DIELS-ALDER REACTIONS IN WATER - ENFORCED HYDROPHOBIC INTERACTION AND HYDROGEN-BONDING

NARCIS (Netherlands)

Engberts, J.B.F.N.

Second-order rate constants have been measured for the Diels-Alder (DA) reactions of cyclopentadiene with dienophiles of varying hydrophobicity and hydrogen-bond acceptor capacity in water, in a series of organic solvents and in alcohol-water mixtures. The intramolecular DA reaction of

A hetero retro Diels-Alder reaction in aqueous solution : A dramatic water-induced increase of the equilibrium constant and inhibition of cycloreversion

NARCIS (Netherlands)

Wijnen, J.W; Engberts, J.B.F.N.

The adduct of the Diels-Alder reaction of nitrosobenzene with cyclopentadiene is not stable in solution. The equilibrium constant for the reaction depends strongly on the medium and water induces a spectacular shift to the adduct. Comparison with the bimolecular addition of nitrosobenzene to

Diels-Alder Reactions in Water. Effects of Hydrophobicity and Hydrogen Bonding

NARCIS (Netherlands)

Otto, Sijbren; Blokzijl, Wilfried; Engberts, Jan B.F.N.

1994-01-01

In order to check whether the activated complex for the Diels-Alder reactions of 5-substituted 1,4-naphthoquinones with cyclopentadiene is more polar in water than in other solvents, we have determined the substituent effects in seven different solvents. The substituent effects gradually decrease

Cycloadditions in mixed aqueous solvents : the role of the water concentration

NARCIS (Netherlands)

Rispens, Theo; Engberts, Jan B. F. N.

We examined the kinetics of a series of cycloaddition reactions in mixtures of water with methanol, acetonitrile and poly(ethylene glycol) (MW 1000). The reactions include the Diels-Alder (DA) reaction between cyclopentadiene and N-n-butylmaleimide or acridizinium bromide, the retro-Diels-Alder

Micellar Catalysis of Diels-Alder Reactions : Substrate Positioning in the Micelle

NARCIS (Netherlands)

Rispens, Theo; Engberts, Jan B.F.N.

2002-01-01

We have studied the kinetics of the Diels-Alder reactions of cyclopentadiene, sorbyl alcohol, and sorbyltrimethylammonium bromide with a series of N-substituted maleimides in micellar media. Micellar rate constants have been determined and were found to be 20-40 times lower than the respective

The Synthesis of "N"-Benzyl-2-Azanorbornene via Aqueous Hetero Diels-Alder Reaction: An Undergraduate Project in Organic Synthesis and Structural Analysis

Science.gov (United States)

Sauvage, Xavier; Delaude, Lionel

2008-01-01

The synthesis of "N"-benzyl-2-azanorbornene via aqueous hetero Diels-Alder reaction of cyclopentadiene and benzyliminium chloride formed in situ from benzylamine hydrochloride and formaldehyde is described. Characterization of the product was achieved by IR and NMR spectroscopies. The spectral data acquired are thoroughly discussed. Numerous…

Non-degenerate 1,2-silyl shift in silyl substituted alkyltrimethylcyclopentadienes

Czech Academy of Sciences Publication Activity Database

Pinkas, Jiří; Kubišta, Jiří; Gyepes, R.; Čejka, Jiří; Meunier, P.; Mach, Karel

2005-01-01

Roč. 690, č. 3 (2005), s. 731-741 ISSN 0022-328X Grant - others:French Government(FR) 20006842 Institutional research plan: CEZ:AV0Z40400503 Keywords : substituted cyclopentadienes * silatropic shift * dynamic NMR spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.025, year: 2005

Preparation of titanocene and zirconocene dichlorides bearing bulky 1,4-dimethyl-2,3-diphenylcyclopentadienyl ligand and their behavior in polymerization of ethylene

Czech Academy of Sciences Publication Activity Database

Horáček, Michal; Pinkas, Jiří; Merna, J.; Gyepes, R.; Meunier, P.

2009-01-01

Roč. 694, č. 2 (2009), s. 173-178 ISSN 0022-328X R&D Projects: GA AV ČR KAN100400701 Institutional research plan: CEZ:AV0Z40400503 Keywords : substituted cyclopentadienes * titanocene * zirconocene Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.347, year: 2009

Specific acid catalysis and Lewis acid catalysis of Diels–Alder reactions in aqueous media

NARCIS (Netherlands)

Mubofu, Egid B.; Engberts, Jan B.F.N.

2004-01-01

A comparative study of specific acid catalysis and Lewis acid catalysis of Diels–Alder reactions between dienophiles (1, 4 and 6) and cyclopentadiene (2) in water and mixed aqueous media is reported. The reactions were performed in water with copper(II) nitrate as the Lewis acid catalyst whereas

DIELS-ALDER REACTIONS IN AQUEOUS-SOLUTIONS - ENFORCED HYDROPHOBIC INTERACTIONS BETWEEN DIENE AND DIENOPHILE

NARCIS (Netherlands)

BLOKZIJL, W; BLANDAMER, MJ; ENGBERTS, JBFN

1991-01-01

Second-order rate constants and isobaric activation parameters for the intermolecular Diels-Alder reactions of cyclopentadiene with alkyl vinyl ketones (2a,b) and 5-substituted-1,4-naphthoquinones (3a-c) as well as for the intramolecular Diels-Alder reaction of N-furfuryl-N-methylmaleamic acid (4)

Effects of the Hydrophobicity of the Reactants on Diels-Alder Reactions in Water

NARCIS (Netherlands)

Meijer, Ale; Otto, Sijbren; Engberts, Jan B.F.N.

1998-01-01

To assess the importance of the hydrophobicity of different parts of diene and dienophile on the aqueous acceleration of Diels-Alder reactions, second-order rate constants have been determined for the reactions of cyclopentadiene (1), 2,3-dimethyl-1,3-butadiene (4), and 1,3-cyclohexadiene (6) with

Specific acid catalysis and Lewis acid catalysis of Diels-Alder reactions in aqueous media

NARCIS (Netherlands)

Mubofu, E.B.; Engberts, J.B.F.N.

A comparative study of specific acid catalysis and Lewis acid catalysis of Diells-Alder reactions between dienophiles (1, 4 and 6) and cyclopentadiene (2) in water and mixed aqueous media is reported. The reactions were performed in water with copper(II) nitrate as the Lewis acid catalyst whereas

The Diels-Alder cyclization of ketenimines.

Science.gov (United States)

Erb, Jeremy; Strull, Jessica; Miller, David; He, Jean; Lectka, Thomas

2012-04-20

A Diels-Alder reaction between cyclopentadiene and a variety of ketenimines is reported. A copper(I)-bis(phosphine complex catalyzes the cycloaddition across the C═N bond of the ketenimine in a [4 + 2] reaction to give an enamine intermediate that is hydrolyzed upon purification to generate aminoketones. © 2012 American Chemical Society

A mechanistic study on the reaction pathways leading to benzene and naphthalene in cellulose vapor phase cracking

International Nuclear Information System (INIS)

Norinaga, Koyo; Yang, Huamei; Tanaka, Ryota; Appari, Srinivas; Iwanaga, Keita; Takashima, Yuka; Kudo, Shinji; Shoji, Tetsuya; Hayashi, Jun-ichiro

2014-01-01

The reaction pathways leading to aromatic hydrocarbons such as benzene and naphthalene in gas-phase reactions of multi-component mixtures derived from cellulose fast pyrolysis were studied both experimentally and numerically. A two-stage tubular reactor was used for evaluating the reaction kinetics of secondary vapor phase cracking of the nascent pyrolysates at temperature ranging from 400 to 900 °C, residence time from 0.2 to 4.3 s, and at 241 kPa. The products of alkyne and diene were identified from the primary pyrolysis of cellulose even at low temperature range 500–600 °C. These products include acetylene, propyne, propadiene, vinylacetylene, and cyclopentadiene. Experiments were also numerically validated by a detailed chemical kinetic model consisting of more than 8000 elementary step-like reactions with over 500 chemical species. Acceptable capabilities of the kinetic model in predicting concentration profiles of the products enabled us to assess reaction pathways leading to benzene and naphthalene via the alkyne and diene from primary pyrolysates of cellulose. C 3 alkyne and diene are primary precursors of benzene at 650 °C, while combination of ethylene and vinylacetylene produces benzene dominantly at 850 °C. Cyclopentadiene is a prominent precursor of naphthalene. Combination of acetylene with propyne or allyl radical leads to the formation of cyclopentadiene. Furan and acrolein are likely important alkyne precursors in cellulose pyrolysis at low temperature, whereas dehydrogenations of olefins are major route to alkyne at high temperatures. - Highlights: • Analytical pyrolysis experiments provided data for kinetic modeling. • Detailed chemical kinetic model was used and evaluated. • Alkyne and diene were important intermediates for aromatic hydrocarbon formation. • Reaction pathways leading to aromatic hydrocarbons were proposed

DNA-based asymmetric catalysis : Sequence-dependent rate acceleration and enantioselectivity

NARCIS (Netherlands)

Boersma, Arnold J.; Klijn, Jaap E.; Feringa, Ben L.; Roelfes, Gerard

2008-01-01

This study shows that the role of DNA in the DNA-based enantioselective Diels-Alder reaction of azachalcone with cyclopentadiene is not limited to that of a chiral scaffold. DNA in combination with the copper complex of 4,4'-dimethyl-2,2'-bipyridine (Cu-L1) gives rise to a rate acceleration of up to

Tetramethyl(perfluoroalkyl)cyclopentadienyl Rhodium(I) Complexes with Ethylene or Diene Ligands. Crystal Structure of [(eta-5-C5Me4C6F13)Rh(CO)2

Czech Academy of Sciences Publication Activity Database

Čermák, Jan; Krupková, Alena; Auerová, Kateřina; Zamrzla, M.; Nguyen Thi, T.H.; Vojtíšek, P.; Císařová, I.

2010-01-01

Roč. 695, č. 3 (2010), s. 375-381 ISSN 0022-328X R&D Projects: GA AV ČR IAA4072203; GA MŠk(CZ) LC06070 Institutional research plan: CEZ:AV0Z40720504 Keywords : fluorous cyclopentadienes * rhodium complexes * alkene complexes Subject RIV: CC - Organic Chemistry Impact factor: 2.205, year: 2010

New uranium compounds preparation and use as catalyst for hydrogenation of non-saturated organic compounds

International Nuclear Information System (INIS)

Arnaudet, L.; Folcher, G.

1985-01-01

Preparation of new organic uranium compounds and their use as catalysts for hydrogenation of non-saturated organic compounds are described. These compounds include Uranium III, a cyclopentadienic group, an alkyl group and an acetylenic derivative C 6 H 5 C triple bonds CR fixed by a π bond. Catalysts can be prepared with depleted uanium for hydrogenation of olefins for example [fr

Enantioselective Diels-Alder Reaction Using Chiral Mg Complexes Derived from Chiral 2-[2-[(Alkyl- or 2-[2-[(Arylsulfonyl)amino]phenyl]-4-phenyl-1,3-oxazoline.

Science.gov (United States)

Ichiyanagi, Tsuyoshi; Shimizu, Makoto; Fujisawa, Tamotsu

1997-11-14

Magnesium complexes derived from (R)-2-[2-[(alkyl- or (R)-2-[2-[(arylsulfonyl)amino]phenyl]-4-phenyl-1,3-oxazolines and methylmagnesium iodide were found to be efficient Lewis acid catalysts for the Diels-Alder reaction of 3-alkenoyl-1,3-oxazolidin-2-one with cyclopentadiene. Chiral ligands were easily prepared from readily available D-phenylglycinol in good yields. The reaction of 3-acryloyl-1,3-oxazolidin-2-one with cyclopentadiene catalyzed by a stoichiometric amount of the Lewis acid gave exclusively the endo-cycloaddition product in up to 92% ee. The sulfonamide group on the chiral ligand strongly influenced the enantiofacial selectivity: the use of a toluene-, benzene-, 1- or 2-naphthalene-, or methanesulfonamide group in the chiral ligand gave the endo-(2R)-cycloaddition product, while a trifluoromethanesulfonamide group predominantly gave its enantiomer, the endo-(2S)-cycloaddition product, in 65% ee. The scope and limitations of the catalytic effect of chiral Mg(II) complexes on the enantioselectivity of the Diels-Alder reaction were investigated. The reaction mechanism of the Mg(II)-catalyzed reaction is also discussed on the basis of the experimental results.

