows a switched reactivity. The position of the equilibrium between the cis- and the trans-dichloro species was found to be the crucial factor governing the reactivity of the complexes.

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

KAUST Repository

Żukowska, Karolina

2015-08-20

Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted compound. The studied complexes are very stable at high temperatures up to 140 °C. The placement of an electron-withdrawing functionality translates into an enhanced activity in RCM. While electronically modified precatalysts, which exist predominantly in the trans-dichloro configuration, gave mostly the RCM and a minor amount of the cycloisomerization product, the unmodified congener, which preferentially exists as its cis-dichloro isomer, shows a switched reactivity. The position of the equilibrium between the cis- and the trans-dichloro species was found to be the crucial factor governing the reactivity of the complexes.

Pyrimidine-pyridine ring interconversion

NARCIS (Netherlands)

Plas, van der H.C.

2003-01-01

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

Metathesis of cardanol over Ru catalysts supported on mesoporousmolecular sieve SBA-15

Czech Academy of Sciences Publication Activity Database

Shinde, Tushar; Varga, Vojtěch; Polášek, Miroslav; Horáček, Michal; Žilková, Naděžda; Balcar, Hynek

2014-01-01

Roč. 478, MAY 2014 (2014), s. 138-145 ISSN 0926-860X R&D Projects: GA ČR(CZ) GAP106/12/0189 Institutional support: RVO:61388955 Keywords : cardanol * metathesis * supported catalysts Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.942, year: 2014

and 8-Membered Oxygen-containing Benzo-fused Rings using ...

African Journals Online (AJOL)

NJD

A number of benzo-fused oxygen-containing heterocycles were synthesized from allyl-3-isopropoxy-4-methoxybenzaldehyde using metathesis or an alkene isomerization-metathesis sequence as key synthetic steps. Benzo-fused compounds thus formed included a 3,6-dihydro-1H-2-benzoxocine, ...

1. Mono([8]annulene)Uranium(4) half-sandwich complexes, 2. Novel syntheses of symmetrically substituted cyclooctatetetraenes

International Nuclear Information System (INIS)

Boussie, T.R.

1991-10-01

A reproducible, high-yield synthesis of mono([8]annulene)uranium(4)dichloride (1) is reported, along with the X-ray crystal structural of the bis(pyridine) adduct. Metathesis reactions of the half-sandwich complex 1 with a variety of simple alkyl and alkoxy reagents failed to generate any isolable mono-ring complexes. Reactions of 1 with polydentate, delocalized anions did produce stable derivatives, including mono([8]annulene)uranium(4)bis(acetylacetonate) (4). An X-ray crystal structure of 4 is reported

1. Mono([8]annulene)Uranium(4) half-sandwich complexes, 2. Novel syntheses of symmetrically substituted cyclooctatetetraenes

Energy Technology Data Exchange (ETDEWEB)

Boussie, Thomas Richard [Univ. of California, Berkeley, CA (United States)

1991-10-01

A reproducible, high-yield synthesis of mono([8]annulene)uranium(4)dichloride (1) is reported, along with the X-ray crystal structural of the bis(pyridine) adduct. Metathesis reactions of the half-sandwich complex 1 with a variety of simple alkyl and alkoxy reagents failed to generate any isolable mono-ring complexes. Reactions of 1 with polydentate, delocalized anions did produce stable derivatives, including mono([8]annulene)uranium(4)bis(acetylacetonate) (4). An X-ray crystal structure of 4 is reported.

1. Mono((8)annulene)Uranium(4) half-sandwich complexes, 2. Novel syntheses of symmetrically substituted cyclooctatetetraenes

Energy Technology Data Exchange (ETDEWEB)

Boussie, T.R.

1991-10-01

A reproducible, high-yield synthesis of mono((8)annulene)uranium(4)dichloride (1) is reported, along with the X-ray crystal structural of the bis(pyridine) adduct. Metathesis reactions of the half-sandwich complex 1 with a variety of simple alkyl and alkoxy reagents failed to generate any isolable mono-ring complexes. Reactions of 1 with polydentate, delocalized anions did produce stable derivatives, including mono((8)annulene)uranium(4)bis(acetylacetonate) (4). An X-ray crystal structure of 4 is reported.

Digital closed orbit feedback system for the advanced photon source storage ring

International Nuclear Information System (INIS)

Chung, Y.; Barr, D.; Decker, G.

1995-01-01

The Advanced Photon Source (APS) is a dedicated third-generation synchrotron light source with a nominal energy of 7 GeV and a circumference of 1104 m. The closed orbit feedback system for the APS storage ring employs unified global and local feedback systems for stabilization of particle and photon beams based on digital signal processing (DSP). Hardware and software aspects of the system will be described in this paper. In particular, we will discuss global and local orbit feedback algorithms, PID (proportional, integral, and derivative) control algorithm, application of digital signal processing to compensate for vacuum chamber eddy current effects, resolution of the interaction between global and local systems through decoupling, self-correction of the local bump closure error, user interface through the APS control system, and system performance in the frequency and time domains. The system hardware including the DSPs is distributed in 20 VME crates around the ring, and the entire feedback system runs synchronously at 4-kHz sampling frequency in order to achieve a correction bandwidth exceeding 100 Hz. The required data sharing between the global and local feedback systems is facilitated via the use of fiber-optically-networked reflective memories

The reaction of 1-tetralones with thallium trinitrate supported on clay: ring contraction vs a-oxidation

Directory of Open Access Journals (Sweden)

Ferraz Helena M. C.

2001-01-01

Full Text Available The reaction of a series of 1-tetralones with thallium trinitrate supported on Montmorillonite K-10 clay led to products of ring contraction (methyl indan-1-carboxylates and/or alpha-oxidation (2-methoxy-1-tetralones, in variable yields.

Catalyst Deactivation Reactions : The Role of Tertiary Amines Revisited

NARCIS (Netherlands)

Novarino, Elena; Rios, Itzel Guerrero; van der Veer, Siebe; Meetsma, Auke; Hessen, Bart; Bouwkamp, Marco W.

2011-01-01

Decamethylzirconocene cation [Cp*2ZrMe](+) (2) decomposes in bromobenzene-d(5) solution to generate sigma-aryl species [Cp*Zr-2(2-C6H4Br-kappa Br,C)][B(C6F5)(4)] (3). This a-bond metathesis reaction is catalyzed by tertiary amines via a two-step mechanism, in which the amine acts as a proton relay.

Alternative loop rings

CERN Document Server

Goodaire, EG; Polcino Milies, C

1996-01-01

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

Bimacrocyclic concave N-heterocyclic carbenes (NHCs): synthesis, structure, and application in catalyses

OpenAIRE

Lüning , Ulrich; Winkelmann , Ole

2009-01-01

Abstract Imidazolinium moieties have been incorporated into bimacrocycles to generate precursors for concave N-heterocyclic carbenes (NHCs). Starting from 2-nitroresorcinol and alkenols, symmetric concave imidazolinium salts 1 were obtained. Bimacrocyclization was achieved via ring closing metathesis (RCM). In an analogous fashion, axially chiral concave imidazolinium salts 2 were obtained by using a naphthalene bridgehead devoid of local C2-symmetry. The concave NHCs derived from ...

Novel phosphanucleoside analogs of dideoxynucleosides

Czech Academy of Sciences Publication Activity Database

Páv, Ondřej; Buděšínský, Miloš; Rosenberg, Ivan

2017-01-01

Roč. 73, č. 34 (2017), s. 5220-5228 ISSN 0040-4020 R&D Projects: GA ČR(CZ) GA17-12703S; GA ČR GA13-26526S; GA MZd NV15-31604A Institutional support: RVO:61388963 Keywords : phosphanucleoside * nucleoside analog * ring-closing metathesis * stereoselective hydroboration * chiral resolution Subject RIV: CC - Organic Chemistry OBOR OECD: Organic chemistry Impact factor: 2.651, year: 2016

Synthesis of allocolchicinoids: a 50 year journey

International Nuclear Information System (INIS)

Sitnikov, N S; Fedorov, A Yu

2013-01-01

Published data on the stereo- and enantioselective synthesis of allocolchicinoids, which are of interest as antitumour agents, are summarized. The stereochemistry of these compounds is described. Two key approaches to their preparation are considered, namely, the synthesis from natural colchicine and total synthesis from commercially available reagents. Various total syntheses of N-acetylcolchicinol are performed using biaryl oxidative and reductive coupling, cyclopropanation–ring expansion and Nicholas reaction. The synthetic routes to allocolchicine are based on Diels–Alder cycloaddition, combination of metathesis and Diels–Alder reaction and direct catalytic CH-arylation. Analogues of the colchicine site ligands incorporating heteroaromatic rings are briefly considered; their structural features and methods of synthesis are discussed. The bibliography includes 144 references.

Thermodynamically consistent Bayesian analysis of closed biochemical reaction systems

Directory of Open Access Journals (Sweden)

Goutsias John

2010-11-01

Full Text Available Abstract Background Estimating the rate constants of a biochemical reaction system with known stoichiometry from noisy time series measurements of molecular concentrations is an important step for building predictive models of cellular function. Inference techniques currently available in the literature may produce rate constant values that defy necessary constraints imposed by the fundamental laws of thermodynamics. As a result, these techniques may lead to biochemical reaction systems whose concentration dynamics could not possibly occur in nature. Therefore, development of a thermodynamically consistent approach for estimating the rate constants of a biochemical reaction system is highly desirable. Results We introduce a Bayesian analysis approach for computing thermodynamically consistent estimates of the rate constants of a closed biochemical reaction system with known stoichiometry given experimental data. Our method employs an appropriately designed prior probability density function that effectively integrates fundamental biophysical and thermodynamic knowledge into the inference problem. Moreover, it takes into account experimental strategies for collecting informative observations of molecular concentrations through perturbations. The proposed method employs a maximization-expectation-maximization algorithm that provides thermodynamically feasible estimates of the rate constant values and computes appropriate measures of estimation accuracy. We demonstrate various aspects of the proposed method on synthetic data obtained by simulating a subset of a well-known model of the EGF/ERK signaling pathway, and examine its robustness under conditions that violate key assumptions. Software, coded in MATLAB®, which implements all Bayesian analysis techniques discussed in this paper, is available free of charge at http://www.cis.jhu.edu/~goutsias/CSS%20lab/software.html. Conclusions Our approach provides an attractive statistical methodology for

Metal-mediated gem-Difluoroallylation of N-Acylhydrazones: Highly Efficient Synthesis of a,a-Difluorohomoallylic Amines

Institute of Scientific and Technical Information of China (English)

YUE Xuyi; QIU Xiaolong; QING Fengling

2009-01-01

Indium-mediated gem-difluoroallylation of aldehyde-derived N-acylhydrazones 1a-1q and 4a-4g with 3-bromo-3,3-difluoropropene 2 afforded a,a-difluorohomoallylic hydrazides 3a-3q and 5a-5g in high yields, re-spectively. Functional groups such as nitro, phenolic hydroxyl, benzyloxy and even C=C bonds of a,fl-unsaturated aldehydes were compatible under this mild and operationally simple gem-difluoroallylic reaction condition. By means of substitution of Zn powder for indium, gem-difluoroallylation of ketone-derived N-acylhydrazones 6a-6d also provided the corresponding a,a-difluorohomoallylic hydrazides 7a-7d in medium yields. The N-N bond cleavage of the hydrazide 3a proceeded smoothly to give the corresponding primary gem-difluorohomoallylic amine 8, which could be converted to gem-difluoro-δ-substituted α,β-unsaturated lactam 11 via acryloylation fol-lowed by ring closing metathesis (RCM) reaction.

Synthesis and characterization of a homogeneous and silica supported homoleptic cationic tungsten(vi) methyl complex: application in olefin metathesis

KAUST Repository

Dey, Raju

2016-08-19

A method for the synthesis of a homogeneous cationic tungsten(VI)penta-methyl complex [(WMe5)(+)(C6F5)(3)BMe-] from neutral tungstenhexamethyl (WMe6) and a silica supported cationic tungstentetramethyl complex [( Si-O-)WMe4+ (C6F5)(3)BMe-] from a neutral silica supported tungstenpentamethyl complex [( Si-O-)WMe5] is described. In both cases a direct demethylation using the B(C6F5)(3) reagent was used. The aforesaid complexes were characterized by liquid or solid state NMR spectroscopy. Interestingly, the homogeneous cationic complex [(WMe5)(+)(C6F5)(3)BMe-] shows moderate activity whereas the supported cationic complex [( Si-O-)WMe4+(C6F5)(3)BMe-] exhibits good activity in olefin metathesis reactions.

Synthesis and characterization of a homogeneous and silica supported homoleptic cationic tungsten(vi) methyl complex: application in olefin metathesis

KAUST Repository

Dey, Raju; Samantaray, Manoja; Poater, Albert; Hamieh, Ali Imad Ali; Kavitake, Santosh Giridhar; Abou-Hamad, Edy; Callens, Emmanuel; Emwas, Abdul-Hamid M.; Cavallo, Luigi; Basset, Jean-Marie

2016-01-01

A method for the synthesis of a homogeneous cationic tungsten(VI)penta-methyl complex [(WMe5)(+)(C6F5)(3)BMe-] from neutral tungstenhexamethyl (WMe6) and a silica supported cationic tungstentetramethyl complex [( Si-O-)WMe4+ (C6F5)(3)BMe-] from a neutral silica supported tungstenpentamethyl complex [( Si-O-)WMe5] is described. In both cases a direct demethylation using the B(C6F5)(3) reagent was used. The aforesaid complexes were characterized by liquid or solid state NMR spectroscopy. Interestingly, the homogeneous cationic complex [(WMe5)(+)(C6F5)(3)BMe-] shows moderate activity whereas the supported cationic complex [( Si-O-)WMe4+(C6F5)(3)BMe-] exhibits good activity in olefin metathesis reactions.

A GLOBAL REGISTRATION ALGORITHM OF THE SINGLE-CLOSED RING MULTI-STATIONS POINT CLOUD

Directory of Open Access Journals (Sweden)

R. Yang

2018-04-01

Full Text Available Aimed at the global registration problem of the single-closed ring multi-stations point cloud, a formula in order to calculate the error of rotation matrix was constructed according to the definition of error. The global registration algorithm of multi-station point cloud was derived to minimize the error of rotation matrix. And fast-computing formulas of transformation matrix with whose implementation steps and simulation experiment scheme was given. Compared three different processing schemes of multi-station point cloud, the experimental results showed that the effectiveness of the new global registration method was verified, and it could effectively complete the global registration of point cloud.

Maternal Punitive Reactions to Children's Negative Emotions and Young Adult Trait Anger: Effect of Gender and Emotional Closeness.

Science.gov (United States)

Perry, Nicole B; Cavanaugh, Alyson; Dunbar, Angel; Leerkes, Esther M

The current study tested whether young adult's recollected reports of their mother's punitive reactions to their negative emotions in childhood predicted anger expression in young adulthood and whether emotional closeness weakens this association. Further, a three-way interaction was tested to examine whether emotional closeness is a stronger protective factor for young women than for young men. Results revealed a significant three-way interaction (gender X emotional closeness X maternal punitive reactions). For young men, maternal punitive reactions to negative emotions were directly associated with increased anger expressions. Maternal punitive reactions to young women's negative emotions in childhood were associated with increased anger in adulthood only when they reported low maternal emotional closeness. Findings suggest that maternal emotional closeness may serve as a buffer against the negative effects of maternal punitive reactions for women's anger expression in young adulthood.

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

OpenAIRE

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

2003-01-01

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

Aziridine- and Azetidine-Pd Catalytic Combinations. Synthesis and Evaluation of the Ligand Ring Size Impact on Suzuki-Miyaura Reaction Issues

Directory of Open Access Journals (Sweden)

Hamza Boufroura

2017-01-01

Full Text Available The synthesis of new vicinal diamines based on aziridine and azetidine cores as well as the comparison of their catalytic activities as ligand in the Suzuki-Miyaura coupling reaction are described in this communication. The synthesis of three- and four-membered ring heterocycles substituted by a methylamine pendant arm is detailed from the parent nitrile derivatives. Complexation to palladium under various conditions has been examined affording vicinal diamines or amine-imidate complexes. The efficiency of four new catalytic systems is compared in the preparation of variously substituted biaryls. Aziridine- and azetidine-based catalytic systems allowed Suzuki-Miyaura reactions from aryl halides including chlorides with catalytic loadings until 0.001% at temperatures ranging from 100 °C to r.t. The evolution of the Pd-metallacycle ring strain moving from azetidine to aziridine in combination with a methylamine or an imidate pendant arm impacted the Suzuki-Miyaura reaction issue.

Carbonyl-Olefin Exchange Reaction: Present State and Outlook

Science.gov (United States)

Kalinova, Radostina; Jossifov, Christo

The carbonyl-olefin exchange reaction (COER) is a new reaction between carbonyl group and olefin double bond, which has a formal similarity with the olefin metathesis (OM) - one carbon atom in the latter is replaced with an oxygen atom. Till now the new reaction is performed successfully only when the two functional groups (carbonyl group and olefin double bond) are in one molecule and are conjugated. The α, β-unsaturated carbonyl compounds (substituted propenones) are the compounds with such a structure. They polymerize giving substituted polyacetylenes. The chain propagation step of this polymerization is in fact the COER. The question arises: is it possible the COER to take place when the two functional groups are not in one molecule and are not conjugated, and could this reaction became an alternative of the existing carbonyl olefination reactions?

Well-Defined Molybdenum Oxo Alkyl Complex Supported on Silica by Surface Organometallic Chemistry: A Highly Active Olefin Metathesis Precatalyst

KAUST Repository

Merle, Nicolas; Le Qué mé ner, Fré dé ric; Bouhoute, Yassine; Szeto, Kai C.; De Mallmann, Aimery; Barman, Samir; Samantaray, Manoja; Delevoye, Laurent; Gauvin, Ré gis M.; Taoufik, Mostafa; Basset, Jean-Marie

2016-01-01

The well-defined silica-supported molybdenum oxo alkyl species (SiO−)MoO(CH Bu) was selectively prepared by grafting of MoO(CH Bu)Cl onto partially dehydroxylated silica (silica) using the surface organometallic chemistry approach. This surface species was fully characterized by elemental analysis and DRIFT, solid-state NMR, and EXAFS spectroscopy. This new material is related to the active species of industrial supported MoO/SiO olefin metathesis catalysts. It displays very high activity in propene self-metathesis at mild (turnover number = 90 000 after 25 h). Remarkably, its catalytic performance outpaces those of the parent imido derivative and its tungsten oxo analogue.

Well-Defined Molybdenum Oxo Alkyl Complex Supported on Silica by Surface Organometallic Chemistry: A Highly Active Olefin Metathesis Precatalyst

KAUST Repository

Merle, Nicolas

2016-12-05

The well-defined silica-supported molybdenum oxo alkyl species (SiO−)MoO(CH Bu) was selectively prepared by grafting of MoO(CH Bu)Cl onto partially dehydroxylated silica (silica) using the surface organometallic chemistry approach. This surface species was fully characterized by elemental analysis and DRIFT, solid-state NMR, and EXAFS spectroscopy. This new material is related to the active species of industrial supported MoO/SiO olefin metathesis catalysts. It displays very high activity in propene self-metathesis at mild (turnover number = 90 000 after 25 h). Remarkably, its catalytic performance outpaces those of the parent imido derivative and its tungsten oxo analogue.

Synthesis of novel aryl brassinosteroids through alkene cross-metathesis and preliminary biological study

Czech Academy of Sciences Publication Activity Database

Kořínková, Petra; Bazgier, V.; Oklešťková, Jana; Rárová, L.; Strnad, Miroslav; Kvasnica, Miroslav

2017-01-01

Roč. 127, NOV (2017), s. 46-55 ISSN 0039-128X R&D Projects: GA ČR GJ15-08202Y; GA MŠk(CZ) LO1204 Institutional support: RVO:61389030 Keywords : Brassinosteroids * BRI1 receptor kinase * Cross-metathesis * Molecular docking * Organic synthesis * Plant bioassays Subject RIV: CC - Organic Chemistry OBOR OECD: Organic chemistry Impact factor: 2.282, year: 2016

Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts

Czech Academy of Sciences Publication Activity Database

Pastva, Jakub; Skowerski, K.; Czarnocki, S. J.; Žilková, Naděžda; Čejka, Jiří; Bastl, Zdeněk; Balcar, Hynek

2014-01-01

Roč. 4, č. 9 (2014), s. 3227-3236 ISSN 2155-5435 R&D Projects: GA ČR(CZ) GAP106/12/0189 Institutional support: RVO:61388955 Keywords : olefin metathesis * heterogeneous catalysts * mesoporous molecular sieves Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 9.312, year: 2014

Effect of Support on Metathesis of n-Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica-Alumina

KAUST Repository

Samantaray, Manoja

2015-03-11

[WMe6] (1) supported on the surface of SiO2-Al2O3(500) (2) has been extensively characterized by solid-state NMR spectroscopy, elemental analysis, and gas quantification, which clearly reveal the formation of a mixture of monopodal and bipodal species with the migration of methyl from W to Al. The supported species SiO2-Al2O3(500) (2) transformed at 120°C into two types of carbynic centers, one of which is cationic and the other neutral. These species are very efficient for the metathesis of n-decane. Comparison with already-synthesized neutral bipodal tungsten indicates that the high increase in activity is due to the cationic character of the grafted tungsten.

Effect of Support on Metathesis of n-Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica-Alumina

KAUST Repository

Samantaray, Manoja; Dey, Raju; Abou-Hamad, Edy; Hamieh, Ali Imad Ali; Basset, Jean-Marie

2015-01-01

[WMe6] (1) supported on the surface of SiO2-Al2O3(500) (2) has been extensively characterized by solid-state NMR spectroscopy, elemental analysis, and gas quantification, which clearly reveal the formation of a mixture of monopodal and bipodal species with the migration of methyl from W to Al. The supported species SiO2-Al2O3(500) (2) transformed at 120°C into two types of carbynic centers, one of which is cationic and the other neutral. These species are very efficient for the metathesis of n-decane. Comparison with already-synthesized neutral bipodal tungsten indicates that the high increase in activity is due to the cationic character of the grafted tungsten.

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-02-28

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

Olefins metathesis, synthesis and properties of homogeneous models of the Re{sub 2}O{sub 7}/Al{sub 2}O{sub 3} catalyst; Methathese des olefines, synthese et proprietes des modeles homogenes du catalyseur Re{sub 2}O{sub 7}/Al{sub 2}O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Doledec, G.

1999-10-05

The aim of this work was to synthesize and to study homogeneous models of the rhenium oxide on alumina catalyst in order to better understand the influence of the alumina environment over the activity in olefin metathesis. A series of aluminium complexes (ArO){sub 2}Al-Y have been synthesised, where ArO is a 4-substituted-2,6-di-tert-butyl-phenoxy, or (ArO){sub 2} is a CH{sub 2{sup -}} or S-ortho bridged-4,4'-di-tert-butyl-di-phenoxy, and Y is an alkyl or chlorine ligand. The reaction of (ArO){sub 2}Al-Cl with AgReO{sub 4} led to new complexes (ArO){sub 2}Al-OReO{sub 3} (A). These complexes exhibit a low to moderate activity in metathesis of 2-pentene (TOF = 0,5 min{sup -1} at 25 deg. C in a toluene solution). Complexes (ArO){sub 2}Al-R (R = iBu, Et) react with Re{sub 2}O{sub 7} in THF or dioxane giving type B complexes including oligomeric linkages like O{sub 3}Re-[Al(OAr)-O){sub 2}-ReO{sub 3}. They show a fairly high activity in the metathesis of 2-pentene, with TOF values as high as 100 min{sup -1}. As far as we know, these are the most active rhenium-based homogeneous metathesis catalysts. Complexes type A may be converted into type B complexes upon reaction with (ArO){sub 2}Al-R in an ether solvent. The high activity of B complexes is tentatively related to the Al-O-Al linkages that are molecular in the homogeneous models or present at the surface of the alumina in the heterogeneous catalyst. These results bear out again the role of the Lewis acidity in these catalysts. We used (ArO){sub 2}Al-R complexes to modify the heterogenous catalyst. It appears that it is an excellent way to reduce the rhenium loading without any loss of activity. (author)

How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

KAUST Repository

Poater, Albert; Falivene, Laura; Urbina-Blanco, Cé sar A.; Manzini, Simone; Nolan, Steven P.; Cavallo, Luigi

2013-01-01

Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. © 2013 The Royal Society of Chemistry.

Ti(Oi-Pr)4-promoted photoenolization Diels-Alder reaction to construct polycyclic rings and its synthetic applications.

Science.gov (United States)

Yang, Baochao; Lin, Kuaikuai; Shi, Yingbo; Gao, Shuanhu

2017-09-20

Stereoselective construction of polycyclic rings with all-carbon quaternary centers, and vicinal all-carbon quaternary stereocenters, remains a significant challenge in organic synthesis. These structures can be found in a wide range of polycyclic natural products and drug molecules. Here we report a Ti(Oi-Pr) 4 -promoted photoenolization/Diels-Alder (PEDA) reaction to construct hydroanthracenol and related polycyclic rings bearing all-carbon quaternary centers. This photolysis proceeds under mild conditions and generates a variety of photo-cycloaddition products in good reaction efficiency and stereoselectivity (48 examples), and has been successfully used in the construction of core skeleton of oncocalyxones, tetracycline and pleurotin. It also provides a reliable method for the late-stage modification of natural products bearing enone groups, such as steroids. The total synthesis of oncocalyxone B was successfully achieved using this PEDA approach.Anthracenols with multiple chiral centres are common motifs in natural products. Here, the authors show a highly stereoselective photoenolization/Diels-Alder methodology involving a key Lewis acid reagent enabling the efficient construction of a family of anthracenol derivatives with quaternary centers.

Energy spectra of quantum rings.

Science.gov (United States)

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

2001-10-25

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

A Short Synthesis of (+)-Cyclophellitol

DEFF Research Database (Denmark)

Hansen, Flemming Gundorph; Bundgaard, Eva; Madsen, Robert

2005-01-01

A new synthesis of (+)-cyclophellitol, a potent b-glucosidase inhibitor, has been completed in nine steps from D-xylose. The key transformations involve a zinc-mediated fragmentation of benzyl-protected methyl 5-deoxy-5-iodo-xylofuranoside followed by a highly diastereoselective indium-mediated c......-mediated coupling with ethyl 4-bromocrotonate. Subsequent ring-closing olefin metathesis, ester reduction, olefin epoxidation, and deprotection then afford the natural product. This constitutes the shortest synthesis of (+)-cyclophellitol reported to date....

C-84 Selective Porphyrin Macrocycle with an Adaptable Cavity Constructed Through Alkyne Metathesis

Energy Technology Data Exchange (ETDEWEB)

Zhang, C. X.; Long, H.; Zhang, W.