Stabilization of wood and lignocellulose materials

International Nuclear Information System (INIS)

Pesek, M.; Dedek, V.; Plander, E.; Jarkovsky, J.

1973-01-01

A method is described consisting in impregnation of wood or of lignocellulose materials with a mixture containing the unsaturated monomers styrene and acrylnitrile, organic solvents and swelling agents, and 1,3-butadiene and/or 2-chloro-1,3-butadiene and/or 1,3-cyclopentadiene at an amount of 40 volume per cent in the initial mixture. Polymerization is effected by ionizing radiation. (B.S.)

{alpha},{beta}-Unsaturated Fischer carbene complexes as chemical multitalents

Energy Technology Data Exchange (ETDEWEB)

Meijere, A. de [Institut fuer Organische Chemie der George-August-Universitaet Goettingen (Germany)

1995-12-31

The well established reaction of {alpha},{beta}-unsaturated Fischer carbenechromium complexes 6(R{sup 1} = H) with alkynes normally proceeds with carbonyl insertion to yield 4-alkoxyphenols 9. Led by the incidental formation of a cyclopentadiene 3 from certain {beta}-aminosubstituted complexes 6(X = NR{sub 2}{sup 3}, R{sup 1} = cPr) the authors have studied the influences of the nature of substituents (R{sup 1}, X on 6; R{sub L}, R{sub S} in the alkyne; R{sup 3} in the amino group), solvents, and temperature on the outcome of the reaction. Imino substitution on complexes 6 leads to 2H-pyrroles 1, a free primary amino group (X = NH{sub 2}) to pyridines 5, and bulky substituents R{sup 1} to cyclopenta[b]pyrans 8 with double insertion of an alkyne. Eventually, appropriate conditions have been developed which permit to selectively prepare either 3-alkoxy-5-(dialkylamino)cyclopentadienes 3 (as synthetic equivalents of cyclopentenones 4), 5-(dialkylaminomethylene)cyclopent-2-enones 7, 3-alkoxy-2-(1{prime}-morpholino-1{prime}-alkenyl)cyclopent-2-enones 10, and 2-acyl-3-(dialkylamino)cyclopent-2-enones 11 from easily accessible carbene complexes 6 (X = NR{sub 2}{sup 3}) in high yields. Mechanistic aspects and implications of these novel transformations will be discussed.

New catalysts for selective hydrogenation of diene and acetylene hydrocarbons into olefins

Energy Technology Data Exchange (ETDEWEB)

Frolov, V.M.; Parenago, O.P.; Shuikina, L.P.

1978-12-01

New catalysts for selective hydrogenation of diene and acetylene hydrocarbons into olefins were obtained by reacting aqueous palladium, rhodium, or nickel chloride (0.005-0.05 mole/l.) at 50/sup 0/C, in an argon atmosphere with chelating nitrogen compounds, i.e., o-phenanthroline, ..cap alpha..,..cap alpha..'-dipyridyl, sodium ethylenediaminetetracetate, morpholine, branched polyethylene imines, or amino acids such as glycine, ..cap alpha..-alanine, ..beta..-phenyl-..cap alpha..-alanine, tyrosine, or histidine, and treating the complexes so obtained with sodium borohydride at 1:1-1:5 NaBH/sub 4/-metal ratios, in an aqueous medium. Palladium-based complexes showed the highest activities (20-98Vertical Bar3< conversion) and selectivities (98-100Vertical Bar3<) in heterogeneous hydrogenation of cyclopentadiene, butadiene, 1-hexyne, 1,3-cyclohexadiene, or 1,3-cyclooctadiene at 20/sup 0/-60/sup 0/C and 0.5-15 atm hydrogen, carried out in a kinetic circulation reactor or a metallic autoclave. Thus, a catalytic system based on PdCl/sub 2/ and ..beta..-phenyl-..cap alpha..-alanine converted 98Vertical Bar3< of cyclopentadiene to cyclopentene with 99Vertical Bar3< selectivity. The palladium-based catalyst did not deactivate on the contact with air.

New L-Serine Derivative Ligands as Cocatalysts for Diels-Alder Reaction

Science.gov (United States)

Sousa, Carlos A. D.; Rodríguez-Borges, José E.; Freire, Cristina

2013-01-01

New L-serine derivative ligands were prepared and tested as cocatalyst in the Diels-Alder reactions between cyclopentadiene (CPD) and methyl acrylate, in the presence of several Lewis acids. The catalytic potential of the in situ formed complexes was evaluated based on the reaction yield. Bidentate serine ligands showed good ability to coordinate medium strength Lewis acids, thus boosting their catalytic activity. The synthesis of the L-serine ligands proved to be highly efficient and straightforward. PMID:24383009

Melting Point and Viscosity Behavior of High Energy Density Missile Fuels

Science.gov (United States)

1982-09-01

CLASSIFICATION OF THIS PAGE (f,n Date Eneed . etrahydrodi(cyclopentadiene) ( XTHDCPD or JP-lO). HNN and HXX each have two crystalline forms. The solid-solid...suggesting solid solution formation on crystallization. The experimental m.p. curves for the binary/isomer I - XTHDCPD system could be used to predict m.p...liquidus temperature, of any/fuel blend of HNN, HXX, isomer I and XTHDCPD of kno composition. It )as found that the maximum m.p. specification of -54 C

Spiro annulation of cage polycycles via Grignard reaction and ring-closing metathesis as key steps

Directory of Open Access Journals (Sweden)

Sambasivarao Kotha

2015-08-01

Full Text Available A simple synthetic strategy to C2-symmetric bis-spiro-pyrano cage compound 7 involving ring-closing metathesis is reported. The hexacyclic dione 10 was prepared from simple and readily available starting materials such as 1,4-naphthoquinone and cyclopentadiene. The synthesis of an unprecedented octacyclic cage compound through intramolecular Diels–Alder (DA reaction as a key step is described. The structures of three new cage compounds 7, 12 and 18 were confirmed by single crystal X-ray diffraction studies.

The preparation of Carbocyclic DDIU (2',3'-DiDeoxy IodoUridine) via electrophilic iodination and biological study

Energy Technology Data Exchange (ETDEWEB)

An, Gwang Gil; Choi, Tae Hyun; Lee, Myung Jin; Ahn, Hyun Seok; Choi, Chang Woon; Lim, Sang Moo; Chun, Kwon Soo [Korea Institute of Radiological and Medical Sciences, Seoul (Korea, Republic of); Rhee, Hak June [Hanyang Univ., Seoul (Korea, Republic of)

2005-07-01

Interest in the synthesis of carbocyclic nucleosides and carbocyclic analogues of normal nucleosides has grown exclusively since the potential antiviral and antitumor therapeutic agents. The replacement of the furanose oxygen by a carbon gives the nucleoside increased in vivo stability. Radioiodinated carobcyclic DDIU was evaluated for monitoring of HSV1-TK (herpes simplex virus type 1 thymidine kinase) gene transduced MCA hepatoma cells and wild-type MCA cells. In this study, we whis to report here an efficient synthetic route for carbocyclic radiopharmaceuticals starting from cyclopentadiene.

Synthesis, characterization and evaluation of biological activities of some 2,3-diaryl bicyclo methanones

Directory of Open Access Journals (Sweden)

Thirunarayanan Ganesamoorthy

2016-06-01

Full Text Available Sixteen (3,4-dichlorophenyl-3-(substituted phenylbicyclo[2.2.1]hept-5-ene-2-yl methanone derivatives have been synthesized by an aqueous phase fly-ash catalyzed [4+2] cycloaddition Diels-Alder reaction of cyclopentadiene and 3,4-dichloro phenyl chalcones. The yields of the methanones were greater than 60%. The synthesized methanones were characterized by their physical constants and spectral data. The antimicrobial and antioxidant activities of the synthesized methanones were evaluated using a variety of bacterial and fungal species and DPPH radical scavenging methods.

Diels-Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels-Alder reaction.

Science.gov (United States)

Cantín, Ángel; Gomez, M Victoria; de la Hoz, Antonio

2016-01-01

Diels-Alder cycloaddition between cyclopentadiene and p -benzoquinone has been studied in the confined space of a pure silica zeolite Beta and the impact on reaction rate due to the concentration effect within the pore and diffusion limitations are discussed. Introduction of Lewis or Brønsted acid sites on the walls of the zeolite strongly increases the reaction rate. However, contrary to what occurs with mesoporous molecular sieves (MCM-41), Beta zeolite does not catalyse the retro-Diels-Alder reaction, resulting in a highly selective catalyst for the cycloaddition reaction.

Artificial Diels–Alderase based on the transmembrane protein FhuA

Directory of Open Access Journals (Sweden)

Hassan Osseili

2016-06-01

Full Text Available Copper(I and copper(II complexes were covalently linked to an engineered variant of the transmembrane protein Ferric hydroxamate uptake protein component A (FhuA ΔCVFtev. Copper(I was incorporated using an N-heterocyclic carbene (NHC ligand equipped with a maleimide group on the side arm at the imidazole nitrogen. Copper(II was attached by coordination to a terpyridyl ligand. The spacer length was varied in the back of the ligand framework. These biohybrid catalysts were shown to be active in the Diels–Alder reaction of a chalcone derivative with cyclopentadiene to preferentially give the endo product.

Rhodium-catalyzed enantioselective intramolecular C-H silylation for the syntheses of planar-chiral metallocene siloles.

Science.gov (United States)

Zhang, Qing-Wei; An, Kun; Liu, Li-Chuan; Yue, Yuan; He, Wei

2015-06-01

Reported herein is the rhodium-catalyzed enantioselective C-H bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)-TMS-Segphos, the reactions took place under very mild conditions to afford metallocene-fused siloles in good to excellent yields and with ee values of up to 97%. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric C-H silylations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron transfer reactions of 1-phenyl-4-vinylpyrazole mediated by cerium(IV) ammonium nitrate

International Nuclear Information System (INIS)

Pitarch-Vinuesa, M.; Miranda, M.A.; Medio-Simon, M.; Sepulveda-Arques, J.

1993-01-01

The title compound is converted into the cyclic ethers 5 and the alcohol 6 upon treatment with ceric ammonium nitrate in acetone. Using methanol as a solvent the dimethoxy derivative 9 and the nitrate ester 10 are formed. No cross cycloaddition is observed in the presence of olefins such as ethyl vinyl ether, DMAD, or indene; however, with cyclopentadiene as co-reagent a mixture of the exo-endo Diels-Alder adducts 14 involving the vinylic system of 1 as 2π component is obtained. The results are rationalized through the intermediacy of the radical cation 1 .+ , generated by single electron transfer (SET) from the neutral precursor 1 to Ce(IV)

Niobium Pentachloride Activation of Enone Derivatives: Diels-Alder and Conjugate Addition Products

Directory of Open Access Journals (Sweden)

Gil Valdo José da Silva

2002-05-01

Full Text Available Niobium pentachloride has proven to be a powerful activating agent for Diels-Alder or conjugate addition reactions of cycloenones. The Diels-Alder product was obtained only with an unsubstituted enone (cyclohexenone and the highly reactive diene cyclopentadiene; substituents in the b-position of enones seem to prevent Diels-Alder reaction: oxygenated substituents favor the formation of vinyl chlorides (ethyl ether or dichloromethane as solvents or enol ethers (ethyl acetate as solvent, while a methyl substituent prevents any kind of transformation with NbCl5. Less reactive dienes, furan and 2-methylfuran gave the conjugate addition products of the furan ring to the enone system.

Reaction between chloromercurocobaltcarborane and undecaborate anion derivatives

International Nuclear Information System (INIS)

Lobanova, I.A.; Khitrova, O.M.; Petrovskij, P.V.; Bregadze, V.I.