2012-06-21

A bisporphyrin macrocycle was constructed from a porphyrin-based diyne monomer in one step through alkyne metathesis. The fullerene binding studies (C{sub 60}, C{sub 70} and C{sub 84}) showed the highest binding affinity of the macrocycle for C{sub 84}, which is in great contrast to its bisporphyrin four-armed cage analogue that showed the strongest binding with C{sub 70}.

Olefin Metathesis with Ru-Based Catalysts Exchanging the Typical N-Heterocyclic Carbenes by a Phosphine–Phosphonium Ylide

Directory of Open Access Journals (Sweden)

Laia Arnedo

2017-03-01

Full Text Available Density functional theory (DFT calculations have been used to describe the first turnover of an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalysts bearing a phosphine–phosphonium ylide ligand, with ethylene as a substrate. Equal to conventional Ru-based catalysts bearing an N-heterocyclic carbene (NHC ligand, the activation of these congeners occurs through a dissociative mechanism, with a more exothermic first phosphine dissociation step. In spite of a stronger electron-donating ability of a phosphonium ylide C-ligand with respect to a diaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/mol higher than those of Ru–NHC standards. Overall, the study also highlights advantages of bidentate ligands over classical monodentate NHC and phosphine ligands, with a particular preference for the cis attack of the olefin. The new generation of catalysts is constituted by cationic complexes potentially soluble in water, to be compared with the typical neutral Ru–NHC ones.

Hoveyda-Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

Czech Academy of Sciences Publication Activity Database

Balcar, Hynek; Shinde, Tushar; Žilková, Naděžda; Bastl, Zdeněk

2011-01-01

Roč. 7, January (2011), s. 22-28 ISSN 1860-5397 R&D Projects: GA AV ČR IAA400400805; GA AV ČR KAN100400701 Institutional research plan: CEZ:AV0Z40400503 Keywords : alkene metathesis * catalyst immobilization * hybrid catalysis Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.517, year: 2011

Polarization Insensitivity in Double-Split Ring and Triple-Split Ring Terahertz Resonators

International Nuclear Information System (INIS)

Wu Qian-Nan; Lan Feng; Tang Xiao-Pin; Yang Zi-Qiang

2015-01-01

A modified double-split ring resonator and a modified triple-split ring resonator, which offer polarization-insensitive performance, are investigated, designed and fabricated. By displacing the two gaps of the conventional double-split ring resonator away from the center, the second resonant frequency for the 0° polarized wave and the resonant frequency for the 90° polarized wave become increasingly close to each other until they are finally identical. Theoretical and experimental results show that the modified double-split ring resonator and the modified triple-split ring resonator are insensitive to different polarized waves and show strong resonant frequency dips near 433 and 444 GHz, respectively. The results of this work suggest new opportunities for the investigation and design of polarization-dependent terahertz devices based on split ring resonators. (paper)

Application of combinatorial biocatalysis for a unique ring expansion of dihydroxymethylzearalenone.

Science.gov (United States)

Rich, Joseph O; Budde, Cheryl L; McConeghey, Luke D; Cotterill, Ian C; Mozhaev, Vadim V; Singh, Sheo B; Goetz, Michael A; Zhao, Annie; Michels, Peter C; Khmelnitsky, Yuri L

2009-06-01

Combinatorial biocatalysis was applied to generate a diverse set of dihydroxymethylzearalenone analogs with modified ring structure. In one representative chemoenzymatic reaction sequence, dihydroxymethylzearalenone was first subjected to a unique enzyme-catalyzed oxidative ring opening reaction that creates two new carboxylic groups on the molecule. These groups served as reaction sites for further derivatization involving biocatalytic ring closure reactions with structurally diverse bifunctional reagents, including different diols and diamines. As a result, a library of cyclic bislactones and bislactams was created, with modified ring structures covering chemical space and structure activity relationships unattainable by conventional synthetic means.

Energetics of the ruthenium-halide bond in olefin metathesis (pre)catalysts

KAUST Repository

Falivene, Laura; Poater, Albert; Cazin, Catherine S J; Slugovc, Christian; Cavallo, Luigi

2013-01-01

A DFT analysis of the strength of the Ru-halide bond in a series of typical olefin metathesis (pre)catalysts is presented. The calculated Ru-halide bond energies span the rather broad window of 25-43 kcal mol-1. This indicates that in many systems dissociation of the Ru-halide bond is possible and is actually competitive with dissociation of the labile ligand generating the 14e active species. Consequently, formation of cationic Ru species in solution should be considered as a possible event. © 2013 The Royal Society of Chemistry.

WMe6 tamed by silica: Si-O-WMe5 as an efficient, well-defined species for alkane metathesis, leading to the observation of a supported W-methyl/methylidyne species

KAUST Repository

Samantaray, Manoja

2014-01-22

The synthesis and full characterization of a well-defined silica-supported ≡Si-O-W(Me)5 species is reported. Under an inert atmosphere, it is a stable material at moderate temperature, whereas the homoleptic parent complex decomposes above -20 °C, demonstrating the stabilizing effect of immobilization of the molecular complex. Above 70 °C the grafted complex converts into the two methylidyne surface complexes [(≡SiO-)W(≡CH) Me2] and [(≡SiO-)2W(≡CH)Me]. All of these silica-supported complexes are active precursors for propane metathesis reactions. © 2013 American Chemical Society.

WMe6 tamed by silica: Si-O-WMe5 as an efficient, well-defined species for alkane metathesis, leading to the observation of a supported W-methyl/methylidyne species

KAUST Repository

Samantaray, Manoja; Callens, Emmanuel; Abou-Hamad, Edy; Rossini, Aaron J.; Widdifield, Cory M.; Dey, Raju; Emsley, Lyndon; Basset, Jean-Marie

2014-01-01

The synthesis and full characterization of a well-defined silica-supported ≡Si-O-W(Me)5 species is reported. Under an inert atmosphere, it is a stable material at moderate temperature, whereas the homoleptic parent complex decomposes above -20 °C, demonstrating the stabilizing effect of immobilization of the molecular complex. Above 70 °C the grafted complex converts into the two methylidyne surface complexes [(≡SiO-)W(≡CH) Me2] and [(≡SiO-)2W(≡CH)Me]. All of these silica-supported complexes are active precursors for propane metathesis reactions. © 2013 American Chemical Society.

Synthesis of the AB ring system of clifednamide utilizing Claisen rearrangement and Diels-Alder reaction as key steps.

Science.gov (United States)

Loke, Inga; Bentzinger, Guillaume; Holz, Julia; Raja, Aruna; Bhasin, Aman; Sasse, Florenz; Köhn, Andreas; Schobert, Rainer; Laschat, Sabine

2016-01-21

In order to construct the functionalized AB ring system of clifednamide, member of the class of macrocyclic tetramic acid lactams, a synthesis was developed which utilized an Ireland-Claisen rearrangement and an intramolecular Diels-Alder reaction. Starting from di-O-isopropylidene-d-mannitol the allyl carboxylate precursor for the sigmatropic rearrangement was prepared. This rearrangement proceeded diastereoselectively only in the presence of an allyl silyl ether instead of the parent enone in the side chain, as suggested by deuteration experiments. A subsequent Diels-Alder reaction yielded the target ethyl hexahydro-1H-indene-carboxylate with high diastereoselectivity. Quantum-chemical investigations of this intramolecular Diels-Alder reaction support the proposed configuration of the final product.

Anomalous regioselective four-member multicomponent Biginelli reaction II: one-pot parallel synthesis of spiro heterobicyclic aliphatic rings.

Science.gov (United States)

Byk, Gerardo; Kabha, Eihab

2004-01-01

In a previous preliminary study, we found that a cyclic five-member ring beta-keto ester (lactone) reacts with one molecule of urea and two of aldehyde to give a new family of spiro heterobicyclic aliphatic rings in good yields with no traces of the expected dihydropyrimidine (Biginelli) products. The reaction is driven by a regiospecific condensation of two molecules of aldehyde with urea and beta-keto-gamma-lactone to afford only products harboring substitutions exclusively in a syn configuration (Byk, G.; Gottlieb, H. E.; Herscovici, J.; Mirkin, F. J. Comb. Chem. 2000, 2, 732-735). In the present work ((a) Presented in part at ISCT Combitech, October 15, 2002, Israel, and Eurocombi-2, Copenhagen 2003 (oral and poster presentation). (b) Also in American Peptide Society Symposium, Boston, 2003 (poster presentation). (c) Abstract in Biopolymers 2003, 71 (3), 354-355), we report a large and exciting extension of this new reaction utilizing parallel organic synthesis arrays, as demonstrated by the use of chiral beta-keto-gamma-lactams, derived from natural amino acids, instead of tetronic acid (beta-keto-gamma-lactone) and the potential of the spirobicyclic products for generating "libraries from libraries". Interestingly, we note an unusual and important anisotropy effect induced by perpendicular interactions between rigid pi systems and different groups placed at the alpha position of the obtained spirobicyclic system. Stereo/regioselectivity of the aldehyde condensation is driven by the nature of the substitutions on the starting beta-keto-gamma-lactam. Aromatic aldehydes can be used as starting reagents with good yields; however, when aliphatic aldehydes are used, the desired products are obtained in poor yields, as observed in the classical Biginelli reaction. The possible reasons for these poor yields are addressed and clarify, to some extent, the complexity of the Biginelli multicomponent reaction mechanism and, in particular, the mechanism of the present

Acyclic Diene Metathesis (ADMET Polymerization for Precise Synthesis of Defect-Free Conjugated Polymers with Well-Defined Chain Ends

Directory of Open Access Journals (Sweden)

Tahmina Haque

2015-03-01

Full Text Available This accounts introduces unique characteristics by adopting the acyclic diene metathesis (ADMET polymerization for synthesis of conjugated polymers, poly(arylene vinylenes, known as promising molecular electronics. The method is more suitable than the other methods in terms of atom efficiency affording defect-free, stereo-regular (exclusive trans polymers with well-defined chain ends; the resultant polymers possess better property than those prepared by the conventional methods. The chain ends (vinyl group in the resultant polymer prepared by ruthenium-carbene catalyst(s can be modified by treating with molybdenum-alkylidene complex (olefin metathesis followed by addition of various aldehyde (Wittig type cleavage, affording the end-functionalized polymers exclusively. An introduction of initiating fragment, the other conjugated segment, and one-pot synthesis of end-functionalized block copolymers, star shape polymers can be achieved by adopting this methodology.

Thallium trinitrate mediated ring contraction of cis-2-decalones

Directory of Open Access Journals (Sweden)

Ferraz Helena M. C.

2001-01-01

Full Text Available The reaction of some cis-2-decalones with TTN in CH2Cl2 at room temperature was investigated. The ring contraction reactions occurred in good yields, however the regio- and diastereoselectivity were low. The effect of the alkyl groups in the regiochemistry of the reaction depends on their position at the decalone ring system.

Poisoning Experiments Aimed at Discriminating Active and Less-Active Sites of Silica-Supported Tantalum Hydride for Alkane Metathesis

KAUST Repository

Saggio, Guillaume; Taoufik, Mostafa; Basset, Jean-Marie; Thivolle-Cazat, Jean

2010-01-01

Only 50% of the silica-supported tantalum hydride sites are active in the metathesis of propane. Indeed, more than 45% of the tantalum hydride can be eliminated by a selective oxygen poisoning of inactive sites with no significant decrease

Effect of cathode porosity on the Lithium-air cell oxygen reduction reaction – A rotating ring-disk electrode investigation

International Nuclear Information System (INIS)

Seo, Jeongwook; Sankarasubramanian, Shrihari; Singh, Nikhilendra; Mizuno, Fuminori; Takechi, Kensuke; Prakash, Jai

2017-01-01

The kinetics of the oxygen reduction reaction (ORR) on the practical air cathode in a Lithium-air cell, which is conventionally composed of porous carbon with or without catalysts supported on it, was investigated. The mechanism and kinetics of the oxygen reduction reaction (ORR) was studied on a porous carbon electrode in an oxygen saturated solution of 0.1 M Lithium bis-trifluoromethanesulfonimide (LiTFSI) in Dimethoxyethane (DME) using cyclic voltammetery (CV) and the rotating ring-disk electrode (RRDE) technique. The oxygen reduction and evolution reactions were found to occur at similar potentials to those observed on a smooth, planar glassy carbon (GC) electrode. The effect of porosity and the resultant increase in surface area were readily observed in the increase in the transient time required for the intermediates to reach the ring and the much larger disk currents (compared to smooth, planar GC) recorded respectively. The RRDE data was analyzed using a kinetic model previously developed by us and the rate constants for the elementary reactions were calculated. The rates constant for the electrochemical reactions were found to be similar in magnitude to the rate constants calculated for smooth GC disks. The porosity of the electrode was found to decrease the rate of desorption of the intermediate and the product and delay their diffusion by shifting it from a Fickian regime in the electrolyte bulk to the Knudsen regime in the film pores. Thus, it is shown that the effect of the electrode porosity on the kinetics of the ORR is physical rather than electrochemical.

A ring polymer molecular dynamics study of the isotopologues of the H + H2 reaction.

Science.gov (United States)

Suleimanov, Yury V; de Tudela, Ricardo Pérez; Jambrina, Pablo G; Castillo, Jesús F; Sáez-Rábanos, Vicente; Manolopoulos, David E; Aoiz, F Javier

2013-03-14

The inclusion of Quantum Mechanical (QM) effects such as zero point energy (ZPE) and tunneling in simulations of chemical reactions, especially in the case of light atom transfer, is an important problem in computational chemistry. In this respect, the hydrogen exchange reaction and its isotopic variants constitute an excellent benchmark for the assessment of approximate QM methods. In particular, the recently developed ring polymer molecular dynamics (RPMD) technique has been demonstrated to give very good results for bimolecular chemical reactions in the gas phase. In this work, we have performed a detailed RPMD study of the H + H(2) reaction and its isotopologues Mu + H(2), D + H(2) and Heμ + H(2), at temperatures ranging from 200 to 1000 K. Thermal rate coefficients and kinetic isotope effects have been computed and compared with exact QM calculations as well as with quasiclassical trajectories and experiment. The agreement with the QM results is good for the heaviest isotopologues, with errors ranging from 15% to 45%, and excellent for Mu + H(2), with errors below 15%. We have seen that RPMD is able to capture the ZPE effect very accurately, a desirable feature of any method based on molecular dynamics. We have also verified Richardson and Althorpe's prediction [J. O. Richardson and S. C. Althorpe, J. Chem. Phys., 2009, 131, 214106] that RPMD will overestimate thermal rates for asymmetric reactions and underestimate them for symmetric reactions in the deep tunneling regime. The ZPE effect along the reaction coordinate must be taken into account when assigning the reaction symmetry in the multidimensional case.

Synthesis and Evaluation of a 2,11-Cembranoid-Inspired Library.

Science.gov (United States)

Welford, Amanda J; Caldwell, John J; Liu, Manjuan; Richards, Meirion; Brown, Nathan; Lomas, Cara; Tizzard, Graham J; Pitak, Mateusz B; Coles, Simon J; Eccles, Suzanne A; Raynaud, Florence I; Collins, Ian

2016-04-11

The 2,11-cembranoid family of natural products has been used as inspiration for the synthesis of a structurally simplified, functionally diverse library of octahydroisobenzofuran-based compounds designed to augment a typical medicinal chemistry library screen. Ring-closing metathesis, lactonisation and SmI2 -mediated methods were exemplified and applied to the installation of a third ring to mimic the nine-membered ring of the 2,11-cembranoids. The library was assessed for aqueous solubility and permeability, with a chemical-space analysis performed for comparison to the family of cembranoid natural products and a sample set of a screening library. Preliminary investigations in cancer cells showed that the simpler scaffolds could recapitulate the reported anti-migratory activity of the natural products. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Topological ring currents in the "empty" ring of benzo-annelated perylenes.

Science.gov (United States)

Dickens, Timothy K; Mallion, Roger B

2011-01-27

Cyclic conjugation in benzo-annelated perylenes is examined by means of the topological π-electron ring currents calculated for each of their constituent rings, in a study that is an exact analogy of a recent investigation by Gutman et al. based on energy-effect values for the corresponding rings in each of these structures. "Classical" approaches, such as Kekulé structures, Clar "sextet" formulas, and circuits of conjugation, predict that the central ring in perylene is "empty" and thus contributes negligibly to cyclic conjugation. However, conclusions from the present calculations of topological ring currents agree remarkably with those arising from the earlier study involving energy-effect values in that, contrary to what would be predicted from the classical approaches, rings annelated in an angular fashion relative to the central ring of these perylene structures materially increase the extent of that ring's involvement in cyclic conjugation. It is suggested that such close quantitative agreement between the predictions of these two superficially very different indices (energy effect and topological ring current) might be due to the fact that, ultimately, both depend, albeit in ostensibly quite different ways, only on an adjacency matrix that contains information about the carbon-carbon connectivity of the conjugated system in question.

On rings generating supernilpotent and special atoms | France ...

African Journals Online (AJOL)

We study prime rings which generate supernilpotent (respectively special) atoms, that is, atoms of the lattice of all supernilpotent (respectively special) radicals. A prime ring A is called a **-ring if the smallest special class containing A is closed under semiprime homomorphic images of A. A semiprime ring A whose every ...

Investigation of the annihilation reaction e+ e- → φ in the Orsay Collider Ring

International Nuclear Information System (INIS)

Richard, Francois

1970-01-01

This research thesis mainly reports an experiment which aimed at measuring the disintegration partial width of the φ into e + e - by studying the annihilation reaction (e + e - → φ) in the Orsay Collider Ring (ACO). In a first part, the author presents the theoretical framework which is based on the Lee-Weinberg-Zumino gauge fields: definition of gauge fields, commutation relationship between them, presentation of Weinberg sum rules, interpretation of sum rules in terms of asymptotic symmetry, formulation of vector dominance meson, application of sum rules, Sugawara model. In a second part, the author discusses the conditions of detection of the two φ modes, and the elimination of parasite reactions. Analysis criteria are then determined after a brief description of the experimental installation. The installation efficiency and some various corrections are also discussed. Results are then interpreted by means of a theory-based curved. A general interpretation of Orsay results is proposed on the ρ, ω and φ within the framework of the theory previously presented

On the predictions and limitations of the Becker–Döring model for reaction kinetics in micellar surfactant solutions

KAUST Repository

Griffiths, I.M.

2011-08-01

We investigate the breakdown of a system of micellar aggregates in a surfactant solution following an order-one dilution. We derive a mathematical model based on the Becker-Döring system of equations, using realistic expressions for the reaction constants fit to results from Molecular Dynamics simulations. We exploit the largeness of typical aggregation numbers to derive a continuum model, substituting a large system of ordinary differential equations for a partial differential equation in two independent variables: time and aggregate size. Numerical solutions demonstrate that re-equilibration occurs in two distinct stages over well-separated timescales, in agreement with experiment and with previous theories. We conclude by exposing a limitation in the Becker-Döring theory for re-equilibration of surfactant solutions. © 2011 Elsevier Inc.

A Short Synthetic Route to the Calystegine Alkaloids

DEFF Research Database (Denmark)

Skaanderup, Philip Robert; Madsen, Robert

2003-01-01

An efficient strategy is described for the synthesis of enantiopure calystegine alkaloids. The key step employs a zinc-mediated fragmentation of benzyl-protected methyl 6-iodo-glycosides followed by in situ formation of the benzyl imine and Barbier-type allylation with zinc, magnesium, or indium...... metal. Stereochemistry in the pivotal allylation is controlled by the choice of the metal. The functionalized 1,8-nonadienes, thus formed, are converted into cycloheptenes by ring-closing metathesis. Regioselective hydroboration and oxidation give the corresponding cycloheptanones, which are deprotected...

Practical route to the left wing of CTX1B and total syntheses of CTX1B and 54-deoxyCTX1B.

Science.gov (United States)

Yamashita, Shuji; Takeuchi, Katsutoshi; Koyama, Takuya; Inoue, Masayuki; Hayashi, Yujiro; Hirama, Masahiro

2015-02-02

Ciguatoxins, the principal causative agents of ciguatera seafood poisoning, are extremely large polycyclic ethers. We report herein a reliable route for constructing the left wing of CTX1B, which possesses the acid/base/oxidant-sensitive bisallylic ether moiety, by a 6-exo radical cyclization/ring-closing metathesis strategy. This new route enabled us to achieve the second-generation total synthesis of CTX1B and the first synthesis of 54-deoxyCTX1B. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metathesis of 2-pentene over Mo and W supported mesoporous molecular sieves MCM-41 and SBA-15

Czech Academy of Sciences Publication Activity Database

Ibrahim, M. A.; Akhtar, M. N.; Čejka, Jiří; Montanari, E.; Balcar, Hynek; Kubů, Martin; Al-Khattaf, S. S.

2017-01-01

Roč. 53, SEP 2017 (2017), s. 119-126 ISSN 1226-086X R&D Projects: GA ČR(CZ) GAP106/12/0189 Institutional support: RVO:61388955 Keywords : metathesis * MCM-41 * SBA-15 Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 4.421, year: 2016

Investigation of Surface Alkylation Strategy in SOMC: In Situ Generation of a Silica-Supported Tungsten Methyl Catalyst for Cyclooctane Metathesis

KAUST Repository

Hamieh, Ali Imad Ali

2016-07-28

An efficient and potentially scalable method is described for the synthesis of the silica-supported complexes [(≡Si-O-)WMe5] and [(≡Si-O-)WMe2(≡CH)] obtained by in situ alkylation of the surface-grafted tungsten chloride [(≡Si-O-)WCl5] (1). [(≡Si-O-)WCl5] can be readily prepared by the reaction of commercially available and stable tungsten hexachloride WCl6 with partially dehydroxylated silica at 700 °C (SiO2-700). Further reaction with ZnMe2 at room temperature rapidly forms a mixture of surface-alkylated tungsten complexes. They were fully characterized by microanalysis, FTIR, mass balance, and solid-state NMR (1H, 13C, 1H-13C HETCOR, 1H-1H double quantum and triple quantum) and identified as [(≡Si-O-)WMe5] and another product, [(≡Si-O-)WMe2(≡CH)]. The latter might have been generated by partial decomposition of the tungsten methyl chloride compound, which is formed during the stepwise alkylation of [(≡Si-O-)WCl5]. DFT calculations were carried out to check the relative stability of the tungsten methyl chloride intermediates and the feasibility of the reaction and corroborate the experimental results. This tungsten complex and its derivative were found to be active catalysts for the metathesis of cyclooctane. © 2016 American Chemical Society.

Investigation of Surface Alkylation Strategy in SOMC: In Situ Generation of a Silica-Supported Tungsten Methyl Catalyst for Cyclooctane Metathesis

KAUST Repository

Hamieh, Ali Imad Ali; Dey, Raju; Samantaray, Manoja; Abdel-Azeim, Safwat; Abou-Hamad, Edy; Chen, Yin; Pelletier, Jeremie; Cavallo, Luigi; Basset, Jean-Marie

2016-01-01

An efficient and potentially scalable method is described for the synthesis of the silica-supported complexes [(≡Si-O-)WMe5] and [(≡Si-O-)WMe2(≡CH)] obtained by in situ alkylation of the surface-grafted tungsten chloride [(≡Si-O-)WCl5] (1). [(≡Si-O-)WCl5] can be readily prepared by the reaction of commercially available and stable tungsten hexachloride WCl6 with partially dehydroxylated silica at 700 °C (SiO2-700). Further reaction with ZnMe2 at room temperature rapidly forms a mixture of surface-alkylated tungsten complexes. They were fully characterized by microanalysis, FTIR, mass balance, and solid-state NMR (1H, 13C, 1H-13C HETCOR, 1H-1H double quantum and triple quantum) and identified as [(≡Si-O-)WMe5] and another product, [(≡Si-O-)WMe2(≡CH)]. The latter might have been generated by partial decomposition of the tungsten methyl chloride compound, which is formed during the stepwise alkylation of [(≡Si-O-)WCl5]. DFT calculations were carried out to check the relative stability of the tungsten methyl chloride intermediates and the feasibility of the reaction and corroborate the experimental results. This tungsten complex and its derivative were found to be active catalysts for the metathesis of cyclooctane. © 2016 American Chemical Society.

[Liesegang's rings resembling helminthiasis].

Science.gov (United States)

Zámecník, M; Riedl, I

1996-12-01

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

An eHealth Approach to Reporting Allergic Reactions to Food and Closing the Knowledge Gap.

Science.gov (United States)

Munro, Christopher; Semic-Jusufagic, Aida; Pyrz, Katarzyna; Couch, Philip; Dunn-Galvin, Audrey; Peek, Niels; Themis, Marina; Mills, Clare; Buchan, Iain; Hourihane, Jonathan; Simpson, Angela

2015-01-01

There is an important knowledge gap in food allergy management in understanding the factors that determine allergic reactions to food, in gathering objective reports of reactions in real time, and in accessing patients' reaction-histories during consultations. We investigate how eHealth methods can close this knowledge gap. We report experiences with an online tool for reporting allergic reactions that we have developed as a web application. This application has been successfully validated by participants from Ireland and the UK, and is currently being used in a pilot where participants report allergic reactions in near-real time.

Fused-Ring Formation by an Intramolecular "Cut-and-Sew" Reaction between Cyclobutanones and Alkynes.

Science.gov (United States)

Deng, Lin; Jin, Likun; Dong, Guangbin

2018-03-01

The development of a catalytic intramolecular "cut-and-sew" transformation between cyclobutanones and alkynes to construct cyclohexenone-fused rings is described herein. The challenge arises from the need for selective coupling at the more sterically hindered proximal position, and can be addressed by using an electron-rich, but less bulky, phosphine ligand. The control experiment and 13 C-labelling study suggest that the reaction may start with cleavage of the less hindered distal C-C bond of cyclobutanones, followed by decarbonylation and CO reinsertion to enable Rh insertion at the more hindered proximal position. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

From ruthenium olefin metathesis catalyst to (η5-3- phenylindenyl)hydrido complex via alcoholysis

KAUST Repository

Manzini, Simone; Nelson, David J.; Lé bl, Tomá š; Poater, Albert; Cavallo, Luigi; Slawin, Alexandra M. Z.; Nolan, Steven P.

2014-01-01

The synthesis and characterisation of [Ru(H)(η5-3- phenylindenyl)(iBu-Phoban)2] 4 is reported ( iBu-Phoban = 9-isobutyl-9-phosphabicyclo-[3.3.1]-nonane). 4 is obtained via alcoholysis of metathesis pre-catalyst M11, in a process that was previously thought to be limited to analogous complex [RuCl 2(PPh3)2(3-phenylindenylidene)] (M 10). This journal is © The Royal Society of Chemistry.

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

Institute of Scientific and Technical Information of China (English)

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

2009-01-01

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

Chemical Reaction Rates from Ring Polymer Molecular Dynamics: Zero Point Energy Conservation in Mu + H2 → MuH + H.

Science.gov (United States)

Pérez de Tudela, Ricardo; Aoiz, F J; Suleimanov, Yury V; Manolopoulos, David E

2012-02-16

A fundamental issue in the field of reaction dynamics is the inclusion of the quantum mechanical (QM) effects such as zero point energy (ZPE) and tunneling in molecular dynamics simulations, and in particular in the calculation of chemical reaction rates. In this work we study the chemical reaction between a muonium atom and a hydrogen molecule. The recently developed ring polymer molecular dynamics (RPMD) technique is used, and the results are compared with those of other methods. For this reaction, the thermal rate coefficients calculated with RPMD are found to be in excellent agreement with the results of an accurate QM calculation. The very minor discrepancies are within the convergence error even at very low temperatures. This exceptionally good agreement can be attributed to the dominant role of ZPE in the reaction, which is accounted for extremely well by RPMD. Tunneling only plays a minor role in the reaction.

Confinement and stability of crystalline beams in storage rings

International Nuclear Information System (INIS)

Haffmans, A.F.

1995-01-01

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

Simple addition of silica to an alkane solution of Wilkinson WMe6 or Schrock W alkylidyne complex give active complex for saturated and unsaturated hydrocarbons metathesis

KAUST Repository

Callens, Emmanuel

2015-08-24

Addition of PDA silica to a solution of the Wilkinson WMe6 as well as the Schrock W neopentilidyne tris neopentyl complex catalyzes linear or cyclic alkanes to produce respectively a distribution of linear alkanes from methane up to triacontane or a mixture of cyclic and macrocyclic hydrocarbons. This single catalytic system transforms also linear α-olefins into higher and lower homologues via isomerization/metathesis mechanism (ISOMET). This complex is also efficient towards functionalized olefins. Unsaturated fatty acid esters (FAEs) are converted into diesters corresponding to self-metathesis products.

The Dynamical History of Chariklo and Its Rings

Energy Technology Data Exchange (ETDEWEB)

Wood, Jeremy [Hazard Community and Technical College, Community College Drive, Hazard, KY 41701 (United States); Horner, Jonti; Marsden, Stephen C. [Computational Engineering and Science Research Centre, University of Southern Queensland, West Street, Toowoomba, QLD 4350 (Australia); Hinse, Tobias C., E-mail: jeremy.wood@kctcs.edu [Korea Astronomy and Space Science Institute, 776 Daedukdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of)

2017-06-01

Chariklo is the only small solar system body confirmed to have rings. Given the instability of its orbit, the presence of rings is surprising, and their origin remains poorly understood. In this work, we study the dynamical history of the Chariklo system by integrating almost 36,000 Chariklo clones backward in time for 1 Gyr under the influence of the Sun and the four giant planets. By recording all close encounters between the clones and planets, we investigate the likelihood that Chariklo’s rings could have survived since its capture to the Centaur population. Our results reveal that Chariklo’s orbit occupies a region of stable chaos, resulting in its orbit being marginally more stable than those of the other Centaurs. Despite this, we find that it was most likely captured to the Centaur population within the last 20 Myr, and that its orbital evolution has been continually punctuated by regular close encounters with the giant planets. The great majority (>99%) of those encounters within 1 Hill radius of the planet have only a small effect on the rings. We conclude that close encounters with giant planets have not had a significant effect on the ring structure. Encounters within the Roche limit of the giant planets are rare, making ring creation through tidal disruption unlikely.

Study of the p + p → π+ + d reaction close to threshold

International Nuclear Information System (INIS)

Drochner, M.; Kemmerling, G.; Zwoll, K.; Frekers, D.; Garske, W.; Klimala, W.; Kolev, D.; Tsenov, R.; Kutsarova, T.

1996-01-01

The p + p → π + + d reaction has been studied at excess energies between 0.275 MeV and 3.86 MeV. The experiments were performed with the external proton beam of the COoler SYnchrotron (COSY) in Julich. Differential and total cross sections were measured employing a high resolution magnetic spectrometer with nearly 4π acceptance in the centre of the mass system. The values of the total cross sections are - when corrected for the Coulomb effects - in agreement with the results obtained from the time reversed reactions as well as from isospin related reactions. The measured anisotropies between 0.008 and 0.29 indicate that the p-wave is not negligible even so close to threshold. The s-wave and p-wave contributions at threshold are deduced. (author)

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

Directory of Open Access Journals (Sweden)

F. G. Orozco

2014-01-01

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

Cis/trans Coordination in olefin metathesis by static and molecular dynamic DFT calculations

KAUST Repository

Poater, Albert; Correa, Andrea; Pump, Eva; Cavallo, Luigi

2014-01-01

In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity. © 2014 Springer Science+Business Media New York.

Cis/trans Coordination in olefin metathesis by static and molecular dynamic DFT calculations

KAUST Repository

Poater, Albert

2014-05-25

In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity. © 2014 Springer Science+Business Media New York.

Change in the reaction kinetics of the deepoxidation of violaxanthine and activity of the xanthophyll ring under the action of γ irradiation

International Nuclear Information System (INIS)

Saakov, V.S.

1993-01-01

This article presents results of a study on the change in the content of the major chloroplast pigments and the activity of the xanthophyll ring as a function of irradiation dose. The data show that photodecomposition of chlorophyll and carotenoids is not associated with the primary action of ionizing radiations but may be manifested as a secondary process which follows inactivation or decomposition of the reaction center. Ionizing radiation affects the activity of the xanthophyll ring, as measured by deepoxidation of violaxanthine (DEV). Disruption of the electron transport chain leads to inhibition of DEV

Combining two-directional synthesis and tandem reactions, part 11: second generation syntheses of (±-hippodamine and (±-epi-hippodamine

Directory of Open Access Journals (Sweden)

Alcaraz Marie-Lyne

2008-01-01

Full Text Available Abstract Background Hippodamine is a volatile defence alkaloid isolated from ladybird beetles which holds potential as an agrochemical agent and was the subject of a synthesis by our group in 2005. Results Two enhancements to our previous syntheses of (±-hippodamine and (±-epi-hippodamine are presented which are able to shorten the syntheses by up to two steps. Conclusion Key advances include a two-directional homologation by cross metathesis and a new tandem reductive amination/double intramolecular Michael addition which generates 6 new bonds, 2 stereogenic centres and two rings, giving a single diastereomer in 74% yield.

Evidence for Dynamic Chemical Kinetics at Individual Molecular Ruthenium Catalysts.

Science.gov (United States)

Easter, Quinn T; Blum, Suzanne A

2018-02-05

Catalytic cycles are typically depicted as possessing time-invariant steps with fixed rates. Yet the true behavior of individual catalysts with respect to time is unknown, hidden by the ensemble averaging inherent to bulk measurements. Evidence is presented for variable chemical kinetics at individual catalysts, with a focus on ring-opening metathesis polymerization catalyzed by the second-generation Grubbs' ruthenium catalyst. Fluorescence microscopy is used to probe the chemical kinetics of the reaction because the technique possesses sufficient sensitivity for the detection of single chemical reactions. Insertion reactions in submicron regions likely occur at groups of many (not single) catalysts, yet not so many that their unique kinetic behavior is ensemble averaged. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Olefin cross metathesis based de novo synthesis of a partially protected L-amicetose and a fully protected L-cinerulose derivative

Directory of Open Access Journals (Sweden)

Bernd Schmidt

2014-05-01

Full Text Available Cross metathesis of a lactate derived allylic alcohol and acrolein is the entry point to a de novo synthesis of 4-benzoate protected L-amicetose and a cinerulose derivative protected at C5 and C1.

Synthesis of Ophiocerins from Non-Carbohydrate Sources

International Nuclear Information System (INIS)

Hong, Hui Jeong; Lee, Dong Min; Kang, Han Young

2010-01-01

Direct and unified synthetic routes to ophiocerin A, B, C, and D have been successfully developed. These syntheses are based on ring-closing metathesis and non-carbohydrate starting materials and are simpler and more efficient than the previous syntheses, as demonstrated in the case of ophiocerin B (2) (eleven steps from methyl α-D-glucopyranoside vs. four steps from 4-penten-2-ol) and ophiocerin A (1) (twelve steps from methyl α-D-glucopyranoside vs. three steps from 4-penten-2-ol). These routes will be useful for the practical synthesis of related natural products. Ophiocerins are comprised of four compounds isolated from the aqueous fungi Ophioceras venezuelense, each bearing a tetrahydropyran ring with an interesting array of substituents (Figure 1). Since substituted tetrahydropyran rings are found in many biologically important natural products, ophiocerins have attracted the attention of synthetic chemists

Tracheal ceramic rings for tracheomalacia: a review after 17 years.

Science.gov (United States)

Göbel, Gyula; Karaiskaki, Niki; Gerlinger, Imre; Mann, Wolf J

2007-10-01

Despite different support techniques, the surgical management of tracheomalacia is still a challenging problem. Satisfactory results after internal stenting are above 80%, whereas, when performing external stenting using biocompatible ceramic rings, results are reported at over 90%. The purpose of this study was to examine the efficiency of surgical treatment in patients with segmentary tracheomalacia using external ceramic ring grafts. In this retrospective study, we collected data from 12 patients who underwent surgery during the last 17 years for symptomatic segmentary tracheomalacia by use of biocompatible aluminum-oxide ceramic rings. All except one patient had undergone previous tracheostomy, six had a history of long-term intubation, two had previous trauma, and two patients had previous cancer treatment including radiotherapy. One of the patients still had an existing tracheostoma, which was closed when a ceramic ring was implanted. Tracheal wall collapse with pseudoglottis formation or flattened anterior-posterior tracheal diameter was documented with fiberoscopy at rest, and both pre- and postoperative airway resistance measurements were performed in all 12 patients using a spirometer. After malacic segments were found to be expandable using rigid tracheoscopy while the patient was under general anesthesia, preparation of the trachea was performed using a midline vertical incision in the neck. Subsequently, the malacic trachea was expanded by placing and suturing proper-sized ceramic ring(s) around it. In all patients, surgical expansion of the malacic segment using ceramic rings was successfully carried out without major complications while inspiratory stridor was resolved. Airway resistance decreased significantly from an average of 0.62 to 0.385 kPascal. Although the results of applying internal tracheal stents are encouraging, complications such as stent migration, granulation tissue and fistula formation, and mucociliary transport arrest are possible

Reaction of Nα-acetyl-L-histidine with diazomethane: A model esterification reaction of carboxylic groups in the presence of imidazole rings

Directory of Open Access Journals (Sweden)

Zamora, R.

1996-10-01

Full Text Available The reaction of Nα-acetyl-L-histidine with diazomethane was studied in order to analyze the esterification reaction of a carboxylic group in the presence of an imidazole ring. The reaction produced the expected Nα-acetyl-L-histidine methyl ester (1 as a major product. However, important amounts of [S]Nα-acetyl-1-methylimidazole-4-alanine methyl ester (2 and [S]Nα-acetyl-1-methylimidazole-5-alanine methyl ester (3 were also produced. These compounds, which could be detected by capillary electrophoresis (HPCE and thin layer chromatography, were fractionated by column chromatography and identified by gas chromatography coupled with mass spectrometry (GC-MS, and ¹H and ¹³C nuclear magnetic resonance spectroscopy. Structures for compounds 1-3 were confirmed by HPCE after acid hydrolysis. These results indicated that the use of diazomethane produces the methyl derivative of the heterocyclic ring in addition to the methyl ester. This reaction should be considered when preparing derivatives for GC-MS analysis.

La reacción de la Nα-acetil-L-histidina con diazometano fue estudiada con objeto de conocer el comportamiento de la reacción de esterificación de un grupo carboxílico en presencia de un anillo de imidazol. La reacción produjo el esperado éster metílico de la Nα-acetil-L-histidina (1 como producto mayoritario. Sin embargo, también se observó la formación de cantidades importantes de los esteres metílicos de la [S]Nα-acetil-1-metilimidazol- 4-alanina (2 y la [S]Nα-acetil-1-metilimidazol-5-alanina (3. Estos compuestos que pudieron ser detectados por electroforesis capilar y cromatografía en capa fina, fueron separados por cromatografía en columna e identificados por cromatografía de gases acoplada a espectrometría de masas, y por espectroscopia de resonancia magnética nuclear de ¹H y ¹³C. Las estructuras de los compuestos

Minimizing guard ring dead space in silicon detectors with an n-type guard ring at the edge of the detector

International Nuclear Information System (INIS)

Palviainen, Tanja; Tuuva, Tuure; Leinonen, Kari

2007-01-01

Detectors with n-type silicon with an n + -type guard ring were investigated. In the present work, a new p + /n/n + detector structure with an n + guard ring is described. The guard ring is placed at the edge of the detector. The detector depletion region extends also sideways, allowing for signal collection very close to the n-guard ring. In this kind of detector structure, the dead space of the detector is minimized to be only below the guard ring. This is proved by simulations done using Silvaco/ATLAS software

Minimizing guard ring dead space in silicon detectors with an n-type guard ring at the edge of the detector

Energy Technology Data Exchange (ETDEWEB)

Palviainen, Tanja [Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta (Finland)]. E-mail: tanja.palviainen@lut.fi; Tuuva, Tuure [Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta (Finland); Leinonen, Kari [Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta (Finland)

2007-04-01

Detectors with n-type silicon with an n{sup +}-type guard ring were investigated. In the present work, a new p{sup +}/n/n{sup +} detector structure with an n{sup +} guard ring is described. The guard ring is placed at the edge of the detector. The detector depletion region extends also sideways, allowing for signal collection very close to the n-guard ring. In this kind of detector structure, the dead space of the detector is minimized to be only below the guard ring. This is proved by simulations done using Silvaco/ATLAS software.

Selective Metathesis of α-Olefins from Bio-Sourced Fischer–Tropsch Feeds

KAUST Repository

Rouen, Mathieu; Queval, Pierre; Borre, Etienne; Falivene, Laura; Poater, Albert; Berthod, Mikael; Hugues, Francois; Cavallo, Luigi; Basle, Olivier; Olivier-Bourbigou, Helene; Mauduit, Marc

2016-01-01

The search for a low-cost process for the valorization of linear alpha-olefins combining high productivity and high selectivity is a longstanding goal for chemists. Herein, we report a soluble ruthenium olefin metathesis catalyst that performs the conversion of linear alpha-olefins to longer internal linear olefins with high selectivity (>99%) under neat conditions at low loadings (50 ppm) and without the need of expensive additives. This robust catalytic process allowed us to efficiently and selectively re-equilibrate the naphtha fraction (C-5-C-8) of a Fischer-Tropsch feed derived from non petroleum resources to a higher-value product range (C-9-C-14), useful as detergent and plasticizer precursors.

Selective Metathesis of α-Olefins from Bio-Sourced Fischer–Tropsch Feeds

KAUST Repository

Rouen, Mathieu

2016-10-14

The search for a low-cost process for the valorization of linear alpha-olefins combining high productivity and high selectivity is a longstanding goal for chemists. Herein, we report a soluble ruthenium olefin metathesis catalyst that performs the conversion of linear alpha-olefins to longer internal linear olefins with high selectivity (>99%) under neat conditions at low loadings (50 ppm) and without the need of expensive additives. This robust catalytic process allowed us to efficiently and selectively re-equilibrate the naphtha fraction (C-5-C-8) of a Fischer-Tropsch feed derived from non petroleum resources to a higher-value product range (C-9-C-14), useful as detergent and plasticizer precursors.

Evaluation of urogenital Chlamydia trachomatis infections by cell culture and the polymerase chain reaction using a closed system

DEFF Research Database (Denmark)

Østergaard, Lars; Traulsen, J; Birkelund, Svend

1991-01-01

the two test systems were compared, the overall sensitivity of the polymerase chain reaction was 96% and the specificity 94% when compared to the cell culture technique. By use of a closed system for DNA extraction and sample transfer for the polymerase chain reaction, contamination of the samples......Two hundred and fifty-four specimens from males and females consulting a clinic for sexually transmitted diseases were analyzed for genital Chlamydia trachomatis infection. Each clinical sample was tested by the cell culture technique and the polymerase chain reaction using a closed system. When...... not detect Chlamydia trachomatis after sufficient antibiotic treatment of the chlamydial infections....

Evaluation of urogenital Chlamydia trachomatis infections by cell culture and the polymerase chain reaction using a closed system

DEFF Research Database (Denmark)

Østergaard, Lars; Traulsen, J; Birkelund, Svend

1993-01-01

the two test systems were compared, the overall sensitivity of the polymerase chain reaction was 96% and the specificity 94% when compared to the cell culture technique. By use of a closed system for DNA extraction and sample transfer for the polymerase chain reaction, contamination of the samples......Two hundred and fifty-four specimens from males and females consulting a clinic for sexually transmitted diseases were analyzed for genital Chlamydia trachomatis infection. Each clinical sample was tested by the cell culture technique and the polymerase chain reaction using a closed system. When...... not detect Chlamydia trachomatis after sufficient antibiotic treatment of the chlamydial infections....

Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins

KAUST Repository

Borguet, Yannick

2015-01-01

© The Royal Society of Chemistry. Deprotonation of 1,3-di(2-tolyl)benzimidazolium tetrafluoroborate with a strong base afforded 1,3-di(2-tolyl)benzimidazol-2-ylidene (BTol), which dimerized progressively into the corresponding dibenzotetraazafulvalene. The complexes [RhCl(COD)(BTol)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BTol)] were synthesized to probe the steric and electronic parameters of BTol. Comparison of the percentage of buried volume (%VBur) and of the Tolman electronic parameter (TEP) of BTol with those determined previously for 1,3-dimesitylbenzimidazol-2-ylidene (BMes) revealed that the two N-heterocyclic carbenes displayed similar electron donicities, yet the 2-tolyl substituents took a slightly greater share of the rhodium coordination sphere than the mesityl groups, due to a more pronounced tilt. The anti,anti conformation adopted by BTol in the molecular structure of [RhCl(COD)(BTol)] ensured nonetheless a remarkably unhindered access to the metal center, as evidenced by steric maps. Second-generation ruthenium-benzylidene and isopropoxybenzylidene complexes featuring the BTol ligand were obtained via phosphine exchange from the first generation Grubbs and Hoveyda-Grubbs catalysts, respectively. The atropisomerism of the 2-tolyl substituents within [RuCl2(=CHPh)(PCy3)(BTol)] was investigated by using variable temperature NMR spectroscopy, and the molecular structures of all four possible rotamers of [RuCl2(=CH-o-OⁱPrC6H4)(BTol)] were determined by X-ray crystallography. Both complexes were highly active at promoting the ring-closing metathesis (RCM) of model α,ω-dienes. The replacement of BMes with BTol was particularly beneficial to achieve the ring-closure of tetrasubstituted cycloalkenes. More specifically, the stable isopropoxybenzylidene chelate enabled an almost quantitative RCM of two challenging substrates, viz., diethyl 2,2-bis(2-methylallyl)malonate and N,N-bis(2-methylallyl)tosylamide, within a few hours at 60°C.

Chemical reaction on solid surface observed through isotope tracer technique

International Nuclear Information System (INIS)

Tanaka, Ken-ichi

1983-01-01

In order to know the role of atoms and ions on solid surfaces as the partners participating in elementary processes, the literatures related to the isomerization and hydrogen exchanging reaction of olefines, the hydrogenation of olefines, the metathesis reaction and homologation of olefines based on solid catalysts were reviewed. Various olefines, of which the hydrogen atoms were substituted with deuterium at desired positions, were reacted using various solid catalysts such as ZnO, K 2 CO 3 on C, MoS 2 (single crystal and powder) and molybdenum oxide (with various carriers), and the infra-red spectra of adsorbed olefines on catalysts, the isotope composition of reaction products and the production rate of the reaction products were measured. From the results, the bonding mode of reactant with the atoms and ions on solid surfaces, and the mechanism of the elementary process were considered. The author emphasized that the mechanism of the chemical reaction on solid surfaces and the role of active points or catalysts can be made clear to the considerable extent by combining isotopes suitably. (Yoshitake, I.)

Ring opening of epoxides with C-nucleophiles.

Science.gov (United States)

Faiz, Sadia; Zahoor, Ameer Fawad

2016-11-01

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

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

DEFF Research Database (Denmark)

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

2015-01-01

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

Chemical Sensors Based on Optical Ring Resonators

Science.gov (United States)

Homer, Margie; Manfreda, Allison; Mansour, Kamjou; Lin, Ying; Ksendzov, Alexander

2005-01-01

Chemical sensors based on optical ring resonators are undergoing development. A ring resonator according to this concept is a closed-circuit dielectric optical waveguide. The outermost layer of this waveguide, analogous to the optical cladding layer on an optical fiber, is a made of a polymer that (1) has an index of refraction lower than that of the waveguide core and (2) absorbs chemicals from the surrounding air. The index of refraction of the polymer changes with the concentration of absorbed chemical( s). The resonator is designed to operate with relatively strong evanescent-wave coupling between the outer polymer layer and the electromagnetic field propagating along the waveguide core. By virtue of this coupling, the chemically induced change in index of refraction of the polymer causes a measurable shift in the resonance peaks of the ring. In a prototype that has been used to demonstrate the feasibility of this sensor concept, the ring resonator is a dielectric optical waveguide laid out along a closed path resembling a racetrack (see Figure 1). The prototype was fabricated on a silicon substrate by use of standard techniques of thermal oxidation, chemical vapor deposition, photolithography, etching, and spin coating. The prototype resonator waveguide features an inner cladding of SiO2, a core of SixNy, and a chemical-sensing outer cladding of ethyl cellulose. In addition to the ring Chemical sensors based on optical ring resonators are undergoing development. A ring resonator according to this concept is a closed-circuit dielectric optical waveguide. The outermost layer of this waveguide, analogous to the optical cladding layer on an optical fiber, is a made of a polymer that (1) has an index of refraction lower than that of the waveguide core and (2) absorbs chemicals from the surrounding air. The index of refraction of the polymer changes with the concentration of absorbed chemical( s). The resonator is designed to operate with relatively strong

Ruthenium Grubbs’ catalyst nanostructures grown by UV-excimer-laser ablation for self-healing applications

International Nuclear Information System (INIS)

Aïssa, B.; Nechache, R.; Haddad, E.; Jamroz, W.; Merle, P.G.; Rosei, F.

2012-01-01

Highlights: ► Successful preparation of 5-Ethylidene-2-Norbornene (5E2N) monomer reacted with Ruthenium Grubbs’ Catalyst (RGC) composite. ► The kinetics of the 5E2N ring opening metathesis polymerization (ROMP) is effective in a large temperature range (−20 to 45 °C). ► The kinetics of the 5E2N ROMP is occurring at very short time scales ( −4 Vol.%, occurring at very short time reaction. This approach opens new prospects for using healing agent nanocomposite materials for self-repair functionality, thereby obtaining a higher catalytic efficiency per unit mass.

Divergent Synthesis of Revised Apratoxin E, 30-epi-Apratoxin E, and 30S/30R-Oxoapratoxin E.

Science.gov (United States)

Mao, Zhuo-Ya; Si, Chang-Mei; Liu, Yi-Wen; Dong, Han-Qing; Wei, Bang-Guo; Lin, Guo-Qiang

2017-10-20

In this report, originally proposed apratoxin E (30S-7), revised apratoxin E (30R-7), and (30S)/(30R)-oxoapratoxin E (30S)-38/(30R)-38 were efficiently prepared by two synthetic methods. The chiral lactone 10, recycled from the degradation of saponin glycosides, was utilized to prepare the key nonpeptide fragment 9. Our alternative convergent assembly strategy was applied to the divergent synthesis of revised apratoxin E and its three analogues. Moreover, ring-closing metathesis (RCM) was for the first time found to be an efficient strategy for the macrocyclization of apratoxins.

Open-ring enhancement sign in diagnosing demyelinating pseudotumor

International Nuclear Information System (INIS)

Fang Liting; Wang Zhiping; Wang Linyou

2010-01-01

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

Concise Synthesis of Macrocycles by Multicomponent Reactions

NARCIS (Netherlands)

Abdelraheem, Eman M. M.; Khaksar, Samad; Dömling, Alexander

2018-01-01

A short reaction pathway was devised to synthesize a library of artificial 18-27-membered macrocycles. The five-step reaction sequence involves ring opening of a cyclic anhydride with a diamine, esterification, coupling with an amino acid isocyanide, saponification, and, finally, macro-ring closure

Solution, thermal and optical properties of bis(pyridinium salt)s as ionic liquids

International Nuclear Information System (INIS)

Jo, Tae Soo; Koh, Jung Jae; Han, Haesook; Bhowmik, Pradip K.

2013-01-01

Bis(pyridinium salt)s containing different alkyl chain lengths and various organic counterions were prepared by the ring-transmutation reaction of bis(pyrylium tosylate) with aliphatic amines in dimethyl sulfoxide at 130–135 °C for 18 h and their tosylate counterions were exchanged to other anions such as triflimide, methyl orange, and dioctyl sulfosuccinate by the metathesis reaction in a common organic solvent. Their chemical structures were established by using 1 H, 19 F, and 13 C NMR spectra. The thermal properties of bis(pyridinium salt)s were studied by DSC and TGA measurements. Some of the dicationic salts provided low melting points below 100 °C and some of them displayed amorphous properties. Polarized optical microscopy studies revealed the crystal structures prior to melting temperatures in some cases. Their optical properties were examined by using UV–Vis and photoluminescent spectrometers; and they emitted blue light both in the solution and solid states regardless of their microstructures, counterions, and the polarity of organic solvents. However, most of these salts exhibited hypsochromic shifts in their emission peaks in the solid state when compared with those of their solution spectra. Due to unique properties of methyl orange anion as a pH indicator, two of the salts showed different color change in varying concentrations of triflic acid in common organic solvents, demonstrating their potential use as an acid sensor in methanol, acetonitrile and acetone. Highlights: ► Luminescent dicationic salts were synthesized by ring-transmutation and metathesis reactions. ► Thermal and optical properties of dicationic salts are affected by the size of anion structures. ► Due to the methyl orange counterions, some dicationic salts showed pH- sensing property

Secondary Interactions Arrest the Hemiaminal Intermediate To Invert the Modus Operandi of Schiff Base Reaction: A Route to Benzoxazinones.