2004-01-01

Interaction of Cs + C 2 B 9 H 12 - and exo-nido-5,6,10-[Cl(Ph 3 P) 2 RU]-5,6,10-(μ-H) 3 -10-H-7,8-C 2 B 9 H 8 with 9-chloromercurocobaltcarborane derivative - 3-(η 5 -Cp)-9-ClHg-3,1,2-CoC 2 B 9 H 10 (η 5 -Cp = cyclopentadiene) in mixed solvent tetrahydrofuran-water-ethanol at room temperature was studied using the methods of elementary analysis and 1 H, 31 P, 11 B NMR. Asymmetric metallocarborane cluster, in which exo-nido-ruthenacarborane and closo-cobalt- or dicarbo-nido-undecaborate fragments are bound via mercury atom, were prepared [ru

Preparation of Bis(polyfluoroalkyl)cyclopentadienes, New Highly Fluorophilic Ligands for Fluorous Biphase Catalysis

Czech Academy of Sciences Publication Activity Database

Bříza, T.; Kvíčala, J.; Paleta, O.; Čermák, Jan

2002-01-01

Roč. 58, č. 20 (2002), s. 3841-3846 ISSN 0040-4020 R&D Projects: GA ČR GA203/99/0135 Keywords : fluorous * fluorophilic * fluorocyclopentadiene Subject RIV: CC - Organic Chemistry Impact factor: 2.420, year: 2002

A facile avenue to conductive polymer brushes via cyclopentadiene-maleimide Diels-Alder ligation

Czech Academy of Sciences Publication Activity Database

Yameen, B.; Rodriguez-Emmenegger, C.; Preuss, C. M.; Pop-Georgievski, Ognen; Verveniotis, Elisseos; Trouillet, V.; Rezek, Bohuslav; Barner-Kowollik, C.

2013-01-01

Roč. 49, č. 77 (2013), s. 8623-8625 ISSN 1359-7345 R&D Projects: GA ČR GBP205/12/G118; GA ČR GAP108/11/1857; GA ČR(CZ) GBP108/12/G108 Institutional support: RVO:61389013 ; RVO:68378271 Keywords : conductive poly(3-hexylthiophen) brushes * Diels-Alder ligation * Kelvin Probe Force Microscopy (KFM) Subject RIV: CD - Macromolecular Chemistry Impact factor: 6.718, year: 2013

Solvent effect on the degree of (a)synchronicity in polar Diels-Alder reactions from the perspective of the reaction force constant analysis.

Science.gov (United States)

Yepes, Diana; Martínez-Araya, Jorge I; Jaque, Pablo

2017-12-29

In this work, we computationally evaluated the influence of six different molecular solvents, described as a polarizable continuum model at the M06-2X/6-31+G(d,p) level, on the activation barrier/reaction rate, overall energy change, TS geometry, and degree of (a)synchronicity of two concerted Diels-Alder cycloadditions of acrolein (R1) and its complex with Lewis acid acrolein···BH 3 (R2) to cyclopentadiene. In gas-phase, we found that both exothermicity and activation barrier are only reduced by about 2.0 kcal mol -1 , and the asynchronicity character of the mechanism is accentuated when BH 3 is included. An increment in the solvent's polarity lowers the activation energy of R1 by 1.3 kcal mol -1 , while for R2 the reaction rate is enhanced by more than 2000 times at room temperature (i.e., the activation energy decreases by 4.5 kcal mol -1 ) if the highest polar media is employed. Therefore, a synergistic effect is achieved when both external agents, i.e., Lewis acid catalyst and polar solvent, are included together. This effect was ascribed to the ability of the solvent to favor the encounter between cyclopentadiene and acrolein···BH 3 . This was validated by the asymmetry of the TS which becomes highly pronounced when either both or just BH 3 is considered or the solvent's polarity is increased. Finally, the reaction force constant κ(ξ) reveals that an increment in the solvent's polarity is able to turn a moderate asynchronous mechanism of the formation of the new C-C σ-bonds into a highly asynchronous one. Graphical abstract A synergistic effect is achieved when both external agents, i.e., Lewis acid catalyst and polar solvent, are included together: lowered energy barriers and increased asynchronicities.

Asymmetric Diels-Alder Reaction of α,β-Unsaturated Oxazolidin-2-one Derivatives Catalyzed by a Chiral Fe(III)-Bipyridine Diol Complex.

Science.gov (United States)

Li, Mao; Carreras, Virginie; Jalba, Angela; Ollevier, Thierry

2018-02-16

An asymmetric Fe III -bipyridine diol catalyzed Diels-Alder reaction of α,β-unsaturated oxazolidin-2-ones has been developed. Among various Fe II /Fe III salts, Fe(ClO 4 ) 3 ·6H 2 O was selected as the Lewis acid of choice. The use of a low catalyst loading (2 mol % of Fe(ClO 4 ) 3 ·6H 2 O and 2.4 mol % of Bolm's ligand) afforded high yields (up to 99%) and high enantiomeric excesses (up to 98%) of endo-cycloadducts for the Diels-Alder reaction between cyclopentadiene and substituted acryloyloxazolidin-2-ones. Other noncyclic dienes led to decreased enantioselectivities. A proposed model supports the observed stereoinduction.

Origins of the Unfavorable Activation and Reaction Energies of 1-Azadiene Heterocycles Compared to 2-Azadiene Heterocycles in Diels-Alder Reactions.

Science.gov (United States)

Fell, Jason S; Martin, Blanton N; Houk, K N

2017-02-17

The reactivities of butadiene, cyclopentadiene, furan, thiophene, pyrrole, and their 1-aza- and 2-aza-derivatives in Diels-Alder reactions with ethylene and fumaronitrile were investigated with density functional theory (M06-2X/6-311G(d,p)). The activation free energies for the Diels-Alder reactions of cyclic 1-azadienes are 10-14 kcal mol -1 higher than those of cyclic 2-azadienes, and the reaction free energies are 17-20 kcal mol -1 more endergonic. The distortion/interaction model shows that the increased activation energies of cyclic 1-azadienes originate from increased transition state distortion energies and unfavorable interaction energies, arising from addition to the nitrogen terminus of the C═N bond.

Using chiral ionic liquid additives to enhance asymmetric induction in a Diels-Alder reaction.

Science.gov (United States)

Goodrich, P; Nimal Gunaratne, H Q; Hall, L; Wang, Y; Jin, L; Muldoon, M J; Ribeiro, A P C; Pombeiro, A J L; Pârvulescu, V I; Davey, P; Hardacre, C

2017-01-31

A bis-oxazoline ligand has been complexed using Cu(ii) and Zn(ii) trifluoromethanesulfonate and a range of chiral ionic liquid (CIL) additives based on natural products were used as a co-catalyst for a Diels-Alder reaction. The catalytic performance of these systems was compared for the asymmetric Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene with and without the presence of a CIL additive. In the absence of the CIL, both catalysts resulted in low enantioselectivities in conventional solvents and ionic liquids. However, whilst only a minor effect of the CIL was observed for the Cu based catalyst, in the case of the Zn based catalyst, significant enhancements in endo enantioselectivity of up to 50% were found on the addition of a CIL.

Sulfur polymer cement, a solidification and stabilization agent for radioactive and hazardous wastes

International Nuclear Information System (INIS)

Darnell, R.G.

1993-01-01

Sulfur polymer cement (SPC) is made by reacting 95% sulfur with 2.5 % dicyclopentadiene and 2.5% cyclopentadiene oligomers, to produce a product that is much better than unmodified sulfur. SPC is being tested as a solidifying and stabilizing agent for low-level radioactive and hazardous wastes. Heavy loadings (5 wt%) of eight toxic metals were combined individually with SPC and 7 wt% sodium sulfide nonahydrate. The leach rates for mercury, lead, chromium and silver oxides were reduced by six orders of magnitude, while those of arsenic and barium were reduced by four. SPC is good for stabilizing incinerator ash. Ion-exchange resins can be stabilized with SPC after heat treatment with asbestos or diatomite at 220-250 deg C. 19 refs

Quantum mechanical/molecular mechanical modeling finds Diels-Alder reactions are accelerated less on the surface of water than in water.

Science.gov (United States)

Thomas, Laura L; Tirado-Rives, Julian; Jorgensen, William L

2010-03-10

Quantum and molecular mechanics calculations for the Diels-Alder reactions of cyclopentadiene with 1,4-naphthoquinone, methyl vinyl ketone, and acrylonitrile have been carried out at the vacuum-water interface and in the gas phase. In conjunction with previous studies of these cycloadditions in dilute solution, a more complete picture of aqueous environmental effects emerges with implications for the origin of observed rate accelerations using heterogeneous aqueous suspensions, "on water" conditions. The pure TIP4P water slab maintains the bulk density and hydrogen-bonding properties in central water layers. The bulk region merges to vacuum over a ca. 5 A band with progressive diminution of the density and hydrogen bonding. The relative free energies of activation and transition structures for the reactions at the interface are found to be intermediate between those calculated in the gas phase and in bulk water; i.e., for the reaction with 1,4-naphthoquinone, the DeltaDeltaG(++) values relative to the gas phase are -3.6 and -7.3 kcal/mol at the interface and in bulk water, respectively. Thus, the results do not support the notion that a water surface is more effective than bulk water for catalysis of such pericyclic reactions. The trend is in qualitative agreement with expectations based on density considerations and estimates of experimental rate constants for the gas phase, a heterogeneous aqueous suspension, and a dilute aqueous solution for the reaction of cyclopentadiene with methyl vinyl ketone. Computed energy pair distributions reveal a uniform loss of 0.5-1.0 hydrogen bond for the reactants and transition states in progressing from bulk water to the vacuum-water interface. Orientational effects are apparent at the surface; e.g., the carbonyl group in the methyl vinyl ketone transition structure is preferentially oriented into the surface. Also, the transition structure for the 1,4-naphthoquinone case is buried more in the surface, and the free energy of

Magnetic nanoparticles conjugated to chiral imidazolidinone as recoverable catalyst

Energy Technology Data Exchange (ETDEWEB)

Mondini, Sara [Consiglio Nazionale delle Ricerche, Laboratorio di Nanotecnologie, Istituto di Scienze e Tecnologie Molecolari (Italy); Puglisi, Alessandra; Benaglia, Maurizio, E-mail: maurizio.benaglia@unimi.it; Ramella, Daniela [Università degli Studi di Milano, Dipartimento di Chimica (Italy); Drago, Carmelo [Consiglio Nazionale delle Ricerche, Istituto di Chimica Biomolecolare (Italy); Ferretti, Anna M.; Ponti, Alessandro, E-mail: alessandro.ponti@istm.cnr.it [Consiglio Nazionale delle Ricerche, Laboratorio di Nanotecnologie, Istituto di Scienze e Tecnologie Molecolari (Italy)

2013-11-15

The immobilization of an ad hoc designed chiral imidazolidin-4-one onto iron oxide magnetic nanoparticles (MNPs) is described, to afford MNP-supported MacMillan’s catalyst. Morphological and structural analysis of the materials, during preparation, use, and recycle, has been carried out by transmission electron microscopy. The supported catalyst was tested in the Diels–Alder reaction of cyclopentadiene with cinnamic aldehyde, affording the products in good yields and enantiomeric excesses up to 93 %, comparable to those observed with the non-supported catalyst. Recovery of the chiral catalyst has been successfully performed by simply applying an external magnet to achieve a perfect separation of the MNPs from the reaction product. The recycle of the catalytic system has been also investigated. Noteworthy, this immobilized MacMillan’s catalyst proved to be able to efficiently promote the reaction in pure water.

A Pyrene-Linked Cavity within a β-Barrel Protein Promotes an Asymmetric Diels-Alder Reaction.

Science.gov (United States)

Himiyama, Tomoki; Taniguchi, Naomasa; Kato, Shunsuke; Onoda, Akira; Hayashi, Takashi

2017-10-23

A unique π-expanded reaction cavity tethering a polycyclic moiety which provides a platform for substrate binding was constructed within the robust β-barrel structure of nitrobindin (NB). NB variants with cavities of different sizes and shapes are coupled with N-(1-pyrenyl)maleimide (Pyr) to prepare a series of NB-Pyr conjugates. The orientation of the pyrene moiety is fixed within the cavity by the coupling reaction. The fluorescent quenching analysis of NB-Pyr indicates that azachalcone (aza), which is a dienophile for a Diels-Alder (DA) reaction, is efficiently incorporated within the pyrene-linked reaction cavity by the aromatic interaction. The DA reaction between aza and cyclopentadiene proceeds within the reaction cavity of NB-Pyr in the presence of Cu II ion in high yield and high enantio- and regioselectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic nanoparticles conjugated to chiral imidazolidinone as recoverable catalyst

International Nuclear Information System (INIS)

Mondini, Sara; Puglisi, Alessandra; Benaglia, Maurizio; Ramella, Daniela; Drago, Carmelo; Ferretti, Anna M.; Ponti, Alessandro

2013-01-01

The immobilization of an ad hoc designed chiral imidazolidin-4-one onto iron oxide magnetic nanoparticles (MNPs) is described, to afford MNP-supported MacMillan’s catalyst. Morphological and structural analysis of the materials, during preparation, use, and recycle, has been carried out by transmission electron microscopy. The supported catalyst was tested in the Diels–Alder reaction of cyclopentadiene with cinnamic aldehyde, affording the products in good yields and enantiomeric excesses up to 93 %, comparable to those observed with the non-supported catalyst. Recovery of the chiral catalyst has been successfully performed by simply applying an external magnet to achieve a perfect separation of the MNPs from the reaction product. The recycle of the catalytic system has been also investigated. Noteworthy, this immobilized MacMillan’s catalyst proved to be able to efficiently promote the reaction in pure water

Vanadocene reactions with mixed acylates of silicon, germanium and tin

International Nuclear Information System (INIS)

Latyaeva, V.N.; Lineva, A.N.; Zimina, S.V.; Gordetsov, A.S.; Dergunov, Yu.I.

1981-01-01

Vanadocene interaction with di-and tri-alkyl (aryl)-derivatives of silicon, tin and germanium is studied. Dibutyltin dibenzoate under mild conditions (20 deg C, toluene) oxidates vanadocene to [CpV(OCOC 6 H 5 ) 2 ] 2 , at that, the splitting off of one Cp group in the form of cyclopentadiene and formation of the products of tin-organic fragment disproportionation (tributyltin benzoate, dibutyltin, metallic tin) take place. Tributyltin benzoate oxidates vanadocene at the mole ratio 2:1 and during prolong heating (120 deg C) in the absence of the solvent, [CpV(OCOC 6 H 5 ) 2 ] 2 and hexabutyldistannate are the products of the reaction. Acetates R 3 SnOCOCH 3 react in the similar way. The reactivity of mono- and diacylates of germanium and silicon decreases in the series of derivatives Sn>Ge>Si [ru

Fullerene derivatives and fullerene superconductors

International Nuclear Information System (INIS)

Wang, H.H.; Schlueter, J.A.; Cooper, A.C.

1993-01-01

A series of 1:1 C 60 Cycloaddition adducts, C 60 A (A = anthracene, butadiene, cyclopentadiene, and methylcyclopentadiene), has been synthesized. The products are cleanly separated and characterized by use of TGA, 1H-NMR, IR, and mass spectrometry. Among these adducts, C 60 (methylcyclopentadiene) showed the highest thermal stability and was doped with three equivalents of rubidium. The resulting Rb 3 C 60 (MeCp) is a semiconductor but can be thermally converted to the superconducting Rb 3 C 60 through a retro-Diels-Alder reaction. A one-step doping process to prepare Rb 3 C 60 crystals has been developed. The optimal doping condition occurs at ∼ 300 degrees C. High superconducting shielding fractions between 60 and 90% and sharp transition widths (ΔT 10--90 between 4 and 0.7 K) were measured for these samples

Functionalized cyclopentadienyl rhodium(III) bipyridine complexes: synthesis, characterization, and catalytic application in hydrogenation of ketones.

Science.gov (United States)

Wang, Wan-Hui; Suna, Yuki; Himeda, Yuichiro; Muckerman, James T; Fujita, Etsuko

2013-07-14

A series of highly functionalized cyclopentadienyl rhodium(III) complexes, [Cp'Rh(bpy)Br](ClO4) (Cp' = substituted cyclopentadienyl), was synthesized from various multi-substituted cyclopentadienes (Cp'H). [Rh(cod)Cl]2 and Cp'H were firstly converted to [Cp'Rh(cod)] complexes, which were then treated with Br2 to give the rhodium(III) dibromides [Cp'RhBr2]2. The novel complexes [Cp'Rh(bpy)Br](ClO4) were obtained readily by the reaction of 2,2'-bipyridine with [Cp'RhBr2]2. These rhodium complexes [Cp'Rh(bpy)Br](ClO4) were fully characterized and utilized in the hydrogenation of cyclohexanone and acetophenone with generally high yields, but they did not exhibit the same reactivity trends for the two substrate ketones. The different activity of these complexes for the different substrates may be due to the influence of the substituents on the Cp' rings.

The Non-Ergodic Nature of Internal Conversion

DEFF Research Database (Denmark)

Kuhlman, Thomas Scheby

The absorption of light by molecules can induce ultrafast dynamics of coupled electronic and nuclear vibrational motion. The ultrafast nature in many cases rests on the importance of several potential energy surfaces in guiding the nuclear dynamics – a concept of central importance in many aspects...... of chemical reaction dynamics. In this thesis, we focus on the non-ergodic nature of internal conversion, i.e. the concept that the nuclear dynamics only sample a reduced phase space potentially resulting in localization of the dynamics in real space. In essence, this is a consequence of vibrational energy...... cyclopentadienes and dithiane. In the case of the cycloketones, the rate of internal conversion varies by more than an order of magnitude between the molecules. This non-ergodic process was found to primarily involve ring-puckering motion, and the different timescales observed could be rationalized on the basis...

Excited State s-cis Rotamers Produced by Extreme Red Edge Excitation of all-trans-1,4-Diphenyl-1,3-butadiene

DEFF Research Database (Denmark)

Wallace-Williams, Stacie E.; Møller, Søren; Goldbeck, Robert A.

1993-01-01

with the wavelength independence observed for the excited singlet-state absorption and fluorescence emission spectra of 1,5-diphenyl-2,3,4,6,7,8- hexahydronaphthalene and for the fluorescence emission spectra of 1,4diphenyl-1,3-cyclopentadiene, s-trans and s-cis structural analogs of DPB, respectively. The spectral...... changes in DPB can be explained in terms of an excitation wavelength-dependent production of s-cis and s-trans rotamer populations in the excited state. The DPB fluorescence emission spectrum was resolved into s-cis and s-trans components. The vibronic structure of the s-cis fluorescence spectrum...... is similar to that of s-trans, but the band origin is red-shifted and there is a slightly larger amplitude on the red edge. The excited-state absorption spectrum of s-cis DPB appears to be red-shifted relative to that of s-trans DPB as well....

1-acetylvinyl acrylates: new captodative olefins bearing an internal probe for the evaluation of the relative reactivity of captodative against electron-deficient double bonds in Diels-Alder and Friedel-Crafts reactions

International Nuclear Information System (INIS)

Herrera, Rafael; Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Mich.; Jimenez-Vazquez, Hugo A.; Delgado, Francisco; Tamariz, Joaquin; Soederberg, Bjoern C.G.

2005-01-01

The captodative olefins 1-acetylvinyl esters of methacrylic and trans-crotonic acids, 3a and 3b, have been prepared. The presence of a second double bond in the molecule, acting as an internal probe, allowed us to compare their relative reactivity in Diels-Alder and Friedel-Crafts reactions. The reactivity was evaluated with cyclopentadiene (6) as diene in Diels-Alder cycloadditions, and with furan (9) and thiophene (10) as heteroaromatic Friedel-Crafts substrates. In both processes, the captodative enone double bond proved to be more reactive than that in the acrylic moiety. FMO theory accounted for this chemo selectivity as a consequence of the major π contribution of the enone to the LUMO of these molecules. The slight exo stereoselectivity observed in the cycloaddition to 6 parallels the higher stability of the corresponding transition state, according to the results of B3LYP/6-311G(d,p) calculations. (author)

Studies on the Diels-Alder adduct from cyclopentadiene and p-benzoquinone: Biotransformation, enantiomeric excess and absolute configuration

Directory of Open Access Journals (Sweden)

Felipe Camargo Braga

2012-06-01

Full Text Available The use of microorganisms or isolated enzymes in synthetic routes has been extensively used by industry and academic research. A great advantage of biotransformation in a synthetic route is highly regio- and enatiosselective control, which can be achieved through microbial catalyzed reaction. Biotransformation is one of the most efficient methods in a production of high purity optical compounds and development of efficient routes for target molecules. Biotransformation by Mucor ramosissimus of enedione 1 gave the keto-alcohol (--2 with enantiomeric excess (ee>99,9% (determined by 1H NMR with [(+-Eu(hfc]3 and their epimer (--3. Determination of the absolute configuration of epimer (--3 was accomplished by controlled reaction and measuring of optical rotation (scheme 1. The fungus M. ramosissimus is a promising species to perform desymmetrization of diketones with high enantioselectivity.

Solvent effects in ionic liquids: empirical linear energy-density relationships.

Science.gov (United States)

Cerda-Monje, A; Aizman, A; Tapia, R A; Chiappe, C; Contreras, R

2012-07-28

Multiparameter linear energy-density relationships to model solvent effects in room temperature ionic liquids (RTILs) are introduced and tested. The model incorporates two solvent dependent and two specific solute-solvent parameters represented by a set of electronic indexes derived from the conceptual density functional theory. The specific solute-solvent interactions are described in terms of the electronic chemical potential for proton migration between the anion or cation and the transition state structure of a specific reaction. These indexes provide a quantitative estimation of the hydrogen bond (HB) acceptor basicity and the hydrogen bond donor acidity of the ionic solvent, respectively. A sound quantitative scale of HB strength is thereby obtained. The solvent dependent contributions are described by the global electrophilicity of the cation and nucleophilicity of the anion forming the ionic liquid. The model is illustrated for the kinetics of cycloaddition of cyclopentadiene towards acrolein. In general, cation HB acidity outweighs the remaining parameters for this reaction.

Artificial Metalloenzymes with the Neocarzinostatin Scaffold: Toward a Biocatalyst for the Diels-Alder Reaction.

Science.gov (United States)

Ghattas, Wadih; Cotchico-Alonso, Lur; Maréchal, Jean-Didier; Urvoas, Agathe; Rousseau, Maëva; Mahy, Jean-Pierre; Ricoux, Rémy

2016-03-02

A copper(II) cofactor coupled to a testosterone anchor, copper(II)-(5-(Piperazin-1-yl)-1,10-phenanthroline)testosterone-17-hemisuccinamide (10) was synthesized and associated with a neocarzinostatin variant, NCS-3.24 (KD =3 μm), thus generating a new artificial metalloenzyme by following a "Trojan horse" strategy. Interestingly, the artificial enzyme was able to efficiently catalyze the Diels-Alder cyclization reaction of cyclopentadiene (1) with 2-azachalcone (2). In comparison with what was observed with cofactor 10 alone, the artificial enzymes favored formation of the exo products (endo/exo ratios of 84:16 and 62:38, respectively, after 12 h). Molecular modeling studies assigned the synergy between the copper complex and the testosterone (KD =13 μm) moieties in the binding of 10 to good van der Waals complementarity. Moreover, by pushing the modeling exercise to its limits, we hypothesize on the molecular grounds that are responsible for the observed selectivity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Is coronene better described by Clar's aromatic π-sextet model or by the AdNDP representation?

Science.gov (United States)

Kumar, Anand; Duran, Miquel; Solà, Miquel

2017-07-05

The bonding patterns in coronene are complicated and controversial as denoted by the lack of consensus of how its electronic structure should be described. Among the different proposed descriptions, the two most representative are those generated by Clar's aromatic π-sextet and adaptative natural density partitioning (AdNDP) models. Quantum-chemical calculations at the density functional theory level are performed to evaluate the model that gives a better representation of coronene. To this end, we analyse the molecular structure of coronene, we estimate the aromaticity of its inner and outer rings using various local aromaticity descriptors, and we assess its chemical reactivity from the study of the Diels-Alder reaction with cyclopentadiene. Results obtained are compared with those computed for naphthalene and phenanthrene. Our conclusion is that Clar's π-sextet model provides the representation of coronene that better describes the physicochemical behavior of this molecule. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

Science.gov (United States)

Xu, Wei; Li, Yani; Yu, Bo; Yang, Jindou; Zhang, Ying; Chen, Xi; Zhang, Guofang; Gao, Ziwei

2015-01-01

A successive anchoring of Ti(NMe2)4, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1‧-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, 13C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands.