Science.gov (United States)

Patel, Ketan; Deshmukh, Satej S; Bodkhe, Dnyaneshwar; Mane, Manoj; Vanka, Kumar; Shinde, Dinesh; Rajamohanan, Pattuparambil R; Nandi, Shyamapada; Vaidhyanathan, Ramanathan; Chikkali, Samir H

2017-04-21

Discovered by Hugo Schiff, condensation between amine and aldehyde represents one of the most ubiquitous reactions in chemistry. This classical reaction is widely used to manufacture pharmaceuticals and fine chemicals. However, the rapid and reversible formation of Schiff base prohibits formation of alternative products, of which benzoxazinones are an important class. Therefore, manipulating the reactivity of two partners to invert the course of this reaction is an elusive target. Presented here is a synthetic strategy that regulates the sequence of Schiff base reaction via weak secondary interactions. Guided by the computational models, reaction between 2,3,4,5,6-pentafluoro-benzaldehyde with 2-amino-6-methylbenzoic acid revealed quantitative (99%) formation of 5-methyl-2-(perfluorophenyl)-1,2-dihydro-4H-benzo[d][1,3]oxazin-4-one (15). Electron donating and electron withdrawing ortho-substituents on 2-aminobenzoic acid resulted in the production of benzoxazinones 9-36. The mode of action was tracked using low temperature NMR, UV-vis spectroscopy, and isotopic ( 18 O) labeling experiments. These spectroscopic mechanistic investigations revealed that the hemiaminal intermediate is arrested by the hydrogen-bonding motif to yield benzoxazinone. Thus, the mechanistic investigations and DFT calculations categorically rule out the possibility of in situ imine formation followed by ring-closing, but support instead hydrogen-bond assisted ring-closing to prodrugs. This unprecedented reaction represents an interesting and competitive alternative to metal catalyzed and classical methods of preparing benzoxazinone.

Effect of support on hydro-metathesis of propene: A comparative study of W(CH 3 ) 6 anchored to silica vs. silica-alumina

KAUST Repository

Tretiakov, Mykyta; Samantaray, Manoja; Saidi, Aya; Basset, Jean-Marie

2018-01-01

Hydro-metathesis of propene was carried out by using well-defined W(CH3)6 supported on silica and silica-alumina. It was observed that W(CH3)6 supported silica-alumina catalyst is much better (TON 4577) than the silica supported catalyst (TON 2104

Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations.

Science.gov (United States)

Trost, Barry M; Frederiksen, Mathias U; Rudd, Michael T

2005-10-21

The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.

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

DEFF Research Database (Denmark)

Beyer, Jürgen; Madsen, Robert

1998-01-01

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

Reactions of Fischer carbene complexes with Electron-deficient olefins: Scope and limitations of this route to donor-acceptor-substituted cyclopropanes

Energy Technology Data Exchange (ETDEWEB)

Wienand, A.; Reissig, H.U. (Inst. fuer Organische Chemie der Technischen Hochschule Darmstadt (West Germany))

1990-12-01

The Fischer carbene complex ((CO){sub 5}Cr{double bond}C(OMe)Ph) (1) is able to transfer its carbene ligand to a variety of electron-deficient olefins and provides donor-acceptor-substituted cyclopropanes in good yields. Apt activating groups with respect to the alkene are ester, amide, nitrile, sulfone, and dialkyl phosphonate functions. Methyl vinyl ketone (19) affords products in low yield that may arise from an intermediate cyclopropane derivative. Phenyl vinyl sulfoxide (24) mainly acts as an oxidizing agent, transforming 1 into methyl benzoate. for olefin 24 and {alpha}-(N-methylanilino)acrylonitrile the authors found products that should be formed on an olefin metathesis pathway. The methyl-substituted carbene complex 48 also affords the expected donor-acceptor-substituted cyclopropanes; however, acyclic isomers are formed in higher amounts. The molybdenum and tungsten complexes 55 and 56, respectively, also furnish cyclopropane derivatives, but the yields are lower than with the chromium compound 1. Disubstituted olefins and complex 1 still give the cyclopropanes in moderate yields, while all trisubstituted and most of the difunctionalized alkenes do not react with this Fischer carbene complex. The cyclopropanes synthesized can be deprotonated and alkylated or transformed into ring-opened products. These model reactions demonstrate the synthetic potentials of donor-acceptor-substituted cyclopropanes prepared via Fischer carbene complexes.

Cross-section of the reaction {sup 7}Li(p,n){sup 7}Be close to the threshold

Energy Technology Data Exchange (ETDEWEB)

Shorin, V S [Institute of Physics and Power Engineering, Obninsk (Russian Federation)

1997-06-01

The status of data on the cross-section of the reaction {sup 7}Li(p,n){sup 7}Be close to the threshold is reviewed. On the basis of recent data on the cross-section of the inverse reaction {sup 7}Be(n,p){sup 7}Li and certain theoretical models, an evaluation is performed of the total cross-section of the {sup 7}Li(p,n)-reaction in the proton energy region up to 2 MeV. (author). 16 refs, 1 fig., 1 tab.

Electrochemically Triggered Co-Conformational Switching in a [2]catenane Comprising a Non-Symmetric Calix[6]arene Wheel and a Two-Station Oriented Macrocycle

Directory of Open Access Journals (Sweden)

Valeria Zanichelli

2018-05-01

Full Text Available Catenanes with desymmetrized ring components can undergo co-conformational rearrangements upon external stimulation and can form the basis for the development of molecular rotary motors. We describe the design, synthesis and properties of a [2]catenane consisting of a macrocycle—the ‘track’ ring—endowed with two distinct recognition sites (a bipyridinium and an ammonium for a calix[6]arene—the ‘shuttle’ ring. By exploiting the ability of the calixarene to thread appropriate non-symmetric axles with directional selectivity, we assembled an oriented pseudorotaxane and converted it into the corresponding oriented catenane by intramolecular ring closing metathesis. Cyclic voltammetric experiments indicate that the calixarene wheel initially surrounds the bipyridinium site, moves away from it when it is reduced, and returns in the original position upon reoxidation. A comparison with appropriate model compounds shows that the presence of the ammonium station is necessary for the calixarene to leave the reduced bipyridinium site.

An Asymmetric Synthetic Approach to the A-ring of the Taxol Family of Anti-Cancer Compounds

Directory of Open Access Journals (Sweden)

M. L. Marin

1998-02-01

Full Text Available A synthetic route developed for the preparation of the A-ring of Taxol family of molecules is reported. By means of an intramolecular Diels-Alder reaction an asymmetric approach to this ring has been accomplished. Also, initial studies to prepare the A ring using an intramolecular Diels-Alder reaction have been successful.

Flexible ring seal

International Nuclear Information System (INIS)

Abbes, Claude; Gournier, Andre; Rouaud, Christian; Villepoix, Raymond de.

1976-01-01

The invention concerns a flexible metal ring seal, able to ensure a perfect seal between two bearings due to the crushing and elastic deformation properties akin to similar properties in elastomers. Various designs of seal of this kind are already known, particularly a seal made of a core formed by a helical wire spring with close-wound turns and with high axial compression ratio, closed on itself and having the shape of an annulus. This wire ring is surrounded by at least one envelope having at rest the shape of a toroidal surface of which the generating circle does not close on itself. In a particular design mode, the seal in question can include, around the internal spring, two envelopes of which one in contact with the spring is composed of a low ductility elastic metal, such as mild steel or stainless steel and the other is, on the contrary, made of a malleable metal, such as copper or nickel. The first envelope evenly distributes the partial crushing of the spring, when the seal is tightened, on the second envelope which closely fits the two surfaces between which the seal operates. The stress-crushing curve characteristic of the seal comprises two separate parts, the first with a relatively sharp slope corresponds to the start of the seal compression phase, enabling at least some of these curves to reach the requisite seal threshold very quickly, then, beyond this, a second part, practically flat, where the stress is appreciably constant for a wide operating bracket [fr

The redox-Mannich reaction.

Science.gov (United States)

Chen, Weijie; Seidel, Daniel

2014-06-06

A complement to the classic three-component Mannich reaction, the redox-Mannich reaction, utilizes the same starting materials but incorporates an isomerization step that enables the facile preparation of ring-substituted β-amino ketones. Reactions occur under relatively mild conditions and are facilitated by benzoic acid.

Rings of Molecular Line Emission in the Disk Orbiting the Young, Close Binary V4046 Sgr

Science.gov (United States)

Dickson-Vandervelde, Dorothy; Kastner, Joel H.; Qi, C.; Forveille, Thierry; Hily-Blant, Pierre; Oberg, Karin; Wilner, David; Andrews, Sean; Gorti, Uma; Rapson, Valerie; Sacco, Germano; Principe, David

2018-01-01

We present analysis of a suite of subarcsecond ALMA Band 6 (1.1 - 1.4 mm) molecular line images of the circumbinary, protoplanetary disk orbiting V4046 Sgr. The ~20 Myr-old V4046 Sgr system, which lies a mere ~73 pc from Earth, consists of a close (separation ~10 Rsun) pair of roughly solar-mass stars that are orbited by a gas-rich crcumbinary disk extending to ~350 AU in radius. The ALMA images reveal that the molecules CO and HCN and their isotopologues display centrally peaked surface brightness morphologies, whereas the cyanide group molecules (HC3N, CH3CN), deuterated molecules (DCN, DCO+), hydrocarbons (as traced by C2H), and potential CO ice line tracers (N2H+, and H2CO) appear as a sequence of sharp and diffuse rings of increasing radii. The characteristic sizes of these molecular emission rings, which range from ~25 to >100 AU in radius, are evident in radial emission-line surface brightness profiles extracted from the deprojected disk images. We find that emission from 13CO emission transitions from optically thin to thick within ~50 AU, whereas C18O emission remains optically thin within this radius. We summarize the insight into the physical and chemical processes within this evolved protoplanetary disk that can be obtained from comparisons of the various emission-line morphologies with each other and with that of the continuum (large-grain) emission on size scales of tens of AU.This research is supported by NASA Exoplanets program grant NNX16AB43G to RIT

The Cryogenic Storage Ring CSR

OpenAIRE

von Hahn, Robert; Becker, Arno; Berg, Felix; Blaum, Klaus; Breitenfeldt, Christian; Fadil, Hisham; Fellenberger, Florian; Froese, Michael; George, Sebastian; Göck, Jürgen; Grieser, Manfred; Grussie, Florian; Guerin, Elisabeth A.; Heber, Oded; Herwig, Philipp

2016-01-01

An electrostatic cryogenic storage ring, CSR, for beams of anions and cations with up to 300 keV kinetic energy per unit charge has been designed, constructed, and put into operation. With a circumference of 35 m, the ion-beam vacuum chambers and all beam optics are in a cryostat and cooled by a closed-cycle liquid helium system. At temperatures as low as (5.5 ± 1) K inside the ring, storage time constants of several minutes up to almost an hour were observed for atomic and molecular, anion a...

Mechanical seal having a double-tier mating ring

Science.gov (United States)

Khonsari, Michael M.; Somanchi, Anoop K.

2005-09-13

An apparatus and method to enhance the overall performance of mechanical seals in one of the following ways: by reducing seal face wear, by reducing the contact surface temperature, or by increasing the life span of mechanical seals. The apparatus is a mechanical seal (e.g., single mechanical seals, double mechanical seals, tandem mechanical seals, bellows, pusher mechanical seals, and all types of rotating and reciprocating machines) comprising a rotating ring and a double-tier mating ring. In a preferred embodiment, the double-tier mating ring comprises a first and a second stationary ring that together form an agitation-inducing, guided flow channel to allow for the removal of heat generated at the seal face of the mating ring by channeling a coolant entering the mating ring to a position adjacent to and in close proximity with the interior surface area of the seal face of the mating ring.

Divergent Total Syntheses of (-)-Huperzine Q, (+)-Lycopladine B, (+)-Lycopladine C, and (-)-4-epi-Lycopladine D.

Science.gov (United States)

Hong, Benke; Hu, Dachao; Wu, Jinbao; Zhang, Jing; Li, Houhua; Pan, Yingming; Lei, Xiaoguang

2017-07-04

We report herein our synthetic efforts towards the divergent syntheses of (-)-huperzine Q (1), (+)-lycopladine B (2), (+)-lycopladine C (3), and (-)-lycopladine D (4). The 10-step total synthesis of (-)-huperzine Q (1) and the first total syntheses of (+)-lycopladines B (2) and C (3) were accomplished through a series of cascade reactions. Our approach involved a Michael addition/aldol/intramolecular C-alkylation sequence to forge the 6/9 spirocycle ring, and this was followed by an ethylene-accelerated carbonyl-olefin metathesis to construct the common 6/5/9 ring system. Finally, late-stage enamine bromofunctionalization enabled us to access (-)-huperzine Q (1), (+)-lycopladine B (2), and (+)-lycopladine C (3), and a tandem C4-epimerization/retro-Claisen condensation furnished (-)-4-epi-lycopladine D (63). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Well-Defined Surface Species [(≡Si - O -)W(=O)Me3] Prepared by Direct Methylation of [(≡Si - O -)W(=O)Cl3], a Catalyst for Cycloalkane Metathesis and Transformation of Ethylene to Propylene

KAUST Repository

Hamieh, Ali Imad Ali

2015-04-03

The silica-supported tungsten oxo-trimethyl complex [(≡Si - O -)W(=O)Me3] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl4 on the surface of silica, partially dehydroxylated at 700 °C (SiO2-700), a well-defined monopodal surface complex [(≡Si - O -)W(=O)Cl3] was produced. The supported complex directly methylated with ZnMe2 and transformed into [(≡Si - O -)W(=O)Me3], which we fully characterized by microanalysis, IR, mass balance and SS NMR (1H, 13C, 1H-13C HETCOR, 1H-1H DQ and TQ). [(≡Si - O)W(=O)Me3] has two conformational isomers on the surface at room temperature. The conversion of one to the other was observed at 318 K by variable-temperature 13C CP/MAS and 1H spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [(≡Si - O)W(=O)Me3] was found to be active in cyclooctane metathesis and to have a wide distribution range in ring-contracted and ring-expanded products. In addition, [(≡Si - O)W(=O)Me3] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes. (Chemical Equation Presented). © 2015 American Chemical Society.

Well-Defined Surface Species [(≡Si - O -)W(=O)Me3] Prepared by Direct Methylation of [(≡Si - O -)W(=O)Cl3], a Catalyst for Cycloalkane Metathesis and Transformation of Ethylene to Propylene

KAUST Repository

Hamieh, Ali Imad Ali; Chen, Yin; Abdel-Azeim, Safwat; Abou-Hamad, Edy; Goh, Li Min Serena; Samantaray, Manoja; Dey, Raju; Cavallo, Luigi; Basset, Jean-Marie

2015-01-01

The silica-supported tungsten oxo-trimethyl complex [(≡Si - O -)W(=O)Me3] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl4 on the surface of silica, partially dehydroxylated at 700 °C (SiO2-700), a well-defined monopodal surface complex [(≡Si - O -)W(=O)Cl3] was produced. The supported complex directly methylated with ZnMe2 and transformed into [(≡Si - O -)W(=O)Me3], which we fully characterized by microanalysis, IR, mass balance and SS NMR (1H, 13C, 1H-13C HETCOR, 1H-1H DQ and TQ). [(≡Si - O)W(=O)Me3] has two conformational isomers on the surface at room temperature. The conversion of one to the other was observed at 318 K by variable-temperature 13C CP/MAS and 1H spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [(≡Si - O)W(=O)Me3] was found to be active in cyclooctane metathesis and to have a wide distribution range in ring-contracted and ring-expanded products. In addition, [(≡Si - O)W(=O)Me3] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes. (Chemical Equation Presented). © 2015 American Chemical Society.

Identification, synthesis and mass spectrometry of a macrolide from the African reed frog Hyperolius cinnamomeoventris

Directory of Open Access Journals (Sweden)

Markus Menke

2016-12-01

Full Text Available The contents of the gular glands of the male African reed frog Hyperolius cinnamomeoventris consist of a mixture of aliphatic macrolides and sesquiterpenes. While the known macrolide gephyromantolide A was readily identified, the structure of another major component was suggested to be a tetradecen-13-olide. The synthesis of the two candidate compounds (Z-5- and (Z-9-tetradecen-13-olide revealed the former to be the naturally occurring compound. The synthesis used ring-closing metathesis as key step. While the Hoveyda–Grubbs catalyst furnished a broad range of isomeric products, the (Z-selective Grubbs catalyst lead to pure (Z-products. Analysis by chiral GC revealed the natural frog compound to be (5Z,13S-5-tetradecen-13-olide (1. This compound is also present in the secretion of other hyperoliid frogs as well as in femoral glands of male mantellid frogs such as Spinomantis aglavei. The mass spectra of the synthesized macrolides as well as their rearranged isomers obtained during ring-closing metathesis showed that it is possible to assign the location of the double bond in an unsaturated macrolide on the basis of its EI mass spectrum. The occurrence of characteristic ions can be explained by the fragmentation pathway proposed in the article. In contrast, the localization of a double bond in many aliphatic open-chain compounds like alkenes, alcohols or acetates, important structural classes of pheromones, is usually not possible from an EI mass spectrum. In the article, we present the synthesis and for the first time elucidate the structure of macrolides from the frog family Hyperoliidae.

WR stars with ring nebulae

International Nuclear Information System (INIS)

Tutukov, A.

1982-01-01

It is shown that most of usually apparently single nitrogen WR stars with ring emission nebulae around them (WN + Neb) are a probable product of the evolution of a massive close binary with initial masses of components exceeding approximately 20 solar masses. (Auth.)

Vanishing of cohomology over Cohen–Macaulay rings

DEFF Research Database (Denmark)

Christensen, Lars Winther; Holm, Henrik Granau

2012-01-01

A 2003 counterexample to a conjecture of Auslander brought attention to a family of rings—colloquially called AC rings—that satisfy a natural condition on vanishing of cohomology. Several results attest to the remarkable homological properties of AC rings, but their definition is barely operational......, and it remains unknown if they form a class that is closed under typical constructions in ring theory. In this paper, we study transfer of the AC property along local homomorphisms of Cohen–Macaulay rings. In particular, we show that the AC property is preserved by standard procedures in local algebra. Our...

Exploratory study for a solid-state charged-particle spectrometer inside the celsius ring: α + 1H reactions at 1.7 and 2.2 GeV/c

International Nuclear Information System (INIS)

Bargholtz, C.; Fransson, K.; Holmberg, L.; Lindh, K.; Sandberg, L.; Tegner, P.E.; Thoerngren-Engblom, P.; Vojdani, D.

1991-08-01

Charged particles emitted in the extreme forward direction can be detected in a particle telescope mounted inside the CELSIUS ring in one of the dipole magnets following the target. Results of a test with a plastic scintillator telescope are reported for α + H reactions at 1.7 and 2.2 GeV/c. The results are consistent with ray-trace calculations. Contributions in the spectrometer from back-ground reactions and scattering in the beam tube are small. (au)

Cycloalkyl-based unsymmetrical unsaturated (U2)-NHC ligands: Flexibility and dissymmetry in ruthenium-catalysed olefin metathesis

KAUST Repository

Rouen, Mathieu

2014-01-01

Air-stable Ru-indenylidene and Hoveyda-type complexes bearing new unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands combining a mesityl unit and a flexible cycloalkyl moiety as N-substituents were synthesised. Structural features, chemical stabilities and catalytic profiles in olefin metathesis of this new library of cycloalkyl-based U2-NHC Ru complexes were studied and compared with their unsymmetrical saturated NHC-Ru homologues as well as a set of commercially available Ru-catalysts bearing either symmetrical SIMes or IMes NHC ligands. © 2014 the Partner Organisations.

Palm oil based polymer materials obtained by ROMP: study by low field NMR

International Nuclear Information System (INIS)

Fernandes, Henrique; Azevedo, Eduardo R. de; Lima-Neto, Benedito S.

2015-01-01

Aiming to study and develop new materials synthesized from sustainable sources, several polymers were prepared using in its monomeric composition, different amounts of NPO (Norbornenyl Palm Oil) monomer. This monomer was developed based on a vegetable oil rather produced in northern Brazil, the Palm Oil. Since this oil have a low content of unsaturation, its use in developing new monomer for ROMP (Ring-Opening Metathesis Polymerization) is not exploited. In this regard, polymeric materials were obtained using the NOP and both the reaction process and the resulting products were analyzed by Nuclear Magnetic Resonance in the time domain (TD-NMR) at low magnetic field. (author)

Palm oil based polymer materials obtained by ROMP: study by low field NMR; Materiais polimericos obtidos via ROMP a partir de oleo de palma: estudo por RMN de baixo campo

Energy Technology Data Exchange (ETDEWEB)

Fernandes, Henrique; Azevedo, Eduardo R. de; Lima-Neto, Benedito S., E-mail: benedito@iqsc.usp.br [Universidade de Sao Paulo (USP), Sao Carlos, SP (Brazil)

2015-07-01

Aiming to study and develop new materials synthesized from sustainable sources, several polymers were prepared using in its monomeric composition, different amounts of NPO (Norbornenyl Palm Oil) monomer. This monomer was developed based on a vegetable oil rather produced in northern Brazil, the Palm Oil. Since this oil have a low content of unsaturation, its use in developing new monomer for ROMP (Ring-Opening Metathesis Polymerization) is not exploited. In this regard, polymeric materials were obtained using the NOP and both the reaction process and the resulting products were analyzed by Nuclear Magnetic Resonance in the time domain (TD-NMR) at low magnetic field. (author)

Palm oil based polymer materials obtained by romp: study by low field NMR; Materiais polimericos obtidos via ROMP a partir de oleo de palma: estudo por RMN de baixo campo

Energy Technology Data Exchange (ETDEWEB)

Fernandes, Henrique; Lima-Neto, Benedito S., E-mail: benedito@iqsc.usp.br [Universidade de Sao Paulo (USP), Sao Carlos, SP (Brazil). Instituto de Quimica de; Azevedo, Eduardo R. de [Universidade de Sao Paulo (USP), Sao Carlos, SP (Brazil). Instituto de Fisica

2013-07-01

Aiming to study and develop new materials synthesized from sustainable sources, several polymers were prepared using in its monomeric composition, different amounts of NPO (Norbornenyl Palm Oil) monomer. This monomer was developed based on a vegetable oil rather produced in northern Brazil, the Palm Oil. Since this oil have a low content of unsaturation, its use in developing new monomer for ROMP (Ring-Opening Metathesis Polymerization) is not exploited. In this regard, polymeric materials were obtained using the NOP and both the reaction process and the resulting products were analyzed by Nuclear Magnetic Resonance in the time domain (TD-NMR) at low magnetic field. (author)

Laparoscopic appendicectomy using endo-ring applicator and fallope rings

International Nuclear Information System (INIS)

Ali, Iyoob V; Maliekkal, Joji I

2009-01-01

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

Electronic bond tuning with heterocyclic carbenes

KAUST Repository

Falivene, Laura

2013-01-01

We discuss the impact of the nature of the heterocyclic carbene ring, when used as a complex forming ligand, on the relative stability of key intermediates in three typical Ru, Pd and Au promoted reactions. Results show that P-heterocyclic carbenes have a propensity to increase the bonding of the labile ligand and of the substrate in Ru-promoted olefin metathesis, whereas negligible impact is expected on the stability of the ruthenacycle intermediate. In the case of Pd cross-coupling reactions, dissociation of a P-heterocyclic carbene is easier than dissociation of the N-heterocyclic analogue. In the case of the Au-OH synthon, the Au-OH bond is weakened with the P-heterocyclic carbene ligands. A detailed energy decomposition analysis is performed to rationalize these results. © 2013 The Royal Society of Chemistry.

Tandem Reaction of Cationic Copolymerization and Concertedly Induced Hetero-Diels-Alder Reaction Preparing Sequence-Regulated Polymers.

Science.gov (United States)

Matsumoto, Suzuka; Kanazawa, Arihiro; Kanaoka, Shokyoku; Aoshima, Sadahito

2017-06-14

A unique tandem reaction of sequence-controlled cationic copolymerization and site-specific hetero-Diels-Alder (DA) reaction is demonstrated. In the controlled cationic copolymerization of furfural and 2-acetoxyethyl vinyl ether (AcOVE), only the furan ring adjacent to the propagating carbocation underwent the hetero-DA reaction with the aldehyde moiety of another furfural molecule. A further and equally important feature of the copolymerization is that the obtained copolymers had unprecedented 2:(1 + 1)-type alternating structures of repeating sequences of two VE and one furfural units in the main chain and one furfural unit in the side chain. The specific DA reaction is attributed to the delocalization of the positive charge to the side furan ring.

Pharmacophore mapping in the laulimalide series: total synthesis of a vinylogue for a late-stage metathesis diversification strategy.

Science.gov (United States)

Wender, Paul A; Hilinski, Michael K; Skaanderup, Philip R; Soldermann, Nicolas G; Mooberry, Susan L

2006-08-31

An efficient synthesis of the macrocyclic core of laulimalide with a pendant vinyl group at C20 is described, allowing for late-stage introduction of various side chains through a selective and efficient cross metathesis diversification step. Representative analogues reported herein are the first to contain modifications to only the side chain dihydropyran of laulimalide and des-epoxy laulimalide. This step-economical strategy enables the rapid synthesis of new analogues using alkenes as an inexpensive, abundantly available diversification feedstock.

Porcine reproductive and respiratory syndrome virus: Interlaboratory ring trial to evaluate real-time reverse transcription polymerase chain reaction detection methods

DEFF Research Database (Denmark)

Wernike, Kerstin; Bonilauri, Paolo; Dauber, Malte

2012-01-01

To compare the real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) assays used for the diagnosis of Porcine reproductive and respiratory syndrome virus (PRRSV), a Europe-wide interlaboratory ring trial was conducted. A variety of PRRSV strains including North American...... (NA) and European (EU) genotype isolates were analyzed by the participants. Great differences regarding qualitative diagnostics as well as analytical sensitivity were observed between the individual RT-qPCR systems, especially when investigating strains from the EU genotype. None of the assays...

TREE SELECTING AND TREE RING MEASURING IN DENDROCHRONOLOGICAL INVESTIGATIONS

Directory of Open Access Journals (Sweden)

Sefa Akbulut

2004-04-01

Full Text Available Dendrochronology is a method of dating which makes use of the annual nature of tree growth. Dendrochronology may be divided into a number of subfields, each of which covers one or more aspects of the use of tree ring data: dendroclimatology, dendrogeomorphology, dendrohydrology, dendroecology, dendroarchaelogy, and dendrogylaciology. Basic of all form the analysis of the tree rings. The wood or tree rings can aid to dating past events about climatology, ecology, geology, hydrology. Dendrochronological studies are conducted either on increment cores or on discs. It may be seen abnormalities on tree rings during the measurement like that false rings, missing rings, reaction wood. Like that situation, increment cores must be extracted from four different sides of each tree and be studied as more as on tree.

Fano resonance and persistent current of a quantum ring

International Nuclear Information System (INIS)

Xiong Yongjian; Liang Xianting

2004-01-01

We investigate electron transport and persistent current of a quantum ring weakly attached to current leads. Assuming there is direct coupling (weakly or strongly) between two leads, electrons can transmit by the inter-lead coupling or tunneling through the quantum ring. The interference between the two paths yields asymmetric Fano line shape for conductance. In presence of interior magnetic flux, there is persistent current along the ring with narrow resonance peaks. The positions of the conductance resonances and the persistent current peaks correspond to the quasibound levels of the closed ring. This feature is helpful to determine the energy spectrum of the quantum ring. Our results show that the proposed setup provides a tunable Fano system

Functionalized linear and cyclic polyolefins

Energy Technology Data Exchange (ETDEWEB)

Tuba, Robert; Grubbs, Robert H.