Fused 1,2,3-Dithiazoles: Convenient Synthesis, Structural Characterization, and Electrochemical Properties

Directory of Open Access Journals (Sweden)

Lidia S. Konstantinova

2016-05-01

Full Text Available A new general protocol for synthesis of fused 1,2,3-dithiazoles by the reaction of cyclic oximes with S2Cl2 and pyridine in acetonitrile has been developed. The target 1,2,3-dithiazoles fused with various carbocycles, such as indene, naphthalenone, cyclohexadienone, cyclopentadiene, and benzoannulene, were selectively obtained in low to high yields. In most cases, the hetero ring-closure was accompanied by chlorination of the carbocyclic moieties. With naphthalenone derivatives, a novel dithiazole rearrangement (15→13 featuring unexpected movement of the dithiazole ring from α- to β-position, with respect to keto group, was discovered. Molecular structure of 4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13 was confirmed by single-crystal X-ray diffraction. Electrochemical properties of 13 were studied by cyclic voltammetry and a complex behavior was observed, most likely including hydrodechlorination at a low potential.

Thermodynamic and molecular origin of interfacial rate enhancements and endo-selectivities of a Diels-Alder reaction.

Science.gov (United States)

Beniwal, Vijay; Kumar, Anil

2017-02-08

Organic reactions in general display large rate accelerations when performed under interfacial conditions, such as on water or at ionic liquid interfaces. However, a clear picture of the physicochemical factors responsible for this large rate enhancements is not available. To gain an understanding of the thermodynamic and molecular origin of these large rate enhancements, we performed a Diels-Alder reaction between cyclopentadiene and methyl acrylate at ionic liquid/n-hexane interfaces. This study describes, for the first time, a methodology for the calculation of the activation parameters of an interfacial reaction. It has been seen that the energy of activation for an interfacial reaction is much smaller than that of the corresponding homogeneous reaction, resulting into the large rate acceleration for the interfacial reaction. Furthermore, the study describes the effects of the alkyl chain length of ionic liquid cations, the extent of heterogeneity, and the polarity of ionic liquids on the rate constants and stereoselectivity of the reaction.

Single-site SBA-15 supported zirconium catalysts. Synthesis, characterization and toward cyanosilylation reaction

Science.gov (United States)

Xu, Wei; Yu, Bo; Zhang, Ying; Chen, Xi; Zhang, Guofang; Gao, Ziwei

2015-01-01

A successive anchoring of Zr(NMe2)4, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1‧-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on dehydroxylated SBA-15 pretreated at 500 °C for 16 h (SBA-15-500) was conducted by SOMC strategy in moderate conditions. The dehydoxylation of SBA-15 was monitored by in situ Fourier transform infrared spectroscopy (in situ FT-IR). The ligand-modified SBA-15-500 supported zirconium complexes were characterized by in situ FT-IR, 13C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MAS) and elemental analysis in detail, verifying that the surface zirconium species are single-sited. The catalytic activity of these complexes was evaluated by cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the structure of surface species and the configuration of the ligands.

Effective charge model in the theory of infrared intensities and its application for study of charge di.stribution in the molecules of organometallic compounds

International Nuclear Information System (INIS)

Aleksanyan, V.T.; Samvelyan, S.Kh.

1984-01-01

General principles of plotting the parametric theory of IR spectrum intensities of polyatomic molecules are outlined. The development of the effective charges model in this theory is considered and the mathematical formalism of the first approximation of the method of effective atom charges is described in detail. The results of calculations of charges distribution in the Mo(CO) 6 , W(CO) 6 , Cp 2 V, Cp 2 Ru and others (Cp-cyclopentadiene), performed in the frame work of the outlined scheme are presented. It is shown that in the investigated carbonyles the effective charge on oxygen and metal atoms is negative, on carbon atom - positive. In dicyclopentavienyl complexes the effective charge on the metal atom is positive and is not over 0.6e; charge values on hydrogen and carbon atoms do not exceed, 0.10-0.15e. The notions of ''electrovalence'' of coordination bond and charge distribution in the case of metallocenes are not correlated

The Hexadehydro-Diels-Alder Cycloisomerization Reaction Proceeds by a Stepwise Mechanism.

Science.gov (United States)

Wang, Tao; Niu, Dawen; Hoye, Thomas R

2016-06-29

We report here experiments showing that the hexadehydro-Diels-Alder (HDDA) cycloisomerization reaction proceeds in a stepwise manner-i.e., via a diradical intermediate. Judicious use of substituent effects was decisive. We prepared (i) a series of triyne HDDA substrates that differed only in the R group present on the remote terminus of the diynophilic alkyne and (ii) an analogous series of dienophilic alkynes (n-C7H15COC≡CR) for use in classical Diels-Alder (DA) reactions (with 1,3-cyclopentadiene). The R groups were CF3, CHO, COMe/Et, CO2Me, CONMe2/Et2, H, and 1-propynyl. The relative rates of both the HDDA cyclization reactions and the simple DA cycloadditions were measured. The reactivity trends revealed a dramatic difference in the behaviors of the CF3 (slowest HDDA and nearly fastest DA) and 1-propynyl (fastest HDDA and slowest DA) containing members of each series. These differences can be explained by invoking radical-stabilizing energies rather than electron-withdrawing effects as the dominating feature of the HDDA reaction.

Practical application of thermoreversibly Cross-linked rubber products

Science.gov (United States)

Polgar, L. M.; Picchioni, F.; de Ruiter, E.; van Duin, M.

2017-07-01

Currently, rubber products cannot simply be reprocessed after their product life, due to the irreversible cross-linking methods traditionally applied. The purpose of this work is to investigate how thermoreversible cross-linking of rubbers via Diels Alder chemistry can be used for the development of recyclable rubber products. Unfortunately, the applicability of the thermoreversible EPM-g-furan/BM system appears to be limited to room temperature applications, because of the rapid deterioration of the compression set at elevated temperatures compared to irreversibly cross-linked EPM. However, the use of EPM rubber modified with thiophene or cyclopentadiene moieties may extend the temperature application range and results in rubber products with acceptable properties. Finally, rubber products generally comprise fillers such as silica, carbon black or fibers. In this context, the reinforcing effect of short cut aramid fibers on the material properties of the newly developed thermoreversibly cross-linked EPM rubbers was also studied. The material properties of the resulting products were found to be comparable to those of a fiber reinforced, peroxide cured reference sample.

Toxicology and metabolism of nickel compounds. Progress report, December 1, 1978-November 30, 1979. [Hamsters and rats

Energy Technology Data Exchange (ETDEWEB)

Sunderman, F.W. Jr.

1979-08-15

The toxicology and metabolism of nickel compounds were investigated in rats and hamsters. The new knowledge includes; demonstration that nickel carbonyl is teratogenic for hamsters; elucidation of physiological factors which influence ..cap alpha..Ni/sub 3/S/sub 2/-induced erythrocytosis in rats; development of a sensitive assay for heme oxygenase activity in renal microsomes for use in studies of renal effects of nickel compounds; demonstration that administration of Ni(CO)/sub 4/ to rats inhibits incorporation of /sup 3/H-thymidine into DNA during hepatic regeneration; demonstration that clones of Syrian hamster fetal cells which have been transformed by in vitro exposure to ..cap alpha..Ni/sub 3/S/sub 2/ consistently cause sarcomas following sc injection into nude mice; demonstration that nickel carbonyl-cyclopentadiene dimer induces rhabdomyosarcomas following im injection in rats; observation of differences in carcinogenic activities of several insoluble nickel compounds; discovery that intraocular injection of ..cap alpha..Ni/sub 3/S/sub 2/ induces amelanotic melanomas in rats; and refinement of analytical methods for nickel in biological materials.

Reactive chemically modified piezoelectric crystal detectors: A new class of high-selectivity sensors

International Nuclear Information System (INIS)

Fadeev, A.Yu.; Filatov, A.L.; Lisichkin, G.V.

1994-01-01

A great number of works have focused on the study of properties of modified piezoelectric quartz crystal detectors (PQCDs) coated with sorbing substrates and on applying sensors based on them for the analysis of diluted gas mixtures and solutions. This work offers a new class of gravemetric sensors characterized by a reversible chemical reaction that occurs on their surface. Silica films are proposed as a sorbing coating of quartz detectors, and a chemical modification of a surface is suggested for covalent fixation of the necessary compounds. PQCDs were chemically modified with reactive diene derivatives that can also act as dienophiles. Hexachlorocyclopentadiene (HCCPD, resonater I) and cyclopentadiene (CPD, resonator II) were fixed on a PQCD surface in several stages. After treatment with the resonaters, the PQCD in a CPD gas phase exhibited time dependent frequency shifts from 20-100 Hz. The results suggest that there is a reversible chemical reaction on the electrode surface of resonators I and II when they interact with CPD vapors. Therefore, PQCDs modified with reactive dienes were prepared for the first time and may be employed as selective sensors for CPD

Multiscale Treatment for the Molecular Mechanism of a Diels-Alder Reaction in Solution: A QM/MM-MD Study.

Science.gov (United States)

Soto-Delgado, Jorge; Tapia, Ricardo A; Torras, Juan

2016-10-11

Thermodynamics and the solvent role in the acceleration of the Diels-Alder reaction between cyclopentadiene (CPD) and methyl vinyl ketone (MVK) have been revisited. In this work we use an ab initio hybrid QM/MM-MD scheme combined with multiple steered molecular dynamics to extract the free energy pofile in water and methanol using the bidirectional Minh-Adib estimator. We obtain 18.7 kcal mol -1 and 20.8 kcal mol -1 free energy barrier for the reaction in water and methanol, respectively. This methodology reproduces experimental values with an absolute error of about 0.8 kcal mol -1 . The experimental difference between the activation free-energy barriers of water and methanol is also reproduced with an absolute error of about 0.1 kcal mol -1 . We explore the charge transfer evolution along reaction coordinates to characterize the electronic behavior for this reaction. It is shown that the solvent molecules around the reaction system produce a global polarization along the reaction coordinate which is consistent with the solvent polarity. The results highlight the role of hydrogen bonding formed in the transition state to stabilize the system charge reorganization in the reaction process.

Liquid-Crystalline Ionic Liquids as Ordered Reaction Media for the Diels-Alder Reaction.

Science.gov (United States)

Bruce, Duncan W; Gao, Yanan; Canongia Lopes, José Nuno; Shimizu, Karina; Slattery, John M

2016-11-02

Liquid-crystalline ionic liquids (LCILs) are ordered materials that have untapped potential to be used as reaction media for synthetic chemistry. This paper investigates the potential for the ordered structures of LCILs to influence the stereochemical outcome of the Diels-Alder reaction between cyclopentadiene and methyl acrylate. The ratio of endo- to exo-product from this reaction was monitored for a range of ionic liquids (ILs) and LCILs. Comparison of the endo:exo ratios in these reactions as a function of cation, anion and liquid crystallinity of the reaction media, allowed for the effects of liquid crystallinity to be distinguished from anion effects or cation alkyl chain length effects. These data strongly suggest that the proportion of exo-product increases as the reaction media is changed from an isotropic IL to a LCIL. A detailed molecular dynamics (MD) study suggests that this effect is related to different hydrogen bonding interactions between the reaction media and the exo- and endo-transition states in solvents with layered, smectic ordering compared to those that are isotropic. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of prostanoids; enantiomeric purity of alcohols by a 31P NMR technique

International Nuclear Information System (INIS)

Penning, T.D.

1985-01-01

The enone, 2,2-diemthyl-3aβ, 6aβ-dihydro-4H-cyclopenta-1,3-dioxol-4-one, has been synthesized in six steps from cyclopentadiene, resolved using sulfoximine chemistry, and converted into (-)-prostaglandin E 2 methyl ester in three steps. Introduction of the optically pure omega side-chain using a conjugate addition of a stabilized organocopper reagent, followed by direct alkylation of the enolate with the α side-chain allylic iodide in the presence of hexamethylphosphoramide, afforded a trans, vicinally disubstituted cyclopentanone. Deprotection of the C-15 alcohol, followed by aluminum amalgam reduction of the C-10/oxygen bond, provided (-)-PGE 2 methyl ester in 47% overall yield from the enone. In an extension of previously described work, 2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide, prepared from l-ephedrine and thiophosphoryl chloride, was used to determine the enantiomeric excess of chiral alcohols in conjunction with 31 P NMR. Chiral primary and secondary alcohols added quantitatively to the phospholidine to give diastereomers which could be analyzed by 31 P NMR and HPLC. A number of other phosphorus heterocycles were also explored as potential chiral derivatizing reagents

How do electron localization functions describe π-electron delocalization?

Science.gov (United States)

Steinmann, Stephan N; Mo, Yirong; Corminboeuf, Clemence

2011-12-14

Scalar fields provide an intuitive picture of chemical bonding. In particular, the electron localization function (ELF) has proven to be highly valuable in interpreting a broad range of bonding patterns. The discrimination between enhanced or reduced electron (de)localization within cyclic π-conjugated systems remains, however, challenging for ELF. In order to clearly distinguish between the local properties of ten highly and weakly π-(de)localized prototype systems, we compare the ELFs of both the canonical wave functions and electron-localized states (diabatic) with those of two closely related scalar fields: the electron localizability indicator (ELI-D) and the localized orbital locator (LOL). The simplest LOL function distinguishes enhanced from weak π-(de)localization in an insightful and reliable manner. LOL offers the finest contrast between annulenes with 4n/4n + 2 π electrons and their inorganic analogues as well as between hyperconjugated cyclopentadiene derivatives. LOL(π) also gives an appealing and intuitive picture of the π-bond. In contrast, the most popular ELF fails to capture subtle contrasting local electronic properties and suffers from the arbitrariness of the σ/π dissection. The orbital separation of the most recent ELI-D is clear-cut but the interpretations sometime less straightforward in the present context.

Computational Investigation of the Competition between the Concerted Diels-Alder Reaction and Formation of Diradicals in Reactions of Acrylonitrile with Non-Polar Dienes

Science.gov (United States)

James, Natalie C.; Um, Joann M.; Padias, Anne B.; Hall, H. K.; Houk, K. N.

2013-01-01

The energetics of the Diels-Alder cycloaddition reactions of several 1,3-dienes with acrylonitrile, and the energetics of formation of diradicals, were investigated with density functional theory (B3LYP and M06-2X) and compared to experimental data. For the reaction of 2,3-dimethyl-1,3-butadiene with acrylonitrile, the concerted reaction is favored over the diradical pathway by 2.5 kcal/mol using B3LYP/6-31G(d); experimentally this reaction gives both cycloadduct and copolymer. The concerted cycloaddition of cyclopentadiene with acrylonitrile is preferred computationally over the stepwise pathway by 5.9 kcal/mol; experimentally, only the Diels-Alder adduct is formed. For the reactions of (E)-1,3-pentadiene and acrylonitrile, both cycloaddition and copolymerization were observed experimentally; these trends were mimicked by the computational results, which showed only a 1.2 kcal/mol preference for the concerted pathway. For the reactions of (Z)-1,3-pentadiene and acrylonitrile, the stepwise pathway is preferred by 3.9 kcal/mol, in agreement with previous experimental findings that only polymerization occurs. M06-2X is known to give more accurate activation and reaction energetics but the energies of diradicals are too high. PMID:23758325

The thermodynamic and structural properties of metallocenes-type random ethylene copolymers

International Nuclear Information System (INIS)

Simanke, Adriane G.; Mauler, Raquel S.; Galland, Griselda B.; Alamo, Rufina G.

2001-01-01

The properties of a series of random ethylene copolymers prepared with the metallocenes catalytic system rac-Et[Ind] 2 ZrCl 2 /MAO were studied for a large variety of comonomer types. These include the classical 1-alkene type with length up to 10 carbons and those of the cyclic type such as cyclopentadiene and dicyclopentadiene. Under rapid crystallization, the melting temperatures of the newly synthesized copolymers followed the relation of model random copolymers indicating a behavior that conforms to that predicted by Flory's phase equilibrium theory. The molar entropy of fusion is not significantly altered by the comonomer type including the dicyclopentadiene type. All types of comonomers studied showed, for a fixed comonomer content, the same change in properties during annealing, except the ethylene 1-butenes. These latter copolymers and the hydrogenated poly butadiene showed a faster rate of change in thermal properties. This is consistent with a higher molecular diffusion for the butene comonomer than for the rest of comonomers analyzed. The properties of the inter lamellar region were also studied as a function of comonomer type and content following the variation of the amorphous halo extracted from the WAXS diffractograms. The observed systematic decrease in the peak scattering angle with increasing comonomer content indicates a variation of the intermolecular liquid structure. (author)

Synthesis of New Silicon-linked Lanthanocene Complexes and Their High Catalytic Activity for Methyl Methacrylate Polymerization with Nanometric Sodium Hydride as Co-catalyst

Institute of Scientific and Technical Information of China (English)

谢小敏; 黄吉玲

2005-01-01

The synthesis and characterization of four new silicon-linked lanthanocene complexes with pendant phenyl groups on cyclopentadiene were reported. Based on the data of elemental analyses, MS and IR, the complexes were presumed to be unsolvated and dimeric complexes [Me2Si(C5H3CMe2C6H5)2LnC1]2 [Ln=Er (1), Gd (2), Sm (3), Dy (4)]. In conjunction with AlEt3 or sodium hydride as the co-catalyst, these complexes could efficiently catalyze the polymerization of methyl methacrylate (MMA). When the nanometric sodium hydride was used as a co-catalyst, the complexes were highly effective for the polymerization of MMA. At low temperature and in short time, in [MeESi(C5H3CMe2C6H5)2LnC1]2/NaH (nanometric) system, the polymer was obtained in more than 80% yield and the molecular weight was greater than 105. The activity reached that of organolanthanide hydride as a single-component catalyst. In ]MeESi(C5H3CMe2C6H5)2ErC1]2/Nail (nanometric) system, the effects of the molar ratio of MMA/catalyst and catalyst/co-catalyst, and the temperature on polymerization were studied.

Direct Lactamization of Azido Amides via Staudinger-Type Reductive Cyclization

Energy Technology Data Exchange (ETDEWEB)

Heo, In Jung; Lee, Su Jeong; Cho, Chang Woo [Kyungpook National University, Daegu (Korea, Republic of)

2012-01-15

The direct lactamization of 1,3- and 1,4-azido amides has been achieved using triphenylphosphine and water, affording various γ- and δ-lactams in good to excellent yields. The direct lactamization of the azido amides was performed via the Staudinger-type reductive cyclization in which the amide group acts as the electrophile for lactam synthesis. This lactamization provides a mild, functional group tolerant and efficient route for the synthesis of various γ- and δ-lactams found in natural products and pharmaceuticals. Further studies will be conducted to develop new synthetic routes for the synthesis of various lactams. The lactam ring system is one of the most ubiquitous structural motifs found in natural products and pharmaceuticals. Owing to the prevalence of lactams, their synthesis has attracted considerable attention. Lactams are usually prepared by the coupling of activated carboxylic acid derivatives with amines. Alternative routes include the Beckmann rearrangement of oximes, the Schmidt reaction of cyclic ketones and hydrazoic acid, the Kinugasa reaction of nitrones and terminal acetylenes, the Diels-Alder reaction of cyclopentadiene and chlorosulfonyl isocyanate, transition metal catalyzed lactamization of amino alcohols, and iodolactamization of amides and alkenes. In particular, the intramolecular Staudinger ligation of azides and activated carboxy acids, including esters, is well known as an environmentally friendly and mild protocol for lactam synthesis.

The Synthesis of the Stable IVDU Derivative for Imaging HSV-1 TK Expression

International Nuclear Information System (INIS)

Kim, Eun Jung; Choi, Tae Hyun; Ahn, Soon Hyuk; Kim, Byoung Soo; Park, Hyun; Cheon, Gi Jeong; An, Gwang Il; Rhee, Hak June

2009-01-01

5-iododeoxyuridine analogues have been exclusively developed for the potential antiviral and antitumor therapeutic agents. In this study, we synthesized carbocyclic radioiododeoxyuridineanalogue (ddIVDU) and carbocyclic intermediate as efficient carbocyclic radiopharmaceuticals. The synthesis is LAH reduction, hetero Diels-Alder reaction as key reactions including Pd(0)-catalyzed coupling reaction together with organotin. MCA-RH7777 (MCA) and MCA-tk (HSV1-tk positive) cells were treated with various concentration of carbocyclic ddIVDU, and GCV. Cytotoxicity was measured by the MTS methods. For in vitro uptake study, MCA and MCA-tk cells were incubated with 1uCi of [ 125 I]carbocyclic ddIVDU. Accumulated radioactivity was measured after various incubation times. The synthesis of ddIVDU and precursor for radioiodination were achieved from cyclopentadiene in good overall yield, respectively. The radioiododemetallation for radiolabeling gave more than 80% yield with > 95% radiochemical purity. GCV was more toxic than carbocyclic ddIVDU in MCA-tk cells. Accumulation of [ 125 I]carbocyclic ddIVDU was higher in MCA-tk cells than MCA cells. Biological data reveal that ddIVDU is stable in vitro, less toxic than ganciclovir (GCV), and selective in HSV1-tk expressed cells. Thus, this new carbocyclic nucleoside, referred to in this paper as carbocyclic 2',3'-didehydro-2',3'-dideoxy-5- iodovinyluridine (carbocyclic ddIVDU), is a potential imaging probe for HSV1-tk

Sources of polyaromatic hydrocarbons (PAH); Kildebestemmelse af polyaromatiske kulbrinter (PAH)

Energy Technology Data Exchange (ETDEWEB)

Egsgaard, H. [Forskningscenetr Risoe, Ald. for Plantebiologi og Biokemi (DK); Larsen, E. [Forskningscenter Risoe, Ald. for Optic og Fluid Dynamik (Denmark)

2000-03-01

Aromatic hydrocarbons including PAH compounds are thermally and chemically very stable compounds and are formed by gasification/pyrolysis of biomass. With reference to the tar compounds present in the produced gas from updraft gasifiers the sources responsible for the formation of naphthalene and poly-aromatic hydrocarbons have been investigated. The focus has been on thermal and oxidative conversions of compounds related to the lignin building blocks. Thus, phenols, 2-methoxy-phenols and 4-substituted-2-methoxy-phenols were investigated by introducing water solutions of the compounds into a continuos flow system operating in the temperature range 600-850 deg. C. The pyrolysis products were identified by GC/MS. The tar compounds reveal a well-defined and characteristic thermal transformation. Phenol is a strong source to naphthalene and indenes while 2-methoxyphenols are sources to aromatic oxo-compounds such as cinnamaldehyde. More complex systems are sources to higer PAH compounds. Thus, oligomers of phenol and 2-methoxyphenol give dibenzofuran and oligomers of isoeugenol are important sources to acenaphthylene. It is characteristic that the simple tar compounds investigated undergo loss of CO and hereby loss of the aromatic structure. The intermediary compounds are very reactive cyclo-pentadienes entering Diels-Alder reactions. The later products are transformed to aromatic compounds. The results may facilitate the determination of optimum conditions for updraft gasifiers and hence a reduction of PAH formation. (au)

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography - Part III: 2,5-Dimethylfuran.

Science.gov (United States)

Togbé, Casimir; Tran, Luc-Sy; Liu, Dong; Felsmann, Daniel; Oßwald, Patrick; Glaude, Pierre-Alexandre; Sirjean, Baptiste; Fournet, René; Battin-Leclerc, Frédérique; Kohse-Höinghaus, Katharina

2014-03-01

This work is the third part of a study focusing on the combustion chemistry and flame structure of furan and selected alkylated derivatives, i.e. furan in Part I, 2-methylfuran (MF) in Part II, and 2,5-dimethylfuran (DMF) in the present work. Two premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of DMF were studied with electron-ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) under two equivalence ratios (φ=1.0 and 1.7). Mole fractions of reactants, products, and stable and radical intermediates were measured as a function of the distance to the burner. Kinetic modeling was performed using a reaction mechanism that was further developed in the present series, including Part I and Part II. A reasonable agreement between the present experimental results and the simulation is observed. The main reaction pathways of DMF consumption were derived from a reaction flow analysis. Also, a comparison of the key features for the three flames is presented, as well as a comparison between these flames of furanic compounds and those of other fuels. An a priori surprising ability of DMF to form soot precursors (e.g. 1,3-cyclopentadiene or benzene) compared to less substituted furans and to other fuels has been experimentally observed and is well explained in the model.