2018-02-13

This invention relates to methods and compositions for preparing linear and cyclic polyolefins. More particularly, the invention relates to methods and compositions for preparing functionalized linear and cyclic polyolefins via olefin metathesis reactions. Polymer products produced via the olefin metathesis reactions of the invention may be utilized for a wide range of materials applications. The invention has utility in the fields of polymer and materials chemistry and manufacture.

Improved direct production of 2,3-dimethylbutenes and 3,3-dimethylbutene from 2-methylpropene on tungsten hydride based catalysts

KAUST Repository

Garron, Anthony; Stoffelbach, Franç ois; Merle, Nicolas; Szeto, Kaï Chung; Thivolle-Cazat, Jean; Basset, Jean-Marie; Norsic, Sé bastien; Taoufik, Mostafa

2012-01-01

2-Methylpropene in the presence of W-H/Ni 1%-Al 2O 3-(500) is transformed in high selectivity into a mixture of 2,3-dimethylbutenes (2,3-DMBs = DMB-1 and DMB-2) and neohexene. 2,3-DMBs arise from the unfavoured 2-methylpropene self-metathesis reaction whereas the neohexene originates from a cascade reaction: 2-methylpropene dimerisation followed by cross metathesis. © 2012 The Royal Society of Chemistry.

Ni(II

African Journals Online (AJOL)

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analytical chemistry, catalysis, electrochemistry, ring-opening metathesis ... Ethanol was dried over anhydrous copper(II) sulfate and distilled over metallic sodium. ... All bacteria were inoculated into Nutrient Broth (Difco) and incubated for 24 h ...

Role of four-membered rings in C32 fullerene stability and mechanisms of generalized Stone-Wales transformation: a density functional theory investigation.

Science.gov (United States)

Wang, Weiwei; Dang, Jingshuang; Zhao, Xiang

2011-08-28

Density functional theory (DFT) methods have been applied to study C(32) fullerenes built from four-, five-, and six-membered rings. The relative energies of pure C(32) fullerenes have been evaluated to locate three most stable structures, 32:D(4d) with two squares, 1:D(3) without square and 5:C(s) with one square. Structural analysis reveals that there is a rearrangement pathway between the lowest energy classical isomer 1:D(3) and the lowest energy non-classical isomer 32:D(4d), and 5:C(s) behaves just as an intermediate between them. The kinetic processes of generalized Stone-Wales transformation (GSWT) with four-membered rings have been explored and two distinct reaction mechanisms are determined by all the transition states and intrinsic reaction coordinates with PBE1PBE/6-31G(d) approach for the first time. One mechanism is the concerted reaction with a rotating dimer closed to the cage surface and another is the stepwise reaction with a carbene-like sp(3) structure, whereas the latter is sorted into two paths based on four-membered ring vanishing before or after the formation of the carbene-like structure. It is indicated that there is no absolute preference for any mechanism, which depends on the adaptability of different reactants on the diverse mechanisms. Furthermore, it's found that the interconversion process with the participation of squares is more reactive than the rearrangement between C(60)_I(h) and C(60)_C(2v), implying some potential importance of non-classical small fullerenes in the fullerene isomerization.

The Jovian rings as observed from Jupiter.

Science.gov (United States)

Malinnikova Bang, A.; Joergensen, J. L.; Joergensen, P. S.; Denver, T.; Connerney, J. E. P.; Bolton, S. J.; Levin, S.

2017-12-01

Juno entered a highly eliptic orbit around Jupiter on the 4. July 2016. Since then, it has completed 8 perijove passages. The Magnetometer experiment consists of two measurement platforms mounted 10m and 12m from the spacecraft spin axis, on one of three large solar panels. Each magnetometer platform is equipped with two star trackers to provide accurate attitude information to the vector magnetometers. The star trackers are pointed 13deg from the (anti) spin vector, and clocked 180deg to avoid simultaneous blinding effects from bright Jupiter only 6000km away, during perijove. This brings Juno well inside the innermost known satellite, Metis. The star trackers pointing close to, and above the Jovian horizon for most of each rotation of Juno, has an excellent view of the Jovian ring systems with a beta-angle close to 180deg. We report on the ring imaging performed during the first 8 orbits, discuss the structure, optical depth and moon sheparding of the inner rings as measured so far.

Saturn’s ring temperatures at equinox

Science.gov (United States)

Spilker, Linda J.; Ferrari, C.; Morishima, R.

2013-10-01

Modeling the thermal emission of Saturn's rings is challenging due to the numerous heating sources as well as the structural properties of the disk and of the particles that are closely related. At equinox, however, the main rings are externally heated by Saturn alone and the problem is somewhat simplified. We test the abilities of our current models to reproduce the temperatures observed with the Cassini CIRS instrument around equinox in August 2009. A simple semi-analytic model which includes mutual shadowing effects can mostly explain the radial profile of the equinox ring temperatures, except the model predicts lower temperatures than those observed for the A ring. The temperature variation at a given saturnocentric radius is primarily caused by observational geometry variations relative to Saturn. The observed temperature increases with decreasing Saturn-ring-observer angle. In addition, we found evidence that the leading hemispheres of particles are warmer than the trailing hemispheres at least for the C ring and probably for the A and B rings as well. This is explained if some fraction of particles has spin rates lower than the synchronous rotation rate as predicted by N-body simulations. The spin model for a monolayer ring (Ferrari, C., Leyrat, C., 2006, Astron. Astrophys. 447, 745-760) can fit the temperature variations with spacecraft longitude observed in the C ring with currently known thermal properties and a mixing of slow and fast rotators. The multilayer model (Morishima, R., Salo, H., Ohtsuki, K., 2009, Icarus 201, 634-654) can reproduce the temperatures of the B and C rings but gives A ring temperatures that are significantly lower than those observed as does the simple semi-analytic model. More advanced models which take into account self-gravity wakes may explain the A ring temperature behavior.

Close correlation between the reaction mechanism and inner structure of loosely halo-nuclei

International Nuclear Information System (INIS)

Liu Jianye; Tianshui Normal Univ., Tianshui; National Laboratory of Heavy Ion Accelerator of Lanzhou, Lanzhou; Guo Wenjun; Ren Zhongzhou; National Laboratory of Heavy Ion Accelerator of Lanzhou, Lanzhou; Xing Yongzhong; National Laboratory of Heavy Ion Accelerator of Lanzhou, Lanzhou

2006-01-01

It was based on the comparisons of the variance properties of fragment multiplicities FM's and nuclear stoppings R's for the neutron-halo colliding system with those of FZ's and R's for the proton-halo colliding system with the increases of beam energy in more detail, the closely correlations between the reaction mechanism and the inner structures of halo-nuclei is found. From above comparisons it is found that the variance properties of fragment multiplicities and nuclear stopping with the increases of beam energy are quite different for the neutron-halo and proton halo colliding systems, such as the effects of loosely bound neutron-halo structure on the fragment multiplicities and nuclear stopping are obviously larger than those for the proton-halo colliding system. This is due to that the structures of halo-neutron nucleus 11 Li is more loosely than that of the proton-halo nucleus 23 Al. In this case, the fragment multiplicity and nuclear stopping of halo nuclei may be used as a possible probe for studying the reaction mechanism and the correlation between the reaction mechanism and the inner structure of halo-nuclei. (authors)

New architectures for molecular materials

International Nuclear Information System (INIS)

Arico, Fabio

2002-01-01

The work described in this thesis is concerned mainly with the synthesis of novel macrocyclic and macropolycyclic oligomers by nucleophilic aromatic substitution under pseudo-high dilution conditions. The cyclic nature of the compounds obtained has been investigated by a range of different analytical techniques, including in some cases single crystal X-ray diffraction. Ring-opening polymerisation of selected macrocycles, in the melt or in solution, was studied as a route to high molecular weight aromatic polymers. In one case the reverse reaction, ring-closing depolymerisation has also been explored for application in the recovery and recycling of a high-value condensation polymer. A potential application of cyclic systems in sub-micron polymer fabrication has been demonstrated using microporous alumina membranes as template for the production of nanoscale polymeric fibrils and tubules. In the present work it is also shown that the previously studied relationship between macrocycles and polymer chains can be extended to a third dimension. Thus, polycondensations involving trifunctional monomers, which would normally afford highly branched or even fully crosslinked polymers, are here shown also to give, under pseudo-high dilution conditions, a series of very large aromatic cage-type molecules. Chemical modification of these macropolycycles was investigated by reducing the carbonyl groups within the cage structures to methylene linkages. The reduced cages so obtained were more tractable and soluble due to the less polar and less rigid methylene groups and the crystals obtained for the latter compounds proved suitable for X-ray crystallographic analysis in order to confirm their macropolycyclic structures. Exploratory studies have shown that a cage-type ether-ketone may be used as a crosslinking agent macrocyclic ring-opening polymerisation. Finally a project, carried out at the University of Strasbourg, under the EU 'Socrates' exchange programme, resulted in the

An N-body Integrator for Planetary Rings

Science.gov (United States)

Hahn, Joseph M.

2011-04-01

A planetary ring that is disturbed by a satellite's resonant perturbation can respond in an organized way. When the resonance lies in the ring's interior, the ring responds via an m-armed spiral wave, while a ring whose edge is confined by the resonance exhibits an m-lobed scalloping along the ring-edge. The amplitude of these disturbances are sensitive to ring surface density and viscosity, so modelling these phenomena can provide estimates of the ring's properties. However a brute force attempt to simulate a ring's full azimuthal extent with an N-body code will likely fail because of the large number of particles needed to resolve the ring's behavior. Another impediment is the gravitational stirring that occurs among the simulated particles, which can wash out the ring's organized response. However it is possible to adapt an N-body integrator so that it can simulate a ring's collective response to resonant perturbations. The code developed here uses a few thousand massless particles to trace streamlines within the ring. Particles are close in a radial sense to these streamlines, which allows streamlines to be treated as straight wires of constant linear density. Consequently, gravity due to these streamline is a simple function of the particle's radial distance to all streamlines. And because particles are responding to smooth gravitating streamlines, rather than discrete particles, this method eliminates the stirring that ordinarily occurs in brute force N-body calculations. Note also that ring surface density is now a simple function of streamline separations, so effects due to ring pressure and viscosity are easily accounted for, too. A poster will describe this N-body method in greater detail. Simulations of spiral density waves and scalloped ring-edges are executed in typically ten minutes on a desktop PC, and results for Saturn's A and B rings will be presented at conference time.

Mucin-producing signet ring cell adenoma of the thyroid

Directory of Open Access Journals (Sweden)

Gulwani Hanni

2008-10-01

Full Text Available Signet ring cell adenoma of the thyroid, though rare, is well documented. This change is chiefly due to intracellular accumulation of thyroglobulin that appears mucinous. Awareness of this entity is important as it may closely simulate a metastatic mucin-secreting signet ring cell carcinoma. Although the mucinous material in signet ring cells has been reported to stain positive with thyroglobulin, in some cases it may not be so. We herein describe a rare case of a 46-year-old man who was hypothyroid and the mass removed from the thyroid showed a mucin-producing signet ring cell adenoma of the thyroid.

Tritium labeling of simple 7-membered ring compounds

International Nuclear Information System (INIS)

Hiltunen, J.; Peng, C.T.; Yang, Z.C.

1990-01-01

Seven-membered ring compounds, from cycloheptane to complex ring structures containing heteroatoms, substituents and fused phenyl rings, were labeled with tritium, using activated and adsorbed tritium. The 7-membered ring structures are generally stable towards reactions with tritium, which allows compounds like 1-benzosuberone, 1-aza-2-methoxy-1-cycloheptane, iminostilbene and clozapine to be labeled to reasonably high specific activities. The best method varies greatly from compound to compound. By optimizing the labeling conditions and use of efficient support exceptionally good results can be obtained. The Pd-on-alumina support gives consistently higher specific activity and less radioimpurity than other supports. Even molecules containing carbon-halogen bond and hydrogen bound to nitrogen can usually be labeled with tritium at stable positions and without dehalogenation. (author)

Some notes on the rings with sacred inscriptions from Pannonia

Directory of Open Access Journals (Sweden)

András Szabó

2015-02-01

Full Text Available More than a hundred rings bearing inscriptions are known from the territory of Roman Pannonia. Among these close to 30 artefacts can be regarded as rings displaying inscriptions of religious significance. Besides the Silvanus-rings, well-known to the archaeological research, some new groups of rings featuring sacred inscriptions can be distinguished according to the dedications. The aim of this paper is to analyse these objects and their religious backgrounds with the help of some archaeological, epigraphical and literary sources and to point out some of the questionable observations of the earlier research.

TRANSVERSE PHASE SPACE PAINTING FOR SNS ACCUMULATOR RING INJECTION.

Energy Technology Data Exchange (ETDEWEB)

BEEBE-WANG,J.; LEE,Y.Y.; RAPARIA,D.; WEI,J.

1999-03-29

The result of investigation and comparison of a series of transverse phase space painting schemes for the injection of SNS accumulator ring [1] is reported. In this computer simulation study, the focus is on the creation of closed orbit bumps that give desired distributions at the target. Space charge effects such as tune shift, emittance growth and beam losses are considered. The results of pseudo end-to-end simulations from the injection to the target through the accumulator ring and Ring to Target Beam Transfer (RTBT) system [2] are presented and discussed.

Collaborative ring trial of the papaya endogenous reference gene and its polymerase chain reaction assays for genetically modified organism analysis.

Science.gov (United States)

Wei, Jiaojun; Li, Feiwu; Guo, Jinchao; Li, Xiang; Xu, Junfeng; Wu, Gang; Zhang, Dabing; Yang, Litao

2013-11-27

The papaya (Carica papaya L.) Chymopapain (CHY) gene has been reported as a suitable endogenous reference gene for genetically modified (GM) papaya detection in previous studies. Herein, we further validated the use of the CHY gene and its qualitative and quantitative polymerase chain reaction (PCR) assays through an interlaboratory collaborative ring trial. A total of 12 laboratories working on detection of genetically modified organisms participated in the ring trial and returned test results. Statistical analysis of the returned results confirmed the species specificity, low heterogeneity, and single-copy number of the CHY gene among different papaya varieties. The limit of detection of the CHY qualitative PCR assay was 0.1%, while the limit of quantification of the quantitative PCR assay was ∼25 copies of haploid papaya genome with acceptable PCR efficiency and linearity. The differences between the tested and true values of papaya content in 10 blind samples ranged from 0.84 to 6.58%. These results indicated that the CHY gene was suitable as an endogenous reference gene for the identification and quantification of GM papaya.

Nuclear transfer reaction measurements at the ESR—for the investigation of the astrophysical 15O(α,γ)19Ne reaction

International Nuclear Information System (INIS)

Doherty, D T; Woods, P J; Davinson, T; Estrade, A; Lotay, G; Litvinov, Yu A; Brandau, C; Dillmann, I; Egelhof, P; Evdokimov, A; Gumberidze, A; Heil, M; Litvinov, S A; Kiselev, O; Najafi, M Ali; Bagchi, S; Kalantar-Nayestanaki, N; Bishop, S; Bo, M; Lederer, C

2015-01-01

Astrophysical x-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The 15 O(α,γ) 19 Ne reaction is one reaction that allows breakout from these CNO cycles and into the rp-process to fuel outbursts. The reaction is expected to be dominated by a single 3/2 + resonance at 4.033 MeV in 19 Ne, however, limited information is available on this key state. This work reports on a pioneering study of the 20 Ne(p,d) 19 Ne reaction, performed in inverse kinematics at the experimental storage ring (ESR) as a means of accessing the astrophysically important 4.033 MeV state in 19 Ne. The unique, background free, high luminosity conditions of the storage ring were utilized for this, the first transfer reaction performed at the ESR. The results of this pioneering test experiment are presented along with suggestions for future measurements at storage ring facilities. (paper)

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-01-28

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

Dynamics of traveling reaction pulses

International Nuclear Information System (INIS)

Dovzhenko, A. Yu.; Rumanov, E. N.

2007-01-01

The growth of activator losses is accompanied by the decay of a traveling reaction pulse. In a ring reactor, this propagation threshold is present simultaneously with a threshold related to the ring diameter. The results of numerical experiments with pulses of an exothermal reaction reveal the transition from pulse propagation to a homogeneous hot regime, established regimes with periodic variations of the pulse velocity, and oscillatory decay of the pulse. When the medium becomes 'bistable' as a result of the variation in parameters, this factor does not prevent the propagation of pulses, but leads to changes in the pulse structure

TSR: A Storage Ring for HIE-ISOLDE

CERN Document Server

Butler, P A; Blaum, K; Grieser, M; Davinson, T; Woods, P J; Flanagan, K; Freeman, S J; Lazarus, I H; Litvinov, Yu A; Raabe, R; Siesling, E; Wenander, F

2016-01-01

It is planned to install the heavy-ion, low-energy ring TSR, currently at the Max-Planck-Institute for Nuclear Physics in Heidelberg, at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored, cooled secondary beams that is rich and varied, spanning from studies of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. In addition to experiments performed using beams recirculating within the ring, the cooled beams can be extracted and exploited by external spectrometers for high-precision measurements. The capabilities of the ring facility as well as some physics cases will be presented, together with a brief report on the status of the project.

Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenylethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

KAUST Repository

Chua, Ming Hui; Huang, Kuo-Wei; Xu, Jianwei; Wu, Jishan

2015-01-01

The straightforward synthesis of 3,5-di(triphenylethylenyl) BODIPYs 1–3 from the condensation of 2-(triphenylethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of 1 resulted in a “1,2-migratory shift” of one triphenylethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry.

Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenylethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

KAUST Repository

Chua, Ming Hui

2015-08-17

The straightforward synthesis of 3,5-di(triphenylethylenyl) BODIPYs 1–3 from the condensation of 2-(triphenylethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of 1 resulted in a “1,2-migratory shift” of one triphenylethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry.

Methods of refining natural oils, and methods of producing fuel compositions

Science.gov (United States)

Firth, Bruce E.; Kirk, Sharon E.

2015-10-27

A method of refining a natural oil includes: (a) providing a feedstock that includes a natural oil; (b) reacting the feedstock in the presence of a metathesis catalyst to form a metathesized product that includes olefins and esters; (c) passivating residual metathesis catalyst with an agent that comprises nitric acid; (d) separating the olefins in the metathesized product from the esters in the metathesized product; and (e) transesterifying the esters in the presence of an alcohol to form a transesterified product and/or hydrogenating the olefins to form a fully or partially saturated hydrogenated product. Methods for suppressing isomerization of olefin metathesis products produced in a metathesis reaction, and methods of producing fuel compositions are described.

Kleinian singularities and the ground ring of c=1 string theory

International Nuclear Information System (INIS)

Ghoshal, D.; Jatkar, D.P.; Mukhi, S.

1993-01-01

We investigate the nature of the ground ring of c=1 string theory at the special ADE points in the c=1 moduli space associated to discrete subgroups of SU(2). The chiral ground rings at these points are shown to define the ADE series of singular varieties introduced by Klein. The non-chiral ground rings relevant to closed-string theory are 3 real dimensional singular varieties obtained as U(1) quotients of the kleinian varieties. The unbroken symmetries of the theory at these points are the volume-preserving diffeomorphisms of these varieties. The theory of kleinian singularities has a close relation to that of complex hyperKaehler surfaces, or gravitational instantons. We speculate on the relevance of these instantons and of self-dual gravity in c=1 string theory. (orig.)

Study of ethylene/2-butene cross-metathesis over W-H/Al2O 3 for propylene production: Effect of the temperature and reactant ratios on the productivity and deactivation

KAUST Repository

Mazoyer, Etienne; Szeto, Kaï Chung; Merle, Nicolas; Norsic, Sé bastien; Boyron, Olivier; Basset, Jean-Marie; Taoufik, Mostafa; Nicholas, Christopher P.

2013-01-01

A highly active and selective catalyst based on supported tungsten hydride for the cross-metathesis between ethylene and 2-butenes yielding propylene has been investigated at low pressure with various temperatures and feed ratios. At low temperature

Injection, compression and stability of intense ion-rings

International Nuclear Information System (INIS)

Sudan, R.N.

1975-01-01

Recent advances in pulsed high power ion beam technology make possible the creation of intense ion-rings with strong self-magnetic fields by single pulse injection. Such ion rings have several uses in controlled fusion e.g., to produce a min parallel B parallel magnetic geometry with a mirror ratio much higher than is possible with external conductors. For even stronger ion rings a min parallel B parallel with closed lines of force (ASTRON type) can be created. For this purpose, since the ion energies required are much higher than are available from high power sources, magnetic compression can be utilized to increase the ion energy. The success of this scheme depends critically on the stability of the ion ring. The low frequency perturbations of the ring-plasma system is examined by means of a generalization of the energy principle which established sufficient conditions for stability. The high-frequency micro-instabilities and their nonlinear consequences are discussed in terms of conventional techniques

Exact wave functions of two-electron quantum rings.

Science.gov (United States)

Loos, Pierre-François; Gill, Peter M W

2012-02-24

We demonstrate that the Schrödinger equation for two electrons on a ring, which is the usual paradigm to model quantum rings, is solvable in closed form for particular values of the radius. We show that both polynomial and irrational solutions can be found for any value of the angular momentum and that the singlet and triplet manifolds, which are degenerate, have distinct geometric phases. We also study the nodal structure associated with these two-electron states.

The generation of efficient supported (Heterogeneous) olefin metathesis catalysts

Energy Technology Data Exchange (ETDEWEB)

Grubbs, Robert H

2013-04-05

Over the past decade, a new family of homogeneous metathesis catalysts has been developed that will tolerate most organic functionalities as well as water and air. These homogeneous catalysts are finding numerous applications in the pharmaceutical industry as well as in the production of functional polymers. In addition the catalysts are being used to convert seed oils into products that can substitute for those that are now made from petroleum products. Seed oils are unsaturated, contain double bonds, and are a ready source of linear hydrocarbon fragments that are specifically functionalized. To increase the number of applications in the area of biomaterial conversion to petrol chemicals, the activity and efficiency of the catalysts need to be as high as possible. The higher the efficiency of the catalysts, the lower the cost of the conversion and a larger number of practical applications become available. Active supported catalysts were prepared and tested in the conversion of seed oils and other important starting materials. The outcome of the work was successful and the technology has been transferred to a commercial operation to develop viable applications of the discovered systems. A biorefinery that converts seed oils is under construction in Indonesia. The catalysts developed in this study will be considered for the next generation of operations.

Kinetic studies on the reaction between dicyanocobinamide and hypochlorous acid.

Directory of Open Access Journals (Sweden)

Dhiman Maitra

Full Text Available Hypochlorous acid (HOCl is a potent oxidant generated by myeloperoxidase (MPO, which is an abundant enzyme used for defense against microbes. We examined the potential role of HOCl in corrin ring destruction and subsequent formation of cyanogen chloride (CNCl from dicyanocobinamide ((CN2-Cbi. Stopped-flow analysis revealed that the reaction consists of at least three observable steps, including at least two sequential transient intermediates prior to corrin ring destruction. The first two steps were attributed to sequential replacement of the two cyanide ligands with hypochlorite, while the third step was the destruction of the corrin ring. The formation of (OCl(CN-Cbi and its conversion to (OCl2-Cbi was fitted to a first order rate equation with second order rate constants of 0.002 and 0.0002 µM(-1 s(-1, respectively. The significantly lower rate of the second step compared to the first suggests that the replacement of the first cyanide molecule by hypochlorite causes an alteration in the ligand trans effects changing the affinity and/or accessibility of Co toward hypochlorite. Plots of the apparent rate constants as a function of HOCl concentration for all the three steps were linear with Y-intercepts close to zero, indicating that HOCl binds in an irreversible one-step mechanism. Collectively, these results illustrate functional differences in the corrin ring environments toward binding of diatomic ligands.

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

Science.gov (United States)

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

2016-02-01

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

On the evolution of vortex rings with swirl

International Nuclear Information System (INIS)

Naitoh, Takashi; Okura, Nobuyuki; Gotoh, Toshiyuki; Kato, Yusuke

2014-01-01

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions

On the evolution of vortex rings with swirl

Energy Technology Data Exchange (ETDEWEB)

Naitoh, Takashi, E-mail: naitoh.takashi@nitech.ac.jp [Department of Engineering Physics, Electronics and Mechanics, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Okura, Nobuyuki, E-mail: ohkura@meijo-u.ac.jp [Department of Vehicle and Mechanical Engineering, Meijo University, 1-501 Shiogamaguchi Tempaku-ku, Nagoya 468-8502 (Japan); Gotoh, Toshiyuki, E-mail: gotoh.toshiyuki@nitech.ac.jp [Department of Scientific and Engineering Simulation, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kato, Yusuke [Controller Business Unit Engineering Division 1, Engineering Department 3, Denso Wave Incorporated, 1 Yoshiike Kusagi Agui-cho, Chita-gun Aichi 470-2297 (Japan)

2014-06-15

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions.

Antiperovskite nitridophosphate oxide Ho{sub 3}[PN{sub 4}]O by high-pressure metathesis

Energy Technology Data Exchange (ETDEWEB)

Kloss, Simon D.; Weidmann, Niels; Schnick, Wolfgang [Department of Chemistry, University of Munich (LMU), Butenandtstrasse 5-13, 81377, Munich (Germany)

2017-04-03

Rare-earth nitridophosphates are a recently discovered class of materials, which are accessible by high-pressure metathesis. Antiperovskite-type Ho{sub 3}[PN{sub 4}]O was synthesized from HoF{sub 3}, LiPN{sub 2}, Li{sub 3}N, and Li{sub 2}O at 5 GPa and ca. 1025 C by this method and the multianvil technique. Ho{sub 3}[PN{sub 4}]O contains rarely observed isolated PN{sub 4} tetrahedra and can be derived by the hierarchical substitution of the ABX{sub 3} perovskite, in which Ho occupies the X positions, O occupies the B position, and the PN{sub 4} tetrahedra occupy the A position. The structure was refined on the basis of powder diffraction data [I4/mcm, a = 6.36112(3), c = 10.5571(1) Aa, Z = 4, R{sub wp} = 0.04, R{sub Bragg} = 0.01, χ{sup 2} = 2.275] starting from the structural model of isotypic Gd{sub 3}[SiN{sub 3}O]O. To characterize Ho{sub 3}[PN{sub 4}]O, elemental analyses were performed through energy-dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Ho{sub 3}[PN{sub 4}]O is paramagnetic down to low temperatures with μ{sub eff} = 10.43(1) μ{sub B} and a Curie temperature (Θ) of 0.11(4) K. It shows the optical characteristics of Ho{sup 3+} ions and vibrations corresponding to isolated PN{sub 4} tetrahedra. On the basis of DFT calculations [generalized gradient approximation (GGA)], Ho{sub 3}[PN{sub 4}]O has an indirect band gap of 1.87 eV. We demonstrate the versatility of high-pressure metathesis by attaining the low end of the P/N atomic ratio κ = 1/4. This confirms the previous assumption that rare-earth nitridophosphates with κ = 1/2 to 1/4 are feasible by this method. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Evidence of Accretion in Saturn's F Ring (Invited)

Science.gov (United States)

Agnor, C. B.; Buerle, K.; Murray, C. D.; Evans, M. W.; Cooper, N. J.; Williams, G. W.

2010-12-01

Lying slightly outside the classical Roche radius and being strongly perturbed by the adjacent moons Prometheus and Pandora, Saturn's F ring represents a unique astrophysical laboratory for examining the processes of mass accretion and moonlet formation. Recent images from the Cassini spacecraft reveal optically thick clumps, capable of casting shadows, and associated structures in regions of the F ring following close passage by Prometheus. Here we examine the accretion environment of the F ring and Prometheus' role in moonlet formation and evolution. Using the observed structures adjacent to these clumps and dynamical arguments we estimate the masses of these clumps and find them comparable to that of ~10-20-km contiguous moonlets. Further, we show that Prometheus' perturbations on the F ring create regions of enhanced density and low relative velocity that may accelerate the accretion of clumps and moonlets.

Synthesis of a new class of fused cyclotetraphosphazene ring systems.

Science.gov (United States)

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

2015-01-05

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

Influence of the acid and basic properties of rhenium oxide supported on alumina catalyst on the catalytic performance in olefin metathesis; Influence des proprietes acido-basiques de l`oxyde de rhenium supporte sur les performances catalytiques en metathese des olefines

Energy Technology Data Exchange (ETDEWEB)

Nahama, F.

1996-11-30

The aim of this work is to study the influence of the acid-basic properties of rhenium oxide supported on alumina catalyst on the catalytic performance in olefin metathesis. The literature data indicate that the environment of the active site does possess acid properties. However, the nature of the acid sites is still matter of debate. Concerning the Re O{sub x} - Al{sub 2}O{sub 3} interactions, we have shown that perrhenate ions are electrostatically absorbed on alumina. The uptake of rhenium is favoured at acidic pH (below 4), and the absorbed rhenium is in equilibrium with rhenium in solution. The results of rhenium extraction by water strongly suggest that the surface compounds of the calcined Re{sub 2}O{sub 7}/Al{sub 2}O{sub 3} materials is aluminium perrhenate. Characterization of surface acidity of the catalyst by infrared spectroscopy reveals that the initiation of the metathesis reaction is governed essentially by Lewis acidity. This strongly supports the role of Lewis acidity, which is exalted by the increase of the rhenium content and the calcination temperature. Finally, we point out by ammonia adsorption-thermodesorption a band at 1320 cm{sup -1} characteristic of the Lewis acidity of aluminium perrhenate. This result is a second indication of the presence of aluminium perrhenate on the Re{sub 2}O{sub 7}/Al{sub 2}O{sub 3} catalyst surface. (author)

Correction of vertical dispersion and betatron coupling for the CLIC damping ring

CERN Document Server

Korostelev, M S

2006-01-01

The sensitivity of the CLIC damping ring to various kinds of alignment errors has been studied. Without any correction, fairly small vertical misalignments of the quadrupoles and, in particular, the sextupoles, introduce unacceptable distortions of the closed orbit as well as intolerable spurious vertical dispersion and coupling due to the strong focusing optics of the damping ring. A sophisticated beam-based correction scheme has been developed to bring the design target emittances and the dynamic aperture back to the ideal value. The correction using dipolar correctors and several skew quadrupole correctors allows a minimization of the closed-orbit distortion, the cross-talk between vertical and horizontal closed orbits, the residual vertical dispersion and the betatron coupling.

The small displacement elastic solution to the ball-on-ring testing method

DEFF Research Database (Denmark)

Frandsen, Henrik Lund

2012-01-01

The ball-on-ring experiment is used for testing of the biaxial strength of ceramics. In this work the solution for the stress distribution and displacements of the disc specimen in the ball-on-ring experiment are determined on closed form. The solution comprises the displacement field and its...

Impact of the Dapivirine Vaginal Ring on Sexual Experiences and Intimate Partnerships of Women in an HIV Prevention Clinical Trial: Managing Ring Detection and Hot Sex.

Science.gov (United States)

Laborde, Nicole D; Pleasants, Elizabeth; Reddy, Krishnaveni; Atujuna, Millicent; Nakyanzi, Teopista; Chitukuta, Miria; Naidoo, Sarita; Palanee-Phillips, Thesla; Baeten, Jared M; Montgomery, Elizabeth T

2018-02-01

Vaginally-inserted HIV prevention methods have been reported to impact the sexual experience for women and their partners, and hence impacts acceptability of and adherence to the method. We analyzed in-depth interviews and focus group discussions about participants' sexual experiences while wearing the ring, collected during the MTN-020/ASPIRE phase 3 safety and effectiveness trial of a dapivirine vaginal ring for HIV prevention in Malawi, South Africa, Uganda, and Zimbabwe. Most women reported that partners did not feel the ring during sex, however, women felt they had to manage their partners' interaction with or reaction to the ring. In maintaining positive relationships, women were concerned about partners' discovering ring use and about ensuring that partners had a good sexual experience with them. Finally women were concerned about how they themselves experienced sex with the ring. Some found that the ring made the vaginal environment more desirable for their partners and themselves.

Impact of the Dapivirine Vaginal Ring on Sexual Experiences and Intimate Partnerships of Women in an HIV Prevention Clinical Trial: Managing Ring Detection and Hot Sex

Science.gov (United States)

Pleasants, Elizabeth; Reddy, Krishnaveni; Atujuna, Millicent; Nakyanzi, Teopista; Chitukuta, Miria; Naidoo, Sarita; Palanee-Phillips, Thesla; Baeten, Jared M.; Montgomery, Elizabeth T.

2018-01-01

Vaginally-inserted HIV prevention methods have been reported to impact the sexual experience for women and their partners, and hence impacts acceptability of and adherence to the method. We analyzed in-depth interviews and focus group discussions about participants’ sexual experiences while wearing the ring, collected during the MTN-020/ASPIRE phase 3 safety and effectiveness trial of a dapivirine vaginal ring for HIV prevention in Malawi, South Africa, Uganda, and Zimbabwe. Most women reported that partners did not feel the ring during sex, however, women felt they had to manage their partners’ interaction with or reaction to the ring. In maintaining positive relationships, women were concerned about partners’ discovering ring use and about ensuring that partners had a good sexual experience with them. Finally women were concerned about how they themselves experienced sex with the ring. Some found that the ring made the vaginal environment more desirable for their partners and themselves. PMID:29151197

Three families of mitered Borromean ring sculptures

NARCIS (Netherlands)

Verhoeff, T.; Verhoeff, K.; Delp, K.; Kaplan, C.S.; McKenna, D.; Sarhangi, R.

2015-01-01

Artists have drawn inspiration from many mathematical structures, such as regular tilings, lattices, symmetry groups, regular polyhedra, knots, and links. A particularly well-known link goes by the name Borromean rings. It consists of three closed loops (“rings”) that cannot be taken apart without

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

Directory of Open Access Journals (Sweden)

Saurabh C. Khadse

2017-02-01

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

Graphene rings in magnetic fields: Aharonov–Bohm effect and valley splitting

International Nuclear Information System (INIS)

Wurm, J; Wimmer, M; Richter, K; Baranger, H U

2010-01-01

We study the conductance of mesoscopic graphene rings in the presence of a perpendicular magnetic field by means of numerical calculations based on a tight-binding model. First, we consider the magnetoconductance of such rings and observe the Aharonov–Bohm effect. We investigate different regimes of the magnetic flux up to the quantum Hall regime, where the Aharonov–Bohm oscillations are suppressed. Results for both clean (ballistic) and disordered (diffusive) rings are presented. Second, we study rings with smooth mass boundary that are weakly coupled to leads. We show that the valley degeneracy of the eigenstates in closed graphene rings can be lifted by a small magnetic flux, and that this lifting can be observed in the transport properties of the system

Contradiction between the results of observations of resistance and critical current quantum oscillations in asymmetric superconducting rings

International Nuclear Information System (INIS)

Gurtovoi, V. L.; Dubonos, S. V.; Karpii, S. V.; Nikulov, A. V.; Tulin, V. A.

2007-01-01

Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta

Biofuel by isomerizing metathesis of rapeseed oil esters with (bio)ethylene for use in contemporary diesel engines.

Science.gov (United States)

Pfister, Kai F; Baader, Sabrina; Baader, Mathias; Berndt, Silvia; Goossen, Lukas J

2017-06-01

Rapeseed oil methyl ester (RME) and (bio)ethylene are converted into biofuel with an evenly rising boiling point curve, which fulfills the strict boiling specifications prescribed by the fuel standard EN 590 for modern (petro)diesel engines. Catalyzed by a Pd/Ru system, RME undergoes isomerizing metathesis in a stream of ethylene gas, leading to a defined olefin, monoester, and diester blend. This innovative refining concept requires negligible energy input (60°C) and no solvents and does not produce waste. It demonstrates that the pressing challenge of increasing the fraction of renewables in engine fuel may be addressed purely chemically rather than by motor engineering.

Catalysts and methods for ring opening metathesis polymerization

Energy Technology Data Exchange (ETDEWEB)

Schrock, Richard Royce; Autenrieth, Benjamin

2018-04-03

The present invention, among other things, provides highly syndiotactic poly(dicyclopentadiene) and/or hydrogenated poly(dicyclopentadiene), compositions thereof, and compounds and methods for preparing the same. In some embodiments, a provided compound is a compound of formula I, II or III. In some embodiments, a provided method comprises providing a compound of formula I, II or III.

Polyurethane Foams with Pyrimidine Rings

Directory of Open Access Journals (Sweden)

Kania Ewelina

2014-09-01

Full Text Available Oligoetherols based on pyrimidine ring were obtained upon reaction of barbituric acid with glycidol and alkylene carbonates. These oligoetherols were then used to obtain polyurethane foams in the reaction of oligoetherols with isocyanates and water. The protocol of foam synthesis was optimized by the choice of proper kind of oligoetherol and synthetic composition. The thermal resistance was studied by dynamic and static methods with concomitant monitoring of compressive strength. The polyurethane foams have similar physical properties as the classic ones except their enhanced thermal resistance. They stand long-time heating even at 200°C. Moreover thermal exposition of foams results generally in increase of their compressive strength.

Rotating circular strings, and infinite non-uniqueness of black rings

International Nuclear Information System (INIS)

Emparan, Roberto

2004-01-01

We present new self-gravitating solutions in five dimensions that describe circular strings, i.e., rings, electrically coupled to a two-form potential (as e.g., fundamental strings do), or to a dual magnetic one-form. The rings are prevented from collapsing by rotation, and they create a field analogous to a dipole, with no net charge measured at infinity. They can have a regular horizon, and we show that this implies the existence of an infinite number of black rings, labeled by a continuous parameter, with the same mass and angular momentum as neutral black rings and black holes. We also discuss the solution for a rotating loop of fundamental string. We show how more general rings arise from intersections of branes with a regular horizon (even at extremality), closely related to the configurations that yield the four-dimensional black hole with four charges. We reproduce the Bekenstein-Hawking entropy of a large extremal ring through a microscopic calculation. Finally, we discuss some qualitative ideas for a microscopic understanding of neutral and dipole black rings. (author)

Hubble again views Saturn's Rings Edge-on

Science.gov (United States)

1995-01-01

Saturn's magnificent ring system is seen tilted edge-on -- for the second time this year -- in this NASA Hubble Space Telescope picture taken on August 10, 1995, when the planet was 895 million miles (1,440 million kilometers) away. Hubble snapped the image as Earth sped back across Saturn's ring plane to the sunlit side of the rings. Last May 22, Earth dipped below the ring plane, giving observers a brief look at the backlit side of the rings. Ring-plane crossing events occur approximately every 15 years. Earthbound observers won't have as good a view until the year 2038. Several of Saturn's icy moons are visible as tiny starlike objects in or near the ring plane. They are from left to right, Enceladus, Tethys, Dione and Mimas. 'The Hubble data shows numerous faint satellites close to the bright rings, but it will take a couple of months to precisely identify them,' according to Steve Larson (University of Arizona). During the May ring plane crossing, Hubble detected two, and possibly four, new moons orbiting Saturn. These new observations also provide a better view of the faint E ring, 'to help determine the size of particles and whether they will pose a collision hazard to the Cassini spacecraft,' said Larson. The picture was taken with Hubble's Wide Field Planetary Camera 2 in wide field mode. This image is a composite view, where a long exposure of the faint rings has been combined with a shorter exposure of Saturn's disk to bring out more detail. When viewed edge-on, the rings are so dim they almost disappear because they are very thin -- probably less than a mile thick.The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Spaced Flight Center for NASA's Office of Space Science.This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/pubinfo/

The kinetics of free radical metathetical and addition reactions in silane solutions

International Nuclear Information System (INIS)

Aloni, R.

1976-12-01

In this work radiolytic technique was employed for the initiation of free radical chainreactions in silane solution. The kinetic analysis of the chain mechanism in various solutions enabled the determination of the Arrhenius parameters for metathesis, addition and unimolecular decomposition reactions which make up the chainpropagation sequence in the systems studied. The following radical reactions were investigated: chlorine atom abstraction from chloromethanes by SiCl 3 and Et 3 Si radicals, and chlorine atom abstraction from chloroethanes by Et 3 Si radicals; unimolecular decomposition reactions and hydrogen atom abstraction, *from the solvent, of chloroethyl radicals in triethylsilane solutions; addition and abstraction reactions of Et 3 Si radicals with chloroolefins. Arrhenius parameters were determined for abstraction of chlorine atom from CH 3 Cl, CH 2 Cl 2 , CHCl 3 and CCl 4 , by SiCl 3 radicals and from CCl 4 , CHCl 3 , CH 2 Cl 2 , CCl 3 CN, C 2 Cl 5 H, sym-C 2 Cl 4 H 2 , asym-C 2 Cl 4 H 2 , 1.1.1-C 2 Cl 3 H 3 , 1.1.1-C 2 Dl 3 F 3 and 1.1-C 2 Cl 2 H 4 by Et 3 Si radicals. (author)

FORMATION OF CENTAURS’ RINGS THROUGH THEIR PARTIAL TIDAL DISRUPTION DURING PLANETARY ENCOUNTERS

Energy Technology Data Exchange (ETDEWEB)

Hyodo, Ryuki; Charnoz, Sébastien [Institut de Physique du Globe, F-75005 Paris, France (France); Genda, Hidenori [Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550 (Japan); Ohtsuki, Keiji [Department of Planetology, Kobe University, Kobe 657-8501 (Japan)

2016-09-01

Centaurs are minor planets orbiting between Jupiter and Neptune that have or had crossing orbits with one or more giant planets. Recent observations and reinterpretation of previous observations have revealed the existence of ring systems around 10199 Chariklo and 2060 Chiron. However, the origin of the ring systems around such a minor planet is still an open question. Here, we propose that the tidal disruption of a differentiated object that experiences a close encounter with a giant planet could naturally form diverse ring–satellite systems around the Centaurs. During the close encounter, the icy mantle of the passing object is preferentially ripped off by the planet's tidal force and the debris is distributed mostly within the Roche limit of the largest remnant body. Assuming the existence of a 20−50 wt% silicate core below the icy mantle, a disk of particles is formed when the objects pass within 0.4–0.8 of the planet's Roche limit with the relative velocity at infinity 3−6 km s{sup −1} and 8 hr initial spin period of the body. The resultant ring mass is 0.1%–10% of the central object's mass. Such particle disks are expected to spread radially, and materials spreading beyond the Roche limit would accrete into satellites. Our numerical results suggest that ring formation would be a natural outcome of such extreme close encounters, and Centaurs can naturally have such ring systems because they cross the orbits of the giant planets.

FORMATION OF CENTAURS’ RINGS THROUGH THEIR PARTIAL TIDAL DISRUPTION DURING PLANETARY ENCOUNTERS

International Nuclear Information System (INIS)

Hyodo, Ryuki; Charnoz, Sébastien; Genda, Hidenori; Ohtsuki, Keiji

2016-01-01

Centaurs are minor planets orbiting between Jupiter and Neptune that have or had crossing orbits with one or more giant planets. Recent observations and reinterpretation of previous observations have revealed the existence of ring systems around 10199 Chariklo and 2060 Chiron. However, the origin of the ring systems around such a minor planet is still an open question. Here, we propose that the tidal disruption of a differentiated object that experiences a close encounter with a giant planet could naturally form diverse ring–satellite systems around the Centaurs. During the close encounter, the icy mantle of the passing object is preferentially ripped off by the planet's tidal force and the debris is distributed mostly within the Roche limit of the largest remnant body. Assuming the existence of a 20−50 wt% silicate core below the icy mantle, a disk of particles is formed when the objects pass within 0.4–0.8 of the planet's Roche limit with the relative velocity at infinity 3−6 km s"−"1 and 8 hr initial spin period of the body. The resultant ring mass is 0.1%–10% of the central object's mass. Such particle disks are expected to spread radially, and materials spreading beyond the Roche limit would accrete into satellites. Our numerical results suggest that ring formation would be a natural outcome of such extreme close encounters, and Centaurs can naturally have such ring systems because they cross the orbits of the giant planets.

Measuring the electron-ion ring parameters by bremsstrahlung

International Nuclear Information System (INIS)

Inkin, V.D.; Mozelev, A.A.; Sarantsev, V.P.

1982-01-01

A system is described for measuring the number of electrons and ions in the electron-ion rings of a collective heavy ion accelerator. The system operation is based on detecting gamma quanta of bremsstrahlung following the ring electron interaction with the nuclei of neutral atoms and ions at different stages of filling the ring with ions. The radiation detector is a scintillation block - a photomultiplier operating for counting with NaI(Tl) crystal sized 30x30 mm and ensuring the detection efficiency close to unity. The system apparatus is made in the CAMAC standard and rems on-line with the TRA/i miniature computer. The block-diagrams of the system and algorithm of data processing are presented. A conclusion is drawn that the results of measuring the ring parameters with the use of the diagnostics system described are in good agreement within the range of measuring errors with those obtained by means of the diagnostics system employing synchrotron radiation and induction sensors

Initial Reactivity of Linkages and Monomer Rings in Lignin Pyrolysis Revealed by ReaxFF Molecular Dynamics.

Science.gov (United States)

Zhang, Tingting; Li, Xiaoxia; Guo, Li

2017-10-24

The initial conversion pathways of linkages and their linked monomer units in lignin pyrolysis were investigated comprehensively by ReaxFF MD simulations facilitated by the unique VARxMD for reaction analysis. The simulated molecular model contains 15 920 atoms and was constructed on the basis of Adler's softwood lignin model. The simulations uncover the initial conversion ratio of various linkages and their linked aryl monomers. For linkages and their linked monomer aryl rings of α-O-4, β-O-4 and α-O-4 & β-5, the C α /C β ether bond cracking dominates the initial pathway accounting for at least up to 80% of their consumption. For the linkage of β-β & γ-O-α, both the C α -O ether bond cracking and its linked monomer aryl ring opening are equally important. Ring-opening reactions dominate the initial consumption of other 4-O-5, 5-5, β-1, β-2, and β-5 linkages and their linked monomers. The ether bond cracking of C α -O and C β -O occurs at low temperature, and the aryl ring-opening reactions take place at relatively high temperature. The important intermediates leading to the stable aryl ring opening are the phenoxy radicals, the bridged five-membered and three-membered rings and the bridged six-membered and three-membered rings. In addition, the reactivity of a linkage and its monomer aryl ring may be affected by other linkages. The ether bond cracking of α-O-4 and β-O-4 linkages can activate its neighboring linkage or monomer ring through the formed phenoxy radicals as intermediates. The important intermediates revealed in this article should be of help in deepening the understanding of the controlling mechanism for producing aromatic chemicals from lignin pyrolysis.

Design studies for the electron storage ring EUTERPE

Energy Technology Data Exchange (ETDEWEB)

Boling, Xi

1995-05-18

The 400 MeV electron storage ring EUTERPE is under construction at Eindhoven University of Technology. The ring is to be used as an experimental tool for accelerator physics studies and synchroton radiation applications. The main task of the current research work is the electron optical design of the ring. Lattice design is a basis for machine design as a whole. Design aspects regarding the basic lattice, based on single particle dynamics, include determination of the equilibrium beam size and bunch length, design of achromatic bending sections, selection of tune values, correction of chromaticity, and minimization of the natural emittance in the ring. The basic lattice designed for the EUTERPE ring has a high flexibility so that different electron optical modes can be realized easily. In low energy storage rings with a high beam current, collective effects can cause a significant change in the bunch length, the transverse emittance and the beam lifetime. In order to ensure a good optical performance for the ring, the choice of suitable parameters concerning the vacuum and RF system are essential as far as collective effects are concerned. An estimation of the collective effects in the ring is given. The injector for EUTERPE is a 75 MeV racetrack microtron which is injected from a 10 MeV linac. In order to get sufficient beam current in the ring, a special procedure of continuous injection with an adjustable locally shifted closed orbit has been presented. Details of the injection procedure and numerical simulations are given. (orig./HSI).

Design studies for the electron storage ring EUTERPE

International Nuclear Information System (INIS)

Xi Boling.

1995-01-01

The 400 MeV electron storage ring EUTERPE is under construction at Eindhoven University of Technology. The ring is to be used as an experimental tool for accelerator physics studies and synchroton radiation applications. The main task of the current research work is the electron optical design of the ring. Lattice design is a basis for machine design as a whole. Design aspects regarding the basic lattice, based on single particle dynamics, include determination of the equilibrium beam size and bunch length, design of achromatic bending sections, selection of tune values, correction of chromaticity, and minimization of the natural emittance in the ring. The basic lattice designed for the EUTERPE ring has a high flexibility so that different electron optical modes can be realized easily. In low energy storage rings with a high beam current, collective effects can cause a significant change in the bunch length, the transverse emittance and the beam lifetime. In order to ensure a good optical performance for the ring, the choice of suitable parameters concerning the vacuum and RF system are essential as far as collective effects are concerned. An estimation of the collective effects in the ring is given. The injector for EUTERPE is a 75 MeV racetrack microtron which is injected from a 10 MeV linac. In order to get sufficient beam current in the ring, a special procedure of continuous injection with an adjustable locally shifted closed orbit has been presented. Details of the injection procedure and numerical simulations are given. (orig./HSI)

Periodic seasonal variation of magnets level of the STB ring

International Nuclear Information System (INIS)

Takahashi, Shigenobu

2003-01-01

The Stretcher-Booster (STB) ring, a 1.2 GeV electron synchrotron, was completed in December, 1997 at the Laboratory of Nuclear Sciences (LNS), Tohoku University. The total weight more than 400 tons were placed near the STB ring, such as concrete blocks for radiation shielding and a spectrometer magnet for nuclear physics experiments after the completion of the STB ring. Re-surveying of magnets alignment was started after 2000. Very recently a new building of an experimental hall was constructed close to the building of the STB ring for use of high energy γ-ray from the electron beam. The building will give rise the changes of magnet levels due to its seasonal distortion. The measurements of the magnet level after construction are continued as well as an expected change of the closed orbit distortion (COD) in the STB ring. The serious influence of the variation of the magnet level may be a change of the beam orbit of extracted beam in the stretcher operation. Difference of the orbit distortion reaches more than 5 mm. Correlation between the COD and the seasonal change of the magnet position is not clear at the moment. However, the machine operation and the beam diagnostics are getting better recently. Continuous surveying of the magnet level will be a useful data for a feed forward correction of the beam orbit. Future subjects and prospects are discussed on surveying. (Y. Tanaka)

Abnormal reaction of 2,5-Dimethylfuran

International Nuclear Information System (INIS)

Pevzner, L.M.; Ignat'ev, V.M.

1987-01-01

The authors have shown that the expected hydroxymethylation at position 3 of the furan ring does not occur in the reaction of 2,5-dimethylfuran with paraform in acetic acid at 70-80 0 C with the dimethylfuran and paraform in molar ratios of 2:1-1:2, but the products from substitution in the side chain are formed. By vacuum distillation of the reaction mass the authors isolated 2-(5-methyl-2-furyl)- ethanol and a hygroscopic viscous product melting at 136 0 C (5 mm Hg). The yield of the reaction products depends on the molar ratio of the dimethylfuran and paraform. The PMR spectrum of the product contains signals for the β-protons of the furan ring with chemical shifts of 5.81 and 5.90 ppm, a signal for the methyl group in the furan ring at 2.22 ppm, a doublet at 3.72 ppm with spin-spin coupling constant of 6 Hz, a weak quintet at 3.20 ppm with the same constant, and a broadened signal in the region of 4.66 ppm for the proton of the hydroxyl group

Reactions of recoil tritium generated by the 3He(n,p)3H reaction with aromatic compounds -intramolecular tritium distribution and radiochemical yield

International Nuclear Information System (INIS)

Nogawa, N.; Morikawa, Naotake; Oohashi, Kunio; Matuoka, H.; Moki, T.; Moriya, T.

1986-01-01

Reactions of recoil tritium with benzoic acid, acetanilide and β-phenethyl alcohol were studied using the 3 He(=n,p) 3 H reaction. The tritium distribution in the aromatic ring is approximately uniform in all the irradiated compounds and the tritium activity per C-H bond in the methyl and ethylene groups is 7 to 8 relative to that of the corresponding ring as standard. These findings are substantially the same as those obtained previously by the 6 Li(n,α) 3 H reactions, suggesting the same mechanism of tritiation for both recoil reactions. The tritiated parent compounds were obtained in high radiochemical yields: 45% for benzoic acid, 30% for acetanilide, 12% for β-phenethyl alcohol. (author)

Ring Theory

CERN Document Server

Jara, Pascual; Torrecillas, Blas

1988-01-01

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

Toluene pyrolysis studies and high temperature reactions of propargyl chloride

Energy Technology Data Exchange (ETDEWEB)

Kern, R.D.; Chen, H.; Qin, Z. [Univ. of New Orleans, LA (United States)

1993-12-01

The main focus of this program is to investigate the thermal decompositions of fuels that play an important role in the pre-particle soot formation process. It has been demonstrated that the condition of maximum soot yield is established when the reaction conditions of temperature and pressure are sufficient to establish a radical pool to support the production of polyaromatic hydrocarbon species and the subsequent formation of soot particles. However, elevated temperatures result in lower soot yields which are attributed to thermolyses of aromatic ring structures and result in the bell-shaped dependence of soot yield on temperature. The authors have selected several acyclic hydrocarbons to evaluate the chemical thermodynamic and kinetic effects attendant to benzene formation. To assess the thermal stability of the aromatic ring, the authors have studied the pyrolyses of benzene, toluene, ethylbenzene, chlorobenzene and pyridine. Time-of-flight mass spectrometry (TOF) is employed to analyze the reaction zone behind reflected shock waves. Reaction time histories of the reactants, products, and intermediates are constructed and mechanisms are formulated to model the experimental data. The TOF work is often performed with use of laser schlieren densitometry (LS) to measure density gradients resulting from the heats of various reactions involved in a particular pyrolytic system. The two techniques, TOF and LS, provide independent and complementary information about ring formation and ring rupture reactions.