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part III: 2,5-Dimethylfuran

Science.gov (United States)

Togbé, Casimir; Tran, Luc-Sy; Liu, Dong; Felsmann, Daniel; Oßwald, Patrick; Glaude, Pierre-Alexandre; Sirjean, Baptiste; Fournet, René; Battin-Leclerc, Frédérique; Kohse-Höinghaus, Katharina

2013-01-01

This work is the third part of a study focusing on the combustion chemistry and flame structure of furan and selected alkylated derivatives, i.e. furan in Part I, 2-methylfuran (MF) in Part II, and 2,5-dimethylfuran (DMF) in the present work. Two premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of DMF were studied with electron-ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) under two equivalence ratios (φ=1.0 and 1.7). Mole fractions of reactants, products, and stable and radical intermediates were measured as a function of the distance to the burner. Kinetic modeling was performed using a reaction mechanism that was further developed in the present series, including Part I and Part II. A reasonable agreement between the present experimental results and the simulation is observed. The main reaction pathways of DMF consumption were derived from a reaction flow analysis. Also, a comparison of the key features for the three flames is presented, as well as a comparison between these flames of furanic compounds and those of other fuels. An a priori surprising ability of DMF to form soot precursors (e.g. 1,3-cyclopentadiene or benzene) compared to less substituted furans and to other fuels has been experimentally observed and is well explained in the model. PMID:24518851

The electronic structure of C60 and its derivatives

International Nuclear Information System (INIS)

Lichtenberger, D.L.; Rempe, M.E.; Gruhn, N.E.; Wright, L.L.

1993-01-01

Molecular orbital calculations are used to examine the electronic structure of C 60 and its interaction with metals and some other atoms. The bonding capabilities of the η 5 , η 6 , and the two possible η 2 sites of C 60 to metals are probed with Fenske-Hall calculations of a silver cation bound in those positions. These results are compared to the bonding capabilities of cyclopentadiene, benzene and ethylene, respectively. It is found that the silver cation bonding to C 60 is favored at the η 2 that is shared between five-membered rings, but that the silver cation bonds more favorably to ethylene than to the η 2 site of C 60 . The electronic structure of the known platinum compound, C 60 Pt(phosphine) 2 , where the bonding is also to this η 2 site, is investigated and compared to the electronic structure of the corresponding ethylene complex. In this more electron-rich metal case, the bonding of the C 60 and ethylene are very similar. A calculation on C 60 OsO 4 (NH 3 ) 2 , where C 60 is bound to two oxygens, shows that the orbital composition correlates with the observed NMR shifts of the carbon atoms. The calculations are used to clarify the interpretations of experimental data obtained from STM, NMR, PES and reactivity. The latest results of these electronic studies will be presented

Direct Lactamization of Azido Amides via Staudinger-Type Reductive Cyclization

International Nuclear Information System (INIS)

Heo, In Jung; Lee, Su Jeong; Cho, Chang Woo

2012-01-01

The direct lactamization of 1,3- and 1,4-azido amides has been achieved using triphenylphosphine and water, affording various γ- and δ-lactams in good to excellent yields. The direct lactamization of the azido amides was performed via the Staudinger-type reductive cyclization in which the amide group acts as the electrophile for lactam synthesis. This lactamization provides a mild, functional group tolerant and efficient route for the synthesis of various γ- and δ-lactams found in natural products and pharmaceuticals. Further studies will be conducted to develop new synthetic routes for the synthesis of various lactams. The lactam ring system is one of the most ubiquitous structural motifs found in natural products and pharmaceuticals. Owing to the prevalence of lactams, their synthesis has attracted considerable attention. Lactams are usually prepared by the coupling of activated carboxylic acid derivatives with amines. Alternative routes include the Beckmann rearrangement of oximes, the Schmidt reaction of cyclic ketones and hydrazoic acid, the Kinugasa reaction of nitrones and terminal acetylenes, the Diels-Alder reaction of cyclopentadiene and chlorosulfonyl isocyanate, transition metal catalyzed lactamization of amino alcohols, and iodolactamization of amides and alkenes. In particular, the intramolecular Staudinger ligation of azides and activated carboxy acids, including esters, is well known as an environmentally friendly and mild protocol for lactam synthesis

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

International Nuclear Information System (INIS)

Xu, Wei; Li, Yani; Yu, Bo; Yang, Jindou; Zhang, Ying; Chen, Xi; Zhang, Guofang; Gao, Ziwei

2015-01-01

A successive anchoring of Ti(NMe 2 ) 4 , cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, 13 C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, 13 C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated

Highly efficient solid-state synthesis of carbon-encapsulated ultrafine MoO{sub 2} nanocrystals as high rate lithium-ion battery anode

Energy Technology Data Exchange (ETDEWEB)

Liu, Boyang, E-mail: byliu@shmtu.edu.cn [Shanghai Maritime University, College of Ocean Science and Engineering (China); Shao, Yingfeng, E-mail: shaoyf@lnm.imech.ac.cn [Chinese Academy of Sciences, State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics (China); Zhang, Yuliang, E-mail: ylzhang@shmtu.edu.cn; Zhang, Fuhua, E-mail: fhzhang@shmtu.edu.cn; Zhong, Ning, E-mail: ningzhong@shmtu.edu.cn [Shanghai Maritime University, College of Ocean Science and Engineering (China); Li, Wenge, E-mail: wgli@shmtu.edu.cn [Shanghai Maritime University, Merchant Marine College (China)

2016-12-15

A simple and highly efficient method is developed for the one-step in situ preparation of carbon-encapsulated MoO{sub 2} nanocrystals (MoO{sub 2}@C) with core-shell structure for high-performance lithium-ion battery anode. The synthesis is depending on the solid-state reaction of cyclopentadienylmolybdenum tricarbonyl dimer with ammonium persulfate in an autoclave at 200 °C for 30 min. The large amount of heat generated during the explosive reaction cleaves the cyclopentadiene ligands into small carbon fragments, which form carbon shell after oxidative dehydrogenation coating on the MoO{sub 2} nanocrystals, resulting in the formation of core-shell structure. The MoO{sub 2} nanocrystals have an equiaxial morphology with an ultrafine diameter of 2–8 nm, and the median size is 4.9 nm. Hundreds of MoO{sub 2} nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 3–5 nm in thickness. The content of MoO{sub 2} nanocrystals in the nanocomposite is about 69.3 wt.%. The MoO{sub 2}@C anode shows stable cyclability and retains a high reversible capacity of 443 mAh g{sup −1} after 50 cycles at a current density of 3 A g{sup −1}, owing to the effective protection of carbon shell.

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

Energy Technology Data Exchange (ETDEWEB)

Xu, Wei; Li, Yani; Yu, Bo; Yang, Jindou; Zhang, Ying; Chen, Xi; Zhang, Guofang, E-mail: gfzhang@snnu.edu.cn; Gao, Ziwei, E-mail: zwgao@snnu.edu.cn

2015-01-15

A successive anchoring of Ti(NMe{sub 2}){sub 4}, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, {sup 13}C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, {sup 13}C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated.

Single-site SBA-15 supported zirconium catalysts. Synthesis, characterization and toward cyanosilylation reaction

International Nuclear Information System (INIS)

Xu, Wei; Yu, Bo; Zhang, Ying; Chen, Xi; Zhang, Guofang; Gao, Ziwei

2015-01-01

Graphical abstract: Ligand-modified signal-site SBA-15 supported zirconium catalysts were synthesized by SOMC method and characterized by a variety of techniques. The zirconium surface complexes show high catalytic efficiency for cyanosilylation of benzaldehyde. - Highlights: • Some Zr active species have been anchored on the surface of SBA-15 by SOMC technique. • The structures of the Zr species have been characterized by a variety of techniques. • The anchored Zr species are single-sited surface complexes. • The Zr surface complexes are catalytic active for cyanosilylation of benzaldehyde. - Abstract: A successive anchoring of Zr(NMe 2 ) 4 , cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on dehydroxylated SBA-15 pretreated at 500 °C for 16 h (SBA-15 -500 ) was conducted by SOMC strategy in moderate conditions. The dehydoxylation of SBA-15 was monitored by in situ Fourier transform infrared spectroscopy (in situ FT-IR). The ligand-modified SBA-15 -500 supported zirconium complexes were characterized by in situ FT-IR, 13 C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MAS) and elemental analysis in detail, verifying that the surface zirconium species are single-sited. The catalytic activity of these complexes was evaluated by cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the structure of surface species and the configuration of the ligands

Single-site SBA-15 supported zirconium catalysts. Synthesis, characterization and toward cyanosilylation reaction

Energy Technology Data Exchange (ETDEWEB)

Xu, Wei; Yu, Bo; Zhang, Ying; Chen, Xi; Zhang, Guofang, E-mail: gfzhang@snnu.edu.cn; Gao, Ziwei, E-mail: zwgao@snnu.edu.cn

2015-01-15

Graphical abstract: Ligand-modified signal-site SBA-15 supported zirconium catalysts were synthesized by SOMC method and characterized by a variety of techniques. The zirconium surface complexes show high catalytic efficiency for cyanosilylation of benzaldehyde. - Highlights: • Some Zr active species have been anchored on the surface of SBA-15 by SOMC technique. • The structures of the Zr species have been characterized by a variety of techniques. • The anchored Zr species are single-sited surface complexes. • The Zr surface complexes are catalytic active for cyanosilylation of benzaldehyde. - Abstract: A successive anchoring of Zr(NMe{sub 2}){sub 4}, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on dehydroxylated SBA-15 pretreated at 500 °C for 16 h (SBA-15{sub -500}) was conducted by SOMC strategy in moderate conditions. The dehydoxylation of SBA-15 was monitored by in situ Fourier transform infrared spectroscopy (in situ FT-IR). The ligand-modified SBA-15{sub -500} supported zirconium complexes were characterized by in situ FT-IR, {sup 13}C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MAS) and elemental analysis in detail, verifying that the surface zirconium species are single-sited. The catalytic activity of these complexes was evaluated by cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the structure of surface species and the configuration of the ligands.

Hepatoprotective Activity of Cichorium endivia L. Extract and Its Chemical Constituents

Directory of Open Access Journals (Sweden)

Ai-Ping Wang

2011-10-01

Full Text Available The objective of the present study was to investigate the in vitro and in vivo hepatoprotective properties of Cichorium endivia L. extract (CEE, and to identify its chemical constituents. CEE significantly blocked the oxidative stress and cytotoxicity induced by tert-butyl hydroperoxide (t-BHP in HepG2 cells. Meanwhile, oral administration of CEE to mice before the treatment of t-BHP exhibited a markedly protective effect by lowering serum levels of ALT and AST, inhibiting the changes in liver biochemistry including MDA, SOD, GSH and GST, as well as ameliorating the liver injuries according to the histopathological observations. According to the acute oral toxicity test, the LD50 of CEE was greater than 5,000 mg/kg, which demonstrates that the CEE can be considered practically non-toxic. Phytochemical analysis of CEE showed the presence of five compounds identified as 2-furanmethanol-(5'→11-1,3-cyclopentadiene-[5,4-c]-1H-cinnoline, which is a new cinnoline derivative derived from a natural source but not synthesis, 2-phenylethyl-β-D-glucopyranoside, kaempferol-3-O-β-D-glucoside, kaempferol, and adenosine. In the ORAC assay, CEE and its constituents kaempferol and kaempferol-3-O-β-D-glucoside had considerable antioxidant potency. Taken together, CEE protects hepatic tissue from oxidative damage in vitro and in vivo, potentially due to its phenolic substances, and does not cause acute oral toxicity, which suggests that CEE may be a valid and safe remedy to cure liver disease.