Development of the first well-defined tungsten oxo alkyl derivatives supported on silica by SOMC: towards a model of WO3/SiO2 olefin metathesis catalyst

KAUST Repository

Mazoyer, Etienne; Merle, Nicolas; Mallmann, Aimery De; Basset, Jean-Marie; Berrier, Elise; Delevoye, Laurent; Paul, Jean Franois; Nicholas, Christopher P.; Gauvin, Ré gis M.; Taoufik, Mostafa

2010-01-01

A well-defined, silica-supported tungsten oxo alkyl species prepared by the surface organometallic chemistry approach displays high and sustained activity in propene metathesis. Remarkably, its catalytic performances outpace those of the parent imido derivative, underlining the importance of the oxo ligand in the design of robust catalysts. © 2010 The Royal Society of Chemistry.

The Pictet-Spengler reaction in solid-phase combinatorial chemistry

DEFF Research Database (Denmark)

Nielsen, Thomas E; Diness, Frederik; Meldal, Morten

2003-01-01

The Pictet-Spengler reaction is an important reaction for the generation of tetrahydro-beta-carbolines and tetrahydroisoquinoline ring systems, which exhibit a range of biological and pharmacological properties. This review covers the solid-phase Pictet-Spengler reaction, as employed in solid...

Functional roles of the pepper RING finger protein gene, CaRING1, in abscisic acid signaling and dehydration tolerance.

Science.gov (United States)

Lim, Chae Woo; Hwang, Byung Kook; Lee, Sung Chul

2015-09-01

Plants are constantly exposed to a variety of biotic and abiotic stresses, which include pathogens and conditions of high salinity, low temperature, and drought. Abscisic acid (ABA) is a major plant hormone involved in signal transduction pathways that mediate the defense response of plants to abiotic stress. Previously, we isolated Ring finger protein gene (CaRING1) from pepper (Capsicum annuum), which is associated with resistance to bacterial pathogens, accompanied by hypersensitive cell death. Here, we report a new function of the CaRING1 gene product in the ABA-mediated defense responses of plants to dehydration stress. The expression of the CaRING1 gene was induced in pepper leaves treated with ABA or exposed to dehydration or NaCl. Virus-induced gene silencing of CaRING1 in pepper plants exhibited low degree of ABA-induced stomatal closure and high levels of transpirational water loss in dehydrated leaves. These led to be more vulnerable to dehydration stress in CaRING1-silenced pepper than in the control pepper, accompanied by reduction of ABA-regulated gene expression and low accumulation of ABA and H2O2. In contrast, CaRING1-overexpressing transgenic plants showed enhanced sensitivity to ABA during the seedling growth and establishment. These plants were also more tolerant to dehydration stress than the wild-type plants because of high ABA accumulation, enhanced stomatal closure and increased expression of stress-responsive genes. Together, these results suggest that the CaRING1 acts as positive factor for dehydration tolerance in Arabidopsis by modulating ABA biosynthesis and ABA-mediated stomatal closing and gene expression.

Report of the eRHIC Ring-Ring Working Group

Energy Technology Data Exchange (ETDEWEB)

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

2015-10-13

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

A new strategy for aromatic ring alkylation in cylindrocyclophane biosynthesis.

Science.gov (United States)

Nakamura, Hitomi; Schultz, Erica E; Balskus, Emily P

2017-08-01

Alkylation of aromatic rings with alkyl halides is an important transformation in organic synthesis, yet an enzymatic equivalent is unknown. Here, we report that cylindrocyclophane biosynthesis in Cylindrospermum licheniforme ATCC 29412 involves chlorination of an unactivated carbon center by a novel halogenase, followed by a previously uncharacterized enzymatic dimerization reaction featuring sequential, stereospecific alkylations of resorcinol aromatic rings. Discovery of the enzymatic machinery underlying this unique biosynthetic carbon-carbon bond formation has implications for biocatalysis and metabolic engineering.

Poisoning Experiments Aimed at Discriminating Active and Less-Active Sites of Silica-Supported Tantalum Hydride for Alkane Metathesis

KAUST Repository

Saggio, Guillaume

2010-10-04

Only 50% of the silica-supported tantalum hydride sites are active in the metathesis of propane. Indeed, more than 45% of the tantalum hydride can be eliminated by a selective oxygen poisoning of inactive sites with no significant decrease in the global turnover. Conversely, cyclopentane induces no such selective poisoning. Hence, the active tantalum hydride sites that show greater resistance to oxygen poisoning correspond to the νTa-H bands of higher wavenumbers, particularly that at 1860cm-1. These active tantalum hydride sites should correspond to tris- or monohydride species relatively far from silica surface oxygen atoms. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

TSR: A storage and cooling ring for HIE-ISOLDE

Energy Technology Data Exchange (ETDEWEB)

Butler, P.A. [Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE (United Kingdom); Blaum, K. [Max-Planck-Institut für Kernphysik, 69117 Heidelberg (Germany); Davinson, T. [School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Flanagan, K.; Freeman, S.J. [School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); Grieser, M. [Max-Planck-Institut für Kernphysik, 69117 Heidelberg (Germany); Lazarus, I.H. [S.T.F.C. Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Litvinov, Yu.A. [Max-Planck-Institut für Kernphysik, 69117 Heidelberg (Germany); GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt (Germany); Lotay, G. [Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); Page, R.D. [Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE (United Kingdom); Raabe, R. [KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven (Belgium); Siesling, E.; Wenander, F. [CERN, 1211 Geneva 23 (Switzerland); Woods, P.J. [School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom)

2016-06-01

It is planned to install the heavy-ion, low-energy ring TSR, currently at the Max-Planck-Institute for Nuclear Physics in Heidelberg, at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored, cooled secondary beams that is rich and varied, spanning from studies of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. In addition to experiments performed using beams recirculating within the ring, the cooled beams can be extracted and exploited by external spectrometers for high-precision measurements. The capabilities of the ring facility as well as some physics cases will be presented, together with a brief report on the status of the project.

A Ring Polymer Molecular Dynamics Approach to Study the Transition between Statistical and Direct Mechanisms in the H2 + H3+ → H3+ + H2 Reaction.

Science.gov (United States)

Suleimanov, Yury V; Aguado, Alfredo; Gómez-Carrasco, Susana; Roncero, Octavio

2018-05-03

Because of its fundamental importance in astrochemistry, the H 2 + H 3 + → H 3 + + H 2 reaction has been studied experimentally in a wide temperature range. Theoretical studies of the title reaction significantly lag primarily because of the challenges associated with the proper treatment of the zero-point energy (ZPE). As a result, all previous theoretical estimates for the ratio between a direct proton-hop and indirect exchange (via the H 5 + complex) channels deviate from the experiment, in particular, at lower temperatures where the quantum effects dominate. In this work, the ring polymer molecular dynamics (RPMD) method is applied to study this reaction, providing very good agreement with the experiment. RPMD is immune to the shortcomings associated with the ZPE leakage and is able to describe the transition from direct to indirect mechanisms below room temperature. We argue that RPMD represents a useful tool for further studies of numerous ZPE-sensitive chemical reactions that are of high interest in astrochemistry.

High pressure photoinduced ring opening of benzene

International Nuclear Information System (INIS)

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

2002-01-01

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

Survey and alignment of photon factory storage ring at KEK

International Nuclear Information System (INIS)

Araki, A.; Honjo, I.; Katoh, M.; Kamiya, Y.; Kihara, M.

1987-01-01

The heights of the magnets for both the ring and the beam transport line (BT-line) have been periodically measured at the Photon Factory. The accumulated data showed that the ring was considerably declined due to the construction of the large experimental hall and the tunnel of the TRISTAN project, and that the BT-line also sank several centimeters at some locations. These displacements of the magnets produce a significantly large closed orbit distortion and the vertical dispersion

Experimental Study of Closed System in the Chlorine Dioxide-Iodide-Sulfuric Acid Reaction by UV-Vis Spectrophotometric Method

Directory of Open Access Journals (Sweden)

Na Li

2011-01-01

Full Text Available The mole ratio r(r=[I−]0/[ClO2]0 has great influence on ClO2-I−-H2SO4 closed reaction system. By changing the initiate concentration of potassium iodide, the curve of absorbance along with the reaction time was obtained at 350 nm and 297 nm for triiodide ion, and 460 nm for iodine. The changing point of the absorbance curve's shape locates at r=6.00. For the reaction of ClO2-I− in the absence of H2SO4, the curve of absorbance along with the reaction time can be obtained at 350 nm for triiodide ion, 460 nm for iodine. The mole ratio r is equal to 1.00 is the changing point of the curve's shape no matter at which wavelength to determine the reaction. For the reaction of ClO2-I−-H+ in different pH buffer solution, the curve of absorbance along with the reaction time was recorded at 460 nm for iodine. When r is greater than 1.00, the transition point of the curve's shape locates at pH 2.0, which is also the point of producing chlorite or chloride for chlorine dioxide at different pH. When r is less than 1.00, the transition point locates at pH 7.0.

Transformation of self-assembled InAs/InP quantum dots into quantum rings without capping.

Science.gov (United States)

Sormunen, Jaakko; Riikonen, Juha; Mattila, Marco; Tiilikainen, Jouni; Sopanen, Markku; Lipsanen, Harri

2005-08-01

Transformation of self-assembled InAs quantum dots (QDs) on InP(100) into quantum rings (QRs) is studied. In contrast to the typical approach to III--V semiconductor QR growth, the QDs are not capped to form rings. Atomic force micrographs reveal a drastic change from InAs QDs into rings after a growth interruption in tertiarybutylphosphine ambient. Strain energy relief in the InAs QD is discussed and a mechanism for dot-to-ring transformation by As/P exchange reactions is proposed.

How to remove the spurious resonances from ring polymer molecular dynamics

Energy Technology Data Exchange (ETDEWEB)

Rossi, Mariana; Manolopoulos, David E. [Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ (United Kingdom); Ceriotti, Michele [Laboratory of Computational Science and Modeling, IMX, École Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)

2014-06-21

Two of the most successful methods that are presently available for simulating the quantum dynamics of condensed phase systems are centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD). Despite their conceptual differences, practical implementations of these methods differ in just two respects: the choice of the Parrinello-Rahman mass matrix and whether or not a thermostat is applied to the internal modes of the ring polymer during the dynamics. Here, we explore a method which is halfway between the two approximations: we keep the path integral bead masses equal to the physical particle masses but attach a Langevin thermostat to the internal modes of the ring polymer during the dynamics. We justify this by showing analytically that the inclusion of an internal mode thermostat does not affect any of the established features of RPMD: thermostatted RPMD is equally valid with respect to everything that has actually been proven about the method as RPMD itself. In particular, because of the choice of bead masses, the resulting method is still optimum in the short-time limit, and the transition state approximation to its reaction rate theory remains closely related to the semiclassical instanton approximation in the deep quantum tunneling regime. In effect, there is a continuous family of methods with these properties, parameterised by the strength of the Langevin friction. Here, we explore numerically how the approximation to quantum dynamics depends on this friction, with a particular emphasis on vibrational spectroscopy. We find that a broad range of frictions approaching optimal damping give similar results, and that these results are immune to both the resonance problem of RPMD and the curvature problem of CMD.

How to remove the spurious resonances from ring polymer molecular dynamics

International Nuclear Information System (INIS)

Rossi, Mariana; Manolopoulos, David E.; Ceriotti, Michele

2014-01-01

Two of the most successful methods that are presently available for simulating the quantum dynamics of condensed phase systems are centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD). Despite their conceptual differences, practical implementations of these methods differ in just two respects: the choice of the Parrinello-Rahman mass matrix and whether or not a thermostat is applied to the internal modes of the ring polymer during the dynamics. Here, we explore a method which is halfway between the two approximations: we keep the path integral bead masses equal to the physical particle masses but attach a Langevin thermostat to the internal modes of the ring polymer during the dynamics. We justify this by showing analytically that the inclusion of an internal mode thermostat does not affect any of the established features of RPMD: thermostatted RPMD is equally valid with respect to everything that has actually been proven about the method as RPMD itself. In particular, because of the choice of bead masses, the resulting method is still optimum in the short-time limit, and the transition state approximation to its reaction rate theory remains closely related to the semiclassical instanton approximation in the deep quantum tunneling regime. In effect, there is a continuous family of methods with these properties, parameterised by the strength of the Langevin friction. Here, we explore numerically how the approximation to quantum dynamics depends on this friction, with a particular emphasis on vibrational spectroscopy. We find that a broad range of frictions approaching optimal damping give similar results, and that these results are immune to both the resonance problem of RPMD and the curvature problem of CMD

Aromatic products from reaction of lignin model compounds with UV-alkaline peroxide

International Nuclear Information System (INIS)

Sun, Y.P.; Wallis, A.F.A.; Nguyen, K.L.

1997-01-01

A series of guaiacyl and syringyl lignin model compounds and their methylated analogues were reacted with alkaline hydrogen peroxide while irradiating with UV light at 254 nm. The aromatic products obtained were investigated by gas chromatography-mass spectrometry (GC-MS). Guaiacol, syringol and veratrol gave no detectable aromatic products. However, syringol methyl ether gave small amounts of aromatic products, resulting from ring substitution and methoxyl displacement by hydroxyl radicals. Reaction of vanillin and syringaldehyde gave the Dakin reaction products, methoxy-1,4-hydroquinones, while reaction of their methyl ethers yielded benzoic acids. Acetoguaiacone, acetosyringone and their methyl ethers afforded several hydroxylated aromatic products, but no aromatic products were identified in the reaction mixtures from guaiacylpropane and syringylpropane. In contrast, veratrylpropane gave a mixture from which 17 aromatic hydroxylated compounds were identified. It is concluded that for phenolic lignin model compounds, particularly those possessing electrondonating aromatic ring substituents, ring-cleavage reactions involving superoxide radical anions are dominant, whereas for non-phenolic lignin models, hydroxylation reactions through attack of hydroxyl radicals prevail

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

Home; Journals; Journal of Chemical Sciences. Krishna P Kaliappan. Articles written in Journal of Chemical Sciences. Volume 120 Issue 1 January 2008 pp 205-216. Synthetic studies on taxanes: A domino-enyne metathesis/Diels-Alder approach to the AB-ring · Krishna P Kaliappan Velayutham Ravikumar Sandip A Pujari.

Resting state networks' corticotopy: the dual intertwined rings architecture.

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Salma Mesmoudi

Full Text Available How does the brain integrate multiple sources of information to support normal sensorimotor and cognitive functions? To investigate this question we present an overall brain architecture (called "the dual intertwined rings architecture" that relates the functional specialization of cortical networks to their spatial distribution over the cerebral cortex (or "corticotopy". Recent results suggest that the resting state networks (RSNs are organized into two large families: 1 a sensorimotor family that includes visual, somatic, and auditory areas and 2 a large association family that comprises parietal, temporal, and frontal regions and also includes the default mode network. We used two large databases of resting state fMRI data, from which we extracted 32 robust RSNs. We estimated: (1 the RSN functional roles by using a projection of the results on task based networks (TBNs as referenced in large databases of fMRI activation studies; and (2 relationship of the RSNs with the Brodmann Areas. In both classifications, the 32 RSNs are organized into a remarkable architecture of two intertwined rings per hemisphere and so four rings linked by homotopic connections. The first ring forms a continuous ensemble and includes visual, somatic, and auditory cortices, with interspersed bimodal cortices (auditory-visual, visual-somatic and auditory-somatic, abbreviated as VSA ring. The second ring integrates distant parietal, temporal and frontal regions (PTF ring through a network of association fiber tracts which closes the ring anatomically and ensures a functional continuity within the ring. The PTF ring relates association cortices specialized in attention, language and working memory, to the networks involved in motivation and biological regulation and rhythms. This "dual intertwined architecture" suggests a dual integrative process: the VSA ring performs fast real-time multimodal integration of sensorimotor information whereas the PTF ring performs multi

Resting State Networks' Corticotopy: The Dual Intertwined Rings Architecture

Science.gov (United States)

Mesmoudi, Salma; Perlbarg, Vincent; Rudrauf, David; Messe, Arnaud; Pinsard, Basile; Hasboun, Dominique; Cioli, Claudia; Marrelec, Guillaume; Toro, Roberto; Benali, Habib; Burnod, Yves

2013-01-01

How does the brain integrate multiple sources of information to support normal sensorimotor and cognitive functions? To investigate this question we present an overall brain architecture (called “the dual intertwined rings architecture”) that relates the functional specialization of cortical networks to their spatial distribution over the cerebral cortex (or “corticotopy”). Recent results suggest that the resting state networks (RSNs) are organized into two large families: 1) a sensorimotor family that includes visual, somatic, and auditory areas and 2) a large association family that comprises parietal, temporal, and frontal regions and also includes the default mode network. We used two large databases of resting state fMRI data, from which we extracted 32 robust RSNs. We estimated: (1) the RSN functional roles by using a projection of the results on task based networks (TBNs) as referenced in large databases of fMRI activation studies; and (2) relationship of the RSNs with the Brodmann Areas. In both classifications, the 32 RSNs are organized into a remarkable architecture of two intertwined rings per hemisphere and so four rings linked by homotopic connections. The first ring forms a continuous ensemble and includes visual, somatic, and auditory cortices, with interspersed bimodal cortices (auditory-visual, visual-somatic and auditory-somatic, abbreviated as VSA ring). The second ring integrates distant parietal, temporal and frontal regions (PTF ring) through a network of association fiber tracts which closes the ring anatomically and ensures a functional continuity within the ring. The PTF ring relates association cortices specialized in attention, language and working memory, to the networks involved in motivation and biological regulation and rhythms. This “dual intertwined architecture” suggests a dual integrative process: the VSA ring performs fast real-time multimodal integration of sensorimotor information whereas the PTF ring performs multi

Energetic ion injection and formation of the storm-time symmetric ring current

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L. Xie

2006-12-01

Full Text Available An extensive study of ring current injection and intensification of the storm-time ring current is conducted with three-dimensional (3-D test particle trajectory calculations (TPTCs. The TPTCs reveal more accurately the process of ring current injection, with the main results being the following: (1 an intense convection electric field can effectively energize and inject plasma sheet particles into the ring current region within 1–3 h. (2 Injected ions often follow chaotic trajectories in non-adiabatic regions, which may have implications in storm and ring current physics. (3 The shielding electric field, which arises as a consequence of enhanced convection and co-exists with the injection and convection electric field, may cause the original open trajectories of injected ions with higher energy to change into closed ones, thus playing a role in the formation of the symmetric ring current.

An unusually strong Einstein ring in the radio source PKS1830-211

International Nuclear Information System (INIS)

Jauncey, D.L.

1991-01-01

RADIO observations of the strong, flat-spectrum radio source PKS1830-211 revealed a double structure, with a separation of 1 arcsec, suggesting that it might be a gravitationally lensed object. We have now obtained high-resolution radio images of PKS1830-211 from several interferometric radiotelescope networks, which show an unusual elliptical ring-like structure connecting the two brighter components. The presence of the ring, and the similarity of the two brighter spots, argue strongly that this is indeed a gravitationally lensed system, specifically an Einstein ring in which lens and lensed object are closely aligned. Although the source is close to the galactic plane, it seems that both the lens and background (lensed) object are extragalactic. This object is one hundred times brighter than either of the two previously discovered radio Einstein rings, and is among the six brightest flat-spectrum sources in the sky. Its brightness makes it a peculiar object: it must involve either a chance alignment of a lensing object with an unusually bright background source, or an alignment with a less bright object but amplified to an unusual degree. (author)

Plug the socket of the main closing valve in a nuclear power plant

International Nuclear Information System (INIS)

Neupauer, J.; Bednar, B.

1988-01-01

The plug is designed for closing the main closing valve socket during a refuelling shutdown of a nuclear power plant. The plug is fixed in the using jaws forced against the socket ring part. The socket is sealed by expanding a ring between two cone trays. A valve provided in the plug allows draining the pipe. The plug is inserted in the socket using a jib suspended on a rail. Following sealing both sockets the inner surfaces of the closing valve can be decontaminated. Following decontamination, a water-proof cover is slid over the plug protecting the plug moving mechanism from damage. (J.B.). 1 fig

Ring distributions leading to species formation: a global topographic analysis of geographic barriers associated with ring species.

Science.gov (United States)

Monahan, William B; Pereira, Ricardo J; Wake, David B

2012-03-12

In the mid 20th century, Ernst Mayr and Theodosius Dobzhansky championed the significance of circular overlaps or ring species as the perfect demonstration of speciation, yet in the over 50 years since, only a handful of such taxa are known. We developed a topographic model to evaluate whether the geographic barriers that favor processes leading to ring species are common or rare, and to predict where other candidate ring barriers might be found. Of the 952,147 geographic barriers identified on the planet, only about 1% are topographically similar to barriers associated with known ring taxa, with most of the likely candidates occurring in under-studied parts of the world (for example, marine environments, tropical latitudes). Predicted barriers separate into two distinct categories: (i) single cohesive barriers (barriers - formed by groups of barriers (each 184,000 to 1.7 million km2) in close geographic proximity (totaling 1.9 to 2.3 million km2) - associated with taxa that differentiate at larger spatial scales (birds: Phylloscopus trochiloides and Larus (sp. argentatus and fuscus)). When evaluated globally, we find a large number of cohesive barriers that are topographically similar to those associated with known ring taxa. Yet, compared to cohesive barriers, an order of magnitude fewer composite barriers are similar to those that favor ring divergence in species with higher dispersal. While these findings confirm that the topographic conditions that favor evolutionary processes leading to ring speciation are, in fact, rare, they also suggest that many understudied natural systems could provide valuable demonstrations of continuous divergence towards the formation of new species. Distinct advantages of the model are that it (i) requires no a priori information on the relative importance of features that define barriers, (ii) can be replicated using any kind of continuously distributed environmental variable, and (iii) generates spatially explicit hypotheses of

A Feeding Strategy in Inner L-Shape Ring Hot Rolling Process

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Wen Meng

2017-01-01

Full Text Available In order to make the inner L-shape ring polling process with a closed die structure (ILRRCDS on the top and bottom of the driven roll stable, at first, this paper established the mathematical model for ILRRCDS. Then, the plastic penetration and biting-in conditions for ILRRCDS were deduced based on plain ring rolling theory. Moreover, a feeding strategy that can realize a constant growth of the ring’s outer radius was proposed and the reasonable value ranges of the feed rate of the mandrel were determined. The numerical simulation model for ILRRCDS is established based on ABAQUS software. Finally, the equivalent plastic strain (PEEQ and temperature distributions of rolled ring were obtained. The results indicated that the proposed feeding strategy can realize a stable ILRRCDS. At the end of ILRRCDS, the PEEQ at the inner radius surface of the ring is maximum, the PEEQ at the outer radius surface of the ring takes the second place, and the PEEQ at the middle part of ring is minimum. With the increase of rolling time, the higher temperature zone of the rolled ring gradually moves from the center part of the ring to the “inner corner zone” of the ring.

Modified lignin: Preparation and use in reversible gel via Diels-Alder reaction.

Science.gov (United States)

Zhou, Wanpeng; Zhang, Hui; Chen, Fangeng

2018-02-01

In this study, popular soda lignin was modified with either furan or maleimide ring, and the modified lignins were subjected to reversible Diels-Alder reaction. A new process was proposed to prepare the functionalized lignin. A long chain was introduced to the hydroxyl groups of lignin, and then either the furan or maleimide ring was added to the other end of the chain. The test results confirmed that either the furan ring or the maleimide ring was bound to lignin. Furan- and maleimide-functionalized lignins were also combined to generate crosslinking via Diels-Alder [4+2] cycloaddition reaction. Under appropriate conditions, the formation of a gel was identified, which reverted to liquid state after retro Diels-Alder reaction upon heating at 120°C. This study reveals the significant versatility and potential of the developed strategy for the utilization of lignin-based recyclable networks. Copyright © 2017 Elsevier B.V. All rights reserved.

Heavy-Atom Tunneling Calculations in Thirteen Organic Reactions: Tunneling Contributions are Substantial, and Bell's Formula Closely Approximates Multidimensional Tunneling at ≥250 K.

Science.gov (United States)

Doubleday, Charles; Armas, Randy; Walker, Dana; Cosgriff, Christopher V; Greer, Edyta M

2017-10-09

Multidimensional tunneling calculations are carried out for 13 reactions, to test the scope of heavy-atom tunneling in organic chemistry, and to check the accuracy of one-dimensional tunneling models. The reactions include pericyclic, cycloaromatization, radical cyclization and ring opening, and S N 2. When compared at the temperatures that give the same effective rate constant of 3×10 -5  s -1 , tunneling accounts for 25-95 % of the rate in 8 of the 13 reactions. Values of transmission coefficients predicted by Bell's formula, κ Bell  , agree well with multidimensional tunneling (canonical variational transition state theory with small curvature tunneling), κ SCT . Mean unsigned deviations of κ Bell vs. κ SCT are 0.08, 0.04, 0.02 at 250, 300 and 400 K. This suggests that κ Bell is a useful first choice for predicting transmission coefficients in heavy-atom tunnelling. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum chemical study of penicillin: Reactions after acylation

Science.gov (United States)

Li, Rui; Feng, Dacheng; Zhu, Feng

The density functional theory methods were used on the model molecules of penicillin to determine the possible reactions after their acylation on ?-lactamase, and the results were compared with sulbactam we have studied. The results show that, the acylated-enzyme tetrahedral intermediate can evolves with opening of ?-lactam ring as well as the thiazole ring; the thiazole ring-open products may be formed via ?-lactam ring-open product or from tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. In virtue of the water-assisted, their energy barriers are obviously reduced.

ASSOCIATIVE RINGS SOLVED AS LIE RINGS

Directory of Open Access Journals (Sweden)

M. B. Smirnov

2011-01-01

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

Homoaromatics as intermediates in the substitution reactions of 1,2,4,5-tetrazines with ammonia and hydrazine

International Nuclear Information System (INIS)

Counotte-Potman, A.D.

1981-01-01

This thesis describes some nucleophilic substitution reactions between the red 1,2,4,5-tetrazines and hydrazine-hydrate or ammonia. Special attention was paid to the occurrence of the Ssub(N) (ANRORC) mechanism in these substitution reactions. This mechanism comprises a sequence of reactions, involving the Addition of a Nucleopile to a heteroaromatic species, followed by a Ring-Opening and Ring Closure reaction to the substitution product. 3-Alkyl(aryl)-1,2,4,5-tetrazines were found to undergo a Chichibabin hydrazination into 6-hydrazino-3-alkyl(aryl)-1,2,4,5-tetrazines on treatment with hydrazine-hydrate. The first step in this reaction sequence was the formation of a homoaromatic sigma-adduct. Subsequently an open-chain intermediate was observed by NMR, on raising the temperature. Finally the hydrazino compound is formed by ring closure. This reaction sequence can be considered as an Ssub(N)(ANRORC) process. With 15 N-labelled hydrazine, only part of the label was found to be built in the 1,2,4,5-tetrazine ring of the 6-hydrazino compounds. This is the first example of a reaction in which both the hydrazino compound with the 15 N-label in the ring and with the 15 N-label in the exocyclic hydrazino group are formed according to the Ssub(N)(ANRORC) mechanism. (Auth.)