Online characterization of isomeric/isobaric components in the gas phase of mainstream cigarette smoke by tunable synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry and photoionization efficiency curve simulation.

Science.gov (United States)

Pan, Yang; Hu, Yonghua; Wang, Jian; Ye, Lili; Liu, Chengyuan; Zhu, Zhixiang

2013-12-17

A newly developed, qualitative and quantitative method based on tunable synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry (SR-VUV-PI-TOFMS) and photoionization efficiency (PIE) curve simulation was applied for the online analysis of isomers and isobaric compounds in the gas phase of mainstream cigarette smoke. After blocking the particulate phase components by the Cambridge filter pad, a puff of fresh gas-phase cigarette smoke was immediately introduced into a vacuum ionization chamber through a heated capillary, then was photoionized, and analyzed by a TOF mass spectrometer. The PIE curves for the mass peaks up to m/z = 106 were measured between 8.0 and 10.7 eV. Some components could be directly identified by their discriminated ionization energies (IEs) on the PIE curve. By simulating the PIE curve with the sum of scaled absolute photoionization cross sections (PICSs), complex isomeric/isobaric compounds along with their mole fractions could be obtained when the best-fitting was realized between experimental and simulated PIE curves. A series of reported toxic compounds for quantification, such as 1,3-butadiene (m/z = 54), 1,3-cyclopentadiene (m/z = 66), benzene (m/z = 78), xylene (m/z = 106), 2-propenal (m/z = 56), acetone and propanal (m/z = 58), crotonaldehyde (m/z = 70), furan and isoprene (m/z = 68), were all found to have other isomers and/or isobaric compounds with considerable abundances. Some isomers have never been reported previously in cigarette smoke, like C5H6 isomers 1-penten-3-yne, 3-penten-1-yne, and 1-penten-4-yne at m/z = 66. Isomeric/isobaric compounds characterization for the mass peaks and mole fraction calculations were discussed in detail below 10.7 eV, an energy value covering several conventional used VUV light sources.

Chemistry of Furan Conversion into Aromatics and Olefins over HZSM-5: A Model Biomass Conversion Reaction

Energy Technology Data Exchange (ETDEWEB)

Cheng, Yu-Ting; Huber, George W.

2011-06-03

The conversion of furan (a model of cellulosic biomass) over HZSM-5 was investigated in a thermogravimetric analysis–mass spectrometry system, in situ Fourier transform infrared analysis, and in a continuous-flow fixed-bed reactor. Furan adsorbed as oligomers at room temperature with a 1.73 of adsorbed furan/Al ratio. These oligomers were polycyclic aromatic compounds that were converted to CO, CO₂, aromatics, and olefins at temperatures from 400 to 600 °C. Aromatics (e.g., benzene, toluene, and naphthalene), oligomer isomers (e.g., benzofuran, 2,2-methylenebisfuran, and benzodioxane), and heavy oxygenates (C₁₂{sub +} oligomers) were identified as intermediates formed inside HZSM-5 at different reaction temperatures. During furan conversion, graphite-type coke formed on the catalyst surface, which caused the aromatics and olefins formation to deactivate within the first 30 min of time on-stream. We have measured the effects of space velocity and temperature for furan conversion to help us understand the chemistry of biomass conversion inside zeolite catalysts. The major products for furan conversion included CO, CO₂, allene, C₂–C₆ olefins, benzene, toluene, styrene, benzofuran, indene, and naphthalene. The aromatics (benzene and toluene) and olefins (ethylene and propylene) selectivity decreased with increasing space velocity. Unsaturated hydrocarbons such as allene, cyclopentadiene, and aromatics selectivity increased with increasing space velocity. The product distribution was selective to olefins and CO at high temperatures (650 °C) but was selective to aromatics (benzene and toluene) at intermediate temperatures (450–600 °C). At low temperatures (450 °C), benzofuran and coke contributed 60% of the carbon selectivity. Several different reactions were occurring for furan conversion over zeolites. Some important reactions that we have identified in this study include Diels–Alder condensation (e.g., two furans form benzofuran and water

Hot atom reactions involving multivalent and univalent species. Progress report, February 1976--January 1977

International Nuclear Information System (INIS)

Tang, Y.N.

1977-01-01

Multivalent hot atoms formed by the nuclear recoil method were studied: 31 Si, 32 P, and 11 C. For the recoil 31 Si reactions, we have completed the study on the reactivities of conjugated dienes towards monomeric 31 SiF 2 . The relative reactivities of 1,3-butadiene, trans-pentadiene, cis-pentadiene and 2-methyl-1,3-butadiene towards 31 SiF 2 have been measured as: 1.0:0.89:0.91:1.06 for singlet 31 SiF 2 ; and as 1.0:0.80:0.52:0.89 for the triplet. The large steric effect detected here between cis- and trans-pentadienes for their reactivities towards triplet 31 SiF 2 -donor indicates that a direct 1,4-addition process is possible for such 31 SiF 2 donating complexes. 2-methyl-1,1-diflorosilacyclopent-3-ene and its 3-methyl isomer were successfully synthesized by the co-pyrolysis technique. Experiments to evaluate the relative addition efficiencies of 31 SiH 2 towards various conjugated dienes; and to study to H- and F-abstraction mechanism by 31 Si atoms were begun. For recoil 32 P reactions, some progress has been made towards evaluating the mechanism of abstraction reactions by recoil 32 P atoms in PF 3 -PCl 3 system, and the moderator effect for recoil 32 P reactions with PF 3 -CH 4 mixtures. The possible formation of 32 PH, and the formation of 32 P atoms via the 32 S(n,p) 32 P process have also been explored. For recoil 11 C reactions, major progress has been obtained in the moderator studies of its reactions with 1,3-butadiene. With the successive addition of Ne as a moderator, the yield of acetylene- 11 C decreased, the yield of cyclopentene- 11 C increased while those of both 1,2,4-pentatriene- 11 C and cyclopentadiene- 11 C went through a minimum. Some progress for the identification of the last unknown 11 C-labeled product from this system has also been made

Steric and electronic effects of 1,3-disubstituted cyclopentadienyl ligands on metallocene derivatives of Cerium, Titanium, Manganese, and Iron

Energy Technology Data Exchange (ETDEWEB)

Sofield, Chadwick Dean [Univ. of California, Berkeley, CA (United States)

2000-05-01

Sterically demanding 1,3-disubstituted cyclopentadienyl ligands were used to modify the physical properties of the corresponding metallocenes. Sterically demanding ligands provided kinetic stabilization for trivalent cerium compounds. Tris(di-t-butylcyclopentadienyl)cerium was prepared and anion competition between halides and cyclopentadienyl groups which had complicated synthesis of the tris(cyclopentadienyl)compound was qualitatively examined. Bis(di-t-butylcyclopentadienyl)cerium methyl was prepared and its rate of decomposition, by ligand redistribution, to tris(di-t-butylcyclopentadienyl)cerium was shown to be slower than the corresponding rate for less sterically demanding ligands. Asymmetrically substituted ligands provided a symmetry label for examination of chemical exchange processes. Tris[trimethylsilyl(t-butyl)cyclopentadienyl]cerium was prepared and the rate of interconversion between the C1 and C3 isomers was examined. The enthalpy difference between the two distereomers is 7.0 kJ/mol. The sterically demanding cyclopentadienyl ligands ansa-di-t-butylcyclopentadiene (Me₂Si[(Me₃C)₂C₅H₃]₂), ansa-bis(trimethylsilyl)cyclopentadiene (Me₂Si[(Me₃Si)₂C₅H₃]₂) and tetra-t-butylfulvalene and metallocene derivatives of the ligands were prepared and their structures were examined by single crystal X-ray crystallography. The effect that substituents on the cyclopentadienyl ring have on the pi-electron system of the ligand was examined through interaction between ligand and metal orbitals. A series of 1,3-disubstituted manganocenes was prepared and their electronic states were determined by solid-state magnetic susceptibility, electron paramagnetic resonance, X-ray crystallography, and variable temperature UV-vis spectroscopy. Spin-equilibria in [(Me₃C)₂C₅H₃]₂Mn and [(Me₃

A Pathway to Artificial Metalloenzymes

KAUST Repository

Fischer, Johannes

2015-12-01

The advancement of catalytic systems and the application thereof has proven to be the key to overcome traditional limitations of industrial-scale synthetic processes. Converging organometallic and biocatalytic principles lead to the development of Artificial Metalloenzymes (ArMs) that comprise a synthetic metal catalyst embedded in a protein scaffold, thereby combining the reactivity of the former with the versatility of the latter. This synergistic approach introduces rationally designed building blocks for the catalytic site and the host protein to assemble enzyme-like structures that follow regio-, chemo-, enantio- and substrate-selective principles. Yet, the identification of suitable protein scaffolds has thus far been challenging. Herein we report a rationally optimized fluorescent protein host, mTFP*, that was engineered to have no intrinsic metal binding capability and, owing to its robust nature, can act as scaffold for the design of novel ArMs. We demonstrate the potential of site-specific modifications within the protein host, use protein X-Ray analysis to validate the respective scaffolds and show how artificial mutant binding sites can be introduced. Transition metal Förster Resonance Energy transfer (tmFRET) methodologies help to evaluate micromolar dissociation constants and reveal structural rearrangements upon coordination of the metal centers. In conjunction with molecular insights from X-Ray crystallographic structure determination, dynamics of the binding pocket can be inferred. The versatile subset of different binding motifs paired with transition metal catalysts create artificial metalloenzymes that provide reactivities which otherwise do not exist in nature. As a proof of concept, Diels-Alder cycloadditions highlight the potential of the present mTFP* based catalysts by stereoselectively converting azachalcone and cyclopentadiene substrates. Screens indicate an enantiomeric excess of up to 60% and provide insights into the electronic and

Chemical signatures of life in modern stromatolites from Lake Alchichica, Mexico. Applications for the search of life on Mars

Science.gov (United States)

Navarro, Karina F.; Navarro-Gonzalez, Rafael; Alcocer, Javier; Escobar, Elva; Morales, Pedro; Cienfuegos, Edith; Coll, Patrice; Raulin, Francois; Stalport, Fabien; Cabane, Michel; Person, Alain; McKay, Chris

hyposaline (8.5-10 g l-1 ) and alkaline (pH 8.9-9.1 and alkalinity of 37 meq l-1 ) with sodium and chloride being the dominant ions but also with bicarbonate and carbonate ions. These conditions are favorable for active carbonate deposition that results in the formation of distinctive stromatolite structures in the littoral region of the lake. These structures generate extended submerged carbonaceous platforms down to a depth of 15 m that slope steeply to the bottom of the lake where soft sediments prevail (Escobar-Briones et al., 1998). The lake is populated by 18 species of cyanobacteria (Tavera and Komárek, 1996) which are the primary producers in the food web a of the lake fixing not only carbon (Escobar-Briones et al., 1998) but also nitrogen (Falcón eto al, 2002). The stromatolite samples were freeze-dried and then were finely grounded with an agate mor-tar mill for analyses. The mineral composition of the sample is essentially hydromagnesite (Mg5 (CO3 )4 (OH)2 , 4 H2 O)) with traces of quartz (SiO2 ) as determined by X-rays diffraction. This is also consistent with differential thermal analysis and thermal gravimetry of the sample. Analysis of the sample by TV-mass spectrometry (MS) using the Phoenix Lander Protocol (Navarro-González et al., 2009) indicates that the major volatile released is carbon dioxide a from 350 C to 1000° C with broad peaks centered at 400° C and 600° C. Organics are also re-° leased from 380° C to 750° C as monitored by a characteristic organic fragment with m/z=41 and that is attributed to the allyl cation: [CH2 CHCH2 ]+ . Analysis of the sample by TV-gas chromatography (GC)-MS using the Viking Lander Protocol but at 750° C (Navarro-González a et al., 2009) demonstrates that a complex suite of organics are released such as 1,3-butadiene, furan, propanal, 2-propenenitrile, 1,3 cyclopentadiene, 2-methyl-1,3-butadiene, propanenitrile, methylfuran, butanal, benzene, 1-methyl-cyclohexene, 1-H-pyrrole, pyridine, methylbenzene, 2