Curing reaction of bisphenol-A based benzoxazine with cyanate ester resin and the properties of the cured thermosetting resin

Directory of Open Access Journals (Sweden)

H. Kimura

2011-12-01

Full Text Available Curing reaction of bisphenol-A based benzoxazine with cyanate ester resin and the properties of the cured thermosetting resin were investigated. The cure behavior of benzoxazine with cyanate ester resin was monitored by model reaction using nuclear magnetic resonance (NMR. As a result of the model reaction, the ring opening reaction of benzoxazine ring and thermal self-cyclotrimerization of cyanate ester group occurred, and then the phenolic hydoroxyl group generated by the ring opening reaction of benzoxazine ring co-reacted with cyanate ester group. The properties of the cured thermosetting resin were estimated by mechanical properties, electrical resistivity, water resistance and heat resistance. The cured thermosetting resin from benzoxazine and cyanate ester resin showed good heat resistance, high electrical resistivity and high water resistance, compared with the cured thermosetting resin from benzoxazine and epoxy resin.

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

Science.gov (United States)

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

2010-10-01

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

Stability and isomerization reactions of phenyl cation C{sub 6}H{sub 5}{sup +} isomers

Energy Technology Data Exchange (ETDEWEB)

Shi, Dandan [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China); Yang, Xue [College of Science, Jilin Institute of Chemical Technology, Jilin 132022 (China); Zhang, Xiaomei; Shan, Shimin [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China); Xu, Haifeng, E-mail: xuhf@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China); Yan, Bing, E-mail: yanbing@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China)

2016-03-01

Highlights: • A total of 60 isomers of C{sub 6}H{sub 5}{sup +} cations were obtained at density functional theory. • The stability and isomerization reactions of C{sub 6}H{sub 5}{sup +} isomers were performed. • The structures, frequencies, thermodynamic properties of isomers were summarized. • Ring to ring or chain isomerization pathways were investigated using IRC method. • Result shows reactions contain hydrogen transfer, bond broken and reconstruction. - Abstract: As a key polyatomic molecular cation that plays a pivotal role in growth of the polycyclic aromatic hydrocarbons, phenyl cation C{sub 6}H{sub 5}{sup +} exhibits various isomers and isomerization reactions. Investigation on the structure and stability of the isomers as well as the isomerization is important for better understanding the chemical reactions involving C{sub 6}H{sub 5}{sup +} cations. In this work, we have performed a theoretical study on the stability and isomerization reactions of C{sub 6}H{sub 5}{sup +} isomers at density functional theory B3LYP/6-311G (d, p) level. We have obtained a total of 60 isomers of C{sub 6}H{sub 5}{sup +} cations, most of which are reported for the first time. The geometries, vibrational frequencies, thermodynamic properties and stability of 28 out of 60 isomers have been summarized in detail. Different ring-to-ring and ring-to-chain isomerization pathways, which are connected via 28 transition states, have been investigated using the intrinsic reaction coordinate method. The results show that the isomerization reactions occur via hydrogen migration followed by bond-breaking and reconstruction.

Saturn's F Ring Core: Calm in the Midst of Chaos

Science.gov (United States)

Cuzzi, J. N.; Whizin, A. D.; Hogan, R. C.; Dobrovolskis, A. R.; Dones, L.; Showalter. M. R.; Colwell, J. E.; Scargle, J. D.

2013-01-01

The long-term stability of the narrow F Ring core has been hard to understand. Instead of acting as "shepherds", Prometheus and Pandora together stir the vast preponderance of the region into a chaotic state, consistent with the orbits of newly discovered objects like S/2004S6. We show how a comb of very narrow radial locations of high stability in semimajor axis is embedded within this otherwise chaotic region. The stability of these semimajor axes relies fundamentally on the unusual combination of rapid apse precession and long synodic period which characterizes the region. This situation allows stable "antiresonances" to fall on or very close to traditional Lindblad resonances which, under more common circumstances, are destabilizing. We present numerical integrations of tens of thousands of test particles over tens of thousands of Prometheus orbits that map out the effect. The stable antiresonance zones are most stable in a subset of the region where Prometheus first-order resonances are least cluttered by Pandora resonances. This region of optimum stability is paradoxically closer to Prometheus than a location more representative of "torque balance", helping explain a longstanding paradox. One stable zone corresponds closely to the currently observed semimajor axis of the F Ring core. While the model helps explain the stability of the narrow F Ring core, it does not explain why the F Ring material all shares a common apse longitude; we speculate that collisional damping at the preferred semimajor axis (not included in the current simulations) may provide that final step. Essentially, we find that the F Ring core is not confined by a combination of Prometheus and Pandora, but a combination of Prometheus and precession.

Multiple Coulomb ordered strings of ions in a storage ring

International Nuclear Information System (INIS)

Hasse, Rainer W.

2002-01-01

We explain that the anomalous frequency shifts of very close masses measured in the high precision mass measurement experiments in the ESR storage ring result from the locking of Coulomb interacting strings of ions. Here two concentric strings which run horizontally close to each other for many revolutions are captured into a single string if their thermal clouds overlap. They give up their identity and lock into an average frequency

Sample preparation techniques based on combustion reactions in closed vessels - A brief overview and recent applications

International Nuclear Information System (INIS)

Flores, Erico M.M.; Barin, Juliano S.; Mesko, Marcia F.; Knapp, Guenter

2007-01-01

In this review, a general discussion of sample preparation techniques based on combustion reactions in closed vessels is presented. Applications for several kinds of samples are described, taking into account the literature data reported in the last 25 years. The operational conditions as well as the main characteristics and drawbacks are discussed for bomb combustion, oxygen flask and microwave-induced combustion (MIC) techniques. Recent applications of MIC techniques are discussed with special concern for samples not well digested by conventional microwave-assisted wet digestion as, for example, coal and also for subsequent determination of halogens

Self-organized formation of GaSb/GaAs quantum rings.

Science.gov (United States)

Timm, R; Eisele, H; Lenz, A; Ivanova, L; Balakrishnan, G; Huffaker, D L; Dähne, M

2008-12-19

Ring-shaped GaSb/GaAs quantum dots, grown by molecular beam epitaxy, were studied using cross-sectional scanning tunneling microscopy. These quantum rings have an outer shape of a truncated pyramid with baselengths around 15 nm and heights of about 2 nm but are characterized by a clear central opening extending over about 40% of the outer baselength. They form spontaneously during the growth and subsequent continuous capping of GaSb/GaAs quantum dots due to the large strain and substantial As-for-Sb exchange reactions leading to strong Sb segregation.

PEGASYS---A proposed internal target facility for the PEP storage ring

International Nuclear Information System (INIS)

Van Biber, K.

1988-07-01

A proposal for an integral gas-jet target and forward spectrometer for the PEP storage ring is described. The beam structure, allowable, luminosity (L = 10 33 cm/sup /minus/2/s/sup /minus/1/ for H 2 , D 2 ) and energy (E/sub e/ ≤ 15 GeV) make the ring ideal for multiparticle coincidence studies in the scaling regime, and where perturbative QCD may be an apt description of some exclusive and semi-inclusive reactions. 14 refs., 7 figs

Spin frustration effects in an odd-member antiferromagnetic ring and the magnetic Mobius strip

International Nuclear Information System (INIS)

Cador, Olivier; Gatteschi, Dante; Sessoli, Roberta; Barra, Anne-Laure; Timco, Grigore A.; Winpenny, Richard E.P.

2005-01-01

The magnetic properties of the first odd-member antiferromagnetic ring comprising eight chromium(III) ions, S=32 spins, and one nickel(II) ion, S=1 spin, are investigated. The ring possesses an even number of unpaired electrons and a S=0 ground state but, due to competing AF interactions, the first excited spin states are close in energy. The spin frustrated ring is visualized by a Mobius strip. The 'knot' of the strip represents the region of the ring where the AF interactions are more frustrated. In the particular case of this bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown that the frustration is delocalized on the chromium chain, while the antiparallel alignment is more rigid at the nickel site

Spin frustration effects in an odd-member antiferromagnetic ring and the magnetic Mobius strip

Energy Technology Data Exchange (ETDEWEB)

Cador, Olivier [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy); Gatteschi, Dante [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy); Sessoli, Roberta [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy)]. E-mail: roberta.sessoli@unifi.it; Barra, Anne-Laure [Laboratoire des Champs Magnetiques Intenses-CNRS, F-38042 Grenoble Cede 9 (France); Timco, Grigore A. [Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Winpenny, Richard E.P. [Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)

2005-04-15

The magnetic properties of the first odd-member antiferromagnetic ring comprising eight chromium(III) ions, S=32 spins, and one nickel(II) ion, S=1 spin, are investigated. The ring possesses an even number of unpaired electrons and a S=0 ground state but, due to competing AF interactions, the first excited spin states are close in energy. The spin frustrated ring is visualized by a Mobius strip. The 'knot' of the strip represents the region of the ring where the AF interactions are more frustrated. In the particular case of this bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown that the frustration is delocalized on the chromium chain, while the antiparallel alignment is more rigid at the nickel site.

The Ring Counter (RCo): A high resolution IC-Si-CsI(Tl) device for heavy ion reaction studies at 10-30 MeV/A

International Nuclear Information System (INIS)

Moroni, A.; Bruno, M.; Bardelli, L.; Barlini, S.; Brambilla, S.; Casini, G.; Cavaletti, R.; Chiari, M.; Cortesi, A.; D'Agostino, M.; De Sanctis, J.; Geraci, E.; Giordano, G.; Giussani, A.; Gramegna, F.; Guiot, B.; Kravchuk, V.; Lanchais, A.; Margagliotti, G.V.; Nannini, A.; Ordine, A.; Piantelli, S.; Vannini, G.; Vannucci, L.

2006-01-01

An annular detector (Ring Counter, RCo) is presented, which has been designed and built to detect and identify in mass and charge light charged particles and fragments with very low energy thresholds and high energy resolution. It complements the GARFIELD apparatus, operating at INFN Laboratori Nazionali di Legnaro, to detect the forward emitted products of nuclear heavy ion reactions. It consists of eight sectors of a three-stage telescope, each one formed by an ionization chamber followed by eight strips of a silicon detector and by two CsI(Tl) scintillators. Construction features and performances are described and discussed in details

ACCELERATORS: Beam based alignment of the SSRF storage ring

Science.gov (United States)

Zhang, Man-Zhou; Li, Hao-Hu; Jiang, Bo-Cheng; Liu, Gui-Min; Li, De-Ming

2009-04-01

There are 140 beam position monitors (BPMs) in the Shanghai Synchrotron Radiation Facility (SSRF) storage ring used for measuring the closed orbit. As the BPM pickup electrodes are assembled directly on the vacuum chamber, it is important to calibrate the electrical center offset of the BPM to an adjacent quadrupole magnetic center. A beam based alignment (BBA) method which varies individual quadrupole magnet strength and observes its effects on the orbit is used to measure the BPM offsets in both the horizontal and vertical planes. It is a completely automated technique with various data processing methods. There are several parameters such as the strength change of the correctors and the quadrupoles which should be chosen carefully in real measurement. After several rounds of BBA measurement and closed orbit correction, these offsets are set to an accuracy better than 10 μm. In this paper we present the method of beam based calibration of BPMs, the experimental results of the SSRF storage ring, and the error analysis.

Conceptual design of a moving-ring reactor

International Nuclear Information System (INIS)

Smith, A.C. Jr.; Ashworth, C.P.; Abreu, K.E.

1983-01-01

A design of a prototype Moving-Ring Reactor has been completed. The fusion fuel is confined in current-carrying rings of magnetically field-reversed plasma (''compact toroids''). The plasma rings, formed by a coaxial plasma gun, undergo adiabatic magnetic compression to ignition temperature while they are being injected into the reactor's burner section. The cylindrical burner chamber is divided into three ''burn stations''. Separator coils and a slight axial guide-field gradient are used to shuttle the ignited toroids rapidly from one burn station to the next, pausing for one third of the total burn time at each station. D-T- 3 He ice pellets refuel the rings at a rate which maintains constant radiated power. The first wall and tritium breeding blanket designs make credible use of helium cooling, SiC and Li 2 O to minimize structural radioactivity. ''Hands-on'' maintenance is possible on all reactor components outside the blanket. The first wall and blanket are designed to shut the reactor down passively in the event of a loss-of-coolant or loss-of-flow accident. Helium removes heat from the first wall, blanket and shield, and is used in a closed-cycle gas turbine to produce electricity. Energy residing in the plasma ring at the end of the burn is recovered via magnetic expansion. Electrostatic direct conversion is not used in this design. The reactor produces a constant net power of 99 MW(e). (author)

Does alkali cation binding to aromatic ring retard the fluxional ...

Indian Academy of Sciences (India)

A Kalpana

2017-11-10

Nov 10, 2017 ... actions can be tuned over a long range by altering the ... where the metal ion moves across the rings.20,24–26 The ..... molecule more susceptible for reaction. ..... Robb M A, Cheeseman J R, Scalmani G, Barone V, Men-.

Large protonation-gated photochromism of an OPE-embedded difurylperfluorocyclopentene

KAUST Repository

Wolf, Jannic Sebastian

2015-01-01

A recently reported protolytic gating effect on the ring closing reaction of an oligo(phenylene ethynylene) (OPE) embedded difurylperfluorocyclopentene (S) with a dimethylaminophenyl chain link in each of the side arms, was quantitatively analyzed in detail. The reaction system (So, SoH+, SoH2 2+, Sc, ScH+, ScH2 2+) comprising three protolytic forms in both open and closed configuration, is characterized by four protolytic equilibrium constants and six photochemical quantum yields of ring closing and ring opening. The absorption spectra, conductivity, and effective photochemical quantum yields were measured in acetonitrile as functions of solvent acidity varied by addition of trifluoroacetic acid and triethylamine and characterized by an effective pHnon-aq. Based on the derivation of a rigorous method for assessing the individual quantum yields of ring closure and ring opening of the six species, it was shown that it is specifically the second protonation step that is responsible for a more than 10-fold increase in the quantum yield of ring closure.

Corneal ring infiltration in contact lens wearers

Directory of Open Access Journals (Sweden)

Seyed Ali Tabatabaei

2017-01-01

Full Text Available To report a case of atypical sterile ring infiltrates during wearing soft silicone hydrogel contact lens due to poor lens care. A 29-year-old woman presented with complaints of pain, redness, and morning discharge. She was wearing soft silicone hydrogel contact lens previously; her current symptoms began 1 week before presentation. On examination, best-corrected visual acuity was 20/40 in that eye. Slit-lamp examination revealed dense, ring-shaped infiltrate involving both the superficial and deep stromal layers with lucid interval to the limbus, edema of the epithelium, epithelial defect, and vascularization of the superior limbus. Cornea-specific in vivo laser confocal microscopy (Heidelberg Retina Tomograph 2 Rostock Cornea Module, HRT 2-RCM, Heidelberg Engineering GmbH, Dossenheim, Germany revealed Langerhans cells and no sign of Acanthamoeba or fungal features, using lid scraping and anti-inflammatory drops; her vision completely recovered. We reported an atypical case of a sterile corneal ring infiltrate associated with soft contact lens wearing; smear, culture, and confocal microscopy confirmed a sterile inflammatory reaction.

Ring distributions leading to species formation: a global topographic analysis of geographic barriers associated with ring species

Directory of Open Access Journals (Sweden)

Monahan William B

2012-03-01

Full Text Available Abstract Background In the mid 20th century, Ernst Mayr and Theodosius Dobzhansky championed the significance of circular overlaps or ring species as the perfect demonstration of speciation, yet in the over 50 years since, only a handful of such taxa are known. We developed a topographic model to evaluate whether the geographic barriers that favor processes leading to ring species are common or rare, and to predict where other candidate ring barriers might be found. Results Of the 952,147 geographic barriers identified on the planet, only about 1% are topographically similar to barriers associated with known ring taxa, with most of the likely candidates occurring in under-studied parts of the world (for example, marine environments, tropical latitudes. Predicted barriers separate into two distinct categories: (i single cohesive barriers (2, associated with taxa that differentiate at smaller spatial scales (salamander: Ensatina eschscholtzii; tree: Acacia karroo; and (ii composite barriers - formed by groups of barriers (each 184,000 to 1.7 million km2 in close geographic proximity (totaling 1.9 to 2.3 million km2 - associated with taxa that differentiate at larger spatial scales (birds: Phylloscopus trochiloides and Larus (sp. argentatus and fuscus. When evaluated globally, we find a large number of cohesive barriers that are topographically similar to those associated with known ring taxa. Yet, compared to cohesive barriers, an order of magnitude fewer composite barriers are similar to those that favor ring divergence in species with higher dispersal. Conclusions While these findings confirm that the topographic conditions that favor evolutionary processes leading to ring speciation are, in fact, rare, they also suggest that many understudied natural systems could provide valuable demonstrations of continuous divergence towards the formation of new species. Distinct advantages of the model are that it (i requires no a priori information on the

13C Kinetic isotopic effect of polymerization on monomers with multiple bond

International Nuclear Information System (INIS)

Berman, E.L.; Polyakov, V.B.; Makovetskij, K.L.; Golenko, T.G.; Galimov, Eh.M.; AN SSSR, Moscow. Inst. Organicheskoj Khimii; AN SSSR, Moscow. Inst. Geokhimii i Analiticheskoj Khimii)

1988-01-01

13 C kinetic isotopic effect (KIE) of anionic and radical polymerization and metathesis reaction of monomers with multiple bonds are studied and correlation between the found KIE values of polymerization and the structure of transition state is established. 13 C KIE of polymerization reactions are investigated using monomers with natural content of the isotope. Polymerization was carried out using high-vacuum equipment: radical polymerization of methyl acrylate (MA) and vinyl acetate in benzene solution under the effect of benzoyl peroxide (60 deg C); anionic polymerization of MA, initiated by potassium butyl cellosolvolate, was realized in mass at 25 deg C; cyclopentene metathesis reaction was conducted in benzene under the effect of initiating system WCl 6 - (C 3 H 5 ) 2 Si(CH 3 ) 2 at -30 deg C; phenylacetylene polymers were prepared by polymerization in benzene solution at 20 deg C under the effect of WCl 6 . It is ascertained that 13 C KIE of radical and anionic polymerization of olefins and cycloolefin metathesis constitutes 2.0 -2.4%. Polymerization of compound with ternary bond is accompanied by a lower value of 13 C KIE (<1%), which is explained by double bond of reacting bond in transition state

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

DEFF Research Database (Denmark)

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

2015-01-01

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

New developments in ultrasonic inspection of retaining rings on generators in operation

International Nuclear Information System (INIS)

Koch-Mathian, A.

1990-01-01

The ultrasonic inspection of retaining rings of operating generators has been operational since 1986. The aim of this presentation is to outline the experience acquired on many retaining rings on different types of generators. In-situ inspections have made it possible to detect more exactly the different shape echoes for the various elements located beneath the retaining ring such as rotor teeth, damping and epoxy insulation. Various methods of identifying these parts are currently being developed. Investigation on corroded retaining rings has made it possible to demonstrate the close correlation between the transverse beam detection and the presence of actual cracks identified by micrograph. The specific facies of these cracks precludes the use of classic dimensioning techniques, but a method based on longitudinal wave detection has already given encouraging results

Factors influencing ring closure through olefin metathesis – A ...

Indian Academy of Sciences (India)

Unknown

the substituents/functional groups present on the alkenes as well as at the allylic position. This article presents an overview of these ... med and (4) functional groups/substituents present in the substrate. The past several years have ..... Ackermann I, Tom D E and Furstner A 2000 Tetra- hedron 56 2196. 13. Holder S and ...

Ruthenium complexes of chelating amido-functionalized N ...

Indian Academy of Sciences (India)

tric transfer hydrogenation reactions,5 metathesis,6 olefin epoxidation reactions,7 hydroformylation reac- tions,8 electrooxidation reactions,9 facial cycloaddition of azides with terminal alkynes regioselectively10 etc. to name a few. The phenomenal success of the N-heterocyclic car- benes in homogeneous catalysis, has ...

Transformation of Zwitterionic Pyridine Derivatives to a Spiro-Fused Ring System: Azoniabenzo[de]fluorine. Synthesis and Mechanistic Rationalization.

Science.gov (United States)

Palkó, Roberta; Egyed, Orsolya; Rokob, Tibor András; Bombicz, Petra; Riedl, Zsuzsanna; Hajós, György

2015-01-02

Reaction of aryl- and benzylsulfanopyridinium amidates bearing a methyl group in position 6 with 2 equiv of diphenylketene afforded a spiro-fused ring system: azoniabenzo[de]fluorine. By use of an excess amount of ketene, a distinct reaction was observed via which a 1H-pyrrolo[3,2-b]pyridin-2(3H)-one derivative was furnished. The structure of the tetracyclic spiro-fused ring system was unambiguously confirmed by X-ray diffraction, and its formation was rationalized by DFT calculations.

Plasma confinement in a magnetic field of the internal ring current

International Nuclear Information System (INIS)

Shafranov, Vitaly; Popovich, Paul; Samitov, Marat

2000-01-01

Plasma confinement in compact region surrounding an internal ring current is considered. As the limiting case of large aspect ratio system the cylindrical plasma is considered initially. Analysis of the cylindrical tubular plasma equilibrium and stability against the most dangerous flute (m=0) and kink (m=1) modes revealed the possibility of the MHD stable plasma confined by magnetic field of the internal rod current, with rather peaked plasma pressure and maximal local beta β(γ)=0.4. In case of the toroidal internal ring system an additional external magnetic field creates the boundary separatrix witch limits the plasma volume. The dependence of the plasma pressure profiles, marginally stable with respect to the flute modes, from the shape of the external plasma boundary (separatrix) in such kind closed toroidal systems is investigated. The internal ring system with circular poloidal magnetic mirror, where the ring supports could be placed, is proposed. (author)

Modes of reaction front propagation and end-gas combustion of hydrogen/air mixtures in a closed chamber

KAUST Repository

Shi, Xian

2017-01-05

Modes of reaction front propagation and end-gas combustion of hydrogen/air mixtures in a closed chamber are numerically investigated using an 1-D unsteady, shock-capturing, compressible and reacting flow solver. Different combinations of reaction front propagation and end-gas combustion modes are observed, i.e., 1) deflagration without end-gas combustion, 2) deflagration to end-gas autoignition, 3) deflagration to end-gas detonation, 4) developing or developed detonation, occurring in the sequence of increasing initial temperatures. Effects of ignition location and chamber size are evaluated: the asymmetric ignition is found to promote the reactivity of unburnt mixture compared to ignitions at center/wall, due to additional heating from asymmetric pressure waves. End-gas combustion occurs earlier in smaller chambers, where end-gas temperature rise due to compression heating from the deflagration is faster. According to the ξ−ε regime diagram based on Zeldovich theory, modes of reaction front propagation are primarily determined by reactivity gradients introduced by initial ignition, while modes of end-gas combustion are influenced by the total amount of unburnt mixture at the time when autoignition occurs. A transient reactivity gradient method is provided and able to capture the occurrence of detonation.

Modes of reaction front propagation and end-gas combustion of hydrogen/air mixtures in a closed chamber

KAUST Repository

Shi, Xian; Ryu, Je Ir; Chen, Jyh-Yuan; Dibble, Robert W.

2017-01-01

Modes of reaction front propagation and end-gas combustion of hydrogen/air mixtures in a closed chamber are numerically investigated using an 1-D unsteady, shock-capturing, compressible and reacting flow solver. Different combinations of reaction front propagation and end-gas combustion modes are observed, i.e., 1) deflagration without end-gas combustion, 2) deflagration to end-gas autoignition, 3) deflagration to end-gas detonation, 4) developing or developed detonation, occurring in the sequence of increasing initial temperatures. Effects of ignition location and chamber size are evaluated: the asymmetric ignition is found to promote the reactivity of unburnt mixture compared to ignitions at center/wall, due to additional heating from asymmetric pressure waves. End-gas combustion occurs earlier in smaller chambers, where end-gas temperature rise due to compression heating from the deflagration is faster. According to the ξ−ε regime diagram based on Zeldovich theory, modes of reaction front propagation are primarily determined by reactivity gradients introduced by initial ignition, while modes of end-gas combustion are influenced by the total amount of unburnt mixture at the time when autoignition occurs. A transient reactivity gradient method is provided and able to capture the occurrence of detonation.

Diverse Reactions of Thiophenes, Selenophenes, and Tellurophenes with Strongly Oxidizing I(III) PhI(L)2 Reagents.

Science.gov (United States)

Egalahewa, Sathsara; Albayer, Mohammad; Aprile, Antonino; Dutton, Jason L

2017-02-06

We report the outcomes of the reactions of aromatic group 16 thiophene, selenophene, and tellurophene rings with the I(III) oxidants PhI(OAc)(OTf) and [PhI(Pyr) 2 ][OTf] 2 (Pyr = pyridine). In all reactions, oxidative processes take place, with generation of PhI as the reduction product. However, with the exception of tellurophene with PhI(OAc)(OTf), +4 oxidation state complexes are not observed, but rather a variety of other processes occur. In general, where a C-H unit is available on the 5-membered ring, an electrophilic aromatic substitution reaction of either -IPh or pyridine onto the ring occurs. When all positions are blocked, reactions with PhI(OAc)(OTf) give acetic and triflic anhydride as the identifiable oxidative byproducts, while [PhI(Pyr) 2 ][OTf] 2 gives pyridine electrophilic aromatic substitution onto the peripheral rings. Qualitative mechanistic studies indicate that the presence of the oxidizable heteroatom is required for pyridine to act as an electrophile in a substantial manner.

Classical swine fever virus detection: results of a real-time reverse transcription polymerase chain reaction ring trial conducted in the framework of the European network of excellence for epizootic disease diagnosis and control

DEFF Research Database (Denmark)

Hoffmann, Bernd; Blome, Sandra; Bonilauri, Paolo

2011-01-01

and specificity values. Nevertheless, some in-house systems had unspecific reactions or suboptimal sensitivity with only a single CSFV genotype. Follow-up actions involved either improvement of suboptimal assays or replacement of specific laboratory assays with the FLI protocol, with or without modifications......The current study reports on a real-time reverse transcription polymerase chain reaction (real-time RT-PCR) ring trial for the detection of Classical swine fever virus (CSFV) genomic RNA undertaken by 10 European laboratories. All laboratories were asked to use their routine in-house real-time RT...